Reprocessable crosslinked polymer dielectrics for high-temperature capacitive energy storage

Polymer dielectrics for mainstream capacitive energy-storage technologies are expected to operate reliably under extreme thermal conditions, yet remain persistently limited by the long-standing trade-off between electrical insulation and thermal tolerance. Although covalent crosslinking can mitigate this conflict by strengthening intermolecular interactions, the poor degradability of permanent covalent networks may incur environmental costs. Here, we report a recyclable polymer topology with dynamically cross-linked rings, namely boroxine rings. Boroxine rings undergo reversible bond dissociation in water-containing polar solvents, thereby enabling polymer recyclability. Meanwhile, these cyclic dynamic covalent motifs impart thermal robustness owing to the strength of the B-O framework. We have confirmed that boroxine incorporation introduces deep localized electronic states and reduces free volume, jointly suppressing high-temperature leakage conduction and enabling a discharged energy density of up to 6.35 J cm^-3 with efficiency above 90% at 200 °C. After secondary recycling, the polymer film maintained 97.8% of its high-temperature capacitive performance. This work proposes a new paradigm for green design of high-temperature capacitors, which is not only environmentally friendly but also significantly reduces the manufacturing cost of high-end capacitor films through recycling.