Second-life applications of supercapacitors: Effective capacitance prognosis and aging

The popularity of supercapacitors (SC) as an energy storage device is growing along with the development of the electrical and electronics applications demanding high operating power. Consequently, the number of retired SC cells is increasing leading to the recycling problem. Supercapacitor reaches its end-of-life (EOL) when its nominal capacitance is decreased by 20% and the initial equivalent series resistance (ESR) is increased by 100%. Under this scenario, the SC is no-longer suitable for its original purpose as a source of high power. However, the aged supercapacitors often retain enough capacity to serve the applications demanding low operating power. This paper investigates the possibility to re-purpose the aged supercapacitors for low power second-life applications. Specifically, we propose a capacitance prognosis model as a function of the operating power of second-life applications. We consider three aged Maxwell supercapacitors to illustrate the proposed scheme. Subsequently, we identify their effective capacitance considering MICAz wireless sensor module as the low power second-life application. Next, we evaluate the sensitivity and robustness of the proposed model. Finally, we study the second-life aging of the aged supercapacitors under low-power charge–discharge cycling.