Carbon-coated positive electrode material and preparation method thereof, and lithium-ion battery

Abstract

The present invention relates to the technical field of lithium-ion batteries, and more particularly to a carbon-coated positive electrode material, a preparation method thereof, and a lithium-ion battery. The carbon-coated positive electrode material comprises: a core and a carbon layer, wherein the core is a high-nickel positive electrode material and the carbon layer contains a carbon material; wherein the carbon layer is physically adsorbed on the surface of the core, and the roughness Δ of the core is 0.1-0.45, wherein the roughness Δ is defined as Formula 1, where V b is the specific surface area BET of the core, m 2 / g;W a is the bulk density of the core, g / cm 3 While maintaining the original structure of the high-nickel positive electrode material, the carbon-coated positive electrode material avoids direct contact between the positive electrode material and the electrolyte through carbon coating, reduces the oxidation of the electrolyte by the positive electrode material during charging, and improves the rate performance and cycle performance of the carbon-coated positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a carbon-coated positive electrode material, a method for preparing the carbon-coated positive electrode material, and a lithium-ion battery containing the carbon-coated positive electrode material. Background Art

[0002] Lithium-ion batteries are green secondary batteries with outstanding advantages, including high voltage, high energy density, excellent cycle performance, low self-discharge, and no memory effect. Since their successful development in the 1990s, they have seen rapid adoption and development. In recent years, lithium-ion batteries have found an increasingly broad range of applications, including energy storage systems such as power, hydropower, thermal, wind, and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0003] The cost of positive electrode materials accounts for about 40% of the total cost of lithium-ion batteries, and their performance also plays a decisive role in lithium-ion batteries. Positive electrode materials are generally prepared by mixing precursors, lithium sources, and additives and then sintering them once. After crushing, screening, and iron removal, the primary sintered material is prepared. However, the positive electrode materials prepared by this process have problems such as poor cycle life, poor storage performance, and low capacity. For this reason, the industry tends to coat the primary sintered materials with ionic compounds and then conduct a secondary sintering. By treating the surface of the particles, the material interface stability is improved, thereby producing materials with better performance. With the rapid development of the new energy industry, conventional nickel-containing multi-element positive electrode materials can no longer meet the further requirements of consumers. High-nickel or ultra-high nickel positive electrode materials have become the mainstream of the market due to their high capacity performance and low cost advantages. The use of coating methods to optimize high-nickel or ultra-high nickel multi-element positive electrode materials is also a current research hotspot.

[0004] Carbon materials have excellent properties such as corrosion resistance, acid and alkali resistance, and good electrical conductivity. Carbon coating can improve the material's rate performance, cycle performance, energy density and chemical stability. For example, lithium iron phosphate is originally an insulator, but after being coated with a layer of conductive carbon, it becomes an excellent positive electrode material. Therefore, carbon coating is a common means of improving the performance of positive electrode materials. However, carbon is reducing and carbon coating can only be achieved under an inert atmosphere, because the traditional carbon coating method is to coat the carbon on the surface of the positive electrode material through low-temperature heat treatment after the positive electrode material is formed. This method will cause the positive electrode material to be partially reduced during the formation of the carbon layer, thereby destroying the original structure of the high-nickel positive electrode material. This has little effect on lithium cobalt oxide, lithium iron phosphate and low-nickel materials, but for high-nickel and ultra-high nickel positive electrode materials, due to their high material activity, if they are not coated under an inert atmosphere, residual alkali conversion will easily form on their surface, increasing the Li2CO3 content, which affects the material capacity. In addition, there is also a method of directly forming a positive electrode material with a carbon-carbon layer by using a high-temperature solid-phase synthesis method for the precursor of the positive electrode material, a lithium source, and a carbon material as a coating agent. However, the solid-phase synthesis of high-nickel and ultra-high nickel positive electrode materials is generally carried out under a high oxygen partial pressure atmosphere, and carbon materials are easily gasified under high temperature and high oxygen partial pressure conditions.

[0005] CN111092202A discloses a high nickel ternary cathode material and its preparation method. The base material is lithium nickel cobalt manganese oxide. The surface of lithium nickel cobalt manganese oxide has two coating layers, which are LiNi from the inside to the outside. x Co y M 1-x-y The preparation method for PO4 and a carbon layer includes: reacting a precursor with a phosphoric acid solution to produce a phosphate-coated high-nickel ternary cathode material; and then preparing a carbon layer from the phosphate-coated high-nickel ternary cathode material through the catalytic action of transition metal ions and olefins. The resulting cathode material exhibits improved rate performance and cycle performance. However, the process is relatively complex, making industrial mass production difficult.

[0006] CN108390022A discloses a carbon-metal oxide composite-coated lithium battery ternary cathode material, comprising a ternary cathode material matrix and a composite coating comprising a carbon-metal oxide compound. By leveraging the respective advantages of the carbon coating and the metal oxide, the material's electronic conductivity and ion diffusion coefficient are effectively improved. Furthermore, the material's structure is stabilized, effectively preventing electrolyte erosion of the cathode material and improving its electronic conductivity, rate capability, and cycle performance. However, the preparation process requires sintering at 300-800°C in an inert atmosphere, which is not conducive to the preparation of high-nickel carbon-coated materials.

[0007] CN108199013A discloses a carbon-coated ternary material and a preparation method thereof, which combines a positive electrode material with a carbon material by multiple ball milling to form a carbon-coated ternary material. However, the method uses multiple ball milling to perform carbon coating, resulting in weak coating strength and small improvement in electrical performance. In addition, the preparation of the carbon-coated material by multiple ball milling is complex, resulting in low preparation efficiency.

[0008] In summary, on the basis of maintaining the original performance of the material, it is an urgent problem to prepare high-nickel and ultra-high-nickel carbon-coated positive electrode materials through a simple, feasible and efficient carbon coating process. Summary of the Invention

[0009] The purpose of the present invention is to overcome the above-mentioned technical problems and provide a new carbon-coated positive electrode material and its preparation method, and a lithium-ion battery. The carbon-coated positive electrode material, while maintaining the original structure of the high-nickel positive electrode material, avoids direct contact between the positive electrode material and the electrolyte through carbon coating, reduces the oxidation of the electrolyte by the positive electrode material in the charging state, and improves the rate performance and cycle performance of the carbon-coated positive electrode material.

[0010] In order to achieve the above object, the first aspect of the present invention provides a carbon-coated positive electrode material, the carbon-coated positive electrode material comprising: a core and a carbon layer, the core being a high-nickel positive electrode material, the carbon layer containing a carbon material;

[0011] The carbon layer is physically adsorbed on the surface of the core, and the roughness Δ of the core is 0.1-0.45, wherein the roughness Δ is defined as Formula I, In Formula I, V b is the specific surface area BET of the core, m 2 / g;W a is the bulk density of the core, g / cm 3 .

[0012] In the present invention, roughness Δ is a self-defined dimensionless parameter; when making comparisons, only numerical comparisons are performed.

[0013] Preferably, the coating layer retention rate δ of the carbon-coated positive electrode material is ≥99%, wherein δ=C0 / C1;

[0014] Among them, C0 is the carbon content of the carbon-coated positive electrode material, wt%; C1 is the carbon content of the upper layer of the carbon-coated positive electrode material after vibration treatment, wt%; the testing method for C1 is to take 200g of the carbon-coated positive electrode material for vibration treatment, the amplitude of the vibration treatment is 3mm, the frequency is 250 times / min, and the time is 60min; then weigh 1g of the upper layer material on the surface of the carbon-coated positive electrode material after vibration treatment, and measure the carbon content of the upper layer material, wt%.

[0015] Preferably, the carbon-coated positive electrode material is prepared by solid-phase dry coating.

[0016] Preferably, the high nickel cathode material has a composition shown in Formula II,

[0017] Among them, Li n Ni 1-x-y-a-b Co x M y E a G b O2(II),

[0018] Wherein, in formula II, 0.9≤n≤1.5, 0≤x<1, 0≤y<1, 0≤a≤0.1, 0≤b≤0.1, 0<x+y+a+b<1, M is Mn and / or Al, E is selected from at least one of P, N, B, Ti, Zr, Y, Al, and Mg; and G is a surface coating layer selected from oxides, sulfides, and fluorides containing at least one of B, Al, and transition elements.

[0019] Preferably, the carbon-coated positive electrode material satisfies: 1.1≤Z≤2.5, preferably satisfies: 1.16≤Z≤2.3; wherein, Among them, PD c , AD c and TD c Respectively represent the compacted density, bulk density and tap density of the carbon-coated positive electrode material, all in g / cm 3 ;PD x , AD x and TD x Respectively represent the compacted density, bulk density and tap density of the core, all in g / cm 3 .

[0020] Preferably, the carbon-coated positive electrode material also satisfies Formula III:

[0021] A second aspect of the present invention provides a method for preparing a carbon-coated positive electrode material, the preparation method comprising:

[0022] In a non-oxidizing atmosphere, the mixed material is subjected to a solid-phase dry coating method, and the filling rate of the processing chamber of the equipment is controlled to be 30-65%. The obtained carbon-coated positive electrode material includes a core and a carbon layer;

[0023] Wherein, the mixed material includes a carbon material and a high nickel positive electrode material as the core;

[0024] The solid-phase dry coating process includes a first mixing coating, a second mixing coating and a third mixing coating; the rotation speed of the first mixing coating is less than the rotation speed of the second mixing coating and less than the rotation speed of the third mixing coating, and the time of the first mixing coating is less than the time of the second mixing coating and less than the time of the third mixing coating.

