Single-crystal nickel-cobalt-manganese positive electrode material, preparation method, positive electrode sheet and lithium ion battery

Abstract

The application provides a single-crystal nickel-cobalt-manganese positive electrode material, a preparation method, a positive electrode sheet and a lithium ion battery. The preparation method comprises the following steps: mixing a nickel-cobalt-manganese precursor, a lithium source and a first additive, first sintering to obtain a first sintered material; mixing the first sintered material and a second additive, second sintering to obtain a second sintered material; mixing the second sintered material and a third additive, third sintering to obtain the single-crystal nickel-cobalt-manganese positive electrode material; the half-peak width a of the (001) crystal face of the nickel-cobalt-manganese precursor and the half-peak width b of the (100) crystal face satisfy the following conditions: 0.30 <= a <= 0.48, 0.38 <= b <= 0.52, and 1.1 <= b / a <= 1.5. The roundness of the single-crystal nickel-cobalt-manganese positive electrode material and the half-peak width of the nickel-cobalt-manganese precursor are combined and quantified, the nickel-cobalt-manganese precursor is screened, and the single-crystal nickel-cobalt-manganese positive electrode material with high roundness and stable structure is prepared by combining the three sintering systems.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to cathode materials, and more particularly to a single-crystal nickel-cobalt-manganese cathode material, its preparation method, cathode sheet, and lithium-ion battery. Background Technology

[0002] Currently, nickel-cobalt-manganese ternary cathode materials (NCM) have become the mainstream choice for power batteries in new energy vehicles due to their excellent comprehensive performance. With the rapid iteration of the new energy vehicle industry, the market's performance requirements for power batteries are becoming increasingly stringent. This has directly driven the breakthrough of ternary cathode materials towards achieving both "high capacity" and "high stability." Single-crystal nickel-cobalt-manganese cathode materials, due to their unique advantages, have become a key area of ​​current research and application.

[0003] However, existing technologies still produce single-crystal nickel-cobalt-manganese cathode materials mostly in the form of near-single crystals or mixtures of near-single crystals and single crystals, and high-purity nickel-cobalt-manganese ternary cathode materials are still difficult to prepare.

[0004] CN111600015A discloses a narrow-distribution, small-particle-size spherical nickel-cobalt-manganese hydroxide precursor material and its preparation method. The prepared spherical nickel-cobalt-manganese hydroxide precursor has good dispersibility, unique morphology, high compaction density, and concentrated pitch distribution. The precursor has a D50 of 2~3μm and has stacked lamellar strips with vertically inserted primary particles with a pitch distribution of 0.7~1.0. The stack thickness of the primary particles is between 2~200nm, and the length of the primary particles is between 40~1000nm. It can be used to prepare single-crystal ternary cathode materials. The preparation method is simple to operate, integrating nucleation-crystallization-growth, and is suitable for industrial production needs.

[0005] CN106602055A discloses a small-particle single-crystal lithium nickel cobalt manganese oxide cathode material and its preparation method. By using a spray drying method, precursor fragments are assembled into spheres to achieve the purpose of embedding metal additives into the interior of the spheres. This solves the problem that in dry mixing, metal additives only coat the surface of the precursor and cannot enter the interior of the precursor. The prepared small-particle single-crystal lithium nickel cobalt manganese oxide cathode material has small and uniform particle size, which improves the structural stability of the cathode material.

[0006] CN109786672A discloses a method for preparing a micron-sized single-crystal ternary cathode material, comprising grinding carbonyl nickel, carbonyl cobalt, carbonyl manganese, and tert-butyl lithium at high speed in a sand mill according to a molar ratio, and then sintering in an air atmosphere to obtain a micron-sized single-crystal ternary cathode material. The micron-sized single-crystal ternary cathode material synthesized by this process has advantages such as low specific surface area, concentrated particle size distribution, and high thermal stability. Furthermore, due to its low specific surface area, the material has a lower contact degree with the electrolyte, resulting in a significantly improved cycle life compared to conventional spherical agglomerated materials.

