Reversible Al³⁺ storage mechanism in anatase TiO₂ cathode material for ionic liquid electrolyte-based aluminum-ion batteries

Rechargeable aluminum ion battery (AIB) with high theoretical specific capacity, abundant elements and low cost engages considerable attention as a promising next generation energy storage and conversion system. Nevertheless, to date, one of the major barriers to pursuit better AIB is the limited applicable cathode materials with the ability to store aluminum highly reversibly. Herein, a highly reversible AIB is proposed using mesoporous TiO₂ microparticles (M-TiO₂) as the cathode material. The improved performance of TiO₂/Al battery is ascribed to the high ionic conductivity and material stability, which is caused by the stable architecture with a mesoporous microstructure and no random aggregation of secondary particles. In addition, we conducted detailed characterization to gain deeper understanding of the Al³⁺ storage mechanism in anatase TiO₂ for AIB. Our findings demonstrate clearly that Al³⁺ can be reversibly stored in anatase TiO₂ by intercalation reactions based on ionic liquid electrolyte. Especially, DFT calculations were used to investigate the accurate insertion sites of aluminum ions in M-TiO₂ and the volume changes of M-TiO₂ cells during discharging. As for the controversial side reactions in AIBs, in this work, by normalized calculation, we confirm that M-TiO₂ alone participate in the redox reaction. Moreover, cyclic voltammetry (CV) test was performed to investigate the pseudocapacitive behavior.