A ternary cathode material, a preparation method thereof, and a lithium-ion battery

Abstract

The present invention discloses a ternary cathode material, a preparation method thereof, and a lithium ion battery, relating to the technical field of battery materials. It includes a cathode material body, a first coating layer coated on the cathode material body, and a second coating layer coated on the first coating layer. The first coating layer is Li<subgt;6< / subgt;PS<subgt;5< / subgt;X, and the second coating layer is Li<subgt;3< / subgt>BO<subgt;3. The cathode material body is a nickel cobalt manganese cathode material containing doping elements M and B, where M is an internal doping element and B is a shallow doping element. The internal doping of element M in the cathode material body plays a role in supporting and stabilizing the material structure; the shallow doping with element B plays a dual role of doping and coating on the primary particles. A solid electrolyte Li<subgt;6< / subgt;PS<subgt;5< / subgt;X is coated on the outside of the cathode material body, and an ion conductor Li<subgt;3BO<subgt;3 is further coated outside the solid electrolyte, which has a protective effect on both the solid electrolyte coating layer and the cathode material, and endows the cathode material with good rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular, to a ternary cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The new energy vehicle industry is developing rapidly. As the heart of new energy vehicles, the performance of power batteries largely determines the performance of new energy vehicles. To meet people's demands for long-range and fast charging of new energy vehicles, power batteries are developing towards high energy density and high-rate charging.

[0003] Ternary materials, especially high-nickel ternary materials (LiNi x Co y Mn z O2, where x + y + z = 1 and x ≥ 0.8) have been widely studied because of their high capacity advantages. Although high-nickel ternary materials have high capacity, due to their high Ni content and low Co content, their cycling and rate performance are poor. People generally use various modification methods to enhance the structural stability and surface stability of the materials, thereby improving the cycling and rate performance of the materials.

[0004] Doping and coating are the most commonly used modification methods. Doping can stabilize the material structure from the inside and provide a more stable framework for the material. Coating can enhance the surface stability of the material, which is equivalent to providing a strong shell for the material. The coating generally uses electrochemically inert substances. Although it can improve the surface stability of the material, it will also reduce the ionic conductivity of the material, thereby increasing the migration energy barrier of lithium ions and reducing the capacity and rate performance of the material.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a ternary cathode material and a preparation method thereof, aiming to improve the capacity and rate performance of the cathode material.

[0007] Another purpose of the present invention is to provide a lithium-ion battery, aiming to improve the rate performance of the battery.

[0008] The present invention is implemented as follows:

[0009] In a first aspect, the present invention provides a ternary cathode material, including a cathode material body, a first coating layer coated on the cathode material body, and a second coating layer coated on the first coating layer. The first coating layer is Li6PS5X, the second coating layer is Li3BO3, and X is selected from at least one of Cl, Br, and I;

[0010] The cathode material body is a nickel-cobalt-manganese cathode material containing doping elements M and B, where M is an internal doping element and B is a shallow doping element. M is selected from at least one of Mg, Al, Si, Ti, Cr, V, Y, Zr, Nb, Mo, Sn, Sb, and W.

[0011] In an alternative embodiment, the general formula of the ternary cathode material is Li(Ni x Co y Mn z M k ) i B j O2@aLi6PS5X@bLi3BO3;

[0012] In the general formula, x + y + z + k = 1, 0.0005 < k < 0.01, 0.98 < i < 0.995, 0.005 < j < 0.02, 0.005 < a < 0.02, and 0.005 < b < 0.02.

[0013] Second, the present invention provides a method for preparing the ternary cathode material in the foregoing embodiment. A ternary precursor containing doping element M is mixed with a boron compound and a lithium source and subjected to a first sintering to obtain a first sintered material;

[0014] A first coating layer is formed on the first sintered material to obtain a first coated material;

[0015] A second coating layer is formed on the first coated material to obtain a second coated material;

[0016] The second coated material is subjected to a second sintering.

[0017] In an alternative embodiment, the preparation process of the first coated material includes: mixing Li2S and P2S5 with a first organic solvent to obtain a first mixed solution, mixing the first sintered material with the first mixed solution to obtain a second mixed solution, adding Li2S to react with LiX in the second mixed solution to obtain a third mixed solution, and drying the third mixed solution to obtain a solid first coated material; where X is selected from at least one of Cl, Br, and I;

[0018] Preferably, under the protection of an inert atmosphere, Li2S and P2S5 are mixed and dissolved in the first organic solvent at a molar ratio of (2 - 3):1, and stirred for 0.5 h - 4 h to obtain a first mixed solution; the first sintered material is mixed with the first mixed solution and stirred for 0.5 h - 2 h to obtain a second mixed solution, Li2S is added to react with LiX in the second mixed solution for 5 h - 15 h to obtain a third mixed solution, and the third mixed solution is vacuum dried at 50°C - 200°C for 2 h - 24 h to dry the solvent;

[0019] More preferably, the mass fractions of Li2S and P2S5 in the first mixed solution are controlled to be 1%-3%, and the mass ratio of the primary sintered material to the first mixed solution is (1.5-3):1;

[0020] More preferably, the first organic solvent is selected from at least one of ethanol, ethyl propionate, N-methylformamide, acetonitrile, anisole, tetrahydrofuran, ethyl acetate, 1,2-dimethoxyethane, ethylenediamine, dimethyl carbonate, hydrazine, and n-hexane.

