Abstract
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.
Data availability
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.
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Acknowledgements
This work is part of the EU-funded FREE4LIB project that has received funding from the European Union’s Horizon Europe research and innovation programme under Grant Agreement No. 101069890.
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Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the granting authority CINEA. Neither the European Union nor the granting authority can be held responsible for them.
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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by J. Castro, M. Gómez, and P. Moretti. Experimental procedures were performed by P.J. Acebes, P. Moretti, M.R. Bermejo, M. Merlo, Y. Belce. and J.J. Biendicho. Diffraction data collection and analysis were conducted by M. Merlo. Electrochemical testing, including electrode fabrication, coin cell testing, and data analysis, was performed by Y Belce. J.J. Biendicho, S. Bolado-Rodriguez and D. Hidalgo were involved in manuscript writing, editing, and reviewing. The first draft of the manuscript was written by J. Castro, and all authors read and approved the final manuscript.
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Castro, J., Gómez, M., Acebes, P.J. et al. Direct recycling of end-of-life lithium-ion batteries cathode active materials by hydrothermal route. Sci Rep (2026). https://doi.org/10.1038/s41598-026-41973-7
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DOI: https://doi.org/10.1038/s41598-026-41973-7