[0007] Therefore, it is of great significance to provide a nickel-cobalt-manganese ternary cathode material with high degree of single crystallization and good structural stability. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a single-crystal nickel-cobalt-manganese (NiCoMn) cathode material, its preparation method, cathode sheet, and lithium-ion battery. This invention combines and quantifies the roundness of the single-crystal NiCoMn cathode material with the full width at half maximum (FWHM) of the XRD characteristic peaks of the NiCoMn precursor to screen the NiCoMn precursor. Simultaneously, it incorporates a three-stage sintering process, adding additives for doping and / or coating during each of the three sintering stages, thereby preparing a single-crystal NiCoMn cathode material with high roundness and good structural stability, thus improving its thermodynamic stability, cycle performance, and high-temperature storage performance.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, the method comprising: mixing a nickel-cobalt-manganese precursor, a lithium source and a first additive, performing a first sintering to obtain a first sintered material; mixing the first sintered material with a second additive, performing a second sintering to obtain a second sintered material; mixing the second sintered material with a third additive, performing a third sintering to prepare the single-crystal nickel-cobalt-manganese cathode material; wherein the half-maximum width a of the (001) crystal plane and the half-maximum width b of the (100) crystal plane of the nickel-cobalt-manganese precursor satisfy: 0.30≤a≤0.48, 0.38≤b≤0.52, 1.1≤b / a≤1.5.

[0011] In this invention, the nickel-cobalt-manganese precursor includes a nickel-cobalt-manganese hydroxide precursor and / or a nickel-cobalt-manganese oxide precursor. The degree of monocrystallization of monocrystalline nickel-cobalt-manganese cathode materials is closely related to their roundness; improving the roundness of monocrystalline nickel-cobalt-manganese cathode materials is an important means to improve their monocrystallization.

[0012] This invention combines and quantifies the roundness of the single-crystal nickel-cobalt-manganese cathode material with the full width at half maximum (FWHM) of the XRD characteristic peaks of the nickel-cobalt-manganese precursor to screen the precursor. Simultaneously, it incorporates a three-stage sintering process, adding additives for doping and / or coating during each of the three sintering stages to prepare a single-crystal nickel-cobalt-manganese cathode material with high roundness and good structural stability, thereby improving the thermodynamic stability, cycle performance, and high-temperature storage performance of the single-crystal nickel-cobalt-manganese cathode material.

[0013] This invention identifies the crystal structure of nickel-cobalt-manganese precursors based on XRD testing technology. The full width at half maximum (FWHM) of the XRD characteristic peaks of the nickel-cobalt-manganese precursors reflects the crystallinity of the corresponding crystal planes. The crystallinity of the (001) and (100) crystal planes of the precursors respectively affects the crystallinity of the (003) and (104) crystal planes during the subsequent preparation of single-crystal nickel-cobalt-manganese cathode materials.

[0014] In single-crystal nickel-cobalt-manganese cathode materials, the crystallinity of the (003) crystal plane mainly affects the roundness of the single-crystal nickel-cobalt-manganese cathode material. When the half-width at half maximum (WHM) of the (001) crystal plane is wide, the (003) crystal plane of the single-crystal nickel-cobalt-manganese cathode material grows preferentially, the lithium-ion diffusion path is better, and the kinetics of the cathode single crystal material are better, but the grain growth is relatively fine. When the WHM of the (001) crystal plane is narrow, the (003) crystal plane of the single-crystal nickel-cobalt-manganese cathode material grows more slowly, the grains tend to be rounder, and the prepared single-crystal nickel-cobalt-manganese cathode material has better thermodynamic stability. The crystallinity of the (104) crystal plane mainly affects the integrity of the layered structure of the single-crystal nickel-cobalt-manganese cathode material. If the half-width of the (100) crystal plane is too wide, it reflects the insufficient crystallinity of the (100) crystal plane, which affects the crystallinity of the (104) crystal plane of the single-crystal nickel-cobalt-manganese cathode material, leading to the intensification of cation mixing in the single-crystal nickel-cobalt-manganese cathode material and causing instability in the material structure. When the half-width of the (100) crystal plane is narrow, it will result in the (003) crystal plane of the single-crystal nickel-cobalt-manganese cathode material being sharp, the grain growth being too fine, and it being difficult to obtain single crystals.

[0015] This invention identifies and filters the full width at half maximum (FWHM) of the (001) and (100) crystal planes, as well as the relationship between their FWHMs, and coordinates their regulation to ensure the preferential growth of the (003) and (104) crystal planes in the single-crystal nickel-cobalt-manganese cathode material during lithiation. This results in more rounded grain growth, leading to a material with higher single-crystallinity and a more complete layered structure, reducing lattice strain during charging and discharging and improving stability. In this invention, the units for FWHMs a and b are "°", corresponding to the diffraction angle "2θ" in the XRD pattern.

