Preparation method of modified high-nickel positive electrode material

Abstract

The application relates to a preparation method of a modified high-nickel positive electrode material. The preparation method comprises the following steps: dispersing a high-nickel positive electrode material matrix in water, mixing the high-nickel positive electrode material matrix with a first coating agent solution immediately after stirring for a first time, obtaining a reaction solution, carrying out solid-liquid separation immediately after continuing to stir for a second time, and vacuum drying to obtain a high-nickel positive electrode material coated with aluminum hydroxide in situ; mixing the high-nickel positive electrode material coated with aluminum hydroxide in situ with a second coating agent in a solid phase, and sintering to obtain the modified high-nickel positive electrode material; the first coating agent solution is an acidic solution of Al 3+ ; and the second coating agent comprises boric acid. In the application, aluminum hydroxide is formed in situ by Al 3+ hydrolysis to perform the first coating, and boric acid is mixed in a solid phase to perform the second coating, so that an aluminum oxide coating layer and a lithium borate fast ion conductor layer with a fused interface are formed in situ during sintering, and the synchronous improvement of the rate performance, the cycle performance and the safety performance is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to high-nickel cathode materials, and more particularly to a method for preparing a modified high-nickel cathode material. Background Technology

[0002] High-nickel ternary cathode materials have attracted much attention in the field of lithium-ion batteries, especially power batteries, due to their outstanding advantages such as high energy density, long cycle life and relatively low cost.

[0003] However, high-nickel ternary materials still face a series of severe challenges in practical industrialization and application. First, the high surface activity of the material easily leads to the formation of a large amount of impurities such as LiOH and Li2CO3, which not only seriously affects the stability of the slurry preparation and coating process of lithium batteries, but also poses a hidden danger to the long-term cycle safety of the battery. Second, driven by the inherent structural instability of the high-nickel components, the cell volume of the material changes significantly during charging and discharging, resulting in microcracks or even breakage inside the particles, failure of active materials and conductive networks, and thus rapid capacity decay. Most importantly, the active impurities remaining on the surface of high-nickel materials and the fresh interfaces exposed by cracks will continue to catalyze the decomposition of electrolyte, continuously generating gas during cycling, leading to increased internal pressure and swelling of the battery, which may even cause thermal runaway in severe cases.

[0004] CN112186157A discloses a water washing method for high-nickel cathode materials, along with the resulting products and applications. The method involves simultaneously mixing, reacting, and washing the high-nickel cathode material in a phosphate solution at room temperature. At room temperature, the phosphate reacts slowly with lithium hydroxide on the surface of the high-nickel cathode material to form a lithium phosphate precipitate that adheres to the surface. Subsequent sintering forms a lithium phosphate coating layer. This lithium phosphate coating layer exhibits good structural and thermal stability, and during sintering, lithium phosphate can penetrate into the shallower secondary particles, further enhancing the structural and thermal stability of the cathode material. However, the reaction between the phosphate and lithium hydroxide on the surface of the high-nickel cathode material is slow, requiring a prolonged water washing process, which can easily lead to over-washing of the high-nickel cathode material.

[0005] CN108023077A discloses a fast-ion conductor-coated modified high-nickel cathode material and its preparation method. The method involves washing and drying the cathode material to reduce the residual alkali content on its surface, minimizing the impact of residual alkali on electrochemical performance and gas expansion. Subsequently, the washed and dried cathode material is coated with a fast-ion conductor, significantly improving the cycle performance, rate performance, and safety performance of the coated material. However, this method requires washing until the pH of the filtrate reaches 7-10, which can easily lead to excessively long washing times and over-washing of the high-nickel cathode material.

[0006] CN109742347A discloses a high-nickel cathode material with a uniform coating layer and its preparation method. First, the high-nickel cathode material is washed in water. Then, two or more inorganic salt substances (such as aluminum phosphate) that can react with each other to form a water-insoluble coating are slowly added. The mixture is thoroughly stirred, vacuum filtered, washed with a low-boiling-point organic solvent or water, dried under vacuum, and then oven-dried to obtain a material containing the coating layer. This material is then placed in a crucible and sintered in a muffle furnace. A new layered lithium metal oxide structure and lithium phosphate or lithium sulfate structure are formed on the surface of the active cathode material, resulting in better adhesion to the active material and providing a channel for rapid lithium-ion transport. This ensures the surface stability of the material while improving rate performance. Although this technical solution reduces the washing time, it cannot achieve in-situ formation of the coating material on the surface of the high-nickel cathode material substrate, resulting in poor stability of the coating layer.

[0007] In the existing technologies for coating high-nickel cathode materials, liquid phase coating takes a long time (usually 5 to 60 minutes), which affects production efficiency. Furthermore, excessive water washing time can lead to over-washing and damage to the material structure. On the other hand, non-liquid phase coating cannot guarantee the uniformity of coating, which affects the consistency of material performance.

