JPS61284507A - Production of cadmium powder for nickel-cadmium battery - Google Patents

Abstract

PURPOSE:To improve overall powder shape and surface shape as well as the condition, etc. of Cd during charging and discharging by executing the deposition of Cd powder while an Ag salt or In salt is allowed to co-exist in an aq. Cd salt soln. CONSTITUTION:The Ag salt such as AgNO3 or In salt such as InCl3 is added to the aq. soln. of Cd salt such as CdSO4. A metallic Zn plate, etc. is immersed into such aq. soln. to effect the substn. reaction of Cd and Zn. A hydrophillic colloid such as glue is added to the aq. soln. to powder the deposited Cd. The Cd powder deposited by the above-mentioned method is fine and has the active shape; in addition, the oxidation of the Cd powder surface is suppressed. The Ag and In contributes to a decrease of the diffusion resistance of Cd<2+> in the intermediate product of Cd in the charging and discharging stage of a battery so that the overall improvement of the utilizing ratio of Cd is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to second, a method for producing cadmium powder for Kel-cadmium batteries.

[Conventional technology]

Cadmium powder is used as a cathode active material in nickel-cadmium batteries. There are two methods for producing cadmium powder: a dry method in which metal cadmium is volatilized in a neutral or reducing atmosphere, condensed and collected, and a sponge-like cadmium is produced by adding a zinc plate or powder to a cadmium salt aqueous solution and performing a substitution reaction. There is a wet method for recovery.

The properties required for the active material obtained in this way include that it is a fine powder and has an active form with high reactivity.
The powder surface is difficult to oxidize, and the Cd utilization rate is good during battery charging and discharging.

However, the active material produced by the dry method has an average particle size of 3 to 3.
It has a spherical shape of 12 μm, and therefore has a small specific surface area.
Reactivity, or utilization rate, is low.

Furthermore, sponge-like Cd produced by the wet method is also disadvantageous in terms of increasing the utilization rate.

On the other hand, in order to increase the utilization rate of Cd, it has been confirmed that additive metals such as Ni are effective in dissolving Cd (OH) 2 generated during charging and discharging, that is, preventing it from becoming passivated. A method has been discovered in which a sponge is obtained by eutectoiding Cd with Cd.

However, until now, no method for producing cadmium powder has been found that can comprehensively improve the shape and surface condition of cadmium powder, the condition of Cd during charging and discharging, and the like.

[Problems to be solved by the invention]

'The present invention solves the above-mentioned problems and comprehensively improves the shape and surface condition of cadmium powder as well as the state of Cd during charging and discharging, thereby increasing the utilization rate of Cd. This invention was made to provide a method for manufacturing a cadmium cathode for a Kel-cadmium battery.

[Means and Effects for Solving the Problems] That is, the above problems involve the step of precipitating cadmium powder for the active material from an aqueous solution of cadmium salt through a substitution reaction with zinc. The problem is solved by the method for producing a cadmium powder for a nickel-cadmium battery of the present invention, which is characterized in that, in the method for producing a cathode, cadmium powder is precipitated by coexisting a silver salt or/and an indium salt in the aqueous solution of the cadmium salt. Ru.

According to the present invention, the precipitated cadmium powder has a fine and highly active shape, and oxidation of the cadmium powder surface is suppressed. Furthermore, Ag and In can lower the diffusion resistance of Cd in the Cd intermediate product during battery charging and discharging, and can increase the overall utilization rate of Cd.

[Detailed description and examples of the invention]

When carrying out the method of the present invention, for example, an aqueous solution of CdSO4 is used as the cadmium salt, and a metal Zn plate, for example, is immersed in the solution to cause a substitution reaction between Cd and Zn. At this time, the precipitated cadmium can be powdered by adding, for example, glue, which is a hydrophilic colloid, to the aqueous solution.

