Non-aqueous electrolyte secondary battery

Description: TECHNICAL FIELD [Detailed description of the invention]

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INDUSTRIAL APPLICABILITY The present invention relates to a non-aqueous electrolyte battery, more particularly a non-aqueous electrolyte secondary battery capable of charging and discharging, and particularly relating to improvement of a positive electrode active material, aiming to increase the charge / discharge capacity of the battery. Is.

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[Conventional Techniques] Non-aqueous electrolyte batteries using alkali metals such as lithium and their alloys and compounds as the negative electrode active material have a large discharge capacity due to the insertion or intercalation reaction of the negative electrode metal ions with the positive electrode active material. Both charge reversibility are achieved. Conventionally, as a secondary battery using lithium as a negative electrode active material, V, which can be an intercalation host with respect to lithium.₂O₅Layered or tunneled oxides such as these are also known. For example, LiCoO is a positive electrode active material having a high reversible discharge region of 4 V or more with respect to a lithium negative electrode.₂, LiNiO₂, LiMn₂O₄Only a very limited number of oxides are known, such as, many of which use rare methyl with an extremely small Clarke number as the central metal, difficult to synthesize, charge / discharge cycle reversibility and thermal stability. There was a problem that it was bad.

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PROBLEM TO BE SOLVED: To solve a problem The present invention has been proposed to improve the above-mentioned problems at present, and an object of the present invention is a large battery having a high discharge voltage and excellent charge / discharge characteristics. The purpose is to provide a non-aqueous electrolyte secondary battery for low cost.

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Means for Solving the Problems If the present invention is outlined, the present invention is an invention relating to a non-aqueous electrolyte secondary battery, and the composition formula, AyMPO._４

[A is an alkali metal, M is a combination of both Co and Fe, represented by 0 <y <2], and contains a phosphoric acid compound having an olivine structure having a hexagonal densely packed oxygen skeleton as a positive electrode active material, and is an alkali. A substance capable of storing and releasing metal, alkaline earth metal, or alkali metal or alkaline earth metal ion is used as a negative electrode active material, and the alkali metal ion undergoes an electrochemical reaction with the positive electrode active material or the negative electrode active material. It is characterized in that the substance capable of moving for the purpose is an electrolyte substance.

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BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. AyMPO, the positive electrode active material of the present invention_４ In (0 <y <2), phosphorus is located at the tetrahedral site, and the alkali metal A has an olivine structure located at the octahedral site together with the central metal and M. Olivine compounds are generally ABCO_４Has a composition formula of. Olivin structure and LiMn_２ O_４The difference in the conventional spinel structure represented by is that oxygen ions are densely packed in six directions or cubes. As described above, the positive electrode active material in the present invention is described as {P}.

[AyM] O_４ (Here, the inside of {} is the tetrahedral site,

([] Indicates an octahedral site) is a transition metal phosphoric acid compound, and examples of such a metal element M include a metal element composed of a combination of both Co and Fe. Although the discharge voltage changes slightly when M is different, the basic characteristics as the positive electrode active material are the same. AyMPO_４The olivine phase of (0 <y <2) is in a divalent oxidation state such as Co and Ni, and is M.²⁺In the case of a stable central metal, it can be easily synthesized by mixing a lithium compound and a phosphoric acid compound such as phosphorus pentoxide with the transition metal compound, firing in the air, and then quenching. On the other hand, trivalent oxidation state like iron, M³⁺In the case of a stable central metal, it is necessary to calcinate in a reducing atmosphere such as in a nitrogen gas stream and react while preventing trivalent oxidation. In order to form a positive electrode using this positive electrode active material, a mixture of the compound powder and a binder powder such as polytetrafluoroethylene is pressure-bonded onto a support such as stainless steel, or the mixture powder is conductive. A conductive powder such as acetylene black is mixed to impart acetylene black, and a binder powder such as polytetrafluoroethylene is further added thereto as required, and this mixture is placed in a metal container, or the above-mentioned mixture is added. It is formed by pressure-bonding molding onto a support such as stainless steel, or by dispersing the above-mentioned mixture in a solvent such as an organic solvent to form a slurry and applying it on a metal substrate. Lithium, which is a negative electrode active material, is formed as a negative electrode by forming a sheet in the same manner as that of a general lithium battery and by crimping the sheet to a conductor net such as nickel or stainless steel. In addition to lithium, the negative electrode active material can store and release lithium alloys, lithium compounds, other conventionally known alkali metals such as sodium, potassium, and magnesium, alkaline earth metals, or alkali metals or alkaline earth metal ions. A substance, for example, an alloy of the metal, a carbon material, or the like can be used. Examples of the electrolytic solution include dimethoxyethane, 2-methyl tetrahydrofuran, ethylene carbonate, methylformate, dimethyl sulfoxide, propylene carbonate, acetonitrile, butyrolactone, dimethylformamide, dimethyl carbonate, diethyl carbonate, sulfolane, ethyl methyl carbonate and the like, and alkali metals. A non-aqueous electrolyte solvent in which Lewis acid containing ions is dissolved, a solid electrolyte, or the like can be used. Further, various conventionally known materials can be used for other elements such as structural materials such as separators and battery cases, and there is no particular limitation.

