Spatial Thermal Conductivity Characterization in Prismatic Formats
Measuring anisotropic conductivity tensors under mechanical stack compression prevents thermal modeling errors in large prismatic lithium battery packs.
Interfacial Thermal Contact Resistance
Meaning
Thermal impedance arising across microscopic surface gaps, roughness asperities, and air voids between two contacting solid surfaces impedes heat conduction across mechanical joints. Minimizing interfacial thermal contact resistance is essential when mounting prismatic battery cells to aluminum cooling plates or connecting module heat sinks. Thermal management specifications dictate surface flatness, roughness tolerances, and the application of thermal interface materials to displace insulating air pockets.
Microscopic Mechanism
Real contact area between mating metallic or polymer surfaces represents only a fraction of nominal geometric contact area under light clamping. Heat transfers through microscopic solid contact points alongside low-conductivity air trapped within interface cavities. Clamping pressure deforms surface asperities elastically and plastically, enlarging direct contact zones and reducing joint resistance.
Thermal gap pads or silicone-free pastes bridge remaining interstitial micro-voids, increasing effective joint conductance across large pack areas.
Cooling Efficiency
Liquid-cooled battery packs rely on rapid heat rejection from cell casings into chilled bottom plates during fast charging cycles. Elevated contact resistance creates sharp thermal gradients, causing internal cell core temperatures to exceed safe operating limits while cooling fluid remains cold. Non-uniform pressure distribution across long cooling plates generates localized hot spots that accelerate differential cell aging within a series pack.
Consistent interface resistance maintains uniform cell temperatures across large multi-module configurations.
Verification Protocol
Test standards such as ASTM D5470 define steady-state heat flow methods to measure thermal impedance across interface materials under varying clamping loads. Purchasing agreements mandate maximum allowable thermal resistance values at nominal module assembly pressures, typically between one hundred and three hundred kilopascals. Quality control engineers verify that thermal interface materials retain elasticity, resist pump-out, and maintain low thermal impedance across accelerated thermal cycling and vibration tests.
Defective interface application invalidates module thermal simulation models and degrades pack fast-charging performance.