JPS601759A - Alkaline storage battery - Google Patents

Abstract

PURPOSE:To increase the utilization rate of an active material principally consisting of nickel hydroxide powder and cobalt powder by stopping the initial charging of a positive plate prepared by packing the active material into an active-material-holding body before the electric potential of the positive plate reaches that at which oxygen is generated. CONSTITUTION:Cobalt powder obtained, for example, by subjecting cobalt oxalate to hydrogen reduction is added to nickel hydroxide powder and nickel carbonyl powder before the mixture is mixed with aqueous carboxymethylcellulose solution to make a paste. The paste is then packed into a spongy porous nickel body having a three-dimentionally continuous structure. The thus obtained body, after being dried with hot air and immersed in a dispersion liquid of a fluorine resin, is again dried with hot air before being pressed, thereby making a positive plate. During the process of formation, charging is stopped before the electric potential of the positive electrode reaches that at which oxygen is generated and which corresponds to about 0.5V relative to a mercuric oxide electrode so that the charged rate of Ni(OH)2 held by the positive plate does not exceed 100%. In this case, a very small amount of oxygen gas is generated from the positive plate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alkaline storage battery having a positive electrode plate formed by holding a powdered active material in an active material holder such as a sponge-like porous nickel material. The purpose of this invention is to improve the performance of the positive electrode plate by terminating the potential before it reaches the oxygen generation potential, thereby obtaining an alkaline storage battery with excellent performance.

A sponge-like porous material with a three-dimensional continuous structure and I
The alkaline storage battery obtained by directly applying nickel hydroxide particles, which is the active substance of the positive electrode active material, along with a binder to an active material support such as a ll-shaped nickel porous material or a nickel net has a high capacity. While this is economically advantageous as it makes filling extremely simple and allows a continuous process, on the other hand, due to the large pore diameter of the porous material, the gap between the nickel porous material, which is the current collector, and the active material powder. Another drawback is that sufficient electrical contact between active material particles cannot be obtained, resulting in a low utilization rate. Therefore, attempts have been made to improve the utilization rate by adding conductive materials such as nickel powder and various additives. It is common to use carbonyl nickel V) powder as this conductive material, and it has been proposed to use cobalt powder as an additive, but these effects are not necessarily sufficient and the use of active materials is high. It has the disadvantage that a large amount must be added in order to obtain the desired ratio.

The present invention discontinues the initial charging of a positive electrode plate, which is formed by holding active material powder mainly composed of nickel hydroxide powder and cobalt powder in an active material holder, before the potential of the positive electrode plate reaches the oxygen generation potential. This is based on the discovery that the active material utilization rate is significantly improved.

Examples of the present invention and its effects will be described in detail below.

The positive electrode plate used in the present invention was manufactured as follows. First, 90 parts of nickel hydroxide powder and 10 parts of carbonyl nickel powder are added with cobalt powder, such as cobalt powder obtained by hydrogen reduction of cobalt oxalate, and made into a paste with an aqueous carboxymethylcellulose solution. .3mm, porosity 96%, thickness 1.2I
A sponge-like porous nickel material having a three-dimensionally continuous structure of lllIl is filled. Next, it was dried with hot air at 80℃ for 1 hour, further immersed in a fluororesin dispersion, and then heated again at 80℃.
After drying with hot air at 0° C. for 1 hour, the positive electrode plate according to the present invention was obtained by pressing at a pressure of 500 kg/cnf. Then, as a chemical formation process, this positive electrode plate was mixed with two nickel plates as a counter electrode and S, G, 1,250 (2
0°C) at 25°C using potassium hydroxide aqueous solution.
I charged it with CA. Here, when a positive electrode plate containing metallic cobalt is charged, a reaction corresponding to the oxidation of cobalt at around 75 V and OV occurs partially on the mercury oxide electrode as shown in Figure 1. It is known that after these oxidation reactions are completed, N+ (01-1>2 is oxidized to the group 00H, leading to oxygen generation. Here, the positive electrode potential is about 05 V with respect to the mercuric oxide electrode. Charging was terminated before reaching the corresponding oxygen evolution potential, that is, so that the charging rate of group (Otl) 2 held on the positive electrode plate became 100% or less.In this case, oxygen gas from the positive electrode plate The occurrence of this positive electrode plate was extremely low.
After discharging the mercuric oxide electrode to OV at 20 A, washing and drying it, and using two sintered negative electrode plates as counter electrodes and electrolyte solution, S , G , 1,250 (20°C) potassium hydroxide. Nominal capacity 1. A flooded type battery of OAh according to the present invention was manufactured. For comparison, the charging time for the first chemical conversion step was adjusted to give a charging rate of nickel hydroxide of 160%, and the charging time was adjusted to 160%.
A flooded type battery (B) was manufactured using the conventional Ah method. These batteries are 0. After charging with IOA for 16 hours, the battery was discharged to 0.2 CA with respect to a mercuric oxide electrode to compare active material utilization rates. Figure 2 shows changes in the active material utilization rate when the amount of cobalt added was changed. From the figure, it can be seen that according to the present invention, an extremely high utilization rate can be obtained even with the addition of a small amount of cobalt. It should be noted that in the positive electrode plates used in both batteries, active material did not fall off due to oxygen gas generation or the like during charging.

