Regeneration method of lithium ion battery positive electrode material based on surface reconstruction and pre-lithiation, positive electrode material and lithium ion battery

Abstract

The invention belongs to the technical field of resource utilization of waste lithium ion batteries, and relates to a regeneration method of a lithium ion battery positive electrode material based on surface reconstruction and pre-lithiation, the positive electrode material and a lithium ion battery. According to the method, the waste positive electrode material and an alkaline aqueous solution capable of providing an ammonia complexing environment and lithium ions at the same time are subjected to a hydrothermal reaction, the concentration of the aqueous solution is 1.0-6.0 mol / L, and the reaction is performed for 2-12 hours at the temperature of 160-250 DEG C; and centrifugally separating and drying the reaction product, mixing with a trace amount of lithium-rich agent, and calcining at 700-950 DEG C for 4-15 hours to obtain the regenerated positive electrode material. Through the one-step hydrothermal process, the structural transformation of the surface rock salt / spinel impure phase and the uniform presetting of the lithium source are synchronously realized, and the dynamic barrier of lithium ion diffusion in the traditional direct regeneration technology is broken through. The obtained regenerated material has a regular layered structure and excellent first charge-discharge capacity and cycle stability, the performance of the regenerated material can be compared favorably with that of a commercial new material, and the process flow is environment-friendly and efficient and is suitable for large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium-ion battery resource utilization technology, and relates to a method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation, as well as cathode materials and lithium-ion batteries. Background Technology

[0002] Currently, the mainstream industrial recycling methods are pyrometallurgy and hydrometallurgy. Pyrometallurgy extracts metals through high-temperature smelting. Although the process is simple, it consumes extremely high amounts of energy and has a low lithium recovery rate, easily causing secondary pollution. Hydrometallurgy uses an acid leaching-extraction-precipitation process, which has a higher metal recovery rate, but the process is lengthy, generates a large amount of acid and alkali-containing waste liquid, and completely destroys the crystal structure of the most valuable cathode material, limiting it to use as a low-grade metallurgical raw material. Both its economic and environmental benefits need improvement.

[0003] Against this backdrop, direct recycling has emerged. This method aims to directly restore the composition, structure, and electrochemical properties of spent cathode materials, enabling them to be reused in battery manufacturing and thus maximizing their added value. Direct recycling boasts significant advantages such as low energy consumption, short process, low carbon emissions, and high economic efficiency, and is considered the most promising next-generation recycling technology.

[0004] However, direct recovery technologies, especially for layered oxide cathodes (such as LiNi), are not ideal. x Co y Mn z The regeneration of O2, NCM, and LiCoO2 (LCO) still faces severe technical bottlenecks. After long-term cycling, the failure of these materials mainly stems from two factors: first, the irreversible loss of active lithium leads to severe lithium deficiency in the bulk phase; second, in the near-surface region of the particles, transition metal (TM) ions (especially Ni)... 2+ The lithium ions migrate to the lithium layer, forming a stable and dense rock salt or spinel phase impurity. This impurity structure fundamentally changes the lithium ion transport path, transforming the low-energy-barrier "1-TM channel" into a high-energy-barrier "2-TM channel," thus creating a huge kinetic barrier to lithium ion diffusion.

[0005] Existing direct regeneration technologies aim to repair the structure and stoichiometry of materials, but all have significant limitations. Existing patent document CN115724474A discloses a method using ammonia water hydrothermal treatment to transform impurity phases (rock salt or spinel phases) into corresponding hydroxide precursors, combined with high-temperature annealing for lithium replenishment to repair the structure. This method utilizes the etching, dissolution, metal ion complexation, and co-precipitation effects of ammonia water at high temperatures to transform the densely packed impurity phase into a layered hydroxide structure, and then uses high-temperature solid-phase annealing for lithium replenishment to repair the material's composition and structure. However, the uneven distribution of lithium salts and insufficient contact with host particles remain, leading to uneven bulk lithium replenishment and the potential presence of unrepaired lithium vacancies within the particles. In addition, some studies have used high-concentration lithium hydroxide (LiOH) for hydrothermal treatment. While this method can open local gaps on the surface through strong alkaline corrosion and achieve limited lithium replenishment, it cannot achieve complete structural reconstruction for thick and stable rock salt phases, resulting in poor long-term cycling stability of the regenerated material. As for the traditional direct solid-state sintering method, the lithium ions cannot diffuse evenly into the bulk phase due to the obstruction effect of the surface rock salt phase, resulting in incomplete repair and low performance recovery rate.

