Unveiling the potential of redox electrolyte additives in enhancing interfacial stability for Zn-ion hybrid capacitors

Zinc-ion hybrid capacitors (ZICs) that combine the characteristics of metal-ion batteries and supercapacitors are emerging to fulfill high energy-power demands. The objective of this study is to address the challenges in the practical implementation of metallic zinc for ZICs. In this work, we explore redox molecules based on anthraquinone compounds as electrolyte additives for the interfacial engineering of Zn anodes. The results reveal that the additives enable favorable solvation of Zn2+ through metal ion-ligand coordination. The redox additives improve the lifespan of Zn//Zn cells from 50 to 1600 cycles at 2 mA cm−2 and 1 mAh cm−2 due to the suppression of parasitic reactions and the mitigation of by-product formations. The redox properties of additives strengthen the pseudocapacitive behavior of the ZICs, enabling efficient interfacial charge and mass transfer. The redox-enhanced device manifests an increased capacity of 195.0 mAh g − 1 with improved cycling stability, compared to that of 149.6 mAh g − 1 for the additive-free electrolyte. The universal strategy, based on the synergistic effects of redox additives, is demonstrated by a collection of molecules with similar structures. This work unveils a conceptually new approach that utilizes redox additives to formulate advanced electrolytes for aqueous energy storage.