Evaluation Of Discharge Performance Parameters Of Power Lithium Ion Batteries

With the rapid development of electric vehicles,lithium-ion batteries are widely used as power batteries in electric vehicles,and their development has attracted more and more attention.At present,there are many kinds of lithium-ion batteries on the market,and the quality of lithium-ion batteries varies from good to bad.The performance parameters of battery products are usually only battery power and battery voltage.For different manufacturers and brands of batteries,even if the battery parameters are the same,the actual performance of the battery often varies greatly.In the existing parameter system of commercial batteries,the parameters that can reflect the electrochemical performance and internal resistance of batteries are actually lacking.In this paper,18650 lithium-ion batteries are taken as the research objects,the structures and principles of lithium-ion battery are discussed,the performance models of lithium-ion battery are expressed,the performance parameters and measurement methods of lithium-ion battery are compared.The method of measuring the polarization curve of a fuel cell is applied to the process of researching lithium ion batteries.In this paper,the polarization curves of lithium ion batteries under different states of charge are measured,and the polarization surface maps reflecting the full performance of the batteries are obtained.By using a new electrochemical kinetic model,the polarization curves of lithium-ion batteries under states of charge are analyzed and fitted,and stable internal resistance values and parameters reflecting the electrochemical characteristics of lithium-ion batteries are obtained.Therefore,the discharge performance of batteries under different charging conditions can be expressed by three parameters:the electromotive force(E),the internal resistance(r)and the power factor(K),which can reflect the electrochemical performance of batteries.The performance parameters of batteries under different charging conditions can be used to reflect and compare the performance of different batteries.This study measured and analyzed 18650 lithium-ion batteries produced by companies such as Sony and Samsung,and obtained the polarization surface of the batteries which could reflect the performance of the batteries,as well as the performance parameters of the batteries under different charging conditions.Through this performance parameter diagram,the performance differences of different batteries can be well compared,and at the same time,the performance of the batteries can be better reversed.The variation of internal resistance and electrochemical performance of batteries during discharging was also shown.The polarization curves of the batteries can be simulated by the obtained performance parameters.The simulated values are in good agreement with the experimental values,which shows the rationality and correctness of using the electrochemical kinetic model to simulate lithium ion batteries.Also the performance parameters proposed in this study can well express the electrochemical performance characteristics and the characteristics of internal resistance.