Nanosized Anatase TiO₂ with Exposed (001) Facet for High-Capacity Mg²⁺ Ion Storage in Magnesium Ion Batteries

Micro-sized anatase TiO₂ displays inferior capacity as cathode material for magnesium ion batteries because of the higher diffusion energy barrier of Mg²⁺ in anatase TiO₂ lattice. Herein, we report that nanosized anatase TiO₂ exposed (001) facet doubles the capacity compared to the micro-sized sample ascribed to the interfacial Mg²⁺ ion storage. First-principles calculations reveal that the diffusion energy barrier of Mg²⁺ on the (001) facet is significantly lower than those in the bulk phase and on (100) facet, and the adsorption energy of Mg²⁺ on the (001) facet is also considerably lower than that on (100) facet, which guarantees superior interfacial Mg²⁺ storage of (001) facet. Moreover, anatase TiO₂ exposed (001) facet displays a significantly higher capacity of 312.9 mAh g^-1 in Mg-Li dual-salt electrolyte compared to 234.3 mAh g^-1 in Li salt electrolyte. The adsorption energies of Mg²⁺ on (001) facet are much lower than the adsorption energies of Li⁺ on (001) facet, implying that the Mg²⁺ ion interfacial storage is more favorable. These results highlight that controlling the crystal facet of the nanocrystals effectively enhances the interfacial storage of multivalent ions. This work offers valuable guidance for the rational design of high-capacity storage systems.