Positive electrode active material and preparation method and application thereof

Abstract

The invention provides a positive electrode active material and a preparation method and application thereof, the positive electrode active material comprises a chemical composition Lim1 (Nia1Cob1Mnc1Ald1Zre1Bf1Tig1Xh1) O2, 0.9 < m1 < 1.05, 0.8 < a1 < 0.96, 0.02 < b1 < 0.1, 0.02 < c1 < 0.1, 0 < d1 < 0.02, 0 < e1 < 0.005, 0 < f1 < 0.01, 0 < = g1 < 0.002, 0 < h1 < = 0.003, a1 + b1 + c1 + d1 + e1 + f1 + g1 + h1 = 1, and X comprises at least one of Sr, Y, W and Nb; and the porosity of the positive electrode active material satisfies a specific relational expression 2. When the positive electrode active material is applied to the lithium ion battery, the cycle performance and the high-temperature storage performance of the battery can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, relates to a positive electrode active material, and particularly relates to a positive electrode active material, a preparation method thereof and an application thereof. Background Art

[0002] Lithium - ion batteries are widely used in portable electronic devices, new energy vehicles, rail transit, energy storage and other fields due to their advantages such as fast charging, wide temperature range, low self - discharge rate, and no pollution. Especially in the field of new energy vehicles, they have great application prospects. However, with the continuous development of technology and the increasing demand of consumers for the performance of electric vehicles, lithium - ion batteries are required to have higher energy density. As one of the main components of lithium - ion batteries, the positive electrode active material plays a crucial role in improving the energy density of the battery.

[0003] Currently, the widely used positive electrode active materials mainly include lithium cobalt oxide, lithium manganate, lithium iron phosphate and ternary materials. Among them, ternary materials have received extensive attention due to their relatively high energy density, mainly because of their relatively high nickel content. Nickel element has a relatively high redox potential, which can enable the battery to work at high voltage, thus achieving a significant increase in energy density. However, due to the relatively low Co element content in ternary materials, it is easy to cause a relatively high lithium - nickel mixing arrangement in the material, reducing the specific capacity of the material and increasing the initial impedance of the material; and the relatively high Ni element content will also lead to higher activity of the material, exacerbating the side reaction between it and the electrolyte, generating a large amount of gas, and deteriorating the high - temperature storage performance of the battery.

[0004] Therefore, it is necessary to further optimize the ternary materials to reduce the material impedance and inhibit the side reaction between them and the electrolyte, effectively improving the cycle performance and high - temperature storage performance of the battery. Summary of the Invention

[0005] Aiming at the above - mentioned defects, the present invention provides a positive electrode active material, which has a relatively low lithium - nickel mixing arrangement rate, can effectively improve the specific capacity of the material and reduce its initial impedance, and improve the cycle stability of the battery; at the same time, the degree of side reaction between this positive electrode active material and the electrolyte is relatively low, which can significantly improve the gas - generation problem and enhance the high - temperature storage performance of the battery.

[0006] The present invention also provides a preparation method of the above - mentioned positive electrode active material. The positive electrode active material prepared by this preparation method can effectively improve the cycle stability and high - temperature storage performance of the battery.

[0007] The present invention also provides a positive electrode sheet, which includes the above - mentioned positive electrode active material or the positive electrode active material prepared by the above - mentioned preparation method. Using this positive electrode sheet in a lithium - ion battery can significantly improve the cycle performance and high - temperature storage performance of the battery.

[0008] The present invention also provides a lithium-ion battery. Since the battery includes the above-mentioned positive electrode active material, or the positive electrode active material prepared by the above-mentioned preparation method, or the above-mentioned positive electrode sheet, the battery has high cycle performance and high-temperature storage performance.

[0009] In the first aspect of the present invention, a positive electrode active material is provided. The positive electrode active material has a chemical composition shown in Formula 1.

[0010] Li m1 (Ni a1 Co b1 Mn c1 Al d1 Zr e1 B f1 Ti g1 X h1 )O2 Formula 1

[0011] In Formula 1, 0.9 < m1 < 1.05, 0.8 < a1 < 0.96, 0.02 < b1 < 0.1, 0.02 < c1 < 0.1, 0 < d1 < 0.02, 0 < e1 < 0.005, 0 < f1 < 0.01, 0 ≤ g1 < 0.002, 0 < h1 ≤ 0.003, a1 + b1 + c1 + d1 + e1 + f1 + g1 + h1 = 1, and X includes at least one of Sr, Y, W, and Nb.

[0012] The positive electrode active material satisfies Formula 2.

[0013]

[0014] In Formula 2, P1 is the porosity of the positive electrode active material between 0 and 4 / 10R1, P2 is the porosity of the positive electrode active material between 4 / 10R1 and 7 / 10R1, and P3 is the porosity of the positive electrode active material between 7 / 10R1 and R1, where R1 is the radius of the positive electrode active material, and P1 > P2 > P3.

[0015] The positive electrode active material as described above, wherein X includes Y and Sr.

[0016] The positive electrode active material as described above, wherein P1 is 1.8 to 3.0%, and / or P2 is 1.5 to 2.7%, and / or P3 is 0.4 to 1.6%.

[0017] The positive electrode active material as described above, wherein the radius R1 of the positive electrode active material is 4 to 7 μm, and / or the specific surface area is 0.4 to 0.7 m 2 / g, and / or D104 is 55 to 65 nm, and / or the lithium-nickel mixing ratio is 0.5 to 2.5%.

[0018] The positive electrode active material as described above, wherein the total dissolution amount contributed by nickel, cobalt, and manganese in each mole of the positive electrode active material is ≤ 2000 ppm;

[0019] Preferably, the nickel dissolution amount contributed by each mole of nickel in the positive electrode active material is ≤ 20 ppm, and / or the cobalt dissolution amount contributed by each mole of cobalt is ≤ 150 ppm, and / or the manganese dissolution amount contributed by each mole of manganese is ≤ 20 ppm.

[0020] The second aspect of the present invention provides a method for preparing the positive electrode active material according to any one of the above, comprising the following steps:

[0021] 1) First sinter the raw materials including the positive electrode active material precursor, lithium source, zirconium source, X source, and first aluminum source at a sintering temperature of 755 - 775 °C for a holding time of 8 - 12 h to obtain a first product;

[0022] Among them, the positive electrode active material precursor satisfies Formula 3,

[0023]

[0024] In Formula 3, P4 is the porosity between 0 and 4 / 10R2 in the positive electrode active material precursor, P5 is the porosity between 4 / 10R2 and 7 / 10R2 in the positive electrode active material precursor, P6 is the porosity between 7 / 10R2 and R2 in the positive electrode active material precursor, where R2 is the radius of the positive electrode active material precursor, and P4 > P5 > P6;

[0025] 2) Crush the first product to obtain a crushed material with a median particle size Dv50 of 8 - 14 μm and a particle size distribution width SPAN of 0.61 - 0.65; mix the crushed material with the raw materials including the cobalt source and titanium source and then perform a second sintering to obtain a second product; among them, the temperature of the second sintering is 670 - 690 °C, and the holding time is 8 - 12 h;

[0026] 3) Mix the second product with the raw materials including the boron source and the second aluminum source and then perform a third sintering at a sintering temperature of 285 - 335 °C for a holding time of 6 - 10 h to obtain the positive electrode active material.

[0027] The method for preparing the positive electrode active material as described above, wherein P4 is 7 - 20%, and / or P5 is 5 - 7%, and / or P6 is 2 - 5%.

[0028] The method for preparing the positive electrode active material as described above, wherein the radius R2 of the positive electrode active material precursor is 4 - 8 μm, and / or the overall porosity is 4 - 10%, and / or the specific surface area is 8 - 12 m 2 / g.

[0029] The method for preparing the positive electrode active material as described above, wherein in the X-ray diffraction pattern of the positive electrode active material precursor, there are a first diffraction peak of the 101 crystal plane and a second diffraction peak of the 001 crystal plane, and the ratio of the peak intensity of the first diffraction peak to the second diffraction peak is (0.8 to 1):1.

[0030] The third aspect of the present invention provides a positive electrode sheet, which includes the positive electrode active material described in the first aspect, or the positive electrode active material prepared by the preparation method described in the second aspect.

[0031] The fourth aspect of the present invention provides a lithium-ion battery, which includes the positive electrode active material described in the first aspect, or the positive electrode active material prepared by the preparation method described in the second aspect, or the positive electrode sheet described in the third aspect.

[0032] By making the positive electrode active material include the chemical composition of the above formula 1, controlling the porosity of the positive electrode active material to gradually decrease from the inside to the outside, and making the porosity satisfy formula 2, the present invention can not only inhibit the migration of nickel to the lithium layer, but also inhibit the cracking of particles caused by stress accumulation, reduce the side reaction between the positive electrode and the electrolyte, thereby effectively improving the cycle performance and high-temperature storage performance of the battery. Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of the positive electrode active material of the present invention;

[0034] Figure 2 It is a schematic structural diagram of the positive electrode active material precursor of the present invention;

[0035] Figure 3 It is a cross-sectional SEM image of the positive electrode active material particles in Example 1 of the present invention;

[0036] Figure 4 It is a cross-sectional SEM image of the positive electrode active material particles in Comparative Example 1 of the present invention.

[0037] Description of the Reference Numerals:

[0038] 1 - The region between 0 and 4 / 10R1 in the positive electrode active material;

[0039] 2 - The region between 4 / 10R1 and 7 / 10R1 in the positive electrode active material;

[0040] 3 - The region between 7 / 10R1 and R1 in the positive electrode active material;

[0041] 4 - The region between 0 and 4 / 10R2 in the positive electrode active material precursor;

[0042] 5 - The region between 4 / 10R2 and 7 / 10R2 in the precursor of the positive electrode active material;

[0043] 6 - The region between 7 / 10R2 and R2 in the precursor of the positive electrode active material; Detailed implementation mode

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] Currently, the energy density of batteries is generally improved by increasing the voltage platform. The higher the voltage platform, the larger the specific capacity and the higher the energy density. The nickel element in the ternary positive electrode active material (such as lithium nickel cobalt manganate, lithium nickel cobalt aluminate) has a relatively high redox potential and a high nickel content, so it can work at a higher voltage, thereby playing a role in increasing the energy density of the battery. However, the cobalt content in the ternary positive electrode active material is relatively low, and nickel and lithium have similar radii, so it is inevitable that lithium ions and nickel ions will exchange positions during the synthesis process, making the diffusion path of lithium ions more complex during the charge and discharge process, affecting the normal insertion and extraction of lithium ions, increasing the diffusion resistance, resulting in capacity decay of the material and an increase in impedance. At the same time, in a high-voltage system, the transition metal ions in the ternary positive electrode active material undergo redox reactions and side reactions with the electrolyte, resulting in the dissolution of transition metal ions and the generation of a large amount of gas, deteriorating the high-temperature storage performance of the battery.

