Single-crystal multi-element positive electrode material, preparation method thereof and lithium ion battery

Abstract

This invention relates to the field of lithium-ion battery technology, and discloses a single-crystal multi-element cathode material, its preparation method, and a lithium-ion battery. The multi-element cathode material comprises quasi-single-crystal particles composed of multiple grains, with G element present at the grain boundaries between the grains. The concentration of G element at the g-sites at the grain boundaries gradually decreases with increasing distance between the g-sites and the surface of the quasi-single-crystal particles. The G element is selected from at least one of Ni, Co, Mn, Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, and B. The single-crystal multi-element cathode material with this special structure can significantly slow down the erosion of the grain boundaries by the electrolyte, improve the grain boundary stability of the cathode material, and significantly improve the cycle life, energy density, rate performance, and impedance increase rate of the lithium-ion battery containing this cathode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a single-crystal multi-element cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid development of the new energy industry, the market has placed higher demands on the performance of lithium-ion batteries. Cathode materials, as the core materials that have the greatest impact on battery performance, are constantly being improved towards higher energy density, longer cycle life, higher safety, and lower cost. Lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA), among other ternary cathode materials, have become one of the most widely used cathode materials due to their excellent energy density advantages. To achieve higher specific capacity, the Ni content in ternary cathode materials is continuously increasing, leading to reduced material stability and consequently deterioration in cycle life and safety performance. Therefore, the application of more stable single-crystal lithium nickel cobalt manganese oxide materials is becoming increasingly widespread.

[0003] Single-crystal multi-element materials can be divided into two states based on their crystal growth arrangement: one is the pure single-crystal state, where each single-crystal particle consists of an independent crystal grain; the other is the near-single-crystal state, which consists of several grains bonded together. Since pure single-crystal particles have no internal pores or interfaces, Li... + The extraction and insertion paths are relatively long, resulting in poor capacity and rate performance. Therefore, current commercially available single-crystal materials typically contain both pure single-crystal particles and quasi-single-crystal particles in varying proportions. However, as described in Zhang et al.'s 2022 article in Nano Letters, "Accelerated Degradation in a Quasi-Single-Crystalline Layered Oxide Cathode for Lithium-Ion Batteries Caused by Residual Grain Boundaries," these quasi-single-crystal particles experience concentrated anisotropic stress at grain boundaries during charge-discharge cycling due to the H2-H3 phase transition causing cell volume changes. This leads to interlayer slip, dislocations, and stacking faults at the grain boundaries, accelerating the loss of reactive oxygen species and irreversible phase transitions, resulting in a decrease in electrochemical capacity. Furthermore, stress concentration can cause cracks along grain boundaries, generating highly active new surfaces that further exacerbate side reactions between the material and the electrolyte, leading to reduced cycle life and increased impedance.

[0004] Common measures to improve the stability of materials include bulk doping and surface coating. However, existing technologies mainly target the stabilization of the internal structure of the crystal and the surface of the particles. There are no effective means to address the grain boundary degradation problem of quasi-single crystal particles. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem of poor electrochemical performance, such as capacity and rate performance, caused by the poor grain boundary stability of quasi-monocrystalline cathode material particles in existing technologies. This invention provides a monocrystalline multi-element cathode material, its preparation method, and a lithium-ion battery. The monocrystalline multi-element cathode material comprises quasi-monocrystalline particles composed of multiple grains, with G elements present at the grain boundaries. The concentration of G elements at the g-sites of the grain boundaries gradually decreases as the distance between the g-sites and the surface of the quasi-monocrystalline particles increases. This significantly slows down the erosion of the grain boundaries by the electrolyte, improves the grain boundary stability of the cathode material, and significantly improves the cycle life, energy density, rate performance, and impedance increase rate of the lithium-ion battery containing this cathode material.

[0006] To achieve the above objectives, the first aspect of the present invention provides a single-crystal multi-element cathode material, characterized in that the multi-element cathode material comprises a single-crystal-like particle composed of multiple grains, and the grain boundaries between the grains contain G elements.

[0007] Among them, the concentration of G element at the grain boundary g site gradually decreases as the distance between the g site and the surface of the single crystal-like particle increases;

[0008] The element G is selected from at least one of Ni, Co, Mn, Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, and B.

[0009] A second aspect of the present invention provides a method for preparing a single-crystal multi-element cathode material, characterized in that the preparation method includes:

[0010] The single-crystal multi-element cathode material matrix is ​​obtained by mixing a grain boundary stabilizer containing G element and then sintering it.

[0011] Wherein, the element G is selected from at least one element selected from Ni, Co, Mn, Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, Ba and B;

[0012] The grain boundary stabilizer has a D50 of 0.01-10 μm, and the grain boundary stabilizer has D10, D50, and D90 satisfying: K90=(D90-D10) / D50≥1.5.

[0013] A third aspect of the present invention provides a single-crystal multi-element cathode material prepared by the above-described preparation method.

[0014] A fourth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned single-crystal multi-element cathode material.

[0015] Through the above technical solutions, the single-crystal multi-element cathode material, its preparation method, and the lithium-ion battery provided by this invention achieve the following beneficial effects:

[0016] The single-crystal multi-element cathode material provided by this invention comprises quasi-single-crystal particles composed of multiple grains, with G element present at the grain boundaries between the grains. The concentration of G element at the g-sites of the grain boundaries gradually decreases as the distance between the g-sites and the surface of the quasi-single-crystal particles increases. The G element fully penetrates and fills the grain boundaries of the cathode material, reducing stress concentration at the grain boundaries caused by changes in cell volume during charge-discharge cycles, thus improving the grain boundary stability of the cathode material. This significantly improves the cycle life of lithium-ion batteries containing this cathode material. Simultaneously, the improved grain boundary stability and fewer grain boundary cracks also reduce the generation of fresh internal interfaces. Under multiple cycles and long-term storage conditions, the impedance increase rate of lithium-ion batteries containing this cathode material is lower. Specifically, compared with conventional cathode materials, lithium-ion batteries containing the cathode material provided by this invention can improve the half-cell cycle capacity retention rate by at least 4% and reduce the impedance increase rate by at least 15% under 45°C conditions and 1C charge-discharge for 80 cycles.

[0017] Furthermore, in the single-crystal multi-element cathode material provided by this invention, the gradient filling of G elements at the grain boundaries serves as a conductive medium, which is more conducive to the conduction of Li deep within the grain boundaries. + The outward diffusion of the cathode material allows its capacity to be fully utilized and its rate performance to be better when used in lithium-ion batteries. Specifically, compared with conventional cathode materials, lithium-ion batteries containing the cathode material provided by this invention can increase the discharge capacity by more than 1 mAh / g in the 0.1C discharge range of 3.0-4.3V at 25°C; and can increase the 1C rate discharge capacity by more than 2%.

