Entropy-Driven Conformational Disorder Enables Outstanding High-Temperature Energy Storage in Dielectric Polymers.

Abstract

The pursuit of high-temperature polymer dielectrics is consistently hindered by the intrinsic tradeoff between ensuring robust electrical insulation and maintaining thermal stability. While aromatic polyimide (PI) has superior thermal resistance, its dense π-π stacking facilitates the formation of charge transfer complexes, causing significant leakage and capacitive failure at elevated temperatures. In this study, we developed an entropy-driven conformational disorder strategy to maximize the conformational entropy of our designed ternary random copolymerized PI (R-PI, ΔS_conf = 5.76 J/(mol·K)). The π-conjugation decoupling and electron localization of the R-PI were achieved by dynamic conformational flipping. Density functional theory and molecular dynamics calculations indicate that the structural randomized state generates a highly fluctuating electrostatic potential field. This field creates high-density deep energy traps that effectively suppress the long-range hopping transport of charge carriers. As a result, the optimal R-PI-0.5 delivers a discharged energy density of 6.12 J/cm³ (η = 91.1%) under an applied field of 650 MV/m at 200°C. This molecular-level design paradigm leverages conformational entropy to exceed traditional dielectric limits, offering a robust pathway for next-generation harsh-environment energy storage.