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 (U_e) 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 (E_b) 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.