Introduction to the internal structure and characteristics of the 18650 cylindrical lithium battery

The internal structure of the 18650 cylindrical lithium battery The 18650 cylindrical lithium ion battery cell is mainly composed of five parts: a metal shell, a positive electrode, a negative electrode, a thin film and an electrolyte. They each perform their duties to ensure normal charging and discharging. The detailed structure is as follows: Positive electrode: The positive electrode material of the 18650 cylindrical lithium ion battery cell is generally lithium iron phosphate, lithium cobalt oxide, etc. The difference of each cathode material will directly affect the characteristics and cost of the 18650 lithium-ion battery. Negative electrode: The negative electrode materials of the 18650 cylindrical lithium ion battery cell include tin-based negative electrode materials, nano-scale negative electrode materials, carbon negative electrode materials, etc. In the battery, the negative electrode material is used for oxidation. The relative potential is low. Electrolyte solution: Taking lithium iron phosphate as an example, it is divided into solute and solvent. Solute: Lithium salt is often used, such as lithium perchlorate, lithium hexafluorophosphate, and lithium tetrafluoroborate. Solvent: Lithium ion batteries often use organic solvents, such as ether, ethylene carbonate, propylene carbonate, and diethyl carbonate. Safety valve: It is the most important explosion-proof barrier for 18650 cylindrical lithium-ion battery cells. When the internal temperature of the battery is abnormal, the safety valve is opened to remove the internal gas to prevent an explosion caused by excessive pressure. Explosion-proof line: also known as vent or explosion-proof hole. When the pressure is overloaded, because the explosion-proof hole is thinner than the rest of the shell, the gas will leak at the explosion-proof hole, so as to prevent the danger of the overall explosion of the battery. Diaphragm: The purpose of the diaphragm is to isolate the positive and negative plates of the cell. When the internal temperature of the battery is too high, the diaphragm will melt, preventing the possibility of battery explosion. When the internal temperature of the battery reaches 130°C, the mesh pores of the diaphragm will be closed to prevent lithium ions from passing through and increase the internal resistance, so as to prevent the internal temperature of the battery from continuing to rise. Features of Cylindrical Lithium Cells Cylindrical lithium batteries, especially 18650, due to their own structural characteristics and standardization of their models, the automation level of cylindrical battery production is the highest among the three important battery cell types. This makes a high degree of consistency possible, and the yield rate is increased accordingly. 1) As mentioned above, the monomer has good consistency; 2) The monomer itself has good mechanical properties. Compared with square and soft-pack batteries, the closed cylinder can obtain the highest bending strength under the approximate size; 3) The technology is mature and the cost is low, but at the same time, the space for cost optimization has been consumed almost; 4) The single energy is small, and the form is easy to control in the event of an accident, but this is also becoming the reason for its replacement. Disadvantages of cylindrical lithium batteries 1) In the context of electric vehicles, the number of cylindrical cells in the battery system is very large, which makes the complexity of the battery system greatly increased. Regardless of the organization or the management system, it is related to the other two types of batteries. The cost of cylindrical batteries is relatively high; 2) Under uneven temperature conditions, the probability of a large number of battery cell characteristics is increased. Of course, the reason why Tesla chose 18650 at the beginning of the design, I believe it is just a helpless choice, because 10 Years ago, the only qualified power lithium batteries that could be mass-produced were cylindrical batteries. The safety and thermal management requirements of the battery are instead the driving force for the research and development of its powerful electronic control system. 3) There is little room for the increase in energy density. In the 2016 news, Chaowei has achieved a single capacity of 4050mAh and a cell specific energy of 306Wh/kg. Since then, no higher records have been seen. In a given space, there are only dead materials, which is recognized as a difficult road. 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 article: How to prevent the misunderstanding of using the battery