Ultrathin and high-strength diaphragm as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and discloses an ultrathin and high-strength diaphragm as well as a preparation method and application thereof. The diaphragm comprises a base layer and a supporting layer, the supporting layer comprises a high polymer material or inorganic ceramic nanofiber, a surfactant and an antistatic agent; the base layer comprises inorganic nano ceramic particles and polyvinylidene fluoride; the inorganic nano ceramic particles are selected from at least one of an oxygen-containing substance of aluminum, an oxygen-containing substance of magnesium, an oxygen-containing substance of silicon, an oxygen-containing substance of titanium and a lithium electrolyte. The composition of the supporting layer and the slurry layer is specifically selected, so that the thickness of the diaphragm prepared by the invention is less than 1.5 mu m, further less than 1 mu m and even less than 0.6 mu m, and the tensile strength of the diaphragm is greater than 5.5 MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to an ultra-thin, high-strength diaphragm, a preparation method thereof, and applications thereof. Background Art

[0002] Improving energy density has long been the development direction of 3C (computer, communication, and consumer electronics) battery cells. Reducing the thickness of the separator, one of the four main components of a battery cell, is a common method for increasing energy density. However, as the separator thickness decreases, its strength, voltage breakdown resistance, and resistance to foreign object penetration all decrease, thus affecting battery cell safety.

[0003] Existing separators typically have a thickness between 30 and 120 μm, which is not conducive to increasing the energy density of battery cells. If the thickness is around 5 μm, the strength of the separator is often less than 5 MPa, which adversely affects the safety of the separator. In other words, existing separators are either too thick or too weak.

[0004] Therefore, there is an urgent need to provide an ultra-thin and high-strength diaphragm. Summary of the Invention

[0005] The present invention aims to address at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides an ultrathin, high-strength diaphragm, a method for preparing the same, and its application. The diaphragm has a thickness of less than 1.5 μm, and can further be less than 1 μm, or even less than 0.6 μm, and has a tensile strength greater than 5.5 MPa.

[0006] A first aspect of the present invention provides an ultra-thin, high-strength diaphragm.

[0007] Specifically, an ultra-thin, high-strength diaphragm includes a stacked base layer and a support layer;

[0008] The support layer comprises polymer materials or inorganic ceramic nanofibers, surfactants, and antistatic agents;

[0009] The base layer comprises inorganic nano-ceramic particles and polyvinylidene fluoride;

[0010] The inorganic nano-ceramic particles are selected from at least one of aluminum oxygen-containing substances, magnesium oxygen-containing substances, silicon oxygen-containing substances, titanium oxygen-containing substances, and lithium electrolytes;

[0011] The volume of the base layer accounts for 40% to 48.5% of the diaphragm, the porosity ratio between the base layer and the diaphragm is 1.45 to 1.70, and the surface roughness Ra of the support layer is 85 to 110 nm.

[0012] Preferably, the polymer material is selected from at least one of polyvinylidene fluoride, polylactic acid, polypropylene, polystyrene, polyvinyl alcohol, polyethersulfone, and cellulose materials.

[0013] Preferably, the molecular weight of the polymer material is 80,000-1.2 million, more preferably 100,000-1 million.

[0014] Preferably, the molecular weight of the polyvinylidene fluoride is 200,000-600,000, more preferably 250,000-500,000.

[0015] Preferably, the inorganic ceramic nanofiber is selected from at least one of alumina nanofiber, zirconium oxide nanofiber, titanium oxide nanofiber, and lead zirconate titanate nanofiber.

[0016] Preferably, the surfactant is selected from at least one of sodium lauryl sulfonate, fatty acid glyceride, fluoroalkyl quaternary ammonium salt, sodium 4-styrene sulfonate, silane surfactant and modified polyol surfactant.

[0017] Preferably, the antistatic agent is selected from at least one of stearyl trimethyl ammonium chloride, alkyl sulfonates, secondary alkyl sulfonates, stearyl dimethyl amyl ammonium chloride and a polymer of polyamide / polyether block amide.

