Nickel cobalt lithium manganate single-crystal positive electrode material and preparation method and application thereof

Abstract

The invention provides a nickel cobalt lithium manganate single-crystal positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: mixing a nickel-cobalt-manganese precursor, a lithium salt and a primary sintering modifier, and then performing primary sintering in a mixed atmosphere to obtain a primary sintering material; the mixed atmosphere comprises oxygen-containing gas and doping gas, and the doping gas comprises CO2 and / or water vapor; and mixing the primary sintering material and a secondary sintering modifier in oxygen-containing gas for secondary sintering, and mixing the primary sintering material and a tertiary sintering modifier in oxygen-containing gas for tertiary sintering to obtain the nickel cobalt lithium manganate single crystal positive electrode material. According to the invention, CO2 and / or water vapor are / is introduced into the atmosphere of the first sintering as doping gas to improve residual alkali of the first sintering material, controllable free lithium is formed on the surface of the material, and the controllable free lithium reacts with the second sintering modifier to form an ultrathin embedded fast ion conductor, so that the effects of reducing the DCR of the material and improving the power performance of a battery cell are achieved, the production cost can be greatly reduced, and the production efficiency is improved. The method is suitable for industrial production of the ternary positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and more particularly, to a single-crystalline lithium nickel cobalt manganese oxide cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing demand for renewable clean energy, lithium-ion batteries (LIBs) have become increasingly important in the fields of electronic devices, mobile communication tools, and large-scale energy storage systems. Excellent properties such as high energy density, high safety, long life, and low cost are crucial for lithium-ion batteries. As the core component of lithium-ion batteries, the cathode material plays a key role in determining the battery cost, safety performance, and electrochemical performance. Among many cathode materials, the nickel-rich cathode material LiNi x Co y Mn (1-x-y) O2 (NCM, 0.5 < x < 1) has received extensive attention due to its energy density advantage and moderate cost.

[0003] However, on the premise of the increasing performance requirements of the cathode material, the cost advantage has also been increasingly emphasized. For ternary cathode materials, it is necessary to reduce costs from aspects such as raw materials, processing technology, and production processes on the premise of meeting performance. Reducing the cobalt content of the precursor in raw materials has become a commonly used means to reduce costs, but it also brings a series of problems, such as poor power performance and rate performance. In the prior art, the rate performance and power performance can also be improved by using the method of generating a fast ion conductor coating layer through the solid-phase reaction of surface residual alkali and additives. However, due to the relatively high sintering temperature of single-crystalline ternary materials, the content of residual alkali (including LiOH and Li2CO3) is generally low, resulting in the inability to generate a uniform fast ion conductor coating layer after coating with additives. To solve this problem, the prior art further adopts the method of additional lithium supplementation and reaction with additives to improve the rate performance of the material and reduce DCR, but the cost is still relatively high. Summary of the Invention

[0004] The main purpose of the present invention is to provide a single-crystalline lithium nickel cobalt manganese oxide cathode material, a preparation method thereof, and an application thereof, so as to solve the problem that ternary cathode materials in the prior art cannot balance low cost and high electrochemical performance.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a preparation method of a single-crystalline lithium nickel cobalt manganese oxide cathode material, and the chemical formula of the single-crystalline lithium nickel cobalt manganese oxide cathode material is LiNi a Co b Mn (1-a-b-c) G cO2, where 0.5≤a≤0.95, 0.02≤b≤0.3, 0.00001≤c≤0.01, G is a modifying element, which includes one or more of Na, Mg, Ca, Al, Zr, W, Sr, Ti, B, Co, Nb, La, V, Y, Mo, and Ce; the preparation method includes the following steps: Step S1, mixing the nickel-cobalt-manganese precursor, lithium salt, and a sintering modifier, and then performing a first sintering in a mixed atmosphere to obtain a sintered material; mixed atmosphere The atmosphere includes oxygen and dopant gas, the dopant gas including CO2 and / or water vapor; step S2, the first sintering material is mixed with the second sintering modifier, and then a second sintering is performed in the oxygen-containing atmosphere to obtain the second sintering material; step S3, the second sintering material is mixed with the third sintering modifier, and then a third sintering is performed in the oxygen-containing atmosphere to obtain lithium nickel cobalt manganese oxide single crystal cathode material; wherein, the first sintering modifier, the second sintering modifier and the third sintering modifier each independently include a compound of modifying element; and the temperature of the second sintering is greater than the temperature of the third sintering.

[0006] By applying the technical solution of this invention, CO2 and / or water vapor are introduced as dopant gases into the atmosphere of the first sintering stage to increase the residual alkali content of the first-sintered material. Furthermore, by controlling the volume ratio of the dopant gas to O2, controllable free lithium is formed on the material surface, which reacts with the second-sintering modifier to form an ultrathin intercalated fast-ion conductor. This reduces the material's DC resistance (DCR) and improves the cell's power performance. The method of controllably introducing CO2 and / or water vapor to increase residual alkali during the first sintering stage significantly reduces production costs, offering advantages such as low energy consumption, safe and reliable production processes, and low production costs. Moreover, the implementation method is simple and controllable, with high production repeatability, making it suitable for the industrial production of ternary cathode materials.

[0007] Furthermore, the volume percentage of the doped gas in the mixed atmosphere is denoted as A, where 0.1% ≤ A ≤ 5%; and / or the oxygen volume content of the oxygen-containing material is 70% to 99.99%, which can effectively improve the residual alkali level of the primary calcined material, form free lithium, provide the necessary lithium for the subsequent secondary calcination modifier reaction, and react with the coating agent to form an ultra-thin intercalated fast ion conductor, significantly reducing the DC internal resistance of the material and improving the power performance of the cell.

[0008] Furthermore, the first sintering process includes a sequential heating section, an isothermal section, and a cooling section, followed by natural cooling to room temperature. The heating section has a heating rate of 2–10 °C / min, a holding temperature of 400–680 °C, and a holding time of 4–7 h; and / or the isothermal section has a heating rate of 2–10 °C / min, a holding temperature of 700–1000 °C, and a holding time of 10–25 h; and / or the cooling section has a heating rate of 2–10 °C / min, a holding temperature of 400–680 °C, and a holding time of 0–5 h. By controlling the temperature program and atmosphere of the first sintering process, controllable free lithium is formed on the particle surface, reacting with the coating agent to form an ultrathin intercalated fast ion conductor. This optimizes the electrochemical performance of the material, simplifies the production process, and achieves a balance between low cost and high performance.

