In view of the worldwide efforts to reduce global CO2-emissions, EVs are seen as a climate-friendly alternative to fossil-based propulsion methods. Therefore, the overall share of EVs is expected to rise even more in the nearer future. This very technology however, not only offers advantages and possibilities, but also poses a great danger int the event of an accident or abuse.
Our goal is to provide a progressive model for simulating the response of Lithium-ion battery (LIB) cells under thermo-mechanical loads. In order to achieve this goal, a precise knowledge of different mechanical and thermal material property parameters is necessary, since the output of a simulation can only be as precise as its input parameters. The majority of measurement errors can be traced back to sample preparation such as opening used cells, separating and washing of the electrode materials as well as test specimen preparation and measurement.
To enhance the most critical aspects of sample preparation, methods from literature and standards were empirically tested for their suitability. These methods were further refined as needed to minimize potential errors at each step and to streamline the entire preparation process, making it easier and more repeatable. One focus was on opening the used cells under inert conditions with rotary cutters followed by separating the sandwiched jelly roll into individual layers. A thorough but gentle leaching of the electrolyte from all materials was then carried out to ensure that they were inert enough for measurements under room conditions and would not affect the health of the experimenter. Experience has shown that tensile forces are primarily absorbed by the metallic collector foils in electrode layers. In addition, the active material tends to complicate tensile experiments due to issues such as delamination. Therefore, it is often beneficial to remove the active material before conducting these experiments. To achieve this, physiochemical separation methods were explored and refined, ensuring the active material can be removed without introducing additional defects into the metallic foils. Finally, a method for cutting samples that avoids adding notches to the sample edges, along with a precise and repeatable technique for accurately measuring all sample dimensions, will complete the sample preparation process. Accurate sample preparation forms the basis for a comprehensive thermomechanical characterization of the battery cell components, which is crucial for the development of a detailed simulation model of the battery cell.