Positive electrode active material with combined large and small particles and preparation method therefor, lithium-ion battery, and electric device

Abstract

Disclosed in the present application are a positive electrode active material with combined large and small particles and a preparation method therefor, a lithium-ion battery, and an electric device. The positive electrode active material with combined large and small particles comprises a large-particle positive electrode active material and a small-particle positive electrode active material, wherein the mass ratio of the large-particle positive electrode active material is not less than 50%, the D50 of the large-particle positive electrode active material is 9-14 μm, and the particle size distribution range (D90-D10) / D50 thereof is 1.0-1.5; and the D50 of the small-particle positive electrode active material is 3-6 μm, and the particle size distribution range (D90-D10) / D50 thereof is 0.6-1.0.

Description

Positive electrode active material with large and small particle matching, preparation method thereof, lithium ion battery and electric device

[0001] Related applications

[0002] The present application claims priority to the Chinese patent application No. 202410731974.0, filed on June 6, 2024, and entitled "Positive electrode active material with large and small particle matching, preparation method thereof, lithium ion battery and electric device", the content of which is hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application belongs to the field of lithium ion batteries, and particularly relates to a positive electrode active material with large and small particle matching, a preparation method thereof, a lithium ion battery and an electric device. BACKGROUND

[0004] In recent years, the demand for cordless electric tool lithium batteries has not decreased, because lithium ion has obvious advantages in energy density, cycle retention rate, charge and discharge rate, etc., is more environmentally friendly, and can meet the market requirements of lightweight and small size. In recent years, electric tools have developed towards professional tools and garden tools, not only requiring power performance, but also requiring energy density of materials. Tool-type lithium batteries are used in high-power output scenarios in actual application process, and are repeatedly used in high-power output, so battery manufacturers have proposed discharge high-rate cycle performance evaluation requirements in the battery design stage. High-rate cycle improvement is one of the key points and difficulties for the improvement of electric tool batteries.

[0005] In the patent application with publication No. CN 115241449 A, the energy density and high power density are improved by using lithium cobaltate secondary ball large particles and lithium cobaltate single crystal small particles. However, compared with lithium cobaltate material, nickel cobalt lithium aluminate has lower cost and higher energy density, and even better power characteristics. However, the mainstream electric tools on the market are all ternary materials rather than lithium cobaltate products.

[0006] In the patent application with publication number CN114464800A, the central part of the positive electrode material has a clear multiple pore structure distribution, increasing the specific surface area of the material and improving the power performance. However, the hollow internal structure sharply reduces the mechanical strength of the material, thereby reducing the compaction density of the pole piece. The improvement of the compaction density is an important means to improve the energy density, but this method can only improve the power density of the material and cannot achieve the improvement of the energy density. In the patent application with publication number CN113903901A, the core-shell structure positive electrode material is prepared to optimize the shell structure, and the pores at the core-shell junction increase, increasing the specific surface area and improving the power performance of the material. However, the increase of pores between the core-shell structure also increases the risk of material breakage during the pole piece rolling process, so it can only improve the power density and cannot improve the energy density. In the patent document with publication number CN116941067A, the use of large and small particles and the difference in Al content of large and small particles allows the material to have high energy density and cycle performance, but it can only improve the small rate cycle and cannot improve the large rate cycle. In the patent document with publication number CN115241449A, large and small particles are also used, and small particles are single crystal particles. Although the problem of rate and compaction is solved, the problem of large rate cycle is still not solved.

[0007] Therefore, how to provide a lithium ion positive electrode material that can simultaneously consider low cost, high energy density and high power density, and has good cycle life in a large rate use scenario is a technical problem to be solved at present. SUMMARY

[0008] The technical problem to be solved by the present application is to overcome the deficiencies and defects mentioned in the above background art, and to provide a positive electrode active material that can simultaneously consider low cost, high energy density and high power density, and has good cycle life in a large rate use scenario, as well as a preparation method thereof, a lithium ion battery and an electric device.

[0009] To solve the above technical problems, the technical solution proposed by the present application is as follows:

[0010] A large and small particle matched positive electrode active material, comprising large particle positive electrode active material and small particle positive electrode active material, the mass fraction of the large particle positive electrode active material is not less than 50%, the D50 of the large particle positive electrode active material is 9-14μm, the particle size distribution range (D90-D10) / D50 is 1.0-1.5, and the D50 of the small particle positive electrode active material is 3-6μm, the particle size distribution range (D90-D10) / D50 is 0.6-1.0.

[0011] The present application can improve the high-rate cycle performance of the material by controlling the particle size distribution range of the large particle positive electrode active material. Compared with the small particle product, the lithium ion transmission path of the large particle product is lengthened. Therefore, the particle size of the large particle product is appropriately widened, the number of small particles with appropriate particle size is increased, the transmission distance of lithium ions is reduced, and the polarization of the large particle is reduced, especially during high-rate discharge. However, when the particle size distribution of the large particle is too wide, the number of small particles in the precursor increases, although the transmission distance of lithium ions is reduced, the small particles with very small particle size are overburned during the actual sintering process, and other performances are affected. When the particle size distribution of the large particle is too narrow, the proportion of large particles in the material increases, which is not conducive to the transmission of lithium ions. Therefore, the particle size distribution of the large particle precursor of the material is within the range of the present application, which can balance the performances of the material and take into account high energy, high power and high-rate cycle performance.

