Manipulating cation solvation equilibrium in sole-solvent electrolyte for fast-charging and wide-temperature-range sodium metal batteries.

Abstract

Sodium metal batteries represent a highly promising solution for grid-scale energy storage. However, their fast-charging capability and wide-temperature operation remain constrained by dynamic interphase degradation and inaccessible sodium coordination chemistry. Central to these challenges is the solvation structures as dictated by cation-dipole (Na⁺-solvent) and cation-anion (Na⁺-anion) interactions. Here, we engineer a sole-solvent electrolyte by tailoring the critical thermodynamic balance between the cation-anion and cation-solvent interactions that fundamentally describes the electrolyte behaviors. By leveraging the methyl-induced electron donation effect in 3-methyltetrahydrofuran, we modulate the Na⁺-anion and Na⁺-solvent interactions, and configure the Na⁺ solvation environment into a balanced anion-solvent-coordinated structure. The weakened Na⁺-solvent attraction enhances anion participation and promotes the formation of inorganic-rich stable interphases on both electrodes as temperature elevates. While a slight decrease in anion participation at low temperatures provides high ionic conductivity, accelerated kinetics and mitigated dendrite growth. Consequently, the Na | |Na₃V₂(PO₄)₃ cells deliver the high-rate capability (up to 100 C with 85 mAh g^-1 at 60 °C) and long cyclability (>1200 cycles, 1 C at -45 °C). This work establishes balanced anion-solvent-solvated chemistry as a design principle for stable wide-temperature batteries.