A method for recovering layered positive electrode material by hydrothermal calcination and regenerated layered positive electrode material

Abstract

The invention relates to a method for recovering layered positive electrode materials by hydrothermal calcination and regenerating layered positive electrode materials. The method comprises the following steps: washing waste battery positive electrode sheets with an organic solvent; then placing the positive electrode sheets in a first solution, ultrasonically treating them, and performing flotation to separate the waste positive electrode materials; then adding the waste positive electrode materials into a second solution, performing a hydrothermal reaction, and then performing solid-liquid separation and drying to obtain a precursor material; and calcining the precursor material to obtain a regenerated positive electrode material. The method of the invention simplifies the recovery process of waste positive electrode materials and can directly achieve in-situ repair of the positive electrode material structure, so that the obtained regenerated positive electrode material has excellent electrochemical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode material recycling, and more specifically, to a method for recovering layered positive electrode materials by hydrothermal calcination and the regenerated layered positive electrode materials obtained by the method. Background Art

[0002] With the increasing demand for batteries in electric vehicles and energy storage devices, commercial lithium-ion batteries have experienced rapid development. After several years of explosive growth, they are widely used in various electronic products. However, due to the expected lifespan of lithium-ion batteries of 3-10 years, a large number of lithium-ion batteries are retired, generating a large amount of lithium-ion battery waste. The main internal causes of lithium-ion battery performance degradation include: lithium migration leading to vacancies in the structure, which causes cation migration within the structure and irreversible phase transitions; the formation of a SEI film resulting in low initial Coulombic efficiency; long-term use of the binder causing expansion and shedding of the cathode material; and electrolyte degradation and decomposition. External environmental conditions such as high and low temperatures, external stress and compression, and casing damage can also render lithium-ion batteries useless. These lithium-ion batteries are often stored in warehouses. However, if improperly handled, the heavy metals contained in the cathode material can cause significant damage to the soil, and the volatilization of the electrolyte can produce toxic gases that pose a significant threat to human health. With the rising price of lithium-ion battery raw materials, the recycling of used lithium-ion batteries has become a focus of considerable research. Therefore, green and environmentally friendly recycling of waste lithium-ion battery positive electrode materials is of great significance to environmental protection and resource recycling. It is urgent to develop a green, efficient, simple and easy recycling method.

[0003] Currently, the commonly used battery recycling methods mainly include: pyrolysis, wet recycling and a combination of wet and pyrolysis. However, wet recycling requires the use of large amounts of acid and alkali solutions, or toxic organic solvents. Pyrolysis has high energy consumption, and the thermal decomposition of organic matter such as polyvinylidene fluoride (PVDF) during the calcination process will also produce fluorine-containing toxic gases. In addition, both methods have complicated steps, and both methods must completely destroy the structure of the positive electrode particles and then reconstruct them again. The direct regeneration method has simple and easy operation steps, which can regenerate waste electrode materials while avoiding high-intensity energy consumption and excessive use of chemicals, which significantly reduces costs and the generation of secondary waste.

[0004] During direct regeneration, the primary method for separating the cathode material is to dissolve or inactivate the PVDF. For example, Chinese patent application CN202010005820.5 discloses a hydrothermal lithium recharge and spray remodeling method for regenerating spent ternary cathode materials. This method uses an alkaline solution to separate the cathode material and the current collector. Following separation, the cathode material is then calcined at high temperature to activate the cathode material, followed by subsequent lithium recharge and other treatments to regenerate the cathode material. This recovery process involves multiple calcinations and requires multiple solvents, resulting in a complex process. Summary of the Invention

[0005] Based on the above-mentioned technical problems existing in the prior art, the present invention aims to provide a method for recovering layered positive electrode materials by hydrothermal calcination. The positive electrode materials are stripped using a mixed solution. During this process, the positive electrode materials can be quickly separated by flotation. Subsequently, the positive electrode materials are regenerated by a second treatment with the mixed solution and hydrothermal reaction. The present invention uses a suitable solution for treatment and can achieve multiple functions such as stripping the positive electrode materials, maintaining the positive electrode material structure, optimizing the lithium replenishment reaction interface, and efficiently replenishing lithium through the same mixed solution. This greatly simplifies the operation steps and achieves the purpose of directly regenerating the positive electrode materials.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for recovering layered positive electrode materials by hydrothermal calcination comprises the following steps:

[0008] S1. Soak and clean the surface of the positive electrode of the used battery with an organic solvent;

[0009] S2. placing the cleaned positive electrode sheet into the first solution, subjecting it to ultrasonic treatment, and then placing it in a flotation device, adding a frother, and flotation; after flotation, filtering and drying to separate the waste positive electrode material;

[0010] S3, adding the waste cathode material to the second solution to carry out a hydrothermal reaction; after the reaction is completed, separating the solid and the liquid, and drying to obtain a precursor material;

[0011] S4, calcining the precursor material to obtain a regenerated positive electrode material;

[0012] The first solution in step S2 and the second solution in step S3 respectively include a lithium-containing compound and an alkali.