[0046] Based on the above problems, in the first aspect of the present invention, a positive electrode active material is provided. The positive electrode active material has a chemical composition shown in Formula 1,

[0047] Li m1 (Ni a1 Co b1 Mn c1 Al d1 Zr e1 B f1 Ti g1 X h1 )O2 Formula 1

[0048] In Formula 1, 0.9 < m1 < 1.05, 0.8 < a1 < 0.96, 0.02 < b1 < 0.1, 0.02 < c1 < 0.1, 0 < d1 < 0.02, 0 < e1 < 0.005, 0 < f1 < 0.01, 0 ≤ g1 < 0.002, 0 < h1 ≤ 0.003, a1 + b1 + c1 + d1 + e1 + f1 + g1 + h1 + i1 = 1, and X includes at least one of Sr, Y, W, and Nb;

[0049] The positive electrode active material satisfies Formula 2,

[0050]

[0051] In Formula 2, P1 is the porosity between 0 and 4 / 10R1 in the positive electrode active material, P2 is the porosity between 4 / 10R1 and 7 / 10R1 in the positive electrode active material, P3 is the porosity between 7 / 10R1 and R1 in the positive electrode active material, where R1 is the radius of the positive electrode active material, and P1 > P2 > P3.

[0052] Exemplarily, the value of Formula 2 is 3.1, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, or 7, or a range composed of any two of these numerical values.

[0053] Figure 1 The following is a schematic structural diagram of the positive electrode active material of the present invention. As Figure 1 shown, with the center of the positive electrode active material particle as the origin, the positive electrode active material particle is divided into three regions. Region 1 is between 0 and 4 / 10R1, that is, the central circular region; Region 2 is between 4 / 10R1 and 7 / 10R1, that is, the annular region in the middle of the particle; Region 3 is between 7 / 10R1 and R1, that is, the annular region on the outside of the particle. The "porosity P1 between 0 and 4 / 10R1" in the present invention refers to the porosity in the circular region, the "porosity P2 between 4 / 10R1 and 7 / 10R1" refers to the porosity in the middle annular region, and the "porosity P3 between 7 / 10R1 and R1" refers to the porosity in the outer annular region.

[0054] The inventors found that by doping specific metal elements in the ternary positive electrode active material and satisfying the chemical composition of Formula 1, the cycle performance and storage performance of the battery can be effectively improved. After analysis, the inventors believe that the reason may be:

[0055] In the positive electrode active material of the present invention, tetravalent zirconium can reduce trivalent nickel to divalent nickel, obtaining a more stable local electron structure and enhancing the structural stability of the positive electrode active material. The ionic radius of element X (including at least one of Sr, Y, W, and Nb) is relatively large, which is beneficial to increasing the layer spacing, thereby improving the lithium-ion diffusion kinetic performance. Aluminum can form aluminum-oxygen tetrahedrons with oxygen, inhibiting nickel / lithium exchange, enhancing the stability of the layered structure, and preventing the migration of nickel to the lithium layer, thereby reducing the lithium-nickel mixing ratio. At the same time, the bond energies of Zr-O, X-O, and Al-O are higher than those of Ni-O, Co-O, and Mn-O, so lattice oxygen can also be fixed. Therefore, when the positive electrode active material is doped with Al, Zr, and X, it is beneficial to improve the cycle performance and high-temperature storage performance of the battery.

[0056] At the same time, Ti and part of Co in the positive electrode active material exist in the form of a coating. Co therein forms cobalt-lithium oxide during the sintering process, and its structure has good lattice matching with the main body structure of the positive electrode active material, which is beneficial to the formation of a uniform coating. Ti can form titanium-lithium oxide, which not only helps to improve the coating uniformity of cobalt-lithium oxide, avoid side reactions between the positive electrode active material and the electrolyte, but also can fix the lattice oxygen on the surface of the positive electrode active material, which is beneficial to the capacity utilization of the positive electrode active material, thereby effectively improving the cycle performance and high-temperature storage performance of the battery.

[0057] Moreover, B and part of Al in the positive electrode active material also exist in the form of a coating and are located on the outer surface of the positive electrode active material, in contact with the electrolyte. B therein forms boron-lithium oxide during the sintering process, which can effectively reduce the specific surface area of the positive electrode active material, repair the surface damage formed during the preparation process, and further reduce side reactions between the surface of the positive electrode active material and the electrolyte. Al can form aluminum-lithium oxide during the sintering process, which can react with hydrofluoric acid generated by the decomposition of the electrolyte, effectively inhibiting the corrosion of the positive electrode active material by hydrofluoric acid, thereby effectively improving the storage performance of the battery.

[0058] In addition, the porosity of the positive electrode active material particles in the present invention gradually decreases from the inside to the outside, that is, the positive electrode active material particles have a porous interior and a dense exterior structure. The porous interior can provide a buffer for stress and strain, effectively reducing particle cracking caused by stress accumulation and further reducing side reactions with the electrolyte. The dense exterior structure can inhibit crack penetration through the particles and further resist electrolyte corrosion. At the same time, when the porosity of the positive electrode active material particles satisfies formula 2, the pores of the positive electrode active material can change non-linearly from the inside to the outside, so that the positive electrode active material will not be affected by the gradual decrease of its internal porosity and its strength.

[0059] Therefore, the positive electrode active material in the present invention can effectively improve the cycle performance and high-temperature storage performance of the battery.

[0060] The "lithium-nickel mixing ratio" in the present invention refers to the proportion of nickel ions occupying the positions of lithium ions in the cathode active material; it can be obtained by testing through conventional methods in the art. For example, it can be obtained by testing through X-ray diffraction (XRD).

[0061] The radius R1 and porosities P1, P2, and P3 of the cathode active material in the present invention can be obtained by the following methods:

[0062] 1) Use a GATAN 697 argon ion polishing instrument to grind the cathode active material particles until the center of the particles is reached;

[0063] 2) Use a Hitachi Regulus 8100 / SU 8010 scanning electron microscope to take a picture of the cross-section of the ground particles at a magnification of 10K to obtain an SEM image of the particle cross-section;

[0064] 3) Use Meits software to process the above-obtained SEM image to automatically calculate the radius R1 of the cathode active material particles and the porosities P1, P2, and P3 of different regions in the cross-section.

[0065] In a specific embodiment, X includes Y and Sr. When X is preferably Y and Sr, the lithium ion diffusivity can be further improved and the lattice oxygen can be stabilized, enabling the battery to have high cycle performance and high-temperature storage performance.

[0066] To further improve the cycle performance and high-temperature storage performance of the lithium ion battery, the structure of the cathode active material can be further adjusted to improve its lithium-nickel mixing and side reactions with the electrolyte.

[0067] In a specific embodiment, the cathode active material includes a core and a coating layer covering at least part of the surface of the core; the coating layer includes a first coating layer and a second coating layer covering at least part of the surface of the first coating layer; the core includes a chemical composition of Formula 1-1, the first coating layer includes a compound composition shown in Formula 1-2, or the compound composition shown in Formula 1-2 and the chemical compositions shown in Formula 1-3 and / or Formula 1-4, and the second coating layer includes the chemical compositions shown in Formula 1-4 and Formula 1-5.

[0068] Li m2 (Ni a2 Co b2 Mn c2 Al d2 Zr e2 X h2 )O2 Formula 1-1

[0069] Li r Co s O t Formula 1-2

[0070] Li j Ti k O l Formula 1-3

[0071] Li x Al y O z Formula 1-4

[0072] Li u B v O w Formula 1-5

[0073] In Formula 1-1, 1.01 < m2 < 1.07, 0.82 < a2 < 0.96, 0.02 < b2 < 0.09, 0.02 < c2 < 0.09, 0 < d2 < 0.015, 0 < e2 < 0.005, 0 < h2 ≤ 0.003, a2 + b2 + c2 + d2 + e2 + h2 = 1, and X includes at least one of Sr, Y, W, and Nb;

[0074] In Formula 1-2, 1 ≤ r ≤ 2, 1 ≤ s ≤ 2, 2 ≤ t ≤ 4;

[0075] In Formula 1-3, 2 ≤ j ≤ 4, 1 ≤ k ≤ 5, 3 ≤ l ≤ 12;

[0076] In Formula 1-4, 0 ≤ x ≤ 1, 1 ≤ y ≤ 2, 2 ≤ z ≤ 3;

[0077] In Formula 1-5, 1 ≤ u ≤ 3, 1 ≤ v ≤ 4, 2 ≤ w ≤ 7.

[0078] When the positive electrode active material has the above structure, the cycle performance and high-temperature storage performance of the battery can be further improved.

[0079] Specifically, the first coating layer includes the compound composition shown in Formula 1-2, or includes the compound composition shown in Formula 1-2 and the compound composition shown in Formula 1-3, or includes the compound composition shown in Formula 1-2 and the chemical composition shown in Formula 1-4, or includes the compound composition shown in Formula 1-2, the compound composition shown in Formula 1-3, and the chemical composition shown in Formula 1-4.

[0080] Specifically, during the preparation of the positive electrode active material, the ratios of the positive electrode active material precursor, lithium source, zirconium source, X source, and first aluminum source, or the conditions of the first sintering (including sintering temperature, heat preservation time, etc.) during the first sintering process can be further controlled to make the chemical composition of the core satisfy Formula 1-1; the ratios of the first product to the cobalt source, or the first product to the cobalt source and the titanium source and / or aluminum source (i.e., the ratio of the first product to the cobalt source, or the ratio of the first product to the cobalt source and the titanium source, or the ratio of the first product to the cobalt source and the aluminum source, or the ratio of the first product to the cobalt source, titanium source, and aluminum source), or the conditions of the second sintering (including sintering temperature, heat preservation time, etc.) during the second sintering process can be further controlled to make the first coating layer include the compound composition shown in Formula 1-2, or the compound composition shown in Formula 1-2 and the chemical compositions shown in Formula 1-3 and / or Formula 1-4; the ratios of the second product to the boron source and the second aluminum source, or the conditions of the third sintering (including sintering temperature, heat preservation time, etc.) during the third sintering process can be further controlled to make the second coating layer have the chemical compositions shown in Formula 1-4 and Formula 1-5.

