Myoungdo Chung

Implementing Realistic Geometry and Measured Diffusion Coefficients into Single Particle Electrode Modeling Based on Experiments with Single LiMn2O4 Spinel Particles

Realistic geometry and diffusion coefficients were measured from a single particle LiMn2O4 electrode and implemented into a three-dimensional multiphysics simulation of a single particle, in order to demonstrate a novel approach to electrode material study. Dispersed particles were used, and electrochemical techniques and atomic force microscopy were performed on isolated single particles. Diffusion coefficients measured from both cyclic voltammetry and the potentiostatic intermittent titration technique ranged between 3.2 � 10 � 12 and 1.2 � 10 � 11 cm 2 /s, which was similar to values measured from thin film LiMn2O4 electrodes. The trend of diffusivity change over potential (versus lithium counter electrode) was similar to those observed from both composite cells and thin film electrodes. The measured diffusion coefficients were then used in simulation of discharge of the irregular particle, by importing the particle morphology into a finite element simulation, in order to simulate intercalation-induced stress generation. Simulation results showed a higher maximum stress generation due to altering diffusivity around the peak current potentials and high local stress concentration on the sharply indented surface area, suggesting that particle irregularities are important in studying both electrochemical performance and local failure mechanisms in cathode materials.

Generation of Realistic Particle Structures and Simulations of Internal Stress: A Numerical/AFM Study of LiMn2O4 Particles

In this paper, the real geometries of cathode particles are reconstructed using atomic force microscopy (AFM). Finite element analysis of intercalation-induced stress is applied to the reconstructed realistic geometries of single and aggregated particles. The reconstructed particle geometry shows rugged surfaces at the boundary for Li-ion flux, which cause larger surface areas than smooth particles. The finite element model of a LiMn2O4 system is simulated under galvanostatic and potentiodynamic control. To investigate the realistic level of boundary flux at particle scale, macroscale simulation results are also applied to intercalationinduced stress analysis of real cathode particles. The numerical results of intercalation-induced stress show that the von Mises stress is concentrated at sharply dented boundaries due to curvature effects when Li ions intercalate or deintercalate and is an order-of-magnitude higher in realistic particle geometries than the stress in ideal smooth particles. It has also been shown that the stress under potentiodynamic control is higher than the stress under galvanostatic control because the high Li-ion flux at two plateaus in the open-circuit potential of a LiMn2O4 system results from linear voltage sweep. We also present results showing that some mesh architectures are preferred for handling these potentially singular regions. V C 2011 The Electrochemical Society. [DOI: 10.1149/1.3552930] All rights reserved.