Severe, particle-level strains induced during both production and cycling have been putatively linked to lifetime limiting damage in lithium-ion cells. Because of the presently unknown contributions of manufacturing and intercalation induced stresses in Li cells, this correlation is critical in determining optimal materials and manufacturing methods for these cells. Both global and localized loads must be estimated, in order to select materials able to resist fracture. Here, we select the LiMn 2 O 4 system for study. We present results of a set of simulation techniques, ranging from one-dimensional finite difference simulations of spherical particles, to fully three-dimensional (3D) simulations of ellipsoidal particles, to systematically study the intercalation-induced stresses developed in particles of various shapes and sizes, with the latter 3D calculations performed using a commercial finite element code. Simulations of spherical particles show that larger particle sizes and larger discharge current densities give larger intercalation-induced stresses. Simulations of ellipsoidal particles show that large aspect ratios are preferred to reduce the intercalation-induced stresses. In total, these results suggest that it is desirable to synthesize electrode particles with smaller sizes and larger aspect ratios to reduce intercalation-induced stress during cycling of lithium-ion batteries.

Numerical Simulation of Intercalation-Induced Stress in Li-Ion Battery Electrode Particles

Evolution of stress within a spherical insertion electrode particle under potentiostatic and galvanostatic operation

We examine the effects of surface tension and surface modulus on diffusion-induced stresses within spherical nanoparticles. We show that both the magnitude and distribution of stresses can be significantly affected by surface mechanics if the particle diameter is in the nanometer range. In particular, a tensile state of stress may be significantly reduced in magnitude or even be reverted to a state of compressive stress with decreasing particle radius. This reduction in tensile stress may be responsible for the observed resilience to fracture and decrepitation of nanoparticles used in various industrial applications.

The influence of surface mechanics on diffusion induced stresses within spherical nanoparticles

Modeling diffusion-induced stress in nanowire electrode structures

A review on modeling of electro-chemo-mechanics in lithium-ion batteries

The effect of chemical stress on diffusion in a hollow cylinder for plane strain and zero axial force has been investigated. Two diffusion processes of constant surface stress and constant surface potential are studied. No matter what the plane strain or zero axial force is the influence of chemical stress on the diffusion process of constant surface potential is similar to that of constant surface stress. Chemical stress enhances both the diffusion coefficient and the concentration. For a given time, the level of concentration becomes lower with a greater ratio of outer radius to inner radius for constant surface potential with given FXf and for constant surface stress with given FXi. F=2EV/[9(1−v)RT] where E, V, R, and T are the Young’s modulus, partial molal volume, gas constant, and absolute temperature, respectively; Xi and Xf are the initial and final mole fractions at boundary surfaces. The results are also compared with those in thin plates and solid cylinders reported in the literature.

W. L. Wang

Papers

Effect of chemical stress on diffusion in a hollow cylinder