Cathode material and preparation method thereof, and lithium ion battery

Abstract

This application relates to a cathode material and its preparation method, and a lithium-ion battery. The cathode material includes a substrate and at least a coating layer disposed on the surface of the substrate. The general chemical formula of the substrate is formula (I): Li a Ni b Co c N d M 2 e In formula (I) of O2(Ⅰ), N includes Mn and / or Al, M 2 It includes at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg, and La; the general chemical formula of the coating layer is shown in formula (II): Li g M 1 (2h‑g) / i O h In equation (II), M 1 Including at least one of Mn, Ti, W, Mo, and Nb; in the diffraction pattern obtained by X-ray diffraction measurement of the cathode material, the cathode material has a diffraction peak 2θ on the (102) plane. 102 The diffraction peak 2θ of the (006) plane 006 The diffraction peak 2θ of the (110) plane 110 The diffraction peak 2θ of the (108) plane 108 ,2θ 102 2θ 006 2θ 110 and 2θ 108 Satisfy the following relationship: 2θ 102 -2θ 006 ≥0.25, 2θ 110 -2θ 108 ≥0.33.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, and particularly relates to a cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] Environmental pollution and the energy crisis have become two major challenges to global development. Addressing the excessive consumption of traditional fossil fuels and the resulting environmental problems is urgent, and the development and utilization of new energy sources are receiving increasing attention worldwide. Developing new energy electric vehicles is a crucial way to improve the competitiveness of my country's automotive industry, ensure energy security, and develop a low-carbon economy. The key to electric vehicle development lies in the development of power batteries. However, new energy electric vehicles are not yet widely accepted, mainly because they lag significantly behind traditional gasoline vehicles in terms of price, driving range, and safety. Lithium-ion power batteries, as the core component and development bottleneck of electric vehicles, play a decisive role. Cathode materials are key factors affecting the cost, energy density, and safety of lithium-ion batteries. The energy densities of lithium cobalt oxide, lithium iron phosphate, and lithium manganese oxide are all below 180 mAh / g, failing to meet the ever-increasing energy density demands of lithium-ion battery applications. High-nickel ternary materials, as a new type of cathode material, possess comprehensive advantages such as high energy density, high operating voltage, and high tap density, and have been widely used in the 3C and power battery fields.

[0003] With the continuous increase in nickel content in high-nickel ternary materials, the high-rate performance and impedance of these materials have faced significant challenges. Currently, the main methods for improving the rate performance and thermal stability of these materials include doping and coating. Conventional coating modification treatments use unary materials, and the coating is performed simultaneously during the preparation of the precursor end. This results in a significant difference in nickel content between the internal matrix and the external coating layer, leading to lower capacity and poorer workability.

[0004] Therefore, there is a need to develop a cathode material that is simple to process and also has high capacity. Summary of the Invention

[0005] The purpose of this invention is to provide a cathode material and its preparation method, as well as a lithium-ion battery. The cathode material of this application has high capacity and rate performance.

[0006] In a first aspect, embodiments of this application provide a positive electrode material, the positive electrode material comprising a matrix and at least a coating layer disposed on the surface of the matrix, the general chemical formula of the matrix being shown in formula (Ⅰ):

[0007] Li a Ni b Co c N d M 2e O2(Ⅰ)

[0008] In equation (Ⅰ), N includes Mn and / or Al, M 2 Includes at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg and La, 0.95≤a≤1.08, 0.3≤b≤1, 0≤c≤0.7, 0≤d≤0.5, 0≤e≤0.1, b+c+d+e=1, 0<x≤1;

[0009] The general chemical formula of the coating layer is shown in formula (II):

[0010] Li g M 1 (2h-g) / i O h (II)

[0011] In formula (II), M 1 Includes at least one of Mn, Ti, W, Mo, and Nb, where i is M 1 The valence values ​​of the ions, and g, h, and (2h-g) / i are all integers;

[0012] In the diffraction pattern obtained by X-ray diffraction measurement of the cathode material, the cathode material has...

[0013] (102) diffraction peak 2θ 102 The diffraction peak 2θ of the (006) plane 006 The diffraction peak 2θ of the (110) plane 110 and

[0014] (108) diffraction peak 2θ 108 The 2θ 102 2θ 006 2θ 110 and 2θ 108 The following relationship must be satisfied:

[0015] 2θ 102 -2θ 006 ≥0.25(Ⅲ)

[0016] 2θ 110 -2θ 108 ≥0.33 (Ⅳ). In some embodiments, the general chemical formula of the matrix is ​​shown in formula (Ⅴ):

[0017] Li a Ni b Co c N d M 2 e M 3 f O2(V)

[0018] In equation (V), M 3 Includes at least one of Mn, Ti, W, Mo, Nb, Zr, Co, Y, Ce, Al and La, 0≤f≤0.1, b+c+d+e+f=1;

[0019] The general chemical formula of the coating layer is shown in formula (VI):

[0020] Li g M 1 (2h-g) / i O h ·NiO·LiMn2O4(VI).

[0021] In some embodiments, the positive electrode material includes at least one of the following features (1) to (10):

[0022] (1) The positive electrode material comprises primary particles, wherein the median particle size of the primary particles is 2.0 μm to 6.0 μm;

[0023] (2) The positive electrode material includes secondary particles, and the secondary particles include a plurality of primary particles;

[0024] (3) Ni in the surface layer of the positive electrode material 2+ The mass and the Ni in the cathode material 2+ and Ni 3+ The ratio of the total mass is greater than or equal to 0.6, wherein the surface layer of the positive electrode material refers to the portion of the positive electrode material extending from the surface of the positive electrode material into the interior of the positive electrode material with a thickness of 0 nm to 20 nm;

[0025] (4) In the XRD pattern of the cathode material, the intensity ratio of the diffraction peaks between the (003) plane and the (104) plane is I. 003 / Ⅰ 104 ≥1.3;

[0026] (5) The 2θ 102 2θ 006 2θ 110 and 2θ 108 It also satisfies the following relationship:

[0027] (2I 102 -2I 006 ) / (2I 110 -2I 108 )≥0.7(VII);

[0028] (6) When the positive electrode material is charged to 4.3V, the lattice parameter change rate of the positive electrode material is ≤5%;

[0029] (7) When the positive electrode material is charged to 4.3V, the cell volume change rate of the positive electrode material is ≤6%;

[0030] (8) When the positive electrode material is charged to 4.3V, the particle strength of the positive electrode material is ≥200MPa;

[0031] (9) The Li g M 1 (2h-g) / i The mass percentage of O in the cathode material is 0% to 1% (excluding O);

[0032] (10) The mass percentage of NiO in the cathode material is 0% to 10%.

[0033] Secondly, embodiments of this application provide a method for preparing a cathode material, comprising the following steps:

[0034] Ni (1-c-d) Co c N d The cathode material is obtained by mixing (OH)2 precursor, lithium salt, metal boride and flux and then subjecting it to a staged heating process; the metal boride includes at least one of Mn, Ti, W, Mo and Nb, and the metal boride can react with the lithium salt; the flux includes at least one oxide, hydroxide or salt of Zr, Sr, Co, Ba, Y, Ce, Al, Mg and La, wherein N includes Al and / or Mn, 0≤c≤0.7, 0≤d≤0.5.

[0035] In some embodiments, the preparation method includes at least one of the following features (1) to (9):

[0036] (1) The Ni (1-c-d) Co c N d The median particle size of the (OH)2 precursor is 2 μm to 6 μm;

[0037] (2) The ratio of the total amount of metal elements in the metal boride to the amount of the cathode material is 0.01% to 1%;

[0038] (3) The metal boride includes at least one of MoB, W2B5, NbB, MbB and TiB2;

[0039] (4) The median particle size of the metal boride is 10 nm to 500 nm;

[0040] (5) The ratio of the total amount of metal elements in the flux to the total amount of the cathode material is 0.02% to 10%;

[0041] (6) The fluxing agent includes at least one of Y2O3, La2O3, ZrO2, Y2O3, Y(OH)3, Mg(OH)2, Al(OH)3 and Cl3Y;

[0042] (7) The median particle size of the flux is 10 nm to 500 nm;

[0043] (8) The lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium phosphate and lithium oxalate;

[0044] (9) The molar ratio of lithium element in the lithium salt to the total metal in the cathode material is (0.95~1.08):1.

