Staircase potential-electrochemical impedance spectroscopy (SPEIS) was performed in 21 steps between 3 to 1.5 V vs. Li/Li + , corresponding to ca. 71 mV increments. Between each EIS measurement, a 10 min chronoamperometric step was performed to reach steady state conditions. The frequency range was set from 1 MHz to 10 mHz. Each frequency was averaged for 3 times, and 10 points per decade were recorded. All measurements were carried out in a temperature-controlled chamber (Binder) at 20 °C using Biologic potentiostats (VMP-3e and VMP-300).