A positive electrode material, a preparation method thereof, a secondary battery, and an electrical device

Abstract

The application provides a positive electrode material, a preparation method thereof, a secondary battery and an electrical device. The positive electrode material comprises secondary particles with a small-angle grain boundary proportion of 10%-30%. From the perspective of positive electrode material domain regulation, the application optimizes grain arrangement and grain boundary orientation, reduces stress and strain between grains and crack propagation caused by anisotropic volume change, solves the cracking problem of polycrystalline materials, improves the cycle performance of the corresponding battery, and thus makes the corresponding battery prepared from the positive electrode material have high capacity and cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy, in particular to a positive electrode material, a preparation method thereof, a secondary battery and an electrical equipment. BACKGROUND

[0002] Lithium ion batteries have been widely used in many fields such as new energy vehicles and energy storage systems due to their high energy density, long service life and environmental friendliness. With the explosive development of new energy vehicles, consumers' demand for further improving the battery mileage is increasing, and improving the energy density and safety performance of lithium ion batteries has become the focus of attention.

[0003] High-nickel positive electrode materials have become the preferred high-energy-density lithium ion battery positive electrode materials for new energy vehicles due to their high specific capacity. For high-nickel polycrystalline positive electrode materials, during the electrochemical reaction process, local stress and strain and micro-cracks are generated, which causes the electrolyte to penetrate into the material particles and induces side reactions, resulting in a decrease in the cycle performance of the battery. Therefore, reducing the generation of local stress and strain and micro-cracks in high-nickel polycrystalline materials, optimizing the ion channels in the particles, and reducing particle cracking are crucial for improving the electrical performance of high-nickel positive electrode materials. SUMMARY

[0004] The present application aims to provide a positive electrode material, a preparation method thereof, a secondary battery and an electrical equipment to solve the above problems.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] The present application first provides a positive electrode material, which includes secondary particles with a small-angle grain boundary proportion of 10% to 30%, and the secondary particles include a plurality of primary particles. In the present application, the small-angle grain boundary is a grain boundary with a phase difference between adjacent grains in the secondary particles of 2-15°.

[0007] For example, the small-angle grain boundary proportion in the secondary particles can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%, or any value between 10% and 30%.

[0008] The small-angle grain boundary proportion is the proportion of grain boundaries with a phase difference between adjacent grains in the secondary particles of 2-15° to all grain boundaries.

[0009] Optionally, the positive electrode material is composed of a plurality of secondary particles, and the average value of the small-angle grain boundary proportion of the secondary particles in the positive electrode material is 10% to 30%. Five secondary particles can be randomly selected, the small-angle grain boundary proportion of each secondary particle is tested, and the arithmetic mean of the small-angle grain boundary proportion is calculated to obtain the average value of the small-angle grain boundary proportion of the secondary particles in the positive electrode material.

[0010] By regulating the small-angle grain boundary proportion of the secondary particles of the positive electrode material within a suitable range, the grain arrangement is optimized, the stress and strain between the grains caused by the anisotropic volume change are reduced, the cracking problem of the polycrystalline material is solved, and the cycle performance of the corresponding battery is improved.

[0011] Optionally, the positive electrode material includes secondary particles with a small-angle grain boundary proportion of 12% to 25%. The average value of the small-angle grain boundary proportion of the secondary particles in the positive electrode material is 12% to 25%.

[0012] Optionally, the secondary particle includes an inner layer and an outer layer covering the inner layer, and the positive electrode material satisfies at least one of the following conditions a to b:

[0013] a. The arrangement mode of the primary particles of the outer layer is different from that of the primary particles of the inner layer, for example, the primary particles of the outer layer are arranged in disorder, and the primary particles of the inner layer are arranged in a radial manner; or the primary particles of the outer layer are arranged perpendicular to the direction of the primary particles of the inner layer, and the primary particles of the inner layer are arranged in a radial manner.

[0014] In an optional embodiment, the primary particles of the inner layer are arranged in a radial manner, and the primary particles of the outer layer are arranged in disorder. The radial arrangement of the primary particles of the inner layer can shorten the lithium ion transmission channel and improve the rate performance; the disordered arrangement of the primary particles of the outer layer can improve the mechanical stability of the secondary particle, inhibit the cracking of the secondary particle during the cycle process, reduce the side reaction with the electrolyte, and improve the cycle stability and safety of the corresponding battery.

