Cathode material with ultrathin surface limiting layer for auxiliary upgrading and regeneration as well as preparation method and application of cathode material

Abstract

The invention provides an ultrathin surface confinement layer assisted upgraded and regenerated positive electrode material and a preparation method and application thereof, the material is a small-particle single-crystal nickel cobalt lithium manganate ternary positive electrode material, the chemical formula of the material is LimNixCoyMnzWnO2, m is more than or equal to 1.00 and less than or equal to 1.03, x + y + z + n is equal to 1, and n is more than or equal to 0.0016 and less than or equal to 0.0271. Elements are efficiently released through a micro-nano scale structure dissociation technology, stoichiometric ratio defects of the material are accurately repaired by combining a lithium source compensation and phase reconstruction technology, and single-crystal structure reconstruction and in-situ construction of a surface limiting layer are synchronously realized in a high-temperature sintering process through a confinement regulation and control grain growth technology of the ultrathin surface limiting layer. The surface limiting layer has dual functions of grain size regulation and surface protection, and the D50 of the prepared single-crystal positive electrode particles is 1-2 microns. Compared with the prior art, the obtained single-crystal positive electrode material shows excellent specific capacity and cycle performance, the recycling of positive electrode metal resources of retired batteries is realized, and an innovative solution is provided for the construction of a closed-loop industrial chain of power batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery material regeneration, and specifically relates to a cathode material assisted by an ultra-thin surface limiting layer for upgraded regeneration and a preparation method thereof. Background Art

[0002] At present, with the rapid development of the new energy vehicle industry, the large-scale recycling and utilization of cathode materials (NCM, NCA) of retired ternary lithium batteries has become a key challenge in the resource cycle of lithium battery material production. Existing recycling and reuse technologies for retired batteries mainly include pyrometallurgy, hydrometallurgy, and direct regeneration and repair, but all three have certain limitations. Among them, pyrometallurgy relies on high-temperature smelting (>1300 °C). Although valuable metals such as nickel and cobalt can be extracted, it has high energy consumption (8 - 10 kWh kg -1 )、low recovery rate, and generates various harmful gases; hydrometallurgy realizes material regeneration through acid leaching - extraction - resynthesis, but the process flow is complex, the reagent cost accounts for more than 60%, and there are problems in the treatment of harmful liquids such as organic waste liquid, harmful acid liquid, and heavy metal wastewater; direct regeneration and repair is represented by the molten salt method, and the material structure is repaired by lithium supplementation - sintering, but limited by the uneven distribution of cracks in the failed material, it is difficult to achieve accurate deep lattice distortion repair, resulting in low specific capacity and cycle life of the regenerated material. At the same time, existing lithium supplementation technologies rely on the mixing degree of materials, and uneven distribution of lithium sources easily causes local over-lithiation, generating excessive residual alkali impurities such as LiOH and Li2CO3, seriously restricting the processing performance and electrochemical performance of the regenerated material.

[0003] At present, some technologies have also improved this situation, but there are still some problems. For example, although the molten salt repair method disclosed in CN116924486A optimizes the repair effect, it requires multi-stage sintering, resulting in high energy consumption and a complex process; the molten salt repair method disclosed in CN116995325A uses a sulfur-based reducing agent, introducing environmental pollution risks. In short, existing molten salt direct regeneration and repair technologies are difficult to meet the requirements of retired battery resource recovery and reuse in terms of energy consumption, environment, performance, etc. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a cathode material assisted by an ultra-thin surface limiting layer for upgraded regeneration, a preparation method thereof, and an application thereof, which overcome the problems of incomplete repair of crystal structure damage and uneven bulk-phase lithium distribution in the regeneration of lithium nickel cobalt manganese oxide ternary cathode materials by the existing molten salt method. By introducing a tungsten-containing surface limiting layer during the molten salt repair process and combining the strategy of component reconstruction - grain size regulation and coordination, the retired material is reduced to a regenerated new material, realizing the restoration of the specific capacity, rate performance, and cycle stability of the material.

