Recycling and upgrading remanufacturing of lithium ion batteries by purification and regeneration integrated material engineering (PRIME)

Abstract

The invention relates to a method for directly recycling a lithium ion battery cathode material. The method comprises the following steps: performing hydrothermal treatment on cathode black powder (CBM) in an alkaline solution to decompose polyvinylidene fluoride (PVDF) and remove electrolyte salt; washing the treated CBM in deionized water to remove redundant alkaline solution, conductive carbon, degraded PVDF and impurities; and annealing the washed material to repair the crystal structure and remove residual carbon.

Description

[0001] Related applications

[0002] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 430,301, filed on December 5, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to the recycling, recovery and regeneration of materials from electrode waste, battery waste and spent lithium-ion batteries. Background Art

[0004] The exponential growth of lithium-ion batteries (LIBs) in consumer electronics over the past few decades has raised concerns about how to deal with the vast amount of end-of-life (EoL) batteries, driven by the high demand for avoiding adverse environmental impacts. The further rapid growth in demand for LIBs for electric vehicles has also put pressure on the supply chain of key materials. Shortages of these key materials, particularly transition metals such as Ni and Co, could soon become a bottleneck in the global transition to battery-powered vehicles. This rapid shift creates an opportunity to promote the "waste-to-wealth" and environmentally friendly aspects of battery recycling by establishing local secondary supply chains for these materials. Direct recycling is one of the most promising solutions for extracting the highest value from EoL batteries because it directly recovers the cathode active material (CAM), maintains target product values, exhibits low energy consumption, and provides a net greenhouse gas (GHG) emission offset. Significant efforts have been made to scale up and streamline this technology to match it with established hydrometallurgical and pyrometallurgical techniques in industry. Some key technical challenges of direct recycling include rigorous pretreatment to remove binder / conductive carbon / aluminum fragments / electrolyte salt impurities and reliable regeneration of high-purity crystalline structures to meet industrial standards, which limit its industrial applicability.

[0005] Direct recycling of cathode materials has been demonstrated on a laboratory scale, where cathodes are processed in small quantities of a few grams and typically involve different pretreatment methods for purification. The cathodes obtained from EoL cells typically have different impurities, including electrolyte salts (typically LiPF6), conductive carbon (typically Super P65 / P45), aluminum fragments, and binders (typically polyvinylidene fluoride (PVDF)), which can be referred to as "cathode black mass" (CBM). The impurity removal process is often referred to as "cleaning." Heating or solvent washing have both been shown to effectively remove impurities, but they also have disadvantages. During the heating process, PVDF, conductive carbon, and LiPF6 introduce fluorine and carbon into the reaction, which compromises the quality of the resulting cathode material. For example, carbon on the surface will provide a CO2 environment when burned, which is known to react with active surface oxygen anions, ultimately leading to the formation of Li2CO3 and irreversible loss of Li in the bulk. PVDF is known to be a low-temperature fluorination reagent for metal oxides and should therefore be avoided. Fluorine compounds (PVDF and LiPF6) lead to the formation of HF during heating, which acts as a dopant within the cathode material, replacing oxygen to form MF2 (M = transition metal), or leading to irreversible loss of Li by forming LiF on the surface. Li loss should be avoided because it makes the circulating NMC material, which is already depleted of Li, more susceptible to oxygen loss. This will promote the formation of the rock salt phase, resulting in a high impedance cell. LiF is also quite insoluble in water and has a very high evaporation temperature. Once formed, it is difficult to remove from the cathode surface and due to its low ionic conductivity (10 -9 / cm), and also increase impedance.

[0006] An alternative impurity removal process is solvent washing, which is effective in removing different impurities. The electrode can be soaked in dimethyl carbonate or other organic solvents to remove electrolyte salt residues. By dissolving PVDF in toxic organic solvents (such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), etc.), the conductive carbon and active material are released in the solvent, and the conductive carbon and PVDF are removed together. Although solvent treatment has high separation yields, the large-scale use of organic solvents raises serious environmental concerns and is subject to strict government regulations, making it impossible to scale up. Other green solvent alternatives have been proposed, such as triethyl phosphate and Cyrene, however, the additional solvent may cause new residues to appear on the cathode surface and should eventually be removed. In addition, the recycling industry typically uses mechanical methods to separate CBM from aluminum foil, which can cause trace amounts of Al fragments to remain in the CBM. Aluminum fragments can act as dopants in CAM and have even been shown to improve electrochemical performance. However, controlling the threshold dopant limit (0.4 t.%) on a large scale will be challenging.

