Relating process parameters to performance: a study on hydrometallurgical recycling and re-production of NMC811 for high-performance batteries

The overarching aim of this doctoral thesis was to advance both the fundamental understanding and the practical feasibility of closed-loop recycling routes for nickel-rich layered oxides (NMC811) used in lithium-ion batteries, in direct connection with the regulatory requirements introduced by Regulation (EU) 2023/1542. The work was structured into four interlinked objectives. First, an extensive literature review was undertaken to critically assess state-of-the-art synthesis routes for NMC-type cathode materials, with particular focus on identifying correlations between process parameters, precursor morphology, and electrochemical performance. This step provided the conceptual framework and highlighted knowledge gaps that guided the experimental program. Second, systematic optimization studies were carried out on the synthesis of NMC811 precursors via oxalate coprecipitation. The influence of solution concentration (0.2, 1.0, and 2.0 M), precipitation pH, and reaction time (3–24 h) on nucleation, growth, and agglomeration phenomena was investigated, enabling a detailed understanding of how these parameters govern primary particle size, secondary aggregate formation, and precursor homogeneity. Third, the study was extended from model systems to real recycling scenarios. A complete mass balance of a hydrometallurgical recycling process was performed, including selective leaching of black mass, oxalate coprecipitation of NMC811-type precursors, and recovery/regeneration of graphite from the anode fraction. This approach enabled quantitative evaluation of metal recovery rates, recycling rates, and overall recycling efficiency, thereby validating the process against the thresholds mandated by EU legislation. Finally, the effect of metallic impurities (Cu, Fe, Al) inherently present in recycled streams was systematically explored. Their impact on the morphology, structural integrity, and size distribution of the precursors was analyzed, and electrochemical tests were conducted on cathodes containing controlled copper contamination. These investigations, carried out in both standard and additive-modified commercial electrolytes, provided direct insights into the tolerance of recycled materials to impurities and possible mitigation strategies. The thesis therefore pursues a dual objective: (i) to optimize key synthesis and recycling parameters in order to ensure reproducible, high-quality NMC811 precursors, and (ii) to verify the feasibility of an integrated recycling scheme for lithium-ion batteries, both in terms of quantitative mass balance and compliance with regulatory targets. By coupling detailed process studies with a regulatory and industrial perspective, this work contributes to bridging the gap between laboratory-scale recycling research and the future implementation of sustainable, regulation-compliant recycling pathways for critical raw materials.