Localized high-concentration electrolyte enhances SEI structure for low-temperature lithium metal batteries

Fluoroethylene carbonate (FEC) is frequently added to the electrolyte in low-temperature lithium metal batteries to improve performance. However, its use results in a Li₂CO₃-rich solid electrolyte interphase (SEI) on the lithium anode, which leads to continuous thickening of the SEI under low-temperature cycling. In this study, the local high-concentration electrolyte was utilized to optimize the solvation structure of Li⁺, thereby adjusting the composition and structure of the SEI. Consequently, the Li∥LiNi_0.8Co_0.1Mn_0.1O₂ cell achieved over 99.5% Coulombic efficiency at −20 °C and sustained over 50 cycles at a 1 C rate at −40 °C, with a specific capacity exceeding 110 mAh/g and a high Coulombic efficiency above 99%. The combined use of ethyl acetate (EA) and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE) promoted the formation of a layered SEI on the lithium anode, enabling efficient Li⁺ desolvation at low temperatures. This provides a novel strategy for designing low-temperature lithium metal battery electrolytes.