A Fully Methylated Cyclic Ether Solvent Enables Graphite Anode Cycling at Low Temperatures.

Graphite anode suffers from great capacity loss and larger cell polarization under low-temperature conditions in lithium-ion batteries (LIBs), which are mainly caused by the high energy barrier for the Li desolvation process and sluggish Li transfer rate across the solid electrolyte interface (SEI). Regulating an electrolyte with an anion-dominated solvation structure could synchronously stabilize the interface and boost the reaction kinetics of the graphite anode. Herein, a highly ionic conductive electrolyte consisting of a fully methylated cyclic ether solvent of 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD) and fluoroethylene carbonate (FEC) cosolvent was designed. The high electron-donating effect and steric hindrance of -(CH) in HMD endow the HMD-based electrolyte with high ionic conductivity but lower coordination numbers with Li, and an anion-dominated solvation structure was formed. Such configuration can accelerate the desolvation process and induce the forming of a LiF-rich SEI film on the anode, avoiding the solvent coembedding into graphite and enhancing the ion migration rate under low temperatures. The assembled Li||graphite cell with the tame electrolyte outperformed the conventional carbonates-based cell, showing 93.8% capacity retention after 227 cycles for the DF-based cell compared to 64.7% after 150 cycles. It also exhibited a prolonged cycle life for 200 rounds with 81% capacity retention under -20 °C. Therefore, this work offers a valuable thought for solvent design and provides approaches to electrolyte design for low-temperature LIBs.