CN116960565A

CN116960565A - Nonwoven fabric composite membrane and preparation method thereof, lithium battery diaphragm, lithium battery and liquid separation membrane

Info

Publication number: CN116960565A
Application number: CN202210392933.4A
Authority: CN
Inventors: 陈莉; 王艳杰; 林陆菁; 杨雪梅; 陈秀峰
Original assignee: Shenzhen Senior Technology Material Co Ltd
Current assignee: Shenzhen Senior Technology Material Co Ltd
Priority date: 2022-04-14
Filing date: 2022-04-14
Publication date: 2023-10-27

Abstract

The embodiment of the application provides a non-woven fabric composite membrane and a preparation method thereof, a lithium battery diaphragm, a lithium battery and a liquid separation membrane, and relates to the field of functional membranes. The non-woven composite film comprises non-woven and a polymer coating overlapped on the non-woven; the polymer coating includes a first pore layer and a second pore layer; the polymer coating is partially embedded in the non-woven fabric, and the first pore layer is far away from the non-woven fabric, or the polymer coating is completely embedded in the non-woven fabric; the first pore layer has a porosity of 50% -95%, the first pore layer has an average pore diameter of 10-200 nm, the second pore layer has an average pore diameter of 0.1-30 μm, and the first pore layer has an average pore diameter smaller than the second pore layer. The non-woven fabric composite membrane formed by combining the non-woven fabric and the polymer coating has good heat resistance and pressure resistance, and also has good selective permeability, and can be used for lithium battery diaphragms and liquid separation membranes.

Description

Nonwoven fabric composite membrane and preparation method thereof, lithium battery diaphragm, lithium battery and liquid separation membrane

Technical Field

The application relates to the field of functional films, in particular to a non-woven fabric composite film and a preparation method thereof, a lithium battery diaphragm, a lithium battery and a liquid separation film.

Background

The non-woven fabric has high porosity and high heat stability, so that the functional film based on the non-woven fabric has wide application. However, some characteristics of the nonwoven fabric also cause problems that are unavoidable when the nonwoven fabric is used in the above-mentioned fields.

Taking a lithium battery separator as an example, in order to prevent short circuits from occurring inside the lithium battery, the lithium battery separator needs to have a smaller pore diameter and a thinner thickness. However, the non-woven fabric with a thin thickness has poor tensile strength and larger aperture, if the non-woven fabric is required to meet the small aperture, the thickness of the non-woven fabric is too large, and if the non-woven fabric is used for preparing the lithium battery diaphragm, the thickness and the aperture of the non-woven fabric are difficult to fully meet the application requirements of the lithium ion battery diaphragm at the same time.

Taking a liquid separation membrane as an example, the liquid separation membrane is usually formed by coating, interfacial polymerization, plasma polymerization, etc. on the surface of a support membrane, and the support membrane is usually formed by compounding an ultrathin skin layer on a non-woven fabric to strengthen the mechanical properties of the support membrane. The supporting film and the ultrathin cortex act together to realize selective separation of the liquid separation film. However, since the non-woven fabric has a larger pore diameter, a large amount of coating liquid is absorbed during coating, and in order to obtain the surface of the support layer film suitable for interfacial polymerization reaction, the thickness of the porous polymer layer on the support film is remarkably increased, so that the membrane permeation resistance of the liquid separation film is greatly increased, and the separation efficiency of the liquid separation film is reduced. And because the aperture of the non-woven fabric is larger, excessive coating permeation and even seepage of the coating to the back of the non-woven fabric easily occur when the surface of the non-woven fabric is directly coated, so that the defect of the obtained coating hole is serious.

Disclosure of Invention

The application aims to provide a non-woven fabric composite membrane, a preparation method thereof, a lithium battery diaphragm, a lithium battery and a liquid separation membrane. When the non-woven fabric composite membrane is used as a lithium battery diaphragm, the integrity can be maintained when the temperature of the lithium battery is too high, and the risk of thermal runaway of the lithium battery can be greatly reduced; when the non-woven fabric composite membrane is used as a liquid separation membrane supporting membrane, the prepared liquid separation membrane still has good water flux and retention rate under the condition of higher pressure, so that liquid can be filtered and separated well.

In a first aspect, embodiments of the present application provide a nonwoven fabric composite film, which includes a nonwoven fabric, and a polymer coating layer laminated on the nonwoven fabric; the polymer coating includes a first pore layer and a second pore layer; the polymer coating is partially embedded in the non-woven fabric, and the first pore layer is far away from the non-woven fabric, or the polymer coating is completely embedded in the non-woven fabric; the first pore layer has a porosity of 50% -95%, the first pore layer has an average pore diameter of 10-200 nm, the second pore layer has an average pore diameter of 0.1-30 μm, and the first pore layer has an average pore diameter smaller than the second pore layer.

The inventor finds that if a layer of polymer coating is embedded in the non-woven fabric with good thermal stability in the process of realizing the application, and the porosity and pore diameter (or pore diameter) of different areas of the polymer coating are controlled, the non-woven fabric composite membrane with an asymmetric pore structure is formed, so that the non-woven fabric composite membrane has good tensile strength, good thermal stability and compression resistance, and good selective permeability, and can well meet the requirements of a diaphragm and a liquid separation membrane by respectively regulating parameters such as pore diameter, porosity, thickness and the like in the coating.

In the implementation process, the special non-woven fabric composite membrane is designed, the non-woven fabric has good mechanical property, the polymer coating can be effectively supported, when the polymer coating is partially embedded in the non-woven fabric, the porosity of a first pore layer far away from the non-woven fabric is 50-95%, the average pore diameter is smaller, the pore structure is similar to a spongy pore, large-volume molecules hardly pass through the first pore layer and pass through the non-woven fabric composite membrane, but small-volume ions or molecules can pass through the first pore layer, and the requirements of separation performance and pressure resistance of a diaphragm and a liquid separation membrane can be met; the average pore diameter of the pores in the second pore layer close to the non-woven fabric is larger, the pore structure is similar to a finger-shaped through hole, and large-volume particles and small-volume particles can pass through the second pore layer and pass through the non-woven fabric composite membrane, so that the requirements of the membrane and the liquid separation membrane on high liquid flux can be met; the first pore layer, the second pore layer and the pore diameter between the non-woven fabrics are graded layer by layer and are mutually matched in a cooperative manner, so that the composite membrane has good selective permeability, and finally realizes high flux, high selectivity and structural stability.

