Method for regenerating waste polycrystalline ternary lithium positive electrode into single crystal ternary lithium positive electrode

Abstract

The invention belongs to the technical field of recycling of waste lithium batteries, and particularly relates to a method for regenerating a waste polycrystalline ternary lithium positive electrode into a single crystal ternary lithium positive electrode. Development of a recovery strategy of waste lithium batteries is extremely urgent, and existing pyrometallurgy and hydrometallurgy processes have the defects of high energy consumption and toxic gas release. In order to solve the problem, the invention provides the method for regenerating the waste polycrystalline ternary lithium positive electrode into the single-crystal ternary lithium positive electrode, which comprises the following steps of: recycling a positive electrode material of a waste lithium battery, immersing the positive electrode material into a dilute acid solution for treatment, mixing the ternary positive electrode material subjected to acid treatment with a lithium source by using a ball mill, and then sintering at different temperatures in stages to obtain the single-crystal ternary lithium positive electrode. The regenerated single crystal ternary positive electrode material is obtained by stabilizing the morphology and reducing natural stress. Through verification, the regenerated single crystal ternary positive electrode material has good stability, the assembled lithium battery has good electrochemical performance, and a good solution strategy is provided for recovery of waste lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling technology, specifically relating to a method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Lithium-ion batteries, with their high energy density and long cycle life, have become the mainstream energy storage solution for portable electronic devices and electric vehicles. Among various cathode materials, ternary lithium batteries stand out in the fields of electric vehicles and high-end energy storage due to their superior energy density and excellent cycle stability. However, the limited lifespan of ternary lithium batteries (typically 3 to 10 years) coupled with their widespread application is expected to lead to a large backlog of used batteries in the coming years. These used lithium-ion batteries contain precious metals such as nickel, cobalt, and lithium, as well as other potentially hazardous components. Improper disposal will pose significant environmental risks, including soil and water pollution. Driven by the dual demands of resource sustainability and environmental protection, developing efficient recycling strategies for used lithium-ion batteries has become an urgent and necessary task in the energy storage field.

[0004] Currently, the commercial recycling of spent ternary lithium batteries mainly relies on pyrometallurgical and hydrometallurgical processes, aiming to recover precious metal resources such as cobalt, nickel, and lithium, and their corresponding compounds, from degraded cathode materials. However, pyrometallurgy is often considered an undesirable option due to its high energy consumption, high operating costs, and the emission of toxic gases. In contrast, hydrometallurgical recycling processes use aqueous solutions to dissolve and extract the target elements. In this process, lithium is typically recovered in the final stage. The additional need for oxidants and precipitants increases the overall cost and raises environmental issues. Therefore, efforts are underway to develop more efficient and environmentally sustainable technologies for recycling spent cathode materials.

[0005] Direct recycling technology, leveraging the layered structure retained in failed ternary lithium-ion battery cathode materials, has become a promising non-destructive recycling method. In practical applications, advanced recycling technologies should prioritize the production of high-value-added or high-performance materials to offset processing costs—the "upgrading and remanufacturing" concept. A promising strategy is to transform the morphology of spent cathodes from polymer aggregates into well-defined single-crystal particles. When recycling ternary lithium-ion battery cathodes that have undergone irreversible morphological degradation, the single-crystalization strategy can significantly improve electrochemical performance, rather than merely restoring reversible capacity. Therefore, recycling spent ternary lithium-ion batteries to prepare single-crystal ternary lithium-ion cathodes is a highly promising direction. Summary of the Invention

[0006] In view of the above situation, the purpose of this invention is to provide a method for recycling and regenerating the cathode material of waste ternary lithium batteries, which has the advantages of low energy consumption, environmental friendliness, and high product added value.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, the method comprising the following steps: (1) Recycling the positive electrode material of ternary lithium batteries; (2) The positive electrode material is treated with dilute sulfuric acid to obtain an acid-treated positive electrode material; (3) The positive electrode material after acidification is mixed with lithium source and then sintered in stages to obtain the final product.

