Biomass‐Derived Polyanionic Interface Modulates the Electrical Double Layer to Achieve Ultrareversible Zinc Metal Anodes

Abstract The widespread use of aqueous zinc‐ion batteries (AZIBs) is greatly limited by reduced cycle stability and shorter service life, mainly caused by the Zn dendrites growth and harmful side reactions. In this work, a scalable, polyanionic biomass‐derived interface is introduced to effectively regulate the ordered transport of zwitterionic species within the electrical double layer on the Zn anode. This interface effectively attracts Zn 2 ⁺ ions, and the high concentration of Zn 2 ⁺ at the interface helps delay ion depletion caused by fast kinetics. It also suppresses the tip effect and enables quick 3D diffusion of Zn 2 ⁺ ions. Additionally, repulsion of OH − and SO 4 2 − ions can effectively prevent side reactions on the zinc anode surface. With these synergistic effects, the C‐CNT@Zn anode maintained stable cycling for over 5000 h in a symmetrical cell at 2 mA cm −2 , 2 mAh cm −2 . At a current density of 5 mA cm −2 , the coulombic efficiency of the Zn//Cu asymmetric cell reached 99.81%, showing excellent reversibility. Importantly, the assembled C‐CNT@Zn//V 2 O 4 full cell demonstrated outstanding long‐term cycling stability. This work offers a simple and effective way to build a stable protective layer, advancing the development of highly reversible AZIBs.