Nonaqueous electrolyte solution for lithium secondary battery and lithium secondary battery using it

The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery using the same.

In recent years, with the miniaturization of electronic devices, the demand for higher capacity for secondary batteries has increased, and lithium secondary batteries, which have a higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries, have attracted attention. There is.

LiPF is a non-aqueous electrolyte solution for lithium secondary batteries.₆, LiBF₄, LiClO₄, LiCF₃SO₃, LiAsF₆, LiN (CF)₃SO₂)₂, LiCF₃(CF₂)₃SO₃Solvents such as ethylene carbonate, cyclic carbonate such as propylene carbonate, chain carbonate such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, methyl acetate, methyl propionate. Such as chain esters, cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, chain ethers such as dimethoxyethane and dimethoxymethane, and non-aqueous solvents such as sulfur-containing organic solvents such as sulfolane and diethyl sulfone. A non-aqueous electrolyte solution dissolved in is used.

In a secondary battery using such a lithium non-aqueous electrolyte solution, the reactivity and ionic conductivity differ depending on the composition of the non-aqueous electrolyte solution, so that the battery characteristics greatly change depending on the non-aqueous electrolyte solution. For example, conventionally, studies have been made to improve the high-temperature storage characteristics and repeated charge / discharge characteristics (cycle characteristics) of batteries by using various methods. Further, as the use of lithium batteries has expanded, it has become necessary to instantaneously extract a large amount of energy, that is, output characteristics. However, when discharging with a large current value, an overvoltage is applied to the battery due to the influence of the internal resistance, which causes a voltage drop, so that there is a problem that a large output cannot be obtained. Therefore, as lithium secondary batteries are used in various electronic devices, as well as automobiles and power tools, there has been a demand for a non-aqueous electrolyte solution that can contribute to the improvement of output characteristics.

Under these circumstances, Patent Document 1 uses a non-aqueous electrolyte solution containing a cyclic siloxane and / or a reaction product thereof, and Patent Document 2 uses a non-aqueous electrolyte solution containing a silicon compound having a specific structure. It is described that it is used, and both can improve the input / output characteristics and the cycle characteristics. However, although these methods are certainly effective, they have not been able to obtain a secondary battery having sufficient characteristics.

Further, Patent Document 3 describes that a non-aqueous electrolyte solution capable of forming a battery having excellent cycle characteristics is provided by setting the hydrogen fluoride (HF) in the non-aqueous electrolyte solution to less than 30 ppm. Patent Document 4 can provide a non-aqueous electrolyte solution that can form a battery having similarly excellent cycle characteristics by using a non-aqueous electrolyte solution characterized in that monoalcohols in a non-aqueous solvent are less than 30 ppm. There is. Further, in Patent Document 5, the non-aqueous solvent contains a high dielectric constant solvent and a low-viscosity solvent, and after purifying them individually, the non-aqueous solvent obtained by mixing and the fluorine-containing electrolyte are mixed. A method for producing an electrolytic solution for a lithium secondary battery is described, wherein the diols in the non-aqueous solvent are less than 20 ppm, and the electrolytic solution produced in this manner has excellent cycle characteristics. An example is shown.

However, these techniques have not contributed to the improvement of output characteristics.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-71458</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2004-87459</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 10-270074</text></patcit><patcit num="4"><text>JP-A-2002-75440</text></patcit><patcit num="5"><text>Japanese Patent No. 3244017</text></patcit>

<p num="0008"> The present invention has been made in view of the background art, and an object of the present invention is to provide a non-aqueous electrolyte solution for a secondary battery which is excellent in output characteristics, high temperature storage characteristics and cycle characteristics. ..</p>

<p num="0009"> As a result of diligent research to solve the above problems, the inventors have found that in a non-aqueous electrolyte solution for a secondary battery obtained by mixing a fluorine-containing lithium salt with a non-aqueous solvent, hydrogen fluoride is contained in the non-aqueous electrolyte solution. We have found that by containing (HF) in a specific range and further containing a specific chemical substance, its effectiveness can be greatly improved by an unexpected method and very good output characteristics can be realized. Reached.</p><p num="0010"> That is, in the present invention, in a non-aqueous electrolyte solution for a secondary battery formed by mixing a fluorine-containing lithium salt with a non-aqueous solvent, hydrogen fluoride (HF) is contained in the entire non-aqueous electrolyte solution at 10 ppm or more and 300 ppm or less. Further, a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an SF bond in the molecule, At least one compound selected from the group consisting of nitrates, nitrites, monofluorophosphates, difluorophosphates, acetates and propionates should be contained in the entire non-aqueous electrolyte solution at a rate of 10 ppm or more. It provides a characteristic non-aqueous electrolyte solution for a secondary battery.<chemistry num="4"><img id="000002" he="38" wi="159" file="JP5740802B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry>[In general formula (1), R¹And R²Represents an organic group having 1 to 12 carbon atoms which may be the same or different from each other, and n represents an integer of 3 to 10. ]<chemistry num="5"><img id="000003" he="10" wi="159" file="JP5740802B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry>[In general formula (2), R³~ R⁵Represents an organic group having 1 to 12 carbon atoms which may be the same or different from each other, x represents an integer of 1 to 3, p, q and r each represent an integer of 0 to 3, and 1 p + q + r 3. ]<chemistry num="6"><img id="000004" he="27" wi="159" file="JP5740802B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry>[In general formula (3), R⁶~ R⁸Represents an organic group having 1 to 12 carbon atoms which may be the same or different from each other, and A represents a group composed of H, C, N, O, F, S, Si and / or P. ]</p><p num="0011"> Further, the present invention is a non-aqueous electrolyte secondary battery including at least a non-aqueous electrolyte solution, a negative electrode capable of occluding and releasing lithium ions, and a positive electrode, and the non-aqueous electrolyte solution is the above-mentioned secondary battery. Provided is a non-aqueous electrolyte secondary battery characterized by being a non-aqueous electrolyte for a battery.</p>

<p num="0012"> According to the present invention, it is possible to provide a non-aqueous electrolyte solution for a secondary battery which is excellent in high temperature storage characteristics and cycle characteristics and has greatly improved output characteristics.</p>

Hereinafter, embodiments of the present invention will be described in detail, but the description of the constituent requirements described below is an example (representative example) of the embodiments of the present invention, and the specific contents thereof are not limited. It can be modified in various ways within the scope of the gist.

&lt;Non-aqueous electrolyte for secondary batteries&gt; The non-aqueous electrolyte solution for a secondary battery of the present invention contains a fluorine-containing lithium salt and a non-aqueous solvent for dissolving the lithium salt. [Fluorine-containing lithium salt] The fluorine-containing lithium salt is not particularly limited as long as it is a fluorine-containing lithium salt known to be usable as an electrolyte for a non-aqueous electrolyte solution for a lithium secondary battery, and examples thereof include the following.

Inorganic fluoride salt: LiPF₆, LiBF₄, LiAsF₆, LiSbF₆etc. Fluorine-containing organolithium salt: LiCF₃SO₃Perfluoroalkane sulfonates such as LiN (CF)₃SO₂)₂, LiN (CF)₃CF₂SO₂)₂, LiN (CF)₃SO₂) (C₄F₉SO₂) Etc. perfluoroalkanesulfonylimide salt; LiC (CF)₃SO₂)₃Perfluoroalkanesulfonylmethide salts such as Li [PF₅(CF₂CF₂CF₃)], Li [PF₄(CF₂CF₂CF₃)₂], Li [PF₃(CF₂CF₂CF₃)₃], Li [PF₅(CF₂CF₂CF₂CF₃)], Li [PF₄(CF₂CF₂CF₂CF₃)₂], Li [PF₃(CF₂CF₂CF₂CF₃)₃] Etc., fluoroalkylfluorophosphate and the like. Oxalatoborate salt: Lithium difluorooxalate borate, etc.

These may be used alone or in combination of two or more in any combination and ratio. Among these, LiPF is easy to generate hydrogen fluoride (HF) in the presence of alcohols, which will be described later.₆, LiBF₄Etc. are preferable. In addition, when comprehensively judging the solubility in non-aqueous solvents, charge / discharge characteristics, output characteristics, cycle characteristics, etc. in the case of a secondary battery, LiPF₆Is preferable.

Further, the non-aqueous electrolyte solution for a secondary battery of the present invention may be used by mixing a lithium salt containing no fluorine in addition to the fluorine-containing lithium salt, and examples thereof include the following. .. Inorganic Lithium Salt: LiClO₄, LiBrO₄, LiIO₄Perhalogenates such as; LiAlCl₄Inorganic chloride salts, etc. Oxalate borate salt: Lithium bis (oxalate) borate, etc.

The concentration of the lithium salt in the non-aqueous electrolyte solution is not particularly limited, but is usually 0.5 mol / L or more, preferably 0.6 mol / L or more, and more preferably 0.7 mol / L or more. The upper limit is usually 2 mol / L or less, preferably 1.8 mol / L or less, and more preferably 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte solution may be insufficient, while if the concentration is too high, the electrical conductivity may decrease due to the increase in viscosity, and the performance of the lithium secondary battery. May decrease.

The concentration of the fluorine-containing lithium salt in the non-aqueous electrolyte solution is not particularly limited, but is usually 0.5 mol / L or more, preferably 0.6 mol / L or more, and more preferably 0.7 mol / L or more. The upper limit is usually 2 mol / L or less, preferably 1.8 mol / L or less, and more preferably 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte solution may be insufficient, or the production of hydrogen fluoride (HF) may be insufficient, while if the concentration is too high, the viscosity may increase. Therefore, the electrical conductivity may decrease or the production of hydrogen fluoride (HF) may proceed excessively, which may reduce the performance of the lithium secondary battery.

The ratio of the fluorine-containing lithium salt to the total lithium salt in the non-aqueous electrolyte solution is preferably 50% by mass or more, and particularly preferably 70% by mass or more, based on the total lithium salt. It is also particularly preferable that all of the lithium salts to be mixed are fluorine-containing lithium salts. If the proportion of the fluorine-containing lithium salt is too low, the production of hydrogen fluoride may be insufficient.

As the lithium salt, one type may be used alone, or two or more types may be used in combination in any combination and ratio, but a preferable example when two or more types of lithium salts are used in combination is LiPF.₆And LiBF₄In this case, LiBF accounts for the total of both.₄The ratio of is particularly preferably 0.01% by mass or more and 20% by mass or less, and further preferably 0.1% by mass or more and 5% by mass or less. In addition, another preferable example is a combination of an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt, in which case the ratio of the inorganic fluoride salt to the total of both is 70% by mass or more and 99% by mass. It is particularly preferably% or less, and even more preferably 80% by mass or more and 98% by mass or less. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

[Non-aqueous solvent] As the non-aqueous solvent, it can be appropriately selected and used from those conventionally proposed as a solvent for a non-aqueous electrolytic solution. For example, the following can be mentioned. 1) Cyclic carbonate: The alkylene group constituting the cyclic carbonate preferably has 2 to 6 carbon atoms, and particularly preferably 2 to 4 carbon atoms. Specific examples thereof include ethylene carbonate, propylene carbonate and butylene carbonate. Of these, ethylene carbonate and propylene carbonate are preferable. 2) Chain carbonate: As the chain carbonate, dialkyl carbonate is preferable, and the number of carbon atoms of the constituent alkyl groups is preferably 1 to 5, particularly preferably 1 to 4, respectively. Specific examples thereof include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate and ethyl-n-propyl carbonate. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable. 3) Cyclic ester: Specific examples thereof include γ-butyrolactone and γ-valerolactone. 4) Chain ester: Specific examples thereof include methyl acetate, ethyl acetate, propyl acetate, methyl propionate and the like. 5) Cyclic ether: Specific examples thereof include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like. 6) Chain ether: Specific examples thereof include dimethoxyethane and dimethoxymethane. 7) Sulfur-containing organic solvent: Specific examples thereof include sulfolane and diethyl sulfone.

These may be used alone or in combination of two or more, but it is preferable to use two or more compounds in combination. For example, it is preferable to use a high dielectric constant solvent such as cyclic carbonates and cyclic esters and a low viscosity solvent such as chain carbonates and chain esters in combination.

One of the preferable combinations of the non-aqueous solvent is a combination mainly composed of cyclic carbonates and chain carbonates. Among them, the total of the cyclic carbonates and the chain carbonates in the non-aqueous solvent is 80% by volume or more, preferably 85% by volume or more, and more preferably 90% by volume or more. Further, the volume of the cyclic carbonates with respect to the total of the cyclic carbonates and the chain carbonates is 5% or more, preferably 10% or more, more preferably 15% or more, and usually 50% or less, preferably 35% or less. More preferably, it is 30% or less. It is particularly preferable that the above-mentioned preferable volume range of the total amount of carbonates in the whole non-aqueous solvent and the above-mentioned preferable volume range of cyclic carbonates relative to cyclic and chain carbonates are combined. It is preferable to use a combination of these non-aqueous solvents because the cycle characteristics of the battery produced using the combination and the high temperature storage characteristics (particularly, the residual capacity after high temperature storage and the high load discharge capacity) are well balanced.