[0013] In some embodiments, in the first solution, Li + The molar ratio of Li and OH- is 1:1-3, + The molar concentration of OH- is ≥0.5M, preferably 1-3M; the molar concentration of OH- is ≥2M, preferably 2.5-9M.

[0014] In some embodiments, the second solution contains Li + The molar ratio of Li and OH- is 1-3:1. + The molar concentration of OH- is ≥2M, preferably 2.5-15M; the molar concentration of OH- is ≥1M, preferably 2.5-5M.

[0015] In some embodiments, the OH- concentration of the first solution is greater than the OH- concentration of the second solution, and the Li + Less than the second solution Li + concentration.

[0016] In some embodiments, the lithium-containing compound is at least one of an inorganic lithium salt, an organic lithium salt, and lithium hydroxide; the inorganic lithium salt includes but is not limited to at least one of LiNO3, LiCl, and Li2SO4; the organic lithium salt includes but is not limited to at least one of lithium formate, lithium acetate, lithium propionate, lithium oxalate, lithium salicylate, lithium lactate, and lithium citrate.

[0017] In some embodiments, in step S1, the organic solvent is at least one of dimethyl carbonate and diethyl carbonate.

[0018] In some embodiments, in step S2, the solid-to-liquid ratio of the positive electrode sheet to the first solution is 1 g: 4-15 mL.

[0019] In some embodiments, in step S2, the ultrasonic treatment temperature is 20-45°C.

[0020] In some embodiments, in step S2, the ultrasonic treatment time is 0.5-2 h.

[0021] In some embodiments, in step S2, the ultrasonic power is 50-1000W.

[0022] In some embodiments, in step S2, during the flotation process, the amount of frother is 0.5-5 mg / g; the rotation speed is 800-1400 r / min; the slurry pH is maintained between 4.5-11; the slurry mass concentration is 0-10%, and the mass concentration is >0; preferably, the slurry mass concentration is 1-10%.

[0023] In some embodiments, in step S3, the hydrothermal temperature is 120-220°C.

[0024] In some embodiments, in step S3, the hydrothermal time is 2-8 hours.

[0025] In some embodiments, in step S3, the solid-to-liquid ratio of the waste positive electrode material to the second solution is 1 g: 3 to 12 mL.

[0026] In some embodiments, in step S4, the calcination temperature is 700-850°C.

[0027] In some embodiments, in step S4, the calcination time is 1-5 hours.

[0028] In some embodiments, the positive electrode material is at least one of a nickel-cobalt-manganese ternary positive electrode (NCM), a nickel-cobalt-aluminum ternary positive electrode (NCA), and a lithium-rich manganese-based positive electrode (LMO), preferably NCM. The molecular formula of the positive electrode material is LiNi x Co y Mn 1-x-yO2, wherein 0<x<1, 0<y<1; more preferably, it is at least one of NCM811, NCM523, NCM622, LiCoO2, and LiNiO2.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The recycling method of the present invention comprises the following steps: after disassembling and separating waste batteries to obtain positive electrode sheets, the electrolyte and impurities on the surface of the positive electrode sheets are first cleaned with an organic solvent; and then a first solution consisting of a lithium-containing compound and an alkaline solution of a specific concentration is added, wherein the alkaline solution attacks the C—F bond in the binder PVDF through hydroxide to generate an unsaturated double bond, causing the PVDF to lose its halogen atomic functional group, thereby reducing its bonding ability and losing its mechanical activity, making it extremely easy to break and degrade. The addition of the lithium-containing compound can effectively inhibit the Li-ionization reaction in the waste positive electrode material. + The leaching of the waste positive electrode material maintains the original structure of the waste positive electrode material; after being treated with the first solution, flotation is performed to effectively separate the waste positive electrode material, and aluminum hydroxide by-products can be obtained by optimizing the treatment conditions of the first solution, thereby improving the economic benefits of the process without increasing the process flow and reagent costs; the waste positive electrode material obtained after separation is then added to a mixed solution composed of a lithium-containing compound and an alkaline solution, and a hydrothermal reaction is carried out to achieve lithium replenishment of the positive electrode material particle structure, wherein the purpose of adding the alkaline solution is to further treat the PVDF remaining on the surface of the positive electrode material particles to effectively replenish the positive electrode material particle structure, and finally, the structurally collapsed positive electrode particles, impurities, etc. are removed by calcination to achieve in-situ regeneration of the positive electrode material particle structure. In addition, by controlling the relationship between the lithium ion and hydroxide ion concentrations in the first solution and the second solution, not only can the lithium and hydroxide ions in each solution be fully utilized to focus on achieving the main functions of steps one and three, but the overall performance and stability of the regenerated material can also be further optimized.

