A positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery

Abstract

The application relates to the technical field of lithium ion battery materials, and provides a positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. The positive electrode material comprises a core, a transition layer and a coating layer. The core comprises lithium cobaltate doped with M elements, the transition layer comprises lithium cobaltate doped with A elements, G elements and M elements, and the coating layer comprises an oxide of D elements. The preparation method of the positive electrode material comprises the following steps: mixing and sintering a cobalt source, a lithium source and an M element source to obtain a lithium cobaltate matrix; treating the lithium cobaltate matrix in an ammonium salt solution to obtain a first pretreated lithium cobaltate matrix through sintering; stirring and treating the first pretreated lithium cobaltate matrix in a solution containing A elements and G elements to obtain a second pretreated lithium cobaltate matrix; and mixing the second pretreated lithium cobaltate matrix and a D element source, and then sintering to obtain the positive electrode material. The positive electrode material has high-pressure stability and can work stably for a long time under the premise of maintaining high capacity.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, and more specifically, to a cathode material, its preparation method, a cathode electrode sheet, and a lithium-ion battery. Background Technology

[0002] Lithium cobalt oxide (LiCoO2) has long dominated the consumer battery market due to its high volumetric energy density, simple production methods, and excellent reliability. Lithium cobalt oxide cathode materials have significant potential for capacity improvement (theoretical specific capacity up to 274 mAh / g), and higher discharge specific capacity can be obtained by increasing the cutoff voltage. However, at high voltages (e.g., 4.5V), the degree of lithium-ion self-intercalation and deintercalation in lithium cobalt oxide is high, leading to instability in its layered structure, severe lattice deformation, and susceptibility to collapse; the Co in lithium cobalt oxide... 3+ Oxidized to Co 4+ The formed Co 4+ Lithium cobalt oxide (LiCO) exhibits strong oxidizing properties and undergoes side reactions with the electrolyte, leading to the loss of the active element cobalt and the consumption of other electrolyte components, resulting in irreversible capacity decay in lithium cobalt oxide batteries. The capacity decay is even more severe at high temperatures. To address these issues, researchers have employed elemental doping of lithium cobalt oxide to improve lattice stability and reduce interfacial side reactions.

[0003] Gradient doping can not only improve the stability of material structures but also reduce structural abrupt changes caused by sudden changes in dopant concentration. Currently, gradient doping is often achieved by co-precipitation of salt solutions with concentration gradients, a process that is difficult to control.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a cathode material, its preparation method, a cathode electrode sheet, and a lithium-ion battery. To overcome the shortcomings and defects of existing technologies, this invention focuses on the research of cathode materials for lithium-ion batteries, particularly improving the structure and composition of lithium cobalt oxide. The cathode material provided by this invention has a three-layer structure consisting of a core, a transition layer, and a coating layer. The synergistic effect of this three-layer structure enables the cathode material to exhibit excellent electrochemical cycling performance at high voltage (4.55V), allowing it to operate stably for extended periods while maintaining high capacity.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a cathode material, the cathode material comprising a core, a transition layer and a coating layer.

[0008] The core comprises lithium cobalt oxide doped with element M, wherein M includes at least one of elements Ni, Mn, Mg, Al, Zr, La, Y and Ti;

[0009] The transition layer is located on the surface of the core; the transition layer comprises lithium cobalt oxide doped with elements A, G and M; the elements A and G are gradient-distributed in the transition layer; the elements A include at least one of F, Cl, S, Br, P, Se and N, and the elements G include at least one of Ni, Co and Mn;

[0010] The coating layer is located on the surface of the transition layer and includes an oxide of element D; the element D includes at least one of elements Ni, Co, Mn, Al, Zr, La, Y, Tb, F, P, Ti, Mg and Li.

[0011] In an optional implementation, the cathode material satisfies at least one of the following (1) to (5):

[0012] (1): The concentrations of the A and G elements in the transition layer increase in the direction away from the core;

[0013] (2): The D element includes Co;

[0014] (3): The thickness of the transition layer is 0.1 nm to 50 nm;

[0015] (4): The thickness of the coating layer is 0.1 nm to 200 nm;

[0016] (5): The Dv50 of the positive electrode material is 3µm~8µm.

[0017] In a second aspect, the present invention provides a method for preparing a cathode material as described in the first aspect, comprising the following steps:

[0018] S1. Mix cobalt source, lithium source and M element source to obtain a first mixture; perform a first sintering on the first mixture to obtain a lithium cobalt oxide matrix;

[0019] S2. The lithium cobalt oxide matrix is ​​dispersed in an ammonium salt solution and stirred for the first time. After solid-liquid separation, it is sintered for the second time to obtain the first pretreated lithium cobalt oxide matrix.

