Insight into the Ionic Transport of Solid Polymer Electrolytes in Polyether and Polyester Blends

Solid polymer electrolytes (SPEs) have been playing a crucial role in the development of a high-performance solid-state lithium metal battery. The safety and the easy tailoring of the polymers designate these materials as promising candidates to be implemented as electrolytes. Poly(ethylene oxide) (PEO) has been widely employed during the past four decades, but its inferior electrochemical stability against high-voltage cathode active materials strongly urges the search for alternative polymers. In recent years, several carbonyl-containing polymers have arisen as possible replacements for PEO, with poly(ε-caprolactone) (PCL) being one of the most representative. In this work, we combine molecular dynamics simulations and a range of experimental measurements to gain in-depth insights into the ionic transport in polyester-based SPEs. Specifically, the physicochemical properties and morphological behaviors of the blend SPEs comprising PEO and PCL including the two end members are comprehensively investigated. The results reveal that the preferential coordination between Li+ cation and ethylene oxide units and partial phase separation between PEO and PCL control the ionic transport in PEO and PCL blends. The present study is believed to inspire novel design strategies for improving the properties of SPEs and batteries made from them.