JPS6215994B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in cathode plates for alkaline storage batteries, particularly cadmium cathode plates. For example, cadmium cathode plates in nickel-cadmium storage batteries are generally produced by a sintering process. This method involves impregnating and retaining an insoluble cadmium compound into the pores of a porous nickel substrate obtained by sintering nickel powder. However, in recent years, due to the complexity and low energy density of the manufacturing method of sintered cathode plates, a review of the manufacturing method has been considered, and a manufacturing method generally called a paste method is being put into practical use. In this method, an active material paste is formed by adding a paste, a solvent, etc. to cadmium oxide or cadmium hydroxide, which is the active material, and this paste is applied to the electrode plate core and dried. Since all or most of the plate except the core can be made of a cadmium compound, it is possible to obtain an energy density that is several times higher than that of a sintered cadmium cathode plate. Therefore, the inventors of the present invention created a battery using the so-called paste-type cadmium cathode plate mentioned above and conducted various performance investigations, and found that it had an extremely important problem. In other words, a battery using a cathode plate whose constituent materials are mostly cadmium compounds, such as those using a paste method, has a sintered cadmium cathode which has a charge/discharge cycle characteristic (hereinafter referred to as cycle characteristic), which is an indispensable performance for a storage battery. It is extremely bad compared to a board, and can cause internal short circuits within a short period of time. After disassembling and investigating the battery that had developed an internal short circuit, it was determined that the cause of the short circuit was the growth of cadmium dendrites due to repeated charging and discharging. It is generally said that the behavior of a cadmium cathode plate during charging and discharging consists in mutual conversion between insoluble metal cadmium (charged state) and insoluble cadmium hydroxide (discharged state), and in this conversion process, cadmium is added to the electrolyte. It is said that it takes the form of an intermediate product that is supported and dissolved. Therefore, the shape of the cadmium cathode plate essentially changes from its initial structure through repeated charging and discharging, and the active material grows in a dendritic shape and extends toward the anode side. However, in the case of a sintered cadmium cathode plate, the porous nickel substrate, which is both a conductor and an active material holder, does not take part in the charge/discharge reaction and maintains its initial structure, and the current inside the plate is maintained. It is thought that the growth of cadmium dendrites is hindered by playing a role in making the distribution uniform. Based on the above speculations, the inventors of the present invention have proposed that in order to solve the above-mentioned problems in cadmium cathode plates such as paste type or compression type, in which all or most of the electrode plates except the plate core are made of cadmium compounds, various types of cadmium compounds are added to the cadmium compound. As a result of investigating the cycle characteristics by adding substances, it was found that when magnesium oxide was added, the cycle characteristics were improved without significantly reducing other characteristics. The present invention has been made based on the above facts, and examples thereof will be described in detail below. First, a conventional paste-type cadmium cathode plate was prepared by the following method. That is, the composition was 90 parts by weight of cadmium oxide powder, 10 parts by weight of metal cadmium powder, 1 part by weight of alkali-resistant fibers, and 0.3 parts by weight of polymer paste, and after adding an aqueous solution containing disodium phosphate and kneading it into a paste, the perforations were plated with nickel. A paste-type cadmium cathode plate obtained by coating and drying the paste on an electrode plate core made of an iron plate is referred to as A. Next, #225 nickel powder, nickel hydroxide powder obtained by alkali treatment of nickel nitrate, and JIS
Special grade magnesium oxide is added to the total of cadmium oxide powder and metal cadmium powder at a ratio of 90:15, respectively.
Paste-type cadmium cathode plates obtained by mixing powders at ratios of 97:3 and 97:3 and using the same method as in the case without additives are referred to as B, C, and D, respectively. The figure is a comparison diagram of the cycle characteristics of a sealed nickel-cadmium battery in which each of these cathode plates A to D is combined with a normal sintered nickel anode plate. As is clear from the figure, it can be seen that the cycle characteristics are improved by adding nickel metal, nickel hydroxide, and magnesium oxide. The addition of nickel metal is thought to be due to a phenomenon similar to the effect of the nickel substrate in the case of the sintered electrode plate described above, and the reason for the improvement due to the addition of nickel hydroxide is that nickel hydroxide is filled with cadmium. It is said to have the effect of helping the change from metal cadmium to cadmium hydroxide in the discharge reaction, and is thought to moderate the growth of cadmium dendrites from the point where they become crystal nuclei of cadmium hydroxide. . However, the effect of adding magnesium oxide, in which some amount becomes in the form of magnesium hydroxide in the assembled state of the battery, is not known. Next, we will compare other characteristics of nickel cadmium batteries using cathode plates A to D.
It is shown in the following table as 100.

[Table] In addition, the amounts of Ni, Ni(OH) ₂ and MgO added in the table are 10%, 2% and 2%, respectively, and *1 is 20℃,
Gas pressure after 24 hours with 0.1c charging, *2 is 0
%, gas pressure after 24 hours with 0.1c charging. As shown in the above table, when compared to the additive-free product A, the Ni-added product B has a significant decrease in electrode plate capacity, and also causes a decrease in storage performance, which is thought to be caused by the structure of the local battery within the cathode plate. In addition, Ni(OH) _2- added C promotes the formation of cadmium hydroxide on the surface of the electrode plate due to the phenomenon described above, and as a result, when the cathode plate is composed mostly of cadmium compounds, the formation of cadmium metal during charging is reduced. Since the conversion begins near the electrode plate core, it is thought that the absence of metal cadmium in the electrode plate surface layer leads to a decrease in oxygen gas absorption ability. In contrast, the cadmium cathode plate D according to the present invention to which magnesium oxide is added can be cycled without any adverse effect on performance as a storage battery, except for a decrease in plate capacity based on the amount of magnesium oxide added. It can improve the characteristics and is extremely useful for cadmium cathode plates such as paste type or compression type in which all or most of the electrode plates except the plate core are made of cadmium active material.

[Brief explanation of the drawing]

The drawing is a cycle characteristic diagram of a nickel-cadmium battery using a cadmium cathode plate according to the present invention.

Claims (1)

[Claims] 1. A cathode plate for an alkaline storage battery, which is a cathode plate formed by adhering a paste or powder mainly composed of cadmium active material to an electrode plate core, the cathode plate being characterized in that magnesium oxide is added to the cadmium active material.