Ternary positive electrode material, positive electrode plate, secondary battery and electronic equipment

Abstract

The invention provides a ternary positive electrode material, a positive electrode plate, a secondary battery and electronic equipment, the ternary positive electrode material comprises crystal particles, the crystal particles comprise a first doping element, a second doping element and a third doping element, and the valence state of the first doping element is 1t; the valence state of the second doping element is lt; the valence state of the third doping element; the first doping element is distributed on the inner layer of the crystal particle, the second doping element is distributed on the middle layer of the crystal particle, and the third doping element is distributed on the shallow surface layer of the crystal particle. The ternary positive electrode material provided by the invention is beneficial to improving the high-temperature cycle performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to ternary cathode materials, cathode plates, secondary batteries, and electronic devices. Background Technology

[0002] Lithium-ion batteries, as a representative of rechargeable batteries, have advantages such as high operating voltage, high energy density, good safety, and no memory effect, and have achieved great success in portable electronic devices, electric vehicles, and hybrid vehicles. Currently, ternary cathode materials are widely used in traditional rechargeable batteries due to their advantages such as high capacity and energy density. However, traditional ternary cathode materials still suffer from poor high-temperature cycling performance. Summary of the Invention

[0003] Based on this, this application provides a ternary cathode material, cathode sheet, secondary battery, and electronic device, which can improve the high-temperature cycle performance of secondary batteries.

[0004] The first aspect of this application provides a ternary cathode material, comprising crystal particles, wherein the crystal particles include a first dopant element, a second dopant element, and a third dopant element, wherein the valence state of the first dopant element is less than the valence state of the second dopant element, and the valence state of the third dopant element is less than the valence state of the third dopant element.

[0005] The first dopant element is distributed in the inner layer of the crystal particle, the second dopant element is distributed in the middle layer of the crystal particle, and the third dopant element is distributed in the shallow surface layer of the crystal particle.

[0006] In the crystal particles, the concentration distribution C of the first dopant element is... A (r) satisfies the following relation (1):

[0007] (1);

[0008] At r=0, the concentration of the first dopant element is: C A (0)=C A0 ;

[0009] At r=r1, the concentration of the first dopant element is: C A (r1)=C A1 ;

[0010] C A0 >C A1 >0;

[0011] Where r represents the distance extending radially from the center of the crystal particle, and r1 represents the distance from the center of the crystal particle to the element distribution boundary of the first doped element.

[0012] C A0 C represents the concentration of the first dopant element at the center of the crystal grain. A1 This indicates the concentration of the first dopant element at the element distribution boundary of the first dopant element;

[0013] In the crystal particles, the concentration distribution C of the second dopant element B (r) satisfies the following relation (2):

[0014] (2);

[0015] At r=r1, the concentration of the second dopant element is: C B (r1) =C B1,edge ;

[0016] At r=r2, the concentration of the second dopant element is: C B (r2)=C B2,edge ;

[0017] At r = (r1 + r2) / 2, the concentration of the second dopant element is: C B (r1+r2) / 2=C B,max ;

[0018] δr B =r2-r1, r2>r1;

[0019] C B,max >C B1,edge >0, C B,max >C B2,edge >0;

[0020] Where r2 represents the distance from the center of the crystal particle along the radial direction to the element distribution boundary of the second doped element;

[0021] C B1,edge C represents the concentration of the second dopant element at the elemental distribution boundary of the first dopant element. B2,edge This indicates the concentration of the second dopant element at the elemental distribution boundary of the second dopant element; C B,max This indicates the concentration of the second dopant element at the center position between the elemental distribution boundary of the first dopant element and the elemental distribution boundary of the second dopant element;

[0022] In the crystal particles, the concentration distribution of the third dopant element satisfies the relationship (3):

[0023] (3);

[0024] At r=r2, the concentration of the third dopant element is: C C (r2)=C C2 ;

[0025] At r=R, the concentration of the third dopant element is: C C (R)=C C3 ;

[0026] 0 <C C2 <C C3 r2 <R;

[0027] Wherein, R represents the distance from the center of the crystal particle along the radial direction to the outer surface of the crystal particle;

[0028] C C2 C represents the concentration of the third dopant element at the elemental distribution boundary of the second dopant element. C3 This indicates the concentration of the third dopant element at the outer surface of the crystal particle.

[0029] In some embodiments of this application, one or more of the following conditions are met:

[0030] (1) (5 / 12)*R≤r1≤(6 / 12)*R, (9 / 12)*R≤r2≤(10 / 12)*R;

[0031] Optionally, 1.2μm≤R≤1.5μm;

[0032] (2) C B1,edge =C B2,edge .

[0033] In some embodiments of this application, one or more of the following conditions are met:

[0034] (1) 2000ppm≤C A0 ≤3000ppm, 800ppm≤C A1 ≤1000ppm;

[0035] (2) 400ppm≤C B1,edge ≤650ppm, 400ppm≤C B2,edge ≤650ppm, 1000ppm≤C B,max ≤1500ppm;

[0036] (3) 0ppm < C C2 ≤330ppm, 330ppm<C C3 ≤1000ppm.

[0037] In some embodiments of this application, one or more of the following conditions are met:

[0038] (1) The first doping element includes Al 3+ Zn 2+ and Mg 2+ One or more of the following, wherein the second doping element includes Ti 4+ and / or Zr 4+ The third doping element includes Nb 5+ Ta 5+ and W 6+ One or more of the following;

[0039] (2) The average particle size of the crystal particles is 2.4μm~3μm, and can be selected as 2.4μm~2.6μm.

[0040] The second aspect of this application provides a positive electrode sheet, including the ternary positive electrode material described in the first aspect of this application.

[0041] A third aspect of this application provides a secondary battery, including the positive electrode sheet described in the second aspect of this application.

[0042] The fourth aspect of this application provides an electrical device including the secondary battery described in the third aspect of this application.

[0043] The electronic device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0044] Figure 1 This is a model diagram showing the distribution of doped elements in a ternary cathode material according to an embodiment of this application.

[0045] Figure 2 The image shows a scanning electron microscope (SEM) image of the ternary cathode material prepared in Example 2.

[0046] Figure 3 The image shows the SEM-Mapping of Al in the ternary cathode material prepared in Example 2.

[0047] Figure 4 The image shows the SEM-Mapping of Ti in the ternary cathode material prepared in Example 2.

