A high-capacity, long-cycle low-cobalt single-crystal cathode material and its preparation method

Abstract

This invention belongs to the field of lithium battery cathode materials and discloses a high-capacity, long-cycle low-cobalt single-crystal cathode material. The particle's interior is divided into two regions from the outside to the inside. The cobalt concentration in the first and second regions decreases in a gradient distribution from the outside to the inside at rates of 6%–20% and 0.1%–6% per 100 nm, respectively. This design significantly improves the initial charge / discharge capacity and rate performance, and also noticeably improves high-temperature cycling. The invention also discloses a method for preparing this low-cobalt single-crystal cathode material. This method is simple and low-cost. By selecting a suitable high-nickel, low-cobalt small-particle precursor, combined with elemental doping and dry sintering processes, the particle size distribution and structure of the low-cobalt single-crystal cathode material are controlled. The crystal structure and surface are modified to form a two-stage decreasing cobalt concentration gradient distribution from the outside to the inside, improving the common problems of high residual lithium, poor power and cycle performance, and poor safety performance of high-nickel, low-cobalt cathode materials.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery cathode material technology, and particularly relates to a high-capacity, long-cycle, low-cobalt single-crystal cathode material and its preparation method. Background Technology

[0002] To meet the ever-increasing demand for longer driving range in the new energy vehicle market, competition for high energy density performance has intensified, leading to significant development in high-energy lithium-ion batteries. In this race for energy density, ternary cathode materials are trending towards higher nickel content and higher voltage, while also facing risks and challenges such as poor cycle life and safety. In recent years, the price of raw materials has risen significantly. As the ultimate goal of ternary cathode materials, high-nickel, low-cobalt cathode materials offer substantial energy density and cost advantages, but they also suffer from common problems such as high residual lithium, poor rate capability, and poor cycle performance.

[0003] Therefore, it is imperative to modify and develop high-nickel, low-cobalt cathode materials to address their risks such as low capacity, poor cycle life, and safety. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a high-capacity, long-cycle low-cobalt single-crystal cathode material and its preparation method.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A high-capacity, long-cycle low-cobalt single-crystal cathode material, wherein the particles of the low-cobalt single-crystal cathode material are analyzed by EPMA, and the region from the particle surface at a distance of 25 nm to 425 nm is the first region, and the region from the particle surface at a distance of 425 nm to the particle center is the second region.

[0007] The cobalt concentration in the first region is distributed in a gradient from the outside to the inside at a rate of 6% to 20% per 100 nm.

[0008] The cobalt concentration in the second region is distributed in a gradient from the outside to the inside at a rate of 0.1% to 6% per 100 nm.

[0009] The low-cobalt single-crystal cathode material of this invention, through EPMA elemental analysis, shows that the cobalt concentration inside the particles exhibits a two-stage decreasing gradient distribution from the outside to the inside. Fully utilizing the promoting effect of cobalt on the lithium-ion diffusion rate, two regions with different cobalt concentration gradients are formed from the surface to the interior, with the cobalt concentration gradient in the interior region being smaller than that in the exterior region. Under the condition of forming a lithium layer channel with a high lithium intercalation state from the outside to the inside and the lithium concentration gradient effect, the first region with a high cobalt concentration gradient greatly promotes lithium-ion entry into the crystal lattice and diffusion into the interior, alleviating the irreversible H2-H3 phase transition in high-nickel, low-cobalt materials, and simultaneously mitigating the high polarization resistance caused by the high lithium intercalation state inside the crystal. The second region with a low cobalt concentration gradient, due to the low lithium concentration in the central lithium layer inside the crystal... Furthermore, the lithium-ion diffusion path is relatively long, and the lithium layer channels are reduced. The promoting effect of cobalt on the lithium-ion diffusion rate gradually decreases with lithium concentration. Combining the low lithium-ion concentration gradient in the second region, a second region with a low cobalt concentration gradient and high nickel composition is designed to further enhance the lithium-ion insertion rate and redox reaction, alleviate the irreversible H1-M phase transition in high-nickel low-cobalt materials, further alleviate the high polarization impedance caused by the high lithium insertion state inside the crystal, improve the capacity utilization at low voltage, and thus achieve higher capacity. It also makes highly efficient use of the gain effect of cobalt, improving capacity while reducing the overall cost of low-cobalt materials. This two-stage cobalt concentration gradient design fully combines the lithium layer channels and lithium concentration gradient effect, greatly improving the lithium-ion insertion rate during discharge. It is extremely suitable for use in low-cobalt single crystal materials, which can improve the high polarization impedance caused by the long diffusion path and slow diffusion rate in low-cobalt single crystal materials, alleviate the irreversible H1-M and H2-H3 phase transitions in high-nickel low-cobalt materials, reduce power loss during cycling, and improve the cycling performance of materials. In addition, the two-stage cobalt concentration gradient design can fully and efficiently utilize the gain effect of cobalt, and has a high overall cost advantage.

