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.