JPS5932865B2 - Manufacturing method of positive electrode for alkaline storage batteries - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement in the manufacturing method of a positive electrode for an alkaline storage battery.
The purpose is to provide an electrode plate that is inexpensive, has excellent discharge characteristics, and has a long life.

Conventionally, methods for producing nickel positive electrodes, which are positive electrodes for alkaline storage batteries, can be broadly classified into the following four types.

The first type is a sintered electrode plate, which is made by chemically or electrochemically filling the pores of a porous sintered nickel substrate obtained by sintering nickel powder with an active material. . This electrode plate has the advantage of being excellent in high rate discharge characteristics and cycle life, but has the disadvantages that the sintered substrate is expensive and the active material filling process is complicated. Second
This is called a pocket type, in which the active material nickel hydroxide is pressure-molded together with a conductive agent, and the molded body is inserted into a pocket container made of porous metal. Although this can be produced at low cost, it has the disadvantage of poor high rate discharge characteristics. The third method uses a porous material called foamed metal, which has a three-dimensional network structure and has been developed in recent years.The porous material is filled with active material powder and pressurized to form an electrode plate. be. Although this has relatively good discharge characteristics, it has the disadvantage that the foamed metal itself has poor performance. The fourth type is a so-called mold type in which active material powder is fixed to a porous metal core together with a binder. Although this electrode plate has the advantage of being inexpensive, it has the disadvantages of poor active material utilization and short cycle life. The present invention relates to an improvement of the conventional manufacturing method, particularly the fourth mold type manufacturing method, which greatly improves the active material utilization rate, and has discharge characteristics and cycle life characteristics that are almost the same as the sintering type. It is also characterized by being able to be manufactured at low cost.

The present invention will be explained below using examples. Example 100 parts by weight of nickel hydroxide powder and 15 parts by weight of nickel powder
A 2% aqueous solution of polyvinyl alcohol is added to this mixed powder and kneaded to form a paste.

This paste is applied to both sides of a nickel-plated perforated steel plate with a thickness of 0.06 m, and if necessary, is then dried and fixed to form a porous semi-finished electrode plate with a thickness of about 0.9 U1. The porosity of the semi-finished electrode plate at this time was about 70%. Next, this porous semi-finished electrode plate was subjected to negative electrolysis at a current density of 10 mA/d with the nickel plate as an anode in a 2 molar nickel sulfate solution with a pH of approximately 2, and nickel was electrodeposited into the pores within the electrode plate. let The amount of nickel electrodeposited was 20% by weight of the amount of nickel hydroxide contained in the electrode plate. After completing this electrodeposition, wash with water,
It is dried, and then impregnated with 5 (Fb fluororesin dispersion 1 Polyflon Dispersion D-1 (manufactured by Daikin Industries), dried, and pressurized to a thickness of about 0.711 and a porosity of about 4
A 3% finished plate was obtained. In order to understand the characteristics of the electrode plate obtained here, a discharge rate test and a cycle life test were conducted in a 30% caustic potassium aqueous solution.

Three discharge rates were used: a 5-hour rate, a 1-hour rate, and a 20-minute rate. The active material utilization rate at each discharge rate is shown in the following table. In addition,
The electrode plate thickness and the amount of active material were the same between the conventional sintered type and molded type and the present invention. Next, a cycle life test was conducted using the same three types of electrode plates as in the previous table, with charging at a 5-hour rate for 8 hours and discharging at a 5-hour rate.

As shown in the figure, the results revealed that the product of the present invention had a cycle life almost equivalent to that of the sintered type, and was superior to the molded type. In the figure, A is a product of the present invention, B is a sintered type, and C is a molded type. As is clear from the table above, the active material utilization rate of the product of the present invention is significantly improved compared to the conventional mold type, and is comparable to that of the sintered type.

