Positive electrode material, preparation method and application thereof, positive electrode sheet of lithium-ion battery and lithium-ion battery

Abstract

The present invention relates to the technical field of secondary batteries, and discloses a positive electrode material, a preparation method and application thereof, a positive electrode sheet for a lithium ion battery, and a lithium ion battery. The positive electrode material comprises polycrystalline particles A and single crystal particles or quasi-single crystal particles B; the particle size D5, D6 of the positive electrode material is as follows: 50 and D 95 Satisfy the relationship shown in formula I: 1.5≤K95=(D 95 ‑D5) / D 50 ≤2.5 formula I. The positive electrode material comprises polycrystalline particles A and single crystal particles or quasi-single crystal particles B, thereby significantly suppressing the generation of microcracks in the positive electrode material and improving the particle strength of the positive electrode material, so that the positive electrode material has a high compaction density and high compressive strength, ensuring that the battery comprising the positive electrode material has a high volume energy density and a long cycle life.

Description

Technical Field

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

[0002] With the rapid development of the electric vehicle industry, high energy density and long life lithium-ion battery cathode materials have received great attention. Layered ternary materials (NCM) have high capacity and great development potential. However, as the nickel content in NCM increases, the stability of the material gradually decreases. The highly active Ni generated during the charging process 4+ The reaction with the electrolyte will generate a NiO rock salt phase, which seriously damages the structure of the layered material and causes the collapse of the positive electrode structure, thereby inducing the dissolution of transition metal ions, phase transformation and lattice oxygen precipitation. At present, the "secondary particles" of conventional polycrystalline NCM are usually composed of many nanometer-scale "primary particles". During the charge and discharge process, the lattice parameters change, which will lead to the formation of microcracks. The formed microcracks will expose the fresh interface inside the particles, further accelerating the structural decay. It is worth noting that the higher the nickel content, the more obvious the destructive effect of the cracks. In summary, the main reason for the decrease in the cycle life of NCM, especially high-nickel NCM, is microcracks. The cracks will cause the thermal stability, structural stability and cycle stability of the positive electrode material to decrease simultaneously.

[0003] To address the serious microcracks that occur in high-nickel NCM materials during cycling, common solutions focus on improving the material's doping and coating processes. However, these two processes have limited effectiveness in improving individual polycrystalline particles, especially for polycrystalline materials with a narrow particle distribution. Therefore, the development of a new polycrystalline material and its corresponding process is needed.

[0004] CN103811744A discloses a method for preparing a ternary positive electrode material for a lithium-ion battery: first, agglomerate material A is prepared from a lithium source and a precursor, and then a single crystal or quasi-single crystal material B is prepared from the lithium source and the precursor. The agglomerate material A and the single crystal or quasi-single crystal material B are then mixed and sintered to form material C. A coating is then wrapped around the powder of material C to obtain a lithium-ion ternary positive electrode material. By grading agglomerates and single crystals or quasi-single crystal ternary materials of different particle sizes and morphologies, single crystal particles can be effectively filled between the particles of the agglomerates, allowing the graded materials to fully contact the conductive agent and binder. At the same time, the spatial utilization rate and compaction density of the material can be improved, thereby increasing the volumetric energy density of the material, which is conducive to the full utilization of the material's electrical properties, while improving the thermal stability of the material and improving the safety of the battery. However, this process is complex and costly, making it unfavorable for actual production.

[0005] CN109524642A discloses a method for preparing a mixed ternary cathode material: 1) mixing ternary material precursor A, ternary material precursor B, and a lithium source to obtain an initial mixture; 2) subjecting the initial mixture to a first sintering, crushing, and then subjecting the mixture to a second sintering to obtain a mixed ternary cathode material; the temperature of the first sintering is 350-550°C, and the temperature of the second sintering is 750-1150°C. The result is a differentiated mixed ternary cathode material with coexisting secondary particle agglomerates and single crystal / single crystal-like morphologies, thereby improving the material's compaction density and cycle performance while reducing preparation costs. It is well known that sintering after adding a lithium source is crucial to the material. Precursors with different Ni contents require different ratios, sintering temperatures, and sintering times to achieve optimal sintering conditions. However, the prior art sinters two precursors with different Ni contents in a unified manner, failing to achieve optimal performance for the cathode material sintered from the two precursors with different Ni contents.

[0006] CN110970602A discloses a positive electrode active material, which mixes low-nickel single crystal material with high-nickel polycrystalline material as the positive electrode active material. The capacity of the final material will be greatly reduced compared to the high-nickel polycrystalline material, making it difficult to truly bring out the advantages of the high-nickel material. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems of reduced stability and capacity of high-nickel positive electrode materials in the prior art due to the presence of microcracks, and to provide a positive electrode material and its preparation method and application, a lithium-ion positive electrode material pole piece, and a lithium-ion battery. The positive electrode material comprises polycrystalline particles A and single crystal particles or quasi-single crystal particles B, thereby significantly inhibiting the generation of microcracks in the positive electrode material and improving the particle strength of the positive electrode material, so that the positive electrode material has a high compaction density and high compressive strength, ensuring that the battery containing the positive electrode material has a high volume energy density and a long cycle life.

[0008] In order to achieve the above object, the present invention provides a positive electrode material in a first aspect, characterized in that the positive electrode material comprises polycrystalline particles A and single crystal particles or quasi-single crystal particles B;

[0009] The particle sizes D5 and D 50 and D 95 Satisfies the relationship shown in formula I:

[0010] 1.5≤K95=(D 95 -D5) / D 50 ≤2.5 Formula I.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned positive electrode material, characterized in that the method comprises the following steps:

[0012] (1) The transition metal precursor Ni x1 Co y1 Mn z1 (OH)2, lithium salt and optional additives are mixed and first sintered to obtain a first sintered material;

[0013] (2) mixing the first sintering material and optional conductive graphite and / or conductive polymer, and performing a second sintering to obtain polycrystalline particles A;

[0014] (3) The transition metal precursor Ni x2 Co y2 Mn z2 (OH)2, lithium salt and optional additives are mixed and sintered for a third time to obtain single crystal particles or single crystal-like particles B;

[0015] (4) mixing the polycrystalline particles A with the single crystal particles or the quasi-single crystal particles B to obtain the positive electrode material;

[0016] x1+y1+z1=1,0.5≤x1≤1,0≤y1≤0.5,0≤z1≤0.5;

[0017] x2+y2+z2=1, 0.5≤x2≤1, 0≤y2≤0.5, 0≤z2≤0.5, -0.05≤x1-x2≤0.05.

