PhD Defense Nov 21st: Thermal Runaway in Large-Format Lithium-Ion Batteries: Experimental, Diagnostic, and Modeling Approaches for Safer Battery Design

• Date: 21 November 2025, 09:15
• Location: Häggsalen, Lägerhyddsvägen 1, Uppsala
• Type: Thesis defence
• Thesis author: Yang Yang
• External reviewer: Jennifer Wen
• Supervisor: Daniel Brandell
• Research subject: Chemistry with specialization in Materials Chemistry
• DiVA

Abstract

Ensuring the safety of lithium-ion batteries requires robust methods to study thermal runaway (TR) and its propagation (TRP). While accelerating rate calorimetry (ARC) has been the standard method, it is costly and limited in applicable cell sizes. This thesis develops empirical and novel approaches that provide cost-effective and scalable alternatives. First, TRP tests on 157 Ah LiNi0.8Mn0.1Co0.1O2 cells using widely available thermocouples were analyzed, enabling the estimation of onset and maximum temperatures, heat release, and temperature increase rates. Results showed close agreement with ARC, while offering broader applicability and lower complexity. Next, pouch and prismatic LiNi0.5Mn0.3Co0.2O2 cells were investigated with multidimensional sensors (i.e., force, gas, voltage, temperature), which allowed for a comprehensive safety characterization and revealed a consistent failure sequence of swelling, venting, gas emission, internal short circuit, and TR. While no significant format differences were found under overcharging, prismatic cells exhibited superior safety under overheating due to their higher mechanical strength and thermal dissipation. Scaling effects were then explored by comparing lab-scale coin cells (8.6 mAh) with industrial-scale cells up to 157 Ah, showing that small-scale tests are highly sensitive to the trigger methods, whereas industrial-scale cells yielded comparatively consistent normalized heat release, highlighting the limitations of downscaling. The TRP methodology was extended to map heat transfer in modules, where busbars and thermal pads were identified as critical heat conduction pathways, and in-situ measurements showed that thermal conductivity of pads under TR conditions deviated substantially from nominal values, strongly influencing TRP time. Finally, computational modeling was employed to simulate aging effects on TR, demonstrating that early aging accelerates TRP due to SEI growth, while late aging reduces total heat release due to further degradations but still sustains faster propagation than fresh batteries. Collectively, these studies integrate empirical diagnostics, module-level analysis, and computational modeling to provide a comprehensive picture of TR across scales, formats, and aging states. The methods and insights developed here support both academic research and industrial applications, offering practical guidelines for safer design and operation of large-format lithium-ion batteries in heavy-duty electric vehicles.