Battery diaphragm, preparation method thereof and secondary battery

Abstract

The invention relates to a battery diaphragm, a preparation method thereof and a secondary battery, and belongs to the technical field of batteries. The battery diaphragm comprises a porous base membrane and a first two-dimensional lamellar material capable of conducting ions, pores of the porous base membrane are filled with the first two-dimensional lamellar material, and the plane direction of the first two-dimensional lamellar material is oriented and arranged in the thickness direction of the porous base membrane. The porous base membrane is filled with the two-dimensional lamellar material capable of conducting ions, and the orientation of the plane direction of the porous base membrane is controlled, so that the ion transmission performance of the battery diaphragm can be effectively improved, and the rate capability of the battery is further improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery separator, a preparation method thereof, and a secondary battery. Background Art

[0002] With the strong global demand for portable electronic products, unmanned equipment, energy storage systems and new energy vehicles, the market size of secondary batteries, as core energy storage components, is growing at an unprecedented rate. Secondary batteries have become a hot topic of current research due to their advantages such as high operating voltage, high energy density and long cycle life. However, the performance of secondary batteries depends largely on the performance of their key component, the diaphragm. An ideal diaphragm should have excellent ion permeability, good thermal stability and mechanical strength to ensure efficient and safe operation of the battery. However, existing diaphragms (such as polyolefin diaphragms) still have limitations in ion transport performance, thermal stability and mechanical properties, making it difficult to meet the growing demand for battery performance.

[0003] Existing research on the modification of diaphragms mainly involves setting a coating on the surface of the diaphragm. The coating materials include inorganic ceramic particles such as alumina and boehmite, or organic polymers such as polyvinylidene fluoride (PVDF). These material coatings can improve the mechanical strength, thermal stability and electrolyte wettability of the diaphragm to a certain extent, but the modification effect on the ion transmission performance is quite limited. In fact, the surface coating may even hinder ion transmission, thereby reducing the rate performance of the battery. Summary of the Invention

[0004] In response to the deficiencies of the prior art, the present application provides a battery separator and a preparation method thereof, and a secondary battery, so as to improve the ion transport performance of the existing battery separator, thereby improving the rate performance of the battery.

[0005] In a first aspect, an embodiment of the present application provides a battery separator, comprising a porous base membrane and a first two-dimensional sheet material capable of conducting ions, wherein the first two-dimensional sheet material is filled in the pores of the porous base membrane, and the planar direction of the first two-dimensional sheet material is oriented in the thickness direction of the porous base membrane.

[0006] In the above technical solution, since the two-dimensional sheet material has ion-conducting properties, and the ion conduction characteristics in the plane direction (corresponding to the crystal a-axis and b-axis) are significantly stronger than those in the thickness direction (corresponding to the crystal c-axis), in this application, by filling the pores of the porous base membrane with a two-dimensional sheet material that can conduct ions and controlling its plane direction to be oriented in the thickness direction of the porous base membrane, the ion transmission path inside the battery separator can be optimized, and the ion transmission efficiency of the battery separator can be effectively improved, thereby improving the rate performance of the battery. Moreover, since the two-dimensional sheet material also has thermal conductivity, it is also beneficial to the heat diffusion inside the battery separator, which can reduce the thermal shrinkage of the battery separator, thereby improving the safety performance of the battery. In addition, filling the two-dimensional sheet material in the pores of the porous base membrane can also improve the mechanical strength of the battery separator to a certain extent, enhance the wettability of the electrolyte, thereby reducing the internal resistance of the battery, improving the cycle performance of the battery, and further improving safety.

[0007] In some embodiments, the first two-dimensional sheet material can be oriented under the action of an electric field, so that the orientation of the first two-dimensional sheet material can be achieved by applying an electric field. Compared with orientation methods such as lamination orientation, the application of an electric field can effectively maintain the pore structure in the battery separator.

[0008] In some embodiments, the first two-dimensional sheet material includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide, or boron nitride. These two-dimensional sheet materials all have excellent ion conductivity and are conducive to achieving fast ion transport.

[0009] In some embodiments, the boron nitride comprises at least one of hexagonal boron nitride or cubic boron nitride. Hexagonal boron nitride and cubic boron nitride, which have insulating properties, have excellent ion and thermal conductivity as two-dimensional sheet materials. In addition, the ion conductivity and / or thermal conductivity of hexagonal boron nitride in the plane direction (corresponding to the crystal a-axis and b-axis) is approximately 20 times that of the thickness direction (corresponding to the crystal c-axis), thereby effectively improving ion transmission efficiency.

[0010] In some embodiments, the pores of the porous base membrane are further filled with solid electrolyte particles. Solid electrolyte particles have high ionic conductivity and low electronic conductivity and can suppress thermal shrinkage and deformation of the separator. Filling the pores of the separator with both the first two-dimensional sheet material and the solid electrolyte particles can further improve ion transmission rate and thermal stability.

[0011] In some embodiments, the first two-dimensional sheet material is boron nitride. Boron nitride has electrical insulation and excellent ion and thermal conductivity. The two-dimensional sheet structure is anisotropic and can provide effective ion and heat transfer channels after being oriented by an electric field.

[0012] In some embodiments, the diameter of the first two-dimensional sheet material is smaller than the pore size of the porous base membrane. By controlling the two-dimensional sheet material and the pore size, the two-dimensional sheet material can be easily spread in the pores, further improving the ion transport efficiency of the battery separator.

[0013] In some embodiments, the average sheet diameter of the first two-dimensional sheet material is between 10 nm and 10 μm, and the average pore diameter of the porous base membrane is between 20 nm and 20 μm. By controlling the average pore diameter of the porous base membrane within a suitable range, filling of the two-dimensional sheet material is facilitated without significantly reducing the mechanical strength of the separator. Furthermore, maintaining the average sheet diameter of the two-dimensional sheet material within a suitable range allows for efficient filling while maintaining ion conductivity.

[0014] In some embodiments, the porous base membrane has a thickness of 3 μm to 30 μm and a porosity of 30% to 80%. By controlling the thickness and porosity of the porous base membrane within an appropriate range, the battery separator can be guaranteed to have sufficient mechanical strength and thermal stability while improving ion transmission efficiency and reducing internal resistance within the battery, thereby ensuring the safety performance, rate performance, and cycle performance of the battery separator.