[0012] In some embodiments, the large particle positive electrode active material has a particle size distribution range of 1.1-1.4, and the small particle positive electrode active material has a particle size distribution range of 0.8-1.0.

[0013] In some embodiments, the large particle positive electrode active material has a particle size distribution range of 1.1-1.4, and the small particle positive electrode active material has a particle size distribution range of 0.8-1.0.

[0014] In some embodiments, the large particle positive electrode active material has a particle size distribution range of 1.1-1.4, and the small particle positive electrode active material has a particle size distribution range of 0.8-1.0.

[0015] The cross-section porosity test of the secondary particle is as follows: the cross-section of the sintered secondary spherical particle is polished by CP cross-section polishing technology, and then observed and photographed by field emission electron microscope, or directly observed by focused ion beam scanning electron microscope. The above methods can obtain the cross-section picture of the secondary particle. The picture is imported into Image J, Photoshop or other software that can calculate the picture to calculate the porosity.

[0016] In some embodiments, the large particle positive active material and the small particle positive active material in the above-mentioned large and small particle combination positive active material have chemical formulas Li a Ni b Co c Al d M e O2, wherein 0.8≤a≤1.1, 0.8

[0017] As a general inventive concept, the present application also provides a method for preparing the above-mentioned large and small particle combination positive active material, comprising the following steps:

[0018] (1) selecting a large particle precursor and a small particle precursor;

[0019] (2) mixing and sintering the large particle precursor with a lithium source to obtain a large particle finished product, and mixing and sintering the small particle precursor with a lithium source to obtain a small particle finished product;

[0020] (3) mixing the large particle finished product and the small particle finished product obtained in step (2) in a certain proportion to prepare the large and small particle combination positive active material.

[0021] In some embodiments, the above-mentioned method for preparing, in step (1), the D50 of the large particle precursor is 11-16 μm, and the particle size distribution range (D90-D10) / D50 is 0.8-1.3.

[0022] In some embodiments, the above-mentioned method for preparing, in step (1), the D50 of the small particle precursor is 2-6 μm, and the particle size distribution range (D90-D10) / D50 is 0.8-1.5.

[0023] In some embodiments, the above-mentioned method for preparing, in step (2), the sintering is divided into first sintering and second sintering, the first sintering is stepwise sintering: first, heating to 400-500 °C for first-stage low-temperature sintering, then heating to 600-700 °C for second-stage medium-temperature sintering, and finally heating to 620-900 °C for third-stage high-temperature sintering, and the temperature of the third-stage high-temperature sintering is 20-200 °C higher than that of the second-stage medium-temperature sintering; further, the temperature of the third-stage high-temperature sintering is 20-120 °C higher than that of the second-stage medium-temperature sintering.

[0024] Further, the second sintering temperature is 600-700℃, and the second sintering time is 6-14h.

[0025] In some embodiments, the preparation method described above, the first low-temperature sintering time is 1-4h, further, the second medium-temperature sintering time is 1-3h, and further, the third high-temperature sintering time is 5-20h.

[0026] In some embodiments, the preparation method described above, the sintering is carried out in an oxygen atmosphere, and further, the sintering temperature rising rate is 3-8℃ / min.

[0027] In some embodiments, the preparation method described above, after the first sintering, the material is cooled, sieved, washed with water, and dried before the second sintering.

[0028] In some embodiments, the preparation method described above, in step (2), the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium nitrate.

[0029] As a general inventive concept, the present application also provides a lithium ion battery comprising the above-mentioned large and small particle combined positive electrode active material or the large and small particle combined positive electrode active material prepared by the above-mentioned preparation method.

[0030] As a general inventive concept, the present application also provides an electrical device comprising the above-mentioned lithium ion battery.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] (1) The positive electrode active material of the present application uses a combination of large particle positive electrode active material and small particle positive electrode active material, widens the particle size of the large particles, increases the number of small particles of appropriate particle size, reduces the lithium ion transmission distance, especially during high-rate discharge, reduces the polarization of large particles, controls the particle size distribution range of large particles to improve the high-rate cycle performance of the material, and controls the particle size distribution range of small particles to avoid the problem of too wide particle size distribution of small particles, which increases the number of large particles in small particles and affects the lithium ion transmission distance, and avoids the problem of too narrow particle size distribution of small particles, which sharply increases the cost.

[0033] (2) In the positive electrode active material of the present application, the combination of secondary spherical large particles and secondary spherical small particles can improve the compaction density of the electrode sheet, the small particles can fill the pores of the large particles, the unit density of the material is improved, and the energy density of the material is improved.

[0034] (3) The positive electrode active material of the present application has a higher external porosity than internal porosity, and the increase of the external porosity can increase the lithium ion insertion area during high-rate cycling, reduce the polarization problem during high-rate cycling, and thus improve the high-rate cycling performance.