[0018] The method for preparing single-crystal multi-element cathode materials provided by this invention is simple, easy to control, and suitable for industrial production. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the single-crystal-like particles of the single-crystal-type multi-element cathode material of the present invention;

[0020] Figure 2 This is a schematic diagram showing that the cobalt hydroxide used as a grain boundary stabilizer in Example 1 contains micron and submicron ions;

[0021] Figure 3 This is a cross-sectional schematic diagram of the single-crystal multi-element cathode material prepared in Example 1. The numbers in the figure are examples of test points for element concentration within the grain boundaries.

[0022] Figure 4This is a comparison graph of the cycling performance of the cathode materials prepared in Example 1, Example 1 and Comparative Example 1 at a 1C rate, where the test temperature is 45℃ and the voltage range is 3.0-4.3V. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of the present invention provides a single-crystal multi-element cathode material, characterized in that the multi-element cathode material comprises a single-crystal-like particle composed of multiple grains, and the grain boundaries between the grains contain G elements;

[0025] Among them, the concentration of G element at the grain boundary g site gradually decreases as the distance between the g site and the surface of the single crystal-like particle increases;

[0026] The element G is selected from at least one of Ni, Co, Mn, Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, and B.

[0027] In this invention, the grain boundary refers to the contact interface and / or gap between multiple grains that make up a single-crystal particle. In this invention, since the single-crystal multi-element cathode material is obtained by the co-growth of a large number of crystal nuclei, most grains will fuse together during crystal growth. When the crystal grows to a certain size, i.e., when the single-crystal multi-element cathode material of this invention is formed, some grains remain that are not completely fused. These grains have different orientations, and their interfaces are the grain boundaries described in this invention.

[0028] In this invention, the single-crystal multi-element cathode material comprises multiple quasi-single-crystal particles, with G elements present at the grain boundaries between the grains. The concentration of G elements at the g-sites of the grain boundaries gradually decreases as the distance between the g-sites and the surface of the quasi-single-crystal particles increases. The G elements fully penetrate and fill the grain boundaries of the cathode material, reducing stress concentration at the grain boundaries caused by cell volume changes during charge-discharge cycles, thus improving the grain boundary stability of the cathode material. This significantly increases the cycle life of lithium-ion batteries containing this cathode material. Simultaneously, the improved grain boundary stability and fewer grain boundary cracks also reduce the generation of fresh internal interfaces. Under multiple cycles and long-term storage conditions, the impedance increase of lithium-ion batteries containing this cathode material is lower.

[0029] Furthermore, the G element is selected from at least one of Mn, Co, W, La, Al, Ti, Zr, and Nb.

[0030] According to the present invention, in the SEM image of the cross-sectional sample of the quasi-single-crystal particles, the concentration of element G at the g site at the grain boundary satisfies the following relationship:

[0031] 1.2C1≥C g ≥0.8C2 Formula I;

[0032]

[0033] Where C1 is the concentration of G element on the surface of the single-crystal-like particles, in mol%; C2 is the concentration of G element in the bulk phase of the single-crystal-like particles, in mol%; C g L is the concentration of element G at the g-site of the grain boundary, in mol%; L is the total length of the grain boundary passing through the g-site, in μm; L g denoted as , the shortest path length from point g along the grain boundary to the surface of the quasi-single-crystal particle, in μm; k is a coefficient, with a value ranging from 0.8 to 1.2.

[0034] In this invention, L represents the total length of the grain boundary passing through point g, which is the approximate sum of the lengths of the two shortest grain boundary segments extending from point g along two opposite directions parallel to the crystal plane to the surface of the quasi-single-crystal grain. g It refers to the approximate length of the shortest grain boundary route extending from the g site along a direction parallel to the grain boundary to the surface of a single-crystal-like particle.

[0035] In this invention, L and L g Approximate values ​​are used because the grain boundary orientation is not a straight line and cannot be actually measured. Therefore, multiple straight lines are drawn along the grain boundary orientation for simulation, and the length of the straight lines is used to approximate the actual length of the grain boundary.

[0036] In this invention, C1, C2 and C g The results were obtained by scanning electron microscopy energy dispersive spectroscopy analysis: a cross-sectional sample of single-crystal multi-element cathode material was prepared by ion milling, and a single-crystal-like single-crystal particle in the cross-sectional sample was selected by scanning electron microscopy energy dispersive spectroscopy analysis. The atomic percentage of elements at different points on the grain boundaries of the particles was obtained. At least 5 sets of data were tested at each position and the average value was taken.

[0037] In this invention, in order to reflect the concentration change trend of element G, multiple different sites need to be randomly selected along the grain boundary for testing and evaluation, and the selected sites should be relatively dispersed to avoid being too concentrated.

[0038] Due to the limitations of the detection method, there may be some abnormal data that exceed the calculation results of Formula II. These data should be removed during evaluation. When more than 75% of the data conform to the law that the concentration of element G at the grain boundary g site gradually decreases with the increase of the distance between the g site and the surface of the single crystal-like particle, as described in this invention, it should be considered to meet the technical effect and requirements of this invention.

[0039] Furthermore, 1.1C1≥C g ≥0.9C2.

[0040] According to the present invention, the total length L of the grain boundary is obtained by scanning electron microscopy energy dispersive spectroscopy analysis, which satisfies 0.01μm≤L≤8μm.

[0041] According to the present invention, C1-C2 ≥ 0.1%.

[0042] Furthermore, C1-C2 ≥ 0.2%.

[0043] According to the present invention, when C1>5%, the value of k ranges from 0.9 to 1.1; when C1≤5%, the value of k ranges from 0.8 to 1.2.

[0044] like Figure 1 As shown, Figure 1 This is a schematic diagram of the single-crystal-like particles of the single-crystal-type multi-element cathode material of the present invention. Figure 1 It can be seen that the cathode material of the present invention comprises a single-crystal-like particle composed of multiple grains as shown in the figure, wherein the contact surface between each grain is the grain boundary of the present invention; taking point g in the figure as an example, the total grain boundary length L from point g along the grain boundary to the surface of the single-crystal-like particle includes two parts: L1 and L2 directions and L3 and L4 directions, and the value of the total length L can be obtained by L1+L2+L3+L4; the shortest path L from point g along the grain boundary direction to the surface of the single-crystal-like particle is... g The concentration of element G on the surface of the single-crystal-like particle, C1, can be obtained by testing at different locations on the surface and taking the average value; the concentration of element G in the bulk phase of the single-crystal-like particle, C2, can be obtained by testing at different central locations inside the grain and taking the average value.

[0045] According to the present invention, the major diameter D1 of the quasi-single crystal particles satisfies 0.1μm≤D1≤20μm, and the minor diameter D2 satisfies 0.1μm≤D2≤20μm.

[0046] According to the present invention, the major diameter D3 of the grain satisfies 0.1μm≤D3≤12μm, and the minor diameter D4 satisfies 0.1μm≤D4≤12μm.

