JP2798700B2 - Method for producing sintered substrate for alkaline storage battery - Google Patents

Description

The present invention relates to a method for producing a sintered substrate for an alkaline storage battery.

(B) Conventional technology A sintered substrate conventionally used as an electrode substrate of an alkaline storage battery such as a nickel-cadmium battery is excellent in mechanical strength and conductivity, and is a holder for an active material. Suitable as. However, the expansion of market applications in recent years has caused a demand for higher capacity of batteries, and active technology development for increasing the capacity of batteries using currently used sintered substrates as electrode substrates is being carried out. .

By the way, a so-called slurry-processed nickel-sintered substrate produced by mixing nickel powder, a thickener and water to form a slurry, applying the slurry to a conductive core, drying and sintering the slurry is usually used. The porosity is about 80%. If the porosity of the sintered substrate is increased, the amount of the active material to be filled can be increased and the capacity can be increased. Therefore, increasing the porosity has been studied variously until now, and the most practical method is to mix a pore-forming agent in a slurry and heat and remove the pore-forming agent. .

In order to use a pore-forming agent in this way and to be able to use it industrially, it must have a uniform pore-forming action, maintain the mechanical strength of the sintered substrate, and easily remove the pore-forming agent. It is necessary to satisfy the requirement that good productivity can be maintained, and most inventions using a spherical organic resin body as a pore-forming agent have been most promising.

However, in order to use a normal organic resin sphere as a pore-forming agent and increase the porosity of the sintered substrate, a large amount of resin is required, and decomposition products of the resin during sintering are generated by a sintering furnace. Or remains in the sintered substrate. On the other hand,
As disclosed in Japanese Patent No. 169773, an organic hollow sphere containing a low-boiling hydrocarbon is used as a pore-forming agent, and this is mixed into a slurry. There is a method of producing a sintered substrate of different degrees. This method is effective because the amount of resin used as a pore-forming agent may be small and is not easily affected by decomposition products. However, variations in temperature during heating and drying, and temperature distribution in the substrate, that is, when a sintered substrate is produced, usually a plurality of rows of slurry are applied to the conductive core at intervals in a strip shape. There is an exposed portion of the conductive core that is not coated with, and the temperature tends to rise near this exposed portion and on the surface of the slurry, and due to these effects, the organic hollow sphere cannot be expanded uniformly, and the uniform It is difficult to obtain a pore distribution. In addition, the organic hollow sphere in the vicinity of or in close contact with the conductive core exerts a force to push up and separate the nickel layer from the conductive core when expanding, thereby causing a gap between the conductive core and the nickel layer. Significantly impairs the adhesion of For this reason,
There was a possibility that the nickel layer was peeled off or dropped off from the conductive core.

(C) Problems to be Solved by the Invention The present invention seeks to provide a highly porous sintered substrate for an alkaline storage battery having uniform pores without peeling and falling off of a nickel layer from a conductive core. Things.

(D) Means for Solving the Problems The sintered substrate for an alkaline storage battery of the present invention is obtained by preliminarily heating and expanding an organic hollow sphere containing a low-boiling hydrocarbon.
The organic hollow sphere is mixed with a nickel powder and a thickener to form a slurry, coated on a conductive core, dried, and then sintered.

Further, the hollowness of the previously expanded organic hollow sphere is 95%.
%, It is possible to obtain a further effect.

(E) Action The organic hollow sphere containing the low-boiling hydrocarbon also affects the material of the resin used for the outer wall of the hollow sphere. As the temperature rises, it rapidly expands to the magnification according to the temperature. FIG. 1 is a diagram showing the relationship between the heating temperature and the expansion ratio. The higher the temperature, the higher the expansion ratio, but beyond a certain temperature, the resin wall breaks down,
Thereafter, the calculated expansion ratio decreases. In the figure, the inflection point of the curve is the expansion limit. At this time, the hollow sphere has the maximum volume, and the contained gas is almost escaping to the outside.

When an organic hollow sphere containing such a low-boiling hydrocarbon is used as a pore-forming agent, the hollow sphere expands when heated, so that the hollow sphere expands when the slurry is dried. Occurs. In the present invention, the organic hollow spheres are heated and expanded in advance, thereby suppressing expansion of the hollow spheres during slurry drying, and preventing peeling and falling off of the nickel layer from the conductive core due to the expansion. It is possible. In addition, even if there is a variation in the temperature distribution in the substrate when the slurry is dried, the hollow spheres are pre-expanded and thus are not easily affected by the expansion. Is much more uniform. If necessary, the uniformity can be further improved by classifying the hollow spheres before mixing the slurry. The removal of hollow spheres is considered most desirable because the same porosity can be achieved with the addition of a minimal amount of resin.

