A method for preparing a positive electrode for a solid-state battery

Abstract

The present invention discloses a method for preparing a positive electrode for a solid-state battery, which belongs to the technical field of lithium-ion batteries. It comprises the following raw materials in parts by weight: 80-100 parts of positive electrode material, 6-12 parts of binder, and 10-20 parts of conductive agent. The positive electrode prepared by the present invention, wherein the positive electrode material is a lithium-rich manganese-based ternary positive electrode material, has a large capacity and low cost, and the positive electrode material is treated with phosphate to improve the electrochemical performance and cycle stability of the positive electrode; wherein the conductive agent is a binary composite conductive agent of carbon nanotubes and carbon black, which can significantly enhance the cycle stability and electrical properties of the electrode. Moreover, by modifying the carbon nanotubes, compared with ordinary carbon nanotubes, it has more defect types and active sites, and less impurities, and can further enhance the long cycle performance and rate performance of the electrode. In summary, the positive electrode prepared by the present invention has important application value in the technical field of lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a method for preparing a positive electrode for a solid-state battery. Background Art

[0002] With oil resources becoming increasingly scarce and environmental pollution becoming increasingly severe, the harmonious development of energy, resources, the environment, and human society has become a growing concern. To address these increasingly severe environmental challenges and reduce dependence on and emissions from fossil fuels, the development of efficient, green, and environmentally friendly new energy sources is urgent. With the increasing emphasis on low-carbon mobility, market demand for low-emission or zero-emission electric vehicles is increasing, driving the development of lithium-ion batteries.

[0003] Lithium-ion batteries offer advantages such as high energy density, long cycle life, and no memory effect. As commercially available, efficient energy storage devices, they are widely used in daily life and production. However, the safety hazards posed by flammable organic electrolytes in commercial lithium-ion batteries remain a major challenge, especially in large-scale applications such as electric vehicles and energy storage power stations. Solid-state batteries contain no liquid, and the gaps within and at the interfaces of electrodes and separators are not filled with liquid. The ion conduction path relies entirely on solid contacts, which can fundamentally solve the safety issues of lithium-ion batteries.

[0004] Currently, research on all-solid-state lithium-ion batteries has mostly focused on solid-state electrolytes, while research on the positive electrode has been relatively limited. A composite positive electrode for a lithium-ion battery consists of a positive electrode active material, an inorganic solid electrolyte, and a conductive additive. The inorganic solid electrolyte provides a transport channel for lithium ions; the conductive additive provides an electron transport channel; and by increasing the contact area between the electrolyte and the positive electrode active material, interfacial issues are effectively resolved, shortening the migration distance of lithium ions in the low-lithium-ion-conductivity positive electrode active material and ensuring sufficient redox reactions of the positive electrode active material during the battery's charge and discharge processes. However, as people's demands continue to increase, traditional positive electrode materials can no longer meet these requirements. Therefore, there is an urgent need to develop a positive electrode for solid-state batteries with excellent electrical performance to meet the higher demands of lithium-ion battery technology. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a method for preparing a positive electrode for a solid-state battery.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a positive electrode for a solid-state battery comprises the following steps:

[0008] A1. Place the positive electrode material, binder, and conductive agent in an oven and dry for 12 hours. Dissolve the binder in N-methylpyrrolidone (NMP), add the conductive agent and positive electrode material, mix, and stir in a homogenizer to obtain a positive electrode slurry.

[0009] A2. Place aluminum foil on the surface of the coating machine, pour in the positive electrode slurry prepared in step A1, adjust the knife scale to 12μm, remove it when it is coated at a uniform speed to the end, and then place it in a 120℃ oven to dry for 1h, then roll it and punch it manually to obtain the positive electrode for solid-state batteries.

[0010] Furthermore, the raw materials are calculated in parts by weight as follows: 80-100 parts of positive electrode material, 6-12 parts of binder, and 10-20 parts of conductive agent.

[0011] Furthermore, in step A1, the stirring conditions are first homogenizing at a speed of 800 rpm for 30 seconds and then homogenizing at a speed of 2000 rpm for 15 minutes.

[0012] Furthermore, in step A1, the binder is one of polyvinylidene fluoride and polytetrafluoroethylene.

[0013] Furthermore, the positive electrode material is prepared by the following steps:

[0014] The lithium-rich manganese-based ternary material and PVP-K30 were dissolved and dispersed in a mixed solution of anhydrous ethanol and distilled water, and then ammonium dihydrogen phosphate was added. After ultrasonication for 15 minutes, the components were evenly dispersed. Then, after continuous stirring for 3 hours, the mixture was dried in a vacuum drying oven at 100°C for 6 hours, and finally calcined at 450°C for 5 hours and naturally cooled to room temperature to obtain the positive electrode material.

