Balanced enhancement of energy storage density and self-healing property of polypropylene-based metallised film

Metallised film capacitors (MFC) can operate under much higher voltage compared to the foil capacitor due to their self-healing (SH) properties, which caters to their application with high energy storage density requirement. Excellent results were achieved on the enhancement of the energy storage density of the dielectric material, whereas the SH properties of the modified material were less concerned. In the present study, the simultaneous improvement of the energy storage density and the SH properties were proposed, by constructing double-layer metallised films of polypropylene (PP) and polymethyl methacrylate (PMMA). The breakdown strength of the PP/PMMA first increased and then decreased with the rising thickness of the PMMA layer. The dielectric constant was also raised because of the introduced ester groups. The highest energy storage density of 5.93 J/cm3 was obtained, which was 62.47% higher than the neat PP, whereas the dielectric loss was maintained around 0.01. The SH properties of PP/PMMA were systematically evaluated, that the SH energy decreased with the increasing PMMA ratio, and the equivalent conductivity at the SH point of the PP/PMMA decreased to only 1% of the neat PP, which largely benefit the stability of the MFC with reduced temperature rise.