Facile preparation of Co@Co₃O₄@Nitrogen doped carbon composite from ionic liquid as anode material for high performance lithium-ion batteries

Co@Co₃O₄@Nitrogen doped carbon (Co@Co₃O₄@NDC) composite is synthesized by high temperature carbonization of ionic liquids followed by low temperature thermal oxidation. In the process of high temperature carbonization, cobalt ions are reduced to metallic cobalt, producing Co@Nitrogen doped carbon (Co@NDC). Co@Co₃O₄@NDC composite is obtained after low temperature oxidation, in which a part of the metallic cobalt is oxidized to Co₃O₄. The structural characterizations indicate that the composite is composed of three crystalline phases (carbon, Co and Co₃O₄). The results of transmission electron microscopy study show that the carbon materials not only coat the Co@Co₃O₄ nanoparticles, but also form carbon network that connects the Co@Co₃O₄ nanoparticles. This conductive carbon network is beneficial to improve the electrochemical performance of the composite. The electrochemical test results show that the Co@Co₃O₄@NDC composite exhibits excellent electrochemical performance, delivering the discharge capacities of 790 and 304 mAh˙g⁻¹ after 1500 cycles at 5 C and 10 C. This excellent electrochemical performance is due to synergistic effects of Co₃O₄, cobalt nanoparticles embedded in carbon which has high conductivity, and nitrogen functional groups.