A Bio‑Chemical Synergy Strategy: Mycelium Separator Breaks the Coupled Degradation Cycle in Aqueous Zn‑I ₂ Batteries

ABSTRACT As global demand for safe, sustainable, and low‐cost energy storage grows, aqueous zinc‐iodine batteries (AZIBs) emerge as promising candidates. However, their practical application is hindered by complex side reactions, including polyiodide shuttling, the hydrogen evolution reaction (HER), and electrolyte acidification. Conventional glass fiber separators fail to mitigate these interfacial issues and pose significant environmental burdens due to high carbon emissions and non‐degradability. This study introduces a bio‐based separator derived from Aspergillus niger mycelium. Its 3D interconnected network and polar‐rich surface (‐OH, ‐NH 2 ) facilitate chemical polyiodide anchoring, water adsorption, and local pH buffering. Operating through a “water‐confining‐promoted‐desolvation” mechanism, the separator suppresses the shuttle effect and HER while stabilizing zinc deposition. AZIBs using this separator exhibit excellent capacity retention over 10 000 cycles at 1.0 A g −1 , achieving an energy density of 208.77 Wh kg −1 and maintaining 153.32 mAh g −1 at −25°C. Life‐cycle assessment shows a 99.4% reduction in carbon emissions compared to glass fiber, with full biodegradability within 50 days. This work offers a sustainable paradigm for high‐performance separators, advancing AZIBs toward environmental compatibility.