Manufacturing process prevents damage to hermetically sealed nickel-cadmium secondary cells by buildup of gas pressure during overcharging and reversed charging conditions. The cells are manufactured with less charge capacity in the positive electrode than in the negative electrode, and two additional electrodes are added

Carson, W. N.

English

NASA Technical Reports Server

December 1966	 Brief 66-10692 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Hermetically Sealed Cells Protected from Internal Gas Pressure 
The problem: 
To prevent damage to hermetically sealed nickel-
cadmium secondary cells by buildup of gas pressure 
during overcharging and reversed charging conditions. 
The solution: 
The cells are manufactured with less charge capac-
ity in the positive electrode than in the negative elec-
trode, and two additional electrodes are added; one 
to detect the evolution of oxygen during overcharge 
at the positive electrode, the second to recombine 
hydrogen evolved at the positive electrode during 
overdischarge. The second electrode is connected to 
the negative electrode by a diode which disconnects 
it during normal charge and discharge conditions. 
How it's done: 
During normal charge, no gas is evolved at either 
electrode. When the positive electrode becomes fully 
charged it generates oxygen. The oxygen is detected 
by the first auxiliary electrode which develops a con-
trol signal to the battery charging power supply. 
During normal discharge no gas is generated at 
either electrode. When the smaller capacity positive 
electrode has discharged, current continues to flow due 
to the potential of series-connected cells still having 
some charge remaining. This causes overdischarge of 
the positive electrode so that it generates hydrogen: 
2H2 0 + 2e-420H + H2 
This hydrogen is recombined by the second auxiliary 
electrode during overdischarge: 
H9 +2OH-2H2O+2e 
the electrons being fed to the external circuit. Thus,
no permanent buildup of hydrogen occurs in opera-
tion, and the cell cannot be harmed by prolonged 
overdischarge. 
An additional benefit is the capability to erase the 
memory effect displayed by NiCd batteries when 
employed at lower than full capacity. This is ac-
complished by periodically subjecting the battery to 
overdischarge for a short time. 
The use of two auxiliary electrodes can be applied 
to other alkaline type cells such as silver-cadmium 
and silver-zinc. 
Note: 
Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B66-10692 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546.
Source: W. N. Carson
of General Electric Company
under contract to
Goddard Space Flight Center 
(GSFC-555) 
Category 01 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000690 2020-03-11T17:42:30+00:00Z


Hermetically sealed cells protected from internal gas pressure

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