Thesis title: Relating Process Parameters to Performance: A Study on Hydrometallurgical Recycling and Re-production of NMC811 for High-Performance Batteries
The overarching objective of this doctoral work was to advance both the mechanistic understanding and the process feasibility of closed-loop recycling routes for nickel-rich layered oxides (LiNi₀.₈Mn₀.₁Co₀.₁O₂, NMC811) used in lithium-ion batteries, in direct alignment with the regulatory framework of Regulation (EU) 2023/1542. The research integrates synthesis science, hydrometallurgical mass-balance quantification, impurity control, and electrochemical validation to establish a technically and regulatorily compliant recycling workflow from black mass to regenerated high-energy cathodes.
A systematic optimization of the oxalate coprecipitation route for NMC811 precursors was first conducted by varying metal-ion concentration (0.2, 1, 2 M), pH, and residence time (6–24 h). Comprehensive characterization (SEM, XRD, ICP-OES, particle-size analysis) demonstrated that increasing concentration and dwell time promotes denser, well-necked secondary aggregates with narrower coarse modes and improved cation ordering, which persist through calcination as a coprecipitation-driven “memory effect.” The 2 M–24 h condition delivered the most favorable microstructure and electrochemical response, attaining specific capacities of ~200 mAh g⁻¹ at C/10 with superior rate retention. The oxalic-acid route is operationally robust, free from complexing agents and controlled-atmosphere constraints, and thus scalable to industrial throughput.
The methodology was then extended to recycling-derived feeds. A full hydrometallurgical mass balance quantified the transformation of mixed-chemistry black mass—comprising NMC fragments and graphite lamellae with fluorinated residues—into high-purity precursors. Controlled H₂O₂ leaching achieved near-quantitative metal extraction, with element-wise recovery/recycling rates of 97.4 % (Ni), 98.4 % (Co), 87.6 % (Mn), and 27.9 % (Li), surpassing EU-mandated thresholds for Ni and Co. The recovered graphite (~32 wt %) was purified to residual metals < 0.2 mg g⁻¹. The overall precursor mass deviation from balance prediction (−0.7 %) confirmed high analytical closure and process reproducibility.
Finally, impurity speciation and purification strategies were quantitatively evaluated as levers for stoichiometric fidelity and structural order. Adjusting leachate pH from spontaneous to 6.0 reduced total impurity load from ~4.22 at.% to ~0.10 at.%. Purified leachates suppressed Cu/Fe contamination (Cu ≤ 0.009 at.%, Fe ≈ 0) but induced Mn sub-stoichiometry (0.74–0.80), whereas controlled-pH (~6.2) coprecipitation from unpurified feeds attained near-ideal Ni₀.₈Co₀.₁Mn₀.₁ stoichiometry with trace Cu/Fe (Cu ≈ 0.015–0.016; Fe 0.024–0.041) and preserved layered ordering (R-3m, I₀₀₃/I₁₀₄ = 1.23–1.38 at 24 h). Preliminary electrochemical tests confirmed that recycled materials exhibit capacities and rate behavior nearly indistinguishable from the optimized synthetic benchmark.
By coupling quantitative process analysis with electrochemical and regulatory validation, this work bridges laboratory-scale recycling research and industrial implementation, defining a reproducible, regulation-compliant, and economically scalable route for the circular regeneration of critical raw materials in advanced lithium-ion batteries.