The poor ionic conductivity and interfacial instability severely limit the application of polyethylene oxide (PEO)-based polymer electrolytes. In this work, we introduce a multifunctional molecular modulated strategy using coumarin, which simultaneously boosts the ionic conductivity and interfacial stability of PEO-coumarin (PLC) membrane. Unlike conventional additives that diminish PEO's crystallinity, coumarin, with its higher Li