[0025] Preferably, the high nickel cathode material has a composition shown in Formula II, Li n Ni 1-x-y-a-b Co x M y E a G b O2(II), wherein 0.9≤n≤1.5, 0≤x<1, 0≤y<1, 0≤a≤0.1, 0≤b≤0.1, 0<x+y+a+b<1, M is selected from Mn and / or Al, E is selected from at least one of P, N, B, Ti, Zr, Y, Al, and Mg; and G is a surface coating layer selected from oxides, sulfides, and fluorides containing at least one of B, Al, and transition elements.

[0026] A third aspect of the present invention provides a lithium-ion battery, comprising: the carbon-coated positive electrode material provided in the first aspect, or the carbon-coated positive electrode material prepared by the preparation method provided in the third aspect.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) The carbon-coated positive electrode material provided by the present invention includes a high-nickel positive electrode material as a core and a carbon layer, wherein the carbon layer is combined with the surface layer of the high-nickel positive electrode material by physical adsorption, and the roughness Δ of the core is 0.1-0.45, thereby making the carbon layer and the core tightly combined, effectively maintaining the original electrical equilibrium state of the core material, so that the carbon-coated positive electrode material has good electronic conductivity, avoids direct contact between the high-nickel positive electrode material and the electrolyte, reduces the dissolution of transition metal ions, reduces the side reaction between the positive electrode material and the electrolyte in the charging state, reduces the corrosion of the positive electrode by hydrofluoric acid and the like generated by the decomposition of lithium salts in the electrolyte, improves the electrode conductivity, and thus improves the capacity and rate performance of the carbon-coated positive electrode material;

[0029] (2) The carbon-coated positive electrode material provided by the present invention is introduced in the form of surface coating before battery production, and is especially combined with a high-nickel positive electrode material with a specific roughness. Through the coating strength gradient design, the carbon material is dispersed more evenly on the surface of the core, so that the Z value of the carbon-coated positive electrode material is in the optimal range, thereby improving the comprehensive performance of the positive electrode material; at the same time, the addition of carbon material in the subsequent battery production process is reduced, thereby improving the battery production efficiency;

[0030] (3) The carbon-coated positive electrode material provided by the present invention is coated by a solid-phase dry coating method, and in particular, a specific solid-phase dry coating method is used to achieve high-strength coating of the carbon material and the core, so that the carbon material and the core are tightly combined to form a carbon-coated positive electrode material; at the same time, this method avoids the heat treatment process under a low oxygen partial pressure atmosphere, prevents the core from being partially reduced, and avoids the resulting damage to the electrochemical performance;

[0031] (4) The preparation method provided by the present invention is a solid-phase dry coating process, does not involve wet processing, and has less environmental pollution; at the same time, the preparation method simplifies the process flow, is simple and easy to operate, has high efficiency, and is suitable for large-scale industrial application;

[0032] (5) The carbon-coated positive electrode material provided by the present invention is used in lithium-ion batteries. Since the surface is coated with a chemically stable carbon layer, it has high corrosion resistance to the electrolyte, avoids direct contact between the positive electrode material and the electrolyte, slows down the oxidation of the electrolyte by the positive electrode material in the charging state, and ensures good cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a SEM image of the agglomerated carbon-coated positive electrode material S1 prepared in Example 1;

[0034] Figure 2 is a SEM image of the single-crystal carbon-coated positive electrode material S5 prepared in Example 5;

[0035] Figure 3 is a SEM image of the agglomerated carbon-coated positive electrode material DS3 prepared in Comparative Example 3;

[0036] Figure 4 1C / 1C cycle curves of button batteries respectively assembled from the agglomerated carbon-coated positive electrode materials of Examples 1-3 and Comparative Example 1 at 45°C and 3-4.3V;

[0037] Figure 5 1C / 1C cycle curves of button cells assembled from the single-crystal carbon-coated positive electrode materials of Example 5 and Comparative Example 2 at 45°C and 3-4.3V are shown. DETAILED DESCRIPTION

[0038] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0039] In the present invention, unless otherwise specified, the terms "first," "second," and "third" do not indicate a sequential order or limit the materials or steps involved. They are used only to indicate that they are not the same materials or steps. For example, in "first mixed coating," "second mixed coating," and "third mixed coating," the terms "first," "second," and "third" are used only to indicate that they are not the same mixed coating.

[0040] A first aspect of the present invention provides a carbon-coated positive electrode material, the carbon-coated positive electrode material comprising: a core and a carbon layer, the core being a high-nickel positive electrode material, the carbon layer comprising a carbon material;

[0041] The carbon layer is physically adsorbed on the surface of the core, and the roughness Δ of the core is 0.1-0.45, wherein the roughness Δ is defined as Formula I, In Formula I, V b is the specific surface area BET of the core, m 2 / g;W a is the bulk density of the core, g / cm 3 .

[0042] The inventors of the present invention have found that: since the carbon material has ultra-high conductivity, when the carbon material and the high-nickel positive electrode material are physically adsorbed and the roughness Δ of the coating layer retention core defined by the present invention is 0.1-0.45, it can not only avoid the heat treatment process under a low oxygen partial pressure atmosphere, prevent the positive electrode material from being partially reduced, and avoid the resulting damage to the electrochemical performance, but also make the carbon material distributed in the pores and surface of the core (high-nickel positive electrode material), so that the carbon material and the core material are tightly combined, and the carbon layer is prevented from falling off during actual application; at the same time, the original electrical equilibrium state of the core material can be effectively changed by carbon coating, so that the carbon-coated positive electrode material has good electronic conductivity, and the carbon layer can avoid direct contact between the positive electrode material and the electrolyte, reduce the dissolution of transition metal ions, slow down the oxidation of the electrolyte by the positive electrode material in the charging state, reduce the corrosion of the positive electrode by hydrofluoric acid and the like generated by the decomposition of lithium salts in the electrolyte, improve the electrode conductivity, and thereby improve the capacity and rate performance of the carbon-coated positive electrode material.

[0043] In the present invention, preferably, the coating layer retention rate δ of the carbon-coated positive electrode material is ≥99%, for example, 99%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, and any value in the range composed of any two numerical values, wherein δ = C0 / C1; C0 is the carbon content of the carbon-coated positive electrode material, wt%; C1 is the carbon content of the upper layer material of the carbon-coated positive electrode material after vibration treatment, wt%; the testing method for C1 is to take 200g of the carbon-coated positive electrode material for vibration treatment, the amplitude of the vibration treatment is 3mm, the frequency is 250 times / min, and the time is 60min; then 1g of the upper layer material is weighed on the surface of the carbon-coated positive electrode material after vibration treatment, and the carbon content of the upper layer material is measured, wt%; further preferably, the coating layer retention rate δ of the carbon-coated positive electrode material is 99.5-99.9%.

[0044] In the present invention, there is physical adsorption between the core and the carbon layer of the carbon-coated positive electrode material. The carbon layer will not form a reduction reaction on the high-nickel positive electrode material during the coating process, thereby avoiding damage to the electrochemical properties of the core. The carbon layer is tightly combined with the core. After vibration treatment, the measured coating layer retention rate δ of the carbon-coated positive electrode material is ≥99%, indicating that the physical adsorption strength between the carbon layer and the core is high, and the obtained carbon-coated positive electrode material is not easy to fall off.

[0045] In the present invention, the measurement principle of the coating layer retention rate δ is as follows: after the carbon-coated positive electrode material undergoes a certain vibration treatment, if the carbon layer is not tightly bonded to the core, a certain amount of carbon layer will be produced. Since the density of the carbon layer is less than the density of the carbon-coated positive electrode material and the core, it will be covered on the surface after the vibration treatment. The present invention respectively detects the carbon content C0 of the carbon-coated positive electrode material that has not been vibration treated and the carbon content C1 of the upper layer material of a fixed mass after the vibration treatment, and obtains the coating layer retention rate δ of the carbon-coated positive electrode material from C0 / C1. It can be understood that if the carbon layer is not tightly bonded to the core, the carbon content of the upper layer material will increase after the vibration treatment, and the value of δ will be small (<99%); if the carbon layer is more tightly bonded to the core, the carbon content of the upper layer material before and after the vibration treatment will be equivalent, and the value of δ will be closer to 1.

[0046] In the present invention, the upper layer material is sampled from the surface of the material after vibration treatment, and the sampling amount of the upper layer material is limited to 0.5wt% of the carbon-coated positive electrode material. It can be understood that the mass proportion of the upper layer material in the carbon-coated positive electrode material is not greater than the mass proportion of the carbon layer in the carbon-coated positive electrode material. In this way, a more accurate value can be obtained, avoiding the situation where the value of C1 is close to C0 when too much upper layer material is sampled, and the difference between the two is less than the measurement error and has no test meaning.

[0047] In a specific embodiment of the present invention, exemplary testing steps for the coating layer retention rate δ include:

[0048] (1) A certain amount of carbon-coated positive electrode material is taken and the carbon content is tested using a high-frequency infrared carbon-sulfur analyzer to obtain the carbon content (wt%) of the oversize material. The testing principle of the high-frequency infrared carbon-sulfur analyzer is to convert the carbon layer on the surface of the inner core into carbon dioxide by high-frequency induction heating of the sample. When infrared light of a specific wavelength passes through the carbon dioxide gas, it can produce strong light absorption. After detection, integration, and normalization, the analysis result of the carbon content of the sample to be tested can be obtained.

[0049] (2) placing the carbon-coated positive electrode material into a device, and then placing it on a powder tap density meter for vibration, with an amplitude of 3 mm and a frequency of 250 times / minute. After vibrating for 60 minutes, 1 g of the upper layer material is weighed from the surface of the carbon-coated positive electrode material after vibration treatment, and the carbon content (%) of the upper layer material is measured to obtain C1;

[0050] (3) According to δ=C0 / C1, the value of δ is calculated, which is the coating layer retention rate.

