Multilayer Structure Design And Energy Storage Performance Of BOPP-Based Composite Films

Polymer film capacitors have significant applications in electrical engineering and power electronics,including new energy vehicle electric drive systems,high-voltage transmission converter stations,and pulsed power supplies for electromagnetic weapons.Biaxially Oriented Polypropylene(BOPP)is the most critical dielectric material in capacitors and determines the capacity and performance of capacitors.However,the conductivity loss of the BOPP film increases sharply under high temperature conditions,leading to a prominent problem of device temperature rise and capacitance degradation,requiring its permitted temperature to be 105℃.Meanwhile,the low relative permittivity of BOPP films leads to low energy storage density.The thesis aims to reduce the high-temperature conductivity loss of BOPP films and improve the relative permittivity,which provides an important reference for the development of high-performance capacitive film materials.In this thesis,BOPP is studied to improve the high temperature energy storage performance of the film by constructing a multilayer structure.The magnetron sputtering technique was used to grow inorganic functional layers on the surface of BOPP films to improve the interfacial potential barrier between metal electrodes and capacitive films,limiting charge injection and reducing high-temperature conductivity losses.Mechanisms and laws influencing the electrical characteristics of inorganic functional layers to BOPP film microstructure and high temperature energy storage performance are systematically studied.It was found that using an inorganic functional layer with wide band gap,medium relative permittivity and proper thickness significantly suppressed charge injection and enhanced the high-temperature energy storage performance of the BOPP composite films.The discharge energy density of the AlN-BOPP-AlN composite film reaches 1.5 J/cm~3 at125℃and the charge/discharge efficiency of 90%.To improve the relative permittivity of BOPP films,Polyvinylidene Fluoride(PVDF)which has high dielectric constant,is laminated and hot-pressed with BOPP to construct multilayer composite films(BP-xL,where x is the number of layers)in this thesis.The effect laws of PVDF film thickness and number of layers on the microstructure and energy storage performance of composite films are systematically studied.The study shows that the best energy storage performance of the composite film is achieved when the number of layers is 7.The discharge energy density of BP-7L composite film is 0.99 J/cm~3 at 125℃and 200 MV/m,which is 106.3%higher than that of BOPP film,and the charge/discharge efficiency is 79.63%.