Composite separator and preparation method therefor, and battery

Abstract

The present application provides a composite separator and a preparation method therefor, and a battery. The composite separator comprises a base film, a first film layer, and a second film layer. The first film layer comprises an electrolyte material capable of achieving efficient lithium-ion transportability, but side reactions may occur between the electrolyte material and an electrode. The second film layer comprises a ceramic oxide material, and a particle size of the ceramic oxide material is defined to be less than that of the electrolyte material, thereby facilitating uniform distribution of the ceramic oxide material on the surface of the first film layer. Thus, the microstructure of a surface layer of the composite separator is optimized.

Description

Composite separator and its preparation method and battery

[0001] This application claims priority to Chinese Patent Application No. 202510147035.6, filed on February 10, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to, but is not limited to, the technical field of batteries, specifically to a composite separator, its preparation method, and a battery. Background Technology

[0003] Lithium-ion batteries are characterized by high energy density, long cycle life, and low self-discharge rate, and are widely used in mobile electronic devices, electric vehicles, and other fields. In recent years, with the increasing demand for high-specific-capacity lithium-ion batteries, they have become a research hotspot in this field. However, these batteries suffer from the problem of uneven lithium-ion deposition on the negative electrode surface, leading to lithium dendrite formation.

[0004] In related technologies, inorganic materials are used to coat and modify the diaphragm, which can improve the mechanical properties and thermal stability of the diaphragm. Invention Overview

[0005] However, inorganic materials are generally insulators, and coatings formed by applying inorganic materials may affect the transport of lithium ions.

[0006] The embodiments of this application provide a composite separator, a method for preparing the same, and a battery, which can improve the technical problems affecting lithium-ion transport caused by the use of inorganic materials.

[0007] In a first aspect, embodiments of this application provide a composite separator, the composite separator comprising:

[0008] Base film;

[0009] A first film layer is disposed on at least one side of the base film;

[0010] The second film layer is disposed on the side of the first film layer that is opposite to the base film;

[0011] The first membrane layer includes an electrolyte material;

[0012] The second film layer comprises a ceramic oxide material, wherein the average particle size of the ceramic oxide material is smaller than the average particle size of the electrolyte material.

[0013] Secondly, embodiments of this application provide a method for preparing a composite diaphragm, the method comprising the following steps;

[0014] Provide base film;

[0015] The first film layer is obtained by coating the base film with the first solution and drying it.

[0016] The second film layer is obtained by coating the first film layer with a second solution on the side opposite to the base film and then drying it.

[0017] The first solution includes an electrolyte material;

[0018] The second solution comprises a ceramic oxide material.

[0019] Thirdly, embodiments of this application provide a battery including the composite separator as described above or a composite separator prepared by the aforementioned method. Beneficial effects

[0020] In the embodiments of this application, by setting a first film layer on the surface of the base film, the first film layer including an electrolyte material can achieve efficient lithium-ion transport. However, the electrolyte material and the electrode may undergo side reactions. A second film layer is set on the side of the first film layer away from the base film. The second film layer is made of ceramic oxide material, and the particle size of the ceramic oxide material is limited to be smaller than that of the electrolyte material. This helps to ensure the uniform distribution of the ceramic oxide material on the surface of the first film layer, thereby optimizing the microstructure of the surface layer of the composite separator. This makes the lithium-ion transport path between the second film layer and the electrode more uniform, thereby improving the problem of lithium-ion transport caused by the use of ceramic oxide material. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 is a schematic diagram of the structure of the composite diaphragm provided in an embodiment of this application;

[0023] Figure 2 is a flowchart of the method for preparing the composite diaphragm provided in the embodiments of this application;

[0024] Figure 3(a) is a SEM planar schematic diagram of the first membrane layer of the composite diaphragm provided in the embodiment of this application;

[0025] Figure 3(b) is a schematic SEM image of the second membrane layer of the composite diaphragm provided in the embodiment of this application.

[0026] Figure label:

[0027] 100. Composite membrane; 110. Base membrane; 120. First membrane layer; 130. Second membrane layer. Embodiments of the present invention

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in actual use or operation, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0029] Lithium-ion batteries are characterized by high energy density, long cycle life, and low self-discharge rate, and are widely used in mobile electronic devices, electric vehicles, and other fields. With increasing energy demand and technological advancements, the demand for high-capacity lithium-ion batteries is constantly rising. However, the electrolyte-anode interface of these batteries is unstable, and lithium ions tend to deposit unevenly on the anode surface, leading to the formation of lithium dendrites. These dendrites may penetrate the separator, causing a short circuit, which can result in battery overheating or even fire.

[0030] Currently, common solutions include modifying the liquid electrolyte or using a solid electrolyte, but these methods are costly and reduce battery material compatibility. In contrast, modified separators are less expensive and can directly improve battery internal safety, compatibility, and versatility.

[0031] Ordinary polyolefin separators on the market are prone to safety issues due to the penetration of lithium dendrites and dead lithium formed at the negative electrode.

