How should a lithium battery fire?

Lithium battery fire condition

Lithium battery is a kind of battery that uses lithium metal or lithium alloy as negative electrode material and uses non-aqueous electrolyte solution. In 1912, lithium metal battery was first proposed and studied by Gilbert N. Lewis. In the 1970s, MSWhittingham proposed and started. Research on lithium-ion batteries, due to the very active chemical properties of lithium metal, the processing, storage and use of lithium metal are very demanding on the environment. Therefore, lithium batteries have not been applied for a long time. With the development of science and technology, lithium batteries have been used now. Become the mainstream.

Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth-generation lithium-metal battery of rechargeable batteries was born in 1996, and its safety, specific capacity, self-discharge rate and performance price ratio are better than lithium-ion batteries. Due to its own high technical requirements, only a few companies in the country are producing such lithium metal batteries.

Chinese name lithium battery foreign name LithiumCell.

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 The chemical reaction of the material 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.

In the preparation stage, the battery is fully charged; an internal short circuit occurs, a large current generates heat through the short-circuit point, and heat diffusion through LiC6 reaches the decomposition temperature of the SEI film, and the SEI film begins to decompose, releasing a small amount of CO2 and C2H4, and the casing is slightly inflated. As the short-circuit position continues to discharge, the battery temperature continues to rise, 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 slower and the heat release is slower. small;

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 rises further. When the internal temperature reaches the decomposition temperature of Li0.5Co02, the positive electrode instantaneously decomposes and releases O2, the latter The electro-hydraulic transient reaction releases a large amount of heat, and at the same time 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;

If the shell is blown up, the pole pieces are scattered, the temperature does not continue to rise, and 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 to rise, but the heating rate Decrease, because the reaction rate is slow, it can be maintained for a long time; 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; the external short circuit: the probability of occurrence of danger in the actual vehicle operation is very low. First, the vehicle system is equipped with a fuse and battery management system BMS, and the second is that the battery can withstand short-time high current impact. 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, resulting in various reactions. A lot of heat is 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.

In the event of a small fire, the flame does not spread to the high-voltage battery section, you can use carbon dioxide or ABC dry powder fire extinguisher to extinguish the fire.

When thoroughly inspecting the fire, do not touch any high-voltage parts and always use an insulated tool for inspection.

Inflatable bottles, gas struts, and other components that store gas can reach extreme temperatures of boiling liquid expansion steam explosions. Before the "hot zone" of the accident is detected, dismantling with appropriate fine protection is required.

If a high-voltage battery is bent, twisted, or damaged in a fire, it may become unsatisfactory or suspect a problem with the battery. Then the amount of water used for fire should not be too small, and the amount of fire water should be sufficient.

It can 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.

If the battery reaches a high enough temperature to leak and release the 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.

The page contains the contents of the machine translation.