[0005] The object of the present invention can be achieved by the following technical solutions: An ultra-thin surface limiting layer-assisted upgraded and regenerated cathode material, which is a small-particle single-crystal nickel cobalt manganese lithium ternary cathode material with the chemical formula Li m Ni x Co y Mn z W n O2, where 1.00 ≤ m ≤ 1.03, x + y + z + n = 1, 0.0016 ≤ n ≤ 0.0271.

[0006] Furthermore, there is a tungsten-containing surface limiting layer with a uniform thickness on the surface of the single-crystal particles. Its thickness L is related to n, where n is the content of W in the aforementioned cathode material. The specific relationship is: 22.34 × e (-n / 0.0124) + 21.87 ≤ L ≤ 22.34 × e (-n / 0.0124) + 23.87, where e is the natural logarithm.

[0007] Furthermore, the particle size distribution and surface residual alkali content of the cathode material meet the following requirements: The small particle size D10 (the particle size with a cumulative distribution of 10%) ≥ 0.5 μm; The median particle size D50 (the particle size with a cumulative distribution of 50%) is 1.0 - 2.0 μm; The large particle size D90 (the particle size with a cumulative distribution of 90%) ≤ 3.0 μm; Calculated as LiOH + Li2CO3, the surface residual alkali content ≤ 0.5 wt%.

[0008] The present invention also provides a preparation method for an ultra-thin surface limiting layer-assisted upgraded and regenerated cathode material, including the following steps: (1) Pretreatment: Subject the retired nickel cobalt manganese lithium ternary cathode material to dealumination pretreatment in an alkaline solution, then calcine and screen it to obtain cathode powder; (2) Molten salt mixing: Mix the cathode powder obtained in step (1), the molten salt containing LiOH, and the tungsten source evenly. Among them: The molar ratio of the cathode powder to LiOH in the molten salt is 1:(1.5 - 2.5); The mass ratio of the tungsten source to the cathode powder is (0.003 - 0.05):1; (3) Two-stage sintering: Subject the mixture obtained in step (2) to two-stage sintering in an oxygen atmosphere. Among them, the first-stage sintering is to heat up to 400 - 600 °C at a rate of 3 - 10 °C / min and hold for 2 - 6 hours; The second-stage sintering is to heat up to 700 - 900 °C at a rate of 3 - 10 °C / min and hold for 8 - 16 hours; (4) Post-treatment: Cool the product sintered in step (3), wash to remove the residual molten salt, and dry to obtain the regenerated nickel cobalt manganese lithium ternary cathode material.

[0009] Further, in step (1), the alkaline solution is a 0.5 - 2.0 M KOH solution; the dealumination pretreatment is to immerse the retired lithium nickel cobalt manganese oxide cathode material in the alkaline solution for 2 - 3 h to remove the aluminum in the material, then take out the remaining solid material and calcine it at 500 - 600 °C for 3 - 8 h; sieving is carried out through a 400 - mesh sieve.

[0010] Further, in step (2), the molten salt containing LiOH contains LiOH and other eutectic components, and the other eutectic components are one or more of NaCl, Na2SO4, KCl, and K2SO4; the molar ratio of LiOH to other eutectic components in the molten salt is 1:(0.1 - 0.5).

[0011] Further, in step (2), the tungsten source is one or more of tungsten trioxide (WO3), tungstic acid (H2WO4), ammonium tungstate ((NH4)2WO4), ammonium metatungstate ((NH4)6[H2W 12 O 40 ·xH2O), tungsten acetylacetonate (W(C5H7O2)6), tungsten acetate (WO2(CH3COO)2), ammonium thiotungstate ((NH4)2WS4).

[0012] Further, in step (3), the oxygen flow rate is 5 - 20 mL / min.

[0013] Further, in step (4), the washing solvent is deionized water, the water temperature is 15 - 30 °C, the washing time is 8 - 15 min, and the washing is carried out until the pH value of the solution is 6.5 - 7.5.

[0014] The present invention also provides an application of the ultrathin surface - restricted layer - assisted upgraded recycled cathode material, which is used as a cathode material for lithium - ion batteries.

