Facile synthesis of a novel P-doped carbon coated nickel phosphides nanorods as sodium storage anode materials

Nickel-based phosphides as anode materials of sodium ion batteries have high capacity, but poor cycle stability and low electrical conductivity. Rational structural design for nickel-based phosphides with carbon provides a new way to address the above shortcomings. This paper presents a simple method to synthesize a novel carbon coated Ni_xP (x = 2.4–3.0, denoted as Ni_xP@PC) nanorods using phosphoric acid resin as phosphorus and carbon sources. The Ni_xP nanocrystals are in-situ generated in the P-doped carbon without further phosphatization. The carbon layer can confine the volume changes during charging/discharging process. Additionally, the enriched P doping in the carbon layer greatly increases the electrical conductivity of the Ni_xP-based composite and provides more active sites for sodium storage. The as-obtained Ni_xP@PC nanorods reveal excellent reversible sodium storage performance (271.6 mA·h/g based on the mass of Ni_xP@PC at 0.1 A/g after 300 cycles) and outstanding cycling stability (0.005% capacity decay per cycle after 5 000 cycles at 2 A/g). Meanwhile, the formation mechanism of Ni_xP@PC is evidenced by monitoring the evolution of morphology and structure during the preparing process. This paper may provide a feasible way for constructing high-performance transitional metal compounds for sodium-ion batteries.