High-capacity, long-cycle, low-cobalt single-crystal positive electrode material and its manufacturing method

Abstract

The present invention relates to the field of lithium battery cathode materials and discloses a high-capacity, long-cycle, low-cobalt single-crystal cathode material, in which the interior of the particle is divided into two regions, a first region and a second region, from the outside to the inside, and the cobalt concentrations in the first region and the second region exhibit a gradient distribution, decreasing at rates of 6% to 20% and 0.1% to 6% per 100 nm, respectively, from the outside to the inside. This design significantly improves the initial charge / discharge capacity and rate performance, and significantly improves high-temperature cycling. The present invention also discloses a method for producing the low-cobalt single crystal positive electrode material, which is simple and inexpensive, by selecting an appropriate high-nickel, low-cobalt small particle precursor, combining element doping coating modification and dry sintering processes, adjusting and controlling the particle size, morphology and structure of the low-cobalt single crystal positive electrode material, and modifying the crystal structure and surface to form a two-stage decreasing cobalt concentration gradient distribution from the outside to the inside, thereby improving the common problems of high-nickel, low-cobalt positive electrode materials, such as high residual lithium, poor power and cycle performance, and poor safety performance.

Description

[Technical Field]

[0001] The present invention relates to the technical field of lithium battery positive electrode materials, and more particularly to a high-capacity, long-cycle, low-cobalt single-crystal positive electrode material and a method for producing the same. [Background technology]

[0002] To meet the ever-increasing demand for driving range in the new energy vehicle market, the competition for high energy density performance is intensifying, leading to the rapid development of high-energy lithium-ion batteries. In the race for energy density, the development of ternary cathode materials is moving toward higher nickel and higher voltage, while at the same time facing risks and challenges such as short cycle life and poor safety. In recent years, the price of raw materials has fluctuated greatly, and as the ultimate goal of ternary cathode materials, high-nickel, low-cobalt cathode materials have the advantages of maximum energy density and cost, but at the same time, they also suffer from common problems such as high residual lithium and poor rate and cycle performance.

[0003] Therefore, it is essential to develop improved high-nickel, low-cobalt positive electrode materials to resolve risk issues such as low capacity, short cycle life, and low safety. Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a high-capacity, long-cycle, low-cobalt single-crystal positive electrode material and a method for manufacturing the same, in order to overcome the deficiencies and defects mentioned in the background art above. [Means for solving the problem]

[0005] In order to solve the above technical problems, the technical solutions provided by the present invention are as follows: A high-capacity, long-cycle low-cobalt single crystal positive electrode material, wherein particles of the low-cobalt single crystal positive electrode material are characterized by an EPMA analysis of a first region being a region from a particle surface at a distance of 25 nm to 425 nm, and a second region being a region from a distance of 425 nm from the particle surface to a particle center; The cobalt concentration in the first region exhibits a gradient distribution with a decrease rate of 6% to 20% per 100 nm from the outside to the inside, The cobalt concentration in the second region exhibits a gradient distribution, decreasing from the outside to the inside by 0.1% to 6% per 100 nm.