[0008] Commonly recycled ternary cathode materials are usually polycrystalline spherical structures composed of secondary particles. To transform them into single-crystal structures, they need to be sintered at high temperatures. The drawback of this high-temperature sintering is that prolonged high-temperature treatment will cause the single-crystal particles to grow excessively, resulting in larger single-crystal particles. This leads to an extended lithium-ion diffusion path and mechanical stress concentration, which will affect subsequent electrochemical performance.

[0009] This invention involves treating the recovered cathode material with dilute sulfuric acid. The low-concentration acid only breaks the bonds between secondary particles, etching the polycrystalline structure into a near-single-crystal precursor structure. Simultaneously, it eliminates surface impurities and rock salt phases that hinder lithium-ion transport without damaging the overall layered structure. This material is then thoroughly mixed with a lithium source and sintered in stages. During the sintering process, low-temperature calcination fuses the cathode material with the lithium source, medium-temperature calcination restores the structure, high-temperature calcination stabilizes the morphology, and then calcination at an intermediate temperature reduces stress. Finally, it is allowed to cool naturally to obtain the regenerated single-crystal ternary cathode material. Verification shows that the advantage of acid treatment is that it lowers the sintering temperature and shortens the sintering time of the near-single-crystal precursor material, resulting in a single-crystal cathode material with a size of only 1~1.5µm and a more uniform distribution. Verification also shows that this regenerated single-crystal ternary cathode material exhibits excellent resistance to cycle degradation, maintaining good electrochemical activity and structural integrity even after long-term charge-discharge cycles. Meanwhile, the above-mentioned regeneration method does not produce toxic or harmful substances, the sintering stage can be carried out in an oxygen or air atmosphere, the process cost is low, and it has good prospects for industrial application.

[0010] Further, in step (1) above, the recycling method of the positive electrode material is as follows: the ternary lithium battery to be recycled is completely discharged, the battery positive electrode is disassembled and recycled, the battery positive electrode is immersed in an organic solvent to remove the residual electrolyte, and the degraded positive electrode material is separated from the aluminum foil surface and sintered at high temperature to obtain powdered positive electrode material.

[0011] The ternary lithium batteries include lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA) types, wherein the cathode material of the lithium nickel cobalt manganese oxide battery is LiNi. x Co y Mn 1-x-y O2, including NCM111(LiNi 0.33 Co 0.33 Mn 0.33 O2), NCM523(LiNi) 0.5 Co 0.2 Mn 0.3 O2), NCM622(LiNi) 0.6 Co 0.2 Mn 0.2 O2), NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 O2) or NCM955 (LiNi) 0.9 Co 0.05 Mn 0.05 Lithium-cobalt-manganese oxide batteries with various nickel-cobalt-manganese ratios (such as O2), wherein the positive electrode material of the lithium-cobalt-aluminum oxide battery is LiNi. x Co y Al 1-x-y O2, including NCA8155 (LiNi 0.8 Co 0.15 Al 0.05 O2), NCA85105 (LiNi) 0.85 Co 0.1 Al 0.05 O2), NCA955 (LiNi) 0.9 Co 0.05 Al 0.05 Lithium-cobalt-aluminum nickel-cobalt-aluminum batteries with various nickel-cobalt-aluminum ratios (such as O2); furthermore, the above-mentioned cathode material is preferably of a type with a high nickel content, and in some embodiments verified by this invention, it is NCM811.

[0012] Furthermore, the complete discharge method is as follows: the ternary lithium battery to be recycled is soaked in salt water for 20-30 hours, wherein the salt water is a 15-25% wt. NaCl aqueous solution.

[0013] Furthermore, the organic solvent is a carbonate solvent, such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), etc., and the immersion time is 3-5 hours.

[0014] Furthermore, the sintering temperature is 400~600℃, the sintering time is 2~6h, and the sintering is carried out in an air atmosphere.

