A lanthanum aluminate-coated lithium nickel cobalt manganate ternary positive electrode material and its preparation method

Abstract

The present invention discloses a lanthanum aluminate-coated nickel-cobalt-manganese-oxide ternary cathode material and its preparation method. The ternary cathode material comprises quasi-spherical nickel-cobalt-manganese-oxide particles as its substrate, with lanthanum aluminate coated on the substrate to form a core-shell structure. The lanthanum aluminate-coated nickel-cobalt-manganese-oxide ternary cathode material retains its unmodified morphology, forming quasi-spherical particles with an average particle size of 9 to 12 μm, a regular morphology, and a uniform particle size distribution. The lanthanum aluminate coating formed on the surface of the cathode material reduces the dissolution of transition metal ions, inhibits side reactions between the material and the electrolyte, and inhibits corrosion by HF acid, thereby improving the material's cycling stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a lanthanum aluminate-coated nickel-cobalt-lithium manganate ternary positive electrode material and a preparation method thereof. Background Art

[0002] Lithium nickel, cobalt, and manganese oxide (NiCoMnO) ternary cathode materials have become one of the most promising lithium-ion battery cathode materials due to their high energy density and operating voltage. However, NiCoMnO ternary cathode materials are prone to reacting with the electrolyte, leading to the dissolution of transition metals, reducing the number of lithium ion insertion sites, and lowering the material's capacity. Furthermore, when highly delithiated, the high-valent transition metal ions within the material undergo redox reactions with oxygen anions, releasing O2, which poses safety concerns. Therefore, in order to further expand the application range of NiCoMnO ternary cathode materials, the cycling stability and safety of NiCoMnO ternary cathode materials need to be further improved. Furthermore, with the increasing performance requirements for lithium-ion batteries in pure electric vehicles, hybrid electric vehicles, and portable energy storage devices, improving the high-temperature and high-voltage performance of NiCoMnO ternary cathode materials is becoming increasingly urgent.

[0003] In order to solve the above problems, surface coating is currently mainly used to modify the nickel cobalt manganese oxide ternary cathode material. Surface coating can inhibit interfacial side reactions, prevent chemical corrosion of the electrolyte, reduce the dissolution of transition metal ions, stabilize the material structure, improve the ionic and electronic conductivity of the material, and promote the transfer of interfacial ionic charges, thereby improving the electrochemical performance of the nickel cobalt manganese oxide ternary cathode material. Currently, wet coating is a commonly used surface coating method, but wet coating will cause the ternary material to come into contact with water, affecting the material performance, especially for high-nickel ternary cathode materials. In addition, the coating process may destroy the surface stoichiometric ratio of the material.

[0004] Based on the above problems, there is an urgent need for a coated modified nickel cobalt manganese oxide ternary positive electrode material with good coating effect, simple process method, low cost and easy industrial production. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a lanthanum aluminate-coated nickel cobalt lithium manganese oxide ternary positive electrode material and a preparation method thereof.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0007] A lanthanum aluminate-coated nickel-cobalt-lithium manganate ternary positive electrode material, wherein the matrix of the ternary positive electrode material is spherical nickel-cobalt-lithium manganate particles, and lanthanum aluminate is coated on the matrix to form a core-shell structure.

[0008] ABO3-type perovskite oxides have attracted considerable attention due to their physical and chemical properties, including high electrical and ionic conductivity and excellent structural stability. Lanthanum aluminate (LaAlO3), an ABO3-type perovskite oxide, exhibits excellent chemical stability and structural stability at high temperatures. It can effectively improve the interfacial stability of high-nickel ternary cathode materials and prevent HF corrosion. Furthermore, LaAlO3 exhibits high ionic conductivity, which facilitates the transport of lithium ions in high-nickel ternary cathode materials, thereby enhancing the electrochemical performance of the materials.

[0009] Therefore, forming a lanthanum aluminate coating on the surface of the positive electrode material can reduce the dissolution of transition metal ions, inhibit side reactions between the material and the electrolyte and corrosion by HF acid, and improve the material's cycling stability. Lanthanum aluminate also has high ionic conductivity, which facilitates lithium ion transport during the charge-discharge cycle. Furthermore, lanthanum aluminate's excellent chemical and thermal stability improves the material's electrochemical performance under high voltage and high temperature conditions.

[0010] Preferably, the chemical formula of the ternary cathode material matrix is ​​LiNi x Co y Mn (1-x-y) O2, wherein 0.6<x<0.9, 0.05<y<0.2; the mass ratio of the generated amount of the lanthanum aluminate coating layer to the ternary precursor matrix material is 0.01-0.1:1, and the coating layer is limited to the nanometer level.

[0011] Under the same technical concept, the present invention also provides a method for preparing a ternary positive electrode material of lanthanum aluminate coated nickel cobalt lithium manganese oxide, comprising the following steps:

[0012] (1) preparing a nickel-cobalt-manganese hydroxide precursor;

[0013] (2) preparing a lanthanum aluminate precursor;

[0014] (3) After uniformly mixing the nickel-cobalt-manganese hydroxide precursor prepared in step (1) and the lanthanum aluminate precursor prepared in step (2) with a lithium source, performing two-stage sintering in an oxidizing atmosphere, and cooling to room temperature, a lanthanum aluminate-coated nickel-cobalt-manganese oxide ternary positive electrode material is obtained.

