ORALS

The study of surfaces and interfaces is one of the main fields of material science. This domain requires specific techniques of surface analysis such as X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Secondary Ion Mass spectrometry (TOF-SIMS) or Scanning Probe Microscopies (AFM a�� STM). In this field, surface and interface phenomena occurring in Li(Na, Mg, Ka��.) batteries during cycling (including liquid or solid electrolyte) play a key role for their performances. Solid Electrolyte Interphase (SEI) formed upon cycling leads to a double-edged problematic: its formation lowers the coulombic efficiency and causes irreversible capacity loss, but it also passivates the electrode from the electrolyte and prevents further aging processes. The present talk aims to obtain new sets of information on the in-depth spatial distribution of SEI species within the electrode over cycling by ToF-SIMS (surface and depth-profile experiments), XPS (using Ag source to increase the depth of analysis compared with the conventional Al source) and Auger Spectroscopy. Several systems were considered to illustrate this talk: First is the study of Full cells as Li4Ti5O12(LTO)/LiNi3/5Co1/5Mn1/5O2 (NMC) and LTO/LiMn2O4 (LMO). The interactions between the two electrodes during cycling are investigated, especially the deposition and insertion of metallic compounds within the LTO electrode, which can directly influence on the stability of the cells and their electrochemical performances. More specifically, we focus this presentation on the results obtained by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Although ToF-SIMS is a recent surface analysis method in the field of battery materials, measurements acquired with this technique could give in-depth elemental and molecular information about the interfacial layers through sputter-depth-profiling experiments. Thanks to a high sensitivity and 2 D and 3D imaging capability, it will be particularly useful to follow the deposition of low amounts of metallic species and especially manganese within the SEI layer. Moreover, the evolution of the SEI chemical composition and spatial distribution upon cycling is also reported to better understand the protective role of the SEI. Secondly, surface modification of LTO, by synthetizing a chemisorbed thin fluorinated layer upon Li4Ti5O12 (LTO) anode material is considered to manage the passivating power of the SEI leading to enhanced electrochemical performances. Overall, this talk presents the relation between electrochemical performances of Li batteries and surface and interface phenomena.

References:
Nicolas Gauthier et al. Journal of The Electrochemical Society, 165(13): A2925-A2934, 2018.