Modulating ion transport properties of PEO-based polymer electrolytes through end-group chemistry

The most widely investigated solid polymer electrolytes to dates are based on polyethylene oxide (PEO) owing to its low glass transition temperature and good solvating capability for wide variety of salts. Inherently poor mechanical stability of PEO has prompted various approaches to improve modulus of PEO-based polymers, mostly by linking hard polymer chains and/or incorporating inorganic fillers. This is to prevent dendrite formation at the electrolyte/electrode interfaces; however, it has been found that these approaches are intimately connected to the reduction of ionic conductivity of the resultant polymer electrolytes. In this study, we show a new methodology for improving ion transport properties and mechanical strength simultaneously by introducing various terminal groups in PEO-based polymers. Particularly, by modifying the chain-end with high dipole moment molecules, significant reduction in PEO crystallinity, noticeable increase in the dielectric constant of PEO, and enhancement of storage modulus of the polymers have been achieved. These positive aspects offer effective solvation of lithium salts and amplified intermolecular interactions, tied to improved lithium ion transport properties.