[0015] Furthermore, the ratio of the amount of the lithium-rich manganese-based ternary material, PVP-K30 and ammonium dihydrogen phosphate is 10g:6.5g:8.4g.

[0016] The prepared positive electrode material is a lithium-rich manganese-based ternary positive electrode material with large capacity and low cost. By treating the positive electrode material with phosphate as a surface inducer, a NiO rock salt phase protective layer can be formed on the surface of the positive electrode material. The protective layer has a stable structure, which improves the stability of the layered structure of the material and inhibits the continuous transformation of the layered structure to the spinel structure, thereby significantly improving the electrochemical performance. Not only that, the modified structure can also prevent oxygen escape, while physically blocking the side reactions of high-valent metal ions and electrolytes, thereby inhibiting surface reconstruction and improving the cycle stability of the electrode.

[0017] Furthermore, the conductive agent is prepared by the following steps:

[0018] S1. Mix multi-walled carbon nanotubes with concentrated sulfuric acid and concentrated nitric acid, and perform ultrasonic treatment for 4 hours at a temperature of 60°C. After ultrasonic treatment, reflux at 100°C for 5 hours. After the reaction is complete, cool, and vacuum filter through a polytetrafluoroethylene filter membrane. Wash the filtrate with distilled water until it is neutral, dry it in a vacuum drying oven at 100°C, and grind it to obtain pre-modified carbon nanotubes. The ratio of multi-walled carbon nanotubes, concentrated sulfuric acid, and concentrated nitric acid is 1g:60mL:40mL.

[0019] S2. In a three-necked flask equipped with a stirring device, vinyltriethoxysilane, AIBN (azobisisobutyronitrile) and N,N-dimethylformamide (DMF) were mixed and stirred evenly, and 2-mercaptopyridine was slowly added. The temperature of the system was maintained at 70°C and the reaction was carried out for 4 hours. After the reaction was completed, part of the solvent was first removed by rotary evaporation, and then purified by column chromatography (the eluent was a mixed solvent of benzene / ethyl acetate in a volume ratio of 1:3). The eluent was removed by rotary evaporation to obtain an intermediate; the ratio of vinyltriethoxysilane, AIBN, N,N-dimethylformamide, and 2-mercaptopyridine was 18.8 g:0.3 g:100 mL:11.1 g;

[0020] Under the action of AIBN, the unsaturated carbon-carbon double bond on the vinyltriethoxysilane molecule undergoes a thiol-ene click reaction with the thiol group of 2-thiopyridine to obtain an intermediate;

[0021] S3, the pre-modified carbon nanotubes were mixed with the ethanol aqueous solution, added to a magnetic stirring device, added a magnet, started stirring, and dispersed for 30 minutes to uniformly disperse the pre-modified carbon nanotubes in the ethanol aqueous solution. The device was evacuated, N2 gas was introduced, and the intermediate was added. The heating was started and set to 80 ° C. The condensation water was turned on and the reaction was allowed to react for 4 hours. After the reaction was completed, the mixture was filtered, washed with ethanol, and then dried in a vacuum drying oven for 3 hours to obtain modified carbon nanotubes; the ratio of the pre-modified carbon nanotubes, ethanol aqueous solution, and intermediate was 1.0g:100mL:8.5g;

[0022] S4, adding the modified carbon nanotubes and carbon black into a ball mill, and ball milling and uniformly mixing to obtain a conductive agent; the ratio of the modified carbon nanotubes to the carbon black is 5g:2g;

[0023] The prepared conductive agent is a binary composite conductive agent. Compared with a single conductive agent, it can construct a multi-dimensional conductive network in the electrode system, improve the probability of contact between active material particles and the conductive agent, increase the active sites of chemical reactions, shorten the transmission distance of ions and electrons in the electrode system, weaken the battery polarization, and enhance the cycle stability of the electrode. In addition, carbon nanotubes have excellent electrical and thermal conductivity, which promotes the transfer of heat in the electrode material and avoids the reduction of battery safety factor due to high temperature at certain points. At the same time, the overlap and entanglement between carbon nanotubes and active materials enhances the toughness of the electrode, making it difficult for the active material to peel off during the charging process. Furthermore, the service life of the positive electrode is improved; more than that, the impurities in the carbon nanotubes are removed and the purity is improved by modifying the carbon nanotubes; the introduced silicon element can form wrinkles on the surface of the carbon nanotubes, further increasing the specific surface area of ​​the carbon nanotubes, thereby enhancing their electrical properties; the introduction of sulfur element can effectively improve the capacity and rate performance of the carbon nanotubes; the introduction of nitrogen element significantly increases the number of defect points and vacancies in the plane of the carbon nanotubes, which can significantly improve the long cycle performance of the battery; finally, compared with single atom doping, this multi-doping can provide carbon nanotubes with more defect types and active sites, further improving the electrical properties of the material.

