Single crystal positive electrode material, preparation method therefor, and lithium-ion battery

Abstract

A single crystal positive electrode material, a preparation method therefor, and a lithium-ion battery. The size distribution B90=(P90-P10) / P50 of single crystal particles of the single crystal positive electrode material satisfies: 0.9≤B90≤1.4; and the Young's modulus E of the positive electrode material measured by means of an atomic force microscope satisfies: 100 GPa≤E≤200 GPa. The single crystal particles of the single crystal positive electrode material have a specific particle size distribution, which enables the single crystal positive electrode material to have high compaction density and have a high Young's modulus, so that the single crystal positive electrode material can bear higher rolling force in a battery preparation process, thereby increasing the volumetric energy density of a lithium-ion battery containing the positive electrode material.

Description

Single crystal positive electrode material and preparation method thereof, and lithium ion battery Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular to a single-crystal positive electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] With the rapid development of the power battery industry, the market demand for lithium-ion batteries is also increasing. Due to the large size of on-board batteries, they occupy a large amount of space in electric vehicles, greatly limiting the comfort and design of the vehicle model. As the largest component in the battery, the positive electrode material can be reduced in size by increasing its volume energy density. Currently, existing technologies often increase battery energy density by increasing the operating voltage window. However, as the voltage increases, the battery performance will deteriorate significantly, and problems such as electrode powdering, cycle diving, and storage gas production often occur. At the same time, the existing electrolyte is extremely susceptible to oxidation and decomposition under high voltage conditions, which also limits the further development of this solution.

[0003] Increasing the compaction density of the cathode material, compressing more cathode material per unit space, can also save space. Increasing the compaction density means that the cathode material particles will be subjected to greater pressure during the electrode preparation process. If the material particles are not strong enough, they will easily crack or even break under such pressure.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem that the compaction density and particle strength of the positive electrode material in the prior art cannot meet the requirements, and to provide a single crystal positive electrode material and its preparation method, and a lithium ion battery. The single crystal particles of the single crystal positive electrode material have a specific particle size distribution, which can enable the single crystal positive electrode material to have a high compaction density and a high Young's modulus so that it can withstand higher rolling pressure during the battery preparation process, thereby improving the volume energy density of the lithium ion battery containing the positive electrode material.

[0006] In order to achieve the above object, the present invention provides a single crystal positive electrode material in a first aspect, wherein the size distribution B of the single crystal particles of the single crystal positive electrode material is 90 =(P 90 -P 10 ) / P 50 Satisfies: 0.9≤B 90 ≤1.4;

[0007] Among them, P 10 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 10% in the SEM image of the positive electrode material; 50is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 50% in the SEM image of the positive electrode material; 90 The particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 90% in the SEM image of the positive electrode material;

[0008] The Young's modulus E of the positive electrode material measured by atomic force microscopy satisfies: 100 GPa≤E≤200 GPa.

[0009] A second aspect of the present invention provides a method for preparing the above-mentioned single crystal positive electrode material, wherein the method comprises the following steps:

[0010] S1, mixing a nickel-cobalt-manganese precursor, a lithium source, and an additive optionally containing a G element to obtain a mixture I;

[0011] S2. In the presence of an oxygen-containing atmosphere, the mixture I is subjected to a first sintering process, and then crushed to obtain a single crystal positive electrode material product II;

[0012] S3, mixing the single crystal cathode material process product II with a coating agent optionally containing an M element to obtain a mixture III;

[0013] S4. Performing a second sintering on the mixture III in the presence of an oxygen-containing atmosphere to obtain the single crystal positive electrode material;

[0014] The crushing makes the size distribution of the single crystal particles of the single crystal positive electrode material B 90 =(P 90 -P 10 ) / P 50 Satisfies: 0.9≤B 90 ≤1.4;

[0015] Among them, P 10 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 10% in the SEM image of the positive electrode material; 50 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 50% in the SEM image of the positive electrode material; 90 The particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 90% in the SEM image of the positive electrode material;

[0016] The first sintering includes: a sintering temperature of T / °C, a heating period from 400°C to T of t1 / h, and a cooling period from T to 400°C of t2 / h, wherein t2 satisfies [ln(T-400)] / t2≤1.

[0017] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the above-mentioned single crystal positive electrode material.

[0018] Through the above technical solution, the single crystal positive electrode material and preparation method thereof, and the lithium ion battery provided by the present invention achieve the following beneficial effects:

[0019] In the present invention, the single crystal particles of the single crystal positive electrode material are found to have a specific size distribution B by SEM. 90 =(P 90 -P 10 ) / P 50 and suitable Young's modulus strength, which enables the single crystal positive electrode material to have a high compaction density and withstand a higher rolling pressure during the battery preparation process, thereby improving the volume energy density of the lithium-ion battery containing the positive electrode material, and having a good cycle retention rate and low impedance.

[0020] In the method for preparing a positive electrode material provided by the present invention, by crushing the product after the first sintering and controlling the single crystal particles of the single crystal positive electrode material to have a specific particle size distribution, the single crystal positive electrode material can have a high compaction density.

