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

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(TCNQ^(x-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.