[0008] Therefore, it is of great significance to provide a method that can reduce residual alkali on the surface of high-nickel cathode materials, effectively reduce the washing time of high-nickel cathode materials, and form a stable coating layer on the surface of high-nickel cathode material substrate. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a modified high-nickel cathode material. This invention utilizes Al... 3+ In-situ hydrolysis forms aluminum hydroxide for the first coating, avoiding the problem of high-nickel cathode material being washed with water during wet coating. It is then mixed with boric acid solid phase for the second coating. During sintering, an aluminum oxide coating layer with a fusion interface and a lithium borate fast ion conductor layer are formed in situ, achieving simultaneous improvement in rate performance, cycle performance and safety performance.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing a modified high-nickel cathode material, the method comprising:

[0012] A high-nickel cathode material matrix is ​​dispersed in water and stirred for a first time. Immediately after stirring, it is mixed with a first coating agent solution to obtain a reaction solution. After stirring for a second time, solid-liquid separation is immediately performed, followed by vacuum drying to obtain an in-situ coated high-nickel cathode material with aluminum hydroxide. The in-situ coated high-nickel cathode material with aluminum hydroxide is then mixed with a second coating agent and sintered to obtain the modified high-nickel cathode material. Residual alkali exists on the surface of the high-nickel cathode material matrix, including lithium hydroxide and lithium carbonate. The first coating agent solution is Al. 3+ The solution is an acidic solution; the pH of the first coating agent solution is 2-4; the concentration of the first coating agent in the first coating agent solution is 50g / L-200g / L; the mass ratio of the first coating agent to the high-nickel cathode material matrix in the reaction solution is (0.0025-0.01):1; the second coating agent includes boric acid; the first time is 5s-15s, and the second time is 10s-30s.

[0013] In this invention, the "high-nickel cathode material matrix" comprises the following chemical formula: Li 1+a Ni x Co y A z M j O2, 0≤a≤0.5, 0.8≤x≤0.96, 0≤y≤0.2, 0≤z≤0.2, 0≤j≤0.01, A includes at least one of Mn or Al, and M includes any one or a combination of at least two of Nb, Mg, Y, Ti, W, Al or Zr.

[0014] This invention uses Al 3+ The acidic solution is used as the first coating agent solution. Through a very short time, the high-nickel cathode material is mixed with the first coating agent solution to coat Al... 3+ Adhering to the surface of high-nickel cathode material, Al, in the locally strongly alkaline environment provided by the residual lithium hydroxide on the surface of the high-nickel cathode material, 3+ While hydrolyzing and consuming lithium hydroxide on the surface of the high-nickel cathode material, a uniform aluminum hydroxide coating layer is formed in situ, significantly reducing the residence time of the high-nickel cathode material in water and avoiding damage to the material structure caused by water washing. Further solid-phase mixing and coating with boric acid allows the boric acid to react with the lithium carbonate remaining after the first coating during subsequent sintering, consuming the lithium carbonate to form a lithium borate fast ion conductor layer. At the same time, the aluminum hydroxide formed during the first coating process decomposes in situ to form an aluminum oxide coating layer. A fusion interface is formed between the two coating layers, avoiding the delamination problem caused by the stress generated by the volume expansion and contraction of the material during charging and discharging.

[0015] This invention utilizes Al 3+In-situ hydrolysis consumes lithium hydroxide, while boric acid consumes lithium carbonate. The two complement each other, achieving not only the full consumption of the two residual alkalis, lithium hydroxide and lithium carbonate, but also complementarity of the coating area. During sintering, an alumina coating layer and a lithium borate fast ion conductor layer with a fusion interface are formed in situ, significantly improving the structural stability of the modified high-nickel cathode material and the bonding stability between the coating layer and the high-nickel cathode material. The formed double coating layer effectively isolates the high-nickel cathode material matrix from the electrolyte, suppressing the occurrence of surface side reactions. The lithium borate fast ion conductor layer effectively improves the lithium-ion transport performance at the interface, achieving simultaneous improvement in rate performance, cycle performance, and safety performance.

[0016] Preferably, the first coating agent in the first coating agent solution includes any one or a combination of at least two of aluminum sulfate, aluminum nitrate, or aluminum chloride.

[0017] Preferably, the mass ratio of the high-nickel cathode material matrix to water is (2~2.5):1.

[0018] Preferably, the method for preparing the reaction solution includes: injecting a first coating agent solution into a dispersion slurry obtained by dispersing a high-nickel cathode material matrix in water, wherein the injection time is 25s to 60s.

[0019] Preferably, the temperature of the first coating agent solution is 10°C to 20°C.

[0020] Preferably, the temperature of the reaction solution is 10℃~15℃.

[0021] Preferably, the solid-liquid separation method includes pressure filtration.

[0022] Preferably, the vacuum drying temperature is 150℃~200℃.

[0023] Preferably, the mass of lithium hydroxide on the surface of the high-nickel cathode material substrate is 0.6wt% to 0.8wt% of the mass of the high-nickel cathode material substrate.

[0024] Preferably, the mass of lithium carbonate on the surface of the high-nickel cathode material substrate is 0.4wt% to 0.6wt% of the mass of the high-nickel cathode material substrate.

[0025] Preferably, the mass ratio of boric acid to the high-nickel cathode material with in-situ coated aluminum hydroxide is (0.003~0.01):1.

[0026] Preferably, the sintering temperature is 250℃~300℃.

[0027] Preferably, the sintering time is 3h to 15h.

[0028] Preferably, the sintering atmosphere includes an oxygen-containing atmosphere.

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

[0030] (1) This invention uses Al 3+ The acidic solution is used as the first coating agent solution. Through a very short time, the high-nickel cathode material is mixed with the first coating agent solution to coat Al... 3+ Adhering to the surface of high-nickel cathode material, Al, in the locally strongly alkaline environment provided by the residual lithium hydroxide on the surface of the high-nickel cathode material, 3+ In-situ hydrolysis forms a uniform aluminum hydroxide coating layer, which significantly reduces the residence time of high-nickel cathode materials in water and avoids damage to the material structure caused by rinsing.

