Li+ Insertion and Extraction Mechanism at Epitaxial Graphene/Solid-State Electrolyte Interfaces

The Li+ insertion/extraction mechanism in cells with a multilayer graphene (MGr) or few-layer graphene anode and a lithium phosphorus oxynitride glass electrolyte (LiPON) was investigated as model interfaces for the graphite anode in all-solid-state batteries. Multiple redox peaks were observed, in the cyclic voltammetry measurements for the cell with MGr obtained by chemical vapor deposition, which were not clearly seen in the cell using an organic liquid electrolyte. These peaks correspond to the stage structure changes associated with the Li+ insertion/extraction. In addition, the charge transfer resistance at the LiPON/MGr interface was significantly smaller than that of the cell using an organic liquid electrolyte. Epitaxial graphene grown by thermal decomposition of SiC was used for the 1–2 layer graphene anode. In this case, redox peaks corresponding to Li+ insertion/extraction were also clearly observed in the cyclic voltammetry measurements, although the current was smaller than that for MGr. Our results in both few-layer and multilayer cases suggest that Li+ ions insert and extract from the edges of graphene, and no significant solid electrolyte interphase or Li+ desolvation reaction occurs at the LiPON/graphene interface.