The role and significance of high-speed discharge equalization for button cell battery cr2025 with consistency problems

　　Charge balancing can only solve the problem of fully charging the battery pack. The actual released power still depends on the smallest capacity battery in the battery pack. Discharge balancing solves the problem of unified deployment of all battery capacities, which can maximize the safe utilization of capacity and optimize the capacity. Optimization, this article explains the importance of balanced discharge through the actual balanced discharge data of two strings of button cell battery cr2025.

　　Battery pack consistency issues

　　The consistency problem of the battery pack is always a lingering pain in the battery management industry. The consistency problem not only reduces the actual discharge capacity of the battery pack, but also affects the power output and battery life of the device. In severe cases, "thermal runaway" may occur. "problems, leading to malfunctions.

　　Based on the principle of safe discharge, the releasable power of the battery pack depends on the battery with the smallest capacity in the battery pack, similar to the "barrel effect". The more strings of batteries, the greater the impact. Take 100 strings of 100Ah lithium button cell battery cr2025 as an example. If the capacity of one string of batteries drops to only 80Ah, then the available capacity of the battery pack is only 80Ah. About 20Ah of capacity cannot be used, which is equivalent to 1/5 of the capacity being wasted. , it is a pity that it cannot be used. The actual charge and discharge rate of the attenuated battery will be higher than the average current of the battery pack, and the attenuation will enter the acceleration channel and form a vicious cycle. The result of the vicious cycle is that the capacity of the battery pack decreases rapidly, accompanied by a serious risk of thermal runaway.

　　Now, the whole world is improving the unit capacity of lithium batteries through technology research and development, but due to technical and other reasons, progress is slow, and the capacity of existing large-capacity button cell battery cr2025 cannot be fully utilized due to consistency issues. In addition to battery production In addition to battery differences caused by factors, temperature during use, high current charging and discharging, and battery management failure will all cause this problem.

　　The decrease in discharge capacity corresponds to a decrease in charging capacity. If it is a vehicle battery pack, the battery will be severely attenuated and the cruising range will be severely reduced.

　　Difficulties in battery balancing technology

　　As far as current battery management technology is concerned, the only technology that can solve the problem of battery pack consistency is battery balancing technology. To fully utilize the battery capacity, the battery equalizer must support discharge equalization, charge equalization and static equalization at the same time. In addition, due to the existence of batteries with different capacities, there is a high voltage difference at the end of charge and discharge. Therefore, the battery equalizer It must also have a wide balancing current and high power conversion efficiency, which can both achieve efficient balancing and reduce losses during full utilization of capacity.

　　The good news is that the battery balancing technology with this technical requirement has been developed by the author after many years of research. After continuous improvement, the performance is getting better and better. A very large balancing current, 5A, can be obtained with a small voltage difference. The design of balancing current within 10~15A can achieve 1A/13mV; the design of 10~15A balancing current can achieve 1A/10mV, thereby achieving high-speed balancing. The distinct advantage of this technology is that it supports both high-speed discharge balancing and high-speed charging balancing, which is a lot Battery equalizer technology does not have it. During the high-speed discharge equalization period, the excess battery capacity released by the large-capacity battery does not pass through the small-capacity battery, but directly enters the discharge channel to supply power to the load. Due to the reduced actual discharge current of the small-capacity battery, the battery temperature rises significantly due to internal resistance. This reduces the risk of thermal runaway.

　　The most important significance of high-speed discharge equalization is to maximize the battery capacity and make full use of the capacity that should do work, such as the 99-string 20Ah capacity in this example, rather than leaving it idle. The true sense of high-speed discharge equalization includes many aspects: real-time equalization, support for large current equalization, and high power conversion efficiency.

　　Still taking the battery pack in this example as an example, assuming that the discharge current of the battery pack is 0.2C, that is, 20A, then the maximum balancing current of the equalizer in this article only needs to reach 4.5~5.0A to satisfy the safe discharge of the battery pack, and all 20Ah The power can be released normally as needed. Similarly, if the discharge current of the battery pack is increased to 0.4C, that is, 40A, the maximum balancing current needs to be 9 to 9.5A. Ordinary battery equalizers cannot meet the requirements, and the synchronous rectification technology used in this article has real-time high power and high efficiency. A transferable battery equalizer can handle this with ease.

　　The greater the balancing current, the stronger the overcharge and over-discharge protection capability of small-capacity batteries, the safer the battery pack operates, and the greater the difference between batteries is allowed.

　　High-speed discharge equalization example

　　The main function of high-speed discharge equalization is to shunt the discharge current of large-capacity batteries to make up for the lack of discharge capacity of small-capacity batteries. The following is an analysis of the balanced charge and discharge examples and data of a group of button cell battery cr2025 with very different capacities. Due to the difference in battery capacity, Therefore, under the condition of high-current balanced charge and discharge, the actual charge and discharge currents of the two batteries are very different, and the difference is very obvious.

　　Figure 1 shows the battery pack of the experimental device. The capacity of the 18650 battery (B1 battery) is only 1Ah, and the capacity of the blue square battery (B2 battery) is as high as 11Ah. The capacity difference is as high as 10Ah, a difference of 10 times. The current total discharge current is 5A. The device under the clamp ammeter is a prototype of the high-efficiency high-power equalizer described in this article, which uses the original "bidirectional synchronous rectification technology" (see the attachment "Bottlenecks and Solutions Affecting Battery Balanced Current and Balanced Efficiency - Bidirectional Synchronous Rectification Technology" "), with the intervention of the equalizer, the balancing current is as high as 9.08A (there is a measurement error, the same below), as shown in Figure 1; the actual discharge current of the square lithium battery is as high as 9.82A, as shown in Figure 2; and 18650 The actual discharge current of the battery is only 0.87A. As shown in Figure 3, under the action of the strong balancing current, the maximum voltage difference is only 0.11V. By the end of the discharge, the two batteries have been completely discharged, and the discharge voltage of the 18650 battery is still Within the safe voltage value.

　　High-speed charging equalization example

　　This battery balancing technology not only supports high-speed discharge balancing, but also supports high-speed charging balancing. Taking the above battery pack as an example, during the same period from 5A constant current charging to automatic switching to constant voltage charging, the 5A current that should pass through the B1 battery The measured maximum charging current is only about 0.84A, as shown in Figure 4; while the measured charging current of the B2 battery is as high as about 8.8A, as shown in Figure 5; the measured maximum balancing current is as high as about 7.97A, which is just close to the two batteries The difference in actual charging current of the battery is shown in Figure 6.

　　During the equalizing charge, the voltage rise rate of the two batteries is basically the same. The maximum voltage difference is only about 0.11V. The maximum voltage of the B1 battery is only about 4.23V, which is always within the safe voltage. The equalizer prototype is under continuous high current balancing. There is only a slight temperature rise, which is why the prototype uses an ABS plastic casing.

　　The ratio of the actual discharge capacity of the battery pack to the initial capacity reflects the operating efficiency of the battery pack. The larger the ratio, the better the health of the battery pack. Charge balancing technology can only fully charge the battery pack, and the actual discharge capacity depends on The battery has the smallest capacity, and the intervention and intervention of discharge equalization maximizes and optimizes the utilization of battery capacity. It can be said that discharge equalization determines the maximum discharge capacity and capability of the battery pack, which is of more practical significance.

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