How to control thermal runaway of lithium-ion battery?

1. Electrolyte flame retardant Electrolyte flame retardant is a very effective way to reduce the risk of battery thermal runaway, but these flame retardants often have a serious impact on the electrochemical performance of lithium-ion batteries, so it is difficult to actually Application. In order to solve this problem, the YuQiao team at the University of California, San Diego [1] used a capsule encapsulation method to store the flame retardant DBA (dibenzylamine) inside the microcapsules and disperse them in the electrolyte. It has an impact on the electrical performance of lithium-ion batteries, but when the battery is damaged by external forces such as squeezing, the flame retardant in these capsules will be released, poisoning the battery and causing battery failure, thereby preventing thermal runaway. In 2018, the YuQiao team [2] used the above technology again, using ethylene glycol and ethylenediamine as flame retardants, and then packaged into the lithium-ion battery to reduce the maximum temperature of the lithium-ion battery in the acupuncture experiment by 70%. Significantly reduces the risk of thermal runaway of lithium-ion batteries. The methods mentioned above are all self-destructive, which means that once the flame retardant is used, the entire lithium-ion battery will be scrapped. The Atsuo Yamada team from the University of Tokyo in Japan [3] developed a method that does not affect lithium A flame-retardant electrolyte for ion battery performance. The electrolyte uses a high concentration of NaN(SO2F)2(NaFSA)orLiN(SO2F)2(LiFSA) as a lithium ion salt, and adds a common flame retardant triphosphate to it. The methyl ester TMP significantly improves the thermal stability of lithium-ion batteries. What's more, the addition of flame retardants does not affect the cycle performance of lithium-ion batteries. The battery using this electrolyte can stably cycle more than 1000 times (C/ 5 cycles of 1200 times, the capacity retention rate is 95%). Making lithium-ion batteries flame-retardant through additives is one of the ways to prevent thermal runaway of lithium-ion batteries. Some people have also tried to prevent the occurrence of internal short-circuits in lithium-ion batteries caused by external forces from the root, so as to achieve the purpose of drawing salaries from the bottom of the pot. Completely prevent the occurrence of thermal runaway. In view of the situation that power lithium batteries may face violent shocks in use, Gabriel M. Veith of Oak Ridge National Laboratory in the United States designed an electrolyte with shear thickening characteristics [4], which uses non-Newtonian fluids. Under normal conditions, the electrolyte is in a liquid state, but when it encounters a sudden impact, it will be in a solid state, becoming extremely strong, and even able to achieve the effect of bulletproof. It prevents the power lithium battery from the root cause. In the event of a collision, there is a risk of thermal runaway caused by a short circuit in the battery. 2. Battery structure Next, let’s take a look at how to brake thermal runaway from the level of battery cells. At present, the problem of thermal runaway has been considered in the structural design of lithium-ion batteries, for example, in the upper cover of the 18650 battery. Generally, there will be a pressure relief valve, which can release the excessively high pressure inside the battery in time when the thermal runaway occurs. Secondly, there will be a positive temperature coefficient material PTC in the upper cover of the battery. When the thermal runaway temperature rises, the resistance of the PTC material will increase significantly. In order to reduce the current to reduce heat generation. In addition, the design of the anti-short circuit between the positive and negative electrodes should be considered in the structural design of the single battery to prevent the battery from being short-circuited due to misoperation, metal excess and other factors, which may cause safety accidents. Secondly, in battery cell design, it is necessary to use safer diaphragms, such as three-layer composite diaphragms that automatically close the cells at high temperatures. However, in recent years, with the continuous improvement of battery energy density and the trend of thinner diaphragms, the three-layer composite diaphragm has been It is gradually eliminated and replaced by ceramic-coated diaphragms. Ceramic coatings can support the diaphragm, reduce the shrinkage of the diaphragm at high temperatures, improve the thermal stability of lithium-ion batteries, and reduce the risk of thermal runaway of lithium-ion batteries. 3. The thermal safety design of the battery pack. The power lithium battery is often composed of dozens, hundreds or even thousands of batteries in series and parallel. For example, the battery pack of Tesla ModelS contains as many as 7000 Only the above 18650 composition, if one of the batteries is thermally out of control, it may spread in the battery pack, causing serious consequences. For example, in January 2013, a Japanese Airlines Boeing 787 passenger plane lithium-ion battery fire occurred in Boston, USA. According to an investigation by the US National Transportation Safety Board, it was caused by a 75Ah square lithium-ion battery in the battery pack. The out-of-control caused thermal runaway of adjacent batteries. After this incident, Boeing required additional measures to prevent thermal runaway spread on all battery packs. In order to prevent thermal runaway from spreading inside lithium-ion batteries, Allcell Technology of the United States has developed a phase change material-based thermal runaway isolation material PCC for lithium-ion batteries [5]. The PCC material is filled between the single lithium-ion batteries. When the lithium-ion battery pack is working normally, the heat generated by the battery pack can be quickly transferred to the outside of the battery pack through the PCC material. When the lithium-ion battery is thermally out of control, the PCC material It can absorb a large amount of heat through the melting of the paraffin material inside, preventing the battery temperature from rising further, thereby preventing heat runaway from spreading inside the battery pack. In the acupuncture experiment, a battery pack with 4 parallels and 10 strings made of 18650 batteries, when PCC material is not used, thermal runaway of one battery eventually caused thermal runaway of 20 batteries in the battery pack, and the use of PCC material In the battery pack, thermal runaway of one battery did not cause thermal runaway of other battery packs. 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.