JPH113703A - Manufacturing method of positive electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide P as a binder without deteriorating the filling property or coating property of an active material powder into a conductive substrate.
An object of the present invention is to provide a method for producing a positive electrode for an alkaline storage battery having a high energy density and a long life by making full use of the capability of TFE. A method for producing a positive electrode for a non-sintered alkaline storage battery using an active material containing a metal oxide as a main material, wherein at least PTFE is added to a metal oxide powder and kneaded, A positive electrode plate for an alkaline storage battery is manufactured by filling or coating a conductive substrate with the powdered active material obtained in the step of pulverizing the kneaded material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode for an alkaline storage battery, particularly to a positive electrode using a metal oxide mainly composed of nickel.

[0002]

2. Description of the Related Art In recent years, the use of portable and cordless electric devices has been progressing, and there is a demand for a small-sized and higher-performance secondary battery. For batteries for such applications, nickel
In addition to the cadmium battery, the energy density is about 1.
Alkaline storage batteries such as nickel-hydrogen storage batteries, which are five times larger, have already been put to practical use. There is an increasing demand for higher capacity and higher energy density in these batteries.

[0003] Conventional alkaline storage batteries such as nickel
As a positive electrode plate of a cadmium storage battery, a sintered nickel positive electrode has been used in which a carbonyl nickel powder or the like is sintered in a reducing atmosphere to form a porous substrate and an active material is retained therein. The electrode plate obtained by this method has a feature that it has excellent high-rate discharge characteristics and a long life due to a robust electrode structure. However, the sintered nickel positive electrode has the disadvantage that the cost is high because the substrate is sintered in a high-temperature reducing atmosphere and the active material filling step is relatively complicated. In addition, the maximum porosity of the porous substrate is about 85% in consideration of the strength of the substrate.
The filling amount of the active material is limited, and there is a limit in improving the packing density.

[0004] In order to improve these disadvantages, non-sintered nickel positive electrodes have been widely developed.
For example, a paste-type nickel positive electrode that is directly filled with a powder mainly composed of an active material using a foamed nickel porous body having a porosity of about 95% as a substrate instead of the above substrate has already been put into practical use (for example, No. 50-36935).

[0005] In addition, a fibrous nickel porous body or the like has been developed as a substrate for a paste-type nickel positive electrode. Since these nickel positive electrodes can use a substrate with high porosity, the amount of the active material to be filled can be increased as compared with the case of the sintering method, and the packing density of the electrode plate can be improved. Further, it has a feature that the filling step can be simplified. However, the substrate used for the paste-type nickel positive electrode is relatively expensive, which is a problem in reducing the cost of the battery. In addition, such a substrate has a problem that the cycle life characteristics are deteriorated because the holding power of the active material is inferior to that of the sintered type. Therefore, a method of adding polytetrafluoroethylene having a molecular weight of about 3,000,000 or less (hereinafter referred to as PTFE) as a binder in order to improve the holding power of the active material is described in JP-A-7-65830. .

[0006]

However, when the method described in the above-mentioned Japanese Patent Application Laid-Open No. 7-65830 is used, a sharp increase in the viscosity of the active material slurry containing PTFE can be suppressed, and the active material holding member can be prevented from being violated. Uniform filling is possible, but when PTFE having a molecular weight of 3,000,000 or less is used, 300
Compared to the case of using PTFE with a molecular weight of 10,000 or more,
Due to the inferior fiber strength at the time of fiberization, sufficient binding force cannot be obtained, and the active material falls off from the holder during charge / discharge, and the cycle life characteristics cannot be sufficiently improved. .

SUMMARY OF THE INVENTION The present invention solves such a problem, and a high energy density positive electrode for an alkaline storage battery having excellent cycle life characteristics without impairing the filling property or coating property of an active material powder onto a substrate. It is an object of the present invention to provide a method for producing the same.

[0008]

SUMMARY OF THE INVENTION In order to solve these problems, the present invention provides a method of manufacturing a positive electrode for a non-sintered alkaline storage battery using an active material mainly composed of a metal oxide.
A step of adding at least PTFE and kneading the metal oxide powder, a step of pulverizing the kneaded product obtained in the step, and filling the conductive substrate with the active material powder obtained in the pulverization step, or It is characterized by having a step of applying.

By obtaining an active material in such a manufacturing process, it is possible to obtain a positive electrode active material powder having an improved binding property between the active materials and excellent cycle life characteristics.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The invention described in claim 1 of the present invention is a method for producing a positive electrode for a non-sintered alkaline storage battery using a metal oxide as a main material, wherein the metal oxide is a main material. A step of adding at least PTFE to the powder and kneading the powder,
A step of pulverizing the kneaded material obtained in the step, and a step of filling or coating the conductive substrate with the active material powder obtained in the pulverization step, and having a cycle life of This has the effect of providing a manufacturing method capable of obtaining a positive electrode for an alkaline storage battery having excellent characteristics and a high energy density.

