Coating electrodes of silver-cadmium cells with thermostable electrodeposits of calcium hydroxide or magnesium hydroxide reduces silver migration and increases cell life. Absence of organic matter enables assembled cells to be sterilized without oxidation of the material of the separators

Carson, W. N., Jr.

Consiglio, J. A.

Mc Quade, J. M.

English

NASA Technical Reports Server

September 1970
	 Brief 70-10462 
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Electrodepo sited Inorganic Separators for Alkaline Batteries 
The problem: 
To design a thin separator for alkaline batteries 
which is resistant to oxidation, is thermally stable, 
and permits more convenient assembly of cells than 
prior techniques. 
The solution: 
Coating the electrodesof silver-cadmium cells with 
thermostable electrodeposits of calcium hydroxide 
or magnesium hydroxide. Thecoating results from the 
increase in pH at an electrode upon cathodic evolution 
of hydrogen from a solution of a soluble salt (such 
as nitrate or acetate) of calcium or magnesium. Mi-
gration of silver and the thickness of separators are 
reduced. Because of the absence of organic matter, 
assembled cells may be sterilized without oxidation 
of the material of the separators. When the new sep-
arators are used in addition to conventional separa-
tors, the cell's life is greatly increased by the reduction 
in migration of silver. 
How it's done:	 - 
The cathode of the electrode to be coated (TBC) 
is placed in a solution of the calcium or magnesium 
salt; the counter electrodes, opposing each face of the 
TBC electrode, may be of platinum, nickel, or stain-
less steel. Passage of electric current between the 
electrodes evolves hydrogen, and the solution imme-
diately adjacent to the cathode becomes alkaline. 
When the calcium hydroxide or magnesium hydroxide 
exceeds it point of solubility it is precipitated in the 
pores and on the surface of the TBC electrode. Cal-
cium or magnesium ions thus lost from the solution 
should be replaced by addition of calcium hydroxide 
or magnesium hydroxide; the solution should be 
stirred.
Following are the reactions at the cathode when 
the TBC electrode is fully discharged: 
H 2 O+2e–. H,+20H	 (I) 
Ca 2 + 20H =Ca(OH),	 (2) 
In the case of an electrode (of silver oxide, for ex-
ample) that may be discharged during the coating 
reaction, the pH may be changed by the electrode 
reactions rather than by the evolution of hydrogen: 
2AgO+1-1,0+2e -
 
- . Ag,O 20H
	
(3) 
A90+H 2 O+2e -. Ag2OH	 (4) 
The opposite effect may be expected during coating of 
an anode—such as a cadmium electrode. The charging 
reaction of a discharged cadmium electrode may 
provide the necessary change in pH for precipitation. 
Coating of the cathode has been found generally pre-
ferable since coating of a cadmium or zinc electrode 
may result in early passivation. 
The preferred parameters for calcium hydroxide 
films are electroyte concentration of calcium acetate, 
70 to 280 g/l (optimum remains undetermined); buff-
ering concentration of calcium hydroxide, 1 to 2. 
g/l; current density, 75 to 155 mA/cm 2 , and coating 
time for 2-mil films, 10 to 15 mm. The more the elec-
trolyte is stirred, the better the coverage and uniform-
ity of thickness of the film. 
So far the coatings have been used only in con-
junction with conventional separators; more expe-
rience is required. In some instances, coating of both 
anode and cathode may be desirable. Because the 
physical nature of the coating varies with the concen-
tration of potassium hydroxide, more information is 
required regarding the concentration of the electro-
(continued os cricaf) 
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lyte. Such separators should be satisfactory on various 
other plates for alkaline cells, and may be useful in 
other electrochemical devices such as metal-air cells. 
Note: 
The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-CR-84002 (N67-26175), Electrodepos-
ited Inorganic Separators
Patent status: 
No patent action is contemplated by NASA. 
Source: W. N. Carson, Jr., J. A. Consiglio, 
and J.M. McQuade of 
General Electric Company 
under contract to 
Goddard Space Flight Center 
(GSC- 10943) 
Brief 70-10462	 Category 01


Electrodeposited inorganic separators for alkaline batteries

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