A rechargeable 6-electron Al–Se battery with high energy density

Rechargeable aluminum ion batteries (AIBs) have attracted substantial interest due to their high theoretical energy density, low cost, and high security. However, the low-energy density and high-cost of the reported cathode materials hinder their further development. Herein, a Se-based 6-electron Al-Se battery was generated by activating the highly reversible Se(−II)/Se(0) couple into Se(0)/Se(IV) couple in AlCl3-based ionic liquid electrolyte, which exhibited an ultra-high theoretical specific capacity (2036 mAh g−1). For further activating the Se cathode and addressing the shuttle effect of the soluble products, the Se/graphene aerogel (Se/GA) and carbon-based modified separator with oxygen-containing functional groups (O-CNT) were collectively employed to promote stable high-energy density for Al-Se battery. Consequently, GA improved the utilization of Se cathode and reduced its overpotential, delivering super-high specific capacity with a sufficient voltage discharge plateau at au. 1.9 V. However, the O-CNT separator effectively blocked these Se-based cationic clusters, such as Sen2+ and SeCl3+, by a dual defense mechanism that integrated the physical barrier of porous structure and powerful chemical adsorption ability of the carboxyl (–COOH) group. Then, a high energy density of 1957 Wh kg−1 (1599 mAh g−1) was delivered at 100 mA g−1 and 624 Wh kg−1 (580 mAh g−1) at 1000 mA g−1. Furthermore, the Al-Se battery exhibited outstanding cycling performance of 421 Wh kg−1 (395 mAh g−1) at 1000 mA g−1 after 200 cycles with the record-setting cyclic performance achieved in the documented AIBs. These results provide useful insight into and a versatile strategy for boosting the performance of Al-Se battery.