A rechargeable lithium metal battery operating at intermediate temperatures using molten alkali bis(trifluoromethylsulfonyl)amide mixture as an electrolyte

The physicochemical properties of molten alkali bis(trifluoromethylsulfonyl)amide, MTFSI (M = Li, K, Cs), mixture (chi(LiTFSI) = 0.20, chi(KTFSI) = 0.10, chi(CsTFSI) = 0.70) were studied to develop a new rechargeable lithium battery operating at intermediate temperature (100-180 degrees C). The viscosity and ionic conductivity of this melt at 150 degrees C are 87.2 cP and 14.2 mS cm(-1), respectively. The cyclic voltammetry revealed that the electrochemical window at 150 degrees C is as wide as 5.0 V, and that the electrochemical deposition/dissolution of lithium metal occurs at the cathode limit. A Li/MTFSI (M = Li, K, Cs)/LiFePO4 cell showed an excellent cycle performance at a constant current rate of C/10 at 150 degrees C; 95% of the initial discharge capacity was maintained after 50 cycles. Except for the initial few cycles, the coulombic efficiencies were approximately 100% for all the cycles, indicating the stabilities of the molten MTFSI mixture and all the electrode materials. (C) 2008 Elsevier B.V. All rights reserved.