Superior Stability Cellulose Composite Separators Enable High-Rate Zinc Ion Batteries with Ultralong Cycle Life

Aqueous zinc ion batteries (AZIBs) are preferred for safety and cost-effectiveness but encounter challenges like zinc dendrite growth and side reactions, reducing their lifespan. Herein, a composite separator (CSC) for AZIBs is prepared using carboxylate sisal fiber (CSF) and sulfonation cotton fiber (SCF), followed by cross-linking with citric acid (CA). The exceptional stability of CSC─including high mechanical strength, wide pH tolerance, and suppression of hydrogen evolution─combined with high zinc ion migration number (t_Zn²⁺ = 0.70), leads to its remarkable electrochemical performance. The cycle life of Zn//Zn batteries with CSC is over 6400 and 400 h at 5 mA cm^-2 and 20 mA cm^-2, respectively. A Zn//MnO₂ full battery exhibits 92.85% capacity retention after 10000 cycles at 5 A g^-1 (∼16C), significantly outperforming the widely used commercial separators in AZIBs like glass fiber (GF). This work presents a highly effective but simple separator design strategy to achieve long-cycling, high-rate AZIBs.