An alternating multilayer architecture boosts ultrahigh energy density and high discharge efficiency in polymer composites

Abstract

Poly(vinylidene fluoride) (PVDF)-based polymers with excellent flexibility and relatively high permittivity are desirable compared to the traditional bulk ceramic in dielectric material applications. However, the low discharge efficiency (<70%) caused by the severe intrinsic dielectric loss of these polymers result in a decrease in their breakdown strength and other problems, which limit their widespread applications. To address these outstanding issues, herein, we used a stacking method to combine poly(methyl methacrylate) (PMMA) with poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) for the synthesis of a series of alternating multilayer films with different layers. Benefitting from the blocking effect of the multilayer structure and excellent insulation performance of PMMA, simultaneous improvements in the breakdown strength and discharge efficiency of the multilayer films were achieved. Compared with the pure polymer films and other multilayer films with different layers, the film with a 9-layer structure exhibited the highest energy storage density of 25.3 J cm^-3 and extremely high discharge efficiency of 84% at 728 MV m^-1. Moreover, the charge and discharge performance of the other multilayer films were also better than that of P(VDF-HFP). In addition, it was also found that for the multilayer composite films with the same components, the blocking effect was reinforced with an increase in the number of layers, which led to a significant improvement in the breakdown strength. We consider that the multilayer structure can correlate with the dielectric properties of different polymer materials to enhance the energy storage of composite materials, and will provide a promising route to design high dielectric performance devices.

Fig. 1. Schematic illustration of the structures of the PMMA/P(VDF-HFP) multilayer composites and the controls (pure PMMA and pure P(VDF-HFP)), respectively.

Fig. 2. (a) Frequency dependence of dielectric constant and (b) dielectric loss for the pure polymer and multilayer composite films.

Fig. 3. (a) Variation in leakage current vs. electric field and (b) TSDC spectra for the pure polymer and multilayer composite films. (c) Young's modulus and breakdown strength for the pure polymer and multilayer composite films. (d) Comparison of the experimental breakdown strength of the multilayer composites films.

Fig. 4. Breakdown evolution procedures for the multilayer composite films with 3L, 5L, 7L and 9L by phase-field simulation.

Fig. 5. (a) Remnant displacement of the multilayer composite films as a function of the electric field summarized from the D-E loops in Fig. S4. (b) Comparison of the energy storage properties of the multilayer composite films.