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

Abstract

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.