Redox-mediated low-temperature hydrothermal relithiation of spent lithium-ion battery cathodes

Abstract

The process for low-temperature hydrothermal relithiation of spent lithium-ion battery cathode materials involves the addition of a reducing agent to an aqueous Li solution at approximately 100 °C, followed by a short annealing, to achieve complete recovery of the composition, crystal structure, and electrochemical performance of severely degraded cathode materials.

Description

[Technical field]

[0001] Related Applications This application claims the benefit of priority to U.S. Provisional Application No. 63 / 313,677, filed February 24, 2022, which is incorporated herein by reference.

[0002] Government Rights This invention was made with Government support under Award No. DE-AC02-06CH11357 (SUB 9F-60081) awarded by the Department of Energy and Award No. CBET1805570 awarded by the National Science Foundation. The Government has certain rights in this invention.

[0003] The present invention relates to a safe and energy-efficient direct regeneration process for lithium-ion battery cathodes. [Background technology]

[0004] Lithium-ion batteries (LIBs) are a widely used power source for portable electronic devices, recreational devices, and electric vehicles (EVs) due to their high energy density and long cycle life. As the average lifespan of LIBs is 5-10 years, a large number of LIBs will be retired in the coming years. It is estimated that approximately 1 million EV batteries will reach end of life (EOL) by 2025, which could cause significant problems if not properly treated. The release of flammable and hazardous wastes (e.g., electrolytes and transition metals) resulting from the improper treatment of used LIBs can pollute soil, water, and air. As a result, there is an urgent imperative to develop effective and environmentally friendly LIB recycling strategies not only to reduce the environmental impact of LIB waste, but also to recover valuable materials such as lithium (Li), cobalt (Co), and nickel (Ni).

[0005] Due to the high value of Co, Ni, and Li, recycling of LIB cathodes has attracted great interest in recent years. Existing approaches employ three main recycling methods: pyrometallurgy, hydrometallurgy, and direct recycling. Pyrometallurgy processes are based on high-temperature smelting processes and often involve the combustion of mixed LIB materials, followed by chemical separation. Pyrometallurgy processes are characterized by low operational complexity and ease of scale-up development, but their recovery efficiency is relatively low. In hydrometallurgy processes, aqueous solution chemistry is generally employed, including leaching in acid, followed by precipitation, chemical separation, and purification. Pyrometallurgy and hydrometallurgy processes represent the state of the art in the recycling industry, but involve high-temperature smelting and use large amounts of acid and base chemicals, which raise concerns about large energy consumption (and high operating costs) and secondary pollution, respectively. The combination of pyrometallurgy and hydrometallurgy recycling methods has provided certain benefits in terms of reducing energy and reagent costs while increasing recovery efficiency. Recent advances in pyrometallurgy are closed-loop "Hydro-to-Cathode" methods that eliminate the complicated chemical separation of Ni, Co, and Mn, resulting in high battery recovery efficiency and reduced operational costs. Nevertheless, these methods require complete decomposition of cathode particles (e.g., NCM) to their basic substances (e.g., CoSO4, NiSO4, Li2CO3), wasting a significant amount of energy that remains within the cathode particle structure. In contrast, direct recycling methods involve physical separation processes to recover cathode and anode materials, with mild post-treatment to repair compositional and structural defects in the electrode particles, while retaining their original compound structure and remaining energy. In this regard, direct recycling appears to be the method with the greatest potential to maximize the value recovered from LIBs.

[0006] In recent years, direct LIB cathode regeneration based on hydrothermal relithiation followed by a short post-annealing step has been reported by many researchers in the field, and has been used to regenerate spent LiCoO2 (LCO), LiNi 0.33Co 0.33 Mn 0.33 O2 (NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), and the morphology, composition, and crystal structure of the LiFePO4 (LFP) cathode are effectively reconstructed, indicating that their electrochemical performance reaches the level equivalent to that of their unused materials. For example, E. Gratz et al., "A closed loop prosess for recycling spent lithium ion batteries", Journal of Power Sources, Vol. 262, 2014, pp. 255 - 262, Y. Shi et al. "Ambient―Pressure Relithiation of Degraded Li x Ni 0.5 Co 0.2 Mn 0.3 O2 (0 < x < 1) via Eutectic Solutions for Direct Regeneration of Lithium―Ion Battery Cathodes (Atmospheric pressure relithiation of degraded Li x Ni 0.5 Co 0.2 Mn 0.3"Direct Regeneration of Lithium-Ion Battery Cathodes by Re-Lithiation of O2(0 < x < 1)", Adv. Energy Mater., Vol. 9, 2019, p. 1900454, S. Sloop et al., "A direct recycling case study from a lithium-ion battery recall", Sustainable Materials and Technologies, Vol. 25, 2020, e00152, L. Brueckner et al., "Industrial Recycling of Lithium-Ion Batteries - A Critical Review of Metallurgical Process Routes", Metals, Vol. 10, 2020, p. 1107, Y. Shi et al., "Effective regeneration of LiCoO2 from spent lithium-ion batteries: A direct approach towards high-performance active particles", Green Chem., Vol. 20, 2018, pp. 851 - 862, and P. Xu et al., "Efficient Direct Recycling of Lithium-Ion Battery Cathodes by Targeted Healing", Joule, Vol. 4, 2020, pp. 2609 - 2626. The described method is characterized by simple operation and low energy consumption, and utilizes a hydrothermal re-lithiation process to recover the cathode composition without concern for the variation of Li loss in different degraded LIB feeds. Further, this process utilizes a short sintering process to restore the microstructure of the cathode with the desired stoichiometric composition and crystallinity.However, to completely recover the Li deficiency and achieve good electrochemical properties, generally, a hydrothermal re-lithiation temperature exceeding 200 °C (e.g., 220 °C) is required. In such an aqueous re-lithiation process, due to the high vapor pressure (e.g., 25 bar at 220 °C) in the re-lithiation reactor, concerns regarding potential safety for large-scale operation arise. Therefore, for the efficient direct recycling of LIBs, a safe and energy-efficient hydrothermal re-lithiation process is still needed. SUMMARY OF THE INVENTION

