Asymmetric fluorinated sulfonamide electrolyte solvent for high-voltage and wide-temperature Li-metal batteries

Stable cycling of Ni-rich positive electrodes under high voltages (≥ 4.6 V) is critically challenging due to severe interfacial parasitic reactions and structural degradation, especially under all-climate conditions (i.e., ≤ −20 °C and ≥ 55 °C). Herein, we rationally design and synthesize an asymmetric fluorinated sulfonamide solvent, N-ethyl-N-methyltrifluoromethane-sulfonamide, where the fluorination of sulfone backbone greatly promotes the oxidation stability, while the introduction of asymmetric amine group bestows the solvent with an low freezing point (below −150 °C). This obtained solvent, with 1 M lithium bis(fluorosulfonyl)imide, delivers high oxidation stability (above 5.0 V) and good Li reversibility (up to 99.8% in Li | |Cu cells). Coupled with its ability to form highly robust LiF-rich solid-electrolyte/cathode-electrolyte interphases, this single-salt single-solvent electrolyte enables stable cycling of Li | |Ni0.8Co0.1Mn0.1 cells under an high voltage of 4.8 V across an wide temperature of −60 to 100 °C. Remarkably, a prototype 5 Ah-level Li | | Ni0.8Co0.1Mn0.1 pouch cell at an cut-off voltage of 4.7 V and 0.1 C demonstrates a high specific energy (based on the mass of all components) of 514 Wh kg−1 over 20 cycles. Stable cycling of Ni-rich positive electrodes at high-voltage (≥ 4.6 V) remains challenging. Here, authors propose a single-salt single-solvent electrolyte based on an asymmetric fluorinated sulfonamide solvent, which sustains stable cycling of 4.8 V LillNCM811 cells from −60 to 100 °C.