JPS6185772A - Manufacture of cadmium anode plate - Google Patents

Abstract

PURPOSE:To suppress the manufacturing steps and processing time and prevent drop of charging efficiency in substrate oxidation by heating a cadmium anode plate being filled with an active substance in the inert gas ambient, charging it in the alkali solution and thereafter washing with water followed by the drying process. CONSTITUTION:When a sintered cadmium cathode plate after it is filled with active substance is heat processed at 250-600 deg.C under the inert ambient, cadmium hydroxide as an active substance changes to cadmium oxide and simultaneously the nitrate remaining in small amount in the active substance reacts, separating silver nitrate. The separated silver nitrate in the electrode is removed from the electrode by the charging of only a short period and it can also be removed by washing with water after the heat processing. Nickel oxide is generated by the heat processing at 230 deg.C on the nickel sintered substrate which is an active substance holding material, and generation of thick nickel oxide is controlled by the heat processing under the inert ambient.

Description

DETAILED DESCRIPTION OF THE INVENTION B) Industrial Application Field The present invention relates to a method for manufacturing a sintered cadmium cathode plate for an alkaline storage battery, and particularly relates to the simplification of the chemical formation process.

(b) Conventional technology Conventionally, a sintered cadmium cathode plate has been produced by impregnating a porous sintered nickel plate with an aqueous cadmium nitrate solution and then treating it with an alkali to convert the cadmium nitrate into cadmium hydroxide, followed by washing with water and drying. By repeating a series of operations, the substrate is filled with a desired amount of active material, and the cathode plate produced in this way is generally (
A chemical conversion process in which charging and discharging are performed one to several times at a relatively low current for the purposes of 1) removing impurities in the electrode plate, (2) improving the charging efficiency of the active material, and (3) imparting flexibility to the electrode plate. Processing is done.

In particular, in cathode plates made of cadmium nitrate as a starting material and filled with active material in the substrate, nitrate radicals remain as impurities.
If a battery is assembled without removing these nitrate radicals, that is, without chemical conversion treatment, the charge storage characteristics will be significantly reduced, so impurities in the electrode plates should be removed. There is a need. However, although the above-mentioned chemical conversion treatment achieves the removal of impurities, the number of man-hours required for chemical conversion is significantly increased, resulting in poor workability, and the treatment time is long, making it unsuitable for continuous treatment of electrode plates.

Further, Japanese Patent Application Laid-Open No. 148235/1984 proposes a method in which a cadmium cathode plate filled with an active material is heat treated and then charged and discharged in an alkaline solution. Although this method can also easily remove nitrate radicals, heat treatment in air oxidizes the nickel sintered substrate, which is the active material support, and creates a gap between the nickel sintered substrate and the active material. The drawback was that nickel oxide, which has poor conductivity, was produced, which adversely affected the charging and discharging characteristics of the electrode plate.

i/S The interlayer point that the invention aims to solve The present invention suppresses the significant increase in man-hours and processing time due to chemical conversion treatment of the cadmium cathode plate after filling the active material, which is performed for the purpose of removing impurities, etc. by heat treatment. At the same time, it is intended to suppress a decrease in charging efficiency due to oxidation of the substrate caused by the heat treatment.

B) Means for solving the problem In the present invention, a cadmium cathode plate filled with an active material is heated in an inert atmosphere, then charged in an alkaline solution, and then washed with water and dried. .

...) Function When the sintered cadmium cathode plate filled with the active material is heat-treated at 250 to 600°C in an inert atmosphere, the active material cadmium hydroxide changes to cadmium oxide, and at the same time, a trace amount of the active material changes into cadmium oxide. The remaining nitrates react to liberate nitrate radicals. The nitrate radicals liberated at this time are hardly volatilized as nitrogen oxide gas by heat treatment (N
It is thought that it remains in the electrode plate in the form of 0s-.

The liberated nitrate radicals in the electrode plate can be easily removed from the electrode plate by charging for a very short time, and can also be easily removed by washing with water after heat treatment.

In addition, the nickel sintered substrate that is the active material holder was heated to 230°C.
It is said that nickel oxide is generated when the above heat treatment is performed, but the generation of this nickel oxide can be suppressed by performing the heat treatment in an inert atmosphere.

(F) Example A series of active material filling operations in which a sintered nickel substrate with a porosity of 80% is immersed in an aqueous cadmium nitrate solution to impregnate the pores of the substrate with cadmium nitrate, followed by drying, alkali treatment, washing with water, and drying. The steps were repeated several times to fill the substrate with the desired amount of active material. The capacity of the electrode plate made in this way is approximately 1250
mAH.

This electrode plate was fired for 20 minutes at various temperatures in a nitrogen atmosphere, and after firing, it was charged to 30% of the plate capacity with an alkaline aqueous solution, washed with water, and dried. Next, the core material of the substrate was removed from these electrode plates, thoroughly crushed in a mortar, the active material was dissolved in acetic acid, the insoluble sintered nickel was removed by filtration, and the nitrate radicals in the filtrate were purified using Yokogawa Electric's ion chromatography. Measurement was performed using Analyzer TC-100 model.

