Niobium-doped ultrahigh-nickel ternary positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to a niobium-doped ultrahigh nickel ternary positive electrode material and a preparation method and application thereof, the chemical general formula of the positive electrode material is LiNi (1-a-b) CoaMnbNbxO2, a is more than 0 and less than or equal to 0.05, b is more than 0 and less than or equal to 0.05, and x is more than or equal to 0.005 and less than or equal to 0.02. Through niobium doping modification, migration of adjacent transition metals to tetrahedral vacancies and lithium layers can be effectively inhibited, so that phase transformation and cation mixing are inhibited; an electrochemical active protection layer can be formed on the niobium-rich surface, so that harmful rock salt phase change and electrolyte erosion can be effectively inhibited; and meanwhile, the interlayer spacing is also increased by doping niobium, and the diffusion coefficient of lithium ions is improved. The method is simple in process, low in cost and capable of achieving large-scale production, and the obtained niobium-doped and modified ultrahigh-nickel ternary positive electrode material has the advantages of being high in specific capacity, good in cycling stability, excellent in rate capability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a niobium-doped ultra-high nickel ternary cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to advantages such as high voltage and energy density, long cycle life, high energy efficiency, low self-discharge, no memory effect, and no pollution, lithium-ion batteries have become the most promising and competitive secondary batteries at present. In recent years, the sales volume of electric vehicles driven by lithium-ion batteries has increased significantly. In order to enable an electric vehicle to travel more than 600 kilometers on a single charge, it is necessary to develop a lithium-ion battery with an energy density exceeding 350 W h kg -1 and the specific energy of the corresponding cathode material is 800 W h kg -1 . However, the currently most advanced high-nickel ternary cathode materials (LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) or LiNi 0.8 Co 0.15 Al 0.05 O2 (NCA)) still cannot meet the requirements of energy and cost. Developing ultra-high nickel ternary cathode materials is an effective way to achieve this goal, but it faces a series of challenges.

[0003] As the nickel content is further increased, especially for ultra-high nickel ternary cathode materials (0.90 ≤ nickel content ≤ 1), the extremely high nickel content not only increases the capacity of the cathode material but also makes the material extremely sensitive to moisture and carbon dioxide, and the content of LiOH and Li2CO3 on the material surface is too high, resulting in poor structural stability, cycle performance, and safety performance of the cathode material, thereby affecting the overall performance of the battery cell. Among them, the excessive residual alkali content is likely to react with the electrolyte to cause an increase in gas production, reducing the safety performance of the battery cell; at the same time, the generation and expansion of microcracks during the cycling of the battery cell cause the anisotropic stress to concentrate at the grain boundaries, resulting in intergranular cracking and particle fragmentation, damaging the morphology and structure of the material, and at the same time, the infiltration of the electrolyte increases the side reactions and the impedance, affecting the transmission of lithium ions, and the structural stability and cycle performance of the cathode material decline. In addition, as the nickel content increases, the lithium-nickel mixing phenomenon in the ternary cathode material will intensify, and the structural stability of the material will be further deteriorated, thereby seriously affecting the cycle stability and rate performance of the material. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above technical deficiencies, provide a niobium-doped ultra-high nickel ternary cathode material, a preparation method thereof, and an application thereof, and solve the technical problems that in the prior art, the ultra-high nickel ternary cathode material is prone to cation mixing and electrolyte erosion, resulting in a decline in structural stability and cycle performance.

[0005] To achieve the above technical objectives, the technical solution provided by the present invention is as follows: In the first aspect, the present invention provides a niobium-doped ultra-high nickel ternary cathode material, the chemical general formula of which is LiNi （1-a-b） Co a Mn b Nb x O2, where 0 < a ≤ 0.05, 0 < b ≤ 0.05, 0.005 ≤ x ≤ 0.02.

