Selective Lithium Ion Transport in Mixed Electron- and Ion- Conducting Radical Polymer-Based Blends

Interest in polymers capable of mixed electron and ion conduction has increased in recent years due to their use in a variety of organic electronic devices. Radical polymers have received less attention than conjugated polymers in this field despite their promise as solid-state charge conductors. To address this, we developed a radical polymer-based system by blending a radical polymer, poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO) with poly[poly(ethylene oxide) methyl ether methacrylate)] (PPEGMA) and lithium hexafluorophosphate. Consistent with previous reports, PPEGMA had a room temperature ionic conductivity of 10^-4 S cm^-1; one of the highest polymer-based lithium-ion conduction values reported. Additionally, PTEO had an ionic conductivity of 10^-6 S cm^-1. A blend of the two polymers at equal weight ratios had a room temperature ionic conductivity similar to PPEGMA and electronic conductivity similar to PTEO. This was due to the clear microscale phase separation between the two polymers, which yielded pathways of distinct ion and charge conduction (i.e., through PPEGMA and PTEO domains respectively) with Li⁺ mostly incorporating in the PPEGMA domains. This work elucidates the impact phase separation has on mixed conduction in radical polymer-based blends.