Tailoring codirectional Zn2+ pathways with biomaterials for advanced hydrogel electrolytes in High-Performance zinc metal batteries

Rechargeable Zinc metal batteries have emerged as promising next-generation energy storage devices, attributed to their affordability, abundant availability, and high safety profile. However, aqueous Zinc anodes encounter challenges such as dendrite formation and electrolyte corrosion. This study addresses these challenges by introducing a biopolymer-based hydrogel electrolyte. The electrolyte is a gelatin (G) hydrogel, enriched with x% β-cyclodextrin (D) grafted onto chitosan (C), designated as G(DC)x. It ensures efficient and uniform Zn2+ ion transport through ionic channels to the zinc anode surface, facilitating the formation of parallel, densely arrayed Zn platelets on the anode. This arrangement minimizes the electrolyte-zinc interface area, mitigating interfacial side reactions and preventing dead zinc formation. The enhanced gelatin network endows the hydrogel electrolyte with considerable mechanical strength (1.49 MPa) and extensive stretchability (400 %), effectively inhibiting dendrite growth and penetration. Additionally, the electrolyte demonstrates excellent ionic conductivity at 24.89 mS cm−1 and a notable transference number of 0.49, synergistically improving the zinc anode's cycling reversibility and lifespan. Symmetric cells using G(DC)2 electrolytes exhibit remarkable cycling stability, exceeding 1200 h at 1 mA cm−2/1 mA h cm−2. Zn-I2 full cells with G(DC)2 hydrogel electrolyte show superior cycling performance, maintaining over 300 cycles at 0.1 A g−1 while retaining excellent mechanical properties. The hydrogel electrolytes, degrading by 85 % in weight within 28 days, also exhibit excellent biodegradability in soil. Consequently, these renewable and biodegradable G(DC)x electrolytes present a viable alternative to liquid electrolytes, paving the way for safer, more stable, and eco-friendly zinc metal batteries.