An experimental investigation on thermal runaway features of lithium-ion cells under tunnel situations

Considering the non-negligible thermal runaway hazards of lithium-ion cells under tunnels (ever-increasing electric vehicles and tunnels), the current work performs an experimental investigation to unveil the thermal runaway features of lithium-ion cells under the tunnel situation; whereby, cells with various states of charge (25%, 50%, and 75% SOC) and tunnels with various ceilings (arc ceiling and flat ceiling) are also considered. There are two smoke beams generated in the thermal runaway process, due to the release of thermal runaway gas and electrolyte evaporation after the safety valve opening and that at the eve of the thermal runaway. With the thermal runaway progresses, the tunnel is eventually fully filled with the smoke, which could induce the visibility inside the tunnel declined by 0.6 m (75% SOC cells). The dimensionless temperature rise of the tunnel ceiling (arc) exponentially decreases as the dimensionless position increases, which is different from that of the flat-ceiling tunnel where a linear decline is demonstrated. Even though the cell with a greater SOC illustrates a more noticeable peak heat radiation, its total heat release during thermal runaway is comparatively less as a result of the short duration of the combustion; in the end, the temperature rise inside the tunnel is inhibited.