[0006] EPMA quantitative analysis of the low-cobalt single crystal positive electrode material of the present invention shows that the cobalt concentration inside the particle exhibits a two-stage decreasing gradient distribution from the outside to the inside. In order to fully utilize the promoting effect of cobalt on the lithium ion diffusion rate, two different cobalt concentration gradient regions are provided from the surface to the inside, and the cobalt concentration gradient in the inner region is smaller than that in the outer region, forming a high-lithium insertion state lithium layer passage and lithium concentration gradient effect from the outside to the inside. The first region with a high cobalt gradient significantly promotes lithium ion entry into the crystal lattice and diffusion into the inside, mitigating the irreversible phase transition of the high nickel, low cobalt material H2-H3, and at the same time mitigating the high polarization resistance caused by the high-lithium insertion state inside the crystal. The second region with a low cobalt gradient allows the lithium concentration in the central lithium layer inside the crystal to be low, and lithium to be inserted into the crystal. The diffusion path of cobalt ions is relatively long, reducing the number of lithium layer passages, and the cobalt's promotion effect on the lithium ion diffusion rate gradually decreases with the lithium concentration. Combined with the low lithium ion concentration gradient in the second region, the low cobalt concentration gradient and high nickel content design of the second region further improves the lithium ion insertion rate and redox reaction, mitigating the irreversible phase transition of the high nickel, low cobalt material H1-M and further mitigating the high polarization resistance caused by the high lithium insertion state inside the crystal, improving the low voltage capacity performance, thereby achieving higher capacity and efficiently utilizing the cobalt gain effect, improving capacity while reducing the overall cost of the low cobalt material. This two-stage cobalt concentration gradient design fully combines the lithium layer pathway and lithium concentration gradient effects, greatly improving the lithium ion insertion rate during the discharge process and is very suitable for application in low-cobalt single crystal materials. It can improve the high polarization resistance caused by the long diffusion path and slow diffusion rate of low-cobalt single crystal materials, mitigate the irreversible phase transitions of high-nickel, low-cobalt materials H1-M and H2-H3, reduce power loss during cycling, and improve the cycling performance of the material. In addition, the two-stage cobalt concentration gradient design can fully and efficiently utilize the gain effect of cobalt, and has the advantage of relatively high overall cost.

[0007] Preferably, the ratio of the cobalt concentration reduction rates in the first region and the second region is 3 to 8:1. In this ratio, in the internal structure of the low-cobalt component, by making the limited cobalt content exhibit a two-step decreasing gradient distribution, the promoting effect of cobalt on the diffusion rate of lithium ions is fully utilized, the insertion rate of lithium ions in the discharge process is improved, and at the same time, in combination with the diffusion path of the spheroidal single-crystal lithium layer, especially in the later stage of discharge, when forming a lithium layer passage and a lithium gradient concentration effect with a high lithium insertion state from the outside to the inside, the first region with a high-concentration cobalt gradient greatly promotes the entry of lithium ions into the crystal lattice, alleviates the high polarization resistance due to the high lithium insertion state inside the crystal, further improves the insertion rate of lithium ions, and thereby exhibits a higher capacity.

[0008] Preferably, 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 where 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, and is at least one or more selected from Al, Mg, Zr, Ti, Y, W, Ta, Nb, Ce, Sn, B, Sr, Mo, and N is a coating element, and is at least one or more selected from B, Ce, Nb, Sn, W, Al, Zr.

[0009] More preferably, M is Zr. Zr for high-temperature co-doping in combination with the Zr-Co element can promote the laminated growth of primary particles, form a stable crystal structure (Zr-O strong bond), and at the same time, the Zr and Co sources can react with the residual lithium on the particle surface to form Li2ZrO3 and LiCoO2 high-speed ion conductors, improve the diffusion rate of lithium ions, protect the surface of the cathode material, suppress the side reaction between the surface of the cathode material and the electrolyte, and thereby improve the cycle stability of the material.

[0010] Preferably, the low-cobalt single crystal positive electrode material has an XRD diffraction pattern with a 104 peak half-width value of 0.08 to 0.10, and a lithium-nickel inclusion value obtained after XRD refinement is 1.8% to 2.5%. The narrower diffraction peak indicates a good crystallinity of the material, and the lower lithium-nickel inclusion can improve the lithium ion diffusion rate, which is beneficial for mitigating adverse phase transitions during cycling and improving structural stability.

[0011] Preferably, the low cobalt single crystal positive electrode material has a D50 particle size of 3.0 to 4.0 μm, a primary particle crystal particle size of 1.5 to 2.0 μm, and a specific surface area of ​​0.4 to 0.8 m 2 / g, with a total residual lithium of 800 to 1400 ppm.

