Ternary positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of positive electrode materials, and particularly relates to a ternary positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: S1, mixing a Ni < x > Co < y > Mn < z > (OH) < 2 > precursor and a lithium source, and performing first sintering to obtain a product A; in the NixCoyMnz (OH) 2 precursor, x is more than or equal to 0.50 and less than or equal to 0.70, y is more than or equal to 0.10 and less than or equal to 0.20, z is more than or equal to 0.20 and less than or equal to 0.30, and x + y + z is equal to 1; s2, mixing the product A with a tungsten-containing dopant, and performing secondary sintering to obtain a product B; the second sintering condition is as follows: the temperature is raised to 600-830 DEG C at the rate of 1.5-5 DEG C / min, and sintering is performed for 3-7 hours; and S3, mixing the product B and a coating agent, and carrying out third sintering to obtain the ternary positive electrode material, the positive electrode material disclosed by the invention has excellent cycling stability when being used in a high-voltage (greater than 4.4 V) environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of positive electrode materials, and specifically relates to a ternary positive electrode material and a preparation method and application thereof. Background Art

[0002] As the application of lithium-ion batteries in the field of new energy vehicles gradually expands, the driving range has become a key factor restricting the development of new energy vehicles. Improving the energy density of lithium-ion batteries is an effective way to solve the anxiety of driving range. The high-voltage route increases the battery charging cut-off voltage so that the positive electrode material can release more lithium ions at a higher voltage, thereby increasing the capacity and working voltage at the same time, thereby achieving the purpose of increasing energy density. The energy density of the high-voltage Ni6 series is close to that of the Ni8 series, but the Ni6 series has better safety and low raw material costs. At the same time, since the nickel content of high-voltage materials is relatively low, the production process is not as complicated as high-nickel ternary materials. Therefore, high-voltage positive electrode materials have certain safety improvements while improving energy density.

[0003] However, under high voltage (>4.4V) environment, with the massive release of lithium ions, the ternary positive electrode material may encounter problems such as decreased crystal structure stability, chaotic ion arrangement and irreversible phase change. These problems will lead to the cycle stability of the battery and cannot be used for a long time. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor cycle stability of existing ternary positive electrode materials when used in a high-voltage environment, thereby providing a ternary positive electrode material and a preparation method and application thereof.

[0005] To this end, the present invention provides the following technical solutions:

[0006] The first aspect of the present invention provides a method for preparing a ternary positive electrode material, wherein the preparation method comprises the following steps:

[0007] S1, Ni x Co y Mn z The (OH)2 precursor and the lithium source are mixed and first sintered to obtain product A;

[0008] The Ni x Co y Mn z In the (OH)2 precursor, 0.50≤x≤0.70, 0.10≤y≤0.20, 0.20≤z≤0.30, x+y+z=1;

[0009] S2, mixing the product A and a tungsten-containing dopant, and performing a second sintering to obtain a product B;

[0010] The conditions for the second sintering include: heating to 600 - 830 °C at a rate of 1.5 - 5 °C / min and sintering for 3 - 7 h;

[0011] S3. Mix product B and the metal oxide coating agent, and conduct the third sintering to obtain the ternary cathode material.

[0012] In the present invention, the mixing in steps S1, S2, and S3 is a conventional mixing in the art, and it is sufficient to achieve uniform mixing.

[0013] In the present invention, the lithium source is a conventional lithium source in the art. Typically and non - restrictively, the lithium source includes at least one of lithium hydroxide and lithium carbonate. The ratio of the total molar amount of nickel ions, cobalt ions, and manganese ions of the metal elements in the Ni x Co y Mn z (OH)₂ precursor to the molar amount of lithium ions in the lithium source is 1:(1.02 - 1.06), ensuring better combination of metal elements such as nickel, cobalt, and manganese with lithium during the sintering process.

[0014] In the present invention, the sintering atmosphere for the first sintering, the second sintering, and the third sintering includes oxygen and / or air.

