Recently, Professor He Xiangming from the Energy Research Institute of Tsinghua University gave a speech on "Consistency and Safety of Lithium Ion Energy Storage Batteries" and introduced a new way to screen consistency: screening batteries by series charge and discharge curves. Because the charge-discharge curve itself reflects all the parameters of the battery. If the parameters are different, the charge-discharge curve must be different. On the contrary, if all the parameters of the battery are theoretically the same, then the charge-discharge curve should be exactly the same.
Consistent screening by series charge and discharge
The so-called series charge and discharge is that the factory battery is connected in series and then charged and discharged. This kind of screening has many advantages. It only needs to select a voltage to be screened. The parameters are simple and simple. In the conventional screening, devices with current accuracy less than 1% are very expensive, and the currents in series are the same, and are filtered by series charge and discharge methods, so that equipment errors can be avoided.
The research team selected five typical batteries. Two Korean manufacturers and one Japanese manufacturer found that the weight error is the biggest gap between domestic and foreign batteries. This gap is mainly reflected in the injection process, and the electrolyte Inevitably, the impact will be consistent.
In contrast to the discharge situation, the voltage of each battery is viewed at the lowest voltage, and then the rebound voltage is observed for 30 minutes. Because statics are 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 of all curve voltages, but these When all the points are put together, the voltage rate dispersion at the end of the discharge is relatively large. If the voltage at the end of the discharge is used for the continuous screening, the battery consistency can be screened with only one parameter.
In addition, comparing the other curves, the team found that the voltage at the end of the discharge was the best for consistent screening. Using this method to test the above five batteries, it can be clearly seen that Japan's battery consistency indicators are the best, and China and South Korea are similar in level of consistency, both behind Japan. Taking the Korean battery as an example, after the battery was screened in series, it was found that the performance of the battery pack was almost the same as that of the single cell. This again proves the effectiveness and convenience of this screening method (only one parameter).
Consistent screening by means of series charge and discharge is simple, fast and effective, because the current of each battery is absolutely the same, so the influence of equipment error on consistency screening is eliminated. It is easier to perform statistics and comparisons by using only one voltage indicator to judge consistency. In addition, due to the relatively high voltage of the device, it can generally be 600-500 volts, which can easily return the discharged electricity to the power grid, thus saving energy.