[0006] In the second aspect, the present invention provides a preparation method of a niobium-doped ultra-high nickel ternary cathode material, including the following steps: mixing an ultra-high nickel ternary precursor, a lithium source and a niobium source uniformly to obtain a mixture; wherein, the ultra-high nickel ternary precursor is Ni （1-a-b） Co a Mn b (OH)2, 0 < a ≤ 0.05, 0 < b ≤ 0.05; subjecting the mixture to staged oxidative calcination to obtain the niobium-doped ultra-high nickel ternary cathode material.

[0007] In the third aspect, the present application provides a positive electrode sheet of a lithium-ion battery, and the positive electrode material of the positive electrode sheet includes the niobium-doped ultra-high nickel ternary cathode material of the first aspect.

[0008] In the fourth aspect, the present application provides a lithium-ion battery, and the lithium-ion battery includes the positive electrode sheet of the third aspect.

[0009] Compared with the prior art, the beneficial effects of the present invention include: Through niobium doping modification, niobium ions are doped into the transition metal layer and are distributed in a gradient. Due to the strong Nb−O bond, it can effectively inhibit the migration of adjacent transition metals to the tetrahedral vacancy and the lithium layer, thereby inhibiting the occurrence of phase transformation and cation mixing; and an electrochemically active protective layer can be formed on the niobium-rich surface, which can effectively inhibit harmful rock salt phase transformation and electrolyte erosion; at the same time, the incorporation of niobium also increases the layer spacing and improves the lithium ion diffusion coefficient, and the electrochemical performance of the niobium-doped ultra-high nickel ternary cathode material of the present invention has been greatly improved. The method of the present invention has the characteristics of simple process, low cost and large-scale production, and the obtained niobium-doped modified ultra-high nickel ternary cathode material has the advantages of high specific capacity, good cycle stability and excellent rate performance. Description of the Drawings

[0010] Figure 1 It is a scanning electron microscope (SEM) image of the niobium-doped ultra-high nickel ternary cathode material prepared in Example 2; Figure 2 It is a scanning electron microscope (SEM) image of the ultra-high nickel ternary cathode material prepared in Comparative Example 1; Figure 3Energy spectrum diagram of niobium-doped ultra-high nickel ternary cathode material prepared in Example 2; Figure 4 X-ray diffraction (XRD) patterns of ultra-high nickel ternary cathode materials prepared in Example 1, Example 2, Example 3, and Comparative Example 1; Figure 5 Charge-discharge specific capacity curves of ultra-high nickel ternary cathode materials prepared in Example 1, Example 2, Example 3, and Comparative Example 1; Figure 6 Cycling performance curves of ultra-high nickel ternary cathode materials prepared in Example 1, Example 2, Example 3, and Comparative Example 1. Detailed implementation manners

[0011] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0012] In order to solve the problems of easy cation mixing and electrolyte erosion in ultra-high nickel ternary cathode materials, a series of constructive methods have been adopted in the prior art, including electrolyte optimization, element doping, and surface coating, etc. Among them, element doping has been proven to be a simple and effective method to improve the electrochemical performance of materials. Common doping elements include aluminum, magnesium, zirconium, titanium, etc. However, which element to choose as the doping element and the doping amount of the doping element have a crucial impact on the material performance. Therefore, in the process of doping ultra-high nickel ternary cathodes, it is necessary to select a more reasonable element as the dopant and regulate its doping amount, so as to maximize the solution of the problems existing in ultra-high nickel ternary cathode materials, thereby promoting the commercialization process of ultra-high nickel ternary cathode materials.

[0013] To address the above deficiencies, the present invention provides a niobium-doped ultra-high nickel ternary cathode material, its preparation method and application. After doping and modification with niobium in the present invention, niobium ions are doped into the transition metal layer and distributed in a gradient manner. It can effectively inhibit the migration of adjacent transition metals to tetrahedral vacancies and lithium layers, thereby inhibiting the occurrence of phase transformation and cation mixing. At the same time, the niobium-rich surface can effectively inhibit harmful rock salt phase transformation and electrolyte erosion, thereby improving the comprehensive electrochemical performance of the ultra-high nickel ternary cathode material.

