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 mu A 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 mu A 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.

Automated summary

Electrochemical energy storage technologies can contribute to achieving a carbon-neutral society by 2050. Aqueous zinc-ion chemistries, using environmentally benign and bio-based materials, show promise in addressing climate change and supply chain issues. This study explores the use of lignin and chitosan to create gel polymer electrolytes for zinc-ion chemistries. The resulting electrolytes demonstrate good mechanical properties, high ionic conductivity, and electrochemical stability, enabling stable cycling of zinc anodes. Compared to traditional configurations, these gel polymer electrolytes exhibit improved performance in terms of short-circuit resistance and Coulombic efficiency. This research highlights the potential of underutilized biomass and marine waste as electrolytes for sustainable energy storage beyond lithium-ion batteries.