Abstract
The increased demand for Li-ion batteries has prompted the scientific community to improve recycling routes in order to reuse the valuable materials in batteries. After their end-of-life, the batteries are collected, discharged, and mechanically disintegrated, generating plastic and metallic streams that are recycled directly; this leaves behind a small particle size fraction known as black mass (BM). BM is composed mainly of graphite and Li-metal complex oxides. Pyrometallurgy is a route known for recycling of BM, in which identifying the BM’s behavior at high temperatures is essential. In this study, two types of BM are characterized in two fractions of 150–700 µm and smaller than 150 µm. The thermal behavior of the BM is studied with thermal analysis techniques. The analyses demonstrate that the mineralogical and morphological properties of the two fractions do not significantly differ, while the amounts of C and organic materials might vary. When the BM was thermally treated, the binders decomposed until a temperature of 500 ℃ was reached, where the volatilization of hydrocarbons was observed, although F mostly persisted in the BM. The Li-metal oxide was partially reduced to lower oxides and Li carbonate at ⁓ 600 ℃, and the main mass loss was caused by carbothermic reduction immediately thereafter. As the products of this process, metallic Co and Ni phases were formed, and part of the graphite remained unreacted. Regarding the Li behavior, it was observed that in the presence of Al, AlLiO2 is the most likely composition to form, and it changes to LiF by increasing the F concentration in the composition.Graphical
Highlights
Since the beginning of the 1990s, Li-ion batteries (LIBs) have been regarded as the most promising energy storage solution for various applications due to their high energy density, low memory effect, low self-discharge, and long lifespan
The main difference is the amount of C, which is much higher in the coarse fraction, while there is a lower amount of the other main elements— e.g., Li, Co, and Ni
A characterization routine including the black mass (BM) thermal behavior was investigated based on chemical, morphological, mineralogical, and thermal analyses
Summary
Since the beginning of the 1990s, Li-ion batteries (LIBs) have been regarded as the most promising energy storage solution for various applications due to their high energy density, low memory effect, low self-discharge, and long lifespan. Valuable metals are recovered at high temperatures based on their physical and chemical properties [4], while in hydrometallurgy, the process of metal recovery is performed based on aqueous chemistry at low temperatures, in which a combination of different techniques, e.g., leaching, solvent extraction, and precipitation, are performed [16–20] These two major methods have pros and cons, such as the emission of hazardous gas in pyrometallurgy and the production of wastewater in hydrometallurgy processes. There are various battery types that generates different BM compositions In this regard, some studies have been performed to investigate the effect of high-temperature treatment on different battery compositions both on the cathode/anode active material, a mix of them, or unaltered BM. To detect the high-temperature behavior of BM in a reductive atmosphere, a Netzsch STA 409 instrument with a detection limit of 1 μg was utilized to conduct thermogravimetric/differential thermal analysis (TGA/DTA) under an Ar atmosphere (flow rate of 100 mL/min) and with a heating rate of 10 °C/min. For the last experiment with LCO + Gr + Al + PVDF, the graphite that was used had the particle size of 7–11 μm
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