[0024] Beneficial effects of the present invention:

[0025] The positive electrode prepared by the present invention has a lithium-rich manganese-based ternary positive electrode material with large capacity and low cost. The electrochemical performance and cycle stability of the positive electrode are improved by treating the positive electrode material with phosphate. The cycle stability and electrical performance of the electrode can be significantly enhanced by adding a binary composite conductive agent of carbon nanotubes and carbon black. Moreover, by modifying the carbon nanotubes, the electrodes have more defect types and active sites than ordinary carbon nanotubes, and have fewer impurities, which can further enhance the long cycle performance and rate performance of the electrode. In summary, the positive electrode prepared by the present invention has important application value in the field of lithium-ion battery technology. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0027] Example 1

[0028] Preparation of conductive agent:

[0029] S1. 1 g of multi-walled carbon nanotubes was mixed with 60 mL of concentrated sulfuric acid and 40 mL of concentrated nitric acid, and subjected to ultrasonic treatment for 4 h at a temperature of 60°C. After ultrasonic treatment, the mixture was refluxed at 100°C for 5 h until the reaction was complete. The mixture was cooled and vacuum filtered through a polytetrafluoroethylene filter membrane. The filtrate was washed with distilled water until neutral, dried in a vacuum drying oven at 100°C, and ground to obtain pre-modified carbon nanotubes.

[0030] S2. In a three-necked flask equipped with a stirring device, 18.8 g of vinyltriethoxysilane, 0.3 g of AIBN and 100 mL of N,N-dimethylformamide were mixed and stirred evenly, and 11.1 g of 2-mercaptopyridine was slowly added. The temperature of the system was maintained at 70°C and the reaction was carried out for 4 hours. After the reaction was completed, part of the solvent was first removed by rotary evaporation, and then purified by column chromatography (the eluent was a mixed solvent of benzene / ethyl acetate, the volume ratio of the two was 1:3), and the eluent was removed by rotary evaporation to obtain an intermediate;

[0031] S3, 1.0g of pre-modified carbon nanotubes was mixed with 100mL of ethanol aqueous solution, added to a magnetic stirring device, added a magnet, started stirring, and dispersed for 30min to uniformly disperse the pre-modified carbon nanotubes in the ethanol aqueous solution. The device was evacuated, N2 gas was introduced, and 8.5g of the intermediate was added. Heating was started, set to 80°C, condensed water was turned on, and the reaction was carried out for 4h. After the reaction was completed, the modified carbon nanotubes were filtered, washed with ethanol, and then dried in a vacuum drying oven for 3h to obtain modified carbon nanotubes;

[0032] S4. Add 5 g of modified carbon nanotubes and 2 g of carbon black into a ball mill, and mix them evenly by ball milling to obtain a conductive agent.

[0033] Example 2

[0034] Preparation of conductive agent:

[0035] S1. Mix 2 g of multi-walled carbon nanotubes with 120 mL of concentrated sulfuric acid and 80 mL of concentrated nitric acid, and perform ultrasonic treatment for 4 h at a temperature of 60°C. After ultrasonic treatment, reflux at 100°C for 5 h until the reaction is complete. Cool the mixture and vacuum filter it with a polytetrafluoroethylene filter membrane. Wash the filtrate with distilled water until it is neutral, dry it in a vacuum drying oven at 100°C, and grind it to obtain pre-modified carbon nanotubes.

[0036] S2. In a three-necked flask equipped with a stirring device, 37.6 g of vinyltriethoxysilane, 0.6 g of AIBN and 200 mL of N,N-dimethylformamide were mixed and stirred evenly, and 22.2 g of 2-mercaptopyridine was slowly added. The temperature of the system was maintained at 70°C and the reaction was carried out for 4 hours. After the reaction was completed, part of the solvent was first removed by rotary evaporation, and then purified by column chromatography (the eluent was a mixed solvent of benzene / ethyl acetate, the volume ratio of the two was 1:3), and the eluent was removed by rotary evaporation to obtain an intermediate;

[0037] S3, 2.0g of pre-modified carbon nanotubes were mixed with 200mL of ethanol aqueous solution, added to a magnetic stirring device, added magnet, started stirring, and dispersed for 30min to uniformly disperse the pre-modified carbon nanotubes in the ethanol aqueous solution. The device was evacuated, N2 gas was introduced, and 17g of the intermediate was added. Heating was started, set to 80°C, condensed water was turned on, and the reaction was carried out for 4h. After the reaction was completed, the modified carbon nanotubes were filtered, washed with ethanol, and then dried in a vacuum drying oven for 3h to obtain modified carbon nanotubes;

[0038] S4. Add 10 g of modified carbon nanotubes and 4 g of carbon black into a ball mill, and mix them evenly by ball milling to obtain a conductive agent.