[0032] In related technologies, coating the membrane surface with inorganic materials can regulate the distribution of lithium ions and improve the mechanical properties and thermal stability of the membrane. However, inorganic materials are usually insulators, and the coating formed by inorganic materials may affect the transport of lithium ions.

[0033] In view of this, this application provides a composite separator, a method for preparing the same, and a battery.

[0034] According to a first aspect of the embodiments of this application, referring to FIG1, a composite separator 100 is provided, wherein the composite separator 100 may include:

[0035] Base film 110;

[0036] The first membrane layer 120 is disposed on at least one side of the base membrane 110;

[0037] The second film layer 130 is disposed on the side of the first film layer 120 that is away from the base film 110;

[0038] The first membrane layer 120 may include an electrolyte material;

[0039] The second membrane layer 130 may include a ceramic oxide material, the average particle size of which is smaller than the average particle size of the electrolyte material.

[0040] This application provides a composite separator comprising a base membrane, a first membrane layer disposed on the surface of the base membrane, and a second membrane layer disposed on the side of the first membrane layer facing away from the base membrane. The first membrane layer comprises an electrolyte material, which, in addition to possessing the characteristics of inorganic materials, can regulate the distribution of lithium ions through efficient lithium-ion transport, thereby suppressing the growth of lithium dendrites. Furthermore, since the electrolyte material is in long-term contact with the electrode, side reactions are prone to occur. By providing the second membrane layer, direct contact between the first membrane layer and the electrode can be effectively prevented. The second membrane layer comprises a ceramic oxide material, and the particle size of the ceramic oxide material is smaller than that of the electrolyte material, which helps to ensure the uniform distribution of the ceramic oxide material on the surface of the first membrane layer. This optimizes the microstructure of the surface layer of the composite separator, making the lithium-ion transport path at the interface between the second membrane layer and the electrode more uniform, thereby improving the problem of lithium-ion transport caused by the use of ceramic oxide materials.

[0041] It should be noted that the projected area of ​​the first film layer is less than or equal to the projected area of ​​the second film layer. The second film layer can completely cover the first film layer, which helps to prevent the first film layer from directly contacting the opposite electrode and thus avoiding a short circuit. If the projected area of ​​the first film layer is greater than the projected area of ​​the second film layer, the first film layer will exceed the coverage area of ​​the second film layer, which may lead to the first film layer directly contacting the opposite electrode and causing a short circuit.

[0042] In some possible implementations, the base film material may be one or more of polypropylene, polyethylene, polyethylene terephthalate, and polyimide.

[0043] In some possible implementations, the electrolyte material may include at least one of lithium titanium aluminum phosphate, lithium germanium aluminum phosphate, and lithium lanthanum zirconium oxide.

[0044] It is understandable that the molecular formula of lithium titanium aluminum phosphate is Li. 1.3 Al 0.3 Ti 1.7 (PO4)3, abbreviated as LATP, has high ionic conductivity and good chemical stability, and can be used in batteries to help improve battery safety and energy density.

[0045] The molecular formula of lithium aluminum germanium phosphate is Li. 1.5 Al 0.5Ge 1.5 (PO4)3, abbreviated as LAGP, has high lithium-ion conductivity and good thermal stability. In addition, LAGP also has excellent high temperature resistance, making it suitable for applications requiring high temperatures.

[0046] The molecular formula of lithium lanthanum zirconium oxide is Li7La3Zr2O 12 Lithium-ion electrolyte, or LLZO for short, has high lithium-ion conductivity and good chemical stability. Its ionic conductivity is close to that of liquid electrolyte materials, making it suitable for applications with high requirements for ionic conductivity.

[0047] Therefore, in addition to possessing the characteristics of inorganic materials, which can improve the mechanical properties and thermal stability of the membrane, any of the above-mentioned electrolyte materials also have high ionic conductivity, which helps to achieve efficient lithium-ion transport.

[0048] In some possible implementations, the ceramic oxide material may include at least one of nano-silica, nano-titanium dioxide, and lithium metasilicate.

[0049] It is understandable that nano-silica, nano-titanium dioxide, and lithium metasilicate possess the inherent characteristics of inorganic materials, such as high mechanical strength and good thermal stability. At the same time, nano-silica, nano-titanium dioxide, and lithium metasilicate all have small particle sizes and large specific surface areas, which makes the ceramic oxide materials have better adsorption performance and higher reactivity. This helps to achieve uniform distribution on the surface of the first film layer, thereby achieving the goal of optimizing the surface microstructure of the electrolyte material in the first film layer.

[0050] In some possible implementations, referring to FIG3(a), the average particle size of the electrolyte material can be from 0.55 μm to 2 μm. Further, the average particle size of the electrolyte material can be from 0.6 μm to 1.5 μm. Exemplarily, the average particle size of the electrolyte material can be 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.05 μm, 1.1 μm, 1.15 μm, 1.2 μm, 1.25 μm, 1.3 μm, 1.35 μm, 1.4 μm, 1.45 μm, 1.5 μm, and any value between two adjacent values. The average particle size can be observed and measured using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to examine the morphology of the powder in the examples.