[0021] Furthermore, the inventors discovered that controlled and slow cooling can lead to a more complete solid-phase reaction, resulting in more rounded and regular particles. This can increase the Young's modulus while reducing residual stress within the particles, thus increasing particle strength. This allows the particles to withstand higher roller pressure during battery fabrication, thereby increasing the volumetric energy density of lithium-ion batteries containing this cathode material.

[0022] In addition, the method for preparing the positive electrode material provided by the present invention is simple and easy to prepare industrially. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a SEM image of a single crystal cathode material of Example 1;

[0024] FIG2 is a SEM image of the single crystal positive electrode material of Example 6;

[0025] FIG3 is a SEM image of the single crystal cathode material of Example 1 after being subjected to 400 MPa pressure treatment;

[0026] FIG4 is a SEM image of the single crystal positive electrode material of Comparative Example 1 after being subjected to a pressure treatment of 400 MPa;

[0027] FIG5 is a SEM image of the single crystal positive electrode material of Comparative Example 2 after being subjected to a pressure treatment of 400 MPa. DETAILED DESCRIPTION

[0028] 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.

[0029] The first aspect of the present invention provides a single crystal positive electrode material, characterized in that the size distribution B of the single crystal particles of the single crystal positive electrode material is 90 =(P 90 -P 10 ) / P 50 Satisfies: 0.9≤B 90 ≤1.4;

[0030] Among them, P 10 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 10% in the SEM image of the positive electrode material; 50 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 50% in the SEM image of the positive electrode material; 90 The particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 90% in the SEM image of the positive electrode material;

[0031] The Young's modulus E of the positive electrode material measured by atomic force microscopy satisfies: 100 GPa≤E≤200 GPa.

[0032] In the present invention, the single crystal particles of the single crystal positive electrode material have a specific size distribution, which enables the single crystal positive electrode material to have a high compaction density, and has a high Young's modulus so that it can withstand higher rolling pressure during the battery preparation process, thereby improving the volume energy density of the lithium-ion battery containing the positive electrode material.

[0033] Specifically, the narrower the size distribution of the single crystal particles, the poorer the gradation of the single crystal particles, and the lower the compaction density; the wider the size distribution, the better the gradation, and the higher the compaction density. However, if the distribution is too wide, it indicates that there are many fine powders and large particles in the material, which is prone to powder loss or even cycle drop during the battery cycle. When the size distribution of the single crystal particles is controlled to meet the above range, it indicates that there is good gradation between large and small particles in the positive electrode material, so that the positive electrode material has a high compaction density.

[0034] In the present invention, based on quantity, P 10 Indicates that 10% of the single crystal particle size of the positive electrode material is smaller than P 10 , P 50 Indicates that 50% of the single crystal particle size of the positive electrode material is smaller than P50 , P 90 Indicates that 90% of the single crystal particle size of the positive electrode material is smaller than P 90 .

[0035] In the present invention, 500 single crystal particles are randomly selected from the SEM image of the positive electrode material, and the average diameter is calculated by converting the projected area of ​​the 500 single crystal particles into a standard circle of equal area, i.e., the particle size P of the single crystal positive electrode material. The 500 particles are randomly selected and can be obtained by cumulatively selecting particles in multiple scanning electron microscope fields of view.

[0036] In the present invention, Young's modulus E refers to the force required to produce a unit deformation of a particle. A higher test value indicates that the particle shape is more difficult to change, i.e., the particle strength is greater. In the present invention, the positive electrode material has a high Young's modulus E, which makes the positive electrode material less susceptible to breakage during the electrode sheet rolling process, and can achieve a higher compaction density of the positive electrode material.

[0037] In the present invention, the Young's modulus E of the positive electrode material is tested by atomic force microscopy (AFM).

[0038] In the present invention, the size distribution of the single crystal particles B 90 =(P 90 -P 10 ) / P 50 Satisfies: 0.9≤B 90 ≤1.4, for example B 90 0.9, 1, 1.1, 1.2, 1.3, 1.4, and any two values ​​in the range. Preferably, 1≤B 90 ≤1.3.

[0039] In the present invention, the Young's modulus E of the positive electrode material measured by atomic force microscopy satisfies: 100 GPa≤E≤200 GPa. For example, the Young's modulus E can be 100 GPa, 110 GPa, 120 GPa, 130 GPa, 140 GPa, 150 GPa, 160 GPa, 170 GPa, 180 GPa, 190 GPa, 200 GPa, and a range consisting of any two values. Preferably, 120 GPa≤E≤200 GPa.

[0040] According to the present invention, 1 μm ≤ P 50 ≤2μm

[0041] In the present invention, the inventors have found that if the particle size is too small, there will be more small particles, the compaction density will be reduced, and problems in processing and application will occur, such as increased viscosity, slurry jelly, and powder loss during electrode cycle. If the particle size is too large, the lithium ion transmission path will increase, resulting in poor electrical performance. At the same time, large particles are more likely to have defects, resulting in reduced particle strength.50 When the content is controlled within the above range, the positive electrode material can have high compaction density, electrical conductivity and particle strength.

[0042] In the present invention, in B 90 If P remains unchanged 50 The larger the size, the greater the difference between large and small particles in the positive electrode material. When 2μm<P 50 When the large particles are too large, the internal residual stress increases and the overall Young's modulus decreases, making the particles more likely to break under the same compaction. 50 When the particle size is less than 1 μm, the compaction density will decrease due to insufficient grading of large and small particles.