[0048] Figure 5 The image shows the SEM-Mapping of Nb in the ternary cathode material prepared in Example 2. Detailed Implementation

[0049] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0050] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be noted that, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items, "above," "below," includes the stated number, and "one or more" with "multiple" means two or more.

[0052] In this document, when referring to numerical intervals (i.e., numerical ranges), unless otherwise specified, the distribution of selectable values ​​within a numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the numerical interval, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, and other numerical interval types.

[0053] In this document, for methods involving multiple steps, unless otherwise explicitly stated herein, there is no strict order constraint on the execution of these steps; they may be executed in any order other than those described. Moreover, any step may include multiple sub-steps or multiple stages, which are not necessarily completed at the same time, but may be executed at different times, and their execution order is not necessarily sequential, but may be executed in turn, alternately, or simultaneously with other steps or parts of the sub-steps or stages of other steps.

[0054] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0055] Currently, commercially available ternary cathode materials generally employ bulk uniform doping with metal elements to improve crystal structure stability. However, the diffusion kinetics of elements with different valence states are not entirely the same, making it difficult to achieve gradient doping effects under traditional doping processes. This fails to maximize the effectiveness of elements with different valence states. Therefore, traditional doping methods can no longer meet the performance requirements of current battery products, especially given the increasingly stringent requirements for capacity decay and thermal instability in automotive power batteries. This necessitates a radical shift in traditional doping methods to optimize or improve the performance of ternary cathode materials, thereby further mitigating the problems of accelerated capacity decay and thermal instability. Based on this, the inventors discovered that the main technical shortcomings of current traditional ternary cathode material doping techniques include:

[0056] (1) The surface structure of the material is similar to the internal bulk structure. Under high temperature cycling and storage conditions, the oxygen released from the surface lattice can easily trigger the degradation of its surface structure, leading to thermal runaway in the presence of electrolyte.

[0057] (2) The doping elements are uniformly distributed on the surface and in the bulk of the material. However, the binding energies of different valence metal elements with oxygen are different. During charging and discharging, the active ions (such as Li) are distributed evenly. + The extraction and insertion of crystals amplify lattice distortion stress, leading to rapid failure of the crystal structure and performance degradation.

[0058] (3) Highly active Ni 4+ Undesirable or severe side reactions with the electrolyte can easily lead to the transformation of the layered structure of the ternary cathode material into an electrochemically inert NiO rock salt structure, hindering the development of active ions (such as Li). + The delivery of ) leads to accelerated capacity decay and deterioration of the cycle during the circulation process.

[0059] To address the aforementioned technical challenges, existing solutions have enabled gradient doping of metal elements with different valence states in ternary cathode materials. However, current gradient doping methods can only qualitatively describe the concentration distribution trends of metal elements with different valence states in ternary cathode materials. There is no definitive concentration distribution model capable of accurately quantifying and predicting these trends, making it difficult to predict the precise concentration values ​​of metal elements with different valence states at a specific point in the ternary cathode material. Therefore, based on existing qualitative studies of concentration distribution trends, accurate quantitative analysis and prediction of the concentration distribution of metal elements with different valence states are crucial for obtaining ideal gradient doped structures and further improving the structural stability of the material.

[0060] In view of this, this application proposes the following technical solution, which conducts experiments and data simulations on the gradient doping structure of the first, second, and third doping elements with different valence states in ternary cathode materials, and obtains a definite concentration distribution model, namely the three parameter formulas in equations (1), (2), and (3) below. This concentration distribution model can perform more accurate quantitative analysis and prediction of the concentration distribution trend of metal elements with different valence states, and can more accurately predict and determine the definite concentration value of metal elements with different valence states at a certain point in ternary cathode materials, thereby better predicting and characterizing the concentration distribution. By combining this concentration distribution model with actual production or experiments, and using this concentration distribution model to guide actual production or experiments, the amount, range, and specific process of gradient doping can be controlled in a targeted manner. Therefore, it has important guiding significance for obtaining an ideal gradient doping structure and is conducive to further improving the structural stability of the material.

[0061] In a first aspect, this application provides a ternary cathode material, comprising crystal particles, wherein the crystal particles comprise a first doping element, a second doping element, and a third doping element, wherein the valence state of the first doping element is less than the valence state of the second doping element, and the valence state of the third doping element is less than that of the third doping element.

[0062] See Figure 1 The first dopant element is distributed in the inner layer of the crystal particle, the second dopant element is distributed in the middle layer of the crystal particle, and the third dopant element is distributed in the shallow surface layer of the crystal particle.

[0063] In the crystal particles, the concentration distribution C of the first dopant element is... A (r) satisfies the following relation (1):

[0064] (1);

[0065] At r=0, the concentration of the first dopant element is: C A (0)=CA0 ;

[0066] At r=r1, the concentration of the first dopant element is: C A (r1)=C A1 ;

[0067] C A0 >C A1 >0;

[0068] Where r represents the distance extending radially from the center of the crystal particle, and r1 represents the distance from the center of the crystal particle to the element distribution boundary of the first doped element.

[0069] C A0 C represents the concentration of the first dopant element at the center of the crystal grain. A1 This indicates the concentration of the first dopant element at the element distribution boundary of the first dopant element;

[0070] In the crystal particles, the concentration distribution C of the second dopant element B (r) satisfies the following relation (2):

[0071] (2);

[0072] At r=r1, the concentration of the second dopant element is: C B (r1) =C B1,edge >0;

[0073] At r=r2, the concentration of the second dopant element is: C B (r2)=C B2,edge >0;

[0074] At r = (r1 + r2) / 2, the concentration of the second dopant element is: C B (r1+r2) / 2=C B,max ;

[0075] δr B =r2-r1, r2>r1;

[0076] C B,max >C B1,edge C B,max >C B2,edge ;

[0077] Where r2 represents the distance from the center of the crystal particle along the radial direction to the element distribution boundary of the second doped element;

[0078] C B1,edgeC represents the concentration of the second dopant element at the elemental distribution boundary of the first dopant element. B2,edge This indicates the concentration of the second dopant element at the elemental distribution boundary of the second dopant element; C B,max This indicates the concentration of the second dopant element at the center position between the elemental distribution boundary of the first dopant element and the elemental distribution boundary of the second dopant element;

[0079] In the crystal particles, the concentration distribution of the third dopant element satisfies the relationship (3):

[0080] (3);

[0081] At r=r2, the concentration of the third dopant element is: C C (r2)=C C2 ;

[0082] At r=R, the concentration of the third dopant element is: C C (R)=C C3 ;

[0083] 0 <C C2 <C C3 r2 <R;

[0084] Wherein, R represents the distance from the center of the crystal particle along the radial direction to the outer surface of the crystal particle;

[0085] C C2 C represents the concentration of the third dopant element at the elemental distribution boundary of the second dopant element. C3 This indicates the concentration of the third dopant element at the outer surface of the crystal particle.

