The comminution of spent lithium-ion batteries (LIBs) produces a powder containing the active cell components, commonly referred to as “black mass.” Recently, froth flotation has been proposed to treat the fine fraction of black mass (<100 µm) as a method to separate anodic graphite particles from cathodic lithium metal oxides (LMOs). So far, pyrolysis has been considered as an effective treatment to remove organic binders in the black mass in preparation for flotation separation. In this work, the flotation performance of a pyrolyzed black mass obtained from an industrial recycling plant was improved by adding a pre-treatment step consisting of mechanical attrition with and without kerosene addition. The LMO recovery in the underflow product increased from 70% to 85% and the graphite recovery remained similar, around 86% recovery in the overflow product. To understand the flotation behavior, the spent black mass from pyrolyzed LIBs was compared to a model black mass, comprising fully liberated LMOs and graphite particles. In addition, ultrafine hydrophilic particles were added to the flotation feed as an entrainment tracer, showing that the LMO recovery in overflow products is a combination of entrainment and true flotation mechanisms. This study highlights that adding kerosene during attrition enhances the emulsification of kerosene, simultaneously increasing its (partial) spread on the LMOs, graphite, and residual binder, with a subsequent reduction in selectivity.

Froth flotation effectively separates anode graphite from cathode active materials (CAMs) of spent lithium-ion batteries when CAM particles are free of organic binders, such as polyvinylidene fluoride (PVDF). This study investigated a bio-based solvent, dihydrolevoglucosenone (Cyrene^TM ), as a pretreatment to remove the PVDF binder from both single chemistry black mass (BM) and industrially produced mixed chemistry black mass (IBM). The subsequent flotation combined with high-intensity attritioning improved CAMs and graphite separation efficiency compared to that of mechanical pretreatment alone, increasing from 0.30 to 0.53 in BM and from 0.37 to 0.54 in IBM. Although pyrolysis resulted in higher separation efficiencies of 0.92 in BM and 0.78 in IBM, Cyrene pretreatment presents advantages in non-emission of toxic gases and in preserving lithium within the CAMs. In the flotation process water, an average lithium dissolution of only 5.5% in BM and 14.7% in IBM was recorded with Cyrene pretreatment, compared to that of 29.3% in BM and 55.4% in IBM with pyrolysis pretreatment. The lower quality of the flotation products obtained with Cyrene pretreatment necessitates further purification steps such as cleaner flotation. Optimizing pretreatment parameters is crucial, including the Cyrene to black mass ratio and contact time. A key challenge is preventing the thermally induced phase separation of PVDF at temperatures lower than 80 °C, which negatively affects the effective separation of graphite and CAMs by froth flotation.

Effective and environmentally benign removal of polyvinylidene fluoride (PVDF) binders from spent battery electrodes remains a critical hurdle in sustainable recycling, primarily due to issues related to the mitigation of fluorinated compound emissions. This work evaluates PVDF binder removal from cathode active material using either a green solvent-based dissolution process or pyrolysis, analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The solvent pretreatment involved mixing dihydrolevoglucosenone (Cyrene™) with PVDF-coated NMC811 at 100 °C, followed by hot filtration to separate the Cyrene-PVDF solution. Pyrolysis was conducted at 800 °C under an argon atmosphere. Positive ToF-SIMS spectra for Cyrene showed characteristic peaks at ketene (42 m/z) and 1,3-dioxole (86 m/z), along with intense C₂H₃O⁺, C₃H₃O⁺, C₄H₇⁺, and C₃H₅O⁺ peaks. The characteristic peaks used to identify PVDF were C₃H₂F₅⁺ (133 m/z), C₃H₂F₃⁺ (95 m/z), and C₃HF₄⁺ (113 m/z). Both processes resulted in PVDF removal, with pyrolysis demonstrating higher effectiveness. Particle agglomeration was observed in both pretreated NMC811 samples, however agglomeration was more pronounced with Cyrene pretreatment due to PVDF redeposition. Following pyrolysis, PVDF was transformed into a defluorinated carbonaceous material.