[0031] The method of the present invention realizes uniform replenishment of lithium sources in an aqueous medium and can realize lithium replenishment and regeneration of the positive electrode material particle structure at a relatively low temperature through a hydrothermal reaction. In addition, in the treatment process, no other organic chemicals are added except for the use of lithium-containing compounds and alkaline solution, and the alkaline solution can be recycled, making the treatment process green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The XRD patterns of the recycled NCM811 ternary materials obtained in Examples 1-2 and Comparative Example 1 are shown;

[0033] Figure 2 The first cycle charge and discharge diagram of the regenerated NCM811 ternary material half-cell obtained in Example 1 and Comparative Example 1;

[0034] Figure 3The rate curves of the regenerated NCM811 ternary material half-cell obtained by the methods provided in Example 1 and Comparative Example 1;

[0035] Figure 4 This is a long cycle curve of the regenerated NCM811 / / graphite full battery obtained according to the method provided in Example 1 and Comparative Example 1.

[0036] Figure 5 This is the XRD pattern of the aluminum hydroxide separated in Example 1. DETAILED DESCRIPTION

[0037] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0039] Example 1

[0040] A method for recovering layered positive electrode materials by hydrothermal calcination comprises the following steps:

[0041] S1. After the used NCM811 batteries were discharged to below 2V at a current density of 0.1C, they were disassembled and sorted in a fume hood to obtain the positive electrode sheet, negative electrode sheet, shell, diaphragm, and tab;

[0042] S2. Soak the positive electrode sheet in a dimethyl carbonate solution for 2 hours, then wash it three times with deionized water, and dry it in a vacuum drying oven at 80° C. for 6 hours to obtain a pretreated positive electrode sheet;

[0043] S3. Mix the pretreated positive electrode sheet with a LiOH aqueous solution with a concentration of 3 mol / L, with a solid-liquid ratio of the positive electrode sheet to the LiOH solution of 1 g:6 mL, and perform ultrasonic treatment at 25°C, an ultrasonic power of 100 W, and an ultrasonic time of 1 h. After ultrasonic treatment, pour the mixture into a flotation machine, add methyl isobutyl carbinol at a dosage of 2 mg / g, adjust the slurry pH to 8.5, and the slurry mass concentration to 8%. Stir at a speed of 1000 r / min and perform flotation for 30 min. After flotation, separate the solid and liquid, dry, and separate to obtain waste positive electrode material and aluminum hydroxide.

[0044] S4. Add the waste cathode material to a mixed solution containing LiNO3 and NaOH (in the mixed solution, the concentration of LiNO3 is 5 mol / L, and the concentration of NaOH is 2 mol / L), the solid-liquid ratio of the waste cathode material to the mixed solution is 1 g:10 mL, and perform a hydrothermal reaction at 120°C for 8 h, followed by solid-liquid separation and drying to obtain a precursor material;

[0045] S5. Place the precursor material obtained in step S4 in a tube furnace, heat it to 750° C. at a rate of 3° C. / min, and then keep it warm for 5 hours to obtain a regenerated NCM811 positive electrode material.

[0046] The obtained regenerated NCM811 cathode material was subjected to XRD detection, and the test results were as follows: Figure 1 shown.

[0047] The electrochemical performance of the regenerated NCM811 cathode material prepared in this example was tested as follows:

[0048] The regenerated NCM811 positive electrode material, conductive carbon and PVDF were ground and mixed evenly in a mass ratio of 8:1:1, stirred into a slurry in N-methylpyrrolidone (NMP) medium, coated on aluminum foil, and cut into pieces after drying to assemble lithium-ion batteries.

[0049] The preparation method of the negative electrode material is to mix sodium carboxymethyl cellulose (CMC): conductive carbon agent: graphite in a ratio of 1.5:1.5:7. Specifically, CMC is dissolved in deionized water, and then the mixed powder of graphite and carbon conductive agent is slowly added multiple times. After stirring on a magnetic stirrer until uniform dispersion, it is coated on copper foil, dried at 80°C for 12 hours, and then cut into pieces to obtain the negative electrode sheet.