[0012] Preferably, the low-cobalt single crystal positive electrode material has a convex reduction peak at 3.4 V to 3.6 V in the 0.1 C rate DQ / DV discharge curve, indicating that the material has a relatively good dynamic diffusion rate, relatively low polarization internal resistance and power loss, and can exhibit higher capacity and better cycle performance.

[0013] As a general inventive concept, the present invention provides a method for producing the above-described low-cobalt single crystal cathode material, the method comprising: Step S1: uniformly mixing a nickel-based hydroxide precursor, a lithium salt, a cobalt source, and a dopant, and then performing two-stage sintering, in which the temperature of the first stage sintering is higher than the temperature of the second stage sintering; and step S2, in which the sintered product obtained after the two-stage sintering in step S1 is crushed and disintegrated, and then uniformly mixed with a coating agent and re-sintered to obtain the low-cobalt single crystal positive electrode material.

[0014] In step S1, a first-stage short-platform ultra-high-temperature sintering is performed to promote the cobalt source to penetrate into the internal structure of the particles, forming a first region with a high cobalt concentration gradient. Subsequently, a second-stage high-temperature platform sintering is performed to promote further crystal growth of the particles and simultaneously form a cobalt concentration gradient within the substrate. Through this sintering process, the diffusion of the cobalt source is fast in the first stage and relatively slow in the second stage, thereby forming a differentiated concentration gradient.

[0015] In the above-described production 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 cobaltous hydroxide, cobalt oxyhydroxide, and tricobalt tetroxide; the dopant is an M salt and a 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 and a compound containing one or more elements of B, Ce, Nb, Sn, W, Al, and Zr; and a molar ratio of lithium element in the lithium salt to the nickel cobalt manganese hydroxide precursor is 1.05 to 1.08:1.

[0016] More preferably, the dopant is a compound containing one or more elements of Al, Mg, Zr, Ti, and Y, and the coating agent is a compound containing one or more elements of B, Nb, W, Al, and Zr.

[0017] Preferably, in step S1, the conditions of the two-stage sintering are that the temperature of the first stage sintering is 800 to 1000°C, the temperature rising rate is 1 to 3°C / min, and the temperature holding time is 2 to 5 hours, the temperature of the second stage sintering is 600 to 800°C, and the temperature holding time is 8 to 20 hours, and both of the two-stage sinterings are performed in an oxygen-containing atmosphere; In step S2, the re-sintering is carried out at a temperature of 200 to 700° C. in an oxygen-containing atmosphere, with a temperature rise rate of 1 to 3° C. / min and a temperature retention time of 4 to 10 hours.

[0018] Preferably, in step S2, the crushing and disaggregation specifically includes pre-crushing the sintered product in sequence using a jaw crusher and a roll crusher, and then crushing it using an air flow crusher, controlling the air pressure to 0.2 to 0.4 MPa, using a classification frequency of 30 to 50 Hz, and using a suction frequency of 30 to 50 Hz. [Effects of the Invention]