[0021] In an alternative embodiment, the preparation process of the second coating material includes: mixing lithium borate and a second organic solvent to obtain a suspension, mixing the first coating material with the suspension and stirring, and then performing vacuum drying to dry the solvent.

[0022] In an alternative embodiment, under the protection of an inert atmosphere, lithium borate powder is mixed with a second organic solvent to obtain a suspension, and the mass fraction of lithium borate in the suspension is 1%-3%; the first coating material and the suspension are mixed and stirred for 1 h-5 h, and then vacuum dried at 50°C-200°C for 2 h-24 h;

[0023] Preferably, the second organic solvent is selected from at least one of ethanol, ethyl propionate, N-methylformamide, acetonitrile, anisole, tetrahydrofuran, ethyl acetate, ethyl propionate, 1,2-dimethoxyethane, ethylenediamine, dimethyl carbonate, hydrazine, n-hexane, and n-pentane.

[0024] In an alternative embodiment, the preparation process of the primary sintered material includes: mixing a ternary precursor containing a doping element M with a boron compound and a lithium source, and performing primary sintering under an atmosphere condition in the presence of oxygen, the temperature of the primary sintering is 700°C-1000°C, and the sintering time is 8 h-24 h;

[0025] Preferably, the dosage of the boron compound is controlled such that the molar ratio of boron to the ternary precursor is (0.005-0.02):1, and the dosage of the lithium source is controlled such that the molar ratio of lithium to the total amount of metal elements in the ternary precursor is (1.01-1.10):1;

[0026] Preferably, the material after primary sintering is crushed to a particle size of 100-500 mesh.

[0027] In an alternative embodiment, a ternary precursor containing a doping element M is prepared by a coprecipitation method, and the general formula of the ternary precursor is Ni x Co y Mn z M k (OH)2; wherein, x + y + z + k = 1, 0.0005 < k < 0.01, and M is selected from at least one of Mg, Al, Si, Ti, Cr, V, Y, Zr, Nb, Mo, Sn, Sb, and W;

[0028] Preferably, the boron compound is selected from at least one of boric acid, boron oxide, ammonium borate, lithium borate, and lithium tetraborate;

[0029] Preferably, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium oxalate.

[0030] In an alternative embodiment, the second coating material is subjected to secondary sintering under the protection of an inert atmosphere, and the temperature of the secondary sintering is controlled to be 400°C - 700°C, and the sintering time is 5h - 10h;

[0031] Preferably, the material after secondary sintering is crushed to 100 - 500 mesh.

[0032] In a third aspect, the present invention provides a lithium-ion battery, which includes the ternary cathode material in the foregoing embodiment or the ternary cathode material prepared by the preparation method of any one of the foregoing embodiments.

[0033] The present invention has the following beneficial effects: M element is doped inside the cathode material body, which plays a role in supporting and stabilizing the material structure; B element is used for shallow doping, which plays a dual role of doping + coating on the primary particles, and partial ionic conductor Li3BO3 will also be formed on the surface of the primary particles, which helps the migration of lithium ions between the primary particles; a layer of solid electrolyte Li6PS5X is coated outside the cathode material body, and a layer of ionic conductor Li3BO3 is further coated outside the solid electrolyte. The weakly basic compound Li3BO3 will not react with Li6PS5X, is less sensitive to air and moisture than Li6PS5X, and has good stability in the electrolyte, which has a protective effect on both the solid electrolyte coating layer and the cathode material, and will not have a great impact on the ionic conductivity of the cathode material coated with the solid electrolyte. The special coating structure and material selection endow the cathode material with good rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0035] Figure 1 XRD pattern of the cathode material prepared in Example 1;

[0036] Figure 2 SEM of the cathode material prepared in Example 1;

[0037] Figure 3SEM of the positive electrode material prepared in Comparative Example 1;

[0038] Figure 4 SEM of the positive electrode material prepared in Comparative Example 2;

[0039] Figure 5 Test results of the rate performance of the positive electrode materials prepared in the examples and comparative examples;

[0040] Figure 6 Comparison of the 5C cycle performance of the positive electrode materials prepared in the examples and comparative examples. Detailed implementation mode

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0042] The embodiments of the present invention provide a method for preparing a ternary positive electrode material, including the following steps:

[0043] S1. Preparation of the precursor

[0044] A ternary precursor containing a doped element M is prepared by a coprecipitation method. The general formula of the ternary precursor is Ni x Co y Mn z M k (OH)2; wherein, x + y + z + k = 1, 0.0005 < k < 0.01, and M is selected from at least one of Mg, Al, Si, Ti, Cr, V, Y, Zr, Nb, Mo, Sn, Sb, and W. The M element can be any one of the above elements. By introducing the M element through the coprecipitation method, the M element can be evenly distributed inside the primary particles of the positive electrode material, playing a role in supporting and stabilizing the material structure.

