Ternary positive electrode material, preparation method thereof, positive electrode sheet, secondary battery and electronic device

Abstract

The application provides a ternary positive electrode material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electronic device. 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, the valence of the first doping element < the valence of the second doping element < the valence of the third doping element, the first doping element is distributed in an inner layer of the crystal particles, the second doping element is distributed in a middle layer of the crystal particles, and the third doping element is distributed in a superficial layer of the crystal particles. The ternary positive electrode material provided by the application 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 a ternary cathode material and its preparation method, cathode sheet, secondary battery and electronic device. 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 and its preparation method, 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] The inner layer of the crystal particle includes a region extending radially from the center of the crystal particle to 6 / 12 of its radius; the middle layer of the crystal particle includes a region extending radially from 5 / 12 of its radius to 10 / 12 of its radius, starting from the center of the crystal particle; and the shallow layer of the crystal particle includes a region extending radially from 9 / 12 of its radius to its outer surface, starting from the center of the crystal particle.

[0007] In some embodiments of this application, 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.

[0008] In some embodiments of this application, one or more of the following conditions are met:

[0009] (1) In the ternary cathode material, the concentration of the first doped element is 2000ppm~3000ppm, the concentration of the second doped element is 1000ppm~1500ppm, and the concentration of the third doped element is greater than 0 and less than or equal to 1000ppm.

[0010] (2) The concentration trends of the first dopant element, the second dopant element, and the third dopant element in the crystal particles are as follows:

[0011] In the inner layer of the crystal particle, the concentration of the first dopant element is uniformly distributed radially from the center of the crystal particle to 5 / 12 of the crystal particle radius, and gradually decreases radially from 5 / 12 of the crystal particle radius to 6 / 12 of the crystal particle radius.

[0012] In the intermediate layer of the crystal particles, the concentration of the second dopant element first increases and then decreases radially from 5 / 12 of the crystal particle radius to 10 / 12 of the crystal particle radius;

[0013] In the shallow layer of the crystal particle, the concentration of the third dopant element gradually increases radially from 9 / 12 of the crystal particle radius to the outer surface of the crystal particle, and is uniformly distributed on the outer surface of the crystal particle.

[0014] In some embodiments of this application, one or more of the following conditions are met:

[0015] (1) The average particle size of the crystal particles is 2.4 μm to 3 μm, and can be selected as 2.4 μm to 2.6 μm;

[0016] (2) In the X-ray diffraction pattern of the ternary cathode material, the peak intensity of the diffraction peak corresponding to the crystal plane (003) is I. 003 The peak intensity of the diffraction peak corresponding to the crystal plane (104) is I. 104 Satisfying: I 003 / I 104 ≥1.8;

[0017] Optionally, I 003 / I 104 It is greater than or equal to 1.8 and less than or equal to 2.5;

[0018] (3) In the X-ray diffraction analysis pattern of the ternary cathode material, the cell parameters a and c of the crystal particles satisfy: 4.9≤c / a≤5, where a represents the side length of the bottom surface of the cell and c represents the height perpendicular to the bottom surface of the cell.

[0019] The second aspect of this application provides a method for preparing a ternary cathode material, comprising:

[0020] 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-heat sintering, and then cooled and crushed to obtain a ternary cathode material.

[0021] 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,

[0022] A first mixture comprising a first compound, nickel cobalt manganese hydroxide and lithium salt is subjected to a first sintering, and then cooled and crushed to obtain a first sintered material. 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.

[0023] The second mixture containing the first sintering material and the second compound is subjected to a second sintering, and then cooled and crushed to obtain the second sintering material. 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 that of the first compound, and the temperature of the second sintering is different from that of the first sintering.

[0024] A third mixture containing the second sintering material and the third compound is subjected to a third sintering, and after cooling and crushing, a ternary cathode material is obtained. 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.

[0025] 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.

[0026] 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.

[0027] The inner layer of the crystal particle includes a region extending radially from the center of the crystal particle to 6 / 12 of the crystal particle's radius; the middle layer of the crystal particle includes a region extending radially from 5 / 12 of the crystal particle's radius to 10 / 12 of the crystal particle's radius; and the shallow layer of the crystal particle includes a region extending radially from 9 / 12 of the crystal particle's radius to the outer surface of the crystal particle.

