The Study On The Correlation With SOH And Impedance Model Of Lithium Ion Battery

Lithium ion battery's SOH is influenced by many factors such as the working environment and the charging and discharging characteristics, so the time of the life cycle can't always achieve the suppliers'promise. It will cause huge economic losses by changing too early or affect the reliability of the system by changing too late. So accurately mastering the battery life state can surely access the best effect on the economy and reliability. Lithium ion battery's SOH is a long-term process, how to accurately measure SOH is a common concern of the battery-users.Many factors that affecting the SOH of the lithium ion battery are analyzed based on the study in the internal structure and working principle in this paper, it make clear the correlation between lithium ion battery's impedance and its SOH, Electrochemical impedance spectroscopy as an important experiment method is adopted in the research of the detection. With electrode dynamics theory and adopt the equivalent circuit of electrode based on electron movement theory, with the impedance model of battery which has specific meaning is established,with other apartment being considered. It is modified according to the actual situation in order to accord with the desired impedance model.Electrochemical impedance spectroscopy as an experiment method is adopted in this research. Combining the experiment of the lithium ion battery's cycle life span, the measure is done to get the SOH of the lithium ion battery by definition. Measuring the electrochemical impedance spectroscopy of battery through electrochemical instrument and getting data of the impedance by the impedance spectroscopy data is getted and analyzed by special electrochemical software Zsimpwin, then the impedance model parameters can be obtained. Through improving traditional genetic programming algorithm, and the accuracy of least-squares fitting method and according the experimental results, the effective experiment data can be analyzed and fitted by GA(Genetic Algorithm) and OLS to get the correlation between lithium ion battery's impedance and its SOH, then realize the forecast for the SOH of lithium ion battery.