Ultrafine CoP Nanoparticles Anchored on Reduced Graphene Oxide Nanosheets as Anodes for Sodium Ion Batteries with Enhanced Electrochemical Performance

Cobalt phosphide/reduced graphene oxide (CoP/RGO) nanohybrid materials have been prepared by a simple chemical precipitation method and a low-temperature phosphorization process. Ultrafine CoP nanoparticles are loaded uniformly onto RGO nanosheets. The diameter of the CoP particle decreases to about 6-8 nm. Sodium ion battery anodes based on the CoP/RGO nanohybrids display significantly improved sodium ion storage performance. These electrode materials demonstrate a large capacity of about 490 mAhg(-1), at a current density of 100 mAg(-1), after 100 cycles. They also deliver good rate performance, demonstrating about 381 mAhg(-1) specific capacity when the current density reaches 2.0 Ag-1. The ultrafine nanoparticles, interconnected porous structure, large surface area, and good electrical conductivity are the major reasons for the excellent electrochemical performance. The synthesis method presented here is general, easy, and efficient, and can be developed for other metal phosphide-graphene composites.