[0018] A third aspect of the present invention provides a use of the above-mentioned positive electrode material in a lithium-ion battery.

[0019] A fourth aspect of the present invention provides a lithium-ion battery positive electrode plate, characterized in that the lithium-ion battery positive electrode plate is made of the above-mentioned positive electrode material.

[0020] A fifth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned lithium-ion battery positive electrode sheet.

[0021] Through the above technical solution, the positive electrode material and its preparation method and application, lithium ion battery positive electrode sheet, and lithium ion battery provided by the present invention achieve the following beneficial effects:

[0022] (1) In the present invention, the positive electrode material includes polycrystalline particles A and single crystal particles or quasi-single crystal particles B, thereby significantly inhibiting the generation of microcracks in the positive electrode material and improving the particle strength of the positive electrode material. Specifically, the polycrystalline particles A can inhibit the generation of microcracks, while the single crystal particles or quasi-single crystal particles can effectively limit the cracking of the particles A, ultimately making the positive electrode material have a high compaction density and high compressive strength, ensuring that the battery containing the positive electrode material has a high volume energy density and a long cycle life.

[0023] (2) Furthermore, in the present invention, the positive electrode material comprises polycrystalline particles A having relatively high particle strength. Furthermore, the polycrystalline particles A comprise a coating layer, which enables the polycrystalline particles A to have a certain elasticity, thereby reducing the proportion of the positive electrode material obtained thereby being crushed during the electrode sheet rolling process, and the squeezing of the current collector is relatively small. On the other hand, the high-strength positive electrode particles can also inhibit the generation of microcracks in the material during the charge and discharge process.

[0024] (3) Furthermore, in the present invention, by separately preparing polycrystalline particles A and single crystal or quasi-single crystal particles B, the two materials can achieve optimal performance respectively, and the polycrystalline particles A are blended with single crystal or quasi-single crystal particles B with similar Ni content. This can significantly improve the safety performance and cycle performance of the positive electrode material while maintaining the high charge and discharge capacity of the high-nickel polycrystalline particles A. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an SEM image of the positive electrode material of Example 1 of the present invention.

[0026] Figure 2 This is a mapping diagram of the C element distribution of the positive electrode material of Example 1 of the present invention.

[0027] Figure 3 This is the rupture pressure-deformation curve of the positive electrode material particles in Example 1 of the present invention under a micro-mechanical testing machine.

[0028] Figure 4 The positive electrode material prepared in Example 1 and the sample of Comparative Example 1 were used to make cycle curves of soft-pack batteries.

[0029] Figure 5 This is a cross-sectional view of the battery electrode prepared in Example 1 after rolling. DETAILED DESCRIPTION

[0030] 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.

[0031] A first aspect of the present invention provides a positive electrode material, characterized in that the positive electrode material comprises polycrystalline particles A and single crystal particles or quasi-single crystal particles B;

[0032] The particle sizes D5 and D 50 and D 95 Satisfies the relationship shown in formula I:

[0033] 1.5≤K95=(D 95 -D5) / D 50 ≤2.5 Formula I.

[0034] In the present invention, the positive electrode material includes polycrystalline particles A and single crystal particles or single crystal-like particles B, and the particle sizes D5 and D 50 and D 95 When the above relationship is met, the generation of microcracks in the positive electrode material can be significantly suppressed and the particle strength of the positive electrode material can be improved. Specifically, the polycrystalline particles A can suppress the generation of microcracks, while the single crystal particles or quasi-single crystal particles can effectively limit the cracking of the particles A, ultimately making the positive electrode material have a high compaction density and high compressive strength, ensuring that the battery containing the positive electrode material has a high volume energy density and a long cycle life.

[0035] In the present invention, the particle size D5 and D 50 and D 95 Measured using a laser particle size analyzer.

[0036] According to the present invention, 1.5≤K95≤2.

[0037] According to the present invention, the particle size D of the polycrystalline particles A is 50 7-22μm.

[0038] Furthermore, the particle size D of the polycrystalline particles A 50 11-20μm.

[0039] According to the present invention, the particle sizes D5 and D 50 and D 95 Satisfies the relationship shown in formula II:

[0040] 0 <K A 95=(D95 -D5) / D 50 ≤1Formula II.

[0041] In the present invention, when the particle sizes D5 and D 50 and D 95 When the above relationship is met, the positive electrode material particles can have excellent consistency and uniformity, so that the positive electrode material particles can have a controllable degree of shrinkage and expansion during long-term use, and the crystal structure of the material surface is more stable, and the long-term cycle performance is better.

[0042] Furthermore, 0.55 <K A 95=(D 95 -D5) / D 50 ≤0.95.

[0043] According to the present invention, the particle size D of the single crystal particles or quasi-single crystal particles B is 50 0.2-7μm.

[0044] Furthermore, the particle size D of the single crystal particles or quasi-single crystal particles B is 50 2-5μm.

[0045] According to the present invention, the particle sizes D5 and D 50 and D 95 Satisfies the relationship shown in formula III:

[0046] 0.2≤K B 95=(D 95 -D5) / D 50 ≤3Formula III.

[0047] Furthermore, 1.5≤K B 95=(D 95 -D5) / D 50 ≤2.5.

