Electrochemical lithiation and passivation mechanisms of iron monosulfide thin film as negative electrode material for lithium-ion batteries studied by surface analytical techniques.

Highlights: [•] XPS, ToF-SIMS analyses are combined with electrochemical control. [•] Conversion/deconversion mechanism of iron monosulfide thin film electrode is reported. [•] Incomplete process of conversion/deconversion and expansion/shrinkage is evidenced. [•] SEI layer thickness variation upon conversion/deconversion is shown. [•] Penetration of SEI layer into the bulk electrode is demonstrated. [Copyright &y& Elsevier]