Measurement of gas pressure in packaged electric double layer capacitors

Abstract Electric double layer capacitors (EDLCs) are popular energy storage devices in part because they have very long life with a highly predictable failure time. EDLCs generate gas during operation, particularly when operated at their maximum rated temperature and voltage, which leads to pressure rise in a sealed package with the possibility of package rupture. However, EDLC package rupture is seldom observed because it can be prevented with proper application engineering, which requires knowledge of the gas generation rate. We demonstrate two approaches for the measurement of gas pressure in packaged EDLCs. The first is indirect and relies on package deformation to infer the internal gas pressure. This is easy to implement and has low cost but it lacks high precision. The second approach measures gas pressure directly using an electronic transducer. It is more cumbersome and costly (a special apparatus is needed) but does provide continuous measurement with high precision. Details of both gas pressure measurement approaches are reported and demonstrated using packaged 100-F-size EDLCs.