Cyclic Ether Derived Stable Solid Electrolyte Interphase on Bismuth Anodes for Ultrahigh‐Rate Sodium‐Ion Storage

Abstract The bismuth anode has garnered significant attention due to its high theoretical Na‐storage capacity (386 mAh g −1 ). There have been numerous research reports on the stable solid electrolyte interphase (SEI) facilitated by electrolytes utilizing ether solvents. In this contribution, cyclic tetrahydrofuran (THF) and 2‐methyltetrahydrofuran (MeTHF) ethers are employed as solvents to investigate the sodium‐ion storage properties of bismuth anodes. A series of detailed characterizations are utilized to analyze the impact of electrolyte solvation structure and SEI chemical composition on the kinetics of sodium‐ion storage. The findings reveal that bismuth anodes in both THF and MeTHF‐based electrolytes exhibit exceptional rate performance at low current densities, but in THF‐based electrolytes, the reversible capacity is higher at high current densities (316.7 mAh g −1 in THF compared to 9.7 mAh g −1 in MeTHF at 50 A g −1 ). This stark difference is attributed to the formation of an inorganic‐rich, thin, and uniform SEI derived from THF‐based electrolyte. Although the SEI derived from MeTHF‐based electrolyte also consists predominantly of inorganic components, it is thicker and contains more organic species compared to the THF‐derived SEI, impeding charge transfer and ion diffusion. This study offers valuable insights into the utilization of cyclic ether electrolytes for Na‐ion batteries.