  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.