[0081] In a specific embodiment, P1 is 1.8 to 3.0%, P2 is 1.5 to 2.7%, and P3 is 0.4 to 1.6%. Within this range, the positive electrode active material particles have a suitable pore distribution inside, enabling the small particles inside to come into full contact with the electrolyte. At the same time, it can also play a buffering role to avoid particle collisions and shrinkage caused by the deintercalation and intercalation of lithium ions. When the porosity of P1, P2, and P3 is lower than the aforementioned range, it will cause the internal structure of the positive electrode active material particles to be too tight, the electrolyte cannot penetrate, and the stress and strain cannot be effectively released, easily leading to particle cracking; when the porosity of P1, P2, and P3 is higher than the aforementioned range, it will cause the structure of the positive electrode active material particles to be too loose, the particle strength to decrease, resulting in the particles being easily broken and pulverized, and the performance will drop significantly.

[0082] Exemplarily, P1 is 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, or 3.0%, or the range composed of any two of these values; P2 is 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, or 2.7%, or the range composed of any two of these values; P3 is 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, or 1.6%, or the range composed of any two of these values.

[0083] In a specific embodiment, the radius R1 of the positive electrode active material is 4 to 7 μm. In this range, the specific surface area of the positive electrode active material particles is more appropriate, which is beneficial to shortening the migration path of lithium ions, improving the diffusion rate of lithium ions, and thus enabling the battery to have higher rate performance; at the same time, it can also further reduce the side reaction with the electrolyte and improve the cycle performance and high-temperature storage performance of the battery.

[0084] Exemplarily, the radius R1 is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm or 7 μm, or the range composed of any two of these values.

[0085] In a specific embodiment, the specific surface area of the positive electrode active material is 0.4 to 0.7 m 2 / g. In this range, the contact area between the electrolyte and the positive electrode active material particles can be effectively reduced, the occurrence of side reactions can be inhibited, thereby further reducing gas generation and improving the high-temperature storage performance of the battery.

[0086] Exemplarily, the specific surface area of the positive electrode active material is 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.55 m 2 / g, 0.6 m 2 / g, 0.65 m 2 / g or 0.7 m 2 / g, or the range composed of any two of these values.

[0087] In a specific embodiment, the D104 of the positive electrode active material is 55 to 65 nm. It should be noted that the positive electrode active material particles in the present invention are secondary particles formed by the aggregation of primary particles. When the D104 of the positive electrode active material is within the foregoing range, the size of the primary particles in the positive electrode active material particles is more appropriate, which is beneficial to making the specific surface area of the material between 0.4 and 0.7 m 2 / g, inhibiting the side reaction between the particles and the electrolyte, and at the same time having a suitable lithium ion diffusion path, so that the material has better rate performance.

[0088] The "D104" in the present invention refers to the average thickness of the crystal grains in the positive electrode active material in the direction perpendicular to the (104) crystal plane, which can be obtained by conventional methods in the art, such as through X-ray diffraction (XRD) testing and fitting the peak corresponding to the 104 crystal plane.

[0089] Exemplarily, D104 is 55 nm, 57 nm, 59 nm, 61 nm, 63 nm or 65 nm, or the range composed of any two of these values.

[0090] Furthermore, the lithium-nickel mixing ratio of the positive electrode active material can be further controlled by adjusting the conditions of the first sintering and the second sintering in the preparation process, such as the sintering temperature, the heat preservation time, and the heating rate, so as to further improve the cycle stability of the battery.

[0091] In a specific embodiment, the lithium-nickel mixing ratio of the positive electrode active material is 0.5-2.5%. Within this range, not only can it ensure that lithium ions can be smoothly deintercalated and intercalated during the cyclic charge and discharge process, but also it can reduce the diffusion barrier of lithium ions in the layered structure to a certain extent, improving the rate performance of the battery. At the same time, an appropriate amount of lithium-nickel mixing can reduce the diffusion barrier of lithium ions in the layered material, thus contributing to improving the rate performance of the material.

[0092] Exemplarily, the lithium-nickel mixing ratio is 0.5%, 1.0%, 1.5%, 2.0% or 2.5%, or a range composed of any two of these values.

[0093] The lithium-nickel mixing ratio in the present invention can be obtained by testing methods commonly used by those skilled in the art. For example, by performing X-ray diffraction analysis (XRD) to obtain the XRD diffraction pattern, the lithium-nickel mixing ratio is the ratio of the diffraction peak intensity of the (003) crystal plane to the diffraction peak intensity of the (104) crystal plane in the pattern.

[0094] Furthermore, the problem of transition metal ion dissolution during the charge and discharge process can be further improved by adjusting the conditions of the second sintering in the preparation method, such as the sintering temperature, the heat preservation time, and the heating rate.

[0095] In a specific embodiment, the total dissolution amount of nickel, cobalt, and manganese per mole of the positive electrode active material ≤ 2000 ppm; preferably, the dissolution amount of nickel contributed by each mole of nickel in the positive electrode active material ≤ 20 ppm, the dissolution amount of cobalt contributed by each mole of cobalt ≤ 150 ppm, and the dissolution amount of manganese contributed by each mole of manganese ≤ 20 ppm.

[0096] When the total dissolution amount contributed by each mole of nickel, cobalt, and manganese in the positive electrode active material is within the aforementioned range, the dissolution amount of transition metal ions in the positive electrode active material is less, which can further reduce the occurrence of side reactions between it and the electrolyte, reduce the gas generation amount, and improve the high-temperature storage performance and cycle performance of the battery.

[0097] Furthermore, when the dissolution amount of nickel contributed by each mole of nickel in the positive electrode active material is within the aforementioned range, excessive nickel ions can be prevented from damaging the negative electrode SEI, improving the high-temperature storage performance of the battery.

[0098] Furthermore, when the dissolution amount of cobalt contributed by each mole of cobalt in the positive electrode active material is within the aforementioned range, excessive cobalt ions can be prevented from damaging the negative electrode SEI, improving the high-temperature storage performance of the battery.

[0099] Further, when the amount of manganese dissolution contributed by each mole of manganese in the positive electrode active material is within the aforementioned range, excessive manganese ions can be prevented from damaging the negative electrode SEI, and the high-temperature storage performance of the battery can be improved.

[0100] The "amount of nickel dissolution contributed by each mole of nickel", "amount of cobalt dissolution contributed by each mole of cobalt", and "amount of manganese dissolution contributed by each mole of manganese" in the present invention can be obtained by the following test methods:

[0101] By digesting 0.4 g of the positive electrode active material in 10 mL of aqua regia, diluting it 100 times with a 2% nitric acid solution, and then performing ICP testing to obtain the chemical formula of the positive electrode active material;

[0102] At an ambient temperature of 25 °C, add 2 g of the positive electrode active material to 0.01 mol / L hydrochloric acid and stir for 2 min. After suction filtration, take the filtrate for ICP testing to obtain the mass contents of nickel, cobalt, and manganese elements in the filtrate respectively. Then, the amount of nickel dissolution contributed by each mole of nickel in the positive electrode active material is the ratio of the mass content of nickel in the filtrate to the molar amount of nickel in the positive electrode active material participating in the test, the amount of cobalt dissolution contributed by each mole of cobalt is the ratio of the mass content of cobalt in the filtrate to the molar amount of cobalt in the positive electrode active material participating in the test, and the amount of manganese dissolution contributed by each mole of manganese is the ratio of the mass content of manganese in the filtrate to the molar amount of manganese in the positive electrode active material participating in the test; among them, the molar amounts of nickel, cobalt, and manganese in the positive electrode active material can be calculated from the mass of the positive electrode active material and the chemical formula obtained by testing.

[0103] The second aspect of the present invention provides a method for preparing the positive electrode active material of the first aspect, including the following steps:

[0104] 1) Perform first sintering on raw materials including a positive electrode active material precursor, a lithium source, a zirconium source, an X source, and a first aluminum source at a sintering temperature of 755-775 °C and a heat preservation time of 8-12 h to obtain a first product;

[0105] Among them, the positive electrode active material precursor satisfies Formula 3,

[0106]

[0107] In Formula 3, P4 is the porosity between 0 and 4 / 10R2 in the positive electrode active material precursor, P5 is the porosity between 4 / 10R2 and 7 / 10R2 in the positive electrode active material precursor, P6 is the porosity between 7 / 10R2 and R2 in the positive electrode active material precursor, where R2 is the radius of the positive electrode active material precursor, and P4 > P5 > P6;

[0108] 2) The first product is pulverized to obtain a pulverized material with a median particle size Dv50 of 8 - 14 μm and a particle size distribution width SPAN of 0.61 - 0.65; the pulverized material is mixed with raw materials including a cobalt source and a titanium source and then subjected to a second sintering to obtain a second product; wherein, the temperature of the second sintering is 670 - 690 °C and the heat preservation time is 8 - 12 h;

[0109] 3) The second product is mixed with raw materials including a boron source and a second aluminum source and then subjected to a third sintering at a sintering temperature of 285 - 335 °C and a heat preservation time of 6 - 10 h to obtain a positive electrode active material.

[0110] Specifically, in step 1), raw materials including a positive electrode active material precursor, a lithium source, a zirconium source, an X source, and an aluminum source are uniformly mixed, and the mixed raw materials are subjected to a first sintering at 755 - 775 °C for a heat preservation time of 8 - 12 h, and a first product is obtained after the sintering ends; wherein, the porosity of the positive electrode active material precursor satisfies the above formula 3.

[0111] Exemplarily, the temperature of the first sintering is 755 °C, 757 °C, 759 °C, 761 °C, 763 °C, 765 °C, 767 °C, 769 °C, 771 °C, 773 °C, or 775 °C, or a range composed of any two of these values; the heat preservation time is 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, or 12 h, or a range composed of any two of these values.

