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

Abstract

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 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).