Solid-phase regeneration method of waste ternary positive electrode material

Abstract

The invention discloses a solid-phase regeneration method of a waste ternary positive electrode material, and belongs to the technical field of recycling of positive electrode materials. The solid phase regeneration method comprises the following steps: preparing a substrate containing a graphene oxide film; the preparation method comprises the following steps: forming a nano titanium dioxide particle layer on the surface of a graphene oxide film, constructing a graphene layer on the surfaces of titanium dioxide particles to obtain a substrate containing a composite layer, stripping the composite layer from the substrate to obtain a graphene oxide-titanium dioxide-graphene composite material, adding ternary material slurry into a suspension of the graphene oxide-titanium dioxide-graphene composite material, stirring, centrifuging, and drying to obtain the graphene oxide-titanium dioxide-graphene composite material. And sintering to obtain the regenerated ternary material. By constructing a composite coating layer, catalyzing PVDF decomposition during low-temperature sintering, protecting the material from HF erosion, reacting with residual alkali on the surface of the material during high-temperature sintering, and constructing a fast ion conductor interface, cleaning and removing of impurities and functional regeneration of the material interface are synchronously realized in a single solid-phase process; the method is short in process flow, environment-friendly and excellent in regenerated material performance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery cathode material recycling and regeneration technology, and in particular to a solid-phase regeneration method for waste ternary cathode materials. Background Technology

[0002] The waste ternary materials (medium and low nickel) generated during the production process are recycled. The recycled ternary electrode sheets are mechanically peeled, ground, and sorted to obtain ternary black powder. This ternary black powder contains impurities such as conductive agents and binders. Among them, the binder polyvinylidene fluoride (PVDF) has a large molecular weight and strong chemical stability, and is currently generally removed by pyrolysis and solvent washing.

[0003] The chemical properties of waste ternary materials (medium and low nickel) do not change significantly. During heat treatment to remove the binder, PVDF decomposes and produces a large amount of HF gas. This gas severely corrodes the ternary material at high temperatures, causing a serious decline in its performance. Therefore, the material purified by heat treatment can generally only be used for hydrometallurgy. The method of solvent washing of PVDF generally involves removing PVDF from the ternary material by dissolving and ultrasonically peeling it off. Although this method can avoid high-temperature HF corrosion, it requires a large amount of solvent, about 15 times the amount of ternary material. These solvents contain PVDF molecules, which can only be separated by evaporation / precipitation from unsuitable solvents. The cost of separating and subsequently purifying N-methylpyrrolidone (NMP) is very high.

[0004] Therefore, there is an urgent need to develop an integrated solid-phase regeneration technology that can remove PVDF harmlessly at lower temperatures, avoid HF corrosion, and directly repair material surface defects and improve performance. This technology is essential for the green and high-value recycling of ternary materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a solid-phase regeneration method for waste ternary cathode materials. This invention designs and constructs a graphene-titanium dioxide-graphene oxide composite coating layer with a "sandwich" structure. At low temperatures, this coating catalyzes the decomposition of PVDF and protects the material from HF corrosion. At high temperatures, it reacts with residual alkali on the material surface to construct a fast-ion conductor interface. Thus, impurity removal and functional regeneration of the material interface are simultaneously achieved in a single solid-phase process. This process is short, does not rely on large amounts of organic solvents, is environmentally friendly, and produces regenerated materials with excellent performance.

[0006] The technical solution of the present invention is as follows:

[0007] The first aspect of this invention protects a solid-phase regeneration method for waste ternary cathode materials, comprising the following steps: S1: Preparation of ternary material slurry; S2: Coat the substrate surface with graphene oxide dispersion and dry to obtain a substrate containing graphene oxide film; S3: Immerse the substrate containing graphene oxide film in a mixture of tetrabutyl titanate and ethanol, and then slowly add a mixture of water and hydrochloric acid. After the addition is completed, nano-titanium dioxide particles are formed on the surface of the graphene oxide film, thus obtaining a substrate containing nano-titanium dioxide / graphene oxide film. S4: Immerse the substrate containing nano-titanium dioxide / graphene oxide film in a graphene dispersion, add water and stir to allow graphene to self-assemble on the surface of the substrate containing nano-titanium dioxide, thereby forming a sandwich structure composite film of graphene oxide-titanium dioxide-graphene on the substrate surface. Wash and dry the substrate of the sandwich structure composite film of graphene oxide-titanium dioxide-graphene to obtain the graphene oxide-titanium dioxide-graphene composite material and the substrate, respectively. S5: The graphene oxide-titanium dioxide-graphene composite material is mixed with a solvent to obtain a composite material suspension; the composite material suspension is added to the ternary material slurry in S1, stirred, centrifuged, and dried to obtain the ternary material coated with the composite material; S6: Sinter the ternary material coated with the composite material obtained in S5 to obtain the recycled ternary material.

[0008] Preferably, in S1, the ternary slurry is obtained by mechanically peeling and sorting waste ternary electrode sheets to obtain a positive current collector and ternary black powder respectively; the ternary black powder is then dispersed with a solvent. Preferably, the solid content of the ternary slurry is 45-55%.