[0112] Exemplarily, the value of formula 3 is 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, or 1.5, or a range composed of any two of these values.

[0113] Figure 2 is a schematic structural diagram of the positive electrode active material precursor of the present invention, as Figure 2 shown. Taking the center of the positive electrode active material precursor particle as the origin, the positive electrode active material precursor particle is divided into three regions. They are region 4 between 0 and 4 / 10R2, that is, the central circular region; region 5 between 4 / 10R2 and 7 / 10R2, that is, the annular region in the middle of the particle; and region 6 between 7 / 10R2 and R2, that is, the annular region on the outside of the particle. The "porosity P4 between 0 and 4 / 10R2" in the present invention refers to the porosity in the circular region, the "porosity P5 between 4 / 10R2 and 7 / 10R2" refers to the porosity in the middle annular region, and the "porosity P6 between 7 / 10R1 and R1" refers to the porosity in the outer annular region.

[0114] The precursor of the positive electrode active material in the present invention refers to a hydroxide containing nickel, cobalt, and manganese. The present invention does not specifically limit the chemical composition of the precursor of the positive electrode active material, and only needs to make the chemical composition of the prepared positive electrode active material satisfy Formula 1.

[0115] The present invention does not specifically limit the source of the precursor of the positive electrode active material, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used. It only needs to make the porosity of the precursor of the positive electrode active material gradually decrease in the direction from its center to the outer surface, and P4, P5, and P6 satisfy Formula 3.

[0116] In the present invention, the test methods for the radius R2 and porosities P4, P5, and P6 of the precursor of the positive electrode active material can be the same as those for the radius R1 and porosities P1, P2, and P3 of the above positive electrode active material, and will not be elaborated here.

[0117] The present invention does not specifically limit the amounts of the precursor of the positive electrode active material, lithium source, zirconium source, X source, and first aluminum source, and only needs to make the prepared positive electrode active material satisfy Formula 1.

[0118] Furthermore, the ratio of the precursor of the positive electrode active material, lithium source, zirconium source, X source, and first aluminum source, or the conditions of the first sintering (including sintering temperature, heat preservation time, etc.) during the first sintering process can be controlled so that the chemical composition of the inner core in the prepared positive electrode active material satisfies Formula 1-1.

[0119] Preferably, the mass content of the zirconium source in the precursor of the positive electrode active material is 3000-5000 ppm; the mass content of the X source in the precursor of the positive electrode active material is 500-4500 ppm; the mass content of the first aluminum source in the precursor of the positive electrode active material is 2500-4500 ppm. Within this range, it is helpful to make the prepared positive electrode active material satisfy Formula 1.

[0120] Preferably, when the X element in the X source includes Sr and Y, the mass content of the strontium source in the precursor of the positive electrode active material is 2000-2500 ppm; the mass content of the yttrium source in the precursor of the positive electrode active material is 1000-2000 ppm.

[0121] In the present invention, the lithium source refers to the raw material providing Li element, the zirconium source refers to the raw material providing Zr element, the X source refers to the raw material providing X element (for example, the yttrium source refers to the raw material providing Y element, and the strontium source refers to the raw material providing Sr element), and the aluminum source refers to the raw material providing Al element. As long as it includes the aforementioned target elements (Li, Zr, Y, Sr, Al), it falls within the definition of the present invention. Exemplarily, the lithium source includes at least one of lithium hydroxide, lithium carbonate, and lithium nitrate; the zirconium source includes at least one of zirconium oxide and zirconium hydroxide; the yttrium source includes at least one of yttrium oxide and yttrium hydroxide; the strontium source includes at least one of strontium oxide and strontium carbonate; the aluminum source includes at least one of aluminum oxide, aluminum hydroxide, and hydroxyaluminum hydroxide.

[0122] The present invention does not specifically limit the sources of the lithium source, zirconium source, X source, and first aluminum source, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0123] The present invention does not specifically limit the mixing method of the raw materials, and it is only necessary to uniformly mix the various materials in the raw materials. For example, mixing can be carried out by using a plowshare mixer.

[0124] In step 2), the above-mentioned first product is subjected to a pulverization treatment, and the median particle size Dv50 of the pulverized material is controlled to be 8 - 14 μm, and the particle size distribution width SPAN is 0.61 - 0.65; subsequently, the pulverized material is uniformly mixed with the raw materials including a cobalt source and a titanium source and then subjected to a second sintering, the sintering temperature is 670 - 690 °C, and the heat preservation time is 8 - 12 h to obtain a second product.

[0125] Exemplarily, the median particle size Dv50 of the pulverized material is 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or 14 μm, or the range composed of any two of these values, and the particle size distribution width SPAN is 0.61, 0.62, 0.63, 0.64 or 0.65, or the range composed of any two of these values.

[0126] Exemplarily, the temperature of the second sintering is 670 °C, 672 °C, 674 °C, 676 °C, 678 °C, 680 °C, 682 °C, 684 °C, 686 °C, 688 °C or 690 °C, or the range composed of any two of these values; the heat preservation time is 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h or 12 h, or the range composed of any two of these values.

[0127] The present invention does not specifically limit the pulverization treatment method, and it is only necessary to make the median particle size Dv50 of the pulverized material be 8 - 14 μm and the particle size distribution width SPAN be 0.61 - 0.65. For example, pulverization can be carried out by mechanical grinding or jet milling.

[0128] The "median particle size Dv50" in the present invention refers to the particle size corresponding to when the cumulative volume distribution percentage of the particles reaches 50%; the "particle size distribution width SPAN" reflects the degree of uniformity of the particle size and can be calculated by (D90 - D10) / D50, where D90 refers to the particle size corresponding to when the cumulative volume distribution percentage of the particles reaches 90%, and D10 refers to the particle size corresponding to when the cumulative volume distribution percentage of the particles reaches 10%; D10, D50, and D90 therein can be obtained by testing with a laser particle size analyzer.

[0129] The present invention does not specifically limit the amounts of the cobalt source and the titanium source, as long as the prepared cathode active material satisfies Formula 1. It should be noted that when i in Formula 1 is 0, the raw materials in step 2) do not include a titanium source.

[0130] Preferably, in the second sintering process, the mass ratio of the titanium source to the cobalt source is (0.08 - 0.16):1. During this process, a coating layer is formed by the cobalt source and the titanium source. When the mass ratio of the cobalt source and the titanium source is within the aforementioned range, it is possible to avoid affecting lithium ion diffusion due to an overly thick coating layer.

[0131] Preferably, the mass content of the titanium source in the cathode active material precursor is 400 - 1000 ppm; preferably, the mass content of the cobalt source in the cathode active material precursor is 5000 - 15000 ppm.

[0132] Furthermore, an aluminum source can also be added during the second sintering process, which can form an aluminum lithium oxide coating layer on the surface and further inhibit the occurrence of side reactions between the surface of the cathode active material and the electrolyte.

[0133] The present invention does not specifically limit the amount of the aluminum source during the second sintering process, as long as the prepared cathode active material satisfies Formula 1.

[0134] Preferably, during the second sintering process, the mass content of the aluminum source in the cathode active material precursor is 500 - 1500 ppm. The type of the aluminum source added during this process can be the same as that in step 1), which will not be elaborated here.

[0135] Furthermore, the ratio of the first product to the cobalt source, or the cobalt source and the titanium source and / or the aluminum source, or the conditions of the second sintering (including sintering temperature, holding time, etc.) during the second sintering process can be controlled such that the first coating layer in the prepared cathode active material has a compound composition shown in Formula 1-2, or a compound composition shown in Formula 1-2 and a chemical composition shown in Formula 1-3 and / or Formula 1-4.

[0136] The cobalt source in the present invention refers to the raw material providing Co element, and the titanium source refers to the raw material providing Ti element. As long as it contains the target elements (Co, Ti), it falls within the scope of the present invention. Exemplarily, the cobalt source includes at least one of cobalt hydroxide, cobalt oxyhydroxide, cobalt nitrate, and cobalt sulfate, and the titanium source includes at least one of titanium oxide and titanium hydroxide.

[0137] The present invention does not specifically limit the sources of the cobalt source and the titanium source, and commercially available products well-known to those skilled in the art or products prepared by conventional preparation methods can be used.

[0138] Further, the product after the sintering can be washed and dried to obtain a second product.

[0139] The present invention does not specifically limit the washing method, and conventional methods in the art can be used for washing. For example, the product after the second sintering can be added to deionized water for stirring and washing; preferably, the mass ratio of the product to deionized water is (0.6 - 1):1.

[0140] The present invention does not specifically limit the drying method, and only the water in the product after washing needs to be evaporated completely. For example, a vibrating dryer can be used for drying. Preferably, the drying temperature is 150 - 180 °C and the drying time is 4 - 6 h.

[0141] In step 3), the above-mentioned second product is uniformly mixed with the raw materials including a boron source and a second aluminum source, and the mixed raw materials are subjected to a third sintering at 285 - 335 °C for a holding time of 6 - 10 h, and a positive electrode active material is obtained after the sintering is completed.

[0142] Exemplarily, the temperature of the third sintering is 285 °C, 290 °C, 295 °C, 300 °C, 305 °C, 310 °C, 315 °C, 320 °C, 325 °C, 330 °C or 335 °C, or the range composed of any two of these values, and the holding time is 6 h, 7 h, 8 h, 9 h or 10 h, or the range composed of any two of these values.

[0143] The present invention does not specifically limit the addition amounts of the boron source and the second aluminum source, as long as the prepared positive electrode active material satisfies formula 1.

[0144] Further, the ratio of the second product to the boron source and the second aluminum source during the third sintering process, or the conditions of the third sintering (including sintering temperature, holding time, etc.) can be controlled so that the second coating layer in the prepared positive electrode active material has the chemical compositions shown in formula 1-4 and formula 1-5.

[0145] Preferably, during the third sintering process, the mass content of the boron source in the precursor of the cathode active material is 1000-1500 ppm; preferably, the mass content of the second aluminum source in the precursor of the cathode active material is 600-1500 ppm.

[0146] The boron source in the present invention refers to a raw material that provides the B element. As long as it contains the target element, it belongs to the definition of the present invention. Exemplarily, the boron source includes at least one of boric acid, metaboric acid, and boron oxide.

