Investigation of High‐Temperature Energy Storage Properties of Polyimide Through Combined Sulfone Grafting and Crosslinking Modification

Polymer dielectrics with miniaturization, lightweighting, and thermal stability are specifically desired for high‐temperature capacitors. However, bandgap ( E g ) and glass transition temperature ( T g ) have an inherent trade‐off, which limits the energy storage performance of these materials at high temperatures. Here, we propose a strategy of synergistic modification combining polar group grafting and crosslinking. Strong polar sulfonyl groups (SO 2 ) are introduced into the backbone of polyimide (PI) to break the trade‐off between E g and T g . Subsequently, charge transport is further inhibited by forming a three‐dimensional network with the crosslinking agent 4,4′,4″‐Methanetriyltrianiline (TAPM). Due to the strong steric hindrance of the sulfonyl group, the sulfone‐grafted polyimide film has a wide E g and high T g . Subsequently, the crosslinking reaction caused by TAPM forms a dense three‐dimensional network structure, which significantly limits charge transport, thus effectively improving the energy storage density ( U e ). The crosslinked film prepared from 2 wt% TAPM and the SO 2  grafted PI chains exhibits an excellent U e of 6.17 J/cm 3 at 150°C and 720 kV/mm, with a charge–discharge efficiency ( η ) above 90%. This study provides theoretical support for the structural design of high‐temperature energy storage dielectrics and offers a feasible technical pathway for their practical application.