Hierarchically dual‐mesoporous TiO2 microspheres have been synthesized by a solvothermal process in the presence of 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMImBF4) and diethylenetriamine (DETA) as co‐templates. Secondary mesostructured defects in the hierarchical TiO2 microspheres produce oxygen vacancies, which not only significantly enhance photocatalytic activity in the degradation of methylene blue (1.7 times that with P25) and acetone (2.9 times that with P25), but are also beneficial for lithium storage. Moreover, we propose a mechanism to rationalize the role of this dual mesoporosity of the TiO2 microspheres in enhancing molecular diffusion, ion transportation, and electronic transitions. Beneficial dual mesoporosity: Hierarchically dual‐mesoporous TiO2 has been synthesized by a co‐templating method. Its mesostructured defects caused by an ionic liquid lead to a high level of oxygen vacancies (see graphic), which significantly enhance its photoelectrochemical performance.