[0007] The method of the present invention provides a safe and energy-efficient direct recycling process based on low-temperature hydrothermal re-lithiation (LTHR) at atmospheric pressure for used LiNi x Co y Mn z O2 (0 < x, y, z < 1, x + y + z = 1, i.e., NCM) cathode materials. By using a low-cost redox mediator at a low concentration, the re-lithiation kinetics of the used NCM material is improved, making it possible to lower the complete re-lithiation temperature from 220 °C to 100 °C or less. The pressure generated in the re-lithiation process can be reduced from about 25 bar to 1 bar, significantly improving the operational safety.

[0008] The effectiveness of the improved method has been demonstrated with various NCM materials, including chemically de-lithiated NCM111, post-cycle (degraded) NCM111, and post-cycle NCM622. These NCM materials are well recycled with complete recovery of composition, crystal structure, and electrochemical performance, achieving the same effectiveness as that achieved by high-temperature processes.

[0009] The method of the present invention provides a versatile low-temperature hydrothermal relithiation (LTHR) process for efficiently and safely recovering the Li composition of depleted NCM cathode materials at ambient pressure. A key aspect of the present process is the use of reducing agents at low concentrations (1%-3% v / v) as green additives (GA) in the aqueous relithiation solution (LiOH solution). These additives can reduce the hydrothermal relithiation temperature and, accordingly, the process pressure. The LTHR process of the present invention shows the same efficiency of relithiation achievable with high-temperature processes, resulting in the complete regeneration of chemically delithiated NCM111, cycled NCM111, and cycled NCM622. This LTHR process can pave the way for more sustainable LIB recycling with high economic benefits, high operational safety, and lower costs.

[0010] In one aspect of the invention, there is a method of regenerating spent lithium ion battery cathode material, where the cathode material is in powder form, the method includes treating the cathode material in an aqueous lithium (Li) solution and a reducing agent at a temperature in the range of 80° C. to 100° C. for a treatment time, washing and drying the treated cathode material, and annealing the treated and dried cathode material in oxygen at an annealing temperature for an annealing time to produce a regenerated cathode material. In some embodiments, the Li solution is LiOH, and the solution may be 0.1 to 4 M LiOH with 1-3% (v / v) reducing agent. The reducing agent is preferably an environmentally friendly reducing additive, and may be one or a combination of ethanol (ET), ethylene glycol (EG), and hydrogen peroxide (HP). The treatment time may be 2 to 20 hours, more preferably 6 to 12 hours, and most preferably 8 hours. The annealing temperature may range from 600 to 1000° C., and the annealing time may be from 1 to 10 hours, and more preferably may be 850° C., in which case the annealing time is 4 hours. The cathode material is LiNi x Co y Mn zIt may be O2, where 0 < x, y, z < 1 and x + y + z = 1 (“NCM”). The cathode material is LiNi 0.33 Co 0.33 Mn 0.33 O2 (NCM111) or LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622). In some embodiments, 5 mol% excess Li2CO3 may be mixed with the treated cathode material before annealing.

[0011] In another aspect of the present invention, a method for treating a lithium-ion battery cathode material from a used battery cell includes separating cathode pieces from the battery cell, treating the cathode pieces in one or more solvent solutions to remove NCM, binder, and carbon black from the cathode piece substrate to extract NCM powder, treating the NCM powder in an aqueous lithium (Li) solution and a reducing agent at a temperature in the range of 80 °C to 100 °C over a treatment time to re-lithiate the NCM powder, washing and drying the re-lithiated powder, and annealing the dried powder in oxygen at an annealing temperature over an annealing time to produce a cathode powder having a recovered composition, crystal structure, and electrochemical performance. The method may further include mixing 5 mol% excess Li2CO3 with the re-lithiated powder before annealing. In some embodiments, the Li solution is LiOH and the solution may be 0.1 to 4 M LiOH containing 1 to 3% (v / v) of a reducing agent. The reducing agent is preferably an environmentally friendly reducing additive and may be one or a combination of ethanol (ET), ethylene glycol (EG), and hydrogen peroxide (HP). The treatment time may be 2 to 20 hours, more preferably 6 to 12 hours. The annealing temperature may be in the range of 600 to 1000 °C, the annealing time is 1 to 10 hours, more preferably 850 °C, in which case the annealing time is 4 hours. The cathode material is LiNi x Co y Mn zIt may be O2, where 0 < x, y, z < 1 and x + y + z = 1 (“NCM”). The cathode material is LiNi 0.33 Co 0.33 Mn 0.33 O2 (NCM111) or LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622).

