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Last week we talked about whether the inconsistent performance of Lithium-ion battery cells will affect the entire battery module. The short answer is YES. Consistency refers to the degree of consistency in the performance of each cell that makes up the battery pack. Due to the effect of production and environment, there are some tiny differences in the consistency of battery cells which will directly reduce the battery service life. So, how to deal with the consistency of battery cells and also improve the performance of battery pack? Let's discover together.
1. Battery sorting
In order to give full play to the best performance of group lithium batteries and increase the service life of lithium batteries, parameter consistency sorting between lithium batteries is an important method. Different batches of Li-ion battery cells are probably best not to use together. Even if the battery cells are from the same batch, battery sorting is needed.
By consistency sorting, the battery cells with similar parameters from the same batch of batteries can be classified as far as possible into a unified range, which is of great importance in the main characteristic parameters of the battery pack. Besides, it also ensures the consistency of the battery pack as well as give full play to the optimal performance of the battery pack, including maximum power generation, maximum current and maximum available capacity of batteries.
There are two main methods for battery sorting, including static sorting and dynamic sorting.
What is static battery sorting?
Static battery sorting refers to screen the battery cells according to the open circuit voltage, internal resistance, capacity and other parameters. By setting a sorting criteria, battery cells of the same batch are finally divided into several groups for subsequent matching.
What is dynamic battery sorting?
Dynamic battery sorting is to screen the battery cells in line with the performance of Li-ion battery cells during the charging and discharging process. There are several ways to help in this process: sorting through constant current & constant voltage charging process, through pulse charging and discharging, and by comparison between the charging and discharging curves of the battery cells.
For UFO Li-ion Battery, we combine static sorting with dynamic sorting method. The static battery sorting is employed as the initial selection, then dynamic sorting method is carried out so as to enhance the sorting accuracy of battery cells. By more detailed battery sorting, battery cells with more similar performance can be selected so as to improve the quality of our Li-ion battery pack.
2. Thermal Management
The internal resistance of battery cells will influence the heat generation within the battery. If the internal resistance of battery cells are inconsistent, the heat they generated will be different as well which will have a bad impact on the performance of the entire battery module. With respect to this problem, it is where thermal management system comes into play. A thermal management system is beneficial for adjusting the temperature differences, keeping them in a certain range when a tiny inconsistency of battery cells existed in the entire battery pack. Although the temperature of the battery cell with more heat generated is higher, the thermal management system is able to control the temperature gap between the battery cells, hence, no obvious difference will occur in the battery degradation.
3. Li-ion battery balancing
Just like a chain, which is only as strong as its weakest link. The inconsistency of battery cells means the differences in voltage. The voltage of some battery cells are higher than the others, reaching the voltage control threshold first, which will lead to a reduction of battery capacity. In regard to this, at the heart of each battery pack, there is a Battery Management System(BMS) to ensure the battery safety. And a balancing function has been designed in the battery management system (BMS) to narrow the gap between battery cells.
Let us suppose, for example, that two battery cells with different capacity are in series, it means that there is same current passing through the battery cells. During the charging, the battery cell with less capacity is bound to be fully charged, reaching ahead of the charging cut off voltage and stop the charging of the entire battery pack, while the voltage of the rest battery cell will lag behind. At this point, the balancing function of the battery management system (BMS) will be triggered off, including connecting to a resistor to release part of the capacity of the high-voltage battery cell or transferring the excess energy to the low-voltage battery cells, so that the charging cut-off condition could be released as well as allowing the battery pack to be recharged with more energy.
No matter how high the energy density of the Lithium-ion battery cell is, the capacity of the Li-ion battery pack will be significantly reduced if there are obvious inconsistencies between the battery cells. Through over a decade of research and development, each UFO lithium-ion battery is equipped with our self-developed battery management system (BMS) to improve the battery ability in storing energy and safety. We use premium materials and the state-of-the-art technologies which lean greater durability to the products, enabling you to procure from us with full confidence to our quality.
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