[0015] Lanthanum aluminate has a melting point greater than 2000°C, while lithium hydroxide in the lithium source melts at 462°C. Two-stage sintering facilitates lithium diffusion and the preparation of positive electrode materials. Therefore, by utilizing a two-stage sintering process with a precursor-mixed lithium mixture to prepare the positive electrode material, a uniformly mixed lanthanum aluminate coating is applied to the material surface, effectively ensuring the formation of a core-shell structured ternary positive electrode material.

[0016] Preferably, the preparation of the nickel-cobalt-manganese hydroxide precursor in step (1) is specifically as follows: under a protective atmosphere, a nickel-cobalt-manganese solution is added to a preheated continuous stirred reactor containing an ammonia solution, a complexing agent and a precipitant are added, and after stirring for co-precipitation reaction, aging, filtering, washing, and drying to obtain a nickel-cobalt-manganese hydroxide precursor; the nickel source is a soluble nickel salt, the cobalt source is a soluble cobalt salt, and the manganese source is a soluble manganese salt; the complexing agent is an ammonia solution, and the hydroxide precipitant is one or more of sodium hydroxide, potassium hydroxide or lithium hydroxide.

[0017] The reaction vessel is a continuous stirred reactor. The growth of the ternary precursor material in the slurry is affected by temperature. The stirred reactor must be preheated to 45°C-55°C before adding to ensure the growth temperature and stirring conditions.

[0018] Preferably, the soluble nickel salt is one or more of nickel sulfate, nickel nitrate, nickel acetate or nickel chloride, and hydrates thereof; the soluble cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt acetate or cobalt chloride, and hydrates thereof; the soluble manganese salt is one or more of manganese sulfate, manganese nitrate, manganese acetate or manganese chloride, and hydrates thereof.

[0019] Preferably, in step (1), the total molar concentration of nickel, cobalt and manganese ions in the solution is 0.1-3.0 mol / L, and the molar ratio of nickel in the nickel source, cobalt in the cobalt source and manganese in the manganese source is 6-9:0.5-2.0:0.5-2.0.

[0020] Preferably, in step (1), the total molar concentration of nickel, cobalt, and manganese ions in the solution is 0.1 to 3.0 mol / L (more preferably 1.5 to 2.5 mol / L). If the concentration of the metal ions is too low, it is not conducive to the subsequent precipitation process, and the precipitation time is long, which is not conducive to improving production efficiency; if the concentration of the metal ions is too high, it is not conducive to the complete dissolution of the metal salt.

[0021] Preferably, in step (1), the feeding rate of the mixed solution is 80 to 120 mL / h (more preferably 90 to 110 mL / h). If the feeding rate is too fast, the pH range will vary widely, making it difficult for the precipitant to effectively precipitate the metal ions, which is not conducive to controlling the formation and growth of crystal nuclei during the reaction process. If the feeding rate is too slow, the particles are likely to agglomerate, which is also not conducive to improving production efficiency.

[0022] Preferably, in step (1), the volume ratio of the ammonia solution, the hydroxide precipitant solution, and the metal solution in the reactor is 0.1 to 10: 1 to 2: 1 to 2. This addition ratio is conducive to the formation of grains and crystal growth during the crystallization process.

[0023] Preferably, in step (1), the molar concentration of the ammonia solution is 0.1 to 5.0 mol / L. If the molar concentration of the ammonia solution is too low, it is difficult for the metal ions to be completely complexed, and if the molar concentration of the ammonia solution is too high, it is not conducive to the formation of hydroxide precipitation by the metal ions.

[0024] Preferably, in step (1), the ammonia concentration of the reaction system is adjusted with ammonia to be maintained at 0.1 to 5.0 mol / L.

[0025] Preferably, in step (1), the mass concentration of the ammonia water used to adjust the ammonia concentration of the reaction system is 25-28%.

[0026] Preferably, in step (1), the pH value of the reaction system is adjusted with a hydroxide precipitant solution to maintain at 10 to 12. At said pH value, it is more advantageous to control the particle growth rate to be neither too fast nor too slow.

[0027] Preferably, in step (1), the molar concentration of the hydroxide precipitant solution is 1.0 to 7.0 mol / L (more preferably 4.0 to 6.0 mol / L). If the molar concentration of the hydroxide precipitant solution is too high or too low, it cannot be accurately controlled.

[0028] Preferably, in step (1), the protective atmosphere is nitrogen or argon atmosphere; the stirring speed of the coprecipitation reaction is 800-1200 r / min, the temperature is 30-60°C, more preferably 40-50°C, and the time is 12-48h; if the stirring speed is too slow, the primary particles are likely to agglomerate, and if the stirring speed is too fast, the growing crystals are likely to break; within the temperature range, it is more conducive to crystal growth; the reaction time is determined by the raw material content and the feeding rate.

[0029] The aging temperature is 30-60°C, more preferably 40-50°C, and the time is 8-24 hours. The aging process can replace anions such as sulfate in the material and is beneficial to the uniformity of the particle surface. If the aging time is too short, it is difficult to ensure the ion exchange of anions, which will also affect the subsequent washing process. If the aging time is too long, it will be detrimental to production applications and the uniformity of the material surface. The aging temperature is consistent with the coprecipitation reaction temperature, which is conducive to the uniform dispersion of the material without agglomeration and ensures that the primary particles grow uniformly into secondary particles.

[0030] The filtrate is washed with deionized water and then ethanol for at least six times in a cross-washing process. The drying temperature is 80-100°C for 12-24 hours. If the temperature is too low or the drying time is too short, the material will be difficult to dry. If the temperature is too high or the drying time is too long, side reactions may occur on the material surface, affecting the material's performance. Furthermore, if the drying time is too long, it is not conducive to industrial production.

