Tesla:behind The Fire

- Dec 06, 2019-

On the journey to the full marketization of electric vehicles, safety has always been a "Sword of Damocles" hanging high.

Before the Shanghai Auto Show ended, the new energy automobile industry immersed in excitement ushered in a "Black Monday" without warning. On the evening of April 21st, an underground garage in a community in Xuhui District, Shanghai, a ModelS spontaneously ignited without a collision. From the video transmitted, a large amount of white smoke was emitted first, and then the fire started to burn, which caused the surrounding vehicles Fire burning. (Fire video: https://v.qq.com/x/page/q0863o0xea5.html)

Throughout the Monday, the video of Tesla's fire spreading wildly in the circle of friends. Just as netizens lamented the frequency of their fires with "double stabbing" again, that afternoon, Xi'an Weilai authorized a service center to repair an ES8. Burning occurred, and pictures circulating on the Internet showed that the ES8 was very damaged and the frame was almost completely burned.

Within one day, two consecutive spontaneous combustion accidents of electric vehicles were caused by domestic and foreign star-rated car companies, which could not help but let the insiders of the electric vehicle market just opened a "sweat".

In fact, if you trace the timeline forward, you will find that the number of fire accidents in electric vehicles is increasing, especially since 2018, there have been too many electric vehicle safety accidents at home and abroad.

Incomplete statistics of high-tech lithium batteries. In 2018, there were more than 40 electric vehicle safety accidents in China alone. These accidents seriously endangered the industry's image and the public's confidence in electric vehicles.

After the electric vehicle has completed from 0 to 1, it is entering the fast track of mass marketization. At this time, safety issues may become an "untimed bomb" in the entire industry. Especially under the current industry trend, high-nickel power batteries with greater safety risks have gradually entered the supporting application stage.

Ouyang Minggao, an academician of the Chinese Academy of Sciences and a professor at Tsinghua University, has repeatedly pointed out in many public places that the biggest risk facing electric vehicles is battery safety.

In fact, Ouyang Minggao's concerns are not “alarms”. Most of the reasons for combing and analyzing domestic electric vehicle fires are directed to the battery. Specifically, most of them are caused by the thermal runaway of the battery.

The so-called thermal runaway means that the power battery will heat up when it is working. When the battery temperature is too high or the charging voltage is too high, a chain of chemical reactions will occur inside the battery, causing the battery internal pressure and temperature to rise sharply, causing the battery to run out of control. And eventually lead to burning.

And if the cause of battery thermal runaway is traced, multiple factors such as overheating, overcharge, internal short circuit, and collision are specifically covered.

After analyzing the fire accidents since last year, Ouyang Minggao concluded that there are still many obvious problems in the product quality of power batteries, which are mainly reflected in three categories. First, insufficient battery product testing and verification; second, Reliability changes during vehicle use. Third, there are problems with charging safety management technology.

If the product quality problem can be used to explain the domestic electric vehicle safety accidents last year, then the self-ignition accidents that Tesla burst out cannot be analyzed from the perspective of quality alone. It may also include the choice of material system, battery cells, etc. Design and system protection to trace and reflect.

From the perspective of power battery companies, a number of industry experts and company technical leaders, including Ouyang Minggao, have emphasized to the high-tech lithium battery that we must focus on the system, material selection and control, and cell-level specification selection. With design, production and quality control, module and pack-level security protection, vehicle verification, use of link operations and other aspects to do more comprehensive.

With regard to the safety implementation of power batteries, from the perspective of battery companies, what specific improvements should be made to truly prevent this "grey rhino"? High-tech lithium batteries have proposed through in-depth exchanges with industry experts and upstream and downstream companies in the industry chain. The following suggestions:

First, in the choice of materials, the choice of core materials will have a direct impact on the final battery product safety.

A technical leader of Rongbai Technology introduced high-tech lithium batteries. The safety of the battery cell depends to a large extent on the core materials, especially for the high nickel ternary system. The metal foreign matter content, residual lithium and pH value of the positive electrode material , Will have a great impact on the safety performance of the battery.