[0015] b. The porosity of the inner layer is 2-10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or any value between 2-10%; the porosity of the outer layer is 0.3%-2%, for example, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or 2.0%, or any value between 0.3%-2%. The porosities of the inner and outer layers are within the above ranges, and the porosity of the outer layer is lower, which can improve the stability of the positive electrode material.

[0016] In order to evaluate the characteristics of the porosity, the image analysis software (avizo) is used to directly obtain the pore area and cross-sectional area of each region, and the porosity of different regions is calculated according to (porosity = pore area of each region / cross-sectional area of each region x 100%).

[0017] Optionally, the inner layer of the secondary particle has a radius of 50-85% of the radius of the secondary particle, for example, it can be 50%, 51%, 52%, 53%, 55%, 56%, 58%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85%, or any value between 50-85%; the outer layer of the secondary particle has a thickness of 15-50% of the radius of the secondary particle, for example, it can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 43%, 45%, 46%, 48%, 49%, or 50%, or any value between 15-50%, wherein the radius of the inner layer plus the thickness of the outer layer is the radius of the secondary particle; the ratio of the radius of the inner layer and the thickness of the outer layer to the radius of the secondary particle is within the above range, which can further improve the stability of the positive electrode material.

[0018] Optionally, the positive electrode material has a general chemical formula of LiNi x Co y M 1-x-y O2, wherein M is selected from one or both of Al and Mn, 0.7≤x<1, 0<y<1, 0<x+y<1;

[0019] Optionally, in the X-ray diffraction pattern of the positive electrode material, the difference a between the peak positions corresponding to the 2θ diffraction angles of the Li layer (003) crystal face in the full charge state and the initial state satisfies: 0<a<0.65°, for example, a can be 0.05°, 0.1°, 0.15°, 0.2°, 0.25°, 0.3°, 0.35°, 0.4°, 0.45°, 0.5°, 0.55°, or 0.6°, or any value between greater than 0 and less than 0.65°. The peak position difference a within the range indicates that the hexagonal layered phase structure has good stability, and the positive electrode material has stronger resistance to side reaction phase change.

[0020] Optionally, the positive electrode material satisfies at least one of the following conditions A-C:

[0021] A. The D50 of the positive electrode material is 10-20 μm, for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, or any value between 10-20 μm;

[0022] B. the mechanical strength of the secondary particles is ≥ 90 MPa;

[0023] C. the sphericity of the secondary particles is 90%-100%, for example, can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%, or any value between 90%-100%. The sphericity of the secondary particles is better, which can effectively improve the filling property of the active material in the positive electrode, thereby improving the energy density of the corresponding battery.

[0024] The application also provides a preparation method of the positive electrode material as described above, comprising:

[0025] mixing and sintering raw materials including a metal N source and a lithium source, and obtaining the positive electrode material after cooling;

[0026] The sintering includes first sintering and second sintering. The temperature of the first sintering is 500-550°C, for example, can be 500°C, 510°C, 520°C, 530°C, 540°C or 550°C, or any value between 500-550°C. The time of the first sintering is 2-6h, for example, can be 2h, 3h, 4h, 5h or 6h, or any value between 2-6h. The temperature of the second sintering is 700-750°C, for example, can be 700°C, 710°C, 720°C, 730°C, 740°C or 750°C, or any value between 700-750°C. The time of the second sintering is 12-18h, for example, can be 12h, 13h, 14h, 15h, 16h, 17h or 18h, or any value between 12-18h. The heating rate during the sintering process is 2-5°C / min, for example, can be 2°C / min, 3°C / min, 4°C / min or 5°C / min, or any value between 2-5°C / min. The cooling rate during the cooling process is 2-5°C / min, for example, can be 2°C / min, 3°C / min, 4°C / min or 5°C / min, or any value between 2-5°C / min.

[0027] Optionally, the metal N source includes a co-precipitation precursor, and the co-precipitation precursor includes NCO3, N(OH)2 or NC2O4, wherein N is one or more of Ni, Co and Al.

