Page 293 - Battery Reference Book

24/16 Lithium batteries
alloys. However, lithium silicon alloys are more cor- to form the cell assembly. Usually a number of cells
rosive in contact with steel cell components. are connected in series together with the thermal man-
More work has been done on lithium-aluminium agement system to produce a battery.
alloys than lithium-silicon alloys. However, Gould, The GouldiWestinghouse battery is the nearest to
Inc. (US) in their cell development have combined commercial production of those being developed by
lithium-silicon alloy with lithium-aluminium alloy various companies. However, further improvement in
in their negative electrode. This increases the specific cycle life, charging systems and thermal management
and volumetric capacity and avoids corrosion of cell are needed before the batteries can find use in vehicle
components. traction applications.
The electrolyte used in lithium (aluminium)-iron These batteries are charged by constant current
sulphide secondary cells is commonly a mixture of methods at the 10 h rate to a termination voltage.
lithium chloride and potassium chloride. A lithium They can also be charged with a constant voltage
fluoride-lithium chloride-lithium bromide mixture source in which case the maximum charge current
has also been used. With the latter electrolyte the should not exceed the 10h rate and the termination
discharge occurs in two steps: voltage should not exceed 2.1-2.2 V per cell. Charging
should be carried out at the 20 h rate at temperatures
2FeS + 2Lif + 2e- 4 LizFeSz + Fe (24.22)
below 0°C and should not be carried out at all at
LizFeSr, + 2Li' + 2e- + 2Li2S + Fe (24.23) temperatures below - 10°C.
In fact, this discharge occurs on a single voltage
plateau because the equilibrium potentials of the above 24.1 1 Lithium - iron disulphide primary
two reactions differ by only 0.02V. Thus the cell batteries
reactions is:
1 Cell reaction
-Li,Al + FeS + LLibAlf LizS + Fe (24.24) Overall: 4Li + FeS2 -+ 2LizS + Fe (24.25)
a-b a-b
In these cells magnesium oxide powder in the form Two companies (Eveready and venture Technology)
of a ceramic plate is used by Gould as a separator. have been involved in the development of these cells.
In a typical cell design (the GouldiWestinghouse The venture Technology AAA type bobbin cell intro-
2OOAh cell), the negative electrode is a lithium alu- duced in 1982 has a stainless steel can with lithium foil
minium alloy, the positive electrode is a solid lithium in contact with the inner surface. The positive electrode
chloride-potassium chloride and the separator is boron is a composite of iron disulphide (FeS2), graphite and
nitride. Magnesium oxide has been used as a separator PTFE binder on an aluminium grid. The separator is
in other batteries. ' porous polypropylene and the electrolyte a solution of
During cell construction three positive plates are lithium perchlorate in a 1 : 1 v/v propylene carbonate
interleaved with four negative plates and separators 1 :2 dimethoxyethane mixture.