NH 4 + Pre-Intercalation and Mo Doping VS 2 to Regulate Nanostructure and Electronic Properties for High Efficiency Sodium Storage.

Sodium-ion hybrid capacitors (SIHCs) have attracted much attention due to integrating the high energy density of battery and high out power of supercapacitors. However, rapid Na + diffusion kinetics in cathode is counterbalanced with sluggish anode, hindering the further advancement and commercialization of SIHCs. Here, aiming at conversion-type metal sulfide anode, taking typical VS 2 as an example, a comprehensive regulation of nanostructure and electronic properties through NH 4 + pre-intercalation and Mo-doping VS 2 (Mo-NVS 2 ) is reported. It is demonstrated that NH 4 + pre-intercalation can enlarge the interplanar spacing and Mo-doping can induce interlayer defects and sulfur vacancies that are favorable to construct new ion transport channels, thus resulting in significantly enhanced Na + diffusion kinetics and pseudocapacitance. Density functional theory calculations further reveal that the introduction of NH 4 + and Mo-doping enhances the electronic conductivity, lowers the diffusion energy barrier of Na + , and produces stronger d-p hybridization to promote conversion kinetics of Na + intercalation intermediates. Consequently, Mo-NVS 2 delivers a record-high reversible capacity of 453 mAh g -1 at 3 A g -1 and an ultra-stable cycle life of over 20 000 cycles. The assembled SIHCs achieve impressive energy density/power density of 98 Wh kg -1 /11.84 kW kg -1 , ultralong cycling life of over 15000 cycles, and very low self-discharge rate (0.84 mV h -1 ).