Composite coating diaphragm as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of new energy batteries, and particularly relates to a composite coating diaphragm and a preparation method and application thereof.The composite coating diaphragm comprises a base membrane and a microcapsule coating at least coating one face of the base membrane, and microcapsules in the microcapsule coating take aluminum-silicon alloy as an inner core and composite ceramic as a shell; the composite ceramic comprises a SiO2-Al2O3 bonding layer which is directly connected with an aluminum-silicon alloy inner core, and an Al2O3 outer layer which is directly connected with the SiO2-Al2O3 bonding layer, and the SiO2-Al2O3 bonding layer is provided with a three-dimensional interpenetrating structure of SiO2 and Al2O3 (silicon dioxide and aluminum oxide). The microcapsule coating not only can meet the requirement of improving the performance of the battery, but also has excellent mechanical performance, high temperature resistance and a certain flame retardant effect, so that the problem of internal short circuit caused by external force or high temperature is effectively prevented, and the safety and reliability of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and in particular relates to a composite coating diaphragm and a preparation method and application thereof. Background Art

[0002] In recent years, with the increasingly serious energy shortage problem caused by the gradual reduction of fossil energy reserves and the continuous increase in environmental protection needs, lithium-ion batteries have been widely used in many fields due to their significant advantages such as high energy density, high power density, long cycle life and low cost. As one of the four main materials of lithium-ion batteries, the separator plays a vital role in the battery. Its main functions include: isolating the positive and negative electrode materials to prevent short circuits caused by direct contact; supporting the internal structure of the battery to prevent deformation of the internal structure due to external mechanical forces; and allowing lithium ions and electrolytes to be freely transmitted between the positive and negative electrodes through its microporous structure, thereby realizing the battery's charge and discharge process. The common battery separators on the market are mainly based on polyethylene (PE) or polypropylene (PP) materials. Through further processing and coating of various functional coatings on its surface, they meet the strict performance and safety requirements of modern batteries.

[0003] With the market's increasingly diverse performance demands for lithium-ion batteries, including higher energy density, higher charge-discharge rates, and lower costs, these demands have become the primary direction of current lithium-ion battery technology development. To meet these performance requirements, the design of lithium-ion battery separators tends to reduce the thickness of the base film and heat-resistant layer to increase the effective space within the battery, thereby improving energy density, reducing manufacturing costs, and reducing internal resistance and heat generation during high-rate charge and discharge. However, this performance improvement also brings potential safety risks: insufficient base film thickness may lead to insufficient mechanical strength, making it more susceptible to deformation under external mechanical stress and easily penetrated by lithium dendrites during battery cycling, causing internal short circuits and thus affecting the battery's cycle life and safety. At the same time, insufficient heat-resistant layer thickness weakens the separator's thermal stability, making it more susceptible to shrinkage or melting in high-temperature environments, increasing the risk of battery short circuits and thermal runaway, thereby posing a threat to the battery's overall safety. Therefore, balancing the separator's mechanical strength and thermal stability with the battery's energy density, cost, and safety while pursuing high performance has become a key challenge in the development of lithium-ion battery separator technology.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to address the problem of poor comprehensive performance of battery separators in the existing technology, especially the deficiencies of traditional alumina or boehmite coated separators in mechanical properties, high temperature resistance and flame retardancy, which makes the battery prone to internal short circuits when subjected to external forces or high temperature environments, affecting the safety and service life of the battery.

[0006] To address the above technical issues, the present invention provides a composite-coated separator that utilizes a microcapsule coating instead of traditional alumina or boehmite coatings. This microcapsule coating not only meets the requirements for improved battery performance but also exhibits excellent mechanical properties, high-temperature resistance, and a certain degree of flame retardancy, effectively preventing internal short circuits caused by external forces or high temperatures, significantly improving battery safety and reliability. The present invention also provides methods for preparing and applying the composite-coated separator.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, a composite coating diaphragm comprises a base membrane and a microcapsule coating coated on at least one side of the base membrane, wherein the microcapsules in the microcapsule coating have an aluminum-silicon alloy as an inner core and a composite ceramic as a shell; the composite ceramic comprises a SiO2-Al2O3 bonding layer directly connected to the aluminum-silicon alloy inner core, and an Al2O3 outer layer directly connected to the SiO2-Al2O3 bonding layer; the SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of SiO2 and Al2O3.

[0009] Furthermore, the mass ratio of aluminum to silicon in the aluminum-silicon alloy is (70-98): (30-2);

[0010] and / or, the composite ceramic is connected to the core by in-situ generation;

[0011] And / or, the composite ceramic has porous SiO2 as a skeleton, which is connected to the core and loaded with Al2O3 to form a structure in which Al2O3 is filled and coated with SiO2;

[0012] and / or, the SiO2-Al2O3 bonding layer is connected to the aluminum-silicon alloy core in the form of Al-O-Si covalent bonds;

[0013] and / or, the SiO2-Al2O3 bonding layer is connected to the Al2O3 outer layer in the form of Al-O-Si covalent bonds;

[0014] And / or, the SiO2-Al2O3 in the SiO2-Al2O3 bonding layer is a composite material of SiO2 and Al2O3 bonded in the form of Al-O-Si covalent bonds;

[0015] And / or, the thickness of the microcapsule coating is 1 to 10 μm.

[0016] Furthermore, the preparation of the microcapsules includes: dissolving aluminum silicon alloy powder in water for surface activation and then adding it to a silica colloidal solution for mixing, then adding hydratable alumina powder, adjusting the pH to be greater than 8, stirring, filtering, drying, and calcining to obtain microcapsules.

