Trap‐Anchored Crosslinked Polyetherimide Networks for Extreme‐Temperature Energy Storage

ABSTRACT Polyetherimide (PEI) is a highly promising high‐temperature dielectric material; however, the exponential increase in conductive loss and severe thermal runaway at high temperatures severely limit its application as a capacitive energy storage material. To address this, we propose a dual‐functional molecular design strategy that constructs a robust, 3D crosslinked network incorporating electron‐deficient boroxine rings (B‐PEI). Experimental and computational analyses indicate that the Lewis acid boron centers act as homogeneously dispersed deep traps, effectively restricting charge carrier mobility. Topological constraints simultaneously decrease free volume, which reduces the mean free path of energetic electrons and increasing the energy barrier for avalanche breakdown. These synergistic mechanisms enable source‐level suppression of leakage current and Joule heating under extreme field conditions. Consequently, the optimized B‐PEI4 film demonstrates exceptional breakdown strengths of 682.2 and 586.2 MV m −1 at 150°C and 200°C, respectively. Notably, it achieves a discharge energy density of 6.78 J cm −3 with an efficiency of 79.3% at 200°C, outperforming most reported polymer dielectrics. This work introduces a “source‐control” paradigm for designing intrinsic high‐temperature dielectrics without compromising flexibility, facilitating advancements in next‐generation electronic and power systems.