Abstract
Lithium-ion batteries are widely used as basic power supplies and storage units for large-scale electric drive products such as electric vehicles. Their reliability is directly related to the life and safe operation of the electric drive products. In fact, the cells have a dependent relationship with the degradation process and they affect the degradation rate of the entire battery pack, thereby affecting its reliability. At present, most research focuses on the reliability of battery packs and assumes that their cells are independent of each other, which may cause the reliability of the evaluation to deviate greatly from the actual level. In order to accurately assess the reliability of lithium-ion batteries, it is necessary to build a reliability model considering the dependency among cells for the overall degradation of lithium-ion battery packs. Therefore, in this study, based on a lithium-ion battery degradation test, the Wiener process is used to analyze the reliability of four basic configurations of lithium-ion battery packs. According to the degradation data of the battery packs, the Copula function is used to quantitatively describe the dependent relationship in the degradation process of a single battery, and the quantitative dependent relationship is combined with the reliability model to form a new reliability model. Finally, taking the battery system of Tesla S as an example, a feasible optimization method for battery pack design is provided based on the model constructed in this work.
Highlights
Lightweight energy storage devices such as lithium-ion batteries and supercapacitors have been widely utilized in electric vehicles, aerospace applications, submarines, and other power fields [1]
Accurate knowledge of the reliability of the battery packs is vital in order to ensure the long life of the electric drive product
By investigating the methods of dependency quantitative analysis, we found that the Copula function is a widely used statistical tool for describing the dependency and reliability of multi-component systems, and this function can be used in the research of dependency measurements [11]
Summary
Lightweight energy storage devices such as lithium-ion batteries and supercapacitors have been widely utilized in electric vehicles, aerospace applications, submarines, and other power fields [1]. As an important clean energy source, lithium-ion batteries have advantages of high energy density, high capacity, low self-discharge rate, good safety, long life, and no pollution. Hundreds of cells are connected, both in series and in parallel, to form battery packs in order to meet the voltage and energy requirements of electric drive products. The reliability of the battery packs is directly related to the overall performance of the electric drive products. For this reason, accurate knowledge of the reliability of the battery packs is vital in order to ensure the long life of the electric drive product. Previous studies have found that the dependency among cells during battery
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