[0015] In some embodiments, at least one surface of the porous base membrane is provided with a functional coating comprising a second two-dimensional sheet material capable of conducting ions. This functional coating can further enhance the mechanical strength of the battery separator, reduce thermal shrinkage, and improve wettability, thereby further reducing the battery's internal resistance and enhancing the battery's cycling performance and safety.

[0016] In some embodiments, the functional coating further includes solid electrolyte particles. Solid electrolyte particles have high ionic conductivity and low electronic conductivity and can suppress thermal shrinkage and deformation of the separator. Coating the two-dimensional sheet material and solid electrolyte particles on the surface of the separator can further improve ion transmission rate and thermal stability.

[0017] In some embodiments, the thickness of the functional coating is 1 μm to 10 μm. By controlling the thickness of the functional coating within a suitable range, it is possible to avoid a reduction in ion transmission efficiency due to excessive thickness.

[0018] In some embodiments, the planar direction of the second two-dimensional sheet material is oriented along the thickness direction of the porous base membrane. By aligning the second two-dimensional sheet material in the functional coating along the thickness direction of the porous base membrane, it can further optimize the ion transport path and improve ion transport efficiency by coordinating with the first two-dimensional sheet material in the pores.

[0019] In some embodiments, the plane direction of the second two-dimensional sheet material is oriented in the plane direction of the porous base membrane. Orienting the two-dimensional sheet material in the functional coating along the plane direction of the porous base membrane facilitates heat diffusion perpendicular to the thickness of the battery separator, further reducing thermal shrinkage of the battery separator and facilitating rapid heat dissipation in the event of localized overheating, thereby improving battery safety.

[0020] In some embodiments, the second two-dimensional sheet material can be oriented under the action of an electric field, so that the orientation of the second two-dimensional sheet material can be achieved by applying a DC electric field. Compared with other orientation methods such as lamination orientation, the application of an electric field can effectively maintain the pore structure in the battery separator.

[0021] In some embodiments, the second two-dimensional sheet material includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide, or boron nitride. These two-dimensional sheet materials all have excellent ion conductivity and thermal conductivity.

[0022] In some embodiments, the boron nitride comprises at least one of hexagonal boron nitride or cubic boron nitride. Hexagonal boron nitride and cubic boron nitride, which have insulating properties, have excellent ion and thermal conductivity as two-dimensional sheet materials. The ion conductivity and / or thermal conductivity of hexagonal boron nitride in the plane direction (corresponding to the crystal a-axis and b-axis) is approximately 20 times that of the thickness direction (corresponding to the crystal c-axis), thereby effectively improving ion transmission efficiency and heat diffusion.

[0023] In some embodiments, the functional coating comprises two or more stacked sub-coatings, at least one of which comprises a second two-dimensional sheet material. By stacking two or more sub-coatings, in addition to the second two-dimensional sheet material, conventional solid electrolyte coatings, inorganic ceramic coatings, polymer coatings, nanofiber coatings, etc. can be added, depending on actual application needs, to further improve the overall performance of the battery separator.

[0024] In a second aspect, an embodiment of the present application provides a method for preparing a battery separator, comprising the following steps:

[0025] Filling the pores of the porous base membrane with a first slurry to obtain a prefabricated diaphragm; wherein the first slurry comprises a first two-dimensional sheet material capable of conducting ions, a binder, and a solvent;

[0026] A first direct current electric field is applied to the prefabricated separator so that the plane direction of the first two-dimensional sheet material is oriented in the thickness direction of the porous base membrane to obtain a battery separator.

[0027] In the above technical solution, since the two-dimensional sheet material has anisotropy, it can be oriented and arranged under the action of an electric field. The present application prepares a modified battery separator by filling the pores of a porous base membrane with a first two-dimensional sheet material, and then applying an electric field so that the plane direction is oriented and arranged in the thickness direction of the porous base membrane, and the preparation method is simple. By utilizing the excellent ion conductivity of the first two-dimensional sheet material in the plane direction, the ion transmission path inside the battery separator can be optimized, the ion transmission efficiency can be improved, and the rate performance of the battery can be improved. Moreover, since the two-dimensional sheet material also has excellent thermal conductivity, it is also beneficial to the heat diffusion inside the battery separator, which can reduce the thermal shrinkage of the battery separator, thereby improving the safety performance of the battery. In addition, filling the pores of the porous base membrane can also improve the mechanical strength of the battery separator to a certain extent, enhance the wettability of the electrolyte, thereby reducing the internal resistance of the battery, improving the cycle performance of the battery, and further improving the safety performance.

[0028] In some embodiments, the first two-dimensional sheet material includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide, or boron nitride; optionally, the boron nitride includes at least one of hexagonal boron nitride or cubic boron nitride. These first two-dimensional sheet materials, particularly boron nitride, have anisotropic ion conductivity. When the planar orientation of the first two-dimensional sheet materials is aligned along the thickness of the porous base membrane, the ion transport efficiency of the battery separator can be effectively improved.

[0029] In some embodiments, the first slurry further includes solid electrolyte particles. Solid electrolyte particles have high ionic conductivity and low electronic conductivity and can suppress thermal shrinkage and deformation of the separator. Adding solid electrolyte particles to the first slurry and filling them into the pores of the separator can further increase the ion transfer rate and further improve the thermal stability of the battery separator, thereby improving the rate performance and safety of the battery.

[0030] In some embodiments, the conditions for applying a first DC electric field to the prefabricated membrane include: placing the prefabricated membrane between two parallel plates of opposite polarity, applying a voltage of 800V to 1200V to the prefabricated membrane via a DC power supply, and treating the prefabricated membrane for 12 to 20 hours. Optionally, the direction of the first DC electric field is switched every 3 to 5 hours. By applying a unidirectional DC electric field to the prefabricated membrane and controlling the applied voltage and treatment time, the two-dimensional sheet material can be reoriented and positioned along the direction of the electric field. Switching the direction of the electric field can also result in a more uniform distribution of the two-dimensional sheet material.

[0031] In some embodiments, the first two-dimensional sheet material in the first slurry is prepared by mixing the first two-dimensional sheet material with a dispersant, ball milling, and drying, such that the average sheet diameter of the first two-dimensional sheet material is smaller than the average pore diameter of the porous base membrane. Pre-treating the two-dimensional sheet material allows for uniform dispersion and effectively controls the particle size range.

