JPS61263047A - Nickel electrode for alkaline battery - Google Patents

Abstract

PURPOSE:To increase utilization of active material by forming a nickel electrode for a alkaline battery by bonding active material layers mainly comprising nickel hydroxide and cobalt oxide on both sides of a cobalt plated nickel foil. CONSTITUTION:A nickel electrode for alkaline battery is formed in such a way that a nickel foil is plated with cobalt in a cobalt plating bath comprising ammonium cobalt sulfate, and a sheet-like active material 2 obtained by kneading nickel hydroxide and cobalt oxide with a solution containing Teflon is pressed on both sides of the cobalt plated sheet 1. Nickel hydroxide particles having poor conductivity is coated with CoOOH produced from cobalt oxide to improve conductivity and bonding with the nickel foil. Thereby, utilization of the active material is increased and the thin nickel electrode having high performance and good productivity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to nickel electrodes for alkaline batteries.

Conventional technology and wishes Conventionally, the nickel electrodes used in small alkaline batteries are
classified into two types.

One of them is what is called a sinter set, and there are 2~
A nickel nitrate solution is impregnated into a microporous sintered substrate, which is made by sintering fine 3μ nickel powder onto a perforated steel plate. The so-called solution impregnation method is then used to fill the active material by changing it into nickel hydroxide in an alkaline solution. In this case, since the active material is held in the pores of the microporous sintered substrate, there is good contact between the active material and the current collector. However, as is known, filling the active material requires a complicated process, resulting in a very expensive electrode plate.

The other method is to make a paste by adding water and a thickener to a nickel hydroxide active material, and directly fill it into a nickel fiber sintered body consisting of pores of several tens to hundreds of microns. This is called a paste type.

Compared to a sinter set, the manufacturing process is greatly simplified since it starts from the nickel monohydroxide active material itself. However, since it consists of larger pores than a sintered substrate, its current collecting properties are very poor. However, in recent years, it has become possible to obtain performance similar to that of a complete sinter set by adding cobalt oxide to nickel hydroxide.

A manufacturing method that is even simpler than this is to directly coat a Nickel-plated perforated steel plate, Nickel foil, or the like with a nickel hydroxide active material. However, since the contact between the active material and the current collector was even worse than that of the above-mentioned electrode plate produced by this manufacturing method, sufficient performance could not be obtained and it could not be put to practical use.

OBJECTS OF THE INVENTION An object of the present invention is to provide an ultra-thin nickel electrode for alkaline batteries with improved active material utilization, high performance, and excellent productivity.

DESCRIPTION OF THE INVENTION In order to achieve the above-mentioned object, the present invention comprises a cobalt-plated nickel foil, and active material layers mainly composed of nickel hydroxide and cobalt oxide are attached to both sides of the foil.

Example An embodiment of the present invention will be described in detail below.

Using a cobalt plating bath consisting of cobalt ammonium sulfate, ammonium acetate, acetic acid, formalin, cadmium sulfate, etc., a nickel foil with a thickness of 20 to 50 μm was coated to a thickness of 1 μm.
~3μ cobalt plating was applied.

The active material is 90% nickel hydroxide and 10% cobalt oxide.
After adding and mixing well, a small amount of an aqueous solution containing 2% Teflon was added and kneaded well, and a sheet of about 40 μm was formed using a roller press.

FIG. 1 shows a state in which an active material layer 2 is pressed onto both sides of a cobalt-plated nickel foil sheet 1 by a roller. The obtained nickel positive electrode plate 4 has a cobalt-plated nickel foil sheet as a core metal, has active material layers on both sides, and has a thickness of 0.08 to 0.11 IIg. This nickel positive electrode plate was cut into pieces of 2 eta x 4 cm+, and a sandwich structure was formed between this positive electrode plate and two cadmium negative electrode plates having a larger capacity than the positive electrode via seven pallets. This was charged and discharged in a caustic potassium aqueous solution with a specific gravity of 1.26, and the active material utilization rate of the positive electrode plate was measured.

For comparison, a positive electrode plate with the same dimensions and composition and the same amount of active material without cobalt plating on nickel foil, and a positive electrode plate with active material composition of only nickel hydroxide and no cobalt oxide, but with cobalt plating treatment. Positive electrode plate 1 using unplated nickel foil: In addition, a positive electrode plate containing only nickel hydroxide and no cobalt oxide was also tested using nickel foil that had been subjected to part plating treatment. Figure 2 shows the results of these tests. After charging at 0.10 current for 15 hours, the active material utilization rate of the positive electrode plate was compared when discharging at 0.20 current, 0vvs, H9/H90.

In Fig. 2, l is a product of the present invention, I is a product in which an active material containing nickel hydroxide and cobalt oxide is bonded to a nickel foil;
(2) is a nickel hydroxide active material crimped onto a nickel foil, and (2) is a nickel hydroxide active material crimped onto a cobalt-plated nickel foil. As is clear from FIG. 2, when the active material contains cobalt oxide, the utilization rate is improved more than when using only nickel hydroxide, but it is further improved when the nickel foil is plated with cobalt. If the nickel foil is not plated with cobalt, the active material utilization rate will be poor even if the active material contains cobalt oxide, and the capacity will decrease significantly as the cycle progresses.The reason for this is as follows. It is analyzed as shown in .

(OoO), which is insoluble in water but soluble in alkaline electrolyte, is a blue HOOO in alkaline solution.
2- produce ions. These ions turn into Co0OH before charging and discharging the positive electrode, change into a highly conductive substance with lattice defects, and precipitate in a form that coats the nickel hydroxide particles, which have poor conductivity. This 0oOOH footing improves the conductivity between the nickel hydroxide particles,
Electrons reach every corner of the active material. This 0oOOH coated nickel hydroxide contacts the nickel foil current collectors, which have much less surface area than they do.

On the other hand, a 0o00H layer is formed on the surface of the nickel foil due to HOOO2- generated from the cobalt oxide added to the active material, but it is uneven and there is some contact between the nickel foil and the active material particles. However, this is still insufficient. When the nickel foil is plated with cobalt, HOOO2- ions due to dissolution of cobalt are effectively supplied to the contact interface between the Niacel foil and the active material particles. Therefore, a perfect bonding state with good conductivity (3o00H) is formed. However, since plated cobalt is a metal, it dissolves faster in an alkaline electrolyte than cobalt oxide, and when immersed in an electrolyte, it dissolves faster than cobalt oxide. It was necessary to leave the electrode for about 15 to 20 hours.Also, the capacity decrease with the progress of the cycle of electrode 1 was due to insufficient contact between the active material particles and the current collector due to Co0OH. This is thought to be due to the fact that the active material is cut due to expansion and contraction due to discharge.

The nickel foil used in the above examples provided with micropores allows easy attachment of the active material layer, has high production efficiency, and is also better as a current collector.

Effects of the Invention As described above, the present invention can provide an ultra-thin nickel electrode for alkaline batteries with improved active material utilization, high performance, and excellent productivity, so its industrial value is It is extremely large.

[Brief explanation of the drawing]

Figure 1 shows the process of attaching the active material to the current collector. Figure 2
The figure is a diagram comparing the characteristics of various positive electrode plates.

Claims (1)

[Claims] A nickel electrode for an alkaline battery, comprising a cobalt-plated nickel foil and an active material layer mainly composed of nickel hydroxide and cobalt oxide attached to both sides of the foil.