Trace LiBF₄ Enabling Robust LiF-Rich Interphase for Durable Low-Temperature Lithium-Ion Pouch Cells

Lithium-ion batteries (LIBs) with electrolytes containing lithium tetrafluoroborate (LiBF₄) can achieve large capacity retention under low temperature, but the accompanying rapid capacity decay inhibits commercialization. Here, the impact of LiBF₄ as a supplemental salt to LiPF₆ is systematically investigated using low ethylene carbonate (EC)-content electrolytes, along with a low-melting-point cosolvent. It is found that rational adjustment of the amount of LiBF₄ could not only regulate the interactions of anions and solvents in Li⁺ solvation sheaths but also tune the composition and morphology of solid electrolyte interphase (SEI). It is worth noting that electrolytes with trace amount of LiBF₄ (0.05 M) show synergetic interaction between PF₆^- and Li⁺ and decreased interaction between EC and Li⁺, achieving a dense and LiF-rich SEI, which enables a 200 mAh pouch cell with less gas generation, long-lived cycling, and higher low-temperature capacity, simultaneously. This work provides new insight into utilizing trace LiBF₄ for stable interface construction of durable low-temperature LIBs.