A high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material and its preparation method

Abstract

A high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material with the chemical formula LiNi x Co y Mn z Al k O2, 0.88≤x<1, 0<y<0.12, 0<z<0.12, 0<k<0.005, x+y+z+k=1. The preparation method includes: mixing a polycrystalline nickel-cobalt-manganese ternary small particle precursor with a lithium source and calcining to obtain polycrystalline nickel-cobalt-manganese ternary small particles; mixing a polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor with a lithium source and calcining to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles; mixing the polycrystalline nickel-cobalt-manganese ternary small particles with nano-alumina particles and calcining to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles; and mixing the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles with the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles to obtain a polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material with high compaction, long cycle life, and high energy density. The present invention separately prepares polycrystalline nickel-cobalt-manganese-aluminum quaternary large and small particles and then grades them to obtain a polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material with high compaction, long cycle life, and high energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material and a preparation method thereof. Background Art

[0002] With the rapid adoption of new energy vehicles in today's society, consumers are also concerned about their range. As one of the core materials in lithium-ion batteries, cathode materials play a decisive role in battery capacity. Therefore, the search for cathode materials with high compaction, long cycle life, and high energy density is urgent.

[0003] High-nickel polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode materials not only possess the high capacity characteristics of high-nickel polycrystalline nickel-cobalt-manganese ternary cathode materials, but also take into account the good cycle stability of high-nickel polycrystalline nickel-cobalt-aluminum ternary cathode materials. Increasing the compaction density of high-nickel polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode materials can achieve higher energy density. Methods for improving the compaction density of cathode materials mainly focus on three aspects: material morphology, material particle size distribution, and electrode processing. Among them, material particle size distribution has the most significant impact on the improvement of compaction density.

[0004] For example, the invention patent with publication number CN113394385A proposes a method for preparing a modified NCMA quaternary cathode material. The method comprises the following steps: 1) in-situ coating of large particles of a high-nickel NCMA quaternary precursor with SiO2; 2) pre-oxidation of small particles of the high-nickel NCMA quaternary precursor; 3) mixing the large particles of the high-nickel NCMA quaternary precursor with the pre-oxidized small particles of the high-nickel NCMA quaternary precursor from step 1 in a certain mass ratio to obtain a graded precursor; 4) uniformly mixing the graded precursor from step 3 with a lithium source and additives, and sintering the mixture in an oxygen atmosphere to obtain a modified NCMA quaternary cathode material.

[0005] Patent publication number CN109888235A proposes a method for grading high-nickel polycrystalline and high-nickel single crystal materials. The method comprises the following steps: 1) mixing a high-nickel polycrystalline precursor, anhydrous LiOH, and a doping additive, sintering the mixture, and then mixing the resulting mixture with a coating additive and sintering the mixture to obtain a high-nickel polycrystalline material; 2) mixing a ternary single crystal precursor, a lithium source, and a doping additive, sintering the mixture, and then mixing the resulting mixture with a coating additive and sintering the mixture to obtain a ternary single crystal material; and 3) mixing the high-nickel polycrystalline material with the ternary single crystal material, or mixing the mixture with the coating additive and sintering the mixture.

[0006] When preparing high-nickel polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode materials with a larger particle size D50, the corresponding sintering temperature is higher, the sintering time is longer, and the lithium content is also relatively increased. This is mainly because the large particle size D50 is not conducive to the diffusion of lithium ions during the sintering process; when preparing high-nickel polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode materials with a smaller particle size D50, the corresponding sintering temperature is lower, the sintering time is shorter, and the lithium content is also relatively reduced, because the small particle size D50 is conducive to the diffusion of lithium ions during the sintering process. Therefore, mixing large and small particles of high-nickel polycrystalline nickel-cobalt-manganese-aluminum quaternary precursors and calcining them with a lithium source can easily lead to overburning of small particles or insufficient sintering of large particles, thereby affecting the performance of electrical properties. In addition, the particle size distribution of high-nickel single-crystal nickel-cobalt-manganese-aluminum quaternary positive electrode materials is generally wide, and there is a small amount of fine powder. After long-term cyclic charge and discharge, structural collapse is prone to occur, resulting in capacity decay. Therefore, it is not suitable for grading with large-particle high-nickel polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode materials.