Brief Description of the Drawings

[0012] [Figure 1A] Shows an overview of the re-lithiation process of degraded NCM111 according to an embodiment of the method of the present invention, and is a schematic diagram of a direct regeneration process based on hydrothermal re-lithiation of the degraded NCM material. [Figure 1B] Shows an overview of the re-lithiation process of degraded NCM111 according to an embodiment of the method of the present invention, and is a diagram showing the role of GA in the LTHR process of the present invention. [Figure 1C] Shows an overview of the re-lithiation process of degraded NCM111 according to an embodiment of the method of the present invention, and is a diagram comparing the saturated vapor pressure of water at temperatures related to different reactor processing conditions. [Diagram 2] It is a flowchart showing the process of an exemplary material recovery process for recycling used LIBs. [Diagram 3] It is a flowchart showing the process of direct recycling of LIBs according to an embodiment of the present invention. [Figure 4A] Shows the re-lithiation kinetics and compares the Li content in different NCM111 particles with and without re-lithiation obtained from the ICP results. [Figure 4B] Shows the re-lithiation kinetics and plots the compositional changes of NCM111 after cycling during re-lithiation via the LTHR process. [Figure 4C] Shows the re-lithiation kinetics and plots the XRD patterns of cathode samples and control samples (T-NCM111) re-lithiated at 100 °C using three different GAs (ET, EG, and HP). [Figure 4D]FIG. 1 shows the relithiation kinetics and plots the unit cell parameters a and c of different NCM111 samples. [Figure 4E] 1 shows the relithiation kinetics, and the XRD patterns of the samples relithiated at 100° C. and the control samples (T-NCM111 and D-NCM111), respectively. [Figure 4F] 1 shows the relithiation kinetics, and the XRD patterns of the samples relithiated at 100° C. and the control samples (T-NCM111 and D-NCM111), respectively. [Figure 5A] SEM images of different samples: post-cycled NCM111 (panel a), T-NCM111 (panel b), and T-NCM111 relithiated at 100 °C without (panel c), with hydrogen peroxide (panel d), with ethanol (panel e), and with ethylene glycol (panel f). The scale bar in each panel is 10 μm. [Figure 5B] SEM images of different samples: cycled NCM111 (panel a), T-NCM111 (panel b), and T-NCM111 relithiated at 100 °C without (panel c), with hydrogen peroxide (panel d), with ethanol (panel e), and with ethylene glycol (panel f). The scale bar in each panel is 4 μm. [Figure 6A] FIG. 1 shows XPS spectra in the Ni 2p region of different NCM111 samples, including C-NCM111. [Figure 6B] FIG. 1 shows XPS spectra in the Ni 2p region of different NCM111 samples, including T-NCM111. [Figure 6C] FIG. 13: XPS spectra in the Ni 2p region of different NCM111 samples: C-NCM111 relithiated at 100° C. without GA. [Figure 6D] FIG. 13 shows XPS spectra in the Ni 2p region of different NCM111 samples, including C-NCM111 relithiated at 100° C. using GA. [Figure 7A] Electrochemical performance of HS-C-NCM111 and HS-C-NCM622 are shown, with voltage profiles of NCM111 samples regenerated at 100 °C using different GAs, and their comparison with virgin and untreated C-NCM111. [Figure 7B] The electrochemical performances of HS-C-NCM111 and HS-C-NCM622 are shown, along with the cycling stability of NCM111 samples regenerated at 100 °C using different GAs, and their comparison with virgin and untreated C-NCM111. [Figure 7C] FIG. 1 shows the electrochemical performance of HS-C-NCM111 and HS-C-NCM622, plotting the cycling stability of virgin NCM111 and regenerated NCM111. [Figure 7D] Electrochemical performance of HS-C-NCM111 and HS-C-NCM622 are shown, with voltage profiles of regenerated, untreated, and virgin NCM622 samples. [Figure 7E] The electrochemical performance of HS-C-NCM111 and HS-C-NCM622 are shown, as well as the cycling stability of regenerated, untreated, and virgin NCM622 samples. [Figure 7F] FIG. 1 shows the electrochemical performance of HS-C-NCM111 and HS-C-NCM622, plotting the cycling stability of virgin and regenerated NCM622. [Figure 7G] FIG. 1 shows the electrochemical performance of HS-C-NCM111 and HS-C-NCM622, plotting the cycling stability of virgin NCM111 and regenerated NCM111. [Figure 7H] FIG. 1 shows the electrochemical performance of HS-C-NCM111 and HS-C-NCM622, plotting the cycling stability of virgin and regenerated NCM622. [Figure 8A] FIG. 13 plots the voltage profiles of NCM111 regenerated at 90° C. and 100° C., as well as the control samples (T-NCM111 and D-NCM111). [Figure 8B] FIG. 13 plots the cycling stability performance of NCM111 regenerated at 90° C. and 100° C., as well as the control samples (T-NCM111 and D-NCM111). [Figure 9A] FIG. 13 shows the full-cell cycling stability of regenerated HS-C-NCM111 using EG as the reducing agent. [Figure 9B] FIG. 13 shows the full-cell cycling stability of HS-C-NCM622 using EG as the reducing agent. [Figure 10A] FIG. 13 shows the XRD patterns of the post-cycle samples T-NCM111, HS-EG, and HS-NoGA in the scanning range of 10° to 80°. [Figure 10B] FIG. 13 shows the XRD patterns of the post-cycle samples T-NCM111, HS-EG, and HS-NoGA in the scanning range of 18° to 19°. [Figure 11A] FIG. 1 compares the energy consumption for direct recycling processes based on treatment at different temperatures. [Figure 11B] FIG. 10 compares GHG emissions for direct recycling methods based on processing at different temperatures. [Figure 12] FIG. 1 compares the energy consumption, GHG emissions, costs, and benefits of pyrometallurgical ("pyro"), hydrometallurgical ("wet"), and direct ("direct") recycling methods based on the LTHR of the present invention for NCM111. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 1A-1C show an overview of the LTHR relithiation process according to the scheme of the present invention. A simple flow diagram of the process is shown in FIG. 3. According to the redox-mediated LTHR process of the present invention for direct recycling, depleted NCM111 particles 200 are treated via relithiation in LiOH solution with the addition of different reducing agents (step 202). To fulfill the key objective of the present process, specifically the objective of reducing / eliminating the need for environmentally unfriendly materials, an environmentally friendly additive, namely "GA", was used as the reducing agent. In the present process, to effectively regenerate depleted NCM111 at low temperature, the Ni in the depleted NCM111 must be removed. 3+ Ni ions 2+ It is important to reduce the Li to Ni ions and compensate for the Li deficiency in the structure for charge balance. 3+ The reduction of Ni in the crystals is facilitated by using a reducing environment that promotes the lowering of the activation barrier (Figure 1A). In the solution treatment method using a reducing agent that promotes the redox reaction, the Ni in the crystals are converted by the donation of electrons from the reducing agent. 3+ ions can be reduced more easily. As a result, Ni 3+ The facile reduction of Li from solution to the cathode material + and promotes the insertion of Li + (FIG. 1B). Three different GAs (ethanol, hydrogen peroxide, and ethylene glycol) were examined to test this mechanism, however, as one of skill in the art will recognize, additional GAs are known and may be used to provide the desired redox properties, including, but not limited to, glycerol, citric acid, L-ascorbic acid, and other known environmentally friendly reducing agents. Additionally, combinations of GAs may also be used. For the three GAs examined herein, the standard reduction potentials are -0.77 V (standard reduction potential of ethanol versus the standard hydrogen electrode or SHE), 0.15 V (hydrogen peroxide), and -0.72 V (ethylene glycol), respectively, all of which are Ni 3+ / Ni 2+ The Gibbs free energy of reaction between NMC material and GA, ΔG = -nFE = -nF (0.7-E GA) is negative, indicating that the relithiation of degraded NCM materials using GA is thermodynamically favorable. NMR spectra were measured to detect the oxidation products of the three reducing agents in the LiOH solution after the hydrothermal process, and the NMR spectra showed that the oxidation products of ethanol, hydrogen peroxide, and ethylene glycol in the LiOH solution were lithium acetate, oxygen, and lithium oxalate, respectively, and the following reactions occurred: [ka]

