JPH05258767A - Alkaline storage battery - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an alkaline storage battery which has little self-discharge during storage and has excellent storage characteristics. [Structure] A highly liquid-absorbing polymer that forms a hydrogel containing a cross-linked sodium polyacrylate or a polyethylene oxide modified product as a main component in an alkaline electrolyte is added in an amount of 0.5 to 10
It is contained by weight%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline storage battery having less self-discharge and excellent storage characteristics.

[0002]

Conventionally, self-discharge of alkaline storage batteries, NO ₃ produced by the decomposition of a separator made of a polyamide nonwoven fabric ^- NO ₃ remaining ions and the positive electrode ^- ions are eluted into the electrolytic solution after the battery assembly, It was believed that the cause was the shuttle reaction between the positive and negative electrodes [eg S. U. Falk & A. J. Sal
kind "Alkaline Storage Ba
tatteries "p631, John Wiley
& Sons, Inc. , (1969)].

Therefore, it has been considered that countermeasures are to improve the separator and clean the positive electrode after fabrication to make a slight bottom.

However, according to the experiments of the present inventor, the biggest factor causing self-discharge is not the generation of NO ₃ ⁻ ions due to the decomposition of the separator as described above or the NO ₃ ⁻ ions remaining in the positive electrode. It was found that the oxygen generated by the decomposition of the positive electrode active material was dissolved in the electrolytic solution to reach the negative electrode, and the oxygen reacted with the negative electrode active material.

That is, when nickel hydroxide [Ni (OH) ₂ ] is used as the positive electrode active material, nickel hydroxide exists as nickel oxyhydroxide (NiOOH) in the charged state, and the following formula is given during storage. The reaction shown occurs, and oxygen is generated from the 2NiOOH + H ₂ O → 2Ni (OH) ₂ + 1 / 2O ₂ positive electrode, which causes self-discharge.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the above-described conventional alkaline storage batteries that cause self-discharge during storage, and provides an alkaline storage battery with less self-discharge and excellent storage characteristics. To aim.

[0007]

DISCLOSURE OF THE INVENTION The present invention has achieved the above object by incorporating a highly liquid-absorbing polymer which forms a hydrogel into an electrolytic solution.

That is, when the electrolytic solution contains a highly absorbent polymer capable of forming a hydrogel, a network-like matrix of the polymer is formed in the electrolytic solution, and this polymeric matrix is generated at the positive electrode. Since it absorbs oxygen, the oxygen rarely reaches the negative electrode, and the self-discharge is suppressed.

In the present invention, examples of the superabsorbent polymer that forms the hydrogel to be contained in the electrolytic solution include crosslinked sodium polyacrylate, crosslinked potassium polyacrylate, and crosslinked ammonium polyacrylate. Crosslinked polyacrylates such as crosslinked polyacrylic acid salt, crosslinked polymethyl acrylate, crosslinked polyethyl acrylate, etc., crosslinked polymethacrylic acid such as crosslinked polymethylmethacrylate, crosslinked polyethylmethacrylate Esters, polyethylene oxide, modified polyethylene oxide, polymers of maleates such as methyl maleate and ethyl maleate, or copolymers of the above maleates with vinyl acetate, isobutylene, starch, cellulose, etc. Polysaccharides and acrylic acid, acrylic acid A copolymer of acrylonitrile, high absorbent polymer as a main component, such as a crosslinked product of polyvinyl alcohol.

The amount of the superabsorbent polymer forming the hydrogel contained in the electrolytic solution is such that the concentration of the superabsorbent polymer forming the hydrogel in the electrolytic solution is 0.5 to
It is preferably set to 10% by weight.

When the concentration of the superabsorbent polymer which forms the hydrogel in the electrolytic solution is less than 0.5% by weight, the formation of the network matrix by the polymer is not sufficient and the oxygen transfer inhibiting ability becomes insufficient. It is sufficient, and when it is more than 10% by weight, the viscosity becomes too high, which may hinder the battery reaction. A particularly preferred concentration of the superabsorbent polymer forming a hydrogel in the electrolytic solution is in the range of 1 to 5% by weight.

When the superabsorbent polymer that forms a hydrogel is contained in the electrolytic solution, the superabsorbent polymer that forms a hydrogel may be added to the prepared electrolytic solution, or electrolysis may be performed. A superabsorbent polymer that forms a hydrogel may be added during the preparation of the liquid to prepare an electrolytic solution containing the superabsorbent polymer that forms a hydrogel.

Examples of the metal oxide or metal hydroxide used for the positive electrode include nickel monoxide (NiO),
Nickel dioxide (NiO ₂ ), nickel hydroxide [Ni
(OH) ₂ ] is a typical example. However, these are when the positive electrode is in a discharged state, and when the positive electrode is in a charged state, the metal oxide or metal hydroxide is present as another compound.

[0014]

EFFECTS OF THE INVENTION According to the present invention, the superabsorbent polymer forming the hydrogel contained in the electrolytic solution absorbs the oxygen generated from the positive electrode, so that the oxygen generated from the positive electrode reaches the negative electrode. Reaction with the negative electrode active material is reduced, self-discharge during storage is suppressed, and storage characteristics are improved.

[0015]

EXAMPLES Next, the present invention will be described more specifically with reference to examples.

