Analysis of several technical points related to the 21700 cylindrical battery

Compared with soft packs and square lithium batteries, the 18650 cylindrical lithium battery was the first commercialized power lithium-ion battery at that time, with the highest degree of automation and the lowest cost. In addition, Tesla has been holding it for many years, maintaining the use of soft bags and square batteries in three parts of the country. Since Tesla announced the Model 3 as 21700, another star has been added to the cylindrical battery family. This article analyzes some skills related to cylindrical batteries. Cylindrical battery, not specified below, refers to 18650. Cylindrical cell structure If you look at the power lithium-ion battery, you will find that the cylindrical 18560 battery is the most discussed battery type and the most discussed battery type. The monomer is mainly composed of a positive electrode, a negative electrode, a diaphragm, a positive electrode and a negative electrode collector, a safety valve, an overcurrent protection device, insulation and a shell. The shells were mostly steel shells in the early days and aluminum shells later. The safety valve and PTC are shown in the figure below. For single overcurrent protection equipment, the plans of each manufacturer are different, and they can be customized at different prices according to different safety requirements. General safety equipment mainly includes two categories: PTC positive temperature coefficient resistor and fuse equipment. When the PTC has an excessive current, the resistance increases, and the accumulation of temperature promotes the increase of the resistance of the PTC. When the temperature exceeds a threshold, it will increase dramatically in the future, which is equivalent to isolating the faulty battery from the entire circuit to prevent further thermal runaway attacks. In principle, the fuse device is a fuse. When too much current is encountered, the fuse will blow and the circuit will be disconnected. The difference between these two types of protection equipment is that the former is recoverable, and the latter is a one-time protection. Once a fault attack occurs, the system must consider the problematic unit to perform normal replacement operations. Cylindrical cell characteristics Cylindrical batteries, especially the 18650 type, have the highest level of automation among the three important battery modes due to their structural features and standardization of types. This makes it possible to obtain a high degree of consistency and yield improvement. Data shows that leading foreign manufacturers such as Samsung and Panasonic can achieve 98% product rates, and Chinese manufacturers can also exceed 90%. The advantages of 1) as mentioned above, the monomer consistency is good; 2) the monomer mechanical properties are good. Compared with square and soft-pack batteries, the closed cylinder can obtain the highest bending strength under similar dimensions; 3) Exquisite technology and low cost, but at the same time the cost optimization space has been almost occupied; 4) Small single energy and easy control In the occurrence of an accident, it has also become the reason for its replacement (popular proverb says, what makes you ruin you, will not kill you makes you strong, is also the same thing) defects, 1) in electric The number of cylinders in the vehicle and battery system is large, which adds to the complexity of the battery system. No matter the organization is still a management system, the cost of the system-level cylindrical battery is higher than the other two types of batteries; 2) In an uneven temperature environment, the probability of dissimilar characteristics of a large number of cells will increase. Of course, Tesla chose 18650 as the beginning of the plan because it was an impossible choice. Starting 10 years ago, only cylindrical batteries were eligible for mass production. The safety and thermal management requirements of the battery are the driving force behind its powerful electronic control system. 3) There is little room for energy density to rise. According to news reports in 2016, the super power supply has a single capacity of 4050mAh and a battery energy of 306Wh/kg. Later, no higher records were found. In a given space, there is only dead data, which is a difficult road. ➤Tesila’s Model 3 battery system now has 21,700 Tesla Model 3s fully using 21,700 ternary lithium batteries, opening a new stage of cylindrical battery improvement capabilities. The energy density of the 21700 battery system of the Tesla Model 3 is about 300Wh/kg, which is more than 20% higher than the energy density of the original 18650 battery, 35% higher than the single capacity, and about 9% lower than the system cost. 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: Analysis of important functional parameters of lithium iron phosphate power lithium ion battery