[0035] (4) The positive electrode active material of the present application has a higher external porosity than internal porosity, and the external porosity is distributed in a discontinuous manner. This non-continuous pore structure and the suitable internal pore structure can enhance the particle strength of the material and help to increase the compaction density of the material during the rolling stage of the electrode sheet.

[0036] (5) The preparation method of the present application uses a segmented calcination method during sintering, which is conducive to the formation of a porous structure and makes the formation of pores more uniform. Gradual and phased increase of the sintering temperature during sintering can avoid the formation of large pores due to excessively high temperature, which affects the strength of the material. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor based on the disclosed drawings.

[0038] FIG. 1 is an SEM image of the large particle positive electrode active material in Example 2.

[0039] FIG. 2 is an SEM image of the large particle positive electrode active material in Example 4.

[0040] FIG. 3 is an SEM image of the large particle positive electrode active material in Example 5.

[0041] FIG. 4 is an SEM image of the large particle positive electrode active material in Comparative Example 3. DETAILED DESCRIPTION

[0042] In order to facilitate understanding of the present application, the present application will be described more fully and specifically below in conjunction with the drawings of the specification and the preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0043] Unless otherwise defined, all terms used in the description herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. The terms used herein are for the purpose of describing specific embodiments and are not intended to limit the scope of the present application.

[0044] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods.

[0045] In the following examples and comparative examples, the external porosity refers to the ratio of the pore area in the part of 0.5R < L≤ R from the center of the cross section to the cross-sectional area in the part of 0.5R < L≤ R from the center of the cross section of the positive electrode active material, and the internal porosity refers to the ratio of the pore area in the part of 0≤ L≤ 0.5R from the center of the cross section to the cross-sectional area in the part of 0≤ L≤ 0.5R from the center of the cross section of the positive electrode active material, R refers to the radius of the secondary sphere of the positive electrode active material, and L refers to the distance from the center of the cross section.

[0046] Example 1:

[0047] A positive electrode active material of the present application with a combination of large and small particles includes large particle positive electrode active material and small particle positive electrode active material, the mass ratio of the large particle positive electrode active material is 80%, the D50 of the large particle positive electrode active material is 10.9 μm, the particle size distribution range (D90-D10) / D50 thereof is 1.36, the D50 of the small particle positive electrode active material is 3.6 μm, and the particle size distribution range (D90-D10) / D50 thereof is 0.63; the external pores of the large particle positive electrode active material are distributed in a discontinuous manner, and the difference between the external porosity and the internal porosity of the large particle positive electrode active material is 5.6%.

[0048] The preparation method of the positive electrode active material with a combination of large and small particles of the present embodiment includes the following steps:

[0049] (1) selecting a large particle precursor Ni 0.90 Co 0.08 Al 0.02 (OH)2, and mixing with lithium hydroxide in a high-speed mixing device at a metal element molar ratio of 1:1.05, while adding 0.15% mol of Zr and mixing uniformly, then placing the mixed material in an oxygen atmosphere furnace for sintering, first sintering at 450℃ for 1h, then increasing the temperature to 640℃ for sintering for 2h, and finally increasing the temperature to 720℃ for sintering for 12h, and then naturally cooling to obtain the base material Li 1.05 Ni 0.9 Co 0.08 Al 0.02 Zr 0.0015O2, wherein the temperature increasing rate is 5°C / min;

[0050] (2) The substrate material obtained in step (1) is sieved, then washed with deionized water at a mass ratio of 1:1.2 for 15 min, filtered, dried in a vacuum drying oven for 8 h, then heated to 625°C at a temperature increasing rate of 5°C / min in an oxygen atmosphere furnace, kept for 10 h, sieved after cooling, to obtain large-particle positive electrode active material with D50=10.9 μm and (D90-D10) / D50=1.36; a part of the sample is selected to take a section by CP section polishing technology combined with field emission electron microscopy, the section picture is imported into Photoshop software for calculation, the external porosity of the large particle is 7.4%, the internal porosity is 1.8%, and the difference between the external porosity and the internal porosity is 5.6%;

[0051] (3) A small-particle precursor Ni 0.90 Co 0.08 Al 0.02 (OH)2 and lithium hydroxide are mixed in a high-speed mixing device at a molar ratio of metal elements of 1:1.05, while 0.15% mol of Mg is added, then the mixture is sintered in an oxygen atmosphere furnace, first sintered at 450°C for 3 h, then sintered at 620°C for 2 h, and finally sintered at 705°C for 12 h, with a temperature increasing rate of 5°C / min, and the substrate material Li 1.05 Ni 0.9 Co 0.08 Al 0.02 Mg 0.0015 O2 is obtained after natural cooling.