[0028] Optionally, the preparation method satisfies at least one of the following (1)-(4):

[0029] (1) the metal N source includes a co-precipitation precursor, and the co-precipitation precursor includes NCO3, N(OH)2 or NC2O4, wherein N is one or more of Ni, Co and Al;

[0030] (2) the metal N source includes a dopant, and the dopant includes one or both of Al and Mn-containing compounds;

[0031] (3) The co-precipitation precursor comprises an inner layer and an outer layer covering the inner layer, the primary particles of the inner layer are arranged in a radial manner, and the primary particles of the outer layer are arranged in a manner different from the arrangement manner of the primary particles of the inner layer, for example, the primary particles of the outer layer can be arranged in a disordered manner or arranged in a direction perpendicular to the direction of the primary particles of the inner layer;

[0032] (4) The D50 of the co-precipitation precursor is 10-20 μm, for example, can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, or any value between 10-20 μm.

[0033] The application also provides a secondary battery comprising the positive electrode sheet.

[0034] The application also provides an electrical equipment comprising the secondary battery.

[0035] The positive electrode material provided by the application comprises secondary particles with a small-angle grain boundary ratio of 10%-30%. From the perspective of positive electrode material domain regulation, the application optimizes grain arrangement and grain boundary orientation, reduces stress and strain between grains and crack propagation caused by anisotropic volume change, solves the cracking problem of polycrystalline materials, improves the cycle performance of the corresponding battery, and thus makes the corresponding battery prepared from the positive electrode material have both high capacity and cycle stability.

[0036] The preparation method of the positive electrode material provided by the application controls the small-angle grain boundary ratio of the positive electrode material by controlling sintering temperature, sintering time and heating rate, so that the corresponding battery prepared from the positive electrode material has both high capacity and cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope of the application.

[0038] Figure 1 The cross-sectional SEM image of the precursor of Example 1 provided by the application;

[0039] Figure 2 The SEM image of the positive electrode material of Example 1 provided by the application;

[0040] Figure 3 The cross-sectional SEM image of the positive electrode material of Example 1 provided by the application;

[0041] Figure 4 The cross-sectional SEM image of the precursor of Example 2 provided by the application;

[0042] Figure 5 SEM image of the positive electrode material of Example 2 provided for the present application;

[0043] Figure 6 SEM image of the positive electrode material of Example 2 provided for the present application;

[0044] Figure 7 SEM image of the precursor of Example 5 provided for the present application;

[0045] Figure 8 EBSD backscattered electron diffraction pattern of the positive electrode material of Example 1 provided for the present application;

[0046] Figure 9 EBSD backscattered electron diffraction pattern of the positive electrode material of Example 2 provided for the present application;

[0047] Figure 10 EBSD backscattered electron diffraction pattern of the positive electrode material of Comparative Example 3 provided for the present application;

[0048] Figure 11 SEM image of the positive electrode material of Example 1 provided for the present application after 0.3 C cycling for 200 cycles;

[0049] Figure 12 SEM image of the positive electrode material of Example 2 provided for the present application after 0.3 C cycling for 200 cycles;

[0050] Figure 13 comsol finite element simulation result of the positive electrode material of Example 2 provided for the present application;

[0051] Figure 14 in-situ charge-discharge XRD test result of the positive electrode material of Example 1 provided for the present application;

[0052] Figure 15 in-situ charge-discharge XRD test result of the positive electrode material of Example 2 provided for the present application. DETAILED DESCRIPTION

[0053] As used herein the terms “about” and “substantially” are used to describe and account for small fluctuations, such as due to measurement or manufacturing tolerances, or other similar factors. For example, the term “about” or “substantially” can mean ± 5% or ± 10% of the value stated.

[0054] “Made by” is synonymous with “comprising”. The terms “comprising,” “including,” “having” or “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a step, a method, an article, or an apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0055] The conjunctive term "comprising," used in the context of describing the chemical components of the compositions of the present application, does not necessarily exclude other components. For example, a jointing employing the term can include other components in addition to or in place of those listed. The term encompasses a wide variety of embodiments and should be affixed the broadest interpretation so as to encompass all possible embodiments. The term "consisting of is to be construed as excluding any element not specified. The term "consisting of is to be construed as excluding any element not specified and further excluding any additional element. The term "consisting essentially of should be construed as excluding any elements not specified, but including additional elements that do not materially affect the basic and novel characteristics of the compositions or methods. Embodiments described herein can suitably comprise, consist of, or consist essentially of, for example, any of the composition or method features set forth herein.

