A single-crystallization upgrading and reconstruction method for high-degradation layered nickel-cobalt-manganese positive electrode material

Abstract

The application relates to a single-crystal upgrading and reconstruction method of a high-degradation layered nickel-cobalt-manganese positive electrode material, which comprises the following steps: S1, after discharging, disassembling and crushing an old ternary lithium ion battery, positive electrode powder is obtained; S2, the obtained positive electrode powder is mixed with selected molten salt at a determined ratio, a ball mill is used for grinding, the mixing of the molten salt and the recovered powder is ensured to be uniform, then a lithium supplement process is carried out under high-temperature conditions, and residual binders and conductive agents and other impurities in the positive electrode powder can also be effectively removed; the lithium supplement heating condition is that the temperature is raised to 600 DEG C and kept for 2h, then the temperature is kept at 910-930 DEG C for 4-6h, the temperature rising speed is 4 DEG C / min, and the gas atmosphere is air; S3, the sample after the lithium supplement is subjected to heat treatment under an oxygen atmosphere, impurity phase structures possibly existing on the surface of the particles are repaired, and the electrochemical performance of the regenerated material is not only similar to that of a commercial battery, but also benefits from a unique single-crystal structure, so that the structural stability is also greatly improved. The method can be applied to the recovery of various ternary lithium ion battery positive electrode materials by simply adjusting the heating temperature and the holding time, and has high application value.

Description

Technical Field

[0001] The present invention belongs to the field of recycling and regeneration of waste ternary lithium-ion battery positive electrode materials, and specifically relates to a single crystal upgrading and reconstruction method for highly degradable layered nickel-cobalt-manganese positive electrode materials with the assistance of high-energy molten salt. Background Art

[0002] With the rapid development of the new energy industry, particularly the growing popularity of electric vehicles, ternary-metal cathodes (NCM) are increasingly dominating the lithium-ion energy storage sector. The penetration of lithium-ion batteries in the new energy sector continues to rise, and the market size is also expanding, with supply exceeding demand. This development is driving a steady increase in the prices of the key metal elements in lithium-ion batteries. Furthermore, lithium batteries typically have a lifespan of 5-8 years. With the advancement of large-scale adoption, battery retirements are expected to peak in the coming years. Unprocessed waste batteries could cause severe environmental damage. Therefore, the recycling of used lithium-ion batteries has become urgent, both for economic and environmental reasons.

[0003] Currently, the main recycling technologies for used batteries include indirect recycling through pyrometallurgy and hydrometallurgy, and direct recycling through regeneration and repair. Although pyrometallurgy has achieved large-scale industrialization, it consumes a lot of energy and produces large amounts of CO, CO2, and dust during the recycling process, causing serious environmental pollution. In contrast, hydrometallurgy offers low waste gas emissions, mild reaction conditions, and high metal recovery rates. However, the organic extractants are expensive, the recovery process is complex, and the organic waste liquid produced is not environmentally friendly.

[0004] In view of the obvious shortcomings of the above-mentioned indirect recycling methods at this stage, direct recycling, as an efficient and environmentally friendly recycling method, has become the research focus of scientific researchers. The standard definition of lithium-ion battery disposal is a capacity loss of more than 20%, which means that there has been obvious lithium loss and irreversible structural phase change in the battery, but the main structure of the battery has not been destroyed, which provides a theoretical basis for direct repair technology. Direct recycling aims to restore battery performance to the level before use by repairing various defects in the positive electrode material. The main ways of positive electrode failure include loss of active lithium ions, particle cracks, cation mixing and changes in surface phase structure. The regeneration methods that have been proven to be effective in repairing positive electrode defects are solid-phase sintering, hydrothermal method, electrochemical method and eutectic molten salt method. Among them, the eutectic molten salt method is considered to be the most promising direct regeneration method due to its cleanliness, efficiency and simple operation.

[0005] The advantage of the eutectic molten salt method is that it accelerates the medium transfer during the lithium replenishment process through a uniform and stable liquid phase environment, making the Li +Under molten conditions, the missing lithium vacancies in the cathode material can be effectively compensated. At the same time, the volatilization of the molten salt under high temperature conditions promotes the single crystal transformation of the regenerated cathode particles, thereby improving the electrochemical and structural stability of the regenerated samples.

[0006] Although the molten salt method for direct regeneration of layered nickel-cobalt-manganese cathode materials has been widely confirmed, the following problems still need to be further optimized before large-scale industrial application: (1) The object of molten salt recovery is only the active material of the battery cathode, so tedious pretreatment steps are required before recycling; (2) In order to ensure a uniform and stable lithium replenishment molten salt environment, an excess of eutectic molten salt is usually added. How to efficiently remove the residual molten salt after the lithium replenishment is completed is a challenge; (3) When lithium replenishment is performed only at the eutectic point temperature, the ideal regeneration effect cannot be obtained; when the temperature rises, the molten lithium salt will evaporate rapidly, and the lithium replenishment molten salt environment will be destroyed; in addition, when the amount of molten salt added is small, the regeneration requirements cannot be met, and excessive use of molten salt will inevitably cause waste of resources. Therefore, how to determine an optimal lithium replenishment condition is also a difficult problem that needs to be overcome before the industrial application of the eutectic molten salt method.

[0007] In summary, developing and optimizing a more efficient, convenient and universal recycling method for upgrading and reconstructing lithium battery positive electrode molten salt is of great significance for the recycling of waste batteries. Summary of the Invention

[0008] To address these issues, the present invention improves and optimizes the existing eutectic molten salt method, proposing a molten salt single crystal reconstruction method suitable for achieving high-level regeneration under high-temperature conditions. This method not only completely eliminates all defects in highly degraded positive electrode materials, but also, compared to the original polycrystalline particles, the regenerated single crystal structure further mitigates the volume phase transition of the regenerated particles during charge and discharge, reducing cracking and significantly improving the battery's cycling stability.

