Dual-Ionic Weakly Solvating Electrolyte Design Enables Efficient Fast-Cycling of High-Voltage Anion Shuttle Batteries

Electrolytes shape solvation structures that govern ionic transport, stability, and interfacial properties in energy storage systems. Sodium-based dual-ion shuttling systems offer high-voltage and fast-charging potential but face challenges such as solvent co-intercalation, electrolyte decomposition, and low Coulombic efficiency, partly due to limited anion-focused electrolyte design. Herein, a low-concentration dual-ionic weakly solvating electrolyte (DWSE) is introduced, leveraging functionalized nano-graphene oxide additives to modulate the solvation environments of Na⁺ and PF₆ ^-. While a conventional cationic weakly solvating electrolyte (CWSE) enhances Na⁺ transport, DWSE simultaneously addresses anion and cation transport for a more balanced approach. DWSE prevents solvent co-intercalation, stabilizes interfaces with NaF-rich layers, and enhances ionic transport. It achieves a reversible capacity of 82.0 mAh g^-1 at 50 C and retains 96.2% capacity after 1500 cycles at 10 C. This study offers a robust framework for advancing dual-ion shuttling systems with optimized cation and anion dynamics.