Tailoring Electrolyte Solvation of Dimethyl Sulfite with Fluoride Dominant via Electrolyte Engineering for Enabling Low-Temperature Batteries

Abstract

Carbonate electrolytes are the primary determinant for the development of low-temperate lithium metal batteries (LT-LMBs). However, conventional ethyl carbonate (EC)-based electrolytes with solvent-dominated solvation configuration suffer from sluggish reaction kinetics, severe interfacial side reactions and high Li⁺ desolvation energy under low temperature. Herein, an EC-free and weakly solvated electrolyte consisting of LiDFOB and mixed solvents including dimethyl sulfite (DMS), ethyl trifluoroacetate (ETFA) and fluoroethylene carbonate (FEC) was designed to facilitate the reaction kinetics and stabilize the interfaces of LT-LMBs, where a fluoride-rich solvation structure including FEC, ETFA and DFOB^- is formed in the designed electrolyte. Such solvation configuration could significantly facilitate the desolvation process and induce the homogeneous Li deposition by forming high ionic conductive and inorganics-rich protective film on the electrode surfaces. With such electrolyte, the Li||NCM811 cell retains a high capacity retention of 81.7% after 1000 cycles, which is far superior to the 31.3% for EC-based electrolyte. Even at -40°C, the cell exhibits a capacity of 125.7 mAh g^-1 with almost no capacity attenuation after 200 cycles. This work confirms the necessity of fluoride-dominated solvation structure in decreasing the desolvation energy and accelerating the ionic transfer, contributing a promising solution to the development of low-temperature LMBs.