[0015] According to the present invention, for the Ni x Co y Mn z (OH)₂ precursor, 0.58 ≤ x ≤ 0.68, 0.10 ≤ y ≤ 0.20, 0.22 ≤ z ≤ 0.30, and x + y + z = 1.

[0016] According to the present invention, the conditions for the second sintering include: heating to 600 - 800 °C at a rate of 2 - 4 °C / min and sintering for 4 - 6 h.

[0017] According to the present invention, the conditions for the first sintering include: heating to 700 - 1000 °C at a rate of 1 - 5 °C / min and sintering for 8 - 15 h.

[0018] According to the present invention, the conditions for the third sintering include: heating to 300 - 500 °C at a rate of 1.5 - 5 °C / min and sintering for 3 - 7 h.

[0019] According to the present invention, the tungsten - containing dopant includes at least one of tungsten oxide and tungstic acid.

[0020] In the present invention, the tungsten oxide is a conventional reagent in the art. Typically and non - restrictively, the tungsten oxide includes tungsten trioxide.

[0021] According to the present invention, the mass ratio of product A to the tungsten - containing dopant is 1:(0.0005 - 0.004).

[0022] According to the present invention, the metal oxide coating agent includes at least one of a tungsten-containing coating agent, an aluminum-containing coating agent, and a titanium-containing coating agent; it may be a tungsten-containing coating agent.

[0023] According to the present invention, the tungsten-containing coating agent includes at least one of tungsten oxide and tungstic acid.

[0024] In the present invention, the aluminum-containing coating agent and the titanium-containing coating agent are conventional oxide coating agents in the art. Typically and non-limitingly, the aluminum-containing oxide is alumina, and the titanium-containing oxide is titanium dioxide.

[0025] According to the present invention, the mass ratio of the product B to the metal oxide coating agent is 1:(0.001 - 0.006).

[0026] According to the present invention, in step S1, an additive is further added for mixing.

[0027] According to the present invention, the additive includes at least one of zirconium oxide, yttrium oxide, and niobium oxide.

[0028] In the present invention, the zirconium oxide, yttrium oxide, and niobium oxide include conventional oxides in the art. Typically and non-limitingly, the zirconium oxide includes zirconia, the yttrium oxide includes yttrium trioxide, and the niobium oxide includes niobium monoxide, niobium dioxide, niobium trioxide, and niobium pentoxide; when multiple additives are selected, the specific dosage is determined according to the actual situation.

[0029] According to the present invention, the Ni x Co y Mn z (OH)2 precursor and the additive have a mass ratio of 1:(0.0005 - 0.008).

[0030] In the second aspect of the present invention, a ternary cathode material prepared by the aforementioned preparation method is protected.

[0031] In the third aspect of the present invention, a secondary battery is protected, wherein the secondary battery includes the aforementioned ternary cathode material.

[0032] In the present invention, the preparation method of the secondary battery includes the following steps: Weigh the ternary cathode material, polyvinylidene fluoride (PVDF), and Super P (SP) according to a mass ratio of (96 - 98):(1 - 1.5):(1 - 1.5) for homogenization, and then lay the aluminum foil flat on the coater for coating (the areal density is 15 - 17 mg / cm 2) Put it in a blast drying oven at 80 - 100 °C and dry for 2 - 4 h; then punch holes, weigh, and bake the electrode sheet. Use a lithium sheet as the negative electrode, and assemble it into a CR2032 button cell in the order of negative electrode case, lithium sheet, electrolyte (lithium perchlorate electrolyte with a concentration of 1 mol / L, and the solvent in the electrolyte is ethylene glycol dimethyl ether and propylene carbonate with a volume ratio of 1:1), PP separator, electrolyte, positive electrode material sheet, gasket, shrapnel, and positive electrode case.

