Designing aggregates-dominated electrolyte via tuning cation-solvent interaction for high-safe and long-life sodium-ion batteries

Sodium-ion batteries (SIBs) have attracted widespread attention as a promising energy storage technology due to the abundant sodium resources and low cost. However, the safety hazard posed by the flammable electrolyte and the low energy density due to insufficient voltage window limit their applicability. Herein, we construct a non-flammable electrolyte with the solvation structure dominated by aggregates (AGGs) via tuning the cation-solvent interaction. This solvation structure allows improved oxidation stability up to 4.8 V (vs. Na⁺/Na), a high Na⁺ transference number, and the formation of a robust anion-derived solid-electrolyte interface (SEI), which facilitates Na⁺ migration to suppress the concentration polarization and achieves rapid de-solvation and diffusion of Na⁺ within the interface, resulting in significant improvement of rate performance and cycle stability. In particular, the hard carbon (HC) anode delivers a high specific capacity of 255.1 mAh g⁻¹ at 0.5 C and a capacity retention of 92.5% even after 1500 cycles. The Na₃V₂(PO₄)₃ (NVP) and NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) cathodes exhibit capacity retention of 96.5% and 90.4% respectively over 800 cycles, and the NVP can deliver a specific capacity of 84.8 mAh g⁻¹ even at the high rate of 10 C. Furthermore, the NVP||HC full cells show stable cycling with a capacity retention of 86.6% after 400 cycles. A commercial NFM||HC pouch cell also shows excellent cycling performance with a capacity retention of 94.6% after 100 cycles. This study provides new insights into electrolyte design by modulating the solvation structure for the development of high-safe and long-life SIBs.