Comprehensive analysis of lithium-ion cells and their aging trajectory toward nonlinear aging

Abstract

More than 30 years after the market introduction of lithium-ion batteries, research still struggles to understand the complex interplay of different aging mechanisms that can lead to a sudden drop in usable capacity. Understanding this nonlinear aging behavior is important to develop optimal strategies regarding the cell design and operation. In this work, we present an extensive analysis of a cycle aging test comprising 62 commercial large-scale pouch-bag type cells in a constant force bracing. The dataset includes eight cells, which exhibit nonlinear aging. Nondestructive methods, such as differential voltage analysis, reveal that the capacity loss is limited by the loss of lithium inventory, which is not homogeneous within the cell . With destructive post-mortem analysis we observe that aging is focused toward the center of the anode. Occurring lithium-plating seems to intensify with aging at high temperatures. Our results point toward a two-step mechanism, where elevated temperatures drive SEI-growth at the electrodes’ center, which, in turn, impair mass transfer kinetics and lead to the deposition of metallic lithium. Ultimately, our work can help to identify the most relevant mechanisms and interactions that provoke nonlinear aging.