[0014] Thus, the reducing additive allows the relithiation to proceed at relatively low temperatures and pressures due to improved redox kinetics, lower energy costs, and improved operational safety (Figure 1C). Although all three GAs were able to assist in the regeneration of NMC, ethylene glycol (EG) was deemed the most suitable for practical applications due to its relatively low cost and for safety reasons (high flash and boiling points). Further evaluation was performed on all three GA candidates, but primarily EG was used as the reducing agent to explore the mechanism of the LTHR process.

[0015] To further evaluate the effectiveness of our LTHR method, two kinds of degraded NCM111 particles were first used to study the effect of redox mediation. One was D-NCM111 with 10% Li loss, which is a model material of the ReCell project, and the other was C-NCM111 from Honda Clarity EV. An initial screening of GAs was performed with D-NCM11, and then the kinetics were systematically studied for C-NCM111. Specifically, C-NCM111 was relithiated in 4 M LiOH solution at 100 °C for 8 h using three different GAs including ethanol (ET), ethylene glycol (EG), and hydrogen peroxide (HP), followed by a short annealing at 850 °C. As a further validation of the important role of the reducing agent, C-NCM111 was treated with LiOH solution under the same conditions without the use of a reducing agent.

[0016] Chemically delithiated NCM111 with Li loss of about 10%, designated as "D-NCM111", was produced by the Materials Engineering Research Facility (MERF) at ARGONNE NATIONAL LABORATORY. Briefly, virgin NCM111 (from Toda America) was reacted with aqueous potassium persulfate to leach Li. The leached material was then washed with water, followed by acetonitrile, and finally dried under vacuum at ambient conditions. This delithiated NCM111 was utilized as starting material for additive screening and was produced in a batch size of 1 kg.

[0017] Referring to FIG. 2, the process flow used to obtain degraded material for evaluating the process of the present invention is shown. Starting at step 100, a commercially available NCM111 cell (20 Ah) was disassembled from a HONDA® Clarity Hybrid EV and separated into three main components: the shell and electrolyte (step 102), the cathode piece (step 104), and the anode piece and separator (step 106). To recover this electrochemically cycled NCM111 material (designated "C-NCM111"), the cathode piece from step 104 was rinsed with dimethyl carbonate (DMC) to remove residual electrolyte. After drying, the cathode piece was immersed in N-methyl-2-pyrrolidone (NMP) (step 108) and then sonicated for 20 minutes to remove the NCM powder, binder, and carbon black (CB) from the aluminum substrate. The resulting solution was centrifuged at 3,500 rpm for 5 minutes to extract the C-NCM111 powder. The precipitate was rinsed multiple times with NMP before recovery and dried for regeneration experiments. CB has a significantly lower density than NCM111, allowing the CB to be isolated by the gravity settling process. Electrochemically cycled and significantly capacity degraded NCM622 (C-NCM622), also obtained from Argonne National Laboratory, was isolated using a similar method.