[0147] The present invention does not specifically limit the type of the second aluminum source, which can be the same as the limitation in step 1) and will not be elaborated here.

[0148] The present invention does not specifically limit the sources of the boron source and the second aluminum source, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0149] In the preparation method of the cathode active material in the present invention, the doping elements (Zr, X, Al) added in the first sintering exist in the form of bulk phase doping. Among them, tetravalent zirconium can reduce trivalent nickel to divalent nickel, obtaining a more stable local electron structure and enhancing the structural stability of the cathode active material; X has a relatively large ionic radius, which can effectively increase the layer spacing and improve the lithium ion diffusion kinetic performance; aluminum can form aluminum-oxygen tetrahedrons with oxygen, inhibiting nickel / lithium exchange and enhancing the stability of the layered structure; the four dopants act synergistically to maintain the structural stability of the material in the high delithiated state. At the same time, the bond energies of Zr-O, X-O, and Al-O are higher than those of Ni-O, Co-O, and Mn-O. Therefore, lattice oxygen can be fixed, which is beneficial to improving the cycle performance and storage performance of the battery.

[0150] During the second sintering process, by pulverizing the first product to obtain a pulverized material with a specific particle size distribution, the dispersion uniformity of the pulverized material particles is improved; on this premise, mixing and sintering the pulverized material with raw materials including a titanium source and a cobalt source can effectively improve the coating effect of the coating layer. The coating layer is formed by the titanium source and the cobalt source under the second sintering conditions and includes cobalt lithium oxide and titanium lithium oxide; among them, the crystal lattice of the cobalt lithium oxide structure and the first product structure has good matching, which is beneficial to forming a uniform coating; at the same time, due to the low diffusion kinetics of Co in the titanium lithium oxide, the diffusion of Co into the bulk phase of the first product during the second sintering process can be avoided, further improving the coating effect and forming a uniform coating layer, which can form a physical isolation between the material body and the electrolyte and inhibit the reaction between the material and the electrolyte; in addition, the strong Ti-O bond energy can fix the surface lattice oxygen, which is beneficial to capacity utilization and cycle stability.

[0151] The elements (B and Al) added during the third sintering exist in the form of surface coating. After the boron source is melted at high temperature, it uniformly covers the surface of the second product particles. Meanwhile, lithium borate oxide is formed, which can reduce the specific surface area of the material surface, repair the surface damage caused by the wet process, and further reduce the side reactions between the cathode active material and the electrolyte. Moreover, the second aluminum source forms lithium aluminum oxide during the sintering process, and this lithium aluminum oxide can react with the decomposition product hydrofluoric acid of the electrolyte to inhibit the corrosion of the cathode active material by hydrofluoric acid and improve the storage performance of the battery.

[0152] Meanwhile, in the preparation method of the cathode active material in the present invention, a special cathode active material precursor is adopted. The porosity of the precursor particles shows a special distribution, which helps to obtain a cathode active material with the porosity gradually decreasing from the inside to the outside and the porosity satisfying Formula 2. This can not only effectively reduce the particle cracking caused by stress accumulation and further reduce the side reactions with the electrolyte, but also reduce the negative impact on the strength of the cathode active material due to the decrease in the internal porosity of the particles.

[0153] Therefore, the cathode active material prepared by the above preparation method can effectively improve the cycle performance and storage performance of the battery.

[0154] In order to further improve the high-temperature storage performance and cycle performance of the battery, the structure of the cathode active material precursor can be further regulated.

[0155] In a specific embodiment, P4 is 7 - 20%, P5 is 5 - 7%, and P6 is 2 - 5%. Within this range, the porosity of the cathode active material precursor is more appropriate, which helps to make the porosity P1 inside the cathode active material particles satisfy 1.8 - 3.0%, P2 satisfy 1.5 - 2.7%, and P3 satisfy 0.4 - 1.6%, further improving the cycle performance and storage performance of the battery.

[0156] Exemplarily, P4 is 7%, 9%, 11%, 13%, 15%, 17%, 19% or 20%, or the range composed of any two of these values; P5 is 5%, 5.5%, 6%, 6.5% or 7%, or the range composed of any two of these values; P6 is 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, or the range composed of any two of these values.

[0157] In a specific embodiment, the radius R2 of the cathode active material precursor is 4 - 8 μm. Within this range, the diffusion path of lithium ions is appropriate, good crystallinity is obtained, and over-sintering of the material caused by too small particles or under-sintering of the material caused by too large particles is avoided.

[0158] Exemplarily, R2 is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm or 8 μm, or a range composed of any two of these values.

[0159] In a specific embodiment, the overall porosity of the cathode active material precursor is 4-10%. Within this range, it is beneficial for the molten lithium salt to penetrate into the interior of the precursor during the sintering process, and at the same time provides a suitable space for grain growth, which is beneficial to improving the crystallinity of the material, thereby improving the battery capacity and cycling performance.

[0160] Exemplarily, the overall porosity is 4%, 5%, 6%, 7%, 8%, 9% or 10%, or a range composed of any two of these values.

[0161] The "overall porosity" in the present invention can be obtained by the following method:

[0162] 1) Grind the cathode active material particles using a GATAN 697 argon ion polishing instrument until the center of the particles is reached;

[0163] 2) Use a Hitachi Regulus 8100 / SU 8010 scanning electron microscope to take a cross-section of the ground particles at a magnification of 10K to obtain an SEM image of the particle cross-section;

[0164] 3) Use Meits software to process the above-obtained SEM image and automatically calculate the overall porosity of the cathode active material particles.

[0165] In a specific embodiment, the specific surface area of the cathode active material precursor is 8-12 m 2 / g. Within this range, the number of active sites in the cathode active material precursor is relatively appropriate, which is beneficial for the reaction with lithium ions and promotes the diffusion of lithium ions.

[0166] Exemplarily, the specific surface area is 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g or 12 m 2 / g, or a range composed of any two of these values.

[0167] In a specific embodiment, in the X-ray diffraction pattern of the precursor of the positive electrode active material, there are a first diffraction peak of the (101) crystal plane and a second diffraction peak of the (001) crystal plane, and the ratio of the peak intensity of the first diffraction peak to the second diffraction peak is (0.8-1):1. At this time, the exposure level of the active crystal plane (101) in the precursor is appropriate, which is beneficial to improving the exposure degree of the active crystal plane (101) in the positive electrode active material, thereby improving the lithium ion diffusion rate of the positive electrode active material and reducing the initial DC internal resistance DCR of the battery.

[0168] Exemplarily, the ratio of peak intensities is 0.8:1, 0.82:1, 0.84:1, 0.86:1, 0.88:1, 0.9:1, 0.92:1, 0.94:1, 0.96:1, 0.98:1 or 1:1, or a range composed of any two of these values.

[0169] The third aspect of the present invention provides a positive electrode sheet, which includes the positive electrode active material of the first aspect or the positive electrode active material prepared by the preparation method of the second aspect. Since the positive electrode active material included therein has a low lithium-nickel mixing ratio and few side reactions with the electrolyte, when this positive electrode sheet is used in a lithium ion battery, the cycle performance and high temperature storage performance of the battery can be effectively improved.

[0170] The fourth aspect of the present invention provides a lithium ion battery, which includes the positive electrode active material of the first aspect, or the positive electrode active material prepared by the preparation method of the second aspect, or the positive electrode sheet of the third aspect. Therefore, this lithium ion battery has a long cycle life and high high temperature storage performance.

[0171] Hereinafter, the sulfide solid electrolyte of the present invention will be introduced in detail through specific examples.

[0172] Example 1

[0173] 1) Add the precursor of the positive electrode active material, fine powder of LiOH monohydrate, zirconia, strontium oxide, yttrium oxide and aluminum hydroxide to a plowshare mixer, with a mixing speed of 36 Hz and mix for 30 min; among them, the molar ratio of the precursor of the positive electrode active material to LiOH monohydrate is 1:1.045, the mass content of zirconia in the precursor is 4000 ppm, the mass content of strontium oxide in the precursor is 2000 ppm, the mass content of yttrium oxide in the precursor is 1000 ppm, and the mass content of aluminum hydroxide in the precursor is 3000 ppm; sinter the mixed material in an oxygen atmosphere (oxygen concentration in the kiln > 95%) for the first time, with a sintering temperature of 770 °C and a holding time of 12 h to obtain a first product;

[0174] Among them, the chemical formula of the precursor of the positive electrode active material is Ni 0.9 Co 0.05Mn 0.05 (OH)2, with a radius R2 of 4.9 μm, the porosity P4 between 0 and 4 / 10R2 is 9.24%, the porosity P5 between 4 / 10R2 and 7 / 10R2 is 5.61%, and the porosity P6 between 7 / 10R2 and R2 is 3.82%. Substituting these values into Equation 3 gives a result of 0.8, the overall porosity is 5%, and the BET specific surface area is 9 m 2 / g. In the XRD of this cathode active material precursor, there are a first diffraction peak of the 101 crystal plane and a second diffraction peak of the 001 crystal plane, and the intensity ratio of the first diffraction peak to the second diffraction peak is 0.92:1;

[0175] 2) Mechanically crush the above first product to obtain a crushed material with a median particle size Dv50 of 9.5 μm and a SPAN of 0.64; mix this crushed material with cobalt hydroxide and titanium oxide in a high-speed mixer for 30 min. Among them, the mass content of cobalt hydroxide in the precursor is 10000 ppm, and the mass content of titanium oxide in the precursor is 800 ppm; then carry out a second sintering on the obtained mixed material in an oxygen atmosphere (oxygen concentration in the kiln > 95%), the sintering temperature is 676 °C, and the heat preservation time is 11 h; mix the sintered product with deionized water (the mass ratio of the product to deionized water is 0.8:1) for cleaning, stir for 1 min and then carry out suction filtration, and dry the solid phase obtained by suction filtration at 150 °C for 5 h to obtain a second product;

[0176] 3) Mix the second product with boric acid and α-aluminum oxide in a high-speed mixer for 30 min. Among them, the mass content of boric acid in the precursor is 1000 ppm, and the mass content of α-aluminum oxide in the precursor is 1000 ppm; then carry out a third sintering on the obtained mixed material again in an oxygen atmosphere (oxygen concentration in the kiln > 95%), the sintering temperature is 330 °C, and the heat preservation time is 10 h to obtain the cathode active material of this example. Through inductively coupled plasma testing (ICP), the chemical composition of this cathode active material is Li 1.00 (Ni 0.855 Co 0.065 Mn 0.05 Al 0.013 Zr 0.004 Sr 0.002 Y 0.001 B 0.0085 Ti 0.0015 )O2, where the chemical composition of the core is Li 1.05 (Ni 0.883 Co 0.05 Mn 0.05 Al 0.01 Zr 0.004 Sr 0.002 Y 0.001)O2, the chemical composition of the first coating layer is LiCoO2, Li2CoO2, Li4Ti5O 12 , Li2TiO3, and the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3;

[0177] It is tested that the specific surface area of the positive electrode active material is 0.56 m 2 / g, D104 is 56 nm, and the lithium-nickel mixing ratio is 0.89%. Through testing, R1 of the positive electrode active material is 5 μm, the porosity P1 between 0 and 4 / 10R1 is 1.94%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.84%, and the porosity P3 between 7 / 10R1 and R1 is 1.19%. Substituting into Equation 2 for calculation, the result is 6.85.