[0009] Furthermore, introducing a mixed atmosphere into one or more temperature zones of the heating, isothermal, and cooling stages, and introducing oxygen-containing atmosphere into the remaining temperature zone, helps to reduce production energy consumption and costs, maintain the safety and controllability of the production process, improve production repeatability, and is suitable for the large-scale industrial production of ternary cathode materials.

[0010] Furthermore, the free lithium content of the first sintered material is denoted as Z, where 800ppm≤Z≤4000ppm; and / or the free lithium content of the first sintered material is denoted as Z, where 1200ppm≤Z≤3600ppm when 0.3%≤A≤0.8%; and / or the temperature of the second sintering is greater than that of the third sintering, with a difference of 150~500℃; and / or the temperature of the second sintering is 500~800℃, with a holding time of 1~7h; and / or the temperature of the third sintering is 200~500℃, with a holding time of 1~7h. This is beneficial for further forming a more suitable amount of residual alkali on the surface of the first sintered material. While improving the electrochemical performance of the material, the coating layer acts as a barrier between the material and the electrolyte, improving structural stability, and ultimately achieving a balance between low cost and high performance.

[0011] Furthermore, the nickel-cobalt-manganese precursor is Ni x Co y Mn (1-x-y) (OH)2 or Ni x Co y Mn (1-x-y) CO3, wherein 0.5≤x≤0.95, 0.02≤y≤0.3; and / or the particle size D of the nickel-cobalt-manganese precursor. 50 The material has a thickness of 2.5–6 μm; and / or the lithium salt includes one or more of lithium oxide, lithium hydroxide, lithium carbonate, and lithium acetate; and / or the sum of the amounts of metal ions in the nickel-cobalt-manganese precursor is in a ratio of 1:(0.95–1.15) to the amount of lithium in the lithium salt, which can further optimize the electrochemical performance and thermal stability of the material.

[0012] Further, in step S1, each modifying element in the calcined modifier accounts for 0.01% to 1% of the weight of the nickel-cobalt-manganese precursor; and / or in step S2, the calcined modifier includes one or more compounds of Al, Zr, W, Ti, Co, Nb, V, Mo, and Ce; and / or each modifying element in the calcined modifier accounts for 0.02% to 2% of the weight of the nickel-cobalt-manganese precursor; and / or in step S3, the tercined modifier includes one or more compounds of Al, Zr, W, Ti, B, Nb, V, Mo, and Ce; and / or each modifying element in the tercined modifier accounts for 0.01% to 1% of the weight of the nickel-cobalt-manganese precursor, which is beneficial to further enhance the structural stability and cycle performance of the material.

[0013] According to another aspect of the present invention, a lithium nickel cobalt manganese oxide single crystal cathode material is provided, which is obtained by using the preparation method of the lithium nickel cobalt manganese oxide single crystal cathode material described above. It has significantly improved rate performance, low preparation cost, and is suitable for large-scale industrial production.

[0014] According to another aspect of the present invention, a positive electrode is provided, comprising a positive current collector and a positive electrode material active layer disposed on at least one side of the positive current collector, wherein the positive electrode material active layer comprises the lithium nickel cobalt manganese oxide single crystal positive electrode material described above in the present invention, which has significantly improved electrochemical performance.

[0015] According to another aspect of the present invention, a secondary battery is provided, comprising the positive electrode sheet described above, which has significantly improved electrochemical performance. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 SEM images of the lithium nickel cobalt manganese oxide single-crystal cathode material according to Embodiment 1 of the present invention are shown;

[0018] Figure 2 SEM images of the lithium nickel cobalt manganese oxide single-crystal cathode material according to Comparative Example 1 of the present invention are shown. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] As described in the background section of this invention, existing ternary cathode materials suffer from the problem of not being able to simultaneously achieve low cost and high electrochemical performance. To address this issue, in a typical embodiment of this invention, a method for preparing a lithium nickel cobalt manganese oxide single-crystal cathode material is provided. The chemical formula of the lithium nickel cobalt manganese oxide single-crystal cathode material is LiNi. a Co b Mn (1-a-b-c) G c O2, where 0.5≤a≤0.95, 0.02≤b≤0.3, 0.00001≤c≤0.01, G is a modifying element, which includes one or more of Na, Mg, Ca, Al, Zr, W, Sr, Ti, B, Co, Nb, La, V, Y, Mo, and Ce; the preparation method includes the following steps: Step S1, mixing the nickel-cobalt-manganese precursor, lithium salt, and a sintering modifier, and then performing a first sintering in a mixed atmosphere to obtain a sintered material; mixed atmosphere The atmosphere includes oxygen and dopant gas, the dopant gas including CO2 and / or water vapor; step S2, the first sintering material is mixed with the second sintering modifier, and then a second sintering is performed in the oxygen-containing atmosphere to obtain the second sintering material; step S3, the second sintering material is mixed with the third sintering modifier, and then a third sintering is performed in the oxygen-containing atmosphere to obtain lithium nickel cobalt manganese oxide single crystal cathode material; wherein, the first sintering modifier, the second sintering modifier and the third sintering modifier each independently include a compound of modifying element; and the temperature of the second sintering is greater than the temperature of the third sintering.

[0021] This invention first mixes a nickel-cobalt-manganese precursor, a lithium salt, and a mono-calcined modifier, then performs high-temperature solid-state sintering in an oxygen-containing atmosphere doped with CO2 and / or water vapor. Oxygen acts as a catalyst in the formation of the ternary cathode material. The metallic elements nickel, cobalt, and manganese are oxidized to form a complete lithium nickel cobalt-manganese oxide structure, resulting in lithium nickel cobalt-manganese oxide particles, i.e., mono-calcined material. The metallic modifying elements in the mono-calcined modifier have high bond energies with O atoms, which can improve the stability of the microcrystalline structure of the material by doping the surface of the lithium nickel cobalt-manganese oxide particles. At the same time, it can reduce the release of O and achieve O fixation. The presence of inert O on the particle surface leads to increased impedance and difficulty in lithium-ion transport. Therefore, the mono-calcined modifier is also beneficial for improving the rate performance of the material. Introducing CO2 and / or water vapor into the atmosphere of the first sintering can increase the residual alkali of the sintered material (for example, when the first sintering includes a heating section, an isothermal section, and a cooling section in sequence, in the initial stage of the heating and isothermal sections of the first sintering, CO2 mainly reacts with Li2O to generate Li2CO3, and in the later stage of the isothermal section and the cooling section, CO2 mainly reacts with Li in the material matrix to generate Li2CO3 (introducing water vapor will generate LiOH accordingly)). Furthermore, by controlling the volume ratio of dopant gas to O2, controllable free lithium can be formed on the surface of the material, while the particles can also grow normally.

