Coupling polyethyleneimine grafting with macropore filling in ultrathin cellulose separator to enable robust aqueous zinc-based batteries

Aqueous zinc-based batteries have emerged as promising candidates for large-scale energy storage owing to their inherent safety and cost-effectiveness. However, their widespread application is impeded by dendritic formation and parasitic reactions at zinc anodes. To address these issues, this study employs polyethyleneimine grafting and macropore filling to synergistically modify the cellulose separator. The zincophilic –NH2 and –NH– groups introduced by polyethyleneimine promote Zn2+ ion desolvation and nucleation processes. Concurrently, the nanocellulose incorporated into macropores not only significantly enhances mechanical properties but also compensates for macroporous defects within the cellulose separator. The optimized separator exhibits ultralow thickness (18 μm), ultrahigh modulus (3.2 GPa), large ionic conductivity (19.0 mS cm−1), high Zn2+ ion transfer number (0.63), and good biodegradability. Comprehensive experimental measurements and theoretical analysis reveal that the utilization of this separator contributes to significantly suppressed zinc dendrites and improved electrochemical kinetics. The assembled Zn//Zn cell demonstrates exceptional cycling stability (over 1000 h lifespan at 10 mA cm−2 and 2 mAh cm−2), and the Zn//MnO2 and Zn//I2 full batteries maintain excellent long-term cyclability under high cathode mass loadings. This work advances our understanding of multifunctional separator design for next-generation electrochemical energy storage systems.