Ternary polycrystalline positive electrode material and preparation method therefor, and lithium-ion battery

Abstract

A ternary polycrystalline positive electrode material, which is a secondary sphere formed by the agglomeration of primary particles. The secondary sphere is partitioned into four equal portions in the direction from the center of the secondary sphere to the surface thereof, i.e., a core layer (a), a first intermediate layer (b), a second intermediate layer (c) and a shell layer (d), respectively. The cross sections of the ternary polycrystalline positive electrode material are observed by using a scanning electron microscope, which shows that the porosity is sequentially decreased from inside to outside. A preparation method therefor comprises: mixing a positive electrode material precursor, a lithium source and a Li-containing polyanionic compound, and then sintering the resulting mixture at a high temperature to obtain a single-fired matrix; and then washing and drying the single-fired matrix, mixing same with a coating agent, and then sintering same to obtain a ternary polycrystalline positive electrode material.

Description

A ternary polycrystalline positive electrode material and preparation method thereof and lithium ion battery

[0001] Related applications

[0002] This application claims priority to the Chinese patent application filed on March 27, 2024, with application number 202410360800.8 and entitled “A ternary polycrystalline positive electrode material, a preparation method thereof, and a lithium-ion battery”, the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present invention relates to the field of lithium-ion batteries, and in particular to a ternary polycrystalline positive electrode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0004] With the rapid development of new energy electric vehicles, the demand for high energy density and low cost in power batteries is increasing. Nickel-rich layered cathode materials are considered the most promising candidates for next-generation lithium-ion batteries for electric vehicles. However, as nickel content increases, material performance gradually deteriorates. Therefore, it is imperative to improve the capacity of cathode materials while ensuring their cycling stability and safety.

[0005] The ternary precursors prepared by traditional preparation methods are simple, but after lithiation, the internal structure of the particles is generally a structure with fewer pores or uneven distribution. This type of structure will further aggravate the diffusion resistance of lithium ions and the anisotropic volume changes, thereby leading to a significant deterioration of electrochemical performance.

[0006] Patent document CN114314692B discloses a ternary positive electrode precursor whose porosity increases radially from the center of the particle. This positive electrode precursor improves the rate performance of the material to a certain extent, but when it is sintered with a lithium source, lithium ions are difficult to diffuse to the center of the particle, resulting in lithium deficiency. At the same time, it reduces the contact with the electrolyte, thereby increasing the transmission barrier of lithium ions and affecting the electrical properties of the material. Summary of the Invention

[0007] The technical solutions proposed in this application are:

[0008] A ternary polycrystalline positive electrode material is a secondary sphere formed by agglomeration of primary particles. The secondary sphere is divided into four equal parts along the direction from the center to the surface of the secondary sphere, namely, an inner core layer, a first intermediate layer, a second intermediate layer, and an outer shell layer. A scanning electron microscope is used to observe the cross-section of the ternary polycrystalline positive electrode material. The cross-sectional porosity decreases from the inside to the outside. The cross-sectional porosity of the inner core layer is 6%-15%, the cross-sectional porosity of the first intermediate layer is 4%-10%, the cross-sectional porosity of the second intermediate layer is 2.5%-8%, and the cross-sectional porosity of the outer shell layer is 0.5%-5%.

[0009] In the above-mentioned ternary polycrystalline positive electrode material, preferably, the difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer is 2%-7%.

[0010] The above-mentioned ternary polycrystalline positive electrode material preferably has a total porosity of 2%-9% in the cross section.

[0011] The above-mentioned ternary polycrystalline positive electrode material, preferably, the median particle size D50 of the secondary spheres of the ternary polycrystalline positive electrode material is 10-16 μm, and the specific surface area is 0.05-0.5 m 2 / g.

[0012] The above-mentioned ternary polycrystalline positive electrode material, preferably, the matrix chemical formula of the ternary polycrystalline positive electrode material includes LimNi 1-x-y Mn x Co y O2, where 0.90≤m≤1.10, 0<x≤0.15, 0<y≤0.15, x+y≤0.2.

[0013] The above-mentioned ternary polycrystalline positive electrode material, preferably, the ternary polycrystalline positive electrode material matrix also contains M element, M element is selected from one or more of S, Ti, P, B, Si, wherein the mass of M element accounts for 0.05% to 0.8% of the total mass of the ternary polycrystalline positive electrode material.

