Porous aluminum oxide and preparation method thereof, and battery separator

Abstract

The present invention relates to the field of batteries, and provides a porous alumina and a preparation method thereof, and a battery separator. The porous alumina includes, from the inside to the outside, an alumina substrate, a first base film layer, and a second base film layer, wherein the surface of the alumina substrate has a porous structure; the first base film layer includes carbon nanotubes, and the carbon nanotubes are embedded in the pores on the surface of the alumina substrate to form the first base film layer; the second base film layer includes aluminum hydroxide, and the second base film layer at least partially covers the surface of the first base film layer. The surface of the alumina substrate has a porous structure and good mechanical properties. The unique tortuous porous structure on the surface can effectively prevent lithium dendrites from piercing, and can improve ionic conductivity. It still has good discharge capacity and capacity retention rate under high-speed current, and is an ideal battery separator material.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to porous alumina and a preparation method thereof, and a battery separator. Background Art

[0002] With the continuous development of science and technology, people have new requirements for batteries, that is, to improve the performance of batteries on the basis of clean battery development. Lithium-ion batteries are one of the most common new energy batteries. Due to their high energy density and long cycle life, lithium-ion batteries have been widely used in consumer electronics, electric vehicles and energy storage systems.

[0003] However, during the charging process of lithium-ion batteries, lithium ions will be unevenly deposited at the negative electrode. This uneven deposition will cause lithium ions to grow at the negative electrode to form lithium dendrites. In severe cases, the lithium dendrites may pierce the battery separator. Mechanical damage to the battery separator may cause battery performance degradation and even cause safety problems. For example, lithium dendrites piercing the battery separator may cause a short circuit inside the lithium-ion battery, causing thermal runaway of the lithium battery and causing combustion and explosion.

[0004] Therefore, the development of porous alumina membrane materials with self-healing function has become an important research direction. Summary of the invention

[0005] The present invention aims to solve at least one of the above technical problems.

[0006] To this end, the first object of the present invention is to provide a porous alumina;

[0007] The second object of the present invention is to provide a method for preparing porous alumina;

[0008] A third object of the present invention is to provide a battery separator.

[0009] To achieve the first purpose of the present invention, the present invention provides a porous alumina, which comprises, from the inside to the outside, an alumina substrate, a first base membrane layer and a second base membrane layer, wherein the surface of the alumina substrate has a porous structure; the first base membrane layer comprises carbon nanotubes, and the carbon nanotubes are embedded in the pores on the surface of the alumina substrate to form the first base membrane layer; the second base membrane layer comprises aluminum hydroxide, and the second base membrane layer at least partially covers the surface of the first base membrane layer.

[0010] Compared with the prior art, the technical effects achieved by adopting this technical solution are as follows: the surface of the alumina substrate has a porous structure and good mechanical properties. The unique tortuous porous structure on the surface can effectively prevent lithium dendrites from piercing, and can improve ion conductivity. It still has good discharge capacity and capacity retention rate under high-speed current, and is an ideal battery separator material; a first base film layer is further provided on the surface of the alumina substrate, and carbon nanotubes (CNTs) are embedded in the pores of the alumina substrate to form the first base film layer. The carbon nanotubes have high strength and high elastic modulus, which can greatly improve the mechanical strength and toughness of the material, and enhance crack resistance and impact resistance; and the carbon nanotubes themselves also have excellent conductivity, so the first base film The layer can also give the entire porous alumina material a certain conductivity, which makes the porous alumina of the present invention suitable for use as a battery separator; the second base film layer is composed of aluminum hydroxide, which can protect the carbon nanotube layer. At the same time, when the alumina substrate is damaged, the carbon nanotubes of the first base film layer can also serve as a trigger for the self-healing reaction, triggering the self-healing mechanism, so that the aluminum hydroxide provides further support during the self-healing process and maintains the structural integrity of the material; by arranging the first base film layer and the second base film layer on the surface of the alumina substrate, the pore structure and surface characteristics of the alumina substrate can be finely controlled, so that the porous alumina material has good performance in terms of mechanical strength, conductivity, chemical stability, etc.

[0011] In addition, the technical solution provided by the present invention may also have the following technical features:

[0012] In the above technical features, the specific surface area of ​​the porous alumina is 100m² / g-300m² / g; and / or the porosity of the porous alumina is 50%-90%; and / or the average pore size of the porous alumina is 2nm-50nm; and / or the mechanical strength of the porous alumina is 100MPa-300MPa.

[0013] Compared with the prior art, the technical effects achieved by adopting this technical solution are as follows: the porous alumina of the present invention has a larger specific surface area and a higher porosity, can provide more active sites and electrolyte penetration channels, and promote the efficiency of ion transmission. The ideal pore structure can effectively increase the transmission path of lithium ions, thereby improving the overall performance of the battery. The performance is better when the specific surface area and porosity are within the above range; the pore size range of 2nm to 50nm covers the scales of micropores, mesopores and some macropores. Such a pore size distribution enables the porous alumina to achieve good ion conductivity, thereby improving the charge and discharge capacity of the battery; the mechanical strength of the porous alumina is within the above range, has a higher structural strength, and can withstand larger mechanical loads and stresses without cracking or deformation. This porous alumina is particularly suitable for battery separators, which can effectively prevent lithium dendrites from piercing the battery separator and ensure the safety of lithium-ion batteries.

[0014] In any of the above technical features, the thickness of the first base film layer is 10nm-100nm; and / or the thickness of the second base film layer is 5nm-50nm.

[0015] Compared with the existing technology, the technical effect achieved by adopting this technical solution is: a layer that is too thick may reduce the porosity of the material and affect the specific surface area; a layer that is too thin may not be sufficient to provide sufficient functionality. Therefore, choosing the right thickness is crucial to balancing the performance of the material so that it maintains a higher porosity and specific surface area.