[0022] The first-calcined material is then pulverized, mixed with a second-calcined modifier, and sintered at high temperature in an oxygen-containing environment. After sieving, the second-calcined material is obtained. The oxygen-containing environment provides a catalytic environment to promote the oxidation process of Mn. At high temperature, the second-calcined modifier can melt and react with the controllable free lithium on the surface of the first-calcined material to form an ultra-thin embedded fast-ion conductor, which is beneficial to improving the migration rate of lithium ions, thereby reducing the material's DCR and improving the cell's power performance. Finally, the second-calcined material is mixed with a third-calcined modifier and sintered at low temperature in an oxygen-containing environment. After sieving and demagnetization, a lithium nickel cobalt manganese oxide single-crystal cathode material is obtained. At low temperature, the third-calcined modifier coats rather than melts and embeds into the material particles, forming a low-temperature coating layer. While acting similarly to a fast-ion conductor, the inert oxide surface coating formed by the third-calcined modifier can act as a protective layer between the material and the electrolyte, slowing down side reactions between the cathode material and the electrolyte, thereby improving the structural stability of the material.

[0023] This invention introduces CO2 and / or water vapor as dopant gases into the atmosphere of the first sintering stage to increase the residual alkali content of the first-sintered material. By controlling the volume ratio of the dopant gas to O2, controllable free lithium is formed on the material surface, reacting with a second-sintering modifier to form an ultrathin intercalated fast-ion conductor. This reduces the material's damping coefficient (DCR) and improves the cell's power performance. The method of controllably introducing CO2 and / or water vapor to increase residual alkali during the first sintering stage significantly reduces production costs, offering advantages such as low energy consumption, safe and reliable production process, and low production cost. Furthermore, the implementation method is simple and controllable, with high production repeatability, making it suitable for the industrial production of ternary cathode materials.

[0024] In a preferred embodiment, the volume percentage of the dopant gas in the mixed atmosphere is denoted as A, where 0.1% ≤ A ≤ 5%, preferably 0.1% ≤ A ≤ 1%; and / or the oxygen volume content is 70%–99.99%, with the remaining gas mainly containing unavoidable impurities such as N2, CO2, and H2O. By introducing an appropriate amount of CO2 and / or water vapor in the first sintering stage, i.e., controlling the range of A, the residual alkali level of the first-sintering material can be effectively increased, forming free lithium, providing the necessary lithium for the subsequent second-sintering modifier reaction, reacting with the coating agent to form an ultra-thin intercalated fast ion conductor, significantly reducing the DC internal resistance of the material and improving the power performance of the cell. Limiting the oxygen volume content within the above range is beneficial for a more complete reaction, resulting in a cathode material with fewer defects and a more complete crystal structure.

[0025] For similar reasons, in some embodiments, the dopant gas includes CO2 and water vapor in a volume ratio of 1:(0.1 to 10).

[0026] To further control the surface residual alkali content of the first sintering material, in a preferred embodiment, the first sintering includes a heating section, a constant temperature section, and a cooling section performed sequentially, followed by natural cooling to room temperature; wherein, the heating rate of the heating section is 2-10℃ / min, the holding temperature is 400-680℃, and the holding time is 4-7h; and / or the heating rate of the constant temperature section is 2-10℃ / min, the holding temperature is 700-1000℃, and the holding time is 10-25h; and / or the heating rate of the cooling section is 2-10℃ / min, the holding temperature is 400-680℃, and the holding time is 0-5h.

[0027] In the heating stage, lithium salt melts at a specific temperature and coats the surface of the nickel-cobalt-manganese precursor, which undergoes initial pyrolysis and structural reorganization. In the high-temperature stage, the high temperature promotes the full reaction between the lithium salt and the precursor, generating a stable lithium nickel-cobalt-manganese oxide single-crystal structure. Simultaneously, the presence of an oxygen-containing atmosphere containing CO2 and / or water vapor increases the residual alkali on the material surface, creating conditions for the subsequent formation of fast-ion conductors, reducing the need for additional lithium replenishment steps, and lowering costs. The raw materials are solid-state sintered to form primary particles, which continue to grow. Some particles fuse and grow larger. Strain occurs during particle cooling; slow cooling and / or low-temperature holding can reduce strain, contributing to the stability of the material's surface structure. Particle integration is achieved in the cooling stage, resulting in a material with more uniform particle size. By controlling the temperature program and atmosphere of the first sintering, controllable free lithium is formed on the particle surface, reacting with the coating agent to form an ultrathin embedded fast-ion conductor. This optimizes the material's electrochemical performance, simplifies the production process, and achieves a balance between low cost and high performance.

[0028] In a preferred embodiment, a mixed atmosphere is introduced into one or more temperature zones of the heating, isothermal, and cooling sections, while oxygen-containing atmospheres are introduced into the remaining temperature zones, all of which can increase the residual alkali content on the material surface. By selectively introducing mixed atmospheres containing CO2 and / or water vapor into different temperature zones (heating, isothermal, and cooling sections) of the first sintering process, and introducing oxygen-containing atmospheres into the remaining temperature zones, it is beneficial to control the residual alkali content on the material surface, providing an abundant lithium source for the subsequent formation of fast ion conductors. This effectively increases the residual alkali content on the surface without affecting the overall quality and structure of the material, synergistically enhancing the conductivity of lithium ions and reducing DCR with subsequent coating, while further reducing the use of CO2 and / or water vapor, lowering production energy consumption and costs, maintaining the safety and controllability of the production process, and improving production repeatability, making it suitable for the large-scale industrial production of ternary cathode materials.

