Ultrahigh Capacity from Complexation-Enabled Aluminum-Ion Batteries with C 70 as the Cathode.

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, we report a novel complexation mechanism for energy storage in RABs by utilizing zero-dimensional 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, we 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. Our work provides a new route to realize high-capacity and long-life batteries following the complexation mechanism. This article is protected by copyright. All rights reserved.