Confining Hyperbranched Star Poly(ethylene oxide)-Based Polymer into a 3D Interpenetrating Network for a High-Performance All-Solid-State Polymer Electrolyte

The original poly(ethylene oxide)-based polymer electrolytes normally show low ionic conductivity and inferior mechanical property, which greatly restrict their practical application in all-solid-state lithium-ion batteries (LIBs). In this work, a hyperbranched star polymer with poly(ethylene glycol) methyl ether methacrylate flexible chain segments is embedded into a three-dimensional (3D) interpenetrating cross-linking network created by the rapid one-step UV-derived photopolymerization of the cross-linker (ethoxylated trimethylolpropane triacrylate) in the presence of lithium salt. The rigid 3D network framework provides the polymer electrolyte with not only enhanced mechanical behavior, including film-forming and dendrite-inhibiting capabilities, but also nanoconfinement effects, which can speed up polymer chain segmental dynamics and reduce the crystallinity of the polymer. Depending on this unique rigid–flexible coupling network, the prepared solid polymer electrolyte shows enhanced ionic conductivity (6.8 × 10–5 S cm–1 at 50 °C), widened electrochemical stability window (5.1 V vs Li/Li+), and enough mechanical stability to suppress the growth of uneven Li dendrite (the Li symmetrical cells can operate steadily at both current densities of 0.05 and 0.1 mA cm–2 for 1000 h). Moreover, the assembled LiFePO4//Li cell also exhibited good cycle performance at 50 °C, making the hyperbranched star polymer electrolyte with a nanoconfined cross-linking structure to have potential application in high-safety and high-performance LIBs.