Safety has always been the focus of new energy vehicles, and since May, a number of spontaneous combustion incidents have occurred in new energy vehicles, again focusing the market's attention on the safety of new energy vehicles. In fact, the power battery as the core of new energy vehicle safety, its safety technology has been constantly upgraded, from a single safety to system safety, to constantly "tamp" the safety bottom line of new energy vehicles.
Concentrate on checking the battery
It is reported that the industry is called "the most serious in history", the key is to have the car sales, inventory of waterproof protection, high-voltage wiring harness, car collision, car power battery, car charging equipment, battery box, mechanical parts and wear parts safety hidden danger investigation work, and according to the actual traffic conditions, take effective technical measures to reduce the vehicle Fire risk.
According to the "New Energy Vehicle Safety Inspection Reference List" issued by the Ministry of Industry and Information Technology, the main content of the safety inspection is the power battery, including appearance inspection, software diagnosis, airtightness test, open box inspection and replacement.
In fact, the policy level of new energy vehicle safety has been on the rise since early May. in early May, the Ministry of Industry and Information Technology (MIIT) released three mandatory national standards, "Electric Vehicle Power Battery Safety Requirements", "Electric Vehicle Safety Requirements" and "Electric Bus Safety Requirements", which will be implemented from January 1, 2021.
It is understood that these three mandatory standards, on the basis of China's original recommended national standards, are fully compliant with the China-led United Nations Global Technical Regulations for Electric Vehicle Safety, further improving and optimizing the safety technical requirements for electric vehicles and power battery products.
On May 26, the Ministry of Industry and Information Technology held a special meeting to strengthen the implementation of national standards for new energy vehicles, requiring all new energy vehicle products to meet national standards.
These policies place the most emphasis on the safety of new energy vehicle power batteries. While optimizing the safety requirements for battery cells and modules, emphasis was placed on the thermal, mechanical, electrical and functional safety requirements for battery systems. Test items include system thermal dispersion, external fire, mechanical shock, simulated collision, wet and thermal cycling, vibration soaking, external short circuit, over temperature, over charging, etc.
Center of gravity steering system safety
With the continuous upgrading of power battery technology, the safety focus of new energy vehicles is gradually shifting from battery technology safety to system safety.
China's automotive power battery safety standards have undergone several upgrades and specifications: When the industry standard was first released in 2006, the new energy vehicle industry was still in the incubation stage, so the main reference was the testing requirements for consumer electronics lithium batteries. 2015 when the new industry standard was released again, 10 years of R&D demonstration experience had been accumulated. On the basis of stand-alone and module testing, the level safety requirements for battery systems were added, which played an important role in guiding the integrated development of the system.
In the past two years, China's new energy vehicle industry has made remarkable achievements. China should also be invited by developed countries such as Europe, the United States and Japan to take the lead in the global electric vehicle safety and technical regulations for the power battery section, forming a mandatory safety standard system. The standard strengthens the thermal safety, mechanical safety, electrical safety, functional safety and other requirements of the battery system, simulating actual scenarios such as external fire, mechanical shock, wet and hot cycles, vibration soaking, over-temperature and over-charging. Single-pin test as an independent project, in this standard is officially canceled. Only as a single-piece thermal control trigger conditions, requiring the battery system in a single piece of thermal control shall not catch fire or explode within 5 minutes after the occurrence, leaving time for the crew to escape safely. In other words, it no longer matters whether the needle is pierced. The key is whether the system can control the spread of uncontrollable heat after the thermal control of a single cell, setting a basic threshold for the safe application of all types of batteries.
In this regard, many industry experts said that the safety standards for power batteries have shifted from a single safety to the overall system safety of the battery. Battery throughout the process of safe use, which is a system engineering, including the single design of the battery, system integration, dynamic monitoring and system protection, and so on, to ensure that the product is safe at all stages of the life cycle, and really improve the safety performance of the battery in practical terms.
Chen Quanshi, a professor at Tsinghua University and director of the Institute of Automotive Research, served as deputy director of the National Electric Vehicle Standards Committee and participated in the development of almost all of China's electric vehicle standards. He said the puncture test has been controversial and there has been a heated debate about whether there should be such a test, which is an optional part of the current standard.
Battery safety continues to improve
In response to the battery safety issue, major new energy vehicle manufacturers and battery manufacturers have been exploring and trying to improve the safety of automotive power batteries through different technical routes and different products.
In the field of power batteries, the mainstream is currently lithium iron phosphate and ternary batteries, other applications such as lithium titanate, lithium manganate, and some new system batteries, including solid-state batteries, magnesium batteries, cobalt-free batteries, hydrogen fuel cells and so on are also in the research and development and exploration stage.
The technical route is the common choice of the market and users. Due to the wide range of new energy vehicle applications and diverse application scenarios, the demand for power batteries is also diversified. Lithium-iron batteries are the characteristics of China, with high safety and long life, mainly used in electric buses, logistics vehicles and other commercial vehicles. Ternary batteries have high energy density and can effectively solve the mileage anxiety of private car users, and have become the mainstream solution for new energy passenger cars worldwide.
Because of this, many automakers and battery manufacturers basically maintain a parallel development of various technology lines. While lithium-iron batteries and ternary batteries are put on the market in large quantities, pre-research and technology reserve of other technology routes are also underway. Taking Ningde Time, which has the highest market share of domestic automotive power battery, as an example, its production and sales of ternary batteries and lithium iron batteries are at the forefront of the industry, maintaining a technical advantage over other battery technology lines.
With the increasing investment in R&D, various battery technology lines are being upgraded to make up for their shortcomings. For the shortcomings of the low energy density of lithium iron batteries, BYD launched the blade battery, through structural changes to make the same volume of lithium iron battery energy has been greatly improved. In order to solve the problem of low stability of ternary batteries, Ningde Time has created the "control short circuit" safety technology after years of research and development. Ternary batteries are subject to severe puncture or external metal foreign body (such as pinprick) impact into the battery, but also to ensure that there is no high current short circuit inside the battery, will not cause thermal control of the battery.
Ningde Times 2017, the first in the world to overcome the problem of high energy density ternary battery needling in response to the demand for a single technology for European automotive companies high energy density ternary batteries can pass the needling test, and sent to Germany Rheinland Rhubarb acid for customer testing and certification. The report results show that in the needling experiment, the ternary battery does not catch fire, does not explode, and the battery temperature is only 35.1°C.
With the acceleration of the "new infrastructure" construction, China's new energy vehicle industry is in a new stage of development. And this will certainly promote the rapid development of related industries, including power batteries. Safety, especially battery safety, as the primary issue of the new energy vehicle industry, will also become an important driving force for the future development of new energy vehicles and battery industry.
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