Fe-doping accelerated magnesium storage kinetics in rutile TiO2 cathode materials

Rutile titanium dioxide (TiO2) 2 ) is theoretically favored as the efficient cathode materials for magnesium secondary batteries, yet rarely reported due to sluggish kinetics, low capacity, and inferior reversibility. Herein, a defect engineering strategy is developed via cationic Fe-doping to enhance the electrochemical magnesium storage kinetics of the rutile TiO2 2 cathode materials and achieve the surface Mg2+ 2+ adsorption/diffusion mechanism. Abundant oxygen vacancies can be generated by Fe cations in rutile TiO2 2 via a molten salt flux method. The optimized rutile TiO2 2 cathode materials show large specific capacity of 204.8 mAh/g at current density of 100 mA g-1, higher than that of the TiO2-based 2-based counterparts reported previously. Additionally, the Mg2+ 2+ diffusion coefficient of Fe-doped rutile TiO2 2 cathode materials are significantly improved to enable rapid magnesium storage. Fe cations can activate the cathode surface and weaken the Coulombic interactions between Mg2+ 2+ and anions in the host material. Oxygen vacancies can provide active adsorption sites for Mg2+ 2+ and MgCl+ + to avoid slow solid-state diffusion and thus accelerate magnesium storage kinetics. Ex-situ XRD and XPS indicate that Fe-doped rutile TiO2 2 cathode materials undergo the energy storage mechanism of Mg2+ 2+ adsorption/diffusion without phase transition or significant lattice expansion.