K2VOP2O7 as a novel high-voltage cathode material for potassium ion batteries

V-based polyanionic electrode materials are attractive in rechargeable batteries for their abundant redox centers, high working voltage and good structural stability. Here we report for the first time the synthesis and application of a novel V-based polyanionic compound K2VOP2O7 as a potential potassium storage material. It is prepared at a relatively low temperature of 550 °C using a conventional solid-state route, followed by sanding or ball milling to reduce the particle size. The material belongs to a tetragonal structure with an open framework, which provides pathways for K+ diffusion. The sanded and ball-milled samples can deliver a specific discharge capacity of 83 and 89 mAh g−1, respectively, both of which are close to the theoretical value of 84 mAh g−1, involving the one-electron-transfer redox of V5+/V4+. The sanded sample runs at a median discharge potential of 3.6 V (vs. K+/K). Combining the merits of facile synthesis and good electrochemical properties, K2VOP2O7 is recognized by this study as a new member of the pyrophosphate cathode family for potassium ion batteries. •We first report a novel V-based polyanionic compound K2VOP2O7 as a K+ storage host.•With an open framework, it provides pathways for K+ diffusion.•As a KIB cathode, it displays a high median discharge voltage of 3.6 V.•Small volume variation of 1.1% during potassiation/depotassiation.•Both crystalline and amorphous samples exhibit good potassium storage performance.