Positive electrode material and preparation method therefor, and lithium ion battery

Abstract

The present application relates to a positive electrode material and a preparation method therefor, and a lithium ion battery. The positive electrode material comprises secondary particles, and the secondary particles comprise: a matrix material having a chemical general formula of LiaNixCoyMzNbO2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, 0≤b<0.4, x+y+z+b=1, M is Mn and / or Al, and N comprises at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti, and Ta; and a first coating located on the surface of the matrix material, wherein the first coating comprises lithium tungstate and / or lithium molybdate. The positive electrode material further comprises a second coating located on the surface of the secondary particles, wherein the second coating comprises at least one of Al2O3, TiO2, MgO, CeO2, ZrO2, Al2O3, TiO2, MgO, CeO2, ZrO2, LiAlO2, Li2TiO3, Li4Ti5O12, Li2CeO3, and Li2ZrO3. The positive electrode material of the present application can reduce the over-potential in a battery electrode, and improve the cycle performance and rate capability thereof.

Description

Positive electrode material and preparation method thereof, and lithium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed on September 27, 2023, with application number 202311289625.X and titled “Positive electrode material, preparation method thereof, and lithium-ion battery”. Technical Field

[0003] The present invention relates to the technical field of positive electrode materials, and in particular to positive electrode materials and preparation methods thereof, and lithium ion batteries. Background Art

[0004] At present, high energy density, high operating voltage, long cycle and high safety are urgent requirements for the widespread and large-scale application of lithium-ion batteries. The positive electrode material has a direct and dominant impact on the performance of lithium-ion battery packs. The quality of its performance will directly affect the overall performance of lithium-ion batteries. Therefore, it is urgent to develop positive electrode materials with excellent performance. High nickel ternary positive electrode material LiMO2 (where M is usually Ni, Co, Mn or Al, and the molar fraction of Ni is above 0.6) has a high specific capacity (200mAh g -1 ), high packing density, and low cost make it one of the most viable options. However, as the nickel content increases, its discharge capacity increases proportionally, but this is accompanied by a series of drawbacks such as rapid capacity decay, structural instability, deteriorating thermal performance, and high residual alkali, which limit its commercial application.

[0005] The main reason for the performance degradation of high-nickel ternary cathode materials is a series of harmful processes that occur during the electrochemical cycle, including bulk and surface phase transitions, intergranular cracking of secondary particles, the formation and growth of the cathode-electrolyte interface, and side reactions that consume valuable liquid organic electrolytes, generate gases, and cause transition metal dissolution. Doping and coating modification are among the most commonly used methods to improve the performance of ternary materials. Coating modification can reduce residual alkali on the material surface, effectively slowing side reactions between the electrolyte and the material surface, thereby inhibiting surface phase transitions and O2 release, thereby improving the material's structural stability and extending its lifespan.

[0006] While conventional coatings currently protect the substrate material, they still cannot address the problem of intergranular cracking in secondary particles. Intergranular cracking in secondary particles can lead to the formation of microcracks, which expose more active sites within the particles to react with the electrolyte, further accelerating the degradation of the cathode material structure, reducing its structural and cycling stability, and ultimately, the cycling performance of lithium-ion batteries.

[0007] Summary of the Invention

[0008] The purpose of the present application is to provide a positive electrode material, a preparation method thereof, and a lithium-ion battery. The positive electrode material provided in the present application has a first coating on the surface of its primary particles, and a second coating on the surface of the secondary particles of the positive electrode material. The first coating is coated on the base material, so that the first coating can form a physical barrier on the surface of the base material, thereby effectively reducing the direct contact between the base material and the electrolyte. The second coating is located on the surface of the secondary particles, so that the second coating can increase the roughness of the secondary particle surface, thereby increasing the interfacial adhesion between the secondary particles, inhibiting the deformation of the secondary particles, and thus inhibiting the expansion of microcracks.

[0009] In a first aspect, the present application provides a positive electrode material, the positive electrode material comprising secondary particles, the secondary particles comprising:

[0010] The matrix material is formed by agglomeration of multiple primary particles, and its general chemical formula is Li a Ni x Co y M z N b O2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, 0≤b<0.4, x+y+z+b=1, M is Mn and / or Al, and N includes at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti and Ta; and

[0011] a first coating located on the surface of the base material, wherein the first coating comprises lithium tungstate and / or lithium molybdate;

[0012] The positive electrode material further includes a second coating, which is located on the surface of the secondary particles; the second coating includes Al2O3, TiO2, MgO, CeO2, ZrO2, LiAlO2, Li2TiO3, Li4Ti5O 12 , Li2CeO3, Li2ZrO3.

[0013] In a second aspect, the present application provides a method for preparing a positive electrode material, comprising the following steps: preparing a mixed solution containing a lithium salt, a first metal oxide, a second metal oxide and / or a second metal hydroxide; adding a matrix material to the mixed solution, performing a heating, dispersion treatment and a drying treatment to obtain a composite material, wherein the matrix material has a general chemical formula of Li a Ni x Co y M z N bO2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, 0≤b<0.4, x+y+z+b=1, M is Mn and / or Al, and N includes at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti and Ta; and the composite material is sintered in an oxygen-containing atmosphere to obtain a positive electrode material.

[0014] In a third aspect, the present application provides a lithium-ion battery, comprising a positive electrode plate, wherein the positive electrode plate comprises the positive electrode material of the first aspect or the positive electrode material prepared by the preparation method of the positive electrode material of the second aspect.

[0015] Compared with the existing technology, the technical solution of this application has at least the following beneficial effects:

[0016] The positive electrode material provided in the present application includes secondary particles, the secondary particles include a matrix material, the matrix material includes multiple primary particles and a first coating located on at least a portion of the surface of the matrix material. On the one hand, first, the first coating forms a physical barrier on the surface of the matrix material, which can reduce the direct contact between the matrix material and the electrolyte. Secondly, the lithium tungstate or lithium molybdate on the first coating is an inert material, so that the coating can inhibit the side reaction between the matrix material and the electrolyte, thereby improving the interface stability between the matrix material and the electrolyte. On the other hand, the lithium tungstate or lithium molybdate on the first coating can provide a lithium ion migration path, so that the first coating can improve the electrical conductivity of the particle body and enhance the lithium ion migration rate, thereby improving the electronic and lithium ion conductivity of the positive electrode material and reducing the overpotential in the battery electrode; in addition, the positive electrode material also includes a second coating, which is located on the surface of the secondary particles. The second coating can increase the roughness of the secondary particle surface, thereby increasing the interfacial adhesion between the secondary particles, inhibiting the deformation of the secondary particles and the expansion of microcracks, thereby improving the structural stability of the positive electrode material and improving the cycle performance of the positive electrode material.

[0017] Thus, the first coating provides more lithium ion migration paths for the migration of lithium ions, enabling the first coating to improve the conductivity of the secondary particles and enhance the lithium ion migration rate. However, after the lithium ion migration rate of the secondary particles is improved, during the lithium insertion process of the positive electrode material, the lithium ions are easily aggregated inside the matrix material after passing through the first coating, causing stress concentration inside the matrix material. The present application further increases the roughness of the secondary particle surface through the metal compound, increasing the interfacial adhesion between the secondary particles, so that the metal compound can inhibit the volume change inside the secondary particles caused by the stress concentration of the matrix material on the surface of the secondary particles, thereby reducing the expansion of microcracks. Furthermore, the coating layer and the metal compound coating layer together construct an integrated structure of the positive electrode material, giving the positive electrode material excellent cycle performance and rate performance.

[0018] The present application provides a method for preparing a positive electrode material, comprising preparing a mixed solution containing a lithium salt, a first metal oxide, a second metal oxide and / or a second metal hydroxide, wherein the lithium salt in the mixed solution reacts with the first metal oxide to form lithium metal oxide, adding a matrix material to the mixed solution, and injecting the lithium metal oxide in the mixed solution into the grain boundaries between the matrix materials. During a heating, dispersion and drying process, the lithium metal oxide coats the matrix material, while the second metal oxide and / or the second metal hydroxide coats the surface of the matrix material to form a composite material. The composite material is sintered in an oxygen-containing atmosphere, and the oxygen can react with the defects on the surface of the positive electrode material to oxidize the reduced state of the metal ions, thereby repairing the surface defects of the positive electrode material during the sintering process. The surface of the base material has a first coating, which provides more lithium ion migration paths for the migration of lithium ions. This first coating can improve the conductivity of the secondary particles and enhance the lithium ion migration rate. The present application further uses a second coating to increase the surface roughness of the secondary particles and increase the interfacial adhesion between the secondary particles. This allows the second coating to inhibit the volume changes within the secondary particles caused by lithium ion migration on the surface of the secondary particles, thereby reducing the expansion of microcracks. Furthermore, the first coating and the second coating together form an integrated structure of the positive electrode material, giving the positive electrode material excellent cycle performance and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and examples.

