Synergy of charge capture and transfer by Ni-MOF nanosheets for enhancing energy storage performance of polyetherimide-based dielectric nanocomposites

Polymer-based dielectric nanocomposites with excellent energy storage performance and good thermal stability are essential to meet the demand for dielectric capacitors operating under high-temperature environments. However, there is still a challenge to high-temperature breakdown strength and energy density due to the increase in leakage current with temperature and applied electric field. In this work, Ni-based metal-organic framework nanosheets (Ni-MOFs) are synthesized by a sonication-assisted solution method and introduced into polyetherimide (PEI) to fabricate Ni-MOFs/PEI dielectric nanocomposites. As a result, the nanocomposites containing 2 wt. % Ni-MOFs exhibit a significantly enhanced breakdown strength of 640 kV/mm and a discharged energy density of 6.37 J/cm3 at 150 °C, which are 48% and 228% higher than those of pure PEI, respectively. This enhancement could be attributed to the synergistic effect of charge capture and transfer induced by wider bandgap and π–d conjugation of Ni-MOFs, which not only act as deep traps to capture charges at the interface but also transfer the charges along the in-plane direction to uniform the local electric field, thus reducing the leakage current and conduction loss. This work provides an effective strategy for the design of high-performance dielectric nanocomposites based on polymer.