Pyrolysis characteristics of cathode from spent lithium-ion batteries using advanced TG-FTIR-GC/MS analysis

Review of lithium-ion batteries' supply-chain in Europe: Material flow analysis and environmental assessment

European legislation stated that electric vehicles' sale must increase to 35% of circulating vehicles by 2030, and concern is associated to the batteries' supply chain. This review aims at analysing the impacts (about material flows and CO2 eq emissions) of Lithium-Ion Batteries' (LIBs) recycling at full-scale in Europe in 2030 on the European LIBs' supply-chain. Literature review provided the recycling technologies' (e.g., pyro- and hydrometallurgy) efficiencies, and an inventory of existing LIBs' production and recycling plants in Europe. European production plants exhibit production capacity adequate for the expected 2030 needs. The key critical issues associated to recycling regard pre-treatments and the high costs and environmental impacts of metallurgical processes. Then, according to different LIBs' composition and market shares in 2020, and assuming a 10-year battery lifetime, the Material Flow Analysis (MFA) of the metals embodied in End of Life (EoL) LIBs forecasted in Europe in 2030 was modelled, and the related CO2 eq emissions calculated. In 2030 the European LIBs' recycling structure is expected to receive 664 t of Al, 530 t of Co, 1308 t of Cu, 219 t of Fe, 175 t of Li, 287 t of Mn and 486 t of Ni. Of these, 99% Al, 86% Co, 96% Cu, 88% Mn and 98% Ni will be potentially recovered by pyrometallurgy, and 71% Al, 92% Co, 92% Fe, 96% Li, 88 % Mn and 90% Ni by hydrometallurgy. However, even if the recycling efficiencies of the technologies applied at full-scale are high, the treatment capacity of European recycling plants could supply as recycled metals only 2%-wt of the materials required for European LIBs' production in 2030 (specifically 278 t of Al, 468 t of Co, 531 t of Cu, 114 t of Fe, 95 t of Li, 250 t of Mn and 428 t of Ni). Nevertheless, including recycled metals in the production of new LIBs could cut up 28% of CO2 eq emissions, compared to the use of virgin raw materials, and support the European batteries' value chain.

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.

Selective Recovery of Cathode Materials from Spent Lithium-Ion Battery Material with a Near-Room-Temperature Separation

Effective separation of cathode materials from the current collector is a critical step in recycling a spent lithium-ion battery (LIB). This typically necessitates the decomposition or dissolution of the organic binder, poly(vinylidene fluoride) (PVDF), to achieve efficient recovery of cathode materials. However, this process requires a high decomposition temperature, typically between 400 and 600 °C, and can lead to side reactions, such as current collector oxidation/brittleness, decomposition of cathode materials, and formation of metal fluorides. In this study, we propose that non-thermal plasma (NTP) treatment can be used to achieve an extremely high separation of cathode materials and aluminum current collector at near room temperature. Instead of relying on PVDF decomposition, which requires high temperatures, PVDF can be deactivated by partially breaking down long molecular chains with appropriate NTP conditions. With a total treatment time of around 2000 s and an environmental temperature of approximately 80 °C, minor side reactions can be avoided. The separation rate can reach up to 95.69%, and high-quality cathode materials can be obtained with only 0.02 wt % aluminum impurity content. This research could potentially offer a new approach toward minimizing recycling steps and reducing energy consumption in the recycling of spent LIBs. It could also be extended to the recovery of a broader range of electronic wastes.

Defluorination and directional conversion to light fuel by lithium synergistic vacuum catalytic co-pyrolysis for electrolyte and polyvinylidene fluoride in spent lithium-ion batteries

To overcome the drawbacks of current recycling technologies and achieve clean utilization of toxic substances in spent lithium-ion batteries, a lithium synergistic vacuum catalytic co-pyrolysis method was proposed to defluorinate electrolyte and polyvinylidene fluoride with directional conversion to light fuel. The gas chromatography-mass spectrometry results indicated, compared to the control group, that adding CaO-ZSM-5 catalyst increased the light fuel (alcohols and hydrocarbons) content of the pyrolysis gas from 61.8 % to 91.47 % under the optimal conditions (530 °C and initial pressure of 100 Pa), whereas the total proportion of esters and toxic organic compounds decreased from 32.58 % to 3.99 %. Moreover, the ethylene carbonate and hexanedinitrile content of the electrolyte was enriched to 85 % in the pyrolysis oil. Notably, fluoride was not detected in the pyrolysis oil and gas, achieving a 98.16 % defluorination rate, implying that hazardous waste was transformed to ordinary waste, thereby greatly avoiding toxic emissions to the environment. The X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy data indicated that fluorine was fixed in the form of CaF2. X-ray photoelectron spectroscopy and XRD analysis of the catalytic pyrolysis residue confirmed that nonferrous metals in the cathode material were converted into simple substances and oxides. Finally, possible co-pyrolysis mechanisms of the organic compounds are proposed, including Li+ generation, chain initiation, catalytic pyrolysis, and directional conversion.

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.

Leaching valuable metals from spent lithium-ion batteries using the reducing agent methanol

When considering resource shortages and environmental pressures, salvaging valuable metals from the cathode materials of spent lithium-ion batteries (LIBs) is a very promising strategy to realize the green and sustainable development of batteries. The reductive acid leaching of valuable metals from cathode materials using methanol as a reducing agent was studied. The results show that the leaching efficiencies of Co and Li are 99% under optimal leaching conditions. The leaching kinetics of cathode materials in a H₂SO₄-methanol system indicate that the leaching of Co and Li is controlled by diffusion, with activation energies of 69.98 and 10.78 kJ/mol, respectively. Detailed analysis of the leaching reaction mechanism indicates that methanol is ultimately transformed into formic acid through a two-step process to further enhance leaching. No side reactions occur during leaching. Methanol can be a sustainable alternative for the reductive acid leaching of valuable metals from spent LIBs due to its high efficiency, application maturity, environmental friendliness, and low cost.

Transformation and migration mechanism of fluorine-containing pollutants in the pyrolysis process of spent lithium-ion battery

Pyrolysis is an effective method to remove organics (e.g. electrolytes and binders) from spent lithium-ion battery (LIB). In this study, the co-pyrolysis characteristics of fluorine-containing substances and active materials from LIB were investigated using thermogravimetric-differential scanning calorimetry (TG-DSC), infrared spectroscopy (IR), and mass spectrometry (MS) analysis. Associated with the pyrolysis, active materials adsorb the residues of electrolyte on the surface and into the pores (20-200 °C), while polyvinylidene fluoride (PVDF) forms a liquid film to cover the local surface of active materials (400-500 °C). These interactions prevent deep removal of organics, leaving fluorine-containing contaminants in active materials. The barrier effect of PVDF liquid mesophase on the removal of organics with secondary liquidous phase formation during pyrolysis was confirmed by in situ optical observation. The migration behavior of fluorine element during the pyrolysis of black mass (BM) from spent LIB was also investigated. With pyrolysis temperature increasing from 100 °C to 600 °C, the dissociable fluorine content in pyrolyzed BM increased from 1.4 wt% to 3.7 wt%. The fluorine-containing contaminants in BM cannot be removed completely by simply increasing pyrolysis temperature. This study provides a better understanding on the transformation of fluorine-containing pollutants during the pyrolysis of BM.