JPH01267956A - Manufacture of hydrogen absorption alloy electrode - Google Patents

Abstract

PURPOSE:To suppress rise of the internal pressure of a battery at the time of overcharging, by mixing fluoric resin with hydrogen absorption alloy, turning the fluoric resin into fibers, pressurizing them into a sheet, recrushing it, filling a support with the powder obtained from recrushing, or otherwise pressure fitting or coating the powder to/over the support. CONSTITUTION:Fluoric resin is mixed with hydrogen absorption alloy powder, and the resultant is pressurized into a sheet, which is crushed. A support is filled with splinters thus obtained, or otherwise they are pressure fitted or coated into/over the support. This provides satisfactory three-phase interface of the surface of hydrogen absorption alloy due to uniform dispersion of PTFE over the surface of the hydrogen absorption alloy. The mentioned re-crushing enhances the oxygen gas permeability of the hydrogen absorption alloy, and the filling, pressure fitting, or coating process is made easy and uniform. Also the internal pressure of the battery at the time of overcharging is dropped with good reproducibility, and the battery performance enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an improvement in the manufacturing method of a hydrogen storage alloy electrode used as a negative electrode of a nickel-hydrogen storage battery or the like.

Conventional technology Nickel-hydrogen storage batteries use a hydrogen storage alloy as the negative electrode material, which has the property of storing and releasing hydrogen at high density.
It can be sealed and is expected to be a high-energy density battery that far exceeds sealed cylindrical nickel-cadmium storage batteries.

The electrode manufacturing process for secondary battery negative electrodes (hereinafter referred to as alloy negative electrodes) using hydrogen storage alloys generally involves supporting hydrogen storage alloy powders (hereinafter referred to as alloy powders) with a suitable binder. Methods of filling, press-fitting, or applying to the body;
Alternatively, there is a method in which alloy powder is sintered at high temperature in an atmosphere such as an inert gas. However, it cannot be created by sintering.
rM has various problems such as a decrease in hydrogen storage capacity and poor formability due to changes in composition after sintering.

From these viewpoints, a common method for producing an electrode is to mix alloy powder and a binder and fill, press fit, or paint the mixture into a support. However, the oxygen reduction performance of the alloy negative electrode may be significantly affected by differences in the type and amount of the binder used, the state of bonding with the alloy powder, the processing method, etc. Therefore, various materials are being considered as binders in this case, including fluorine resin, polyethylene, and polyvinyl alcohol (hereinafter referred to as PTFE, PE, and PVA, respectively). .

When creating an alloy negative electrode using the above method, basically the following method can be adopted.

(1) In the case of nickel-cadmium storage batteries, as is already known, a hydrophilic binder such as PVA is mixed with alloy powder, and the mixture is filled, press-fitted or coated into a support, and then a predetermined thickness is obtained. How to apply pressure.

(2) A method in which a water-repellent fluororesin such as PTFE and alloy powder are mixed, filled, press-fitted, or painted onto a support, and then pressed to a desired thickness.

(3) A method in which a water-repellent fluororesin such as PTFE and alloy powder are mixed, formed into a sheet, and then filled, press-fitted, or painted onto a support and pressurized to the desired thickness (Japanese Patent Laid-Open No. 8
2-216163).

Problems to be Solved by the Invention In order to completely seal a nickel-metal hydride storage battery that uses a hydrogen storage alloy as the negative electrode, it is necessary to prevent hydrogen gas from being generated from the negative electrode during overcharging and to transfer oxygen gas generated from the positive electrode to the negative electrode. It must be reduced to water at the surface. Therefore,
Generally, a configuration is used in which the capacity of the negative electrode is made larger than that of the positive electrode so that the negative electrode absorbs oxygen gas generated from the positive electrode during overcharging. The oxygen gas absorption reaction is expressed by the following formulas (1) and (2).

3A02 + H2O+ 2 e″″−+ 20 H−
--(1) MH! +20H"'-+MH!-2+2H2
0+2e'''...(2) Here, the oxygen ionization reaction in equation (1) is rate-determining, and in order to improve the oxygen gas absorption capacity in the battery, the reaction rate in equation (1) must be To achieve this, it is necessary to increase the three-phase interface of solid phase, liquid phase, and gas phase on the surface of the negative electrode to expand the effective reaction area of reaction 1.

