Synergistic effects of ionic liquid and redox species for improved aqueous-based Zn-ion capacitor

Abstract

As the demand for high-performance energy storage devices grow, aqueous zinc-ion hybrid capacitors (ZICs) have gained significant attention for their ability to combine the high energy density of zinc-ion batteries (ZIBs) with the high-power density of supercapacitors (SCs). However, their application is limited by poor stability caused by zinc dendrite growth from uneven Zn deposition/stripping. Ionic liquids (ILs) and redox species in ZICs are an emerging area of research focused on improving the performance and efficiency of energy storage devices. The combination of IL and redox species can enhance the charge storage capacity, stability, and cycling performance of ZICs, potentially providing high energy and power densities with long-term durability. Herein, synergistic effects of 1-Ethyl-3-methylimidazoliumtriflate (EMImTfO) and 1-Ethyl-3-methylimidazolium iodide (EMImI) were investigated on aqueous electrolyte of Zn(TfO)2. The Zn/graphene ZIC delivers capacities of 82 and 96 mAh g−1 at 0.5 A g−1 in Zn(TfO)2 and Zn(TfO)2/ EMImTfO electrolytes, respectively, while the redox additive of EMImI boosts the capacity to 182 mAh g−1 under the same conditions. Moreover, even at a high current density of 5 A g−1, the capacity was found to be 100 mAh g−1, indicating improved rate capability. These findings offer a promising strategy for the development of redox-active electrolytes tailored for next-generation sustainable energy storage systems.