What are the difficulties in the high-temperature nail penetration test for the new-generation Xiaomi SU7?
The new-generation Xiaomi SU7 Max version successfully passed the high-temperature, fully charged nail penetration challenge for ternary lithium batteries. Compared with the new national battery standards, this challenge features a higher operating temperature, a higher state of charge, and uses nail penetration, which is recognized by the industry as a more stringent trigger for thermal runaway, making it much more difficult;
First are the temperature and state of charge. In the thermal runaway test of the new national battery standards, the required battery temperature is 22±5°C and the battery SOC is ≥95%. In this test, the new-generation Xiaomi SU7 heated the battery to 55°C and fully charged it. The higher the battery temperature and the higher the state of charge, the more violent the thermal runaway reaction;
In addition, there is the nail penetration. The new national standards recommend two common methods for triggering battery thermal runaway: heating (external heating/internal heating) and nail penetration. Nail penetration directly destroys structures such as the cell separator and electrode sheets, causing an instantaneous short circuit in the cell. The energy is released rapidly, the release area is more concentrated, and the local temperature rises sharply. Therefore, nail penetration is recognized by the industry as a more stringent thermal runaway trigger method;
After the new-generation Xiaomi SU7 triggered thermal runaway in a single cell via nail penetration, there was no thermal propagation to other cells, the battery pack did not catch fire or explode, the alarms inside and outside the vehicle were activated normally, the cloud alarm was activated normally, the doors unlocked normally, and there was no visible smoke inside the vehicle. The test challenge was successful.