# Prospects for the Development of High Energy Density Dielectric Capacitors
###### Abstract  
In this paper, the design of high energy density dielectric capacitors for energy storage in vehicle, industrial, and electric utility applications have been considered in detail. The performance of these devices depends primarily on the dielectric constant and breakdown strength characteristics of the dielectric material used. A review of the literature on composite polymer materials to assess their present dielectric constants and the various approaches being pursued to increase energy density found that there are many papers in which materials having dielectric constants of 20-50 were reported, but only a few showing materials with very high dielectric constants of 500 and greater. The very high dielectric constants were usually achieved with nanoscale metallic or carbon particles embedded in a host polymer and the maximum dielectric constant occurred near the percolation threshold particle loading. In this study, an analytical method to calculate the dielectric constant of composite dielectric polymers with various types of nanoparticles embedded is presented. The method was applied using an Excel spreadsheet to calculate the characteristics of spiral wound battery cells using various composite polymers with embedded particles. The calculated energy densities were strong functions of the size of the particles and thickness of the dielectric layer in the cell. For a 1000 V cell, an energy density of 100-200 Wh/kg was calculated for 3-5 nm particles and 3-5 u thick dielectric layers. The results of this study indicate that dielectric materials with an effective dielectric constant of 500-1000 are needed to develop dielectric capacitor cells with battery-like energy density. The breakdown strength would be 300-400 V/u in a reverse sandwich multilayer dielectric arrangement. The leakage current of the cell would be determined from appropriate DC testing. These high energy density dielectric capacitors are very different from electrochemical capacitors that utilize conducting polymers and liquid electrolytes and are constructed much like batteries. The dielectric capacitors have a very high cell voltage and are constructed like conventional ceramic capacitors. dielectric materials; embedded nano-carbon; high energy density; batteries; and electrochemical supercapacitors +
Footnote †: journal: Applied Sciences  
The energy density of the capacitor is  
\[\mathrm{Wh/L}=1/2\ \epsilon_{0}\ \epsilon_{\mathrm{r}}\ (V/\delta)^{2}\]  
A key material parameter is \(\epsilon_{\mathrm{r}}\), the effective dielectric constant of the material from which the capacitor is assembled. The energy density of all dielectric capacitor devices is proportional to the voltage squared, but the maximum voltage is limited by the breakdown strength of the dielectric material V/\(\mu\). Hence the key material property is \(\epsilon_{\mathrm{r}}\ (V/\delta)^{2}\). In most cases, attempts to increase the effective dielectric constant have resulted in a significant decrease in breakdown strength. This report is focused on increasing the effective dielectric constant of a polymer composite, but consideration of the breakdown strength of the composite is at least of equal importance. The general approach discussed in this paper to increase the effective dielectric constant of a polymer composite has its roots in Dr. [PERSON]'s familiarity [1; 2; 3; 4] with electrochemical supercapacitors (ECSCs)--carbon/carbon electric double-layer capacitors (EDLCs) and hybrid ECSCs that utilize microporous carbon and a liquid electrolyte. The charge separation in the electrodes occurs in the double-layer formed in the micro-pores of the carbon at the interface between the liquid electrolyte and the carbon. The capacitance of the electrode is proportional to the specific capacitance (F/g) of the microporous material used to form the electrodes in the cell.