[0051] In some possible implementations, referring to FIG3(b), the average particle size of the ceramic oxide material can be from 10 nm to 500 nm. Further, the average particle size of the ceramic oxide material can be from 30 nm to 120 nm. Exemplarily, the average particle size of the ceramic oxide material can be 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, and any value between two adjacent values ​​mentioned above.

[0052] It should be noted that, since the particle size limit for ceramic oxide materials is smaller than that limit for electrolyte materials, the greater the difference in average particle size between the electrolyte materials and ceramic oxide materials, the more favorable it is for the ceramic oxide materials to be evenly distributed when coated on the first film layer containing the electrolyte materials, thereby achieving the goal of optimizing the microstructure of the electrolyte material surface.

[0053] It should be noted that nano-silica, due to its high specific surface area and reactivity, can improve the affinity of the separator for the electrolyte, allowing the electrolyte to spread more evenly and quickly onto the surface of the separator. Moreover, nano-silica also has a porous structure, which allows the electrolyte to penetrate and remain in the separator more easily, thereby reducing the interfacial resistance between the electrolyte and the separator and improving battery performance and safety.

[0054] In some possible implementations, the porosity of the ceramic oxide material can be from 70% to 99%. Further, the porosity of the ceramic oxide material can be from 80% to 98%. Exemplarily, the porosity of the ceramic oxide material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and any value between two adjacent values.

[0055] It should be noted that the porosity of ceramic oxide materials refers to the proportion of pores in the ceramic oxide material, and the porosity can be calculated using the following formula;

[0056] Porosity = (1 - ρ / ρ0) × 100%;

[0057] Where ρ is the apparent density of the ceramic oxide material;

[0058] ρ0 is the theoretical density of the ceramic oxide material, which is the density assuming the material has no pores.

[0059] In some possible implementations, the porosity of nano-silica can be 90% to 98%, which gives nano-silica a large specific surface area, thereby exhibiting stronger reactivity and adsorption capacity. At the same time, the high porosity of nano-silica helps to further improve the wettability of the electrolyte on the membrane surface, thereby significantly reducing the interfacial resistance between the electrolyte and the membrane.

[0060] In some possible implementations, the porosity of the electrolyte material can be from 20% to 35%. Further, the porosity of the electrolyte material can be from 25% to 30%. Exemplarily, the porosity of the electrolyte material can be 25%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30%, and any value between two adjacent values.

[0061] It should be noted that the porosity of an electrolyte material refers to the proportion of pores in the electrolyte material, and the porosity can be calculated using the following formula;

[0062] Porosity = (1 - ρ / ρ0) × 100%;

[0063] Where ρ is the apparent density of the electrolyte material;

[0064] ρ0 is the theoretical density of the electrolyte material, which is the density assuming the material has no pores.

[0065] It is understandable that porosity and specific surface area are positively correlated. The greater the porosity of a material, the larger its specific surface area, which is more conducive to improving reactivity; conversely, the smaller the porosity of a material, the smaller its specific surface area, which is detrimental to its reactivity.

[0066] In some possible implementations, the thickness of the first film layer can be from 2 μm to 3 μm. Further, the thickness of the first film layer can be from 2.2 μm to 2.8 μm. Exemplarily, the thickness of the first film layer can be 2.2 μm, 2.25 μm, 2.3 μm, 2.35 μm, 2.4 μm, 2.45 μm, 2.5 μm, 2.55 μm, 2.6 μm, 2.65 μm, 2.7 μm, 2.75 μm, 2.8 μm, and any value between two adjacent values ​​mentioned above.

[0067] It is understandable that the thickness of the first membrane layer is related to efficient ion transport. As the thickness of the first membrane layer increases, the content of electrolyte material in the first membrane layer increases, which is beneficial to improving the ion transport of the first membrane layer. However, as the thickness of the first membrane layer continues to increase, it may lead to an increase in the internal resistance of the battery, thereby reducing the electrochemical performance of the battery.

[0068] In some possible implementations, the thickness of the second film layer can be from 1 μm to 2 μm. Further, the thickness of the second film layer can be from 1.2 μm to 1.8 μm. Exemplarily, the thickness of the second film layer can be 1.2 μm, 1.25 μm, 1.3 μm, 1.35 μm, 1.4 μm, 1.45 μm, 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, 1.75 μm, 1.8 μm, or any value between two adjacent values ​​mentioned above.

[0069] It is understandable that a larger thickness of the second film layer is beneficial for protecting the first film layer and preventing side reactions when the first film layer is in long-term contact with the electrode. Also, since the particle size of the ceramic oxide material in the second film layer is smaller than that of the electrolyte material, the second film layer is beneficial for optimizing the microstructure of the electrolyte material in the first film layer. However, if the thickness of the second film layer is further increased, it will increase the internal resistance of the battery, leading to increased energy loss during charging and discharging and reducing the performance of the battery. Therefore, the thickness of the second film layer should not be too large.

[0070] In some possible implementations, the first film layer may further include an adhesive material. Further, the adhesive material may include one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polyethylene oxide, polyphenylene ether, or polydimethylsiloxane.