[0015] In step (2) above, the positive electrode material is immersed in a dilute sulfuric acid solution and stirred for a period of time. The treated positive electrode material is washed to remove the acid solution and dried to obtain the acid-treated positive electrode material.

[0016] Furthermore, the concentration of the sulfuric acid solution is 0.3~1 mol / L, the solid-liquid ratio of the positive electrode material to the sulfuric acid solution is 50~200 g / L, and the temperature is room temperature.

[0017] Furthermore, the stirring speed is 1000~1500 rpm, and the stirring time is 5~7 hours.

[0018] After the above stirring is completed, the positive electrode material can be separated by centrifugation or other methods. After thoroughly removing the residual acid by washing with deionized water multiple times, it is dried to obtain the final product.

[0019] In step (3) above, if the nickel content in the cathode material of the ternary lithium battery to be recycled in step (1) is greater than or equal to 60%, the segmented sintering needs to be sintered under oxygen, and the lithium source is lithium hydroxide monohydrate; if the nickel content is less than 60%, the segmented sintering is sintered under air, and the required lithium source is lithium carbonate; the dosage of the lithium source added is 0.3-0.4 times the mass of the cathode material. The main reason for adopting the above operation is that when the nickel content in the cathode material is high (greater than or equal to 60%), the required sintering temperature is relatively low. Since lithium hydroxide has higher reactivity, it can react completely even at a relatively low sintering temperature; at the same time, using oxygen as the sintering atmosphere helps to completely oxidize divalent nickel and avoid lithium-nickel mixing. When the nickel content in the cathode material is low (less than 60%), a higher sintering temperature is required. At this temperature, lithium carbonate can be completely decomposed, and the demand for oxygen is also reduced when the nickel content is low. At this time, air can be used as the sintering atmosphere.

[0020] Furthermore, the above-mentioned nickel content indicates that in the cathode material, the mass fraction of nickel among the three elements nickel, cobalt, and manganese or nickel, cobalt, and aluminum reaches 60% or more.

[0021] Furthermore, the temperature setting method for the segmented sintering is as follows: the heating rate is 3~10℃ / min, the low temperature section is sintered at 400~600℃ for 2~4h, the medium temperature section is sintered at 650~800℃ for 3~5h, and the high temperature section is sintered at 750~900℃ for 2~4h. During sintering, the temperature of the high temperature section is higher than that of the medium temperature section, and then the temperature is reduced to the medium temperature section for sintering for 1~2h.

[0022] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention adopts a direct recycling method to directly recycle waste polycrystalline ternary cathode materials into regenerated monocrystalline ternary cathode materials. Compared with traditional wet and pyrometallurgical recycling and metal extraction, it significantly reduces processing steps and optimizes costs.

[0023] 2. The present invention allows for the extraction of lithium salts from the acid solution generated after acid etching. Further processing can enable the acid etching step to be repeated, thus realizing the recovery and internal circulation of process products and reducing costs.

[0024] 3. The recycled single-crystal ternary lithium-ion battery cathode material obtained by this invention has a low cost. Compared with the polycrystalline ternary cathode material on the market, the single-crystal material obtained by this invention has a size concentrated in the range of 1~1.5µm, which is smaller and has obvious advantages in performance.

[0025] 4. The regenerated single-crystal ternary lithium battery cathode process provided by this invention is simple to operate and environmentally friendly, avoiding the large-scale discharge of wastewater and waste gas that would affect the environment. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is a flowchart of the regeneration method for the single-crystal ternary cathode material described in this invention; Figure 2 The image shows a SEM image of the failed ternary cathode material described in Example 1. Figure 3 This is a SEM image of the regenerated single-crystal ternary cathode material in Example 1; Figure 4 SEM images of regenerated ternary cathode materials that are sintered directly without acid etching. Figure 5 SEM images of commercially available monocrystalline ternary cathode materials; Figure 6 This is a graph showing the cycle performance of a half-cell assembled from the regenerated single-crystal ternary cathode material described in Example 1. Figure 7 This is a rate performance test diagram of the half-cell assembled from the regenerated single-crystal ternary cathode material described in Example 1; Figure 8 The electrochemical impedance spectroscopy of the half-cell assembled from the regenerated single-crystal ternary cathode material described in Example 1 is shown. Figure 9 The graph shows the cycle performance of a soft-pack full cell assembled from the recycled single-crystal ternary cathode material described in Example 1. Detailed Implementation