[0032] In some embodiments, after the first slurry is filled into the pores of the porous base membrane, a drying step is further included; optionally, the drying temperature is 60°C to 80°C and the drying time is 4 hours to 24 hours. Drying can prevent the slurry from flowing and can initially position the two-dimensional sheet material.

[0033] In some embodiments, the average pore size of the porous base membrane is 20 nm to 20 μm, and the average sheet size of the first two-dimensional sheet material is 10 nm to 10 μm. By controlling the average sheet size of the porous base membrane and the first two-dimensional sheet material within a suitable range, the first two-dimensional sheet material can be more easily and more fully filled into the pores of the porous base membrane, thereby further improving ion transport efficiency. Furthermore, a suitable average pore size of the porous base membrane ensures sufficient mechanical strength for the battery separator. Furthermore, a suitable average sheet size of the first two-dimensional sheet material can further enhance ion transport performance.

[0034] In some embodiments, the preparation method further includes applying a second slurry to at least one surface of the porous base membrane, which is dried to form a functional coating. The second slurry comprises a second 2D sheet material capable of conducting ions, a binder, and a solvent. The functional coating further enhances the mechanical strength and thermal stability of the battery separator and improves its wettability, thereby enhancing the electrochemical performance and safety of the battery.

[0035] In some embodiments, the preparation method further includes applying a second DC electric field to the functional coating to orient the second two-dimensional sheet material in the plane of the porous base membrane; wherein the second DC electric field is perpendicular to the first DC electric field. By applying the second DC electric field separately to the functional coating, the two-dimensional sheet material in the functional coating is oriented in the plane of the porous base membrane, which facilitates heat diffusion perpendicular to the thickness of the battery separator and facilitates rapid heat dissipation in the event of local overheating in the battery, thereby improving battery safety.

[0036] In a third aspect, an embodiment of the present application further provides a secondary battery, comprising the battery separator of the first aspect or the battery separator prepared by the preparation method of the second aspect.

[0037] In the above technical solution, since the battery separator has fast ion transport performance, high mechanical strength and thermal stability, the secondary battery has excellent rate performance, cycle performance and safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 A schematic cross-sectional view of a battery separator provided in an embodiment of the present application.

[0040] Figure 2 A process flow chart of a method for preparing a battery separator provided in an embodiment of the present application.

[0041] Figure 3 A schematic cross-sectional view of another battery separator provided in an embodiment of the present application.

[0042] Figure 4 Schematic diagram of a device for applying a first DC electric field to a prefabricated diaphragm in an embodiment of the present application.

[0043] Figure 5 A schematic cross-sectional view of another battery separator provided in an embodiment of the present application.

[0044] Figure 6 A schematic cross-sectional view of another battery separator provided in an embodiment of the present application.

[0045] Figure 7 Schematic diagram of a device for applying a second DC electric field to a prefabricated diaphragm in an embodiment of the present application.

[0046] Description of reference numerals:

[0047] 10-porous base membrane; 12-pores; 14-first two-dimensional sheet material; 16, 24-solid electrolyte particles; 20-functional coating; 22-second two-dimensional sheet material; A-DC power supply; B-plate; x-plane direction; z-thickness direction. DETAILED DESCRIPTION

[0048] Below, the battery separator of the present application, the method for preparing the battery separator, and the embodiment of the secondary battery including the battery separator are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0049] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0051] In existing research, the main method for modifying battery separators is to set a coating on the surface of the separator. The coating materials include inorganic ceramic particles such as alumina and boehmite, or organic polymers such as polyvinylidene fluoride (PVDF). These material coatings can improve the mechanical strength, thermal stability and electrolyte wettability of the separator to a certain extent, but the modification effect on the ion transmission performance is quite limited, and the surface coating may even hinder the transmission of ions.

[0052] Based on this, an embodiment of the present application provides a battery separator, which includes a porous base membrane and a first two-dimensional sheet material capable of conducting ions. The first two-dimensional sheet material is filled in the pores of the porous base membrane, and the planar direction of the first two-dimensional sheet material is oriented in the thickness direction of the porous base membrane.

[0053] In this application, the term "two-dimensional sheet material" refers to a class of very thin materials in which electrons can only move freely in two dimensions, usually only one or a few layers of atoms thick, and usually including three crystal axes, respectively referred to as the a-axis, b-axis and c-axis. Among them, the a-axis and the b-axis are perpendicular to each other, corresponding to the length and width of the crystal, respectively, and the plane direction formed by the two constitutes the plane direction described in this application; the c-axis is perpendicular to both the a-axis and the b-axis and usually represents the height or thickness direction of the crystal. Two-dimensional sheet materials have excellent anisotropic mechanical, electrical, optical, thermal and other physical and chemical properties, and the performance in the plane direction (i.e., the plane formed by the a-axis and the b-axis) is far better than the performance in the thickness / height direction (i.e., the c-axis). Moreover, because the two-dimensional sheet material has an ultra-thin layered structure and a large aspect ratio as well as a high specific surface area and rich surface functional groups, ions can move more easily between and inside the sheets, thereby facilitating the transmission of ions on the surface and inside the material. That is, the two-dimensional sheet material has excellent ion conductivity along its plane direction. Furthermore, the plane direction in the present application may specifically refer to the length direction (ie, the a-axis) of the two-dimensional sheet material.

[0054] In this application, "oriented arrangement" refers to the specific arrangement of the first two-dimensional sheet material in the porous base membrane, and "the planar direction of the first two-dimensional sheet material is oriented in the thickness direction of the porous base membrane" means that in the pores of the porous base membrane, the planar direction of the first two-dimensional sheet material is (or mostly) arranged along the thickness direction of the porous base membrane, and the angle between the planar direction of the first two-dimensional sheet material and the thickness direction of the porous base membrane is within 30°. Furthermore, the planar direction of the first two-dimensional sheet material is parallel to the thickness direction of the porous base membrane.

[0055] Since the two-dimensional sheet material has ion conductivity, and the ion conductivity in the plane direction (corresponding to the crystal a-axis and b-axis) is significantly stronger than that in the thickness direction (corresponding to the crystal c-axis), the present application can optimize the ion transmission path by filling the pores of the porous base membrane with the first two-dimensional sheet material that can conduct ions and orienting its plane direction along the thickness direction of the diaphragm, thereby effectively improving the ion transmission efficiency of the battery diaphragm and thus improving the rate performance of the battery. Moreover, since the two-dimensional sheet material also has thermal conductivity, it is also beneficial to the heat diffusion inside the diaphragm, reducing the thermal shrinkage of the diaphragm, thereby improving the safety performance of the battery. In addition, filling the first two-dimensional sheet material in the pores of the porous base membrane can also improve the mechanical strength of the battery diaphragm to a certain extent, enhance the wettability of the electrolyte, thereby reducing the internal resistance of the battery, improving the cycle performance of the battery, and further improving safety.