[0016] To achieve the second object of the present invention, the present invention provides a method for preparing porous alumina, which is used to prepare the porous alumina according to any one of the above technical features, and the preparation method comprises:

[0017] S100, preparing a precursor solution: dissolving an aluminum oxide precursor in a solvent, adding a template, and stirring uniformly to obtain a precursor solution;

[0018] S200, preparing a porous alumina template: subjecting a precursor solution to gelation treatment, calcination treatment and activation treatment in sequence, and then placing the precursor solution in a carbon nanotube solution for immersion treatment and first drying treatment in sequence to obtain a porous alumina template;

[0019] S300, preparing porous alumina: spraying a porous alumina template with a microcapsule emulsion containing aluminum hydroxide, and performing a second drying process to obtain porous alumina;

[0020] The carbon nanotubes are modified carbon nanotubes, and the preparation method of the modified carbon nanotubes includes:

[0021] S201, subjecting the carbon nanotubes to plasma treatment under vacuum conditions, and cooling them to room temperature to obtain modified carbon nanotubes;

[0022] The plasma treatment uses oxygen as the plasma gas.

[0023] Compared with the prior art, the technical effects achieved by adopting this technical solution are as follows: the alumina precursor is dissolved in a solvent and a template is added to generate a uniform precursor solution, which ensures gelation and the formation of a pore structure in the subsequent process. The addition of the template helps to control the pore size and porosity of the final porous alumina so that it meets the required structural requirements and ensures the porous characteristics of the material; the gelation treatment and calcination treatment can effectively form a porous structure, and the surface activity of the material is improved by activation treatment. The introduction of carbon nanotubes helps to enhance the mechanical strength and conductivity of the material. The drying treatment ensures the stability of the pore structure of the material. This process can give the material high strength and conductivity while maintaining the porosity of the material, so that the prepared porous alumina is suitable for use as a battery separator; the carbon nanotubes are modified by plasma treatment, and the use of oxygen as plasma gas can introduce oxygen content on the surface of the material to form oxides or functional groups such as hydroxyl groups, carboxyl groups, etc. The introduction of these functional groups can enhance the compatibility of the carbon nanotubes with the polymer matrix, so that the carbon nanotubes are better dispersed in the material, and A stronger interfacial bonding force is formed, and the introduced functional groups can participate in the self-healing reaction through chemical or physical interactions to promote the healing process. For example, carboxyl and hydroxyl groups can react with functional groups in the polymer to form new chemical bonds to help restore the integrity of the material. Under appropriate conditions, the carbon nanotubes after plasma treatment can still maintain good conductivity; the porous alumina template is treated by spraying aluminum hydroxide in the microcapsule emulsion, and aluminum hydroxide is introduced into the surface of the porous alumina. Its main purpose is to fill the microscopic cracks or pores in the material by physical or chemical means to enhance the self-healing ability of the material. When the material is subjected to stress or other external damage, aluminum hydroxide can form a new aluminum oxide layer in the damaged area to play a repairing role, thereby extending the service life of the material; through meticulous process steps and material processing, a porous alumina material with high mechanical strength, specific pore structure and potential self-healing ability is prepared. These characteristics make the material have significant performance advantages in a variety of applications, especially suitable for battery separators for lithium-ion batteries.

[0024] In any of the above technical features, in S100, the alumina is γ-alumina; and / or the mass ratio of alumina to solvent is 1:(5-20); and / or the template includes an organic template, a surfactant and a hard template; and / or the mass ratio of the template to alumina is (0.1-2):1.

[0025] Compared with the prior art, the technical effects achieved by adopting this technical solution are as follows: γ-alumina is an alumina phase with a high specific surface area and a good pore structure. Compared with other alumina phases such as α-alumina, γ-alumina is easier to form a porous structure and has higher activity; the mass ratio of alumina to solvent determines the concentration and viscosity of the precursor solution, which directly affects the gelation and pore-forming process. By adjusting the ratio of alumina to solvent, the pore size, porosity and specific surface area of ​​porous alumina can be precisely controlled to meet the needs of different applications; templates are usually used to control the pore structure and size of porous materials. When preparing porous alumina, templates can help form a uniform pore structure. There are usually organic templates, surfactants and hard templates. Among them, organic templates and surfactants are often used in the synthesis of microporous or mesoporous materials. Hard templates can be removed after calcination, leaving pores. By adjusting the ratio of template to alumina, porous alumina with the most suitable porosity and pore size can be obtained.

[0026] In any of the above technical features, in S200, the gelation treatment is to add propylene oxide for gelation treatment; and / or the activation treatment includes any one of an ammonia activation treatment or a nitric acid activation treatment.

[0027] Compared with the prior art, the technical effects achieved by adopting this technical scheme are as follows: the introduction of propylene oxide can induce sol-gel transformation quickly and evenly to form a stable three-dimensional network structure, which helps to control the microscopic pore structure of porous alumina, make its pore distribution more uniform, and enhance the mechanical strength and stability of the material; the surface of porous alumina after ammonia treatment may become more hydrophilic, which is conducive to interaction with aqueous solutions, and may also improve the activity of the material in certain catalytic reactions; nitric acid treatment can increase the surface acidity of porous alumina, thereby enhancing its activity in acidic catalytic reactions, and such activation treatment can also help remove organic residues on the surface of the material, further purify and enhance the surface activity of the material; by introducing propylene oxide for gelation treatment, the pore structure and stability of porous alumina can be better controlled, and the use of ammonia activation treatment or nitric acid activation treatment can adjust the surface chemical properties of porous alumina according to different needs, thereby improving the adaptability and functionality of the material.

[0028] In S300 in any of the above technical features, the particle size of the spray treatment is 1nm-20nm.

