Lignin-Chitosan Gel Polymer Electrolytes for Stable Zn Electrodeposition

Electrochemical energy storage technologies offer means to transition toward a decarbonized society and carbon neutrality by 2050. Compared to conventional lithium-ion batteries, aqueous zinc-ion chemistries do not require scarce materials or toxic and flammable organic-based electrolytes to function, making them favorable contenders in the scenario of intensifying climate change and supply chain crisis. However, environmentally benign and bio-based materials are needed to substitute fossil-based battery materials. Accordingly, this work taps into the possibilities of lignin together with chitosan to form gel polymer electrolytes (GPEs) for zinc-ion chemistries. A simple fabrication process enabling free-standing sodium lignosulfonate-chitosan and micellar lignosulfonate-kraft lignin-chitosan GPEs with diameters exceeding 80 mm is developed. The GPEs combine tensile strength with ductility, reaching Young’s moduli of 55 ± 4 to 940 ± 63 MPa and elongations at break of 14.1 ± 0.2 to 43.9 ± 21.1%. Competitive ionic conductivities ranging from 3.8 to 18.6 mS cm^-1 and electrochemical stability windows of up to +2.2 V vs Zn²⁺/Zn were observed. Given the improved interfacial adhesion of the GPEs with metallic Zn promoted by the anionic groups of the lignosulfonate, a stable cycling of the Zn anode is obtained. As a result, GPEs can operate at 5000 μA cm^-2 with no short-circuit and Coulombic efficiencies above 99.7%, outperforming conventional separator-liquid electrolyte configurations such as the glass microfiber separator soaked into 2 M ZnSO₄ aqueous electrolyte, which short-circuits after 100 μA cm^-2. This work demonstrates the potential of underutilized biorefinery side-streams and marine waste as electrolytes in the battery field, opening new alternatives in the sustainable energy storage landscape beyond LIBs.