[0071] It is understandable that using any of the above-mentioned bonding materials helps to increase the network structure during the molding of the first film layer, helps to enhance the structural stability of the first film layer, and also helps to give the first film layer good flexibility and bending resistance.

[0072] In some possible implementations, the electrolyte material may comprise 90% to 98% by mass in the first membrane layer, and / or the binder material may comprise 1% to 5% by mass. As can be seen, the electrolyte material has a high mass percentage in the first membrane layer, thereby ensuring that the first membrane layer has efficient ion transport.

[0073] According to a second aspect of this application, referring to FIG2, a method for preparing a composite diaphragm is provided, the method comprising the following steps;

[0074] S100, provides base film;

[0075] S200: A first solution is coated onto a base film and dried to obtain a first film layer; wherein, the first solution may include an electrolyte material;

[0076] S300, The second film layer is obtained by coating the first film layer with a second solution on the side opposite to the base film and drying it; wherein, the second solution may include a ceramic oxide material.

[0077] This application provides a method for preparing a composite separator. A first solution is coated onto a base membrane and dried to obtain a first membrane layer. A second solution is then coated onto the side of the first membrane layer facing away from the base membrane and dried to obtain a second membrane layer. The first solution includes an electrolyte material, which helps ensure the first membrane layer has efficient ion transport. The second solution includes a ceramic oxide material. The second membrane layer formed by the second solution effectively protects the first membrane layer, preventing side reactions that may occur during long-term contact between the first membrane layer and the electrode. Furthermore, since the average particle size of the ceramic oxide material is smaller than that of the electrolyte material, it helps to ensure uniform distribution of the ceramic oxide material on the surface of the first membrane layer. This optimizes the microstructure of the electrolyte material in the first membrane layer, resulting in uniformity of the lithium-ion transport path at the interface between the second membrane layer and the electrode, thereby improving the problem of lithium-ion transport issues caused by the use of ceramic oxide materials.

[0078] In some possible implementations, the first solution can be prepared by the following method:

[0079] The electrolyte material and the binder material are mixed and stirred to obtain the first solution.

[0080] It is understandable that the electrolyte material is mixed with the binder material so that the electrolyte material is uniformly coated by the binder material, and a uniform first solution is obtained by stirring. The first film layer obtained by coating and drying the first solution has high efficiency in lithium ion transport.

[0081] In some possible implementations, the electrolyte material can be prepared using the following methods:

[0082] Lithium salt, aluminum salt, titanium salt and phosphate salt are added to the first solvent, stirred and mixed, and dried to obtain the electrolyte precursor;

[0083] The electrolyte precursor is calcined and cooled to obtain the electrolyte material.

[0084] By adopting the above scheme, lithium salt, aluminum salt, titanium salt and phosphate salt are first made into electrolyte precursors, and then the electrolyte precursors are calcined to obtain lithium titanium aluminum phosphate electrolyte material with high lithium ion transport efficiency.

[0085] In some possible implementations, the first solvent includes propanol. Propanol has good solubility and environmental friendliness, which helps to fully dissolve lithium salts, aluminum salts, titanium salts, and phosphate salts to prepare homogeneous and stable solutions.

[0086] In some possible implementations, calcination may include preheating at 350°C to 450°C for 20 to 40 minutes, followed by calcination at 800°C to 1000°C for 1.5 to 2.5 hours.

[0087] Understandably, the calcination process involves preheating at a lower temperature to help remove and volatilize small molecule components from the electrolyte precursor, followed by calcination at a higher temperature to help form a porous structure. This significantly increases the specific surface area of ​​the electrolyte material, providing more active sites for electrochemical reactions. The porous structure also helps improve lithium-ion transport, thereby enhancing the electrochemical performance of the battery.

[0088] In some possible implementations, the ceramic oxide material can be prepared using the following methods:

[0089] Tetraethyl orthosilicate is dissolved in a second solvent to obtain a first mixture;

[0090] Deionized water was dissolved in a second solvent and mixed. The pH was adjusted to 10 to 11 using ammonia water to obtain a second mixture.

[0091] The first mixture and the second mixture are mixed and stirred until a sol is formed, and then aged to obtain a ceramic oxide material.

[0092] By adopting the above scheme, the prepared ceramic oxide material can form a uniform porous structure, providing more active sites and ion transport channels; it also helps to optimize the crystal structure, improve the thermal expansion coefficient of the ceramic oxide material, and effectively improve the high-temperature stability of the composite membrane.

[0093] According to a third aspect of this application, a battery is provided, comprising the composite separator of the first aspect described above.

[0094] This application provides a battery including the aforementioned composite separator. The composite separator further includes a first film layer and a second film layer. The first film layer enables highly efficient lithium-ion transport, while the second film layer protects the first film layer, preventing side reactions from occurring due to prolonged contact between the first film layer and the electrode. Simultaneously, the second film layer optimizes the microstructure of the electrolyte material in the first film layer, resulting in uniformity of the lithium-ion transport path at the interface between the second film layer and the electrode. Therefore, the battery containing the aforementioned composite separator exhibits excellent battery performance.

