Mitigating Interfacial Diluting and Space Charge Layer Effects in Diluted Electrolytes Through a Biomacromolecule Additive for Long‐Lifespan Aqueous Zn Metal Batteries

Abstract Aqueous Zn metal batteries (AZMBs) are promising candidates for large‐scale energy storage due to their intrinsic safety and low cost. Employing diluted electrolytes further enhances cost effectiveness, but also exacerbates interfacial challenges, including Zn 2 ⁺ concentration polarization and elevated free H 2 O content within the electric double layer (EDL), resulting in aggravated dendrite formation and hydrogen evolution reaction (HER). Herein, a biomacromolecule additive of sodium hyaluronate (HA) is introduced to reconfigure the EDL structure in a super‐diluted 0.3 m ZnSO 4 electrolyte, effectively alleviating interfacial diluting and space charge layer effects during Zn plating. HA molecules spontaneously assemble into a compact interfacial layer on Zn, where their hydrophilic functional groups immobilize free water, while the long‐chain anionic backbone forms a fixed negative charge network within the EDL. This dual functionality suppresses HER, mitigates space‐charge‐layer‐induced Zn 2 ⁺ polarization, and transforms the dilute interface into a self‐supplementing Zn 2 ⁺ reservoir. Consequently, Zn metal anodes achieve ultra‐stable cycling for over 5000 hours with a 95.1% reduction in salt usage, and Zn‐I 2 full cells sustain stable cycling over 10 000 cycles with neglectable capacity decay. This HA‐engineered interfacial strategy successfully simultaneously reduces cost while enhancing performance d, offering a new paradigm for safe, durable, and economically viable AZMBs.