Nanostructured CuP2/C composites as highperformance anode materials for sodium ion batteries

Research on sodium ion batteries has recently been revived. Attention is now placed on the development of high-capacity and stable electrode materials at low costs. Among them, compounds operating on the conversion mechanism represent a promising class of anode materials. Unfortunately, they are generally plagued by poor electrical conductivity and large volume changes during repeated cycling. In this study, we exploit a new type of composite material made of copper phosphide and Super P carbon black (CuP2/C) as a potential anode candidate. The final products consisted of crystalline CuP2 cores coated with carbon black nanoparticles on the surface. Electrochemical measurements and multiple ex situ studies demonstrate that CuP2/C composites are capable of fast and reversible sodiation and desodiation based on the conversion mechanism. They deliver a large capacity in excess of 500 mA h g(-1), high rate capability and decent short-term cycling stability. Our study suggests that these transition metal phosphides with a suitable carbon coating may hold great opportunities as anode materials for sodium ion batteries for effective and economical energy storage.