[0018] Preferably, the aluminum oxygen-containing substance is selected from at least one of Al2O3, Al(OH)3, and AlOOH (boehmite).

[0019] Preferably, the magnesium oxygen-containing substance is selected from at least one of Mg(OH)2 and MgO.

[0020] Preferably, the silicon oxygen-containing substance is SiO2.

[0021] Preferably, the titanium oxygen-containing substance is TiO2.

[0022] Preferably, the lithium electrolyte is selected from at least one of LATP (lithium aluminum titanium phosphate), LLZO (lithium lanthanum zirconium oxide), and LZO (Li8ZrO6).

[0023] Preferably, the composition of the support layer, by mass, includes 10-28 parts of polymer material or inorganic ceramic nanofiber, 0.1-2.8 parts of surfactant, and 0.5-3.5 parts of antistatic agent; further preferably, the composition of the support layer, by mass, includes 12.5-25 parts of polymer material or inorganic ceramic nanofiber, 1-2.5 parts of surfactant, and 1-2.5 parts of antistatic agent.

[0024] Preferably, the composition of the base layer, calculated by mass, includes 0.5-10 parts of inorganic nano-ceramic particles and 1 part of polyvinylidene fluoride; further preferably, the composition of the base layer, calculated by mass, includes 1-6 parts of inorganic nano-ceramic particles and 1 part of polyvinylidene fluoride; more preferably, the composition of the base layer, calculated by mass, includes 2-2.5 parts of inorganic nano-ceramic particles and 1 part of polyvinylidene fluoride.

[0025] Preferably, the particle size of the inorganic nano-ceramic particles is 10-300 nm; more preferably, 50-200 nm.

[0026] Preferably, the support layer includes one or more support sublayers, and the composition of the support sublayer is the same as that of the support layer.

[0027] Preferably, the support layer comprises 1-10 support sublayers; further preferably, the support layer comprises 1-5 support sublayers.

[0028] Preferably, the support layer or support sublayer is in a fibrous shape.

[0029] Preferably, the thickness of the separator is less than 1.5 μm, more preferably less than 1 μm, and more preferably less than 0.6 μm. Specifically, the thickness of the separator may be 0.50-1.22 μm.

[0030] Preferably, the tensile strength of the diaphragm is greater than 5.5 MPa, more preferably greater than 5.8 MPa. Specifically, the tensile strength of the diaphragm is 5.6-6.5 MPa. The diaphragm of the present invention has a tensile strength of 5.6-6.5 MPa when the thickness is 0.50-1.22 μm.

[0031] A second aspect of the present invention provides a method for preparing an ultra-thin, high-strength diaphragm.

[0032] Specifically, a method for preparing an ultra-thin, high-strength diaphragm includes the following steps:

[0033] Mixing polymer materials or inorganic ceramic nanofibers, surfactants, antistatic agents, and solvents to prepare a support layer slurry;

[0034] Mixing inorganic nano-ceramic particles, polyvinylidene fluoride, and a solvent to prepare a base layer slurry;

[0035] A wet film support layer is prepared by an electrostatic spinning method and a support layer slurry, and then a wet film base layer is prepared on the wet film support layer by a micro-concave roller coating method and a base layer slurry, and the wet film base layer is dried to prepare the ultra-thin, high-strength diaphragm.

[0036] Preferably, the solvent is selected from at least one of acetone, N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), ethanol, methyl carbonate, and tetrahydrofuran.

[0037] More preferably, acetone is used as the solvent when preparing the support layer slurry, and N-methylpyrrolidone (NMP) or dimethylacetamide (DMAC) is used as the solvent when preparing the base layer slurry.

[0038] Preferably, in the support layer slurry, the mass proportion of the solvent is 68-88%, more preferably 70-85%.

[0039] Preferably, the mass proportion of the solvent in the base layer slurry is 65-85%, more preferably 70-80%.

[0040] Preferably, the drying temperature is 55-75° C., and the drying time is 4-6 hours.