[0029] The residual alkali content can be quantitatively controlled by adjusting the volume ratio of CO2 or water vapor to O2, thus offering the advantages of controllable and convenient operation. To further form a more suitable amount of residual alkali on the surface of the primary calcined material, providing a richer lithium source for the reaction between the secondary calcined modifier and free lithium, thereby promoting the formation of ultra-thin embedded fast ion conductors, further reducing the DC internal resistance of the material, and improving the power performance of the battery cell, in a preferred embodiment, the free lithium content of the primary calcined material is denoted as Z, where 700ppm≤Z≤25000ppm; preferably, 800ppm≤Z≤4000ppm; more preferably, when 0.3%≤A≤0.8%, 1200ppm≤Z≤3600ppm; and even more preferably, when 0.3%≤A≤0.8%, 1000ppm≤Z≤2200ppm. In some implementations, when 0.1% ≤ A ≤ 0.5%, 700ppm ≤ Z ≤ 2800ppm; when 0.5% < A ≤ 1%, 1400ppm < Z ≤ 4000ppm; and when 1% < A ≤ 5%, 4000ppm < Z ≤ 25000ppm.

[0030] Free lithium refers to the free lithium on the surface of a calcined material, used to characterize the total residual alkali on the surface of the calcined material. LiOH The mass fraction of lithium carbonate is expressed as ω. Li2CO3 The total free lithium content A in lithium hydroxide and lithium carbonate is calculated as ω. Li Calculated using the following formula:

[0031] In a preferred embodiment, the temperature of the second sintering is greater than that of the third sintering, with a difference of 150–500°C; and / or the temperature of the second sintering is 500–800°C, with a holding time of 1–7 hours; and / or the temperature of the third sintering is 200–500°C, with a holding time of 1–7 hours. Setting the temperature difference between the second and third sintering within the above range is beneficial for the second-sintering modifier to form a fast-ion conductor at high temperatures, while the third-sintering modifier forms an inert oxide coating layer at lower temperatures. The synergistic effect of these two modifiers improves the electrochemical performance of the material, while the coating layer acts as a barrier between the material and the electrolyte, enhancing structural stability and ultimately achieving a balance between low cost and high performance.

[0032] By adjusting the ratio of Ni, Co, and Mn in the precursor, the electrochemical performance and thermal stability of the material can be further optimized, achieving a balance between high energy density and long cycle life. In a preferred embodiment, the nickel-cobalt-manganese precursor is Ni. x Co y Mn (1-x-y) (OH)2 or Ni x Co y Mn (1-x-y)CO3, wherein 0.5≤x≤0.95, 0.02≤y≤0.3; and / or the particle size D of the nickel-cobalt-manganese precursor. 50 The particle size is 2.5–6 μm; and / or the lithium salt includes one or more of lithium oxide, lithium hydroxide, lithium carbonate, and lithium acetate; and / or the sum of the amounts of metal ions in the nickel-cobalt-manganese precursor is in a ratio of 1:(0.95–1.15) to the amount of lithium in the lithium salt. Wherein, the particle size D... 50 This refers to the particle size Dv 50 Controlling the precursor particle size within the aforementioned range is beneficial for increasing the material's compaction density, while simultaneously accelerating lithium-ion transport and improving rate performance. The aforementioned amount of lithium salt facilitates a sufficient supply of lithium, reducing material costs while maintaining high performance, and promoting more efficient solid-state reactions. This contributes to the formation of a uniform and stable single-crystal structure, thereby enhancing the material's electrochemical performance.

[0033] In a preferred embodiment, in step S1, each modifying element in the calcined modifier accounts for 0.01% to 1% of the weight of the nickel-cobalt-manganese precursor; and / or in step S2, the bis-calcined modifier includes one or more compounds of Al, Zr, W, Ti, Co, Nb, V, Mo, and Ce; and / or each modifying element in the bis-calcined modifier accounts for 0.02% to 2% of the weight of the nickel-cobalt-manganese precursor; and / or in step S3, the ter-calcined modifier includes one or more compounds of Al, Zr, W, Ti, B, Nb, V, Mo, and Ce; and / or each modifying element in the ter-calcined modifier accounts for 0.01% to 1% of the weight of the nickel-cobalt-manganese precursor.

[0034] Controlling the addition ratio of each modifying element in the primary calcination modifier within the aforementioned range not only effectively improves the stability of the material's microstructure and reduces disordered oxygen release, but also reduces structural defects caused by excessive modifying elements, thus contributing to the material's high activity and long-term stability. Under the aforementioned conditions, the secondary calcination modifier is more conducive to reacting with free lithium on the surface of the primary calcined material, generating an ultrathin intercalated fast ion conductor, further increasing the lithium-ion migration rate and reducing the material's DC internal resistance. The addition ratio of the tertiary calcination modifier within the aforementioned range facilitates the formation of an inert oxide coating layer at low temperatures, acting as a protective barrier between the material and the electrolyte, effectively suppressing side reactions, and further enhancing the material's structural stability and cycle performance.

[0035] In order to further improve the uniformity of material mixing and promote the sintering reaction, in some embodiments, in step S2, the first sintering material is pulverized and then mixed with the second sintering modifier; the pulverization method is air jet milling, the pulverization pressure is 0.4-0.8 MPa, the grading frequency is 80-130 Hz, and the induced draft fan frequency is 35-60 Hz.

[0036] In some embodiments, the mixing equipment includes one or more of a 3D mixer, a high-speed mixer (such as an FM20 high-speed mixer), and a ball mill; and / or the sintering equipment includes one or more of a tube furnace, a box furnace, and a roller kiln.

[0037] In some embodiments, the weight percentage of C in the calcined material is 0.05% to 0.40%, preferably 0.08% to 0.26%, more preferably 0.08% to 0.15%, and the weight percentage of S is 0.05% to 0.06%.

[0038] In another typical embodiment of the present invention, a lithium nickel cobalt manganese oxide single crystal cathode material is also provided, which is obtained by using the preparation method of the lithium nickel cobalt manganese oxide single crystal cathode material described above. It has significantly improved rate performance, low preparation cost, and is suitable for large-scale industrial production.

[0039] In another typical embodiment of the present invention, a positive electrode sheet is also provided, including a positive current collector and a positive electrode material active layer disposed on at least one side of the positive current collector. The positive electrode material active layer includes the lithium nickel cobalt manganese oxide single crystal positive electrode material described above in the present invention, which has significantly improved electrochemical performance.

[0040] In another typical embodiment of the present invention, a secondary battery is also provided, including the positive electrode sheet described above, which has significantly improved electrochemical performance.

[0041] Typical, but not restrictive, A is a range of 0.1%, 0.5%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these values.

