Characterization of lithium-ion batteries in recycling processes and assessment of the liberation efficiency of black mass components using automated mineralogy

Lithium-ion batteries (LIBs) are currently the most important electrochemical energy storage sys-tems for electronic mobile devices and electric vehicles. The growing global demand for LIBs is accompanied by an increase in the need for Co, Mn, Ni, Li and graphite. In order to narrow the gap between supply and demand and to achieve the European sustainability goals, the recycling of LiBs has attracted a lot of attention in recent years. Here, the focus is on valuable metals such as cobalt, nickel and lithium as well as graphite. In addition, due to its chemical and phase compositions, the battery material remains to be a huge challenge for a proper materials characterization. Hence, there is not only a need to find innovative and comprehensive LiB recycling process solutions but also to develop new analytical workflows to enhance the understanding of the battery material.
In this study, LIBs are fed to a mechanical and thermo-mechanical recycling process route to release active materials from electrodes foils. In addition to the valuable metals, the focus is particularly on the recovery of graphite. The mechanical route works with an impact shear crusher, while for the thermo-mechanical tests the batteries were vacuum pyrolyzed at 500-650 °C before crushing. The so-called black mass fraction smaller than 1 mm was separated and further classified into four size fractions. Accurate characterization of both the main chemistry and detailed characterization of the phases contained in the recycled material remains a major challenge. Therefore, each fraction has been characterized by different analytical methods, including X-ray fluorescence (XRF), inductively coupled plasma optical emission spectroscopy (ICP-OES). For a good visualization and quantifica-tion of the results of the processing success and process efficiency, a more detailed analytical char-acterization is required. This study proposes an innovative and novel characterization method based on automated mineralogy. Various important particle parameters such as size, composition and ad-hesion are analyzed and quantitatively evaluated. The Mineral Liberation Analyzer (MLA) system used for the measurements uses a combination of scanning electron microscopy (SEM) image analy-sis and energy-dispersive X-ray spectroscopy (EDS) and is established as a powerful method in the primary raw materials sector. However, there are no dedicated databases for use in the secondary raw materials sector in order to analyze black mass material in a fast and precise manner. An analyti-cal challenge of this study is therefore to create a database for battery characterization and to be able to use it for a wide range of applications.
Results of this study display a selective liberation of electrode foils during the beneficiation process. The thermo-mechanical process releases more active particles from the foils than a mechanical pro-cess alone. Hence, most of the graphite particles are liberated and concentrated in the < 63 μm frac-tion, in particular in the case of thermo-mechanically treated samples. Cu foils are generally better liberated than aluminium foils. However, it was found that the process type has different effects on Al foil liberation. The thermomechanical process liberates more metal oxides from the Al foil than the mechanical process alone but Al breakage is more affected by thermal treatment, resulting in finer Al particles.