Research On Rapid Evaluation Of Residual Value Of Decommissioned Lithium-ion Power Battery

In order to get rid of the double dilemma of environmental pollution and energy shortage,vigorously promoting clean electric energy to replace traditional fuel has become an important way for the green development of automobile industry.As a common source of power supply for electric vehicles,power batteries must be decommissioned when their comprehensive performance declines to insufficient to support the power requirements of electric vehicles.If a large number of decommissioned batteries are not properly and effectively handled,it will not only cause a waste of renewable resources,but also lead to the deterioration of social environment and frequent safety accidents.Therefore,if we can properly solve the problem of echelon utilization of power batteries,we can not only make full use of the life cycle of power batteries,but also further reduce the energy storage cost and effectively improve the level of resource recycling,so as to promote the long-term development of China’s electric vehicle industry.In this study,the basic performance of decommissioned lithium iron phosphate power battery under different conditions is explored through the constructed rapid detection platform of decommissioned power battery,a new electrochemical equivalent circuit model is proposed,a model for rapid evaluation of battery residual value is established,and a method for rapid screening and reorganization of decommissioned cells is also proposed.Firstly,in order to study the basic characteristics of decommissioned lithium iron phosphate power battery,a fast detection platform of decommissioned power battery with the functions of constant current and constant voltage charge and discharge,pulse charge and discharge,high and low temperature test and electrochemical impedance spectroscopy measurement is constructed.By designing various test schemes of decommissioned power batteries under different temperatures,different state of charge and different state of charge health,this study analyzes the correlation of decommissioned battery capacity,open circuit voltage,DC internal resistance and electrochemical characteristics with the surrounding environment and the actual state.It lays a foundation for the subsequent comparative study of equivalent circuit models,the rapid prediction method of SOC and SOH,and the research of rapid sorting and reorganization method.Secondly,based on the electrochemical impedance spectroscopy test results of decommissioned lithium-ion power batteries under different SOH and SOC,the fitting results of the newly constructed electrochemical equivalent circuit model and several equivalent circuit model parameters commonly used in the literature are compared and analyzed.The grey correlation analysis method between the slope and SOC parameters is improved.The analysis results show that the newly constructed equivalent circuit model can well fit the impedance spectra under different SOH and SOC.At the same time,the constant phase element has a close relationship with the SOH and SOC of decommissioned power batteries,indicating that it has the potential to further predict the health state of decommissioned power batteries.Thirdly,based on the analysis results of multiple groups of exploration experiments designed,the correlation model between health state and charged state and multiple characteristic parameters such as open circuit voltage and equivalent circuit parameters of electrochemical impedance spectrum is established,so as to judge the safety state and effectively predict the remaining life of decommissioned power batteries.The main research process is as follows: 1)Charge and discharge the decommissioned power battery of the recycling plant to determine the capacity;2)Analyze the capacity distribution and adopt high-temperature cycle gradient aging for some batteries to obtain decommissioned batteries with different health states;3)Discharge experiments with equal 10% SOC,equal 5% SOC and equal time interval were carried out on the fully charged decommissioned batteries with different SOH,and EIS test was carried out in the discharge gap;4)Analyze and process the experimental data,establish the EIS equivalent circuit model,and study the relationship between the parameters and the decommissioned battery SOH and SOC;5)The correlation model between SOH and SOC and multiple characteristic parameters such as open circuit voltage and equivalent circuit parameters is established to predict the health state of decommissioned batteries.The experimental results show that this method can greatly reduce the test time,save energy and realize the rapid estimation of battery with unknown state of charge and healthy state.Finally,Aiming at the problems of low screening efficiency,high energy consumption and low grouping rate of decommissioned power batteries at this stage,a fast screening and recombinant method based on short-time pulse discharge and electrochemical impedance spectroscopy for decommissioned power batteries(EIS)is proposed.More than 200 decommissioned lithium iron phosphate power batteries of the same type and different batches were tested and analyzed by short-time pulse discharge and EIS.Then,the obtained pulse voltage difference,DC internal resistance,EIS curve shape characteristics and EIS equivalent circuit model parameters are used as screening indexes,and a mathematical model is established to realize the rapid and effective sorting and reorganization of decommissioned power batteries.The experimental results show that this method has low energy consumption,the average test time of single cell is less than 20 min,and the consistency index is good after grouping,so it has great practical value in engineering.