Nickel-cobalt-manganese ternary positive electrode material and preparation method and application thereof

Abstract

The invention discloses a nickel-cobalt-manganese ternary positive electrode material and a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials. The preparation method of the material comprises the following steps: dissolving nickel salt, cobalt salt and manganese salt in a solvent, and adding a mixed solution composed of organic carboxylic acid and ammonia water to obtain a solution B; preparing a solution C containing lithium bicarbonate and ammonium bicarbonate; and mixing the solution B and the solution C, performing hydrothermal reaction to obtain a precursor of the ternary positive electrode material, and roasting the precursor to obtain the nickel-cobalt-manganese ternary positive electrode material. In the hydrothermal reaction process, the pyrolysis of bicarbonate radicals and the precipitation of four metal ions of nickel, cobalt, manganese and lithium are simultaneously carried out in the whole system, so that nickel, cobalt, manganese and lithium in the prepared precursor are uniformly distributed, and the migration path of each element of the precursor with uniformly distributed components is short in the subsequent calcination process; the generation of a layered phase and the integrity of material crystal lattices are facilitated, so that the effect of improving the electrochemical performance of the material is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a nickel-cobalt-manganese ternary cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] The nickel-cobalt-manganese ternary cathode material is a key lithium-ion battery material with the chemical formula LiNi x Co y Mn 1-x-y O 2 , where x and y represent the ratios of nickel, cobalt, and manganese, which can be adjusted according to actual needs. It is used for the positive electrode of lithium-ion batteries and has various advantages, including high voltage resistance, high specific capacity, and low cobalt content. This makes it have broad prospects in electronic products and power applications and become an important pillar in the field of new energy materials. In recent years, thanks to the rapid rise and continuous expansion of the electric vehicle market, the demand for nickel-cobalt-manganese ternary cathode materials has also shown a rapid growth trend and is expected to maintain high-speed growth in the next few years.

[0003] At the same time, the nickel-cobalt-manganese ternary cathode material industry has also achieved remarkable results in technological innovation. On the one hand, by optimizing the material ratio and preparation process, the energy density and cycle stability of the material have been improved; on the other hand, by introducing new additives and modification technologies, the thermal stability and safety of the material have been improved. These technological innovations have not only promoted industrial upgrading but also laid a solid foundation for the sustainable development of the industry.

[0004] Currently, the mainstream method for preparing the positive electrode of ternary cathode materials is to mix two powders, namely a ternary cathode precursor, generally hydroxides of nickel, cobalt, and manganese, and lithium carbonate or lithium hydroxide, at high speed to obtain a mixed powder containing four elements of lithium, nickel, cobalt, and manganese. Then, the mixed powder is subjected to aerobic calcination and pulverization to obtain the ternary cathode material. The disadvantage of this method is that it is difficult to make the components in the cathode material distribute evenly during powder mixing, thus limiting the performance of the material. In view of the defect of powder mixing, there are also studies in the prior art to prepare ternary materials in a wet environment, but there are still some problems. For example, in order to ensure the sufficiency and uniformity of the reaction between raw materials, the required environment often requires high temperature and high pressure, resulting in harsh preparation process conditions, high equipment investment, and high cost investment; when using coprecipitation for raw material mixing, it is difficult to control the precipitation rate between reactants, resulting in too fast precipitation and uneven dispersion of the phases. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a nickel-cobalt-manganese ternary cathode material, a preparation method thereof, and an application thereof. By improving the preparation process of the ternary cathode material, the present invention makes the phases of the ternary cathode material more uniform and obtains a product with good electrochemical performance.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a method for preparing a nickel-cobalt-manganese ternary cathode material, comprising the following steps: (1) Preparation of transition metal solution: Using soluble salts of nickel, cobalt, and manganese, such as nickel sulfate, cobalt sulfate, manganese sulfate, or nickel chloride, cobalt chloride, manganese chloride, etc., as the source of nickel, cobalt, and manganese metal ions, dissolve them in a solvent to obtain solution A (transition metal salt solution). The solvent can be pure water, a mixed solvent composed of pure water and an alcohol reagent such as ethanol or ethylene glycol. The total concentration of nickel, cobalt, and manganese metal ions in solution A is 1 - 2.5 mol / L. When the concentration of nickel, cobalt, and manganese metal ions in solution A is too low, the metal nucleation and growth processes in the liquid phase will be slow, and at the same time, the solid content of the resulting slurry will also be low, resulting in poor economic benefits. If the metal ion concentration is too high, on the one hand, excess metal salts will not dissolve, and on the other hand, the nucleation and growth processes in the liquid phase will be too fast to effectively control the reaction process.

