High-surface-area mesoporous TiO₂ microspheres via one-step nanoparticle self-assembly for enhanced lithium-ion storage

Mesoporous TiO₂ microspheres assembled from TiO₂ nanoparticles with specific surface areas as high as 150 m² g^-1 were synthesized via a facile one-step solvothermal reaction of titanium isopropoxide and anhydrous acetone. Aldol condensation of acetone gradually releases structural H₂O, which hydrolyzes and condenses titanium isopropoxide, forming TiO₂ nanocrystals. Simultaneous growth and aggregation of TiO₂ nanocrystals leads to the formation of high-surface-area TiO₂ microspheres under solvothermal conditions. After a low-temperature post-synthesis calcination, carbonate could be incorporated into TiO₂ as a dopant with the carbon source coming from the organic byproducts during the synthesis. Carbonate doping modifies the electronic structure of TiO₂ (e.g., Fermi level, E_f), and thus influences its electrochemical properties. Solid electrolyte interface (SEI) formation, which is not common for titania, could be initiated in carbonate-doped TiO₂ due to elevated E_f. After removing carbonate dopants by high-temperature calcination, the mesoporous TiO₂ microspheres showed much improved performance in lithium insertion and stability at various current rates, attributed to a synergistic effect of high surface area, large pore size and good anatase crystallinity.