Why are 18650 lithium-ion batteries made into a cylindrical shape

The meaning of the cylindrical lithium-ion battery: such as 18650 type, that is, the diameter of the battery is 18mm, the length is 65mm, and the cylindrical battery. In fact, the cylindrical steel shell battery is not only 18650, there are other sizes such as 26650. In the early days, lithium-ion batteries were made of steel shell cells, and the outer shell was made of steel. Because the metal expansion coefficient of steel material is not as good as that of aluminum shell material, when the battery is short-circuited, the probability of explosion is higher than that of aluminum shell. Early lithium-ion batteries are used in the consumer electronics field. The important thing is to use it on laptops and mobile phones. The laptop uses 18650. The mobile phone is the first to use a square aluminum shell battery to replace the steel shell battery (the mobile phone battery will be swollen after a long time). Due to the development of ultra-thin smart phones, the mobile phone lithium-ion battery has now developed to the third generation, aluminum plastic film Material polymer batteries. The rounded side can distribute the pressure, and can improve the safety performance of the battery in the case of strong squeezing. Another advantage of cylindrical batteries is that the batch processing is simpler. When the winding machine winds the separator and the positive and negative electrodes, it can be automated. A single size such as 18650 can produce batteries of the same size and different capacity formulations. cost. Why is a cylinder? It can be viewed from two aspects. 1. Strength: Lithium-ion batteries are very dangerous, especially the current high-nickel ternary, steel needle puncture, external shock impact and deformation of the battery core, etc., as long as there is a problem with the film, it will cause The internal short circuit will explode at that moment, and the burning temperature after the frying can still reach 6,700 degrees. The arc shape is conducive to the dispersion of force. The square is slightly worse in this respect. Therefore, a cylinder is the first choice for a safe angle. 2. Manufacturing cost. From the perspective of strength, the honeycomb rhombus is also good. However, the processing cost is much worse. The corner folding process is more troublesome, the efficiency is not as high as the winding, and the cost is higher than that of the circular winding. The prismatic batteries are currently relatively large in size, so the cost is controlled by reducing the frequency of the corner folding process per unit Wh. Therefore, when manufacturers are positioning to manufacture small batteries, they will give priority to the cylinder (the soft case is essentially wound, but it is finally placed in a square mold to heat and press the aluminum-plastic film, which is better than the hard case. Low cost) Therefore, it depends on product positioning and users. In applications with more power, larger volume, and relatively regular battery space, it is suitable for large square hard-shell batteries, which can reduce a lot of difficulties in group wiring and management. And cost. For example, electric buses. And for some applications that are changeable, not very regular, or use less, the most important thing is the cylinder. For example, if power tools are extremely strict with space, they will be soft-packed. For example, mobile phones, digital wearable devices, etc. 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: What are the important reasons for the bulging of lithium-ion batteries