Ultrahigh Capacity from Complexation‐Enabled Aluminum‐Ion Batteries with C70 as the Cathode

Abstract Restricted by the available energy storage modes, currently rechargeable aluminum‐ion batteries (RABs) can only provide a very limited experimental capacity, regardless of the very high gravimetric capacity of Al (2980 mAh g −1 ). Here, a novel complexation mechanism is reported for energy storage in RABs by utilizing 0D fullerene C 70 as the cathode. This mechanism enables remarkable discharge voltage (≈1.65 V) and especially a record‐high reversible specific capacity (750 mAh g −1 at 200 mA g −1 ) of RABs. By means of in situ Raman monitoring, mass spectrometry, and density functional theory (DFT) calculations, it is found that this elevated capacity is attributed to the direct complexation of one C 70 molecule with 23.5 (super)halogen moieties (superhalogen AlCl 4 and/or halogen Cl) in average, forming (super)halogenated C 70 ·(AlCl 4 ) m Cl n‐m complexes. Upon discharging, decomplexation of C 70 ·(AlCl 4 ) m Cl n‐m releases AlCl 4 − /Cl − ions while preserving the intact fullerene cage. This work provides a new route to realize high‐capacity and long‐life batteries following the complexation mechanism.