[Autohome? Industry]? Currently, summer is approaching across the country, and electric vehicles are gradually becoming "restless" as the weather gets hotter. Since May 2020, the national supervision platform for new energy vehicles has discovered 79 safety accidents. Among the identified vehicles on fire, 58% of the vehicle fires were caused by battery problems, and 19% were caused by collision problems. This forces people to re-examine the quality and safety issues of new energy vehicles. Why do new energy vehicles always spontaneously ignite? Do all the "sins" behind it have to be shouldered by the battery?
"Sun Tzu: Military Strength": "Thus, those who are good at fighting look for the strength and do not blame others, so they can choose people and follow the strength." This means that the army is not strict and the teaching is unclear. The defeat was all the general's fault. Each cell in the battery pack is a soldier that adds energy to the electric vehicle. How to command these soldiers to prevent them from "thermal runaway" and spontaneous combustion, and to "welcome" them in extreme weather, so that they can obtain stronger power? The battery life needs an excellent "general" - the thermal management system.
■In summer, how to curb the murderer of spontaneous combustion?
Judging from the application status of pure electric models in 2020, some models are equipped with ternary lithium battery systems with energy densities as high as 180Wh/kg or even 190Wh/kg. If the vehicle's thermal management system fails to meet standards, such high-energy-density batteries can easily lead to safety hazards.
"This standard of the Ministry of Industry and Information Technology undoubtedly sets a new threshold for battery safety in the field of new energy vehicles." Dr. Gu Jianmin, Chief Technology Officer of Valeo China, said when communicating with Autohome. But in his view, this standard is a bit of a "temporary solution, not the root cause", because the ultimate goal of electric vehicle safety is not to give a 5-minute warning, but to continuously improve the design and manufacturing level, and ultimately achieve a single battery cell that does not lose control, or a single battery cell. Loss of control will not cause the entire battery pack to catch fire or explode.
In fact, as an energy carrier, there is no intrinsically completely safe battery. There are great differences in the thermal runaway process of each type of cell and battery system. Not every car company has the ability to build this 5-minute "life wall". It is not appropriate to simply transfer the pressure to the power battery. The safety of electric vehicles is also related to the technical strength of the car companies themselves. The battery thermal management system is an important link.
In order to prevent the battery from spontaneous combustion, the primary responsibility of the "general" of the thermal management system is to "control the temperature" to prevent the soldiers (battery cells) underneath from spontaneous combustion due to thermal runaway. The habits of batteries are similar to humans. They neither tolerate too much heat nor like too cold. The most suitable operating temperature is between 10-30℃. When the temperature is too high, the battery thermal management system usually has two ways to cool the battery, namely air cooling and liquid cooling.
『Tesla uses a liquid-cooled battery thermal management system』
Air cooling, in one sentence, means "walking with the wind". Its technology is simple and low-cost (about 1200 Yuan) and easy to maintain, but it is difficult to achieve heat dissipation balance, and the entire temperature inside the battery can easily vary. In the early days of the development of electric vehicles, because the dominant lithium iron phosphate battery had good thermal stability and relatively low heat dissipation requirements, the thermal management system did not need to be too complicated and could only use air-cooling technology. Early representative models include the Nissan Leaf, BAIC New Energy EC, Toyota Prius, etc.
However, the current energy density of batteries is getting higher and higher. Whether it is the mainstream high-nickel ternary battery or the lithium iron phosphate battery with a major structural transformation, higher requirements are put forward for the battery thermal management system. requirements, the current battery cooling system is tilting from air cooling to liquid cooling. Liquid cooling mainly controls the temperature of the battery through the liquid in the battery pipe. It has a better cooling effect and balances the temperature of the entire battery. However, the disadvantages are also obvious. Its technical difficulty is greater than that of air cooling and its cost is high (about 3,500 yuan). , and large size. If the car manufacturer does not design the thermal management system well, the energy density of the entire battery will decrease. According to statistics, golf GTE, NIO ES6, BYD Tang New Energy, Tesla Model 3 and other models all use liquid cooling. It is estimated that the market penetration rate of liquid cooling technology has exceeded 60%.
As the saying goes, one rat droppings spoils the whole pot of porridge. If a certain battery cell undergoes thermal runaway, adjacent cells will also experience thermal runaway and spread.
Is there any way to prevent it early? Or "cut off" a battery cell as soon as possible when it is discovered that it has thermal runaway?
