Preparation method of MOF-derived bimetallic sulfide-coated high-nickel ternary positive electrode material

Abstract

The invention discloses a preparation method of an MOF-derived bimetallic sulfide coated high-nickel ternary positive electrode material. The preparation method comprises the following steps: step 1, preparing a precursor solution containing cobalt ions, second metal ions and an organic ligand; the second metal ions are zinc ions, copper ions, nickel ions, iron ions or ferrous ions; step 2, dispersing high-nickel ternary material powder into the precursor solution, and performing in-situ growth of bimetal MOF on the surface of the high-nickel ternary material powder to obtain an intermediate material; and 3, mixing the intermediate material with a sulfur source, and carrying out heating treatment in an inert atmosphere to obtain the MOF derived bimetallic sulfide coated high-nickel ternary positive electrode material. According to the preparation method provided by the invention, the bimetallic MOF is used as a single precursor, and uniform mixing of two sulfides and in-situ construction of a nano heterojunction coating layer can be realized through one-step vulcanization, so that the cycle life, the rate capability and the thermal stability of the positive electrode material are improved.

Description

Preparation method of MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a method for preparing a high-nickel ternary cathode material coated with MOF-derived bimetallic sulfide. Background Technology

[0002] High-nickel ternary cathode materials mainly refer to ternary cathode materials with a high nickel content (such as NCM811), which are key to improving the energy density of lithium batteries and are widely used in new energy vehicles, consumer electronics and other fields. Their core advantages are that they can significantly improve the specific capacity (up to 220mAh / g) and energy density of batteries, while reducing the amount of expensive cobalt and lowering costs.

[0003] Coating high-nickel ternary cathode materials with single-metal sulfides is an effective way to improve their performance, especially in sulfide all-solid-state batteries. The sulfide coating can significantly suppress interfacial side reactions between the high-nickel ternary cathode material and the sulfide solid electrolyte, reduce the formation of the space charge layer (SCL), thereby ensuring the smooth flow of lithium-ion diffusion channels and improving the battery's discharge specific capacity and cycle life.

[0004] While coating with single-metal sulfides can improve the performance of high-nickel ternary cathode materials, limitations remain. For example, cobalt sulfide itself may undergo structural changes during long-term cycling, and its single band structure and catalytic properties have limited ability to optimize the conversion of polysulfides and interfacial ion transport. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a method for in-situ constructing a bimetallic sulfide heterojunction coating layer on the surface of a high-nickel ternary cathode material using a bimetallic MOF precursor through a one-step sulfidation process. This heterojunction coating layer can simultaneously leverage the advantages of both sulfides and utilizes the built-in electric field effect at the interface to achieve synergistic optimization of interfacial ion / electron transport, thereby comprehensively improving the electrochemical performance of the high-nickel cathode material. This invention is achieved using the following technical solution: This invention proposes a method for preparing a high-nickel ternary cathode material coated with a MOF-derived bimetallic sulfide, comprising the following steps: Step 1: Preparing a precursor solution containing cobalt ions, a second metal ion, and an organic ligand; the second metal ion is zinc ions, copper ions, nickel ions, iron ions, or ferrous ions; Step 2: Dispersing high-nickel ternary material powder in the precursor solution, and in-situ growing a bimetallic MOF on the surface of the high-nickel ternary material powder to obtain an intermediate material; Step 3: Mixing the intermediate material with a sulfur source, and heating under an inert atmosphere to obtain the MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material.

[0006] Optionally, the second metal ion is a zinc ion.

[0007] Optionally, the organic ligand is 2-methylimidazole or hexamethylenetetramine.

[0008] Optionally, the solvent for the precursor solution is methanol or ethanol.

[0009] Optionally, the molar ratio of the cobalt ion to the second metal ion is 1:0.1 to 1:1.

[0010] Optionally, the concentration of cobalt ions in the precursor solution is 0.01-1 mol / L, and the concentration of organic ligands is 0.02-1.2 mol / L.

