Comparative study of hydrogel electrolytes synthesized by different polymerization methods for enhanced zinc battery performance

Development of high-performance hydrogel electrolytes (HEs) via a facile synthesis route is crucial for advancing aqueous zinc-ion batteries (AZIBs). This work presents a comparative study of HEs synthesized by three one-pot polymerization methods: UV-activated, thermal-activated (80 °C), and CuSO₄/tannic acid (TA) redox catalytic system. Among these HEs, HE-CuSO₄/TA is synthesized with the shortest time (less than 3 min) at ambient temperature. Moreover, the HE-CuSO₄/TA demonstrates superior properties, including enhanced ionic conductivity and robust adhesion to zinc foil. Additionally, the HE-CuSO₄/TA effectively regulates the Zn2+ desolvation process and suppresses water-induced side reactions, thereby promoting uniform zinc deposition/stripping. Consequently, the symmetric cell with HE-CuSO₄/TA achieves exceptional cycling stability of 1950 h at 0.5 mA cm−2 and 0.5 mAh cm−2, significantly outperforming its counterparts. The full cell Zn||MnO₂@CNT with HE-CuSO₄/TA exhibits enhanced reaction kinetics and maintains capacity retention more than 85% after 1500 cycles at 1.0 A g−1. Furthermore, this transition metal salt-TA strategy is applicable for synthesizing a diversity of HEs, even with high-concentration salts. This work provides an efficient and scalable polymerization platform, paving the way for durable AZIBs.