[0020] FIG1 is a flow chart of a process for preparing a positive electrode material according to an embodiment of the present application;

[0021] FIG2 is a SEM image of the positive electrode material prepared in Example 1 of the present application;

[0022] FIG3 is a SEM image of the positive electrode material prepared in Comparative Example 1 of the present application;

[0023] FIG4a is a particle strength curve of the positive electrode material prepared in Example 1 of the present application;

[0024] FIG4 b is a particle strength curve of the positive electrode material prepared in Comparative Example 1 of the present application;

[0025] FIG5a is a comparison diagram of the positive electrode material prepared in Example 1 of the present application before and after compression;

[0026] FIG5 b is a comparison diagram of the positive electrode material prepared in Comparative Example 1 of the present application before and after compression;

[0027] FIG6 is an EIS graph of the positive electrode materials prepared in Examples 1, 5, and 6 of the present application;

[0028] FIG7 is an XRD diagram of the positive electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0029] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0030] It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0031] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "an", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0032] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0033] In the first aspect, the present application provides a positive electrode material, the positive electrode material includes secondary particles and a metal compound, the secondary particles include the matrix material, the matrix material is formed by agglomeration of multiple primary particles, and the chemical formula of the matrix material is Li a Ni x Co y M z N b O2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, 0≤b<0.4, x+y+z+b=1, M is Mn and / or Al, N includes at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti and Ta, a represents the molar ratio of Li element to Ni+Co+M+N element, and x, y, z, b represent the molar content of the corresponding element respectively; the secondary particles further include a first coating, the first coating is located on at least a portion of the surface of the base material, the first coating includes lithium tungstate and / or lithium molybdate; the second coating is located on the surface of the secondary particles; the second coating includes Al2O3, TiO2, MgO, CeO2, ZrO2, LiAlO2, Li2TiO3, Li4Ti5O 12, Li2CeO3, Li2ZrO3.

[0034] It can be understood that in the present application, the surface of the secondary particles includes a first type of area and a second type of area, the first type of area includes the first coating and the second coating, the second coating is located on the surface of the first coating, the second type of area includes the primary particles and the second coating, and the second coating is located on the surface of the primary particles. The matrix material is formed by the aggregation of multiple primary particles, and the multiple primary particles are arranged radially outward from the center of the matrix material. The first coating is located on the outer surface of all or part of the outermost primary particles. For the outermost primary particles whose outer surface is covered by the first coating, the surface of the secondary particles is the first coating, that is, the first type of area. For the outermost primary particles whose outer surface is not covered by the first coating, the surface of the secondary particles is the outer surface of the primary particles, that is, the second type of area. That is, the second coating can be located on the surface of the first coating or on the outer surface of the outermost primary particles. It should be noted that the outer surface of the outermost primary particles refers to the surface of the outermost primary particles away from the center of the matrix material.

[0035] The positive electrode material provided in the present application includes secondary particles, the secondary particles include a matrix material, the matrix material includes multiple primary particles and a first coating located on at least a portion of the surface of the matrix material. On the one hand, first, the first coating forms a physical barrier on the surface of the matrix material, which can reduce the direct contact between the matrix material and the electrolyte. Secondly, the lithium tungstate or lithium molybdate on the first coating is an inert material, so that the coating can inhibit the side reaction between the matrix material and the electrolyte, thereby improving the interface stability between the matrix material and the electrolyte. On the other hand, the lithium tungstate or lithium molybdate on the first coating can provide a lithium ion migration path, so that the first coating can improve the electrical conductivity of the particle body and enhance the lithium ion migration rate, thereby improving the electronic and lithium ion conductivity of the positive electrode material and reducing the overpotential in the battery electrode; in addition, the positive electrode material also includes a second coating, which is located on the surface of the secondary particles. The second coating can increase the roughness of the secondary particle surface, thereby increasing the interfacial adhesion between the secondary particles, inhibiting the deformation of the secondary particles and the expansion of microcracks, thereby improving the structural stability of the positive electrode material and improving the cycle performance of the positive electrode material.

[0036] Thus, the first coating provides more lithium ion migration paths for the migration of lithium ions, enabling the first coating to improve the conductivity of the secondary particles and enhance the lithium ion migration rate. However, after the lithium ion migration rate of the secondary particles is improved, during the lithium insertion process of the positive electrode material, the lithium ions are easily aggregated inside the matrix material after passing through the first coating, causing stress concentration inside the matrix material. The present application further increases the roughness of the secondary particle surface through the metal compound, increasing the interfacial adhesion between the secondary particles, so that the metal compound can inhibit the volume change inside the secondary particles caused by the stress concentration of the matrix material on the surface of the secondary particles, thereby reducing the expansion of microcracks. Furthermore, the coating layer and the metal compound coating layer together construct an integrated structure of the positive electrode material, giving the positive electrode material excellent cycle performance and rate performance.

[0037] Specifically, the value of a can be, for example, 0.95, 0.98, 1.01, 1.02, 1.03, 1.05 or 1.1. When the molar content of Li in the positive electrode material (the molar content of Li here refers to the molar ratio of Li element to Ni+Co+M+N element) is within the above range, the battery using the positive electrode material has a higher charge and discharge specific capacity; when the molar ratio of Li in the positive electrode material is less than the above range, Ni easily enters the Li layer, and the cation mixing is obvious, resulting in poor stability of the electrochemical cycle. When the molar ratio of Li in the positive electrode material is higher than the above range, excess residual alkali will form on the surface of the material, and it is easy to form a jelly-like shape during the preparation of the slurry, affecting the coating effect; secondly, the effect of the residual alkali on the electrochemical performance is mainly reflected in the increase of irreversible capacity loss and the deterioration of the cycle performance.

[0038] The value of x can be, for example, 0.6, 0.7, 0.8, 0.85, 0.86, 0.87, 0.88, 0.9, 0.92, 0.95, 0.97 or 0.99, the value of y can be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.3, 0.37 or 0.39, and the value of z can be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.3, 0.37 or 0.39, etc., and are not limited thereto. When the total molar content of Ni, Co and M in the positive electrode material is within the above range, the battery has good electrochemical performance. When the total molar content of Ni, Co and M in the positive electrode material is lower than the above range, the battery's first irreversible capacity is high, and the cycle and rate performance are poor; when the total molar content of Ni, Co and M in the positive electrode material is higher than the above range, the battery's capacity is low and cannot meet the energy density requirements, affecting practical applications.

[0039] The value of b may be, for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.35 or 0.39, etc., and is not limited here.

[0040] In some embodiments, the thickness of the coating layer formed by the first coating is 3 nm to 30 nm, specifically 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm or 30 nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0041] In some embodiments, the second coating is granular, and the particle size of the granular second coating is 10nm to 100nm, specifically 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0042] In some embodiments, the mass proportion of the second coating in the positive electrode material is 0.05wt% to 0.8wt%, specifically 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt% or 0.8wt%, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0043] In some embodiments, the second coating forms a coating layer with a thickness of 2nm to 40nm on at least part of the surface of the secondary particles, which can be 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm or 40nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here. The thickness of the second coating refers to the distance between the outer surface of the second coating layer and the surface in contact with the secondary particles. It can be understood that since the trace water in the battery will react with the lithium salt in the electrolyte to generate hydrogen fluoride HF, the coating thickness of the second metal compound is too thin, and the effect of resisting HF corrosion on the active material in the positive electrode material is poor, thereby affecting the cycle performance of the positive electrode material; if the coating thickness of the second metal compound is too thick, it will hinder the Li + diffusion, leading to higher Li + The ion migration barrier, in turn, affects the rate performance and cycle performance of the cathode material. Controlling the coating thickness of the second metal compound within the above range can, on the one hand, effectively block direct contact between the cathode material and the electrolyte, reducing side reactions between the cathode material and the electrolyte, and on the other hand, increase the lithium ion migration rate, thereby improving the rate performance and cycle performance of the cathode material.

[0044] In some embodiments, the average particle strength of the positive electrode material is ≥45 MPa. The average particle strength of the positive electrode material can specifically be 45 MPa, 46 MPa, 47 MPa, 48 MPa, 49 MPa, 50 MPa, 55 MPa, or 60 MPa, etc., without limitation herein. Controlling the average particle strength of the positive electrode material within the above range can reduce the formation and expansion of microcracks, improve the structural stability of the positive electrode material, and further enhance the cycling stability of the positive electrode material.

[0045] In some embodiments, the compacted density of the positive electrode material is 2.1 g / cm 3 ~4.6g / cm 3 Specifically, the compaction density of the positive electrode material can be 2.1 g / cm 3 , 2.5g / cm 3 , 2.8g / cm 3 , 3g / cm 3 、3.5g / cm 3 , 4g / cm 3 , 4.3g / cm 3 , 4.5g / cm 3 or 4.6g / cm 3 etc., not limited here.

[0046] In some embodiments, the tap density of the positive electrode material is 1.7 g / cm 3 ~4.1g / cm 3 , specifically 1.7g / cm 3 , 2g / cm 3 , 2.2g / cm 3 , 2.5g / cm 3 , 3g / cm 3 、3.5g / cm 3 , 4g / cm 3 or 4.1 g / cm 3 Of course, it can also be other values ​​within the above range, which is not limited here.

[0047] In some embodiments, the ratio of the compacted density to the tapped density of the positive electrode material is 1.05 to 1.3, specifically 1.05, 1.08, 1.1, 1.15, 1.2, 1.25, or 1.3, and of course other values ​​within the above range are also possible, and are not limited here. By controlling the ratio of the compacted density to the tapped density of the positive electrode material within the above range, the compactness between particles in the battery electrode sheet made of the positive electrode material can be improved, the mass per unit volume of the electrode sheet and the shear strength can be improved, thereby giving the battery high capacity and safety and stability.

[0048] In some embodiments, the average particle size D50 of the positive electrode material is 9 μm to 20 μm, specifically 9 μm, 9.5 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, etc., and of course other values ​​within the above range are also possible, and are not limited here. Controlling the particle size of the positive electrode material within the above range is beneficial to improving the structural stability, thermal stability, and long-cycle stability of the positive electrode material.