[0009] Preferably, in step S2, the concentration of the graphene oxide dispersion is 0.1~1.0 mg / mL; The graphene oxide dispersion is obtained by dispersing graphene oxide with water. The substrate includes at least one of silicon wafers and quartz glass.

[0010] Preferably, in step S3, the volume concentration of tetrabutyl titanate in the tetrabutyl titanate-ethanol mixture is 5% to 15%. The ethanol is anhydrous ethanol; The pH value of the water-hydrochloric acid mixture is 1 to 3.

[0011] Preferably, in S3, the volume ratio of the tetrabutyl titanate-ethanol mixture to the water-hydrochloric acid mixture is 100:1.5~3.5.

[0012] Preferably, in S4, the graphene dispersion is obtained by dispersing graphene in a solvent; The concentration of the graphene dispersion is 0.1~1.0 mg / mL; The solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide; Preferably, the graphene is few-layer graphene with ≤10 layers.

[0013] Preferably, in step S4, the volume ratio of water to graphene dispersion is 1.5-2.5:1; The stirring time is 1-2 hours; The drying process is freeze-drying.

[0014] Preferably, in step S5, the concentration of the composite material suspension is 10~20 mg / mL; The solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide; The mass of the composite material in the composite material suspension accounts for 2-4 wt% of the mass of the ternary material in the ternary material slurry; The stirring time is 2-3 hours.

[0015] Preferably, in S6, the sintering is a three-stage sintering; In the three-stage sintering process: the first stage sintering temperature is 460~480℃, the time is 3~4h, and the atmosphere is nitrogen; the second stage sintering temperature is 650~680℃, the time is 1~2h, and the atmosphere is oxygen; the third stage sintering temperature is 720~750℃, the time is 6~8h, and the atmosphere is air or oxygen.

[0016] A second aspect of this invention protects a ternary material obtained by the solid-phase regeneration method described in the first aspect above.

[0017] The beneficial technical effects of this invention are as follows: This invention constructs a graphene-titanium dioxide-graphene oxide "sandwich" composite structure and coats the ternary material to be treated with this structure to obtain a ternary material with a coating layer. Further sintering yields a regenerated ternary material, achieving low-temperature catalytic decomposition and harmless treatment of PVDF in the ternary material, protecting it from HF corrosion. Furthermore, during the high-temperature sintering stage, the titanium dioxide in the composite material can react with residual alkali on the surface of the ternary material to form a fast-ion conductor interface. This invention's regeneration method simultaneously achieves the clean removal of impurities and the functional regeneration of the material interface in a single solid-phase process, while avoiding HF corrosion of the ternary material during sintering. Specifically, in the graphene-titanium dioxide-graphene oxide "sandwich" composite structure constructed in this invention, the titanium dioxide positioned between the graphene and graphene oxide acts as a catalyst, lowering the decomposition temperature of PVDF and causing it to initially decompose at low temperatures, avoiding the large amount of HF generated during concentrated decomposition at high temperatures that directly corrodes the cathode material. The outer graphene layer acts as a physical barrier during the initial calcination stage, mitigating the HF corrosion of the titanium dioxide and ternary material. The inner layer of graphene oxide preferentially binds to the residual alkali sites in the ternary material, preventing uneven coating that could lead to preferential reaction between hydrogen fluoride and residual alkali. Furthermore, the graphene / titanium dioxide / graphene oxide "sandwich" composite structure protects titanium dioxide from HF corrosion, allowing F to escape as a gas and preventing its introduction into the titanium dioxide and ternary material.

[0018] This invention achieves synergistic "impurity removal-repair-enhancement" by constructing a multifunctional integrated coating layer. The "sandwich" coating layer constructed by this method plays a triple role in the regeneration process: "catalyst / protective layer," "sacrificial template," and "interface modifier." The lithium titanate or titanium-doped interface layer ultimately generated in situ on the material surface effectively eliminates residual alkali and provides a high-speed lithium-ion transport channel, thereby improving the overall first-cycle efficiency, rate performance, and long cycle life of the regenerated ternary material.

[0019] Furthermore, the entire regeneration process of this invention is primarily a solid-phase reaction, using only twice the solvent of ternary materials. Moreover, it is recovered through direct evaporation and condensation, resulting in absolutely no solid waste or waste liquid generation, thus avoiding the use of large amounts of solvent and complex wastewater treatment. The NMP solvent can be centrifuged for recycling, conforming to green chemistry principles. The three-stage sintering process is ingeniously designed, with clear objectives for each stage, facilitating industrial-scale production. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the embodiments.

[0021] To address the existing problems in recycling waste ternary materials, this invention provides a solid-phase regeneration method for waste ternary materials.

