Meaning
Dimensional increases in the metallic housing of rectangular batteries result from the internal pressure generated by intercalating ions and secondary gas production. While prismatic cell expansion is expected during charging, excessive growth can deform the cell can and damage neighboring components in a module. Stiff aluminum or steel walls provide more resistance to this motion than pouch cell materials.
Internal Force
Lithiation of the anode forces the electrode stack to push against the wide faces of the can. This prismatic cell expansion is most noticeable at high states of charge when material density is at its lowest. Engineers use external spacers to absorb this energy without failing the end plates.
Stress Calculation
Wall thickness determines the amount of elastic deflection possible before permanent deformation starts. Overcharging triggers gas release that pushes expansion beyond the limits of pure physical intercalation. Internal safety vents are designed to rupture before the case walls fail.
Module Spacing
Gaps between cells in a pack must accommodate the worst case scenario for prismatic cell expansion over years of use. Tight packing improves energy density but raises the risk of module warping. Elastic foams are placed between cells to maintain consistent contact pressure.