[0016] Preferably, the first sintering includes sintering sequentially on a first temperature platform and a second temperature platform, wherein the temperature of the first temperature platform is 40°C to 90°C lower than the temperature of the second temperature platform.

[0017] Preferably, the temperature of the second temperature platform is 800℃~1000℃.

[0018] Preferably, the sintering time on the first temperature platform is 5h to 12h.

[0019] Preferably, the sintering time on the second temperature platform is 8h to 12h.

[0020] Preferably, the temperature of the second sintering is 100°C to 200°C lower than the temperature of the second temperature platform.

[0021] Preferably, the second sintering time is 8h to 15h.

[0022] Preferably, the temperature of the third sintering is 300°C to 600°C lower than the temperature of the second temperature platform.

[0023] Preferably, the third sintering time is 6h to 12h.

[0024] Preferably, the first, second, and third additives each independently include any one or a combination of at least two of ZrO2, Co3O4, Co(OH)2, CoOOH, TiO2, WO3, MoO3, Nb2O5, MnO2, CeO2, La2O3, Y2O3, SrCO3, Al2O3, MgO, B2O3, NaF, P2O5, or SiO2.

[0025] Preferably, the amount of the first additive is 0.3 wt.% to 1.5 wt.% of the mass of the nickel-cobalt-manganese precursor.

[0026] Preferably, the amount of the second additive added is 1 wt.% to 3 wt.% of the mass of the first sintering material.

[0027] Preferably, the amount of the third additive is 0.1 wt.% to 0.5 wt.% of the mass of the second sintering material.

[0028] In a second aspect, the present invention provides a single-crystal nickel-cobalt-manganese cathode material, which is prepared by the preparation method described in the first aspect; the roundness of the single-crystal nickel-cobalt-manganese cathode material is ≥0.8.

[0029] In this invention, the roundness Fc is calculated as follows: using SEM, the average projected area S and average projected perimeter P of the particles are measured respectively. The roundness Fc is then calculated according to Formula 1, where Fc ≤ 1, and the closer Fc is to 1, the closer the particle is to a sphere. Formula 1 is as follows:

[0030] Formula 1.

[0031] In this invention, the general chemical formula of the single-crystal nickel-cobalt-manganese cathode material is Li. 1+p Ni x Co y Mn z M mO2, 0.55≤x<0.96, 0≤y≤0.20, 0.04≤z≤0.40, 0<m≤0.03, 0<p≤0.1, M is a metallic or non-metallic element in the first, second, or third auxiliary agent.

[0032] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising the single-crystal nickel-cobalt-manganese positive electrode material as described in the second aspect.

[0033] Fourthly, the present invention provides a lithium-ion battery comprising a single-crystal nickel-cobalt-manganese cathode material as described in the second aspect, or a cathode sheet as described in the third aspect.

[0034] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention combines and quantifies the roundness of the single-crystal nickel-cobalt-manganese cathode material with the full width at half maximum (FWHM) of the XRD characteristic peaks of the nickel-cobalt-manganese precursor to screen the precursor. Simultaneously, it incorporates a three-stage sintering process, adding additives for doping and / or coating during each of the three sintering stages to prepare a single-crystal nickel-cobalt-manganese cathode material with high roundness and good structural stability, thereby improving the thermodynamic stability, cycle performance, and high-temperature storage performance of the single-crystal nickel-cobalt-manganese cathode material. Attached Figure Description

[0037] Figure 1 The image shows a SEM of the nickel-cobalt-manganese precursor provided in Example 1.

[0038] Figure 2 This is a SEM image of the single-crystal nickel-cobalt-manganese cathode material prepared in Example 1.

[0039] Figure 3 The image shows the SEM of the nickel-cobalt-manganese precursor provided in Comparative Example 1.

[0040] Figure 4 This is a SEM image of the single-crystal nickel-cobalt-manganese cathode material prepared in Comparative Example 1. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0042] 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 invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. In this invention, "a combination of at least two" means, unless otherwise specified, a quantity greater than or equal to two. For example, "any combination of one or at least two" means one or more of two. It is understood that when referring to "a combination of at least two," it means any suitable combination of multiple items, i.e., a combination of "at least two" items carried out in a manner that does not conflict with and allows for the implementation of the invention.

