Cation‐Anion Redox Active Organic Complex for High Performance Aqueous Zinc Ion Battery

Abstract

Organic redox compounds are attractive cathode materials in aqueous zinc‐ion batteries owing to their low cost, environmental friendliness, multiple‐electron‐transfer reactions, and resource sustainability. However, the realized energy density is constrained by the limited capacity and low voltage. Herein, copper‐tetracyanoquinodimethane (CuTCNQ), an organic charge–transfer complex is evaluated as a zinc‐ion battery cathode owing to the good electron acceptation ability in the cyano groups that improves the voltage output. Through electrochemical activation, electrolyte optimization, and adoption of graphene‐based separator, CuTCNQ‐based aqueous zinc‐ion batteries deliver much improved rate performance and cycling stability with anti‐self‐discharge properties. The structural evolution of CuTCNQ during discharge/charge are investigated by ex situ Fourier transform infra‐red (FT‐IR) spectra, ex situ X‐ray photoelectron spectroscopy (XPS), and in situ ultraviolet visible spectroscopy (UV–vis), revealing reversible redox reactions in both cuprous cations (Cu+) and organic anions (TCNQx‐1), thus delivering a high voltage output of 1.0 V and excellent discharge capacity of 158 mAh g−1. The remarkable electrochemical performance in Zn//CuTCNQ is ascribed to the strong inductive effect of cyano groups in CuTCNQ that elevated the voltage output and the graphene‐modified separator that inhibited CuTCNQ dissolution and shuttle effect in aqueous electrolytes.