Lithium battery fire is extreme but highly publicized and scary. From energy storage stations to electric bicycles, the cause of a battery fire may not be the battery itself. It can be a failure of the battery system. The main reason of lithium battery fire is caused by thermal runaway. Today, when we talk about fire extinguishing, we need to understand the real reason of thermal runaway first.
The cause of lithium battery fire
The nature of lithium battery fire is that the heat in the battery fails to release according to the design intention, causing fire after the ignition point of internal and external combustion objects. The main reasons are external short circuit, external high temperature and internal short circuit.
1, internal short circuit:
Due to abuse of the battery as the overcharge before putting in crystal, the impurities such as dust in the process of producing batteries, exacerbating generated pierced diaphragm, produce micro short circuit. This is the electric energy that causes temperature rise of temperature of material chemistry and enlarged the short-circuit path, forming the bigger short-circuit current. The accumulation of each other enhances each other's damage, leading to thermal runaway.
2.External short circuit:
Take electric vehicles as an example. The probability of actual vehicle operation is very low. First, the vehicle system is equipped with a fuse and battery management system BMS. Secondly, the battery can withstand a short period of high current impact. In extreme cases, the short circuit point exceeds the vehicle fuse, and BMS fails at the same time. A long time of external short circuit will generally lead to the burning of the weak connection in the circuit. It rarely leads to thermal runaway events of the battery. Now, companies have adopted the practice of adding fusing wire in the loop. This can more effectively avoid the harm caused by external short circuit.
3.External high temperature:
Due to the structural characteristics of lithium battery, decomposition reactions occur in SEI film, electrolyte and EC at high temperature. Decomposition substances of electrolyte will also react with positive and negative electrodes. The cell diaphragm will melt and decompose, resulting in a large amount of heat generation. The melting of the diaphragm causes an internal short circuit, and the release of electrical energy increases heat production. This kind of cumulative mutually reinforcing damage effect leads to the cell explosion-proof film rupture, electrolyte ejection, and combustion fire.
Lithium battery fire extinguishing scheme
After analyzing the cause of battery fire, let's take a look at Tesla's recommended solution when lithium battery fire needs to be put out:
1.If there is a small fire and the flame does not spread to the high voltage battery part, carbon dioxide or ABC dry powder fire extinguisher can be used to extinguish the fire.
2, when thoroughly checking the fire, do not contact with any high-pressure parts, always use insulation tools to check.
3.if the high-voltage battery is bent, twisted or damaged in a fire, it will become deformed or suspect that there is a problem with the battery. So the water consumption of fire fighting can not be too little, fire water to have enough amount.
A battery fire may take 24 hours to completely extinguish. Using a thermal imaging camera ensures that the high-voltage battery is completely cooled before the accident is over. If you don't have a thermal camera, you have to monitor the battery to see if it refires. Smoke indicates that the battery is still hot and should be monitored until the battery is no longer smoking for at least an hour.
Gm volt's emergency rescue manual instructs electric vehicle firefighting: If the battery reaches a high enough temperature to leak and release electrolytes, the electrolyte must be flammable. This requires a large amount of water to cool the battery and extinguish the fire. Because the DC and AC systems are not grounded, firefighters can safely use water as their primary extinguishing agent without the risk of electric shock. ABC dry powder extinguishers do not extinguish battery flames. Firefighters should avoid direct internal contact with any high voltage assembly during fire suppression or relief operations, which could potentially cause an electric shock.
To sum up, lithium battery fire requires a lot of water, long time and patience, cooling is key, lithium battery is not explosive, will not explode under normal circumstances.