Why does a lithium-ion battery catch fire?

The direct cause of 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 important 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 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 to cause an internal short circuit and release huge heat. The most typical example is an electric truck rear-end school bus accident that occurred 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 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 made NOTE7 happen. 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 output is pressed to the ATL lithium-ion battery. The rapid increase in production has caused the quality of this batch of batteries to decline. The content of debris and burrs adhering to the negative copper plate inside the battery exceeds the standard. It is easy to puncture the diaphragm and cause an internal short circuit. In electric vehicles, overcharging and high-current fast charging are the main culprits in inducing 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, which will cause the lithium to form dendrites like branches 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 internal short circuits. Not only that, the charging pile is not compliant and may be overcharged. When the battery is fully charged and continues to be charged, more lithium will be inserted into the negative electrode of the battery. When the maximum capacity of the negative electrode is exceeded, it will collapse. The battery is swollen, and it causes an internal short circuit. The recent fire incident of an electric vehicle in Dongguan is likely to be related to both overcharging and fast charging. When it comes to temperature runaway, the important 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 summer now, 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 field of 3C batteries such as mobile phones, since the explosion of NOTE7, the lithium-ion batteries used have basically switched from lithium-ion batteries to lithium-polymer batteries, and the flammable liquid electrolyte in the previous lithium-ion batteries has been replaced with a gel. Even if the battery is punctured after replacement, it will be swollen at best, and deflagration will not occur. On electric vehicles, as the gel-like power lithium battery temporarily fails to meet the loading requirements, 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. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: How to charge the battery of a new electric vehicle?