<i>In Situ</i> Observation of Lithiation and Delithiation Reactions of a Silicon Thin Film Electrode for All-Solid-State Lithium-Ion Batteries by X-ray Photoelectron Spectroscopy

Abstract

<i>In situ</i> X-ray photoelectron spectroscopy is applied to electrochemical lithiation/delithiation processes of an amorphous Si electrode sputter-deposited on a Li_6.6La₃Zr_1.6Ta_0.4O₁₂ solid electrolyte. After the first lithiation, a broad Li peak appears at the Si surface, and peaks corresponding to bulk Si and Si suboxide significantly shift to lower binding energy. The appearance of the Li peak and shift of the Si peaks confirm the formation of lithium-silicide and lithium-silicates due to the lithiation of Si and native suboxide. The composition of lithium-silicide is estimated to be Li_3.44Si by quantitative analysis of electrochemical response and photoelectron spectra. Peak fitting analysis shows the formation of Li₂O and Li₂CO₃ due to side reactions. Upon the following delithiation, the peak corresponding to Li_3.44Si phase shifts back to higher binding energy to form Li_0.15Si phase, while lithium-silicates, Li₂O, and Li₂CO₃ remained as irreversible species. Thus, electrochemical reactions accompanied with lithiation/delithiation processes are successfully observed.