A few days ago, a video uploaded to Weibo showing the battery of a domestically produced new energy vehicle spontaneously combusting and exploding on a roadside in Guangzhou attracted nationwide attention. Six days prior, a similar incident involving a WM Motor new energy vehicle occurred at its Chengdu research institute. Even Tesla, a competitor in the new energy vehicle market, has not been immune to such situations. BAIC, Yema, Roewe, and BYD have also been reported to have experienced spontaneous combustion issues. Ouyang Minggao, an academician of the Chinese Academy of Sciences and a professor at Tsinghua University, directly pointed out that the biggest risk currently facing pure electric vehicles is battery safety.
Why have batteries become a hindrance to new energy sources?
As we all know, the advantage of new energy vehicles lies in their lower carbon footprint and greater environmental friendliness compared to gasoline-powered vehicles. They use unconventional automotive fuels as their power source, such as lithium batteries and hydrogen fuel. Lithium batteries also have a wide range of applications, including not only new energy vehicles, but also mobile phones, laptops, tablets, power banks, electric bicycles, power tools, and more.
Currently, mainstream new energy vehicles, whether globally renowned like Tesla or domestically prominent like XPeng Motors, NIO, and BYD, all use lithium-ion batteries. These lithium-ion batteries, classified by their cathode materials, can be categorized into: lithium iron phosphate batteries, ternary lithium batteries (including NCA and NCM), lithium manganese oxide batteries, lithium cobalt oxide batteries, nickel-metal hydride batteries, and lithium titanate batteries. Among them, Tesla, BAIC E200/150, GAC Trumpchi GA5EV, Beijing Benz, Brilliance BMW 5 Series, and NIO all use ternary lithium-ion batteries. BYD, which previously used lithium iron phosphate batteries, later switched to ternary lithium-ion batteries.
However, neither ternary lithium batteries nor lithium iron phosphate batteries can escape the hidden dangers of being flammable and explosive.
Lithium is the most reactive metal in the world. Due to its highly reactive chemical properties, lithium metal reacts violently with oxygen when exposed to air, easily leading to explosions and combustion. Furthermore, redox reactions also occur internally during the charging and discharging process of lithium batteries. Explosions and spontaneous combustion are primarily caused by the accumulation of heat generated by the lithium battery, which cannot dissipate and release in time. Simply put, lithium batteries generate a large amount of heat during charging and discharging, leading to increased internal temperature and uneven temperature distribution between individual cells, resulting in unstable battery performance.
In August of this year, an Apple retail store in Amsterdam, Netherlands, was forced to temporarily close and evacuate customers after an iPad battery exploded, releasing potentially harmful substances into the air. Previously, Samsung, Xiaomi, and Huawei have also been reported to have experienced mobile phone spontaneous combustion incidents. These incidents demonstrate that improper charging or excessively high ambient temperatures can easily cause lithium batteries to spontaneously combust or explode, a major concern for manufacturers.
Why must we use lithium batteries?
The limitations in battery selection largely depend on the development and commercialization of batteries themselves. The world's first battery, the "Voltaic pile," was made of zinc and tin plates. Zinc and copper batteries, wet batteries, and dry batteries followed. Due to their portability and ease of carrying, dry batteries were widely used for a long time before being replaced by Edison's rechargeable nickel-iron battery. Ultimately, lithium-ion batteries, using lithium cobalt oxide as the positive electrode and metallic lithium as the negative electrode, became the final choice in the market.
Compared to other batteries, lithium batteries have significant advantages. They have a long lifespan, exceeding six years, and are small in size with high energy density, reaching 460-600 Wh/kg, which is 6 to 7 times that of lead-acid batteries. Currently, Tesla has announced that its 21700 battery system, jointly developed with Panasonic, has an energy density of 300 Wh/kg. Meanwhile, lithium batteries possess high power handling capacity; lithium iron phosphate batteries used in new energy vehicles can achieve charge-discharge capabilities of 15-30C, facilitating high-intensity starting and acceleration of vehicles. Lithium batteries also exhibit strong adaptability to high and low temperatures, are environmentally friendly, and consume virtually no water during production.
In terms of commercial applications, only a handful of batteries are suitable for large-scale commercial use due to limitations in size and weight, energy storage and release capacity, storage time, lifespan, cost, ease of use, and mass production. For both reasons, lithium-ion batteries have become the optimal solution.
While the inherent properties of lithium batteries dictate their "flammable and explosive" nature, it is not entirely impossible to mitigate these risks and ensure safety. Whether it's a mobile phone manufacturer or a new energy vehicle company, through proper battery management and thermal management systems, batteries can be made safe and prevent explosions or spontaneous combustion.
How to solve this?
Batteries release heat during operation, and if this heat cannot be dissipated in time, it can spontaneously combust or explode. Therefore, a battery thermal management system can manage this heat. The thermal management system in new energy vehicles is a subsystem of the battery management system. This system cools the battery when it gets too hot and preheats it when it gets too cold, thus better utilizing the battery's performance. Tesla's unique battery management system is a typical example.
Tesla equips its vehicles with thousands of lithium cobalt oxide batteries for power. The 18650 batteries it uses have a lifespan of over 1000 charge cycles, but due to their high density, they also carry a higher risk of spontaneous combustion and fire. Tesla addresses this through its battery management system, which monitors various physical parameters of the battery in real time, assesses its condition, and provides online diagnostics and warnings. It also manages discharge and pre-charge, battery equalization, and thermal management. For example, its battery thermal management uses liquid cooling—a 50% water + 50% ethylene glycol mixture—to control the battery's temperature rise.
In fact, manufacturers have long been aware of the limitations of lithium batteries, and fuel cells, graphene batteries, and lithium-air batteries are all areas of research and development. Among fuel cells, hydrogen fuel cells have attracted the most attention, and hydrogen fuel cell vehicles, as a branch of new energy vehicles, have been continuously explored for commercial use.
In 2008, my country's independently developed fuel cell vehicle, based on the Volkswagen Passat and modified and integrated into the model, held a launch ceremony in Beijing at the New Energy Vehicle Engineering Center of Tongji University and was put into operation during the Beijing Olympics. Now, ten years later, at this year's CES Asia in Shanghai, Hyundai showcased its new generation hydrogen fuel cell vehicle, the NEXO. This model's fuel cell system efficiency reaches 60%, placing it at the forefront of the world.
Compared to lithium batteries, fuel cells offer greater safety. Because hydrogen requires extremely high concentrations to explode, it often begins to burn before ignition, making an explosion much more difficult. Furthermore, hydrogen's density is lower than air, so even if a fire breaks out, it occurs above the gas source, unlike lithium batteries or gasoline where the fuel is at the bottom of the vehicle, quickly rendering the entire vehicle unusable. In addition, fuel cells boast advantages such as high power generation efficiency, low environmental pollution, low noise, high reliability, and ease of constructing fuel cell power plants.
Of course, the high cost, transportation, and storage of fuel cells are also disadvantages compared to lithium batteries.
at last
Mobile phones, which also use lithium batteries, have repeatedly encountered difficulties regarding spontaneous combustion and explosions. This is even more true for new energy vehicles, which face even greater challenges. New energy vehicles are an inevitable trend driven by the times, and their widespread application is undeniable. Although funding and mass production are pressing issues for new energy vehicles, product safety must always be the top priority.
