γ‐Ray Irradiation Significantly Enhances Capacitive Energy Storage Performance of Polymer Dielectric Films

Polymer dielectric capacitors are fundamental in advanced electronics and power grids but suffer from low energy density, hindering miniaturization of compact electrical systems. It is shown that high‐energy and strong penetrating γ‐irradiation significantly enhances capacitive energy storage performance of polymer dielectrics. γ‐irradiated biaxially oriented polypropylene (BOPP) films exhibit an extraordinarily high energy density of 10.4 J cm−3 at 968 MV m−1 with an efficiency of 97.3%. In particular, an energy density of 4.06 J cm−3 with an ultrahigh efficiency of 98% is reliably maintained through 20 000 charge–discharge cycles under 600 MV m−1. At 125 °C, the γ‐irradiated BOPP film still delivers a high discharged energy density of 5.88 J cm−3 with an efficiency of 90% at 770 MV m−1. Substantial improvements are also achieved for γ‐irradiated cycloolefin copolymers at a high temperature of 150 °C, verifying the strategy generalizability. Experimental and theoretical analyses reveal that the excellent performance should be related to the γ‐irradiation induced polar functional groups with high electron affinity in the molecular chain, which offer deep energy traps to impede charge transport. This work provides a simple and generally applicable strategy for developing high‐performance polymer dielectrics. A universal strategy is proposed to improve dielectric energy storage performance of polymers by γ‐ray irradiation. Utilizing this strategy to the biaxially oriented polypropylene (BOPP), a record‐high energy density of 10.4 J cm−3 with >95% efficiency is achieved, surpassing commercial polymers, reported all‐organic polymers and PP‐based composites. Substantial improvements are also achieved for γ‐irradiated cycloolefin copolymer at 150 °C.