A study on the wettability of metal oxides as cathode active materials to improve lithium-ion battery recycling

One of the main tasks for today’s researchers in order to ensure the supply of critical raw materials is the efficient recovery and recycling of secondary resources. Lithium-ion batteries (LIB) are the key technology to electrify transport, which is one of the multiple measures proposed to prevent global warming. Therefore, the recycling of spent LIBs is of great interest and unvoidable. A major challenge in spent LIBs recycling, is the beneficiation of fine powder resulting from the battery crushing, so-called “black mass”, which contains the valuable lithium metal oxides (from the cathode) and the critical graphite (from the anode). One promising way to separate the graphitic material from the lithium metal oxides is through froth flotation, which separates the particles according to their differences in wettability.
In order to improve the separation process, one must first have a proper understanding of the particle properties. In particular, the lithium metal oxides are rather declared as hydrophilic and should therefore be easily separated from the hydrophobic graphite. Nevertheless, many studies report on their recovery into the froth product, along with the graphite, thus lowering its grade, which is most probably due to the residual hydrophobic binder that causes a change in their wettability.
In this study, different battery materials, including fresh lithium metal oxides and graphite, as well as real spent materials from LIBs were used. The particles were analysed for their wettability and wetting ability using optical contour analysis, inverse gas chromatography, particle attachment to bubbles, analytical particle solvent extraction as well as the Washburn method. These results are set into context with flotation tests and shed light on the particle wettability and its effect on the flotation separation efficiency, as well as the difficulties that arise when it comes to the recycling of spent LIBs.