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.
Transient Plane Source Method
Meaning
Non-destructive photothermal measurement technique utilizing a flat, double-spiral resistive nickel sensor element embedded inside an insulating polymer film evaluates thermal conductivity, thermal diffusivity, and volumetric heat capacity of solid materials. Employing the transient plane source method delivers accurate thermal transport measurements for battery electrode sheets, separator films, thermal interface materials, and solid electrolyte discs. Sourcing teams specify this test method because it measures directional thermal transport without requiring extensive sample destruction.
Operating Principle
A thin sensor acts simultaneously as a precise heat source and dynamic resistance thermometer during test cycles. Applying a continuous electrical current pulse heats the sensor, causing heat to diffuse outward into contacting test specimens positioned on both sides. The rate of sensor temperature increase depends directly on the thermal transport properties of surrounding materials.
Recording electrical resistance changes over test periods ranging from seconds to minutes generates temperature-versus-time curves analyzed to extract thermal parameters.
Anisotropic Resolution
Layered battery materials, such as laminated pouch cells and calendered electrode foils, exhibit strong thermal anisotropy where in-plane conductivity far exceeds through-plane conductivity. Specialized analytical models within the test framework decouple in-plane and through-plane thermal conductivity tensors from a single test run. Clamping fixtures apply uniform mechanical pressure to minimize interfacial contact resistance between the flat sensor and compliant battery specimens.
This capability provides essential material properties needed for multi-dimensional thermal simulations of battery packs.
Standardization Framework
ISO 22007-2 governs the experimental setup, sensor sizing, power output limits, and calculation algorithms for transient plane source testing. Sourcing agreements require test documentation verifying sensor radius selection, probing depth compliance, and boundary condition limits to prevent edge reflection errors. Qualified testing laboratories supply certified thermal conductivity datasheets across varying compression loads and cell states of charge.
Defensible thermophysical data ensure accurate battery thermal management sizing and reliable module cooling design.