[0015] Compared with the prior art, the advantages and technical effects of the present invention are as follows: 1) The present invention realizes the efficient release of elements through the micro - nano scale structure dissociation technology, combines the lithium source compensation and phase reconstruction process, and by introducing a trace amount of tungsten element, during the repair of the retired cathode material, confines the growth range of the primary particles of the cathode material, not only realizes the homogeneous regulation of lithium source compensation, but also uses the high - temperature solid - state reaction to promote the material to reconstruct into a single - crystal phase with a stable layered structure within the limited space of the ultrathin tungsten - containing restricted layer, ultimately realizing the efficient re - activation of elements in the failed material, the repair of stoichiometric ratio defects, and the structural regeneration of single - crystal particles, thereby restoring its electrochemical performance.

[0016] While precisely repairing the material's stoichiometric defects, the failed material is prepared into a new single-crystal positive electrode material. Furthermore, through the confinement control of grain growth by an ultra-thin surface restriction layer, single-crystal structure reconstruction and in-situ construction of the surface restriction layer are simultaneously achieved during high-temperature sintering. This surface restriction layer has the dual functions of grain size control and surface protection. The D50 of the prepared single-crystal positive electrode particles is 1-2 μm. Thanks to this preparation method, the resulting single-crystal positive electrode material exhibits excellent specific capacity and cycle performance, achieving efficient recycling of retired battery positive electrode metal resources and providing an innovative solution for the construction of a closed-loop power battery industry chain.

[0017] 2) The present invention removes impurities on the surface of retired positive electrode materials through dealumination, and then achieves precise lithium compensation and synchronous tungsten surface doping in a LiOH molten salt system containing a tungsten source: the high-temperature molten salt environment promotes lithium ion diffusion and restores the Li ratio in the material to 1.00-1.03. At the same time, the intrinsic characteristic of tungsten ions (large radius, making it difficult for them to diffuse into the bulk phase of lithium nickel cobalt manganese oxide materials) is utilized to form a uniform Li-WO confinement layer (approximately nanometer thick) on the surface of the single crystal, which enhances structural stability by inhibiting lattice oxygen precipitation and transition metal dissolution. During the calcination process, the fluidity of the molten salt optimizes lattice rearrangement, while the tungsten confinement layer can reduce surface residual alkali. While controlling the residual alkali content (≤0.5 wt%), it synergistically reduces interfacial side reactions and restores the continuity of the lithium ion diffusion channel, thereby reconstructing the complete layered structure of the single crystal particles and achieving regeneration of specific capacity, rate performance and cycle stability.

[0018] 3) This invention forms an ultra-thin surface restriction layer by introducing a trace amount of tungsten into the molten salt. This layer limits the growth size of the reconstructed single crystal particles while repairing them, thereby increasing the specific surface area and the active sites for the lithium storage reaction. Furthermore, the tungsten-containing surface restriction layer can also limit the replenished lithium source to a certain range within the failed material, more effectively repairing the crystal structure of the nickel-cobalt-manganese oxide ternary cathode material, reducing lithium ion loss, reducing phase change damage, and restoring the material's capacity. Within the voltage range of 3.0-4.3V, the 0.5 C discharge capacity is greater than 160 mAh g -1 . The regenerated single crystal particles have a larger specific surface area, which is beneficial to improving the rate performance of the material. Generally, a large specific surface area will increase the side reactions on the surface of the material during the charge and discharge process. However, in the positive electrode material of the present invention that is upgraded and regenerated with the assistance of an ultra-thin surface restriction layer, the tungsten-containing surface restriction layer serves as a dense lithium tungsten oxide protective layer on the surface of the material, which can effectively reduce the occurrence of surface side reactions during the cycle of the electrode material and improve the cycle life of the material. The capacity retention rate of the recycled material after 100 cycles at 0.5 C is ≥90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1X-ray diffraction pattern of the product obtained in Example 1.

[0020] Figure 2 X-ray diffraction pattern of the product obtained in Comparative Example 1.

[0021] Figure 3 Scanning electron microscope photos of the product obtained in Example 1 at different magnifications.

[0022] Figure 4 Half-cell rate performance of the products obtained in Example 1 and Comparative Example 1.