[0086] In the ternary cathode material provided in this application, the concentration distributions of the first doped element, the second doped element and the third doped element satisfy the above relationships (1), (2) and (3), respectively. That is, equations (1), (2) and (3) construct a concentration distribution model for doped elements with different valence states.

[0087] Equation (1) indicates that the concentration of the first dopant element gradually decreases radially outward from the center of the crystal particle, and the distribution area of ​​the first dopant element is between the center of the crystal particle and r1 (including the center of the crystal particle and r=r1); within the range of r>r1, the concentration of the first dopant element is zero. That is, the concentration of the first dopant element is highest at the center of the crystal particle (C). A0 At r=r1, the concentration of the first dopant element is the lowest (at C). A1 The concentration of the first dopant element is highest at the center of the crystal grain (r=0), C.A0 decreases linearly in the radial direction to the lowest value C at the boundary of its element distribution (r = r1). A1 .

[0088] Relationship (2) shows that from r1 to r2 in the radial direction, the concentration of the second doping element first increases and then decreases, and the distribution region of the second doping element is between r1 and r2 (including r = r1 and r = r2); in the range of r < r1 and r > r2, the concentration of the second doping element is zero. That is, at r = r1, the second doping element starts to appear, and its concentration is a relatively low value (which is C B1,edge ); at r = r2, the concentration of the second doping element is also a relatively low value (which is C B2,edge ); between r1 and r2, the concentration of the second doping element first increases from C B1,edge to C B,max , and then decreases from C B,max to C B2,edge , and the maximum concentration value C B,max is located at the midpoint between r1 and r2 (i.e., (r1 + r2) / 2).

[0089] Relationship (3) shows that from r2 to R in the radial direction, the concentration of the third doping element gradually increases outwards, and the distribution region of the third doping element is between r2 and R (including r = r2 and r = R); in the range of r < r2, the concentration of the third doping element is zero. That is, at r = r2, the third doping element starts to appear, and its concentration is the lowest (which is C C2 ); at r = R, the concentration of the third doping element is the highest (which is C C3 ); the concentration of the third doping element linearly increases from the lowest value C C2 at r = r2 to the highest value C C3 at the boundary of its element distribution (r = R).

[0090] The concentration function of each of the above doping elements is continuous within its distribution region, but the overall concentration profile may not be continuous between different elements (only coexists at the boundary points); outside its distribution region, the concentration of each element is zero. In addition, at the junction, at r = r1, the first doping element and the second doping element coexist in a coupled manner; at r = r2, the second doping element and the third doping element coexist in a coupled manner. Therefore, the distribution region of the first doping element is from the center of the crystal grain to r1 (including the center of the crystal grain and r = r1), the distribution region of the second doping element is between r1 and r2 (including r = r1 and r = r2), and the distribution region of the third doping element is between r2 and R (including r = r2 and r = R). In addition, the coexistence at r1 and r2 means that the concentration of the doping elements at these coexistence points is continuous or has an overlap.

[0091] The first, second, and third doping elements form a gradient doping structure. This gradient doping structure facilitates the formation of crystal particles with a more stable and robust structure from the inside out, exhibiting a difference between the surface structure and the internal bulk structure. Specifically, the surface structure of the crystal particles is relatively robust, while the bulk structure is relatively flexible and stable. In this differentiated crystal structure, the more robust surface structure effectively blocks electrolyte erosion, while the relatively flexible and stable bulk structure greatly buffers structural damage caused by intracrystalline stress. This comprehensively improves the stability of the material's crystal and interface structures, thereby enhancing the cycle performance of the ternary cathode material and further improving its storage performance and / or thermal stability.

[0092] When the concentration distribution of the high-valence dopant element (i.e., the third dopant element) in the outermost layer satisfies the above relationship (3), it is beneficial to improve its binding energy with oxygen, thereby improving the binding strength between the metal and oxygen on the surface of the material, effectively suppressing the release of oxygen from the surface lattice, improving the surface structure stability, reducing the risk of thermal runaway of the material, and improving safety performance; at the same time, due to the charge balance effect, the presence of the high-valence dopant element in the surface layer is beneficial to the high-valence Ni ions (such as Ni) in the surface layer (such as Ni) 4+ The reduced proportion of Ni ions and surface oxygen defects helps to reduce adverse reactions between high-valence Ni ions and electrolytes, stabilizes the oxidation state of Ni on the particle surface, and inhibits the mixing of Li / Ni cations. This helps to suppress the transformation of layered structures into disordered rock salt phases, reduces the probability of layered structures transforming into inert NiO rock salt phases, and improves the stability of the material structure.

[0093] In addition, the gradual gradient change in valence state and concentration distribution of dopants from the inside to the outside can effectively reduce lattice stress, mitigate lattice distortion and the generation of intergranular microcracks, buffer structural failure caused by lattice stress, and improve the service life of the material. Furthermore, the coupling and coexistence at the junctions of adjacent dopants with different valence states is conducive to further improving the stability of the crystal structure and interface structure of the material, which in turn is conducive to improving the cycle performance of ternary cathode materials, and further conducive to improving storage performance and / or thermal stability.

[0094] Accordingly, based on the gradient doping structure formed by doping elements of different valence states, the concentration distribution model provided in this application can perform more accurate quantitative analysis and prediction of the concentration distribution trend of metal elements of different valence states. It can accurately predict and determine the specific concentration value of metal elements of different valence states at a certain point in the ternary cathode material, thus enabling better prediction and characterization of the concentration distribution. By combining this concentration distribution model with actual production or experiments, and using it to guide actual production or experiments, the amount, range, and specific processes of gradient doping can be specifically controlled. Therefore, it has important guiding significance for obtaining an ideal gradient doping structure and is conducive to further improving the structural stability of the material.

[0095] It is understood that the "center of the crystal grain" mentioned in this application refers to the geometric center of the crystal grain as a regular or irregular geometric entity.