[0007] (2) Solution complexation and pH adjustment: Add a mixed solution composed of organic carboxylic acid and ammonia water to solution A to obtain solution B with a pH of 6 - 8; preferably, the organic carboxylic acid is citric acid or acetic acid, and the molar ratio of NH 3 ·H 2 O to the organic carboxylic acid is (1.5 - 3):1, that is, the amount of ammonia water is more than that of the organic carboxylic acid. This is because when citric acid and ammonia water are mixed in equimolar amounts, the pH can be considered neutral and will not affect the pH of the system. In the present invention, the transition metal salt solution is generally acidic. To adjust its pH to neutral, ammonia water needs to be more than citric acid. Preferably, the molar ratio of NH 3 ·H 2 O to citric acid is limited to (1.5 - 3):1. The mixed solution plays a role in complexing transition metal ions and adjusting the pH range. Its principle of action is as follows: Citric acid or acetic acid contains carboxyl groups and is an organic substance itself. During the subsequent calcination process, it can be completely removed from the material under high-temperature conditions and will not affect the material properties due to residual products. The principle of complexation of the mixed solution is as follows: It contains carboxylic acid groups and amino groups. The carboxylic acid groups and amino groups can form polydentate coordination bonds with metal ions. Compared with using ammonia water alone as a complexing agent, the mixed solution containing organic carboxylic acid has a stronger metal ion chelating ability and can form stable complexes with metal ions (Ni 2+ , Co 2+ , Mn 2+ ). Through the synergistic effect of organic carboxylic acid and ammonia water, the complexation efficiency is improved, laying a foundation for obtaining a product with uniform phase dispersion in the subsequent preparation.

[0008] (3) Preparation of precipitation solution: After adding battery-grade lithium carbonate or industrial-grade lithium carbonate into water to make a slurry, carbon dioxide is introduced to obtain a lithium bicarbonate solution, and then ammonium bicarbonate is added to obtain solution C. Since lithium carbonate has low solubility in water, it is difficult to disperse it with a solvent, which is why the solid-phase mixing method is basically used to prepare ternary materials using lithium carbonate as the lithium source in the prior art. In this patent, by introducing carbon dioxide into the lithium carbonate solution, carbon dioxide reacts with water to form carbonic acid, which further promotes the conversion of lithium carbonate into lithium bicarbonate with higher solubility, effectively increasing the lithium content in the solution. The ratio of the amount of substance of lithium element in solution C to the total amount of substance of nickel, cobalt, and manganese metal ions is (1.1 - 1.2):1, that is, there is a certain excess coefficient of lithium. The ratio of the amount of substance of ammonium bicarbonate in solution C to the total amount of substance of nickel, cobalt, and manganese metal ions is (1.5 - 3.0):1. During the reaction process, the system temperature needs to be strictly controlled. Preferably, the temperatures of the lithium bicarbonate solution and solution C are controlled at 25 - 30 °C. If the temperature is too high, the solubility of carbon dioxide will decrease, and lithium bicarbonate is easily decomposed by heat, which will affect the progress of the reaction. If the temperature is too low, it will also affect the solubility of carbon dioxide in water, and thus affect the concentration of the obtained lithium bicarbonate solution.

[0009] (4) Pyrolysis precipitation: Mix solution B and solution C into a kettle to obtain mixed solution D, transfer it into a hydrothermal reaction kettle, and slowly heat it under stirring conditions. The heating rate is not higher than 1 °C / min. Heat it to 60 - 95 °C for hydrothermal reaction for 1 - 6 h. After the reaction is completed, filter, wash, dry, and crush the obtained product, and then obtain the precursor of the nickel-cobalt-manganese ternary cathode material through screening. (5) Preparation of ternary cathode material: Further heat the precursor of the nickel-cobalt-manganese ternary cathode material in an oxidizing atmosphere such as air or oxygen at a heating rate of 3 - 5 °C / min to 700 - 950 °C, and obtain the ternary cathode material after roasting and crushing.