[0029] Compared with the existing technology, the technical effect achieved by adopting this technical scheme is: when the particle size of the spray droplets is small, the aluminum hydroxide healing agent can be evenly distributed on the surface of the porous alumina to form a dense and uniform repair layer. This delicate coverage helps to improve the overall strength and durability of the material, especially for the healing effect of micro cracks. At the same time, due to the high structural match between aluminum hydroxide and porous alumina materials, the durability and service life of the material can be significantly improved. By precisely controlling the particle size of the spray treatment, the distribution effect of the healing agent can be optimized to ensure that the mechanical properties, pore structure and surface characteristics of the material are effectively maintained and enhanced.

[0030] In any of the above technical features, in S200, the temperature of the first drying treatment is 50°C-150°C; and / or in S300, the temperature of the second drying treatment is 100°C-200°C; and / or in S200, the time of the first drying treatment is 2h-12h; and / or in S300, the time of the second drying treatment is 1h-6h.

[0031] Compared with the prior art, the technical effects achieved by adopting this technical solution are as follows: the selection of drying temperature affects the drying rate and the thermal stability of the material. Too high a temperature may cause deformation of the material or cracking, while too low a temperature may lead to incomplete drying, affecting the quality of the final material. Using the above-mentioned temperature for the first drying treatment and the second drying treatment can reduce thermal stress, prevent material deformation or cracking, and accelerate the drying process, which helps to remove the solvent faster. The length of the drying time determines the degree of removal of the solvent or moisture in the material. The appropriate time ensures uniform drying and avoids structural defects or functional degradation caused by insufficient drying. Using the above-mentioned time for the first drying treatment and the second drying treatment can reduce thermal stress, maintain its structural stability, and ensure that the healing agent is completely cured and the material surface is uniform.

[0032] In any of the above technical features, in S201, the flow rate of oxygen is 50sccm-300sccm; and / or the temperature of plasma treatment is 25°C-100°C; and / or the time of plasma treatment is 60s-300s.

[0033] Compared with the existing technology, the technical effects achieved by adopting this technical solution are: using the above-mentioned temperature for plasma treatment can avoid damage or deformation of carbon nanotubes caused by high temperature, and help to improve the activity of plasma and enhance the treatment effect; using the above-mentioned time for plasma treatment, the surface activity and adhesion are significantly improved, which is suitable for most standard surface treatment requirements.

[0034] To achieve the third objective of the present invention, the present invention provides a battery separator, which comprises a porous alumina having any one of the above technical features.

[0035] The battery separator of the present invention includes the porous alumina in any technical solution of the present invention. The battery separator of the present invention has all the beneficial effects of the porous alumina in any technical solution of the present invention, which will not be described in detail here.

[0036] After adopting the technical solution of the present invention, the technical effects that can be achieved are as follows:

[0037] 1. The surface of the alumina substrate has a porous structure and good mechanical properties. Its unique tortuous porous structure can effectively prevent lithium dendrites from piercing and improve ion conductivity. It still has good discharge capacity and capacity retention rate under high-speed current, making it an ideal battery separator material;

[0038] 2. Carbon nanotubes are embedded in the pores of the alumina substrate to form the first base film layer. Carbon nanotubes can greatly improve the mechanical strength and toughness of the material, enhance crack resistance and impact resistance, and carbon nanotubes themselves also have excellent electrical conductivity, so the first base film layer can also give the entire porous alumina material a certain electrical conductivity;

[0039] 3. The second base film layer is composed of aluminum hydroxide, which can protect the carbon nanotube layer. When the aluminum oxide substrate is damaged, the carbon nanotubes in the first base film layer can act as a trigger or enhancer for the self-healing reaction, triggering the self-healing mechanism, so that the aluminum hydroxide can provide further support in the self-healing process and maintain the structural integrity of the material;

[0040] 4. The preparation method of porous alumina of the present invention prepares a porous alumina material with high mechanical strength, specific pore structure and potential self-healing ability through meticulous process steps and material treatment. These characteristics make the material have significant performance advantages in a variety of applications, and it is particularly suitable for use as a battery separator for lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a SEM image of porous alumina according to an embodiment of the present invention;

[0042] Figure 2 This is a graph showing the DCR growth rate of a lithium-ion battery having a battery separator made of porous alumina according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0044] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the following Figure 1 and Figure 2 The specific embodiments of the present invention are described in detail.

[0046] In the related art, lithium ions are unevenly deposited at the negative electrode during the charging process of lithium-ion batteries. This uneven deposition will cause lithium ions to grow at the negative electrode to form lithium dendrites. In severe cases, the lithium dendrites may pierce the battery separator. Mechanical damage to the battery separator may cause battery performance degradation and even lead to safety issues. For example, lithium dendrites piercing the battery separator may cause a short circuit inside the lithium-ion battery, resulting in thermal runaway of the lithium battery and causing combustion and explosion.

[0047] In view of this, the present invention provides a porous alumina, which can improve the mechanical strength and conductivity while arranging a first base membrane layer and a second base membrane layer on the surface of the alumina substrate. The porous alumina is suitable for use as a battery separator, can effectively prevent lithium dendrites from piercing, and improve ionic conductivity.

[0048] Specifically, if Figure 1 As shown, an embodiment of the present invention provides a porous alumina, which includes, from the inside out, an alumina substrate, a first base membrane layer and a second base membrane layer, wherein the surface of the alumina substrate has a porous structure; the first base membrane layer includes carbon nanotubes, and the carbon nanotubes are embedded in the pores on the surface of the alumina substrate to form the first base membrane layer; the second base membrane layer includes aluminum hydroxide, and the second base membrane layer at least partially covers the surface of the first base membrane layer.

