How to extinguish a lithium battery fire

Lithium battery fire protection requires the establishment of multiple lines of defense with strategic depth. In addition to the use of non-flammable or flame-retardant materials inside the battery to make the battery intrinsically safe, the first line of defense outside the battery is to prevent various causes of battery overheating, such as overcharge, short circuit, impact, etc. The electrical system needs to be designed safely.

When the first line of defense is broken (for example, the battery management system fails to cut off the charging power supply in time), the battery temperature rises, and the temperature sensor or gas, smoke detector, etc. in the monitoring system should promptly find the fault and alarm, reminding the work. Personnel handle failures and eliminate fire incentives. This is the second line of defense.

When the fault is not dealt with in time and the second line of defense is broken, the battery burning (smoldering) is unavoidable. At this time, the fire system needs to limit the combustion to the defective battery box (or box). It also isolates adjacent unfired batteries and equipment to avoid fire isolation. Due to the extremely high temperature of the lithium ion battery after thermal runaway, the existing non-aqueous fire extinguishing agents such as gas and dry powder cannot quickly lower the battery temperature, and the fire extinguishing effect is not ideal. Therefore, setting the battery fire prevention target to controlled burn-down is a relatively realistic solution with strong technical economy. This is the third line of defense.

If the fire control failure expands and poses a serious threat to the safety of personnel, it is necessary to start a fixed water-based fire-extinguishing system installed in the vehicle or wait for the fire brigade to extinguish the fire.

In general, the first and second lines of defense are considered by battery manufacturers or electric vehicle manufacturers. As a fire protection professional, we can establish a solid third line of defense for our customers. We can customize the solution according to the specific model specifications of the battery. The components used in the program come from all over the world, not limited to a certain equipment or material.

In order to ensure the effect of fire control, a separate fire extinguishing tube can be installed in the battery case (or box). The fire extinguishing tube is thermally broken after the battery is on fire. And the fire extinguishing gas is automatically released, and the battery fire is extinguished.

Lithium battery fire extinguishing is mainly caused by thermal runaway. If you need to extinguish the fire, you first need to understand the real cause of thermal runaway. The main causes of thermal runaway of lithium batteries are external short circuit, external high temperature and internal short circuit. Internal short circuit: due to the abuse of the battery, such as the over-charge and over-distribution of the crystal, the magazine dust during the battery production process, will deteriorate the formation of the piercing diaphragm, resulting in a micro-short circuit, the release of electrical energy leads to temperature rise, temperature rise band The chemical reaction of the material further expands the short-circuit path and creates a larger short-circuit current. This mutual accumulation of mutually enhanced damage leads to thermal runaway. Taking a lithium cobalt oxide battery as an example, a typical thermal runaway process is briefly described. A: During the preparation phase, the battery is fully charged; B: an internal short circuit occurs, a large current generates heat through the short-circuit point, and is thermally diffused by LiC6 to reach the decomposition temperature of the SEI film, and the SEI film begins to decompose, releasing a small amount of CO2 and C2H4, and the shell The body swells slightly. As the short-circuit position continues to discharge, the battery temperature rises continuously, and the chain solvent in the electro-hydraulic begins to disperse. LiC6 and electro-hydraulic also begin to react and exotherm, accompanied by C2H5F\C3H6\C3H8, but the reaction is slow. The heat release is small; C: As the discharge progresses, the temperature of the short-circuit position continues to rise. The partial shrinkage of the diaphragm melts, the short-circuit position expands, and the temperature further rises. When the internal temperature reaches the decomposition temperature of Li0.5Co02, the positive electrode decomposes instantaneously. And release O2, the latter reacts a large amount of heat in the electro-hydraulic reaction, and releases a large amount of CO2 gas, causing the internal pressure of the battery to increase. If the pressure is large enough, the battery casing is broken, causing the battery to explode; D: if the casing is blasted The pole piece is scattered, the temperature does not continue to rise, the reaction is terminated; but if the shell is only cracked, the pole piece is not scattered, then LiC6 continues to react with the electro-hydraulic, the temperature will continue High, but the heating rate decreases, because the reaction rate is slow, so it can be maintained for a long time; E: When the heat generation rate of the internal reaction of the battery is less than the heat dissipation rate, the battery begins to cool down until the internal reaction is completed; External short circuit: The actual vehicle probability of danger during operation is very low. First, the vehicle system is equipped with a fuse and battery management system BMS. Second, the battery can withstand short-time high current surges. In the extreme case, the short-circuit point crosses the fuse of the vehicle, and the BMS fails. The external short-circuit for a long time generally causes the weak connection point in the circuit to burn, which rarely causes the battery to have a thermal runaway event. Nowadays, more PACK companies adopt the practice of adding fuses in the loop, which can effectively avoid the hazards caused by external short circuits. External high temperature: Due to the characteristics of the lithium battery structure, the SEI film, electrolyte solution, EC, etc. will decompose at high temperature, and the decomposition product of the electrolyte will react with the positive electrode and the negative electrode, and the cell diaphragm will melt and decompose, and various reactions Causes a lot of heat to be generated. The melting of the diaphragm leads to an internal short circuit, which in turn increases the production of heat. This cumulative mutual reinforcement damage has the effect of causing the explosion-proof membrane of the battery core to rupture, the electrolyte to be ejected, and the combustion to ignite.