Gu Jianmin told Autohome, "Battery safety is not a problem of a certain technical point, but a problem of the entire system. The fundamental function of the battery thermal management system is to make the battery work within a certain appropriate temperature range and maintain Optimum usage and efficiency are used to ensure the performance and life of the battery system, rather than to prevent the battery cell from thermal runaway. ”
Previous cases of spontaneous combustion of electric vehicles have vividly demonstrated that electric vehicles are not suitable for electric vehicles. Once a car spontaneously ignites, unless a large amount of water is used to cool it down, it cannot be stopped with just some small dry powder fire extinguishers. In most cases, you can just watch it burn out. "It can be seen that battery thermal management needs to be intervened in the early stage of design, using an integrated optimization platform to realize the coupling of structure, heat, fatigue and life to prevent thermal runaway. Once thermal runaway occurs, it must be able to detect it immediately and give an alarm in advance, so that the driver can The officers had enough time to escape to a safe place," Gu Jianmin said.
Of course, for the ultimate goal, the industry is still exploring battery thermal management technology. It is reported that the American company Allcell Technology has developed a battery thermal runaway isolation material PCC based on phase change materials (a material that can switch between liquid and solid states). In the acupuncture experiment, a battery pack of 4 parallel and 10 strings composed of 18650 cells did not use PCC material. Thermal runaway of one cell eventually caused thermal runaway of 20 cells in the battery pack. When PCC material was used, In the battery pack, the thermal runaway of one cell did not cause thermal runaway of other battery packs. This method is considered the most promising development direction for battery thermal management, but it is still in the laboratory stage.
■How to "extend life" of frozen batteries in winter?
In addition to re-examining the safety of electric vehicles, battery life is also a major anxiety issue for consumers buying electric vehicles. At present, many new models claim that their driving range can reach 600km or even more than 700km when applying, but what is the real actual effect? "The declared battery life of an electric vehicle will be discounted by 20% for actual use, and an additional 40% discount will be given if the air conditioner is turned on." An industry insider joked. Since the battery is not resistant to heat or cold, a lot of power must be consumed to ensure that the battery works at the most suitable temperature.
Compared with summer, extreme cold weather is even more damaging to batteries. For example, some current mobile phones, in the cold Northeast, will only have 60% power left in a few minutes if you don't put a warm baby on the back of the phone, and will shut down after a while. It’s already miserable for a mobile phone to turn into a “brick”. If this happens to a moving electric car, it’s like a nightmare.
For traditional cars, the engine itself carries a lot of heat and consumes very little warm air power in winter. But for electric cars, without the engine as a heat source, the power battery must not only provide power for driving the car Energy needs to be allocated to the power consumption of heating air, which is a huge loss. Therefore, a complete battery thermal management system also needs to preheat the battery at this critical moment in winter and cooperate with the air-conditioning thermal management system to maximize the battery life.
At present, most electric vehicle heaters and air conditioners are equipped with an additional PTC heater as a supplement. Its working principle is similar to the "heat fast" we use. It can quickly heat the coolant in the pipe to heat the battery pack. It has a simple structure and low cost, but it consumes huge power energy.
The above is still a conservative algorithm. Using PTC solution for heating in winter still puts a huge burden on the battery. If the heating efficiency is not up to par, it is not an exaggeration to say that the range of electric vehicles will be halved in winter.
Isn’t there a better way to “preserve” battery life? The answer is yes. The new heat pump air conditioner can effectively alleviate the battery life problems caused by electric vehicle heating. Compared with PTC's "electric energy conversion into heat", the heat pump system "electric energy transfers heat", there is no energy loss, and the heating efficiency is more efficient. According to Hanon research, under the same environment, the heating efficiency of heat pump heating is 1.8-2.4 times that of PTC, and the energy saving effect is significant, which can reduce the mileage loss caused by heating to half.
With heat pump air conditioners having such advantages, traditional car companies will naturally not stand by and watch indifferently, including Audi R8 e-tron, BMW i3, Nissan Leaf, Kia Soul and Jaguar I-PACE, etc., which have already adopted heat pump systems.
In China, Huayu Sanden is the first parts company to achieve mass production of heat pump air conditioners. Its heat pump air conditioners are equipped with two electric vehicles, the Roewe Marvel X and Ei5, owned by SAIC Motor Passenger Cars.
『Roewe Marvel question. "In low temperature conditions (-10°C to 0°C range), Valeo's heat pump technology can reduce energy consumption by up to about 30% compared to traditional PTC heating technology, but in extremely cold conditions (below -10°C ℃), it is generally recommended to use heat pumps and PTCs to provide heat, which is also the current common sense in the industry." Gu Jianmin said.