[0045] In some embodiments, the preparation method includes at least one of the following features (1) to (4):

[0046] (1) The segmented heating process is carried out in an oxygen or air atmosphere;

[0047] (2) The segmented heating process includes: first heating to 300℃~750℃, holding for 2h~24h, then heating to 750℃~1000℃, holding for 5h~24h;

[0048] (3) The step after the segmented heating treatment is to crush the material obtained from the segmented heating treatment.

[0049] (4) The step of pulverizing the material obtained from the segmented heating process after the segmented heating process is further included. The pulverization includes at least one of grinding, ball milling and crushing.

[0050] In some embodiments, after obtaining the cathode material, the process further includes: mixing the cathode material with a mixture containing lithium permanganate and a metal compound with a valence of +3 or greater, followed by heat treatment.

[0051] In some embodiments, the preparation method includes at least one of the following features (1) to (6):

[0052] (1) The metal compounds with a valence of +3 or greater include at least one oxide, boride, hydroxide or salt of at least one of the elements selected from Mn, Ti, W, Mo, Nb, Zr, Co, Y, Ce, Al and La;

[0053] (2) The ratio of the total amount of metal elements in the metal compound with a valence of +3 or greater to the total amount of transition metal elements in the heat-treated cathode material is 0.02 wt% to 10 wt%.

[0054] (3) The median particle size of the metal compounds with a valence of +3 or greater is 10 nm to 500 nm;

[0055] (4) The concentration of lithium permanganate in the mixture containing lithium permanganate and a metal compound with a +3 valence greater than or equal to is 0.02 g / L to 10 g / L;

[0056] (5) The ratio of the total amount of transition metal elements in the lithium permanganate to the total amount of transition metal elements in the heat-treated cathode material is 0.01 wt% to 2 wt%.

[0057] (6) After the positive electrode material and the mixture containing lithium permanganate and a metal compound with a valence greater than or equal to +3 are mixed with the positive electrode material and before heat treatment, the mixture further includes a step of drying the mixture containing lithium permanganate and a metal compound with a valence greater than or equal to +3 with the positive electrode material.

[0058] In some embodiments, the preparation method includes at least one of the following features (1) to (3):

[0059] (1) The heat treatment is carried out in an oxygen or air atmosphere;

[0060] (2) The temperature of the heat treatment is 200℃~800℃;

[0061] (3) The heat treatment holding time is 5h to 24h.

[0062] Thirdly, embodiments of this application provide a lithium-ion battery, the lithium-ion battery comprising the positive electrode material described in the first aspect or the positive electrode material prepared by the preparation method described in the second aspect.

[0063] Compared with the prior art, the present invention has the following advantages:

[0064] The cathode material of this application, M 1 M exists in the coating layer 1 Including at least one of Mn, Ti, W, Mo and Nb, M 1 Elements form a lithium boron oxide coating layer, which coats the surface of the substrate. This coating inhibits the grain growth of primary particles in the substrate material, improves ionic conductivity, reduces the impedance of the material, and thus enhances the rate performance of the material; M 2 The element exists in the kernel, M 2 Including at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg and La, and a specific M 2The presence of elements can promote and optimize the directional growth of crystal faces in materials, which is beneficial for forming layered structures, thereby improving the structural stability of the material and further enhancing its rate performance and capacity. The cathode material of this application satisfies equations (III) and (IV) during X-ray diffraction measurements, indicating that the cathode material has fewer lattice defects on its surface and can form single-crystal particles with complete surfaces. That is, this application achieves this through M... 1 Element and M 2 Synergistic effects of elements can help the growth of material grains and adjust the size of primary particles to obtain single crystal particles with a more complete layered structure, which is beneficial to improve the insertion and extraction of lithium ions and enhance the capacity and rate performance of cathode materials.

[0065] The metal borides in this application possess strong metal-oxygen bond energy. Under segmented heating conditions, the metal borides react completely with lithium salts to form fast-ion conductor lithium boron oxide, which coats the surface of the primary particles to form a coating layer. This inhibits the growth of the primary particles, while the presence of the lithium boron oxide significantly increases the diffusion rate of lithium ions in the material, thereby increasing the material's capacity. Furthermore, the addition of a flux helps alleviate the inhibition of grain growth by the metal borides, solving the problem of metal borides being unable to be added to the cathode material alone or causing increased energy consumption. Simultaneously, the addition of the flux promotes the directional growth of the material's crystal faces, optimizing crystal growth and facilitating the formation of a layered structure, thus improving the material's structural stability and further enhancing its rate performance and thermal stability. This application utilizes a segmented heating process and an in-situ synthesis method to form dopants (flux metal elements and boron elements) inside the precursor particles, creating layered single-crystal materials. This improves the structural stability and capacity of the material. Simultaneously, it can form a coating layer (metal elements of metal borides) on the surface of the precursor particles, inhibiting grain growth, increasing ionic conductivity, reducing the impedance of the material, and thus enhancing the rate performance of the material. Attached Figure Description

[0066] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0067] Figure 1 This is a flowchart illustrating the preparation process of the cathode material in this application;

[0068] Figure 2 SEM image of the cathode material prepared in Example 1;

[0069] Figure 3The image shows the XRD pattern of the cathode material prepared in Example 1.

[0070] Figure 4 SEM image of the cathode material prepared in Example 2;

[0071] Figure 5 SEM image of the cathode material prepared in Example 3;

[0072] Figure 6 SEM image of the cathode material prepared in Comparative Example 1;

[0073] Figure 7 Here is a SEM image of the cathode material prepared in Comparative Example 2;

[0074] Figure 8 Here is a SEM image of the cathode material prepared in Comparative Example 3;

[0075] Figure 9 The image shows the SEM image of the cathode material prepared in Comparative Example 4. Detailed Implementation

[0076] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0077] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0078] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0079] For ease of understanding of this invention, specific terms have been appropriately defined in this application. Unless otherwise defined herein, the scientific and technical terms used in this invention have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0080] In the embodiments and comparative examples of this invention, the "%" addition amount refers to the total amount of the cathode material; the "wt%" addition amount refers to the total mass of the cathode material.

[0081] As used herein, the term "matrix" refers to a lithium-based composite oxide synthesized by a high-temperature solid-state reaction of a precursor and a lithium salt, and includes both lithium and metal elements.

[0082] This application provides a cathode material, which includes a substrate and a coating layer disposed on at least a portion of the surface of the substrate. The general chemical formula of the substrate is shown in formula (I):

[0083] Li a Ni b Co c N d M 2 e O2(Ⅰ)

[0084] In equation (Ⅰ), N includes Mn and / or Al, M 2 It includes at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg and La, with 0.95≤a≤1.08, 0.3≤b≤1, 0≤c≤0.7, 0≤d≤0.5, 0≤e≤0.1, and b+c+d+e=1;

[0085] The general chemical formula of the coating layer is shown in formula (II):

[0086] Li g M 1 (2h-g) / i O h (II)

[0087] In formula (II), M 1 Includes at least one of Mn, Ti, W, Mo, and Nb, where i is M 1 The valence values ​​of the ions, and g, h, and (2h-g) / i are all integers;

[0088] In the diffraction pattern obtained by X-ray diffraction measurement of the cathode material, the cathode material has a diffraction peak 2θ on the (102) plane. 102 The diffraction peak 2θ of the (006) plane 006 The diffraction peak 2θ of the (110) plane 110 The diffraction peak 2θ of the (108) plane 108 ,2θ 102 2θ 006 2θ 110 and 2θ 108 The following relationship must be satisfied:

[0089] 2θ 102 -2θ 006 ≥0.25(Ⅲ)

[0090] 2θ 110 -2θ 108 ≥0.33 (Ⅳ).

[0091] It should be noted that 2θ in this application 102 This refers to 2θ corresponding to the diffraction peak of the (102) plane, and the others are the same.

[0092] In the above scheme, the cathode material of this application, M 1 M exists in the coating layer 1 Including at least one of Mn, Ti, W, Mo and Nb, M 1 Elements form a lithium boron oxide coating layer, which coats the surface of the substrate. This coating inhibits the grain growth of primary particles in the substrate material, improves ionic conductivity, reduces the impedance of the material, and thus enhances the rate performance of the material; M 2 Elements exist in the kernel, M 2 Including at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg and La, and a specific M 2 The presence of elements can promote and optimize the directional growth of crystal faces in materials, which is beneficial for the formation of layered structures, thereby improving the structural stability of the material and further enhancing its rate performance and thermal stability; the cathode material of this application satisfies the following equation when X-ray diffraction measurements are performed.

