Collector, electrode, and battery

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a battery and a current collector and electrodes used therein.

【0002】

[Conventional technology]

The remarkable progress of electronic technology in recent years has made electronic devices smaller and lighter one after another. Along with this, batteries as a portable power source are also required to be smaller and lighter and have a high energy density. In addition, electronic devices that frequently charge and discharge, such as notebook personal computers, mobile phones or PHS (Personal Handyphone System), or pure electric vehicles (PEVs), hybrid electric vehicles; As a power source for HEVs) or electric vehicles, there is a demand for the development of batteries with excellent energy density and cycle characteristics. Therefore, as a secondary battery that meets these demands, research and development of a lithium ion secondary battery that uses a lithium composite oxide for the positive electrode, a carbon material or alloy for the negative electrode, and a non-aqueous solvent for the electrolyte has been carried out. ing.

【0003】

[Problems to be Solved by the Invention]

However, the lithium ion secondary battery has a problem that it is difficult to simultaneously improve the high load characteristic and other characteristics such as capacity or charge / discharge cycle characteristics. For example, in order to increase the capacity, it is conceivable to increase the packing density of the active material in the active material layer of the electrode and increase the input amount of the active material. The characteristics deteriorate. This is because the gap between the active materials is reduced and it becomes difficult for the electrolyte to reach the details of the electrode. Further, when a high pressure is applied to increase the filling property, the active material on the electrode surface is crushed and the surface is smoothed, so that it becomes difficult for the electrolyte to penetrate into the active material layer, and the productivity is also lowered.

【0004】

Further, in order to obtain excellent charge / discharge cycle characteristics, for example, a method of increasing the amount of the binder added to the active material layer to increase the peel strength between the active material layer and the current collector can be considered. According to the method, the high load characteristic deteriorates. This is because many of the widely used polymer binders have electrical insulating properties, and as the amount added increases, the internal resistance increases. For example, even if an attempt is made to atomize an active material to improve high load characteristics, a binder is further required, and considering the performance as a battery, it is very difficult to set the balance.

【0005】

The present invention has been made in view of such problems, and an object of the present invention is to provide a current collector, an electrode, and a battery capable of simultaneously improving high load characteristics and other characteristics.

【0006】

[Means for solving problems]

The current collector according to the present invention has a first layer having a porosity of 30% or more and less than 100%, and a second layer provided on at least one surface of the first layer and having a porosity of 5% or less. It is prepared.

【0007】

The electrode according to the present invention is a stack of a current collector and an active material layer, and has a through hole penetrating the current collector and the active material layer.

【0008】

The first battery according to the present invention is provided with an electrolyte together with a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode is a first layer having a porosity of 30% or more and less than 100%. It includes a current collector provided on at least one surface of the first layer and having a second layer having a porosity of 5% or less.

【0009】

The second battery according to the present invention is provided with an electrolyte together with a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode has a laminated current collector and an active material layer, and these collections are provided. A through hole is provided to penetrate the electric body and the active material layer.

【0010】

In the current collector according to the present invention, a first layer having a porosity of 30% or more and less than 100% and a second layer provided on at least one surface of the first layer and having a porosity of 5% or less are provided. Therefore, for example, when the active material layer is formed on the surface, the interfacial resistance with the active material layer is reduced. In addition, the physical binding force with the active material layer is strengthened.

【0011】

Since the electrode according to the present invention has through holes penetrating the current collector and the active material layer, the electrolyte permeates smoothly, for example, when used in a battery equipped with an electrolyte.

【0012】

Since the current collector of the present invention is used in the first battery according to the present invention, excellent high load characteristics and charge / discharge cycle characteristics can be obtained.

【0013】

Since the second battery according to the present invention uses the electrodes of the present invention, high capacity and excellent high load characteristics can be obtained.

【0014】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

【0015】

[First Embodiment] FIG. 1 shows a cross-sectional structure of a secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called cylindrical type, and is wound around a substantially hollow cylindrical battery can 11 in which a strip-shaped positive electrode 21 and a negative electrode 22 which are electrodes are wound via a separator 23. It has an electrode body 20. The battery can 11 is made of, for example, nickel (Ni) plated iron (Fe), one end of which is closed and the other end of which is open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

【0016】

At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14, and a heat-sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are connected via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via a heat-sensitive resistance element 16, and the disk plate 15a is inverted when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Then, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. The heat-sensitive resistance element 16 limits the current by increasing the resistance value when the temperature rises, and prevents abnormal heat generation due to a large current. For example, the heat-sensitive resistance element 16 is made of barium titanate-based semiconductor ceramics. The gasket 17 is made of, for example, an insulating material, and the surface is coated with asphalt.

【0017】

The wound electrode body 20 is wound around the center pin 24, for example. A lead wire 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the wound electrode body 20, and a lead wire 26 made of nickel or the like is connected to the negative electrode body 22. The lead wire 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the lead wire 26 is welded to the battery can 11 and electrically connected.

