Why 18650 power lithium-ion battery pack is the first choice for new energy vehicles

18650 battery is the earliest, most mature and most stable lithium battery, widely used in electronic products. In contrast, laminated lithium batteries are far from mature. Common batteries include square batteries, soft-pack batteries, and even the size and position of the tabs are not even. The processing technology possessed by the battery manufacturer cannot meet the conditions. Most of them rely on human control. The consistency of the battery is lower than that of the 18650 battery. If the consistency of the battery does not meet the requirements, the management of a large number of battery strings and parallel batteries will not allow the performance of each battery to be better. The 18650 core can handle this problem. Under normal circumstances, the single capacity of the 18650 battery is small, the number of required monomers is 7104 type (S type), but the compatibility is very good. The capacity of the cascade battery can be very large (the number of cells is reduced from 20Ah to 60Ah), but the consistency is poor. In contrast, at this stage, it is difficult to invest a lot of manpower and material resources together with battery suppliers to improve the processing technology of cascade batteries. Therefore, when developing Roadster and ModelS, Tesla's only option is to buy batteries from the market and develop its own battery system. It should not be so difficult to develop a battery system that manages more than 6000 cells with good consistency and a battery system with more than 6000 cells with poor consistency. Even if the number of individual batteries increases, if the performance of these batteries is reliable, it is easier to manage. Compared with another successful all-electric car-Nissan's Leaf-it uses a cascaded lithium battery. This is because Nissan has been cooperating with NEC for many years and has accumulated a large amount of battery technology and considerable energy in quality control. Ye's battery comes from a joint venture between AESC-Nissan and NEC. The laminated battery has thin thickness, large surface, average heat dissipation, and good heat dissipation capability. Therefore, Nissan Blade is very bold in adopting a passive thermal management system (in fact, not a management system!), which takes heat away through natural convection air. Energy density-in terms of the energy density of a single battery, the 18650 battery is higher than the stacked lithium battery. The energy density of the 33Ah lithium battery used by Nissan LEAF is 157Wh/kg, the energy density of the stacked battery used in GMVolt is about 150Wh/kg, and the energy density of the 18650 battery is about 211Wh/kg by the speed of a sports car. . However, the 18650 battery management system is more complicated, so the extra weight will make the energy density of the battery pack much lower than the energy density of a single cell. The Roadster battery pack weighs 450 kg and has an energy density of 118Wh/kg, while the LEAF battery pack weighs 225 kg and has an energy density of 107 watts/kg. At the battery level, the energy density of the two is already comparable. Safety The above analysis of the advantages of cascaded lithium batteries, but there are also some disadvantages. Since laminated lithium batteries are usually packaged in aluminum-plastic film, the thickness of the aluminum-plastic film is thin, and the mechanical strength is poor. In extreme cases such as a car collision, the aluminum-plastic film is easily damaged, causing safety accidents. This also explains why Nissan added an aluminum casing to the four battery modules. The 18650 battery is generally a steel shell with better safety. As mentioned above, with the continuous improvement of the 18650 battery processing technology, the safety is also constantly improving. 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. Previous post: Analysis of knowledge about battery charging