[0045] The coprecipitation method is a conventional method. It is to drop nickel salt, cobalt salt, manganese salt, and a salt solution containing metal element M into the reaction kettle together, and use ammonia water and sodium hydroxide in the reaction kettle to maintain the reaction pH value to form a ternary precursor by precipitation. When preparing various raw materials, the ingredients are prepared according to the chemical composition of the ternary precursor to make the chemical formula of the prepared ternary precursor meet the requirements.

[0046] S2. Primary sintering

[0047] Mix the ternary precursor containing the doped element M with a boron compound and a lithium source and perform primary sintering to obtain a primary sintered material. By introducing the B element through primary sintering, because of its strong binding ability with O, it will form BO3 3-In this form, a gradient shallow doping is formed on the surface layer of the primary particles, which plays a dual role of doping and coating on the primary particles. Moreover, a partial ionic conductor - Li3BO3 will also be formed on the surface of the primary particles, which helps the migration of lithium ions between the primary particles.

[0048] In some embodiments, the preparation process of the primary sintered material includes: mixing a ternary precursor containing a doping element M with a boron compound and a lithium source, and performing a primary sintering in an atmosphere with the presence of oxygen. The temperature of the primary sintering is 700°C - 1000°C, and the sintering time is 8h - 24h. Specifically, the temperature of the primary sintering can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, etc., or any value between adjacent values above; the sintering time can be 8h, 10h, 12h, 15h, 17h, 20h, 24h, etc., or any value between adjacent values above.

[0049] In some embodiments, the dosage of the boron compound is to control the molar ratio of boron to the ternary precursor to be (0.005 - 0.02):1, specifically it can be 0.005:1, 0.010:1, 0.015:1, 0.020:1, etc., or any value between adjacent values above; the dosage of the lithium source is to control the molar ratio of lithium to the total amount of metal elements in the ternary precursor to be (1.01 - 1.10):1, that is, Li / Me = (1.01 - 1.10):1, such as it can be 1.01:1, 1.03:1, 1.05:1, 1.07:1, 1.10:1, etc., or any value between adjacent values above.

[0050] In some embodiments, the boron compound is selected from at least one of boric acid, boron oxide, ammonium borate, lithium borate, and lithium tetraborate, and can be a mixture formed by one or several of them; the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium oxalate, and can be a mixture formed by one or several of them.

[0051] In some embodiments, the material after the primary sintering is crushed to a particle size of 100 - 500 mesh to better control the particle size range of the final product and prepare a product with uniform performance.

[0052] S3. Primary coating

[0053] A first coating layer is formed on the primary sintered material to obtain a first coated material. The first coating layer is Li6PS5X, and X is selected from at least one of Cl, Br, and I, and can be one or several of them. By coating a layer of solid electrolyte Li6PS5X outside the material, the ionic conductivity of the material is greatly improved. X can be any one or two, or three of Cl, Br, and I.

[0054] In the actual operation process, the preparation process of the first coating material includes: mixing Li2S, P2S5 with a first organic solvent to obtain a first mixed solution, mixing the primary sintered material with the first mixed solution to obtain a second mixed solution, adding Li2S and LiX to the second mixed solution to react to obtain a third mixed solution, and drying the third mixed solution to obtain a solid first coating material; wherein, X is selected from at least one of Cl, Br, and I. The dosages of Li2S, P2S5, Li2S and LiX can be proportioned according to Li6PS5X. During the reaction process, the total reaction is 5Li2S + 2P2S5 + 2LiX → 2Li6P2S5X.

[0055] In some embodiments, under the protection of an inert atmosphere, Li2S and P2S5 are mixed and dissolved in the first organic solvent according to a molar ratio of (2 - 3):1, and stirred for 0.5 h - 4 h to obtain a first mixed solution; the primary sintered material is mixed with the first mixed solution and stirred for 0.5 h - 2 h to obtain a second mixed solution, Li2S and LiX are added to the second mixed solution to react for 5 h - 15 h to obtain a third mixed solution, and the third mixed solution is vacuum dried at 50°C - 200°C for 2 h - 24 h to dry the solvent. Among them, the mass fraction of Li2S and P2S5 in the first mixed solution is controlled to be 1% - 3%, and the mass ratio of the primary sintered material to the first mixed solution is (1.5 - 3):1. By precisely controlling the dosages, concentrations of each raw material and the mixing reaction time, the raw materials react fully to obtain Li6PS5X.

[0056] Specifically, the molar ratio of Li2S to P2S5 can be 2:1, 2.5:1, 3.0:1, etc., or any value between the adjacent values above; the mass fraction of Li2S and P2S5 in the first mixed solution can be 1%, 1.5%, 2%, 2.5%, 3%, etc., or any value between the adjacent values above; the mass ratio of the primary sintered material to the first mixed solution can be 1.5:1, 2.0:1, 2.5:1, 3.0:1, etc., or any value between the adjacent values above.

[0057] In some embodiments, the first organic solvent is selected from at least one of ethanol, ethyl propionate, N - methylformamide, acetonitrile, anisole, tetrahydrofuran, ethyl acetate, 1,2 - dimethoxyethane, ethylenediamine, dimethyl carbonate, hydrazine (hydrazine) and n - hexane, and can be any one of the above solvents, or a mixed solvent formed by several of them.