Specific examples of preferable combinations of cyclic carbonates and chain carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate. And ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate and the like. A combination in which propylene carbonate is further added to the combination of these ethylene carbonates and chain carbonates is also mentioned as a preferable combination. When propylene carbonate is contained, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99: 1 to 40:60, particularly preferably 95: 5 to 50:50. Furthermore, propi in the whole non-aqueous solvent The amount of len carbonate should be 0.1% by volume or more, preferably 1% by volume, more preferably 2 volumes. Amount% or more, usually 10% by volume or less, preferably 8% by volume or less, more preferably 5% by volume or less Then, the characteristics of the combination of ethylene carbonate and chain carbonates were maintained. As it is, it is preferable because it has excellent low temperature characteristics.

Among these, those containing asymmetric chain carbonates are more preferable, and in particular, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl. Those containing ethylene carbonate such as methyl carbonate, symmetrical chain carbonates and asymmetric chain carbonates are preferable because they have a good balance between cycle characteristics and large current discharge characteristics. Among them, those in which the asymmetric chain carbonates are ethyl methyl carbonates are preferable, and the alkyl groups constituting the dialkyl carbonates preferably have 1 to 2 carbon atoms.

Another example of a preferred non-aqueous solvent is one containing a chain ester. In particular, those containing a chain ester in the above-mentioned mixed solvent of cyclic carbonates and chain carbonates are preferable from the viewpoint of improving the low temperature characteristics of the battery, and methyl acetate and ethyl acetate are particularly preferable as the chain ester. preferable. The volume of the chain ester in the non-aqueous solvent is usually 5% or more, preferably 8% or more, more preferably 15% or more, usually 50% or less, preferably 35% or less, more preferably 30% or less, More preferably, it is 25% or less.

Examples of other preferred non-aqueous solvents are from one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone, or from two or more organic solvents selected from the group. The mixed solvent occupies 60% by volume or more of the whole. Such a mixed solvent preferably has a flash point of 50 ° C. or higher, and particularly preferably 70 ° C. or higher. A non-aqueous electrolyte solution using this solvent reduces evaporation and leakage of the solvent even when used at a high temperature. Among them, those in which the amount of γ-butyrolactone in the non-aqueous solvent is 60% by volume or more, and the total of ethylene carbonate and γ-butyrolactone in the non-aqueous solvent is 80% by volume or more, preferably 90% by volume or more. Yes, and the volume ratio of ethylene carbonate to γ-butyrolactone is 5:95 to 45:55, or the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 80% by volume or more, preferably 90% by volume. If a solvent having a volume ratio of% or more and a volume ratio of ethylene carbonate to propylene carbonate of 30:70 to 60:40 is used, the balance between cycle characteristics and large current discharge characteristics is generally improved.

[Hydrogen fluoride (HF)] LiPF in a non-aqueous solvent as described above₆In many cases, hydrogen fluoride (HF) is contained in a non-aqueous electrolyte solution in which a fluorine-containing lithium salt such as the above is dissolved. Causes of hydrogen fluoride (HF) content include those derived from impurities in the fluorine-containing lithium salt and those produced by the reaction of a trace amount of water or alcohol in a non-aqueous solvent with the fluorine-containing lithium salt. .. In Patent Document 3 described above, it is said that hydrogen fluoride (HF) in the non-aqueous electrolyte solution needs to be removed as much as possible, particularly preferably 15 ppm or less, and in the examples, the cycle characteristics of the non-aqueous electrolyte solution of 9 ppm are The best result was obtained.

In the case of the present invention, the content of hydrogen fluoride (HF) is usually 10 ppm or more, preferably 12 ppm or more, particularly preferably 15 ppm or more, further preferably 20 ppm or more, and usually 300 ppm or less, preferably 250 ppm or less, particularly. It is preferably 200 ppm or less, more preferably 150 ppm or less. If the content is too low, the effect of improving the output may be insufficient, and if the content exceeds this range, the output and the cycle characteristics may be adversely affected.

&lt;Method of containing hydrogen fluoride (HF)&gt; In order to contain hydrogen fluoride (HF), it may be added directly to a non-aqueous electrolyte solution or a non-aqueous solvent as a raw material, or it may be non-aqueous by utilizing the reaction of water or alcohols with a fluorine-containing lithium salt. It may be generated inside the electrolytic solution, and for that purpose, a method such as adding water or alcohols to the non-aqueous electrolytic solution or preliminarily containing these components in a non-aqueous solvent of the raw material at an appropriate concentration is used. be able to. In this case, it may take a certain amount of time to complete the reaction. That is, when a fluorine-containing lithium salt is dissolved in a non-aqueous solvent containing water or alcohols and an electrolytic solution containing a specific compound is prepared, it takes time for the reaction between water or alcohols and the fluorine-containing lithium salt to be completed. However, when using this for manufacturing a battery, it is not always necessary to wait for the completion of the reaction. In the present invention, hydrogen fluoride (HF) in a specific concentration range may be present when functioning as a battery, and may be generated in the battery. When hydrogen fluoride (HF) is generated in the non-aqueous solvent of the raw material, hydrogen fluoride (HF) is generated in a part of the non-aqueous solvent used as the raw material, and water and alcohols are contained in it. It is also possible to mix non-aqueous solvents.

When water or alcohols are contained in the non-aqueous solvent in advance, depending on the purity of the solvent used, more water or alcohols than required may be contained from the beginning. In that case, it is preferable to purify the non-aqueous solvent by a method such as adsorption treatment, distillation, or crystallization to remove water and alcohols before use. A non-aqueous solvent in which water or alcohol is removed and a predetermined amount of water or alcohol remains may be used as it is, or water or alcohol may be mixed with a purified non-aqueous solvent so as to have a predetermined amount. You may.

The adsorption treatment can be carried out in a liquid state, and can be dissolved in a non-aqueous solvent such as alumina, activated carbon, silica gel, Molecular Sieves (trade name) 4A and / or Molecular Sieves 5A, or reacted with a non-aqueous solvent. It can be purified with an adsorbent that does not drip. In this case, raw materials that are liquid at room temperature, such as dimethyl carbonate, can be individually purified, but raw materials that are solid at room temperature, such as ethylene carbonate, are also mixed with other raw materials to make a liquid, and are collectively purified. You can also do it. Examples of the contact method include a method of continuously passing a non-aqueous solvent through the liquid (hereinafter referred to as a continuous method), or a method of adding an adsorbent to the non-aqueous solvent and allowing it to stand or agitate (hereinafter referred to as a batch method). Be done. In the case of the continuous method, the contact time is preferably 0.1 to 5 / hour as the liquid space velocity (LHSV). The contact temperature is preferably 10 to 60 ° C. In the case of the batch method, it is preferable to add 0.1 to 30% by mass of the adsorbent to the non-aqueous solvent and treat for 0.25 hours to 24 hours.

Further, a raw material that is solid at room temperature, such as ethylene carbonate, can be subjected to a crystallization treatment. Crystallization can be carried out using solvents such as acetonitrile, acetone and toluene.

It is preferable to appropriately adjust such purification conditions according to the type and purity of the raw material used and the content of the target water or alcohol.

[Water, alcohol] In producing the non-aqueous electrolyte solution of the present invention without adding hydrogen fluoride (HF), water or alcohols are contained in the non-aqueous solvent used for the non-aqueous electrolyte solution. That is, it is used with water or alcohol added, or used without removing water or alcohol. Alcohols, particularly monohydric or divalent alcohols, are preferably contained. The alcohols are not particularly limited, and the type of alkyl group and the valence of the alcohol are not particularly limited. Specifically, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, etc. Monoalcohols such as t-butyl alcohol; diols such as ethylene glycol and propylene glycol; triols such as glycerin and the like are preferable. Particularly preferable "water and alcohols" to be added include methyl alcohol, ethyl alcohol, ethylene glycol, propylene glycol and the like.

It is industrially preferable to use alcohols mixed due to the manufacturing process or the like as the non-aqueous solvent for the electrolytic solution to be used from the viewpoint of productivity, cost and the like. Methyl alcohol, ethyl alcohol, ethylene glycol or propylene glycol are particularly preferred as they may be contained in the preferred non-aqueous solvent used.

The non-aqueous solvent used in the non-aqueous electrolyte solution of the present invention is 3 ppm or more, preferably 10 ppm or more, particularly preferably 20 ppm or more, further preferably 30 ppm or more, and the upper limit is 150 ppm or less, preferably 130 ppm or less, particularly preferably 120 ppm. Below, it is more preferable that water and alcohols of 100 ppm or less are contained. If the content of water or alcohols in the non-aqueous solvent is too small, the high output characteristics characteristic of the present invention may not be sufficiently obtained, and if it is too large, the cycle characteristics and high temperature storage characteristics may deteriorate. There is

Of these, the monoalcohols are preferably 5 ppm or more, particularly preferably 10 ppm or more, further preferably 15 ppm or more, preferably 100 ppm or less, particularly preferably 80 ppm or less, still more preferably 50 ppm or less in a non-aqueous solvent. is there. The diols are 3 ppm or more, preferably 10 ppm or more, particularly preferably 15 ppm or more, further preferably 20 ppm or more, preferably 100 ppm or less, particularly preferably 90 ppm or less, more preferably 80 ppm or less, and further in a non-aqueous solvent. It is preferably 70 ppm or less. The amount of water in a non-aqueous solvent is 3 ppm or more, preferably 5 ppm or more, particularly preferably 10 ppm or more, preferably 100 ppm or less, particularly preferably 80 ppm or less, and further preferably 70 ppm or less.

[Specific compound] The non-aqueous electrolyte solution of the present invention includes a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and SF in the molecule. At least one compound selected from the group consisting of a compound having a bond, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate and a propionate (hereinafter, these are referred to as "specific compounds"). It is characterized by containing (may be abbreviated).

[[Cyclic siloxane compound represented by general formula (1)]] R in the cyclic siloxane compound represented by the general formula (1)¹And R²Are organic groups with 1 to 12 carbon atoms that may be the same or different from each other, but R¹And R²Chain alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group and t-butyl group; cyclic alkyl group such as cyclohexyl group and norbornanyl group; Alkenyl groups such as vinyl group, 1-propenyl group, allyl group, butenyl group, 1,3-butadienyl group; alkynyl group such as ethynyl group, propynyl group, butynyl group; alkyl halide group such as trifluoromethyl group; 3 -Alkyl group having a saturated heterocyclic group such as pyrrolidinopropyl group; aryl group such as phenyl group which may have an alkyl substituent; aralkyl group such as phenylmethyl group and phenylethyl group; tri such as trimethylsilyl group Alkylsilyl group; Trialkylsiloxy group such as trimethylsiloxy group and the like can be mentioned.

Among them, those having a small number of carbon atoms are more likely to exhibit characteristics, and an organic group having 1 to 6 carbon atoms is preferable. In addition, the alkenyl group acts on the non-aqueous electrolyte solution and the coating film on the electrode surface to improve the input / output characteristics, and the aryl group has the effect of capturing radicals generated in the battery during charging and discharging to improve the overall battery performance. Therefore, it is preferable. Therefore, R¹And R²A methyl group, a vinyl group or a phenyl group is particularly preferable.

In the general formula (1), n represents an integer of 3 to 10, but an integer of 3 to 6 is preferable, and 3 or 4 is particularly preferable.

Examples of the cyclic siloxane compound represented by the general formula (1) include hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane, hexaphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5. -Cyclotrisiloxane such as trivinylcyclotrisiloxane, cyclotetrasiloxane such as octamethylcyclotetrasiloxane, cyclopentasiloxane such as decamethylcyclopentasiloxane, and the like can be mentioned. Of these, cyclotrisiloxane is particularly preferable.

[[Fluorosilane compound represented by the general formula (2)]] R in the fluorosilane compound represented by the general formula (2)³~ R⁵Is an organic group having 1 to 12 carbon atoms which may be the same or different from each other, but R in the general formula (1)¹And R²Examples of the above-mentioned chain alkyl group, cyclic alkyl group, alkenyl group, alkynyl group, alkyl halide group, alkyl group having a saturated heterocyclic group, aryl group such as phenyl group which may have an alkyl group, In addition to aralkyl group, trialkylsilyl group, trialkylsiloxy group, carbonyl group such as ethoxycarbonylethyl group; carboxyl group such as acetoxy group, acetoxymethyl group, trifluoroacetoxy group; methoxy group, ethoxy group, propoxy group, butoxy Examples include an oxy group such as a group, a phenoxy group and an allyloxy group; an amino group such as an allylamino group; and a benzyl group.

In the general formula (2), x represents an integer of 1 to 3, p, q and r each represent an integer of 0 to 3, and 1 p + q + r 3. Also, x + p + q + r = 4.

Examples of the fluorosilane compound represented by the general formula (2) include trimethylfluorosilane, triethylfluorosilane, tripropylfluorosilane, phenyldimethylfluorosilane, triphenylfluorosilane, vinyldimethylfluorosilane, vinyl diethylfluorosilane, and the like. In addition to monofluorosilanes such as vinyldiphenylfluorosilane, trimethoxyfluorosilane, and triethoxyfluorosilane, difluorosilanes such as dimethyldifluorosilane, diethyldifluorosilane, divinyldifluorosilane, and ethylvinyldifluorosilane; methyltrifluorosilane, Examples thereof include trifluorosilanes such as ethyl trifluorosilane.