[0009] The technical solutions adopted in the present invention are as follows:

[0010] A method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt, comprising the following steps:

[0011] Step S1: After the used ternary lithium-ion battery is completely discharged, it is mechanically disassembled and separated to obtain an aluminum current collector coated with a positive electrode active material, which is crushed with a grinder and then simply sieved to remove the aluminum foil to obtain a positive electrode powder with degraded performance;

[0012] Step S2: The obtained positive electrode powder is mixed with the selected molten salt in proportion, and ground with a ball mill to ensure that the molten salt and the recovered powder are evenly mixed. Then, the lithium replenishment process is carried out under high temperature conditions. At the same time, the residual binder and conductive agent impurities in the positive electrode powder can also be effectively removed after thermal decomposition;

[0013] The lithium replenishment heating conditions are to heat the temperature to 600°C and keep it for 2 hours, then keep it at 910-930°C for 4-6 hours, with a heating rate of 4°C / min. The gas atmosphere is air, and the gradient heating method can provide a more stable lithium replenishment molten salt environment.

[0014] Step S3: After the lithium-supplemented sample is centrifuged, washed, and dried, it is heat-treated in an oxygen atmosphere to repair the impurity phase structure that may exist on the particle surface.

[0015] Furthermore, the complete discharge process in step S1 is carried out in a Na2SO4 solution with a concentration of 5%-10% for 48-72 hours;

[0016] And / or, after the aluminum foil is initially removed by sieving through a 400 mesh in step S1, the positive electrode powder is alkaline-soaked with a NaOH solution, and the impurity aluminum can be completely removed after filtration.

[0017] Furthermore, the selection and molar ratio of the molten salt in step S2 are LiOH:Li2CO3:KCl=0.84x:0.16x:(1-x), x=0.5-0.7.

[0018] Furthermore, in step S2, the molar ratio of the total amount of lithium ions in the molten salt to the amount of lithium ions lost in the positive electrode powder is 1:1-8:1;

[0019] And / or, the volume ratio of the molten salt to the positive electrode powder in step S2 should be 1:1-4:1 to ensure that the molten salt can fully cover the positive electrode powder after grinding.

[0020] Furthermore, in step S2, the ball mill is rotated at a speed of 400-500 r / min for 20-30 min, and dispersant ethanol is added for thorough grinding;

[0021] And / or, the main components of the binder and the conductive agent mentioned in step S2 are polyvinylidene fluoride and carbon black, which will decompose when heated to a temperature above 800°C.

[0022] Furthermore, since the molten salts selected in step S2 are all water-soluble salts, residual molten salts can be effectively removed by filtering with deionized water in step S3.

[0023] Furthermore, the heat treatment temperature in step S3 is 600-800° C., and an oxidizing gas atmosphere, such as oxygen, is selected.

[0024] Furthermore, this molten salt method is applicable to layered nickel-cobalt-manganese ternary lithium-ion battery positive electrodes with different transition metal element ratios, such as NCM523, NCM622 and NCM811, and the best repair effect can be achieved by changing the heating conditions.

[0025] A highly degradable layered nickel-cobalt-manganese cathode material is prepared by the above-mentioned single crystal upgrading and reconstruction method of a highly degradable layered nickel-cobalt-manganese cathode material with the assistance of high-energy molten salt.

[0026] A lithium-ion battery comprises a battery positive electrode made of the above-mentioned highly degradable layered nickel-cobalt-manganese positive electrode material.

[0027] Compared with conventional eutectic molten salt regeneration technology, the present invention has the following advantages:

[0028] (1) The molten salt single crystal reconstruction method of the highly degradable layered nickel-cobalt-manganese positive electrode material provided by the present invention abandons the advantage of the conventional molten salt method in completing lithium replenishment under medium and low temperature conditions, and instead chooses to achieve high-level repair and regeneration of discarded ternary lithium battery positive electrode materials under high temperature conditions with the help of the high-energy melting environment of the molten salt. When the temperature rises, on the one hand, it can accelerate the conduction and transportation process of the reaction ions in the molten salt environment, and the lithium replenishment process is more efficient and thorough, greatly reducing the reaction time and improving industrial production efficiency. On the other hand, the volatilization of the molten salt at high temperature can serve as a driving force for the regeneration and growth of the positive electrode particles. At the same time, under the action of the co-solvent KCl, it can ensure that the molten salt provides the driving force for the growth of single crystal particles while maintaining the stability and uniformity of the entire molten salt lithium replenishment environment. Under the action of high-temperature molten salt, all defects of the waste positive electrode material are effectively restored, and the regenerated single crystal structure has better structural stability and excellent electrochemical performance.

[0029] (2) The molten salt single crystal reconstruction method for highly degradable layered nickel-cobalt-manganese positive electrode materials provided by the present invention has the following optimizations compared with the traditional eutectic molten salt method: first, molten salt regeneration performed only at the eutectic point temperature is not sufficient to completely repair all defects of highly degradable materials, while repair performed at a higher temperature can ensure that the defect repair has sufficient driving force, and even positive electrode samples with serious defects can be fully restored after regeneration; secondly, the molten salt volatilization that is difficult to avoid at high temperatures is also well solved in the present invention. Under the action of KCl, the volatilization effect is suppressed within an acceptable range, and the entire lithium replenishment environment is sufficient to ensure the regeneration of waste materials; finally, while repairing the defects, the final sample obtained by the molten salt single crystal reconstruction method provided by the present invention successfully grows into a single crystal structure with better stability, which greatly improves the capacity retention rate during the battery cycle, and is even better than standard commercial products.

[0030] (3) The molten salt single crystal reconstruction method of the highly degradable layered nickel-cobalt-manganese positive electrode material provided by the present invention has obvious advantages over the traditional indirect recovery method: almost no toxic and harmful gases are generated during the recovery process, and no organic waste liquid is generated, which is environmentally friendly; the molten salt raw materials are all cheap and clean inorganic metal salts, and the production cost is low; in addition, the entire process has no complicated processing steps, and the main operations only include basic pretreatment, molten salt lithium supplementation and heat treatment, which are simple and efficient to operate; finally, as a direct recovery method, there is no need to consider the purification and separation of various metal elements of waste positive electrode materials, but to achieve the recycling of waste batteries in the most ideal closed-loop recovery method.

[0031] (4) The molten salt single crystal reconstruction method of the highly degradable layered nickel-cobalt-manganese positive electrode material provided by the present invention can greatly simplify the pretreatment process of the battery. It only needs to separate the positive electrode material and the aluminum foil. The remaining other components such as PVDF, conductive carbon and electrolyte decomposition product LiF can decompose by themselves in a high-temperature molten salt environment and will not affect the performance of the regenerated positive electrode.