[0018] Referring again to FIG. 3, the depleted cathode powders 200 (chemically delithiated NCM111, and electrochemically depleted NCM111 and NCM622) were doped with 1%-3% (v / v) of a reducing agent, specifically an environmentally friendly additive (GA), stirred in an aqueous LiOH solution (step 202) and relithiated at 80°C-100°C for 2 to 20 hours ("treatment time") (step 204). The LiOH solution may have a concentration in the range of 0.1-4M. In the majority of the tests, the LiOH concentration was 4M, the temperature was 100°C, and the treatment time was 8 hours. This step was followed by washing with deionized water to remove Li salt residues. After drying, the relithiated powders were mixed with 5 mol% excess Li2CO3 (to compensate for Li loss during the post-annealing process) and "short annealed". (As known in the art, a "short anneal" can be distinguished from a "full anneal" in terms of the conditions and the resulting changes in the material.) In most of the evaluation process, annealing parameters of 850°C for 4 hours (step 206) in oxygen with a heating rate of 5°C / min were used to produce regenerated cathode material (step 208). Overall, the "short anneal" conditions used in the process of the present invention may vary between 1 and 10 hours at temperatures of about 600 to 1000°C. It should be noted that leaching of transition metals may occur during extended cycling, especially in the chopping conditions of spent cathodes. The extent of leaching is influenced by the cycling conditions (temperature, upper cutoff voltage, etc.), the microstructure of the cathode, the type of cathode material (especially Mn-rich cathode materials), etc. However, for the present NCM, leaching of transition metals is not believed to be a significant issue. ICP results did not identify any obvious changes in transition metal composition and dissolution of transition metal ions in the spent NCM compared to the equivalent virgin material. Leaching of transition metals was minimal.

[0019] The chemical composition of the various cathode powders was evaluated by inductively coupled plasma mass spectrometry (ICP-MS, Thermo Fisher Scientific, iCAP RQ model). The surface composition of the samples was analyzed by X-ray photoelectron spectroscopy (XPS). XPS data was collected using a PHI5000 VersaProbe II system (Physical Electronics, Inc.) with AlKα radiation (1486.6 eV). X-ray powder diffraction (XRD) utilizing CuKα radiation (λ = 1.5406 Å, Bruker, D2 Phaser) was used to determine the crystal structure. Rietveld refinement was performed on the XRD results using General Structure Analysis System (GSAS) software with EXPGUI interface. A scanning electron microscope (SEM, FEI XL30) was used to observe the surface structure and morphology of the various cathode particles.

[0020] The electrochemical performance of all samples was measured at approximately 10 mg cm -2 The NCM cathode materials were evaluated by coin cells (half cells) with a cathode mass loading of 10 ... Galvanostatic charge-discharge tests were performed using a Neware battery cycler in the potential range of 3.0–4.3 V, with four activation cycles at a rate of C / 10, followed by 50 cycles at a constant rate of C / 3.

[0021] 4A-4F show the relithiation kinetics according to the method of the present invention. As shown by the ICP-MS results in FIG. 4A, the relithiation kinetics at 100° C. (x Li After the regeneration process with C-NCM111(x = 1.06), Li =0.62) Li content (x Li ) recovered well, and T-NCM111(x Li The stoichiometric composition of the LTHR process was maintained at the same value (Li content = 1.06). The three GAs (ET, HP, and EG) each showed almost the same composition recovery effect. In contrast, in the absence of GA under the same conditions, the Li content is only achieved to 0.98. This effect was also observed in the case of D-NCM111, where the Li content was recovered from 0.9 to 1.06 by the use of GA (see Table 1 below). Furthermore, the inventors evaluated the relithiation kinetics in the composition recovery of the LTHR process (FIG. 4B). By utilizing GA, the LTHR process at 100° C. for 8 hours can achieve the same 100% composition recovery rate as the conventional 220° C. process (see, for example, FIG. 1C).

[0022] The morphology of the regenerated and control samples was further compared. The LTHR process did not affect the morphology of the particles (Figure 5A-5B), which may be attributed to the mild regeneration conditions. The XRD results also confirm the effectiveness of the LTHR process on the recovery of the crystal structure of the C-NCM111 and D-NCM111 samples (Figure 4C-4F). Overall, the diffraction peaks of all samples were in good agreement with the typical α-NaFeO2 structure with the R3m space group. This indicated that the bulk structure of NCM111 was not affected by the electrochemical cycle (C-NCM111), chemical delithiation (D-NCM111), and our regeneration method, again demonstrating the feasibility of the direct regeneration process based on LTHR.

[0023] Throughout the regeneration process, the microstructural changes were clearly observed. C-NCM111 showed a shift of the (003) peak to lower angles (Figure 4D), which is due to the Li +This can be explained by the increase in electrostatic repulsion between oxygen layers along the c-axis direction in the depleted state. On the other hand, the spacing between the peaks of the (108) / (110) doublet increases, which is due to the increase in the Ni 2+ More than Ni 3+ The decrease in the α lattice constant is due to the decrease in the average intermetallic distance caused by the small effective ionic radius of . A similar peak shift can also be observed in D-NCM111 (Figure 4E-F). The lattice constants of unit cell a and unit cell c determined by Rietveld refinement are shown in Table 1. [Table 1]

[0024] The lattice constant a decreased from 2.860 Å (T-NCM111) to 2.837 Å (C-NCM111) and 2.848 Å (D-NCM111), respectively. The lattice constant c increased from 14.247 Å (T-NCM111) to 14.383 Å (C-NCM111) and 14.311 Å (D-NCM111), respectively, which is consistent with the peak shifts in the XRD results. After the LTHR process, the (003), (108), and (110) peaks obviously shifted back to their original positions similar to those of virgin T-NCM111, indicating the restoration to the original microstructure (Figures 4D and 4F). The lattice constants a and c of the regenerated samples were close to those of T-NCM111, indicating that Li was introduced into the lattice structure despite the lower relithiation temperature. + This indicated that the ions had reached an equilibrium state. Furthermore, the Li / Ni mixing ratios of C-NCM111 decreased from 5.47 to 2.40 (ET), 2.43 (HP), and 2.41 (EG), respectively (Figure 4E), reaching almost the same mixing ratio as that of virgin T-NCM111 (2.39). In contrast, the Li / Ni mixing ratio did not fully recover to the original state without GA, which again demonstrates that GA is helpful in regenerating NCM111 in the LTHR process.

