Cotton-derived cellulose film as a dendrite-inhibiting separator to stabilize the zinc metal anode of aqueous zinc ion batteries

Benefiting from high safety, low cost, and competitive energy density, aqueous zinc-ion batteries (AZIBs) have become a very promising technique for grid-scale energy storage. However, the life span of AZIBs is severely influenced by the uncontrolled zinc dendritic growth and undesirable side reactions. To address this issue, this work employs cotton-derived cellulose film prepared by a facile filtration method as the separator for AZIBs. The obtained separator offers dense and uniform nanopores, abundant hydroxyl groups, excellent mechanical properties (29.2 MPa in strength and 4.16 GPa in modulus), and large ionic conductivity (56.95 mS cm–1). These properties enable this separator to increase the zinc ion transfer number, lower the desolvation barrier of hydrated zinc ions, reduce the zinc nucleation overpotential, and accelerate the zinc deposition kinetics, in comparison with the commonly used glass fiber separator. Therefore, the cellulose film separator can effectively inhibit zinc dendrites and harmful side reactions. Impressively, the Zn//Zn symmetric cell with this separator remains stable at a cumulative zinc plating capacity of 1000 mAh cm−2 and can endure ultra-large areal capacity of 20 mAh cm−2. The assembled Zn-MnO2 battery also achieves significantly improved rate capability and cyclability compared to those using other separators. This study provides new insights into designing reliable, efficient, and cost-effective separators of electrochemical energy storage devices.