Study On Performance Analysis And Remaining Life Of Second Use LiFePO₄ Battery

Currently,China's new energy electric vehicle industry is at a rapid developing stage.Power lithium-ion batteries as the core components of electric vehicles,the service period is only 5⁸ years.A large amount of retired lithium-ion batteries will be generated in the next few years.These retired lithium-ion batteries without proper treatment may cause a series of environmental and safety issues.The green recycling of lithium-ion batteries has become an urgent problem to be solved.The secondary use of retired lithium-ion batteries,as one of the effective means to solve the problems of battery recycling,has been recognized by industry and scholars and been encouraged and supported by national policies.However,in the process of the secondary use of retired lithium-ion batteries,the cycle aging performance,the aging mechanism and the remaining life of retired batteries have become the critical problem that constrains the use of these batteries in a large-scale.Based on the analysis of the aging mechanism of lithium-ion batteries,this thesis has designed experiments to study the cycle aging performance,aging mechanism and remaining life prediction of retired lithium-ion Li FePO₄ batteries during the secondary use,so as to provide technical and data.The main research contents of the paper are as follows:?1?The design of aging test program for the secondary used LiFePO₄ batteries.A test platform has been established for testing the residual energy of LiFePO₄ batteries and their internal resistance.Through the preliminary assessment of the health status of the retired LiFePO₄ battery,feasible batteries were selected for the secondary utilization test.By measuring the capacity and internal resistance of the battery,the battery charge-discharge rate during LiFePO₄ secondary utilization and the effect of different SOC cycle intervals on the lithium-ion battery health status were studied.?2?There are different aging mechanisms for lithium-ion batteries in different life cycles.Using the incremental capacity analysis and reconstructing the battery voltage curve,the aging mechanism of the phase-out phase of retired LiFePO₄ batteries is studied and analyzed.This provides theoretical guidance for rational,reliable and safe use charge-discharge strategies for retired LiFePO₄ batteries.?3?Aiming at the remaining life of the process of retired lithium-ion batteries,a Least Square Support Vector Machine?SVM?prediction model based on Bayesian model is firstly proposed to verify the feasibility of the prediction algorithm through the lithium-ion battery test data published by NASA Research Center.Then the retired LiFePO₄ battery cycle aging test was designed for the collection of battery capacity degradation data,using the proposed algorithm model to predict the remaining life of the retired LiFePO₄ battery.