Epoxy-Functional Hyperbranched Polysiloxane Hybridized Water-Synthesized Polyimide Dielectrics for High-Temperature Capacitive Energy Storage.

Water-synthesized polymer dielectrics with reliable high-temperature energy storage capability are highly desirable for sustainable power electronic applications. Herein, a topology-engineered organic-inorganic hybrid dielectric is constructed by integrating epoxy-functionalized hyperbranched polysiloxane (EPHPSi) into water-synthesized fluorinated polyimide (W-PI). During thermal imidization, the epoxy groups of EPHPSi undergo ring-opening reactions with the polymer matrix, forming a robust cross-linked hybrid network. The hyperbranched siloxane nanoarchitecture regulates molecular packing, suppresses segmental relaxation, and introduces additional charge-trapping sites, thereby helping to reduce charge transport and improve the dielectric performance under elevated temperatures. As a result, the optimized W-PIEPHPSi-10% film exhibits a high breakdown strength of 669 MV m-1 at room temperature and retains 630 MV m-1 at 200°C, with a relatively narrow Weibull distribution. Meanwhile, the composite film achieves a high discharge energy density of 8.75 J cm-3 with a charge-discharge efficiency of 94.7% at room temperature. More importantly, an ultrahigh discharge energy density of 8.52 J cm-3 is maintained at 200°C under 600 MV m-1. This work provides a sustainable strategy for developing environmentally friendly polymer dielectrics for high-temperature capacitive energy storage.