[0093] The relationship between equation (III) and equation (IV) indicates that the cathode material of this application has fewer lattice defects on its surface, enabling the formation of single-crystal particles with complete surfaces. In other words, this application achieves this through M... 1 Element and M 2 Synergistic effects of elements can help the growth of material grains and adjust the size of primary particles to obtain single crystal particles with a more complete layered structure, which is beneficial to improve the insertion and extraction of lithium ions and enhance the capacity and rate performance of cathode materials.

[0094] In this application, 2θ 102 -2θ 006 It can be 0.25, 0.28, 0.30, 0.33, 0.35, and 0.38, or other values ​​within the above range; this application does not impose any restrictions. If 2θ 102 -2θ 006 A value less than 0.25 indicates that the surface of the cathode material is incomplete and contains certain lattice defects. 2θ 110 -2θ 108 It can be 0.33, 0.5, 0.38,

[0095] 0.40, 0.45, and 0.48, etc., and other values ​​within the above range, are not limited herein. If 2θ 110 -2θ 108 If the value is less than 0.33, it indicates that the surface of the cathode material is incomplete and has certain lattice defects.

[0096] In some embodiments, the general chemical formula of the matrix is ​​shown in formula (V):

[0097] Li a Ni b Coc N d M 2 e M 3 f O2(V)

[0098] In equation (V), N includes Mn and / or Al, M 2 Including at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg, and La, M 3 It includes at least one of Mn, Ti, W, Mo, Nb, Zr, Co, Y, Ce, Al and La, with 0.95≤a≤1.08, 0.3≤b≤1, 0≤c≤0.7, 0≤d≤0.5, 0≤e≤0.1, 0≤f≤0.1, b+c+d+e+f=1, and 0≤y≤0.01.

[0099] The general chemical formula of the coating layer is shown in formula (VI):

[0100] Li g M 1 (2h-g) / i O h ·NiO·LiMn2O4(VI)

[0101] In equation (VI), M 1 Includes at least one of Mn, Ti, W, Mo, and Nb, where i is M 1 The valence values ​​of the ions, and g, h, and (2h-g) / i are all integers.

[0102] In the above scheme, M 2 Element and M 3 Elements exist in the kernel, M 2 Element and M 3 The presence of this element can promote the directional growth of crystal faces in materials, optimize crystal face growth, facilitate the formation of layered structures, and improve the structural stability of materials; the coating layer in this application is Li. g M 1 (2h-g) / i O h A mixed phase coating of NiO and LiMn2O4 phases, wherein M 1The NiO phase is a rock salt phase and the LiMn2O4 phase is a spinel phase, which are metal ions that inhibit single crystal growth. The above-mentioned mixed coating layer has a three-dimensional tunnel structure, which can significantly improve the rate of lithium ion insertion and extraction in the crystal lattice, making the material structure more stable. Lithium ions can be reversibly inserted and extracted from the mixed phase lattice without causing structural collapse. It reduces the transformation of H2 phase to H3 phase under high voltage, which is beneficial to improve the particle strength of the material and reduce the risk of cracks and pulverization and large-scale gas generation during cycling. It can significantly improve the structural stability, rate performance, safety performance and gas generation problem of the material.

[0103] In the matrix material of this application, a can be, for example, 0.95, 0.98, 1.01, 1.03, 1.05 or 1.08, b can be, for example, 0.3, 0.5, 0.7, 0.8, 0.83, 0.88, 0.91, 0.94 or 0.98, c can be, for example, 0.02, 0.06, 0.1, 0.2, 0.5 or 0.7, d can be, for example, 0.02, 0.06, 0.1, 0.2 or 0.5, e can be, for example, 0.02, 0.04, 0.06 or 0.1, and f can be, for example, 0.02, 0.04, 0.06 or 0.1.

[0104] In some embodiments, the cathode material includes secondary particles and / or primary particles. The secondary particles include a plurality of primary particles and a coating layer covering the surface of the primary particles. It is understood that the primary particles are individual fine grains, and the secondary particles are particles formed by the aggregation of primary particles. Preferably, the secondary particles are aggregates formed by the aggregation of primary particles after coating. The cathode material of this application can be primary particles, secondary particles, or a mixture of primary and secondary particles.

[0105] In some implementations, the median particle size of the primary particles is 2 μm to 6 μm. Specifically, the median particle size of the primary particles can be 2 μm, 3 μm, 4 μm, 5 μm, and 6 μm, or other values ​​within the above range, which are not limited here. If the median particle size of the primary particles is less than 2 μm, the primary particles are too small, causing severe agglomeration of the single crystal particles and resulting in poor material quality. If the median particle size of the primary particles is greater than 6 μm, the single crystal primary particles are too large, resulting in low capacity, high impedance, and poor rate performance of the material.

[0106] In some implementations, Ni in the surface layer of the cathode material 2+ quality and Ni 2+ and Ni 3+ The ratio of the total mass is greater than or equal to 0.6. The surface layer of the cathode material refers to the portion extending from the surface of the cathode material into its interior with a thickness of 0 nm to 20 nm. Specifically, the Ni in the surface layer of the cathode material... 2+quality and Ni 2+ and Ni 3+ The ratio of the total mass can be 0.6, 0.65, 0.7, 0.8, 0.9, etc., or other values ​​within the above range, which are not limited here. Within the above range, the Ni in the surface layer of the positive electrode material... 2+ The high content of Ni indicates a relatively stable layered structure in the cathode material. In this application, the Ni content in the cathode material... 2+ and Ni 3+ The quality was determined by powder XPS.

[0107] In some embodiments, in the XRD pattern of the cathode material, the intensity ratio of the diffraction peaks between the (003) plane and the (104) plane is I. 003 / Ⅰ 104 ≥1.3, specifically, Ⅰ 003 / Ⅰ 104 The ratio can be 1.3, 1.4, 1.5, 1.6, and 1.7, or other values ​​within the above range, which are not limited here. Within the above range, it indicates that the cathode material of this application can reduce lithium-nickel mixing, reduce the impedance of the material, and thus improve the capacity and rate performance of the material.

[0108] In some implementations, 2θ 102 2θ 006 2θ 110 and 2θ 108 Satisfying the relationship described in equation (Ⅶ):

[0109] (2θ 102 -2θ 006 ) / (2θ 110 -2θ 108 )≥0.7(Ⅶ)

[0110] Specifically, (2θ) 102 -2θ 006 ) / (2θ 110 -2θ 108 The value can be 0.70, 0.72, 0.75, or 0.79, or any other value within the above range, which is not limited here. Satisfying the above relationship indicates that the layered structure of the cathode material of this application is more complete, which is beneficial to the insertion and extraction of lithium ions, and makes the cathode material have better capacity and rate performance.

[0111] In some implementations, the rate of change of the lattice parameters of the cathode material when charged to 4.3V is...

[0112] ≤5%, specifically, when the cathode material is charged to 4.3V, the rate of change of the lattice parameters of the cathode material can be 1%, 2%, 3%, 4%, and 5%, etc., or other values ​​within the above range, which are not limited here. Within the above range, it indicates that the cathode material of this application has excellent structural stability.

[0113] In some embodiments, when the cathode material is charged to 4.3V, the rate of change of the unit cell volume of the cathode material is...

[0114] ≤6%, specifically, when the cathode material is charged to 4.3V, the cell volume change rate of the cathode material can be, for example, 1%, 2%, 3%, 4%, 5%, and 6%, etc., or other values ​​within the above range, which are not limited here. Within the above range, it indicates that the cathode material of this application has excellent structural stability.

[0115] In some implementations, when the positive electrode material is charged to 4.3V, the particle strength of the positive electrode material is...

[0116] ≥200MPa. Specifically, when the positive electrode material is charged to 4.3V, the particle strength of the positive electrode material can be, for example, 200MPa, 300MPa, 400MPa, 500MPa and 600MPa, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0117] When the cathode material is charged to 44.3V, the rate of change of lattice parameters and the rate of change of unit cell volume decrease with increasing particle strength, indicating that the cathode material of this application has excellent structural stability. Furthermore, the higher the particle strength, the smaller the decrease in lattice parameter c and the smaller the rate of change of unit cell volume as lithium ions are extracted during charging. Conversely, low particle strength indicates an unstable lattice structure, resulting in a larger decrease in lattice parameter c and a larger rate of change of unit cell volume as lithium ions are extracted during charging.