[0056] The following is a further detailed description of the preparation method of the battery separator.

[0057] Figure 1 This is a schematic cross-sectional view of a battery separator provided in an embodiment of the present application. Figure 1 The battery separator includes a porous base membrane 10 and a first two-dimensional sheet material 14 capable of conducting ions. The first two-dimensional sheet material 14 is filled in the pores 12 of the porous base membrane 10, and the plane direction of the first two-dimensional sheet material 14 is arranged in the z-oriented direction of the thickness direction of the porous base membrane 10.

[0058] Figure 2 This is a process flow chart of a method for preparing a battery separator provided in an embodiment of the present application. Figure 1 and Figure 2 , the preparation method comprises the following steps:

[0059] S10: Filling the pores 12 of the porous base membrane 10 with a first slurry to obtain a prefabricated diaphragm; wherein the first slurry includes a first two-dimensional sheet material 14 capable of conducting ions, a binder, and a solvent.

[0060] In some embodiments, the porous base membrane 10 can be a commercially available polyolefin base membrane or an industrially prepared polyolefin base membrane, including a polyethylene base membrane, a polypropylene base membrane, a polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite membrane, polyimide (PI), polyethylene terephthalate (PET), non-woven fabric, aramid, etc.

[0061] In some embodiments, the thickness of the porous base membrane 10 may be 3 μm to 30 μm, for example, 3 μm, 5 μm, 10 μm, 12 μm, 15 μm, 20 μm, 25 μm, 30 μm, etc.

[0062] In some embodiments, the average pore size of the pores 12 in the porous base membrane 10 is 20 nm to 20 μm, for example, 20 nm, 50 nm, 100 nm, 500 nm, 1 μm, 10 μm, 20 μm, etc.

[0063] In some embodiments, the porosity of the porous base membrane 10 is 30% to 80%, for example, 30%, 40%, 50%, 60%, 70%, 80%, etc.

[0064] Porosity refers to the percentage of the total volume of pores in the porous base membrane to the total volume of the porous base membrane in its natural state. Common testing methods in the art can be used to determine the average pore size and porosity of the porous base membrane 10. For example, the average pore size and porosity of the porous base membrane 10 can be measured according to the standard GB / T 21650.1-2008, "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion and Gas Adsorption."

[0065] The porous base film 10 has a plane direction x and a thickness direction z perpendicular to the plane direction x. In the embodiment of the present application, the pores 12 may be a honeycomb network structure or a straight through hole structure parallel to the thickness direction z.

[0066] In some embodiments, the first two-dimensional sheet material 14 can be oriented under the action of an electric field.

[0067] The phrase "capable of aligning under the action of an electric field" means that the first two-dimensional sheet material can be polarized and charged under the action of an electric field, and can then be induced to move under electrophoresis so that the plane direction is roughly parallel to the direction of the electric field, i.e., aligned along the direction of the electric field. By controlling the target direction to be parallel to the direction of the electric field, the first two-dimensional sheet material 14 can be oriented in a specific direction.

[0068] In some embodiments, the first two-dimensional sheet material 14 includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide, or boron nitride, wherein the boron nitride includes at least one of hexagonal boron nitride and cubic boron nitride.

[0069] Furthermore, the first two-dimensional sheet material 14 is boron nitride. Further still, the first two-dimensional sheet material 14 is hexagonal boron nitride.

[0070] In some embodiments, the average sheet diameter of the first two-dimensional sheet material 14 is smaller than the average pore diameter of the porous base membrane 10. The average sheet diameter of the first two-dimensional sheet material 14 is 10 nm to 10 μm, for example, 10 nm, 50 nm, 100 nm, 500 nm, 1 μm, 5 μm, 10 μm, etc.

[0071] The sheet diameter refers to the length or width of the two-dimensional sheet material, typically taking the larger value of the length or width. The average sheet diameter refers to the average sheet diameter of the first two-dimensional sheet material 14 filled in the pores 12. The sheet diameter of the two-dimensional sheet material can be measured using an AFM (Atomic Force Microscope), a SEM (Scanning Electron Microscope), a TEM (Transmission Electron Microscope), an STM (Scanning Tunneling Microscope), or the like, and statistically analyzed using statistical analysis software (e.g., Image J software) to obtain the average sheet diameter.

[0072] In some embodiments, the first slurry may further include solid electrolyte particles 16 .

[0073] The solid electrolyte particles 16 may include at least one of an oxide solid electrolyte, a sulfide solid electrolyte, a polymer solid electrolyte, or a halide solid electrolyte.

[0074] Among them, oxide solid electrolytes can be classified into crystalline and glassy (amorphous) types according to their material structures. Crystalline electrolytes include perovskite type, NASICON type, LISICON type, garnet type, etc., and glassy oxide electrolytes such as LiPON type electrolytes. As an example, oxide solid electrolytes can include Li 3.3 La 0.56 TiO3, LiTi2(PO4)3, Li 14 Zn(GeO4)4, Li7La3Zr2O 12 , Li 1+x Al x Ti 2-x (PO4)3 (0 < x < 2), Li 7-a La3Zr 2-a MaO 12 (M = Ta, Nb; 0 < a < 2), Li b La 2 / 3-b TiO3 (0 < b < 2), LiAlO2, Li2ZrO3 and Li4Ti5O 12 at least one of.

[0075] As an example, the oxide solid electrolyte can be lithium aluminum titanium phosphate (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, abbreviated as LATP), lanthanum lithium titanate (Li 3.3 La 0.56 TiO3, abbreviated as LLTO), lithium lanthanum zirconium oxide (Li7La3Zr2O 12 , abbreviated as LLZO), etc.