[0022] The first aspect of this invention provides a solid-phase regeneration method for waste ternary cathode materials, comprising the following steps: S1: Preparation of ternary material slurry; S2: The graphene oxide dispersion is coated onto the substrate surface and dried to form an ultrathin graphene oxide film that is completely attached to the substrate surface, thus obtaining a substrate containing the graphene oxide film. S3: Immerse the substrate containing graphene oxide film in a mixture of tetrabutyl titanate and ethanol, and then slowly add a mixture of water and hydrochloric acid. After the addition is completed, nano-titanium dioxide particles are formed on the surface of the graphene oxide film, thus obtaining a substrate containing nano-titanium dioxide and graphene oxide film. S4: Immerse the substrate containing nano-titanium dioxide-graphene oxide film in a graphene dispersion, add pure water dropwise at room temperature, and stir slowly to allow graphene sheets to self-assemble on the surface of the substrate containing nano-titanium dioxide, thereby forming a sandwich structure composite film of graphene oxide-titanium dioxide-graphene on the substrate surface. Wash and dry the substrate containing the sandwich structure composite film of graphene oxide-titanium dioxide-graphene to separate the graphene oxide-titanium dioxide-graphene composite material from the substrate, thus obtaining the graphene oxide-titanium dioxide-graphene composite material. S5: The graphene oxide-titanium dioxide-graphene composite material is mixed and dispersed with a solvent to obtain a composite material suspension; the composite material suspension is added dropwise to the ternary material slurry in S1, stirred, centrifuged, and dried to obtain the ternary material coated with the composite material. S6: Sinter the ternary material coated with the composite material obtained in S5 to obtain the recycled ternary material.

[0023] It is understood that this invention constructs a graphene-titanium dioxide-graphene oxide "sandwich" composite structure and coats the ternary material to be treated with this structure to obtain a ternary material with a coating layer. Further sintering yields a regenerated ternary material, achieving low-temperature catalytic decomposition and harmless treatment of PVDF in the ternary material, protecting it from HF corrosion. Furthermore, during the high-temperature sintering stage, the titanium dioxide in the composite material can react with residual alkali on the surface of the ternary composite material to form a fast ion conductor interface. Therefore, the regeneration method of this invention simultaneously achieves the clean removal of impurities and the functional regeneration of the material interface in a single solid-phase process, while avoiding the corrosion of the ternary material by HF during sintering.

[0024] In some embodiments, in S1, the ternary slurry is obtained by mechanically peeling and sorting waste ternary electrode sheets to obtain a positive current collector and ternary black powder respectively; the ternary black powder is dispersed with a solvent, wherein the solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide.

[0025] In this invention, the method for obtaining ternary black powder by stripping and sorting from waste ternary electrode sheets is not limited, and any method that can achieve the effects of this invention is within the scope of protection of this invention. The ternary black powder is a low- to medium-nickel ternary material, that is, a ternary material of NCM6 series or below.

[0026] In some embodiments, the solid content of the ternary slurry is 45-55%, including but not limited to 45%, 50%, and 55%.

[0027] In some embodiments, in S2, the concentration of the graphene oxide dispersion is 0.1~1.0 mg / mL; including but not limited to 0.1 mg / mL, 0.5 mg / mL, and 1.0 mg / mL.

[0028] In some embodiments, in S2, the graphene oxide dispersion is obtained by dispersing graphene oxide with water.

[0029] In some embodiments, in S2, the substrate is a hydrophilic substrate, preferably comprising at least one of a silicon wafer and quartz glass. The silicon wafer is a silicon wafer with a silicon dioxide layer.

[0030] In some embodiments, in S2, the coating method includes at least one of spin coating, drop coating, and dip coating.

[0031] In some embodiments, in S2, the drying is performed under reduced pressure at a low temperature, where the low temperature refers to 50~70°C, including but not limited to 50°C, 60°C, and 70°C.

[0032] In some embodiments, in S3, the volume concentration of tetrabutyl titanate in the tetrabutyl titanate-ethanol mixture is 5% to 15%; including but not limited to 5%, 10%, and 15%.

[0033] In some embodiments, in S3, the ethanol is anhydrous ethanol; In some embodiments, in S3, the pH value of the water-hydrochloric acid mixture is 1 to 3, including but not limited to 1, 2, and 3.

[0034] In some embodiments, in S3, the volume ratio of the tetrabutyl titanate-ethanol mixture to the water-hydrochloric acid mixture is 100:1.5 to 3.5, including but not limited to 100:1.5, 100:2, 100:2.5, 100:3, and 100:3.5.

[0035] In step S3 of this invention, the substrate containing the graphene oxide film is immersed in a tetrabutyl titanate-ethanol mixture. Then, a water-hydrochloric acid mixture is slowly added dropwise. During this process, the tetrabutyl titanate hydrolyzes to generate positively charged nano-titanium dioxide. The titanium dioxide is generated and loaded in situ on the graphene oxide surface, forming a composite layer. In this reaction, the tetrabutyl titanate undergoes hydrolysis in a trace amount of water and a strongly acidic environment. The resulting nascent titanium dioxide hydrate nanoparticles, under the low pH conditions of the system, undergo surface protonation and carry a stable positive charge (Ti-OH2). + Since one side of the two-dimensional graphene oxide film is attached to the substrate and is in an inactive state, while the other side contains abundant negatively charged oxygen-containing functional groups, positively charged nano-titanium dioxide particles are selectively and firmly adsorbed on one side of the graphene oxide film through electrostatic interactions, thus achieving uniform unilateral loading.

