Heterogeneity of the Dominant Causes of Performance Loss in End‐of‐Life Cathodes and Their Consequences for Direct Recycling

Direct recyling of Li-ion battery materials promises a low-cost path towards a secure domestic supply of critical materials for batteries. Using cathode material from an end-of-life commercial Li-ion cell, this work identifies the primary degradation mechanisms that diminish the performance of directly reused cathode materials and includes a discussion on what is needed to overcome such limitations.

Abstract

Recycling Li-ion batteries from electric vehicles is critical for reducing costs and supporting the development of a domestic battery supply chain. Direct recycling of cathodes, like LiNi _x Mn _y Co _z O₂ (NMC), is attractive due to its low cost, energy use, and emissions compared to traditional recycling techniques. However, a comprehensive understanding of the active material properties at end-of-life is needed to guide direct recycling processes and the performance-dependent reuse applications. Here, NMC material from an end-of-life commercial pouch cell is characterized and bench-marked against pristine non-cycled counterparts with respect to capacity, impedance, crystallography, morphology, and microstructure to identify major degradation modes and understand variability in the end-of-life material. The spatial heterogeneity of each property throughout the cell is also quantified. While the degraded material demonstrated similar capacity as the pristine, its impedance and rate capability are severely diminished. Furthermore, samples from the periphery of the electrode layers showed more severe performance loss compared to samples extracted from central regions. The dominant culprit of performance loss is the material microstructure, where the magnitude of particle cracking showed the strongest correlation to the impedance components that are most unfavorably impacted. This work suggests severe cracks in cathode active materials are the primary challenge that direct recycling methods must overcome.