Composite separator, manufacturing method thereof, and battery

Abstract

The present invention provides a composite separator comprising a base membrane, a first nanofiber layer, and a ceramic powder, the first nanofiber layer being located on a first side of the base membrane, and the ceramic powder forming a first ceramic coating located between the first nanofiber layer and the base membrane, or the ceramic powder being added to the first nanofiber layer. The present invention also provides a method for manufacturing the composite separator, and a battery.

Description

[Technical Field]

[0001] The present invention relates to the technical field of battery separators, and more particularly to a composite separator, a method for manufacturing the composite separator, and a battery. [Background technology]

[0002] Lithium-ion batteries, one of the core technologies in the development of new energy technologies, boast high capacity, high operating voltage, high energy density, long cycle life, excellent safety, and no memory effect. They are widely used in electronics, electric vehicles, space technology, defense, and other industries. As electronic products become more sophisticated, the demand for higher energy density and capacity in batteries is also increasing. To accommodate more electrode material in a smaller volume, separators must provide more space for the electrode material. However, this requires separators to be lighter and thinner, which places greater demands on separator safety.

[0003] Lithium-ion batteries primarily consist of a positive electrode, a negative electrode, a separator, and an electrolyte. As one of the key components, the separator plays a crucial role in battery performance. The separator's primary role is to isolate the positive and negative electrodes, preventing the free passage of electrons within the battery, while allowing ions in the electrolyte to freely pass between the positive and negative electrodes, forming a charge-discharge circuit and allowing ions to shuttle between the positive and negative electrodes during charge-discharge cycles. The safety performance of the separator is directly related to the overall performance of the battery. Batteries generate large amounts of heat during repeated charge-discharge cycles, and the separator must be able to withstand high temperatures without rupture, resist penetration by lithium dendrites, and prevent short circuits. Currently, conventional lithium battery separators use a ceramic material coated on a polyolefin substrate to improve the separator's overall thermal and mechanical properties. However, further improvements are needed in the electrolyte's wettability and mechanical properties.

[0004] As described above, in order to improve the safety of lithium-ion batteries and extend their service life, it is urgent to provide separators with high support strength and puncture strength. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a battery composite separator that is excellent in one or more of wettability with an electrolyte, mechanical properties, thermal stability, and battery cycle stability. [Means for solving the problem]

[0006] Therefore, the present invention proposes a composite separator comprising a base membrane, a first nanofiber layer, and a ceramic powder, wherein the first nanofiber layer is located on a first side of the base membrane, and the ceramic powder forms a first ceramic coating located between the first nanofiber layer and the base membrane, or is added to the first nanofiber layer.

[0007] In the present invention, the nanofibers are entangled to form a mesh-like structure, which allows lithium ions to be uniformly deposited on the mesh-like structure, preventing excessive deposition of lithium ions in specific areas, which would result in the formation of lithium dendrites. Furthermore, the force applied to a single point on the mesh-like structure is uniformly distributed from the point level to the surface level, improving the structural strength and puncture strength of the separator and more effectively preventing lithium dendrites from piercing the separator. Furthermore, because the mesh-like structure formed by the nanofibers has a nearly two-dimensional planar shape, the thickness of the nanofiber layer can be controlled, which, when used in a lithium-ion battery, can increase the battery capacity of the lithium-ion battery or reduce the volume of the lithium-ion battery without affecting the capacity, allowing the lithium-ion battery to be installed in smaller or more precise devices and instruments.

[0008] The present invention further proposes a method for manufacturing the above-mentioned composite separator, which includes a step (S1) of applying a slurry containing nanofibers to a first side of the base film and a step (S2) of drying the slurry containing nanofibers to form the first nanofiber layer, and further includes, before step (S1), a step (S01) of applying a slurry containing ceramic powder to the first side of the base film and a step (S02) of drying the slurry containing ceramic powder to form the first ceramic coating, or further includes, before step (S1), a step (S0) of adding the ceramic powder to the slurry.

[0009] The present invention further proposes a battery comprising a separator, said separator comprising the composite separator described above. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic view showing a composite separator according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic view showing a composite separator according to an embodiment of the present invention. [Figure 3] FIG. 2 is a schematic view showing a composite separator according to an embodiment of the present invention. [Figure 4] FIG. 2 is a schematic view showing a composite separator according to an embodiment of the present invention. [Figure 5] 1 is a scanning electron microscope photograph showing a nanofiber layer according to an embodiment of the present invention. [Figure 6] 1 is a scanning electron microscope photograph showing a nanofiber layer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011]

[0030] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for the purpose of explanation and interpretation of the present invention, and are not intended to limit the present invention.

[0012] The endpoints of the ranges and any values ​​disclosed herein are not intended to be limiting to the exact ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. With respect to numerical ranges, the endpoints of each range, the endpoints of each range and individual dot values, and the individual dot values ​​can be combined to obtain one or more new numerical ranges, which are considered to be specifically disclosed herein.

[0013] 1 and 2 show composite separators proposed in the first and second embodiments, respectively. The composite separators include a base film (1) and a first nanofiber layer (2) located on a first side (11) of the base film (1). The base film (1) may contain one or more of polyethylene and polypropylene to provide the separator with excellent thermal stability to withstand the thermal energy generated during the charge and discharge process of the battery, excellent electrochemical strength to prevent organic solvents contained in the electrolyte from corroding the separator and causing contact between the positive and negative electrodes of the battery, and excellent insulation to mechanically isolate the positive and negative electrodes. The thickness of the base film (1) may be 3 μm to 10 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, to improve battery performance. In some embodiments, the composite separator further comprises a ceramic powder (3). In the embodiment shown in Figure 1, the ceramic powder (3) forms a first ceramic coating (31) located between the first nanofiber layer (2) and the base membrane (1), and in the embodiment shown in Figure 2, the ceramic powder (3) is added to the first nanofiber layer (2).

[0014] The embodiment shown in FIG. 1 will now be further considered.

[0015] The first nanofiber layer (2) can uniformly deposit lithium ions, prevent the growth of lithium dendrites, and improve the puncture strength of the separator, preventing lithium dendrites from penetrating the separator. Specifically, the first nanofiber layer (2) protects the base film (1), improves the puncture strength of the separator, and prevents lithium dendrites from penetrating the separator. To avoid the separator affecting the electrolyte absorption or retention rate, compressing the battery's storage space, and affecting battery capacity, the first nanofiber layer (2) must be lightweight, thin, and have uniform porosity while maintaining sufficient strength. The thickness of the first nanofiber layer (2) may be 1 μm to 2 μm, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm.

[0016] The first nanofiber layer (2) contains at least nanofibers. Because nanofibers are flexible and flexible, when they are arranged crosswise, they can form a network structure with many pores. That is, the nanofibers are alternately stacked and connected to form a two-dimensional network structure. Specifically, when lithium ions are deposited on the current collector, spherical protrusions are formed, and a high electric field is generated, which further deposits lithium ions and forms lithium dendrites. Meanwhile, the network structure composed of nanofibers allows metallic lithium to be deposited uniformly, suppressing the growth of lithium dendrites. Furthermore, the large surface area and porous structure of the network structure significantly reduce the local electric field in the separator, allowing for the storage of more lithium. Furthermore, the volume change of the separator during charge-discharge cycles is reduced, allowing for the maintenance of high battery capacity even with repeated charge-discharge cycles. The nanofibers may include one or more of barium dititanate nanowires, hydroxyapatite nanowires, calcium phosphate nanowires, calcium silicate nanowires, and carboxymethyl cellulose nanowires. To provide breathability and avoid excessively high internal resistance, the surface density of the first nanofiber layer (2) must be controlled so that the separator as a whole has sufficient structural stability, heat resistance, and puncture strength, while achieving a lightweight and thin design, thereby reducing the volume of the battery and increasing the battery capacity. The surface density of the first nanofiber layer (2) must be 0.1 g / m or less. 2 ~3g / m 2 , e.g., 0.1 g / m 2 , 0.2g / m 2 , 0.3 g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1g / m 2 , 1.1g / m 2 , 1.2g / m 2 , 1.3g / m 2 , 1.4g / m 2 , 1.5g / m 2 , 1.6g / m2 , 1.7g / m 2 , 1.8g / m 2 , 1.9g / m 2 , 2g / m 2 , 2.1g / m 2 , 2.2g / m 2 , 2.3g / m 2 , 2.4g / m 2 , 2.5g / m 2 , 2.6g / m 2 , 2.7g / m 2 , 2.8g / m 2 , 2.9g / m 2 , or 3 g / m 2 The aspect ratio of the nanofibers can be adjusted to control the probability of nanofibers becoming entangled with each other. If the aspect ratio is too large, the nanofibers are prone to entanglement, making it difficult to effectively control the uniformity of the nanofiber coating. Furthermore, the density of the resulting network structure varies. If the separator surface is not flat, gaps form between the separator and the electrode. Lithium dendrites grow in these gaps, creating a risk of the battery separator being punctured by the lithium dendrites. If the aspect ratio is too small, the nanofibers cannot effectively entangle with each other, resulting in an insufficiently dense network structure that cannot effectively withstand thermal energy and does not provide sufficient puncture strength. Furthermore, when the nanofibers are stacked, they extend in the height direction, and the fibers intersect perpendicularly, forming a three-dimensional alternating structure rather than being arranged in a two-dimensional plane. This results in an increase in separator thickness and variations in thickness, leading to a decrease in battery capacity. Therefore, in order for the nanofibers to form a two-dimensional network structure with an extremely thin thickness, the aspect ratio of the nanofibers may be 20 to 100, for example, 20, 40, 60, 80, or 100. In order to reduce the surface energy and avoid aggregation of the nanofiber slurry, the particle size and specific surface area of ​​the nanofibers can be controlled. The particle size D50 of the nanofibers may be 0.5 μm to 6.5 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or 6.5 μm, but the specific surface area may be 2 μm or less. 2 / g~20m 2 / g, e.g., 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g, 19m 2 / g, or 20m 2 / g. In addition to the nanofibers, the first nanofiber layer (2) may contain a binder. The binder may include one or more of polymethacrylates, polyacrylic acid amides, phenyl cinnamates, cinnamates, polyvinylidene fluoride, and polyvinyl alcohol.

