One-step surface nitridation of CoO for high-energy-density lithium-ion batteries

The surface of micrometer-sized CoO particles is finely tuned by a nitride produced through one-step process with various heat treatments with solid-state urea, which has been frequently used as a surfactant for the nanosynthesis of CoO in aqueous media. After conducting simple surface nitridation processes without a solvent using an autogenic reactor, it is found that the CoO surface is clearly modified by a cobalt-rich nitride (Co_5.47N) by X-ray diffraction analyses. As the heat treatment temperature increases, the content of the cobalt nitride also grows. A temperature above 500°C for the surface modification causes an initial specific capacity loss because of the growth of the inert cobalt nitride; however, the surface-modified samples exhibit a more prolonged cycle life than the pristine CoO due to decreased kinetic barrier and enhanced surface stability. Additionally, the surface nitridation leads to a high rate capability, which can solve poor power density for conversion-type anode materials. It is found that the surface nitridation allows a high electrical conductivity and reduces the surface charge transfer resistance.