Research on Pouch Cell Thermography in the Monroe Research Group, Department of Engineering Science, University of Oxford

Owing to their large gravimetric and volumetric energy densities, large-format prismatic Li-ion cells are becoming ubiquitous in civilian vehicle applications and are also under consideration for heavy military vehicle hybridization and robotic platforms. In prismatic cells, electro-thermal coupling of the in-plane distributions of temperature and current density have also been shown to cause self-heating, which can lead to the onset of thermal instability. Two-dimensional simulations have also shown that instabilities occur under specific local perturbations or boundary conditions. Temperature within a cell can increase due to poor heat transfer at cell edges, or because heat transfer is slowed by local changes in properties such as electric conductivity, reaction rate constants, or thermal conductivity that occur as the distributions of temperature or electrolyte content vary. Under certain conditions (say, if electric conductivity rises with temperature as thermal conductivity stays constant) constructive feedback can develop, causing a potentially catastrophic "thermal runaway" situation where temperature rises without bound. For this research, we derived an analytic solution using porous electrode theory (Newman & Tobias model) and global thermal energy balance with thermodynamic analysis in 1-D geometry. After that, we compared the analytic solution with numerical result from COMSOL (PDE solver).

We have designed an experimental setup to measure temperature profiles when cycling the battery. Using an IR camera to track surface temperature we should be able to determine the physical properties of the system using our numerical tool generated in 3-D in COMSOL.