Significantly improve capacitive properties of alicyclic polyimide dielectrics at high temperatures via hard/soft segment engineering

Abstract

The demand for high energy storage density and efficiency of polymer film capacitors at high temperatures is urgently increasing in the electronics and electrical field. However, most traditional high temperature resistant polymers exhibit the low bandgap and high conductive loss because of the presence of conjugated aromatic structures, resulting in a significant decrease in the energy storage performance at high temperatures and high fields. In this paper, a series of alicyclic polyimide dielectric films containing hard segment of phenyl imide and soft segment of cyclohexyl imide are designed and prepared. On the one hand, the introduction of non-coplanar alicyclic ring into main-chain of polyimide can break long distance conjugation effect, weaken the intermolecular and intramolecular charge transfer interaction and improve the bandgap. On the other hand, the physical crossing point formed by the soft segments can sharply increase Young's modulus of the polyimide films. As a result, the terpolymer polyimide film (CPI90) with copolymerization ratio of phenyl/cyclohexyl dianhydride of 9:1 achieves a highest discharge energy density (U_d) of 5.59 J cm⁻³ at 150 °C. Importantly, the CPI90 film can obtain the U_d of 2.74 J cm⁻³ at 200 °C. In addition, the CPI90 film possesses a good self-healing ability attributing to a small ratio for the carbon to hydrogen and oxygen. This work offers a new strategy for synergistically promoting the bandgap and Young's modulus of polymer dielectrics via molecular and hard/soft segment engineering.