Enhanced Dielectric Energy Storage Performance of Polyimide/γ-Ga2O3 Nanocomposites under Dual Trap Mechanisms

The rapid development of advanced electronics, hybrid vehicles, etc. has imposed heightened requirements on the performance of polymer dielectrics. However, the energy density (Ue) of polymer dielectrics significantly decreases due to increased leakage current and dielectric loss under high temperatures and high electric fields. Herein, γ phase Ga2O3 (γ-Ga2O3) nanoplates with wide-bandgap (∼4.7 eV) and moderate dielectric constant (∼10.0) were synthesized and incorporated into a polyimide (PI) matrix. The γ-Ga2O3 nanoplates impede charge injection and transport within the nanocomposites under dual trap mechanisms, namely, deep traps introduced by band alignment at the interface between γ-Ga2O3 and PI and the defective spinel structure of γ-Ga2O3 with lattice defects that function as additional charge carrier traps. Additionally, γ-Ga2O3 nanoplates also serve as electron scattering centers and act as electrical barriers; thus, the leakage current and conduction loss get reduced. Consequently, the nanocomposite with 1 wt % γ-Ga2O3 exhibits a discharge energy density of 4.591 J cm–3 and a breakdown strength (Eb) of 501.49 MV m–1 at 150 °C, which are significantly higher than those of commercial biaxially oriented polypropylene (BOPP) at 25 °C. Moreover, the nanocomposite exhibits remarkable cyclic stability over 120,000 cycles with only 1.2% fluctuation. This work provides a semiconductor filler strategy in the design of polymer nanocomposites for capacitive energy storage at high-temperature and high electric field environments.