[0014] The above-mentioned ternary polycrystalline positive electrode material, preferably, comprises a boron coating layer on the surface of the ternary polycrystalline positive electrode material, wherein the boron element in the boron coating layer accounts for 0.05% to 0.2% of the total mass of the ternary polycrystalline positive electrode material.

[0015] As a general inventive concept, the present application also provides a method for preparing the above-mentioned ternary polycrystalline positive electrode material, comprising the following steps:

[0016] (1) mixing a lithium source, a cathode material precursor, and a Li-containing polyanion compound in a stoichiometric ratio and sintering at a high temperature to obtain a monoalkyl matrix; wherein the Li-containing polyanion compound is at least one of Li2SO4, Li2TiO3, Li3PO4, Li2B4O7, LiBO2, and Li2SiO3;

[0017] (2) The monoalkyl matrix is ​​washed with water, dried, mixed with a coating agent, and then sintered to obtain a ternary polycrystalline positive electrode material.

[0018] In the above-mentioned preparation method, preferably, in step (1), the high-temperature sintering process includes: first, heating to 450-550°C at a rate of 1-5°C / min in an air or oxygen atmosphere for a first heat preservation period of 3-7 hours, then heating to 600-750°C at a rate of 1-5°C / min for a second heat preservation period of 8-15 hours, then cooling to 550-700°C at a rate of 5-10°C / min for a third heat preservation period of 2-4 hours, and finally naturally cooling to room temperature to obtain a sintered matrix. In the sintering process of the present application, the use of this specific cooling program can ensure that the Li-containing polyanion compound dopant can better enter the interior of the particles, thereby better achieving the purpose of high internal porosity and low external porosity.

[0019] In the above preparation method, preferably, in step (1), the temperature of the second insulation stage is 50-150° C. higher than the temperature of the third insulation stage.

[0020] In the above preparation method, preferably, in step (2), the sintering process includes heating to 300-400°C at a rate of 1-5°C / min in air or oxygen atmosphere and keeping the temperature for 3-12 hours.

[0021] In the above preparation method, preferably, the lithium source includes one or both of lithium hydroxide and lithium carbonate, and the coating agent includes one or both of boric acid and boron oxide.

[0022] As a general inventive concept, the present application also provides a lithium-ion battery, wherein the positive electrode material used in the lithium-ion battery is the above-mentioned ternary polycrystalline positive electrode material or the ternary polycrystalline positive electrode material prepared by the above-mentioned preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a schematic diagram showing a cross section of a ternary polycrystalline cathode material divided into four equal parts according to radius length in the present application;

[0024] FIG2 is a cross-sectional electron microscope image of the ternary polycrystalline positive electrode material in Example 1 of the present application;

[0025] FIG3 is a cross-sectional electron microscope image of the ternary polycrystalline positive electrode material in Comparative Example 1 of the present application;

[0026] FIG4 is a comparison chart of the first-cycle discharge capacity of the ternary polycrystalline positive electrode materials in the examples of the present application and the comparative examples.

[0027] In the figure, a, inner core layer; b, first intermediate layer; c, second intermediate layer; d, outer shell layer. DETAILED DESCRIPTION

[0028] To facilitate understanding of the present application, the present application will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the scope of protection of the present application is not limited to the following specific embodiments.

[0029] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this application.

[0030] Compared with traditional technologies, the beneficial effects of this application are:

[0031] (1) The cross-sectional porosity of the ternary polycrystalline positive electrode material of the present application decreases from the inside to the outside. This unique gradient structure enables the positive electrode material to be in more complete contact with the electrolyte, forming more diffusion paths, reducing the transmission barrier of lithium ions, and effectively improving the transmission rate of lithium ions, thereby improving the discharge performance of the positive electrode material and improving the cycle performance of the material.

[0032] (2) The cross-sectional porosity of the outer shell layer of the ternary polycrystalline positive electrode material of the present application is the smallest, which is 0.5%-5%, presenting a relatively dense outer shell structure, so that the overall positive electrode material exhibits a dense outer structure and a relatively loose inner structure, which can better adapt to the anisotropic volume change caused by the H2-H3 phase transition of the material under high voltage, and improve the stability of the overall structure.

[0033] (3) In the preparation method of the present application, the ternary precursor prepared by the traditional method can be directly synthesized through multi-stage lithiation sintering and doping to synthesize a positive electrode material with a porosity gradually decreasing from the inside to the outside. The sintering cost is low and the process is stable, which is suitable for large-scale production.