It is effective that the above-mentioned organic hollow sphere used in the present invention is expanded as much as possible, and a particularly great effect is obtained when expanded to a hollowness of 95% or more. However, from the practical point of view, it is difficult to uniformly expand to the expansion limit, so that the resin wall is heated at a temperature slightly lower than the inflection point in consideration of the temperature variation at the time of heating, and the resin wall does not break. Should be so.

(F) Example As an organic hollow sphere, a methyl methacrylate-acrylonitrile copolymer containing a low-boiling hydrocarbon was used, and this was heated and expanded to obtain hollowness of 85%, 90%, 95% and
97% of each were produced. Then, nickel powder 100
Parts by weight, 100 parts by weight of pure water, 3 parts by weight of methylcellulose, and 100 vol% of the heat-expanded organic hollow spheres with respect to nickel powder are mixed to form a slurry, and this slurry is formed into a conductive core made of punching metal. After coating and drying, sintering was performed in a reducing atmosphere at 900 ° C. to obtain a sintered substrate. As shown in the table below,
The substrates A to D were determined according to the hollowness of the used organic hollow spheres, and the porosity of the sintered substrate is shown in the table below.

Here, the reason why the porosity of the substrates A and B is higher than that of the substrates C and D is that the organic hollow spheres expand when the slurry is dried. On the other hand, it is considered that the porosity of the substrates C and D using the organic hollow spheres having a hollowness of 95% has almost no change and no expansion has occurred.

Next, the substrates A to D were filled with nickel hydroxide by using a normal chemical impregnation method in which the sintered substrate was immersed in an aqueous solution of nickel nitrate and then subjected to an alkali treatment, thereby producing a nickel electrode.

The nickel electrode was spirally wound with a separator interposed between the nickel electrode and a cadmium electrode and then unwound, and the weight difference between the nickel electrode before and after the treatment was measured.
The result is shown in FIG.

Further, an overcharge test was performed in which the nickel electrode was used without being wound and the counter electrode was charged with a current of 2 C for 3 hours in a potassium hydroxide aqueous solution using a nickel plate as a counter electrode. The weight difference between the nickel electrodes before and after the test was measured, and the results are shown in FIG.

As is clear from FIGS. 2 and 3, as the hollowness of the organic hollow sphere increases, the weight change rate of the nickel electrode decreases, and when the hollowness exceeds 95%, the weight change rate becomes very small. It can be seen that it can be suppressed. In addition, the change in weight was mainly due to peeling and falling off of the nickel sintered layer filled with the active material, that is, the so-called active material layer from the conductive core. As described above, the smaller the hollowness of the organic hollow sphere, the larger the weight change rate is.The smaller the hollowness, the more room for expansion by heating, and the smaller the hollowness, the larger the volume due to expansion. It is thought to be due to the increase. Therefore, the smaller the hollowness, the greater the force to separate the nickel layer from the conductive core due to expansion during slurry drying, and as a result, the adhesion between the conductive core and the nickel sintered body on the completed substrate Properties are reduced, and peeling and falling off occur.

In addition, when an organic hollow sphere having a hollowness of 95% is used and when an organic hollow sphere having a hollowness of 90% is used, the resin amount of the organic hollow sphere for obtaining the same porosity is smaller than that in the case of using a hollow hollow sphere of 95% It was confirmed by other experiments that 2/3 of the case of 90% was good. This shows that the use of an organic hollow sphere having a hollowness of 95% or more increases the strength of the substrate and the effect of reducing the amount of resin.

(G) Effect of the Invention According to the present invention, when an organic hollow sphere containing a low-boiling hydrocarbon is used as a pore-forming agent, the nickel layer can be prevented from peeling and falling off from the conductive core, and can be highly porous. In addition to providing a sintered substrate for alkaline storage batteries, the amount of resin used as a pore-forming agent is reduced, and the decomposition products of the resin generated during sintering can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the heating temperature and the expansion ratio of the organic hollow sphere, and FIGS. 2 and 3 are diagrams showing the relationship between the organic hollow sphere and the weight change rate of the electrode plate.

Continuation of the front page (56) References JP-A-63-114068 (JP, A) JP-A-61-34861 (JP, A) JP-A-60-65464 (JP, A) JP-A-61-34861 (JP) , A) JP-A-58-66267 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/64-4/84 B22F 5/00, 7/04

Claims (2)

(57) [Claims] An organic hollow sphere containing a low-boiling hydrocarbon is heated and expanded in advance, and then the organic hollow sphere is mixed with a nickel powder and a thickener to form a slurry, which is applied to a conductive core. And drying and then sintering the sintered substrate for an alkaline storage battery. 2. The method for producing a sintered substrate for an alkaline storage battery according to claim 1, wherein the hollowness of the previously expanded organic hollow sphere is 95% or more.