Potential change during intercalation of sulfuric acid in host carbons with different textures

From the electric potential changes, the intercalation reaction of sulfuric acid in graphite was divided into two elemental processes: the charging process of the interface between graphite layer and intercalated sulfuric acid in pure stages, which corresponded to a steep increase in potential, and the stage transformation process caused by further intercalation, which showed a plateau on the potential change due to equilibrium between two stage structures. On the assumption that a part of the electric quantity applied to further intercalation during the stage transformation process was consumed on extra-charging of graphite layers, the potential curve against electric quantity could be simulated. The simulated potential curves were compared with experimental ones observed by galvanostatic and chemical intercalations in three host carbon materials with different nanotextures, natural graphite flakes, mesophase-pitch-based carbon fiber and vapor-grown carbon fiber. The host with high crystallinity as natural graphite flakes showed distinct plateaux in potential, suggesting a lower degree of overlapping of extracharging of graphite layers into the stage transformation process. On the other two hosts, a higher degree of overlapping was observed. The effect produced by host carbon texture on the intercalation was discussed by mutual comparison.