[0032] (5) The molten salt single crystal reconstruction method of the highly degradable layered nickel-cobalt-manganese positive electrode material provided by the present invention can comprehensively repair various defects in waste positive electrode materials. Various causes of positive electrode failure such as active lithium loss, structural phase change, oxygen vacancies and cation mixing can be effectively eliminated in a high-temperature molten salt environment.

[0033] (6) The molten salt single crystal reconstruction method of the highly degradable layered nickel-cobalt-manganese positive electrode material provided by the present invention is the best measure to cope with resource recycling under the dual carbon background. It can effectively solve the environmental pressure and economic burden brought about by the peak of lithium-ion battery retirement, and at the same time achieve low-cost recycling and resource reuse.

[0034] (7) The molten salt single crystal reconstruction method of the highly degradable layered nickel-cobalt-manganese positive electrode material provided by the present invention has good universality and flexibility, and can be applied to retired lithium-ion battery positive electrode materials with various transition metal ratios (such as NCM523, NCM622, NCM811, etc.). It only needs to formulate different heating schemes according to different materials to achieve direct repair of waste positive electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 、 2XRD comparison diagrams of the repaired regenerated samples (R-NCM, r-NCM) in implementation cases 1 and 2, the untreated sample (S-NCM) and the commercial sample (C-NCM).

[0037] Figure 3 These are the XRD refinement patterns of various samples in implementation cases 1 and 2.

[0038] Figure 4 SEM images of various materials in implementation cases 1 and 2.

[0039] Figure 5 Electrochemical cycle diagrams of various samples in implementation cases 1 and 2.

[0040] Figure 6 Electrochemical rate diagrams of various samples in implementation cases 1 and 2.

[0041] Figure 7 The capacity-voltage comparison diagram of various samples in implementation cases 1 and 2.

[0042] Figure 8 XPS spectra of Ni and O of various samples in implementation cases 1 and 2.

[0043] Figure 9 These are actual pictures of the operations in Cases 1 and 2 and actual pictures of the samples after lithium supplementation with high-temperature molten salt.

[0044] Figure 10 This is a comparison of the XRD patterns of the samples after repair and regeneration in Cases 3 and 4.

[0045] Figure 11 SEM comparison images of samples after repair and regeneration in implementation cases 3 and 4.

[0046] Figure 12 Electrochemical performance diagram of the regenerated samples in implementation cases 3 and 4.

[0047] Figure 13 XRD and refined patterns of the regenerated sample in implementation case 5.

[0048] Figure 14 This is the SEM image of the regenerated sample in implementation case 5.

[0049] Figure 15 This is the electrochemical cycle diagram of the regenerated sample in implementation case 5.

[0050] Figure 16 SEM comparison images of samples after repair and regeneration in implementation cases 6 and 7.

[0051] Figure 17 Electrochemical cycle diagram of the regenerated samples in implementation cases 6 and 7. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation methods of the present invention are further described below.

[0053] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0054] Implementation Case 1

[0055] (1) After being completely discharged in a Na2SO4 solution, the spent commercial NCM523 battery was disassembled to obtain aluminum foil loaded with positive electrode active material. After drying in a drying oven, the aluminum foil was crushed using a crusher, and the positive electrode powder and aluminum foil were separated using a 400-mesh sieve. The positive electrode powder to be recycled was then collected and recorded as S-NCM.

[0056] (2) Weigh 1 g of the powder in (1) (lithium loss is 41.3%), then add a specific proportion of eutectic molten salt and co-solvent (molar ratio of LiOH:Li2CO3:KCl=0.84x:0.16x:1-x, x=0.5), specifically weighing 0.42 g, 0.14 g and 0.88 g of LiOH.H2O, Li2CO3 and KCl respectively, then mix the S-NCM powder with the molten salt-co-solvent and put it into a ball mill, grind for 20 minutes at a speed of 400 r / min, and add dispersant ethanol at the same time to ensure that the powder to be recovered is completely and evenly distributed in the molten salt system. At the same time, the initial polycrystalline structure is broken to a certain extent, which is more conducive to the generation of single crystal structure in the regeneration reaction. After ball milling is completed and dried, the mixture is placed in an Al2O3 crucible.

[0057] (3) The crucible in (2) was placed in a muffle furnace and heated using a gradient heating method to ensure the completeness of the reaction. The temperature was first raised to 600°C and held for 2 hours, then heated to 910°C and held for 6 hours, with a heating rate of 4°C / min. The gas atmosphere was air. After heating, the sample was filtered through deionized water to remove residual lithium salts and co-solvents. The powder material was then placed in a drying oven and dried at 60°C for 8 hours.

[0058] (4) Calculate the molar weight of the dried sample, add approximately 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. To ensure that the impurity phase structure that hinders lithium ion diffusion is completely restored to a layered structure, the sample is then heated at 600°C in a tube furnace under an O2 atmosphere for 4 hours at a heating rate of 2°C / min. The sample after heat treatment is the repaired positive electrode powder, denoted as R-NCM.

[0059] (5) The powder samples were subjected to XRD, SEM and XPS tests. The powders were made into slurry and assembled into half-cells, and the electrochemical data of the cells were tested.

[0060] Implementation Case 2

[0061] (1) Weigh 1 g of the powder of (1) in Implementation Case 1 (lithium loss is 41.3%), and then add a specific proportion of eutectic molten salt (molar ratio of LiOH:Li2CO3=0.84:0.16). Compared with Case 1, the cosolvent KCl is not added in this case to explore its role in the molten salt system. LiOH.H2O, Li2CO3 0.42 g and 0.14 g are weighed respectively, and then the S-NCM powder and the molten salt are mixed evenly using a ball mill.

[0062] (2) The crucible in (1) was placed in a muffle furnace and heated. The temperature was first raised to 600°C and held for 2 h, then heated to 910°C and held for 6 h, with a heating rate of 4°C / min. The atmosphere was air. After heating, the residual molten salt was removed by filtration with deionized water, and then dried in a drying oven at 60°C for 8 h.

[0063] (3) Calculate the molar weight of the dried sample, add approximately 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. Then, heat in a tube furnace at 600°C for 4 h under an O2 atmosphere at a heating rate of 4°C / min to restore the impurity phase structure in the degraded powder. The sample after heat treatment is the repaired cathode powder, denoted as r-NCM.

