Positive electrode material and preparation method therefor, positive electrode sheet, lithium ion battery, and electric device

Abstract

A positive electrode material and a preparation method therefor, a positive electrode sheet, a lithium ion battery, and an electric device. The particles of the positive electrode material are of a core-shell structure, and the core-shell structure comprises a nickel-rich core and a lithium nickel cobalt manganese oxide shell covering the surface of the nickel-rich core. The content of nickel in the nickel-rich core is higher than the content of nickel in the lithium nickel cobalt manganese oxide shell. The content of cobalt and the content of manganese in the lithium nickel cobalt manganese oxide shell are respectively higher than the content of cobalt and the content of manganese in the nickel-rich core. The content of nickel in the core of the positive electrode material is high, so that the capacity can be improved; the content of manganese in the shell is high, so that the safety and stability of the positive electrode material can be improved; the content of cobalt in the shell is high, so that the initial coulombic efficiency and rate capability of the positive electrode material can be improved; and the manganese-rich cobalt-rich shell effectively improves the cycle performance of the positive electrode material, and reduces gas production and heat release.

Description

Positive electrode material and preparation method thereof, positive electrode sheet, lithium-ion battery and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application number 202410332260.2 filed with the State Intellectual Property Office of China on March 22, 2024, entitled “A positive electrode material and its preparation method, positive electrode sheet, lithium-ion battery and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the technical field of lithium-ion batteries, and in particular to a positive electrode material and a preparation method thereof, a positive electrode sheet, a lithium-ion battery and an electrical device. Background Art

[0004] Lithium-ion batteries are widely used in portable electronics, household appliances, electric vehicles, and energy storage due to their high energy density. However, high-nickel ternary cathode materials suffer from the problem of surface nickel transforming into a rock salt phase during charge and discharge, causing a rapid decline in cycling performance.

[0005] In addition, in the prior art, the Mn source and the Co source are mixed by a solid phase method. Since Mn diffuses slowly and the solid phase mixing is uneven, Co can often diffuse and coat into a shell well, while Mn segregates severely.

[0006] In view of this, the present invention is proposed.

[0007] Summary of the Invention

[0008] The first object of the present invention is to provide a positive electrode material having a high nickel content in the core, which can increase the capacity, and a high content of cobalt and manganese in the shell. The higher manganese content in the shell can improve the safety and stability of the positive electrode material, and the higher cobalt content in the shell can improve the first efficiency and rate performance of the positive electrode material. The manganese-rich and cobalt-rich shell effectively improves the cycle performance of the positive electrode material and reduces gas production and heat release. This solves the problem that it is impossible to produce a positive electrode material with a surface that is simultaneously cobalt-rich and manganese-rich in the prior art, and that the high-valent nickel on the surface of a high-nickel ternary positive electrode material is converted into a rock salt phase during charge and discharge, resulting in a rapid decrease in cycle performance.

[0009] The second object of the present invention is to provide a method for preparing a positive electrode material. Based on the difference in diffusion rates of Mn and Co elements under high-temperature calcination, the present invention first forms a surface manganese-rich material by first calcining a surface-rich Mn core-shell precursor, and then coats cobalt by a second calcination to form a ternary core-shell positive electrode material with a surface rich in manganese and cobalt. The gradient of manganese and cobalt elements is controllable and the process is simple. This not only solves the problem of being unable to produce a positive electrode material with both cobalt and manganese-rich surfaces, but also solves the problem of severe segregation caused by slow Mn diffusion.

[0010] A third object of the present invention is to provide a positive electrode sheet.

[0011] A fourth object of the present invention is to provide a lithium ion battery.

[0012] A fifth object of the present invention is to provide an electrical device.

[0013] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0014] The present invention first provides a positive electrode material, wherein the particles of the positive electrode material have a core-shell structure, wherein the core-shell structure comprises a nickel-rich core and a lithium nickel cobalt manganese oxide shell coated on the surface of the nickel-rich core;

[0015] The nickel content in the nickel-rich core is higher than the nickel content in the lithium nickel cobalt manganese oxide shell;

[0016] The cobalt content and the manganese content in the lithium nickel cobalt manganese oxide shell are respectively higher than the cobalt content and the manganese content in the nickel-rich core.

[0017] The present invention further provides a method for preparing the positive electrode material, comprising the following steps:

[0018] A core-shell precursor and a first lithium source are first mixed and first calcined to obtain a surface manganese-rich material; in the core-shell precursor, the nickel content of the core layer is higher than the nickel content of the shell layer, and the manganese content of the core layer is lower than the manganese content of the shell layer;

[0019] The surface manganese-rich material and the cobalt source are subjected to a second mixing and a second calcination to obtain the positive electrode material.

[0020] The present invention further provides a positive electrode sheet, comprising the positive electrode material, or the positive electrode material obtained by the method for preparing the positive electrode material.

[0021] The present invention also provides a lithium-ion battery comprising the positive electrode sheet.

[0022] The present invention further provides an electrical device comprising the lithium-ion battery.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The positive electrode material provided by the present invention has a nickel-rich core and a cobalt-rich and manganese-rich shell. The higher content of nickel in the core can improve the capacity, and the content of cobalt and manganese in the shell is relatively high. The higher content of manganese in the shell can improve the safety and stability of the positive electrode material. The higher content of cobalt in the shell can improve the first efficiency and rate performance of the positive electrode material. The manganese-rich and cobalt-rich shell effectively improves the cycle performance of the positive electrode material and reduces gas production and heat release.

[0025] (2) The preparation method of the positive electrode material provided by the present invention is based on the difference in diffusion rates of Mn and Co elements under high-temperature calcination. A surface manganese-rich material is first formed by the first calcination of a surface manganese-rich core-shell precursor, and then cobalt is coated by a second calcination to form a surface manganese-rich and cobalt-rich ternary core-shell positive electrode material. The gradients of manganese and cobalt elements are controllable and the process is simple.