[0048] According to the present invention, the positive electrode material has a composition shown in formula (1):

[0049] [Li 1+a (Ni x Co y Mn z M 1-x-y-z )N k O 2-w J w ](1);

[0050] In formula (1), 0≤a≤0.3, 0<x≤1, 0≤y≤1, 0≤z≤1, 0≤k≤0.1, 0≤w≤0.1; M is selected from at least one of B, Na, K, Mg, Al, Ca, Ti, Fe, Zn, Sr, Y, Zr, Nb, Mo, Sn, Ba, Ta, and W;

[0051] N is selected from at least one of B, Mg, Al, Ti, V, Sr, Y, Zr, Nb, Mo, and W;

[0052] J is at least one of F, Cl, and P.

[0053] According to the present invention, the surface of the polycrystalline particle A is coated with a coating layer P.

[0054] In the present invention, the surface of the polycrystalline particle A is coated with a coating layer P, whereby the polycrystalline particle A can have a certain elasticity, thereby reducing the proportion of the cathode material crushed during the preparation of the cathode electrode sheet, and can reduce the extrusion of the current collector and inhibit the generation of microcracks in the cathode material during charge and discharge.

[0055] According to the present invention, based on the total weight of the polycrystalline particle A, the mass ratio of the polycrystalline particle A to the coating layer is 1:0 - 0.05.

[0056] Further, based on the total weight of the polycrystalline particle A, the mass ratio of the polycrystalline particle A to the coating layer is 1:0.001 - 0.02.

[0057] According to the present invention, the coating layer P is provided by conductive graphite and / or a conductive polymer.

[0058] According to the present invention, the conductive polymer is selected from at least one of polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene sulfide, poly(3,4-ethylenedioxythiophene), and polyphenylacetylene.

[0059] In the present invention, the polycrystalline particle A has the composition shown in formula (2):

[0060] [Li 1+a1 (Ni x1 Co y1 Mn z1 M’ 1-x1-y1-z1 )N’ k1 O 2-w1 J’ w1 (2);

[0061] In formula (1), 0≤a1≤0.3, 0<x1≤1, 0≤y1≤1, 0≤z1≤1, 0≤k1≤0.1, 0≤w1≤0.1; M’ is selected from at least one of B, Na, K, Mg, Al, Ca, Ti, Fe, Zn, Sr, Y, Zr, Nb, Mo, Sn, Ba, Ta, and W;

[0062] N’ is selected from at least one of B, Mg, Al, Ti, V, Sr, Y, Zr, Nb, Mo, and W;

[0063] J’ is at least one of F, Cl, and P.

[0064] In the present invention, the single crystal particles or quasi-single crystal particles B have the composition shown in formula (3):

[0065] [Li 1+a2 (Ni x2 Co y2 Mn z2 M” 1-x2-y2-z2 )N” k2 O 2-w2 J” w2 (3); ​​​​​​​​​​​​​​​​​​​​​​ Figure 4 As shown in the figure, under low pressure, the particle's deformation initially shows a slow change. This change represents the strength of polycrystalline particle A. The greater the strength, the longer the slowly growing displacement diameter. As pressure increases, the particle cracks, and its deformation rapidly increases, showing a linear change. This change is significantly influenced by the internal crystalline structure of the initial polycrystalline particle A. In other words, under pressure, the slower the growth of the polycrystalline particle's displacement diameter before the linear change, and the greater the deformation before rupture, indicating a higher particle strength.

[0073] In the present invention, in the micro-mechanical testing machine test, the single particle strength of the polycrystalline particle A is 50-200 MPa; the deformation of the polycrystalline particle A before fracture is D 50 ×(10-25%).

[0074] According to the present invention, under the pressure of 20kN, the powder compaction density of the positive electrode material is ≥3.5g / cm 3 .

[0075] Furthermore, under a pressure of 20 kN, the powder compaction density of the positive electrode material is 3.5-4.5 g / cm 3 .

[0076] According to the present invention, the specific surface area of ​​the positive electrode material is A1, and after being fractured at a pressure of 4.5 T, the specific surface area of ​​the positive electrode material is A2;

[0077] Among them, (A2-A1) / A1×100%≤40%.

[0078] Furthermore, A2-A1) / A1×100% is 5-30%.

[0079] A second aspect of the present invention provides a method for preparing the above-mentioned positive electrode material, characterized in that the method comprises the following steps:

[0080] (1) The transition metal precursor Ni x1 Co y1 Mn z1 (OH)2, lithium salt and optional additives are mixed and first sintered to obtain a first sintered material;

[0081] (2) mixing the first sintering material and optional conductive graphite and / or conductive polymer, and performing a second sintering to obtain polycrystalline particles A;

[0082] (3) The transition metal precursor Ni x2 Co y2 Mn z2 (OH)2, lithium salt and optional additives are mixed and sintered for a third time to obtain single crystal particles or single crystal-like particles B;

[0083] (4) mixing the polycrystalline particles A with the single crystal particles or the quasi-single crystal particles B to obtain the positive electrode material;

[0084] Among them, x1+y1+z1=1, 0.5≤x1≤1, 0≤y1≤0.5, 0≤z1≤0.5;

[0085] x2+y2+z2=1, 0.5≤x2≤1, 0≤y2≤0.5, 0≤z2≤0.5, -0.05≤x1-x2≤0.05.

[0086] In the present invention, polycrystalline particles A and single crystal or quasi-single crystal particles B are prepared separately so that the two materials can achieve optimal performance respectively, and the polycrystalline particles A and the single crystal or quasi-single crystal particles B are blended. This can significantly improve the safety performance and cycle performance of the positive electrode material while maintaining the high charge and discharge capacity of the high-nickel polycrystalline particles A.

[0087] According to the present invention, the additive is at least one selected from the group consisting of lithium compounds, boron compounds, tungsten compounds, neodymium compounds, aluminum compounds, zirconium compounds, magnesium compounds and chlorides.

[0088] In the present invention, the lithium compound is selected from at least one of Li2O, LiOH, Li2CO3, LiCl, LiF, Li3PO4 and LiBO2.

[0089] The boron compound is selected from at least one of B2O3, H3BO3, Na2B4O7 and Li2B4O7.

