From：Internet Info Agency 2018-09-27 18:00:33
Recently, new energy vehicles have triggered a wave of attention, because both domestic and foreign, in the past two months, there have been incidents of spontaneous combustion of pure electric vehicles. In addition, we also found an interesting trend from the incidents of electric vehicles: when a fuel car catches fire, people often say, "VW is on fire" or "Ford is on fire", while one pure electric vehicle catches fire, almost all the people may only say "The NEV is on fire." Although it is just a joke, this phenomenon is indeed worth pondering. Isn't the NEV, which has always been called the future trend of automobile, so unpopular? Are NEVs really prone to spontaneous combustion than fuel vehicles?
Debate!
Which side are you on?
The claim: NEV is easier to be caught on fire.
NEVs often pursue such indicators as cruising range and charging speed, while ignoring the stability of the power battery, which easily leads to spontaneous combustion. Moreover, the self-ignition of the power battery is difficult to be extinguished.
The counterclaim: We should treat this issue rationally.
NEV has always been a hot topic in the auto sector. Almost every spontaneous combustion incident has caused widespread concern and even been over-reported. This has left people with the impression that NEVs are easy to get spontaneous combustion. What more, the probability of spontaneous combustion of fuel vehicles is also very high.
It is no need to be hasty to answer whether NEVs are prone to spontaneous combustion or not. But let us first see what incidents to the pure electric vehicles recently, and what causes the fire. At last, how should we deal with the power battery when it is on fire?
Q: Are NEVs really that unreliable?
Aspect 1: What is the reason of spontaneous combustion of pure electric vehicles recently?
Aspect 2: What are the factors that cause the power battery to catch fire?
Aspect 3: Why is it more dangerous when the pure electric vehicles on fire?
Aspect 4: How do consumers deal with the fire?
Aspect 5: How to avoid it in daily use?
＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
(We apologize for the low resolution of the screenshot picture for videos.)
As one of the new automakers, Weltmeister (WM Motor) has always been concerned by the industry. On August 25, the EX5, the only pure electric model of WM Motor, caught fire in the park of its own research institute. The video of the fire incident on the Internet caused great concern. Seeing from the video, the fire was started from the tail and chassis, and emitted a lot of smoke. Finally, the entire car was swallowed by flames.
Subsequently, WM Motor issued an official statement on August 26 and 29 respectively to clarify the cause and effect of the EX5 fire incident. According to the two statements, this EX5 was an early test vehicle, which was specially used for experimental certification. It had carried a total of 57,000 kilometers on various test road conditions and had conducted a 50 km/h rear crash test. It also had taken many water wading tests. The vehicle had been decided to be scrapped, and some parts were to be removed, such as the vehicle system and the emergency switches. However, some staff violated the regulations to electrify the car, which eventually triggered the risk of short-circuiting the vehicle and caused a spontaneous combustion fire on the power battery mounted on the vehicle.
(We apologize for the low resolution of the screenshot picture for videos.)
Early this month, one video of the LIFAN pure electric vehicle 650EV caught the attention of netizens in Weibo (a Chinese microblogging website, similar with Twitter). In the video, LIFAN 650EV parked on the side of the road, a burst of crackling noise and fire from the chassis. In addition, a large amount of smoke was emitted. It was apparent that the power battery at the chassis was on fire, which eventually caused the whole vehicle to be swallowed by flames.
Subsequently, LIFAN responded to the media, saying that they had found that the vehicle had abnormal power battery conditions on the monitoring platform before the fire, and had informed the car owner to wait for the service personnel to go to the maintenance. However, the car had already caught fire before the service personnel had arrived. After that, LIFAN conducted the on-the-spot investigation and preliminary determined that the cause of the vehicle battery fire was due to heavy rain in Guangzhou. The vehicle was exposed to rain for more than 2 hours, and the battery leaked slightly and a short circuit occurred, which eventually caused the power battery to catch fire. However, regarding the 650 EV fire incident, LIFAN did not issue a written statement. Whether the cause of the fire is related to rain exposure or not needs further investigation.
(We apologize for the low resolution of the screenshot picture for videos.)
ZOTYE Cloud 100 (Z100) is a pure electric mini-car. For it is relatively affordable and can enjoy the subsidies of NEVs, it has certain competitiveness in the market, and is also favored by shared travel in some areas. But, on September 5 in Zhuhai, Guangdong province, a Z100 shared EV was on fire when it was charging. In addition, another Z100 model, which is also charging next to it, also started to burn from the tail. The video was largely reposted, arousing an extremely high attention.
In the video, the left Z100 pure electric vehicle started to burn first. The whole vehicle has been surrounded by flames, and the red cloud 100 model on the right had a dazzling flame at the tail. But, up till now, ZOTYE has not yet issued the results of the investigation into the cause of the fire when the two cars were charging.