[0023] Figure 5 Half-cell cycling performance of the products obtained in Example 1 and Comparative Example 1. Detailed implementation manners

[0024] The following will describe the specific content and implementation manners of the present invention in conjunction with the embodiments of the present invention. However, the described embodiments are only a part of the embodiments of the present invention, and the implementation manners of the present invention are not limited thereto.

[0025] All raw materials involved in the present invention are commercially available raw materials. The retired ternary lithium nickel cobalt manganese oxide cathode material comes from a conventional electric vehicle recycling company. For example, the retired ternary lithium nickel cobalt manganese oxide cathode material in the following examples comes from Hebei Zhonghua Lithium Battery Technology Co., Ltd.

[0026] The electrochemical performance test method of the material is as follows: Mix the cathode material, polyvinylidene fluoride (PVDF) and acetylene black evenly according to a mass ratio of 8:1:1, then put it into a certain amount of N-methylpyrrolidone (NMP (electronic grade, purity 99.9%)) and continuously stir for 12 hours to form a uniformly dispersed slurry. Then use a scraper to coat the slurry on the aluminum foil, and then quickly put it into a blast drying oven at 80 °C until NMP is completely evaporated. Then transfer it to a vacuum drying oven at 80 °C and dry for 12 hours. After that, cut it into discs with a diameter of 10 mm for standby, and the active material loading on its surface is about 3 mg cm -2 .

[0027] The button cell assembly uses a CR2032 type battery case. The above - cut circular wafer is used as the positive electrode, a pure PE membrane is used as the separator, lithium metal (diameter 16 mm) is used as the negative electrode, and the electrolyte is an electrolyte of 1 M LiPF6 dissolved in dimethyl carbonate (DMC): ethylene carbonate (EC) = 7:3 (Vol%) + 5% fluoroethylene carbonate (FEC). After the button cell is prepared, it is left standing for 10 hours, and then electro - chemical performance tests are carried out at different current densities (at a nominal specific capacity of 1C = 150 mAh g -1 ) within a voltage range of 3.0 - 4.3V.

[0028] Example 1 A preparation method of a small - particle single - crystal nickel - cobalt - manganese lithium - rich layered oxide cathode material assisted by an ultra - thin surface - limiting layer for upgrading and regeneration includes the following steps: Step 1: Immerse the retired nickel - cobalt - manganese lithium - rich layered oxide cathode material in 1 M KOH solution for 2h for dealumination pretreatment, then calcine at 600 °C for 8h to obtain the dealuminated cathode powder, and then sieve it through a 400 - mesh sieve for standby.

[0029] Step 2: Mix the cathode powder obtained in Step 1, the molten salt formed by LiOH and NaCl, and tungsten trioxide evenly. Among them, the molar ratio of the cathode powder to LiOH is 1:2; the mass ratio of tungsten trioxide to the cathode powder is 0.01:1; the molar ratio of LiOH to NaCl is 1:0.2.

[0030] Step 3: Sinter the mixture obtained in Step 2 in two stages under an oxygen flow rate of 10 mL / min: The first stage: Heat up to 500 °C at a rate of 5 °C / min and keep the temperature for 5 hours; The second stage: Heat up to 850 °C at a rate of 5 °C / min and keep the temperature for 10 hours.

[0031] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 25 °C for 15 min until the pH = 7.0, and dry it in vacuum for 12 hours.

[0032] Comparative Example 1 (retired material) Immerse the retired nickel - cobalt - manganese lithium - rich layered oxide cathode material in NMP for 24h to obtain the cathode powder, remove iron impurities by magnetic separation, and then sieve it through a 400 - mesh sieve.

[0033] Perform phase and electro - chemical performance tests on the materials obtained in Example 1 and Comparative Example 1: As Figure 1 shown is the X-ray diffraction pattern of the product obtained in Example 1. It can be seen from the figure that the repaired material has clear XRD diffraction peaks after the repair in Example 1, indicating that the crystallinity of the material after repair is restored well. Compared with Figure 2 the X-ray diffraction pattern of the retired lithium nickel cobalt manganese oxide material obtained in Comparative Example 1 shown, the intensity ratio of the (003) / (104) crystal plane peaks in Example 1 is higher, and the splitting degree of the (108) / (110) crystal plane peaks is more obvious, proving the transformation to a layered structure during the material repair process.

