Visualization of solvation structure on Li4Ti5O12(111)/ ionic liquid-based electrolyte interface by atomic force microscopy

Abstract

Ionic liquids (ILs) have been intensively studied as one promising candidate for an electrolyte in 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-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide (EMI-TFSI), and a spinel-type lithium titanate (Li4Ti5O12) electrode in the presence and absence of Li-salt by frequency modulation atomic force microscopy (FM-AFM) utilizing a quartz tuning fork sensor. Solvation structures on the interface were successfully visualized by two-dimensional frequency shift mapping. Electrochemical impedance spectroscopy measurement was also performed to measure the rate of Li+-ion insertion/extraction on the interface and we found that the interfacial ion-transfer may prevent the formation of layered solvation structure.