Unique hollow NiO nanooctahedrons fabricated through the Kirkendall effect as anodes for enhanced lithium-ion storage

The Kirkendall effect, which is a simple and novel phenomenon, has been widely employed for the fabrication of hollow metal oxide nanostructures with designed pore structures. For the first time, we demonstrate the application of the Kirkendall effect to nickel selenides (NiSe₂) as precursors for the preparation of unique hollow NiO nanooctahedrons. The NiSe₂ precursors prepared via a facile hydrothermal method underwent post-treatment in air. During the controlled oxidation process, the outward diffusion of Ni cations and the Se component in NiSe₂ was quicker than the inward diffusion of O₂ gas, resulting in the formation of NiO nanooctahedrons with hollow voids. As lithium-ion battery anode materials, these nanooctahedrons exhibited stable cycling performance (a specific discharge capacity of 1234 mA h g⁻¹ after 150 cycles at 1 A g⁻¹) and high rate capability (specific discharge capacities of 895, 887, 853, 808, 761, and 713 mA h g⁻¹ at 0.5, 0.7, 1.0, 1.5, 2.0, and 3.0 A g⁻¹, respectively). The excellent electrochemical properties of the unique hollow NiO nanooctahedrons can be ascribed to the substantial void space, which increases the contact area between the electrolyte and active materials and accommodates the volume expansion of NiO during cycling.