Coordination of Monovalent AlCl₂⁺ by Redox-Active Carbonyl Groups in Perylene Polyimide for Aluminum Batteries Using Urea-Based Ionic Liquids

Rechargeable aluminum-organic batteries (AOBs) represent a significant evolution from traditional aluminum-ion batteries, utilizing innovative electrolytes with cationic aluminum complexes ([AlCl x ] (3– x )+, x = 0–2). However, AOBs can suffer from cathode intercalation irregularities, slow aluminum-ion kinetics, and organic material dissolution, which detract from their broader application. To address these hurdles, we report a perylene polyimide-anthraquinone/graphene (PI-AQ/G) composite cathode. This cathode efficiently attracts and retains Al complex ions using redox-active carbonyl groups, which are enhanced by cost-effective AlCl 3 /urea-based ionic liquid analogues (ILAs) to boost electrochemical efficiency. The Al||PI-AQ/G cells with 1.3:1 AlCl 3 /urea (A:U) and 1.4:1 AlCl 3 / N -ethylurea (A:EU) ionic liquids achieve excellent discharge capacities of 265 and 256 mAh g –1, respectively, at 100 mA g –1 . The Al||PI-AQ/G (A:U) display a significant reversible capacity of 69 mAh g –1, which maintains at 42 mAh g –1 after 200 cycles at 0.5 A g –1 and shows exceptional long cycle life over 1000 cycles at 1 A g –1, showcasing exceptional cyclic stability. Extensive analytical assessments for PI-AQ/G (A:U) electrodes using ex situ scanning electron microscopy and energy dispersive spectroscopy identify monovalent AlCl 2 + as the primary active species. This species interacts with the carbonyl groups in PI-AQ, facilitating energy storage via the formation of stable O–Al–Cl bonds. Our research highlights perylene-based organic polyimides as highly effective cathode materials for AOBs, enhancing both performance and cost efficiency. These advancements address substantial challenges in the field and pave the way for the development of high-capacity and cost-effective aluminum-based energy storage solutions.