Cobalt-containing modified positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the field of positive electrode materials, and particularly relates to a cobalt-containing modified positive electrode material and a preparation method and application thereof.The preparation method comprises the following steps that S1, a precursor and a lithium source are mixed and pre-sintered, and a pre-sintered material is obtained; and S2, mixing the pre-sintered material with a cobalt element additive and a lithium element additive, and sintering to obtain the cobalt-containing modified positive electrode material, wherein in terms of the mass of the precursor, the use amount of the cobalt element additive is 2000 to 12000 ppm, and the use amount of the lithium element additive is 500 to 5000 ppm; according to the invention, island-shaped coating of the pre-sintered material can be realized by specific dosages of the cobalt element additive and the lithium element additive, the production cost is reduced, and the prepared positive electrode material has excellent electrical properties.

Description

Technical Field

[0001] The present invention belongs to the field of positive electrode materials, and in particular relates to a cobalt-containing modified positive electrode material and a preparation method and application thereof. Background Art

[0002] Nickel-rich oxides and lithium-rich layered oxide materials have been widely used in lithium-ion batteries in recent years due to their high energy density. In particular, lithium-rich manganese-based layered oxides (LRMO) have been widely studied and discussed due to their theoretical specific energy of up to 900Wh / kg and high discharge capacity of about 250mAh / g. The crystal structure of LRMO consists of rhombohedral R-3m (LiMO2) and monoclinic C / 2m (Li2MnO3) phases, in which the Li-O-Li configuration in the Li2MnO3 phase triggers a partial redox mechanism, thus giving LRMO a higher capacity.

[0003] However, LRMO materials face some severe challenges in practical applications, such as oxygen loss, which can lead to significant irreversible capacity loss and low initial Coulombic efficiency (ICE). In addition, as the cycle progresses, the transformation of the material from a layered structure to a spinel structure will cause a significant drop in capacity and voltage decay. At present, in order to improve the structural stability and electrochemical performance of LRMO positive electrode materials, researchers have explored a variety of methods, including doping with heterogeneous ions, surface coating or modification, encapsulation, and morphology optimization through nanosizing.

[0004] Traditional doping and coating may cause local structural distortion and uneven performance. Excessive coating will affect the diffusion of lithium ions. During the charge and discharge process of lithium-ion batteries, lithium ions are released from the positive electrode, migrate through the electrolyte to the negative electrode and embed. Therefore, the diffusion of lithium ions will affect the capacity performance of the battery. However, if the coating is too little, the purpose of coating cannot be achieved.

[0005] At the same time, residual alkali will appear during the use of positive electrode materials. The residual alkali reacts with the electrolyte to generate gas, which further causes battery bloating and affects battery safety. The current method to solve the problem of residual alkali is through water washing, but the water washing process is cumbersome and increases costs. At the same time, water washing will cause lithium to precipitate from the positive electrode material, reducing the performance of the positive electrode material. Summary of the invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the residual alkali phenomenon existing in the use of existing positive electrode materials and the defects of low capacity of positive electrode materials, thereby providing a cobalt-containing modified positive electrode material and its preparation method and application.

[0007] To this end, the present invention provides the following technical solutions:

[0008] The first aspect of the present invention protects a method for preparing a cobalt-containing modified positive electrode material, wherein the preparation method comprises the following steps:

[0009] S1, mixing a precursor and a lithium source and pre-sintering them to obtain a pre-sintered material;

[0010] S2, mixing the pre-sintered material with a cobalt element additive and a lithium element additive and sintering them to obtain a cobalt-containing modified positive electrode material;

[0011] Wherein, based on the mass of the precursor, the amount of the cobalt element additive is 2000-12000ppm, and the amount of the lithium element additive is 500-5000ppm.

[0012] In the present invention, after the pre-sintering, the sintered product is cooled to room temperature and then crushed and sieved to obtain a pre-sintered material.

[0013] In the present invention, the "amount of the cobalt element additive" in "the amount of the cobalt element additive is 2000-12000ppm" is the mass of the cobalt element additive divided by the mass of the precursor; the "amount of the lithium element additive" in "the amount of the lithium element additive is 500-5000ppm" is the mass of the lithium element additive divided by the mass of the precursor.

