Lithium batteries cannot be made into a large one, so we have to organize many small cells together, and everyone can work together with sincerity, even if we can take electric vehicles to fly. At this point, we need to face the issue of consistency.

Our daily experience is that two dry batteries, with the positive and negative poles connected, can emit light from a flashlight. Who cares if they are consistent or inconsistent. The large-scale application of lithium batteries is not so simple.

The inconsistency of lithium battery parameters mainly refers to the inconsistency of capacity, internal resistance, and open circuit voltage. Inconsistent battery cell strings used together can cause the following problems.

1) Capacity loss refers to the formation of a battery pack consisting of individual cells, which conforms to the "barrel principle" in terms of capacity. The capacity of the worst cell determines the capacity of the entire battery pack.

To prevent overcharging and discharging of the battery, the logic of the battery management system is set as follows: during discharge, when the lowest individual voltage reaches the discharge cut-off voltage, the entire battery pack stops discharging; When charging, stop charging when the highest unit voltage touches the charging cutoff voltage.https://www.greenwayalu.com/aluminum_products_series/

Take two batteries connected in series as an example. One battery has a capacity of 1C, while the other has a capacity of only 0.9C. In a series connection, two batteries pass through the same amount of current.

When charging, batteries with small capacity must first be fully charged, reaching the charging cut-off condition, and the system will no longer continue to charge. When discharging, batteries with small capacity will inevitably discharge all available energy first, and the system will immediately stop discharging.

In this way, cells with small capacity are always fully charged and discharged, while cells with large capacity are always using a portion of their capacity. A portion of the entire battery pack's capacity is always idle

2) Life loss, similarly, the lifespan of a battery pack is determined by the battery cell with the shortest lifespan. It is highly possible that the battery cell with the shortest lifespan is the one with a small capacity. Small capacity battery cells are always fully charged and discharged, with excessive output, which is likely to reach the key point of their lifespan first. As the lifespan of the battery cells comes to an end, a group of battery cells welded together will die with it.

3) As the internal resistance increases, different internal resistances flow through the same current, and cells with high internal resistance generate relatively more heat. If the battery temperature is too high, it will accelerate the degradation rate and further increase the internal resistance. Internal resistance and temperature rise form a pair of negative feedback, accelerating the degradation of high internal resistance cells.