# MANLY battery# Winter is over, which one is better, lithium iron phosphate battery or ternary lithium battery?
Yesterday the author and the team's technical experts discussed the technical route of the power battery pack currently selected for mainstream electric vehicles. In particular, the impact of safety, long battery life, and cycle life on the realization of electric vehicles are particularly important.
Judging from the use of the product, the reliability and safety in a high-temperature environment, and the cycle life of the battery pack after years of actual use, iron phosphate currently has obvious advantages. However, from the perspective of product design on the product side, ternary lithium is more excellent in terms of battery energy density under the same volume and low-temperature performance in the northern area under the actual use environment. The characteristics of these two materials, the safety, and stability of lithium iron phosphate batteries are higher, while the safety and stability of ternary lithium are relatively low.
Compared with the previously used ternary lithium battery, the lithium iron phosphate battery on the new Model 3 has a lower energy density and a much worse discharge performance in a low-temperature environment in the north. For example, under the same low-temperature conditions, the attenuation of lithium iron phosphate batteries is as high as 30%, while the attenuation of ternary lithium batteries is less than 15%. The attenuation of low temperature also directly led to the instability of the remaining power measurement of the lithium iron phosphate battery at low temperatures. The two-year supply agreement reached by CATL (Ningde Times) and Tesla did not experience a During the complete low-temperature winter test cycle, the BMS (Battery Management System) did not accumulate more comprehensive data for adjustments, and more accurately understand the battery conditions. As a result, many Tesla owners need to calibrate the battery. Previously, Tesla used the 21700 battery jointly developed with Panasonic, and its development cycle was 23 months, while CATL’s lithium iron phosphate battery took only about 9 months from requesting to mass production.
From the perspective of charging speed and energy density, the ternary lithium battery is undoubtedly the best choice in the future; from the perspective of cycle life, it is longer. The lithium iron phosphate battery will start to decay after more than 3500 cycles of charge and discharge. The number of charge-discharge cycles for ternary lithium batteries is only 2000; from a safety point of view, the thermal stability of lithium iron phosphate is currently the best among automotive batteries. The reason is that its internal chemical composition will start to decompose when the battery temperature is above 500 degrees. The ternary lithium battery is lower than 300 degrees, so the risk of spontaneous combustion of the lithium iron phosphate battery during impact and rapid charging is low.
When it comes to the safety of lithium batteries, what is worth paying attention to is the debate on the wear test by battery manufacturers in the previous period. What is a puncture test? The author's previous intelligent hardware R&D team has a global first-line lithium battery manufacturer in the supply chain. Fortunately, he has learned about the key steps of lithium battery testing institutions, of which the puncture test is very important! In a laboratory environment, a steel needle is used to pierce the battery cell or battery module, forcibly destroying the internal structure of the battery and causing an internal short circuit, causing thermal runaway. The national standard GB/T 31485-2015 "Safety requirements and test methods for power batteries for electric vehicles" also has clear requirements, that is, it can pass the test without deflagration or fire within 1 hour after acupuncture penetration.
Of course, some experts pointed out that puncture is too demanding for batteries. For example, Wang Binggang, the leader of the National New Energy Vehicle Innovation Engineering Expert Group, said that from the current battery, there are few batteries that can pass the puncture experiment. The ternary lithium battery is because of its high material activity. , It is more difficult to pass the acupuncture test, and oxygen will be released after reaching the decomposition temperature, which will accelerate the chain thermal runaway under the action of high temperature. The puncture test standard is too harsh, and it is difficult to puncture the battery in actual use. Therefore, the national standard cancels this test. For electric vehicles, it is more important to consider the safety architecture of the entire vehicle, to avoid thermal runaway through sensors, electronic control systems, insulating materials, and a more rigid shell. Now that there are nearly 4 million new energy vehicles, the market promotion proves that the battery of ternary material is safe, and the specific cause of the fire of electric vehicles cannot be proved to be the cause of the ternary lithium battery. Until now, the cause of the fire cannot be excluded from the internal short circuit caused by the gold absorption of the electrode and the external short circuit caused by the high voltage overcharge.
Song Jian, executive vice president of Tsinghua University Automotive Engineering Development Research Institute and deputy director of the State Key Laboratory of Automotive Safety and Energy, also said that the balance between energy density and safety needs to be resolved urgently. No company can guarantee that the battery pack will not break when it is collided. The puncture test is equivalent to simulating a situation where foreign objects are squeezed in after a high-strength impact. Similarly, many batteries are now difficult to undergo vibration testing. The battery diaphragm in the ternary lithium battery will break at 10kpa, and the high-frequency applied force of the vibration test will also break the battery diaphragm's tolerance limit, causing an internal short circuit. In the same way, the puncture is also used to verify the internal short circuit of the battery.
However, the author believes that in the case of existing raw materials, the puncture test of lithium batteries is still necessary. In order to more realistically simulate the actual use of the environment, the temperature after the collision may cause a fire, and the battery pack manufacturer and the vehicle are urged. Only by increasing R&D investment in the use of anti-collision structures and high-temperature protection materials can companies further ensure the safety of vehicles during use. On the other hand, with the advent of new energy and new technologies and large-scale applications, it is also necessary to use new materials to ensure the safety of electric vehicle battery compliance components.