[0050] After testing, such as Figure 2-4 As shown, the regenerated positive electrode material recovered by direct hydrothermal calcination according to the method of the present invention maintains excellent cycle and rate performance, as shown in FIG. Figure 3 , the discharge capacity can reach 120mAh / g at a rate of 10C, showing excellent electrochemical performance; Figure 4 After being assembled into a full battery, the test showed that the capacity retention rate could reach 96.95% after 100 cycles at a rate of 1C (1C = 180mAh / g) in the voltage range of 2.7-4.2V.

[0051] Example 2

[0052] A method for recovering layered positive electrode materials by hydrothermal calcination comprises the following steps:

[0053] S1. After the used NCM811 batteries were discharged to below 2V at a current density of 0.1C, they were disassembled and sorted in a fume hood to obtain the positive electrode sheet, negative electrode sheet, shell, diaphragm, and tab;

[0054] S2. Soak the positive electrode sheet in a dimethyl carbonate solution for 2 hours, then wash it three times with deionized water, and dry it in a vacuum drying oven at 80° C. for 6 hours to obtain a pretreated positive electrode sheet;

[0055] S3. Add the pretreated positive electrode sheet to a mixed solution containing LiNO3 and NaOH (in the mixed solution, the concentration of LiNO3 is 1 mol / L, and the concentration of NaOH is 3 mol / L), the solid-liquid ratio of the positive electrode sheet to the mixed solution is 1 g:5 mL, and ultrasonic treatment is performed at 30°C, the ultrasonic power is 100 W, and the ultrasonic time is 0.75 h; after ultrasonic treatment, pour it into a flotation machine, add methyl isobutyl carbinol in an amount of 2 mg / g, adjust the slurry pH to 8.5, the slurry mass concentration is 8%, stir at a speed of 1000 r / min, and flotation is performed for 30 min. After flotation is completed, the solid-liquid separation is carried out, and the waste positive electrode material and aluminum hydroxide are separated.

[0056] S4. Add the waste cathode material to a mixed solution containing LiNO3 and NaOH (in the mixed solution, the concentration of LiNO3 is 2 mol / L, and the concentration of NaOH is 2 mol / L), the solid-liquid ratio of the waste cathode material to the mixed solution is 1 g:10 mL, and perform a hydrothermal reaction at 120° C. for 8 h, followed by solid-liquid separation and drying to obtain a precursor material;

[0057] S5. Place the precursor material obtained in step S4 in a tube furnace, heat it to 750° C. at a rate of 3° C. / min, and then keep it warm for 5 hours to obtain a regenerated NCM811 positive electrode material.

[0058] The obtained regenerated NCM811 cathode material was subjected to XRD detection, and the test results were as follows: Figure 1 shown.

[0059] The electrochemical performance of the regenerated NCM811 cathode material prepared in this example was tested as follows:

[0060] The recycled NCM811 cathode material, conductive carbon and PVDF were ground and mixed evenly in a mass ratio of 8:1:1, stirred into a slurry in an NMP medium, coated on aluminum foil, and cut into pieces after drying to assemble lithium-ion batteries.

[0061] The preparation method of the negative electrode material is to mix CMC: conductive carbon agent: graphite in a ratio of 1.5:1.5:7. Specifically, CMC is dissolved in deionized water, and then the mixed powder of graphite and carbon conductive agent is slowly added multiple times. After stirring on a magnetic stirrer until uniform dispersion, it is coated on a copper foil, dried at 80°C for 12 hours, and then cut into pieces to obtain the negative electrode sheet.

[0062] Testing has shown that the regenerated cathode material recovered through direct hydrothermal calcination in this example maintains excellent cycle and rate performance. In a half-cell system, the discharge capacity at a rate of 10C can reach 125 mAh / g, demonstrating excellent electrochemical performance. In a full-cell system, the capacity retention rate can reach 91.01% after 100 cycles at a rate of 1C in the voltage range of 2.7-4.2V.

[0063] Example 3

[0064] A method for recovering layered positive electrode materials by hydrothermal calcination comprises the following steps:

[0065] S1. After the waste lithium cobalt oxide batteries are discharged to below 2V at a current density of 0.1C, they are disassembled and sorted in a fume hood to obtain the positive electrode sheet, negative electrode sheet, shell, diaphragm, and tab;

[0066] S2. Soak the positive electrode sheet in a dimethyl carbonate solution for 2 hours, then wash it three times with deionized water, and dry it in a vacuum drying oven at 80° C. for 6 hours to obtain a pretreated positive electrode sheet;

[0067] S3. The pretreated positive electrode sheet was mixed with a 2 mol / L lithium formate and 5 mol / L NaOH solution, with a solid-liquid ratio of the positive electrode sheet to the mixed solution of 1 g:10 mL. The mixture was ultrasonically treated at 20°C, with an ultrasonic power of 800 W and an ultrasonic time of 0.5 h. After ultrasonic treatment, the mixture was poured into a flotation machine, and methyl isobutyl carbinol was added at a dosage of 4 mg / g. The slurry pH was adjusted to 11 and the slurry mass concentration was 5%. The mixture was stirred at a speed of 800 r / min and flotation was performed for 30 min. After flotation, the solid-liquid separation was performed and the mixture was dried to separate the waste positive electrode material.