[0043] In the present invention, the positive electrode material P 50 Satisfy 1μm≤P 50 ≤2μm, for example, it can be 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, and a range consisting of any two values. Preferably, 1.3μm≤P 50 ≤1.7μm.

[0044] According to the present invention, the coverage X of the positive electrode material measured by SEM satisfies: 5%≤X.

[0045] In the present invention, coating the surface of the positive electrode material improves contact between single crystal particles, thereby increasing the material's compaction density. The coating layer on the surface of the positive electrode material also enhances the material's particle strength. Furthermore, when the positive electrode material's coating ratio falls within the aforementioned range, it can improve the surface interface, compensate for surface defects, reduce impedance, and increase the positive electrode material's Young's modulus (E) and particle strength. However, excessively high coating ratios increase the interface for electron transmission, increasing the material's impedance.

[0046] In the present invention, the coverage rate X = total area of ​​the coating on the surface of the single crystal particles / total surface area of ​​the single crystal particles, wherein the total area of ​​the coating on the surface of the single crystal particles and the total area of ​​the single crystal particles are measured by SEM images. Specifically, the total area of ​​the single crystal particles is the total projected area of ​​the coating on the surface of 100 random single crystal particles measured by SEM images, and the total area of ​​the coating on the surface of the single crystal particles is the total projected area of ​​100 random corresponding single crystal particles measured by SEM images. The ratio of the two is the coverage rate.

[0047] In the present invention, the coverage X of the positive electrode material measured by SEM satisfies: 5%≤X, where X can be, for example, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, and a range consisting of any two values. Preferably, 5%≤X≤30%.

[0048] According to the present invention, the residual stress of the positive electrode material measured by XRD is 0-0.2%.

[0049] In the present invention, the positive electrode material has low residual stress, indicating that the positive electrode material has many internal defects and is not easy to break.

[0050] In the present invention, the residual stress of the positive electrode material is obtained by refined calculation after XRD testing.

[0051] In the present invention, the residual stress of the positive electrode material measured by XRD is 0-0.2%, for example, it can be 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, and a range consisting of any two values. Preferably, the residual stress of the positive electrode material measured by XRD is 0.01-0.15%.

[0052] According to the present invention, the median particle size D of the positive electrode material measured by a particle size analyzer is 50 Satisfy: 2μm≤D 50 ≤6μm, for example, it can be 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 3μm, 3.2μm, 3.4μm, 3.6μm, 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6μm, and a range consisting of any two values. Preferably, 3μm≤D 50 ≤5μm.

[0053] According to the present invention, after the pressure treatment of 400 MPa, the particle size change rate ΔD of the positive electrode material measured by the particle size analyzer is 10 =D 10 -D' 10 Satisfy: △D 10 ≤0.2μm; where D 10 is the particle size before pressure treatment, D' 10 It is the particle size after pressure treatment.

[0054] In the present invention, after being treated with a certain pressure, the particle size change rate of the positive electrode material is low, indicating that the positive electrode material has high particle strength and the positive electrode material particles are not easily crushed during the battery manufacturing process;

[0055] According to the present invention, the compaction density of the positive electrode material is 3.3-3.7 g / cm 3 .

[0056] In the present invention, the positive electrode material has high compaction density and high particle strength, and the battery prepared thereby has high volume energy density.

[0057] According to the present invention, the single crystal cathode material has a composition shown in Formula I:

[0058] Li 1+a (Ni x Mn y Co z G b )M c O2 Formula I;

[0059] Among them, 0≤a≤0.2, 0<b≤0.05, 0<c≤0.05, 0.4≤x<1, 0 <y<0.5,0≤z<0.5;

[0060] M is selected from at least one of B, Nb, Co, Mo, W, Si, Mg, and Al;

[0061] G is selected from at least one of Ta, Nb, Hf, Zr, Ti, Al, W, Y, Sb, Sr and Si.

[0062] In the present invention, in addition to Li, the main elements distributed inside the single crystal positive electrode material particles are Ni, Co, Mn and G, and the main metal element distributed on the surface of the single crystal positive electrode material particles is M.

[0063] In the present invention, the metal element M in the positive electrode material is the main metal element in the coating, and the coating includes a lithium oxygen compound of the M element and / or an oxide containing the M element, and may also include at least one element of Ni, Co, Mn, and G from the matrix.

[0064] In one embodiment of the present invention, M and G are different.

[0065] In one embodiment of the present invention, M is selected from at least one of Al, W, Nb, B, and Mg.

[0066] In one embodiment of the present invention, M is selected from at least one of Al, W, B, and Mg.

[0067] In a specific embodiment of the present invention, G is selected from at least one of Ta, Nb, Hf, Zr, Ti, Al, W, and Y.

[0068] In a preferred embodiment of the present invention, G satisfies E G-O ≥500kJ / mol, where E G-O is the G-O bond energy. In the present invention, when G is selected in the positive electrode material, which has a high G-O bond energy after bonding with O, G can enter the crystal interior and participate in lattice construction, further improving the Young's modulus of the positive electrode material. More preferably, G is selected from at least one of Ta, Nb, Hf, Zr, and Ti.