[0041] Although the electrostatic spinning method and the micro-concave roller coating method are conventional methods in the art, the present invention makes targeted selections of the process parameters involved in the electrostatic spinning method and the micro-concave roller coating method.

[0042] Preferably, the parameters involved in the electrospinning method are: the micropump pushing speed is 0.5-2.5 m / min, the voltage is 20-40 kV; the distance from the syringe needle to the receiving roller is 10-15 cm; and the electrospinning time is 4-10 h.

[0043] Preferably, the parameters of the micro-concave roller coating method are as follows: the diameter of the micro-concave roller is 60 to 100 mm and the number of lines is 180 to 250; and the coating speed is 5 to 10 m / min.

[0044] The process of preparing the diaphragm is as follows: in the electrospinning method, the high-voltage electrode of the high-voltage liquid injection system generates an electric field, which introduces charges into the support layer slurry. Through the action of the electric field, the molecules in the support layer slurry are charged, and a charged polymer solution is generated. Since the charged polymer solution will move in the direction of the electric field under the action of the electric field, the polymer solution is stretched into a very fine liquid stream and eventually reaches a rotating collector connected to the ground wire, forming a fibrous support layer woven together. Then, a scraper and a micro-gravure are used to coat the base slurry into the support layer. After drying, a composite structure diaphragm can be obtained.

[0045] The thickness of the final separator is determined by the coating speed and the number of supporting sublayers.

[0046] The more and denser the fibrous support layers are, not only will the thickness of the diaphragm become thicker, but the surface density of the diaphragm will also increase, thereby increasing the tensile strength of the diaphragm and reducing the air permeability.

[0047] A third aspect of the present invention provides an application of an ultra-thin, high-strength separator in the preparation of a battery cell.

[0048] A battery cell comprises the above-mentioned diaphragm.

[0049] The application of the above-mentioned ultra-thin, high-strength diaphragm in the preparation of battery cells.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) Due to the specific selection of the support layer and the slurry layer composition, the thickness of the diaphragm prepared by the present invention is less than 1.5 μm, further less than 1 μm, or even less than 0.6 μm, and the tensile strength of the diaphragm is greater than 5.5 MPa.

[0052] (2) The support layer is formed by electrospinning technology to form a high-strength fibrous support layer, which is then combined with traditional micro-concave roller coating technology to ensure the formation of an ultra-thin base layer. The strength and air permeability of this composite structure membrane are determined by the number and density of the fibrous support sublayers; the thickness of the final membrane is determined by the coating speed and the number of support sublayers. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the process for preparing a diaphragm according to Example 1 of the present invention;

[0054] Figure 2 This is a schematic structural diagram of the diaphragm according to Example 1 of the present invention. DETAILED DESCRIPTION

[0055] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0056] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0057] Example 1: Preparation of diaphragm

[0058] An ultra-thin, high-strength diaphragm consisting of a stack of support and base layers;

[0059] The support layer comprises, by mass, 10 parts of polyvinylidene fluoride, 1.5 parts of a surfactant (sodium lauryl sulfonate), and 1.0 parts of an antistatic agent (stearyl trimethyl ammonium chloride);

[0060] The base layer comprises 7.5 parts of Al(OH)3 and 3.5 parts of polyvinylidene fluoride in parts by mass.

[0061] A method for preparing an ultrathin, high-strength diaphragm comprises the following steps:

[0062] Preparation of electrospinning solution: 60 g of acetone and 1.5 g of surfactant (sodium dodecyl sulfate) were weighed and placed in a container. The mixture was mechanically stirred at 500 rpm at room temperature for 30 min. 10 g of polyvinylidene fluoride (average molecular weight approximately 200,000) and 1.0 g of antistatic agent (stearyltrimethylammonium chloride) were then weighed and mixed in the stirring container. The mixture was stirred continuously for 8 h until the solution became clear and transparent. This yielded the polyvinylidene fluoride electrospinning solution (or support layer slurry).