[0052] (4) The sample after sintering in step (3) is sieved, then washed with deionized water at a ratio of 1:1.2 for 15 min, filtered, dried in a vacuum drying oven for 8 h, then heated to 630°C at a temperature increasing rate of 5°C / min in an oxygen atmosphere furnace, kept for 10 h, sieved after cooling, to obtain small-particle positive electrode active material with D50=3.6 μm and (D90-D10) / D50=0.63;

[0053] (5) The large-particle positive electrode active material obtained in step (2) and the small-particle positive electrode active material obtained in step (4) are mixed in a high-speed mixing device at a mass ratio of 8:2, to obtain positive electrode active material with large and small particles.

[0054] Example 2:

[0055] The positive electrode active material of the size particle matching of the application comprises a large particle positive electrode active material and a small particle positive electrode active material, the mass percentage of the large particle positive electrode active material is 70%, the D50 of the large particle positive electrode active material is 11.8 μm, the particle size distribution range (D90-D10) / D50 of the large particle positive electrode active material is 1.22, the D50 of the small particle positive electrode active material is 3.7 μm, and the particle size distribution range (D90-D10) / D50 of the small particle positive electrode active material is 0.68; the external pores of the large particle positive electrode active material are distributed in a discontinuous manner, and the difference between the external porosity and the internal porosity of the large particle positive electrode active material is 7.7%.

[0056] The preparation method of the positive electrode active material of the size particle matching of the embodiment comprises the following steps:

[0057] (1) selecting a large particle precursor Ni 0.90 Co 0.08 Al 0.02 (OH)2, and mixing the lithium hydroxide in a high-speed mixing device at a metal element molar ratio of 1:1.04, while adding 0.08% mol of Mg and 0.10% mol of Ti, and then uniformly mixing, then placing the mixed material in an oxygen atmosphere furnace for sintering, first sintering at 450℃ for 1.5 h, then sintering at 650℃ for 3 h, and finally sintering at 725℃ for 12 h, and then naturally cooling to obtain a matrix material Li 1.04 Ni 0.9 Co 0.08 Al 0.02 Mg 0.0008 Ti 0.001 O2, wherein the temperature rising rate is 5℃ / min;

[0058] (2) screening the matrix material obtained in step (1), then washing for 15 min according to the mass ratio of the matrix material: deionized water = 1:1.0, then filtering, then placing in a vacuum drying box for drying for 8 h, then heating to 630℃ in an oxygen atmosphere furnace, keeping warm for 10 h, and then screening and dissociating after cooling to obtain a large particle positive electrode active material with D50 = 11.8 μm and (D90-D10) / D50 = 1.22, and the SEM image is shown in FIG. 1, the large particle pore distribution is a discontinuous distribution, the external porosity is 9.3% and the internal porosity is 1.6% according to the same way of measuring as in Example 1, and the external porosity is 7.7% larger than the internal porosity;

[0059] (3) selecting a small particle precursor Ni 0.90 Co 0.08 Al 0.02(OH)2 with lithium hydroxide, according to the molar ratio of metal elements 1:1.04, mixed in a high-speed mixing device, while adding 0.08% mol of Mg and 0.10% mol of Ti, and then placing the mixture in an oxygen atmosphere furnace for sintering, first sintering at 450°C for 3h, then sintering at 620°C for 2h, and finally sintering at 705°C for 12h, with a heating rate of 5°C / min, and after natural cooling, the matrix material Li 1.04 Ni 0.9 Co 0.08 Al 0.02 Mg 0.0008 Ti 0.001 O2;

[0060] (4) The sample after sintering in step (3) is sieved, then washed according to the ratio of matrix material: deionized water = 1:1.2 for 13min, filtered, then placed in a vacuum drying oven for 8h, then heated to 620°C at a heating rate of 5°C / min in an oxygen atmosphere furnace, and held for 10h, then sieved after cooling to dissociate, to obtain a small-particle positive electrode active material with D50 = 3.7μm, (D90-D10) / D50 = 0.68;

[0061] (5) The large-particle positive electrode active material obtained in step (2) and the small-particle positive electrode active material obtained in step (4) are mixed in a high-speed mixing device according to a mass ratio of 7:3 to obtain a large-small particle mixed positive electrode active material.

[0062] Example 3:

[0063] A large-small particle mixed positive electrode active material of the present application includes a large-particle positive electrode active material and a small-particle positive electrode active material, the mass ratio of the large-particle positive electrode active material being 80%, the D50 of the large-particle positive electrode active material being 10.3μm, the particle size distribution range (D90-D10) / D50 of the large-particle positive electrode active material being 1.28, the D50 of the small-particle positive electrode active material being 3.9μm, and the particle size distribution range (D90-D10) / D50 of the small-particle positive electrode active material being 0.87; the external porosity of the large-particle positive electrode active material is distributed in a non-continuous manner, and the difference between the external porosity and the internal porosity of the large-particle positive electrode active material is 10.5%.