[0095] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0096] Example 1

[0097] A battery includes a negative electrode, a composite separator, a positive electrode, and the composite separator stacked sequentially. The composite separator is prepared by the following method:

[0098] Preparation of LATP electrolyte materials:

[0099] Li2CO3, Al2O3, TiO2 and NH4H2PO4 weighed in a molar ratio of 0.65:0.15:1.7:1 were added to a ball mill jar, ball milled for 3 hours with propanol as solvent, and dried to remove the solvent to obtain the electrolyte precursor.

[0100] The electrolyte precursor was placed in a muffle furnace, preheated at 400℃ for 30 min, then heated to 900℃ for 2 h, and then cooled at room temperature and ground to obtain LATP electrolyte material; wherein the average particle size of LATP electrolyte material is 550 nm to 650 nm.

[0101] Preparation of ceramic oxide materials:

[0102] Tetraethyl orthosilicate (TEOS) and ethanol were mixed at a volume ratio of 1:10 to obtain the first mixture;

[0103] Deionized water and ethanol were mixed at a volume ratio of 2:1, and the pH value was adjusted to 10 using ammonia water to obtain a second mixture.

[0104] The first mixture and the second mixture were mixed and stirred until a sol was formed. The mixture was aged for 4 days under dark conditions to obtain a ceramic oxide material. The particle size of the nano-silica in the ceramic oxide material was 35nm to 45nm.

[0105] Preparation of composite membrane:

[0106] A first solution was coated on both sides of a PP base film to a thickness of 2 μm. The film was then placed in an oven and dried at 110°C for 1 hour to obtain the first film layer. The first solution was prepared by mixing LATP electrolyte material and binder material, with LATP electrolyte material comprising 95% by mass and binder material comprising 5% by mass.

[0107] A second solution is coated on the side of the first membrane layer away from the base membrane. The second solution uses the aforementioned ceramic oxide material, and the coating thickness is 1.5 μm. After drying, the second membrane layer is obtained, thus obtaining the composite membrane.

[0108] The positive electrode sheet is prepared using the following method:

[0109] LATP material (Li 1.3 Al 0.3 Ti 1.7 (PO4)3), carbon nanotubes (CNT), polyvinylidene fluoride (PVDF), and polyvinylpyrrolidone (PVP) were mixed in a mass ratio of 97.9:0.4:1.5:0.2 to prepare a slurry. After mixing, the slurry was uniformly coated onto an aluminum foil current collector, dried, and cold-pressed into a positive electrode sheet with a thickness of 200 μm.

[0110] The negative electrode sheet is prepared using the following method:

[0111] A slurry was prepared by mixing graphite, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and binder (SBR) in a mass ratio of 96.9:0.4:1.4:1.3. The slurry was then uniformly coated onto a copper foil current collector, dried, cold-pressed, and the negative electrode sheet was cut to a thickness of 150 μm.

[0112] Example 2

[0113] A battery differs from Example 1 in that the average particle size of the nano-silica in the electrolyte material and the ceramic oxide material is different. In this example, the average particle size of the electrolyte material is 750 nm to 850 nm, and the average particle size of the nano-silica is 35 nm to 45 nm.

[0114] Example 3

[0115] A battery differs from Example 1 in that the average particle size of the nano-silica in the electrolyte material and the ceramic oxide material is different. In this example, the average particle size of the electrolyte material is 850 nm to 950 nm, and the average particle size of the nano-silica is 25 nm to 35 nm.

[0116] Example 4

[0117] A battery differs from Example 1 in that the average particle size of the nano-silica in the electrolyte material and the ceramic oxide material is different. In this example, the average particle size of the electrolyte material is 850 nm to 950 nm, and the average particle size of the nano-silica is 85 nm to 95 nm.

[0118] Example 5

[0119] A battery differs from Example 1 in that the average particle size of the nano-silica in the electrolyte material and the ceramic oxide material is different. In this example, the average particle size of the electrolyte material is 1550 nm to 1650 nm, and the average particle size of the nano-silica is 35 nm to 45 nm.

[0120] Example 6

[0121] A battery differs from Example 1 in that the average particle size of the nano-silica in the electrolyte material and the ceramic oxide material is different. In this example, the average particle size of the electrolyte material is 950 nm to 1050 nm, and the average particle size of the nano-silica is 195 nm to 205 nm.

[0122] Example 7

[0123] A battery differs from Example 1 in that the average particle size of the nano-silica in the electrolyte material and the ceramic oxide material is different. In this example, the average particle size of the electrolyte material is 950 nm to 1050 nm, and the average particle size of the nano-silica is 145 nm to 155 nm.

[0124] Example 8

[0125] A battery differs from Example 1 in that the thicknesses of the first and second films are different. In this example, the thickness of the first film is 2 μm, and the thickness of the second film is 1 μm.

[0126] Example 9

[0127] A battery differs from Example 1 in that the thicknesses of the first and second films are different. In this example, the thickness of the first film is 2 μm, and the thickness of the second film is 2 μm.

