JP3035384B2 - Alkaline secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery.

[0002]

2. Description of the Related Art Conventionally, sintered nickel positive electrodes are generally used in alkaline secondary batteries such as nickel cadmium batteries and nickel hydrogen batteries. In recent years, a paste-type nickel positive electrode has been proposed as an electrode in place of the sintered nickel positive electrode, and is partially put into practical use. Such a paste-type nickel positive electrode is manufactured by forming nickel hydroxide as a main active material into a paste, filling the paste into a porous conductive substrate, and then rolling the conductive substrate with a roller press.

In the paste-type nickel positive electrode, it is necessary to hold nickel hydroxide having no self-binding property on the conductive substrate without falling off. For this reason, a three-dimensional porous body such as a fibrous nickel substrate or a felt-like nickel substrate is used as a conductive substrate,
An active material is bound to a conductive substrate by adding a binding agent such as polytetrafluoroethylene to nickel hydroxide to impart a binding property to the active material mixture. For example, in Japanese Patent Publication No. 59-31833, after a nickel sponge-like three-dimensional porous body is filled with nickel hydroxide in the form of a paste, the electrode strength is increased by spraying or impregnating a binder.

However, in an alkaline secondary battery in which the paste-type nickel positive electrode is wound with a negative electrode such as a cadmium electrode or a hydrogen electrode via a separator and accommodated in a battery can, the paste-type nickel positive electrode has poor flexibility. Since a crack is generated by the stretching force applied at the time of winding, there is a problem that the conductive substrate protrudes from the crack generation location, breaks through the separator, and causes an internal short circuit.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, and has been made in consideration of an alkaline secondary battery which suppresses the occurrence of cracks during winding of a paste-type nickel positive electrode to prevent internal short circuit. It is intended to provide a battery.

[0006]

According to the present invention, there is provided an alkaline secondary battery in which a paste-type nickel positive electrode and a negative electrode are wound and housed in a battery can with a separator interposed therebetween. An active material mixture containing nickel hydroxide and polytetrafluoroethylene (PTFE) is filled into a conductive substrate made of a body so that the surface of the substrate is covered with the mixture, and the substrate is rolled by a roller press. Wherein the paste-type nickel positive electrode is wound together with the negative electrode and the separator in the same direction as the rolling direction in the roller press and is housed in the battery can. It is.

The conductive substrate of the paste-type nickel positive electrode is formed of a three-dimensional porous body such as a net, a sponge, a fiber, and a felt, and is made of a metal such as nickel or stainless steel or a resin plated with nickel. Which has been given.

The active material mixture of the paste-type nickel positive electrode may contain additives such as cobalt oxide and a thickener such as carboxymethylcellulose as required in addition to nickel hydroxide and PTFE. The above-mentioned paste-type nickel positive electrode can be manufactured by, for example, the method (a) described below,
(B).

(A) First, a dispersion of PTFE is uniformly mixed with a kneading liquid such as nickel hydroxide, an additive, a thickener, and water to prepare an active material paste. Subsequently, this active material paste is filled into the conductive substrate inside the substrate, and simultaneously molded so that the surface is covered with the active material paste,
dry. Subsequently, the conductive substrate is rolled by a roller press to produce a paste-type nickel positive electrode.

(B) First, an active material paste containing no PTFE is prepared by uniformly mixing a kneading liquid such as nickel hydroxide, an additive, a thickener, and water. Subsequently, the active material paste is filled in the conductive substrate into the inside of the substrate, and at the same time, the surface is covered with the active material paste, and dried. Subsequently, the conductive substrate is sprayed or impregnated with a dispersion of PTFE and dried. Then, the paste-type nickel positive electrode is manufactured by rolling the conductive substrate by a roller press. Examples of the negative electrode include a cadmium negative electrode and a hydrogen storage alloy negative electrode.

[0011]

In a conventional paste-type nickel positive electrode of an alkaline secondary battery, a stretching force is applied when wound to be accommodated in a battery can, so that a crack or the like is generated on the outer peripheral side of a conductive substrate made of a three-dimensional porous body. This was the starting point, and cracks had occurred in the nickel positive electrode. This was because the flexibility of the nickel positive electrode was affected by the strength of the conductive substrate alone.

According to the present invention, a paste type nickel positive electrode obtained by filling a conductive substrate made of a three-dimensional porous body with an active material mixture containing nickel hydroxide and PTFE and rolling the conductive substrate by a roller press is used. By winding the negative electrode and the separator together with the negative electrode and the separator in the same direction as the rolling direction in the roller press and housing the negative electrode and the separator in the battery can, it is possible to suppress the occurrence of cracks during the winding of the paste nickel positive electrode.

That is, in the case of a paste-type nickel positive electrode in which PTFE is mixed in an active material mixture, by rolling with a roller press and applying a shearing force, the PTFE becomes fibrous and entangles and captures nickel hydroxide particles. In addition, the binding strength of the active material particles is increased. This binding strength increases in the rolling direction, especially since the fibrous PTFE is oriented in the rolling direction near the surface. For this reason, cracking of the nickel positive electrode during winding in the same direction as the rolling direction can be suppressed.