[0049] In some embodiments, the peak intensity I of the (006) crystal plane of the positive electrode material obtained by X-ray diffraction pattern measurement is 006 , the peak intensity of (101) crystal plane I 101 and the peak intensity I of the (102) crystal plane 102 The relationship between satisfies: 0.6≤(I 006 +I 102 ) / I 101 ≤0.85. (I 006 +I 102 ) / I 101 The specific value of can be 0.6, 0.65, 0.7, 0.72, 0.75, 0.78, 0, 0.79, 0.8, 0.83 or 0.85, etc., which is not limited here.

[0050] It should be noted that when I 006 , I 101 , I 102 The relationship between satisfies: 0.6≤(I 006 +I 102 ) / I 101 When ≤0.85, it indicates that the positive electrode material has good hexagonal crystal structure order and the positive electrode material is a layered structure. Ideally, Li + Occupies the 3b position, transition metals such as Ni, Co, and Mn randomly occupy the 3a position, but due to Li + and Ni 2+ Ionic radii are similar and tend to occupy each other's positions, forming a mixed arrangement of cations. When Ni atoms occupy the sites of the lithium layer, the intensity of the 101 peak decays rapidly, resulting in a decrease in the structural order of the positive electrode material.

[0051] When(I 006 +I 102 ) / I 101When the value is greater than 0.85, the degree of cation mixing in the positive electrode material is high, the structural order of the material is reduced, and the deintercalation of lithium ions in the material is hindered. The structural order of the positive electrode material includes the structural order of the bulk material inside and on the surface. The formation of residual alkali on the surface of the positive electrode material will lead to ion rearrangement on the surface of the material, thereby reducing the structural order of the material. However, appropriate residual alkali will help Li + diffusion, promoting the improvement of electrochemical performance, so when (I 006 +I 102 ) / I 101 When the value is less than 0.6, although the orderliness of the material structure increases, the overall performance is not optimal. (I 006 +I 102 ) / I 101 The positive electrode material with a value between 0.6 and 0.85 has good structural stability and good overcharge resistance (as shown in Figure 7).

[0052] In some embodiments, the peak intensity I of the (110) crystal plane of the positive electrode material obtained by X-ray diffraction pattern measurement is 110 The peak intensity I of (108) crystal plane 108 The relationship between them satisfies: |I 110 -I 108 |=0.39~0.46. |I 110 -I 108 The specific value of | can be 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45 or 0.46, etc., which is not limited here. 108 -I 110 When the value of | is within the above range, as shown in Figure 7, the (108) and (110) diffraction peaks split significantly, indicating that the positive electrode material forms a better layered structure, which can promote the Li + The rapid deintercalation in the bulk structure and surface layer gives the positive electrode material high rate performance and better kinetic stability.

[0053] In some embodiments, the surface free lithium content and specific surface area of ​​the positive electrode material satisfy the relationship: P = G + 819.8H, and satisfy: 1400 ≤ G + 819.8H ≤ 1600, wherein G represents the mass content of the surface free lithium of the positive electrode material in ppm, and H represents the specific surface area of ​​the positive electrode material in m 2 / g.

[0054] It should be noted that the free lithium on the surface of cathode materials primarily comes from residual alkali on the surface of the material. The formation of residual alkali on the surface can lead to ion rearrangement on the surface of the material, thereby reducing the order of the material structure. The cathode material has a large specific surface area (i.e., a porous structure), so that cracks encounter a large number of pore walls during the propagation process. The pore walls force the cracks to change direction, thereby consuming the potential energy during the propagation of microcracks, thereby inhibiting the expansion of intercrystalline cracks. On the basis of the above-mentioned positive electrode material increasing the roughness of the secondary particle surface through the first coating and the second coating to increase the interfacial adhesion between the secondary particles, thereby inhibiting the microcracks of the secondary particles, the present application further limits the specific surface area H and the surface free lithium content G of the positive electrode material to satisfy the above-mentioned relationship, so that the surface free lithium content G of the positive electrode material is less and the specific surface area H is relatively large. Therefore, on the one hand, the surface free lithium content G of the positive electrode material is less, which reduces the possibility of free lithium causing ion rearrangement on the surface of the material, and makes the positive electrode material have a higher structural order. On the other hand, the specific surface area H is relatively large, so that the positive electrode material has a porous structure, thereby consuming the potential energy in the process of microcrack diffusion. In this way, the positive electrode material has a higher structural order and structural stability, further inhibits the expansion of microcracks, and thus improves the cycle performance and rate performance of the battery.

[0055] In some embodiments, the specific surface area of ​​the positive electrode material is 0.2 m 2 / g~1.3m 2 / g, specifically 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g or 1.3m 2 When the specific surface area of ​​the positive electrode material is controlled within the above range, it is beneficial to improve the cycle performance of the lithium battery made of the positive electrode material.

[0056] In some embodiments, the surface free lithium content of the positive electrode material is 500ppm to 1300ppm, specifically 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm or 1300ppm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0057] In some implementations, the value of P may be 1400, 1430, 1500, 1520, 1530, or 1600, etc., which is not limited here.

[0058] In some embodiments, there is a negative correlation between the specific surface area of ​​the positive electrode material and the surface free lithium content, that is, when the specific surface area of ​​the positive electrode material increases, the surface free lithium content of the positive electrode material decreases accordingly.

[0059]

[0060] In a second aspect, the present application provides a method for preparing a positive electrode material, as shown in FIG1 , comprising the following steps: step S10, preparing a mixed solution containing a lithium salt, a first metal oxide, a second metal oxide and / or a second metal hydroxide; step S20, adding a matrix material to the mixed solution, performing a heating, dispersion treatment and a drying treatment to obtain a composite material containing the matrix material, wherein the general chemical formula of the matrix material is Li a Ni x Co y M z N b O2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, 0≤b<0.4, x+y+z+b=1, M is Mn and / or Al, N includes at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti and Ta, a represents the molar ratio of Li element to Ni+Co+M+N element, and x, y, z, and b represent the molar content of the corresponding elements respectively; step S30, sintering the composite material in an oxygen-containing atmosphere to obtain a positive electrode material.

[0061] The present application provides a method for preparing a positive electrode material, comprising preparing a mixed solution containing a lithium salt, a first metal oxide, a second metal oxide, and / or a second metal hydroxide, wherein the lithium salt in the mixed solution reacts with the first metal oxide to form a lithium metal oxide, adding a matrix material to the mixed solution, and injecting the lithium metal oxide in the mixed solution into the grain boundaries between the matrix materials. During a heating, dispersion, and drying process, the lithium metal oxide and the matrix material are coated, and at the same time, the second metal oxide and / or the second metal hydroxide coat the matrix material to form a composite material; sintering the composite material in an oxygen-containing atmosphere, wherein oxygen can react with defects on the surface of the positive electrode material to oxidize the reduced state of the metal ions, thereby repairing the surface defects of the positive electrode material during the sintering process. The positive electrode material has a first coating, and a second coating also exists on the surface of the secondary particles. The second coating is a product of high-temperature calcination of the second metal oxide and / or the second metal hydroxide. The second coating may include the second metal oxide and / or a second metal oxide containing Li. The first coating provides a lithium ion migration path for lithium ions, reducing stress concentration within the secondary particles during lithium ion migration and minimizing volume changes during lithium ion migration. The second coating then provides structural support on the surface of the secondary particles, inhibiting volume changes within the secondary particles caused by lithium ion migration, thereby reducing the propagation of microcracks. Furthermore, the first and second coatings together form an integrated structure for the positive electrode material, giving it excellent cycle performance and rate capability.

[0062] The preparation method of the present application is described in detail below with reference to the examples:

[0063] Before step S10, the method further includes: x Co y M z Oxide or Ni x Co y M z The hydroxide and the lithium source are mixed to obtain a mixture, and the mixture is sintered to obtain a matrix material, wherein M is Mn and / or Al. 0.6≤x<1, 0<y<0.4, 0<z<0.4.

[0064] In some embodiments, the amount of the lithium source added is such that the ratio of the sum of the molar contents of Ni, Co and M to the molar content of Li is 1:(0.95-1.1), specifically 1:0.95, 1:0.99, 1:1.01, 1:1.02, 1:1.03, 1:1.05, 1:1.06, 1:1.08 and 1:1.1, etc., are not limited here. Controlling the ratio of the sum of the molar contents of Ni, Co and M to the molar content of Li within the above range is beneficial to the formation of matrix material grains and the improvement of the electrochemical properties of the material. Preferably, the amount of the lithium source added is such that the ratio of the sum of the molar contents of Ni, Co and M to the molar content of Li is 1:1.01.

[0065] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate, and lithium oxalate.

[0066] In some embodiments, the mixture further comprises a compound containing a doping element N, wherein N comprises at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti, and Ta.

[0067] In some embodiments, the compound containing the doping element N includes at least one of an oxide of the element N and a hydroxide of the element N.

[0068] In some embodiments, the amount of the compound containing the doping element N is such that the ratio of the total molar content of Ni, Co, and M to the molar content of N is 1:(0-0.4). Specifically, the ratio may be 1:0, 1:0.1, 1:0.2, 1:0.3, or 1:0.4, etc., which is not limited here.

