JPH0734364B2 - Nickel electrode for alkaline batteries - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nickel electrode for alkaline batteries such as nickel-cadmium batteries and nickel-hydrogen batteries.

2. Description of the Related Art Lead storage batteries and alkaline storage batteries are widely used as secondary batteries among various power sources. The most widely used of the latter alkaline batteries is the nickel-cadmium battery. The adoption of a closed structure has become a major factor in expanding the range of practical applications. This battery has fairly excellent characteristics such as high-rate charge / discharge, life, temperature characteristics, and storage characteristics, and its ease of use and high reliability contributed to its practical use.

By the way, the sintering type has been adopted for the nickel electrode constituting the Alcal battery because of its excellent characteristics. However, the sintering method is expensive because the manufacturing method is particularly complicated, and it has been a long time since the non-sintering method has received attention. Generally, in a non-sintering method such as a paste method, it is usual to bind an active material or an active material holding material with a binder to form an electrode.
This binder is required to have strong binding strength with a small amount of addition, be scientifically stable, and not interfere with the battery reaction. Ion-permeable resins such as alcohol and carboxymethyl cellulose and insulating resins such as polyethylene, polystyrene, polyvinyl chloride and rubber-based or fluorine-based resins have been proposed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the nickel electrodes using these binders, when the amount of the binder is small, deterioration of the electrode performance due to repeated charging / discharging is recognized, and when a large amount of the binder is used, the life is improved but the discharge is improved. The characteristics deteriorate. Therefore, it is an important issue to obtain excellent performance for a long time by improving the binder used.

By the way, the nickel electrode changes between nickel hydroxide and nickel oxyhydroxide by charging / discharging, and has a property of swelling due to repeated charging / discharging in addition to the volume change. Therefore, a large amount of binder is required to suppress such volume expansion, but when used in large amounts, both nickel hydroxide and nickel oxyhydroxide may be inferior in terms of conductivity, and this time the performance will drop drastically. Will bring.

An object of the present invention is to provide a nickel electrode that solves the above problems.

Means for Solving the Problems Therefore, styrene-ethylene-butylene-styrene copolymer (SEBS) is used as a binder for nickel electrodes. The amount of addition is preferably about 2 to 20 (Wt)% with respect to the active material. In addition, you may use together other resin centering on this resin.

Action Conventionally, styrene-butadiene copolymers, styrene-isoprene copolymers and the like have been tried as rubber-based resins as binders for nickel electrodes, but they have not been sufficiently effective. The reason why excellent properties can be exhibited for a long period of time by using a styrene-ethylene-butylene-styrene copolymer containing ethylene is not clear. However, the incorporation of ethylene resulted in a synergistic effect of the rubber type, which rather contributes to binding, and the ethylene type, which contributes to electrolytic solution resistance and oxidation resistance.

Example A paste type nickel electrode will be described below as an example.

75 parts of commercially available nickel hydroxide powder, 6 parts of cobalt powder, 15 parts of phosphorous graphite as a conductive agent, 0.8 part of acrylonitrile-based short fiber as a reinforcing agent (weight ratio) and styrene-
3% by weight of ethylene-butylene-styrene copolymer
Toluene solution is added to this resin in an amount of 3.5 parts by weight with respect to the nickel hydroxide powder to form a paste. This paste was applied to an iron-made nickel-plated punching metal plate having a thickness of 0.17 mm, a hole diameter of 1.8 mm, and a porosity of 53%, smoothed through a slit having a width of 0.7 mm, and dried at 120 ° C. for 1 hour. The resulting electrode was pressed three times between rollers that were embossed and pressed to a thickness of 0.6 m.
Adjusted to m. Then, it was further dipped in a 0.3% solution of fluorine resin and dried again at 120 ° C. for 1 hour, and then applied to a sealed nickel-cadmium battery by using the Pate nickel electrode thus obtained.
The battery was a C type. The electrode was cut into a width of 3.9 cm and a length of 26 cm, and lead plates were attached to two predetermined places by spot welding. As a counter electrode, a known paste type cadmium electrode was selected and used with a width of 3.9 cm and a length of 22 cm. Also in this case, the lead plates were attached at two places.

The separator is a polyamide nonwoven fabric, and the electrolyte is 20 g of lithium hydroxide in a caustic potash aqueous solution with a specific gravity of 1.20.
L was used after dissolving. The nominal capacity is 2.8Ah. The battery thus obtained was designated as (A).

For comparison, a battery of nickel electrodes obtained by using the same amount of styrene-butadiene copolymer as the binder (A) in (B) was also added with the same amount of polyethylene in the same high temperature benzene solution. The case was added as (C).

The discharge capacities of these batteries were examined by normal charge / discharge. Charge to 130% at 0.2C (5 hour rate), 0.5C
As a result of discharging to a final voltage of 1.0 V at (2 hour rate), all showed 2.8 to 3.0 Ah and there was no big difference.

Next, a change in discharge capacity was examined by a charge / discharge cycle test. Similarly, charging is up to 130% at 0.2C (5-hour rate),
The discharge was repeated at 0.5C (2 hour rate) until the final voltage was 1.0V.
As a result, the battery (A) of the present invention has 400
It was revealed that the discharge capacity was 2.5 to 2.7 Ah up to about a cycle and the capacity was extremely constant, and the life characteristics were excellent.

On the other hand, in batteries (B) and (C), 5 out of 10 batteries showed an extreme decrease in capacity by 300 cycles, and the remaining 5 batteries.
The discharge capacity of the Ko battery was distributed between 1.8 and 2.1 Ah after 300 cycles.

In the present embodiment, an example in which a punching metal plate having a two-dimensional structure is used as an electrode support, which can obtain the most inexpensive electrode, is shown. It is also effective when used.

The amount of the binder added is small when the three-dimensional structure such as a foamed or fibrous support is used, for example, 2
About 4% is preferable, and for punching metal plates and the like, slightly more than 3% is preferable. In addition, when only life is particularly emphasized, the amount may be further increased up to about 20%.

Further, in this example, an example using a solution of styrene-ethylene-butylene-styrene copolymer was shown, but when an emulsion or dispersion aqueous solution of this resin is used,
Carboxymethyl cellulose and a polyvinyl alcohol aqueous solution, which have been often tried, can be used in combination.

Effects of the Invention As described above, the non-sintered nickel electrode for alkaline batteries obtained by using the styrene-ethylene-butylene-styrene copolymer (SEBS) as the binder can exhibit excellent characteristics for a long period of time.

Claims (2)

[Claims] 1. A nickel electrode for an alkaline battery, which is characterized by using styrene-ethylene-butylene-styrene copolymer (SEBS) as a binder and not sintering. 2. The nickel electrode for an alkaline battery according to claim 1, wherein the content of the styrene-ethylene-butylene-styrene copolymer (SEBS) is 2 to 20% with respect to the active material.