CA1151846A - Method for producing nickel hydroxide - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A nickel hydroxlde precipitated from nickel-salt solutions acquires, as an active electrode material for alkaline batteries, a highly favourable specific capacity and a reduced tendency to swelling, as a result of a special drying process which is carried out in two stages. In the first stage, using temperatures between 40 and, at the most 80°C, the water content is reduced to a residual humidity of about 10% by weight and then final drying is carried in a second stage at temperatures between 100 and 160°C thereby greatly reduc-ing recrystallization during the first stage and not affecting the capacity of the compound during high temperature drying in the second stage.

Description

The invention relates to a method for producing nickel hydroxide as the active material for positive electrodes in aIkaline batteries. A special field of application for the method according to the invention is the productionof active compound for button cells.
Two important criteria o the quality of positive paste (? ground) electrodes are their capacity and the extent to which they swell. Swelling is to be understood in this case to mean the increase in thickness of -the electrode as it absorbs electr~lyte which occurs independently of subsequent changes in volume during electrical operation. If swelling due to electrolyte absorption occurs, problems arise when the cell is assembled. `The steps used in the pre-paration of the compound have a definite influence upon both the capacity of theelectrode and its tendency to swell. Drying is one of these steps.
m e nickel hydroxide precipitated from nickel-salt solutions is washed after filtering or centrifuging, and is then dried in a drying cabinet. The so-called thick slurry or filter cake contains between 50 and 90% by weight of water at the beginning of the drying operation.
Drying has hitherto been carried out in one operation at temperatures no hi~her than 80&, based upon the knowledge that high drying te~peratures im-pair capacity.
It is the purpose of the present invention to carry out further pro-cessing of the Ni(OH)2 in such a manner as to produce a positive electrode in which capacity and the redu~tion in the tendency to swell attain the best possi-ble values.
In the invention, the Ni(OH)2 precipitated from nickel-salt solutions is predried in a first stage, at a lcw temFerature, to a predeterndned residual moisture content, and is finish-dried in a second stage at a higher temperature.It has been found particularly advan-tageous -to maintain, un the first drying stage, a relatively low temperature of only 40 to 60C, and under no cir-~; cumstances more than 80&, until the water content has reduced to a predeter-mlned residual m~isture content. This residual moisture content is preferably between 5 and 20% by weight, and more preferably 10% by weight.
~ rying is then ccmpleted in the second stage at a temperature between 100 and 160C, and this may be carried out in the same drying cabinet.
The resulting product, processed into a compacted-powder electrode, is noted for its high capacity and little tendency to swell.
e result of the method according to the invention is that a surpris-ingly favourable co~,prQmise has been found between two quality characteristicswhich are in antagonism with each other as the temperature rises. It is assumed that predrying plays an important part in this result.
By way oE explanation, it is conceivable that, at the low drying temperature during the first drying stage, no appreciable crystallization takes place, although enough mother liquor is initially available as the recrystalliz-ing medium. Increased conversion of the initially rontgen-amorphous, fresh pre-cipitation product requires a higher temperature, and this is by no means unde-sirable, since recrystallization produces a reduction in surface and thus a de-cline in activity in the nickel-hydroxide compound. m is disadvantage is associ-ated with known drying processes which operate at high temperatures right fromthe start.
If, however, in the first drying stage according to the present inven tion, the water ocntent of the ccmpound is reduced to about 10% by weight, recry~
stallization is also prevented by a lack of mother liquor and paths for ion transportation. A temperature of 100 C is now unobjectionable and, in the - second drying stage, this may be increased to 160 C.

- 2 -'.~

Tests have shown that subsequent drying no longer reduces substan-tially the capacity of a compound predried according to the invention. On the other hand, subsequent drying reduces swelling by up to 50%.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for preparing nickel hydroxide for use as active material for positive electrodes in alkaline storage batteries or cells, wherein nickel hydroxide (Ni(OH)2) is precipitated from a nickel-salt solution, the nickel hydroxide is dried in a first stage at a temperature of less than 80°C
to a predetermined residual moisture content and is then dried in a second stage at a temperature above 100°C.

2. A method according to claim 1, characterized in that the drying temperature in the second stage is between 100 and 160°C

3. A method according to claim 1 or 2, characterized in that the residual moisture content of the nickel hydroxide after the first drying stage is between 5 and 20% by weight.

4. A method according to claim 2 wherein the drying temperature in the first stage is between about 40 and 60°C.

5. A method according to claim 1 or 2 wherein the residual moisture content of the nickel hydroxide after the first drying stage is about 10% by weight.