[0064] The preparation method of the large-small particle mixed positive electrode active material of the present embodiment includes the following steps:

[0065] (1) Select a large-particle precursor Ni 0.90 Co 0.08 Al 0.02(OH)₂ and lithium hydroxide were mixed in a high-speed mixing apparatus at a metal element molar ratio of 1:1.05, while 0.1% mol of Zr was added and mixed thoroughly. The mixture was then placed in an oxygen atmosphere furnace for sintering. The sintering was first performed at 450℃ for 3 hours, then at 650℃ for 2 hours, and finally at 725℃ for 12 hours. The mixture was then allowed to cool naturally to obtain the matrix material Li. 1.05 Ni 0.9 Co 0.08 Al 0.02 Zr 0.001 O2, wherein the heating rate is 5℃ / min;

[0066] (2) The matrix material obtained in step (1) was sieved, and then washed for 15 min at a mass ratio of matrix material:deionized water = 1:1.3. After filtration, it was dried in a vacuum drying oven for 8 h, and then heated to 650℃ in an oxygen atmosphere furnace and kept at that temperature for 10 h. After cooling, it was sieved and dissociated to obtain a large particle positive electrode active material with D50 = 10.3 μm and (D90-D10) / D50 = 1.28. The pore distribution of the large particles was discontinuous and uniform. The external porosity was measured to be 16.1% and the internal porosity was 5.6% in the same way as in Example 1. The external porosity was 10.5% greater than the internal porosity.

[0067] (3) Select Ni small particle precursor with D50 = 3.3 μm and particle size distribution range (D90-D10) / D50 = 1.24. 0.90 Co 0.08 Al 0.02 (OH)₂ and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.04, with 0.1% mol of Mg added simultaneously. The mixture was then placed in an oxygen atmosphere furnace for sintering, first at 450℃ for 3 hours, then at 620℃ for 2 hours, and finally at 713℃ for 12 hours, with a heating rate of 5℃ / min. After natural cooling, the matrix material Li was obtained. 1.04 Ni 0.9 Co 0.08 Al 0.02 Mg 0.001 O2;

[0068] (4) After sintering in step (3), the sample is sieved, washed for 12 min with matrix material: deionized water = 1:1.3, filtered, dried in a vacuum drying oven for 8 h, heated to 640 °C at a heating rate of 5 °C / min in an oxygen atmosphere furnace, held for 10 h, cooled and sieved to dissociate, to obtain small particle positive electrode active material with D50 = 3.9 μm and (D90-D10) / D50 = 0.87;

[0069] (5) The large particle positive electrode active material obtained in step (2) is mixed with the small particle positive electrode active material obtained in step (4) in a mass ratio of 8:2 in a high-speed mixing device to obtain a large-small particle mixed positive electrode active material.

[0070] Example 4:

[0071] A large-small particle mixed positive electrode active material of the present application comprises a large particle positive electrode active material and a small particle positive electrode active material, the mass ratio of the large particle positive electrode active material being 75%, the D50 of the large particle positive electrode active material being 11.4 μm, the particle size distribution range (D90-D10) / D50 of the large particle positive electrode active material being 1.26, the D50 of the small particle positive electrode active material being 3.6 μm, and the particle size distribution range (D90-D10) / D50 of the small particle positive electrode active material being 0.93; the external pores of the large particle positive electrode active material are distributed in a discontinuous manner, and the difference between the external porosity and the internal porosity of the large particle positive electrode active material is 18.1%.

[0072] The preparation method of the large-small particle mixed positive electrode active material of the present embodiment comprises the following steps:

[0073] (1) A large particle precursor Ni 0.90 Co 0.08 Al 0.02 (OH)2 with a D50 of 12.3 μm and a particle size distribution range (D90-D10) / D50 of 1.15 is mixed with lithium hydroxide in a high-speed mixing device at a metal element molar ratio of 1:1.04, 0.10% mol of La and 0.3% mol of Ti are added at the same time, and the mixture is uniformly mixed, then the mixture is placed in an oxygen atmosphere furnace for sintering, first sintered at 450°C for 3 h, then heated to 620°C for 2 h, and finally heated to 725°C for 12 h, and then naturally cooled to obtain a matrix material Li 1.04 Ni 0.9 Co 0.08 Al 0.02 La 0.001 Ti 0.003 O2, wherein the heating rate is 5°C / min;

[0074] (2) The substrate material obtained in step (1) is sieved, then washed with deionized water at a mass ratio of substrate material: deionized water = 1:1.0 for 15 min, filtered, then dried in a vacuum drying oven for 8 h, then heated to 660°C in an oxygen atmosphere furnace, held for 10 h, then sieved and separated after cooling, to obtain a large-particle positive electrode active material with D50 = 11.4 μm, (D90-D10) / D50 = 1.26, and the SEM image is shown in Figure 2. The large-particle pore distribution is a non-continuous distribution, and the external porosity is 22.7%, the internal porosity is 4.6%, and the external porosity is 18.1% greater than the internal porosity, measured in the same way as in Example 1.

