Lithium nickel composite oxide positive electrode material and its manufacturing method

Abstract

The present invention discloses a lithium-nickel composite oxide positive electrode material. By observing the cross section of the lithium-nickel composite oxide using a scanning electron microscope, the cross section was divided into four equal parts along the radial length. The porosity of each cross section was measured to be 3% to 8%, and the total porosity of the cross section was 3% to 8%. The manufacturing method includes the steps of: mixing nickel-cobalt-manganese hydroxide with an M-containing sulfate, followed by stepwise pre-sintering at low temperatures to obtain a pre-sintered precursor; mixing the pre-sintered precursor with a lithium source and then sintering at high temperatures to obtain a primary sintered substrate; and washing the primary sintered substrate with deionized water, drying, mixing with a coating agent, and sintering to obtain a lithium-nickel composite oxide positive electrode material. The lithium-nickel composite oxide positive electrode material of the present invention has abundant, uniformly sized, and uniformly distributed pores within the particles, which are favorable for electrolyte infiltration, ensure sufficient contact between the cathode material and the electrolyte, shorten the lithium ion transport path, improve the discharge capacity of the cathode material, reduce the internal resistance of lithium batteries, and exhibit better rate performance.

Description

[Technical Field]

[0001] The present invention relates to the field of positive electrode materials for lithium ion batteries, and more particularly to a lithium nickel composite oxide positive electrode material that is rich in pores and has the pores uniformly distributed within the material, and a method for producing the same. [Background technology]

[0002] In recent years, lithium-ion batteries have been rapidly developed and widely applied in the fields of mobile electronics and automobile manufacturing. In particular, with the rapid expansion of the new energy automobile industry, market demand for lithium-ion batteries has increased significantly, and lithium-ion batteries are required to have high energy density, long life, low cost, high safety, and environmental friendliness. Among various conventional battery materials, high-nickel ternary lithium-ion cathode materials have shown significant advantages and have become a major research topic.

[0003] To meet consumer demands for long driving range and fast charging, lithium-ion batteries must possess higher energy density and excellent rate performance. From the perspective of cathode materials, the most effective way to improve energy density is to increase the nickel content in the material. However, increasing the nickel content rapidly reduces battery stability and can pose serious safety issues. On the other hand, improving rate performance is typically achieved by designing the precursor to be porous or by applying a surface coating. However, porous precursors can have reduced porosity or uneven pore distribution after sintering. This uneven pore distribution can cause anisotropic stress within the material during charge and discharge, ultimately leading to particle fracture and rapid degradation of electrical performance. Furthermore, the formation of fast-ion conductors through surface coating, a common method for improving rate performance, often comes at the expense of capacity. Positive electrode materials with both high energy density and good rate performance are currently the focus of industry research, but conventional modification methods have difficulty simultaneously improving both capacity and rate performance of positive electrode materials. Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to overcome the drawbacks and deficiencies described in the background art above and to provide a lithium-nickel composite oxide positive electrode material having a high discharge capacity and excellent rate performance, and a method for producing the same. [Means for solving the problem]

[0005] In order to solve the above technical problems, the present invention provides a lithium nickel composite oxide positive electrode material, and by performing cross-sectional observation using a scanning electron microscope, the cross section of the lithium nickel composite oxide is divided into four equal parts along the radial length, and the porosity of each measured cross section is 3% to 8%, the pores are uniformly distributed from the inside to the outside within the particle, and the total porosity of the cross section is 3% to 8%.

[0006] The porosity of the lithium-nickel composite oxide positive electrode material was measured as follows: Positive electrode material particles were cut using an ion beam milling machine (CP) to obtain a sample that allowed observation of the particle cross section, and cross-sectional images were taken using a scanning electron microscope (SEM). Next, the particle pore area was extracted from the photograph using the image analysis software ImageJ, and a Python script was used to divide the particle pore area into four equal regions by dividing the radius of the particle pore area into four. Finally, the script program was used to calculate the porosity within each region and the total porosity of the particle cross section.

[0007] In the lithium nickel composite oxide positive electrode material, the specific surface area of ​​the lithium nickel composite oxide positive electrode material is preferably 0.5 to 1.0 m 2 / g.

