Meaning
Physical breakdown of a battery cell caused by structural stresses, volume changes, pressure fluctuations or external vibrations. This process results in the loss of active material or the compromise of internal components like the separator and current collectors. Engineers track cell mechanical degradation to predict when physical fatigue will lead to an electrical failure or a safety event.
Expansion Stress
Repeated swelling and shrinking during lithiation creates internal pressure that deforms the casing. These volumetric changes strain the binders that hold the electrode particles together, eventually leading to delamination from the copper or aluminum foil. As the electrical contact weakens, the capacity of the cell drops.
Fatigue Mechanism
Cyclic loading induces micro-cracks in the active material and the solid electrolyte interphase layer. Once the surface is breached, fresh lithium reacts with the electrolyte to thicken the resistive film and consume active ions. Over thousands of miles, the cumulative effect of road vibrations and thermal expansion cycles weakens the weld points between the tabs and the jelly roll.
If a tab snaps or a separator pinches, the cell may experience an internal short circuit that triggers a thermal event. The rate of this wear depends on the depth of discharge and the rigidity of the module housing.
Environmental Exposure
External impacts and temperature extremes accelerate the weakening of structural bonds. High heat softens polymer separators, making them more vulnerable to penetration by the expanding active materials.