[0020] S3. The first pretreated lithium cobalt oxide matrix is ​​placed in a solution containing element A and element G, and the mixture is stirred for the second time and the solvent is evaporated to obtain the second pretreated lithium cobalt oxide matrix.

[0021] S4. The second pretreated lithium cobalt oxide matrix and the D element source are mixed, and after the third sintering, they are crushed and sieved to obtain the cathode material.

[0022] In an optional embodiment, the ammonium salt in the ammonium salt solution includes at least one of ammonium chloride, ammonium fluoride, ammonium sulfate, ammonium nitrate, and ammonium carbonate, and the concentration of the ammonium salt solution is 2 mol / L to 10 mol / L.

[0023] In an optional implementation, step S1 satisfies at least one of the following (6) to (10):

[0024] (6): The M element of the M element source includes at least one of Ni, Mn, Mg, Al, Zr, La, Y and Ti;

[0025] (7): The source of element M includes at least one of the following: hydroxide, oxide, carbonate, nitrate, sulfate, soluble halide and acetate of element M;

[0026] (8): The mass of the M element source is 0.03% to 0.2% of the mass of the first mixture.

[0027] (9): The molar ratio of cobalt ions in the cobalt source to lithium ions in the lithium source is 1: (1~1.05).

[0028] (10): The temperature of the first sintering is 800℃~1000℃ and the duration is 5h~10h.

[0029] In an optional implementation, step S2 satisfies at least one of the following (11) to (12):

[0030] (11): The first stirring time is 10h~48h;

[0031] (12): The second sintering temperature is 400℃~800℃ and the duration is 3h~6h.

[0032] In an optional implementation, step S3 satisfies at least one of the following (13) to (15):

[0033] (13): The A element source includes at least one of F, Cl, S, Br, P, Se and N, and the G element source includes at least one of Ni, Co and Mn.

[0034] (14): The total mass of the A element source and the G element source is 0.5% to 1.5% of the mass of the first pretreated lithium cobalt oxide matrix, and the molar ratio of A in the A element source to G in the G element source is 0.3-1:1;

[0035] (15): The temperature of the second stirring is 100℃~150℃.

[0036] In an optional implementation, step S4 satisfies at least one of the following (16) to (18):

[0037] (16): The D element in the D element source includes at least one of the elements Ni, Co, Mn, Al, Zr, La, Y, Tb, F, P, Ti, Mg and Li;

[0038] (17): The mass of the D element source is 0.3% to 2.5% of the mass of the second pretreated lithium cobalt oxide matrix;

[0039] (18): The temperature of the third sintering is 500℃~900℃ and the duration is 5h~10h.

[0040] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising the positive electrode material provided in the first aspect or the positive electrode material prepared by the preparation method provided in the second aspect.

[0041] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode as provided in the third aspect.

[0042] The present invention has the following beneficial effects:

[0043] (1) The cathode material provided by this invention has a three-layer structure consisting of a core, a transition layer, and a coating layer. The core comprises lithium cobalt oxide doped with a metal element M in the bulk phase. Element doping at the bulk level can expand the lattice spacing and improve the Li... + The diffusion rate is high; the transition layer includes anions of element A and cations of element G. Co-doping of these anions and cations stabilizes the crystal lattice structure and reduces oxygen evolution on the crystal surface. Furthermore, the gradient distribution of these two ions in the transition layer improves the stability of the material structure while reducing structural abrupt changes caused by sudden changes in dopant concentration. The coating layer is an oxide containing element D, which reduces the contact between the active material and the electrolyte in the cathode material. The synergistic effect of these three layers results in a cathode material that not only has good discharge specific capacity but also high-voltage stability, enabling it to operate stably for extended periods while maintaining high capacity.

[0044] (2) This invention utilizes ammonium ions in an ammonium salt solution to replace lithium ions in lithium cobalt oxide, and then removes the ammonium ions by sintering to obtain lithium cobalt oxide with gradient lattice vacancies on the surface, which facilitates subsequent gradient co-doping of anions and cations. This method is simple to operate. The ammonium salt solution spontaneously diffuses from the surface of lithium cobalt oxide to the interior of lithium cobalt oxide, resulting in a gradient distribution of the amount of replaced lithium ions that decreases from the surface to the interior. This gradient distribution is relatively uniform and easy to achieve. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used 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 should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 The image shows a scanning electron microscope (SEM) image of the cathode material prepared in Example 1.

[0047] Figure 2 The image shows a scanning electron microscope (SEM) image of the cathode material prepared for Comparative Example 1. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. However, there may be instances where unnecessary detailed descriptions are omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0049] Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the invention and are not intended to limit the subject matter of the claims. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0050] For the sake of brevity, this invention specifically discloses several numerical ranges, which can be combined to form corresponding embodiments. The endpoints and values ​​of the ranges disclosed herein are not limited to precise ranges or values; these ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0051] Unless otherwise stated, the terminology used in this invention has the common meaning as generally understood by those skilled in the art.

