A single-crystal layered cathode material, its preparation method and application

Abstract

This invention provides a single-crystal layered cathode material, its preparation method, and its application. The preparation method of the single-crystal layered cathode material includes the following steps: S1, ozone oxidation of the cathode precursor to obtain an oxidation product; S2, wet mixing of the oxidation product with a lithium source and heating to obtain a lithiation product; S3, sintering the lithiation product to obtain the single-crystal layered cathode material. The preparation method of the single-crystal layered cathode material provided by this invention, through ozone oxidation and wet mixing, achieves the preservation of the layered structure; it maximally suppresses the generation of Li / Ni mixing, lattice defects, and internal pores, allowing more active materials in the final single-crystal layered cathode material to participate in the electrochemical reaction, thereby achieving a higher discharge specific capacity.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a single-crystal layered cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have become the preferred power source for portable electronics and electric vehicles due to their high energy density and long cycle life. To meet the increasing demand for longer driving ranges, developing cathode materials with higher energy density is crucial. Nickel-based layered oxides (chemical formula LiNi) are a suitable choice. a Co b Mn c O2, abbreviated as NCM or nickel-rich LiTMO2 (where α ≥ 0.8), possesses high theoretical specific capacity and relatively low cost, and is considered one of the most promising cathode materials for next-generation high-energy-density lithium-ion batteries. The electrochemical performance of a material is closely related to its crystal structure and microstructure. An ideal nickel-rich LiTMO2 material should have a complete α-NaFeO2 layered structure (R-3m space group), where transition metal ions form a stable MO6 octahedral framework with oxygen, and lithium ions reside in the lithium layers between the transition metal layers. This structure provides a two-dimensional channel for the rapid extraction / insertion of lithium ions.

[0003] Currently, the mainstream method for large-scale industrial production of nickel-based cathode materials is the high-temperature solid-state sintering method. A typical process involves using a co-precipitation method to prepare a hydroxide precursor (TM(OH)2, such as Ni...) x Co y Mn z (OH)2) is mechanically mixed with a lithium source (such as LiOH·H2O) and then calcined once or multiple times at high temperature (usually above 700℃) and in an oxygen atmosphere. However, this method has the following inherent defects that severely limit the final properties of the material.

[0004] Irreversible destruction and reconstruction of the MO6 framework: During heating, the TM(OH)2 precursor decomposes at around 200℃, causing its original layered MO6 framework to collapse and initially generate rock salt phase (TMO) or spinel phase intermediates. Subsequently, at higher temperatures, these intermediate phases need to react with the lithium source to reconstruct the layered structure. This "destruction-reconstruction" process is thermodynamically discontinuous, easily leading to incomplete reconstruction or the generation of crystal defects such as lattice distortion, dislocations, and porosity.

[0005] Li / Ni cation mixing: due to Ni 2+ (0.69 Å) and Li + The ionic radii of Ni (0.76 Å) are similar, and at high temperatures, some Ni... 2+Lithium ions readily migrate from the transition metal layer to the lithium layer, occupying lithium sites and forming so-called Li / Ni antisite defects. This mixing blocks lithium-ion diffusion channels, increases the diffusion barrier, and leads to decreased kinetic performance and capacity loss. Especially in materials with extremely high nickel content (Ni ≥ 0.9%), more Ni is needed to maintain charge balance. 3+ , but Ni 2+ The existence and migration issues of [the species] are even more prominent.

[0006] Inhomogeneity caused by competing reactions: In solid-state sintering, precursors and lithium salts exist as micron-sized particles, resulting in limited and non-uniform solid-phase contact area. This leads to asynchronous lithiation, precursor decomposition, and oxidation reactions occurring both within and between particles. Some regions may undergo "topological lithiation" and initially form a layered structure, while other regions decompose into a rock salt phase. This competing reaction (lithiation versus decomposition) results in spatial inhomogeneity of chemical composition and phase distribution within the particles. These inactive or low-activity intermediate phase residues ultimately become "dead zones" in the cathode material, reducing effective capacity and initial coulombic efficiency.

