Regulating Diffusion Coefficient of Li⁺ by High Binding Energy Anion towards Ultra‐Low Temperature Lithium‐ion Batteries

Electrolyte design is the optimal strategy to achieve extremely low temperature operation of lithium‐ion batteries. Here, the diffusion coefficient of Li + is proposed to improve the ion transport kinetics at low temperatures. The diffusion coefficient of Li + is improved by constructing a Li + solvation sheath with weak steric effects. Specifically, high binding energy BF 4 − anions are added to a 1 M LiPF 6 in propyl acetate ( PA ) electrolyte. Since the binding energy of Li + with BF 4 − is greater than that of PA. Therefore, the small‐sized BF 4 − replaces the large‐sized PA molecule to form a Li + solvation sheath with a weak steric effect, which increases the diffusion coefficient of Li + . Using the high diffusion coefficient electrolyte, the 800 mAh pouch cell retain 91 % and 75 % of its room temperature capacity at −40 °C(0.5 C rate) and −60 °C (0.2 C rate), respectively. And it also shows stable cycling at −40 °C. This work provides a new strategy for designing low‐temperature electrolytes of lithium‐ion batteries.