[0025] To further understand the role of GA in the LTHR process, XPS measurements were performed to determine the Ni valence state in different NCM111 before annealing (Figure 6A-D). 3+ / Ni 2+ Due to the lower redox potential of Ni, only the valence state of Ni is expected to change, since the maximum Li deficiency in this case is 0.4. As shown in Figure 6A, in C-NCM111, 40.78% of Ni is Ni. 3+ In the presence of GA, i.e., in LiOH with GA, Ni 2+ Ni reduced to 3+ After relithiation in LiOH alone (Figure 6C), about 21.07% of Ni was converted to Ni 3+ In this case, H2O was left as Ni 3+ Ni 2+ In contrast, in the presence of GA, Ni 3+ All Ni is produced through the LTHR process. 2+ Similar results were observed for D-NCM111, where relithiation in GA-containing LiOH solution was more effective than in LiOH without GA. Specifically, 24.68% Ni 2+ However, chemical delithiation results in Ni 3+ After LTHR treatment without GA, 22.79% of Ni was still converted to Ni 3+ This is 1.89% Ni. 3+ Only at low temperatures 2+ These results indicate that Ni 3+ From Ni 2+ This confirms the importance of GA in promoting the reduction of Li to LiCl from the solution to the Li-deficient sites in the NCM cathode. + This further promotes reinsertion of the charge, compensating for the charge.

[0026] The electrochemical performance of C-NCM111 regenerated by the LTHR process followed by a short annealing at 850 °C (denoted as "HS-C-NCM111") was evaluated by half-cell testing. Figures 7A-7B plot the voltage profile and cycling stability for various materials and processing conditions. Significant Li loss (38%) and crystal structure degradation reduced the initial capacity of C-NCM111 to 51 mAhg. -1 Ni 3+ The effective ionic radius of Ni 2+ is smaller than 0.01, so when Li is deficient, Ni 3+ The higher the cation mixing ratio, the more readily the Li sites are occupied by Li. + Blocking the transport of Li + After regeneration, the regenerated and unused samples had a storage capacity of approximately 155 mAhg at C / 10 in Gen2 electrolyte. -1 The C-NCM111 processed without GA showed only 92% capacity retention at C / 3 after 60 cycles. In contrast, the NCM111 regenerated with different GAs from the LTHR process all retained similar capacity retention at C / 3 after 60 cycles, about 96%, showing the same cycling stability as the virgin T-NCM111. A similar trend was also observed in the D-NCM111 samples with LP40 in the half cells.

[0027] D-NCM111 is 134.0mAhg at C / 10 -1 After LTHR followed by a short annealing, the initial capacity of HS-D-NCM111 was 154 mAhg at C / 10. -1 The capacity retention after 50 cycles improved to 91% at C / 3. This result was comparable to that of virgin T-NCM111. Half-cell tests were performed using a 10 mg / cm 2 Under these conditions, the cycling performance was limited by the poor stability of the lithium metal anode. 2The rate and half-cell performance (200 cycles at 1C) of HS-C-NCM111-GA (with EG) was evaluated at a cathode loading of 100 mAhg at 1C (Figure 7C, G). -1 The capacity of HS-C-NCM111-GA was 157mAhg at 0.1C, 0.3C, 1C, 3C, and 5C, respectively, with a capacity retention of 83% after 200 cycles, which was similar to that of virgin T-NCM111. -1 , 151mAhg -1 , 140mAhg -1 , 130mAhg -1 , 113mAhg -1 The capacity of the unused T-NCM111 was 156mAhg at 0.1C, 0.3C, 1C, 3C, and 5C, respectively. -1 , 151mAhg -1 , 140mAhg -1 , 129mAhg -1 , 113mAhg -1 These results indicated that the rate capability of the regenerated NCM111 was restored. HS-C-NCM111-GA paired with a graphite anode (cathode loading: 10 mg / cm 2 As shown in Figure 9A, in the full cell test, HS-C-NCM111-GA showed 138 mAhg at 1C. -1 It showed an initial capacity of 120mAhg after 100 cycles. -1 The capacity of the HS-C-NCM111-GA was maintained at 100%. This result was comparable to that of virgin T-NCM111 under the same conditions. The HS-C-NCM111-GA was able to achieve the same electrochemical performance as T-NCM111 in rate, half-cell, and full-cell tests, confirming the success of the regeneration method of the present invention.

[0028] Also in Figures 8A and 8B, the delithiated NCM111 regenerated by the LTHR process at 90°C and 100°C followed by short annealing was designated as "HS-D-NCM111-GA-90°C" and "HS-D-NCM111-GA-100°C". The initial capacity of HS-D-NCM111-GA-90°C was 154.0 mAhg at C / 10.-1 At C / 3, the capacity reached 149.8mAhg, which is the same level as that of virgin NCM111. -1 The initial capacity of 10 ...

[0029] Considering the growing interest in high-Ni NCM cathodes, we extended the testing to NCM622 by comparing the electrochemical properties between cycled (C-NCM622), LTHR regenerated (denoted as HS-C-NCM622), and virgin samples using Gen2 electrolyte (Figure 7D-F, H). As mentioned before, all three GAs performed well for the regeneration of NMC111, but EG was deemed the most suitable for practical applications due to its advantages of low cost and safety. Therefore, in the extended testing of NCM622, EG was used as the reducing agent for the LTHR process.