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[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In the examples, the batteries were prepared and measured in a dry box under an argon atmosphere. Further, Example 1 is shown as a reference example of the present invention.

Example 1 FIG. 1 is a cross-sectional view of a coin-type battery which is a specific example of the battery according to the present invention. In the figure, 1 is a sealing plate, 2 is a gasket, 3 is a positive electrode case, 4 is a negative electrode, 5 is a separator, and 6 is a positive electrode combination. The agent pellets are shown. For the positive electrode active material, lithium carbonate, cobalt trioxide, and phosphorus pentoxide are weighed and mixed according to the reaction formula (Chemical formula 1) of the following formula, calcined in the air at 780 ° C. for 15 hours, and then rapidly cooled. LiCoPO obtained₄Was used.

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[Chemical formula 1] Reaction formula: 3Li₂CO₃+ 2Co₃O₄+ 3P₂O₅ 6LiCoPO₄+ 3CO₂+ O₂

An X-ray diffraction pattern of the obtained powder sample is shown in FIG. The X-ray diffraction pattern was identified as the very orthorhombic olivine structure (JCPDS # 32-552). In FIG. 2, the vertical axis represents the X-ray diffraction intensity (arbitrary unit), and the horizontal axis represents 2θ (°). Let this sample be a. This sample a is crushed into a powder, mixed with a conductive agent (acetylene black) and a binder (polytetrafluoroethylene), and then rolled and molded into a positive electrode mixture pellet 6 (thickness 0.5 mm, diameter 15 mm). And said. Next, a metal lithium negative electrode 4 is pressure-arranged on a stainless steel sealing plate 1 and inserted into a recess of a polypropylene gasket 2, and a polypropylene microporous separator 5 and a positive electrode mixture are placed on the negative electrode 4. The pellets 6 are arranged in this order, and LiPF is used as an electrolytic solution in a single solvent of propylene carbonate.₆A coin-type lithium battery having a thickness of 2 mm and a diameter of 23 mm was produced by injecting an appropriate amount of a 1N solution in which the above-mentioned solution was dissolved and impregnating the battery with a positive electrode case 3 made of stainless steel and crimping the battery.

Example 2 Lithium carbonate, cobalt tetraoxide, iron dihydrate iron oxalate, and diammonium hydrogen phosphate were mixed as the positive electrode active material according to the reaction formula (Chemical formula 2) of the following formula, and then weighed and mixed in a nitrogen stream at 780. LiCo obtained by firing at ° C for 15 hours_0.75Fe_0.25PO₄ Was used.

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[Chemical equation 2] Reaction formula: 2Li₂CO₃+ Co₃O₄+ FeC₂O₄2H₂O + 4 (NH₄）₂HPO₄ 4LiCo_0.75Fe_0.25PO₄+ 4CO₂+ 8H₂O + 8NH₃

The X-ray diffraction pattern of the obtained powder sample is LiCoPO.₄And LiFePO₄Similarly, it was identified as having an orthorhombic olivine structure. Let this sample be b.

Example 3 Lithium carbonate, cobalt tetraoxide, iron dihydrate iron oxalate, and diammonium hydrogen phosphate were mixed as the positive electrode active material according to the reaction formula (Chemical equation 3) of the following formula, weighed and mixed, and 780 in a nitrogen stream. LiCo obtained by firing at ° C for 15 hours_0.5 Fe_0.5 PO₄ Was used.

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[Chemical formula 3] Reaction formula: 3Li₂CO₃+ Co₃O₄+ 3FeC₂O₄2H₂O + 6 (NH₄）₂HPO₄ 6LiCo_0.5Fe_0.5PO₄+ 9CO₂+ 13H₂O + 12NH₃+ 2H₂

The X-ray diffraction pattern of the obtained powder sample is LiCoPO.₄And LiFePO₄Similarly, it was identified as having an orthorhombic olivine structure. Let this sample be c.

Example 4 Lithium carbonate, cobalt tetraoxide, iron dihydrate iron oxalate, and diammonium hydrogen phosphate were mixed as the positive electrode active material according to the reaction formula (Chemical formula 4) of the following formula, weighed and mixed, and 780 in a nitrogen stream. LiCo obtained by firing at ° C for 15 hours_0.25Fe_0.75PO₄ Was used.