[0069] In some embodiments, the mixing conditions for obtaining the mixture are: dry grinding at 10° C. to 50° C. for 0.3 to 2 hours. The dry grinding temperature can be 10° C., 20° C., 30° C., 40° C., and 50° C., and can also be other values ​​within the above range. The dry grinding time can be 0.3 h, 0.5 h, 0.8 h, 1 h, 1.5 h, or 2 h, and can also be other values ​​within the above range.

[0070] In some embodiments, the sintering conditions for obtaining the matrix material are: pre-sintering the mixture at 400° C. to 600° C. for 3 h to 9 h in an oxygen-containing atmosphere, and then sintering at 650° C. to 950° C. for 8 h to 16 h.

[0071] Specifically, the temperature in the first stage of sintering can be 400°C, 420°C, 450°C, 470°C, 480°C, 500°C, 520°C, 550°C, 580°C, and 600°C, and other values ​​within the aforementioned range are also possible and are not limited herein. The holding time in the first stage of sintering can be 3 hours, 3.5 hours, 4 hours, 5.5 hours, 6 hours, 7.5 hours, or 9 hours, and other values ​​within the aforementioned range are also possible and are not limited herein.

[0072] The second stage sintering temperature can be 650°C, 720°C, 750°C, 770°C, 780°C, 800°C, 820°C, 850°C, 880°C, and 920°C, and other values ​​within the aforementioned range are also possible and are not limited herein. The second stage sintering holding time can be 8 hours, 10 hours, 12 hours, 12.5 hours, 13 hours, 15 hours, or 16 hours, and other values ​​within the aforementioned range are also possible and are not limited herein.

[0073] In some embodiments, the sintering equipment includes a stationary box furnace or a roller hearth continuous furnace.

[0074] Step S10: preparing a mixed solution containing a lithium salt, a first metal oxide, a second metal oxide and / or a second metal hydroxide.

[0075] In some embodiments, the step of preparing a mixed solution containing a lithium salt, a first metal oxide, a second metal oxide and / or a second metal hydroxide comprises adding the lithium salt to a solvent, heating and stirring at 40°C to 80°C to form a transparent solution, adding the first metal oxide thereto and continuing to heat and stir at 40°C to 80°C until a transparent solution is formed again, then adding the second metal oxide and / or second metal hydroxide thereto, and ultrasonically dispersing at 50Hz to 100Hz for 10min to 60min.

[0076] In some embodiments, the mass ratio of the lithium salt to the first metal oxide is 1:(1-3), specifically 1:1, 1:1.2, 1:1.5, 1:2, 1:2.3, 1:2.5 or 1:3, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0077] In some embodiments, the mass ratio of the lithium salt to the second metal oxide and / or second metal hydroxide is 1:(0.5-3), specifically 1:0.5, 1:0.8, 1:1, 1:1.5, 1:1.8, 1:2, 1:2.3, 1:2.5 or 1:3, etc., which is not limited here.

[0078] In some embodiments, the mixed solution further includes a solvent.

[0079] In some embodiments, the mass ratio of the total mass of the lithium salt and the first metal oxide to the solvent is 1:(2-6), specifically 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5 or 1:6, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0080] In some embodiments, the solvent includes at least one of water, ethanol, and acetone.

[0081] In some embodiments, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate, and lithium oxalate.

[0082] In some embodiments, the first metal oxide includes at least one of tungsten oxide and molybdenum oxide.

[0083] In some embodiments, the second metal oxide includes at least one of aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, and ceria.

[0084] In some embodiments, the second metal hydroxide includes at least one of aluminum hydroxide, magnesium hydroxide, titanium hydroxide, zirconium hydroxide, and cerium hydroxide.

[0085] Step S20: adding a matrix material to the mixed solution, performing a heating, dispersion and drying process to obtain a composite material containing the matrix material, wherein the general chemical formula of the matrix material is Li a Ni x Co y M z N b O2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, x+y+z+b=1, 0≤b<0.4, M is Mn and / or Al, and N includes at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti and Ta.

[0086] In some embodiments, the average particle size D50 of the matrix material is 9 μm to 18 μm, specifically 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or 18 μm, etc., and other values ​​within the above range are also possible and are not limited here. Controlling the particle size of the matrix material within the above range is beneficial to improving the structural stability, thermal stability, and long-cycle stability of the positive electrode material.

[0087] In some embodiments, the mass ratio of the matrix material to the mixed solution is 1:(0.3-1.5), specifically 1:0.3, 1:0.4, 1:0.5, 1:0.8, 1:1, 1:1.1, 1:1.2 or 1:1.3, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0088] In some embodiments, the heat dispersion treatment includes adding the matrix material to the mixed solution and performing ultrasonic dispersion treatment and heat stirring treatment.

[0089] In some embodiments, the frequency of the ultrasonic dispersion treatment is 50 Hz to 100 Hz, and the time is 10 min to 60 min.

[0090] Specifically, the frequency of the ultrasonic dispersion treatment can be 50 Hz, 60 Hz, 70 Hz, 80 Hz, 90 Hz, or 100 Hz, etc., and is not limited here. The time of the ultrasonic dispersion treatment can be 10 min, 15 min, 20 min, 30 min, 40 min, 45 min, 50 min, or 60 min, etc., and is not limited here.

[0091] In some embodiments, the heating and stirring treatment is performed at a temperature of 60° C. to 100° C. and for a time of 1 hour to 3 hours.

[0092] Specifically, the temperature of the heating and stirring treatment can be 60° C., 65° C., 70° C., 75° C., 80° C., 90° C., or 100° C., etc., and is not limited here. The time of the heating and stirring treatment can be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.5 hours, or 3 hours, etc., and is not limited here.

[0093] In some embodiments, the drying temperature is 100°C to 200°C, specifically 100°C, 120°C, 130°C, 150°C, 160°C, 170°C, 180°C or 200°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0094] In some embodiments, the drying time is 12 hours to 48 hours, and specifically can be 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, 24 hours, 25 hours, 28 hours, 30 hours, 35 hours, 35 hours, 40 hours, 43 hours, 45 hours or 48 hours, etc., which is not limited here.

[0095] Step S30: sintering the composite material in an oxygen-containing atmosphere to obtain a positive electrode material.

[0096] In some embodiments, the sintering temperature is 300°C to 800°C, specifically 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0097] In some embodiments, the sintering time is 3 h to 15 h, specifically 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0098] In a third aspect, the present application provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, a non-aqueous electrolyte and a casing, wherein the positive electrode sheet comprises a current collector and a positive electrode active material coated on the current collector, and the positive electrode active material comprises the positive electrode material as described above or the positive electrode material prepared by the preparation method of the positive electrode material as described above, as well as a conductive agent and a binder.

[0099] In some embodiments, the conductive agent is one of conductive carbon black, Ketjen black, graphite, and acetylene black.

[0100] In some embodiments, the binder is one of sodium carboxymethyl cellulose, cyclodextrin, and polyvinylidene fluoride.

[0101] In some embodiments, the solvent in the positive electrode active material is selected from one of deionized water, N-methylpyrrolidone, and N,N-dimethylformamide.

[0102] The following further describes the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0103] Example

[0104] Example 1

[0105] (1) Weigh appropriate amounts of LiOH and binary material nickel-cobalt precursor Ni in a molar ratio of 1.04:1. 0.90 Co 0.10 (OH)2, and according to Ni 0.90 Co 0.10 The mass ratio of (OH)2 to Al(OH)3 is 78:1. An appropriate amount of Al(OH)3 is weighed, and the three powders are mixed and crushed to obtain a mixture.

[0106] (2) The mixture was calcined at 550°C in a muffle furnace for 4 h, ground into fine particles, and then transferred to a tube furnace in an oxygen atmosphere for high-temperature sintering for 14 h. The sintering temperature was controlled at 750°C. The sintered matrix material was crushed to a D50 of approximately 11 μm, and the crushed material was stored in a polyethylene plastic bag and sealed with aluminum-plastic film.

[0107] (3) In a stirrable water-washed reactor, 8 g of lithium hydroxide was added to 50 ml of deionized water. After heating and stirring at 60° C. to form a transparent solution, 10 g of WO 3 was weighed and added thereto. The mixture was heated and stirred at 60° C. until a transparent solution was formed. 9 g of TiO 2 was then added to the transparent solution. Ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension.

[0108] (4) Weigh 100 g of the matrix material and add it to the suspension. After ultrasonic dispersion at 60 Hz for 45 min, heat and stir at 80 °C for 2 h to evaporate the water solvent. Heat in a vacuum drying oven at 100 °C for 24 h to obtain a composite material.

[0109] (5) The composite material was calcined at 550°C in an oxygen atmosphere for 10 h to obtain a modified positive electrode material.

[0110] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer (i.e., a coating layer formed by the first coating) located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-1, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (i.e., the coating formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0111] Among them, the thickness of the lithium tungstate coating layer is 6.3nm, the thickness of the TiO2 coating layer is 5.6nm, the average particle size D50 of the positive electrode material is 11.5μm, and the specific surface area is 0.69m 2 / g, the mass content of free lithium on the surface is 931ppm, P=1496.7.

[0112] FIG2 is an SEM image of the positive electrode material prepared in Example 1 of the present application. As shown in FIG2 , a first coating layer and nanoparticles located on the surface of the first coating layer exist on the surface of the base material in the positive electrode material.

