Based on the packaging form, lithium batteries can be divided into three forms: square, cylindrical and soft-pack. The packaging form refers to the packaging structure of a single lithium battery. Different packaging forms correspond to different process steps and also correspond to different forms of battery precision structural parts. At present, the technical routes of lithium battery packaging mainly include three forms: cylindrical, square and soft-pack.
(1)Prismatic Cell: Usually winding or lamination process is used to make bare cells, and prismatic cell aluminum shell or steel shell is used as packaging material. prismatic cell have the advantages of high group efficiency, large single cell capacity and simple structure. The size, model and volume are fixed, and the shape is not easy to change, which may limit the battery design of some equipment. In addition,prismatic cell have low consistency and difficult heat dissipation. Because prismatic cell are larger than cylindrical batteries, fewer cells are required to achieve the same energy. This means that for the same volume, the use of prismatic cell requires fewer electrical connections to be welded, reducing the number of required structural parts and improving volume utilization. Development prospects: In the past few years, the performance of prismatic cell has been rapidly improved with the support of the domestic industrial chain. prismatic cell now account for more than 90% of the domestic power battery market share.
(2) Pouch cell: Because pouch cell use a stacking manufacturing method, they are thinner and have the highest energy density (using aluminum-plastic film packaging that is lighter than aluminum shells). They are considered to be a powerful tool for solving endurance and safety concerns, and can also make a good connection to solid-state batteries. Considering the layout of the entire vehicle (there is more room for imagination in shape, more changes, not limited to rectangles. It can be composed of a small battery pack placed under the trunk, or it can be made into a T-shaped layout.) pouch cell have the advantages of high single-cell energy density, good electrochemical performance, high safety, flexible design, variable shape, strong adaptability, and high energy density. However, their product consistency requirements are higher, the grouping efficiency is relatively low, and the cost is relatively high. Development prospects: In today’s battery development trend, pouch cell have been unpopular for a long time. Even in theory, compared with square and cylindrical batteries using hard shell packaging, pouch cell are less likely to explode after thermal runaway. But in reality, the factor that has the greatest impact on the entire automotive battery system is the consistency of the single cell, which is precisely one of the disadvantages of pouch cell and has also led to frequent safety accidents in electric vehicles equipped with pouch cell.
(3) Cylindrical: Cylindrical batteries are usually packaged in cylindrical steel shells, and the bare cells are made using a winding process. Cylindrical batteries are one of the best practices for lithium batteries and are also standardized and universal products. As early as 1992, Japan’s SONY company developed the 18650 battery. Currently, cylindrical batteries can be divided into 14650, 18650, 21700, 32650, 4680 and other models, which are named after the battery size. 18650 is the most mature technology, while 21700 is the new battery that Tesla has been promoting in recent years. Due to its geometric shape, the gap between cylindrical batteries is larger, which is conducive to air circulation, thereby improving heat dissipation efficiency. There are relatively more cylindrical cells, and higher requirements for thermal management systems. Cylindrical batteries have good consistency, high production efficiency, and strong heat dissipation capabilities at the system level. After the size upgrade, it can improve its original low single energy density, many cells required for the module, and the resulting poor lifespan and complex management. But in general, its low energy density and low product grouping efficiency are still obvious disadvantages.