[0043] In the description of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0044] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0046] In one specific embodiment, the present invention provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, the method comprising: mixing a nickel-cobalt-manganese precursor, a lithium source, and a first additive, performing a first sintering to obtain a first sintered material; mixing the first sintered material with a second additive, performing a second sintering to obtain a second sintered material; mixing the second sintered material with a third additive, performing a third sintering to prepare the single-crystal nickel-cobalt-manganese cathode material; wherein the half-maximum width α of the (001) crystal plane of the nickel-cobalt-manganese precursor is equal to the half-maximum width α of the (100) crystal plane. b satisfies: 0.30≤a≤0.48, for example, a can be 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46 or 0.48; 0.38≤b≤0.52, for example, b can be 0.38, 0.40, 0.42, 0.44, 0.46, 0.48, 0.50 or 0.52; 1.1≤b / a≤1.5, for example, b / a can be 1.1, 1.2, 1.3, 1.4 or 1.5.

[0047] The fibrous morphology of the nickel-cobalt-manganese precursor that satisfies the relationship between the half-peak width a of the (001) crystal plane and the half-peak width b of the (100) crystal plane is short and thick. The nickel-cobalt-manganese precursor with short and thick fibrous morphology requires a higher temperature during sintering and lithiation, which is more conducive to the melting and growth of grains along the periphery. At the same time, due to the inheritance of crystal morphology, the primary grain growth of the cathode is also shorter and thicker, thereby obtaining a material with high roundness and improving the degree of single crystallization.

[0048] This invention identifies the crystal structure of nickel-cobalt-manganese precursors based on XRD testing technology. The full width at half maximum (FWHM) of the XRD characteristic peaks of the nickel-cobalt-manganese precursors reflects the crystallinity of the corresponding crystal planes. The crystallinity of the (001) and (100) crystal planes of the precursors respectively affects the crystallinity of the (003) and (104) crystal planes during the subsequent preparation of single-crystal nickel-cobalt-manganese cathode materials.

[0049] In single-crystal nickel-cobalt-manganese cathode materials, the crystallinity of the (003) crystal plane mainly affects the roundness of the single-crystal nickel-cobalt-manganese cathode material. When the half-width at half maximum (WHM) of the (001) crystal plane is wide, the (003) crystal plane of the single-crystal nickel-cobalt-manganese cathode material grows preferentially, the lithium-ion diffusion path is better, and the kinetics of the cathode single crystal material are better, but the grain growth is relatively fine. When the WHM of the (001) crystal plane is narrow, the (003) crystal plane of the single-crystal nickel-cobalt-manganese cathode material grows more slowly, the grains tend to be rounder, and the prepared single-crystal nickel-cobalt-manganese cathode material has better thermodynamic stability. The crystallinity of the (104) crystal plane mainly affects the integrity of the layered structure of the single-crystal nickel-cobalt-manganese cathode material. If the half-width of the (100) crystal plane is too wide, it reflects the insufficient crystallinity of the (100) crystal plane, which affects the crystallinity of the (104) crystal plane of the single-crystal nickel-cobalt-manganese cathode material, leading to the intensification of cation mixing in the single-crystal nickel-cobalt-manganese cathode material and causing instability in the material structure. When the half-width of the (100) crystal plane is narrow, it will result in the (003) crystal plane of the single-crystal nickel-cobalt-manganese cathode material being sharp, the grain growth being too fine, and it being difficult to obtain single crystals.

[0050] This invention identifies and filters the half-peak widths (WHM) of the (001) and (100) crystal planes and the relationship between them, and coordinates and controls them so that the (003) and (104) crystal planes of the single-crystal nickel-cobalt-manganese cathode material grow preferentially during the lithiation process, making the grains more rounded and obtaining a material with higher single crystallinity. At the same time, the layered structure is more complete, reducing lattice strain during the charging and discharging process and improving stability.

[0051] In some embodiments, the first sintering includes sintering sequentially at a first temperature platform and a second temperature platform. The first temperature platform allows for sufficient lithiation and the discharge of waste gases (carbon dioxide and water), while the second temperature platform is used for grain melting and growth. The temperature difference between the first and second temperature platforms affects the rate and sufficiency of waste gas (carbon dioxide and water) discharge, as well as the speed of crystal growth. If the temperature difference is too large, carbon dioxide and water may not be fully discharged before grain growth begins, resulting in impurities within the crystal lattice, poor grain roundness, and easily broken single crystals. If the temperature difference is too small, including situations where the first temperature platform is too high or the second temperature platform is too low, when the first temperature platform is too high, the discharge of carbon dioxide and water occurs simultaneously with grain growth, resulting in impurities within the crystal lattice, poor grain roundness, and easily broken single crystals. If the second temperature platform is too low, it is difficult for grains to melt and grow into single crystals.

