Why does the electric vehicle lithium-ion battery explode, can the technology prevent it?

　　Author ：Iflowpower – Portable Power Station Supplier

We are entering the new era of the energy revolution, but when we continue to overlook the beautiful future of electric energy, it will not worry, is the lithium-ion battery safe? Explosion accidents caused by electric car batteries: Why do Xinhua.com feel frequent in recent years in recent years? Whether it is electric cars or storage power stations, you are inseparable from a key device - battery. Almost all electric vehicles and more than 70% of chemical energy storage power stations are all lithium ion batteries, which is the battery used in our mobile phones and laptops.

Since the lithium-ion battery excels the portability of electric energy, the development of our information age is boosted. Therefore, there are three scientists who have contributed the development of lithium-ion battery technology to Nobel Chemical Award. Thanks to the development of lithium-ion batteries, the use scene is very close, our mobile phone, camera and Bluetooth headphones must be it, but why is it applied to electric cars, the lithium-ion battery has happened so many accidents? This is actually a probability problem.

For example, an imported battery used in an imported electric vehicle is only one million, but 8,000 such batteries must be installed on a car, which is equivalent to 10,000 batteries to install 1250 electric vehicles. That is, in theory 1250 electric vehicles, there is a battery in a car may have an accident. If this accident belongs to the battery burning or an explosion level, it is possible to cause a chain reaction in which the battery around it, thereby causing an accident of electric vehicle burning.

The same is true for accommodation in the energy storage power station, compared to an electric vehicle to store 50 to 100 degrees, the container body of a battery can generally store 1000 degrees, and a medium large energy storage power station is often dozens of dozens Collection of such energy storage battery containers. It is understood that such a large-scale battery is used, occasionally occasionally occurs. On the other hand, the combustion of electric vehicles and energy storage power plants, the consequences of explosion accidents are obviously more serious than mobile phone batteries, and the current fire protection measures are almost impossible.

Of course, we can't ignore this news that this news spreads so rapidly, and the serious incidents that causing casualties have caused a large social impact. Why will the lithium ion battery burn or even explode? Lithium-ion battery is a component-containing component, which is important consisting of positive electrode, negative electrode, electrolyte and diaphragm. After charging, its positive is generally a transition metal oxide, which has strong oxidation resistance; negative electrode is embedded in a large amount of lithium, which has a very strong reductive.

The electrolyte is generally organic esters, which has the characteristics of low melting point and flammable. It is important to note that firecrackers in our lives are also a device that understands the ingredients containing gunpowder into a sulfur (sulfur, chemical formula s) diit (stone, chemical type KNO3) three charcoal, of which nitrosite is Strong oxidizing agent, sulfur and charcoal are reducing agents. After the outside is given more than 120 degrees of stimulation, the oxidation reducing reaction in the firecracker occurs dramatically, releases a lot of gas and heat, fireproof, firecrackers exploded.

It can be seen that theoretical lithium-ion battery has a highly released redox reaction, and its internal combustible electrolyte also can help this reaction, bringing the consequences of burning or even explosion. How big is the power of lithium ion batteries burning or exploding? Light from its storing electrical energy, 150WH / kg energy density ordinary lithium ion battery electrical energy is about 1/10 of TNT explosive explosion, thermal energy density. In recent years, the research conclusively, the positive negative electrode in the lithium-ion battery accident can directly occur in special circumstances, or even aluminum and copper concentration fluids can also directly participate in the reaction in the manner of reducing agents, and the heat of heat should be significantly higher than Battery storage corresponding to energy.

In general, a safety accident in the closed space, the maximum temperature can reach 800 ° C, and a 43.4G heavy lithium ion battery takes a burst of the explosion of 5.45 gtnt, reaching the TNT equivalent 1 / 8.

The reason why the lithium ion battery does not respond to a strenuous redox reaction but is constantly converted into electrical energy in an electrochemical reaction, and it is constantly converted to electrical energy because the diaphragm is effectively physically isolated and Electronic conduction insulation (and existence of the electrolyte). However, when various internal or external causes cause the diaphragm failure, then the positive and negative pole is directly contacted, this internal short circuit will bring electrical energy to be released, there is a lot of heat and bring high temperature, instant damage to the internal chemical system of the battery, resulting in stability The negative electrolyte, the positive electrolyte, the negative electrode and the positive electrode, and even the redox reaction also involved in the current fluid, instantaneously heats up, resulting in instantaneous gasification of the electrolyte, and inclusing the positive negative electrode active material powder ejecting the battery housing, Bring the consequences of burning or even explosion, this process is called heat out of control (referred to as TR). According to the statistics of electric vehicle accident scenes in recent years, most accidents are "self-ignition", including standing (battery-free discharge), while driving (battery discharge) and charging.