【0018】

FIG. 2 is an enlarged view of a part of the wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which active material layers 21b are provided on both sides of a current collector 21a having a pair of facing surfaces. Although not shown, the active material layer 21b may be provided on only one side of the current collector 21a. The current collector 21a has a thickness of, for example, about 5 μm to 50 μm, and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The active material layer 21b has a thickness of, for example, 10 μm to 300 μm, and is composed of, for example, a positive electrode active material. If necessary, a conductive agent such as carbon black or graphite and a binder such as polyvinylidene fluoride are further added. And include. The thickness of the active material layer 21b is the total thickness when the active material layer 21b is provided on both sides of the current collector 21a.

【0019】

As the positive electrode active material, for example, a metal oxide, a metal sulfide, a specific polymer material, or the like is preferable, and any one or two or more of them are selected depending on the purpose of use of the battery.

【0020】

Metal oxides include lithium composite oxides containing lithium or V containing no lithium.₂O₅And so on. In particular, some lithium composite oxides have a high potential and can increase the energy density, which is preferable. As this lithium composite oxide, for example, the chemical formula Li_xMO₂There is something represented by. In the formula, M represents one or more kinds of transition metal elements, and at least one of the group consisting of cobalt (Co), nickel and manganese (Mn) is particularly preferable. The value of x varies depending on the charge / discharge state of the battery, and is usually 0.05 x 1.10. As a specific example of such a lithium composite oxide, LiCO₂, LiNiO₂, Li_yNi_zCo_1-zO₂(Y and z depend on the charge / discharge state of the battery and are usually 0 <y <1, 0.7 <z <1.02) or LiMn with a spinel-type structure₂O₄And so on.

【0021】

As a metal sulfide, TiS₂Or MoS₂Examples of the polymer material include polyacetylene and polypyrrole.

【0022】

The positive electrode 21 also has a through hole 21c that penetrates the current collector 21a and the active material layer 21b. This is to increase the permeability of the electrolyte. The electrolyte will be described later.

【0023】

The through hole 21c may be distributed over the entire positive electrode 21 or may be present in a part of the positive electrode 21, but is 1 cm.²It is preferable that there are 1 or more and 200 or less per unit. The total area of the through holes 21c is preferably in the range of 0.1% or more and 10% or less, and more preferably in the range of 0.5% or more and 3% or less with respect to the area of the active material layer 21b. This is because if the number of through holes is small and the total area is small, the permeability is low, and if the number of through holes is large and the total area is large, the amount of active material decreases and the capacity decreases. The total area of the through holes 21c is the total area of each through hole 21c in a plane parallel to the extending direction of the electrode.

【0024】

The diameter of the through hole 21c is preferably in the range of 10 μm or more and 10 mm or less, and more preferably in the range of 100 μm or more and 1 mm or less. This is because if it is small, the permeability is low due to clogging or the like, and if it is large, the amount of active material is reduced and the capacity is reduced.

【0025】

Like the positive electrode 21, the negative electrode 22 has a structure in which active material layers 22b are provided on both sides of a current collector 22a having a pair of facing surfaces. Although not shown, the active material layer 22b may be provided only on one side of the current collector 22a. The current collector 22a has a thickness of, for example, 6 μm to 40 μm, and is made of a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil. The active material layer 22b has, for example, a thickness of 10 μm to 300 μm, and is composed of, for example, containing one or more of negative electrode materials capable of occluding and releasing lithium, which is a negative electrode active material. If necessary, a binder such as polyvinylidene fluoride may be further contained. The thickness of the active material layer 22b is the total thickness when the active material layer 22b is provided on both sides of the current collector 22a.

【0026】

Examples of the negative electrode material capable of occluding and releasing lithium include simple substances, alloys or compounds of metal elements or metalloid elements capable of forming an alloy with lithium. In the present specification, in addition to alloys composed of two or more kinds of metal elements, alloys including one or more kinds of metal elements and one or more kinds of metalloid elements are also included. Some of the structures are solid solutions, eutectic (eutectic mixtures), intermetallic compounds, or two or more of them coexist.

【0027】

Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), copper, cobalt, antimony (Sb), Bismuth (Bi), cadmium (Cd), magnesium, boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr) and indium (Y) ). Examples of these alloys or compounds include the chemical formula Ma._sMb_tLi_uOr the chemical formula Ma_pMc_qMd_rThe ones represented by are mentioned. In these chemical formulas, Ma represents at least one of the metallic and semi-metallic elements capable of forming an alloy with lithium, and Mb represents at least one of the metallic and semi-metallic elements other than lithium and Ma. Mc represents at least one non-metallic element, and Md represents at least one of metal and semi-metallic elements other than Ma. The values of s, t, u, p, q and r are s> 0, t 0, u 0, p> 0, q> 0 and r 0, respectively.

【0028】

Among them, elemental substances, alloys or compounds of group 4B metal elements or metalloid elements are preferable, and silicon or tin, or alloys or compounds thereof are particularly preferable. These may be crystalline or amorphous.

【0029】

Specific examples of such alloys or compounds are LiAl, AlSb, CuMgSb, SiB.₄, SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄, Si₂N₂O, SiO_v(0 <v 2), SnO_w(0 <w 2), SnSiO₃, LiSiO or LiSnO.

