Enhanced High-Temperature Capacitive Energy Storage in Poly(tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride) via Chemical Grafting Modification

Polymer dielectric films with high energy storage density and efficiency are urgently needed for electric vehicles and power electronics. However, commercial dielectric films often suffer from increased energy loss and leakage current at elevated temperatures, which substantially compromises their energy density and efficiency. Herein, a C–F bond activation strategy was adopted to successfully graft poly(glycidyl methacrylate) (PGMA) segments onto the side chains of poly(tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride), significantly enhancing its high-temperature energy storage performance. The polar groups in PGMA enhance dipole polarization and thus dielectric constant of material. Meanwhile, epoxy groups form a crosslinked network during hot-pressing, which synergistically improves the mechanical modulus and breakdown strength. Combined density functional theory calculations and thermally stimulated depolarization current analysis confirm that PGMA acts as deep traps to effectively capture carriers, suppressing leakage current and enhancing insulation performance. As a result, the graft copolymer with 4.5 wt % PGMA achieves a discharge energy density of 10.0 J/cm³ and a charge-discharge efficiency of 82.1% at room temperature under 600 MV/m. Notably, it retains a discharge energy density of 8.1 J/cm³ and an efficiency of 71.9% at 125 °C and 500 MV/m. This work not only provides a theoretical foundation for designing high-temperature-resistant and high-energy-density polymer dielectrics but also proposes an innovative material modification approach.