High temperature dielectric breakdown and energy storage properties of polyetherimide nanocomposites improved by hindering molecular motion

Abstract Polyetherimide (PEI) has excellent thermal and electrical properties, and is widely used as a dielectric material for high-temperature high-power film capacitors in power systems, new energy vehicles and other fields. However, as the operating temperature increases, the electrical conductivity increases and the breakdown strength decreases, reducing the energy storage density of capacitors significantly and limiting the practical applications. To clarify the influencing mechanism of high temperature on breakdown properties and energy storage performance of dielectrics, this paper establishes a charge transport and molecular displacement modulated (CTMD) breakdown model based on the expansion movement of molecular chain segments to investigate change regularity in charge transport and molecular chain motion of PEI nanocomposites (PNCs) at high temperatures. The results show that at high temperatures of 100°C, PEI PNCs with an appropriate nanoparticle content (3wt%) show a 5.35% reduction in maximum internal temperature, a 28.79% reduction in maximum molecular displacement and an 11.20% increase in breakdown strength compared to pure PEI. Nano-doping can effectively increase the difficulty of molecular segment motion, thereby reducing the excitation volume in which they provide energy for charge transport. Thus, charge transport is inhibited, current density is reduced and excess Joule heat is avoided. Eventually, high temperature dielectric breakdown and energy storage properties of PEI PNCs can be significantly improved.