[0052] The following is a detailed description of the positive electrode material, its preparation method, positive electrode sheet, and lithium-ion battery provided by the present invention.

[0053] Currently, lithium cobalt oxide cathode materials exhibit poor high-voltage stability; while high capacity can be achieved at high voltages, they cannot operate stably for extended periods and suffer from poor cycle performance. To address these technical problems, this invention proposes the following solution.

[0054] The present invention provides a cathode material comprising a core, a transition layer and a coating layer.

[0055] The core comprises lithium cobalt oxide doped with element M, wherein M includes at least one of Ni, Mn, Mg, Al, Zr, La, Y, and Ti. Bulk-doped lithium cobalt oxide with metal element M can increase the lattice spacing and improve the Li-phase conductivity at the bulk level. + The diffusion rate.

[0056] The transition layer is located on the surface of the core; the transition layer comprises lithium cobalt oxide doped with elements A, G, and M; the A and G elements are distributed in a gradient in the transition layer; the A element includes at least one of F, Cl, S, Br, P, Se, and N, and the G element includes at least one of Ni, Co, and Mn. The A-containing ions are anions, and the G-containing ions are cations; co-doping of anions and cations can stabilize the crystal lattice structure and reduce oxygen evolution on the crystal surface.

[0057] The coating layer, located on the surface of the transition layer, comprises an oxide of element D; the element D includes at least one of Ni, Co, Mn, Al, Zr, La, Y, Tb, F, P, Ti, Mg, and Li. This coating layer can reduce the contact between the active material and the electrolyte in the cathode material, thereby reducing the generation of interfacial side reactions.

[0058] The synergistic effect of the three-layer structure enables the resulting cathode material to not only have good discharge specific capacity, but also high voltage stability, and to operate stably for a long time while maintaining high capacity.

[0059] In some implementations, the concentrations of elements A and G in the transition layer increase in the direction away from the core, meaning that the closer to the surface of the material particles, the more elements A and G are doped. This can stabilize the crystal lattice structure on the crystal surface and reduce the precipitation of oxygen on the crystal surface.

[0060] In some embodiments, element D includes Co. Oxides of Co have high electrical conductivity and... + The diffusion rate will not significantly affect the Li in the cathode material. + The insertion / extraction rate, as a coating layer, can stabilize the surface structure of the cathode material.

[0061] In some implementations, the thickness of the transition layer is 0.1 nm to 50 nm.

[0062] In some implementations, the thickness of the coating layer is 0.1 nm to 200 nm.

[0063] In some implementations, the Dv50 of the cathode material is 3µm to 8µm.

[0064] Accordingly, the present invention provides a method for preparing a cathode material, comprising the following steps:

[0065] S1. Mix the cobalt source, lithium source and M element source to obtain a first mixture; perform a first sintering on the first mixture to obtain a lithium cobalt oxide matrix.

[0066] In some embodiments, the cobalt source particle size Dv50 is 3µm to 5µm, which is beneficial for improving the discharge specific capacity of the cathode material.

[0067] In some embodiments, the M element source includes at least one of Ni, Mn, Mg, Al, Zr, La, Y, and Ti. Doping with the M element can increase the c-axis spacing of the lithium cobalt oxide crystal and improve the Li... + The diffusion rate is reduced, while the phase transition of the lithium cobalt oxide crystal layered structure is suppressed during cycling.

[0068] In some embodiments, the source of element M includes at least one of the following: hydroxide, oxide, carbonate, nitrate, sulfate, soluble halide, and acetate of element M.

[0069] In some implementations, the mass of the M element source is 0.03% to 0.2% of the mass of the first mixture.

[0070] In some embodiments, the molar ratio of cobalt ions in the cobalt source to lithium ions in the lithium source is 1:(1~1.05).

[0071] In some embodiments, the temperature of the first sintering is 800℃~1000℃, and the duration is 5h~10h.

[0072] S2. The lithium cobalt oxide matrix is ​​dispersed in an ammonium salt solution and stirred for the first time. After solid-liquid separation, it is sintered for the second time to obtain the first pretreated lithium cobalt oxide matrix.

[0073] In some embodiments, the solid-liquid separation process further includes washing, drying, and grinding the solid product obtained from the solid-liquid separation with deionized water, followed by a second sintering.

[0074] A lithium cobalt oxide matrix is ​​dispersed in an ammonium salt solution. Ammonium ions in the ammonium salt solution can displace lithium ions in the lithium cobalt oxide matrix, resulting in an ammonium ion-doped lithium cobalt oxide matrix. After removing the ammonium ions through a second sintering process, O and Li vacancies are left on the surface of the first pretreated lithium cobalt oxide matrix, facilitating subsequent doping. Because the ammonium salt solution diffuses from the surface of the lithium cobalt oxide matrix into its interior, the number of vacancies increases from the inside out. The amount of vacancies on the surface of the first pretreated lithium cobalt oxide matrix can be controlled by adjusting the concentration of the ammonium salt solution or the initial stirring time.

