Conversion of MoS2 to a Ternary MoS2- xSe 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 MoS2- xSe x alloy through the selenizing process in order to boost the electrochemical performance for Na-ion batteries. Conversion of MoS2 to MoS2- xSe 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 MoS1.2Se0.8/graphene (MoS1.2Se0.8/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 MoS1.2Se0.8/G electrode also displays a relatively high reversible capacity of 178 mA h g-1. Full cells assembled with Na3V2(PO4)2F3 cathodes and MoS1.2Se0.8/G anodes reveal high charge/discharge capacities. This work demonstrates that the ternary MoS2- xSe x alloy could be a potential anode material for Na-ion storage.