Nanoscale characterization of the site‐specific degradation of electric double‐layer capacitor using scanning electrochemical cell microscopy

Abstract

Abstract Electric double‐layer capacitors (EDLCs) that store electrical energy in the interface between an electrolyte and a solid electrode are favorable energy storage systems that demonstrate high‐power density, excellent cycle stability, and low environmental impact. To increase the operating voltage and improve the capacitance of EDLCs, it is essential to investigate the relationship between the degradation process and structural properties of activated carbon. In the current study, we used scanning electrochemical cell microscopy (SECCM) to assess the site‐specific degradation mechanisms caused by electrolyte decomposition. To simplify the structural properties of activated carbon, we used the highly oriented pyrolytic graphite (HOPG) as a model substrate to distinguish the edge and the basal planes of activated carbon. The mobile and nanoscale electrochemical cell provides local cyclic voltammetry (CV) to examine the difference in the degradation process at the edge and basal planes of HOPG. SECCM's nanoscale electrochemical cell can suppress the impact of capacitive current and can therefore be used to clearly measure the current associated with degradation caused by electrolyte decomposition. SECCM's local CV measurements directly exposed the degradation reaction that occurred at the edge plane in the positive potential range.

Keywords

• electrical double‐layer capacitor
• electrochemical degradation
• HOPG
• scanning electrochemical cell microscopy