[0068] S4. Add the waste cathode material to a mixed solution containing lithium nitrate and NaOH (in the mixed solution, the concentration of lithium nitrate is 4 mol / L, and the concentration of NaOH is 2 mol / L), the solid-liquid ratio of the waste cathode material to the mixed solution is 1 g:8 mL, and perform a hydrothermal reaction at 170° C. for 5 h, followed by solid-liquid separation and drying to obtain a precursor material;

[0069] S5. Place the precursor material obtained in step S4 in a tube furnace, heat it to 850° C. at a rate of 5° C. / min, and then keep it warm for 3 hours to obtain a regenerated lithium cobalt oxide positive electrode material.

[0070] The electrochemical performance of the regenerated lithium cobalt oxide positive electrode material prepared in this example was tested as follows:

[0071] The regenerated lithium cobalt oxide positive electrode material, conductive carbon and PVDF were ground and mixed evenly in a mass ratio of 8:1:1, stirred into a slurry in an NMP medium, coated on an aluminum foil, and cut into pieces after drying to assemble a lithium-ion battery.

[0072] The preparation method of the negative electrode material is to mix CMC: conductive carbon agent: graphite in a ratio of 1.5:1.5:7. Specifically, CMC is dissolved in deionized water, and then the mixed powder of graphite and carbon conductive agent is slowly added multiple times. After stirring on a magnetic stirrer until uniform dispersion, it is coated on a copper foil, dried at 80°C for 12 hours, and then cut into pieces to obtain the negative electrode sheet.

[0073] Testing has shown that the regenerated cathode material recovered through direct hydrothermal calcination in this example maintains excellent cycle and rate performance. In a half-cell system, the discharge capacity can reach 131 mAh / g at a rate of 5C. In a full-cell system, the capacity retention rate can reach 86.53% after 100 cycles at a rate of 1C in the voltage range of 2.7-4.2V.

[0074] Example 4

[0075] A method for recovering layered positive electrode materials by hydrothermal calcination comprises the following steps:

[0076] S1. After the used NCM523 batteries were discharged to below 2V at a current density of 0.1C, they were disassembled and sorted in a fume hood to obtain the positive electrode sheet, negative electrode sheet, shell, diaphragm, and tab;

[0077] S2. Soak the positive electrode sheet in a dimethyl carbonate solution for 2 hours, then wash it three times with deionized water, and dry it in a vacuum drying oven at 80° C. for 6 hours to obtain a pretreated positive electrode sheet;

[0078] S3. The pretreated positive electrode sheet was mixed with a 0.5 mol / L lithium sulfate and 2.5 mol / L NaOH solution, with a solid-liquid ratio of the positive electrode sheet to the mixed solution of 1 g: 4 mL. The mixture was ultrasonically treated at 45°C, with an ultrasonic power of 1000 W and an ultrasonic time of 1.5 h. After ultrasonic treatment, the mixture was poured into a flotation machine, and methyl isobutyl carbinol was added at a dosage of 5 mg / g. The slurry pH was adjusted to 8.0 and the slurry mass concentration was 6%. The mixture was stirred at a speed of 900 r / min and flotation was performed for 45 min. After the flotation was completed, the solid-liquid separation was carried out and the mixture was dried to separate the waste positive electrode material and aluminum hydroxide.

[0079] S4. Add the waste cathode material to a mixed solution containing Li2SO4 and NaOH (in the mixed solution, the concentration of Li2SO4 is 3 mol / L, and the concentration of NaOH is 2 mol / L), the solid-liquid ratio of the waste cathode material to the mixed solution is 1 g:6 mL, and perform a hydrothermal reaction at 150°C for 3.5 hours, followed by solid-liquid separation and drying to obtain a precursor material;

[0080] S5. Place the precursor material obtained in step S4 in a tube furnace, then heat it to 750° C. at a rate of 3° C. / min, and then keep it warm for 5 hours to obtain a regenerated NCM523 positive electrode material.

[0081] The electrochemical performance of the regenerated NCM523 cathode material prepared in this example was tested as follows:

[0082] The recycled NCM523 cathode material, conductive carbon and PVDF were ground and mixed evenly in a mass ratio of 8:1:1, stirred into a slurry in an NMP medium, coated on aluminum foil, and cut into pieces after drying to assemble lithium-ion batteries.

