(1) Overview of cell sorting. Cell sorting is a key process in the production of modules or packs. The purpose is to select cells with good electrical properties through sorting and match them into a group to ensure that the modules or packs The consistency of electrical performance extends the service life of the Pack.
A module is generally composed of multiple cells in series and parallel. If the consistency of the single cells is not good, the life of the module will be shortened, and the performance of the module will ultimately be determined by the worst single cell. Although the degree of automation of battery cell manufacturing is getting higher and higher, its manufacturing process is complicated, and each link of raw materials, parts and environment may cause inconsistencies between single cells, and this inconsistency will gradually accumulate during use. expand. Therefore, battery cell manufacturers not only need to strictly control every aspect of cell production to ensure the consistency of battery production; Pack manufacturers also need to adopt appropriate sorting methods to reduce the initial gap between the single cells in the battery pack. Difference, improve the performance and life of the battery pack.
(2) Cell sorting method
At present, the sorting methods of power cells mainly include single parameter sorting method, multi-parameter sorting method, dynamic characteristic curve sorting method and electrochemical impedance spectroscopy sorting method.
(3) Single parameter sorting method.
Separate sorting using the external characteristic parameters of the cells (voltage, internal resistance, capacity). The open circuit voltage method is simple to operate, but the accuracy is poor; the internal resistance method measurement will cause the polarization of the battery to produce a polarized internal resistance; the capacity method sorting has a certain effect, but it cannot reflect the working characteristics of the battery pack under different working conditions.
(4) Multi-parameter sorting method.
Select multiple parameters for sorting, and the parameters can be selected for capacity, voltage, internal resistance, self-discharge rate, etc. According to the matching requirements, set the conditions of comprehensive capacity difference, internal resistance difference, voltage difference, and self-discharge rate difference to improve the accuracy of sorting.
(5) Sorting method of dynamic characteristic curve.
The charge-discharge curve is a concentrated expression of capacity, internal resistance, charge-discharge voltage plateau and polarization degree. Carry out specific charging and discharging experiments on the batteries, and sort the batteries according to the similarity between the charge and discharge curves.
((6) Electrochemical impedance spectroscopy sorting method
This method is to apply a small amplitude AC signal with different frequencies, and measure the relationship between the ratio of AC signal voltage to current (impedance) and the frequency of the sine wave.