What are the indications and sorting methods for the divergence of lithium-ion battery packs?

At this moment, the power lithium-ion battery pack has steadily occupied the position of the leader of the electric vehicle power supply. The service life is long, the energy density is high, the security can be changed, and the energy density can continue to rise. The energy density of lead-acid batteries is around 40Wh/kg, while the energy density of lithium-ion batteries is already higher than 150Wh/kg. Lithium-ion battery packs have high energy density and are afraid to design too large capacity, because while the energy convergence is improved, the requirements for safety are also rising. First of all, only a lithium-ion battery with an excessive amount of energy can cause accidents, and the ignition will be out of control, and the internal reverberation of the battery will be sharp. In a short period of time, too much energy is nowhere to be released. Especially when the growth of security skills and control skills is not sufficient, the capacity of each battery should be prohibited. Since lithium-ion batteries cannot be made into a large one, string together one small one and one small one. At this time, we must face a problem, consistency. The divergence of lithium-ion battery packs mainly refers to the divergence of the parameters of capacity, internal resistance, and open circuit voltage. The divergence of battery core functions is formed during the production process. The batteries in the same lithium-ion battery pack are always weaker and weaker faster. The discrete level of the parameters between the single cells increases with the deepening of the aging level. If the inconsistent batteries are used in series and connected together, the following problems will arise. Lithium-ion battery packs are inconsistent in the expression 1. Capacity loss, the battery cell constitutes a lithium-ion battery pack, and the capacity is in line with the principle of a wooden barrel. The capacity of the worst battery cell determines the ability of the entire lithium-ion battery pack. Take two batteries in series as an example. One battery has a capacity of C, and the other has a capacity of only 0.9C. Connected in series, the two batteries pass current of the same size. When charging, the battery with small capacity must be full first, and when the charging deadline is reached, the system will no longer continue to charge. When discharging, a battery with a small capacity must first emit all available energy, and the system immediately stops the discharge. In this way, cells with small capacity are always full, but cells with large capacity have been using departmental capacity. The capacity of the entire lithium-ion battery pack is always in an idle state. 2. Life loss is determined by the cell with the shortest lifespan. Small-capacity batteries are full of discharge every time, with too much effort, and large batteries are probably the first to reach the point of life. The life of the battery cell has ended, and a group of battery cells that are welded together will come to an end. 3. The internal resistance increases, the different internal resistance, the current flowing through the communication, the battery with large internal resistance has more fever. The battery temperature is too high, causing the deterioration rate to accelerate, and the internal resistance will further increase. Internal resistance and temperature rise form a pair of negative feedback, which accelerates the deterioration of high internal resistance cells. Although the internal resistance of a battery with a deep aging level is larger, the capacity attenuation is also more. Lithium-ion battery packs are divided into different sorting methods, and the individual cells are different, and it is important to consider three aspects. Single cells are sorted and heated after grouping. When there is a small amount of inconsistency, the battery management system provides balance results; different batches of cells are not put together for use; even if the batches of cells are communicated, the parameters are different. Discrepancies must be screened; lithium-ion battery packs are mainly divided into two categories: static sorting and dynamic sorting: 1. Static sorting, which screens and selects the open circuit voltage, internal resistance, capacity and other characteristic parameters of the battery cell. Policy parameters, introduce statistical comparisons, set screening criteria, and finally divide the same batch of cells into several groups. 2. Dynamic screening is based on the characteristics of the battery cell during the charging and discharging process. Some select the constant current and constant voltage charging process, some select the pulse attack charge and discharge process, and some compare their own charging and discharging curves. The relationship between. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.