[0017] Furthermore, the average particle size of the aluminum-silicon alloy powder is 100 nm to 1 μm;

[0018] And / or, the silicon dioxide content in the silicon dioxide colloidal solution accounts for 5 to 15% of the mass of the aluminum-silicon alloy powder;

[0019] And / or, the amount of the hydratable alumina powder added is 10 to 30% by mass of the aluminum-silicon alloy powder;

[0020] and / or, the average particle size of the hydratable alumina powder is 50 to 200 nm;

[0021] And / or, the specific surface area of ​​the hydratable alumina is 100-300m 2 / g.

[0022] Furthermore, the surface activation temperature is 80-100°C;

[0023] And / or, the surface activation time is 6 to 18 hours;

[0024] And / or, the pH is adjusted to 9-10;

[0025] and / or, the calcination temperature is 200-300° C.;

[0026] And / or, the calcination time is 4 to 6 hours.

[0027] Furthermore, the microcapsule coating includes a binder;

[0028] And / or, the base film is selected from one of polypropylene film, polyethylene film and polypropylene and polyethylene composite film

[0029] Furthermore, the binder is selected from polyvinylidene fluoride or polymethyl methacrylate;

[0030] And / or, the mass ratio of the microcapsules to the binder is (70-90):(30-10).

[0031] In a second aspect, a method for preparing the composite coating membrane according to the first aspect is provided, comprising roller coating a slurry containing the microcapsules on at least one surface of the base film to obtain the composite coating membrane.

[0032] In a third aspect, a battery separator is provided, which is the composite coating separator described in the first aspect, or the composite coating separator prepared by the preparation method described in the second aspect.

[0033] In a fourth aspect, a lithium-ion battery comprises the battery separator described in the third aspect.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] The composite coating diaphragm of the present invention is a microcapsule particle coating diaphragm that can be used to improve the performance of batteries. The microcapsules therein are a particle structure with an aluminum-silicon alloy as the core, porous silica as the outer shell skeleton, and a composite ceramic formed by filling and covering silica with a high specific surface area of ​​modified boehmite (aluminum oxide) as the shell. Specifically, the composite ceramic includes a SiO2-Al2O3 bonding layer as an intermediate layer directly connected to the aluminum-silicon alloy, and an Al2O3 outer layer as the outermost layer directly connected to the SiO2-Al2O3 bonding layer. The SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of silica and alumina. The special particle structure of the microcapsule has high-strength bonding stability, which can improve the mechanical properties, high temperature resistance, corrosion resistance of the diaphragm, and reduce internal resistance. Porous silica and high specific surface area alumina can improve high temperature performance while having good processing performance, making the microcapsule particles easier to coat, making the diaphragm structure more stable while having good liquid retention capacity.

[0036] The battery separator of the present invention is a composite coating separator containing a microcapsule particle coating. When used in a lithium-ion battery, it can improve the safety performance of the battery because it has excellent mechanical properties, high temperature resistance and a certain flame retardant effect, thereby effectively preventing internal short circuit problems caused by external force or high temperature; moreover, it is corrosion-resistant, has low internal resistance and strong liquid retention capacity, and can meet the requirements for improving battery performance to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the microcapsule structure in the microcapsule coating in the composite coating membrane of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0039] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0040] In a first aspect, the present invention provides a composite coating diaphragm comprising a base membrane and a microcapsule coating coated on at least one side of the base membrane, wherein the microcapsules in the microcapsule coating have an aluminum-silicon alloy as an inner core and a composite ceramic as a shell; the composite ceramic comprises a SiO2-Al2O3 bonding layer directly connected to the aluminum-silicon alloy inner core, and an Al2O3 outer layer directly connected to the SiO2-Al2O3 bonding layer; the SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of SiO2 and Al2O3.

[0041] The composite coating diaphragm of the present invention is formed by modifying boehmite (γ-AlO(OH)) into a part of the shell to form microcapsules coated on a base film. The microcapsules have a particle structure with an aluminum-silicon alloy as the core and a composite ceramic as the shell. Figure 1 Specifically, the composite ceramic includes a SiO2-Al2O3 bonding layer as the middle layer, directly connected to the aluminum-silicon alloy, and an Al2O3 outer layer as the outermost layer, directly connected to the SiO2-Al2O3 bonding layer. The SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of silicon dioxide and aluminum oxide. The unique particle structure of the microcapsules provides high-strength bonding stability, which can improve the mechanical properties and high-temperature resistance of the diaphragm and reduce internal resistance.

[0042] Among them, the aluminum-silicon alloy serving as the core is relatively light in weight, has good heat resistance, good wear resistance, a relatively low thermal expansion coefficient, and good corrosion resistance, making it suitable for the internal use environment of lithium battery DQ (battery cells); in addition, since the interior is an alloy rather than traditional alumina or ceramics, the resistivity of the alloy is smaller, and the resistivity of the diaphragm is also smaller. Under the same working conditions, a diaphragm with low resistance can have a better discharge rate and reduce heat generation.

[0043] In the composite ceramics serving as the shell, the three-dimensional interpenetrating silica and alumina have a porous structure and a high specific surface area, which can improve high-temperature performance while having good processing properties, making the microcapsule particles easier to coat, making the diaphragm structure more stable while having good liquid retention capabilities.

[0044] Therefore, the diaphragm containing this microcapsule coating can improve the safety performance of the battery when used as a lithium-ion battery diaphragm, because it has excellent mechanical properties, high temperature resistance and a certain flame retardant effect, thereby effectively preventing internal short circuit problems caused by external force or high temperature; and it is corrosion-resistant, has low internal resistance and strong liquid retention capacity, which can meet the requirements of improving battery performance to a certain extent.

