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

Abstract

A ternary polycrystalline positive electrode material is a secondary ball formed by agglomerating primary particles, the secondary ball is equally divided into four parts in the direction from the center to the surface of the secondary ball, the four parts are an inner core layer, a first middle layer, a second middle layer and a shell layer, and the section of the ternary polycrystalline positive electrode material is observed through a scanning electron microscope. The porosity is sequentially reduced from inside to outside. The preparation method comprises the following steps: mixing a positive electrode material precursor, a lithium source and a Li-containing polyanion compound, and sintering at a high temperature to obtain a primary sintered matrix; and washing and drying the primary sintering substrate, mixing the primary sintering substrate with a coating agent, and sintering to obtain the ternary polycrystalline positive electrode material. The invention also discloses a lithium ion battery. The porosity of the section of the positive electrode material is sequentially reduced from inside to outside, so that the positive electrode material can be in more sufficient contact with an electrolyte, more diffusion paths are formed, the transmission obstruction of lithium ions is reduced, and the transmission rate of the lithium ions is effectively improved, so that the discharge performance of the positive electrode material is improved, and the cycle performance of the material is improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and in particular relates to a ternary polycrystalline positive electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] 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.

[0003] 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.

[0004] 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

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a ternary polycrystalline positive electrode material and a preparation method thereof and a lithium ion battery.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0007] 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%.

[0008] 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%.

[0009] The above-mentioned ternary polycrystalline positive electrode material preferably has a total porosity of 2%-9% in the cross section.

[0010] 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.

[0011] The above-mentioned ternary polycrystalline positive electrode material, preferably, 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.

[0012] 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.

[0013] 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.

[0014] As a general inventive concept, the present invention also provides a method for preparing the above-mentioned ternary polycrystalline positive electrode material, comprising the following steps:

[0015] (1) A lithium source, a cathode material precursor, and a Li-containing polyanion compound are mixed in a stoichiometric ratio and then sintered at a high temperature to obtain an alkyl matrix; wherein the Li-containing polyanion compound is Li2SO4, Li2TiO 3、 At least one of Li3PO4, Li2B4O7, LiBO2, and Li2SiO3;

[0016] (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.

[0017] 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 invention, 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] As a general inventive concept, the present invention 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.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The cross-sectional porosity of the ternary polycrystalline positive electrode material of the present invention 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.

[0024] (2) The cross-sectional porosity of the outer shell layer of the ternary polycrystalline positive electrode material of the present invention is the smallest, which is 0.5%-5%, presenting a relatively dense outer shell structure, so that the positive electrode material as a whole exhibits a dense outer structure and a 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.

[0025] (3) During the preparation method of the present invention, 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.

[0026] (4) The preparation method of the present invention 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the present invention dividing the cross section of the ternary polycrystalline positive electrode material into four equal parts according to the radius length;

[0028] Figure 2 This is a cross-sectional electron microscope image of the ternary polycrystalline positive electrode material in Example 1 of the present invention;

[0029] Figure 3 This is a cross-sectional electron microscope image of the ternary polycrystalline positive electrode material in Comparative Example 1 of the present invention;

[0030] Figure 4 2 is a comparison chart of the first-cycle discharge capacity of the ternary polycrystalline positive electrode materials in the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0031] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0032] 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 the present invention.

[0033] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0034] The cross sections involved in the following embodiments and comparative examples are all central cross sections of the ternary polycrystalline positive electrode material.

[0035] Example 1:

[0036] A ternary polycrystalline positive electrode material of the present invention 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, which are the inner core layer, the first intermediate layer, the second intermediate layer and the outer shell layer. The structural diagram is shown as follows: Figure 1 As shown, 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 4.8%, and the cross-sectional porosity decreased from the inside to the outside. The cross-sectional porosity of the inner core layer was 6.4%, the porosity of the first intermediate layer was 5.9%, the porosity of the second intermediate layer was 4.9%, and the cross-sectional porosity of the outer shell was 3.9%. The difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer was 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.

[0037] The preparation method of the ternary polycrystalline positive electrode material in this embodiment comprises the following steps:

[0038] (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;

[0039] (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.

[0040] (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 heated to 350°C at 3°C / min in an air atmosphere and maintained for 5h. The material was then naturally cooled to room temperature to obtain a ternary polycrystalline positive electrode material. The cross-sectional electron microscope image is shown in FIG. Figure 2 shown.

[0041] Example 2:

[0042] A ternary polycrystalline positive electrode material of the present invention 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, which are the inner core layer, the first intermediate layer, the second intermediate layer and the outer shell layer. The structural diagram is shown as follows: Figure 1 As shown, 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 5.28%, and the cross-sectional porosity decreased from the inside to the outside. The cross-sectional porosity of the inner core layer was 7.9%, the porosity of the first intermediate layer was 6.9%, the porosity of the second intermediate layer was 5.8%, and the cross-sectional porosity of the outer shell was 2.1%. The difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer was 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.