[0113] Example 2

[0114] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washing reactor device, and heated and stirred at 60° C. to form a transparent solution. Then, 10 g of WO3 was weighed and added thereto, and heating and stirring were continued at 60° C. until a transparent solution was formed. Then, 9 g of MgO was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0115] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-2, the positive electrode material also includes MgO nanoparticles (i.e., the granular second coating) and an MgO coating layer (a coating layer formed by the second coating) located on the surface of the secondary particles, the MgO nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the MgO coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0116] The thickness of the lithium tungstate coating layer is 6.6 nm, the thickness of the MgO coating layer is 6.1 nm, the average particle size D50 of the positive electrode material is 11.1 μm, and the specific surface area is 0.70 m 2 / g, the mass content of free lithium on the surface is 923ppm, P=1496.9.

[0117] Example 3

[0118] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washing reactor device, and heated and stirred at 60° C. to form a transparent solution. Then, 10 g of WO3 was weighed and added thereto, and heating and stirring were continued at 60° C. until a transparent solution was formed. Then, 9 g of ZrO2 was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0119] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02O2-3, the positive electrode material also includes ZrO2 nanoparticles (i.e., formed by a granular second coating) and a ZrO2 coating layer (a coating layer formed by the second coating) located on the surface of the secondary particles, the ZrO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the ZrO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0120] Among them, the thickness of the lithium tungstate coating layer is 6.1nm, the thickness of the ZrO2 coating layer is 5.7nm, the average particle size D50 of the positive electrode material is 11.8μm, and the specific surface area is 0.68m 2 / g, the mass content of free lithium on the surface is 935ppm, P=1492.5.

[0121] Example 4

[0122] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washing reactor device, and heated and stirred at 60° C. to form a transparent solution. Then, 10 g of WO3 was weighed and added thereto. The heating and stirring at 60° C. were continued until a transparent solution was formed. Then, 9 g of Al(OH)3 was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0123] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-4, the positive electrode material also includes Al2O3 nanoparticles (i.e., the granular second coating) and an Al2O3 coating layer (a coating layer formed by the second coating) located on the surface of the secondary particles, the Al2O3 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the Al2O3 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0124] Among them, the thickness of the lithium tungstate coating layer is 6.8nm, the thickness of the Al2O3 coating layer is 5.3nm, the average particle size D50 of the positive electrode material is 11.3μm, and the specific surface area is 0.70m 2 / g, the mass content of free lithium on the surface is 919 ppm, P = 1492.9, and the formula 1400 ≤ P = Y + 819.8X ≤ 1600 is satisfied, where X represents the specific surface area and Y represents the mass content of free lithium on the surface.

[0125] Example 5

[0126] The difference from Example 1 is that (5) the composite material is calcined at 700° C. in an oxygen atmosphere for 10 h to obtain a modified positive electrode material. The remaining operations are the same as in Example 1.

[0127] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-5, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0128] Among them, the thickness of the lithium tungstate coating layer is 6.1nm, the thickness of the TiO2 coating layer is 5.2nm, the average particle size D50 of the positive electrode material is 11.6μm, and the specific surface area is 0.35m 2 / g, the mass content of free lithium on the surface is 1210ppm, P=1496.9.

[0129] Example 6

[0130] The difference from Example 1 is that (5) the composite material is calcined at 400° C. in an oxygen atmosphere for 10 h to obtain a modified positive electrode material. The remaining operations are the same as in Example 1.

[0131] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-6, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0132] Among them, the thickness of the lithium tungstate coating layer is 6.4nm, the thickness of the TiO2 coating layer is 6.2nm, the average particle size D50 of the positive electrode material is 11.2μm, and the specific surface area is 0.89m 2 / g, the mass content of free lithium on the surface is 750ppm, P=1479.6.

[0133] Example 7

[0134] The difference from Example 1 is that (1) appropriate amounts of LiOH and binary nickel-cobalt composite material Ni are weighed in a molar ratio of 1.04:1. 0.90 Co 0.10 (OH)2, and according to Ni 0.90 Co 0.10 The mass ratio of (OH)2 to Al(OH)3 is 78:1. Weigh an appropriate amount of Al(OH)3 and then 0.90 Co 0.10 The mass ratio of (OH)2 to Zr(OH)4 is 350:1. Weigh an appropriate amount of Zr(OH)4, mix the four powders and grind them to obtain a mixture. The remaining operations are the same as in Example 1.

[0135] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.8838 Co 0.0971 Al 0.0177 Zr 0.0014 O2-7, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0136] Among them, the thickness of the lithium tungstate coating layer is 6.9nm, the thickness of the TiO2 coating layer is 5.9nm, the average particle size D50 of the positive electrode material is 11.7μm, and the specific surface area is 0.71m 2 / g, the mass content of free lithium on the surface is 910ppm, P=1492.1.

[0137] Example 8

[0138] The difference from Example 1 is that the NCM811 nickel cobalt manganese oxide matrix material is purchased directly from the market, and the same scheme as steps (3)(4)(5) is used to obtain the modified positive electrode material.

[0139] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is a secondary particle, which is formed by agglomeration of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10Mn 0.10 O2, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0140] Among them, the thickness of the lithium tungstate coating layer is 6.9nm, the thickness of the TiO2 coating layer is 6.0nm, the average particle size D50 of the positive electrode material is 11.9μm, and the specific surface area is 0.72m 2 / g, the mass content of free lithium on the surface is 902ppm, P=1492.3.

[0141] Example 9

[0142] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washed reactor apparatus, and heated and stirred at 60° C. to form a transparent solution. Then, 12 g of MoO 3 was weighed and added thereto. The heating and stirring at 60° C. were continued until a transparent solution was formed. Then, 9 g of TiO 2 was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0143] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium molybdate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-8, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (a coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0144] Among them, the thickness of the lithium molybdate coating layer is 6.8nm, the thickness of the TiO2 coating layer is 5.4nm, the average particle size D50 of the positive electrode material is 11.6μm, and the specific surface area is 0.72m 2 / g, the mass content of free lithium on the surface is 905ppm, P=1495.3.

[0145] Example 10

[0146] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washed reactor device, and heated and stirred at 60° C. to form a transparent solution. Then, 5 g of WO3 and 6 g of MoO3 were weighed and added thereto. The mixture was heated and stirred at 60° C. until a transparent solution was formed. Then, 9 g of TiO2 was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0147] The positive electrode material prepared in this embodiment includes secondary particles, which include a matrix material and a lithium molybdate and lithium tungstate coating layer located on the surface of the matrix material. The matrix material is formed by the aggregation of multiple primary particles. The general chemical formula of the matrix material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-9, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0148] The thickness of the lithium molybdate and lithium tungstate coating layers is 7.0 nm, the thickness of the TiO2 coating layer is 5.5 nm, the average particle size D50 of the positive electrode material is 11.5 μm, and the specific surface area is 0.71 m 2 / g, the mass content of free lithium on the surface is 913ppm, P=1495.1.

[0149] Example 11

[0150] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washed reactor device, and heated and stirred at 60° C. to form a transparent solution. Then, 10 g of WO3 was weighed and added thereto, and heating and stirring were continued at 60° C. until a transparent solution was formed. Then, 75 g of TiO2 was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0151] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02O2-10, the positive electrode material also includes TiO2 nanoparticles (i.e., the material formed by the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0152] Among them, the thickness of the lithium tungstate coating layer is 6.8nm, the thickness of the TiO2 coating layer is 39.6nm, the average particle size D50 of the positive electrode material is 11.5μm, and the specific surface area is 0.67m 2 / g, the mass content of free lithium on the surface is 939ppm, P=1488.3.

[0153] Example 12

[0154] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washed reactor device, and heated and stirred at 60° C. to form a transparent solution. Then, 10 g of WO3 was weighed and added thereto. The heating and stirring at 60° C. were continued until a transparent solution was formed. Then, 3 g of TiO2 was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0155] The positive electrode material prepared in this comparative example includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by agglomeration of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-11, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0156] Among them, the thickness of the lithium tungstate coating layer is 6.3nm, the coating thickness of the TiO2 coating layer is 2.7nm, the average particle size D50 of the positive electrode material is 11.0μm, and the specific surface area is 0.69m 2 / g, the mass content of free lithium on the surface is 927ppm, P=1492.7.

[0157] Example 13

[0158] The difference from Example 1 is that (2) the mixture is calcined at 550°C in a muffle furnace for 4 h, ground into fine particles, and then transferred to a tube furnace in an oxygen atmosphere for high-temperature sintering for 14 h. The sintering temperature is controlled at 730°C. The sintered matrix material is crushed to a D50 of approximately 11 μm, and the crushed material is stored in a polyethylene plastic bag and sealed with an aluminum-plastic film. The remaining operations are the same as in Example 1.

[0159] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The general chemical formula of the base material is Li 1.00 N i0.88 Co 0.10 Al 0.02 O2-12, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0160] Among them, the thickness of the lithium tungstate coating layer is 6.3nm, the thickness of the TiO2 second coating layer is 5.5nm, the average particle size D50 of the positive electrode material is 11.9μm, and the specific surface area is 0.79m 2 / g, the mass content of free lithium on the surface is 850ppm, P=1497.6.

[0161] Example 14

[0162] The difference from Example 1 is that (2) the mixture is calcined at 550°C in a muffle furnace for 4 h, ground into fine particles, and then transferred to a tube furnace in an oxygen atmosphere for high-temperature sintering for 14 h. The sintering temperature is controlled at 770°C. The sintered matrix material is crushed to a D50 of approximately 11 μm, and the crushed material is stored in a polyethylene plastic bag and sealed with an aluminum-plastic film. The remaining operations are the same as in Example 1.

