Fire safety knowledge of lithium batteries

What causes of lithium battery fires?

1.Internal short circuit
Because of the abuse of the battery as the overcharge before put in crystal, the impurities such as dust in the process of producing batteries, exacerbating generated pierced diaphragm, produce micro short circuit, the electric energy that cause temperature rise of temperature of material chemistry and enlarged the short-circuit path, formed the bigger short-circuit current, the accumulation of each other and enhance each other's damage, leading to thermal runaway.

2. External short circuit
Take electric cars. The probability of actual vehicle operation is very low. First, the vehicle system is equipped with fuse and battery management system BMS, and second, 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, and rarely lead to thermal runaway events of the battery. Now, more PACK enterprises have adopted the practice of adding fusing wire in the loop, which can more effectively avoid the harm caused by external short circuit.

3. External high temperature
Due to the structural characteristics of lithium batteries, decomposition reactions occur in SEI film, electrolyte and EC at high temperature. Decomposition substances of electrolyte will also react with positive and negative electrodes, and 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, its consequence is to lead to the cell explosion-proof film rupture, electrolyte ejection, combustion fire.

How to prevent lithium battery fire? Four measures we can do about it

• Positive and negative electrode ingredients When mixing powder and homogenizing, dust absorption device should be set up to prevent the explosion of dust such as toner. Clean up the scattered dust on the equipment and in the workshop in time to prevent accumulation, and prohibit fireworks, take anti-static measures.

(2) Electrode coating
High temperature heating device in electrode coating process should be managed by special person. Dry powder fire extinguishers and other fire fighting facilities should be set up nearby. In welding process, dust absorption device should be set up to reduce the probability of dust explosion.
(3) Inject electrolyte
Electrolyte should be far away from open fire and high temperature, the workshop should be limited storage, fire with dry powder, carbon dioxide and other extinguishers.
(4) Other requirements
Lithium ion battery production plant, warehouse for class C fire risk, should be a grade 1, 2 fire resistance grade building, good ventilation, and equipped with fire fighting equipment and equipment. Storehouse should be waterproof and moistureproof.

In addition to using some dry powder fire extinguishers, as well as dust fire extinguishers, automatic sprinklers should be installed to avoid penny wise and pound foolish

What should we do when lithium batteries catch fire?

Analyzing the causes of battery fires, when lithium batteries need to be put out to fight fires, let's look at Tesla's recommendations:

1.If encountered a small fire, the flame did not spread to the high-pressure battery part, can use carbon dioxide or ABC dry powder fire extinguisher.

2.In a thorough inspection of the fire, do not come into contact with any high-voltage components, always use insulation tools to check.

3.If the high voltage battery in the fire bending, twisting, damage, in short, become not like, or suspect that the battery problem. Then the water consumption when extinguishing the fire should not be too small, fire water should be sufficient.

4.Battery fire may take 24 hours to completely extinguish. Using a thermal camera ensures that the high voltage battery is completely cooled before the accident is completely complete. If you do not have a thermal camera, you must monitor the battery for re-ignition. Smoke indicates that the battery is still hot and monitoring will remain in control until at least an hour after the battery is no longer smoking.

According to the U.S. Fire Protection Agency, electric vehicles can catch fire "over 2,760 degrees Celsius" and "the use of water or foam can cause violent flames, as water molecules break down into explosive hydrogen and oxygen." So it's not safe to put out a small amount of water, and an electric car alone requires dozens of tons of water.

Simply, lithium battery fire fighting uses a lot of water to cool the battery, it takes a long time and patience, cooling is the key.

Ten tips on how to keep and maintain the lithium battery warehouse

1. Battery warehouse and aging room must be separated from other areas and set up independently
2. Battery warehouse and aging room must be separated by solid brick wall and normally closed fire door
3. The battery warehouse and aging room must be equipped with explosion-discharging Windows;
4. The battery warehouse and aging room must take ventilation, cooling and moisture-proof measures
5. Smoke alarm and automatic fire extinguishing devices must be installed in battery warehouse and aging room
6. Battery warehouse and aging room must be equipped with 24-hour video monitoring device;
7. Shelves, pads and pallets of battery warehouse and aging room must be made of non-combustible materials
8. When batteries are stored in multiple layers and stacked, shelves must be used for layering and isolation
9. Insulation measures must be taken for the exposed parts of positive (negative) poles of storage batteries
10. Faulty batteries and abandoned batteries must be placed in a special treatment cabinet for isolation and disposal. It is recommended to use explosion-proof sand buckets to deal with the batteries in accidents,and prepare a big bucket of water for emergency use.

remark:

1. Battery warehouse temperature and humidity requirements: indoor temperature 20±5 °C, relative humidity 65±20%;
2. Battery warehouse, aging room should use explosion-proof electrical equipment

All in all,We know what causes lithium-ion battery fires, and we know that lithium-ion battery fires are extremely difficult to control. Therefore, once we found smoke, fire and other signs, follow the right steps,and be sure to escape the first time, not penny wise and pound foolish!