[0047] According to the present invention, the width of the grain boundary is 1-50 nm, and the difference between the maximum width of the grain boundary and the minimum width of the grain boundary is less than or equal to 20 nm.

[0048] In the present invention, the width of the grain boundary refers to the distance between the surfaces of adjacent grains on both sides of the grain boundary along the direction perpendicular to the surface of the material. The width of the grain boundary is measured by a scanning electron microscope method. When the difference between the maximum value and the minimum value of the width of the grain boundary exceeds 20 nm, the concentration of element G at the position where the grain boundary is relatively wide increases, and the concentration of element G at this site does not apply to the formula shown in Formula II.

[0049] In the present invention, the addition of the grain boundary stabilizer does not change the total length L of the grain boundaries, the major diameter D1 of the single-crystal-like grains, the minor diameter D2 of the single-crystal-like grains, the major diameter D3 of the grains, the minor diameter D4 of the grains, the width (H) of the grain boundary, and the difference between the maximum value (H max ) and the minimum value (H min ) of the width of the grain boundary of the polycrystalline cathode material. The total length L of the grain boundaries, the major diameter D1 of the single-crystal-like grains, the minor diameter D2 of the single-crystal-like grains, the major diameter D3 of the grains, the minor diameter D4 of the grains, the width (H) of the grain boundary, and the difference between the maximum value (H max ) and the minimum value (H max ) of the width of the grain boundary of the single-crystalline polycrystalline cathode material are the same as those of the polycrystalline cathode matrix material before being mixed and sintered with the grain boundary stabilizer.

[0050] In the present invention, the total length L of the grain boundaries, the major diameter D1 of the single-crystal-like grains, the minor diameter D2 of the single-crystal-like grains, the major diameter D3 of the grains, the minor diameter D4 of the grains, the width (H) of the grain boundary, the maximum value (H max ) and the minimum value (H max ) of the width of the grain boundary in the polycrystalline cathode material are measured by SEM. Specifically, 300 single-crystal-like grains of the polycrystalline cathode material are randomly selected as samples in the SEM image of the polycrystalline cathode material, and the average value is taken.

[0051] According to the present invention, the single-crystalline polycrystalline cathode material includes a matrix and a coating layer coated on the matrix;

[0052] The matrix has the composition shown in Formula III:

[0053] Li 1+a (Ni x Co y Me z M w )O2 Formula III;

[0054] Where, -0.1 ≤ a ≤ 0.1, 0 < x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.6, 0 ≤ w ≤ 0.2; Me is selected from Mn and / or Al; M is at least one element selected from Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, and Ba;

[0055] The coating layer is selected from lithium oxide compounds of element G and / or oxides of element G;

[0056] G is at least one element selected from Ni, Co, Mn, Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, and B;

[0057] The molar ratio of the coating layer to the matrix, calculated as [n(G) + n(Co) + n(Me) + n(M)], is 0.001-0.05.

[0058] Furthermore, -0.06 ≤ a ≤ 0.06, 0.4 <x<1,0<y≤0.3,0<z≤0.5,0<w≤0.1。

[0059] Furthermore, Me is selected from Mn and / or Al.

[0060] Furthermore, M is at least one element selected from W, La, Al, Y, Ti, Zr, Nb, Ce, Mg, and Sr.

[0061] Furthermore, G is at least one element selected from Mn, Co, W, La, Al, Ti, Zr, and Nb.

[0062] Furthermore, the molar ratio of the coating layer to the matrix, calculated as [n(G) + n(Co) + n(Me) + n(M)], is 0.005-0.04.

[0063] A second aspect of the present invention provides a method for preparing a single-crystal multi-element cathode material, characterized in that the preparation method includes:

[0064] The single-crystal multi-element cathode material matrix is ​​obtained by mixing a grain boundary stabilizer containing G element and then sintering it.

[0065] Wherein, the element G is selected from at least one of Ni, Co, Mn, Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, Ba and B;

[0066] The grain boundary stabilizer has a D50 of 0.01-10 μm, and the grain boundary stabilizer has D10, D50, and D90 satisfying: K90=(D90-D10) / D50≥1.5.

[0067] In this invention, a multi-element cathode material matrix is ​​mixed with a grain boundary stabilizer containing G element and having a specific particle size and distribution, and then sintered to obtain the single-crystal multi-element cathode material described in the first aspect of this invention. Specifically, the cathode material comprises quasi-single-crystal particles composed of multiple grains, and G element is present at the grain boundaries between the grains. The concentration of G element at the g-site of the grain boundary gradually decreases as the distance between the g-site and the surface of the quasi-single-crystal particle increases. The G element fully penetrates and fills the grain boundaries of the cathode material, which can reduce the stress concentration at the grain boundaries caused by the change in unit cell volume during charge-discharge cycles, improve the grain boundary stability of the cathode material, and significantly improve the cycle life of lithium-ion batteries containing this cathode material. At the same time, the improved grain boundary stability and fewer grain boundary cracking phenomena also reduce the generation of fresh internal interfaces. Under multiple cycles and long-term storage conditions, the impedance increase of lithium-ion batteries containing this cathode material is lower.

[0068] In particular, the preparation method of the single-crystal multi-element cathode material provided by the present invention is simple in process and easy to control, and is suitable for industrial production.

[0069] Furthermore, the G element is selected from at least one of Mn, Co, W, La, Al, Ti, Zr, and Nb.

[0070] Furthermore, the grain boundary stabilizer is selected from at least one of oxides, hydroxy oxides, hydroxides, fluorides, sulfates, nitrates, carbonates, and oxalates containing the element G.

[0071] Furthermore, the grain boundary stabilizer has a D50 of 0.1-8 μm, and the grain boundary stabilizer has D10, D50, and D90 satisfying: K90=(D90-D10) / D50≥2.

[0072] According to the present invention, the specific surface area of ​​the grain boundary stabilizer is greater than or equal to 10 m². 2 / g.

[0073] In this invention, an interface stabilizer with a large specific surface area is used, which is beneficial for its uniform dispersion with the material during the mixing process. Furthermore, the high specific surface area of ​​the interface stabilizer enables it to achieve higher reactivity, which is beneficial for diffusion into the grain boundary during the sintering process, thereby achieving a better grain boundary gradient filling effect.

[0074] Furthermore, the specific surface area of ​​the grain boundary stabilizer is 20-100 m². 2 / g.

[0075] According to the present invention, the amount of the grain boundary stabilizer added is 0.001≤n(G)n[n(Ni)+n(Co)+n(Me)+n(M)]≤0.05 according to the stoichiometric ratio.