[0031] Preferably, the preparation of the nickel cobalt manganese hydroxide precursor in step (2) is specifically as follows: grinding the aluminum source, the lanthanum source and the complexing agent together, mixing them uniformly, and drying them to obtain a lanthanum aluminate precursor.

[0032] Preferably, in step (2), the molar ratio of the aluminum source, the lanthanum source and the complexing agent is 1:1:1; the aluminum source includes one or more of aluminum nitrate, aluminum oxalate or aluminum hydroxide and hydrates thereof, the lanthanum source includes one or more of lanthanum nitrate, lanthanum carbonate or lanthanum acetate and hydrates thereof, and the complexing agent includes one or more of citric acid monohydrate, ethylenediaminetetraacetic acid or tartaric acid; more preferably, the aluminum source is aluminum nitrate, the lanthanum source is lanthanum nitrate, and the complexing agent is citric acid monohydrate.

[0033] Preferably, in step (2), the grinding time is 20 to 40 minutes. If the grinding time is too short, the aluminum source, lanthanum source, and complexing agent cannot be fully refined and mixed unevenly; if the grinding time is too long, the experimental cycle is too long, which is not conducive to industrial production.

[0034] Preferably, in step (2), the drying temperature is 100-120°C and the drying time is 2-6 hours. If the drying temperature is too low or the drying time is too short, the material will be difficult to dry; if the temperature is too high or the drying time is too long, the aluminum source and lanthanum source will decompose, resulting in side reactions and affecting the material properties.

[0035] Preferably, in step (3), the mass ratio of the amount of the lanthanum aluminate coating layer generated to the ternary precursor matrix material is 0.01 to 0.1:1. If too much lanthanum aluminate is generated, the coating layer on the surface of the material will be too thick, which will reduce the specific capacity of the material and affect the reaction kinetics of the ternary material; if too little lanthanum aluminate is generated, it will be difficult to achieve uniform coating on the surface of the ternary material, and the electrochemical performance of the nickel-cobalt-manganese-lithium ternary cathode material cannot be effectively improved.

[0036] The molar ratio of the total molar number of nickel, cobalt and manganese elements in the nickel-cobalt-manganese hydroxide to the lithium in the lithium source is 1:1.02-1.10; if the lithium source is too little, the volatilization of Li during the high-temperature process will affect the material structure, so that the ternary material cannot form a good layered structure, thereby affecting the electrochemical properties of the material; if the lithium source is too much, an excessively thick residual lithium layer will appear on the surface of the ternary material, inhibiting the diffusion of lithium ions and increasing the impedance of the ternary material.

[0037] The two-stage temperature-raising sintering refers to: first, heating to 350-550°C, more preferably 400-500°C, at a rate of 1-10°C / min, more preferably 3-7°C / min; sintering for 2-8 hours, more preferably 3-6 hours; then heating to 550-1000°C, more preferably 600-900°C, at a rate of 1-10°C / min, more preferably 3-7°C / min; sintering for 8-20 hours, more preferably 10-16 hours; in the two-stage temperature-raising sintering process, the temperature of the second stage sintering is higher than the temperature of the first stage sintering. During the first stage sintering process, the decomposition reaction of the precursor and the lithium source mainly occurs, and in the second stage sintering process, the chemical reaction of the precursor and the oxide decomposed by the lithium source in an oxygen atmosphere mainly occurs. If the sintering temperature is too high or the sintering time is too long, the material will easily agglomerate or even clump, making it difficult to release capacity during the charge and discharge process. If the sintering temperature is too low or the sintering time is too short, it will be difficult to form the desired morphology, affecting the electrochemical performance. If the heating rate is too fast, it will be difficult to ensure that the material reacts fully, especially affecting the diffusion of lithium ions into the material structure. If the heating rate is too slow, it will be unfavorable for industrial production.

[0038] The lithium source is lithium hydroxide monohydrate and / or lithium carbonate; the oxidizing atmosphere is air atmosphere and / or oxygen atmosphere.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The lanthanum aluminate-coated lithium nickel cobalt manganese oxide ternary positive electrode material maintains the morphology before modification, which is spherical particles with an average particle size of 9 to 12 μm, regular morphology, and uniform particle size distribution.

[0041] (2) The lanthanum aluminate coating formed on the surface of the positive electrode material can reduce the dissolution of transition metal ions, inhibit the side reaction between the material and the electrolyte and the corrosion of HF acid, and improve the cycle stability of the material. Lanthanum aluminate has high ionic conductivity and is beneficial for lithium ion transport during the charge and discharge cycle as a coating. Lanthanum aluminate also has excellent chemical and thermal stability, which is beneficial for improving the electrochemical performance of the material under high voltage and high temperature conditions.

[0042] (3) The battery assembled by the method of coating lanthanum aluminate with nickel cobalt oxide ternary positive electrode material of the present invention has an initial discharge capacity of 208.3 mAh / g and a charge capacity of 239.4 mAh / g at a charge and discharge voltage of 2.7 to 4.5 V and a current density of 1C (200 mA / g). The initial charge and discharge coulombic efficiency is 87.01%. After 100 cycles, the discharge capacity can still be as high as 175.6 mAh / g, the capacity retention rate is 90.61%, and the discharge capacity at a current density of 10C can reach more than 152.2 mAh / g. This shows that the method of coating lanthanum aluminate with nickel cobalt oxide ternary positive electrode material of the present invention can promote the transmission of lithium ions during the charge and discharge process, stabilize the structure of the ternary material under high voltage, and improve the electrochemical performance of the material.

