Fading analyses of commercial lithium-ion batteries with blended cathodes using synchrotron X-ray diffraction measurement and discharge curve analysis

We investigated the fading behavior of commercial lithium-ion batteries with blended cathodes. Synchrotron X-ray diffraction measurements revealed the constituent materials of the blended cathode and the degradation state of the cathode due to particle cracking. A particle model was newly introduced to the discharge curve analysis in order to explain the voltage change due to particle cracking, which is not considered in the conventional discharge curve analyses. Herein, blended cathode and particle models to advance the conventional discharge curve analyses have been presented. We have implemented these models besides basic model within our discharge curve analysis code called VOLCALO (VOLtage CALculation and Optimization). The blended cathode model could reproduce the measured values of the discharge curve of cycled batteries better than the conventional method and obtain a change in blend weight ratio due to degradation. The particle model analysis revealed that considering the particle size change due to particle cracking, changes in the discharge curves near the discharge end could be explained by the increase of surface sites.