[0026] (3) The present invention provides a method for preparing a positive electrode material, wherein the positive electrode material is a secondary particle, and the preparation method forms a positive electrode intermediate through a single calcination. The cobalt element of the secondary calcination has a faster diffusion rate, and can not only diffuse inward to form a core-shell structure in the outer layer of the secondary particle, but also penetrate into the interior of the secondary particle along the grain boundary, coating the primary particle, enhancing the interaction between the primary particles, and effectively inhibiting the cracking of the particles and the decomposition of the electrolyte at the positive electrode interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] FIG1 is a cross-sectional element distribution diagram of the positive electrode material of Example 1 provided by the present invention;

[0029] FIG2 is a cross-sectional element quantitative analysis diagram of the positive electrode material of Example 1 provided by the present invention;

[0030] FIG3 is a cross-sectional element distribution diagram of the positive electrode material of Comparative Example 1 provided by the present invention;

[0031] FIG4 is a cross-sectional element quantitative analysis diagram of the positive electrode material of Comparative Example 1 provided by the present invention;

[0032] FIG5 is the XRD data of the positive electrode material prepared in Example 1 provided by the present invention and its Rietveld refinement result;

[0033] FIG6 is a graph showing the cycle performance of lithium-ion batteries made from the positive electrode materials of Example 2, Comparative Example 1, and Comparative Example 3 provided by the present invention. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0035] Unless otherwise specified, in the present invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, terms such as "first," "second," "third," and "fourth" serve only as non-exhaustive enumeration and description, and should not constitute closed-ended limitations on quantity.

[0036] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0037] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or any two or more.

[0038] In a first aspect, the present invention provides a positive electrode material, wherein particles of the positive electrode material have a core-shell structure, wherein the core-shell structure includes a nickel-rich core and a lithium nickel cobalt manganese oxide shell coated on the surface of the nickel-rich core.

[0039] The nickel content in the nickel-rich core is higher than the nickel content in the lithium nickel cobalt manganese oxide shell.

[0040] The cobalt content and manganese content of the lithium nickel-cobalt-manganese oxide shell are respectively higher than the cobalt content and manganese content of the nickel-rich core. That is, the cobalt content of the lithium nickel-cobalt-manganese oxide shell is higher than the cobalt content of the nickel-rich core, and the manganese content of the lithium nickel-cobalt-manganese oxide shell is higher than the manganese content of the nickel-rich core.

[0041] The cathode material provided by the present invention has a nickel-rich core and a cobalt- and manganese-rich shell. A higher nickel content in the core can improve capacity, while the shell contains higher cobalt and manganese content. The higher manganese content in the shell can improve the safety and stability of the cathode material, while the higher cobalt content in the shell can improve the initial efficiency and rate performance of the cathode material. The manganese- and cobalt-rich shell effectively improves the cycle performance of the cathode material and reduces gas production and heat release. This invention solves the existing problem of simultaneously enriching the surface of the cathode material with manganese and cobalt.

[0042] In some specific embodiments, the nickel content in the positive electrode material decreases gradually from the center of the particle to the surface of the particle, wherein the gradient decrease means that the nickel content gradually decreases from the center of the particle to the surface of the particle.

[0043] In some specific embodiments, the cobalt content in the positive electrode material increases in a gradient from the center of the particle to the surface of the particle, wherein the gradient increase means that the cobalt content gradually increases from the center of the particle to the surface of the particle.

[0044] In some specific embodiments, the manganese content in the positive electrode material increases in a gradient from the center of the particle to the surface of the particle, wherein the gradient increase means that the manganese content gradually increases from the center of the particle to the surface of the particle.

[0045] Among them, the gradient changes of various elements, especially the gradient changes of Ni elements, can reduce the stress accumulation of the positive electrode material during the charging and discharging process, and reduce particle cracking and core-shell separation.

[0046] In some specific embodiments, in the positive electrode material, the difference between the mass fraction of nickel at the center of the particle and the mass fraction of nickel at the surface of the particle is ≥5%, including but not limited to any one of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 18%, and 20%, or a range of values ​​therebetween. This configuration enables the positive electrode material to have a high nickel content inside to increase high capacity and a low nickel content outside to reduce surface side reactions, thereby improving the safety performance and cycle life of the positive electrode material.

[0047] In some specific embodiments, in the positive electrode material, the difference between the mass fraction of cobalt at the particle surface and the mass fraction of cobalt at the particle center is ≥ 2%, including but not limited to any one of 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, and 8%, or any range therebetween. The Co element can improve the conductivity of the positive electrode material, and a surface rich in Co is particularly beneficial for improving the electrochemical performance of the positive electrode material.

[0048] In some specific embodiments, in the positive electrode material, the difference between the mass fraction of manganese at the particle surface and the mass fraction of manganese at the particle center is ≥ 3%, including but not limited to any one of 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 8.5%, 9%, and 10%, or any range therebetween. Mn can improve the stability of the positive electrode material, and surface Mn enrichment is particularly beneficial for improving the safety and cycling performance of the positive electrode material.

[0049] In some specific embodiments, the diameter of the nickel-rich core is 4 to 16 μm, including but not limited to any point value of 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, or a range value between any two of them.

[0050] In some specific embodiments, the thickness of the lithium nickel cobalt manganese oxide shell is 0.1 to 2 μm, including but not limited to any one of 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, and 2 μm, or a range between any two of them.

[0051] The positive electrode material provided by the present invention has a large core diameter and a high core mass ratio, which can ensure that the overall Ni content is sufficiently high and maintain the capacity advantage of the high-nickel positive electrode.

[0052] In some specific embodiments, the average chemical formula of the nickel-rich core is LiNi x Co y Mn 1-x-y O2, wherein 0.5<x<1, 0<y<0.5, x+y<1. Wherein, x includes but is not limited to any one of 0.51, 0.53, 0.55, 0.58, 0.6, 0.7, 0.8, 0.9, 0.95, 0.98, or any range between two of them; y includes but is not limited to any one of 0.001, 0.01, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.45, 0.49, or any range between two of them.

[0053] The average chemical formula of the lithium nickel cobalt manganese oxide shell is LiNi a Co b Mn 1-a-b O2, where 0<a<x, 1>b>y, 1-ab>1-xy.

[0054] In some specific embodiments, the microstrain of the positive electrode material is ≥0.05%, including but not limited to any point value of 0.05%, 0.052%, 0.055%, 0.058%, 0.06%, 0.063%, 0.065%, 0.068%, 0.7%, or any range value between any two of them.

[0055] The positive electrode material provided by the present invention has higher microscopic strain, indicating that the positive electrode material has a core-shell structure.

