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

TL;DR: High-temperature electrostatic energy storage using covalent organic frameworks in polymer composites achieves impressive energy density and efficiency through an energy level cascade mechanism.

Abstract: 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 (EA) of the outer COF shell to create energy traps, thereby capturing free charges and limiting electrical conduction. Concurrently, the low EA 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.