In one possible implementation, the average pore size of the nonwoven composite membrane is no greater than 0.2 μm, and the maximum pore size/average pore size ratio is 1-50; and/or the ratio of the longitudinal tensile strength to the transverse tensile strength of the non-woven fabric is 1.05-4; and/or the non-woven fabric is one of PET non-woven fabric, polyester non-woven fabric, PE non-woven fabric, PP non-woven fabric, polyolefin non-woven fabric, PVC non-woven fabric, polyamide non-woven fabric, PI non-woven fabric, PTFE non-woven fabric, PPS non-woven fabric, PAN non-woven fabric, cellulose non-woven fabric or aramid non-woven fabric.

In the above-mentioned implementation process, if the average pore diameter of the nonwoven composite membrane is greater than 0.2 μm and the maximum pore diameter/average pore diameter ratio is greater than 50, the nonwoven composite membrane having an excessively large pore diameter as a support layer for interfacial polymerization may absorb a large amount of water phase reaction monomer, which may result in: on one hand, a large amount of polymerization reaction products are formed in the membrane holes of the support membrane, so that the membrane permeation resistance of liquid is increased, and the flux of the membrane is reduced; on the other hand, the diffusion speed of the water phase reaction monomer from the membrane hole to the reaction interface is slowed down, so that the water phase monomer at the polymerization reaction interface is insufficient in supply, the crosslinking degree of the formed polymer cortex is low, and the rejection rate of the membrane is reduced; if the average pore diameter of the non-woven composite membrane is smaller than 0.2 μm and the maximum pore diameter/average pore diameter ratio is smaller than 50, the water phase monomer is less stored in the surface and pores of the support membrane, so that the water phase monomer is not supplied enough during interfacial polymerization, and the crosslinking degree of the ultrathin separation layer is reduced, and the non-woven composite membrane is difficult to have good selective permeability.

In one possible implementation, the nonwoven composite film has a thickness of 5-40 μm, the first pore layer has a porosity of 70% -95%, and the second pore layer has an average pore diameter of 0.1-10 μm.

In the implementation process, the non-woven composite membrane has high electrolyte absorption and retention rate and can ensure high-efficiency and rapid migration of lithium ions by limiting the thickness of the non-woven composite membrane and the parameters of the first pore layer and the second pore layer, and the non-woven composite membrane is more suitable for being used as a lithium battery diaphragm.

The thickness of the non-woven composite film is controlled to be 5-40 mu m, so that the loss of the energy density of the battery can be reduced under the condition of ensuring the tensile strength of the non-woven composite film, and the good battery cycle performance can be obtained. The porosity of the first pore layer is 70% -95%, the liquid retention rate of the non-woven composite membrane to the electrolyte can be improved, the smooth flow of the electrolyte is facilitated, and the advantages of high capacity and quick charging are provided for the battery. The composite membrane layer is compatible with the small aperture and the large aperture simultaneously under the synergistic effect of the mutual matching of the second pore layer and the non-woven fabric, so that a large specific surface area and an ion migration channel in the battery can be provided to the greatest extent, and high liquid absorption and retention performance is obtained; the average pore diameter of the second pore layer is 0.1-10 mu m, which is beneficial to improving the holding rate of the non-woven composite membrane to electrolyte and also beneficial to improving the lithium ion transmission rate.

In one possible implementation, not less than 10% of the polymer coating in the thickness direction is embedded in the nonwoven fabric; and/or the thickness of the polymer coating is 1-25 mu m, and the thickness of the first pore layer is 1-10% of the thickness of the polymer coating; and/or the surface density of the non-woven fabric is 5-25 g/cm ² The method comprises the steps of carrying out a first treatment on the surface of the And/or the nonwoven fabric has a cross-directional tensile strength greater than 0.2kN/m.

In the realization process, the part of the polymer coating which is not less than 10 percent in the thickness direction is embedded in the non-woven fabric, so that the polymer coating is not easy to peel off from the non-woven fabric; if the depth of embedding is less than 10%, the bonding strength between the polymer coating and the nonwoven fabric is low, and the polymer coating is easily peeled from the nonwoven fabric.

The thickness of the polymer coating is 1-25 mu m, so that the thickness of the lithium battery diaphragm can be well ensured not to be too large, and the loss of the battery energy density is reduced. And because the aperture of the first pore layer is small, the transmission resistance to lithium ions is the largest under the same thickness, if the thickness of the first pore layer exceeds 10% of the thickness of the porous polymer layer, the transmission resistance to lithium ions can be overlarge, so that the internal resistance of the lithium battery is obviously increased, and the battery performance is reduced.

In one possible implementation, the nonwoven composite film has a thickness greater than 40 μm and no greater than 210 μm, the first pore layer has a porosity of 50% to 90%, and the second pore layer has an average pore diameter of 0.5 to 30 μm.

In the implementation process, the non-woven composite membrane has high rejection rate and high water flux performance by limiting the thickness of the non-woven composite membrane and the parameters of the first pore layer and the second pore layer, so that the non-woven composite membrane is more suitable for being used as a liquid separation membrane.

The porosity of the first pore layer is 50% -90%, and the diameter of the pores in the first pore layer is micro-nano, so that the impurities can be prevented from passing through. If the porosity and average pore diameter are too small, the separation effect of the non-woven fabric composite membrane can be improved, but when impurities are trapped, the pores are easy to be blocked, so that the liquid separation efficiency is reduced; if the porosity and average pore diameter are too large, the separation effect of the liquid separation membrane cannot be ensured.

The average pore diameter of the second pore layer is in the range of 0.5-30 mu m, so that the resistance to liquid can be reduced to the greatest extent, the requirement of high water flux can be met, the structural strength of the second pore layer can be ensured, and the first pore layer is supported to a certain extent. If the average pore diameter of the second pore layer is too large, the structure of the second pore layer is too loose and is easy to break under high pressure; if the average pore diameter of the pores is too small, the resistance to the liquid is too large, and the requirement of high water flux cannot be met.

In one possible implementation, the roughness Ra of the side of the first pore layer remote from the second pore layer is 5-35 nm.