[0052] In some embodiments, the temperature of the first temperature platform is 40°C to 90°C lower than the temperature of the second temperature platform. For example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, preferably 75°C to 85°C.

[0053] In some embodiments, the temperature of the second temperature platform is 800°C to 1000°C, for example, it can be 800°C, 825°C, 850°C, 875°C, 900°C, 925°C, 950°C, 975°C or 1000°C.

[0054] In some embodiments, the sintering time on the first temperature platform is 5h to 12h, for example, it can be 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h.

[0055] In some embodiments, the sintering time on the second temperature platform is 8h to 12h, for example, it can be 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h.

[0056] In this invention, a second sintering process is performed by mixing a first sintering material and a second additive at a temperature below the second temperature plateau. This process modifies the roundness of the grains in the first sintering material and utilizes the second additive for surface doping, improving grain boundary stability and thus enhancing the thermodynamic stability and kinetic properties of the material. Controlling the second sintering temperature ensures that the second additive is doped onto the material surface. If the second sintering temperature is too high, the second additive will be over-doped into the grain interior, affecting the bulk composition. If the second sintering temperature is too low, the second additive will only form a coating layer and will not achieve surface doping.

[0057] In some embodiments, the temperature of the second sintering is 100°C to 200°C lower than the temperature of the second temperature platform, for example, it can be 100°C, 120°C, 140°C, 160°C, 180°C or 200°C.

[0058] In some embodiments, the second sintering time is 8h to 15h, for example, it can be 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13.5h, 14h, 14.5h or 15h.

[0059] In some embodiments, the temperature of the third sintering is 300°C to 600°C lower than the temperature of the second temperature platform, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C.

[0060] The purpose of mixing the second sintering material with the third additive is to coat the surface of the second sintering material, forming a nano-coating layer on the material surface to reduce the contact between the material and the electrolyte and prevent the electrolyte from corroding the base material.

[0061] In some embodiments, the third sintering time is 6h to 12h, for example, it can be 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h.

[0062] In some embodiments, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium nitrate, lithium acetate, or lithium hydroxide.

[0063] In some embodiments, the first, second, and third additives each independently include any one or at least two combinations of ZrO2, Co3O4, Co(OH)2, CoOOH, TiO2, WO3, MoO3, Nb2O5, MnO2, CeO2, La2O3, Y2O3, SrCO3, Al2O3, MgO, B2O3, NaF, P2O5, or SiO2. Typical but non-limiting combinations include combinations of ZrO2 and Co3O4, TiO2 and WO3, MoO3 and Nb2O5, MnO2 and CeO2, La2O3 and Y2O3, SrCO3 and Al2O3, MgO and B2O3, NaF and P2O5, or SiO2 and ZrO2.

[0064] In some embodiments, the amount of the first additive added is 0.3 wt.% to 1.5 wt.% of the nickel-cobalt-manganese precursor. For example, it can be 0.3 wt.%, 0.5 wt.%, 0.7 wt.%, 0.9 wt.%, 1.1 wt.%, 1.3 wt.%, or 1.5 wt.%.

[0065] In some embodiments, the amount of the second additive added is 1 wt.% to 3 wt.% of the mass of the first sintering material, for example, it can be 1 wt.%, 1.2 wt.%, 1.4 wt.%, 1.6 wt.%, 1.8 wt.%, 2 wt.%, 2.2 wt.%, 2.4 wt.%, 2.6 wt.%, 2.8 wt.% or 3.0 wt.%.

[0066] In some embodiments, the amount of the third additive added is 0.1 wt.% to 0.5 wt.% of the mass of the second sintering material, for example, it can be 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.% or 0.5 wt.%.

[0067] In another specific embodiment, the present invention provides a single-crystal nickel-cobalt-manganese cathode material, which is prepared by the preparation method described in the preceding specific embodiment; the roundness of the single-crystal nickel-cobalt-manganese cathode material is ≥0.8, for example, it can be 0.8, 0.81, 0.83, 0.84, 0.85, 0.86, 0.87 or 0.88.

[0068] The roundness factor Fc is calculated as follows: Using SEM, the average projected area S and average projected perimeter P of the particles are measured respectively. The roundness factor Fc is then calculated according to Formula 1. Fc ≤ 1, and the closer Fc is to 1, the closer the particle is to a sphere. Formula 1 is as follows:

[0069] Formula 1.

