A nanocellulose-mediated, multiscale ion-sieving separator with selective Zn²⁺ channels for durable aqueous zinc-based batteries

A heterostructure engineered, multiscale ion-sieving separator with desired macro‑meso-molecular pores that can render selective Zn²⁺ permeability and homogeneous Zn²⁺ distribution at the separator-electrode interface is designed to achieve durable aqueous Zn-ion batteries. The proposed separator is fabricated by stacking an intermediate nanocellulose layer and a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) upper layer on a glass fiber substrate, wherein the nanocellulose layer contains uniform mesopores favoring a homogeneous Zn²⁺ flux and endowing the attainment of a PEDOT:PSS layer. While the PEDOT:PSS layer features intrinsic ionic/electronic conductivity and rich sulfonate groups enabling uniform electrical field distribution and inhibiting anions migration. The combination of mesoporous nanocellulose and cation-permeable PEDOT:PSS used in the heterostructure separator yields a high ionic transference number and fast Zn²⁺ desolvation kinetics. This unique separator enables highly compact and dendrite-free Zn deposition at 4 mA cm⁻²/8 mAh cm⁻², and sustains the symmetric Zn||Zn cell over 400 h at 10 mA cm⁻²/4 mAh cm⁻². Such advantages bring remarkable reversibility to full AZBs with high I₂ mass loading cathodes of 13.0 mg cm⁻², delivering a discharge capacity of 172.1 mAh g⁻¹ after 1000 cycles. This multiscale ion-sieving design principle provides new insight into separator engineering for ultra-stable Zn metal batteries.