Tailoring the Orientation of Electron‐Delocalized Conjugated Structures in Polyimide Dielectrics for High‐Temperature Capacitive Energy Storage

ABSTRACT Dielectric polymers for high‐temperature capacitive energy storage require both high thermal stability and electrical insulation. Although the rigid conjugated structure of polyimide affords a high glass transition temperature, making it a promising candidate, it also introduces compromised electrical insulation through electron delocalization. Here, we propose and demonstrate that regulating the spatial orientation of localized π‐containing/electron‐delocalized conjugated structures in polyimide can effectively break the trade‐off between thermal stability and electrical insulation. The out‐of‐plane orientation of localized conjugated structures reduces the spatial connectivity of short‐range electron‐delocalization sites along the electric‐field direction, thereby suppressing continuous carrier migration. Consequently, under high temperature and elevated electric field, the out‐of‐plane‐oriented semi‐aromatic polyimide exhibits an electrical conductivity reduced by over an order of magnitude compared to its in‐plane‐oriented counterpart. It achieves a high discharge energy density ( U e ) of 7.16 J cm − 3 with a charge–discharge efficiency ( η ) exceeding 90% at 200°C, surpassing its in‐plane‐oriented analogue ( U e = 3.44 J cm − 3 , η = 90%). Furthermore, analysis of the dual gas‐phase and condensed‐phase mechanism demonstrates the exceptional breakdown self‐healing ability of the designed polymer, highlighting the promise of the out‐of‐plane conjugation orientation for high‐performance polymer capacitors operating at elevated temperatures.