Three-dimensional simulation of transport processes within blended electrodes on the particle scale

An electrochemical model that is capable to simulate charge and species transport within the three-dimensional particulate cathode structure of lithium-ion battery half-cells is applied to blended electrodes. The electrodes are assumed to consist of physical mixtures of LiMn2O4 (LMO) and Li[Ni1/3Co1/3Mn1/3]O-2 (NMC) as cathode active materials. The results of the numerical simulations reveal that there is a significant temporal variation in the distribution of the intercalation current between the active materials on the particulate level. In this context, the LMO component was found to be electrochemically inactive at the beginning and at the end of a simulated discharge process that leads to the identification of a suitable operating window of the half-cells between 0.2 DOD . It is shown that within this range, a relaxation of the maximum lithium concentration gradients within the NMC component is achievable. As this provides indications of reduced mechanical stresses within the active material particles, an increased cycling stability of this kind of blended electrodes is expectable. Because of the NMC component's higher volumetric capacity compared with LMO, the separator-near arrangement of NMC allows the magnitude of ionic current density to be reduced by up to 11% compared with a random particle arrangement. As this indicates a reduction of potential temperature-induced side reactions of the electrolyte, an increased cycle life of the half-cells, especially for high-performance applications, is anticipated. Consequently, multiple-layer coating processes appear particularly attractive for the production of optimized blended positive electrodes for lithium-ion batteries.