[0010] Preferably, in the aforementioned low-cobalt single-crystal cathode material, the ratio of the cobalt concentration reduction rate in the first region to that in the second region is 3 to 8:1. With this ratio, within the internal structure of the low-cobalt composition, by distributing the limited cobalt content in a two-stage decreasing gradient, the promoting effect of cobalt on the lithium-ion diffusion rate is fully utilized, increasing the lithium-ion insertion rate during discharge. Simultaneously, combined with the spherical single-crystal lithium layer diffusion path, especially in the later stages of discharge, the formation of lithium layer channels with high lithium-intercalation states from the outside in, along with the lithium gradient concentration effect, greatly promotes lithium-ion entry into the crystal lattice through the high-concentration cobalt gradient in the first region. This alleviates the high polarization resistance caused by the high lithium-intercalation states within the crystal, further enhancing the lithium-ion insertion rate and thus achieving a higher capacity.

[0011] Preferably, the general formula of the low-cobalt single-crystal cathode material is Li. u Ni 1-x-y-z Co x Mn y Mz N v O 2-w Wherein, 0.9≤u≤1.1, 0<x≤0.10, 0<y≤0.1, 0≤z≤0.05, 0≤v≤0.05, -0.05≤w≤0.05; M is a doping element, which is selected from at least one or more of Al, Mg, Zr, Ti, Y, W, Ta, Nb, Ce, Sn, B, Sr, and Mo; N is a coating element, which is selected from at least one or more of B, Ce, Nb, Sn, W, Al, and Zr.

[0012] More preferably, M is Zr. High-temperature co-doping of Zr with Zr-Co elements promotes primary particle stacking growth, forming a stable crystal structure (Zr-O strong bond). Simultaneously, Zr and Co source energy react with residual lithium on the particle surface to form Li2ZrO3 and LiCoO2 fast ion conductors, increasing the lithium-ion diffusion rate, protecting the cathode material surface, and suppressing side reactions between the cathode material surface and the electrolyte, thereby improving the material's cycle stability.

[0013] Preferably, the low-cobalt single-crystal cathode material has a full width at half maximum (FWHM) of 0.08–0.10 for peak 104 in its XRD diffraction pattern, and a lithium-nickel mix ratio of 1.8%–2.5% after XRD refinement. Narrower diffraction peaks indicate better crystallinity, and lower lithium-nickel mix ratios can increase the lithium-ion diffusion rate, which is beneficial for mitigating adverse phase transitions during cycling and improving structural stability.

[0014] Preferably, the D50 particle size of the low-cobalt single-crystal cathode material is 3.0~4.0μm, the primary particle grain size is 1.5~2.0μm, and the specific surface area is 0.4~0.8m². 2 / g, with total residual lithium of 800~1400ppm.

[0015] Preferably, the low-cobalt single-crystal cathode material exhibits a prominent reduction peak at 3.4V to 3.6V in the 0.1C rate DQ / DV discharge curve. This indicates that the material possesses a good kinetic diffusion rate, low polarization resistance, and low power loss, enabling it to achieve higher capacity and better cycle performance.

