In situ preparation of cobalt doped ZnO@C/CNT composites by the pyrolysis of a cobalt doped MOF for high performance lithium ion batteries

Abstract

Co doped ZnO embedded in carbon/carbon nanotube composites (CZO@C/CNT) was prepared in situ during the calcination of Co-MOF-105 at 600 °C. A lower crystallinity demonstrated weaker binding force in Co-MOF-105, which made it possible for Co ions to break away from the crystal and reduce to metal Co during the pyrolysis process. The formation of CNTs was catalyzed by Co metal and the carbon source was terephthalic acid, which acted as the organic linker in the MOF. Moreover, the sp² hybridization of the carbon atoms in terephthalic acid decreased the energy barrier during the growth of CNTs. From TEM and SEM observation, the CNTs were interspersed in the material and connected the CZO@C nanoparticles together, which made the electron transfer easier. The other advantages of Co doping were enhancing the conductivity of ZnO and increasing the graphitization degree of the carbon on the surface of the CZO@C nanoparticles. When the CZO@C/CNT composite was used as an anode material for lithium ion batteries, an enhanced electrochemical performance of 758 mA h g⁻¹ after 100 cycles at a current density of 100 mA g⁻¹ was obtained.