[0045] As an optional embodiment of the composite coating diaphragm of the present invention, the mass ratio of aluminum to silicon in the aluminum-silicon alloy is (70-98): (30-2);

[0046] And / or, the thickness of the microcapsule coating is 1 to 10 μm (such as 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 9.5 μm, etc.).

[0047] In the above technical solution, the mass ratio of aluminum (Al) and silicon (Si) in the aluminum-silicon alloy (Al-Si) is controlled to (70-98): (30-2), typically but not limitatively, it can be controlled to 70:30, 73:27, 75:25, 77:23, 80:20, 82:18, 85:15, 87:13, 90:10, 92:8, 94:6, 96:4, 98:2, etc., to avoid excessive silicon increasing the surface resistance of the overall microcapsule, affecting the ion conduction rate of the diaphragm, and reducing the dynamic performance of the diaphragm. At the same time, the expansion of silicon is larger than that of aluminum. Excessive expansion of silicon during the electrical cycle will affect the stability of the microcapsule structure. Under this condition, a thicker coating layer is required to ensure the stability of the microcapsule structure. However, too thick a coating layer will increase the surface resistance of the diaphragm and reduce the dynamic performance of the diaphragm. At the same time, it will cause the thickness of the diaphragm to increase, thereby occupying the battery cell space, and also increase the cost of using the diaphragm. Too little silicon can easily lead to weak bonding strength of the microcapsules. The Al and Si contents in the aluminum-silicon alloy respectively determine the number of amphoteric Al-OH (aluminum hydroxyl) and Si-OH (silicon hydroxyl) groups produced on its surface. Compared with Al-OH, Si-OH has stronger bonding strength with SiO2. Because the surface energy of Si-OH is close to that of SiO2 colloid, it has better wettability and is easy to spread evenly. At the same time, Si-OH and SiO2 match at the atomic level on the bonding interface, and the defect density is low. Therefore, in order to ensure bonding strength, it is not advisable to have too little silicon.

[0048] As an optional embodiment of the composite coating diaphragm of the present invention, the composite ceramic is connected to the core by in-situ generation;

[0049] And / or, the composite ceramic has porous SiO2 as a skeleton, which is connected to the core and loaded with Al2O3 to form a structure in which Al2O3 is filled and coated with SiO2;

[0050] and / or, the SiO2-Al2O3 bonding layer is connected to the aluminum-silicon alloy core in the form of Al-O-Si covalent bonds;

[0051] and / or, the SiO2-Al2O3 bonding layer is connected to the Al2O3 outer layer in the form of Al-O-Si covalent bonds;

[0052] And / or, the SiO2-Al2O3 in the SiO2-Al2O3 bonding layer is a composite material of SiO2 and Al2O3 bonded in the form of Al-O-Si covalent bonds.

[0053] In the above technical solution, the composite ceramic can be connected to the core by in-situ generation to strengthen the bonding strength between the shell and the core; porous silica can also be used as the shell skeleton, and while connecting to the core, alumina with a high specific surface area can be filled into its porous structure to form a three-dimensional interpenetrating structure of SiO2 and Al2O3, forming a SiO2-Al2O3 bonding layer, and on the other hand, it can be covered on the outside of the skeleton to form a coating on the skeleton, forming an Al2O3 outer layer, and the porous silica can be used as a bridge to strengthen the connection between the alumina and the core. When the core and the composite ceramic are connected, the formation of covalent bonds can be controlled to strengthen the bonding strength, for example, the SiO2-Al2O3 bonding layer can be controlled to connect to the aluminum-silicon alloy core and / or the Al2O3 outer layer in the form of Al-O-Si covalent bonds, and / or the SiO2-Al2O3 in the SiO2-Al2O3 bonding layer can be controlled to bond SiO2 and Al2O3 in the form of Al-O-Si covalent bonds.

[0054] As an optional embodiment of the composite coating diaphragm of the present invention, the preparation of the microcapsules includes: dissolving aluminum silicon alloy powder in water for surface activation and then adding silica colloidal solution to mix, then adding hydratable alumina powder, adjusting the pH to >8, stirring, filtering, drying, and calcining to obtain microcapsules.

[0055] In the above technical solution, when preparing microcapsules, first, the aluminum-silicon alloy powder Al-Si is dispersed in water for surface activation, so that the aluminum active sites and silicon active sites exposed on the surface can respectively adsorb OH in the water to produce amphoteric Al-OH and Si-OH. This process expands the specific surface area of ​​the Al-Si core and provides more loading sites.

[0056] Then, silica colloidal solution is added and mixed and dispersed, so that the charged SiO2 micelles are initially combined with the amphoteric Al-OH and Si-OH on the Al-Si surface through limited hydrogen bonding.

[0057] After that, hydrated alumina (ρ-Al2O3) was added and pH was adjusted to 8 to promote the increase of ρ-Al2O3 hydration product γ-AlO(OH) and its surface positive charge, and the hydration product [Al(H2O)6] 3+ The increase of Si-O - On the one hand, SiO2 micelles can bridge with γ-AlO(OH) through electrostatic interaction, and on the other hand, they can form a stable hydrogen bond network with Al-OH and Si-OH on the Al-Si surface, thereby allowing the in-situ generated ρ-Al2O3 hydration product to combine with Al-Si.