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The low-cobalt, high-nickel positive electrode material of the present invention has a particle interior with a cobalt concentration that exhibits a two-stage, gradually decreasing gradient distribution from the outside to the inside, which can significantly improve the initial charge / discharge capacity and rate performance, and can also significantly improve high-temperature cycling. This can significantly solve the common problems of low-cobalt, high-nickel materials in the industry, such as high residual lithium, poor rate and cycling performance, and poor safety performance. (2) The manufacturing method of the present invention employs appropriate surface coating elements and a dry sintering process to react with and reduce the residual lithium on the material surface, while simultaneously forming a thin and uniform coating layer on the material surface, solving the common problem of high residual lithium in high-nickel materials and avoiding the problem of surface structure damage caused by the removal of residual lithium in the water washing process. Furthermore, while establishing a lithium ion transmission path, it also fixes surface oxygen atoms, inhibiting side reactions between the material surface and the electrolyte, thereby improving the rate and cycle performance of the material. (3) The manufacturing method of the present invention uses an appropriate grinding process to control the dissociation effect of single crystal particles, and at the same time ensure the integrity of the single crystal particles during dissociation, forming particles with uniform and narrow distribution and excellent dispersibility, improving the dispersibility of particle size, obtaining a narrower particle range, and improving the consistency of material use. (4) The manufacturing method of the present invention has a simple overall process and relatively low costs. It selects an appropriate high-nickel, low-cobalt small particle precursor, combines element doping, coating modification, and dry sintering processes, and adjusts and controls the internal nickel-cobalt-manganese component design, particle size morphology, and structure of the ternary low-cobalt single crystal positive electrode material. The material's crystal structure and surface are modified to form a two-stage cobalt concentration gradient distribution from the outside to the inside. This solves the common problems of high-nickel, low-cobalt positive electrode materials, such as high residual lithium, poor power and cycling performance, and poor safety performance. This alleviates the irreversible phase transitions of H1-M (low voltage kinetics) and H2-H3 in high-nickel, low-cobalt materials, improving the mechanical strength of the material. This achieves both high capacity and long cycle life, while also providing relatively good power performance and a stable crystal structure, resulting in batteries with high safety, high capacity, and long cycle life. This meets the safe and high-performance requirements of high-range luxury vehicles and has the advantage of relatively high overall cost, making it suitable for the needs of long-range EV batteries. [Brief explanation of the drawings]

[0020] In order to more clearly describe the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the description of the embodiments or the prior art. It is clear that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative work. [Figure 1] FIG. 1 is an SEM image of a high-capacity, long-cycle, low-cobalt, high-nickel positive electrode material prepared in Example 1. [Figure 2] 1 is an EPMA image of a cross section of a high-capacity, long-cycle, low-cobalt, high-nickel positive electrode material prepared in Example 1. FIG. [Figure 3] FIG. 1 is an SEM image of a high-capacity, long-cycle, low-cobalt, high-nickel positive electrode material prepared in Example 2. [Figure 4] 1 is a DQ / DV graph of the positive electrode materials prepared in Example 1 and Comparative Example 1. [Figure 5] FIG. 2 is a graph showing the high-temperature cycle performance of the positive electrode materials produced in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order to facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the drawings and preferred embodiments in the specification, but the scope of protection of the present invention is not limited to the following specific examples.

[0022] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used in this specification are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0023] Unless otherwise specified, the various raw materials, reagents, instruments, and devices used in the present invention may be commercially available or may be produced by known methods.

[0024] Example 1 The high-capacity, long-cycle, low-cobalt single-crystal cathode material has the chemical formula Li 1.0 Ni 0.929 Co 0.030 Mn 0.039 Zr 0.002 B 0.0005 Al 0.002 O2, composed of small primary single crystal particles, with a D50 particle size of 3.5 μm, a primary particle crystal size of 1.7 μm, and a specific surface area of ​​0.65 m 2 / g, the total residual lithium is 1189 ppm, the half width value of the XRD diffraction 014 peak is 0.082, and the XRD refined lithium nickel inclusion value is 1.82%.

[0025] The manufacturing method includes the following steps. In step 1), purchased nickel cobalt manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04(OH)2, lithium hydroxide monohydrate, nanoscale zirconium oxide, and cobaltous 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. The mixture was then heated to 900°C at a rate of 3°C / min in a box furnace with an oxygen concentration of ≥96% and maintained at that temperature for 2 hours. The mixture was then further cooled to 786°C and maintained at that temperature for 12 hours, after which it was naturally cooled to room temperature to obtain a sintered material. In step 2), the sintered material is pre-crushed by a jaw crusher and a roll crusher in sequence, and then crushed by an airflow crusher, the air pressure is controlled at 0.35 MPa, the classification frequency is 45 Hz, and the suction frequency is 40 Hz, so that the sintered agglomerates can be fully dissociated and the particle size can be controlled; The crushed material, boric acid, and aluminum oxide were added to a high-speed mixer in a molar ratio of 1:0.0005:0.001 and stirred at 1800 r / min for 30 minutes. The mixture was then heated to 320°C at a rate of 3°C / min in a box furnace under an oxygen atmosphere and kept at that temperature for 8 hours. After that, the mixture was allowed to cool naturally to room temperature to obtain a sintered material, which was then sieved through a 300-mesh screen to obtain a ternary positive electrode material.