In the implementation process, the roughness Ra of one surface of the first pore layer, which is far away from the second pore layer, is not more than 35nm, and the ultra-thin separation layer of the liquid separation membrane is prepared by using the non-woven fabric composite membrane as the support membrane by using an interfacial polymerization method, so that the spreading of the aqueous phase reaction monomer on the surface of the support membrane in the interfacial polymerization process is more uniform, the rapid migration of the aqueous phase monomer is promoted, the interfacial polymerization reaction speed is accelerated, a primary membrane for separating the skin layer is rapidly formed on the surface of the support membrane, the further diffusion of the aqueous phase monomer is further inhibited, and the formation of a thinner compact skin layer is facilitated, so that the ultra-thin separation layer with few defects and high uniformity with thickness is prepared.

In one possible implementation, the polymer coating has not less than 10% of its portion embedded in the nonwoven fabric in the thickness direction; and/or the thickness of the polymer coating is 25-120 mu m, and the thickness of the first pore layer is 1-15% of the thickness of the polymer coating; and/or the surface density of the non-woven fabric is 30-90 g/cm ² The method comprises the steps of carrying out a first treatment on the surface of the And/or the nonwoven fabric has a cross-directional tensile strength greater than 2kN/m.

In the implementation process, if the penetration depth of the polymer coating in the non-woven fabric is greater than 50% of the thickness of the porous polymer layer, the polymer coating fills too much pores in the non-woven fabric, the graded filtering function of the non-woven fabric is not fully utilized, the resistance to fluid is increased, and the water flux is reduced. If the penetration depth of the polymer coating into the nonwoven fabric is less than 10% of the thickness of the porous polymer layer, the polymer coating is not tightly bonded to the nonwoven fabric.

The thickness of the polymer coating is 25-120 mu m, the thickness of the first pore layer is 1-15% of the thickness of the polymer coating, the pore defect on the surface of the membrane is avoided by proper thickness, the non-woven fabric composite membrane can be ensured to have higher interception performance, and the separation treatment efficiency is not influenced. If the polymer coating is too thick, or the thickness of the first pore layer exceeds 15%, the length of a path through which water molecules pass when penetrating through the membrane body is greatly increased, the resistance of the non-woven fabric separation membrane to liquid is increased, and the treatment efficiency is seriously reduced; if the polymer coating is too thin, or the thickness of the first porous layer is less than 1%, it is difficult for the nonwoven composite membrane to have high rejection performance.

In a second aspect, an embodiment of the present application provides a method for preparing the nonwoven fabric composite film, which includes the following steps: and dissolving the polymer in a solvent to form a casting solution with the mass fraction of 5% -50%, coating the casting solution on the surface of the carrier film, covering non-woven fabrics on the liquid surface of the casting solution to obtain a composite film to be solidified, immersing the composite film to be solidified in a coagulating bath solution until the casting solution is solidified, and cleaning and stripping the carrier film.

In the above implementation, the polymer coating layers at different positions have different liquid-liquid phase separation speeds, so that the composite film to be cured can form different layer structures when immersed into a coagulation bath solution for curing.

When the film casting liquid is solidified, the carrier film can block the direct contact between the solution in the coagulating bath and the solvent in the film casting liquid at one side of the film casting liquid coating close to the carrier film, and the diffusion direction of the solution in the coagulating bath from the non-woven fabric side to the carrier film side is controlled, so that the mass transfer exchange rate between the coagulating bath solution and the solvent in the film casting liquid is greatly reduced, the film casting liquid system is subjected to time delay phase separation, the liquid-liquid phase separation speed is reduced, the formation of a macroporous structure in the film can be effectively eliminated, and a first pore layer with smooth and flat surface and smaller pore diameter can be formed during solidification; on the side of the casting solution coating close to the non-woven fabric, the loose porous non-woven fabric can not block the direct contact between the solution in the coagulating bath and the solvent in the casting solution, the rate of mutual diffusion exchange between the casting solution and the coagulating bath solution on the side close to the non-woven fabric is high, the instantaneous liquid-liquid phase separation of the system is realized, and a second pore layer with larger pore diameter can be formed during solidification.

In addition, during preparation, the carrier film is coated with the film casting solution, then the non-woven fabric is covered on the film casting solution, and the thickness of the polymer coating in the functional film embedded into the non-woven fabric can be well controlled by adjusting the thickness of the film casting solution layer, so that the thickness of the non-woven fabric composite can be accurately regulated and controlled; the problems that in the traditional preparation method, the penetration depth of the casting solution is different or even the penetration is excessive on the surface of the non-woven fabric so as to leak the solution are effectively solved; further, since the casting solution is permeated into the nonwoven fabric and is cured, the nonwoven fabric becomes a part of the nonwoven fabric composite film when forming the nonwoven fabric composite film, and the heat stability and pressure resistance of the functional film can be increased. The carrier film and the nonwoven fabric cooperate to produce the nonwoven fabric composite film of the first aspect.

In one possible implementation, the carrier film is any one of a release film, an anti-sticking film, a waterproof film and silicone paper; optionally, the release film is any one of a PE release film, a PET release film, an OPP release film, a PC release film, a PS release film, a PMMA release film, a BOPP release film, a TPX release film, a PVC release film, a PTFE release film, a PPS release film or a composite release film; and/or the polymer is at least one of polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, polyarylsulfone amide, polyetherimide, polycarbonate, polyvinyl chloride, polyimide, polyether sulfone, polysulfone, polyarylsulfone, sulfonated polysulfone, sulfonated polyether sulfone, polyacrylonitrile, polyamide, polyether ether ketone, polyarylether ketone, sulfonated polyarylether ketone, polytetrafluoroethylene, sulfonated polyphenylene ether sulfone, polyvinylidene fluoride or cellulose acetate; and/or the solvent is at least one of N, N-dimethylformamide, dimethylacetamide, diethylformamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, acetone and tetrahydrofuran; and/or the coagulating bath solution comprises at least one of pure water, alcohol compounds, 1-40% solvent aqueous solution and acetone.

In one possible implementation, the polymer mass fraction of the casting solution is 5% -30%, and the thickness of the casting solution is 1-25 μm when the casting solution is coated on the surface of the carrier film.

In the realization process, the casting film liquid with specific mass fraction and specific thickness is beneficial to forming the non-woven fabric composite film which can be used for the lithium battery diaphragm.

