The Scanning Electron Microscopy (SEM) image of the thin-film LNMO electrode was captured using a Nova 600 NanoLab. An in-house designed 3-electrode electrochemical-ellipsometry cell (Redox.me) was used for cyclic voltammetry (CV), galvanostatic cycling, and EIS characterizations. In this work, we exploited only the air-tight feature of the cell. For relevant ellipsometry studies, we direct readers to our previous works . The electrochemical-ellipsometry cell was assembled inside an Ar-filled glovebox (Jacomex) with thin-film LNMO as the working electrode (WE), Li metal as both CE and RE, and 1 M LiPF 6 in propylene carbonate (PC) as the electrolyte. The geometrical surface area of WE is 1.13 cm 2 (12 mm diameter). Potentiostatic EIS measurements were carried out using BioLogic SP-200 potentostat with a 7.07 mV root-mean-squre (RMS) amplitude and a frequency range of 10 mHz to 200 kHz. Due to the pronounced self-discharge rate of the thin-film LNMO electrode , EIS was conducted at a quasisteady state after holding at the designated potential levels for 30 minutes. After the EIS measurement, the electrode was (galvanostatically) charged to the next target potential level. All the potential values appeared in this work are versus Li/Li + .