Research On Characteristic Parameters And Performance Evaluation Of Power Lithium-Ion Batteries

In recent years,new energy vehicles have been developed rapidly,and as the core component of new energy vehicles,the performance of batteries has attracted much attention from the world.At present,the expression of battery performance is mostly focused on the study of battery capacity,internal resistance,health status,and aging,and there is a lack of a parameter system to express the electrochemical kinetic performance characteristics of batteries.Based on this status,the group proposes a new polarization curve model to evaluate the battery performance based on the principle of electrical power conservation and uses three physical parameters to evaluate the battery performance.The group applies the concept of fuel cell polarization curve to the performance evaluation of lithium-ion batteries by measuring the polarization curves of the batteries under different charge states to obtain a polarization surface that reflects the full performance of the batteries.In the actual polarization curve fitting process,there is a problem that the fitted electric potential is smaller than the open-circuit voltage;in this work,based on the study of previous data and methods,it is found that the key factor causing this problem is the neglect of the offset of the charge state during the polarization curve measurement,and the method of using the feeder to measure the battery polarization curve is proposed to address this problem.Through extensive experiments,it is shown that this method can reduce the loss of battery energy during curve measurement,which can well solve the above problem and improve the accuracy of curve fitting.When the new model is used to fit the polarization curve of a powerful Li-ion battery,there will be too large an electric power conversion coefficient and a very small internal resistance value,which affects the results of battery performance evaluation.To address this problem,this work proposes the use of a battery series measurement method.The method establishes a theoretical relationship between the discharge characteristics of a single battery and a series battery,which can reduce the electrical power conversion coefficient and increase the internal resistance value,and effectively improve the accuracy of the fitted parameters;the method is verified by establishing simulations and testing the polarization characteristics of the series battery,and the test results show that there is a quantitative relationship between the series battery and the discharge characteristics of the single battery.Finally,based on the battery performance evaluation method developed in this work,the discharge characteristics of six common ternary material 18650 power Li-ion batteries on the market were evaluated to study the changes in battery performance after over-discharge.The test results show that the method can accurately express the discharge performance characteristics of the battery and can evaluate the performance of the battery,which has some practical engineering application value.