How to control lithium-ion battery thermal out of control?

　　Author ：Iflowpower – Portable Power Station Supplier

1. Electrolytic liquid flame retardant electrolyte flame retardant is a very effective way to reduce battery thermal out-of control, but these flame retardants often have a serious impact on electrochemical properties of lithium ion batteries, so it is difficult to actually Chinese application. In order to solve this problem, the Yuqiao team of Sheng Diego, California, China [1] stores the flame retardant DBA (dibenzylamine) in the interior of the microcapsules in the case of the capsule package, dispersion in the electrolyte, will not The electrical properties of the lithium-ion battery have an effect, but when the battery is destroyed by extrusion, the flame retardant in these capsules is released, and the battery is toxic to cause the battery to fail, thereby preventing the occurrence of heat loss.

2018 Yuqiao Team [2] Re-utilized the above technology, using ethylene glycol and ethylenediamine as a flame retardant, encapsulated into the lithium ion battery inside so that the lithium ion battery has dropped at the highest temperature in the acupuncture experiment. 70%. Significantly reduced the risk of thermal out of control of lithium ion batteries.

The way mentioned above is self-destruction, that is, once the flame retardant is used, the entire lithium-ion battery will be scrapped, and the Atsuoyamada team of Tokyo University, Japan [3] has developed a kind of resulting from lithium Flame-retardant electrolyte of ion battery properties, the electrolytic solution using high concentrations of NaN (SO2F) 2 (Nafsa) orlin (SO2F) 2 (LIFSA) as a lithium ion salt, and the common flame retardant is added thereto. Methyl ester TMP, significantly increases the thermal stability of the lithium ion battery, which is even more powerful, and does not affect the cycle performance of lithium ion battery, and the battery adopts the electrolyte can be stabilized more than 1000 times (C / 5 cycle 1200 times, capacity retention rate 95%). Through the additive, the lithium-ion battery has a flame retardant characteristic to prevent the path of thermal out of control of the lithium-ion battery, and some people have another way, trying to occur from the occurrence of short-circuited in the lithium-ion battery caused by roasting, thus achieving the suction of the bottom of the suction, Thoroughly eliminate the occurrence of thermal out of control.

For the case of the dynamic lithium-ion battery, it may face violent impacts in use, GabrielM.Veith, US Oak Lace National Laboratory, designed an electrolyte with shear thickening characteristics [4], the electrolyte used non-Newton The fluid is characterized, in normal state, the electrolyte is presented in a liquid state, but in the case of sudden impact, it will present a solid state, becomes unusually sturdy, and can even achieve the effect of bulletproof, and prevent lithium from the roots. The risk of short-circuit caused by heat-out of the battery when the ion battery collides.

2. The battery structure takes us to see how to take a hot out of control, and the current lithium-ion battery has considered the problem of thermal out of control in structural design, such as in the upper cover of the 18650 battery. There is generally a pressure relief valve, and it is possible to release the pressure inside the battery during thermal out of control.

The positive temperature coefficient material PTC in the second battery upper cover is significantly increased when the heat loss temperature increases. Reduce current to reduce heat. In addition, in the design of the cell structure, it is necessary to consider the short-circuit design between the positive and negative electrodes, and prevent the battery, which causes the battery, causes a safety accident due to erroneous operation, metal excessive objects.

Second, when the battery is designed, a more secure diaphragm is used, for example, three-layer composite diaphragm of automatic shuttle at high temperatures, but in recent years, with the continuous improvement of battery energy density, the three-layer composite diaphragm has been The ceramic coating diaphragm that gradually eliminated, the ceramic coating can be used to support the diaphragm, reducing the shrinkage of the separator at high temperature, improve the thermal stability of the lithium ion battery, reducing the risk of thermal out of control of lithium ion batteries. 3. Battery pack heat safety design The power lithium-ion battery is often from dozens, hundreds or even thousands of batteries consisting in parallel, such as Tesla's Models battery packs.

More than 7,000 18650, if one of the batteries is thermal out of control, it may spread in the battery pack, causing serious consequences. For example, in January 2013, a Japanese airline of Boston, USA, a Japanese airline, a fire event, according to the investigation of the US National Transport Safety Commission, is due to a 75AH square lithium-ion battery in the battery pack. After retaining, the adjacent battery thermal out-of-control is raised.

After the incident, Boeing requires measures to prevent thermal out-of-control spread on all battery packs. In order to prevent thermal out of control in the interior of lithium ion batteries, US AllCelltechnology has developed a lithium-ion battery thermal out-of-control isolation material based on phase change materials [5]. The PCC material is filled between the monomer lithium ion battery, and when the lithium ion battery pack is normal, the heat of the battery pack can be quickly transmitted to the battery pack through the PCC material, and the PCC material is in the lithium ion battery.

It can be melted by the paraffin material therethrough to absorb a large amount of heat, preventing the battery temperature from further increase, thereby prevention of heat loss in the battery pack. In the acupuncture experiment, a battery pack packaged from 18650 batteries, when the PCC material is not used, one battery thermal out-of-control will eventually lead to 20 batteries in the battery pack, and use PCC materials In the battery pack, a battery thermal out of control does not trigger other battery packs. .