Hyperbranched PEO-Based Hyperstar Solid Polymer Electrolytes with Simultaneous Improvement of Ion Transport and Mechanical Strength

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) with nonflammability, shape flexibility, and high SPE/Li interfacial stability are poised to be an enabler for solid-state lithium batteries, but their application is restricted by low room-temperature ionic conductivity and poor mechanical strength at elevated temperatures. Herein, hyperstar polymers are synthesized with hyperbranched PEO serving as the star core and linear polystyrene (PS) serving as the arms. The hyperbranched topological structure suppresses crystallization and facilitates PEO segmental motion, and the steric hindrance for PEO segmental motion is tuned by controlling the average chain length of the branched PEO segments. The rigid PS arms entangle during phase separation and form mechanically strong physical cross-links. An all-solid-state Li/LiFePO4 battery based on our hyperstar SPE delivers a stable capacity of 142 mAh g–1 at 0.2C owing to fast ion transport and stable electrolyte/electrode interfaces.