[0063] Preparation of base slurry: Weigh 7.5 g of Al(OH)3 and 3.5 g of PVDF into a container containing 50 g of NMP and stir at 500 rpm for 4 h to obtain base slurry;

[0064] Preparation of the diaphragm: The electrospinning method is used to push the support layer slurry out of the high-pressure liquid injection system at a speed of 1.5mL / h, and a high voltage of 40kV is applied. Under the action of the electric field force, the support layer slurry will be injected into the rotating collector to form a fibrous wet film support layer; then use a scraper and a micro-concave roller to apply the base layer slurry to the wet film support layer through a micro-concave coating method. A micro-concave roller with a diameter of 100mm and a line number of 180 is selected and coated on the wet film support layer at a coating speed of 5m / min. The total thickness of the wet film is about 2.3μm. Then it is placed in 65℃ for drying for 6h to remove the solvent to obtain a composite structure diaphragm.

[0065] Figure 1 Schematic diagram of the process for preparing a diaphragm according to Example 1 of the present invention; Figure 2 Schematic diagram of the structure of the diaphragm of Example 1 of the present invention ( Figure 2 In the figure, "MD" means machine direction and "TD" means transverse direction.

[0066] Example 2: Preparation of diaphragm

[0067] An ultra-thin, high-strength diaphragm consisting of a stack of support and base layers;

[0068] The support layer comprises, by weight, 9.5 parts of polystyrene, 1.5 parts of a surfactant (sodium lauryl sulfonate), and 1.0 parts of an antistatic agent (alkyl sulfonate);

[0069] The base layer comprises 7.5 parts of Al2O3 and 3.5 parts of polyvinylidene fluoride, calculated by mass.

[0070] A method for preparing an ultrathin, high-strength diaphragm comprises the following steps:

[0071] Preparation of electrospinning solution: 60 g of acetone and 1.5 g of surfactant (sodium dodecyl sulfate) were weighed and placed in a container. The mixture was mechanically stirred at 500 rpm at room temperature for 30 min. Then, 9.5 g of polystyrene (average molecular weight approximately 150,000) and 1.5 g of antistatic agent (alkyl sulfonate) were weighed and mixed. The mixture was placed in a stirring container and stirred continuously for 8 h until the solution became clear and transparent. This yielded the polystyrene electrospinning solution (or support layer slurry).

[0072] Preparation of base slurry: Weigh 7.5 g of Al2O3 and 3.5 g of PVDF into a container containing 40 g of NMP and stir at 500 rpm for 4 h to obtain base slurry;

[0073] Preparation of the diaphragm: The electrospinning method is used to push the support layer slurry out of the high-pressure liquid injection system at a speed of 1.5mL / h, and a high voltage of 40kV is applied. Under the action of the electric field force, the support layer slurry will be injected into the rotating collector to form a fibrous wet film support layer; then a scraper and a micro-concave roller are used to apply the base layer slurry to the wet film support layer through a micro-concave coating method. A micro-concave roller with a diameter of 60mm and a line number of 200 is selected and coated at a coating speed of 5m / min. The total thickness of the wet film is about 1.9μm. Then it is placed in 65℃ for drying for 8h to remove the solvent to obtain a composite structure diaphragm.

[0074] Example 3: Preparation of diaphragm

[0075] An ultra-thin, high-strength diaphragm consisting of a stack of support and base layers;

[0076] The support layer comprises, by mass, 12 parts of polypropylene, 1.0 part of surfactant (fatty acid glyceride), and 1.0 part of antistatic agent (alkyl sulfonate);

[0077] The base layer includes 8.5 parts of AlOOH (boehmite) and 4.5 parts of polyvinylidene fluoride in parts by mass.

[0078] A method for preparing an ultrathin, high-strength diaphragm comprises the following steps:

[0079] Preparation of electrospinning solution: 60 g of acetone and 1.0 g of surfactant (fatty acid glyceride) were weighed and placed in a container. The mixture was mechanically stirred at 500 rpm at room temperature for 30 min. 12 g of polypropylene (average molecular weight approximately 200,000) and 1.0 g of antistatic agent (alkyl sulfonate) were then weighed and mixed in the stirring container. The mixture was stirred continuously for 8 h until the solution became clear and transparent. This provided the polypropylene electrospinning solution (or support layer slurry).

