Electrochimica Acta, Volume 431, September 2022, 141143, DOI:10.1016/j.electacta.2022.141143

Degradation Modes and Mechanisms Analysis of Lithium-ion Batteries with Knee Points

Weiping Diao2, Jonghoon Kim1, Michael H. Azarian2 and Michael Pecht2
1 Department of Electrical Engineering, Chungnam National University, Daejeon 34134, South Korea
2 Center for Advanced Life Cycle Engineering, University of Maryland, College Park, MD, 20742, USA

For more information about this article and related research, please contact Prof. Michael G. Pecht


The capacity of lithium-ion batteries decreases during usage (cycling) and storage (rest). After some initial charge-discharge cycling, 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 above the end-of-life capacity threshold leads to a shorter life than expected based on the initial capacity fade rate. Although various degradation mechanisms and their effects on lithium-ion batteries are generally known, the degradation mechanisms for the knee point phenomenon have been in contention in the literature. In this paper, aging tests are conducted on custom three-electrode lithium-ion pouch cells to distinguish the contribution of all degradation modes to the cell's capacity fade and determine the one that causes the knee point, which is the acceleration of cathode resistance increase due to the increased degradation rate in cathode interfacial kinetics. Incremental capacity analysis and destructive analysis were further conducted to determine the degradation mechanisms that lead to the acceleration of cathode resistance increase.

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