Mesoscale Models for Mechanics of Active Materials in Li-Ion Batteries

Most deformation models for Li-ion batteries are based on device-level empirical fits to the integral battery responses under the external and internal loadings. One of the main obstacles to establishing physics-based mechanical models formulations for Li-ion batteries is a lack of insight into the underlying kinematic micro-mechanisms of deformation of active materials. The active materials are compressed between current collectors, separators and other thermal management or structural layers that exert constraints and interlaminar forces that further complicate the material characterization.

            We are using recently measured [1] microstructures of different lithium nickel manganese cobalt oxide  (NMC) cathode configurations. The microstructures were determined by X-ray tomography under various pressure conditions.  The experimental data on microstructure for increasing pressure is particularly convenient for identification kinematic mechanisms of deformation and formulation of interaction models between particles in electrodes. We use these reconstructed microstructures to generate computational models and to correlate the models to the experiments. Discrete element particle-based methods are used for modeling of mechanics of electrode materials at mesoscale where the meso-scale effects dominate the through-thickness response. Individual particle response can be decoupled from the assembly response and analyzed individually for possible non-linear deformation, fracture, crushing or crumbling. In this work we concentrate on the particle models that use particle size, shape, spatial distributions and inter-particle bonding. Various computational models for the microstructure are used in this study.

            An example of a reconstructed battery electrode microstructure with weight ratio of 90:5:5 (active material : C : binder) and the mechanical compression simulation for the equivalent spherical particle model is shown in the figure below . The effects of postulated deformation mechanisms and their parameters are compared with the measures of microstructure configuration at increasing pressures. The developed models are used for modeling the mechanics of active materials in a computational framework for physics-based models of batteries [2].

References:

[1] Ebner M, Geldmacher F, Marone F, Stampanoni M, Wood V. X-Ray Tomography of Porous, Transition Metal Oxide Based Lithium Ion Battery Electrodes. Advanced Energy Materials. 2013;3:845-50.

[2] Allu, S., Kalnaus, S., Elwasif, W., Simunovic, S., Turner, J.A., Pannala, S., “A new open computational framework for highly-resolved coupled three-dimensional multiphysics simulations of Li-ion cells”, J. Power Sources 246 (2014), 876-886.