Improving Energy Storage Density of Biaxially Oriented Polypropylene Film by Quickly Repairing Surface Insulation Defects

Surface defects are the key challenges to the properties of insulation and energy storage for biaxially oriented polypropylene (BOPP) films, limiting the application of BOPP films in harsh environments such as high temperatures and strong electric fields. The industrial process is the main factor responsible for surface insulation defects. It is difficult to solve fundamentally in the short term. Therefore, surface insulation defects must be repaired by post-treatment. The post-treatment should be fast enough to accommodate the industrial demand for BOPP films. Here, a modified method for rapidly reconstructing the defective surface of a BOPP film by pressure spray is reported. It is found that the surface insulation defects of the BOPP film are covered by the modified layer, and the insulation and energy storage properties are significantly improved. The high-temperature breakdown field strength of the modified films increased by 28.3%. The discharge energy density at 120 °C is also significantly increased, up to 4.9 J/cm3. Notably, the modified film has self-healing properties after metallization. In addition, the high-temperature performance is significantly improved. The pyrolysis activation energy of the modified BOPP film is up to 1.1 eV, which is 54.9% higher than that of the unmodified BOPP film, which is 0.71 eV. Tensile strength and other mechanical properties are also well maintained. This modification strategy has the characteristics of fast, cheap, environmental protection, and easy availability of raw materials and opens up a novel way for practical modification schemes.