[0014] In the first aspect, the present invention provides a niobium-doped ultra-high nickel ternary cathode material, whose chemical general formula is LiNi （1-a-b） Co a Mn b Nb x O2, where 0 < a ≤ 0.05, 0 < b ≤ 0.05, 0.005 ≤ x ≤ 0.02.

[0015] Preferably, the chemical general formula of the niobium-doped ultra-high nickel ternary cathode material is LiNi 0.95 Co 0.025 Mn 0.025 Nb x O2, where 0.005 ≤ x ≤ 0.02.

[0016] In a second aspect, the present invention provides a method for preparing a niobium-doped ultra-high nickel ternary cathode material, comprising the following steps: Mix an ultra-high nickel ternary precursor, a lithium source, and a niobium source uniformly to obtain a mixture; wherein, the ultra-high nickel ternary precursor is Ni （1-a-b） Co a Mn b (OH)2, 0 < a ≤ 0.05, 0 < b ≤ 0.05; Perform segmented oxidative calcination on the mixture to obtain a niobium-doped ultra-high nickel ternary cathode material.

[0017] Preferably, the molar ratio of the lithium element in the lithium source to the total molar amounts of nickel, cobalt, and manganese elements in the ultra-high nickel ternary precursor is (1.02 - 1.08):1.

[0018] More preferably, n(Li):n(Ni+Co+Mn):n(Nb) = 1.05:1.

[0019] Preferably, the ultra-high nickel ternary precursor, the lithium source, and the niobium source are mixed uniformly by ball milling.

[0020] Preferably, the ultra-high nickel ternary precursor is vacuum dried and then mixed with the lithium source and the niobium source; the temperature of the vacuum drying is 80 - 150 °C.

[0021] Preferably, the ultra-high nickel ternary precursor is Ni 0.95 Co 0.025 Mn 0.025 (OH)2.

[0022] Preferably, the lithium source is LiOH·H2O; the niobium source is niobium pentoxide or niobium(V) ethoxide. In the present invention, the niobium source is preferably niobium pentoxide; there are no special restrictions on the sources of niobium pentoxide and LiOH·H2O in the present invention, and commercially available products or self-made products well-known to those skilled in the art can be used.

[0023] Preferably, the conditions for the segmented oxidative calcination include: in an air or oxygen atmosphere, first keep the temperature at 500 °C - 550 °C for 4 h - 6 h, then keep the temperature at 680 °C - 780 °C for 10 h - 15 h, and then naturally cool to room temperature.

[0024] Further preferably, in the staged oxidation calcination, the calcination temperature in the first stage is 500 °C and the heat preservation time is 5 h, and the calcination temperature in the second stage is 720 °C and the heat preservation time is 10 h.

[0025] Preferably, after the staged oxidation calcination, it is further ground and sieved to obtain the niobium-doped ultra-high nickel ternary cathode material, and the sieving is carried out with a 100-500 mesh sieve.

[0026] In a third aspect, the present application provides a positive electrode sheet for a lithium-ion battery, and the positive electrode material of the positive electrode sheet includes the niobium-doped ultra-high nickel ternary cathode material of the second aspect.

[0027] In a fourth aspect, the present application provides a lithium-ion battery, and the lithium-ion battery includes the positive electrode sheet of the third aspect.

[0028] The following further describes the present invention in detail through specific examples; unless otherwise specified, the equipment and reagents used in the present invention are conventional commercially available products in the technical field. The purity of niobium pentoxide is 99%.

[0029] Example 1 Weigh 2 g of the ultra-high nickel ternary precursor Ni 0.95 Co 0.025 Mn 0.025 (OH)2, 0.952 g of LiOH·H2O and 0.029 g of niobium pentoxide, where n(Li):n(Ni+Co+Mn):n(Nb) = 1.05:1:0.005 (molar ratio). Put the above three substances into a ball mill and mix them evenly to obtain the first mixture.

[0030] Place the above first mixture in a corundum boat and put it into a tube furnace for staged sintering and introduce oxygen. First, keep it at 500 °C for 5 h, then keep it at 720 °C for 12 h, and finally cool it naturally to room temperature to obtain the first sintered product.