[0039] Example 3

[0040] Preparation of positive electrode materials:

[0041] 10g of lithium-rich manganese-based ternary material and 6.5g of PVP-K30 were dissolved and dispersed in a mixed solution of anhydrous ethanol and distilled water, followed by the addition of 8.4g of ammonium dihydrogen phosphate. After ultrasonication for 15min, the components were evenly dispersed. After continuous stirring for 3h, the mixture was dried in a vacuum drying oven at 100°C for 6h, and finally calcined at 450°C for 5h and naturally cooled to room temperature to obtain the positive electrode material.

[0042] Example 4

[0043] Preparation of positive electrode materials:

[0044] 20g of lithium-rich manganese-based ternary material and 13.0g of PVP-K30 were dissolved and dispersed in a mixed solution of anhydrous ethanol and distilled water, followed by the addition of 16.8g of ammonium dihydrogen phosphate. After ultrasonication for 15 minutes, the components were evenly dispersed. After continuous stirring for 3 hours, the mixture was dried in a vacuum drying oven at 100°C for 6 hours, and finally calcined at 450°C for 5 hours and naturally cooled to room temperature to obtain the positive electrode material.

[0045] Example 5

[0046] A1. 80 g of the positive electrode material prepared in Example 3, 6 g of polyvinylidene fluoride, and 10 g of the conductive agent prepared in Example 1 were placed in an oven and dried for 12 h. The polyvinylidene fluoride was first dissolved in 200 mL of N-methylpyrrolidone, and the conductive agent and the positive electrode material were added and mixed. The mixture was placed in a homogenizer and stirred at 800 rpm for 30 s and then at 2000 rpm for 15 min to obtain a positive electrode slurry.

[0047] A2. Place aluminum foil on the surface of the coating machine, pour in the positive electrode slurry prepared in step A1, adjust the knife scale to 12μm, remove it when it is coated at a uniform speed to the end, and then place it in a 120℃ oven to dry for 1h, then roll it and punch it manually to obtain the positive electrode for solid-state batteries.

[0048] Example 6

[0049] A1. 90 g of the positive electrode material prepared in Example 4, 9 g of polytetrafluoroethylene, and 15 g of the conductive agent prepared in Example 2 were placed in an oven and dried for 12 h. The polytetrafluoroethylene was first dissolved in 200 mL of N-methylpyrrolidone, and the conductive agent and the positive electrode material were added and mixed. The mixture was then placed in a homogenizer and stirred. The mixture was first homogenized at 800 rpm for 30 s and then at 2000 rpm for 15 min to obtain a positive electrode slurry.

[0050] A2. Place aluminum foil on the surface of the coating machine, pour in the positive electrode slurry prepared in step A1, adjust the knife scale to 12μm, remove it when it is coated at a uniform speed to the end, and then place it in a 120℃ oven to dry for 1h, then roll it and punch it manually to obtain the positive electrode for solid-state batteries.

[0051] Example 7

[0052] A1. 100 g of the positive electrode material prepared in Example 3, 12 g of polytetrafluoroethylene, and 20 g of the conductive agent prepared in Example 2 were placed in an oven and dried for 12 h. Polytetrafluoroethylene was first dissolved in 200 mL of N-methylpyrrolidone, and the conductive agent and the positive electrode material were added and mixed. The mixture was then placed in a homogenizer and stirred. The mixture was first homogenized at 800 rpm for 30 s and then at 2000 rpm for 15 min to obtain a positive electrode slurry.

[0053] A2. Place aluminum foil on the surface of the coating machine, pour in the positive electrode slurry prepared in step A1, adjust the knife scale to 12μm, remove it when it is coated at a uniform speed to the end, and then place it in a 120℃ oven to dry for 1h, then roll it and punch it manually to obtain the positive electrode for solid-state batteries.

[0054] Comparative Example 1

[0055] The conductive agent in Example 7 was replaced by conductive carbon black of equal mass, and the remaining steps were the same as those in Example 7 to prepare a positive electrode.

[0056] Comparative Example 2

[0057] A commercially available solid-state battery positive electrode was used.