[0118] In some implementations, Li g M 1 (2h-g) / i The mass percentage of oxygen in the cathode material is 0% to 1% (excluding 0). For example, Li g M 1 (2h-g) / i The mass percentage of oxygen in the cathode material can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, and 1%, or other values ​​within the above range, which are not limited here.

[0119] In some embodiments, the mass percentage of NiO in the cathode material is 0% to 10%. For example, the mass percentage of NiO in the cathode material can be 0%, 0.05%, 0.1%, 1%, 3%, 5%, and 10%, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0120] This application also provides a method for preparing the above-mentioned positive electrode material, such as... Figure 1 The diagram shown is a flowchart of the preparation process of the cathode material of this application, including the following steps:

[0121] Ni (1-c-d) Co c N d The cathode material is obtained by mixing (OH)2 precursor, lithium salt, metal boride and flux and then performing a segmented heating process. The metal boride includes at least one of Mn, Ti, W, Mo and Nb, and the metal boride can react with lithium salt. The flux includes at least one oxide, hydroxide or salt of Zr, Sr, Co, Ba, Y, Ce, Al, Mg and La, wherein N includes at least one of Co, Al and Mn, 0≤c≤0.7, 0≤d≤0.5.

[0122] In the above-mentioned scheme, the metal borides of this application have strong metal-oxygen bond energy. Under segmented heating treatment conditions, the metal borides react completely with lithium salts to form fast ion conductor lithium boron oxide, which coats the surface of the primary particles to form a coating layer. While inhibiting the growth of the primary particles, the presence of lithium boron oxide can significantly increase the diffusion rate of lithium ions in the material and improve the capacity of the material. The addition of flux can alleviate the inhibition of grain growth by metal borides, solving the problem that metal borides cannot be added to the cathode material alone or that the addition of metal borides to the cathode material alone will lead to increased energy consumption. At the same time, the addition of flux can promote the directional growth of the crystal faces of the material, optimize the crystal face growth, and facilitate the formation of a layered structure, improving the structural stability of the material and further enhancing the rate performance and thermal stability of the material. This application utilizes a segmented heating process and an in-situ synthesis method to form dopants (flux metal elements and boron elements) within the precursor particles, creating a layered single-crystal material. This improves the material's structural stability and capacity. Simultaneously, it forms a coating layer (metal boride elements) on the surface of the precursor particles, inhibiting grain growth, increasing ionic conductivity, reducing impedance, and ultimately enhancing the material's rate performance. Without this segmented heating process, it is impossible to form a stable layered coating layer on the substrate surface.

[0123] It is understandable that adding metal borides alone results in smaller primary particle growth of the cathode material during the preparation process, making it impossible to generate single crystals at the same sintering temperature. If single crystals are required, the sintering temperature needs to be significantly increased, resulting in higher energy consumption.

[0124] The preparation method of this application is described in detail below with reference to the embodiments:

[0125] Before step S100, Ni is prepared. (1-c-d) Co c N d (OH)2 precursor, comprising the following steps:

[0126] Ni was obtained by co-precipitation, which involved mixing a metal salt solution with a complexing agent and a pH adjuster. (1-c-d) Co c N d (OH)2 precursor.

[0127] In some embodiments, the mass ratio of the metal salt solution, complexing agent, and pH adjuster is 1:(0.01 to 0.10):(0.1 to 0.8). Specifically, the mass ratio of the metal salt solution, complexing agent, and pH adjuster can be 1:0.01:0.1, 1:0.05:0.3, 1:0.1:1.5, and 1:0.08:0.8, etc.

[0128] In some embodiments, the metal salt solution includes at least one of a nickel salt solution, a cobalt salt solution, a manganese salt solution (or an aluminum salt solution).

[0129] Specifically:

[0130] Nickel salt solutions include at least one of nickel sulfate, nickel chloride, nickel sulfamate, nickel bromide, nickel hydroxide, and nickel carbonyl.

[0131] Cobalt salt solutions include at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate.

[0132] Manganese salt solutions include at least one of manganese sulfate, manganese nitrate, and manganese chloride.

[0133] Aluminum salt solutions include at least one of sodium aluminate, aluminum sulfate, aluminum chloride, and potassium aluminate.

[0134] In some embodiments, the complexing agent is selected to be capable of forming a complex with nickel, cobalt, manganese or aluminum ions in an aqueous solution. Specifically, the complexing agent includes at least one of ammonium ion donor, hydrazine, ethylenediaminetetraacetic acid, hypozoxytriacetic acid, uracil diacetic acid and glycine. The ammonium ion donor includes at least one of ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate and ammonium fluoride.

[0135] In some embodiments, the mixing temperature is between 10°C and 80°C. Specifically, the mixing temperature is 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, and 80°C, etc., and other values ​​within the above range are also possible and are not limited here. Preferably, the mixing temperature is between 20°C and 70°C. Controlling the temperature of the co-precipitation reaction within the above range is beneficial to the growth of precursor grains.

[0136] In some implementations, the pH adjuster includes alkali metal hydroxides.

[0137] In some embodiments, the alkali metal oxide includes at least one of sodium hydroxide and potassium hydroxide.

[0138] In some embodiments, the pH of the mixed treatment is 9 to 13. Specifically, the pH of the mixed treatment is 9, 10, 11, 12, and 13, etc. Of course, other values ​​within the above range are also possible and are not limited here. Preferably, the pH of the mixed treatment is 11 to 13.

[0139] In some embodiments, the mixing process takes place for 10 hours to 200 hours. The specific mixing time can be 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, 60 hours, 70 hours, 80 hours, 90 hours, 100 hours, 110 hours, 120 hours, 130 hours, 140 hours, 150 hours, 160 hours, 180 hours, 180 hours, 190 hours, and 200 hours, or other values ​​within the above range. No limitation is made here.

[0140] In some embodiments, the mixing process is carried out under stirring conditions, with a stirring rate of 800 rpm to 1200 rpm. The stirring rate can be 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, and 1200 rpm, or other values ​​within the above range, which are not limited here.

[0141] In some embodiments, the mixing process is carried out in a reaction vessel, which is at least one of a continuous type that allows the formed metal complex hydroxide to overflow, or an intermittent type that does not discharge to the outside of the system until the reaction is completed.

[0142] In some embodiments, the metal composite hydroxide precursor prepared by the mixing process is a slurry-like suspension, which is then subjected to solid-liquid separation, washing, and drying to obtain the metal composite hydroxide precursor.

[0143] Of course, Ni can also be prepared by other methods. (1-c-d) Co c N d (OH)2 precursors, or obtained by directly purchasing products, are not limited herein.

[0144] Step S100: Ni (1-c-d) Co c N d The cathode material is obtained by mixing (OH)2 precursor, lithium salt, metal boride and flux and then performing a segmented heating process.

[0145] In some implementations, Ni (1-c-d) Co c N d The median particle size of the (OH)₂ precursor is 2 μm to 6 μm. Specifically, Ni (1-c-d) Co c N d The median particle size of the (OH)₂ precursor can be 2 μm, 3 μm, 4 μm, 5 μm, and 6 μm, or other values ​​within the above range, and is not limited herein. Within the above particle size range, it indicates that the Ni of this application... (1 - c-d) Co c N d The (OH)2 precursor has a suitable particle size, which is beneficial for generating near-spherical particles during the preparation process. If Ni... (1-c-d) Co c N d If the median particle size of the (OH)₂ precursor is less than 2 μm, the precursor material particle size is too small to form near-spherical particles; if Ni (1-c-d) Co c N d If the median particle size of the (OH)2 precursor is greater than 6 μm, it will be difficult to generate single crystals due to the excessively large particle size of the precursor material.