[0036] In some embodiments, in S4, the graphene dispersion is obtained by dispersing graphene in a solvent. The concentration of the graphene dispersion is 0.1~1.0 mg / mL; including but not limited to 0.1 mg / mL, 0.5 mg / mL, and 1.0 mg / mL.

[0037] The solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide.

[0038] Preferably, the graphene is few-layer graphene with ≤10 layers.

[0039] In some embodiments, in S4, the volume ratio of water to graphene dispersion is 1.5 to 2.5:1, including but not limited to 1.5:1, 2:1, and 2.5:1. In some embodiments, the stirring time in S4 is 1 to 2 hours, including but not limited to 1 hour, 1.5 hours, and 2 hours.

[0040] Understandably, step S4 involves immersing the substrate containing the nano-titanium dioxide-graphene oxide film into a graphene dispersion, then slowly stirring with pure water added dropwise at room temperature. This allows the graphene sheets to self-assemble onto the side of the titanium dioxide particles loaded in step S3, forming a "sandwich" composite film of graphene oxide-titanium dioxide-graphene. During this process, the selected dispersion system effectively maintains the stability of the graphene sheets, preventing re-aggregation. After the addition of water, the lack of solvation between the graphene sheets leads to a spontaneous and tight stacking of the sp² carbon network with the aromatic domains of graphene oxide and the surface of titanium dioxide, along with van der Waals forces. This results in a complete, continuous, and highly conductive encapsulation layer on the titanium dioxide side, and the sequential formation of a sandwich composite film of graphene oxide-titanium dioxide-graphene on the substrate surface.

[0041] Understandably, after obtaining the substrate of the sandwich-structured composite film containing graphene oxide-titanium dioxide-graphene, it is washed and dried. During the drying process, the substrate will gradually peel off from the composite film, resulting in the graphene oxide-titanium dioxide-graphene composite material and the substrate, respectively.

[0042] In some embodiments, in S5, the concentration of the composite material suspension is 10~20 mg / mL; including but not limited to 10 mg / mL, 15 mg / mL, and 20 mg / mL.

[0043] In some embodiments, in S5, the solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide.

[0044] In some embodiments, in S5, the mass of the composite material in the composite material suspension accounts for 2 to 4 wt% of the ternary material slurry, including but not limited to 2 wt%, 3 wt%, and 4 wt%.

[0045] In some embodiments, the stirring time in S5 is 2-3 hours.

[0046] Understandably, when the composite material suspension is added to the ternary material slurry, the graphene oxide side of the graphene oxide-titanium dioxide-graphene composite material still contains abundant oxygen-containing negatively charged active groups, which can adsorb onto the residual alkali on the surface of the ternary material, thus loading onto the surface of the ternary material and forming a composite-coated ternary material. This strategy of preferentially binding to the residual alkali sites of the ternary material can achieve directional and uniform coating, thereby avoiding the erosion of the material body and surface residual alkali by hydrogen fluoride generated by PVDF cracking during subsequent sintering.

[0047] In some embodiments, in S6, the sintering is a three-stage sintering; In the three-stage sintering process: the first stage sintering temperature is 460~480℃, including but not limited to 460℃, 470℃, and 480℃, for 3~4 hours, including but not limited to 3 hours, 3.5 hours, and 4 hours, with a nitrogen atmosphere; the second stage sintering temperature is 650~680℃, including but not limited to 650℃, 660℃, and 680℃, for 1~2 hours, including but not limited to 1 hour, 1.5 hours, and 2 hours, with an oxygen atmosphere; the third stage sintering temperature is 720~750℃, including but not limited to 720℃, 730℃, and 750℃, for 6~8 hours, including but not limited to 6 hours, 7 hours, and 8 hours, with an air or oxygen atmosphere.

[0048] Understandably, during the sintering process, in the first stage under nitrogen protection, the nano-titanium dioxide within the graphene-coated layer generates surface oxygen vacancies and Lewis acid sites upon heating. These active sites catalyze the breaking of the CF bonds in PVDF, significantly reducing its decomposition temperature from the conventional ~550℃ to below 480℃. Titanium dioxide provides electron transfer channels, promoting the defluorination of PVDF and generating carbonaceous residues and gaseous HF and fluorocarbon molecules. The HF is temporarily physically blocked by the outer graphene layer, mitigating its direct impact on the ternary material. In the second stage of sintering, the sintering temperature is increased, and the atmosphere is switched to an oxygen atmosphere. The outer graphene layer, residual conductive agent, and carbonaceous residues generated in the first stage are completely oxidized and burned, volatilizing completely in the form of CO2 and H2O. Simultaneously, the remaining trace amounts of PVDF decomposition products are further oxidized and decomposed into harmless gases. During this process, graphene oxide is completely oxidized, burned, and decomposed into harmless volatile gases. After this stage, nano-titanium dioxide is exposed in situ and firmly adheres to the surface of the purified ternary material. The ternary material itself remains structurally intact due to the protection of the carbon layer and the final titanium dioxide layer throughout the process. In the third sintering stage, the sintering temperature is further increased, and the atmosphere is switched to air or an oxidizing atmosphere. At this point, the exposed nano-titanium dioxide reacts with residual alkalis (such as Li₂O, LiOH, Li₂CO₃) on the surface of the ternary material in a solid-state reaction. At high temperatures, titanium dioxide acts as a titanium source, reacting with lithium compounds to generate a layer of lithium titanate (such as Li₄Ti₅O) with a spinel structure. 12 Alternatively, a titanium-doped surface reconstruction layer can be formed. This layer is an excellent lithium-ion conductor, which not only completely eliminates the adverse effects of residual alkali on electrochemical performance, but also constructs a stable interface structure on the surface of the cathode particles that facilitates rapid lithium-ion transport, significantly improving the rate performance and cycle stability of the recycled material.