[0010] The present invention also provides a nickel-cobalt-manganese ternary cathode material, which is prepared by the preparation method as described above. This nickel-cobalt-manganese ternary cathode material has good electrochemical performance and has good application prospects in lithium-ion batteries.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The preparation method of the ternary cathode material provided by the present invention is as follows: First, the soluble salts of nickel, cobalt, and manganese are dissolved in a solvent, and a mixed solution containing nickel, cobalt, manganese, and lithium ions is obtained under the dual complexing action of an organic carboxylic acid and ammonia water; lithium carbonate is converted into lithium bicarbonate and ammonium bicarbonate is used in combination. During the subsequent hydrothermal reaction process, the thermal decomposition of ammonium bicarbonate and lithium bicarbonate is caused by slow heating to release carbonate ions. At this time, the carbonate ions will cause the precipitation of nickel, cobalt, manganese, and lithium to obtain a mixed salt of lithium nickel cobalt manganate, that is, the precursor of the ternary cathode material of nickel, cobalt, and manganese; finally, the precursor is calcined at high temperature to obtain the ternary cathode material. During the above reaction process, the thermal decomposition of bicarbonate and the precipitation of metal ions occur simultaneously in the system, and the four metal ions of nickel, cobalt, manganese, and lithium in the solution co-precipitate. Compared with the traditional method of co-precipitation by mixing two solutions, the method provided by this patent will not cause segregation due to inconsistent local solution components. In the precursor prepared by the present invention, the elements of nickel, cobalt, manganese, and lithium are evenly distributed. The precursor can be obtained by high-temperature aerobic calcination to obtain the ternary cathode material of nickel, cobalt, and manganese. The precursor with such an even element distribution has a short migration path for each element during the subsequent calcination process, which is beneficial to the formation of a layered phase and the integrity of the material lattice, thereby improving the electrochemical performance of the material. The preparation method provided by the present invention provides a new method and idea for technological innovation in the ternary cathode material industry of nickel, cobalt, and manganese. Description of the Drawings

[0012] Figure 1 SEM pattern of the ternary cathode material of nickel, cobalt, and manganese prepared in Example 1 of the present invention. Detailed Description of the Embodiments

[0013] The following further illustrates the present invention with reference to embodiments, so that those skilled in the art can better understand the present invention and implement it, but the embodiments cited do not limit the present invention.

[0014] In addition, in the preparation processes of the following embodiments, unless otherwise specified, they are all conventional means in the prior art in this field, and therefore will not be described in detail; the raw materials used in the following embodiments are all commercially available products and can be obtained by purchase.

[0015] Example 1 A preparation method of a ternary cathode material of nickel, cobalt, and manganese includes the following steps: (1) Preparation of the transition metal solution: Nickel sulfate, cobalt sulfate, and manganese sulfate are dissolved in pure water to obtain solution A. At this time, the solution contains Ni 2+ , Co 2+ , Mn 2+ and SO 4 2- , Ni 2+ , Co 2+ , Mn 2+The molar ratio of the substances is 55:10:35, and the total metal ion concentration of nickel, cobalt, and manganese is 1.5 mol / L; (2) Solution complexation and pH adjustment: Mix NH 3 ·H 2 O and citric acid in a molar ratio of 1.5:1 to obtain a mixed solution; add this mixed solution to solution A to complex transition metal ions and adjust the pH to 6.5, obtaining solution B; (3) Precipitation solution preparation: Pulverize battery-grade lithium carbonate with pure water and then introduce carbon dioxide to obtain a lithium bicarbonate solution. Control the temperature of the lithium bicarbonate solution at 25 °C, where the molar ratio of lithium element to the total amount of nickel, cobalt, and manganese metal ions is 1.2:1. Then add ammonium bicarbonate, and the molar ratio of ammonium bicarbonate to the total amount of nickel, cobalt, and manganese metal ions is 2.0:1, obtaining solution C; (4) Pyrolysis precipitation: Mix solution B and solution C into a kettle to obtain a mixed solution D. Transfer it into a hydrothermal reaction kettle and slowly heat it under stirring conditions. The heating rate is 0.5 °C / min, heat it up to 70 °C for a hydrothermal reaction for 2 h, and then filter, wash, dry, and crush it, and pass through a 200-mesh sieve to obtain the precursor; (5) Preparation of ternary cathode material: Roast the precursor powder in an air atmosphere at a heating rate of 3 °C / min to 950 °C for 9 h, and obtain the ternary cathode material after pulverization.

