JPS61143941A - Manufacture of nickel positive electrode for battery - Google Patents

Abstract

PURPOSE:To increase life and reliability by applying paste whose binder concentration is larger than that of base paste on both sides of an electrode, drying it, and pressing it with a flat plate to form the surface layer whose porosity is larger than that of filled material. CONSTITUTION:500g of 0.5wt% polyvinyl alcohol aqueous solution is added to a mixture of nickel hydroxide, nickel powder and cobalt powder, and they are kneaded to obtain paste. The paste is filled in a spongy nickel porous body having a porosity of 95% and a mean pore diameter of 200mum and dried, then compressed so as to form an irregular surface. 50g of 3wt% polyvinyl alcohol aqueous solution is added to 100g of the mixture having the same mixing ratio as the above mixture to prepare paste. The paste is sprayed on the surface of the substrate and dried, then they are compressed with a flat plate. Thereby, since the surface of the substrate is porous and the large amount of hydrophilic binder exists thereon, electrolyte retention ability on the surface of the substrate is increased. The movement of electrolyte inside the electrode is suppressed and decrease in discharge capacity is retarded. By smoothing the surface of the electrode, short-circuit is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a nickel positive electrode for an alkaline storage battery, which is constructed in combination with a negative electrode for an alkaline battery such as a cadmium electrode, a zinc electrode, or a hydrogen electrode.

Conventional technology Conventionally, for the purpose of achieving high capacity and simplifying the manufacturing process for sintered nickel electrodes, there was a method in which nickel hydroxide, an active material, was directly injected into a highly porous foamed nickel porous material. It has been proposed. In this method, a foamed nickel porous body is filled with an active material and then pressurized to improve electrode strength and increase the packing density of the active material. As for the pressure pressing method, a roller press has been used rather than a flat plate press in consideration of mass production, but due to the weak strength of the foamed Nisokel support, deformation and curvature occurred during pressurization.

In order to solve this problem, a method has been proposed in which pressure is applied using a roller press with an uneven surface.

Problems to be Solved by the Invention As described above, by pressurizing the electrode with a roller having projections and depressions, a nickel electrode filled with active material at a high density can be obtained without being deformed or curved.

When a sealed nickel-cadmium storage battery is constructed using these nickel electrodes and actually operated, the amount of electricity discharged is 1.3 to 1.4 times that of a general-purpose battery, but the charge/discharge cycle is repeated. It was found that the decrease in discharge capacity becomes large. In order to investigate the cause of this problem, they disassembled the battery whose capacity had decreased, and found that the thickness of the Niackel positive electrode was 1.4 times that of the initial thickness. This is due to the fact that in electrode plates, such as porous nickel foam, in which a relatively weak support is filled with active material at a high density, the volume changes repeatedly due to repeated charging and discharging, that is, due to oxidation and reduction of the active material. This is due to the fact that the electrode plate itself has swelled. Since the active material layer density of electrodes with bulging in this way has decreased from the initial stage, the absorption of electrolyte increases, and therefore the electrolyte inside the separator, where electrolyte is most needed, is depleted. . This is considered to be the cause of the decrease in capacity. Furthermore, another problem is that the irregularities provided on the surface of the electrode plate often cause short circuits in the battery.

The present invention eliminates the above-mentioned disadvantages of nickel electrodes that are densely filled with active materials, and provides a nickel electrode that not only has a high capacity but also has a long life and high reliability.

Means for Solving the Problems The present invention allows electrolyte to be retained on the surface of the nickel electrode, that is, on the interface between the nickel electrode and the separator, for a long period of time. Fill the active material in the form of a paste from an aqueous binder solution, dry it, press it with an uneven roller, then apply a paste with a higher binder concentration than the above paste to both sides of the electrode and dry it. Afterwards, perform flat plate pressing. At this time, the amount of the coating should be at least such that unevenness on the surface of the electrode plate is not recognized, and the porosity should be larger than that of the filling material filled inside the foam metal. A cross-sectional view of the nickel electrode thus obtained is shown in FIG.

1 is an active material layer filled into the porous body, and 2 is an active material layer coated on the surface thereof.

Function: In the above-mentioned electrode plate configuration, the surface of the electrode plate has a higher porosity and a larger amount of hydrophilic binder than the inside. Therefore, the electrolyte retention force on the surface of the electrode plate increases. As a result, movement of the electrolytic solution into the electrode is suppressed, and a decrease in discharge capacity is reduced.