[0178] Example 2

[0179] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 2), during the second sintering process, titanium oxide is replaced by aluminum hydroxide, and at the same time, the doping amount of cobalt hydroxide is adjusted to 5000 ppm, and the others remain unchanged.

[0180] It is obtained by inductively coupled plasma testing (ICP) that the chemical composition of the positive electrode active material in this example is Li 1.00 (Ni 0.861 Co 0.0575 Mn 0.05 Al 0.016 Zr 0.004 Sr 0.002 Y 0.001 B 0.0085 )O2, where the chemical composition of the core is Li 1.05 (Ni 0.883 Co 0.05 Mn 0.05 Al 0.01 Zr 0.004 Sr 0.002 Y 0.001 )O2, the chemical composition of the first coating layer is Li2CoO2, LiAlO2, and the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3; It is tested that the specific surface area of the positive electrode active material is 0.54 m 2 / g, D104 is 60 nm, and the lithium-nickel mixing rate is 1.08%. Through testing, the R1 of the positive electrode active material is 4.78 μm, the porosity P1 between 0 and 4 / 10R1 is 2.12%, the porosity P2 between 4 / 10R1 and 7 / 10R1 μm is 1.92%, and the porosity P3 between 7 / 10R1 and R1 μm is 1.32%. Then, Equation 2 is 3.31.

[0181] Example 3

[0182] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 2), the pulverized material is mixed with 5000 ppm cobalt hydroxide, 800 ppm titanium oxide, and 1000 ppm aluminum hydroxide, and the others remain unchanged.

[0183] The chemical composition of the positive electrode active material in this example obtained by inductively coupled plasma testing (ICP) is Li 1.00 (Ni 0.8595 Co 0.0575 Mn 0.05 Al 0.016 Zr 0.004 Sr 0.002 Y 0.001 B 0.0085 Ti 0.0015 )O2, where the chemical composition of the core is Li 1.05 (Ni 0.883 Co 0.05 Mn 0.05 Al 0.01 Zr 0.004 Sr 0.002 Y 0.001 )O2, the chemical composition of the first coating layer is Li2CoO2, LiAlO2, Li4Ti5O 12 , the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3; the specific surface area is 0.58 m 2 / g, D104 is 59 nm, and the lithium-nickel mixing rate is 0.92%. Through testing, the R1 of the positive electrode active material is 4.92 μm, the porosity P1 between 0 and 4 / 10R1 is 2.01%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.86%, and the porosity P3 between 7 / 10R1 and R1 is 1.05%. Then, Equation 2 is 5.84.

[0184] Example 4

[0185] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 1), the specific surface area of the positive electrode active material precursor is 8 m 2 / g, and the others remain unchanged.

[0186] In this embodiment, the specific surface area of the positive electrode active material is 0.53 m 2 / g, D104 is 58 nm, and the lithium-nickel mixing ratio is 0.91%. Through testing, the R1 of the positive electrode active material is obtained as 4.9 μm. The porosity P1 between 0 and 4 / 10R1 is 2.15%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.98%, and the porosity P3 between 7 / 10R1 and R1 is 0.96%. Then, Equation 2 is 6.52.

[0187] Example 5

[0188] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 1), the specific surface area of the positive electrode active material precursor is 12 m 2 / g, and the others remain unchanged.

[0189] In this embodiment, the specific surface area of the positive electrode active material is 0.61 m 2 / g, D104 is 59 nm, and the lithium-nickel mixing ratio is 0.81%. Through testing with a laser particle size analyzer, the R1 of the positive electrode active material is obtained as 4.91 μm. The porosity P1 between 0 and 4 / 10R1 is 2.02%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.85%, and the porosity P3 between 7 / 10R1 and R1 is 1.24%. Then, Equation 2 is 3.92.

[0190] Example 6

[0191] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 1), the overall porosity of the positive electrode active material precursor is 4%, the P4 porosity is 7.27%, the P5 porosity is 5.01%, and the P6 porosity is 2.63%. Substituting into Equation 3 for calculation, the result is 1.5, the radius R2 is 5.1 μm, and the BET specific surface area is 9.3 m 2 / g;

[0192] In this embodiment, the specific surface area of the positive electrode active material is 0.52 m 2 / g, D104 is 59 nm, and the lithium-nickel mixing ratio is 1.01%. Through testing, the R1 of the positive electrode active material is obtained as 4.81 μm. The porosity P1 between 0 and 4 / 10R1 is 1.88%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.53%, and the porosity P3 between 7 / 10R1 and R1 is 0.52%. Then, Equation 2 is 3.55.

[0193] Example 7

[0194] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1. The difference is that in step 1), the overall porosity of the positive electrode active material precursor is 10%, the P4 porosity is 16.32%, the P5 porosity is 6.81%, and the P6 porosity is 4.96%. Substituting into Equation 3, the calculated value is 0.5, the radius R2 is 4.8 μm, and the specific surface area BET is 9.6 m 2 / g.

[0195] The specific surface area of the positive electrode active material in this embodiment is 0.66 m 2 / g, D104 is 60 nm, and the lithium-nickel mixing ratio is 0.91%. Through testing, R1 of the positive electrode active material is obtained as 4.94 μm, the porosity P1 between 0 and 4 / 10R1 is 2.91%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 2.68%, and the porosity P3 between 7 / 10R1 and R1 is 1.22%. Then Equation 2 is 6.89.

[0196] Example 8

[0197] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1. The difference is that in step 1), the chemical composition of the positive electrode active material precursor is Ni 0.94 Co 0.03 Mn 0.03 (OH)2; the radius R2 is 5.3 μm, and the specific surface area BET is 9.5 m 2 / g;

[0198] By inductively coupled plasma testing (ICP), the chemical composition of the positive electrode active material in this embodiment is Li 1.03 (Ni 0.895 Co 0.045 Mn 0.02 Al 0.013 Zr 0.004 Sr 0.002 Y 0.001 B 0.0085 Ti 0.0015 )O2, where the chemical composition of the core is Li 1.063 (Ni 0.923 Co 0.03 Mn 0.03 Al 0.01 Zr 0.004 Sr 0.002 Y 0.001 )O2, the chemical composition of the first coating layer is LiCoO2, Li2CoO2, Li4Ti5O 12 , Li2TiO3, and the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3; through testing, it is obtained that the specific surface area of this positive electrode active material is 0.53 m2 / g, D104 is 58 nm, and the lithium-nickel mixing rate is 1.01%. Through testing, the R1 of the positive electrode active material is 4.87 μm, the porosity P1 between 0 and 4 / 10R1 is 1.95%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.86%, and the porosity P3 between 7 / 10R1 and R1 is 1.31%. Then, Equation 2 is 6.41.

[0199] Example 9

[0200] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 1), the chemical composition of the precursor is Ni 0.88 Co 0.07 Mn 0.05 (OH)2, the radius R2 is 5.2 μm, and the specific surface area BET is 8.8 m 2 / g;

[0201] Through inductively coupled plasma testing (ICP), the chemical composition of the positive electrode active material in this example is obtained as Li 1.02 (Ni 0.835 Co 0.085 Mn 0.05 Al 0.013 Zr 0.004 Sr 0.002 Y 0.001 B 0.0085 Ti 0.0015 )O2, where the chemical composition of the core is Li 1.057 (Ni 0.863 Co 0.07 Mn 0.05 Al 0.01 Zr 0.004 Sr 0.002 Y 0.001 )O2, the chemical composition of the first coating layer is LiCoO2, Li2CoO2, Li4Ti5O 12 , Li2TiO3, and the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3; through testing, the specific surface area of this positive electrode active material is 0.56 m 2 / g, D104 is 59 nm, and the lithium-nickel mixing rate is 1.12%. Through testing, the R1 of the positive electrode active material is 4.93 μm, the porosity P1 between 0 and 4 / 10R1 is 1.98%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.84%, and the porosity P3 between 7 / 10R1 and R1 is 1.02%. Then, Equation 2 is 6.30.

[0202] Example 10

[0203] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 1), during the first sintering process, strontium oxide and yttrium oxide are replaced with tungsten trioxide, and the mass content of tungsten oxide in the precursor is 3000 ppm, and the others remain unchanged;

[0204] The chemical composition of the positive electrode active material in this example obtained by inductively coupled plasma testing (ICP) is Li 1.00 (Ni 0.87 Co 0.065 Mn 0.05 Al 0.013 Zr 0.004 W 0.0015 B 0.0085 Ti 0.0015 )O2, where the chemical composition of the core is Li 1.05 (Ni 0.899 Co 0.05 Mn 0.05 Al 0.01 Zr 0.004 W 0.0015 )O2, the chemical composition of the first coating layer is LiCoO2, Li2CoO2, Li4Ti5O 12 , Li2TiO3, and the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3; it is obtained by testing that the specific surface area of this positive electrode active material is 0.60 m 2 / g, D104 is 56 nm, and the lithium-nickel mixing ratio is 1.22%. Through testing, the R1 of the positive electrode active material is 4.88 μm, the porosity P1 between 0 and 4 / 10R1 is 2.03%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.91%, and the porosity P3 between 7 / 10R1 and R1 is 1.12%, then formula 2 is 7.00.