Further, a paste type nickel positive electrode is formed by coating the surface of the conductive substrate with an active material mixture having a high binding strength in the rolling direction, and this positive electrode is wound in the same direction as the rolling direction. In addition, the vicinity of the surface of the conductive substrate which receives the largest stretching force at the time of winding is sufficiently reinforced by the active material mixture, and the flexibility of the nickel positive electrode in the winding direction is increased. For this reason, cracks in the nickel positive electrode during winding can be suppressed. Therefore, it is possible to obtain an alkaline secondary battery in which an internal short circuit due to cracking of the nickel positive electrode during winding is prevented.

[0015]

Embodiments of the present invention will be described below in detail. Example 1

First, 90 parts by weight of nickel hydroxide, 10 parts by weight of cobalt oxide, 0.3 part of carboxymethyl cellulose
4.2 parts by weight of PTFE dispersion (solid content 60% by weight)
The active material paste was prepared by kneading 40 parts by weight of water and 40 parts by weight of water.

Further, polyethylene terephthalate (PE)
After nickel plating was applied to the felt-shaped nonwoven fabric manufactured by T), this was annealed to produce a felt-like nickel substrate having a thickness of 1.5 mm.

Then, the inside of the felt-like nickel substrate was filled with the above-mentioned active material paste, and simultaneously, both sides of the substrate were molded so as to be covered with the paste having a thickness of 0.2 mm. This was dried at 100 ° C. for 30 minutes and then rolled by a roller press to a thickness of 0.6 mm. Further cutting,
Current collector welding was performed to produce a paste nickel positive electrode.

The paste-type nickel positive electrode thus obtained was wound together with a paste-type cadmium electrode using a punched metal as a conductive substrate through a polyamide separator in the same direction as the rolling direction in the roller press.
After storing this in a battery can, an alkaline electrolyte was further injected to assemble an alkaline secondary battery. Comparative Example 1 An alkaline secondary battery similar to that of Example 1 was assembled except that a paste-type nickel positive electrode was wound in a direction perpendicular to a rolling direction in a roller press. Comparative Example 2

The filling of the felt-like nickel substrate with the active material paste was performed so that the surface of the substrate was exposed.
A paste-type nickel positive electrode was manufactured in the same manner as in Example 1. Subsequently, an alkaline secondary battery was assembled in the same manner as in Example 1 using the paste-type nickel positive electrode thus obtained.

The internal resistance between both electrodes was measured for each of the 100 alkaline secondary batteries of Example 1 and Comparative Examples 1 and 2. Those having an internal resistance value of less than 1 kΩ were evaluated as defectives due to internal short circuits, and the defective rate (the number of defectives / 10
0). The results are shown in Table 1 below.

Table 1 Surface condition of nickel positive electrode Rolling direction of nickel positive electrode Failure rate Example 1 Same as rolling direction covered with active material mixture 1/100 Comparative Example 1 Rolling covered with active material mixture Perpendicular to the direction 5/100 Comparative Example 2 Nickel substrate is exposed Same as rolling direction 6/100

As is apparent from Table 1, the alkaline secondary battery of Example 1 has a reduced defective rate due to an internal short circuit as compared with Comparative Examples 1 and 2. In this method, an active material mixture is filled into a felt-like nickel substrate of a paste-type nickel positive electrode so that the surface of the substrate is covered with the mixture and rolled, and the paste-type nickel positive electrode is wound in the same direction as the rolling direction. This is due to the fact that the flexibility of the nickel positive electrode in the winding direction can be increased due to the rotation, and the occurrence of cracks in the nickel positive electrode during winding can be suppressed.

The PTFE-free active material paste was filled in a felt-like nickel substrate, dried, and impregnated with a solution obtained by diluting a PTFE dispersion liquid 15 times with water, dried, and then rolled by a roller press. As a result, a paste-type nickel positive electrode in which the surface of the nickel substrate was covered with the active material mixture was produced. The same effect as in Example 1 was obtained for an alkaline secondary battery in which the paste-type nickel positive electrode thus obtained was incorporated in the same manner as in Example 1.

[0025]

As described above in detail, according to the present invention, there is provided an alkaline secondary battery which can suppress occurrence of cracks at the time of winding a paste-type nickel positive electrode to prevent an internal short circuit, and have excellent reliability and mass productivity. Can be provided.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Katsuyuki Hata 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (56) References JP-A-54-110440 (JP, A) JP-A 55-80274 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/32 H01M 10/24-10/30

Claims (1)

(57) [Claims] 1. An alkaline secondary battery in which a paste-type nickel positive electrode and a negative electrode are wound and housed in a battery can with a separator interposed therebetween, wherein the paste-type nickel positive electrode comprises:
An active material mixture containing nickel hydroxide and polytetrafluoroethylene is filled in a conductive substrate made of a three-dimensional porous body so that the surface of the substrate is covered with the mixture, and the substrate is rolled by a roller press. Wherein the paste-type nickel positive electrode is wound in the same direction as the rolling direction in the roller press together with the negative electrode and the separator and housed in the battery can. .