[0058] The positive electrodes obtained in Examples 5, 6, and 7 and Comparative Examples 1 and 2 were assembled into button-type batteries and performance tests were performed. The results are shown in the following table:

[0059]

[0060] As can be seen from the above table, the positive electrode prepared in the embodiment of the present invention has a higher capacity, rate performance, electrical performance and cycle performance as a battery than the comparative example, and it can be seen from Examples 5, 6, 7 and Comparative Example 1 that as the content of the conductive agent continues to increase, the various performances of the battery are improved. Therefore, the present invention has important application value in the field of lithium-ion battery technology.

[0061] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0062] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode for a solid-state battery, characterized in that: The following steps are involved: A1. Place the positive electrode material, binder, and conductive agent in an oven, dissolve the binder in N-methylpyrrolidone, add the conductive agent and positive electrode material, mix, and place in a homogenizer to stir to obtain a positive electrode slurry; A2. Place aluminum foil on the surface of the coating machine, pour the positive electrode slurry prepared in step A1, adjust the knife scale to 12μm, remove it when it is coated at a uniform speed to the end, and then place it in a 120℃ oven to dry for 1 hour. Then, roll it and punch it manually to obtain the positive electrode for solid-state batteries; Wherein, the conductive agent is prepared by the following steps: S1. Mix multi-walled carbon nanotubes with concentrated sulfuric acid and concentrated nitric acid, and perform ultrasonic treatment for 4 hours at a temperature of 60°C. After the ultrasonic treatment, reflux at 100°C for 5 hours until the reaction is complete. Cool, filter, and wash the filtrate with distilled water until it is neutral, dry, and grind to obtain pre-modified carbon nanotubes. S2. Vinyltriethoxysilane, AIBN and N,N-dimethylformamide were mixed and stirred evenly, 2-mercaptopyridine was slowly added, and the mixture was reacted at 70° C. for 4 h. After the reaction was completed, the mixture was rotary evaporated, purified by column chromatography, and rotary evaporated to obtain an intermediate; S3, mixing the pre-modified carbon nanotubes with ethanol aqueous solution, adding them to a magnetic stirring device, starting stirring, and dispersing for 30 minutes, evacuating the device, introducing N2 gas, then adding the intermediate, starting heating, setting the temperature to 80°C, turning on condensation water, reacting for 4 hours, and after the reaction is complete, filtering, washing, and drying to obtain modified carbon nanotubes; S4. Add the modified carbon nanotubes and carbon black into a ball mill, and mix them evenly by ball milling to obtain a conductive agent.

2. The method for preparing a positive electrode for a solid-state battery according to claim 1, characterized in that: In step S1, the ratio of the amount of multi-walled carbon nanotubes, concentrated sulfuric acid, and concentrated nitric acid is 1 g:60 mL:40 mL.

3. The method for preparing a positive electrode for a solid-state battery according to claim 1, characterized in that: In step S2, the ratio of vinyltriethoxysilane, AIBN, N,N-dimethylformamide, and 2-mercaptopyridine is 18.8 g:0.3 g:100 mL:11.1 g.

4. The method for preparing a positive electrode for a solid-state battery according to claim 1, wherein: In step S3, the ratio of the amount of pre-modified carbon nanotubes, ethanol aqueous solution, and intermediate is 1.0 g:100 mL:8.5 g.

5. The method for preparing a positive electrode for a solid-state battery according to claim 1, wherein: In step S4, the ratio of modified carbon nanotubes to carbon black is 5g:2g.

6. The method for preparing a positive electrode for a solid-state battery according to claim 1, characterized in that: The positive electrode material is prepared by the following steps: The lithium-rich manganese-based ternary material and PVP-K30 were dissolved and dispersed in a mixed solution of anhydrous ethanol and distilled water, and then ammonium dihydrogen phosphate was added. After ultrasonication for 15 minutes, the components were evenly dispersed. Then, after continuous stirring for 3 hours, the mixture was dried in a vacuum drying oven at 100°C for 6 hours, and finally calcined at 450°C for 5 hours and naturally cooled to room temperature to obtain the positive electrode material.

7. The method for preparing a positive electrode for a solid-state battery according to claim 6, characterized in that: The ratio of the lithium-rich manganese-based ternary material, PVP-K30 and ammonium dihydrogen phosphate is 10g:6.5g:8.4g.

8. The method for preparing a positive electrode for a solid-state battery according to claim 1, characterized in that: The raw materials are calculated in parts by weight as follows: 80-100 parts of positive electrode material, 6-12 parts of binder, and 10-20 parts of conductive agent.

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