Example 1 30% by weight of water containing 2% by weight of a superabsorbent polymer [Rheozic 835H (trade name) manufactured by Nippon Pure Chemical Co., Ltd.] containing cross-linked branched polyacrylic acid sodium as a main component An aqueous potassium oxide solution was prepared, and using this, an AA alkaline storage battery having the structure shown in FIG. 1 was produced.

Explaining the battery shown in FIG. 1, 1 is a positive electrode, 2 is a negative electrode, 3 is a separator, 4 is a spiral electrode body,
5 is a battery case, 6 is an annular gasket, 7 is a lid, and 8
Is a terminal plate, 9 is a sealing plate, 10 is a metal spring, 11 is a valve body,
Reference numeral 12 is a positive electrode lead body, 13 is a negative electrode insulator, and 14 is a positive electrode insulator.

The positive electrode 1 uses a sintered nickel electrode and is in the form of a sheet containing nickel hydroxide as a positive electrode active material, and the negative electrode 2 is a hydrogen storage alloy capable of reversibly storing and releasing hydrogen. This hydrogen storage alloy was used as an active material and was pressure-bonded to a collector made of nickel expanded metal.

The separator 3 is made of nylon non-woven fabric,
The positive electrode 1 and the negative electrode 2 are stacked via the separator 3 and are spirally wound to form a spiral electrode body 4.

The spiral electrode body 4 is housed in the battery case 5, the positive electrode 1 in the spiral electrode body 4 is connected to the lower portion of the sealing plate 9 by the positive electrode lead body 12, and the negative electrode 2 is The outermost peripheral portion contacts the inner peripheral surface of the battery case 5,
Thereby, the negative electrode 2 and the battery case 5 are electrically connected.

The negative electrode 2 is made by pressing a hydrogen storage alloy onto a current collector, and the positive electrode 1 also uses a nickel sintered body as its substrate. In FIG. 1, these are shown in detail. The internal configurations of the negative electrode 2 and the positive electrode 1 are not shown because they are complicated.

Prior to accommodating the spiral electrode body 4 in the battery case 5, the negative electrode insulator 13 is formed on the bottom of the battery case 5.
, And the positive electrode insulator 14 is arranged on the upper part of the spiral electrode body 4.

The sealing lid 7 is composed of a terminal plate 8 and a sealing plate 9, and the opening of the battery case 5 is sealed by the sealing lid 7 and the annular gasket 6.

The terminal plate 8 is provided with a gas discharge hole 8a,
A gas detection hole 9a is provided in the sealing plate 9, and a metal spring 10 and a valve body 11 are arranged between the terminal plate 8 and the sealing plate 9. Then, the outer peripheral portion of the sealing plate 9 is bent to bend the terminal plate 8
The terminal plate 8 and the sealing plate 9 are fixed by sandwiching the outer peripheral part of the.

Then, 2 ml of an electrolytic solution containing 2% by weight of the superabsorbent polymer whose main component is the cross-linked branched type sodium polyacrylate is injected into this battery.

Also, in this battery, under normal circumstances, the valve body 11 closes the gas detection hole 9a by the pressing force of the metal spring 10, so that the inside of the battery is kept sealed, but the inside of the battery is kept closed. When gas is generated in the battery and the internal pressure of the battery rises abnormally, the metal spring 10 contracts to form a gap between the valve body 11 and the gas detection hole 9a, and the gas inside the battery is detected by the gas detection hole 9a and the gas detection hole 9a. The gas is discharged through the gas discharge hole 8a to the outside of the battery, and the battery is prevented from bursting.

Example 2 30% by weight hydroxylation containing 3% by weight of a superabsorbent polymer [R-30F (trade name) manufactured by Sumitomo Chemical Co., Ltd.] containing a polyethylene oxide modified product as a main component An AA alkaline storage battery having the structure shown in FIG. 1 was produced in the same manner as in Example 1 except that an aqueous potassium solution was used as the electrolytic solution.

Comparative Example 1 The structure shown in FIG. 1 was obtained in the same manner as in Example 1 except that a 30 wt% potassium hydroxide aqueous solution containing no superabsorbent polymer for forming a hydrogel was used as the electrolytic solution. AA
A type alkaline storage battery was produced.

The batteries of Examples 1 and 2 and Comparative Example 1 were charged at 20 ° C. and 0.1 C for 15 hours, stored at 45 ° C. for 3 days, and discharged at 20 ° C. and 0.2 C to obtain a discharge capacity. The measurement was performed, and the capacity retention ratio of the discharge capacity after storage to the discharge capacity before storage was obtained. The results are shown in Table 1.

[0030]

[Table 1]

As shown in Table 1, the batteries of Examples 1 and 2 have a larger capacity retention rate than the battery of Comparative Example 1. This result indicates that the batteries of Examples 1 and 2 of the present invention have less self-discharge and are excellent in storage characteristics as compared with the battery of Comparative Example 1 corresponding to the conventional product.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an enlarged embodiment of an alkaline storage battery of the present invention.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator

Claims (1)

[Claims] 1. A positive electrode containing a metal oxide or metal hydroxide as a positive electrode active material, and a negative electrode containing cadmium, zinc, iron, their oxides, their hydroxides or hydrogen storage alloys as a negative electrode active material. An alkaline storage battery having an electrolytic solution composed of an aqueous alkaline solution, wherein the electrolytic solution contains a highly liquid-absorbent polymer that forms a hydrogel.