# Prospects for the Development of High Energy Density Dielectric Capacitors
## 8 Summary and Conclusions  
In this paper, the design of high energy density dielectric capacitors for energy storage in vehicle, industry, and electric utility applications has been considered in detail. The literature on composite polymer materials was reviewed to assess the present state-of-the-art of the dielectric constant of dielectric materials being developed to increase energy density. It was found that there were a number of papers in which dielectric materials having dielectric constants of 20-30 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 occurring near the percolation threshold particle  
Figure 11: Porous spherical carbon particles for supercapacitor electrodes. Representative electron micrographs showing (**A**) Pristine carbon nanospheres prepared by HTS; (**B**) Carbon spheres after carbonization; (**C**) Carbon spheres after graphitization. Figure 12: High-resolution transmission electron microscopy (HRTEM) measurement of a spherical carbon particle [58]. loading. Unfortunately, the tangent loss associated with the high dielectric constant was high. In general, the breakdown strength of the composite polymer was significantly less than the host polymer. All the dielectric material testing was done at relatively high frequency and no DC data was available. For some composite polymer materials, the dielectric constant was nearly independent of frequency, but for most materials, the dielectric constant decreased markedly with frequency. The second step in the study was to develop an analytical method to calculate the dielectric constant of composite polymers with various types of nanoparticles embedded in the host polymer. In the analysis, it was assumed the particles were arranged uniformly and that the effects of the interfaces between the host polymer and the particles were negligible. The analytical results were used in 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, but for a 1000 V cell, an energy density of 100-200 Wh/kg was calculated for 3-5 nm particles and 3-5\(\upmu\) thick layers. The analytical method and calculations did not include the effects of percolation and any losses related to changes in molecular polarizability with electric field. Nonetheless, the calculations indicated that the development of dielectric capacitor cells with battery-like energy density may be possible. These devices will be especially useful for electric utility energy storage because of their high cell voltage, long cycle life, and solid-state construction. The results of this study indicate that dielectric materials with a dielectric constant of 500-1000 are needed to design dielectric capacitor cells with battery-like energy density. These cells would likely use a mix of polymers as the host polymer with nm size carbon and/or graphene particles embedded and a voltage of 800-1000 V. The breakdown strength would be 300-400 MV/m in reverse sandwich multilayer dielectric arrangements. The leakage current of the cell would be determined from appropriate DC testing. Work was funded part by consulting with Capacitance Sciences Inc.: Menlo Park, CA, USA, 2005. There are no conflict of interest. In 2006-2010, a company **EEstor** in Austin, Texas was claiming to develop a high energy density dielectric capacitor system using sub-micron size Barium Titanate particles in a host polymer that had higher energy density than Lithium batteries. The voltage of the capacitor system was 3500 V. Those claims persist to today (2021) and **EEstor** has not released any data showing the performance of their cell or produced any product.