Nanoparticles*

Dielectric capacitors inherently possess ultra-high-power density, especially required in electric vehicles, medical devices, and pulse-power systems. However, their ultra-low energy densities hinder the real potential of dielectric capacitors. Polymer nanocomposites (PNCs) promise a realistic solution to increase the energy density of dielectric capacitors by mixing high κ nanoparticles (NPs) with high electrical breakdown polymers. However, NP agglomerations and random distributions of the nanoparticles become challenges to overcome to

replace available high-energy-density devices such as supercapacitors or batteries. A sandwiched multi-layer (SML) design of PNCs has attracted significant academic attention, even though it is still in its infancy. SML PNCs can eliminate or decrease some drawbacks of NP blending with polymer matrices. Critical parameters that affect the dielectric capacitors are investigated: the thickness of the dielectric material and the NP ratio inside the SML PNCs. We thoroughly investigated the effect of BaTiO₃ NP and the thickness of the polymer thin

films in SML design. We found that the low NP ratio can drastically affect the dielectric properties of the PNCs. 1 vol % NP in the SML structure has increased the dielectric breakdown strength from 583 kV/mm to 814 kV/mm for 450 nm dielectric thickness, but 3 vol % NP in SML has decreased the electrical breakdown strength, whereas the electrical breakdown strength of PNCs normally decreases with the addition of NPs. In this work, we used a sandwiched structure to increase the energy density of the PNC by implementing different ratios of NPs. The maximum ultra-high energy of 15.5 j cm^-3 with the 1 vol % NP is successfully achieved by SML PNCs.