[0058] Finally, after calcination, Al-OH, Si-OH and hydrogen bonds connected to Al-Si and SiO2 or connected to SiO2 and ρ-Al2O3 hydration products are in situ dehydrated to form covalent bonds Al-O-Si, and γ-AlO(OH) interspersed in the porous SiO2 skeleton and enriched on the other side of the porous SiO2 skeleton are in situ dehydrated to form γ-Al2O3, forming a double-layer continuous composite ceramic shell. The composite ceramic shell includes an intermediate layer that is connected to the aluminum-silicon alloy. The core consists of a SiO2-Al2O3 bonding layer directly connected to the SiO2-Al2O3 bonding layer via covalent Al-O-Si bonds, and an Al2O3 outer layer, the outermost layer, directly connected to the SiO2-Al2O3 bonding layer via covalent Al-O-Si bonds. A small amount of γ-Al2O3 interspersed and filled in the porous SiO2 skeleton and a large portion of γ-Al2O3 concentrated in the outer layer provide thermal stability and corrosion resistance. The porous SiO2 skeleton provides thermal stability and porous ion channels, and the Al-O-Si bonds stabilize the interface. The resulting microcapsule particle structure has an aluminum-silicon alloy core and a γ-Al2O3-SiO2 composite ceramic shell, consisting of a SiO2-Al2O3 bonding layer and an Al2O3 outer layer, three-dimensionally interpenetrating SiO2 and Al2O3. Due to the in-situ generation of Al-O-Si and γ-Al2O3, the core-shell bond is strong and the structure is strong and stable. It should be further explained that dehydration between the core and the shell generates Al-O-Si bonds, and SiO2 and γ-Al2O3 in the shell also generate Al-O-Si bonds. At the same time, the chemical bonds in these places are not only Al-O-Si bonds, but this bond plays a major role because the Al-O-Si bond has a larger bond energy and can provide high-strength bonding and stability. At the same time, the directionality of this chemical bond is relatively strong and has fewer defects. The other bonding bonds are Al 3+ There are ionic bonds formed with Si-O, Al-O-Al aluminum-oxygen bonds formed by the unreacted Al atoms on the surface of the Al-Si core and the Al2O3 in the shell, as well as residual hydrogen bonds.

[0059] It is worth noting that the hydrated alumina is compounded with the modified aluminum-silicon alloy powder through the silica colloidal solution as a bridge and forms a firmly bonded microcapsule particle structure after calcination. This is because the silica in the silica colloidal solution exists in the form of micelle particles (micelles / particles), the interior of the particles is a siloxane (Si-O-Si) network structure, and the surface is Si-OH generated by the hydrolysis of silica. Under alkaline conditions, Si-OH continues to dissociate to generate Si-O - , at this time the particle is negatively charged; the surface of ρ-Al2O3 hydrated to generate γ-AlO(OH) is rich in Al-OH, and OH is continuously consumed during the hydration process. - It will change Al-OH from amphoteric to positively charged Al-OH 2+ At this time, the particle is positively charged, and in the process of generating γ-AlO(OH), positively charged [Al(H2O)6] 3+ Therefore, after adjusting the pH to 8, SiO2 micelles can act as bridges, using the increased Si-O - , so that the ρ-Al2O3 hydration products such as [Al(H2O)6] 3+ and Al-OH on the surface 2+ The γ-AlO(OH) is electrostatically adsorbed and bridged with SiO2, while forming a stable hydrogen bond network with Al-OH and Si-OH on the Al-Si surface, or with Al-OH on the γ-AlO(OH) surface at the same time. The hydrogen bond network exists stably before calcination, maintaining the temporary structure of the coating layer. After calcination and solidification, the hydrogen bonds begin to dehydrate and transform into covalent bonds, and the γ-AlO(OH) also continues to react to form alumina. After calcination, the hydrogen bonds are completely converted into Al-O-Si, and the γ-AlO(OH) dehydrates to form γ-Al2O3, forming a continuous, complete and firmly bonded composite ceramic as a microcapsule particle structure with an aluminum-silicon alloy core coated.

[0060] The present invention uses hydrated alumina (ρ-Al2O3) as raw material, which is a transitional alumina with low crystallinity and in a metastable state. It contains a large number of closed pores and through pores, so the specific surface area is relatively high, about 100-300m 2 / g. The special crystal structure and high specific surface area of ​​hydrated alumina make it more chemically active than other types of alumina, and it can quickly undergo hydration reaction after contact with water. When hydrating alumina undergoes hydration reaction, the OH groups on the surface of hydrated alumina particles in the adsorbed water - After hydroxylation, some particles will dissolve in water and dissociate into free Al 3+ , Al in aqueous solution 3+ and OH -The combined reaction forms pseudo-boehmite AlO(OH)·xH2O, which precipitates on the surface of the non-hydrating particles (i.e., aluminum-silicon alloy particles) to form a gel. Subsequently, a portion of the pseudo-boehmite gel crystallizes to form boehmite.

[0061] As an optional embodiment of the composite coating diaphragm of the present invention, the average particle size of the aluminum-silicon alloy powder is 100 nm to 1 μm;

[0062] And / or, the silicon dioxide content in the silicon dioxide colloidal solution accounts for 5-15% (e.g., 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, etc.) of the mass of the aluminum-silicon alloy powder;

[0063] And / or, the addition amount of the hydratable alumina powder accounts for 10-30% (such as 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 29.5%, etc.) of the mass of the aluminum-silicon alloy powder;

[0064] and / or, the average particle size of the hydratable alumina powder is 50 to 200 nm;

[0065] And / or, the specific surface area of ​​the hydratable alumina is 100-300m 2 / g.