[0007] First Irreversible Capacitance Loss: Materials prepared by conventional methods typically exhibit an initial coulombic efficiency (ICE) hovering around 90%, making further improvement difficult. Studies have shown that a significant portion of the irreversible capacity loss occurs in the low-voltage range (e.g., below 3.8V relative to Li / Li). + This is related to the inherently slow lithium-ion diffusion kinetics of the material at low voltages, and this kinetic characteristic stems from structural defects in the material. Currently, there is a lack of effective means to precisely control the structure in the low-voltage region to reduce irreversible capacity. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is that the existing high-temperature solid-state sintering method for preparing cathode materials leads to irreversible destruction and reconstruction of the MO6 framework, Li / Ni cation mixing, non-uniformity caused by competitive reactions, and first irreversible capacity loss, which in turn leads to a decline in electrical performance. In order to overcome the above defects, a single-crystal layered cathode material, its preparation method and application are provided.

[0009] Therefore, the present invention provides the following technical solution: The first aspect of this invention protects a method for preparing a single-crystal layered cathode material, wherein the preparation method includes the following steps: S1, the positive electrode precursor is oxidized with ozone to obtain the oxidation product; S2, the oxidation product is wet-mixed with a lithium source and heated to obtain the lithiation product; S3, the lithiation products are sintered to obtain a single-crystal layered cathode material.

[0010] In this invention, step S1 involves ozone oxidation to remove Ni from the positive electrode precursor. 2+ Oxidized to Ni 3+ Meanwhile, while maintaining its layered MO6 framework, layered hydroxyl oxide TMOOH is obtained; in step S2, in a liquid phase environment, using Li + / H + The exchange mechanism allows lithium ions to be embedded in the interlayer of TMOOH, generating a lithiation product LiTMO2 with a layered structure, while avoiding structural decomposition at high temperatures; step S3 involves sintering the lithiation product, which can eliminate residual trace amounts of unlithiation phase, promote grain growth, and improve the crystal structure, thereby obtaining a final product with optimal electrochemical performance.

[0011] In one alternative embodiment, the nickel content is ≥80wt% based on the metal elements in the positive electrode precursor.

[0012] Optionally, the general chemical formula of the positive electrode precursor is Ni. x Co y Mn z (OH)₂, where 0.8 ≤ x ≤ 0.92, 0.03 ≤ y ≤ 0.12, 0.03 ≤ z ≤ 0.12, x + y + z = 1; as an example, (x, y, z) can be (0.80, 0.10, 0.10), (0.85, 0.08, 0.07), (0.88, 0.06, 0.06), (0.90, 0.05, 0.05), (0.92, 0.04, 0.04), or within any range of the above values; optionally, the general chemical formula for the nickel content in the positive electrode precursor is Ni. x Co y Mn z (OH)2, where 0.85≤x≤0.9, 0.04≤y≤0.06, 0.04≤z≤0.06, x+y+z=1; as an example, (x, y, z) can be (0.90, 0.05, 0.05), (0.88, 0.06, 0.06), (0.89, 0.05, 0.06), or within any of the above values.

[0013] In this invention, the positive electrode precursor undergoes ozone oxidation at room temperature (20-30°C), where the oxidation potential of ozone is higher than that of Ni. 2+ / Ni 3+ The oxidation potential of Ni enables efficient and clean oxidation of Ni. 2+ Oxidized to Ni 3+ At the same time, it decomposes into oxygen without introducing any impurities.

[0014] In one optional embodiment, during ozone oxidation, the flow rate of the oxidizing gas is 1-10 L / min. For example, the flow rate of the oxidizing gas can be 1 L / min, 3 L / min, 5 L / min, 10 L / min, or within any range of the above values; alternatively, it can be 5-8 L / min. For example, the flow rate of the oxidizing gas can be 5 L / min, 6 L / min, 7 L / min, 8 L / min, or within any range of the above values.

