Strain Propagation in Lithium-Ion Batteries from the Crystal Structure to the Electrode Level

The propagation of strain within a commercial LiCoO2 (LCO) electrode for lithium-ion batteries is investigated during cycling. An experimental multiscale approach is combined with microstructural, mechanical simulations. The crystal structure exhibits a volume change of 2.32% measured by in operando X-ray diffraction (XRD) measurements. The resulting change in the electrode thickness is about 1.8% and is measured by electrochemical dilatometry. The width of the electrode, volume fraction of active material, and binder geometry all affect the electrode deformation; this is investigated using a representative spherical particle model (RSPM). Thereby, the anisotropic swelling behavior of the electrode is verified, as the in-plane expansion of the electrode is restricted by interactions between the particles, binder, and the current collector. SEM images of the electrode are used to model the electrode expansion in a realistic microstructure. The simulation reveals that load paths form inside the electrode and cause stress peaks inside the binder material. To compare the 2D simulations with experimental data, a 3D RSPM is constructed. Based on these findings, we propose an equation that predicts the expansion of electrodes based on characteristics of the crystal structure.