Research on the consistency of the power battery based on multi-points impedance spectrum

For the great need of the high power output and high capacity power battery of electric vehicle, this article presents a method which classify the battery by EIS, and this method can get more information about the dynamics and electrode interface structure than the traditional ones. In order to make it closer to actual production, improvement was made for the disadvantages of the long time consuming and difficulty in sorting. Select a specific spectrum to measure the battery impedance, and use the results to simulate the impedance curve, and then sort the batteries. The actual data have showed that the method is efficient in batteries sorting. Through measuring the EIS of the lithium battery, this article established a reasonable equivalent circuit. By setting the categories range of the equivalent parameters, this is a reasonable sorting method at the moment. However, the long time required makes it impossible to be used in production. To solve the problem, a new method, multi-points EIS is introduced. It just selected some characteristic frequency points in the impedance cure, and it substitutes point for line in the test. The selection of spectrum point plays a vital role in the multi-points EIS sorting, and spectrum point may vary with the internal structure of the battery. EIS curves of the battery are composed of circle and lines, so Hough transform algorithm is use identify the curve and get an approximate subsection equation. After repeated tests and experiments, it won´t effectively fit the original state of the battery impedance and calculate the equivalent circuit when the test points are less then five. Test results have shown that multi-points EIS improve the accuracy of battery sorting; therefore it has great practical value. This method can explore the internal structure of the battery, reduce test time and simplify the sorting steps, providing a new ways for the development of battery management system.