Stress Evolution in Composite Silicon Electrodes during Lithiation/Delithiation

TL;DR

This study measures real-time stress in composite silicon electrodes during lithiation/delithiation, revealing how binder properties influence stress evolution and indicating plastic deformation impacts cycling stability.

Contribution

First in-situ stress measurements on composite Si electrodes, demonstrating binder-dependent stress behavior and plasticity effects during electrochemical cycling.

Findings

Stress in CMC-based electrodes reaches 70 MPa during lithiation.

PVDF-based electrodes exhibit lower peak stress (~12 MPa).

Stress response depends on cycling history due to plastic deformation.

Abstract

We report real-time average stress measurements on composite silicon electrodes made with two different binders [Carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF)] during electrochemical lithiation and delithiation. During galvanostatic lithiation at very slow rates, the stress in a CMC-based electrode becomes compressive and increases to 70 MPa, where it reaches a plateau and increases slowly thereafter with capacity. The PVDF-based electrode exhibits similar behavior, although with lower peak compressive stress of about 12 MPa. These initial experiments indicate that the stress evolution in a Si composite electrode depends strongly on the mechanical properties of the binder. Stress data obtained from a series of lithiation/delithiation cycles suggests plasticity induced irreversible shape changes in contacting Si particles, and as a result, the stress response of the system during any given lithiation/delithiation cycle depends on the cycling history of the electrode. While these results constitute the first in-situ stress measurements on composite Si electrodes during electrochemical cycling, the diagnostic technique described herein can be used to assess the mechanical response of a composite electrode made with other active material/binder combinations.