Aqueous Zn-ion chemistry has emerged as a promising energy storage technology yet suffers from severe irreversibility due to poor management of water and Zn²⁺ flows, leading to dendrite formation, parasitic reactions, and structural collapse of many cathode materials. To address these challenges, we turned to eggshell membranes (ESM), which have evolved over millions of years to regulate water and Ca²⁺ flows, ensuring the formation of well-defined hard shells and protecting chicken embryos during incubation. We discovered ESM, especially after denaturation, can effectively retard water, regulate Zn²⁺ flow, and self-concentrate Zn²⁺ at the electrode interfaces, thus achieving dendrite-free Zn plating/striping at a coulombic efficiency of ∼99.8% over 500 cycles, steady charge/discharge beyond a half year, and capacity retention of 90.1% over 10 000 cycles for Zn–V full cells. To demonstrate scalability, we fabricated prototyped ESM-based papers, showing dual-electrode protection capability and long-term stability. This work also inspires bionic structures in batteries and beyond.