[0051] In the present invention, there is no limitation on the sampling method of the upper layer material, but it is necessary to ensure that the upper layer material is taken from a specified amount of material from top to bottom in the apparatus after the vibration treatment;

[0052] For example, scraping can be used to sequentially obtain the required amount of upper layer material layer by layer. For example, if the material after vibration treatment includes three layers, namely the first layer, the second layer and the third layer from top to bottom, the upper layer material should be obtained first from the first layer. If the required amount is insufficient, the material is scraped from the surface of the second layer until a sufficient amount of upper layer material is obtained. It is not possible to directly extend from the first layer along the depth direction of the material to the second layer or even the third layer to obtain the required amount of upper layer material.

[0053] Alternatively, an apparatus with an openable and closable discharge port at the bottom may be used. For example, the apparatus may include a cylinder with a thread at one end and a base threadedly connected to the thread of the cylinder. When the material needs to be taken, the apparatus is suspended above the weighing device, the base is unscrewed, and the weight of the material on the weighing device is controlled to obtain the required amount of upper material. When this method is used, taking 200g of material as an example, the discharge rate is preferably controlled below 1g / s. It is understandable that, if conditions permit, the larger the aspect ratio of the cylinder, the better, so as to control the flow rate and obtain a more accurate amount of residual material, i.e., the upper material. Of course, it is also possible to set a scale on the cylinder to estimate the volume occupied by the required amount of upper material in the apparatus and discharge an appropriate amount of material, thereby continuously fine-tuning the required upper material. Alternatively, a negative pressure device can be connected to the top of the measuring cylinder to adjust the negative pressure to suck out a specified amount of upper material, etc. In this application, only exemplary sampling methods are given, and the specific sampling steps or forms are not limited, as long as the sampling amount of the upper material can be achieved.

[0054] In some embodiments of the present invention, the carbon-coated cathode material is preferably produced by solid-phase dry coating. Solid-phase dry coating achieves physical adsorption between the carbon layer and the core. Compared to existing technologies, this avoids the heat treatment process under a low oxygen partial pressure atmosphere, prevents partial reduction of the cathode material, and avoids the resulting degradation of electrochemical performance.

[0055] In some embodiments of the present invention, preferably, the high nickel cathode material has a composition shown in Formula II, wherein Li n Ni 1-x-y-a-b Co x M y E a G b O2(II),

[0056] Wherein, 0.9≤n≤1.5, 0≤x<1, 0≤y<1, 0≤a≤0.1, 0≤b≤0.1, 0<x+y+a+b<1, M is selected from Mn and / or Al, E is selected from at least one of P, N, B, Ti, Zr, Y, Al, and Mg; G is a surface coating layer selected from oxides, sulfides, and fluorides containing at least one of B, Al, and transition elements. In the present invention, transition elements include, but are not limited to, W, Ti, Sr, Y, Zr, Nb, V, and Mo.

[0057] In the present invention, unless otherwise specified, in Formula II, when a≠0 and b≠0, the core formula is Li n Ni 1-x-y-a-b Co x M y E a G b O2; when a=0 and b≠0, or a≠0 and b=0, the core formula is Li n Ni 1-x-y- b Co x M y G b O2, or Li n Ni 1-x-y-a Co x M y E a O2; when a=0 and b=0, the core formula is Li n Ni 1-x-y Co x M y O2.

[0058] In some embodiments of the present invention, in Formula II, 0.9≤n≤1.5, preferably 0.95≤n≤1.25; 0≤x<1, preferably 0.01≤x≤0.2; 0≤y<1, preferably 0.01≤y≤0.1; 0≤a≤0.1, for example, 0, 0.001, 0.002, 0.003, 0.005, 0.01, 0.02, 0.05, 0.1, and any value in the range consisting of any two numerical values, preferably 0<a≤0.05; 0≤b≤0.1, for example, 0, 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, and any value in the range consisting of any two numerical values, 0<b≤0.05; 0<x+y+a+b<1, preferably 0.02<x+y+a+b≤0.4.

[0059] In some embodiments of the present invention, the roughness Δ of the inner core is 0.1-0.45, for example, 0.1, 0.12, 0.15, 0.2, 0.22, 0.25, 0.3, 0.35, 0.38, 0.45, and any value in a range consisting of any two values, preferably 0.12-0.38.

[0060] In some embodiments of the present invention, preferably, the average particle size D of the core 50 2-16 μm, for example, 2 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 16 μm, and any value in the range of any two values, preferably 3-14 μm; BET is 0.1-2 μm 2 / g, for example, 0.1m 2 / g, 0.2m 2 / g, 0.5m 2 / g, 0.8m 2 / g、1m 2 / g, 1.3m 2 / g, 2m 2 / g, any value in the range of any two values, preferably 0.2-1.3m 2 The core that meets the above conditions is more conducive to improving the coating strength of the core and the carbon layer, thereby improving the performance of the carbon-coated positive electrode material.

[0061] In the present invention, the first sintering conditions (such as temperature, time, etc.) are adjusted so that the core meets the above parameter limitations.

[0062] In the present invention, unless otherwise specified, the average particle size D 50The parameters were measured using a Malvern Mastersizer 3000 laser particle size analyzer; the specific surface area BET parameters were measured using a Micromeritics ASAP 2020 fully automatic specific surface area and porosity analyzer; and the bulk density parameters were measured using a powder bulk density analyzer.

[0063] In some embodiments of the present invention, it is further preferred that when the core is selected from agglomerated particles, the roughness Δ of the agglomerated particles is 0.1-0.35, for example, 0.1, 0.12, 0.15, 0.2, 0.22, 0.25, 0.3, 0.35, and any value in the range of any two values, preferably 0.12-0.25; the average particle size D of the primary particles in the agglomerated particles is 50 The carbon material preferably fills the gaps between the primary particles during the carbon coating process of the agglomerates meeting the above conditions. The carbon layer and the particles are "interlocked" to form a structure through gradient coating, further enhancing the bonding strength between the "carbon layer" and the primary particles.

[0064] In some embodiments of the present invention, further preferably, when the core is selected from single crystal particles, the roughness Δ of the single crystal particles is 0.15-0.45, for example, 0.15, 0.2, 0.22, 0.25, 0.3, 0.35, 0.38, 0.45, and any value in the range of any two values, preferably 0.22-0.38; the average particle size D of the single crystal particles is 50 It is 0.6-3 μm, for example, 0.6 μm, 1 μm, 1.5 μm, 2 μm, 3 μm, and any value in a range consisting of any two values, and is preferably 1-2 μm.

[0065] In some embodiments of the present invention, preferably, the thickness of the carbon layer is 10-200 nm, for example, 10 nm, 50 nm, 60 nm, 70 nm, 80 nm, 100 nm, 150 nm, 200 nm, and any value in a range consisting of any two values, preferably 50-100 nm. In the present invention, when the thickness of the carbon layer meets the above conditions, it means that the carbon layer is densely coated on the surface of the core, which can effectively change the original electrical equilibrium state of the high-nickel positive electrode material, improve the electrode conductivity, and thus improve the capacity and rate performance of the carbon-coated positive electrode material.

[0066] In the present invention, the carbon layer thickness is measured by ion milling the carbon-coated positive electrode material to prepare a sample, then observing the location of the coating layer using a scanning electron microscope, and finally determining the carbon layer thickness using an energy spectrum scanner. The carbon layer thickness is measured by randomly selecting 20 areas along the periphery of a specific particle, and the average of these areas is defined as the carbon layer thickness of that specific particle. To improve test accuracy, 40-60 particles are selected for testing each time, and the average of these carbon layer thicknesses is used as the carbon layer thickness of the sample.

[0067] In some embodiments of the present invention, preferably, the standard deviation of the carbon content test values ​​at any three points in the carbon-coated positive electrode material is ≤0.005, for example, 0.0005, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.005, and any value within a range consisting of any two values, preferably ≤0.0025. When the above conditions are met, the carbon layer of the carbon-coated positive electrode material has good uniformity, which can improve the overall performance of the carbon-coated positive electrode material, and can reduce the addition of conductive carbon in the subsequent battery manufacturing process, thereby improving the battery manufacturing efficiency.

[0068] In the present invention, the carbon layer that meets the above parameter requirements is more easily attached to the core, thereby improving the coating strength of the carbon-coated positive electrode material.

[0069] In some embodiments of the present invention, preferably, the carbon layer consists of the carbon material.

[0070] In some embodiments of the present invention, preferably, the carbon material is selected from at least one of acetylene black, furnace black, Ketjen black, carbon nanotubes, carbon nanofibers, graphite particles, porous carbon, soft carbon, hard carbon and artificial graphite.

[0071] In some embodiments of the present invention, preferably, the volume impedance ratio of the carbon-coated positive electrode material to the core is 20-70:100, for example, 20:100, 30:100, 40:100, 50:100, 60:100, 70:100, preferably 30-50:100. In the present invention, satisfying the volume impedance ratio within the above range indicates that the carbon layer is densely coated on the surface of the core, which can effectively change the original electrical equilibrium state of the high-nickel positive electrode material, improve the electrode conductivity, and thereby improve the capacity and rate performance of the carbon-coated positive electrode material.

[0072] In some embodiments of the present invention, preferably, based on the total weight of the carbon-coated positive electrode material, the content of the carbon layer is 0.1-5wt%, for example, 0.1wt%, 0.19wt%, 0.48wt%, 0.96wt%, 0.97wt%, 0.98wt%, 1.47wt%, and any value in the range of any two values, preferably 0.96-1.47wt%. In the present invention, the carbon layer content is greater than 5wt%, which will not only affect the Li + The transmission will cause the kinetics to deteriorate, and the coating strength will also deteriorate, and the cost is too high; if the carbon layer content is less than 0.1wt%, the coating effect is poor, and it is difficult to play the role of carbon coating in improving conductivity.

