The previous section indicated a loss of crystallinity of KSC during discharge which could not be reversed after charging indicating a decomposition of pristine KSC in the first cycle. In order to shed light on this decomposition we have performed periodic density functional theory calculations. For the computational details, we refer to the experimental section. As a potential degradation mechanism, we considered reactions of the type K 2 SnCl 6 + Li → K 2 SnCl x + LiCl 6-x where K2SnClx is the reduced KSC species with the preserved crystal structure. To create potential K2SnClx configurations, chlorine vacancies were introduced in the unit cell of pristine KSC. The cell contains n = 24 results in an acceptable number of structures for k = 0, 1, 2, 3, 4 (Figure ) i.e. in total 156 input structures corresponding to the stoichiometry K2SnClx with 5 ≤ 𝑥 ≤ 6.