[0042] Typical, but not limiting, Z is a range of values ​​consisting of 700ppm, 1000ppm, 1400ppm, 2000ppm, 2800ppm, 3500ppm, 4000ppm, 5000ppm, 8000ppm, 10000ppm, 15000ppm, 25000ppm, or any two of these values.

[0043] Typical, but not limiting, oxygen volume content is 70%, 75%, 80%, 85%, 90%, 92%, 95%, 99.99%, or any two of these values.

[0044] Typical, but not limiting, the holding temperature of the first sintering heating section is 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 680℃, or any two of these values; the holding time is 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, or any two of these values. The holding temperature of the first sintering isothermal section is 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 10h ... The holding temperature is 00℃ or any two of these values, and the holding time is 10h, 12h, 15h, 18h, 20h, 22h, 25h or any two of these values; the holding temperature of the cooling section of the first sintering is 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 680℃ or any two of these values, and the holding time is 0h, 1h, 2h, 3h, 4h, 5h or any two of these values.

[0045] Typically, but not limitingly, the temperature of the second sintering is greater than the temperature of the third sintering, with the difference being a range of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, or any two of these values.

[0046] Typical, but not limiting, the second sintering temperature is 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃ or any two of these values, and the holding time is 1h, 2h, 3h, 4h, 5h, 6h, 7h or any two of these values.

[0047] Typical, but not limiting, the third sintering temperature is 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃ or any two of these values, and the holding time is 1h, 2h, 3h, 4h, 5h, 6h, 7h or any two of these values.

[0048] Typical, but not limiting, values ​​for each modifying element in the calcined modifier as a percentage of the nickel-cobalt-manganese precursor by weight are 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, or any two of these values; values ​​for each modifying element in the bis-calcined modifier as a percentage of the nickel-cobalt-manganese precursor by weight are 0.02%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, or any two of these values; and values ​​for each modifying element in the tertiary-calcined modifier as a percentage of the nickel-cobalt-manganese precursor by weight are 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, or any two of these values.

[0049] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0050] Unless otherwise specified, in the following examples and comparative examples, the content of the modified additives is the weight percentage of each modified element in the nickel-cobalt-manganese precursor.

[0051] Example 1

[0052] Step S1, the particle size D 50 Ni is a 5μm nickel-cobalt-manganese precursor. 0.65 Co 0.1 Mn 0.25 (OH)₂ and LiOH·H₂O were weighed and added to a high-speed mixer according to the specified ratio. The ratio of the sum of the amounts of metal ions in the nickel-cobalt-manganese precursor to the amount of lithium in the lithium source was 1:1.06. Zirconium oxide, alumina, titanium oxide, and strontium carbonate were added. After mixing in the high-speed mixer for 20 minutes, a homogeneous mixture was obtained. The material was then placed in a box furnace for the first sintering. The atmosphere throughout the process was 0.5% CO₂ + 99.5% oxygen (oxygen content of 92-95%). The box furnace temperature was set as follows: in the heating section, the temperature was first increased from room temperature to 650℃ at a rate of 2℃ / min and held for 5 hours; then in the isothermal section, the temperature was increased to 925℃ at a rate of 2℃ / min and held for 15 hours; finally, in the cooling section, the temperature was decreased to 650℃ at a rate of 2℃ / min and allowed to cool naturally to room temperature to obtain the first-burnt material.

[0053] Step S2: The first-burn material is subjected to airflow pulverization at a pressure of 0.5 MPa, a grading frequency of 90 Hz, and a blower frequency of 40 Hz. After pulverization, the material is collected and stored. The pulverized material is then added to a high-speed mixer, and 2% cobalt hydroxyl oxide and 0.1% zirconium oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering. Oxygen (with an oxygen content of 92-95%) is introduced, and the temperature is raised from room temperature to 700°C at a rate of 2°C / min. The temperature is held for 5 hours, and after natural cooling to room temperature, the material is sieved to obtain the second-burn material.

[0054] Step S3: The secondary sintered material is added to a high-speed mixer, followed by 0.05% alumina, 0.05% boric acid, and 0.3% tungsten oxide. After mixing for 20 minutes in the high-speed mixer, a homogeneous mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (92-95% oxygen content) is introduced. The temperature is increased from room temperature to 400℃ at a rate of 2℃ / min, held for 5 hours, and then naturally cooled to room temperature. After sieving and demagnetization, lithium nickel cobalt manganese oxide single-crystal cathode material with the chemical formula LiNi is obtained. 0.65 Co 0.1Mn 0.2492 G 0.0008 O2 (G=Zr, Al, Ti, Sr, Co, W, B).

[0055] Example 2

[0056] The difference from Example 1 is that in step S1, the atmosphere is 1% CO2 + 99% oxygen throughout the process.

[0057] Example 3

[0058] The difference from Example 1 is that in step S1, the atmosphere is 0.5% water vapor + 99.5% oxygen throughout the process.

[0059] Example 4

[0060] The difference from Example 1 is that in step S1, during the first sintering process of placing the material into the box furnace, 0.7% CO2 + 99.3% oxygen is introduced in the constant temperature section, and oxygen is introduced in the heating and cooling sections.

[0061] Example 5

[0062] The difference from Example 1 is that in step S1, during the first sintering process of placing the material into the box furnace, 0.5% CO2 + 99.5% oxygen is introduced into the constant temperature section and the cooling section, and oxygen is introduced into the heating section.

[0063] Example 6

[0064] The difference from Example 1 is that in step S1, during the first sintering process of placing the material into the box furnace, 0.7% CO2 + 99.3% oxygen is introduced into the heating section and the constant temperature section, and oxygen is introduced into the cooling section.

[0065] Example 7

[0066] The difference from Example 1 is that in step S1, the particle size D is... 50 Ni is a 5μm nickel-cobalt-manganese precursor. 0.5 Co 0.2 Mn 0.3(OH)₂ and Li₂CO₃ were weighed and added to a high-speed mixer according to a specified ratio. The ratio of the sum of the metal ions in the nickel-cobalt-manganese precursor to the amount of lithium in the lithium source was 1:1.08. Zirconium oxide, alumina, titanium oxide, and strontium carbonate were added. After mixing in the high-speed mixer for 20 minutes, a homogeneous mixture was obtained. The material was then placed in a box furnace for the first sintering. The atmosphere throughout the process was 1% CO₂ + 99% oxygen (oxygen content of 92-95%). The box furnace temperature was set as follows: first, the temperature was increased from room temperature to 650℃ at a rate of 2℃ / min and held for 5 hours; then, the temperature was increased to 960℃ at a rate of 2℃ / min and held for 15 hours; subsequently, the temperature was decreased to 650℃ at a rate of 2℃ / min and held for 2 hours. After natural cooling to room temperature, the first sintered material was obtained.