[0015] In one optional embodiment, during ozone oxidation, the mass concentration of ozone in the oxidizing gas is 20-60 g / m³. 3 As an example, the mass concentration of ozone in an oxidizing gas can be 20 g / m³. 3 30g / m 3 40g / m 3 50g / m 3 60g / m 3 Or within the range of any of the above values; 40-50 g / m³ is an option. 3 As an example, the mass concentration of ozone in the oxidizing gas can be selected as 40 g / m³. 3 42g / m 3 45g / m 3 48g / m 3 50g / m 3 , or within the range of any of the above values.

[0016] In one optional embodiment, the ozone oxidation time is 4-12 hours. For example, the ozone oxidation time can be 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, or any range of these values. The oxidation time of 4-12 hours ensures that the oxidation depth reaches at least 95% (which can be determined by chemical titration). During the oxidation process, the precursor color changes from its natural color (such as Ni) to its original color. 0.9 Co 0.05 Mn 0.05 The transformation of (OH)2 (from brownish-red) to black signifies the successful formation of TMOOH. The reaction equation is: 2TM(OH)2 + O3 → 2TMOOH + H2O + O2; the time can be selected as 8-10h. As an example, the ozone oxidation time can be 8h, 8.5h, 9h, 9.5h, 10h, or any range of the above values.

[0017] In one optional embodiment, the wet mixing includes the following steps: mixing the oxidation product with a saturated lithium source solution at 25°C; dispersing the oxidation product (generally in powder form) in an excess of saturated lithium source solution to obtain a mixture; transferring the mixture to a hydrothermal reactor and heating it under closed and autogenous pressure. + H replaces the interlayer of TMOOH + The reaction equation is: TMOOH + LiOH → LiTMO2 + H2O. The purpose of using a saturated lithium source solution is twofold: firstly, to provide extremely high Li... + Concentration serves as the driving force for the reaction; secondly, maintaining a strongly alkaline environment (pH≈14) inhibits Ni. 3+ Hydrolysis and Li + / H + Reverse exchange protects the product structure.

[0018] In this invention, the lithium source is a conventional lithium source in the art, typically and non-limitingly including at least one of lithium hydroxide and lithium carbonate.

[0019] In one optional embodiment, the heating conditions include heating to 60-180°C for 1-10 hours; as an example, the heating temperature can be 60°C, 90°C, 120°C, 150°C, 180°C, or any range thereof; the heating time can be 1 hour, 3 hours, 5 hours, 7 hours, 10 hours, or any range thereof. The lithiation step of this invention is transferred from a high-temperature solid phase to a low-temperature liquid phase, resulting in mild reaction conditions that are easy to control precisely. The use of a saturated lithium source solution not only provides a uniform reaction medium but also prevents the hydrolysis of high-nickel materials, and the mother liquor can be recycled, reducing lithium salt waste and conforming to the concept of green chemistry. Furthermore, this method has been successfully applied to LiNiO2 and NCM materials with different nickel contents, demonstrating its great potential as a universal synthesis platform. Optionally, heating to 90-120℃ for 4-8 hours is performed. For example, the heating temperature can be 90℃, 95℃, 100℃, 110℃, 120℃, or any range of the above values. The heating time can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any range of the above values.

[0020] In this invention, after heating, the product is naturally cooled to room temperature (20-30°C), filtered to separate the solid product, and then quickly rinsed with a small amount of saturated lithium source solution (or not rinsed at all, depending on subsequent requirements) to remove surface soluble substances. The saturated lithium source solution can be recycled.

[0021] In one optional embodiment, the sintering conditions include: heating to 500-750°C at a heating rate of 2-10°C / min, and holding for 5-15 hours; as an example, the heating rate can be 2°C / min, 4°C / min, 6°C / min, 8°C / min, 10°C / min, or any range thereof; the sintering temperature can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or any range thereof; the holding time can be 5 hours, 7 hours, 9 hours, 11 hours, 13 hours, 15 hours, or any range thereof; this temperature is lower than the sintering temperature of conventional solid-state methods (typically >750°C), but sufficient. The crystallization process is completed by driving short-range atomic migration without causing excessive primary particle growth or inducing unfavorable phase transitions, and energy consumption is also reduced. Optionally, the temperature is raised to 600-700°C at a heating rate of 5-8°C / min and held for 10-12 hours. As an example, the heating rate can be selected as 5°C / min, 6°C / min, 7°C / min, 8°C / min, or within any range of the above values. The sintering temperature can be selected as 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, or within any range of the above values. The holding time can be selected as 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, or within any range of the above values.