[0017] The first nanofiber layer (2) may be formed by drying the nanofiber slurry. To control the fluidity or viscosity of the nanofiber slurry, the nanofiber slurry may contain nanofibers, a binder, and a coating material. The coating material may include one or more of a dispersant, a thickener, a solvent, and a wetting agent. Adding a solvent to the nanofiber slurry improves the coating properties of the nanofiber slurry, and the first nanofiber layer (2) obtained by evaporating the solvent has a uniform thickness and a dense structure. The solvent may include one or more of ethanol, acetone, NMP, isopropyl alcohol, and deionized water. The dispersant may include one or more of ammonium polyacrylate, amine polyacrylate, styrene-maleic anhydride polymer, and phosphate esters. The thickener may include one or more of sodium carboxymethylcellulose, flaked bentonite, and associative polyurethane. The wetting agent may include one or more of succinic acid, acetylene glycol, and organosiloxane. In order to provide the first nanofiber layer (2) with good structural stability and heat resistance, the content of the nanofibers may be 5 wt% to 10 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, based on the total weight of the nanofiber slurry, and the content of the binder may be 1 wt% to 2 wt%, for example, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2 wt%, based on the total weight of the nanofibers. Specifically, the nanofiber slurry may contain 5 wt% to 10 wt% nanofibers based on the nanofiber slurry, 0.5 wt% to 1.5 wt% dispersant based on the nanofibers, 1.2 wt% to 1.8 wt% thickener based on the nanofibers, 1 wt% to 2 wt% binder based on the nanofibers, and 0.01 wt% to 0.5 wt% wetting agent based on the nanofibers, with the remainder being solvent.

[0018] The first ceramic coating (31) supports the base film (1) and prevents thermal energy from directly contacting the base film (1), thereby preventing the base film (1) from being torn during the charge / discharge process of the battery or when subjected to an acting force. The ceramic powder (3) in the first ceramic coating (31) may include one or more of alumina, boehmite, barium titanate, silica, and inorganic magnesium hydroxide, and may have a particle diameter D50 of 0.3 μm to 1 μm and a specific surface area of ​​2 m or more. 2 / g~12m 2 / g. In order to provide sufficient support for the base film (1), the areal density of the first ceramic coating (31) applied to the base film (1) must not be too low. The areal density of the first ceramic coating (31) is 0.5 g / m 2 ~3g / m 2 , e.g., 0.5 g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1g / m 2 , 1.1g / m 2 , 1.2g / m 2 , 1.3g / m 2 , 1.4g / m 2 , 1.5g / m 2 , 1.6g / m 2 , 1.7g / m 2 , 1.8g / m 2 , 1.9g / m 2 , 2g / m 2 , 2.1g / m 2 , 2.2g / m 2 , 2.3g / m 2 , 2.4g / m 2 , 2.5g / m 2 , 2.6g / m 2 , 2.7g / m 2 , 2.8g / m 2 , 2.9g / m 2 , or 3 g / m 2The areal density of the first ceramic coating (31) and the first nanofiber layer (2) must be controlled to provide thermal insulation to the base membrane (1) so that the first ceramic coating (31) can effectively support the base membrane (1), to provide a predetermined structural strength to the separator, and to prevent lithium dendrites from puncturing the separator. The areal density ratio between the first ceramic coating (31) and the first nanofiber layer (2) may be 6:1 or less. The first ceramic coating (31) may contain a binder in addition to the ceramic powder (3). The binder may include one or more of polymethacrylates, polyacrylic acid amides, phenylcinnamates, cinnamates, polyvinylidene fluoride, and polyvinyl alcohol.

[0019] The first ceramic coating (31) may be formed by drying the ceramic slurry. The ceramic slurry may include ceramic powder (3), a binder, and coating ingredients. The coating ingredients may include one or more of a dispersant, a thickener, and a solvent to control the fluidity or viscosity of the ceramic slurry. The solvent may include one or more of ethanol, acetone, NMP, isopropyl alcohol, and deionized water. The dispersant may include one or more of ammonium polyacrylate, amine polyacrylate, styrene maleic anhydride polymer, and phosphate esters. The thickener may include one or more of sodium carboxymethylcellulose, flaked bentonite, and associative polyurethane.

[0020] The nanofiber slurry may contain a lower percentage of solids and binder than the ceramic slurry to ensure that the nanofibers are intersected and stacked within an extremely thin thickness, spreading flatly, and forming a dense two-dimensional network structure. This also prevents the nanofibers from extending and entangling in the height direction, making the separator too thick overall, reducing the density of the first nanofiber layer (2) and making it vulnerable to puncture by lithium dendrites. Specifically, the ceramic slurry may contain 25 wt% to 35 wt% of ceramic powder (3) based on the ceramic slurry, 0.5 wt% to 1.2 wt% of dispersant based on the ceramic powder (3), 1 wt% to 1.5 wt% of thickener based on the ceramic powder (3), and 3 wt% to 6 wt% of binder based on the ceramic powder (3), with the remainder being solvent.

[0021] Furthermore, the ceramic slurry or nanofiber slurry can be applied by a gravure roller or a wire bar, and the application process can be any method commonly used in the art.

[0022] To control the overall thickness of the separator and provide corresponding thermal protection, puncture strength, or battery capacity retention, the separator may further include a second ceramic coating (4) disposed on a second side (12) opposite the first side (11) of the base membrane (1), as shown in Figure 3. To control the overall thickness of the separator and provide corresponding thermal protection, puncture strength, or battery capacity retention, the separator may further include a second ceramic coating (4) disposed on a second side (12) opposite the first side (11) of the base membrane (1), and a second nanofiber layer (5) disposed on the second side (12) of the base membrane (1) to position the second ceramic coating (4) between the base membrane (1) and the second nanofiber layer (5), as shown in Figure 4. Since the second nanofiber layer (5) and the second ceramic coating (4) are arranged corresponding to the first nanofiber layer (2) and the first ceramic coating (31), respectively, the composition and physical and chemical properties of the second nanofiber layer (5) and the second ceramic coating (4) can be referred to the relevant description of the first nanofiber layer (2) and the first ceramic coating (31), and will not be further described.

[0023] Here, we will explain the method for manufacturing the separator shown in Figure 1. First, a slurry containing ceramic powder (3) (also referred to as "ceramic slurry") is applied to the first side (11) of the base film (1), then the slurry containing ceramic powder (3) is dried to form a first ceramic coating (31), and then a slurry containing nanofibers (also referred to as "nanofiber slurry") is applied to the side of the first ceramic coating (31) that is not in contact with the base film (1), and finally the slurry containing nanofibers is dried to form a first nanofiber layer (2).

[0024] 3, the manufacturing method may further include applying a slurry containing ceramic powder (3) (also referred to as "ceramic slurry") to the second side (12) of the base film (1) and drying the slurry containing ceramic powder (3) to form a second ceramic coating (4). It should be understood that these two steps may occur before applying the slurry containing ceramic powder (3) to the first side (11) of the base film (1), between the step of drying the slurry containing ceramic powder (3) to form the first ceramic coating (31) and the application of the nanofiber slurry to the side of the first ceramic coating (31) not contacting the base film (1), or after the step of drying the nanofiber slurry to form the first nanofiber layer (2).

[0025] In the structure shown in FIG. 4, the manufacturing method may further include applying a slurry containing ceramic powder (3) (also referred to as a "ceramic slurry") to the second side (12) of the base film (1), drying the slurry containing ceramic powder (3) to form a second ceramic coating (4), applying another slurry containing nanofibers (also referred to as a "nanofiber slurry") to the side of the second ceramic coating (4) not in contact with the base film (1), and drying the slurry containing nanofibers to form a second nanofiber layer (5). It should be understood that the first two steps may be performed before the step of applying the slurry containing ceramic powder (3) to the first side (11) of the base film (1), or may be performed between the step of drying the slurry containing ceramic powder (3) to form the first ceramic coating (31) and the step of applying the nanofiber slurry to the side of the first ceramic coating (31) that is not in contact with the base film (1), or may be performed after the step of drying the nanofiber slurry to form the first nanofiber layer (2); and the latter two steps may also be performed before the application of the slurry containing ceramic powder (3) to the first side (11) of the base film (1), or may be performed between the step of drying the slurry containing ceramic powder (3) to form the first ceramic coating (31) and the step of applying the nanofiber slurry to the side of the first ceramic coating (31) that is not in contact with the base film (1), or may be performed after the step of drying the nanofiber slurry to form the first nanofiber layer (2). In each case, however, the first two steps precede the latter two.

[0026] The nanofiber slurry manufacturing process is as follows: First, the dispersant and nanofibers are mixed by stirring for at least one hour, and then the nanofibers are ball-milled to uniformly disperse in the dispersant to obtain a first mixture. Next, the first mixture is mixed with a thickener and stirred for at least 30 minutes to obtain a second mixture. After that, the second mixture, binder, and wetting agent are mixed by stirring to obtain the nanofiber slurry.

[0027] In this embodiment, by selecting an appropriate coating material and controlling the surface density when applying the coating, it is possible to achieve protection of the first ceramic coating (31) and base film (1) by the first nanofiber layer (2), or protection of the second ceramic coating (4) and base film (1) by the second nanofiber layer (5). In addition, the two-dimensional mesh-like porous structure improves the liquid absorption and retention of the composite separator sample, allowing it to perform better when used in lithium-ion batteries.