Tesla’s fire incidents also received widespread attention. On August 23, one Tesla Model S was on fire while running on the New Jersey highway. The Model S in the picture stopped on the side of the highway with obvious fire at the front and the chassis and lots of black smoke emitted.
Since the power battery of a pure electric vehicle is usually arranged on the chassis of the vehicle, when the chassis is bumped, it is likely that the power battery case is broken or the battery core is penetrated, which leads a huge fire risk of the power battery. But Tesla did not issue a formal written statement about the cause of the fire.
Is thermal runaway the basic cause of power battery fire?
From the fire cases of pure electric vehicles mentioned above, we can easily find that almost all pure electric vehicles cannot avoid the fire of the power battery, and even the power battery is always the first to catch fire. So, what is the real reason for inducing a fire in a pure electric vehicle power battery?
Actually, all power battery fires can be blamed to thermal runaway that is the case that the exothermic reaction is out of control.
We all know that lithium batteries generate a certain amount of heat during discharge and charging, and the higher the temperature of the battery itself, the faster the current will be released or charged. The higher current will continue to release more heat, and eventually causes the battery temperature to be continued to rise until the the battery temperature lost control.
Battery overheat can cause the electrodes and electrolyte inside the battery cell to decompose to generate gas and expand, forcing the safety valve to open. After the electrode is in contact with the air, an acute oxidation reaction will occur, and the high temperature will continue to rise until the fire occurs.
The electric control system of pure electric vehicles can limit the current when charging and discharging. The liquid cooling system set in the power battery can also well control the battery temperature during charging and discharging. Both systems, to the greatest extent, eliminate the hidden danger of thermal runaway. Therefore, it is difficult to occur spontaneous combustion in the case where the two systems are both designed and operated normally.
What factors can cause thermal runaway?
1. A serious collision can cause an internal short circuit or electrolyte leakage:
The battery cells are neatly held together at a predetermined spacing. If the vehicle collided, it is likely to cause the battery pack shell or a single battery cell to be deformed by an external force.
In the case above, hard objects collided directly with the Tesla Model S chassis, even lifted up the vehicle, causing the power battery to catch fire eventually. It is more likely because the power battery was damaged by external force. As a result, the power battery may be short-circuited due to deformation, and heat is generated continuously, which eventually leads to thermal runaway. Another possibility is that the independent shell of the battery cell is broken, resulting in leakage of flammable electrolyte. This is also a certain possibility to cause a fire.
However, the fire caused by the internal short circuit or electrolyte leakage during the collision is only a probabilistic accident. It is even more dangerous that the conductive material directly penetrates into the power battery.
For example, if some sharp objects, like rebar that are extremely conductive directly, directly penetrated into the power battery during a collision, a short circuit between the positive and negative electrodes of the battery will occur, and the heat generated by the short circuit will be more and faster, which will cause a fire in a short time.
2.Water wading, slight collision or power port fouling cause external short circuit of the power battery:
External short circuit of power battery is also common in the daily use of pure electric vehicles. For example, the waterproof performance of pure electric vehicle battery is not up to standard and frequent wading in the rainy season, slight vehicle collision, and fouling at the power port, all these may cause an external short circuit. In the case above, if the fire of the LIFAN 650EV is really caused by a long-term water wading, it would be a right example to this.
The danger of an external short circuit is not as straightforward as the internal short circuit caused by a collision. Because the heat generated by the external short circuit does not directly act on the inside of the power battery to cause thermal runaway. However, if the heat of the external short circuit cannot be dissipated but heated the power battery, there is also the possibility of igniting the power battery.
3. The electric control system malfunctions cause overcharging or over-discharging:
The electric control system of the pure electric vehicle can ensure that the power battery does not overcharge and over-discharge, but we can still see some battery fire incidents when charging, which is likely to be caused by the unreasonable design of or malfunction of the electric control system, or the failure of the charging pile.
For example, the Z100 charging fire incident mentioned at the beginning of the article is most likely caused by overcharging of the power battery. When overcharged, the internal heat generated inside the battery cell directly induces thermal runaway, which eventually causes the power battery to catch fire. When over-discharged, the copper ions in the electrolyte will crystallize on the negative electrode and proliferate, and penetrate the inner diaphragm of the cell, causing internal short circuit to induce thermal runaway and ignite the power battery ultimately.
4. The external high temperature heating power battery triggers the thermal runaway:
The last reason for the fire of the power battery is that the high temperature of the external environment directly heats the power battery to trigger the thermal runaway, such as direct ignition by an open flame.
Why is it more dangerous when a pure electric vehicle to catch fire?
Due to its active chemical nature, the ternary lithium battery boasts advantages of high energy density and fast charging time. It satisfies the requirements of the current pure electric vehicle for the cruising range and charging time to a certain extent, allowing it is widely used in NEVs’ power battery.
