X-ray photoelectron spectroscopy (XPS) and symmetric electrochemical impedance spectroscopy (EIS) are carried out to identify and determine the nature of the solid electrolyte interface (SEI) formation on TiO2 rutile anodes in lithium ion batteries. The recorded XPS spectra (O1s, C1s, P2p and Li1s and Ti2p) evidence an SEI layer formation at 0.8 V vs. Li/Li+ in a TiO2/Li cell with a lithium reference and an organic electrolyte (LiPF6 in EC : DMC (1 : 1 by wt%)). When the cell is discharged down to 0.1 V, the SEI mainly consists of ether and carbonyl groups and some alcohol or alkoxide groups. Upon charge the SEI additionally evidences some carboxylic groups. EIS measurements exhibit an additional RQ element at 0.8 V, supporting the formation of the SEI at this potential. The EIS evaluation shows that the SEI is mainly formed in the first cycle but evolves further on in the following cycles. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.085206jes] All rights reserved.