Molten salt electrolytes for high-temperature lithium cells

The composition and melting point of the molten salt electrolyte play a key role in the performance of high-temperature Li-alloy/metal sulfide cells. For example, the performance of the LiAl/FeS cell operated under flooded-electrolyte conditions improves markedly with an increase in the LiCl content of the LiClKCl electrolyte. A similar cell, when operated in a starved-electrolyte state, requires the use of an all-lithium cation electrolyte (e.g., LiFLiClLiBr) to achieve good performance. Both these electrolytes have fairly high melting points, >400 °C. The LiAl/FeS2 cell, on the other hand, has been found to operate well as an upper-plateau cell in an electrolyte (25mol%LiCl–37mol%LiBr–38mol%KBr) with a low melting point, 310 °C. Recent laboratory investigations have also demonstrated that the LiAl/(NiFe)S2 cell operates very well in an Li2S saturated, all-lithium, cation electrolyte at high temperatures, 475 °C.