A novel zinc ion supercapacitor with ultrahigh capacity and ultralong cycling lives enhanced by redox electrolyte

It remains a great challenge to design an energy storage device with high energy density, high power density, and low cost simultaneously. To overcome this challenge, a novel Zn-ion energy storage device that combines multiple energy storage mechanisms is proposed by introducing redox electrolyte in Zn-ion hybrid capacitor. In this design, an aqueous solution with 2 M ZnSO4 and 0.3 M KI is optimized as redox electrolyte for Zn-ion device. Thanks to the redox reaction of polyiodide, reversible ion adsorption, and reversible electrodeposition, the fabricated Zn-ion hybrid device using as designed electrolyte shows a high-rate performance, ultrahigh specific capacity (428 mAhg−1 based on activated carbon), and an ultra-long cycling stability with a retention rate of 99.1 % up to 16,000 cycles. With ultralong cycling life, a facile fabrication, and low costs, the as fabricated device will be a very promising energy storage device in the future. This work illustrates the advantages of multiple storage mechanisms in aqueous devices toward high energy density and power density.