Comparing the structure and performance of cylindrical 32650 lithium battery

Power lithium battery generally refers to a lithium battery that can supply power to equipment, appliances, vehicles, etc. through high current discharge. Power lithium batteries have the characteristics of high specific energy, high current charge and discharge, and long cycle life, and have been widely used. Power lithium batteries are divided into ternary, lithium cobalt oxide, lithium manganate, lithium iron phosphate and other types according to the different cathode materials; according to the different shapes, they are divided into square batteries (prismaTIc), cylindrical batteries (cylindrical), etc. In order to increase the cruising range, the energy of the power lithium battery through the series-parallel combination is generally larger, the capacity ranges from a few ampere hours to hundreds of ampere hours, and the voltage ranges from more than ten volts to hundreds of volts. With the increase in carrying energy, the potential danger of the battery also increases. Therefore, how to improve the safety of power lithium-ion batteries has become an important prerequisite for the continued development of electric vehicles. In the development process of power lithium batteries, there have always been two development directions. One direction is large single cells, which are combined in a small amount in parallel; the other direction is small cells, which are combined in a large number of parallels. Companies represented by South Korea’s LG and domestic BYD are taking the generous route; the US A123 and domestic companies represented by Waterma are taking the small cylindrical route. These two routes are currently inconclusive, and different power lithium-ion battery manufacturers choose different process routes according to their own understanding. But in the face of the indicator of safety, the results of the two process routes are very different. This article compares and decomposes the structure and performance of power lithium-ion batteries, especially in terms of safety, to illustrate the safety advantages of small cylindrical batteries used in electric vehicles. Battery structure and performance comparison Decomposing cylindrical batteries and square batteries are currently the two mainstream directions in the industry. The basic structure of the cylindrical battery is shown in Figure 1. The positive and negative electrodes are separated by a separator, and the core is formed by winding. Normally, the positive and negative pole pieces are welded with positive and negative pole lugs and led out through both sides respectively. The tabs are welded to the positive and negative housings. The electrolyte is filled in the shell. Figure 2 shows the structure of a square battery. The structure of the square battery is divided into a laminated structure and a winding structure. The laminated square lithium battery is composed of n positive electrode sheets and n+1 negative electrode sheets to form a battery cell. The positive and negative sheets are separated by a separator, and the positive and negative sheets are reserved on one side of the positive and negative sheets. In the negative ear area, the positive and negative ears respectively extend symmetrically from both sides of the core cell when they are stacked into a core cell. The winding structure of the square battery is similar to that of the cylindrical battery. The difference is that the core is flat rather than cylindrical. Due to the different shapes of cylindrical batteries and square batteries, the structure is quite different. Under normal circumstances, the capacity of cylindrical batteries cannot be too large due to the current density of the core and the limitation of heat dissipation. The capacity of the square battery can be increased by increasing the length and width on the premise that the thickness is appropriate. The capacity of a single cell can generally exceed 10 times that of a cylindrical battery. Table 1 compares the performance of cylindrical and square batteries. It can be seen that the two batteries have their own characteristics. Cylindrical battery has simple structure design, close positive and negative interface, mature processing line, low cost, good heat dissipation in groups, and excellent safety performance. The disadvantage is that the internal resistance is relatively high, and the grouping requirements are high. The advantage of the square battery is the large single capacity and simple combination. The disadvantage is that the processing technology is complicated, and the consistency of large-capacity battery monomers is difficult to control. In addition, the square shell is prone to stress accumulation, the shell is easily broken, and the electrolyte splashes cause safety hazards. From the perspective of the global market, both large-capacity square batteries and small-capacity cylindrical batteries are used in the power field. At present, a benchmark company in the lithium iron phosphate battery industry, the main products of A123 in the United States are three types of cylindrical batteries of 18650/26650/32113, with a single capacity of 2.5Ah-5Ah. 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 the application of small low-speed lithium battery electric vehicles