【0030】

Negative electrode materials capable of absorbing and removing lithium also include carbon materials, metal oxides, polymer materials and the like. Examples of the carbon material include non-graphitizable carbon, artificial graphite, cokes, graphites, glassy carbons, calcined organic polymer compounds, carbon fibers, activated carbon and carbon blacks. Among these, coke includes pitch coke, needle coke, petroleum coke, etc., and the organic polymer compound fired body is carbonized by firing a polymer material such as phenol resin or furan resin at an appropriate temperature. The thing that was done. Examples of the metal oxide include iron oxide, ruthenium oxide and molybdenum oxide, and examples of the polymer material include polyacetylene and polypyrrole.

【0031】

The separator 23 is impregnated with an electrolytic solution which is a liquid electrolyte. This electrolytic solution is composed of, for example, a solvent and a lithium salt which is an electrolyte salt. The solvent dissolves and dissociates the electrolyte salt. Examples of the solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and the like. Non-aqueous solvents such as 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetate, butyrate or propionate are preferred, and any one of these is preferred. Species or a mixture of two or more species are used.

【0032】

As a lithium salt, for example, LiBF₄, LiPF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, LiN (CF)₃SO₂)₂, LiN (C₂F₅SO₂)₂, LiC (CF)₃SO₂)₃, LiAlCl₄And LiSiF₆However, any one or two or more of these are used in combination.

【0033】

This secondary battery can be manufactured, for example, as follows.

【0034】

First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a paste-like positive electrode mixture. Use as an agent slurry. Next, for example, this positive electrode mixture slurry is applied to the current collector 21a, the solvent is dried, and then compression molding is performed by a roll press or the like to form the active material layer 21b. After that, for example, a through hole 21c is formed in the current collector 21a and the active material layer 21b to prepare a positive electrode 21. Alternatively, for example, the positive electrode mixture slurry may be applied to the current collector 21a, the solvent may be dried, the through holes 21c may be opened, and then compression formation may be performed to form the active material layer 21b. At that time, the through hole 21c is formed, for example, by sandwiching the positive electrode 21 with a roll or a flat plate having needle-shaped protrusions, or by irradiating a laser.

【0035】

Next, for example, a negative electrode material capable of occluding / removing lithium and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a paste. Negative electrode mixture slurry. This negative electrode mixture slurry is applied to the current collector 22a to dry the solvent, and then compression molding is performed by a roll press or the like to form the active material layer 22b to prepare the negative electrode 22.

【0036】

Subsequently, the lead wire 25 is attached to the current collector 21a by welding or the like, and the lead wire 26 is attached to the current collector 22a by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, the tip of the lead wire 25 is welded to the safety valve mechanism 15, and the tip of the lead wire 26 is welded to the battery can 11 and wound. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and housed inside the battery can 11. After the positive electrode 21 and the negative electrode 22 are housed inside the battery can 11, the electrolytic solution is injected into the battery can 11 to impregnate the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat-sensitive resistance element 16 are fixed to the open end of the battery can 11 by caulking via the gasket 17. As a result, the secondary batteries shown in FIGS. 1 and 2 are formed.

【0037】

This secondary battery operates as follows.

【0038】

In this secondary battery, for example, when charging is performed, lithium ions are released from the positive electrode 21 and are occluded in the negative electrode 22 via the electrolytic solution impregnated in the separator 23. When the electric discharge is performed, for example, lithium ions are separated from the negative electrode 22, and are occluded in the positive electrode 21 via the electrolytic solution impregnated in the separator 23. Here, since the positive electrode 21 has the through hole 21c, the electrolytic solution is sufficiently permeated into the positive electrode 21, and the electrode reaction is sufficiently performed.

【0039】

As described above, according to the present embodiment, since the positive electrode 21 has the through hole 21c, the permeability of the electrolyte to the positive electrode 21 can be increased. Therefore, for example, even if the active material layer 21b is thickened or at the time of high output discharge, the lithium ions can be smoothly moved. Therefore, high capacity and excellent high load characteristics can be obtained. In addition, productivity can be increased.

【0040】

In particular, the total area of the through holes 21c is within the range of 0.1% or more and 10% or less with respect to the area of the active material layer 21b, or the number of through holes 21c is 1 cm.²A higher effect can be obtained by setting the diameter of the through hole 21c to be within the range of 10 μm or more and 10 mm or less.

【0041】

In the above embodiment, the positive electrode 21 is provided with a through hole 21c, but the negative electrode 22 may be provided with a through hole penetrating the current collector 22a and the active material layer 22b, and the positive electrode 21 and the negative electrode may be provided. It may be held in both of 22. If it is provided on both the positive electrode 21 and the negative electrode 22, a higher effect can be obtained. When the negative electrode 22 is provided with through holes, the total area, number, and diameter of the through holes in the negative electrode are the same as those in the above embodiment.

【0042】

[Second Embodiment] FIG. 3 shows a cross-sectional configuration of a positive electrode in a secondary battery according to a second embodiment of the present invention. This secondary battery is the same as that of the first embodiment except that the current collector 21a and the active material layer 21b are replaced with another current collector 41a and the active material layer 41b having no through hole 21c. It has the configuration of. Therefore, here, the same components are designated by the same reference numerals, and detailed description of the same parts will be omitted.

