Chelation-frustrated molecular design enables diverse solvation structures for wide-temperature sodium metal batteries

Abstract The practical application of sodium metal batteries (SMBs) in grid-scale energy storage requires electrolytes that remain stable over a wide temperature range. Although high-entropy electrolytes (HEEs) can improve temperature adaptability by enriching Na+ solvation environments through multiple salts and solvents, their complex formulations and high cost hinder practical application. Herein, we report a compositionally simple single-salt and single-solvent electrolyte, 1 M NaPF6 in 2-(ethoxymethyl) tetrahydrofuran (EMTHF), that achieves diverse solvation structures through chelation-frustrated molecular design. The spatially separated ring and chain ether oxygen sites in EMTHF enable three concurrent Na+ coordination modes, namely κ1-Oring-coordinated, κ1-Ochain-coordinated, and κ2-Oring, Ochain-chelated Na+–EMTHF configurations. This diverse yet weakly solvating environment facilitates Na+ desolvation and promotes the formation of anion-derived interphases, thereby stabilizing Na anodes. Consequently, Na–Cu cells sustain stable cycling for more than 1000 cycles at 5 mA·cm−2 and 5 mAh·cm−2. Na–Na3V2(PO4)3 (NVP) cells exhibit excellent temperature adaptability, retaining 86.5% of their capacity after 3000 cycles at −20 °C and 72.9% after 300 cycles at 80 °C. Moreover, a Na–NVP full cell assembled with a 70 μm Na anode and an NVP cathode loading of 10 mg·cm−2 delivered highly stable long-term cycling, with a capacity retention of 97.0% after 1000 cycles. These findings demonstrate that diverse solvation structures can be achieved through rational solvent molecular design, offering a simple route toward wide-temperature SMBs.