[0128] Example 10

[0129] A battery differs from Example 1 in that the thicknesses of the first and second films are different. In this example, the thickness of the first film is 3 μm, and the thickness of the second film is 2 μm.

[0130] Example 11

[0131] A battery differs from Example 1 in that the thicknesses of the first and second films are different. In this example, the thickness of the first film is 3 μm, and the thickness of the second film is 1 μm.

[0132] Example 12

[0133] A battery differs from Example 1 in that the thicknesses of the first and second films are different. In this example, the thickness of the first film is 1.5 μm, and the thickness of the second film is 2.5 μm.

[0134] Example 13

[0135] A battery differs from Example 1 in that the thicknesses of the first and second films are different. In this example, the thickness of the first film is 1.5 μm, and the thickness of the second film is 3 μm.

[0136] Comparative Example 1

[0137] A battery that differs from Example 1 in that it does not contain a second film layer.

[0138] The battery in this comparative example was prepared using the following method:

[0139] Preparation of LATP electrolyte materials:

[0140] Li2CO3, Al2O3, TiO2 and NH4H2PO4 weighed in a molar ratio of 0.65:0.15:1.7:1 were added to a ball mill jar, ball milled for 3 hours with propanol as solvent, and dried to remove the solvent to obtain the electrolyte precursor.

[0141] The electrolyte precursor was placed in a muffle furnace, preheated at 400℃ for 30 min, then heated to 900℃ for 2 h, and then cooled at room temperature and ground to obtain LATP electrolyte material; wherein the average particle size of LATP electrolyte material is 550 nm to 650 nm.

[0142] Preparation of composite membrane:

[0143] A first solution is coated on both sides of a PP base membrane with a coating thickness of 2 μm. The membrane is then placed in an oven and dried at 110°C for 1 hour to obtain the first membrane layer. The first solution is prepared by mixing LATP electrolyte material and binder material. The mass percentage of LATP electrolyte material is 95%, and the mass percentage of binder material is 5%, thus obtaining the composite membrane.

[0144] Comparative Example 2

[0145] A battery that differs from Example 1 in that it does not contain a first film layer.

[0146] The battery in this comparative example was prepared using the following method:

[0147] Preparation of ceramic oxide materials:

[0148] Tetraethyl orthosilicate (TEOS) and ethanol were mixed at a volume ratio of 1:10 to obtain the first mixture;

[0149] Deionized water and ethanol were mixed at a volume ratio of 2:1, and the pH value was adjusted to 10-11 using ammonia water to obtain a second mixture.

[0150] The first mixture and the second mixture were mixed and stirred until a sol was formed. The mixture was aged for 4 days under dark conditions to obtain a ceramic oxide material. The particle size of the nano-silica in the ceramic oxide material was 35nm to 45nm.

[0151] Preparation of composite membrane:

[0152] A second solution is coated on both sides of the PP base membrane. The second solution uses the above-mentioned ceramic oxide material and the coating thickness is 1.5 μm. After drying, the second membrane layer is obtained, thus obtaining the composite separator.

[0153] Comparative Example 3

[0154] A battery differs from Example 1 in that the electrolyte material and the ceramic oxide material have the same particle size. In this comparative example, the particle size of the electrolyte material and the ceramic oxide material is 450 nm to 550 nm.

[0155] Detection method:

[0156] 1. Capacity retention and 50% SOC 10s DCR are based on the following test steps:

[0157] Step 1: Charge at 0.33C constant current and constant voltage to 3.65V (cutoff current 0.05C), let stand for 5 minutes, discharge at 0.33C constant current to 2.5V, let stand for 5 minutes. Repeat this step 13 times, and record the discharge capacity of the 13th cycle as Q0.

[0158] Step 2: Charge at 0.5C constant current and constant voltage to 3.65V (cutoff current 0.05C), let stand for 5 minutes, discharge at 0.5C constant current to 2.5V, let stand for 5 minutes. Repeat this step 3 times, and record the discharge capacity in the 3rd week as Q1.

[0159] Step 3: Charge 0.5Q1 with constant current and constant voltage to 3.65V (cutoff voltage 0.05Q1), let stand for 5 minutes; discharge 0.2Q1 with constant current to 2.5V (cutoff capacity 50%Q1), let stand for 1 hour; discharge Q1 with constant current for 10 seconds (cutoff voltage 2.5V), let stand for 5 minutes; discharge Q1 with constant current to 2.5V, let stand for 5 minutes.

[0160] Step 4: Charge according to the 4C rate (0~100% SOC, cutoff voltage 3.65V), let it rest for 5 minutes, discharge Q1 at a constant current to 2.5V (100~0% SOC), repeat this step 50 times, then return to step 2 and continue the cycle.

[0161] The capacity retention rate is calculated using the following formula: Capacity retention rate = (Qn / Qmax) × 100%;

[0162] Where Qn is the discharge capacity at the nth cycle, and Qmax is the maximum discharge capacity;

[0163] The formula for calculating DCR at 50% SOC 10s is as follows: DCR = (VD10 - VD0) / I;

[0164] Where VD0 is the end voltage after 1 hour of rest, VD10 is the end voltage after Q1 discharges for 10 seconds, and I is the current corresponding to 1C.

