Diluent modified weakly solvating electrolyte for fast-charging high-voltage lithium metal batteries

Weakly solvating electrolyte (WSE) demonstrates superior compatibility with lithium (Li) metal batteries (LMBs). However, its application in fast-charging high-voltage LMBs is challenging. Here, we propose a diluent modified WSE for fast-charging high-voltage LMBs, which is formed by adding diluent of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) into the tetrahydropyran (THP) based WSE. A relatively loose solvation structure is formed due to the formation of weak hydrogen bond between TTE and THP, which accelerates the de-solvation kinetics of Li+. Besides, more anions are involved in solvation structure in the presence of TTE, yielding inorganic-rich interphases with improved stability. Li (30 µm)||LiNi0.5 Co0.2Mn0.3O2 (4.1 mAh/cm2) batteries with the TTE modified WSE retain over 64 % capacity retention after 175 cycles under high rate of 3 C and high-voltage of 4.5 V, much better than that with pure THP based WSE. This work points out that the combination of diluent with weakly solvating solvent is a promising approach to develop high performance electrolytes for fast-charging high-voltage LMBs.