Carbene‐Mediated Cross‐linking of Aromatic Dielectric Polymers for Capacitive Energy Storage at 250°C

Reliable energy storage in electrostatic capacitors requires dielectric materials that can withstand extreme thermal and electrical stresses, a demand that exceeds the capabilities of many commercial polymers. Cross‐linking offers a promising route to improved thermal and electrical robustness, but existing strategies often depend on polymer‐specific reactive groups, harsh activation conditions, or byproducts that limit broader adoption. Herein, we report a post‐polymerization cross‐linking strategy based on carbene‐mediated C–H insertion, enabled by a stepwise thermal activation protocol. Using commercial fluorinated polyimide (FPI) and the commercial bis‐diazirine cross‐linker BLD201 as a model system, this approach yields free‐standing cross‐linked films with a high cross‐linking efficiency of 95.8% at only 2 wt.% BLD201, despite the exclusive presence of aromatic/ sp 2 C–H bonds in the polymer backbone. The resulting cross‐linked FPI films exhibit outstanding capacitive energy storage performance, along with excellent spatial uniformity and long‐term durability. A maximum discharged energy density of 4.4 J cm −3 is achieved at 250°C, which is among the highest values reported for state‐of‐the‐art polymer films under comparable conditions. This work establishes thermally activated carbene cross‐linking as a versatile route for transforming commercial aromatic polymers into thermally resilient electrostatic energy storage materials.