[0034] (4) The preparation method of the present application introduces a Li-containing polyanion compound, which can enable the positive electrode material to form an internal porous structure. At the same time, combined with a period of insulation at a higher temperature, the polyanion compound can more effectively penetrate into the center of the particle, and more effectively form a ternary positive electrode material with a porosity that decreases radially from the center of the particle.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0036] The cross sections involved in the following embodiments and comparative examples are all central cross sections of the ternary polycrystalline positive electrode material.

[0037] Example 1:

[0038] A ternary polycrystalline positive electrode material of the present application is a secondary ball of primary particle agglomeration. The secondary ball is divided into four equal parts along the direction from the center to the surface of the secondary ball, namely, an inner core layer, a first intermediate layer, a second intermediate layer and an outer shell layer. The structural schematic diagram is shown in Figure 1. The cross section of the ternary polycrystalline positive electrode material is observed using a scanning electron microscope. The total porosity of the cross section is 4.8%, and the cross-sectional porosity decreases from the inside to the outside. The cross-sectional porosity of the inner core layer is 6.4%, the porosity of the first intermediate layer is 5.9%, the porosity of the second intermediate layer is 4.9%, and the cross-sectional porosity of the outer shell layer is 3.9%. The difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer is 2.5%; the matrix chemical formula of the ternary polycrystalline positive electrode material is Li 1.02 Ni 0.94 Co 0.04 Mn 0.02 O2·0.01Li3PO4, and the substrate surface is coated with a boron coating layer, and the mass of the boron element in the boron coating layer accounts for 0.1% of the total mass of the ternary polycrystalline positive electrode material; the median particle size D50 of the secondary ball of the ternary polycrystalline positive electrode material is 13.5μm, and the specific surface area is 0.21m 2 / g.

[0039] The preparation method of the ternary polycrystalline positive electrode material in this embodiment comprises the following steps:

[0040] (1) LiOH·H2O, cathode material precursor Ni 0.94 Co 0.04 Mn 0.02 (OH)2 and Li3PO4 were ground and mixed in a molar ratio of 1.02:1:0.01, placed in a calcining furnace, and heated to 500°C at a rate of 5°C / min in a pure oxygen atmosphere, kept warm for 5 hours, then heated to 725°C at a rate of 3°C / min, kept warm for 10 hours, then cooled to 600°C at a rate of 10°C / min, kept warm for 4 hours, and naturally cooled to room temperature to obtain a monoalkyl matrix;

[0041] (2) The monoalkyl matrix was washed with deionized water for 10 min, with a solid-liquid mass ratio of 1:1 during washing. The temperature of the deionized water was controlled at 10°C. After washing, the sample was placed in a vacuum oven at 150°C and vacuum dried for 8 h. It was then naturally cooled to room temperature and passed through a 300-mesh sieve to obtain a washed sample.

[0042] (3) The washed sample was mixed evenly with H3BO3, wherein the ratio of the total molar number of metal elements in the precursor to the molar number of boron elements was 1:0.01. The mixed material was placed in a calcining furnace, and in an air atmosphere, the temperature was raised to 350°C at 3°C / min and maintained for 5h. The material was then naturally cooled to room temperature to obtain a ternary polycrystalline positive electrode material, and its cross-sectional electron microscope image is shown in Figure 2.

[0043] Example 2:

[0044] A ternary polycrystalline positive electrode material of the present application is a secondary ball of primary particle agglomeration. The secondary ball is divided into four equal parts along the direction from the center to the surface of the secondary ball, namely, an inner core layer, a first intermediate layer, a second intermediate layer and an outer shell layer. The structural schematic diagram is shown in Figure 1. The cross section of the ternary polycrystalline positive electrode material is observed using a scanning electron microscope. The total porosity of the cross section is 5.28%, and the cross-sectional porosity decreases from the inside to the outside. The cross-sectional porosity of the inner core layer is 7.9%, the porosity of the first intermediate layer is 6.9%, the porosity of the second intermediate layer is 5.8%, and the cross-sectional porosity of the outer shell is 2.1%. The difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer is 5.8%; the matrix chemical formula of the ternary polycrystalline positive electrode material is Li 1.02 Ni 0.94 Co 0.04 Mn 0.02 O2·0.01Li2TiO3, and the substrate surface is coated with a boron coating layer, the mass of the boron element in the boron coating layer accounts for 0.1% of the total mass of the ternary polycrystalline positive electrode material; the median particle size D50 of the secondary ball of the ternary polycrystalline positive electrode material is 13.5μm, and the specific surface area is 0.16m 2 / g.

