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

Abstract 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 BF₄⁻ anions are added to a 1 M LiPF₆ in propyl acetate (PA) electrolyte. Since the binding energy of Li⁺ with BF₄⁻ is greater than that of PA. Therefore, the small‐sized BF₄⁻ 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.