In one possible implementation, after the composite film is cured, a drying step is further included; alternatively, the drying temperature is 40-90 ℃.

In one possible implementation, the polymer mass fraction of the casting solution is 10% -50%, and the thickness of the casting solution is 25-120 μm when the casting solution is coated on the surface of the carrier film.

In the above-described implementation, the use of a casting solution of a specific mass fraction and a specific thickness is advantageous in forming a nonwoven fabric composite membrane that can be used as a support membrane in a liquid separation membrane.

In a third aspect, the present application provides a lithium battery separator comprising the nonwoven fabric composite film described above and a nonwoven fabric composite film produced by using the production method of the second aspect.

In a fourth aspect, the present application provides a liquid separation membrane comprising the nonwoven fabric composite membrane described above and a nonwoven fabric composite membrane produced by the production method of the second aspect.

In a fifth aspect, the present application provides a lithium battery comprising the lithium battery separator of the third aspect.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments of the present application will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and should not be considered as limiting the scope, and other related drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flow chart of the preparation of a nonwoven fabric composite film according to an embodiment of the present application;

FIG. 2 is a schematic structural view of the composite film to be cured in examples 1 to 5 of the present application;

fig. 3 is a schematic structural view of a lithium battery separator according to embodiment 1 of the present application;

fig. 4 is a schematic structural view of a lithium battery separator according to embodiment 2 of the present application;

FIG. 5 is a schematic structural view of the composite film to be cured in examples 6 to 11 of the present application;

FIG. 6 is a schematic view showing the structure of a liquid separation membrane in example 6 of the present application;

fig. 7 is a schematic structural view of a lithium battery separator according to comparative example 1 of the present application;

fig. 8 is a schematic structural view of a liquid separation membrane in comparative example 6 of the present application.

Icon: 1-a carrier film; 2-polymer coating; 3-non-woven fabric; 4-polymer coating.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

The nonwoven fabric composite film and the method for preparing the same according to the embodiment of the application are specifically described below.

A non-woven fabric composite membrane comprises a non-woven fabric 3 and a polymer coating 2 which is overlapped on at least one surface of the non-woven fabric 3 and is partially or completely embedded in the non-woven fabric 3, wherein the polymer coating 2 is divided into a first pore layer and a second pore layer, and the second pore layer is partially or completely embedded in the non-woven fabric 3; the thickness of the non-woven composite membrane is 5-210 mu m, the average pore diameter is not more than 0.2 mu m, and the maximum pore diameter/average pore diameter ratio is 1-50; the ratio of the longitudinal tensile strength to the transverse tensile strength of the non-woven fabric 3 is 1.05-4; the first pore layer has porosity of 50-95%, average pore diameter of 10-200 nm, and average pore diameter of 0.1-30 μm.

It should be noted that "the second porous layer is partially or completely embedded in the nonwoven fabric 3" means that the nonwoven fabric composite film of the present application may or may not be embedded in the nonwoven fabric 3 according to actual conditions. For example, a part of the second porous layer may be embedded in the nonwoven fabric 3, and the first porous layer may not be embedded in the nonwoven fabric 3; the second porous layer may be entirely embedded in the nonwoven fabric 3, and the first porous layer may not be embedded in the nonwoven fabric 3; the second porous layer may be entirely embedded in the nonwoven fabric 3, and part of the first porous layer may be embedded in the nonwoven fabric 3; it is also possible that the first and second porous layers are all embedded in the nonwoven fabric 3, and the degree to which the polymer coating 2 is embedded in the nonwoven fabric 3 may be changed according to the actual application needs.

In the embodiment of the application, the first pore layer is a sponge pore layer, the pore structure of the first pore layer is in a sponge shape, the pores are fine, the pressure resistance is high, and the average pore diameter parameter is generally used for characterization; the second cell layer is a finger-like cell layer whose cell structure is finger-like through-holes and is therefore generally characterized by an average cell diameter parameter.

In the implementation process, the non-woven fabric 3 has good thermal stability and compression resistance, the polymer coating 2 is divided into a first pore layer and a second pore layer, the average pore diameter of the first pore layer is small, the pore structure is similar to a spongy pore, and large-volume particles can be well prevented from penetrating through the first pore layer and penetrating through the non-woven fabric composite membrane, but small-volume particles can be easily penetrated; the average pore diameter of the second pore layer is large, the pore structure is similar to a finger-shaped through hole, and particles with large volume or particles with small volume can easily penetrate through the second pore layer. The non-woven fabric 3 can play a role in supporting the embedded polymer coating 2, so that the formed non-woven fabric composite film not only has good thermal stability and compression resistance of the non-woven fabric 3, but also can selectively penetrate particles, and can still keep integrity when the temperature of a lithium battery is too high when the non-woven fabric composite film is used as a lithium battery diaphragm, prevent thermal runaway and reduce potential safety hazards; when used as a support membrane of a liquid separation membrane, the membrane still has good water flux and retention rate under the condition of higher pressure, and simultaneously ensures the separation effect and efficiency. In the embodiment of the application, parameters such as the thickness or the embedding degree of the non-woven fabric composite membrane can be specifically adjusted according to the needs, so that the non-woven fabric composite membrane can be used for a lithium battery diaphragm or a liquid separation membrane. Moreover, when the nonwoven fabric composite membrane of the present application is used for a liquid separation membrane, it can be used not only as a support membrane for the liquid separation membrane but also as a microfiltration membrane or an ultrafiltration membrane, and for simplicity of explanation, the present application is analyzed only with the support membrane for the liquid separation membrane.

For example, the nonwoven fabric composite film has a thickness of 5 to 40 μm; the porosity of the first pore layer is 70% -95%, the thickness is 1% -10% of the thickness of the polymer coating 2, the average pore diameter of the first pore layer is 10-200 nm, and optionally 10-80 nm; the average pore diameter of the second pore layer is 0.1-10 μm, for example, may be 0.1-6.5 μm; the thickness of the polymer coating 2 is 1-25 mu m, and the part of the polymer coating which is not less than 10% in the thickness direction is embedded in the non-woven fabric 3; the surface density of the non-woven fabric 3 is 5-25 g/cm ² The transverse tensile strength is greater than 0.2kN/m. The non-woven fabric composite film is suitable for being used as a lithium battery diaphragm.