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[Chemical formula 4] Reaction formula: 6Li₂CO₃+ Co₃O₄+ 9FeC₂O₄2H₂O + 12 (NH₄）₂HPO₄ 12LiCo_0.25Fe_0.75PO₄+ 24CO₂+ 28H₂O + 8O₂+ 24NH₃+ 8H₂O

The X-ray diffraction pattern of the obtained powder sample is shown in FIG. The X-ray diffraction pattern is LiCoPO₄And LiFePO₄

[JCPDS # 40-1499, Triphylite] Similarly, it was identified as having an orthorhombic olivine structure. The vertical axis and the horizontal axis of FIG. 3 have the same meaning as those of FIG. Let this sample be d. The positive electrode active material is LiCo prepared as described above._0.25Fe_0.75PO₄A coin-type lithium battery was produced in the same manner as in Example 1 except that the above was used.

0. Of the batteries prepared in this manner using both samples a (Example 1), b (Example 2), c (Example 3), and d (Example 4) as positive electrode active materials. 25mA / cm²Table 1 shows the 1V termination discharge capacities after the initial charging at 5.3V termination.

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[Table 1] <img file="000002.tif" id="000002" he="070" wi="110" img-format="tif" img-content="drawing" />

As an example, 0.25 mA / cm of sample a.²The initial charge at the end of 5.3 V and the subsequent discharge curve at the current density of 5 are shown in FIG. That is, FIG. 4 shows LiCoPO, which is an embodiment of the present invention.₄It is a characteristic diagram which shows the 5.3V initial charge and the subsequent initial discharge curve of. In FIG. 4, the vertical axis represents the battery voltage (V) and the horizontal axis represents the discharge time (hr). Further, as an example showing the cycle reversibility of the present invention, sample a0.25 mA / cm.²The charge / discharge curve during the voltage regulation charge / discharge cycle test between 5.3V and 4.0V at the current density of is shown in FIG. That is, FIG. 5 shows LiCoPO, which is an embodiment of the present invention.₄It is a characteristic diagram which shows the charge / discharge curve at the time of the voltage regulation test between 5.3V and 4.0V of. In FIG. 5, the vertical axis represents the battery voltage (V) and the horizontal axis represents the charge / discharge time (hr). As is clear from Table 1 and FIG. 4, in the olivine-type phosphoric acid compound positive electrode of the present invention, the higher the cobalt content ratio, the higher the discharge voltage, and the voltage of the discharge voltage flat portion exceeds 4.5 V. On the other hand, when the iron content ratio increases, the 4V region decreases, but instead a flat portion of the discharge voltage of 3V appears, and the discharge voltage can be freely designed by changing the content ratio. Further, as is clear from FIG. 5, it can be seen that the high voltage portion has good cycleability.

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INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to construct a highly practical non-aqueous electrolyte secondary battery having a variable discharge voltage, and it has an advantage that it can be used in various fields.

[Simple explanation of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a coin-type battery according to an embodiment of the present invention.

FIG. 2 is LiCoPO, which is an embodiment of the present invention.₄It is a figure which shows the X-ray diffraction figure of.

FIG. 3 is LiCo, which is an embodiment of the present invention._0.25Fe_0.75PO₄It is a figure which shows the X-ray diffraction figure of.

FIG. 4 is LiCoPO, which is an embodiment of the present invention.₄It is a characteristic diagram which shows the 5.3V initial charge and the subsequent initial discharge curve of.

FIG. 5 is LiCoPO, which is an embodiment of the present invention.₄It is a characteristic diagram which shows the charge / discharge curve at the time of the voltage regulation test between 5.3V and 4.0V of.

[Explanation of symbols] 1: Seal plate, 2: Gasket, 3: Positive electrode case, 4: Negative electrode, 5: Separator, 6: Positive electrode mixture pellet

Continuation of front page (72) Inventor Hideaki Otsuka 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Yoji Sakurai 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Junichi Yamaki 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (56) References Japanese Patent Application Laid-Open No. 6-275277 (JP, A) Japanese Patent Application Laid-Open No. 7-130357 (JP, A) J. Electrochem. S oc. , 1994, Vol. 141, No. 9, pp. 2279-2482 "Electrochemistry and Industrial Physical Chemistry", Electrochemical Association, 1993, Vol. 61, No. 61 No. 2, pp. 224-227 (58) Surveyed field (Int.Cl.⁷, DB name) H01M 4/00 --4/04 H01M 4/36 --4/62 H01M 10/40