Entropy-Driven Solvation toward Low-Temperature Sodium-Ion Batteries with Temperature-Adaptive Feature

Salt precipitation at temperatures far above the freezing point of solvents is primarily responsible for performance decay of rechargeable batteries at low temperature, yet is still challenged by a lack of in-depth understanding of the design principle and ultimate solutions. Here, this is resolved via tuning the entropy of solvation in a strong-solvation (SS) and weak-solvation (WS) solvent mixture, in which a solvation structure can spontaneously transform at low temperature to avoid salt precipitation, endowing the electrolyte with a temperature-adaptive feature. The results affirm that such temperature-adaptive electrolyte ensures encouraging low-temperature performance in a hard carbon||Na2/3Ni1/4Cu1/12Mn2/3O2 full cell with 90.6% capacity retention over 400 cycles at -40 degrees C. The generality of the concept is further expanded to construct a series of SS-WS electrolytes as potential candidates for rechargeable low-temperature sodium-ion batteries. The work shed lights on the importance of entropy tuning and affords a rational viewpoint on designing low-temperature electrolytes.