[0076] In this invention, when the amount of grain boundary stabilizer is too low, i.e., n(G) / [n(Ni)+n(Co)+n(Me)+n(M)] is less than 0.001, the proportion of G element added is too low, and the gradient effect cannot be achieved. When the amount of grain boundary stabilizer is too high, i.e., n(G) / [n(Ni)+n(Co)+n(Me)+n(M)] is greater than 0.05, it will cause excessive accumulation of G element on the particle surface, thereby inhibiting the electrochemical activity of the multi-element cathode material, and the excessive G element consumes more active Li. + This reduces the capacity of the battery containing the multi-element cathode material; when the amount of grain boundary stabilizer is controlled within the above range, the optimal grain boundary concentration gradient of element G can be achieved, thereby realizing the technical effect of the present invention.

[0077] Furthermore, the amount of the grain boundary stabilizer added is based on a stoichiometric ratio of 0.005≤n(G) / [n(Ni)+n(Co)+n(Me)+n(M)]≤0.04.

[0078] In this invention, when two or more grain boundary stabilizers are mixed with a multi-element cathode material matrix to prepare a single-crystal multi-element cathode material, there is no particular limitation on the amount of each of the various grain boundary stabilizers, as long as the total amount of grain boundary stabilizers added meets the above-mentioned range.

[0079] According to the present invention, the mixing conditions include: mixing is carried out in a device containing an agitator, wherein the linear velocity of the blade tip of the agitator is greater than or equal to 20 m / s.

[0080] In this invention, mixing under the above conditions can provide high mixing intensity, ensuring that the grain boundary stabilizer and the multi-element cathode material are fully and uniformly mixed, while also having a certain grinding effect on the grain boundary stabilizer, causing the tiny powder to gather at the grain boundaries on the surface of the single-crystal particles, so that it can more easily penetrate and fill into the grain boundaries during sintering.

[0081] In this invention, there is no particular limitation on the equipment containing a stirring paddle, as long as the equipment contains a stirring paddle, such as a rotary mixing equipment with a stirring paddle, such as a plow mixer, a high-speed mixer, a mechanical fusion machine, etc.

[0082] In this invention, the linear velocity v at the blade tip is equal to the blade diameter × π × rotational speed.

[0083] Furthermore, the mixing conditions include mixing in a device containing an agitator, wherein the blade tip linear velocity of the agitator is 30-50 m / s.

[0084] According to the present invention, the sintering conditions include: a sintering temperature of 400°C or higher; and a sintering time of 4 hours or higher.

[0085] In the present invention, sintering under the above conditions can achieve the effective diffusion and reaction of the grain boundary stabilizer, ensure that it enters the grain boundary to a sufficient depth, and form the effect of gradient filling. When the temperature is too low or the time is too short, the sufficient reaction of the grain boundary stabilizer cannot be achieved, and the technical effect of the present invention cannot be achieved. When the temperature is too high or the time is too long, the crystal structure of the multi-component material will change, resulting in the performance loss of the cathode material.

[0086] Furthermore, the conditions for the sintering include: the sintering temperature is 600 - 900 °C; the sintering time is 6 - 10 h.

[0087] In the present invention, there is no particular limitation on the type of the multi-component cathode material, which can be a conventional multi-component cathode material in the art, preferably a lithium nickel cobalt manganese oxide cathode material and / or a lithium nickel cobalt aluminum oxide cathode material.

[0088] In a specific embodiment of the present invention, the multi-component cathode material matrix has the composition shown in Formula IV:

[0089] Li 1+a (Ni x Co y Me z M w )O2 Formula IV;

[0090] Where, -0.1 ≤ a ≤ 0.1, 0 < x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.6, 0 ≤ w ≤ 0.2; Me is selected from Mn and / or Al; M is at least one of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr and Ba. <00​​​​​​​​​​​​​​​​After mixing the cathode material precursor, lithium source, and dopant, heat treatment is carried out to obtain the multi-component cathode material.

[0097] In the present invention, the cathode material precursor has the composition shown in Formula V:

[0098] Ni x Co y Me z (OH)2 Formula V;

[0099] where 0 < x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.6; Me is selected from Mn and / or Al.

[0100] In the present invention, the lithium source can be a conventional lithium source in the art, such as Li2CO3 and / or LiOH, etc.

[0101] In the present invention, the dopant is a compound containing M, where M is selected from at least one element of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, and Ba.

[0102] In the present invention, the amounts of the lithium source and the cathode material precursor are such that 0.9 ≤ n(Li) / [n(Ni) + n(Co) + n(Me) + n(M)] ≤ 1.1, preferably, 0.94 ≤ n(Li) / [n(Ni) + n(Co) + n(Me) + n(M)] ≤ 1.06.

[0103] In the present invention, the amounts of the dopant and the cathode material precursor are such that 0 ≤ n(M) / [n(Ni) + n(Co) + n(Me) + n(M)] ≤ 0.2, preferably, 0 ≤ n(M) / [n(Ni) + n(Co) + n(Me) + n(M)] ≤ 0.1.

[0104] In the present invention, the dopant can undergo mixed-site with Ni, Co, and Me in the cathode material precursor, such that n(Ni) + n(Co) + n(Me) + n(M) = 1 in the prepared cathode material. However, when the amount of the dopant is low, its content cannot be accurately measured by existing detection means; at this time, the influence of the doping element M on the proportion of Ni, Co, and Me is small, making n(Ni) + n(Co) + n(Me) + n(M) in the expression slightly greater than 1. [[ID=3l]]

[0105] In the present invention, the conditions of the heat treatment include: the heat treatment temperature is 850 - 950 °C, and the heat treatment time is 8 - 10 h.

[0106] In the third aspect of the present invention, a single-crystalline multi-component cathode material prepared by the above preparation method is provided.

[0107] A fourth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned single-crystal multi-element cathode material.

[0108] The present invention will be described in detail below through embodiments. In the following embodiments,

[0109] The composition of the single-crystal multi-element cathode material was determined by inductively coupled plasma spectroscopy.

[0110] The concentration of G element in the single-crystal multi-element cathode material was determined by scanning electron microscopy energy dispersive spectroscopy.

[0111] The grain boundary length, grain boundary width, major axis, and minor axis of the quasi-single-crystal particles in the single-crystal type multi-element cathode material were measured by scanning electron microscopy.

[0112] The major and minor axes of the grains in the single-crystal multi-element cathode material were measured using scanning electron microscopy.

[0113] The D10, D50, and D90 of the grain boundary stabilizer were measured by laser diffraction according to GB / T 19077-2016.

[0114] The specific surface area of ​​the grain boundary stabilizer was measured using the BET method according to GB-T19587-2017.

[0115] The cycle life, energy density, and rate performance of lithium-ion batteries were tested using 2025 coin cells.

[0116] The specific manufacturing process of the 2025 coin cell is as follows:

[0117] Electrode preparation: A homogeneous slurry is formed by thoroughly mixing a multi-element positive electrode material, acetylene black, and polyvinylidene fluoride (PVDF) at a mass ratio of 95:3:2 with an appropriate amount of N-methylpyrrolidone (NMP). The slurry is coated onto aluminum foil and dried at 120°C for 12 hours. Then, it is pressed into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. The loading of the multi-element positive electrode material is 15-16 mg / cm³. 2 .

