An ammonium acetate-modulated gel electrolyte induces uniform zinc deposition for long-term cycling of zinc-ion hybrid supercapacitors

Abstract

Aqueous zinc-based energy storage devices utilizing metallic zinc as the anode exhibit high theoretical capacity, superior safety, environmental friendliness, and cost-effectiveness, demonstrating broad prospects for energy storage applications. However, severe dendrite growth and parasitic side reactions degrade the durability and reversibility of the zinc anode, thereby hindering the large-scale application of zinc-based devices. Gel electrolytes, which combine the mechanical properties of polymer matrices with the ionic conductivity of conventional liquid electrolytes, can meet the requirements for flexible devices while ensuring electrochemical performance. Although the polymer network can partially restrict water activity to mitigate interfacial side reactions, the issues of the zinc anode remain pronounced in traditional gel electrolytes. Studies have shown that introducing functional charged groups into gel electrolytes can regulate zinc deposition behavior and suppress side reactions, thereby effectively protecting the zinc anode. Based on this rationale, a PAM/AAT/ZnSO₄ hydrogel electrolyte (PAAHE) was synthesized via thermally initiated polymerization using acrylamide (AM) as the monomer, ammonium acetate (AAT) as the additive, and ZnSO₄ as the electrolyte salt. The polar carboxylate groups with high interfacial energy effectively inhibit zinc dendrite growth. Enhanced by AAT, the PAAHE exhibits outstanding mechanical properties. Simultaneously, the charged carboxylate groups from AAT can induce the preferential deposition of zinc along the (002) crystal plane. Experimental results demonstrate that side reactions and dendrite growth on the zinc anode are significantly suppressed in the PAAHE. Benefiting from these advantages, the optimized Zn//Cu cell achieves a cycle life of 480 cycles, and the Zn//Zn symmetric cell operates stably for over 750 h. Furthermore, the quasi-solid-state ZHC based on the PAAHE delivers a long cycle life of 28 000 cycles at 10 A g⁻¹ and demonstrates excellent practicality in the field of flexible energy storage. This work provides an effective strategy for fabricating multifunctional hydrogel electrolytes.