【0043】

The current collector 41a has, for example, a first layer 40a having a void 41d and a second layer 40b provided on both sides of the first layer 40a and having a porosity smaller than that of the first layer 40a. Although not shown, the second layer 40b may be provided on only one side of the first layer 40a. That is, the current collector 41a has a void 41d inside, and a dent is easily formed when a force is applied from the outside. Therefore, as shown in FIG. 4, the active material layer 41b is partially sunk into the current collector 41a by being pressed toward the current collector 41a during molding, and is three-dimensionally different from the current collector 41a. Is in contact with. Further, since the current collector 41a has the second layer 40b having a smaller porosity than the first layer 40a, the contact area between the active material layer 41b and the current collector 41a is larger. As a result, the interfacial resistance between the current collector 41a and the active material layer 41b is reduced, and the physical binding force is also strengthened. In FIG. 4, only the positive electrode active material 41c is shown as a component of the active material layer 41b, and the conductive agent and the binder are omitted.

【0044】

The porosity of the first layer 40a is preferably in the range of 30% or more and less than 100%, and more preferably 50% or more and 90% or less. If the porosity is low, the sinking during molding becomes small, the interfacial resistance between the current collector 41a and the active material layer 41b becomes large, and the physical binding force cannot be sufficiently obtained. This is because the strength and conductivity of the material are reduced. The porosity of the second layer 40b is preferably 5% or less, and may be zero. This is to secure a sufficient contact area between the current collector 41a and the active material layer 41b.

【0045】

In such a current collector 41a, for example, a first layer 40a made of expanded metal, punched metal, or metal non-woven fabric is fused and laminated with rolled metal foil, pressure-bonded and laminated, or metal-deposited or plated. It is produced by forming the second layer 40b.

【0046】

As described above, according to the present embodiment, since the current collector 41a having the first layer 40a and the second layer 40b is used, the interfacial resistance between the current collector 41a and the active material layer 41b is reduced. At the same time, the physical binding force between the current collector 41a and the active material layer 41b can be strengthened. Therefore, it is possible to prevent an increase in interfacial resistance even during long-term use, and it is possible to improve high load characteristics and charge / discharge cycle characteristics.

【0047】

Although the current collector 41a of the positive electrode 21 has been described here, the current collector 22a of the negative electrode 22 may be configured as described above, and both the positive electrode 21 and the negative electrode 22 may be configured as such. You may. It is preferable to apply it to both the positive electrode 21 and the negative electrode 22 because a higher effect can be obtained.

【0048】

[Third Embodiment] FIG. 5 shows a cross-sectional configuration of a positive electrode in a secondary battery according to a third embodiment of the present invention. This secondary battery has the same configuration as that of the first embodiment except that the configuration of the positive electrode is different, and is manufactured in the same manner. Therefore, here, the same components are designated by the same reference numerals, and detailed description of the same parts will be omitted.

【0049】

The positive electrode 21 has the same configuration as the first embodiment, except that the current collector 51a is configured in the same manner as in the second embodiment. That is, the positive electrode 21 is provided with a through hole 51c penetrating the current collector 51a and the active material layer 51b, and the current collector 51a has a first layer 50a having a void 51d and a porosity higher than that of the first layer 50a. Has a small second layer 50b. Therefore, according to the present embodiment, the effects of both the first embodiment and the second embodiment can be obtained. That is, high load characteristics can be improved, and high capacity and excellent charge / discharge cycle characteristics can be obtained.

【0050】

Although the positive electrode 21 has been described here, the negative electrode 22 or both the positive electrode 21 and the negative electrode 22 may be configured in this way.

【0051】

[Example]

Further, specific examples of the present invention will be described in detail.

【0052】

(Examples 1-1 to 1-3) The secondary batteries shown in FIGS. 1 and 2 were produced. Here, the same reference numerals will be used with reference to FIGS. 1 and 2.

【0053】

First, the positive electrode active material, lithium-cobalt composite oxide (LiCoO)₂) 95 parts by mass of powder and lithium carbonate (Li)₂CO₃) 5 parts by mass of powder was mixed, and 91 parts by mass of this mixture was mixed with 6 parts by mass of scaly graphite as a conductive agent and 3 parts by mass of polyvinylidene fluoride as a binder to prepare a positive electrode mixture. Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone, which is a solvent, to form a positive electrode mixture slurry, which is uniformly applied to both sides of a current collector 21a made of a strip-shaped aluminum foil having a thickness of 20 μm and dried. , The active material layer 21b was formed by compression molding. After the active material layer 21b was formed, a through hole 21c having a diameter of about 300 μm was provided by sandwiching the active material layer 21b with a roll having needle-like protrusions to prepare a positive electrode 21. At that time, 1 cm²The number of through holes 21c per hit and the total area of the through holes 21c with respect to the active material layer 21b were changed as shown in Table 1 in Examples 1-1 to 1-3. After that, an aluminum lead wire 25 was attached to one end of the current collector 21a.

【0054】

[table 1]

<img file="JP2003123767A_D0001.tif" />【0055】

Further, 90 parts by mass of graphite powder as a negative electrode active material was mixed with 10 parts by mass of polyvinylidene fluoride as a binder to prepare a negative electrode mixture. Subsequently, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, and then uniformly applied to both sides of a current collector 22a made of a strip-shaped copper foil having a thickness of 10 μm. The negative electrode 22 was prepared by drying and compression molding to form the active material layer 22b. After that, a nickel lead wire 26 was attached to one end of the current collector 22a.

