Enhancing capacitor lifetime by alternate constant polarization

This paper reports the successful attempts of symmetric aqueous electrochemical capacitor (EC) lifespan extension. A novel exploitation procedure, i.e., alternate floating, is herein proposed. Since only the positive electrode ages remarkably in EC systems with LiNO3 as the electrolyte, it is demonstrated that alternate polarization allows the properties of the negative electrode to be fully exploited. In our approach both electrodes play the role of the positive electrode and the negative one alternately; carbon electrodes were subjected to standard and alternate voltage-holding polarization. To observe the capacitor behavior under alternate floating at different conditions, various electrolyte concentrations of LiNO3 (0.2–5.0 mol L−1) were used. It was found that the utilization of alternate polarization during the aging test allows the lifespan of the capacitor to be noticeably prolonged. Moreover, the lifetime improvement strongly depends on the electrolyte concentration. A maximum improvement of 83% of capacitor operation time is achieved for 0.2 mol L−1 LiNO3, i.e., almost doubling the operation time. The aged electrodes were tested postmortem using SEM, TEM, XPS and N2 sorption at 77 K. The results demonstrated that the alternate floating protocol ages both electrodes almost equally.