Operando 3D Imaging of Electrolyte Motion in Cylindrical Li-Ion Cells

Electrolyte motion in commercial Li-ion batteries has become an important topic as researchers seek to understand patterns of degradation that occur in large-format cells. Recent work has linked the motion of excess electrolyte to Li plating on the anode of large-format cells after repeated fast charging - an effect known as electrolyte motion induced salt inhomogeneity (EMSI). Mapping the distribution and flow patterns of electrolyte in the cell is critical to understanding these phenomena and predicting the patterns of Li plating that can result. In this work, we used time-resolved, synchrotron computed tomography (CT) to directly image the flow of electrolyte in two commercial 18650 cells during cycling, with one cell containing SiOx in the negative electrode and the other containing only graphite. The former cell shows significantly more electrolyte "pumping" during charge and discharge as well as asymmetric redistribution of salt along the jelly roll after hundreds of cycles. The results yield new insights into how electrolyte motion and its effects are influenced by the composition, geometry, and orientation of the cell.