[0028] In some embodiments of this application, one or more of the following conditions are met:

[0029] (1) 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℃;

[0030] (2) The sintering time of the first stage, the sintering time of the second stage, and the sintering time of the third stage are each 2h to 6h independently.

[0031] In some embodiments of this application, one or more of the following conditions are met:

[0032] (1) 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℃~800℃, 840℃~880℃, and 920℃~960℃;

[0033] Optionally, the first sintering temperature is 920℃~960℃, the second sintering temperature is 840℃~880℃, and the third sintering temperature is 760℃~800℃;

[0034] (2) The time for the first sintering, the time for the second sintering, and the time for the third sintering are each independently 2h~6h;

[0035] (3) 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.

[0036] The third aspect of this application provides a positive electrode sheet, including the ternary positive electrode material described in the first aspect of this application or the ternary positive electrode material prepared by the preparation method described in the second aspect of this application.

[0037] A fourth aspect of this application provides a secondary battery, including the positive electrode sheet described in the third aspect of this application.

[0038] The fifth aspect of this application provides an electrical device including the secondary battery described in the fourth aspect of this application.

[0039] 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.

[0040] The ternary cathode material provided in this application features a spiral gradient doping pattern where the valence state of the dopant elements gradually increases from low to high along the crystal particle center to the outer surface. Furthermore, a coupling coexistence exists at the junctions of adjacent dopant elements with different valence states. This spiral gradient doping facilitates the formation of a crystal structure that is more stable and robust from the inside out, with a differentiated surface structure and internal bulk structure. Specifically, the particle surface structure 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 both the crystal structure and interface structure of the material, thereby enhancing the cycle performance of the ternary cathode material and further improving its storage performance and / or thermal stability. Attached Figure Description

[0041] 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.

[0042] Figure 2 The image shows a scanning electron microscope (SEM) image of the ternary cathode material prepared in Example 2.

[0043] Figure 3 The image shows the SEM-Mapping of Al in the ternary cathode material prepared in Example 2.

[0044] Figure 4 The image shows the SEM-Mapping of Ti in the ternary cathode material prepared in Example 2.

[0045] Figure 5 The image shows the SEM-Mapping of Nb in the ternary cathode material prepared in Example 2.

[0046] Figure 6The images show the XRD patterns of the ternary cathode materials prepared in Examples 1-5 and Comparative Example 10. Detailed Implementation

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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:

[0054] (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.

[0055] (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.

[0056] (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.

[0057] To solve the above technical problems, the inventors have proposed the following technical solution in this application.

[0058] 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.

[0059] 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.

[0060] The inner layer of the crystal particle includes a region extending radially from the center of the crystal particle to 6 / 12 of its radius; the middle layer of the crystal particle includes a region extending radially from 5 / 12 of its radius to 10 / 12 of its radius, starting from the center of the crystal particle; and the shallow layer of the crystal particle includes a region extending radially from 9 / 12 of its radius to its outer surface, starting from the center of the crystal particle.

[0061] The ternary cathode material provided in this application features a spiral gradient doping pattern where the valence state of the dopant elements gradually increases from low to high along the crystal particle center to the outer surface. Furthermore, a coupling coexistence exists at the junctions of adjacent dopant elements with different valence states. This spiral gradient doping facilitates the formation of a crystal structure that is more stable and robust from the inside out, with a differentiated surface structure and internal bulk structure. Specifically, the particle surface structure 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 both the crystal structure and interface structure of the material, thereby enhancing the cycle performance of the ternary cathode material and further improving its storage performance and / or thermal stability.