[0064] (4) The powder samples were subjected to XRD, SEM and XPS tests. The powders were made into slurry and assembled into half-cells, and the electrochemical data of the cells were tested.

[0065] Figure 1 、 2The XRD comparison diagrams of the regenerated samples (R-NCM, r-NCM) after repair in implementation cases 1 and 2, the untreated samples (S-NCM) and the commercial samples (C-NCM). As can be seen from the figure, the four samples are all α-NaFeO2 layered structures (R-3m space group). By comparison, it can be seen that the (003) peak intensity of S-NCM is relatively low, indicating that the cations in the sample before treatment are seriously mixed. After regeneration and repair, combined with the data in Table 2, it can be seen that the I (003) / (104) values ​​of R-NCM and r-NCM are significantly increased, almost at the same level as C-NCM, indicating that the regenerated samples have a good layered structure; In addition, the (003) peak of the treated sample migrates to a low angle, and the unit cell expands along the c-axis direction, indicating that due to Li + The crystal structure collapse caused by the loss was restored, and the degeneracy of the (108) and (110) peaks further confirmed that the Li vacancies in the regenerated sample were effectively replenished under the action of high-temperature molten salt.

[0066] Figure 3 The XRD refinement patterns of various samples in implementation cases 1 and 2 are shown. Combining the refinement data in Tables 1 and 2, it can be seen that compared with the untreated S-NCM powder, the unit cell parameter c values ​​of the regenerated R-NCM and r-NCM are increased, confirming that the Li vacancies in both implementation cases are effectively supplemented. However, the a value in r-NCM is reduced, while the a value in R-NCM is increased, which indicates that there are still Ni vacancies with smaller ionic radius in r-NCM. 2+ / Ni 3+ The Li / Ni mixing data in Table 1 also confirm the situation of Li sites being occupied. Therefore, in Implementation Case 2, although the high-temperature molten salt without KCl can also replenish the Li loss in S-NCM, due to the rapid volatilization of LiOH+Li2CO3, the ultimate repair degree is limited, and the degree of cation mixing is still at a high level; on the contrary, in Implementation Case 1, under the action of KCl-stabilized molten salt environment, the crystal structure of the regenerated R-NCM is fully restored, and all performances are close to those of C-NCM materials.

[0067] Table 1: XRD refinement data of various samples in implementation cases 1 and 2

[0068]

[0069] Table 2: XRD peak (003) / (104) intensity ratios of various samples in implementation cases 1 and 2

[0070]

[0071] Figure 4The SEM images of various materials in Implementation Cases 1 and 2 are shown. By comparison, it can be found that the particle surface of the S-NCM sample is rough and finely divided, and there are impurities such as conductive carbon and PVDF between the particles. In the R-NCM material repaired by Implementation Case 1, not only the particle surface is smooth and the size is uniform, but also compared with the secondary spherical particles of C-NCM, under the action of high-temperature molten salt, the particles grow into a more stable single crystal structure, avoiding the generation of intercrystalline cracks. Compared with the r-NCM material in Implementation Case 2, it can be clearly seen that the particle size is extremely uneven. Due to the unstable growth driving force provided by the rapid volatilization of the molten salt, a small amount of particles have grown abnormally. At the same time, there are still small particles similar to those in S-NCM. Therefore, a stable and uniform molten salt environment is the key factor in effectively repairing the particle morphology. Under the fluxing and stabilizing effect of KCl, the eutectic system of LiOH+Li2CO3 is milder at high temperatures, which not only provides a stable medium transfer environment, but also ensures the uniformity of particle growth.

[0072] Table 3: Electrochemical data of various samples in implementation cases 1 and 2

[0073]

[0074] Figure 5 、 6 7 are comparison diagrams of the electrochemical performance of various samples in implementation cases 1 and 2. First, the constant current charge and discharge performance of the repaired materials under the two implementation cases was tested. Figure 5 As can be seen from the data given in Table 3, the R-NCM sample repaired by the synergistic action of LiOH+Li2CO3+KCl in Implementation Case 1 has the best cycle stability, and still has a capacity retention rate of 81.2% after 200 cycles of charge and discharge at a 1C rate, which is significantly higher than the r-NCM material repaired only under the LiOH+Li2CO3 eutectic conditions in Implementation Case 2 (56.1% in 200 cycles). It is worth mentioning that although the first-cycle capacity of R-NCM (156.8mAh / g) is slightly lower than that of C-NCM material (157.7mAh / g), in the subsequent cycle process, the capacity attenuation rate of the former is significantly lower than that of commercial powder (75.1% in 200 cycles), which is due to the more stable single crystal structure of R-NCM, further confirming that molten salt repair at high temperature can effectively improve the regeneration performance of waste positive electrode materials. Comparison Figure 6From the rate performance test graph, we can find that at different charge and discharge rates, R-NCM has a discharge capacity that is not inferior to C-NCM. At the same time, after a high rate cycle of 5C, both can still recover to the initial level under 0.1C conditions. Compared with the r-NCM and untreated S-NCM materials in Implementation Case 2, the capacity gap at different rates is more obvious, which fully proves the key stabilizing role of KCl for the entire molten salt system under high temperature conditions. Figure 7 The capacity-voltage diagram can more intuitively compare the capacity attenuation rate and cycle stability of different materials. As the number of battery cycles increases, the image curve of r-NCM in Implementation Case 2 gradually deforms, and the cycle stability is significantly reduced. Compared with R-NCM in Implementation Case 1, the difference is very significant. Although the capacity of R-NCM is constantly attenuating during the cycle, its charge and discharge curve remains regular, and its capacity also decreases the slowest among several materials. Through the comparison of various electrochemical properties, R-NCM in Implementation Case 1 has the best comprehensive performance. Under the action of high-temperature molten salt, the lost Li + After replenishment, the capacity is restored to the same level as C-NCM. In addition, due to its unique single crystal structure, it is even better than C-NCM in cycle stability performance. In Implementation Case 2, although the capacity of r-NCM is improved compared to S-NCM, all performances have not reached the qualified level. The rapidly volatilizing eutectic molten salt cannot provide an ideal repair environment, resulting in the final regeneration effect being significantly worse than R-NCM. Although high-temperature conditions can achieve high-level regeneration, a stable regeneration environment is also an indispensable element. In summary, traditional eutectic molten salts cannot directly adapt to the volatilization effect under high-temperature conditions, making it difficult to achieve an ideal repair effect. The LiOH+Li2CO3+KCl regeneration system proposed in this patent not only effectively alleviates the uncontrollable volatilization process of molten salts under high-temperature conditions, but also achieves high-level repair and regeneration of waste positive electrode materials with the help of a high-energy environment at a higher temperature.