[0007] Therefore, how to solve the above-mentioned deficiencies in the prior art has become the subject to be studied and solved by the present invention. Summary of the Invention

[0008] The purpose of the present invention is to provide a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material and a preparation method thereof.

[0009] In order to achieve the above objectives, the technical solutions adopted by the present invention at the product level are:

[0010] A high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material with the chemical formula LiNi x Co y Mn z Al k O2, wherein 0.88≤x<1, 0<y<0.12, 0<z<0.12, 0<k<0.005, and x+y+z+k=1.

[0011] Further technical solutions, D50 is 12-16um, and tap density is 2.45-2.75g / cm 3 , with a specific surface area of ​​0.2 to 0.4 m 2 / g, particle size distance 1.15<(D90-D10) / D50<1.25.

[0012] A further technical solution is that the positive electrode material is composed of a gradation of polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles and polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles, wherein the mass of the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles accounts for 18-22% of the total mass of the positive electrode material, and the mass of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles accounts for 78-82% of the total mass of the positive electrode material.

[0013] Further technical solution, the D50 of the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles 小 3~3.8um, D10 小 ≥1.5um, D90 小 ≤6um, particle size distance meets 0.5<(D90 小 -D10 小 ) / D50 小 <0.9, tap density is 2.35~2.45g / cm 3 , the specific surface area is 0.4~0.5m 2 / g;

[0014] The D50 of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles 大 14.5~17.5um, D10 大 ≥10um, D90 大 ≤22um, particle size distance meets 0.3<(D90 大 -D10 大 ) / D50 大 <0.7, tap density is 2.55~2.75g / cm 3 , with a specific surface area of ​​0.2 to 0.3 m 2 / g;

[0015] The polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles and the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles also satisfy the following relationship: 3.5<(D90 大 -D90 小 ) / D90 小 <4.3,3.5<(D50 大 -D50 小 ) / D50 小 <3.9,3.5<(D10 大 -D10 小 ) / D10 小 <4.2.

[0016] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention at the method level is:

[0017] A method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material, comprising:

[0018] Step 1: uniformly mix a polycrystalline nickel-cobalt-manganese ternary small particle precursor and a lithium source, calcine at 600-720° C. for 8-18 hours under oxygen flow, and then naturally cool to room temperature to obtain polycrystalline nickel-cobalt-manganese ternary small particles. The heating rate in the calcination stage is 1-5° C. / min.

[0019] Furthermore, a polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor is uniformly mixed with a lithium source, calcined at 740-880° C. for 20-30 hours under oxygen flow, and then naturally cooled to room temperature to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles. The heating rate during the calcination stage is 1-5° C. / min.

[0020] Step 2: uniformly mix the polycrystalline nickel-cobalt-manganese ternary small particles obtained in step 1 with nano-alumina particles, calcine at 450-550° C. for 4-6 hours under oxygen flow, and then naturally cool to room temperature to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles;

[0021] Step 3: Mix the large polycrystalline nickel-cobalt-manganese-aluminum quaternary particles in step 1 and the small polycrystalline nickel-cobalt-manganese-aluminum quaternary particles in step 2 evenly to obtain a polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material with high compaction, long cycle time and high energy density.

[0022] A further technical solution is that in step 1, the chemical formula of the polycrystalline nickel-cobalt-manganese ternary small particle precursor is Ni x / x+y+z Co y / x+y+z Mn z / x+y+z The molar ratio of (OH)2, the total amount of polycrystalline nickel-cobalt-manganese ternary small particle precursor and the lithium source is 1:(1.01-1.05);

[0023] The chemical formula of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor is Ni x Co y Mn z Al k (OH)2, the molar ratio of the total amount of polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor and the lithium source is 1:(1.06-1.12).

