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 degrees C(0.5 C rate) and -60 degrees C (0.2 C rate), respectively. And it also shows stable cycling at -40 degrees C. This work provides a new strategy for designing low-temperature electrolytes of lithium-ion batteries.