[0030] C-NCM622 is 121mAhg at C / 10 -1 The initial capacity of HS-C-NCM622 was 175 mAh at C / 10 and showed 76% capacity retention at C / 3 after 60 cycles. Due to the LTHR process and short annealing, the initial capacity of HS-C-NCM622 was 175 mAh at C / 10. -1 The capacity retention improved to 92% at C / 3 after 60 cycles. This result is equivalent to that of virgin T-NCM622. To demonstrate the electrochemical performance of the regenerated NCM622, we performed electrochemical experiments using 3 mg / cm 2 The rate capability and cycling stability in half cells (200 cycles at 1C) of HS-C-NCM622-GA (regenerated using EG as GA) were evaluated at a cathode loading of 10 mg / cm (Figure 7F, Figure 7H). HS-C-NCM622-GA yielded similar rate capability and long cycling stability as T-NCM622. HS-C-NCM622-GA paired with graphite anode (cathode loading: 10 mg / cm) was also evaluated at 10 mg / cm. 2In the full cell test, HS-C-NCM622-GA achieved 154 mAhg at 1C in the first cycle (Figure 9B). -1 capacity of 130mAhg after 100 cycles at 1C. -1 The capacity of the HS-C-NCM622-GA was maintained at 100%. This result is close to the capacity of virgin T-NCM111 under the same conditions. In summary, the HS-C-NCM622-GA was able to achieve the same electrochemical performance as that of T-NCM622 in the rate, half-cell, and full-cell tests. Thus, the successful regeneration of NCM622 was confirmed. The successful regeneration of both NCM111 and NCM622 using different GAs suggests that the direct recycling method based on the LTHR of the present invention has high efficiency and versatility. These results generally indicate that the Ni 3+ This supports the use of a reducing environment to lower the activation barrier for reduction and relithiation of .

[0031] To investigate the difference in structural stability between the regenerated and virgin materials, the cycled HS-EG, HS-NoGA, and T-NCM111 electrodes (denoted as "cycled HS-EG," "cycled HS-NoGA," and "cycled T-NCM111," respectively) were characterized by XRD (Figure 10A-B). The XRD diffraction peaks of these samples remained in good agreement with a typical layered structure without major impurity phases, indicating that the bulk structures of virgin and regenerated NCM111 were not affected by electrochemical cycling. No obvious structural differences were observed between cycled HS-EG and cycled T-NCM111, which also demonstrated the feasibility of the direct regeneration method based on LTHR. However, as mentioned above, without the addition of GA, the Li content, Li / Ni mixing ratio, transition metal valence, electrochemical stability, etc. of the regenerated materials cannot be fully restored to their original states. Due to the more significant Li deficiency and lattice expansion along the c-axis, the (003) peak of cycled HS-NoGA shifted to lower angles after cycling compared with cycled HS-EG and cycled T-NCM111. Overall, this again demonstrates that GA can promote the regeneration of NCM111 in the LEHR process, maintain its structural stability, and provide a certain degree of recovery effect.

[0032] In conventional hydrothermal relithiation processes, NCM materials require a high-pressure reactor (typically an autoclave) to maintain pressures above 25 bar (the saturation pressure of water) at 220° C. (see FIG. 1C). Using the method of the present invention, the enhanced relithiation kinetics enabled by GA allows LTHR to be carried out at temperatures below the boiling point of water. This allows the relithiation process to be carried out at ambient pressure, eliminating the need for a high-pressure reactor. Specifically, lowering the relithiation temperature to 100° C. can reduce the pressure required for the LTHR process of the present invention to about 1 bar. Replacing conventional high-pressure reactors with low-cost vessels increases the feasibility of large-scale direct regeneration for industrial applications without the need for additional safety precautions required by conventional methods.

[0033] An assessment of the environmental and economic impacts of LTHR-based direct regeneration was performed using the EverBatt model developed by Argonne National Laboratory, with a throughput of 10,000 tonnes of spent LIBs per year. A life cycle analysis (LCA) was performed for the entire LTHR direct recycling process and the conventional high-pressure reaction in terms of energy consumption (Figure 11A), greenhouse gas (GHG) emissions (Figure 11B), operating costs, and overall benefits. Modelling assuming the same pre- and post-treatment results in a total energy consumption of 5.28 MJ kg of spent batteries in the conventional high-pressure regeneration reaction. -1 Only 4.22MJkg of used batteries in LTHR -1 It is shown that the GHG emissions are reduced by approximately 0.03 kg per kg of battery by using LTHR for the direct regeneration process compared to the conventional high-pressure regeneration reaction at 220 °C (Figure 5, panel a).

[0034] By reducing the temperature of the relithiation process, low-grade industrial waste heat could potentially be utilized as the heat source for the LTHR process. The total costs of the direct recycling process of NCM batteries were estimated to be US$ 2.07 and US$ 2.25 for spent battery cells processed at 100°C and 220°C, respectively. Therefore, the production of regenerated cathodes using LTHR has the potential to bring an additional profit of US$ 0.18 per kg of spent battery. In addition, significant cost savings can be achieved due to the relaxed safety requirements.

