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

Abstract

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||Na2/3 Ni1/4 Cu1/12 Mn2/3 O2 full cell with 90.6% capacity retention over 400 cycles at -40 °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.