Influence of the lithium salt nature over the surface film formation on a graphite electrode in Li-ion batteries: An XPS study

摘要

The formation of a passivation film (solid electrolyte interphase, SEI) at the surface of the negative electrode of full LiCoO_2/graphite lithium-ion cells using different salts (LiBF_4, LiPF_6, LiTFSI, LiBETI) in carbonate solvents as electrolyte was investigated by X-ray photoelectron spectroscopy (XPS). The analyzes were carried out at different potential stages of the first cycle, showing the potential-dependent character of the surface film species formation and the specificity of each salt. At 3.8 V, for all salts, we have mainly identified carbonated species. Beyond this potential, the specific behavior of LiPF_6 was identified with a high LiF deposit, whereas for other salts, the formation process of the SEI appears controlled by the solvent decomposition of the electrolyte.