[0073] In some embodiments of the present invention, preferably, the carbon-coated positive electrode material satisfies: 1.1≤Z≤2.5, for example, Z is selected from 1.1, 1.16, 1.18, 1.2, 1.23, 1.25, 1.3, 1.5, 1.72, 1.8, 2, 2.13, 2.2, 2.3, 2.5, and any value in the range of any two values, preferably satisfying: 1.16≤Z≤2.3; wherein, Among them, PD c , AD c and TD c Respectively represent the compacted density, bulk density and tap density of the carbon-coated positive electrode material, all in g / cm 3 ;PD x , AD x and TD x Respectively represent the compacted density, bulk density and tap density of the core, all in g / cm 3 In the present invention, the Z value satisfies the above range, the carbon-coated positive electrode material particles are in close contact with each other, the density index is high, and the carbon layer can be tightly bonded to the surface of the positive electrode material.

[0074] In some embodiments of the present invention, further preferably, when the core is selected from an agglomerated high-nickel positive electrode material, the positive electrode material satisfies: 1.1≤Z≤1.3, for example, Z is selected from 1.1, 1.16, 1.18, 1.2, 1.23, 1.25, 1.3, and any value in a range consisting of any two values, preferably satisfying: 1.16≤Z≤1.23. Carbon-coated agglomerated positive electrode materials that meet the above ranges have excellent capacity and cycle performance.

[0075] In some embodiments of the present invention, further preferably, when the core is selected from a single crystal high-nickel positive electrode material, the positive electrode material satisfies: 1.5≤Z≤2.5, for example, Z is selected from 1.5, 1.72, 1.8, 2, 2.13, 2.2, 2.3, 2.5, and any value in a range consisting of any two values, preferably satisfying: 1.72≤Z≤2.3. Lithium-ion batteries composed of carbon-coated single crystal positive electrode materials that meet the above ranges not only have a high initial charge capacity, but also have good capacity retention.

[0076] In some embodiments of the present invention, preferably, the carbon-coated positive electrode material further satisfies Formula III: In the present invention, the above limitations are met, indicating that the carbon layer of the carbon-coated positive electrode material is not only tightly bonded to the core, but also has a smaller surface roughness, that is, the surface of the core particles is smoother after being coated, which can effectively improve the wettability of the material surface with the electrolyte, increase the active area of ​​the electrolyte contact reaction, and effectively improve the rate performance.

[0077] In the present invention, the compaction density parameter can be measured by the compaction test system of the powder resistance meter, especially the MCP-PD51. Add the sample to the mold and adjust the load to 20KN. By adjusting the pressure rod to 20KN, the test report can be output to read the compaction density in g / cm 3 .

[0078] In the present invention, the bulk density parameter can be measured using the Scott bulk density meter, which is a powder bulk density test developed in accordance with GB / T1479.2-2011 (Determination of bulk density of metal powders - Part 2: Scott volumetric method). 3 ). For details, please refer to the following method: For testing the loose density in the experiment, weigh the cylindrical cup and record it as G1. Use a spoon to place the carbon-coated positive electrode material lightly on the screen of the upper combined funnel, and use a small brush to gently brush the material (do not vibrate the equipment, especially the cylindrical cup) to pass through the screen, through the cloth box, and into the square funnel until it is full and powder overflows. Take out the cylindrical cup and use a stainless steel ruler to scrape the part of the material that overflows the cylindrical cup. Take out the cup and wipe off the powder attached to the outer surface, and weigh the cylindrical cup and powder G2, accurate to 0.01g. The loose density can then be calculated using the following equation, g / cm 3 , that is, bulk density = (weight of cylindrical cup and powder - weight of cup) / cup volume = (G2-G1) / S.

[0079] In the present invention, the tap density can be measured with reference to GB / T 21354-2008, General method for determination of tap density of powder products, which is the national standard for measuring tap density in China. The tap density parameter can be measured in the laboratory as follows:

[0080] Place a 10mL measuring cylinder (material: glass) on a balance, calibrate the balance to 0, add the carbon-coated positive electrode material to the measuring cylinder, adjust the line of sight to the height of the carbon nanotubes and read the scale to measure the volume of the carbon nanotubes. Stop adding when the volume is 8-10mL. Then place the measuring cylinder containing the positive electrode material on a calibrated balance and weigh it, and record the weight m (g). Vibrate it about 100 times on a rubber mat, rotate the measuring cylinder after every 20 vibrations, and control the amplitude to 1-1.5cm. Measure the volume of the carbon nanotubes by reading the scale of the measuring cylinder and record it as V (mL). The tap density g / cm can be calculated by the following equation 3 , that is, tap density = m / V.

[0081] A second aspect of the present invention provides a method for preparing a carbon-coated positive electrode material, the preparation method comprising:

[0082] In a non-oxidizing atmosphere, the mixed material is subjected to a solid-phase dry coating method, and the filling rate of the processing chamber of the equipment is controlled to be 30-65%. The obtained carbon-coated positive electrode material includes a core and a carbon layer;

[0083] Wherein, the mixed material includes a carbon material and a high nickel positive electrode material as the core;

[0084] The solid-phase dry coating process includes a first mixing coating, a second mixing coating and a third mixing coating; the rotation speed of the first mixing coating is less than the rotation speed of the second mixing coating and less than the rotation speed of the third mixing coating, and the time of the first mixing coating is less than the time of the second mixing coating and less than the time of the third mixing coating.

[0085] In the present invention, unless otherwise specified, the non-oxidizing atmosphere includes but is not limited to nitrogen, helium, argon, neon, etc., preferably nitrogen.

[0086] In the present invention, unless otherwise specified, controlling the filling rate of the device processing chamber to 30-65% refers to the effective volume ratio of the mixture containing the high-nickel cathode material and the carbon material to the processing chamber. The filling rate is controlled to ensure that the entire system has a reasonable compressive stress, and the specific device type and material have little influence. A filling rate less than 30% or greater than 65% will affect the coating effect.

[0087] In the present invention, the equipment for solid phase dry coating includes but is not limited to high-speed mixer equipment, wherein the high-speed mixer is lined with ceramic material for metal isolation treatment, and the high-speed mixer is physically cooled by introducing chilled water during the coating process.

[0088] In the present invention, unless otherwise specified, the first mixed coating enables the carbon material to be evenly dispersed in the gaps between the particles of the high-nickel positive electrode material; the second mixed coating enables the carbon material to adhere to the particle surface of the high-nickel positive electrode material; and the third mixed coating achieves a close combination of the carbon material and the high-nickel positive electrode material.

[0089] In some embodiments of the present invention, preferably, the conditions for the first mixing and coating include: a rotation speed of 600-800 rpm, and a time of 10-30 min; the conditions for the second mixing and coating include: a rotation speed of 70-1000 rpm, and a time of 15-60 min; and the conditions for the third mixing and coating include: a rotation speed of 900-1200 rpm, and a time of 20-90 min.

[0090] In some embodiments of the present invention, it is further preferred that the speed ratio of the first, second, and third mixing coatings is 1:1.2-1.3:1.4-1.5; and the time ratio of the first, second, and third mixing coatings is 1:1.5-2:2-3. Meeting these conditions can achieve high-strength, uniform coating while preventing particle cracking or pulverization during the coating process.

[0091] In some embodiments of the present invention, preferably, the high nickel cathode material has a composition shown in Formula II, Li n Ni 1-x-y-a-b Co x M y E a G b O2(II), wherein 0.9≤n≤1.5, 0≤x<1, 0≤y<1, 0≤a≤0.1, 0≤b≤0.1, 0<x+y+a+b<1, M is selected from Mn and / or Al, E is selected from at least one of P, N, B, Ti, Zr, Y, Al, and Mg; and G is a surface coating layer selected from oxides, sulfides, and fluorides containing at least one of B, Al, and transition elements.

[0092] In some embodiments of the present invention, further preferably, in Formula II, 0.95≤n≤1.25, 0.01≤x≤0.2, 0.01≤y≤0.1, 0<a≤0.05, 0<b≤0.05, 0.02<x+y+a+b≤0.4.

[0093] In some embodiments of the present invention, preferably, the mass ratio of the inner core to the carbon layer is 95-99.9:0.1-5, for example, 95:5, 97:3, 98:2, 98.53:1.47, 99:1, 99.04:0.96, 99.9:0.1, and any value in the range consisting of any two values, preferably 98.53-99.04:0.96-1.47.

[0094] In the present invention, unless otherwise specified, since the solid-phase dry coating results in a trace amount of carbon material (1-5 wt%) loss, the carbon material content in the carbon-coated positive electrode material is lower than the percentage of the core added.

[0095] In the present invention, the source of the high nickel cathode material can be selected from a wide range and can be purchased or prepared. Preferably, the high nickel cathode material is prepared by the following method:

[0096] S1. A lithium salt, a cathode material precursor, and an E source are first dry-mixed, and then first sintered. The obtained primary product is crushed and sieved in sequence to obtain a substrate;

[0097] S2, performing a second dry mixing of the substrate and the G source, and then performing a second sintering to obtain a second sintered product, which is then crushed and sieved in sequence to obtain a high-nickel positive electrode material having a composition represented by Formula II;

[0098] Wherein, the cathode material precursor has the composition shown in Formula IV: Ni 1-α-β Co α M β (OH)2(IV), 0≤α<1, 0≤β<1, 0<α+β<1, M is selected from Mn and / or Al.

