Cell to Cell Thermal Runaway protection systems for battery packs in Electric Vehicles

With the significant increase of the Electric Vehicles (EV) in the automotive market, the safety standards and regulations for these kinds of products are becoming more restrictive. One of the new problems for the EV is the Thermal Runaway (TR) event management. When this unwanted phenomenon happens, the uncontrolled rise of the temperature in one cell it can spread to the entire pack. The consequence of this chain reaction is the generation of a huge quantity of heat with flames and gasses venting which is very dangerous for the vehicle occupants. To make the Electric Vehicle safer, the Chinese legislation of 2018 establishes that the flame should not penetrate inside the passenger compartment earlier than 5 minutes after the onset of the Thermal Runaway. Cell to cell barriers can be employed to prevent or delay the thermal runaway. The barriers protect and thermally insulate one cell from the others. A set of tests and a 1D model have been therefore developed to evaluate and assess the performances of different thermal barrier solutions. The 1D model has been used to have a previous forecast of which is the possible behaviour of the barriers. The laboratory tests instead allow to assess the capability of the materials to perform in real conditions. The tests try to emulate the abuse condition when the Thermal Runaway event occurs. During the TR event, flames can develop and release a big amount of hot gasses from the burning cells. So to assess the capability of the materials to resist direct flame contact specific tests should be tuned. The flame temperature and the duration of the test should be representative of the average TR process of the cell. To evaluate the thermal performance of the barrier a Hot-Cold Plate test has been employed. Also in that case the parameter of temperature and average thermal energy should be comparable with the real condition case. By means of the temperature profile on the cold side is possible to have an indication of which is the level of protection of the next cell. The core activity of the barriers is to insulate the cells from the others. The results of the tests highlight which are the barriers that can accomplish better their mission. The barriers should pass all the tests to be valid. The temperature profile, measured on the cold side, gives an indication of the performance having the possibility to make a rank of solutions. The results highlight a significant improvement in the protection performance of the barriers that are capable to absorb heat due to chemical reactions or phase change. The experiment showed that the low thermal conductivity of the barriers is not enough to compete with the thermal energy absorption of the other solutions.