[0075] Figure 8 The XPS spectra of Ni and O of various samples in implementation cases 1 and 2. As can be seen from the figure, Ni on the surface of S-NCM sample 2+ The proportion is 52.8%, while Ni 3+ The content is only 41.2%, which indicates that there is a large amount of NiO rock salt impurity phase on the surface of the waste material. This is due to the appearance of Li vacancies, which leads to the 2+ Irreversibly migrates to the surface of the material through the Li layer and combines with lattice oxygen to form a barrier to Li + The migrated spinel phase and rock salt phase hinder the diffusion channel of lithium ions and deteriorate the electrochemical performance of the material. 2+ / Ni 3+The change in the proportion of can be used to analyze the degree of repair of the crystal structure of the material. After the repair of implementation cases 1 and 2, the Ni 2+ / Ni 3+ The proportions are 41.8% / 58.2% and 53.5% / 46.5% respectively. Ni in R-NCM 2+ The content of Ni ions in the r-NCM in case 2 did not change significantly, which shows that the impurity phase on the surface of the regenerated sample in case 1 has been effectively eliminated, and Li + The diffusion channel was successfully restored, corresponding to the significant improvement of the electrochemical performance of R-NCM; however, there are still a large number of non-layered phase structures in r-NCM. + The transport process of NCM is hindered, so the electrochemical performance is obviously inferior to that of R-NCM.

[0076] Figure 9 The diagrams are of the actual operation in implementation cases 1 and 2 and the actual diagram of the sample after high-temperature molten salt lithium supplementation. The upper half of the diagram is the flow chart of the entire implementation case. Through simple pretreatment and disassembly, the waste positive electrode powder containing conductive carbon and binder is obtained, which is then evenly mixed with the molten salt. During the high-temperature lithium supplementation process, the residual impurities are removed at the same time, and finally the layered structure of the material is further repaired by heat treatment under an O2 atmosphere to obtain a regenerated sample. It can be seen from the actual diagram of the sample after lithium supplementation that in Example 2, due to the lack of KCl, the molten salt in the eutectic system of LiOH+Li2CO3 evaporates rapidly, resulting in the final sample being in a block-like sintered state. The sample after molten salt regeneration through the synergistic action of LiOH+Li2CO3+KCl has a morphology that is a condensed state after melting and cooling. A simple morphological analysis can reveal the lithium replenishment process of the molten salt in Cases 1 and 2. The addition of KCl makes the molten salt environment in Case 1 more stable and uniform, and the medium transfer process in the high-temperature molten state is more complete and efficient. In contrast, in Case 2, the low-eutectic LiOH+Li2CO3 system rapidly evaporates and loses at higher temperatures. The entire process is similar to traditional solid-state sintering. Furthermore, due to the evaporation of the molten salt, sufficient lithium source replenishment cannot be guaranteed, ultimately resulting in poor regeneration results. Comparing the different experimental results in Cases 1 and 2 clearly demonstrates the critical role of KCl in the high-temperature molten salt. Efficient regeneration and recovery of spent cathode materials can only be achieved through the synergistic effect of high temperature conditions and the stable, high-energy molten salt environment of KCl.

[0077] Implementation Case 3

[0078] (1) Weigh 1 g of the powder of Example 1 (lithium loss is 41.3%), then add a specific proportion of eutectic molten salt and co-solvent (molar ratio of LiOH:Li2CO3:KCl=0.84x:0.16x:1-x, x=0.5), specifically weighing 0.42 g, 0.14 g, and 0.88 g of LiOH.H2O, Li2CO3, and KCl, respectively. Then, mix the S-NCM powder and molten salt evenly, grind them in a ball mill for 20 min at a speed of 400 r / min, and place the mixture in an Al2O3 crucible after ball milling.

[0079] (2) Place the crucible in (1) in a muffle furnace and heat it. First, heat it to 600°C and hold it for 2 hours, then heat it to 900°C and hold it for 6 hours. The heating rate is 4°C / min. The gas atmosphere is air. After heating, remove the residual molten salt by filtration. Then, place it in a drying oven and dry it at 60°C for 8 hours.

[0080] (3) Calculate the molar weight of the dried sample, add approximately 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. Heat in a tube furnace at 600°C for 4 h under an O2 atmosphere, with a heating rate of 2°C / min. The sample after heat treatment is the repaired cathode powder, designated R-NCM-2.

[0081] (4) The powder samples were subjected to XRD and SEM tests. The powders were made into slurry and assembled into half-cells, and the electrochemical data of the cells were tested.

[0082] Implementation Case 4

[0083] (1) Weigh 1 g of the powder of Example 1 (lithium loss is 41.3%), then add a specific proportion of eutectic molten salt (molar ratio of LiOH:Li2CO3=0.84:0.16), specifically weighing 0.42 g of LiOH.H2O and 0.14 g of Li2CO3, then mix the S-NCM powder and molten salt evenly, grind them in a ball mill for 20 min at a speed of 400 r / min, and place the mixture in an Al2O3 crucible after ball milling.

[0084] (2) Place the crucible in (1) in a muffle furnace and heat it. First, heat it to 600°C and hold it for 2 hours, then heat it to 900°C and hold it for 6 hours. The heating rate is 4°C / min. The gas atmosphere is air. After heating, filter out the residual molten salt. Then, place the sample in a drying oven at 60°C and dry it for 8 hours.

[0085] (3) Calculate the molar weight of the dried sample, add approximately 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. Heat in a tube furnace at 600°C for 4 h under an O2 atmosphere, with a heating rate of 2°C / min. The sample after heat treatment is the repaired cathode powder, designated r-NCM-2.

[0086] (4) The powder samples were subjected to XRD and SEM tests. The powders were made into slurry and assembled into half-cells, and the electrochemical data of the cells were tested.