[0016] As a general inventive concept, this invention provides a method for preparing the above-mentioned low-cobalt single-crystal cathode material, comprising the following steps:

[0017] S1. After uniformly mixing the nickel-based hydroxide precursor, lithium salt, cobalt source and dopant, perform two-stage sintering, with the temperature of the first stage sintering being higher than that of the second stage sintering.

[0018] S2. The sintered products obtained after the two sintering stages in step S1 are crushed and dissociated, then mixed evenly with the coating agent and sintered again to obtain the low cobalt single crystal cathode material.

[0019] In step S1, the cobalt source is promoted to enter the internal structure of the particles through the first short platform ultra-high temperature sintering, forming a high-concentration cobalt gradient first region; then the second platform high temperature sintering is used to promote further crystal growth of the particles, while a cobalt concentration gradient is formed inside the matrix. This sintering process allows the cobalt source to diffuse faster in the first stage and relatively slower in the second stage, thus forming a differentiated concentration gradient.

[0020] In the above preparation method, preferably, the lithium salt is one or two of lithium carbonate, lithium hydroxide, lithium nitrate, lithium fluoride, and lithium phosphate; the cobalt source is one or two of cobalt hydroxide, cobalt hydroxyl oxide, and cobalt tetroxide; the dopant is an M salt, which is a compound or compound containing one or more elements selected from Al, Mg, Zr, Ti, Y, W, Ta, Nb, Ce, Sn, B, Sr, and Mo; the coating agent is an N salt, which is a compound or compound containing one or more elements selected from B, Ce, Nb, Sn, W, Al, and Zr; and the molar ratio of lithium to nickel cobalt manganese hydroxide precursor in the lithium salt is 1.05~1.08:1.

[0021] More preferably, the dopant is a compound containing one or more elements selected from Al, Mg, Zr, Ti, and Y, and the coating agent is a compound containing one or more elements selected from B, Nb, W, Al, and Zr.

[0022] Preferably, in step S1, the conditions for the two-stage sintering are as follows: the temperature of the first stage sintering is 800~1000℃, the heating rate is 1~3℃ / min, and the holding time is 2~5h; the temperature of the second stage sintering is 600~800℃, and the holding time is 8~20h. Both stages of sintering are carried out in an oxygen-containing atmosphere.

[0023] In step S2, the re-sintering temperature is 200~700℃, carried out in an oxygen-containing atmosphere, the heating rate is 1~3℃ / min, and the holding time is 4~10h.

[0024] Preferably, in step S2, the crushing and dissociation specifically includes the following steps: the sintered product is initially crushed by a jaw crusher and a roller mill, and then crushed by an air jet mill, with the air pressure controlled at 0.2~0.4MPa, the grading frequency at 30~50Hz, and the induced draft frequency at 30~50Hz.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The low cobalt high nickel cathode material of the present invention has a two-stage decreasing gradient distribution of cobalt concentration inside the particles from the outside to the inside, which can significantly improve the first charge / discharge capacity and rate performance, and can significantly improve high temperature cycling. It largely solves the common problems of high residual lithium, poor rate and cycle performance, and poor safety performance of low cobalt high nickel materials in the industry.

[0027] (2) The preparation method of the present invention uses appropriate surface coating elements and dry sintering process to react with residual lithium on the surface of the material, thereby reducing residual lithium and coating a thin and uniform coating layer on the surface of the material. This solves the common problem of high residual lithium in high nickel materials and avoids the surface structure damage caused by the water washing process to remove residual lithium. It can also fix oxygen atoms on the surface while establishing lithium ion transport channels, suppressing side reactions between the material surface and the electrolyte, and improving the rate and cycle performance of the material.

[0028] (3) The preparation method of the present invention controls the dissociation effect of single crystal particles through a suitable crushing process, and ensures the integrity of single crystal particles while dissociating them, forming uniform, narrowly distributed particles with good dispersion, improving the dispersion of particle size, obtaining a narrower particle range, and improving the consistency of material use.