[0056] When expressing a value or parameter, such as equivalent weight, concentration, or the like, as a range, preferably a range, or a series of upper preferred values and lower preferred values, it should be understood that all ranges formed by any pairings of an upper range limit or preferred value with a lower range limit or preferred value are expressly disclosed, whether or not the range is explicitly disclosed. For example, when a range "1-5" is disclosed, the described range should be interpreted to include ranges "1-4," "1-3," "1-2," "1-2 and 4-5," "1-3 and 5," and the like. When numerical ranges are described herein, unless otherwise stated, the range is intended to include the endpoints and all integers and fractions within that range.

[0057] In these examples, the parts and percentages are by mass unless otherwise indicated.

[0058] "and / or" is used to indicate one or both stated cases can occur, for example A and / or B includes (A and B) and (A or B).

[0059] The embodiments of the present application will be described in detail with specific examples, but those skilled in the art will understand that the following examples are for illustration only and should not be construed as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0060] Example 1

[0061] The precursor of Example 1 was prepared by co-precipitation of nickel sulfate, cobalt sulfate (Ni / Co molar ratio of 92 / 8) and sodium hydroxide, ammonia water, and the chemical formula was Ni 0.92 Co 0.08 (OH)2, the cross-sectional SEM image of which is as shown in Figure 1As shown, the primary particles are arranged radially. The precursor was dried in a vacuum oven at 110°C for 10 hours, and then the precursor, dopant (Al(OH)3), and lithium hydroxide were evenly mixed at a ratio of (Ni+Co+Al):Li of 1:1.05, and sintered in a tube furnace under an oxygen atmosphere. The sample was heated from 25°C to 550°C and maintained for 2 hours, and then further heated to 710°C and maintained for 12 hours. The heating rate was set to 2°C / min. Then, under a constant oxygen flow, the furnace was cooled to 25°C at a cooling rate of 1°C / min to obtain the positive electrode material sample powder of Example 1. As shown Figure 2 As shown, the positive electrode material is a spherical secondary particle with a D50 of 16.67 μm; its cross-sectional SEM image is shown in Figure 3 As shown, it can be seen that the primary particles of the positive electrode material of Example 1 are also arranged radially, and the overall porosity of the secondary particles is measured to be 3.86%.

[0062] Example 2

[0063] The precursor of Example 2 was prepared by coprecipitation of nickel sulfate, cobalt sulfate (Ni / Co molar ratio is 92 / 8) with sodium hydroxide and ammonia water, and the chemical formula is Ni 0.92 Co 0.08 (OH)2, its cross-sectional SEM image is as follows Figure 4 As shown, the primary particles in the inner layer are arranged radially, and the primary particles in the outer layer are arranged disorderly. The precursor was dried at 110°C in a vacuum oven for 10 hours, and then the precursor, dopant (Al(OH)3), and lithium hydroxide were evenly mixed at a ratio of (Ni+Co+Al):Li of 1:1.05, and sintered in an oxygen atmosphere in a tube furnace. The sample was heated from 25°C to 550°C and maintained for 2 hours, and then further heated to 710°C and maintained for 12 hours. The heating rate was set to 2°C / min. Then, under a constant flow of oxygen, the furnace was cooled to 25°C at a cooling rate of 1°C / min to obtain the positive electrode material sample powder of Example 2. Its SEM picture is as shown below. Figure 5 As shown, it is a spherical secondary particle with a measured D50 of 16.82 μm; its cross-sectional SEM image is shown in Figure 6 As shown, the inner primary particles of the cathode material of Example 2 are radially arranged, while the outer primary particles are disorderly arranged. The inner layer porosity is measured to be 4.07%, and the outer layer porosity is 0.67%. The radius of the inner layer accounts for 78.6% of the radius of the secondary particles, and the thickness of the outer layer accounts for 21.4% of the radius of the secondary particles.