[0043] The battery assembled using the method of coating lanthanum aluminate with nickel cobalt oxide ternary positive electrode material of the present invention has an initial discharge capacity of 203.5 mAh / g, a charge capacity of 225.4 mAh / g, and an initial charge and discharge coulombic efficiency of 90.27% at a charge and discharge voltage of 2.7 to 4.3 V and a current density of 1 C (200 mA / g) at 50° C. After 100 cycles, the discharge capacity can still reach 170.2 mAh / g, with a capacity retention rate of 92.75%. This indicates that the method of coating lanthanum aluminate with nickel cobalt oxide ternary positive electrode material of the present invention is beneficial for improving the electrochemical performance of the material at high temperatures.

[0044] (4) The modification method of the present invention can stabilize the crystal structure of the high-nickel ternary cathode material during the cycle, reduce side reactions between the material and the electrolyte, and improve lithium ion transport performance, thereby improving the electrochemical performance of the material under high voltage and high temperature conditions and expanding the application range of the nickel-cobalt-manganese oxide ternary cathode material. The method of the present invention has a simple process, significant modification effect, low raw material cost, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 This is the XRD pattern of the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material of Example 1 of the present invention;

[0047] Figure 2 This is an SEM image of the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material of Example 1 of the present invention;

[0048] Figure 3The charge-discharge cycle curve and charge-discharge coulomb curve of the battery assembled using the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material and its preparation method according to Example 1 of the present invention;

[0049] Figure 4 The charge-discharge cycle curve and charge-discharge coulomb curve of the battery assembled with the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material and its preparation method at 50°C in Example 1 of the present invention;

[0050] Figure 5 This is a discharge rate curve of a battery assembled using the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material and its preparation method according to Example 1 of the present invention;

[0051] Figure 6 This is the XRD pattern of the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material of Example 3 of the present invention;

[0052] Figure 7 The charge-discharge cycle curve and charge-discharge Coulomb curve of a battery assembled using the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material and its preparation method according to Example 3 of the present invention;

[0053] Figure 8 The charge-discharge cycle curve and charge-discharge Coulomb curve of a battery assembled using the nickel-cobalt-manganese oxide ternary positive electrode material and its preparation method in Comparative Example 1 of the present invention are shown;

[0054] Figure 9 This is the charge and discharge cycle curve and charge and discharge Coulomb curve of the battery assembled using the aluminum and lanthanum doped nickel cobalt manganese oxide ternary positive electrode material and its preparation method in comparative example 2 of the present invention. DETAILED DESCRIPTION

[0055] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0056] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0057] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0058] Example 1:

[0059] A lanthanum aluminate coated nickel cobalt lithium manganate ternary positive electrode material, wherein the lanthanum aluminate coating layer covers a spherical nickel cobalt lithium manganate matrix to form a core-shell structure; the chemical formula of the nickel cobalt lithium manganate matrix is ​​LiNi 0.83 Co0.12 Mn 0.05 O2, the amount of lanthanum aluminate coating layer generated accounts for 2wt% of the ternary precursor matrix material.

[0060] (1) 4 L of a mixed solution of nickel sulfate, cobalt sulfate and manganese sulfate (wherein the total molar concentration of Ni, Co and Mn ions is 2.0 mol / L and the molar ratio of Ni, Co and Mn is 0.83:0.12:0.05) was pumped into a reactor containing 2 L of a 2 mol / L ammonia solution at a feeding rate of 100 mL / h, and at the same time, the ammonia concentration of the reaction system was adjusted to 2 mol / L with 25% ammonia water, and the pH value of the reaction system was adjusted to 11.4 with 4 L of a 5 mol / L sodium hydroxide precipitant solution. The mixture was heated and stirred at 1000 r / min and 50° C. under a high-purity nitrogen atmosphere for 40 h and then aged at 45° C. with stirring for 12 h, filtered, and the filtrate was cross-washed 6 times with deionized water and ethanol, respectively, and dried at 90° C. for 12 h to obtain a nickel-cobalt-manganese hydroxide precursor;

[0061] (2) Weigh 0.0351 g (0.0935 mmol) of Al(NO3)3·9H2O, 0.0405 g (0.0935 mmol) of La(NO3)3·6H2O, and 0.0197 g (0.0935 mmol) of citric acid monohydrate in an agate mortar and grind them together to mix thoroughly and grind them into a white paste. Then, place the white paste in an oven and dry it to constant weight to obtain a light yellow loose foamy lanthanum aluminate precursor;

[0062] (3) 1 g of the nickel cobalt manganese hydroxide precursor obtained in step (1) was mixed with the lanthanum aluminate precursor obtained in step (2) and 0.4784 g (11.4013 mmol) of lithium hydroxide monohydrate and ground. In a high-purity oxygen atmosphere, the temperature was first raised to 450° C. at a rate of 5° C. / min, sintered for 4 h, and then raised to 750° C. at a rate of 5° C. / min, sintered for 12 h, and sintered in two stages. The mixture was cooled to room temperature to obtain a lanthanum aluminate-coated nickel cobalt manganese oxide lithium ternary positive electrode material.

[0063] like Figure 1 As shown in FIG, the XRD diffraction pattern of the nickel cobalt manganese oxide ternary positive electrode material coated with lanthanum aluminate in the embodiment of the present invention is basically consistent with the XRD diffraction pattern of the uncoated nickel cobalt manganese oxide ternary positive electrode material, which shows that the lanthanum aluminate coating does not change the phase structure of the ternary material.