[0006] Therefore, there is an urgent need in this field to develop a new direct regeneration method that must be able to: (1) fundamentally “transform” rather than “bypass” or “destroy” the rock salt / spinel phase barrier on the surface; (2) create optimal kinetic conditions for subsequent deep lithium replenishment while removing the barrier; and (3) ultimately achieve a thorough and uniform repair of the waste cathode material from the surface to the bulk phase, so that its electrochemical performance is restored to a level comparable to that of commercial new materials. Summary of the Invention

[0007] Based on this, the purpose of this invention is to provide a method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation. This method has a reasonable process flow. Through a one-step hydrothermal reaction, the reconstruction of the surface rock salt / spinel phase and the uniform pre-positioning of the lithium source are realized simultaneously, creating an ideal precursor state for the subsequent high-temperature solid-phase reaction. This method is an efficient, thorough and industrially promising method for regenerating waste lithium-ion battery cathode materials.

[0008] This invention also provides a cathode material prepared using the regeneration method provided by this invention and a lithium-ion battery containing the cathode material. The material is thoroughly regenerated and has a high performance recovery rate; the lithium-ion battery exhibits excellent electrochemical performance.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation, comprising the following steps: S1, the waste positive electrode material is mixed with the hydrothermal reaction solution in a certain proportion and subjected to hydrothermal treatment to obtain the reaction slurry; The reaction slurry described in S2 and S1 is cooled and then centrifuged to obtain centrifuged products, which are then dried to obtain intermediates. S3, the intermediate described in S2 is mixed with the lithium-rich agent in a certain proportion and calcined in an oxygen-containing atmosphere to obtain the lithium-ion battery cathode material based on surface reconstruction and pre-lithiation.

[0010] Furthermore, the waste cathode material mentioned in S1 is cathode black powder, and the main components of the cathode black powder include LiCoO2 or LiNi. x Co y Mn z The cathode black powder contains layered oxides of O2, conductive carbon, binder, and electrolyte salt; the molar ratio of lithium (Li) to transition metal (TM) in the cathode black powder is Li / TM = 0.70~0.95; the general chemical formula is LiNi. x Co y Mn z In O2, x + y + z = 1.

[0011] Furthermore, the conductive carbon includes acetylene black or Super P, the binder includes polyvinylidene fluoride (PVDF), and the electrolyte includes trace amounts of lithium hexafluorophosphate (LiPF6); the particle surface of the positive electrode black powder is coated with a rock salt phase and / or spinel phase with a thickness of 5~50 nm.

[0012] Furthermore, the concentration of the hydrothermal reaction solution in S1 is 1.0~6.0 mol / L, preferably 4.0 mol / L, including an aqueous solution of lithium amino acid or a mixed aqueous solution of ammonia / lithium hydroxide.

[0013] Furthermore, the preparation process of the amino lithium aqueous solution is as follows: solid amino lithium is dissolved in low-temperature deionized water and stirred until completely dissolved.

[0014] Further, the preparation process of the ammonia / lithium hydroxide mixed aqueous solution is as follows: a certain volume of concentrated ammonia is measured and dissolved together with a calculated amount of lithium hydroxide solid in deionized water, the volume is adjusted and stirred evenly to obtain the solution; the mass concentration of the concentrated ammonia is 25~28wt%; the concentration of ammonia in the ammonia / lithium hydroxide mixed aqueous solution is 1.0~6.0 mol / L, and the concentration of lithium hydroxide is also 1.0~6.0 mol / L.

[0015] Furthermore, in S1, the solid-liquid ratio of the waste cathode material to the hydrothermal reaction solution is 1g: 95~560 mL, preferably 1g: 140 mL; the hydrothermal treatment conditions are: heating to 160~250℃ at a rate of 1~5℃ / min, holding the reaction at this temperature for 2~12 hours, preferably reacting at 180℃ for 6 hours; during this process, ammonia complexation and the strong alkaline environment work synergistically to complete the conversion of the surface phase of the waste cathode material and lithium pre-positioning.

