1. Capacity loss, the single cell constitutes a lithium-ion battery pack, and the capacity conforms to the barrel principle. The capacity of the worst cell determines the capacity 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. In series relationship, 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, the battery with small capacity must discharge all available energy first, and the system stops discharging immediately. In this way, the small-capacity cells are always fully discharged, while the large-capacity cells have been using part of the capacity and a part of the entire lithium-ion battery pack's capacity is always in an idle state.
2. The loss of life is determined by the cell with the shortest life. Small-capacity cells are fully discharged every time, and the output is too strong, and it is likely to reach the key point of life first. As the battery life ends, a group of batteries welded together will also end of life.
3. The internal resistance increases, different internal resistances flow the same current, and the cells with large internal resistance generate more heat. If the temperature of the battery is too high, the deterioration speed will be accelerated, and the internal resistance will further increase. The internal resistance and temperature rise form a pair of negative feedback, which accelerates the deterioration of the high internal resistance cell. Of course, the internal resistance of the cells with deep aging degree is relatively large, and the capacity attenuation is also more.