[0007] Therefore, there remains a need for a sustainable and environmentally sound battery recycling process that can scale to the industrial level required to support a large-scale global transition to batteries as a primary energy source. Summary of the Invention

[0008] The method of the present invention addresses the rapidly growing problem of battery waste accumulation by integrating the purification and relithiation processes of CBM, providing a more environmentally friendly, cost-effective and scalable recycling technology. By purifying the CBM from unwanted binders, electrolyte residues, aluminum fragments and conductive carbon, the resulting purified product can be integrated with existing relithiation and sintering steps. No organic solvents are required in the process of the present invention, where a 100g batch of CBM (NCM111) was successfully regenerated to its original state. The process of the present invention has steps derived and designed from existing hydrothermal and sintering technologies for cathode synthesis and is therefore safe and easy to scale to industrial levels. The process can be extended to NCM622, NCM811 (or higher nickel up to 99wt.%), NCA, NCMA and mixed CBMs in various states, and the chemical solution can be reused to maximize process efficiency. The method of the present invention solves one of the main challenges of scaling up direct recycling in an eco-friendly and economical manner, making it suitable for further industrial adoption.

[0009] The method of the present invention, called "Purification and Regeneration Integrated Materials Engineering" or "PRIME", provides full recycling capabilities, including recovery and regeneration of materials from electrode waste, battery waste and spent batteries, including cathode active materials (CAMs) with different chemistries, such as LiCoO2 (LCO), LiNix Co y Mn z O2(x+y+z=1)(NCM or NMC), LiNi x Co y Al z O2(NCA), LiMn2O4(LMO), LiFePO4(LFP), LiMn x Fe y PO4(LMFP), etc. Although these different cathode materials may involve different amounts of dopants, or may have surface coatings, the recycled CAM produced by the method of the present invention can be used to make new batteries with electrochemical properties equivalent to those of the original batteries.

[0010] Direct recycling methods typically involve multiple complex steps, which increase the complexity and cost of processing spent batteries, making these processes less economically viable and more challenging to scale. Compared to other direct recycling processes, the method of the present invention provides an integrated process for recycling cathode materials that significantly reduces the number of physical and chemical processing steps required, integrating purification and regeneration in a single step.

[0011] In one aspect, a method for directly recycling cathode materials for lithium-ion batteries comprises: hydrothermally treating cathode black material (CBM) in a lithium-ion-containing solution to decompose polyvinylidene fluoride (PVDF) and remove electrolyte salts; washing the treated CBM in a washing solution to remove excess lithium-ion-containing solution, conductive carbon, degraded PVDF, and impurities; and annealing the washed material to repair the crystal structure and remove residual carbon, thereby recovering cathode active material (CAM), wherein the CAM can be used to make new batteries. In some embodiments, the lithium-ion-containing solution can be one or a combination of LiOH, NaOH, KOH, an alkali metal hydroxide solution, a water-soluble lithium salt, and an electrolyte salt. The lithium-ion-containing solution can be an alkali metal hydroxide solution comprising one or a combination of Li2CO3, lithium acetate, Li2SO4. The lithium ion-containing solution may include an electrolyte salt comprising one or a combination of LiPF6, LiBF4, LiClO4, lithium bis(oxalato)borate (C4BLiO8) and lithium difluoro(oxalato)borate (C2BF2LiO4). The lithium ion-containing solution may have a lithium concentration in the range of 0.1 to saturation at 25°C. In some embodiments, the lithium ion-containing solution may be 0.1 to 5.34M LiOH. The hydrothermal treatment step includes subjecting the CBM to a temperature in the range of 50 to 300°C in the lithium ion-containing solution for a duration in the range of 1 to 10 hours. The washing step may include mechanically agitating the CBM in the washing solution. In some embodiments, the lithium ion-containing solution may be a recaptured and reused solution from one or more previous hydrothermal treatments. The CBM may be one or more of NCM111, NCM622, NCM811, NCA, NCMA, and a hybrid CBM.

[0012] In another aspect, a method for directly recycling cathode materials for lithium-ion batteries may include: hydrothermally treating cathode black material (CBM) in a treatment solution comprising an alkaline solution for decomposing polyvinylidene fluoride (PVDF) and removing electrolyte salts, and a lithium ion solution for relithiating the CBM; washing the treated CBM in a wash solution to remove excess treatment solution, conductive carbon, degraded PVDF, and impurities; and annealing the washed material to repair the crystal structure and remove residual carbon, thereby recovering cathode active material (CAM), wherein the CAM can be used to make new batteries. In some embodiments, the treatment solution may be one or a combination of LiOH, NaOH, KOH, an alkali metal hydroxide solution, a water-soluble lithium salt, and an electrolyte salt. The treatment solution may be an alkali metal hydroxide solution comprising one or a combination of Li2CO3, lithium acetate, Li2SO4. The treatment solution may include an electrolyte salt comprising one or a combination of LiPF6, LiBF4, LiClO4, lithium bis(oxalato)borate (C4BLiO8) and lithium difluoro(oxalato)borate (C2BF2LiO4). The lithium concentration of the treatment solution at 25°C may be in the range of 0.1 to saturation. In some embodiments, the solution containing lithium ions may be 0.1 to 5.34M LiOH. The hydrothermal treatment step includes subjecting the CBM to a temperature in the range of 50 to 300°C in the treatment solution for a duration in the range of 1 to 10 hours. The washing step may include mechanically agitating the CBM in the washing solution. In some embodiments, the treatment solution may be a recaptured and reused solution from one or more previous hydrothermal treatments. The CBM may be one or more of NCM111, NCM622, NCM811, NCA, NCMA, and a mixed CBM.

