Electrochemical Modeling on Crack Propagation within Ni-Rich Layered Cathode Materials

Abstract

Rechargeable lithium-ion batteries (LIBs) are being actively applied to energy storage systems (ESSs) and electric vehicles (EVs) because of their high energy density and long-life characteristics. Essential to the success of these efforts is warranty for not only battery performance but also reliability, which needs to understand the underlying degradation mechanism. Particularly, as the Ni content in cathode active materials increases, crack formation and propagation within the particle has been investigated as one of main causes for LIB degradation. However, although the formation of this crack is highly related to the number of cycles and the state of charge (SOC), the related research is still stayed in place. In this study, a new electrochemical model for lithium ion batteries is proposed based on theoretical equations of crack propagation. We aim to model the phenomenon of crack propagation after cycling in different depth of discharge (DOD) levels using 18650 cells, whose chemistry is LiNi0.8Co0.15Al0.05O2/Graphite. In particular, since LiNi0.8Co0.15Al0.05O2 has a form of secondary particle, its degradation is closely related to cracks within the particle when it is charged to high voltage over long-term cycling. And it has been found the range of SOC has a greater impact on degradation than the number of cycles. We try to establish the model by giving the degradation impact of SOC and the number of cycles differently. This choice of model brings a cycle life prediction with a few parameters to be fitted to particular cells.