[0033] The technical solution of the present invention has the following advantages:

[0034] 1. The present invention provides a preparation method of a ternary positive electrode material. Among them, the preparation method includes the following steps: S1, mix the Ni x Co y Mn z (OH)2 precursor and a lithium source, and perform the first sintering to obtain product A; in the Ni x Co y Mn z (OH)2 precursor, 0.50 ≤ x ≤ 0.70, 0.10 ≤ y ≤ 0.20, 0.20 ≤ z ≤ 0.30, and x + y + z = 1; S2, mix product A and a tungsten-containing dopant, and perform the second sintering to obtain product B; the conditions of the second sintering include: heating to 600 - 830 °C at a rate of 1.5 - 5 °C / min and sintering for 3 - 7 h; S3, mix product B and a coating agent, and perform the third sintering to obtain the ternary positive electrode material; the precursor with a specific composition of the present invention acts synergistically with the second sintering conditions. The higher manganese content in the precursor can provide a large number of vacancies and defect channels, ensuring that after the second sintering at a lower temperature and for a shorter time, the tungsten-containing dopant can enter the lattice of the positive electrode material, and tungsten atoms replace the atoms in the lattice of the positive electrode material, inhibiting the phase change of the crystal structure during charge and discharge and maintaining crystal stability; it can also improve the electron transport efficiency inside the material, facilitating the insertion and extraction of lithium ions; and after adding a metal oxide coating agent and sintering, a coating layer is formed, which can isolate product B from the electrolyte, reduce the interfacial resistance between the positive electrode material and the electrolyte, and improve the charge transport efficiency during charge and discharge; the positive electrode material of the present invention has excellent cycle stability when used in a high-voltage (>4.4 V) environment.

[0035] 2. The specific precursor of the present invention can further provide a stable lattice framework that is conducive to the uniform distribution of the dopant, and further affects the site preference and diffusion path of the dopant in the lattice.

[0036] 3. The specific second sintering conditions of the present invention can further enable the doped substance to migrate in the lattice of the positive electrode material, making the distribution more uniform and forming a more stable doped structure.

[0037] 4. The inventors unexpectedly found that when the dopant and the coating agent contain tungsten, the doped tungsten element forms a coupling with the coated tungsten element. It is speculated that the reason is that the doped tungsten element has a specific electronic configuration, while the coated tungsten element also has a specific electronic state. The electron orbits of the two interact with each other, reducing the charge transfer resistance and making it more convenient for the charge to transfer multiple times, further improving the cycle stability.

[0038] 5. Adding additives in the present invention can further improve the grain boundary stability, change the electron state density distribution in the material, thereby improving electron conduction and enhancing the cycle stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 It is the SEM picture of Product B in Example 1;

[0041] Figure 2 It is the SEM picture of the ternary cathode material in Example 1;

[0042] Figure 3 It is the SEM picture of Product B in Comparative Example 3;

[0043] Figure 4 It is the SEM picture of Product B in Comparative Example 4;

[0044] Figure 5 It is the SEM picture of Product B in Comparative Example 5;

[0045] Figure 6 It is the SEM picture of the ternary cathode material in Comparative Example 7. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The following embodiments are provided to better further understand the present invention. They are not limited to the best embodiments, and do not constitute a limitation to the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0047] For those embodiments where specific experimental steps or conditions are not indicated, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0048] Example 1

[0049] This example provides a method for preparing a ternary cathode material, comprising the following steps:

[0050] S1, Mix the Ni 0.60 Co 0.20 Mn 0.20 (OH)2 precursor, lithium carbonate, zirconia, and yttria evenly, and under an oxygen atmosphere, heat to 960 °C at a rate of 2.5 °C / min and sinter for 10 h, then naturally cool to room temperature to obtain product A; among them, the molar total of nickel ions, cobalt ions, and manganese ions in the Ni 0.60 Co 0.20 Mn 0.20 (OH)2 precursor and the molar amount of lithium ions in lithium carbonate is 1:1.04; the mass ratio of the Ni 0.60 Co 0.20 Mn 0.20 (OH)2 precursor, zirconia, and yttria is 1:0.001:0.002;

