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In order to satisfy the miniaturization trends of power electronic devices and safe operation in harsh environments, high-temperature dielectric polymers with excellent energy density and great reliability are desired in advanced electronic and power systems as electrostatic capacitors. Herein, the all-polymer dielectric composite films, consisting of ferroelectric polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as filler and linear polymer polyimide (PI) as matrix, were fabricated by in situ polymerization method for electrostatic energy storage scenarios. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results indicated that the P(VDF-HFP) was successfully compounded into the PI matrix. The dielectric permittivity of PI/P(VDF-HFP) energy storage composites was enhanced, while the breakdown strength and electrical resistivity values were wrecked slightly with enhancive mass fraction of P(VDF-HFP). Consequently, the discharged energy density (U d) of PI-10, PI-20 and PI-30 were 2.60, 2.90, and 3.16 J/cm3 at 30 ℃ and 400 MV/m, respectively, which were 1.05, 1.17 and 1.27 times than those of neat PI film (2.48 J/cm3). Notably, an interesting phenomenon was observed that the charge-discharge efficiency (η) of all-organic composites was dramatically improved situated in high-temperature conditions. When the mass ratio of P(VDF-HFP) to PI was 1:4, the corresponding U d and η of PI-20 could be significantly improved to 2.25 J/cm3 and 76.9% at 382 MV/m and 150 ℃, which were 6.7 and 10.5 times than those of neat PI film (0.336 J/cm3 and 7.3%) at 300 MV/m, respectively. Impressively, PI-30 film delivers an enhanced U d of 1.81 J/cm3 and η of 71% at 200 ℃ and 308 MV/m. The significant improvement in the efficiency of composites under high-temperature environment is attributed to the suppression of space charges, which was verified by the TSDC results. In addition, the all-polymer composites exhibited outstanding cycling stability under harsh conditions of high temperature and high electric field. Our fabricated PI/P(VDF-HFP) composite films present potential energy storage applications in the high temperature environments with demand for flexible dielectric materials with upgraded permittivity, excellent energy density as well as reliable cycling stability. [Display omitted] • All-organic composites with PI matrix and P(VDF-HFP) filler are proposed to enhance energy storage properties. • The optimized PI based composite exhibits excellent energy density of 2.25 J/cm3 and efficiency of 76.9% at 150 ℃. • The all-organic composites show outstanding cycling stability under harsh conditions. [ABSTRACT FROM AUTHOR]

With the renewable energy application fields of film capacitors gradually expanding, mining film capacitors' data is an important issue. When the aging mechanism and environment are unfamiliar, it will be hard to extract the capacitance's variation law and predict its changes. At the same time, the parallel operation of film capacitor components also brings practical needs and data basis for collaborative prediction. In this work, the capacitance of five film capacitors at room temperature and humidity for 70 days was measured and the characteristics of capacitance variation were analyzed. Then, the capacitance law extraction, single prediction, and collaborative prediction methods for film capacitors were proposed based on the smoothing splines theory. Finally, the effectiveness and application potential of the single prediction and collaborative prediction methods were verified by actual data. The performance of the single prediction and collaborative prediction methods is evaluated by error analysis. The single prediction and collaborative prediction methods proposed in this work can also provide a reference for the prediction and evaluation of other parameters like equivalent series resistance of film capacitors, and help to effectively and accurately explore the aging mechanism. • We measured the capacitance for 70 days at room temperature and humidity and analyzed the characteristics. • Based on smooth splines theory, the law extraction, single prediction, and collaborative prediction methods were constructed. • This work will provide a reference for predicting and evaluating other parameter such as the equivalent series resistance of film capacitors, helping to monitor the state and explore the aging mechanism effectively and accurately. [ABSTRACT FROM AUTHOR]