[0096] It is understood that the "inner layer of the crystal particle" in this application refers to the region surrounded by the center of the crystal particle to r=r1; the "middle layer of the crystal particle" refers to the region surrounded by r=r1 to r=r2; and the "shallow layer of the crystal particle" refers to the region surrounded by r=r2 to r=R.

[0097] In some implementations, (5 / 12)*R≤r1≤(6 / 12)*R, (9 / 12)*R≤r2≤(10 / 12)*R. This configuration is beneficial for promoting the formation of crystal structures that are more stable and robust from the inside out, with a difference between the surface structure and the internal bulk structure. That is, the surface structure of the crystal particles is relatively robust, while the bulk structure is relatively flexible and stable. This is beneficial for improving the stability of the crystal structure and interface structure of the material, and for obtaining a more ideal gradient doping structure. This, in turn, is beneficial for improving the cycle performance of the ternary cathode material, and further beneficial for improving storage performance and / or thermal stability.

[0098] In some implementations, 1.2 μm ≤ R ≤ 1.5 μm. For example, R can be 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or any value within the range above. This setting is beneficial for further improving the stability of the crystal structure and interface structure of the material, and for obtaining a more ideal gradient doping structure, which in turn is beneficial for further improving the cycle performance of the ternary cathode material, and further beneficial for improving storage performance and / or thermal stability.

[0099] In some implementations, C B1,edge =C B2,edgeThis configuration facilitates a more regular concentration distribution of the second dopant element, promotes the formation of a more stable and robust crystal structure from the inside out, and differentiates the surface structure from the internal bulk structure. In other words, the surface structure of the crystal particles is relatively robust, while the bulk structure is relatively flexible and stable. This improves the stability of the crystal structure and interface structure of the material, and helps to obtain a more ideal gradient doping structure. This, in turn, helps to improve the cycle performance of the ternary cathode material, and further helps to improve storage performance and / or thermal stability.

[0100] In some implementations, 2000ppm≤C A0 ≤3000ppm, 800ppm≤C A1 ≤1000ppm. For example, C A0 It can be 2000ppm, 2300ppm, 2500ppm, 2700ppm, 3000ppm, or within any range of the above values; C A1 The concentration can be 800ppm, 830ppm, 900ppm, 960ppm, 1000ppm, or within any range of these values. This is beneficial for further improving the stability of the crystal and interface structures of the material, and for obtaining a more ideal gradient doping structure, which in turn helps to further improve the cycle performance of the ternary cathode material, and further improves its storage performance and / or thermal stability.

[0101] In some implementations, 400ppm≤C B1,edge ≤650ppm, 400ppm≤C B2,edge ≤650ppm, 1000ppm≤C B,max ≤1500ppm. For example, C B1,edge and C B2,edge Each of these values ​​can be independently 400ppm, 440ppm, 500ppm, 570ppm, 650ppm, or within any range of these values; C B,max The concentration can be 1000ppm, 1200ppm, 1400ppm, 1500ppm, or within any range of these values. This is beneficial for further improving the stability of the crystal and interface structures of the material, and for obtaining a more ideal gradient doping structure, which in turn is beneficial for further improving the cycle performance of the ternary cathode material, and further beneficial for improving storage performance and / or thermal stability.

[0102] In some implementations, 0ppm < C C2 ≤330ppm, 330ppm<C C3 ≤1000ppm. For example, C C2It can be 5ppm, 10ppm, 60ppm, 100ppm, 140ppm, 210ppm, 270ppm, 330ppm, or within any range of the above values; C C3 The values ​​can be 331ppm, 420ppm, 530ppm, 640ppm, 760ppm, 870ppm, 950ppm, 1000ppm, or any range thereof. This is beneficial for further improving the stability of the crystal and interface structures of the material, and for obtaining a more ideal gradient doping structure, which in turn is beneficial for further improving the cycle performance of the ternary cathode material, and further beneficial for improving storage performance and / or thermal stability.

[0103] In some embodiments, the first doping element includes Al. 3+ Zn 2+ and Mg 2+ One or more of the following, wherein the second doping element includes Ti 4+ and / or Zr 4+ The third doping element includes Nb 5+ Ta 5+ and W 6+ One or more of these can be used. This is beneficial for improving the stability of the crystal and interface structures of ternary cathode materials, and for obtaining more ideal gradient doping structures, which in turn is beneficial for improving the cycle performance of ternary cathode materials, and further beneficial for improving storage performance and / or thermal stability.

[0104] In some embodiments, the average particle size of the crystal particles is 2.4 μm to 3 μm, optionally 2.4 μm to 2.6 μm. For example, the average particle size of the crystal particles can be 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or within any range of the above values. This is beneficial for improving the cycle performance of the ternary cathode material, and further beneficial for improving storage performance and / or thermal stability.

[0105] Currently, elemental gradient doping of ternary cathode materials is typically achieved through the design of a core-shell structure in the precursor, resulting in a gradient distribution of the main elements Ni, Co, and Mn. After designing the core-shell structure of the precursor, its structural characteristics can be inherited during the subsequent synthesis of the cathode material, allowing the Ni, Co, and Mn content to also exhibit a gradient distribution, thereby improving or optimizing the cathode material's performance. However, designing a gradient distribution of main elements Ni, Co, and Mn through the precursor presents two challenges: firstly, the synthesis technology for achieving a gradient distribution of main elements in the precursor is quite difficult; secondly, during the high-temperature calcination of the subsequent cathode material, the main elements Ni, Co, and Mn can diffuse into each other, leading to an indistinct gradient distribution of main elements after the cathode material is synthesized.

[0106] In view of this, in a second aspect, this application provides a method for preparing a ternary cathode material, which can be used to prepare the ternary cathode material of the first aspect of this application, and may include the following steps:

[0107] S1. A mixture containing nickel-cobalt-manganese hydroxide, a compound containing a first doping element, a compound containing a second doping element, a compound containing a third doping element, and a lithium salt is subjected to step heating sintering, and then cooled and crushed to obtain a ternary cathode material.

[0108] The stepped heating sintering includes a first-stage sintering, a second-stage sintering, and a third-stage sintering, wherein the temperature of the first-stage sintering is less than the temperature of the second-stage sintering, and the temperature of the third-stage sintering is less than the temperature of the second-stage sintering; or,

[0109] S1' The first mixture containing the first compound, nickel cobalt manganese hydroxide and lithium salt is subjected to a first sintering, and after cooling and crushing, a first sintered material is obtained. The first compound includes one of a compound containing a first doping element, a compound containing a second doping element, and a compound containing a third doping element.