[0075] In some embodiments, the ammonium salt in the ammonium salt solution includes at least one of ammonium chloride, ammonium fluoride, ammonium sulfate, ammonium nitrate, and ammonium carbonate; the concentration of the ammonium salt solution is 2 mol / L to 10 mol / L, for example, it can be any one of 2 mol / L, 5 mol / L, 7 mol / L, 10 mol / L, or a range between any two.

[0076] In some implementations, the duration of the first stirring is 10h to 48h, for example, it can be any one or any two of 10h, 15h, 24h, 30h, and 48h.

[0077] In some implementations, the drying temperature is 80°C and the drying time is 24 hours.

[0078] In some embodiments, the temperature of the second sintering is 400°C to 800°C, for example, it can be any one or any two of 400°C, 500°C, 600°C, 700°C, and 800°C; the duration of the second sintering is 3h to 6h, for example, it can be any one or any two of 3h, 4h, 5h, and 6h.

[0079] S3. The first pretreated lithium cobalt oxide matrix is ​​placed in a solution containing element A and element G, and the mixture is stirred for the second time and the solvent is evaporated to obtain the second pretreated lithium cobalt oxide matrix.

[0080] In some embodiments, drying is also included after evaporating the solvent.

[0081] In some embodiments, the A element source includes at least one of F, Cl, S, Br, P, Se, and N, and the A-containing ion is an anion or a polyanion, doped into the vacancy of the first pretreated lithium cobalt oxide matrix. The G element source includes at least one of Ni, Co, and Mn, and the G-containing ion is a cation, doped into the vacancy of the first pretreated lithium cobalt oxide matrix.

[0082] Since different radii and diffusion coefficients affect the diffusion of ions in lithium cobalt oxide crystals, gradient doping of lithium cobalt oxide can be achieved by doping with different ions. Atom-containing ions, due to their low diffusion coefficient, can only remain on the surface lattice, stabilizing the oxygen in the surface lattice, reducing oxygen evolution, and helping to suppress Co. 4+ Interaction with the electrolyte. Radius of the G-containing ion and Li. + Because the atoms are close together, the G-containing ions diffuse to occupy lithium vacancies in the first pretreated lithium cobalt oxide matrix, preventing drastic lattice changes in the layered structure of the cathode material under high delithiation conditions and improving lattice stability. In summary, simultaneous doping with both A-containing anions and G-containing cations can improve the high-voltage stability of the cathode material.

[0083] In S2, the number of vacancies on the surface of the first pretreated lithium cobalt oxide substrate exhibits a decreasing gradient distribution from the outside to the inside; in S3, gradient doping can be achieved by doping with ions of different radii and diffusion coefficients. Therefore, the combined use of S2 and S3 can achieve excellent gradient doping of cations and anions containing A and G elements on the surface of the cathode material, thus preparing the second pretreated lithium cobalt oxide substrate.

[0084] In some embodiments, the total mass of element A source and element G source is 0.5% to 1.5% of the mass of the first pretreated lithium cobalt oxide matrix, and the molar ratio of A source A to G source G is 0.3-1:1.

[0085] In some embodiments, the temperature of the second stirring is 100°C to 150°C.

[0086] In some embodiments, the second stirring speed is 500 rpm to 800 rpm, and the first and second stirring speeds may be the same or different.

[0087] S4. The second pretreated lithium cobalt oxide matrix and the D element source are mixed, and after the third sintering, they are crushed and sieved to obtain the cathode material.

[0088] It should be noted that the D element source generates an oxide of D element after the third sintering reaction. The oxide of D element is the coating layer, which can prevent the active material in the positive electrode material from directly contacting the electrolyte, reduce Co dissolution, and inhibit oxygen evolution.

[0089] In some embodiments, the D element source includes at least one of Ni, Co, Mn, Al, Zr, La, Y, Tb, F, P, Ti, Mg, and Li. Among these, oxides of Co have high electrical conductivity, and Li... + The diffusion rate will not significantly affect the Li in the cathode material. + De-embedding speed.

[0090] In some embodiments, the mass of the D element source is 0.3% to 2.5% of the mass of the second pretreated lithium cobalt oxide matrix.

[0091] In some embodiments, the temperature of the third sintering is 500°C to 900°C, and the duration is 5 hours to 10 hours.

[0092] The features and performance of the present invention will be further described in detail below with reference to the accompanying drawings, embodiments and comparative examples.