[0118] Battery Assembly: In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into a 2025 coin cell and then left to stand for 6 hours. The negative electrode used a 17 mm diameter, 1 mm thick lithium metal sheet; the separator used a 25 μm thick polyethylene porous membrane (Celgard 2325); and the electrolyte used was a 1 mol / L mixture of equal parts LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0119] Electrochemical performance testing:

[0120] In the following examples and comparative examples, the electrochemical performance of the 2025 coin cell was tested using the Shenzhen Xinwei Battery Testing System, with a charge / discharge current density of 200 mA / g at 0.1C.

[0121] The charge / discharge voltage range was controlled between 3.0 and 4.3V. At room temperature, the coin cell was charged and discharged at 0.1C to evaluate the initial discharge specific capacity of the multi-element cathode material.

[0122] Cyclic performance test: The charge and discharge voltage range was controlled at 3.0-4.3V. At a constant temperature of 45℃, the coin cell was charged and discharged twice at 0.1C and then charged and discharged 80 times at 1C to evaluate the high-temperature capacity retention of the multi-element cathode material.

[0123] Rate performance testing: The charge / discharge voltage range was controlled at 3.0-4.3V. At room temperature, the coin cell was cycled twice at 0.1C, and then once each at 0.2C, 0.33C, 0.5C, and 1C. The rate performance of the multi-element cathode material was evaluated by the ratio of the initial discharge specific capacity at 0.1C to the discharge specific capacity at 1C. The initial discharge specific capacity at 0.1C is the discharge specific capacity of the coin cell in the first cycle, and the discharge specific capacity at 1C is the discharge specific capacity of the coin cell in the sixth cycle.

[0124] Impedance increase rate test: The charge / discharge voltage range was controlled between 3.0-4.3V. The coin cell was capacitively charged at 0.1C at room temperature, and the HPPC-DCR at 50% SOC was tested, marked as the initial impedance R1. Then, the coin cell was charged and discharged twice at 0.1C at a constant temperature of 45℃, and then charged and discharged 80 times at 1C. After cycling, the coin cell was capacitively charged at 0.1C at room temperature, and the HPPC-DCR at 50% SOC was tested, marked as the post-cycle impedance R2. The impedance increase rate of the material was calculated using the formula (R2-R1) / R1×100%.

[0125] Preparation Example

[0126] This is used to illustrate the preparation method of multi-element cathode materials.

[0127] Preparation Example 1

[0128] Ni 0.6 Co 0.2 Mn 0.2The (OH)2 precursor, lithium source Li2CO3, LiOH, and dopant containing Al were mixed at molar ratios of n(Li) / [n(Ni)+n(Co)+n(Mn)+n(Al)]=1.05 and n(Al) / [n(Ni)+n(Co)+n(Mn)+n(Al)]=0.1, and then heat-treated at 900℃ for 10 h to prepare the multi-element cathode material P1, whose composition is: Li 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 O2.

[0129] Preparation Example 2

[0130] Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor, lithium source LiOH, and dopant containing Zr compound were mixed in molar ratios of n(Li) / [n(Ni)+n(Co)+n(Mn)+n(Zr)]=1.05 and (n(Zr) / [n(Ni)+n(Co)+n(Mn)+n(Zr)]=0.002, and then heat-treated at 850℃ for 10 h to prepare the multi-element cathode material P2, whose composition is Li 1.05 Ni 0.8 Co 0.1 Mn 0.1 Zr 0.002 O2.

[0131] Preparation Example 3

[0132] Ni 0.96 Co 0.02 Al 0.02 The (OH)2 precursor, lithium source LiOH, and Ti-containing dopant compound were mixed at n(Li) / [n(Ni)+n(Co)+n(Al)+n(Ti)]=1.03 and n(Ti) / [n(Ni)+n(Co)+n(Al)+n(Ti)]=0.001, and then heat-treated at 800℃ for 10 h to prepare the multi-element cathode material P3, whose composition is Li 1.03 Ni 0.96 Co 0.0 2Al 0.02 Ti 0.001 O2.

[0133] Preparation Example 4

[0134] Ni 0.6 Co 0.2 Mn 0.2The (OH)2 precursor, lithium source Li2CO3, and LiOH were mixed at a molar ratio of n(Li) / [n(Ni)+n(Co)+n(Mn)]=1.05, and then heat-treated at 900℃ for 10 h to prepare the multi-element cathode material P4, whose composition is: Li 1.05 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0135] The total length L, width (H), and maximum width (H) of grain boundaries in the multi-element cathode material in the preparation example are discussed. max ) and minimum value (H) min The differences between the two, the major diameter D1 and minor diameter D2 of the single-crystal-like particles, and the major diameter D3 and minor diameter D4 of the grains were tested, and the results are shown in Table 1.

[0136] Table 1

[0137] L H <![CDATA[H max -H min ]]> <![CDATA[D1]]> <![CDATA[D2]]> <![CDATA[D3]]> <![CDATA[D4]]> Preparation Example 1 4.7 23 4 6.2 4.6 2.6 1.8 Preparation Example 2 3.5 19 6 4.5 4.1 1.7 1.3 Preparation Example 3 3.2 20 4 3.7 3.4 1.6 1 Preparation Example 4 4.5 22 5 5.3 5.1 2.3 2

[0138] Example 1

[0139] (1) The multi-element cathode material P1 is mixed with cobalt hydroxide powder to obtain a mixture. The mixing equipment is a high-speed mixer with a blade tip linear velocity of 35 m / s. The multi-element cathode material and cobalt hydroxide are added according to a stoichiometric ratio of n(Co) / [n(Ni)+n(Co)+n(Mn)+n(Al)]=0.025. The cobalt hydroxide powder contains both nano- and submicron-sized particles with a D50=0.5μm and K90=2.3 and a specific surface area of ​​20m². 2 / g.

[0140] (2) The mixture is sintered at 750°C for 6 hours in an oxygen atmosphere to obtain the single-crystal multi-element cathode material Al, which includes a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Mn)+n(Al)], is 0.025.

[0141] Example 2

[0142] (1) The multi-element cathode material P1 is mixed with tungsten oxide powder to obtain a mixture. The mixing equipment is a high-speed mixer with a blade tip linear velocity of 35 m / s. The multi-element cathode material P1 and tungsten oxide are added according to a stoichiometric ratio of n(W) / [n(Ni)+n(Co)+n(Mn)+n(Al)]=0.025. The tungsten oxide powder contains both nano- and submicron-sized particles with a D50=4μm, K90=3.4, and a specific surface area of ​​14m². 2 / g.

[0143] (2) The mixture is sintered at 750°C for 6 hours in an oxygen atmosphere to obtain the single-crystal multi-element cathode material A2, which includes a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 The coating layer is mainly composed of lithium tungsten oxide, with a small amount of tungsten oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Mn)+n(Al)], is 0.025.