[0026] SEM and EPMA images of the above ternary positive electrode material are shown in Figures 1 and 2. The EMPA elemental distribution map shows that the cobalt concentration gradient is distributed in two stages, from the outside to the inside. In the first high-cobalt gradient region, which extends from 25 nm from the particle surface to 425 nm from the surface, the cobalt concentration decreases at a rate of 12.37% per 100 nm toward the center. In the second low-cobalt gradient region, which extends from 425 nm from the particle surface to the center, the cobalt concentration decreases at a rate of 3.18% per 100 nm toward the center. The ratio of the cobalt concentration decrease rates in the first and second regions is 3.89. This ensures rapid lithium ion insertion and extraction, while stabilizing the lattice structure of the material and mitigating the irreversible H1-M (low-voltage kinetics) and H2-H3 phase transitions of the high-nickel, low-cobalt material, improving both the capacity and mechanical strength of the material, thereby enhancing its cycling performance.

[0027] Example 2 The high-capacity, long-cycle, low-cobalt single-crystal cathode material has the chemical formula Li 1.0 Ni 0.928 Co 0.030 Mn 0.040 Al 0.004 B 0.0005 O2, composed of small primary single crystal particles, with a D50 particle size of 3.5 μm, a primary particle crystal size of 1.7 μm, and a specific surface area of ​​0.59 m 2 / g, the total residual lithium is 1312 ppm, the half width value of the XRD diffraction 014 peak is 0.085, and the XRD refined lithium nickel inclusion value is 1.87%.

[0028] The manufacturing method includes the following steps. In step 1), purchased nickel cobalt manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, aluminum oxide, and cobaltous 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. The mixture was then heated to 900°C at a rate of 3°C / min in a box furnace with an oxygen concentration of ≥96% and maintained at that temperature for 2 hours. The mixture was then further cooled to 786°C and maintained at that temperature for 12 hours, after which it was naturally cooled to room temperature to obtain a sintered material. In step 2), the sintered material is pre-crushed by a jaw crusher and a roll crusher in sequence, and then crushed by an airflow crusher, the air pressure is controlled at 0.35 MPa, the classification frequency is 45 Hz, and the suction frequency is 40 Hz, so that the sintered agglomerates can be fully dissociated and the particle size can be controlled; The crushed material, boric acid, and aluminum oxide were added to a high-speed mixer in a molar ratio of 1:0.0005:0.001 and stirred at 1800 r / min for 30 minutes. The mixture was then heated to 320°C at a rate of 3°C / min in a box furnace under an oxygen atmosphere and kept at that temperature for 8 hours. After that, the mixture was allowed to cool naturally to room temperature to obtain a sintered material, which was then sieved through a 300-mesh screen to obtain a ternary positive electrode material.

[0029] The SEM image of the above ternary positive electrode material is shown in Figure 3.

[0030] Example 3 The high-capacity, long-cycle, low-cobalt single-crystal cathode material has the chemical formula Li 1.0 Ni 0.929 Co 0.030 Mn 0.039 Zr 0.002 W 0.0015 O2, composed of small primary single crystal particles, with a wavy single crystal surface morphology, a D50 particle size of 3.8 μm, a primary particle crystal size of 1.7 μm, and a specific surface area of ​​0.64 m 2 / g, the total residual lithium is 1385 ppm, the half width value of the XRD diffraction 014 peak is 0.084, and the XRD refined lithium nickel inclusion value is 1.94%.