[0093] Example 1

[0094] This embodiment provides a cathode material, the preparation method of which includes:

[0095] S1. Mix 7 kg Co3O4, 3.3 kg Li2CO3, 8 g Mg(OH)2 and 6 g Al2O3 evenly to obtain the first mixture. Sinter the first mixture at 1000℃ for 10 h, then pulverize and sieve to obtain the lithium cobalt oxide matrix.

[0096] S2. The lithium cobalt oxide matrix was dispersed in a 5 mol / L NH4Cl aqueous solution and stirred for the first time. After solid-liquid separation, a solid product was obtained. The solid product was washed with deionized water, dried at 80°C for 24 h, ground, and sintered at 500°C for 6 h to obtain the first pretreated lithium cobalt oxide matrix.

[0097] The duration of the first stirring is 24 hours, and the stirring speed is 500 rpm.

[0098] S3. The first pretreated lithium cobalt oxide matrix is ​​placed in an anhydrous ethanol solution containing H3PO4 and Ni(CH3COO)2 (solid-liquid ratio of 1g:2g), stirred for the second time, and the solvent is evaporated. Then, it is dried at 120°C to obtain the second pretreated lithium cobalt oxide matrix.

[0099] The total mass of H3PO4 and Ni(CH3COO)2 is 0.75% of the mass of the first pretreated lithium cobalt oxide matrix; the molar ratio of P to Ni is 0.3:1; the temperature of the second stirring is 110℃ and the speed of the second stirring is 600rpm.

[0100] S4. Take 80g of the second pretreated lithium cobalt oxide matrix, 0.63g of Co(OH)2, 0.25g of MnO2, 0.21g of Y2O3 and 0.12g of AlOOH, mix them, sinter at 500℃ for 5h, then crush and sieve to obtain the cathode material.

[0101] The cathode material obtained in this embodiment has a transition layer thickness of 30nm~40nm and a coating layer thickness of 100nm~150nm.

[0102] Instruction manual attached Figure 1 The image shows a scanning electron microscope (SEM) image of the cathode material obtained in this embodiment. It can be seen from the image that the cathode material particles are about 5 μm in size, with good dispersion and no obvious agglomeration. The surface of the cathode material particles is rough and has a coating layer.

[0103] Example 2

[0104] This embodiment provides a cathode material, the preparation method of which includes:

[0105] S1. Mix 7 kg Co3O4, 3.3 kg Li2CO3, 3 g Mg(OH)2 and 2 g Al2O3 evenly to obtain the first mixture. Sinter the first mixture at 1000℃ for 5 h, then pulverize and sieve to obtain the lithium cobalt oxide matrix.

[0106] S2. The lithium cobalt oxide matrix was dispersed in a 2 mol / L NH4F aqueous solution and stirred for the first time. After solid-liquid separation, a solid product was obtained. The solid product was washed with deionized water, dried at 80°C for 24 h, ground, and sintered at 800°C for 3 h to obtain the first pretreated lithium cobalt oxide matrix.

[0107] The duration of the first stirring is 48 hours, and the stirring speed is 500 rpm.

[0108] S3. The first pretreated lithium cobalt oxide matrix is ​​placed in an anhydrous ethanol solution containing H3PO4 and Ni(CH3COO)2 (solid-liquid ratio of 1g:2g), stirred for the second time, and the solvent is evaporated. Then, it is dried at 120°C to obtain the second pretreated lithium cobalt oxide matrix.

[0109] The total mass of H3PO4 and Ni(CH3COO)2 is 0.9% of the mass of the first pretreated lithium cobalt oxide matrix; the molar ratio of P to Ni is 0.4:1; the temperature of the second stirring is 100℃ and the speed of the second stirring is 600rpm.

[0110] S4. Take 80g of the second pretreated lithium cobalt oxide matrix, 0.25g of Co(OH)2, 0.04g of MnO2, 0.03g of Y2O3 and 0.09g of AlOOH, mix them, sinter at 900℃ for 5h, then crush and sieve to obtain the cathode material.

[0111] The cathode material obtained in this embodiment has a transition layer thickness of 25nm~40nm and a coating layer thickness of 5nm~50nm.

[0112] Example 3

[0113] This embodiment provides a cathode material, the preparation method of which includes:

[0114] S1. Mix 7 kg Co3O4, 3.3 kg Li2CO3, 13 g Mg(OH)2 and 7.1 g TiO2 evenly to obtain the first mixture. Sinter the first mixture at 800℃ for 10 h, then pulverize and sieve to obtain the lithium cobalt oxide matrix.

[0115] S2. The lithium cobalt oxide matrix was dispersed in a 10 mol / L NH4Cl aqueous solution and stirred for the first time. After solid-liquid separation, a solid product was obtained. The solid product was washed with deionized water, dried at 80°C for 24 h, ground, and sintered at 400°C for 6 h to obtain the first pretreated lithium cobalt oxide matrix.