[0163] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is a secondary particle, which is formed by agglomeration of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02O2-13, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0164] Among them, the thickness of the lithium tungstate coating layer is 6.0nm, the coating thickness of the TiO2 coating layer is 5.3nm, the average particle size D50 of the positive electrode material is 11.7μm, and the specific surface area is 0.60m 2 / g, the mass content of free lithium on the surface is 1002ppm, P=1493.9.

[0165] Example 15

[0166] The difference from Example 1 is that in (1), appropriate amounts of LiOH and binary material nickel-cobalt precursor Ni are weighed in a molar ratio of 1.04:1. 0.80 Co 0.20 (OH)2, and according to Ni 0.80 Co 0.20 The mass ratio of (OH)2 to Al(OH)3 is 78:1. Weigh an appropriate amount of Al(OH)3, mix the three powders and grind them to obtain a mixture. The remaining operations are the same as in Example 1.

[0167] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.78 Co 0.20 Al 0.02 O2-14, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0168] Among them, the thickness of the lithium tungstate coating layer is 6.8nm, the thickness of the TiO2 coating layer is 5.8nm, the average particle size D50 of the positive electrode material is 11.3μm, and the specific surface area is 0.73m 2 / g, the mass content of free lithium on the surface is 895ppm, P=1493.5.

[0169] Example 16

[0170] The difference from Example 1 is that in (1), appropriate amounts of LiOH and binary material nickel-cobalt precursor Ni are weighed in a molar ratio of 1.04:1. 0.70 Co 0.30 (OH)2, and according to Ni 0.70 Co 0.30 The mass ratio of (OH)2 to Al(OH)3 is 78:1. Weigh an appropriate amount of Al(OH)3, mix the three powders and grind them to obtain a mixture. The remaining operations are the same as in Example 1.

[0171] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.68 Co 0.30 Al 0.02 O2-15, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0172] Among them, the thickness of the lithium tungstate coating layer is 6.6nm, the thickness of the TiO2 coating layer is 5.5nm, the average particle size D50 of the positive electrode material is 11.6μm, and the specific surface area is 0.77m 2 / g, the mass content of free lithium on the surface is 862ppm, P=1493.2.

[0173] Example 17

[0174] The difference from Example 1 is that in (1), appropriate amounts of Li2CO3 and binary material nickel-cobalt precursor Ni 0.90 Co 0.10 (OH)2, and according to Ni 0.90 Co 0.10 The mass ratio of (OH)2 to Al(OH)3 is 78:1. Weigh an appropriate amount of Al(OH)3, mix the three powders and grind them to obtain a mixture. The remaining operations are the same as in Example 1.

[0175] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02O2-16, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0176] Among them, the thickness of the lithium tungstate coating layer is 6.3nm, the coating thickness of the TiO2 coating layer is 5.2nm, the average particle size D50 of the positive electrode material is 11.1μm, and the specific surface area is 0.70m 2 / g, the mass content of free lithium on the surface is 920ppm, P=1493.9.

[0177] Example 18

[0178] The difference from Example 1 is that in (1), appropriate amounts of LiNO3 and binary material nickel-cobalt precursor Ni are weighed in a molar ratio of 1.04:1. 0.90 Co 0.10 (OH)2, and according to Ni 0.90 Co 0.10 The mass ratio of (OH)2 to Al(OH)3 is 78:1. Weigh an appropriate amount of Al(OH)3, mix the three powders and grind them to obtain a mixture. The remaining operations are the same as in Example 1.

[0179] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-17, the positive electrode material also includes TiO2 nanoparticles (i.e., the granular second coating) and a TiO2 coating layer (the coating layer formed by the second coating) located on the surface of the secondary particles, the TiO2 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the TiO2 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0180] Among them, the thickness of the lithium tungstate coating layer is 6.1nm, the thickness of the TiO2 coating layer is 5.6nm, the average particle size D50 of the positive electrode material is 11.8μm, and the specific surface area is 0.75m 2 / g, the mass content of free lithium on the surface is 880ppm, P=1494.9.

[0181] Example 19

[0182] The difference from Example 1 is that in (3), 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washed reactor. After heating and stirring at 60° C. to form a transparent solution, 10 g of WO 3 was weighed and added thereto. Heating and stirring at 60° C. were continued until a transparent solution was formed. Then, 9 g of CeO 2 was added to the transparent solution, and ultrasonic dispersion was performed at 100 Hz for 30 minutes to obtain a suspension. The remaining operations were the same as in Example 1.

[0183] The positive electrode material prepared in this embodiment includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by the aggregation of multiple primary particles. The chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-17, the positive electrode material further includes Li2CeO3 nanoparticles (i.e., particles formed by the second coating) and a Li2CeO3 coating layer (a coating layer formed by the second coating) located on the surface of the secondary particles. The Li2CeO3 nanoparticles are located on the surface of the lithium tungstate coating layer or the surface of the primary particles, and the Li2CeO3 coating layer is located on the surface of the lithium tungstate coating layer or the surface of the primary particles.

[0184] Among them, the thickness of the lithium tungstate coating layer is 6.3nm, the thickness of the Li2CeO3 coating layer is 5.9nm, the average particle size D50 of the positive electrode material is 11.3μm, and the specific surface area is 0.71m 2 / g, the mass content of free lithium on the surface is 912ppm, P=1494.1.

[0185] Comparative Example 1

[0186] (1) Weigh appropriate amounts of LiOH and binary nickel-cobalt composite material Ni in a molar ratio of 1.04:1. 0.90 Co 0.10 (OH)2, and according to Ni 0.90 Co 0.10 The mass ratio of (OH)2 to Al(OH)3 is 78:1. An appropriate amount of Al(OH)3 is weighed, and the three powders are mixed and crushed to obtain a mixture.

[0187] (2) The mixture was calcined at 550°C in a muffle furnace for 4 h, ground into fine particles, and then transferred to a tube furnace in an oxygen atmosphere for high-temperature sintering for 14 h. The sintering temperature was controlled at 750°C. The sintered matrix material was crushed to a D50 of approximately 11 μm, and the crushed material was stored in a polyethylene plastic bag and sealed with aluminum-plastic film.

[0188] (3) Weigh 100 g of the matrix material and add it into 50 ml of deionized water. After ultrasonic dispersion at 60 Hz for 45 min, heat and stir at 80 °C for 2 h to evaporate the water solvent. Heat in a vacuum drying oven at 100 °C for 24 h to obtain a composite material.

[0189] (4) The composite material was calcined at 550°C in an oxygen atmosphere for 10 h to obtain a modified positive electrode material.

[0190] The chemical formula of the positive electrode material prepared in this comparative example is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-12; the surface of the positive electrode particles is not coated, the average particle size of the positive electrode material is 11.0μm, and the specific surface area is 0.70m 2 / g; the mass content of free lithium on the surface is 1033 ppm, P=1606.9.

[0191] FIG3 is an SEM image of the positive electrode material prepared in Comparative Example 1 of the present application. As shown in FIG3 , the surfaces of the primary particles of the positive electrode material and the spaces between the primary particles are relatively smooth, and there is no coating layer or particulate matter on the surface of the positive electrode material.

[0192] Comparative Example 2

[0193] The difference from Example 1 is that (3) 8 g of lithium hydroxide was added to 50 ml of deionized water in a stirrable water-washing reactor device, and after heating and stirring at 60° C. to form a transparent solution, 10 g of WO3 was weighed and added thereto, and heating and stirring at 60° C. were continued until a transparent solution was formed. The remaining operations were the same as in Example 1.

[0194] The positive electrode material prepared in this comparative example includes secondary particles, which include a base material and a lithium tungstate coating layer located on the surface of the base material. The base material is formed by agglomeration of multiple primary particles. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-13.

[0195] The thickness of the lithium tungstate coating layer is 6.1 nm, the average particle size D50 of the positive electrode material is 11.0 μm, and the specific surface area is 0.67 m 2 / g, the mass content of free lithium on the surface is 820ppm, P=1369.3.

[0196] Comparative Example 3

[0197] The difference from Example 1 is that (3) 9 g of TiO2 was added to a stirrable water-washing reactor and dissolved in 50 ml of deionized water, and ultrasonic dispersion was performed at 100 Hz for 30 min to obtain a suspension. The remaining operations were the same as in Example 1.

[0198] The positive electrode material prepared in this comparative example includes a base material (the base material is formed by agglomeration of multiple primary particles) and TiO2 nanoparticles and a TiO2 coating layer located on the surface of the base material. The general chemical formula of the base material is Li 1.00 Ni 0.88 Co 0.10 Al 0.02 O2-14, the TiO2 nanoparticles and the TiO2 coating layer are located on the surface of the base material.

[0199] The coating thickness of the TiO2 coating layer is 5.1 nm, the average particle size D50 of the positive electrode material is 11.3 μm, and the specific surface area is 0.68 m 2 / g, the mass content of free lithium on the surface is 1123ppm, P=1680.

[0200] Test Method

[0201] (1) Testing method for the thickness of the coating formed by the first coating and the thickness of the coating formed by the second coating:

[0202] The thickness of the first cladding layer and the second cladding layer was measured using a transmission electron microscope (TEM) with a built-in ruler at a magnification of 50k to 100k.

[0203] (2) Testing method for particle size of granular second coating:

[0204] The particle size of the nanoparticles was measured using a scanning electron microscope (SEM) with a built-in ruler at a magnification of 20k to 100k.