【0056】

After preparing the positive electrode 21 and the negative electrode 22, respectively, a separator 23 made of a microporous polypropylene film having a thickness of 25 μm is prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 are laminated in this order and wound many times to have an outer diameter. A 17.2 mm spiral wound electrode body 20 was produced.

【0057】

After manufacturing the wound electrode body 20, the wound electrode body 20 is sandwiched between a pair of insulating plates 12 and 13, and the lead wire 26 is welded to the battery can 11, and the lead wire 25 is welded to the safety valve mechanism 15. The wound electrode body 20 was housed inside a nickel-plated iron battery can 11. After that, the electrolytic solution was injected into the battery can 11. The electrolytic solution is a solvent in which 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate are mixed, and LiPF is used as a lithium salt.₆1 mol / dm³The one dissolved at the concentration of was used.

【0058】

After injecting an electrolytic solution into the inside of the battery can 11, the battery lid 14 is crimped to the battery can 11 via a gasket 17 coated with asphalt on the surface to maintain the airtightness inside the battery. For 1-3, cylindrical secondary batteries with a diameter of 18 mm and a height of 65 mm were obtained.

【0059】

The obtained Examples 1-1 to 1-3 secondary batteries were subjected to a charge / discharge test to determine the initial discharge capacity and the high load capacity retention rate. At that time, charging was performed with a constant current of 400 mA until the battery voltage reached 4.2 V, and then with a constant voltage of 4.2 V until the total charging time reached 5 hours. Discharge was performed with a constant current of 400mA, 800mA, 2A or 5A until the battery voltage reached 2.75V. The initial discharge capacity is the discharge capacity of the first cycle, and the high load capacity retention rate is the ratio of the discharge capacity when discharged at 400 mA to the discharge capacity when discharged at 5 A, that is, the discharge capacity when discharged at (5 A). It was calculated as (discharge capacity when discharged at / 400mA) x 100. The results obtained are shown in Table 1. In addition, Fig. 6 shows the relationship between the discharge current and the discharge capacity, and Fig. 7 shows the relationship between the total area of the through holes 21c with respect to the active material layer 21b, the high load capacity retention rate, and the discharge capacity when discharged at 400 mA. ..

【0060】

Further, as Comparative Example 1-1 with respect to this Example, a secondary battery was produced in the same manner as in this Example except that the positive electrode was not provided with a through hole. For the secondary battery of Comparative Example 1-1, the initial discharge capacity and the high load capacity retention rate were also determined. The results are also shown in Table 1, Fig. 6 and Fig. 7.

【0061】

As can be seen from Table 1 and FIG. 6, the discharge capacity of this example was larger and the decrease of the discharge capacity was smaller than that of Comparative Example 1-1. Further, according to this embodiment, a sufficient value of 1350 mAh or more was obtained for the discharge capacity when discharging at 400 mA. That is, it was found that if the positive electrode 21 has a through hole 21c, the high load characteristic can be improved while maintaining the discharge capacity.

【0062】

Further, as can be seen from Table 1 and FIG. 7, when the total area of the through holes 21c with respect to the active material layer 21b was increased, the high load capacity retention rate tended to increase and the discharge capacity tended to decrease. That is, it was found that if the total area of the through holes 21c with respect to the active material layer 21b is 0.1% or more and 10% or less, a high discharge capacity and excellent high load characteristics can be obtained.

【0063】

(Examples 1-4 to 1-7) A secondary battery was produced in the same manner as in Example 1-1, except that the negative electrode 22 was provided with a through hole having a diameter of about 300 μm instead of the positive electrode 21. At that time, 1 cm²The number of through holes per hit and the total area of through holes with respect to the active material layer 22b were changed as shown in Table 2 in Examples 1-4 to 1-7. For the secondary batteries of Examples 1-4 to 1-7, the initial discharge capacity and the high load capacity retention rate were determined in the same manner as in Example 1-1. The obtained results are shown in Table 2, FIG. 8 and FIG. 9 together with the results of Comparative Example 1-1.

【0064】

[Table 2]

<img file="JP2003123767A_D0002.tif" />【0065】

As can be seen from Table 2 and FIG. 8, in the same manner as in Examples 1-1 to 1-3, the discharge capacity at the time of high current discharge is larger than that of Comparative Example 1-1, and the discharge capacity is lowered. Was able to be made smaller. In addition, a sufficient value of 1500 mAh or more was obtained for the discharge capacity when discharging at 400 mA. That is, it was found that even if the negative electrode 22 has a through hole, the high load characteristic can be improved while maintaining the discharge capacity.

【0066】

Further, as can be seen from Table 2 and FIG. 9, the relationship between the total area of the through holes with respect to the active material layer 22b, the high load capacity retention rate, and the discharge capacity has the same tendency as in Examples 1-1 to 1-3. It was observed. That is, it was found that if the total area of the through holes with respect to the active material layer 22b is 0.1% or more and 10% or less, a high discharge capacity and excellent high load characteristics can be obtained.

