Graphene nanosheets (GNS) were used as anodes in full Li-ion cells and LiFePO4 (LFPO) was used as the cathode. A rapid decrease in capacity was observed following the first cycle, the origin of which was assigned to Li consumption in the solid-electrolyte interface (SEI) formation. A reduction of the irreversible capacity from 120 to a value as low as 20 mAh g(-1), similar to a commercial graphite anode, was possible through a prelithiation treatment prior to cell assembling. However, the GNS electrode barely delivered a capacity ca. 40 mAh g(-1) at the end of cycle 50, notably lower than that of the graphite electrode (ca. 100 mAh g(-1)). X-ray photoelectron spectroscopy spectra of the pristine electrodes at the end of 6th and 22nd charges, combined with depth profile analysis, supplied valuable information on the thickness and composition of the SEI. The spectra revealed that the SEI formed on the graphite electrode was much thicker than that formed on the GNS electrode and that its composition was controlled mainly by Li2CO3. The strength and the stability of Li2CO3 are two requisites for establishing a good SEI, which is the reason why the cell made from graphite performed better.