There is a classic case recently. Tesla recently announced a new patent on a heat pump system, which is expected to be first applied to Model Y. This technology cancels the traditional PTC in the design, but integrates a low-voltage PTC (playing an auxiliary role) in the heat pump air conditioner, and then integrates the battery system, power electronic drive system and vehicle system circuit to establish a set of Modular system. "Tesla's 'play' has changed the relationship between software and hardware, and also changed the concept of collaboration between different system designs within car companies. This new organizational method will be difficult for traditional car companies to keep up in the short term." An automotive electronics engineer commented on this.
『Source: Model Y Owner’s Manual』
■Thermal management of electric vehicles, the new cheese of domestic manufacturers?
Compared with traditional fuel vehicles, the thermal management system of electric vehicles has added components such as electric compressors, electronic expansion valves, battery coolers, and PTC heaters. The system integration and complexity are higher. The cost has increased from about 1,910 yuan for traditional cars to 5,280-9,920 yuan for electric cars (2020 forecast data). For parts companies, electric vehicle thermal management systems are a new piece of cheese.
Looking back on the past, in the traditional field of automotive thermal management, the four overseas parts giants Denso, Hanon, Valeo, and Mahle together account for 54% of the global automotive thermal management market ( 2017 data). Because of this, these companies are comfortable switching to the field of thermal management of electric vehicles and have a preemptive advantage.
"Schematic diagram of Valeo's new energy vehicle thermal system (including heat pump and battery thermal management system)"
For example, Valeo currently occupies 15% of the global battery thermal management system share. It provides cooling plates for models such as Tesla Model 3, and won orders for battery thermal management and heat pumps such as Volkswagen ID.3 and Peugeot e-208 in 2019. It achieved a total revenue of 36.2 billion yuan, accounting for 10% of the company's total revenue. 23.7%; the new heat pump developed by Denso in 2017 is installed on the Toyota Prius Prime PHEV. The working range can be extended to -10°C, saving 63% energy than the original version, increasing the vehicle’s cruising range by 21%; Mahler uses heat pumps Based on this, an integrated thermal management system has been developed that can increase the winter cruising range of electric vehicles by up to 20%, and is currently being tested on prototype vehicles.
Looking at it this way, the core technology of electric vehicle thermal management has been blocked by overseas companies again? Not entirely. Because the air conditioning system has fewer technological updates, traditional thermal management giants can smoothly shift their advantages. However, the battery thermal management system is a completely new field, and no company has yet been able to build technical barriers.
Domestic thermal management companies such as Yinlun Co., Ltd., Sanhua Intelligent Control, Aoteka, and Songzhi Co., Ltd. have also been actively expanding the field of electric vehicle thermal management in recent years. Although domestic companies have the opportunity to touch the cheese of electric vehicle thermal management, they are more involved in the thermal management Tier 2 field. Compared with international thermal management giants, they are still lacking in system integration capabilities. For example, although Tenglong Co., Ltd. has supplied Tesla with Thermal management components are provided, but they still need to be integrated through Hanon America.
Judging from the trend, it has become inevitable for domestic traditional automobile thermal management manufacturers to expand from single components to system integration. For example, Yinlun Co., Ltd. signed an agreement with Tesla in March 2020 to provide it with automobiles. Heat exchange module products; the company's heat pump systems will be supplied in batches to Jiangling New Energy in the second half of this year; starting in 2021, heat exchange assembly products will be supplied to Geely PMA pure electric platforms.
It can be seen that the opportunities brought by new energy vehicles may re-rank the thermal management market, and the competitive advantages of domestic manufacturers come from two points: close to the market and low cost. In the future, they need to rise from Tier2 to Tier1, binding OEMs develop more sophisticated thermal management systems to enhance their voice.
■Written at the end:
Nowadays, the new policy of subsidy for new energy vehicles has been extended, and the "stable technical indicators" have also been emphasized, which has given car companies a longer buffer period. It is hoped that car companies will no longer blindly pursue "energy density", nor cut corners to reduce costs, causing consumers to suffer from multiple anxieties such as halved battery life and safety. If electric vehicles want to make waves, thermal management must first keep up.
Regarding the development of thermal management of new energy vehicles in the future, Gu Jianmin proposed two trends: First, intelligent thermal management. The thermal management system will definitely be combined with smart cockpits in the future to bring users a more comfortable experience. For example, it automatically adjusts the most suitable cabin ambient temperature; secondly, it supports fast charging and overcharging. Difficulty in charging and slow charging are currently the two major pain points that affect the user experience of electric vehicles. Shortening the charging time, for example, with the Tesla V3 supercharger, Heat needs to be taken away quickly, which also requires a battery thermal management system to assist. (Text/Auto Home Peng Fei)