Intercalation into and film formation on pyrolytic graphite in a supercapacitor-type electrolyte (C2H5)4NBF4/propylene carbonate

Highly oriented pyrolytic graphite (HOPG) in a solution of (C2H5)4NBF4 in propylene carbonate (PC) was investigated as a model system for the electrochemical double-layer capacitor (EDLC) negative electrode. For the first time the intercalation of (C2H5)4N+ into HOPG could be monitored by means of in situ atomic force microscopy (AFM). In analogy to the behavior in Li+ containing solution the formation of a surface film on the negative electrode could be detected. The question is addressed if this film might serve as a solid electrolyte interphase preventing sustained solvent decomposition.