[0058] S4. Secondary coating

[0059] A second coating layer is formed on the first coating material to obtain a second coating material, and the second coating layer is Li3BO3. Since the solid electrolyte Li6PS5X (X = Cl, Br, I) is sensitive to air and moisture and is extremely prone to deterioration, thus losing its due effect, in the embodiments of the present invention, a layer of ion conductor Li3BO3 is further coated outside the solid electrolyte. Its sensitivity to air and moisture is lower than that of Li6PS5X, and it has good stability in the electrolyte solution. It has a protective effect on both the solid electrolyte coating layer and the positive electrode material, and will not have a great impact on the ionic conductivity of the positive electrode material coated with the solid electrolyte.

[0060] It should be noted that Li3BO3 is a weakly basic compound and will not react with Li6PS5X. If H3BO3 or BO3 is directly coated, it will react with Li6PS5X, causing the denaturation of Li6PS5X and resulting in the failure of the coating.

[0061] In some embodiments, the preparation process of the second coating material includes: mixing lithium borate and a second organic solvent to obtain a suspension, mixing the first coating material with the suspension and stirring, and then performing vacuum drying to remove the second organic solvent by vacuum drying.

[0062] In actual operation, under the protection of an inert atmosphere, lithium borate powder is mixed with a second organic solvent to obtain a suspension, and the mass fraction of lithium borate in the suspension is 1% - 3%; the first coating material and the suspension are mixed and stirred for 1 h - 5 h, and then vacuum dried at 50°C - 200°C for 2 h - 24 h to remove the second organic solvent.

[0063] Specifically, the mass fraction of lithium borate in the suspension can be 1%, 2%, 3%, etc., or any value between the adjacent values above; the mass ratio of the first coating material to the suspension can be 1.5:1, 2.0:1, 2.5:1, 3.0:1, etc., or any value between the adjacent values above.

[0064] Furthermore, the second organic solvent is selected from at least one of ethanol, ethyl propionate, N - methylformamide, acetonitrile, anisole, tetrahydrofuran, ethyl acetate, ethyl propionate, 1,2 - dimethoxyethane, ethylenediamine, dimethyl carbonate, hydrazine, n - hexane, and n - pentane. It can be any one of the above organic solvents, or a mixed solvent formed by several solvents.

[0065] S5, Secondary sintering

[0066] The second coating material is subjected to secondary sintering. To protect Li6PS5X, the secondary sintering is carried out under the protection of an inert atmosphere, controlling the temperature of the secondary sintering to be 400°C - 700°C and the sintering time to be 5h - 10h. Specifically, the temperature of the secondary sintering can be 400°C, 500°C, 600°C, 700°C, etc., or any value between the adjacent values above; the sintering time can be 5h, 6h, 7h, 8h, 9h, 10h, etc., or any value between the adjacent values above.

[0067] In some embodiments, the material after secondary sintering is crushed to 100 - 500 meshes to obtain a cathode material product with uniform particle size, preventing the particle size from being too large or too small.

[0068] An embodiment of the present invention also provides a ternary cathode material, including a cathode material body, a first coating layer coated on the cathode material body, and a second coating layer coated on the first coating layer. The first coating layer is Li6PS5X, the second coating layer is Li3BO3, and X is selected from at least one of Cl, Br, and I; the cathode material body is a nickel-cobalt-manganese cathode material containing doping elements M and B, M is an internal doping element, B is a shallow doping element, and M is selected from at least one of Mg, Al, Si, Ti, Cr, V, Y, Zr, Nb, Mo, Sn, Sb, and W.

[0069] It should be noted that the ternary cathode material provided in the embodiments of the present invention can be prepared by the above preparation method. M as an internal doping element can be introduced when preparing the precursor by the coprecipitation method, and B as a shallow doping can be introduced during the primary sintering. Li3BO3 has a protective effect on both the solid electrolyte coating layer Li6PS5X and the cathode material, and will not cause a large impact on the ionic conductivity of the cathode material with a solid electrolyte coating, making the prepared cathode material have good rate performance.

[0070] In some embodiments, the general formula of the ternary cathode material provided in the embodiments of the present invention can be expressed as Li(Ni x Co y Mn z M k ) i B j O2@aLi6PS5X@bLi3BO3; Li(Ni x Co y Mn z M k ) i B jO2 represents the cathode material body, Li6PS5X represents the first coating layer, and Li3BO3 represents the second coating layer. In the general formula, x + y + z + k = 1, 0.0005 < k < 0.01, 0.98 < i < 0.995, 0.005 < j < 0.02, 0.005 < a < 0.02, 0.005 < b < 0.02.

[0071] In some embodiments, the ternary cathode material provided in the embodiments of the present invention can be further used to prepare a lithium battery, and the lithium battery has good rate performance.

[0072] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0073] Example 1

[0074] The ternary material prepared in this example is:

[0075] Li(Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 ) 0.99 B 0.01 O2@0.01Li6PS5Cl@0.01Li3BO3.

[0076] This example also provides a preparation method of the ternary material, including the following steps:

[0077] (1) Prepare a ternary precursor Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 (OH)2 doped with element Al by the co-precipitation method.

[0078] Mix nickel sulfate, cobalt sulfate, manganese sulfate and aluminum sulfate according to a molar ratio of 82:6:11:1 to form a 2 mol / L (total metal element concentration, the same below) mixed solution.