[0205] (3) Test method for average particle size of positive electrode material:

[0206] The volume particle size distribution of the positive electrode particles dispersed in a certain aqueous solution was tested using a Malvern laser particle size analyzer 3000.

[0207] (4) Testing method for specific surface area of ​​positive electrode material:

[0208] The specific surface area of ​​the cathode material was measured by the gas adsorption method. Specifically, Micromeritics TristarⅡ was used to perform N2 adsorption test, and the adsorption amount values ​​at different equilibrium pressures were calculated. The isothermal adsorption line was obtained and the specific surface area of ​​the cathode material was calculated.

[0209] (5) Test method for compaction density of positive electrode materials:

[0210] The compaction density of the positive electrode particles is measured by the American 4350CARVER compaction density meter. Specifically, a certain mass of positive electrode material powder sample is placed in a metal sleeve and the ratio of the mass of the sample to the compacted volume after maintaining it under a certain pressure for a certain period of time is obtained.

[0211] (6) Test method for tap density of positive electrode material:

[0212] The tap density of the positive electrode particles was measured by BT-303, specifically the mass per unit volume of the positive electrode material powder in the container after being tapped under specified conditions.

[0213] (7) Test method for average particle strength of positive electrode material:

[0214] The strength of the cathode particles was measured using a dynamic ultramicrohardness tester DUH-211S.

[0215] (8) Test method for surface free lithium content of positive electrode material:

[0216] The residual alkali free lithium of the positive electrode material was determined by using a Mettler Toledo automatic potentiometric titrator G20S. Specifically, the titration was performed using a hydrochloric acid standard titration solution on the automatic potentiometric titrator in an equivalence point titration mode. The OH in the sample was calculated based on the jump point and the amount of hydrochloric acid standard titration solution (0.025 mol / L) consumed. - and CO3 2- The content is then converted into surface free lithium content.

[0217] (9) Electrochemical performance test:

[0218] The positive electrode materials prepared in Examples 1 to 14 and Comparative Examples 1 to 3 were assembled into button cells: 0.8 g of positive electrode material, 0.1 g of conductive carbon black and 0.1 g of polyvinylidene fluoride were weighed and placed in a ball mill, 15 mL of N-methylpyrrolidone was added, and ball milling was performed to form a uniform positive electrode slurry, which was then evenly coated on aluminum foil and vacuum dried at 80°C for 12 h to obtain a positive electrode sheet. The lithium sheet was used as the negative electrode and assembled into a 2016 button cell in a glove box.

[0219] The battery was tested in the 3.0V-4.3V discharge range and with a theoretical capacity of 250mAh / g at 1C using the CT2001A battery testing system from Wuhan Blue Electric Electronics Co., Ltd. The test results are detailed in Table 2.

[0220] Table 1 Physicochemical properties of the positive electrode materials prepared in each embodiment and comparative example

[0221] Table 2 Electrochemical properties of the positive electrode materials prepared in each embodiment and comparative example

[0222] As shown in Tables 1 and 2, according to the test data of Examples 1 to 19, the positive electrode material includes secondary particles, the secondary particles include a matrix material and a first coating, the matrix material is formed by the agglomeration of multiple primary particles, and the surface of the matrix material has a first coating. The first coating can form a physical barrier on the surface of the matrix material, thereby effectively avoiding direct contact between the positive electrode material and the electrolyte, and improving the stability of the coating / main interface; the presence of the second coating can improve the electrical conductivity of the particle body and enhance the lithium ion migration rate, thereby improving the electronic and lithium ion conductivity of the positive electrode material, reducing the overpotential in the battery electrode, and at the same time effectively reducing the residual alkali on the surface of the positive electrode material, significantly improving the cycle performance and rate performance of the positive electrode material; in addition, the presence of the second coating on the surface of the secondary particles of the positive electrode material can further isolate the contact between the positive electrode material and the electrolyte, further construct the integration of the positive electrode material, and inhibit the expansion of microcracks, thereby improving the particle strength, further improving the structural stability of the positive electrode material, and thus improving the cycle performance of the positive electrode material.

[0223] Figures 4a and 4b are the particle strength curves of the positive electrode materials obtained in Example 1 and Comparative Example 1 of the present application, respectively. A controlled force is applied to the particles and their displacement is recorded. In the initial stage of the test, the displacement increases rapidly with the increase of the compressive force, after which a slow increase in displacement is observed. Finally, the particles break at the critical point, and the displacement rises sharply under almost constant stress. The particle strength is calculated by measuring the breaking force and cross-sectional area of ​​the particles. As can be seen from Figure 4a, the average particle strength of the positive electrode material obtained in Example 1 can reach 57.6 MPa; as can be seen from Figure 4b, the average particle strength of the positive electrode material obtained in Comparative Example 1 is 36.1 MPa. Obviously, the particle strength of the positive electrode material obtained in Example 1 is significantly higher than that of the particles in Comparative Example 1. This is because the positive electrode material of Example 1 has a first coating on the surface of its base material, and there is also a second coating on the surface of the positive electrode material secondary particles, which enhances the integrity and stability of the positive electrode material particles. Therefore, its average particle hardness is stronger than that of the particles in Comparative Example 1 without the first coating and the second coating on the surface.

[0224] Figures 5a and 5b are comparison diagrams of the positive electrode materials prepared in Example 1 and Comparative Example 1 of the present application before and after compression, respectively. As shown in Figures 5a and 5b, the positive electrode material prepared in Comparative Example 1 does not have the first coating and the second coating on the surface, so the positive electrode particles are broken into dispersed small particles after compression. However, the positive electrode material prepared in Example 1 can still maintain a block shape after compression due to the presence of the first coating and the second coating on the surface, which further indicates that the presence of the first coating and the second coating can further construct an integrated structure of the positive electrode material, inhibit the expansion of microcracks, enhance the particle strength, and thus improve the structural stability of the positive electrode material.

[0225] Figure 6 is an EIS (electrochemical impedance spectroscopy) graph of the positive electrode materials prepared in Examples 1, 5 and 6 of the present application. It can be seen from Figure 6 that with the increase of the sintering temperature (i.e., the calcination temperature of the composite material in an oxygen atmosphere in step (5)), the impedance of the positive electrode material first decreases and then increases, indicating that an appropriate sintering temperature can repair the surface defects of the positive electrode material and thereby reduce the impedance.

[0226] By (I 006 +I 102 ) / I 101 The value is used to evaluate the orderliness of the hexagonal close-packed structure of the positive electrode material, and the structural orderliness is closely related to the performance of the positive electrode material. According to the test data of Examples 1, 5, and 6, under the driving force of high-temperature annealing (i.e., sintering and cooling of the composite material after sintering), Li + Diffusion from the interior of the particle to the surface, with the increase of the secondary sintering temperature (i.e., the temperature at which the composite material is sintered), more Li+ diffuses from the interior of the particle to the surface, which leads to a serious degree of cation mixing inside the particle and a deterioration of the structural order. When Ni atoms occupy the site of the lithium layer, the intensity of the 101 peak decays rapidly. As shown in Table 1, in the range of 0.6≤(I006+I102) / I101≤0.850, (I 006 +I 102 ) / I 101 The value gradually increases with the increase of secondary sintering temperature. In addition, the specific surface area of ​​the positive electrode material gradually decreases with the increase of secondary sintering temperature, that is, (I 006 +I 102 ) / I 101 The value is inversely proportional to the specific surface area of ​​the material. The larger the specific surface area, the more complete the contact between the positive electrode material and the electrolyte, which in turn leads to an increase in the capacity value, that is, (I 006 +I 102 ) / I 101 The value is inversely proportional to the capacity. FIG7 is an XRD diagram of the positive electrode material prepared in Example 1 of the present application. As shown in FIG7 , the (108) and (110) diffraction peaks are obviously split, indicating that the positive electrode material forms a good layered structure, that is, (I006 +I 102 ) / I 101 The value is inversely proportional to the absolute value of the difference between the positions 2θ of the (108) and (110) diffraction peaks |110-108|. Therefore, in the temperature range of 300-800℃, (I 006 +I 102 ) / I1 01 The value reaches the optimal value, the hexagonal close-packed structure of the positive electrode material is more ordered, and the positive electrode material has the best electrochemical performance.

[0227] In addition, a properly porous structure (i.e., a relatively large specific surface area) can effectively relieve stress and change the path of microcrack propagation, avoid particle crushing, and hinder the electrolyte from penetrating into new microcrack interfaces and forming a passivation film that causes loss of active lithium ions and increased impedance. During high-temperature annealing (i.e., the process of sintering the composite material) and the subsequent cooling process, the Li2O3 diffused to the surface + It reacts with O2, CO2 and H2O molecules to form LiOH and Li2CO3 on the sample surface, which participates in the formation of residual lithium and causes ion rearrangement on the surface of the material, that is, the orderliness of the hexagonal close-packed structure of the positive electrode material is reduced, destroying the structural stability of the material, and then causing the capacity and capacity retention rate of the positive electrode material to decay rapidly. In addition, excessive residual alkali on the surface will affect the processing performance of the positive electrode material and cause the slurry to appear "jelly". In addition, free lithium on the surface helps Li + Diffusion, too low free lithium and too high specific surface area will lead to an increase in impedance, so there is an optimal free lithium content, that is, an optimal specific surface area, so that the positive electrode material has the best electrochemical performance. For example, the positive electrode materials in Examples 1, 5, and 6 have significantly different specific surface areas. Example 5 has the smallest specific surface area and is not effective in relieving stress and changing the microcrack propagation path. At the same time, its residual alkali is the highest and the free lithium content is high. (I 006 +I 102 ) / I 101 The largest surface area, i.e., the lowest structural order, results in the worst capacity and cycle performance among the three. Example 6 has the largest specific surface area. Due to its large contact area with the electrolyte, its capacity is higher. Although it can effectively relieve stress and change the microcrack propagation path, excessive pores can easily cause crack penetration, ultimately leading to a significant reduction in capacity retention. Example 1 has an appropriate specific surface area and free lithium content, resulting in higher capacity, rate performance, and cycle stability. Therefore, the temperature at which the composite material is sintered has a certain impact on the performance of the positive electrode material, and a sintering temperature of 550°C is more effective.

