JPH01151158A - Manufacture of positive electrode for nonaqueous solvent cell - Google Patents

Abstract

PURPOSE:To obtain a positive electrode for a cell excellent in large-current characteristic by kneading, granulating and drying a positive electrode active material, conducting material powder, a thickener and the dispersion of polytetra fluoroethylene(PTFE), coating PTFE on the surface, then forming them into pellets. CONSTITUTION:A positive electrode active material such as MnO, conducting material powder such as graphite, a thickener solution solved with polyacrylic acid or the like in water and polytetra fluoroethylene(PTFE) in water are added and kneaded. The mixture is pressure-extruded into grains, which are dried by a centrifugal granulating machine or the like. The water PTEF dispersion is spray-coated on the surface of the granular black mix. Finally, the coating black mix thus obtained is press-molded into a pellet by a press-molding machine. The positive electrode for a button cell thus produced has the strong binding force among the granular black mix and suppresses the rise of the internal resistance of the cell and shows the excellent large-current characteristic.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a positive electrode for a non-aqueous solvent battery, and more specifically, a method for manufacturing a positive electrode for a non-aqueous battery with excellent battery performance. Regarding the law.

(Prior Art and Problems) An example of a non-aqueous solvent battery that is currently widely used is shown in FIG. The figure is a longitudinal cross-sectional view of a button-type non-aqueous solvent battery.

In the figure, 1 is the positive electrode. The positive electrode l is MnO2, V
205, an active material such as CuO is kneaded with a conductive material, a binder, etc. and formed into pellets or sheets.

2 is a negative electrode crimped to the negative electrode container 3, and is made of Li foil or L
It is composed of an alkali metal foil mainly composed of i.

4 is a separator, for example, porous polypropylene.

The positive electrode 1 is made of a liquid-retentive material such as a polypropylene thin film or a polypropylene nonwoven fabric, and is placed on the positive electrode 1 . This separator 4 contains propylene carbonate, 1.2
- Aprotic organic solvents such as dimethoxyethane LiCI O4 + LiA 04, LiBF4
, LiPF6.

It is impregnated with a non-aqueous electrolyte of a predetermined concentration in which an electrolyte such as L i As F6 is dissolved.

These positive electrode 1, separator (non-aqueous electrolyte) 4, and negative electrode 2 constitute a power generation element as a whole.

Then, this power generation element is housed in a battery container consisting of a positive electrode container 6 and a negative electrode container 3, and a battery is assembled. 5 is an insulating backing.

The positive electrode in such a nonaqueous solvent battery is produced by, for example, kneading a powder of a positive electrode active material and a conductive material, a thickener solution, and a dispersion of polytetrafluoroethylene (binder), followed by granulation and drying. It is produced by a method in which the granular mixture is made into a granular mixture, which is then filled into a mold and pressure-molded to form pellets (JP-A-55-93671, JP-A-55-9).
However, as the demand for large current discharge characteristics for batteries has increased in recent years, a problem has arisen in that the positive electrode mixture expands during discharge, increasing internal resistance and making it impossible to extract large current.

Accordingly, an object of the present invention is to provide a non-aqueous solvent battery that is resistant to increases in internal resistance and has excellent large current discharge characteristics.

[Structure of the Invention] (Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned problems, the present inventors discovered that the granular mixture was pressurized during the production of the positive electrode. It has been found that the objective can be achieved by adding a step of forming a polytetrafluoroethylene (PTFE) film before molding.

That is, the method for producing a positive electrode for a non-aqueous solvent battery of the present invention is as follows: (1) A mixture is prepared by kneading a positive electrode active material, a conductive material powder, a thickener solution, and a polytetrafluoroethylene (PTFE) dispersion. Process; (2)
A step of granulating the mixture and drying it into a granular mixture;
(3) Forming a polytetrafluoroethylene (PTFE) film on the surface of the granular mixture to obtain a coating mixture; (4) Filling the coating mixture into a mold and press-molding it into pellets. It is characterized by consisting of four steps:

The manufacturing process of the present invention will be sequentially explained.

First, as the positive electrode active material used in the first step, positive electrode active materials used in conventional nonaqueous solvent batteries can be used, such as MnO2, V205
, CuO, etc. The positive electrode active material is used in powder form, and preferably has an average particle size of 20 particles or less.

As the conductive substance, for example, fine powder of graphite, acetylene black, carbon black, etc. is used, and the specific surface area is preferably 1Om'/g or more.

As a thickener solution, for example, polyacrylic acid, polyacrylic acid alkali metal group, polyvinyl alcohol, etc. are mixed with water,
It is dissolved in a solvent such as alcohol at a concentration of 1 to 5% by weight.

Polytetrafluoroethylene 7 (P
A dispersion of TFE has a solid content of 30 to 70% by weight and is dispersed in a dispersion medium such as water or alcohol. If the solid content is less than this range, the binding properties of the product will be poor, and if it is too large, the PTFE will not be present uniformly, which is not preferred.

85 to 95 parts by weight of positive electrode active material as described above, 5 to 15 parts by weight of conductive material, 20 to 40 parts by weight of thickener solution, PTF
1 to 5 parts by weight of E-dispersion are mixed and stirred and kneaded to obtain a viscous wetting agent. Stirring and cross-mixing can be carried out in a conventional manner.

