Conversion of MoS₂ to a Ternary MoS_{2- x}Se _x Alloy for High-Performance Sodium-Ion Batteries

MoS₂ has attracted tremendous attention as an anode for Na-ion batteries (NIBs) owing to its high specific capacity and layered graphite-like structure. Herein, MoS₂ is converted to a ternary MoS_{2- x}Se _x alloy through the selenizing process in order to boost the electrochemical performance for Na-ion batteries. Conversion of MoS₂ to MoS_{2- x}Se _x expands interlayer spacing, improves electronic conductivity, and creates more defects. The expanded interlayer spacing decreases Na⁺ diffusion resistance and facilitates Na⁺ fast transfer. The integrated graphene as a conductive network offers effective pathway for electron migration and maintains structural stability of electrodes during cycles. The ternary MoS_1.2Se_0.8/graphene (MoS_1.2Se_0.8/G) electrode demonstrates an extremely high reversible capacity of 509 mA h g^-1 after 200 cycles at 0.1 A g^-1 (capacity retention of 109%) as an anode for sodium-ion batteries. Even at 2 A g^-1 and after 700 cycles, the MoS_1.2Se_0.8/G electrode also displays a relatively high reversible capacity of 178 mA h g^-1. Full cells assembled with Na₃V₂(PO₄)₂F₃ cathodes and MoS_1.2Se_0.8/G anodes reveal high charge/discharge capacities. This work demonstrates that the ternary MoS_{2- x}Se _x alloy could be a potential anode material for Na-ion storage.