Determination of retirement points by using a multi-objective optimization to compromise the first and second life of electric vehicle batteries

Abstract

Reusing the retired batteries of electric vehicles (EVs) in the second life applications can improve the economic and environmental benefits of the whole life cycle of batteries. It is imperative to accurately identify the retirement points of the reusing EV batteries for the second life applications. A quantitative method to determine the retirement points of the EV batteries was proposed in this work, which features the compromise between the first life application scenario in electric buses and the second life application scenario in energy storage systems. A multi-objective optimization approach is adopted to obtain the optimal retirement points by minimizing the total cost of the electric bus (TCB) and the total cost of the energy storage system (TCE) simultaneously. The Pareto fronts of the TCB and the TCE and a trade-off strategy were obtained by using the ε−constraint method and the evaluation function method to solve the proposed multi-objective optimization problems. A case study was employed to verify the effectiveness of the proposed method. The influence of the end of life points of the batteries on determining the retirement points of the batteries was also analyzed and discussed. The results show that the selection range of the retirement points depends upon the two ends of the Pareto front, which are the minimum TCB and the minimum TCE, respectively. The decrease of the end of life of the batteries narrows the selection range of the retirement points of the batteries. The proposed strategy is a quantitative analysis tool to determine the retirement points of reusing batteries in different application scenarios.