Synthesis and Electrochemical Properties of NixCo3−xO4 with Porous Hierarchical Structures for Na-Ion Batteries

Highly crystallized cubic NixCo3−xO4 with porous hierarchical structures was synthesized through a simple coprecipitation method followed by calcination at temperatures above 400°C in air. The performances of the samples as anode materials for Na-ion batteries were evaluated. At 100 mA g−1 in the 50th cycle, the nanorod-like Co3O4 sample that was calcined at 400°C delivered a discharge capacity of 169.4 mA h g−1, which corresponded to 27.7% of the second discharge capacity. By contrast, at 100 mA g−1 in the 50th cycle, the flower-like Ni0.3Co2.7O4 sample delivered a discharge capacity of 274.6 mA h g−1, which corresponded to 42.9% of the second discharge capacity. The improved performance shown by this anode material was attributed to the formation of additional mesopores and the stabilization of cubic Ni0.3Co2.7O4 after doping with Ni2+ ions. The above results showed that the electrochemical properties of metal oxide electrode materials can be effectively improved by controlling compositions and nanostructures.