Viability of Low Molecular Weight Lignin in Developing Thiol-Ene Polymer Electrolytes with Balanced Thermomechanical and Conductive Properties

Polymer electrolytes with high aromatic content are prepared through thiol-ene polymerization with functionalized, low molecular weight fractions of softwood pine Kraft lignin, and wheat straw/Sarkanda grass soda lignin. Differing solubility, functionality, and aromatic content of the lignin fractions vary the glass transition temperatures of the resulting polymers and the suitability for electrolyte applications. The softwood pine Kraft lignin is used as a precursor for a gel polymer electrolyte (GPE) with room temperature conductivity of 72 × 10^–7 S cm^–1, while the wheat straw/Sarkanda grass soda lignin is utilized in solid polymer electrolytes (SPEs) with room temperature conductivity values in the range of 5 × 10^–5– 7 × 10^–5 S cm^–1. The lignin-based GPE displays similar conductivity but improved thermal stability to a comparable, recently reported GPE containing an allylated, monophenolic, lignin-derived, vanillin-derived monomer. The lignin-based SPEs exhibit excellent cationic transport with ion transference values up to 0.90. The promising conductivity and ion transference results reveal the potential for use of functionalized, low molecular weight wheat straw/Sarkanda grass soda lignin in SPE applications as a way to improve thermal stability, electrochemical performance, and incorporate an abundant, sustainable resource in a high performance application.