Next, a second step in which the wet mixture obtained in the first step is granulated and dried to form a granular mixture will be described. Granulation is carried out by extruding the wet mixture under pressure through holes with a hole diameter of 0.2 to 0.8 mm, and cutting out a cylindrical mixture with a length of 0.5 to 1.0 mm. Next, this is dried, for example, in a centrifugal granulator through which hot dry air of 80 to 120°C is aerated, at a rotation speed of 500 to 1000 rpm,
By drying for 0.5 to 1 hour, the average particle size is 0.2
It can be made into a spherical granular mixture of ~0.8 mm.

Next, PTFE was applied to the surface of the granular mixture obtained in the second step.
The third step of forming a film to obtain a coating mixture will be described. Coating can be carried out by a spraying method, a dipping method, etc. In the case of a spraying method, for example, an aqueous PTFE dispersion having a solid content of 30 to 70% by weight is sprayed using, for example, a spray coating machine. The coating amount is such that the coated PTFE has a solid content of 0.2 to 1.5% by weight based on the granular mixture.

Finally, the fourth step will be described in which the coating mixture obtained in the third step is filled into a mold and pressure-molded into pellets. Fill a mold with a predetermined amount of the coating mixture according to the size of the desired positive electrode, and apply 2 to 6 tOn/Cff1.
In step 2, pressure molding is performed using, for example, a press molding machine.

When the positive electrode thus obtained is incorporated into a battery as shown in FIG.
Due to the coating of E, the binding force between the granular mixture is strengthened, the expansion of the positive electrode mixture during battery discharge is suppressed, and the rate at which the electrolyte is absorbed into the positive electrode mixture is reduced, resulting in the absorption of the electrolyte at the lithium interface or within the separator. Therefore, an increase in internal resistance is suppressed and large current discharge characteristics are improved.

The invention will be explained in more detail by the following examples.

(Example) (1) Production of positive electrode 95 parts by weight of calcined manganese dioxide powder and fine graphite powder (
Specific surface area 20rrf/g) mixed with 5 parts by weight10
00 g, a thickener aqueous solution prepared by dissolving 30 g of polyacrylic acid in 300 g of water, and aqueous PTF with a solid content of 60% by weight.
After adding 50 g of E-dispersion, the mixture was sufficiently stirred and kneaded to produce a viscous wetting agent.

Next, this wet mixture was extruded under pressure through a wire mesh with a hole diameter of 0.5 mm, and a diameter of 0.5 mm and a length of 0.2-0.
An 8 mm cylindrical mixture was cut out.

This was processed in a centrifugal granulator with LOOO'C hot dry air at 11,000 rpm for 0.5 hours, and the particle size was 0.
．． A spherical granular mixture with a size of 2 to 0.8 mm was obtained.

Furthermore, when this granular mixture was spray-coated with a PTFE dispersion having a solid content of 60% by weight using a spray coating machine, a film of PTFE of 0.3% by weight with respect to the granular mixture was formed.

Finally, 0.4 g of this coating mixture was pressure-molded using a press molding machine under conditions of 5 tons/Cm2, and a diameter of 15
A pellet with a thickness of 0.65 mm was obtained, and this was used as a positive electrode.

(2) Assembling the battery The positive electrode pellets are placed in a stainless steel positive electrode container, and on top of the positive electrode pellets made of polypropylene nonwoven fabric, propylene carbonate and 1,2-dimethoxyethane are mixed in l:1
A separator impregnated with an electrolytic solution prepared by dissolving lithium perchlorate at a concentration of 1 mole/liter in a mixed solvent of (volume ratio) is placed, and a metal lithium foil is placed on top of it as a negative electrode. , constituted the power generation element. Next, a stainless steel negative electrode container was mounted on top of this, and an insulating backing (sealing body) made of polypropylene was interposed around the periphery.
The upper part of the positive electrode container was bent inward and the whole was caulked to assemble a button type non-aqueous solvent battery as shown in FIG.

(3) Continuous discharge performance test Regarding the thus manufactured battery equipped with the positive electrode according to the present invention, the drop in terminal voltage over time when a load resistance of IKΩ was applied at 20°C was measured, and the results are shown in Figure 2. (
Shown in A).

As a comparative example, P
A battery equipped with a positive electrode manufactured in the same manner except that it was not coated with TFE dispersion was assembled in the same manner, and a continuous discharge performance test was conducted under the same conditions as above. The results are shown as (B).

[Effects of the Invention] Since the positive electrode manufactured according to the present invention is coated with a PTFE dispersion before the granular mixture is pressure-molded, the granular mixture has a strong binding force among itself and has little expansion.

Therefore, an increase in internal resistance of the battery is suppressed, and a battery with excellent large current discharge characteristics and long life can be provided.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a button-type nonaqueous solvent battery, and FIG. 2 is a battery (A
) and a battery (B) equipped with a positive electrode manufactured by a conventional method.

Claims (1)

[Claims] A step of kneading a powder of a positive electrode active material and a conductive material, a thickener solution, and a dispersion of polytetrafluoroethylene (PTFE) to form a wetting agent; granulating the wetting agent; , drying to form a granular mixture; polytetrafluoroethylene (PTFE) on the surface of the granular mixture.
1. A method for producing a positive electrode for a non-aqueous battery, comprising the following steps: forming a film to obtain a coating mixture; filling the coating mixture into a mold and press-molding it into pellets;