[0064] Example 3

[0065] The precursor of Example 3 was prepared by coprecipitation of nickel sulfate, cobalt sulfate, aluminum sulfate (Ni / Co / Al molar ratio is 90 / 8 / 2) with sodium hydroxide and ammonia water, and the chemical formula is Ni 0.90Co 0.08 Al 0.02 (OH)2, the precursor was dried at 110 ° C in a vacuum oven for 10 hours, and then the precursor and lithium hydroxide were evenly mixed according to (Ni + Co + Al): Li at a ratio of 1:1.05, and sintered in an oxygen atmosphere in a tube furnace. The sample was heated from 25 ° C to 540 ° C and maintained for 3 hours, and then further heated to 710 ° C and maintained for 12 hours. The heating rate was set to 2 ° C / min. Then, under a constant oxygen flow, the furnace was cooled to 25 ° C at a cooling rate of 1 ° C / min to obtain the positive electrode material sample powder of Example 3, which was spherical secondary particles, and the D50 was measured to be 10.22 μm.

[0066] Example 4

[0067] The precursor of Example 4 was prepared by coprecipitation of nickel sulfate, cobalt sulfate, aluminum sulfate (Ni / Co / Al molar ratio of 85 / 13 / 2) with sodium hydroxide and ammonia water. The precursor was dried in a vacuum oven at 110°C for 10 hours, and then the precursor and lithium hydroxide were evenly mixed at a ratio of (Ni+Co+Al):Li of 1:1.05. The mixture was sintered in a tube furnace under an oxygen atmosphere. The sample was heated from 25°C to 550°C and maintained for 4 hours, and then further heated to 730°C and maintained for 12 hours. The heating rate was set to 2°C / min. Then, under a constant oxygen flow, the furnace was cooled to 25°C at a cooling rate of 2°C / min to obtain the positive electrode material sample powder of Example 4, which was spherical secondary particles with a measured D50 of 17.15μm.

[0068] Example 5

[0069] The precursor of Example 5 was prepared by coprecipitation of nickel sulfate, cobalt sulfate (Ni / Co molar ratio is 92 / 8) with sodium hydroxide and ammonia water, and the chemical formula is Ni 0.92 Co 0.08 (OH)2, its cross-sectional SEM image is as follows Figure 7 As shown, the primary particles are arranged in a disordered manner and have a porosity of 5.14%. The precursor was dried in a vacuum oven at 110°C for 10 hours, and then the precursor, dopant (Al(OH)3), and lithium hydroxide were evenly mixed at a ratio of (Ni+Co+Al):Li of 1:1.05. The mixture was sintered in a tube furnace under an oxygen atmosphere. The sample was heated from 25°C to 550°C and maintained for 4 hours, and then further heated to 720°C and maintained for 15 hours. The heating rate was set to 2°C / min. Then, under a constant oxygen flow, the furnace was cooled to 25°C at a cooling rate of 2°C / min to obtain the positive electrode material sample powder of Example 5, which was spherical secondary particles, and the measured D50 was 17.42μm.

[0070] Comparative Example 1

[0071] The precursor of Comparative Example 1 is the same as that of Example 1, and the dopant is Al(OH)3. The precursor is dried in a vacuum oven at 110°C for 10 hours, and then the precursor, the dopant, and lithium hydroxide are mixed uniformly at (Ni+Co+Al):Li = 1:1.05, and sintering is performed in a tube furnace under an oxygen atmosphere, the sample is heated from 25°C to 480°C and kept for 2 hours, and then further heated to 650°C and kept for 9 hours. The heating rate is set to 2°C / min. Then, the furnace is cooled to 25°C at a cooling rate of 1°C / min under a constant oxygen flow, to obtain a positive electrode material sample powder of Comparative Example 1, which is spherical secondary particles, and the D50 is measured to be 16.58 μm.

[0072] Comparative Example 2

[0073] The precursor of Comparative Example 2 is the same as that of Example 2, and the precursor is dried in a vacuum oven at 110°C for 10 hours, and then the precursor and lithium hydroxide are mixed uniformly at (Ni+Co+Al):Li = 1:1.05, and sintering is performed in a tube furnace under an oxygen atmosphere, the sample is heated from 25°C to 560°C and kept for 2 hours, and then further heated to 950°C and kept for 20 hours. The heating rate is set to 2°C / min. Then, the furnace is cooled to 25°C at a cooling rate of 1°C / min under a constant oxygen flow, to obtain a positive electrode material sample powder of Comparative Example 2, which is irregularly shaped non-spherical morphology.

