The role of battery sorter in the battery pack making process

In the battery pack assembly production line, the battery sorter is an essential battery pack making equipment. So, what is the role of the battery sorter machine in the battery pack making process?

As we all know, in order to meet the energy and voltage requirements, hundreds or even thousands of single lithium-ion battery cells need to be assembled into battery packs in series and parallel before use.

In theory, these single battery cells should have exactly the same characteristics. However, in fact, due to the fluctuation of related process parameters in the manufacturing and production processes, even the same batch of lithium-ion battery cells still have certain differences in performance (such as capacity, internal resistance, voltage, and decay speed, etc.).

On the one hand, these differences will continue to accumulate as the number of battery cycles increases during use, resulting in the continuous expansion of performance differences between single battery cells.

On the other hand, due to the huge number of battery cells in the battery pack, there must be a certain temperature gradient inside the battery pack during use. The existence of the temperature gradient will also cause the inconsistency of the internal resistance of the battery cell and the inconsistency of the current distribution, resulting in the decay rate of single battery cell is inconsistent.

The above two factors will cause the cycle life of the battery pack to be much lower than that of the single battery cell. For example, the cycle life of a single battery cell can reach more than 1000 times, but after only 150 cycles of assembled battery packs, serious capacity degradation occurs. It is found through random inspection that the capacity of some single battery cells has been lower than 80% of the rated capacity.

Why is this? This is mainly because the small differences in the coulombic efficiency, decay rate and internal resistance increase of the single battery cells continue to accumulate in the cycle, which ultimately leads to the excessive decline of some single battery cells.

The inconsistency between single lithium-ion battery cells mainly includes indicators such as temperature, voltage, SoC, capacity and internal resistance. If we take the time factor into consideration, the inconsistency of lithium-ion batteries should also include self-discharge, coulomb efficiency, Capacity decline rate, etc.

In summary, before assembling the battery pack, we must test and sort the battery cells to improve the consistency of the battery cells as much as possible.

Therefore, we will first use the battery cell cycler to perform a certain number of cycles of charge and discharge tests on the battery cells. Through this step, we can initially grade the battery cells according to their actual capacity and capacity attenuation speed.

After the battery cell capacity classification is completed, we use a battery sorter to test and sort the battery cells according to the voltage and internal resistance test values.

Based on the above two battery cell grading and sorting tests, the consistency of the battery cells has been as high as possible. After selecting a suitable battery management system, the battery pack can be assembled. Of course, it is essential to test the battery management system. Battery pack and BMS test systems, battery PCM tester or battery pack protection board test equipment are necessary.