Enhanced interfacial compatibility of FeS@N,S-C anode with ester-based electrolyte enables stable sodium-ion full cells

The development of sodium-ion full cells is seriously suppressed by the incompatibility between electrodes and electrolytes. Most representatively, high-voltage ester-based electrolytes required by the cathodes present poor interfacial compatibility with the anodes due to unstable solid electrode interphase (SEI). Herein, FeS@N,S-C (spindle-like FeS nanoparticles individually encapsulated in N,S-doped carbon) with excellent structural stability is synthesized as a potential sodium anode material. It exhibits exceptional interfacial stability in ester-based electrolyte (1 M NaClO4 in ethylene carbonate/propylene carbonate with 5% fluoroethylene carbonate) with long-cycling lifespan (294 days) in Na|FeS@N,S-C coin cell and remarkable cyclability in pouch cell (capacity retention of 82.2% after 170 cycles at 0.2 A g−1). DFT calculation reveals that N,S-doping on electrode surface could drive strong repulsion to solvated Na+ and preferential adsorption to ClO4− anion, guiding the anion-rich inner Helmholtz plane. Consequently, a robust SEI with rich inorganic species (NaCl and Na2O) through the whole depth stabilizes the electrode–electrolyte interface and protects its integrity. This work brings new insight into the role of electrode’s surface properties in interfacial compatibility that can guide the design of more versatile electrodes for advanced rechargeable metal-ion batteries.