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 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.