Page 261 - Battery Reference Book

Silver-cadmium secondary batteries 20/5
gas bursts the diaphragms and forces the electrolyte Negative terminal
into the manifold and cells. In this cell design a \ Filter and vent plug
vented system enhances the rapid clearing of the
manifold and eliminates excessive intercell leakage
paths. The battery has no moving parts and has
an extended shelf life. It can be activated directly
into a load or in parallel with a mains system. The
open-circuit voltage of this battery is 1.6-1.87V
with a working voltage of 1.20-1.55V. The battery
operating temperature is -29 to +71"C and, with
water assistance, -48 to +71"C. The energy density
is 11-66Whkg or 24-213WNdm3, depending on
battery size. Units are available in the weight in the
weight range 0.14-135kg. The dry storage charge
retention characteristics of this battery are excellent
at temperatures up to 52°C.
Eagle Picher supply gas-generating pyrotechnic
devices, which can be used for the activation of
remotely activated batteries by transferring electrolyte
from a reservoir to the battery cells. Eagle Picher
have developed over 70 gas-generator configurations
with capabilities ranging from 20 to 200 000 cm3
(standard condition gas output), many of which Figure 20.3 Yardney Silvercel silver-zinc battery construction.
have been used in a majority of missile/spacecraft Positive electrode manufactured from special grades of silver with
or without silver collectors. Negative electrode manufactured from
systems. zinc with or without collectors. Semipermeable and ion-exchange
separators designed and patented by Yardney. Strong electrolyte
solution of potassium hydroxide. Positive and negative terminals of
20.2 Silver-zinc secondary batteries silver-plated steel for maximum corrosion resistance and minimum
contact resistance, or special nonmagnetic alloys. The filling vent
allows activation of the cell with electrolyte, while the vent plug
These cells are leakproof, spillproof and have high or screw valve, when placed in the cell, will allow gassing and
impact strength. The assembled cells can be enclosed prevent electrolyte spillage. Vent trap, designed to be moulded as
part of the cover, prevents leakage and spillage, and so allows
in sturdy lightweight cases for special mechanical the cell to operate in any position. Case and cover moulded in
and environmental conditions. Batteries can also plastics such as ABS, SAN, nylon, modif polypropylene oxide,
be designed and built to meet the most stringent polyarylether or polysulphone (Courtesy of Yardney)
requirements.
A typical battery design is shown in Figure 20.3. 20.3 Silver-cadmium secondary
This battery contains silver oxide as the positive elec-
trode and zinc as the negative electrode, and has an batteries
alkaline electrolyte. The design of this battery is very similar to that of the
Separators are made from cellophane or non-woven silver-zinc battery, with the exception that the zinc
polyamide. Cells are fitted with a safety valve. Dry negative electrode is replaced by one fabricated from
charged cells can be stored indefinitely. cadmium.