1. FeS LiAl LiCl-KCl 450oC 60-100 1.33 [12]
2. FeS2Li4Si LiCl-KCl 450oC 120 -180 1.8/1.3 [12]
3. FeS2CaAl1.2Si0.4LiCl-NaCl-CaCl2-BaCl2480oC 610 2.0/1.2 [12] CoS2Li LiBr-KBr-LiCl 450-480oC 70-90 1.97 [11-15]
4. Asignificant problem with conventional thermal batteries may be self-discharge at operating temperature16-19. The typical mission for thermal batteries is for high power, short duration missions, and while the self-discharge rate during storage is extremely low, once the battery has been raised to operating temperature, self-discharge may be high. This could limit the mission lifetime, and make conventional thermal batteries unsuitable for longer duration missions2. The self-discharge rate varies considerably depending on details of the battery construction; for example, Knödler18measured self-discharge rates of about 1% per day for fully-charged engineering-scale LiAl/FeS cells at an operating temperature of 470° C, but notes that the rate goes down to about 0.5% per day when the battery is in a semi-charged state, and decreases with time when the battery is held at open-circuit conditions. Guidotti, Reinhardt and Saga19, on the other hand, observed about 25% loss of capacity on LiSi/Fe2S batteries held at open circuit voltage for one hour, although this rate was decreased considerably by the use of fused, lithiated catholytes, most particularly with the LiCl/KCl electrolyte, where the capacity loss decreased to about 2% over the 60 minute test. Del Castillo, et al.2noted considerably higher self-discharge rates for the Li alloy/FeS2cells they tested, with performance dropping within 40 minutes of operation.