Bifunctional Keratin Enables Highly Stable Zinc Anodes via Interfacial Nucleation Regulation

ABSTRACT Currently, various protein molecules are being applied to aqueous zinc‐ion batteries to enhance their cycle life. However, traditional proteins exhibit limited functionality, and due to their low content of zinc‐affinity groups, they struggle to form uniform and stable solid electrolyte interlayers. In this study, sulfonated modified keratin (SBKP) with enhanced zinc affinity was obtained through SBMA modification. SBKP self‐assembles into a SEI layer on the zinc foil surface. The sulfonic acid groups (─SO ₃ ^{2 −} ) in SBKP effectively regulate interfacial charge transfer through strong Lewis acid‐base interactions, enhancing nucleation driving forces and promoting rapid, uniform Zn ^{2 +} deposition. Furthermore, SBKP reconstructs the hydrogen‐bond network in the outer solvated shell layer, achieving a favorable balance between ion transport kinetics and corrosion resistance. Leveraging these properties, the SBKP@Zn symmetric cell demonstrates an exceptionally long cycle life of 3281 h at a current density of 1 mA cm ^{− 2} . In a full‐cell configuration with a MnO ₂ cathode, stable cycling performance is maintained even after 1000 cycles. This study proposes a scalable and effective interfacial engineering strategy for stabilizing zinc anodes, offering valuable insights for developing long‐lasting, high‐performance aqueous micro‐energy storage systems suitable for flexible electronic devices.