[0069] In a specific embodiment of the present invention, in Formula I, a can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, and a range consisting of any two values, preferably 0≤a≤0.1; b can be 0.01, 0.02, 0.03, 0.04, 0.05, and a range consisting of any two values, preferably 0<b≤0.03; c can be 0.01, 0.02, 0.03, 0.04, 0.05, and a range consisting of any two values, preferably 0<c≤0.03.

[0070] A second aspect of the present invention provides a method for preparing the above-mentioned single crystal positive electrode material, characterized in that the method comprises the following steps:

[0071] S1, mixing a nickel-cobalt-manganese precursor, a lithium source, and an additive optionally containing a G element to obtain a mixture I;

[0072] S2. In the presence of an oxygen-containing atmosphere, the mixture I is subjected to a first sintering process, and then crushed to obtain a single crystal positive electrode material product II;

[0073] S3, mixing the single crystal cathode material process product II with a coating agent optionally containing an M element to obtain a mixture III;

[0074] S4. Performing a second sintering on the mixture III in the presence of an oxygen-containing atmosphere to obtain the single crystal positive electrode material;

[0075] The crushing makes the size distribution of the single crystal particles of the single crystal positive electrode material B 90 =(P 90 -P 10 ) / P 50 Satisfies: 0.9≤B 90 ≤1.4;

[0076] Among them, P10 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 10% in the SEM image of the positive electrode material; 50 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 50% in the SEM image of the positive electrode material; 90 The particle size corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 90% in the SEM image of the positive electrode material;

[0077] The first sintering includes: a sintering temperature of T / °C, a heating period from 400°C to T of t1 / h, and a cooling period from T to 400°C of t2 / h, wherein t2 satisfies [ln(T-400)] / t2≤1.

[0078] In the present invention, by crushing the product after the first sintering and controlling the single crystal particles of the single crystal positive electrode material to have a specific size distribution and the time of the cooling section during the first sintering, the single crystal positive electrode material can have a high compaction density, thereby improving the volume energy density of the lithium-ion battery containing the positive electrode material.

[0079] Specifically, when the time of the cooling section in the first sintering is controlled to meet the above range, the cooling rate of the cooling section is low. The inventors have found that by slowly cooling, the solid-phase reaction can be more complete, the particles can be more rounded and regular, and the residual stress inside the particles can be reduced while increasing the Young's modulus, thereby increasing the strength of the particles. This allows the material to withstand higher rolling pressure during the battery preparation process, ensuring that the positive electrode particles are not damaged when preparing lithium-ion batteries with high volumetric energy density.

[0080] In the present invention, there is no particular limitation on the crushing equipment and / or conditions, as long as the size distribution B of the single crystal particles of the single crystal positive electrode material can be made 90 It suffices to satisfy the limitations of the present invention.

[0081] In the present invention, t2 satisfies [ln(T-400)] / t2≤1, for example, it can be 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, and a range consisting of any two values. Preferably, t2 satisfies [ln(T-400)] / t2≤0.9. In this relationship, the unit of T is ℃ and the unit of t2 is h, which reflects the relationship between the sintering temperature T and the cooling time t2 and limits the cooling rate.

[0082] According to the present invention, 0<t1 / t2≤1.

[0083] In the present invention, when the time t1 of the heating section and the time t2 of the cooling section are controlled to meet the above ranges, it indicates that during the first sintering process, the material has the characteristics of fast heating and slow cooling, thereby increasing the Young's modulus of the obtained positive electrode material particles and further reducing the residual stress inside the particles.

[0084] In the present invention, 0<t1 / t2≤1, for example, t1 / t2 is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and a range consisting of any two values. Preferably, 0.1≤t1 / t2≤0.8.

[0085] According to the present invention, 800°C≤T≤1000°C.

[0086] In the present invention, the particle size P can be controlled by controlling the sintering temperature T of the first sintering. 50 When it meets the above range, the obtained particle size is moderate. If the temperature is too high, the particle size increases and the capacity decreases; at the same time, if the temperature is too low, the particle size decreases and the cycle becomes worse.

[0087] In the present invention, the sintering temperature T of the first sintering satisfies 800℃≤T≤1000℃, for example, it can be 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, and a range consisting of any two values. Preferably, 850℃≤T≤970℃.

[0088] According to the present invention, in step S1, the additive containing the G element is selected from at least one of G oxides, G hydroxides and G carbonates.

[0089] According to the present invention, the G element is selected from at least one of Ta, Nb, Hf, Zr, Ti, Al, W, Y, Sb, Sr and Si.

[0090] In a specific embodiment of the present invention, G is selected from at least one of Ta, Nb, Hf, Zr, Ti, Al, W, and Y.

[0091] According to the present invention, G satisfies E G-O ≥500kJ / mol, where E G-O It is the GO key function.

[0092] In the present invention, when a compound of a G element that can bond with O and has a high G-O bond energy is selected as an additive, G can enter the crystal interior and participate in lattice construction, thereby further improving the Young's modulus of the positive electrode material. Preferably, G is selected from at least one of Ta, Nb, Hf, Zr, and Ti.

