Mo-doped TiO₂ Nanomaterials with Rich Cation Vacancies as High-Rate Cathodes for Mg-Li Hybrid-Ion Batteries

Transition metal oxides (TMOs) hold promise as cathode materials for Mg-Li hybrid-ion batteries (MLIBs) due to their exceptional chemical stability, cost-effectiveness, non-toxicity, and minimal volume changes upon cycling. However, their low intrinsic conductivity and limited active sites seriously impede their practical application. Herein, a series of Mo-doped TiO₂ (MTO) nanomaterials with Ti vacancies were successfully developed via a one-step solvothermal followed by a calcination process as the advanced cathode materials for MLIBs. Doping Mo in TiO₂ contributes to broadening the ion diffusion channels and reducing the transfer resistance of Li⁺, leading to enhancement of the kinetic performance. Additionally, the formation of Ti vacancies in TiO₂ can increase its conductivity and provide extra ion storage sites. Based on the above advantages, MTO-3 (the molar ratio of Mo and Ti is 3%) exhibits higher specific capacity (324.3 mAh g^-1 at 100 mA g^-1) and superior rate specific capacity (117.5 mAh g^-1 at 2000 mA g^-1). The analysis of the pseudocapacitance-like contribution in conjunction with the galvanostatic intermittent titration technique further demonstrates the enhanced Li⁺ storage kinetics during the electrochemical reaction process. Furthermore, based on theoretical calculation, it can uncover the fact that the electron structure reconstruction induced by Mo doping and Ti vacancies can greatly improve the Li⁺ storage performance of MTO. Our doping and vacancy engineering strategies provide valuable insights for developing transition metal oxide cathode materials.