[0016] Figure 1 Figure 16 is the SEM pattern of the nickel-cobalt-manganese ternary cathode material prepared in Example 1. It can be seen that the obtained single-crystal ternary material is microscopically uniform micron-sized particles, and the surface of these micron-sized particles is round. This is due to the uniform distribution of nickel, cobalt, manganese, and lithium elements in the basic particles of the prepared precursor. Further, by subjecting the precursor to high-temperature aerobic calcination and pulverization, a nickel-cobalt-manganese-lithium-ion ternary cathode material can be obtained. The short migration paths of each element of this precursor with uniform element distribution during the subsequent calcination process are beneficial to the formation of lamellar phases and the integrity of the material lattice, thereby improving the electrochemical performance of the material.

[0017] Example 2 A preparation method of a nickel-cobalt-manganese ternary cathode material, comprising the following steps: (1) Preparation of transition metal solution: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in pure water to obtain solution A. At this time, the solution contains Ni 2+ , Co 2+ , Mn 2+ and SO 4 2- , Ni 2+ , Co 2+ , Mn 2+The molar ratio of the substances is 65:7:28, and the total concentration of nickel, cobalt, and manganese metal ions is 2 mol / L; (2) Solution complexation and pH adjustment: Mix NH 3 ·H 2 O and citric acid in a molar ratio of 2:1 to obtain a mixed solution; Add this mixed solution to solution A to complex transition metal ions and adjust the pH to 7, obtaining solution B; (3) Precipitation solution preparation: Add industrial-grade lithium carbonate to pure water to make a slurry, then introduce carbon dioxide to obtain a lithium bicarbonate solution. Control the temperature of the lithium bicarbonate solution at 25 °C, where the molar ratio of lithium element to the total amount of nickel, cobalt, and manganese metal ions is 1.15:1. Then add ammonium bicarbonate, and the molar ratio of ammonium bicarbonate to the total amount of nickel, cobalt, and manganese metal ions is 2.2:1, obtaining solution C; (4) Pyrolysis precipitation: Mix solution B and solution C into a kettle to obtain a mixed solution D. Transfer it into a hydrothermal reaction kettle and slowly heat it under stirring conditions. The heating rate is 0.6 °C / min. Heat it to 80 °C and carry out a hydrothermal reaction for 3 h, and then filter, wash, dry, and crush it through a 200-mesh sieve to obtain powder E; (5) Preparation of ternary cathode material: Further calcine powder E in an air atmosphere at a heating rate of 4 °C / min to 900 °C and pulverize it to obtain the ternary cathode material.

[0018] Example 3 A preparation method of a nickel-cobalt-manganese ternary cathode material, comprising the following steps: (1) Preparation of transition metal solution: Dissolve soluble salts of nickel, cobalt, and manganese, namely nickel chloride, cobalt chloride, and manganese chloride, in pure water to obtain solution A. At this time, the solution contains Ni 2+ , Co 2+ , Mn 2+ and Cl - etc. The molar ratio of Ni 2+ , Co 2+ , Mn 2+ is 88:07:05, and the total concentration of nickel, cobalt, and manganese metal ions is 2.5 mol / L; (2) Solution complexation and pH adjustment: Mix NH 3 ·H 2 O and citric acid in a molar ratio of 2.5:1 to obtain a mixed solution; Add this mixed solution to solution A to complex transition metal ions and adjust the pH to 7.5, obtaining solution B; (3) Preparation of precipitation solution: Lithium carbonate of battery grade is added to pure water to make a slurry, and then carbon dioxide is introduced to obtain a lithium bicarbonate solution. The temperature of the lithium bicarbonate solution is controlled at 25 °C, where the molar ratio of lithium element to the total molar amount of nickel, cobalt and manganese metal ions is 1.1:1. Then ammonium bicarbonate is added, and the molar ratio of ammonium bicarbonate to the total molar amount of nickel, cobalt and manganese metal ions is 2.5:1 to obtain solution C; (4) Pyrolysis precipitation: Solution B and solution C are mixed and put into a kettle to obtain a mixed solution D. The mixed solution D is transferred into a hydrothermal reaction kettle and slowly heated under stirring conditions. The heating rate is 0.7 °C / min. The temperature is raised to 85 °C for hydrothermal reaction for 4 h, and then filtered, washed, dried and crushed through a 200-mesh sieve to obtain powder E; (5) Preparation of ternary cathode material: The powder E is further calcined at 850 °C at a heating rate of 5 °C / min in an oxygen atmosphere and then pulverized to obtain the ternary cathode material.