[0074] Comparative Example 3

[0075] The precursor of Comparative Example 3 is prepared by coprecipitation of nickel sulfate, cobalt sulfate (Ni / Co molar ratio of 92 / 8), sodium hydroxide, and ammonia, and the chemical formula is Ni 0.92 Co 0.08 (OH)2, and the precursor is dried in a vacuum oven at 110°C for 10 hours, and then the precursor and lithium hydroxide are mixed uniformly at (Ni+Co):Li = 1:1.05, and sintering is performed in a tube furnace under an oxygen atmosphere, the sample is heated from 25°C to 550°C and kept for 2 hours, and then further heated to 710°C and kept for 12 hours. The heating rate is set to 2°C / min. Then, the furnace is cooled to 25°C at a cooling rate of 1°C / min under a constant oxygen flow, to obtain a positive electrode material sample powder of Comparative Example 3, which is spherical secondary particles, and the D50 is measured to be 15.97 μm.

[0076] EBSD backscattering electron diffraction technology is used to characterize the positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-3, and the phase difference between adjacent grains can be accurately identified by EBSD technology. Figure 8 EBSD backscattering electron diffraction pattern of the positive electrode material of Example 1, Figure 9EBSD backscattered electron diffraction pattern of the positive electrode material of Example 2, Figure 10 EBSD backscattered electron diffraction pattern of the positive electrode material of Comparative Example 3, in the characterization of grain boundaries and orientation differences, green grain boundaries are small-angle grain boundaries with a phase difference between adjacent grains of 2-15° identified, red grain boundaries are large-angle grain boundaries with a phase difference angle > 15° between adjacent grains identified, and the proportion of small-angle grain boundaries of the positive electrode materials of each example and comparative example is shown in Table 1.

[0077] The average particle size D50 of the positive electrode material can be conveniently measured by a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK, and the D50 of the positive electrode materials of each example and comparative example is shown in Table 1.

[0078] The sphericity of the positive electrode material is calculated by avizo software, and the sphericity of the positive electrode materials of each example and comparative example is shown in Table 1.

[0079] Table 1 Parameters of the positive electrode materials of each example and comparative example

[0080]

[0081] The positive electrode materials prepared from Examples 1 to 5 and Comparative Examples 1 to 3 were respectively prepared into half-cell batteries for testing electrochemical performance, the preparation method of the half-cell batteries was as follows: the positive electrode material, conductive agent (Super C) and binder (PVDF) were mixed in a mass ratio of 90:5:5, the corresponding mass of the mixture was weighed and uniformly mixed, then a slurry was prepared in a homogenizer, the solid content was controlled at 20-50%, and the slurry was uniformly coated on a 16 μm aluminum foil using a coating machine, the coating thickness was 0.25 mm, and after drying and rolling, a positive electrode sheet with a diameter of 14 mm was prepared. The negative electrode used metal lithium, and a CR2032 button cell was assembled using LiPF6 / EC / EMC electrolyte and PE separator. The button cell was tested at 0.1C charge-discharge at 2.7-4.3V, and the charge-discharge cycle was 200 cycles at 0.3C.

[0082] The electrochemical performance of the half-cell batteries prepared from the positive electrode materials of Examples 1 to 5 and Comparative Examples 1 to 3 is shown in Table 2.

[0083] Table 2 Electrochemical performance of the half-cell batteries of each example and comparative example

[0084]

[0085] As can be seen from Table 1 and Table 2, the small-angle grain boundary proportion of the positive electrode materials of Examples 1-5 is in the range of 10-30%, reducing the stress and strain between grains and crack propagation caused by anisotropic volume change, solving the problem of cracking of polycrystalline materials and improving the cycle performance, so that the half-batteries prepared from the positive electrode materials of Examples 1-5 have high discharge specific capacity performance and good cycle performance. The small-angle grain boundary proportion of the positive electrode materials of Comparative Examples 1 and 3 is less than 10%, and the cycle performance of the half-batteries prepared therefrom is poor. Moreover, the positive electrode material of Comparative Example 3 does not contain aluminum, and the cycle retention rate rapidly decreases to 71.4% at 100 cycles. The small-angle grain boundary proportion of the positive electrode material of Comparative Example 2 is greater than 30%, and the positive electrode material is non-spherical. Although the cycle retention rate is high, the capacity and rate performance are poor.

