Molecular Engineering Enabling High Initial Coulombic Efficiency and Rubost Solid Electrolyte Interphase for Hard Carbon in Sodium‐Ion Batteries

Abstract Hard carbon (HC) as a potential candidate anode for sodium‐ion batteries (SIBs) suffers from unstable solid electrolyte interphase (SEI) and low initial Coulombic efficiency (ICE), which limits its commercial applications and urgently requires the emergence of a new strategy. Herein, an organic molecule with two sodium ions, disodium phthalate (DP), was successfully engineered on the HC surface (DP‐HC) to replenish the sodium loss from solid electrolyte interphase (SEI) formation. A stabilized and ultrathin (≈7.4 nm) SEI was constructed on the DP‐HC surface, which proved to be simultaneously suitable in both ester and ether electrolytes. Compared to pure HC (60.8 %), the as‐designed DP‐HC exhibited a high ICE of >96.3 % in NaPF 6 in diglyme (G2) electrolyte, and is capable of servicing consistently for >1600 cycles at 0.5 A g −1 . The Na 3 V 2 (PO 4 ) 3 (NVP)|DP‐HC full‐cell with a 98.3 % exceptional ICE can be cycled stably for 450 cycles, demonstrating the tremendous practical application potential of DP‐HC. This work provides a molecular design strategy to improve the ICE of HC, which will inspire more researchers to concentrate on the commercialization progress of HC.