Nanoporous Anatase TiO₂ Mesocrystals: Additive-Free Synthesis, Remarkable Crystalline-Phase Stability, and Improved Lithium Insertion Behavior

Unique spindle-shaped nanoporous anatase TiO₂ mesocrystals with a single-crystal-like structure and tunable sizes were successfully fabricated on a large scale through mesoscale assembly in the tetrabutyl titanate−acetic acid system without any additives under solvothermal conditions. A complex mesoscale assembly process involving slow release of soluble species from metastable solid precursors for the continuous formation of nascent anatase nanocrystals, oriented aggregation of tiny anatase nanocrystals, and entrapment of in situ produced butyl acetate as a porogen was put forward for the formation of the anatase mesocrystals. It was revealed that the acetic acid molecules played multiple key roles during the nonhydrolytic processing of the [001]-oriented, single-crystal-like anatase mesocrystals. The obtained nanoporous anatase mesocrystals exhibited remarkable crystalline-phase stability (i.e., the pure phase of anatase can be retained after being annealed at 900 °C) and improved performance as anode materials for lithium ion batteries, which could be largely attributed to the intrinsic single-crystal-like nature as well as high porosity of the nanoporous mesocrystals.