If the boiling point of the fluorosilane compound represented by the general formula (2) is low, it may volatilize, making it difficult to contain a predetermined amount in the non-aqueous electrolyte solution. Further, even after being contained in a non-aqueous electrolyte solution, there is a possibility that the battery may volatilize under conditions such as heat generation of the battery due to charging and discharging and high temperature of the external environment. Therefore, those having a boiling point of 50 ° C. or higher at 1 atm are preferable, and those having a boiling point of 60 ° C. or higher are particularly preferable.

Further, as with the compound of the general formula (1), the organic group having a small number of carbon atoms is more likely to exhibit the effect, and the alkenyl group having 1 to 6 carbon atoms acts on the non-aqueous electrolyte solution and the coating film on the electrode surface. The aryl group has the effect of capturing radicals generated in the battery during charging and discharging to improve the overall battery performance. Therefore, from this viewpoint, the organic group is preferably a methyl group, a vinyl group or a phenyl group, and examples of the compound are particularly preferably trimethylfluorosilane, vinyl dimethyl fluorosilane, phenyl dimethyl fluoro silane, vinyl diphenyl fluoro silane and the like. ..

[[Compound represented by general formula (3)]] R in the compound represented by the general formula (3)⁶~ R⁸Is an organic group having 1 to 12 carbon atoms which may be the same or different from each other. As an example, R in the general formula (2)³~ R⁵Examples of the above-mentioned chain alkyl group, cyclic alkyl group, alkenyl group, alkynyl group, alkyl halide group, alkyl group having a saturated heterocyclic group, aryl group such as phenyl group which may have an alkyl group, The aralkyl group, trialkylsilyl group, trialkylsiloxy group, carbonyl group, carboxyl group, oxy group, amino group, benzyl group and the like can be similarly mentioned.

A in the compound represented by the general formula (3) is not particularly limited as long as it is a group composed of H, C, N, O, F, S, Si and / or P, but the general formula (3) As the element directly bonded to the oxygen atom inside, C, S, Si or P is preferable. Examples of the existing form of these atoms include a chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, an alkyl halide group, a carbonyl group, a sulfonyl group, a trialkylsilyl group, a phosphoryl group, a phosphinyl group and the like. Is preferable. The molecular weight of the compound represented by the general formula (3) is preferably 1000 or less, particularly preferably 800 or less, and even more preferably 500 or less.

Examples of the compound represented by the general formula (3) include siloxane compounds such as hexamethyldisiloxane, 1,3-diethyltetramethyldisiloxane, hexaethyldisiloxane, and octamethyltrisiloxane; methoxytrimethylsilane and ethoxy. Alkoxysilanes such as trimethylsilane; peroxides such as bis (trimethylsilyl) peroxide; carboxylic acid esters such as trimethylsilyl acetate, triethylsilyl acetate, trimethylsilyl propionate, trimethylsilyl methacrylate, trimethylsilyl trifluoroacetate; methanesulfonic acid Sulfate esters such as trimethylsilyl, trimethylsilyl ethanesulfonate, triethylsilyl methanesulfonate, trimethylsilyl fluoromethanesulfonate; sulfate esters such as bis (trimethylsilyl) sulfate; borate esters such as tris (trimethylsiloxy) boron; tris Examples thereof include phosphates such as (trimethylsilyl) phosphate and tris (trimethylsilyl) phosphite, or phosphite esters.

Of these, siloxane compounds, sulfonic acid esters, and sulfate esters are preferable, and sulfonic acid esters are particularly preferable. Hexamethyldisiloxane is preferable as the siloxane compound, trimethylsilyl methanesulfonic acid is preferable as the sulfonic acid ester, and bis (trimethylsilyl) sulfate is preferable as the sulfate ester.

[[Compound with SF bond in the molecule]] The compound having an SF bond in the molecule is not particularly limited, but sulfonyl fluorides and fluorosulfonic acid esters are preferable. For example, methanesulfonyl fluoride, ethanesulfonylfluoride, methanebis (sulfonylfluoride), ethane-1,2-bis (sulfonylfluoride), propane-1,3-bis (sulfonylfluoride), butane-1,4 -Bis (sulfonyl fluoride), difluoromethane bis (sulfonyl fluoride), 1,1,2,2-tetrafluoroethane-1,2-bis (sulfonyl fluoride), 1,1,2,2,3, Examples thereof include 3-hexafluoropropane-1,3-bis (sulfonyl fluoride), methyl fluorosulfonate, ethyl fluorosulfonate and the like. Of these, methanesulfonyl fluoride, methanebis (sulfonyl fluoride) or methyl fluorosulfonate are preferred.

[[Nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate]] The counter cations of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, and propionate are not particularly limited, but metal elements such as Li, Na, K, Mg, Ca, Fe, and Cu. Besides, NR⁹R¹⁰R¹¹R¹²(In the formula, R⁹~ R¹²Independently represent a hydrogen atom or an organic group having 1 to 12 carbon atoms. ), Ammonium and quaternary ammonium can be mentioned. Where R⁹~ R¹²Examples of the organic group having 1 to 12 carbon atoms include an alkyl group which may be substituted with a halogen atom, a cycloalkyl group which may be substituted with a halogen atom, an aryl group which may be substituted with a halogen atom, and nitrogen. Examples include atomic-containing heterocyclic groups. R⁹~ R¹²As, hydrogen atom, alkyl group, cycloalkyl group, nitrogen atom-containing heterocyclic group and the like are preferable. Among these counter cations, lithium, sodium, potassium, magnesium, calcium or NR from the viewpoint of battery characteristics when used in a lithium secondary battery.⁹R¹⁰R¹¹R¹²Is preferable, and lithium is particularly preferable. Further, among them, nitrate or difluorophosphate is preferable in terms of battery cycle and high temperature storage characteristics, in addition to having a large output improving effect, and lithium difluorophosphate is particularly preferable. Further, as these compounds, those synthesized in a non-aqueous solvent may be used substantially as they are, and those synthesized separately and substantially isolated may be used in a non-aqueous solvent or a non-aqueous electrolyte solution. May be added to.

Specific compounds, that is, cyclic siloxane compounds represented by the general formula (1), fluorosilane compounds represented by the general formula (2), compounds represented by the general formula (3), and compounds having an SF bond in the molecule. , Nitrite, nitrite, monofluorophosphate, difluorophosphate, acetate or propionate may be used alone, or two or more compounds may be used in combination in any combination and ratio. May be good. Further, among the specific compounds classified into each of the above, one type may be used alone, or two or more types of compounds may be used in combination in any combination and ratio.

The ratio of these specific compounds in the non-aqueous electrolyte solution is essential to be 10 ppm or more (0.001% by mass or more) in total with respect to the total non-aqueous electrolyte solution, but is preferably 0.01% by mass or more, more preferably 0.05% by mass. % Or more, more preferably 0.1% by mass or more. The upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and further preferably 3% by mass or less. If the concentration of the specific compound is too low, it may be difficult to obtain the effect of improving the low temperature characteristics, while if the concentration is too high, the charge / discharge efficiency may decrease.

Further, when these specific compounds are actually used as a non-aqueous electrolyte solution for manufacturing a secondary battery, even if the battery is disassembled and the non-aqueous electrolyte solution is taken out again, the content in the non-aqueous electrolyte solution is significantly reduced. There are many. Therefore, those in which at least the above-mentioned specific compound can be detected from the non-aqueous electrolyte solution extracted from the battery are considered to be included in the present invention.

When the above-mentioned constant amount of hydrogen fluoride (HF) and such a specific compound coexist in a non-aqueous electrolyte solution, it is possible to improve the output of the lithium secondary battery without adversely affecting the cycle characteristics. ..

In the non-aqueous electrolyte solution of the present invention, the reason why the coexistence of a certain amount of hydrogen fluoride (HF) and a specific compound improves the output without adversely affecting the cycle characteristics is not clear, but it is considered as follows. .. The present invention is not limited to the following principle of action. That is, the specific compound may have a certain degree of output characteristic improving effect regardless of the content of hydrogen fluoride (HF). It is considered that this is because the specific compound exerts some action on the electrodes of the battery and reduces the reaction resistance involved in the deinsertion and insertion of lithium ions. Here, hydrogen fluoride (HF) may play a role in reinforcing or mediating this effect. For example, the specific compound and hydrogen fluoride (HF) act together on the electrode, or hydrogen fluoride (HF) plays an intermediary role when the specific compound acts on the electrode. In addition, hydrogen fluoride (HF) given the role in this way can be stably present in the battery, and it is considered that it is less likely to have an adverse effect such as deterioration of cycle characteristics.

[Other compounds] The non-aqueous electrolyte solution of the present invention contains a fluorine-containing lithium salt as an electrolyte and a specific compound as essential components in a non-aqueous solvent containing a specific amount of hydrogen fluoride (HF), but other components may be required. The compound can be contained in any amount as long as the effects of the present invention are not impaired. Specific examples of such other compounds include, for example, (1) Aromatic compounds such as biphenyl, alkylbiphenyl, tarphenyl, partially hydride of tarphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluoro Partially fluorinated compounds of the aromatic compounds such as benzene and p-cyclohexylfluorobenzene; fluorine-containing anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole and 3,5-difluoroanisole Anti-charge agents such as compounds; (2) Vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride, etc. Negative film forming agent; (3) Ethylene sulfite, propylene sulfite, dimethyl sulfone, propane sulton, butane sulton, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulforan, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sul Positive protective agents such as foxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide; And so on.

As the overcharge inhibitor, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, a partially hydride of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran are preferable. These may be used in combination of two or more types. When two or more kinds are used in combination, it is particularly preferable to use cyclohexylbenzene or terphenyl (or a partially hydrogenated product thereof) in combination with t-butylbenzene or t-amylbenzene.

As the negative electrode film forming agent, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, succinic anhydride, and maleic anhydride are preferable. These may be used in combination of two or more types. As the positive electrode protective agent, sulfite ethylene sulfite propylene, propane sultone, butane sultone, methyl methanesulfonate, Busurufa is down preferred. These may be used in combination of two or more types. Further, it is particularly preferable to use the negative electrode film forming agent and the positive electrode protective agent in combination, or the overcharge inhibitor, the negative electrode film forming agent and the positive electrode protective agent in combination.

The content ratio of these other compounds in the non-aqueous electrolyte solution is not particularly limited, but is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, and further preferably 0.2% by mass with respect to the entire non-aqueous electrolyte solution. % Or more, and the upper limit is preferably 5% by mass or less, particularly preferably 3% by mass or less, and further preferably 2% by mass or less. By adding these compounds, it is possible to suppress the explosion and ignition of the battery in the event of an abnormality due to overcharging, and to improve the capacity maintenance characteristics and cycle characteristics after high temperature storage.

&lt;Non-aqueous electrolyte secondary battery&gt; The non-aqueous electrolyte secondary battery of the present invention will be described in detail below.

[Battery shape] The shape of the battery is not particularly limited, and examples thereof include a bottomed tubular shape, a bottomed square shape, a thin shape, a sheet shape, and a paper shape. When incorporated into a system or device, it may have a horseshoe shape, a comb shape, or the like in consideration of fitting into a peripheral system arranged around the battery in order to improve volumetric efficiency and storability. .. From the viewpoint of efficiently releasing the heat inside the battery to the outside, a square shape having at least one surface that is relatively flat and has a large area is preferable.

Since the outer surface area of the battery to be filled with the bottomed tubular shape is small, it is preferable to design the battery to efficiently escape the Joule heat generated by the internal resistance during charging and discharging. Further, it is preferable to design so that the filling ratio of the substance having high thermal conductivity is increased and the internal temperature distribution is reduced.

In the bottomed square shape, the area S of the largest surface (the product of the width and height of the external dimensions excluding the terminal part, unit cm²) To the thickness T (unit: cm) of the outer shape of the battery. The value of 2S / T is preferably 100 or more, and more preferably 200 or more. By enlarging the maximum surface, it is possible to improve the characteristics such as cycle performance and high temperature storage even with a high output and large capacity battery, and also to improve the heat dissipation efficiency at the time of abnormal heat generation, "valve operation" and "burst It is possible to suppress the dangerous state of ".

[Battery configuration] The chargeable and dischargeable secondary battery of the present invention includes a positive electrode and a negative electrode capable of storing and discharging lithium ions, the non-aqueous electrolyte solution of the present invention, a separator disposed between the positive electrode and the negative electrode, a current collecting terminal, and an exterior. It is composed of at least a case and the like. If necessary, a protective element may be mounted inside the battery and / or outside the battery.

[Positive electrode] The positive electrode used in the non-aqueous electrolyte secondary battery of the present invention will be described below. [[Positive electrode active material]] The positive electrode active material used for the positive electrode will be described below. [[[composition]]] The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. A substance containing lithium and at least one transition metal is preferable, and examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphoric acid compound.

V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable as the transition metal of the lithium transition metal composite oxide, and LiCoO is a specific example.₂Lithium-cobalt composite oxide, such as LiNiO₂Lithium-nickel composite oxide, LiMnO, etc.₂, LiMn₂O₄, Li₂MnO₃Lithium-manganese composite oxides such as, and some of the transition metal atoms that are the main constituents of these lithium transition metal composite oxides are Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Examples thereof include those substituted with other metals such as Mg, Ga, Zr, and Si. Specific examples of the substituted ones include, for example, LiNi._0.5Mn_0.5O₂, LiNi_0.85Co_0.10Al_0.05O₂, LiNi_0.33Co_0.33Mn_0.33O₂, LiMn_1.8Al_0.2O₄, LiMn_1.5Ni_0.5O₄And so on.

