High-energy-density aqueous zinc-based hybrid supercapacitor-battery with uniform zinc deposition achieved by multifunctional decoupled additive

Aqueous Zn-based hybrid supercapacitors (ZHSs) are promising energy storage devices, benefiting from their safety, high power density, low-cost and environmental benignity. However, the major issues of Zn dendrites and low energy density severely hinder their further rapid development. Herein, a multifunctional decoupled additive, 1-methyl-1-ethyl pyrrolidinium bromide (MEP∙Br), is proposed to update the traditional ZHS to Zn-based hybrid supercapacitor-battery (ZHSB) with higher energy density. Thanks to the merits of the uniform Zn deposition induced by MEP+, reduced polarization derived from alteration of solvation structure by Br−, increased capacity from rapid electrochemical reversible reaction of Br2/Br−, and the fixation of charged Br2-containing species in cathode realized by robust complexation of MEP∙Br, compared with the traditional ZHS, the ZHSB with MEP∙Br demonstrates a much higher average energy density of 383.2 W h kg−1 (265.8 mAh g−1) and long-term cycling durability (over 5000 cycles) at a high power density of 16.8 kW kg−1 (10 A g−1). Interestingly, even at an ultrahigh current density of 20 A g−1, the ZHSB can still deliver a high specific capacity of 252.4 mAh g−1 (about three times higher than that of ZHS). This work provides a new option for the next generation energy storage technologies.