Meaning
Physical deformation property describes the temporary expansion and contraction of cell components during rapid temperature swings. High power applications cause transient thermal strain when the internal resistance generates heat faster than the cooling system can remove it. This mechanical stress fluctuates as the load on the battery changes.
Components return to their original dimensions once the temperature stabilizes.
Expansion Coefficient
Material selection determines the magnitude of the movement during a heat event. Different parts of the battery, such as the copper current collector and the ceramic separator, experience transient thermal strain at different rates. This mismatch creates shear stress at the interfaces between layers.
Engineers use materials with matched coefficients to minimize the risk of internal cracking.
Interface Fatigue
Mechanical bonds between the active material and the substrate can weaken over thousands of cycles. Each time transient thermal strain occurs, the layers are pulled in different directions. Over time, this leads to delamination and a loss of electrical contact.
Testing involves rapid thermal cycling to observe the degradation of the internal structure.
Structural Tolerance
Repeated exposure to these forces requires a housing that can flex without breaking. Transient thermal strain is most dangerous during extreme fast charging where temperatures can rise by forty degrees in minutes. A well designed cell assembly includes enough internal clearance to allow for this expansion.
Designs that accommodate these movements prevent the delamination of active materials from the current collector.
