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

Abstract

Recycling black mass (BM) obtained from NMC-based end-of-life lithium-ion batteries (LIBs) is intricate and multifaceted due to the complex physicochemical properties of BM and the presence of impurities such as metallic current collectors (Al and Cu), PVDF (polyvinylidene fluoride) binder, and residual electrolytes. A judicious combination of characterization techniques is essential for understanding the physicochemical properties of BM. This understanding is also vital for optimizing pre-treatment processes designed to remove impurities in BM and for creating a decision framework to efficiently plan subsequent recycling processes. Here, industrial BM samples from end-of-life NMC622, NMC111, and NMC901 LIBs are characterized. Focused Beam Reflectance Measurement (FBRM) was used to develop a method to estimate BM particle size by applying square weighting to chord length distribution, enabling real-time size monitoring during recycling processes. Quantitative phase analysis of XRD patterns was conducted to calculate the fraction (wt. %) of crystalline and amorphous phases in BM. Electron microscopy was used to visualize particle morphology and the deposition of PVDF, while inert thermogravimetry with mass spectrometry (TGA/MS) helped with the identification of carbonaceous and fluorinated gases that evolved during PVDF decomposition. A key contribution of this study was the development of a novel method using oxidative TGA/MS for the quantification of graphite in BM. Additionally, graphite particles were also characterized using Raman spectroscopy providing insights into the carbonaceous deposits and structural order. Explored characterization techniques highlight the impact of the physicochemical properties of BM and provide a decision framework for selecting pre-treatment methods and optimizing recycling strategies.