Several studies on the degradation mechanism of electrochemical capacitors have been conducted, but they have not predicted and analyzed the lifetime of the capacitors. A capacitor's life is normally considered to end when its capacity is reduced to 20% of the initial level or its ac equivalent series resistance (ESR) increases by 200% compared its initial value. Once the ac ESR reaches a failure state, it becomes impractical to use it as a factor to determine the failure of an electrochemical capacitor; hence, only the capacity is considered as a factor when determining a capacitor's failure. This method, which is used for small-scale electrochemical capacitors employed as capacitance backup, cannot be applied to new electrochemical capacitors with high output and low resistance. Therefore, we analyzed a failure mechanism by conducting a load-life test on high-output cylindrical-shaped electrochemical capacitors under different voltages (2.5, 2.7, and 2.9 V) and temperatures (333.15 K, 343.15 K, and 353.15 K) for 1000-1500 h, using the simulation software ALTA 8 PRO and Weibull ++8. By proposing an appropriate dc ESR as a life-determining factor for existing capacitors and by analyzing different failure conditions (150%, 180%, and 200%) through comparison, we found that a 180% increase in the dc ESR over its initial level is the most appropriate factor to be used as a failure condition for electrochemical capacitor performance. In addition, in the case of performance degradation due to voltage and temperature changes, an acceleration factor for each condition has been deduced, facilitating a preliminary performance evaluation w an accelerated life test.
Bibliographical noteFunding Information:
This work was supported by the Energy Efficiency and Resources R&D program ( 2012T100201571 ) under the Ministry of Knowledge Economy, Republic of Korea.
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All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Safety, Risk, Reliability and Quality
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Electrical and Electronic Engineering