Stress State Characterization of Li-Ion Batteries Based on a Membrane Sensor

Uneven force distribution in the cell may cause material deformation and stress concentration, affecting the performance and life of the cell. The uneven force distribution phenomenon present in the cell is artificially constructed and exacerbated by applying a cross tape to the surface of a Li-ion pouch cell. The flexibility of the membrane sensor allows it to conform better to cells and enables an accurate measurement of the stress distribution. In the early charging stage, the active material in the tape region undergoes preferential Li+ insertion, resulting in a rapid increase in stress. In the latter charging stage, the lithiation phenomenon becomes more pronounced in the vicinity of the tape. By disassembling and inspecting the aged electrodes, we observe that the tape-overlapped region experiences the highest and evenly distributed force, resulting in partial electrode structure alteration and crack formation. However, the regions at the outer edge of the tape experience a significant stress gradient, leading to noticeable differences in particle appearance and the formation of Li dendrites. Hence, uneven stress distribution results in uneven utilization of the capacity. This work exemplifies the importance of membrane sensors in cell stress monitoring and explores the effect of inhomogeneous forces on Li+ insertion and electrode changes in cells.