DEGRADATION ANALYSIS OF LITHIUM-ION BATTERIES WITH KNEE POINTS

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2021

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Abstract

The commercialization of lithium-ion batteries has enabled applications ranging from portable consumer devices to high-power electric vehicles to become commonplace. The capacity, which has been used to determine if lithium-ion batteries have reached the end of life, decreases during usage (cycling) and storage (rest). After some charge-discharge cycles, the capacity fade rate has been observed to increase, and the capacity fade curve visibly bends, the onset of which is described as a knee point. The occurrence of the knee point during the useful life of the battery leads a shorter life than expected based on the initial capacity fade rate.

Although various degradation mechanisms are generally known in the literature, the degradation mechanisms responsible for the knee point phenomenon have been in contention. Understanding why and when the knee point will appear on the capacity fade curves is valuable to battery manufacturers and device companies to predict or mitigate the knee point. This study presents the degradation behavior with knee point identification algorithms, experimental analysis that identifies the degradation mechanisms for the knee point, and accelerated aging tests and modeling methods to predict the capacity fade trend, including the knee point. Finally, this study discusses how to delay the knee point from chemical design perspectives and how battery users should qualify batteries

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