This is because after the active material mainly composed of nickel hydroxide is fixed to the porous core metal, nickel is electrodeposited in the nickel salt solution, and the presence of nickel near the active material improves the conductivity and makes it active. This is thought to improve the reactivity of the substance. Since this electrodeposited nickel must be present inside the electrode plate, the semi-finished electrode plate must have a certain level of porosity before the electrodeposition operation begins. This porosity is also related to the current density during the electrodeposition operation, and the greater the porosity, the more nickel will be electrodeposited inside the electrode plate even if the current density is increased. That is, the porosity before the electrodeposition operation needs to be 50% or more, and is usually preferably kept at 60 to 80 (:!). In addition, in order to improve the electrodeposition effect, it is necessary to add a conductive agent to the main active material, nickel hydroxide, in advance.
Adding nickel powder as in the example is effective. It was confirmed that at least about 10 parts by weight of the nickel powder should be added to 100 parts by weight of nickel hydroxide. The key point of the present invention is the amount of electrodeposited nickel in addition to the porosity of the semi-finished electrode plate and the effect of adding nickel as described above.

The amount of electrodeposited nickel is related to the active material utilization rate, and as a result of various experiments, in order to ensure the active material utilization rate of 90% or more at a 5-hour rate, the amount of electrodeposited nickel must be approximately It was confirmed that 15% by weight or more is required. The nickel salt solution used for electrodeposition must be one that deposits nickel on the cathode by negative electrolysis, such as nickel sulfate, and as with nickel nitrate, a reduction reaction of nitrate ions occurs to cause the electrodeposition of nickel. Those that are inhibited cannot be used. The present invention also requires impregnation with a fluororesin dispersion and subsequent pressurization after nickel electrodeposition.

That is, after the electrodeposition is completed, the nickel salt solution is removed by washing with water, and then dried. When this is impregnated with a fluororesin dispersion and pressurized, the active material and the electrode are entangled due to the mesh-like entanglement of the fluororesin. A porous core made of nickel and a thin metal sheet is firmly fixed. Therefore, even a porous core made of a thin metal sheet that does not itself have the function of an active material holding container, such as a sintered substrate or foamed metal, can be sufficiently used as a current collector and core material. be. In this way, the strength of the electrode plate is improved and flexibility is ensured, so even when the electrode plate is wound in a spiral, the active material does not fall off. Note that the above pressure may be applied either in the undried state after impregnation with the fluororesin dispersion or in the dry state. In the present invention, the active material utilization rate of nickel hydroxide is improved by electrodeposition of nickel, but this improvement in the active material utilization rate is further enhanced by the addition of cobalt or a cobalt compound. In other words, if cobalt or a cobalt compound such as cobalt hydroxide or cobalt acetate is added to nickel hydroxide, the electrodeposited nickel will precipitate near the nickel hydroxide and the cobalt or cobalt compound. It is thought that the reactivity of nickel oxide is further increased, and the utilization rate is improved by about 5 to 7% compared to the case of using nickel hydroxide alone. In the manufacturing method of the present invention, a paste mainly composed of nickel hydroxide is first fixed to a porous core metal, but a binder with high viscosity is required to maintain the paste state, and polyvinyl alcohol In addition, an aqueous solution of a cellulose derivative substance such as carboxymethyl cellulose, or polyethylene dissolved in an organic solvent can be used. In addition,
After fixing this paste to the core metal, nickel is deposited inside the electrode plate by electrodeposition. If too much binder is used, the deposition will not be sufficient, so the amount of binder must be set appropriately. There is. As described above, the nickel positive electrode manufactured by the manufacturing method of the present invention has improved performance compared to conventional molded electrode plates, and can be manufactured at a low cost without the need for complicated processes like the sintering method. be.

[Brief explanation of drawings]

The figure shows the cycle life characteristics of the electrode plate. A: Electrode plate of the present invention, B: Conventional sintered electrode plate, C: Conventional molded electrode plate.

Claims (1)

[Claims] 1. A porous semi-finished electrode is produced by fixing a paste mainly composed of nickel hydroxide powder and containing at least 10 parts by weight of nickel powder per 100 parts by weight of the nickel hydroxide powder to both sides of a porous core metal. For use in alkaline storage batteries, the plate is then electrolyzed in a nickel salt solution to electrodeposit metallic nickel, washed with water, dried, impregnated with a fluororesin dispersion, and pressurized. Manufacturing method of positive electrode. 2. The method for producing a positive electrode for an alkaline storage battery according to claim 1, wherein the paste is mainly composed of nickel hydroxide and contains nickel, cobalt or a cobalt compound, and a binder.