"If we don't investigate the causes of fires in new energy vehicles, spontaneous combustion incidents may continue to occur in the domestic market." A week ago, Sun Liqing, associate professor at the School of Mechanical Engineering and Vehicle Engineering of Beijing Institute of Technology, asserted this in an interview with a reporter from China Consumer News.
Unexpectedly, just a few days later, on May 12, a Tesla Model S parked at the Harbour Plaza in Hong Kong for about half an hour suddenly started smoking and caught fire. Simultaneously, an explosion was heard at the scene, causing the front of the vehicle to be destroyed by fire.
A series of spontaneous combustion incidents have sparked widespread concern about the safety of new energy vehicles, with the blame pointing directly to the power batteries that provide energy to these vehicles.
The development of power batteries cannot be separated from safety.
According to the latest data from the China Association of Automobile Manufacturers, sales of new energy vehicles reached 360,000 units from January to April 2019, representing a year-on-year increase of 59.8%.
The performance of new energy vehicles bucking the trend and rising during a period of continued sluggishness in the overall auto market is truly remarkable.
Many automakers see new energy vehicles as the hope for tomorrow's car market, naturally increasing their investment in this segment. However, it is precisely these new energy vehicles, expected to lead the future and whose market position is rising, that have encountered safety issues while developing rapidly.
In fact, the recent spontaneous combustion incidents are just the tip of the iceberg of the problems exposed by new energy vehicles.
In January of this year, the China EV100 released the "Lithium Battery Industry Development Report (2019)" (hereinafter referred to as the "Report"). Statistics show that from 2011 to October 2018, there were 108 cases of new energy vehicle fires in China. With the continuous growth in the number of vehicles on the road, the number of accidents involving new energy vehicles is showing a rapid upward trend.
Wang Binggang, head of the expert group for the National New Energy Vehicle Innovation Project, said that safety issues of new energy vehicles cover the entire life cycle, including the design and development stage, manufacturing and use process, and monitoring. For example, if the production process is not strictly controlled or the charging management is inadequate, a fire accident may occur if any link is not properly controlled.
So, which part of the process went wrong?
Data released by the China EV100 brings people closer to the truth. The data shows that in the past eight years, 92 out of every 100 new energy vehicle fires in China were related to power batteries, accounting for a staggering 86%. From an internal perspective, spontaneous combustion caused by battery thermal runaway is the primary cause. Battery thermal runaway is a complex and serious safety issue for electric vehicles.
This shows that battery quality issues have become a major cause of vehicle fires.
In 2018, domestic sales of new energy vehicles reached 1.256 million units, while the number of new energy vehicles recalled reached 138,000 units, involving seven automakers including Zotye Auto, Denza, Tesla, and Lifan Motors, with a recall rate as high as 13%.
According to recall information released by the State Administration for Market Regulation, JAC Motors recalled 4,248 new energy vehicles. The reason for the recall is that local overheating may occur during vehicle use, leading to battery thermal runaway and posing a safety hazard. It is clear that the problem lies with the power battery.
The quality of power batteries varies.
"The domestic new energy vehicle market is entering a period of rapid development, but it is an undeniable fact that some brands have an excessively high frequency of fires," said Ye Shengji, deputy secretary-general of the China Association of Automobile Manufacturers. He added that this indicates there is still much room for improvement in key issues concerning the safety of consumers' lives and property, and power batteries are a very important aspect of this.
In fact, with the rapid rise of new energy vehicles, once the market overheats, a situation will naturally arise where production capacity exceeds market demand.
Currently, apart from a few automakers such as BYD and Denza that use self-produced power batteries, other automakers rely on external procurement to meet their power battery needs. In other words, most automakers do not have absolute say in the most crucial aspect of new energy vehicles.
Wang Binggang stated that the research and development of power batteries is a relatively slow process, requiring full consideration of factors such as the materials used, cell quality, internal resistance, voltage, and power. It is similar to a traditional fuel vehicle engine; it is easy to make, but it requires a lot of effort to make it well.