[0049] Preferably, the surface of the alumina substrate has a porous structure and good mechanical properties. The unique tortuous porous structure on the surface can effectively prevent lithium dendrites from piercing, and can improve ionic conductivity. It still has good discharge capacity and capacity retention rate under high-speed current, and is an ideal battery separator material; a first base film layer is further provided on the surface of the alumina substrate, and carbon nanotubes (CNTs) are embedded in the pores of the alumina substrate to form the first base film layer. The carbon nanotubes have high strength and high elastic modulus, which can greatly improve the mechanical strength and toughness of the material, enhance crack resistance and impact resistance, and the carbon nanotubes themselves also have excellent electrical conductivity, so the first base film layer can also give the entire porous alumina substrate good electrical conductivity. Aluminum materials have a certain electrical conductivity, which makes the porous alumina of the present invention particularly suitable for use as a battery separator; the second base film layer is composed of aluminum hydroxide, which can protect the carbon nanotube layer. At the same time, when the alumina substrate is damaged, the carbon nanotubes of the first base film layer can also serve as a trigger or enhancer for the self-healing reaction, triggering the self-healing mechanism, so that the aluminum hydroxide provides further support during the self-healing process and maintains the structural integrity of the material; by arranging the first base film layer and the second base film layer on the surface of the alumina substrate, the pore structure and surface characteristics of the alumina substrate can be finely controlled, so that the porous alumina material has good performance in terms of mechanical strength, electrical conductivity, chemical stability, etc.

[0050] Preferably, the specific surface area of ​​porous alumina is 100m² / g-300m² / g, where the specific surface area refers to the total surface area of ​​a material per unit mass. A higher specific surface area means that the material surface has more opportunities to contact external substances. The porosity of porous alumina is 50%-90%, where the porosity is the ratio of the pore volume to the total volume in the material. A high porosity means that there are more pores inside the material. Materials with high porosity usually exhibit good permeability and lower density. High porosity can also improve the energy storage performance of the material. For example, in supercapacitors or battery electrode materials, more pores can accommodate more electrolytes and improve electrochemical performance. Porous alumina has a larger specific surface area and a higher porosity, which can provide more active sites and electrolyte permeation channels, thereby promoting the efficiency of ion transmission. An ideal pore structure can effectively increase the transmission path of lithium ions, thereby improving the overall performance of the battery. The specific surface area and porosity have better performance within the above range.

[0051] Furthermore, the specific surface area of ​​the porous alumina is preferably 200m² / g-250m² / g, and the porosity is preferably 60%-80%, at which point the performance of the porous alumina is optimal.

[0052] Preferably, the average pore size of the porous alumina is 2nm-50nm. The average pore size refers to the average diameter of the pores in the material. The pore size range of 2nm to 50nm covers the scales of micropores, mesopores and some macropores. Such a pore size distribution enables the porous alumina to achieve good ionic conductivity, thereby improving the charge and discharge capacity of the battery. The average pore size is preferably 10nm-20nm, at which time the ionic conductivity of the porous alumina is optimal.

[0053] Furthermore, the mechanical strength of porous alumina is 100MPa-300MPa, which has high structural strength and can withstand large mechanical loads and stresses without cracking or deforming. This porous alumina is particularly suitable for battery separators, which can effectively prevent lithium dendrites from piercing the battery separator and ensure the safety of lithium-ion batteries.

[0054] Furthermore, the thickness of the first base film layer is 10nm-100nm; and / or the thickness of the second base film layer is 5nm-50nm. Preferably, a layer that is too thick may reduce the porosity of the material and affect the specific surface area; a layer that is too thin may not be sufficient to provide sufficient functionality, so choosing the right thickness is crucial to balancing the performance of the material so that it maintains a higher porosity and specific surface area.

[0055] In some implementations of the embodiments of the present invention, the present invention provides a method for preparing porous alumina, which is used to prepare porous alumina according to any one of the above technical features, and the preparation method comprises:

[0056] S100, preparing a precursor solution: dissolving an aluminum oxide precursor in a solvent, adding a template, and stirring uniformly to obtain a precursor solution;

[0057] S200, preparing a porous alumina template: subjecting a precursor solution to gelation treatment, calcination treatment and activation treatment in sequence, and then placing the precursor solution in a carbon nanotube solution for immersion treatment and first drying treatment in sequence to obtain a porous alumina template;

[0058] S300, preparing porous alumina: spraying a porous alumina template with a microcapsule emulsion containing aluminum hydroxide, and performing a second drying process to obtain porous alumina;

[0059] The carbon nanotubes are modified carbon nanotubes, and the preparation method of the modified carbon nanotubes includes:

[0060] S201, subjecting the carbon nanotubes to plasma treatment under vacuum conditions, and cooling them to room temperature to obtain modified carbon nanotubes;

[0061] The plasma treatment uses oxygen as the plasma gas.

[0062] Preferably, the alumina precursor is dissolved in a solvent and a template is added to generate a uniform precursor solution to ensure gelation and formation of a porous structure in the subsequent process. The solvent is preferably any one of dichloromethane, toluene or ethanol. The addition of the template helps to control the pore size and porosity of the final porous alumina so that it meets the required structural requirements and ensures the porous characteristics of the material.

[0063] The gelation treatment and calcination treatment can effectively form a porous structure. The calcination treatment is preferably carried out at 900°C-1100°C for 4h-18h, and the surface activity of the material is improved by activation treatment. The introduction of carbon nanotubes helps to enhance the mechanical strength and conductivity of the material. The material is preferably immersed in a carbon nanotube solution at 60°C for 3.5h-12h. The drying treatment ensures the stability of the pore structure of the material. This process can give the material high strength and conductivity while maintaining the porosity of the material, so that the prepared porous alumina is suitable for use as a battery separator.