However, every rose has its thorn. The chemical nature of the ternary lithium battery also gives it a certain instability. As many factors mentioned above, the power battery may be triggered thermal runaway and eventually catch fire. Different from the internal combustion engine vehicle, when pure electric vehicle catch fire, most of the flame will first appear in the car chassis with a burst of crackling noise. Apart from that, what are the other differences between a fire in a pure electric vehicle and that in an internal combustion engine vehicle?
1. The power battery is burning very fast:
First, the speed of burning. Spread speed of the flame is affected by the wind and other factors, and the nature of the combustion is one of the main reasons for determining the speed of flame spread. Since most of the engine compartment is incombustible metal and rubber material with certain flame-retardant ability, when an internal combustion engine vehicle is on fire, there will be a pungent burnt smell before the violent combustion, then the smoke emitted, and finally flame appeared, which is a relatively slow process. Of course, except for a condition of fuel leakage.
However, for a pure electric vehicle, if the power battery is on fire, its active chemical nature itself determines its extremely flammable feature. First of all, the electrolyte in the cell is a kind of flammable dangerous substance; secondly, the electrode in the cell contacts the air and undergoes an acute oxidation reaction, which exacerbates combustion. Therefore, the power battery will produce a huge flame within a few seconds after the smoke appears.
2. Fast speed of burning spread
Since the cells in the power battery pack is closely and neatly arranged. If any one of the battery cells triggers thermal runaway, the surrounding cells will be heated or even burning, just like dominoes. The burst of crackling noise we heard in the videos is caused by the explosion of the battery cells in the power battery.
3. Extremely high temperature
When the battery is on fire, the heat generated from the oxidation reaction of the electrode, the combustion of the electrolyte, and the thermal runaway of other adjacent cells can reach 1000℃, which is twice as high as the 500℃ of an internal combustion engine.
4. Fire is difficult to be extinguished
Thermal runaway is an irreversible and acute reaction. Once thermal runaway occurs, it must cause a fire. Moreover, after the power battery is ignited, it no longer relies on the oxygen in the air for combustion. And its internal electrolyte and electrode will decompose to generate the gas involved in the combustion, so the common fire extinguisher cannot extinguish the flame. At the same time, the power battery is usually located at the bottom of the vehicle, which also makes it difficult to accurately extinguish the fire at the fire point.
5. Toxic gases
According to the test of the DNV GL Group, lithium batteries will release a lot of toxic gases when burning, including CH4, CO, C2H4, H2S, HF, HCl, SO2, HCN, and etc. Except for CH4, the rest of the gas will do harm to the human body. Smoke inhalation can also cause dizziness, headache, coma, loss of consciousness, or even death.
What should we do when a pure electric vehicle is on fire?
The only way for ordinary consumers to deal with the fire of pure electric vehicles is rapid evacuation and call 911 timely. Conditions permitting, try to park your car in an open area and inform the rear cars or pedestrians to avoid it.
1. Evacuate the vehicle ASAP
Since electric vehicles only take a few seconds from the start of smoke to the appearance of flames, and can also emit a lot of toxic gases, so the occupants should quickly evacuate the vehicle.
2. Timely call for professional firefighters
The fire of the power battery requires professional firefighters to use a large amount of water to continuously spray against the fire point to reduce the temperature of the battery core to suppress its thermal runaway. It also should be noted that, since thermal runaway is a continuous process and heat is continuously generated, even if the open flame is extinguished, it is still possible to re-ignite.
3. Pay attention to the risk of electric shock during the fire extinguishing process
At the beginning of the power battery burning, some battery cells are still intact, which means there is still a certain amount of electricity in it. Therefore, it is not recommended for consumers to extinguish the fire personally. When using more water with more impurities to extinguish the fire, it is very prone to electric shock.
4.Try to avoid driving on uneven roads during daily driving, keeping in mind the vehicle model and the location of the power battery.
Driving on uneven roads may directly cause damage or penetration of the power battery, resulting in a fire accident. In addition, the driver should also bear in mind the model of the vehicle being driven and the position of the power battery to facilitate the firefighters to locate the fire point more accurately and improve efficiency.
Summary:
For many people, pure electric vehicles are still a new-comer. And, because of this, pure electric vehicles receive much attention. Any fire accident of a pure electric vehicle will trigger great concern on the Internet, even been overexposed, leaving an unreliable impression. But people should rationally treat such incidents.
More importantly, we should fully understand the countermeasures in the accident of a pure electric vehicle fire. First of all, we should evacuate the vehicle asap. Safety comes first. Drivers should be familiar with the layout of the power battery of the vehicle being driven, so that firefighters can be more effectively in performing fire-fighting operations. Finally, after experiencing collisions, dragging, and severe wading, the vehicle's power battery should be inspected in time to avoid the risk of thermal runaway.
Author’s speculation: NEVs are easier to be caught on fire than fuel ones?
Conclusion: Yes, but we should treat those incidents rationally.
