Assessment of the liberation efficiency of lithium-ion battery components in recycling processes by using automated mineralogy

Mechanical recycling processes aim at separating individual particles based on their properties, such as size, shape, density and composition. However, secondary material such as spent lithium ion battery are highly heterogeneous and complex in element and also material form. In order to improve recycling efficiency, characterization of the recycled products, on a particle level, is crucial. Nevertheless, conventional characterization techniques, such ICP-OES, XRF or XRD, provide bulked information for the products only. Tis research presents the development of a new analytical procedure based on individual particle characterization in order to monitor and diagnose lithium ion battery (LiB) recycling.
In this study, cylindrical lithium-ion batteries (INR18650-29E) are fed to a mechanical and thermo-mechanical recycling process route to release coated particles from the electrodes foils. In addition to the valuable metals, the focus is particularly on the recovery of graphite. The mechanical route works with a shear crusher, while for the thermo-mechanical tests the batteries were vacuum pyrolyzed at 500-650 °C before crushing. The fraction smaller than 1 mm, called black mass, was separated and classified into 4 size fractions based on the particle size distribution. The samples were analysed by automated mineralogy, this analytical tool enables the acquisition of particle-based information such as elemental and phase composition, morphology, association and degree of liberation. The Mineral Liberation Analyzer (MLA) system used for the measurements uses a combination of scanning electron microscopy (SEM) image analysis 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 analytical 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. The analysis shows a selective liberation of the anode components in comparison to the cathode components for the beneficiation processes, but with different liberation patterns of the Al foil. The lamination structure of the electrodes was conserved during mechanical process, which resultes in coarse aggregates. The thermo-mechanical process releases more individual and small aggregates of active particles from the foils than a mechanical process alone.