Functionalized Separator with Integrated Mass Transfer Selectivity and Kinetics Regulation toward Durable Zn Anodes

The limited durability of Zn anodes in aqueous zinc-ion batteries (AZIBs) can largely be attributed to disordered ion transport and sluggish kinetics. In this work, a functional separator comprising bacterial cellulose functionalized with boehmite (BM/BC) is developed to regulate the ion flux, enhancing both the selectivity and kinetics of Zn²⁺ transport. The BM/BC separator leverages strong coordination between its polar surface functional groups and electrolyte species to effectively anchor H₂O molecules and SO₄^2- anions. This anchoring effect facilitates Zn²⁺ desolvation and selective migration, yielding an exceptional Zn²⁺ transference number of 0.81 and significant suppression of interfacial side reactions. Furthermore, the nucleophilic property of boehmite mitigates the strong adsorption of Zn²⁺ by the cellulose chains, thereby conferring the BM/BC interfaces with low Zn²⁺ diffusion barriers, which can accelerate Zn²⁺ transport and homogenize the Zn²⁺ flux. Consequently, the BM/BC separator effectively suppresses interfacial degradation of the Zn anode, as collectively demonstrated by the extended lifespan (>2900 h) in Zn||Zn symmetric batteries, stable cycling (>1000 cycles) in Zn||MnO₂ full batteries, and robust performance in pouch configurations. This work provides a feasible strategy and fundamental insights for the design of advanced separators for high-performance AZIBs.