Reliability of High-Voltage Electrochemical Capacitors: Predictions for Statistically Independent Cells from a Single Distribution

摘要

Several application areas for electrochemical capacitors that require high-voltage systems were described. The reliability of such systems was examined and related to the reliability of individual cells used in their assembly. Examples were presented that showed the impact that the cell life distribution has on system life. Approaches were suggested for increasing the reliability of high-voltage electrochemical capacitor systems. The underlying assumption used throughout this treatment was that capacitor cells were statistically independent components having a common life distribution. This requires that cell voltage and cell temperature uniformity in the series-string be maintained. If such conditions do not exist, then the cells become statistically dependent and the mathematical relationship between cell and system reliability can become extremely complicated. Irrespective, system reliability under such situations will not be any better than the results presented here for statistically independent cells selected from the same life distribution. One final statement is needed concerning the applicability of these results. The temperature influence on cell life, as described, generally holds for all types of electrochemical capacitors. Activation energies may vary somewhat, but this exponential behavior is universal. However, the voltage influence on life may not hold for all types of electrochemical capacitors. The described life increase arising from cell voltage derating does holds for electrochemical capacitors having a symmetric construction, that is devices with electrodes of the same material at approximately the same mass. Such devices most commonly use activated carbon electrode materials and a non-aqueous electrolyte.