[0110] S2'. The second mixture containing the first sintering material and the second compound is subjected to a second sintering, and after cooling and crushing, a second sintering material is obtained. The second compound includes one of a compound containing a first doping element, a compound containing a second doping element, and a compound containing a third doping element. The doping element of the second compound is different from the doping element of the first compound, and the temperature of the second sintering is different from the temperature of the first sintering.

[0111] S3'. A third mixture containing the second sintering material and the third compound is subjected to a third sintering, cooled, and crushed to obtain a ternary cathode material. The third compound includes one of a compound containing a first doping element, a compound containing a second doping element, and a compound containing a third doping element. The doping element of the third compound is different from the doping element of the first compound and the doping element of the second compound. The temperature of the third sintering is different from the temperature of the first sintering and the temperature of the second sintering.

[0112] The ternary cathode material includes crystal particles, and the crystal particles include a first doping element, a second doping element, and a third doping element, wherein the valence state of the first doping element is less than the valence state of the second doping element, and the valence state of the third doping element is less than that of the third doping element.

[0113] The first dopant element is distributed in the inner layer of the crystal particle, the second dopant element is distributed in the middle layer of the crystal particle, and the third dopant element is distributed in the shallow surface layer of the crystal particle.

[0114] In the crystal particles, the concentration distribution C of the first dopant element is... A (r) satisfies the following relation (1):

[0115] (1);

[0116] At r=0, the concentration of the first dopant element is: C A (0)=C A0 ;

[0117] At r=r1, the concentration of the first dopant element is: C A (r1)=C A1 ;

[0118] C A0 >C A1 >0;

[0119] Where r represents the distance extending radially from the center of the crystal particle, and r1 represents the distance from the center of the crystal particle to the element distribution boundary of the first doped element.

[0120] C A0 C represents the concentration of the first dopant element at the center of the crystal grain. A1 This indicates the concentration of the first dopant element at the element distribution boundary of the first dopant element;

[0121] In the crystal particles, the concentration distribution C of the second dopant element B (r) satisfies the following relation (2):

[0122] (2);

[0123] At r=r1, the concentration of the second dopant element is: C B (r1) =C B1,edge >0;

[0124] At r=r2, the concentration of the second dopant element is: C B (r2)=C B2,edge >0;

[0125] At r = (r1 + r2) / 2, the concentration of the second dopant element is: C B (r1+r2) / 2=C B,max ;

[0126] δr B =r2-r1, r2>r1;

[0127] C B,max >C B1,edge C B,max >C B2,edge ;

[0128] Where r2 represents the distance from the center of the crystal particle along the radial direction to the element distribution boundary of the second doped element;

[0129] C B1,edge C represents the concentration of the second dopant element at the elemental distribution boundary of the first dopant element. B2,edge This indicates the concentration of the second dopant element at the elemental distribution boundary of the second dopant element; C B,max This indicates the concentration of the second dopant element at the center position between the elemental distribution boundary of the first dopant element and the elemental distribution boundary of the second dopant element;

[0130] In the crystal particles, the concentration distribution of the third dopant element satisfies the relationship (3):

[0131] (3);

[0132] At r=r2, the concentration of the third dopant element is: C C (r2)=C C2 ;

[0133] At r=R, the concentration of the third dopant element is: C C (R)=C C3 ;

[0134] 0 <CC2 <C C3 r2 <R;

[0135] Wherein, R represents the distance from the center of the crystal particle along the radial direction to the outer surface of the crystal particle;

[0136] C C2 C represents the concentration of the third dopant element at the elemental distribution boundary of the second dopant element. C3 This indicates the concentration of the third dopant element at the outer surface of the crystal particle.

[0137] The above preparation method provided in this application includes step S1 or steps S1' to S3'. Both of these methods involve elemental gradient doping during the synthesis stage of ternary cathode material, rather than achieving gradient doping through the design of the precursor. This helps to reduce the difficulty of synthesizing elemental gradient distribution and facilitates obtaining ternary cathode materials with obvious elemental gradient distribution characteristics.

[0138] Specifically, this application performs gradient doping based on the ionic radius or diffusion kinetics of doping elements with different valence states, and selects appropriate sintering temperatures for different doping elements and / or calcination stages. This facilitates the formation of the concentration distribution structure corresponding to each doping element mentioned above in this application (i.e., the concentration distribution model constituted by equations (1), (2) and (3)) in the ternary cathode material according to the ease of doping of the doping elements), so that the structure of the ternary cathode material formed after doping tends to be more stable from the inside out and can form a robust doped shell, thereby improving the stability of the material's crystal structure and interface structure, and at the same time improving cycle performance and storage performance.

[0139] For example, in step S1, the sintering temperature of the first stage is more conducive to the diffusion of the first dopant element, allowing it to diffuse into the inner layer. By adjusting the sintering temperature of the first stage, it is beneficial to form the concentration distribution structure shown in the aforementioned equation (1) in the inner layer. Then, at the sintering temperature of the second stage, it is more conducive to the diffusion of the second dopant element, allowing it to diffuse into the intermediate layer. By adjusting the sintering temperature of the second stage, it is beneficial to form the concentration distribution structure shown in the aforementioned equation (2) in the intermediate layer. Finally, at the sintering temperature of the third stage, it is more conducive to the diffusion of the third dopant element, allowing it to diffuse into the shallow layer. By adjusting the sintering temperature of the third stage, it is beneficial to form the concentration distribution structure shown in the aforementioned equation (3) in the shallow layer. Steps S1' to S3' diffuse dopant elements of different valence states in steps and match the corresponding diffusion temperatures based on the different dopant elements, which is also beneficial to obtain a doped structure with a concentration gradient distribution. Furthermore, by adjusting the diffusion temperatures matched with different dopant elements, it is also beneficial to obtain the concentration distribution structures shown in equations (1), (2), and (3).

[0140] In some embodiments, the sintering temperature of the first stage is 760℃~800℃, the sintering temperature of the second stage is 840℃~880℃, and the sintering temperature of the third stage is 920℃~960℃. This facilitates the formation of a doped structure in the ternary cathode material where the valence state of the dopant element gradually increases from low to high along the crystal particle center to the outer surface of the crystal particle, and where adjacent dopant elements with different valence states coexist and are coupled, thus obtaining a ternary cathode material with a dopant element concentration gradient distribution according to equations (1), (2), and (3).