[0019] Performance test and results Using the ternary cathode materials prepared in Examples 1, 2, and 3 as the cathode materials of the battery, coin cells are made. The specific preparation method is as follows: The cathode material, carbon-based conductive agent Super P, and polyvinylidene fluoride are mixed and slurried in N-methylpyrrolidone according to a mass ratio of 80:10:10. The slurry is coated on an aluminum foil, dried, and sliced to prepare a working electrode. Among them, the areal density of the composite electrode material is 1 mg / cm 2 ; Test method: A lithium sheet is used as a reference electrode in a lithium-ion half-cell, and the electrolyte is a mixed solution of ethylene carbonate / dimethyl carbonate (mass ratio 1:1) containing 1 M lithium hexafluorophosphate; The charge and discharge tests of the battery are carried out on a Neware battery test system, and the voltage range is selected as 2.75 - 4.35 V (vs Li + / Li). The results are shown in Table 1. At the same time, commercially available conventional method ternary cathode materials (obtained by high-speed mixing of nickel-cobalt-manganese precursor and lithium carbonate followed by calcination and pulverization) with the same components as those in Examples 1, 2, and 3 (referring to the elemental compositions of the materials in Examples 1, 2, and 3 respectively) are purchased and tested and compared with the ternary cathode materials prepared by the present invention, which are respectively recorded as Comparative Example 1, Comparative Example 2, and Comparative Example 3. The obtained results are as follows in Table 1: Table 1

[0020] It can be seen that compared with the conventional ternary cathode materials with the same components on the market, the batteries assembled with the materials prepared in the present invention have certain improvements in the electrical performance in terms of the capacities at 0.2C and 1C and the first efficiency. The increase in capacity means that the batteries prepared with this material will have a higher energy density. Among them, the improvement in the first efficiency (the first efficiency) is more practically significant. The first efficiency reflects the degree of side reactions and the proportion of available lithium ions during the charge and discharge process, and is an important indicator of the material performance. The first efficiency of the batteries composed of the materials prepared in this patent all exceeds 88%, and can reach up to 89.12% at most, which is difficult to achieve in the prior art and is at the leading level in the industry.

[0021] Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-cobalt-manganese ternary positive electrode material, characterized in that: The following steps are involved: Dissolving nickel salt, cobalt salt and manganese salt in a solvent to obtain solution A; Adding a mixed solution consisting of an organic carboxylic acid and aqueous ammonia to solution A to obtain a solution B having a pH of 6-8; Lithium carbonate is added to water and carbon dioxide is introduced to obtain a lithium bicarbonate solution; Then add ammonium bicarbonate to obtain solution C; The solution B and the solution C are mixed and subjected to a hydrothermal reaction, and the obtained product is separated, dried, and crushed to obtain a precursor; After the precursor is calcined in an oxygen-containing atmosphere, a nickel-cobalt-manganese ternary positive electrode material is obtained.

2. The method for preparing the nickel-cobalt-manganese ternary positive electrode material according to claim 1, characterized in that: The nickel salt is nickel sulfate or nickel chloride; the cobalt salt is cobalt sulfate or cobalt chloride; and the manganese salt is manganese sulfate or manganese chloride.

3. The method for preparing the nickel-cobalt-manganese ternary positive electrode material according to claim 1, characterized in that: The solvent is water or a mixed solvent consisting of water and an alcohol reagent; the alcohol reagent is ethanol or ethylene glycol.

4. The method for preparing the nickel-cobalt-manganese ternary positive electrode material according to claim 1, characterized in that: The organic carboxylic acid is citric acid or acetic acid.

5. The method for preparing the nickel-cobalt-manganese ternary positive electrode material according to claim 1, characterized in that: The temperature of the lithium bicarbonate solution and the solution C is 25-30°C.

6. The method for preparing the nickel-cobalt-manganese ternary positive electrode material according to claim 1, characterized in that: The ratio of the amount of lithium element in the solution C to the total amount of nickel, cobalt and manganese metal ions is (1.1-1.2):1; the ratio of the amount of ammonium bicarbonate in the solution C to the total amount of nickel, cobalt and manganese metal ions is (1.5-3.0):

1.

7. The method for preparing the nickel-cobalt-manganese ternary positive electrode material according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 60-95°C and the time is 1-6 h.

8. The method for preparing the nickel-cobalt-manganese ternary positive electrode material according to claim 1, characterized in that: The calcination temperature is 700-950°C.

9. A nickel-cobalt-manganese ternary positive electrode material, characterized in that: The nickel-cobalt-manganese ternary positive electrode material is prepared by the preparation method described in any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery contains the nickel-cobalt-manganese ternary positive electrode material as claimed in claim 9.

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