[0014] According to the present invention, based on the mass of the precursor, the amount of the cobalt element additive is 2500-10000 ppm, and the amount of the lithium element additive is 800-4000 ppm.

[0015] According to the present invention, the molar ratio of the sum of the metal elements in the precursor to the lithium element in the lithium source is 1:1.1-1.5.

[0016] According to the present invention, the pre-sintering includes a first sintering and a second sintering.

[0017] According to the present invention, the first sintering conditions include: heating to 500-850° C. at a heating rate of 2-6° C. / min, and sintering for 4-8 hours.

[0018] According to the present invention, the second sintering conditions include: heating to 900-1000° C. at a heating rate of 2-6° C. / min, and sintering for 8-16 hours.

[0019] In the present invention, the first sintering and the second sintering are each independently performed in an air or oxygen atmosphere, and the air can be compressed air with a gas flow rate of 10-15 L / min.

[0020] According to the present invention, the sintering conditions include: heating to 700-950° C. at a heating rate of 3-6° C. / min, and sintering for 4-8 hours.

[0021] In the present invention, the sintering is carried out in an air or oxygen atmosphere, and the gas flow rate is at a conventional level in the art.

[0022] According to the present invention, the chemical formula of the precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.1 < x ≤ 1 and 0 < y ≤ 0.5. Typically and non-limitingly, the chemical formula of the precursor is Ni 0.33 Co 0.33 Mn 0.33 (OH)2 and / or Ni 0.16 Co 0.16 Mn 0.68 (OH)2.

[0023] In the present invention, the specific surface area of the precursor is 40 - 50 m 2 / g, the tap density is 1.5 - 2 g / cm 3 , and the size of the median particle size D50 is 5 - 8 μm.

[0024] According to the present invention, the lithium source is a lithium-containing compound.

[0025] According to the present invention, the lithium-containing compound includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0026] According to the present invention, the cobalt element additive is a cobalt-containing compound.

[0027] According to the present invention, the cobalt-containing compound includes at least one of cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt tetroxide, and may be optionally cobalt hydroxide.

[0028] According to the present invention, the lithium element additive is a lithium-containing inorganic substance.

[0029] According to the present invention, the lithium-containing inorganic substance includes lithium hydroxide and / or lithium carbonate.

[0030] The second aspect of the present invention protects a cobalt-modified cathode material prepared by the aforementioned preparation method.

[0031] The third aspect of the present invention protects a secondary battery, wherein the secondary battery includes the aforementioned cobalt-modified cathode material.

[0032] The preparation method of the battery is as follows: the prepared positive electrode material is used as the positive electrode main material to prepare a positive electrode plate, N-methylpyrrolidone is used as a dispersant, the positive electrode material: carbon black: PVDF (polyvinylidene fluoride) is mixed with the dispersant in a mass ratio of 8: (1-1.2): (1-1.2) (the amount of the dispersant is not limited, as long as it can be mixed evenly), to prepare a positive electrode slurry, the positive electrode slurry is evenly coated on an aluminum foil, and the dispersant is removed at 80-85° C. in an oven for 2-3 hours to remove the dispersant to obtain a positive electrode plate; in an argon atmosphere of a glove box, a lithium metal sheet is used as a negative electrode plate, lithium hexafluorophosphate (LiPF6) is used as a solute in an electrolyte, a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 is used as a solvent, and the electrolyte concentration is 1-1.2 mol / L, and the prepared positive electrode plate and Celgard 2500 type diaphragm, CR2032 battery is assembled in the order of negative electrode plate, electrolyte, diaphragm, electrolyte and positive electrode plate.

[0033] The technical solution of the present invention has the following advantages:

[0034] 1. The present invention provides a method for preparing a cobalt-modified positive electrode material, wherein the preparation method comprises the following steps: S1, pre-sintering a precursor and a lithium source to obtain a pre-sintered material; S2, mixing the pre-sintered material with a cobalt element additive and a lithium element additive and sintering the pre-sintered material to obtain a cobalt-modified positive electrode material; wherein, based on the mass of the precursor, the amount of the cobalt element additive is 2000-12000ppm, and the amount of the lithium element additive is 500-5000ppm; the specific amounts of the cobalt element additive and the lithium element additive in the present invention can achieve island-shaped coating of the pre-sintered material, thereby reducing the amount of raw materials and production costs; during the coating process, the cobalt element additive can react with the residual alkali on the surface of the positive electrode material to reduce the residual alkali content and generate LiCoO3, so that the prepared positive electrode material has excellent capacity performance.

