Understanding ageing mechanism of carbon electrodes in double layer capacitors operating in organic electrolytes

Understanding the ageing mechanisms of porous carbon electrodes used in electrochemical double layers supercapacitors (EDLCs) is of high importance to improve their lifetime. In this work, we studied ageing of two different porous carbons with different pore size distribution and surface functionalities in 1.5 M tetraethyl ammonium tetrafluoroborate (Et4NBF4) in acetonitrile (AN) electrolyte. The combination of Raman spectroscopy, thermogravimetric analysis (TGA), gas sorption and electrochemical impedance spectroscopy techniques allowed us to identify two different behaviors depending on the porous carbon used. A microporous carbon experiences an ionic/electronic resistance increase leading to a capacitance fall off upon cycling, associated with pore clogging. This resulted from the electrolyte degradation taking place at the positive electrode combined with porous carbon oxidation. Differently, only an increase of the series resistance was observed for the mesoporous carbon tested, following the creation of defects at the positive carbon electrode.