[0064] The carbon nanotubes are modified by plasma treatment, preferably using oxygen as plasma gas, and functional groups such as hydroxyl and carboxyl groups can be introduced. The introduction of these functional groups can enhance the compatibility of the carbon nanotubes with the polymer matrix, so that the carbon nanotubes are better dispersed in the material and form a stronger interface bonding force. The introduced functional groups can participate in the self-healing reaction through chemical or physical interactions to promote the healing process. For example, carboxyl and hydroxyl groups can react with functional groups in the polymer to form new chemical bonds to help restore the integrity of the material. Under appropriate conditions, the carbon nanotubes after plasma treatment can still maintain good conductivity;

[0065] The porous alumina template is sprayed with a microcapsule emulsion containing aluminum hydroxide. The introduction of the healing agent gives the porous alumina self-healing properties, which can self-repair when the material is microscopically damaged, thereby extending the service life of the material and maintaining its performance, so that the final product has the required physical and chemical properties. The microcapsule emulsion ensures that the aluminum hydroxide can be evenly distributed on the surface of the material and released when necessary. The second drying treatment further stabilizes the material structure, so that the final product has the required physical and chemical properties;

[0066] Through meticulous process steps and material treatment, a porous alumina material with high mechanical strength, specific pore structure and potential self-healing ability was prepared. These properties give the material significant performance advantages in a variety of applications, especially for use as battery separators in lithium-ion batteries.

[0067] Preferably, in S100, the alumina is γ-alumina, which is converted by dehydration of boehmite at a specific temperature. γ-alumina is an alumina phase with a high specific surface area and a good pore structure. Compared with other alumina phases such as α-alumina, γ-alumina is more likely to form a porous structure and has higher activity.

[0068] Preferably, the mass ratio of alumina to solvent is 1:(5-20). The mass ratio of alumina to solvent determines the concentration and viscosity of the precursor solution, which directly affects the gelation and pore-forming process. The precursor solution with a low solvent ratio has a higher concentration and a higher viscosity, which may form a pore structure with a smaller pore size and help to generate a denser porous alumina; the precursor solution with a high solvent ratio has a lower concentration and a lower viscosity, which may generate a pore structure with a larger pore size and lead to a higher porosity; by adjusting the ratio of alumina to solvent, the pore size, porosity and specific surface area of ​​the porous alumina can be precisely controlled to meet the needs of different applications.

[0069] Preferably, the template includes an organic template, a surfactant and a hard template. The template is usually used to control the pore structure and size of the porous material. The template can help form a uniform pore structure when preparing porous alumina. There are usually organic templates, surfactants and hard templates, among which organic templates and surfactants are often used in the synthesis of microporous or mesoporous materials. The hard template can be removed after calcination, leaving pores. By adjusting the ratio of template to alumina, porous alumina with the most suitable porosity and pore size can be obtained.

[0070] Furthermore, the organic template includes at least one of polyvinyl alcohol (PVA), polyacrylamide (PAM), and polyvinyl pyrrolidone (PVP); the surfactant includes at least one of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS); and the hard template includes at least one of silica nanoparticles and polystyrene microspheres.

[0071] Preferably, the mass ratio of the template to alumina is (0.1-2):1. By adjusting the ratio of the template to alumina, porous alumina with the most suitable porosity and pore size can be obtained.

[0072] Preferably, in S200, the gelation treatment is to add propylene oxide for gelation treatment. Propylene oxide is a commonly used gelling agent. After propylene oxide is added to the precursor solution, a ring-opening reaction of propylene oxide will occur, resulting in accelerated hydrolysis and condensation reactions in the solution to form a uniform gel structure; the introduction of propylene oxide can quickly and uniformly induce sol-gel transformation to form a stable three-dimensional network structure, which helps to control the microscopic pore structure of porous alumina, making its pore distribution more uniform and enhancing the mechanical strength and stability of the material; at the same time, this gelation treatment method can also improve the controllability and efficiency of the preparation process and reduce defects that may occur in the preparation process, such as uneven pore size or unstable structure.

[0073] Preferably, the activation treatment includes any one of an ammonia activation treatment or a nitric acid activation treatment. The ammonia activation treatment is usually used to introduce alkaline conditions, which can adjust the chemical properties of the alumina surface, promote the formation of specific functional groups, and enhance the interaction with its carbon nanotubes or healing agents; the porous alumina surface after ammonia treatment may become more hydrophilic, which is conducive to the interaction with aqueous solutions, and may also increase the activity of the material in certain catalytic reactions. In addition, ammonia treatment may also improve the conductivity or other functional properties of the material.

[0074] Furthermore, nitric acid activation treatment is an acidic treatment method. Nitric acid treatment can increase the acidic functional groups on the surface of the material, thereby adjusting the surface chemical properties; nitric acid treatment can increase the surface acidity of porous alumina, thereby enhancing its activity in acidic catalytic reactions. Such activation treatment can also help remove organic residues on the surface of the material, further purify and enhance the surface activity of the material; at the same time, this treatment may increase the degree of surface oxidation and improve the stability of the material in certain environments.

[0075] Preferably, aluminum hydroxide is introduced into the surface of porous alumina as a healing agent. Its main purpose is to fill the microscopic cracks or pores in the material by physical or chemical means to enhance the self-healing ability of the material. Aluminum hydroxide can form a dense covering layer on the surface of porous alumina to improve the mechanical strength and durability of the material. When the material is subjected to stress or other external damage, aluminum hydroxide can form a new aluminum oxide layer in the damaged area to play a repairing role, thereby extending the service life of the material.

[0076] Preferably, the preparation method of the microcapsule emulsion containing aluminum hydroxide comprises:

[0077] S310, preparing a capsule core solution: mixing aluminum hydroxide powder and a solvent in a mass ratio of 1:(2-3) to obtain a capsule core solution;

[0078] S320, preparing a capsule wall solution: uniformly mixing porous cyclodextrin and deionized water in a mass ratio of 1:5.5, adding an emulsifier and a cross-linking agent, and continuing to mix uniformly to obtain a capsule wall solution;

[0079] S330, preparing a microcapsule emulsion: slowly dripping the capsule core solution into the capsule wall solution while stirring, so that the capsule core is gradually wrapped by the capsule wall, and obtaining a microcapsule emulsion containing aluminum hydroxide;

[0080] The solvent is anhydrous ethanol or deionized water; and the porous cyclodextrin is porous cyclodextrin modified with acryloyl chloride.

