Research On The Method Of Second Use Battery Screening And Comprehensive Performance Evaluation

With the purpose of coping with the restrictions of countries on China’s energy,the government vigorously promotes the development of electric vehicles.At the same time,a large number of vehicle power batteries are gradually eliminated.Even if it is retired,the vehicle power battery still has about 80% of the capacity.After scientific screening and classification,it can be used in other fields with low requirements on battery performance,which can maximize the life cycle value of lithium-ion batteries.However,Lithium-ion batteries have a wide range of application scenarios,leading to great inconsistency of retired batteries,and direct group use will cause safety problems to a certain extent.In this paper,the screening of second use lithium-ion batteries and the comprehensive performance evaluation method of second use batteries after screening are the research contents,and the following research is mainly carried out:(1)A series of performance tests were carried out on the lithium iron phosphate battery selected in this paper,including the residual energy detection of retired lithiumion batteries,capacity test at different temperatures,the discharge ohmic resistance test,and the battery charge-discharge temperature rise test at different temperatures and different rates.Through the above tests,the characteristics of lithium-ion batteries with different aging degrees under different experimental conditions are obtained,and the data obtained provides support for the comprehensive performance evaluation of the second use battery in the following steps.(2)The changes of Incremental Capacity Curve of batteries in different SOH under the influence of single factors at different temperatures and rates were studied.It was found that the indicators of the IC curves of different batteries had different degrees of divergence at different temperatures and rates,which indicated that there were some limitations in screening retired lithium-ion batteries only by capacity parameters has certain limitations.For second use batteries,the Incremental Capacity Analysis method can be adopted,Based on the principle of electrochemical reaction,combined with the residual energy detection data of lithium-ion batteries,the second use batteries can be screened into groups.(3)The improved fuzzy C-means clustering algorithm is used as the algorithm for second use lithium-ion batteries screening,and then some parameters of the lithium-ion batteries IC curves at different temperatures and different rates are extracted.Combined with the residual energy test data of lithium-ion batteries as the clustering object,the effectiveness index is used to determine the number of battery screening,the the battery screening category is determined by the effectiveness index.Then,the screened batteries are connected in series as the experimental group and the batteries screened by capacity screening method as the control group,and charge and discharge experiments are carried out at the screened temperature,and the effectiveness of this method is proved by comparing the voltage of each battery.(4)In view of the possibility that the performance of retired lithium-ion batteries may have some randomness,a comprehensive performance evaluation method of batteries with second use is proposed by combining the grey cloud model with randomness.Firstly,determine the evaluation index,and then use the gray system theory to divide each index into different gray categories,and then combine it with the cloud model theory to form a gray cloud model.At the same time,the subjective AHP method and the objective entropy weight method are combined to obtain the combined weight value of each battery performance evaluation index,which makes the index weight of cascade utilization lithium-ion battery more scientific and reasonable.The gray cloud model is used to obtain the gray category of each performance index of the second use lithium-ion batteries.Finally,the comprehensive performance evaluation value of each battery is obtained by combining the TOPSIS method and sorted.