Advancing high-temperature electrostatic energy storage via linker engineering of metal–organic frameworks in polymer nanocomposites

High-performance, thermally resilient polymer dielectrics are essential for film capacitors used in advanced electronic devices and renewable energy systems, particularly at elevated temperatures where conventional polymers fail to perform. Compositing polymers with nanofillers is a well-established approach to enhancing energy storage performance, though there remains a strong need for fillers with broad structural tunability and a clear structure-property relationship to further improve performance at elevated temperatures. Herein, we unravel the untapped potential of UiO-66 metal–organic framework (MOF) derivatives as exceptional nanofillers for tuning the properties of the widely used polyetherimide (PEI). By systematically varying the linker structures, we create a series of isostructural MOF fillers that exhibit contrasting capabilities in regulating the charge transport and energy storage capacities of the resulting composite films. Notably, capacitors based on composite films using the electron-deficient UiO-66-F4 show remarkable long-term charge-discharge stability and achieve ultrahigh discharged energy densities of 9.87 J cm−3 at 150 °C and 9.21 J cm−3 at 200 °C, setting a new benchmark for high-temperature flexible polymer composites. Through comprehensive experimental and theoretical analyses, we establish an unprecedented correlation between the MOF fillers' electronic structures and the composites’ improved electrical breakdown strength and energy storage properties. These findings offer a rational pathway to harness the exceptional structural diversity of MOFs for the development of composite materials suitable for high-temperature electrostatic energy storage.