The Research Of The Battery Consistency Based On Multi-spectral Method

The electrical power field which is electrical vehicles-based has a rapidly increasing demand for power batteries currently. And the batteries should be assembled to achieve the high power output and high-capacity requirements. However, the inconsistency in single cell battery pack in the initial performance will accelerate the decay of single battery capacity, and Increase internal resistance, further premature battery failure. Finally, it will result in material waste. Therefore, it is necessary to improve the consistency of cell battery during sorting group.Detections technology at this stage mainly against the external characteristics of the battery, limits the multiple characteristic measured values within a certain range to ensure the consistency of the battery comprehensive performance. The electrochemical impedance spectroscopy (EIS) in this article can detect the internal electrode structure of the battery systerm without damaging the battery, and reflect the internal details such as the condition of the battery, electrolyte concentration, the deterioration level of the exchange membrane accurately. In this way, it can ensure the compatibility of internal structure of sorted batteries, and increase accuracy greatly, so as to solve the shortage of the traditional detection methods.This article uses the lithium-iron phosphate power batteries as the study object, analyses the measurements of the EIS making use of the class circle target recognition algorithm, and builds the impedance equivalent circuit of the lithium iron phosphate power batteries. In order to solve the time-consuming of the EIS's measurement, I propose multi-spectral analysis based on EIS, which use the figure of the EIS as the theoretical basis, measure the impedance response at particular spectrumpoints, and calculate the equivalent circuit model parameters of the batteries using the least-squares fitting. Because EIS curve is smooth, coherent and regular, using fewer frequencies can improve accuracy, shorten time and reduce the number of step. Through the study, the steps of the conformity analysis and the frequencies are determined by repeat comparison, which proves the consistency and practicality of the multi-spectral method by MATLAB simulation software and testing the actual batteries'lifetime.For the combined use of the batteries, multi-spectrum method is fast non-destructive and energy-saving. It can sort the batteries whose performances close to each other and assemble them.It can make each group batteries achieving the best state, improve the efficiency of every battery, extend the lifetime of each group batteries, and reduce the repair costs. It has proposed a new direction for the practical application.