[0056] In some specific embodiments, the first discharge specific capacity of the lithium-ion battery containing the positive electrode material is ≥228 mAh / g; including but not limited to any one of 228 mAh / g, 229 mAh / g, 230 mAh / g, 231 mAh / g, 232 mAh / g, 233 mAh / g, and 235 mAh / g, or a range between any two of the values.

[0057] In some specific embodiments, the first coulombic efficiency of the lithium-ion battery containing the positive electrode material is ≥90%, including but not limited to any point value of 90%, 91%, 92%, 93%, 94%, 95%, 96%, or any range value between two of them.

[0058] In some specific embodiments, the capacity retention rate of a lithium-ion battery containing the positive electrode material after 100 cycles is ≥91.5%, including but not limited to any one of 91.5%, 91.9%, 92%, 92.5%, 92.8%, 93%, 93.6%, 94%, 95%, and 96%, or a range between any two of the values.

[0059] In a second aspect, the present invention provides a method for preparing the above-mentioned positive electrode material, comprising the following steps:

[0060] The core-shell precursor and the first lithium source are sequentially subjected to a first mixing and a first calcination, and after cooling, a surface manganese-rich material is obtained.

[0061] Wherein, in the core-shell precursor, the nickel content of the core layer is higher than that of the shell layer, and the manganese content of the core layer is lower than that of the shell layer.

[0062] In some specific embodiments, in the core-shell precursor, the cobalt content of the core layer is no greater than the cobalt content of the shell layer. Specifically, the core layer and the shell layer may both contain no cobalt, in which case the cobalt content of the core layer and the shell layer is equal, namely, 0. When both the core layer and the shell layer contain cobalt, the cobalt content of the core layer is lower than that of the shell layer.

[0063] The surface manganese-rich material and the cobalt source are sequentially mixed and calcined for a second time, and then cooled to obtain the positive electrode material.

[0064] This invention leverages the differences in the diffusion rates of Co and Mn elements. A Mn gradient is formed in the core-shell precursor and retained during the first calcination, while a Co gradient is formed during the second calcination. This effectively maintains the Mn-Co gradient, fully leveraging the advantages of the core-shell structure of the cathode material. This not only addresses the difficulty of producing cathode materials with simultaneously cobalt- and manganese-rich surfaces, but also solves the problem of severe segregation caused by slow Mn diffusion.

[0065] The positive electrode material prepared by this method has the advantages of high capacity, high first efficiency (i.e., first coulomb efficiency), and good cycle performance when made into a lithium-ion battery.

[0066] In some specific embodiments, the average chemical formula of the core layer of the core-shell precursor is Ni p Co q Mn 1-p-q (OH)2, wherein 0.5<p<1, 0≤q<0.5, and p+q<1. Wherein, p includes but is not limited to any one of 0.51, 0.53, 0.55, 0.58, 0.6, 0.7, 0.8, 0.9, 0.95, and 0.98, or any range between two of them; q includes but is not limited to any one of 0, 0.001, 0.01, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.45, and 0.49, or any range between two of them.

[0067] The average chemical formula of the shell layer of the core-shell precursor is Ni w Co s Mn 1-w-s (OH)2, where 0<w<p, 1>s≥q, 1-ws>1-pq.

[0068] The present invention utilizes a precursor with a surface rich in manganese, which is retained during the first calcination, forming an intermediate material with a surface rich in manganese. A gradient of cobalt can be formed during the second calcination, effectively maintaining the gradient concentrations of manganese and cobalt.

[0069] In some specific embodiments, the diameter of the core layer of the core-shell precursor is 4 to 16 μm, including but not limited to any point value of 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, and 16 μm, or a range value between any two of them.

[0070] The thickness of the shell layer of the core-shell precursor is 0.1-2 μm, including but not limited to any one of 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, and 2 μm, or a range between any two of them.

[0071] In some specific embodiments, the volume median particle size D of the core-shell precursor is 50 4 to 18 μm, including but not limited to any one of 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 16 μm, and 18 μm, or a range between any two of the values.

[0072] Using the above D 50 The core-shell precursor with a small particle size can achieve both high rate performance and high compaction density.

[0073] In some specific embodiments, the specific surface area of ​​the core-shell precursor is 4 to 20 m 2 / g, including but not limited to 4m 2 / g、5m 2 / g、8m 2 / g、10m 2 / g、13m 2 / g、15m 2 / g、18m 2 / g, 20m 2 / g, or any range of values ​​between them.

[0074] The specific surface area of ​​the core-shell precursor is within the above range, which is conducive to controlling the morphology of the precursor and thus ensuring the effective synthesis of the positive electrode material.

[0075] In some specific embodiments, the tap density of the core-shell precursor is 1.9 to 2.1 g / cm 3 ; Including but not limited to 1.9g / cm 3 , 1.95 / cm 3 , 2.0 / cm 3 , 2.05 / cm 3 , 2.1g / cm 3 Any point value in or any range of values ​​between them.

[0076] The tap density of the core-shell precursor is within the above range, which can increase the compaction density of the positive electrode material prepared therefrom, and further increase the volume energy density of the lithium battery obtained after assembly.

[0077] In some specific embodiments, the core-shell precursor exhibits a radial distribution, which helps reduce strain and enhance lithium-ion transport performance. Radial distribution refers to the radial arrangement of primary particles from the center of the sphere toward the surface. This optimizes the lithium-ion transport pathway and significantly enhances its dynamic performance. Furthermore, the radial distribution effectively dissipates stress, effectively mitigating particle cracking caused by volume changes in high-nickel or ultra-high-nickel materials, and effectively improving cycling performance.

[0078] In some specific embodiments, the molar ratio of the core-shell precursor to the lithium element in the first lithium source is 1:(1-1.07); including but not limited to any one of 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07 or a range between any two of them.

[0079] In some specific embodiments, the first calcination comprises a two-stage calcination.

[0080] Compared to a single-stage calcination, a two-stage calcination provides a lower temperature holding platform, which facilitates the thorough mixing and diffusion of the lithium salt in the precursor, improving reaction uniformity. Directly increasing the temperature to the high temperature stage, i.e., using a traditional single-stage calcination, can result in localized lithium enrichment or depletion.

