UV Irradiation Treatment for Enhanced Sodium Storage Performance Based on Wide-Interlayer-Spacing Hollow C@MoS2@CN Nanospheres.

The photochemistry and sodium storage process have been generally considered as two separated approaches without strong connection. Here, we dedicate to improve the electrochemical performance of MoS2 based composite via ultraviolet (UV) irradiation. C@MoS2@CN nanospheres consist of double protective structures, including inner hollow carbon spheres with thin wall (C) and outer N-doping carbon nanosheets (CN) derived from polydopamine. The special nanostructure possesses the virtues such as wide-interlayer spacing, flexible feature with great structure integrity and rich active sites, which endow the fast electron transfer and shorten the ion diffusion pathways. Under the excitation of UV-light, intense electrons and holes are accumulated within MoS2 based composite. The excited electrons can promote the pre-insertion of Na+. And more importantly, they can promote the decomposing of electrolyte on the surface of electrode material to get a stable solid electrolyte interphase (SEI) in advance. After UV-light irradiation treatment in electrolyte, the initial Coulombic efficiency of C@MoS2@CN electrodes increased from 48.2% to 79.6%. And benefiting from the fine nanostructure, the C@MoS2@CN electrode with UV irradiation treatment delivered a great rate performance of 116 mAh g-1 in 20 s and super cycling stability that 87.6% capacity was retained after 500 cycles at 500 mA g-1. When employed as anode for sodium-ion hybrid capacitors (SIHCs), it delivered a maximum power density of 6.84 kW kg-1 (with 114.07 Wh kg-1 energy density) and a maximum energy density of 244.15 Wh kg-1 (with 152.59 W kg-1 power density). This work sheds new viewpoints into the applications of photochemistry in the development of energy storage devices.