[0062] Specifically, the high-valence dopants in the outermost layer have a higher binding energy with oxygen, which is beneficial for improving the binding strength between the surface metal and oxygen, effectively suppressing the release of surface lattice oxygen, improving surface structural stability, reducing the risk of thermal runaway, and enhancing safety performance. Simultaneously, due to the charge balance effect, the presence of high-valence dopants in the surface layer is beneficial for the formation of high-valence Ni ions (such as Ni...) in the surface layer. 4+The reduced proportion of Ni ions and surface oxygen defects helps to minimize adverse reactions between high-valence Ni ions and the electrolyte, stabilizes the oxidation state of Ni on the particle surface, and inhibits Li / Ni cation mixing. This, in turn, helps to suppress the transformation of the layered structure into a disordered rock salt phase, reducing the probability of the layered structure transforming into the inert NiO rock salt phase and improving the stability of the material structure. Furthermore, the gradual gradient change of the valence state of the dopant elements from the inside out effectively reduces lattice stress, mitigates lattice distortion and the generation of intergranular microcracks, buffers structural failures caused by lattice stress, and extends the material's lifespan. Moreover, the coupling and coexistence at the junctions of adjacent dopant elements with different valence states further enhances the stability of the crystal and interface structures of the material, thereby improving the cycle performance of the ternary cathode material and further enhancing storage performance and / or thermal stability.

[0063] 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.

[0064] 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 elements. This facilitates the formation of a helical gradient doped element structure in the ternary cathode material, thereby comprehensively improving the stability of the crystal structure and interface structure of the material, which in turn improves the cycle performance of the ternary cathode material, and further improves its storage performance and / or thermal stability.

[0065] In some embodiments, in the ternary cathode material, the concentration of the first dopant element is 2000ppm~3000ppm, the concentration of the second dopant element is 1000ppm~1500ppm, and the concentration of the third dopant element is greater than 0 and less than or equal to 1000ppm. Based on the helical gradient doping element doping structure, this concentration distribution of dopant elements is beneficial to further improve the stability of the crystal structure and interface structure of the material, thereby improving the cycle performance of the ternary cathode material, and further beneficial to improving storage performance and / or thermal stability.

[0066] For example, the concentration of the first dopant element can be 2000ppm, 2300ppm, 2500ppm, 2700ppm, 2900ppm, 3000ppm or within any of the above values; the concentration of the second dopant element can be 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm or within any of the above values; and the concentration of the third dopant element can be 10ppm, 50ppm, 100ppm, 300ppm, 500ppm, 700ppm, 900ppm, 1000ppm or within any of the above values.

[0067] In some embodiments, the concentration trends of the first dopant element, the second dopant element, and the third dopant element in the crystal particles are as follows:

[0068] In the inner layer of the crystal particle, the concentration of the first dopant element is uniformly distributed radially from the center of the crystal particle to 5 / 12 of the crystal particle radius, and gradually decreases radially from 5 / 12 of the crystal particle radius to 6 / 12 of the crystal particle radius.

[0069] In the intermediate layer of the crystal particles, the concentration of the second dopant element first increases and then decreases radially from 5 / 12 of the crystal particle radius to 10 / 12 of the crystal particle radius;

[0070] In the shallow surface layer of the crystal particles, the concentration of the third dopant element gradually increases radially from 9 / 12 of the crystal particle radius towards the outer surface of the crystal particles, and is uniformly distributed on the outer surface of the crystal particles. This facilitates the formation of a helical gradient doped element structure in the ternary cathode material, thereby comprehensively improving the stability of the material's crystal and interface structures, which in turn improves the cycle performance of the ternary cathode material, and further enhances its storage performance and / or thermal stability.

[0071] 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.

[0072] In some embodiments, the peak intensity of the diffraction peak corresponding to the crystal plane (003) in the X-ray diffraction analysis pattern of the ternary cathode material is I. 003The peak intensity of the diffraction peak corresponding to the crystal plane (104) is I. 104 Satisfying: I 003 / I 104 ≥1.8; optionally, I 003 / I 104 It is greater than or equal to 1.8 and less than or equal to 2.5. For example, I 003 / I 104 The values ​​can be 1.8, 2.0, 2.1, 2.3, 2.5, or any range of these values. This indicates that the ternary cathode material possesses good crystallinity and a layered structure, which is beneficial for its high cycle performance, and further beneficial for its high storage performance and / or thermal stability.