[0099] In some embodiments of the present invention, further preferably, in Formula IV, 0.01≤α≤0.2, 0.01≤β≤0.1, and 0.02≤α+β≤0.3.

[0100] In some embodiments of the present invention, preferably, when the core is selected from agglomerated high nickel cathode material, the average particle size D of the cathode material precursor is 50 The surface area is 6-14 μm, and the BET surface area is 4-16 m 2 / g, bulk density ≥1.4g / cm 3 , tap density ≥1.8g / cm 3 Or, when the core is selected from a single crystal high nickel cathode material, the average particle size D of the cathode material precursor is 50 The surface area is 2-6 μm, and the BET surface area is 4-30 m 2 / g, bulk density ≥1g / cm3 , tap density ≥1.4g / cm 3 .

[0101] In some embodiments of the present invention, preferably, the usage ratio of the lithium salt, the positive electrode material precursor and the E source satisfies n(Li):n(Ni+Co+M):n(E)=n(Li):1:n(E), wherein, 0.9≤n(Li)≤1.5, for example, 0.9, 0.95, 1, 1.1, 1.2, 1.25, 1.5, and any value in the range consisting of any two numerical values, preferably 0.95≤n(Li)≤1.25; 0≤n(E)≤0.1, for example, 0, 0.001, 0.002, 0.003, 0.005, 0.01, 0.02, 0.05, 0.1, and any value in the range consisting of any two numerical values, preferably 0<n(E)≤0.05.

[0102] In some specific embodiments of the present invention, the lithium salt is selected from at least one of lithium oxide, lithium hydroxide, lithium carbonate and lithium nitrate; the E source is selected from oxides, hydroxides and carbonates containing at least one of the elements P, N, B, Ti, Zr, Y, Al and Mg.

[0103] In some embodiments of the present invention, preferably, the conditions of the first dry mixing and the second dry mixing each independently include: a mixing time of 0.5-6 h, and a mixing frequency of 30-150 Hz.

[0104] In some embodiments of the present invention, preferably, the first sintering conditions include: being carried out in an atmosphere with an oxygen content of 90-99.5 volume %, a temperature of 650-1200° C., a heating rate of 2-10° C. / min, and a constant temperature time of 6-20 h.

[0105] In some embodiments of the present invention, preferably, in step S1, when the core is selected from an agglomerated high-nickel positive electrode material, the first sintering temperature T satisfies formula V:

[0106]

[0107] Among them, C Ni is the molar percentage of nickel in the mixture of the nickel source, the cobalt source and the M source calculated as metal;

[0108] Alternatively, when the core is selected from a single crystal high nickel positive electrode material, the first sintering temperature T satisfies Formula VI:

[0109]

[0110] Among them, C Niis the mole percentage of nickel in the mixture of the nickel source, the cobalt source and the M source calculated as metal.

[0111] In the present invention, the first sintering temperature within the above range is satisfied, and the roughness Δ is 0.1-0.45 and the average particle size D is obtained. 50 2-16 μm and a BET surface area of ​​0.1-2 m 2 / g high nickel positive electrode material.

[0112] In some embodiments of the present invention, preferably, the G source is selected from oxides, sulfides and fluorides containing at least one of B, Al and transition elements; transition elements include but are not limited to W, Ti, Sr, Y, Zr, Nb, V, Mo, etc., preferably W.

[0113] In some embodiments of the present invention, preferably, the amount of the G source satisfies n(G):n(Ni+Co+M+E+G)=n(G):1, wherein 0≤n(G)≤0.1, for example, 0, 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, and any value in the range consisting of any two numerical values, preferably 0<n(G)≤0.05.

[0114] In some embodiments of the present invention, preferably, the second sintering conditions include: in an atmosphere with an oxygen content of ≥20 volume %, a temperature of 300-800°C, a heating rate of 2-10°C / min, and a constant temperature time of 6-20h.

[0115] In a specific embodiment of the present invention, when the core is selected from an agglomerated high-nickel cathode material, Formula I is prepared by the following method:

[0116] S1, lithium salt, general formula Ni 1-α-β Co α M β The positive electrode material precursor of (OH)2 and the E source are mixed evenly by a first dry mixing method, and then a first sintering is performed, and the obtained primary product is crushed, pulverized, and sieved in sequence to obtain an agglomerated substrate;

[0117] Wherein, the particle size D of the positive electrode material precursor is 50 The surface area is 6-14 μm, and the BET surface area is 4-16 m 2 / g, bulk density ≥1.4g / cm 3 , tap density ≥1.8g / cm 3 The mixing time of the first dry mixing method is 0.5-6h, and the mixing frequency is 30-150Hz; the first sintering temperature T satisfies formula V: Among them, C Niis the molar percentage of nickel in the mixture of the nickel source, the cobalt source and the M source calculated as metal;

[0118] S2. The agglomerated substrate and the G source are mixed uniformly by a second dry mixing method (mixing time is 0.5-6h, mixing frequency is 30-150Hz), and then a second sintering is performed to obtain a second sintered product, which is crushed and sieved in sequence to obtain an agglomerated high-nickel positive electrode material.

[0119] In another specific embodiment of the present invention, when the core is selected from a single crystal high nickel cathode material, Formula I is prepared by the following method:

[0120] S1, lithium salt, general formula Ni 1-α-β Co α M β The positive electrode material precursor of (OH)2 and the E source are mixed evenly by a first dry mixing method, and then a first sintering is performed, and the obtained primary product is crushed, pulverized, and sieved in sequence to obtain a single crystal substrate;

[0121] Wherein, the particle size D of the positive electrode material precursor is 50 The surface area is 2-6 μm, and the BET surface area is 4-30 m 2 / g, bulk density ≥1g / cm 3 , tap density ≥1.4g / cm 3 The mixing time of the first dry mixing method is 0.5-6h, and the mixing frequency is 30-150Hz; the first sintering temperature T satisfies formula VI: Among them, C Ni is the molar percentage of nickel in the mixture of the nickel source, the cobalt source and the M source calculated as metal;

[0122] S2. The above-mentioned single crystal substrate and G source are mixed evenly by a second dry mixing method (mixing time is 0.5-6h, mixing frequency is 30-150Hz), and then a second sintering is performed to obtain a second sintered product, which is crushed and sieved in turn to obtain a single crystal high-nickel positive electrode material.

[0123] In the present invention, the general formula is Ni 1-α-β Co α M β The cathode material precursor of (OH)2 is prepared by a co-precipitation method, specifically comprising:

[0124] (1) preparing a mixed salt solution of a nickel source, a cobalt source, and a M source according to a molar ratio of n(Ni):n(Co):n(M)=(1-α):α:β; preparing a precipitant solution and a complexing agent solution, respectively;

[0125] (2) Add the mixed salt solution, precipitant solution and complexing agent solution into the reactor, carry out coprecipitation reaction in an inert atmosphere, and filter, wash, dry and sieve the obtained solid-liquid mixed slurry to obtain the general formula Ni 1-α-β Co α M β (OH)2 cathode material precursor.

[0126] In some embodiments of the present invention, in step (1), the concentration of the mixed salt solution in terms of metal is 1-3 mol / L, preferably 1.5-2.5 mol / L; the concentration of the precipitant solution is 2-15 mol / L, preferably 5-10 mol / L; and the concentration of the complexing agent solution is 1-15 mol / L, preferably 5-10 mol / L.

[0127] In some embodiments of the present invention, in step (1), the nickel source, cobalt source, and M source are each independently selected from at least one of sulfates, nitrates, chlorides, oxalates, acetates, and citrates containing nickel, cobalt, and M; further preferably, the nickel source is selected from at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, nickel acetate, and nickel citrate; the cobalt source is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, cobalt acetate, and cobalt citrate; and the M source is selected from at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, manganese acetate, and manganese citrate. The precipitant includes, but is not limited to, sodium hydroxide and / or potassium hydroxide; and the complexing agent includes, but is not limited to, aqueous ammonia, sodium edetate, ammonium nitrate, ammonium chlorate, ammonium sulfate, and the like.

[0128] In some embodiments of the present invention, in step (2), the coprecipitation reaction conditions include: pH value of 10-13, preferably 11-12; temperature of 40-80°C, preferably 50-70°C; time of 5-50h, preferably 8-32h.

[0129] In the present invention, the filtration in step (2) is intended to remove the liquid in the solid-liquid mixture, and the filtration includes but is not limited to suction filtration, filter pressing, centrifugation, etc.; the washing is intended to remove residual impurities in the filtered product; the drying is intended to remove residual moisture in the washed product, and includes but is not limited to hot air drying, infrared drying, microwave drying, etc.; the screening is intended to obtain a positive electrode material precursor with a specific particle size range.

[0130] A third aspect of the present invention provides a lithium-ion battery, which contains the carbon-coated positive electrode material provided by the first aspect, or the carbon-coated positive electrode material prepared by the preparation method provided by the second aspect.

[0131] The carbon-coated positive electrode material provided by the present invention has a high carbon layer content. When preparing the electrode sheet later, only 0.1wt% of carbon nanotubes need to be added, and no other conductive agents need to be added. At the same time, the carbon coating of the present invention has high bonding strength, so it will not fall off during the subsequent tableting process. At the same time, even if the carbon nanotubes added to the slurry undergo bridging, due to the high carbon content of the carbon-coated positive electrode material itself, a natural conductive channel will be formed, thereby improving the transmission rate of lithium ions.

[0132] The present invention will be described in detail below through examples.

[0133] The physical properties of the high nickel cathode materials prepared in Preparation Examples 1-5 are listed in Table 1.