[0087] Figure 10 The XRD comparison diagram of the samples after repair and regeneration in implementation cases 3 and 4. Under the heating condition of 900℃, the crystal structure of R-NCM-2 is effectively restored, and the intensity ratio of I(003) / I(104) is greater than 1.2, indicating that the regenerated sample has a very standard layered structure. At the same time, the degree of splitting of the (108) and (110) peaks also confirms that the Li loss in the sample has been successfully replenished. It is worth noting that in r-NCM-2, compared with the lithium replenishment process at 910℃, when the temperature is lowered, the layered structure of the regenerated sample is not well restored. The intensity ratio of the (003) peak to the (104) peak is only 1.06, which is lower than the standard value (1.2) recorded in the literature. In addition, the (108) and (110) double peaks are also significantly split, indicating that the sample may still be in a lithium-deficient state at this time. Secondly, the fluctuation of the XRD curve is more obvious, proving that the crystallinity of the material is also poor. Therefore, the method in case 4 cannot achieve the expected regeneration effect.

[0088] Figure 11 The SEM images of the samples heated at 910℃ and 900℃ with and without KCl were compared. Under the same observation magnification, it can be seen that the particle size at 910℃ is larger than that at 900℃, which proves that the temperature has a significant effect on the growth of particles. The higher the temperature, the more energy there is in the molten salt environment. + Faster transport also promotes particle growth, but once the upper temperature limit is exceeded, the rapid volatilization of the molten salt inevitably leads to an imbalance in the molten environment, deteriorating the regeneration effect. Secondly, as can be seen from the figure, the R-NCM particles have a smoother surface and a more regular shape, a significant contrast to the particle morphology of the r-NCM. Therefore, only a stable eutectic molten salt under the action of KCl can promote uniform particle growth, ultimately resulting in a single crystal structure with superior performance.

[0089] Figure 12Figure 4 shows the electrochemical performance of the regenerated samples in cases 3 and 4. The cycling performance difference between the two regenerated samples is very obvious. Combined with the data in Table 4, it can be seen that the first cycle capacity of R-NCM-2 is 152.2 mAh / g, while the first cycle capacity of r-NCM-2 is only 122.9 mAh / g. After 100 cycles, R-NCM-2 still has a capacity retention rate of 87.2%, which is much higher than the 67.8% of r-NCM-2. At the same time, the rate performance of the two is also quite different, further confirming the key role played by KCl under high-temperature molten salt conditions. It is worth noting that the performance of the samples regenerated at 900°C in Cases 3 and 4 is lower than that of the samples regenerated at 910°C in Cases 1 and 2. However, compared with the first-cycle capacity of 103.2 mAh / g of the untreated sample, the heating condition of 900°C also played a role in lithium replenishment to a certain extent, but did not achieve the maximum optimization of the regeneration performance. Combined with the data of Case 1, it further shows that the final repair level of the sample can be improved at a higher temperature. Therefore, considering various factors, 910°C is the optimal high-temperature molten salt lithium replenishment temperature.

[0090] Table 4: Electrochemical data of regenerated samples and comparative samples of implementation cases 3 and 4

[0091]

[0092] Implementation Case 5

[0093] (1) Weigh 1 g of the powder of Example 1 (lithium loss is 41.3%), then add a specific proportion of eutectic molten salt (molar ratio of LiOH:Li2CO3=0.84:0.16), specifically weighing 0.42 g of LiOH.H2O and 0.14 g of Li2CO3, then mix the S-NCM powder and molten salt evenly, grind them in a ball mill for 20 min at a speed of 400 r / min, and place the mixture in an Al2O3 crucible after ball milling.

[0094] (2) Place the crucible from (1) in a muffle furnace and heat it at the eutectic temperature of LiOH:Li2CO3, 440°C, for 12 h at a heating rate of 4°C / min in an air atmosphere. After heating, remove the residual molten salt by filtration and then dry it in a drying oven at 60°C for 8 h.

[0095] (3) Calculate the molar weight of the dried sample, add approximately 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. Then, heat in an O2 atmosphere in a tube furnace at 600°C for 4 hours at a heating rate of 2°C / min. The sample after heat treatment is the repaired cathode powder, designated r-NCM-3.

[0096] (4) The powder samples were subjected to XRD and SEM tests. The powders were made into slurry and assembled into half-cells, and the electrochemical data of the cells were tested.

[0097] Table 5: XRD refinement data of the regenerated sample and the comparative sample in Example 5

[0098]

[0099]

[0100] Table 6: Electrochemical data of regenerated samples and comparative samples in Example 5

[0101]

[0102] Figure 13 The XRD and corresponding refined images of the regenerated sample in Case 5 are shown. Combining the data in Table 5, it can be seen that when molten salt lithium supplementation was performed at the eutectic temperature of LiOH+Li2CO3, although the values ​​of the unit cell parameters a and c were consistent with the trend of lithium supplementation under high temperature conditions and increased compared to S-NCM, its I(003) / (104) value was 1.18, which did not reach the standard of 1.2, and the layered structure was not fully restored. In addition, the degree of cation mixing was 5.9% after repair, which was also higher than the 4.1% after regeneration treatment in Case 1. This shows that although the regeneration reaction carried out at medium and low temperatures can play a certain role in repair, the repair level is not as good as the high temperature and high energy lithium supplementation environment in Case 1.

[0103] Figure 14 This is an SEM image of the regenerated sample in Implementation Case 5. At different magnifications, it can be seen that there are still many incomplete spherical secondary particles in the regenerated sample. This is the result of increased cracks and eventual particle breakage after the battery has been cycled for a long time. After the lithium replenishment reaction at 440°C, these degraded particles are not effectively repaired. Instead, they continue to exist in a fragmented form between the particles. Compared with the uniform and regular single crystal particles in Case 1, this fragmented structure inevitably leads to reduced battery performance. This shows that under the conditions of 440°C, the growth driving force provided by the entire molten salt environment is very limited, and it can neither repair the complete secondary particles nor fully grow into a single crystal structure.

