Meaning
Internal mechanical tension residing within a material after the removal of external loads influences its dimensional stability and resistance to fracture. During electrode manufacturing, residual stress develops in the active coatings and current collector foils as a result of drying, calendering, and winding. This tension affects the mechanical cohesion of the layers during cell operation.
Sourcing managers must monitor these stresses to ensure cell lifetime targets are met.
Mechanical Origins
Solvent evaporation during the drying of slurries causes polymer binders to shrink, which creates tensile forces within the coating. When the dried electrode is compressed during the calendering step, residual stress builds up as the metal foil plastically deforms while the active material is crushed against it. If the pressure distribution across the roller is uneven, it leaves a pattern of variable stress across the width of the foil.
These internal stresses can cause the finished electrode strip to curl, twist, or buckle during the subsequent high-speed winding process.
Delamination Risk
Repeated volume changes during cycling lead to localized mechanical failures. In high-nickel electrodes, residual stress accelerates the formation of microcracks and increases the risk of the active coating peeling away from the current collector. The presence of stress concentrations can also trigger lithium plating by altering the local electric field.
Over time, these mechanical issues degrade the electronic connectivity of the electrode.
Measurement Technique
Non-destructive X-ray diffraction calculates stress by measuring changes in the lattice spacing.