[0011] PTFE is fiberized by mechanical shearing force at the time of kneading the active material powder and at the time of rolling the electrode plate, and obtains an active material retaining force. However, when PTFE is contained in the active material powder, fibrillation occurs during kneading, and a sharp increase in viscosity occurs, which makes it difficult to fill or coat the substrate, which is the active material holder, by a normal method.

However, as described in claim 1 of the present invention, if there is a step of pulverizing the kneaded material containing fibrous PTFE, the above-mentioned problem does not occur and the substrate can be easily filled. Or can be painted. Further, as shown in claim 4 of the present invention, if the pulverized active material powder has passed through a 30-mesh sieve having a mesh size of 500 μm according to Japanese Industrial Standards, it is easier to fill or coat the substrate. Can be worn.

By the way, commercially available PTFE is insoluble in almost all solvents except for special cases, and has a melt viscosity of 3%.
Since it is as high as 10 ¹¹ to ¹² poise at 80 ° C., it is very difficult to determine the molecular weight by a general measuring method. Often used as a measure of practical molecular weight is the specific gravity of a molded article produced under certain molding and heat treatment conditions. The smaller the specific gravity, the larger the molecular weight. In commercial PTFE, it is often expressed using the SSG (standard specific gravity) of a molded product by the American Society for Testing and Materials (hereinafter referred to as ASTM), and is used as an index indicating the physical properties of PTFE. Is more in line with the object of the present invention than expressed in molecular weight.

[0014] The fiber strength at the time of fiberization is PT
The higher the molecular weight of FE, that is, the lower the SSG value, the stronger. Therefore, by using PTFE having an SSG value of less than 2.20 as described in claim 2 of the present invention, the active material holding power when the electrode plate is formed is improved, and the cycle life characteristics of the battery are improved. In addition, fiberized PTFE
Has the effect of preventing the additive from agglomerating and improving the dispersibility of the additive, thus improving the active material utilization of the positive electrode,
The amount of the additive for improving the utilization can be reduced, and the energy density of the electrode can be increased.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the present invention will be described below.

(Example 1) Spherical nickel hydroxide powder 1
100 parts by weight, 10 parts by weight of cobalt hydroxide powder having a particle size of about 1 μm, 3 parts by weight of graphite powder, 2 parts by weight of zinc oxide powder, and PTFE having an SSG value of 2.11.
Ethanol was added to 1 part by weight of the powder, and the mixture was kneaded until the PTFE powder was sufficiently fibrous to prepare an active material kneaded material f.
Further, the active material kneaded material f was pulverized until it passed through a 30-mesh sieve having an opening of 500 μm to prepare an active material powder a as an example of the present invention.

Next, an active material powder b, which is an example of the present invention, was prepared in exactly the same manner as the active material powder a except that PTFE powder having an SSG value of 2.19 was used. Also, an active material powder c as a comparative example was produced in exactly the same manner as the active material powders a and b except that PTFE powder having an SSG value of 2.20 was used.

The active material kneaded material f and the active material powders a to a
c into a foamed nickel porous body as a conductive substrate,
Drying and rolling were performed to produce a non-sintered nickel positive electrode plate. However, when the active material kneaded material f is used, although the electrode plate can be manufactured, the apparent density is low and the particle size is larger than the diameter of the substrate perforation, so that the packing density is 400 mAh / c.
Only about c electrode plates were obtained, which was not very suitable for a high-capacity battery configuration.

Next, a positive electrode plate having a packing density of about 600 mAh / cc prepared by using the active material powders a to c is swirled through a general-purpose hydrogen storage alloy negative electrode and a separator made of a nonwoven fabric made of polypropylene and subjected to hydrophilic treatment. Thus, an AA sealed nickel-metal hydride storage battery was manufactured. The nominal capacity of these batteries is 1200 mAh. As the electrolyte, a solution prepared by dissolving 20 g of lithium hydroxide per liter in an aqueous solution of potassium hydroxide having a specific gravity of 1.30 was used. The battery produced in this way corresponds to the sign of the active material powder used,
Let A to C respectively.

The charging / discharging cycle of these batteries A to C (charging: 1200 mA × 1.5 hours, discharging: 1200
mA, a final voltage of 0.9 V). The measurement was performed for each of five batteries, and the average was taken. With charge and discharge cycle,
FIG. 1 shows a change in battery capacity with respect to the battery capacity in the first cycle.
Shown in The battery life is defined as the time when the battery capacity becomes 60% or less of the capacity in the first cycle.
The battery C has a life of more than 00 cycles,
The capacity deteriorated in about 50 cycles. this is,
In the positive electrode using the PTFE powder having an SSG value of 2.20, the strength of the fiber when fiberized is inferior, so that the active material powder falls off from the substrate and the contact between the substrate and the active material decreases. It is thought to be.

