Leveraging the anion-binding ability of lignin-inspired compounds to enhance Li+ transference number in solid polymer electrolytes

• Jenna Hess, Chemical Engineering, University of Delaware

• Thomas Epps, Chemical Engineering, University of Delaware

Lithium‑ion batteries (LiBs) are widely used in consumer electronic devices, electric vehicles, and national power grids. The electrolyte is a critical component in a LiB as it controls the transport of ions and impacts long-term battery stability. Commercial liquid electrolytes, in which a lithium salt is dissolved in flammable organic solvents, offer high conductivities to support practical applications, but their flammability poses a significant safety concern. Moreover, the unconstrained mobility of both cations and anions leads to low cationic current fractions (as represented by a low lithium transference number, <0.5). Solid polymer electrolytes (SPEs) can mitigate these concerns if the anion can be sufficiently immobilized to favor lithium‑ion conduction. Lignin-inspired molecules are particularly attractive options to constrain anion motion through ion–dipole interactions due to the presence of various functional groups (e.g., methoxy group). In this work, a lignin‑inspired compound was incorporated into a traditional polymer electrolyte material. The thermal and transport (ion conduction) properties of the polymer electrolyte were investigated by differential scanning calorimetry, alternating current impedance spectroscopy, and potentiostatic polarization. A four-fold higher lithium transference number was achieved in the composite electrolyte, which could portend significantly faster charging and discharging rates. Overall, this work demonstrates that lignin‑inspired compounds have a strong potential to enable safer, higher‑performance SPEs for LiBs.