JP2000011994A - Positive electrode for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the conductivity of a positive pole for obtaining a large- capacity battery improved in charge and discharge cycle characteristic by adhering a conductive high polymer to the surface of a porous sintered body which is formed of lithium transition metal oxide. SOLUTION: The vacancy rate of a porous sintered body is set to 15-60% of the total volume, a mixed powder formed of lithium compound and transition metal compound which are made into an oxide by heat treatment is temporarily burnt, then formed into a designated shape and sintered to form a porous sintered body, and conductive high polymer is adhered to the surface of the sintered body. The conductive high polymer is preferably polyacethylene, polyparaphenylene, polyphenylene vinylene or the like. A nonaqueous secondary battery is preferably formed by the positive electrode, a negative electrode containing negative active material, and an electrolyte obtained by dissolving a lithium compound in an organic solvent, or a solid electrolyte containing lithium ion conductive nonaqueous electrolyte retaining an organic solvent obtained by dissolving a lithium compound in high polymer or dissolving a lithium compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode for a non-aqueous secondary battery using a porous sintered body made of a lithium transition metal oxide and a non-aqueous secondary battery using the same.

[0002]

2. Description of the Related Art With the spread of mobile phones and notebook computers, high-capacity lithium secondary batteries have attracted attention.
Among them, a demand for a thin and space-saving prismatic battery is increasing. Current prismatic batteries use positive and negative electrodes in which a paint mixture of an electrode active material, a binder, and a conductive material is applied on a strip-shaped metal foil to increase the efficiency of the battery reaction by increasing the electrode area. After these are wound together with the separator, they are crushed and stored in the battery can.

The ratio of the active material in this electrode is about 40%.
% By volume, the remainder being binder, conductive material, metal foil, etc.
% By volume and 30 to 40% by volume of pores.
Therefore, there is a problem that a material that does not originally contribute to the capacity of the electrode, such as a binder, a conductive material, or a metal foil, limits the battery capacity per volume. Further, when the wound electrode is housed in a rectangular battery can, the corners of the battery can cannot be filled and wasteful space is created, so that the capacity per unit volume is further reduced.

Therefore, as one means for increasing the capacity per unit volume, attempts have been made to form an electrode from a sintered body substantially made of an active material. When the electrode is formed of a sintered body, the binder is not included, and the conductive material can be unnecessary or reduced to a small amount. Therefore, the packing density of the active material can be increased, and the capacity per unit volume can be increased. At the same time, an improvement in the conductivity of the electrode can be expected. For example, JP-A-5-299090 discloses a negative electrode in which a copper foil is pressed on a sintered body of petroleum pitch or a carbonaceous material, and JP-A-8-180904 discloses a positive electrode made of a sintered body of a lithium composite oxide. Have been.

[0005]

However, at a high current density (for example, 10 mA / cm ² ), it cannot be said that sufficient capacity can be obtained, and the cause is that the internal resistance of the battery is not sufficiently reduced. There's a problem. In particular, the lithium transition metal oxide, which is the active material of the positive electrode, has a large electric resistance, and the reduction of the electric resistance is not sufficient even as a sintered body.

Accordingly, an object of the present invention is to provide a positive electrode for a non-aqueous secondary battery which has improved conductivity and provides high capacity.

[0007]

In order to achieve the above-mentioned object, the present invention solves the above-mentioned problems by using a porous sintered body made of a lithium transition metal oxide having a conductive polymer layer on its surface as a positive electrode. It was completed after finding that it could be solved. That is, the positive electrode for a non-aqueous secondary battery of the present invention is a porous sintered body made of a lithium transition metal oxide, having a conductive polymer layer adhered to the surface of the sintered body. Is what you do. Since the conductive polymer layer is provided on the surface of the porous sintered body, the conductivity of the positive electrode is greatly improved and the internal resistance of the battery can be greatly reduced as compared with the case where a conventional coating film is used.

Preferably, the sintered body is porous and has a porosity of 15 to 60% of the total volume. The dead space in the positive electrode can be reduced, and the active material and the electrolyte can be sufficiently contacted, so that the capacity per unit volume can be increased.

In the method of manufacturing a positive electrode for a non-aqueous secondary battery according to the present invention, a mixed powder comprising a lithium compound and a transition metal compound which becomes an oxide by heat treatment is calcined in an air atmosphere and then formed into a predetermined shape. A heat treatment is performed in an air atmosphere to form a sintered body, and a conductive polymer is applied to the surface of the sintered body.