In the realization process, the thickness of the non-woven fabric composite film is 5-40 mu m, and the loss of the energy density of the battery can be reduced under the condition of ensuring the tensile strength of the non-woven fabric composite film. The porosity of the first porous layer is 70% -95%, the liquid retention rate of the non-woven composite membrane to the electrolyte can be improved, the porosity is 70% -95%, the smooth flow of the electrolyte is facilitated, and the advantages of high capacity and quick charge are provided for the battery. However, since the pore diameter of the first pore layer is small and the transmission resistance to lithium ions is large, the thickness of the first pore layer needs to be controlled to be 1% -10% of the total thickness of the polymer coating 2, more than 10% can increase the internal resistance of the battery, reduce the battery efficiency, less than 1% can hardly avoid pore defects on the surface of the membrane, and the puncture-resistant strength is low and the porous electrode with uneven surface is difficult to prevent from puncturing the membrane, so that short circuit is caused. The average pore diameter of the second pore layer is 0.1-10 mu m, which is beneficial to improving the electrolyte holding rate and the ion transmission rate of the non-woven composite membrane.

The parameters of the nonwoven composite film may also be set to the following types:

the thickness of the non-woven fabric composite film is more than 40 mu m and not more than 210 mu m; the porosity of the first pore layer is 50% -90%, the thickness is 1% -15% of the thickness of the polymer coating 2, the average pore diameter of the first pore layer is 10-200 nm, and the average pore diameter of the first pore layer is 50-200 nm; the average pore diameter of the second pore layer is 0.5-30 mu m, and can be 0.5-15 mu m; the thickness of the polymer coating 2 is 25-120 mu m, and at least 10% of the polymer coating is embedded in the non-woven fabric 3 in the thickness direction, and further, 10% -50% of the polymer coating is embedded in the non-woven fabric; the roughness Ra of one surface of the first pore layer far away from the second pore layer is 5-35 nm; the surface density of the non-woven fabric 3 is 30-90 g/cm ² Specifically, the areal density may be 40 to 80g/cm ² The transverse tensile strength is greater than 2kN/m. The nonwoven composite membrane is suitable for use as a liquid separation membrane.

In the realization process, the thickness of the non-woven composite membrane is larger than 40 mu m and not larger than 210 mu m, so that the non-woven composite membrane has high interception rate and good water flux under the condition of ensuring the tensile strength of the non-woven composite membrane. The porosity of the first pore layer is 50% -90%, which is favorable for preventing impurities from passing through. If the porosity and average pore diameter are too small, although the separation effect of the non-woven fabric composite membrane can be improved, the pores are easily blocked when the impurities are trapped, so that the water treatment efficiency is reduced; if the porosity and average pore diameter are too large, the separation effect of the liquid separation membrane cannot be ensured. The average pore diameter of the second pore layer is 0.5-30 mu m, so that the resistance to liquid can be reduced to the greatest extent, the requirement of high water flux can be met, the structural strength of the second pore layer can be ensured, and the first pore layer can be supported to a certain extent. If the average pore diameter of the second pore layer is too large, the structure of the second pore layer is too loose and is easy to break under high pressure; if the average pore diameter of the pores is too small, the resistance to the liquid is too large, and the requirement of high water flux cannot be met.

The embodiment of the application also provides a preparation method of the non-woven fabric composite film, which comprises the following steps:

(1) Preparing a casting film liquid: and dissolving the polymer in a solvent to form a casting film solution with the mass fraction of 5-50%.

Wherein the polymer is at least one of polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, polyarylsulfone amide, polyetherimide, polycarbonate, polyvinyl chloride, polyimide (PI), polyethersulfone, polysulfone (PSF), polyarylsulfone, sulfonated polysulfone, sulfonated polyethersulfone, polyacrylonitrile, polyamide, polyetheretherketone, polyaryletherketone, sulfonated polyaryletherketone, polytetrafluoroethylene, sulfonated polyphenylene ether sulfone, polyvinylidene fluoride (polyvinylidene fluoride, PVDF) or cellulose acetate; the solvent is at least one of N, N-Dimethylformamide (DMF), N-Dimethylacetamide (DAMc), diethylformamide, N-methylpyrrolidone (NMP), N-ethylpyrrolidone, dimethylsulfoxide, acetone and tetrahydrofuran.

In this step, the mass fraction of the polymer may be changed according to the application scenario. If the non-woven fabric composite membrane is used for a lithium battery diaphragm, the mass fraction is controlled to be 5% -30%; if the prepared non-woven fabric composite membrane is used as a liquid separation membrane, the mass fraction can be controlled to be 10% -50%.

(2) Coating a casting film liquid: and uniformly coating the casting solution on the surface of the carrier film 1, and then covering the non-woven fabric 3 on the liquid surface of the casting solution to obtain the composite film to be solidified.

The carrier film 1 is a film with slight or no adhesiveness after contacting with the polymer coating, such as any one of a release film, a waterproof film and silicone paper; wherein the release film can be any one selected from PE release film, PET release film, OPP release film, PC release film, PS release film, PMMA release film, BOPP release film, TPX release film, PVC release film, PTFE release film, PPS release film or composite release film, and the non-woven fabric 3 can be any one selected from PET non-woven fabric, polyester non-woven fabric, PE non-woven fabric, PP non-woven fabric, polyolefin non-woven fabric, PVC non-woven fabric, polyamide non-woven fabric, PI non-woven fabric, PTFE non-woven fabric, PPS non-woven fabric, PAN non-woven fabric, cellulose non-woven fabric or aramid non-woven fabric.

In the step, the casting solution is firstly coated on the surface of the carrier film 1, then the non-woven fabric 3 is covered on the liquid level, at the moment, the casting solution is immersed into the non-woven fabric 3 from bottom to top, and when the casting solution is subsequently solidified, the thickness of the polymer coating 2 embedded into the non-woven fabric 3 can be well controlled, so that the thickness of the non-woven fabric 3 compounded can be accurately regulated. In addition, in the step, the thickness of the casting solution is required to be controlled within the range of 1-120 mu m, so that the occurrence of instability can be effectively inhibited, the defect holes on the surface of the film are reduced, and the thickness of the prepared non-woven fabric composite film meets the practical requirements. If the thickness of the casting solution is too small, the interface is more easily disturbed, and the probability of defect holes on the surface of the film is larger. If the thickness of the casting solution is too large, the propagation of particles is likely to be hindered, and the demand for a lithium battery separator or a liquid separation membrane cannot be satisfied.