[0011] Optionally, in step two, the high-nickel ternary material powder is dispersed in the precursor solution and then allowed to stand for 4-12 hours at a temperature of 15-50°C to obtain the intermediate material.

[0012] Optionally, in step three, the heat treatment procedure is as follows: heating to 350-550°C at a rate of 1-5°C / min and holding at that temperature for 2-5 hours; optionally, the sulfur source is elemental sulfur; the weight ratio of the intermediate material to the sulfur source is 0.1-2:1.

[0013] The present invention also proposes a high-nickel ternary cathode material coated with MOF-derived bimetallic sulfide obtained by the above preparation method.

[0014] This invention also proposes the application of the above-mentioned MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material in lithium batteries.

[0015] The present invention has the following beneficial effects: The method for preparing high-nickel ternary cathode materials coated with MOF-derived bimetallic sulfides provided by the present invention utilizes bimetallic MOF as a "single precursor" and can achieve uniform mixing of two sulfides and in-situ construction of the nano-heterojunction coating layer through one-step sulfidation. CoS x (e.g., Co9S8) has good electronic conductivity and electrocatalytic activity, while ZnS can effectively physically block electrolyte erosion; the pn heterojunction coating layer formed by the cobalt and zinc bimetals can more effectively capture and catalyze the conversion of harmful polysulfides, reducing the damage of harmful polysulfides to the interface between the cathode material and the electrolyte, thereby improving the cycle life, rate performance and thermal stability of the ternary cathode material. Detailed Implementation

[0016] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0017] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0018] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0019] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0020] The nickel ternary material powder used in the following examples is NCM811 powder, with the chemical formula LiNi. 0.8 Co 0.1 Mn 0.1 O2, D50 3-8μm, tap density ≥2.3g / cm3, specific surface area 0.3-0.7g / cm3. 3 .

[0021] Example 1: Preparation of CoS in this example x / ZnS heterojunction-coated NCM811.

[0022] Step 1: Dissolve 1.5 mmol cobalt nitrate hexahydrate and 0.5 mmol zinc nitrate hexahydrate in 50 mL of methanol (Solution A). Dissolve 8 mmol 2-methylimidazole in 50 mL of methanol (Solution B). Quickly pour Solution B into Solution A and stir for 5 minutes.

[0023] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 6 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0024] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:3. Under an argon atmosphere, heat to 450°C at 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0025] Example 2: Preparation of CoS in this example x / ZnS heterojunction-coated NCM811.

[0026] Step 1: Dissolve 1 mmol cobalt nitrate hexahydrate and 0.1 mmol zinc nitrate hexahydrate in 50 mL of methanol (Solution A). Dissolve 8 mmol 2-methylimidazole in 50 mL of methanol (Solution B). Quickly pour Solution B into Solution A and stir for 5 minutes.

[0027] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 6 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0028] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:3. Under an argon atmosphere, heat to 450°C at 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0029] Example 3: CoS was prepared in this example. x / ZnS heterojunction-coated NCM811.

[0030] Step 1: Dissolve 1 mmol of cobalt nitrate hexahydrate and 1 mmol of zinc nitrate hexahydrate in 50 mL of methanol (solution A). Dissolve 8 mmol of 2-methylimidazole in 50 mL of methanol (solution B). Quickly pour solution B into solution A and stir for 5 minutes.

[0031] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 6 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0032] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:3. Under an argon atmosphere, heat to 450°C at 3°C / min and hold for 5 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0033] Example 4: CoS was prepared in this example. x / CuS heterojunction-coated NCM811.

[0034] Step 1: Dissolve 1.5 mmol cobalt nitrate hexahydrate and 0.5 mmol copper nitrate in 50 mL of ethanol (Solution A). Dissolve 8 mmol 2-methylimidazole in 50 mL of ethanol (Solution B). Quickly pour Solution B into Solution A and stir for 5 minutes.