[0016] Furthermore, the hydrothermal treatment described in S1 is preferably carried out in a high-pressure reactor. First, the old positive electrode material and the hydrothermal reaction solution are added to the high-pressure reactor, and the solid and liquid are fully mixed by mechanical stirring or shaking. Then, the high-pressure reactor is placed in an oven and heated. The high-pressure reactor includes a stainless steel reactor with a polytetrafluoroethylene liner.

[0017] Further, in step S2, the centrifugation time is 5-10 minutes, and the centrifugation speed is 3000-8000 rpm, preferably 8 minutes and 6000 rpm; the centrifuged product is dried at 60-120°C for 4-24 hours, preferably at 100°C for 12 hours. Through centrifugation and drying in step S2, residual alkaline substances, dissolved fluorides, decomposed binder products, and conductive carbon after the hydrothermal reaction can be removed; ultimately, a dried, phase-reconstruction-induced layered hydroxide and lithium-rich hydroxide composite precursor intermediate is obtained.

[0018] Furthermore, the amount of lithium-rich agent added in S3 is 3 to 10 wt% of the mass of the intermediate, preferably 4 to 6 wt%, and this excess is used to compensate for lithium volatilization at high temperatures and ensure sufficient lithium replenishment; the lithium-rich agent includes at least one of lithium hydroxide, lithium carbonate and lithium nitrate.

[0019] Furthermore, the intermediate and lithium-rich agent described in S3 are preferably first mechanically mixed in a mortar or mixer to ensure uniformity; then the uniformly mixed powder is placed in a high-temperature resistant container (such as an alumina crucible) and then placed in a muffle furnace or tube furnace for sintering.

[0020] Furthermore, the oxygen volume fraction in the oxygen-containing atmosphere described in S3 is ≥20 vol%, including air, oxygen, or a mixture of oxygen and argon.

[0021] Furthermore, the selection of the oxygen-containing atmosphere mentioned in S3, for cathode materials with a nickel content ≥60% (such as NCM622, NCM811), must be carried out in a pure oxygen atmosphere to prevent nickel reduction and oxygen loss.

[0022] Furthermore, the calcination conditions described in S3 are as follows: the temperature is increased to 700-950°C at a rate of 2-10°C / min and held for 4-15 hours; preferably, the temperature is increased to 850°C at a rate of 5°C / min and held for 10 hours to complete the solid-state reaction, grain growth and structural repair.

[0023] Furthermore, after the calcination treatment in S3 is completed, the power is cut off, and the sample is allowed to cool naturally to room temperature (25±5℃) with the furnace. After removal, it is lightly ground, preferably for 10~20 minutes, to obtain a high-performance cathode material for lithium-ion batteries based on surface reconstruction and pre-lithiation, which has a standard layered structure.

[0024] This invention further provides a lithium-ion battery cathode material prepared by the above-mentioned method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation. This material not only recovers its chemical composition but also achieves reconstruction in its microstructure, enabling its electrochemical performance to rival that of commercially available new materials.

[0025] Furthermore, the general formula of the positive electrode material is Li. 1+a M1 x M2 y M3 z O2, wherein: M1, M2, and M3 are transition metal elements, each independently selected from at least two of Ni, Co, and Mn, with 0.5 ≤ x ≤ 0.9, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.3, and x + y + z = 1; 'a' is a lithium stoichiometric excess set to ensure electrochemical performance, ranging from 0.02 ≤ a ≤ 0.15, preferably a = 0.05 ~ 0.08. This design ensures that the material has sufficient reversible lithium capacity. Furthermore, the general formula Li 1+a M1 x M2 y M3 z The O2 may contain a dopant element M' with an atomic percentage not exceeding 5 at% (i.e., k ≤ 0.05), wherein M' is selected from at least one of Al, Mg, Zr, Ti, W, Ta, and F, to further improve the structural stability and cycle life of the material. This doped material is an extension application based on regenerated cathode materials; during the preparation of this doped material, a certain amount of dopant element precursor can be added during the hydrothermal treatment process to achieve element predoping, and element doping is achieved in the subsequent annealing process.

[0026] Furthermore, the cathode material has a typical α-NaFeO2 type layered crystal structure, belonging to the trigonal crystal system, with a space group of R3m, and is composed of secondary spherical or near-spherical particles formed by the aggregation of primary particles.

