Sandwich-like MoS2 @SnO2 @C with High Capacity and Stability for Sodium/Potassium Ion Batteries.

Sandwich-like MoS2 @SnO2 @C nanosheets are prepared by facile hydrothermal reactions. SnO2 nanosheets can attach to exfoliated MoS2 nanosheets to prevent restacking of adjacent MoS2 nanosheets, and carbon transformed from polyvinylpyrrolidone is coated on MoS2 @SnO2 , forming a sandwich structure to maintain cycling stability. As an anode for sodium-ion batteries, the electrode greatly deliverers a high initial discharge specific capacity of 530 mA h g-1 and maintains at 396 mA h g-1 after 150 cycles at 0.1 A g-1 . Even at a large current density of 1 A g-1 , it can hold 230 mA h g-1 after 450 cycles. Besides, as an anode for K+ storage, the electrode also shows a discharge capacity of 312 mA h g-1 after 25 cycles at 0.05 A g-1 . This work may provide a new strategy to prepare other composites which can be applied to new kind of rechargeable batteries.

Improved Na+/K+ Storage Properties of ReSe2-Carbon Nanofibers Based on Graphene Modifications.

Rhenium diselenide (ReSe2) has caused considerable concerns in the field of energy storage because the compound and its composites still suffer from low specific capacity and inferior cyclic stability. In this study, ReSe2 nanoparticles encapsulated in carbon nanofibers were synthesized successfully with simple electrospinning and heat treatment. It was found that graphene modifications could affect considerably the microstructure and electrochemical properties of ReSe2-carbon nanofibers. Accordingly, the modified compound maintained a capacity of 227 mAh g-1 after 500 cycles at 200 mA g-1 for Na+ storage, 230 mAh g-1 after 200 cycles at 200 mA g-1, 212 mAh g-1 after 150 cycles at 500 mA g-1 for K+ storage, which corresponded to the capacity retention ratios of 89%, 97%, and 86%, respectively. Even in Na+ full cells, its capacity was maintained to 82% after 200 cycles at 1C (117 mA g-1). The superior stability of ReSe2-carbon nanofibers benefitted from the extremely weak van der Waals interactions and large interlayer spacing of ReSe2, in association with the role of graphene-modified carbon nanofibers, in terms of the shortening of electron/ion transport paths and the improvement of structural support. This study may provide a new route for a broadened range of applications of other rhenium-based compounds.