[0064] like Figure 2 As shown, the lanthanum aluminate-coated nickel-cobalt-lithium manganese oxide ternary positive electrode material of the embodiment of the present invention is a secondary spherical particle formed by the agglomeration of blocky primary particles, with an average particle size of 10 μm.

[0065] Battery assembly: Weigh 0.08 g of the high-nickel ternary positive electrode material coated with the manganese-rich material obtained in the embodiment of the present invention, add 0.01 g of acetylene black as a conductive agent and 0.01 g of PVDF polyvinylidene fluoride as a binder, and mix and grind with N-methylpyrrolidone as a solvent to form a positive electrode material; the obtained positive electrode material is coated on the surface of an aluminum foil to form a pole piece; in a closed glove box filled with argon, use the pole piece as the positive electrode, the metal lithium sheet as the negative electrode, the microporous polypropylene membrane as the separator, and 1 mol / L LiPF6 / EC:DMC:DEC (volume ratio 1:1:1) as the electrolyte to assemble a CR2025 button battery, and perform a charge and discharge performance test.

[0066] like Figure 3 As shown, the battery assembled with the lanthanum aluminate-coated nickel cobalt manganese oxide ternary positive electrode material and its preparation method obtained in the embodiment of the present invention has an initial discharge specific capacity of 208.3 mAh / g, a charge specific capacity of 239.4 mAh / g, and an initial charge and discharge coulombic efficiency of 87.01% at a charge and discharge voltage of 2.7 to 4.5 V and a current density of 0.1C (1C = 200 mA / g). At a current density of 1C, the initial discharge specific capacity is 193.8 mAh / g, the charge specific capacity is 214.9 mAh / g, and the initial charge and discharge coulombic efficiency is 90.22%. After 100 cycles at a current density of 1C, the discharge specific capacity can still be as high as 175.6 mAh / g, and the capacity retention rate is 90.61%. This shows that the method of the present invention for coating the lanthanum aluminate-coated nickel cobalt oxide ternary positive electrode material can promote the transmission of lithium ions during the charge and discharge process, stabilize the structure of the ternary material under high voltage, and improve the electrochemical performance of the material.

[0067] like Figure 4 As shown in FIG5 , the rate curve of the battery assembled using the lanthanum aluminate-coated nickel cobalt manganese oxide ternary positive electrode material and the preparation method thereof obtained in the embodiment of the present invention shows that the discharge capacity at a 10C current density can reach more than 152.2 mAh / g, further indicating that after the high nickel ternary material is coated with lanthanum aluminate, the lithium ion transmission performance during the charge and discharge cycle is improved.

[0068] like Figure 5As shown, the battery assembled with the lanthanum aluminate-coated nickel cobalt manganese oxide ternary positive electrode material and its preparation method obtained in the embodiment of the present invention has an initial discharge capacity of 203.5 mAh / g, a charge capacity of 225.4 mAh / g, and an initial charge and discharge coulombic efficiency of 90.27% at a charge and discharge voltage of 2.7 to 4.3 V and a current density of 0.1 C (1 C = 200 mA / g) at 50°C. At a current density of 1 C, the initial discharge capacity is 183.5 mAh / g, the charge capacity is 203.1 mAh / g, and the initial charge and discharge coulombic efficiency is 90.36%. After 100 cycles at a current density of 1 C, the discharge capacity can still be as high as 170.2 mAh / g, and the capacity retention rate is 92.75%. This shows that the method of coating the nickel cobalt oxide ternary positive electrode material of the present invention with lanthanum aluminate is beneficial to improving the electrochemical performance of the material at high temperatures.

[0069] Example 2

[0070] A lanthanum aluminate coated nickel cobalt lithium manganate ternary positive electrode material, wherein the lanthanum aluminate coating layer covers a spherical nickel cobalt lithium manganate matrix to form a core-shell structure; the chemical formula of the nickel cobalt lithium manganate matrix is ​​LiNi 0.83 Co 0.1 Mn 0.07 O2, the amount of lanthanum aluminate coating layer generated accounts for 1wt% of the ternary precursor matrix material.

[0071] (1) 4 L of a mixed solution of nickel sulfate, cobalt sulfate and manganese sulfate (wherein the total molar concentration of Ni, Co and Mn ions is 2.0 mol / L and the molar ratio of Ni, Co and Mn is 0.83:0.1:0.07) was pumped into a reactor containing 2 L of a 2 mol / L ammonia solution at a feeding rate of 100 mL / h, and at the same time, the ammonia concentration of the reaction system was adjusted to 2 mol / L with 25% ammonia water, and the pH value of the reaction system was adjusted to 11.4 with 4 L of a 5 mol / L sodium hydroxide precipitant solution. The mixture was heated and stirred at 1000 r / min and 50° C. under a high-purity nitrogen atmosphere for 40 h and then aged at 45° C. with stirring for 12 h, filtered, and the filtrate was cross-washed 6 times with deionized water and ethanol, respectively, and dried at 90° C. for 12 h to obtain a nickel-cobalt-manganese hydroxide precursor;

[0072] (2) Weigh 0.0175 g (0.0468 mmol) of Al(NO3)3·9H2O, 0.0202 g (0.0468 mmol) of La(NO3)3·6H2O, and 0.0098 g (0.0468 mmol) of citric acid monohydrate in an agate mortar and grind them together to mix thoroughly and grind them into a white paste. Then, place the white paste in an oven and dry it to constant weight to obtain a light yellow loose foamy lanthanum aluminate precursor;

[0073] (3) 1 g of the nickel-cobalt-manganese hydroxide precursor obtained in step (1) was mixed with the lanthanum aluminate precursor obtained in step (2) and 0.4672 g (11.1344 mmol) of lithium hydroxide monohydrate and ground. In a high-purity oxygen atmosphere, the temperature was first raised to 450° C. at a rate of 5° C. / min, sintered for 4 h, then raised to 775° C. at a rate of 5° C. / min, sintered for 15 h, and sintered in two stages. The mixture was cooled to room temperature to obtain a lanthanum aluminate-coated nickel-cobalt-manganese oxide lithium ternary positive electrode material.

