Sn@C Composite with an Ultra-high Initial Coulombic Efficiency via Interfacial Engineering for Sodium-Ion Battery Anodes

Tin (Sn)-based anodes are attractive candidates for sodium-ion batteries due to their high theoretical capacity and low operating potential. However, their practical viability is severely constrained by drastic volume changes, unstable solid–electrolyte interphase (SEI) formation, and intrinsically low initial Coulombic efficiency (ICE). Herein, an interfacial regulation strategy to enhance the ICE and cycling stability of Sn-based anodes is proposed. That is, we construct Sn-MOF-derived Sn@C composites with submicron Sn particles uniformly confined in a conductive carbon matrix via hydrothermal synthesis and subsequent pyrolysis. This architecture yields an exceptional ICE of 96.4% (725/752 mA h g–1 at 0.1 A g–1), far surpassing that of commercial Sn powder (77.9%). Mechanistic investigations reveal a reversible stepwise alloying pathway from Sn to Na9Sn4 and subsequently to Na15Sn4, while the carbon matrix promotes a thin, uniform NaF-rich SEI that curbs electrolyte decomposition and Na+ loss. In situ EIS-DRT analysis further corroborates the progressive reduction of interfacial resistances during sodiation–desodiation. As a result, the anode sustains 378 mA h g–1 after 500 cycles at 1 A g–1. A Sn@C-900∥Na3V2(PO4)3 full cell can deliver an energy density of 188 W h kg–1 and retain 107 mA h g–1 over 400 cycles, underscoring the practical feasibility of this high-ICE Sn@C anode.