[0031] Grind and crush the above first sintered product, and then screen it with a 300-mesh sieve to obtain the niobium-doped ultra-high nickel ternary cathode material.

[0032] Example 2 The difference from Example 1 is only that: weigh 2 g of the ultra-high nickel ternary precursor Ni 0.95 Co 0.025 Mn 0.025 (OH)2, 0.952 g of LiOH·H2O and 0.057 g of niobium pentoxide, where n(Li):n(Ni+Co+Mn):n(Nb) = 1.05:1:0.01 (molar ratio). Other steps and conditions are the same as in Example 1 to obtain the niobium-doped ultra-high nickel ternary cathode material.

[0033] Example 3 The difference from Example 1 is only that: weigh 2 g of ultra-high nickel ternary precursor Ni 0.95 Co 0.025 Mn 0.025 (OH)2, 0.952 g of LiOH·H2O and 0.115 g of niobium pentoxide, where n(Li):n(Ni+Co+Mn):n(Nb) = 1.05:1:0.02 (molar ratio), and other steps and conditions are the same as those in Example 1, to obtain niobium-doped ultra-high nickel ternary cathode material.

[0034] Comparative Example 1 The difference from Example 1 is only that: no niobium is doped, that is, weigh 2 g of ultra-high nickel ternary precursor Ni 0.95 Co 0.025 Mn 0.025 (OH)2, 0.952 g of LiOH·H2O, where n(Li):n(Ni+Co+Mn) = 1.05:1 (molar ratio), and other steps and conditions are the same as those in Example 1, to obtain ultra-high nickel ternary cathode material.

[0035] Performance Test I. The test methods adopted in the present invention: Morphology test: Use a scanning electron microscope (SEM) to observe and analyze the morphology characteristics and changes of the ultra-high nickel ternary cathode materials prepared in the examples and comparative examples; Structure analysis: Use X-ray diffraction (XRD) to analyze the structures of the ultra-high nickel ternary cathode materials prepared in the examples and comparative examples; Electrical performance test: Use a coin cell to test the electrical performance of the ultra-high nickel ternary cathode materials prepared in the examples and comparative examples. The specific steps are as follows: (1) Weigh the above ultra-high nickel ternary cathode material, conductive acetylene black (SP) and polyvinylidene fluoride (PVDF) according to a mass ratio of 90:5:5. First, dissolve PVDF in an appropriate amount of N-methylpyrrolidone (NMP), and then add the evenly mixed ultra-high nickel cathode material and acetylene black powder to NMP and stir evenly to make a slurry; (2) Uniformly coat the above slurry on an aluminum foil substrate, then transfer the wet electrode sheet to a vacuum drying oven and dry it at 120 °C for 12 h. Then, use a punching machine to punch the dried electrode sheet into a positive electrode sheet with a diameter of 12 mm; (3) Assemble 2025 coin cells in a glove box (where the O2 content < 1 ppm and the H2O content < 1 ppm), using the self-prepared electrode as the positive electrode, a lithium metal sheet as the negative electrode, a Celgard 2500 membrane as the separator, and an electrolyte of 1 mol / L LiPF6 dissolved in a solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 3:7 and adding 2 vol.% fluoroethylene carbonate (FEC). The voltage test window for the electrochemical performance is 2.70 - 4.30 V.

[0036] II. Result Analysis Figure 1 and Figure 2 are the scanning electron microscope images corresponding to the ultra-high nickel ternary cathode materials prepared in Example 2 and Comparative Example 1, respectively. From Figure 1 and Figure 2 it can be seen that the ultra-high nickel ternary cathode materials of Example 2 and Comparative Example 1 are both secondary micron spheres formed by the accumulation of nano-scale primary particles. Among them, the particle size of the primary particles in Example 2 is about 0.2 - 0.5 μm, and the particle size of the primary particles in Comparative Example 1 is about 0.5 - 1 μm, indicating that niobium doping does not change the overall morphology of the ultra-high nickel ternary cathode material, but will reduce the size of the primary particles on the micron spheres. At the same time, it can also be seen through Figure 3 that the nickel, cobalt, manganese, and niobium elements in the niobium-doped ultra-high nickel ternary cathode material prepared in Example 2 are uniformly distributed.

