Positive Role of Fluorine Impurity in Recovered LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Materials

Abstract

Lithium-ion battery (LIB) recycling is considered as an important component to enable industry sustainability. A massive number of LIBs in portable electronics, electric vehicles, and grid storage will eventually end up as wastes, leading to serious economic and environmental problems. Hence, tremendous efforts have been made to improve the hydrometallurgical recycling process because it is the most promising option for handling end-of-life LIBs owing to its wide applicability, low cost, and high productivity. Despite these advantages, some extra elements (Al, Fe, C, F, and so forth) remain as impurities in the removal process and are retained in the solution, which is a great challenge to obtain high-quality cathode materials. In this work, the impacts caused by fluorine impurity on the LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode are intensively investigated via hydrometallurgical coprecipitation for the first time. Our results show that up to 1 at. % fluorine impurity brings a positive influence on the recovered material due to a higher Ni2+ ratio on the surface of cathode particles. In addition, the presence of fluoride ions during coprecipitation could lead to the formation of holes in cathode particles, which improves the rate capability and cyclability dramatically. Compared to the virgin material, the capacity of the NCM622 material with 0.2 at. % fluorine impurity is boosted by ∼8% (167.7 mA h/g) with a remarkable capacity retention of 98.0% after 100 cycles at 0.33 C. Besides, the cathode with 0.2 at. % fluorine impurity shows a far better rate performance, especially at high rates (∼7% increased at 5 C) than that of virgin. These results convince that a low concentration of fluorine impurity is desirable in the hydrometallurgical recycling process. More importantly, this study offers implications in the design of high-performance NCM622 cathode materials via coprecipitation production with ion doping in the near future.

Advances in Intelligent Regeneration of Cathode Materials for Sustainable Lithium‐Ion Batteries

“…[156][157][158][159] Note that, the peeled cathode materials from retired LIBs in an industrial process usually contain impurities, such as PVDF binders, carbon-based conductive agents, etc. [67,71,160] It is significant to realize the direct renovation of degraded cathode materials in such a complex system for the large-scale production. Intriguingly, Deng and co-workers found that, in a suitable molten salt medium, the spent cathode materials with acetylene black impurities could be directly regenerated, showing the comparable electrochemical performance to that of the fresh samples.…”

“…[64][65][66][67] Recently, several innovative direct regeneration strategies, such as solid-state, hydrothermal, eutectic, and electrochemical methods, have been proposed accordingly and applied to degraded cathode materials to restore their electrochemical performance without breaking down the microstructures, which exhibit gigantic potential in solving the forthcoming retired LIBs storm (Figure 4). [68][69][70][71] However, the current development of these direct regeneration techniques is still in infancy. Although the substantial researches have been carried out and published, [50,72] it is absent in the thorough summary and assessment of this kind of advanced route, which is much significant and pressing for the quick progress of direct regeneration technique and future practical application in industrial scale.…”

Preferential Extraction of Lithium from Spent Cathodes and the Regeneration of Layered Oxides for Li/Na-Ion Batteries

“…Due to the higher leaching rates and lower energy consumption, hydrometallurgy has been extensively adopted in industry. In general, the spent cathodes are first dissolved with acid with the addition of a reductive agent, followed by a complex separation process involving chemical precipitation or solvent extraction . Even if all metal ions can be leached out, the subsequent multistep separation usually leads to huge loss of metal ions, especially lithium, whose final recovery rate is even below 72% .…”

“…In general, the spent cathodes are first dissolved with acid with the addition of a reductive agent, followed by a complex separation process involving chemical precipitation or solvent extraction. 10 Even if all metal ions can be leached out, the subsequent multistep separation usually leads to huge loss of metal ions, especially lithium, whose final recovery rate is even below 72%. 11 Furthermore, excessive employment of chemical reagents means serious flaws in terms of recycling costs.…”

The Effects of Phosphate Impurity on Recovered LiNi0.6Co0.2Mn0.2O2 Cathode Material via a Hydrometallurgy Method

“…Based on our previous work, insoluble carbon is determined to be a negative factor in hydrometallurgical recycling . Anion impurities such as fluorine (F – ) is found to be beneficial to the process, resulting in a degree of performance improvement for the recovered cathode compared to virgin . However, there is still further investigation needed to uncover the influence of other anion impurities in the hydrometallurgy process.…”