[0080] Preparation of base slurry: 8.5 g of AlOOH (boehmite) and 4.5 g of PVDF were weighed and placed in a container containing 40 g of NMP and stirred at 500 rpm for 10 h to obtain base slurry;

[0081] Preparation of the diaphragm: The electrospinning method is used to push the support layer slurry out of the high-pressure liquid injection system at a speed of 0.5mL / h, and a high voltage of 40kV is applied. Under the action of the electric field force, the support layer slurry will be injected into the rotating collector to form a fibrous wet film support layer; then use a scraper and a micro-gravure plate to apply the base layer slurry to the wet film support layer through a micro-gravure coating method. A micro-gravure roller with a diameter of 80mm and a line number of 180 is selected and coated on the wet film support layer at a coating speed of 5m / min. The total thickness of the wet film is about 3.2μm. Then it is placed in 65℃ for drying for 6h to remove the solvent to obtain a composite structure diaphragm.

[0082] Example 4: Preparation of diaphragm

[0083] An ultra-thin, high-strength diaphragm consisting of a stack of support and base layers;

[0084] The support layer comprises, by weight, 10 parts of polypropylene, 1.0 parts of a surfactant (a fluoroalkyl quaternary ammonium salt), and 1.5 parts of an antistatic agent (a secondary alkyl sulfonate);

[0085] The base layer comprises 8.5 parts of LATP (lithium aluminum titanium phosphate) and 4.5 parts of polyvinylidene fluoride, calculated by weight.

[0086] A method for preparing an ultrathin, high-strength diaphragm comprises the following steps:

[0087] Preparation of electrospinning solution: 60 g of acetone and 1.0 g of a surfactant (fluoroalkyl quaternary ammonium salt) were weighed and placed in a container. The mixture was mechanically stirred at 500 rpm at room temperature for 30 min. 10 g of polypropylene (average molecular weight approximately 250,000) and 1.5 g of an antistatic agent (secondary alkyl sulfonate) were then weighed and mixed in the stirring container. The mixture was stirred continuously for 8 h until the solution became clear and transparent. This provided the polypropylene electrospinning solution (or support layer slurry).

[0088] Preparation of base slurry: 8.5 g of LATP (lithium aluminum titanium phosphate) and 4.5 g of PVDF were weighed and placed in a container containing 40 g of DMAC and stirred at 500 rpm for 4 h to obtain base slurry;

[0089] Preparation of the diaphragm: The electrospinning method is used to push the support layer slurry out of the high-pressure liquid injection system at a speed of 2.0mL / h, and a high voltage of 30kV is applied. Under the action of the electric field force, the support layer slurry will be injected into the rotating collector to form a fibrous wet film support layer; then a scraper and a micro-concave roller are used to apply the base layer slurry to the wet film support layer through a micro-concave coating method. A micro-concave roller with a diameter of 100mm and a line number of 200 is selected and coated at a coating speed of 5m / min. The total thickness of the wet film is about 2.8μm. Then it is placed in 65℃ for drying for 6h to remove the solvent to obtain a composite structure diaphragm.

[0090] Comparative Example 1

[0091] A method for preparing a diaphragm comprises the following steps:

[0092] 60g of acetone and 1.5g of surfactant were weighed and placed in a container, and mechanically stirred at room temperature for 30min at a speed of 500rpm; then 9.5g of polystyrene (average molecular weight of about 150,000) and 1.5g of antistatic agent were weighed and mixed and placed in a stirring container, and stirred continuously for 8h to dissolve until the solution was clear and transparent, thereby obtaining a polystyrene electrospinning solution. The polystyrene electrospinning solution was pushed out of the high-pressure liquid injection system at a speed of 1.5ml / h by the electrospinning method, and a high voltage of 40kV was applied. Under the action of the electric field force, the polystyrene electrospinning solution was injected into the rotating collector to form a fibrous support layer; then the polystyrene electrospinning solution was coated on the support layer by a micro-concave coating method using a scraper and a micro-concave plate. A micro-concave roller with a diameter of 60mm and a line number of 200 was selected and coated on the support layer at a coating speed of 5m / min. The total thickness of the wet film was about 1.8μm, and then it was placed in 65℃ for drying for 8h to remove the solvent to obtain a diaphragm.