[0081] Furthermore, in S300, the particle size of the spray treatment is 1nm-20nm. The smaller spray particle size can make the aluminum hydroxide healing agent evenly distributed on the surface of the porous alumina to form a dense and uniform repair layer. This delicate coverage helps to improve the overall strength and durability of the material, especially for the healing effect of micro cracks.

[0082] Preferably, the choice of drying temperature affects the drying rate and thermal stability of the material. Too high a temperature may cause deformation or cracking of the material, while too low a temperature may lead to incomplete drying, affecting the quality of the final material. The length of the drying time determines the degree of removal of solvents or moisture in the material. Appropriate time ensures uniform drying and avoids structural defects or functional degradation due to insufficient drying. Therefore, in S200, the temperature of the first drying treatment is 50°C-150°C, and the time of the first drying treatment is 2h-12h. In S300, the temperature of the second drying treatment is 100°C-200°C, and the time of the second drying treatment is 1h-6h. This can reduce thermal stress, prevent material deformation or cracking, and accelerate the drying process, which helps to remove the solvent faster, maintain its structural stability, and ensure that the healing agent is fully cured and the material surface is uniform.

[0083] Preferably, plasma treatment uses oxygen as plasma gas. Oxygen plasma treatment can introduce oxygen content on the surface of the material to form oxides or functional groups such as hydroxyl groups, carboxyl groups, etc. These functional groups can not only enhance the interfacial interaction between the carbon nanotubes and the polymer matrix, but also serve as anchor points for the self-healing agent, thereby improving the healing efficiency; the oxygen flow rate is 50sccm-300sccm, preferably 100sccm-250sccm, the oxygen concentration is appropriate, the surface modification effect is significant, and the surface polarity and adhesion can be effectively increased without causing excessive oxidation. More oxygen functional groups can be introduced, and the performance of the carbon nanotubes can be optimized; the temperature of the plasma treatment is 25°C-100°C, which can avoid damage or deformation of the carbon nanotubes caused by high temperature, and help to improve the activity of the plasma and enhance the treatment effect; the time of the plasma treatment is 60s-300s, preferably 120s-180s, the surface activity and adhesion are significantly improved, and the treatment effect is the best.

[0084] [Example 1]

[0085] This embodiment provides a porous alumina, which includes, from the inside out, an alumina substrate, a first base film layer, and a second base film layer. The surface of the alumina substrate has a porous structure, the first base film layer has a thickness of 10 nm, and the second base film layer has a thickness of 5 nm. The porous alumina is prepared by the following steps:

[0086] S100, preparing a precursor solution: dissolving a γ-alumina precursor in dichloromethane, wherein the mass ratio of γ-alumina to dichloromethane is 1:20, adding polyvinyl alcohol, wherein the mass ratio of polyvinyl alcohol to γ-alumina is 0.1:1, and stirring evenly to obtain a precursor solution;

[0087] S200, preparing a porous alumina template: adding propylene oxide to the precursor solution for gelation treatment, calcining at 900° C. for 18 h, then activating with ammonia, then immersing in a carbon nanotube solution at 60° C. for 3.5 h, and performing a first drying treatment at 50° C. for 12 h to obtain a porous alumina template;

[0088] S300, preparing porous alumina: spraying the porous alumina template with a microcapsule emulsion containing aluminum hydroxide, wherein the particle size of the sprayed alumina template is 1 nm, and performing a second drying treatment at 100° C. for 6 hours to obtain porous alumina;

[0089] The method for preparing carbon nanotubes comprises:

[0090] S201, subjecting the carbon nanotubes to plasma treatment with oxygen under vacuum conditions for 300 seconds, with an oxygen flow rate of 50 sccm and a temperature of 25° C., and cooling to room temperature to obtain modified carbon nanotubes;

[0091] The microcapsule emulsion containing aluminum hydroxide was purchased from outside.

[0092] [Example 2]

[0093] This embodiment provides a porous alumina, which includes, from the inside out, an alumina substrate, a first base film layer, and a second base film layer. The surface of the alumina substrate has a porous structure. The first base film layer has a thickness of 100 nm, and the second base film layer has a thickness of 50 nm. The porous alumina is prepared by the following steps:

[0094] S100, preparing a precursor solution: dissolving a γ-alumina precursor in toluene, wherein the mass ratio of γ-alumina to toluene is 1:5, adding hexadecyltrimethylammonium bromide, wherein the mass ratio of hexadecyltrimethylammonium bromide to γ-alumina is 2:1, and stirring evenly to obtain a precursor solution;

[0095] S200, preparing a porous alumina template: adding propylene oxide to the precursor solution for gelation treatment, calcining at 1100° C. for 4 hours, then activating with ammonia, then immersing in a carbon nanotube solution at 60° C. for 12 hours, and performing a first drying treatment at 150° C. for 2 hours to obtain a porous alumina template;

[0096] S300, preparing porous alumina: spraying the porous alumina template with a microcapsule emulsion containing aluminum hydroxide, wherein the particle size of the sprayed alumina template is 20 nm, and performing a second drying treatment at 200° C. for 1 h to obtain porous alumina;

[0097] The method for preparing carbon nanotubes comprises:

[0098] S201, subjecting the carbon nanotubes to oxygen plasma treatment for 60 seconds under vacuum conditions, with an oxygen flow rate of 300 sccm and a temperature of 100° C., and cooling to room temperature to obtain modified carbon nanotubes; the microcapsule emulsion containing aluminum hydroxide is purchased externally.