[0075] (3) A small-particle precursor Ni 0.90 Co 0.08 Al 0.02 (OH)2 and lithium hydroxide, at a molar ratio of metal elements of 1:1.04, are mixed in a high-speed mixing device, while 0.3% mol of Ti is added, then the mixture is placed in an oxygen atmosphere furnace for sintering, first sintered at 450°C for 2 h, then heated to 600°C for 2 h, and finally heated to 705°C for 12 h, at a heating rate of 5°C / min, and after natural cooling, the substrate material Li 1.04 Ni 0.9 Co 0.08 Al 0.02 Ti 0.003 O2;

[0076] (4) The sample after sintering in step (3) is sieved, then washed with deionized water at a ratio of substrate material: deionized water = 1:1.0 for 15 min, filtered, then dried in a vacuum drying oven for 8 h, then heated to 660°C in an oxygen atmosphere furnace at a heating rate of 5°C / min, held for 10 h, then sieved and separated after cooling, to obtain a small-particle positive electrode active material with D50 = 3.6 μm, (D90-D10) / D50 = 0.93.

[0077] (5) The large-particle positive electrode active material obtained in step (2) and the small-particle positive electrode active material obtained in step (4) are mixed in a high-speed mixing device at a mass ratio of 7.5:2.5, to obtain a large-small particle positive electrode active material.

[0078] Example 5:

[0079] The positive electrode active material of the size particle matching of the application comprises large particle positive electrode active material and small particle positive electrode active material, the mass percentage of the large particle positive electrode active material is 80%, the D50 of the large particle positive electrode active material is 11.2 μm, the particle size distribution range (D90-D10) / D50 thereof is 1.16, the D50 of the small particle positive electrode active material is 4.2 μm, and the particle size distribution range (D90-D10) / D50 thereof is 0.84; the external pores of the large particle positive electrode active material are distributed in a discontinuous manner, and the difference between the external porosity and the internal porosity of the large particle positive electrode active material is 15.6%.

[0080] The preparation method of the positive electrode active material of the size particle matching of the embodiment comprises the following steps:

[0081] (1) selecting a large particle precursor Ni 0.92 Co 0.06 Al 0.02 (OH)2 with a D50 of 12.1 μm and a particle size distribution range (D90-D10) / D50 of 0.85, mixing the precursor with lithium hydroxide in a high-speed mixing device at a metal element molar ratio of 1:1.05, simultaneously adding 0.15% mol of Zr, and uniformly mixing, then placing the mixture in an oxygen atmosphere furnace for sintering, first sintering at 450 ℃ for 3 h, then increasing the temperature to 620 ℃ for sintering for 2 h, and finally increasing the temperature to 725 ℃ for sintering for 12 h, and then naturally cooling to obtain a matrix material Li 1.05 Ni 0.92 Co 0.06 Al 0.02 Zr 0.0015 O2, wherein the temperature increasing rate is 5 ℃ / min;

[0082] (2) screening the matrix material obtained in step (1), then washing for 15 min according to a mass ratio of the matrix material: deionized water = 1:1.3, filtering, then placing in a vacuum drying box for drying for 8 h, then increasing the temperature to 640 ℃ in an oxygen atmosphere furnace, keeping the temperature for 10 h, screening after cooling, to obtain a large particle positive electrode active material with a D50 of 11.2 μm and a (D90-D10) / D50 of 1.16, and the SEM image thereof is shown in FIG. 3, the large particle pore distribution is a discontinuous distribution, the external porosity is 19.5% according to the same manner as in embodiment 1, the internal porosity is 3.9%, and the external porosity is 15.6% larger than the internal porosity;

[0083] (3) selecting a small particle precursor Ni 0.92 Co 0.06 Al 0.02(OH)₂ and lithium hydroxide were mixed in a high-speed mixer at a metal element molar ratio of 1:1.04, with 0.15% mol of Zr added simultaneously. The mixture was then sintered in an oxygen atmosphere furnace, first at 450℃ for 3 hours, then at 610℃ for 2 hours, and finally at 705℃ for 12 hours, with a heating rate of 5℃ / min. After natural cooling, the matrix material Li was obtained. 1.04 Ni 0.92 Co 0.06 Al 0.02 Zr 0.0015 O2;

[0084] (4) The sample after sintering in step (3) is sieved, washed for 15 min with matrix material: deionized water = 1:1.5, filtered, dried in a vacuum drying oven for 8 h, heated to 640 °C in an oxygen atmosphere furnace at a heating rate of 5 °C / min, held for 10 h, cooled and sieved to dissociate, to obtain small particle positive electrode active material with D50 = 4.2 μm and (D90-D10) / D50 = 0.84;

[0085] (5) The large-particle positive electrode active material obtained in step (2) and the small-particle positive electrode active material obtained in step (4) are mixed in a high-speed mixing device at a mass ratio of 8:2 to obtain a positive electrode active material with a combination of large and small particles.

[0086] Comparative Example 1:

[0087] This comparative example uses a combination of large and small particle positive electrode active materials. The large particle positive electrode active material accounts for 80% of the total mass. The large particle positive electrode active material has a D50 of 12.3 μm and a particle size distribution range (D90-D10) / D50 of 0.85. The small particle positive electrode active material has a D50 of 3.6 μm and a particle size distribution range (D90-D10) / D50 of 0.63. The difference between the external and internal porosity of the large particle positive electrode active material is 11.3%.

