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In this paper, a novel deashing method is proposed to prepare polypropylene (PP) materials with different ash contents (60–500 ppm). Effects of the ash on dielectric and energy storage characteristics of PP in polymer film capacitors are studied. The experimental results reveal that a low content of ash will help to improve the dielectric properties. Compared to the sample with 500 ppm of ash content, the PP film with 60 ppm ash possesses a higher breakdown strength (587.1 kV/mm), a lower DC conductivity (1.12 ×10−14 S/m) and dielectric loss factor (3 ×10−4). In addition, the energy storage property also shows a remarkabe improvement, the discharge energy density can be up to 3.22 J/cm3 and the discharge efficiency remains at a high level. After the purification, the decline of the ash content in PP prevents the local electric field distortion and enhances the breakdown strength, which is beneficial for the improvement of the discharge energy density. Meanwhile, the reduction in the number of carriers ionized by the ash weakens the transport behavior and reduces the conductivity. It is concluded that the PP with high purity shows a great potential in polymer film capacitors. [ABSTRACT FROM AUTHOR]

In this paper, an advanced surface-grafting method is reported to improve the high-temperature performance of biaxially oriented polypropylene (BOPP) membranes. The leakage conductivity of the surface-grafted films decreases by 98% at 85 °C. The decline in the leakage loss contributes to the 99% charge-efficiency at 85 °C. The dielectric constant increases by 7%. The DC breakdown strength grows by 43% at 85 °C. The maximum energy storage density goes up from 1.45 to 2.77 J/cm3 at 85 °C. The surface-grafted BOPP film exhibits outstanding energy density and charge-discharge efficiency characteristics. This research provides a theoretical reference for improving the performance of capacitor film based on surface modification. [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of the nano Polyhedral oligomericsilsesquioxanes (POSS) with three similar molecular structures on the thermal and electrical properties of polypropylene (PP) films, aiming to propose a comprehensive modification method. After doping with micro amount of nano POSS, the crystallinity and regularity of films are elevated. Correspondingly, PP with optimized microstructure has the lowest conductivity, due to the interaction between the nanoparticles and the matrix, as well as the strong binding force of the crystal region to the carriers. The loss of the sample is restricted, especially in the low frequency region, since the combined effect of polarization and conduction. The DC breakdown strength of the modified PP is higher than that of the PP, with an increase of above 20% at 25–85 °C. Based on quantum chemical calculations, the energy level distributions are analyzed. By selecting appropriate additives, deep trap sites can be introduced to catch carriers, preventing the breaks of polymer molecular chains. This modification of PP films shows huge potential in the improvement of dielectric properties in the field of DC capacitors. [ABSTRACT FROM AUTHOR]

In this article, a surface modification method is proposed for improving the breakdown strength and the energy density of polypropylene (PP) films for power capacitors based on chemical vapor deposition (CVD). The results indicate that after 5% thickness deposition, the leakage conductivity of the composite films decreases by 77% at 30 °C and declines by 96.2% at 85 °C compared with the pristine PP samples. The dielectric constant is increased from 2.19 to 2.34 at 1 kHz. The dielectric loss decreases from 0.0425 to 0.0047. The dc breakdown strength is enhanced from 553.7 to 658.5 kV/mm, and the energy density is improved by 40%–50%. The parylene deposition successfully increases the withstand voltage and the energy density by inhibiting charge injection. The results provide a reference for optimizing the performance of capacitor by interface modification. [ABSTRACT FROM AUTHOR]

This article presents novel all-ceramic composite films used as a screen-printed capacitors on polymer surface and their characterization at 45-MHz to 10-GHz frequency range. All-ceramic composite paste is based on lithium molybdate (Li2MoO4), barium titanate (BaTiO3), and water manufactured by the room temperature fabrication (RTF) method. For the determination of the permittivity and the loss tangent of the materials, ceramic thick films are printed on the top of an interdigital-shaped microwave capacitors using pastes with 0, 10, and 20 vol.% of BaTiO3 filler in Li2MoO4 followed by a drying process at 120 °C. The electrical properties of the capacitors, capacitance, and quality value are derived from measured ${S}$ -parameter results, whereas the electrical properties of the ceramic thick-film materials, real, and imaginary values of permittivity are derived from the measured results through computer simulations. The electrical properties of the ceramic material, such as moderate permittivity and moderately low-loss tangent, could be adjusted by changing the volume fraction of the BaTiO3 filler to match the demands of different areas of applications. The obtained results are verified with five samples of each ceramic composition. The results show the capacitance values of 0.30 pF for an uncoated capacitor and 0.55, 0.67, and 0.95 pF with coatings of Li2MoO4 with 0, 10, and 20 vol.% of BaTiO3 composites, respectively, at 2.5-GHz frequency. The calculated relative permittivity ($\varepsilon _{r}$) values for the same materials are 3.70, 5.23, and 6.43, and loss tangent values are 0.035, 0.027, and 0.036 at 2.5 GHz. These novel all-ceramic capacitor composite materials are applicable for the RF components used in telecommunication applications in the frequency range of 45 MHz–10 GHz, thus widening the technology roadmap in terms of material choices for different applications, especially high thermal resistant materials. [ABSTRACT FROM AUTHOR]

Temperature rise is one of the major causes for all-film pulsed capacitor (AFPC) failure under high repetitive high-voltage pulse discharge operations. To study the thermal characteristics, a thermal simulation model is established. In this model, the actual operation conditions of capacitors are applied. The practical internal structure and heat production transfer of the AFPC are considered. The validation of the model is proved by the simulation and the experimental results. Based on the finite element method (FEM), the overall temperature field distribution of the AFPC, and the mathematical model between discharge voltage, frequency and temperature rise can be calculated. This model is capable of evaluating the temperature rise characteristics of an AFPC in repetitive high-voltage pulse discharge and can provide certain instructive suggestions for the safe operation and the optimal design of AFPC. [ABSTRACT FROM AUTHOR]