[0146] In some embodiments, the ratio of the total amount of metal elements in the metal boride to the total amount of the cathode material is 0.01% to 1%, wherein the metal element in the metal boride refers to at least one of Mn, Ti, W, Mo, and Nb, that is, the coating layer of the cathode material contains M. 1Specifically, the ratio of the total amount of metal elements in the lithium metal oxide to the total amount of the cathode material can be, for example, 0.01%, 0.02%, 0.05%, 0.057%, 0.1%, 0.2%, 0.5%, 0.8%, and 1%, or other values ​​within the above range, without limitation. If the ratio of the total amount of metal elements in the metal boride to the total amount of the cathode material is less than 0.01%, the amount added is too small, and a complete coating layer cannot be formed during the segmented heating process, thus failing to achieve the coating effect. If the ratio of the total amount of metal elements in the metal boride to the total amount of the cathode material is greater than 1%, the amount added is too large, resulting in an excessively thick coating layer, and even after adding flux, single crystals cannot be formed. Preferably, the ratio of the total amount of metal elements in the metal boride to the total amount of the cathode material is 0.02% to 0.5%, and more preferably, the ratio of the total amount of metal elements in the metal boride to the total amount of the cathode material is 0.07% to 0.2%.

[0147] In some embodiments, the metal boride includes at least one of MoB, W2B5, NbB, MbB, and TiB2.

[0148] In some embodiments, the median particle size of the metal borides is 10 nm to 500 nm. Specifically, the median particle size of the metal borides is 10 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, and 500 nm, etc. Of course, other values ​​within the above range are also possible and are not limited here. Preferably, the median particle size of the metal borides is 20 nm to 300 nm, and more preferably, the median particle size of the metal borides is 30 nm to 200 nm.

[0149] In some embodiments, the ratio of the total amount of metal elements in the flux to the total amount of the cathode material is 0.02% to 10%. It is understood that the metal elements in the flux include at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg, and La. Specifically, the ratio of the total amount of metal elements in the flux to the total amount of the cathode material can be 0.02%, 0.07%, 0.1%, 0.3%, 0.5%, 1%, 3%, 5%, 8%, and 10%, etc., and of course, other values ​​within the above range are also possible and are not limited here. If the ratio of the total amount of metal elements in the flux to the total amount of the cathode material is less than 0.02%, the doping amount is too small, the fluxing effect is not obvious, and the generated primary particles are small; if the ratio of the total amount of metal elements in the flux to the total amount of the cathode material is greater than 10%, the amount of flux added is too large, which seriously affects the capacity of the material. Preferably, the ratio of the total amount of metal elements in the flux to the total amount of the cathode material is 0.02% to 5%, and more preferably, the ratio of the total amount of metal elements in the flux to the total amount of the cathode material is 0.07% to 3%.

[0150] In this application, the size of primary particles can be controlled by adjusting the addition ratio of metal borides and flux. Within the defined range of metal borides and flux, the particle size of the generated single crystal particles can be increased by increasing the addition ratio of flux, resulting in a cathode material with high stability. Alternatively, smaller single crystal particles can be obtained by reducing the addition ratio of flux or increasing the addition ratio of metal borides, resulting in a cathode material with good rate performance, high capacity, and low impedance.

[0151] In some embodiments, the median particle size of the flux is 10 nm to 500 nm. Specifically, the median particle size of the flux is 10 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm and 500 nm, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0152] The median particle size of both the metal boride and the flux in this application is in the nanometer range, and the addition of Ni... (1-c-d) Co c N d In the (OH)2 precursor, uniform doping can be achieved through mixing operations, which is beneficial to improving the structural stability of the material.

[0153] In some embodiments, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium phosphate, and lithium oxalate, preferably lithium hydroxide.

[0154] In some embodiments, the molar ratio of lithium element in the lithium salt to the total metal in the cathode material is (0.95 to 1.08):1. Specifically, the molar ratio of lithium element in the lithium salt to the total metal in the cathode material can be 0.95:1, 0.98:1, 1:1, 1.03:1, 1.05:1 and 1.08:1, etc., or other values ​​within the above range, which are not limited here.

[0155] In some implementations, the staged heating process is carried out in an oxygen or air atmosphere.

[0156] In some embodiments, the segmented heating process includes a two-stage heating process, wherein the segmented heating process includes:

[0157] First, raise the temperature to 300℃~750℃ and hold it for 2h~24h. Then, raise the temperature to 750℃~1000℃ and hold it for 5h~24h.

[0158] In some embodiments, the temperature of the first stage of the segmented heating process is 300℃ to 750℃. Specifically, the temperature of the first stage of the segmented heating process can be 300℃, 400℃, 500℃, 600℃, 700℃, and 750℃, etc., or other values ​​within the above range, which are not limited here. Controlling the temperature of the first stage of the segmented heating process within the above range is beneficial for forming Li on the surface of the primary particles of the material. g M 1 (2h-g) / i O h The layered coating promotes the directional growth of particles.

[0159] In some implementations, the holding time of the first stage of the segmented heating process is 2h to 24h. Specifically, the holding time of the segmented heating process is 2h, 5h, 8h, 10h, 12h, 15h, 18h, 20h and 24h, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0160] In some embodiments, the second stage temperature of the segmented heating process is 750℃ to 1000℃. Specifically, the first stage temperature of the segmented heating process can be 750℃, 800℃, 900℃, 950℃, and 1000℃, or other values ​​within the above range, which are not limited here. Controlling the temperature of the second stage of the segmented heating process within the above range is beneficial for forming a layered structure and generating single crystals in the material, without causing material decomposition.

[0161] In some implementations, the holding time of the second stage of the segmented heating process is 5h to 24h. Specifically, the holding time of the segmented heating process is 5h, 8h, 10h, 12h, 15h, 18h, 20h and 24h, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0162] In some embodiments, the step of pulverizing the material obtained from the segmented heating process after the segmented heating process is further included, and the pulverization includes at least one of grinding, ball milling and crushing.

[0163] In some implementations, the equipment for segmented heating processes includes stationary box furnaces, roller kiln continuous furnaces, etc.

[0164] In some implementations, the method further includes the following after step S100:

[0165] Step S200: The positive electrode material is mixed with a mixture containing lithium permanganate and a metal compound with a +3 valence greater than or equal to that of the precursor and then subjected to heat treatment.

[0166] In the above steps, this application adds lithium permanganate and a metal compound with a valence of +3 or higher. The metal ions in the metal compound with a valence of +3 or higher enter Ni. (1-c-d) Co c N d The crystal lattice interior of the (OH)2 precursor and Ni in the material 3+ A reaction occurs, causing the Ni layer on the material surface to... 2+ The increased content of lithium boron oxide leads to the formation of a rock salt phase NiO on the surface, while lithium permanganate forms a spinel LiMn2O4 phase on the surface, creating a mixed coating layer with the layered structure of lithium boron oxide. This mixed coating layer of lithium boron oxide, rock salt NiO, and spinel LiMn2O4 possesses a three-dimensional tunnel structure, allowing lithium ions to reversibly intercalate and deintercalate from the mixed phase lattice without causing structural collapse. This reduces the H2-to-H3 phase transition under high voltage, improving the material's structural and thermal stability. Furthermore, the synergistic effect of lithium boron oxide, rock salt NiO, and spinel LiMn2O4 significantly increases the rate of lithium ion intercalation and deintercalation in the lattice, enhancing the material's rate performance. Additionally, the formation of the spinel LiMn2O4 phase significantly reduces gas production, thereby improving the material's safety performance.

[0167] In this application, due to Ni 2+ The formation of rock salt phase NiO can lead to the formation of Ni within the material matrix. 2+ The boron compounds in this application can generate lithium boron oxide during the segmented heating process, which can significantly improve the diffusion rate of lithium ions in the material, increase the material's capacity, and thus reduce the concentration of Ni in the material. 3+Capacity loss due to conversion to rock salt phase NiO.

[0168] Understandably, compared to a single spinel LiMn2O4 phase coating, which can only provide lithium-ion transport channels, the hybrid coating of this application can not only provide lithium-ion transport channels but also improve the particle strength of the material, reduce the risk of cracks and subsequent pulverization and gas generation during material cycling, and significantly improve the structural stability and safety of the material while reducing gas generation.

[0169] Specifically: a metal compound with a valence of +3 or greater is dispersed in a lithium permanganate solution to obtain a first solution, and the cathode material obtained by segmented heating treatment is mixed with the first solution and then subjected to heat treatment.

[0170] In some embodiments, the metal compound with a valence of +3 or higher includes at least one oxide, boride, hydroxide, or salt of at least one element selected from Mn, Ti, W, Mo, Nb, Zr, Co, Y, Ce, Al, and La. Exemplarily, the metal compound with a valence of +3 or higher includes at least one selected from Mn₂O₅, TiCl₄, CeO₂, MoO₃, and Ti(OH)₄.