As the transition metal of the lithium-containing transition metal phosphoric acid compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable, and specific examples thereof include LiFePO.₄, Li₃Fe₂(PO₄)₃, LiFeP₂O₇Iron phosphates such as LiCoPO₄Cobalts such as cobalt phosphates, some of the transition metal atoms that are the main constituents of these lithium transition metal phosphate compounds are Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, etc. Examples thereof include those substituted with other metals such as Ga, Zr, Nb, and Si.

[[[Surface coating]]] Further, it is also possible to use a substance having a composition different from that of the substance constituting the main positive electrode active material attached to the surface of the positive electrode active material. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide and other oxides, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate. , Sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate and the like.

These surface adhering substances are, for example, dissolved or suspended in a solvent and impregnated with the positive electrode active material and dried, or the surface adhering substance precursor is dissolved or suspended in the solvent and impregnated with the positive electrode active material and then heated. It can be attached to the surface of the positive electrode active material by a method of reacting with the above, a method of adding to the positive electrode active material precursor and firing at the same time, or the like.

The amount of the surface adhering substance is preferably 0.1 ppm or more, more preferably 1 ppm or more, further preferably 10 ppm or more, and the upper limit is preferably 20 mass% or less, more preferably 10 by mass with respect to the positive electrode active material. It is used in an amount of mass% or less, more preferably 5 mass% or less. The surface-adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material and improve the battery life, but if the adhering amount is too small, the effect is not sufficiently exhibited. If it is too much, the resistance may increase because it inhibits the ingress and egress of lithium ions.

[[[shape]]] As the shape of the positive electrode active material particles in the present invention, lumps, polyhedrons, spheres, elliptical spheres, plates, needles, columns, etc., which are conventionally used, are used. Among them, the primary particles are aggregated and secondary. It is preferable that the particles are formed and the shape of the secondary particles is spherical or elliptical spherical. Normally, in an electrochemical element, the active material in the electrode expands and contracts with the charge and discharge, so that the stress tends to cause deterioration such as destruction of the active material and breakage of the conductive path. Therefore, it is preferable that the primary particles aggregate to form the secondary particles rather than the single particle active material containing only the primary particles because the stress of expansion and contraction is alleviated and deterioration is prevented. In addition, since spherical or elliptical spherical particles have less orientation during molding than plate-shaped equiaxed particles, the expansion and contraction of the electrode during charging and discharging is also smaller, and the electrode is created. It is also preferable to mix it with the conductive material because it is easy to mix uniformly.

[[[Tap Density]]] The tap density (bulk density) of the positive electrode active material is usually 1.3 g / cm.³Above, preferably 1.5 g / cm³Above, more preferably 1.6 g / cm³Above, most preferably 1.7 g / cm³That is all. When the tap density of the positive electrode active material is less than the above lower limit, the amount of dispersion medium required for forming the positive electrode active material layer increases, and the required amount of the conductive material and the binder increases, so that the positive electrode activity on the positive electrode active material layer increases. The filling rate of the material is restricted, and the battery capacity may be restricted. By using the metal composite oxide powder having a high tap density, a high density positive electrode active material layer can be formed. Generally, the larger the tap density is, the more preferable it is, and there is no particular upper limit. However, if it is too large, the diffusion of lithium ions through the non-aqueous electrolyte solution as a medium in the positive electrode active material layer becomes rate-determining, and the load characteristics may easily deteriorate. , Usually 2.5g / cm³Below, preferably 2.4 g / cm³It is as follows.

In the present invention, the tap density is 20 cm after passing through a sieve having a mesh size of 300 μm.³After dropping the sample into the tapping cell of No. 1 to fill the cell volume, tapping with a stroke length of 10 mm was performed 1000 times using a powder density measuring instrument (for example, a tap denser manufactured by Seishin Enterprise Co., Ltd.) to obtain the volume at that time. The density obtained from the weight of the sample is defined as the tap density.

[[[Median diameter d₅₀]]] Particle median diameter d₅₀(Secondary particle diameter when primary particles are aggregated to form secondary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, most preferably 3 μm or more, and the upper limit is , Usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, most preferably 15 μm or less. If it falls below the above lower limit, a high tap density product may not be obtained, and if it exceeds the upper limit, it takes time to diffuse lithium in the particles, resulting in deterioration of battery performance or making a positive electrode for the battery, that is, as an active material. When a conductive material, a binder, or the like is slurried with a solvent and applied in a thin film form, problems such as streaks may occur. Where different median diameter d₅₀By mixing two or more types of positive electrode active materials having a positive electrode, the filling property at the time of producing a positive electrode can be further improved.

The median diameter d in the present invention₅₀Is measured by a known laser diffraction / scattering particle size distribution measuring device. When LA-920 manufactured by HORIBA is used as the particle size distribution meter, 0.1 mass% sodium hexametaphosphate aqueous solution is used as the dispersion medium used for the measurement, and the measured refractive index is set to 1.24 after ultrasonic dispersion for 5 minutes. To.

[[[Average primary particle size]]] When the primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, and most preferably 0.08 μm or more. It is 0.1 μm or more, and the upper limit is usually 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. If it exceeds the above upper limit, it is difficult to form spherical secondary particles, which adversely affects the powder filling property and greatly reduces the specific surface area, so that there is a high possibility that the battery performance such as output characteristics will deteriorate. is there. On the contrary, if it falls below the above lower limit, problems such as inferior reversibility of charge / discharge may occur because the crystal is usually underdeveloped.

The primary particle size is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph with a magnification of 10000 times, the longest value of the intercept by the left and right boundary lines of the primary particles with respect to the horizontal straight line is obtained for any 50 primary particles, and the average value is obtained. Be done.

[[[BET specific surface area]]] The BET specific surface area of the positive electrode active material used in the secondary battery of the present invention is 0.2 m.²/ g or more, preferably 0.3m²/ G or more, more preferably 0.4m²Above / g, upper limit is 4.0m²/ G or less, preferably 2.5m²/ G or less, more preferably 1.5m²It is less than / g. If the BET specific surface area is smaller than this range, the battery performance tends to deteriorate, and if it is large, the tap density does not easily increase, and a problem may easily occur in the coatability at the time of forming the positive electrode active material.

The BET specific surface area is determined by using a surface meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken) to pre-dry the sample at 150 ° C for 30 minutes under nitrogen flow, and then the relative pressure of nitrogen with respect to atmospheric pressure. It is defined by the value measured by the nitrogen adsorption BET 1-point method by the gas flow method using a nitrogen-helium mixed gas accurately adjusted so that the value of is 0.3.

[[[Manufacturing method]]] As a method for producing a positive electrode active material, a general method is used as a method for producing an inorganic compound. In particular, various methods can be considered for producing spherical or elliptical spherical active materials. For example, transition metal raw materials such as transition metal nitrates and transition metal sulfates and, if necessary, raw materials of other elements are used as water. Dissolve or pulverize and disperse in a solvent such as, etc., adjust the pH while stirring to prepare and recover a spherical precursor, dry it if necessary, and then LiOH, Li.₂CO₃, LiNO₃A method of adding a Li source such as, and firing at a high temperature to obtain an active material, a transition metal raw material such as a transition metal nitrate, a transition metal sulfate, a transition metal hydroxide, a transition metal oxide, and other materials as required. The raw material of the element is dissolved or pulverized and dispersed in a solvent such as water, and dried and molded with a spray dryer or the like to form a spherical or elliptical spherical precursor, which is then LiOH or Li.₂CO₃, LiNO₃A method of adding a Li source such as, etc. and firing at a high temperature to obtain an active material, a transition metal raw material such as a transition metal nitrate, a transition metal sulfate, a transition metal hydroxide, a transition metal oxide, and LiOH, Li.₂CO₃, LiNO₃Li source such as, and if necessary, raw materials of other elements are dissolved or pulverized and dispersed in a solvent such as water, and dried and molded with a spray dryer or the like to obtain a spherical or elliptical precursor. A method of obtaining an active material by firing at a high temperature can be mentioned.

[[Positive electrode configuration]] The configuration of the positive electrode used in the present invention will be described below. [[[Electrode structure and fabrication method]]] The positive electrode is produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be produced by a conventional method. That is, a positive electrode active material, a binder, and if necessary, a conductive material, a thickener, and the like are mixed in a dry manner to form a sheet, which is then pressure-bonded to the positive electrode current collector, or these materials are used as a liquid medium. A positive electrode can be obtained by forming a positive electrode active material layer on the current collector by applying the slurry as a slurry to the positive electrode current collector and drying the slurry.

The positive electrode active material may be used by mixing two or more of them in advance, or may be mixed by adding them at the same time when preparing the positive electrode.

[[[Positive electrode active material]]] In the present invention, the content of the positive electrode active material used for the positive electrode in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 95% by mass or less, more preferably 93% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. On the contrary, if the content is too high, the strength of the positive electrode may be insufficient.

[[[Conductive material]]] As the conductive material, a known conductive material can be arbitrarily used. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite (graphite); carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. It should be noted that one of these may be used alone, or two or more thereof may be used in any combination and ratio.

The conductive material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the positive electrode active material layer, and the upper limit is usually 50% by mass or less, preferably 30% by mass or less. , More preferably, it is used so as to contain 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. On the contrary, if the content is higher than this range, the battery capacity may decrease.

[[[Binder]]] The binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of the coating method, any material may be used as long as it is dissolved or dispersed in the liquid medium used in the production of the electrode. , Polyethylene, Polypropylene, Polyethylene terephthalate, Polymethylmethacrylate, Polygonide, Aromatic polyamide, Cellulose, Nitrocellulose and other resin-based polymers; SBR (Styrene-butadiene rubber), NBR (Acrylonitrile-butadiene rubber), Fluoro rubber, Isoprene rubber , Butadiene rubber, rubber-like polymers such as ethylene / propylene rubber; styrene / butadiene / styrene block copolymer or hydrogen additive thereof, EPDM (ethylene-propylene-diene ternary copolymer), styrene / ethylene / butadiene Thermoplastic elastomeric polymers such as ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymers, Soft resinous polymers such as propylene / α-olefin copolymers; Fluorine polymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers; Examples thereof include a polymer composition having ionic conductivity of alkali metal ions (particularly lithium ions). In addition, as these substances, 1 type may be used alone, and 2 or more types may be used together in arbitrary combinations and ratios.

The proportion of the binder in the positive electrode active material layer is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and the upper limit is usually 80% by mass or less, preferably 60% by mass or less. , More preferably 40% by mass or less, and most preferably 10% by mass or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained, the mechanical strength of the positive electrode is insufficient, and the battery performance such as cycle characteristics may be deteriorated. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

[[[Liquid medium]]] As the liquid medium for forming the slurry, any solvent can be used as long as it can dissolve or disperse the positive electrode active material, the conductive material, the binder, and the thickener used as needed. There is no particular limitation, and either an aqueous solvent or an organic solvent may be used.

Examples of the aqueous medium include water, a mixed medium of alcohol and water, and the like. Examples of the organic medium include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; and ketones such as acetone, methylethylketone and cyclohexanone. Classes; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine, N, N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide and tetrahydrofuran (THF); N-methylpyrrolidone (NMP) , Amides such as dimethylformamide and dimethylacetamide; aprotonic polar solvents such as hexamethylphosphalamide and dimethylsulfoxide can be mentioned.

[[[Thickener]]] In particular, when an aqueous medium is used, it is preferable to use a thickener and a latex such as styrene-butadiene rubber (SBR) to form a slurry. Thickeners are commonly used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used alone or in combination of two or more in any combination and ratio. When a thickener is further added, the ratio of the thickener to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 5% by mass. It is in the range of% or less, preferably 3% by mass or less, and more preferably 2% by mass or less. Below this range, the coatability may be significantly reduced. If it exceeds, the ratio of the active material in the positive electrode active material layer decreases, which may cause a problem that the capacity of the battery decreases and a problem that the resistance between the positive electrode active materials increases.

[[[Consolidation]]] The positive electrode active material layer obtained by coating and drying is preferably consolidated by a hand press, a roller press, or the like in order to increase the packing density of the positive electrode active material. The density of the positive electrode active material layer is preferably 1.5 g / cm as the lower limit.³Above, more preferably 2 g / cm³Above, more preferably 2.2 g / cm³As mentioned above, the upper limit is preferably 3.5 g / cm.³Below, more preferably 3 g / cm³Below, more preferably 2.8 g / cm³The range is as follows. If it exceeds this range, the permeability of the non-aqueous electrolyte solution to the vicinity of the current collector / active material interface may decrease, and the charge / discharge characteristics may decrease, especially at a high current density. If it is lower than that, the conductivity between the active materials may decrease and the battery resistance may increase.

[[[Current collector]]] The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium and tantalum; carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials, especially aluminum, are preferable.

Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, foamed metal, etc. in the case of metal material, and carbon plate in the case of carbonaceous material. Examples include a carbon thin film and a carbon column. Of these, a metal thin film is preferable. The thin film may be formed in a mesh shape as appropriate. The thickness of the thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. On the contrary, if the thin film is thicker than this range, the handleability may be impaired.

The ratio of the thickness of the current collector to the positive electrode active material layer is not particularly limited, but (thickness of the active material layer on one side immediately before injection of the non-aqueous electrolyte solution) / (thickness of the current collector) is 20 or less. It is preferably 15 or less, most preferably 10 or less, and the lower limit is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during high current density charging / discharging. Below this range, the volume ratio of the current collector to the positive electrode active material may increase and the capacity of the battery may decrease.

[[[Electrode area]]] When the non-aqueous electrolyte solution of the present invention is used, the area of the positive electrode active material layer is preferably larger than the outer surface area of the battery outer case from the viewpoint of improving the stability at high output and high temperature. Specifically, the total area of the electrode areas of the positive electrode with respect to the surface area of the exterior of the secondary battery is preferably 15 times or more, and more preferably 40 times or more in terms of area ratio. The outer surface area of the outer case means the total area calculated from the vertical, horizontal, and thickness dimensions of the case part filled with the power generation element excluding the protruding part of the terminal in the case of the bottomed square shape. .. In the case of a bottomed cylindrical shape, the geometric surface area approximates the case portion filled with the power generation element excluding the protruding portion of the terminal as a cylinder. The total electrode area of the positive electrode is the geometric surface area of the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which the positive electrode mixture layer is formed on both sides via a current collector foil. , Refers to the sum of the areas calculated separately for each surface.

[[[Discharge capacity]]] When the non-aqueous electrolyte solution for a secondary battery of the present invention is used, the electric capacity of the battery element housed in the exterior of one battery of the secondary battery (the electric capacity when the battery is discharged from a fully charged state to a discharged state). ) Is 3 amper hour (Ah) or more, which is preferable because the effect of improving the low temperature discharge characteristics is large. Therefore, the positive electrode plate is preferably designed so that the discharge capacity is fully charged and is 3 amp-hours (Ah) or more and 20 Ah or less, and more preferably 4 Ah or more and 10 Ah or less. If it is less than 3Ah, the voltage drop due to the electrode reaction resistance becomes large when a large current is taken out, and the power efficiency may deteriorate. At 20Ah or higher, the electrode reaction resistance becomes smaller and the power efficiency improves, but the temperature distribution due to the internal heat generation of the battery during pulse charging / discharging is large, the durability of repeated charging / discharging is inferior, and abnormalities such as overcharging and internal short circuit occur. When the heat dissipation efficiency deteriorates due to the sudden heat generation at that time, the internal pressure rises and the gas discharge valve operates (valve operation), and the battery contents explode violently to the outside (burst). There is.

[[[Thickness of positive electrode plate]]] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer obtained by subtracting the metal leaf thickness of the core material is the thickness of the mixture layer with respect to one side of the current collector. The lower limit is preferably 10 μm or more, more preferably 20 μm or more, and the upper limit is preferably 200 μm or less, more preferably 100 μm or less.

[Negative electrode] The negative electrode used in the non-aqueous electrolyte secondary battery of the present invention will be described below. [[Negative electrode active material]] The negative electrode active material used for the negative electrode will be described below.

[[[composition]]] The negative electrode active material is not particularly limited as long as it can electrochemically store and release lithium ions, and is a carbonaceous material, a metal oxide such as tin oxide or silicon oxide, a metal composite oxide, or lithium alone. , Lithium alloys such as lithium-aluminum alloys, and metals that can be alloyed with lithium such as Sn and Si. These may be used alone or in combination of two or more in any combination and ratio. Of these, carbonaceous materials or lithium composite oxides are preferably used from the viewpoint of safety.

The metal composite oxide is not particularly limited as long as it can occlude and release lithium, but it is preferable that titanium and / or lithium is contained as a constituent component from the viewpoint of high current density charge / discharge characteristics.

As a carbonaceous material, (1) Natural graphite, (2) Artificial carbonaceous substances and artificial graphite substances; carbonaceous substances {for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or oxidation-treated pitches, needle coke, pitch. Thermal decomposition products of coke and organic substances such as furnace black, acetylene black, and pitch-based carbon fibers, carbonizable organic substances (for example, coal tar pitch from soft pitch to hard pitch, or dry distillate). Coal-based heavy oil such as oil, normal pressure residual oil, DC heavy oil of reduced pressure residual oil, crude oil, decomposition-based petroleum heavy oil such as ethylene tar produced as a by-product during thermal decomposition of naphtha, as well as acenaftylene, decacyclene, Aromatic hydrocarbons such as anthracene and phenanthrene, N-ring compounds such as phenazine and acrydin, S-ring compounds such as thiophene and bithiophene, polyphenylene such as biphenyl and terphenyl, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, and insolubilization of these Treated products, organic polymers such as nitrogen-containing polyacrylonitrile and polypyrrole, organic polymers such as sulfur-containing polythiophene and polystyrene, polysaccharides typified by cellulose, lignin, mannan, polygalactouronic acid, chitosan and saccharose. Natural polymers such as, polyphenylene sulfide, thermoplastic resins such as polyphenylene oxide, thermocurable resins such as furfuryl alcohol resin, phenol-formaldehyde resin, imide resin) and their charcoal or carbonizable organic substances are benzene and toluene. , A solution of xylene, quinoline, n-hexane or other low molecular weight organic solvents and their charcoal} heat-treated at least once in the range of 400 to 3200 ° C. (3) A carbon material in which the negative electrode active material layer is composed of at least two or more kinds of carbon substances having different crystallinities and / or has an interface in which the different crystalline carbon substances are in contact with each other. (4) A carbon material in which the negative electrode active material layer is composed of at least two kinds of carbon substances having different orientations and / or has an interface in which the carbon substances having different orientations are in contact with each other. The one selected from is preferable because it has a good balance of initial irreversible capacitance and high current density charge / discharge characteristics.

[[Construction, physical properties, preparation method of negative electrode]] Regarding the properties of carbonaceous materials, negative electrode electrodes containing carbonic materials, electrodeization methods, current collectors, and lithium ion secondary batteries, any one or more of the following items (1) to (19) It is desirable to satisfy at the same time.

(1) X-ray parameters For carbonaceous materials, the d value (interlayer distance) of the lattice planes (002 planes) determined by X-ray diffraction by the Gakushin method is preferably 0.335 nm or more, usually 0.360 nm or less, preferably 0.350 nm or less. More preferably, it is 0.345 nm or less. Further, the crystallite size (Lc) of the carbonaceous material determined by X-ray diffraction by the Gakushin method is preferably 1 nm or more, and more preferably 1.5 nm or more.

(2) Ash The ash content contained in the carbonaceous material is preferably 1% by mass or less, particularly 0.5% by mass or less, particularly 0.1% by mass or less, and the lower limit is 1 ppm or more, based on the total mass of the carbonaceous material. If it exceeds the above range, the deterioration of battery performance due to the reaction with the non-aqueous electrolyte solution during charging / discharging may not be negligible. Below this range, manufacturing requires a great deal of time, energy and pollution control equipment, which can increase costs.

(3) Volume-based average particle size As for the volume-based average particle diameter of the carbonaceous material, the volume-based average particle diameter (median diameter) obtained by the laser diffraction / scattering method is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, still more preferably 7 μm. That is all. The upper limit is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and particularly preferably 25 μm or less. Below the above range, the irreversible capacity may increase, leading to a loss of initial battery capacity. On the other hand, if it exceeds the above range, a non-uniform coating surface is likely to occur when the electrode is produced by coating, which may not be desirable in the battery manufacturing process.

In the present invention, the volume-based average particle size is a laser diffraction / scattering type particle size distribution meter in which carbon powder is dispersed in a 0.2 mass% aqueous solution (about 10 mL) of polyoxyethylene (20) sorbitan monolaurate, which is a surfactant. It is defined by the median diameter measured using (for example, LA-700 manufactured by HORIBA, Ltd.).

(4) Raman R value, Raman half width The Raman R value of the carbonaceous material measured by the argon ion laser Raman spectroscopy is usually 0.01 or more, preferably 0.03 or more, more preferably 0.10 or more, and the upper limit is 1.50 or less, preferably 1.2 or less, more preferably 1.0. Hereinafter, it is more preferably in the range of 0.50 or less. If the Raman R value falls below this range, the crystallinity of the particle surface becomes too high, and there may be fewer sites where Li enters the layers during charging and discharging. That is, the charge acceptability may decrease. Further, when the negative electrode is densified by pressing after being applied to the current collector, the crystals are likely to be oriented in the direction parallel to the electrode plate, which may lead to deterioration of the load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the non-aqueous electrolyte solution is increased, and the efficiency may be lowered and the gas generation may be increased.

Also, 1580 cm of carbonaceous material^-1The Raman half width in the vicinity is not particularly limited, but it is usually 10 cm.^-1Above, preferably 15 cm^-1Above, and as an upper limit, usually 100 cm^-1Below, preferably 80 cm^-1Below, more preferably 60 cm^-1Below, more preferably 40 cm^-1The range is as follows. If the Raman half width falls below this range, the crystallinity of the particle surface becomes too high, and there may be fewer sites where Li enters the layers during charging and discharging. That is, the charge acceptability may decrease. Further, when the negative electrode is densified by pressing after being applied to the current collector, the crystals are likely to be oriented in the direction parallel to the electrode plate, which may lead to deterioration of the load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the non-aqueous electrolyte solution is increased, and the efficiency may be lowered and the gas generation may be increased.

The Raman spectrum is measured by using a Raman spectroscope (for example, a Raman spectroscope manufactured by JASCO Corporation), the sample is naturally dropped into the measurement cell and filled, and the surface of the sample in the cell is irradiated with argon ion laser light. , By rotating the cell in a plane perpendicular to the laser beam. About the obtained Raman spectrum, 1580 cm^-1Near peak P_AStrength I_AAnd 1360 cm^-1Near peak P_BStrength I_BAnd its intensity ratio R (R = I)_B/ I_A) Is calculated and defined as the Raman R value of the carbonaceous material. Also, the obtained Raman spectrum of 1580 cm^-1Near peak P_AThe half width of the carbonaceous material is measured and defined as the Raman half width of carbonaceous materials.

The Raman measurement conditions here are as follows. Argon ion laser wavelength: 514.5 nm Laser power on sample: 15 ~ 25mW Resolution: 10 ~ 20cm^-1 Measurement range: 1100 cm^-1~ 1730cm^-1 Raman R value, half width analysis: Background processing Smoothing process: Simple average, 5 points for convolution

(5) BET specific surface area The specific surface area of the carbonaceous material of the present invention measured using the BET method is usually 0.1 m.²/ g or more, preferably 0.7m²/ g or more, more preferably 1.0 m²/ G or more, more preferably 1.5m²It is more than / g. The upper limit is usually 100m²/ G or less, preferably 25m²/ G or less, more preferably 15m²/ G or less, more preferably 10m²It is less than / g. If the value of the specific surface area is less than this range, the acceptability of lithium tends to deteriorate during charging when used as a negative electrode material, and lithium may easily precipitate on the electrode surface. On the other hand, if it exceeds this range, the reactivity with the non-aqueous electrolyte solution increases when used as the negative electrode material, gas generation tends to increase, and it may be difficult to obtain a preferable battery.

The specific surface area by the BET method is determined by pre-drying the sample with a nitrogen meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken) at 350 ° C for 15 minutes under nitrogen flow, and then nitrogen to atmospheric pressure. Use a nitrogen-helium mixed gas that is accurately adjusted so that the relative pressure value is 0.3, and use the value measured by the nitrogen adsorption BET 1-point method by the gas flow method.

(6) Pore diameter distribution The pore size distribution of the carbonaceous material is determined by Hg porosometry (mercury injection method), and the pores in the particles corresponding to the pore diameters of 0.01 μm or more and 1 μm or less, irregularities due to steps on the particle surface, and between particles The amount of the contact surface or the like is 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and the upper limit is 0.6 mL / g or less, preferably 0.4 mL / g or less, more preferably 0.3. The range is mL / g or less. If it exceeds this range, a large amount of binder may be required at the time of electrode plate formation. If it is lower than that, the high current density charge / discharge characteristics may be deteriorated, and the effect of relaxing the expansion / contraction of the electrode during charge / discharge may not be obtained.

The total pore volume corresponding to the pore diameter in the range of 0.01 μm to 100 μm is preferably 0.1 mL / g or more, more preferably 0.25 mL / g or more, further preferably 0.4 mL / g or more, and the upper limit is 10 mL / g. The range is g or less, preferably 5 mL / g or less, and more preferably 2 mL / g or less. If it exceeds this range, a large amount of binder may be required at the time of electrode plate formation. If it is lower than that, the effect of dispersing the thickener and the binder may not be obtained at the time of electrode plate formation.

The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, still more preferably 0.5 μm or more, and the upper limit is 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. Beyond this range, a large amount of binder may be required. If it is lower than that, the high current density charge / discharge characteristics may deteriorate.

