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

Abstract

In situ X-ray photoelectron spectroscopy is applied to electrochemical lithiation/delithiation processes of an amorphous Si electrode sputter-deposited on a Li 6.6 La 3 Zr 1.6 Ta 0.4 O 12 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 3.44 Si by quantitative analysis of electrochemical response and photoelectron spectra. Peak fitting analysis shows the formation of Li 2 O and Li 2 CO 3 due to side reactions. Upon the following delithiation, the peak corresponding to Li 3.44 Si phase shifts back to higher binding energy to form Li 0.15 Si phase, while lithium-silicates, Li 2 O, and Li 2 CO 3 remained as irreversible species. Thus, electrochemical reactions accompanied with lithiation/delithiation processes are successfully observed.

Electrochemical Lithiation and Delithiation in Amorphous Si Thin Film Electrodes Studied by Operando X-ray Photoelectron Spectroscopy

“…32−39 In our previous study, the chemical states of an amorphous Si thin-film electrode sputter-deposited on a Li 6.6 La 3 Zr 1.6 Ta 0.4 O 12 (LLZT) solid electrolyte after the first lithiation and successive delithiation steps were quantitatively analyzed by electrochemical techniques coupled with XPS. 40 In addition to the lithium silicide (Li x Si) quasi-reversibly responding to the lithiation/delithiation, a few irreversible species such as Li 2 O, Li 2 CO 3 , and lithium silicates (Li silicates) were formed due to the side reactions of Li x Si with residual gases and lithiation of Si native oxides. In the present study, the lithiation/delithiation processes of amorphous Si electrodes were dynamically tracked by sequentially generating a series of XPS spectra composed of Li 1s, C 1s, O 1s, and Si 2p regions for comprehensive analysis.…”

“…The preparation method for a Si thin-film cell with a structure of Cu/amorphous Si/Li 6.6 La 3 Zr 1.6 Ta 0.4 O 12 (LLZT)/ Li metal cell was reported previously. 40 Initially, the garnettype LLZT solid electrolyte sheets (Toshima Manufacturing Co., Ltd.) were heated at ca. 600 °C for 2 h in a tubular furnace under an O 2 flow rate of 0.2 L/min to remove the adsorbed water molecules.…”

Design of Robust, Lithiophilic, and Flexible Inorganic‐Polymer Protective Layer by Separator Engineering Enables Dendrite‐Free Lithium Metal Batteries with LiNi0.8Mn0.1Co0.1O2 Cathode

“…For the Si 2p XPS spectrum (Figure 2g), the Si 2p peaks located at ≈101.6, and ≈103.2 eV could correspond to Li y SiO x and SiO x , respectively. [35,[48][49][50] In addition, on the basis of the binary phase diagrams ( Figure S11, Supporting Information) and Gibbs free energy which is less than zero, [43] Si is easy to form Si-Li alloy (i. e. lithium-silicide, Li x Si) with the presence of Li metal, which account for the Si 2p peak at ≈98.9 could assign to the overlap peak of Li x Si and Si. [50][51][52] As shown in the O 1s XPS spectrum (Figure 2h), one component at ≈531.5 eV is associated with O environments in the LiPAA binder and in the Li y SiO x .…”

“…[35,[48][49][50] In addition, on the basis of the binary phase diagrams ( Figure S11, Supporting Information) and Gibbs free energy which is less than zero, [43] Si is easy to form Si-Li alloy (i. e. lithium-silicide, Li x Si) with the presence of Li metal, which account for the Si 2p peak at ≈98.9 could assign to the overlap peak of Li x Si and Si. [50][51][52] As shown in the O 1s XPS spectrum (Figure 2h), one component at ≈531.5 eV is associated with O environments in the LiPAA binder and in the Li y SiO x . [49,[53][54][55] The other peaks are detected at ≈528.7 and ≈532.1 eV, which can be respectively attributed to Li 2 O and SiO x .…”

Lithiation of Single-Crystalline Ge(111) and Si(111) Investigated by X-ray Photoelectron Spectroscopy

“…Nevertheless, Ge exhibits high lithium-ion diffusivity (400 times faster than Si), enabling an ultrafast charging rate of up to 1000 C, and high electrical conductivity (∼100 times higher than Si); furthermore, it is less sensitive to surface oxidation than Si. − In addition, it was reported that Si and Ge have markedly different responses to electrochemical lithiation/delithiation. − For example, the lithiation of crystalline Si (c-Si) exhibits a strong orientation-dependence (anisotropy), with the predominant expansion along the (110) directions and little expansion along the (111) directions. , Recent in situ transmission electron microscopy (TEM) and first-principles studies showed that lithium diffusion into crystalline silicon occurs more exclusively along the (110) and (112) surfaces than along the (111) surface, and a layer-by-layer peeling mechanism was suggested. , In contrast, the lithiation of crystalline Ge (c-Ge) is largely isotropic. , Furthermore, in comparison to Ge, the lithiation of Si is more sensitive to the change of doping conditions and electrical conductivity, resulting from their differences in band structures and electronic properties. , …”