JPH0724216B2 - Non-sintered cadmium cathode for alkaline storage batteries - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cadmium cathode, and more specifically, it is used as a cathode of an alkaline storage battery such as a nickel-cadmium storage battery, and cadmium oxide or hydroxide as a main active material. The present invention relates to an improvement of a cadmium cathode produced by applying a kneaded product containing cadmium powder and metal cadmium powder as a precharge product to a conductive core body.

(B) Conventional technology As a cadmium cathode used in nickel-cadmium storage batteries and the like, a non-sintering type cadmium cathode such as a paste type, which has a simple manufacturing process and a low manufacturing cost, is widely used industrially. This type of cadmium cathode is formed by kneading an active material such as cadmium oxide powder or cadmium hydroxide powder together with a paste solution onto a conductive core, coating and filling the paste, and then after drying and chemical conversion treatment. It is manufactured by washing with water, drying, etc., but since the binding force between the active material and the conductive core is weak, the active material peels off or falls off during the chemical conversion process, etc. Has the drawback of being large.

Therefore, for example, as disclosed in JP-B-58-32744, a mixture of cadmium oxide powder or the like as a main active material as an active material to be contained in the paste and metal cadmium powder as a precharge product. It has been proposed that by using, the chemical conversion step in the paste type cadmium cathode is substantially unnecessary, and thus the deterioration of the battery capacity due to the progress of the charge / discharge cycle is prevented.

(C) Problems to be Solved by the Invention However, as a metal cadmium powder used for such a purpose, a mixture of zinc powder and nickel powder in a cadmium salt solution disclosed in the above Japanese Patent Publication No. 58-32744 is used. It was obtained by using a powder obtained by pulverizing spongy metal cadmium containing nickel produced by a substitution reaction utilizing the difference in ionization tendency between cadmium and zinc. The metal cadmium powder has a low utilization rate, and the utilization rate of the electrode itself is also low.

On the other hand, in order to improve the utilization rate of the cadmium electrode, JP-A-51-150643 proposes to add iron such as ferric oxide, but with the progress of charge / discharge cycle. There is a problem that the eluted iron ions migrate to the anode, causing a decrease in the anode capacity, and further, a large amount of self-discharge.

(D) Means for Solving the Problems The non-sintered cadmium cathode for alkaline storage batteries of the present invention is
It is characterized by holding a mixture of cadmium oxide or cadmium hydroxide as a main active material, metal cadmium as a precharge generation material, and indium or an indium compound. The amount of addition is preferably 0.01 to 5.00% by weight in terms of indium, based on the active material cadmium. The indium compound can be added in the form of oxide, hydroxide or salt.

(E) Action A mixture of cadmium oxide or cadmium hydroxide as the main active material, metal cadmium as a precharge product, and indium or an indium compound is held in the cadmium cathode, so that it is evenly distributed over the entire active material. Indium is dispersed. Therefore, when the cadmium cathode is charged and discharged in an alkaline electrolyte, the indium atoms are replaced in the cadmium metal crystal at the time of charging, and the lattice defects of the cadmium metal crystal of both the main active material and the precharge product are uniform. The resulting crystalline state becomes unstable. This is because the atomic number of indium is 49 and the atomic number of cadmium is 48, and the atomic weights are very close. Since this structure has a great influence on the state of electrons, an electrochemical reaction is activated, metal cadmium having a high utilization rate is generated, and the utilization rate of the cadmium cathode itself is improved.

(F) Example 80 parts by weight of cadmium oxide as a cadmium active material, 20 parts by weight of metallic cadmium, and 0.5% by weight of metal indium powder with respect to the cadmium active material were added, and 38 parts by weight of water and methylcellulose 1.5 as a water-soluble paste were added. Parts by weight and 1.8 parts by weight of acrylic short fibers as a reinforcing material are mixed to obtain an active material paste. This active material paste was applied to a punching metal current collector, dried and cut into a predetermined size to obtain a cadmium cathode of the present invention. A nickel plate was used as a counter electrode for this cathode, and charge and discharge was performed in a potassium hydroxide solution having an electrolyte concentration of 25% to calculate the utilization rate of the cathode. At this time, charging is 0.15C
The discharge was performed for 15 hours at a current of 0.3 C, and the discharge end voltage was -1.0 V (VS, Hg / HgO).

The figure shows the relationship between the content of indium with respect to the cadmium active material and the utilization factor of the cathode, and the utilization factor of the cathode was calculated as follows.

As shown in the figure, when indium is added to the cadmium active material, the utilization factor of the cathode is improved. The amount of indium or indium compound added is 0.01 to the cadmium active material in terms of indium.
5.00% by weight is preferable, and the maximum utilization is obtained especially in the range of 0.01 to 2.00% by weight.

Although indium metal was used as an additive in the examples, indium oxide, indium hydroxide, or an indium salt may be added as an indium compound.

(G) Effect of the invention The non-sintered cadmium cathode for alkaline storage batteries of the present invention has cadmium oxide or cadmium hydroxide as a main active material, and metal cadmium as a precharge generation material,
Since it holds indium or a mixture with an indium compound, indium is uniformly dispersed in the entire active material, and a cadmium cathode having a high utilization rate can be obtained. Therefore, the capacity of the cathode can be improved, and the capacity of the anode can be set higher by the increase in the capacity of the cathode, so that the battery capacity is increased. Further, when the anode capacity is set in the conventional manner, the utilization factor of the cathode is high and it is difficult for the cathode to be dominant, so that the overcharge characteristic can be improved.

[Brief description of drawings]

The figure shows the relationship between the indium content with respect to the cadmium active material and the cathode utilization rate.

Claims (3)

[Claims] 1. A non-sintering type alkaline storage battery characterized by holding a mixture of cadmium oxide or cadmium hydroxide as a main active material, metal cadmium as a precharge product, and indium or an indium compound. Cadmium cathode. 2. The unburned alkaline storage battery according to claim 1, wherein the amount of the indium or indium compound added is 0.01 to 5.00% by weight in terms of indium with respect to the cadmium active material. Type cadmium cathode. 3. The non-sintered cadmium cathode for an alkaline storage battery according to claim 1, wherein the indium compound is selected from indium hydroxide, indium oxide, and indium oxalate.