[0035] 2. The present invention further limits the types of cobalt element additives, which can further improve the performance of the positive electrode material.

[0036] 3. The specific sintering conditions of the present invention can further reduce the residual alkali content of the positive electrode material and improve the electrical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 This is an electron microscope image of the cobalt-modified positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0039] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0040] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0041] Example 1

[0042] This embodiment provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0043] S1, according to the molar ratio of lithium element to the total metal elements in the precursor of 1.5:1, weigh 0.75mmol lithium carbonate and 1mmol Ni 0.33 Co 0.33 Mn 0.33 The (OH)2 precursor was mixed in a high speed mixer to obtain a mixed powder, wherein the specific surface area of ​​the precursor was 41m 2 / g, tap density is 1.82g / cm 3 , the median particle size D50 is 5.7μm; the mixed powder is heated to 500℃ in a box furnace at a heating rate of 2℃ / min for the first sintering for 5h, and then heated to 900℃ at a heating rate of 2℃ / min for the second sintering for 10h. The sintering atmosphere is compressed air with an air flow rate of 10L / min. The mixture is naturally cooled to room temperature and crushed to obtain a pre-sintered material;

[0044] S2, mixing the obtained pre-sintered material with 5000ppm of cobalt hydroxide as a cobalt element additive and 2000ppm of lithium carbonate as a lithium element additive, heating the material to 900°C at a heating rate of 5°C / min in a box furnace under a compressed air atmosphere, and sintering the material for 5h to obtain a cobalt-containing modified positive electrode material;

[0045] The electron microscope image of the prepared cobalt-containing modified positive electrode material is as follows Figure 1 As shown, from Figure 1 It can be seen that there is a coating layer on the surface of the cobalt-modified positive electrode material, and the coating is relatively uniform.

[0046] Example 2

[0047] This embodiment provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0048] S1, according to the molar ratio of lithium element to the total metal elements in the precursor of 1.5:1, weigh 0.75mmol lithium carbonate and 1mmol Ni 0.33 Co 0.33 Mn 0.33 The (OH)2 precursor was mixed in a high speed mixer to obtain a mixed powder, wherein the specific surface area of ​​the precursor was 41m 2 / g, tap density is 1.82g / cm 3 , the median particle size D50 is 5.7μm; the mixed powder is heated to 500℃ in a box furnace at a heating rate of 2℃ / min for the first sintering for 5h, and then heated to 900℃ at a heating rate of 2℃ / min for the second sintering for 10h. The sintering atmosphere is compressed air with an air flow rate of 10L / min. The mixture is naturally cooled to room temperature and crushed to obtain a pre-sintered material;

[0049] S2, mixing the obtained pre-burned material with 5000ppm of cobalt element additive cobalt hydroxide and 5000ppm of lithium element additive lithium carbonate, heating the mixture to 900°C at a heating rate of 5°C / min in a box furnace under a compressed air atmosphere, and sintering the mixture for 5h to obtain a cobalt-modified positive electrode material.

[0050] Example 3

[0051] This embodiment provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0052] The method of Example 1 is the same, except that in S2, "cobalt hydroxide" is changed to "cobalt oxide".

[0053] Example 4

[0054] This embodiment provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0055] According to the method of Example 1, the difference is that in S1, "Ni 0.33 Co 0.33 Mn 0.33 (OH)2" was changed to "Ni 0.16 Co 0.16 Mn 0.68 (OH)2”.