For the above reasons, the lithium battery is fire-extinguishing. Let us look at the recommendations of Tesla and GM: 1. If there is a small fire, the flame does not spread to the high-voltage battery, you can use carbon dioxide or ABC dry powder fire extinguisher to extinguish the fire. 2. When thoroughly inspecting the fire, do not touch any high-voltage parts. Always use insulation tools for inspection. 3. The gas cylinder, gas column and other components that store the gas can reach the extreme temperature of the boiling liquid expansion steam explosion. Before the "hot zone" of the accident is detected, dismantling with appropriate fine protection is required. 4. If the high-voltage battery is bent, twisted, or damaged in a fire, it may become unsatisfactory or suspect battery problems. Then the amount of water used for firefighting should not be too small, and the amount of fire water should be sufficient. 5. It may take up to 24 hours for the battery to catch fire. Using a thermal imaging camera ensures that the high voltage battery is completely cooled before the end of the accident. If you do not have a thermal imaging camera, you must monitor if the battery will re-ignite. Smoke indicates that the battery is still hot, and monitoring is maintained until at least one hour after the battery no longer smokes. In the emergency rescue manual of General Volanda, the fire extinguishing of electric vehicles is guided as follows: If the battery reaches a high enough temperature to leak and release electrolyte, 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 use water safely as the primary fire extinguishing agent and there is no risk of electric shock. ABC dry powder fire extinguishers do not extinguish the battery flame. Firefighters should avoid direct internal contact in any high-voltage components that are extinguished or released, which can potentially result in electric shock.

The fire extinguishing agent that can really extinguish the battery fire is not present at present. An effective attempt is to use water to cool and suffocate control, but there is pressure inside the battery and electrolyte (chemical), so the combustion is complicated and cannot directly extinguish the fire. In addition, for electric vehicles, Shenzhen is said to use a small aerosol automatic fire extinguishing device. The size of the canned fish is magnetized on the side of the battery inside the vehicle. A small amount of blasting aerosol is used to spread the fire. The small space is very easy to use.

1. The battery is usually charged with a semi-electric state when it leaves the factory. When riding for the first time, it is best to fill the battery. On the one hand, the self-discharge will reduce the charge of the lithium battery, and activate the active substance.

2. Do not run out of battery power every time you ride, long-term over-discharge will reduce battery life by 3 times. When the electric vehicle is in low battery, you should stop the ride decisively.

3. Lithium battery is effective at any time, even if there is 50% power before charging, it is because it is different from nickel-metal hydride battery, the latter has memory effect and lithium battery does not. However, it should be noted that lithium batteries cannot be over-discharged, and excessive discharge can cause irreversible capacity loss. When the machine reminds you that the battery is low, it will start charging immediately.

4. Never overcharge. When the charging completion indicator is on, stop charging. If the battery is not used for a long time, remove the battery from the instrument and store it in a dry and cool place, and charge it once in 60~90 days to avoid too long storage time. The battery is too low due to self-discharge, resulting in irreversible capacity loss, because the best storage state of lithium battery is semi-electric storage.

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