Thermally Robust Piezoelectric KNN/Polyimide Separator for Regulating Lithium Deposition in Lithium Metal Batteries

ABSTRACT Lithium‐metal batteries offer exceptionally high theoretical energy density but are hindered by dendrite‐induced short circuits and the limited thermal stability of conventional separators. Here, we report a thermally robust piezoelectric composite separator composed of highly fluorinated polyimide and potassium sodium niobate (KNN), fabricated through an electrospinning/imidization strategy. Molecular dipole engineering, preferential through‐thickness polarization, and ceramic‐polymer electromechanical coupling collectively enable regulation of the local interfacial electric field, homogenized Li + flux, and suppressed lithium dendrite growth during cycling. Meanwhile, the rigid polyimide framework endows the separator with excellent thermal tolerance and structural integrity at elevated temperatures. Consequently, LiFePO 4 ||Li cells retain 88.5% of their initial capacity after 1900 cycles at 2 C. This work demonstrates an electromechanically active separator that integrates intrinsic thermal stability with interfacial regulation, providing a potential strategy for improving the durability of lithium‐metal batteries.