Furthermore, since the surface of the electrode plate is smoothed, short-circuit phenomena are reduced.

Example nickel hydroxide powder 8807. A paste obtained by kneading 60 y of a 0.5 wt% aqueous solution of polyvinyl alcohol into a mixture of 80 y of nickel powder and 40 y of cobalt powder was sufficiently stirred to form a paste with a porosity of 95 cm and an average pore diameter of 200 μm.
1 A foamed nickel porous body with a thickness of 1.4 m and a size of 300 x 200 rm was filled. After that, it was dried at 110°C for 30 minutes, and then two rollers with a diameter of 300B each having a surface having cubic convex parts with a negative side of 0.3 mm and a height of 0.1 + l1 m1 at intervals of 0.8 cm were used. The material was passed through the film three times while adjusting the interval, and compressed under pressure to a thickness of 0.68 m.

Next, to 1 ooy of mixed powder of nickel hydroxide, nickel powder, and cobalt powder in the same blending ratio as above, 50 ml of a 3% by weight aqueous solution of polyvinyl alcohol was added to form a paste, and the unevenly processed electrode plate surface was Spray it on and after drying, press it to 300 Kg/cM with a flat plate press.
It was compressed at a pressure of .

The average porosity of the coating layer at this time was around 46 inches, and the average porosity of the nickel porous body filled with roughness was 3.
It was higher than 6%.

Electrodes without this coating layer are called a1, electrodes with coating layers in various proportions are called b-d, and electrodes with a coating formed only with a 3% by weight aqueous solution of polyvinyl alcohol instead of the coating layer are called e. do. These electrode plates were cut to a width of 38 m and a length of 216 m, equivalent to a size AA size.

Table 1 shows the electrode manufacturing conditions, theoretical amount of electricity, amount of surface layer coating, thickness, etc. at this time.

Next, these electrodes a to e, a known paste-type cadmium negative electrode, a separator made of a polyamide nonwoven fabric, and an electrolyte solution containing lithium hydroxide saturated in a 30% by weight aqueous solution of potassium hydroxide were added to each cell. .5cc was used to construct AA size sealed storage batteries A-E with a nominal capacity of 2.8Ah. Each battery erodes.

℃, the charge is 0. Charging and discharging were repeated, with each cycle consisting of charging and discharging at a current of I CmA for 16 hours and discharging at a current of 0.20 mA to a final voltage of 0.9 V.

Figure 2 shows the changes in the number of cycles and discharge capacity.
, 1, 2 CmA, and the discharge capacity and capacity ratio (ratio when the discharge capacity at a discharge current of 0, 2 CmA is taken as 100%) are shown in Table 2.

As shown in Figure 2, positive electrode a without a coating layer on the surface
In battery A using the above, a decrease in capacity was observed after about 160 cycles, and the capacity decreased to about 60% of the initial capacity after about 20 cycles. Positive electrodes with varying amounts of coating on the surface 1), c, d
No significant difference was observed between batteries B, C, and D using the same battery, but the change in discharge capacity increased in the order of C, B, and D. Therefore, battery C is considered to be optimal. Also,
Battery E also showed relatively little change in discharge capacity, but as shown in Table 2, the voltage and capacity decreased significantly during large current discharge. This is considered to be because the surface layer increases the internal resistance and decreases the diffusion rate of ions.

Effects of the Invention As described above, the present invention provides a method for producing an electrode that can stably operate a nickel electrode for a long period of time, in which a foamed nickel porous material with relatively low strength is filled with an active material at a high density. ,
It is useful in constructing high capacity batteries.

In addition, although a sealed battery was shown in the examples,
Similar effects can be obtained with ordinary open batteries. Furthermore, it can be applied not only to nickel-cadmium storage batteries but also to battery systems using nickel positive electrodes, such as nickel-water X, nickel-iron, and nickel-zinc battery systems.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a main part showing a configuration example of a nickel positive electrode according to the present invention, and FIG. 2 is a diagram comparing changes in discharge capacity due to charge/discharge cycles of batteries using various nickel electrodes.

Claims (1)

[Claims] An active material mainly composed of nickel hydroxide powder is made into a paste form with an aqueous binder solution and filled into a foamed nickel porous body.
After applying sufficient pressure with a roller with an uneven surface and drying,
A nickel for battery, characterized in that a paste of an active material having a higher binder concentration than the above paste is applied to both sides, and then pressure is applied with a flat plate press to form a surface layer with greater porosity than the previous filled layer. Manufacturing method of positive electrode.