On plastic deformation and fracture in Si films during electrochemical lithiation/delithiation cycling

TL;DR

This study investigates how silicon thin films deform and fracture during charge-discharge cycles in lithium-ion batteries, revealing high stress levels, fracture resistance, and damage evolution through in situ measurements and microscopy.

Contribution

It provides the first in situ stress measurements of silicon thin films during lithiation/delithiation, estimating fracture resistance and analyzing damage mechanisms.

Findings

Peak compressive stress during lithiation was 1.48 GPa

Estimated fracture resistance of lithiated Si is 9-11 J/m^2

Fracture initiation and crack density increase with cycle number

Abstract

An in situ study of deformation, fracture, and fatigue behavior of silicon as a lithium-ion battery electrode material is presented. Thin films (100-200 nm) of silicon are cycled in a half-cell configuration with lithium metal foil as counter/reference electrode, with 1M lithium hexafluorophosphate in ethylene carbonate, diethylene carbonate, dimethyl carbonate solution (1:1:1, wt.%) as electrolyte. Stress evolution in the Si thin-film electrodes during electrochemical lithiation and delithiation is measured by monitoring the substrate curvature using the multi-beam optical sensing method. The stress measurements have been corrected for contributions from residual stress arising from sputter-deposition. An indirect method for estimating the potential errors due to formation of the solid-electrolyte-interphase layer and surface charge on the stress measurements was presented. The films undergo extensive inelastic deformation during lithiation and delithiation. The peak compressive stress during lithiation was 1.48 GPa. The stress data along with the electron microscopy observations are used to estimate an upper bound fracture resistance of lithiated Si, which is approximately 9-11 J/m^2. Fracture initiation and crack density evolution as a function of cycle number is also reported.