[0066] As an optional embodiment of the composite coating membrane of the present invention, the surface activation temperature is 80-100° C. (such as 82° C., 85° C., 87° C., 90° C., 92° C., 95° C., 97° C., etc.);

[0067] And / or, the surface activation time is 6 to 18 hours (such as 7 hours, 9 hours, 11 hours, 13 hours, 15 hours, 17 hours, etc.);

[0068] And / or, the pH is adjusted to 9-10 (e.g., 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, etc.); pH adjustment is not recommended to exceed 10, and a relatively mild environment is selected to stabilize the reaction rate and facilitate coating uniformity;

[0069] And / or, the calcination temperature is 200-300°C (such as 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, etc.), and the calcination is mainly to complete the formation of covalent bonds (Al-O-Si) and alumina, such as the conversion of hydrogen bonds to covalent bonds (Al-O-Si) and the conversion of γ-AlO(OH) to γ-Al2O3. Low temperature will lead to incomplete conversion and weak interface bonding. Excessively high temperature will cause the sintering and densification of silica, reduce the porosity of the overall structure, and affect the ion conduction efficiency and infiltration effect;

[0070] And / or, the calcination time is 4 to 6 hours (such as 4.5 hours, 5 hours, 5.5 hours, etc.).

[0071] As an optional embodiment of the composite coating membrane of the present invention, the microcapsule coating includes a binder; further, the binder is selected from polyvinylidene fluoride or polymethyl methacrylate; further, the mass ratio of the microcapsules to the binder is (70-90): (30-10), typically but not limited to 70:30, 73:27, 75:25, 77:23, 80:20, 82:18, 85:15, 87:13, 90:10, etc.;

[0072] And / or, the base film is selected from one of a polypropylene film, a polyethylene film and a composite film of polypropylene and polyethylene. Further, the base film includes but is not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PP, double-layer PP / PE and triple-layer PP / PE / PP and the like.

[0073] In a second aspect, the present invention provides a method for preparing the composite coating membrane, comprising roller-coating a slurry containing the microcapsules onto at least one surface of the base film to obtain the composite coating membrane.

[0074] As an optional embodiment of the preparation method of the present invention, the preparation method further comprises: mixing the microcapsules with a binder and then roller coating the mixture on the surface of the base film to obtain a composite coating membrane.

[0075] As an optional embodiment of the preparation method of the present invention, the preparation method comprises:

[0076] First, aluminum-silicon alloy powder is placed in water at 80-100° C. and magnetically stirred for 6-18 hours, and then the solution is filtered and dried to obtain surface-activated aluminum-silicon alloy powder.

[0077] Secondly, adding the surface-activated aluminum-silicon alloy powder to a silica colloidal solution, wherein the silica content in the silica colloidal solution accounts for 5-15% of the mass of the aluminum-silicon alloy powder, and magnetically stirring for a certain time, such as 30 minutes, adding hydratable aluminum oxide (ρ-Al2O3) accounting for 10-30% of the mass of the aluminum-silicon alloy powder, controlling the pH between 9 and 10 and continuously stirring for a certain time, such as 4 to 6 hours, and then filtering the mixture, washing it with deionized water, and drying it in an oven at 130°C for a certain time, such as 6 hours, to obtain a dried mixed powder;

[0078] The dried mixed powder is then calcined at 200-300°C for 4-6 hours to obtain a microcapsule having an aluminum-silicon alloy core and a composite ceramic shell. The composite ceramic comprises a SiO2-Al2O3 bonding layer directly connected to the aluminum-silicon alloy core and an Al2O3 outer layer directly connected to the SiO2-Al2O3 bonding layer. The SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of SiO2 and Al2O3.

[0079] Finally, the microcapsules were made into a slurry of PVDF+microcapsules (the mass ratio of microcapsules to PVDF was 90:10, and the solid content of the roller-coated slurry was controlled at about 30%), which was then roller-coated on the base film to form a microcapsule coating with a thickness of 1 to 10 μm to obtain a composite coating diaphragm.

[0080] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0081] Example 1

[0082] 100g of aluminum-silicon alloy powder (Al-12Si: aluminum-silicon mass ratio of 88:12, average particle size 500nm) was magnetically stirred in 500mL of water at 95°C for 12 hours at a stirring speed of 1200r / min. After stirring, the mixture was filtered and dried to obtain surface-activated aluminum-silicon alloy powder. The surface-activated aluminum-silicon alloy powder was added to a colloidal silica solution (10g of solute silica) and magnetically stirred for 30 minutes, controlling the solid content of the mixed solution to 20%. 20g of hydrated alumina (ρ-Al2O3, average particle size 100nm) was then added, the pH was adjusted to 10, and stirring was continued for 4 hours. The mixture was filtered, washed with deionized water, and dried at 130°C for 6 hours. The dried mixed powder is calcined at 300°C for 6 hours to obtain microcapsules. The microcapsules have an aluminum-silicon alloy core and a composite ceramic shell. The composite ceramic includes a SiO2-Al2O3 bonding layer directly connected to the aluminum-silicon alloy core and an Al2O3 outer layer directly connected to the SiO2-Al2O3 bonding layer. The SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of SiO2 and Al2O3.

[0083] Then, PVDF and microcapsules were prepared into a slurry at a mass ratio of 1:9 and a solid content of 30%, and the slurry was roller-coated onto a maximum surface of the single-layer PE base film with a roller coating thickness of 3 microns to form a microcapsule coating to make a composite coating diaphragm.