[0035] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 6 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0036] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:3. Under an argon atmosphere, heat to 450°C at 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0037] Example 5: Preparation of CoS in this example x / NiS heterojunction-coated NCM811.

[0038] Step 1: Dissolve 1.5 mmol cobalt nitrate hexahydrate and 0.5 mmol nickel nitrate in 50 mL methanol (solution A). Dissolve 8 mmol 2-methylimidazole in 50 mL methanol (solution B). Quickly pour solution B into solution A and stir for 5 minutes.

[0039] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 6 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0040] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:3. Under an argon atmosphere, heat to 350°C at a rate of 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0041] Example 6: Preparation of CoS in this example x / NiS heterojunction-coated NCM811.

[0042] Step 1: Dissolve 0.1 mmol cobalt nitrate hexahydrate and 1 mmol nickel nitrate in 50 mL of methanol (solution A). Dissolve 8 mmol 2-methylimidazole in 50 mL of methanol (solution B). Quickly pour solution B into solution A and stir for 5 minutes.

[0043] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 6 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0044] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:3. Under an argon atmosphere, heat to 450°C at 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0045] Example 7: Preparation of CoS in this example x / ZnS heterojunction-coated NCM811.

[0046] Step 1: Dissolve 1.5 mmol cobalt nitrate hexahydrate and 0.5 mmol zinc nitrate hexahydrate in 50 mL of methanol (Solution A). Dissolve 8 mmol hexamethylenetetramine in 50 mL of methanol (Solution B). Quickly pour Solution B into Solution A and stir for 5 minutes.

[0047] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 8 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0048] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:1. Under an argon atmosphere, heat to 550°C at 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0049] Example 8: Preparation of CoS in this example x / ZnS heterojunction-coated NCM811.

[0050] Step 1: Dissolve 1.5 mmol cobalt nitrate hexahydrate and 0.5 mmol zinc nitrate hexahydrate in 50 mL of methanol (Solution A). Dissolve 8 mmol 2-methylimidazole in 50 mL of methanol (Solution B). Quickly pour Solution B into Solution A and stir for 5 minutes.

[0051] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 12 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0052] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 2:1. Under an argon atmosphere, heat to 450°C at 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0053] Comparative Example 1: This comparative example uses the above-mentioned NCM811 raw material without any coating treatment.

[0054] Comparative Example 2: Single-metal CoS was prepared in this example. x NCM811 encapsulated.

[0055] Step 1: Dissolve 2 mmol of cobalt nitrate hexahydrate in 50 mL of methanol (solution A). Dissolve 8 mmol of 2-methylimidazole in 50 mL of methanol (solution B). Quickly pour solution B into solution A and stir for 5 minutes.

[0056] Step 2: Take 2.0 g of dry NCM811 powder, disperse it in the above mixed solution, sonicate for 30 minutes, and then let it stand at room temperature for 6 hours. Centrifuge, wash with methanol, and vacuum dry at 80℃ to obtain MOF-coated NCM811 precursor.

[0057] Step 3: Thoroughly grind and mix the MOF-coated NCM811 precursor with excess sulfur powder, with a precursor-to-sulfur powder mass ratio of 1:3. Under an argon atmosphere, heat to 450°C at 3°C / min and hold for 3 hours. After cooling, grind and sieve to obtain the MOF-derived bimetallic sulfide heterojunction-coated high-nickel ternary cathode material.

