Acetic Anhydride as an Oxygen Donor in the Non-Hydrolytic Sol–Gel Synthesis of Mesoporous TiO2 with High Electrochemical Lithium Storage Performances

An original, halide-free non-hydrolytic sol–gel route to mesoporous anatase TiO₂ with hierarchical porosity and high specific surface area is reported. This route is based on the reaction at 200 °C of titanium(IV) isopropoxide with acetic anhydride, in the absence of a catalyst or solvent. NMR spectroscopic studies indicate that this method provides an efficient, truly non-hydrolytic and aprotic route to TiO₂. Formation of the oxide involves successive acetoxylation and condensation reactions, both with ester elimination. The resulting TiO₂ materials were nanocrystalline, even before calcination. Small (about 10 nm) anatase nanocrystals spontaneously aggregated to form mesoporous micron-sized particles with high specific surface area (240 m² g⁻¹ before calcination). Evaluation of the lithium storage performances shows a high reversible specific capacity, particularly for the non-calcined sample with the highest specific surface area favouring pseudo-capacitive storage: 253 mAh g⁻¹ at 0.1 C and 218 mAh g⁻¹ at 1 C (C=336 mA g⁻¹). This sample also shows good cyclability (92 % retention after 200 cycles at 336 mA g⁻¹) with a high coulombic efficiency (99.8 %). Synthesis in the presence of a solvent (toluene or squalane) offers the possibility to tune the morphology and texture of the TiO₂ nanomaterials.