Direct recycling of end-of-life lithium-ion batteries cathode active materials by hydrothermal route

At the present time, the increasing use of lithium-ion batteries in electric vehicles has created unprecedented pressure for end-of-life management and resource recovery. This article reports on a direct recycling approach to regenerate spent cathode active materials, in particular Ni-rich NMC622, via a hydrothermal re-lithiation strategy and thermal annealing. An initial screening process was established to separate high purity spent cathode active materials from disassembled LG Chem pouch cells from Hyundai KONA battery packs. A full factorial design was applied to provide a meaningful statistical analysis of the influence of hydrothermal variables - LiOH concentration, temperature and reaction time. The results indicate that lithium concentration and temperature have a strong main effect on regeneration efficiency, while interaction effects with time are more influential for lithium incorporation. The regenerated cathode active materials exhibited structural, morphological and electrochemical performance comparable to commercial NMC622, especially for samples treated at 160 °C, 4 M LiOH and 1 h reaction time. This process demonstrates the feasibility of regenerating degraded cathode active materials for reuse in new batteries, contributing to circular economy strategies and critical raw material independence in Europe. On the other hand, detailed material characterization validated the recovery of layered crystalline structure and localized cation mixing, conditions required for best battery performance. Regenerated electrodes retained high specific capacity during electrochemical testing and displayed good stability over 50 cycles under the conditions tested. Interactions were quantitatively significant and through the statistical analysis approach, optimal synthesis conditions were directed based on interaction limits. Against this background, the proposed method circumvents the high energy consumption and material losses of the pyrometallurgical route and the secondary pollution and reagents needed in the hydrometallurgical leaching process. In summary, direct recycling appears to be a more resource-efficient and sustainable route for the recovery of cathode materials in future battery supply chains.