Dynamic Zn 2+ ‐Coordinating Oxygen Sites and Electric Field Modulation in Boron‐Integrated Cellulose Nanofiber Separators for Stable Zinc‐Ion Batteries

Abstract Aqueous zinc‐ion battery (AZIB) separators face critical challenges, including poor interfacial stability, dendrite formation, and limited ion transport kinetics, which significantly hinder their practical application. To address these issues, a boron‐integrated cellulose nanofiber (B/CNF) separator with an ultrathin thickness of 64 µm, fabricated via a scalable dispersion‐dehydration strategy, is developed. The incorporation of boron leads to the formation of B─O and B─O─C structures, in which oxygen atoms bearing lone electron pairs act as Lewis base sites capable of coordinating with Zn 2+ ions. This coordination enhances Zn 2+ transport across the separator and reduces the desolvation energy barrier. Concurrently, boron doping homogenizes the interfacial electric field, mitigating localized charge accumulation and dendrite growth. This synergistic mechanism significantly enhances ion mobility, improves cycling stability, and suppresses unwanted side reactions. As a result, Zn||Zn symmetric cells incorporating B/CNF separators demonstrate ultralong lifespans exceeding 1200 h at 1 mA cm −2 and 250 h at 30 mAh cm −2 (Depth of Discharge (DOD) = 51.24%), while Zn||VO 2 full cells retain 80.38% of their initial capacity after 500 cycles at 1 A g −1 . These results highlight the potential of B/CNF separators to overcome the limitations of conventional separators and advance the development of high‐performance AZIBs.