[0104] Figure 15The electrochemical performance diagram of the regenerated sample in Example 5 is shown in the figure. From the 100-cycle cycle data in the figure, it can be seen that the performance of the regenerated sample has recovered to a certain extent after the lithium replenishment reaction at 440°C. At a charge and discharge rate of 1C, the first cycle capacity reaches 154.8 mAh / g. This shows that in the case of lithium loss, the molten salt at medium and low temperatures can achieve the lithium replenishment process. However, in the subsequent cycle process, it can be found that the capacity decreases very rapidly. After 100 cycles, the capacity is only 117.5 mAh / g, and the capacity retention rate is 75.8%. This is much lower than the 93.4% capacity retention rate of 100 cycles in Example 1. This may be related to the particle morphology observed in the SEM image. Due to the presence of broken particles, the material structure becomes very unstable during the charge and discharge process, and the irreversible volume strain and cracks are generated, which ultimately lead to the reduction of the electrochemical performance of the regenerated sample. Therefore, although the regeneration reaction carried out at the LiOH+Li2CO3 eutectic point temperature can repair the defects of S-NCM such as particle cracking, lithium loss and cation mixing during long-term cycling to a certain extent, the performance of the final material cannot achieve the expected effect. On the contrary, when the temperature is raised to 910℃ and KCl is added at the same time to prevent the rapid volatilization of the molten salt and stabilize the lithium replenishment environment, it can not only completely repair various defects in S-NCM, but also its electrochemical performance is comparable to that of commercial powder.

[0105] Implementation Case 6

[0106] (1) Weigh 1 g of the powder of Example 1 (lithium loss is 41.3%), and then add a specific proportion of eutectic molten salt (molar ratio of LiOH:Li2CO3:KCl=0.84x:0.16x:1-x, x=0.5), specifically weighing 0.42 g, 0.14 g, and 0.88 g of LiOH.H2O, Li2CO3, and KCl, respectively. Then, mix the S-NCM powder and the molten salt evenly, grind them in a ball mill for 20 min at a speed of 400 r / min, and place the mixture in an Al2O3 crucible after ball milling.

[0107] (2) Place the crucible in (1) in a muffle furnace and heat it. First, heat it to 600°C and hold it for 2 hours, then heat it to 950°C and hold it for 6 hours. The heating rate is 4°C / min. The gas atmosphere is air. After heating, filter out the residual molten salt in the sample and then dry it in a forced air drying oven at 60°C for 8 hours.

[0108] (3) Calculate the molar weight of the dried sample, add 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. Then, heat in a tube furnace at 600°C for 4 hours under an O2 atmosphere at a heating rate of 2°C / min. The sample after heat treatment is the repaired cathode powder, designated R-NCM-3.

[0109] (4) The powder samples were subjected to SEM testing. At the same time, the powders were made into slurry and assembled into half-cells, and the electrochemical data of the cells were tested.

[0110] Implementation Case 7

[0111] (1) Weigh 1 g of the powder of Example 1 (lithium loss is 41.3%), and then add a specific proportion of eutectic molten salt (molar ratio of LiOH:Li2CO3:KCl=0.84x:0.16x:1-x, x=0.5), specifically weighing 0.42 g, 0.14 g, and 0.88 g of LiOH.H2O, Li2CO3, and KCl, respectively. Then, mix the S-NCM powder and the molten salt evenly, grind them in a ball mill for 20 min at a speed of 400 r / min, and place the mixture in an Al2O3 crucible after ball milling.

[0112] (2) The crucible in (1) was placed in a muffle furnace and heated. The temperature was first raised to 600°C and held for 2 h, then heated to 930°C and held for 6 h, with a heating rate of 4°C / min. The atmosphere was air. After heating, the residual molten salt was removed by filtration with deionized water, and then dried in a drying oven at 60°C for 8 h.

[0113] (3) Calculate the molar weight of the dried sample, add 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. Heat in a tube furnace at 600°C for 4 h under an O2 atmosphere, with a heating rate of 2°C / min. The sample after heat treatment is the repaired cathode powder, designated R-NCM-4.

[0114] (4) The powder samples were subjected to SEM testing. At the same time, the powders were made into slurry and assembled into half-cells, and the electrochemical data of the cells were tested.

[0115] Table 7: Electrochemical data of regenerated samples and comparative samples in implementation cases 6 and 7

[0116]

[0117]

[0118] Figure 16 、 17The following are SEM images of the regenerated samples from Cases 6 and 7. As can be seen from the figure, when the temperature is raised to 950°C, the regenerated particle morphology exhibits a distorted structure similar to that in Case 2. This extremely uneven growth pattern is caused by the uncontrolled volatilization of the molten salt, indicating that the added KCl is no longer sufficient to alleviate the volatilization of the lithium salt. The unbalanced lithium replenishment environment leads to the coexistence of particles with greatly varying sizes. However, the particle morphology after treatment at 930°C remains relatively regular, and the large and uniform single crystal particles ensure excellent electrochemical performance after regeneration. Figure 17 Comparing the electrochemical performance of the regenerated samples in this case with that of the untreated samples, the deteriorated particle morphology under heating conditions at 950°C led to a sharp decline in the regeneration performance. The first-cycle capacity of 142.7 mAh / g was much lower than that of the sample treated at 910°C in Case 1. At the same time, the capacity retention rate of only 71.8% after 100 cycles also demonstrated the instability of the particle structure. In contrast, the regenerated sample treated at 930°C not only had a capacity of 155.2 mAh / g in the first cycle, but also maintained a capacity retention rate of 90.3% after 100 cycles. This case shows that the treatment conditions of 950°C have exceeded the upper limit of the stability of the high-temperature molten salt, and the performance of the regenerated sample will be severely degraded at this time. However, the regenerated sample treated at 930°C still has good electrochemical performance (155.2 mAh / g / 90.3%). Combined with the experimental data in Case 1, it is confirmed that the regeneration temperature of 910-930°C can maximize the regeneration performance of highly degraded lithium-ion ternary layered cathode materials.

[0119] Implementation Case 8

[0120] (1) Weigh 1 g of the powder of (1) in Example 1 (lithium loss is 41.3%), then add a specific proportion of eutectic molten salt and co-solvent (molar ratio of LiOH:Li2CO3:KCl=0.84x:0.16x:1-x, x=0.7), specifically weighing 0.46 g, 0.15 g and 0.42 g of LiOH.H2O, Li2CO3 and KCl respectively, then mix the S-NCM powder with the molten salt-co-solvent and put it into a ball mill, grind for 20 minutes at a speed of 400 r / min, and add dispersant ethanol at the same time to ensure that the powder to be recovered is completely and evenly distributed in the molten salt system. At the same time, the initial polycrystalline structure is broken to a certain extent, which is more conducive to the generation of single crystal structure in the regeneration reaction. After ball milling is completed and dried, the mixture is placed in an Al2O3 crucible.

