Takuya Masuda1
NIMS1
We developed in-situ X–ray photoelectron spectroscopy (XPS) and bimodal atomic force microscopy (AFM) systems and applied them to electrochemical lithiation and delithiation reactions of a silicon electrode deposited on a solid electrolyte sheet in an all-solid-state lithium-ion battery configuration. XPS showed that not only lithium silicide but also lithium oxide, lithium silicate and lithium carbonate were formed due to the lithiation of silicon and native oxide, followed by undesired side reactions with residual gasses such as oxygen and carbon dioxide in the inert condition. The spectral features of lithium silicide reversibly responded to the successive lithiation and delithiation cycles, while lithium oxide, lithium silicate and lithium carbonate formed at the surface remained unchanged as irreversible species. As long as the lithiation and delithiation cycles were repeated in the range of Li content x= 0 – 2.4 in Li<sub>x</sub>Si, the position of lithium silicide peak in the Si 2p region shifted monotonically. However, a drastic shift was observed in the successive delithiation after inserting lithium in silicon electrode up to Li<sub>3.5</sub>Si. This drastic shift was assignable to the phase transformation of crystalline Li<sub>15</sub>Si<sub>4</sub> to amorphous Li<sub>x</sub>Si. AFM showed that the Young’s modulus of silicon/lithium silicide changes consistently with change in lithium content x in Li<sub>x</sub>Si. Such spectroscopic chemical information and nanoscale mechanical information will be discussed in detail in the context of mechanical degradation.<br/><br/>References<br/>[1] R. Endo, T. Ohnishi, K. Takada, T. Masuda, “In Situ Observation of Lithiation and Delithiation Reactions of a Silicon Thin Film Electrode for All-Solid-State Lithium-Ion Batteries by X–ray Photoelectron Spectroscopy”, J. Phys. Chem. Lett., 2020, 11, 6649−6654.<br/>[2] R. Endo, T. Ohnishi, K. Takada, T. Masuda, “Instrumentation for tracking electrochemical reactions by x-ray photoelectron spectroscopy under conventional vacuum conditions”, J. Phys. Commun., 2021, 5, 015001.<br/>[3] R. Endo, T. Ohnishi, K. Takada, T. Masuda, “Electrochemical Lithiation and Delithiation in Amorphous Si Thin Film Electrodes Studied by Operando X–ray Photoelectron Spectroscopy”, J. Phys. Chem. Lett., 2022, 13, 7363-7370.<br/>[4] H. Sakai, Y. Taniguchi, K. Uosaki, T. Masuda, “Quantitative cross-sectional mapping of nanomechanical properties of composite films for lithium ion batteries using bimodal mode atomic force microscopy”, J. Power Sources, 2019, 413, 29-33.