Wide-bandgap fluorides/polyimide composites with enhanced energy storage properties at high temperatures

In advanced electronics and electrical power systems, polymer dielectric capacitors are favored for their high power density and great reliability. However, the low energy density at high temperatures constrains their use in emerging applications. To address this vital issue, herein, a novel calcium fluoride (CaF2) nanoparticle with a wide bandgap (∼12.1 eV) and moderate permittivity (∼10.0) is prepared by a simple direct precipitation method and then introduced into the polyimide (PI) matrix. The incorporation of the CaF2 nanoparticles increases the permittivity and reduces conduction loss simultaneously. Consequently, at 150 ℃, the PI film with 3 vol% CaF2 exhibits enhanced discharged energy density and breakdown field of 2.68 J cm−3 and 455.4 MV m−1, respectively. Besides, the composite shows a higher power density of 0.36 MW cm−3 and a faster discharge speed of 2.09 μs at 150 ℃ than that 2.93 μs of biaxially oriented polypropylene (BOPP) measured at 85 ℃. Notably, CaF2 nanofiller, as a deep trap, captures injected charges and alleviates the local electric distortion, as revealed by finite element simulation and thermally stimulated discharge current (TSDC) measurement. This work proposes a novel fluoride nanofiller to rationalize the energy storage improvement of high-temperature composites with potential wide application.