[0028] Furthermore, compared with the prior art, the advantages of this embodiment are as follows. First, by forming a highly dense first ceramic coating (31) on the base film (1), the support performance of the base film (1) is strengthened. Therefore, when the separator is subjected to a force, it can maintain its structural strength and not bend or deform. Furthermore, the first ceramic coating (31) acts as a heat-resistant layer on the base film (1), improving the thermal stability of the entire composite separator of the lithium-ion battery, raising the separator's rupture temperature and widening the safety zone when the separator is subjected to heat. This improves the safety of the lithium-ion battery during long-term charge / discharge cycles and at high temperatures. Furthermore, in this embodiment, nanofibers with specific particle diameters, specific surface areas, and aspect ratios are prepared into a nanofiber slurry, which is then applied to the first ceramic coating (31). This allows the nanofibers to intertwine alternately within an extremely thin thickness, forming a two-dimensional network structure. Lithium ions are uniformly deposited on the network structure, preventing excessive lithium ion deposition in specific areas, which would result in the formation of lithium dendrites. Furthermore, the force applied to a single point on the network structure is uniformly distributed from the point to the surface, significantly improving the structural strength and puncture strength of the separator and effectively preventing lithium dendrites from piercing the separator. Furthermore, because the network structure formed by the nanofibers has a nearly two-dimensional planar shape, the thickness of the first nanofiber layer (2) can be controlled. When the separator is used in a lithium ion battery, this can increase the battery capacity of the lithium ion battery or reduce the volume of the lithium ion battery without affecting the capacity of the lithium ion battery, allowing the lithium ion battery to be installed in smaller or more precise devices and instruments.

[0029] The embodiment shown in FIG. 2 will now be further considered. The first nanofiber layer (2) contains at least nanofibers and ceramic powder (3). The thickness of the first nanofiber layer (2) may be 1 μm to 1.5 μm, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm. The nanofibers may be amphiphilic nanofibers, which may contain one or more of amphiphilic nanocellulose, amphiphilic cellulose nanowhiskers, amphiphilic cellulose nanofilaments, and amphiphilic microfibrillated cellulose. The ceramic powder (3) may contain one or more of alumina, titanium oxide, boehmite, silicon nitride, boron carbide, and barium sulfate. The hydrophilicity of amphiphilic nanofibers increases the separator's liquid absorption capacity and increases the wetting rate of the electrolyte, while the lipophilicity enhances the nanofibers' ability to bind to the base film (1), allowing the nanofibers to intertwine and form a three-dimensional mesh structure. When combined with ceramic powder (3) and a binder, the bonding strength between the first nanofiber layer (2) and the base film (1) is further enhanced, reducing problems such as powder shedding and improving the separator's mechanical properties. Furthermore, the addition of nanofibers can somewhat increase the bonding strength between the first nanofiber layer (2) and the base film (1), allowing for a reduction in the amount of binder used while still achieving good bonding strength. This allows for the addition of more ceramic powder (3) and nanofibers, improving the mechanical properties and thermal stability of the first nanofiber layer (2). The total mass of the ceramic powder (3) and the amphiphilic nanofibers may be 95 wt% to 99 wt% of the mass of the first nanofiber layer (2), for example, 95 wt%, 95.5 wt%, 96 wt%, 96.5 wt%, 97 wt%, 97.5 wt%, 98 wt%, 98.5 wt%, or 99 wt%. Specifically, the total mass of the ceramic powder (3) and the amphiphilic nanofibers is 97 wt% to 99 wt% of the mass of the first nanofiber layer (2).The mass ratio of the amphiphilic nanofibers to the ceramic powder (3) may be (1-20):100, for example, 1:100, 2:100, 4:100, 6:100, 8:100, 10:100, 12:100, 14:100, 16:100, 18:100, or 20:100, which increases the bonding strength between the first nanofiber layer (2) and the base membrane (1), improves membrane density, and improves the tensile strength and puncture resistance of the separator. Furthermore, the amount of ceramic powder (3) added is also somewhat satisfied. The combination of amphiphilic nanofibers further improves the breathability of the separator and increases its wettability, liquid absorption, and liquid retention. Specifically, the mass ratio of the amphiphilic nanofibers to the ceramic powder (3) is (5-10):100.

[0030] The first nanofiber layer (2) may further contain a binder, which may include one or more of polyacrylamide, polybutyl methacrylate, polyhydroxyethyl methacrylate, and polyvinyl alcohol. The hydrophilic groups of the amphiphilic nanofiber may include one or more of hydroxyl groups, carboxyl groups, amino groups, quaternary amine groups, aldehyde groups, sulfonic acid groups, and phosphate groups, while the lipophilic groups may include one or more of alkyl groups, phenyl groups, and cycloalkyl groups. The presence of hydroxyl groups is advantageous for accelerating the wetting rate of the separator. Furthermore, since a large number of active hydroxyl groups are inherently present on the surface of natural fibers, simply converting only a portion of the active hydroxyl groups to lipophilic groups (e.g., alkyl groups) can impart a high wetting rate, high liquid absorption rate, and high liquid retention rate to the separator, and can further increase the bonding strength between the first nanofiber layer (2) and the base film (1). Specifically, the hydrophilic groups of the amphiphilic nanofiber may include hydroxyl groups, and the lipophilic groups may include alkyl groups.

[0031] The higher the thermal decomposition temperature of the amphiphilic nanofiber, the more improved the heat resistance and thermal stability of the separator. In the high-temperature environment of battery operation, the separator can release stress and not experience significant thermal shrinkage, thereby preventing contact between the positive and negative electrode materials inside the battery and causing a short circuit, improving battery safety. The thermal decomposition temperature of the amphiphilic nanofiber may be 275°C or higher, for example, 275°C, 280°C, 285°C, 290°C, 295°C, 300°C, 305°C, 310°C, 315°C, 320°C, 325°C, 330°C, 335°C, 340°C, 345°C, or 350°C. Specifically, the thermal decomposition temperature of the amphiphilic nanofiber 122 may be between 275°C and 340°C.

[0032] The density of the amphiphilic nanofibers is 1.6 g / cm 3 For example, 1.05 g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.35g / cm 3 , 1.4g / cm 3 , 1.45g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , or 1.6 g / cm 3 Specifically, the density of the amphiphilic nanofiber may be 1.0 g / cm 3 ~1.6g / cm 3 Furthermore, since the density of the amphiphilic nanofibers is at least one time lower than the density of the ceramic powder (3), the wetting speed of the separator can be further increased and at the same time, the mechanical properties of the separator can be improved. Therefore, if the density of the amphiphilic nanofibers is represented by A1 and the density of the ceramic powder (3) is represented by A2, and the units of A1 and A2 are the same, A1<1 / 2×A2 may be satisfied.

[0033] The diameter of the amphiphilic nanofibers may be 4 nm to 20 nm, e.g., 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, or 20 nm, the length may be 100 nm to 500 nm, e.g., 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm, and the aspect ratio may be 5 to 125, e.g., 5, 10, 15, 20, 25, 30, 35, 40, 45, 55, 65, 75, 85, 95, 105, 115, or 125. Under the condition that the thickness of the first nanofiber layer 2 is the same, the above size allows more nanofibers to be stacked in the first nanofiber layer 2, thereby improving the deposition of the first nanofiber layer 2 on the base film 1 and improving the heat resistance of the separator. Furthermore, the above size specification allows the nanofibers to form a relatively reasonable porosity, reduce internal resistance, form a mesh structure, and improve the cooperation effect with the ceramic powder 3, thereby increasing both the tensile strength and puncture strength of the separator and contributing to better mechanical properties.

[0034] Since amphiphilic nanofibers with various pyrolysis temperatures and densities are commercially available, the production of amphiphilic nanofibers with various pyrolysis temperatures and densities will not be described in detail herein. Furthermore, most commercially available nanocellulose, cellulose nanowhiskers, cellulose nanofilaments, or microfibrillated cellulose have a hydrophilic structure. The amphiphilic nanocellulose (hydrophilic and lipophilic) referred to herein is different from commercially available nanocellulose (hydrophilic), the amphiphilic cellulose nanowhiskers (hydrophilic and lipophilic) referred to herein are different from commercially available cellulose nanowhiskers (hydrophilic), the amphiphilic cellulose nanofilaments (hydrophilic and lipophilic) referred to herein are different from commercially available cellulose nanofilaments (hydrophilic), and the amphiphilic microfibrillated cellulose (hydrophilic and lipophilic) referred to herein is different from commercially available microfibrillated cellulose (hydrophilic). Furthermore, since the amphiphilic nanocellulose, amphiphilic cellulose nanowhiskers, amphiphilic cellulose nanofilaments, and amphiphilic microfibrillated cellulose referred to herein are commercially available, the production of amphiphilic nanocellulose, amphiphilic cellulose nanowhiskers, amphiphilic cellulose nanofilaments, and amphiphilic microfibrillated cellulose will not be described in detail herein.

[0035] The particle diameter D50 of the ceramic powder (3) may be 100 nm to 1000 nm, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, or 1000 nm. The combination of this size of the ceramic powder (3) with the size of the amphiphilic nanofibers (diameter 4 nm to 20 nm, length 100 nm to 500 nm, aspect ratio 5 to 125) simultaneously provides heat resistance, improving the heat resistance of the separator. Furthermore, when the particle diameter D50 of the ceramic powder (3) and the length of the amphiphilic nanofibers are expressed in the same unit, the ratio of the particle diameter D50 of the ceramic powder (3) to the length of the amphiphilic nanofibers is 1:(1 to 2).

