Deep eutectic electrolytes for fast charging and wide temperature lithium metal batteries

Lithium metal batteries offer high energy density. However, it requires electrolytes that remain stable under fast-charging and wide temperature fluctuation. Here, we develop a sulfonyl-based deep eutectic electrolyte (DEE) that is nonflammable, thermally stable, and highly conductive (4.1 mS cm⁻¹at 30 °C). The tailored solvation structure of this DEE reduced Li⁺–anion binding and lowered desolvation barriers, as confirmed by spectroscopy, molecular dynamics, and density functional theory. The DEE formed a robust LiF/SO_x-rich solid electrolyte interphase that enabled long-term cycling. The Li/LFP cells delivered 92 % capacity retention after 1200 cycles at 2C and 30 °C. Moreover, Li/LMFP cells retained 75 % after 500 cycles at 2C and 30 °C. The electrolyte maintained stability under fast charging and repeated thermal transitions between 4 and 70 °C, highlighting its adaptability to demanding operating conditions. These findings establish sulfonyle-based DEEs as a design platform for safe, high-rate lithium metal batteries in grid storage and electric vehicles.