Optimized Ti Doping in CoMoO4 Nanorods as Anodes with Enhanced Electrochemical Performance for Lithium-Ion Batteries

In this work, we have optimized titanium doping (Ti4+) into the CoMoO4 nanorod anode material to improve its intrinsic behavior, such as low electrical conductivity, poor cycling stability, and large volume expansion/contraction during (de) lithiation for lithium-ion battery applications. Among all the doping concentrations of 5, 20, and 40 wt %, the CoMoO4 nanorod anode with 20 wt % doping exhibits high reversible capacity, better cycling stability, and superior rate capability. It is believed that Ti4+ doping generates two extra electrons corresponding to cationic (Mo6+) vacancy and leads to anionic (O2-) vacancy in the CoMoO4 crystal lattice. In addition, though XPS results demonstrate the partial reduction of Mo6+ to Mo5+ species after doping, it is believed that one extra electron in the d-orbital may also help to alleviate the electronic conductivity and enhance the diffusion rate of Li+ ions. As per the structural refinement results, it is found that the 5 wt % Ti-doped sample forms a solid solution, whereas 20 and 40 wt % Ti-doped samples show excess Ti, which is present in the form of TiO2 as an additional phase, resulting in the generation of the CoMoO4@TiO2 nanocomposite. The superior electrochemical performances of the 20 wt % Ti-doped CoMoO4 anode can be accounted for the high mobility of Li+ ions due to the optimum doping concentration, proper defects, and synergistic effect of TiO2 nanoparticles, which are stuck to the surface of the CoMoO4 nanorods, resulting in improved electronic conductivity and excellent cycling stability of the host material.