[0073] In some embodiments, in the X-ray diffraction analysis pattern of the ternary cathode material, the cell parameters a and c of the crystal particles satisfy the following relationship: 4.9 ≤ c / a ≤ 5, where a represents the side length of the bottom face of the cell, and c represents the height perpendicular to the bottom face of the cell. For example, c / a can be 4.9, 4.91, 4.93, 4.95, 4.97, 4.99, 5, or any value within the range of these values. This indicates that the ternary cathode material possesses good crystallinity and a layered structure, which is beneficial for its high cycle performance, and further beneficial for its high storage performance and / or thermal stability.

[0074] 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.

[0075] 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:

[0076] 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.

[0077] 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,

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] The inner layer of the crystal particle includes a region extending radially from the center of the crystal particle to 6 / 12 of its radius; the middle layer of the crystal particle includes a region extending radially from 5 / 12 of its radius to 10 / 12 of its radius, starting from the center of the crystal particle; and the shallow layer of the crystal particle includes a region extending radially from 9 / 12 of its radius to its outer surface, starting from the center of the crystal particle.

[0084] 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.

[0085] Specifically, this application performs gradient doping based on the ionic radius or diffusion kinetics of dopants with different valence states, and selects appropriate sintering temperatures for different dopants and / or calcination stages. This facilitates the formation of helical gradient doping based on the ease of doping of dopants, making the structure of the ternary cathode material formed after doping more stable from the inside out and forming a robust doped shell, thereby improving the stability of the material's crystal structure and interface structure, while also improving cycle performance and storage performance.

[0086] For example, in step S1, the sintering temperature in the first stage is more conducive to the diffusion of the first dopant element, allowing it to diffuse into the inner layer; then, the sintering temperature in the second stage is more conducive to the diffusion of the second dopant element, allowing it to diffuse into the intermediate layer; finally, the sintering temperature in the third stage is conducive to the diffusion of the third dopant element, allowing it to diffuse into the shallow surface layer, thereby obtaining a spiral gradient doped structure. Steps S1' to S3', by diffusing dopant elements of different valence states step by step and matching the diffusion temperature according to the different dopant elements, also ultimately facilitate the obtaining of a spiral gradient doped structure.

[0087] 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 spiral gradient doping structure in the ternary cathode material, where the valence state of the doping element gradually increases from low to high along the crystal grain center to the outer surface of the crystal grain, and where adjacent doping elements with different valence states coexist and are coupled at their junctions. This results in a ternary cathode material with a clear gradient distribution of doped elements.

[0088] In some embodiments, the sintering times for the first stage, the second stage, and the third stage are each independently 2 to 6 hours. This facilitates the formation of a spiral gradient doped structure and helps obtain ternary cathode materials with a clear gradient distribution of doped elements.

[0089] 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;

[0090] 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 spiral gradient doping structure in the ternary cathode material, where the valence state of the doping element gradually increases from low to high along the crystal particle center to the outer surface of the crystal particle, and where adjacent doping elements with different valence states coexist and are coupled at their junctions. This results in a ternary cathode material with a clear gradient distribution of doped elements.

[0091] In some embodiments, the times for the first sintering, the second sintering, and the third sintering are each independently 2 to 6 hours. This facilitates the formation of a spiral gradient doped structure and helps obtain ternary cathode materials with a clear gradient distribution of doped elements.

[0092] 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.

[0093] 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。

[0094] 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.

[0095] 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.

[0096] 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.

[0097] In some embodiments, the lithium salt includes one or more of lithium hydroxide, lithium carbonate, and lithium dihydrogen phosphate.

[0098] 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.

[0099] Fourthly, this application provides a secondary battery, including the positive electrode sheet of the third aspect of this application.

[0100] 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.

[0101] Fifthly, this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0102] 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.

[0103] Example

[0104] 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.

[0105] Example 1

[0106] 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.

[0107] 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.

[0108] Example 2

[0109] 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:

[0110] 1) Ni cobalt manganese hydroxide Ni 0.72 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] Example 3

[0116] 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.

[0117] Example 4

[0118] 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.

