How do you control the thermal loss of lithium ion batteries?

　　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 In use. 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 When the electrical properties of the lithium-ion battery, the flame retardant in these capsules will be released when the battery is destroyed by extrusion, and the battery has caused battery failure, thus the occurrence of heat loss.

2018 Yuqiao team [2] once again utilizes the above technique, ethylene glycol and ethylenediamine are used as a flame retardant, and the internal portion of the lithium ion battery is loaded into the lithium-ion battery has dropped by 70% in the acupuncture test. 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 employs high concentrations of NaN (SO2F) 2 (Nafsa) orlin (SO2F) 2 (LIFSA) as a lithium salt, and a common flame retardant is added thereto.

The ester TMP significantly increases the thermal stability of the lithium ion battery, which is more powerful. The addition of the flame retardant does not affect the cycle performance of the lithium ion battery, and the battery adopts the electrolyte can be stably circulated more than 1000 times (C / 5) 1200 times in circulation, capacity retention rate 95%). Through the additive, the lithium ion battery has a flame retardant characteristic is one of the ways of the heat loss of the lithium ion battery, and some people have another way, trying to occur short-circuited in the lithium-ion battery from the root of the roots, thus achieving the purpose of the bottom of the kettle, 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 of the American Oak Ridge National Laboratory has designed an electrolyte with shear thickening characteristics [4], the electrolyte uses non-Newton The fluid is characterized, in normal state, the electrolyte is presented in a liquid state, but in the case of a sudden impact, the solid state is presented, it becomes unusually sturdy, and can even achieve the effect of the bulletproof, from the root alert in power lithium The risk of short-circuit caused by heat-out of the battery when the ion battery collides.

2. Battery structure Next, we will see how to give heat out of control, and the current lithium-ion battery is currently considering the problem of thermal out of control in structure design, such as on the 18650 battery. There will be a pressure relief valve in the cover, and it can be released in time when the heat is out of control, and there will be a positive temperature coefficient material in the second battery upper cover.

The electrical resistance of the PTC material is significantly increased during the heat loss temperature rise. Large to reduce current reduction. In addition, in the design of the cell structure, consider the short-circuit design between the positive and negative electrodes, and the alert is caused by mistakes, and the metal excessive objects cause the battery to have a foreign short circuit, causing safety accidents.

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 company of Boston, USA, a Japanese company, is a survey of the US National Transport Safety Commission, is due to a 75AH square lithium-ion battery in the battery pack. After the adjacent battery heat is out of control, the Boeing requires the measures to add a hot out-of-control spread on all battery packs.

In order to prevent thermal out of control in the interior of the lithium ion battery, 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 through the paraffin material in which it is used to absorb a large amount of heat, preventing the battery temperature from further rising, so that the hotness is unfained in the battery pack.

In the acupuncture test, a battery pack packaged from 18650 batteries, and when there is no PCC material, a 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. .