A Trilayer Polymer Composite with Macroscopic Gradient Dielectric Constant Distribution for Advanced Energy Storage Capacitors

With the increased demand for electrical devices, there is an urgent requirement to explore advanced materials for capacitors. Composite is an effective way to improve performance through materials and structure design. Herein, an asymmetric three-layer structure with gradient dielectric constant through the solution casting method is reported. This unique design of construction consists of a buffer layer pristine poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) embedded between high insulation linear materials polyurea (PUA) and high polarization non-linear materials P(VDF-HFP)/BT nanocomposite. The experimental and simulation results demonstrate that the linear layer ensures high insulation of the composite and relatively high efficiency, while the nanocomposite layer acts as a high dielectric layer to enhance polarization. Typically, the buffer layer could effectively avoid overconcentration of the electric field on the PUA layer, which results in high breakdown strength of the trilayer composite. As a result, an ultrahigh breakdown strength of 5970 kV/cm and excellent energy storage density of 8.2 J/cm 3 can be obtained, which were 45% and 2.15 times higher than that of pristine P(VDF-HFP). This asymmetric structure strategy provides a successful case in exploring high-performance energy storage materials.