Polymer composites with high dielectric constant (high-k) have a broad application in the energy storage field. However, the balance between high dielectric constant, low dielectric loss, and low filler content is hardly achieved. In this work, single-layered MXene nanosheets with a thickness of ∼1 nm and a lateral size of ∼560 nm were prepared by in situ hydrofluoric acid (HF) method, and MXene/poly­(vinylidene fluoride-co-hexafluoropropylene) composites were prepared by a simple solution casting method. The morphologies, crystalline behaviors, and dielectric properties of the composites were fully investigated. At 1 kHz, composites have a high dielectric constant of 539 and a low dielectric loss of 0.06 when the content of MXene is 4.0 wt%. High dielectric constant is strongly related to the enhancement of interfacial polarization and the formation of microcapacitor structure. Possible microscopic mechanisms about the role of MXene in improving the dielectric constant of composites were elucidated by means of Ag nanoparticles. Moreover, finite element modeling conducted by COMSOL Multiphysics shows that low dielectric loss is attributed to the parallel arrays of nanosheets that can inhibit the conduction of leakage current. This work brings a good inspiration for the structure design of dielectric materials.

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