[0093] According to the present invention, the amounts of the nickel-cobalt-manganese precursor, the lithium source and the additive containing the G element are such that 1≤n(Li) / [n(Ni)+n(Co)+n(Mn)]≤1.2; 0<n(G) / [n(Ni)+n(Co)+n(Mn)]≤0.05.

[0094] Furthermore, the amounts of the nickel-cobalt-manganese precursor, the lithium source and the additive containing the G element are such that 1≤n(Li) / [n(Ni)+n(Co)+n(Mn)]≤1.1; 0<n(G) / [n(Ni)+n(Co)+n(Mn)]≤0.03.

[0095] In the present invention, the nickel-cobalt-manganese precursor is selected from nickel-cobalt-manganese oxide and / or nickel-cobalt-manganese hydroxide.

[0096] In the present invention, there is no particular limitation on the type of lithium source, and conventional lithium sources in the art, such as lithium carbonate and / or lithium hydroxide, may be used.

[0097] According to the present invention, the M element is selected from at least one of B, Nb, Co, Mo, W, Si, Mg and Al.

[0098] In one embodiment of the present invention, the M element is different from the G element.

[0099] In a specific embodiment of the present invention, the M element is selected from at least one of Al, W, B, and Mg.

[0100] In the present invention, there is no particular limitation on the type of the coating agent, as long as it can provide the M element, such as oxides, hydroxides or carbonates containing the M element.

[0101] According to the present invention, the dosage of the single crystal positive electrode material process product II and the coating agent containing the M element is such that: 0<n(M) / [n(Ni)+n(Co)+n(Mn)]≤0.05.

[0102] Furthermore, the dosage of the single crystal positive electrode material process product II and the coating agent containing the M element is such that: 0<n(M) / [n(Ni)+n(Co)+n(Mn)]≤0.03.

[0103] According to the present invention, the second sintering conditions include: a sintering temperature of 300-800° C. and a sintering time of 4-12 hours.

[0104] Furthermore, the second sintering conditions include: a sintering temperature of 400-750° C. and a sintering time of 6-10 hours.

[0105] In the present invention, the oxygen-containing atmosphere is oxygen and / or air.

[0106] In the present invention, there is no special requirement for the equipment used for crushing, and it can be any conventional equipment in the art that can achieve crushing, such as one or more of a soybean milk machine, a jaw crusher, a roller crusher, a colloid mill, a mechanical mill, and a jet mill.

[0107] In the present invention, the method further comprises crushing and screening the product after the second sintering.

[0108] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the above-mentioned single crystal positive electrode material.

[0109] The present invention will be described in detail below through examples. In the following examples, the raw materials of the examples and comparative examples are all commercially available products.

[0110] Example 1

[0111] 1) Preparation of cathode material process products: nickel cobalt manganese hydroxide precursor (Ni 0.6 Co 0.2 Mn 0.2 )(OH)2 is mixed evenly with lithium carbonate and additive ZrO2 in a ratio of [n(Ni)+n(Co)+n(Mn)]:n(Li):n(Zr)=1:1.04:0.002 using a high-speed mixer; the mixture is then sintered in an oxygen atmosphere, and the sintering process is as follows: heating to 970°C, keeping the temperature constant for 10 hours, and then cooling, wherein the time t1 from 400°C to 970°C is 6 hours, and the time from 970°C to 400°C is 8 hours; after sintering, the sintered material is crushed by a jet mill to obtain a positive electrode material process product;

[0112] 2) Preparation of finished cathode material: The cathode material obtained by the above method and the coating agent WO3 are mixed uniformly in a high-speed mixer according to the ratio of [n(Ni)+n(Co)+n(Mn)]:n(M)=1:0.01; the mixture is then sintered in an air atmosphere, and the sintering process is as follows: heating to 500℃ and keeping the temperature constant for 8h; the sintered material is crushed by a colloidal mill to obtain the finished cathode material, and its D 50 It is 3.8μm.

[0113] Example 2

[0114] Except that the sintering temperature in step 1) is adjusted to 940° C., the other process parameters are exactly the same as those in Example 1, as shown in Table 2.

[0115] Example 3

[0116] Except for step 1), the precursor composition is adjusted to (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2, the lithium source is adjusted to lithium hydroxide and the addition amount is: [n(Ni)+n(Co)+n(Mn)]:n(Li):n(Zr)=1:1.03:0.002, and the sintering temperature is adjusted to 890℃;

[0117] In step 2), WO3 is replaced by Co(OH)2 and the sintering temperature is increased to 700°C. The other process parameters are exactly the same as those in Example 1. See Table 2 for details.

[0118] Example 4

[0119] Except that the ratio of the cathode material in-process product and the coating agent WO3 in step 2) is adjusted to [n(Ni)+n(Co)+n(Mn)]:n(M)=1:0.04, the other process parameters are exactly the same as those in Example 1, as shown in Table 2.

[0120] Example 5

[0121] Except that the sintering temperature in step 1) is adjusted to 1050° C., the other process parameters are exactly the same as those in Example 1, as shown in Table 2.

[0122] Example 6

[0123] Except that in step 2), the cathode material process product and the coating agent were uniformly mixed in a high-speed mixer at a ratio of [n(Ni)+n(Co)+n(Mn)]:n(M)=1:0.0005; the other process parameters were exactly the same as those in Example 1, as shown in Table 2.

