The SBSs presented in Figure ,f,h were obtained from 100 AIMD snapshots for each concentration (for further details see SI). They provide a more detailed picture than the DoS of the structure of the band gap and its gradual narrowing and filling with increasing alkali metal concentration. SBS also lends further insights into EMT, providing information about the electron energy and momentum dispersion relations. In the following, we first perform a detailed temporal analysis of the AIMD data. Finally, we compare the calculated DoS with our reanalysed experimental data.