An Ultrafast and Stable Li-Metal Battery Cycled at −40 °C

Li-metal battery (LMB) suffers from the unexpected Li dendrite growth and unstable solid-electrolyte interphase (SEI), especially in the extreme conditions, such as high rates and low temperatures (LT). Herein, a high-rate and stable LT LMB is realized by regulating electrolyte chemistry. A weak Li⁺-solvating solvent 2-methyltetrahydrofuran is used as electrolyte solvent to mitigate the kinetic barrier for Li⁺ de-solvation. Moreover, a co-solvent tetrahydrofuran with a high donor number is incorporated to improve the LT solubility of Li salts, achieving an improved ionic conductivity while maintaining the weak Li⁺-solvation effect. Furthermore, abundant FSI^- anions in contact-ion pairs are presented, facilitating the formation of a stable LiF-enriched SEI. Consequently, the Li||Li battery can be operated at 10 mA cm^-2 with a small polarization of 154 mV at −40 °C. Meanwhile, an outstanding cumulative cycling capacity of 4000 mAh cm^-2 at 8.0 mA cm^-2 is achieved, reaching a record high level in LT alkali metal symmetric batteries. Also, rechargeable high-rate and stable full batteries are achieved at −40 °C. This work demonstrates the superiority of electrolyte chemistry for synergistic regulation of both ion transfer kinetics and SEI toward ultrafast and stable rechargeable LMBs at LT.