[0081] The temperature of the first calcination in the two-stage calcination is 300-600°C, including but not limited to any one of 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, and 600°C, or a range between any two of them; the holding time of the first calcination is ≥2h, including but not limited to any one of 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 12h, 15h, 20h, and 24h, or a range between any two of them, and is preferably held for 3-9h.

[0082] In some specific embodiments, the heating rate of the first calcination in the two-stage calcination is 1 to 6°C / min, including but not limited to any one of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, and 6°C / min, or a range between any two of them.

[0083] The temperature of the second calcination in the two-stage calcination is 650-850°C, including but not limited to any one of 650°C, 700°C, 750°C, 800°C, and 850°C, or a range between any two of them; the holding time of the second calcination is ≥4h, including but not limited to any one of 4h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 24h, and 30h, or a range between any two of them, preferably 4-20h.

[0084] In some specific embodiments, the heating rate of the second calcination in the two-stage calcination is 1 to 6°C / min, including but not limited to any one of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, and 6°C / min, or a range between any two of them.

[0085] In some specific embodiments, a second lithium source is further added during the second mixing process, and the molar ratio of the surface manganese-rich material, the cobalt element in the cobalt source, and the lithium element in the second lithium source is 1: (0.002-0.06): (0.0001-0.12);

[0086] The purpose of adding the second lithium source in the second mixing process is to replenish lithium, thereby avoiding the deterioration of electrochemical performance due to a low Li:NCM ratio.

[0087] In some specific embodiments, the temperature of the second calcination is 500-800°C, including but not limited to any one of 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, and 800°C, or a range between any two thereof; the holding time of the second calcination is ≥2h, including but not limited to any one of 2h, 3h, 5h, 8h, 10h, 12h, 15h, 16h, 18h, 20h, and 24h, or a range between any two thereof, preferably for 2-16h.

[0088] The second calcination using the above temperature range is beneficial to controlling element diffusion, thereby ensuring that the core and shell have a sufficient concentration difference.

[0089] In some specific embodiments, the heating rate of the second calcination is 1 to 6°C / min, including but not limited to any one of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, and 6°C / min, or a range between any two of them.

[0090] In some specific embodiments, the first calcination and the second calcination are carried out in an oxygen atmosphere. Preferably, the oxygen intake rate is 100 to 400 L / min, including but not limited to any one of 100 L / min, 200 L / min, 300 L / min, and 400 L / min, or a range between any two of them.

[0091] In some specific embodiments, the cobalt source includes a compound containing cobalt, including but not limited to one or more of cobalt oxides, hydroxides, oxyhydroxides, nitrates, and acetates.

[0092] In some specific embodiments, the first lithium source and / or the second lithium source includes any lithium-containing compound commonly used in the art, such as one or more of LiOH, Li2CO3, Li2SO4, LiCl and LiNO3, but is not limited thereto.

[0093] In a third aspect, the present invention provides a positive electrode sheet comprising the above-mentioned positive electrode material, or the positive electrode material obtained by the above-mentioned method for preparing the positive electrode material.

[0094] The lithium-ion battery made from the positive electrode sheet has the advantages of high capacity, high first coulombic efficiency and good cycle performance.

[0095] In some specific embodiments, the positive electrode sheet includes a current collector and a positive electrode active layer disposed on the current collector.

[0096] In some specific embodiments, the current collector includes but is not limited to aluminum foil.

[0097] In some specific embodiments, the positive electrode active layer includes, in addition to the above-mentioned positive electrode material, at least one of a binder and a conductive agent.

[0098] The binder includes any bonding material commonly used in the art, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber and water-based glue, but is not limited thereto.

[0099] The conductive agent includes any conductive material commonly used in the art, such as at least one of conductive graphite, acetylene black, carbon nanotubes, nanopowder, and graphene, but is not limited thereto.

[0100] In some specific embodiments, the conductive carbon black includes at least one of conductive carbon black SP (super p), acetylene black (AB) and Ketjen black (KB), but is not limited thereto.

[0101] In a fourth aspect, the present invention provides a lithium-ion battery comprising the above-mentioned positive electrode sheet.

[0102] This lithium-ion battery has excellent electrochemical performance, not only high capacity, but also high initial efficiency and excellent cycle performance.

[0103] In some specific embodiments, the lithium-ion battery includes, in addition to the above-mentioned positive electrode sheet, at least one of a negative electrode sheet, a separator, and an electrolyte.

[0104] The negative electrode sheet, separator and electrolyte may be any commercially available negative electrode sheet, separator and electrolyte, or any negative electrode sheet, separator and electrolyte prepared according to any prior art, and the present invention does not limit this.

[0105] In a fifth aspect, the present invention provides an electrical device comprising the above-mentioned lithium-ion battery.

[0106] The electrical equipment includes any device, equipment or system containing the above-mentioned lithium-ion battery.

[0107] Electrical equipment containing the above-mentioned lithium-ion batteries can be widely used in various fields, such as transportation, electronic products, aerospace, medical and energy storage, but not limited thereto.

[0108] As examples, the electrical equipment mentioned above include electric vehicles, electric motorcycles, electric bicycles, power tools, starting power supplies, energy storage systems, electronic products, household appliances, and office equipment, but are not limited thereto.

[0109] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0110] Example 1

[0111] The method for preparing the positive electrode material provided in this embodiment includes the following steps:

[0112] (1) A spherical core-shell precursor (purchased from Huayou Cobalt) with an overall molar ratio of Ni element: Mn element = 94.7:5.3 was obtained, and its average chemical formula is Ni 0.947 Mn 0.053 (OH)2, its volume median particle size D 50 The surface area is 10 μm and the specific surface area is 12.5 m 2 / g, and the tap density is 1.95g / cm 3 The core diameter is 9.6 μm and the average chemical formula of the core is Ni 0.986 Mn 0.014 (OH)2, the shell thickness is 0.2μm, and the average chemical formula of the shell is Ni 0.65 Mn 0.35 (OH)2.

[0113] According to LiOH: the above core-shell precursor Ni 0.947 Mn 0.053 The ingredients were prepared in a molar ratio of (OH)2=1.03:1, and mixed evenly in a high-speed mixer at a rotation speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then mixing was continued for 20 minutes to obtain a mixture.

