Analysis of the thermal runaway phenomenon of Nickel-Manganese-Cobalt cells induced by nail penetration through high-speed infrared imaging

Gradual replacement of fossil fuels by clean and renewable energies is crucial to minimize the greenhouse effect from the transport sector. The electric vehicle is intended to be the leading technology for this purpose, for which clean and renewable energy must be stored as chemical energy in the battery. From the safety point of view, the main issue of this technology is related to the risk of thermal runaway. Among other factors, a collision can be one of the causes of a battery electric vehicle explosion, as damage to the surface of the battery can generate a short circuit, resulting in a battery thermal runaway. To replicate this situation at a system level, the nail penetration test is reproduced in laboratories. In this work, the effect of the nail penetration position, battery state of charge (SOC) and initial ambient temperature on the thermal runaway behavior of a Nickel-Manganese-Cobalt 811 cell is investigated. Infrared images were used to evaluate the temperature distribution in the battery surface, revealing the root causes for the scattering observed in the surface temperature when measured through thermocouples. Furthermore, a methodology to correct the thermographic images is described, abording the main uncertainties related to the characteristics of the optical access. The results show that the battery state of charge has a strong effect on the heat release than nail position and initial ambient temperature, increasing in 20 % from SOC 50 % to SOC 100 %. Regarding the position, nail penetration tests at the top of the battery lead to lower temperatures when compared to the other positions, representing 10 % less heat release than middle and bottom nail position. Furthermore, the thermographic images showed a variability in the spatial distribution of temperature between the test cells of up to 40 degrees C, with case rupture being mainly responsible for the higher values.