[0067] Example 8

[0068] The difference from Example 1 is that in step S1, the particle size D is... 50 Ni is a 5μm nickel-cobalt-manganese precursor. 0.95 Co 0.02 Mn 0.03 (OH)₂ and LiOH·H₂O were weighed and added to a high-speed mixer according to the specified ratio. The ratio of the sum of the metal ions in the nickel-cobalt-manganese precursor to the amount of lithium in the lithium source was 1:1.01. 0.3% zirconium oxide, 0.1% alumina, 0.1% titanium oxide, and 0.1% strontium carbonate were added. After mixing in the high-speed mixer for 20 minutes, a homogeneous mixture was obtained. The material was then placed in a box furnace for the first sintering. The atmosphere throughout the process was 0.3% CO₂ + 99.7% oxygen (oxygen content of 92-95%). The box furnace temperature was set as follows: first, the temperature was increased from room temperature to 500℃ at a rate of 2℃ / min and held for 5 hours; then, the temperature was increased to 780℃ at a rate of 2℃ / min and held for 15 hours; subsequently, the temperature was decreased to 500℃ at a rate of 2℃ / min and held for 2 hours. After natural cooling to room temperature, the first-burnt material was obtained.

[0069] Example 9

[0070] The difference from Example 1 is that in step S1, the atmosphere introduced throughout is 0.1% CO2 + 99.9% oxygen (the oxygen content in the oxygen is 92-95%).

[0071] Example 10

[0072] The difference from Example 1 is that in step S1, the atmosphere introduced throughout is 0.9% CO2 + 99.1% oxygen (the oxygen content in the oxygen is 92-95%).

[0073] Example 11

[0074] The difference from Example 1 is that in step S1, the particle size D is... 50 Ni is a 2.5 μm nickel-cobalt-manganese precursor. 0.95 Co 0.02 Mn 0.03 (OH)2 and lithium oxide are weighed and added to a high-speed mixer according to the specified ratio. The ratio of the sum of the amounts of metal ions in the nickel-cobalt-manganese precursor to the amount of lithium in the lithium source is 1:0.95. 0.3% zirconium oxide, 0.1% aluminum oxide, 0.1% titanium oxide and 0.01% strontium carbonate are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for the first sintering. The atmosphere throughout the process is 0.5% CO2 + 99.5% oxygen (the oxygen content in the oxygen is 92-95%). The temperature settings for the box furnace are as follows: in the heating section, the temperature is first increased from room temperature to 400℃ at a heating rate of 3℃ / min and held for 7 hours; then in the constant temperature section, the temperature is increased to 700℃ at a heating rate of 3℃ / min and held for 25 hours; subsequently, in the cooling section, the temperature is decreased to 400℃ at a cooling rate of 3℃ / min and held for 5 hours. After natural cooling to room temperature, a batch of calcined material is obtained.

[0075] Example 12

[0076] The difference from Example 1 is that in step S1, the particle size D is... 50 Ni, a nickel-cobalt-manganese precursor with a diameter of 6 μm 0.5 Co 0.2 Mn 0.3 (OH)₂ and lithium acetate were weighed and added to a high-speed mixer according to the specified ratio. The ratio of the sum of the metal ions in the nickel-cobalt-manganese precursor to the amount of lithium in the lithium source was 1:1.15. Zirconium oxide, alumina, titanium oxide, and strontium carbonate were added. After mixing in the high-speed mixer for 20 minutes, a homogeneous mixture was obtained. The material was then placed in a box furnace for the first sintering. The atmosphere throughout the process was 0.5% CO₂ + 99.5% oxygen (oxygen content of 92-95%). The box furnace temperature was set as follows: in the heating section, the temperature was first increased from room temperature to 680℃ at a rate of 10℃ / min and held for 4 hours; then in the isothermal section, the temperature was increased to 1000℃ at a rate of 10℃ / min and held for 10 hours; finally, in the cooling section, the temperature was decreased to 680℃ at a rate of 10℃ / min and allowed to cool naturally to room temperature to obtain the first-sintered material.

[0077] Example 13

[0078] The difference from Example 1 is as follows:

[0079] In step S2, the first-burn material is subjected to airflow pulverization at a pressure of 0.5 MPa, a grading frequency of 90 Hz, and a blower frequency of 40 Hz. After pulverization, the material is collected and stored. The pulverized material is then added to a high-speed mixer, and 2% cobalt hydroxyl oxide and 0.1% zirconium oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (containing 92-95% oxygen) is introduced. The temperature is raised from room temperature to 500°C at a rate of 2°C / min, held for 7 hours, and then naturally cooled to room temperature before sieving to obtain the second-burn material.

[0080] In step S3, the secondary sintered material is added to a high-speed mixer, and then 0.05% alumina, 0.05% boric acid, and 0.3% tungsten oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (containing 92-95% oxygen) is introduced. The temperature is raised from room temperature to 200°C at a rate of 2°C / min, held for 7 hours, and then naturally cooled to room temperature. After sieving and demagnetizing, lithium nickel cobalt manganese oxide single crystal cathode material is obtained.

[0081] Example 14

[0082] The difference from Example 1 is as follows:

[0083] In step S2, the first-burn material is subjected to airflow pulverization at a pressure of 0.5 MPa, a grading frequency of 90 Hz, and a blower frequency of 40 Hz. After pulverization, the material is collected and stored. The pulverized material is then added to a high-speed mixer, and 2% cobalt hydroxyl oxide and 0.1% zirconium oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (containing 92-95% oxygen) is introduced. The temperature is raised from room temperature to 800°C at a rate of 2°C / min, held for 1 hour, and then naturally cooled to room temperature before sieving to obtain the second-burn material.

