Electrical short-circuit behavior and temporary localized overcharge conditions during thermal runaway in lithium-ion battery packs

Thermal propagation remains a safety challenge for lithium-ion traction batteries in the growing electric-vehicle market. While mitigation strategies have largely focused on limiting thermal interactions between cells, electrical coupling effects during and after cell failure have received comparatively less systematic attention. This study examines electrical cell-to-cell interactions during thermal runaway using a three-module assembly containing cylindrical 21700 cells. To characterize the electrical response, row voltages and selected cell surface temperatures were recorded during thermal runaway. The measured voltage response indicates internally driven electrical redistribution through the parallel network during thermal runaway, influenced by the effective short-circuit resistance established in the trigger cell. The three-module experiments further indicate temporary overcharge conditions in modules connected in series to the failing module, with the corresponding cell groups temporarily exceeding their normal operating window. Dedicated single-cell nail-penetration tests revealed substantial variation in the effective post-failure short-circuit resistance, resulting in a wide range of estimated short-circuit currents and electrical loading within the investigated assembly. A simplified electrical model of the three-module assembly reproduced the measured redistribution trends and provided insight into the electrical behavior of individual cells within the assembly. Overall, the results provide experimentally supported insight into topology-dependent electrical redistribution and temporary localized overcharge conditions during thermal runaway under representative local module-level boundary conditions.