Donor–Acceptor Covalent Organic Framework Enables Ambipolar Charge Storage in Aluminum‐Ion Energy Storage

ABSTRACT The development of sustainable high‐performance energy storage systems (ESS) beyond lithium‐ion technology has become a global priority due to lithium's geopolitical and supply‐chain constraints. Among emerging alternatives, aluminum‐ion ESS (Al‐ESS) offer remarkable advantages, including aluminum's natural abundance, high theoretical volumetric capacity, and intrinsic safety. However, progress in Al‐ESS is hindered by the scarcity of effective cathode materials capable of reversible Al‐ion storage. In this context, covalent organic frameworks (COFs) offer tunable structures and abundant redox‐active sites, which enable multi‐electron reactions and fast ion transport. However, their practical implementation is often undermined by poor electronic conductivity and limited accessibility of redox centers. Herein, 2D donor–acceptor COF integrating electron‐rich tetrakis(4‐aminophenyl)‐1,4‐phenylenediamine (TPA) and electron‐deficient naphthalenediimide (NDI) units is reported as an ambipolar cathode for Al‐ESS. The highly crystalline, microporous framework exhibits intrinsic charge‐transport pathways, enabling operation without conductive carbon‐nanotube additives. COF TPA‐NDI delivers a high specific capacity of 270 mAh/g, a specific energy of 447 Wh/kg, and exceptional cycling stability. Ex situ analyses reveal a reversible multi‐electron redox process involving amine, imine, and carbonyl sites coordinating both cationic and anionic species. These findings demonstrate that donor–acceptor engineering in COFs can yield intrinsically conductive organic cathodes, providing a new design paradigm for next‐generation Al‐ESS.