[0051] S2, Mix product A and tungstic acid evenly according to a mass ratio of 1:0.002, and under an air atmosphere, heat to 600 °C at a rate of 2 °C / min and sinter for 4 h, then naturally cool to room temperature to obtain product B. The SEM image of product B is as shown in Figure 1 the figure. It can be seen from the figure that the surface of product B is smooth and no obvious dopant is seen on the surface; it indicates that the tungsten-containing dopant enters the cathode material;

[0052] S3, Mix product B, tungsten oxide, alumina, and titanium oxide evenly according to a mass ratio of 1:0.002:0.002:0.001, and under an oxygen atmosphere, heat to 400 °C at a rate of 2 °C / min and sinter for 4 h, then naturally cool to room temperature to obtain the ternary cathode material. The SEM image of the ternary cathode material is as shown in Figure 2 the figure. It can be seen from the figure that the metal oxide coating agent is evenly coated on the surface of the cathode material.

[0053] Example 2

[0054] This example provides a method for preparing a ternary cathode material, comprising the following steps:

[0055] S1, Mix the Ni 0.70 Co 0.10 Mn 0.20 (OH)2 precursor, lithium hydroxide, zirconia, yttria, and niobium pentoxide evenly, and under an oxygen atmosphere, heat to 890 °C at a rate of 2.5 °C / min and sinter for 10 h, then naturally cool to room temperature to obtain product A; among them, the Ni 0.70 Co 0.10 Mn0.20 (OH)2 precursor, the ratio of the total molar amount of nickel ions, cobalt ions and manganese ions to the molar amount of lithium ions in lithium carbonate is 1:1.05; Ni 0.70 Co 0.10 Mn 0.20 (OH)2 precursor, zirconia, yttria and niobium pentoxide have a mass ratio of 1:0.001:0.002:0.001;

[0056] S2, mix product A and tungsten oxide evenly according to a mass ratio of 1:0.002, and under an oxygen atmosphere, heat it to 700 °C at a rate of 2 °C / min and sinter for 4 h, then cool it naturally to room temperature to obtain product B;

[0057] S3, mix product B, tungsten oxide, alumina and titanium oxide evenly according to a mass ratio of 1:0.003:0.002:0.001, and under an oxygen atmosphere, heat it to 400 °C at a rate of 2 °C / min and sinter for 4 h, then cool it naturally to room temperature to obtain the ternary cathode material.

[0058] Example 3

[0059] This example provides a method for preparing a ternary cathode material. Compared with Example 1, the difference is that Ni 0.65 Co 0.10 Mn 0.25 (OH)2 precursor is used.

[0060] Example 4

[0061] This example provides a method for preparing a ternary cathode material. Compared with Example 1, the difference is that in step S2, it is heated to 820 °C at a rate of 5 °C / min and sintered for 7 h.

[0062] Example 5

[0063] This example provides a method for preparing a ternary cathode material. Compared with Example 1, the difference is that the composition of the metal oxide coating agent is different. Specifically, in step S3, product B, alumina and titanium oxide are mixed evenly according to a mass ratio of 1:0.002:0.001; in this example, the total mass of product B, alumina and titanium oxide is equal to the total mass of product B, tungsten oxide, alumina and titanium oxide in Example 1.

[0064] Example 6

[0065] This example provides a method for preparing a ternary cathode material, including the following steps:

[0066] S1, Ni 0.60 Co 0.20 Mn 0.20(OH)2 precursor and lithium carbonate are mixed evenly, and under an oxygen atmosphere, the temperature is raised to 960 °C at a rate of 2.5 °C / min and sintered for 10 h, and then naturally cooled to room temperature to obtain product A; among them, Ni 0.60 Co 0.20 Mn 0.20 The molar total amount of nickel ions, cobalt ions and manganese ions in the (OH)2 precursor and the molar amount of lithium ions in lithium carbonate have a ratio of 1:1.04;

[0067] S2, in the manner of step S2 in Example 1;

[0068] S3, in the manner of step S3 in Example 1.

