Enhancing the Energy Density of Zn-Ion Capacitors Using Redox-Active Choline Anthraquinone Electrolyte

Abstract

Owing to ease of recyclability, high theoretical capacity (820 mAh g−1), safety, facile manufacture, and high energy density, Zinc-ion capacitors (ZICs) are emerging as promising capacitors and have attracted substantial attention. However, aqueous ZICs frequently encounter several difficulties, comprising low coulombic efficiency, low Zn anode deposition/stripping efficiency, hydrogen evolution, fast capacity decay, and Zn dendrite formation. Hence, to inhibit the formation of Zn dendrites, it is important to tune the electrolyte and the electrode/electrolyte interface. Herein, the key problems are tackled by using choline-based electrolytes. ZIC with ZnCl2 in the presence of choline chloride yields good capacity and inhibits Zn dendrite formation due to the adsorption of choline at the interface. To further increase the energy density of the device, redox-active choline anthraquinone sulphonate (ChAQS) additives are synthesized and incorporated into the ChCl/ZnCl2 system. The constructed graphene-based aqueous ZIC with the novel (ChCl/ ChAQS /ZnCl2) electrolyte system shows a high specific capacity of 460 F g−1 and a high energy density of 185 Wh kg−1 at 0.25 A g−1. These outcomes demonstrate an innovative pathway to fabricate biobased redox electrolytes for emerging sustainable energy storage devices.