[0035] The direct recycling method based on the LTHR of the present invention for recycling NCM was also compared with the conventional pyrometallurgical and hydrometallurgical recycling processes using LCA. Figure 12 shows the results of this comparison. The energy consumption of the pyrometallurgical and hydrometallurgical recycling processes of spent NCM cells was 18.497 MJ kg, respectively. -1 and 30.710 MJ kg -1 This means that the energy consumption is only 4.166MJkg -1The GHG emissions from pyrometallurgy (2.457 kg) and hydrometallurgy (2.258 kg) were significantly higher than that from the direct recycling process based on LTHR (panel a) for 1 kg of spent NCM cells, as shown in panel b. These can be explained by the generation of large amounts of chemicals used in the pyrometallurgical and hydrometallurgical recycling processes in the pyrometallurgical process. The costs and benefits associated with the three recycling processes are also modeled and analyzed, as shown in panels c and d of Figure 12. The total costs for pyrometallurgy, hydrometallurgy, and direct recycling based on LTHR for 1 kg of spent NCM cells are US$3.10, US$2.54, and US$2.04, respectively. This is due to the expensive equipment, the use of large amounts of chemicals, and the large energy consumption of the pyrometallurgical and hydrometallurgical recycling processes. Due to the high value of Ni and Co, pyrometallurgical and hydrometallurgical recycling of 1 kg of spent NCM cells can provide profits of US$2.16 and US$3.07, respectively. The total energy usage, GHG emissions, and processing costs are significantly reduced, making the LTHR-based direct regeneration method of the present invention a preferred option for closed-loop safe LIB recycling. Overall, the LTHR-based direct recycling method meets each element of the "4H" approach of battery recycling (high efficiency, high economic benefit, high environmental benefit, and high safety), and represents a new trend in sustainable LIB recycling.

Claims

1. 1. A method for regenerating spent lithium ion battery cathode material, wherein the cathode material is in powder form, the method comprising: treating the cathode material in an aqueous lithium (Li) solution and a reducing agent at a temperature in the range of 80° C. to 100° C. for a treatment time sufficient to relithiate the cathode material; washing and drying the treated cathode material; and annealing the treated, dried cathode material in oxygen at an annealing temperature for an annealing time to produce a regenerated cathode material; A method comprising:

2. The method of claim 1 , wherein the aqueous Li solution comprises LiOH.

3. The method of claim 1, wherein the cathode material is treated at approximately 1 bar.

4. 2. The method of claim 1, wherein the reducing agent is one or a combination of ethanol (ET), ethylene glycol (EG), hydrogen peroxide (HP), glycerol, citric acid, and L-ascorbic acid.

5. 10. The method of claim 1, wherein the treatment time is from 2 to 20 hours.

6. The method of claim 5, wherein the treatment time is about 8 hours at 100°C.

7. 2. The method of claim 1, wherein the annealing temperature is in the range of 600°C to 1000°C and the annealing time is in the range of 1 to 10 hours.

8. 8. The method of claim 7, wherein the annealing temperature is 850°C and the annealing time is 4 hours.

9. The cathode material is LiNi ｘ Co ｙ Mn ｚ O ２ 2. The method of claim 1, wherein 0<x, y, z<1 and x+y+z=1.

10. The NCM is LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ 10. The method of claim 9, wherein the compound is (NCM111).

11. The NCM is LiNi ０．６ Co ０．２ Mn ０．２ O ２ 10. The method of claim 9, wherein the compound is (NCM622).

12. 2. The method of claim 1, wherein the aqueous Li solution contains 1 to 3% (v / v) of the reducing agent and 0.1 to 4 M LiOH.

13. Before annealing, 5 mol% excess Li ２ CO ３ 10. The method of claim 1, further comprising mixing a fluorine-containing compound with the treated cathode material.

14. 1. A method for treating lithium ion battery cathode material from spent battery cells, comprising: Separating a cathode strip comprising a cathode strip substrate from the battery cell; treating the cathode pieces in one or more solvent solutions to remove NCM powder, binder, and carbon black from the cathode piece substrate and extract the NCM powder; treating the NCM powder in an aqueous lithium (Li) solution and a reducing agent at a temperature in the range of 80° C. to 100° C. for a treatment time sufficient to produce a relithiated NCM powder; washing and drying the relithiated NCM powder; and annealing the dried powder in oxygen at an annealing temperature for an annealing time to produce a cathode powder having a restored composition, crystalline structure, and electrochemical performance; A method comprising:

15. Before annealing, 5 mol% excess Li ２ CO ３ 15. The method of claim 14, further comprising mixing a tetrahydrofuran with the relithiated powder.

16. 15. The method of claim 14, wherein the aqueous Li solution comprises LiOH.

17. The method of claim 14, wherein the NCM powder is treated at approximately 1 bar.

18. 15. The method of claim 14, wherein the environmentally friendly reducing additive is one or a combination of ethanol (ET), ethylene glycol (EG), hydrogen peroxide (HP), glycerol, citric acid, and L-ascorbic acid.

19. 15. The method of claim 14, wherein the treatment time is from 2 to 20 hours.

20. The method of claim 19, wherein the treatment time is 8 hours at 100°C.

21. 15. The method of claim 14, wherein the annealing temperature is in the range of 600°C to 1000°C and the annealing time is in the range of 1 to 10 hours.

22. 22. The method of claim 21, wherein the annealing temperature is 850°C and the annealing time is 4 hours.

23. The cathode material is LiNi ｘ Co ｙ Mn ｚ O ２ 15. The method of claim 14, wherein 0<x, y, z<1 and x+y+z=1.

24. The NCM powder is LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ 24. The method of claim 23, wherein the compound is (NCM111).

25. The NCM powder is LiNi ０．６ Co ０．２ Mn ０．２ O ２ 24. The method of claim 23, wherein the compound is (NCM622).

26. 15. The method of claim 14, wherein the aqueous Li solution contains 1-3% (v / v) of the reducing agent and 0.1 to 4 M LiOH.

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