Hydrogel Electrolyte with Regulated Water Activity and Hydrogen Bond Network for Ultra-Stable Zinc Electrode

Quasi-solid-state zinc-ion batteries (QZIBs) have attracted wide attention due to their excellent dimensional stability and high safety. However, poor ion conduction capabilities, severe dendrite growth, and rampant side reactions still hinder their commercialization. The regulation of the solvation structure of Zn²⁺ is considered to be an effective method to address these issues. Herein, a hydrogel electrolyte with a regulated solvation structure (HE-RS) is designed via the combination of tetramethyl urea (TMU) additive and polyvinyl alcohol (PVA) matrix. The hydrophilic ─C═O group of TMU exhibits strong affinity with the PVA chains, improving the mechanical strength of the PVA matrix. The ─N(CH₃)₂ groups at both ends of TMU exhibit strong hydrophobic characteristics, which leads to local hydrophobicity and decreased water activity. Additionally, abundant oxygen-containing (electronegative) groups on both PVA and TUM can adsorb Zn²⁺ and provide sites for Zn²⁺ transference. Benefiting from these merits, Zn²⁺ solvation structure and deposition behavior are regulated. Consequently, the Zn||Zn symmetric cell with HE-RS exhibits a stable cycling life exceeding 2000 h. Moreover, the HE-RS-based Zn||NH₄V₄O₁₀ cell exhibits a capacity retention of 96.4% after 1000 cycles at 2 A g⁻¹.