[0086] The positive electrode material of Example 2 has good sphericity, and the inner layer of primary particles is arranged in a radial manner and the outer layer of primary particles is arranged in a disordered manner, which not only shortens the lithium ion transmission channel, but also improves the mechanical stability of the material particles, thereby improving the rate performance, cycle stability and safety of the corresponding battery. As can be seen from the data in Table 2, the half-batteries prepared from the positive electrode material of Example 2 have high discharge specific capacity, cycle performance and rate performance. The primary particles of Example 1 are arranged in a radial manner as a whole, and the primary particles of Example 5 are arranged in a disordered manner as a whole, and the overall performance is lower than that of Example 2.

[0087] The SEM characterization results of the secondary particles of the positive electrode materials of Examples 1 and 2 after 0.3C cycle for 200 cycles are shown in Figure 11 and Figure 12 respectively. The positive electrode material of Example 2 has different arrangement manners of primary particles between the inner layer and the outer layer, and the primary particles arranged in a disordered manner in the outer layer hinder the expansion of internal stress of the secondary particles to the surface, so that the secondary particles still have good spherical particle morphology after 200 cycles, the ion channel in the particles is still complete, and the cycle performance is best.

[0088] Similarly, the electrochemical-mechanical model of the positive electrode particles of Example 2 is built by using the comsol finite element simulation software. The key parameters in the model are set according to the actual crystallography and electrochemical parameters of the nickel-cobalt-manganese positive electrode material, and the results are shown in Figure 13 respectively. The finite element calculation results show that, under the state of 100% SOC (state of charge), the stress of the positive electrode material of Example 2 is mainly concentrated on the junction between the inner layer and the outer layer. The disordered outer layer in the positive electrode material of Example 2 is beneficial to disrupting the strain extension direction of the grains arranged in a radial manner in the inner layer, and is conducive to preventing the internal stress from expanding to the surface of the particles, and is more conducive to inhibiting particle cracking and electrolyte penetration and corrosion.

[0089] The mechanical strength of 50 secondary particles of the positive electrode material of Example 1, Example 2 and Comparative Example 1 was tested respectively, and the results showed that the particle strength of the positive electrode material was 78.41 MPa, 98.77 MPa and 73.67 MPa respectively. The mechanical strength of the positive electrode material particles of Example 2 was higher than that of Example 1 and Comparative Example 1. The increase in particle strength was conducive to inhibiting the cracking of the positive electrode particles during the cycle process, reducing the side reaction with the electrolyte, improving the ability of the material to resist the phase change of the side reaction, and further helping to improve the cycle stability and safety of the battery.

[0090] The ability of the three positive electrode materials of Example 1, Example 2 and Comparative Example 1 to resist the phase change of the side reaction was tested by in-situ charge-discharge XRD test and data refinement. The voltage range of the test was 2.7-4.3V, including the charging process and the discharging process at 0.1C. The results of Example 1 and Example 2 are shown in Figure 14 and Figure 15 The refinement results of the Li layer (003) crystal plane showed that the peak positions corresponding to the 2θ diffraction angle of Example 1 in the initial state and the full charge state were 18.767° and 19.419° respectively, the peak positions corresponding to the 2θ diffraction angle of Example 2 in the initial state and the full charge state were 18.749° and 19.354° respectively, and the peak positions corresponding to the 2θ diffraction angle of Comparative Example 1 in the initial state and the full charge state were 18.728° and 19.427° respectively. The peak position difference a corresponding to the 2θ diffraction angle of Example 1, Example 2 and Comparative Example 1 in the full charge state and the initial state was 0.65°, 0.61° and 0.70° respectively. The smaller the peak position difference a, the better the stability of the hexagonal layered phase structure. This indicated that the small-angle crystallinity of the positive electrode material of Example 1-2 was in a suitable range, the structure stability of the positive electrode material was better, and the positive electrode material of Example 2 had better ability to resist the phase change of the side reaction due to the improvement of the mechanical strength of the positive electrode particles and the different arrangement of the inner and outer primary particles.

