How to kill an ultracapacitor

August 25, 2014 //By Mike Everett
How to kill an ultracapacitor
Mike Everett, CTO at Maxwell Technologies, gives an overview of how to cause an ultracapacitor to fail and assesses it to be difficult.

When working within their specified operating parameters, ultracapacitors will provide a stubbornly long and trouble-free existence. Ultracapacitors will outlast most other electronic components in any given application, which is why they are the perfect power delivery device in the most demanding environments.

However, an ultracapacitor can meet an early demise if you really want it to -- though the list of things you can do to kill it is pretty limited. Paying attention to the following circumstances will ensure the maximum lifetime of your system's ultracapacitors.

Operating temperature: An ultracapacitor doesn’t rely on electrochemical reactions to generate or deliver power or energy. It operates (simplistically speaking) electrostatically. So it stands to reason that electrochemical reactions in an ultracapacitor are not only absent by design, but also unwanted. Increasing temperature catalyzes chemical reaction rates. This generally applies to ultracapacitors, as they are chemical systems. Therefore, if you want to kill an ultracapacitor, operate it outside of its specified operating temperature, and you will be sure to degrade its capacitance excessively, increase its resistance at unacceptable rates, and decrease its efficiency dramatically. The magnitude of the effects is proportionate to the temperature beyond specification and the time spent at that temperature.

Operating voltage: Electrochemical systems generally exhibit a stable operating voltage range beyond which the system becomes unstable, electrochemically speaking. Similar to over-temperature, the effects of overvoltage include increasing decay rate in capacitance and increasing rate of resistance rise. Overvoltage will also increase the gas generation rate inside the cell. If the overvoltage is severe enough, the gas will increase to a level that will result in over-pressuring the cell from the inside out and venting, followed by cessation of function. Ultracapacitors, unlike some other electrochemical storage technologies, do not have an under-voltage limit. In fact, reverse voltage, while not desirable, will generally not kill an ultracapacitor or create a dangerous situation, as long as the reverse voltage is not over the absolute value of the voltage specification when normally operated. As with temperature, the impacts of overvoltage are dependent on the overvoltage magnitude and the time spent at that condition.

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