[0022] In this invention, sintering is carried out in an atmosphere furnace, and after the heat preservation is completed, it is naturally cooled to room temperature (20-30℃).

[0023] The second aspect of this invention protects the single-crystal layered cathode material prepared by the aforementioned preparation method, wherein the prepared single-crystal layered cathode material has good crystallinity and a complete layered structure.

[0024] A third aspect of this invention protects a secondary battery, wherein the battery comprises the aforementioned monocrystalline layered cathode material.

[0025] The advantages of the present invention compared to the prior art are as follows: The method for preparing single-crystal layered cathode material provided by this invention achieves the preservation of the layered structure from TM(OH)2 (layered) to TMOOH (layered) to LiTMO2 (layered) through ozone oxidation and wet mixing. In steps S1 and S2, the MO6 octahedral framework remains unchanged, and the phase transformation is completed only through proton de-intercalation and lithium ion intercalation. This reaction mechanism fundamentally avoids the collapse and reconstruction process of the MO6 framework in traditional methods, and suppresses the generation of Li / Ni mixing, lattice defects and internal pores to the greatest extent. This results in good integrity and chemical homogeneity of the layered structure of the final single-crystal layered cathode material, allowing more active materials in the material to participate in the electrochemical reaction, thereby achieving a higher discharge specific capacity (up to 220.5 mAh / g at 0.1C). Meanwhile, due to the more stable material structure, the H2-H3 phase change is smoother and more reversible during cycling, especially under high voltage, and the cell volume change is smaller, which effectively delays the generation of microcracks and particle pulverization. Therefore, the cycling stability is significantly improved (the capacity retention rate can reach 80% after 160 cycles, which is better than the approximately 70% of traditional materials). Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is the XRD pattern of the lithiation product from Example 1. Detailed Implementation

[0028] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having” and any variations thereof in the text of this invention are intended to cover non-exclusive inclusion.

[0030] In the description of the embodiments of the present invention, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This range can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] In the description of the embodiments of the present invention, the term "and / or" is merely a description of the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0034] In the description of the embodiments of the present invention, the term "at least one" refers to one or more (including two).

[0035] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0036] Example 1 This embodiment provides a single-crystal layered cathode material, the preparation method of which includes the following steps: S1, 100 g of Ni 0.9 Co 0.05 Mn 0.05(OH)₂ precursor powder was placed in a fluidized bed reactor, and ozone with a mass concentration of 50 g / m³ was introduced into the reactor at 25°C, using oxygen as the carrier gas. 3 A mixed gas was used, with a flow rate of 5 L / min, and oxidation was continued for 8 hours. After the reaction was completed, the black oxide product Ni was collected. 0.9 Co 0.05 Mn 0.05 The oxidation degree of OOH, determined by chemical titration, was 95.48%. S2, 50g of the oxidation product was dispersed in 500 mL of saturated LiOH solution (5.3 mol / L at 25°C), transferred to a 1L hydrothermal reactor, sealed, and heated to 90°C with a stirring speed of 100 rpm for 10 h. After the reaction, it was naturally cooled to 25°C, the solid product was separated by filtration, rapidly washed with a small amount of saturated LiOH solution, and vacuum dried at 80°C for 12 h to obtain the lithiation product; XRD analysis was performed. Figure 1 It can be seen that the product shows obvious characteristic diffraction peaks of the (003), (101), and (104) crystal planes at 18.8°, 36.5°, and 44.8°. The peaks are sharp and free of impurities, indicating that the LiTMO2 phase with α-NaFeO2 layered structure has been successfully formed and has good crystallization. S3, the lithiation product was placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under an oxygen atmosphere (flow rate 100 mL / min), held at that temperature for 10 h, and then naturally cooled to 25°C to obtain the single-crystal layered cathode material LiNi. 0.9 Co 0.05 Mn 0.05 O2.

