Carbon Coated SnS/SnO 2 Heterostructures Wrapping on CNFs as an Improved-Performance Anode for Li-Ion Batteries: Lithiation-Induced Structural Optimization upon Cycling.

Carbon coated SnS/SnO2 heterostructures wrapping on carbon nanofibers (C@SnS/SnO2 @CNFs) was demonstrated to have excellent performance as an anode material for Li-ion batteries. C@SnS/SnO2 @CNFs electrode delivers high reversible capacity of 826.8 mA h g-1 (500th cycle) at the current density of 1.0 A g-1 . However, an interesting phenomenon of increasing capacity on cycling can be observed. According to the analysis of the evolution of structure and electrochemical property, C@SnS/SnO2 @CNFs is demonstrated to experience the progress of conversion from nanowalls containing polycrystals into amorphous nanosheets with high porosity and larger surface upon cycling. The above lithiation-induced structural optimization provides larger effective surface areas and encourages the conversion reactions, which can promote charge transfer and also enhance the reversibility of the conversion reactions of SnS and SnO2 inducing the increasing reversible capacity. The study explains the progress of increasing capacity of C@SnS/SnO2 @CNFs and likewise provides a perspective on optimization of the electrochemical performance of electrodes.