A small part is an accident that occurs when an external heat source, collision, and control circuit failure. "Spontaneous combustion" belongs to spontaneous heat loss, the latter is collectively referred to as the thermal out of control of thermal abuse, mechanical abuse, electrical abuse). Although the two types of scenarios are ultimately brought about by the ultimate temperature, combustion and other mechanisms are similar, there is a big difference in the difficulty of launching research.

At present, the thermal out of control under the abuse is controlled by the excitation conditions. In recent years, it has made great progress, which is basically able to quantitatively describe the mechanisms of various abuse conditions and the mechanism and subsequent hazards. However, spontaneous thermal out of control, due to its complicated incomprehensibility, the battery after thermal out-of-control is completely damaged, it is difficult to recover the micro situation before the heat loss, become a difficult research.

Why is it difficult to predict a lithium-ion battery thermal out of control? Spontaneous thermal out-of control is the current electric car's largest security anxiety. Why is it difficult to prevent? This should be said from the manufacture of batteries. If each battery is completely consistent from the micro electrode material particles, the diaphragm to the macroscopic plate, the housing package is 100.

000000,000%, which will definitely have a battery pack made of thousands or hundreds of thousands of such batteries. Better security features. You may notice that hundreds of percent expressions here is a bit different, there are ten zeros behind, which represents an ideal expected - battery full scale high.

As is well known, the consequence of battery inconsistency is that the performance degraded battery will decay faster, some passivation is deactivated, directly invalid; there is also a partially different road - internal short circuits and heat out of control, burning, explosion. Is there any short-term short-term short circuit in this harm? The reason is that this decay is very slow and the external voltage signal is not obvious. The second is that the battery is directly entering the destructive thermal out-of control in a few minutes, the battery is complete, the evidence cannot be traced, which also makes this field Research progress.

Really accurately simulating short-term short circuits, still a problem. In addition, the battery is similar to a black box, although we can use some electrochemical spectrometers and in situ CT technical means to monitor individual battery changes and internal microstructure, but we cannot predict which tens of millions of batteries It will be meticulously study in "sudden death" in several months or after several years. Each battery is almost no self-inventive risk, but which is "sudden death" after half a year or three years later or in winter Chen, causing a large-scale burning accident? It's hard to predict now.

This is like unlike our body? Battery material parameters and manufacturing processes Similar to our genes, battery charge and discharge system is like our eating habits, battery use ambient temperature changes like growing environment. With the growth, there are always some people's body, there will be long-term inflammation or more serious vascular lesions, thereby possible development into cancer or cause stroke in a short time, which is similar to the battery short circuit and subsequent thermostat. If we have the ability to perform real-time monitoring on the health of each person 24h on the earth, we can discover an abnormality and dispose of cancer and stroke, but this is obviously not actual.

Similarly, we are also difficult to bear the most comprehensive real-time monitoring of each battery, now able to assemble a module that makes dozens of batteries to monitor the voltage and overall temperature, and this is spontaneous from the study and prevention of battery cells The requirements of thermal out of control are obviously gap. One thing that can be determined is to improve the consistent performance of the battery to improve the security and reliability of the battery pack. However, the perfect consistency cannot be done, the particles of the battery positive and negative active substances, each of the shapes, surface conditions, defects, etc.

of the battery, as long as the resolution is sufficiently high, it can be seen. In addition to raw materials, battery preparation involves dozens of complex processes, wanting to keep battery consistent very difficult. Although the powerful lithium-ion battery industry investment is now in order to achieve higher processing accuracy, the number of raw materials and complex preparation processes of lithium-ion batteries make consistency to become a never-ending task.

Electric cars will of course continue to develop, my country will continue to promote large-scale storage technology in energy systems. According to the status quo of energy structure in China, electric vehicles have an important role in my country's medium and long-term energy strategy and future sustainable development. I believe that with the continued rapid development of the battery technology system, its reliability and safety will be significantly improved in the next 5-10 years.

However, completely preventing the lithium-ion battery burning accident, almost impossible. Of course, in the case of respecting objective reality, there are many ways to improve safety. The first is the innovative warning technology, such as Stanford University's recent report of the sensitive capture of the hydrogen signal can push the warning lithium-ion battery thermal out of control, which is enough to escape the personnel on the electric car.

In addition, the "self-toxic" technique of the battery is also more effective, and its mechanism is when the battery generates thermal out of control, some special chemicals can be released to passivate "痪" inside the battery, interrupt the thermal out-of control chain. Regarding the safety of lithium-ion battery, vigorously develop innovative and efficient safety improvement technology, continuously improve battery manufacturing consistency. One day, this kind of "explosive" news will no longer appear in our lives, we can use electric vehicles with peace of mind.

Acknowledgments: Thanks to Tsinghua University, Wang Li and Vehicle College, Feng Xunning, two teachers, supplied to the relevant materials and useful discussions.