[0076] Among them, sulfide solid electrolytes can include lithium and sulfur, and can further include other elements. For example, they can include at least one of elements such as P, Si, Ge, Sn, Al, etc. Specifically, the general structural formula of sulfide solid electrolytes can be expressed as yLi2S - (100 - y)LS, where 0 < y < 100, and the LS can be one or more of substances such as P2S5, SiS2, GeS2, SnS2, Al2S3, etc. The solid electrolyte systems formed by them can be one or more of systems such as Li2S - P2S5 system, Li2S - SiS2 system, Li2S - GeS2 system, Li2S - SnS2 system, Li2S - Al2S3 system. The state of the sulfide solid electrolyte can be crystalline, amorphous or a composite state of crystalline - amorphous.

[0077] As an example, sulfide solid electrolytes include Li 10 GeP2S12 、Li6PS5Cl、Li 10 SnP2S 12 , at least one of Li2S-P2S5, Li2S-SiS2 and Li2S-B2S3.

[0078] Among them, the polymer solid electrolyte (SPE) is composed of a polymer matrix (such as polyester, polyenzyme and polyamine, etc.) and a metal salt (such as LiClO4, LiAsF4, LiPF6, LiBF4, etc.). The polymer matrix can be selected from at least one of polyester, polyenzyme and polyamine, and the lithium salt can be selected from at least one of LiClO4, LiAsF4, LiPF6, LiBF4.

[0079] Common SPEs include polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene oxide (PPO), polyvinylidene chloride (PVDC), and single-ion polymer electrolytes.

[0080] Among them, halide solid electrolyte is a kind of solid compound composed of halide ions (such as fluoride ions, chloride ions, etc.) and metal ions (such as lithium ions, sodium ions, etc.). As an example, halide solid electrolyte may include Li3YC l6 、Li3ErC l6 , at least one of Li3YBr6, Li3InBr6 or Li3InCl6.

[0081] In some embodiments, the binder may include at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), an acrylic copolymer, a styrene-acrylic copolymer, or a vinylidene fluoride-hexafluoropropylene copolymer.

[0082] Among them, the mass ratio of the binder to the first two-dimensional sheet material 14 (or a mixture of the first two-dimensional sheet material 14 and the solid electrolyte particles 16) can be (1:7.33) to (1:1), for example, 1:1, 1:2, 1:5, 1:7, etc.

[0083] In some embodiments, the solvent may be one of N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

[0084] In some embodiments, the solid content of the first slurry is 30% to 60%, for example, 30%, 40%, 50%, 60%, etc.

[0085] The first slurry may be prepared by mixing and stirring the first ion-conducting two-dimensional sheet material 14, a binder, and a solvent, preferably at 1000 rpm for 24 hours.

[0086] In some embodiments, before forming the first slurry, the process may further include: mixing the first two-dimensional sheet material 14 with a dispersant, ball milling, and drying, so that the average sheet diameter of the first two-dimensional sheet material 14 is smaller than the average pore diameter of the porous basement membrane 10. Furthermore, the two-dimensional sheet material and the dispersant are mixed at a mass ratio of 1:5, wherein the dispersant may be in excess, and zirconium oxide beads (1 mm:2 mm:5 mm mass ratio of 1:1:1) are added. The mixture is placed in a ball milling jar and stirred uniformly. The mixture is then placed in a ball mill and ball milled at 300 rpm for 1 hour. The ball-milled slurry is filtered through a 300-mesh screen and then dried in a 55°C oven for 6 hours to obtain the first two-dimensional sheet material 14.

[0087] The dispersant may be a commonly used anhydrous organic solvent, such as anhydrous ethanol, anhydrous methanol, N,N-dimethylformamide (DMF), etc. The dispersant is preferably anhydrous ethanol, which is low in cost and easy to evaporate.

[0088] In some embodiments, the method for filling the pores 12 of the porous base membrane 10 with the first slurry can be vacuum coating under negative pressure, specifically comprising: applying a vacuum on one side of the porous base membrane 10 to place the pores 12 under negative pressure, and coating the first slurry on the other side of the porous base membrane 10 so that the first slurry enters the pores 12 under the action of the negative pressure. Preferably, the micro-dimpled coating method plus vacuum coating is used.

[0089] In some embodiments, after the first slurry is filled into the pores 12 of the porous base membrane 10 , the prefabricated separator is further dried. The drying conditions include: baking at 60° C. to 80° C. for 4 to 24 hours, for example, baking at 80° C. for 12 hours.

[0090] See Figure 3 After the first slurry fills the pores 12 of the porous base membrane 10, a second slurry may be applied to one or both sides of the porous base membrane 10 to form a functional coating 20. The second slurry includes a second two-dimensional sheet material 22 capable of conducting ions, a binder, and a solvent.

[0091] In some embodiments, the second two-dimensional sheet material 22 includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide, or boron nitride. The boron nitride may include at least one of hexagonal boron nitride and cubic boron nitride. Furthermore, the second two-dimensional sheet material 22 is boron nitride.

[0092] The second two-dimensional sheet material 22 may be the same as or different from the first two-dimensional sheet material 14. It is understood that when the second two-dimensional sheet material 22 is the same as the first two-dimensional sheet material 14, the first slurry may be directly coated on the surface of the porous basement membrane 10 to form the functional coating 20 while the first slurry fills the pores 12 of the porous basement membrane 10.

[0093] Any method that can achieve uniform coating can be used, including knife coating, dip coating, curtain coating, spray coating, etc. Furthermore, the functional coating 20 is coated by micro-dimpled coating.

[0094] In some embodiments, the second slurry may further include solid electrolyte particles 24. The type of solid electrolyte particles 24 may be the same as that of the solid electrolyte particles 16.

[0095] It should be noted that the functional coating 20 may include two or more stacked sub-coatings, as long as at least one sub-coating includes the second two-dimensional sheet material 22. Other sub-coatings can be selected as needed to contain solid electrolyte particles 24, inorganic ceramic particles such as alumina and boehmite, or organic polymers such as PVDF, nanofibers, etc.

[0096] As an example, the functional coating 20 may include a first sub-coating (not shown) and a second sub-coating (not shown) stacked in sequence on the surface of the porous base membrane 10, wherein the first sub-coating includes a second two-dimensional sheet material 22, and the second sub-coating includes solid electrolyte particles 24. The first sub-coating may be the surface of one side of the porous base membrane 10, or the second sub-coating may be the surface of one side of the porous base membrane 10.

[0097] In some embodiments, the thickness of the functional coating 20 may be 1 μm to 10 μm, for example, 1 μm, 2 μm, 5 μm, 7 μm, 10 μm, etc.

