According to incomplete statistics, since 2018, there have been nearly 50 problems of spontaneous combustion or explosion of new energy vehicles. Frequent spontaneous combustion accidents have furthered the society's concerns about the safety of electric vehicles in high temperature environments and battery stability. What is the cause of such an incident? Recently, the Economic Daily reporter interviewed Professor Lu, a professor at Peking University and chairman of the academic committee of Lithium Davos.
In order to ensure the safe operation of all electric buses in the 2008 Beijing Olympic Games, the Lu team has conducted research. It was found that the safety of electric vehicles is not only determined by batteries, but also the improper use of lithium batteries.
In his view of Lu, the cause of fire accidents was 31%, which was mainly due to improper selection of lithium battery materials and the quality of the battery itself. "When charging quickly, a lithium battery with poor conductivity is prone to generate a lot of heat, and the temperature rises sharply, resulting in thermal runaway." Lu said.
According to the statistics of the fire accidents of new energy vehicles since 2017, the charging place is a high-risk area with fire, accounting for 50%.
Lithium batteries contain a large amount of flammable substances, such as water-insoluble liquid electrolytes, which burn when exposed to air at temperatures of 60 to 70 degrees Celsius. He said that the reasons for the various problems in electric vehicles should not be completely attributed to lithium batteries. Analog fuel vehicles, in fact, fuel is more flammable, and the occurrence of combustion and explosion accidents is even more terrible, but the probability of spontaneous combustion or explosion of fuel vehicles in the world every year is still very low.
In recent years, electric vehicles with high energy density and long battery life have attracted attention. Some batteries with a density of 180Wh/kg and even up to 200Wh/kg have begun to be applied. However, the materials of these lithium batteries are more prone to heat during charging and discharging, and as the energy density continues to increase, the probability of thermal runaway also rises sharply.
At the same time, when the car collides, the battery pack is deformed, causing the battery diaphragm to be torn and an internal short circuit, and it is also easy to cause a fire due to leakage of the flammable electrolyte.
“The design of electric vehicles is always at the heart of the problem.” Lu said that because during the driving or charging process, the battery has to work to generate heat. But as of now, there is no good solution for achieving rapid heat dissipation of lithium batteries. Therefore, it is imperative to accelerate the development of lithium battery core materials and battery technology. But to completely solve the safety problem of electric vehicles in the future, it is not simply a problem with batteries.
He Lu believes that in the near future, electric vehicles should have a very important role in the development of hydrogen fuel cells and lithium batteries in order to develop and solve safety problems. “I have been encouraging the promotion of methanol fuel cells. We have been working on this for more than ten years. The working principle of methanol fuel is the same as that of hydrogen fuel, but it does not need low temperature and high pressure. It can be combined with lithium battery. In terms of hybrid or incremental power, it is expected to rapidly promote the development of electric vehicles."