[0141] In some embodiments, the sintering time of the first stage, the sintering time of the second stage, and the sintering time of the third stage are each independently 2h to 6h. This is beneficial for promoting the formation of a doped structure in which the valence state of the dopant element gradually increases from low to high along the crystal grain center to the outer surface of the crystal grain, and where there is coupling and coexistence at the junction of adjacent dopant elements with different valence states. It is also beneficial for obtaining a ternary cathode material with a concentration gradient distribution of dopant elements as shown in equations (1), (2), and (3).

[0142] In some embodiments, the temperature of the first sintering, the temperature of the second sintering, and the temperature of the third sintering are each independently one of 760°C~800°C, 840°C~880°C, and 920°C~960°C;

[0143] Optionally, the first sintering temperature is 920℃~960℃, the second sintering temperature is 840℃~880℃, and the third sintering temperature is 760℃~800℃. This facilitates the formation of a doped structure where the valence state of the dopant element gradually increases from low to high along the crystal grain center to the outer surface of the crystal grain, and where there is coupling and coexistence at the junctions of adjacent dopant elements with different valence states. It also facilitates obtaining a ternary cathode material with a dopant element concentration gradient distribution as shown in equations (1), (2), and (3).

[0144] In some embodiments, the first sintering time, the second sintering time, and the third sintering time are each independently 2h to 6h. This is beneficial for promoting the formation of a doped structure in which the valence state of the dopant element gradually increases from low to high along the crystal grain center to the outer surface of the crystal grain, and where there is coupling and coexistence at the junction of adjacent dopant elements with different valence states. It is also beneficial for obtaining a ternary cathode material with a dopant element concentration gradient distribution as shown in equations (1), (2), and (3).

[0145] In some embodiments, the first doping element includes Al. 3+ Zn 2+ and Mg 2+One or more of the following, wherein the second doping element includes Ti 4+ and / or Zr 4+ The third doping element includes Nb 5+ Ta 5+ and W 6+ One or more of them.

[0146] In some embodiments, nickel-cobalt-manganese hydroxide satisfies the chemical formula Ni x Co y Mn (1-x-y) (OH)₂, where 0.5 ≤ x < 1.0, 0 <y<1.0。

[0147] In some embodiments, the compound containing the first dopant element includes one or more of the oxide, carbonate, and hydroxide of the first dopant element.

[0148] In some embodiments, the compound containing the second dopant element includes one or more of the oxides, carbonates, and hydroxides of the second dopant element.

[0149] In some embodiments, the compound containing the third dopant element includes one or more of the oxides, carbonates, and hydroxides of the third dopant element.

[0150] In some embodiments, the lithium salt includes one or more of lithium hydroxide, lithium carbonate, and lithium dihydrogen phosphate.

[0151] Thirdly, this application provides a positive electrode sheet, including the ternary positive electrode material of the first aspect of this application or the ternary positive electrode material prepared by the preparation method of the second aspect of this application.

[0152] Fourthly, this application provides a secondary battery, including the positive electrode sheet of the third aspect of this application.

[0153] In some embodiments, the secondary battery also includes a negative electrode, an electrolyte, and a separator. During battery charging and discharging, lithium ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0154] Fifthly, this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0155] In some implementations, the type of electrical equipment is not particularly limited, and it can be any electronic device known in the prior art. For example, the electrical equipment may include, but is not limited to, power tools, electric vehicles, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, etc.

[0156] The following are specific embodiments, which describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0157] Example 1

[0158] 1) Ni cobalt manganese hydroxide Ni 0.72 Co 0.05 Mn 0.23 (OH)2, Al2O3, TiO2, Nb2O5, and Li2CO3 are placed in a high-speed mixer and dispersed using a dry mixing method at high speed to ensure thorough mixing and homogeneity, resulting in a homogeneous mixture I; wherein, Li2CO3 and Ni 0.72 Co 0.05 Mn 0.23 (OH)2 is quantified according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23; the mass ratio of the metal oxides Al2O3, TiO2, and Nb2O5 is 20:6:25.

[0159] 2) The material I is evenly spread into a square sagger, and then the sagger containing material I is placed in a roller kiln for firing. The temperature is increased to 780℃ at a heating rate K1 and held for 4 hours. Then the temperature is increased to 860℃ at the same heating rate K1 and held for 4 hours. Finally, the temperature is increased to 940℃ at the same heating rate K1 and held for 4 hours for reaction. After that, the temperature is cooled, crushed, sieved, and demagnetized to obtain the final product material II. Among them, the boat-shaped sagger is a high-temperature refractory ceramic sagger, the oxygen inlet flow rate is 150 liters / min, and the furnace pressure of the tubular furnace is 5 Pa.

[0160] Example 2

[0161] Similar to the preparation method in Example 1, the main difference lies in the mixing method in step 1) and the sintering and heat preservation method in step 2), as detailed below:

[0162] 1) Ni cobalt manganese hydroxide Ni0.72 Co 0.05 Mn 0.23 (OH)2, Al2O3 and Li2CO3 are placed in a high-speed mixer and dispersed by high-speed rotation using a dry mixing method to fully stir and mix them evenly to obtain a homogeneous mixture III.

[0163] 2) Spread the material III evenly into a square sagger, place the sagger containing material III in a roller kiln for firing, heat it to 940℃ at a heating rate K1 and hold it for 4 hours, then cool it down and crush it to obtain material IV.

[0164] 3) Repeat steps 1) and 2) above. The only difference is that in step 1), material IV and TiO2 are placed in a high-speed mixer and stirred thoroughly to obtain a homogeneous mixture V; in step 2), the sintering temperature is changed to 860℃ and held for 4 hours, then cooled and crushed to obtain material VI.

[0165] 4) Repeat step 3) above. The only difference is that in step 3), material VI and Nb2O5 are placed in a high-speed mixer and stirred thoroughly to obtain a homogeneous mixture material VII; in step 3), the sintering temperature is changed to 780℃ and held for 4 hours, then cooled and crushed to obtain the final product material VIII.

[0166] Among them, Li2CO3 and Ni 0.72 Co 0.05 Mn 0.23 (OH)2 is measured according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23; the mass ratio of metal oxides Al2O3, TiO2, and Nb2O5 is 20:6:25.

[0167] Example 3

[0168] Similar to the preparation method in Example 2, the main differences are: in step 1), Al2O3 is replaced with Nb2O5 and in step 2), the sintering temperature is 780℃ and the holding time is 4h; in step 4), Nb2O5 is replaced with Al2O3 and the sintering temperature is 940℃ and the holding time is 4h.

