Real-time Measurement of Stress and Damage Evolution During Initial Lithiation of Crystalline Silicon

TL;DR

This study measures stress and damage during the initial lithiation of crystalline silicon in lithium-ion batteries, revealing how phase transformation induces stress, fracture, and damage, impacting anode design.

Contribution

It provides in situ measurements of stress evolution and fracture mechanisms during silicon lithiation, highlighting the role of phase boundary dynamics and mechanical failure.

Findings

Stress jumps cause fractures in silicon anodes.

Biaxial compressive stress reaches ~0.5 GPa during lithiation.

Cracks propagate into crystalline silicon upon delithiation.

Abstract

Crystalline to amorphous phase transformation during initial lithiation in (100) silicon-wafers is studied in an electrochemical cell with lithium metal as the counter and reference electrode. It is demonstrated that severe stress jumps across the phase boundary lead to fracture and damage, which is an essential consideration in designing silicon based anodes for lithium ion batteries. During initial lithiation, a moving phase boundary advances into the wafer starting from the surface facing the lithium electrode, transforming crystalline silicon into amorphous LixSi. The resulting biaxial compressive stress in the amorphous layer is measured in situ and it was observed to be ca. 0.5 GPa. HRTEM images reveal that the crystalline-amorphous phase boundary is very sharp, with a thickness of ~ 1 nm. Upon delithiation, the stress rapidly reverses, becomes tensile and the amorphous layer begins to deform plastically at around 0.5 GPa. With continued delithiation, the yield stress increases in magnitude, culminating in sudden fracture of the amorphous layer into micro-fragments and the cracks extend into the underlying crystalline silicon.