Characterization of lithium ion battery recycling processes and estimation of liberation efficiency of electrodes using automated mineralogy

Lithium-ion batteries (LIBs) are currently one of the most important electrochemical energy storage devices, powering electronic mobile devices and electric vehicles. Growing global demands for Co, Mn, Ni, Li, and graphite which are all used and present in LIBs as energy storage added difficulties to the already deficit and imbalance supply of sources of raw materials worldwide, which resulted to supply risks, price fluctuations and monopoly of market. In fact, Co and natural graphite are listed as critical raw materials (CRMs) in Europe since 2010 and Mn, and Li are on the boundary of criticality. While recycling is identified as a solution to potentially reduce the gap between the demand and supply. Recycling of lithium ion battery (LIB) has attracted a lot of attention in the recent years and focuses primarily on valuable metals such as cobalt, nickel and lithium. During the recycling processes, considerable amount of the components are lost like electrolyte, separator or graphite. For instance, graphite can either be slagged-off or consumed as a reductant agent during pyrometallurgical treatment. Some other loses are due to a lack of liberation of the targeted particles, elements such as Co are lost in the coarse fractions and a not recovered in the right product. Hence, there is a need to find innovative and comprehensive LIB recycling operations.
For understanding and be able to quantify the loses and recycling process efficiency a deeper characterization is required. This research proposes a new characterization method based on automated mineralogy. In this study, the particles morphologies (size, composition and phases associations) are analysed. The liberation of active materials from electrodes is quantified by comparing two recycling processes: mechanical and thermochemical-mechanical. The mechanical route operates with an impact shear crusher while for the thermomechanical operation the batteries were vacuum pyrolyzed at 500-650oC before to be crushed. The black mass, fraction below 1 mm from the recycling processes, were classified in 4 size fractions based on the particles size distribution. Each fraction was characterized by various analytical methods, including X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Atomic Absorption Spectrometry (AAS) and SEM-based automated mineralogy. The latter consists in the combination of a scanning electron microscopy (SEM) image analysis and energy dispersive X-ray spectroscopy (EDS). It is a powerful and well-known method for primary material characterization; however, it has not yet been applied to secondary material such as black mass, which is a challenging material to analyse due fine alloys particles and to the lack of an existing dedicated database.
In this research, a database for battery characterization is also aimed aside from the determination of the liberation efficiency of the processes employed. Furthermore, a unique procedure was used in preparing the grain mounts for SEM-EDS analysis. Here, iodoform is added to modify the grey level of resin, which improves the contrast with the carbon phases. This technic allows the quantification of the carbon phases which is also a limitation of XRF and XRD aside from the fact that these methods cannot provide images for qualitative evaluation. This study showed that the thermo-mechanical process liberates more active particles from the foils than only a mechanical process. For both processes, a liberation selectivity of the electrode foils was observed. Cu foil is better liberated than Al foils. By consequence, most of the graphite particles are concentrated in the <63μm fraction. 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 only mechanical process, but Al breakage is more affected by thermal treatment, which creates finer Al particles, which can be problematic for further hydrometallurgy routes.