[0008] In the lithium nickel composite oxide positive electrode material, preferably, the lithium nickel composite oxide positive electrode material is Li a Ni 1-x-y-z Co x Mn y M zThe substrate is made of O2, and the surface of the substrate is coated with a boron coating layer, and M represents at least one element selected from Li, Na, K, Mg, Ti, Co, Zn, Zr, Ce, and Al, and 0.90≦a≦1.10, 0 <x≦0.15、0<y≦0.15、0<z≦0.02、x+y+z≦0.2である。

[0009] In the lithium nickel composite oxide positive electrode material, preferably, the substrate further contains an S element, and the S element accounts for 0.02% to 0.2% of the total mass of the lithium nickel composite oxide positive electrode material.

[0010] In the lithium nickel composite oxide positive electrode material, the boron element in the boron coating layer preferably accounts for 0.05% to 0.2% of the total mass of the lithium nickel composite oxide positive electrode material.

[0011] As a general concept of the present invention, the present invention further provides a method for producing the above-mentioned lithium nickel composite oxide positive electrode material, the method comprising: Step (1) of mixing nickel-cobalt-manganese hydroxide with M-containing sulfate, followed by stepwise pre-sintering at low temperature to obtain a pre-sintered precursor; (2) mixing the lithium source and the pre-sintering precursor according to a stoichiometric ratio, followed by high-temperature sintering to obtain a primary sintered body; and (3) washing the primary sintered substrate with deionized water, drying, mixing with a coating agent, and sintering to obtain a lithium nickel composite oxide positive electrode material.

[0012] In the above manufacturing method, preferably, in step (1), the low-temperature pre-sintering process is carried out in an air or oxygen atmosphere by first increasing the temperature to 150-200°C at a rate of 3-5°C / min, sintering at that temperature for 1-2 hours, then increasing the temperature to 300-400°C at a rate of 1-3°C / min, sintering at that temperature for 2-5 hours, and finally cooling naturally to room temperature.

[0013] In the above manufacturing method, preferably, in step (2), the high-temperature sintering process is carried out in an air or oxygen atmosphere by first increasing the temperature to 450 to 550°C at a rate of 1 to 5°C / min, sintering at that temperature for 3 to 7 hours, then increasing the temperature to 600 to 750°C at a rate of 1 to 5°C / min, maintaining that temperature for 8 to 15 hours, and finally cooling naturally to room temperature.

[0014] In the above manufacturing method, preferably, in step (3), the sintering process involves raising the temperature to 300 to 400°C at a rate of 1 to 5°C / min in an air or oxygen atmosphere, maintaining the temperature for 3 to 12 hours, and then naturally cooling to room temperature.

[0015] In the above manufacturing method, preferably, in step (3), the coating agent is one or more of boric acid and boron oxide.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) The total porosity of the cross section of the lithium nickel composite oxide positive electrode material according to the present invention is 3% to 8%, and the porosity of each measured portion after dividing the cross section into four equal parts along the radius is also 3% to 8%. This indicates that the particles are characterized by abundant, uniformly sized, and uniformly distributed pores within them, which is favorable for electrolyte infiltration, ensures sufficient contact between the positive electrode material and the electrolyte, shortens the lithium ion transport path, improves the discharge capacity of the positive electrode material, reduces the internal resistance of lithium batteries, and exhibits better rate performance.

[0018] (2) In the present invention, by adding a metal sulfate in the pre-sintering step during the manufacturing process of a lithium-nickel composite oxide positive electrode material, the internal porous structure formed during the pre-sintering step is maintained in a uniformly distributed state even after primary sintering, thereby ensuring that abundant and uniform pores are distributed within the manufactured lithium-nickel composite oxide positive electrode material, which is advantageous for improving the rate performance of lithium batteries. In contrast, conventional hydroxide precursors undergo dehydration after pre-sintering, forming sparsely porous oxide precursors, and such sparsely porous structures are difficult to maintain after sintering and are distributed very non-uniformly.

[0019] (3) In the manufacturing process of the lithium nickel composite oxide positive electrode material, the present invention can increase the bulk density of the precursor by pre-sintering, thereby increasing the loading amount during primary sintering. In addition, since a variety of sulfates can be selected, the present invention is suitable for large-scale production. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 2 is a schematic diagram of four regions obtained by dividing the cross section of a particle into four equal radius regions in the process of measuring particle porosity according to the present invention. [Figure 2] 1 is an electron microscope photograph at 20,000 magnifications of a lithium nickel composite oxide positive electrode material in Example 1 of the present invention. [Figure 3] 1 is an electron microscope photograph of a lithium nickel composite oxide positive electrode material in Comparative Example 1 of the present invention at a magnification of 20,000. [Figure 4] FIG. 1 is a comparison diagram of the capacities of batteries made of lithium nickel composite oxide positive electrode materials of Examples of the present invention and Comparative Examples. [Figure 5] FIG. 1 is a graph comparing the rates of batteries made of lithium nickel composite oxide positive electrode materials of Example 1 of the present invention and each of the comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order to facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the drawings and preferred embodiments of the specification, but the scope of protection of the present invention is not limited to the following specific examples.