[0056] Example 5

[0057] This embodiment provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0058] S1, according to the molar ratio of lithium element to the total metal elements in the precursor of 1.5:1, weigh 0.75mmol lithium carbonate and 1mmol Ni 0.33 Co 0.33 Mn 0.33 The (OH)2 precursor was mixed in a high speed mixer to obtain a mixed powder, wherein the specific surface area of ​​the precursor was 41m 2 / g, tap density is 1.82g / cm 3 , the median particle size D50 is 5.7μm; the mixed powder is heated to 900℃ at a heating rate of 2℃ / min and sintered for 10h, the sintering atmosphere is compressed air, the air flow rate is 10L / min, and the mixture is naturally cooled to room temperature, and the pre-sintered material is obtained after crushing;

[0059] S2, in accordance with the method of Example 1.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0062] S1, according to the method of Example 1;

[0063] S2, in the manner of Example 1, except that the obtained pre-burned material is mixed with 1000ppm of cobalt element additive cobalt hydroxide and 5000ppm of lithium element additive lithium carbonate, and the temperature is raised to 900°C at a heating rate of 5°C / min in a box furnace under a compressed air atmosphere and sintered for 5h to obtain a cobalt-modified positive electrode material.

[0064] Comparative Example 2

[0065] This comparative example provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0066] S1, according to the method of Example 1;

[0067] S2, in the manner of Example 1, except that the obtained pre-burned material is mixed with 20000ppm of cobalt element additive cobalt hydroxide and 200ppm of lithium element additive lithium carbonate, and the temperature is raised to 900°C at a heating rate of 5°C / min in a box furnace under a compressed air atmosphere and sintered for 5h to obtain a cobalt-modified positive electrode material.

[0068] Comparative Example 3

[0069] This comparative example provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0070] S1, according to the method of Example 1;

[0071] S2, in the manner of Example 1, except that the obtained pre-burned material is mixed with 15000ppm of cobalt element additive cobalt hydroxide and 10000ppm of lithium element additive lithium carbonate, and the temperature is raised to 900°C at a heating rate of 5°C / min in a box furnace under a compressed air atmosphere and sintered for 5h to obtain a cobalt-modified positive electrode material.

[0072] Comparative Example 4

[0073] This comparative example provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0074] S1, according to the molar ratio of lithium element to the total metal elements in the precursor of 1.5:1, weigh 0.75mmol lithium carbonate and 1mmol Ni 0.33 Co 0.33 Mn 0.33 (OH)2 precursor, and then add 5000ppm of cobalt element additive cobalt hydroxide in a high-speed mixer to mix to obtain a mixed powder, wherein the specific surface area of ​​the precursor is 41m 2 / g, tap density is 1.82g / cm 3 , the median particle size D50 is 5.7μm; the mixed powder is heated to 500℃ in a box furnace at a heating rate of 2℃ / min for the first sintering for 5h, and then heated to 900℃ at a heating rate of 2℃ / min for the second sintering for 10h. The sintering atmosphere is compressed air with an air flow rate of 10L / min. The mixture is naturally cooled to room temperature and crushed to obtain a pre-sintered material;

[0075] S2, mixing the obtained pre-burned material with 2000 ppm of lithium carbonate as a lithium element additive, heating the temperature to 900° C. at a heating rate of 5° C. / min in a box furnace under a compressed air atmosphere, and sintering for 5 hours to obtain a cobalt-containing modified positive electrode material.

[0076] Comparative Example 5

[0077] This comparative example provides a method for preparing a modified positive electrode material, which is as follows:

[0078] S1, according to the method of Example 1;

[0079] S2, in the manner of Example 1, except that the obtained pre-burned material is mixed with 2000 ppm of lithium carbonate as a lithium element additive, and the temperature is increased to 900°C at a heating rate of 5°C / min in a box furnace under a compressed air atmosphere, and sintered for 5 hours to obtain a modified positive electrode material.

[0080] Comparative Example 6

[0081] This comparative example provides a method for preparing a cobalt-containing modified positive electrode material, which is as follows:

[0082] S1, according to the method of Example 1;

[0083] S2, in the manner of Example 1, except that the obtained pre-burned material is mixed with 5000 ppm of cobalt element additive cobalt hydroxide, and the temperature is increased to 900°C at a heating rate of 5°C / min in a box furnace under a compressed air atmosphere, and sintered for 5 hours to obtain a cobalt-containing modified positive electrode material.