[0074] After testing, the XRD diffraction pattern of the nickel-cobalt-manganese-oxide ternary positive electrode material coated with lanthanum aluminate in the embodiment of the present invention is basically consistent with the XRD diffraction pattern of the uncoated nickel-cobalt-manganese-oxide ternary positive electrode material, which shows that the lanthanum aluminate coating does not change the phase structure of the ternary material.

[0075] After testing, the lanthanum aluminate-coated nickel, cobalt, and lithium manganese oxide ternary positive electrode material of the embodiment of the present invention is a secondary spherical particle formed by the agglomeration of blocky primary particles, with an average particle size of 9 μm.

[0076] Battery assembly: Same as Example 1.

[0077] The battery assembled with the lanthanum aluminate-coated nickel-cobalt-manganese oxide ternary positive electrode material and its preparation method obtained in the embodiment of the present invention has an initial discharge specific capacity of 216.8 mAh / g, a charge specific capacity of 242.6 mAh / g, and an initial charge and discharge coulombic efficiency of 89.36% at a charge and discharge voltage of 2.7 to 4.5 V and a current density of 0.1C (1C = 200 mA / g). At a current density of 1C, the initial discharge specific capacity is 196.8 mAh / g, the charge specific capacity is 216.6 mAh / g, and the initial charge and discharge coulombic efficiency is 90.85%. After 100 cycles at a current density of 1C, the discharge specific capacity can still be as high as 168.8 mAh / g, and the capacity retention rate is 85.77%. This shows that the method of the present invention for coating the lanthanum aluminate-coated nickel-cobalt-manganese oxide ternary positive electrode material can promote the transmission of lithium ions during the charge and discharge process, stabilize the structure of the ternary material under high voltage, and improve the electrochemical performance of the material.

[0078] Example 3

[0079] A lanthanum aluminate coated nickel cobalt lithium manganate ternary positive electrode material, wherein the lanthanum aluminate coating layer covers a spherical nickel cobalt lithium manganate matrix to form a core-shell structure; the chemical formula of the nickel cobalt lithium manganate matrix is ​​LiNi 0.8 Co 0.1 Mn 0.1O2, the amount of lanthanum aluminate coating layer generated accounts for 3wt% of the ternary precursor matrix material. (1) 4 L of a mixed solution of nickel sulfate, cobalt sulfate and manganese sulfate (wherein the total molar concentration of Ni, Co and Mn ions is 2.0 mol / L and the molar ratio of Ni, Co and Mn is 0.8:0.1:0.1) was pumped into a reactor containing 2 L of a 2 mol / L ammonia solution at a feeding rate of 100 mL / h, and at the same time, the ammonia concentration of the reaction system was adjusted to 2 mol / L with 25% ammonia water, and the pH value of the reaction system was adjusted to 11.45 with 4 L of a 5 mol / L sodium hydroxide precipitant solution. The mixture was heated and stirred at 1000 r / min and 50° C. under a high-purity nitrogen atmosphere for 40 h and then aged at 45° C. with stirring for 12 h, filtered, and the filtrate was cross-washed 6 times with deionized water and ethanol, and dried at 90° C. for 12 h to obtain a nickel-cobalt-manganese hydroxide precursor;

[0080] (2) Weigh 0.0525 g (0.1404 mmol) of Al(NO3)3·9H2O, 0.0606 g (0.1404 mmol) of La(NO3)3·6H2O, and 0.0294 g (0.1404 mmol) of citric acid monohydrate in an agate mortar and grind them together to mix thoroughly and grind them into a white paste. Then, place the white paste in an oven and dry it to constant weight to obtain a light yellow loose foamy lanthanum aluminate precursor;

[0081] (3) 1 g of the nickel cobalt manganese hydroxide precursor obtained in step (1) was mixed with the lanthanum aluminate precursor obtained in step (2) and 0.4784 g (11.4013 mmol) of lithium hydroxide monohydrate and ground. In a high-purity oxygen atmosphere, the temperature was first raised to 480° C. at a rate of 5° C. / min, sintered for 4 h, then raised to 760° C. at a rate of 5° C. / min, sintered for 12 h, and sintered in two stages. The mixture was cooled to room temperature to obtain a lanthanum aluminate-coated nickel cobalt manganese oxide lithium ternary positive electrode material.

[0082] like Figure 6 As shown in FIG, the XRD diffraction pattern of the nickel cobalt manganese oxide ternary positive electrode material coated with lanthanum aluminate in the embodiment of the present invention is basically consistent with the XRD diffraction pattern of the uncoated nickel cobalt manganese oxide ternary positive electrode material, which shows that the lanthanum aluminate coating does not change the phase structure of the ternary material.

[0083] After testing, the lanthanum aluminate-coated nickel cobalt manganese oxide ternary positive electrode material of the embodiment of the present invention is a secondary spherical particle formed by the agglomeration of blocky primary particles, with an average particle size of 10 μm.

[0084] Battery assembly: Same as Example 1.

