Lewis Acid-Base Regulated Novel Eutectic Electrolyte of 1,4-Butane Sultone and LiTFSI Enables High-Voltage Lithium Metal Batteries via F/S-Rich Interphases

Abstract

Conventional carbonate electrolytes oxidatively decompose at high voltages, limiting the cycling life of lithium metal batteries (LMBs). Herein, we report a deep eutectic electrolyte (DEE) composed of 1,4-butane sultone (BS) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), in which BS coordinates with Li⁺ through its S=O group via Lewis acid–base interactions to promote LiTFSI dissociation. The sulfonate group in BS enables DEE to exhibit good compatibility with Li and robust oxidative stability under high-voltage operation. Its effective decomposition promotes the formation of F/S-rich interphases with an ultrathin cathode electrolyte interface (CEI) of ~6 nm, synergistically boosting interfacial ionic conductivity and mechanical stability. Consequently, Li||Li symmetric cells sustain stable stripping/plating for over 2,000 hours. LiCoO2||Li cells achieve 81.7% capacity retention after 1,000 cycles at 0.5C with a 4.3 V cutoff. At elevated cutoff voltages of 4.5 V and 4.6 V (1C), the cells retain 83.6% capacity after 500 cycles and 83.2% after 300 cycles, respectively, far outperforming cells with commercial carbonate electrolytes. Even at 50 ℃, the capacity loss remains only 19.2% after 800 cycles. This work highlights the potential of sulfonate-based DEEs for high-voltage, high-temperature and long-life LMBs.