NH4+ Pre‐Intercalation and Mo Doping VS2 to Regulate Nanostructure and Electronic Properties for High Efficiency Sodium Storage

Abstract

AbstractSodium‐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 VS2 as an example, a comprehensive regulation of nanostructure and electronic properties through NH4+ pre‐intercalation and Mo‐doping VS2 (Mo‐NVS2) is reported. It is demonstrated that NH4+ 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 NH4+ 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‐NVS2 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).