[0013] Direct recycling of active materials from spent batteries and manufacturing waste is highly desirable for battery recycling, where the cathode mixture remains intact. Several challenges hinder the development and scaling of direct recycling, including impurity removal, batch uniformity, and scalability, all of which are required to be economically viable. Regarding impurity removal, the binder in cathode black material (CBM) presents one of the greatest challenges. Polyvinylidene fluoride (PVDF), the most commonly used binder in cathode manufacturing, inherently binds the active cathode material to the conductive carbon. Conventional purification steps for direct recycling involve dissolution or decomposition to remove the PVDF, which is either economically unfeasible or faces challenges with the removal of fluorine impurities (LiF). Batch uniformity is another challenge, as cathode materials from different cells typically have different SOCs after long-term cycling. Lithium replenishment needs to be well controlled. Finally, scalability remains an issue for direct recycling. PRIME uses an innovative approach to bridge the gap between laboratory-scale direct recycling and current industrial recycling methods. PRIME is compatible with both spent batteries and manufacturing waste. PRIME removes impurities; some components dissolve, while others decompose. PRIME relithiates cathode materials with varying lithium contents, returning them to the same original lithium ratio. Crucially, PRIME promises to be scalable to ton-scale cathode recycling yields. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of one embodiment of the inventive process indicating scalable regeneration of CAM via multi-step integrated direct recirculation.

[0015] Figure 2A is a schematic diagram of the mechanism of binder decomposition and active material release; Figure 2B FTIR spectra showing chemical degradation of PVDF were plotted; and Figure 2C The results of thermogravimetric analysis (TGA) of CBM (NCM111) compared to cathode material recycled using the process of the present invention are plotted, and the binder and carbon contents are estimated.

[0016] Figures 3A-3C SEM images of pCAM, CBM, and rCAM, respectively; Figure 3D is a wide-angle SEM image of rCAM; Figure 3E is the XRD comparison of pCAM, CBM, and rCAM, indicating the bulk relithiation of the recycled materials; Figure 3F The XPS spectra of fluorine in pCAM, CBM, and rCAM were compared; Figure 3G provided DTA and DSC data of CBM and rCAM; Figure 3H and 3I The XPS data of oxygen and carbon were compared separately.

[0017] Figure 4A is an elemental analysis chart comparing the carbon content of pCAM and rCAM; Figure 4B EDS analysis results of aluminum tracer are provided.

[0018] Figures 5A-5E The electrochemical performance of the regenerated cathode material is shown, where Figure 5A shows the voltage curve in the first cycle; Figure 5B The cycling stability in half-cells is plotted; Figure 5C The extended cycling stability of the recycled cathode presented in a half-cell is shown; Figure 5D Plotting the rate performance of the regenerated cathode compared to the original cathode; and Figure 5E The cycling stability in the full cell is plotted.

[0019] Figure 6A A schematic diagram of the use of LiOH to replenish the solution during the hydrothermal step is provided; Figure 6B The first cycle voltage curve of NCM111 (rCAM) recovered in the reused LiOH supplement solution is plotted; Figure 6C is a comparison of the (003) XRD peak data of different samples; and Figure 6D The first cycle voltage curve of recycled NCM 622 (rCAM 622) using the process of the present invention is shown.

[0020] Figure 7A The initial cycles of original NCM811 (pCAM NCM811) and recycled NCM811 (rCAM NCM811) are shown. Figure 7B and Figure 7C Results are presented separately for NCA and NCMA materials. DETAILED DESCRIPTION

[0021] Figure 1The schematically illustrated cathode recycling process of the present invention involves three main steps: (step 102) hydrothermal ("HT") relithiation with PVDF decomposition and electrolyte salt removal; (step 104) washing to remove excess alkaline solution, conductive carbon, degraded PVDF, and other impurities; and (step 106) annealing to repair the crystal structure and remove residual carbon. In comparison, a typical laboratory-scale direct recycling process involves multiple purification steps using toxic organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl carbonate (DMC) to dissolve the PVDF binder and release the cathode material (sometimes accelerated by sonication), plus centrifugation to separate the conductive carbon from the cathode active material (CAM), making the entire process time-consuming. The cathode electrode typically includes PVDF and carbon black as significant inactive materials, however, such materials are generally not conducive to recycling / upcycling processes.

