Constructing interfacial charge-transfer complexes to suppress charge injection and bulk transport for boosting high-temperature energy storage in cyclo-olefin copolymers

Developing high-performance polymer dielectrics is the core pathway to drive technological breakthroughs in high-power electrostatic energy storage capacitors. Cyclo-olefin Copolymer (COC) is recognized as an ideal high-temperature-resistant polymer dielectric material. However, the energy storage properties of COC is constrained by the exponential surge in conductive losses under extremes conditions. To address this problem, this study proposes a simple and efficient modification strategy aimed at enhancing dielectric properties and energy storage density of COC films at high-temperature. Through binary graft copolymerization to construct interfacial charge-transfer complexes, an energy barrier layer is constructed on the film surface while deep level surface charge traps are simultaneously introduced, dually suppressing charge injection behavior at electrode interfaces and bulk charge migration processes. The modified film exhibits a 96.96% reduction in leakage current density and a 34.7% increase in breakdown strength, reaching 5.41 × 10 − 10 A/cm 2 and 644.1 kV/mm at 125 ℃, respectively. Furthermore, the discharge energy density of the modified film significantly improves, achieving a 4.87 J/cm 3 at 125 ℃. After 50,000 charge-discharge cycles, both discharge energy density and charge-discharge efficiency maintain stable reliability. This study provides new insights for polymer interfacial structure design and establishes novel approaches for developing high-property polymer dielectric materials.