How to give a lithium-ion battery "thermal out of control" to install brakes!

Autor: Iflowpower - Dodavatel přenosných elektráren

Heat out-of-control is the most serious safety accident in the use of lithium-ion batteries. The thermal out of control is often due to the lithium ion battery in which the diaphragm is destroyed, or the diaphragm is broken, or due to the external short circuit outside the battery. It has caused a large amount of heat, which causes a large amount of heat, initiates a positive and negative electrode active substance and electrolyte, causing a lithium-ion battery to prevent and explode, seriously threaten the lives and property safety of users.

Therefore, the lithium-ion battery will generally be required in lithium ion battery safety detection, and the lithium ion battery is required to pass overcharge, overprint, short circuit and extrusion, acupuncture, but with the continuous improvement of the power lithium battery energy density and battery capacity, the battery passed acupuncture The test became more and more difficult, so the acupuncture test is not implemented in the "Lithium Ion Power Battery Safety Requirements for Electric Vehicles] announced in the Ministry of Industry and Information Technology. However, the new version requires nothing to do with the acupuncture test. Subsequent, it is not possible to restore it.

If the manufacturer achieves large capacity, high-energy density power lithium battery is smooth through the acupuncture test, then it will be significant in competition. The advantages. Today we will talk about those techniques that "brake" to loses "brakes" to lithium-ion batteries.

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 influence on electrochemical performance of lithium-ion batteries, so it is difficult to use in actual 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 The electrical performance of the lithium-ion battery is influenced, but when the battery is destroyed by extrusion, the flame retardant in these capsules will be released, and the battery is "toxic" causes the battery failure, thereby preventing the occurrence of thermal out of control.

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 has significantly improved the thermal stability of the lithium-ion battery, which is even 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 property to prevent one of the pathways of thermal out of control of lithium ion batteries, and some people have another way, trying to prevent the occurrence of short circuits in lithium ion batteries caused by root from the root cause, thereby achieving the purpose of picking up the bottom of the kettle.

Thoroughly eliminate the occurrence of thermal out of control. For the case of the dynamic lithium battery in use, it may face violent impact, the Gabrielm of the American Oak Ridge National Laboratory. Veith has designed an electrolyte [4] with a shear thickening property, which utilizes the characteristics of a non-Newtonian fluid.

In normal state, the electrolyte presents liquid state, but when encountering a sudden impact The solid state will be made abnormally, and it can even achieve the effect of the bulletproof. From the root cause, the risk of heat loss in the battery is prevented during the crash in the power lithium battery. 2.

The battery structure takes us to 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 in the upper cover of 18650. 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, the short-circuit design between the positive and negative electrodes is considered in the design of the monomer battery structure, and the factors such as malfunction, metallic substances, etc., 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 battery is often used in use, hundreds or even thousands of batteries consisting in parallel, such as Tesla's Models battery packs from more than 7,000.

The 18650 composition, if one of the batteries occur, it may spread in the battery pack, causing serious consequences. For example, in January 2013, a Japanese Airlines of Boston, USA, the Boeing 787 passenger plane, based on the investigation of the US National Transport Safety Commission, is due to a 75AH square lithium-ion battery in the battery pack. After the loss of control, the adjacent battery thermal out-of control was raised.

After the incident, Boeing requested measures to add a hot out-of-control spread on all battery packs. In order to prevent heat from being out of control in the interior of the lithium ion battery, US AllCelltechnology has developed a lithium-ion battery thermal out-control isolation material based on phase change materials [5]. PCC material is filled between the monomer lithium ion battery, in the case where the lithium ion battery pack is working properly, the heat of the battery pack can be quickly transmitted to the battery pack through the PCC material, and when the heat loss of the lithium ion battery, PCC material It can be melted through the paraffin material therethrough to absorb a large amount of heat, preventing the battery temperature from further increase, thereby preventing thermal out of control spreading inside 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. Lithium-ion battery thermal out-of control is our most reluctant to see the safety accident of a strong prevention, improve the safety of lithium-ion batteries, prevent thermal out-of-control, and heat management design from battery formula design, structural design and battery pack.

Under the upper tube, co-improvement of thermostability of lithium-ion battery, reduce the possibility of heat loss control. .