High‑Temperature Polymer Nanocomposite Enabled by Thermally Conductive 2D Covalent Organic Frameworks for Capacitive Energy Storage

ABSTRACT Dielectric polymers for high‐temperature capacitive energy storage are often limited by low thermal conductivity and resulting Joule heat accumulation. Although high‐thermal‐conductivity inorganic fillers have been introduced, their poor interfacial compatibility with organic matrices restricts overall performance improvement. Here, we develop an all‐organic nanocomposite by integrating two‐dimensional (2D) covalent organic framework nanosheets (COF‐NS) into a polyetherimide (PEI) matrix. The COF‑NS exhibits high intrinsic thermal conductivity and forms strong interfacial interactions with PEI via B─O coordination bonds. Multi‑scale simulations combining molecular dynamics and phase‑field modeling confirm that the organic similarity between COF‑NS and PEI ensures effective phonon matching and minimizes interfacial thermal resistance, significantly enhancing thermal conduction through efficient in‑plane heat dissipation pathways. Additionally, the wide bandgap of COF‑NS introduces charge traps that suppress leakage current, while the robust interface enhances mechanical strength, and the 2D morphology inhibits electrical treeing. These combined effects significantly improve the breakdown strength and energy storage performance at high temperatures. The resulting PEI/COF‑NS composite achieves a high energy density of 5.89 J cm −3 at 200°C, with an efficiency above 90%, outperforming most reported polymer dielectrics. This work underscores the significant potential of organic 2D materials in developing high‑temperature dielectric polymers for advanced electronic and electrical systems.