(Example 2) Next, the following test was conducted to examine the optimal pulverization conditions for obtaining the active material powder.

An active material powder d as a comparative example was prepared in exactly the same manner as the active material powder a of Example 1 except that the material was crushed until it passed through a 22-mesh sieve having an opening of 710 μm. Further, an active material powder e as another comparative example was produced in exactly the same manner as the active material powder a of Example 1, except that the material was pulverized until it passed through a 42-mesh sieve having an opening of 355 μm.

Batteries D and E were produced in exactly the same manner as in Example 1 using a positive electrode using these active material powders.

Example 1 for these batteries D and E
A charge / discharge cycle was performed under exactly the same conditions. FIG. 2 shows a change in the battery capacity with respect to the battery capacity in the first cycle accompanying the charge / discharge cycle at this time together with the result of the battery A. The measurement was performed for each of five batteries, and the average was taken. Assuming that the time when the battery capacity becomes 60% or less of the capacity in the first cycle is the life of the battery, the batteries A and D are 500
The battery E shows a life of more than 350 cycles,
The capacity deteriorated in about a cycle. In the battery E, the PTFE fibers in the active material powder are finely cut because the active material powder that has been pulverized until it passes through a 42-mesh sieve having an aperture of 355 μm is used to produce the positive electrode. Therefore, it is considered that the active material holding power was reduced, the active material powder was dropped from the substrate and the contact between the substrate and the active material was reduced, and the cycle life characteristics were reduced.

On the other hand, although the battery D shows good cycle life characteristics, the positive electrode is manufactured using an active material powder which has been pulverized only until it passes through a 22-mesh sieve having a mesh size of 710 μm. The filling property of the active material powder into the foamed nickel body is poor. Accordingly, an energy density of only about 450 mAh / cc in the case of using an electrode plate was obtained, which proved that this was not suitable as a method for manufacturing a positive electrode of an alkaline storage battery requiring a high energy density.

Although powdery PTFE is used here, it goes without saying that the same result can be obtained by using a dispersion in which PTFE powder is dispersed in a solvent such as water. In addition, here, as a method of manufacturing an electrode plate, a method was described in which a foamed nickel porous body was used for a substrate serving as an active material holding body, and the active material powder was filled in the porous nickel porous body. The same result can be obtained in a method of applying an active material powder by using a substrate whose surface has been processed into an irregular shape as a substrate.

From the above, PTFE is added to a powder mainly composed of a metal oxide and kneaded, and the kneaded material is pulverized to obtain an active material powder. It is preferable to use PTFE having an SSG value of less than 2.20. In order to maintain the active material holding power without lowering the filling property or the coating property on the conductive substrate, a mesh having an aperture of 500 μm is required. It has been found desirable to grind until it passes through a 30 mesh sieve.

[0028]

As described above, according to the present invention, it is possible to maximize the ability of PTFE as a binder without deteriorating the filling property or coating property of an active material powder into a conductive substrate. This is advantageous in that a positive electrode for an alkaline storage battery having a high energy density and a long life can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing cycle life characteristics of batteries A and B according to an embodiment of the present invention and a battery C of a comparative example.

FIG. 2 is a diagram showing cycle life characteristics of a battery A according to an example of the present invention and batteries D and E as comparative examples.

Claims (4)

[Claims] 1. A method for producing a positive electrode for a non-sintered alkaline storage battery using an active material containing a metal oxide as a main material, wherein at least polytetrafluoroethylene is added to a metal oxide powder and kneaded. A method for producing a positive electrode for an alkaline storage battery, comprising a step, a step of pulverizing the kneaded product obtained in the step to obtain an active material powder, and a step of filling or applying the active material powder to a conductive substrate. 2. A method for producing a positive electrode for a non-sintered alkaline storage battery using an active material containing a metal oxide as a main material, wherein at least polytetrafluoroethylene is added to a metal oxide powder and kneaded. And a step of filling or coating the conductive substrate with the active material powder obtained by pulverizing the kneaded material, wherein the polytetrafluoroethylene has an SSG value representing a standard specific gravity according to the American Society for Testing and Materials. 2.20
A process for producing a positive electrode for an alkaline storage battery. 3. The method for producing a positive electrode for an alkaline storage battery according to claim 1, wherein the metal oxide is an oxide mainly composed of nickel. 4. The method for producing a positive electrode for an alkaline storage battery according to claim 1, wherein the active material powder after the pulverizing step is passed through a 30-mesh sieve having a mesh size of 500 μm according to Japanese Industrial Standards.