[0114] (2) The mixture obtained in step (1) was calcined at 600°C for 2 hours (i.e., the first calcination step), then taken out and stirred and mixed uniformly in a high-speed mixer at a speed of 900 r / min. After stirring for 20 minutes, it was calcined at 770°C for 12 hours (i.e., the second calcination step) to obtain a calcined product. During the above calcination process, the heating rate was 2.5°C / min, the atmosphere was oxygen, and the oxygen inlet rate was 200 L / min.

[0115] The calcined product was crushed and sieved to obtain a product with a surface rich in manganese and an average chemical formula of LiNi 0.947 Mn 0.053 Intermediate material of O2.

[0116] (3) The intermediate material obtained in step (2) was mixed with Co(OH)2 and LiOH in a molar ratio of 1:0.05:0.05, and mixed evenly in a high-speed mixer at a speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then continued to mix for 20 minutes to obtain a mixed material. The mixed material was roasted at 720°C for 8 hours (i.e., the second roasting), wherein the heating rate was 2.5°C / min, the atmosphere was oxygen, and the oxygen intake rate was 200L / min. After cooling, the obtained roasted product was crushed and sieved to obtain an average chemical formula of LiNi 0.90 Co 0.05 Mn 0.05 O2 positive electrode material.

[0117] The particles of the positive electrode material prepared in this embodiment have a core-shell structure, which includes a nickel-rich core and a lithium nickel cobalt manganese oxide shell coated on the surface of the nickel-rich core. The nickel content in the positive electrode material decreases gradually from the center of the particle to the surface of the particle; the cobalt content in the positive electrode material increases gradually from the center of the particle to the surface of the particle; and the manganese content in the positive electrode material increases gradually from the center of the particle to the surface of the particle. The diameter of the nickel-rich core is 9.2 μm, and the thickness of the lithium nickel cobalt manganese oxide shell is 0.3 μm. The average chemical formula of the nickel-rich core is LiNi 0.926 Co 0.040 Mn 0.034 O2, the average chemical formula of the lithium nickel cobalt manganese oxide shell is LiNi 0.811 Co 0.084 Mn 0.105 O2.

[0118] The element distribution analysis of the cross section of the positive electrode material was performed by electron probe microanalysis (EPMA). The results are shown in FIG1 . It can be seen that Mn and Co are enriched on the particle surface.

[0119] The cross-section of the above-mentioned cathode material was subjected to elemental quantitative analysis by energy dispersive spectrometer (EDS). The results are shown in FIG2 . It can be seen that the Mn and Co elements are distributed in a gradient from the center of the particle to the surface of the particle, with the concentration being high outside and low inside.

[0120] Example 2

[0121] The method for preparing the positive electrode material provided in this embodiment includes the following steps:

[0122] (1) A spherical core-shell precursor (purchased from Huayou Cobalt) with an overall molar ratio of Ni:Co:Mn = 91.4:3.55:5.05 was obtained, and its average chemical formula is Ni 0.914 Co 0.0355 Mn 0.0505 (OH)2, its volume median particle size D 50 The surface area is 10 μm and the specific surface area is 11.3 m 2 / g, and the tap density is 2.01g / cm 3 The core diameter is 9.5 μm and the average chemical formula of the core is Ni 0.9484 Co 0.0355 Mn 0.0161 (OH)2, the shell thickness is 0.25μm, and the average chemical formula of the shell is Ni 0.653 Co 0.0325 Mn 0.3145 (OH)2.

[0123] According to LiOH: the above core-shell precursor Ni 0.914 Co 0.0355 Mn 0.0505 The ingredients were prepared in a molar ratio of (OH)2=1.02:1, and mixed evenly in a high-speed mixer at a rotation speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then mixing was continued for 20 minutes to obtain a mixture.

[0124] (2) The mixture obtained in step (1) was calcined at 550°C for 3 hours (i.e., the first calcination step), then taken out and stirred and mixed uniformly in a high-speed mixer at a speed of 900 r / min. After stirring for 20 minutes, it was calcined at 760°C for 12 hours (i.e., the second calcination step) to obtain a calcined product. During the above calcination process, the heating rate was 2.5°C / min, the atmosphere was oxygen, and the oxygen inlet rate was 200 L / min.

[0125] The calcined product was crushed and sieved to obtain a product with a surface rich in manganese and an average chemical formula of LiNi 0.914 Co 0.0355 Mn 0.0505 Intermediate material of O2.

[0126] (3) The intermediate material obtained in step (2) was mixed with CoO(OH) and LiOH in a molar ratio of 1:0.015:0.01 and mixed evenly in a high-speed mixer at a speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off and the mixture was mixed for 20 minutes to obtain a mixed material. The mixed material was calcined at 700°C for 5 hours (i.e., the second calcination) at a heating rate of 2.5°C / min, in an oxygen atmosphere, and at an oxygen inlet rate of 200 L / min. After cooling, the calcined product was crushed and sieved to obtain a product with an average chemical formula of LiNi 0.90 Co 0.05 Mn 0.05 O2 positive electrode material.

[0127] The particles of the positive electrode material prepared in this embodiment have a core-shell structure, which includes a nickel-rich core and a lithium nickel cobalt manganese oxide shell coated on the surface of the nickel-rich core. The nickel content in the positive electrode material decreases gradually from the center of the particle to the surface of the particle; the cobalt content in the positive electrode material increases gradually from the center of the particle to the surface of the particle; and the manganese content in the positive electrode material increases gradually from the center of the particle to the surface of the particle. The diameter of the nickel-rich core is 9.3 μm, and the thickness of the lithium nickel cobalt manganese oxide shell is 0.35 μm. The average chemical formula of the nickel-rich core is LiNi 0.912 Co 0.046 Mn 0.042 O2, the average chemical formula of the lithium nickel cobalt manganese oxide shell is LiNi 0.826 Co 0.076 Mn 0.098 O.

