Stress Evolution in Lithium-ion Composite Electrodes during Electrochemical Cycling and Resulting Internal Pressures on the Cell Casing

TL;DR

This study investigates how internal stresses in lithium-ion composite electrodes evolve during electrochemical cycling and how these stresses influence internal pressures on the cell casing, providing insights into mechanical stability.

Contribution

It introduces real-time stress measurement in composite electrodes during cycling and correlates stress features with phase changes, offering new understanding of mechanical behavior in lithium-ion batteries.

Findings

Peak tensile stress during delithiation is ~1.5 MPa.

Peak compressive stress during lithiation is ~6 MPa.

Stress evolution correlates with phase transformations in the oxide.

Abstract

Composite cathode coatings made of a high energy density layered oxide (Li1.2Ni0.15Mn0.55Co0.1O2, theoretical capacity ~377 mAh/g), polyvinylidene fluoride (PVdF) binder, and electron-conduction additives, were bonded to an elastic substrate. An electrochemical cell, built by pairing the cathode with a capacity-matched graphite anode, was electrochemically cycled and the real-time average stress evolution in the cathode coating was measured using a substrate-curvature technique. Features in the stress evolution profile showed correlations with phase changes in the oxide, thus yielding data complementary to in situ XRD studies on this material. The stress evolution showed a complex variation with lithium concentration suggesting that the volume changes associated with phase transformations in the oxide are not monotonically varying functions of lithium concentration. The peak tensile stress in the cathode during oxide delithiation was approximately 1.5 MPa and the peak compressive stress during oxide lithiation was about 6 MPa. Stress evolution in the anode coating was also measured separately using the same technique. The measured stresses are used to estimate the internal pressures that develop in a cylindrical lithium-ion cell with jelly-roll electrodes.