[0169] Example 4

[0170] Similar to the preparation method in Example 1, the main difference is that in step 2), the material I is heated to 940°C in a roller kiln at a heating rate K1 and kept at that temperature for 12 hours, followed by cooling, crushing, sieving, and demagnetizing to obtain the final product.

[0171] Example 5

[0172] Similar to the preparation method in Example 1, the main difference is that in step 2), the material I is heated to 860°C in a roller kiln at a heating rate K1 and kept at that temperature for 12 hours. Then, it is cooled, crushed, sieved, and demagnetized to obtain the final product.

[0173] Comparative Example 1

[0174] Following step 1) of Example 2, a homogeneous mixture III was obtained by dry mixing. Then, following step 2), the mixture was reacted at 940°C for 12 hours to obtain the final product. No further processing was performed. Li₂CO₃ and Ni... 0.72 Co 0.05 Mn 0.23 (OH)2 is measured according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23.

[0175] Comparative Example 2

[0176] Similar to the preparation method of Comparative Example 1, the main difference is that in step 2), the reaction is carried out at 860℃ for 12 hours to obtain the final product.

[0177] Comparative Example 3

[0178] Similar to the preparation method of Comparative Example 1, the main difference is that in step 2), the reaction is carried out at 780℃ for 12 hours to obtain the final product.

[0179] Comparative Example 4

[0180] Similar to the preparation method in Example 2, the main difference is that in step 1), Al2O3 is replaced with TiO2, and the reaction is carried out at 940℃ for 12 hours as in step 2) to obtain the final product, without proceeding to the next step; wherein, Li2CO3 and Ni 0.72 Co 0.05 Mn 0.23 (OH)2 is measured according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23.

[0181] Comparative Example 5

[0182] Similar to the preparation method of Comparative Example 4, the main difference is that in step 2), the reaction is carried out at 860℃ for 12 hours to obtain the final product.

[0183] Comparative Example 6

[0184] Similar to the preparation method of Comparative Example 4, the main difference is that in step 2), the reaction is carried out at 780℃ for 12 hours to obtain the final product.

[0185] Comparative Example 7

[0186] The preparation method is similar to that in Example 2, the main difference being that in step 1), Al2O3 is replaced with Nb2O5, and the reaction is carried out at 940℃ for 12 hours as described in step 2) to obtain the final product, without proceeding to the next step; wherein, Li2CO3 and Ni 0.72 Co 0.05 Mn 0.23 (OH)2 is measured according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23.

[0187] Comparative Example 8

[0188] Similar to the preparation method of Comparative Example 7, the main difference is that in step 2), the reaction is carried out at 860℃ for 12 hours to obtain the final product.

[0189] Comparative Example 9

[0190] Similar to the preparation method of Comparative Example 7, the main difference is that in step 2), the reaction is carried out at 780℃ for 12 hours to obtain the final product.

[0191] Comparative Example 10

[0192] Similar to the preparation method in Example 1, the main difference is that in step 2), the material I is heated to 780°C in a roller kiln at a heating rate K1 and kept at that temperature for 12 hours, followed by cooling, crushing, sieving, and demagnetizing to obtain the final product.

[0193] The ternary cathode materials or coin cells prepared in Examples 1-5 and Comparative Examples 1-10 were subjected to relevant performance tests, and the test results are shown in Tables 1-4 below; in Tables 1-4, " / " indicates that the parameter is not present. In all the above examples and comparative examples, the heating rate K1 was 2.5℃ / min.

[0194] The test conditions or standards for each performance test item are as follows:

[0195] (1) Average particle size test: The ternary cathode material was tested by scanning electron microscopy (SEM), and the size of 300 to 500 particles was manually measured on the SEM image under the calibrated scale using NanoMeasurer software. The software automatically generated the average particle size value.

[0196] (2) Element concentration distribution test: Scanning electron microscope combined with energy dispersive spectroscopy (EDS) was used for the test.

[0197] (3) Electrochemical performance testing:

[0198] The ternary cathode material is assembled into an LR2032 coin cell. Among them, the positive electrode sheet is prepared from a ternary cathode material, acetylene black, and a binder PVDF with a mass ratio of 90:6:4.

[0199] Initial specific capacity and DCR test: Under the condition of 25 ± 2 °C, the coin cell is charged at a constant current of 0.1C to 4.5V, charged at a constant voltage of 4.5V until 0.05C, and then discharged at a constant current of 0.1C to 3.0V;

[0200] High-temperature cycle test: Under the condition of 45 ± 2 °C, the coin cell is charged at a constant current of 0.5C to 4.5V, charged at a constant voltage of 4.5V until 0.05C, and then discharged at a constant current of 1.0C to 3.0V. The charge-discharge equipment used is a Blue-Energy charge-discharge instrument; Cycle capacity retention rate = (discharge specific capacity at 50 cycles / initial discharge specific capacity) × 100%.

[0201] Table 1

[0202]

[0203] Table 2

[0204]

[0205] Table 3

[0206]

[0207] Table 4

[0208]

[0209] Combined with Tables 1, 2, and 3, it can be seen that in the ternary cathode material particles of Examples 1 to 5, the first doping element, the second doping element, and the third doping element form a gradient doping structure, and this gradient doping structure satisfies the concentration distribution model of this application. That is, in the range of 0 ≤ r ≤ r1, the concentration of the first doping element gradually decreases from C at r = 0 A0 to C at r = r1 A1 ; and in the range of 0 ≤ r < r1, the concentrations of the second doping element and the third doping element are zero, and in the range of r1 < r ≤ R, the concentration of the first doping element is zero; at the same time, at the coupling point, that is, at r = r1, the second doping element (whose concentration is C B1,edge ) starts to appear, and the first doping element and the second doping element coexist.

[0210] In the range of r1 ≤ r ≤ (r1 + r2) / 2, the concentration of the second doping element gradually increases from C at r = r1 B1,edge to C at r = (r1 + r2) / 2 B,max, then within the range of (r1 + r2) / 2 ≤ r ≤ r2, the concentration of the second doping element decreases gradually from C at r = (r1 + r2) / 2 B,max to C at r = r2. B2,edge ; within the range of r1 ≤ r < r2, the concentration of the third doping element is zero; meanwhile, at the coupling point, i.e., r = r2, the third doping element starts to appear (with a concentration of C C2 ), and the second doping element and the third doping element coexist.

