Trace LiBF<sub>4</sub> Enabling Robust LiF-Rich Interphase\nfor Durable Low-Temperature Lithium-Ion Pouch Cells

Lithium-ion batteries (LIBs) with\nelectrolytes containing\nlithium\ntetrafluoroborate (LiBF<sub>4</sub>) can achieve large capacity retention\nunder low temperature, but the accompanying rapid capacity decay inhibits\ncommercialization. Here, the impact of LiBF<sub>4</sub> as a supplemental\nsalt to LiPF<sub>6</sub> is systematically investigated using low\nethylene carbonate (EC)-content electrolytes, along with a low-melting-point\ncosolvent. It is found that rational adjustment of the amount of LiBF<sub>4</sub> could not only regulate the interactions of anions and solvents\nin Li<sup>+</sup> solvation sheaths but also tune the composition\nand morphology of solid electrolyte interphase (SEI). It is worth\nnoting that electrolytes with trace amount of LiBF<sub>4</sub> (0.05\nM) show synergetic interaction between PF<sub>6</sub><sup>–</sup> and Li<sup>+</sup> and decreased interaction between EC and Li<sup>+</sup>, achieving a dense and LiF-rich SEI, which enables a 200\nmAh pouch cell with less gas generation, long-lived cycling, and higher\nlow-temperature capacity, simultaneously. This work provides new insight\ninto utilizing trace LiBF<sub>4</sub> for stable interface construction\nof durable low-temperature LIBs.