Thermal runaway induced gas hazard for cell-to-pack (CTP) lithium-ion battery pack

The Cell-To-Pack (CTP) structure improves the energy density of the battery system, thereby increasing the driving range of electric vehicles. However, a more compact structure leads to high level of failure hazard, especially for the intensive gas venting caused by battery thermal runaway. This study conducts the thermal runaway experiment of a CTP battery pack, and establishes a gas eruption model to reveal the influence of the venting gas temperature, concentration, and pressure on the thermal hazard of the CTP battery pack, once a single cell undergoes thermal runaway failure. Results show that the hot gas (>670 degrees C) can melt the sheet molding compound (SMC) cover whose melting point is about 260 degrees C within 60 min. Hot flammable gas was selfignited after it burst out from a melt hole on the cover. Simulation results point out that hot vent gas accelerates the thermal runaway propagation to adjacent cells. The vented carbonate electrolyte will liquefy and accumulate at the bottom corners of the battery pack. The pressure of the vent gas causes the obvious deformation of the pack cover, and the maximum stress and plastic strain of the cover can be as high as 70.59 MPa and 1.9 %, respectively. The results help guide the safety design of a high-compact and high-energy battery pack.