[0098] S20: applying a first direct current electric field to the prefabricated separator so that the plane direction of the first two-dimensional sheet material 14 is arranged in a z-orientation in the thickness direction of the porous base membrane 10 to obtain a battery separator.

[0099] See Figure 4 The conditions for applying the first DC electric field to the prefabricated diaphragm may include: placing the prefabricated diaphragm between two plates B with opposite polarities in a parallel direction, applying a voltage of 800V to 1200V between the two plates B through a DC power supply A to form a unidirectional DC electric field, and treating for 12h to 20h.

[0100] Furthermore, the direction of the electric field is switched every 3 to 5 hours. For example, the treatment is carried out at a voltage of 1000 V for 16 hours, and the two plates B are swapped every 4 hours to switch the direction of the electric field.

[0101] The DC power supply A is a high-voltage DC control power supply that can provide a high voltage of 1000V or above and can change polarity at regular intervals. The electrode plates B can be made of stainless steel, with a spacing of 180mm between the two electrode plates.

[0102] See Figure 3When the functional coating 20 is also formed on the surface of the porous base membrane 10, the planar direction of the second two-dimensional sheet material 22 is also arranged in the z-orientation along the thickness direction of the porous base membrane 10. In this case, the orientation of the second two-dimensional sheet material 22 can further improve the ion transport rate of the battery separator, while the functional coating 20 can also improve the mechanical properties and electrolyte wettability of the battery separator.

[0103] "Electrolyte wettability" refers to the ability of the electrolyte to spread and penetrate the surface of the battery separator. Good wettability allows the electrolyte to quickly and evenly penetrate the pores of the separator, thereby reducing the battery's internal resistance and improving the battery's charge and discharge efficiency and overall performance. The provision of the functional coating 20 effectively enhances the electrolyte wettability of the battery separator.

[0104] In other embodiments, the functional coating layer 20 may be formed after step S20 . That is, after step S20 , the process further includes: coating a second slurry on one or both sides of the porous base membrane 10 to form the functional coating layer 20 .

[0105] It can be understood that by applying the second slurry after applying the first DC electric field, the second two-dimensional sheet material 22 can be oriented at different times from the first two-dimensional sheet material 14. The second two-dimensional sheet material 22 can be arranged in a non-oriented manner or in an oriented direction different from that of the first two-dimensional sheet material 14.

[0106] See Figure 5 In some embodiments, the battery separator includes a functional coating 20 comprising a second two-dimensional sheet material 22 and solid electrolyte particles 24. The second two-dimensional sheet material 22 may be randomly distributed. In this case, due to the excellent ion and thermal conductivity of the second two-dimensional sheet material 22, the ion transport rate and thermal stability of the battery separator can be improved to a certain extent. Furthermore, the functional coating 20 can improve the mechanical properties and electrolyte wettability of the battery separator.

[0107] In some embodiments, the preparation method may further include: Figure 6 and Figure 7 , a second DC electric field is applied to the functional coating 20 so that the planar direction of the second two-dimensional sheet material 22 is oriented in the planar direction x of the porous base membrane 10 .

[0108] The conditions for applying the second DC electric field may include: placing a prefabricated separator having a functional coating 20 on its surface perpendicular to two electrode plates B, aligning the electrode plates B with the functional coating 20, and applying a voltage of 800-1200V to the functional coating 20 via a DC power supply for 12-20 hours. Optionally, the direction of the electric field may be switched every 3-5 hours.

[0109] It can be understood that the electric field directions of the second DC electric field and the first DC electric field are perpendicular to each other.

[0110] Among them, "the planar direction of the second two-dimensional sheet material 22 is oriented in the planar direction x of the porous base membrane 10" means that in the functional coating 20, the planar direction of the second two-dimensional sheet material 22 is (or most of) arranged along the planar direction x of the porous base membrane 10, and the angle between the planar direction of the second two-dimensional sheet material 22 and the planar direction x of the porous base membrane 10 is within 30°.

[0111] In addition, the present application also provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and the above-mentioned battery separator arranged between the positive electrode sheet and the negative electrode sheet.

[0112] It is understandable that the present application does not limit the type of secondary battery, which may be a lithium-ion battery, a sodium-ion battery, a lithium-sulfur battery, etc. Similarly, the present application does not specifically limit the positive electrode sheet and the negative electrode sheet.

[0113] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0114] Example 1

[0115] This embodiment provides a battery separator, the preparation method of which includes the following steps:

[0116] (1) Hexagonal boron nitride (h-BN, average sheet diameter 500 nm), lithium aluminum titanium phosphate (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, abbreviated as LATP) and anhydrous ethanol are mixed in a mass ratio of 1:1:5, and zirconium oxide beads (average particle size of 1 mm, 2 mm, and 5 mm in a mass ratio of 1:1:1) are added. The mixture is placed in a ball mill and stirred evenly. The mixture is then placed in a ball mill and ball milled at 300 rpm for 1 hour. The milled slurry is filtered through a 300-mesh sieve and dried in a 55°C oven for 6 hours to obtain a dried mixed powder.

[0117] (2) The binder polyvinylidene fluoride (PVDF) and the above mixed powder were mixed in a mass ratio of 1:7.33, and then the solvent N-methylpyrrolidone (NMP) was added to make the solid content 40%. After mixing, the mixture was stirred at room temperature at 1000 rpm for 24 hours to obtain a slurry.

[0118] (3) The slurry was filled into the pores of a polyethylene porous base film (PE base film, thickness of 12 μm, porosity of 60%, average pore size of 1 μm) by micro-concave coating and vacuum negative pressure of a coating roller, and dried with hot air at 80°C for 12 h to obtain a prefabricated diaphragm.

[0119] (4) At room temperature, the prefabricated diaphragm is placed in a first DC electric field. The prefabricated diaphragm is placed parallel to the two plates and a high-voltage DC power supply is applied. The diaphragm is treated at a voltage of 1000 V for 16 hours. During this period, the positions of the two plates are swapped every 4 hours to switch the direction of the electric field so that the plane direction of the hexagonal boron nitride is oriented in the thickness direction of the porous base membrane.

[0120] (5) The slurry in step (2) was evenly coated on both sides of the diaphragm obtained in step (4) by micro-concave coating. After coating, the slurry was dried with hot air at 80°C for 12 hours to form a functional coating (with a thickness of 7 μm).