[0022] Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used in this specification are only for describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0023] Unless otherwise specified, the various raw materials, reagents, instruments, and devices used in the present invention can all be purchased from the market or prepared by conventional methods.

[0024] The particle cross-sectional images and porosity calculations in the following examples and comparative examples were obtained as follows: Positive electrode material particles were cut using an ion beam milling (CP) machine to obtain samples that allowed observation of the particle cross-section, and cross-sectional images were taken using a scanning electron microscope (SEM). Next, the particle pore area was extracted from the photograph using the image analysis software ImageJ, and the particle pore area was divided into four equal radius regions using a Python script, as shown in Figure 1. Finally, the script program calculated the porosity within each region and the total porosity of the particle cross-section.

[0025] Example 1 The lithium nickel composite oxide positive electrode material of the present invention was subjected to cross-sectional observation using a scanning electron microscope. The cross section of the lithium nickel composite oxide was divided into four equal parts along the radial length, and the porosities of the four regions were measured. From the inside to the outside, the porosities were 5.02%, 5.63%, 5.57%, and 4.82%, respectively. The total porosity of the cross section was 5.22%, and the specific surface area was 0.64 m 2 / g, and the lithium nickel composite oxide positive electrode material is Li 1.03 Ni 0.82 Co 0.10 Mn 0.07 Ti 0.01 O 2.00and the substrate further contains an S element, the mass of which accounts for 0.041% of the total mass of the lithium nickel composite oxide positive electrode material. The surface of the substrate is coated with a boron coating layer, and the boron element in the coating layer accounts for 0.1% of the total mass of the lithium nickel composite oxide positive electrode material.

[0026] The method for producing a lithium nickel composite oxide positive electrode material of the present invention includes the following steps (1) to (3).

[0027] In step (1), the high-nickel cathode material precursor Ni 0.83 Co 0.10 Mn 0.07 (OH)2 and Ti(SO4)2 were mixed in a molar ratio of 1:0.01 into a high-speed mixer. The rotation speed of the high-speed mixer was 1500 rpm / min. After 30 minutes of high-speed mixing, the mixture was placed in a sintering furnace, heated to 150°C at a rate of 3°C / min in an oxygen atmosphere, and sintered at that temperature for 2 hours. Thereafter, the temperature was raised to 300°C at a rate of 1°C / min, and sintered at that temperature for 3 hours. The mixture was then naturally cooled to room temperature to obtain a pre-sintered precursor.

[0028] In step (2), the pre-sintered precursor prepared in step (1) and LiOH·H2O were mixed in a high-speed mixer at a molar ratio of 1:1.03. The rotation speed of the high-speed mixer was 1500 rpm / min. After 30 minutes of high-speed mixing, the mixture was placed in a sintering furnace and heated to 500°C at a rate of 4°C / min in an oxygen atmosphere. The mixture was then sintered for 6 hours, then heated to 720°C at a rate of 1.5°C / min and sintered for 12 hours. The mixture was then naturally cooled to room temperature, crushed, and sieved through a 300-mesh sieve to obtain a primary sintered body.

[0029] In step (3), the primary sintered substrate was washed with deionized water for 15 minutes at a solid-liquid ratio of 1:1, with the deionized water temperature controlled at 10°C. After washing, the sample was placed in a vacuum oven and vacuum-dried at 160°C for 8 hours. Then, it was naturally cooled to room temperature and sieved through a 300-mesh sieve to obtain a washed sample. The washed sample and boric acid were mixed in a mass ratio of 1:0.0019 in a high-speed mixer at a rotation speed of 1500 rpm / min for 30 minutes. After high-speed mixing, the mixture was placed in a sintering furnace and heated to 350°C at a rate of 2°C / min in an oxygen atmosphere. The mixture was then sintered for 8 hours. It was then naturally cooled to room temperature and sieved through a 300-mesh sieve to obtain a lithium-nickel composite oxide cathode material.