A mercury porosimeter (Autopore 9520: manufactured by Micromeritex) was used as a device for mercury porosimeter. Approximately 0.2 g of the sample was sealed in a powder cell, degassed at room temperature under vacuum (50 μmHg or less) for 10 minutes, and pretreatment was performed. Subsequently, the pressure was reduced to 4 psia (about 28 kPa), mercury was introduced, the pressure was increased stepwise from 4 psia (about 28 kPa) to 40,000 psia (about 280 MPa), and then the pressure was lowered to 25 psia (about 170 kPa). The number of steps at the time of pressurization was 80 points or more, and in each step, the amount of mercury injection was measured after an equilibrium time of 10 seconds. From the mercury intrusion curve thus obtained, the pore size distribution was calculated using Washburn's formula. The surface tension (γ) of mercury was 485 dyne / cm, and the contact angle (ψ) was 140 °. For the average pore diameter, the pore diameter when the cumulative pore volume was 50% was used.

(7) Circularity Circularity is used as the degree of sphere of the carbonaceous material, and the circularity of the particles having a particle size in the range of 3 to 40 μm is preferably 0.1 or more, particularly preferably 0.5 or more, more preferably 0.8 or more, still more preferably 0.85. The above is most preferably 0.9 or more. A large circularity is preferable because the high current density charge / discharge characteristics are improved. The circularity is defined by the following formula, and when the circularity is 1, it becomes a theoretical true sphere. Circularity = (Peripheral length of an equivalent circle with the same area as the projected particle shape) / (Actual peripheral length of the projected particle shape)

As the value of circularity, for example, a flow type particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.) was used, and about 0.2 g of the sample was used, and 0.2 of the surfactant polyoxyethylene (20) sorbitan monolaurate Disperse in a mass% aqueous solution (about 50 mL), irradiate 28 kHz ultrasonic waves at an output of 60 W for 1 minute, specify the detection range to 0.6 to 400 μm, and measure the values for particles with a particle size in the range of 3 to 40 μm. Use.

The method for improving the circularity is not particularly limited, but a spherical shape obtained by subjecting it to a spherical shape is preferable because the shape of the interparticle voids when the electrode body is formed is adjusted. Examples of spheroidizing treatment include a method of mechanically approaching a sphere by applying a shearing force and a compressive force, and a mechanical / physical treatment method of granulating a plurality of fine particles by a binder or the adhesive force of the particles themselves. Can be mentioned.

(8) True density The true density of carbonaceous materials is usually 1.4 g / cm³Above, preferably 1.6 g / cm³Above, more preferably 1.8 g / cm³Above, more preferably 2.0 g / cm³That's all, and the upper limit is 2.26 g / cm.³It is as follows. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of carbon may be too low and the initial irreversible capacity may increase. In the present invention, the true density is defined as measured by the liquid phase substitution method (pycnometer method) using butanol.

(9) Tap density The tap density of carbon material is usually 0.1 g / cm³That's all, preferably 0.5g / cm³Above, more preferably 0.7 g / cm³Above, particularly preferably 1 g / cm³It is hoped that the above is the case. Also, preferably 2 g / cm³Below, more preferably, 1.8 g / cm³Below, particularly preferably 1.6 g / cm³It is as follows. If the tap density is lower than this range, the filling density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if it exceeds this range, the voids between the particles in the electrode become too small, it becomes difficult to secure the conductivity between the particles, and it may be difficult to obtain preferable battery characteristics. The tap density is measured and defined by the same method as described in the section of positive electrode active material.

(10) Orientation ratio The orientation ratio of the carbonaceous material is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically in the range of 0.67 or less. If it falls below this range, the high-density charge / discharge characteristics may deteriorate.

The orientation ratio is measured by X-ray diffraction after pressure molding the sample. Fill a molding machine with a diameter of 17 mm with 0.47 g of sample and 600 kgf / cm.²The molded body obtained by compressing with is set using clay so as to be flush with the surface of the sample holder for measurement, and X-ray diffraction is measured. From the peak intensities of (110) diffraction and (004) diffraction of the obtained carbon, the ratio expressed by (110) diffraction peak intensity / (004) diffraction peak intensity is calculated and defined as the orientation ratio of the active material.

The X-ray diffraction measurement conditions here are as follows. In addition, "2θ" indicates a diffraction angle. Target: Cu (Kα ray) graphite monochromator Slit: Divergence slit = 0.5 degrees, light receiving slit = 0.15 mm, scattering slit = 0.5 degrees Measurement range and step angle / measurement time: (110) Surface: 75 degrees 2θ 80 degrees 1 degree / 60 seconds (004) Surface: 52 degrees 2θ 57 degrees 1 degree / 60 seconds

(11) Aspect ratio (powder) The aspect ratio is theoretically 1 or more, and the upper limit is 10 or less, preferably 8 or less, and more preferably 5 or less. If it exceeds the upper limit, streaks may occur during electrode plate formation, a uniform coated surface may not be obtained, and the high current density charge / discharge characteristics may deteriorate.

The aspect ratio is expressed as A / B when the longest diameter of the carbon material particles when observed three-dimensionally is A and the shortest diameter orthogonal to it is B. Observation of carbon particles is performed with a scanning electron microscope capable of magnified observation. Select any 50 graphite particles fixed to the end face of a metal with a thickness of 50 μm or less, rotate and incline the stage on which the sample is fixed for each, measure A and B, and average the A / B. Find the value.

(12) Mixing auxiliary materials The secondary material mixture means that two or more kinds of carbonaceous materials having different properties are contained in the negative electrode and / or the negative electrode active material. The properties described here are one or more of X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, circularity, and ash content. Shows the characteristics.

Particularly preferable embodiments are that the volume-based particle size distribution is not symmetrical when centered on the median diameter, that two or more carbon materials having different Raman R values are contained, and that the X-ray parameters are different. And so on. As an example of the effect, carbonaceous materials such as natural graphite, graphite such as artificial graphite (graphite), carbon black such as acetylene black, and amorphous carbon such as needle coke are contained as a conductive material to increase electrical resistance. For example, to reduce the amount. These may be used alone or in combination of two or more in any combination and ratio. When added as a conductive material, it is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 45% by mass or less, preferably 40% by mass. If it falls below this range, it may be difficult to obtain the effect of improving conductivity. If it exceeds, the initial irreversible capacity may increase.

(13) Electrode fabrication The electrode may be manufactured by a conventional method. For example, a binder, a solvent, and if necessary, a thickener, a conductive material, a filler, etc. are added to a negative electrode active material to form a slurry, which is applied to a current collector, dried, and then pressed to form a slurry. Can be done. The thickness of the negative electrode active material layer per side at the stage immediately before the non-aqueous electrolyte injection step of the battery is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is 150 μm or less, preferably 120 μm. Hereinafter, it is more preferably 100 μm or less. If it exceeds this range, the non-aqueous electrolyte solution does not easily permeate to the vicinity of the current collector interface, so that the high current density charge / discharge characteristics may deteriorate. If it falls below this range, the volume ratio of the current collector to the negative electrode active material may increase and the capacity of the battery may decrease. Further, the negative electrode active material may be roll-molded to form a sheet electrode, or may be compression-molded to form a pellet electrode.

(14) Current collector As the current collector, a known one can be arbitrarily used. Examples of the current collector of the negative electrode include metal materials such as copper, nickel, stainless steel, and nickel-plated steel, and copper is particularly preferable from the viewpoint of ease of processing and cost. When the current collector is made of a metal material, the shape of the current collector may be, for example, a metal foil, a metal column, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, a foamed metal, or the like. Among them, a metal thin film is preferable, a copper foil is more preferable, and a rolled copper foil by a rolling method and an electrolytic copper foil by an electrolytic method are more preferable, both of which can be used as a current collector. When the thickness of the copper foil is thinner than 25 μm, a copper alloy having higher strength than pure copper (phosphor bronze, titanium copper, Corson alloy, Cu-Cr-Zr alloy, etc.) can be used.

The current collector made of copper foil produced by the rolling method is suitable for small cylindrical batteries because the copper crystals are lined up in the rolling direction and therefore it is hard to break even if the negative electrode is rounded tightly or at an acute angle. be able to. In the electrolytic copper foil, for example, a metal drum is immersed in a non-aqueous electrolytic solution in which copper ions are dissolved, and a current is passed while rotating the drum to deposit copper on the surface of the drum and peel it off. It is obtained by Copper may be deposited on the surface of the rolled copper foil by an electrolytic method. One side or both sides of the copper foil may be roughened or surface-treated (for example, chromate treatment having a thickness of several nm to 1 μm, base treatment such as Ti, etc.).

The following physical characteristics are further desired for the current collector substrate. (1) Average surface roughness (Ra) The average surface roughness (Ra) of the negative electrode active material thin film forming surface of the current collector substrate specified by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.05 μm or more, preferably 0.1 μm or more, particularly preferable. Is 0.15 μm or more, usually 1.5 μm or less, preferably 1.3 μm or less, and particularly preferably 1.0 μm or less. Good charge / discharge cycle characteristics can be expected by setting the average surface roughness (Ra) of the current collector substrate within the range between the above lower limit and upper limit. By setting the value to the above lower limit or more, the area of the interface with the negative electrode active material thin film becomes large, and the adhesion with the negative electrode active material thin film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, but a foil having an average surface roughness (Ra) of more than 1.5 μm is generally difficult to obtain as a foil having a practical thickness as a battery. It is preferably 1.5 μm or less.

(2) Tensile strength The tensile strength of the current collector substrate is not particularly limited, but is usually 100 N / mm.²Above, preferably 250 N / mm²Above, more preferably 400 N / mm²Above, particularly preferably 500 N / mm²That is all. The tensile strength is the maximum tensile force required for the test piece to break, divided by the cross-sectional area of the test piece. The tensile strength in the present invention is measured by the same device and method as the elongation rate. If the current collector substrate has a high tensile strength, cracks in the current collector substrate due to expansion and contraction of the negative electrode active material thin film due to charging and discharging can be suppressed, and good cycle characteristics can be obtained.

(3) 0.2% proof stress The 0.2% proof stress of the current collector substrate is not particularly limited, but is usually 30 N / mm.²Above, preferably 150 N / mm²Above, particularly preferably 300 N / mm²That is all. 0.2% proof stress is the magnitude of the load required to apply 0.2% plastic (permanent) strain, and means that it is deformed by 0.2% even if it is unloaded after applying a load of this magnitude. ing. The 0.2% proof stress in the present invention is measured by the same device and method as the elongation rate. If the current collector substrate has a high proof stress of 0.2%, plastic deformation of the current collector substrate due to expansion / contraction of the active material thin film due to charging / discharging can be suppressed, and good cycle characteristics can be obtained.

The thickness of the metal thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more. The upper limit is usually 1 mm or less, preferably 100 μm or less, and more preferably 30 μm or less. If it is thinner than 1 μm, the strength will decrease and it may be difficult to apply. If it is thicker than 100 μm, the shape of the electrode such as winding may be deformed. Further, the metal thin film may be in the form of a mesh.

(15) Ratio of current collector to active material layer thickness The ratio of the thickness of the current collector to the active material layer is not particularly limited, but (thickness of the active material layer on one side immediately before injection of the non-aqueous electrolyte solution) / (thickness of the current collector) is 150 or less. It is preferable, particularly preferably 20 or less, more preferably 10 or less, and the lower limit is preferably 0.1 or more, particularly preferably 0.4 or more, and more preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during high current density charging / discharging. Below this range, the volume ratio of the current collector to the negative electrode active material may increase and the capacity of the battery may decrease.

(16) Electrode density The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the active material existing on the current collector is preferably 1 g / cm.³Above, more preferably 1.2 g / cm³, More preferably 1.3 g / cm³That's all, and the upper limit is 2g / cm.³Below, preferably 1.9 g / cm³Below, more preferably 1.8 g / cm³Below, more preferably 1.7 g / cm³The range is as follows. If it exceeds this range, the active material particles may be destroyed, resulting in an increase in the initial irreversible capacity and deterioration of the high current density charge / discharge characteristics due to a decrease in the permeability of the non-aqueous electrolyte solution near the current collector / active material interface. .. If it is lower than that, the conductivity between active materials may decrease, the battery resistance may increase, and the capacity per unit volume may decrease.

(17) Binder The binder for binding the active material is not particularly limited as long as it is a non-aqueous electrolyte solution or a material stable to the solvent used in electrode production. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR ( Acrylonitrile-butadiene rubber), rubber-like polymers such as ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogen additive thereof; EPDM (ethylene / propylene / diene ternary copolymer), styrene / ethylene / Thermoplastic elastomeric polymers such as butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers or their hydrogenated products; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer Soft resinous polymers such as coalesced and propylene / α-olefin copolymers; fluoropolymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers; alkalis Examples thereof include a polymer composition having ionic conductivity of metal ions (particularly lithium ions). These may be used alone or in combination of two or more in any combination and ratio.

The type of solvent for forming the slurry is particularly limited as long as it is a solvent capable of dissolving or dispersing the negative electrode active material, the binder, and the thickener and the conductive material used as needed. However, either an aqueous solvent or an organic solvent may be used. Examples of aqueous solvents include water, alcohols and the like, and examples of organic solvents include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, etc. N, N-dimethylaminopropylamine, propylene oxide, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane And so on. In particular, when an aqueous solvent is used, a dispersant or the like is added in addition to the above-mentioned thickener, and a latex such as SBR is used to form a slurry. It should be noted that these may be used alone or in combination of two or more in any combination and ratio.