[0088] The preparation method of this comparative example differs from that of Example 1 in that, in step (1), a large-particle precursor Ni with D50 = 13.1 μm and a particle size distribution range (D90-D10) / D50 = 0.55 is selected. 0.90 Co 0.08 Al 0.02 (OH)2, other processes and parameters are the same as in Example 1.

[0089] Comparative Example 2:

[0090] The positive electrode active material of the comparative example of large and small particle matching includes large particle positive electrode active material and small particle positive electrode active material, the mass percentage of the large particle positive electrode active material is 70%, the D50 of the large particle positive electrode active material is 12.0 μm, the particle size distribution range (D90-D10) / D50 thereof is 1.69, and the D50 of the small particle positive electrode active material is 3.7 μm, the particle size distribution range (D90-D10) / D50 thereof is 0.68.

[0091] The preparation method of the comparative example is different from that of example 2 in that in step (1), a large particle precursor with D50=12.3 μm and a particle size distribution range (D90-D10) / D50=1.51 is selected, and other processes and parameters are completely consistent with those of example 2.

[0092] Comparative example 3:

[0093] The positive electrode active material of the comparative example of large and small particle matching includes large particle positive electrode active material and small particle positive electrode active material, the mass percentage of the large particle positive electrode active material is 80%, the D50 of the large particle positive electrode active material is 10.6 μm, the particle size distribution range (D90-D10) / D50 thereof is 0.89, the D50 of the small particle positive electrode active material is 3.3 μm, the particle size distribution range (D90-D10) / D50 thereof is 0.48, and the difference between the external porosity and the internal porosity of the large particle positive electrode active material is 0.6%. The SEM image of the large particle positive electrode active material is shown in FIG. 4.

[0094] The preparation method of the comparative example is different from that of example 3 in that in step (1), a large particle precursor with D50=11.6 μm and a particle size distribution range (D90-D10) / D50=0.59 is selected, and a small particle precursor with D50=3.5 μm and a particle size distribution range (D90-D10) / D50=0.79 is selected, and other processes and parameters are completely consistent with those of example 3.

[0095] Comparative example 4:

[0096] The positive electrode active material of the comparative example of large and small particle matching includes large particle positive electrode active material and small particle positive electrode active material, the mass percentage of the large particle positive electrode active material is 80%, the D50 of the large particle positive electrode active material is 11.9 μm, the particle size distribution range (D90-D10) / D50 thereof is 0.75, the D50 of the small particle positive electrode active material is 4.2 μm, the particle size distribution range (D90-D10) / D50 thereof is 0.84, and the difference between the external porosity and the internal porosity of the large particle positive electrode active material is 3.6%.

[0097] The preparation method of the present comparative example is different from example 5 in that in step (1), a large particle precursor with D50 = 13.5 μm and a particle size distribution range (D90-D10) / D50 = 0.37 is selected, and other processes and parameters are completely consistent with example 5.

[0098] Comparative example 5:

[0099] The present comparative example is different from example 4 in that the large particle precursor and the small particle precursor of example 4 are mixed in a high-speed mixing device at a mass ratio of 7.5:2.5, and lithium hydroxide is mixed at a transition metal to lithium molar ratio of 1:1.04, and 0.03% mol of Ti is added and uniformly mixed, and then the mixture is placed in an oxygen atmosphere furnace for sintering, first sintered at 450°C for 1.5 h, then heated to 650°C for 3 h, and finally heated to 720°C for 12 h, and the same post-treatment conditions are used to obtain a positive electrode active material.

[0100] The positive electrode active materials finally obtained in the examples and comparative examples are made into button cells with lithium metal sheets as negative electrodes for evaluation and test, and the 0.1C charging is carried out at room temperature and in the voltage range of 3.0-4.3V, and then the 0.1C discharging is carried out, the room temperature is 25°C, the 1C charging and 1C discharging 50-week cycle retention rate test, or the 1C charging and 3C discharging 50-week cycle retention rate test, and the physical and chemical index test and button cell results are shown in Table 1 below.

[0101] Table 1: Performance comparison of positive electrode materials of comparative examples 1-5 and examples 1-5

[0102] Comparative example 1 and example 1 are compared, and both the capacity and the cycle are worse, which is because the particle size distribution range of the large particles of comparative example 1 is too small, and the particle distribution is too concentrated, which will affect the compaction and thus affect the capacity, and because the particle size distribution range is too small, the overall particle size distribution of the large particles is concentrated and too large, which will also adversely affect the large rate cycle. By comparing comparative example 2 and example 2, it can be seen that the particle size distribution range of the large particles of comparative example 2 is too large, which leads to poor large rate cycle, because the particle size distribution range is too large, the number of large particles near Dmax increases, the transmission path of Li + becomes longer, and the number of small particles near Dmin increases, which is easy to cause over-sintering during the sintering process, affecting the Li + transport rate, thereby leading to poor large rate cycle performance. The particle size of the large particles and the small particles of comparative example 3 meets the requirements, but the particle size distribution range of both the large particles and the small particles does not meet the requirements, and both are too small, which leads to a narrow particle size range, the number of large particles in the large particles increases, the number of large particles in the small particles increases, the porosity decreases, which affects the contact between the material and the electrolyte, and is not conducive to the transmission of Li +Transmission. Compared with Example 4, the large rate cycle deviation of Comparative Example 5 is due to the use of co-sintering in the sintering process. Due to the different heating conditions of large and small particles in the co-sintering process, the same temperature cannot match large and small particles at the same time. If the temperature meets the large particles, the small particles are over-sintered. If the temperature meets the small particles, the sintered large particles are not fully crystalline, which will affect the performance of the material. Therefore, the performance is worse than that of Example 4. Moreover, compared with Example 5, the porosity of Comparative Example 4 is low, and the particle size distribution range of the large particles is also narrow. The above two factors are not conducive to the large rate, resulting in poorer performance.