The nonaqueous secondary battery of the present invention is characterized in that a porous sintered body made of a lithium transition metal oxide having a conductive polymer layer on the surface is used as a positive electrode. A negative electrode containing a negative electrode active material and an electrolyte solution in which a lithium compound is dissolved in an organic solvent, or a lithium ion conductive nonaqueous electrolyte in which a lithium compound is dissolved in a polymer or an organic solvent in which a lithium compound is dissolved is held It is preferable to use a solid electrolyte containing Further, it is preferable to use a porous sintered body also for the negative electrode, whereby a further increase in capacity can be achieved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As the positive electrode material used for the positive electrode of the present invention, any known lithium transition metal oxide can be used, but LiCoO ₂ , LiNi
It is preferable to use any of O ₂ , LiMn ₂ O _{4 having} a spinel structure, and LiCoO ₂ doped with Mg.

The positive electrode of the present invention is obtained by calcining a mixed powder containing a Li compound and a transition metal compound which becomes an oxide by heat treatment at 500 to 900 ° C. for about 0.1 to 10 hours in an air atmosphere, and And 700 ~
By sintering at 1100 ° C. for about 0.5 to 24 hours, a sintered body can be obtained. Here, what becomes an oxide by heat treatment is a hydroxide of Li and a transition metal,
Oxides, nitrates and carbonates.

Further, a conductive polymer is applied to the surface of the sintered body. In the deposition method used in the present invention, the sintered body is used as an anode, and electrolytic oxidative polymerization is performed by immersing the sintered body in an electrolytic solution containing a monomer, or a sintered body is alternately used in a monomer solution and an oxidant solution, or a monomer and an oxidant are used. Examples of the method include liquid-phase chemical oxidative polymerization in which a sintered body is immersed in a solution containing the oxidizing agent at once, or gas-phase chemical oxidative polymerization in which a sintered body is immersed in an oxidizing agent solution and then brought into contact with a gaseous monomer. Alternatively, a method of immersing the sintered body in a solution in which the conductive polymer is dissolved and then removing the solvent may be used.

In the electrolytic oxidation polymerization, oxidation polymerization is performed at a constant voltage or a constant current for a predetermined time in an organic solvent containing a monomer and a supporting electrolyte, using a sintered body as an anode and platinum or the like as a cathode.
A conductive polymer is applied to the surface of the sintered body. The supporting electrolyte includes ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , and AsF as anions.
^{_{6 -, SbF 6 -, AlCl}} 4 -, CF 3 SO 3 - and p- toluenesulfonate and the like can be used quaternary ammonium salts of the alkyl group substituted from 1 to 4 carbon atoms including.

In the chemical oxidative polymerization, a sintered body is immersed in a monomer solution and then immersed in an oxidizing agent solution containing Fe (III) chloride, sulfate, hydrogen peroxide or the like as an oxidizing agent.
The polymer is removed from the solution and left for a predetermined time and temperature to polymerize. When using a gaseous monomer, after immersing the sintered body in the oxidizing agent solution, withdrawing from the solution, fixing the sintered body in a closed container, and introducing the gaseous monomer into the container for a predetermined time to polymerize .

The conductive polymer used in the present invention includes polyacetylene, polyparaphenylene, polyphenylenevinylene, polyphenylene sulfide, polypyrrole, polythiophene, poly (3-methylthiophene), polyaniline, polyperinaphthalene, and the like.

The positive electrode of the present invention has a porosity of 15 to 6
It is preferably a 0% porous body. Although there is a method of simply forming powder and heat-treating the way of opening the holes, it is desirable to use the method described below in order to prevent the electrolyte solution from sufficiently penetrating and obstructing the flow of ions. . That is, organic fibers such as nylon, acrylic, acetate, and polyester (having a diameter of 0.1 to 10) are used as the raw material powder.
0 μm) or organic polymer particles having a diameter of 0.1 to 100 μm are mixed and baked to oxidize and decompose the fibers and the like. Concentration polarization hardly occurs, and the voltage drop can be reduced for a large current. The organic fibers or particles used at this time are preferably completely oxidized and decomposed at a high temperature in an air atmosphere.

The porosity referred to here is an open porosity, and was measured by the Archimedes method described below. Archimedes method: W ₁ , the original sample weight is decompressed or boiled in water, the air in the pores is expelled, cooled and the weight measured in water W ₂ , taken out of the water, wiped only on the surface to remove the water droplet When was the weight and W _3, porosity = apparent porosity (open _{porosity) = (W 3 -W 1)} / (W
₃ −W ₂ ) × 100.

As the negative electrode active material used in the present invention, any material known as a negative electrode active material of a lithium ion secondary battery can be used. For example, carbon materials such as natural graphite, coke and glassy carbon, silicon , Metal lithium, and a metal capable of forming an alloy with metal lithium such as aluminum.