The replacement liquid, ie, the CdSO4 aqueous solution, is adjusted to about -=5. The reason for this is that when - is low, Cd'', Ag'' rI
This is because glue, which is a hydrophilic colloid, is suspended, aggregated, emulsified, and becomes hydrophobic in the presence of an electrolyte such as n3+.

Therefore, if - is low, the effect of glue will be weakened, and Cd will be obtained in the form of a thread rather than a powder.

The silver salt can be added to the Cd50 aqueous solution, for example in the form of an AgNO3 aqueous solution. Industrially, it is preferable to use Ag dissolved by heating with a small amount of HNO3, evaporated to dryness, and redissolved in pure water. The reason for this is free HNO3
This is because the precipitated Cd powder is redissolved when H is present.
NO3 needs to be completely removed.

Furthermore, when using an indium salt, it can be added to the aqueous cadmium salt solution in the form of, for example, I nCJ s, in the same manner as when using a silver salt.

Note that Zn remains as an impurity in the cadmium powder precipitated and recovered in this way, and in order to remove this, conventionally, for example, washing with dilute sulfuric acid has been performed, but in the method of the present invention, such acid washing and alkali ( For example, the Zn content in the cadmium powder can be lowered to about 0.01 to 0.3 wt% by combining washing with (for example, NaOH aqueous solution).

Hereinafter, the present invention will be explained in more detail with reference to specific examples.

Example 1 CdO was leached with dilute sulfuric acid, and an aqueous solution of CdSO4 was leached with Cd2
It was prepared at 401/l as +. Ag is AgN0. I added it. Ag+ concentration is 0 (Blank) and 0, respectively.
．． 25.0.50.1.00,2. It was set as OOg/no.

Glue concentrations were all set to 0.1 fl/l, and 21 of each of the five types of substitution liquids were prepared. p) of the substitution liquid (b5.
0, and the temperature was room temperature (12 to 14° C. as liquid temperature), and two Zn plates each having a size of 100+a+X 50wX 15W were immersed and reacted for 24 hours. Pure water was used in all preparations of the replacement liquid. The voices after the replacement are 6 each.
．． It was 0.

After completion of substitution, the obtained slurry powder is 101/l after washing with water.
After washing with dilute sulfuric acid for 1 hour, further washing with water and then K 1001
Washed with 1/13 NaOH aqueous solution for 1 hour.

Then, after washing with water and dehydrating with methyl alcohol,
After drying at a temperature of ~70°C, it was classified using a 325 mesh to obtain metal Cd powder.

Table 1 shows the composition and properties of the metal Cd powder obtained by the above operation. Further, FIG. 1 shows the relationship between the Ag+ concentration in the replacement liquid and the specific surface area (curve 1) and average particle diameter (curve 2) of the cadmium powder. Furthermore, FIG. 2 shows the relationship between the Ag concentration and Aget in the cadmium powder. No Ag oxide was present, and Ag was an alloy phase of AgCd and AgCd5.

According to Figure 1, the specific surface area is Og/1 (Bla
n) From c), it increases almost linearly until around 1.0 OI/11, and shows a value of 2 to 3 m2/g. Moreover, the average particle size decreases almost linearly, and it is also possible to make it 1.0 μm or less.

Further, when the cadmium powder is observed with a scanning electron microscope, it appears to be in the form of andrites with a diameter of 10 to 20 μm, but when observed in detail, as shown in FIG. 3, very fine particles are attached to the surface of the dendrites.

Further, the precipitation form of Ag was determined by X-ray diffraction to be an alloy phase of (AgCd)2H and (ca,Ag)40.

(AgCd)2H is two of a phase of AgCd.
toms parunit cell and hex
agonal, (Cd μg) 40 is fo in Cd, Ag phase
ur of atom+s per unit cell
l and primitiveorthorhomb
It is ic. Moreover, these alloy phases are Ag
A clear peak was also observed as the concentration decreased.

