Microwave-assisted self-template synthesis of mesoporous anatase TiO2 spheres for non-aqueous Al-ion batteries: Textural property optimization and enhanced reversible Al3+ storage

Mesoporous anatase TiO2 spheres (MATS) are elaborated via microwave-assisted rapid crystallization of hydrous TiO2 colloidal spheres (HTCS) self-template. Tuning the hydrothermal and calcination temperatures allow for textural property-controllable synthesis. The optimal MATS are demonstrated as a promising cathode material of aluminium-ion batteries (AIBs) and show superior rate and capacity performances. Their large surface area and porous structure offer a robust and interconnected scaffold for Al3+ insertion/exertion with higher reversibility. The constructed non-aqueous AIBs with RTILs electrolyte deliver the highest initial capacity of 145.3 mA h g(-1) at 0.2C with high Coulombic efficiency of asymptotic to 96.5%, and a reversible capacity of 78.0 mA h g(-1) at 1C can be retained after 200 cycles with high Coulombic efficiency of asymptotic to 98.6%. Our study on the Al storage mechanism further shows the charge/discharge process involves the extraction/insertion of Al species (Al3+, AlCl4-, Al2Cl7-, etc.) into the TiO2 crystal lattices with the formation of intermediate aluminium titanium oxides (Al2Ti7O15 and Al2TiO5) and non-oxides (Ti(AlCl4)(2) and Ti(ClO4)(4)). The continuous enrichment of the latter during cycling greatly deteriorates the reversibility of AIBs.