The ratio of the binder to the active material is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 20% by mass or less, preferably 15% by mass or less, more preferably. Is in the range of 10% by mass or less, more preferably 8% by mass or less. If it exceeds this range, the proportion of the binder, which is a component that does not contribute to the battery capacity, becomes excessive in the negative electrode active material layer, which may lead to a decrease in the battery capacity. If it is lower than that, the strength of the negative electrode may decrease. In particular, when a rubbery polymer typified by SBR is contained in the main component, the ratio of the binder to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more. The upper limit is 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. When a fluorine-based polymer typified by polyvinylidene fluoride is contained in the main component, the ratio to the active material is 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more. The upper limit is 15% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less.

Thickeners are commonly used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used alone or in combination of two or more in any combination and ratio. When a thickener is further added, the ratio of the thickener to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 5% by mass or less. It is preferably in the range of 3% by mass or less, more preferably 2% by mass or less. Below this range, the coatability may be significantly reduced. If it exceeds, the ratio of the active material to the negative electrode active material layer decreases, which may cause a problem that the capacity of the battery decreases or a problem that the resistance between the negative electrode active materials increases.

(18) Plate orientation ratio The plate orientation ratio is preferably 0.001 or more, particularly preferably 0.005 or more, more preferably 0.01 or more, and the upper limit is the theoretical value of 0.67 or less. If it falls below this range, the high-density charge / discharge characteristics may deteriorate. The measurement of the electrode plate orientation ratio is as follows. For the negative electrode after pressing to the target density, the active material orientation ratio of the electrode is measured by X-ray diffraction. The specific method is not particularly limited, but as a standard method, peak separation is performed by fitting the peaks of carbon (110) diffraction and (004) diffraction by X-ray diffraction using an asymmetric Pearson VII as a profile function. Is performed, and the integrated intensities of the peaks of (110) diffraction and (004) diffraction are calculated respectively. From the obtained integrated intensity, the ratio expressed by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated. The active material orientation ratio of the electrode calculated by the measurement is defined as the electrode plate orientation ratio.

The X-ray diffraction measurement conditions here are as follows. In addition, "2θ" indicates a diffraction angle. Target: Cu (Kα ray) graphite monochromator Slit: divergent slit = 1 degree, light receiving slit = 0.1 mm, scattering slit = 1 degree Measurement range and step angle / measurement time: (110) Surface: 76.5 degrees 2θ 78.5 degrees 0.01 degrees / 3 seconds (004) Surface: 53.5 degrees 2θ 56.0 degrees 0.01 degrees / 3 seconds Sample preparation: Fix the electrodes to the glass plate with double-sided tape with a thickness of 0.1 mm.

(19) Impedance The resistance of the negative electrode when charged from the discharged state to 60% of the nominal capacity is preferably 100 Ω or less, particularly preferably 50 Ω or less, more preferably 20 Ω or less, and / or the double layer capacity is 1 × 10.^-6F or higher is preferable, and 1 × 10 is particularly preferable.^-5F, more preferably 1x10^-4F. Within this range, the output characteristics are good and preferable.

The resistance and double layer capacitance of the negative electrode are measured by the following procedure. The lithium-ion secondary battery to be measured is charged with a current value that can charge the nominal capacity in 5 hours, then remains uncharged and discharged for 20 minutes, and then discharges at a current value that can discharge the nominal capacity in 1 hour. Use a battery with a capacity of 80% or more of the nominal capacity. The lithium-ion secondary battery in the discharged state described above is charged to 60% of the nominal capacity with a current value capable of charging the nominal capacity in 5 hours, and the lithium-ion secondary battery is immediately transferred into a glove box under an argon gas atmosphere. Here, the lithium ion secondary battery is quickly disassembled and taken out without the negative electrode being discharged or short-circuited, and if it is a double-sided coated electrode, the electrode active material on one side is peeled off without damaging the electrode active material on the other side, and the negative electrode is used. Two electrodes are punched to 12.5 mmφ, and the active material surfaces are opposed to each other through a separator so that they do not shift. 60 μL of the non-aqueous electrolyte solution used in the battery is dropped between the separator and both negative electrodes to bring them into close contact with each other, and the current collectors of both negative electrodes are conducted with conductivity while keeping them out of contact with the outside air, and the AC impedance method is performed. To do. The measurement is at a temperature of 25 ° C, 10^-2~10⁵The complex impedance is measured in the Hz frequency band, and the arc of the negative resistance component of the obtained call-call plot is approximated by a semicircle to obtain the surface resistance (R) and the double layer capacitance (Cdl).

The area of the negative electrode plate is not particularly limited, but it is designed to be slightly larger than the facing positive electrode plate so that the positive electrode plate does not protrude from the negative electrode plate. From the viewpoint of suppressing the life of the cycle of repeated charging and discharging and the deterioration due to high temperature storage, it is preferable to make the area as close to the positive electrode as possible because the proportion of electrodes that work more uniformly and effectively is increased and the characteristics are improved. In particular, the design of this electrode area is important when used at a large current.

The thickness of the negative electrode plate is designed according to the positive electrode plate to be used, and is not particularly limited, but the thickness of the mixture layer after subtracting the metal leaf thickness of the core material is usually 15 μm or more. It is preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is 150 μm or less, preferably 120 μm or less, and more preferably 100 μm or less.

[Separator] The separator used in the non-aqueous electrolyte secondary battery of the present invention has a predetermined mechanical strength that electronically insulates between the two electrodes, has high ion permeability, and is oxidative and negative electrode on the side in contact with the positive electrode. It is not particularly limited as long as it also has resistance to reducing property on the side. Resins, inorganic substances, glass fibers and the like are used as the material of the separator having such required characteristics. As the resin, an olefin polymer, a fluoropolymer, a cellulosic polymer, a polyimide, nylon and the like are used. Specifically, it is preferable to select from materials that are stable against non-aqueous electrolytes and have excellent liquid retention properties, and it is preferable to use a porous sheet or non-woven fabric made from polyolefin such as polyethylene or polypropylene. preferable. As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used, and those having a particle shape or a fiber shape are used. As the form, a thin film such as a non-woven fabric, a woven cloth, or a microporous film is used. As the thin film shape, a thin film having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used.

In addition to the independent thin film shape, a separator obtained by forming a composite porous layer containing the inorganic particles on the surface layer of the positive electrode and / or the negative electrode using a resin binder can be used. For example, alumina particles having a 90% particle size of 1 μm or less are formed on both sides of the positive electrode as a porous layer using a fluororesin binder.

[Electrode group] The electrode group has a laminated structure in which the above-mentioned positive electrode plate and the negative electrode plate are formed by the above-mentioned separator, and a structure in which the above-mentioned positive electrode plate and the negative electrode plate are spirally wound through the above-mentioned separator. Either may be used. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is preferably 40% to 90%, and more preferably 50% to 80%. When the electrode group occupancy rate is less than 40%, the battery capacity is small, and when it is 90% or more, the void space is small, and the member expands due to the high temperature of the battery or the vapor pressure of the liquid component of the electrolyte is high. As a result, the internal pressure rises, which reduces various characteristics such as repetitive charge / discharge performance and high-temperature storage as a battery, and further, a gas discharge valve that releases the internal pressure to the outside may operate.

[Current collector structure] The current collecting structure is not particularly limited, but in order to more effectively improve the output characteristics of the non-aqueous electrolyte solution for a secondary battery of the present invention, a structure that reduces the resistance of the wiring portion and the joint portion. Need to be. When such internal resistance is small, the effect of using the non-aqueous electrolyte solution of the present invention is particularly well exhibited. When the electrode group has the above-mentioned laminated structure, a structure formed by bundling the metal core portions of each electrode layer and welding them to the terminals is preferably used. When the area of one electrode becomes large, the internal resistance becomes large. Therefore, it is also preferably used to reduce the resistance by providing a plurality of terminals in the electrode. In the wound structure in which the electrode group is described above, the internal resistance can be reduced by providing a plurality of lead structures on the positive electrode and the negative electrode and bundling them in the terminals.

By optimizing the above-mentioned structure, the internal resistance can be reduced as much as possible. For batteries used at large currents, the impedance measured by the 10kHz AC method (hereinafter abbreviated as "DC resistance component") is preferably 10 milliohms (mΩ) or less, and the DC resistance component is 5 milliohms (mΩ). More preferably: When the DC resistance component is set to 0.1 milliohm or less, the high output characteristics are improved, but the ratio of the current collecting structural material used increases, and the battery capacity may decrease.

The non-aqueous electrolyte solution for a secondary battery of the present invention is effective in reducing the reaction resistance associated with the deinsertion and insertion of lithium into the electrode active material, which is a factor that can realize good output characteristics. However, it was found that in a normal battery with a DC resistance greater than 10 mΩ, the effect of reducing the reaction resistance may not be reflected 100% in the output characteristics due to the DC resistance. This can be improved by producing a battery having a small DC resistance component, and the effect of the non-aqueous electrolyte solution for a secondary battery of the present invention can be fully exhibited. In addition, from the viewpoint of drawing out the effect of the non-aqueous electrolyte solution and producing a high-output battery, this requirement and the electric capacity (battery) of the battery element housed in the outer battery of one of the secondary batteries described above It is particularly preferable to simultaneously satisfy the requirement that the electric capacity when discharged from the fully charged state to the discharged state) is 3 amper hours (Ah) or more.

[Exterior case] The material of the outer case is not particularly limited as long as it is a substance stable to the non-aqueous electrolyte used. Specifically, a nickel-plated steel plate, stainless steel, aluminum or aluminum alloy, metals such as magnesium alloy, or a laminated film (laminated film) of resin and aluminum foil is used. From the viewpoint of weight reduction, aluminum or aluminum alloy metal or laminated film is preferably used.

In the outer case using the metals, the metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed and sealed structure, or the metals are used to caulk the structure via a resin gasket. There are things to do.

Examples of the outer case using the laminated film include a case in which resin layers are heat-sealed to form a sealed and sealed structure. In order to improve the sealing property, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when the resin layer is heat-sealed via the current collector terminal to form a closed structure, the metal and the resin are bonded to each other. Resin is preferably used.

[Protective element] As the above-mentioned protective elements, PTC (Positive Temperature Coefficient), which increases resistance when abnormal heat generation or excessive current flows, thermal fuse, thermistor, current flowing in the circuit due to a sudden rise in battery internal pressure or internal temperature during abnormal heat generation. Examples include a valve (current cutoff valve) that shuts off the current. It is preferable to select the protective element under conditions that do not operate under normal use of high current, and from the viewpoint of high output, it is more preferable to design the protective element so as not to cause abnormal heat generation or thermal runaway even without the protective element.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples as long as the gist thereof is not exceeded. &lt;Preparation of non-aqueous solvent&gt; Commercially available ethylene carbonate (EC) was adsorbed with Molecular Sieves 4A (50 ° C, LHSV; 1 / hour). On the other hand, dimethyl carbonate and ethyl methyl carbonate were sufficiently precisely distilled at a reflux ratio of 1 and a theoretical plate number of 30, respectively, and then adsorbed with Molecular Sieves 4A (25 ° C, LHSV; 1 / hour). Then, these are mixed at a ratio of EC: DMC: EMC (volume ratio 3: 3: 4), and further adsorbed with Molecular Sieves 4A (25 ° C, LHSV; 1 / hour) to prepare a mixed non-aqueous solvent. did. At this time, no water or alcohols were detected in the non-aqueous solvent.

&lt;Making a secondary battery&gt; [Preparation of positive electrode] Lithium cobalt oxide (LiCoO) as positive electrode active material₂) 90% by mass, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in an N-methylpyrrolidone solvent to form a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 80 μm with a press. The size of the active material layer was 100 mm in width, 100 mm in length, and 30 mm in width. It was cut into a shape having a working part and used as a positive electrode.

[Preparation of negative electrode] 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by Timcal), 100 parts by weight of aqueous dispersion of sodium carboxymethyl cellulose (1% by mass of sodium carboxymethyl cellulose) as a thickener and binder, respectively. Two parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by mass) was added and mixed with a disperser to form a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm with a press, and uncoated with a width of 104 mm, a length of 104 mm, and a width of 30 mm as the size of the active material layer. It was cut into a shape having a working part and used as a negative electrode.

[Battery assembly] The 32 positive electrodes and 33 negative electrodes were arranged alternately, and laminated so that a porous polyethylene sheet separator (thickness 25 μm) was sandwiched between the electrodes. At this time, the positive electrode active material surface was faced so as not to come off from the negative electrode active material surface. The uncoated parts of each of the positive electrode and the negative electrode were welded together to form a current collecting tab, and the electrode group was enclosed in a battery can (outer dimensions: 120 x 110 x 10 mm) with a gas discharge valve. .. Then, 20 mL of a non-aqueous electrolyte solution was injected into a battery can loaded with the electrode group, sufficiently permeated into the electrodes, and sealed to prepare a square battery. The rated discharge capacity of this battery is as high as about 6Ah, and the DC resistance measured by the 10kHz AC method is about 5 milliohms.

