# Electrochemical Lithiation and Delithiation of Amorphous Nonstoichiometric Silicon Oxide Thin-Film Electrode Studied by Operando X‑ray Photoelectron Spectroscopy

## TL;DR

This study uses X-ray spectroscopy to observe how lithium interacts with a silicon oxide electrode during charging and discharging.

## Contribution

The paper reveals the depth-dependent lithiation mechanism in nonstoichiometric SiOx thin films using operando XPS.

## Key findings

- Lithiation initially occurs at the SiOx/Li6.6La3Zr1.6Ta0.4O12 interface, forming LiySi and Li silicates.
- Lithiation propagates into the bulk as the composition reaches Li∼2.0Si, increasing the ion conductive pathway.
- Lithiation/delithiation becomes uniform across the SiOx film at higher capacities.

## Abstract

Electrochemical lithiation/delithiation of a nonstoichiometric
silicon oxide (SiO
x
) thin-film electrode
on a Li6.6La3Zr1.6Ta0.4O12 were analyzed using operando X-ray
photoelectron spectroscopy (XPS). At the pristine SiO
x
surface, bulk Si and SiO
x
peaks were observed and remained unchanged in the capacity density
from 0 to ∼1300 mAh gSi
–1. At
the capacity density of ∼1400 mAh gSi
–1, however, new peaks corresponding to Li∼2.0Si
and Li silicates appeared simultaneously with a substantial decrease
in the bulk Si and SiO
x
peaks. These results
imply that, in the initial stage, lithiation of SiO
x
occurred at the SiO
x
/Li6.6La3Zr1.6Ta0.4O12 interface
to form Li
y
Si and Li silicates, which
was beyond the probing depth of XPS. Subsequently, lithiation gradually
propagated into the bulk and approached the probing depth of XPS as
the composition reached Li∼2.0Si, thereby elongating
the ion conductive pathway. Thereafter, the position of the Li
y
Si peak reversibly responded to the state
of charge because lithiation/delithiation occurred uniformly across
the SiO
x
thin film.