[0024] According to a further technical solution, in step 2, the molar ratio of the polycrystalline nickel-cobalt-manganese ternary small particles to the nano-alumina particles is 2(x+y+z):k.

[0025] According to a further technical solution, in step 2, the size of the nano-alumina particles is 10 to 30 nm.

[0026] A further technical solution is that in step three, the mass ratio of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles to the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles meets (78-82):(18-22).

[0027] The working principle and advantages of the present invention are as follows:

[0028] 1. The present invention develops corresponding sintering processes according to the different particle sizes D50 of large and small particles of polycrystalline nickel-cobalt-manganese-aluminum quaternary, so that the electrical properties of large and small particles can be optimized, solving the problem of poor capacity after mixing large and small particles of high-nickel polycrystalline nickel-cobalt-manganese-aluminum quaternary precursors and calcining them with a lithium source.

[0029] 2. When preparing polycrystalline nickel-cobalt-manganese-aluminum quaternary particles separately, the large particles are made of Ni x Co y Mn z Al k The (OH)2 precursor is mixed with the lithium source and sintered. The large particles have a larger particle size D50. The internal stress of the material is larger during the charge and discharge process, and cracks are prone to occur. The uniform doping of Al can effectively alleviate the volume expansion of lithium ions during the deintercalation process of the positive electrode material and reduce the internal stress. The small particles are made of Ni x / x+y+z Co y / x+y+z Mn z / x+y+z The (OH)2 precursor is mixed with a lithium source, sintered, and then calcined with nano-alumina. The small particles have a large specific surface area and are prone to side reactions with the electrolyte during the charge and discharge process. By doping aluminum with di-sintering, the aluminum content on the surface of the material can be increased, isolating it from direct contact with the electrolyte and effectively preventing the occurrence of side reactions.

[0030] 3. When preparing polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles, the present invention uses 10-30 nm alumina for surface doping. Alumina with a small particle size has higher reactivity, which is conducive to doping at a lower reaction temperature and preventing overburning.

[0031] 4. When the size of polycrystalline nickel-cobalt-manganese-aluminum quaternary particles is graded, the D50 of the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles is 小 3~3.8um, D10 小 ≥1.5um, D90 小 ≤6um, particle size distance meets 0.5<(D90 小 -D10 小 ) / D50 小 <0.9; D50 of large polycrystalline nickel-cobalt-manganese-aluminum quaternary particles 大 14.5~17.5um, D10 大 ≥10um, D90 大 ≤22um, particle size distance meets 0.3<(D90 大 -D10 大 ) / D50 大<0.7, by limiting the particle size D10, D50, D90 and particle size distance of large and small particles respectively, the consistency of the performance of large and small particle products is improved, which facilitates the full play of electrochemical performance after grading. In addition, the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles and the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles also meet the following relationship: 3.5 < (D90 大 -D90 小 ) / D90 小 <4.3,3.5<(D50 大 -D50 小 ) / D50 小 <3.9,3.5<(D10 大 -D10 小 ) / D10 小 <4.2, the mass ratio of the mixture of large polycrystalline nickel-cobalt-manganese-aluminum quaternary particles and small polycrystalline nickel-cobalt-manganese-aluminum quaternary particles satisfies (78~82):(18~22). By adjusting the ratio of the particle sizes D10, D50, and D90 of large and small particles, the filling of small particles in the voids between large particles is improved, the compaction density is increased, and thus the energy density is increased. The mixing ratio of large and small particles needs to be strictly controlled. Too many large particles can easily lead to too many voids between particles, reduce the compaction density, and thus reduce the energy density. Too few large particles will lead to reduced cycle performance.