[0031] The manufacturing method includes the following steps. In step 1), purchased nickel cobalt manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, nanoscale zirconium oxide, and cobaltous 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. The mixture was then heated to 900°C at a rate of 3°C / min in a box furnace with an oxygen concentration of ≥96% and maintained at that temperature for 2 hours. The mixture was then further cooled to 786°C and maintained at that temperature for 12 hours, after which it was naturally cooled to room temperature to obtain a sintered material. In step 2), the sintered material is pre-crushed by a jaw crusher and a roll crusher in sequence, and then crushed by an airflow crusher, the air pressure is controlled at 0.35 MPa, the classification frequency is 45 Hz, and the suction frequency is 40 Hz, so that the sintered agglomerates can be fully dissociated and the particle size can be controlled; The crushed material and tungsten oxide were added to a high-speed mixer in a molar ratio of 1:0.0015 and stirred at 1800 r / min for 30 minutes. The mixture was then heated to 450°C at a rate of 3°C / min in a box furnace under an oxygen atmosphere and kept at that temperature for 8 hours. After that, the mixture was allowed to cool naturally to room temperature to obtain a sintered material, which was then sieved through a 300-mesh screen to obtain a ternary positive electrode material.

[0032] (Comparative Example 1) Low cobalt single crystal cathode material has the chemical formula Li 1.0 Ni 0.948 Co 0.01 Mn 0.04 Zr 0.002 O2, composed of small primary single crystal particles, with a D50 particle size of 3.7 μm, a primary particle crystal size of 1.7 μm, and a specific surface area of ​​0.71 m 2 / g, the total residual lithium is 3278 ppm, the half width value of the XRD diffraction 014 peak is 0.114, and the XRD refined lithium nickel contamination value is 3.12%. Compared with the examples, the crystallinity of the material is poor and the lithium nickel contamination is relatively serious.

[0033] The manufacturing method includes the following steps. In step 1), purchased nickel cobalt manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04 (OH)2, lithium hydroxide monohydrate, and nanoscale zirconium oxide were added to a high-speed mixer in a molar ratio of 1:1.07:0.002 and stirred at 1800 r / min for 30 min. The mixture was then heated to 786°C at a rate of 3°C / min in a box furnace with an oxygen concentration of ≥96%, and kept at this temperature for 12 hours. The mixture was then naturally cooled to room temperature to obtain a sintered material. In step 2), the sintered material is pre-crushed by a jaw crusher and a roll crusher in sequence, and then crushed by an airflow crusher, the air pressure is controlled at 0.35 MPa, the classification frequency is 45 Hz, and the suction frequency is 40 Hz, so that the sintered agglomerates can be fully dissociated and the particle size can be controlled; The crushed material was sieved through a 300 mesh screen to obtain a ternary positive electrode material.

[0034] 4 is a graph showing the DQ / DV at a 0.1C rate of the positive electrode materials prepared in Example 1 and Comparative Example 1. As can be seen from the graph, Comparative Example 1 has generally low reduction peaks and no reduction peak at around 3.5V, resulting in relatively large polarization and a relatively low discharge capacity, whereas Example 1 has generally high reduction peaks, particularly the H2-H3 phase transition peak at around 4.2V and the H1-M reduction peak at around 3.5V. This indicates that the two-stage tapered cobalt concentration gradient design in Example 1 alleviates the irreversible H1-M and H2-H3 phase transitions, resulting in a higher gram capacity.

[0035] 5 is a graph showing the high-temperature cycle performance of the positive electrode materials prepared in Example 1 and Comparative Example 1. As can be seen from the graph, the high-temperature cycle performance of Example 1 is much better than that of Comparative Example 1 due to the two-step decreasing cobalt concentration gradient and coating layer design.

[0036] (Comparative Example 2) Low cobalt single crystal cathode material has 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, composed of small primary single crystal particles, with a D50 particle size of 4.2 μm, a primary particle crystal size of 1.7 μm, and a specific surface area of ​​0.49 m 2 / g, the total residual lithium was 2545 ppm, the half width value of the XRD diffraction 014 peak was 0.109, and the XRD refined lithium nickel contamination value was 2.97%, which means that compared with the examples, the crystallinity of the material was poor and the lithium nickel contamination was relatively serious.

