Cross-linked interfacial network obviously enhancing energy storage property of semi-alicyclic polyimide-based dielectric nanocomposites

Abstract

The energy storage performance of polyimide film capacitor is poor in high temperature and high field environment because the conjugated π bond of aromatic structures produces excited electron and provides a channel for the movement of free electrons. In this paper, semi-alicyclic polyimide-based BaTiO₃ nanocomposites (POSS@BT/PIS1) are designed and synthesized via combining molecular engineering with cross-linked interfacial engineering. The integration of non-coplanar dicyclohexyl units into the polyimide framework substantially diminishes molecular conjugation and increases the band gap. The polar functional group -SO₂- induces a significant inductive effect, altering the direction of electron movement within the aromatic ring. This leads to the formation of localized deep traps and consequently inhibits carrier transport. Furthermore, BaTiO₃ nanoparticles covered by polyhedral oligosiloxane (POSS) with epoxy group are added into the semi-alicyclic polyamide acid by solution blending method. After high temperature imide processing, a hybrid covalent cross-linked network is constructed to promote the increase of dielectric constant and breakdown strength. As a result, discharge energy density (U_e) of 10.82 J cm⁻³ and an efficiency (η) of 88 % are obtained in 1 wt% POSS@BT/PIS1. More importantly, 1 wt% POSS@BT/PIS1 deliveries the U_e of 6.9 J cm⁻³ and η of 80 % at 150 °C.