On May 28, an electric car in Heyuan City, Guangdong Province, suddenly burst into flames after an hour of charging, the owner immediately unplugged the power supply to stop charging, then firefighters arrived to prepare to put out the fire, the vehicle suddenly burst into flames, flames quickly swept the entire body; May 15, Guangxi Baise College new energy ferry in charging spontaneous combustion, the vehicle from smoke to fire engulfed in just 3 seconds; May 6, Zhengzhou City, Henan Province Road and Talent Street intersection, a green electric truck fire spontaneous combustion accident ...... According to the GGII incomplete statistics, from January to May 2021, a total of 34 domestic electric vehicle fire accidents, an increase of 20 over the same period last year; involving 38 vehicles, an increase of 73% over the same period last year.
As the number of new energy vehicles grows and the temperature rises after summer, electric vehicle fires and spontaneous combustion accidents are also at their traditional high. So, how safe are electric cars? Are they more prone to spontaneous combustion than fuel cars? This reporter recently conducted an interview to investigate these issues.
More difficult to put out than fuel cars
The "Small Pure Electric Passenger Vehicle Travel Data Report" released by the National Alliance for New Energy Vehicles last year shows that the probability of a domestic new energy vehicle fire in 2019 is 0.0049%; since 2020, the probability of a fire has dropped to 0.0026%. Meanwhile, relevant data from the Ministry of Public Security shows that the annual fire accident rate of traditional fuel vehicles is about 0.01%-0.02%, compared with the probability of fire and spontaneous combustion accidents of new energy vehicles, which is significantly lower than that of traditional fuel vehicles.
"Electric car battery, motor, electric control composed of drive system thermal efficiency is much higher than fuel cars, under normal circumstances into the waste heat to less than the engine, that is, internal and external working temperature are lower than the engine system, and the system is relatively simple, volume regulation or even can be designed to be smaller, so the probability of igniting the surrounding wiring harness and other flammable media is also lower, which is the probability of tram fire is lower than This is the fundamental reason why trams are less likely to catch fire than oil vehicles." Cao Guangping, an independent researcher in the new energy vehicle industry, said in an interview with reporters.
Even so, the risk of fire in electric vehicles still requires vigilance, Cao Guangping warned, "Although the probability of fire in components outside the drive system of electric vehicles is low, it is more difficult to put out a fire inside the battery, especially after a short circuit inside the electric core, than in a fuel car, so the danger of fire accidents in electric vehicles may be higher."
The potential for spontaneous combustion in the middle and later stages of charging is high
The cause of spontaneous combustion in electric vehicles is both unexplained spontaneous combustion during charging and external collision, which basically originates from the power battery. This reporter found that most electric car fires occur during or just after charging. "This is because the probability of a battery fire is positively correlated with the state of charge, which means that the more electrical energy is charged into the battery, the greater the potential difference between the positive and negative electrodes of each cell, and the more likely it is to catch fire, and the greater the danger of catching fire." Cao Guangping pointed out.
It is understood that the lithium-ion battery charging fire there is a U-shaped curve law, that is, the early stage of charging because of the current is larger, in the charging plug, socket, cable, charger or charging pile, as well as charging the battery circuit is easy to overheat, the possibility of spontaneous combustion; charging late, although the current is getting smaller, but the battery potential will gradually rise, easy to breakdown or damage the battery and other insulation structure, also prone to spontaneous combustion.
How to eradicate the hidden danger of spontaneous combustion in power battery charging? Cao Guangping pointed out that car companies, battery companies need to strengthen the battery pack and other preventive design, the group users in the early stages of vehicle charging need to check the temperature and temperature rise rate of each link of the charging circuit, and at the end of charging to check the battery accumulation temperature rise. "Charging should be stopped immediately if the temperature rise is abnormal. At the same time, individual users should try to charge in a cool, ventilated place to avoid the risk of spontaneous combustion due to overheating of the battery caused by exposure to the sun."
The whole industry chain needs to work together to solve the problem
As power batteries are prone to fire under the action of various factors such as overcharging, overheating, short-circuiting and mechanical triggering, and are difficult to put out and have a high risk of re-ignition, this has put forward new requirements for enterprise design and development.
Cao Guangping pointed out that maintenance is an important task to prevent battery fires. "Many car companies have built data monitoring platforms in the background of vehicle operation, which helps to discover hidden battery problems of specific users, and according to the data to curb the seeds of accidents in a timely manner, and try to do their best to prevent 'unburned'." At the same time, battery use should be reduced as much as possible to meet range requirements, which can also reduce the probability of fire. "Because the more batteries on board, the more complex the system becomes, the more difficult it is to manage thermally and battery management, and the greater the probability of failure."
"If hydrogen fuel cells and lithium batteries are used in combination, they will play an important role." Beijing University professor Qi Lu has pointed out that "the promotion of the use of methanol fuel cells should be encouraged, which work like hydrogen fuel, but do not require low temperature and high pressure use, and can be combined with lithium batteries, which will be oriented to hybrid or extended power in terms of technology, and will be expected to promote the rapid development of electric vehicles."
In addition, Cao Guangping also pointed out that battery fire prevention is not only a matter for car and battery companies, but a problem that the whole industry chain needs to face together. "The consistency of materials and equipment and process requirements before the production of batteries are strictly enforced in order to have a comprehensive prevention and control effect."
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