[0036] Here, we will explain a method for manufacturing the separator shown in Figure 2. First, a coating slurry containing ceramic powder (3) and nanofibers is applied to the first side (11) of the base film (1), and then the coating slurry is dried to form the first nanofiber layer (2). Specifically, first, a ceramic powder (3) dispersion, a nanofiber dispersion, and a binder are mixed to form a coating slurry, then the coating slurry is applied to the first side (11) of the base film (1), and finally, the coating slurry is dried to form the first nanofiber layer (2). This process allows the ceramic powder (3) and nanofibers to be dispersed relatively uniformly in the coating slurry, resulting in a separator in which the ceramic powder (3) and nanofibers are uniformly distributed. The hydrophilicity of the nanofibers improves the separator's ability to absorb liquid, accelerating the wetting rate of the battery fluid. The lipophilicity of the nanofibers enhances the separator's ability to bind to the base film (1). Furthermore, the nanofibers are entangled to form a three-dimensional mesh structure, which, when combined with the binder and ceramic powder (3), further enhances the bonding strength between the ceramic powder (3) and the base film (1), improving the mechanical properties of the separator.

[0037] More specifically, a solvent, a dispersant, and the ceramic powder (3) are mixed to form a ceramic powder dispersion. The dispersant not only uniformly disperses the ceramic powder (3) in the ceramic powder dispersion and reduces agglomeration of the ceramic powder (3), but also serves as a dispersant in the coating slurry to better disperse other components in the coating slurry. The dispersant may include one or more of sodium polyacrylate, amine polyacrylate, and polyphosphate. The solvent may include one or more of water, NMP, isopropyl alcohol, and acetone. The amount of ceramic powder (3) added may be 10 wt% to 50 wt% of the ceramic powder dispersion, for example, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%, which contributes to better dispersing the small particle size ceramic powder (3).

[0038] Next, the solvent and nanofibers are mixed to form a nanofiber dispersion. Because the nanofibers are amphiphilic, they can be dispersed well in solvents, whether aqueous or oil-based, without the need for a dispersant. The solvent may include one or more of water, NMP, isopropyl alcohol, and acetone. The amount of nanofibers added may be 1 wt% to 10 wt%, for example, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%, or 10 wt%, of the nanofiber dispersion, which contributes to the well-dispersed nanofibers.

[0039] The ceramic powder (3) dispersion and the nanofiber dispersion are then mixed, followed by the addition of a binder to form a coating slurry. Other additives, such as a wetting agent, may be added to the coating slurry. The wetting agent may include one or more of siloxane, alkylphenol polyoxyethylene ether, and succinic acid. The components of the coating slurry may be adjusted using a solvent, and the total amount of solvent may be 88 wt% to 99 wt% of the coating slurry, for example, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, or 99 wt%. A higher total amount of solvent in the coating slurry can improve the orientation of the nanofibers, which in turn contributes to the regular crosslinking of the fibers in the first nanofiber layer (2) to be formed later, thereby improving the performance of the nanofibers. Specifically, the total amount of the solvent added is 95 wt% to 99 wt% of the coating slurry. The total amount of the ceramic powder (3) added may be 1 wt% to 10 wt% of the coating slurry, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, and the total amount of the nanofibers added may be 0.1 wt% to 1 wt% of the coating slurry, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, or 10 wt%. The total amount of binder added may be 0.01 wt% to 0.4 wt% of the coating slurry, for example, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, or 0.4 wt%. The total amount of dispersant added may be 0.01 wt% to 0.1 wt% of the coating slurry, for example, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, or 0.1 wt%.

[0040] Finally, the coating slurry is applied to the first side (11) of the base film (1) and dried to obtain a separator. The coating method may be a gravure roller, a wire bar, or a spray coat, and drying may be performed in an oven.

[0041] Conventionally, a ceramic coating is formed on a base film as a separator. However, poor electrolyte wettability of the ceramic coating makes it difficult for the separator to absorb the electrolyte, hindering the transport and movement of lithium ions. Adding nanofibers to the ceramic coating to improve the separator's electrolyte wettability has been reported. The nanofibers possess a large number of active hydroxyl groups on their surface, making them hydrophilic and improving the coating's wettability. However, it has been discovered that the addition of nanofibers creates new problems for separators. For example, separators are often manufactured and used in aqueous environments. However, nanofibers, due to their hydrophilic nature and the large number of active hydroxyl groups on their surface, easily break internal hydrogen bonds under the action of water molecules, resulting in poor mechanical properties in high-humidity environments. Furthermore, while the base film of a separator is generally hydrophobic, the hydrophilic nature of nanofibers results in insufficient bonding between the coating and the base film, making them prone to delamination, which in turn causes the separator to bend and significantly deteriorate its mechanical properties. In this embodiment, the hydrophilicity of the nanofibers can improve the separator's liquid absorption capacity and increase the wetting rate of the electrolyte, while the lipophilicity can improve the bonding ability between the nanofibers and the base film (1). The nanofibers are entangled to form a three-dimensional network structure, which, when combined with the binder and ceramic powder (3), further enhances the bonding strength between the first nanofiber layer (2) and the base film (1), thereby improving the mechanical properties of the separator. Based on this, the separator of this embodiment can be used in battery manufacturing.

[0042] The present invention will now be described by way of example. Examples A1-A19 and Comparative Examples A1-A3 illustrate the effect of various layered structures and the properties of the materials used in the layered structures on the performance parameters of the resulting composite separator samples.

[0043] Example A1 The composite separator sample of this example includes, in the elongation direction, a base film, a first ceramic coating formed by applying and drying a ceramic slurry to a first side of the base film, and a first nanofiber coating formed by applying and drying a nanofiber slurry to the side of the first ceramic coating not in contact with the base film. The base film used in this example is a polyethylene film with a thickness of 7 μm, which has high porosity, high mechanical strength, a low closing temperature, and a high film rupture temperature. The base film has good uniformity due to its complete manufacturing process, and excellent mechanical properties and heat resistance. Therefore, combining the base film with the first ceramic coating allows for an increased thickness and space for the first ceramic coating. The areal density of the first ceramic coating used in this example is 1.5 g / m. 2 The areal density of the first nanofiber coating used in this example is 0.6 g / m 2 is.

[0044] The method for producing the ceramic slurry used includes the steps of: (S1a) mixing ammonium polyacrylate and alumina powder in a weight ratio of 1:200 by stirring for at least 1 hour, and then ball milling the alumina powder to uniformly disperse it in the ammonium polyacrylate to obtain a first mixture; (S2a) mixing the first mixture and sodium carboxymethylcellulose by stirring for 30 minutes to obtain a second mixture, in which the sodium carboxymethylcellulose is a 4% clear solution obtained by stirring water and CMC at 2000 rpm for at least 1 hour, and the CMC accounts for 1% of the total solid weight of the alumina powder; and (S3a) mixing the second mixture with polyacrylamide and succinic acid by stirring to obtain a ceramic slurry with a solid content of 35 wt%, in which the polyacrylamide accounts for 3% of the total solid weight of the alumina powder and the succinic acid accounts for 0.01% of the total solid weight of the alumina powder.

[0045] The nanofiber slurry used is prepared by mixing ammonium polyacrylate and barium dititanate nanowires by stirring for at least 1 hour, and then ball milling the barium dititanate nanowires to uniformly disperse them in the ammonium polyacrylate to obtain a third mixture (S1b), in which the weight ratio of the ammonium polyacrylate to the barium dititanate nanowires is 1:200, and the barium dititanate nanowires have a particle diameter D50 of 2 μm and a specific surface area of ​​15 m 2 / g and aspect ratio of 60; step (S2b) of mixing and stirring the third mixture and sodium carboxymethylcellulose for 30 minutes to obtain a fourth mixture, in which the sodium carboxymethylcellulose is a 4% clear solution obtained by stirring water and CMC at 2000 rpm for 1 hour or more, and the CMC is 1.5 wt% of the total solid weight of the barium dititanate nanowires; and step (S3b) of stirring and mixing the fourth mixture with polyacrylamide and succinic acid to obtain a nanofiber slurry with a solid content of 10 wt%, in which the polyacrylamide is 1.5% of the total solid weight of the nanofiber powder and the succinic acid is 0.01% of the total solid weight of the nanofiber powder.

[0046] Examples A2 to A5 Examples A2 to A5 illustrate the influence of nanofiber particle size and specific surface area on the performance parameters of composite separator samples.

[0047] In Example A2, compared to Example A1, the nanofibers used have a particle diameter of 0.5 μm and a specific surface area of ​​20 m 2 The difference is that the saturation is / g.

[0048] In Example A3, compared to Example A1, the nanofibers used have a particle diameter of 6.5 μm and a specific surface area of ​​2 m 2 The difference is that the saturation is / g. In Example A4, compared to Example A1, the nanofibers used have a particle diameter of 0.3 μm and a specific surface area of ​​27 m 2 The difference is that the saturation is / g.

[0049] In Example A5, compared to Example A1, the nanofibers used have a particle diameter of 7 μm and a specific surface area of ​​1.5 m 2 The difference is that the saturation is / g.

[0050] Examples A6 to A9 Examples A6-A9 demonstrate the effect of nanofiber aspect ratio on the performance parameters of composite separator samples. Example A6 differs from Example A1 in that the aspect ratio of the nanofibers used is 20.

[0051] Example A7 differs from Example A1 in that the aspect ratio of the fibers used is 120.

[0052] Example A8 differs from Example A1 in that the aspect ratio of the nanofibers used is 10. Example A9 differs from Example A1 in that the aspect ratio of the nanofibers used is 100.

[0053] Examples A10 to A12 Examples A10 to A12 illustrate the effect of the mass ratio of binder to the total weight of nanofibers in the nanofiber slurry on the performance parameters of composite separator samples.

