Enhancing Robustness and Charge Transfer Kinetics of Sodium-Ion Batteries through Introduction of Anionic Anchoring Separators

Ionic transport critically dictates the performance of the batteries. Here, we proposed an anion anchoring strategy for enhancing Na⁺ transport kinetics that was based on introducing a separator with a positive surface potential. Besides, we developed a nuclear magnetic resonance-assisted Hittorf approach to address the limitation of the traditional Bruce-Vincent approach itself in order to accurately quantify the migration dynamics of anions on the time scale. Results indicate that this strategy effectively anchors free anions and increases the proportion of solvent-separated ion pairs in the bulk, reduces the cation transfer energy barrier at the anode, and mitigates parasitic reactions at the cathode. The symmetric Na||Na cells efficiently operate over 1600 h, and the Na||Na₃V₂(PO₄)₃ cells show stable cycling performance under limited Na excess and lean electrolyte conditions. The assembled HC||Na₃V₂(PO₄)₃ pouch cells achieve an energy density of up to 225.7 W h kg^-1. Our strategy offers a new option for high-energy and long-cycle sodium-ion batteries.