Analysis of lithium-ion battery performance and degradation presents many multi-physics challenges as we look to understand the plethora of coupled mechanisms occurring within a single electrode. Electrochemical reactions in the active material introduce mechanical stresses as cathode particles swell upon lithium intercalation. Over numerous charge-discharge cycles, this behavior can lead to mechanical degradation, and thus, capacity fade. The presence of a secondary conductive binder phase additionally complicates these mechanisms, altering ionic and electronic conduction pathways, masking available surface area for reaction, and buffering mechanical contacts. As these mechanisms are largely governed by effects at the mesoscale (structures of 100s of active material particles joined by binder), we focus our computational efforts on resolved cathode mesostructures.

In this talk, we will present a variety of different simulations which study half-cell performance at constant current discharge. The Conformal Decomposition Finite Element Method (CDFEM) algorithm is used to generate conformal mesoscale meshes of particle, conductive binder, and electrolyte phases, derived directly from 3D computed tomography data of NMC333 cathodes. This mesoscale approach for coupled electrochemical and mechanical simulations allows exploration of phenomena at the particle scale, while also providing insight on macroscale effective properties. Here, we will discuss the manifestation of local stresses from lithiation-induced swelling, as well as the impact of concentration gradients and local mesostructure on half-cell discharge curves and other macroscopic behavior. Additionally, we will investigate the influence of manufacturing processes on cell performance by studying a range of calendering pressures and binder loading fractions.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.