How to ensure the consistency of the 18650 battery pack?button cell battery cr1620

　　Everyone knows that electric vehicles and large energy storage devices nowadays are composed of many 18650 batteries, so how can we ensure that each battery in our battery pack can match consistently? Currently, in the industry, batteries are screened through a series of parameters such as capacity, voltage, and internal resistance. This screening process is complex and has limitations, such as measurement errors. The current measurement error in China is around 1%, which cannot meet the market demand for power batteries. So the Energy Research Institute of Tsinghua University proposed a new screening method: to screen batteries through series charging and discharging curves. Because in fact, the charge discharge curve itself reflects all the parameters of the battery. If the parameters are different, there must be differences in the charge discharge curve. On the contrary, if all the parameters of the battery are theoretically the same, then the charge discharge curve should be exactly the same.

　　A combination power battery is never a single battery, just like a Tesla car battery, which consists of approximately 9600 Panasonic 18650 lithium batteries combined in series and parallel, making battery consistency the most important issue. Due to the differences in the parameters of each battery cell, there will be differences in its working state. If not controlled, it will damage the battery and cause safety issues; But with control, the capacity cannot be fully utilized.

　　So only by combining multiple 18650 lithium batteries in series and parallel, and conducting consistency screening, can we effectively distinguish the consistency of the batteries. Series charging and discharging refers to the charging and discharging of factory batteries after being connected in series. This type of screening has many advantages, as it only needs to select a voltage for screening, with relatively simple parameters and is simple and fast. In traditional screening, devices with current accuracy less than 1% are very expensive, while the absolute values of series currents are the same. By using the series charging and discharging method for screening, equipment errors can be avoided. The Pinshangtong R&D team selected five typical batteries, including two Korean manufacturers and one Japanese manufacturer. Through comparison, it was found that the weight error is the biggest difference between domestic and foreign batteries, mainly reflected in the liquid injection process, and the amount of electrolyte inevitably affects consistency. Therefore, compare the discharge situation, that is, put it at the lowest voltage to see the voltage of each battery, and then stand still for 30 minutes to see the rebound VC voltage. Because static is generally used to study the impedance characteristics of batteries, the voltage of static rebound is actually a very important factor in battery characteristics. These points are also the largest among all curve voltages. However, when these points are compared together, it can be found that the voltage dispersion at the discharge end is relatively large, If the voltage at the discharge end is used for consistency screening, only one parameter can be used to screen battery consistency. Then compared to other curves, the research team found that the voltage at the discharge end was the most excellent for consistency screening. Using this method to test the above five batteries, it is evident that Japan's battery consistency indicators are the best, while China and South Korea have similar levels of consistency, all lagging behind Japan. Taking Korean batteries as an example, after screening the series connection of batteries, it was found that the performance of their battery pack was almost the same as that of individual cells. This also once again proves the effectiveness and convenience of this series parallel screening method.

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