[0049] A second aspect of the present invention provides a ternary material obtained by the solid-phase regeneration method described in the first aspect above.

[0050] The present invention will be further described below through examples and other means.

[0051] Example 1 A method for recycling waste ternary materials includes the following steps: (1) Select waste NCM523 ternary electrode sheets from low-nickel plants, remove the current collector by mechanical peeling, and grind and sort to obtain ternary black powder; disperse the ternary black powder in N-methylpyrrolidone (NMP) solvent, control the solid content to 50%, and stir evenly to form ternary slurry.

[0052] (2) Substrate functionalization: Quartz glass was selected as the substrate. After cleaning, a 0.5 mg / mL graphene oxide aqueous dispersion was coated onto the substrate surface by dip coating. The substrate was dried under reduced pressure at 60°C for 2 hours to form a graphene oxide anchoring layer, thus obtaining a substrate coated with a graphene oxide film.

[0053] (3) Interfacial chemical bonding: A substrate coated with a graphene oxide film was immersed in a tetrabutyl titanate-anhydrous ethanol mixture (the volume content of tetrabutyl titanate in the mixture was 10%). A deionized water-hydrochloric acid mixture with pH=2 was slowly added dropwise to the tetrabutyl titanate-anhydrous ethanol mixture at a volume ratio of 100:2.0 to the water-hydrochloric acid mixture. After the addition was completed, a titanium dioxide layer was deposited in situ on the surface of the graphene oxide, and a composite film containing titanium dioxide and graphene oxide was obtained on the substrate.

[0054] (4) Physical self-assembly: The substrate containing the composite film was immersed in a 0.5 mg / mL few-layer graphene NMP dispersion. Pure water was added dropwise to the graphene dispersion at a volume ratio of 1.5:1, and the mixture was stirred at room temperature for 1 hour. A graphene layer was formed on the surface of the titanium dioxide layer. At this point, the substrate surface contained a composite film of graphene, titanium dioxide, and graphene oxide in sequence. The substrate was then washed once with deionized water and freeze-dried at -50°C for 12 hours. During the drying process, the substrate gradually peeled off from the composite film, resulting in a graphene oxide-titanium dioxide-graphene composite material.

[0055] (5) Construction of the coating layer: The above composite material was dispersed in NMP and the concentration was controlled at 15 mg / mL to obtain a composite material solution. The composite material solution was added dropwise to the ternary slurry in step (1) at a mass ratio of 2:100. After stirring at room temperature for 2 hours, the mixture was centrifuged and the resulting material was dried at 120°C and normal pressure for 4 hours to obtain the ternary material coated with the composite material.

[0056] (6) Solid-phase regeneration: The resulting coated ternary material was subjected to solid-state regeneration: specifically, a three-stage sintering process was adopted. The first stage was carried out at 470℃ in a nitrogen atmosphere for 3.5 hours; the second stage was carried out at 660℃ in an oxygen atmosphere for 1.5 hours; and the third stage was carried out at 730℃ in an air atmosphere for 7 hours. After sintering, the material was cooled to obtain regenerated NCM523 material.

[0057] Example 2 A method for recycling waste ternary materials includes the following steps: (1) Recycling of waste ternary materials: Waste NCM622 ternary electrode sheets from a nickel plant were selected. After mechanical stripping to remove the current collector, the ternary black powder was obtained by grinding and sorting. The ternary black powder was dispersed in NMP solvent, and the solid content was controlled at 45%. The mixture was stirred evenly to form a ternary slurry.

[0058] (2) Substrate functionalization: Quartz glass was selected as the substrate. After cleaning, a 0.3 mg / mL graphene oxide aqueous dispersion was coated onto the substrate surface by spin coating. The substrate was dried under reduced pressure at 50 °C for 3 h to form a graphene oxide anchoring layer, thus obtaining a substrate coated with a graphene oxide film.

[0059] (3) Interfacial chemical bonding: A substrate coated with a graphene oxide film was immersed in a tetrabutyl titanate-anhydrous ethanol mixture (tetrabutyl titanate volume content 5%). A deionized water-hydrochloric acid mixture with pH=2.8 was slowly added dropwise to the tetrabutyl titanate-anhydrous ethanol mixture at a volume ratio of 100:2.5, while stirring. The addition was stopped after 1.8 hours, and a titanium dioxide layer was deposited in situ on the graphene oxide surface, resulting in a composite film containing titanium dioxide and graphene oxide on the substrate.