[0084] In step S3, the secondary sintered material is added to a high-speed mixer, and then 0.05% alumina, 0.05% boric acid, and 0.3% tungsten oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (containing 92-95% oxygen) is introduced. The temperature is raised from room temperature to 500°C at a rate of 2°C / min, held for 1 hour, and then naturally cooled to room temperature. After sieving and demagnetizing, lithium nickel cobalt manganese oxide single crystal cathode material is obtained.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that in step S1, the atmosphere is oxygen-containing throughout, with an oxygen volume content of 92-95%.

[0087] Comparative Example 2

[0088] The difference from Example 1 is as follows:

[0089] In step S2, the first-burn material is subjected to airflow pulverization at a pressure of 0.5 MPa, a grading frequency of 90 Hz, and a blower frequency of 40 Hz. After pulverization, the material is collected and stored. The pulverized material is then added to a high-speed mixer, along with 2% cobalt hydroxyl oxide and 0.1% zirconium oxide. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (containing 92-95% oxygen) is introduced. The temperature is raised from room temperature to 600°C at a rate of 2°C / min, held for 5 hours, and then naturally cooled to room temperature before sieving to obtain the second-burn material.

[0090] In step S3, the secondary sintered material is added to a high-speed mixer, and then 0.05% alumina, 0.05% boric acid, and 0.3% tungsten oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (containing 92-95% oxygen) is introduced. The temperature is raised from room temperature to 600°C at a rate of 2°C / min, held for 5 hours, and then naturally cooled to room temperature. After sieving and demagnetizing, lithium nickel cobalt manganese oxide single crystal cathode material is obtained.

[0091] Comparative Example 3

[0092] The difference from Example 1 is as follows:

[0093] In step S2, the first-burn material is subjected to airflow pulverization at a pressure of 0.5 MPa, a grading frequency of 90 Hz, and a blower frequency of 40 Hz. After pulverization, the material is collected and stored. The pulverized material is then added to a high-speed mixer, and 2% cobalt hydroxyl oxide and 0.1% zirconium oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (containing 92-95% oxygen) is introduced. The temperature is raised from room temperature to 400°C at a rate of 2°C / min, held for 5 hours, and then naturally cooled to room temperature before sieving to obtain the second-burn material.

[0094] In step S3, the secondary sintered material is added to a high-speed mixer, and then 0.05% alumina, 0.05% boric acid, and 0.3% tungsten oxide are added. After mixing in the high-speed mixer for 20 minutes, a uniform mixture is obtained. The material is then placed in a box furnace for sintering, and oxygen (with an oxygen content of 92-95%) is introduced. The temperature is raised from room temperature to 700°C at a rate of 2°C / min, held for 5 hours, and then naturally cooled to room temperature. After sieving and demagnetizing, lithium nickel cobalt manganese oxide single crystal cathode material is obtained.

[0095] Performance testing:

[0096] The materials of the above embodiments and comparative examples were analyzed and tested as follows.

[0097] Carbon and sulfur testing of calcined materials: The test shall be conducted in accordance with GB / T 20123-2006.

[0098] Residual alkali test of calcined materials: The test shall be conducted in accordance with GB / T 41704-2022.

[0099] DCR test of lithium nickel cobalt manganese oxide cathode material: Lithium nickel cobalt manganese oxide material was mixed with binder (PVDF) and conductive agent (carbon black) in a mass ratio of 98:1:1, coated, dried and cut into sheets to obtain cathode sheets. The cathode sheets were then assembled with graphite anode sheets, separator (PE separator) and electrolyte (1.0 mol / L LiPF6, solvent is EC+DEC+EMC) into 3Ah soft pack batteries. After formation and capacity testing, the DCR at 30% SOC at -25℃ was tested. The test steps are shown in Table 1.

[0100] Table 1

[0101]

[0102]

[0103] Rate performance test of lithium nickel cobalt manganese oxide cathode material: Assemble a 3Ah soft pack battery according to the DCR test item. The test steps are shown in Table 2. Rate performance = 1C discharge capacity ÷ 0.33C discharge capacity × 100%.

[0104] Table 2

[0105]

[0106]

[0107] The carbon and sulfur content, residual alkali content, DCR, and rate performance test data of the above embodiments and comparative examples are shown in Table 3.

[0108] Table 3

[0109]

[0110]

[0111] SEM images of the lithium nickel cobalt manganese oxide single-crystal cathode material in Example 1 are shown below. Figure 1 The SEM image of the lithium nickel cobalt manganese oxide single-crystal cathode material of Comparative Example 1 is shown below. Figure 2 .

[0112] In Comparative Example 2, because the second and third sintering temperatures were the same, the temperature for the reaction between the coating agent and residual alkali and the formation of the coating layer was not reached. Although sufficient residual alkali was formed in the first sintering, the solid-phase reaction in the second sintering was incomplete, and the coating layer could not be fully formed, resulting in a negligible decrease in DCR and poor rate performance. In Comparative Example 3, because the second sintering temperature was lower, the residual alkali did not react completely with the coating agent, resulting in a higher DCR. At the same time, the third sintering temperature was higher, and the coating agent was overburned, thus significantly reducing all performance aspects, including rate performance. Furthermore, if CO2 gas is introduced after a stable first-sintering sample is formed, and then high-temperature sintering is performed with the coating agent to form a positive electrode material, a two-step heat treatment is used to form a fast-ion conductor coating agent on the material surface. The introduced CO2 reacts with LiOH on the surface of the positive electrode material to form Li2CO3. Therefore, sufficient LiOH on the material surface must be ensured to generate enough Li2CO3, which not only increases the material processing cost but also reduces production capacity and efficiency.

[0113] The DCR data shows that when the residual alkali level is increased, there is sufficient free lithium on the material surface to react with the modified additives, thereby generating a surface coating layer with excellent lithium-ion conductivity. This is beneficial to improving the migration rate of lithium ions, thereby reducing the impedance of the material itself and significantly improving the rate performance of the cell. At the same time, it can also act as a protective layer between the material and the electrolyte, which can slow down the side reactions between the cathode material and the electrolyte, thereby improving the structural stability of the material.

[0114] As can be seen, compared with the oxygen-containing sintered sample of Comparative Example 1, all embodiments of the present invention introduce oxygen-containing materials doped with different volumes of CO2 and / or water vapor, which significantly improves the residual alkali content. Furthermore, SEM images of Example 1 and Comparative Example 1 show that even with the introduction of CO2 or water vapor, the particle size of the final material is not affected. The average particle size of Example 1 is 1.91 μm, and the average particle size of Comparative Example 1 is 1.94 μm, indicating that the particle size is essentially the same. This demonstrates that introducing a certain proportion of CO2 and / or water vapor can improve the residual alkali content while allowing the particles to grow normally. Therefore, this method has the advantages of being simple to operate and easy to implement, and it does not produce side effects.

