Method for analyzing in-situ volume change of large format lithium-ion hard case cells

To achieve high volumetric energy density in li-ion battery systems, it is relevant to predict the required space for reversible and irreversible volume change of the battery cells. In prismatic hard case cells, a locally inhomogeneous change in thickness occurs due to the rigid housing, which makes geometric analysis much more difficult. This publication highlights the challenges of analyzing prismatic hard case cells with existing test benches. In addition, an innovative test method is presented, in which the cells are both, compressed by air pressure and measured three-dimensionally. Influences such as gas inclusions between the electrode layers or plastic deformations of the housing can be reduced or even eliminated. This method enables a clear description of the local cell thickness at defined pressure, state of charge (SOC) and energy throughput (ETP). The resulting data can be used for a 3D simulation to estimate the required installation space within a battery system and the resulting force and pressure.