Superior High‐Temperature Energy Storage Performance in All‐Organic Composite Dielectrics Achieved by Synergistic Regulation of Free Volume and Charge Distribution

Developing polymer dielectrics with stable high-temperature energy storage performance remains a pivotal challenge for next-generation electrical systems. However, the exponentially increasing conduction loss at elevated temperatures results in a decline in both energy storage density and efficiency. Herein, a cross-scale synergistic regulation strategy that integrates mesoscale free volume and molecular-scale charge trap, effectively addressing the issue of free volume collapse and space charge accumulation under thermal-electric coupling stress is proposed. By blending polyimide with polyetherimide and introducing a low-cost n-type organic semiconductor, 1,4,5,8-naphthalenetetracarboxylic dianhydride, the resulting single-layer composite achieved a discharge energy density (U_d) of 5.01 J cm^-3 with a charge-discharge efficiency (η) close to 90% under 500 MV m^-1 at 150 °C. Additionally, multi-layer gradient architecture is employed to further enhance the high-temperature energy storage properties of the composites. Ultimately, the resultant 0.5-2.0-0.5 three-layer composite demonstrates a U_d of 6.95 J cm^-3 at 150 °C with a η of 84.5%. Even under 200 °C, 0.5-2.0-0.5 delivers a U_d of 3.24 J cm^-3 with a η of 90.1%. This research presents a novel strategy for enhancing the energy storage performance of all-organic polymer dielectrics under high-temperature conditions.