In method 1 above, since hydrophilic PVA is used as a binder, the amount of components forming the three-phase interface is insufficient, resulting in poor oxygen gas absorption. As a result, the internal pressure of the battery increases, the safety valve of the battery operates, gas scatters outside the battery, the amount of electrolyte decreases, and various battery performances such as discharge capacity deteriorate. Furthermore, in method 2, PTFE, which is a water-repellent binder, is insufficiently bonded to the surface of the hydrogen storage alloy, resulting in a problem in that the internal pressure of the battery increases. In addition, in method 3, the three-phase interface is easily formed, but P
The dispersibility of TFE into the hydrogen storage alloy electrode layer is poor. That is, PTFE is distributed intensively on the electrode surface, smoothing the electrode surface and coating the electrode surface, resulting in poor oxygen gas permeability. In addition, it does not form into a sheet, has poor uniformity in filling, press-fitting, or coating the support, and has no reproducibility in characteristics such as battery internal pressure at the end of charging. In particular, when a three-dimensional support is used, the filling process becomes extremely difficult due to the formation of a sheet.

The present invention is intended to solve these problems, and aims to uniformly and easily fill, press fit, or apply a hydrogen storage alloy to a support, and further to suppress an increase in battery internal pressure during battery charging. That is.

Means for Solving the Problems In order to solve these problems, the present invention mixes a hydrogen storage alloy powder and a fluorine resin, pressurizes the mixture to form a notebook, and then crushes this sheet to obtain a notebook. The pulverized material is filled, press-fitted, or coated onto a support.

Function: With this configuration, the three-phase interface on the surface of the hydrogen storage alloy becomes sufficient due to uniform dispersion of PTFE on the surface of the hydrogen storage alloy. In addition, re-grinding improves the permeability of oxygen gas to the hydrogen storage alloy, making the filling, press-fitting, or coating process into the support easy and uniform, and the battery internal pressure during overcharging is reproducible. This results in improved battery performance.

EXAMPLES Hereinafter, the present invention will be explained with reference to examples. The hydrogen storage alloy used for the negative electrode is MmN i 3. s5”o, 4”o
, a"o, 7s. Mitsushmetal Mm (La: about 26% by weight, Co
: Approximately 52% by weight.

Nd: about 18% by weight, Pr: about 6% by weight, etc.) and Ni
, Mn.

Each sample of Al and Co was put into an arc melting furnace and heated to 1o-4.
After creating a vacuum to ~10-" Torr, arc discharge was performed in an argon gas atmosphere (reduced pressure) to heat and melt the sample. In order to homogenize the sample, it was heated to 1060" in vacuum.
Heat treatment was performed at C for 6 hours. The obtained alloy was coarsely ground and then made into powder with a particle size of 38 μm or less using a ball mill.

Using the alloy powder obtained as described above, as an example, (a) using PTFE powder as a binder, PTFE
3 wt% and 97 wt. The powder was re-pulverized to give a powder, mixed with an organic solvent to form a paste, and then filled into a foamed nickel porous body with a porosity of 96%.

As a comparative example, (b) using PTFE powder as a binder, PTFE
3 wt % of the powder and 97 wt % of the alloy powder were mixed with an organic solvent and made into a paste, which was then filled into a foamed nickel porous body with a porosity of 95 inches.

(C) A 1.5 wt % PVA aqueous solution and alloy powder were mixed as a binder to form a paste, which was then filled into a foamed nickel porous body with a porosity of 96%.

After drying, (a), (b), and (c) were respectively immersed in a KOH aqueous solution with a specific gravity of 1.30 at 50B for 12 hours, washed with water, dried, and pressurized to obtain the dimensions of AA size (39
Negative electrode plate (a), Φ) cut into ×80 x o, 5fl) and having a charge/discharge capacity of 1600mAh,
Cc) was obtained. This electrode was combined with a known foamed metal nickel positive electrode to construct an AA size sealed storage battery with a capacity of 100,100 O. The internal pressure of the battery was measured by making a 1φ hole in the bottom of the battery case and fixing the battery to a fixing device equipped with a pressure sensor. Charging at the time of battery internal pressure measurement was performed at various charging rates up to I CmA, and the positive electrode capacity was 16
The battery was charged to 0%, and the battery internal pressure at that point was taken as the battery internal pressure at that charging rate.

FIG. 1 shows an example (a) and a comparative example (b), respectively.

A battery containing the negative electrode plate of (C) was charged at a charging rate of 0.60 mA.
The behavior of the battery internal pressure increasing with respect to the charging capacity when charging is shown. A is a battery constructed using the negative electrode of Example (a), b is a comparative example (b), and C is a battery constructed using the negative electrode of comparative example (C), respectively. As is clear from comparing a and C, when water-repellent PTFE is used as a binder, the internal pressure of the battery at 1ao% charge is 3.2 kV, and when hydrophilic PVA is used as a binder, (s, skg when charging at 16°
-CM).

This is because in Example A, a three-phase interface is provided to the surface of the hydrogen storage alloy by PTFE, so that the oxygen gas absorption ability is improved7 compared to Comparative Example C. Further, in Comparative Example 2, the battery internal pressure is higher than in Example A. this is,
In Comparative Examples, the PTFE was not fibrous, so it had poor binding properties with the hydrogen storage alloy, and the area covered by the hydrogen storage alloy with PTFH was small, so a three-phase interface was not formed sufficiently. This is because the battery internal pressure increases in Example A as well.

