Improved Electrochemical Performance of Self-Assembled Hierarchical Nanostructured Nickel Phosphide as a Negative Electrode for Lithium Ion Batteries

Hierarchical, nanostructured nickel phosphide (h-Ni 2 P) spheres are synthesized by a one-pot reaction from an organic-phase mixture of nickel acetylacetonate, trioctylphosphine, tri- n -octylamine, and oleylamine (OAm). OAm is used as a surfactant to modify the surface morphology of Ni 2 P spheres. The h-Ni 2 P spheres are composed of ordered nanoparticles with 5–10 nm sizes and filled by amorphous carbon. The hierarchical structure can greatly increase the contact area between Ni 2 P and electrolyte, which provides more sites for Li + accommodation, shortens the diffusion length of Li +, and enhances the reactivity of the electrode reaction. Also, the amorphous carbon and the hierarchical Ni 2 P nanostructures can buffer volume expansion and thus increase the electrode stability during cycling. In the context of storage behavior, the h-Ni 2 P electrode exhibits high capacity as well as Coulombic efficiency. After 50 cycles, the reversible capacity of h-Ni 2 P spheres is 365.3 mA h g –1 at 0.5 C and 257.8 mA h g –1 at 1 C, much higher than that of Ni 2 P spheres (97.2 mA h g –1 at 0.5 C). At a high rate of 3 C, the specific capacity of h-Ni 2 P is still as high as 167.1 mA h g –1 .