Material Characterization of NMC Black Mass from End-of-Life Lithium-Ion Batteries for Enhanced Recycling Strategies

Recycling black mass (BM) obtained from NMC-based end-of-life lithium-ion batteries (LIBs) is hindered by metallic impurities (Al and Cu), residual electrolytes, and PVDF (polyvinylidene fluoride) binder. Pre-treatment of BM, such as milling and pyrolysis, to remove these impurities necessitates characterizing its physicochemical properties that affect such pre-treatment methods. More importantly, a judicious combination of characterization techniques can provide an integrated framework for efficiently planning pre-treatment and recycling processes. In this study, industrial BM samples from end-of-life NMC622, NMC111, and NMC901 LIBs are characterized. The comparative characterization of BM using FBRM (focused beam reflectance measurement) and laser diffraction techniques showed that applying square weighting to the chord length distribution measured by FBRM yields values close to the actual particle size, while also providing a method that can be used for real-time analysis of recycling processes. XRD (x-ray diffraction), complemented by SEM (scanning electron microscopy) and metal composition data confirmed that crystalline NMC phases remain intact in untreated BM and graphite exists as a mixture of 2H and 3R phases. Additionally, Raman spectroscopy with SEM elemental analysis provided insights into the carbonaceous deposits and metal particles on graphite surfaces. Qualitative TGA/MS (thermogravimetry with mass spectrometry) of BM under pyrolytic conditions allowed the identification of residual electrolytes and PVDF through the evolution of carbonaceous and fluorinated gases. Quantitative TGA/MS under oxidative conditions allowed quantification of total carbon in BM and estimation of PVDF. Explored characterization techniques highlight the impact of pre-treatment processes and provide a decision framework for selecting and optimizing recycling strategies.