Abstract:In order to improve battery thermal safety and vehicle reliability, the thermal runaway propagation of battery modules was carried out. Aiming at the thermal runaway propagation characteristics of cylindrical 21700 lithium-ion batteries, the effects of charging state, cell distance and other factors on the multi-dimensional thermal runaway propagation behavior of 21700 lithium-ion battery modules were investigated experimentally. It is found that the thermal runaway propagation of the battery is faster in the axial direction than it in the radial direction. When the battery is fully charged and the spacing is 2.0 mm, the thermal runaway propagation is 97 s faster in the axial direction than in the radial direction, and with the decrease of the battery power and the increase of the spacing, the thermal runaway propagation speed becomes slower. When the battery spacing is 2.0 mm, the 30% and 50% charging states are safe charging states for axial and radial batteries, respectively. When the battery is fully charged, 6.0 mm and 4.0 mm are the safe distances for axial and radial batteries, respectively. The research results can provide reference for battery storage, transportation and battery module design of electric vehicles.