[0069] Comparative Example 1

[0070] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0071] S1, Mix Ni 0.60 Co 0.20 Mn 0.20 (OH)2 precursor, lithium carbonate, zirconia, and yttria evenly, and under an oxygen atmosphere, the temperature is raised to 960 °C at a rate of 2.5 °C / min and sintered for 10 h, and then naturally cooled to room temperature to obtain product A; among them, Ni 0.60 Co 0.10 Mn 0.30 The molar total amount of nickel ions, cobalt ions and manganese ions in the (OH)2 precursor and the molar amount of lithium ions in lithium carbonate have a ratio of 1:1.04; Ni 0.60 Co 0.20 Mn 0.20 (OH)2 precursor, zirconia, and yttria have a mass ratio of 1:0.001:0.002;

[0072] S2, Mix product A, tungsten oxide, alumina, and titanium oxide evenly according to a mass ratio of 1:0.002:0.002:0.001, and under an oxygen atmosphere, raise the temperature to 400 °C at a rate of 2 °C / min and sinter for 4 h, and then naturally cool to room temperature to obtain the ternary cathode material.

[0073] Comparative Example 2

[0074] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0075] S1, Mix Ni 0.70 Co 0.10 Mn 0.20(OH)2 precursor, lithium hydroxide, zirconium oxide, yttrium oxide, and niobium pentoxide are mixed evenly. Under an oxygen atmosphere, it is heated to 890 °C at a rate of 2.5 °C / min and sintered for 10 h, then naturally cooled to room temperature to obtain product A; among them, Ni 0.70 Co 0.10 Mn 0.20 The ratio of the total molar amount of nickel ions, cobalt ions, and manganese ions in the (OH)2 precursor to the molar amount of lithium ions in lithium carbonate is 1:1.05; Ni 0.70 Co 0.10 Mn 0.20 The mass ratio of the (OH)2 precursor, zirconium oxide, yttrium oxide, and niobium pentoxide is 1:0.001:0.002:0.001;

[0076] S2, Product A, tungsten oxide, alumina, and titanium oxide are mixed evenly according to the mass ratio of 1:0.003:0.002:0.001. Under an oxygen atmosphere, it is heated to 400 °C at a rate of 2 °C / min and sintered for 4 h, then naturally cooled to room temperature to obtain the ternary cathode material.

[0077] Comparative Example 3

[0078] This comparative example provides a preparation method of a ternary cathode material. Compared with Example 3, the difference lies in that the type of precursor is different, and Ni 0.80 Co 0.10 Mn 0.10 (OH)2 precursor is used;

[0079] The SEM image of product B in step S2 is as Figure 3 shown. It can be seen from the figure that the dopant remains on the surface and the doping is not successful. The reason is that the diffusion rate of tungsten element is slow. Ni 0.80 Co 0.10 Mn 0.10 The Mn content in the (OH)2 precursor is relatively low, and Mn can provide vacancies and defect channels in the lattice. When the content is low, the number of vacancies decreases; as a result, most of the dopants cannot enter the lattice of the cathode material at a lower temperature and shorter sintering time and can only remain outside.

[0080] Comparative Example 4

[0081] This comparative example provides a preparation method of a ternary cathode material. Compared with Example 3, the difference lies in that, specifically in step S2, it is heated to 300 °C at a rate of 2 °C / min and sintered for 6 h. The SEM image of product B in step S2 is as Figure 4 shown. It can be seen from the figure that there are a large number of tungsten-containing dopants on the surface of the cathode material, indicating that the tungsten-containing dopants have not all entered the cathode material.