[0116] The duration of the first stirring is 15 hours, and the stirring speed is 500 rpm.

[0117] S3. The first pretreated lithium cobalt oxide matrix is ​​placed in an anhydrous ethanol solution containing H3PO4 and Ni(CH3COO)2 (solid-liquid ratio of 1g:2g), stirred for the second time, and the solvent is evaporated. Then, it is dried at 120°C to obtain the second pretreated lithium cobalt oxide matrix.

[0118] The total mass of H3PO4 and Ni(CH3COO)2 is 1.5% of the mass of the first pretreated lithium cobalt oxide matrix; the molar ratio of P to Ni is 1:1; the temperature of the second stirring is 150℃ and the speed of the second stirring is 800 rpm.

[0119] S4. Take 80g of the second pretreated lithium cobalt oxide matrix, 0.81g of Co(OH)2, 0.25g of MnO2, 0.63g of CoPO4 and 0.23g of AlOOH, mix them, sinter at 500℃ for 10h, then crush and sieve to obtain the cathode material.

[0120] The cathode material obtained in this embodiment has a transition layer thickness of 40nm~50nm and a coating layer thickness of 150nm~200nm.

[0121] Example 4

[0122] This embodiment provides a cathode material, which differs from Embodiment 1 only in that, in S2, the lithium cobalt oxide matrix is ​​dispersed in a 3 mol / L NH4Cl aqueous solution and stirred for the first time.

[0123] The cathode material obtained in this embodiment has a transition layer thickness of 25nm~35nm and a coating layer thickness of 100nm~150nm.

[0124] Example 5

[0125] This embodiment provides a cathode material, which differs from Embodiment 1 only in that, in S2, the lithium cobalt oxide matrix is ​​dispersed in an 8 mol / L NH4Cl aqueous solution and stirred for the first time.

[0126] The cathode material obtained in this embodiment has a transition layer thickness of 40nm~50nm and a coating layer thickness of 100nm~150nm.

[0127] Example 6

[0128] This embodiment provides a cathode material, which differs from Embodiment 1 only in that, in S3, the total mass of H3PO4 and Ni(CH3COO)2 is 0.6% of the mass of the first pretreated lithium cobalt oxide matrix.

[0129] The cathode material obtained in this embodiment has a transition layer thickness of 20nm~35nm and a coating layer thickness of 100nm~150nm.

[0130] Example 7

[0131] This embodiment provides a cathode material, which differs from Embodiment 1 only in that, in S3, the total mass of H3PO4 and Ni(CH3COO)2 is 1.3% of the mass of the first pretreated lithium cobalt oxide matrix.

[0132] The cathode material obtained in this embodiment has a transition layer thickness of 40nm~50nm and a coating layer thickness of 100nm~150nm.

[0133] Example 8

[0134] This embodiment provides a cathode material, which differs from Embodiment 1 only in that, in S3, the molar ratio of P to Ni is 0.6:1.

[0135] The cathode material obtained in this embodiment has a transition layer thickness of 25nm~35nm and a coating layer thickness of 100nm~150nm.

[0136] Example 9

[0137] This embodiment provides a cathode material, which differs from Embodiment 1 only in that the molar ratio of P to Ni is 0.8:1.

[0138] The cathode material obtained in this embodiment has a transition layer thickness of 20nm~30nm and a coating layer thickness of 100nm~150nm.

[0139] Comparative Example 1

[0140] This comparative example provides a cathode material that differs from Example 1 in that it only includes step S1 (i.e., no subsequent processing is performed on the lithium cobalt oxide substrate).

[0141] Instruction manual attached Figure 2 The image shows a scanning electron microscope (SEM) image of the cathode material obtained in Comparative Example 1. It can be seen from the image that the cathode material has a smooth surface and a small amount of agglomeration.

[0142] Comparative Example 2

[0143] This comparative example provides a cathode material, the preparation method of which includes:

[0144] S1. Mix 7 kg Co3O4, 3.3 kg Li2CO3, 8 g Mg(OH)2 and 6 g Al2O3 evenly to obtain the first mixture. Sinter the first mixture at 1000℃ for 10 h, then pulverize and sieve to obtain the lithium cobalt oxide matrix.

[0145] S2. The lithium cobalt oxide matrix was dispersed in a 5 mol / L NH4Cl aqueous solution and stirred for the first time. After solid-liquid separation, a solid product was obtained. The solid product was washed with deionized water, dried at 80°C for 24 h, ground, and sintered at 500°C for 6 h to obtain the first pretreated lithium cobalt oxide matrix.

[0146] The duration of the first stirring is 24 hours, and the stirring speed is 500 rpm.

