Quantitative analysis on the heat transfer modes in the process of thermal runaway propagation in lithium-ion battery pack under confined and semi-confined space

摘要

Thermal runaway (TR) may propagate in a lithium-ion battery (LIB) pack in confined and semi-confined spaces, because of insufficient heat dissipation. This may induce accidents and lead to significant losses. However, the heat transfer modes between cells when TR propagates in an LIB pack have not been revealed. In this work, aluminium foil (AF), which has low emissivity and high thermal conductivity, and refractory ceramic fibre (RCF), which has low thermal conductivity, were employed to reduce the heat transferred between two cells through conduction and radiation via the air, respectively. Therefore, the differences in heat transfer properties in these two materials were used to quantitatively analyse the heat transfer modes in the process of TR propagation in an LIB pack under confined and semi-confined spaces. The TR propagation process was roughly divided into three stages, and the maximum temperature of the cell experiencing TR in a confined space was lower than that in a semi-confined space. TR propagation speed decreased from 7.84×10~(-3) s~(-1) to 6.14×10~(-3) s~(-1) and from 11.9×10~(-3) s~(-1) to 9.62×10~(-3) s~(-1) owing to the use of RCF in confined and semi-confined spaces, respectively. Furthermore, the TR propagation speed decreased from 7.84×10~(-3) s~(-1) to 5.1×10~(-3) s~(-1) and from 10.87×10~(-3) s~(-1) to 7.46×10~(-3) s~(-1) owing to the use of AF. In the LIB pack, the heat was mainly transferred through conduction via the air between two neighbouring cells, in a proportion of approximately 50-83.8%. Then, the main heat transfer mode changed to radiation when the neighbouring cell underwent TR. However, when one cell was wrapped with AF on its surface to decrease the radiation heat absorbed from the neighbouring cell, the main heat transfer mode was conduction, and it did not change even though the neighbouring cell underwent TR. This is different from the aforementioned phenomenon. Therefore, the radiation heat influences the TR propagation more significantly than the conduction heat. A detailed analysis of the main heat transfer mode can provide valuable guidelines for the safety design and prevention of TR propagation in LIB packs.