[0029] (4) The preparation method of the present invention has a simple overall preparation process and low cost. By selecting a suitable high-nickel and low-cobalt small particle precursor, combined with element doping coating modification and dry sintering process, the internal nickel, cobalt and manganese composition of the ternary low-cobalt single crystal cathode material is designed, the particle size morphology and structure are controlled, and the crystal structure and surface of the material are modified to form a two-stage decreasing cobalt concentration gradient distribution from the outside to the inside. This improves the common problems of high residual lithium, poor power and cycle performance and poor safety performance of high-nickel and low-cobalt cathode materials, alleviates the H1-M (low voltage kinetics) and H2-H3 irreversible phase transition of high-nickel and low-cobalt materials, improves the mechanical strength of the material, and has good power performance while taking into account high capacity and high cycle life. At the same time, the crystal structure is stable, making the battery safe, high-capacity and long cycle, meeting the safety and high performance requirements of long-range high-end vehicles, and has a high comprehensive cost advantage, which is suitable for the needs of EV long-range vehicle batteries. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1SEM image of the high-capacity, long-cycle, low-cobalt, high-nickel cathode material prepared in Example 1;

[0032] Figure 2 EPMA image of a cross section of the high-capacity, long-cycle, low-cobalt, high-nickel cathode material prepared in Example 1;

[0033] Figure 3 SEM image of the high-capacity, long-cycle, low-cobalt, high-nickel cathode material prepared in Example 2;

[0034] Figure 4 The DQ / DV curves of the cathode materials prepared in Example 1 and Comparative Example 1 are shown.

[0035] Figure 5 The graph shows the high-temperature cycling performance of the cathode materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0039] Example 1:

[0040] A high-capacity, long-cycle, low-cobalt single-crystal cathode material with the chemical formula Li 1.0 Ni 0.929 Co 0.030 Mn 0.039 Zr 0.00 2B 0.0005 Al 0.002 O2 is composed of primary single-crystal particles with a D50 particle size of 3.5 μm, a primary particle grain size of 1.7 μm, and a specific surface area of ​​0.65 m². 2 / g, total residual lithium is 1189ppm, XRD diffraction 104 peak full width at half maximum is 0.082, XRD refined lithium-nickel mixture value is 1.82%.

[0041] Its preparation method includes the following steps:

[0042] 1) The purchased nickel-cobalt-manganese hydroxide precursor Ni 0.95 Co0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, nano-sized zirconium oxide and cobalt hydroxide were added to a high-speed mixer in a molar ratio of 1:1.07:0.002:0.02 and stirred at 1800 r / min for 30 min. Then, in a box furnace with an oxygen concentration ≥96%, the temperature was increased to 900℃ at a heating rate of 3℃ / min and held for 2 h. The temperature was then decreased to 786℃ and held for 12 h. The material was then naturally cooled to room temperature to obtain the sintered material.

[0043] 2) The sintered material is first crushed by a jaw crusher and a double roller mill, and then pulverized by an air jet mill. The air pressure is controlled at 0.35MPa, the grading frequency is 45Hz, and the induced draft frequency is 40Hz, which can effectively dissociate the sintered agglomerates and control the particle size.

[0044] The pulverized material was added to a high-speed mixer with boric acid and alumina at a molar ratio of 1:0.0005:0.001 and stirred at 1800 r / min for 30 min. Then, in a box furnace under an oxygen atmosphere, the temperature was raised to 320℃ at a heating rate of 3℃ / min and held for 8 h. After naturally cooling to room temperature, the sintered material was obtained. The sintered material was sieved using a 300-mesh sieve to obtain the ternary cathode material.