[0134] Preparation Example 1

[0135] S1, preparation formula is Ni 0.83 Co 0.11 Mn 0.06 (OH)2 cathode material precursor Q1:

[0136] (1) nickel salt (nickel sulfate), cobalt salt (cobalt sulfate) and manganese salt (manganese sulfate) were prepared into a mixed salt solution with a concentration of 2 mol / L at a molar ratio of 83:11:6 based on the metal elements; a precipitant (sodium hydroxide) and a complexing agent (ammonia water) were prepared into a precipitant solution with a concentration of 2 mol / L and a complexing agent solution with a concentration of 6 mol / L, respectively;

[0137] (2) The mixed salt solution, precipitant solution and complexing agent solution were added to a reactor and co-precipitated in an inert atmosphere (pH 11.5, temperature 65°C, synthesis time 80 h) to obtain a solid-liquid mixed slurry, which was filtered, washed, dried for a third time, and sieved for a second time to obtain a cathode material precursor Q1;

[0138] S2. The lithium salt (LiOH·H2O), the cathode material precursor Q1 and the E source (nano-zirconia) were dry mixed in a ball mill (mixing time was 4 h, mixing frequency was 35 Hz), and then the first sintering was carried out (in an atmosphere with an oxygen content of 95% by volume, temperature was 825°C; heating rate was 3°C / min; holding time was 10 h). The obtained primary product was crushed, pulverized and sieved in turn to obtain an average particle size D 50 The surface area is 14.0 μm and the BET surface area is 0.55 m 2 / g agglomerated substrate W1;

[0139] Wherein, the usage ratio of the above-mentioned lithium salt, cathode material precursor Q1 and E source satisfies n(Li):n(Ni+Co+M):n(E)=1.02:1:0.002;

[0140] S3. After washing and drying the above-mentioned agglomerated substrate W1, G source (tungsten oxide) was added and dry-mixed under high-speed ball milling conditions. The mixing time was 3 hours and the mixing frequency was 35 Hz. In an air atmosphere, a second sintering was performed (temperature was 350 ° C, heat preservation was 10 hours). The obtained second sintered product was cooled to room temperature, crushed and sieved in turn to obtain an agglomerated high-nickel positive electrode material P1 with the general formula of Li 1.02 Ni 0.826 Co 0.11 Mn 0.06 Zr 0.002 W 0.002 O2;

[0141] Wherein, the usage ratio of the above-mentioned G source satisfies n(G):n(Ni+Co+M+E+G)=0.002:1;

[0142] Among them, the physical properties of the above-mentioned agglomerated high-nickel positive electrode material P1 are listed in Table 1.

[0143] Preparation Example 2

[0144] S1, preparation formula is Ni 0.91 Co 0.05 Mn 0.04 (OH)2 cathode material precursor Q2:

[0145] (1) Based on the metal elements, nickel salt (nickel sulfate), cobalt salt (cobalt sulfate) and manganese salt (manganese sulfate) are prepared into a mixed salt solution with a concentration of 2 mol / L at a molar ratio of 91:5:4; a precipitant (sodium hydroxide) and a complexing agent (ammonia water) are prepared into a precipitant solution with a concentration of 2 mol / L and a complexing agent solution with a concentration of 6 mol / L, respectively;

[0146] (2) The mixed salt solution, precipitant solution and complexing agent solution were added to a reactor and co-precipitated in an inert atmosphere (pH 11.0, temperature 55°C, synthesis time 80h) to obtain a solid-liquid mixed slurry, which was filtered, washed, dried for a third time, and sieved for a second time to obtain a cathode material precursor Q2;

[0147] S2. The difference from Preparation Example 1 is that the first sintering temperature is replaced with 760° C., and the usage ratio of the above lithium salt, positive electrode material precursor Q2 and E source satisfies n(Li):n(Ni+Co+M):n(E)=1.01:1:0.003;

[0148] Get the average particle size D 50 The surface area is 13.0 μm and the BET surface area is 0.61 m 2 / g agglomerated substrate W2;

[0149] S3. Different from Preparation Example 1, an agglomerated high-nickel positive electrode material P2 is obtained;

[0150] Among them, the physical properties of the above-mentioned agglomerated high-nickel positive electrode material P2 are listed in Table 1.

[0151] Preparation Example 3

[0152] S1, preparation formula is Ni 0.83 Co 0.11 Mn 0.06 (OH)2 cathode material precursor Q3:

[0153] Different from Preparation Example 1, the pH value of the coprecipitation reaction in step (2) is 11.8, the temperature is 50°C, the synthesis time is 60h, and the average particle size D of the positive electrode material precursor Q3 is obtained. 50 5.2μm;

[0154] S2. The difference from Preparation Example 1 is that the first sintering temperature is replaced with 850° C., and the usage ratio of the lithium salt, the positive electrode material precursor Q3 and the E source satisfies n(Li):n(Ni+Co+M):n(E)=1:1:0.003;

[0155] Get the average particle size D 50 The surface area is 4.6 μm and the BET surface area is 0.65 m 2 / g single crystal substrate W3;

[0156] S3. Different from Preparation Example 1, the temperature of the second sintering is replaced with 650° C. to obtain a single crystal high nickel positive electrode material P3.

[0157] Among them, the physical properties of the above-mentioned single crystal high nickel positive electrode material P3 are listed in Table 1.

[0158] Preparation Example 4

[0159] The difference from Preparation Example 1 is that in step S2, the first sintering temperature is replaced with 831°C, and the average particle size D 50 The agglomerated substrate DW1 is 16.4 μm;

[0160] In step S3, an agglomerated high-nickel positive electrode material DP1 is obtained.

[0161] Among them, the physical properties of the above-mentioned agglomerated high-nickel positive electrode material DP1 are listed in Table 1.

[0162] Preparation Example 5

[0163] The difference from Preparation Example 3 is that in step S2, the first sintering temperature is replaced with 816°C, and the average particle size D 50 The single crystal substrate DW2 is 3.2 μm;

[0164] In step S3, a single-crystal high-nickel positive electrode material DP2 is obtained.

[0165] The physical properties of the single crystal high nickel cathode material DP2 are listed in Table 1.

[0166] Table 1

[0167]

[0168] Note: *- When the core is selected from agglomerated high nickel cathode material, the first sintering temperature T satisfies formula V: When the core is selected from a single crystal high nickel cathode material, the first sintering temperature T satisfies Formula VI: Among them, C Ni is the molar percentage of nickel in the mixture of the nickel source, the cobalt source and the M source calculated as metal;

[0169] For example, in Preparation Example 1, the temperature T of the first sintering satisfies Formula V: In Preparation Example 3, the first sintering temperature T satisfies VI:

[0170] Table 1

[0171]

[0172] Note: 1- average particle size D of the core 50 , μm; 2- average particle size D of primary particles in agglomerated particles 50 Or the average particle size D of the single crystal particles 50 , nm; 3-Formula I is the roughness V b is the specific surface area of ​​the core BET, m 2 / g;W a is the bulk density of the core, g / cm 3 .

[0173] It can be seen from the results in Table 1 that compared with Preparation Examples 4-5, the high-nickel positive electrode materials (agglomerated high-nickel positive electrode materials, single crystal high-nickel positive electrode materials) prepared in Preparation Examples 1-3 have higher roughness, which will be more conducive to the close bonding of the carbon material and the matrix material during the carbon coating process, thereby improving the bonding strength of the carbon coating material.

[0174] Example 1

[0175] In a nitrogen atmosphere, a carbon material (conductive carbon black) and an agglomerated high-nickel cathode material P1 were added to a high-speed mixer at a mass ratio of 1:99 for solid-phase dry coating. The filling rate of the processing chamber of the equipment was controlled to 45%. The speed of the first mixed coating was controlled to be 600 rpm and the time was 20 min; the speed of the second mixed coating was controlled to be 750 rpm and the time was 30 min; the speed of the third mixed coating was controlled to be 1050 rpm and the time was 40 min to obtain a carbon-coated cathode material S1;

[0176] Among them, the SEM image of the carbon-coated positive electrode material S1 is as follows Figure 1 As shown by Figure 1 It can be seen that the surface of the carbon-coated positive electrode material S1 is smooth and the primary particles are round, indicating that the carbon layer is evenly coated on the surface of the primary particles and is very dense.

[0177] The physical properties of the carbon-coated cathode material S1 are listed in Table 2.

[0178] Example 2

[0179] According to the method of Example 1, the difference is that

[0180] The agglomerated high-nickel positive electrode material P1 was replaced by the agglomerated high-nickel positive electrode material P2, and the other conditions were the same to obtain the carbon-coated positive electrode material S2.

[0181] Among them, the physical properties of the above-mentioned carbon-coated positive electrode material S2 are listed in Table 2.

[0182] Example 3

[0183] According to the method of Example 1, the difference is that

[0184] Solid phase dry coating was performed according to the process parameters in Table 2 to obtain carbon-coated positive electrode material S3.

[0185] The physical properties of the carbon-coated cathode material S3 are listed in Table 2.

[0186] Example 4

[0187] According to the method of Example 1, the difference is that

[0188] The carbon material was replaced with porous carbon, and the other conditions were the same to obtain the carbon-coated positive electrode material S4.

[0189] The physical properties of the carbon-coated cathode material S4 are listed in Table 2.

[0190] Example 5

[0191] According to the method of Example 1, the difference is that

[0192] The agglomerated high-nickel positive electrode material P1 was replaced with the single-crystal high-nickel positive electrode material P3, and solid-phase dry coating was performed according to the process parameters in Table 2 to obtain the carbon-coated positive electrode material S5.

[0193] The physical properties of the carbon-coated positive electrode material S5 are listed in Table 2.

[0194] Among them, the SEM image of the carbon-coated positive electrode material S5 is as follows: Figure 2 As shown by Figure 2 It can be seen that the surface of the carbon-coated positive electrode material S5 is smooth, indicating that the carbon layer is evenly coated on the surface of the single crystal particles and is very dense.