[0045] The preparation method of the ternary polycrystalline positive electrode material in this embodiment comprises the following steps:

[0046] (1) LiOH·H2O, cathode material precursor Ni 0.94 Co 0.04 Mn 0.02 (OH)2 and Li2TiO3 were ground and mixed in a molar ratio of 1.02:1:0.01, placed in a calcining furnace, and heated to 500°C at a rate of 5°C / min in a pure oxygen atmosphere, then kept at this temperature for 5 hours, then heated to 725°C at a rate of 3°C / min, kept at this temperature for 10 hours, then cooled to 600°C at a rate of 10°C / min, kept at this temperature for 4 hours, and naturally cooled to room temperature to obtain a monoalkyl matrix;

[0047] (2) The monoalkyl matrix was washed with deionized water for 10 min, with a solid-liquid mass ratio of 1:1 during washing. The temperature of the deionized water was controlled at 10°C. After washing, the sample was placed in a vacuum oven at 150°C and vacuum dried for 8 h. It was then naturally cooled to room temperature and passed through a 300-mesh sieve to obtain a washed sample.

[0048] (3) The washed sample was mixed evenly with H3BO3, wherein the ratio of the total molar number of the metal elements of the precursor to the molar number of the boron element was 1:0.01. The mixed material was placed in a calcination furnace, and in an air atmosphere, the temperature was raised to 350°C at 3°C / min and maintained for 5h. The mixture was naturally cooled to room temperature to obtain a ternary polycrystalline positive electrode material.

[0049] Example 3:

[0050] A ternary polycrystalline positive electrode material of the present application is a secondary ball of primary particle agglomeration. The secondary ball is divided into four equal parts along the direction from the center to the surface of the secondary ball, namely, an inner core layer, a first intermediate layer, a second intermediate layer and an outer shell layer. The structural schematic diagram is shown in Figure 1. The cross section of the ternary polycrystalline positive electrode material is observed using a scanning electron microscope. The total porosity of the cross section is 5.73%, and the cross-sectional porosity decreases from the inside to the outside. The cross-sectional porosity of the inner core layer is 8.5%, the porosity of the first intermediate layer is 7.2%, the porosity of the second intermediate layer is 5.7%, and the cross-sectional porosity of the outer shell layer is 3.0%. The difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer is 5.5%; the chemical formula of the ternary polycrystalline positive electrode material is Li 1.02 Ni 0.90 Co 0.06 Mn 0.04 O2·0.01Li2SO4, and the surface of the matrix is ​​coated with boron element, the mass of which accounts for 0.1% of the total mass of the ternary polycrystalline positive electrode material; the median particle size D50 of the secondary ball of the ternary polycrystalline positive electrode material is 14.0μm, and the specific surface area is 0.19m 2 / g.

[0051] The preparation method of the ternary polycrystalline positive electrode material in this embodiment comprises the following steps:

[0052] (1) LiOH·H2O, cathode material precursor Ni 0.90 Co 0.06 Mn 0.04 (OH)2 and Li2SO4 were ground and mixed in a molar ratio of 1.02:1:0.01, placed in a calcining furnace, and heated to 500°C at a rate of 5°C / min in a pure oxygen atmosphere, then kept at that temperature for 5 hours, then heated to 735°C at a rate of 3°C / min, kept at that temperature for 10 hours, then cooled to 615°C at a rate of 10°C / min, kept at that temperature for 4 hours, and naturally cooled to room temperature to obtain a monoalkyl matrix;

[0053] (2) The monoalkyl matrix was washed with deionized water for 10 min, with a solid-liquid mass ratio of 1:1 during washing. The temperature of the deionized water was controlled at 10°C. After washing, the sample was placed in a vacuum oven at 150°C and vacuum dried for 8 h. It was then naturally cooled to room temperature and passed through a 300-mesh sieve to obtain a washed sample.

[0054] (3) The washed sample was mixed evenly with H3BO3, wherein the ratio of the total molar number of the metal elements of the precursor to the molar number of the boron element was 1:0.01. The mixed material was placed in a calcination furnace, and in an air atmosphere, the temperature was raised to 350°C at 3°C / min and maintained for 5h. The mixture was naturally cooled to room temperature to obtain a ternary polycrystalline positive electrode material.

