Three-dimensional hierarchical Ni5P4 nanospheres encapsulated in graphene as high-performance anode materials of sodium ion batteries

Transition metal phosphides have received extensive attention as anode materials of sodium ion batteries due to their high theoretical specific capacity and low redox potentials. However, the large volume change during the insertion/extraction of sodium ions often leads to a poor electrochemical performance and thus limits their practical application. Herein, we rationally designed three-dimensional hierarchical Ni5P4 nanospheres wrapped by rGO nanostructures (Ni5P4@rGO) through a sequential hydrothermal synthesis and phosphidation of highly folded spherical α-Ni(OH)2. The graphene nanosheets can effectively prevent the collapse of spherical α-Ni(OH)2 and aggregation of Ni5P4 active materials during phosphidation. Besides, the strong coupling between the nickel phosphide and graphene layers leads to excellent electrochemical performance of Ni5P4@rGO composite as anode materials of SIBs, delivering a specific capacity of 304 mA h g–1 at 0.2 A g–1 after 200 cycles. The strategy developed in this paper may shed light on the morphology-controlled synthesis of transition metal phosphides with high performance for energy storage devices.