Yolk–shell-structured microspheres composed of N-doped-carbon-coated NiMoO4 hollow nanospheres as superior performance anode materials for lithium-ion batteries

Abstract

Novel yolk–shell-structured microspheres consisting of N-doped-carbon-coated metal–oxide hollow nanospheres are designed as efficient anode materials for lithium-ion batteries and synthesized via a spray pyrolysis process. A NiMoO₄ yolk–shell architecture formed via spray pyrolysis is transformed into equally structured NiSe₂–MoSe₂ composite microspheres. Because of the complementary effect between the Ni and Mo components that prevents severe crystal growth during selenization, NiSe₂–MoSe₂ nanocrystals are uniformly distributed over the yolk–shell structure. Then, the yolk–shell-structured NiSe₂–MoSe₂ microspheres are oxidized, which yields microspheres composed of NiMoO₄ hollow nanospheres by nanoscale Kirkendall diffusion. Uniform coating with polydopamine and a subsequent carbonization process produce uniquely structured microspheres consisting of N-doped-carbon-coated NiMoO₄ hollow nanospheres. The discharge capacity of the yolk–shell-structured NiMoO₄–C composite microspheres for the 500^th cycle at a current density of 3.0 A g⁻¹ is 862 mA h g⁻¹. In addition, the NiMoO₄–C composite microspheres show a high reversible capacity of 757 mA h g⁻¹ even at an extremely high current density of 10 A g⁻¹. The synergetic effect between the hollow nanospheres comprising the yolk–shell structure and the N-doped carbon coating layer results in the excellent lithium-ion storage performance of the NiMoO₄–C composite microspheres.