[0079] Place ammonia water and water in a reaction kettle to form a bottom solution, the ammonia water concentration in the bottom solution is 8 g / L, inject the mixed solution into the reaction kettle, and at the same time add ammonia water solution and sodium hydroxide solution. During the precipitation process, control the ammonia water concentration to be 6 ± 0.3 g / L and the pH value to be 11.5 ± 0.1. After the injection is completed, react for 24 h, filter, wash and dry.

[0080] (2) Mix the ternary precursor and boron oxide evenly according to a molar ratio of B: precursor of 1:99, and then add lithium hydroxide for secondary mixing, with a molar ratio of Li / Me = 1.04.

[0081] (3) Place the mixture prepared in step (2) under an oxygen atmosphere, keep it sintered at 790 °C for 16 h, then crush the sintered material and sieve it through a 300-mesh sieve to obtain the primary sintered material Li(Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 ) 0.99 B 0.01 O2.

[0082] (4) Under the protection of an Ar atmosphere, dissolve Li2S and P2S5 in ethanol at a molar ratio of Li2S:P2S5 = 3:1 and continuously stir for 1 h, where the sum of the masses of Li2S and P2S5 accounts for 1.67 wt.% of the total mass of the mixed solution.

[0083] (5) Add the primary sintered material to the mixed solution in step (4), continuously stir for 1 h, then add a certain amount of Li2S and LiCl to the mixed solution, where the molar ratio of Li2S:LiCl = 1:1, continue to stir and react for 8 h, where the molar ratio of P2S5 added in step (4) to LiCl added in step (5) = 1:2, and the mass concentration of Li6PS5Cl obtained from the reaction is 2.5 wt.%, and the mass ratio of the primary sintered material to the mixed solution = 5:2.

[0084] (6) Vacuum-dry the mixed solution in step (5) at 120 °C for 3 h to dry the solvent and obtain solid powder A.

[0085] (7) Under the protection of an Ar atmosphere, add a certain amount of lithium borate powder to n-hexane and continuously stir to prepare a suspension, where the content of lithium borate in the suspension is 1.63 wt.%, then add the solid powder A in step (6) to the suspension, and the mass ratio of the solid powder A to the suspension = 2:1, continue to stir for 2 h, and then vacuum-dry it at 80 °C for 3 h to dry the solvent and obtain solid powder B.

[0086] (8) Place the solid powder B under the protection of an Ar atmosphere, sinter it at 550 °C for 6 h, then crush it and sieve it through a 300-mesh sieve to obtain the finished positive electrode material, and this positive electrode material is Li(Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 ) 0.99 B 0.01 O2@0.01Li6PS5Cl@0.01Li3BO3.

[0087] Example 2

[0088] The ternary material prepared in this example is:

[0089] Li(Ni 0.82 Co0.06 Mn 0.11 W 0.01 ) 0.98 B 0.02 O2@0.01Li6PS5Br@0.01Li3BO3。

[0090] This embodiment also provides a preparation method for ternary materials, including the following steps:

[0091] (1) Prepare a ternary precursor Ni 0.82 Co 0.06 Mn 0.11 W 0.01 (OH)2 doped with element W by coprecipitation method.

[0092] Prepare a 2 mol / L mixed solution by mixing nickel sulfate, cobalt sulfate, manganese sulfate and sodium tungstate in a molar ratio of 82:6:11:1.

[0093] Place ammonia water and water in a reaction kettle to prepare a bottom solution with an ammonia water concentration of 6 g / L in the bottom solution. Inject the mixed solution into the reaction kettle, and at the same time add ammonia water solution and sodium hydroxide solution. During the precipitation process, control the ammonia water concentration to be 4 ± 0.3 g / L and the pH value to be 11.3 ± 0.1. After the injection is completed, react for 24 h, filter, wash and dry.

[0094] (2) Mix the ternary precursor and ammonium borate evenly at a molar ratio of B:precursor = 2:98, and then add lithium hydroxide for secondary mixing with a molar ratio of Li / Me = 1.03.

[0095] (3) Place the mixture prepared in step (2) under an oxygen atmosphere and keep it sintered at 780 °C for 18 h. Then crush the sintered material and pass it through a 300-mesh sieve to obtain a primary sintered material Li(Ni 0.82 Co 0.06 Mn 0.11 W 0.01 ) 0.98 B 0.02 O2;

[0096] (34) Dissolve Li2S and P2S5 in ethyl acetate at a molar ratio of Li2S:P2S5 = 3:1 under the protection of an Ar atmosphere and stir continuously for 2 h, where the sum of the masses of Li2S and P2S5 accounts for 1.15 wt.% of the total mass of the mixed solution;

[0097] (5) Add the once-sintered material into the mixture in step (4), continuously stir for 1.5 h, and then add a certain amount of Li2S and LiBr into the mixture, where the molar ratio of Li2S:LiBr = 1:1. Continue to stir and react for 12 h. The molar ratio of P2S5 added in step (4) to LiBr added in step (5) = 1:2. The mass concentration of Li6PS5Br obtained from the reaction is 2.0 wt.%, and the mass ratio of the once-sintered material to the mixture = 2:1.

[0098] (6) Vacuum-dry the mixture in step (5) at 120 °C for 3 h to dry the solvent and obtain solid powder A.