[0090] The tungsten compound is selected from at least one of WO2, WO3, Na2WO4, Li2W2O7 and Li2WO4.

[0091] The neodymium compound is selected from at least one of Nb2O5, NbO2, Nb2O3 and NbCl5.

[0092] The aluminum compound is selected from at least one of Al2O3, Al(OH)3 and AlOOH.

[0093] The zirconium compound is selected from at least one of ZrO2, Zr(OH)4, and ZrSiO4.

[0094] The magnesium compound is selected from at least one of MgO, MgCl2 and Mg(OH)2.

[0095] The chloride is selected from at least one of NaCl, KCl and BaCl2.

[0096] According to the present invention, in step (1), the transition metal precursor Ni x1 Co y1 Mn z1 The molar ratio of (OH)2, the lithium salt and the additive is 1:0.99-1.1:0-1.

[0097] According to the present invention, the first sintering conditions include: a sintering temperature of 650-850° C. and a sintering time of 15-30 hours.

[0098] Furthermore, the first sintering conditions include: a sintering temperature of 680-800° C. and a sintering time of 16-25 hours.

[0099] According to the present invention, in step (1), the ratio of the sintering heating time tr to the constant temperature time tc satisfies:

[0100] 0.5≤t r / t c ≤2.5 (4).

[0101] In the present invention, when the ratio of the sintering heating time to the holding time falls within the aforementioned range, the reaction process during the synthesis of the material can be effectively controlled, resulting in a more uniform and smooth surface for the primary particles and a denser secondary particle size. This also effectively controls residual alkali on the surface and significantly enhances the strength of the particles. Consequently, over long-term use, the material's cracking is effectively reduced, improving its cyclic performance and safety.

[0102] Furthermore, 0.6≤t r / t c ≤2.

[0103] According to the present invention, the mass ratio of the first sintering material to the graphite and / or the conductive polymer is 1:0-0.05.

[0104] Furthermore, the mass ratio of the first sintering material to the graphite and / or the conductive polymer is 1:0.001-0.02.

[0105] In a specific embodiment of the present invention, the first sintering material, the conductive graphite and the conductive polymer are mixed and then sintered for the second time to obtain polycrystalline particles A.

[0106] Specifically, the mass ratio of the first sintering material, the conductive graphite and the conductive polymer is 1:0.001-0.01:0.001-0.01, preferably 1:0.002-0.008:0.002-0.008.

[0107] According to the present invention, the conditions for the second sintering include: a sintering temperature of 100-500° C. and a sintering time of 4-12 hours.

[0108] Furthermore, the second sintering conditions include: a sintering temperature of 200-400° C. and a sintering time of 6-10 hours.

[0109] According to the present invention, in step (3), the transition metal precursor Ni x2 Co y2 Mn z2 The molar ratio of (OH)2, the lithium salt and the additive is 1:0.99-1.1:0-1.

[0110] According to the present invention, the conditions of the third sintering include: a sintering temperature of 800-1200° C. and a sintering time of 15-30 hours.

[0111] Furthermore, the conditions of the third sintering include: a sintering temperature of 850-1000° C. and a sintering time of 15-25 hours.

[0112] According to the present invention, the mass ratio of the polycrystalline particles A to the single crystal particles or quasi-single crystal particles B is 0.01:9:1, preferably 0.25-4:1.

[0113] A third aspect of the present invention provides a use of the above-mentioned positive electrode material in a lithium-ion battery.

[0114] A fourth aspect of the present invention provides a lithium-ion battery positive electrode plate, characterized in that the lithium-ion battery positive electrode plate is made of the above-mentioned positive electrode material.

[0115] In the present invention, the lithium-ion battery positive electrode sheet can be prepared according to conventional methods in the art. Specifically, the positive electrode material, the conductive agent and the binder are dispersed in an organic solvent, such as NMP, in a mass ratio of 90-98:0-8:0.5-8, stirred evenly and then slurried. The prepared slurry is coated on aluminum foil, dried, cut and rolled to prepare the lithium-ion battery positive electrode sheet.

[0116] In the present invention, when the compaction density of the positive electrode sheet of the lithium ion battery is 3.4-3.6 g / cm 3 When the positive electrode particles are within the specified range, the deformation of the aluminum foil caused by the extrusion of the positive electrode particles on the aluminum foil is less than 30%.

[0117] In the present invention, the deformation of the aluminum foil is measured using a ruler.

[0118] A fifth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned lithium-ion battery positive electrode sheet.

[0119] In the present invention, conventional methods in the art can be used to prepare lithium-ion batteries. Specifically, the positive electrode sheet, negative electrode sheet, and separator of the lithium-ion battery are wound, shelled, injected with liquid, and sealed to form a lithium-ion battery.

[0120] The present invention will be described in detail below by way of examples.

[0121] Polycrystalline particles A, single crystal particles or single crystal particles B and D5, D 50 and D 95 Measured using the following method:

[0122] Use a Mastersizer 2000 laser particle size analyzer for testing. In the "Measurement" section of the software, change the "Sample Test Time" and "Background Test Time" settings to 6 seconds. In the "Measurement Cycles" section, change the number of cycles to 3 and the delay to 5 seconds. Click "Create Average Results from Measurement" to record the average results. Next, click "Start" to automatically measure the background. After the automatic measurement is complete, add 40 ml of sodium pyrophosphate, then use a medicine spoon to add a small amount of sample until the obscuration reaches 1 / 2 of the visual 10-20% area. Click "Start." Finally, record the three results and the average.

[0123] The compaction density of the positive electrode sheet is measured using the following method:

[0124] Use an MCP-PD51 powder resistance meter to perform the test. Take clean, dry aluminum foil, weigh 4g of the sample to be tested, and add it to the assembled mold, ensuring the inner walls are free of material. Gently shake the mold from side to side to level the material inside. Enter the sample weight and batch number into the test software. Then, apply pressure to the material for approximately 15-20 minutes. When the pressure reaches 20 kN, stop applying pressure and maintain it steady for 30 seconds. If the pressure drops, return it to 20 kN. Then, begin testing the sample. After the resistance test is complete, record the thickness. Finally, calculate the compacted density.

