Designing Anti-Swelling Nanocellulose Separators with Stable and Fast Ion Transport Channels for Efficient Aqueous Zinc-Ion Batteries

Separators swelling in aqueous electrolytes can cause inhomogeneous ion flux and unregulated dendrite propagation, yet the corresponding phenomenon and mitigation strategy are rarely studied. This article deals with the issue of pore structure variation caused by separator swelling in aqueous zinc-ion batteries (AZBs) by employing nanocellulose separator as a representative example. A multifunctional separator composed of Zr⁴⁺-hydrolysate-coated nanocellulose (Zr-CNF) is developed by in situ hydrolysis of Zr⁴⁺, which demonstrates excellent swelling resistance, pore-structure stability, and percolating porosity due to cross-linking and hydrogen bond shielding effect. Consequently, the homogeneous Zn-ion flux, high ionic conductivity, and Zn²⁺ transfer number are maintained upon cycling. Moreover, the amorphous ZrO containing coating induces a homogeneous directional electric field around the interface, accelerating the Zn²⁺ influx, reducing the nucleation overpotential, and promoting homogeneous nucleation for Zn deposition. The Zr-CNF separator enable dendrite-free Zn anode with high Coulombic efficiency (99.7%) and exceptional cyclability for 680 h under 5 mA cm⁻²/5 mAh cm⁻². The feasibility of the Zr-CNF separator is verified in PANI/V₂O₅-based AZBs and activated carbon-based Zn-ion capacitors. This study provides a facile approach to address separator swelling issue, enlightening novel insights into the efficient and sustainable aqueous battery technologies in the future.