Electrochemical Li+ Insertion/Extraction Reactions at LiPON/Epitaxial Graphene Interfaces

Redox reactions of the Li+ insertion/extractionfromone to two interlayers of graphene (Gr) on area-defined single-crystallineSiC substrates are investigated using lithium phosphorus oxynitrideglass (LiPON) as the solid-state electrolyte. Unlike an organic liquidelectrolyte, this glassy electrolyte does not induce a reduction currentand excludes the desolvation reaction of Li+. Gr electrodeswith less than two Gr layers show a single reduction peak and oneor two oxidation peaks below +0.21 V (vs Li+/Li), differingdistinctly from those of graphite and multilayer Gr, which displaymultiple peaks (multiple stage transitions). However, this findingaligns with the conventional understanding that graphite stage structuretransitions proceed with stepwise increases or decreases in the numberof Gr layers between adjacent Li-inserted interlayers. Cyclic voltammetrymeasurements indicate the presence of surface capacity due to Li+ adsorption/desorption at the LiPON/Gr interface. Moreover,Li+ insertion and extraction induce different charge transferresistances at the level of a single interlayer. These sensitive measurementsare achieved using high-quality epitaxial Gr and LiPON electrolyte,which prevent the formation of a solid electrolyte interphase andthe desolvation reaction of Li+. Similar measurements usingbilayer Gr produced by chemical vapor deposition coupled with a Grtransfer method and an ethylene carbonate/dimethyl carbonate liquidelectrolyte are not reliable. Thus, the proposed method is effectivefor electrochemical measurement of Gr electrodes with a controllednumber of layers.

Automated summary

In this study, redox reactions of Li+ insertion/extraction from one to two interlayers of graphene on SiC substrates were investigated using LiPON glass as the solid-state electrolyte. The glassy electrolyte did not induce a reduction current and excluded the desolvation reaction of Li+. Single-layer and double-layer graphene electrodes showed a single reduction peak and one or two oxidation peaks, differing from graphite and multilayer graphene. Cyclic voltammetry measurements indicated surface capacity due to Li+ adsorption/desorption at the LiPON/graphene interface. The proposed method is effective for electrochemical measurement of graphene electrodes with a controlled number of layers.