# Prospects for the Development of High Energy Density Dielectric Capacitors
## 6 Review of Research on High Voltage, Film Capacitors  
The analysis and calculations in Sections 3 and 4 indicate that dielectric cells assembled using a host polymer with nm size carbon elements embedded can have high energy density and very high power. The dielectric layer will be thin (1-5 \(\upmu\)) and the carbon particles must be arranged very uniformly and have very good contact with the host polymer. In other words, the calculated results correspond to an ideal dielectric cell. In addition, the dielectric layers in the devices are very thin films. There are clearly serious questions regarding how closely the ideal assembly of the cells can be approached in practice even after extensive development. A survey of the literature has not found research using carbon elements in composite polymers to increase their dielectric constant at high voltage (1000 V), but there has been successful research [51; 52; 53; 54] using other types of particles for that purpose in thin films. Also, there has been much research on electrochemical capacitors [52; 53; 54; 55; 56] using particulate carbon and graphene sheets/plates to increase the specific capacitance (F/g) of electrodes. In this section, a review of some of the relevant research is presented, and its relevance to the development of the proposed dielectric devices indicated. Some relevant high voltage research can be found in [51; 52; 53; 54; 55]. Ref. [51] is a recent review of the properties of polymer composites used in high voltage applications. It treats many of the same filler particles at high voltage that were considered at lower voltages in Section 2. In [16], a study is described in detail of mixed polymers of various properties to yield a composite with high dielectric constant and high breakdown strength. Thin films of the composite were tested up to 4 kV. The results of the testing are shown in Figure 7, which indicate an energy density of the film of about 6 Wh/L (22 J/cm\({}^{3}\)) at 370 V/\(\upmu\). The thickness of the film is not given in [51], but the breakdown value of 4 kV indicates a thickness of 10-15 \(\upmu\). Ref. [53] is a good review of the state-of-the-art of thin film plastic capacitors and a discussion of the characteristics of available dielectric polymer materials. The paper is concerned with spiral wound capacitors developed using a new polymer HED (modified polyethylene terephthalate). Test data for the new capacitors are shown in Table 6 and Figure 8. The data indicate an energy density of 1.3 Wh/L (4.7 J/cm\({}^{3}\)). \begin{table}
\begin{tabular}{c c c} \hline  & **“3 mm” Control Mylar®** & **“3 mm” Control Mylar®** \\  & **PET(WO 279132)** & **PET(WO 279133)** \\ \hline Avg.Capacitance, DF (120 Hz) & 63 mF, 0.6\% & 70 mF, 0.7\% \\ \hline Active Length & 9492 cm & 8710 cm \\ \hline Thickness & 3.35 micron & 2.80 micron \\ \hline  & **“4 mm” control Mylar®** & **“4 mm” control Mylar®** \\  & **PET(WO 279277)** & **PET(WO 279279)** \\ \hline Avg.Capacitance & 40 mF, 0.6\% & 39 mF, 0.6\% \\ \hline Active Length & 6137 cm & 6017 cm \\ \hline Thickness & 3.53 micron & 4.24 micron \\ \hline \end{tabular}
\end{table} 
Table 6: Characteristics of the HED film capacitors [53]. Figure 7: Energy density and breakdown data for mixed- polymer thin films. (**a**) The energy density of PVDF-TrFE-CFE/ArPTU composite films with different composite ratios; (**b**) Comparing of discharge energy density of our works with reported works [16]. Ref. [54] is a presentation by General Electric of the development of a DC bus film capacitor on a DOE contract. That work utilized polyetherimide (PEI) as the polymer dielectric. The film thicknesses were 3-5u with a breakdown strength of 500-600 V/\(\mu\). The results of the development are summarized in Table 7. The energy density of the 800 \(\mu\)F film capacitor shown in the table is 1.5 Wh/L tested at about 1600 V.  
Ref. [55] involves the fabrication of spiral wound capacitors from flexible alkali glass (\(\varepsilon\) = 5.7) ribbons of thickness 50 \(\mu\).