Achieving Superior High‐Temperature Capacitive Energy Storage in All‐Organic Dielectric Random Copolymer

ABSTRACT There is a growing demand for heat‐resistant dielectric polymers, such as Polyetherimide (PEI), for use in electrical devices operating in harsh environments. However, the relatively narrow bandgap ( E g ) of PEI facilitates charge transport at elevated temperatures, thereby limiting the enhancement of its high‐temperature DC breakdown strength ( E b ) and, consequently, energy density ( U e ). In this work, it is proposed that constructing deep traps in PEI to capture carriers is an effective method for improving its high‐temperature performance. The diamine‐terminated siloxane (DMS) segments with a large‐ E g are randomly incorporated into fluorinated PEI (FPEI) backbones through in situ polymerization. The distinct E g characteristics (narrow vs . wide) of the FPEI and DMS segments result in a high density of deep traps in the random copolymer. The deep trap depth of the FPEI‐based copolymer with 7% DMS (FPEI‐S07) increases from 2.8 to 3.0 eV, which effectively suppresses charge transport at high temperatures. This endows FPEI‐S07 with a maximum U e of 6.31 J cm −3 and a charge‐discharge efficiency ( η ) of 90.02% at 650 MV m −1 and 200°C, which significantly surpass those of previously reported dielectric polymers. This strategy provides a novel avenue for the structural design of dielectric polymers for achieving high‐energy‐storage capacitors at elevated temperatures.