[0125] The specific surface area of ​​the positive electrode material is measured according to the following method:

[0126] Use MCP-PD51 powder resistance meter for testing. Take clean and dry aluminum foil, weigh 5g of the sample to be tested, add it to the installed mold, require that the inner wall of the mold is not stained with material, gently shake the mold left and right to make the material inside the mold flat, and enter the sample weight and batch number in the test software. Install the mold on the lifting instrument, apply 0T (ton) (Ref), 1.5T, 2.5T, 3.5T and 4.5T pressure for testing. The pressurization time is controlled at about 15-20min. Stop pressurizing when the pressure reaches the target value, stabilize the pressure for 30s, and then take out the fracturing particles for specific surface area testing;

[0127] Use a Tri-star 3020 surface area analyzer for testing. Weigh 3g of sample and install the sample tube on the vacuum connector on the degassing station. Set the heating temperature to 300℃ and the degassing time to 120min. After degassing, cool the sample tube. Enter the mass of the empty sample tube and the mass of the degassed sample and sample tube in the tester software interface, record the specific surface area data calculated by the software (BET method), and complete the specific surface area test of the positive electrode material sample.

[0128] The particle strength of the positive electrode material is measured using the following method:

[0129] Measurements were performed using an MCT-210 micro compression tester. First, open the MCT-210 testing software and clamp the sample stage to the center of the platen, ensuring it remains at least 3 cm below the objective lens. Turn on the LED light on the main unit and adjust the stage height until the sample particle image is clear in the CCD image display window by turning the handwheel on the lower right. Click "Start Testing," measure the particle diameter, and save the pre-compression image. Rotate the handwheel to bring the particle's apex to the lens's focal point. Push the sample stage right under the platen to begin the compression test. After compression is complete, push the stage left under the objective lens and rotate the handwheel until the compressed image is clear. Save the image.

[0130] The surface morphology of the cathode material and the surface element distribution of the cathode material were measured using SEM;

[0131] Lithium-ion batteries are tested for electrochemical and safety performance according to the national lithium-ion standard GB / T18287-2000.

[0132] Example 1

[0133] (1) Preparation of polycrystalline particles A: The following compounds are calculated according to the molar ratio, wherein the transition metal hydroxide precursor Ni 0.83 Co 0.06 Mn 0.11 The molar ratio of (OH)2:LiOH:LiF:ZrO2 is 1:1.03:0.01:0.005, and after being uniformly mixed, the mixture is sintered at 780°C for 24 hours to obtain a first sintered material; wherein, the heating time is 12 hours and the constant temperature time is 12 hours;

[0134] (2) The first sintering material, artificial graphite and conductive polyaniline were mixed in a mass ratio of 1:0.005:0.005, mixed using a high-speed mixer, and then sintered at 350°C for 10 hours to obtain polycrystalline particles A with a coating layer P on the surface, the composition of which is (Li 1.03 (Ni 0.83 Co 0.06 Mn 0.11 Zr0.005 )O2F 0.01 )0.01P. The particle size D5 and D 50 and D 95 They are 8.5μm, 12.6μm, 18.4μm, K A 95 is 0.78, and the average particle strength is 98MPa when tested by a micro-mechanical testing machine. The particle deformation before crushing is 2.5μm, accounting for the particle D before rupture. 50 19.8% of the total.

[0135] (3) Preparation of single crystal particles or quasi-single crystal particles B: The following compounds are calculated according to the molar ratio: transition metal hydroxide precursor Ni 0.83 Co 0.06 Mn 0.11 The molar ratio of (OH)2:LiOH:ZrO2 is 1:1.01:0.005. After mixing evenly, sintering at 870℃ for 24h obtains Li 1.01 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2 single crystal particles or single crystal-like particles B, wherein the particle size D5, D 50 and D 95 They are 2.6μm, 5.6μm, 11.3μm, K B 95 is 1.55.

[0136] (4) Preparation of positive electrode material: Polycrystalline particles A and single crystal particles or quasi-single crystal particles B are mixed in a mass ratio of 70:30 and mixed in a high-speed mixer to obtain a positive electrode material. The composition of the positive electrode material is (Li 1.024 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2F 0.007 )0.007P. The particle size D5, D 50 and D 95 They are 2.3μm, 10.7μm, and 20.5μm respectively, and K95 is 1.70.

[0137] According to the test, under the pressure of 20kN, the powder compaction density of the cathode material can reach 3.65g / cm 3 The specific surface area A1 of the positive electrode material is 0.56m 2 / g, after 4.5T pressing, the specific surface area A2 of the positive electrode material is 0.68m 2 / g, (A2-A1) / A1×100% is 21%.

[0138] The SEM and C element distribution mapping diagrams of the positive electrode material of Example 1 are as follows: Figure 1 and Figure 2 As shown, from Figure 1 It can be seen that the positive electrode material is composed of polycrystalline particles and single crystal or quasi-single crystal particles, among which a layer of coating material is evenly dispersed on the surface of the large particles. Figure 2 for Figure 1 The mapping diagram of the C element distribution confirms that an elastic coating layer is evenly dispersed on the surface of the large particles.

[0139] The fracture pressure-deformation curve of a single particle in the polycrystalline particle A of Example 1 in the micro-mechanical testing machine test is as follows: Figure 3 As shown by Figure 3 It can be seen that as the pressure increases, the displacement diameter of the particles increases slowly at first, and then increases sharply as the pressure continues to increase, and eventually rupture occurs.