[0084] Example 2

[0085] Take 100g of aluminum-silicon alloy powder (Al-30Si: aluminum-silicon mass ratio of 70:30, average particle size 100nm) and magnetically stir it in 500mL of water at 95°C for 6 hours at a stirring speed of 1200r / min. After stirring, filter and dry to obtain surface-activated aluminum-silicon alloy powder. Add the surface-activated aluminum-silicon alloy powder to a colloidal silica solution (5g of solute silica) and magnetically stir for 30 minutes. Control the solid content of the mixed solution to 20%. Add 10g of hydratable alumina (ρ-Al2O3, average particle size 50nm), adjust the pH to 10, and continue stirring for 4 hours. Filter, rinse with deionized water, and dry at 130°C for 6 hours. The dried mixed powder is calcined at 300°C for 6 hours to obtain microcapsules. The microcapsules have an aluminum-silicon alloy core and a composite ceramic shell. The composite ceramic includes a SiO2-Al2O3 bonding layer directly connected to the aluminum-silicon alloy core and an Al2O3 outer layer directly connected to the SiO2-Al2O3 bonding layer. The SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of SiO2 and Al2O3.

[0086] Then, PVDF and microcapsules were prepared into a slurry at a mass ratio of 1:9 and a solid content of 30%, and the slurry was roller-coated onto a maximum surface of the single-layer PE base film with a roller coating thickness of 3 microns to form a microcapsule coating to make a composite coating diaphragm.

[0087] Example 3

[0088] 100g of aluminum-silicon alloy powder (Al-2Si: aluminum-silicon mass ratio of 98:2, average particle size 1μm) was magnetically stirred in 500mL of water at 80°C for 18 hours at a stirring speed of 1200r / min. After stirring, the mixture was filtered and dried to obtain surface-activated aluminum-silicon alloy powder. The surface-activated aluminum-silicon alloy powder was added to a colloidal silica solution (15g of solute silica) and magnetically stirred for 30 minutes. The solid content of the mixed solution was controlled to 20%. 30g of hydratable alumina (ρ-Al2O3, average particle size 200nm) was added, the pH was adjusted to 9, and stirring was continued for 6 hours. The mixture was filtered, washed with deionized water, and dried at 130°C for 6 hours. The dried mixed powder is calcined at 200°C for 4 hours to obtain microcapsules. The microcapsules have an aluminum-silicon alloy core and a composite ceramic shell. The composite ceramic includes a SiO2-Al2O3 bonding layer directly connected to the aluminum-silicon alloy core and an Al2O3 outer layer directly connected to the SiO2-Al2O3 bonding layer. The SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of SiO2 and Al2O3.

[0089] Then, PVDF and microcapsules were prepared into a slurry at a mass ratio of 1:9 and a solid content of 30%, and the slurry was roller-coated onto a maximum surface of the single-layer PE base film with a roller coating thickness of 3 microns to form a microcapsule coating to make a composite coating diaphragm.

[0090] Comparative Example 1

[0091] 100g of aluminum-silicon alloy powder (Al-12Si:Al-Si mass ratio of 88:12, average particle size 500nm) was magnetically stirred in 500mL of water at 95°C for 12 hours at a stirring speed of 1200r / min. After stirring, the powder was filtered and dried to obtain the pretreated aluminum-silicon alloy powder. The pretreated aluminum-silicon alloy powder was added to a colloidal silica solution (10g of solute silica) and magnetically stirred for 30 minutes, controlling the solid content of the mixed solution to 20%. 20g of hydratable alumina (ρ-Al2O3, average particle size 100nm) was added, the pH was adjusted to 8, and stirring was continued for 2 hours. The mixture was filtered, washed with deionized water, and dried at 130°C for 6 hours. The dried mixed powder was calcined at 300°C for 6 hours to obtain a microcapsule material with a heterogeneous structural composition. Then, PVDF and microcapsule material are prepared into a slurry according to a mass ratio of 1:9 and a solid content of 30%, and the microcapsule material with uneven structural composition is roller-coated onto a largest surface of a single-layer PE base film with a roller coating thickness of 3 microns to form a composite coating diaphragm.

[0092] The preparation method of the comparative example diaphragm is basically the same as that of Example 1, except that the pH is adjusted to 8 after adding ρ-Al2O3 and the stirring time is 2 h.

[0093] Comparative Example 2

[0094] 100g of aluminum-silicon alloy powder (Al-12Si:Al-Si mass ratio of 88:12, average particle size 500nm) was magnetically stirred in 500mL of water at 95°C for 12 hours at a stirring speed of 1200r / min. After stirring, the powder was filtered and dried to obtain surface-activated aluminum-silicon alloy powder. The surface-activated aluminum-silicon alloy powder was mixed with 10g of silica powder, and deionized water was added to control the solid content of the mixed solution to 20%. The mixture was magnetically stirred for 30 minutes. 20g of hydratable alumina (ρ-Al2O3, average particle size 100nm) was then added, the pH was adjusted to 10, and stirring was continued for 4 hours. The mixture was filtered, washed with deionized water, and dried at 130°C for 6 hours. The dried mixed powder was calcined at 300°C for 6 hours to obtain a mixture in which the aluminum-silicon alloy and silica were each coated with the ρ-Al2O3 product. Then, PVDF and the mixture were prepared into a slurry at a mass ratio of 1:9 and a solid content of 30%, and the slurry was roller-coated onto a maximum surface of the single-layer PE base film with a roller coating thickness of 3 microns to prepare a composite coating diaphragm.

[0095] The preparation method of the diaphragm of this comparative example is basically the same as that of Example 1, except that silicon dioxide particles are used instead of silicon dioxide colloidal solution.