[0034] As Figure 3 shown are the scanning electron microscope photos of the product obtained in Example 1 at different magnification factors. It can be seen from the figure that after repair by the method described in Example 1, the morphology of the material is single crystal small particles, and its particle size distribution is D10 = 0.7 μm, D50 = 1.8 μm, D90 = 2.9 μm; the residual alkali content on its surface is 0.3 wt%; As Figure 4 shown are the half-cell rate performances of the products obtained in Example 1 and Comparative Example 1. It can be seen from the figure that the rate performance of the material repaired by the method described in Example 1 is greatly improved compared with that of the retired material described in Comparative Example 1.

[0035] As Figure 5 shown are the half-cell cycle performances of the products obtained in Example 1 and Comparative Example 1. It can be seen from the figure that the material repaired by the method described in Example 1 has excellent cycle stability, and the discharge capacity reaches 164.1 mAh g -1 at 0.1 C, and the capacity retention rate is 96.5% after 50 cycles, while the capacity of the retired material described in Comparative Example 1 decays significantly after 50 cycles, and the capacity retention rate is only 55.8%.

[0036] Example 2 Step 1: Immerse the retired lithium nickel cobalt manganese oxide ternary cathode material in 0.5 M KOH solution for 3 h for dealumination pretreatment, then calcine at 600 °C for 5 h to obtain the dealuminated cathode powder, and then sieve it through a 400-mesh sieve for standby.

[0037] Step 2: Mix evenly the cathode powder obtained in Step 1, the molten salt formed by LiOH and NaCl, and tungsten trioxide. Among them, the molar ratio of the cathode powder to LiOH is 1:1.5; the mass ratio of tungsten trioxide to the cathode powder is 0.003:1; the molar ratio of LiOH to NaCl is 1:0.1.

[0038] Step 3: Perform two-stage sintering on the mixture obtained in Step 2 under an oxygen flow rate of 20 mL / min: The first stage: Heat up to 600 °C at a rate of 3 °C / min and hold for 2 hours; The second stage: Heat up to 900 °C at a rate of 3 °C / min and hold for 8 hours.

[0039] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 15 °C for 10 min until the pH reaches 6.5, and dry it under vacuum for 12 hours.

[0040] Example 3 Step 1: Immerse the retired ternary lithium nickel cobalt manganese oxide cathode material in a 2.0 M KOH solution for 2 h for dealumination pretreatment, then calcine it at 500 °C for 3 h to obtain the dealuminated cathode powder, and then sieve it through a 400-mesh sieve for standby.

[0041] Step 2: Mix the cathode powder obtained in Step 1, the molten salt formed by LiOH and KCl, and sodium tungstate evenly. Among them, the molar ratio of the cathode powder to LiOH is 1:2.5; the mass ratio of sodium tungstate to the cathode powder is 0.05:1; the molar ratio of LiOH to KCl is 1:0.5.

[0042] Step 3: Sinter the mixture obtained in Step 2 in two stages under an oxygen flow rate of 15 mL / min: The first stage: Heat up to 400 °C at a rate of 8 °C / min and hold for 6 hours; The second stage: Heat up to 700 °C at a rate of 8 °C / min and hold for 16 hours.

[0043] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 30 °C for 10 min until the pH reaches 7.5, and dry it under vacuum for 12 hours.

[0044] Example 4 Step 1: Immerse the retired ternary lithium nickel cobalt manganese oxide cathode material in a 1.0 M KOH solution for 2 h for dealumination pretreatment, then calcine it at 550 °C for 5 h to obtain the dealuminated cathode powder, and then sieve it through a 400-mesh sieve for standby.

[0045] Step 2: Mix the cathode powder obtained in Step 1, the molten salt formed by LiOH and Na2SO4, and ammonium tungstate evenly. Among them, the molar ratio of the cathode powder to LiOH is 1:1.8; the mass ratio of ammonium tungstate to the cathode powder is 0.01:1; the molar ratio of LiOH to Na2SO4 is 1:0.3.

