A Ternary Co-polyimide for High-temperature Capacitive Energy Storage

The development of modern power electronic systems places increasing demands on polymer dielectrics for continuous operation under extreme conditions of high temperature and high electric field. However, the insulating and thermal stability of current polymer dielectrics are often contradictory and mutually exclusive. Herein, we report a ternary co-polyimide that introduces both a highly rigid main-chains and saturated alicyclic side-chains. The former ensures the stability of the copolymer at elevated temperatures and reduces intrachain charge transfer due to its isopropyl structural units with large dihedral angles. The latter increases the molecular chain spacing and decreases interchain charge transfer due to its bulky alicyclic side groups. The resultant copolymer shows decent discharge energy density with 90% charge-discharge efficiency at 200 °C (6.1 J/cm3) and 250 °C (3.1 J/cm3), far exceeding those of conventional dielectric polymers and polymer composites. Here a completely new dimension is offered for the molecular design of polymers, giving rise to well-balanced thermal and dielectric properties, and ultimately the desired capacitive energy storage performance at high temperatures. The molecular design strategy in this work regulates the charge transfer process based on the intrinsic structure of the polymer and provides a new perspective for the future development of advanced high-temperature polymer dielectrics.