XPS was used to investigate the elemental composition and the chemical oxidation states of KSC in the pristine, fully discharged, and charged electrodes. Most importantly, Figure compares the XPS deconvoluted spectra in the Sn 3d5/2 region. Similarly, deconvoluted spectra of the Cl 2p region are shown in Figure . For pristine KSC, a single Sn 3d5/2 peak is observed at 488.0 eV, which can be assigned to the hexachlorostannate (SnCl6 2-) ion of KSC. For the discharged electrode, the disappearance of this peak indicates complete decomposition of KSC while the detection of two new peaks at lower binding energy (Sn 3d5/2 peaks at 483.8 eV and 486.2 eV), indicates that at least partial reduction of Sn. In addition, the first (smaller) peak could be assigned to K-Sn alloy(s) since its binding energy is well below the expected value for metallic Sn (of ~ 485 eV) and the second one could be due to the formation of SnCl2 or KSnCl3, which is consistent with the DFT findings, involvement of other Sn 2+ /Sn 4+ species cannot be excluded, however, since the binding energies of compounds with these two oxidation states are usually close to each other. After the charged state, only one peak remains, which is shifted to 486.5 eV. This shift could point to an increase in the average Sn oxidation state, i.e., the presence of a larger amount of Sn 4+ species. In any case, the reformation of KSC can be excluded based on this result.