[0055] Comparative Example 1:

[0056] The ternary polycrystalline positive electrode material of this comparative example was cut into particles, and its cross-sectional electron microscope image is shown in Figure 3. The cross-sectional view of the ternary polycrystalline positive electrode material was observed using a scanning electron microscope. The total porosity of the cross-sectional view was 4.7%. The particle pore area was divided into four regions with a radius of four equal parts, including an inner core layer, a first intermediate layer, a second intermediate layer, and an outer shell layer from the inside to the outside. The cross-sectional porosity of the inner core layer was 4.8%, the porosity of the first intermediate layer was 4.4%, the porosity of the second intermediate layer was 5.8%, and the cross-sectional porosity of the outer shell layer was 5.4%.

[0057] The preparation method of the ternary polycrystalline positive electrode material in this comparative example is compared with that in Example 1, the only difference being that Li3PO4 is not added during the pre-calcination process. The remaining steps are the same and will not be repeated here.

[0058] Comparative Example 2:

[0059] The ternary polycrystalline positive electrode material of this comparative example was cut into particles and the cross-section of the ternary polycrystalline positive electrode material was observed using a scanning electron microscope. The total porosity of the cross-section was 3.3%. The particle pore area was divided into four regions with a radius of four equal parts, including an inner core layer, a first intermediate layer, a second intermediate layer and an outer shell layer from the inside to the outside. The cross-sectional porosity of the inner core layer was 3.6%, the porosity of the first intermediate layer was 3.5%, the porosity of the second intermediate layer was 3.8%, and the cross-sectional porosity of the outer shell layer was 3.0%.

[0060] The preparation method is compared with Example 3, the only difference being that Li2SO4 is not added during the pre-calcination process, and the remaining steps are the same and will not be described in detail.

[0061] Comparative Example 3:

[0062] The ternary polycrystalline positive electrode material of this comparative example was cut into particles and the cross-section of the ternary polycrystalline positive electrode material was observed using a scanning electron microscope. The total porosity of the cross-section was 3.8%. The particle pore area was divided into four regions with a radius of four equal parts, including an inner core layer, a first intermediate layer, a second intermediate layer and an outer shell layer from the inside to the outside. The cross-sectional porosity of the inner core layer was 3.2%, the porosity of the first intermediate layer was 3.5%, the porosity of the second intermediate layer was 5.3%, and the cross-sectional porosity of the outer shell layer was 4.8%.

[0063] The preparation method of the ternary polycrystalline positive electrode material of this comparative example is different from that of Example 3, except that the cooling process of step (1) is different, and the other steps are the same. The preparation process of step (1) of this comparative example is: LiOH·H2O, positive electrode material precursor Ni 0.90 Co 0.06 Mn 0.04(OH)2 and Li2SO4 were ground and mixed in a molar ratio of 1.02:1:0.01, placed in a calcination furnace, and heated to 500°C at a rate of 5°C / min under a pure oxygen atmosphere, then kept warm for 5 hours, then heated to 735°C at a rate of 3°C / min, kept warm for 10 hours, and then naturally cooled to room temperature to obtain a monoalkyl matrix.

[0064] Performance testing:

[0065] (1) Porosity test of ternary polycrystalline cathode materials

[0066] The positive electrode material particles were cut using an ion beam milling device (CP) to obtain samples with observable particle cross-sections. The cross-sectional images were captured using a scanning electron microscope (SEM). The particle pore area was then extracted from the captured photos using the image analysis software ImageJ. The particle pore area was then divided into four regions with a radius of four equal parts using a python script. Finally, the porosity in each region and the total porosity of the particle cross-section were calculated using the script.

[0067] (2) Power-off performance test

[0068] The positive electrode material was mixed with the conductive agent SP and binder (PVDF) in a ratio of 8:1:1. Using a pipette, an appropriate amount of NMP solution was added to the mixed powder material as a solvent. The mixture was stirred, coated, and dried. The mixture was assembled into CR2032 button cells, packaged, and allowed to stand for 12 hours. The resulting button cells were then placed on a blue battery test system for electrochemical performance testing.

[0069] The test items include: charge and discharge tests in the voltage range of 3.0~4.3V, 25℃ and current density of 0.5C. The results are shown in Table 1 and Figure 4.

[0070] Table 1: Electrical performance test of Examples 1-3 and Comparative Examples 1-2

[0071] The electrical performance test results of Examples 1 and 2 and Comparative Example 1, and Example 3 and Comparative Examples 2 and 3 show that the ternary polycrystalline positive electrode material in the examples of the present application has a structure in which the porosity decreases from the inside to the outside, which can effectively improve the transmission rate of lithium ions and the stability of the overall structure, as reflected in the improvement of discharge capacity and cycle retention rate. It can be seen from this that the ternary polycrystalline positive electrode material of the present application has excellent discharge capacity and cycle stability.