[0037] Example 2 This embodiment provides a single-crystal layered cathode material, the preparation method of which includes the following steps: S1, as described in S1 of Example 1; S2, the same as S2 in Example 1, except that after sealing, it is heated to 180°C; S3 is the same as S3 in Example 1, except that it is heated to 700°C at a heating rate of 5°C / min.

[0038] Example 3 This embodiment provides a single-crystal layered cathode material, the preparation method of which includes the following steps: S1, following the method in Example 1, differs in that Ni 0.9 Co 0.05 Mn 0.05 (OH)2 precursor powder was replaced with Ni 0.825 Co0.115 Mn 0.06 (OH)2 precursor powder was used to prepare the oxidation product Ni. 0.825 Co 0.115 Mn 0.06 The oxidation degree of OOH, determined by chemical titration, was 95.32%. S2, the same as S2 in Example 1, except that after sealing, it is heated to 120°C; S3 is the same as S3 in Example 1, except that it is heated to 700°C at a heating rate of 5°C / min.

[0039] Example 4 This embodiment provides a single-crystal layered cathode material, the preparation method of which includes the following steps: S1, following the method in Example 1, differs in that Ni 0.9 Co 0.05 Mn 0.05 The (OH)2 precursor powder was replaced with Ni(OH)2 precursor powder, and the oxidation product was NiOOH. The oxidation depth was determined to be 96.15% by chemical titration. S2, the same as S2 in Example 1, except that after sealing, it is heated to 180°C; S3 is the same as S3 in Example 1, except that it is heated to 700°C at a heating rate of 5°C / min.

[0040] Example 5 This embodiment provides a single-crystal layered cathode material, the preparation method of which includes the following steps: S1, following the method in Example 1, differs in that the oxidation time is 4 hours, yielding the oxidation product Ni. 0.9 Co 0.05 Mn 0.05 The oxidation degree of OOH, determined by chemical titration, was 82.50%. S2, in accordance with the method of S2 in Example 1; S3, in accordance with the method of S3 in Example 1.

[0041] Example 6 This embodiment provides a single-crystal layered cathode material, the preparation method of which includes the following steps: S1, the method is the same as S1 in Example 1, except that oxygen is introduced into the reactor as the carrier gas and ozone mass concentration is 20 g / m³. 3 A mixed gas was used, with a flow rate of 5 L / min, and oxidation was continued for 12 h. After the reaction was completed, the oxidation product Ni was collected. 0.9 Co 0.05 Mn 0.05The oxidation degree of OOH, determined by chemical titration, was 93.50%. S2, in accordance with the method of S2 in Example 1; S3. The lithiation product is placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under an oxygen atmosphere (flow rate of 100 mL / min). The temperature is held for 10 hours and then naturally cooled to 25°C to obtain a single-crystal layered cathode material.

[0042] Comparative Example 1 This comparative example provides a cathode material, the preparation method of which includes the following steps: S1, according to Ni 0.9 Co 0.05 Mn 0.05 The molar ratio of total metal elements in (OH)₂ to the molar ratio of lithium in LiOH·H₂O is 1:1.05. This is used to measure 100 g of Ni... 0.9 Co 0.05 Mn 0.05 (OH)2 precursor and LiOH·H2O powder were mixed in a ball mill at 300 rpm for 4 hours to obtain mixed powder. S2. The mixed powder is placed in a tube furnace and heated to 480°C at a heating rate of 5°C / min under an oxygen atmosphere (oxygen flow rate of 100 mL / min). The temperature is held for 5 hours, then the temperature is increased to 750°C and held for 15 hours. After sintering, the material is naturally cooled to 25°C to obtain the cathode material.