[0121] (2) The crucible in (1) was placed in a muffle furnace and heated using a gradient heating method to ensure the completeness of the reaction. The temperature was first raised to 600°C and held for 2 hours, then heated to 910°C and held for 6 hours, with a heating rate of 4°C / min. The gas atmosphere was air. After heating, the sample was filtered through deionized water to remove residual lithium salts and co-solvents. The powder material was then placed in a drying oven and dried at 60°C for 8 hours.

[0122] (3) Calculate the molar weight of the dried sample, add approximately 5% molar ratio of Li2CO3, mix thoroughly in a mortar, and place in an Al2O3 crucible. To ensure that the impurity phase structure that hinders lithium ion diffusion is completely restored to a layered structure, the sample is then heated at 600°C in a tube furnace under an O2 atmosphere for 4 hours at a heating rate of 2°C / min. The sample after heat treatment is the repaired positive electrode powder, denoted as R-NCM-5.

[0123] (4) After the powder is made into a slurry and assembled into a half-cell, the electrochemical data of the battery are tested.

[0124] Table 8: Electrochemical data of regenerated samples and comparative samples in Example 8

[0125]

[0126] The electrochemical data of each sample in Case 8 are shown in Table 8. When the x value in the molten salt ratio increases, the content of the co-solvent KCl decreases. When x = 0.7, the inhibitory effect on the volatilization of lithium salts at high temperatures is also reduced. Compared with the electrochemical data of x = 0.5 in Case 1, the first cycle capacity of R-NCM-5 is 153.6 mAh / g, slightly lower than 156.8 mAh / g. At the same time, the capacity retention rate of 100 cycles (88.1%) is also slightly lower than that of the commercial standard sample (88.6%). However, its various performances are still significantly better than those of the untreated sample (109.8 mAh / g / 68.4%). This case shows that when the KCl content decreases, the volatilization effect of the lithium salt is intensified, affecting the electrochemical performance of the final regenerated sample. However, compared with the performance of S-NCM without adding KCl (126.7 mAh / g) in Case 2, the treatment conditions of Case 8 still have a great advantage. Therefore, under appropriate temperature conditions (910-930°C), when the molten salt ratio is LiOH:Li2CO3:KCl=0.84x:0.16x:1-x, x=0.5-0.7, excellent regenerated electrochemical performance can be obtained.

[0127] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations made to these embodiments without departing from the principles and spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt, characterized in that: The steps include: Step S1: After the used ternary lithium-ion battery is completely discharged, it is mechanically disassembled and separated to obtain an aluminum current collector coated with a positive electrode active material, which is crushed with a grinder and then simply sieved to remove the aluminum foil to obtain a positive electrode powder with degraded performance; Step S2: The obtained positive electrode powder is mixed with the selected molten salt in proportion, and ground with a ball mill to ensure that the molten salt and the recovered powder are evenly mixed. Then, the lithium replenishment process is carried out under high temperature conditions. At the same time, the residual binder and conductive agent impurities in the positive electrode powder can also be effectively removed; The lithium replenishment heating conditions are to heat the temperature to 600°C and hold for 2 hours, then hold at 910-930°C for 4-6 hours, with a heating rate of 4°C / min. The gas atmosphere is air, wherein a gradient heating method can provide a more stable lithium replenishment molten salt environment. The selection and molar ratio of the molten salt are LiOH:Li2CO3:KCl=0.84x:0.16x:(1-x), x=0.5-0.7; the molar ratio of the total lithium ion amount in the molten salt to the lithium ion loss amount of the positive electrode powder is 1:1-8:1; Step S3: After the lithium-supplemented sample is centrifuged, washed, and dried, it is heat-treated in an oxygen atmosphere to repair the impurity phase structure that may exist on the particle surface.

2. The method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt as claimed in claim 1, characterized in that: The complete discharge process in step S1 is carried out in a Na2SO4 solution with a concentration of 5%-10% for 48-72 hours; And / or, after the aluminum foil is initially removed by sieving through a 400-mesh sieve in step S1, the positive electrode powder is alkaline-soaked with a NaOH solution, and the impurity aluminum can be completely removed after filtration.

3. The method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt as claimed in claim 1, characterized in that: In step S2, the ball mill rotates at a speed of 400-500 r / min for 20-30 min, and dispersant ethanol is added for thorough grinding.

4. The method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt as claimed in claim 1 or 3, characterized in that: In step S2, the volume ratio of the molten salt to the positive electrode powder should be 1:1-4:1 to ensure that the molten salt can fully cover the positive electrode powder after grinding.

5. The method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt as claimed in claim 1, characterized in that: The main components of the binder and the conductive agent mentioned in step S2 are polyvinylidene fluoride and carbon black, which will decompose when heated to a temperature above 800°C.

6. The method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt as claimed in claim 1, characterized in that: Since the molten salts selected in step S2 are all water-soluble salts, residual molten salts can be effectively removed by filtering with deionized water in step S3.

7. The method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt as claimed in claim 1, characterized in that: The heat treatment temperature in step S3 is 600-800° C., and an oxidizing gas atmosphere is selected.

8. The method for upgrading and reconstructing a highly degradable layered nickel-cobalt-manganese cathode material to a single crystal by using a high-energy molten salt as claimed in claim 1, characterized in that: This molten salt method is suitable for layered nickel-cobalt-manganese ternary lithium-ion battery positive electrodes with different transition metal element ratios, and the best repair effect can be achieved by changing the heating conditions.

9. A highly degradable layered nickel-cobalt-manganese cathode material, characterized by: It is prepared by the single crystal upgrading and reconstruction method of the highly degradable layered nickel-cobalt-manganese positive electrode material under the assistance of high-energy molten salt as described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that: The invention comprises a battery positive electrode made of the highly degradable layered nickel-cobalt-manganese positive electrode material according to claim 9.

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