[0027] Furthermore, the cathode material was tested by XRD, and its (003) crystal plane diffraction peak was located at 2θ = 18.65° ± 0.25°. The (104) crystal plane diffraction peak was located at 2θ = 44.50° ± 0.25°. The intensity ratio of the (003) peak to the (104) peak, I(003) / I(104) ≥ 1.20, preferably I(003) / I(104) ≥ 1.35; this ratio is the core indicator for measuring the degree of Li / Ni cation mixing, and a high ratio indicates that the layered structure is highly regular. The (006) and (102) diffraction peaks, as well as the (108) and (110) diffraction peaks, exhibit a clearly distinguishable bimodal separation. This demonstrates that, compared to waste cathode materials, the rock salt and spinel phase impurities in the particles within a depth of at least 50 nm are effectively removed, transforming the material into a regular layered structure with fast one-dimensional lithium-ion transport channels.

[0028] Furthermore, X-ray photoelectron spectroscopy testing of the cathode material showed that no characteristic signal of F element could be detected in the bulk phase of the material (detection limit <0.1 at%), proving that fluoride impurities originating from the binder and electrolyte have been effectively removed.

[0029] Finally, this invention provides a lithium-ion battery comprising a positive electrode containing the aforementioned lithium-ion battery positive electrode material. This lithium-ion battery exhibits excellent electrochemical performance.

[0030] The beneficial effects of this invention are: 1. High degree of thorough repair and excellent cycle performance: After 100 cycles at 1C, the capacity retention of the regenerated lithium-ion battery cathode material can reach 96.3%, which is superior to the traditional LiOH hydrothermal method (~90%) and direct sintering method (~85%). This advantage stems from the core technology (S1 hydrothermal reconstruction reaction), in which the ammonia complexing agent selectively dissolves the surface rock salt / spinel phase and transforms it into a layered hydroxide precursor, fundamentally eliminating the kinetic barrier to lithium-ion diffusion.

[0031] 2. Excellent lithium replenishment efficiency and uniformity: First-week discharge capacity recovery rate >92%, and low voltage decay rate. This advantage stems from the (S1 hydrothermal reconstruction reaction), where, under a strongly alkaline environment, the lithium source (coated / adsorbed lithium) and the newly formed hydroxide form a nanoscale close contact, creating a "lithium-rich hydroxide composite precursor." This allows for nanoscale contact between the lithium source and the host material during (S3 high-temperature crystallization treatment), achieving efficient short-range bulk diffusion, which helps lower the lithium-ion diffusion barrier and promotes deep lithiation. Furthermore, the uniform distribution of lithium effectively avoids the potential for localized lithium excess (forming low-melting-point corrosion particles) or localized lithium deficiency caused by agglomeration in traditional solid-state mixing.

[0032] 3. High applicability: This method is applicable to LiCoO2 and LiNi. x Co y Mn z O2 (including NCM111, NCM523, NCM622, NCM811) and other layered cathode materials are regenerated. This advantage stems from the universality of the ammonia complexation reaction for various transition metal ions, and the effective promotion of pre-lithiation by the strong alkaline lithium environment.

[0033] 4. The process is environmentally friendly and economical: it avoids the use of toxic organic solvents such as NMP, and the hydrothermal solution has the potential to be recycled, reducing costs and environmental footprint. Attached Figure Description