[0043] Comparative Example 2 This comparative example provides a cathode material, the preparation method of which includes the following steps: S1, 100 g of Ni 0.9 Co 0.05 Mn 0.05 (OH)2 precursor powder was dispersed in 500 mL of saturated LiOH solution (5.3 mol / L at 25 °C), transferred to a 1 L hydrothermal reactor, sealed, heated to 90 °C, stirred at 100 rpm, and kept at this temperature for 10 h. After the reaction was completed, the mixture was naturally cooled to 25 °C, filtered to separate the solid product, rapidly washed with a small amount of saturated LiOH solution, and vacuum dried at 80 °C for 12 h to obtain the lithiation product. S2, according to Ni 0.9 Co 0.05 Mn 0.05 The molar ratio of total metal elements in (OH)₂ to the molar ratio of lithium in LiOH·H₂O is 1:1.05. This is used to measure 100 g of Ni... 0.9 Co 0.05 Mn 0.05The (OH)2 precursor and LiOH·H2O powder were mixed in a ball mill and heated to 700℃ at 5℃ / min under an oxygen atmosphere (oxygen flow rate of 100 mL / min) and held for 10 h to obtain the cathode material.

[0044] Comparative Example 3 This comparative example provides a cathode material, the preparation method of which includes the following steps: S1, according to the method of Example 1; S2, according to Ni 0.9 Co 0.05 Mn 0.05 The molar ratio of total metal elements in (OH)₂ to the molar ratio of lithium in LiOH·H₂O is 1:1.05. The oxidation product Ni... 0.9 Co 0.05 Mn 0.05 OOH and LiOH·H2O powders were mixed in a ball mill and heated to 700℃ at a heating rate of 5℃ / min under an oxygen atmosphere (oxygen flow rate of 100 mL / min). The mixture was held at this temperature for 10 h and then naturally cooled to 25℃ after sintering to obtain the cathode material.

[0045] Test case Battery preparation method: The materials obtained in the examples and comparative examples, Super P, and PVDF were mixed at a mass ratio of 92:4:4 to obtain a positive electrode mixture. The positive electrode mixture was then mixed with N-methylpyrrolidone (NMP) to form a slurry, wherein the ratio of the positive electrode mixture to NMP was 2:1 (g / mL). The slurry was coated on aluminum foil with an areal density of 10 mg / cm³. 2 After drying, a positive electrode sheet is prepared. A negative electrode mixture is obtained by mixing graphite, binder (LA133), and carbon nanotubes (CNTs) in a mass ratio of 90:5:5. The negative electrode mixture and NMP are then coated onto copper foil in a ratio of 2:1 (g / mL), resulting in an areal density of 10 mg / cm³. 2 After drying, a negative electrode sheet is prepared; the electrolyte is a 1 mol / L LiPF6 ethylene carbonate (EC) and dimethyl carbonate (DMC) solution, wherein the volume ratio of EC to DMC is 1:1; the positive electrode sheet, separator (PE / PP composite membrane), negative electrode sheet and electrolyte are assembled into a 2025 type button cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm.

[0046] At 25℃, the vehicle was first charged at a constant current rate of 0.1C to 4.3V to obtain the initial charge capacity of 0.1C. Then, it was first discharged at a rate of 0.1C to 2.7V to obtain the initial discharge capacity of 0.1C. The specific discharge capacity of 0.1C was then calculated. Initial coulombic efficiency: 0.1C initial discharge capacity / 0.1C initial charge capacity × 100%; Cycle stability test method: At 25℃, the battery is charged to 4.3V at a constant current of 0.5C and discharged to 2.7V at a constant current of 0.5C, for 160 charge-discharge cycles; the capacity retention rate after the 160th cycle = (0.5C discharge capacity after the 160th cycle / 0.5C discharge capacity after the first cycle) × 100%; The test results are shown in Table 1; Table 1