[0037] Figure 4 are the X-ray diffraction patterns of the ultra-high nickel ternary cathode materials prepared in Example 1, Example 2, Example 3, and Comparative Example 1. It can be seen from the figure that the peak shapes and peak positions of the ultra-high nickel ternary cathode materials prepared in the examples and comparative examples are basically the same, strong characteristic peaks can be observed, and there are no impurity peaks, indicating that niobium doping does not affect the α-NaFeO2 structure of the ultra-high nickel ternary cathode material. At the same time, the two groups of peaks (006) / (102) and (018) / (110) of the spectrum are both significantly split, indicating that the ultra-high nickel ternary cathode materials all have a good layered structure. In addition, the peak intensity ratio of (003) to (104) is related to the Li + / Ni 2+ cation mixing degree of the ternary cathode material. The larger the peak intensity ratio I (003) / I (104) , the lower the cation mixing degree. It can be seen from the spectrum that the I (003) / I (104) peak intensity ratios of the ultra-high nickel ternary cathode materials prepared in Examples 1 - 3 are all greater than the I (003) / I (104)The peak intensity ratio indicates that the cation mixing of the ultra-high nickel ternary cathode material has been inhibited after niobium doping. Finally, it can also be seen from the spectrogram that the peak positions of (003) and (104) of the ultra-high nickel ternary cathode materials prepared in Examples 1-3 shift to the left, indicating that the layer spacing of the ultra-high nickel ternary cathode material increases after niobium doping, which is beneficial to the electrical properties of the ultra-high nickel ternary cathode.

[0038] Figure 5 are the charge-discharge specific capacity curves of the ultra-high nickel ternary cathode materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1. Figure 6 are the cyclic performance curves of the ultra-high nickel ternary cathode materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1. Among them, the tested voltage range is 2.7 V - 4.3 V, the tested current density is 1 C (1 C = 180 mA / g), and the test temperature is 25°C; the specific results are shown in Table 1 below.

[0039] Table 1 Electrical property test results of the ultra-high nickel ternary cathode materials of Examples 1-3 and Comparative Example 1

[0040] From Figure 5 and Table 1, it can be seen that after niobium doping, the specific capacity and efficiency of the ultra-high nickel ternary cathode material have been improved. The discharge specific capacity reaches 220.3 - 228.9 mAh / g, and the initial efficiency is 86.8 - 91.2%; and the specific capacity and efficiency of the ultra-high nickel ternary cathode material prepared in Example 2 are the best.

[0041] From Figure 6 and Table 1, it can be seen that after 80 cycles, the capacity retention rate of the ultra-high nickel ternary cathode material prepared in the examples of the present invention can still be maintained at 84.9 - 91.4%, while that of Comparative Example 1 is reduced to 77.8%. This shows that the cyclic performance of the ultra-high nickel ternary cathode material has been significantly improved after niobium doping.

[0042] Comparative Example 2 The difference from Example 1 is only that: one-step sintering is adopted, that is, directly heating to 720°C and holding for 12 h, and other steps and conditions are the same as those in Example 1.

[0043] It is found that without the first-stage calcination, the mixture fails to be fully melted and homogenized and is directly sintered, resulting in uneven composition and particle size of the obtained material.

[0044] Comparative Example 3 The difference from Example 1 is only that: the first-stage sintering temperature is adjusted from 500°C to 400°C, and other steps and conditions are the same as those in Example 1.

[0045] It was found that if the sintering temperature of the first stage was too low, it would also cause insufficient melting and unevenness.

