Analysis and prediction of the open circuit potential of lithium-ion cells

A model is presented, which allows quantitative analysis as well as prediction of the open circuit potential of lithium-ion cells. Furthermore, the model determines half-cell potentials of already stressed lithium-ion cells, using a data set accomplished just once from half-cell potentials of a new reference cell. Its capability to describe thereby two relevant degradation processes, namely, (i) loss of active mass, and, (ii) loss of active lithium, is experimentally verified on a LiNi0.8Co0.15Al0.05O2 (NCA)/LiCoO2 (LCO) blend cell. A further extension of the model allows the prediction of the open circuit potential of a blend cathode with various blend ratios as well as the analysis of unknown blend ratios. This ability is experimentally verified for cathodes made of LiNi0.8Co0.15Al0.05O2 (NCA)/LiMn2O4 (LMO) blends. ► A model for the quantitative OCV analysis of Li-ion cells is introduced. ► In-situ diagnosis of aging mechanisms is experimentally verified. ► Loss of active lithium and contact loss of active material are separated. ► A novel model to describe the OCV of a blend cathode is introduced. ► The active masses of the blend components are determined using the OCV model.