[0046] Step 3: Sinter the mixture obtained in Step 2 in two stages under an oxygen flow rate of 5 mL / min: The first stage: Heat up to 550 °C at a rate of 5 °C / min and hold for 4 hours; The second stage: Heat up to 800 °C at a rate of 5 °C / min and hold for 10 hours.

[0047] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 25 °C for 15 min until the pH reaches 7.0, and dry it in vacuum for 12 hours.

[0048] Example 5 Step 1: Immerse the retired lithium nickel cobalt manganese oxide cathode material in 1.0 M KOH solution for 3 h for dealumination pretreatment, then calcine it at 500 °C for 8 h to obtain the dealuminated cathode powder, and then sieve it through a 400-mesh sieve for standby.

[0049] Step 2: Mix the cathode powder obtained in Step 1, the molten salt formed by LiOH and K2SO4, and ammonium thiotungstate evenly. Among them, the molar ratio of the cathode powder to LiOH is 1:1.6; the mass ratio of ammonium thiotungstate to the cathode powder is 0.03:1; the molar ratio of LiOH to K2SO4 is 1:0.3.

[0050] Step 3: Carry out two-stage sintering on the mixture obtained in Step 2 at an oxygen flow rate of 10 mL / min: The first stage: Heat it to 450 °C at a rate of 7 °C / min and hold for 5 hours; The second stage: Heat it to 750 °C at a rate of 3 °C / min and hold for 11 hours.

[0051] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 25 °C for 8 min until the pH reaches 7.0, and dry it in vacuum for 12 hours.

[0052] Example 6 Step 1: Immerse the retired lithium nickel cobalt manganese oxide cathode material in 2.0 M KOH solution for 2 h for dealumination pretreatment, then calcine it at 500 °C for 3 h to obtain the dealuminated cathode powder, and then sieve it through a 400-mesh sieve for standby.

[0053] Step 2: Mix the cathode powder obtained in Step 1, the molten salt formed by LiOH and K2SO4, and tungstenyl acetylacetone evenly. Among them, the molar ratio of the cathode powder to LiOH is 1:1.6; the mass ratio of tungstenyl acetylacetone to the cathode powder is 0.03:1; the molar ratio of LiOH to K2SO4 is 1:0.3.

[0054] Step 3: Carry out two-stage sintering on the mixture obtained in Step 2 at an oxygen flow rate of 20 mL / min: The first stage: Heat it to 600 °C at a rate of 10 °C / min and hold for 3 hours; The second stage: Heat it to 900 °C at a rate of 10 °C / min and hold for 9 hours.

[0055] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 25 °C for 15 min until the pH = 7.0, and dry it under vacuum for 12 hours.

[0056] Comparative Example 2 (Regeneration by traditional high-temperature sintering method) Step 1: Immerse the retired lithium nickel cobalt manganese oxide cathode material in 1.0 M KOH solution for 2 h, then calcine it at 600 °C for 8 h to obtain the cathode powder, and then screen it through a 400-mesh sieve.

[0057] Step 2: Mix the cathode powder obtained in Step 1 with LiOH in a molar ratio of 1:0.5 by ball milling until homogeneous. The specific conditions are a rotation speed of 500 rpm, a ball milling time of 30 min, and a ball-to-material ratio of 10:1.

[0058] Step 3: Carry out two-stage sintering on the mixture obtained in Step 2 under an oxygen flow rate of 10 mL / min: The first stage: Heat it up to 500 °C at a rate of 5 °C / min and hold for 5 hours; The second stage: Heat it up to 850 °C at a rate of 5 °C / min and hold for 10 hours.

[0059] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 25 °C for 15 min until the pH = 7.0, and dry it under vacuum for 12 hours.

[0060] Comparative Example 3 (Regeneration by molten salt method, but without introducing a tungsten-containing surface limiting layer) Step 1: Immerse the retired lithium nickel cobalt manganese oxide cathode material in 1 M KOH solution for 2 h for dealumination pretreatment, then calcine it at 600 °C for 8 h to obtain the dealuminated cathode powder, and then screen it through a 400-mesh sieve for standby.

[0061] Step 2: Mix the cathode powder obtained in Step 1 with the molten salt formed by LiOH and NaCl until homogeneous. Among them, the molar ratio of the cathode powder to LiOH is 1:1.2; the molar ratio of LiOH to NaCl is 1:0.2.