【0067】

(Example 2-1) A positive electrode was prepared using a current collector having a void inside, and its characteristics were investigated. First, as a positive electrode active material, a lithium-manganese composite oxide (LiMn) having a spinel structure with an average particle size of 20 μm₂O₄), 92% by mass of this lithium-manganese composite oxide, 5% by mass of polyvinylidene fluoride as a binder, 1% by mass of carbon black as a conductive agent, and 2% by mass of scaly artificial graphite are mixed to form a positive electrode. The mixture was adjusted. Subsequently, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture slurry. Further, as a current collector, a non-woven fabric made of aluminum is pressed, and a porous aluminum foil having a thickness of 40 μm is prepared by heat-sealing a thin film made of aluminum. Was applied to and dried, and compression molding was performed with an elastic roll press to form an active material layer, which was used as a positive electrode.

【0068】

The peel strength of the prepared positive electrode of Example 2-1 was measured. The peel strength was measured by attaching a tape to the surface of the active material layer and pulling it at a constant speed with a tensile strength tester. The results are shown in Table 3. Next, the positive electrode was punched into a circular shape with a diameter of 15 mm, and the coin-shaped cell shown in FIG. 10 was produced using this as a working electrode. In this coin-shaped cell, the working electrode 61 of this embodiment composed of the current collector 61a and the active material layer 61b and the counter electrode 62 made of lithium metal are laminated via a separator 63, and the electrolytic solution 64 is injected. is there. A polypropylene film having a thickness of 25 μm was used for the separator 63. LiPF as a lithium salt in a solvent in which 50% by volume of ethylene carbonate and 50% by volume of propylene carbonate are mixed in the electrolytic solution 64.₆1.0 mol / dm³The one dissolved at the concentration of was used. These working poles 61 and counter poles 62 were housed inside the outer can 65 and the outer cup 66, and the outer can 65 and the outer cup 66 were sealed by caulking via a gasket 67.

【0069】

[Table 3]

<img file="JP2003123767A_D0003.tif" />【0070】

The produced coin-shaped cell was subjected to a charge / discharge test to investigate its high load characteristics. The results are shown in FIG. In Fig. 11, the horizontal axis is the discharge current density (mA / cm).²), And the vertical axis shows the high load capacity retention rate (%). Charging was performed with a constant current of 1 mA until the battery voltage reached 4.2 V, and then with a constant voltage of 4.2 V until the current value reached 0.01 mA. Discharge is 0.5mA / cm², 3.0mA / cm², 6.0mA / cm²Or 12.0mA / cm²This was done until the battery voltage reached 2.8V at the constant current density of. High load capacity retention rate is 0.5mA / cm²It was calculated as the ratio of the discharge capacity when discharged at each discharge current density to the discharge capacity when discharged in.

【0071】

In addition, a charge / discharge test was performed on the produced unused coin-shaped cell to investigate the charge / discharge cycle characteristics. The results are shown in Fig. 12. In FIG. 12, the horizontal axis shows the number of charge / discharge cycles (times), and the vertical axis shows the capacity retention rate (%). The charging / discharging conditions are the same as those for the high load characteristic measurement described above, and the current density during discharging is 3.0 A / cm.²And said. The capacity retention rate was calculated as the ratio of the discharge capacity in each cycle to the initial discharge capacity (discharge capacity in the first cycle).

【0072】

As Comparative Example 2-1 with respect to this example, a positive electrode was prepared using a current collector made of an aluminum foil having a thickness of 30 μm, and the peel strength of the active material layer on the positive electrode was examined in the same manner as in this example. The results are shown in Table 3. Further, using the positive electrode of Comparative Example 2-1 prepared, a coin-shaped cell was prepared in the same manner as in this example, and the high load characteristic and the charge / discharge cycle characteristic were examined. The results are also shown in FIGS. 11 and 12.

【0073】

As can be seen from Table 3, according to this example, the peel strength per unit width was about 7 times that of Comparative Example 2-1. That is, it was found that if a current collector having voids inside is used, the interfacial binding property between the current collector and the active material layer can be improved.

【0074】

Further, as can be seen from FIG. 11, the deterioration of the high load capacity retention rate was smaller in this example than in Comparative Example 2-1. Further, as can be seen from FIG. 12, in this example, the deterioration of the capacity due to the charge / discharge cycle was smaller than that in Comparative Example 2-1. That is, it was found that the high load characteristics and the charge / discharge cycle characteristics can be improved by using a current collector having a void inside.

【0075】

(Example 2-2) Instead of the positive electrode, a negative electrode using a current collector having an internal void was prepared, and its characteristics were investigated. First, a massive artificial graphite having an average particle size of 15 μm was used as the negative electrode active material, and 95% by mass of the massive artificial graphite was mixed with 5% by mass of polyvinylidene fluoride as a binder to prepare a negative electrode mixture. Subsequently, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode mixture slurry. Further, as a current collector, a non-woven fabric made of copper is pressed, and a porous copper foil having a thickness of 30 μm is prepared by heat-sealing a thin film made of copper to the non-woven fabric. The active material layer was formed by compression molding with an elastic roll press machine to form a negative electrode.

