Regulating Solvation Chemistry via Strongly Coordinating Anion and Weakly Solvating Cosolvent for Low-Temperature Sodium Metal Batteries.

Abstract

Sodium metal batteries (SMBs) hold great promise for next-generation energy storage systems due to their abundant sodium resources, high theoretical specific capacity, and low redox potential. However, they suffer from rapid capacity degradation at low operating temperatures, which inevitably hinders their practical application. In this work, we employ a strongly coordinating anion and a weakly solvating cosolvent to fabricate anion-rich and varied solvation structures, aiming to enhance the low-temperature electrochemical performance of SMBs. This unique solvation configuration efficiently reduces the Na+ desolvation energy barrier, alleviates concentration polarization, accelerates liquid-phase ion transport, and facilitates the in-situ formation of a stable, highly ion-conductive electrode-electrolyte interphase. Benefiting from the synergistic regulation of interfacial stability and ion transport kinetics, dendrite-free sodium deposition is achieved at -20°C, enabling stable cycling for over 500 h at 0.5 mA cm-2 and 0.5 mAh cm-2. Additionally, the assembled SMBs exhibit excellent rate performance and cycling stability, delivering a high capacity retention of 70.54% and 68.28% after 1000 cycles at -20°C and -40°C, respectively. This work provides a novel perspective for the rational design of advanced electrolytes for high-performance low-temperature SMBs and lays a solid foundation for their practical application in cold environments.