[0144] Example 3

[0145] (1) The multi-element cathode material P1 is mixed with titanium boride powder to obtain a mixture. The mixing equipment is a high-speed mixer with a blade tip linear velocity of 35 m / s. The cathode material and titanium boride are added according to a stoichiometric ratio of n(Ti) / [n(Ni)+n(Co)+n(Mn)+n(Al)]=0.025. The titanium boride powder contains both nano- and submicron-sized particles with a D50=1μm, K90=5.6, and a specific surface area of ​​45m². 2 / g.

[0146] (2) The mixture is sintered at 750°C for 6 hours in an oxygen atmosphere to obtain the single-crystal multi-element cathode material A3, which includes a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 The coating layer is mainly composed of lithium titanium oxide, and also contains a small amount of titanium oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ti)], is 0.025.

[0147] Example 4

[0148] (1) The multi-element cathode material P1 is mixed with alumina powder to obtain a mixture. The mixing equipment is a high-speed mixer with a blade tip linear velocity of 35 m / s. The cathode material and alumina are added according to a stoichiometric ratio of n(Al) / [n(Ni)+n(Co)+n(Mn)+n(Al)]=0.025. The alumina powder contains both nano- and submicron-sized particles with a D50=3.8μm and K90=2, and a specific surface area of ​​78m². 2 / g.

[0149] (2) The mixture is sintered at 750°C for 6 hours in an oxygen atmosphere to obtain the single-crystal multi-element cathode material A4, which includes a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 The O2 coating layer mainly consists of lithium aluminum oxide, with a small amount of aluminum oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Al)], is 0.025.

[0150] Example 5

[0151] (1) The multi-element cathode material P1 is mixed with alumina and zirconium oxide powder to obtain a mixture. The mixing equipment is a high-speed mixer with a blade tip linear velocity of 35 m / s. The alumina is added according to the stoichiometric ratio of n(Al) / [n(Ni)+n(Co)+n(Mn)+n(Al)] = 0.025. The zirconium oxide is added according to the stoichiometric ratio of n(Zr) / [n(Ni)+n(Co)+n(Mn)+n(Al)] = 0.025. The alumina powder contains nano- and submicron-sized particles with D50 = 3.8 μm, K90 = 2, and a specific surface area of ​​78 m². 2 / g; the zirconium oxide powder contains nano- and submicron-sized particles with D50 = 6 μm, K90 = 2.8, and a specific surface area of ​​34 m². 2 / g.

[0152] (2) The mixture is sintered at 600°C for 8 hours in an oxygen atmosphere to obtain a single-crystal multi-element cathode material A5, which includes a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1The O2 coating layer mainly comprises lithium aluminum oxide and lithium zirconium oxide, and also contains a small amount of aluminum oxide and zirconium oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Al) + n(Zr)], is 0.05. In the coating layer, the molar ratio of aluminum oxide and lithium aluminum oxide to the substrate, calculated as [n(Ni) + n(Co) + n(Mn) + n(Al)], is 0.025. Similarly, the molar ratio of zirconium oxide and lithium zirconium oxide to the substrate, calculated as [n(Ni) + n(Co) + n(Mn) + n(Al)], is 0.025.

[0153] Example 6

[0154] A single-crystal multi-element cathode material was prepared according to the method of Example 1, except that P2 was used instead of P1. A single-crystal multi-element cathode material A6 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.05 Ni 0.8 Co 0.1 Mn 0.1 Zr 0.002 The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Mn)+n(Zr)], is 0.025.

[0155] Example 7

[0156] A single-crystal multi-element cathode material was prepared according to the method of Example 1, except that P3 was used instead of P1. A single-crystal multi-element cathode material A7 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.03 Ni 0.96 Co 0.02 Al 0.02 Ti 0.001 The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Al)+n(Ti)], is 0.025.

[0157] Example 8

[0158] A single-crystal multi-element cathode material was prepared according to the method of Example 1, except that P4 was used instead of P1. A single-crystal multi-element cathode material A8 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.05 Ni 0.6 Co 0.2 Mn0.2 The coating layer is mainly composed of lithium cobalt oxide, with a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Co)], is 0.025.

[0159] Example 9

[0160] A single-crystal multi-element cathode material was prepared according to the method of Example 1, except that the multi-element cathode material and cobalt hydroxide were added at a stoichiometric ratio of n(Co) / [n(Ni)+n(Co)+n(Mn)+n(Al)] = 0.001. A single-crystal multi-element cathode material A9 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.05 Ni 0.6 Co 0.2 Mn 0.2 The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni) + n(Co) + n(Mn)], is 0.001.

[0161] Example 10

[0162] A single-crystal multi-element cathode material was prepared according to the method of Example 1, except that the linear velocity at the tip of the stirring impeller was 10 m / s. A single-crystal multi-element cathode material A10 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Mn)+n(Al)], is 0.025.

[0163] Example 11

[0164] Single-crystal multi-element cathode material was prepared according to the method of Example 1, except that the sintering temperature was 400℃. Single-crystal multi-element cathode material A11 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Mn)+n(Al)], is 0.025.

[0165] Example 12

[0166] Single-crystal multi-element cathode material was prepared according to the method of Example 1, except that the sintering time was 2 hours. Single-crystal multi-element cathode material A12 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Mn)+n(Al)], is 0.025.

[0167] Comparative Example 1

[0168] Single-crystal multi-element cathode material was prepared according to the method of Example 1, except that the cobalt hydroxide powder contained only submicron particles with D50 = 14 μm and K90 = 1; the specific surface area was 6 m². 2 / g. A single-crystal multi-element cathode material D1 was obtained, comprising a matrix and a coating layer covering the matrix, wherein the matrix is ​​composed of Li. 1.05 Ni 0.54 Co 0.18 Mn 0.18 Al 0.1 The coating layer is mainly composed of lithium cobalt oxide, and also contains a small amount of cobalt oxide. The molar ratio of the coating layer to the substrate, calculated as [n(Ni)+n(Co)+n(Mn)+n(Al)], is 0.025.

[0169] Comparative Example 2

[0170] Ni 0.6 Co 0.2 Mn 0.2The (OH)2 precursor, lithium sources Li2CO3 and LiOH, and Al-containing dopants were mixed at molar ratios of n(Li) / [n(Ni)+n(Co)+n(Mn)+n(Al)] = 1.05 and n(Al) / [n(Ni)+n(Co)+n(Mn)+n(Al)] = 0.1. Then, cobalt hydroxide powder was added at a molar ratio of n(Co) / [n(Ni)+n(Co)+n(Mn)+n(Al)] = 0.025. The cobalt hydroxide powder contained both nano- and submicron-sized particles with a D50 of 0.5 μm, K90 of 2.3, and a specific surface area of ​​20 m². 2 / g, and heat-treated at 900℃ for 10h to prepare the multi-element cathode material D2, whose composition is Li 1.05 Ni 0.53 Co 0.2 Mn 0.18 Al 0.09 O2.

