1. Internal short circuit:
Due to the abuse of the battery, such as dendrites caused by overcharge and overdischarge, impurities and dust in the battery production process, etc., will deteriorate to pierce the diaphragm, resulting in micro-short circuit, the release of electrical energy leads to temperature rise, and the material chemical The reaction expands the short-circuit path again, creating a larger short-circuit current, which accumulates and reinforces each other, leading to thermal runaway.
2. External short circuit:
Take electric cars, for example. The probability of danger in actual vehicle operation is very low. First, the vehicle system is equipped with fuses and battery management system BMS, and second, the battery can withstand a short-term high-current shock. In the extreme case, the short-circuit point crosses the fuse of the whole vehicle, and the BMS fails at the same time. The external short-circuit for a long time will generally cause the weak point of the connection in the circuit to be burned, and rarely cause the thermal runaway of the battery. Now, more PACK companies have adopted the practice of adding fuses in the loop, which can more effectively prevent the harm caused by external short circuits.
3. External high temperature:
Due to the characteristics of the lithium-ion battery structure, the SEI film, electrolyte, EC, etc. will decompose at high temperatures, and the decomposed products of the electrolyte will also react with the positive and negative electrodes, and the cell separator will melt and decompose, and various reactions will cause a lot of heat. Appear. The melting of the membrane causes an internal short circuit, and the release of electrical energy increases the production of heat. This cumulative and mutually reinforcing destructive purpose results in the rupture of the explosion-proof membrane of the battery cell, the ejection of the electrolyte, and the occurrence of combustion and fire.
As an energy source for pure electric vehicles, the cause of lithium-ion battery pack fire is thermal runaway caused by battery overheating, which is most likely to occur during battery charging and discharging. Because the lithium-ion battery itself has a certain internal resistance, a certain amount of heat will appear while outputting electric energy to supply power for pure electric vehicles, which will increase its own temperature. When its own temperature exceeds its normal operating temperature range, it will damage the entire battery. longevity and safety. In pure electric vehicles, the power lithium battery system is composed of multiple power lithium battery cells. During the working process, a large amount of heat accumulates in the small battery box. If the heat cannot be quickly dissipated in time, the high temperature will Affect the life of the power lithium battery or even thermal runaway, resulting in accidents such as fire and explosion