[0228] Combining the test results in Table 1 and Table 2, we can see that:

[0229] Compared with Example 1, the thickness of the second coating layer in the positive electrode material prepared in Example 11 is increased, which can effectively block the direct contact between the base material and the electrolyte, increase the particle strength of the positive electrode material, and improve the structural stability of the positive electrode material. It can still maintain good rate performance (such as the sizes of 1C / 0.1C and 2C / 0.1C in Table 2 can be used to represent the rate performance) and capacity retention rate. It can be seen from the data in Tables 1 and 2 that its rate performance and capacity retention rate are still higher than those of Comparative Examples 1-3.

[0230] Compared to Example 1, the positive electrode material prepared in Example 12 has a thinner second coating layer, which may result in a slight decrease in the particle strength of the positive electrode material, affecting its effectiveness in resisting HF corrosion of the active material and the material's capacity retention. However, as can be seen from the data in Tables 1 and 2, the capacity retention of Example 12 is still higher than that of Comparative Examples 1-3.

[0231] Compared with Example 1, the positive electrode material prepared in Example 13 has (I 006 +I 102 ) / I 101 The value of is less than 0.6. Although the structural orderliness of the positive electrode material is improved, the structural stability of the positive electrode material is reduced compared with Example 1. The side reaction between the electrolytes of the positive electrode material is aggravated, resulting in a decrease in the capacity and cycle performance of the positive electrode material.

[0232] Compared with Example 1, the positive electrode material prepared in Example 14 has (I 006 +I 102 ) / I 101 The value of |I in the positive electrode material is greater than 0.85, the degree of cation mixing inside the positive electrode material particles is high, and the structural order of the positive electrode material is reduced, resulting in the obstruction of the deintercalation of lithium ions in the positive electrode material; at the same time, the |I 110 -I 108 The value of | is less than 0.39, the layered structure of the positive electrode material is weakened, and Li + The rapid deintercalation in the bulk structure and surface layer slows down, resulting in a decrease in the capacity and cycle performance of the positive electrode material. Therefore, in the process of preparing the matrix material, the sintering temperature is controlled at 750℃ for better results.

[0233] Compared with Example 1, the surface of the base material prepared in Comparative Example 1 has no coating material, the base material is in direct contact with the electrolyte, the side reaction between the active substance in the base material and the electrolyte is serious, the surface structure of the material is destroyed, the secondary particles are prone to cracking to form microcracks, and the expansion of the microcracks is difficult to suppress. At the same time, the formed microcracks expose more active sites of the positive electrode material particles to undergo side reactions with the electrolyte, further accelerating the decay of the positive electrode material structure, resulting in a significant decrease in the strength of the positive electrode material particles, a decrease in the structural stability of the material, and further a decrease in the capacity decay and cycle performance of the material.

[0234] Compared with Example 1, the positive electrode material of Comparative Example 2 does not add the second metal oxide during the preparation process, and there is no second coating on the surface of the secondary particles of the obtained positive electrode material. The strength of the positive electrode material particles is reduced, and the microcracks formed by intercrystalline cracking of the secondary particles increase, which intensifies the side reaction between the positive electrode material and the electrolyte, further accelerates the decay of the positive electrode material structure, resulting in a decrease in the overall structural stability and cycle stability of the material, thereby reducing the cycle performance of the lithium-ion battery.

[0235] Compared with Example 1, the positive electrode material of Comparative Example 3 does not add the first metal oxide during the preparation process, and the surface of the base material of the prepared positive electrode material does not have the first coating, which increases the direct contact between the positive electrode material and the electrolyte. The side reaction between the positive electrode material and the electrolyte is serious, which reduces the electrical conductivity of the positive electrode material particles and the lithium ion migration rate, thereby reducing the electronic and lithium ion conductivity of the positive electrode material, increasing the overpotential in the battery electrode, and increasing the residual alkali on the surface of the positive electrode material, which reduces the cycle performance and rate performance of the positive electrode material.

[0236] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that: The positive electrode material includes secondary particles, and the secondary particles include: A matrix material, the matrix material comprising a plurality of primary particles, the general chemical formula of the matrix material being Li a Ni x Co y M z N b O2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, 0≤b<0.4, x+y+z+b=1, M is Mn and / or Al, and N includes at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti and Ta; and A first coating located on at least a portion of the surface of the base material, wherein the first coating comprises lithium tungstate and / or lithium molybdate; The positive electrode material further includes a second coating, which is located on the surface of the secondary particles; the second coating includes Al2O3, TiO2, MgO, CeO2, ZrO2, LiAlO2, Li2TiO3, Li4Ti5O 12 , Li2CeO3, Li2ZrO3.

2. The positive electrode material according to claim 1, characterized in that The surface of the secondary particle includes a first type of region and a second type of region, the first type of region includes the first coating and the second coating, the second coating is located on the surface of the first coating, the second type of region includes the primary particle and the second coating, the second coating is located on the surface of the primary particle.

3. The positive electrode material according to claim 1, characterized in that It meets at least one of the following technical features: (1) The thickness of the coating layer formed by the first coating is 3 nm to 30 nm; (2) The second coating is in a granular form, and the particle size of the granular second coating is 10 nm to 100 nm; (3) The second coating forms a coating layer with a thickness of 2 nm to 40 nm on at least a portion of the surface of the secondary particles.

4. The positive electrode material according to claim 1, characterized in that It meets at least one of the following technical features: (1) The mass proportion of the second coating in the positive electrode material is 0.05wt% to 0.8wt%; (2) The compaction density of the positive electrode material is 2.1 g / cm 3 ~4.6g / cm 3 ; (3) The tap density of the positive electrode material is 1.7 g / cm 3 ~4.1g / cm 3 ; 5. The positive electrode material according to claim 1, characterized in that It meets at least one of the following technical features: (1) The specific surface area of ​​the positive electrode material is 0.2 m 2 / g~1.3m 2 / g; (2) The mass content of free lithium on the surface of the positive electrode material is 500ppm to 1300ppm; (3) The average particle strength of the positive electrode material is ≥45 MPa.

6. The positive electrode material according to claim 1, characterized in that It meets at least one of the following technical features: (1) The ratio between the compaction density and the tap density of the positive electrode material is 1.05 to 1.3; (2) The average volume distribution particle size D50 of the positive electrode material is 9 μm to 20 μm; (3) The peak intensity I of the (006) crystal plane of the positive electrode material obtained by X-ray diffraction pattern measurement 006 , the peak intensity of (101) crystal plane I 101 and the peak intensity I of the (102) crystal plane 102 The relationship between satisfies: 0.6≤(I 006 +I 102 ) / I 101 ≤0.850; 7. The positive electrode material according to claim 1, characterized in that The peak intensity I of the (110) crystal plane of the positive electrode material obtained by X-ray diffraction spectrum measurement is 110 The peak intensity I 108 The relationship between them satisfies: 0.39≤∣I 110 -I 108 ∣≤0.

850.

8. The positive electrode material according to claim 1, characterized in that The positive electrode material satisfies the following formula: 1400≤G+819.8H≤1600; Wherein, G represents the mass content of free lithium on the surface of the positive electrode material, in ppm, and H represents the specific surface area of ​​the positive electrode material, in m 2 / g.

9. A method for preparing a positive electrode material, characterized in that: The following steps are involved: preparing a mixed solution containing a lithium salt, a first metal oxide, a second metal oxide and / or a second metal hydroxide; The matrix material is added to the mixed solution, and subjected to heating, dispersion and drying treatment to obtain a composite material, wherein the matrix material has a chemical formula of Li a Ni x Co y M z N b O2, wherein 0.95≤a≤1.1, 0.6≤x<1, 0<y<0.4, 0<z<0.4, 0≤b<0.4, x+y+z+b=1, M is Mn and / or Al, and N includes at least one of Zr, Mg, Sr, V, Y, Nb, B, S, Ba, Ti and Ta; The composite material is sintered in an oxygen-containing atmosphere to obtain a positive electrode material.

10. The preparation method according to claim 9, characterized in that: It meets at least one of the following technical features: (1) The mass ratio of the lithium salt to the first metal oxide is 1:(1-3); (2) The mass ratio of the lithium salt to the second metal oxide and / or the second metal hydroxide is 1:(0.5-3); (3) The mixed solution further includes a solvent, and the mass ratio of the total mass of the lithium salt and the first metal oxide to the solvent is 1:(2-6).

11. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode plate, and the positive electrode plate comprises the positive electrode material according to any one of claims 1 to 8 or a positive electrode material prepared by the method for preparing the positive electrode material according to any one of claims 9 to 10.

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