Ni2P Nanoflake Array/Three Dimensional Graphene Architecture as Integrated Free-Standing Anode for Boosting the Sodiation Capability and Stability

Research on transition-metal phosphides for sodium-ion battery anodes has received increasing attention owing to their high theoretically specific capacity. Unfortunately, the high volume expansion limits their further applications. Herein, a nanoflakes array Ni2P/three-dimensional graphene in-situ grown on Ni foam (Ni2P/3DG) is designed as free-standing anode material. The structure characterization indicated that the Ni2P nanoflakes were combined with 3DG uniformly. The ultrasmall particle size and uniform distribution of the Ni2P/3DG particles plays a major role for the excellent reversible capacity (402.6 mAh g(-1) at 200 mA g(-1) over 100 cycles), remarkable rate capability (273.3 mAh g(-1) at 1000 mA g(-1), the capacity return to 603.6 mAh g(-1) at 50 mA g(-1)) and high initial coulombic efficiency (about 88.28 %). Moreover, the Ni2P/3DG showed low volume expansion (166.9 %) and no obvious sharp dendrite growth after 200 cycles. The enhanced electrochemical performance is ascribed to the synergistic effect between 3DG and Ni2P. The nanoflake array can buffer the volume expansion and shorten the Na+ diffusion path. 3DG provides a conductive channel for charge transfer. The storage mechanism is related to a diffusion-controlled process and capacitive behavior. Additionally, the Ni2P/3DG also reduces dendritic problems, improving safety and stability and has a great potential for Na-storage.