Ion Conduction in Poly(ethylene oxide) Ionically Assembled Complexes

We report on relationships between conductivity and materials properties in novel complexes comprised of positively and negatively charged PEO-containing ionomers, where oppositely charged poly(ethylene oxide) (PEO) ionomers were blended with lithium salt to form a new class of PEO-based ionically associated complexes. The complexes were evaluated as potential solid polymer electrolytes using differential scanning calorimetry, impedance spectroscopy, tensile testing, and infrared spectroscopy. Under all salt concentrations investigated, the PEO complexes were amorphous and their glass transition temperatures increased with salt concentration. The glass transition temperature of the complex was elevated relative to the homopolymers, indicating a strong electrostatic interaction between the oppositely charged PEO ionomers. The maximum conductivity was 3.7 × 10–6 S cm–1 at 105 °C for an EO:Li+ ratio of 40:1. As salt concentration further increased, ionic conductivity decreased due to an increase in glass transition temperature of the salt-doped complex and a decrease in free salt ions. These complexes present a new concept to control glass transition temperature, conductivity, and segmental relaxation in solid-state polymer electrolytes while maintaining robust mechanical properties compared to homopolymer PEO.