[0171] In some embodiments, the median particle size of the metal compounds with a valence of +3 or higher is 10 nm to 500 nm. Specifically, the median particle size of the metal compounds with a valence of +3 or higher is 10 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, and 500 nm, etc., and of course, other values ​​within the above range are also possible and are not limited here. Preferably, the median particle size of the metal compounds with a valence of +3 or higher is 20 nm to 300 nm, and more preferably, the median particle size of the metal compounds with a valence of +3 or higher is 30 nm to 200 nm. The median particle size of the metal compounds with a valence of +3 or higher and the median particle size of the single crystal growth inhibition in this application are both at the nanometer level, which can form uniform doping during the reaction process, thereby improving the structural stability of the material.

[0172] In some embodiments, the ratio of the total amount of metal elements in the +3 valence metal compound to the total amount of transition metals in the heat-treated cathode material is 0.02% to 10%. Specifically, the ratio can be 0.02%, 0.07%, 0.1%, 0.3%, 0.5%, 1%, 3%, 5%, 8%, and 10%, or other values ​​within the above range, which are not limited here. Preferably, the ratio of the total amount of metal elements in the +3 valence metal compound to the total amount of transition metals in the heat-treated cathode material is 0.02% to 5%. More preferably, the ratio is 0.07% to 3%.

[0173] In some embodiments, the concentration of lithium permanganate in the first solution is 0.02 g / L to 10 g / L. Specifically, the concentration of lithium permanganate in the first solution can be 0.02 g / L, 0.07 g / L, 0.1 g / L, 0.5 g / L, 1 g / L, 3 g / L, 5 g / L, 8 g / L, and 10 g / L, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Preferably, the concentration of lithium permanganate in the first solution is 0.2 g / L to 10 g / L, and more preferably, the concentration of lithium permanganate in the first solution is 0.3 g / L to 5 g / L.

[0174] In some embodiments, the mass ratio of lithium permanganate to the heat-treated cathode material is 0.01 wt% to 2 wt%. Specifically, the mass ratio of lithium permanganate to the heat-treated cathode material is 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.3 wt%, 1.7 wt%, and 2 wt%, etc., and other values ​​within the above range are also possible and are not limited here. Preferably, the mass ratio of lithium permanganate to the heat-treated cathode material is 0.02 wt% to 1 wt%, and more preferably, the mass ratio is 0.03 wt% to 0.5 wt%.

[0175] In some embodiments, after mixing the cathode material obtained by the segmented heating process with the first solution and before heat treatment, the method further includes a step of drying the cathode material obtained by the segmented heating process with the first solution.

[0176] In some embodiments, the drying process may be, for example, spray drying.

[0177] In some embodiments, the drying temperature is 150°C to 300°C. Specifically, the drying temperature can be, for example, 150°C, 170°C, 200°C, 220°C, 250°C, and 300°C, or other values ​​within the above range, which are not limited here. Within the above drying temperature range, the moisture in the material can be rapidly reduced, resulting in a uniform coating of lithium permanganate and high-valence metal oxides on the surface of the material. Preferably, the drying temperature is 150°C to 250°C.

[0178] In some embodiments, the heat treatment is carried out in an oxygen or air atmosphere.

[0179] In some embodiments, the heat treatment temperature is 200–800°C. Specifically, the heat treatment temperature can be, for example, 200°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, and 800°C, or other values ​​within the above range, which are not limited here. Preferably, the heat treatment temperature is 300°C–750°C.

[0180] In some embodiments, the heat treatment holding time is 5h to 24h. Specifically, the heat treatment holding time is 5h, 8h, 10h, 12h, 15h, 18h, 20h and 24h, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0181] In some embodiments, the heat treatment process includes a step of sieving the heat-treated material to prevent the final product from agglomerating due to the heat treatment. For example, the mesh size of the sieve is 200 to 600 mesh. Specifically, the mesh size can be 200, 300, 400, 500, and 600 mesh, or other values ​​within the above range, which are not limited here.

[0182] This application also provides a lithium-ion secondary battery, including a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and a casing. The positive electrode includes a current collector and a positive electrode material prepared by the above-described positive electrode material or by the above-described positive electrode material preparation method coated on the current collector.

[0183] The embodiments of the present invention are described, but the present invention is not limited to these examples as long as it does not depart from its spirit.

[0184] Example 1

[0185] (1) The Ni / Co / Mn precursor with a molar ratio of 88 / 9 / 3 was mixed with lithium hydroxide, MoB and La2O3 evenly, sintered at 600℃ for 5h, and then heated to 830℃ for 15h. The mixture was then crushed to obtain material A. The median particle size of MoB was 50nm, and the amount of Mo in MoB was equivalent to 0.1% of the amount of the final product. The median particle size of La2O3 was 20nm, and the amount of La was equivalent to 0.5% of the amount of the final product. The molar ratio of lithium in lithium hydroxide to the total metal in the final product was Li / Me = 1.05.

[0186] (2) Add CeO2 to the lithium permanganate solution and stir evenly to obtain material B. The median particle size of CeO2 is 200 nm, the mass percentage of Ce element in the final product is 0.2 wt%, the concentration of lithium permanganate solution is 5 g / L, and the mass percentage of lithium permanganate in the final product is 0.5 wt%.

[0187] (3) Add material A to material B for spray drying at a temperature of 200°C to obtain material C.

[0188] (4) Material C is sintered at high temperature in an oxygen atmosphere. The sintering temperature is 700℃ and the sintering time is 12h. After sintering, it is crushed to obtain the positive electrode material, which is the final product.

[0189] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.8966% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.001 Ce 0.0001 O2. The chemical formula of the mixed coating layer is: 0.1% Li2MoO4·0.0014% NiO·0.002% LiMn2O4; the percentages in the molecular formula refer to the molar ratio, and the same applies to other embodiments.

[0190] like Figure 2 The image shown is a SEM image of the cathode material prepared in Example 1 of this invention. Figure 1 It can be seen that the cathode material has a moderate particle size and a distinct layered coating.

[0191] Example 2

[0192] (1) The Ni / Co / Mn precursor with a molar ratio of 75 / 0 / 25 was mixed with lithium hydroxide, W2B5 and Y2O3 evenly, sintered at 550℃ for 5h, and then heated to 930℃ for 15h. The mixture was then crushed to obtain material A. The median particle size of W2B5 was 50nm, and the W element was equivalent to 0.02% of the final product. The median particle size of Y2O3 was 100nm, and the Y element was equivalent to 0.3% of the final product. The molar ratio of lithium element in lithium hydroxide to the total metal in the final product was Li / Me = 1.03.

[0193] (2) Add MoO3 to the lithium permanganate solution and stir evenly to obtain material B. The median particle size of MoO3 is 20 nm, the mass percentage of Mo in the final product is 0.4 wt%, the concentration of lithium permanganate solution is 8 g / L, and the mass percentage of lithium permanganate in the final product is 7 wt%.

[0194] (3) Add material A to material B and spray dry at a temperature of 170°C to obtain material C.

[0195] (4) Material C is sintered at high temperature in an oxygen atmosphere. The sintering temperature is 600℃ and the sintering time is 20h. After sintering, it is crushed to obtain the positive electrode material, which is the final product.

[0196] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 98.64% Li 1.03 Ni 0.747 Mn 0.2485 La 0.003 Y 0.0003 The chemical formula of the O2 mixed coating layer is: 0.04% Li4WO5·1.3% NiO·0.02% LiMn2O4.

[0197] like Figure 4 The image shown is a SEM image of the cathode material prepared in Example 1 of this invention. Figure 4 It can be seen that the cathode material has a moderate particle size and a distinct layered coating.

[0198] Example 3

[0199] (1) The Ni / Co / Mn precursor with a molar ratio of 60 / 10 / 30 was mixed with lithium carbonate, NbB, Y2O3 and ZrO2 and sintered at 750℃ for 8h in air atmosphere, and then heated to 970℃ for 10h. The mixture was then crushed to obtain material A. The median particle size of NbB was 50nm, and the Nb element was equivalent to 0.3% of the final product. The median particle size of Y2O3 was 100nm, and the Y element was equivalent to 0.2% of the final product. The median particle size of ZrO2 was 200nm, and the Zr element was equivalent to 0.5% of the final product. The molar ratio of lithium element in lithium carbonate to the total metal in the final product was Li / Me = 1.06.

