Solid State Module Spring Plate Compression Allowances under Cycling
Solid state spring plate allowances absorb 10 to 18 percent cell volumetric strain while bounding contact pressure between 1.0 and 4.0 MPa across cell life.
Thermal CTE Expansion Mismatch
Meaning
Divergences in how different materials expand or contract when heated create internal stresses at their bonded interfaces. In battery assembly, the thermal cte expansion mismatch between metal cooling plates and polymer cell holders can lead to joint failure under temperature extremes.
Interfacial Stress
Every component in a battery pack expands at a unique rate determined by its coefficient of thermal expansion. When these parts are fixed together, a thermal cte expansion mismatch generates shear forces across the contact surfaces during thermal cycling. These forces are concentrated at the edges of the joints.
This local stress can exceed the yield strength of the adhesives used to secure the assembly.
Joint Degradation
Repetitive thermal cycling caused by rapid charging and harsh ambient conditions degrades the physical connection between layers. If the thermal cte expansion mismatch is large, it can cause the thermal interface material to pump out or delaminate from the cooling plate. This separation creates air gaps that reduce heat transfer efficiency.
The resulting hotspot accelerates cell aging in those localized regions.
Mitigation Technique
To address these mechanical stresses, design teams select materials with closely aligned coefficients of thermal expansion. Where this is not possible, flexible adhesive compounds are utilized to absorb the physical displacement without breaking the bond. This strategy allows the different materials to slide slightly against one another while maintaining thermal contact.
Using these compliant bonding materials prevents structural failures and maintains the integrity of the thermal path throughout the design life of the vehicle.