[0099] [Example 3]

[0100] This embodiment provides a porous alumina, which includes, from the inside out, an alumina substrate, a first base film layer, and a second base film layer. The surface of the alumina substrate has a porous structure, the first base film layer has a thickness of 70 nm, and the second base film layer has a thickness of 30 nm. The porous alumina is prepared by the following steps:

[0101] S100, preparing a precursor solution: dissolving a γ-alumina precursor in ethanol, wherein the mass ratio of γ-alumina to ethanol is 1:10, adding silica nanoparticles, wherein the mass ratio of silica nanoparticles to γ-alumina is 1:1, and stirring evenly to obtain a precursor solution;

[0102] S200, preparing a porous alumina template: adding propylene oxide to the precursor solution for gelation treatment, calcining at 1000° C. for 10 h, then activating with ammonia, then immersing in a carbon nanotube solution at 60° C. for 10 h, and performing a first drying treatment at 120° C. for 8 h to obtain a porous alumina template;

[0103] S300, preparing porous alumina: spraying a porous alumina template with a microcapsule emulsion containing aluminum hydroxide, wherein the particle size of the sprayed alumina template is 10 nm, and performing a second drying treatment at 180° C. for 5 h to obtain porous alumina;

[0104] The method for preparing carbon nanotubes comprises:

[0105] S201, subjecting the carbon nanotubes to plasma treatment with oxygen under vacuum conditions for 180 seconds, with an oxygen flow rate of 100 sccm and a temperature of 80° C., and cooling to room temperature to obtain modified carbon nanotubes;

[0106] The preparation method of the microcapsule emulsion containing aluminum hydroxide comprises:

[0107] S310, preparing a capsule core solution: mixing aluminum hydroxide powder and anhydrous ethanol in a mass ratio of 1:2 to obtain a capsule core solution;

[0108] S320, preparing a capsule wall solution: mixing the porous cyclodextrin modified with acryloyl chloride and deionized water in a mass ratio of 1:5.5, adding Tween-80 and glutaraldehyde, and continuing to mix to obtain a capsule wall solution;

[0109] S330, preparing microcapsule emulsion: slowly dripping the capsule core solution into the capsule wall solution while stirring, so that the capsule core is gradually wrapped by the capsule wall to obtain a microcapsule emulsion containing aluminum hydroxide.

[0110] [Example 4]

[0111] This embodiment provides a porous alumina, which includes, from the inside out, an alumina substrate, a first base film layer, and a second base film layer. The surface of the alumina substrate has a porous structure, the first base film layer has a thickness of 55 nm, and the second base film layer has a thickness of 25 nm. The porous alumina is prepared by the following steps:

[0112] S100, preparing a precursor solution: dissolving a γ-alumina precursor in ethanol, wherein the mass ratio of γ-alumina to ethanol is 1:15, adding polyvinyl pyrrolidone, wherein the mass ratio of polyvinyl pyrrolidone to γ-alumina is 0.8:1, and stirring evenly to obtain a precursor solution;

[0113] S200, preparing a porous alumina template: adding propylene oxide to the precursor solution for gelation treatment, calcining at 1100° C. for 10 h, then activating with ammonia, then immersing in a carbon nanotube solution at 60° C. for 8 h, and performing a first drying treatment at 140° C. for 7 h to obtain a porous alumina template;

[0114] S300, preparing porous alumina: spraying a porous alumina template with a microcapsule emulsion containing aluminum hydroxide, wherein the particle size of the sprayed alumina template is 12 nm, and performing a second drying treatment at 160° C. for 5 h to obtain porous alumina;

[0115] The method for preparing carbon nanotubes comprises:

[0116] S201, subjecting the carbon nanotubes to plasma treatment with oxygen under vacuum conditions for 120 seconds, with an oxygen flow rate of 250 sccm and a temperature of 82° C., and cooling to room temperature to obtain modified carbon nanotubes;

[0117] The preparation method of the microcapsule emulsion containing aluminum hydroxide comprises:

[0118] S310, preparing a capsule core solution: mixing aluminum hydroxide powder and deionized water in a mass ratio of 1:3 to obtain a capsule core solution;

[0119] S320, preparing a capsule wall solution: mixing the porous cyclodextrin modified with acryloyl chloride and deionized water in a mass ratio of 1:5.5, adding Tween-80 and glutaraldehyde, and continuing to mix to obtain a capsule wall solution;

[0120] S330, preparing microcapsule emulsion: slowly dripping the capsule core solution into the capsule wall solution while stirring, so that the capsule core is gradually wrapped by the capsule wall to obtain a microcapsule emulsion containing aluminum hydroxide.

[0121] [Comparative Example 1]

[0122] This comparative example provides a porous alumina, which is purchased from outside.

[0123] [Comparative Example 2]

[0124] This comparative example provides a porous alumina, which includes, from the inside to the outside, an alumina substrate, a first base membrane layer, and a second base membrane layer. The surface of the alumina substrate has a porous structure, the first base membrane layer has a thickness of 10 nm, and the second base membrane layer has a thickness of 5 nm. The preparation method is the same as that of Example 1, except that the alumina precursor is an α-alumina precursor.

[0125]

Performance test

[0126] BET Test

[0127] 0.2 g of the porous alumina samples of Examples 1-4 and Comparative Examples 1-2 were respectively sampled and BET tests were performed using nitrogen as the adsorbent. The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130] Mechanical strength test

[0131] The porous alumina of Examples 1-4 and Comparative Examples 1-2 were subjected to mechanical strength tests. The test results are shown in Table 2.

[0132] Table 2

[0133]

[0134] According to Table 1 and Table 2, the specific surface area, porosity and mechanical strength of the porous alumina in Examples 1-4 are greater than those in Comparative Examples 1-2, indicating that the porous alumina in Examples 1-4 has better performance, especially the porous alumina in Examples 3-4 has better performance. This may be due to the selection of the first base film layer and the second base film layer of appropriate thickness in Examples 3-4 and the selection of appropriate parameters in the preparation process. The mechanical properties of Comparative Example 1 are poor, which is due to the larger average pore size in Comparative Example 1, which affects its mechanical properties. Although the mechanical properties of the porous alumina in Comparative Example 2 are better than those in Example 1, its specific surface area, porosity and average pore size are smaller. This may be due to the selection of an α-alumina precursor in Comparative Example 2. Although it has better mechanical properties, it is not easy to form a porous structure.

