Scalable High‐Permittivity Polyimide Copolymer with Ultrahigh High‐Temperature Capacitive Performance Enabled by Molecular Engineering

Abstract Polymer capacitors are essential components of advanced electronic and power systems. However, the deficient high‐temperature capacitive performance of polymer dielectrics fails to meet the demand for harsh condition applications, due to the mutually restrictive relationships in permittivity ( ε r ), glass transition temperature (T g ), and bandgap ( E g ). Here, a modularized molecular engineering strategy is reported to enhance the high‐temperature capacitive performance of polymer dielectrics. First, the potential influences of multiple structural units on ε r , T g , and E g of polymers are elucidated by comparing a set of polyimides (PIs). After screening out an excellent sulfonated PI with concurrently high ε r (4.2), E g (3.4 eV), and T g (311.2 °C), a semi‐alicyclic sulfonyl‐containing PI copolymer is further synthesized that exhibits a superior discharged energy density of 4.3 J cm −3 above 90% efficiency at 200 °C and 485 MV m −1 . Density functional theory calculations demonstrate that the combination of polar sulfonyl group, ether linkage, and alicyclic group in the backbones of the copolymer decouples the dipole orientation and the segmental motion of backbones, and reduces conjugation effects of aromatic groups, thereby minimizing the polarization relaxation loss and the conduction loss while retaining excellent thermal stability and high permittivity.