[0034] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Appendix Figure 1 The image shows the ICP-OES test results of different samples (waste cathode material S-NCM523, intermediate H-NCM523 and recycled cathode material R-NCM523-A) in Example 1 of the present invention. Appendix Figure 2 The images show the SEM test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-A) in Example 1 of this invention; the scale bar is 100 nm, Figure a is S-NCM523, and Figure b is R-NCM523-A. Appendix Figure 3 The figures show the HRTEM test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-A) in Example 1 of this invention; where the scale bar is 2nm, Figure a is S-NCM523 and Figure b is R-NCM523-A. Appendix Figure 4 The XPS test results of different samples (waste cathode material S-NCM523, intermediate H-NCM523, and recycled cathode material R-NCM523-A) in Example 1 of this invention are shown in the figure. Appendix Figure 5 This is a comparison chart of the XRD test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-A) and commercial C-NCM523 material in Example 1 of the present invention; Appendix Figure 6The images show refined XRD test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-A) and commercial C-NCM523 material in Example 1 of this invention; wherein, Figure a is S-NCM523, Figure b is R-NCM523-A, and Figure c is C-NCM523. Appendix Figure 7 The first charge-discharge curve of the regenerated cathode material R-NCM523-A in Example 1 of this invention; Appendix Figure 8 The graph shows the cycle stability test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-A) and commercial C-NCM523 material in Example 1 of the invention. Appendix Figure 9 This is a comparison of the XRD test results of different samples (waste cathode material S-NCM111 and recycled cathode material R-NCM111) in Example 2 of the present invention; Appendix Figure 10 The graph shows the cycle stability test results of different samples (waste cathode material S-NCM111 and recycled cathode material R-NCM111) and commercial C-NCM111 material in Example 2 of the present invention. Appendix Figure 11 This is a comparison chart of XRD test results for different samples (waste cathode material S-LCO and recycled cathode material R-LCO) in Example 3 of the present invention; Appendix Figure 12 The first charge-discharge curve of the regenerated cathode material R-LCO in Example 3 of this invention; Appendix Figure 13 The graph shows the cycle stability test results of different samples (waste cathode material S-LCO and recycled cathode material R-LCO) in Example 3 of the present invention. Appendix Figure 14 This is a comparison chart of the XRD test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-D) in Comparative Example 1 of the present invention and commercial C-NCM523 material. Appendix Figure 15 The image shows the SEM test results of the regenerated cathode material R-NCM523-D in Comparative Example 1 of this invention; the scale bar is 1 μm. Appendix Figure 16 The graph shows the cycle stability test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-D) in Comparative Example 1 of the invention. Appendix Figure 17This is a comparison of the XRD test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-E) and commercial C-NCM523 material in Comparative Example 2 of this invention; Appendix Figure 18 The image shows the SEM test results of the regenerated cathode material R-NCM523-E in Comparative Example 2 of this invention; the scale bar is 1 μm. Appendix Figure 19 The figure shows the cycle stability test results of different samples (waste cathode material S-NCM523 and recycled cathode material R-NCM523-E) in Comparative Example 2 of this invention. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All mentioned embodiments are implemented based on the technical solutions of the present invention, and detailed implementation processes are given. However, it should be stated that the scope of protection of the present invention is not limited to the following embodiments.

[0037] The following embodiments provide detailed implementation procedures for the technical solutions of the present invention. Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0038] Example 1

[0039] NCM523 was regenerated using 4M lithium amino acid solution. Raw materials: NCM523 (S-NCM523) cathode sheets obtained from dismantled retired power batteries. Black powder was scraped off from the aluminum foil current collector and dried in a vacuum drying oven to obtain cathode black powder. ICP-MS testing showed that its Li / TM ratio was 0.85.

[0040] Hydrothermal reconstruction: Weigh 1g of the above black powder and place it in a 500mL high-pressure reactor. Add 140mL of a 4mol / L lithium amino acid aqueous solution. After sealing, place the reactor in an oven and react at 180℃ for 6 hours.

[0041] Centrifugal drying: After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The slurry was removed and centrifuged at 4500 rpm for 6 min. The resulting product was dried in a vacuum drying oven at 100℃ for 12 hours to obtain intermediate H-NCM523.

[0042] High-temperature crystallization: The dried intermediate H-NCM523 was thoroughly mixed with 5% of the intermediate lithium hydroxide monohydrate (LiOH•H2O) in a mixer. The mixture was placed in an alumina crucible and then placed in a box furnace. The temperature was increased to 850°C at 5°C / min under air atmosphere and held for 10 hours. After that, it was naturally cooled to room temperature. The resulting material was then ground to obtain the final recycled material R-NCM523-A.

[0043] Battery fabrication: Weigh out powdered positive electrode active materials (recycled positive electrode material S-NCM523, commercial new material C-NCM523, or recycled material R-NCM523-A), acetylene black conductive agent, and PVDF binder in a mass ratio of 8:1:1. Mix them evenly in an agate mortar. Then, add N-methylpyrrolidone (NMP) in small amounts several times as a solvent for PVDF and to participate in dispersion. The total amount of NMP added is 10:1 in mass ratio to PVDF. Grind thoroughly to obtain a slurry with good viscosity and flowability. Then, coat the obtained slurry evenly on a clean and dry aluminum foil current collector. Use a four-sided coating machine to make an electrode sheet with a thickness of 100 μm. Place it in a vacuum drying oven for overnight drying at a drying temperature of 120℃. After drying, take it out and use a cutting machine to cut it into round pieces with a diameter of 12 mm, which are the positive electrode sheets of button batteries.

