Article | Wang Yibo
Grade for review | Clefable
In the early morning of February 23rd, a fire occurred in 6 Mingxi Garden in Yuhuatai District, Nanjing, causing 15 people to die and 44 people injured.After preliminary analysis, the fire was caused by the electric bicycle (this article mainly refers to the battery car) that was parked on the ground.According to information, the fire was burned for more than an hour before being extinguished.
If you focus on the first battery car, it may burn above 750 ° C within a few seconds or a few minutes.Specifically,The lithium ion battery used by battery carsEssence
Today, as more and more electric bicycles and electric vehicles explosion occurred, people’s impression of lithium ion batteries is not very good, especially lithium ion batteries used in electric bicycles.
For example, since the dead fire caused by electric bicycles in New York, USA in December 2021, the New York City Fire Bureau (FDNY) began to ban FDNY headquarters from parking electric bicycles and electric scooters, except for the equipment used by the disabled.By April 2022, FDNY will also be limited to a area, and transportation equipment such as electric bicycles parked or charging shall not exceed 5 vehicles.In addition, the British government has announced that the Palace of Westminster prohibits the parking of electric bicycles and electric scooters, although it has been strongly opposed by bicycle advocate groups.
But according to the accident that happened in the past,Fire involving electric bicycles and electric scooters is usually attributed to inferior battery and related equipmentEssenceSome people think that these cheaper battery products have brought bad reputation to lithium ion batteries.
Security Risk
In fact, when Sony launched the first charging lithium -ion battery in 1991, they knew their potential safety risks.At that time, high -temperature gas generated by mobile phone batteries burned a man’s face, and a large number of charging lithium -ion batteries had to be recalled.Sony knows that granular pollution during the manufacturing process of lithium -ion batteries, such as copper, aluminum, iron and nickel, may cause short circuits inside the battery.
In addition, battery manufacturers often fill a lot of active materials in the battery and make the diaphragm between the electrode thinner to improve the energy density of the battery.But when the battery is unfortunately pierced, overcharged or overheated,The interval in the middle will collapse, causing the two positive and negative electrodes to connect and the internal short circuit occurs.Essence
If it is a slight short circuit, it will not produce too much calories; but if severe short circuit occurs, there will be a considerable current between positive and negative electrodes, which will cause the temperature to riseHeat out of control(Thermal Runaway).
As the name implies, heat out of control means that too much calories accumulated in the internal accumulation of lithium ion batteries.Feng Xuning, an associate professor of the School of Vehicles and Launival of Tsinghua University, passed the 25AH (Ashishi) Sanyo Lithium -ion Power Battery during his study at Tsinghua University.The battery temperature curve will rise rapidly with nearly vertical straight linesEssence
The fact is that the reaction releases heat and the temperature is increased, and the increase in temperature means that the response is faster, which generates more calories.It is important that this will constitute an index -level positive feedback ring, so that the battery temperature can be increased from about 200 ° C to 750 ° C within a few seconds.
During this period, the battery diaphragm collapsed completely, and a large area was short -circuited between the positive and negative poles.At the same time, the orthodox and electrolytes begin to decompose reactions.The metal oxides will release oxygenAnd oxygen can promote combustion reactions, thereby generating more gas and calories.It is worth mentioning that electric vehicles and electric bicycles will be burnedOxygen is generated by autonomy, and recovery may occurThis is a major reason why the fire is difficult to extinguish.
For example, in April 2021, a 2019 Tesla Model S rushed out of the road and hit a tree after hitting a tree.Initially, the fire was extinguished within a few minutes, but then it continued to reunite, bringing challenges to firefighters. They spent about 4 hours and used more than 11,000 liters of water -The world’s largest fire -fighting aircraft can only carry about 75,000 water liters.
How to improve
Today, the battery basically has a safety system, so under normal circumstances, the battery will be directly powered off when the battery occurs.But if it is inside the batteryInherent defectFor example, metal particle pollution, the battery safety system is difficult to monitor and prevents potential thermal outfolding.In this regard, battery manufacturers have been working hard to reduce the presence of metal particles and improve the safety of lithium -ion batteries.However, the battery failure rate exists. For example, the battery failure rate of laptop computers made by Dell and Apple is about one -half hundred thousand, resulting in nearly 600,000 lithium -ion battery packs recalled.
In addition to further improving the manufacturing process of lithium -ion battery, scientists are still trying other technologies, such as developing sodium ion batteries, solid -state batteries, and even “water batteries”.
In order to find the alternative of lithium -ion batteries that may be on fire, the team led by Professor Ma Tianyi, Royal Melbourne University of Science and Technology in Australia, set her sights on“Water battery”And in February this year, in “Advanced Materials” (Advanced Materials) The latest progress in the magazine.
The electrolytes often used in lithium -ion batteries are mixtures of organic intangible sub -solvents and lithium salt. The Ma Tianyi’s team wants to use water to replace the electrolyte in it to reduce the possibility of battery explosion.Of course, the “water” here is not pure water, but a mixture of water and inorganic salts.Then, theyUse zinc anode(The team also pays attention to magnesium anode), andApply oxidation on the two poles, Further improve the life of the water battery.At present, their vision is to use such batteries in cases where electric scooter does not require a lot of electricity.
With the transformation of energy, more and more electric transportation equipment poured into the market, and security problems may also emerge.At present, related numbers are still shocking -according to statistics from the National Fire Rescue Bureau,In 2023, the country received a total of about 20,000 electric bicycle fires from fire.It rose about 17.4%from 2022.The use of electric vehicles safely, there is still a long time to go.
Reference link:
https://www.nfpa.org/news-hogs-nd-rad-rin-nfpa-journal/2022/08/04/e-bikes
https://www.newscientist.com/article/2418258-batteries-with-water-Power-scoors-without-Exploding/
https://sciteChDaiLY.com/what-makes-electric- “fires-diffult-to-extinguish- video/
https://batteryniversity.com/article/lithium-te-saflety-concerns