[0115] As can be seen from the above, compared with the comparative example, the embodiments of the present invention introduce CO2 and / or water vapor as dopant gases into the atmosphere of the first sintering to increase the residual alkali of the first-sintered material. Furthermore, by controlling the volume ratio of the dopant gas to O2, controllable free lithium is formed on the material surface, which reacts with the second-sintering modifier to form an ultrathin intercalated fast ion conductor, thereby reducing the material's DCR (DC internal resistance) and improving the cell's power performance. The method of controllably introducing CO2 and / or water vapor to increase residual alkali in the first sintering stage can significantly reduce production costs, offering advantages such as low energy consumption, safe and reliable production process, and low production cost. Moreover, the implementation method is simple and controllable, with high production repeatability, making it suitable for the industrial production of ternary cathode materials.

[0116] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a single-crystal cathode material of lithium nickel cobalt manganese oxide, characterized in that, The chemical formula of the lithium nickel cobalt manganese oxide single crystal cathode material is LiNi a Co b Mn (1-a-b-c) G c O2, wherein 0.5≤a≤0.95, 0.02≤b≤0.3, 0.00001≤c≤0.01, and G is a modifying element, which includes one or more of Na, Mg, Ca, Al, Zr, W, Sr, Ti, B, Co, Nb, La, V, Y, Mo, and Ce; the preparation method includes the following steps: Step S1: Mix the nickel-cobalt-manganese precursor, lithium salt and sintering modifier, and then perform a first sintering in a mixed atmosphere to obtain a sintering material; the mixed atmosphere includes oxygen-containing and doped gas, and the doped gas includes CO2 and / or water vapor. Step S2: Mix the first calcined material with the second calcined modifier, and then perform a second sintering in the oxygen-containing environment to obtain the second calcined material; Step S3: Mix the second-calcined material with the third-calcined modifier, and then perform a third sintering in the oxygen-containing environment to obtain the lithium nickel cobalt manganese oxide single crystal cathode material; Wherein, the first sintering modifier, the second sintering modifier, and the third sintering modifier each independently include a compound of the modifying element; and the second sintering temperature is greater than the third sintering temperature.

2. The method for preparing lithium nickel cobalt manganese oxide single-crystal cathode material according to claim 1, characterized in that, The volume percentage of the doped gas in the mixed atmosphere is denoted as A, where 0.1% ≤ A ≤ 5%; and / or The oxygen-containing oxygen has an oxygen volume content of 70% to 99.99%.

3. The method for preparing lithium nickel cobalt manganese oxide single-crystal cathode material according to claim 1 or 2, characterized in that, The first sintering process includes a sequential heating section, a isothermal section, and a cooling section, followed by natural cooling to room temperature; wherein, The heating rate of the heating section is 2–10℃ / min, the holding temperature is 400–680℃, and the holding time is 4–7h; and / or The heating rate of the constant temperature section is 2–10℃ / min, the holding temperature is 700–1000℃, and the holding time is 10–25h; and / or The heating rate of the cooling section is 2–10℃ / min, the holding temperature is 400–680℃, and the holding time is 0–5h.

4. The method for preparing lithium nickel cobalt manganese oxide single-crystal cathode material according to claim 3, characterized in that, The mixed atmosphere is introduced into one or more temperature zones of the heating zone, the isothermal zone, and the cooling zone, while the oxygen-containing zone is introduced into the remaining temperature zone.

5. The method for preparing lithium nickel cobalt manganese oxide single-crystal cathode material according to claim 1 or 2, characterized in that, The free lithium content of the calcined material is denoted as Z, where 800ppm ≤ Z ≤ 4000ppm; and / or The free lithium content of the calcined material is denoted as Z. When 0.3% ≤ A ≤ 0.8%, 1200ppm ≤ Z ≤ 3600ppm; and / or The temperature of the second sintering is greater than the temperature of the third sintering, with a difference of 150–500 °C; and / or The second sintering temperature is 500–800℃, and the holding time is 1–7 hours; and / or The third sintering temperature is 200–500℃, and the holding time is 1–7 hours.

6. The method for preparing lithium nickel cobalt manganese oxide single-crystal cathode material according to claim 1 or 2, characterized in that, The nickel-cobalt-manganese precursor is Ni x Co y Mn (1-x-y) (OH)2 or Ni x Co y Mn (1-x-y) CO3, where 0.5 ≤ x ≤ 0.95, 0.02 ≤ y ≤ 0.3; and / or The particle size D of the nickel-cobalt-manganese precursor 50 2.5–6 μm; and / or The lithium salt includes one or more of lithium oxide, lithium hydroxide, lithium carbonate, and lithium acetate; and / or The sum of the amounts of metal ions in the nickel-cobalt-manganese precursor is in the ratio of the amount of lithium in the lithium salt to the amount of metal ions in the precursor to 1:(0.95-1.15).

7. The method for preparing lithium nickel cobalt manganese oxide single-crystal cathode material according to claim 1 or 2, characterized in that, In step S1, each modifying element in the calcination modifier accounts for 0.01% to 1% of the weight percentage of the nickel-cobalt-manganese precursor; and / or In step S2, the sintered modifier includes one or more compounds of Al, Zr, W, Ti, Co, Nb, V, Mo, and Ce; and / or each modifying element in the sintered modifier accounts for 0.02% to 2% of the weight of the nickel-cobalt-manganese precursor; and / or In step S3, the tri-calcined modifier includes one or more compounds of Al, Zr, W, Ti, B, Nb, V, Mo, and Ce; and / or each modifying element in the tri-calcined modifier accounts for 0.01% to 1% of the weight of the nickel-cobalt-manganese precursor.

8. A lithium nickel cobalt manganese oxide single-crystal cathode material, characterized in that, The lithium nickel cobalt manganese oxide single crystal cathode material was prepared using any one of claims 1 to 7.

9. A positive electrode sheet, comprising a positive current collector and a positive electrode material active layer disposed on at least one side of the positive current collector, characterized in that, The active layer of the cathode material includes the lithium nickel cobalt manganese oxide single crystal cathode material as described in claim 8.

10. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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