Synergistic mechanism of oxygen-deficient and Co-doped homojunction anatase/rutile TiO2 anodes for LiBs conductivity/Li+ transport enhancement

Abstract

The electronic conductivity of TiO₂-based anodes was improved fundamentally by co-integrating the oxygen vacancy of TiO₂ into the homogeneous structure with cobalt doping. The results showed that the introduction of oxygen vacancies and Co expanded the lattice space, reduced the charge transfer resistance, and effectively increased the electronic conductivity and ionic transport. Density functional theory (DFT) calculations illustrated that Co doping resulted in a continuous distribution of electronic states at the Fermi energy level, which permitted the sample Co-A/R-TiO₂ to have enhanced metallic properties. The presence of abundant grain boundaries, interfacial and vacancy defects in the hollow microsphere anode all served as additional active sites for Li⁺ storage. The Co-A/R-TiO₂ anode had a high reversible specific capacity of 443 mAh/g after 500 cycles at 0.5 C current density. The high capacity was mainly attributed to the synergistic effect of the perfect defect structure of the hollow spheres and the heterogeneous interfaces. This strategy of using defects combined with homo/heterojunction engineering could be extended to the design of other conventional semiconductor materials as energy storage electrodes.