[0060] (4) Physical self-assembly: The substrate containing the composite film was immersed in a 0.3 mg / mL few-layer graphene NMP dispersion. Pure water was added dropwise to the graphene dispersion at a volume ratio of 2.0:1, and the mixture was stirred at room temperature for 2 hours. A graphene layer was formed on the surface of the titanium dioxide layer. At this point, the substrate surface contained a composite film of graphene, titanium dioxide, and graphene oxide in sequence. The substrate was then washed once with deionized water and freeze-dried at -45°C for 10 hours. During the drying process, the substrate gradually peeled off from the composite film, resulting in a graphene oxide-titanium dioxide-graphene composite material.

[0061] (5) Construction of the coating layer: The above composite material was dispersed in NMP and the concentration was controlled at 10 mg / mL to obtain a composite material solution. The composite material solution was added dropwise to the ternary slurry in step (1) at a mass ratio of 3:100. After stirring at room temperature for 3 hours, the mixture was centrifuged and the resulting material was dried at 110°C and atmospheric pressure for 5 hours to obtain the ternary material coated with the composite material.

[0062] (6) Solid-phase regeneration: The resulting coated ternary material is subjected to solid-phase regeneration: specifically, a three-stage sintering process is adopted. The first stage is held at 460℃ in a nitrogen atmosphere for 4 hours; the second stage is held at 650℃ in an oxygen atmosphere for 2 hours; and the third stage is held at 720℃ in an air atmosphere for 8 hours.

[0063] After sintering and cooling, recycled NCM523 material is obtained.

[0064] Example 3 A method for recycling waste ternary materials includes the following steps: (1) Recycling of waste ternary materials: Waste NCM523 ternary electrode sheets from low-nickel plants were selected. After mechanical stripping to remove the current collector, the ternary black powder was obtained by grinding and sorting. The ternary black powder was dispersed in NMP solvent, and the solid content was controlled to be 55%. The mixture was stirred evenly to form a ternary slurry.

[0065] (2) Substrate functionalization: Quartz glass was selected as the substrate. After cleaning, a 0.8 mg / mL graphene oxide aqueous dispersion was coated onto the substrate surface by drop coating. The substrate was dried under reduced pressure at 70°C for 1.5 h to form a graphene oxide anchoring layer, thus obtaining a substrate coated with a graphene oxide film.

[0066] (3) Interfacial chemical bonding: A substrate coated with a graphene oxide film was immersed in a tetrabutyl titanate-anhydrous ethanol mixture (the volume content of tetrabutyl titanate in the mixture was 15%). A deionized water-hydrochloric acid mixture with pH=3 was slowly added dropwise to the tetrabutyl titanate-anhydrous ethanol mixture at a volume ratio of 100:3.5 to the water-hydrochloric acid mixture. The mixture was stirred and stirred for 2.5 hours. After stirring, a titanium dioxide layer was deposited in situ on the surface of the graphene oxide, and a composite film containing titanium dioxide and graphene oxide was obtained on the substrate.

[0067] (4) Physical self-assembly: The substrate containing the composite film was immersed in a 0.8 mg / mL few-layer graphene NMP dispersion. Pure water was added dropwise to the graphene dispersion at a volume ratio of 1.5:1, and the mixture was stirred at room temperature for 2 hours. A graphene layer was formed on the surface of the titanium dioxide layer. At this point, the substrate surface contained graphene, titanium dioxide, and graphene oxide composite film in sequence. The substrate was then washed once with deionized water and freeze-dried at -55°C for 14 hours. During the drying process, the substrate gradually became encapsulated by the composite film, resulting in a graphene oxide-titanium dioxide-graphene composite material.

[0068] (5) Construction of the coating layer: The above composite material was dispersed in NMP and the concentration was controlled at 20 mg / mL to obtain a composite material solution. The composite material solution was added dropwise to the ternary slurry in step (1) at a mass ratio of 4:100. After stirring at room temperature for 4 hours, the mixture was centrifuged and the resulting material was dried at 130°C and normal pressure for 3 hours to obtain the ternary material coated with the composite material.

[0069] (6) Solid-phase regeneration: The resulting coated ternary material was subjected to solid-phase regeneration: specifically, a three-stage sintering process was adopted. The first stage was carried out at 480℃ under a nitrogen atmosphere for 3 hours; the second stage was carried out at 680℃ under an oxygen atmosphere for 1 hour; and the third stage was carried out at 750℃ under an air atmosphere for 6 hours. After sintering, the material was cooled to obtain regenerated NCM523 material.

[0070] Comparative Example 1 A method for recycling waste ternary materials includes the following steps: The recycled NCM523 ternary material was directly processed using a two-stage sintering method. The first stage sintering temperature was 550℃ for 3 hours, and the second stage sintering temperature was 750℃ for 7 hours. The sintering atmosphere was air. After sintering, recycled ternary material was obtained.