[0128] Example 3

[0129] The method for preparing the positive electrode material provided in this embodiment comprises the following steps:

[0130] (1) A spherical core-shell precursor (purchased from Huayou Cobalt) with an overall molar ratio of Ni:Co:Mn = 90.9:4.04:5.06 was obtained, and its average chemical formula is Ni 0.909 Co 0.0404 Mn 0.0506 (OH)2, its volume median particle size D 50 The surface area is 11 μm and the specific surface area is 10.9 m 2 / g, and the tap density is 1.97g / cm 3 , the core diameter is 9.8μm, and the average chemical formula of the core is Ni 0.9451 Co 0.0538 Mn 0.0011 (OH)2, the shell thickness is 0.6μm, and the average chemical formula of the shell is Ni 0.8 Mn0.2 (OH)2.

[0131] According to LiOH: the above core-shell precursor Ni 0.909 Co 0.0404 Mn 0.0506 The ingredients were prepared in a molar ratio of (OH)2=1.04:1, and mixed evenly in a high-speed mixer at a rotation speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then mixing was continued for 20 minutes to obtain a mixture.

[0132] (2) The mixture obtained in step (1) was calcined at 600°C for 2 hours (i.e., the first calcination step), then taken out and stirred and mixed uniformly in a high-speed mixer at a speed of 900 r / min. After stirring for 20 minutes, it was calcined at 755°C for 14 hours (i.e., the second calcination step) to obtain a calcined product. During the above calcination process, the heating rate was 2.5°C / min, the atmosphere was oxygen, and the oxygen inlet rate was 200 L / min.

[0133] The calcined product was crushed and sieved to obtain a product with a surface rich in manganese and an average chemical formula of LiNi 0.909 Co 0.0404 Mn 0.0506 Intermediate material of O2.

[0134] (3) The intermediate material obtained in step (2) was mixed with Co(OH)2 in a molar ratio of 1:0.01 and mixed evenly in a high-speed mixer at a speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off and then continued to mix for 20 minutes to obtain a mixed material. The mixed material was roasted at 650°C for 6 hours (i.e., the second roasting) at a heating rate of 2.5°C / min, in an oxygen atmosphere, and at an oxygen inlet rate of 200 L / min. After cooling, the obtained roasted product was crushed and sieved to obtain a product with an average chemical formula of LiNi 0.90 Co 0.05 Mn 0.05 O2 positive electrode material.

[0135] The particles of the positive electrode material prepared in this embodiment have a core-shell structure, which includes a nickel-rich core and a lithium nickel cobalt manganese oxide shell coated on the surface of the nickel-rich core. The nickel content in the positive electrode material decreases gradually from the center of the particle to the surface of the particle; the cobalt content in the positive electrode material increases gradually from the center of the particle to the surface of the particle; and the manganese content in the positive electrode material increases gradually from the center of the particle to the surface of the particle. The diameter of the nickel-rich core is 9.6 μm, and the thickness of the lithium nickel cobalt manganese oxide shell is 0.6 μm. The average chemical formula of the nickel-rich core is LiNi 0.92 Co 0.044 Mn 0.036O2, the average chemical formula of the lithium nickel cobalt manganese oxide shell is LiNi 0.851 Co 0.065 Mn 0.084 O2.

[0136] Example 4

[0137] The preparation method of the positive electrode material provided in this embodiment is basically the same as that in Example 3, except that in step (3), the molar ratio of the intermediate material obtained in step (2) to Co(OH)2 is replaced with 1:0.03.

[0138] Example 5

[0139] The preparation method of the positive electrode material provided in this embodiment is basically the same as that in Example 3, except that, in step (2), the temperature and time of the first calcination step are replaced by calcination at 400°C for 6 hours, and the temperature and time of the second calcination step are replaced by calcination at 680°C for 16 hours.

[0140] Example 6

[0141] The preparation method of the positive electrode material provided in this embodiment is basically the same as that in Example 3, except that in step (3), the temperature and time of the second calcination are replaced by calcination at 550° C. for 8 h.

[0142] Comparative Example 1

[0143] The preparation method of the positive electrode material with uniform distribution of Ni, Co and Mn provided in this comparative example comprises the following steps:

[0144] (1) Obtaining a spherical precursor Ni with a molar ratio of Ni element: Co element: Mn element = 90:5:5 0.90 Co 0.05 Mn 0.05 (OH)2, its volume median particle size D 50 The surface area is 10 μm and the specific surface area is 9.7 m 2 / g, and the tap density is 2.06g / cm 3 .

[0145] According to LiOH: precursor Ni 0.90 Co 0.05 Mn 0.05 The ingredients were prepared in a molar ratio of (OH)2=1.02:1, and mixed evenly in a high-speed mixer at a rotation speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then mixing was continued for 20 minutes to obtain a mixture.

[0146] (2) The mixture obtained in step (1) was calcined at 600°C for 2h, then taken out and stirred and mixed uniformly in a high-speed mixer at a speed of 900r / min. After stirring for 20min, it was calcined at 770°C for 12h to obtain a calcined product. The heating rate during the above calcination process was 2.5°C / min, the atmosphere was oxygen, and the oxygen inlet rate was 200L / min. The calcined product was crushed and sieved to obtain the positive electrode material LiNi 0.90 Mn 0.05 Co 0.05 O2.

[0147] The element distribution analysis of the cross section of the positive electrode material was performed by electron probe microanalysis (EPMA). The results are shown in FIG3 . It can be seen that the Ni, Co, and Mn elements are uniformly distributed.

[0148] The cross section of the positive electrode material was subjected to elemental quantitative analysis by energy dispersive spectroscopy (EDS). The results are shown in FIG4 . It can be seen that the Ni, Co, and Mn elements are evenly distributed.

[0149] Comparative Example 2

[0150] The method for preparing the positive electrode material provided in this comparative example comprises the following steps:

[0151] (1) Obtain a spherical precursor (purchased from Huayou Cobalt) with an overall molar ratio of Ni:Co:Mn = 90:5:5, and its average chemical formula is Ni 0.90 Co 0.05 Mn 0.05 (OH)2, its volume median particle size D 50 The surface area is 10 μm and the specific surface area is 10.7 m 2 / g, and the tap density is 2.01g / cm 3 , the core diameter is 9μm, and the average chemical formula of the core is Ni 0.974 Co 0.013 Mn 0.013 (OH)2, the shell thickness is 0.5μm, and the average chemical formula of the shell is Ni 0.70 Co 0.15 Mn 0.15 (OH)2.