As we all know, most mainstream new energy vehicles in China currently use lithium batteries. Although lithium batteries offer a significant improvement in safety performance compared to lead-acid batteries, some problems are still inevitable.
Recently, the most frequently heard reports of power battery fires are mainly caused by the internal resistance of the battery cells under different vehicle conditions. When outputting electrical energy, the cells release heat, causing their own temperature to rise and accumulating a large amount of heat within the battery pack. Ultimately, the inability to dissipate heat leads to a fire. The report shows that my country adopts a notification management system for electric vehicle companies and products, requiring electric vehicles to meet both conventional vehicle and electric vehicle-specific inspection standards. However, this notification management only covers prototype vehicles, and the quality of some products varies considerably. For example, inconsistent battery module designs and defects in the BMS (Battery Management System) for charging management can all potentially lead to electric vehicle safety accidents.
Sun Liqing stated frankly that lithium batteries are in the early stages of industrialization, and there are practical factors such as imperfect production processes and low levels of automation in production equipment, making it difficult to guarantee the initial consistency of lithium batteries when they leave the factory.
As the market share of new energy vehicles increases, the development of pouch batteries is gradually gaining recognition from major automakers. More than ten automakers, including BAIC New Energy, SAIC Motor, and Chery Automobile, have already made this choice. However, pouch batteries also face technical limitations. "Pouch batteries don't have a thick outer casing, making them lighter and more flexible in shape. However, the lack of a protective casing weakens the mechanical strength of the cells, and the sealing process is more difficult, resulting in slightly lower cell consistency. This directly leads to a decrease in the overall stability of the battery pack," said Sun Liqing.
In addition, my country inspects electric vehicles in accordance with the national motor vehicle safety technical inspection standards. However, under the existing technical inspection model, without disassembly, the inspection department finds it difficult to effectively inspect the special requirements of electric vehicle batteries, motors, electronic controls, etc., and cannot detect actual problems in a timely manner.
All of these factors will have a certain impact on the safety of new energy vehicles.
The accumulation of domestic battery technology still needs to be improved.
Currently, domestically branded new energy vehicles hold over 50% of the market share in China. Unlike traditional gasoline vehicles, domestic new energy vehicles primarily use domestically produced power batteries, rather than core components from foreign brands.
Does this indicate that domestically produced batteries have a high level of technology? The report shows that after years of development, domestic battery manufacturers, leveraging their first-mover advantage in new energy vehicles, have become major global producers of lithium-ion batteries. However, in terms of core technologies, South Korea leads in chemical battery materials and possesses comprehensive technological reserves in the four key material areas: cathode, anode, electrolyte, and separator; Japan's power battery products have the highest energy density globally. And in terms of the depth of technological accumulation by companies, the competitiveness of domestically produced batteries remains limited.
From a technological potential perspective, the theoretical energy density of lithium iron phosphate batteries is about 170 Wh/kg, while that of ternary lithium batteries is 300-350 Wh/kg. Both of them have safety issues such as low thermal decomposition temperature and easy combustion and explosion. Therefore, the potential for improving the energy density of both is relatively small.
According to a reporter from the China Consumer News, the energy density of all-solid-state lithium batteries has great potential for improvement in the future. The biggest difference between solid-state lithium batteries and traditional lithium batteries lies in their use of solid-state electrolyte materials, which changes the traditional structure of lithium batteries. Separators and other components are no longer essential, bringing significant technological advantages and potential.
It is understood that the main technological advantages of solid-state lithium batteries lie in their high safety, significantly reducing the risk of battery combustion and explosion. Furthermore, and most importantly for consumers, they offer high energy density, with the estimated maximum potential energy density of all-solid-state lithium batteries reaching 900 Wh/kg.
Sun Liqing stated that current technology development is still some distance from industrialization, and it remains uncertain whether it can replace existing battery systems within a certain period. However, it is certain that the emergence of new batteries is expected to break through the current technological bottlenecks of power batteries, reduce battery costs, improve driving range, and bring better products to consumers.
