Page 312 - Battery Reference Book

Lithium anode thermal batteries 2719
Table 27.2 Comparison of properties of calcium-calcium chromate and lithium-iron sulphide systems

Calcium-calcium chromate Lithium-iron sulphide
Energy density (W/s) 600 1600
Activation time (s) 0.03 possible, 0.3 typical 0.3 possible
Voltage range 2.5-500 2.5-500
Multiple voltage taps Up to 5 voltagedunit are common 4 voltagedunit currently employed
Dependability 0.995 0.995
Maintenance Nil Nil
Shelf life (years) 15 >15 expected
Severe environrnents
Operating temperature (" C) -55 to +93 -54 to +74
Units of shock during activated life 10 000 10000
g acceleration during activated life 2500 2500
Humidity/pressure Unaffected Unaffected
Activation Electrical percussion mechanical shock Electrical percussion mechanical shock

Table 27.3 Types of thermal battery
Electrochemical system: Operating cell Characteristics andor applications
anodeielectrolyteicathode voltage (V)

CalLiCl-KCl/WO3 2.4-2.6 Used principally for fuse applications where a low level of
electrical noise is essential and where dynamic environments
are not severe
CdLiCl-KCVCaCrQ4 2.2-2.6 Used in applications requiring short-term operation in severe
dynamic environments
MgLiCl-KCVJ205 2.2 - 2. I Used in applications requiring short-term operation in severe
dynamic environments
Li(M)/LiCl - KCVFeS2 1.6-2.1 Overall advantages: low electrical noise, can operate in severe
dynamic environments, long service life (up to 1 h)

Iron disulphide begins to decompose thermally at are in production and are capable of operating at elec-
about 550°C, into sulphur and iron sulphide, but good trode current densities of up to 2.0A/cm2, with long
cathode efficiencies have been obtained up to 600°C. battery durations. A capability has been demonstrated
Above 600°C. the rate of decomposition increases, of achieving 100 W h/kg compared with approximately
but experience with this system shows that thermal 20 W h/kg in designs of conventional calcium batter-
runaway is not as much a problem as with cal- ies, such as the CaLiCl-KC1 and CaCrOs/Fe systems.
cium - calcium chromate. These latter designs, although they give very satisfac-
Another advantage to the lithium-iron disulphide tory performance for applications with durations of up
system is the absence of high-melting salt phases to approximately 5 min, show a very significant drop in
such as CaC12.KC1. The cell can thus operate close electrode current density, which results in a reduction
to 352°C. While calcium-calcium chromate may in the power and energy density as discharge durations
be used with homogeneous electrolyte-depolarizer are extended.
blends, iron disulphide must be separated from the Capabilities of lithium alloy -iron disulphide ther-
anode by a distinct electrolyte layer. Otherwise, the mal cells include complete inertness during storage, the
iron disulphide, which is a fairly good conductor, will ability to operate at very low temperatures without pre-
be electronically shorted to the anode. heating, resistance to mechanical vibration and shock,
One of the constraints in designs of calcium anode- and the ability to deliver very high currents for a short
based thermal batteries has been the limited duration period of time. Outputs can vary from 1 W for 10m
at high current densities due to a low electrochemical seconds to several kW for tens of minutes. Lithium-
efficiency of the calcium anode, arising from the exis- based systems do not suffer to any major extent from
tence of side-reactions involving the electrolyte and the efficiency reducing and exothermic side reactions and
electrode active materials. It has been demonstrated by are now allowing thermal batteries to remain active
Mine Safety Appliances Ltd that significant improve- longer and be made in much larger sizes.
ments in thermal battery performance can be achieved Cells using lithium or the lithium-aluminium
by the use of lithium as the active anode material in alloy -iron disulphide system with a lithium chlor-
the cell, coupled with new cathodes. These batteries ide-potassium chloride electrolyte have an on-load