From a DFT perspective, an accurate treatment of dopant, polaron, surface, and other defect states as function of the electrode potential is required to understand how defects modify the SCEs' properties. For instance, the potential-dependent formation of polaronic states has been shown to greatly impact the electrochemical thermodynamics and kinetics of SCEs while the localized surface states fundamentally change the proton-coupled electron transfer chemistry at metal-oxide surfaces. Furthermore, polaronic and surfaces states change the differential capacitance and e.g. Fermipinning leads to a sharply peaked differential capacitance (C SS , Eq. ( ))