[0047] A comparison of Example 1 and Comparative Example 1 shows that the present invention first performs ozone oxidation in step S1, followed by wet lithiation in step S2, and then sintering in step S3. This fundamentally avoids the irreversible process of the precursor MO6 octahedral framework collapsing and decomposing before high-temperature reconstruction in the traditional solid-state method, significantly reducing lattice defects. The single-crystal layered cathode material prepared by the method provided by the present invention is significantly superior to the traditional high-temperature solid-state method in terms of 0.1C discharge specific capacity, initial coulombic efficiency, and capacity retention after 160 cycles. This indicates that the present invention can effectively suppress structural defects and Li / Ni mixing, thereby improving the electrochemical performance of the material. A comparison of Example 1 and Comparative Example 2 shows that omitting the ozone oxidation step significantly reduces the specific capacity, initial coulombic efficiency, and cycle stability of the material. This is mainly because, with the ozone oxidation step omitted, the precursor is still predominantly divalent nickel, which cannot maintain its layered topology during lithiation. This leads to decomposition and phase transition competition, resulting in uneven lithiation and an increase in impurities. This demonstrates that precursor pre-oxidation is crucial for stabilizing the layered structure and improving lithiation efficiency. A comparison of Example 1 and Comparative Example 3 shows that direct solid-phase mixing and sintering without wet lithiation leads to a significant decrease in the various properties of the material. This is mainly because the solid-solid contact is limited, the lithium diffusion path is long and uneven, causing asynchronous lithiation and decomposition, resulting in uneven phase and composition distribution and a large amount of low-activity intermediate phase remaining. Liquid-phase homogeneous lithiation can significantly improve reaction uniformity and reduce dead zones and irreversible phases, which is a key step in obtaining high-performance single-crystal cathode materials.

[0048] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a single-crystal layered cathode material, characterized in that, The preparation method includes the following steps: S1, the positive electrode precursor is oxidized with ozone to obtain the oxidation product; S2, the oxidation product is wet-mixed with a lithium source and heated to obtain the lithiation product; S3, the lithiation products are sintered to obtain a single-crystal layered cathode material.

2. The preparation method according to claim 1, characterized in that, The nickel content is ≥80 wt% based on the metal elements in the positive electrode precursor. Optionally, the general chemical formula for the nickel content in the positive electrode precursor is Ni. x Co y Mn z (OH)2, where 0.8≤x≤0.92, 0.03≤y≤0.12, 0.03≤z≤0.12, x+y+z=1; Optionally, the general chemical formula for the nickel content in the positive electrode precursor is Ni. x Co y Mn z (OH)2, where 0.85≤x≤0.9, 0.04≤y≤0.06, 0.04≤z≤0.06, and x+y+z=1.

3. The preparation method according to claim 1, characterized in that, During ozone oxidation, the flow rate of the oxidizing gas is 1-10 L / min; And / or, during ozone oxidation, the mass concentration of ozone in the oxidizing gas is 20-60 g / m³. 3 ; And / or, the ozone oxidation time is 4-12 hours.

4. The preparation method according to claim 3, characterized in that, During ozone oxidation, the flow rate of the oxidizing gas is 5-8 L / min; And / or, during ozone oxidation, the mass concentration of ozone in the oxidizing gas is 40-50 g / m³. 3 ; And / or, the ozone oxidation time is 8-10 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The wet mixing process includes the following steps: mixing the oxidation product with a saturated lithium source solution at 25°C; And / or, the heating conditions include: heating to 60-180°C for 1-10 hours.

6. The preparation method according to claim 5, characterized in that, The heating conditions include heating to 90-120℃ for 4-8 hours.

7. The preparation method according to any one of claims 1-6, characterized in that, The sintering conditions include heating to 500-750℃ at a heating rate of 2-10℃ / min and holding for 5-15 hours.

8. The preparation method according to claim 7, characterized in that, Heat to 600-700℃ at a heating rate of 5-8℃ / min, and hold for 10-12 hours.

9. A single-crystal layered cathode material prepared by the preparation method according to any one of claims 1-8.

10. A secondary battery, characterized in that, The battery comprises the single-crystal layered cathode material as described in claim 9.

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