[0200] (2) Add Ti(OH)4 to the lithium permanganate solution and stir evenly to obtain material B. The median particle size of Ti(OH)4 is 300nm, the Ti element is equivalent to 0.1wt% of the final product, the concentration of lithium permanganate solution is 3g / L, and the mass percentage of permanganate in the final product is 0.2wt%.

[0201] (3) Add material A to material B and spray dry at a temperature of 220°C to obtain material C.

[0202] (4) Material C is sintered at high temperature in an oxygen atmosphere. The sintering temperature is 750℃ and the sintering time is 8h. After sintering, it is crushed to obtain the positive electrode material, which is the final product.

[0203] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.6976% Li. 1.06 Ni 0.5951 Co 0.0992 Mn 0.2975 Y 0.003 Zr 0.005 Ti 0.0002 O2. The chemical formula of the mixed coating layer is: 0.3% LiNbO3·0.002% NiO·0.0004% LiMn2O4.

[0204] like Figure 5 The image shown is a SEM image of the cathode material prepared in this embodiment. Figure 5 It can be seen that the cathode material has a moderate particle size and a distinct layered coating.

[0205] Example 4

[0206] Unlike Example 1, only step (1) is performed.

[0207] The positive electrode material obtained in this embodiment includes a matrix and a coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.8966% Li1.05 Ni 0.879 Co 0.09 Mn0.03La 0.001 Ce 0.0001 O2, the chemical formula of the coating layer is 0.1034% Li2MoO4.

[0208] Example 5

[0209] Unlike Example 1, in step (1), the amount of Mo element in MoB is equivalent to 0.01% of the amount of the final product.

[0210] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.9866% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.001 Ce 0.0001 O2. The chemical formula of the mixed coating layer is: 0.01% Li2MoO4·0.0014% NiO·0.002% LiMn2O4.

[0211] Example 6

[0212] Unlike Example 1, in step (1), the amount of Mo element in MoB is equivalent to 1% of the amount of the final product.

[0213] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.0006% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.001 Ce 0.0001 O2. The chemical formula of the mixed coating layer is: 1% Li2MoO4·0.0014% NiO·0.002% LiMn2O4.

[0214] Example 7

[0215] Unlike Example 1, in step (1), the amount of Mo element in MoB is equivalent to 1.5 wt% of the amount of the final product.

[0216] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 98.5006% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.001 Ce 0.0001O2. The chemical formula of the mixed coating layer is: 1% Li2MoO4·0.0014% NiO·0.002% LiMn2O4.

[0217] Example 8

[0218] Unlike Example 1, the amount of La element in step (1) is equivalent to 0.02% of the amount of the final product.

[0219] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.8966% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.00004 Ce 0.0001 O2. The chemical formula of the mixed coating layer is: 0.1% Li2MoO4·0.0014% NiO·0.002% LiMn2O4.

[0220] Example 9

[0221] Unlike Example 1, the amount of La element in step (1) is equivalent to 5% of the amount of the final product.

[0222] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.8966% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.01 Ce 0.0001 O2. The chemical formula of the mixed coating layer is: 0.1% Li2MoO4·0.0014% NiO·0.002% LiMn2O4.

[0223] Example 10

[0224] Unlike Example 1, the amount of La element in step (1) is equivalent to 10% of the amount of the final product.

[0225] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.8966% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.02 Ce 0.0001 O2. The chemical formula of the mixed coating layer is: 0.1% Li2MoO4·0.0014% NiO·0.002% LiMn2O4.

[0226] Example 11

[0227] Unlike Example 1, the amount of La element in step (1) is equivalent to 15% of the amount of the final product.

[0228] The positive electrode material obtained in this embodiment includes a matrix and a mixed coating layer covering the surface of the matrix. The chemical formula of the matrix is: 99.8966% Li 1.05 Ni 0.879 Co 0.09 Mn0.03La 0.03 Ce 0.0001 O2. The chemical formula of the mixed coating layer is: 0.1% Li2MoO4·0.0014% NiO·0.002% LiMn2O4.

[0229] Comparative Example 1

[0230] Unlike Example 1, MoB is not added in step (1).

[0231] Comparative Example 2

[0232] Unlike Example 1, La2O3 is not added in step (1).

[0233] Comparative Example 3

[0234] Unlike Example 1, MoB is not added in step (1). Instead, MoB is added to materials A and B in step (3) and then spray-dried and sintered at high temperature.

[0235] Comparative Example 4

[0236] Unlike Example 1, La2O3 in step (1) is replaced with ZrBr4, and the amount of Zr is equivalent to 0.5% of the amount of the final product.

[0237] Comparative Example 5

[0238] Unlike Example 1, in step (1), “sintering at 600°C for 5 hours and then sintering at 830°C for 15 hours” is replaced with “sintering at 830°C for 15 hours”.

[0239] Performance testing

[0240] (1) The peak intensity ratio of the cathode material was tested by XRD.

[0241] (2) Ni on the surface of the positive electrode material 2+ And Ni in cathode materials 2+ and Ni 3+ XPS was used for testing.

[0242] (3) The rate of change of lattice parameters and the rate of change of unit cell volume of the cathode material were calculated after refinement by XRD testing.

[0243] (4) Electrochemical performance testing of cathode materials:

[0244] The electrochemical performance of the prepared positive electrode material was evaluated using a coin cell. The specific method is as follows: The positive electrode material, SP, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 96:2:2. NMP was added at a solid content of 50%, and the mixture was prepared into a viscous slurry using a high-speed disperser. The slurry was then uniformly coated onto aluminum foil using a scraper, dried in an oven at 80°C, and rolled to form positive electrode sheets with a diameter of 14 mm. A 16 mm diameter lithium sheet was used as the negative electrode, a Celgard polyethylene PP film was used as the separator, and a 1 mol / L LiPF6 carbonate solution (DEC / EC volume ratio 1:1) was used as the electrolyte. The assembly was carried out in an argon-filled glove box.

[0245] The capacity, first efficiency and rate performance were tested using the LAND battery testing system at 25℃ and 3.0V~4.3V. The reference capacity was set to 200mA / g and the current density corresponding to 1C was 200mA / g.

[0246] Impedance tests were performed at -25°C and 25°C with 50% SOC, 0.03–105 Hz, and an amplitude of 5 mV to obtain EIS data. The electrode material was a coin cell fully charged after 2.5 cycles at 0.1C.

[0247] The test results are shown in Tables 1 and 2.

[0248] Table 1. Parameters of the cathode materials prepared in each embodiment and comparative example

[0249]

[0250]

[0251] Table 2. Performance parameters of the cathode materials prepared in each embodiment and comparative example

[0252]

[0253]

[0254] As shown in Examples 1-11 and Comparative Examples 1-5, this application will use Ni (1-c-d) Co c N dThe (OH)2 precursor, lithium salt, metal borides, and flux are mixed and subjected to a staged heating process. This process gives the metal borides a strong metal-oxygen bond energy, which readily reacts with the lithium salt to form fast-ion conductor lithium boron oxide. This oxide coats the surface of the primary particles, inhibiting their growth. Simultaneously, the presence of the lithium boron oxide significantly increases the diffusion rate of lithium ions in the material, improving its capacity. The addition of flux further mitigates the growth inhibition caused by the metal borides, addressing the issues of metal borides being unable to be added alone to the cathode material or the increased energy consumption resulting from their addition. Furthermore, the flux promotes directional crystal growth, optimizes crystal plane growth, and facilitates the formation of a layered structure, improving the material's structural stability and further enhancing its rate performance.

[0255] In Examples 7 and 11, excessive addition of metal borides or flux resulted in overdoping, making it impossible to generate single crystals and leading to poor capacity and uniformity of the cathode material.

[0256] like Figure 5 As shown in Comparative Example 1, no boron metal oxide was added during the preparation process, which could not suppress grain growth, resulting in larger primary particles. This led to the final cathode material having disadvantages such as low capacity, high cell volume change rate, low particle strength, and poor cycle life.

[0257] like Figure 6 As shown in Comparative Example 2, no flux was added during the preparation process, resulting in an indistinct layered coating structure in the prepared material. Ultimately, this led to the cathode material exhibiting drawbacks such as high cell volume change rate, low particle strength, and poor cycle life.