[0030] Example 2 The cross section of the lithium nickel composite oxide positive electrode material of the present invention was observed using a scanning electron microscope. The cross section of the lithium nickel composite oxide was divided into four equal parts along the radial length, and the porosities of the four regions were measured. From the inside to the outside, the porosity was 4.28%, 4.56%, 5.03%, and 4.55%, respectively. The total porosity of the cross section was 4.68%, and the specific surface area was 0.75 m 2 / g, and the lithium nickel composite oxide positive electrode material is Li 1.03 Ni 0.88 Co 0.05 Mn 0.05 La 0.02 O 2.00 The substrate further contains an S element, the mass of which accounts for 0.036% of the total mass of the lithium nickel composite oxide positive electrode material. The surface of the substrate is coated with a boron coating layer, and the boron element in the coating layer accounts for 0.1% of the total mass of the lithium nickel composite oxide positive electrode material.

[0031] The method for producing a lithium nickel composite oxide positive electrode material of the present invention includes the following steps (1) to (3).

[0032] In step (1), the high-nickel cathode material precursor Ni 0.90 Co 0.05 Mn 0.05(OH)2 and La2(SO4)3 were mixed in a high-speed mixer in a molar ratio of 1:0.01. The rotation speed of the high-speed mixer was 1500 rpm / min. After 30 minutes of high-speed mixing, the mixture was placed in a sintering furnace, heated to 150°C at a rate of 3°C / min in an oxygen atmosphere, sintered for 2 hours, then heated to 300°C at a rate of 1°C / min, sintered for 3 hours, and then naturally cooled to room temperature to obtain a pre-sintered precursor.

[0033] In step (2), the pre-sintering precursor and LiOH·H2O were mixed in a high-speed mixer at a molar ratio of 1:1.03. The rotation speed of the high-speed mixer was 1500 rpm / min. After 30 minutes of high-speed mixing, the mixture was placed in a sintering furnace and heated to 520°C at a rate of 3°C / min in an oxygen atmosphere. The mixture was then sintered for 6 hours, then heated to 700°C at a rate of 2°C / min, and sintered for 11 hours. The mixture was then naturally cooled to room temperature, crushed, and sieved through a 300-mesh sieve to obtain a primary sintered body.

[0034] In step (3), the primary sintered substrate was washed with deionized water for 15 minutes at a solid-liquid ratio of 1:1. The temperature of the deionized water was controlled at 10°C. After washing, the sample was placed in a vacuum oven and vacuum dried at 160°C for 8 hours. Then, it was naturally cooled to room temperature and sieved through a 300-mesh sieve to obtain a washed sample. The washed sample and boric acid were then introduced into a high-speed mixer in a mass ratio of 1:0.0019 and mixed. The high-speed mixer had a rotation speed of 1500 rpm / min. After 30 minutes of high-speed mixing, the mixture was obtained. After that, the mixture was placed in a sintering furnace and heated to 350°C at a heating rate of 2°C / min in an oxygen atmosphere. The mixture was then kept at this temperature and sintered for 5 hours. Then, it was naturally cooled to room temperature and sieved through a 300-mesh sieve to obtain a lithium-nickel composite oxide positive electrode material.

[0035] Example 3 The lithium nickel composite oxide positive electrode material of the present invention was subjected to cross-sectional observation using a scanning electron microscope. The cross section of the lithium nickel composite oxide was divided into four equal parts along the radial length, and the porosities of the four regions were measured. From the inside to the outside, the porosities were 6.84%, 6.99%, 7.32%, and 6.62%, respectively. The total porosity of the cross section was 6.92%, and the specific surface area was 0.86 m 2 / g, and the lithium nickel composite oxide positive electrode material is Li 1.07 Ni 0.92 Co 0.04 Mn 0.04 O 2.00 and the substrate further contains an S element, the mass of which accounts for 0.054% of the total mass of the lithium nickel composite oxide positive electrode material. The surface of the substrate is coated with a boron coating layer, and the boron element in the coating layer accounts for 0.1% of the total mass of the lithium nickel composite oxide positive electrode material.

[0036] The method for producing a lithium nickel composite oxide positive electrode material of the present invention includes the following steps (1) to (3).

[0037] In step (1), the high-nickel cathode material precursor Ni 0.92 Co 0.04 Mn 0.04 (OH)2 and Li2SO4 were mixed in a molar ratio of 1:0.02 into a high-speed mixer. The rotation speed of the high-speed mixer was 1500 rpm / min. After 30 minutes of high-speed mixing, the mixture was placed in a sintering furnace, heated to 150°C at a rate of 3°C / min in an oxygen atmosphere, and sintered at that temperature for 2 hours. Thereafter, the temperature was raised to 300°C at a rate of 1°C / min, and sintered at that temperature for 3 hours. The mixture was then naturally cooled to room temperature to obtain a pre-sintered precursor.