[0091] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit them. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features. These modifications or substitutions do not change the essence of the corresponding technical solutions, which are within the scope of the technical solutions of the embodiments of the present application.

[0092] Furthermore, to the extent that the terms "comprises", "comprising", "includes", "including" and "has" or any variation thereof are used in the following description and / or claims, such terms are intended to include a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, where appropriate to context, the above description and / or claims can refer to actions to be taken by a person or apparatus. Such actions are sometimes referred to as being taken "by the person" or "by the apparatus". Although some embodiments can be described in singular tense where specific language is used, the singular form can include plural forms unless the context clearly indicates otherwise. The terms "comprise", "comprising", "include", "including" and "has" or any variation thereof are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited only to those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, where appropriate to context, the above description and / or claims can refer to actions to be taken by a person or apparatus. Such actions are sometimes referred to as being taken "by the person" or "by the apparatus". Although some embodiments can be described in

Claims

1. A positive electrode material, characterized in that The positive electrode material includes secondary particles having a low-angle grain boundary ratio of 10% to 30%, and the secondary particles include a plurality of primary particles; Among them, the proportion of small-angle grain boundaries is the proportion of grain boundaries with a phase difference of 2-15° between adjacent grains in the secondary particles to all grain boundaries.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material includes secondary particles in which the low-angle grain boundaries account for 12% to 25%.

3. The positive electrode material according to claim 1, characterized in that The secondary particles include an inner layer and an outer layer covering the inner layer, and the positive electrode material satisfies at least one of the following conditions a to b: a. The arrangement of the primary particles in the outer layer is different from the arrangement of the primary particles in the inner layer; b. The inner layer porosity is 2-10%, and the outer layer porosity is 0.3%-2%.

4. The positive electrode material according to claim 1, characterized in that The chemical formula of the positive electrode material is LiNi x Co y M 1-x-y O2, wherein M is selected from one or both of Al and Mn, 0.7≤x<1, 0 <y<1,0<x+y<1。 5. The positive electrode material according to claim 4, characterized in that In the X-ray diffraction pattern of the positive electrode material, the difference a between the peak positions corresponding to the 2θ diffraction angles of the fully charged state and the initial state of the Li layer (003) crystal plane satisfies: 0<a<0.65°.

6. The positive electrode material according to any one of claims 1 to 5, characterized in that The positive electrode material satisfies at least one of the following conditions AC: A. The D50 of the positive electrode material is 10-20 μm; B. The mechanical strength of the secondary particles is ≥90 MPa; C. The sphericity of the secondary particles is 90%-100%.

7. A method for preparing a positive electrode material according to any one of claims 1 to 6, characterized in that: include: Mixing raw materials including a metal N source and a lithium source, sintering, and cooling to obtain the positive electrode material; The metal N source includes a co-precipitation precursor, and the co-precipitation precursor includes NCO3, N(OH)2 or NC2O4, wherein N is one or more of Ni, Co, and Al; The sintering includes a first sintering and a second sintering. The temperature of the first sintering is 500-550°C and the time is 2-6 hours; the temperature of the second sintering is 700-750°C and the time is 12-18 hours. The heating rate during the sintering process is 2-5°C / min, and the cooling rate during the cooling process is 2-5°C / min.

8. The method for preparing the positive electrode material according to claim 7, wherein: The preparation method satisfies at least one of the following conditions (1)-(3): (1) The metal N source includes a dopant, and the dopant includes one or two compounds containing Al and Mn; (2) The coprecipitated precursor includes an inner layer and an outer layer covering the inner layer, the primary particles of the inner layer are arranged radially, and the arrangement of the primary particles of the outer layer is different from the arrangement of the primary particles of the inner layer; (3) The D50 of the coprecipitated precursor is 10-20 μm.

9. A secondary battery, characterized in that: It comprises a positive electrode plate, wherein the positive electrode plate comprises the positive electrode material according to any one of claims 1 to 6.

10. An electrical equipment, characterized in that: The secondary battery according to claim 9 is included.

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