Durable low-temperature sodium metal batteries enabled by solvent−interaction regulation in solvation structure

Sodium metal batteries (SMBs) have emerged as a promising option for next-generation electrochemical energy storage technologies. Unfortunately, restricted by the sluggish Na⁺ transport kinetics and unstable electrode/electrolyte interphase, SMBs suffer from severe performance deterioration under extreme temperatures. Herein, a low-concentration electrolyte with weak Na⁺−solvent interaction is constructed, which endows facile desolvation and fast ionic conduction at low temperature. Furthermore, we investigated the interaction mechanism between solvents and elucidated its crucial influence in regulating the solvation structure. This synergistic effect facilitates the formation of a thin, dense, and inorganic-rich cathode/electrolyte interphase, optimizing the interfacial chemistry and accelerating the interfacial dynamics at low temperature. As a result, Na_0.67Ni_0.33Mn_0.67O₂//Na batteries employing this electrolyte display a high capacity retention of 92.6% after 200 cycles under −40 °C. This work presents valuable insights into the critical role of solvent−solvent interactions in electrolyte design, and provides a feasible guideline for developing low-temperature electrolytes.