JPS61190860A - Manufacture of cadmium anode plate - Google Patents

Abstract

PURPOSE:To easily remove the residual nitrate group by impregnating the desired amount of active material in a substrate, and baking it in the mixed atmosphere of inactive gas and hydrogen gas whose content is below the explosion limit to manufacture a cadmium anode plate. CONSTITUTION:Cadmium nitrate is impregnated in a porous sintered nickel substrate and converted into cadmium hydroxide in an alkaline solution. By repeating these processes, active material is filled in the substrate. Then, the substrate is baked in the mixed atmosphere of inactive gas such as argon, nitrogen, and hydrogen gas whose content is below the explosion limit at 210-310 deg.C to manufacture a cadmium anode for alkaline storage battery. Since a nitrate group is easily removed from the anode plate impregnated with active material, the storage performance of the battery is increased and decrease in charging efficiency caused by oxidation, in sintering, of the surface of the substrate can be prevented. Therefore, workability and safety are improved.

Description

[Detailed Description of the Invention] Field of Industrial Application The present invention relates to a method for manufacturing a sintered cadmium anode plate for an alkaline storage pond, and features: (i) residual nitrate in the electrode plate; This relates to removal and improvement of charge/discharge efficiency C;

(b) Conventional technology The sintered cadmium anode plate has two branches C: After impregnating a porous nickel sintered substrate with a cadmium nitrate solution, cadmium nitrate is mixed with cadmium hydroxide f2 in an alkaline solution such as sodium hydroxide. C: The substrate is prepared by filling the required amount of active material. In this method of manufacturing electrode plates, one plate (
; It is known that if nitrate radicals remain and are trapped in the battery, they will significantly reduce the storage quality, and must be removed from the battery. Yes, but C; it cannot be removed.

Conventional methods for removing nitrate from the cadmium negative plate thus prepared include 3-1 electrochemical treatment, that is, chemical conversion treatment in which charging and discharging are performed one to several times at a relatively low current; Special Publication No. 54-148255 1;
There is a firing process as proposed in .

However, the method of charging and discharging one to several times does not achieve the activation of the active material (particularly the removal of nitrate radicals), which is the purpose of chemical formation, but requires a large number of man-hours for chemical formation. Since the workability is poor and the processing time is long, continuous processing of electrode plates C: is not suitable.Furthermore, the removal of nitrate radicals can be easily achieved by the method of baking, but ■JP-A-54-14823
Publication No. 5 C: As shown in C: When the firing process is performed in air, the surface of the C nickel sintered substrate is oxidized during firing and the insulating nickel oxide (; changes, so the conductivity between the substrate and the active material changes. There is a phenomenon in which the properties of the battery decrease and the charging and discharging efficiency decreases.Furthermore, as a result of firing experiments conducted in various atmospheres,
■When firing in a nitrogen atmosphere, when introducing the nickel sintered substrate into the firing furnace, a small amount of air C: Oxidized. In order to prevent this, C; requires complicated operations such as deaerating the substrate before introducing it into the firing furnace. ■When firing in a hydrogen atmosphere, oxidation of the substrate can be prevented; however, since the metal cadmium produced during this firing is extremely reactive, it is necessary to perform a treatment to prevent dioxide after firing. When using C; the biggest problem that arises is the problem of explosion.Hydrogen exceeds the lower explosive limit at a concentration of 4% or more, so firing in a hydrogen atmosphere always poses a risk of explosion. There are major restrictions in terms of equipment design and safety measures.

(C) Problems to be Solved by the Invention The present invention solves the problem of a significant increase in man-hours when removing nitrate radicals from a cadmium anode plate after filling the active material and activating the active material. Increase in processing time and oxidation of the surface of the sintered substrate in firing process C: Decrease in charge/discharge efficiency and risk of explosion This invention solves the problem of reducing the cadmium anode plate after filling with the active material with an inert gas. It is fired in a mixed atmosphere with hydrogen below the lower explosive limit.

(E) Effect: Using cadmium nitrate as a starting material, it becomes porous metal, and at the same time, the remaining nitrate in the active material reacts to liberate nitrate radicals. The reaction rate of cadmium oxide to cadmium oxide is slow, so it is not suitable for practical use, and if the temperature exceeds 310°C, cadmium melts.

Problems such as volatilization occur. Therefore, the firing temperature is 210℃
It is necessary to carry out the process within the range of ~310°C.