[0147] S3. The first pretreated lithium cobalt oxide substrate was placed in an anhydrous ethanol solution containing H3PO4 and Ni(CH3COO)2 (solid-liquid ratio of 1g:2g), stirred for the second time, and the solvent was evaporated. Then, it was dried at 120°C to obtain the second pretreated lithium cobalt oxide substrate. The second pretreated lithium cobalt oxide substrate was directly sintered at 500°C for 5 hours, then crushed and sieved to obtain the cathode material of Comparative Example 2.

[0148] The total mass of H3PO4 and Ni(CH3COO)2 is 0.75% of the mass of the first pretreated lithium cobalt oxide matrix; the molar ratio of P to Ni is 0.3:1; the temperature of the second stirring is 110℃ and the speed of the second stirring is 600rpm.

[0149] Comparative Example 3

[0150] This comparative example provides a cathode material, the preparation method of which includes:

[0151] 7 kg Co3O4, 3.3 kg Li2CO3, 8 g Mg(OH)2 and 6 g Al2O3 were mixed evenly to obtain a first mixture. The first mixture was sintered at 1000℃ for 10 h, and then pulverized and sieved to obtain a lithium cobalt oxide matrix.

[0152] 80g of lithium cobalt oxide matrix, 0.63g of Co(OH)2, 0.25g of MnO2, 0.21g of Y2O3 and 0.12g of AlOOH were mixed and sintered at 500℃ for 5h. The mixture was then pulverized and sieved to obtain the cathode material of Comparative Example 3.

[0153] Comparative Example 4

[0154] This comparative example provides a cathode material, the preparation method of which includes:

[0155] 7 kg Co3O4, 3.3 kg Li2CO3, 8 g Mg(OH)2 and 6 g Al2O3 were mixed evenly to obtain a first mixture. The first mixture was sintered at 1000℃ for 10 h, and then pulverized and sieved to obtain a lithium cobalt oxide matrix.

[0156] 80g of lithium cobalt oxide matrix, 0.51g of Ni(CH3COO)2, 0.09g of H3PO4, 0.63g of Co(OH)2, 0.25g of MnO2, 0.21g of Y2O3 and 0.12g of AlOOH were mixed and sintered at 500℃ for 5h. The mixture was then pulverized and sieved to obtain the cathode material of Comparative Example 4.

[0157] Experimental Example 1

[0158] The size and distribution of the cathode material were tested using a laser particle size analyzer. The particle size test results are expressed as the median particle size Dv50. The test results are shown in Table 1.

[0159] Experimental Example 2

[0160] The obtained positive electrode material, along with conductive agents Super P and PVDF, is uniformly coated onto aluminum foil in a ratio of 92:4:4, and then pressed into a positive electrode sheet. The positive electrode sheet, graphite negative electrode sheet, electrolyte, and separator are then assembled into a battery.

[0161] The discharge specific capacity of each battery was tested at a current density of 0.1C within the range of 3V to 4.55V.

[0162] After activation by charge-discharge, each battery was stored in a 60°C oven. The batteries were then charged and discharged at 0.1C every two days, and the capacity retention rate was calculated after 10 days. The test results are shown in Table 1.

[0163] Table 1

[0164]

[0165] Table 1, comparing Examples 1-9 and Comparative Examples 1-4, shows that the cathode material prepared by this invention exhibits excellent electrical properties under high-temperature storage conditions of 60°C and high-voltage charge-discharge conditions of 4.55V, with a battery capacity retention rate of up to 70.3%, while the battery capacity retention rate of Comparative Example 1 is only 5.2%. When the cathode material lacks the aforementioned transition layer or coating layer, its battery capacity retention rate does not achieve good performance, demonstrating that the simultaneous presence of both the transition layer and the coating layer is necessary to impart superior high-temperature and high-pressure stability to the cathode material.

[0166] Comparative Example 4 used the same mass of raw materials as Example 1 to modify the lithium cobalt oxide matrix. Due to the different modification methods, Comparative Example 4 exhibited better discharge specific capacity, but lower capacity retention. Comparative Example 4 did not perform liquid-phase treatment on the lithium cobalt oxide matrix, resulting in the presence of common residual lithium on the matrix surface. Direct coating of the lithium cobalt oxide matrix could absorb this residual lithium, generating compounds that facilitate lithium-ion intercalation and deintercalation, leading to a higher discharge specific capacity. Comparing the data from Example 1 and Comparative Example 4 demonstrates that a coating layer alone, without an anion-cation doped transition layer, is insufficient to improve the high-temperature and high-pressure stability of the cathode material.