[0044] After drying, the raw materials used for assembling coin cells were transferred to a glove box filled with high-purity argon gas for assembling CR2032 coin cells. The water and oxygen content in the glove box was less than 0.1 ppm. The lithium-ion battery separator used was Celgard 2400 with a diameter of 16 mm, and the counter electrode was a commercially available lithium sheet with a diameter of 15.6 mm and a thickness of 4.5 mm. The electrolyte was prepared using 1.0 M LiPF6 as the solute and EC:DMC:EMC in a 1:1:1 vol% ratio as the solvent. The battery assembly method involved sequentially placing the lithium metal sheet, separator, electrolyte, positive electrode, gasket, and spring onto the negative electrode shell, and finally covering it with the positive electrode shell. The coin cells were then sealed using a packaging machine and left to stand for later use.

[0045] Implementation effect test

[0046] This invention employed inductively coupled plasma optical emission spectrometry (ICP-OES) to compare the elemental contents of S-NCM523, H-NCM523, and R-NCM523-A. Figure 1The results showed that, compared with S-NCM523, the relative molar ratio of lithium in H-NCM523 after hydrothermal reaction treatment was 1.087. During the high-temperature annealing process, in order to prevent the evaporation or overflow of lithium, a small amount of lithium-rich agent was added, which made the obtained R-NCM523-A still maintain a Li molar ratio of 1.078, and the Li:Ni:Co:Mn ratio was close to that of commercial materials.

[0047] This invention used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to test the morphological characteristics of the material. The test results showed that, relative to the cracks on the surface of the waste particles ( Figure 2 a) The surface of the repaired material is smooth. Figure 2 b), and high-resolution transmission electron microscopy (HRTEM) revealed the rock salt phase relative to the surface of S-NCM523 ( Figure 3 a) The crystal structure of the repaired material has been restored to a layered structure. Figure 3 b).

[0048] This invention employs X-ray photoelectron spectroscopy to perform elemental analysis on the materials. The analysis results show that, compared to waste particles, no characteristic signal of fluorine (F) was detected in H-NCM523 after hydrothermal reaction treatment (detection limit <0.1 at%). After high-temperature annealing, no characteristic signal of F was also detected in the bulk phase of R-NCM523-A material (detection limit <0.1 at%). This fully demonstrates that fluoride impurities originating from binders and electrolytes have been effectively removed. Figure 4 ).

[0049] This invention uses Cu Kα rays (wavelength λ = 1.5406 Å) to perform XRD tests on different materials. The XRD test results show that the (003) peak position (2θ ≈ 18.7°) is consistent with that of the commercial new material (C-NCM523), and the (003) / (104) peak intensity ratio is >1.2. Figure 5 XRD refinement results indicate a severe lithium-nickel mixture relative to the waste (Li / Ni = 12.41%). Figure 6 a) The repaired material exhibits a low Li / Ni mixture (3.1%). Figure 6 b) Close to the lithium-nickel blending value of commercial materials (3.91%) Figure 6 c).

[0050] Half-cell test (2.5~4.2V vs. Li) + The first-cycle discharge capacity at 0.1C is 162.2 mAh / g, and the first-cycle efficiency is 93.9%. Figure 7 After 100 cycles at a 0.5C rate, the capacity retention is 96%. Figure 8 ).

[0051] Example 2

[0052] NCM111 was regenerated using a 4M ammonia / 4M LiOH mixed solution. Raw material: waste NCM111 (S-NCM111) black powder, Li / TM ratio is 0.92.

[0053] Hydrothermal reconstruction: Weigh 1g of black powder and carry out a hydrothermal reaction with 140mL of a mixed aqueous solution containing 4 mol / L ammonia and 4 mol / L LiOH, under the same conditions as in Example 1.

[0054] Centrifugal drying: Same as in Example 1.

[0055] High-temperature crystallization: After mixing 5% of the intermediate LiOH•H2O, calcine at 850℃ for 10 hours under an oxygen atmosphere at a rate of 5℃ / min.

[0056] Implementation effect test: The (003) peak of the recycled material R-NCM111 returned to its original position ( Figure 9 Furthermore, after 100 cycles, the capacity retention rate is 92.2%, comparable to that of commercial material (C-NCM111). Figure 10 ).