[0022] The release mechanism of the cathode material that occurs in steps 102 and 104 is Figure 2A Schematically shown in . To determine the mechanism of PVDF degradation in the HT process, pure PVDF membranes were produced by coating a glass plate with PVDF, drying it, and peeling it off the glass plate. The transparent membrane was treated with HT reaction in an alkaline solution (e.g., 0.1 to 4 M LiOH solution) under the same conditions typically used for cathode HT relithiation (i.e., 220°C for 4 hours). After the reaction, the transparent PVDF membrane decomposed into a black, brittle film. The decomposed membrane product completely lost its mechanical integrity during washing and decomposed into powder. Reference Figure 2B , Fourier-transform infrared spectra (FTIR) analysis of the dried decomposed membrane showed that the characteristic fluorocarbon peaks (1000-1250 cm -1 ) disappears, and the broad peak of double bond carbon appears at 1600 cm -1 This result is consistent with earlier studies showing that PVDF membranes undergo defluorination in alkaline environments. This result confirms two key points: first, that PVDF can be defluorinated / decomposed under the same HT conditions used for cathode relithiation, and second, that the decomposition products have lost enough mechanical integrity to be easily broken apart by gentle agitation during washing.

[0023] Variations of HT treatment are known in the art to be effective for relithiation, including different combinations of temperature, time, pressure, and atmosphere. For example, PCT Publication WO2023 / 164073, incorporated herein by reference, discloses a low-temperature HT process for relithiation. Therefore, the specific temperatures and times cited herein are provided as examples of HT treatment, the key objective being to decompose PVDF and substantially remove other impurities by the alkaline solvent used in the HT process and subsequent washing. In addition, HT treatment is not limited to LiOH, and a variety of different treatment solutions can be used to perform the relithiation and removal steps of the electrolyte salt. The treatment solution can include one or a combination of the following: LiOH, NaOH, KOH, an alkali metal hydroxide solution (e.g., one or a combination of Li2CO3, lithium acetate, Li2SO4), a water-soluble lithium salt, and an electrolyte salt (e.g., one or a combination of LiPF6, LiBF4, LiClO4, lithium bis(oxalato)borate (CBLiO8), and lithium difluoro(oxalato)borate (CBF2LiO4)).

[0024] Cathode regeneration based on hydrothermal relithiation, followed by a short post-annealing step, has been widely reported in the art. Many workers have demonstrated the regeneration of spent LiCoO2 (LCO), LiNi 0.33 Co 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 The morphology, composition and crystal structure of O2 (NCM622) and LiFePO4 (LFP) cathodes were effectively reconstructed, resulting in electrochemical performance levels comparable to those of the original materials. See, for example, E. Gratz et al., “A closed loop process for recycling spent lithium ion batteries”, Journal of Power Sources 262 (2014) 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", Adv. Energy Mater. 9 (2019) 1900454; S. Sloop et al., "A direct recycling case study from a lithium-ion battery recall", Sustainable Materials and Technologies 25 (2020) e00152; L. Brückner et al., "Industrial Recycling of Lithium-Ion Batteries—A Critical Review of Metallurgical Process Routes", Metals 10 (2020) 1107; Y. Shi et al., "Effective regeneration of LiCoO2 from spent lithium-ion batteries: A direct approach towards high-performance active particles", Green Chem. 20 (2018) 851 - 862; and P. Xu et al., "Efficient Direct Recycling of Lithium-Ion Battery Cathodes by Targeted Healing", Joule 4 (2020) 2609 - 2626. The described methods are characterized by simple operation and low energy consumption, using a hydrothermal relithiation process to recycle the cathode composition without considering the variation of Li loss in different feedstocks of degraded LIBs. The process also uses a short sintering process to restore the cathode microstructure with the desired stoichiometry and crystallinity.

[0025] It has been shown that HT relithiation in an alkaline environment is an important step for regenerating cathode materials. By reacting hydroxides in solution with the side PVDF binder, the efficiency of the relithiation conditions can be further improved. The obtained CBM (NCM111) with 3 wt.% PVDF (by Figure 2CThermogravimetric analysis (TGA) shown) was directly processed under the same HT relithiation conditions for further processing. Washing (step 104) was performed after the hydrothermal treatment with deionized water (DI) to remove decomposed PVDF, alkali, and carbon impurities. In some embodiments, other washing solutions can be used, for example, low concentration alkaline solutions, and mild inorganic / organic acid solutions can be used instead of DI water or in addition to DI water.

[0026] After the washing process, most of the carbon impurities are removed, which is beneficial for the subsequent annealing process. To provide a direct comparison, Figure 3A -C are backscattered mode scanning electron microscopy (SEM) images of pristine CAM (pCAM), CBM, and recycled CAM (rCAM), respectively. Figure 3B The CBM shown in clearly shows that the binder and carbon cover most of the cathode surface. This observation confirms Figure 2C TGA data plotted in , which shows the presence of about 9 wt% total binder and conductive carbon. Figure 3G The corresponding differential thermal analysis (DTA) and differential scanning calorimetry (DSC) data are provided in . Figure 3C The rCAMs seen in Figure 3 exhibited a very clean surface, indicating a successful purification process. Meanwhile, the secondary spherical shape was well preserved, which could help maintain packing density after electrode casting.