[0195] Example 6

[0196] According to the method of Example 1, the difference is that

[0197] The mass ratio of carbon material to cathode material was changed to 1.5:98.5, and the other conditions were the same to obtain carbon-coated cathode material S6.

[0198] Among them, the physical properties of the above-mentioned carbon-coated positive electrode material S6 are listed in Table 2.

[0199] Example 7

[0200] According to the method of Example 1, the difference is that

[0201] The mass ratio of carbon material to core was changed to 0.5:99.5, and solid phase dry coating was performed according to the process parameters in Table 2 to obtain carbon-coated positive electrode material S7.

[0202] Among them, the physical properties of the above-mentioned carbon-coated positive electrode material S7 are listed in Table 2.

[0203] Example 8

[0204] According to the method of Example 1, the difference is that

[0205] The mass ratio of carbon material to core was changed to 0.2:99.8, and solid-phase dry coating was performed according to the process parameters in Table 2 to obtain carbon-coated positive electrode material S8.

[0206] Among them, the physical properties of the above-mentioned carbon-coated positive electrode material S8 are listed in Table 2.

[0207] Comparative Example 1

[0208] (1) 1 g of conductive carbon black was placed in a planetary ball mill. The inner lining of the ball mill was treated with ceramic material for metal isolation. The ball mill beads were made of zirconium oxide with a particle size of 1 mm. The ball mill was milled at a speed of 350 rpm / min for 2 h to adhere a layer of carbon material to the surface of the ball mill beads and the inner surface of the ball mill. The remaining carbon material powder and the ball mill beads were separated by sieving. After separation, the ball mill beads were returned to the ball mill jar for use in the next process.

[0209] (2) Add 99 g of agglomerated high-nickel cathode material P1 to a ball mill at a 1:1 ball-to-material ratio and mill at 350 rpm for 4 h. The resulting ternary material coated with a small amount of carbon material and the milling beads are separated by sieving. After separation, the milling beads are returned to the milling jar for use in the next step.

[0210] While the ternary material is being ball-milled, prepare another ball mill (same as above) and repeat step (1) to ball-mill the carbon material. After the ball milling is completed, the remaining carbon material powder and the ball milling beads are separated by sieving, and the separated ball milling beads are returned to the ball milling tank.

[0211] Repeat step (2) to treat the high nickel cathode material, and continuously increase the carbon coating amount of the high nickel cathode material. Repeat the above steps 15 times to obtain the carbon-coated cathode material DS1.

[0212] The physical properties of the carbon-coated cathode material DS1 are listed in Table 2.

[0213] Comparative Example 2

[0214] According to the method of comparative example 1, the difference is that

[0215] The agglomerated high-nickel positive electrode material P1 was replaced by the single-crystal high-nickel positive electrode material P3, and the other conditions were the same to obtain the carbon-coated positive electrode material DS2.

[0216] Among them, the physical properties of the above-mentioned carbon-coated positive electrode material DS2 are listed in Table 2.

[0217] Comparative Example 3

[0218] According to the method of Example 1, the difference is that

[0219] Solid phase dry coating was performed according to the process parameters in Table 2 to obtain carbon-coated positive electrode material DS3.

[0220] Among them, the physical properties of the above-mentioned carbon-coated positive electrode material DS3 are listed in Table 2.

[0221] Among them, the SEM image of the carbon-coated positive electrode material DS3 is as follows: Figure 3 As shown by Figure 3It can be seen that the carbon layer coating uniformity is poor when the material is not gradient coated, which is not conducive to the electrical performance.

[0222] Comparative Example 4

[0223] According to the method of Example 1, except that

[0224] The agglomerated high-nickel positive electrode material P1 was replaced by the agglomerated high-nickel positive electrode material DP1, and the other conditions were the same to obtain the carbon-coated positive electrode material DS4.

[0225] Among them, the physical properties of the above-mentioned carbon-coated positive electrode material DS4 are listed in Table 2.

[0226] Comparative Example 5

[0227] According to the method of Example 1, except that

[0228] The agglomerated high-nickel positive electrode material P1 was replaced by the single-crystal high-nickel positive electrode material DP2, and the other conditions were the same to obtain the carbon-coated positive electrode material DS5.

[0229] The physical properties of the carbon-coated cathode material DS5 are listed in Table 2.

[0230] Table 2

[0231]

[0232] Note: 4-mass ratio of carbon material and high nickel positive electrode material; 5-carbon material content in carbon-coated positive electrode material, wt%.

[0233] Table 2

[0234]

[0235] Note: Among them, PD c , AD c and TD c Respectively represent the compacted density, bulk density and tap density of carbon-coated positive electrode materials, all in g / cm 3 ;PD x , AD x and TD x Represents the compacted density, bulk density and tapped density of the core, all in g / cm 3 ;

[0236] Formula III:

[0237] Table 2

[0238]

[0239] It can be seen from the data in Table 2 that, compared with Comparative Examples 1-5, the carbon-coated positive electrode materials prepared by the preparation method provided by the present invention in Examples 1-8 are so that the carbon layer and the core are tightly combined, so that the carbon-coated positive electrode material not only satisfies: the coating layer retention rate δ ≥ 99%, but also satisfies: the standard deviation of the carbon content test values ​​at any three points in the carbon-coated positive electrode material is ≤ 0.005, the volume impedance ratio of the carbon-coated positive electrode material and the core is 20-70:100, 1.1 ≤ Z ≤ 2.5, thereby improving the capacity and cycle performance of the carbon-coated positive electrode material.

[0240] Compared with Comparative Examples 1 and 3-4, the agglomerated carbon-coated positive electrode materials prepared by the preparation method provided by the present invention in Examples 1-4 and 6-8 have a Z value of 1.1-1.3. Compared with Comparative Examples 2 and 5, the single crystal carbon-coated positive electrode material prepared by the preparation method provided by the present invention in Example 5 has a Z value of 1.5-2.5, which is more conducive to improving the performance of the carbon-coated positive electrode material.

[0241] Test Case

[0242] The carbon-coated positive electrode materials (S1-S8 and DS1-DS5) prepared in Examples 1-8 and Comparative Examples 1-5 were used as positive electrodes, and button batteries were assembled respectively.

[0243] The discharge specific capacity of the button cell was measured at 0.1C discharge capacity, 4.3-2.8V and 25°C, and the 80-week cycle retention rate was measured at 1C and 45°C. The test results are listed in Table 3.

[0244] The 1C / 1C cycle curves of button cells assembled from the agglomerated carbon-coated positive electrode materials of Examples 1-3 and Comparative Example 1 at 45°C and 3-4.3V are shown in FIG. Figure 4 As shown by Figure 4 It can be seen that compared with Comparative Example 1, the button batteries assembled from the agglomerated carbon-coated positive electrode materials of Examples 1-3 have a higher capacity retention rate.

[0245] The 1C / 1C cycle curves of button cells assembled from the single crystal carbon coated positive electrode materials of Example 5 and Comparative Example 2 at 45°C and 3-4.3V are shown in FIG. Figure 5 As shown by Figure 5 It can be seen that compared with Comparative Example 2, the button battery assembled with the single crystal carbon-coated positive electrode material of Example 5 has a higher capacity retention rate.

[0246] Table 3

[0247]

[0248]

[0249] It can be seen from the data in Table 3 that compared with Comparative Examples 1-5, the button batteries with carbon-coated positive electrode material tissues prepared in Examples 1-8 have higher discharge specific capacity.

[0250] At the same time, compared with Comparative Example 1, the button batteries assembled with the carbon-coated positive electrode materials prepared in Examples 1-3 also have a higher capacity retention rate; compared with Comparative Example 2, the button batteries assembled with the carbon-coated positive electrode materials prepared in Example 5 also have a higher capacity retention rate.

[0251] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A carbon-coated positive electrode material, characterized in that The carbon-coated positive electrode material comprises: a core and a carbon layer, wherein the core is a high-nickel positive electrode material and the carbon layer contains a carbon material; The carbon layer is physically adsorbed on the surface of the core; the roughness ∆ of the core is 0.12-0.38, wherein the roughness ∆ is defined as in formula I, ∆= (I); In formula I, V b is the specific surface area BET of the core, m 2 / g;W a is the bulk density of the core, g / cm 3 ; Wherein, when the core is selected from agglomerated particles, the roughness ∆ of the agglomerated particles is 0.12-0.35; or, when the core is selected from single crystal particles, the roughness ∆ of the single crystal particles is 0.15-0.38; Wherein, the high nickel cathode material has the composition shown in formula II, Li n Ni 1-x-y-a-b Co x M y E a G b O2 (II), in formula II, 0.9≤n≤1.5, 0≤x<1, 0≤y<1, 0≤a≤0.1, 0≤b≤0.1, 0<x+y+a+b<1, M is Mn and / or Al, E is selected from at least one of P, N, B, Ti, Zr, Y, Al, and Mg elements; G is a surface coating layer selected from oxides, sulfides, and fluorides containing at least one of B, Al, and transition elements.

2. The carbon-coated positive electrode material according to claim 1, wherein The coating layer retention rate δ of the carbon-coated positive electrode material is ≥99%, wherein δ=C0 / C1; Wherein, C0 is the carbon content of the carbon-coated positive electrode material, wt%; C1 is the carbon content of the upper layer of the carbon-coated positive electrode material after vibration treatment, wt%; The test method of C1 is to take 200g of the carbon-coated positive electrode material and perform vibration treatment, wherein the amplitude of the vibration treatment is 3mm, the frequency is 250 times / min, and the time is 60min; then, 1g of the upper layer material is weighed from the surface of the carbon-coated positive electrode material after the vibration treatment, and the carbon content of the upper layer material is measured, wt%.