[0119] Example 5

[0120] 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.

[0121] Comparative Example 1

[0122] 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 quantified according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23.

[0123] Comparative Example 2

[0124] 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.

[0125] Comparative Example 3

[0126] 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.

[0127] Comparative Example 4

[0128] 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 quantified according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23.

[0129] Comparative Example 5

[0130] 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.

[0131] Comparative Example 6

[0132] 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.

[0133] Comparative Example 7

[0134] 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 quantified according to the molar ratio of Li:Ni:Co:Mn = 1.02:0.72:0.05:0.23.

[0135] Comparative Example 8

[0136] 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.

[0137] Comparative Example 9

[0138] 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.

[0139] Comparative Example 10

[0140] 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.

[0141] 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 1-3 below. In all the examples and comparative examples above, the heating rate K1 was 2.5℃ / min.

[0142] The test conditions or standards for each performance test item are as follows:

[0143] (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.

[0144] (2) X-ray diffraction analysis test: The test is performed using an X-ray diffractometer.

[0145] (3) Elemental distribution test: The test was conducted using a scanning electron microscope combined with an energy dispersive spectroscopy (EDS).

[0146] (4) Electrochemical performance testing:

[0147] The ternary cathode material was assembled into an LR2032 coin cell, wherein the cathode electrode sheet was prepared by ternary cathode material, acetylene black and PVDF binder in a mass ratio of 90:6:4.

[0148] First specific capacity and DCR test: Under the condition of 25±2℃, the button cell was charged to 4.5V with constant current of 0.1C, charged to 0.05C with constant voltage of 4.5V, and then discharged to 3.0V with constant current of 0.1C.

[0149] High-temperature cycle test: Under the condition of 45±2℃, the button cell is charged to 4.5V at a constant current of 0.5C, charged to 0.05C at a constant voltage of 4.5V, and then discharged to 3.0V at a constant current of 1.0C. The charging and discharging equipment used is the Blue Electric Charge-Discharge Tester; Cycle capacity retention rate = (50-cycle discharge specific capacity / first discharge specific capacity) × 100%.

[0150] Table 1

[0151]

[0152] Table 2

[0153]

[0154] Table 3

[0155]

[0156] from Figure 2It can be seen that the ternary cathode material prepared in this application has a good crystal particle morphology. Figures 3-5 Based on the elemental distribution, it can be determined that Al is distributed in the inner layer of the particles, Ti in the middle layer, and Nb in the shallow surface layer. Figure 6 As shown in Table 2, the single-crystal ternary cathode material prepared using the stepwise doping process in Example 2 exhibits a good layered structure and crystallinity. Meanwhile, the Ic of the single-crystal material... 003 / I 104 The larger value indicates that the lithium-nickel mixing degree of the ternary cathode material prepared by the method of this application is significantly reduced.

[0157] It is particularly important to emphasize that, as shown in Tables 1-3, the samples prepared using the experimental scheme of Comparative Example 10 exhibit poor electrochemical performance and micro-strain characteristics. This is because the temperature of 780℃ is insufficient for the hydroxide to completely decompose, nucleate, and crystallize to form a single-crystal cathode material (the precursor contains some form of nickel, cobalt, and manganese-based oxides, such as...). Figure 6 XRD of Comparative Example 10).

[0158] As can be seen from the comparison of the electrochemical performance of Examples 1-5 and Comparative Examples 1-10 in Table 3 above, there is an electrochemical synergistic effect among the gradient doping elements, which can effectively improve the electrochemical performance and give full play to the electrochemical efficacy of each element; at the same time, it can be seen that the overall electrochemical performance of Example 2 is better, because Al(3) + Ti (4) + ), Nb (5 + The doping process, when calcined at 940℃, 860℃, and 780℃ respectively, exhibits a good spiral gradient distribution effect and forms a multidimensional structure, which can significantly improve the stability of the bulk phase and interface structure of the cathode material particles.

[0159] 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.

