fig4

Figure 4. X-ray photoelectron spectra of Cu electrodes recovered from Cu||Li cells, cycled either with QSPE-2 (upper panels) or QSPE-3 (lower panels) as electrolyte. Cycling was performed at room temperature, with two and a half cycles at 2 mAh cm^-2 and 0.1 mA cm^-2, followed by 50 cycles at 0.2 mAh cm^-2 and 0.1 mA cm^-2. (A) F 1s, (B) O 1s, (C) N 1s, (D) C 1s, (E) B 1s and( F) S 2p core levels with corresponding fittings based on internal references as well as^[38,60,61] and refs therein.