In situ X-ray diffraction of the intercalation of (C2H5)4N+ and BF4- into graphite from acetonitrile and propylene carbonate based supercapacitor electrolytes

The intercalation of (C2H5)4N+ and BF4- from acetonitrile (AN) and propylene carbonate (PC) solutions into bound graphite electrodes during cyclic voltammetry was investigated by in situ X-ray diffraction (XRD) using synchrotron radiation. The disappearance of the 002 reflection of graphite in the XRD patterns upon intercalation of (C2H5)4N+ indicates that the cations are accumulated between the graphene layers. For the intercalation of BF4-, the appearance of 00l reflexes in the intercalated state provides clear evidence of staging. In both cases, the in-plane periodicity was not significantly altered by the intercalation process apart from slight changes in the CC bond length. The intercalation of BF4- from the PC-based electrolyte was found to have the least destructive effect on the periodicity of the graphite structure during initial cycling in the anodic potential range along with the highest charge/discharge efficiency.