[0152] According to LiOH: the above core-shell precursor Ni 0.90 Co 0.05 Mn 0.05 The ingredients were prepared in a molar ratio of (OH)2=1.02:1, and mixed evenly in a high-speed mixer at a rotation speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then mixing was continued for 20 minutes to obtain a mixture.

[0153] (2) The mixture obtained in step (1) was calcined at 600°C for 2 hours, then taken out and stirred in a high-speed mixer at a speed of 900 r / min to mix uniformly. After stirring for 20 minutes, it was calcined at 770°C for 12 hours to obtain a calcined product. During the above calcination process, the heating rate was 2.5°C / min, the atmosphere was oxygen, and the oxygen inlet rate was 200 L / min.

[0154] The calcined product was crushed and sieved to obtain the positive electrode material LiNi 0.90 Co 0.05 Mn 0.05 O2.

[0155] Comparative Example 3

[0156] The preparation method of the positive electrode material provided in this comparative example comprises the following steps:

[0157] (1) Obtaining a spherical precursor Ni with a molar ratio of Ni element: Co element: Mn element = 93.8:3.1:3.1 0.938 Co 0.031 Mn 0.031 (OH)2, its volume median particle size D 50 The surface area is 10 μm and the specific surface area is 10.3 m 2 / g, and the tap density is 1.98g / cm 3 .

[0158] According to LiOH: precursor Ni 0.938 Co 0.031 Mn 0.031 The ingredients were prepared in a molar ratio of (OH)2=1.02:1, and mixed evenly in a high-speed mixer at a rotation speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then mixing was continued for 20 minutes to obtain a mixture.

[0159] (2) The mixture obtained in step (1) was calcined at 550°C for 4 hours, then taken out and stirred in a high-speed mixer at a speed of 900 r / min to mix uniformly. After stirring for 20 minutes, it was calcined at 740°C for 12 hours to obtain a calcined product. During the above calcination process, the heating rate was 2.5°C / min, the atmosphere was oxygen, and the oxygen inlet rate was 200 L / min.

[0160] The calcined product was crushed and sieved to obtain the intermediate material LiNi 0.938 Co 0.031 Mn 0.031 O2.

[0161] (3) The intermediate material obtained in step (2) was mixed with Mn(OH)2, CoO(OH) and LiOH in a molar ratio of 1:0.02:0.02:0.04, and mixed evenly in a high-speed mixer at a speed of 900 r / min. After mixing for 20 minutes, the material hanging on the inner wall of the high-speed mixer was scraped off, and then continued to mix for 20 minutes to obtain a mixed material. The mixed material was calcined at 720°C for 6 hours, wherein the heating rate was 2.5°C / min, the atmosphere was oxygen, and the oxygen intake rate was 200 L / min. After cooling, the calcined product was crushed and sieved to obtain an average chemical formula of LiNi 0.90 Mn 0.05 Co 0.05 O2 positive electrode material.

[0162] Comparative Example 4

[0163] The preparation method of the positive electrode material provided in this comparative example is basically the same as that of Example 3, except that in step (1), the spherical core-shell precursor is replaced by a spherical precursor Ni with a molar ratio of Ni element: Co element: Mn element = 93.8:3.1:3.1. 0.938 Co 0.031 Mn 0.031 (OH)2 (in which nickel, cobalt and manganese elements are evenly distributed), its volume median particle size D 50 The surface area is 11 μm and the specific surface area is 11.8 m 2 / g, and the tap density is 1.92g / cm 3 .

[0164] Comparative Example 5

[0165] The preparation method of the positive electrode material provided in this comparative example is basically the same as that of Example 3, except that the calcination in step (2) is: calcining the mixture obtained in step (1) at 755°C for 16 hours to obtain a calcined product (i.e., not calcined in steps).

[0166] XRD analysis was performed on the cathode materials prepared in each Example and Comparative Example, and microstrain data were obtained. The results are shown in Table 1. Specifically, the obtained XRD data were further analyzed using the William-Hall equation in the refinement software Topas to determine the microstrain of the cathode materials. The XRD data and Rietveld refinement results for the cathode material prepared in Example 1 are shown in Figure 5 . It can be seen that this cathode material has a hexagonal layered structure and good crystallinity.

[0167] Button-type lithium-ion batteries were made using the positive electrode materials prepared in each embodiment and each comparative example, and the electrochemical performance of each lithium-ion battery was tested (first-week charge specific capacity, first-week discharge specific capacity, first-week coulombic efficiency, and capacity retention rate after 100 cycles). The results are shown in Table 1.

[0168] The preparation method of lithium-ion battery includes: mixing the above-mentioned positive electrode material with acetylene black and polyvinylidene fluoride in a mass ratio of 90:6:4, adding an appropriate amount of N-methylpyrrolidone as a dispersant, and grinding into a slurry; then evenly coating the slurry on aluminum foil, vacuum drying at 120°C for 10 hours, rolling the dried electrode sheet with a roller machine, and then cutting the electrode sheet with a slicer into a circular electrode sheet with a diameter of 1.3 cm. The loading amount of the positive electrode material on the circular electrode sheet is controlled at 15 mg / cm 2 Half-cells were assembled in an argon atmosphere glove box with a water partial pressure ≤ 0.1 ppm and an oxygen partial pressure ≤ 0.1 ppm. Metallic lithium was used as the counter electrode, and a 1 M LiPF6 (FEC / EC / DMC, 1:1:1 by volume) solution was used as the electrolyte. The assembled battery was a CR2032 button-type lithium-ion secondary battery.

[0169] The electrochemical performance test method is: using constant current charge and discharge mode, the capacity test is 0.1C charge and 0.1C discharge, 2.5~4.3V, vs.Li + / Li; Cycle test: 0.5C charge and 0.5C discharge at 45℃, 2.7~4.25V vs.Li + / Li, the number of cycles is 100.

[0170] Table 1 Electrochemical performance test results

[0171] The cycle data of lithium-ion batteries prepared using the positive electrode materials of Example 2, Comparative Example 1 and Comparative Example 3 are shown in FIG6 .

[0172] From the data in Table 1 we can see that:

[0173] Compared with Comparative Example 1, Examples 1 to 3 have higher microscopic strain, indicating that the core-shell structure of the positive electrode material particles prepared in each Example is retained.

