Lithium-ion batteries are a common choice for portable electronic devices that require compact, efficient and long-life cycle secondary batteries. However, the dangers of liquid electrolytes used in lithium-ion batteries are well known and include leaks, erosion and toxicity. Improving the electrolytes in lithium-ion batteries entails fixing safety concerns, refining the electrical, mechanical and thermal properties, and creating cost-effective and environmentally friendly production methods. Solid polymer electrolytes (SPEs) act as physical separators while also allowing for the flow of ions and are liquid-free, thereby mitigating safety concerns. In this work, bio-based monomers derived from lignocellulosics were explored as monomers in the development of polymer electrolytes. Employing aromatic compounds, such as those derived from lignin, are known to increase the mechanical and thermal stability of resulting polymer networks. Additionally, photo-initiated thiol-ene polymerizations was explored as a green polymerization method as it is are fast, easy and relatively low-energy, making the process industrially desirable. The SPEs were formed by mixing solid lithium salt in a resin consisting of a bio-based functionalized monomer, ETTMP 1300, and a photo-initiator. The free radical-step growth thiol-ene polymerization was performed in a UV curing oven at 365 nm. The thermomechanical properties of the polymers were tested using TGA, DSC and DMA. The room temperature conductivities of the SPEs were determined to be on the order of 10-4 S cm-1. The relationship between Tg and conductivity was studied by changing the concentration of lithium salt in the resin. It was found that as concentration of lithium salt increased, the Tg of the SPEs increased. Conductivity also increased up to a certain point after which the segmental motion of the polymer chains was too limited and conductivity values subsequently dropped. In addition to conductivity, cationic flow was analyzed by determination of the lithium-ion transference numbers. The SPEs had lithium-ion transference values in the average range for such systems, with the highest at 0.38. The SPEs with the highest transference values had the lowest observed ion aggregations, as determined via FTIR, and the lowest host polymer polarities, as determined by dielectric constants. This study shows that there are many factors that affect current flow and ion transport in polymer electrolyte materials.

Conductivity and ion transport in lignin-derived solid polymer electrolytes

2019 Spring National Meeting

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