[0211] Within the range of r2 ≤ r ≤ R, the concentration of the third doping element increases gradually from C at r = r2 C2 to C at r = R. C3 ; and within the range of r2 < r ≤ R, the concentration of the second doping element is zero.

[0212] Thus, in the concentration distribution model provided in this application, each determined and different gradient doping structure can be obtained by adjusting parameters according to the three formulas (1), (2), and (3), and the determined concentration value of metal elements with different valence states at a certain point can be predicted and determined, and it is repeatable and feasible. And under the concentration distribution model of this application, within the overall value range of r, relatively excellent electrochemical performance is shown (Table 4 shows typical data). Thus, the concentration distribution model constructed by formulas (1), (2), and (3) provided in this application creatively provides a new method for improving battery performance through gradient doping. This method can be combined with actual production or experiments, and has important guiding significance for obtaining an ideal gradient doping structure.

[0213] In addition, it can be seen from Figure 2 that the ternary cathode material prepared in this application has a good crystal particle morphology. Figures 3-5 In, according to the element distribution state, it can be judged that Al is distributed in the inner layer of the particle, Ti is distributed in the middle layer of the particle, and Nb is distributed in the shallow surface layer of the particle.

[0214] Furthermore, it should be noted that, due to different preparation conditions compared to this application, Comparative Examples 1-2, 4-5, and 7-8, although single-crystal particles were also formed, only a single element was doped in the single-crystal particles, and a gradient doping structure satisfying the concentration distribution model of this application was not formed. Therefore, their cycle performance and storage performance were worse than those of Examples 1-5 (see Table 4). Comparative Examples 3, 6, 9, and 10, due to their low sintering temperatures, could not form single-crystal morphologies like those in the examples. The particles formed were quasi-single-crystal structures formed by the aggregation of small particles (primary particle radius much smaller than 1.3 μm), and therefore could not form a gradient doping structure satisfying the concentration distribution model of this application. The overall concentrations of the first, second, and third doping elements in Comparative Examples 3, 6, and 9 were 2026 ppm, 795 ppm, and 704 ppm, respectively; the overall concentrations of the first, second, and third doping elements in Comparative Example 10 were 2077 ppm, 798 ppm, and 702 ppm, respectively.

[0215] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0216] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A ternary cathode material, characterized in that, The crystal particle comprises a first doping element, a second doping element and a third doping element, and the valence state of the first doping element < the valence state of the second doping element < the valence state of the third doping element; The first doping element is distributed in an inner layer of the crystal particle, the second doping element is distributed in an intermediate layer of the crystal particle, and the third doping element is distributed in a superficial layer of the crystal particle; In the crystal particle, the concentration distribution C of the first dopant element A (r) satisfies the following relational expression (1): （1）； At r = 0, the concentration of the first doping element is: C A (0) = C A0 ; At r = r1, the concentration of the first dopant element is: C A (r1)=C A1 ; C A0 >C A1 >0; Wherein, r represents a distance extending radially from the center of the crystal particle as a starting point, r1 represents a distance from the center of the crystal particle to the element distribution boundary of the first doping element in the radial direction; C A0 denotes the concentration of the first doped element at the center of the crystal particle, C A1 denotes the concentration of the first doped element at the element distribution boundary of the first doped element; In the crystal particle, the concentration distribution C of the second dopant element B (r) satisfies the following relation (2): （2）； At r = r1, the concentration of the second dopant element is: C B (r1) = C B1,edge ; At r = r2, the concentration of the second dopant element is: C B (r2) = C B2,edge ; At r = (r1 + r2) / 2, the concentration of the second dopant element is: C B (r1 + r2) / 2 = C B,max ; dr B = r2- r1, r2> r1; C B,max >C B1,edge >0,C B,max >C B2,edge >0; Wherein, r2 represents a distance from the center of the crystal particle to the element distribution boundary of the second doping element in the radial direction; C B1,edge denotes the concentration of the second doping element at the element distribution boundary of the first doping element, C B2,edge denotes the concentration of the second doping element at the element distribution boundary of the second doping element; C B,max denotes the concentration of the second doping element at a center position between the element distribution boundary of the first doping element and the element distribution boundary of the second doping element; In the crystal particle, the concentration distribution of the third doping element satisfies the relationship (3): （3）； At r = r2, the concentration of the third dopant element is: C C (r2) = C C2 ; At r = R, the concentration of the third dopant element is: C C (R) = C C3 ; 0 < C C2 < C C3 r2 < R; Wherein, R represents a distance from the center of the crystal particle to the outer surface of the crystal particle in the radial direction; C C2 denotes the concentration of the third dopant element at the element distribution boundary of the second dopant element, C C3 denotes the concentration of the third dopant element at the outer surface of the crystal grain.

2. The ternary cathode material of claim 1, characterized in that, One or more of the following conditions are satisfied: (1) (5 / 12)*R≤r1≤(6 / 12)*R, (9 / 12)*R≤r2≤(10 / 12)*R; Optionally, 1.2 μm≤R≤1.5 μm; (2) C B1,edge = C B2,edge .

3. The ternary cathode material according to claim 1 or 2, characterized in that, 2000 ppm < C A0 ≤ 3000 ppm, 800 ppm < C A1 ≤ 1000 ppm. 4.The ternary positive electrode material of claim 1 or 2, characterized in that, 400 ppm < C B1,edge ≤ 650 ppm, 400 ppm < C B2,edge ≤ 650 ppm, 1000 ppm < C B,max ≤ 1500 ppm.

5. The ternary cathode material according to claim 1 or 2, characterized in that, 0 ppm < C C2 ≤ 330 ppm, 330 ppm < C C3 ≤ 1000 ppm. 6.The ternary positive electrode material of claim 1 or 2, characterized in that, The first doping element includes one or more of Al 3+ , Zn 2+ , and Mg 2+ , the second doping element includes Ti 4+ and / or Zr 4+ , and the third doping element includes one or more of Nb 5+ , Ta 5+ , and W 6+ .

7. The ternary cathode material according to claim 1 or 2, characterized in that, The average particle size of the crystal particle is 2.4 μm~3 μm, and is optionally 2.4 μm~2.6 μm.

8. A positive electrode sheet characterized by comprising: The ternary positive electrode material of any one of claims 1~7.

9. A secondary battery characterized by comprising: The positive electrode sheet of claim 8.

10. An electronic device, comprising: The secondary battery of claim 9.

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