Unlocking the Potential of Cellulose Separators for High‐Rate Performance in Zinc‐Ion Batteries via Interface‐Engineered Tandem Chemistry

Abstract Cellulose separators for aqueous zinc‐ion batteries face challenges at high‐rate conditions owing to the inherent limitations of slow Zn 2 ⁺ diffusion due to extensive intermolecular hydrogen bonding, and interfacial instability from excessive water activity. Herein, an interface‐engineered tandem chemistry is proposed by integrating chitosan‐trimesoyl chloride (CS‐TMC) layer on a bacterial cellulose separator. The inner CS cross‐linked with cellulose, rich in zincophilic ─OH groups, enhances the wettability, electrolyte uptake rate, and rapid transportation of Zn 2+ through the bulk separator. Simultaneously, the outer grafted TMC with hydrophobic groups such as benzene rings and acyl chlorides can assist to facilitate desolvation of hydrated Zn 2+ and suppress the interfacial side reactions by reducing the amount of active water. Consequently, Zn||Zn symmetrical cells with CS‐TMC separator deliver long lifespan over 4500 cycles at a high current density of 40 mA cm −2 , surpassing most reported cellulose‐based separators. Moreover, the CS‐TMC separator can also protect vanadium oxide cathode from dissolution, which can render 270 mAh g −1 at 10 A g −1 with 98.2% capacity retention after 10 000 cycles, highlighting the promising potential of the tandem chemistry design for cellulose separator in practical applications.