JP3267156B2 - Nickel hydride rechargeable battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen secondary battery, and more particularly to an improvement in the utilization of nickel hydroxide, which is the main active material of the positive electrode.

[0002]

2. Description of the Related Art In recent years, with the spread of portable equipment and the reduction in size and weight of nickel-metal hydride secondary batteries, there has been a strong demand for miniaturization and high capacity as power sources.

[0003] A typical configuration and manufacturing method of a conventional nickel-metal hydride secondary battery will be described below.

First, an electrode group including a positive electrode, a negative electrode, and a separator for electrically insulating both of them is inserted into a metal battery case, and a predetermined amount of an alkaline electrolyte is injected. After that, the upper part of the case is sealed with a sealing plate provided with terminals. The positive electrode used here has a three-dimensionally continuous porosity of 9 made of nickel metal.
A non-sintering type in which a sponge-like porous substrate of 5% or more is filled with nickel hydroxide as an active material is typical, and is widely used as a positive electrode of a high-capacity secondary battery at present. With respect to this non-sintered positive electrode,
No. 765 proposes filling spherical nickel hydroxide. According to this method, the active material can be uniformly and densely filled in the substrate, and a higher capacity can be achieved as compared with the sintered positive electrode. However, the pore diameter of the sponge-like porous substrate is about 200 to 500 μm, and since these pores are filled with spherical nickel hydroxide having a particle diameter of several μm to several tens μm, nickel hydroxide near the skeleton made of nickel metal is used. However, the charge / discharge reaction proceeds smoothly because the conductivity is ensured, but the reaction of nickel hydroxide far away from the skeleton does not proceed sufficiently as near the skeleton because of insufficient conductivity. Therefore, in this non-sintered positive electrode, it is necessary to connect the spherical nickel hydroxide particles with a conductive substance in addition to the spherical nickel hydroxide to be filled. Generally, cobalt hydroxide, cobalt oxide, metal cobalt, or the like is used as the conductive agent.

[0005] In the nickel-hydrogen secondary battery constructed as described above, the alkaline electrolyte sufficiently penetrates between the electrodes, and the electrolytic solution dissolves and precipitates cobalt hydroxide and the like added to the positive electrode active material. After the initial charge / discharge cycle,
Next, aging is performed in an atmosphere at an increased temperature for activation of the hydrogen storage alloy. Here, when cobalt hydroxide is used as the conductive agent, the cobalt hydroxide dissolves in the strong alkaline electrolyte as cobaltate ions. Its solubility is about 100 ppm. The cobaltate ions dissolved in the alkaline electrolyte as described above are reprecipitated in the form of fine particles on the surface of the nickel hydroxide particles during the charging process as a battery to become cobalt hydroxide. It is considered that the nickel hydroxide particles are electrically coupled to each other by forming a thin conductive layer on the surface of the nickel hydroxide particles. Also,
Cobalt hydroxide in the solid state that did not dissolve in the electrolyte,
By the initial charge, the surface is changed to cobalt oxyhydroxide and acts as a conductive agent for electrically connecting the nickel hydroxide particles.

[0006]

However, in the above-described structure, the solubility of the conductive agent added to the positive electrode, such as cobalt hydroxide, in the alkaline electrolyte is at most 2%.
Since it is about 00 ppm, the conductive layer of cobalt oxyhydroxide formed on the surface of the nickel hydroxide particles by dissolution precipitation is extremely thin and weak. Therefore, when the battery is discharged at a high rate or stored at a high temperature, the thin and weak conductive layer is broken and the conductive network is damaged.
Also, cobalt hydroxide in a solid state not dissolved in the alkaline electrolyte is changed to cobalt oxyhydroxide by the initial charge and becomes a conductive agent. In this state, it hardly dissolves in the alkaline electrolyte. After the first charge,
No new conductive layer is formed on the surface of the nickel hydroxide particles. Further, the mixture of nickel hydroxide, which is the main active material, and cobalt hydroxide added as a conductive agent to the sponge-like porous substrate, and the mixture is filled into the sponge-like porous substrate. The utilization rate of nickel hydroxide is affected. For these reasons, the conventional nickel-metal hydride secondary battery has a problem that the utilization rate of nickel hydroxide is greatly reduced or becomes unstable when the battery is subjected to high-rate discharge or high-temperature storage.

An object of the present invention is to provide a nickel-hydrogen secondary battery which has a high active material utilization rate and exhibits stable battery characteristics by enhancing the conductivity between particles of nickel hydroxide which is a main active material of a positive electrode. With the goal.

[0008]

In order to solve the above-mentioned problems, a nickel-hydrogen secondary battery of the present invention comprises a positive electrode having nickel hydroxide as a main active material, a separator, and a negative electrode comprising a hydrogen storage alloy powder. Inside a metal battery case containing an alkaline electrolyte and at least one of cobalt hydroxide, cobalt oxide and metal cobalt in an electrically neutral state not conducting with the electrode and the battery case, and It is positioned so as to be in contact with the alkaline electrolyte.