[0070] In this invention, the general chemical formula of the single-crystal nickel-cobalt-manganese cathode material is Li. 1+p Ni x Co y Mn z M mO2, x+y+z=1, 0.55≤x<0.96, for example, it could be 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.96, 0≤y≤0.20, for example, it could be 0, 0.05, 0.1, 0.15 or 0.2, 0.04≤z≤0.4, for example, it could be 0.04, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.4, 0≤m≤0.02, for example it can be 0, 0.005, 0.01, 0.015 or 0.02, 0<p≤0.1, for example it can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, M is a metallic or non-metallic element in the first, second or third auxiliary agent.

[0071] In yet another embodiment, the present invention provides a positive electrode sheet comprising a single-crystal nickel-cobalt-manganese positive electrode material as described in another preceding embodiment.

[0072] In another specific embodiment, the present invention provides a lithium-ion battery comprising a single-crystal nickel-cobalt-manganese cathode material as described in another specific embodiment above, or comprising a cathode sheet as described in yet another specific embodiment above.

[0073] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0074] To clearly illustrate the technical solution of the present invention, the test methods for the full width at half maximum (FWHM) a of the (001) crystal plane and the full width at half maximum (FWHM) b of the (100) crystal plane in the specific embodiment are as follows:

[0075] An X-ray diffractometer was used with a scanning range of 10-90°, a continuous scanning mode, a step size of 0.02° / step, and a dwell time of 0.2s / step. The fitting angle range of the (001) crystal plane was 18°~22°, and the fitting angle of the (100) crystal plane was 32°~35°. The values ​​of a and b were read from the XRD-PDXL software.

[0076] The above description is only for clearly illustrating the technical solution of the present invention and should not be regarded as a further limitation of the present invention.

[0077] Example 1

[0078] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, the method comprising:

[0079] Ni with a full width at half maximum (FWHM) of 0.35 for the (001) crystal plane, a FWHM of 0.47 for the (100) crystal plane, and a b / a ratio of 1.3 0.6 Co 0.1 Mn 0.3 (OH)₂ precursor, mixed with lithium hydroxide and ZrO₂ to obtain a mixture, wherein Ni 0.6 Co 0.1 Mn 0.3 The molar ratio of (OH)₂ precursor to lithium hydroxide is 1:1.03, and the mass of ZrO₂ is Ni. 0.6 Co 0.1 Mn 0.3 0.5 wt.% of (OH)2 precursor.

[0080] Under an oxygen atmosphere, the mixture is first heated to 930℃ and sintered for 10 hours, then heated to 990℃ and sintered for 10 hours to obtain the first sintered material; the first sintered material is mixed with 1.5 wt% Co(OH)2 and sintered at 840℃ for 10 hours to obtain the second sintered material; the second sintered material is mixed with 0.2 wt% Al2O3 and sintered at 540℃ for 10 hours to obtain the single-crystal nickel-cobalt-manganese cathode material.

[0081] Example 2

[0082] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, the method comprising:

[0083] Ni with a full width at half maximum (FWHM) of 0.3 for the (001) crystal plane, a FWHM of 0.44 for the (100) crystal plane, and a b / a ratio of 1.47 was used. 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor, mixed with lithium hydroxide and TiO₂ to obtain a mixture, wherein Ni 0.8 Co 0.1 Mn 0.1 The molar ratio of (OH)₂ precursor to Li in lithium hydroxide is 1:1.05, and the mass of TiO₂ is Ni. 0.8 Co 0.1 Mn 0.1 0.3 wt.% of (OH)2 precursor.

[0084] Under an oxygen atmosphere, the mixture is first heated to 860℃ and sintered for 5 hours, then heated to 900℃ and sintered for 8 hours to obtain the first sintered material; the first sintered material is mixed with WO3 accounting for 1 wt% of the mass of the first sintered material and sintered at 800℃ for 8 hours to obtain the second sintered material; the second sintered material is mixed with Nb2O5 accounting for 0.1 wt% of the mass of the second sintered material and sintered at 600℃ for 6 hours to obtain the single crystal nickel-cobalt-manganese cathode material.