[0031] (2) In this invention, boric acid is further coated on the surface of the aluminum hydroxide coating layer. During the subsequent sintering process, the boric acid reacts further with the lithium carbonate that remains after the first coating to form a lithium borate fast ion conductor layer. At the same time, the aluminum hydroxide formed during the first coating process decomposes in situ to form an aluminum oxide coating layer. A fusion interface is formed between the two coating layers, which avoids the problem of delamination caused by the stress generated by the volume expansion and contraction of the material during charging and discharging.

[0032] (3) The preparation method provided by the present invention forms a double coating layer in situ on the surface of the high nickel cathode material substrate, which effectively isolates the contact between the high nickel cathode material substrate and the electrolyte, suppresses the occurrence of surface side reactions, and the lithium borate fast ion conductor layer effectively improves the lithium ion transport performance at the interface, thus achieving simultaneous improvement in rate performance, cycle performance and safety performance. Attached Figure Description

[0033] Figure 1 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Example 1.

[0034] Figure 2 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Example 2.

[0035] Figure 3 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Example 4.

[0036] Figure 4 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Example 10.

[0037] Figure 5 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Comparative Example 3.

[0038] Figure 6 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Comparative Example 5.

[0039] Figure 7 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Comparative Example 6.

[0040] Figure 8 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Comparative Example 7.

[0041] Figure 9 This is the FESEM image of the high-nickel cathode material with in-situ aluminum hydroxide coating in Comparative Example 8. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0043] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0044] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0045] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0046] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0047] In one specific embodiment, the present invention provides a method for preparing a modified high-nickel cathode material, the method comprising:

[0048] A high-nickel cathode material matrix is ​​dispersed in water and stirred for a first time. Immediately after stirring, it is mixed with a first coating agent solution to obtain a reaction solution. After stirring for a second time, solid-liquid separation is immediately performed, followed by vacuum drying to obtain an in-situ coated high-nickel cathode material with aluminum hydroxide. The in-situ coated high-nickel cathode material with aluminum hydroxide is then mixed with a second coating agent and sintered to obtain the modified high-nickel cathode material. Residual alkali exists on the surface of the high-nickel cathode material matrix, including lithium hydroxide and lithium carbonate. The first coating agent solution is Al. 3+ The solution is an acidic solution; the pH of the first coating agent solution is 2-4, for example, it can be 2, 2.5, 3, 3.5 or 4; the concentration of the first coating agent in the first coating agent solution is 50 g / L-200 g / L, for example, it can be 50 g / L, 70 g / L, 90 g / L, 100 g / L, 120 g / L, 140 g / L, 160 g / L, 180 g / L or 200 g / L; in the reaction solution, the mass ratio of the first coating agent to the high-nickel cathode material matrix is ​​(0.0025-0.01):1, for example, it can be 0.0025:1, 0.003:1, 0.0035:1, 0.004:1, 0.0045 The first coating agent is 0.005:1, 0.0055:1, 0.006:1, 0.0065:1, 0.007:1, 0.0075:1, 0.008:1, 0.0085:1, 0.009:1, 0.0095:1, or 0.01:1; the second coating agent includes boric acid; the first time is 5s to 15s, for example, it can be 5s, 6s, 7s, 8s, 9s, 10s, 11s, 12s, 13s, 14s, or 15s; the second time is 10s to 30s, for example, it can be 10s, 12s, 14s, 16s, 18s, 20s, 22s, 24s, 26s, 28s, or 30s.

[0049] This invention uses Al 3+ The acidic solution is used as the first coating agent solution. Through a very short time, the high-nickel cathode material is mixed with the first coating agent solution to coat Al... 3+ Adhering to the surface of high-nickel cathode material, Al, in the locally strongly alkaline environment provided by the residual lithium hydroxide on the surface of the high-nickel cathode material, 3+While hydrolyzing and consuming lithium hydroxide on the surface of the high-nickel cathode material, a uniform aluminum hydroxide coating layer is formed in situ, significantly reducing the residence time of the high-nickel cathode material in water and avoiding damage to the material structure caused by water washing. Further solid-phase mixing and coating with boric acid allows the boric acid to react with the lithium carbonate remaining after the first coating during subsequent sintering, consuming the lithium carbonate to form a lithium borate fast ion conductor layer. At the same time, the aluminum hydroxide formed during the first coating process decomposes in situ to form an aluminum oxide coating layer. A fusion interface is formed between the two coating layers, avoiding the delamination problem caused by the stress generated by the volume expansion and contraction of the material during charging and discharging.

[0050] This invention utilizes Al 3+ In-situ hydrolysis consumes lithium hydroxide, while boric acid consumes lithium carbonate. The two complement each other, achieving not only the full consumption of the two residual alkalis (lithium hydroxide and lithium carbonate) but also complementarity in the coating region. During sintering, an alumina coating layer and a lithium borate fast-ion conductor layer with a fusion interface are formed in situ, significantly improving the structural stability of the modified high-nickel cathode material and the bonding stability between the coating layer and the high-nickel cathode material. Furthermore, the formed double coating layer effectively isolates the high-nickel cathode material matrix from the electrolyte, suppressing the occurrence of surface side reactions. The lithium borate fast-ion conductor layer effectively improves the lithium-ion transport performance at the interface, achieving simultaneous improvement in rate performance, cycle performance, and safety performance.