[0103] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present disclosure.

[0104] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A positive electrode active material with a size particle matching, comprising a large particle positive electrode active material and a small particle positive electrode active material, the mass percentage of the large particle positive electrode active material being not less than 50%, the D50 of the large particle positive electrode active material being 9μm-14μm, the particle size distribution range (D90-D10) / D50 of the large particle positive electrode active material being 1.0-1.5, the D50 of the small particle positive electrode active material being 3μm-6μm, and the particle size distribution range (D90-D10) / D50 of the small particle positive electrode active material being 0.6-1.

0.

2. The size particle combination positive electrode active material according to claim 1, wherein, The particle size distribution range of the large particle positive electrode active material is 1.1-1.4, and the particle size distribution range of the small particle positive electrode active material is 0.8-1.

0.

3. The size particle blended positive electrode active material according to any one of claims 1 to 2, wherein, The difference between the external porosity and the internal porosity of the large particle positive electrode active material is 5%-20%, the external porosity being the ratio of the pore area to the cross-sectional area of the part with a distance of 0.5R<L≤R from the center of the cross section of the positive electrode active material, and the internal porosity being the ratio of the pore area to the cross-sectional area of the part with a distance of 0≤L≤0.5R from the center of the cross section of the positive electrode active material, R being the radius of the secondary sphere of the positive electrode active material, and L being the distance from the center of the cross section.

4. The size particle blended positive electrode active material according to any one of claims 1 to 3, wherein, The external pores of the large particle positive electrode active material are discontinuous, the external pores being the pores with a distance of 0.5R<L≤R from the center of the cross section of the positive electrode active material, R being the radius of the secondary sphere of the positive electrode active material, and L being the distance from the center of the cross section.

5. The size particle paired positive electrode active material according to any one of claims 1 to 4, wherein, The chemical formula of the large particle positive electrode active material and the small particle positive electrode active material are independently Li a Ni b Co c Al d M e O2, 0.8≤a≤1.1, 0.8 6.A method for preparing the positive electrode active material with a size particle matching according to any one of claims 1-5, comprising the following steps: (1) selecting a large particle precursor and a small particle precursor; (2) mixing the large particle precursor with a lithium source and sintering to obtain a large particle finished product; mixing the small particle precursor with a lithium source and sintering to obtain a small particle finished product; (3) mixing the large particle finished product and the small particle finished product obtained in step (2) in a certain proportion to prepare the positive electrode active material with a size particle matching.

7. The production method according to claim 6, wherein In step (1), the D50 of the large particle precursor is 11μm-16μm, and the particle size distribution range (D90-D10) / D50 is 0.8-1.

3. The D50 of the small particle precursor is 2μm-6μm, and the particle size distribution range (D90-D10) / D50 is 0.8-1.

5.

8. The production process according to any one of claims 6 to 7, wherein In step (2), the sintering is divided into first sintering and second sintering, the first sintering is staged sintering: first, heating to 400℃-500℃ for first-stage low-temperature sintering, then heating to 600℃-700℃ for second-stage medium-temperature sintering, and finally heating to 620℃-900℃ for third-stage high-temperature sintering, and the temperature of the third-stage high-temperature sintering is 20℃-200℃ higher than that of the second-stage medium-temperature sintering. The temperature of the second sintering is 600℃-700℃, and the time of the second sintering is 6h-14h.

9. The production method according to claim 8, wherein The first low-temperature sintering time is 1-4 hours, the second medium-temperature sintering time is 1-3 hours, and the third high-temperature sintering time is 5-20 hours.

10. The production process according to any one of claims 6 to 9, wherein The sintering is carried out in an oxygen atmosphere, and the temperature rising rate during the sintering is 3-8℃ / min.

11. The production process according to any one of claims 8 to 10, wherein After the first sintering, the material is cooled, sieved, washed with water, dried, and then sintered again.

12. The production process according to any one of claims 6 to 9, wherein In step (2), the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium nitrate.

13. A lithium ion battery comprising the size particle matched positive electrode active material of any one of claims 1-5 or the size particle matched positive electrode active material prepared by the preparation method of any one of claims 6-12.

14. An electrical device comprising the lithium ion battery of claim 13.

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