With the gradual popularization of new energy vehicles, their safety issues have been paid more and more attention by the whole society. At present, the spontaneous combustion and explosion events caused by the power battery of energy vehicles emerge in endlessly, which casts a cloud over the development prospect of the new energy vehicle market that is on the rise. In this context, it is urgent to solve the safety problem of power battery.
Recently, BMW (China) Automobile Trading Co., Ltd. filed a recall plan with the State Administration of Market Supervision and Administration in accordance with the requirements of the Regulations on the Administration of Defective Automobile Product Recall and the Implementation Measures of the Regulations on the Administration of Defective Automobile Product Recall. It is worth noting that BMW plans to recall three imported electric vehicles due to the fire risk of batteries.
With the gradual popularization of new energy vehicles, their safety issues have been paid more and more attention by the whole society. At present, the spontaneous combustion and explosion events caused by the power battery of energy vehicles emerge in endlessly, which casts a cloud over the development prospect of the new energy vehicle market that is on the rise. In this context, it is urgent to solve the safety problem of power battery.
Frequent battery safety accidents
With the increase of the number of new energy vehicles and the increase of their service life, the self ignition rate of new energy vehicles remains high. According to the data released by the Emergency Management Department, there were 640 new energy vehicle fires in the first quarter of 2022, an increase of 32% over the same period last year, higher than the average fire growth rate of 8.8% for vehicles. On average, more than 7 new energy vehicle fires occur every day.
The Emergency Management Department pointed out that the current fire causes of new energy vehicles mainly include the aging of battery components, external collision, high temperature weather, battery thermal runaway and high load. Among them, more than half of the fire accidents are caused by fire and electricity, and the other main reason is the battery fire caused by external collision. From this point of view, battery is the main cause of fire of new energy vehicles. "It is difficult to extinguish a fire in the battery of a new energy vehicle, especially after the internal short circuit of the battery cell catches fire, and the subsequent hazards are relatively large. Therefore, it cannot be taken lightly." An industry expert told the reporter.
The frequent occurrence of tram fires also sounded an alarm for the brand side, urging it to "find and solve early". In addition to BMW, since this year, many car enterprises have solved most of the discovered battery safety problems through recalls. For example, in September, Volvo Car Sales (Shanghai) Co., Ltd., Daqing Volvo Car Manufacturing Co., Ltd. and Zhejiang Haoqing Automobile Manufacturing Co., Ltd. filed a recall plan with the State Administration of Market Supervision and Administration. It is reported that among the vehicles recalled this time, some plug-in hybrid vehicles have internal short circuit due to the battery cell of the power battery module. When the power battery is in a high energy state, the battery module may overheat. In extreme cases, the power battery may lose control of heat, which may lead to potential safety hazards.
It is widely believed in the industry that the recall system is a mechanism guarantee for error correction and improvement and a responsible attitude of enterprises. Enterprises can find problems in a timely manner and implement recall before problems cause accidents in a large area, which is more trustworthy for consumers.
The problem of "thermal runaway" is highlighted
However, the causes of the spontaneous combustion event caused by the power battery are more complex. In addition to the potential quality hazards of the battery itself, there are also safety problems caused by the characteristics of battery materials.
At present, the mainstream type of power battery used in pure electric vehicles is lithium battery. The reporter found that many electric vehicle fire accidents occurred during or just after charging. "When the positive pole of the lithium battery is overcharged, it is easy to have dendrites, that is, lithium ions in the positive material seep out to form dendritic crystals. As the dendrites become larger and larger, they are easy to break the lithium battery diaphragm, causing a short circuit between the positive and negative electrodes, which causes heat and explosion." Zhang Xiang, a researcher at the Automotive Innovation Center of North China University of Technology, said in an interview earlier.
The potential safety hazards in the charging link cannot be ignored. So, how should consumers avoid thermal runaway caused by overcharging? "At the initial stage of charging, due to the large charging current, it is easy to overheat in some parts of the whole circuit, such as the charging plug, charging socket, charging cable, charger or charging pile, and the charged battery; while at the later stage of charging, although the current is getting smaller and smaller, the potential in the battery will become higher and higher, which is easy to break down or destroy the insulation structure of the battery, and also prone to fire." Cao Guangping, an independent researcher of new energy and intelligent connected vehicle, pointed out that "in view of this rule, in addition to the need to strengthen the preventive design of vehicle enterprises and battery enterprises in the design process of battery packs, it is recommended that users pay attention to checking the temperature and temperature rise speed of each link of the entire charging circuit at the initial stage of vehicle charging, and check the cumulative temperature rise of the battery at the end of charging. If there is any abnormality, the charging should be stopped immediately."
In addition, at the enterprise level, some battery suppliers and car enterprises have launched technological innovation against the "thermal runaway" of batteries. For example, Lando officials have said that the mica battery carried by Lando Free uses three-dimensional thermal insulation technology, which can withstand the high temperature of more than 2000 degrees. When the battery is out of control due to heat, the battery pack of Lando Free can still be kept "free from smoke, fire and explosion" after 50 days. In terms of active safety measures, it can not only monitor in real time, but also predict key faults such as smoke, fire and explosion 2 hours in advance.
Common responsibilities of the industrial chain
In general, in order to improve the safety of new energy vehicles and effectively reduce the probability of fire, it is particularly important to use them in a reasonable and standardized manner. In addition, the key is to continuously strengthen the supervision on the policy side and continuously optimize the product side.
In July this year, Guo Shougang, head of the First Equipment Industry Division of the Ministry of Industry and Information Technology, stressed that in terms of power battery safety prevention and control, it is necessary to improve the performance level of power battery thermal runaway alarm, safety protection, low temperature adaptation, etc; In April, the Ministry of Industry and Information Technology, the Ministry of Public Security, the Ministry of Transport, the Ministry of Emergency Management, and the State and Municipal Administration of Supervision jointly issued the Guiding Opinions on Further Strengthening the Safety System Construction of New Energy Automobile Enterprises, which clearly pointed out that the safety level of power batteries should be improved.
"The power battery should not blindly pursue high energy density while ignoring safety. The main reason for the ignition of the power battery is the problem of manufacturing process and consistency. In addition to paying attention to the management of battery thermal runaway, we should not blindly reduce costs and bury potential safety hazards." Wu Hui, general manager of the research department of Ivey Economic Research Institute, once said.
At present, the battery safety of new energy vehicles has become the top priority. According to the interviewed insiders, power battery safety is an important task that battery manufacturers and car enterprises need to shoulder together. Battery safety actually comes from the design safety of battery material system, which is what power battery manufacturers need to do. In addition, automobile enterprises are also responsible for battery safety in terms of battery loading and application. "In particular, the vehicle enterprise project team should put battery safety first in the process of technical connection with battery manufacturers, and should not excessively reduce costs. It is necessary to comprehensively balance various factors and implement battery safety requirements in the entire vehicle model project."
