A new look at the solid electrolyte interphase on graphite anodes in Li-ion batteries

The solid electrolyte interphase (SEI) of graphite electrodes has been extensively studied using surface sensitive techniques such as photoelectron spectroscopy (PES) and soft X-ray spectroscopy. By combining measurements of reference compounds with graphite electrodes cycled in different electrolytes and under different conditions, knowledge of the solid electrolyte interphase (SEI) chemistry can be obtained. In this article, conclusive results concerning the chemical composition of the inorganic part of the SEI is described. The results show that Li2O often reported to be present in the SEI could be an artifact from abusive Ar+ sputtering. The presence of Li2CO3 is a matter of debate; the compound is not observed in anodes extracted from hermetically sealed cells that are never exposed to air. The results show that cell-design and sample handling are crucial to the observed chemical composition of the SEI.