[0032] In summary, the present invention obtains a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material by separately preparing polycrystalline nickel-cobalt-manganese-aluminum quaternary particles of different sizes and then grading them. The preparation method is reliable, simple and easy to operate, and easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Attachment Figure 1 A Malvern 2000 particle size diagram of the positive electrode material prepared according to an embodiment of the present invention;

[0034] Attachment Figure 2 This is a Malvern 2000 particle size diagram of the positive electrode material prepared in Comparative Example 1 of the present invention;

[0035] Attachment Figure 3 This is a Malvern 2000 particle size diagram of the positive electrode material prepared in Comparative Example 3 of the present invention;

[0036] Attachment Figure 4 This is a Malvern 2000 particle size diagram of the positive electrode material prepared in Comparative Example 5 of the present invention;

[0037] Attachment Figure 5 This is a SEM image of the positive electrode material prepared in an embodiment of the present invention;

[0038] Attachment Figure 6 This is a SEM image of the positive electrode material prepared in Comparative Example 1 of the present invention;

[0039] Attachment Figure 7 This is an SEM image of the positive electrode material prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0041] The present invention will be described in detail below to clearly illustrate the present invention. After understanding the embodiments of the present invention, any person skilled in the art can make changes and modifications based on the techniques taught by the present invention without departing from the spirit and scope of the present invention.

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure.

[0043] Unless otherwise noted, the terms used herein generally have their ordinary meanings in the art, within the context of the present invention, and in the specific context. Certain terms used to describe the present invention are discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art regarding the present invention.

[0044] Example:

[0045] A method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material comprises the following steps:

[0046] Step 1: Mix the polycrystalline nickel-cobalt-manganese ternary small particle precursor and lithium source evenly, calcine at 700℃ for 15h under oxygen flow, and then cool naturally to room temperature to obtain polycrystalline nickel-cobalt-manganese ternary small particles. The heating rate is 1.5℃ / min. The chemical formula of the polycrystalline nickel-cobalt-manganese ternary small particles is LiNi 0.92 Co 0.03 Mn 0.05 O2; the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor is mixed evenly with the lithium source, calcined at 800℃ for 25h under oxygen flow, and then naturally cooled to room temperature to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles. The heating rate is 2℃ / min. The chemical formula of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles is LiNi 0.916 Co 0.03 Mn 0.05 Al 0.004 O2, D50 大 17.216um, D10 大 12.625um, D90 大 The particle size is 23.398um, the particle size distance is 0.626, and the tap density is 2.58g / cm 3 , with a specific surface area of ​​0.23m 2 / g;

[0047] The chemical formula of the polycrystalline nickel-cobalt-manganese ternary small particle precursor is Ni 0.92 Co 0.03 Mn 0.05 (OH)2, the molar ratio of the total amount of polycrystalline nickel-cobalt-manganese ternary small particle precursor and lithium source is 1:1.03, and the chemical formula of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor is Ni 0.916 Co 0.03 Mn 0.05 Al 0.004 The molar ratio of (OH)2, the total amount of polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor and the lithium source is 1:1.08;

[0048] Step 2: uniformly mixing the polycrystalline nickel-cobalt-manganese ternary small particles obtained in step 1 with nano-alumina particles, wherein the molar ratio of the polycrystalline nickel-cobalt-manganese ternary small particles to the nano-alumina particles is 498:1, and the size of the nano-alumina particles is 15 nm; calcining the mixture at 500° C. for 5 hours under oxygen flow and then naturally cooling the mixture to room temperature to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles;

[0049] The chemical formula of polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles is LiNi 0.916 Co 0.03 Mn 0.05 Al 0.004 O2, D50 小 3.636um, D10 小 2.638um, D90 小 The particle size is 5.026um, the particle size distance is 0.657, and the tap density is 2.43g / cm 3 , with a specific surface area of ​​0.48m 2 / g;

[0050] Step 3: The polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles in step 1 are mixed with the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles in step 2 in a mass ratio of 4:1 to obtain a polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material product with high compaction, long cycle and high energy density. The chemical formula is LiNi 0.916 Co 0.03 Mn 0.05 Al 0.004 O2, D50 is 15.936um, particle size spacing is 1.188, and tap density is 2.52g / cm 3 , with a specific surface area of ​​0.28m 2 / g, compacted density is 3.65g / cm 3 ;

[0051] Among them, (D90 大 -D90 小 ) / D90 小 The value of (D50 大 -D50小 ) / D50 小 The value of (D10 is 3.7, 大 -D10 小 ) / D10 小 The value is 3.8, and the relevant data are shown in Table 1.