As a result, cobalt hydroxide or the like located in the battery case dissolves in the alkaline electrolyte to form cobaltate ions, which are formed as cobalt oxyhydroxide on the surface of the nickel hydroxide particles of the positive electrode during the initial charge of the battery. Deposit to form a thin conductive layer. Even after the initial charge, the supply source of this conductive layer, such as cobalt hydroxide, is electrically isolated from the electrodes and the battery case, and is located in a neutral state where no potential is applied. It has no effect and is not oxidized. Therefore, cobalt hydroxide or the like always dissolves in a small amount in the alkaline electrolyte to form cobaltate ions, which are precipitated as cobalt oxyhydroxide on the surface of nickel hydroxide particles, which is the active material of the positive electrode, every time charging is performed. Since a conductive layer is formed to maintain a conductive network connecting the nickel hydroxide particles, the conductivity of the nickel hydroxide particles is increased, and a battery with high active material utilization and stable characteristics is obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention described in claim 1 of the present application is
A positive electrode containing nickel hydroxide as a main active material, a separator, a negative electrode made of a hydrogen storage alloy powder, and a metal battery case containing an alkaline electrolyte are filled with cobalt hydroxide, cobalt oxide, and metallic cobalt. At least one of the electrodes and the battery case is located in a neutral state that is not electrically conductive, in a state in contact with the alkaline electrolyte, cobalt hydroxide and the like here,
Nickel hydroxide particles, which are active materials for the positive electrode, are not oxidized by the charge and discharge of the battery, are dissolved in a small amount in the alkaline electrolyte, and become cobaltate ions at each charge as well as at the first charge. Deposits as cobalt oxyhydroxide on the surface of the surface, constantly forming a thin conductive layer and maintaining the conductive network between the nickel hydroxide particles, increasing the conductivity of the active material and increasing the active material utilization Can be done.

According to a second aspect of the present invention, the positive electrode contains at least one of cobalt hydroxide, cobalt oxide and metallic cobalt as an additive. It changes to conductive cobalt oxyhydroxide at the time of charging, and enhances the conductivity of the positive electrode itself to further improve the utilization rate of nickel hydroxide as an active material.

According to a third aspect of the present invention, there are provided two plate-shaped or film-shaped insulating members which are in contact with an alkaline electrolyte and have ion diffusibility, provided between the inner bottom of the battery and cobalt hydroxide, cobalt oxide and metal. It is arranged in a so-called sandwich shape with at least one of cobalt interposed. The cobalt hydroxide and the like here are electrically isolated from the electrode and the battery case and are in an electrically neutral state, so that no potential is applied even after charging, and the cobalt hydroxide or the like always dissolves in the electrolytic solution. In particular, when this cobalt hydroxide or the like is located between the two insulating members disposed at the bottom of the battery case, a special place is not required, and the insertion of the electrode group into the battery case is obstructed. And it can always be in good contact with the alkaline electrolyte.

[0013]

Next, an embodiment of the present invention will be described with reference to a cylindrical nickel-metal hydride secondary battery shown in FIG.

