Significantly enhanced high-temperature capacitive energy storage in cyclic olefin copolymer dielectric films via ultraviolet irradiation

Polymer dielectrics with high operation temperature (similar to 150 degrees C) and excellent capacitive energy storage performance are vital for electric power systems and advanced electronic devices. Here, a very convenient and competitive strategy by preparing ultraviolet-irradiated cyclic olefin copolymer films is demonstrated to be effective in improving the energy storage performance at high temperatures. Compared with the unirradiated film, irradiated films exhibit a higher dielectric constant, higher breakdown strength and stronger mechanical properties as a result of the emergence of the carbonyl group and cross-linking network. Consequently, with a high efficiency above 95%, a superior discharged energy density of similar to 3.34 J cm(-3) is achieved at 150 degrees C, surpassing the current dielectric polymers and polymer nanocomposites. In particular, the energy storage performance remains highly reliable over 20 000 cycles under actual operating conditions (200 MV m(-1) at 150 degrees C) in hybrid electric vehicles. This research offers a valuable pathway to build high-energy-density polymer-based capacitor devices working under harsh environments.