Ultrahigh Capacity from Complexation-Enabled Aluminum-Ion Batteries with C₇₀ 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, a novel complexation mechanism is reported for energy storage in RABs by utilizing 0D fullerene C₇₀ 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 C₇₀ molecule with 23.5 (super)halogen moieties (superhalogen AlCl₄ and/or halogen Cl) in average, forming (super)halogenated C₇₀ ·(AlCl₄ )_m Cl_n-m complexes. Upon discharging, decomplexation of C₇₀ ·(AlCl₄ )_m Cl_n-m releases AlCl₄ ^- /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.