[0062] Step 3: Carry out two-stage sintering on the mixture obtained in Step 2 under an oxygen flow rate of 10 mL / min: The first stage: Heat it up to 500 °C at a rate of 5 °C / min and hold for 5 hours; The second stage: Heat it up to 850 °C at a rate of 5 °C / min and hold for 10 hours.

[0063] Step 4: Cool the product sintered in Step 3, then wash it with deionized water at 25 °C for 15 min until the pH = 7.0, and dry it under vacuum for 12 hours.

[0064] The following table shows the electrochemical performance test results of the materials obtained in each example and comparative example: Sample Name Particle Size D50 (μm) Residual Alkali (wt%) <![CDATA[0.1 C specific capacity (mAh g -1 )]]> Retention Rate after 50 Cycles at 0.1 C (%) <![CDATA[0.5 C specific capacity (mAh g -1 )]]> Retention Rate after 100 Cycles at 0.5 C (%) Example 1 1.8 0.3 164.1 96.5 161.2 92.3 Example 2 1.8 0.3 163.2 95.6 160.1 90.6 Example 3 1.5 0.4 161.1 95.0 160.3 90.5 Example 4 1.7 0.3 162.0 96.1 160.8 91.0 Example 5 1.6 0.5 163.9 94.8 160.6 91.3 Example 6 1.9 0.3 163.3 96.0 160.0 90.4 Comparative Example 1 10.8 0.0 110.1 72.6 57.8 55.8 Comparative Example 2 9.0 0.9 132.1 82.0 107.3 73.5 Comparative Example 3 3.5 1.1 144.2 88.8 128.3 80.3 As can be seen from the above table, a ternary cathode material of small particle single crystal nickel cobalt manganese lithium oxide assisted by an ultra-thin surface limiting layer for upgraded regeneration proposed by the present invention exhibits excellent lithium storage performance. Within the voltage window of 3.0 - 4.3 V, the repaired material can maintain long-term stable cycling with a high reversible specific capacity at current densities of 0.1 C and 0.5 C. In sharp contrast, the reversible capacity and cycling stability of the retired material of Comparative Example 1 without regeneration and repair both show significant deterioration. In Comparative Example 2, traditional high-temperature sintering method was used for regeneration. Although the performance of the obtained material is slightly better than that of the retired material, its specific capacity is much lower than that of the repaired material in the examples. At the same time, due to the lack of the fluxing effect of molten salt during sintering, the particle size of the material repaired by the method described in Comparative Example 2 is close to that of the retired material described in Comparative Example 1, and no single crystal is formed, thus greatly reducing the cycling performance of the material. In Comparative Example 3, the molten salt method without introducing tungsten element was used for repair. Due to the lack of growth control of the ultra-thin tungsten-containing surface limiting layer on the material particles, although the obtained material forms single crystal, its particle size is large, increasing the ion diffusion path between particles, resulting in its specific capacity being lower than that of the material repaired in the examples. Therefore, a ternary cathode material of small particle single crystal nickel cobalt manganese lithium oxide assisted by an ultra-thin surface limiting layer for upgraded regeneration and its preparation method of the present invention can effectively restore the lithium ion storage capacity and cycling stability of the electrode material, providing a new design idea for the recycling of retired ternary cathode materials of lithium ion batteries.

[0065] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A cathode material assisted by an ultra-thin surface limiting layer for upgraded regeneration, characterized in that The positive electrode material is a small-particle single-crystal ternary nickel cobalt manganese lithium oxide positive electrode material, and its chemical formula is Li m Ni x Co y Mn z W n O2, where 1.00 ≤ m ≤ 1.03, x + y + z + n = 1, and 0.0016 ≤ n ≤ 0.0271.

2. The ultra-thin surface-limiting layer-assisted upgraded and regenerated cathode material according to claim 1, wherein There is a tungsten-containing surface limiting layer with a uniform thickness on the surface of the single crystal particles. The thickness L is related to n, where n is the content of W in the positive electrode material. The specific relationship is: 22.34×e (-n / 0.0124) +21.87 ≤ L ≤ 22.34×e (-n / 0.0124) +23.87, where e is the natural constant.

