Hyperbranched dielectric polymer networks exhibiting giant energy storage density at 250 °C

Harsh-environment requirements of electrical and electronic systems demand advanced dielectrics with high energy storage density at elevated temperatures. Heat-resistant polymers are usually designed with densely packed molecular chains to maintain structural integrity. Unfortunately, the narrowed inter-chain spacing causes severe charge transfer under high electro-thermal fields, prohibiting capacitive energy storage beyond 200 °C. Here we report hyperbranched dielectric polymer networks as a solution to the persistent challenge. The hyperbranched topological junctions not only transform the linear polymer chains into a robust network to tolerate thermal stress, but also expand the inter-chain spacing to inhibit charge transfer. Results suggest that the hyperbranched networks exhibit suppressed secondary chain relaxation alongside expanded free volume. Moreover, the customizable chemical structure of hyperbranched centers renders this method general to capacitive polymer design. The hyperbranched polymer networks exhibit an exceptionally high discharged energy density of 4.9 J/cm3 above 90% efficiency at 250 °C, surpassing the existing polymeric dielectrics. To overcome charge transfer and achieve efficient capacitive energy storage in dielectric polymers at thermal extremes, hyperbranched networks are designed to expand inter-chain spacing and suppress secondary relaxation, delivering 4.9 J/cm³ energy density with 90% efficiency at 250 °C.