[0052] Comparative Example 1:

[0053] The difference from the embodiment is that the nickel-cobalt-manganese ternary small particles prepared in step 1 are different. In this comparative example, calcination at 920°C for 15 hours is performed, followed by natural cooling to room temperature, and then pulverization to obtain single crystal / quasi-single crystal nickel-cobalt-manganese ternary small particles. The rest is exactly the same as in Example 1. Relevant data are shown in Table 1.

[0054] Comparative Example 2:

[0055] The difference from the embodiment is that the polycrystalline nickel-cobalt-manganese ternary small particles prepared in step 1 are different. In this comparative example, the chemical formula is Ni 0.916 Co 0.03 Mn 0.05 Al 0.004 The (OH)2 precursor is mixed with a lithium source to directly prepare polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles, which are then directly mixed with polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles in step three. The rest is exactly the same as in Example 1. The relevant data are shown in Table 1.

[0056] Comparative Example 3:

[0057] The difference from the embodiment is that the particle size spacing of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles prepared in step 1 is different. The particle size spacing of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles prepared in this comparative example is 0.98, and the rest is exactly the same as in Example 1. The relevant data are shown in Table 1.

[0058] Comparative Example 4:

[0059] The difference from the embodiment is that the size of the nano-alumina particles used in step 2 is different. The size of the nano-alumina particles used in this comparative example is 60 nm. The rest is exactly the same as in embodiment 1. The relevant data are shown in Table 1.

[0060] Comparative Example 5:

[0061] The difference from the embodiment is that in step three, the mixing mass ratio of polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles and polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles is different. In this comparative example, the mixing mass ratio of polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles and polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles is 3:1. The rest is exactly the same as Example 1. Relevant data are shown in Table 1.

[0062] Table 1 Relevant test data of the products obtained in each example

[0063]

[0064] Comparing the data of each example in Table 1, it can be seen that: when the quaternary size particles of polycrystalline nickel-cobalt-manganese-aluminum are graded, when the small particles are single crystal / single crystal-like (Comparative Example 1), the compaction density of the obtained product is the highest, but its first discharge capacity and cycle performance are not good. When the mass ratio of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles to the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles is 3: 1 (Comparative Example 5), the compaction density is low, and the first discharge capacity and cycle performance are poor. In Comparative Example 2, the small particles obtained by directly mixing and calcining the nickel-cobalt-manganese-aluminum precursor with the lithium source are much worse than those of the embodiment in terms of cycle performance. When the particle size distance of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles is wide (Comparative Example 3), the consistency of the product deteriorates, and the first discharge capacity and capacity retention rate decrease. In addition, the activity of large-sized alumina is low (Comparative Example 4), which leads to a decrease in the doping effect, which in turn causes a decrease in electrical performance.

[0065] Figures 1 to 4 The Malvern 2000 particle size diagrams of the products prepared in Example, Comparative Example 1, Comparative Example 3 and Comparative Example 5 are respectively. Figures 5-7 They are SEM images of the products prepared in Example, Comparative Example 1 and Comparative Example 3. As can be seen from the figure, Comparative Example 3 ( Figure 7 ) The particle sizes of the positive electrode materials prepared are wide and the consistency is poor, resulting in poor initial discharge capacity and cycle performance.