[0082] Comparative Example 5

[0083] This comparative example provides a method for preparing a ternary cathode material. Compared with Example 3, the difference lies in that, specifically, in step S2, the temperature is raised to 900 °C at a rate of 5 °C / min and sintered for 8 h. The SEM image of product B in step S2 is as Figure 5 shown. It can be seen from the figure that there are a small amount of tungsten-containing dopants on the surface of product B. It is speculated that the reason is that tungsten acid decomposes to produce tungsten oxide at this temperature, and tungsten oxide sublimes, resulting in the inability to control the actual reaction amount of the tungsten-containing dopant.

[0084] Comparative Example 6

[0085] This comparative example provides a method for preparing a ternary cathode material. Compared with Example 3, the difference lies in that, specifically, in step S2, product A and molybdenum oxide are mixed evenly at a mass ratio of 1:0.002.

[0086] Comparative Example 7

[0087] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0088] S1, Mix Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor, lithium carbonate, zirconium oxide, and yttrium oxide evenly. Under an oxygen atmosphere, the temperature is raised to 960 °C at a rate of 2.5 °C / min and sintered for 10 h, and then naturally cooled to room temperature to obtain product A; among them, the molar total of nickel ions, cobalt ions, and manganese ions in the Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor and the molar amount of lithium ions in lithium carbonate is 1:1.04; the mass ratio of Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor, zirconium oxide, and yttrium oxide is 1:0.001:0.002;

[0089] S2, Mix product A and tungstic acid evenly at a mass ratio of 1:0.002. Under an air atmosphere, the temperature is raised to 600 °C at a rate of 2 °C / min and sintered for 4 h, and then naturally cooled to room temperature to obtain the ternary cathode material. The SEM image of the ternary cathode material is as Figure 6 shown. It can be seen from the figure that the surface of the ternary cathode material is smooth and there is no obvious residue of tungsten-containing dopants.

[0090] Test Example

[0091] Weigh the ternary cathode materials, polyvinylidene fluoride (PVDF), and Super P (SP) provided in each example and comparative example according to the mass ratio of 97.2:1.3:1.5 respectively for homogenization, and then lay the aluminum foil flat on the coater for coating (surface density is 15 mg / cm 2 ), and place it in a blast drying oven at 80 °C for 2 h; then punch holes, weigh, and bake the electrode sheet. Use a lithium sheet as the negative electrode, and assemble it in the order of negative electrode shell, lithium sheet, electrolyte (lithium perchlorate electrolyte with a concentration of 1 mol / L, and the solvent in the electrolyte is ethylene glycol dimethyl ether and propylene carbonate with a volume ratio of 1:1), PP separator, electrolyte, positive electrode material sheet, gasket, shrapnel, and positive electrode shell to make a CR2032 button cell;

[0092] Put the prepared battery into the BlueTEC test system, charge it to 4.5 V at a charging rate of 1 C, and then discharge it to 3.0 V at a discharging rate of 1 C for 100 cycles. The capacity retention rate = (discharge capacity of the 100th cycle / first discharge capacity) × 100%, and take the average value after testing 3 times. The results are shown in Table 1;

[0093] Table 1

[0094] Capacity retention rate (%) Example 1 94.3 Example 2 94.0 Example 3 95.2 Example 4 93.6 Example 5 93.7 Example 6 93.1 Comparative Example 1 91.6 Comparative Example 2 90.5 Comparative Example 3 88.5 Comparative Example 4 91.0 Comparative Example 5 89.5 Comparative Example 6 87.6 Comparative Example 7 88.9

[0095] It can be seen from the comparison between the examples and the comparative examples that the ternary cathode material of the present invention has a more excellent capacity retention rate.

[0096] It can be seen from the comparison between Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2 that after adding the tungsten-containing dopant in the present invention and performing the second sintering, it is ensured that the tungsten-containing dopant can enter the lattice of the cathode material, the tungsten atoms replace the atoms in the lattice of the cathode material, inhibit the phase change of the crystal structure during charge and discharge, and maintain the crystal stability; it can also improve the electron transport efficiency inside the material and facilitate the insertion and extraction of lithium ions.

