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. (C) 2016 The Electrochemical Society. All rights reserved.