Contributed Commentary by Anton Beck, Battery Product Manager, Epec When a lithium battery pack is designed using multiple cells in series, it is very important to design the electronic features to continually balance the cell voltages. This is not only for the performance of the battery pack, but also for optimal life cycles.
Uneven electrical current distribution in a parallel-connected lithium-ion battery pack can result in different degradation rates and overcurrent issues in the cells. Understanding the electrical current dynamics can enhance configuration design and battery management of parallel connections.
Parallel connection of lithium-ion batteries significantly aggravates the unbalanced discharging phenomenon between the cells. A simplified capacity loss model was proposed for the lithium-ion batteries and was used to assess the capacity degradation performances for the parallel-connected cells.
For lithium-ion batteries, a simplified capacity loss model was proposed and used to assess the capacity degradation performances for parallel-connected cells. The capacity loss rate increases as the temperature difference between the cells increases.
An uneven temperature distribution within a battery pack leads to mismatch of internal resistance among cells. For battery packs with series combination, all cells have the same charging/discharging current.
In a battery pack with series combination, all the cells have the same charging/discharging current. The cutoff voltage is determined by the weakest cell among the series-connected cells, which affects the overall capacity of the battery pack. For a series battery pack, this means that the cells are connected in such a way that the voltage of each cell adds up to provide the desired output voltage.