[0045] The SEM and EPMA images of the above ternary cathode materials are as follows: Figures 1-2 As shown in the EMPA elemental distribution map, a two-stage cobalt concentration gradient distribution is formed from the outside to the inside. The first region, with a high cobalt concentration gradient from 25 nm from the particle surface to 425 nm from the surface, shows a gradient distribution of cobalt concentration decreasing at a rate of 12.37% per 100 nm towards the center. The second region, with a low cobalt concentration gradient from 425 nm from the particle surface to the particle center, shows a gradient distribution of cobalt concentration decreasing at a rate of 3.18% per 100 nm towards the center. The ratio of the cobalt concentration reduction rate of the first and second regions is 3.89. This ensures rapid lithium-ion insertion and extraction while stabilizing the crystal structure of the material, alleviating the H1-M (low voltage kinetics) and H2-H3 irreversible phase transition in high-nickel, low-cobalt materials, improving the material's capacity and mechanical strength, thereby enhancing the material's cycle performance.

[0046] Example 2:

[0047] A high-capacity, long-cycle, low-cobalt single-crystal cathode material with the chemical formula Li 1.0 Ni 0.928 Co 0.030 Mn 0.040 Al 0.00 4B 0.0005O2 is composed of primary single-crystal particles with a D50 particle size of 3.5 μm, a primary particle grain size of 1.7 μm, and a specific surface area of ​​0.59 m² / g. 2 / g, total residual lithium is 1312ppm, XRD diffraction 104 peak full width at half maximum is 0.085, XRD refined lithium-nickel mixture value is 1.87%.

[0048] Its preparation method includes the following steps:

[0049] 1) The purchased nickel-cobalt-manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, aluminum oxide and cobalt hydroxide were added to a high-speed mixer in a molar ratio of 1:1.07:0.001:0.02 and stirred at 1800 r / min for 30 min. Then, in a box furnace with an oxygen concentration ≥96%, the temperature was increased to 900℃ at a heating rate of 3℃ / min and held for 2 h. The temperature was then decreased to 786℃ and held for 12 h. The material was then naturally cooled to room temperature to obtain the sintered material.

[0050] 2) The sintered material is first crushed by a jaw crusher and a double roller mill, and then pulverized by an air jet mill. The air pressure is controlled at 0.35MPa, the grading frequency is 45Hz, and the induced draft frequency is 40Hz, which can effectively dissociate the sintered agglomerates and control the particle size.

[0051] The pulverized material was added to a high-speed mixer with boric acid and alumina at a molar ratio of 1:0.0005:0.001 and stirred at 1800 r / min for 30 min. Then, in a box furnace under an oxygen atmosphere, the temperature was raised to 320℃ at a heating rate of 3℃ / min and held for 8 h. After naturally cooling to room temperature, the sintered material was obtained. The sintered material was sieved using a 300-mesh sieve to obtain the ternary cathode material.

[0052] SEM images of the above ternary cathode materials are shown below. Figure 3 As shown.

[0053] Example 3:

[0054] A high-capacity, long-cycle, low-cobalt single-crystal cathode material with the chemical formula Li 1.0 Ni 0.929 Co 0.030 Mn 0.039 Zr 0.00 2W 0.0015 O2 is composed of primary single-crystal particles with a wavy surface morphology. The D50 particle size is 3.8 μm, the primary particle grain size is 1.7 μm, and the specific surface area is 0.64 m². 2 / g, total residual lithium is 1385ppm, XRD diffraction 104 peak full width at half maximum is 0.084, XRD refined lithium-nickel mixture value is 1.94%.

[0055] Its preparation method includes the following steps:

[0056] 1) The purchased nickel-cobalt-manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, nano-sized zirconium oxide and cobalt hydroxide were added to a high-speed mixer in a molar ratio of 1:1.07:0.002:0.02 and stirred at 1800 r / min for 30 min. Then, in a box furnace with an oxygen concentration ≥96%, the temperature was increased to 900℃ at a heating rate of 3℃ / min and held for 2 h. The temperature was then decreased to 786℃ and held for 12 h. The material was then naturally cooled to room temperature to obtain the sintered material.

[0057] 2) The sintered material is first crushed by a jaw crusher and a double roller mill, and then pulverized by an air jet mill. The air pressure is controlled at 0.35MPa, the grading frequency is 45Hz, and the induced draft frequency is 40Hz, which can effectively dissociate the sintered agglomerates and control the particle size.

