Sustainable Aloe‐Emodin as an Advanced Organic Cathode for High‐Performance Aluminum‐Ion Batteries

Abstract Anthraquinone derivatives, known for their redox properties, are widely recognized as promising cathode materials for aluminum‐ion batteries. This study presents an environmentally benign extraction of aloe‐emodin from aloe dry powder, a sustainable and economically viable resource, using ferric chloride as an oxidizing agent in an acidic medium. Emodin and its isomer, aloe‐emodin, share a symmetrical polycyclic chemical architecture and carbonyl functionalities, but differ in the position of their hydroxyl groups. The shift of a hydroxyl group from the aromatic ring to the methyl moiety in emodin results in aloe‐emodin, enhancing its redox potential. As a cathode material in aluminum‐ion batteries, aloe‐emodin demonstrates enhanced electrochemical performance compared to emodin, showcasing a high reversible specific capacity of 85.9 mAh/g at 50 mA/g, superior rate capability with 42.0 and 32.0 mAh/g at 1000 and 2000 mA/g, respectively, and remarkable long‐term cyclability with a capacity retention of 50.3 mAh/g and a Coulombic efficiency of 99.05 % after 6000 cycles at 1000 mA/g. These findings contribute to a deeper understanding of the design principles for aluminum‐ion batteries that leverage anthraquinone‐based cathode materials.