【0076】

The peel strength of the prepared negative electrode of Example 2-2 was measured in the same manner as in Example 2-1. The results are shown in Table 4. Next, this negative electrode was punched into a circular shape having a diameter of 15 mm, and using this as a working electrode, a coin-shaped cell shown in FIG. 10 was produced in the same manner as in Example 2-1. A lithium metal was used as the counter electrode.

【0077】

[Table 4]

<img file="JP2003123767A_D0004.tif" />【0078】

The produced coin-shaped cell was subjected to a charge / discharge test to investigate its high load characteristics. The results are shown in FIG. In Fig. 13, the horizontal axis is the discharge current density (mA / cm).²), And the vertical axis shows the high load capacity retention rate (%). Charging was performed with a constant current of 1 mA until the battery voltage reached 4.2 V, and then with a constant voltage of 4.2 V until the current value reached 0.01 mA. Discharge is 0.5mA / cm², 3.0mA / cm², 6.0mA / cm²Or 12.0mA / cm²This was done until the battery voltage reached 2.8V at the constant current density of. High load capacity retention rate is 0.5mA / cm²It was calculated as the ratio of the discharge capacity when discharged at each discharge current density to the discharge capacity when discharged in.

【0079】

In addition, a charge / discharge test was conducted on the produced unused coin-shaped cell to investigate the charge / discharge cycle characteristics. The results are shown in FIG. In FIG. 14, the horizontal axis shows the number of charge / discharge cycles (times), and the vertical axis shows the capacity retention rate (%). The charging / discharging conditions are the same as those for the high load characteristic measurement described above, and the current density during discharging is 3.0 A / cm.²And said. The capacity retention rate was calculated as the ratio of the discharge capacity in each cycle to the initial discharge capacity (discharge capacity in the first cycle).

【0080】

As Comparative Example 2-2 with respect to this example, a negative electrode was prepared using a current collector made of a copper foil having a thickness of 20 μm, and the peel strength between the current collector and the active material layer in the negative electrode was examined in the same manner as in this example. It was. The results are shown in Table 4. In addition, using the negative electrode of Comparative Example 2-2 that was prepared, a coin-shaped cell was prepared in the same manner as in this example, and the high load characteristics and charge / discharge cycle characteristics were examined. The results are also shown in FIGS. 13 and 14.

【0081】

As can be seen from Table 4, according to this example, the peel strength per unit width was about 5 times that of Comparative Example 2-2. That is, it was found that the interfacial bondability between the current collector and the active material layer can be improved by using a current collector having an internal void in the negative electrode as well as the positive electrode.

【0082】

Further, as can be seen from FIG. 13, the deterioration of the high load capacity retention rate was smaller in this example than in Comparative Example 2-2. Further, as can be seen from FIG. 14, in this example, the deterioration of the capacity due to the charge / discharge cycle was smaller than that in Comparative Example 2-2. That is, it was found that the high load characteristics and the charge / discharge cycle characteristics can be improved by using a current collector having an internal void in the negative electrode as well as the positive electrode.

【0083】

Although the present invention has been described above with reference to embodiments and examples, the present invention is not limited to the above embodiments and examples, and can be variously modified. For example, in the above-described embodiments and examples, through holes are provided so as to penetrate the active material layers provided on both sides of the current collector, but even if they are provided so as to penetrate only one of the active material layers. Good.

【0084】

Further, in the above-described embodiments and examples, the materials and manufacturing methods of the metal foil or alloy foil constituting the current collector 22a have been described with specific examples, but the current collector is made of other materials. A metal foil or an alloy foil may be used, or a metal foil or an alloy foil obtained by another production method may be used.

【0085】

Further, in the above-described embodiments and examples, the case where an electrolytic solution which is a liquid electrolyte is used as the solvent has been described, but another electrolyte may be used instead of the electrolytic solution. Other electrolytes include, for example, a gel-like electrolyte in which an electrolytic solution is held in a polymer compound, a solid electrolyte having ionic conductivity, a mixture of a solid electrolyte and an electrolytic solution, or a solid electrolyte and a gel-like electrolyte. A mixture of and can be mentioned.

【0086】

In addition, various polymer compounds can be used as the gel-like electrolyte as long as it absorbs the electrolytic solution and gels. Examples of such a polymer compound include a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, and an ether-based polymer such as polyethylene oxide or a crosslinked product containing polyethylene oxide. Molecular compounds, polyacrylonitrile, and the like can be mentioned. In particular, a fluorine-based polymer compound is desirable from the viewpoint of redox stability.

【0087】

As the solid electrolyte, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ionic conductivity, or an inorganic solid electrolyte composed of ionic conductive glass or ionic crystals can be used. At this time, as the polymer compound, for example, an ether-based polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester-based polymer compound such as polymethacrylate, or an acrylate-based polymer compound may be used alone or mixed. Alternatively, it can be used by copolymerizing it in a molecule. Further, as the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.

【0088】

Furthermore, in the above-described embodiments and examples, a cylindrical or coin-shaped secondary battery having a wound structure has been described, but the present invention has an elliptical or polygonal secondary battery having a wound structure. The same can be applied to a battery or a secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. In addition, it can be applied to a so-called button type or card type secondary battery. Further, it can be applied not only to a secondary battery but also to a primary battery.