[0093] Comparative Example 2

[0094] An ultra-thin, high-strength diaphragm consisting of a stack of support and base layers;

[0095] The support layer comprises, by mass, 10 parts of polyvinylidene fluoride, 1.5 parts of a surfactant (sodium lauryl sulfonate), and 1.0 parts of an antistatic agent (stearyl trimethyl ammonium chloride);

[0096] The base layer comprises 7.5 parts of Ca(OH)2 and 3.5 parts of polyvinylidene fluoride, calculated by weight.

[0097] A method for preparing an ultrathin, high-strength diaphragm comprises the following steps:

[0098] Preparation of electrospinning solution: 60 g of acetone and 1.5 g of surfactant (sodium dodecyl sulfate) were weighed and placed in a container. The mixture was mechanically stirred at 500 rpm at room temperature for 30 min. 10 g of polyvinylidene fluoride (average molecular weight approximately 200,000) and 1.0 g of antistatic agent (stearyltrimethylammonium chloride) were then weighed and mixed in the stirring container. The mixture was stirred continuously for 8 h until the solution became clear and transparent. This yielded the polyvinylidene fluoride electrospinning solution (or support layer slurry).

[0099] Preparation of base slurry: Weigh 7.5 g of Al(OH)3 and 3.5 g of PVDF into a container containing 50 g of NMP and stir at 500 rpm for 4 h to obtain base slurry;

[0100] Preparation of the diaphragm: The electrospinning method is used to push the support layer slurry out of the high-pressure liquid injection system at a speed of 1.5mL / h, and a high voltage of 40kV is applied. Under the action of the electric field force, the support layer slurry will be injected into the rotating collector to form a fibrous wet film support layer; then use a scraper and a micro-concave roller to apply the base layer slurry to the wet film support layer through a micro-concave coating method. A micro-concave roller with a diameter of 100mm and a line number of 180 is selected and coated on the wet film support layer at a coating speed of 5m / min. The total thickness of the wet film is about 2.3μm. Then it is placed in 65℃ for drying for 6h to remove the solvent to obtain a composite structure diaphragm.

[0101] Product effect testing

[0102] The thickness and tensile strength of the membranes prepared in the above examples and comparative examples were tested. The results are shown in Table 1.

[0103] The thickness test method is: use Malvern thickness tester to test the thickness of the diaphragm. First, take a 1m long composite diaphragm, measure a data on each side every 20cm, measure a total of five times, and take the average value.

[0104] Tensile strength test method: Refer to the standard "GB / T 36363-2018 Polyolefin separator for lithium-ion batteries" and perform a tensile test on the separator sample.

[0105] Table 1

[0106]

[0107]

[0108] As can be seen from Table 1, the diaphragm prepared in the present invention can still maintain a tensile strength of 5.6-6.2 MPa when the thickness is 0.52-1.22 μm, that is, the diaphragm of the present invention can meet the requirements of ultra-thinness and high strength at the same time.

[0109] In addition, referring to the preparation method of Example 2, diaphragms with support layers of 2, 3, 4, and 5 layers (that is, the support layer is composed of 2, 3, 4, and 5 support sublayers, and when there are more than 2 support layers, the support layers are adjacent) were prepared (the support layer of Example 2 is 1 layer), and then the total thickness, membrane surface density, tensile strength, and air permeability of the diaphragm were tested. The results are shown in Table 2.

