Flower-like Spherical α-Ni(OH)2 Derived NiP2 as Superior Anode Material of Sodium-Ion Batteries.

Abstract

Transition metal phosphides (TMPs) are promising anode candidates for sodium-ion batteries, due to their high theoretical specific capacity and working potential. However, the low conductivity and excessive volume variation of TMPs during insertion/extraction of sodium ions result in a poor rate performance and long-term cycling stability, largely limiting their practical application. In this paper, NiP2 nanoparticles encapsulated in three-dimensional graphene (NiP2 @rGO) were obtained from the flower-like spherical α-Ni(OH)2 by phosphating and carbon encapsulation processes. When used as a sodium-ion batteries anode material, the NiP2 @rGO composite shows an excellent cycling performance (117 mA h g-1 at 10 A g-1 after 8000 cycles). The outstanding electrochemical performance of NiP2 @rGO is ascribed to the synergistic effect of the rGO and NiP2 . The rGO wrapped on the NiP2 nanoparticles build a conductive way, improving ionic and electronic conductivity. The effective combination of NiP2 nanoparticles with graphene greatly reduces the aggregation and pulverization of NiP2 nanoparticles during the discharge/charge process. This study may shed light on the construction of high-performance anode materials for sodium-ion batteries and to other electrode materials.