What Affects the Consistency of Lithium-ion Batteries?

Lithium-ion battery packs face consistency issues during use, which not only affects the overall performance of the battery pack, but may also cause safety hazards. Therefore, in-depth research on the factors affecting the consistency of lithium-ion battery packs is of great practical significance.

1.Cell capacity difference: In a battery pack, if the capacity of each cell is inconsistent, some cells will reach full charge or over discharge state first during the charge and discharge process, while other cells are still working normally. This not only reduces the overall capacity utilization of the battery pack, but also accelerates the aging of the cells and shortens the service life of the battery pack。

2.Difference in internal resistance of battery cells: The internal resistance of a battery cell will affect its voltage drop and heat generation during the charge and discharge process. When charging and discharging at high rates, the voltage drop of a battery cell with a larger internal resistance is more obvious, resulting in reduced output power; at the same time, the heat generation is also greater, which may cause local overheating and affect the stability and safety of the battery.

3.Differences in self-discharge rates of cells: Cells with high self-discharge rates lose power faster in the battery pack, resulting in inconsistent overall SOC of the battery pack. This inconsistency causes the battery management system to frequently perform balancing operations, increasing system complexity and energy consumption.

4.Initial SOC differences of cells: Before the battery pack is assembled, if the SOC of each cell is inconsistent, then in the subsequent use, this difference will gradually accumulate and amplify. Even if it is adjusted through balancing measures later, it is difficult to completely eliminate the impact of the initial SOC difference.

5.Differences in manufacturing processes and materials: For example, uneven coating of pole pieces, differences in electrolyte injection amounts, inconsistent diaphragm thickness, etc., will all lead to discreteness in battery cell performance。

6.Influence of use environment and working conditions: When the battery pack is used in different environments with different temperatures, humidity, charge and discharge depth, the aging speed and performance changes of each battery cell will also be different. The consistency of the battery pack that works in harsh environment for a long time is more likely to be destroyed.