How can lithium-ion batteries catch fire?

We often see some safety accidents caused by lithium-ion batteries. The most impressive thing is the explosion and fire caused by lithium-ion batteries. If an electric car with 50 kilowatt-hours of electricity is completely out of control and catches fire, the energy released is as high as 180 million joules, which is equivalent to the energy released by 43 kilograms of TNT explosives. Why does lithium-ion battery catch fire spontaneously? The direct cause of the fire and spontaneous combustion of lithium-ion batteries is the thermal runaway of the battery. The so-called thermal runaway refers to the internal short circuit caused by various stimuli of the battery, which causes the internal temperature of the battery to rise by thousands of degrees, and the flammable electrolyte boils and ejects. It will burn when exposed to air. At present, there are three main causes of short circuit in the battery, mechanical out of control, electrochemical out of control and temperature out of control. In mechanical out-of-control, the most common thing is that the battery is squeezed or damaged by needle puncture, which will cause the battery diaphragm to be pierced, and the positive and negative plates are directly connected, causing an internal short circuit and releasing huge heat. The most typical example is an electric truck rear-end school bus accident in Shenzhen recently. The rear-end collision caused the truck's battery pack to be excessively squeezed, causing a large-area internal short circuit, and finally the truck was burned into an empty shell. If the battery layout is unreasonable, problems will also occur after long-term use. In the past, the NOTE7 of Samsung SDI lithium-ion battery was used because the space left for the battery was too small, and the external negative plate was squeezed and deformed and short-circuited, which eventually caused NOTE7. Many spontaneous combustion accidents. There are many reasons for electrochemical runaway, and poor battery quality is an important cause. It is this NOTE7. When the SDI lithium-ion battery has a problem, the production capacity is pressed to the ATL lithium-ion battery. The rapid increase in production capacity has caused the quality of these batteries to decline. The content of debris and burrs adhering to the negative copper plate inside the battery exceeds the standard. During the charging and discharging process of the battery, a large amount of copper metal debris and burrs are mixed into the electrolyte. It is easy to puncture the diaphragm and cause an internal short circuit. In electric vehicles, overcharging and high-current fast charging are the 'culprits' that induce electrochemical runaway. When an electric vehicle uses a non-compliant charging pile, the charging pile may output a large current that the lithium-ion battery cannot withstand. In the battery, the charging speed is too fast, and the lithium ion will form a branch-like branch on the surface of the negative electrode. These dendrites are as thin and hard as a needle tip. When the dendrites grow to a certain length, they will puncture the diaphragm and induce an internal short circuit. Not only that, the charging pile is not compliant and may be overcharged. When the battery is fully charged and continues to be charged, the negative electrode of the battery will be filled with more lithium ions. When the maximum capacity of the negative electrode is exceeded, it will collapse. Cause the battery to bulge, or cause an internal short circuit. The recent fire incident of an electric car in Dongguan is likely to be related to both overcharging and fast charging. When it comes to temperature runaway, the main reason is that lithium-ion batteries are very heat-resistant. When lithium-ion batteries are charged and discharged at high temperatures, the positive and negative plates will react with the electrolyte, releasing oxygen and additional heat. The impact of multiple heat can easily cause the membrane to melt, and then a large-area short circuit occurs. It is already summer, and many electric vehicles are charged under the scorching sun. If they do not dissipate heat well, it is easy to cause thermal runaway and fire in the battery. The explosion of a battery is very dangerous and even life-threatening in severe cases. Therefore, car and mobile phone manufacturers have also come up with many ways to protect the battery. In the category of 3C batteries such as mobile phones, since the explosion of NOTE7, the lithium-ion batteries used have basically switched from lithium batteries to lithium-ion polymer batteries, replacing the flammable liquid electrolyte in the previous lithium-ion batteries with gelatinous solutions. Even if the battery is punctured after replacement, it will be swollen at best, and deflagration will not occur. In electric vehicles, since the gel-like power battery temporarily fails to meet the requirements for loading, we can only think of ways to protect the battery as much as possible. Lithium-ion batteries are afraid of being poked and squeezed, so anti-collision materials are added to the outside of the battery pack, and the bottom is smeared with anti-scratch coating. Lithium-ion batteries are afraid of fast charging and overcharging, so build a battery management system to control the current of charging and discharging in real time, and monitor the health of each battery. Lithium-ion batteries are also afraid of heat, so make a liquid cooling system for lithium-ion batteries to ensure that they will not overheat in summer. According to the latest national standards, after a thermal runaway occurs in the lithium-ion battery of an electric vehicle, it must not fire or explode within 5 minutes. If your electric car accidentally catches fire, quickly cover your mouth and nose, find a way to get out of the car, and leave the electric car more than 15m, do not try to extinguish the fire, you will have a chance to survive the battery fire. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Lead-acid batteries and lithium-ion batteries are charged differently and cannot be mixed!