[0124] Example 7

[0125] Except that the additive in step 1) is replaced with TiO2 and the mixture is uniformly mixed in a high-speed mixer in a ratio of [n(Ni)+n(Co)+n(Mn)]:n(Li):n(Ti)=1:1.04:0.002; the remaining process parameters are exactly the same as those in Example 1, as shown in Table 2.

[0126] Example 8

[0127] In step 1), the additives are replaced with Y2O3 and Al2O3 and mixed uniformly in a high-speed mixer according to the ratio of [n(Ni)+n(Co)+n(Mn)]:n(Li):n(Y):n(Al)=1:1.04:0.001:0.001. The sintering temperature is 960°C, t1 is 5h, and t2 is 7h.

[0128] In step 2), the coating agent was replaced with B2O3 and mixed evenly in a high-speed mixer at a ratio of [n(Ni)+n(Co)+n(Mn)]:n(M)=1:0.005; the sintering temperature was 350°C, and the other process parameters were shown in Table 2.

[0129] Example 9

[0130] In step 1), the additive is replaced with Al2O3 and mixed uniformly in a high-speed mixer according to the ratio of [n(Ni)+n(Co)+n(Mn)]:n(Li):n(Al)=1:1.04:0.002. The sintering temperature is 940°C, t1 is 5h, and t2 is 9h.

[0131] In step 2), the coating agent was replaced with B2O3 and WO3 and mixed evenly in a high-speed mixer at a ratio of [n(Ni)+n(Co)+n(Mn)]:n(B):n(W)=1:0.001:0.001; the sintering temperature was 400°C, and the other process parameters were shown in Table 2.

[0132] Comparative Example 1

[0133] In addition to step 1) increasing the crushing strength during the crushing process, the particle distribution B is obtained. 90 The remaining process parameters are exactly the same as those in Example 1, as shown in Table 2.

[0134] Comparative Example 2

[0135] Except that the time t2 for cooling to 400° C. in step 1) is 4 h, the other process parameters are exactly the same as those in Example 1, as shown in Table 2.

[0136] Table 1

[0137] Table 2

[0138] Table 2 continued

[0139] Table 2 continued

[0140] Test and equipment:

[0141] ① Particle size D 10 、D 50 、D' 10 : Measured by Marvern's Hydro 2000mu laser particle size analyzer;

[0142] ② Compaction density (hereinafter referred to as PD): obtained by testing with the BT-30 compaction density tester of Baxter Company;

[0143] Pressure test: Carver compaction density test is performed. The test method is as follows: First, accurately weigh 3g of sample and place it in the compaction mold, cover it with the upper anvil and plunger. Then, slowly pressurize to 7.5t, pressurize for 10 minutes, maintain constant pressure for 30 seconds, and test the sample D' after compression. 10 ;

[0144] ③Electron microscopy test: obtained by scanning electron microscope S-4800 model of Hitachi HITACHI Company of Japan;

[0145] The projected area of ​​each single crystal particle in the electron microscope is counted with the help of measurement software, and then its particle size is calculated. The specific method is as follows: the average diameter is calculated by converting the projected area of ​​500 random particles in the scanning electron microscope image into a standard circle of equal area, that is, the particle size P of the single crystal positive electrode material; the diameter data of the above 500 particles are statistically calculated to obtain the particle size P corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 10%. 10 The particle size P corresponding to the cumulative single crystal particle size distribution percentage of the sample reaching 50% 50 The particle size P corresponding to the cumulative single crystal particle size distribution percentage of the sample reaches 90% 90 , the size distribution of single crystal particles B 90 =(P 90 -P 10 ) / P 50 500 particles were randomly selected, which can be obtained by cumulative selection in multiple scanning electron microscope fields.

[0146] The total projected area of ​​100 single crystal particles and the total projected area of ​​the coatings on their surfaces were counted using measurement software, and the coverage ratio was calculated as X = total area of ​​coatings on the surface of single crystal particles / total area of ​​single crystal particles;

[0147] The cracks in the cross section of the cathode material were observed by SEM images of the cross section.

[0148] ④ Young's modulus: obtained by observation with a Bruker atomic force microscope and testing with Keysight's Agilent Nano Indenter G200. Ten particles are randomly selected from each batch of samples and the average value is taken as the Young's modulus E of the material.

[0149] ⑤ Residual stress: measured by Rigaku Smartlab 9KW rotating target diffractometer and calculated by XRD refinement;

[0150] ⑥Battery preparation and electrical performance testing:

[0151] In the above embodiments and comparative examples, the electrochemical performance of the positive electrode material was tested using a CR2025 button cell, and the preparation process thereof was as follows:

[0152] Pole sheet preparation: The positive electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) were mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 95:3:2 to form a uniform electrode slurry (whose solid content at 25°C was 60%). The slurry was coated on aluminum foil and dried at 120°C for 12 hours. It was then stamped using a pressure of 100 MPa to form a positive electrode sheet with a diameter of 15.8 mm and a thickness of 3.2 mm. The positive electrode material loading was 15.5 mg / cm 2 In an argon-filled glove box with water and oxygen contents less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into a CR2025 button cell and left to stand for 6 hours. The negative electrode used a 15.8 mm diameter, 1 mm thick lithium metal sheet; the separator used a 25 μm thick polypropylene microporous membrane (Celgard 2325); and the electrolyte used a 1 mol / L mixture of equal parts LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0153] Capacity Testing: Electrochemical performance testing of CR2025 button cells was conducted using a Shenzhen Xinweier battery testing system. The charge and discharge current density at 0.1C was 100 mA / g. The charge and discharge voltage range was controlled between 3.0 and 4.45 V. At room temperature, the button cells were charged and discharged at 0.1C to evaluate the specific charge and discharge capacity of the positive electrode material. Example 3, a high-nickel material, was tested between 3.0 and 4.35 V.

