Fluorine-Rich Interphase and Desolvation Regulation for a Long-Life and High-Rate TiS2-Based Li-Metal Battery

Structural stability and electrochemical stability make titanium disulfide (TiS2) a promising cathode material for Li-metal battery. Building the good compatibility of electrolyte with TiS2 and Li metal is key to improving the performance of TiS2; based Li-metal battery, and related tricky issues are the unstable solid electrolyte interphase (SEI) and slow Li+ transportation kinetics. Here we design an electrolyte of lithium bis(fluorosulfonyl)imide (LiFSI) in methyl 2,2,2-trifluoroethyl carbonate (FEMC) for a TiS2-based Li-metal battery. On the one hand, the reduction of LiFSI and FEMC generates robust fluorine-rich SEIs on both the surfaces of TiS2 and Li metal, thereby elevating the cycling stability. On the other hand, the weak solvation ability of FEMC enables fast charge transfer, thus improving the rate capability. The Li+ transportation kinetics processes of Li+ conduction in bulk electrolyte, Li+ desolvation, Li+ migration across SEI, and Li+ diffusion in bulk TiS2 are studied with different electrolytes. The results reveal that the Li+ transportation kinetics in the TiS2-based Li-metal cell is mainly controlled by Li+ desolvation. This electrolyte regulation for interphase stability and Li+ kinetics is also applicable to other battery systems.