[0038] In step (2), the pre-sintering precursor and LiOH·H2O were mixed in a high-speed mixer in a molar ratio of 1:1.03. The mixer rotation speed was 1500 rpm / min. After 30 minutes of high-speed mixing, the mixture was placed in a sintering furnace and heated to 520°C at a rate of 3°C / min in an oxygen atmosphere. The mixture was then sintered for 6 hours, then heated to 680°C at a rate of 2°C / min, and sintered for 10 hours. The mixture was then naturally cooled to room temperature, crushed, and sieved through a 300-mesh sieve to obtain the primary sintered body.

[0039] In step (3), the primary sintered substrate was washed with deionized water for 15 minutes at a solid-liquid ratio of 1:1, with the temperature of the deionized water controlled at 10°C. After washing, the sample was placed in a vacuum oven and vacuum-dried at 160°C for 8 hours. Then, it was naturally cooled to room temperature and sieved through a 300-mesh sieve to obtain a washed sample. The washed sample and boric acid were then mixed in a high-speed mixer at a mass ratio of 1:0.0019, with the mixer rotating at 1500 rpm / min, for 30 minutes to obtain a mixture. Finally, the mixture was placed in a sintering furnace and heated to 350°C at a rate of 2°C / min in an oxygen atmosphere. The mixture was then sintered for 5 hours, naturally cooled to room temperature, and sieved through a 300-mesh sieve to obtain a lithium-nickel composite oxide cathode material.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is that Ti(SO4)2 is not added in the pre-sintering process of step (1), and all other conditions and parameters are the same as those of Example 1.

[0041] Comparative Example 2 The difference between this comparative example and Example 1 is that in the pre-sintering step (1), a stepwise pre-sintering process was not used, but the temperature was raised to 300°C at a rate of 1°C / min and then kept at that temperature for 3 hours. All other conditions and parameters were the same as those in Example 1.

[0042] Figure 2 is an electron microscope photograph of the lithium nickel composite oxide positive electrode material in Example 1 of the present invention, and Figure 3 is an electron microscope photograph of the lithium nickel composite oxide positive electrode material in Comparative Example 1 of the present invention. As can be seen from Figure 2, after adding sulfate in the pre-sintering step, the number and pore area of ​​pores are significantly increased and the pore distribution is uniform, while as can be seen from Figure 3, the pore area of ​​the cross section of the material particles produced without adding sulfate in the pre-sintering step is small and unevenly distributed, with few pores in the interior and center of the particles and many pores on the exterior.

[0043] Table 1 shows a comparison of the S element content, specific surface area, and pore distribution of the lithium nickel composite oxide positive electrode materials of each Example and Comparative Example.

[0044] Table 1. S element content, specific surface area and pore distribution of lithium nickel composite oxide positive electrode materials of Examples and Comparative Examples [Table 1]

[0045] Comparing the porosity test results of Example 1 and Comparative Example 1, it can be seen that adding sulfate during pre-sintering can significantly improve the porosity of the material particles. Furthermore, comparing the porosity of each region of the particle cross section, it can be seen that Example 1 has a more uniform pore distribution. Comparing the porosity test results of Example 1 and Comparative Example 2, it can be seen that stepwise pre-sintering is beneficial for forming more abundant pores in the material, thereby improving the electrical performance of the material.

[0046] The lithium-nickel composite oxide cathode materials of Examples 1, 2, Comparative Examples 1, and 2 were thoroughly and uniformly mixed with carbon black (Super-P) and binder (PVDF) in a ratio of 92.5:5:2.5. An appropriate amount of organic solvent, N-methylpyrrolidone (NMP), was then added to prepare a slurry. The cathode slurry was then uniformly coated onto aluminum foil using a coating machine. The coated cathode sheet was placed in a ventilation drying box, dried at 120°C for 20 hours, and finally cut into circular cathode sheets with a diameter of 14 mm. The anode (metallic lithium sheet), electrolyte (solute: 1 mol / L LiPF6, solvent volume ratio: EC / DEC = 1:2), separator, and cathode sheet were assembled into CR2032 button cells in a glove box for electrical performance testing. The test voltage of the button battery is 3.0 to 4.3 V, the initial charge capacity is the charge capacity at 25°C and 0.1 C rate, and the initial discharge capacity is the discharge capacity at 25°C and 0.1 C rate. The room temperature cycle test measures the cycle retention rate at 25°C and 1 C / 1 C charge / discharge rate, and the high temperature cycle test measures the cycle retention rate at 45°C and 0.5 C / 0.5 C charge / discharge rate.

