Detailed explanation of the improvement direction of lithium battery safety performance

It is feasible to add flame retardant on the basis of the original electrolyte, but a particularly suitable flame retardant has not yet been discovered. The flame retardant effect of Buddha compounds is better, but the cost is high; the alkyl phosphate ester, after adding electrolyte, reduces the conductivity, and the flame retardant effect is also general, so it can not be regarded as a good choice; the flame retardant effect of nitride is unclear and has Toxic, basically not feasible. Flame retardant is a more practical technical route, but it also requires time and manpower investment. The solid electrolyte polymer electrolyte is an intermediate form between the real solid electrolyte and the electrolyte, and is the coexistence state of the dry polymer electrolyte and the electrolyte. However, the safety of polymer electrolytes has been greatly improved compared to electrolytes, and there have been improvements in leakage and flammability. I saw in the news that a company invented a non-burning electrolyte. If it is as advertised, it will be a revolutionary result. Choosing the proper electrolyte reduces the probability of SEI membrane dissolution by selecting the type of electrolytic salt. 3.2 Positive and negative electrode materials From the perspective of improving the thermal stability of the material, select materials with a more stable molecular structure. As for the negative electrode, for carbon materials, the spherical structure is more stable than the layered structure; across the types, the spinel structure of lithium titanate is more stable than all graphite materials. The various safety issues mentioned in 2.3, lithium titanate does not exist, and it is the safest one of the current negative electrode materials. The range of options for cathode materials is not large, and lithium cobalt oxide, due to its poor stability, has become increasingly smaller. There are three mainstream cathode materials for power lithium-ion batteries, lithium iron phosphate, lithium manganate and ternary materials. From the perspective of safety, lithium iron phosphate has the best safety, followed by lithium manganate, and the ternary is relatively poor. 4 Safety auxiliary measures When the potential safety hazards of positive and negative materials and electrolytes cannot be completely dealt with, people take the second place and adopt some auxiliary methods to play the role of blocking, alarming, and isolation. These measures include the following in detail. The design purpose of the safety valve is that when the internal pressure of the battery cell increases to a certain value, it is expected to open, and to guard against the explosion of the battery cell, which will cause bad effects. But after the safety valve is opened, it is often accompanied by the leakage of electrolyte. If the electrolyte is flammable, it will have the effect of replenishing the east wall. In the stage when the battery cell actually burns after thermal runaway, the safety valve may also become a small flame ejector, allowing the burning material to spread in a larger area. Therefore, the design of the safety valve must be considered comprehensively. Temperature sensitive resistors Add temperature sensitive resistors with positive temperature coefficients to the connecting conductors between telecommunication circuits or modules. In normal operation, its resistance is similar to a piece of wire. When a large current occurs, its temperature rises to a certain value under the influence of the thermal effect of the current, and the internal resistance rises suddenly, achieving the purpose of basically blocking the short-circuit current. Such a device can often only be effective in the process of external short-circuit, and it is less useful for thermal runaway caused by internal short-circuit. The fuse is similar to the temperature-sensitive resistor mentioned above, except that the fuse actively cuts off the circuit after encountering a large current, which is an irreversible safety method. The selected value of the fuse should reserve a relatively large margin to guard against the influence of misoperation. The insulation wall is designed to isolate the thermally runaway batteries, and the entire battery pack is divided into several areas. When a thermal runaway occurs in a certain area, alert other areas to be implicated. It is a means of passively reducing casualties. Smoke alarms and fire extinguishers are currently mandatory for use in passenger cars. The smoke alarm detects fire alarm information, and the battery management system immediately activates the fire extinguisher to spray fire extinguishing agent to extinguish the fire. The effectiveness of this method often depends on the sensitivity and accuracy of the sensor that detects the danger. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: What are the reasons why lithium batteries are not suitable for recharging when they are dead?