[0099] (7) Under the protection of an Ar atmosphere, add a certain amount of lithium borate powder into dimethyl carbonate and continuously stir to prepare a suspension. The content of lithium borate in the suspension is 2.04 wt.%. Then add the solid powder A in step (6) into the suspension. The mass ratio of the solid powder A to the suspension = 5:2. Continue to stir for 2 h, and then vacuum-dry it at 140 °C for 3 h to dry the solvent and obtain solid powder B.

[0100] (8) Place the solid powder B under the protection of an Ar atmosphere, sinter at 520 °C for 7 h, then crush it, and pass through a 300-mesh sieve to obtain the finished positive electrode material, which is Li(Ni 0.82 Co 0.06 Mn 0.11 W 0.01 ) 0.98 B 0.02 O2@0.01Li6PS5Br@0.01Li3BO3.

[0101] Example 3

[0102] The ternary material prepared in this example is:

[0103] Li(Ni 0.82 Co 0.06 Mn 0.10 Mg 0.02 ) 0.98 B 0.02 O2@0.01Li6PS5Br@0.01Li3BO3.

[0104] This example also provides a preparation method of a ternary material, including the following steps:

[0105] (1) Prepare a ternary precursor Ni 0.82 Co 0.06 Mn 0.10 Mg 0.02 (OH)2 by the co-precipitation method.

[0106] Prepare a 2 mol / L mixed solution by mixing nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate in a molar ratio of 82:6:11:1.

[0107] Place ammonia water and water in a reaction kettle to prepare a bottom liquid with an ammonia water concentration of 7 g / L in the bottom liquid. Inject the mixed solution into the reaction kettle, and at the same time add ammonia water solution and sodium hydroxide solution. During the precipitation process, control the ammonia water concentration to be 5 ± 0.3 g / L and the pH value to be 11.4 ± 0.1. After the injection is completed, react for 24 h, filter, wash and dry. (2) Mix the ternary precursor and boric acid evenly in a molar ratio of B:precursor = 2:98, and then add lithium hydroxide for secondary mixing with a molar ratio of Li / Me = 1.03.

[0108] (3) Place the mixture prepared in step (2) under an oxygen atmosphere and keep it sintered at 795 °C for 12 h. Then crush the sintered material and pass it through a 300-mesh sieve to obtain a primary sintered material Li(Ni 0.82 Co 0.06 Mn 0.10 Mg 0.02 ) 0.98 B 0.02 O2.

[0109] (4) Under the protection of an Ar atmosphere, dissolve Li2S and P2S5 in ethyl propionate in a molar ratio of Li2S:P2S5 = 3:1 and stir continuously for 3 h, where the sum of the masses of Li2S and P2S5 accounts for 1.00 wt.% of the total mass of the mixed solution.

[0110] (5) Add the primary sintered material to the mixed solution in step (4) and stir continuously for 2 h. Then add a certain amount of Li2S and LiI to the mixed solution, where the molar ratio of Li2S:LiI = 1:1. Continue to stir and react for 12 h, where the molar ratio of P2S5 added in step (4) to LiI added in step (5) = 1:2. The mass concentration of Li6PS5I obtained by the reaction is 2.0 wt.%, and the mass ratio of the primary sintered material to the mixed solution = 2:1.

[0111] (6) Vacuum-dry the mixed solution in step (45) at 150 °C for 3 h to dry the solvent and obtain solid powder A.

[0112] (7) Under the protection of an Ar atmosphere, add a certain amount of lithium borate powder to ethyl formate and stir continuously to prepare a suspension, where the content of lithium borate in the suspension is 2.04 wt.%. Then add the solid powder A in step (6) to the suspension, and the mass ratio of the solid powder A to the suspension = 5:2. Continue to stir for 2 h, and then vacuum-dry it at 110 °C for 3 h to dry the solvent and obtain solid powder B.

[0113] (8) Place solid powder B under the protection of an Ar atmosphere, sinter it at 540 °C for 6 h, then crush it and pass it through a 300-mesh sieve to obtain the finished cathode material, which is Li(Ni 0.82 Co 0.06 Mn 0.10 1Mg 0.02 ) 0.98 B 0.02 O2@0.01Li6PS5Br@0.01Li3BO3.

[0114] Comparative Example 1

[0115] This comparative example provides a method for preparing a ternary material, including the following steps:

[0116] (1) Mix the ternary precursor Ni 0.82 Co 0.06 Mn 0.12 (OH)2 with alumina and boron oxide in a molar ratio of Al:B:precursor = 1:1:98, mix evenly, and then add lithium hydroxide for secondary mixing, with a molar ratio of Li / Me = 1.04.

[0117] (2) Place the mixture obtained in step (1) under an oxygen atmosphere, keep it sintering at 790 °C for 16 h, then crush the sintered material and pass it through a 300-mesh sieve to obtain the first sintered material Li(Ni 0.82 Co 0.06 Mn 0.12 ) 0.98 Al 0.01 B 0.01 O2.