Claims

1. A ternary polycrystalline positive electrode material, characterized in that: The ternary polycrystalline positive electrode material is a secondary ball formed by agglomeration of primary particles. The secondary ball is divided into four equal parts along the direction from the center to the surface of the secondary ball, namely, an inner core layer, a first intermediate layer, a second intermediate layer and an outer shell layer. The cross-section of the ternary polycrystalline positive electrode material was observed using a scanning electron microscope. The cross-sectional porosity decreased from the inside to the outside. The cross-sectional porosity of the inner core layer was approximately 6%-15%, the cross-sectional porosity of the first intermediate layer was approximately 4%-10%, the cross-sectional porosity of the second intermediate layer was approximately 2.5%-8%, and the cross-sectional porosity of the outer shell layer was approximately 0.5%-5%.

2. The ternary polycrystalline cathode material according to claim 1, wherein: The difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer is approximately 2%-7%.

3. The ternary polycrystalline positive electrode material according to claim 1 or 2, characterized in that: The total porosity of the cross section of the ternary polycrystalline positive electrode material is about 2%-9%.

4. The ternary polycrystalline cathode material according to any one of claims 1 to 3, characterized in that The median particle size D50 of the secondary spheres of the ternary polycrystalline positive electrode material is approximately 10-16 μm.

5. The ternary polycrystalline cathode material according to any one of claims 1 to 4, characterized in that: The specific surface area of ​​the secondary spheres of the ternary polycrystalline positive electrode material is about 0.05-0.5m 2 / g.

6. The ternary polycrystalline cathode material according to any one of claims 1 to 5, characterized in that The matrix chemical formula of the ternary polycrystalline positive electrode material includes Li m Ni 1-x-y Mn x Co y O2, where 0.90≤m≤1.10, 0<x≤0.15, 0<y≤0.15, x+y≤0.

2.

7. The ternary polycrystalline cathode material according to claim 6, wherein: The matrix also contains M element, which is selected from one or more of S, Ti, P, B, and Si. The mass of M element accounts for about 0.05% to 0.8% of the total mass of the ternary polycrystalline positive electrode material.

8. The ternary polycrystalline positive electrode material according to claim 6 or 7, characterized in that: The surface of the ternary polycrystalline positive electrode material comprises a boron coating layer, wherein the boron element in the boron coating layer accounts for approximately 0.05% to 0.2% of the total mass of the ternary polycrystalline positive electrode material.

9. A method for preparing a ternary polycrystalline cathode material according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) mixing a positive electrode material precursor, a lithium source, and a Li-containing polyanion compound in a stoichiometric ratio and sintering at a high temperature to obtain a monoalkyl matrix; wherein the Li-containing polyanion compound is at least one of Li2SO4, Li2TiO3, Li3PO4, Li2B4O7, LiBO2, and Li2SiO3; (2) The monoalkyl matrix is ​​washed with water, dried, mixed with a coating agent, and then sintered to obtain a ternary polycrystalline positive electrode material.

10. The preparation method according to claim 9, characterized in that In step (1), the high-temperature sintering process includes: first, heating to 450-550°C at a rate of about 1-5°C / min in air or oxygen atmosphere for a first heat preservation period of about 3-7 hours, then heating to 600-750°C at a rate of 1-5°C / min for a second heat preservation period of about 8-15 hours, then cooling to 550-700°C at a rate of 5-10°C / min for a third heat preservation period of about 2-4 hours, and finally naturally cooling to room temperature to obtain a sintered matrix.

11. The preparation method according to claim 9 or 10, characterized in that: In step (1), the temperature of the second insulation stage is about 50-150° C. higher than the temperature of the third insulation stage.

12. The preparation method according to any one of claims 9 to 11, characterized in that In step (2), the sintering process refers to heating the material to 300-400° C. at a rate of about 1-5° C. / min in an air or oxygen atmosphere and keeping the temperature for about 3-12 hours.

13. The preparation method according to any one of claims 9 to 12, characterized in that The lithium source includes lithium hydroxide and / or lithium carbonate.

14. The preparation method according to any one of claims 9 to 13, characterized in that The coating agent includes boric acid and / or boron oxide.

15. A lithium ion battery, characterized in that: The positive electrode material used in the lithium-ion battery is the ternary polycrystalline positive electrode material according to any one of claims 1 to 8 or the ternary polycrystalline positive electrode material prepared by the preparation method according to any one of claims 9 to 14.

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