Metal-organic framework tin doped nickel phosphide/carbon composites for high performance sodium ion batteries

Metal phosphide has aroused great interest in energy storage materials because of its unique crystal structure and high theoretical specific capacity. However, its practical application is seriously restricted by the problems such as poor cycle stability and rapid capacity attenuation. In this paper, tin doped nickel phosphide/carbon composites (NiSnP/C) are prepared by calcination of metal-organic framework precursors with phosphorus source at 350 degrees C. Crystalline Ni2P phase is generated, and electron interaction exists between the Sn and Ni sites in NiSnP/ C. When used as the anode material for sodium ion storage, the reversible specific capacity of NiSnP/C-2 under 1 A g-1 is 285 mAh g-1. The high specific capacity of sodium ion battery with NiSnP/C-2 is owing to its porous structure, high specific surface area and abundant electrochemical active sites, which reduces the charge transfer resistance and accelerates ion diffusion. The transition from crystalline Ni2P phase to crystalline Ni and Na3P phase is observed during Na+ storage. The carbon skeleton also maintains the structural integrity during the charge-discharge process, and improves the rate performance and cycle stability.