[0140] Example 2

[0141] (1) Preparation of polycrystalline particles A: The following compounds are calculated according to the molar ratio, wherein the transition metal hydroxide precursor Ni 0.83 Co 0.06 Mn 0.11 The molar ratio of (OH)2:LiOH:ZrO2 is 1:1.04:0.005, and after being uniformly mixed, the mixture is sintered at 700°C for 15 hours to obtain a first sintered material; wherein, the heating time is 7 hours and the constant temperature time is 8 hours;

[0142] (2) The first sintering material, artificial graphite and conductive polyaniline were mixed in a mass ratio of 1:0.005:0.005, mixed using a high-speed mixer, and then sintered at 350°C for 10 hours to obtain polycrystalline particles A with a coating layer P on the surface, the composition of which is (Li 1.04 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2)0.01P. The particle size D5 and D 50 and D 95 They are 11.4μm, 16.7μm, 24.5μm, K A 95 is 0.78, and the average particle strength is 95MPa when tested by a micro-mechanical testing machine. The particle deformation before crushing is 3.2μm, accounting for the particle D before rupture. 50 19.2% of the total.

[0143] (3) Preparation of single crystal particles or quasi-single crystal particles B: The following compounds are calculated according to the molar ratio: transition metal hydroxide precursor Ni0.83 Co 0.06 Mn 0.11 The molar ratio of (OH)2:LiOH is 1:1.02. After mixing evenly, sintering at 870℃ for 24h obtains a composition of Li 1.02 (Ni 0.83 Co 0.06 Mn 0.11 )O2 single crystal particles or single crystal-like particles B, wherein the particle size D5, D 50 and D 95 They are 1.8μm, 3.7μm, 7.3μm, K B 95 is 1.48.

[0144] (4) Preparation of positive electrode material: Polycrystalline particles A and single crystal particles or quasi-single crystal particles B are mixed in a mass ratio of 70:30 and mixed in a high-speed mixer to obtain a positive electrode material. The composition of the positive electrode material is (Li 1.034 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.0035 )O2)0.007P. The particle size D5, D 50 and D 95 They are 2.0μm, 13.2μm, and 26.6μm respectively, and K95 is 1.86.

[0145] According to the test, under the pressure of 20kN, the powder compaction density of the cathode material can reach 3.60g / cm 3 ; The specific surface area A1 of the positive electrode material is 0.61m 2 / g, after 4.5T pressing, the specific surface area A2 of the positive electrode material is 0.74m 2 / g, (A2-A1) / A1×100% is 21%.

[0146] Example 3

[0147] (1) Preparation of polycrystalline particles A: The following compounds are calculated according to the molar ratio, wherein the transition metal hydroxide precursor Ni 0.83 Co 0.06 Mn 0.11 (OH)2:LiOH:LiF:ZrO2 with a molar ratio of 1:1.03:0.01:0.005 were mixed evenly and sintered at 780°C for 24 hours to obtain a first sintered material; wherein, the heating time was 12 hours and the constant temperature time was 12 hours;

[0148] (2) The first sintered material and artificial graphite were mixed in a mass ratio of 1:0.01, mixed using a high-speed mixer, and then sintered at 350°C for 10 hours to obtain polycrystalline particles A with a coating layer P on the surface, the composition of which is (Li 1.03 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2F 0.01 )0.01P. The particle size D5 and D 50 and D 95 They are 8.4μm, 12.5μm, 18.3μm, K A 95 is 0.79, and the average particle strength is 89MPa when tested by a micro-mechanical testing machine. The particle deformation before crushing is 2.7μm, accounting for 1.3% of the particle D before crushing. 50 21.6%.

[0149] (3) Single crystal particles or single crystal-like particles B are prepared according to step (3) of Example 1.

[0150] (4) Preparation of positive electrode material: Polycrystalline particles A and single crystal particles or quasi-single crystal particles B are mixed in a mass ratio of 70:30 and mixed in a high-speed mixer to obtain a positive electrode material. The composition of the positive electrode material is (Li 1.024 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2F 0.007 )0.007P. The particle size D5, D 50 and D 95 They are 2.3μm, 10.7μm, and 20.4μm respectively, and K95 is 1.69.

[0151] According to the test, under the pressure of 20kN, the powder compaction density of the cathode material can reach 3.63g / cm 3 The specific surface area A1 of the positive electrode material is 0.58m 2 / g, after 4.5T pressing, the specific surface area A2 of the positive electrode material is 0.71m 2 / g, (A2-A1) / A1×100% is 22%.

[0152] Example 4

[0153] (1) Preparation of polycrystalline particles A: The following compounds are calculated according to the molar ratio, wherein the transition metal hydroxide precursor Ni 0.83 Co 0.06 Mn 0.11(OH)2:LiOH:LiF:ZrO2 is 1:1.03:0.01:0.005, mixed evenly and sintered at 780°C for 24 hours to obtain a first sintered material; wherein, the heating time is 18 hours and the constant temperature time is 9 hours;

[0154] (2) The same as step (2) of Example 1. 1.03 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2F 0.01 )0.01P polycrystalline particles A. The particle size D5, D 50 and D 95 They are 6.2μm, 11.9μm, 17.3μm, K A 95 is 0.93, and the average particle strength is 102MPa when tested by a micro-mechanical testing machine. The particle deformation before crushing is 2μm, accounting for the particle D before rupture. 50 16.8% of.

[0155] (3) The same as step (3) of Example 1.

[0156] (4) Preparation of positive electrode material: Polycrystalline particles A and single crystal particles or quasi-single crystal particles B are mixed in a mass ratio of 80:20 and mixed in a high-speed mixer to obtain a positive electrode material. The composition of the positive electrode material is (Li 1.026 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2F 0.008 )0.008P. The particle size D5, D 50 and D 95 They are 2.6μm, 11.4μm, and 21.2μm respectively, and K95 is 1.63.

[0157] According to the test, under the pressure of 20kN, the powder compaction density of the cathode material can reach 3.70g / cm 3 ; The specific surface area A1 of the positive electrode material is 0.50m 2 / g, after 4.5T pressing, the specific surface area A2 of the positive electrode material is 0.58m 2 / g, (A2-A1) / A1×100% is 16%.