[0051] In this invention, it is preferable to use an inorganic acid of the same anionic type as the first coating agent to adjust the pH. For example, sulfuric acid, nitric acid or hydrochloric acid can be used to adjust the pH to the target range.

[0052] In some embodiments, the first coating agent in the first coating agent solution includes any one or a combination of at least two of aluminum sulfate, aluminum nitrate, or aluminum chloride.

[0053] In some embodiments, the mass ratio of the high-nickel cathode material matrix to water is (2~2.5):1, for example, it can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1 or 2.5:1.

[0054] In some embodiments, the preparation of the reaction solution includes: injecting a first coating agent solution into a dispersion slurry obtained by dispersing a high-nickel cathode material matrix in water, wherein the injection time is 25s to 60s, for example, 25s, 30s, 35s, 40s, 45s, 50s, 55s, or 60s. By using the feeding method of injecting the first coating agent solution into the dispersion slurry, and by controlling the injection time, it avoids excessively high concentrations of coating solution coming into contact with the high-nickel cathode material matrix for a short time, thus preventing localized Al2O3 formation. 3+ Rapid hydrolysis can affect the uniformity of the coating layer.

[0055] In some embodiments, the temperature of the first coating agent solution is 10°C to 20°C, for example, it can be 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C or 20°C.

[0056] In some embodiments, the temperature of the reaction solution is 10°C to 15°C, for example, 10°C, 11°C, 12°C, 13°C, 14°C or 15°C.

[0057] In some embodiments, the solid-liquid separation method includes pressure filtration.

[0058] In some embodiments, the vacuum drying temperature is 150°C to 200°C, for example, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C.

[0059] In some embodiments, the mass of lithium hydroxide on the surface of the high-nickel cathode material substrate is 0.6wt% to 0.8wt% of the mass of the high-nickel cathode material substrate, for example, it can be 0.6wt%, 0.62wt%, 0.64wt%, 0.68wt%, 0.7wt%, 0.72wt%, 0.74wt%, 0.76wt%, 0.78wt%, or 0.8wt%.

[0060] In some embodiments, the mass of lithium carbonate on the surface of the high-nickel cathode material substrate is 0.4wt% to 0.6wt% of the mass of the high-nickel cathode material substrate, for example, it can be 0.4wt%, 0.42wt%, 0.44wt%, 0.46wt%, 0.48wt%, 0.5wt%, 0.52wt%, 0.54wt%, 0.56wt%, 0.58wt%, or 0.6wt%.

[0061] In this invention, by testing the content of lithium hydroxide and lithium carbonate on the surface of high-nickel cathode materials, high-nickel cathode materials with specific lithium hydroxide or lithium carbonate content are selected as the high-nickel cathode material matrix in this invention. High-nickel cathode materials with the above-mentioned lithium hydroxide and lithium carbonate content can effectively convert lithium hydroxide and lithium carbonate to generate the target coating layer, and will not cause the electrochemical performance and safety performance of high-nickel cathode materials to deteriorate due to excessive residual alkali.

[0062] In some embodiments, the mass ratio of boric acid to the in-situ coated aluminum hydroxide high-nickel cathode material is (0.003~0.01):1, for example, it can be 0.003:1, 0.004:1, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1 or 0.01:1.

[0063] In some embodiments, the sintering temperature is 250°C to 300°C, for example, 250°C, 260°C, 270°C, 280°C, 290°C or 300°C.

[0064] In some embodiments, the sintering time is 3h to 15h, for example, it can be 3h, 5h, 7h, 9h, 11h, 13h or 15h.

[0065] In some embodiments, the sintering atmosphere includes an oxygen-containing atmosphere, which includes air and / or oxygen.

[0066] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0067] To clearly illustrate the technical solution of the present invention, in all the following embodiments and comparative examples, Li was selected with an initial lithium carbonate content of 0.58 wt% and a lithium hydroxide content of 0.74 wt%. 1.05 Ni 0.85 Co 0.15 O2 is used as the matrix for high-nickel cathode materials.

[0068] The testing methods used for the lithium carbonate and lithium hydroxide content on the surface of the high-nickel cathode material matrix and the prepared modified high-nickel cathode material include:

[0069] The material was dispersed in water, stirred thoroughly, and allowed to stand. The filtrate was divided into two portions. One portion was treated with excess mannitol to mask borate ions, and the other portion was treated with excess mannitol and barium chloride to mask borate and carbonate ions. The treated filtrates were titrated with hydrochloric acid, and the content of LiOH and Li2CO3 on the surface of the material was calculated.

[0070] The above description is only for clearly illustrating the technical solution of the present invention and should not be regarded as a further limitation of the present invention.

