Lithium battery pack inconsistency performance and analysis of sorting methods

The performance of the inconsistency of lithium battery packs 1. Capacity loss, the battery cells form a lithium battery pack, and the capacity conforms to the barrel principle. The capacity of the worst battery cell determines the capacity of the entire lithium 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. In a series connection, the two batteries pass the same amount of current. When charging, a battery with a small capacity must overflow first, and the charging cut-off condition is reached, and the system will no longer continue to charge. When discharging, a battery with a small capacity will inevitably emit all available energy first, and the system will stop discharging immediately. In this way, the batteries with small capacity are always overflowing, but the batteries with large capacity have been using part of the capacity, and part of the capacity of the entire lithium battery pack is always in an idle state. 2. Life loss is determined by the cell with the shortest lifespan. Small-capacity batteries are overflowing every time, and the output is too strong, which is likely to reach the focus of life first. The life of the battery cell has ended, and a group of battery cells that are welded together will die. 3. The internal resistance increases, the same current flows through different internal resistances, and the cells with large internal resistance generate more heat. 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. Of course, the internal resistance of the battery with a deep aging degree is relatively large, and the capacity attenuation is also more. Lithium battery packs are inconsistent and the sorting method is inconsistent with single cells, which must be considered from three aspects. Single battery sorting, thermal management after grouping, the battery management system provides equalization function when a small amount of inconsistency occurs; batteries of different batches are not used together; even if the battery cells of the same batch are inconsistent due to inconsistent parameters, It must be screened; lithium battery packs must be divided into two categories: static sorting and dynamic sorting: 1. Static sorting, which is based on the open circuit voltage, internal resistance, capacity and other characteristic parameters of the battery cell, selects target parameters, and introduces statistical algorithms , Set the screening criteria, and finally divide the cells of the same batch into several groups. 2. Dynamic screening is based on the characteristics of the battery cell during the charging and discharging process. Some choose the constant current and constant voltage charging process, some choose the pulse shock charging and discharging process, and some compare their own charging and discharging curves. Relationship between. Combining dynamic and static sorting, static screening is used for preliminary grouping, and dynamic screening is carried out on this basis, so that more groups can be divided and screening accuracy is higher, but the cost will rise accordingly. 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 is the capacity of a common 18650 lithium battery?