Dealing with SOC and C/E Mismatch Problems Using Cell Balancing Technology -Lithium - Ion Battery Equipment
Lithium-ion battery packs are generally composed of multiple batteries connected in series, but if the capacity of the batteries does not match, the capacity of the entire battery pack will be affected. To do this, we balance the mismatched cells. This article discusses the concept of cell balancing and some considerations.
A lithium-ion battery pack usually consists of one or several battery packs connected in parallel, and each battery pack consists of 3 to 4 batteries connected in series. This combination can simultaneously meet the voltage and power requirements required for notebook computers, medical equipment, detection instruments, and industrial use. However, this commonly used configuration usually does not work to its full potential because a mismatch in the capacity of one cell in series with the others will reduce the capacity of the entire battery pack.(Lithium - Ion Battery Equipment)
Mismatches in battery capacity include state-of-charge (SOC) mismatches and capacity/energy (C/E) mismatches. In both cases, the total capacity of the battery pack is only up to the capacity of the weakest cell. In most cases, the cause of battery mismatch is imperfect process control and testing methods, rather than changes in the chemical properties of lithium ions themselves. Prismatic lithium-ion batteries (LiIonprismaticcell) require stronger mechanical stress during processing, and differences between batteries are more likely to occur. In addition, lithium-ion polymer batteries will also have differences between batteries due to the adoption of new processes.
The performance of series-connected Li-ion battery packs can be improved by employing cell balancing solutions to address SOC and C/E mismatch issues. The battery mismatch problem can be corrected by balancing the battery during the initial adjustment process. After that, it only needs to be balanced during the charging process, while the C/E mismatch must be balanced during the charging and discharging process. Although the product defect rate may be very low for a certain battery manufacturer, in order to guard against the problem of short battery life, we still need to provide further quality assurance.
Meaning of battery balancing
Portable devices with an operating voltage of 6V or above are powered by series-connected battery packs, in which case the total voltage of the battery pack is the sum of the voltages of the individual series-connected batteries. The battery pack of a portable computer is usually composed of three or four batteries connected in series, and the nominal voltage is 10.8V or 14.4V. In most of these uses, a single series-connected battery pack cannot supply the energy required by the device. At present, the largest battery (such as 18650) can supply 2,000mAh (milliamp middot; hour) energy, and the computer needs 50-60Whr (5,000-6,000mAh) energy, so it is necessary to connect three batteries in parallel for each battery in series.
Cell balancing refers to the application of differential current to different cells (or battery packs) in a series battery pack. The current of each cell in a series battery pack is usually the same, so additional components and circuitry must be added to the battery pack to achieve cell balancing. Only when the batteries in the battery pack are connected in series, and the batteries in series are equal to or greater than three levels, the battery balancing problem will be considered. Cell balancing is achieved when all cells in the battery pack meet the following two conditions:
1. Cell balancing is achieved when their relative states of charge are the same, provided all cells have the same capacity. SOC is usually expressed as a percentage of current capacity and rated capacity. Therefore, open circuit voltage (OCV) can be used as a measure of SOC. Provided that all cells in an unbalanced battery pack can be differentially charged to full capacity (balance point), they can be charged and discharged normally without any additional adjustments, usually one-time. When users use a new battery, they usually require to charge the battery for a long time, and this process actually includes a complete discharge-charge. This process minimizes the load and maximizes the battery charging time, reducing the demands on the battery balancing circuitry.
2. If the capacities of the batteries are different, they are also considered to be balanced when the SOC is the same. But SOC is only a relative value, and the absolute value of each battery capacity is different. In order to make the SOC of batteries with different capacities the same, it is necessary to use a differential current every time the batteries connected in series are charged and discharged. The normal charge and discharge time is shorter than the initial charge and discharge, and requires a larger current.
A lithium-ion battery pack usually consists of one or several battery packs connected in parallel, and each battery pack consists of 3 to 4 batteries connected in series. This combination can simultaneously meet the voltage and power requirements required for notebook computers, medical equipment, detection instruments, and industrial use. However, this commonly used configuration usually does not work to its full potential because a mismatch in the capacity of one cell in series with the others will reduce the capacity of the entire battery pack.(Lithium - Ion Battery Equipment)
Mismatches in battery capacity include state-of-charge (SOC) mismatches and capacity/energy (C/E) mismatches. In both cases, the total capacity of the battery pack is only up to the capacity of the weakest cell. In most cases, the cause of battery mismatch is imperfect process control and testing methods, rather than changes in the chemical properties of lithium ions themselves. Prismatic lithium-ion batteries (LiIonprismaticcell) require stronger mechanical stress during processing, and differences between batteries are more likely to occur. In addition, lithium-ion polymer batteries will also have differences between batteries due to the adoption of new processes.
The performance of series-connected Li-ion battery packs can be improved by employing cell balancing solutions to address SOC and C/E mismatch issues. The battery mismatch problem can be corrected by balancing the battery during the initial adjustment process. After that, it only needs to be balanced during the charging process, while the C/E mismatch must be balanced during the charging and discharging process. Although the product defect rate may be very low for a certain battery manufacturer, in order to guard against the problem of short battery life, we still need to provide further quality assurance.
Meaning of battery balancing
Portable devices with an operating voltage of 6V or above are powered by series-connected battery packs, in which case the total voltage of the battery pack is the sum of the voltages of the individual series-connected batteries. The battery pack of a portable computer is usually composed of three or four batteries connected in series, and the nominal voltage is 10.8V or 14.4V. In most of these uses, a single series-connected battery pack cannot supply the energy required by the device. At present, the largest battery (such as 18650) can supply 2,000mAh (milliamp middot; hour) energy, and the computer needs 50-60Whr (5,000-6,000mAh) energy, so it is necessary to connect three batteries in parallel for each battery in series.
Cell balancing refers to the application of differential current to different cells (or battery packs) in a series battery pack. The current of each cell in a series battery pack is usually the same, so additional components and circuitry must be added to the battery pack to achieve cell balancing. Only when the batteries in the battery pack are connected in series, and the batteries in series are equal to or greater than three levels, the battery balancing problem will be considered. Cell balancing is achieved when all cells in the battery pack meet the following two conditions:
1. Cell balancing is achieved when their relative states of charge are the same, provided all cells have the same capacity. SOC is usually expressed as a percentage of current capacity and rated capacity. Therefore, open circuit voltage (OCV) can be used as a measure of SOC. Provided that all cells in an unbalanced battery pack can be differentially charged to full capacity (balance point), they can be charged and discharged normally without any additional adjustments, usually one-time. When users use a new battery, they usually require to charge the battery for a long time, and this process actually includes a complete discharge-charge. This process minimizes the load and maximizes the battery charging time, reducing the demands on the battery balancing circuitry.
2. If the capacities of the batteries are different, they are also considered to be balanced when the SOC is the same. But SOC is only a relative value, and the absolute value of each battery capacity is different. In order to make the SOC of batteries with different capacities the same, it is necessary to use a differential current every time the batteries connected in series are charged and discharged. The normal charge and discharge time is shorter than the initial charge and discharge, and requires a larger current.