[0083] The preparation method of the negative electrode material is to mix CMC: conductive carbon agent: graphite in a ratio of 1.5:1.5:7. Specifically, CMC is dissolved in deionized water, and then the mixed powder of graphite and carbon conductive agent is slowly added multiple times. After stirring on a magnetic stirrer until uniform dispersion, it is coated on a copper foil, dried at 80°C for 12 hours, and then cut into pieces to obtain the negative electrode sheet.

[0084] Testing has shown that the regenerated cathode material recovered through direct hydrothermal calcination in this example maintains excellent cycle and rate performance. In a half-cell system, the discharge capacity can reach 105 mAh / g at a rate of 10C. In a full-cell system, the capacity retention rate can reach 82.95% after 100 cycles at a rate of 1C in the voltage range of 2.7-4.2V.

[0085] Comparative Example 1

[0086] A method for recovering layered positive electrode materials by hydrothermal calcination comprises the following steps:

[0087] S1. After the used NCM811 batteries were discharged to below 2V at a current density of 0.1C, they were disassembled and sorted in a fume hood to obtain the positive electrode sheet, negative electrode sheet, shell, diaphragm, and tab;

[0088] S2. Soak the positive electrode sheet in a dimethyl carbonate solution for 2 hours, then wash it three times with deionized water, and dry it in a vacuum drying oven at 80° C. for 6 hours to obtain a pretreated positive electrode sheet;

[0089] S3. Mix the pretreated positive electrode sheet with a NaOH solution with a concentration of 3 mol / L at a solid-liquid ratio of 1 g:6 mL, and ultrasonically treat at 25°C with an ultrasonic power of 100 W and an ultrasonic time of 1 h. After ultrasonic treatment, pour the pretreated positive electrode sheet into a flotation machine, add methyl isobutyl carbinol at a dosage of 2 mg / g, adjust the slurry pH to 8.5, and the slurry mass concentration to 8%. Stir at a speed of 1000 r / min and flotate for 30 min. After flotation, separate the solid and liquid, dry, and separate to obtain waste positive electrode material and aluminum hydroxide.

[0090] S4. Add the waste positive electrode material to a mixed solution containing LiNO3 and NaOH (in the mixed solution, the concentration of LiNO3 is 5 mol / L and the concentration of NaOH is 2 mol / L), the volume ratio of the waste positive electrode material to the mixed solution is 1 g:10 mL, and perform a hydrothermal reaction at 120°C for 8 hours, followed by solid-liquid separation and drying to obtain a precursor material;

[0091] S5. Place the precursor material obtained in step S4 in a tube furnace, heat it to 750° C. at a rate of 3° C. / min, and then keep it warm for 5 hours to obtain a regenerated NCM811 positive electrode material.

[0092] The obtained regenerated NCM811 cathode material was subjected to XRD detection, and the test results were as follows: Figure 1 shown.

[0093] The electrochemical performance of the regenerated NCM811 cathode material obtained by the method of this comparative example was tested as follows:

[0094] The positive electrode sheet is prepared by grinding and mixing the regenerated NCM811 positive electrode material, conductive carbon, and PVDF in a mass ratio of 8:1:1, stirring the mixture into a slurry in an NMP medium, coating the mixture on aluminum foil, and cutting the mixture into pieces after drying to obtain the positive electrode sheet.

[0095] The negative electrode sheet is prepared by mixing CMC, conductive carbon agent, and graphite in a ratio of 1.5:1.5:7. Specifically, CMC is dissolved in deionized water, and then the mixed powder of graphite and carbon conductive agent is slowly added multiple times. After stirring on a magnetic stirrer until uniform dispersion, the mixed powder is coated on a copper foil, dried at 80°C for 12 hours, and cut into pieces to obtain the negative electrode sheet.

[0096] The positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled into a lithium ion battery according to conventional methods in the art, and then the electrochemical performance test is carried out. The test results are as follows Figure 2-Figure 4 shown.

[0097] like Figure 2-4 In the voltage range of 2.7-4.2V, after 100 cycles at a rate of 1C, the capacity retention rate can reach 80.97%, and the discharge specific capacity at a rate of 10C is 54mAh / g.

[0098] Depend on Figure 2-4 It can be seen that the electrochemical performance of the regenerated NCM811 positive electrode material obtained in this comparative example is significantly lower than the electrochemical performance of the regenerated NCM811 positive electrode material obtained in Example 1.

