The Health Parameter Estimation Method for LiFePO₄ Battery Echelon Use

The echelon use of aged batteries is one of the key issues after the development of electric vehicles, In this paper, LiFePO₄ secondary battery is regard as the research object, based on the pseudo-two-dimensional electrochemical reaction mechanism model, the battery terminal voltage is simulated and analyzed under different charge-discharge rate and working conditions, it can be concluded that the over-potential of battery terminal voltage is approximate constant under the low constant current or pulse current working condition. Based on this phenomenon, the method for the battery health status characteristic parameters extraction is designed. Firstly, the battery capacity parameters are estimated based on the nonlinear least squares method under the low rate constant charge-discharge current. Then, combined with battery open circuit voltage and internal impedance estimation method, the extraction of battery impedance characteristic and capacity characteristics parameters under pulse conditions are realized. Finally, the method is verified by the experiments, this article can provide a basis method for LiFePO₄ battery health state evaluation, re-classification, and re-use.