Mixed electron- and ion-conducting polymers have received considerable interest over the last few years due to their applicability in a variety of organic electronic devices. To achieve this mixed conduction, researchers tend to rely on copolymerizing or blending two polymers, where one conducts ions and the other conducts electrons. Despite their potential as solid-state charge conductors, radical polymers have received less attention than their conjugated counterparts. This work addresses this unmet opportunity by developing a blended radical polymer poly­(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO), poly­(poly­(ethylene oxide) methyl ether methacrylate) (PPEGMA), and lithium hexafluorophosphate system. PPEGMA, similar to previous publications, had one of the highest polymer-based room-temperature ionic conductivity of 10–4 S cm–1. In addition to conducting charges, 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 of 10–4 S cm–1 and an electronic conductivity of 10–2 S cm–1 similar to pristine PPEGMA and PTEO thin films, respectively. This similarity resulted from the formation of distinct pathways of ion (i.e., through PPEGMA domains) and electron (i.e., through PTEO domains) conduction due to microscale phase separation between the two polymers with the lithium ions mainly incorporating in the PPEGMA domains. With the addition of lithium salt, the electronic conductivity of the blend increased by 1.7 times. However, at [Li+]/[O] ratios higher than 0.08, the electronic conductivity suffered due to poor film quality. Ultimately, this effort establishes a template for determining mixed conduction in radical polymer-based blends and for developing the next generation of simultaneous conduction devices.

Hybrid electrolyte materials comprising polymer-ionic salt matrixes embedded with garnet particles constitute a promising class of materials for the realization of all-solid-state batteries. In addition to providing solutions to the safety issues inherent to current liquid electrolytes, hybrid polymer electrolytes offer advantages over other solid-state electrolytes. This is because their functional properties such as ionic conductivity, electrochemical stability, and mechanical and thermal properties can be tailored to a particular application by independently optimizing the properties of the constituent materials. This independent optimization permits the rational design of solid-state electrolytes, thereby solving the current bottlenecks that prevent their practical implementation into battery devices. This Mini-Review starts with a survey of solid-state electrolytes, focusing on their materials and ion transport limitations. Next, we summarize the current understanding of transport mechanisms in composite polymer electrolytes (CPEs) with the purpose of identifying materials' solutions for further improving their properties. The overall goal of the Mini-Review is to foster heightened research interest in these hybrid structures to rapidly advance development of future all-solid-state battery devices.

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