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

Abstract

Mesoporous anatase TiO ₂ spheres (MATS) are elaborated via microwave-assisted rapid crystallization of hydrous TiO ₂ 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 Al ³⁺ 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 ≈ 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 ≈ 98.6%. Our study on the Al storage mechanism further shows the charge/discharge process involves the extraction/insertion of Al species (Al ³⁺, AlCl ₄ ⁻, Al ₂Cl ₇ ⁻, etc.) into the TiO ₂ crystal lattices with the formation of intermediate aluminium titanium oxides (Al ₂Ti ₇O ₁₅ and Al ₂TiO ₅) and non-oxides (Ti(AlCl ₄) ₂ and Ti(ClO ₄) ₄₎. The continuous enrichment of the latter during cycling greatly deteriorates the reversibility of AIBs.

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