[0154] High-temperature cycle performance test: In both the examples and comparative examples, the charge and discharge voltage range was controlled to be 3.0-4.45V. At a constant temperature of 60°C, the button battery was charged and discharged twice at 0.1C, and then charged and discharged 80 times at 1C to evaluate the high-temperature cycle capacity retention rate of the positive electrode material.

[0155] Impedance test: Before the battery is fully charged and tested at 50% SOC, this is the initial impedance. After the battery has completed the high-temperature cycle test, it is fully charged and tested again at 50% SOC, this is the final impedance. The impedance growth rate is (%) = (final impedance - initial impedance) / initial impedance × 100%.

[0156] Table 3

[0157] Table 3 continued

[0158] As can be seen from Table 3, the single crystal cathode material provided by the present invention has a specific particle size distribution B 90 and a high Young's modulus, resulting in a button-type battery with high capacity, excellent high-temperature cycle retention, and low impedance performance. Specifically, by regulating the conditions of the first sintering, the method provided by the present invention can eliminate residual stress within the single crystal particles, thereby improving the particle strength of the positive electrode material.

[0159] In the single crystal positive electrode material provided in Comparative Example 2, since the cooling rate of the first sintering during the preparation process is too fast, not only can the existing internal stress not be eliminated, but the sudden cooling during the cooling process will also cause new stress and strain, which ultimately leads to excessively high residual stress inside the particles and low Young's modulus, that is, reduced hardness; during the battery manufacturing and cycling process, the sharp corners on the surface of the particles are easily broken during the rolling process, and cracks are more likely to occur inside the particles, resulting in poor cycle performance and a significant increase in impedance after the cycle.

[0160] Comparative Example 1 is based on Example 1, and the particle size distribution B is adjusted by adjusting the crushing strength after the first sintering. 90 , when the particle size is the same, B 90 A small value indicates that the gradation of the material particles is poor, so its compaction density is low; the crushing strength is high during the preparation process, and the surface / interior of the particles will be damaged, so the residual stress is large and the particle strength is low; at the same time, a large crushing strength will inevitably bring fine powder / micro powder, resulting in a decrease in its high-temperature cycle retention rate and an increase in impedance.

[0161] Furthermore, the change value of the particle size D10 of the positive electrode material before and after the pressure test △D 10 =D 10 -D' 10 It was found that the particles of the positive electrode material would break after the pressure test, resulting in the D' 10 The value will also be higher than the previous D 10 The smaller the hardness of the material, the easier it is to break. 10 Compared with the embodiment, the Young's modulus of the comparative example is smaller and its particles are easier to crush, so △D 10 The value changes are also large.

[0162] Figure 1 is an SEM image of the single crystal positive electrode material of Example 1. The raised islands on its surface are coating agent particles, which can improve the compaction density of the positive electrode material, and at the same time share the force exerted on the material particles, thereby increasing their particle strength. Figure 2 is an SEM image of the single crystal positive electrode material of Example 6. Due to the small amount of coating agent added, there are almost no coating agent particles on its surface. Accordingly, the compaction density of Example 6 is low and the particle strength is also poor.

[0163] Figures 3, 4 and 5 are electron microscope images of the positive electrode materials of Example 1, Comparative Example 1 and Comparative Example 2 after pressure testing, respectively. It can be seen from the figures that the positive electrode material particles of Example 1 have almost no cracks in the individual particles after the pressure test, while Comparative Examples 1 and 2 have cracks to varying degrees, which is consistent with the Young's modulus test law, confirming that the material particles have low strength.

[0164] In Example 2, the size of the single crystal particles is slightly smaller, and the ion transmission distance is shorter, resulting in a slight increase in the battery capacity.

[0165] In Example 3, the Ni content is relatively high, and under the same test system, the battery capacity is higher than that of the examples with lower Ni content.

[0166] In Example 5, due to the high temperature, the particle size exceeds the upper limit. The ultra-high temperature and large particle size will reduce the particle strength of the material and make it more easily broken, so the Young's modulus test value is low; at the same time, its particle size is large, and the lithium ion transmission capacity will be reduced, so the electrical performance data such as capacity and impedance are also poor.

[0167] Compared with Example 1, the amount of additive added in Example 4 is larger, resulting in a relatively high coating rate. A large amount of coating agent gives it a larger particle strength (Young's modulus value), but the number of interfaces through which electrons are transmitted will also increase, so the initial impedance value and growth rate are both increased.