[0165] 2. Average particle size: The morphology of the powder in the examples was observed and the particle size was measured using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

[0166] 3. Porosity: refers to the proportion of pores in a material;

[0167] Porosity can be calculated using the following formula: Porosity = (1 - ρ / ρ0) × 100%;

[0168] Where ρ is the apparent density of the material;

[0169] ρ0 is the theoretical density of the material, which is the density assuming the material has no pores. Let ρ0 be 1.05 cm³. 3 / g.

[0170] The detection results of the examples and comparative examples are shown in Table 1.

[0171] Table 1

[0172] Sample Cycle Number (N) Capacity Retention Rate (%) 50% SOC 10s DCR (Ω) Example 1 1500 92.4 0.0295 Example 2 1500 92.8 0.0297 Example 3 1501 93.2 0.0308 Example 4 1498 91.9 0.0301 Example 5 1500 91.6 0.0291 Example 6 1501 91.4 0.0293 Example 7 1500 91.2 0.0305 Example 8 1499 Example 91.80.0296 Example 91500 Example 10 Example 11 Example 12 Example 13 Example 14 Example 14 Example 15 Example 14 Example 15 Example 16 Example 17 Example 18 Example 19 Example 19 Example 19 Example 19 Example 19 Example 19 Example 10 Example 19 Example 19 Example 19 Example 19 Example 10 Example 19 Example 11 Example 19 Example 12 Example 19 Example 13 Example 19 Example 14 Example 15 Example 19 Example 14 Example 15 Example 16 Example 17 Example 18 Example 19 ...

[0173] Based on the test results of Example 1, Comparative Examples 1-2, and Table 1, Example 1 includes a base film, a first film layer, and a second film layer. The first film layer includes LATP electrolyte material, ensuring the composite membrane has high-efficiency lithium-ion transport. The second film layer includes ceramic oxide material, protecting the LATP electrolyte material and optimizing its microstructure, thus ensuring uniformity of the lithium-ion transport path at the interface between the second film layer and the electrode. Therefore, the first and second film layers can produce a synergistic effect. Comparative Example 1 includes a base film and a first film layer, but lacks a second film layer. Therefore, the LATP electrolyte material in the first film layer may undergo side reactions when in long-term contact with the electrode, significantly affecting the battery's capacity retention and DCR value. Comparative Example 2 includes a base film and a second film layer, but lacks a first film layer. The absence of LATP electrolyte material affects lithium-ion transport, thereby impacting the battery's capacity retention and DCR value.

[0174] As can be seen from Examples 1 to 7, the particle sizes of nano-silica in the electrolyte material and ceramic oxide material in Examples 2-7 are different from those in Example 1. In Example 1, the particle size of the electrolyte material is 550 nm to 650 nm, and the particle size of the ceramic oxide material is 35 nm to 45 nm. At this time, the ratio of the particle size of the electrolyte material to the particle size of the ceramic oxide material is approximately 15. Similarly, in Examples 2-7, the ratios of the particle size of the electrolyte material to the particle size of the ceramic oxide material are 20, 30, 10, 40, 5, and 7, respectively. Table 1 shows that after 1500 cycles, the capacity retention rate of the batteries in Examples 1-3 remained above 92%, while the capacity retention rate of the samples in Examples 4-7 was only slightly over 91%. This suggests that when the average particle size ratio of the electrolyte material to the ceramic oxide material is between 15 and 30, the prepared battery can maintain a high capacity retention rate for a longer period. However, when the average particle size ratio is below 10 or below 40, the capacity retention rate decreases after 1500 cycles. This may be because a particle size ratio of 15 to 30 provides better interfacial contact and ion transport network, which is beneficial for lithium ion migration, thus maintaining a high capacity retention rate. A larger or smaller particle size ratio may increase the internal resistance of the battery, affecting its capacity retention rate.

[0175] Compared with Example 1, Examples 8-13 all changed the thickness of the first and second films. In Examples 1 and 8-11, the thickness of the first film was 2 μm to 3 μm, and the thickness of the second film was 1 μm to 2 μm. As shown in Table 1, in Examples 12 and 13, the thickness of the first film was 1.5 μm, and the thickness of the second film was 2.5 μm and 3 μm, respectively. The ratio of the thickness of the first film to the second film was 0.5 to 0.6. In this case, the first film formed by the LATP electrolyte material is too thin, which may restrict the lithium-ion transport path and affect the battery's capacity retention rate and DCR value.

[0176] Table 1 further reveals that, compared to Example 1, the thickness ratio of the first film layer to the second film layer in Examples 8-10 is 1 to 2, and both Examples 1 and 8-10 can achieve high capacity retention. However, in Example 11, the thickness ratio of the first film layer to the second film layer is 3, indicating a large difference in thickness between the two layers. As shown in Table 1, the capacity retention of Example 11 is slightly lower. This may be due to a side reaction between the LATP electrolyte material and the electrode, resulting in lithium dendrite growth on the electrode surface, which affects the capacity retention and DCR value of the sample.