[0071] Comparative Example 2 A method for recycling waste ternary materials includes the following steps: This is essentially the same as Example 1, except that only graphene oxide is used for surface coating. The specific steps are as follows: (1) Select waste NCM523 ternary electrode sheets from low-nickel plants, remove the current collector by mechanical peeling, and grind and sort to obtain ternary black powder; disperse the ternary black powder in N-methylpyrrolidone (NMP) solvent, control the solid content to 50%, and stir evenly to form ternary slurry.

[0072] (2) The graphene oxide-NMP dispersion with a concentration of 15 mg / mL was added to the ternary slurry at a mass ratio of 3:100. After stirring at room temperature for 2 h, the NMP was recovered by centrifugation. The resulting material was dried at 120 °C under normal pressure for 4 h to obtain the ternary material coated with graphene oxide.

[0073] (3) Solid phase regeneration, which is the same as the solid phase regeneration in step (6) of Example 1.

[0074] Comparative Example 3 A method for recycling waste ternary materials includes the following steps: The process is basically the same as in Example 1, except that only graphene oxide loaded with titanium dioxide is used for surface coating. The specific steps are as follows: (1) Select waste NCM523 ternary electrode sheets from low-nickel plants, remove the current collector by mechanical peeling, and grind and sort to obtain ternary black powder; disperse the ternary black powder in N-methylpyrrolidone (NMP) solvent, control the solid content to 50%, and stir evenly to form ternary slurry.

[0075] (2) Substrate functionalization: Quartz glass was selected as the substrate. After cleaning, a 0.5 mg / mL graphene oxide aqueous dispersion was coated onto the substrate surface by dip coating. The substrate was dried under reduced pressure at 60°C for 2 hours to form a graphene oxide anchoring layer, thus obtaining a substrate coated with a graphene oxide film.

[0076] (3) Interfacial chemical bonding: A substrate coated with a graphene oxide film was immersed in a tetrabutyl titanate-anhydrous ethanol mixture (the volume content of tetrabutyl titanate in the mixture was 5%). At a volume ratio of tetrabutyl titanate-ethanol mixture to water-hydrochloric acid mixture of 100:2.0, a deionized water-hydrochloric acid mixture with pH=2 was slowly added dropwise to the tetrabutyl titanate-anhydrous ethanol mixture. After stirring for 2 hours, a titanium dioxide layer was deposited in situ on the surface of the graphene oxide, and a composite film containing titanium dioxide and graphene oxide was obtained on the substrate.

[0077] The substrate was then washed once with deionized water and freeze-dried at -50°C for 12 hours. During the drying process, the substrate gradually peeled off from the composite film, yielding a graphene oxide-titanium dioxide composite material.

[0078] (4) Construction of the coating layer: The above graphene oxide-titanium dioxide composite material was dispersed in NMP and the concentration was controlled at 15 mg / mL to obtain a composite material solution. The composite material solution was added dropwise to the ternary slurry in step (1) at a mass ratio of 2:100. After stirring at room temperature for 3.5 h, the mixture was centrifuged and the resulting material was dried at 120 °C under normal pressure for 4 h to obtain the ternary material coated with the composite material.

[0079] (5) Solid phase regeneration, which is the same as the solid phase regeneration in step (6) of Example 1.

[0080] Comparative Example 4 A method for recycling waste ternary materials includes the following steps: The process is basically the same as in Example 1, except that hydrolyzed nano-titanium dioxide particles are added only to the ternary slurry. The specific steps are as follows: (1) Select waste NCM523 ternary electrode sheets from low-nickel plants, remove the current collector by mechanical peeling, and grind and sort to obtain ternary black powder; disperse the ternary black powder in N-methylpyrrolidone (NMP) solvent, control the solid content to 50%, and stir evenly to form ternary slurry.

[0081] (2) Prepare a tetrabutyl titanate-anhydrous ethanol mixture with a volume ratio of 1:10. Add a deionized water-hydrous acid mixture with pH=3 dropwise to the tetrabutyl titanate-anhydrous ethanol mixture with a volume ratio of 100:2.0. Stir for 2 hours to obtain nano-titanium dioxide particles. Then, centrifuge and dry the nano-titanium dioxide.

[0082] (3) Disperse the collected nano-titanium dioxide in NMP and control the concentration to 15 mg / mL to obtain a nano-titanium dioxide solution. According to the mass ratio of nano-titanium dioxide to ternary material in ternary slurry of 2:100, add titanium dioxide-NMP dispersion with a concentration of 15 mg / mL to the ternary slurry in step (1). Stir at room temperature for 3.5 h, centrifuge, recover NMP, and dry the obtained material at 120℃ and normal pressure for 4 h to obtain titanium dioxide-ternary material mixture.

[0083] (4) Solid phase regeneration, which is the same as the solid phase regeneration in step (6) of Example 1.

[0084] Comparative Example 5 A method for recycling waste ternary materials includes the following steps: It is basically the same as Example 1, except that in step (6), the temperature of the first sintering stage is 550°C.

[0085] Comparative Example 6 A method for recycling waste ternary materials includes the following steps: It is basically the same as Example 1, except that in step (5), the amount of composite material added accounts for 1 wt% of the mass of the ternary material.