In FIG. 1, an insulating member 2a formed by punching a polyethylene film having a microporous shape into a disk is placed on the inner bottom of a nickel-plated iron battery case 1, and a particle size of 0.1 μm is placed thereon. １．０1.0 μm of cobalt hydroxide powder 3 is sprinkled, and an insulating member 2b similar to 2a is further placed thereon to form a sandwich shape as a whole. At this time, the amount of the cobalt hydroxide powder 3 was 2% by weight based on nickel hydroxide, which is the main active material of the positive electrode 4. Next, an electrode group in which a strip-shaped positive electrode 4, a polypropylene separator 5, and a negative electrode 6 made of hydrogen storage alloy powder are spirally wound is inserted into the battery case 1 and placed on the insulating member 2b.
Next, a predetermined amount of an alkaline electrolyte 7 is injected into the battery case 1, and then an upper insulating plate 8 made of polyethylene is disposed on the electrode group. A positive electrode lead 9 is spot-welded to the positive electrode 4, and the other end of the positive electrode lead 9 is
The safety valve 10 and the terminal cap 11 are connected to the lower surface of a dish-shaped metal cover 12 which forms a sealing plate together with the terminal cap 11. In addition, 1
Reference numeral 3 denotes an insulating gasket for insulating the battery case 1 from the sealing plate. On the other hand, the negative electrode 6 forms a current collecting structure by directly contacting the core material exposed at the outermost periphery with the inner wall of the battery case 1. The positive electrode used here was 88% by weight of nickel hydroxide powder and 10% by weight of cobalt hydroxide powder.
And 2% by weight of zinc oxide powder were dry-mixed, and 25 parts by weight of pure water was further added to 100 parts by weight of this mixture to prepare a slurry-like active material paste, which was made of a sponge made of nickel and having a porosity of 95%. A porous substrate was filled and dried. This is 1A. In the same manner, a positive electrode made of 98% by weight of nickel hydroxide powder and 2% by weight of zinc oxide powder without mixing cobalt hydroxide powder was designated as 1B. The negative electrode 6 was prepared by applying a paste prepared mainly with a hydrogen storage alloy powder to both sides of a nickel-plated iron sheet and drying the paste. Using the positive electrode 1A, the negative electrode 6 and the separator 5 made of a nonwoven fabric made of polypropylene, a theoretical capacity of 1600
An electrode group of mAh was formed. This was inserted into the battery case 1 according to the above-described procedure, and the opening of the battery case 1 was sealed with a sealing plate to produce a battery A having a size of 4 / 5A. Similarly, a battery having the same configuration as described above was prepared using the positive electrode 1B, and this was designated as Battery B. For comparison, battery case 1
Do not place cobalt hydroxide powder 3 on the inner bottom of
Other than the above, the battery A was the same as the battery A, and the battery prepared using the positive electrode 1B was D. The four types of batteries A, B, C, and D were repeatedly charged and discharged with a current of 1.6 A. FIG. 2 shows the utilization rate of nickel hydroxide as the positive electrode active material at this time. As shown in FIG.
The battery B of the present invention in which the cobalt hydroxide powder 3 is located at the inner bottom of the battery case 1 is an active material more than the batteries C and D in which the cobalt hydroxide powder 3 is not located at the inner bottom of the battery case 1. It can be seen that the utilization rate of nickel hydroxide is improved, and that a stable utilization rate can be obtained even when the battery is repeatedly charged and discharged. This is because the electrode group impregnated with the alkaline electrolyte 7 is in contact with the insulating member 2b, so that the insulating member 2b is also impregnated with the alkaline electrolyte 7 and the cobalt hydroxide in contact with the insulating member 2b is alkaline. Electrolyte 7
This is because a thin conductive layer of cobalt oxyhydroxide is formed on the surface of the nickel hydroxide particles every time the battery is charged. Further, when comparing the batteries A and B, the positive electrode contains cobalt hydroxide in a state mixed with the active material more than the battery B in which the cobalt hydroxide powder 3 is merely located at the inner bottom of the battery case 1. It can be seen that the battery A has the utilization rate of the active material improved by almost 2%. This is because not only the formation of a thin conductive layer of cobalt oxyhydroxide on the surface of the nickel hydroxide particles, but also the number of contact points between the nickel hydroxide particles and the cobalt hydroxide particles located therebetween,
The number of active sites is increased, which means that formation of these reliable conductive networks is effective in increasing active material utilization.

As described above, according to the present embodiment, the cobalt hydroxide powder 3 is located at the inner bottom of the battery case 1 and is dissolved in the alkaline electrolyte 7 so that the conductive oxyhydr By precipitating it as cobalt oxide, a stable and high utilization rate of the active material can be obtained.

In this embodiment, the cobalt hydroxide powder 3 is located at the inner bottom of the battery case 1. However, not only cobalt hydroxide but also cobalt oxide or metallic cobalt is almost the same. The same effect can be obtained by using either one of them alone or in combination of two or more.
In addition, in the battery case 1, not only the inner bottom portion of the case 1 but also the above-mentioned sandwich-shaped spiral electrode group is placed above the separator 5 in contact with the upper end of the separator 5.
May be provided, or may be provided in a part of the inner peripheral surface of the case 1 by lining in a sandwich shape.

[0017]

As described above, according to the present invention, at least one of cobalt hydroxide, cobalt oxide and metal cobalt is electrically neutralized without conducting to the electrode and the battery case inside the battery case. But in contact with the alkaline electrolyte, conductive cobalt oxyhydroxide is deposited on the surface of the nickel hydroxide particles, which is the main active material of the positive electrode, every time the battery is charged. It is possible to provide a nickel-metal hydride secondary battery in which the conductivity of nickel is increased and the utilization rate of an active material is high.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a nickel-metal hydride secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a charge / discharge cycle of a battery and an active material utilization rate in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2a Insulating member 2b Insulating member 3 Cobalt hydroxide 4 Positive electrode 5 Separator 6 Negative electrode 7 Alkaline electrolyte 8 Upper insulating plate 9 Positive electrode lead 10 Safety valve 11 Cap 12 Cover 13 Insulating gasket

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-213317 (JP, A) JP-A-7-135020 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/30

Claims (3)

(57) [Claims] A positive electrode comprising nickel hydroxide as a main active material;
A separator, a negative electrode made of a hydrogen storage alloy powder, and an inside of a battery case that also serves as a terminal of one of the electrodes containing an alkaline electrolyte, at least one of cobalt hydroxide, cobalt oxide, and metallic cobalt. A nickel-hydrogen secondary battery, wherein the nickel-hydrogen secondary battery is located in contact with the alkaline electrolyte and not in conduction with the positive electrode, the negative electrode and the battery case. 2. The positive electrode comprises nickel hydroxide as a main active material,
2. The nickel-metal hydride secondary battery according to claim 1, further comprising at least one of cobalt hydroxide, cobalt oxide and metallic cobalt as an additive. 3. An inner bottom portion of a battery case is provided with two plate-like or film-like insulating members which are in contact with an alkaline electrolyte and have ion diffusibility, and between these two insulating members, cobalt hydroxide and cobalt oxide are provided. And at least one of cobalt and metal cobalt.
Or the nickel-metal hydride secondary battery according to 2.