Designing High Donor Number Anion Additive for Stable Lithium Metal Batteries

The electrolytes in energy-dense lithium metal batteries (LMBs) face the challenge of being compatible with both the lithium anode and the high voltage cathodes. Adjusting the solvation structures of the electrolytes by regulating the interaction between ions and solvents is an effective strategy to improve the stability of LMBs. Herein, lithium trifluoroacetate (LiTFA) endowed with high donor number is introduced into ether-based electrolytes as an additive to regulate the solvation structure and further stabilize the interphase as well as accelerate the interfacial kinetic of LMBs. Due to the strong interaction between TFA^- with Li⁺, the anion-rich solvation structure with reduced solvent coordination capability is constructed, contributing to the formation of inorganic-rich interphase layers and facilitate charge transfer reaction. Consequently, the designed electrolyte improves the reversibility of Li plating/stripping with high Coulombic efficiency of 99.24% and enables long-term cycling of Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) over 100 cycles with a capacity retention of 84.37% under the condition of lean electrolyte, limited Li source and conventional Li-salt concentration. This work provides an effective and low-cost strategy to adjust the solvation structure and improve the stability of LMBs without largely sacrificing the intrinsic physicochemical property (viscosity, wettability, ionic conductivity etc.) of electrolytes.