Coupled TCNQ–Cu ²⁺ Redox Forms Conductive CuTCNQ for High‐Rate Aqueous Copper‐Ion Batteries

Aqueous copper‐ion batteries are attractive for their cost, safety, and sustainability but are limited by a narrow voltage window and modest rate performance. A coupled‐redox strategy is proposed in which the organic molecular cathode 7,7,8,8‐ tetracyanoquinodimethane (TCNQ) and Cu ²⁺ each accept one electron to form TCNQ ^– and Cu ⁺ , which then coordinate into a conductive CuTCNQ phase formed in situ. This phase accelerates charge transport and stabilizes the redox process, delivering a specific capacity of 171 mAh g ⁻¹ at 0.5 A g ⁻¹ . Owing to the fast kinetics of CuTCNQ, the cell retains a specific capacity of 82 mAh g ⁻¹ after 700 cycles at a high current density of 5 A g ⁻¹ . Extending the concept to a decoupled Zn//TCNQ aqueous battery with a TCNQ cathode and Zn anode yields an operating voltage of 1.32 V. These results show that pairing an organic‐molecule with Cu ²⁺ to form a conductive coordination phase is an effective route to high‐rate, long‐life aqueous copper‐ion storage and broadens the role of organic electrodes in aqueous batteries.