# Prospects for the Development of High Energy Density Dielectric Capacitors
###### Abstract
In order to increase the energy density of EDLCs (5-10 Wh/kg for a device), hybrid ECSCs have been developed that consist of carbon in one electrode and the second electrode formed from nanoporous carbon coated with metal oxides or conducting polymers that have much higher specific capacitance than the carbon. The charge transport in electrochemical capacitors is due to the diffusion of ions in the electrolyte. The high capacitance of the ECSC is due to the sum of the capacitance of millions of micro-capacitors formed in and around the nano-carbon particles. The dielectric, in this case, is the liquid electrolyte with a rather high dielectric constant (20-80), and the maximum voltage (1-4 V) of the cell depends on the decomposition of the electrolyte. The high capacitance of the cell is due to the distributed charge separation in the double-layer on the surface of the electrically conductive porous carbon and/or its coatings. This charge separation is very much larger (>10\({}^{6}\)) than it could be on the surface of the metal current collector of the cell. The source/sink of the electrical current through the ECSC is by way of the current collector as in a battery. The concept of distributed charge separation and millions of micro-capacitors in a host dielectric can be used as the approach to achieve a high effective dielectric constant in a dielectric cell. ECSC devices are characterized in terms of their capacitance C and resistance R. The charge stored is given by Q = CV and the energy stored is E = 1/2 CVr\({}^{2}\), where Vr is the rated voltage of the device. The response time of the ECSC is RC. These are the same relationships given previously to describe the performance of a dielectric capacitor. Energy storage in a dielectric material is much different than in the electrode of an EC in which there is a physical transport of ions through the liquid electrolyte. In the dielectric material, the material becomes polarized in response to an electric field generated between two electrical conducting surfaces on which surface charge forms. There is no physical movement of atomic material as the dielectric cell is charged and discharged. In the case of the dielectric cells analyzed in this paper, the distance between the conducting surfaces is the spacing of the carbon particles and it is the host dielectric material that is polarized. The maximum electric field possible between the particles depends on the effective breakdown strength characteristics of the host dielectric material. In the dielectric cell, there is no need for a separator because the dielectric material has an extremely low electrical conductivity. It acts as an insulator. In principle, the calculation of performance of the cell is straightforward after its capacitance is known. This paper consists of several sections. Section 2 is a review of recent research on approaches to achieving significant increases in the dielectric constants of polymer composites for use in energy storage devices. Section 3 is the analytical basis of the present proposed approach for increasing the effective dielectric constant of polymer compositesusing various embedded elements, including carbon in various forms. Section 4 is the application of the results of Section 3 to the design of high energy density dielectric cells via an Excel spreadsheet model. Section 5 discusses the DC testing of the dielectric cells and the metrics used to describe their performance. Section 6 is a review of selected research on the development of high voltage, film capacitors. Section 7 is a review of recent electrochemical supercapacitor research dealing with carbon, graphene, and polymers to increase the specific capacitance (F/g) of their electrodes. Section 8 is a summary of the paper and important aspects of the development of high energy density dielectric capacitors that make their development uncertain.