Boosting the Zn-ion energy storage capability of graphene sandwiched nanoporous VOx derived from MXene

Abstract

Aqueous rechargeable zinc-ion batteries (ZIBs) are emerging in grid energy storage due to zinc abundance and intrinsic safety. However, developing suitable cathode materials with satisfactory stability and rate capacity remains a great challenge. Herein, a structure of layered MXene derived nanoporous VO_x wrapped with graphene nanosheets (rGO–VO_x) is constructed as a cathode for ZIBs. The incorporation of two typical 2D materials imparts composites with shortened diffusion pathways and increased electrical conductivity. Thus, the rGO–VO_x cathode exhibits a remarkable rate capability of 196 mA h g⁻¹ at 8 A g⁻¹ and long-term stability with 90% retention after over 1200 cycles at 5 A g⁻¹ in an aqueous coin cell. The Zn storage mechanism is also systematically investigated. The layered V₂O₅ transforms into layered Zn_xV₂O₅·nH₂O with larger interspacing upon cycling. NaV₆O₁₅ and the in situ formed Zn_xV₂O₅·nH₂O co-contribute to the subsequent insertion and extraction process.