In Situ Measurements of Stress Evolution in Silicon Thin Films During Electrochemical Lithiation and Delithiation

TL;DR

This study uses in situ stress measurements to analyze the mechanical behavior of silicon thin films during lithiation and delithiation, revealing elastic and plastic deformation processes and their impact on energy dissipation and electrochemical potential.

Contribution

It provides the first in situ stress evolution data in silicon electrodes during cycling, linking mechanical energy dissipation to electrochemical polarization.

Findings

Plastic deformation dissipates mechanical energy during cycling.

Stress relaxation correlates with electrode potential relaxation.

Plastic flow stress varies with lithium concentration.

Abstract

We report in situ measurements of stress evolution in a silicon thin-film electrode during electrochemical lithiation and delithiation by using the Multi-beam Optical Sensor (MOS) technique. Upon lithiation, due to substrate constraint, the silicon electrode initially undergoes elastic deformation, resulting in rapid rise of compressive stress. The electrode begins to deform plastically at a compressive stress of ca. -1.75 GPa; subsequent lithiation results in continued plastic strain, dissipating mechanical energy. Upon delithiation, the electrode first undergoes elastic straining in the opposite direction, leading to a tensile stress of ca. 1 GPa; subsequently, it deforms plastically during the rest of delithiation. The plastic flow stress evolves continuously with lithium concentration. Thus, mechanical energy is dissipated in plastic deformation during both lithiation and delithiation, and it can be calculated from the stress measurements; we show that it is comparable to the polarization loss. Upon current interrupt, both the film stress and the electrode potential relax with similar time-constants, suggesting that stress contributes significantly to the chemical potential of lithiated-silicon.