[Battery evaluation] (Capacity measurement) For a new battery that has not undergone a charge / discharge cycle, the voltage range is 4.2V to 3.0V at 25 ° C, and the current value is 0.2C (the current value that discharges the rated capacity based on the 1-hour discharge capacity in 1 hour is 1C. The initial charge / discharge was performed for 5 cycles (the same applies hereinafter). The 0.2C discharge capacity in the 5th cycle at this time was used as the initial capacity.

(Output measurement) In a 25 ° C environment, the battery was charged with a constant current of 0.2C for 150 minutes, discharged at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C for 10 seconds, and the voltage at the 10th second was measured. The area of the triangle surrounded by the current-voltage straight line and the lower limit voltage (3V) was defined as the output (W).

(Cycle test) A cycle test was conducted in a high temperature environment of 60 ° C, which is considered to be the upper limit temperature for actual use of lithium secondary batteries. After charging with the constant current constant voltage method of 2C up to the upper limit voltage of 4.2V, the charging / discharging cycle of discharging with the constant current of 2C up to the discharge end voltage of 3.0V was set as one cycle, and this cycle was repeated up to 500 cycles. The battery after the cycle test was charged and discharged for 3 cycles in a 25 ° C environment, and the 0.2 C discharge capacity in the 3rd cycle was defined as the post-cycle capacity. The ratio of the capacity after this cycle to the initial capacity was defined as the capacity retention rate.

Example 1 Under a dry argon atmosphere, methanol in an amount of 10 ppm was mixed with the above-mentioned mixed non-aqueous solvent, and lithium hexafluorophosphate (LiPF) was mixed.₆) Was added to 0.8 mol / L and dissolved. The amount of hydrogen fluoride (HF) in the solution after 1 day was 12 ppm, and when measured again 2 weeks later, it was 14 ppm. Hexamethylcyclotrisiloxane was mixed in an amount of 0.3% by mass with respect to this mixed solution (2 weeks after mixing) to prepare a non-aqueous electrolyte solution. A battery was prepared by the above method using this non-aqueous electrolyte solution, and the output and capacity retention rate were measured. The results are shown in Table 1.

Example 2 In Example 1, a battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 1 except that the mixing amount of methanol was changed to 20 ppm with respect to the mixed non-aqueous solvent, and the output and capacity were maintained. The rate was measured. The results are shown in Table 1. LiPF₆The amount of hydrogen fluoride (HF) in the mixed solution 1 day after mixing was 16 ppm, and when measured again 2 weeks later, it was 19 ppm.

Example 3 In Example 1, a battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 1 except that the mixing amount of methanol was changed to 35 ppm with respect to the mixed non-aqueous solvent, and the output and capacity were maintained. The rate was measured. The results are shown in Table 1. LiPF₆The amount of hydrogen fluoride (HF) in the mixed solution 1 day after mixing was 22 ppm, and when measured again 2 weeks later, it was 27 ppm.

Example 4 In Example 1, a battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 1 except that ethylene glycol (EG) was mixed with a mixed non-aqueous solvent in an amount of 15 ppm instead of methanol. Output and capacity retention were measured. The results are shown in Table 1. LiPF₆The amount of hydrogen fluoride (HF) in the mixed solution 1 day after mixing was 14 ppm, and when measured again 2 weeks later, it was 16 ppm.

Example 5 In Example 1, a battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 1 except that ethylene glycol was mixed with a mixed non-aqueous solvent in an amount of 35 ppm instead of methanol, and the output and capacity were obtained. The maintenance rate was measured. The results are shown in Table 1. LiPF₆The amount of hydrogen fluoride (HF) in the mixed solution 1 day after mixing was 23 ppm, and when measured again 2 weeks later, it was 27 ppm.

Example 6 In Example 1, a battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 1 except that methanol was mixed with a mixed non-aqueous solvent in an amount of 25 ppm and ethylene glycol was mixed in an amount of 25 ppm, and the output and capacity were increased. The maintenance rate was measured. The results are shown in Table 1. LiPF₆The amount of hydrogen fluoride (HF) in the mixed solution 1 day after mixing was 31 ppm, and when measured again 2 weeks later, it was 36 ppm.

Example 7 In Example 1, instead of hexamethylcyclotrisiloxane, the amount of lithium difluorophosphate (Inorganic Nuclear Chemistry Letters (1969), 5 (7), pp. 581 to 582) is 0.3% by mass based on the mixed solution. A battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 1 except that the mixture was prepared according to the method described in (1), and the output and capacity retention rate were measured. The results are shown in Table 1.

Example 8 In Example 3, a battery was used using a non-aqueous electrolyte solution prepared in the same manner as in Example 3 except that lithium difluorophosphate was mixed in an amount of 0.3% by mass with respect to the mixed solution instead of hexamethylcyclotrisiloxane. Was prepared, and the output and capacity retention rate were measured. The results are shown in Table 1.

Example 9 In Example 4, a battery was used using a non-aqueous electrolyte solution prepared in the same manner as in Example 4 except that lithium difluorophosphate was mixed in an amount of 0.3% by mass with respect to the mixed solution instead of hexamethylcyclotrisiloxane. Was prepared, and the output and capacity retention rate were measured. The results are shown in Table 1.

Example 10 In Example 6, a battery was used using a non-aqueous electrolyte solution prepared in the same manner as in Example 6 except that lithium difluorophosphate was mixed in an amount of 0.3% by mass with respect to the mixed solution instead of hexamethylcyclotrisiloxane. Was prepared, and the output and capacity retention rate were measured. The results are shown in Table 1.

Example 11 In Example 6, a battery was used using a non-aqueous electrolyte solution prepared in the same manner as in Example 6 except that trimethylsilyl methanesulfonate was mixed in an amount of 0.3% by mass with respect to the mixed solution instead of hexamethylcyclotrisiloxane. Was prepared, and the output and capacity retention rate were measured. The results are shown in Table 1.

Example 12 &lt;Making a secondary battery-2&gt; [Preparation of positive electrode] Lithium cobalt oxide (LiCoO) as positive electrode active material₂) 90% by mass, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in an N-methylpyrrolidone solvent to form a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm with a press, and cut into a width of 52 mm and a length of 830 mm to obtain a positive electrode. However, both the front and back sides are provided with a 50 mm uncoated part in the length direction, and the length of the active material layer is 780 mm.

[Preparation of negative electrode] 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by Timcal), 100 parts by weight of aqueous dispersion of sodium carboxymethyl cellulose (1% by mass of sodium carboxymethyl cellulose) as a thickener and binder, respectively. Two parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by mass) was added and mixed with a disperser to form a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm, which is a negative electrode current collector, dried, rolled to a thickness of 85 μm with a press, and cut into a width of 56 mm and a length of 850 mm. It was used as the negative electrode. However, both the front and back sides are provided with a 30 mm uncoated part in the length direction.

[Preparation of non-aqueous electrolyte solution] A non-aqueous electrolyte solution similar to that in Example 6 was prepared. [Battery assembly] The positive electrode and the negative electrode were stacked and wound together with a polyethylene separator so that the positive electrode and the negative electrode did not come into direct contact with each other to form an electrode body. The positive electrode and negative electrode terminals were housed in the battery can so as to be exposed to the outside. Next, after injecting 5 mL of a non-aqueous electrolyte solution described later into this, caulking was performed to prepare an 18650 type cylindrical battery. The rated discharge capacity of this battery was about 0.7 amp-hours (Ah), and the DC resistance measured by the 10kHz AC method was about 35 milliohms (mΩ). In the above-mentioned battery, the output and the capacity retention rate were measured in the same manner as in Example 6. The results are shown in Table 1.

Comparison Example 1 In Example 3, a battery was prepared using a non-aqueous electrolyte solution prepared without mixing hexamethylcyclotrisiloxane, and the output and capacity retention rate were measured. The results are shown in Table 1.

Comparison example 2 In Example 5, a battery was prepared using a non-aqueous electrolyte solution prepared without mixing hexamethylcyclotrisiloxane, and the output and capacity retention rate were measured. The results are shown in Table 1.

Comparison example 3 In Example 6, a battery was prepared using a non-aqueous electrolyte solution prepared without mixing hexamethylcyclotrisiloxane, and the output and capacity retention rate were measured. The results are shown in Table 1.

Comparison example 4 In Example 1, a battery was prepared using a non-aqueous electrolytic solution prepared without mixing methanol with a mixed non-aqueous solvent, and the output and capacity retention rate were measured. The results are shown in Table 1. LiPF₆The amount of hydrogen fluoride (HF) in the solution 1 day after mixing was 9 ppm, and when measured again 2 weeks later, it was also 9 ppm.

Comparison Example 5 In Comparative Example 4, a battery was prepared using a non-aqueous electrolyte solution prepared by mixing 0.3% by mass of lithium difluorophosphate instead of hexamethylcyclotrisiloxane, and the output and capacity retention rate were measured. The results are shown in Table 1.

Comparison Example 6 In Comparative Example 4, a battery was prepared using a non-aqueous electrolyte solution prepared by mixing 0.3% by mass of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane, and the output and capacity retention rate were measured. The results are shown in Table 1.

Comparison example 7 In Example 1, a battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 1 except that the mixing amount of methanol was changed to 700 ppm with respect to the mixed non-aqueous solvent, and the output and capacity were maintained. The rate was measured. The results are shown in Table 1. LiPF₆The amount of hydrogen fluoride (HF) in the solution 1 day after mixing was 321 ppm, and when measured again 2 weeks later, it was 403 ppm.

Comparison Example 8 In Example 1, a battery was prepared using a non-aqueous electrolytic solution prepared without mixing methanol with a mixed non-aqueous solvent and without mixing hexamethylcyclotrisiloxane, and the output and capacity retention rate were measured. .. The results are shown in Table 1.

Comparison Example 9 In Example 12, a battery was prepared using a non-aqueous electrolyte solution prepared in the same manner as in Example 12 except that hexamethylcyclotrisiloxane was not mixed, and the output and capacity retention rate were measured. The results are shown in Table 1.

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As is clear from Table 1, the lithium secondary batteries of Comparative Examples 1 to 3 containing a larger amount of hydrogen fluoride (HF) are inferior in both output characteristics and cycle characteristics to the lithium secondary batteries of Comparative Example 8. However, the lithium secondary batteries of Examples 1 to 11 to which a specific compound was added showed improvements in both output characteristics and cycle characteristics. Further, in terms of output, the lithium secondary batteries of Examples 1 to 11 have higher performance than the lithium secondary batteries of Comparative Examples 4 to 6 which contain a specific compound but have a low hydrogen fluoride (HF) content. The surprising result was that the presence of hydrogen fluoride (HF) enhances the output improving effect of the specific compound. However, in the lithium secondary battery of Comparative Example 7 containing an excess of hydrogen fluoride (HF), the cycle characteristics were particularly inferior.

Further, the output improvement rate of Example 12 was only about 19% with respect to Comparative Example 9 which is a battery structure having a low capacity and a high DC resistance, while Example 6 which is a battery structure having a high capacity and a low DC resistance. The output improvement rate for Comparative Example 3 (both containing 25 ppm of methanol and 25 ppm of ethylene glycol) was about 29%, and the output improvement rate for Comparative Example 2 of Example 5 (both containing 35 ppm of ethylene glycol) was about 26. The output improvement rate was about 26% with respect to Comparative Example 1 of Example 3 (both containing 35 ppm of methanol), which was large. From this, it was found that the effect of the present invention is specifically large in a battery structure having a high capacity and a low DC resistance.

As described above, in the non-aqueous electrolyte solution of the present invention, that is, the non-aqueous electrolyte solution for a secondary battery formed by mixing a fluorine-containing lithium salt with a non-aqueous solvent, the hydrogen fluoride (HF) in the non-aqueous electrolyte solution Is 10 ppm or more and 300 ppm or less, and further, a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and a compound in the molecule. At least one compound selected from the group consisting of compounds having SF bonds, nitrates, nitrites, monofluorophosphates, difluorophosphates, acetates and propionates is added to the entire non-aqueous electrolyte solution. By using a non-aqueous electrolyte solution for secondary batteries, which is characterized by containing 10 ppm or more, it has become possible to obtain large output characteristics without deteriorating cycle characteristics.

In this example, the effect is exhibited by adding alcohols to the purified non-aqueous solvent, but if the non-aqueous solvent originally contains alcohols or water, the purification conditions for the non-aqueous solvent should be changed. By adjusting, the same effect can be obtained without adding alcohols. In general, purification of a non-aqueous solvent is troublesome and industrially causes a cost. However, in the present invention, a high-performance non-aqueous electrolyte solution can be prepared without requiring excessive purification. Its value is enormous.

The use of the non-aqueous electrolyte solution for a secondary battery and the non-aqueous electrolyte solution secondary battery of the present invention is not particularly limited, and can be used in various known applications. Specific examples include laptops, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copies, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, mini disks, transceivers. , Electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, bikes, motorized bicycles, bicycles, lighting equipment, toys, game machines, watches, power tools, strobes, cameras, etc. Can be done. In particular, since the non-aqueous electrolyte secondary battery of the present invention can obtain good cycle characteristics and high output characteristics, a particularly large effect can be obtained when used in an application requiring a large instantaneous current. Therefore, it is widely used in such fields.