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.
In-Plane Conductivity
Meaning
Transport property metrics quantify the ease with which electrons or ions move parallel to the surface of an electrode layer. Measuring the in-plane conductivity is essential for designing electrodes that can handle high currents without excessive heat generation. This lateral movement is considerable in large format cells where the current must travel a distance to reach the tab or collector.
Lateral Diffusion
Efficiency in a battery depends on the uniform distribution of current across the entire electrode area. High in-plane conductivity prevents the formation of hot spots near the tabs where the current density is naturally higher. If the material resists this lateral flow, the center of the electrode may not be fully utilized during fast charging.
Engineers optimize the carbon black and binder ratios to create a continuous network for electron transport. This network must remain stable during the expansion and contraction of the active materials.
Electrode Uniformity
Consistency in the coating process ensures that the resistance is the same at every point on the foil. Variation in in-plane conductivity can lead to uneven aging of the active material as some areas work harder than others. Testing this property involves using a four-point probe or an eddy current sensor to scan the surface of the dried coating.
A uniform conductive path is the mark of a well-controlled manufacturing line.
Power Density
Delivering high bursts of energy requires a low overall internal resistance. Improving the in-plane conductivity allows for thinner current collectors which reduces the total weight of the battery pack. This change increases the energy per kilogram while still meeting the power requirements of the application.
The relationship between the thickness of the coating and its lateral resistance is a primary consideration during the slurry formulation phase.
Thermal Gradient Effects on Active Material Loss in Prismatic Formats
Internal thermal gradients accelerate prismatic cell active material loss by driving localized current crowding, high-temperature SEI growth, and particle cracking.