[0171] Table 2

[0172]

[0173] Table 2 (continued)

[0174]

[0175] The coherence C1 and C2 at different sites of G element in the preparation examples, embodiments, and comparative examples of the multi-element cathode materials were compared. g The C2 (mol%) was tested, and the results are shown in Table 3.

[0176] It should be noted that in Table 3, the standard used to calculate the proportion of data that satisfy Equation II is related to the content of element G. Specifically, when C1>5%, the value of k ranges from 0.9 to 1.1; when C1≤5%, the value of k ranges from 0.8 to 1.2.

[0177] Table 3

[0178]

[0179]

[0180] Table 3 (continued)

[0181]

[0182] Table 3 (continued)

[0183]

[0184]

[0185] Table 3 (continued)

[0186]

[0187] Table 3 (continued)

[0188]

[0189]

[0190] Table 3 (continued)

[0191]

[0192] Table 3 (continued)

[0193]

[0194]

[0195] Table 3 (continued)

[0196]

[0197] Table 3 (continued)

[0198]

[0199] Table 4 shows the coefficient k values ​​calculated according to Equation II at each point in the embodiments and comparative examples.

[0200] It should be noted that in Table 4, the standard used to calculate whether the data meets the data ratio of Equation II is related to the content of element G. Specifically, when C1>5%, the value of k ranges from 0.9 to 1.1; when C1≤5%, the value of k ranges from 0.8 to 1.2.

[0201] Table 4

[0202]

[0203]

[0204] Table 4 (continued)

[0205]

[0206] Table 4 (continued)

[0207]

[0208] Table 4 (continued)

[0209]

[0210] Table 4 (continued)

[0211]

[0212] Table 4 (continued)

[0213]

[0214]

[0215] Table 4 (continued)

[0216]

[0217] Table 4 (continued)

[0218]

[0219]

[0220] Table 4 (continued)

[0221]

[0222] Figure 2 This is a schematic diagram showing that cobalt hydroxide, a grain boundary stabilizer, contains micron and submicron ions. Figure 2 It can be seen that the grain boundary stabilizer has a wide particle size distribution and obvious differences in particle size; Figure 3 This is a cross-sectional schematic diagram of the single-crystal multi-element cathode material prepared in Example 1. The numbers in the figure are examples of test points for element concentration within the grain boundaries.

[0223] The cathode materials prepared in the examples, embodiments, and comparative examples were assembled into lithium-ion batteries, and the electrochemical performance of the lithium-ion batteries was tested. The results are shown in the table below.

[0224] Table 5

[0225]

[0226]

[0227] As can be seen from Tables 3, 4, and 5, compared to Preparation Example 1 and Comparative Examples 1-2, the cathode materials prepared by Examples 1-12 of this invention all contain interface stabilizer elements, and the concentration of G element at the grain boundary g-site gradually decreases as the distance between the g-site and the surface of the single-crystal-like particle increases. When the above cathode materials are used in lithium-ion batteries, they can significantly improve and enhance the initial discharge capacity, rate performance, and cycle performance of lithium-ion batteries, and reduce the impedance increase rate.

[0228] Furthermore, compared to Examples 9-12, the concentration gradient of the grain boundary stabilizer in the grain boundaries of the cathode materials prepared in Examples 1-8 is more significant. In Examples 9-12, the uniformity of the gradient distribution is slightly worse, the concentration of the material is higher at the surface, while the concentration difference near the interior of the particles is smaller, and there are some data that exceed the calculation range of Formula II. When the cathode materials prepared in Examples 1-8 are used in lithium-ion batteries, the lithium-ion batteries can simultaneously have high initial discharge specific capacity, rate performance, and cycle performance, with a lower impedance increase rate, and the battery has the best overall performance.

[0229] Furthermore, Examples 2-4 show cathode materials prepared with different types of grain boundary stabilizers, all of which have good grain boundary concentration gradient filling effect. When the above cathode materials are used in lithium-ion batteries, they can improve and enhance the first discharge capacity, rate performance, cycle performance and impedance increase rate of lithium-ion batteries.

[0230] Furthermore, Example 5 presents cathode materials prepared with two different types of grain boundary stabilizers. It can be seen that both stabilizers have a concentration gradient filling effect. However, due to the larger total amount of grain boundary stabilizer added, the capacity of the battery decreases slightly when used in lithium-ion batteries, but the cycle performance is relatively better.

[0231] Furthermore, it can be seen from Examples 6 and 7 that the same effect can be obtained for different NCM compositions; in particular, in Example 7, due to the overall low concentration, the calculation range of Formula II is narrow. Due to the limitations of test stability, the percentage of points that meet the calculation range is 89%. However, this situation does not affect the determination of the gradient concentration effect or the improvement of various battery performances when it is used in lithium-ion batteries.

[0232] Furthermore, as can be seen from Example 8, whether the cathode material is doped or not does not affect the improvement effect of the grain boundary stabilizer filling the concentration gradient at the grain boundary.

[0233] In the cathode material prepared in Comparative Example 1, since the grain boundary stabilizer only contains micron-sized particles with a narrow particle size distribution, the overall reactivity is low. The main element of the grain boundary stabilizer is enriched on the outer surface of the single-crystal-like particles and cannot diffuse smoothly into the grain boundary. The effect of filling the concentration gradient in the grain boundary is not achieved. When used in lithium-ion batteries, the overall performance is close to that of Preparation Example 1 and cannot reach the performance level of Example 1. Figure 4 This is a comparison chart of the cycling performance of the cathode materials prepared in Example 1, Example 1, and Comparative Example 1 at a 1C rate. Figure 4 The performance difference is obvious.

[0234] The cathode material prepared in Comparative Example 2 was prepared by adding a grain boundary stabilizer during the precursor and lithium salt mixing stage and then sintering. The results show that there is no concentration difference between the surface and the bulk phase, and there is no concentration gradient distribution effect at the grain boundaries. When applied to lithium-ion batteries, its performance is not significantly improved compared to that of Preparation Example 1.

