Separator‐Mediated Pre‐Desolvation Regulation via Oxygen‐Doped Carbon Nitride for Efficient Sodium Storage in Hard Carbon

ABSTRACT

Hard carbon (HC) is a highly promising anode for sodium‐ion batteries, yet its practical reversibility is still limited by uncontrolled electrolyte reduction at the HC/electrolyte interface. Herein, we developed a separator‐mediated pre‐desolvation regulation strategy via oxygen‐doped carbon nitride (CNOI) modified separator that enables concurrent interfacial passivation and rapid Na ⁺ transport. The CNOI with abundant polar N/O sites electrostatically interacts with Na ⁺ and preconditions its local solvation environment before interfacial charge transfer. As a result, the Na ⁺ flux across the separator becomes more homogeneous, and the interfacial desolvation barrier is reduced, thereby promoting the in situ formation of a thin, ion‐conductive SEI. Accordingly, HC|Na half‐cells with the CNOI‐modified separator exhibit an initial Coulombic efficiency of 93.0%, sustain a capacity of 297.7 mAh g ⁻¹ after 600 cycles at 1 C, and deliver 247.3 mAh g ⁻¹ even at an elevated rate of 15 C. It also realizes remarkable low‐temperature adaptability, delivering a capacity of 163.5 mAh g ⁻¹ at 0.5 C even at −40°C. This work establishes separator‐driven pre‐desolvation regulation as a transferable interfacial engineering strategy for high‐performance HC anodes of practical sodium‐ion batteries.