Parameters for lithium battery cell sorting

Lithium battery capacity

Lithium battery capacity is generally used as the primary selection of battery cell sorting, which is the most important parameter performance of battery cell inconsistency. There are many reasons for the inconsistency in capacity, and most are the result of inconsistencies in the manufacturing process.

Lithium battery capacity testing equipment is one of the essential testing equipment for battery manufacturers. Lithium battery manufacturers will complete the battery capacity test before leaving the factory.

Lithium battery open circuit voltage (OCV) and internal resistance (IR)

The voltages are inconsistent. After the formation, they undergo the same charging and discharging process, and are left for a sufficient time. Under the same ambient temperature, the cells to be evaluated are charged to the same SOC. Measure the open circuit voltage, and the voltage difference reflected at this time is the voltage inconsistency of the single cell. Studies have shown that the open circuit voltage of a single cell conforms to a normal distribution. That is to say, all our efforts to improve consistency can only change the concentration of parameters.

The internal resistance is inconsistent. The internal resistance of the cell is an important characterization of the power characteristics of the cell. It is also one of the reasons why the cell performance parameters are further discretized after the cell is grouped. Inconsistent internal resistance can cause inconsistent temperature rise, which is a type of cause that causes further discretization of other parameters.

Internal resistance is also the detection index after the module is grouped. The assembly of cells from a single cell to a module requires a grouping process such as welding or mechanical structure clamping. The consistency of the grouping process is reflected in the molded module, which is the internal resistance of the module.

The battery cell sorting machine is to finely sort the cells according to the set parameter range by detecting the voltage and internal resistance of each cell.

Usually, the parameters used for static sorting include battery capacity, open circuit voltage and internal resistance.

Some methods are to directly divide the interval according to the value of the parameter, and the cells that fall in the same interval are a group; some after the initial grouping, then use another parameter as the object of investigation in the group and continue to do the cells more detailed grouping. For example, after being divided into 5 groups according to capacity, each group is further divided into 3 groups according to the open circuit voltage and internal resistance. Finally, a batch of cells is divided into 15 groups.