[0028] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] In the context of this specification, the word "comprising" is considered to mean "especially including". It should not be interpreted as "consisting of only".

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0032] Example 1 This embodiment provides a method for regenerating single-crystal ternary lithium cathodes from waste polycrystalline ternary lithium cathodes. The method uses waste high-nickel ternary cathode material as raw material to recycle cathode material. The failed cathode material is acid-etched and mixed with a lithium source, then sintered in stages to obtain the regenerated single-crystal ternary cathode material. The process is as follows: Figure 1 As shown; specifically, it includes the following steps: (1) Cathode material recycling: Waste NCM811 ternary lithium batteries were completely discharged in a 20% wt. NaCl aqueous solution. The discharged batteries were disassembled and the cathode aluminum foil was recycled. The foil was then immersed in dimethyl carbonate for 5 hours to remove residual electrolyte. The degraded cathode material was carefully separated from the aluminum foil. The SEM image of the material is shown below. Figure 2 As shown, the recycled cathode material consists of spherical secondary particles with rough and irregular surfaces. This reflects the degradation of the original layered structure and particle cracking of the waste cathode material after charge-discharge cycles.

[0033] The recovered cathode powder was sintered at 500℃ for 4 hours to remove binders and acetylene black impurities, resulting in treated and degraded cathode material. (2) Acid etching: The above-mentioned failed positive electrode material is immersed in dilute sulfuric acid solution and stirred at 1000 rpm for 6 hours. The acid solution and positive electrode material are separated by centrifugation. The positive electrode material after acid etching is washed 3 times with deionized water and then dried to obtain the positive electrode material after acid etching. The concentration of the dilute sulfuric acid is 0.3~1 mol / L.

[0034] (3) Segmented sintering: The above-acidified cathode material was mixed with 0.3 times the amount of LiOH·H2O by ball milling, and then heated to 450℃ in an oxygen environment at a heating rate of 5℃ / min. It was then calcined at 450℃ for 2h, heated to 650℃ for 5h, heated to 800℃ for 2h, cooled to 650℃ for 1h, and then naturally cooled to obtain the regenerated single-crystal ternary cathode material LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0035] SEM images of the regenerated monocrystalline ternary lithium battery cathode material obtained in step (3) above are shown below. Figure 3 As shown, the particles of the recycled material are mainly octahedral in shape, and the size of a single particle is much smaller than that of the cathode material recovered in step (1) above. The size is between 1 and 1.5 μm, which is consistent with the morphological characteristics of single crystallization products.

[0036] Example 2 This embodiment provides another method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, which differs from Embodiment 1 in that: In step (1), the cathode material of the waste ternary lithium battery is NCM622.

[0037] In step (2), the recovered cathode powder is sintered at 400°C for 6 hours.

[0038] In step (3), the acidified cathode material is mixed with 0.4 times the amount of LiOH·H2O by ball milling, and then heated to 500℃ in an oxygen environment at a heating rate of 5℃ / min. It is then calcined at 500℃ for 2 hours, then heated to 700℃ for 3 hours, then heated to 830℃ for 2 hours, and finally cooled to 700℃ for 1 hour. Afterward, it is naturally cooled to obtain the regenerated single-crystal ternary cathode material LiNi. 0.6 Co 0.2 Mn 0.2 O2.

[0039] The remaining settings are the same as in Example 1.

[0040] Example 3 This embodiment provides another method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, which differs from Embodiment 1 in that: In step (1), the cathode material of the waste ternary lithium battery is NCM523.