[0121] Example 2

[0122] This embodiment provides a battery separator, and its preparation method is substantially the same as that in Example 1, except that:

[0123] In step (1), h-BN and LATP were replaced by MoS2 (average sheet diameter of 500nm) and lithium lanthanum titanate (Li 3.3 La 0.56 TiO3, referred to as LLTO);

[0124] In step (4), the treatment is carried out at a voltage of 1000 V for 20 h.

[0125] Example 3

[0126] This embodiment provides a battery separator, and its preparation method is substantially the same as that in Example 1, except that:

[0127] In step (1), h-BN and LATP were replaced by WS2 (average sheet diameter of 500 nm) and lithium lanthanum zirconium oxide (Li7La3Zr2O 12 , referred to as LLZO).

[0128] Example 4

[0129] This embodiment provides a battery separator, and its preparation method is substantially the same as that in Example 1, except that:

[0130] In step (2), the binder PVDF is replaced with styrene-butadiene rubber (SBR).

[0131] Example 5

[0132] This embodiment provides a battery separator, and its preparation method is substantially the same as that in Example 1, except that:

[0133] In step (2), the mass ratio of the binder PVDF to the mixed powder is 1:5;

[0134] In step (3), the porosity of the PE base film is 40%.

[0135] Example 6

[0136] This embodiment provides a battery separator, and its preparation method is substantially the same as that in Example 1, except that:

[0137] In step (2), the mass ratio of the binder PVDF to the mixed powder is 1:1;

[0138] In step (3), the porosity of the PE base film is 80%.

[0139] Example 7

[0140] This embodiment provides a battery separator, and its preparation method is substantially the same as that in Example 1, except that step (5) is not included.

[0141] Comparative Example 1

[0142] This comparative example provides a battery separator, the preparation method of which differs from that of Example 1 in that step (3) and step (4) are not included.

[0143] Comparative Example 2

[0144] This comparative example provides a battery separator, the preparation method of which differs from that of Example 1 in that step (4) is not included.

[0145] Comparative Example 3

[0146] This comparative example provides a conventional commercially available battery separator, which is a PE separator with a thickness of 12 μm, a porosity of 60%, and a pore size of 1 μm.

[0147] Some of the preparation parameters of Examples 1 to 7 and Comparative Examples 1 to 3 are shown in Table 1.

[0148] Table 1 Some preparation parameters of battery separators in Examples and Comparative Examples

[0149]

[0150] Performance testing and result analysis

[0151] 1. Battery separator

[0152] The ion transport performance, mechanical properties and thermal shrinkage performance of the above-mentioned battery separator were tested. The test method is as follows:

[0153] (1) Ionic conductivity: The test is conducted in accordance with the standard GB / T36363-2018, including the following steps: placing the battery separator in an electrolyte solution containing 1 mol / L lithium hexafluorophosphate, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, keeping the solution sealed, and soaking for 2 hours. The electrolyte is injected into a resistance test mold, the battery separator is placed in it, and its AC impedance resistance R is tested. The ionic conductivity is: σ = d / (R*S), where d is the thickness of the battery separator and S is the area of the battery separator.

[0154] (2) Tensile strength: The above battery separators were cut into strips of 7 cm in length and 1 cm in width. The cut battery separators were fixed on a tensile testing machine and subjected to a tensile test at a speed of 4.8 cm / s. The maximum stress data at break was recorded. The transverse direction (MD) and longitudinal direction (TD) were tested separately.

[0155] (3) Heat shrinkage: Cut the battery separator into 10 cm × 10 cm squares and lightly mark 8 cm × 8 cm squares in the center of the square separator along the MD and TD directions with a pencil. Place the marked separator in a paper clamp and fix it. Then, heat treat it in an oven at 150°C and 180°C for 1 hour respectively. After heat treatment, remeasure the length of the pencil-marked squares and calculate the shrinkage rate according to the following formula:

[0156]

[0157] The above performance test results are shown in Table 2.

[0158] Table 2 Performance test results of battery separators

[0159]

[0160] As can be seen from Table 2, the battery separators prepared in Examples 1 to 7 all have high ionic conductivity, as well as high tensile strength and thermal stability. Comparing the performance test results of Example 1 and Example 7, it can be seen that adding a functional coating to the surface of the battery separator can further improve the ionic conductivity of the battery separator, increase the tensile strength, and reduce the thermal shrinkage. Among them, the ionic conductivity of the battery separator is greater than or equal to 0.86mS / cm, and can reach up to 1.22mS / cm; the transverse tensile strength of the battery separator is greater than or equal to 147MPa, and the longitudinal tensile strength is greater than or equal to 142.7MPa; the shrinkage rate of the battery separator after treatment at 150°C for 1h is less than or equal to 12.5%, and the shrinkage rate after treatment at 180°C for 1h is less than or equal to 22%.

[0161] By comparing the performance test results of Example 1 and Comparative Examples 1 to 3, it can be seen that filling the pores of the battery separator with two-dimensional sheet materials and controlling the orientation arrangement in the thickness direction can effectively improve the ionic conductivity of the battery separator, increase the tensile strength of the battery separator, and reduce the thermal shrinkage rate of the battery separator.

[0162] 2. Secondary batteries

[0163] The above diaphragm was assembled into a soft pack battery for rate performance and battery internal resistance (DCR) test, in which the positive electrode of the soft pack battery was made of ternary high nickel material (LiNi 0.8 Co 0.1 Mn 0.1 O2, NCM811), the negative electrode uses silicon carbon negative electrode for experiment, the specific test method is as follows:

[0164] (1) Rate performance

[0165] Rate charge capacity retention rate: Maintaining a discharge rate of 0.2C, the discharge capacities at charge rates of 0.2C, 0.5C, 1C, 2C, and 3C were tested respectively. The rate conditions were recorded as: 0.2C / 0.2C, 0.5C / 0.2C, 1C / 0.2C, 2C / 0.2C, and 3C / 0.2C. The rate charge capacity retention rate was calculated as follows:

[0166]

[0167] Rate discharge capacity retention rate: Maintaining a charge rate of 0.2C, the discharge capacities at discharge rates of 0.2C, 0.5C, 1C, 2C, and 3C were tested respectively. The rate conditions were recorded as: 0.2C / 0.2C, 0.2C / 0.5C, 0.2C / 1C, 0.2C / 2C, and 0.2C / 3C. The rate discharge capacity retention rate was calculated as follows:

[0168]

[0169] The above performance test results are shown in Table 3.

