Entropy-Driven Solvation towards 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, we resolve this via tuning the entropy of solvation in a strong-solvation (SS) and weak-solvation (WS) solvent mixture, in which the solvation structure can spontaneously transform at low temperature to avoid the salt precipitation, endowing the electrolyte with a temperature-adaptive feature. Our results affirm that such temperature-adaptive electrolyte ensures encouraging low-temperature performance in a hard carbon||Na 2/3 Ni 1/4 Cu 1/12 Mn 2/3 O 2 full cell with 90.6% capacity retention over 400 cycles at -40 °C. We further expand the generality of the concept to construct a series of SS-WS electrolytes as potential candidates for rechargeable low-temperature sodium-ion batteries. Our work shed lights on the importance of entropy tuning and affords a rational viewpoint on designing low-temperature electrolytes. This article is protected by copyright. All rights reserved.