[0205] Example 11

[0206] The preparation method of the positive electrode active material in this example is basically the same as that in Example 1, except that in step 1), during the first sintering process, strontium oxide and yttrium oxide are replaced with niobium pentoxide, and the mass content of niobium pentoxide in the precursor is 3000 ppm, and the others remain unchanged;

[0207] The chemical composition of the positive electrode active material in this example obtained by inductively coupled plasma testing (ICP) is Li 1.00 (Ni 0.855 Co 0.065 Mn 0.05 Al 0.013 Zr 0.004 Nb 0.003 B0.0085 Ti 0.0015 )O₂, where the chemical composition of the core is Li 1.05 (Ni 0.884 Co 0.05 Mn 0.05 Al 0.01 Zr 0.004 Nb 0.003 )O₂, the chemical composition of the first coating layer is LiCoO₂, Li₂CoO₂, Li₄Ti₅O 12 , Li₂TiO₃, and the chemical composition of the second coating layer is Li₂B₄O₇, LiBO₂, Al₂O₃; it is obtained through testing that the specific surface area of this positive electrode active material is 0.61 m 2 / g, D104 is 57 nm, and the lithium-nickel mixing ratio is 1.23%. Through testing, it is obtained that R1 of the positive electrode active material is 4.89 μm, the porosity P1 between 0 and 4 / 10R1 is 2.04%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.90%, and the porosity P3 between 7 / 10R1 and R1 is 1.10%, then Equation 2 is 6.14.

[0208] Comparative Example 1

[0209] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, the difference is that in step 1), the internal and external distribution of the porosity of the positive electrode active material precursor is uniform, the radius R2 is 5.0 μm, the overall porosity is 3.5%, and the specific surface area is 13 m 2 / g. In the XRD of this positive electrode active material precursor, there are a first diffraction peak of the 101 crystal plane and a second diffraction peak of the 001 crystal plane, and the peak intensity ratio of the first diffraction peak to the second diffraction peak is 0.62:1, and the others remain unchanged.

[0210] The specific surface area of the positive electrode active material in this comparative example is 0.65 m 2 / g, D104 is 53 nm, and the lithium-nickel mixing ratio is 1.89%. Through testing, it is obtained that R1 of the positive electrode active material is 4.96 μm, the porosity P1 between 0 and 4 / 10R1 is 1.33%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.12%, and the porosity P3 between 7 / 10R1 and R1 is 0.98%, then Equation 2 is 0.79.

[0211] Comparative Example 2

[0212] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, the difference is that in step 1), zirconium oxide, strontium oxide, yttrium oxide, and aluminum hydroxide are not added during the sintering process, and the others remain unchanged.

[0213] The chemical composition of the positive electrode active material in this comparative example was obtained by inductively coupled plasma testing (ICP) as Li 0.996 (Ni 0.87 Co 0.065 Mn 0.05 Ti 0.0015 Al 0.005 B 0.0085 )O2, where the chemical composition of the core was Li 1.048 (Ni 0.90 Co 0.05 Mn 0.05 )O2, the chemical composition of the first coating layer was LiCoO2, Li2CoO2, Li4Ti5O 12 , Li2TiO3, and the chemical composition of the second coating layer was Li2B4O7, LiBO2, Al2O3; it was obtained by testing that the specific surface area of this positive electrode active material was 1.3 m 2 / g, D104 was 81 nm, and the lithium-nickel mixing ratio was 5.36%. By testing with a laser particle size analyzer, the R1 of the positive electrode active material was obtained as 4.93 μm, the porosity P1 between 0 and 4 / 10R1 was 1.98%, the porosity P2 between 4 / 10R1 and 7 / 10R1 was 1.00%, the porosity P3 between 7 / 10R1 and R1 was 0.93%, and then Equation 2 was 0.14.

[0214] Comparative Example 3

[0215] The preparation method of the positive electrode active material in this comparative example was basically the same as that in Example 1, except that in step 1), the internal and external distribution of the porosity of the positive electrode active material precursor was uniform, the radius R2 was 4.8 μm, the overall porosity was 15%, and the specific surface area was 19 m 2 / g. In the XRD of this positive electrode active material precursor, there were a first diffraction peak of the 101 crystal plane and a second diffraction peak of the 001 crystal plane, and the peak intensity ratio of the first diffraction peak to the second diffraction peak was 0.71:1, with the others remaining unchanged;

[0216] The specific surface area of the positive electrode active material in this comparative example was 0.72 m 2 / g, D104 was 71 nm, and the lithium-nickel mixing ratio was 2.01%. By testing, the R1 of the positive electrode active material was obtained as 5.06 μm, the porosity P1 between 0 and 4 / 10R1 was 3.11%, the porosity P2 between 4 / 10R1 and 7 / 10R1 was 2.97%, the porosity P3 between 7 / 10R1 and R1 was 1.66%, and then Equation 2 was 9.80.

[0217] Comparative Example 4

[0218] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, except that in step 2), cobalt hydroxide and titanium oxide are not added during the sintering process, and the others remain unchanged;

[0219] Through inductively coupled plasma testing (ICP), the chemical composition of the positive electrode active material in this comparative example is found to be Li 0.991 (Ni 0.8515 Co 0.05 Mn 0.05 Al 0.013 Zr 0.004 Sr 0.002 Y 0.001 B 0.0085 )O2, where the chemical composition of the core is Li 1.041 (Ni 0.883 Co 0.05 Mn 0.05 Al 0.01 Zr 0.004 Sr 0.002 Y 0.001 )O2, there is no first coating layer, and the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3; the specific surface area is 0.65 m 2 / g, D104 is 53 nm, and the lithium-nickel mixing ratio is 1.89%. Through laser particle size analyzer testing, the R1 of the positive electrode active material is 4.78 μm, the porosity P1 between 0 and 3.82 μm is 2.11%, the porosity P2 between 3.82 and 6.69 μm is 1.80%, and the porosity P3 between 6.69 and 9.56 μm is 1.77%, then formula 2 is 0.11.

[0220] Comparative Example 5

[0221] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, except that in step 2), the crushed material is mixed with 800 ppm of titanium oxide, and the others remain unchanged.

[0222] Through inductively coupled plasma testing (ICP), the chemical composition of the positive electrode active material in this comparative example is found to be Li 0.998 (Ni 0.85 Co 0.05 Mn 0.05 Al 0.013 Zr 0.004 Sr 0.002 Y 0.001 B 0.0085 Ti 0.0015 )O2, where the chemical composition of the core is Li 1.038 (Ni 0.883 Co 0.05 Mn 0.05 Al0.01 Zr 0.004 Sr 0.002 Y 0.001 )O2, the chemical composition of the first coating layer is Li4Ti5O 12 , Li2TiO3, and the chemical composition of the second coating layer is Li2B4O7, LiBO2, Al2O3; the specific surface area is 0.63 m 2 / g, D104 is 54 nm, and the lithium-nickel mixing ratio is 1.72%. Through testing, the R1 of the positive electrode active material is 4.77 μm, the porosity P1 between 0 and 4 / 10R1 is 2.02%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.83%, and the porosity P3 between 7 / 10R1 and R1 is 1.72%. Then, Equation 2 is 0.64.

[0223] Comparative Example 6

[0224] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 1, except that in step 3), boric acid and α-aluminum oxide are not added during the sintering process, and the others remain unchanged;

[0225] Through inductively coupled plasma testing (ICP), the chemical composition of the positive electrode active material in this comparative example is obtained as Li 0.998 (Ni 0.8685 Co 0.065 Mn 0.05 Al 0.008 Zr 0.004 Sr 0.002 Y 0.001 Ti 0.0015 )O2, where the chemical composition of the core is Li 1.038 (Ni 0.883 Co 0.05 Mn 0.05 Al 0.01 Zr 0.004 Sr 0.002 Y 0.001 )O2, the chemical composition of the first coating layer is LiCoO2, Li2CoO2, Li4Ti5O 12 , Li2TiO3, and there is no second coating layer; the specific surface area is 1.12 m 2 / g, D104 is 53 nm, and the lithium-nickel mixing ratio is 2.19%. Through testing, the R1 of the positive electrode active material is 4.93 μm, the porosity P1 between 0 and 4 / 10R1 is 2.09%, the porosity P2 between 4 / 10R1 and 7 / 10R1 is 1.86%, and the porosity P3 between 7 / 10R1 and R1 is 1.66%. Then, Equation 2 is 0.89.

[0226] The basic parameters are shown in Table 1.

[0227] Table 1

[0228]

[0229] Test Example

[0230] 1. At an ambient temperature of 25 °C, weigh 2 g of the positive electrode active material prepared in the above-mentioned examples and comparative examples, add the weighed positive electrode active material to 0.01 mol / L hydrochloric acid, stir for 2 min, perform suction filtration, and conduct ICP tests on the filtrate to obtain the mass contents of nickel, cobalt, and manganese elements in the filtrate respectively. Then, the nickel dissolution amount contributed by each mole of nickel in the positive electrode active material is the ratio of the mass content of nickel in the filtrate to the molar amount of nickel in the positive electrode active material participating in the test, the cobalt dissolution amount contributed by each mole of cobalt is the ratio of the mass content of cobalt in the filtrate to the molar amount of cobalt in the positive electrode active material participating in the test, and the manganese dissolution amount contributed by each mole of manganese is the ratio of the mass content of manganese in the filtrate to the molar amount of manganese in the positive electrode active material participating in the test; among them, the molar amounts of nickel, cobalt, and manganese in the positive electrode active material can be calculated from the mass of the positive electrode active material and the chemical composition obtained by ICP test. The test and calculation results are shown in Table 2.

[0231] Table 2

[0232]

[0233] As can be seen from Table 2:

[0234] Compared with Comparative Examples 1 - 6, the positive electrode active materials prepared in Examples 1 - 11 have lower nickel, cobalt, and manganese dissolution amounts. From this, it can be known that the positive electrode active material in the present invention can effectively reduce the occurrence of side reactions between it and the electrolyte, reduce the gas generation amount, and improve the high-temperature storage performance and cycling performance of the battery.

