The inconsistency of lithium battery packs is mainly affected by time, and the reasons mainly include two aspects:1. First of all, there are problems in the process and uneven materials in the manufacturing process, which makes the materials of lithium batteries and so on have very small differences; after the lithium battery pack is put into use, the electrolyte density of each battery in the battery pack , Temperature and ventilation conditions, self-discharge degree and charging and discharging process, etc., the capacity and internal resistance of the same model of batteries shipped from the same batch may vary.
2. When loading and using, the influence of differences in electrolyte density, temperature and ventilation conditions, self-discharge degree and charging and discharging process of each battery in the lithium battery pack.
What equipment is needed for lithium battery cell sortingThe lithium battery cell automatic sorting machine can directly sort out the set open circuit voltage, AC internal resistance and other parameters. And the sorting efficiency is high, 10 channels are sorted together, 9 OK channels, 1 NG channel. The consistency of the lithium battery pack is guaranteed.
What harm and problems will be caused by inconsistent lithium battery packs?First of all, if a lithium battery with too much energy alone encounters an accident, it will cause thermal runaway, and the inside of the battery will react sharply. In a short period of time, there will be nowhere to release the excessive energy, which is very dangerous. Especially when the development of security technology and control capabilities is not sufficient, the capacity of each battery should be restrained. The inconsistency of lithium battery parameters mainly refers to the inconsistency of capacity, internal resistance, and open circuit voltage. Inconsistent batteries are used in series and used together, the following problems will occur.
1. Capacity loss. The single cells form 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 overcharge and overdischarge of the battery, the logic of the battery management system is set as follows: when discharging, when the voltage of the lowest cell reaches the discharge cut-off voltage, the entire battery pack stops discharging; when charging, when the voltage of the highest cell reaches the cut-off voltage of charging When the voltage is low, stop charging.
Take two batteries connected 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 system will not continue to charge when the charging cut-off condition is reached. When discharging, a battery with a small capacity must first emit all available energy, and the system stops discharging immediately. In this way, the batteries with small capacity are always fully charged and discharged, while the batteries with large capacity are always using part of the capacity. A portion of the capacity of the entire battery pack is always idle.
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 battery cell with the shortest life is the one with the small capacity. The small-capacity battery is fully charged every time, and the output is too strong, and it is likely to reach the point of life first. Until the end of battery life, a group of welded batteries will also end their life.
3. The internal resistance increases. Different internal resistances flow the same current, and the cells with large internal resistances 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. Internal resistance and temperature rise form a pair of negative feedback, which accelerates the deterioration of high internal resistance cells.
