Understanding the effect of nonmetallic impurities in regenerated cathode materials for lithium-ion battery recycling by tracking down impurity elements

From Li battery leachate to cathodes: Unveiling the role of boron impurity in Ni-rich LiNixCoyMnzO2 resynthesis by simulated leachate

As the demand for lithium-ion batteries (LIBs) grows, recycling spent LIBs has become critical for resource conservation and environmental sustainability. Among various cathode active materials (CAMs), Ni-rich LiNixCoyMnzO2 (NCM) is favored for its high capacity. This study investigates the impact of boron, a common coating element, as an impurity during the resynthesis of LiNi0.9Co0.05Mn0.05O2 from LIB leachate. The boron content in industrial LIB leachate is confirmed as 0.6 mol% (vs. Ni + Co + Mn) by leaching commercial Ni-rich CAMs. Also, it is designed that boron is introduced with 0, 0.06, 0.6, and 6 mol% during coprecipitation, and the resulting CAMs are denoted as NCM, NCMB0.06, NCMB0.6, and NCMB6, respectively. Boron predominantly localizes in the core of precursor, leading to the formation of internal pores during calcination. These internal pores act as buffers that reduce the compressive and tensile stresses exerted on CAM particles during cycling. Consequently, the NCMB samples exhibit superior cycle retention compared to NCM. The rate performance is also enhanced, as evidenced by the increased lithium-ion diffusion coefficient, supported by cycling voltammetry results. On the other hand, NCMB6 shows deteriorated initial discharge capacity with the highest cation disorder. These findings demonstrate that the current boron level in LIB leachate can enhance capacity retention and rate performance, offering valuable insights for facilitating the recycling process of spent LIBs. This study would expand the understanding of impurities in the resynthesis of CAM by associating impurities with the origin of coating materials for NCM, contributing to the commercialization of the resynthesis process.

Ferrioxalate photolysis-assisted green recovery of valuable resources from spent lithium iron phosphate batteries

Recovering valuable resources from spent cathodes while minimizing secondary waste generation is emerging as an important objective for the future recycling of spent lithium-ion batteries, including lithium iron phosphate (LFP) batteries. This study proposes the use of oxalic acid leaching followed by ferrioxalate photolysis to separate and recover cathode active material elements from spent LFP batteries. The cathode active material can be rapidly dissolved at room temperature using appropriate quantities of oxalic acid and hydrogen peroxide, as determined through thermodynamic calculations. The dissolved ferrioxalate complex ion (Fe(C2O4)33-) is selectively precipitated through subsequent photolysis at room temperature. Depending on the initial concentration, the decomposition ratio can exceed 95 % within 1-4 h. Molecular mechanism analysis reveals that the decomposition of the Fe(C2O4)33- complex ion into water-insoluble FeC2O4·2H2O results in the precipitation of iron and the separation of metal elements. Lithium can be recovered as dihydrogen phosphates through filtration and water evaporation. No additional precipitant is needed and no other side products are generated during the process. Oxalic acid leaching followed by photolysis offers an environmentally friendly and efficient method for metal recovery from spent LFP cathodes. The photochemical process is a promising approach for reducing secondary waste generation in battery recycling.

Cathode active materials using rare metals recovered from waste lithium-ion batteries: A review

Large-scale lithium-ion batteries (LIBs) are overtaking as power sources for electric vehicles and grid-scale energy-storage systems for renewable sources. Accordingly, large amounts of LIBs are expected to be discarded in the near future. Recycling technologies for waste LIBs, particularly for valuable rare metals (Li, Co, and Ni) used in cathode active materials, need to be developed to construct continuous LIB supply chains. Various recovery methodologies, such as pyrometallurgy, hydrometallurgy, and direct recycling, as well as their advantages, disadvantages, and technical features, are briefly introduced. We review the electrochemical performances of these cathode active materials based on recycled rare metals from LIB waste. Moreover, the physicochemical properties and electrochemical performance of the cathode active materials with impurities incorporated during recycling, which have high academic significance, are outlined. In hydrometallurgy-based LIB recycling, the complete removal of impurities in cathode active materials is not realistic for the mass and sustainable production of LIBs; thus, optimal control of the impurity levels is of significance. Meanwhile, the studies on the direct recycling of LIB showed the necessity of almost complete impurity removal and restoration of physicochemical properties in cathode active materials. This review provides a survey of the technological outlook of reusing cathode active materials from waste LIBs.