[0066] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material, characterized by: include: Step 1: uniformly mix a polycrystalline nickel-cobalt-manganese ternary small particle precursor and a lithium source, calcine at 600-720° C. for 8-18 hours under oxygen flow, and then naturally cool to room temperature to obtain polycrystalline nickel-cobalt-manganese ternary small particles. The heating rate in the calcination stage is 1-5° C. / min. Furthermore, a polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor is uniformly mixed with a lithium source, calcined at 740-880° C. for 20-30 hours under oxygen flow, and then naturally cooled to room temperature to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles. The heating rate during the calcination stage is 1-5° C. / min. Step 2: uniformly mix the polycrystalline nickel-cobalt-manganese ternary small particles obtained in step 1 with nano-alumina particles, calcine at 450-550° C. for 4-6 hours under oxygen flow, and then naturally cool to room temperature to obtain polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles; Step 3: The large polycrystalline nickel-cobalt-manganese-aluminum quaternary particles prepared in step 1 are mixed evenly with the small polycrystalline nickel-cobalt-manganese-aluminum quaternary particles prepared in step 2 to obtain a polycrystalline nickel-cobalt-manganese-aluminum quaternary positive electrode material having high compaction, long cycle life, and high energy density; The chemical formula of the polycrystalline nickel-cobalt-manganese ternary small particle precursor is Ni x / x+y+z Co y / x+y+z Mn z / x+y+z (OH)2, the chemical formula of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor is Ni x Co y Mn z Al k (OH)2; The mass percentage of the polycrystalline nickel-cobalt-manganese ternary small particles to the total mass of the positive electrode material is 18-22%, and D50 小 3~3.8um, D10 小 ≥1.5um, D90 小 ≤6um, particle size distance meets 0.5<(D90 小 -D10 小 ) / D50 小 <0.9; The mass percentage of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles accounts for 78-82% of the total mass of the positive electrode material, and D50 大 14.5~17.5um, D10 大 ≥10um, D90 大 ≤22um, particle size distance meets 0.3<(D90 大 -D10 大 ) / D50 大 <0.7; The polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles and the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles also satisfy the following relationship: 3.5<(D90 大 -D90 小 ) / D90 小 <4.3,3.5<(D50 大 -D50 小 ) / D50 小 <3.9,3.5<(D10 大 -D10 小 ) / D10 小 <4.

2.

2. The method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material according to claim 1, characterized in that: In the step 1, the molar ratio of the total amount of the polycrystalline nickel-cobalt-manganese ternary small particle precursor to the lithium source is 1:(1.01-1.05); The molar ratio of the total amount of polycrystalline nickel-cobalt-manganese-aluminum quaternary large particle precursor to the lithium source is 1:(1.06-1.12).

3. The method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material according to claim 1, characterized in that: In the step 2, the molar ratio of the polycrystalline nickel-cobalt-manganese ternary small particles to the nano-alumina particles is 2(x+y+z):k.

4. The method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material according to claim 1, characterized in that: In the step 2, the size of the nano-alumina particles is 10-30 nm.

5. The method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material according to claim 1, characterized in that: In step 3, the chemical formula of the positive electrode material is LiNi x Co y Mn z Al k O2, wherein 0.88≤x<1, 0<y<0.12, 0<z<0.12, 0<k<0.005, and x+y+z+k=1.

6. The method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material according to claim 5, characterized in that: The D50 of the positive electrode material is 12-16 μm, and the tap density is 2.45-2.75 g / cm 3 , with a specific surface area of ​​0.2~0.4m 2 / g, particle size distance 1.15<(D90-D10) / D50<1.

25.

7. The method for preparing a high-density, long-cycle, high-energy-density polycrystalline nickel-cobalt-manganese-aluminum quaternary cathode material according to claim 1, characterized in that: The tap density of the polycrystalline nickel-cobalt-manganese-aluminum quaternary small particles is 2.35-2.45 g / cm 3 , with a specific surface area of ​​0.4~0.5m 2 / g; the tap density of the polycrystalline nickel-cobalt-manganese-aluminum quaternary large particles is 2.55~2.75g / cm 3 , with a specific surface area of ​​0.2~0.3m 2 / g.

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