[0235] 2. Fabricate lithium-ion batteries with the positive electrode active materials in the above-mentioned examples and comparative examples, including the following steps:

[0236] Mix the above-prepared positive electrode active material with conductive material carbon black and binder polyvinylidene fluoride (PVDF) according to a mass ratio of 94.5:3:2.5, and add the mixed material to N-methyl-2-pyrrolidone (NMP). After stirring evenly, obtain a positive electrode active paste; coat the positive electrode active paste on both sides of the aluminum foil, and after drying, rolling, and slitting, obtain a positive electrode sheet. The double-sided areal density of this positive electrode sheet is 0.014 g / cm 2 , and the tap density is 3.35 g / cm 3 .

[0237] Artificial graphite is mixed with CMC, SBR, and a conductive agent in a mass ratio of 95.5:1.5:2:1, and the obtained mixture is added to deionized water. After stirring evenly, a negative electrode active paste is obtained; the negative electrode active paste is coated on both sides of a copper foil, and after drying, rolling, and slitting, a negative electrode sheet is obtained. The double-sided areal density of the negative electrode sheet is 10 g / cm 2 , and the tap density is 1.55 g / cm 3 .

[0238] The separator uses a porous polyethylene separator. The lithium salt in the electrolyte is lithium hexafluorophosphate (LiPF6), the concentration is 1 M, and the organic solvent is ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a volume ratio of 1:1.

[0239] After stacking the positive electrode sheet, the separator, and the negative electrode sheet, winding is carried out to obtain a bare battery cell, and then the bare battery cell is placed in an aluminum-plastic film package; the above-mentioned electrolyte is injected into the dried bare battery cell, and after vacuum packaging and standing at room temperature, high-temperature formation is carried out. The formation mechanism is: charge at 0.05C for 1 h, then charge at a constant current and constant voltage of 0.2C until 4.25V, the cut-off current is 0.05C, and then discharge at 0.5C until 2.8V to obtain a lithium-ion battery.

[0240] The lithium-ion battery prepared above is tested as follows:

[0241] 1) Capacity

[0242] At 25°C, charge at a constant current of 1C until 4.25V, then charge at a constant voltage of 4.25V until the current is equal to 0.05C, then stand for 5 min, and then discharge at a constant current of 0.33C until the voltage is 2.8V. The discharge capacity this time is recorded as the battery capacity.

[0243] 2) Initial DC internal resistance DCR at 50% SOC

[0244] At 25°C, make the battery at 50% SOC, and perform a pulse test by discharging at a rate of 4C for 10 s. Record the change in voltage ΔU during the 10 s discharge. ΔU (V) = the voltage value at the start of the battery test - the voltage value at the end of the battery test. Then the battery impedance (mΩ) = ΔU / 4C.

[0245] 3) High-temperature storage capacity retention rate

[0246] At 25 °C, it is charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V until the current equals 0.05C, then left standing for 5 minutes, and then discharged at a constant current of 0.33C until the voltage is 2.8V. Record the initial discharge capacity as Q1; then charge it to 4.25V according to the aforementioned charging mechanism, place the fully charged battery in an incubator at 70 °C for 28 days, then take out the battery and discharge it at a constant current of 0.33C until the voltage is 2.8V to obtain the discharge capacity after storage as Q2; then charge and discharge according to the aforementioned charging and discharging mechanism to obtain the discharge capacity as Q3; then the high-temperature storage capacity retention rate (%) = Q2 / Q1 * 100%, and the high-temperature storage capacity recovery rate (%) = (Q3 / Q1) × 100%.

[0247] 4) Cycle performance

[0248] At 45 °C, it is charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 0.5C to 4.25V, and then discharged at a discharge rate of 1C to 2.8V. Record the initial discharge capacity as C4; cycle 300 times according to the aforementioned charge and discharge mechanism to obtain the discharge capacity C5 after cycling, then the cycle capacity retention rate (%) = (C5 / C4) × 100%. The test results are shown in Table 3.

[0249] Table 3

[0250]

[0251] As can be seen from Table 3:

[0252] Compared with Comparative Examples 1 - 6, the lithium-ion batteries in Examples 1 - 11 have higher comprehensive performance. Among them, for the lithium-ion battery in Example 9, its initial DCR at 50% SOC is as low as 73.2 mΩ. Correspondingly, its high-temperature storage capacity retention rate is as high as 87.7%, its high-temperature storage capacity recovery rate is as high as 94.2%, its high-temperature storage capacity recovery rate is as high as 93.5%, and the full charge capacity of this battery is also relatively high, being 208.8 mAh / g. It can be seen from this that the positive electrode active material in the present invention can effectively improve the cycle performance and high-temperature storage performance of the battery.

[0253] 2. Conduct SEM tests on the positive electrode active materials in Example 1 and Comparative Example 1, and the test results are as Figure 3 and Figure 4 shown.

[0254] Figure 3 is the cross-sectional SEM image of the positive electrode active material particles in Example 1. From Figure 3 it can be seen that the porosity inside the positive electrode active material particles gradually decreases from the inside to the outside. Figure 4 is the cross-sectional SEM image of the positive electrode active material particles in Comparative Example 1. FromFigure 4 It can be seen that although there are pores inside the positive electrode active material particles, the number of pores is small. Combining with Table 1, it can be known that the porosity of the positive electrode active material in Example 1 satisfies Equation 1, while the positive electrode active material in Comparative Example 1 does not satisfy Equation 1. Correspondingly, its cycle performance and high-temperature storage performance are significantly reduced. Thus, it can be known that by making the positive electrode active material particles satisfy a special relationship, the cycle performance and high-temperature storage performance of the battery can be effectively improved.

[0255] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material has a chemical composition represented by Formula 1, Li m1 (Ni a1 Co b1 Mn c1 Al d1 Zr e1 B f1 Ti g1 X h1 )O₂ of formula 1 wherein in Formula 1, 0.9 < m1 < 1.05, 0.8 < a1 < 0.96, 0.02 < b1 < 0.1, 0.02 < c1 < 0.1, 0 < d1 < 0.02, 0 < e1 < 0.005, 0 < f1 < 0.01, 0 ≤ g1 < 0.002, 0 < h1 ≤ 0.003, a1 + b1 + c1 + d1 + e1 + f1 + g1 + h1 = 1, and X includes at least one of Sr, Y, W, and Nb; The positive electrode active material satisfies Formula 2, wherein in Formula 2, P1 is the porosity of the positive electrode active material between 0 and 4 / 10R1, P2 is the porosity of the positive electrode active material between 4 / 10R1 and 7 / 10R1, P3 is the porosity of the positive electrode active material between 7 / 10R1 and R1, wherein R1 is the radius of the positive electrode active material, and P1 > P2 > P3.

2. The positive electrode active material according to claim 1, wherein X includes Y and Sr.

3. The cathode active material according to any one of claims 1 or 2, characterized in that, P1 is 1.8 to 3.0%, and / or P2 is 1.5 to 2.7%, and / or P3 is 0.4 to 1.6%.

4. The cathode active material according to any one of claims 1-3, characterized in that, The radius R1 of the positive electrode active material is 4 to 7 μm, and / or the specific surface area is 0.4 to 0.7 m 2 / g, and / or D104 is 55 to 65 nm, and / or the lithium-nickel mixing ratio is 0.5 to 2.5%.

5. The cathode active material according to any one of claims 1-4, characterized in that, The total dissolution amount of nickel, cobalt, and manganese per mole of the positive electrode active material ≤ 2000 ppm; Preferably, the dissolution amount of nickel contributed by each mole of nickel in the positive electrode active material ≤ 20 ppm, and / or the dissolution amount of cobalt contributed by each mole of cobalt ≤ 150 ppm, and / or the dissolution amount of manganese contributed by each mole of manganese ≤ 20 ppm.

6. A method for preparing the cathode active material according to any one of claims 1-5, characterized in that, comprising the following steps: 1) Subjecting raw materials including a positive electrode active material precursor, a lithium source, a zirconium source, an X source, and a first aluminum source to a first sintering at a sintering temperature of 755 to 775 °C and a heat preservation time of 8 to 12 h to obtain a first product; wherein the positive electrode active material precursor satisfies Formula 3, wherein in Formula 3, P4 is the porosity of the positive electrode active material precursor between 0 and 4 / 10R2, P5 is the porosity of the positive electrode active material precursor between 4 / 10R2 and 7 / 10R2, P6 is the porosity of the positive electrode active material precursor between 7 / 10R2 and R2, wherein R2 is the radius of the positive electrode active material precursor, and P4 > P5 > P6; 2) Crushing the first product to obtain a crushed material with a median particle size Dv50 of 8 to 14 μm and a particle size distribution width SPAN of 0.61 to 0.65; mixing the crushed material with raw materials including a cobalt source and a titanium source and then subjecting them to a second sintering to obtain a second product; wherein the temperature of the second sintering is 670 to 690 °C and the heat preservation time is 8 to 12 h; 3) Mixing the second product with raw materials including a boron source and a second aluminum source and then subjecting them to a third sintering at a sintering temperature of 285 to 335 °C and a heat preservation time of 6 to 10 h to obtain the positive electrode active material.

7. The method for preparing the positive electrode active material according to claim 6, characterized in that, P4 is 7 to 20%, and / or P5 is 5 to 7%, and / or P6 is 2 to 5%.

8. The method for preparing the positive electrode active material according to claim 6 or 7, characterized in that, The radius R2 of the precursor of the positive electrode active material is 4 to 8 μm, and / or the overall porosity is 4 to 10%, and / or the specific surface area is 8 to 12 m 2 / g.

9. The preparation method of the cathode active material according to any one of claims 6-8, characterized in that, In the X-ray diffraction pattern of the positive electrode active material precursor, there are a first diffraction peak of the 101 crystal plane and a second diffraction peak of the 001 crystal plane, and the peak intensity ratio of the first diffraction peak to the second diffraction peak is (0.8 to 1):

1.

10. A positive electrode sheet, characterized in that, The positive electrode sheet includes the positive electrode active material according to any one of claims 1-5, or the positive electrode active material prepared by the preparation method according to any one of claims 6-9.

11. A lithium-ion battery, characterized in that, The lithium ion battery includes the positive electrode active material according to any one of claims 1-5, or the positive electrode active material prepared by the preparation method according to any one of claims 6-9, or the positive electrode sheet according to claim 10.

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