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 500th 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.