[0027] To verify the effectiveness of the relithiation process, both X-ray diffraction patterns (XRD) and inductively coupled mass spectrometry (ICP-MS) were performed. Figure 3E XRD patterns of pCAM, CBM and rCAM are provided. All samples showed The α-NaFeO2 structure of the space group indicates that there is no phase change in the bulk structure during the entire process. Figure 3E As shown in the center figure, in CBM, the (003) peak indicating the c-lattice parameter exhibits a leftward peak shift compared to pCAM, indicating that the increase in the c-lattice constant is due to the increased electrostatic repulsion between oxygen layers caused by lithium deficiency. As shown in the right figure, the spacing between the (108) / (110) doublets is larger than that of the pristine sample, indicating that the a-lattice parameter in CBM is reduced, which is due to the higher oxidation state of nickel (Ni) in the lithium-deficient state. 3+ Rather than Ni 2+ In contrast, the (003) peak in rCAM shifts to the right, and the (108) / (110) doublet spacing decreases, aligning with that of the pristine sample, indicating successful relithiation. Figure 3C It is also shown that the annealing step removes residual carbon or decomposed binder impurities, leaving a clean and clear morphology of the rCAM. Figure 3DA wider SEM image of rCAM in Figure 4 highlights the general morphology preservation in the process of the present invention.

[0028] X-ray photoelectron spectroscopy (XPS) was performed to track the fluorine on the surface. Figure 3F As shown in Figure 3, a clear signal of F from the binder in the energy range of 680-690 eV was observed in the CBM, where both C-F bonds and metal-F bonds were present, indicating the presence of both the binder and the cathode electrolyte interface (CEI). For rCAM, no fluorine signal was detected as for pCAM, indicating that the fluorine element was successfully removed from the CBM. Figure 3H and 3I XPS data for oxygen and carbon are provided separately, confirming the removal of the cathode electrolyte interface from the recycled cathode. Figure 3H The O1s from CBM after treatment has a clear TM-O peak around 528 eV and no peak around 533 eV, further confirming the removal of CEI. For C1s, the disappearance of the C-F bond around 290 eV in the rCAM sample also verifies the removal of PVDF.

[0029] Transition metal (TM) leaching is a potential cause of LIB degradation. To identify CBMs before and after the recycling process, ICP-MS was performed to verify the Ni / Co / Mn ratios, and the relevant results are shown in Table 1.

[0030]

[0031] Table 1

[0032] As shown in the table, the TM ratios of both samples were the same and remained constant as in the original material. Therefore, the recovery process of the present invention maintains the TM stoichiometry and avoids any leaching. To further evaluate the carbon residue of the samples, combustion elemental analysis was performed to quantify the carbon from pCAM and rCAM, and the results are shown in Figure 2. Figure 4A The carbon residue weight ratio of rCAM is similar to that of pCAM, further confirming the efficiency of carbon removal. EDS was performed to track aluminum impurities. The results are shown in Figure 4B The signal of aluminum present in CBM disappears in rCAM, indicating the effective removal of aluminum impurities.

[0033] After confirming the impurity removal and the quality of rCAM, the electrochemical performance was evaluated in half-cell and full-cell configurations, and the relevant results are shown in Figures 5A-5E In. Figure 5AAs shown in Figure 2, the discharge capacity of rCAM is 155 mAh / g, while that of pCAM is 154 mAh / g, compared to the voltage curves obtained from the first cycle at C / 10. The initial coulombic efficiency (ICE%) of rCAM (89%) is very similar to that of pCAM (88%), so that the curves are almost indistinguishable. Half-cell cycling at C / 3 shows that the discharge capacity retention of rCAM after 100 cycles is 98%, which essentially overlaps with the results of pCAM, as shown in Figure 2. Figure 5B The longer half-cell cycle of rCAM is shown in Figure 5C As shown, the discharge capacity retention is 90% after more than 400 cycles, further highlighting the remarkable quality of rCAM, whose results are indistinguishable from those of pCAM. The rate performance was evaluated in a half-cell configuration and the data are shown in Figure 5D The curves for the two samples completely overlap. The well-matched performance between pCAM and rCAM validates the direct recycling process. Finally, a full cell was assembled using graphite as the anode. Figure 5E Similar trends are shown for pCAM and rCAM with capacity retention greater than 94% after 100 cycles at 1 C. Thus, rCAM clearly exhibits electrochemical performance that is competitive with pCAM in all respects.

[0034] To establish the sustainability feature of the process of the present invention, the HT replenishment solution was recovered as supernatant after a single process to regenerate a new batch of CBM.

[0035] refer to Figure 6A As shown in the process schematic, the 4M LiOH supplemented alkaline solution used for the hydrothermal treatment of a 100g batch of CBM (NCM111) was stored. The same solution was used for the hydrothermal treatment of an additional batch of CBM, referred to as "Batch 2". The HT-CBM was washed with a large amount of deionized water to remove surface alkali, decomposed PVDF and carbon impurities. Batch 2 was dried in a convection oven at 80°C overnight, then mixed with 5mol% Li2CO3 and annealed in a box furnace at 850°C for 4 hours with a temperature increase of 5°C per minute and allowed to cool naturally after annealing. The product obtained was labeled "rCAM-G2" (or rCAM generated in 2× used LiOH). After the same procedure using the same supplementary solution, another product "rCAM-G3" (or rCAM generated in 3× used LiOH) was obtained again. The obtained product was used to cast electrodes.