3. The carbon-coated positive electrode material according to claim 2, wherein The coating layer retention rate δ of the carbon-coated positive electrode material is 99.5-99.9%; And / or, the carbon-coated positive electrode material is prepared by solid-phase dry coating.

4. The carbon-coated positive electrode material according to claim 1, wherein In formula II, 0.95≤n≤1.25, 0.01≤x≤0.2, 0.01≤y≤0.1, 0<a≤0.05, 0<b≤0.05, 0.02<x+y+a+b≤0.

4.

5. The carbon-coated positive electrode material according to claim 1, wherein The average particle size D of the core 50 2-16 μm; BET specific surface area is 0.1-2 m 2 / g.

6. The carbon-coated positive electrode material according to claim 5, wherein The average particle size D of the core 50 3-14 μm; BET specific surface area is 0.2-1.3 m 2 / g.

7. The carbon-coated positive electrode material according to claim 5, wherein When the core is selected from agglomerated particles, the roughness ∆ of the agglomerated particles is 0.12-0.25; the average particle size D of the primary particles in the agglomerated particles is 50 300-700nm; or, When the core is selected from single crystal particles, the roughness ∆ of the single crystal particles is 0.22-0.38; the average particle size D of the single crystal particles 50 0.6-3μm.

8. The carbon-coated positive electrode material according to claim 7, wherein The average particle size D of the primary particles in the agglomerated particles 50 The average particle size D of the single crystal particles is 350-500 nm; 50 1-2μm.

9. The carbon-coated positive electrode material according to claim 1, wherein The thickness of the carbon layer is 10-200 nm; And / or, the standard deviation of the carbon content test values ​​at any three points in the carbon-coated positive electrode material is ≤0.005; And / or, the carbon layer is composed of the carbon material.

10. The carbon-coated positive electrode material according to claim 9, wherein The thickness of the carbon layer is 50-100 nm; And / or, the standard deviation of the carbon content test values ​​at any three points in the carbon-coated positive electrode material is ≤0.0025; And / or, the carbon material is at least one selected from conductive carbon black, acetylene black, furnace black, Ketjen black, carbon nanotubes, carbon nanofibers, graphite particles, porous carbon, soft carbon, hard carbon and artificial graphite.

11. The carbon-coated positive electrode material according to claim 1, wherein The volume impedance ratio of the carbon-coated positive electrode material and the core is 20-70:100; And / or, based on the total weight of the carbon-coated positive electrode material, the content of the carbon layer is 0.1-5 wt %.

12. The carbon-coated positive electrode material according to claim 11, wherein The volume impedance ratio of the carbon-coated positive electrode material and the core is 30-50:100; And / or, based on the total weight of the carbon-coated positive electrode material, the content of the carbon layer is 0.96-1.47 wt %.

13. The carbon-coated positive electrode material according to any one of claims 1 to 12, wherein The carbon-coated positive electrode material satisfies: 1.1≤Z≤2.5; wherein Z= , among which, PD c , AD c and TD c Respectively represent the compacted density, bulk density and tap density of the carbon-coated positive electrode material, all in g / cm 3 ;PD x , AD x and TD x Respectively represent the compacted density, bulk density and tap density of the core, all in g / cm 3 .

14. The carbon-coated positive electrode material according to claim 13, wherein The carbon-coated positive electrode material satisfies: 1.16≤Z≤2.

3.

15. The carbon-coated positive electrode material according to claim 13, wherein When the core is selected from agglomerated high-nickel positive electrode materials, the carbon-coated positive electrode material satisfies: 1.1≤Z≤1.3; When the core is selected from a single crystal high nickel positive electrode material, the carbon-coated positive electrode material satisfies: 1.5≤Z≤2.

5.

16. The carbon-coated positive electrode material according to claim 15, wherein When the core is selected from agglomerated high-nickel positive electrode materials, the carbon-coated positive electrode material satisfies: 1.16≤Z≤1.23; When the core is selected from a single crystal high nickel positive electrode material, the carbon-coated positive electrode material satisfies: 1.72≤Z≤2.

3.

17. The carbon-coated positive electrode material according to claim 13, wherein The carbon-coated positive electrode material also satisfies Formula III: (III).

18. A method for preparing the carbon-coated positive electrode material according to any one of claims 1 to 17, characterized in that: The preparation method comprises: In a non-oxidizing atmosphere, the mixed material is subjected to a solid-phase dry coating method, and the filling rate of the processing chamber of the equipment is controlled to be 30-65%. The obtained carbon-coated positive electrode material includes a core and a carbon layer; Wherein, the mixed material includes a carbon material and a high nickel positive electrode material as the core; The solid-phase dry coating process includes a first mixing coating, a second mixing coating and a third mixing coating; the rotation speed of the first mixing coating is less than the rotation speed of the second mixing coating and less than the rotation speed of the third mixing coating, and the time of the first mixing coating is less than the time of the second mixing coating and less than the time of the third mixing coating.

19. The preparation method according to claim 18, wherein The conditions for the first mixing and coating process include: a rotation speed of 600-800 rpm and a time of 10-30 min; the conditions for the second mixing and coating process include: a rotation speed of 700-1000 rpm and a time of 15-60 min; the conditions for the third mixing and coating process include: a rotation speed of 900-1200 rpm and a time of 20-90 min; And / or, the rotation speed ratio of the first mixing coating, the second mixing coating and the third mixing coating is 1:1.2-1.3:1.4-1.5; the time ratio of the first mixing coating, the second mixing coating and the third mixing coating is 1:1.5-2:2-3.

20. The preparation method according to claim 18, wherein The mass ratio of the core to the carbon layer is 95-99.9:0.1-5.

21. The preparation method according to claim 20, wherein The mass ratio of the inner core to the carbon layer is 98.53-99.04:0.96-1.

47.

22. The preparation method according to claim 20, wherein The high nickel cathode material is prepared by the following method: S1. A lithium salt, a cathode material precursor, and an E source are first dry-mixed, and then first sintered. The obtained primary product is crushed and sieved in sequence to obtain a substrate; S2, performing a second dry mixing of the substrate and the G source, and then performing a second sintering to obtain a second sintered product, which is then crushed and sieved in sequence to obtain a high-nickel positive electrode material having a composition shown in Formula II; Wherein, the positive electrode material precursor has the composition shown in Formula IV: Ni 1-α-β Co α M β (OH)2(IV), 0≤α<1, 0≤β<1, 0<α+β<1, M is selected from Mn and / or Al.

23. The preparation method according to claim 22, wherein In formula IV, 0.01≤α≤0.2, 0.01≤β≤0.1, and 0.02≤α+β≤0.

3.

24. The preparation method according to claim 22, wherein In step S1, when the core is selected from agglomerated high nickel cathode material, the average particle size D of the cathode material precursor is 50 The surface area is 6-14 μm, and the BET surface area is 4-16 m 2 / g, bulk density ≥1.4g / cm 3 , tap density ≥1.8g / cm 3 ; Alternatively, when the core is selected from a single crystal high nickel cathode material, the average particle size D of the cathode material precursor is 50 The surface area is 2-6 μm, and the BET surface area is 4-30 m 2 / g, bulk density ≥1g / cm 3 , tap density ≥1.4g / cm 3 .

25. The preparation method according to claim 22, wherein The usage ratio of the lithium salt, the positive electrode material precursor and the E source satisfies n(Li):n(Ni+Co+M):n(E)=n(Li):1:n(E), wherein 0.9≤n(Li)≤1.5, 0≤n(E)≤0.1; And / or, the E source is selected from oxides, hydroxides, and carbonates containing at least one of the elements P, N, B, Ti, Zr, Y, Al, and Mg; and / or, the G source is selected from oxides, sulfides and fluorides containing at least one of B, Al and transition elements; And / or, the amount of the G source satisfies n(G):n(Ni+Co+M+E+G)=n(G):1, wherein 0≤n(G)≤0.1; And / or, the conditions of the first dry mixing and the second dry mixing each independently include: a mixing time of 0.5-6h, a mixing frequency of 30-150Hz; And / or, the first sintering conditions include: in an atmosphere with an oxygen content of 90-99.5% by volume, a temperature of 650-1200° C., a heating rate of 2-10° C. / min, and a constant temperature time of 6-20 h; And / or, the second sintering conditions include: being carried out in an atmosphere with an oxygen content of ≥20% by volume, at a temperature of 300-800° C., a heating rate of 2-10° C. / min, and a constant temperature time of 6-20 h.

26. The preparation method according to claim 25, wherein The usage ratio of the lithium salt, the positive electrode material precursor and the E source satisfies n(Li):n(Ni+Co+M):n(E)=n(Li):1:n(E), wherein 0.95≤n(Li)≤1.25, 0<n(E)≤0.05; And / or, the amount of the G source satisfies n(G):n(Ni+Co+M+E+G)=n(G):1, wherein 0<n(G)≤0.

05.

27. The preparation method according to claim 22, wherein In step S1, when the core is selected from an agglomerated high-nickel positive electrode material, the first sintering temperature T satisfies formula V: （V）， Among them, C Ni is the molar percentage of nickel in the mixture of the nickel source, the cobalt source and the M source calculated as metal; Alternatively, when the core is selected from a single crystal high nickel positive electrode material, the first sintering temperature T satisfies Formula VI: (WE), Among them, C Ni is the mole percentage of nickel in the mixture of the nickel source, the cobalt source and the M source calculated as metal.

28. A lithium ion battery, characterized in that: The lithium-ion battery contains the carbon-coated positive electrode material according to any one of claims 1 to 17.

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