[0118] (3) Mix the first sintered material in step (2) with lithium borate in a molar ratio of Li3BO3:Li(Ni 0.82 Co 0.06 Mn 0.12 ) 0.98 Al 0.01 B 0.01 O2 = 1:100, mix evenly, then place the mixture under an oxygen atmosphere, sinter it at 550 °C for 6 h, then crush it and pass it through a 300-mesh sieve to obtain the finished cathode material, which is Li(Ni 0.82 Co 0.06 Mn 0.12 ) 0.98 Al 0.01 B 0.01 O2@0.01Li3BO3.

[0119] Comparative Example 2

[0120] This comparative example provides a method for preparing a ternary material. On the basis of Comparative Example 1, the ternary precursor Ni0.82 Co 0.06 Mn 0.12 (OH)2 is replaced with an Al-doped precursor Ni prepared by the co-precipitation method 0.82 Co 0.06 Mn 0.11 Al 0.01 (OH)2, and the molar ratio of boron oxide to the precursor is B:precursor = 1:100. The remaining steps are the same as in Comparative Example 1. Finally, the cathode material Li(Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 ) 0.99 B 0.01 O2@0.01Li3BO3 is obtained.

[0121] That is, the difference between Comparative Example 2 and Example 1 is only that: no Li6PS5Cl coating layer is introduced.

[0122] Comparative Example 3

[0123] This comparative example provides a method for preparing a ternary material. The difference from Example 1 is only that: the Li6PS5Cl coating layer is replaced with Li3PS4. The specific coating steps are as follows:

[0124] Replace step (5) of Example 1 with "Add the once-sintered material to the mixed solution in step (4), and continuously stir for 4 h. The mass ratio of the once-sintered material to the mixed solution = 2:1." The remaining steps remain unchanged, and Li(Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 ) 0.99 B 0.01 O2@0.01Li3PS4@0.01Li3BO3 can be obtained.

[0125] Comparative Example 4

[0126] This comparative example provides a method for preparing a ternary material. The difference from Example 1 is only that: the coating amount of the Li6PS5Cl coating layer is different, specifically as follows:

[0127] Change "wherein the sum of the masses of Li2S and P2S5 accounts for 1.67 wt.% of the total mass of the mixed solution" in step (4) of Example 1 to "wherein the sum of the masses of Li2S and P2S5 accounts for 0.42 wt.% of the total mass of the mixed solution", and the remaining steps remain unchanged, and Li(Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 ) 0.99 B 0.01O2@0.0025Li6PS5Cl@0.01Li3BO3

[0128] Comparative Example 5

[0129] This comparative example provides a method for preparing a ternary material, which is only different from Example 1 in that the coating amount of the Li6PS5Cl coating layer is different, specifically as follows:

[0130] Change "wherein the total mass of Li2S and P2S5 accounts for 1.67 wt.% of the total mass of the mixed solution" in step (4) of Example 1 to "wherein the total mass of Li2S and P2S5 accounts for 5.01 wt.% of the total mass of the mixed solution", and keep the rest of the steps unchanged, then Li(Ni 0.82 Co 0.06 Mn 0.11 Al 0.01 ) 0.99 B 0.01 O2@0.03Li6PS5Cl@0.01Li3BO3

[0131] Comparative Example 6

[0132] This comparative example provides a method for preparing a ternary material, which is only different from Example 1 in that the Li3BO3 coating layer is not introduced.

[0133] Test Example 1 - Material Characterization

[0134] The XRD pattern of the positive electrode material prepared in Example 1 is as Figure 1 shown, and the scanning electron microscope image is as Figure 2 shown. It can be seen that the material prepared in Example 1 has a double coating layer of solid electrolyte + Li3BO3, and the gaps between the primary particles on the surface are filled with coating materials.

[0135] The scanning electron microscope image of the positive electrode material prepared in Comparative Example 1 is as Figure 3 shown, and the scanning electron microscope image of the positive electrode material prepared in Comparative Example 2 is as Figure 4 shown. It can be seen that the morphology of the product prepared in Comparative Example 2 is similar to that of Comparative Example 1.

[0136] Test Example 2 - Comparison of Electrochemical Performance

[0137] The coin cell was used to test the electrochemical performance at 25 °C, and the test equipment was LAND. Table 1 shows the comparison of the electrochemical performance of the positive electrode materials prepared in Example 1 and each comparative example.

[0138] Table 1 Comparison of 0.1C coin cell performance of different schemes

[0139]

[0140] The test results of rate performance of different schemes are as follows Figure 5 shown.

[0141] The first cycle capacity of the positive electrode prepared in Example 1 and Comparative Examples 1-6 was shown in Table 2. The 5C cycle performance of different schemes was compared. Figure 6 shown.

[0142] Table 2 Comparison of the first-week capacity of 5C cycle for different schemes

[0143]

[0144] From Table 2 and Figure 6 It can be seen that the cycle performance of the embodiment of the present invention is significantly better than that of the comparative example.

[0145] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A ternary cathode material, characterized in that, It includes a cathode material body, a first coating layer coated on the cathode material body, and a second coating layer coated on the first coating layer. The first coating layer is Li6PS5X, and the second coating layer is Li3BO3, where X is selected from at least one of Cl, Br, and I; The cathode material body is a nickel-cobalt-manganese cathode material containing doping elements M and B. M is an internal doping element, and B is a shallow doping element. M is selected from at least one of Mg, Al, Si, Ti, Cr, V, Y, Zr, Nb, Mo, Sn, Sb, and W; The general formula of the ternary cathode material is Li(Ni x Co y Mn z M k ) i B j O2@aLi6PS5X@bLi3BO3; In the general formula, x + y + z + k = 1, 0.0005 < k < 0.01, 0.98 < i < 0.995, 0.005 < j < 0.02, 0.005 < a < 0.02, 0.005 < b < 0.

