fig2

Figure 2. Exemplar characterizations used for the EEI studies. (A) XPS characterization for C 1s, F 1s, and S 2p spectra of the CEI components on the NaCu_1/9Ni_2/9Fe_1/3Mn_1/3O₂ (Na-CNFM) cathode after the 10th cycle in the electrolytes of 1 M NaPF₆/EC+DMC and NaFSI-triethyl phosphate (TEP)/1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) Reproduced from ref^[17]; copyright 2020 American Chemical Society; (B) Soft XAS Mn L-edge spectra in the TEY mode for the NaNi_1/3Fe_1/3Mn_1/3O₂ cathode after different cycling histories. Reproduced from ref^[18], copyright 2018 Wiley; (C) Cryo-TEM of the Na dendrite at low magnification in FEC-free EC:DMC-based electrolyte at the first cycle. Reproduced from ref^[19], copyright 2021 Springer Nature; (D) SEM images of charged NaFeO₂ electrodes before and after an aging cycling step (inset image: glass fiber separator after aging). Reproduced from ref^[20], copyright 2022 IOP Publishing Limited; (E) TOF-SIMS depth profiles of inorganic secondary ion fragments on the surfaces of the one-cycle Na_0.67Fe_0.5Mn_0.5O₂ electrodes showing the evolution of CO₃^- species in the CEI layer formed on the electrode surface. Reproduced from ref^[21], copyright 2021 Elsevier. CEI: Cathode electrolyte interphase; DMC: dimethyl carbonate; EC: ethylene carbonate; EEI: electrode-electrolyte interphase; FEC: fluoroethylene carbonate; SEI: solid electrolyte interphase; SEM: scanning electron microscopy; TEM: transmission electron microscopy; TEY: total electron yield; TOF-SIMS: time-of-flight secondary ion mass spectrometry; XAS: X-ray absorption spectroscopy; XPS: X-ray photoelectron spectroscopy.