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 µ 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/µ 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.
Highlights
The most common and simplest electrical energy storage device is the ceramic capacitor that uses a very thin dielectric layer between two metal plates to separate positive and negative charge
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/μ
Attempts to increase the effective dielectric constant have resulted in a significant decrease in breakdown strength
Summary
The most common and simplest electrical energy storage device is the ceramic capacitor that uses a very thin dielectric layer between two metal plates to separate positive and negative charge. The general approach discussed in this paper to increase the effective dielectric constant of a polymer composite has its roots in Dr Burke’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 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.
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