1. Classification
Batteries from different batches should theoretically not be used together. Even batteries from the same batch need to be screened, and batteries with relatively similar parameters should be placed in separate battery packs.
The purpose of sorting is to select cells with similar parameters. Sorting methods, studied for many years, are mainly divided into static sorting and dynamic sorting.
Static sorting: The characteristic parameters of the battery, such as open circuit voltage, internal resistance, and capacity, are screened. Target parameters are selected, statistical algorithms are introduced, screening criteria are set, and finally, cells from the same batch are divided into several groups.
Dynamic screening involves selecting batteries based on their characteristics during the charging and discharging process. Some batteries are selected based on constant current and constant voltage charging, others on pulse charge and discharge, and still others on their own charge and discharge curves.
Combining static filtering and dynamic sorting, with static filtering as the initial grouping and dynamic filtering on this basis, results in more groups and higher filtering accuracy, but the cost will also increase accordingly.
This illustrates the importance of scale in the production of power lithium-ion batteries. Large-scale shipments allow manufacturers to perform more precise sorting and obtain battery packs with more similar performance. If production volume is too small and there are too many packs, even the best methods cannot be put into use if a batch cannot be matched with battery packs.
2. Heat Management
To address the issue of varying heat levels in batteries with inconsistent internal resistance, a thermal management system can be implemented to regulate the temperature difference across the entire battery pack, keeping it within a relatively small range. Batteries generating more heat will still experience a higher temperature rise, but the difference in temperature between them and other batteries will not be significant, and the degree of degradation will not be noticeably different.
3. Balance
Inconsistent cell voltages cause some cells to consistently reach the control threshold before others, resulting in a reduction in the overall system capacity. To address this issue, the Battery Management System (BMS) incorporates a balancing function.