[0047] FIG. 4 is a graph comparing the capacities of the batteries made of the positive electrode materials of each Example and Comparative Example, and FIG. 5 is a graph comparing the rates of the batteries made of the positive electrode materials of Example 1 and each Comparative Example. Table 2 shows the results of the electrochemical performance of each Example and Comparative Example.

[0048] Table 2. Electrochemical performance of lithium nickel composite oxide positive electrode materials of Examples and Comparative Examples [Table 2]

[0049] Comparing the electrical performance test results of Example 1 and Comparative Example 1, it can be seen that adding sulfate during pre-sintering significantly improves the discharge capacity and rate performance of the material, while also maintaining good room temperature and high temperature cycle retention. Comparing the electrical performance test results of Example 1 and Comparative Example 2, it can be seen that stepwise pre-sintering can further improve the discharge capacity and rate performance of the material. This demonstrates that the lithium nickel composite oxide positive electrode material of the present invention exhibits good discharge capacity and excellent rate performance.

Claims

1. A lithium nickel composite oxide positive electrode material, A lithium nickel composite oxide positive electrode material, characterized in that the porosity of each cross section measured by dividing the cross section of the lithium nickel composite oxide into four equal parts along the radial length using a scanning electron microscope is 3% to 8%, and the total porosity of the cross section is 3% to 8%.

2. The specific surface area of ​​the lithium nickel composite oxide positive electrode material is 0.5 to 1.0 m ２ 2. The lithium nickel composite oxide positive electrode material according to claim 1, wherein the SiO 2 content is 1 / g.

3. The lithium nickel composite oxide positive electrode material is Li ａ Ni １－ｘ－ｙ－ｚ Co ｘ Mn ｙ M ｚ O ２ a 1.10≦a≦1.10, 0<x≦0.15, 0<y≦0.15, 0<z≦0.02, and x+y+z≦0.

2.

4. 4. The lithium nickel composite oxide positive electrode material according to claim 3, wherein the substrate further contains an S element, and the S element accounts for 0.02% to 0.2% of the total mass of the lithium nickel composite oxide positive electrode material.

5. 4. The lithium nickel composite oxide positive electrode material according to claim 3, wherein the boron element in the boron coating layer accounts for 0.05% to 0.2% of the total mass of the lithium nickel composite oxide positive electrode material.

6. A method for producing the lithium nickel composite oxide positive electrode material according to any one of claims 1 to 5, Step (1) of mixing nickel-cobalt-manganese hydroxide with M-containing sulfate, followed by stepwise pre-sintering at low temperature to obtain a pre-sintered precursor; (2) mixing the lithium source and the pre-sintering precursor according to a stoichiometric ratio, followed by high-temperature sintering to obtain a primary sintered body; and (3) washing the primary sintered substrate with deionized water, drying, mixing with a coating agent, and sintering the mixture to obtain a lithium nickel composite oxide positive electrode material.

7. 7. The method of claim 6, wherein in step (1), the stepwise pre-sintering at low temperatures comprises first heating the material to 150-200°C at a rate of 3-5°C / min in an air or oxygen atmosphere, sintering at that temperature for 1-2 hours, then heating the material to 300-400°C at a rate of 1-3°C / min, sintering at that temperature for 2-5 hours, and finally cooling the material to room temperature.

8. 7. The method of claim 6, wherein in step (2), the high-temperature sintering process comprises first heating the material to 450-550°C at a rate of 1-5°C / min in an air or oxygen atmosphere, maintaining the temperature for 3-7 hours, then heating the material to 600-750°C at a rate of 1-5°C / min, maintaining the temperature for 8-15 hours, and finally cooling the material to room temperature.

9. 7. The method according to claim 6, wherein in step (3), the sintering process comprises heating the material to 300-400°C at a rate of 1-5°C / min in an air or oxygen atmosphere, maintaining the temperature for 3-12 hours, and then naturally cooling the material to room temperature.

10. 7. The method of claim 6, wherein in step (3), the coating agent is one or more of boric acid and boron oxide.

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