3. The ultra-thin surface-limiting layer-assisted upgraded and regenerated cathode material according to claim 1, wherein The particle size distribution and surface residual alkali content of the positive electrode material meet the following requirements: The small particle size D10 (the particle size with a cumulative distribution of 10%) ≥ 0.5 μm; The median particle size D50 (the particle size with a cumulative distribution of 50%) is 1.0 - 2.0 μm; The large particle size D90 (the particle size with a cumulative distribution of 90%) ≤ 3.0 μm; Based on LiOH + Li2CO3, the surface residual alkali content ≤ 0.5 wt%.

4. A method for preparing a cathode material with ultra-thin surface limiting layer-assisted upgraded regeneration as described in any one of claims 1-3, characterized in that, It includes the following steps: (1) Pretreatment: The retired ternary lithium nickel cobalt manganese oxide positive electrode material is subjected to dealumination pretreatment in an alkali solution, then calcined and sieved to obtain the positive electrode powder; (2) Molten salt mixing: The positive electrode powder obtained in step (1), the molten salt containing LiOH and the tungsten source are mixed evenly. Among them: the molar ratio of the positive electrode powder to LiOH in the molten salt is 1:(1.5 - 2.5); the mass ratio of the tungsten source to the positive electrode powder is (0.003 - 0.05):1; (3) Two-stage sintering: The mixture obtained in step (2) is subjected to two-stage sintering in an oxygen atmosphere. Among them, the first-stage sintering is to heat up to 400 - 600 °C at a rate of 3 - 10 °C / min and keep it warm for 2 - 6 hours; the second-stage sintering is to heat up to 700 - 900 °C at a rate of 3 - 10 °C / min and keep it warm for 8 - 16 hours; (4) Post-treatment: The product after sintering in step (3) is cooled, washed to remove the residual molten salt, and dried to obtain the regenerated ternary lithium nickel cobalt manganese oxide positive electrode material.

5. The preparation method of the ultra-thin surface-limiting layer-assisted upgraded and regenerated cathode material according to claim 4, wherein, In step (1), the alkali solution is a 0.5 - 2.0 M KOH solution; The dealumination pretreatment is to immerse the retired ternary lithium nickel cobalt manganese oxide positive electrode material in the alkali solution for 2 - 3 h to remove the aluminum in the material, then take out the remaining solid material and calcine it at 500 - 600 °C for 3 - 8 h; sieving is carried out through a 400-mesh sieve.

6. The preparation method of the ultra-thin surface-limiting layer-assisted upgraded and regenerated cathode material according to claim 4, characterized in that, In step (2), the molten salt containing LiOH contains LiOH and other eutectic components, and the other eutectic components are one or more of NaCl, Na2SO4, KCl, K2SO4; the molar ratio of LiOH to the other eutectic components in the molten salt is 1:(0.1 - 0.5).

7. The preparation method of the ultra-thin surface-limiting layer-assisted upgraded and regenerated cathode material according to claim 4, characterized in that, In step (2), the tungsten source is one or more of tungsten trioxide (WO3), tungstic acid (H2WO4), ammonium tungstate ((NH4)2WO4), ammonium metatungstate ((NH4)6[H2W 12 O 40 ·xH2O), tungsten acetylacetonate (W(C5H7O2)6), tungsten acetate (WO2(CH3COO)2), and ammonium thiotungstate ((NH4)2WS4).

8. The preparation method of the ultra-thin surface-limiting layer-assisted upgraded and regenerated cathode material according to claim 4, wherein, In step (3), the oxygen flow rate is 5 - 20 mL / min.

9. The preparation method of the ultra-thin surface-limiting layer-assisted upgraded and regenerated cathode material according to claim 4, characterized in that In step (4), the washing solvent is deionized water, the water temperature is 15 - 30 °C, the washing time is 8 - 15 min, and the washing is carried out until the pH value of the solution is 6.5 - 7.

5.

10. Application of a cathode material assisted by an ultra-thin surface limiting layer for upgraded regeneration as described in any one of claims 1-3, characterized in that, The application of the material as a positive electrode material for lithium-ion batteries.

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