[0085] like Figure 7As shown, the battery assembled with the lanthanum aluminate-coated nickel cobalt manganese oxide ternary positive electrode material and its preparation method obtained in the embodiment of the present invention has an initial discharge specific capacity of 206.7 mAh / g, a charge specific capacity of 240.2 mAh / g, and an initial charge and discharge coulombic efficiency of 86.08% at a charge and discharge voltage of 2.7 to 4.5 V and a current density of 0.1C (1C = 200 mA / g). At a current density of 1C, the initial discharge specific capacity is 194.4 mAh / g, the charge specific capacity is 215.6 mAh / g, and the initial charge and discharge coulombic efficiency is 90.16%. After 200 cycles at a current density of 1C, the discharge specific capacity can still be as high as 159.9 mAh / g, and the capacity retention rate is 82.25%. This shows that the method of coating the nickel cobalt manganese oxide ternary positive electrode material with lanthanum aluminate can improve the cycle stability of the nickel cobalt manganese oxide ternary positive electrode material under high voltage.

[0086] Comparative Example 1

[0087] A lithium nickel cobalt manganese oxide positive electrode material with the chemical formula LiNi 0.83 Co 0.12 Mn 0.05 O2.

[0088] (1) Same as Example 1;

[0089] (2) 1 g of the nickel-cobalt-manganese hydroxide precursor obtained in step (1) and 0.4784 g (11.4013 mmol) of lithium hydroxide monohydrate were mixed and ground. In a high-purity oxygen atmosphere, the temperature was first raised to 450° C. at a rate of 5° C. / min, sintered for 4 h, and then raised to 750° C. at a rate of 5° C. / min, sintered for 12 h, and sintered in two stages. The mixture was cooled to room temperature to obtain a nickel-cobalt-manganese oxide lithium ternary positive electrode material.

[0090] After testing, the XRD diffraction pattern of the nickel-cobalt-lithium manganese oxide ternary positive electrode material in this comparative example is completely consistent with that of the lithium nickel oxide standard card.

[0091] After testing, it was found that the nickel-cobalt-lithium manganese oxide ternary positive electrode material of this comparative example was secondary spherical particles formed by the agglomeration of blocky primary particles, with an average particle size of 9 μm.

[0092] Battery assembly: Same as Example 1.

[0093] like Figure 8As shown, the battery assembled with the nickel cobalt manganese oxide ternary positive electrode material and its preparation method obtained in the comparative example of the present invention has an initial discharge specific capacity of 218.6 mAh / g, a charge specific capacity of 245.2 mAh / g, and an initial charge and discharge coulombic efficiency of 89.16% at a charge and discharge voltage of 2.7 to 4.5 V and a current density of 0.1 C (1 C = 200 mA / g). At a current density of 1 C, the initial discharge specific capacity is 197.7 mAh / g, the charge specific capacity is 216.8 mAh / g, and the initial charge and discharge coulombic efficiency is 91.18%. After 100 cycles at a current density of 1 C, the discharge specific capacity is 154.9 mAh / g, and after 200 cycles, the discharge specific capacity rapidly decreases to 108.1 mAh / g, with a capacity retention rate of only 54.67%. This indicates that the capacity retention rate of the nickel cobalt oxide lithium ternary positive electrode material in this comparative example is low.

[0094] Comparative Example 2

[0095] A lithium nickel cobalt manganese oxide cathode material co-doped with aluminum and lanthanum, with the chemical formula Al / La-LiNi 0.83 Co 0.1 Mn 0.07 O2, wherein the doping amount of Al and La each accounts for 1wt% of the ternary precursor matrix material.

[0096] (1) Same as Example 2.

[0097] (2) Weigh 0.0615 g (0.0605 mmol) of Al2O3·3H2O and 0.0197 g (0.0605 mmol) of La2O3 in an agate mortar and grind them thoroughly to obtain a dopant precursor;

[0098] (3) 1 g of the nickel cobalt manganese hydroxide precursor obtained in step (1) was mixed with the dopant precursor obtained in step (2) and 0.4672 g (11.1344 mmol) of lithium hydroxide monohydrate and ground. In a high-purity oxygen atmosphere, the temperature was first raised to 450° C. at a rate of 5° C. / min, sintered for 4 h, and then raised to 775° C. at a rate of 5° C. / min, sintered for 15 h, and sintered in two stages. The mixture was cooled to room temperature to obtain an aluminum- and lanthanum-doped nickel cobalt manganese oxide lithium ternary positive electrode material.

[0099] After testing, the XRD diffraction pattern of the aluminum and lanthanum doped nickel cobalt manganese oxide ternary positive electrode material in this comparative example is basically consistent with the XRD diffraction pattern of the unmodified nickel cobalt manganese oxide ternary positive electrode material, which shows that a small amount of aluminum and lanthanum doping will not change the phase structure of the ternary material.

[0100] After testing, the aluminum and lanthanum doped nickel cobalt manganese oxide ternary positive electrode material of the embodiment of the present invention is a secondary spherical particle formed by the agglomeration of blocky primary particles, with an average particle size of 9 μm.

[0101] Battery assembly: Same as Example 1.