Leaching kinetics of fluorine during the aluminum removal from spent Li-ion battery cathode materials

The high content of aluminum (Al) impurity in the recycled cathode powder seriously affects the extraction efficiency of Nickel, Cobalt, Manganese, and Lithium resources and the actual commercial value of recycled materials, so Al removal is crucially important to conform to the industrial standard of spent Li-ion battery cathode materials. In this work, we systematically investigated the leaching process and optimum conditions associated with Al removal from the cathode powder materials collected in a wet cathode-powder peeling and recycling production line of spent Li-ion batteries (LIBs). Moreover, we specifically studied the leaching of fluorine (F) synergistically happened along with the removal process of Al, which was not concerned about in other studies, but one of the key factors affecting pollution prevention in the recovery process. The mechanism of the whole process including the leaching of Al and F from the cathode powder was indicated by using NMR, FTIR, and XPS, and a defluoridation process was preliminarily investigated in this study. The leaching kinetics of Al could be successfully described by the shrinking core model, controlled by the diffusion process and the activation energy was 11.14 kJ/mol. While, the leaching of F was attributed to the dissolution of LiPF6 and decomposition of PVDF, and the kinetics associated was described by Avrami model. The interaction of Al and F is advantageous to realize the defluoridation to some degree. It is expected that our investigation will provide theoretical support for the large-scale recycling of spent LIBs.

In-situ pyrolysis based on alkaline medium removes fluorine-containing contaminants from spent lithium-ion batteries

Pyrolysis is an effective method for removing organic contaminants (e.g. electrolytes, solid electrolyte interface (SEI), and polyvinylidene fluoride (PVDF) binders) from spent lithium-ion batteries (LIBs). However, during pyrolysis, the metal oxides in black mass (BM) readily react with fluorine-containing contaminants, resulting in a high content of dissociable fluorine in pyrolyzed BM and fluorine-containing wastewater in subsequent hydrometallurgical processes. Herein, an in-situ pyrolysis process is proposed to control the transition pathway of fluorine species in BM using Ca(OH)₂-based materials. Results show that the designed fluorine removal additives (FRA@Ca(OH)₂) can effectively scavenge SEI components (Li_xPOF_y) and PVDF binders from BM. During the in-situ pyrolysis, potential fluorine species (e.g. HF, PF₅, and POF₃) are adsorbed and converted to CaF₂ on the surface of FRA@Ca(OH)₂ additives, thereby inhibiting the fluorination reaction with electrode materials. Under the optimal experimental conditions (temperature = 400 °C, BM: FRA@Ca(OH)₂ = 1: 4, holding time = 1.0 h), the dissociable fluorine content in BM was reduced from 3.84 wt% to 2.54 wt%. The inherent metal fluorides in BM feedstock hinder the further removal of fluorine with pyrolysis treatment. This study provides a potential strategy for source control of fluorine-containing contaminants in the recycling process of spent LIBs.

Challenges in Recycling Spent Lithium-Ion Batteries: Spotlight on Polyvinylidene Fluoride Removal

In the recycling of retired lithium-ion batteries (LIBs), the cathode materials containing valuable metals should be first separated from the current collector aluminum foil to decrease the difficulty and complexity in the subsequent metal extraction. However, strong the binding force of organic binder polyvinylidene fluoride (PVDF) prevents effective separation of cathode materials and Al foil, thus affecting metal recycling. This paper reviews the composition, property, function, and binding mechanism of PVDF, and elaborates on the separation technologies of cathode material and Al foil (e.g., physical separation, solid-phase thermochemistry, solution chemistry, and solvent chemistry) as well as the corresponding reaction behavior and transformation mechanisms of PVDF. Due to the characteristic variation of the reaction systems, the dissolution, swelling, melting, and degradation processes and mechanisms of PVDF exhibit considerable differences, posing new challenges to efficient recycling of spent LIBs worldwide. It is critical to separate cathode materials and Al foil and recycle PVDF to reduce environmental risks from the recovery of retired LIBs resources. Developing fluorine-free alternative materials and solid-state electrolytes is a potential way to mitigate PVDF pollution in the recycling of spent LIBs in the EV era.