[0041] In step (2), the recovered cathode powder is sintered at 600°C for 2 hours.

[0042] In step (3), the acidified cathode material is mixed with 0.3 times the amount of Li2CO3 by ball milling, and then heated to 550°C in air at a heating rate of 5°C / min. It is then calcined at 550°C for 2 hours, then heated to 750°C for 3 hours, then heated to 850°C for 2 hours, and finally cooled to 750°C for 1 hour. Afterward, it is naturally cooled to obtain the regenerated single-crystal ternary cathode material LiNi. 0.5 Co 0.2 Mn 0.3 O2.

[0043] The remaining settings are the same as in Example 1.

[0044] Example 4 This embodiment provides another method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, which differs from Embodiment 1 in that: In step (1), the cathode material of the waste ternary lithium battery is NCM111.

[0045] In step (2), the recovered cathode powder is sintered at 600°C for 4 hours.

[0046] In step (3), the acidified cathode material is mixed with 0.4 times the amount of Li2CO3 by ball milling, and then heated to 600°C in air at a heating rate of 5°C / min. It is then calcined at 600°C for 2 hours, then heated to 800°C for 3 hours, then heated to 900°C for 2 hours, and finally cooled to 800°C for 1 hour. After natural cooling, the regenerated single-crystal ternary cathode material LiNi is obtained. 0.33 Co 0.33 Mn 0.33 O2.

[0047] The remaining settings are the same as in Example 1.

[0048] Example 5 This embodiment provides another method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, which differs from Embodiment 1 in that: In step (1), the cathode material of the waste ternary lithium battery is NCA8155.

[0049] In step (3), the acidified cathode material is mixed with 0.35 times the amount of LiOH·H2O by ball milling, and then heated to 500°C in air at a heating rate of 5°C / min. It is then calcined at 500°C for 2 hours, then heated to 700°C for 3 hours, then heated to 780°C for 2 hours, then cooled to 700°C for 1 hour, and finally allowed to cool naturally to obtain the regenerated single-crystal ternary cathode material LiNi. 0.8 Co 0.15 Al0.05 O2.

[0050] The remaining settings are the same as in Example 1.

[0051] Example 6 This embodiment provides another method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, which differs from Embodiment 1 in that: In step (1), the cathode material of the waste ternary lithium battery is NCA955.

[0052] In step (3), the acidified cathode material is mixed with 0.35 times the amount of LiOH·H2O by ball milling, and then heated to 480°C in an oxygen environment at a heating rate of 5°C / min. It is then calcined at 480°C for 2 hours, then heated to 680°C for 3 hours, then heated to 750°C for 2 hours, cooled to 750°C for 1 hour, and finally allowed to cool naturally to obtain the regenerated single-crystal ternary cathode material LiNi. 0.9 Co 0.05 Al 0.05 O2.

[0053] The remaining settings are the same as in Example 1.

[0054] Comparative Example This embodiment provides another method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, which differs from Embodiment 1 in that: The acid hydrolysis process in step (2) is omitted; the rest of the setup is the same as in Example 1. The resulting product is as follows: Figure 4 As shown, the resulting product is distributed in an irregular spherical shape. This is because simple high-temperature sintering cannot repair the cracks on the failed spherical cathode material and the primary particle expansion during high-temperature sintering.

[0055] Commercially available single-crystal SEM images such as Figure 5 As shown, the size of the single crystal is between 2 and 4 µm, while the size of the single crystal obtained by acid etching combined with segmented sintering is between 1 and 1.5 µm. The commercially available single crystal particles are larger and have a more dispersed size distribution, which makes the regenerated single crystal cathode material have better electrochemical performance in subsequent electrochemical tests.