[0071] Example 1

[0072] This embodiment provides a method for preparing a modified high-nickel cathode material, the method comprising:

[0073] (1) Sulfuric acid and aluminum sulfate were dissolved in water to prepare a first coating agent solution with an aluminum sulfate concentration of 100 g / L, a pH of 3.2, and a temperature of 15 °C;

[0074] (2) According to Li 1.05 Ni 0.85 Co 0.15The mass ratio of O2 matrix to water is 2.2:1. Li 1.05 Ni 0.85 Co 0.15 O2 matrix was dispersed in water and stirred for 10 seconds to obtain a dispersion slurry. Immediately afterward, the first coating agent solution was injected into the dispersion slurry over a period of 30 seconds, resulting in a reaction solution at 12°C. The reaction solution was stirred for another 20 seconds, and then immediately separated into solid and liquid phases by pressure filtration. The solid was then vacuum-dried at 160°C to obtain Li-coated aluminum hydroxide in situ. 1.05 Ni 0.85 Co 0.15 O2; In the reaction solution, aluminum sulfate and Li 1.05 Ni 0.85 Co 0.15 The mass ratio of the O2 matrix is ​​0.006:1;

[0075] (3) According to the Li of boric acid and in-situ coated aluminum hydroxide 1.05 Ni 0.85 Co 0.15 The mass ratio of O2 is 0.0043:1, and the solid phase is mixed with the in-situ coated aluminum hydroxide Li 1.05 Ni 0.85 Co 0.15 O2 and boric acid are sintered at 280°C for 7 hours in an oxygen atmosphere to obtain the modified high-nickel cathode material.

[0076] Example 2

[0077] This embodiment provides a method for preparing a modified high-nickel cathode material, the method comprising:

[0078] (1) Sulfuric acid and aluminum sulfate were dissolved in water to prepare a first coating agent solution with an aluminum sulfate concentration of 200 g / L, a pH of 2, and a temperature of 10 °C.

[0079] (2) According to Li 1.05 Ni 0.85 Co 0.15 The mass ratio of O2 matrix to water is 2:1, and Li 1.05 Ni 0.85 Co 0.15 O2 matrix was dispersed in water and stirred for 5 seconds to obtain a dispersion slurry. Immediately afterward, the first coating agent solution was injected into the dispersion slurry over a period of 60 seconds, resulting in a reaction solution at 10°C. The reaction solution was stirred for another 10 seconds, and then immediately separated into solid and liquid phases by pressure filtration. The solid was then vacuum-dried at 200°C to obtain Li-coated aluminum hydroxide in situ. 1.05 Ni 0.85 Co 0.15 O2; In the reaction solution, aluminum sulfate and Li 1.05Ni 0.85 Co 0.15 The mass ratio of the O2 matrix is ​​0.01:1;

[0080] (3) According to the Li of boric acid and in-situ coated aluminum hydroxide 1.05 Ni 0.85 Co 0.15 The mass ratio of O2 is 0.0043:1, and the solid phase is mixed with the in-situ coated aluminum hydroxide Li 1.05 Ni 0.85 Co 0.15 O2 and boric acid are sintered at 250°C for 15 hours in an oxygen atmosphere to obtain the modified high-nickel cathode material.

[0081] Example 3

[0082] This embodiment provides a method for preparing a modified high-nickel cathode material, the method comprising:

[0083] (1) Nitric acid and aluminum nitrate were dissolved in water to prepare a first coating agent solution with an aluminum nitrate concentration of 50 g / L, a pH of 4, and a temperature of 20 °C.

[0084] (2) According to Li 1.05 Ni 0.85 Co 0.15 The mass ratio of O2 matrix to water is 2.5:1. Li 1.05 Ni 0.85 Co 0.15 O2 matrix was dispersed in water and stirred for 15 seconds to obtain a dispersion slurry. Immediately afterward, the first coating agent solution was injected into the dispersion slurry over a period of 25 seconds, resulting in a reaction solution at 15°C. The reaction solution was stirred for another 30 seconds, and then immediately separated into solid and liquid phases by pressure filtration. The solid was then vacuum-dried at 150°C to obtain Li-coated aluminum hydroxide in situ. 1.05 Ni 0.85 Co 0.15 O2; In the reaction solution, aluminum nitrate reacts with Li 1.05 Ni 0.85 Co 0.15 The mass ratio of the O2 matrix is ​​0.0025:1;

[0085] (3) According to the Li of boric acid and in-situ coated aluminum hydroxide 1.05 Ni 0.85 Co 0.15 The mass ratio of O2 is 0.003:1, and the solid phase is mixed with the in-situ coated aluminum hydroxide Li 1.05 Ni 0.85 Co 0.15 O2 and boric acid are sintered at 300°C for 3 hours in an oxygen atmosphere to obtain the modified high-nickel cathode material.

[0086] Example 4

[0087] This embodiment provides a method for preparing a modified high-nickel cathode material, wherein the preparation method, except for step (3) involving boric acid and in-situ coated aluminum hydroxide Li 1.05 Ni 0.85 Co 0.15 Except for the O2 mass ratio of 0.01:1, everything else is the same as in Example 1.

[0088] Example 5

[0089] This embodiment provides a method for preparing a modified high-nickel cathode material. The preparation method is the same as in Example 1, except that aluminum sulfate is replaced with aluminum nitrate in step (1).

[0090] Example 6

[0091] This embodiment provides a method for preparing a modified high-nickel cathode material, wherein the preparation method, except for step (3) involving boric acid and in-situ coated aluminum hydroxide Li 1.05 Ni 0.85 Co 0.15 Except for the O2 mass ratio of 0.0025:1, everything else is the same as in Example 1.

[0092] Example 7

[0093] This embodiment provides a method for preparing a modified high-nickel cathode material, wherein the preparation method, except for step (3) involving boric acid and in-situ coated aluminum hydroxide Li 1.05 Ni 0.85 Co 0.15 Except for the O2 mass ratio of 0.015:1, everything else is the same as in Example 1.

[0094] Example 8

[0095] This embodiment provides a method for preparing a modified high-nickel cathode material. Except for the sintering temperature of 200°C in step (3), the preparation method is the same as that in Example 1.

