Meaning
Thermal barrier values representing the opposition to heat flow at the boundaries between cells and cooling plates determine pack cooling efficiency. Sourcing specialists analyze this interfacial thermal resistance to evaluate how effectively heat can be extracted from the active cell matrices. This metric is measured in kelvin square centimeters per watt and depends on the contact pressure and the presence of thermal interface materials.
It is not applicable to liquid immersion cooling designs where the cooling fluid directly contacts the cell casings.
Boundary Condition
Microscopic air gaps between the rigid cell surfaces and the cold plates act as highly effective thermal barriers that trap heat. This interfacial thermal resistance arises because metal surfaces are not perfectly flat, resulting in very low physical contact area. Applying a compliant thermal pad or paste is necessary to fill these air gaps and create a continuous path for heat transfer.
Sourcing specifications mandate the maximum allowed roughness of the cell casings to minimize this initial thermal resistance.
Heat Transfer
High thermal resistance at these contact boundaries leads to elevated internal cell temperatures and faster capacity loss during cycling. This interfacial thermal resistance must be minimized to ensure that the active cooling system can quickly respond to sudden spikes in cell heat generation. Measuring this parameter requires thermal test vehicles that simulate the actual mechanical compression and heat flux of the final pack assembly.
It is critical to monitor how this resistance changes over time, as material aging, thermal cycling and cell breathing can cause the interface material to pump out or dry up. This degradation leads to a rise in thermal resistance, which increases the risk of thermal runaway during fast charging.
Pack Design
Sourcing agreements define the minimum compression force required during assembly to ensure the interface material performs as specified. This interfacial thermal resistance is a key input for thermal simulation models used to size the cooling channels and liquid flow rates. Contracts with cell suppliers include warranties that limit the swelling of the cell over its lifetime, preventing excessive compression force that could squeeze the interface material out of the contact zone.
This limit ensures consistent thermal performance over the vehicle’s operating life.
