Self-discharge mechanisms in electrochemical capacitors

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Electrochemical capacitors, or "supercapacitors", can store the energy produced by intermittent alternative energy sources (e.g. solar panels or windmills). They can also complement fuel cells and batteries for hybrid car applications, where the battery or fuel cell provides the energy required to drive long distances, and the capacitor delivers the high power needed for acceleration. Electrochemical capacitors are essentially maintenance free and have a much higher cycle life than batteries (they can be charged millions of times, rather than hundreds or thousands of times for batteries), making them ideal for remote applications. One poorly understood aspect of electrochemical capacitor behaviour is self-discharge, the spontaneous loss of voltage as the electrochemical capacitor sits for long periods of time. This is of practical importance as one would like to know that the electrochemical capacitor is ready for use, whether it has been unused for a day or a year. At this point, it is unclear why and how it loses this voltage, and this is under study in the Andreas laboratory.