Specifically, if the non-woven fabric composite film is used for a lithium battery diaphragm, the thickness of the casting film liquid is generally 1-25 μm; if the nonwoven fabric composite membrane is intended to be used as a liquid separation membrane, the thickness of the casting solution is generally 25 to 120. Mu.m.

(3) Curing: and transferring the composite film to be solidified into a coagulating bath solution until the film casting solution is solidified. Specifically, the curing time may be selected to be 3 to 60 minutes, and the temperature may be 25 to 35 ℃. The coagulating bath solution comprises at least one of pure water, an alcohol compound, an aqueous solution of 1-40 wt% of a solvent and acetone.

The composite film to be cured is transferred into a coagulation bath solution, and the polymer coating layer undergoes liquid-liquid phase separation due to the difference in solubility of the solution in the coagulation bath and the solvent in the polymer solution. Moreover, since the carrier film 1 is denser than the non-woven fabric 3, the polymer coating layer has different liquid-liquid phase separation speeds at the side close to the carrier film 1 and the side close to the non-woven fabric 3, and when the casting film liquid is solidified in the coagulating bath solution, the position close to the carrier film 1 and the position close to the non-woven fabric 3 can form different layer structures, so that the non-woven fabric composite film with asymmetric pore structures at two sides of the coating layer is formed.

When the film casting liquid is solidified, the carrier film can block the direct contact between the solution in the coagulating bath and the solvent in the film casting liquid at one side of the film casting liquid coating close to the carrier film, and the diffusion direction of the coagulating bath solution from the non-woven fabric side to the carrier film side is controlled, so that the mass transfer exchange rate between the coagulating bath solution and the solvent in the film casting liquid is greatly reduced, the film casting liquid system is subjected to time delay phase separation, the liquid-liquid phase separation speed is slowed down, the formation of a macroporous structure in the film can be effectively eliminated, a first pore layer with smooth and flat surface and smaller average pore diameter is formed during solidification, and the pores in the first pore layer are similar to sponge-shaped pores; on the side of the casting solution coating close to the non-woven fabric, the loose porous non-woven fabric 3 cannot block direct contact between the solution in the coagulating bath and the solvent in the casting solution, the mutual diffusion exchange speed of the casting solution and the coagulating bath solution on the side close to the non-woven fabric 3 is high, instantaneous liquid-liquid phase separation of a system occurs, instantaneous liquid-liquid phase separation of the casting solution and the non-solvent occurs, a second pore layer with larger pore diameter is formed during solidification, and the pore structure in the second pore layer is similar to a finger-shaped through hole.

(4) Forming a non-woven fabric composite film: and (3) after the casting solution is solidified, washing the composite membrane structure in the step (3), and peeling the carrier membrane 1 to form the non-woven fabric composite membrane.

If a lithium battery separator is to be formed, the step (4) needs to be dried while washing, and specifically, the temperature during drying can be selected to be 40-90 ℃; in the step (1), the mass fraction of the polymer of the casting solution is 5-30%; in the step (2), when the casting solution is applied to the surface of the carrier film, the thickness of the casting solution is 1 to 25. Mu.m, and the thickness of the nonwoven fabric is 5 to 35. Mu.m, preferably 5 to 24. Mu.m.

If a liquid separation membrane is to be formed, drying is not required; in the step (1), the mass fraction of the polymer in the casting solution is 10% -50%; in the step (2), when the casting solution is applied to the surface of the carrier film, the thickness of the casting solution is 25 to 120. Mu.m, preferably 25 to 80. Mu.m, and the thickness of the nonwoven fabric is 40 to 150. Mu.m, preferably 50 to 105. Mu.m.

After the carrier film 1 is peeled off, a structure in which the polymer coating 2 is embedded in the nonwoven fabric 3 is formed, which is the nonwoven fabric composite film in the present application.

It should also be noted that since the nonwoven fabric 3 has a loose porous structure, the polymer solution fills the pores of the nonwoven fabric 3 when immersed in the nonwoven fabric 3, and the average pore size of the nonwoven fabric composite film is regarded as the same as that of the polymer coating layer 2 after the polymer solution is cured.

The features and capabilities of the present application are described in further detail below in connection with the examples.

Example 1

As shown in fig. 1 to 3, the present embodiment provides a lithium battery separator including a non-woven fabric 3 and a polymer coating layer 2 stacked on an upper surface of the non-woven fabric 3 and embedded in the non-woven fabric 3, the polymer coating layer 2 including a first pore layer and a second pore layer. The specific preparation steps of the lithium battery separator are as follows:

(1) Preparing a casting film liquid: and adding PVDF into NMP, stirring until the PVDF is completely dissolved, and obtaining the casting solution with the PVDF mass fraction of 10% after vacuum defoaming.

(2) Coating a casting film liquid: uniformly coating the casting solution on the surface of PE release film (see figure 1), wherein the thickness of the casting solution is 2 mu m, the thickness is 10 mu m, and the surface density is 8g/m ² A PET nonwoven fabric having a transverse tensile strength of 1.43kN/m and a tensile strength aspect ratio of 1.42 was covered over the liquid film and bonded thereto (see FIG. 1) so that the casting solution was thickThe part with 20% of the degree direction is immersed into the PET non-woven fabric to form a composite film to be cured, and the structure of the composite film to be cured can be seen in fig. 2.

(3) Curing: the composite film to be cured in step (2) was transferred into a coagulation bath solution using a 1% nmp aqueous solution as the coagulation bath solution, so that the casting solution was cured for 10min at a curing temperature of 25 ℃.

(4) Forming a lithium battery separator: after the casting solution is solidified, the composite membrane structure in the step (3) is washed, and then is dried at 50 ℃, and the carrier membrane 1 is peeled off to form the lithium battery diaphragm.

The specific process of preparation (excluding the step of preparing the casting solution) is shown in fig. 1, and as can be seen from fig. 1, the preparation is carried out by coating the casting solution on the surface of the carrier film, then covering the non-woven fabric, curing, washing with deionized water, drying, and then stripping the carrier film to form the lithium battery separator.

