Study On Identification Of SEI Film Model And Charging Pattern For Lithium Battery

As a new energy battery,lithium ion batteries offer several advantages including high open circuit voltage,high energy density,high charging rate and good safety,have been applied in electric driven vehicles.The solid electrolyte interface(SEI film)formed during the formation of lithium batteries is crucial to the performance of lithium batteries.However,different charging and discharging strategies lead to the difference of SEI film's morphology and electrical characteristics.Using the traditional constant-current and constant-voltage charging method(CC-CV),SEI film is thicker and not compact,resulting large capacity loss and longer charging time in the formation of the battery.These problems hinder the popularization and application of Li-ion battery.To deal with problems of CC-CV,the SEI electrochemical model was established in this paper based on the study of the formation mechanism of the solid electrolyte interface.The optimal charging mode based on dynamic programming algorithm and the optimal 5 constant current charging mode based on particle swarm optimization(PSO)and fuzzy control algorithm have been studied for shorter charge time and better performance of the film.The specific contents are as follows:(1)A SEI electrochemical model was established and simplified and SEI membrane electrical parameters were obtained through analyzing the formation of the film.MATLAB software was used to simulate and analyze the model;(2)Using dynamic programming algorithm and electrochemical lithium battery model,the ideal optimum charging curve was obtained considering the performance of SEI film;(3)The corresponding experimental environment was built,mainly including the construction of the software part.The optimal 5 stage constant current charging mode was obtained through PSO.By analyzing results and changing the weight of PSO,the number of experiments was shortened by 50%.Finally,the comparison between the optimal 5 stage constant current charging method and the optimal charging mode based on dynamic programming algorithm was carried out,then the optimal 5 stage constant current charging method was validated.Through charging and discharging test,the optimal 5 stage constant current charging method was compared with the traditional CC-CV.The charging time was shortened by 17.8%,and capacity loss and the thickness of film was smaller compared with the CC-CV.The optimal 5 phase constant current charging mode is better than the CC-CV for cycling performance through cycling test.