ZrO ₂ -Functionalized Glass Fiber/Bacterial Cellulose Composite Separator for Dendrite-Free Zn Anode and Ultrastable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) hold great promise for large-scale energy storage; however, their development is hindered by Zn anode instability, including dendrite growth, parasitic hydrogen evolution, and interfacial passivation. Here, we report a low-cost and scalable composite separator (GB50-ZrO₂-40) fabricated by ball milling and vacuum filtration of glass fiber, bacterial cellulose (BC), and 40 wt % ZrO₂ nanoparticles. The resulting three-phase network exhibits high mechanical strength (∼44 MPa), hierarchical porosity, and strong water/ZrO₂ interactions, which together provide multiple functions: it resists dendrite penetration through mechanical reinforcement, homogenizes the local electric field and Zn²⁺ flux via interfacial Maxwell-Wagner polarization, and promotes partial desolvation of Zn²⁺ by preferential water adsorption on ZrO₂. These synergistic effects inhibit side reactions and promote uniform, dense Zn deposition. As a result, Zn||Zn symmetric batteries with GB50-ZrO₂-40 deliver ultrastable cycling performance exceeding 4500 h at 0.5 mA cm^-2 with 0.25 mAh cm^-2 and 1307 h at 10 mA cm^-2 with 5 mAh cm^-2. Furthermore, Zn||NaV₃O₈·1.5H₂O full batteries retain more than 92% of their capacity after 1000 cycles at 5 A g^-1. The underlying mechanisms are supported by combined electrochemical measurements, in situ microscopy, finite-element simulations, and density functional theory (DFT) adsorption calculations, highlighting the practical scalability of the GB50-ZrO₂-40 separator for high-performance AZIBs.