[0096] Example 9

[0097] This embodiment provides a method for preparing a modified high-nickel cathode material. Except for the sintering temperature of 400°C in step (3), the preparation method is the same as in Example 1.

[0098] Example 10

[0099] This embodiment provides a method for preparing a modified high-nickel cathode material. Except for step (2), in which the first coating liquid is rapidly injected into the dispersion slurry within 3 seconds, the preparation method is the same as in Example 1.

[0100] Comparative Example 1

[0101] This comparative example provides a method for preparing a modified high-nickel cathode material. The preparation method is the same as in Example 1, except that a dispersion of aluminum hydroxide of equal concentration is used to replace the first coating agent solution.

[0102] Comparative Example 2

[0103] This comparative example provides a method for preparing a modified high-nickel cathode material. The method, except that step (3) does not involve the addition of boric acid, only involves the in-situ coating of Li with aluminum hydroxide. 1.05 Ni 0.85 Co 0.15 Except for the use of O2 for sintering, everything else is the same as in Example 1.

[0104] Comparative Example 3

[0105] This comparative example provides a method for preparing a modified high-nickel cathode material, wherein the preparation method, except for step (2), first uses Li to disperse Li 1.05 Ni 0.85 Co 0.15 The O2 matrix water is mixed with the first coating agent solution to obtain a mixed solution, and then Li is added. 1.05 Ni 0.85 Co 0.15 Except for the addition of the O2 matrix to the above mixed solution and stirring for 30 seconds, everything else was the same as in Example 1.

[0106] Comparative Example 4

[0107] This comparative example provides a method for preparing a modified high-nickel cathode material. Except for step (2), in which the stirring time is adjusted from 30s to 10min after injecting the first coating agent solution into the dispersion slurry, the preparation method is the same as in Example 1.

[0108] Comparative Example 5

[0109] This comparative example provides a method for preparing a modified high-nickel cathode material, wherein the preparation method, except for step (2) involving aluminum sulfate and Li... 1.05 Ni 0.85 Co 0.15 Except for the O2 matrix mass ratio of 0.002:1, everything else is the same as in Example 1.

[0110] Comparative Example 6

[0111] This comparative example provides a method for preparing a modified high-nickel cathode material, wherein the preparation method, except for step (2) involving aluminum sulfate and Li... 1.05 Ni 0.85 Co 0.15Except for the O2 matrix mass ratio of 0.015:1, everything else is the same as in Example 1.

[0112] Comparative Example 7

[0113] This comparative example provides a method for preparing a modified high-nickel cathode material. Except for the pH of the first coating solution in step (1) being 1.5, the preparation method is the same as in Example 1.

[0114] Comparative Example 8

[0115] This comparative example provides a method for preparing a modified high-nickel cathode material. Except for the pH of the first coating solution in step (1) being 4.5, the preparation method is the same as in Example 1.

[0116] Performance testing:

[0117] 1. Residual alkali content test:

[0118] The LiOH and Li2CO3 content on the surface of the modified high-nickel cathode material in all the above examples and comparative examples was tested, and the test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] 2. Field Emission Scanning Electron Microscopy (FESEM): The modified high-nickel cathode materials prepared in Examples 1, 2, 4, 10, Comparative Example 3, and Comparative Examples 5 to 8 were subjected to FESEM testing. The test results are shown in [Figure number missing]. Figures 1 to 9 .

[0122] 3. Electrical performance testing:

[0123] The modified high-nickel cathode material provided in all the above embodiments and comparative examples was uniformly dispersed in N-methylpyrrolidone with conductive carbon black and polyvinylidene fluoride at a mass ratio of 94:3:3. After being mixed evenly, it was coated on aluminum foil, dried, pressed, and sliced ​​to obtain the cathode sheet.

[0124] Assembled button cell: with lithium metal sheet as negative electrode, polyethylene (PE) microporous membrane as separator, and 1 mol / L LiPF6 EC / DMC (volume ratio 1:1) solution as electrolyte.

[0125] Assemble the soft-pack battery: Graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are uniformly dispersed in water at a mass ratio of 94:3:2:1. After being mixed evenly, the mixture is coated onto aluminum foil, dried, pressed, and sliced ​​to obtain the negative electrode sheet. The positive electrode sheet is matched with the graphite negative electrode sheet, the separator is a polyethylene (PE) microporous separator, and the electrolyte is a 1 mol / L LiPF6 EC / DMC (volume ratio of 1:1) solution to assemble the soft-pack battery.

[0126] At 25℃ and within a voltage range of 2.5V to 4.25V, the coin cell was charged and discharged at a rate of 0.2C to test the initial discharge specific capacity and initial efficiency. Then, it was charged and discharged at a rate of 1C to test the 1C rate capacity retention rate. The 1C rate capacity retention rate = 1C discharge specific capacity / 0.2C discharge specific capacity × 100%.

[0127] The coin cell battery was charged and discharged at a rate of 0.5C and 1C within a voltage range of 3.0V to 4.5V at 25℃ for 50 cycles to test the cycle capacity retention rate.

[0128] At 45℃, within a voltage range of 2.75V to 4.5V, the soft-pack battery was charged at a rate of 0.5C and discharged at a rate of 1C for 600 cycles. The gas production was then tested using the following method:

[0129] The volume of the battery before cycling (V0, in mL) and the volume of the battery after cycling (V1, in mL) were measured using the water displacement method. The gas production rate was calculated as (V1 - V0) / C, where C is the initial discharge capacity of the battery (Ah).

