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 BF4‐ anions are added to a 1M 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℃(0.5C rate) and ‐60℃ (0.2C rate), respectively. And it also shows stable cycling at ‐40℃. This work provides a new strategy for designing low‐temperature electrolytes of lithium‐ion batteries.