[0235] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A single-crystal multi-element cathode material, characterized in that, The multi-component cathode material comprises single-crystal-like particles composed of multiple grains, and element G exists at the grain boundaries between the grains; Among them, the concentration of element G at the g-site of the grain boundary gradually decreases as the distance between the g-site and the surface of the single-crystal-like particle increases; The element G is selected from at least one of Ni, Co, Mn, Ta, Cr, Mo, W, La, Y, Ti, V, Nb, Ce, Er, and B; Among them, in the SEM image of the cross-sectional sample of the single-crystal-like particle, the concentration of element G at the g-site of the grain boundary satisfies the following relationship: 1.2 C1≥C g ≥0.8 C2 Formula I; Among them, C1 is the concentration of element G on the surface of the single-crystal-like particle, mol%; C2 is the concentration of element G in the bulk phase of the single-crystal-like particle, mol%; In the SEM image of the cross-sectional sample of the single-crystal-like particle, the concentration of element G at the g-site of the grain boundary satisfies the following relationship: Formula II; wherein C g is the concentration of G element at the g site of the grain boundary, mol%; L is the total length of the grain boundary passing through the g site, pm; L g is the shortest path length from the g site to the surface of the single-crystal-like particle along the grain boundary, pm; k is a coefficient, and the value range of k is 0.8-1.2; the single-crystal-type multi-element positive electrode material comprises a matrix and a coating layer coated on the matrix; The matrix has the composition shown in Formula III: Li 1+a (Ni x Co y Me z M w )O2formula III; Among them, -0.1 ≤ a ≤ 0.1, 0.8 ≤ x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.6, 0 ≤ w ≤ 0.2; Me is selected from Mn and / or Al; M is at least one element of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, and Ba; The coating layer is selected from lithium oxides of element G and / or oxides of element G; Calculated by n(G), the molar ratio of the coating layer to the matrix calculated by [n(Ni) + n(Co) + n(Me) + n(M)] is 0.001 - 0.05; The major axis D1 of the single-crystal-like particle satisfies 3.7 μm ≤ D1 ≤ 20 μm, and the minor axis D2 satisfies 3.4 μm ≤ D2 ≤ 20 μm; The major axis D3 of the grain satisfies 0.1 μm ≤ D3 ≤ 2.6 μm, and the minor axis D4 satisfies 0.1 μm ≤ D4 ≤ 2 μm.

2. The single-crystal multi-element cathode material according to claim 1, wherein, The element G is selected from at least one of Mn, Co, W, La, Ti, and Nb.

3. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, 1.1 C1≥C g ≥0.9 C2.

4. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, The total length L of the grain boundary obtained by scanning electron microscopy energy spectrum analysis satisfies 0.01 μm ≤ L ≤ 8 μm.

5. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, The total length L of the grain boundary obtained by scanning electron microscopy energy spectrum analysis satisfies 0.1 μm ≤ L ≤ 5 μm.

6. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, C1 - C2 ≥ 0.1%.

7. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, C1 - C2 ≥ 0.2%.

8. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, The width of the grain boundary is 1 - 50 nm, and the difference between the maximum value and the minimum value of the width of the grain boundary is less than or equal to 20 nm.

9. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, -0.06 ≤ a ≤ 0.06, 0.8 ≤ x < 1, 0 < y ≤ 0.3, 0 < z ≤ 0.5, 0 < w ≤ 0.

1.

10. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, Me is selected from Mn and / or Al; M is at least one element of W, La, Al, Y, Ti, Zr, Nb, Ce, Mg, and Sr.

11. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, G is at least one element of Mn, Co, W, La, Al, Ti, Zr, and Nb.

12. The single-crystal multi-element cathode material according to claim 1 or 2, wherein, Calculated by n(G), the molar ratio of the coating layer to the matrix calculated by [n(Ni) + n(Co) + n(Me) + n(M)] is 0.005 - 0.

04.

13. A method for preparing a single-crystal multi-element cathode material according to any one of claims 1-12, characterized in that, The preparation method includes: Mixing the multi-component cathode material matrix with a grain boundary stabilizer containing element G, and then performing sintering treatment to obtain the single-crystal-type multi-component cathode material; Among them, the G element is selected from at least one of Ni, Co, Mn, Ta, Cr, Mo, W, La, Y, Ti, V, Nb, Ce, Er, and B; The D50 of the grain boundary stabilizer is 0.5 - 10 μm, and the D10, D50, and D90 of the grain boundary stabilizer satisfy: K90 = (D90 - D10) / D50 ≥ 1.

5.

14. The preparation method according to claim 13, wherein, The G element is selected from at least one of Mn, Co, W, La, Ti, and Nb.

15. The preparation method according to claim 13 or 14, wherein, The grain boundary stabilizer is selected from at least one of oxides, hydroxyoxides, hydroxides, fluorides, sulfates, nitrates, carbonates, and oxalates containing the G element.

16. The preparation method according to claim 13 or 14, wherein, The D50 of the grain boundary stabilizer is 0.5 - 8 μm, and the D10, D50, and D90 of the grain boundary stabilizer satisfy: K90 = (D90 - D10) / D50 ≥ 2.

17. The preparation method according to claim 13 or 14, wherein, The specific surface area of ​​the grain boundary stabilizer is greater than or equal to 10 m². 2 / g.

18. The preparation method according to claim 13 or 14, wherein, The specific surface area of ​​the grain boundary stabilizer is 20-100 m². 2 / g.

19. The preparation method according to claim 13 or 14, wherein, The addition amount of the grain boundary stabilizer is added according to the stoichiometric ratio of 0.001 ≤ n(G) / [n(Ni) + n(Co) + n(Me) + n(M)] ≤ 0.05; And / or, the conditions for mixing include: mixing in a device with a stirring paddle, and the linear velocity at the end of the paddle of the stirring paddle is greater than or equal to 20 m / s; And / or, the conditions for sintering include: the sintering temperature is above 400 °C; the sintering time is above 4 h.

20. The preparation method according to claim 19, wherein, The addition amount of the grain boundary stabilizer is added according to the stoichiometric ratio of 0.005 ≤ n(G) / [n(Ni) + n(Co) + n(Me) + n(M)] ≤ 0.04; And / or, the conditions for mixing include: mixing in a device with a stirring paddle, and the linear velocity at the end of the paddle of the stirring paddle is 30 - 50 m / s; And / or, the conditions for sintering include: the sintering temperature is 600 - 900 °C; the sintering time is 6 - 10 h.

21. The preparation method according to claim 13 or 14, wherein, The matrix of the polycrystalline cathode material has the composition shown in Formula IV: Li 1+a (Ni x Co y Me z M w )O₂ type IV; Among them, -0.1 ≤ a ≤ 0.1, 0.8 ≤ x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.6, 0 ≤ w ≤ 0.2; Me is selected from Mn and / or Al; M is at least one of Ta, Cr, Mo, W, La, Al, Y, Ti, Zr, V, Nb, Ce, Er, Mg, Sr, and Ba.

22. The preparation method according to claim 21, wherein, -0.06 ≤ a ≤ 0.06, 0.8 ≤ x < 1, 0 < y ≤ 0.3, 0 < z ≤ 0.5, 0 < w ≤ 0.

1.

23. The preparation method according to claim 21, wherein, Me is selected from Mn and / or Al.

24. The preparation method according to claim 21, wherein, M is at least one of W, La, Al, Y, Ti, Zr, Nb, Ce, Mg, and Sr.

25. A lithium-ion battery, characterized in that, The lithium-ion battery includes the single-crystalline polycrystalline cathode material according to any one of claims 1 - 12.

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