[0056] Performance testing 1. Half-cell cycle performance The single-crystal ternary cathode material LiNi prepared in Example 1 above... 0.8 Co 0.1 Mn 0.1O2, PVDF, and carbon black were mixed in a ratio of 8:1:1 to form a slurry. After coating with aluminum foil, the mixture was vacuum dried at 110°C for 12 hours, followed by coating with electrodes (load 3 mg / cm²). The positive electrode and separator were then placed sequentially in a CR2032 casing, and 50 μL of electrolyte was added for wetting. Lithium foil, gaskets, and spring contacts were then placed on top and compacted for sealing. The casing was left to stand for 6 hours. Using a battery testing system, the battery was cycled 300 times at 1C and 25°C within a voltage range of 2.8–4.3V, recording the capacity and coulombic efficiency per cycle.

[0057] The results are as follows Figure 6 As shown, the initial capacity was 183 mAh / g. After 300 cycles at 2.8-4.3V, 1C rate, and 25℃, the half-cell's discharge capacity remained stable at approximately 157.8 mAh / g, with a decay rate of 13.8%, indicating that the regenerated single-crystal material has extremely strong resistance to cycle degradation. The coulombic efficiency during cycling was close to 100%, indicating very few side reactions during charge and discharge, and excellent electrochemical reversibility of the material. The ability to maintain stable performance even at a high 1C rate also demonstrates good ion transport efficiency of the regenerated material.

[0058] 2. Half-cell rate performance The single-crystal ternary cathode material LiNi prepared in Example 1 above... 0.8 Co 0.1 Mn 0.1 O2, PVDF, and carbon black were mixed in a ratio of 8:1:1 to form a slurry. After coating with aluminum foil, the slurry was vacuum dried at 110°C for 12 hours, followed by coating with an electrode sheet (load 3 mg / cm²). Then, the positive electrode sheet and separator were placed sequentially in a CR2032 casing, and 50 μL of electrolyte was added for wetting. A lithium sheet, gasket, and spring were then placed on top and compacted for sealing. The casing was left to stand for 6 hours. The battery was then tested using a battery testing system within a voltage range of 2.8–4.3 V.

[0059] The results are as follows Figure 7 As shown, the specific capacity of the regenerated monocrystalline cathode material at 0.1C is 198.1 mAh / g, slightly higher than the 194.3 mAh / g specific capacity of the commercial polycrystalline cathode. However, the capacity gap widens further with increasing C rate. Especially at 5C, the regenerated monocrystalline cathode material achieves a discharge capacity of 145.3 mAh / g, significantly exceeding the 132.5 mAh / g specific capacity of the commercial polycrystalline cathode. This indicates that the relithiation and recrystallization processes endow the regenerated monocrystalline cathode material with superior structural integrity, directly resulting in its excellent high-rate performance.

[0060] 3. Half-cell impedance test The single-crystal ternary cathode material LiNi prepared in Example 1 above... 0.8 Co 0.1 Mn 0.1O2, PVDF, and carbon black were mixed in a ratio of 8:1:1 to form a slurry. After coating with aluminum foil, the mixture was vacuum dried at 110°C for 12 hours and then coated with an electrode (load 3 mg / cm²). Subsequently, the positive electrode and the separator were placed in a CR2032 shell, and 50 μL of electrolyte was added for wetting. Then, lithium sheets, gaskets, and springs were placed in the shell and compacted and sealed. The mixture was left to stand for 6 hours.

[0061] Electrochemical impedance spectroscopy (EIS) further verified the regenerated single-crystal LiNi material. 0.8 Co 0.1 Mn 0.1 O2 exhibits excellent electrochemical reversibility and (de)lithiation kinetics. The EIS plot obtained after the 300th cycle ( Figure 8 The fitting results derived from the equivalent circuit model indicate that the polycrystalline cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 and regenerated single-crystal cathode material LiNi 0.8 Co 0.1 Mn 0.1 The charge transfer resistance (R) of O2 ct The surface impedance (Rp) of the regenerated single-crystal cathode material increases with the number of cycles. Notably, the regenerated single-crystal cathode material has an impedance of 142.5 Ω after 300 cycles, significantly lower than the 245.3 Ω of the polycrystalline cathode material. Furthermore, the surface impedance (Rp) of the regenerated single-crystal cathode material also increases with the number of cycles. f The size of the ions is also significantly smaller, which strongly demonstrates that the reconstructed ordered layered structure can effectively suppress harmful surface side reactions, thereby significantly improving the (de)lithiation kinetics.

