Effect of thermal shock on energy density of biaxially oriented polypropylene films for pulsed power capacitors

Abstract In this paper, thermal shock experiments are performed on the biaxially oriented polypropylene (BOPP) films, and the changes in dielectric and energy storage properties before and after the experiments are explored. The experimental results show that the films have reduced comprehensive performance with the thermal shock time and frequency increasing. After the thermal shock, both the permittivity and the dielectric loss increase slightly. And, the direct current (DC) conductivity has risen by 73.6%–714.2%. The lowest DC breakdown strength of film is 604.4 kV mm −1 , showing a 13.5% reduction compared to that of pristine film. In addition, energy storage performance has also deteriorated. The maximum discharge energy density decreased from 4.62 J cm −3 of pristine film to 3.26 J cm −3 of treated film. There is a decrease in charge and discharge efficiency under the same electric field. The metallization layer of the film receives less influence; the capacitance is reduced by only 0.37%. The causes and mechanisms of performance changes are analyzed and discussed. The disruption of molecular chains during thermal shock is the most important factor leading to the degradation of films. This paper provides a powerful perspective and reference for studying the performance degradation and failure of polymer dielectrics under extreme operating conditions.