Structure and Defect Engineering of VSSe Quantum Dots Confined in a Nitrogen-Doped Carbon Framework for High-Performance Sodium-Ion Storage.

Constructing quantum dot-scale metal sulfides with defects and strongly coupled with carbon is significant for advanced sodium-ion batteries (SIBs). Herein, Se substituted VS quantum dots with anionic defects confined in nitrogen-doped carbon matrix (VSSe/NC) are fabricated. Introducing element Se into VS crystal expands the interlayer distance of VS, and triggers anionic defects, which can facilitate Na diffusions and act as active sites for Na storage. Meanwhile, the quantum dots tightly encapsulated by conductive carbon framework improve the stability and conductivity of the electrode. Theoretical calculations also unveil that the presence of Se enhances the conductivity and Na adsorption ability of VSSe. These properties contribute to the VSSe/NC with high specific capacity of 447 mAh g at 0.2 A g, and prominent rate and cyclic performance with 504 mAh g after 1000 cycles at 10 A g. The sodium-ion hybrid capacitors (SIHCs) with VSSe/NC anode and activated carbon cathode can achieve high energy/power density (maximum 144 Wh kg/5960 W kg), capacity retention ratio of 71% after 4000 cycles at 2 A g. This work not only synthesizes VSSe/NC, but also provides a promising opportunity for designing quantum dots and utilizing defects to improve the electrochemical properties.