[0096] Comparative Example 3

[0097] 100g of aluminum-silicon alloy powder (Al-12Si:Al-Si mass ratio of 88:12, average particle size of 500nm) was magnetically stirred in 500mL of water at 95°C for 12 hours at a stirring speed of 1200r / min. After stirring, the powder was filtered and dried to obtain surface-activated aluminum-silicon alloy powder. The surface-activated aluminum-silicon alloy powder was added to 500mL of deionized water and stirred continuously for 30 minutes. Then, 20g of hydrated alumina (ρ-Al2O3, average particle size of 100nm) was added, the pH was adjusted to 10, and stirring was continued for 4 hours. The mixture was filtered, washed with deionized water, and dried at 130°C for 6 hours. The dried mixed powder was calcined at 300°C for 6 hours to obtain highly porous microcapsules. A slurry of PVDF and the highly porous microcapsules was then prepared at a mass ratio of 1:9 and a solids content of 30%. The slurry was then roll-coated onto one of the largest surfaces of a single-layer PE base film to a thickness of 3 microns to form a composite coating separator.

[0098] The preparation method of the diaphragm of this comparative example is basically the same as that of Example 1, except that no silica colloidal solution is used.

[0099] Comparative Example 4

[0100] The only difference from Example 1 is that conventional boehmite (γ-AlO(OH)) is used as a coating material instead of microcapsules, and a composite coating separator is prepared in the same manner.

[0101] Experimental example

[0102] The electrochemical properties of the composite coating membranes prepared in various embodiments and comparative examples were tested.

[0103] The test method is as follows:

[0104] (1) Mechanical Properties Test: The membranes prepared in the Examples and Comparative Examples were used as samples for testing. Each group of samples was cut into strips with a width of 15 mm and a length of 150 mm. The initial distance between the clamps of the electronic tensile testing machine was set to 100 mm. The test strips were placed in the upper and lower ends of the clamps along the length direction, and the clamps were clamped. During the test, the strips and the clamps were kept in the same vertical direction, and there was no obvious tensile deformation. After the preparation was completed, the tensile test was carried out at a rate of 200 mm / min. Each group of samples was tested three times and the average value was obtained.

[0105] (2) Surface resistance: After punching the diaphragm into sheets, it is immersed in lithium-ion battery electrolyte (calculated by mass percentage, LiPF6 (lithium hexafluorophosphate): 15%, ethylene carbonate (EC): 33%, dimethyl carbonate (DMC): 30%, ethyl methyl carbonate (EMC): 20%, vinylene carbonate (VC): 1%, vinyl sulfate (DTD): 0.7%, LiODFB: 0.3%) for 2 hours in a sealed environment. The soaked diaphragm is clamped between two electrode plates and placed in the electrolyte. The electrode plates are connected to the electrochemical workstation. The tested resistance value is plotted on the diaphragm layer number-resistance value coordinate system, and the diaphragm test is stacked layer by layer. The slope of the resistance discrete point can then be calculated based on the experimental results. Diaphragm surface resistance = slope × test clamping area.

[0106] (3) Puncture: Use a puncture test machine and set the needle speed to 50 mm / min. Place the diaphragm to be tested flat in the middle of the fixture and tighten it with the screws. Adjust the distance between the needle and the diaphragm to 5 mm and the position of the limit block to 20 mm from the moving paddle. Then start the device for puncture. After the diaphragm is punctured, the test is completed and the corresponding data is recorded.

[0107] (4) Thermal shrinkage: Take a sample of the diaphragm to be tested, draw a corresponding rectangle on the surface of the diaphragm with a 40*60 standard part, use a two-dimensional testing instrument to measure the length and width of the corresponding rectangle and record the corresponding values ​​as the data before shrinkage. Afterwards, place an A4 paper on the glass plate, place the sample on the A4 paper, cover the sample with another A4 paper, and then place a glass plate on the A4 paper (glass plate + A4 paper + sample + A4 paper + glass plate). Then place the glass plate to be tested in an oven and set the oven temperature to 130°C for 1 hour. After heating, cool the sample to be tested to room temperature and use a two-dimensional testing instrument to measure the length and width of the rectangle as the data after shrinkage to calculate the thermal shrinkage rate (shrinkage rate = (before shrinkage - after shrinkage) / before shrinkage * 100%).

[0108] (5) Air permeability: Use an air permeability tester, the experimental test standard is GB / T36383-2018, set the penetration time to 10s, and the penetration area to 6.45cm 2 The upper chamber pressure was 1.21 kPa, and then the diaphragm was flatly covered on the designated test platform to begin testing and obtain experimental data. This test measures the diaphragm's air permeability, which is primarily related to the porosity of the diaphragm and coating. The test result is the time it takes for gas to pass through a unit volume, so the lower the test result, the better the air permeability.

[0109] The results of the above tests are shown in Table 1:

[0110] Table 1 Comparison of the diaphragms obtained in each embodiment and comparative example

[0111]

[0112] Description: Compared with the composite membrane prepared using the method of the present invention in Comparative Example 4, which is a composite membrane prepared using conventional boehmite, the composite membranes of Examples 1, 2, and 3 show significant improvements in mechanical properties (tensile strength, puncture strength) and heat shrinkage resistance. Furthermore, because the core material of the microcapsule structure is an alloy rather than a metal oxide, its surface resistance is significantly reduced, which is more conducive to high-rate charge and discharge of the battery cell and improves the life of long-term cycles. Furthermore, the air permeability test results show that the separator of the present invention has a high porosity, better electrolyte infiltration, can store more electrolyte, and provide more lithium ion transmission paths.

