C-P/C-Se dual-bond interfacial regulation: A synergistic strategy for efficient sodium storage in bimetallic...

Transition metal phosphides (TMPs) are considered promising anode candidates for sodium-ion batteries (SIBs) because of their high theoretical capacity and favorable electrochemical activity. Their electrochemical performance, however, is often restricted by sluggish charge-transfer kinetics, pronounced interfacial polarization, and structural instability caused by substantial volume variations during conversion reactions. To address these challenges, a C-P/C-Se dual-bond interfacial regulation strategy is proposed to construct Fe_0.9Co_0.1P_1-xSe_x@C (x = 0.2), a carbon-confined bimetallic phosphoselenide composite with chemically coupled interfaces. The dual interfacial bonds effectively anchor active phosphoselenide phases onto the carbon framework, enhancing electronic coupling, maintaining structural integrity, and mitigating volume variations during conversion reactions. Meanwhile, Se incorporation modifies the local electronic and coordination environments, providing more favorable pathways for Na⁺ transport. As a result, the coupled regulation of interfacial bonding and Se substitution enables faster electron/ion transport and improved reaction reversibility. At 1 A g^-1, Fe_0.9Co_0.1P_1-xSe_x@C achieves an initial Coulombic efficiency of 81.9% and delivers 463.0 mAh g^-1 after 1000 cycles. When operated at 5 A g^-1, the electrode still provides 356.7 mAh g^-1 after 500 cycles. In addition, the assembled Fe_0.9Co_0.1P_1-xSe_x@C||Na₃V₂(PO₄)₃ full cell exhibits favorable rate capability and long-term cycling stability. These results establish a feasible route for regulating chemically bonded interfaces in phosphide-based anodes for efficient Na⁺ storage.