In OSLiB, safety-critical conditions for lithium-ion batteries are investigated from the cell to the system level and methods for detecting them are developed and validated. The investigations are carried out on commercial reference cells as well as cells with targeted defects that result in safety-relevant issues such as lithium plating. For the online diagnosis, two classes of methods are considered which either require additional excitation and hardware or only rely on the "classical" battery management system data (voltage, current, temperature) and variables derived thereof. The objective of OSLiB is the reliable detection of safety-critical conditions, such as lithium plating, critical temperatures and the detection of dendrite formation at the cell and also the module level. The scaling from the cell to the battery system level focuses on the localization of safety-critical cells within a parallel and/or serial network by analysing inhomogeneities in the network. The validation of the online diagnostic methods developed in the project is based on post-mortem analyses of the cells under investigation. Based on the results, requirements enabling the integration of diagnostic procedures into the battery system and the BMS will be specified.