[0160] 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, It includes crystal particles, wherein the crystal particles include a first doping element, a second doping element, and a third doping element, and the valence state of the first doping element is less than the valence state of the second doping element, which is less than the valence state of the third doping element. 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. The inner layer of the crystal particle includes a region extending radially from the center of the crystal particle to 6 / 12 of its radius; the middle layer of the crystal particle includes a region extending radially from 5 / 12 of its radius to 10 / 12 of its radius, starting from the center of the crystal particle; and the shallow layer of the crystal particle includes a region extending radially from 9 / 12 of its radius to its outer surface, starting from the center of the crystal particle.

2. The ternary cathode material according to claim 1, characterized in that, 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.

3. The ternary cathode material according to claim 1 or 2, characterized in that, In the ternary cathode material, the concentration of the first dopant element is 2000ppm~3000ppm, the concentration of the second dopant element is 1000ppm~1500ppm, and the concentration of the third dopant element is greater than 0 and less than or equal to 1000ppm.

4. The ternary cathode material according to claim 1 or 2, characterized in that, One or more of the following conditions must be met: (1) The average particle size of the crystal particles is 2.4 μm to 3 μm; (2) In the X-ray diffraction pattern of the ternary cathode material, the peak intensity of the diffraction peak corresponding to the crystal plane (003) is I. 003 The peak intensity of the diffraction peak corresponding to the crystal plane (104) is I. 104 Satisfying: I 003 / I 104 ≥1.8; (3) In the X-ray diffraction analysis pattern of the ternary cathode material, the cell parameters a and c of the crystal particles satisfy: 4.9≤c / a≤5, where a represents the side length of the bottom surface of the cell and c represents the height perpendicular to the bottom surface of the cell.

5. The ternary cathode material according to claim 4, characterized in that, One or more of the following conditions must be met: (1) The average particle size of the crystal particles is 2.4 μm to 2.6 μm; (2) I 003 / I 104 It is greater than or equal to 1.8 and less than or equal to 2.

5.

6. A method for preparing a ternary cathode material, characterized in that, include: 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-heat sintering, and then cooled and crushed to obtain a ternary cathode material. 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, A first mixture comprising a first compound, nickel cobalt manganese hydroxide, and lithium salt is subjected to a first sintering, and then cooled and crushed to obtain a first sintered material; wherein, 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; A second mixture comprising the first sintering material and the second compound is subjected to a second sintering, and then cooled and crushed to obtain a second sintering material; wherein, 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, and 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. A third mixture containing the second sintering material and the third compound is subjected to a third sintering, and then cooled and crushed to obtain a ternary cathode material; wherein, 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, and 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, and the third sintering temperature is different from the first sintering temperature and the second sintering temperature; 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. 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. The inner layer of the crystal particle includes a region extending radially from the center of the crystal particle to 6 / 12 of its radius; the middle layer of the crystal particle includes a region extending radially from 5 / 12 of its radius to 10 / 12 of its radius, starting from the center of the crystal particle; and the shallow layer of the crystal particle includes a region extending radially from 9 / 12 of its radius to its outer surface, starting from the center of the crystal particle.

7. The method for preparing the ternary cathode material according to claim 6, characterized in that, One or more of the following conditions must be met: (1) 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℃; (2) The sintering time of the first stage, the sintering time of the second stage, and the sintering time of the third stage are each 2h to 6h independently.

8. The method for preparing the ternary cathode material according to claim 6 or 7, characterized in that, One or more of the following conditions must be met: (1) 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℃~800℃, 840℃~880℃, and 920℃~960℃; (2) The time for the first sintering, the time for the second sintering, and the time for the third sintering are each independently 2h~6h; (3) 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.

9. The method for preparing the ternary cathode material according to claim 8, characterized in that, The first sintering temperature is 920℃~960℃, the second sintering temperature is 840℃~880℃, and the third sintering temperature is 760℃~800℃.

10. A positive electrode plate, characterized in that, This includes the ternary cathode material as described in any one of claims 1 to 5, or the ternary cathode material prepared by the preparation method of the ternary cathode material as described in any one of claims 6 to 9.

11. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 10.

12. An electronic device, characterized in that, Includes the secondary battery as described in claim 11.

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