Carbonized polymer dots/polyimide dielectric composites with enhanced breakdown strength for a high-temperature flexible capacitor

High-temperature polyimide (PI) dielectrics with high energy density are urgently needed for capacitive energy storage fields. However, the breakdown strength ( E b ) and energy storage ( U e ) capabilities significantly deteriorate due to large conduction losses at high temperatures, limiting the practical applications of PI dielectrics. To address this issue, carbonized polymer dots (CPDs) with tunable band gaps were introduced into PI to prepare CPDs/PI composites. CPDs can also form physical entanglement and chemical crosslinking with PI molecular chains. Moreover, the wide band gap CPDs provide the composites with a higher energy barrier at the electrode/composite interface, effectively inhibiting the charge injection. Additionally, longer alkyl chains on the surface of CPDs are more conducive to their entanglement with PI molecular chains, which facilitates the formation of charge traps. Among the composites, the 12CPDs exhibit the largest band gap and longest alkyl chains. As a result, at a high temperature of 150 °C, the 12CPDs/PI0.2% film exhibits an exceptional U e of 4.0 J cm −3 , which is 2.47 J cm −3 higher than that of pristine PI with a U e of 1.53 J cm −3 , respectively.