Research On Modeling Of Lithium-Sulfur Batteries And Battery Universal Model

Lithium-ion batteries play an important role as the key part of energy supply of electric vehicles(EVs).But due to their intrinsic lower energy density(200-250Wh/kg),it restricts the mileage of EVs and further hinders the popularization and development of EVs.With the advantages of high energy density(2600Wh/kg),low cost(S is abundant in natural environment)and environmental benignity,lithium-sulfur batteries have been attracted great interests in recent years.The battery model connects both the internal and external characteristics of batteries,which is the theoretical basis of battery monitoring in BMS(Battery Management System)and ensures the safe and reliable operation of batteries.Therefore,battery modeling is necessary for the application of batteries.Thus,in this paper,several studies on the modeling of lithium-sulfur batteries were conducted from the view of equivalent circuit model,based on their particular charging-discharging mechanism and relevant test results.Besides,we proposed the concept of universal battery model according to the various existing battery models.The detailed research and achievement are as follows:Firstly,the basic structure and working principle of lithium-sulfur batteries were described.And then experimental tests on relevant characteristic were carried out to provide the theoretical basis for battery modeling and parameter estimation.It is essential for determining the specific implementation details of the experiment(such as temperature,current rate and static time).Secondly,based on the current modeling of lithium-ion battery modeling and the obtained background knowledge of lithium-sulfur batteries,lithium-sulfur batteries modeling were established first-order and second-order equivalent circuit simultaneously from the view of the impedance spectrum characteristics of each SOC(State of Charge)point.Model parameters off-line identification were conducted based on the interval constant current charging-discharging test.Corresponding simulation platform was built according to the characteristics of lithium-sulfur batteries and then the model was verified by simulation through both constant current condition and dynamic condition.The results showed that the first-order RC equivalent circuit model is more suitable for lithium-sulfur battery modeling.Thirdly,based on the cycling life test of lithium-sulfur batteries,the applicability of lithium-sulfur battery model in its whole life cycle was comprehensively analyzed for the first time.Theoretically analysis on the variation of model parameters during aging was also studied.Based on the result,the corresponding relationship between the parameters and cycle times was finally established.Finally,according to the established lithium-sulfur battery model and the existing models of different types of batteries,model topology was finally summarized and the universal battery model was concluded.