Growth of nickel phosphide films as anodes for lithium-ion batteries: Based on a novel method for synthesis of nickel films using ionic liquids

Nickel phosphide (Ni-P) films were fabricated through four types of Ni films electrodeposited using a choline chloride-based ionic liquid (choline chloride-ethylene glycol) at room temperature. Sheet-like morphology of Ni films can be obtained when 0.5 M of Ni2+ is used; and sphere-like one is presented by 1.0 M of Ni2+. Consequently, the surface morphologies of these Ni-P films were affected by the initial Ni films. And different phases of Ni12P5 and Ni2P in the Ni-P films would be obtained after the phosphorization process. As anodes for Li-ion batteries, the electrochemical properties of these Ni-P films were investigated by cyclic voltammetry and galvanostatic charge-discharge tests. The surface morphology and thickness of thin films had a significant effect on their electrochemical performance. The Ni2P films delivered a large reversible discharge capacity around 398.5 mAh g−1 with the capacity retention of 91.4% after 50 cycles.