Two-dimensional analysis on interfacial solvation structure of ionic liquid electrolyte on a hydrogen-terminated Si electrode by atomic force microscopy

Abstract

Abstract Ionic liquids (ILs) have been intensively studied as a new electrolyte for lithium-ion batteries (LIBs). Structural analysis of interfaces between an IL-based electrolyte and a LIB electrode would provide beneficial information for improving LIBs. In this study, we investigated the interfacial structures between an IL, 1-methyl-1-propyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py13-TFSI), and an H-terminated Si(111) electrode in the presence and absence of Li-salt by frequency modulation atomic force microscopy (FM-AFM) utilizing a quartz tuning fork sensor. Two-dimensional frequency shift mapping imaging of the solvation structure at the interface showed that the layered solvation structure was only observed in the absence of Li salts in the ILs, which was in good agreement with our previous studies performed on the IL/lithium titanate interfaces. Combined with the electrochemical measurements, the partial disappearance of the layered solvation structure in the Li-salt-doped IL was strongly suggested to be due to the Li-ion insertion/extraction at the IL/Si interface.