Cobalt nickel nitride coated by a thin carbon layer anchoring on nitrogen-doped carbon nanotube anodes for high-performance lithium-ion batteries

Cobalt nickel nitrides coated by a thin carbon layer anchoring on nitrogen-doped carbon nanotubes, named NiCo2N@C–NCNT nanocomposites, were obtained by a facile fabrication method. The work reveals that the NiCo2N structures possess extensive Li+ channels and high electrical conductivity for the rapid electron/ion transfer in lithium-ion batteries (LIBs). These materials were applied as anodes for the first time, and a nanobattery was constructed and examined using a transmission electron microscope (TEM) to directly verify the in situ structural evolution during lithiation/delithiation processes. The results show a small dimensional expansion of the NiCo2N@C–NCNT nanocomposites during the lithiation process; this is due to the disciform expansion of the lithiated NiCo2N nanoparticles which cover the surface of the NCNTs. It was found that some of the lithiated NiCo2N nanoparticles moved along the surface of the NCNTs and entered the NCNTs – thus acting to ‘protect’ themselves. Moreover, electrodes composed of interconnected NCNTs alleviate the volumetric expansion of NiCo2N@C–NCNT nanocomposites. The NiCo2N@C–NCNT nanocomposite electrode exhibits excellent lithium storage properties in electrochemical tests in coin cell configurations. This material synthesis route and ‘self-protection’ mechanism provide the basis of a design strategy for developing effective electrode materials in LIBs and a broader sphere of metal-ion batteries.