Multifunctional hydroquinone additive for enhanced zinc–iodine hybrid battery capacitors: suppressing polyiodide shuttle effects and dendrite growth

Abstract

The development of zinc–iodine hybrid battery capacitors (ZIHBCs), integrating the advantages of zinc–iodine batteries (ZIBs) and zinc-ion hybrid capacitors (ZHCs), aims to combine the high energy density of ZIBs with the superior power density of ZHCs. However, the practical application of ZIHBCs is hindered by significant challenges, including polyiodide shuttle effects on the cathode and dendrite growth on the anode. In this study, a trifunctional hydroquinone (HQ) additive was introduced to address these issues by acting as a redox mediator, suppressing polyiodide diffusion and stabilizing the Zn anode. HQ enhanced the faradaic redox reactions at the interface of the chitosan/activated carbon (CAC) cathode, reduced the polyiodide concentration through preferential coordination with I₂, suppressed the shuttle effect, and improved the iodine redox kinetics. At the same time, HQ interacted with Zn²⁺ ions via a Lewis acid–base mechanism, mitigating dendrite growth, protecting Zn from polyiodide corrosion, and enhancing the long-term cycling stability as well as the coulombic efficiency. Consequently, the ZIHBC with added HQ exhibited a high capacity of 243 mA h g⁻¹, an energy density of 258 W h kg⁻¹ at 0.5 A g⁻¹, and a remarkable cycling stability over 5000 cycles at 10 A g⁻¹, with a coulombic efficiency of 99.9%. Furthermore, Zn/Zn symmetric cells with added HQ achieved superior stability, reaching ∼1300 h at a capacity/current density of 1 mA h cm⁻²/1 mA cm⁻². These results highlight the transformative potential of HQ as an additive for ZIHBCs, representing a critical advancement in energy storage technology.