Excellent energy storage performance in cross-linked polyimide dielectric with positively charged cross-linking points

Abstract

The conjugation effect of the benzene ring in the main chain of PI and the secondary relaxation of the polymer caused by the movement of local chain segments, the leakage current density and dielectric loss (tanδ) of the PI increase under high temperature, resulting in a decrease in discharge energy density (Ud) and charge-discharge efficiency (η). In order to satisfy the stable operation of polymer dielectric capacitors and enhance their energy storage performance in high-temperature environments, in this work, cross-linked PI (MPI) with cross-linked structure were prepared by using melamine (MA) as cross-linker. The Ud of MPI can reach 2.89 J/cm3 under 150 ℃ and 471.53 kV/mm when the MA content is 1.5 wt%. The cross-linked structure not only limits losses from polarization of the polymer molecular chains, but also restricts the thermal movement of the molecular chains at elevated temperatures, which improves the η. Additionally, the positively charged cross-linked points act as traps to capture carriers, suppressing carrier conduction at both normal and high temperatures, thereby significantly increasing the breakdown strength (Eb) and Ud at high temperatures. This work provides a new insight for enhance the high temperature stability of polymer dielectric capacitors.