[0085] Example 3

[0086] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, the method comprising:

[0087] Ni with a full width at half maximum (FWHM) of 0.47 for the (001) crystal plane, a FWHM of 0.52 for the (100) crystal plane, and a b / a ratio of 1.11 was used. 0.94 Co 0.03 Mn 0.03 (OH)₂ precursor, mixed with lithium hydroxide and ZrO₂ to obtain a mixture, wherein Ni 0.94 Co 0.03 Mn 0.03 The molar ratio of (OH)₂ precursor to lithium hydroxide is 1:1.03, and the mass of ZrO₂ is Ni. 0.94 Co 0.03 Mn 0.03 1.5 wt.% of (OH)2 precursor.

[0088] Under an oxygen atmosphere, the mixture is first heated to 710℃ and sintered for 12 hours, then heated to 800℃ and sintered for 12 hours to obtain the first sintered material; the first sintered material is mixed with 3 wt% Co(OH)2 and sintered at 600℃ for 15 hours to obtain the second sintered material; the second sintered material is mixed with 0.5 wt% B2O3 and sintered at 200℃ for 12 hours to obtain the single-crystal nickel-cobalt-manganese cathode material.

[0089] Example 4

[0090] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which uses Ni with a (001) crystal plane half-width a of 0.3, a (100) crystal plane half-width b of 0.38, and a b / a ratio of 1.27. 0.6 Co 0.1 Mn 0.3 Except for the (OH)2 precursor, everything else is the same as in Example 1.

[0091] Example 5

[0092] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material. Except for the temperature of the first sintering temperature plateau being 960°C, the rest is the same as in Embodiment 1.

[0093] Example 6

[0094] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material. Except for the temperature of the first sintering temperature plateau being 890°C, the rest is the same as in Embodiment 1.

[0095] Example 7

[0096] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material. Except for the second sintering temperature of 910°C, the rest is the same as in Example 1.

[0097] Example 8

[0098] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material. Except for the second sintering temperature of 770°C, the rest is the same as in Example 1.

[0099] Example 9

[0100] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material. Except for the third sintering temperature of 705°C, the rest is the same as in Example 1.

[0101] Example 10

[0102] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material. Except for the third sintering temperature of 375°C, the rest is the same as in Example 1.

[0103] Example 11

[0104] This embodiment provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material. Except for the first sintering which is only sintered at 930°C for 20 hours, the rest is the same as in Example 1.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which uses Ni with a (001) crystal plane half-width a of 0.53, a (100) crystal plane half-width b of 0.55, and a b / a ratio of 1.04. 0.6 Co 0.1 Mn 0.3 Except for the (OH)2 precursor, everything else is the same as in Example 1.

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which uses Ni with a (001) crystal plane half-width a of 0.25, a (100) crystal plane half-width b of 0.47, and a b / a ratio of 1.88. 0.6 Co 0.1 Mn 0.3 Except for the (OH)2 precursor, everything else is the same as in Example 1.

[0109] Comparative Example 3

[0110] This comparative example provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which uses Ni with a (001) crystal plane half-width a of 0.36, a (100) crystal plane half-width b of 0.35, and a b / a ratio of 0.97. 0.6 Co 0.1 Mn 0.3 Except for the (OH)2 precursor, everything else is the same as in Example 1.

[0111] Comparative Example 4

[0112] This comparative example provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which uses Ni with a (001) crystal plane half-width a of 0.33, a (100) crystal plane half-width b of 0.54, and a b / a ratio of 1.64. 0.6 Co 0.1 Mn 0.3 Except for the (OH)2 precursor, everything else is the same as in Example 1.

[0113] Comparative Example 5

[0114] This comparative example provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which is the same as that in Example 1 except that only the first sintering is performed.

[0115] Comparative Example 6

[0116] This comparative example provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which is the same as that in Example 1 except that only the first and second sintering are performed.

[0117] Comparative Example 7

[0118] This comparative example provides a method for preparing a single-crystal nickel-cobalt-manganese cathode material, which is the same as that in Example 1 except that only the first and third sintering processes are performed.

[0119] Performance testing:

[0120] SEM tests were performed on the nickel-cobalt-manganese precursors provided in Example 1 and Comparative Example 1, and the prepared single-crystal nickel-cobalt-manganese cathode material. The SEM images of the nickel-cobalt-manganese precursors provided in Example 1 and the prepared single-crystal nickel-cobalt-manganese cathode material are shown below. Figure 1 and Figure 2 As shown, the SEM images of the nickel-cobalt-manganese precursor provided in Comparative Example 1 and the prepared single-crystal nickel-cobalt-manganese cathode material are respectively shown in Figure 1. Figure 3 and Figure 4 As shown. According to Figure 1 and Figure 3 The comparison results show that the primary granular fibers of the nickel-cobalt-manganese precursor provided in Example 1 are shorter and thicker than those in Comparative Example 1, which is more conducive to the melting and growth of grains along the periphery during the subsequent lithiation sintering process, improving roundness. Figure 2and Figure 4 The comparison results show that the single-crystal nickel-cobalt-manganese cathode material prepared in Example 1 has better particle shape uniformity, higher roundness, and better dispersibility, while the roundness, size inhomogeneity, and particle dispersibility provided by Comparative Example 1 are poor.

