Mesoporous TiO₂ microparticles formed by the oriented attachment of nanocrystals: A super-durable anode material for sodium-ion batteries

Spindle-shaped anatase TiO₂ secondary particles were successfully fabricated via the oriented attachment of primary nanocrystals. By adjusting the concentration of tetrabutyl titanate, the size of the TiO₂ nanocrystals and particles could be controlled, resulting in pore evolution. Pores for the random aggregation of secondary particles gradually transformed to nanopores originating from the oriented attachment of the primary nanocrystals, resulting in an excellent micro/nanostructure that increased the performance of a sodium-ion battery. The mesoporous TiO₂ microparticle anode, with its unique combination of nanocrystals and uniform nanopores, displays super durability (95 mAh/g after 11, 000 cycles at 1 C), high initial efficiency (61.4%), and excellent rate performance (265 and 77 mAh/g at 0.1 and 20 C, respectively). In particular, at slow discharge (0.1 C) and fast charge (5, 50, and 100 C) rates, the anatase TiO₂ shows remarkable initial charge capacities of 200, 119, and 56 mAh/g, corresponding to 172, 127, and 56 mAh/g, after 150 cycles, respectively, thus meeting the requirements for fast energy storage. This excellent performance can be attributed to the stability of the material and its high ionic conductivity, resulting from the stable architecture with a mesoporous microstructure and without the random aggregation of secondary particles. A fundamental understanding of the pore structure and controllable pore construction has been proven to be effective in increasing the rate capability and durability of nanostructured electrode materials.