Ultrathin, high-strength, and bio-derived sulfated bacterial cellulose nanofiber separators for stable aqueous zinc...

Herein, we demonstrate that sulfated bacterial cellulose nanofibers (SBCNF) can be facilely exfoliated from their natural ingredients by using chlorosulfonic acid to heterogeneously sulfated BC in anhydrous N, N-dimethylformamide. Controlled heterogeneous sulfation with chlorosulfonic acid enables precise tuning of sulfate substitution, which promotes electrostatic disintegration of bacterial cellulose into highly dispersible nanofibers during high-pressure homogenization. The resulting SBCNF dispersions form transparent (∼90%), mechanically strong (∼207 MPa), and highly ordered lamellar films with anisotropic swelling and reduced porosity, arising from their dense layer-by-layer nanofiber assemblies. Leveraging their hydrophilicity, ion-sieving capability, and tortuous nanochannels, ultrathin SBCNF separators (∼8 μm) effectively suppress Zn dendrite propagation and facilitate uniform Zn deposition. Symmetric cells incorporating SBCNF exhibit low overpotential, stable plating/stripping behavior, and exceptional cycling stability exceeding 5200 h. Full Zn||MnO₂ cells using SBCNF separators demonstrate high capacities, excellent rate reversibility, and 79.17% capacity retention with ∼100% Coulombic efficiency over 100 cycles. These results position SBCNF as a compelling class of bio-derived separators, enabling high-efficiency ion transport and durable Zn storage in next-generation aqueous batteries.