Aging and Electrode Inhomogeneity in Commercial 18650 Lithium-Ion Cells during Long-Term Cycling

Abstract

Li-ion battery production has increased dramatically in the past decade. The concerns over the limited source and environmental impact suggest the recycling of Li-ion battery after usage, especially the functional ceramic oxide cathode materials. Recently, a new approach to recycling cathode materials has been investigated: direct recycling method. The key concept of this method is that the aged cathode materials are chemically and/or thermally re functionalized, and we have previously reported that the properties of the aged cathode materials, including level of lithiation,1 SEI layer,2 and surface reconstruction layer,3 can have an effect on the direct-recycled cathode materials. As such, in this work, we characterized the aging level, in terms of chemical, physical and electrochemical properties, of cathode materials (NCA) harvested from 18650 cells after long-term cycling under different conditions. Specifically, different charge protocols and testing temperatures were used. Different failure mechanisms and rates capacity loss were observed, which we document and explain using a phenomenological model Additionally, we observed significant area-specific inhomogeneities in the cycled electrodes; certain patterned regions of were found to have different degrees of SEI formation as well as different degrees of lithiation. The potential mechanism behind this phenomenon will be discussed. Reference: Wang, Han, and Jay F. Whitacre. "Direct Recycling of Aged LiMn2O4 Cathode Materials used in Aqueous Lithium‐ion Batteries: Processes and Sensitivities." Energy Technology.Xiong, Xunhui, et al. "Washing effects on electrochemical performance and storage characteristics of LiNi8Co0.1Mn0.1O2 as cathode material for lithium-ion batteries." Journal of Power Sources 222 (2013): 318-325.Jung, Sung‐Kyun, et al. "Understanding the degradation mechanisms of LiNi5Co0.2Mn0.3O2 cathode material in lithium ion batteries." Advanced Energy Materials4.1 (2014): 1300787. Figure 1