Interfacial Engineering Using Covalent Organic Frameworks in Polymer Composites for High-Temperature Electrostatic Energy Storage

The use of inorganic nanofillers has been an effective method to improve high-temperature capacitive performance of dielectric polymers, though there are unmet challenges such as undesirable organic–inorganic compatibility, and low efficiencies and energy densities. Herein, a surface functionalization strategy using covalent organic frameworks (COFs) is employed to address such challenges in realizing high-performing polymer composites. Specifically, core–shell structured nanoparticles, where ZrO₂ nanoparticles act as the core and a COF material forms the shell, are constructed and composited with the polyetherimide (PEI) matrix. The design leverages the high electron affinity (E_A) of the outer COF shell to create energy traps, thereby capturing free charges and limiting electrical conduction. Concurrently, the low E_A and wide bandgap of the ZrO₂ core introduce energy barriers to impede charge injection and migration. This orchestrated “energy level cascade” results in a marked reduction of leakage current and energy loss. The resulting polymer composite showcases an impressive discharged energy density of 6.21 J cm⁻³ at an efficiency above 90%, with a maximum discharged energy density reaching 7.43 J cm⁻³ at 150 °C. These performance metrics position the PEI/ZrO₂@COF polymer composite to surpass or be on par with state-of-the-art high-temperature PEI composites and other advanced polymer dielectrics.