Monodispersed copper phosphide nanocrystals in situ grown in a nitrogen-doped reduced graphene oxide matrix and their superior performance as the anode for lithium-ion batteries

Abstract

A nanocomposite anode material consisting fully of monodispersed copper phosphide (Cu₃P) nanocrystals in situ grown in three-dimensional (3D) nitrogen-doped reduced graphene oxide (N-RGO) matrices has been manufactured via a “heating-up” synthesis, which involves nucleation, nitrogen-doping, crystallization and ligand exchange. The “heating-up” synthesis approach, using stable and relatively low-toxicity precursors and 3D porous N-RGO as the matrix, is straightforward, cost-effective and up-scalable. The Cu₃P nanocrystals with an average size of 25–40 nm are wrapped, without aggregation, within the interior and on the surface of the curling N-RGO matrices. The resultant Cu₃P/N-RGO nanocomposites possess a 3D porous nanostructure with a BET surface area as high as 405.71 m² g⁻¹. In this nanostructure, the N-RGO's properties of excellent conductivity and an interconnected porous network enable the Cu₃P/N-RGO nanocomposites to provide pathways for rapid electron transfer and lithium ion transport, and the Cu₃P nanocrystals with their small size and monodispersed phase can accommodate the volume change during charging/discharging processes. Hence, Cu₃P/N-RGO nanocomposites reveal an excellent lithium-storage performance in terms of a long-life cycling stability (705.5 mA h g⁻¹ at 10C, 88.8% capacity retention over 1000 cycles at 25 °C), a high heat-resistance capability (674.6 mA h g⁻¹ under 10C, 88.9% capacity retention over 1000 cycles at 55 °C), and a high rate capability (604.6 mA h g⁻¹ at 50C).