Coordination structure regulation in non-flammable electrolyte enabling high voltage lithium electrochemistry

Abstract

High-voltage battery systems bring significant increases in energy density but are also accompanied by fast degradation of electrochemical performance and serious safety issues. Herein, Li+ coordination structure regulation was conducted to formulate a non-flammable electrolyte, which consists of 1.5 M lithium bis (fluor sulfonyl) imide (LiFSI) in triethyl phosphate and methyl 2,2,2-trifluoromethyl carbonate (FEMC). The renamed TEP-FEMC-FEC (TFF) electrolyte exhibits an FSI−-dominated solvation structure contributed by the weakly-solvating ability of FEMC. The generated inorganic-rich interfacial layers are conducive to stabilizing the phase transition of high-voltage cathodes while suppressing the dendritic growth on lithium metal or co-intercalation behavior in graphite anode. This TFF electrolyte enables LiCoO2 || Li batteries to achieve capacity maintenance over 79% after 400 cycles with high-rate of 5 C at an ultra-high voltage of 4.6 V, and an outstanding capacity exceeding 100 mA h g−1 even at a super-high current density of 20 C. Additionally, the Ah-level LiCoO2 || graphite pouch cells also exhibit high capacity retention and satisfactory safety performance even under fast charging. This work provides a novel research direction for the pursuit of high energy density non-flammable electrolytes.