[0036] The samples relithiated from the spent solutions were further processed using the same procedure. Figure 6BThe voltage curve for the first cycle of operation at C / 10 in a half-cell configuration is shown. Interestingly, the capacity achieved for this sample, 155 mAh / g, is also similar to the original capacity, as is the CBM regenerated from fresh solution. The same LiOH solution was reused multiple times to demonstrate robustness. Correlated XRD analysis and electrochemical performance indicate that the accumulated impurities observed during material regeneration have a negligible impact on the quality of the final product. Comparison of the corresponding energy efficiencies between pCAM, rCAM, rCAM-G2, and rCAM-G3 shows negligible differences between the samples.

[0037] In real life, CBMs obtained from EoL cells with various states of health have different Li deficiencies. To show the flexibility of our process in handling such CBM mixtures, we mixed NCM111 CBMs obtained from two different cells (i.e., CBM#1 and CBM#2) and evaluated them in a 1:1 ratio (mixed black powder or MBM). To verify the different Li deficiencies, the XRD of CBM#1 and CBM#2 were compared with rCAM. Figure 6C As shown, the change in the (003) peak shift indicates the difference in Li deficiency between CBM#1 and CBM#2. After the recycling process of the present invention, rCAM-MBM exhibits a fully recovered Li composition, with the 003 peak shifted back to match the original NCM111. In addition, the electrochemical performance was analyzed to ensure the quality of the obtained product, with the capacity consistent with rCAM for several cycles.

[0038] The same direct recycling process was applied to NCM622 CBM (CBM 622). As shown in Table 1, CBM 622 obtained from the cycled cells was analyzed by ICP-MS, TGA and XRD to evaluate the black powder. CBM 622 was found to be lithium deficient by ICP-MS and XRD, while TGA showed 6.5 wt% PVDF and carbon impurities. CBM 622 was treated with the same process as NCM111 CBM, except for the annealing step, which was carried out under a pure oxygen flow rather than an air flow. The oxygen atmosphere is a key factor in the annealing of Ni-rich NCM cathodes because it is Ni-free due to the preference of Ni for Ni. 2+ Oxidation state and oxygen deficiency tend to form a rock salt phase. CBM622 washed in NMP was used as a control for this material. Figure 6DThe voltage profiles of the first cycle in half-cells made from recycled NCM622 cathodes (rCAM 622) and control CBM 622 washed in NMP are compared. The NCM622 CBM half-cell had an ICE% of 79%, likely due to impurities, and only a discharge capacity of 119 mAh / g. ICP-MS and XRD confirmed the lithium-deficient and deformed bulk phase shown in Table 1. In contrast, the half-cell made from rCAM 622 exhibited an ICE of 82% and a discharge capacity of 176 mAh / g, which closely matches commercial-grade NCM622. Long-term cycling of the half-cell data showed a capacity retention of 94% after 200 cycles, demonstrating the high quality of the recycled cathode material.

[0039] Figure 7A Initial cycles of original NCM811 (pCAM NCM811) and recycled NCM811 (rCAM NCM811) are shown, with nearly identical curves indicating successful regeneration. Figure 7B and Figure 7C Similar results are provided for NCA and NCMA materials, respectively.

[0040] From a technical perspective, the process of the present invention bridges the gap between laboratory-scale direct recycling and industrial-scale processes, taking into account economic and ecological considerations. The Everbatt model, developed by Argonne National Laboratory, was used to compare different recycling pathways to highlight the economic and ecological impact of organic solvents on direct recycling processes. Many reported processes use NMP (or similar toxic organics) as a solvent to remove PVDF, while others use DMC. Comparisons between older pyrometallurgical processes, currently practiced hydrometallurgical processes, existing laboratory-scale versions of direct recycling (using NMP and DMC), and the organic-free direct recycling method of the present invention reveal several economic benefits. By avoiding the use of expensive NMP and DMC organics, processing material costs can be reduced by approximately $5 per kilogram of battery. In addition to the initial material cost of these organic liquids, the general and plant overhead costs associated with their use (including labor, supervision, management, and maintenance costs) can also be saved, amounting to approximately $2.16 per kilogram of battery. On an industrial scale, direct recycling processes that rely on organic solvents could potentially be less profitable than current pyrometallurgical and hydrometallurgical technologies. Processes that rely on organic solvents are even more impractical for scaling up recycling operations because the large amounts of toxic materials increase the risk of accidents and environmental damage that could occur at any of the multiple stages, including handling, storage, disposal, and transportation. Therefore, the effectiveness of the present method in avoiding these economic and environmental obstacles makes it not only practical on an ecological scale but also profitable for businesses.

[0041] Examples : The following examples provide details of the procedures used during the processing and evaluation of the process of the present invention.

