Modeling Battery Cell Reversible Expansion Using the Discrete Element Method
Authors: Teel Hunter , Garrick Taylor R. , Srinivasan Srikant , Wang Fengkun , Zeng Yangbing , Shimpalee Sirivatch 
Published: December 2024

Intercalation type electrodes experience a volume change due to insertion of guest species in the host lattice.1 For lithium-ion batteries, and in particular the anode electrode, this volume change can be significant and is necessary to consider2,3 when designing these batteries, in order to link the cell level volume change to pack and system level implications4. For graphitic anodes, volume expansion can range from zero to ten percent as charging occurs5,6. Silicon based anodes, which comparatively offer a much higher theoretical energy density, can expand up to four hundred percent of its initial size7,8. If the design of the cells does not allow enough space for these expansions to occur, resultant stress on the electrode structure can cause fracturing of the active material. This leads to capacity loss9,10, reducing performance of the cell and driving other destructive behaviors during electrochemical operation.

Numerical simulation can be used to predict volumetric expansion of the electrodes and the resultant stresses in the electrode structure as lithiation occurs. One simulation method used for capturing this volume expansion is the discrete element method (DEM), which can include hundreds of particles with unique dimensions and tracks what happens in the particle phase as expansion occurs. Through use of DEM simulations we are able to capture electrode strains at a microscale level, and extrapolate these results to a cell level response. This is coupled with experimental measurements that quantify electrode level volume expansion to increase accuracy of the simulation results.

In this work, we present the expansion for a composite Active Material-Binder electrode structure and the resultant stress-strain behavior observed. Expansion of the electrode is linked to the half-cell potential11 and state-of-lithiation as well as design properties, which are quantified to give a full picture of the resultant electrode-electrolyte continuum.

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