[0158] Example 5

[0159] The positive electrode material was prepared according to the method of Example 1, except that step (2) was not performed, and the first sintered material obtained in step (1) was polycrystalline particles A, whose composition was Li 1.03 (Ni0.83 Co 0.060 Mn 0.11 Zr 0.005 )O2F 0.01 The particle size D5 and D 50 and D 95 They are 9.0μm, 13.1μm, 19μm, K A 95 is 0.76, and the average particle strength is 82MPa when tested by a micro-mechanical testing machine. The particle deformation before crushing is 1.8μm, accounting for the particle D before rupture. 50 13.7%.

[0160] Step (3) and step (4) are carried out according to step (3) and step (4) of Example 1. The final product is composed of (Li 1.024 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.005 )O2F 0.007 )0.007P positive electrode material. The particle size D5, D 50 and D 95 They are 2.5μm, 10.9μm, and 20.5μm respectively, and K95 is 1.65.

[0161] According to the test, under the pressure of 20kN, the powder compaction density of the cathode material can reach 3.55g / cm 3 The specific surface area A1 of the positive electrode material is 0.54. After being pressed at a pressure of 4.5T, the specific surface area A2 of the positive electrode material is 0.71, and (A2-A1) / A1×100% is 30%.

[0162] Comparative Example 1

[0163] The positive electrode material was prepared according to the method of Example 1, except that steps (3) and (4) were not performed. Polycrystalline particles A were used as the positive electrode material. The particle sizes of the polycrystalline particles A were D5, D 50 and D 95 They are 8.5μm, 12.6μm, 18.4μm, K A 95 is 0.78, and the average particle strength is 98MPa when tested by a micro-mechanical testing machine. The particle deformation before crushing is 2.5μm, accounting for the particle D before rupture. 50 19.8% of the total.

[0164] After testing, under the pressure of 20kN, the powder compaction density of the positive electrode material is 3.2g / cm 3 ;

[0165] The specific surface area A1 of the positive electrode material is 0.42. After being pressed at a pressure of 4.5T, the specific surface area A2 of the positive electrode material is 0.68, and (A2-A1) / A1×100% is 62%.

[0166] Comparative Example 2

[0167] (1) Preparation of polycrystalline particles A: The following compounds are calculated according to the molar ratio, wherein the transition metal hydroxide precursor Ni 0.83 Co 0.06 Mn 0.11 The molar ratio of (OH)2:LiOH is 1:1.09, and after being uniformly mixed, the mixture is sintered at 600°C for 10 hours to obtain a first sintered material; wherein, the heating time is 6 hours and the constant temperature time is 4 hours;

[0168] (2) The first sintering material, artificial graphite and conductive polyaniline were mixed in a mass ratio of 1:0.05:0.05, mixed using a high-speed mixer, and then sintered at 200°C for 6 hours to obtain polycrystalline particles A with a coating layer P on the surface, the composition of which is (Li 1.09 Ni 0.83 Co 0.06 Mn 0.11 O2)0.1P. The particle size of polycrystalline particles A is D5, D 50 and D 95 They are 4.5μm, 10.5μm, 21.5μm, K A 95 is 1.6, tested by micro mechanical testing machine, 100MPa, the deformation of the particle before crushing is 1.9μm, accounting for the particle D before rupture 50 18.1%.

[0169] (3) Preparation of single crystal particles or quasi-single crystal particles B: The following compounds are calculated according to the molar ratio: transition metal hydroxide precursor Ni 0.83 Co 0.06 Mn 0.11 The molar ratio of (OH)2: LiOH: ZrO2 is 1:1.02:0.01. After mixing evenly, sintering at 1000℃ for 24h to obtain a composition of Li 1.02 (Ni 0.83 Co 0.06 Mn 0.11 Zr 0.01 )O2 single crystal particles or single crystal-like particles B, wherein the particle size D5, D 50 and D 95 They are 1.8μm, 4.3μm, 11.5μm, K B 95 is 2.25.

[0170] (4) The mixing method is the same as that in Example 1, and the positive electrode material is obtained by mixing with a high-speed mixer. The particle size of the positive electrode material is D5, D 50 and D 95 They are 1.6μm, 9μm, 24.5μm respectively, and K95 is 2.54.

[0171] According to the test, under the pressure of 20kN, the powder compaction density of the cathode material can reach 3.46g / cm 3 The specific surface area A1 of the positive electrode material is 0.33m 2 / g, after 4.5T pressing, the specific surface area A2 of the positive electrode material is 0.45m 2 / g, (A2-A1) / A1×100% is 36%.

[0172] Table 1 Performance parameters of cathode materials

[0173]

[0174] It can be seen from Table 1 that, first, the compaction density of polycrystalline particles A after mixing with particles B and the BET increase after fracturing under 4.5T pressure conditions are greatly improved; secondly, the elastic coating layer on the surface of polycrystalline particles A can effectively enhance the strength of single particles and slow down the cracking degree of particles during long cycles; the K95 positive electrode material prepared in the comparative example is not within the scope of protection of the present invention, its particles are relatively dispersed and weak in strength, which is not conducive to long-term cyclic use.

[0175] Test Case

[0176] (1) Lithium-ion battery positive electrode:

[0177] The positive electrode material, carbon black, and polyvinylidene fluoride (PVDF) prepared in the examples and comparative examples were mixed in a weight ratio of 95:2.5:2.5 and coated on aluminum foil, dried, cut, and rolled to prepare a positive electrode sheet for a lithium-ion battery.

[0178] (2) Soft-pack batteries

[0179] Artificial graphite is used as the negative electrode, PE is used as the separator, and the positive electrode sheet of the lithium-ion battery is used as the positive electrode sheet. Specifically: the negative electrode is made of artificial graphite coated on copper foil, dried, cut, and rolled into a negative electrode sheet. A PE separator is added in the middle to wind, shell, inject liquid, and seal, and then processed into a wound soft-pack battery. The performance of the soft-pack battery is shown in Table 2.

[0180] The SEM cross-sectional view of the positive electrode sheet made of the positive electrode material of Example 1 after rolling is as follows: Figure 5 As shown by Figure 5 It can be seen that single crystal or single crystal-like particles exist, indicating that the positive electrode material of Example 1 can reduce the squeezing of the current collector.