[0042] Example 1: Collecting cathode black powder: Scrapped prismatic cells (20 Ah) were manually disassembled in a fume hood, and the long cathode strips were carefully separated and cut into approximately 5×5 inch pieces. After disassembly, the cathode strips were stored in a fume hood for 2 days and then stored in a vacuum oven at 80° C. overnight to dry. 100 g of CBM of NCM111 was obtained as starting material by scraping the cathode strips with a blade. Cathode strips of NCM622 were obtained from Argonne National Laboratory, and its cathode black powder was obtained by scraping with a blade using the same process. Original NCM111 (Toda Kogyo Corp., Japan) or pCAM and NCM622 or “pCAM622” (Targray, Montreal, CA) were used as controls.

[0043] Example 2: Regeneration of cathode active material: 100g NMC111 CBM was added directly to a 500ml autoclave reactor with 300ml 4M LiOH solution and heated at 220°C for 4 hours (optimization was obtained from P.Xu et al., ACSStain.Chem.Eng.2021, 9, 4543, which is incorporated herein by reference). After hydrothermal heating, the supernatant was gently poured out and stored for subsequent reuse. Deionized water was added to the settled product, and mechanical agitation was provided by stirring at 500rpm for 30 minutes. The product was stirred in deionized water, then filtered using vacuum filtration and further washed with plenty of water. The product was collected from the filter and dried overnight at 80°C in a convection oven. The yield at this point was 91wt.% based on the weight of CAM. The product was then ground with 5mol% excess Li2CO3 and annealed in a box furnace for 4 hours, heated to 850°C at 5°C / min and cooled naturally. A batch of NCM622 CBM was also processed using the same process up to the annealing step, which was performed in a tube furnace under oxygen flow.

[0044] Example 3: Mechanism study:A 5 wt.% PVDF (KYNAR 2800) adhesive solution was prepared by stirring the ingredients together overnight using NMP as a solvent. The solution was cast as a thin PVDF film on glass with a thickness of approximately 50 μm using a doctor blade method. After drying, the transparent film was easily peeled off with tweezers. A 50 mg PVDF membrane portion was cut and placed in a 4 M LiOH solution, followed by hydrothermal heating at 220°C for 4 hours. (As mentioned above, HT parameters can vary) After HT treatment, the film turned black and disintegrated into a powder. It was washed with deionized water to remove the LiOH, and FTIR spectroscopy was performed using a Thermo Scientific Nicolet 6700FTIR instrument equipped with a Smart iTR diamond ATR fixture. FTIR analysis was also performed on a portion of the film retained as a control.

[0045] Example 4: Characterization of black powder and recycled materials: TGA, DTA and DSC were performed on the two CBM samples using an SDT650 instrument heated to 1000°C at 10°C / min in air. SEM images were obtained using a FEI Apreo SEM (Thermo Scientific) in backscattering mode. The voltage and current were set to 1 kV and 0.1 nA, respectively. Bulk crystal structure analysis of the powder samples was performed using a Rigaku Miniflex XRD device. Stoichiometric compositions and ratios were calculated using ICP-MS, Thermo Scientific, iCAP RQ model. XPS was performed by Kratos Supra with a 10 -8 A 15 kV Al anode source at Torr vacuum was used for the measurements, with a step size of 1.0 eV for the measurement scan and 0.1 eV for the high-resolution scan. The C1s peak at 284.6 eV was used for calibration.

[0046] Example 5: Electrochemical analysis:The original NCM111 was used as a control for comparison with the regenerated sample. Typically, the cathode powder was mixed with PVDF (KYNAR 2800) and carbon black (Super P65) in NMP (Sigma-Aldrich, anhydrous 99.5%) in a mass ratio of 8: 1: 1 to form a uniform slurry. The slurry was cast by a doctor blade and then dried overnight at 120 ° C under vacuum. The 12 mm cathode disc was cut, rolled and used to assemble CR2032 button cells in an argon environment glove box, with Li metal as the anode. The electrolyte used was a battery-grade lithium hexafluorophosphate (LiFP6) solution in ethylene carbonate (EC) and ethyl methyl carbonate (EMC), consisting of 1.0 M LiPF6 in EC / EMC=30 / 70 (v / v) (Gen2, from Gotion, US). The mass loading was 4-5 mg / cm 2 For the anode in the full cell, the same procedure was followed with PVDF and NMP mixed in a mass ratio of 8:1:1, replacing graphite with cathode powder (Superior Graphite). Graphite anode discs were cut to 13 mm (active material loading 4-5 mg / cm 2 ) and pre-lithiated by direct contact with Li metal for 10 minutes to compensate for future lithium loss during cycling. The battery was left to rest for 8 hours and then tested for constant current charge-discharge cycling between the 3-4.3 V voltage window using a Neware battery cycler, with 4 activation cycles at a C / 10 (1C=155 mA / g) rate, and long cycling at C / 3 for half cells and 1C for full cells.