[0102] like Figure 9 As shown, the battery assembled with the aluminum-lanthanum doped nickel cobalt manganese oxide ternary positive electrode material and its preparation method obtained in the embodiment of the present invention has an initial discharge specific capacity of 218.6 mAh / g, a charge specific capacity of 252.1 mAh / g, and an initial charge and discharge coulombic efficiency of 86.73% at a charge and discharge voltage of 2.7 to 4.5 V and a current density of 0.1C (1C = 200 mA / g). At a current density of 1C, the initial discharge specific capacity is 194.1 mAh / g, the charge specific capacity is 214.2 mAh / g, and the initial charge and discharge coulombic efficiency is 90.59%. After 200 cycles at a current density of 1C, the discharge specific capacity is 140.2 mAh / g, and the capacity retention rate is 72.23%. This shows that the aluminum-lanthanum doped nickel cobalt oxide ternary positive electrode material of the present invention can improve the capacity retention rate, but compared with the lanthanum aluminate coating of the present invention, the initial coulombic efficiency of the aluminum-lanthanum doped material is low, and the improvement of the cycle stability is limited.

Claims

1. A method for preparing a ternary positive electrode material of lanthanum aluminate coated nickel cobalt lithium manganese oxide, characterized in that: The matrix of the ternary positive electrode material is spherical lithium nickel cobalt manganese oxide particles, and lanthanum aluminate is coated on the matrix to form a core-shell structure. The preparation method includes the following steps: (1) preparing a nickel-cobalt-manganese hydroxide precursor, wherein the nickel-cobalt-manganese hydroxide precursor is prepared by adding a nickel-cobalt-manganese solution to a preheated continuous stirring reactor containing an ammonia solution under a protective atmosphere, adding a complexing agent and a precipitant, stirring to perform a coprecipitation reaction, aging, filtering, washing, and drying to obtain a nickel-cobalt-manganese hydroxide precursor; (2) preparing a lanthanum aluminate precursor, wherein the preparation of the lanthanum aluminate precursor comprises: grinding an aluminum source, a lanthanum source, and a complexing agent together, mixing them uniformly, and drying them to obtain a lanthanum aluminate precursor; (3) After uniformly mixing the nickel cobalt manganese hydroxide precursor obtained in step (1) and the lanthanum aluminate precursor obtained in step (2) with a lithium source, performing two-stage sintering in an oxidizing atmosphere and cooling to room temperature to obtain a lanthanum aluminate-coated nickel cobalt manganese oxide ternary positive electrode material, the two-stage sintering refers to: first heating to 350-550°C at a rate of 1-10°C / min, sintering for 2-8 h, and then heating to 550-1000°C at a rate of 1-10°C / min, and sintering for 8-20 h.

2. The preparation method according to claim 1, wherein In step (1), the nickel in the nickel-cobalt-manganese solution is a soluble nickel salt, the cobalt is a soluble cobalt salt, and the manganese is a soluble manganese salt; the complexing agent is an ammonia solution, and the precipitant is one or more of sodium hydroxide, potassium hydroxide, or lithium hydroxide.

3. The preparation method according to claim 2, wherein The soluble nickel salt is one or more of nickel sulfate, nickel nitrate, nickel acetate or nickel chloride, and their hydrates; the soluble cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt acetate or cobalt chloride, and their hydrates; the soluble manganese salt is one or more of manganese sulfate, manganese nitrate, manganese acetate or manganese chloride, and their hydrates.

4. The preparation method according to claim 2 or 3, wherein In the step (1), the total molar concentration of nickel, cobalt and manganese ions in the nickel-cobalt-manganese solution is 0.1-3.0 mol / L, and the molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese solution is 6-9:0.5-2.0:0.5-2.0; the feeding rate of the nickel-cobalt-manganese solution is 80-120 mL / h; the molar concentration of the ammonia solution is 0.1-5.0 mol / L; the ammonia concentration of the reaction system is adjusted by ammonia water to be maintained at 0.1-5.0 mol / L; the mass concentration of ammonia water used to adjust the ammonia concentration of the reaction system is 25-28%; the pH value of the reaction system is adjusted by hydroxide precipitant solution to be maintained at 10-12; the molar concentration of the hydroxide precipitant solution is 1.0-7.0 mol / L; the volume ratio of the ammonia solution, hydroxide precipitant solution and nickel-cobalt-manganese solution in the reactor is 0.1-10:1-2:

1.

5. The preparation method according to claim 2 or 3, wherein In the step (1), the protective atmosphere is nitrogen or argon atmosphere; the stirring speed of the coprecipitation reaction is 800-1200 r / min, the temperature is 30-60°C, and the time is 12-48 h; the aging temperature is 30-60°C, and the time is 8-24 h; the washing is to cross-wash the filtrate with deionized water and ethanol respectively for ≥6 times; the drying temperature is 80-100°C, and the time is 12-24 h.

6. The preparation method according to claim 5, wherein In step (2), the molar ratio of the aluminum source, the lanthanum source and the complexing agent is 1:1:1; the aluminum source includes aluminum nitrate, aluminum oxalate or aluminum hydroxide, and one or more of their hydrates; the lanthanum source includes lanthanum nitrate, lanthanum carbonate or lanthanum acetate, and one or more of their hydrates; the complexing agent includes one or more of citric acid monohydrate, ethylenediaminetetraacetic acid or tartaric acid; the grinding time is 20 to 40 minutes; the drying temperature is 100 to 120° C., and the drying time is 2 to 6 hours.

7. The preparation method according to claim 1, wherein In step (3), the mass ratio of the lanthanum aluminate coating layer to the nickel cobalt manganese oxide ternary positive electrode material matrix is ​​0.01-0.1:1; the molar ratio of the total molar number of nickel, cobalt and manganese elements in the nickel cobalt manganese hydroxide precursor to the molar ratio of lithium in the lithium source is 1:1.02-1.10; the lithium source is lithium hydroxide monohydrate and / or lithium carbonate; and the oxidizing atmosphere is air atmosphere and / or oxygen atmosphere.

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