[0181] The cycle curves of the soft pack battery using the positive electrode sheet made of the positive electrode materials of Example 1 and Comparative Example 1 as the positive electrode are as follows: Figure 4 As shown by Figure 4 It can be seen that compared with Comparative Example 1, the cycle performance of the soft-pack battery containing the positive electrode sheet made of the positive electrode material of Example 1 is significantly improved.

[0182] Table 2

[0183]

[0184] As can be seen in Table 2, the positive electrode sheet produced using the positive electrode material of the present invention has a significantly improved compaction density, effectively suppressing the formation of microcracks in the material during charge and discharge, and significantly improving cycle life and gas production. Furthermore, the elastic coating on the surface of the polycrystalline particles A effectively buffers the compression of the particles on the current collector, while substantially not affecting the capacity, thereby improving cycle life.

[0185] 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 positive electrode material, characterized in that The positive electrode material includes polycrystalline particles A and single crystal particles or quasi-single crystal particles B; The particle sizes D5 and D 50 and D 95 Satisfies the relationship shown in formula I: 1.5 ≤ K95 = (D 95 - D5) / D 50 ≤ 2.5 Formula I; The positive electrode material has the composition shown in formula (1): In formula (1), 0≤a≤0.3, 0.83<x≤1, 0≤y≤1, 0≤z≤1, 0≤k≤0.1, 0≤w≤0.1; M is selected from at least one of B, Na, K, Mg, Al, Ca, Ti, Fe, Zn, Sr, Y, Zr, Nb, Mo, Sn, Ba, Ta, and W; N is selected from at least one of B, Mg, Al, Ti, V, Sr, Y, Zr, Nb, Mo, and W; J is at least one of F, Cl, and P; Among them, the surface of the polycrystalline particles A is coated with a coating layer P; Among them, based on the total weight of the polycrystalline particles A, the mass ratio of the polycrystalline particles A to the coating layer P is 1:0 - 0.05; Among them, the coating layer P is provided by conductive graphite and / or conductive polymer; Among them, in the micro-mechanical testing machine test, the strength of a single particle of the polycrystalline particles A is ≥50 MPa; Wherein, under the pressure of 20kN, the powder compaction density of the positive electrode material is ≥3.5g / cm 3 .

2. The positive electrode material according to claim 1, wherein 1.5≤K95≤2。 3. The positive electrode material according to claim 1 or 2, wherein The particle size D of the polycrystalline particles A 50 7-22μm.

4. The positive electrode material according to claim 1, wherein The particle sizes D5 and D 50 and D 95 Satisfies the relationship shown in formula II: 0 <K A 95=(D 95 -D5) / D 50 ≤1Formula II.

5. The positive electrode material according to claim 1, wherein The particle size D of the single crystal particles or quasi-single crystal particles B 50 0.2-7μm.

6. The positive electrode material according to claim 1, wherein The particle sizes D5 and D 50 and D 95 Satisfies the relationship shown in formula III: 0.2≤K B 95=(D 95 -D5) / D 50 ≤3Formula III.

7. The positive electrode material according to claim 1, wherein The conductive polymer is selected from at least one of polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene sulfide, poly(3,4-ethylenedioxythiophene), and poly(phenylacetylene).

8. The positive electrode material according to claim 1, wherein In the positive electrode material, the mass ratio of the polycrystalline particles A to the single crystal particles or quasi-single crystal particles B is 0.01 - 9:

1.

9. The positive electrode material according to claim 1, wherein The deformation amount of the polycrystalline particle A before breaking is D of the polycrystalline particle A. 50 × (5-25%).

10. The positive electrode material according to claim 1, wherein The specific surface area of the positive electrode material is A1, and after being fractured under a pressure of 4.5 T, the specific surface area of the positive electrode material is A2; Among them, (A2 - A1) / A1×100%≤40%.

11. A method for preparing the positive electrode material according to any one of claims 1 to 10, characterized in that: The method includes the following steps: (1) The transition metal precursor Ni x1 Co y1 Mn z1 (OH)2, lithium salt and optional additives are mixed and first sintered to obtain a first sintered material; (2) Mix the first sintered material with conductive graphite and / or conductive polymer and conduct secondary sintering to obtain polycrystalline particles A; (3) The transition metal precursor Ni x2 Co y2 Mn z2 (OH)2, lithium salt and optional additives are mixed and sintered for a third time to obtain single crystal particles or single crystal-like particles B; (4) Mix the polycrystalline particles A with single crystal particles or quasi-single crystal particles B to obtain the positive electrode material; Among them, x1 + y1 + z1 = 1, 0.83≤x1≤1, 0≤y1≤0.5, 0≤z1≤0.5; x2 + y2 + z2 = 12. The preparation method according to claim 11, wherein ​ 13. The preparation method according to claim 11 or 12, wherein In step (1), the transition metal precursor Ni x1 Co y1 Mn z1 The molar ratio of (OH)2, the lithium salt and the additive is 1:0.99-1.1:0-1.

14. The preparation method according to claim 11, wherein ​ 15. The preparation method according to claim 14, wherein ​ 16. The preparation method according to claim 11, wherein ​ 17. The preparation method according to claim 11, wherein ​ 18. The preparation method according to claim 11, wherein In step (3), the transition metal precursor Ni x2 Co y2 Mn z2 The molar ratio of (OH)2, the lithium salt and the additive is 1:0.99-1.1:0-1.

19. The preparation method according to claim 11, wherein ​ 20. The preparation method according to claim 11, wherein ​ 21. Use of the positive electrode material according to any one of claims 1 to 10 in a lithium ion battery.

22. A positive electrode plate for a lithium-ion battery, characterized in that: The lithium-ion battery positive electrode plate is made of the positive electrode material according to any one of claims 1 to 10.

23. A lithium ion battery, characterized in that: The lithium-ion battery comprises the lithium-ion battery positive electrode sheet according to claim 22.

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