Structural tailoring enables ultrahigh energy density and charge–discharge efficiency of PAEK copolymer dielectrics at high temperatures

•A novel polymer dielectric (c-P(AEK-BBP)) was prepared by molecular structure design.•c-P(AEK-BBP) exhibits a breakdown strength of up to 644 MV·m−1 at 150 °C.•At 150 ℃, c-P(AEK-BBP) delivers a maximum discharged energy density 7.3 J·cm−3.•The excellent recycling stability and fast charge–discharge capability.