[0121] SEM tests were performed on the first sintered material and the single-crystal nickel-cobalt-manganese cathode material provided in all the above embodiments and comparative examples. The average projected area S and average projected perimeter P of the particles were tested using ImageJ. The roundness Fc1 of the first sintered material and the roundness Fc2 of the single-crystal nickel-cobalt-manganese cathode material were calculated according to Formula 1. The test results are shown in Table 1.

[0122] The monocrystalline nickel-cobalt-manganese cathode material provided in all the above embodiments and comparative examples was dispersed in NMP with conductive carbon black and PVDF at a mass ratio of 92:4:4 to prepare a slurry, which was then coated on the surface of aluminum foil to prepare a cathode sheet. Lithium sheets and graphite anodes were matched respectively, and coin half cells and coin full cells were assembled.

[0123] The cycle performance of the prepared lithium-ion half-cell was tested: at 45℃ and within a voltage range of 3.0-4.4V, the capacity retention rate was tested after 50 charge-discharge cycles at a rate of 0.5C / 1C.

[0124] The high-temperature storage performance of the prepared lithium-ion full battery was tested: the capacity retention rate and capacity recovery rate of the battery were tested after 72 hours of storage at 45℃, 3.0-4.4V, and 0.33C.

[0125] The electrical performance test results are shown in Table 1.

[0126] Table 1

[0127]

[0128] In summary, this invention combines and quantifies the roundness of the single-crystal nickel-cobalt-manganese cathode material with the full width at half maximum (FWHM) of the XRD characteristic peaks of the nickel-cobalt-manganese precursor to screen the precursor. Simultaneously, by combining a three-stage sintering process and controlling the temperature between the three sintering stages, and by adding additives for doping and / or coating during each of the three sintering stages, a single-crystal nickel-cobalt-manganese cathode material with high roundness and good structural stability is prepared, thereby improving the thermodynamic stability, cycle performance, and high-temperature storage performance of the single-crystal nickel-cobalt-manganese cathode material.

[0129] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a single-crystal nickel-cobalt-manganese cathode material, characterized in that, The preparation method includes: A first sintering material is prepared by mixing a nickel-cobalt-manganese precursor, a lithium source, and a first additive; the first sintering material is then mixed with a second additive and sintered a second time to obtain a second sintering material; the second sintering material is then mixed with a third additive and sintered a third time to prepare the single-crystal nickel-cobalt-manganese cathode material. The half-peak width a of the (001) crystal plane and the half-peak width b of the (100) crystal plane of the nickel-cobalt-manganese precursor satisfy the following: 0.30≤a≤0.48, 0.38≤b≤0.52, 1.1≤b / a≤1.5; The first auxiliary agent is ZrO2; The second auxiliary agent is Co(OH)2; The third auxiliary agent is Al2O3; The first sintering includes sintering sequentially on a first temperature platform and a second temperature platform, wherein the temperature of the first temperature platform is 40°C to 90°C lower than the temperature of the second temperature platform; the temperature of the second sintering is 100°C to 200°C lower than the temperature of the second temperature platform; the temperature of the third sintering is 300°C to 600°C lower than the temperature of the second temperature platform; and the temperature of the second temperature platform is 800°C to 1000°C.

2. The preparation method according to claim 1, characterized in that, The sintering time at the first temperature platform is 5h~12h; And / or, the sintering time on the second temperature platform is 8h~12h.

3. The preparation method according to claim 1, characterized in that, The second sintering time is 8h~15h.

4. The preparation method according to claim 1, characterized in that, The third sintering time is 6h~12h.

5. The preparation method according to claim 1, characterized in that, The amount of the first additive added is 0.3 wt.% to 1.5 wt.% of the mass of the nickel-cobalt-manganese precursor; And / or, the amount of the second additive added is 1 wt.% to 3 wt.% of the mass of the first sintering material; And / or, the amount of the third additive added is 0.1 wt.% to 0.5 wt.% of the mass of the second sintering material.

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