Detailed explanation of lithium-ion battery consistency problems

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 together in series, the following problems will occur. 1) Capacity loss, the battery pack is composed of single cells, and 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 overcharge and overdischarge of the battery, 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 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, the battery with 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 life. 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. When the battery cell's life ends all the time, a group of battery cells 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. The above three parameters are not completely independent. The internal resistance of the battery with a deep aging degree is relatively large, and the capacity attenuation is also more. Separate explanations, just to express clearly their respective directions of influence. 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: How to charge to protect the battery?