[0062] 4. Full battery cycle performance The single-crystal ternary cathode material LiNi prepared in Example 1 above 0.8 Co 0.1 Mn 0.1 A full cell was constructed using O2 as the positive electrode and graphite as the negative electrode: The positive and negative electrodes were prepared separately and coated with aluminum and copper foil respectively. After vacuum drying at 100℃ for 12 hours, electrode sheets were formed (positive electrode loading 3 mg / cm², negative electrode capacity excess 10%-15%). The cells were assembled, compacted, and sealed in an Ar glove box, and allowed to stand at room temperature for 4 hours. Testing was performed using a testing system within a voltage range of 2.8-4.3V: 300 cycles at 1C were performed simultaneously, and the charge / discharge capacity and coulombic efficiency per cycle were recorded.

[0063] The results are as follows Figure 9 As shown, the initial capacity was 173 mAh / g, which decreased to 141.6 mAh / g after 300 cycles. Compared with the results of the half-cell above, the full cell showed a slight decrease after 300 cycles, but still maintained excellent cycle performance overall.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for regenerating waste polycrystalline ternary lithium cathodes into monocrystalline ternary lithium cathodes, characterized in that, The method includes the following steps: (1) Recycling the positive electrode material of ternary lithium batteries; the positive electrode material is the positive electrode material of nickel cobalt manganese lithium batteries or nickel cobalt aluminum lithium batteries, wherein the positive electrode material of nickel cobalt manganese lithium batteries is selected from NCM111, NCM523, NCM622, NCM811 or NCM955; the positive electrode material of nickel cobalt aluminum lithium batteries is selected from NCA8155, NCA85105 or NCA955; the recycling method of the positive electrode material is as follows: the ternary lithium battery to be recycled is completely discharged, and the positive electrode of the battery is disassembled and immersed in a carbonate solvent to remove impurities. The degraded positive electrode material is separated from the aluminum foil surface and sintered at high temperature to obtain powdered positive electrode material; the carbonate solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate or methyl ethyl carbonate, and the immersion time is 3~5h; the sintering temperature is 400~600℃, the sintering time is 2~6h, and the sintering is carried out in an air atmosphere; (2) The positive electrode material is immersed in dilute sulfuric acid solution and stirred for a period of time. The treated positive electrode material is washed to remove the acid solution and dried to obtain the acid-treated positive electrode material. (3) The acidified cathode material is mixed with a lithium source and then sintered in sections; if the nickel content in the cathode material of the ternary lithium battery to be recycled in step (1) is greater than or equal to 60%, the section sintering needs to be sintered under oxygen, and the lithium source is lithium hydroxide monohydrate; if the nickel content is less than 60%, the section sintering is sintered under air, and the lithium source is lithium carbonate; the section sintering is set as follows: the heating rate is 3~10℃ / min, the low temperature section is sintered at 400~600℃ for 2~4h, the medium temperature section is sintered at 650~800℃ for 3~5h, the high temperature section is sintered at 750~900℃ for 2~4h, and the temperature of the high temperature section is higher than that of the medium temperature section during sintering, and then the temperature is reduced to the medium temperature section for 1~2h to obtain the product.

2. The method as described in claim 1, characterized in that, In step (2), the concentration of the dilute sulfuric acid solution is 0.3~1mol / L, the solid-liquid ratio of the positive electrode material to the dilute sulfuric acid solution is 30~200g / L, and the temperature is room temperature.

3. The method as described in claim 1, characterized in that, In step (2), the stirring speed is 1000-1500 rpm and the stirring time is 4-12 h.

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