[0054] Example A10 differs from Example A1 in that the mass ratio of the binder used in producing the nanofiber slurry to the total weight of the nanofibers is 1 wt %.

[0055] Example A11 differs from Example A1 in that the mass ratio of the binder used in producing the nanofiber slurry to the total weight of the nanofibers is 2 wt %. Example A12 differs from Example A1 in that the mass ratio of the binder used in producing the nanofiber slurry to the total weight of the nanofibers is 3 wt %.

[0056] Examples A13 to A15 Examples A13 to A15 illustrate the effect of the mass ratio of nanofibers in the nanofiber slurry relative to the total weight of the nanofiber slurry on the performance parameters of composite separator samples.

[0057] Example A13 differs from Example A1 in that the mass ratio of the nanofibers used in producing the nanofiber slurry to the total weight of the nanofiber slurry is 5 wt %.

[0058] Example A14 differs from Example A1 in that the mass ratio of the nanofibers used in producing the nanofiber slurry to the total weight of the nanofiber slurry is 2 wt %.

[0059] Example A15 differs from Example A1 in that the mass ratio of the nanofibers used in producing the nanofiber slurry to the total weight of the nanofiber slurry is 15 wt %.

[0060] Examples A16 and A17 Examples A16 and A17 illustrate the effect of the areal density of the first nanofiber coating and the areal density of the first ceramic coating on the performance parameters of composite separator samples.

[0061] In Example A16, the areal density of the first ceramic coating formed on the base film was 1.8 g / m 2 and the surface density of the first nanofiber coating formed on the first ceramic coating is 0.3 g / m 2 The difference is that

[0062] In Example A17, the areal density of the first ceramic coating formed on the base film was 1.9 g / m 2 and the surface density of the first nanofiber coating formed on the first ceramic coating is 0.2 g / m 2 The difference is that

[0063] Examples A18 and A19 Example A18 differs from Example A1 in that a second ceramic coating is formed on the second side of the base film.

[0064] Example A19 differs from Example A18 in that a second nanofiber coating is further formed on the side of the second ceramic coating that is not in contact with the base film.

[0065] Comparative Example A1 In Comparative Example A1, compared to Example A1, a first ceramic coating and a second ceramic coating were formed on the first side and the second side of the base film, respectively, but the first ceramic coating and the second ceramic coating were not formed with a nanofiber coating, and the areal density of the first ceramic coating and the second ceramic coating was 2.1 g / m 2 The difference is that

[0066] Comparative example A2 In Comparative Example A2, compared to Example A1, a first nanofiber coating was formed on the first side of the base film, and the areal density of the first nanofiber coating was 2.1 g / m 2 The difference is that

[0067] Comparative example A3 In Comparative Example A3, compared with Example A1, the ceramic slurry and the nanofiber slurry were mixed to form a mixed slurry, which was then applied to the first side of the base film, and the mixed slurry was cooled to form a mixed coating to obtain a composite separator sample, and the areal density of the mixed coating was 2.1 g / m 2 The difference is that

[0068] For testing the performance parameters of the composite separator samples of Examples A1-A19 and Comparative Examples A1-A3, refer to the following methods.

[0069] Thickness The measurement tool used was a Mahr Millimar thickness gauge. First, the surface of the composite separator sample was kept flat, and the thickness was measured at 5 to 10 random points along the longitudinal direction (MD) of the composite separator sample. The obtained measurement results were averaged to obtain the thickness of the composite separator sample.

[0070] areal density

[0071] Three test samples of the same area are cut out from the composite separator sample, and the thickness (H), area (S), and mass (m) of each test sample are obtained using a weighing method. The areal density of the test samples is calculated according to the standards specified in GB / T 6343-2009, and the calculation formula for areal density (ρ) is ρ = m / (H × S). The calculation results are then averaged to obtain the areal density of the composite separator sample.

[0072] Scanning electron microscope (SEM)

[0073] A test sample measuring 0.5 cm x 0.5 cm was cut from the composite separator sample, attached to a sample stage with conductive adhesive, and placed in an ion sputtering device to spray gold. Finally, the gold-sprayed test sample was scanned and examined using a scanning electron microscope to capture a photograph of the coating morphology on the test sample. Figure 5 shows the image of the first nanofiber coating on the test sample taken with a scanning electron microscope.

[0074] Ventilation rate Using the EG01 Oken air permeability tester as the measurement tool, select any three points on the composite separator sample, measure the average time required for 100 ml of gas to permeate at each point, and average the three sets of test results to obtain the air permeability of the composite separator sample.

[0075] Puncture Strength Three test samples with a length and width of 5 cm or more were cut out from the composite separator sample, and the test samples were fixed on a sample stage. The diameter (φ) was measured using a puncture needle with a 0.5 mm tip (SR) and an electronic puncture strength tester. After the test was completed, the three test results were averaged to obtain the puncture strength of the composite separator sample.

[0076] Liquid absorption rate and liquid retention rate Three test samples measuring 100 mm x 100 mm in length and width were cut from the composite separator sample, and the initial weight (m0) of each test sample was weighed. The test sample was placed in the electrolyte and soaked for 1 hour, then removed. The electrolyte on the surface of the test sample was wiped off with a clean wiper, and the absorbed weight (m1) of the test sample was weighed. The weighed test sample was spread flat and left at room temperature for 1 hour, and the liquid-retained weight (m2) of the test sample was weighed. Here, the liquid absorption rate of the test sample = ((m1 - m0)) / m0 x 100%, and the liquid retention rate = ((m2 - m0)) / m0 x 100%. Finally, the three sets of experimental data were averaged to obtain the liquid absorption rate and liquid retention rate of the composite separator sample.

[0077] Cycle characteristics An electrochemical test is performed on the composite separator sample, and the composite separator sample is charged and discharged 500 times. The capacity retention rate after the test is measured to determine the cycle characteristics of the composite separator sample.

[0078] The selection of coating materials used in Examples A1 to A19 and Comparative Examples A1 to A3, the areal density of the coating application, and the performance parameters of the composite separator samples produced are summarized in Tables 1 and 2 below.

[0079] Table 1. Measurement results of parameters of composite separator samples JPEG2025527985000002.jpg220170

[0080] Table 2. Parameter measurement results for composite separator samples JPEG2025527985000003.jpg231170

[0081] The structural features of the composite separator samples of Examples A1 to A19 and Comparative Examples A1 to A3 are described in detail below. The lithium-ion battery composite separators of Examples A1 to A17 have a structure including a base film, a first ceramic coating, and a first nanofiber coating, in this order, as shown in FIG. 1. The lithium-ion battery composite separator of Example A18 has a structure including a first nanofiber coating, a first ceramic coating, a base film, and a second ceramic coating, in this order, as shown in FIG. 3. The lithium-ion battery composite separator of Example A19 has a structure including a first nanofiber coating, a first ceramic coating, a base film, a second ceramic coating, and a second nanofiber coating, in this order, as shown in FIG. 4. The composite separator sample of Comparative Example A1 has a structure including a first ceramic coating, a base film, and a second ceramic coating, in this order. The composite separator sample of Comparative Example A2 includes a first nanofiber coating and a base film, in that order. The composite separator sample of Comparative Example A3 includes a mixed coating formed by drying a mixed slurry of nanofiber slurry and ceramic slurry, and a base film, in that order.

[0082] In Example A1, a first ceramic coating is formed on a base film, and then a light and thin first nanofiber coating is formed on the first ceramic coating, thereby improving the heat resistance and puncture strength of the composite separator sample and extending its cycle life. Specifically, in Example A1, nanofibers with a specific aspect ratio are selected, allowing the nanofibers to be entangled to form a porous network structure. Furthermore, the nanofibers are entangled with each other, enhancing the interaction between molecular chains, thereby improving the overall structural strength of the composite separator sample. When force is applied to the composite separator sample, the force is distributed from the point of application to the surface, thereby uniformly distributing the external puncture and compression forces experienced by the composite separator sample. The resistance of the first nanofiber coating to breakage improves the withstand voltage and puncture resistance of the composite separator sample. Furthermore, the light and thin first nanofiber coating reduces the overall thickness of the composite separator sample, thereby further reducing the weight and thickness of lithium-ion batteries or increasing the battery capacity of a given battery volume.

[0083] Example A1 will be described below in comparison with other examples and comparative examples. See the test results for Examples A1 to A5. In Example A4, when the nanofiber particle size was too small and the specific surface area was too large, the nanofibers had too high a surface energy, tending to aggregate and entangle with each other, failing to form a planar network structure. This resulted in a localized application of the first nanofiber coating that was too thick or too dense, and the first nanofiber coating was not uniformly adhered to the first ceramic coating or base film, resulting in large areas of uncoated material. In Example A5, when the nanofiber particle size was too large and the specific surface area was too small, the entanglement density of the nanofibers was too low for the same surface density or thickness of the first nanofiber coating. As a result, the resulting coating structure was loose and unable to effectively form a network structure. As described above, when the nanofiber particle size and specific surface area were inappropriate, performance parameters such as thermal properties, cycle characteristics, liquid absorption rate, and liquid retention rate of the composite separator sample were affected. Specifically, referring to Examples A1 to A3, the particle diameter and specific surface area of ​​the nanofibers used are appropriate, so compared to Examples A4 and A5, the heat shrinkage rate is reduced, the withstand voltage strength is increased, and the membrane rupture temperature, puncture strength, liquid absorption rate, liquid retention rate, and capacity retention rate are relatively high.