[0046] Different from the prior art, the present invention provides a niobium-doped ultra-high nickel ternary cathode material, a preparation method thereof and an application; by using a niobium source oxide as a dopant, the niobium element is uniformly mixed with the ultra-high nickel ternary cathode material precursor by a ball milling method, and then the niobium-doped ultra-high nickel ternary cathode material is obtained through a high-temperature heat treatment process. The preparation method includes the following steps: uniformly mixing the ultra-high nickel ternary precursor, a lithium source and a niobium source by ball milling, placing the uniformly mixed reactants in a corundum boat and putting them into a tube furnace for segmented sintering and introducing oxygen, first keeping the temperature at 500 °C to 550 °C for 4 h to 6 h, then keeping the temperature at 680 °C to 780 °C for 10 h to 15 h, and then naturally cooling to room temperature, grinding and screening the sintered product to obtain the niobium-doped ultra-high nickel ternary cathode material. In addition, the niobium-doped ultra-high nickel ternary cathode material prepared by the present invention has the advantages of uniform chemical composition, high purity, uniform particle size, precisely controllable chemical stoichiometry, simple operation method, easy control of production conditions, good product reproducibility, stable electrochemical performance, etc.

[0047] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A niobium-doped ultra-high nickel ternary cathode material, characterized in that, The chemical general formula of the niobium-doped ultra-high nickel ternary cathode material is LiNi （1-a-b） Co a Mn b Nb x O2, where 0 < a ≤ 0.05, 0 < b ≤ 0.05, and 0.005 ≤ x ≤ 0.

02.

2. The niobium-doped ultra-high nickel ternary cathode material according to claim 1, wherein The chemical general formula of the niobium-doped ultra-high nickel ternary cathode material is LiNi 0.95 Co 0.025 Mn 0.025 Nb x O2, where 0.005 ≤ x ≤ 0.

02.

3. The preparation method of the niobium-doped ultra-high nickel ternary cathode material according to any one of claims 1-2, characterized in that, It includes the following steps: Mix the ultra-high nickel ternary precursor, lithium source and niobium source uniformly to obtain a mixture; wherein, the ultra-high nickel ternary precursor is Ni （1-a-b） Co a Mn b (OH)2, 0 < a ≤ 0.05, 0 < b ≤ 0.05; Subject the mixture to segmented oxidative calcination to obtain a niobium-doped ultra-high nickel ternary cathode material.

4. The preparation method of the niobium-doped ultra-high nickel ternary cathode material according to claim 3, characterized in that, The molar ratio of the lithium element in the lithium source to the total molar amount of nickel, cobalt, and manganese elements in the ultra-high nickel ternary precursor is (1.02 - 1.08):

1.

5. The preparation method of the niobium-doped ultra-high nickel ternary cathode material according to claim 3, characterized in that, The ultra-high nickel ternary precursor, the lithium source, and the niobium source are uniformly mixed by ball milling; and / or The ultra-high nickel ternary precursor is vacuum dried and then mixed with the lithium source and the niobium source; the temperature of the vacuum drying is 80 - 150 °C.

6. The preparation method of the niobium-doped ultra-high nickel ternary cathode material according to claim 3, characterized in that, The ultra-high nickel ternary precursor is Ni 0.95 Co 0.025 Mn 0.025 (OH)2; The lithium source is LiOH·H2O; the niobium source is niobium pentoxide or niobium ethoxide.

7. The preparation method of the niobium-doped ultra-high nickel ternary cathode material according to claim 3, characterized in that, The conditions for the segmented oxidative calcination include: in an air or oxygen atmosphere, first hold at 500 °C - 550 °C for 4 h - 6 h, then hold at 680 °C - 780 °C for 10 h - 15 h, and then naturally cool to room temperature.

8. The preparation method of the niobium-doped ultra-high nickel ternary cathode material according to claim 3, characterized in that, After the segmented oxidative calcination, it is also ground and sieved to obtain the niobium-doped ultra-high nickel ternary cathode material, and the sieving is carried out with a 100 - 500 mesh sieve.

9. A positive electrode sheet of a lithium-ion battery, characterized in that, The cathode material of the cathode sheet includes the niobium-doped ultra-high nickel ternary cathode material according to any one of claims 1 - 2.

10. A lithium-ion battery, characterized in that, It includes the cathode sheet according to claim 9.

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