[0058] In the experimental example, the positive electrode material (high-nickel ternary positive electrode material prepared in Examples 1-8 and Comparative Examples 1-2), the binder being polyvinylidene fluoride (PVDF), and the conductive agent being conductive carbon black (SP) were mixed in a mass ratio of 8:1:1, and an appropriate amount of NMP was added. The mixture was stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain a positive electrode sheet. Lithium hexafluorophosphate (LiPF6) was used as the electrolyte, and a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was used as the solvent to prepare an electrolyte solution with a concentration of 1 mol / L. A lithium metal sheet was used as the counter electrode, and a polypropylene (PP) membrane was used as the separator. The cells were assembled into a button cell in an argon-filled glove box. The tests were conducted using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 2.5~4.25V. The test process was as follows: 0.2C charge / 0.2C discharge for 1 week, and 0.2C charge / 1C discharge for 50 weeks. The initial coulombic efficiency at 0.2C and the cycle capacity retention rate after 50 cycles were recorded. After 50 cycles, the battery was fully charged at 0.2C, and the positive electrode was removed. Differential scanning calorimetry (DSC) was performed at 30~500℃ with a heating rate of 5℃ / min and nitrogen protection (nitrogen flow rate of 50mL / min). The onset temperature of the exothermic peak of the DSC charging state was recorded.

[0059] Table 1 Performance Test Results

[0060] As shown in Table 1, the CoS prepared in Examples 1-8 of this invention... x The ZnS heterojunction-coated NCM811 ternary cathode material exhibits excellent cycle life, rate performance, and thermal stability. CoS x (e.g., Co9S8) exhibits good electronic conductivity and electrocatalytic activity, while ZnS effectively blocks electrolyte erosion. The pn heterojunction coating layer formed by the cobalt and zinc bimetals can more effectively capture and catalyze the conversion of harmful polysulfides, reducing the damage caused by harmful polysulfides to the interface between the cathode material and the electrolyte. The cycle capacity retention and the onset temperature of the DSC exothermic peak are significantly improved after 50 cycles. Comparative Example 1 shows the NCM811 ternary cathode material lacking a coating layer, and Comparative Example 2 shows the single-metal CoS811. x The coated NCM811 ternary cathode material has poor stability, resulting in poor battery performance. Therefore, compared to uncoated and single-metal sulfide-coated ternary cathode materials, the ternary cathode material prepared in this invention exhibits significant improvements in cycle life, rate performance, and thermal stability.

[0061] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material, characterized in that, The process includes the following steps: Step 1: Prepare a precursor solution containing cobalt ions, a second metal ion, and an organic ligand; the second metal ion is zinc ion, copper ion, nickel ion, iron ion, or ferrous ion; Step 2: Disperse high-nickel ternary material powder in the precursor solution, and grow a bimetallic MOF in situ on the surface of the high-nickel ternary material powder to obtain an intermediate material; Step 3: Mix the intermediate material with a sulfur source and heat it under an inert atmosphere to obtain the MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material.

2. The method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material according to claim 1, characterized in that, The second metal ion is a zinc ion.

3. The method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material according to claim 1, characterized in that, The organic ligand is 2-methylimidazolium or hexamethylenetetramine.

4. The method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material according to claim 1, characterized in that, The solvent for the precursor solution is methanol or ethanol.

5. The method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material according to claim 1, characterized in that, The molar ratio of cobalt ions to the second metal ions is 1:0.1 to 1:

1.

6. The method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material according to claim 1, characterized in that, The concentration of cobalt ions in the precursor solution is 0.01-1 mol / L, and the concentration of organic ligands is 0.02-1.2 mol / L.

7. The method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material according to claim 1, characterized in that, In step two, the high-nickel ternary material powder is dispersed in the precursor solution and then allowed to stand at 15-50°C for 4-12 hours to obtain the intermediate material.

8. The method for preparing MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material according to claim 1, characterized in that, In step three, the heat treatment procedure is as follows: the temperature is increased to 350-550°C at a rate of 1-5°C / min, and held for 2-5 hours; preferably, the sulfur source is elemental sulfur; the weight ratio of the intermediate material to the sulfur source is 0.1-2:

1.

9. The MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the MOF-derived bimetallic sulfide-coated high-nickel ternary cathode material as described in claim 9 in lithium batteries.

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