[0057] Example 3

[0058] LiCoO2 was regenerated using a 2M ammonia / 2M LiOH mixed solution. Raw material: Waste LiCoO2 black powder (S-LCO), Li / Co ratio is 0.92.

[0059] Hydrothermal reconstruction: The hydrothermal solution was a 2M ammonia / 2M LiOH mixed solution, the reaction temperature was 200℃, and the time was 4 hours.

[0060] Centrifugal drying: Same as in Example 1.

[0061] High-temperature crystallization: After mixing with 5% intermediate Li2CO3, calcination was carried out at 850°C for 12 hours in air atmosphere.

[0062] Implementation effect test: The impurity phase Co3O4 in the recycled material (R-LCO) completely disappeared. Figure 11 Electrochemical performance was tested at 3~4.3V. Figure 12 This indicates that the R-LCO has a first-cycle discharge capacity of 145.5 mAh / g, and retains 93.5% of its capacity after 100 cycles at 0.5C. Figure 13 ).

[0063] Comparative Example 1 Traditional LiOH hydrothermal method The steps are basically the same as in Example 1, except that the hydrothermal reaction solution is replaced with a 4 mol / L LiOH aqueous solution (ammonia-free). The resulting recycled material is R-NCM523-D.

[0064] Implementation effect test: Its XRD pattern showed that the (003) peak position was slightly restored, but the (104) peak was broadened, indicating that the improvement of cation mixing was limited. Figure 14 SEM images showed that the repaired R-NCM523-D material contained particles of varying sizes. Figure 15 Furthermore, after the repaired material was stably cycled for 100 cycles at 0.5C, the capacity retention rate was 79.6%. Figure 16 The capacity retention rate of the repair material is lower than that of the repair material in a mixture of lithium amino acid or ammonia and lithium hydroxide. This is attributed to the fact that the secondary particles of varying sizes after repair cause differences in lithium ion diffusion paths, resulting in excessively high local current density, decreased electrochemical performance, and increased safety risks.

[0065] Comparative Example 2 Direct solid-state sintering method 100g of raw NCM523 waste black powder was directly mixed with 7 mol% excess LiOH•H2O, and then calcined at 850℃ for 10 hours in air atmosphere to obtain recycled material C-NCM523-E.

[0066] Implementation effect test: Its XRD pattern showed that the (003) peak position was slightly restored, but the (104) peak was broadened, indicating that the improvement of cation mixing was limited. Figure 17 SEM results show that pores still exist on the surface of the waste. Figure 18 Furthermore, after 100 cycles at 0.5C, the capacity retention was 66.1%, significantly lower than the capacity retention of the hydrothermally pre-lithiated sample (R-NCm523-D) after high-temperature annealing repair. Figure 19 This indicates the limitations of its repair.

[0067] In summary, the lithium-ion battery cathode material regeneration method based on surface reconstruction and pre-lithiation provided by this invention has strong universality and is applicable to LiCoO2 and LiNi. x Co y Mn z The regeneration of various layered cathode materials, including O2 (such as NCM111, NCM523, NCM622, and NCM811), is an advantage stemming from the universality of the ammonia complexation reaction for various transition metal ions and the effective promotion of lithiation by the strong alkaline lithium environment. The process is environmentally friendly and economical, avoiding the use of toxic organic solvents such as NMP, and the hydrothermal solution has the potential for recycling, reducing costs and environmental footprint.

[0068] The cathode material prepared using the surface reconstruction and pre-lithiation-based lithium-ion battery cathode material regeneration method provided by this invention exhibits high repair thoroughness and excellent cycle performance. After 100 cycles at 1C rate, the regenerated lithium-ion battery cathode material retains 96.3% of its capacity, which is superior to the traditional LiOH hydrothermal method (~90%) and direct sintering method (~85%). This advantage stems from the core technology (S1 hydrothermal reconstruction reaction), where the ammonia complexing agent selectively dissolves and transforms the surface rock salt / spinel phase, fundamentally eliminating the kinetic barrier to lithium-ion diffusion. It also demonstrates excellent lithium replenishment efficiency and uniformity, with a first-cycle discharge capacity recovery rate >92% and a low voltage decay rate. This advantage stems from the fact that in the (S1 hydrothermal reconstruction reaction), under a strongly alkaline environment, the lithium source (coated / adsorbed lithium) and the newly formed hydroxide are in close nanoscale contact, forming a "lithium-rich hydroxide composite precursor." This allows the lithium source and the host material to achieve nanoscale contact in the (S3 high-temperature crystallization treatment), enabling efficient short-range bulk diffusion, which helps lower the lithium-ion diffusion barrier and promotes deep lithiation. Furthermore, the uniform distribution of lithium effectively avoids the localized lithium excess (forming low-melting-point corrosion particles) or localized lithium deficiency that can occur with traditional solid-state mixing, which may result in agglomeration.