Gaogong Lithium Power learned that, in fact, international companies including Ningde Times, Samsung, and Vision AESC have strict requirements on core key indicators of cathode materials. For example, residual lithium needs to be controlled within 2000ppm, pH value is within 11, and metal foreign matter is within 20ppb. In this regard, the suggestions of industry experts are that domestic electric battery companies should put forward clear requirements on the core index control of materials.

Second, in the design of battery cells, modules, packs and process settings, safety redundancy and monitoring and early warning must be done.

In the design process, the first is to ensure the chemical stability of the battery cell, select a stable material, and test its stability through rigorous evaluation; in the module part, protect the battery cell from impact through the structure. The third stage is pack. In addition to physical protection measures, the key is to diagnose the battery module through BMS, monitor the occurrence of abnormalities, and predict possible problems to control the problems.

Among them, many head power battery companies have emphasized to high-tech lithium batteries, whether in batteries, modules or packs, we must fully consider FMEA to ensure that the design leaves a safety margin.

At the same time, in the process setting, add safety process settings to eliminate defective cells and ensure product consistency; strictly control the quality of manufacturing to ensure that it covers all the monitoring points of the FMEA failure mode, so that product production data can be traced, Traceable.

In addition, in the design of pack and BMS, it is necessary to have a safety warning strategy. Develop a device safety warning system in the battery system. In an emergency, cut off the circuit in advance to avoid thermal runaway. The BMS must protect the battery, and it must call the police when it detects a sharp rise in temperature, even if it is parked or locked. The vehicle must be able to receive the BMS alarm and respond in a timely manner (audible and visual alarm to notify the owner).

The third is to fully verify the test and verification before mass production.

In fact, this is also the biggest problem currently facing the domestic power battery field. On the one hand, product replacement is rapid, and on the other hand, test verification requires time and energy and lacks design reference experience. This is also an important reason for frequent accidents in recent years.

Stones from other hills, can learn. Representative of the National People's Congress and CEO of Vision Group Zhang Lei mentioned in this year ’s two sessions that the development process of internationally renowned well-known car companies is quite sufficient, and the safety risk has been controlled to a minimum level before the product launch. These car companies also master the core parameters of the car's operating conditions, and the test and verification schemes at the module and pack levels are more adequate and reasonable. Like Zhang Lei's point of view, most people in the industry have suggested that power battery companies should learn from the experience of traditional car companies in the development process and test links, and do a good job in product testing.

At the vision AESC strategy conference held at the Shanghai Auto Show last week, Zhang Lei also expressed a similar view with Ouyang Minggao. He believed that safe battery safety is the largest "gray rhino" in the electric vehicle industry. Based on safety considerations, Vision chose the Japanese company AESC, a battery company jointly established by Nissan and NEC, when it entered the field of power batteries. In the past 12 years, this company has created 430,000 electric vehicles, 9 Accumulated a record of 0 serious accidents.

The fourth is based on the Internet of Things technology to achieve security protection throughout the life cycle.

Batteries are organic chemical systems: every physical quantity such as temperature, power, voltage, current, power, internal resistance, etc., affects the safety and health of the battery cell at all times. And affected by the driver's operating habits and driving environment. By collecting real-time battery pack-related data and driving behavior and the relationship between the environment, and then analyzing and comparing big data, it is a feasible solution to achieve battery health prediction and safety management.

By analyzing the relationship between battery performance and safety-related parameters and driving behavior and driving environment parameters through big data, assessing the health of the battery and giving a quantification, the health of the battery and the entire vehicle can be presented to the driver in a quantitative form in real time Some parts are at high risk, and the system can prompt the driver to replace them or take precautionary measures. At the same time, it presents health in real time, and informs the driver how to adjust the driving style to improve the health of the battery and the entire vehicle. In order to achieve a benign interaction with the driver and improve the safety of the entire system.

The unanimous judgment of industry insiders, including Ouyang Minggao, is that safety technology is the first core technology of power batteries, the first focus of a revolutionary breakthrough in battery technology, and the lifeline of sustainable development of electric vehicles.

Facing the "grey rhino" of power battery safety, whether it can make greater breakthroughs and progress will determine how far power battery companies can go in the future: "In the era of high nickel, safety will always be a must for car and battery companies. The alert sword of Damocles, from material-battery-module-pack-car, negligence in every link may lead to irreparable losses. "