Central-Atom-Differentiated Solvent Chemistry Enables Anion-Reinforced Solvation for Ultra-Long Cycling Ah-Level Sodium-Ion Pouch Cells.

Abstract

Conventional carbonate-based electrolytes for sodium-ion batteries (SIBs) provide high salt solubility and high-voltage compatibility. However, their inherent Na+ solvation behavior and interfacial reactions remain largely governed by carbon-centered carbonate motifs, making it difficult to concurrently achieve rapid Na+ desolvation and durable electrode-electrolyte interphases under practical operating conditions. Here, we introduce a central-atom-differentiated solvent chemistry by incorporating ethylene sulfite (ES) into a conventional carbonate electrolyte. The sulfur-centered sulfite motif creates an oxygen-donor environment electronically distinct from that of the carbon-centered carbonate motif, thereby rebalancing solvent-anion competition and promoting PF6 - participation in the inner Na+ solvation sheath. The resulting anion-reinforced solvation substantially lowers the Na+ desolvation barrier. Concurrently, the distinct interfacial conversion chemistry of ES, combined with the enhanced anion participation, favors the formation of robust, inorganic-rich interphases on both the cathode and anode. Consequently, a 2.34 Ah NaNi0.33Fe0.33Mn0.33O2||hard carbon pouch cell retains 81.29% of its initial capacity after 3500 cycles at room temperature (corresponding to over one year of continuous cycling) and maintains stable cycling across a 70°C operating window from -20°C to 50°C. This work demonstrates that differentiating solvent central-atom chemistry provides a compositionally simple route to simultaneously regulate Na+ solvation and dual-electrode interphases for practical SIBs.