In this example, the total thickness of the lithium battery separator was 11.6 μm, the average pore diameter was 53.5nm, and the maximum pore diameter/average pore diameter ratio was 8.6; the total thickness of the PVDF coating is 2 μm, 20% of the PVDF coating is partially embedded into the PET non-woven fabric in the thickness direction, the first pore layer is positioned on the side far away from the non-woven fabric relative to the second pore layer, the thickness of the first pore layer is 0.2 μm, the porosity is 90%, the average pore diameter is 53.5nm, and the average pore diameter of the second pore layer is 3.5 μm. In this example, the polymer coating 2 was not completely embedded in the nonwoven fabric 3, and the lithium battery separator had no hole defect.

Example 2

As shown in fig. 1 to 2 and fig. 4, the present embodiment provides a lithium battery separator including a nonwoven fabric 3 and a polymer coating layer 2 stacked on an upper surface of the nonwoven fabric 3 and embedded in the nonwoven fabric 3, the polymer coating layer 2 including a first pore layer and a second pore layer. The specific preparation steps of the lithium battery separator are as follows:

(1) Preparing a casting film liquid: and adding PI into DMAc, stirring until the PI is completely dissolved, and obtaining the casting film liquid with the PI mass fraction of 5% after vacuum defoaming.

(2) Coating a casting film liquid: uniformly coating the casting solution on the surface of the PET release filmThe thickness of the casting solution was 8. Mu.m, the thickness was 8. Mu.m, and the areal density was 6g/m ² A PP nonwoven fabric having a transverse tensile strength of 0.75kN/m and a tensile strength aspect ratio of 1.81 was covered over the liquid film and bonded so that the casting film liquid was entirely immersed in the PP nonwoven fabric in the thickness direction to form a composite film to be cured (see fig. 2).

(3) Curing: and (3) transferring the composite film to be solidified in the step (2) into the coagulating bath solution by using pure water as the coagulating bath solution, so that the casting solution is solidified, the solidifying time is 30min, and the solidifying temperature is 25 ℃.

(4) Forming a lithium battery separator: after the casting solution is solidified, the composite membrane structure in the step (3) is washed, then dried at 60 ℃, and the carrier membrane 1 is peeled off to form the lithium battery diaphragm.

In this example, the total thickness of the lithium battery separator was 8 μm, the average pore diameter was 82.9nm, and the maximum pore diameter/average pore diameter ratio was 13.0; the total thickness of the PI coating was 8 μm and was fully embedded in the nonwoven fabric 3, the thickness of the first pore layer was 0.24 μm, the porosity was 95%, the average pore diameter was 82.9nm, and the average pore diameter of the second pore layer was 4.8 μm. In this example, the polymer coating 2 was completely embedded in the nonwoven fabric 3, and the lithium battery separator was produced without hole defects.

Example 3

As shown in fig. 1 to 2, the present embodiment provides a lithium battery separator including a non-woven fabric 3 and a polymer coating layer 2 stacked on an upper surface of the non-woven fabric 3 and embedded in the non-woven fabric 3, the polymer coating layer 2 including a first pore layer and a second pore layer. The specific preparation steps of the lithium battery separator are as follows:

(1) Preparing a casting film liquid: and adding PSF into DMF, stirring until the PSF is completely dissolved, and obtaining the casting film liquid with the mass fraction of PSF of 30% after vacuum defoaming.

(2) Coating a casting film liquid: uniformly coating the casting solution on the surface of the PP/PET release film, wherein the thickness of the casting solution is 3 mu m, the thickness is 15 mu m, and the surface density is 13g/m ² The PP/PET non-woven fabric with the transverse tensile strength of 2.58kN/m and the tensile strength aspect ratio of 1.53 is covered on the liquid film and is attached, so that 40 percent of the casting film liquid in the thickness direction is immersed into PIn the P/PET nonwoven, a composite film to be cured was formed (see fig. 2).

(3) Curing: and (3) transferring the composite film to be solidified in the step (2) into a coagulating bath by using pure water as the coagulating bath, so that the casting solution is solidified, the solidifying time is 15min, and the solidifying temperature is 30 ℃.

(4) Forming a lithium battery separator: after the casting solution is solidified, the composite membrane structure in the step (3) is washed, then the composite membrane structure is dried at 55 ℃, and the carrier membrane 1 is peeled off to form the lithium battery diaphragm.

In this example, the total thickness of the lithium battery separator was 16.8 μm, the average pore diameter was 13.2nm, and the maximum pore diameter/average pore diameter ratio was 3.1; the total thickness of the polymer coating 2 was 3 μm, 40% of the portion in the thickness direction was embedded in the nonwoven fabric 3, the first pore layer was located on the side away from the nonwoven fabric with respect to the second pore layer, the thickness of the first pore layer was 0.15 μm, the porosity was 70%, the average pore diameter was 13.2nm, and the average pore diameter of the second pore layer was 0.53 μm.

Example 4

(1) Preparing a casting film liquid: PVDF is added into DMSO, stirred until the PVDF is completely dissolved, and vacuum defoamed to obtain the casting solution with the mass fraction of 18%.

(2) Coating a casting film liquid: uniformly coating the casting solution on the surface of the PET release film, wherein the thickness of the casting solution is 14 mu m, the thickness is 24 mu m, and the surface density is 20g/m ² A PI nonwoven fabric having a transverse tensile strength of 3.78kN/m and a tensile strength aspect ratio of 2.24 was covered over the liquid film and bonded so that 90% of the casting film liquid in the thickness direction was immersed in the PP nonwoven fabric to form a composite film to be cured (see fig. 2).

(3) Curing: and (3) transferring the composite film to be solidified in the step (2) into a coagulating bath by using pure water as the coagulating bath, so that the casting solution is solidified, the solidifying time is 40min, and the solidifying temperature is 35 ℃.

(4) Forming a lithium battery separator: and (3) after the casting solution is solidified, washing the composite membrane structure in the step (3), drying at 65 ℃, and stripping the carrier membrane 1 to obtain the lithium battery diaphragm.

In this example, the total thickness of the lithium battery separator was 25.4 μm, the average pore diameter was 42.6 μm, and the maximum pore diameter/average pore diameter ratio was 6.4; the total thickness of the polymer coating 2 was 14 μm, 90% of the portion in the thickness direction was embedded in the nonwoven fabric 3, the first pore layer was located on the side away from the nonwoven fabric with respect to the second pore layer, the thickness of the first pore layer was 0.7 μm, the porosity was 82%, the average pore diameter was 42.6nm, and the average pore diameter of the second pore layer was 6.5 μm. In this example, the polymer coating 2 was not completely embedded in the nonwoven fabric 3, and the lithium battery separator was produced without hole defects.