[0069] Regarding the above technical solution, those skilled in the art can conceive of several alternative solutions without departing from the core concept of the present invention, and these solutions can also achieve the purpose of the present invention: Alternatives for ammonia sources: In addition to ammonia water, other reagents that can provide an environment for ammonia complexation can be used, such as urea (which decomposes under hydrothermal conditions to produce NH3), ammonium carbonate, ammonium bicarbonate and other volatile ammonium salts.

[0070] Lithium source alternatives: In the (S1 hydrothermal reconstruction reaction), in addition to LiOH and LiOH produced by the hydrolysis of LiNH2, some lithium acetate, lithium nitrate, lithium nitride, etc. can also be used in combination with ammonia water, but their lithium replenishment effect may be inferior to that of strongly alkaline LiOH.

[0071] Process parameters can be adjusted: hydrothermal temperature, time, and concentration can be adjusted within the specified range to suit materials with different failure levels. Annealing temperature and time can also be adjusted accordingly to optimize oxygen partial pressure conditions for materials with different nickel contents.

[0072] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation, characterized in that, Includes the following steps: S1, the waste positive electrode material is mixed with the hydrothermal reaction solution in a certain proportion and subjected to hydrothermal treatment to obtain the reaction slurry; The reaction slurry described in S2 and S1 is cooled and then centrifuged to obtain centrifuged products, which are then dried to obtain intermediates. S3, the intermediate described in S2 is mixed with the lithium-rich agent in a certain proportion and calcined in an oxygen-containing atmosphere to obtain the lithium-ion battery cathode material based on surface reconstruction and pre-lithiation.

2. The method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation as described in claim 1, characterized in that, The waste cathode material mentioned in S1 is cathode black powder, the main components of which include LiCoO2 or have the chemical formula LiNi. x Co y Mn z The cathode powder comprises a layered oxide of O2, conductive carbon, a binder, and an electrolyte salt; the molar ratio of lithium to transition metal in the cathode black powder is 0.70~0.95; the general chemical formula is LiNi. x Co y Mn z In O2, x + y + z = 1.

3. The method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation as described in claim 1, characterized in that, The concentration of the hydrothermal reaction solution mentioned in S1 is 1.0~6.0 mol / L, including aqueous solutions of lithium aminohydride or mixed aqueous solutions of ammonia and lithium hydroxide.

4. The method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation as described in claim 1, characterized in that, The solid-liquid ratio of the waste cathode material to the hydrothermal reaction solution in S1 is 1g : 95~560 mL; the hydrothermal treatment conditions are: heating to 160~250℃ and holding the reaction for 2~12 hours.

5. The method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation as described in claim 1, characterized in that, The centrifugation time in S2 is 5-10 minutes, and the centrifugation speed is 3000-8000 rpm; the centrifuged product is dried at 60-120℃ for 4-24 hours.

6. The method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation as described in claim 1, characterized in that, The amount of lithium-rich agent added in S3 is 3 to 10 wt% of the mass of the intermediate; the lithium-rich agent includes at least one of lithium hydroxide, lithium carbonate and lithium nitrate.

7. The method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation as described in claim 1, characterized in that, The oxygen volume fraction in the oxygen-containing atmosphere described in S3 is ≥20 vol%, including air, oxygen, or a mixture of oxygen and argon.

8. The method for regenerating lithium-ion battery cathode materials based on surface reconstruction and pre-lithiation as described in claim 1, characterized in that, The calcination conditions described in S3 are: heating to 700~950℃ and holding for 4~15 hours.

9. A lithium-ion battery cathode material prepared by the lithium-ion battery cathode material regeneration method based on surface reconstruction and pre-lithiation as described in any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, wherein the positive electrode sheet contains the lithium-ion battery positive electrode material as described in claim 9.

Images