Bifunctional electrolyte addition for longer life and higher capacity of aqueous zinc-ion hybrid supercapacitors

Owing to uncontrolled and uneven electrodeposition and side reactions, Zn metal anodes inevitably suffer from issues such as dendrite growth, hydrogen evolution reactions, and surface passivation. This paper proposes an efficient strategy to address these critical issues for realizing long-life and high-capacity aqueous zinc-ion hybrid supercapacitors (ZHSCs) by incorporating low-concentration (0.05 mol·L⁻¹) redox RbI electrolyte additives. Specifically, rubidium cations have the ability to influence the negative Zn electrode surface via an electrostatic shielding mechanism, effectively protecting the electrode and minimizing undesired side reactions. In an aqueous solution, iodide anions actively solvate Zn²⁺ ions by stabilizing and modulating the solvation shell surrounding Zn²⁺. Moreover, the presence of iodide ions promotes the uniform deposition of Zn²⁺ species by selective adsorption onto the electrode surface. The synergistic effect of the electrostatic shielding and halogen ions enables the realization of aqueous symmetric Zn||Zn cells with a substantial cycle life of more than 2000 h. Additionally, when applied to commercial activated carbon (AC), the proposed strategy facilitates the development of aqueous ZHSCs, exhibiting high specific capacitances (148.8 F·g⁻¹ at 4 A·g⁻¹) and ultra-long cycling stability. Graphical abstract: (Figure presented.)