Study On Aging Characteristics Of Ternary Lithium Ion Batteries Under Different Charge And Discharge Strategies

High nickel ternary lithium-ion power battery is an ideal power battery for electric vehicles due to its high energy density and good low temperature performance.However,the safety problems caused by thermal runaway have attracted increasing attention in recent years.Since the battery aging has a direct impact on the thermal safety of the battery,in order to study the influence of different factors on the battery aging,the control variable method is adopted in this paper.The ternary NMC811lithium-ion battery is taken as the research object,and the cycle characteristics of the battery under different charge and discharge strategies are studied.The influence of cycle conditions such as charge rate,discharge rate and charge and discharge interval on the aging process of the lithium-ion battery is mainly studied,and the relationship between capacity attenuation,internal resistance change and battery aging characteristics is also studied.The main research contents and conclusions are as follows :(1)Aiming at the problem of battery cycle capacity attenuation under different charging and discharging strategies,the difference of battery cycle capacity attenuation under different charging rates,different discharge rates and different charging and discharging intervals was analyzed.The results show that the charging rate has the greatest impact on the battery capacity attenuation.When the capacity attenuation is the same,the cycle number of 2C charging is about half that of 1C charging.According to the difference of capacity attenuation law in different stages,discharge rate has little effect on battery capacity attenuation.Different charge and discharge intervals also have a great influence on the battery capacity attenuation rate,and the battery capacity attenuation is the fastest under the full charge and full discharge modes.In the process of battery capacity attenuation,there are generally two inflection points.Before reaching the first inflection point,the battery capacity decays rapidly.After reaching the first turning point,the battery capacity decay is more linear.Then reach the second turning point,the battery capacity decay parabolic trend.(2)Combined with two non-destructive internal resistance test methods,i.e.,hybrid pulse power performance test and electrochemical impedance spectroscopy test,the internal resistance of batteries in different aging states was tested,and the variation characteristics of internal resistance were studied.The results show that with the increase of cycles,the increase trend of polarization resistance is more intuitive,while the ohmic resistance is on the increase trend as a whole,but its numerical fluctuation is large.According to the analysis of electrochemical impedance spectroscopy,the increase of charge transfer resistance in polarization resistance is the main reason for the increase of polarization resistance.During the cycling test,the active particles inside the lithium ion battery are continuously embedded / deembedded on the electrode material,the interface structure of the electrode material is constantly changing,and the internal resistance characteristics of the battery are constantly changing.(3)Finally,particle filter algorithm is used to predict the development trend of lithium-ion battery health status.The health status development data of three batteries were selected to train the prediction model and obtain the initialization model.The particle filter algorithm is used to update the model parameters according to the real-time data of lithium-ion batteries to be predicted No.4 and No.5,and predict the development trend of the healthy state of the battery.By analyzing the error between the predicted data and the experimental data,the prediction accuracy of the particle filter algorithm under different future cycles of the battery was studied.