Urea-intercalated montmorillonite quasi-solid-state electrolyte enabling selective Zn2+ transport and reduced water reactivity for durable aqueous zinc-ion batteries

The corrosion of zinc anodes, hydrogen evolution reaction, dendrite growth, and by-product formation are major obstacles to the practical application of aqueous zinc-ion batteries. In the electrolyte system, free water molecules that do not participate in ion hydration can disrupt solution stability, thereby becoming a major factor causing electrochemical barriers. To mitigate the adverse effects of free water molecules on AZIBs, this study utilized urea-intercalated montmorillonite as a raw material to prepare a novel clay-based quasi-solid-state electrolyte, based on the unique layered structure, negatively charged sheets, and strong ion exchange capacity of montmorillonite. This electrolyte effectively reduced the free water content and water activity in the system, thereby inhibiting corrosion and HER. Additionally, the intercalation of urea widened the interlayer spacing of montmorillonite, enhancing the attraction of Zn 2+ to construct interlayer cation channels. Meanwhile, the unique electric field structure on its surface determined the ion-selective transport characteristics, and the Zn 2+ transfer number of this clay-based quasi-solid-state electrolyte reached 0.82. Furthermore, the clay-based quasi-solid-state electrolyte promoted uniform deposition of Zn 2+ on the Zn anode surface, inhibiting dendrite growth and by-product formation. When this electrolyte was applied to a Zn//MnO₂ full cell at a current density of 300 mA g −1 , the battery could stably cycle for 1000 cycles, with the discharge specific capacity remaining at 193.2 mAh g −1 after cycling, a capacity retention rate of approximately 86.6%, and a stable CE close to 100%, demonstrating excellent capacity performance and cycle stability. • The abundant hydrophilic groups (-OH) in UMMT formed hydrogen bonds with water molecules, reducing the free water content in the quasi-solid-state electrolyte and suppressed side reactions involving free water at the electrodes. • The intercalation of urea widened the interlayer spacing of montmorillonite, enhancing the attraction of Zn 2+ to construct interlayer cation channels. • The negatively charged surface of UMMT enables cation-selective transport. • The assembled full cell can achieve stable zinc deposition and long-term cycling performance.