Characterisation of the solid electrolyte interface during lithiation/delithiation of germanium in an ionic liquid

In this paper, we present investigations of the interface of electrodeposited Ge during lithiation/delithiation in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide containing 0.5 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI/[Py-1,Py-4]TFSI). Cyclic voltammetry (CV) and infrared spectroscopy were used to study the electrochemistry and the changes in the electrolyte during the Li intercalation/deintercalation processes. From infrared spectroscopic analysis, it was found that the TFSI anion decomposes during the lithiation process, resulting in the formation of a solid-liquid interface (SEI) layer. X-ray photoelectron spectroscopy was used to analyse the composition of the SEI layer and the changes in the electrodeposited germanium. Furthermore, atomic force microscopy (AFM) was used to evaluate the changes in the SEI layer which showed that the SEI layer was inhomogenous and changed during the lithiation/delithiation processes.