Ladderphane copolymers for high-temperature capacitive energy storage

For capacitive energy storage at elevated temperatures1–4, dielectric polymers are required to integrate low electrical conduction with high thermal conductivity. The coexistence of these seemingly contradictory properties remains a persistent challenge for existing polymers. We describe here a class of ladderphane copolymers exhibiting more than one order of magnitude lower electrical conductivity than the existing polymers at high electric fields and elevated temperatures. Consequently, the ladderphane copolymer possesses a discharged energy density of 5.34 J cm−3 with a charge–discharge efficiency of 90% at 200 °C, outperforming the existing dielectric polymers and composites. The ladderphane copolymers self-assemble into highly ordered arrays by π–π stacking interactions5,6, thus giving rise to an intrinsic through-plane thermal conductivity of 1.96 ± 0.06 W m−1 K−1. The high thermal conductivity of the copolymer film permits efficient Joule heat dissipation and, accordingly, excellent cyclic stability at elevated temperatures and high electric fields. The demonstration of the breakdown self-healing ability of the copolymer further suggests the promise of the ladderphane structures for high-energy-density polymer capacitors operating under extreme conditions. A class of dielectric copolymers called ladderphanes is shown to outperform existing dielectric polymers and composites, with high discharged energy density and charge–discharge efficiency even at temperatures up to 200 °C.