[0058] The pulverized material and tungsten oxide were added to a high-speed mixer at a molar ratio of 1:0.0015 and stirred at 1800 r / min for 30 min. Then, in a box furnace under an oxygen atmosphere, the temperature was raised to 450℃ at a heating rate of 3℃ / min and held for 8 h. After natural cooling to room temperature, the sintered material was obtained. The sintered material was sieved using a 300-mesh sieve to obtain the ternary cathode material.

[0059] Comparative Example 1:

[0060] A low-cobalt single-crystal cathode material with the chemical formula Li 1.0 Ni 0.948 Co 0.01 Mn 0.04 Zr 0.002 O2 is composed of primary single-crystal particles with a D50 particle size of 3.7 μm, a primary particle grain size of 1.7 μm, and a specific surface area of ​​0.71 m². 2 / g, total residual lithium is 3278ppm, XRD diffraction 104 peak half width at half maximum is 0.114, XRD refined lithium-nickel mixing value is 3.12%. Compared with the example, the material has poor crystallinity and serious lithium-nickel mixing.

[0061] Its preparation method includes the following steps:

[0062] 1) The purchased nickel-cobalt-manganese hydroxide precursor Ni 0.95 Co0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, and nano-sized zirconium oxide were added to a high-speed mixer at a molar ratio of 1:1.07:0.002 and stirred at 1800 r / min for 30 min. Then, in a box furnace with an oxygen concentration ≥96%, the temperature was increased to 786℃ at a heating rate of 3℃ / min and held for 12 h. The mixture was then naturally cooled to room temperature to obtain the sintered material.

[0063] 2) The sintered material is first crushed by a jaw crusher and a double roller mill, and then pulverized by an air jet mill. The air pressure is controlled at 0.35MPa, the grading frequency is 45Hz, and the induced draft frequency is 40Hz, which can effectively dissociate the sintered agglomerates and control the particle size.

[0064] The pulverized material is sieved through a 300-mesh sieve to obtain ternary cathode material.

[0065] Figure 4 The figures show the DQ / DV curves of the cathode materials prepared in Example 1 and Comparative Example 1 at a 0.1C rate. As can be seen from the figures, the reduction peaks in Comparative Example 1 are generally lower, with no reduction peak around 3.5V, indicating greater polarization and lower discharge capacity. In contrast, the reduction peaks in Example 1 are generally higher, especially the H2-H3 phase transition peak around 4.2V and the H1-M reduction peak around 3.5V. This indicates that through a two-stage decreasing cobalt concentration gradient design, Example 1 mitigates the irreversible phase transitions of H1-M and H2-H3, resulting in a higher specific capacity.

[0066] Figure 5 The graph shows the high-temperature cycling performance of the cathode materials prepared in Example 1 and Comparative Example 1. As can be seen from the graph, through the two-stage decreasing cobalt concentration gradient and the coating layer design, the high-temperature cycling performance of Example 1 is far superior to that of Comparative Example 1.

[0067] Comparative Example 2:

[0068] A low-cobalt single-crystal cathode material with the chemical formula Li 0.99 Ni 0.948 Co 0.01 Mn 0.04 Zr 0.002 B 0.0005 Al 0.002 O2 is composed of primary single-crystal particles with a D50 particle size of 4.2 μm, a primary particle grain size of 1.7 μm, and a specific surface area of ​​0.49 m². 2 / g, total residual lithium is 2545ppm, XRD diffraction 104 peak half width at half maximum is 0.109, XRD refined lithium-nickel mixing value is 2.97%. Compared with the example, the material has poor crystallinity and serious lithium-nickel mixing.

[0069] Its preparation method includes the following steps:

[0070] 1) The purchased nickel-cobalt-manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, and nano-sized zirconium oxide were added to a high-speed mixer at a molar ratio of 1:1.07:0.002 and stirred at 1800 r / min for 30 min. Then, in a box furnace with an oxygen concentration ≥96%, the temperature was increased to 786℃ at a heating rate of 3℃ / min and held for 12 h. The mixture was then naturally cooled to room temperature to obtain the sintered material.

