Recently, many electric vehicle fire and explosion incidents have once again pushed the safety of power batteries to the forefront. The replacement of lithium iron phosphate battery by ternary materials has brought about an increase in the mileage of electric vehicles, and also led to a decrease in battery safety. In the event of a collision, it is easy to cause a safety accident such as burning of the power battery. In order to increase the escape time of the passengers in the vehicle during a burning accident, it is generally necessary to add a fire extinguishing system inside the battery box to suppress the spread of thermal runaway inside the battery box. Unlike traditional organic combustion, the battery system contains a reducing agent and an oxidant. Therefore, simple air isolation does not prevent the burning of lithium-ion batteries. That is, traditional fire extinguishing agents are not necessarily suitable for extinguishing power battery fires.
Power lithium-ion battery fire has the following characteristics:
1. Fast fire, long duration
According to the NFPA (American Fire Protection Association) experiment, the fire spreads quickly within the power battery module in just a few seconds, lasting about 27 minutes.
2. High combustion temperature
A major feature of power battery combustion is high temperature. According to NFPA experiments, the maximum external temperature of the battery in combustion can reach 283-1090 degrees Celsius, and the internal temperature of the battery can reach 572-1121 degrees Celsius. Such a high temperature is enough to ignite the inside of the battery module. And other combustible materials in the car, resulting in a bigger fire.
3. Fighting difficulties
For the power battery, most of the combustion reaction takes place inside the battery casing, and the battery casing hinders the action of the fire extinguishing agent. In practice, the fire time of the power battery fire often exceeds the oxygen supply time of the oxygen bottle carried by the firefighter. The personal safety of firefighters poses a certain threat.
In order to verify the extinguishing effect of different fire extinguishing agents on power battery fires, the Federal Aviation Administration FAA tested aqueous solutions based on water, such as water, AF-31, AF-21, etc., gas fire extinguishing agents such as FM-200, FE-36 , and dry powder fire extinguishing agent, research shows that the cooling effect of fire extinguishing agent is the key factor affecting the fire extinguishing effect, so water-based fire extinguishing agent has the best effect on extinguishing lithium-ion battery, while dry powder and gas fire extinguishing agent have basically no effect on lithium-ion battery fire. .
Some research institutes in China, such as the University of Science and Technology of China, have shown that carbon dioxide, dry powder and other fire extinguishing agents have little effect on extinguishing lithium-ion battery fires. In fact, this is not difficult to understand. This is mainly because of the main working principle of these fire extinguishing agents. By insulating the oxygen in the air, the combustion reaction cannot be carried out, but in the lithium ion battery, the positive electrode material, especially in the charged state, is a strong oxidant itself, and the negative electrode active material, electrolyte, etc. The reducing agent already has the basic combustion conditions, so the ordinary air-insulating agent does not have the effect on the lithium-ion battery fire. Only the fire extinguishing agent capable of rapid cooling can quickly take away the heat generated by the combustion, so that the combustion The reaction does not have the conditions to continue, in order to extinguish the lithium-ion battery fire.
Although water as a fire extinguishing agent is very effective in extinguishing a power battery fire, there are still many problems in actual use, such as long extinguishing time and large water consumption, so water is not a very efficient fire extinguishing agent. Bosch, Germany, 2009 The company tested the effects of water, foam, dry powder and F-500 (a microcyst-extinguishing agent developed by Americandangerous Goods Control Arts Inc), and Bosch's tests showed that F-500 fire extinguishing agent is the most fire-fighting battery fire. Good choice, the test of the German Motor Vehicle Inspection Association (DEKRA) in 2013 also shows that the F-500 is an efficient power battery fire extinguishing agent, which can greatly shorten the time of extinguishing the power battery fire and reduce the consumption of fire extinguishing agent.
The working principle of F-500 fire extinguishing agent is mainly to reduce the surface tension of water by additives, so that tiny water droplets can be formed during spraying. These water droplets can diffuse into the interior of lithium ion battery and absorb heat quickly to achieve the effect of fire extinguishing. .
At the International Symposium on Fire Science and Fire Engineering held in 2017, Weitao Luo (first author) and Shunbing Zhu (corresponding author) of Nanjing University of Technology analyzed the effects of different fire extinguishing agents on extinguishing power battery fires. 18650 battery was used as the research object, and the effect of pure water, 5% F-500 solution and 5% solution (anionic/nonionic surfactant) configured on the lithium-ion battery fire was tested, and the water mist was also tested. The extinguishing effect of the lithium-ion battery fire. From the experimental results (as shown in the figure below), the F-500 fire extinguishing agent and the anion prepared by the author, the effect of the non-ionic solution fire extinguishing agent is significantly better than the pure water fire extinguishing agent. The temperature of the battery with two kinds of fire extinguishing agent drops rapidly, and the lithium-ion battery fire is quickly extinguished. Compared with pure water, the fire extinguishing time is greatly shortened. The author's experiments show that even with spray fire extinguishing, F-500 fire extinguishing agent and the author's preparation The effect of anionic, non-ionic solution fire extinguishing agent is also significantly better than pure water. It can effectively inhibit the burning of lithium-ion battery in only 4 seconds.
It is not difficult to see from the above analysis that although pure water can extinguish a lithium-ion battery fire, it has low efficiency, long extinguishing time and large water consumption, so it is not suitable for occasions where the space of electric vehicles is limited and the escape time is very precious. The F-500 fire extinguishing agent reduces the surface tension of the water, so that the water forms tiny droplets, which greatly improves the fire extinguishing efficiency, greatly shortens the fire extinguishing time, and greatly reduces the amount of fire extinguishing agent, which is very suitable for use in electric vehicles. Even In special occasions such as airplanes, the use of such fire-extinguishing agents can quickly extinguish fires and reduce risks when the battery of electronic equipment burns.