【0089】

In addition, in the above embodiments and examples, the case where lithium is used for the electrode reaction has been described, but other alkali metals such as sodium (Na) or potassium (K), or magnesium or calcium (Ca), etc. The present invention can be applied to the case where an alkaline earth metal or another light metal such as aluminum, or lithium or an alloy thereof is used, and the same effect can be obtained. In that case, the positive electrode active material, the negative electrode active material and the electrolyte salt are appropriately selected according to the light metal. Others can be configured in the same manner as in the above embodiment.

【0090】

[Effect of the invention]

As described above, according to the current collector according to claim 1 or the battery according to any one of claims 5 to 7, the first layer having a porosity of 30% or more and less than 100% and the first layer. Since the second layer provided on at least one surface of the first layer and having a porosity of 5% or less is provided, the interfacial resistance with the active material layer can be reduced and the active material layer can be reduced. It is possible to strengthen the physical binding force with. Therefore, it is possible to prevent an increase in interfacial resistance even during long-term use, and it is possible to improve high load characteristics and charge / discharge cycle characteristics.

【0091】

Further, according to the electrode according to any one of claims 2 to 4 or the battery according to any one of claims 8 to 12, a through hole penetrating the current collector and the active material layer. Therefore, the permeability of the electrolyte can be increased. Therefore, for example, even if the active material layer is thickened or even during high-power discharge, the lithium ions can be smoothly moved. Therefore, high capacity and excellent high load characteristics can be obtained. In addition, productivity can be increased.

【0092】

In particular, according to the electrode according to claim 3 or the battery according to claim 9, the total area of the through holes is set to be within the range of 0.1% or more and 10% or less with respect to the area of the active material layer. , Higher effect can be obtained.

【0093】

Further, according to the electrode according to claim 4 or the battery according to claim 12, since a gap is provided inside the current collector, high load characteristics can be improved, and the capacity and capacity are excellent. Charge / discharge cycle characteristics can be obtained.

[Simple explanation of drawings]

[Figure 1]

It is sectional drawing which shows the structure of the secondary battery which concerns on 1st Embodiment of this invention.

[Figure 2]

It is sectional drawing which shows the part of the wound electrode body shown in FIG. 1 enlarged.

[Fig. 3]

It is sectional drawing which shows the structure of the positive electrode which concerns on 2nd Embodiment of this invention.

[Fig. 4]

FIG. 5 is a cross-sectional view schematically showing the state of the interface between the current collector and the active material layer shown in FIG.

[Fig. 5]

It is sectional drawing which shows the structure of the positive electrode which concerns on 3rd Embodiment of this invention.

[Fig. 6]

It is a characteristic figure which shows the relationship between the discharge current and the discharge capacity which concerns on Examples 1-1 to 1-3 of this invention in comparison with Comparative Example 1-1.

[Fig. 7]

A comparative example of the relationship between the total area of through holes for the active material layer in the positive electrode according to Examples 1-1 to 1-3 of the present invention and the discharge capacity when discharged at a high load capacity retention rate and a constant current of 400 mA. It is a characteristic diagram shown in comparison with 1-1.

[Fig. 8]

FIG. 5 is a characteristic diagram showing the relationship between the discharge current and the discharge capacity according to Examples 1-4 to 1-7 of the present invention in comparison with Comparative Example 1-1.

[Fig. 9]

Comparative example of the relationship between the total area of through holes for the active material layer in the negative electrode according to Examples 1-4 to 1-7 of the present invention and the discharge capacity when discharged at a high load capacity retention rate and a constant current of 400 mA. It is a characteristic diagram shown in comparison with 1-1.

[Fig. 10]

It is sectional drawing which shows the structure of the coin-shaped cell produced in the Example of this invention.

[Fig. 11]

It is a characteristic figure which shows the relationship between the discharge current density and the high load capacity retention rate which concerns on Example 2-1 of this invention in comparison with Comparative Example 2-1.

[Fig. 12]

It is a characteristic diagram which shows the relationship between the number of charge / discharge cycles and the capacity retention rate which concerns on Example 2-1 of this invention in comparison with Comparative Example 2-1.

[Fig. 13]

It is a characteristic diagram which shows the relationship between the discharge current density and the high load capacity retention rate which concerns on Example 2-2 of this invention in comparison with Comparative Example 2-2.

[Fig. 14]

It is a characteristic diagram which shows the relationship between the number of charge / discharge cycles and the capacity retention rate which concerns on Example 2-2 of this invention in comparison with Comparative Example 2-2.

[Explanation of symbols]

11 ... Battery can, 12,13 ... Insulation plate, 14 ... Battery lid, 15 ... Safety valve mechanism, 15a ... Disc plate, 16 ... Thermal resistance element, 17,67. .. Gasket, 20 ... wound electrode body, 21 ... positive electrode, 21a, 22a, 41a, 51a, 61a ... current collector, 21b, 22b, 41b, 51b, 61b ... active material layer , 21c, 51c ... Through hole, 22 ... Negative, 23,63 ... Separator, 24 ... Center pin, 25,26 ... Lead wire, 40a, 50a ... First layer, 40b, 50b ... 2nd layer, 41c ... positive active material, 41d, 51d ... void, 61 ... working electrode, 62 ... counter electrode, 64 ... electrolyte, 65 ... Exterior can, 66 ... Exterior cup