[0099] Comparative Example 2

[0100] A method for recovering layered positive electrode materials by hydrothermal calcination comprises the following steps:

[0101] S1. After the used NCM811 batteries were discharged to below 2V at a current density of 0.1C, they were disassembled and sorted in a fume hood to obtain the positive electrode sheet, negative electrode sheet, shell, diaphragm, and tab;

[0102] S2. Soak the positive electrode sheet in a dimethyl carbonate solution for 2 hours, then wash it three times with deionized water, and dry it in a vacuum drying oven at 80° C. for 6 hours to obtain a pretreated positive electrode sheet;

[0103] S3. The pretreated positive electrode sheet was mixed with a LiOH solution with a concentration of 3 mol / L at a solid-liquid ratio of 1 g:6 mL, and ultrasonically treated at 25°C with an ultrasonic power of 100 W and an ultrasonic time of 1 h. After ultrasonic treatment, the pretreated positive electrode sheet was poured into a flotation machine, and methyl isobutyl carbinol was added at a dosage of 2 mg / g. The slurry pH was adjusted to 8.5 and the slurry mass concentration was 8%. The slurry was stirred at a speed of 1000 r / min and flotation was performed for 30 min. After the flotation was completed, the solid-liquid separation was carried out and the waste positive electrode material and aluminum hydroxide were separated.

[0104] S4. Add the waste cathode material to a NaOH solution with a concentration of 2 mol / L, with a solid-liquid ratio of the waste cathode material to the NaOH solution of 1 g:10 mL, perform a hydrothermal reaction at 120° C. for 8 h, separate the solid and liquid, and dry to obtain a precursor material;

[0105] S5. Place the precursor material obtained in step S4 in a tube furnace, heat it to 750° C. at a rate of 3° C. / min, and then keep it warm for 5 hours to obtain a regenerated NCM811 positive electrode material.

[0106] The electrochemical performance of the regenerated NCM811 cathode material prepared in this comparative example was tested as follows:

[0107] Preparation of positive electrode sheet: Regenerated NCM811 positive electrode material, conductive carbon, and PVDF were ground and mixed uniformly in a mass ratio of 8:1:1, stirred into a slurry in NMP medium, coated on aluminum foil, dried, and cut into pieces to obtain positive electrode sheets;

[0108] Preparation of the negative electrode sheet: CMC was dissolved in deionized water in a mass ratio of CMC: conductive carbon agent: graphite = 1.5:1.5:7. A mixed powder of graphite and carbon conductive agent was then slowly added multiple times. The mixture was stirred on a magnetic stirrer until uniformly dispersed, then coated on copper foil. The mixture was dried at 80°C for 12 hours and cut into pieces to obtain the negative electrode sheet.

[0109] The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte were assembled into a lithium-ion battery according to conventional methods in the art, and then the electrochemical performance test was performed.

[0110] After testing, it was found that in the voltage range of 2.7-4.2V, after 100 cycles at a rate of 1C, the capacity retention rate could reach 79.89%, and the discharge specific capacity was 45mAh / g at a rate of 10C.

[0111] This indicates that after direct hydrothermal treatment and subsequent water washing, there is no lithium hydroxide shell coating the outside of the particles, resulting in a large amount of unrepaired rock salt phase inside the particles after the same calcination time, and the electrical performance of the obtained regenerated positive electrode material is significantly reduced.

[0112] Comparative Example 3

[0113] A method for recovering positive electrode layered materials by hydrothermal calcination comprises the following steps:

[0114] S1. After the used NCM811 batteries were discharged to below 2V at a current density of 0.1C, they were disassembled and sorted in a fume hood to obtain the positive electrode sheet, negative electrode sheet, shell, diaphragm, and tab;

[0115] S2. Soak the positive electrode sheet in a dimethyl carbonate solution for 2 hours, then wash it three times with deionized water, and dry it in a vacuum drying oven at 80° C. for 6 hours to obtain a pretreated positive electrode sheet;

[0116] S3. Mix the pretreated positive electrode sheet with a LiOH solution with a concentration of 3 mol / L, with a solid-liquid ratio of the positive electrode sheet to the LiOH solution of 1 g:6 mL, and ultrasonically treat at 25°C, with an ultrasonic power of 100 W and an ultrasonic time of 1 h. After ultrasonic treatment, pour the mixture into a flotation machine, add methyl isobutyl carbinol at a dosage of 2 mg / g, adjust the slurry pH to 8.5, and the slurry mass concentration to 8%. Stir at a speed of 1000 r / min and flotate for 30 min. After flotation, separate the solid and liquid, dry, and separate to obtain waste positive electrode material and aluminum hydroxide.