[0130] The test results are shown in Table 2.

[0131] Table 2

[0132]

[0133] In summary, based on the test results of Examples 1 to 5, the present invention, through Al... 3+ In-situ hydrolysis forms aluminum hydroxide for the first coating, avoiding the problem of high-nickel cathode material being washed with water during wet coating. It is then mixed with boric acid solid phase for the second coating. During sintering, an aluminum oxide coating layer with a fusion interface and a lithium borate fast ion conductor layer are formed in situ, achieving simultaneous improvement in rate performance, cycle performance and safety performance.

[0134] like Figures 1 to 3 As shown, the aluminum hydroxide-coated Li obtained after the first coating in Examples 1 to 3 1.05 Ni 0.85 Co 0.15The FESEM image of O2 shows a light-colored, semi-transparent coating on the particle surface, which is an aluminum hydroxide coating. The image also shows that as the concentration of the coating agent in the first coating agent solution increases, the reaction between the first coating agent and Li in the reaction solution... 1.05 Ni 0.85 Co 0.15 The increased mass ratio of the O2 matrix leads to coating of Li 1.05 Ni 0.85 Co 0.15 The increased aluminum hydroxide content on the O2 matrix surface leads to an increase in Li 1.05 Ni 0.85 Co 0.15 The aluminum hydroxide layer on the surface of the O2 substrate gradually thickens. In Example 3, the content of the light-colored, semi-transparent aluminum hydroxide coating layer on the material surface decreases significantly, indicating that the thickness of the coating layer is significantly reduced. However, the coating layer on the surface of the material prepared in Examples 1 to 3 is uniform and there are no agglomerated particles.

[0135] Based on the test results of Examples 1 and 6 to 7, if boric acid reacts with Li coated with aluminum hydroxide in situ... 1.05 Ni 0.85 Co 0.15 If the mass ratio of O2 is too small, boric acid cannot coat the Li in situ of aluminum hydroxide. 1.05 Ni 0.85 Co 0.15 O2 forms a complete coating layer on the surface, preventing the formation of a complete lithium borate fast-ion conductor layer, resulting in unsatisfactory rate performance improvement; while boric acid and in-situ coated aluminum hydroxide Li 1.05 Ni 0.85 Co 0.15 An excessively high O2 mass ratio will cause boric acid to coat the Li in situ with aluminum hydroxide. 1.05 Ni 0.85 Co 0.15 Local aggregation of O2 on the surface leads to excessively thick local coating, increased impedance, and a greater likelihood of side reactions, resulting in decreased cycle performance and safety performance. These side reactions also increase gas production.

[0136] According to the test results of Examples 1, 8, and 9, if the sintering temperature is too low, aluminum hydroxide cannot be fully decomposed to form an alumina coating layer, and boric acid cannot fully consume the residual lithium carbonate to form a lithium borate fast ion conductor layer; if the sintering temperature is too high, boric acid will be lost, and a lithium borate fast ion conductor layer cannot be formed, resulting in a decrease in the performance of the modified high-nickel cathode material.

[0137] Based on the test results of Examples 1 and 10, if the first coating agent solution is rapidly poured into the dispersion slurry instead of being slowly injected over a specific time period, it will cause Li 1.05 Ni 0.85Co 0.15 Local areas of Al on the surface of O2 matrix 3+ The concentration increases sharply and hydrolysis occurs rapidly, such as Figure 4 As shown, the aluminum hydroxide formed by hydrolysis in Li 1.05 Ni 0.85 Co 0.15 Severe aggregation occurred on the surface of the O2 matrix.

[0138] Based on the test results of Example 1 and Comparative Example 1, if aluminum hydroxide is used as the first coating agent, short-term mixing cannot achieve the desired effect in Li. 1.05 Ni 0.85 Co 0.15 A complete coating layer is formed on the surface of the O2 substrate, but the coating effect is poor, resulting in unsatisfactory improvement in electrical performance.

[0139] Based on the test results of Example 1 and Comparative Example 2, if only in Li 1.05 Ni 0.85 Co 0.15 The surface of the O2 substrate is coated with aluminum hydroxide in situ without boric acid. In other words, the surface of the modified high-nickel cathode material only includes an aluminum oxide coating layer and does not include a lithium borate fast ion conductor layer. Therefore, it cannot effectively improve the rate performance of the modified high-nickel cathode material and cannot synergistically improve cycle stability with the aluminum oxide coating layer.

[0140] Based on the test results of Example 1 and Comparative Example 3, if Li is not pre-treated... 1.05 Ni 0.85 Co 0.15 The O2 matrix is ​​dispersed in water to obtain a dispersion slurry, and Li is then added. 1.05 Ni 0.85 Co 0.15 If the O2 matrix surface is fully wetted, it will be detrimental to the Al content in the first coating agent solution. 3+ In Li 1.05 Ni 0.85 Co 0.15 O2 adheres uniformly to the surface of the substrate and hydrolyzes in situ to form an aluminum hydroxide coating layer, such as Figure 5 As shown, Li 1.05 Ni 0.85 Co 0.15 The severe agglomeration of aluminum hydroxide on the surface of the O2 matrix leads to the inability to obtain a uniform aluminum oxide coating layer on the surface of the modified high-nickel cathode material, resulting in poor performance in improving structural stability and suppressing side reactions.

