Rational Conversion of V2CTx MXene into VS4-Carbon Composites as Superior Anode Materials for High-Rate and Durable Potassium/Sodium Storage

MXenes with unique physical and chemical properties have been extensively applied in various energy storage systems. Nevertheless, the limited capacity and instability of MXene hamper its practical applications in alkali-ion batteries. Herein, for the first time, V2CTx MXene is rationally converted into VS4-carbon composite, which is strategically engineered with a hollow morphological configuration and an integrated reduced graphene oxide (rGO) layer. Regarding potassium storage, the as-designed hollow VS4/C/rGO composite shows a capacity of 549 mA h/g at 0.1 A/g and durable cyclic behavior exceeding 2000 cycles at 1 A/g. What's more, this composite displays a remarkable capacity of 202 mA h/g at a high rate of 20 A/g, surpassing most V-based and MXene-based anodes. For sodium storage, it also manifests exceptional rate capability and long-term cycling life. As disclosed by kinetics analysis and ex-situ characterizations, the unique merits of the hollow structure, small VS4 particles, and protective rGO coating are desirable for the good structural stability and fast charge transportation, thus accounting for the excellent battery performance of the V2CTx-derived hollow VS4/C/rGO composite.