Analysis of the interface between lithium and organic electrolyte solution

The interfacial reaction between lithium and 1 mol/dm3 LiPF6/EC+DMC solution was investigated by in situ Fourier transform infrared (FTIR) spectroscopy. The double modulation FTIR (DMFTIR) spectra after immersion for 1 and 15 h indicate the formation of new reduction products of the solvent on lithium. Morphological changes by the surface reaction were observed after immersion for 15 h by in situ AFM. Some parts of lithium surface were raised as particles or ridgelines. Measurements of force–distance curves in AFM observation were carried out to investigate the interfacial layer on lithium. An attempt was also made to estimate the thickness of passive layer on lithium, and whether polymeric layer exists on lithium or not. The interfacial layer on lithium in LiPF6/EC+DMC solution was estimated to be about 5 nm in thickness. The morphology of deposited lithium in LiPF6/EC+DMC was investigated and compared with that in LiClO4/EC+DMC by in situ AFM. The morphological change of lithium deposition in the initial stages occurred mainly on the ridgelines.