Lithium-ion batteries (LIB) play a key role in the electrification of mobility, but resource management and reuse are still a major challenge. To improve this, new recycling methods must be developed to increase efficiency and recovery rates, facilitating the reuse of critical raw materials (CRMs) from spent LIBs. Currently, inorganic acids are widely used for metals recovery, despite their environmental and economic limitations. Research into greener solvent alternatives is underway, highlighting the need for sustainable options like natural deep eutectic solvents (NADES). These solvents are typically non-toxic, biodegradable, and stable across various temperatures and pH levels, making them promising substitutes for conventional inorganic solvents and aligning well with green chemistry principles.

Within the framework of my PhD thesis, we have developed a new hydrometallurgical process based on NADES. Successfully recovering lithium phosphate and Ni-Co-Mn oxalate as precursor materials for new battery manufacturing. The total recovery yields of Co, Ni and Li exceed the European Commission’s established recovery targets, achieving rates of 99.9%, 99.7%, and 53%, respectively. These values were attained through cathode direct recycling strategies rather than conventional black mass leaching methods. The cathode direct recycling process involved conducting solid-liquid metal extraction directly on the cathode material. Cathodes were carefully dismantled from NMC (Nickel-Manganese-Cobalt) cells sourced from electric vehicles.

Aluminium foil was separated using citric acid, and the cathode active material underwent further processing through a leaching step. First, a solvent screening was conducted under the same temperature and molar ratios to identify the most effective solvent.

Among the tested NADES, a formulation composed of choline chloride, ascorbic acid, and lactic acid was selected for its exceptional performance. This NADES was then optimized based on key parameters such as temperature, bulk density, and scalability. Following optimization, the recovery yields for Li, Mn, Ni, and Co reached 99.8%.

The strong bonds that are formed during the extraction between organic solvents and metals require the synthesis of very insoluble species to precipitate Ni, Mn and Co from solution. Metal oxalates are known for being highly insoluble, thus oxalic acid was added to precipitate a mix Ni-Mn-Co oxalate. The resulting precipitation recovery yields were 99.9% for Mn, 99.9% for Co, and 99.7% for Ni.

Lithium in solution was recovered as lithium phosphate adding sodium phosphate to the solution, increasing the pH and evaporating part of the volume, to concentrate the lithium phosphate beyond the solubility limit. The result of the lithium recovery yield for the NADES route was 58% of the initial concentration in solution.

The mix Ni-Mn-Co oxalate can be used as precursor for new NMC cathode active materials, and lithium phosphate is used in the synthesis of lithium iron phosphate battery industry.