Lithiation of Silicon Anode based on Soft X-ray Emission Spectroscopy: A Theoretical Study

TL;DR

This study uses soft X-ray emission spectroscopy combined with DFT and MD simulations to analyze the electronic and structural changes in lithium silicides during silicon lithiation, revealing spectral signatures of structural disintegration.

Contribution

It demonstrates that SXES can effectively analyze silicon lithiation, providing new spectral insights into Si-Si network disintegration in lithium silicides.

Findings

Si coordination decreases with lithium concentration in LiₓSi.

Amorphous LiₓSi shows Si clustering and covalent bonds.

Spectral shifts in Si-L₂,₃ emission bands reflect lithiation stages.

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.