Conversion of MoS 2 to a Ternary MoS 2- x Se x Alloy for High-Performance Sodium-Ion Batteries.

MoS ₂ has attracted tremendous attention as an anode for Na-ion batteries (NIBs) owing to its high specific capacity and layered graphite-like structure. Herein, MoS ₂ 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 MoS ₂ 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 _1.2 Se _0.8 /graphene (MoS _1.2 Se _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 _1.2 Se _0.8 /G electrode also displays a relatively high reversible capacity of 178 mA h g ^-1 . Full cells assembled with Na ₃ V ₂ (PO ₄ ) ₂ F ₃ cathodes and MoS _1.2 Se _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.