[0168] 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 single-crystal cathode material, characterized in that, The size distribution B of the single crystal particles of the single crystal cathode material 90 =(P 90 -P 10 ) / P 50 satisfies: 0.9 ≤ B 90 ≤ 1.4; Among them, P 10 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of 10% in the SEM image of the positive electrode material; P 50 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of 50% in the SEM image of the positive electrode material; P 90 is the particle size corresponding to the cumulative single crystal particle size distribution percentage of 90% in the SEM image of the positive electrode material; The Young's modulus E of the positive electrode material measured by an atomic force microscope satisfies: 100 GPa ≤ E ≤ 200 GPa.

2. The single crystal cathode material according to claim 1, wherein, 1≤B 90 ≤1.3； Preferably, 120 GPa ≤ E ≤ 200 GPa; Preferably, 1 μm ≤ P 50 ≤ 2 μm, preferably, 1.3 μm ≤ P 50 ≤ 1.7 μm.

3. The single crystal cathode material according to claim 1 or 2, wherein The coating rate X of the positive electrode material measured by SEM satisfies: 5% ≤ X, preferably, 5% ≤ X ≤ 30%; Preferably, the residual stress of the positive electrode material measured by XRD is 0 - 0.2%; Preferably, the median particle size D of the positive electrode material measured by a particle size analyzer 50 satisfies: 2 μm ≤ D 50 ≤ 6 μm; Preferably, after the pressure treatment at 400 MPa, the particle size change rate △D of the positive electrode material measured by a particle size analyzer 10 = D 10 - D' 10 satisfies: △D 10 ≤ 0.2 μm; where D 10 is the particle size before the pressure treatment, and D' 10 is the particle size after the pressure treatment; Preferably, the tap density of the positive electrode material is 3.3-3.7 g / cm 3 .

4. The single-crystalline cathode material according to any one of claims 1 to 3, wherein, The single crystal cathode material has a composition shown in Formula I: Li 1+a (Ni x Mn y Co z G b )M c O2 Formula I; Wherein, 0 ≤ a ≤ 0.2, 0 < b ≤ 0.05, 0 < c ≤ 0.05, 0.4 ≤ x < 1, 0 < y < 0.5, 0 ≤ z < 0.5; M is selected from at least one of B, Nb, Co, Mo, W, Si, Mg, and Al; G is selected from at least one of Ta, Nb, Hf, Zr, Ti, Al, W, Y, Sb, Sr, and Si.

5. A method for preparing the single-crystal cathode material according to any one of claims 1-4, characterized in that, The method includes the following steps: S1. Mix a nickel-cobalt-manganese precursor, a lithium source, and optionally an additive containing element G to obtain mixture I; S2. In the presence of an oxygen-containing atmosphere, after the first sintering of mixture I, it is crushed to obtain the process product II of the single-crystal positive electrode material; S3. Mix the process product II of the single-crystal positive electrode material with an optional coating agent containing element M to obtain mixture III; S4. In the presence of an oxygen-containing atmosphere, perform the second sintering on mixture III to obtain the single-crystal positive electrode material; Among them, the fragmentation results in the size distribution B of the single crystal particles of the single crystal cathode material 90 =(P 90 -P 10 ) / P 50 satisfies: 0.9 ≤ B 90 ≤ 1.4; Among them, P 10 is the particle size corresponding to the cumulative single-crystal particle size distribution percentage of the sample reaching 10% in the SEM image of the positive electrode material; P 50 is the particle size corresponding to the cumulative single-crystal particle size distribution percentage of the sample reaching 50% in the SEM image of the positive electrode material; P 90 is the particle size corresponding to the cumulative single-crystal particle size distribution percentage of the sample reaching 90% in the SEM image of the positive electrode material; The first sintering includes: the sintering temperature is T / °C, the time for the heating section from 400 °C to T is t1 / h, and the time for the cooling section from T to 400 °C is t2 / h, wherein, t2 satisfies [ln(T - 400)] / t2 ≤ 1.

6. The method according to claim 5, wherein, 0 < t1 / t2 ≤ 1; And / or, 800 °C ≤ T ≤ 1000 °C.

7. The method according to claim 5 or 6, wherein In step S1, the additive containing element G is selected from at least one of an oxide of G, a hydroxide of G, and a carbonate of G; Preferably, element G is selected from at least one of Ta, Nb, Hf, Zr, Ti, Al, W, Y, Sb, Sr, and Si; Preferably, G satisfies E G-O ≥500 kJ / mol, where E G-O is the bond energy of the G-O bond; Preferably, the dosages of the nickel-cobalt-manganese precursor, the lithium source, and the additive containing element G are such that 1 ≤ n(Li) / [n(Ni) + n(Co) + n(Mn)] ≤ 1.2; 0 ≤ n(G) / [n(Ni) + n(Co) + n(Mn)] ≤ 0.

05.

8. The method according to any one of claims 5-7, wherein Element M is selected from at least one of B, Nb, Co, Mo, W, Si, Mg, and Al; Preferably, the dosages of the process product II of the single-crystal positive electrode material and the coating agent containing element M are such that: 0 ≤ n(M) / [n(Ni) + n(Co) + n(Mn)] ≤ 0.

05.

9. The method according to any one of claims 5-8, wherein, The conditions for the second sintering include: the sintering temperature is 300 - 800 °C, and the sintering time is 4 - 12 h.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the single-crystal positive electrode material according to any one of claims 1 - 4.

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