Pinning and elongating of electric treeing induced by wrinkled nanosheets in polymer dielectrics towards significantly enhanced high-temperature energy storage performance†

Abstract

Polymer film capacitors are key components in pulsed energy storage systems. However, at high temperatures, polymers often suffer from sharp deterioration in breakdown strength and energy storage performance. Here, pinning and elongating of breakdown paths induced by wrinkled ceramic nanosheets are proposed to enhance the high-temperature energy storage performance of polymers. The simulations show that wrinkled nanosheets can more effectively pin charge transport and elongate the breakdown path compared to flat nanosheets, yielding greatly increased breakdown time. Based on that, wrinkled alumina nanosheets (WAO) are prepared via a facile ion exchange process and then incorporated into polyetherimide (PEI) film, forming WAO/PEI nanocomposites. The composite film with merely 0.2 wt% WAO exhibits an ultrahigh energy density of 8.27 J cm⁻³ (efficiency > 90%) at 150 °C, which reaches 420% that of pure PEI film and is superior to most of the state-of-the-art polymer composites filled with other types of nanofillers. Meanwhile, excellent cycling stability (>50 000 cycles at 300 MV m⁻¹) and power density (1.16 MW cm⁻³) at 200 °C are achieved. In addition, the novel wrinkled nanosheets are further demonstrated to be able to remarkably enhance the high-temperature energy storage performance of other polymers, including polymethyl methacrylate, polycarbonate and polyimide.