Closing the battery loop: Choline citrate-based deep eutectic solvent to unlock direct cathode resynthesis via chlorine-free solvometallurgy

The science and technology behind end-of-life lithium-ion batteries (EoL-LIBs) is a fast-evolving field. Among various solutions proposed to recycle cathode active materials, the solvometallurgy exploiting deep eutectic solvents (DESs) for the leaching of cathode materials is one of the leading research technology due to high efficiencies, low costs of reagents, and absence of wastewater production. In literature, up to now, this method has been exploited to dissolve selected cathode materials and subsequently recover the critical raw materials in the form of salts to be reused for the synthesis of new cathodes. With this work, we propose and demonstrate the feasibility of an innovative and alternative solvometallurgical process, based on the design of a conceptually new DES formulation based on the presence of choline citrate substituting the always-exploited choline chloride, combined with ethylene glycol. This new method enables the leaching of the most relevant and common cathode materials - LiCoO 2 (LCO), Li(Ni/Mn/Co)O 2 (NMC), LiMn 2 O 4 (LMO), LiFePO 4 (LFP), thus providing high flexibility combined with high efficiency. The leap forward and innovation is the new possibility of the direct resynthesis of cathodes, avoiding the step of metals separation; this is intrinsically linked to the new formulation of the DES, avioiding the presence of chlorine. This new strategy can open new ways for the further development of solvometallurgy and efficient recycling of EoL-LIBs.