[0117] S4, adding the waste cathode material to a LiNO3 solution with a concentration of 5 mol / L, with a solid-liquid ratio of the waste cathode material to the LiNO3 solution of 1 g:10 mL, carrying out a hydrothermal reaction at 120° C. for 8 h, followed by solid-liquid separation and drying to obtain a precursor material;

[0118] S5. Place the precursor material obtained in step S4 in a tube furnace, heat it to 750°C at a rate of 3°C / min, and then keep it warm for 5 hours to obtain a regenerated NCM811 positive electrode material. The electrochemical performance of the regenerated NCM811 positive electrode material prepared in this comparative example was tested as follows:

[0119] Preparation of positive electrode sheet: Regenerated NCM811 positive electrode material, conductive carbon, and PVDF were ground and mixed uniformly in a mass ratio of 8:1:1, stirred into a slurry in NMP medium, coated on aluminum foil, and cut into pieces after drying to obtain positive electrode sheets;

[0120] Preparation of the negative electrode sheet: CMC was dissolved in deionized water in a mass ratio of CMC: conductive carbon agent: graphite = 1.5:1.5:7. A mixed powder of graphite and carbon conductive agent was then slowly added multiple times. The mixture was stirred on a magnetic stirrer until uniformly dispersed, then coated on copper foil. The mixture was dried at 80°C for 12 hours and cut into pieces to obtain the negative electrode sheet.

[0121] The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte were assembled into a lithium-ion battery according to conventional methods in the art, and then the electrochemical performance test was performed.

[0122] After testing, it was found that in the voltage range of 2.7-4.2V, after 100 cycles at a rate of 1C, the capacity retention rate could reach 83.89%, and the discharge specific capacity at a rate of 10C was 97mAh / g.

[0123] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0124] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for recovering layered cathode materials by hydrothermal calcination, characterized in that: The following steps are involved: S1. Soak and clean the surface of the positive electrode of the used battery with an organic solvent; S2. placing the cleaned positive electrode sheet into the first solution, subjecting it to ultrasonic treatment, and then placing it in a flotation device, adding a frother, and flotation; after flotation, filtering and drying to separate the waste positive electrode material; S3, adding the waste cathode material to the second solution to carry out a hydrothermal reaction; after the reaction is completed, separating the solid and the liquid, and drying to obtain a precursor material; S4, calcining the precursor material to obtain a regenerated positive electrode material; Wherein, the first solution in step S2 and the second solution in step S3 respectively include a lithium-containing compound and an alkali; In the first solution, Li + and OH - The molar ratio is 1:1-3, Li + The molar concentration of OH is ≥0.5M, - Molar concentration ≥ 2M; Li in the second solution + and OH - The molar ratio is 1-3:1, Li + The molar concentration of OH is ≥2M, - Molar concentration ≥1M.

2. The method for recovering layered positive electrode materials by hydrothermal calcination according to claim 1, characterized in that: OH of the first solution - The concentration is greater than that of the second solution - Concentration, Li of the first solution + Less than the second solution Li + concentration.

3. The method for recovering layered positive electrode materials by hydrothermal calcination according to claim 1, characterized in that: The lithium-containing compounds selected from the first solution and the second solution are each independently at least one of an inorganic lithium salt, an organic lithium salt, and lithium hydroxide, and the bases include at least one of LiOH, NaOH, and KOH.

4. The method for recovering layered positive electrode materials by hydrothermal calcination according to claim 3, characterized in that: The inorganic lithium salt includes at least one of LiNO3, LiCl, and Li2SO4; the organic lithium salt includes at least one of lithium formate, lithium acetate, lithium propionate, lithium oxalate, lithium salicylate, lithium lactate, and lithium citrate.

5. The method for recovering layered positive electrode materials by hydrothermal calcination according to claim 1, characterized in that: In step S1, the organic solvent is at least one of dimethyl carbonate and diethyl carbonate; and / or in step S3, the solid-liquid ratio of the waste positive electrode material to the second solution is 1g:3-12mL; and / or the hydrothermal temperature is 120-220°C; and / or the hydrothermal time is 0.5-8h.

6. The method for recovering layered cathode materials by hydrothermal calcination according to claim 1, characterized in that: In step S4, the calcination temperature is 700-850° C.; and / or the calcination time is 1-10 hours.

7. The method for recovering layered cathode materials by hydrothermal calcination according to claim 1, characterized in that: In step S2, the solid-liquid ratio of the positive electrode sheet and the first solution is 1g:4-15mL, and / or the ultrasonic treatment temperature is 20-45°C; and / or the treatment time is 0.5-2h; and / or the ultrasonic power is 50-1000W; and / or, during the flotation process, the amount of the frother is 0.5-5mg / g; the rotation speed is 800-1400r / min; the slurry pH is maintained between 4.5-11; and the slurry mass concentration is 0-10% and not 0.

8. A regenerated layered positive electrode material, characterized in that The material is prepared by the method for recovering layered positive electrode materials by hydrothermal calcination as described in any one of claims 1 to 7.

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