It should be noted that the more liberated nitrate radicals can be removed more easily by washing with water or by short-time photoelectric or electrical discharge.

If the atmosphere during the above firing is a mixed atmosphere of an inert gas such as argon or nitrogen and hydrogen below the lower explosive limit, it is possible to prevent the conductivity from decreasing due to oxidation of the sintered substrate. can be converted. Furthermore, during firing C: no explosion occurred; Perform the usual active material filling operation for conversion C; Thus, a cadmium hydroxide electrode plate was produced.The electrode plate was fired at 300° C. for 10 minutes in an atmosphere of Hz 2 vol 1% and Nz 98 vol 1% to obtain the electrode plate of the present invention. (As a binary comparison, the cadmium hydroxide electrode plate was fired at the same temperature and for the same time in air and N2 to obtain a comparative electrode plate.

The amount of residual nitrate roots and amount of nickel oxide were measured.

Next table: Shows the results. Incidentally, the amount of nickel oxide is expressed in weight % with respect to the electrode plate type tc.

As is clear from the table, the electrode plate of the present invention and the comparative electrode plate are both C
The nitrate radicals in the electrode plate were almost completely removed, and no influence of the atmosphere during firing was observed. The amount of nickel oxide increases in the comparative electrode plates fired in air and N2, and slightly decreases in the reverse C: electrode plate of the present invention.

Next, the measurement results of the charging efficiency of these electrode plates are shown in Figure I:. The measurement was carried out using a sample electrode plate Y8511 x 41 m in size C; cut it and immersed it in a 20% potassium hydroxide aqueous solution at 50 mAx.
Charging at 1oHrs & discharging at 50#lA C: Therefore, this was done. The capacitance of the electrode plate thus obtained is approximately 100,100 O. In the drawing, the vertical axis represents the potential of the electrode plate relative to the mercury oxide reference electrode I, and the horizontal axis represents the amount of discharge. For example, if we take Ov as the reference g2, the charging efficiency of the electrode plate of the present invention is 84% (420mAH15
00mAH).

The comparison electrode plate fired in N2 had 71% (355mAH15
00mAH). As can be seen from the drawings, the photoelectric efficiency of the comparison electrode plates fired in air and N2 is considerably lower than that of the electrode plate C before firing.In addition, these comparison electrode plates have a potential at the end of discharge C: It is thought that these phenomena are caused by the decrease in the conductivity of the sintered body and the active substance due to the increase in nickel oxide.On the other hand, the charging efficiency of the electrode plate of the present invention is lower than that before firing. has increased compared to
The potential drop at the end of discharge is also sharp. The cause of this improvement in charging efficiency is estimated. .

In addition, the amount of nickel oxide is only slightly decreased compared to before firing, so it is difficult to think that this is due to nickel oxide. Therefore, although it is unclear what effect is responsible, the active material is more active than Hzc. It is thought that this may have led to an increase in charging efficiency.

(g) Effects of the Invention The method for producing a cadmium anode plate of the present invention includes: step C of impregnating a porous metal substrate C with cadmium nitrate, and then converting the cadmium nitrate into cadmium hydroxide C; After filling the desired amount of active material, the substrate is fired in a mixed atmosphere of inert gas and hydrogen below the lower explosive limit.

Nitrate radicals can be easily removed from the cadmium anode plate after being impregnated with the active material. In addition, it is possible to prevent a decrease in charging efficiency due to oxidation on the surface of the sintered substrate that occurs during firing, and it can be used in a hydrogen atmosphere. If there is no need to carry out zeta dioxide prevention treatment during firing, there will be no risk of explosion, which will have great benefits in terms of equipment design and safety measures, and it will also be possible to simultaneously activate the active material. It is.

[Brief explanation of the drawing]

The drawing shows the charging efficiency of the electrode plate of the present invention and the comparative electrode plate.

Claims (2)

[Claims] (1) After filling the porous metal substrate with a desired amount of active material by impregnating the substrate with cadmium nitrate and then converting the cadmium nitrate into cadmium hydroxide,
A method for manufacturing a cadmium anode plate, characterized in that the substrate is fired in a mixed atmosphere containing an inert gas and hydrogen below the lower explosive limit. (2) The method for manufacturing a cadmium anode plate according to claim (1), wherein the firing temperature is 210°C to 310°C.