[0113] Comparative Example 1, based on Example 1, reduced the pH and stirring time after adding hydratable alumina. Compared with Example 1, the overall performance of Comparative Example 1 differed significantly, and compared with the conventional boehmite separator in Comparative Example 4, the performance was similar, not significantly improving performance. This result is because in the microcapsules of the present invention, the formation of Al-O-Si bonds is key to connecting the aluminum-silicon alloy core and the silica (SiO2) / alumina (Al2O3) shell. At pH = 8, ρ-Al2O3 hydrates incompletely and with low efficiency, primarily forming amorphous Al(OH)3 rather than γ-AlO(OH). Without amorphous Al(OH)3, it cannot effectively connect to SiO2 and has a weak interface with the Al-Si surface, resulting in an uneven shell structure. Furthermore, in this case, the overall reaction rate is low, and the ρ-Al2O3 is insufficient for complete hydration. Residual unreacted ρ-Al2O3 results in uneven shell composition. Therefore, Comparative Example 1 is a product of an incomplete reaction and only partially contributes to the performance effects of the microcapsules of the present invention.

[0114] Comparative Examples 2 and 3 are based on Example 1, respectively replacing silica colloid with silica particles and directly adding hydrated alumina after discarding the silica colloid solution. From the experimental results, Comparative Examples 2 and 3 both exhibit mechanical properties and heat resistance far lower than those of Example 1, and also lower than the conventional boehmite composite membrane of Comparative Example 4. This is because Comparative Examples 2 and 3 lose the key adsorption effect of silica gel as a bridge, and are unable to form the Al-O-Si bond in the microcapsules of the present invention. Therefore, these two comparative examples can only rely on the gel precipitated on the particle surface after the hydration of ρ-Al2O3 to form a loose boehmite shell layer. The microcapsules finally formed have weak interface bonding and the shell structure is easy to peel off. The performance of Comparative Example 2 is further reduced compared with Comparative Example 3. This is because the silica particles are easy to agglomerate and have basically no adsorption properties. It is difficult to adsorb on the surface of the aluminum-silicon alloy particles and combine with the aluminum-silicon alloy through stirring. Instead, it will affect the precipitation gel of ρ-Al2O3 on the surface of the aluminum-silicon alloy, resulting in a further decrease in the thickness of the microcapsule shell. At the same time, the final sintered product is a mixture of aluminum-silicon alloy particles coated with alumina and silica particles coated with alumina. The new impurities introduced further affect the performance of the composite diaphragm.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite coating diaphragm, characterized in that: It includes a base film and a microcapsule coating coated on at least one side of the base film, wherein the microcapsules in the microcapsule coating have an aluminum-silicon alloy as an inner core and a composite ceramic as a shell; the composite ceramic includes a SiO2-Al2O3 bonding layer directly connected to the aluminum-silicon alloy inner core, and an Al2O3 outer layer directly connected to the SiO2-Al2O3 bonding layer; the SiO2-Al2O3 bonding layer has a three-dimensional interpenetrating structure of SiO2 and Al2O3.

2. The composite coating diaphragm according to claim 1, characterized in that: The mass ratio of aluminum to silicon in the aluminum-silicon alloy is (70-98): (30-2); and / or, the composite ceramic is connected to the core by in-situ generation; And / or, the composite ceramic has porous SiO2 as a skeleton, which is connected to the core and loaded with Al2O3 to form a structure in which Al2O3 is filled and coated with SiO2; and / or, the SiO2-Al2O3 bonding layer is connected to the aluminum-silicon alloy core in the form of Al-O-Si covalent bonds; and / or, the SiO2-Al2O3 bonding layer is connected to the Al2O3 outer layer in the form of Al-O-Si covalent bonds; And / or, the SiO2-Al2O3 in the SiO2-Al2O3 bonding layer is a composite material of SiO2 and Al2O3 bonded in the form of Al-O-Si covalent bonds; And / or, the thickness of the microcapsule coating is 1 to 10 μm.

3. The composite coating diaphragm according to claim 1, characterized in that: The preparation of the microcapsules includes: dissolving aluminum silicon alloy powder in water for surface activation and then adding it to silica colloidal solution for mixing; then adding hydratable aluminum oxide powder; adjusting the pH to be greater than 8; stirring; filtering; drying; and calcining to obtain microcapsules.

4. The composite coating diaphragm according to claim 3, characterized in that: The average particle size of the aluminum-silicon alloy powder is 100nm to 1μm; And / or, the silicon dioxide content in the silicon dioxide colloidal solution accounts for 5 to 15% of the mass of the aluminum-silicon alloy powder; And / or, the amount of the hydratable alumina powder added is 10 to 30% by mass of the aluminum-silicon alloy powder; and / or, the average particle size of the hydratable alumina powder is 50 to 200 nm; And / or, the specific surface area of ​​the hydratable alumina is 100-300m 2 / g.

5. The composite coating diaphragm according to claim 3, characterized in that: The surface activation temperature is 80-100°C; And / or, the surface activation time is 6 to 18 hours; And / or, the pH is adjusted to 9-10; and / or, the calcination temperature is 200-300° C.; And / or, the calcination time is 4 to 6 hours.

6. The composite coating diaphragm according to claim 1, characterized in that: The microcapsule coating includes a binder; And / or, the base film is selected from one of a polypropylene film, a polyethylene film and a composite film of polypropylene and polyethylene.

7. The composite coating diaphragm according to claim 6, characterized in that: The binder is selected from polyvinylidene fluoride or polymethyl methacrylate; And / or, the mass ratio of the microcapsules to the binder is (70-90):(30-10).

8. A method for preparing the composite coating membrane according to any one of claims 1 to 7, characterized in that: The slurry containing the microcapsules is roll-coated on at least one surface of the base film to obtain the composite coating separator.

9. A battery separator, characterized in that: The battery separator is the composite coating separator according to any one of claims 1 to 7, or the composite coating separator prepared by the preparation method according to claim 8.

10. A lithium-ion battery, characterized in that: The battery separator according to claim 9 is included.

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