Electrochemical lithium-ion intercalation and deintercalation at carbonaceous materials in propylene carbonate (PC)-based electrolyte solution depends on the graphitization degree of the material. In this study, graphitized carbon nanospheres (GCNSs) heat-treated at 2900°C (GCNS-2900) and 2600°C (GCNS-2600) showed the reversible lithium-ion intercalation and deintercalation in PC-based electrolyte solutions, despite their high graphitization degree. Moreover, in situ Raman spectroscopy and transmission electron microscopy (TEM) were performed to further understand the electrochemical behavior. According to the Raman spectra, the cointercalation of PC with lithium ions and partial exfoliation was observed only in GCNS-2900. The TEM images revealed that GCNS-2900 exhibited structural collapses due to the concentration of stress in the ridges of a polyhedron during the graphitization process. Such collapses were responsible for the cointercalation of PC with lithium ions and partial exfoliation in GCNS-2900. The control of the graphitization degree, including the stacking order, suppression of edges and structural collapses, and a suitable arrangement of graphene layers should effectively suppress the destruction of graphite and improve the first coulombic efficiency in PC-based electrolyte solutions.
Published in: "Journal of the Electrochemical Society".