[0110] Table 2

[0111]

[0112] It can be seen from Table 2 that the more and denser the supporting layers are, not only the thickness of the composite diaphragm will become thicker, but also the surface density of the diaphragm will become larger, thereby increasing the tensile strength of the diaphragm and reducing the air permeability.

[0113] Within the scope of protection claimed in the present invention, when the types of polymer materials, inorganic ceramic nanofibers or inorganic nano-ceramic particles are changed, the effect of the prepared diaphragm product is similar to that of the diaphragm in Example 3.

Claims

1. A diaphragm, characterized in that: including stacked base and support layers; The support layer comprises polymer materials or inorganic ceramic nanofibers, surfactants, and antistatic agents; The base layer comprises inorganic nano-ceramic particles and polyvinylidene fluoride; The inorganic nano-ceramic particles are selected from at least one of aluminum oxygen-containing substances, magnesium oxygen-containing substances, silicon oxygen-containing substances, titanium oxygen-containing substances, and lithium electrolytes; The volume of the base layer accounts for 40% to 48.5% of the diaphragm, the porosity ratio between the base layer and the diaphragm is 1.45 to 1.70, and the surface roughness Ra of the support layer is 85 to 110 nm.

2. The diaphragm according to claim 1, characterized in that The polymer material is selected from at least one of polyvinylidene fluoride, polylactic acid, polypropylene, polystyrene, polyvinyl alcohol, polyethersulfone, and cellulose materials.

3. The diaphragm according to claim 1, characterized in that The inorganic ceramic nanofiber is selected from at least one of alumina nanofiber, zirconium oxide nanofiber, titanium oxide nanofiber, and lead zirconate titanate nanofiber.

4. The diaphragm according to claim 1, characterized in that The oxygen-containing substance of aluminum is selected from at least one of Al2O3, Al(OH)3, and AlOOH; and / or, the oxygen-containing substance of magnesium is selected from at least one of Mg(OH)2 and MgO; and / or, the oxygen-containing substance of silicon is SiO2; and / or, the oxygen-containing substance of titanium is TiO2; and / or, the lithium electrolyte is selected from at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium oxide, and Li8ZrO6.

5. The diaphragm according to any one of claims 1 to 4, characterized in that: The supporting layer comprises, by weight, 10-28 parts of polymer material or inorganic ceramic nanofiber, 0.1-2.8 parts of surfactant, and 0.5-3.5 parts of antistatic agent.

6. The diaphragm according to any one of claims 1 to 4, characterized in that: The composition of the base layer, calculated by mass, includes 0.5-10 parts of inorganic nano-ceramic particles and 1 part of polyvinylidene fluoride.

7. The diaphragm according to any one of claims 1 to 4, characterized in that: The thickness of the separator is less than 1.5 μm, and the tensile strength of the separator is greater than 5.5 MPa.

8. The method for preparing a diaphragm according to any one of claims 1 to 7, characterized in that: The following steps are involved: Mixing polymer materials or inorganic ceramic nanofibers, surfactants, antistatic agents, and solvents to prepare a support layer slurry; Mixing inorganic nano-ceramic particles, polyvinylidene fluoride, and a solvent to prepare a base layer slurry; A wet film support layer is prepared by an electrostatic spinning method and a support layer slurry, and then a wet film base layer is prepared on the wet film support layer by a micro-concave roller coating method and a base layer slurry, and the mixture is dried to prepare the separator.

9. The preparation method according to claim 8, characterized in that The parameters involved in the electrospinning method are: a micropump pushing speed of 0.5 to 2.5 m / min and a voltage of 20 to 40 kV; a distance from the syringe needle to the receiving roller of 10 to 15 cm; an electrospinning time of 4 to 10 hours; and / or, the parameters involved in the micro-concave roller coating method are: a micro-concave roller diameter of 60 to 100 mm and a line number of 180 to 250; and a coating speed of 5 to 10 m / min.

10. A battery cell, characterized in that: The diaphragm comprises the diaphragm according to any one of claims 1 to 7.

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