[0071] 2) The sintered material is first crushed by a jaw crusher and a double roller mill, and then pulverized by an air jet mill. The air pressure is controlled at 0.35MPa, the grading frequency is 45Hz, and the induced draft frequency is 40Hz, which can effectively dissociate the sintered agglomerates and control the particle size.

[0072] The pulverized material was added to a high-speed mixer with boric acid and alumina at a molar ratio of 1:0.0005:0.001 and stirred at 1800 r / min for 30 min. Then, in a box furnace under an oxygen atmosphere, the temperature was raised to 320℃ at a heating rate of 3℃ / min and held for 8 h. After naturally cooling to room temperature, the sintered material was obtained. The sintered material was sieved using a 300-mesh sieve to obtain the ternary cathode material.

[0073] Performance testing:

[0074] The electrochemical performance of the cathode materials in the above examples and comparative examples was studied using CR2032 coin cells. The experimental methods are as follows:

[0075] Positive electrode sheet: The positive electrode materials of Examples 1 and 2 and Comparative Examples 1 and 2, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were stirred and dispersed with solvent NMP in a mass ratio of 92.5:5:2.5, coated on an aluminum foil substrate, and rolled to obtain a positive electrode sheet.

[0076] Negative electrode: Lithium metal sheet.

[0077] Electrolyte: 1 mol / L LiPF6 solution, with EC and DMC mixed in a ratio of 1:2, and 1% VC as additive.

[0078] The CR2032 button cell was assembled and tested. The charging cutoff voltage was 4.25V and the discharging cutoff voltage was 3.0V.

[0079] The following are the test results of the electrical properties of the cathode materials prepared in Examples 1-3 and Comparative Examples 1-2. The test results of the electrical properties are shown in Table 1.

[0080] Table 1: Electrical performance test results of cathode materials

[0081]

[0082] As shown in Table 1, the low-cobalt single-crystal cathode materials prepared in Examples 1-3 of this invention not only have a simple preparation method but also significantly improve the initial charge / discharge capacity and rate performance, and can significantly improve high-temperature cycling. They largely solve the common problems of high residual lithium, poor rate performance, and poor cycling performance in low-cobalt, high-nickel materials in the industry. In contrast, Comparative Examples 1-2 did not employ the doping and coating modification and two-stage high-temperature sintering process of this invention. Therefore, no cobalt concentration gradient distribution was formed inside the material, resulting in higher residual lithium on the material surface, larger polarization resistance, and poorer capacity, rate performance, and cycling performance compared to the examples. Overall, their electrochemical performance was significantly worse.

[0083] This invention, through the selection of suitable high-nickel, low-cobalt small-particle precursors, combined with elemental doping and coating modification and dry sintering processes, designs the internal nickel, cobalt, and manganese composition of ternary cathode materials, controls the particle size morphology and structure, and modifies the crystal structure and surface of the materials, forming a two-stage decreasing cobalt concentration gradient distribution from the outside to the inside. This improves the common problems of high residual lithium, poor power and cycle performance of high-nickel, low-cobalt cathode materials, alleviates the H1-M (low voltage kinetics) and H2-H3 irreversible phase transitions of high-nickel, low-cobalt materials, improves the mechanical strength of the materials, and achieves good power performance while balancing high capacity and long cycle life. At the same time, the crystal structure is stable, and the batteries used have high safety, high capacity and long cycle life, meeting the safety and high performance requirements of long-range high-end vehicles. It also has a high overall cost advantage and is suitable for the needs of EV long-range vehicle batteries.

Claims

1. A high-capacity, long-cycle, low-cobalt single-crystal cathode material, characterized in that, The low-cobalt single-crystal cathode material particles were analyzed by EPMA. The region from the particle surface to the particle surface, ranging from 25 nm to 425 nm, was designated as the first region, and the region from the particle surface to the particle center, ranging from 425 nm, was designated as the second region. The cobalt concentration in the first region is distributed in a gradient from the outside to the inside at a rate of 6% to 20% per 100 nm. The cobalt concentration in the second region is distributed in a gradient from the outside to the inside at a rate of 0.1% to 6% per 100 nm. The ratio of the rate of decrease in cobalt concentration in the first region to that in the second region is 3 to 8:

1.