[0084] See Examples A1 and A6-A9. In Example A8, if the aspect ratio of the nanofibers is too small, it becomes difficult for the nanofibers to cross and stack, resulting in a loose structure of the first nanofiber coating. Specifically, because the nanofibers cross perpendicularly and stack vertically, the coating is arranged in a three-dimensional mesh rather than a flat surface. Furthermore, because the gaps between the nanofibers are large and the frictional force is low, the mechanical properties are poor and the applied force cannot be effectively transmitted. When a force is applied to a single point, powder shedding and puncture holes are likely to occur. In addition, in Example A9, if the aspect ratio of the nanofibers is too large, the nanofibers are likely to entangle with each other, resulting in poor nanofiber distribution uniformity or uneven mesh density, which affects application. As described above, in Examples A8 and A9, the first nanofiber coating fails to provide heat resistance and puncture resistance during use. Furthermore, it is difficult to control the thickness during the application process, resulting in unevenness on the surface. In Examples A1, A6, and A7, nanofibers with appropriate aspect ratios were used, and the nanofibers were alternately stacked and arranged to form a two-dimensional mesh structure, which significantly improved the mechanical strength and properties of the composite separator samples and prevented the separator from being perforated. Furthermore, the formation of the mesh structure improved the liquid absorption and retention rates of the composite separator samples.

[0085] The test results of Examples A1 to A9 combined show that by adjusting the particle size, specific surface area, or aspect ratio of the nanofibers, the density at which the nanofibers intersect with one another can be increased, further increasing the deposition density of the first nanofiber coating at a very high thickness. Furthermore, when the nanofibers form a denser, porous two-dimensional network structure in the plane, the heat resistance and mechanical properties of the first nanofiber coating can be improved without increasing the coating thickness or internal resistance.

[0086] See Examples A1 and A10-A12. The binder is an important substance that determines the bonding strength between the coatings. If the binder content is too low, the first nanofiber coating will not stably adhere to the first ceramic coating. To reduce internal resistance, the amount of binder used in the first nanofiber coating must be reduced. Specifically, in Example A12, the binder content is twice that of Example A1. As a result, the composite separator sample of Example A12 has higher air permeability and internal resistance than Example A1. Furthermore, in Examples A1, A10, and A11, the content of high-molecular-weight and high-viscosity polymers is reduced, improving the spreadability of the nanofiber slurry and preventing the internal nanofibers from agglomerating or entangling, which would increase the coating thickness and affect overall performance.

[0087] See Examples A1 and A13 to A15. In Example A14, the mass ratio of nanofibers was too low, resulting in a low density of the network structure formed by applying the nanofiber slurry to the first ceramic coating and curing it, and a low coverage rate for the first ceramic coating. In Example A15, the mass ratio of nanofibers was too high, resulting in a two-dimensional network structure formed by arranging the nanofibers in the forward direction when the resulting nanofiber slurry was produced and applied, and a three-dimensional structure in which the nanofibers intersect perpendicularly was likely to be formed.

[0088] See Examples A1 and A16-A17. The first ceramic coating has a high density and a predetermined thickness and weight, while the first nanofiber coating is light, thin, flexible, and has an intersecting network structure with many pores. Therefore, if the ratio of the areal density of the first ceramic coating to the areal density of the first nanofiber coating is too high, pore clogging occurs, resulting in high air permeability, high internal resistance, and poor heat resistance for the entire composite separator of a lithium-ion battery. In Example A1, the areal density ratio of the first ceramic coating to the first nanofiber coating is 2.5:1; in Example A16, the areal density ratio of the first ceramic coating to the first nanofiber coating is 6:1; and in Example A17, the areal density ratio of the first ceramic coating to the first nanofiber coating is 9.5:1. In Example A17, the areal density ratio was too high, so the resulting composite separator sample had high air permeability, high internal resistance, and poor heat resistance, while Examples A1 and A16 did not have such problems.

[0089] See Examples A1 and A18. In Example A18, a first ceramic coating and a second ceramic coating are formed on both sides of the base film, respectively, and the thickness and areal density of the first ceramic coating and the second ceramic coating are higher than those of Example A1. The separator of Example A18 has similar heat resistance, puncture strength, and cycle stability to those of Example A1.

[0090] See Examples A1 and A19. Example A19 is a preferred embodiment of the present invention, in which a first ceramic coating and a first nanofiber coating are formed sequentially from the inside to the outside on one side of the base film, and a second ceramic coating and a second nanofiber coating are formed sequentially from the inside to the outside on the other side of the base film. The composite separator sample of Example A19 exhibited a lower thermal shrinkage rate, a higher withstand voltage, a higher membrane rupture temperature, a higher puncture strength, a higher liquid absorption rate, and a higher liquid retention rate than the other examples. Furthermore, even after 500 charge-discharge cycles, the capacity retention rate of the composite separator sample of Example A19 exceeded 95%, demonstrating that forming a first nanofiber coating and a second nanofiber coating on both sides of the composite separator sample reliably improved the charge-discharge cycle stability of the composite separator sample.

[0091] Example A1 will be described below in comparison with Comparative Example A1. In Comparative Example A1, the first ceramic coating has a high surface density, resulting in a dense structure. This results in a composite separator sample with a higher overall thickness and surface density than Example A1. However, Comparative Example A1 has poor heat resistance, is prone to shrinkage due to heat generated during the battery charge / discharge process, and has a lower puncture strength than the composite separator sample of Example A1. Therefore, the composite separator sample of Comparative Example A1 has poor structural strength and is prone to breakage due to heat or punctures from lithium dendrites, causing the battery's positive and negative electrodes to come into contact with each other and resulting in a short circuit. In contrast, the composite separator sample of Example A1 stably transports lithium ions during the battery charge / discharge process and mechanically separates the positive and negative electrodes, thereby improving safety in use and maintaining service life.

[0092] Example A1 will be described below in comparison with Comparative Examples A2 and A3.

[0093] Nanofibers with high surface energy tend to aggregate and entangle in the polymer matrix. Therefore, whether the nanofiber slurry is applied directly to the base film or mixed with a ceramic slurry and then applied to the base film, the density distribution of the slurry becomes uneven, resulting in areas that are left uncoated. The nanofibers in the first nanofiber coating are not uniformly dispersed and aligned longitudinally, resulting in the first nanofiber coating failing to perform its function properly. Due to the poor heat resistance and load characteristics of the base film, if the first ceramic slurry or first nanofiber slurry does not completely coat the base film, the exposed surface layer of the base film is subject to heat and force, resulting in puncture, rupture, or breakage, and the base film loses its ability to separate the positive and negative electrodes. Furthermore, the base film is highly hydrophobic, which makes its surface less compatible with the electrolyte, hindering its ability to be fully wetted by the electrolyte. Therefore, if the first nanofiber coating does not completely cover the base film, the overall internal resistance of the composite separator sample will increase, adversely affecting the cycle characteristics and charge / discharge efficiency of the battery.

[0094] As described above, by appropriately selecting the coating materials and controlling the surface density when applying the coating, the first nanofiber coating can protect the first ceramic coating and base film, or the second nanofiber coating can protect the second ceramic coating and base film. Furthermore, the two-dimensional mesh-like porous structure can improve the liquid absorption and retention properties of the composite separator sample, allowing it to perform better when used in lithium-ion batteries.

[0095] Examples B1-B12 and Comparative Examples B1-B4 illustrate the effect of various properties of the nanofibers used in the layered structure on the performance parameters of the resulting composite separator samples.

[0096] Examples B1 to B12, Comparative Examples B1 to B4 The composite separators of Examples B1 to B12 and Comparative Examples B1 to B4 were all produced by the following steps, but the differences between them are shown in Tables 3 and 4.

[0097] (1) A dispersant (BYK Additives (Shanghai) Co., Ltd.) was added to deionized water and stirred at high speed for 10 minutes. Alumina ceramic powder with a mass concentration of 30% was added to the dispersion in two batches, and the mixture was stirred and pulverized uniformly to a mass ratio of dispersant to alumina ceramic powder of 1:100.

[0098] (2) Amphiphilic nanocellulose at a mass concentration of 4% was added to deionized water and stirred to obtain an amphiphilic nanofiber dispersion.

[0099] (3) The obtained amphiphilic nanofiber dispersion was added to the obtained ceramic powder dispersion and stirred to mix uniformly, thereby obtaining a mixed solution.

[0100] (4) A binder polyacrylamide (purchased from Hunan Gaorui Power Materials Co., Ltd.) was added to the mixed solution and stirred uniformly.

[0101] (5) A wetting agent (purchased from BYK Additives (Shanghai) Co., Ltd.) was added to the uniformly stirred solution, and the mixture was further stirred. Deionized water was then added to obtain a finished coating slurry with a wetting agent to dispersant ratio of 1:1.

[0102] (6) The resulting coating slurry was then applied using a gravure roller. The coating process used was a common industry standard, with the ceramic fibers coated on one side of the base film. A 7 μm thick PE film (purchased from Shanghai Enjie New Materials Technology Co., Ltd.) was used as the base film, resulting in a ceramic fiber coating thickness of 1.5 μm.

[0103] Table 3. Materials and parameters of composite separator JPEG2025527985000004.jpg200170

[0104] Table 4. Materials and parameters of composite separator JPEG2025527985000005.jpg119170

[0105] For testing the parameters of the composite separators of Examples B1 to B12 and Comparative Examples B1 to B4, the following methods were used.

[0106] Thickness The thickness of the composite separator is measured using a Mahr Millimar thickness gauge. The test method is as follows: Keep the measurement surface flat and measure 5 to 10 points along the MD direction, then average the measurements to obtain the thickness of the composite separator.

[0107] areal density Three test samples of the same area are cut out from the composite separator sample, and the thickness (H), area (S), and mass (m) of the samples are obtained using a weighing method. The areal density of the samples, ρ=m / (H×S), is calculated and averaged according to the standards specified in GB / T 6343-2009.

[0108] SEM A separator sample measuring 0.5 cm x 0.5 cm is cut out, attached to a sample stage with conductive adhesive, and placed in an ion sputtering device to spray with gold. The gold-sprayed separator sample is scanned and examined using a scanning electron microscope to take photographs of the coating morphology.