Next, the optimum value of the amount of PTFE added in the present invention was determined. As the hydrogen storage alloy electrode, in Example a, P
The amount of TFE added was 0. Electrodes prepared by the same manufacturing method were used while changing δ~5 and Ow within the ranges shown above. FIG. 2 shows the relationship between the amount of PTFE added and the battery internal pressure when the battery was charged to 150% of the positive electrode capacity at charging rates of 0 and 50 mA.

From this figure, the amount of PTFE added is 0.5 to 4.5wt.
In the range of 0.50 mA, the internal pressure of the battery became 6°C.(Ig-2 or less).

Although a very small amount of PTFE is effective, it is appropriate to add 0.5 wt% or more from a practical standpoint such as the strength of the electrode plate. Also, considering the high energy density of the negative electrode,
A content of 4.5 wt% or more is not preferable. From the above, PTFE
The appropriate amount of addition is 0.5 to 4.5 wt%.

Next, the porosity of the hydrogen storage alloy 7-t in Example a was varied in the range of 10 to 70%, and a hydrogen storage alloy electrode prepared by the same manufacturing method was used as a negative electrode, and the porosity of the sheet was adjusted to the optimum value. It was investigated.

In the process of pressurizing a mixture of PTFE and hydrogen storage alloy to form a sheet, if the porosity of the sheet is 50% or more, the internal pressure of the battery when charged to 150% at a charging rate of 0.5 CmA is 6.9-011 -2 or more, and the battery internal pressure increases by 1.8 h.α or more when the sheet porosity is 50%, which is 3.2 h.α-2. When the porosity of the sheet is 50% or less, the battery internal pressure at 150% charge hardly changes even if the porosity is further reduced. From this, in the process of pressurizing PTFE and hydrogen storage alloy to form a sheet, the porosity of the sheet is set to 60.
% or less is appropriate.

Furthermore, the relationship between the average particle diameter of the mixture powder of the hydrogen storage alloy and PTFE after re-pulverization and the battery internal pressure was investigated. At that time, the negative electrode had an average particle size of the mixture in Example h' of 5 μm.
Hydrogen storage alloy electrodes made using the same manufacturing method were used, with the thickness being varied within the range of ~900 μm.

When the average particle diameter of the mixture is 10 μm or less, 0.50 m
The internal pressure of the battery at 150% overcharging at charging rate A is 6k.
y-Qll-2, and the battery characteristics deteriorated.

However, the larger the average particle diameter of the mixture, the worse the uniformity of filling, press-fitting, or coating onto the support. According to the present invention, the average particle diameter of the mixture is 10 μm to 600 μm.
μm is preferred.

In addition to PTFE, examples of water-repellent binders include tetrafluoroethylene-hexafluoropropylene copolymer,
Fluororesins such as propylene hexafluoride, vinylidene chloride,
Polystyrene, polyisobutylene, etc. can also be used.

Effects of the Invention As described above, according to the present invention, a hydrogen storage alloy and a fluororesin are mixed, the fluororesin is made into fibers, and then,
By pressurizing it into a sheet, re-pulverizing the sheet, and filling, press-fitting or coating the powder into a support,
When fibrous fluororesin is used as a binder for the hydrogen storage alloy, it facilitates uniform filling, press-fitting, and adhesion to the support, and the hydrogen storage alloy surface of the entire electrode has water repellency. As a result of improving the oxygen gas absorption capacity, it is possible to provide a sealed alkaline storage battery that suppresses an increase in battery internal pressure during overcharging.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the amount of electricity charged and battery internal pressure at 0 and 50 mA charging rates depending on the binder used, and Figure 2 shows the relationship between the amount of binder added and the 160-chi charge at 0.50 mA charging rate. FIG. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (4)

[Claims] (1) A step of pressurizing a mixture of a fluororesin and a hydrogen storage alloy powder that electrochemically absorbs and releases hydrogen as an active material into a sheet, a step of pulverizing the sheet, and
A method for producing a hydrogen storage alloy electrode, comprising the step of filling, press-fitting or coating the pulverized material into a support, and then pressurizing it to a desired thickness. (2) The hydrogen storage according to claim 1, wherein the fluororesin is in a powder or dispersion state and is contained in the mixture in an amount of 0.5 to 4.5 wt%. Method for manufacturing alloy electrodes. (3) The method for producing a hydrogen storage alloy electrode according to claim 1, wherein in the step of forming the sheet, pressure is applied until the porosity of the sheet becomes 50% or less. (4) The average particle diameter of the mixture obtained in the step of pulverizing the sheet to obtain a mixture powder of the hydrogen storage alloy and the fluororesin is 10 to 500 μm. A method for producing a hydrogen storage alloy electrode according to item 1.