Thermal runaway properties of power cells under tunnel scenarios: Impact of state of charge, capacity, and chemistry

The thermal runaway risk of power cells inside tunnels is non-negligible, particularly considering the dramatic increase in electric vehicles and tunnels with the development of cities, thus an experimental investigation is performed in this research to disclose the thermal runaway properties of power cells at tunnel scenarios; in which, the impact of cell state of charge (SOC), capacity, and chemistry is involved. Power cells demonstrate two times gas/smoke releasing in the thermal runaway process, which occur after the safety valve opening and on the eve of the thermal runaway, respectively. The considerable gases released cause a dramatic decline of visibility inside the tunnel; taking the 40 Ah ternary (NMC) cell with 50 % SOC as the example, its thermal runaway results in an extinction coefficient of ∼ 0.67 m⁻¹, indicating that the walking speed of human within the tunnel lower than that of a blind. It should be noted that the severity would further aggravate at the case with a lower SOC or higher capacity. There is an exponential decline between dimensionless temperature rise and dimensionless position for the tunnel ceiling, and the ceiling's maximum temperature rise is found to grow linearly with the increasing the average heat release rate to the power of two-thirds and the tunnel's height to the power of five-thirds. Finally, the smoke and toxic hazards inside the tunnel caused by the LFP cell's thermal runaway are even worse than the NMC cell, due to the considerable amount of smoke released.