02.

2. A preparation method of the ternary cathode material described in claim 1, characterized in that Mix a ternary precursor containing doping element M with a boron compound and a lithium source and conduct a first sintering to obtain a first sintered material; Form the first coating layer on the first sintered material to obtain a first coated material; Form the second coating layer on the first coated material to obtain a second coated material; Conduct a second sintering on the second coated material.

3. The preparation method according to claim 2, characterized in that, The preparation process of the first coated material includes: mixing Li2S and P2S5 with a first organic solvent to obtain a first mixed solution, mixing the first sintered material with the first mixed solution to obtain a second mixed solution, adding Li2S to react with LiX in the second mixed solution to obtain a third mixed solution, and drying the third mixed solution to obtain the solid first coated material; where X is selected from at least one of Cl, Br, and I.

4. The preparation method according to claim 3, characterized in that, Under the protection of an inert atmosphere, mix Li2S and P2S5 in a molar ratio of (2 - 3):1 and dissolve them in the first organic solvent, stir for 0.5h - 4h to obtain a first mixed solution; mix the first sintered material with the first mixed solution and stir for 0.5h - 2h to obtain a second mixed solution, add Li2S to react with LiX in the second mixed solution for 5h - 15h to obtain a third mixed solution, and vacuum dry the third mixed solution at 50°C - 200°C for 2h - 24h to dry the solvent.

5. The preparation method according to claim 4, characterized in that, Control the mass fraction of Li2S and P2S5 in the first mixed solution to be 1% - 3%, and the mass ratio of the first sintered material to the first mixed solution to be (1.5 - 3):

1.

6. The preparation method according to claim 4, wherein The first organic solvent is selected from at least one of ethanol, ethyl propionate, N-methylformamide, acetonitrile, anisole, tetrahydrofuran, ethyl acetate, 1,2-dimethoxyethane, ethylenediamine, dimethyl carbonate, hydrazine, and n-hexane.

7. The preparation method according to claim 3 or 4, characterized in that, The preparation process of the second coated material includes: mixing lithium borate with a second organic solvent to obtain a suspension, mixing the first coated material with the suspension and stirring, and then vacuum drying to dry the solvent.

8. The preparation method according to claim 7, wherein Under the protection of an inert atmosphere, lithium borate powder is mixed with the second organic solvent to obtain a suspension, and the mass fraction of lithium borate in the suspension is 1%-3%; the first coating material and the suspension are mixed and stirred for 1 h-5 h, and then vacuum dried at 50 °C-200 °C for 2 h-24 h.

9. The preparation method according to claim 8, characterized in that, The second organic solvent is selected from at least one of ethanol, ethyl propionate, N-methylformamide, acetonitrile, anisole, tetrahydrofuran, ethyl acetate, ethyl propionate, 1,2-dimethoxyethane, ethylenediamine, dimethyl carbonate, hydrazine, n-hexane, and n-pentane.

10. The preparation method according to claim 2, characterized in that, The preparation process of the primary sintered material includes: mixing a ternary precursor containing a doping element M with a boron compound and a lithium source, and performing primary sintering in an atmosphere with oxygen present, the temperature of the primary sintering is 700 °C-1000 °C, and the sintering time is 8 h-24 h.

11. The preparation method according to claim 10, wherein The dosage of the boron compound is to control the molar ratio of boron to the ternary precursor to be (0.005-0.02):1, and the dosage of the lithium source is to control the molar ratio of lithium to the total amount of metal elements in the ternary precursor to be (1.01-1.10):

1.

12. The preparation method according to claim 10, wherein, The material after the primary sintering is crushed to a particle size of 100-500 mesh.

13. The preparation method according to claim 10, characterized in that, The ternary precursor containing the doping element M is prepared by a coprecipitation method, and the general formula of the ternary precursor is Ni x Co y Mn z M k (OH)2; wherein, x + y + z + k = 1, 0.0005 < k < 0.01, and M is selected from at least one of Mg, Al, Si, Ti, Cr, V, Y, Zr, Nb, Mo, Sn, Sb, and W.

14. The preparation method according to claim 10, characterized in that The boron compound is selected from at least one of boric acid, boron oxide, ammonium borate, lithium borate, and lithium tetraborate.

15. The preparation method according to claim 10, characterized in that, The lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium oxalate.

16. The preparation method according to claim 2, characterized in that, The second coating material is subjected to secondary sintering under the protection of an inert atmosphere, and the temperature of the secondary sintering is controlled to be 400 °C-700 °C, and the sintering time is 5 h-10 h.

17. The preparation method according to claim 16, wherein The material after the secondary sintering is crushed to 100-500 mesh.

18. A lithium-ion battery, characterized in that, It includes the ternary cathode material described in claim 1 or the ternary cathode material prepared by the preparation method described in any one of claims 2-17.

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