[0174] Comparing Examples 1 to 3 with Comparative Example 2, it can be seen that the positive electrode materials obtained by controlling the Mn / Co gradient through secondary sintering (i.e., Examples 1 to 3) have higher microscopic strain than the positive electrode materials obtained by single sintering of conventional core-shell precursors (i.e., Comparative Example 2), indicating that the core-shell gradient is better retained.

[0175] Compared with Comparative Examples 1 to 3, Examples 1 to 3 have better discharge specific capacity and cycle stability in electrochemical tests. This is because the difference in nickel, cobalt and manganese concentrations in the core-shell improves the stability of the positive electrode material, and the surface Co-rich structure improves the material's kinetic performance.

[0176] Compared with Comparative Example 1, Example 2 has a core-shell structure, while Comparative Example 1 has a homogeneous structure. Example 2 has better capacity and significantly improved cycle performance.

[0177] Compared with Comparative Example 2, Example 2 and Comparative Example 2 both have core-shell structures, but the core-shell gradient of Example 2 is better retained, which effectively stabilizes the surface of the particles and improves the cycle performance of the positive electrode material.

[0178] Compared with Example 3, the solid phase coating method used in Example 3 will lead to Mn segregation, and its capacity and cycle rate will decrease year-on-year.

[0179] Compared with Example 3 and Comparative Example 4, Comparative Example 4 uses a precursor with a homogeneous structure in which nickel, cobalt and manganese elements are evenly distributed, and the capacity and cycle performance are reduced.

[0180] Compared with Example 3 and Comparative Example 5, the first calcination of Comparative Example 5 was performed in only one step, resulting in reduced capacity and cycle performance.

[0181] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A positive electrode material, characterized in that The particles of the positive electrode material have a core-shell structure, wherein the core-shell structure comprises a nickel-rich core and a lithium nickel cobalt manganese oxide shell coated on the surface of the nickel-rich core; The nickel content in the nickel-rich core is higher than the nickel content in the lithium nickel cobalt manganese oxide shell; The cobalt content and the manganese content in the lithium nickel cobalt manganese oxide shell are respectively higher than the cobalt content and the manganese content in the nickel-rich core.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material satisfies at least one of the following conditions: (1) The nickel content in the positive electrode material decreases gradually from the center of the particle to the surface of the particle; (2) The cobalt content in the positive electrode material increases gradually from the center of the particle to the surface of the particle; (3) The manganese content in the positive electrode material increases gradually from the center of the particle to the surface of the particle; (4) In the positive electrode material, the difference between the mass fraction of nickel element at the center of the particle and the mass fraction of nickel element at the surface of the particle is ≥5%; (5) In the positive electrode material, the difference between the mass fraction of cobalt element at the particle surface and the mass fraction of cobalt element at the particle center is ≥ 2%; (6) In the positive electrode material, the difference between the mass fraction of manganese element at the particle surface and the mass fraction of manganese element at the particle center is ≥3%.

3. The positive electrode material according to claim 1, characterized in that The positive electrode material satisfies at least one of the following conditions: (1) The diameter of the nickel-rich core is 4 to 16 μm; (2) The thickness of the lithium nickel cobalt manganese oxide shell is 0.1 to 2 μm.

4. The positive electrode material according to claim 1, characterized in that The average chemical formula of the nickel-rich core is LiNi x Co y Mn 1-x-y O2, where 0.5<x<1, 0<y<0.5, x+y<1; The average chemical formula of the lithium nickel cobalt manganese oxide shell is LiNi a Co b Mn 1-a-b O2, where 0<a<x, 1>b>y, 1-ab>1-xy.

5. The positive electrode material according to claim 1, characterized in that The positive electrode material satisfies at least one of the following conditions: (1) The microstrain of the positive electrode material is ≥0.05%; (2) The initial discharge capacity of the lithium-ion battery containing the positive electrode material is ≥228 mAh / g; (3) The initial coulombic efficiency of the lithium-ion battery containing the positive electrode material is ≥90.0%; (4) The capacity retention rate of a lithium-ion battery containing the positive electrode material after 100 cycles is ≥91.5%.

6. The method for preparing the positive electrode material according to any one of claims 1 to 5, wherein: The steps include: A core-shell precursor and a first lithium source are first mixed and first calcined to obtain a surface manganese-rich material; in the core-shell precursor, the nickel content of the core layer is higher than the nickel content of the shell layer, and the manganese content of the core layer is lower than the manganese content of the shell layer; The surface manganese-rich material and the cobalt source are subjected to a second mixing and a second calcination to obtain the positive electrode material.

7. The method for preparing the positive electrode material according to claim 6, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The average chemical formula of the core layer of the core-shell precursor is Ni p Co q Mn 1-p-q (OH)2, wherein 0.5<p<1, 0≤q<0.5, p+q<1; the average chemical formula of the shell of the core-shell precursor is Ni w Co s Mn 1-w-s (OH)2, where 0<w<p, s≥q, 1-ws>1-pq; (2) The core layer of the core-shell precursor has a diameter of 4 to 16 μm and a thickness of 0.1 to 2 μm; (3) The volume median particle size of the core-shell precursor is 4 to 18 μm, and the specific surface area is 4 to 20 m 2 / g, tap density is 1.9~2.1g / cm 3 ; (4) The molar ratio of the core-shell precursor to the lithium element in the first lithium source is 1:(1-1.07); (5) The first calcination includes two-stage calcination; the temperature of the first calcination in the two-stage calcination is 300-600°C, and the temperature is kept at 300-600°C. The temperature of the second step of the two-stage calcination is 650-850 ° C, and the holding time is ≥ 4h; (6) A second lithium source is further added during the second mixing process, and the molar ratio of the surface manganese-rich material, the cobalt element in the cobalt source, and the lithium element in the second lithium source is 1: (0.002-0.06): (0.0001-0.12); (7) The temperature of the second roasting is 500-800°C, and the holding time is ≥2h.

8. A positive electrode sheet, characterized in that: The positive electrode material comprises the positive electrode material according to any one of claims 1 to 5, or the positive electrode material obtained by the preparation method of the positive electrode material according to any one of claims 6 to 7.

9. A lithium-ion battery, characterized in that: Including the positive electrode sheet as claimed in claim 8.

10. An electrical device, characterized in that: Comprising the lithium-ion battery as claimed in claim 9.

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