In the use of batteries, users may often encounter some problems. Take electric bike batteries as an example, since the battery packs of electric vehicles are used in series, they are prone to capacity imbalance after a period of time. Battery cell imbalance occurs when individual cells within a battery pack exhibit different charge levels, capacities or performance. Prolonged battery imbalance can lead to shorter operating hours and safety issues.
What Causes Battery Cell Imbalance?
A battery pack is in fact a cluster of cells’ batteries that are in a very deep connection. However, when any of these cells vary in nature, the whole team loses its balance. Thus, this unbalance not only decreases the energy utilization but also accelerates the deterioration of the battery. As a result, the batteries that are not balanced cannot be fully charged or discharged, causing a faster degradation and a shorter lifespan. This affects the revenue and the longevity of the operation in the long term.
Cell-to-cell discrepancies may occur at the same time during the manufacturing process and operation. Manufacturing can be the source of such a problem due to the cells with different levels of state of charge (SoC), capacities, impedances, or ages which can be mixed together, thereby putting the battery pack on an imbalanced path right from the beginning. The operational factors such as the way cells are arranged and the position of the current collectors are other issues that can contribute to the problem. Even environmental factors such as sunlight exposure affect them, particularly in major packs like energy storage systems.
Following are some of the most common factors that cause battery imbalance:
- Manufacturing Variations: Despite the strict quality control measures taken, slight variations in the manufacturing process may lead to differences in cell properties thus the cause for imbalance over time.
- Differences in Self-Discharge Rates: Cells that are part of the same battery pack can have different rates of self-discharge which means that some cells are drained faster than others, thus causing an imbalanced situation.
- Uneven Temperature Distribution: Temperature has a great impact on battery performance and unbalanced allocation of heat among the cells in the pack may cause some cells to age faster than others, which results in imbalance.
- Overcharging or Undercharging: Inappropriate charging methods including overcharging or undercharging the cells can result in imbalance within them by making some cells more stressed than others.
- Aging Effects: With time, the cells that are constantly undergoing cycling and degradation tend to show different symptoms from other battery cells, making the problem of cell imbalance worse.
What May Occur If Battery Cell Imbalance?
Ignoring battery cell imbalance can have severe consequences, ranging from reduced performance to potential safety hazards.
| Consequence | Description |
|---|---|
| Reduced Battery Capacity | As cells become imbalanced, the overall capacity of the battery pack is limited by the weakest cells, leading to a noticeable decrease in runtime. |
| Decreased Runtime | Directly related to the reduced capacity, cell imbalance can result in shorter operating times for your devices or electric vehicles. |
| Accelerated Aging and Degradation | Imbalanced cells experience uneven stress, causing some cells to degrade faster than others, ultimately shortening the overall lifespan of the battery pack. |
| Safety Concerns | In extreme cases, severe cell imbalance can lead to overheating, thermal runaway, and potential safety risks, emphasizing the importance of addressing this issue promptly. |
How to Fix Battery Cell Imbalance
Fortunately, there are several techniques and solutions available to mitigate and even resolve battery cell imbalance, including cell balancing methods and BMS.
Cell Balancing Methods
a. Passive Balancing
This method is based on taking energy away from the stronger cells and, as a result, the weaker ones can catch up and develop a bit slower. Passive balancing is mainly done by incorporating resistors or bypass circuits that selectively draw up charge from the stronger cells. Although the passive balancing method is simple and inexpensive, it is very slow and inefficient, especially regarding an acute imbalance.
More sophisticated systems will recharge the cells and even out the charge level throughout the whole pack. Active balancing uses complex circuits and algorithms to transfer charge from stronger cells to weaker ones, thus achieving equal charge distribution among cells. This technique is usually quicker and more effective than the passive balancing approach, but sometimes it may be more complicated and costly.
Battery Management System Solutions
Highly advanced BMS systems consist of continuous monitoring and balancing of the cells which utilize both passive and active techniques to deliver optimum performance.
Replacement of Faulty Cells
In extreme situations, it might be the case that locating and substituting damaged or severely imbalanced cells becomes an important step to restore the total health of the battery pack.
Preventing Battery Cell Imbalance with a BMS
While addressing cell imbalance after it occurs is essential, prevention is always the best approach. This is when the Battery Management System (BMS) is introduced and put to use. A well-designed BMS is of much help in avoiding the imbalance of cells.
- Cell Monitoring and Balancing: The BMS continuously monitors each cell’s condition individually and detects imbalances at an early stage by using balancing algorithms to restore equilibrium to the pack.
- Overcharge and Overdischarge Protection: The BMS prevents overcharging and overdischarging, thus reducing the tendency of any one cell to be subjected to excessive stress, minimizing the risk of imbalance.
- Temperature Monitoring and Control: The BMS regulates and monitors the temperature of the battery pack, this prevents the uneven temperature distribution and the consequent imbalances.
A BMS of good quality is the first step in preventing the premature decline in the life and performance of your batteries that can lead to a waste of time, money, and nerves due to the problem being solved in the distant future.
By knowing the causes, results, and available options, you can take effective measures to guarantee the maximum performance, safety, and life of the battery systems. Whether you’re a consumer, a professional, or a leader in the industry, the issue of battery cell imbalance should be your main concern. The future of batteries lies in the implementation of sophisticated Battery Management Systems, such as MOKOEnergy’s balancing BMS, which have the power to take you one step ahead and fully exploit the capabilities of your battery-powered devices and applications.
Note that a good battery is a contented and a high-performing battery.