[0037] The manufacturing method includes the following steps. In step 1), purchased nickel cobalt manganese hydroxide precursor Ni 0.95 Co 0.01 Mn 0.04(OH)2, lithium hydroxide monohydrate, and nanoscale zirconium oxide were added to a high-speed mixer in a molar ratio of 1:1.07:0.002 and stirred at 1800 r / min for 30 min. The mixture was then heated to 786°C at a rate of 3°C / min in a box furnace with an oxygen concentration of ≥96%, and kept at this temperature for 12 hours. The mixture was then naturally cooled to room temperature to obtain a sintered material. In step 2), the sintered material is pre-crushed by a jaw crusher and a roll crusher in sequence, and then crushed by an airflow crusher, the air pressure is controlled at 0.35 MPa, the classification frequency is 45 Hz, and the suction frequency is 40 Hz, so that the sintered agglomerates can be fully dissociated and the particle size can be controlled; The crushed material, boric acid, and aluminum oxide were added to a high-speed mixer in a molar ratio of 1:0.0005:0.001 and stirred at 1800 r / min for 30 minutes. The mixture was then heated to 320°C at a rate of 3°C / min in a box furnace under an oxygen atmosphere and kept at that temperature for 8 hours. After that, the mixture was allowed to cool naturally to room temperature to obtain a sintered material, which was then sieved through a 300-mesh screen to obtain a ternary positive electrode material.

[0038] Performance test: The electrochemical performance of the positive electrode materials in the above examples and comparative examples was investigated using a CR2032 coin-type battery. The experimental method is as follows: 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 in a mass ratio of 92.5:5:2.5 with NMP solvent, and the dispersion was applied to an aluminum foil substrate and roll-pressed to obtain a positive electrode sheet. Negative electrode sheet: a lithium metal sheet. Electrolyte: 1 mol / L LiPF6 solution, the solvent is a mixed solvent of EC and DMC, the ratio of the two is 1:2, and the additive is 1% VC. Assembled into a CR2032 coin cell battery for battery testing, the charge cut-off voltage is 4.25V and the discharge cut-off voltage is 3.0V.

[0039] Below are the test results of the electrical performance of the positive electrode materials produced in Examples 1 to 3 and Comparative Examples 1 and 2. Table 1 shows the test results of the electrical performance.

[0040] [Table 1]

[0041] As can be seen from Table 1, the low-cobalt single crystal positive electrode materials prepared in Examples 1 to 3 of the present invention not only have simple manufacturing methods, but also significantly improve initial charge / discharge capacity and rate performance, and significantly improve high-temperature cycling, significantly solving the common problems of low-cobalt, high-nickel materials in the industry, such as high residual lithium and poor rate and cycling performance.Comparative Examples 1 and 2 do not use the doping coating modification and two-stage high-temperature sintering process of the present invention, and therefore do not form a cobalt concentration gradient distribution within the material, have relatively high residual lithium on the material surface, relatively large polarization internal resistance, relatively poor capacity, rate and cycling performance, and have relatively poor overall electrochemical performance compared to the Examples.

[0042] The present invention selects an appropriate high-nickel, low-cobalt small particle precursor, and combines element doping, coating modification, and dry sintering processes to adjust and control the internal nickel-cobalt-manganese component design, particle size morphology, and structure of the ternary positive electrode material. This modifies the material's crystal structure and surface, forming a two-stage cobalt concentration gradient distribution from the outside to the inside. This solves the common problems of high-nickel, low-cobalt positive electrode materials, such as high residual lithium and poor power and cycle performance. This alleviates the irreversible phase transitions of H1-M (low voltage kinetics) and H2-H3 in high-nickel, low-cobalt materials, improving the mechanical strength of the material. This achieves both high capacity and long cycle life, while also providing relatively good power performance and a stable crystal structure. This makes the battery highly safe, high-capacity, and long-cycle, meeting the safe and high-performance requirements of high-range luxury vehicles and offering the advantage of relatively high overall cost, making it suitable for the needs of long-range EV batteries.