[0170] (2) Battery internal resistance (DCR)

[0171] At 25°C, charge the secondary battery at a constant current of 0.33C to 4.3V, then charge it at a constant voltage of 4.3V to a current of 0.05C, and record the voltage V1. Then discharge it at a constant current of 1C to a certain state of charge (SOC) (90%, 80%, 70%, 60%, 50%, 45%, 30%, 15%), and record the voltage V2. The DC internal resistance DCR of the battery is 3×(V2-V1) / C.

[0172] The above performance test results are shown in Table 4.

[0173] Table 3 Rate performance test results of the embodiments and comparative examples

[0174]

[0175] Table 4 Battery internal resistance test results of the embodiment and comparative example

[0176]

[0177] As can be seen from Table 3, the batteries prepared in Examples 1 to 7 can maintain a high capacity retention rate at different charge and discharge rates, especially when charging and discharging at high rates (2C, 3C), the capacity retention rate is significantly higher than that of Comparative Examples 1 to 3, indicating that filling the battery separator with a two-dimensional sheet material and controlling the orientation of the plane direction in the thickness direction of the base film can effectively improve the rate performance of the battery.

[0178] As can be seen from Table 4, the batteries prepared with the battery separators in Examples 1 to 7 have lower internal resistance at different states of charge (SOC), and are significantly lower than those in Comparative Examples 1 to 3, indicating that filling the battery separator with a two-dimensional sheet material and controlling the orientation of the plane in the thickness direction of the base film in the present application can effectively reduce the internal resistance of the battery, thereby improving the cycle performance of the battery.

[0179] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A battery separator, characterized in that: It includes a porous base membrane and a first two-dimensional sheet material capable of conducting ions, wherein the first two-dimensional sheet material is filled in the pores of the porous base membrane, and the plane direction of the first two-dimensional sheet material is oriented in the thickness direction of the porous base membrane.

2. The battery separator according to claim 1, characterized in that The first two-dimensional sheet material can be oriented and arranged under the action of an electric field; Optionally, the first two-dimensional sheet material includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide or boron nitride; Optionally, the boron nitride includes at least one of hexagonal boron nitride or cubic boron nitride; Optionally, the pores of the porous base membrane are also filled with solid electrolyte particles.

3. The battery separator according to claim 1, characterized in that The first two-dimensional sheet material is boron nitride.

4. The battery separator according to claim 1, characterized in that The sheet diameter of the first two-dimensional sheet material is smaller than the pore diameter of the pores of the porous base membrane filled therein; Optionally, the average sheet diameter of the first two-dimensional sheet material is 10 nm to 10 μm; Optionally, the average pore size of the porous base membrane is 20 nm to 20 μm; Optionally, the porous base membrane has a thickness of 3 μm to 30 μm and a porosity of 30% to 80%.

5. The battery separator according to any one of claims 1 to 4, characterized in that A functional coating is provided on at least one surface of the porous base membrane, wherein the functional coating comprises a second two-dimensional sheet material capable of conducting ions; Optionally, the functional coating further comprises solid electrolyte particles; Optionally, the functional coating has a thickness of 1 μm to 10 μm.

6. The battery separator according to claim 5, characterized in that The plane direction of the second two-dimensional sheet material is oriented in the thickness direction of the porous base membrane; or, the plane direction of the second two-dimensional sheet material is oriented in the plane direction of the porous base membrane; Optionally, the second two-dimensional sheet material can be oriented and arranged under the action of an electric field; Optionally, the second two-dimensional sheet material includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide or boron nitride; Optionally, the boron nitride includes at least one of hexagonal boron nitride or cubic boron nitride.

7. The battery separator according to claim 5, characterized in that The functional coating comprises two or more stacked sub-coatings, wherein at least one of the sub-coatings comprises the second two-dimensional sheet material.

8. A method for preparing a battery separator, characterized in that: The following steps are involved: Filling the pores of the porous base film with a first slurry to obtain a prefabricated diaphragm; wherein the first slurry comprises a first two-dimensional sheet material capable of conducting ions, a binder, and a solvent; A first direct current electric field is applied to the prefabricated separator so that the plane direction of the first two-dimensional sheet material is oriented in the thickness direction of the porous base membrane to obtain a battery separator.

9. The preparation method according to claim 8, characterized in that The first two-dimensional sheet material includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide or boron nitride; Optionally, the boron nitride includes at least one of hexagonal boron nitride or cubic boron nitride; Optionally, the first slurry further includes solid electrolyte particles.

10. The preparation method according to claim 8, characterized in that The conditions for applying the first DC electric field to the prefabricated diaphragm include: placing the prefabricated diaphragm between two plates with opposite polarities in a parallel direction, applying a voltage of 800V to 1200V to the prefabricated diaphragm through a DC power supply, and treating for 12 hours to 20 hours; Optionally, the direction of the first DC electric field is switched every 3 hours to 5 hours.

11. The preparation method according to claim 8, characterized in that In the first slurry, the preparation method of the first two-dimensional sheet material comprises: mixing the first two-dimensional sheet material and a dispersant, ball milling, and drying, so that the average sheet diameter of the first two-dimensional sheet material is smaller than the average pore diameter of the porous base membrane; Optionally, after the first slurry is filled into the pores of the porous base membrane, a drying step is further included; Optionally, the average pore size of the porous base membrane is 20 nm to 20 μm; Optionally, the average sheet diameter of the first two-dimensional sheet material is 10 nm to 10 μm; Optionally, the drying temperature is 60° C. to 80° C., and the drying time is 4 hours to 24 hours.

12. The preparation method according to claim 8, characterized in that Also includes: A second slurry is applied to at least one side of the porous base membrane to form a functional coating after drying; wherein the second slurry comprises a second two-dimensional sheet material capable of conducting ions, a binder, and a solvent; Optionally, the second two-dimensional sheet material includes at least one of molybdenum disulfide, tungsten disulfide, rhenium disulfide or boron nitride; Optionally, the second slurry further comprises solid electrolyte particles.

13. The preparation method according to claim 12, characterized in that Also includes: Applying a second DC electric field to the functional coating so that the plane direction of the second two-dimensional sheet material is oriented in the plane direction of the porous base membrane; The electric field directions of the second DC electric field and the first DC electric field are perpendicular to each other.

14. A secondary battery, characterized in that: A battery separator comprising the battery separator according to any one of claims 1 to 7; or a battery separator prepared by the preparation method according to any one of claims 8 to 13.

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