2. The low-cobalt single-crystal cathode material according to claim 1, characterized in that, The general formula of the low-cobalt single-crystal cathode material is Li. u Ni 1-x-y-z Co x Mn y M z N v O 2-w Wherein, 0.9≤u≤1.1, 0<x≤0.10, 0<y≤0.1, 0≤z≤0.05, 0≤v≤0.05, -0.05≤w≤0.05; M is a doping element, which is selected from at least one or more of Al, Mg, Zr, Ti, Y, W, Ta, Nb, Ce, Sn, B, Sr, and Mo; N is a coating element, which is selected from at least one or more of B, Ce, Nb, Sn, W, Al, and Zr.

3. The low-cobalt single-crystal cathode material according to claim 1, characterized in that, The low-cobalt single-crystal cathode material has a full width at half maximum (FWHM) of 0.08 to 0.10 for the 104 peak in the XRD diffraction pattern, and the lithium-nickel mixture ratio obtained after XRD refinement is 1.8% to 2.5%.

4. The low-cobalt single-crystal cathode material according to claim 1, characterized in that, The low-cobalt single-crystal cathode material has a D50 particle size of 3.0~4.0μm, a primary particle grain size of 1.5~2.0μm, and a specific surface area of ​​0.4~0.8m². 2 / g, with total residual lithium of 800~1400ppm.

5. The low-cobalt single-crystal cathode material according to any one of claims 1 to 4, characterized in that, The low-cobalt single-crystal cathode material exhibits a prominent reduction peak at 3.4V to 3.6V in the 0.1C rate DQ / DV discharge curve.

6. A method for preparing a low-cobalt single-crystal cathode material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. After uniformly mixing the nickel-based hydroxide precursor, lithium salt, cobalt source and dopant, perform two-stage sintering, with the temperature of the first stage sintering being higher than that of the second stage sintering. S2. The sintered products obtained after the two sintering stages in step S1 are crushed and dissociated, then mixed evenly with the coating agent and sintered again to obtain the low cobalt single crystal cathode material.

7. The preparation method according to claim 6, characterized in that, The lithium salt is one or two of lithium carbonate, lithium hydroxide, lithium nitrate, lithium fluoride, and lithium phosphate; the cobalt source is one or two of cobalt(II) hydroxide, cobalt(II) hydroxyl oxide, and cobalt(III) oxide; the dopant is an M salt, which is a compound or compound containing one or more elements of Al, Mg, Zr, Ti, Y, W, Ta, Nb, Ce, Sn, B, Sr, and Mo; the coating agent is an N salt, which is a compound or compound containing one or more elements of B, Ce, Nb, Sn, W, Al, and Zr; and the molar ratio of lithium to nickel cobalt manganese hydroxide precursor in the lithium salt is 1.05~1.08:

1.

8. The preparation method according to claim 6, characterized in that, In step S1, the conditions for the two-stage sintering are as follows: the temperature of the first stage sintering is 800~1000℃, the heating rate is 1~3℃ / min, and the holding time is 2~5h; the temperature of the second stage sintering is 600~800℃, and the holding time is 8~20h. Both stages of sintering are carried out in an oxygen-containing atmosphere. In step S2, the re-sintering temperature is 200~700℃, carried out in an oxygen-containing atmosphere, the heating rate is 1~3℃ / min, and the holding time is 4~10h.

9. The preparation method according to any one of claims 6 to 8, characterized in that, In step S2, the crushing and dissociation specifically includes the following steps: the sintered product is initially crushed by a jaw crusher and a roller mill, and then crushed by an air jet mill, with the air pressure controlled at 0.2~0.4MPa, the grading frequency at 30~50Hz, and the induced draft frequency at 30~50Hz.

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