The synergistic effect of fluorinated solvents and LiDFOB on stable cycling of Li metal batteries with limited Li

Abstract

Practical Li metal batteries (LMBs) demand electrolytes that stabilize ultra-thin (<20 μm) or Li-free anodes while resisting extreme temperatures. Herein, we design a dual-salt electrolyte combining LiPF₆ and LiDFOB in fluorinated carbonate/carboxylate ester solvents, leveraging a fluorine-induced solvation structure. The Li‖NCM811 cell employing the designed electrolyte (1 M LiPF₆ 0.1 M LiDFOB in FEC/ETFP 3 : 7 v/v) exhibits outstanding performance under thin Li conditions at room temperature (25 °C). After 100 cycles, it retains a high capacity of 67.35%, with an average coulombic efficiency (CE) of 99.90%. Moreover, it maintains 75.92% of room-temperature capacity at −40 °C (145.6 mA h g⁻¹), in addition to the inherent flame-retardancy. Mechanistic studies reveal that fluorinated solvents cooperate with LiDFOB to form anion-rich solvation structures, promoting the formation of compact inorganic-rich interphases. The dual fluorine sources (solvent/DFOB⁻) synergistically enhance Li⁺ desolvation kinetics and interface stability, accounting for the improved cycling efficiency and temperature resilience. This work provides a robust strategy for advancing practical LMBs with limited Li anodes, addressing key challenges in energy density, cycle stability, low-temperature performance, and safety.