Unusual Interface Phenomena between Graphite and Propylene Carbonate-Based Electrolyte Solutions

In the present study, the surface reactions occurring at the graphite negative electrodes of lithium secondary batteries in propylene carbonate (PC)-based media were examined. The electrode reactions were significantly affected by the electrolyte concentration. In a concentrated solution (3.27 mol kg LiClO4/PC), lithium ions were reversibly intercalated within graphite. In contrast, continual electrolyte decomposition and exfoliation of the graphene layers occurred in a low concentration solution (2.45 mol kg LiClO4/PC). In situ electrochemical atomic force microscopy revealed the formation of an effective surface film on the graphite surface after potential cycling in the 3.27 mol kg LiClO4/PC solution. The results of Raman analysis indicated the absence of free PC molecules in the concentrated solution, which suggested that ion–solvent interactions are an important factor for regulating the formation of stable surface films on graphite negative electrodes in PC-based solutions.