[0043] The preparation method of the ternary polycrystalline positive electrode material in this embodiment comprises the following steps:

[0044] (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;

[0045] (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.

[0046] (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.

[0047] Example 3:

[0048] A ternary polycrystalline positive electrode material of the present invention 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, which are the inner core layer, the first intermediate layer, the second intermediate layer and the outer shell layer. The structural diagram is shown as follows: Figure 1 As shown, 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 5.73%, and the cross-sectional porosity decreased from the inside to the outside. The cross-sectional porosity of the inner core layer was 8.5%, the porosity of the first intermediate layer was 7.2%, the porosity of the second intermediate layer was 5.7%, and the cross-sectional porosity of the outer shell was 3.0%. The difference between the cross-sectional porosity of the inner core layer and the cross-sectional porosity of the outer shell layer was 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.

[0049] The preparation method of the ternary polycrystalline positive electrode material in this embodiment comprises the following steps:

[0050] (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;

[0051] (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.

[0052] (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.

[0053] Comparative Example 1:

[0054] The ternary polycrystalline positive electrode material of this comparative example is cut into particles, and its cross-sectional electron microscope image is as follows: Figure 3 As shown, 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 4.7%. The particle pore area was divided into four regions with a radius of four equal parts, including the inner core layer, the first intermediate layer, the second intermediate layer and the 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%.

[0055] The specific 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.

[0056] Comparative Example 2:

[0057] 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%.

[0058] The specific preparation method is compared with Example 3, the only difference is that Li2SO4 is not added during the pre-calcination process, and the remaining steps are the same and will not be repeated here.

[0059] Comparative Example 3:

[0060] 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%.

[0061] The specific preparation method of the ternary polycrystalline positive electrode material of this comparative example is compared with that of Example 3, the only difference being the cooling process of step (1), while the other steps are the same. The preparation process of step (1) of this comparative example is as follows: LiOH·H2O, positive electrode material precursor Ni 0.90 Co0.06 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.

[0062] Performance testing:

[0063] (1) Porosity test of ternary polycrystalline cathode materials

[0064] 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.

[0065] (2) Power-off performance test

[0066] 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.

[0067] 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 shown.

[0068] Table 1: Electrical performance test of Examples 1-3 and Comparative Examples 1-2

[0069] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 0.1C charging capacity mAh / g 248.0 248.5 242.4 246.0 241.5 241.9 0.1C discharge capacity mAh / g 227.8 228.5 223.6 222.5 215.0 217.1 0.1C charge and discharge efficiency% 91.9 92.0 92.2 90.4 89.0 89.7 50-cycle cycle retention rate (1C)% 96.2 96.8 95.9 94.2 94.8 95.0

[0070] 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 embodiments of the present invention 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 invention 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 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. The cross-section of the ternary polycrystalline positive electrode material is observed using a scanning electron microscope. The cross-sectional porosity decreases from the inside to the outside. Among them, 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%.

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 2%-7%.

3. The ternary polycrystalline cathode material according to claim 1, wherein: The total porosity of the cross section of the ternary polycrystalline positive electrode material is 2%-9%.

4. The ternary polycrystalline cathode material according to claim 1, wherein: 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.

5. The ternary polycrystalline cathode material according to claim 1, wherein: 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.

6. The ternary polycrystalline cathode material according to claim 5, 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 0.05% to 0.8% of the total mass of the ternary polycrystalline positive electrode material.

7. The ternary polycrystalline cathode material according to claim 5, wherein: 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 0.05% to 0.2% of the total mass of the ternary polycrystalline positive electrode material.

8. A method for preparing a ternary polycrystalline positive electrode material according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) A positive electrode material precursor, a lithium source, and a Li-containing polyanion compound are mixed in a stoichiometric ratio and then sintered at a high temperature to obtain an alkyl matrix; wherein the Li-containing polyanion compound is Li2SO4, Li2TiO 3、 At least one of 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.

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

10. The preparation method according to claim 8, characterized in that In step (1), the temperature of the second insulation stage is 50-150° C. higher than the temperature of the third insulation stage.

11. The preparation method according to claim 8, wherein In step (2), the sintering process refers to heating the material 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.

12. The preparation method according to claim 8, wherein The lithium source includes lithium hydroxide and / or lithium carbonate, and the coating agent includes boric acid and / or boron oxide.

13. 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 7 or the ternary polycrystalline positive electrode material prepared by the preparation method according to any one of claims 8 to 12.

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