Enhancing high‐temperature breakdown strength of polyetherimide dielectric nanocomposites with MgO nanosheets by inhibiting charge migration

Abstract Polymer‐based dielectric nanocomposites with excellent high‐temperature energy storage performance are highly desirable in advanced electronic and power systems, but it remains a challenge to achieve superior breakdown strength at elevated temperatures. In this work, two‐dimensional (2D) magnesium oxide nanosheets (MgO NSs) are prepared by a hydrothermal method and used as fillers to fabricate MgO NSs/polyetherimide (PEI) dielectric nanocomposites. The effect of MgO NSs addition (1–4 wt%) on breakdown strength of MgO NSs/PEI nanocomposites is studied from 25 to 150°C. As a result, the nanocomposites containing 3 wt% MgO NSs obtain maximum breakdown strength of 538 kV mm −1 at 150°C, which is 25% higher than that of pure PEI and remains 92% of the room‐temperature value, accompany with an excellent discharged energy density of 3.66 J cm −3 . The enhancement of breakdown strength could be attributed to the 2D structure and wide band gap (~7.8 eV) of MgO NSs, which act as barriers to suppress the electrical tree growth and create deep traps to capture charge, thus inhibiting the migration of charge carriers and suppressing electrical conduction. This work provides an effective approach for developing high‐temperature polymer‐based dielectric nanocomposites with high breakdown strength and discharged energy density.