The reason why a high active material utilization rate can be obtained when the initial charging is terminated before the positive electrode potential reaches the oxygen evolution potential is considered to be due to the following reason.

5- That is, as mentioned above, metallic cobalt reacts with the mercuric oxide electrode at -0.75V and around OV, and eventually becomes Co with high conductivity.

It is thought to be oxidized to OH. However, part of the initial charging process, the sum of the amount of electricity required for the reaction near 75 V and 0.
Less than the amount of electricity assuming that it changes to OH,
It is thought that a part of the cobalt does not completely change to 000H and remains in the electrode plate in the form of metallic cobalt or (support) (OH) 2 . Then, it is thought that it gradually changes to Q100H in the subsequent charging process. Here, it is known that in the presence of water and oxygen, C0(OH)2 chemically changes into a substance called 01 H02, which has an extremely low S degree and is electrochemically inert. Therefore, cobalt is not sufficiently oxidized during the first charge and C11
When a large amount of oxygen is generated from the positive electrode plate when it exists in the positive electrode plate as (OH)2, the 0(Of-1>2 changes to On HO2 and good conductivity within the electrode plate is obtained. However, according to the present invention, cobalt is not sufficiently oxidized during the first charge and remains in the electrode plate as CO(OH)2. However, since the generation of oxygen gas is extremely small, so(7)CO(Ol
It is thought that a good utilization rate can be obtained because 2 hardly changes to C11HO2, and smoothly changes to Co001 in the next charging process, fully demonstrating its effect as an additive. .

As described above, according to the present invention, an alkaline storage battery with excellent performance can be achieved by improving the utilization rate of a positive electrode plate in which an active material holder holds active material powder mainly composed of nickel hydroxide powder and cobalt powder. can be supplied.

In the examples, a sponge-like porous nickel material was used as the active material holder, but a nickel mesh or! It goes without saying that similar effects can be obtained by using an I-shaped nickel porous body.

Further, in the embodiment, the positive electrode plate was charged for the first time before the positive electrode plate was assembled into the battery, but the same effect can be obtained even if the first charge is performed after the uncharged positive electrode plate is assembled into the battery.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing typical charging characteristics of a positive electrode plate containing cobalt, and FIG. 2 is a diagram showing changes in active material utilization when the amount of cobalt added is changed. A: Invention product, B: Conventional product φ)
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Claims (1)

[Claims] 1. A positive electrode formed by holding an active material powder mainly composed of nickel hydroxide powder and cobalt powder in an active material holder, such as a sponge-like porous nickel material, a fibrous nickel porous material, or a nickel mesh. An alkaline '7B battery having a plate, characterized in that the initial charge of the positive plate is terminated before its potential reaches an oxygen evolution potential. 2. The alkaline storage battery according to claim 1, wherein the positive electrode plate is charged for the first time before being assembled into the battery. 3. The alkaline storage battery according to claim 1, wherein the first charging of the positive electrode plate is performed after the positive electrode plate is assembled into the battery.