[0109] ventilation Using an EG01 Oken type air permeability tester, three points are selected, and the time t required for 100 ml of gas to permeate is measured and averaged.

[0110] moisture Three separator samples of approximately 0.1 g each were weighed and sealed in sample bottles. The sealed sample bottles were placed in a heating furnace and heated at 150°C for 300 seconds. Testing was then performed using a Karl Fischer moisture meter. After the test was completed, the measured values ​​of the three test samples were averaged.

[0111] Peel strength

[0112] Three 15mm wide samples were cut out from the test sample along the MD direction, and the cut test samples were attached to a glass slide with double-sided adhesive tape. The free end of the test sample was then folded 180°, and the adhesive surface was peeled off by hand for 20mm. The test was then carried out using a tensile tester, and the measured values ​​of the three test samples were averaged after the test was completed.

[0113] Tensile strength Five test samples, each 15 mm wide and 150 mm long, were cut out from the product (the test gauge for the sample was 100 mm). Measurements were taken using a microcomputer-controlled electronic universal (tensile) testing machine, CMT series, and after the test was completed, the measured values ​​of the five test samples were averaged. Puncture Strength

[0114] The diameter of the puncture needle is φ1.65 mm, and the tip SR is 0.5 mm. Three test samples of 5 cm x 5 cm or more are cut out from the product, fixed to the sample stage, and measured using an electronic puncture strength tester. After the test is completed, the measured values ​​of the three test samples are averaged.

[0115] Membrane rupture temperature Temperature-rising internal resistance method: A circular separator sample with a diameter of 50 mm is cut out and sealed in a mold filled with a conductive liquid. The mold containing the sample is placed in an oven and heated at a rate of 5°C / min. The change in internal resistance due to the temperature of the mold during the heating process is recorded.

[0116] Closure temperature Tc: The temperature at which the internal resistance value begins to increase significantly. Breakdown temperature Tb: The temperature at which the internal resistance value begins to decrease significantly.

[0117] Liquid absorption rate and liquid retention rate Three separator samples measuring 100mm x 100mm are cut out and weighed to determine their weight m0. The test sample is placed in the electrolyte and left sealed for 1 hour, then removed. The electrolyte on the sample's surface is wiped off with a clean wiper, and the weight m1 is weighed. The weighed sample is spread flat and left to stand at room temperature for 1 hour, after which the weight m2 is weighed. Here, the liquid absorption rate = ((m1 - m0)) / m0 x 100%, and the liquid retention rate = ((m2 - m0)) / m0 x 100%. After the test is completed, the measured values ​​of the three test samples are averaged.

[0118] Wettability Using a needle, 2 μL of the PC solution was taken and dropped onto the surface of the separator coating, and the MD and TD penetration sizes at 0 min and 5 min were measured and calculated at three points using an optical microscope.

[0119] contact angle Using a contact angle meter DSA, place a 2 µL drop of water on the separator-coated surface using a needle, take three points, stay for 5–15 s, measure the angle, and average it.

[0120] Heat shrink The test sample was cut to a size of 100mm x 100mm, marked in the MD and TD directions, sandwiched between two thick glass plates from the outside, baked in an oven at 150°C for 1 hour, removed, and measured using an optical projector after shrinkage in the MD / TD directions. The specific shrinkage rate was calculated using the following formula:

[0121] Lateral shrinkage MD: ΔM=(M1-M2) / M1×100%

[0122] Longitudinal shrinkage TD: ΔT = (T1 - T2) / T1 x 100%

[0123] In the above formula, M1, T1: initial length, unit: mm; M2, T2: final length, unit: mm. Internal Resistance Five separators were cut to fit the mold for the resistance test, and the separators were placed in a 1 mol / L solution of lithium hexafluorophosphate (LiPF6) and ethylene carbonate (EC), sealed, and immersed. One layer of the immersed separator was placed to test the AC impedance resistance, then another layer was placed and its AC impedance was tested, and five layers were placed to obtain five AC impedances. The horizontal axis represents the number of separator layers, and the vertical axis represents the separator resistance. The slope of the curve and the degree of linear fitting were calculated, and the slope when the degree of linear fitting was greater than 0.99 was taken as the separator impedance. This was done using a proprietary testing device, the Solatron analytical 1400 CellTest System. Three measurements were taken and averaged.

[0124] Table 5. Composite separator parameters and performance JPEG2025527985000006.jpg188170

[0125] Table 6. Parameters and performance of composite separator JPEG2025527985000007.jpg122170

[0126] Figure 6 is a scanning electron microscope image of the composite separator of Example B1. The coating of the composite separator contains particles and fibers, and the particles are distributed within the fiber network structure. This suggests that a ceramic fiber layer structure is obtained.

[0127] As can be seen from Tables 3-6, in Examples B1-B5, compared to Comparative Example B1, hydrophilic nanocellulose exhibited poor mechanical properties and thermal stability in the coating, poor wetting, and high moisture content. The separators exhibited poor puncture resistance, low rupture temperatures, and reduced wetting values. The reasons for this are as follows: Because the hydrophilic nanofibers have a large number of highly active hydroxyl groups on their surfaces, the material's internal hydrogen bonds are easily broken by the action of water molecules in a high-humidity environment, resulting in the destruction of the entire network structure and a sudden decline in mechanical properties. Furthermore, aqueous environments are unavoidable in the manufacturing and use processes of raw materials, which impacts performance and is unhelpful for coating application. They are also a major factor in separator bending and high moisture content. From the above, it is clear that the addition of amphiphilic nanofibers not only accelerates the wetting speed of the electrolyte, improves the degree of wetting, and increases the liquid absorption and retention rates, but also maintains the mechanical properties of the material in high humidity environments, enhances the puncture resistance of the fiber skeleton, and solves problems such as coating bending and high moisture content caused by the hydrophilicity of the raw materials. Furthermore, amphiphilic nanofibers act as a bridge between the hydrophilic alumina and the hydrophobic base film, improving the adhesion between the coating and the base film, reducing the amount of adhesive used, and contributing to a decrease in internal resistance.

[0128] As can be seen from Tables 3-6, comparing Examples B1-B5 with Comparative Example B2, the addition of amphiphilic nanofibers reduces the surface density of the coating compared to conventional ceramic separators. This allows for the formation of multiple heat-resistant layers at the same coating thickness. The resulting fiber skeleton provides support, improving the separator's heat resistance, membrane rupture temperature, puncture strength, tensile strength, and electrolyte wettability. The coating combines the performance advantages of the nanofibers themselves, such as their high heat resistance and high thermal decomposition temperature, with the structural advantages of high-aspect-ratio fibers forming a porous entangled network structure, which has polar molecules, strong interchain interactions, and intertwining fibers. The nanofibers' lightweight nature reduces the surface density of the coating, resulting in high heat resistance, lightweight, and thin separators.

[0129] As can be seen from Tables 3-6, comparing Examples B1-B5 with Comparative Example B3, nanofibers exhibit superior performance, but the higher the fiber content, the better the coating film performance. Comparative Example B3 met the heat resistance requirements, and due to its amphiphilic properties, the separator exhibited good wettability but poor coating properties. Because only nanofibers were present on the coating surface, their small particle size and dimensions meant that excessive density could lead to entanglement and clumping. The presence of hydroxyl groups on the surface of the fibers resulted in self-forming membranes, which could result in pore clogging and abnormal internal resistance, affecting the separator's basic physical properties. Therefore, blending fibers with ceramic particles is a suitable physical bonding method, reducing the fiber content in the coating slurry, smoothing fiber elongation, and preventing entanglement. The formation of a network-entangled structure facilitates ceramic particle filling, increasing pore space, and ensuring breathability. Fibers also have the advantages of improving heat resistance, puncture resistance, and tensile strength.

[0130] As can be seen from Tables 3 to 6, comparing Examples B1 to B5 with Comparative Example B4, hydrophobic nanocellulose reduces the peel strength between the coating and the base film in the coating, and also reduces the separator's liquid absorption and retention rates, resulting in poor electrolyte wettability. The reasons for this are as follows: Because the surface of the hydrophobic nanofibers contains a large amount of hydrophobic groups, the adhesion between the nanofibers and the base film is low. In thermal property tests (MD heat shrinkage and TD heat shrinkage), the coating's function of resisting base film shrinkage is difficult to achieve, resulting in poor separator heat shrinkability. Furthermore, the hydrophobic groups also reduce the electrolyte's wetting effect.

[0131] Comparing Examples B1 and B2, when the fiber aspect ratio is increased within a certain range, the higher the interaction due to fiber entanglement, the better the tensile strength of the composite coating. The physical entanglement between the nanofibers and between the nanofibers and the ceramic results in a denser arrangement. The denser the porous entangled structure formed by the fibers as the main framework, the stronger the mechanical support provided, the more puncture resistance it provides, and the lower the film rupture temperature.

[0132] Comparison of Examples B3, B4, and B2 revealed that amphiphilic nanofibers are key to improving the overall performance of the separator, and adjusting the proportion of amphiphilic nanofibers affects the separator's heat resistance, membrane rupture temperature, puncture strength, tensile strength, and wettability. When the mass ratio of amphiphilic nanofibers to ceramic powder is (6-10:100), the membrane surface has excellent density, and the separator's tensile strength and puncture resistance are all improved, increasing breathability and reducing internal resistance, thereby improving separator performance.

[0133] As can be seen from a comparison of Examples B5 to B7, the content of the water solvent in the coating slurry is approximately 90% by mass (estimated to be 85% to 92%), which gives the coating excellent applicability and high density, and the nanofibers easily spread in a plane, which contributes to the packing of the ceramic powder and improves the heat resistance, film rupture temperature, and puncture strength of the separator.

