In Situ Atomic Force Microscopic Studies of LiFSI-[Py_1,4]FSI Interfacial Nanostructure on Au(111): Solid Electrolyte Interphase and Lithium Underpotential Deposition

Abstract

In this paper, the structure of the LiFSI-[Py1,4]­FSI interface on Au(111) was investigated using in situ atomic force microscopy and cyclic voltammetry. Raman and IR vibrational spectroscopy was applied to evaluate the coordination of Li+ ions with the FSI– anion. It was found that [Li­(FSI)3]2– species are present in the solutions. The solvation layer number and the forces decrease at higher concentration of Li+ ions. Therefore, the driving force, which is required for the [Li­(FSI)3]2– species to pass through the solvation layer to reach the electrode surface, is lowered. This increases the onset potentials of the SEI layer formation and lithium underpotential deposition (Li-UPD) at high Li+ concentrations. It was found that the onset potentials are −0.8, −0.7, −0.6, and −0.4 V for the Li-UPD and −2.0, −1.6, −1.4, and −1.3 V for the SEI layer formation, vs the Pt-(quasi)­reference electrode, corresponding to Li+ concentrations of 0.1, 0.25, 0.5, and 1 M, respectively.

In Situ Electrochemical Surface Plasmon Resonance Study on Lithium Underpotential Deposition and Stripping in Bis(fluorosulfonyl)amide-Based Ionic Liquids

“…For [Li­(G4) + ]­[FSA – ], the scan range was from −3 to −1.8 V, while for [C 4 mim + ]­[FSA – ], it was from −2.8 to −1.5 V because the UPD/UPS peaks were 0.2 V more positive for the latter (see the discussion below). In each CV, a current peak pair assignable to the Li UPD/UPS was observed as in previous studies of Li UPD/UPS in organic electrolytes , and ILs , on gold. For the solvate IL, [Li­(G4) + ]­[FSA – ], the reductive deposition peak of Li UPD appeared at −2.9 V in the negative-going scan, just before the start of the bulk Li deposition.…”

“…Above the ILs, the atmosphere of the Ar gas (99.9%) was kept over the whole measurement. In the simultaneous cyclic voltammetry and ESPR measurements, a PC-controlled potentiostat (Autolab Type III) controlled the potential of the working electrode vs Ag/AgCl, E , with the scan rate of 50 mV s –1 , which is in the range of 10–100 mV s –1 adopted in the previous CV studies on Li UPD. ,− Before each scan, E was held at −2 V for 1000 s to stabilize the SPR angle and current.…”

“…Scanning electron microscopy (SEM) − ,, is a powerful method to visualize the electrode surface in an ex situ manner after the Li electrodeposition process in ILs. As for the in situ experimental methods to study Li electrodeposition in ILs, scanning tunneling microscopy (STM), optical microscopy observation, , atomic force microscopy (AFM), , and electrochemical quartz crystal microbalance (EQCM) , were used to study not only the electrode surface morphology − but also the IL structure on the electrode. ,− …”

Suppressing water clusters by using “hydrotropic” ionic liquids for highly stable aqueous lithium-ion batteries

“…Typically, the FTIR peaks for FSI À anions in the ranges of 540-620 cm À1 and 700-900 cm À1 are highly sensitive to the coordination environment of FSI À anions. [36][37][38] The peaks at 582 cm À1 , 592 cm À1 and 850 cm À1 are ascribed to [Li(H 2 O) x ] + ions in the H 2 O-Li + -FSI À solvation structures. 39 However, the addition of ionic liquid PP 13 FSI tends to largely isolate different H 2 O-Li + -FSI À solvation clusters with the suppression of H 2 O-H 2 O interactions as shown in the simulated structures in Fig.…”