Yolk-shell-structured microspheres composed of N-doped-carbon-coated NiMoO ₄ hollow nanospheres as superior performance anode materials for lithium-ion batteries

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 NiMoO ₄ yolk-shell architecture formed via spray pyrolysis is transformed into equally structured NiSe ₂ -MoSe ₂ composite microspheres. Because of the complementary effect between the Ni and Mo components that prevents severe crystal growth during selenization, NiSe ₂ -MoSe ₂ nanocrystals are uniformly distributed over the yolk-shell structure. Then, the yolk-shell-structured NiSe ₂ -MoSe ₂ microspheres are oxidized, which yields microspheres composed of NiMoO ₄ 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 NiMoO ₄ hollow nanospheres. The discharge capacity of the yolk-shell-structured NiMoO ₄ -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 NiMoO ₄ -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 NiMoO ₄ -C composite microspheres.