Claims

1. A high-capacity, long-cycle low-cobalt single crystal positive electrode material, wherein particles of the low-cobalt single crystal positive electrode material are characterized by an EPMA analysis of a first region located at a distance of 25 nm to 425 nm from the particle surface, and a second region located at a distance of 425 nm from the particle surface to the particle center; The cobalt concentration in the first region exhibits a gradient distribution at a rate of decreasing from the outside to the inside by 6% to 20% per 100 nm; The cobalt concentration in the second region exhibits a gradient distribution at a rate of decreasing from the outside to the inside by 0.1% to 6% per 100 nm.

2. 2. The low-cobalt single crystal positive electrode material according to claim 1, wherein the ratio of the cobalt concentration reduction rate in the first region to the cobalt concentration reduction rate in the second region is 3 to 8:

1.

3. 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 and is at least one or more elements selected from Al, Mg, Zr, Ti, Y, W, Ta, Nb, Ce, Sn, B, Sr, and Mo, and N is a coating element and is at least one or more elements selected from B, Ce, Nb, Sn, W, Al, and Zr. The low cobalt single crystal positive electrode material according to claim 1,

4. The low cobalt single crystal positive electrode material has a half width value of 0.08 to 0.10 of the 104 peak in the XRD diffraction pattern, and the lithium nickel inclusion value obtained after XRD refinement is 1.8% to 2.5%. The low cobalt single crystal positive electrode material according to claim 1.

5. The low cobalt single crystal positive electrode material has a D50 particle size of 3.0 to 4.0 μm, a primary particle crystal particle size of 1.5 to 2.0 μm, and a specific surface area of ​​0.4 to 0.8 m ２ / g and a total residual lithium of 800-1400 ppm.

6. The low cobalt single crystal positive electrode material according to any one of claims 1 to 5, characterized in that it has a convex reduction peak at 3.4 V to 3.6 V in a 0.1 C rate DQ / DV discharge curve. The low cobalt single crystal positive electrode material according to any one of claims 1 to 5.

7. Step S1: uniformly mixing a nickel-based hydroxide precursor, a lithium salt, a cobalt source, and a dopant, and then performing two-stage sintering, in which the temperature of the first stage sintering is higher than the temperature of the second stage sintering; and Step S2 of subjecting the sintered product obtained after the two-stage sintering in Step S1 to pulverization and disintegration, followed by uniformly mixing the sintered product with a coating agent and then re-sintering the resulting low-cobalt single crystal positive electrode material.

8. 8. The method according to claim 7, wherein 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 cobaltous hydroxide, cobalt oxyhydroxide, and trimocobalt tetroxide; the dopant is an M salt, which is a 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 containing one or more elements of B, Ce, Nb, Sn, W, Al, and Zr; and a molar ratio of lithium element in the lithium salt to the nickel cobalt manganese hydroxide precursor is 1.05 to 1.08:

1.

9. In step S1, the conditions of the two-stage sintering are that the temperature of the first stage sintering is 800 to 1000°C, the temperature rising rate is 1 to 3°C / min, and the temperature holding time is 2 to 5 hours, the temperature of the second stage sintering is 600 to 800°C, and the temperature holding time is 8 to 20 hours, and both of the two stages are performed in an oxygen-containing atmosphere; 8. The method of claim 7, wherein in step S2, the re-sintering is performed at a temperature of 200 to 700°C in an oxygen-containing atmosphere, with a heating rate of 1 to 3°C / min and a heat-keeping time of 4 to 10 hours.

10. The manufacturing method according to any one of claims 7 to 9, characterized in that in step S2, the pulverization and disaggregation specifically includes steps of pre-crushing the sintered product in sequence using a jaw crusher and a roll crusher, and then pulverizing it using an air flow pulverizer, controlling the air pressure to 0.2 to 0.4 MPa, using a classification frequency of 30 to 50 Hz, and using a suction frequency of 30 to 50 Hz.

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