Hotspots in Lithium-Ion Battery Pouch Cells: Models and Bounds

Lithium-ion batteries have grown larger in recent years in response to the need to increase pack-level energy densities. One of the main issues that emerges in these large format cells are heterogeneities. In particular, temperature hotspots in large pouch cells have been shown to influence degradation rates and fast charging limits. Motivated by these issues, this paper proposes computationally efficient models and bounds to characterise thermal hotspots in pouch cells. The models are validated against experimental data and shown to capture the spread in temperature across the pouch cell. The bounds exploit external positivity of the underlying system to improve scalability and are shown to be tight under constant current cycling. Through these results, bounds for the maximum temperature a pouch cell will experience during an arbitrary use-profile can be computed at scale and so be used to support battery safety and control.