Pyrolysis-Ultrasonic-Assisted Flotation Technology for Recovering Graphite and LiCoO₂ from Spent Lithium-Ion Batteries

Abstract

An environmentally-friendly technology of pyrolysis-ultrasonic-assisted flotation for recovering graphite and LiCoO2 from spent lithium-ion batteries has been evaluated in this paper. Surface properties and morphology of graphite and LiCoO2 derived from spent lithium-ion batteries were carefully studied, and on this basis, their pyrolysis characteristics were investigated by thermogravimetry–gas chromatography–mass spectroscopy. Advanced analysis techniques, scanning electron microscopy, X-ray fluorescence spectrometry, and X-ray photoelectron spectroscopy, were utilized to analyze the effect of pyrolysis and ultrasound on the surface properties and morphology of graphite and LiCoO2. Flotation tests were conducted to evaluate the reinforcing effect of pyrolysis–ultrasound on flotation behavior. Results show that organic binder and electrolyte are the main reasons that graphite and LiCoO2 are hard to separate by flotation; meanwhile, pyrolysis can effectively decompose organic binders at a pyrolysis temperature of 500 °C, and ultrasonic cleaning can effectively remove residual pyrolysis products. Pyrolysis-ultrasonic-assisted flotation can make the LiCoO2 grade improve from 67.25% to 93.89% with the recovery improving from 74.62% to 96.88%. This research work may provide an alternative process for the preparation of high purity LiCoO2 particles for the subsequent chemical metallurgy.

A review of physical processes used in the safe recycling of lithium ion batteries

“…Similar investigations into temperature and duration of heat treatment processes were conducted by other authors [97,64,96,80]. As discussed in section 4.4, heat treatment is used extensively by authors in order to remove or degrade the binder on electrode coatings, and restore hydrophobicity or hydrophilicity prior to froth flotation [96,79,80,65,64,97]. Dissolution of PVDF can be achieved by using hot solvents such as N-Methyl-2-pyrrolidone (NMP), N-N-dimethylacetamide (DMAC), N,N-Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), and Ethanol [106,10,21].…”

“…The current collectors; copper and aluminium, can also be found within this mass, and their concentration will vary depending on comminution conditions. Laboratory scale experiments often generate black mass through comminution and sieving, relying on preferential comminution of electrode coatings to keep the Al and Cu content of the black mass low [79,15,71,80]. Current collectors need to be removed from the black mass prior to hydrometallurgical extraction, in order to maximise cost-effectiveness [81,82,83].…”

“…This was due to the hydrophobic PVDF binder which was still stuck to the LiCoO 2 and graphite powders. If heat treated to 500°C to decompose and remove the PVDF, froth flotation can separate carbons from the cathode materials successfully [75,70,96,79,80,65,64,97]. The heat treatment decomposes the binder (producing HF [98,64]) and may modify the carbon present in the sample.…”

A Sustainable Process for the Recovery of Anode and Cathode Materials Derived from Spent Lithium-Ion Batteries

“…Two main problems need to be solved in this process: (a) Electrode particles are attached to foils by organic binder and they are difficult to liberate under only the action of mechanical crushing force, which results in some electrode materials remaining on the foils and decreases the recovery efficiency; (b) electrode materials from this flowchart are still enveloped by electrolyte and organic binder, which will decrease their flotation efficiency because the hydrophilic/hydrophobic differences between cathode materials and anode materials are decreased. Therefore, the removal of organic binder and electrolyte is an essential process in order to obtain high purity cathode materials [18,19]. Some chemical agents, including N-methyl-2-pyrrolidone, dimethylformamide, dimethyl acetamide, and dimethyl sulfoxide, have been utilized to dissolve the organic binder [20,21].…”

Oxidizing Roasting Behavior and Leaching Performance for the Recovery of Spent LiFePO4 Batteries

“…The main peak at 284.7 eV was caused by the carbon black. Two peaks of C-OR and C=O attributed to organic solvents were detected at 285.5 and 288.9 eV [39]. The peaks located at 286.7 and 291.1 eV are attributed to CH2 and (CF2CHF)n which are from binder PVDF [40].…”