Tuning Separator Chemistry: Improving Zn Anode Compatibility via Functionalized Chitin Nanofibers

ABSTRACT Aqueous zinc batteries (AZBs) face significant challenges due to the limited compatibility of Zn anodes with conventional separators, leading to dendrite growth, hydrogen evolution reaction (HER), and poor cycling stability. While separator design is crucial for optimizing battery performance, its potential remains underexplored. Commonly used glass fiber filters were not originally designed as battery separators, and their properties have a limited impact on these challenges. To address these limitations, nanochitin derived from waste shrimp shells was used to fabricate separators with varying concentrations of amine and carboxylic functional groups. This study investigates how the type and concentration of these groups influence separator properties and performance, inhibiting dendrite growth, local HER formation, and poor cycling stability. In a mild acidic electrolyte, the density of ammonium and carboxylic groups significantly affected water structure and ionic conductivity. Quasi‐elastic neutron scattering revealed that low‐functionalized chitin, particularly with only ammonium groups, promotes strongly bound water with restricted mobility, enhancing Zn plating and stripping kinetics. These separators exhibit exceptional Zn stability over 2000 h at 0.5 mA/cm 2 , maintaining low overpotentials and stable polarization. Full cells of ZnǁNaV 3 O 8 ·1.5H 2 O achieved over 2000 cycles at 2 A/g, demonstrating that simple, low‐functionalized nanochitin separators significantly improve AZB performance.