[0167] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode material, characterized in that, It includes a core, a transition layer, and a coating layer; the core includes lithium cobalt oxide doped with element M, wherein M includes at least one of Ni, Mn, Mg, Al, Zr, La, Y, and Ti; the transition layer is located on the surface of the core; The transition layer comprises lithium cobalt oxide doped with elements A, G, and M; the elements A and G are distributed in a gradient in the transition layer; The element A includes at least one of F, Cl, S, Br, P, Se, and N, and the element G includes at least one of Ni, Co, and Mn; The coating layer is located on the surface of the transition layer and includes an oxide of element D; the element D includes at least one of elements Ni, Co, Mn, Al, Zr, La, Y, Tb, F, P, Ti, Mg and Li. The method for preparing the cathode material includes the following steps: S1. Mix cobalt source, lithium source and M element source to obtain a first mixture; perform a first sintering on the first mixture to obtain a lithium cobalt oxide matrix; S2. The lithium cobalt oxide matrix is ​​dispersed in an ammonium salt solution and stirred for the first time. After solid-liquid separation, it is sintered for the second time to obtain the first pretreated lithium cobalt oxide matrix. S3. The first pretreated lithium cobalt oxide matrix is ​​placed in a solution containing element A and element G, and the mixture is stirred for the second time and the solvent is evaporated to obtain the second pretreated lithium cobalt oxide matrix. S4. The second pretreated lithium cobalt oxide matrix and the D element source are mixed, and after the third sintering, they are crushed and sieved to obtain the cathode material.

2. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following (1) to (5): (1): The concentrations of the A and G elements in the transition layer increase in the direction away from the core; (2): The D element includes Co; (3): The thickness of the transition layer is 0.1 nm to 50 nm; (4): The thickness of the coating layer is 0.1 nm to 200 nm; (5): The Dv50 of the positive electrode material is 3µm~8µm.

3. A method for preparing the cathode material according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Mix cobalt source, lithium source and M element source to obtain a first mixture; perform a first sintering on the first mixture to obtain a lithium cobalt oxide matrix; S2. The lithium cobalt oxide matrix is ​​dispersed in an ammonium salt solution and stirred for the first time. After solid-liquid separation, it is sintered for the second time to obtain the first pretreated lithium cobalt oxide matrix. S3. The first pretreated lithium cobalt oxide matrix is ​​placed in a solution containing element A and element G, and the mixture is stirred for the second time and the solvent is evaporated to obtain the second pretreated lithium cobalt oxide matrix. S4. The second pretreated lithium cobalt oxide matrix and the D element source are mixed, and after the third sintering, they are crushed and sieved to obtain the cathode material.

4. The method for preparing the cathode material according to claim 3, characterized in that, The ammonium salt in the ammonium salt solution includes at least one of ammonium chloride, ammonium fluoride, ammonium sulfate, ammonium nitrate, and ammonium carbonate, and the concentration of the ammonium salt solution is 2 mol / L to 10 mol / L.

5. The method for preparing the cathode material according to claim 3, characterized in that, Step S1 satisfies at least one of the following (6) to (10): (6): The M element of the M element source includes at least one of Ni, Mn, Mg, Al, Zr, La, Y and Ti; (7): The source of element M includes at least one of the following: hydroxide, oxide, carbonate, nitrate, sulfate, soluble halide and acetate of element M; (8): The mass of the M element source is 0.03% to 0.2% of the mass of the first mixture. (9): The molar ratio of cobalt ions in the cobalt source to lithium ions in the lithium source is 1: (1~1.05). (10): The temperature of the first sintering is 800℃~1000℃ and the duration is 5h~10h.

6. The method for preparing the cathode material according to any one of claims 3 or 4, characterized in that, Step S2 satisfies at least one of the following (11)~(12): (11): The first stirring time is 10h~48h; (12): The second sintering temperature is 400℃~800℃ and the duration is 3h~6h.

7. The method for preparing the cathode material according to claim 3, characterized in that, Step S3 satisfies at least one of the following (13) to (15): (13): The A element source includes at least one of F, Cl, S, Br, P, Se and N, and the G element source includes at least one of Ni, Co and Mn. (14): The total mass of the A element source and the G element source is 0.5% to 1.5% of the mass of the first pretreated lithium cobalt oxide matrix, and the molar ratio of A in the A element source to G in the G element source is 0.3-1:1; (15): The temperature of the second stirring is 100℃~150℃.

8. The method for preparing the cathode material according to claim 3, characterized in that, Step S4 satisfies at least one of the following (16) to (18): (16): The D element in the D element source includes at least one of the elements Ni, Co, Mn, Al, Zr, La, Y, Tb, F, P, Ti, Mg and Li; (17): The mass of the D element source is 0.3% to 2.5% of the mass of the second pretreated lithium cobalt oxide matrix; (18): The temperature of the third sintering is 500℃~900℃ and the duration is 5h~10h.

9. A positive electrode sheet, characterized in that, The cathode material includes the cathode material described in any one of claims 1 to 2 or the cathode material prepared by the preparation method described in any one of claims 3 to 8.

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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