Thermal runaway propagation behavior of the Cell-to-Pack battery system

Structurally compact battery packs significantly improve the driving range of electric vehicles. Technologies like Cell-to-Pack increase energy density by 15%–20%. However, the safety implications of multiple tightly-packed battery cells still require in-depth research. This paper studies thermal runaway propagation behavior in a Cell-to-Pack system and assesses propagation speed relative to other systems. The investigation includes temperature response, extent of battery damage, pack structure deformation, chemical analysis of debris, and other considerations. Results suggest three typical patterns for the thermal runaway propagation process: ordered, disordered, and synchronous. The synchronous propagation pattern displayed the most severe damage, indicating energy release is the largest under the synchronous pattern. This study identifies battery deformation patterns, chemical characteristics of debris, and other observed factors that can both be applied to identify the cause of thermal runaway during accident investigations and help promote safer designs of large battery packs used in large-scale electric energy storage systems.