Phase-separated solvothermal high yields recovery of lithium and cobalt cathode precursors from end-of-life LiCoO₂ lithium-ion batteries

Lithium-ion batteries (LIBs) recycling is one of the most urgent challenges affecting this technological sector. Indeed, their continuously growing production and demand is already leading to the creation of large volumes of end-of-life LIBs (EoL-LIBs). At the same time, the growing demand for LIBs is not sustainable from the point of view of supply of the critical raw materials needed to produce the essential components of LIBs. The development of efficient and sustainable recycling strategies provides a solution to these two urgent issues. Here we propose a new ternary deep eutectic solvent (DES) composition based on choline chloride, citric acid, and ethylene glycol in molar ratio 1:1:1 for the reductive degradation of LiCoO₂ cathode. The optimized leaching process (5g of DES for 100 mg of black mass for 30 min at 140 °C) leads to the full degradation of the cathode with extraction yields above 97% for both Li and Co. Simple electrochemical tests confirm irreversible DES degradation, making its recovery and reuse impractical. We demonstrate that a subsequent thermal treatment, using DES as a sacrificial agent, allows to separate and recover Co₃O₄ and LiCl with adequate purity to be exploited for LiCoO₂ resynthesis. As a proof of concept, a new batch of LiCoO₂ is synthesized and used for new cells' assembly. The performance of the resynthesized material is comparable with that of the commercial benchmark material, demonstrating the possibility of a full closed-loop recycling route.