Multi-level electrolyte regulation toward a stable Zn anode in aqueous zinc-ion capacitors

The aqueous zinc (Zn)-based energy storage system (AZESS) offers low cost and high safety, making it a promising candidate for energy storage devices. However, its practical application is hindered by dendritic growth and side reactions at the anode side. To overcome these challenges, a multi-level modulation strategy is proposed based on a multi-component hydrogel electrolyte to precisely regulate the Zn 2+ solvation structure, hydrogen-bond (H-bond) network, and deposition behavior. This tailored electrolyte suppresses interfacial water aggregation, mitigates water-induced side reactions, and enables uniform Zn deposition/dissolution, thereby effectively inhibiting dendrite growth and enhancing interfacial stability. As a result, the Zn//Zn symmetric cell using this hydrogel demonstrates remarkable durability, along with a high coulombic efficiency. Moreover, the assembled Zn//Activated carbon (AC) capacitor exhibits outstanding long-term performance, maintaining an impressive capacity retention of 99.55 % and high coulombic efficiency (CE) of 99.8 % after 35,000 cycles. This strategy provides a promising pathway for the rational design of advanced electrolytes toward high-performance Zinc-ion capacitors (ZICs). A hydrogel electrolyte is designed to enhance the stability of Zn-metal anode by optimizing Zn 2+ solvation, reconstructing the hydrogen-bonding network and tuning Zn deposition behavior. This multi-level regulation strategy effectively suppresses dendrite growth and H 2 O-induced side reactions, enabling good reversibility and long-term cycling stability in Zn//Zn cells and Zn//AC capacitors, offering new insights for advanced electrolyte design for aqueous Zn-based energy storage systems. • A multi-level modulation strategy enables regulation of Zn 2+ solvation structure and hydrogen-bond networks through a hydrogel electrolyte. • Interfacial water activity, dendrites and side reactions are greatly suppressed. • Regulated Zn nucleation enables uniform plating/stripping and long-term interfacial stability. • The Zn//AC capacitor achieves 99.55 % capacity retention and 99.8 % CE after 35,000 cycles.