The non-aqueous electrolyte used in the present invention is a non-aqueous electrolyte in which a lithium compound is dissolved in an organic solvent, or a polymer in which a lithium compound is dissolved or an organic solvent in which a lithium compound is dissolved is held. A polymer solid electrolyte can be used. The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used for this type of battery. Examples of the organic solvent include propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane,
1,2-diethoxyethanemethylformate, butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxofuran, 4-methyl-1,
3-dioxofuran, diethyl ether, sulfolane,
Methylsulfolane, acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, 1,2-dichloroethane, 4-methyl-2-pentanone, 1,4-dioxane, anisole, diglyme,
Dimethylformamide, dimethylsulfoxide and the like. Two or more of these solvents can be used in combination.

As the electrolyte, for example, LiClO ₄ , L
iAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C
_{6 H 5) 4, LiCl,} LiBr, LiI, LiCH 3 SO
₃ , LiCF ₃ SO ₃ , LiAlCl _4, etc., and these can be used alone or in combination of two or more.

The solid polymer electrolyte used in the present invention comprises:
A solution obtained by dissolving an electrolyte selected from the above electrolytes in the following polymer can be used. For example, a polymer having a polyether chain such as polyethylene oxide or polypropylene oxide, a polymer having a polyester chain such as polyethylene succinate and polycaprolactam, a polymer having a polyamine chain such as polyethyleneimine, and a polyalkylene sulfide. Such a polymer having a polysulfide chain is exemplified.

Further, as the polymer solid electrolyte used in the present invention, polyvinylidene fluoride, vinylidene fluoride-
It is also possible to use a polymer such as a tetrafluoroethylene copolymer, polyethylene oxide, polypropylene oxide, polyacrylonitrile, or polymethyl methacrylate in which the above non-aqueous electrolyte is retained and plasticized to polymerize the above polymer.

[0024]

【Example】

Embodiment 1 Lithium carbonate powder and cobalt carbonate powder are mixed in a molar ratio of Li / Co = 1/1 and calcined at 800 ° C. for 1 hour in an air atmosphere. Next, this was pulverized, compacted, and fired at 800 ° C. for 10 hours in an air atmosphere to obtain a positive electrode having a diameter of 19 mm and a thickness of 0.5 mm. Pyrrole was electrolytically oxidized and polymerized on the positive electrode for 2 hours in a solution of tetraethylammonium p-toluenesulfonate in acetonitrile (0.05 mol / l) using a SUS plate as a counter electrode and the positive electrode as an electrode. The resistance of this positive electrode was 1 kΩ.

Using a vibration mill, 80 parts of crystalline silicon powder having a purity of 99.9% and an average particle diameter of 1 μm manufactured by Kojundo Chemical Co., Ltd. and 20 parts of pitch-based carbon (residual carbon ratio: 50%) are mixed. Disperse, press-harden this mixed powder, and raise the temperature to 100 ° C./hour;
A molded body fired at 1100 ° C. for 3 hours in a nitrogen atmosphere was used as a negative electrode. The molded body after firing has a diameter of 20 mm and a thickness of 0.1 mm.
5 mm, specific gravity 1.1 g / cm ³ .

A porous polyethylene film is sandwiched between the positive electrode and the negative electrode thus obtained as a separator, and the volume ratio of ethylene carbonate and dimethyl carbonate is 1: 1:
A battery was formed using the mixed solvent of No. 1 and lithium hexafluorophosphate. The cycle characteristics of this battery were good.

[0027]

Comparative Example 1 A positive electrode was produced in the same manner as in Example 1 except that electrolytic oxidation polymerization was not performed. The resistance of the positive electrode was 1000 kΩ.

[0028]

As is apparent from the above description, the positive electrode for a non-aqueous secondary battery of the present invention is a porous sintered body made of a lithium transition metal oxide having a conductive polymer layer adhered to the surface. By using as a positive electrode, the conductivity of the positive electrode can be greatly improved, and the charge / discharge cycle characteristics are improved, so that a nonaqueous secondary battery having a large capacity can be provided.

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Claims (4)

[Claims] 1. A positive electrode for a non-aqueous secondary battery having a porous sintered body made of a lithium transition metal oxide and having a conductive polymer layer adhered to the surface of the sintered body. 2. The porosity of the sintered body is 15 to 6 of the total volume.
The positive electrode for a non-aqueous secondary battery according to claim 1, which is 0%. 3. A calcined mixed powder composed of a lithium compound and a transition metal compound that becomes an oxide by heat treatment, molded into a predetermined shape, and calcined to form a porous sintered body.
A method for producing a positive electrode for a non-aqueous secondary battery, comprising applying a conductive polymer to the surface of the sintered body. 4. A positive electrode made of a porous sintered body of a lithium transition metal oxide having a conductive polymer layer on the surface, a negative electrode containing a negative electrode active material, an electrolytic solution obtained by dissolving a lithium compound in an organic solvent, Alternatively, a non-aqueous secondary battery comprising a solid electrolyte containing a lithium ion conductive non-aqueous electrolyte in which a lithium compound is dissolved in a polymer or an organic solvent in which the lithium compound is dissolved is held.