Introduction to lithium-ion battery consistency issues

Our daily relevant experience is that if the positive and negative poles of two dry batteries are connected, the flashlight can emit light. Who cares about the same and inconsistent things. The large-scale application of lithium-ion batteries is not so simple. The inconsistency of lithium-ion battery parameters mainly refers to the inconsistency of capacity, internal resistance, and open circuit voltage. If inconsistent batteries are used in series and used together, the following problems will occur. 1) Capacity loss. Cells make up a battery pack. The capacity conforms to the barrel principle. The capacity of the worst cell determines the capacity of the entire battery pack. In order to prevent the battery from overcharging and overdischarging, the logic of the battery management system is set as follows: when discharging, when the lowest cell voltage reaches the discharge cut-off voltage, the entire battery pack stops discharging; when charging, when the highest cell voltage touches the charge cut-off voltage To stop charging. Take two batteries in series as an example. One battery has a capacity of 1C, 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, the battery with a small capacity must be fully charged first, and the charging cut-off condition is reached, and the system will not 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, batteries with small capacity are always fully discharged, while batteries with large capacity always use part of the capacity. Part of the capacity of the entire battery pack is always in an idle state. 2) Life loss. Similarly, the life of the battery pack is determined by the cell with the shortest lifespan. It is very likely that the cell with the shortest life span is the cell with a small capacity. Small-capacity batteries are fully charged and discharged 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. 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: Comparison of the performance of the five major cathode materials for electric vehicle lithium-ion batteries