Lithiation Products of a Silicon Anode Based on Soft X-ray Emission Spectroscopy: A Theoretical Study

Abstract

Due to its exceptional lithium storage capacity silicon is considered as a promising candidate for anode material in lithium-ion batteries (LIBs). In the present work we demonstrate that methods of the soft X-ray emission spectroscopy (SXES) can be used as a powerful tool for the comprehensive analysis of the electronic and structural properties of lithium silicides Li x Si forming in LIB's anode upon Si lithiation. On the basis of density functional theory (DFT) and molecular dynamics (MD) simulations it is shown that coordination of Si atoms in Li x Si decreases with increase in Li concentration both for the crystalline and amorphous phases. In amorphous a-Li x Si alloys Si tends to cluster forming Si-Si covalent bonds even at the high lithium concentration. It is demonstrated that the Si-L 2,3 emission bands of the crystalline and amorphous Li x Si alloys show different spectral dependencies reflecting the process of disintegration of Si-Si network into Si clusters and chains of the different sizes upon Si lithiation. The Si-L 2,3 emission band of Li x Si alloys become narrower and shifts towards higher energies with an increase in Li concentration. The shape of the emission band depends on the relative contribution of the X-ray radiation from the Si atoms having different coordination. This feature of the Si-L 2,3 spectra of Li x Si alloys can be used for the detailed analysis of the Si lithiation process and LIB's anode structure identification.

Lithiation/Delithiation Properties of Lithium Silicide Electrodes in Ionic-Liquid Electrolytes

“…(c) Correlative relationship between the A ′/ A and x in Li x Si. The black squares and black or blue circles represent the A ′/ A estimated from Figure 3 in ref and the results that we investigated from parts (a) and (b), respectively. It should be noted that the peak intensities in parts (a) and (b) were normalized by the peak at 92.0 eV.…”

“…Figure c displays the relationship between the peak intensity ratio ( A ′/ A ) and x in Li x Si. Black squares denote the peak intensity ratio A ′/ A estimated from Figure 3 in ref , while black and blue circles represent the results obtained from the SXE spectra in the ionic- and organic-liquid electrolytes, respectively. The A ′/ A decreased with an increase in x (the black squares in Figure c).…”

“…(b) XRD pattern and (c) Raman spectra of the Li 1.00 Si electrode immersed in 1 M LiFSA/Py13-FSA with 2 vol % VC or FEC for 12 h. (d) Correlative relationship between the A ′/ A in the SXE spectra and x in Li x Si. The black squares and black or blue circles represent the A ′/ A estimated from Figure 3 in ref and the results from Figure S10, respectively. (e) EDS of the Li 1.00 Si electrode immersed in 1 M LiFSA/Py13-FSA with 2 vol % VC or FEC for 12 h.…”

Effects of HF on the Lithiation Behavior of the Silicon Anode in LiPF6 Organic Electrolyte Solution

“…Figure c shows SXE spectra for the first, second, and third layers, in addition to those for Li metal and c-Si as references , in the photon energy region of 50–105 eV, which covers Li K α and Si L 2,3 X-ray emissions. Combined with density of states calculations, the peak energy of 53.3 eV in Li K α and 91.8 eV in Si L 2,3 has been indicated to be relative to the c-Li 15 Si 4 alloy, and a peak energy of 53.6 eV in Li K α and 91.6 eV in Si L 2,3 is relative to the a-Li 13 Si 4 alloy . The peak energies were used to determine the compositions of the Li–Si alloys.…”

Lithiation-Induced Structural Rearrangement and Stress Change in SiCO-Derived Porous Carbon: A First-Principles Study

“…The increasing requirements of energy density in applications such as electric vehicles demand new-generation electrode materials of lithium-ion batteries (LIBs). − Graphite is currently used as an anode in commercial LIBs due to its low cost and excellent reversibility; however, it shows a relatively low capacity (372 mAh g –1 ) and limited rate capability during the insertion of lithium. , Silicon presented a very high specific capacity of 4200 mA g –1 , however, corresponding to poor cycling performance because of the large volume expansion during lithiation (around 300%) and poor electrical conductance. , Many efforts were made to develop silicon–carbon composites using carbon as a volume buffer and conductive additive, while large capacity loss during cycling is still a great challenge for these materials. − …”