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.