[0135] Self-healing ability test

[0136] The porous alumina of Examples 1-4 and Comparative Examples 1-2 were subjected to post-mechanical damage heating treatment, and their healing effects were evaluated using dynamic mechanical analysis (DMA). The results show that as the temperature increases, the storage modulus G' of the porous alumina of Examples 1-4 and Comparative Example 2 rises after a short drop, indicating that the healing degree of the porous alumina gradually increases, and the healed diaphragm is almost restored to its original state; while the storage modulus G' of the porous alumina of Comparative Example 1 gradually decreases as the temperature increases, indicating that the porous alumina in Comparative Example 1 does not have self-healing ability.

[0137] Cyclic performance test

[0138] The porous alumina in Examples 1-4 and Comparative Examples 1-2 were made into battery separators and assembled into lithium-ion batteries, and the cycle performance was tested. The test results are as follows: Figure 2 As shown, the DCR growth rate of the lithium-ion batteries with the porous alumina battery separators in Examples 1-4 is less than 1.25 after 200 cycles, while the DCR growth rate of the lithium-ion batteries with the porous alumina battery separators in Comparative Examples 1-2 is about 1.3 after 200 cycles, indicating that the lithium-ion batteries with the porous alumina battery separators in the embodiments of the present invention still have good performance after multiple cycles.

[0139] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0140] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A porous alumina, characterized in that: The porous alumina includes, from inside to outside, an alumina substrate, a first base film layer, and a second base film layer. The surface of the aluminum oxide substrate has a porous structure; The first base film layer includes carbon nanotubes, and the carbon nanotubes are embedded in the pores on the surface of the aluminum oxide substrate to form the first base film layer; The second base film layer comprises aluminum hydroxide, and the second base film layer at least partially covers the surface of the first base film layer; The preparation method of the porous alumina comprises: S100, preparing a precursor solution: dissolving an aluminum oxide precursor in a solvent, adding a template, and stirring the mixture to obtain the precursor solution; S200, preparing a porous alumina template: subjecting the precursor solution to gelation treatment, calcination treatment and activation treatment in sequence, and then placing the precursor solution in a carbon nanotube solution for immersion treatment and first drying treatment in sequence to obtain the porous alumina template; S300, preparing porous alumina: spraying the porous alumina template with a microcapsule emulsion containing aluminum hydroxide and performing a second drying process to obtain the porous alumina; The carbon nanotubes are modified carbon nanotubes, and the preparation method of the modified carbon nanotubes includes: S201, subjecting the carbon nanotubes to plasma treatment under vacuum conditions, and cooling them to room temperature to obtain the modified carbon nanotubes; The plasma treatment uses oxygen as the plasma gas.

2. The porous alumina according to claim 1, characterized in that The specific surface area of ​​the porous alumina is 100m² / g-300m² / g; and / or The porosity of the porous alumina is 50%-90%; and / or The average pore size of the porous alumina is 2nm-50nm; and / or The mechanical strength of the porous alumina is 100MPa-300MPa.

3. The porous alumina according to claim 1, characterized in that The thickness of the first base film layer is 10nm-100nm; and / or The thickness of the second base film layer is 5nm-50nm.

4. A method for preparing porous alumina, characterized in that: For preparing the porous alumina according to any one of claims 1 to 3, the preparation method comprises: S100, preparing a precursor solution: dissolving an aluminum oxide precursor in a solvent, adding a template, and stirring the mixture to obtain the precursor solution; S200, preparing a porous alumina template: subjecting the precursor solution to gelation treatment, calcination treatment and activation treatment in sequence, and then placing the precursor solution in a carbon nanotube solution for immersion treatment and first drying treatment in sequence to obtain the porous alumina template; S300, preparing porous alumina: using a microcapsule emulsion containing aluminum hydroxide to spray the porous alumina template and perform a second drying process to obtain the porous alumina; Wherein, the carbon nanotubes are modified carbon nanotubes, and the preparation method of the modified carbon nanotubes comprises: S201, subjecting the carbon nanotubes to plasma treatment under vacuum conditions, and cooling them to room temperature to obtain the modified carbon nanotubes; The plasma treatment uses oxygen as the plasma gas.

5. The preparation method according to claim 4, characterized in that In the S100, The alumina is γ-alumina; and / or The mass ratio of the aluminum oxide to the solvent is 1:(5-20); and / or The template comprises an organic template, a surfactant and a hard template; and / or The mass ratio of the template to the alumina is (0.1-2):

1.

6. The preparation method according to claim 4, characterized in that In the S200, The gelation treatment is to add propylene oxide for gelation treatment; and / or The activation treatment includes any one of an ammonia activation treatment or a nitric acid activation treatment.

7. The preparation method according to claim 4, characterized in that In the S300, the particle size of the spray-treated particles is 1 nm-20 nm.

8. The preparation method according to claim 4, characterized in that In S200, the temperature of the first drying process is 50° C.-150° C.; and / or In the S300, the temperature of the second drying process is 100° C.-200° C.; and / or In S200, the first drying process lasts for 2 hours to 12 hours; and / or In the S300, the second drying process is performed for 1 hour to 6 hours.

9. The preparation method according to claim 4, characterized in that In the S201, The flow rate of the oxygen gas is 50 sccm-300 sccm; and / or The temperature of the plasma treatment is 25°C-100°C; and / or The plasma treatment time is 60s-300s.

10. A battery separator, characterized in that: The battery separator comprises the porous alumina according to any one of claims 1 to 3.

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