In addition, we also prepared an electrode plate that was immediately washed with ion-exchanged water and completely dried at 70°C after firing, and for comparison, a fully chemically formed electrode plate that was heat-treated after being filled with the active material, and a fully chemically formed electrode plate that was heated at 450°C after being filled with the active material. An electrode plate that was only fired at ℃ was prepared, and nitrate radicals were measured using the same treatment as described above. The results are shown in Table 1.
Shown below. In the table, NOs- is the nitrate contained in the crushed sample 2P.

Table 1 From Table 1, it can be seen that the amount of nitrate radicals in the electrode plates fired at 250 DEG C. to 700 DEG C. and then charged or washed with water was significantly reduced to almost the same level as the fully chemically formed electrode plates. However, when the capacitance of the electrode plate was measured, it was found that the capacity of the electrode plate fired at 700° C. deteriorated by about 10%, and the active material was inactivated. Therefore, it is appropriate that the upper limit of the firing temperature is 600°C, and the appropriate lower limit temperature is 250°C.

In addition, considering the reason why the amount of nitrate radicals in the electrode plate that was charged or washed with water after firing at 250°C to 700°C was significantly reduced, the amount of residual nitrate radicals in the electrode plate that was only fired at 450°C was 250°C to 700°C, although slightly decreased compared to the plate.
The number of nitrate radicals is much higher than that of a plate that has been charged or washed with water after firing, so a small amount of the nitrate radicals are removed as nitrogen oxides by heating, and most of the nitrate radicals still remain in the plate. Due to this heating, the nitrate radicals in the electrode plate, which are difficult to remove with normal water washing, are also easily removed when the active material cadmium hydroxide changes to cadmium oxide, and the subsequent charging or water washing makes it easier to remove them. It is assumed that it was easily removed.

Next, a comparative experiment was conducted by changing the firing atmosphere. Table 2 shows the amount of nickel oxide 1 in the electrode plate 2P when the firing was performed at 450°C for 20 minutes in nitrogen and in air, and for comparison, the nickel oxide 1 in the electrode plate after being filled with active material The amount is also indicated at the same time. The measurement method was to dissolve the fired electrode plate 2F in a 1:2 mixture of concentrated nitric acid and water (for 3 hours), filter it, and then measure the weight of the residue.

The residue was identified as nickel oxide only by X-ray analysis.

Table 2 From Table 2, a large amount of nickel oxide, which has poor conductivity, is generated in the electrode plate fired in air, forming a poor conductor layer, whereas the generation of nickel oxide is suppressed in the electrode plate fired in nitrogen. I can see that it is being done. As a result, the electrode plate fired in nitrogen has less influence of nickel oxide than the electrode plate fired in air, and has better charge-discharge characteristics.

In addition, the results of the battery prototype test are shown below. Similar to the above, a sintered substrate filled with cadmium hydroxide was heated for 5 minutes in a nitrogen atmosphere.
The cathode obtained by firing at 00° C. for 20 minutes and washing with water is charged with a %C current for 18 minutes, washed with water, and dried. The cathode thus obtained was combined with a fully chemicalized 4/1 sintered nickel anode to produce four types of batteries (IA).
I got it. For comparison, we used a battery in which the cathode was completely chemically formed without heat treatment, and
A battery ICI was produced using a battery that was baked for 0 minutes, washed with water, and then dried. The cycle characteristics diagram of these batteries is shown in the drawing. The cycle conditions are a, i- at 20°C.
The battery is charged at s current for 16 hours and then discharged at 20° C. with 10 current, and the capacity is determined by the discharge time. Battery 1 using a cathode that was not charged after firing
cI showed significant deterioration and was subject to cathode regulation, but batteries 4 and (B) showed little cycle deterioration and were in good condition. Furthermore, the flexibility of the cathode that was charged after firing was superior to that of the cathode that was completely chemically formed.

(1) Effects of the Invention The method for producing a cadmium cathode plate of the present invention is to heat-treat a porous sintered nickel substrate filled with hydroxide at a temperature of 250 to 600°C in an inert atmosphere. Since charging is carried out in an alkaline solution, followed by washing and drying, nitrate radicals can be removed in much the same way as complete chemical formation, and flexibility can be imparted to the electrode plate, as well as a significant increase in the number of man-hours associated with complete chemical formation. In addition, it is possible to suppress an increase in processing time, and it is also possible to suppress a decrease in charge/discharge characteristics due to oxidation of the substrate caused by heat treatment.

[Brief explanation of the drawing]

The drawing is a cycle characteristic diagram of a battery using the cathode plate according to the present invention and a comparative battery.

Claims (1)

[Claims] (1) After filling a desired amount of active material into the substrate by impregnating a porous nickel sintered substrate with cadmium nitrate and then performing an alkali treatment to change the cadmium nitrate into cadmium hydroxide, Cadmium, characterized in that the substrate is heat treated in an inert atmosphere at a temperature within the range of 250 to 600°C, the substrate after the heat treatment is charged in an alkaline solution, and then washed with water and dried. A method of manufacturing a cathode plate.