[0086] Comparative Example 7 A method for recycling waste ternary materials includes the following steps: It is basically the same as Example 1, except that in step (6), the second sintering time is 0.5h.

[0087] Test example: The F element content of the recycled ternary materials obtained by ICP testing in the examples and comparative examples is shown in Table 1.

[0088] The performance of the batteries corresponding to the recycled materials prepared in each embodiment and comparative example was also measured. The specific methods are as follows: The recycled ternary materials prepared in each embodiment and comparative example of the present invention were mixed with binder and conductive agent, then slurryed, coated, rolled and cut. Then, a coin cell was prepared using a lithium sheet as the counter electrode. The cell was cycled twice at a rate of 0.1C, with a voltage range of 3.0-4.35V. The specific capacity was recorded and the first efficiency was calculated.

[0089] The mass ratio of ternary material, binder, and conductive agent is 97.5:1.5:1.0; the binder is PVDF; the conductive agent is Super P; and the coating thickness is 90 micrometers.

[0090] The results are shown in Table 1.

[0091] Table 1. Performance tests of batteries using recycled materials from the embodiments and comparative examples of the present invention.

[0092] As shown in Table 1, the batteries prepared from the recycled materials obtained in the examples have a larger specific capacity, excellent first-time efficiency, and a lower F content.

[0093] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A solid-phase regeneration method for waste ternary cathode materials, characterized in that, Includes the following steps: S1: Preparation of ternary material slurry; S2: Coat the substrate surface with graphene oxide dispersion and dry to obtain a substrate containing graphene oxide film; S3: Immerse the substrate containing graphene oxide film in a mixture of tetrabutyl titanate and ethanol, and then add a mixture of water and hydrochloric acid dropwise. After the dropwise addition is completed, nano-titanium dioxide particles are formed on the surface of the graphene oxide film, thus obtaining a substrate containing nano-titanium dioxide and graphene oxide film. S4: Immerse the substrate containing nano-titanium dioxide-graphene oxide film in graphene dispersion, add water and stir to allow graphene to self-assemble on the surface of the substrate containing nano-titanium dioxide, and sequentially form a sandwich structure composite film of graphene oxide-titanium dioxide-graphene on the substrate surface. After washing and drying, obtain graphene oxide-titanium dioxide-graphene composite material. S5: The graphene oxide-titanium dioxide-graphene composite material is mixed with a solvent to obtain a composite material suspension; the composite material suspension is added to the ternary material slurry in S1, stirred, centrifuged, and dried to obtain the ternary material coated with the composite material; S6: Sinter the ternary material coated with the composite material obtained in S5 to obtain the recycled ternary material.

2. The solid-phase regeneration method according to claim 1, characterized in that, In S1, the ternary slurry is obtained by mechanically peeling and sorting waste ternary electrode sheets to obtain a positive current collector and ternary black powder respectively; the ternary black powder is then dispersed with a solvent. Preferably, the solid content of the ternary slurry is 45-55%.

3. The solid-phase regeneration method according to claim 1, characterized in that, In S2, the concentration of the graphene oxide dispersion is 0.1~1.0 mg / mL; The graphene oxide dispersion is obtained by dispersing graphene oxide with water. The substrate includes at least one of silicon wafers and quartz glass.

4. The solid-phase regeneration method according to claim 1, characterized in that, In S3, the volume concentration of tetrabutyl titanate in the tetrabutyl titanate-ethanol mixture is 5%~15%; The ethanol is anhydrous ethanol; The pH value of the water-hydrochloric acid mixture is 1 to 3.

5. The solid-phase regeneration method according to claim 1, characterized in that, In S3, the volume ratio of the tetrabutyl titanate-ethanol mixture to the water-hydrochloric acid mixture is 100: 1.5~3.

5.

6. The solid-phase regeneration method according to claim 1, characterized in that, In S4, the graphene dispersion is obtained by dispersing graphene in a solvent; The concentration of the graphene dispersion is 0.1~1.0 mg / mL; The solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide; Preferably, the graphene is few-layer graphene with ≤10 layers.

7. The solid-phase regeneration method according to claim 1, characterized in that, In S4, the volume ratio of water to graphene dispersion is 1.5~2.5:1; The stirring time is 1-2 hours; The drying process is freeze-drying.

8. The solid-phase regeneration method according to claim 1, characterized in that, In S5, the concentration of the composite material suspension is 10~20 mg / mL; The solvent includes at least one of N-methylpyrrolidone and N,N-dimethylformamide; The mass of the composite material in the composite material suspension accounts for 2-4 wt% of the mass of the ternary material in the ternary material slurry; The stirring time is 2-3 hours.

9. The solid-phase regeneration method according to claim 1, characterized in that, In S6, the sintering is a three-stage sintering; In the three-stage sintering process: the temperature of the first stage sintering is 460~480℃, the time is 3~4h, and the atmosphere is nitrogen; the temperature of the second stage sintering is 650~680℃, the time is 1~2h, and the atmosphere is oxygen. The third sintering temperature is 720~750℃, the time is 6~8h, and the atmosphere is air or oxygen.

10. A ternary material obtained by the solid-phase regeneration method according to any one of claims 1-9.

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