[0084] Test Case

[0085] Preparation method of the battery: The cobalt-modified positive electrode material prepared in the embodiment and the comparative example is used as the positive electrode main material to prepare the positive electrode plate, N-methylpyrrolidone is used as a dispersant, and the positive electrode material: carbon black: PVDF (polyvinylidene fluoride) is mixed with the dispersant in a mass ratio of 8:1:1 (the amount of the dispersant is not limited, as long as it can be mixed evenly) to prepare a positive electrode slurry, and the positive electrode slurry is evenly coated on an aluminum foil, and dried in an oven at 80°C for 2h to remove the dispersant to obtain a positive electrode plate; in an argon atmosphere of a glove box, a lithium metal sheet is used as a negative electrode plate, and an electrolyte is lithium hexafluorophosphate (LiPF6) as a solute, and a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 is used as a solvent, and the electrolytic solute concentration is 1 mol / L, and the positive electrode plate and Celgard prepared above are used. 2500 type diaphragm, CR2032 battery is assembled in the order of negative electrode plate, electrolyte, diaphragm, electrolyte and positive electrode plate.

[0086] A potentiometric titrator is used to detect the residual alkali content on the surface of the ternary positive electrode material.

[0087] Test of electrical performance: charge to 4.65V at a rate of 0.2C, record the charge capacity, and then discharge to 2.5V at a rate of 0.2C, record the discharge capacity. The specific results are shown in Table 1.

[0088] Table 1

[0089] Residual alkali content (wt%) First cycle discharge capacity (mAh / g) Example 1 0.63 260.3 Example 2 0.55 257.8 Example 3 0.69 258.9 Example 4 0.65 257.3 Example 5 0.63 255.7 Comparative Example 1 0.74 248.9 Comparative Example 2 0.81 250.5 Comparative Example 3 1.12 236.4 Comparative Example 4 0.74 246.7 Comparative Example 5 0.75 253.5 Comparative Example 6 0.77 245.5

[0090] The specific dosage of the cobalt element additive and the lithium element additive in the present invention can achieve island-shaped coating of the pre-sintered material, reducing the amount of raw materials and production costs; during the coating process, the cobalt element additive reacts with the residual alkali on the surface of the positive electrode material to generate LiCoO3, reducing the residual alkali content, so that the prepared positive electrode material has excellent electrical properties.

[0091] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing a cobalt-modified positive electrode material, characterized in that: The preparation method comprises the following steps: S1, mixing a precursor and a lithium source and pre-sintering them to obtain a pre-sintered material; S2, mixing the pre-sintered material with a cobalt element additive and a lithium element additive and sintering them to obtain a cobalt-containing modified positive electrode material; Wherein, based on the mass of the precursor, the amount of the cobalt element additive is 2000-12000ppm, and the amount of the lithium element additive is 500-5000ppm.

2. The preparation method according to claim 1, characterized in that: Based on the mass of the precursor, the amount of the cobalt element additive is 2500-10000 ppm, and the amount of the lithium element additive is 800-4000 ppm.

3. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of the total metal elements in the precursor to the lithium element in the lithium source is 1:1.1-1.

5.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The pre-sintering includes a first sintering and a second sintering; Optionally, the first sintering conditions include: heating to 500-850° C. at a heating rate of 2-6° C. / min, and sintering for 4-8 hours; Optionally, the second sintering conditions include: heating to 900-1000° C. at a heating rate of 2-6° C. / min, and sintering for 8-16 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The sintering conditions include: heating to 700-950° C. at a heating rate of 3-6° C. / min and sintering for 4-8 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The precursor chemical formula is Ni x Co y Mn 1-x-y (OH)2, 0.1 <x≤1,0<y≤0.5。 7. The preparation method according to any one of claims 1 to 6, characterized in that: The lithium source is a lithium-containing compound; Optionally, the lithium-containing compound includes at least one of lithium carbonate, lithium hydroxide and lithium acetate.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The cobalt element additive is a cobalt-containing compound; Optionally, the cobalt-containing compound includes at least one of cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt tetroxide, and may be cobalt hydroxide; And / or, the lithium element additive is a lithium-containing inorganic substance; Optionally, the lithium-containing inorganic substance includes lithium hydroxide and / or lithium carbonate.

9. A cobalt-containing modified positive electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. A secondary battery, characterized in that: The secondary battery comprises the cobalt-containing modified positive electrode material according to claim 9.

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