Tailored preparation methods of TiO₂ anatase, rutile, brookite: Mechanism of formation and electrochemical properties

Using a simple aqueous precipitation method based on a low-cost titanium oxysulfate precursor, we have prepared three TiO₂ polymorphs: anatase, rutile, and brookite. Although the anatase form can be directly obtained from the thermolysis reaction of an oxysulfate solution, the rutile and the brookite have been prepared by the addition of oxalate species. Depending on the concentration, the oxalate anions have been shown to act either as a ligand with the stabilization of a titanium oxalate hydrate, Ti ₂O₃(H₂O)₂(C₂O ₂)H₂O, or as a chelating agent with the isolation of the rutile phase. The brookite form was obtained by thermal decomposition of the oxalate hydrate at a temperature as low as 300 °C. The resulting solid consisted of nanodomains of TiO₂ brookite embedded in large micrometer-size particles and exhibited a high specific surface area of 255 m²/g because of the mesoporosity arising from the removal of water from the oxalate species. This type of morphology is of interest for lithium-ion batteries because of an easier coating process and a higher surface contact between the material and the electrolyte that enhanced the electrochemical activity. Finally, based on electrochemical characterizations, TiO₂ brookite provided higher volumetric energy density than comparable nanomaterials.