Temperature-Responsive Solvation of Deep Eutectic Electrolyte Enabling Mesocarbon Microbead Anode for High-Temperature Li-Ion Batteries

Deep eutectic electrolytes (DEEs) provide a safe solution for high-temperature batteries. While promising, the DEEs/electrode interphase chemistry and the underlying temperature mechanism remain unclear. Herein, the DEE is formulated with succinonitrile (SCL) and lithium bis(fluorosulfonyl) imide (LiFSI) to promote the mesocarbon microbead (MCMB) anode in high-temperature Li-ion batteries. The temperature-sensitive mechanism of solid electrolyte interphase (SEI) evolution on the MCMB is deciphered, the core of which is temperature-regulated solvation chemistry. Specifically, high temperature can result in the enhanced interaction between Li⁺ and FSI^- anions in the solvation structure, thus elevating the LiF content in the SEI. Due to the synergy of DEE (featuring rapid ion conduction and thermal stability) and high-temperature optimized interphase, MCMB/Li and LiFePO₄/MCMB cells exhibit improved cycling stability at high temperature. This work promotes a fundamental understanding of the intrinsic relationship between the temperature factor and SEI evolution, illuminating the future of DEEs in high-temperature batteries.