To make this clear in Figure 4, the Cd
(Cd3Ag)2 when d peak is normalized to 1
The relative intensities of the 5-econd peaks of H (A in the figure) and (Agca)4o (B in the figure) are shown. These peaks were used for Cd, (AgCd)40
.

The main peaks of (Cd3Ag)2H each have a diffraction angle of 2
This is because it is difficult to separate the peaks because they are close to each other at θ. These alloy phases are used as contact materials in electronic materials and are believed to have a positive influence on the utilization rate of Cd powder.

Example 2 In Example 1, a method for cleaning cadmium powder will be explained in detail. Since the CdSO4 aqueous solution is replaced with a Zn plate, Zn as an impurity becomes a problem due to an increase in Zn2+ ions in the aqueous solution. Moreover, the metal Cd powder obtained by the present invention has a porous surface shape, and this Zn
In the subsequent water washing process, hydrolysis occurs and remains as an impurity of Zn(OH)2.

Moreover, when washed with conventional dilute sulfuric acid, the metal Cd powder becomes
Zn tends to aggregate and fuse, and Zn remains in the porous portion of the surface, making it impossible to remove it effectively. Therefore, first, a certain amount of Zn was removed by pickling, and then the metal Cd was removed with an NaOH aqueous solution.
To efficiently remove Znf remaining on the porous part of the powder surface.

Next, a specific method will be described. The concentration of dilute sulfuric acid cleaning is 10φ
, NaOH aqueous solution concentration is 1001/l, each 1
Stir for hours. Also, before and after each washing, washing was performed with water. Table 2 shows a comparison between the conventional case of using only dilute sulfuric acid and the case of pickling and alkaline washing according to the present invention.

Table 2 Example 3 Metal Cd powder added with In, which exhibits the same effect as Ag regarding the utilization rate of metal Cd powder as an active material, was prepared according to Example 1. The specific method will be described below.

CdSO4 aqueous solution cd Concentration I, Te 409/1.
P)! = 5.0, and In was added as InCl2 after removing HCl. In concentration is 2.0i/l
The glue concentration was 0.11/l. The amount of replacement liquid is 2
1. Two Zn plates (100 w x 50 wm x l 5 m) were immersed in gold at room temperature (20 to 22°C as liquid temperature), and the reaction time was 24 hours. - after the substitution was completed was 6.0. The slurry powder obtained after the substitution was washed in the same manner as in Example 2.

The obtained metal Cd powder is very porous, with a composition of total amount Cd = 92.47 wt, metal powder Cd = 8
9.43 wt%, total amount In = 5.56 wt%,
The total amount of Zn = 0.01 wt*S04 is a trace amount, the specific surface area is as high as 3.16 m/lil, and it is highly active, and the average particle size is 1.47 μm, h-v, which is smaller than when In is not added. Further, the form of the precipitated In was metal In.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the relationship between the Ag+ concentration in the cadmium salt aqueous solution and the specific area and average particle size of the precipitated cadmium powder when carrying out the method of the present invention, and Figure 2 is a curve diagram showing the relationship between the Ag concentration and the precipitated cadmium powder. FIG. 2 is a curve diagram showing the relationship between the Ag content of Figure 3 is an electron micrograph showing the particle morphology of cadmium powder obtained by the method of the present invention, and Figure 4 is an X-ray image of this powder.
It is a line diffraction diagram. Agent Patent Attorney Seki Yamashita Flat AQ, f (wt%) Surface area (m2/Q)

Claims (2)

[Claims] (1) A method for producing cadmium powder for a nickel-cadmium battery, which includes a step of precipitating cadmium powder for an active material by a substitution reaction with zinc from an aqueous solution of a cadmium salt, in which a silver salt or/and A method for producing cadmium powder for a nickel-cadmium battery, which comprises precipitating cadmium powder in the presence of an indium salt. (2) The nickel powder according to claim (1), wherein the cadmium powder obtained in the precipitation step is subjected to acid washing and alkali washing to remove impurity zinc.
A method for producing cadmium powder for cadmium batteries.