[0258] like Figure 7 As shown in Comparative Example 3, MoB was not added in step (1), but in step (3), which resulted in larger primary particles in the prepared material. This led to the final cathode material having disadvantages such as low capacity, high cell volume change rate, low particle strength, and poor cycle life.

[0259] like Figure 8 As shown, ZrBr4 was used as the flux in Comparative Example 4. Because bromides react with borides to generate boron bromide and hydrogen bromide, they severely corrode the material and damage its surface structure. This results in an indistinct layered structure in the prepared cathode material, leading to drawbacks such as low capacity, high cell volume change rate, low particle strength, and poor cycle life.

[0260] However, in Comparative Example 5, step (1) of the sintering process did not employ segmented sintering, 2θ 102 -2θ 006 and 2θ 110 -2θ 108If the value is too small, a stable layered coating cannot be obtained, resulting in poor structural stability of the material, which in turn leads to poor capacity, initial efficiency and cycle performance.

[0261] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes a matrix and a coating layer covering at least a portion of the surface of the matrix, wherein the general chemical formula of the matrix is ​​shown in formula (I): Li a Ni b Co c N d M 2 e O2(Ⅰ) In equation (Ⅰ), N includes Mn and / or Al, M 2 It includes at least one of Zr, Sr, Co, Ba, Y, Ce, Al, Mg and La, with 0.95≤a≤1.08, 0.3≤b≤1, 0<c≤0.7, 0<d≤0.5, 0<e≤0.1, and b+c+d+e=1; The coating layer comprises a compound with the general chemical formula (II); Li g M 1 (2h-g) / i O h (II) In formula (II), M 1 Includes at least one of Mn, Ti, W, Mo, and Nb, where i is M 1 The valence values ​​of the ions, and g, h, and (2h-g) / i are all positive integers; In the diffraction pattern obtained by X-ray diffraction measurement of the cathode material, the cathode material has a diffraction peak 2θ of the (102) plane. 102 The diffraction peak 2θ of the (006) plane 006 The diffraction peak 2θ on the (110) plane 110 The diffraction peak 2θ of the (108) plane 108 The 2θ 102 2θ 006 2θ 110 and 2θ 108 The following relationship must be satisfied: 2θ 102 -2θ 006 ≥0.25 (Ⅲ) 2θ 110 -2θ 108 ≥0.33 (Ⅳ) (2θ 102 -2θ 006 ) / (2θ 110 -2θ 108 )≥0.7 (Ⅶ); The cathode material includes primary particles, and the cathode material also includes lithium boron oxide coated on the primary particles.

2. The cathode material according to claim 1, characterized in that, The general chemical formula of the matrix is ​​shown in formula (V): Li a Ni b Co c N d M 2 e M 3 f O2(Ⅴ) In equation (V), M 3 It includes at least one of Mn, Ti, W, Mo, Nb, Zr, Co, Y, Ce, Al and La, where 0 < f ≤ 0.1 and b + c + d + e + f = 1; The coating layer comprises a compound with the general chemical formula (VI); Li g M 1 (2h-g) / i The h ·NiO·LiMn2O4(Ⅵ) The cathode material includes primary particles, and the cathode material also includes lithium boron oxide coated on the primary particles.

3. The cathode material according to claim 1 or 2, characterized in that, The cathode material includes at least one of the following features (1) to (8): (1) The median particle size of the primary particles is 2.0 μm to 6.0 μm; (2) The positive electrode material includes secondary particles, and the secondary particles include multiple primary particles; (3) Ni in the surface layer of the cathode material 2+ The mass and the Ni in the cathode material 2+ and Ni 3+ The ratio of the total mass is greater than or equal to 0.6, wherein the surface layer of the positive electrode material refers to the portion of the positive electrode material extending from the surface of the positive electrode material into the interior of the positive electrode material with a thickness of 0nm to 20nm; (4) In the XRD pattern of the cathode material, the intensity ratio of the diffraction peaks between the (003) plane and the (104) plane is I. 003 / Ⅰ 104 ≥1.3; (5) When the positive electrode material is charged to 4.3V, the rate of change of the lattice parameters of the positive electrode material is ≤5%; (6) When the positive electrode material is charged to 4.3V, the cell volume change rate of the positive electrode material is ≤6%; (7) When the positive electrode material is charged to 4.3V, the particle strength of the positive electrode material is ≥200MPa; (8) The Li g M 1 (2h-g) / i O accounts for 0% to 1% of the mass of the cathode material, excluding 0.

4. The cathode material according to claim 2, characterized in that, The mass percentage of NiO in the cathode material is 0% to 10%.

5. A method for preparing a positive electrode material, characterized in that, Includes the following steps: Ni (1-c-d) Co c N d A cathode material is obtained by mixing (OH)₂ precursor, lithium salt, metal boride, and flux and then subjecting the mixture to a staged heating process. The metal boride contains at least one of Mn, Ti, W, Mo, and Nb, and the metal boride can react with the lithium salt. The ratio of the total amount of metal elements in the metal boride to the amount of the cathode material is 0.01% to 1%. The flux contains at least one of the oxides, hydroxides, or salts of Zr, Sr, Co, Ba, Y, Ce, Al, Mg, and La. The ratio of the total amount of metal elements in the flux to the total amount of the cathode material is 0.02% to 10%. N includes Al and / or Mn, 0 < c ≤ 0.7, and 0 < d ≤ 0.

5.

6. The preparation method according to claim 5, characterized in that, The preparation method includes at least one of the following features (1) to (6): (1) The Ni (1-c-d) Co c N d The median particle size of the (OH)2 precursor is 2 μm to 6 μm; (2) The metal boride includes at least one of MoB, W2B5, NbB, MnB and TiB2; (3) The median particle size of the metal boride is 10 nm to 500 nm; (4) The fluxing agent includes at least one of Y2O3, La2O3, ZrO2, Y(OH)3, Mg(OH)2, Al(OH)3 and Cl3Y; (5) The median particle size of the flux is 10 nm to 500 nm; (6) The lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium phosphate and lithium oxalate.

7. The preparation method according to claim 5, characterized in that, The preparation method includes at least one of the following features (1) to (4): (1) The segmented heating process is carried out in an oxygen or air atmosphere; (2) The segmented heating process includes: first heating to 300℃~750℃, holding for 2h~24h, then heating to 750℃~1000℃, holding for 5h~24h; (3) The step after the segmented heating treatment is to crush the material obtained from the segmented heating treatment; (4) The step of pulverizing the material obtained from the segmented heating process after the segmented heating process is further included, wherein the pulverization includes at least one of grinding and crushing.

8. The preparation method according to claim 5, characterized in that, After obtaining the cathode material, the process further includes: mixing the cathode material with a mixture containing lithium permanganate and a metal compound with a valence of +3 or greater, and then subjecting it to heat treatment.

9. The preparation method according to claim 8, characterized in that, The preparation method includes at least one of the following features (1) to (6): (1) The metal compounds with a valence of +3 or greater include at least one oxide, boride, hydroxide or salt of at least one of the elements selected from Mn, Ti, W, Mo, Nb, Zr, Co, Y, Ce, Al and La; (2) The ratio of the total amount of metal elements in the metal compound with a valence of +3 or higher to the total amount of transition metal elements in the heat-treated cathode material is 0.02% to 10%; (3) The median particle size of the metal compounds with a valence of +3 or greater is 10 nm to 500 nm; (4) The concentration of lithium permanganate in the mixture containing lithium permanganate and a metal compound with a +3 valence greater than or equal to is 0.02 g / L to 10 g / L; (5) The ratio of the total amount of lithium permanganate to the total amount of transition metal elements in the heat-treated cathode material is 0.01% to 2%; (6) After the cathode material is mixed with the mixture containing lithium permanganate and a metal compound with a valence greater than or equal to +3, and before heat treatment, the method further includes the step of drying the mixture containing lithium permanganate and a metal compound with a valence greater than or equal to +3 with the cathode material.

10. The preparation method according to claim 8, characterized in that, The preparation method includes at least one of the following features (1) to (3): (1) The heat treatment is carried out in an oxygen or air atmosphere; (2) The temperature of the heat treatment is 200 ℃~800 ℃; (3) The heat treatment holding time is 5h~24h.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes the cathode material according to any one of claims 1 to 4 or the cathode material prepared by the preparation method according to any one of claims 5 to 10.

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