Hollow core-shell structured Si/C nanocomposites were prepared to adapt for the large volume change during a charge-discharge process. The Si nanoparticles were coated with a SiO2 layer and then a carbon layer, followed by etching the interface SiO2 layer with HF to obtain hollow core-shell structured Si/C nanocomposites. The Si nanoparticles are well encapsulated in a carbon matrix with an internal void space between the Si core and the carbon shell. The hollow core-shell structured Si/C nanocomposites demonstrate a high specific capacity and excellent cycling stability, with capacity decay as small as 0.02% per cycle. The enhanced electrochemical performance can be attributed to the fact that the internal void space can accommodate the volume expansion of Si during lithiation, thus preserving the structural integrity of electrode materials, and the carbon shell can increase the electronic conductivity of the electrode.

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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. KEYWORDS: sodium ion batteries, anode, MoS 2 , MoS 2−x Se x , selenizing