Developing Polymer Electrolytes with Balanced Thermomechanical and Conductive Properties through Incorporation of High Aromatic Content

Abstract

Thermomechanical and electrochemical properties of thiol-ene polymers with high aromatic content afforded by lignocellulosic biomass were evaluated to explore feasibility and advantages in polymer electrolyte applications. Polymer electrolytes have the potential to mitigate stability and safety concerns accompanying incumbent liquid electrolyte systems in lithium-ion batteries. The thermal properties associated with low glass transition temperature (T g) polymers are thought to improve contact with electrodes and ionic flow through the membranes compared to other liquid electrolyte alternatives such as solid electrolytes. Additionally, the high aromatic content of the lignin macromolecule can impart mechanical and thermal stability, making it attractive for use in applications that require robust polymers.Low molecular weight fractions of wheat straw/Sarkanda grass soda lignin were functionalized and prepared through thiol-ene polymerization into polymer electrolytes. In combination with previous work, it was determined that differing solubility, functionality, and aromatic content of lignin fractions vary the glass transition temperatures of the resulting polymers and the suitability for electrolyte applications. The wheat straw/Sarkanda grass soda lignin utilized in solid polymer electrolytes (SPEs) displayed room temperature conductivity values in the range of 5 – 7 x 10-5 S cm-1. The lignin-based SPEs exhibited excellent cationic transport with ion transference values up to 0.90. Voltage stability and compatibility with electrode materials were also explored. 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.