VPO4@C/graphene microsphere as a potential anode material for lithium-ion batteries

Three-dimensional PO4-based polyanionic structures composed of interconnected MO6 octahedra and PO4 tetrahedra, such as VPO4, are potential anode materials for Li-ion batteries given their excellent cyclic stability. However, the application of VPO4 as an anode material has been limited by its low conductivity and drastic volume expansion. Herein, VPO4@C/graphene microspheres are designed and synthesised. P covalently bridges VPO4 and graphene through P-C bonding and acts as a buffer layer to maintain structural stability during continuous charge-discharge cycling. Graphene and C improve the electrical conductivity of VPO4 and reduce volume expansion during charge-discharge cycling. When applied as a Li-ion battery anode, the VPO4@C/graphene microspheres can achieve a specific capacity of 432.8 mA h g(-1) after 100 cycles under the current densities of 100 mA g(-1). This performance is superior to that of commercial graphite. The VPO4@C/graphene microspheres provide a good rate performance with a capacity of 562.1, 494, 424.2 and 356 mAh g(-1) under 200, 400, 1000 and 2, 000 mA g(-1), respectively. Furthermore, the VPO4@C/graphene microspheres achieve high tap density of > 1.2 g cm(-3), which is higher than that of other nanomaterials ( < 1.0 g cm(-3)) and is compatible with commercially available anode materials. Thus, VPO4@C/graphene microspheres are a promising anode material for Li-ion batteries.