[0141] Based on the test results of Example 1 and Comparative Example 4, if the second stirring time is too long, it will lead to over-washing, Li 1.05 Ni 0.85 Co 0.15 The structure of O2 is disrupted, resulting in impurity phases, which leads to a decrease in the electrochemical performance of the modified high-nickel cathode material.

[0142] Based on the test results of Example 1 and Comparative Examples 5 to 6, if aluminum sulfate and Li 1.05 Ni 0.85 Co 0.15 If the mass ratio of the O2 matrix is ​​too small, Li will adhere to the reaction solution. 1.05 Ni 0.85 Co 0.15 Al on the surface of O2 matrix 3+ If the amount is too small, it cannot hydrolyze to form a complete aluminum hydroxide coating layer, resulting in poor coating integrity. Figure 6 As shown, some areas on the particle surface lack an aluminum hydroxide coating layer, thus failing to effectively strengthen Li. 1.05 Ni 0.85 Co 0.15 The structure of the O2 matrix cannot effectively isolate the electrolyte; if aluminum sulfate and Li 1.05 Ni 0.85 Co 0.15 An excessively high O2 matrix mass ratio will lead to excessive accumulation of aluminum hydroxide in some areas, such as... Figure 7 As shown, the island-like or dot-like concentrated distribution is not conducive to improving the interaction with Li. 1.05 Ni 0.85 Co 0.15 The bonding strength and stability between the O2 matrix and the subsequently formed lithium borate fast ion conductor layer. Therefore, aluminum sulfate and Li 1.05 Ni 0.85 Co 0.15 Both excessively high and low O2 matrix mass ratios can lead to deterioration of the electrical performance of modified high-nickel cathode materials.

[0143] Based on the test results of Example 1, Comparative Examples 7 and 8, optimizing the pH of the first coating agent solution is more beneficial for Al. 3+ Encapsulated in Li 1.05 Ni 0.85 Co 0.15 On the surface of the O2 matrix, in-situ hydrolysis forms a complete and dense aluminum hydroxide coating layer. A pH that is too low will be detrimental to Al... 3+ Hydrolysis, such as Figure 8 As shown, Li 1.05 Ni 0.85 Co 0.15 The coating layer on the surface of the O2 matrix is ​​relatively thin, and the pH is too high, Al 3+ Premature hydrolysis will result in the coating layer containing not only the aluminum hydroxide formed by in-situ hydrolysis, but also pre-hydrolyzed aluminum hydroxide particles, such as... Figure 9 As shown, Li 1.05 Ni 0.85 Co 0.15The unevenness of the coating layer on the O2 substrate surface deteriorates, affecting the interaction between the aluminum hydroxide coating layer and Li. 1.05 Ni 0.85 Co 0.15 The binding force between O2 matrices is reduced, which in turn leads to a decrease in cycle stability.

[0144] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a modified high-nickel cathode material, characterized in that, The preparation method includes: A high-nickel cathode material matrix is ​​dispersed in water and stirred for a first time. Then, it is immediately mixed with a first coating agent solution to obtain a reaction solution. After stirring for a second time, solid-liquid separation is immediately performed, followed by vacuum drying to obtain an in-situ coated aluminum hydroxide high-nickel cathode material. The in-situ coated aluminum hydroxide high-nickel cathode material is then mixed with a second coating agent in a solid phase and sintered to obtain the modified high-nickel cathode material. The high-nickel cathode material substrate has residual alkali on its surface, and the residual alkali includes lithium hydroxide and lithium carbonate. The first coating agent solution is Al 3+ An acidic solution; the pH of the first coating agent solution is 2-4; In the first coating agent solution, the concentration of the first coating agent is 50 g / L to 200 g / L; In the reaction solution, the mass ratio of the first coating agent to the high-nickel cathode material matrix is ​​(0.0025~0.01):1; The second coating agent includes boric acid; The first time is 5s~15s, and the second time is 10s~30s.

2. The preparation method according to claim 1, characterized in that, The first coating agent in the first coating agent solution includes any one or a combination of at least two of aluminum sulfate, aluminum nitrate, or aluminum chloride.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the high-nickel cathode material matrix to water is (2~2.5):

1.

4. The preparation method according to claim 1, characterized in that, The method for preparing the reaction solution includes: The first coating agent solution is injected into a dispersion slurry obtained by dispersing a high-nickel cathode material matrix in water, and the injection time is 25s~60s.

5. The preparation method according to claim 1, characterized in that, The temperature of the first coating agent solution is 10℃~20℃.

6. The preparation method according to claim 1, characterized in that, The temperature of the reaction solution is 10℃~15℃.

7. The preparation method according to claim 1, characterized in that, The solid-liquid separation method includes pressure filtration; And / or, the temperature of the vacuum drying is 150℃~200℃.

8. The preparation method according to claim 1, characterized in that, The mass of lithium hydroxide on the surface of the high-nickel cathode material substrate is 0.6wt%~0.8wt% of the mass of the high-nickel cathode material substrate; And / or, the mass of lithium carbonate on the surface of the high-nickel cathode material substrate is 0.4wt% to 0.6wt% of the mass of the high-nickel cathode material substrate.

9. The preparation method according to claim 1, characterized in that, The mass ratio of boric acid to the high-nickel cathode material with in-situ coated aluminum hydroxide is (0.003~0.01):

1.

10. The preparation method according to claim 1, characterized in that, The sintering temperature is 250℃~300℃; And / or, the sintering time is 3h~15h; And / or, the sintering atmosphere includes an oxygen-containing atmosphere.

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