Solvation-structure-preserved electrolyte breaks the low temperature barrier for sodium metal battery

Abstract

Sodium metal batteries (SMBs) are expected to become an alternative solution for energy storage and power systems in the future due to their abundant resources, substantial energy–density, and all-climate performance. However, uneven Na deposition and slow charge transfer kinetics still significantly impair their low temperature and rate performance. Herein, we report a non-solvating trifluoromethoxy benzene (PhOCF₃) that modulates dipole–dipole interactions in the solvation structure. This modulation effectively reduces the affinity between Na⁺ and solvents, promoting an anion-rich solvation sheath formation and significantly enhancing room temperature electrochemical performance in SMBs. Furthermore, temperature-dependent spectroscopic characterizations and molecular dynamics simulations reveal that these dipole–dipole interactions thermodynamically exclude solvent molecules from inner Na⁺ solvation sphere at low temperatures, which endows the electrolyte with exceptional temperature adaptability, leading to remarkable improvement in low temperature SMB performance. Consequently, Na||Vanadium phosphate sodium (NVP) cells with the optimized electrolyte achieve 10,000 cycles at 10 C with capacity retention of 90.2% at 25 °C and over 650 cycles at 0.5 C with a capacity of 92.1 mA h g⁻¹ at −40 °C. This work probed the temperature-responsive property of Na⁺ solvation structure and designed the temperature-adaptive electrolyte by regulating solvation structure via dipole–dipole interactions, offering a valuable guidance for low temperature electrolytes design for SMBs.