Optimizing the gradient of electric field distribution and inhibiting charge injection in multilayer dielectric films for high capacitive performance

Dielectric polymer materials are capable of storing energy stably and are utilized in numerous fields such as modern electronic devices and power systems. Thus far, the unappealable discharged energy density of the current dielectric polymer film has mainly been caused by insufficient breakdown strength and lower discharged efficiency. Herein, multilayer dielectric films consisting of polyethersulfone (PESU) as the outer layer and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) doped with Ni-MOF as the middle layer were constructed. The PESU layer could block charge injection and effectively disperse the electric field strength of the single-layer film; moreover, the PESU with multiple active sites facilitates restricting the motion of carriers. Consequently, an elevated breakdown strength of 824 MV m-1 is exhibited in multilayer nanocomposites, which is 164.8% that of PESU films, concomitant with a surged efficiency of 87.3%, which is 24.9% higher than that of pure P(VDF-HFP), and a superior discharged energy density of 20.8 J cm-3 is achieved. The multilayer dielectric material provides a feasible example for fabricating energy storage devices with the coupling of ultrahigh breakdown strength and efficiency. Nanocomposite films obtain superior energy storage density, which is by far the most energy storage performance reported to date.