[0177] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A composite diaphragm, comprising: Base film; A first film layer is disposed on at least one side of the base film; and The second film layer is disposed on the side of the first film layer that is opposite to the base film; The first membrane layer includes an electrolyte material; The second film layer comprises a ceramic oxide material, wherein the average particle size of the ceramic oxide material is smaller than the average particle size of the electrolyte material.

2. The composite diaphragm according to claim 1, wherein, The average particle size of the electrolyte material is 0.55 μm to 2 μm; preferably, the average particle size of the electrolyte material is 0.6 μm to 1.5 μm.

3. The composite diaphragm according to claim 1 or 2, wherein, The ceramic oxide material has an average particle size of 10 nm to 500 nm; preferably, the ceramic oxide material has an average particle size of 30 nm to 120 nm.

4. The composite diaphragm according to claim 1, wherein, The thickness of the first film layer is 2 μm to 3 μm; and / or The thickness of the second film layer is 1 μm to 2 μm.

5. The composite diaphragm according to claim 1, wherein, The porosity of the electrolyte material is 20% to 35%.

6. The composite diaphragm according to claim 1 or 5, wherein, The porosity of the ceramic oxide material is 90% to 98%.

7. The composite diaphragm according to claim 1, wherein, The electrolyte material includes at least one of lithium titanium aluminum phosphate, lithium germanium aluminum phosphate, and lithium lanthanum zirconium oxide; and / or The ceramic oxide material includes at least one of nano-silica, nano-titanium dioxide, and lithium metasilicate.

8. The composite diaphragm according to claim 1, wherein, The first membrane layer further includes an adhesive material, preferably one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polyethylene oxide, polyphenylene ether, or polydimethylsiloxane.

9. A method for preparing a composite diaphragm, The composite diaphragm comprises: Base film; A first film layer is disposed on at least one side of the base film; and The second film layer is disposed on the side of the first film layer that is opposite to the base film; The first membrane layer includes an electrolyte material; The second film layer comprises a ceramic oxide material, wherein the average particle size of the ceramic oxide material is smaller than the average particle size of the electrolyte material; The preparation method includes the following steps; Provide base film; The first film layer is obtained by coating the base film with the first solution and drying it. The second film layer is obtained by coating the first film layer with a second solution on the side opposite to the base film and then drying it. The first solution includes an electrolyte material; The second solution comprises a ceramic oxide material.

10. The method for preparing the composite diaphragm according to claim 9, wherein, The first solution was prepared by the following method: The electrolyte material and the binder material are mixed and stirred to obtain the first solution.

11. The method for preparing the composite diaphragm according to claim 9, wherein, The electrolyte material is prepared using the following method: Lithium salt, aluminum salt, titanium salt and phosphate salt are added to the first solvent, stirred and mixed, and dried to obtain the electrolyte precursor; The electrolyte precursor is calcined and cooled to obtain the electrolyte material; Preferably, the first solvent includes propanol; preferably, the calcination includes preheating at 350°C to 450°C for 20 to 40 minutes, and then calcining at 800°C to 1000°C for 1.5 to 2.5 hours.

12. The method for preparing the composite diaphragm according to claim 9, wherein, The ceramic oxide material is prepared using the following method: Tetraethyl orthosilicate is dissolved in a second solvent to obtain a first mixture; Deionized water was dissolved in a second solvent and mixed. The pH was adjusted to 10 to 11 using ammonia water to obtain a second mixture. The first mixture and the second mixture are mixed and stirred until a sol is formed, and then aged to obtain a ceramic oxide material.

13. The method for preparing the composite diaphragm according to claim 9, wherein, The average particle size of the electrolyte material is 0.55 μm to 2 μm; preferably, the average particle size of the electrolyte material is 0.6 μm to 1.5 μm.

14. The method for preparing the composite diaphragm according to claim 9 or 13, wherein, The ceramic oxide material has an average particle size of 10 nm to 500 nm; preferably, the ceramic oxide material has an average particle size of 30 nm to 120 nm.

15. The method for preparing the composite diaphragm according to claim 9, wherein, The thickness of the first film layer is 2 μm to 3 μm; and / or The thickness of the second film layer is 1 μm to 2 μm.

16. The method for preparing the composite diaphragm according to claim 9, wherein, The porosity of the electrolyte material is 20% to 35%.

17. The method for preparing the composite diaphragm according to claim 9 or 16, wherein, The porosity of the ceramic oxide material is 90% to 98%.

18. The method for preparing the composite diaphragm according to claim 9, wherein, The electrolyte material includes at least one of lithium titanium aluminum phosphate, lithium germanium aluminum phosphate, and lithium lanthanum zirconium oxide; and / or The ceramic oxide material includes at least one of nano-silica, nano-titanium dioxide, and lithium metasilicate.

19. The method for preparing the composite diaphragm according to claim 9, wherein, The first membrane layer further includes an adhesive material, preferably one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polyethylene oxide, polyphenylene ether, or polydimethylsiloxane.

20. A battery comprising the composite separator according to any one of claims 1 to 8.

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