[0047] The inventive method described herein is highly effective for directly recycling recycled CAM from cathode black powder. All impurities, including PVDF binder, conductive carbon, electrolyte salts, and aluminum fragments were successfully removed. The hydrothermal and washing steps completely removed fluorine, aluminum, and most conductive carbon residues, while the annealing step helped to recover the CAM phase and remove any remaining trace carbon. The process provided 100% recovery of the electrochemical performance of the recycled CAM, replicating the performance metrics of pCAM. Direct recycling of active materials from spent batteries and manufacturing waste is critical for battery recycling. Previous challenges have hindered the development and scale-up of direct recycling.

[0048] The PRIME process of the present invention bridges the gap between direct laboratory-scale recycling and current industrial recycling methods. PRIME is compatible with both spent batteries and manufacturing waste. PRIME removes impurities and relithiates cathode materials with varying lithium contents, restoring them to the same original lithium ratio. Importantly, PRIME offers the ability to scale to ton-scale cathode recovery yields.

Claims

1. A method for directly recycling lithium-ion battery cathode materials, the method comprising: hydrothermally treating cathode black mass (CBM) in a lithium-ion-containing solution to decompose polyvinylidene fluoride (PVDF) and remove electrolyte salts; washing the treated CBM in a washing solution to remove excess lithium ion-containing solution, conductive carbon, degraded PVDF, and impurities; as well as The washed material is annealed to repair the crystal structure and remove residual carbon, thereby recovering the cathode active material (CAM), which can be used to make new batteries. 2 . The method according to claim 1 , wherein the lithium ion-containing solution comprises one of LiOH, NaOH, KOH, an alkali metal hydroxide solution, a water-soluble lithium salt, and an electrolyte salt, or a combination thereof.

3. The method according to claim 1, wherein the lithium ion-containing solution comprises an alkali metal hydroxide solution, and the alkali metal hydroxide solution comprises one of Li2CO3, lithium acetate, Li2SO4, or a combination thereof.

4. The method according to claim 1, wherein the lithium ion-containing solution comprises an electrolyte salt, the electrolyte salt comprising one of LiPF6, LiBF4, LiClO4, lithium bis(oxalato)borate (C4BLiO8) and lithium difluoro(oxalato)borate (C2BF2LiO4) or a combination thereof. The method according to claim 1 , wherein the lithium concentration of the lithium ion-containing solution at 25° C. is in the range of 0.1 to saturation. The method of claim 1 , wherein the lithium ion-containing solution comprises 0.1 to 5.34 M LiOH.

7. The method of claim 1, wherein the hydrothermal treatment comprises subjecting the CBM to a temperature in the range of 50 to 300°C in the lithium ion-containing solution for a duration in the range of 1 to 10 hours.

8. The method of claim 1, wherein washing comprises mechanically agitating the CBM in the wash solution.

9. The method of claim 1 , wherein the lithium ion-containing solution comprises recaptured and reused solution from one or more previous hydrothermal treatments.

10. The method of claim 1, wherein the CBM is one or more of NCM111, NCM622, NCM811, NCA, NCMA, and a hybrid CBM.

11. A method for directly recycling lithium-ion battery cathode materials, the method comprising: hydrothermally treating cathode black powder (CBM) in a treatment solution comprising an alkaline solution for decomposing polyvinylidene fluoride (PVDF) and removing electrolyte salts and a lithium ion solution for relithiating the CBM; washing the treated CBM in a washing solution to remove excess treatment solution, conductive carbon, degraded PVDF, and impurities; as well as The washed material is annealed to repair the crystal structure and remove residual carbon, thereby recovering the cathode active material (CAM). 12 . The method according to claim 11 , wherein the treatment solution comprises one of LiOH, NaOH, KOH, an alkali metal hydroxide solution, a water-soluble lithium salt, and an electrolyte salt, or a combination thereof.

13. The method of claim 11, wherein the treatment solution comprises an alkali metal hydroxide solution comprising one of Li2CO3, lithium acetate, Li2SO4, or a combination thereof.

14. The method of claim 11, wherein the treatment solution comprises an electrolyte salt comprising one of LiPF6, LiBF4, LiClO4, lithium bis(oxalato)borate (C4BLiO8), and lithium difluoro(oxalato)borate (C2BF2LiO4), or a combination thereof.

15. The method of claim 11, wherein the lithium concentration of the treatment solution at 25°C is in the range of 0.1 to saturation.

16. The method of claim 11, wherein the treatment solution comprises 0.1 to 5.34 M LiOH.

17. The method of claim 11, wherein hydrothermal treatment comprises subjecting the CBM to a temperature in the treatment solution in the range of 50 to 300°C for a duration in the range of 1 to 10 hours.

18. The method of claim 11, wherein washing comprises mechanically agitating the CBM in the wash solution.

19. The method of claim 11, wherein the treatment solution comprises recaptured and reused solution from one or more previous hydrothermal treatments.

20. The method of claim 11, wherein the CBM is one or more of NCM111, NCM622, NCM811, NCA, NCMA, and a hybrid CBM.

Images