[0134] As can be seen from the results of Examples B5, B8, and B9, if the density A1 of the amphiphilic nanofibers is less than 1 / 2 × the density A2 of the ceramic powder, the coating has the advantages of being lighter and thinner. At this ratio, the nanofibers exhibit a good mesh-like porous structure, and the fibers are entangled to form pores, which shortens the ventilation time, reduces internal resistance, makes the pores less likely to clog, and improves the liquid absorption effect of the separator.

[0135] As a result of comparing Example B5 and Example B10, the higher the thermal decomposition temperature of the amphiphilic nanofiber, the more improved both the heat resistance and the membrane rupture temperature.

[0136] Comparing Example B5 and Example B11, the binder content was low, ranging from 1 wt% to 3 wt% (2.7% in Example B5). The addition of amphiphilic nanofibers increased the adhesion between the coating and the base film, allowing the binder content to be reduced to a certain extent, i.e., the amount of ceramic and amphiphilic nanofibers added could be increased. Because the polymer binder exhibits rigidity and brittleness, while the nanofibers exhibit flexibility and toughness, increasing the nanofiber content contributes to improving the separator's mechanical properties, such as tensile strength, and further improves the composite separator's liquid absorption. This avoids fiber entanglement and aggregation, which can be caused by adhesives with high surface energy, and is advantageous for application. Because the polymer adhesive exhibits rigidity and brittleness, while the fibers exhibit flexibility, increasing the fiber content improves mechanical properties, such as tensile strength, and also reduces internal resistance, shortens ventilation time, and improves heat resistance and liquid absorption.

[0137] Comparing Example B5 and Example B12, when the ceramic has a low D50 (within the length range of the amphiphilic nanofibers) and the same thickness, the smaller the particle size of the ceramic particles, the more layers can be stacked, and the more support layers and protective layers there are that act on the base membrane. In the porous skeleton of the nanofibers, the smaller the particle size of the ceramic particles, the lower the filling range, the greater the filling amount and filling thickness, the denser the membrane surface, and the better the overall properties of the composite separator.

[0138] As described above, by controlling the aspect ratio of the amphiphilic nanofibers and the ratio of nanofibers to ceramic, a lightweight, thin, heat-resistant coated separator can combine the performance and structural advantages of amphiphilic nanofibers with the heat resistance and breathability advantages of ceramics. In the above example, the aspect ratio of the amphiphilic nanocellulose is 50-125, and the mass ratio of amphiphilic nanofibers to alumina is (4-6:100). Taking into account both the performance advantages and structural properties of the material, the high-aspect-ratio nanofibers are oriented in the forward direction at the appropriate slurry concentration, forming an entangled network structure on the coating, which increases the bonding sites of the ceramic particles and contributes to the adhesion and packing of the ceramic particles. This provides strong support, resistance to puncture and tension, and an improved film rupture temperature, demonstrating the fiber's excellent heat resistance. The hydrophilic and lipophilic properties of the fiber not only promote wetting by the electrolyte and increase the liquid absorption rate and retention rate, but also enhance the adhesive strength between the coating and the polyolefin substrate, reducing the amount of adhesive required, which is advantageous for shortening the separator's ventilation time, lowering its internal resistance, and reducing moisture.

[0139] The above content relating to well-known content will not be described in detail, but can be understood by those skilled in the art. The above description is merely a few specific embodiments of the present invention and does not limit the present invention, and any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and principle of the present invention should be included in the protection scope of the present invention. The technical scope of the present invention is not limited to the content of the specification, but should be determined based on the scope of the claims.

Claims

1. A composite separator, 1. A composite separator comprising: a base membrane; a first nanofiber layer; and a ceramic powder, wherein the first nanofiber layer is located on a first side of the base membrane; and the ceramic powder forms a first ceramic coating located between the first nanofiber layer and the base membrane or is added to the first nanofiber layer.

2. 2. The composite separator of claim 1, wherein when the ceramic powder forms the first ceramic coating located between the first nanofiber layer and the base film, the first nanofiber layer includes nanofibers and a binder.

3. 3. The composite separator of claim 2, wherein when the ceramic powder forms the first ceramic coating located between the first nanofiber layer and the base film, the nanofibers are alternately stacked and connected to each other to form a two-dimensional network structure.

4. 3. The composite separator of claim 2, wherein the ceramic powder forms the first ceramic coating located between the first nanofiber layer and the base film; the nanofibers include one or more of barium dititanate nanowires, hydroxyapatite nanowires, calcium phosphate nanowires, calcium silicate nanowires, and carboxymethyl cellulose nanowires; and / or the binder includes one or more of polymethacrylates, polyacrylic acid amides, phenyl cinnamates, cinnamates, polyvinylidene fluoride, and polyvinyl alcohol; and / or the ceramic powder includes one or more of alumina, boehmite, barium titanate, silica, and inorganic magnesium hydroxide.

5. When the ceramic powder forms the first ceramic coating located between the first nanofiber layer and the base film, the areal density of the first nanofiber layer is 0.1 g / m ２ ~3g / m ２ and / or the areal density of the first ceramic coating is 0.5 g / m ２ ~3g / m ２ 2. The composite separator according to claim 1, wherein:

6. 6. The composite separator of claim 5, wherein when the ceramic powder forms the first ceramic coating located between the first nanofiber layer and the base film, the areal density ratio of the first ceramic coating to the first nanofiber layer is 6:1 or less.

7. When the ceramic powder forms the first ceramic coating located between the first nanofiber layer and the base film, the aspect ratio of the nanofibers is 20 to 100, and / or the particle diameter D50 of the nanofibers is 0.5 μm to 6.5 μm, and / or the specific surface area of ​​the nanofibers is 2 m ２ / g to 20m ２ 3. The composite separator of claim 2, wherein the tensile strength is 1 / g.

8. When the ceramic powder forms the first ceramic coating located between the first nanofiber layer and the base film, the particle diameter D50 of the ceramic powder is 0.3 μm to 1 μm, and / or the specific surface area of ​​the ceramic powder is 2 m ２ / g~12m ２ 3. The composite separator of claim 2, wherein the tensile strength is 1 / g.

9. 2. The composite separator of claim 1, wherein when the ceramic powder is added to the first nanofiber layer, the first nanofiber layer comprises amphiphilic nanofibers and the ceramic powder.

10. 10. The composite separator of claim 9, wherein when the ceramic powder is added to the first nanofiber layer, the amphiphilic nanofibers comprise one or more of amphiphilic nanocellulose, amphiphilic cellulose nanowhiskers, amphiphilic cellulose nanofilaments, and amphiphilic microfibrillated cellulose; and / or the ceramic powder comprises one or more of alumina, titanium oxide, boehmite, silicon nitride, boron carbide, and barium sulfate.

11. When the ceramic powder is added to the first nanofiber layer, the thermal decomposition temperature of the amphiphilic nanofiber is 275°C or more, and / or the density of the amphiphilic nanofiber is 1.6 g / cm ３ and / or the diameter of the amphiphilic nanofibers is 4 nm to 20 nm, and / or the length of the amphiphilic nanofibers is 100 nm to 500 nm, and / or the aspect ratio of the amphiphilic nanofibers is 5 to 125.

12. 10. The composite separator of claim 9, wherein when the ceramic powder is added to the first nanofiber layer, the particle size D50 of the ceramic powder is 100 nm to 1000 nm.

13. 10. The composite separator of claim 9, wherein when the ceramic powder is added to the first nanofiber layer, the mass ratio of the amphiphilic nanofiber to the ceramic powder is (1-20):100, and / or, when the density of the amphiphilic nanofiber is represented by A1 and the density of the ceramic powder is represented by A2, and A1 and A2 have the same unit, A1<1 / 2×A2.

14. 10. The composite separator of claim 9, wherein when the ceramic powder is added to the first nanofiber layer, the first nanofiber layer further comprises a binder.

15. 15. The composite separator of claim 14, wherein when the ceramic powder is added to the first nanofiber layer, the binder comprises one or more of polyacrylamide, polybutyl methacrylate, polyhydroxyethyl methacrylate, and polyvinyl alcohol.

16. 15. The composite separator of claim 14, wherein when the ceramic powder is added to the first nanofiber layer, the total mass of the ceramic powder and the amphiphilic nanofibers accounts for 95 wt % to 99 wt % of the mass of the first nanofiber layer.

17. 10. The composite separator of claim 9, wherein when the ceramic powder is added to the first nanofiber layer, the hydrophilic groups of the amphiphilic nanofibers include one or more of a hydroxy group, a carboxy group, an amino group, a quaternary amine group, an aldehyde group, a sulfonic acid group, and a phosphate group, and the lipophilic groups of the amphiphilic nanofibers include one or more of an alkyl group, a phenyl group, and a cycloalkyl group.

18. 2. The method for manufacturing a composite separator according to claim 1, comprising: a step (S1) of applying a slurry containing nanofibers to a first side of the base film; and a step (S2) of drying the slurry containing nanofibers to form the first nanofiber layer; and further comprising, before step (S1), a step (S01) of applying a slurry containing ceramic powder to the first side of the base film and a step (S02) of drying the slurry containing ceramic powder to form the first ceramic coating; or further comprising, before step (S1), a step (S0) of adding the ceramic powder to the slurry.

19. When step (S01) is included before step (S1), the aspect ratio of the nanofibers is 20 to 100, the particle diameter D50 of the nanofibers is 0.5 μm to 6.5 μm, and the specific surface area of ​​the nanofibers is 2 m ２ / g to 20m ２ / g and further comprising step (S0) before step (S1), the nanofibers are amphiphilic nanofibers.

20. A battery comprising a separator, the separator comprising the composite separator of claim 1.

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