An experimental study on the effectiveness of conventional state-of-health diagnosis schemes for second-use supercapacitors

Reuse of the retired/aged supercapacitors plays an important role in production sustainability and environmental concerns. Therefore, appropriate health characterization methods along with proper guidelines to identify the remaining useful capacitance of the retired supercapacitor cells are required. This paper focuses on conventional approach based capacitance diagnosis of retired supercapacitors, since there is a lack of technological development for the same. In particular, we evaluate the effectiveness of Maxwell six-step process-based time domain approach and electrochemical impedance spectroscopy based frequency domain approach in identifying the remaining capacitance of the retired supercapacitors. This work considers a retired cell of the commercially available Maxwell supercapacitors to demonstrate the approach. The results obtained from the conventional approaches via cyclic voltammetry test is validated. Subsequently, the effectiveness of the test methods are experimentally verified by considering a new specimen of the Maxwell 100 F supercapacitor. The obtained results confirm that both the approaches are showing promising results, however, for different operating voltage range. This clearly indicates the need for future research towards second-life application of retired supercapacitors. Finally, the importance of choosing proper capacitance characterization scheme for reliable use of retired supercapacitors considering a wireless sensor network based realistic second-life application is discussed.