[0097] It can be seen from the comparison between Example 3 and Comparative Example 3 that the specific precursor of the present invention can further provide a stable lattice framework that is beneficial to the uniform distribution of the dopant, and further affect the site preference and diffusion path of the dopant in the lattice.

[0098] It can be seen from the comparison between Example 3, Comparative Example 4, and Comparative Example 5 that the specific second sintering conditions of the present invention can further enable the doped substance to migrate in the lattice of the cathode material, make the distribution more uniform, and form a more stable doped structure.

[0099] It can be seen from the comparison between Example 3 and Comparative Example 6 that the tungsten-containing dopant has a better effect than other dopants. The tungsten-containing dopant can enter the lattice of the cathode material, the tungsten atoms replace the atoms in the lattice of the cathode material, inhibit the phase change of the crystal structure during charge and discharge, and maintain the crystal stability.

[0100] Comparing Example 1 with Comparative Example 7, it can be seen that after sintering with the metal oxide coating agent, a coating layer is formed, which can isolate Product B from the electrolyte, reduce the interfacial resistance between the positive electrode material and the electrolyte, improve the charge transfer efficiency during charge and discharge, and thus improve the cycle stability.

[0101] Obviously, the above examples are only for illustration purposes and are not intended to limit the implementation methods. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. The obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing a ternary positive electrode material, characterized in that: The preparation method comprises the following steps: S1, Ni x Co y Mn z The (OH)2 precursor and the lithium source are mixed and first sintered to obtain product A; The Ni x Co y Mn z In the (OH)2 precursor, 0.50≤x≤0.70, 0.10≤y≤0.20, 0.20≤z≤0.30, x+y+z=1; S2, mixing the product A and a tungsten-containing dopant, and performing a second sintering to obtain a product B; The second sintering conditions include: heating to 600-830°C at a rate of 1.5-5°C / min and sintering for 3-7h; S3, mixing the product B and the metal oxide coating agent, and performing a third sintering to obtain a ternary positive electrode material.

2. The preparation method according to claim 1, characterized in that: The Ni x Co y Mn z In the (OH)2 precursor, 0.58≤x≤0.68, 0.10≤y≤0.20, 0.22≤z≤0.30, x+y+z=1.

3. The preparation method according to claim 1 or 2, characterized in that: The second sintering conditions include: heating to 600-800° C. at a rate of 2-4° C. / min and sintering for 4-6 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The first sintering conditions include: heating to 700-1000° C. at a rate of 1-5° C. / min and sintering for 8-15 hours; And / or, the conditions of the third sintering include: heating to 300-500° C. at a rate of 1.5-5° C. / min and sintering for 3-7 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The tungsten-containing dopant includes at least one of tungsten oxide and tungstic acid; And / or, the mass ratio of the product A to the tungsten-containing dopant is 1:(0.0005-0.004).

6. The preparation method according to any one of claims 1 to 5, characterized in that: The metal oxide coating agent includes at least one of a tungsten-containing coating agent, an aluminum-containing coating agent, and a titanium-containing coating agent; and may be a tungsten-containing coating agent; Optionally, the tungsten-containing coating agent includes at least one of tungsten oxide and tungstic acid; And / or, the mass ratio of the product B to the metal oxide coating agent is 1:(0.001-0.006).

7. The preparation method according to any one of claims 1 to 6, characterized in that: In step S1, additives are also added for mixing.

8. The preparation method according to claim 7, characterized in that: The additive includes at least one of zirconium oxide, yttrium oxide, and niobium oxide; Optionally, the Ni x Co y Mn z The mass ratio of (OH)2 precursor and additive is 1:(0.0005-0.008).

9. A ternary positive electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. A secondary battery, characterized in that: The secondary battery comprises the ternary positive electrode material according to claim 9.

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