Example 5

As shown in fig. 1 and 2, the present embodiment provides a lithium battery separator, which includes a non-woven fabric 3 and a polymer coating 2 stacked on an upper surface of the non-woven fabric 3 and embedded in the non-woven fabric 3, the polymer coating 2 including a first porous layer and a second porous layer. The specific preparation steps of the lithium battery separator are as follows:

(1) Preparing a casting film liquid: PVDF-HFP is added into NMP, stirred until the PVDF-HFP is completely dissolved, and the casting solution with the mass fraction of 25% is obtained after vacuum defoaming.

(2) Coating a casting film liquid: uniformly coating the casting solution on the surface of the PE release film, wherein the thickness of the casting solution is 25 mu m, the thickness is 32 mu m, and the surface density is 25g/m ² PAN non-woven fabric with transverse tensile strength of 4.92k N/m and longitudinal tensile strength/transverse tensile strength ratio of 1.65 is covered above the liquid film and is attached, so that 70% of the casting film liquid in the thickness direction is immersed into the PAN non-woven fabric to form a composite film to be solidified.

(3) Curing: and (3) transferring the composite film to be solidified in the step (2) into a coagulating bath by using pure water as the coagulating bath, so that the casting solution is solidified, the solidifying time is 50min, and the solidifying temperature is 30 ℃.

(4) Forming a lithium battery separator: and (3) after the casting solution is solidified, washing the composite membrane structure in the step (3), drying at 70 ℃, and stripping the carrier membrane 1 to obtain the lithium battery diaphragm.

In this example, the total thickness of the lithium battery separator was 39.5 μm, the average pore diameter was 27.5 μm, and the maximum pore diameter/average pore diameter ratio was 4.6; the total thickness of the polymer coating 2 was 25 μm, 70% of the portion in the thickness direction was embedded in the nonwoven fabric 3, the first pore layer was located on the side away from the nonwoven fabric with respect to the second pore layer, the first pore layer had a thickness of 1.25 μm, a porosity of 75%, an average pore diameter of 27.5nm, and an average pore diameter of 8.1 μm.

Specific parameters of the lithium battery separators in examples 1 to 5 are shown in table 1:

table 1 specific parameters during the preparation of examples 1 to 5

Example 6

As shown in fig. 1 and 5, the present embodiment provides a support film for a liquid separation membrane, comprising a nonwoven fabric 3 and a polymer coating layer 2 stacked on the upper surface of the nonwoven fabric 3 and embedded in the nonwoven fabric 3, the polymer coating layer 2 comprising a first pore layer and a second pore layer. The specific preparation steps of the liquid separation membrane support membrane are as follows:

(1) Preparing a casting film liquid: and adding polyethersulfone into DMF, stirring until the polyethersulfone is completely dissolved, and obtaining the casting solution with the mass fraction of the polyethersulfone of 10 percent after vacuum defoaming.

(2) Coating a casting film liquid: uniformly coating the casting solution on the surface of the PET release film, wherein the thickness of the casting solution is 25 mu m, the thickness is 90 mu m, and the surface density is 70g/m ² The PP non-woven fabric with the transverse tensile strength of 3.62kN/m and the longitudinal tensile strength/transverse tensile strength ratio of 1.46 is covered above the liquid film and is attached, so that 40% of the casting film liquid in the thickness direction is immersed into the PP non-woven fabric to form the composite film to be solidified.

(3) Curing: and (3) transferring the composite film to be solidified in the step (2) into a coagulating bath by using pure water as the coagulating bath, so that the casting solution is solidified, wherein the solidifying time is 10min, and the solidifying temperature is 30 ℃.

(4) Forming a composite non-woven fabric: and (3) after the casting solution is solidified, washing the composite membrane in the step (3), and stripping the carrier membrane 1 to obtain the composite non-woven fabric for the liquid separation membrane support membrane.

In this example, the total thickness of the composite nonwoven fabric for a liquid separation membrane support membrane was 105 μm, the average pore diameter was 0.17 μm, and the maximum pore diameter/average pore diameter ratio was 25.9; the total thickness of the polymer coating layer 2 was 25 μm, 40% of the portion in the thickness direction was embedded in the nonwoven fabric 3, the first pore layer was located on the side away from the nonwoven fabric with respect to the second pore layer, the first pore layer had a thickness of 0.25 μm, a porosity of 90%, an average pore diameter of 0.17nm, an average pore diameter of 18 μm, and a roughness Ra of the surface of the first pore layer away from the second pore layer of 32nm.

Examples 7 to 11

Examples 7 to 11 respectively provide a support film of a liquid separation membrane comprising a nonwoven fabric 3 and a polymer coating layer 2 laminated on an upper surface of the nonwoven fabric 3 and embedded in the nonwoven fabric 3, the polymer coating layer 2 comprising a first pore layer and a second pore layer. The preparation methods of the support films in examples 7 to 11 are mainly different from example 6 in that specific parameters in the preparation processes of examples 6 to 11 are shown in table 2, and are as follows:

Table 2 specific parameters during the preparation of examples 6 to 11

Comparative example 1

As shown in fig. 7, the present comparative example provides a lithium battery separator comprising a non-woven fabric 3 and a polymer coating layer 4 stacked on the upper surface of the non-woven fabric 3 and embedded in the non-woven fabric 3, and is prepared as follows:

(1) Preparing a casting film liquid: and adding PVDF into DMF, stirring until the PVDF is completely dissolved, and obtaining the casting solution with the PVDF mass fraction of 30% after vacuum defoaming.

(2) Coating a casting film liquid: the casting solution is uniformly coated on the surface of the non-woven fabric 3 to ensureThe thickness of the casting solution was 3. Mu.m, and 90% of the casting solution was immersed in the nonwoven fabric 3 in the thickness direction to form a composite film to be cured. Wherein the nonwoven fabric 3 is made of PET, has a thickness of 15 μm and an areal density of 12g/m ² The transverse tensile strength was 1.39kN/m and the tensile strength aspect ratio was 1.25.

(3) Curing: and (3) transferring the composite film to be cured in the step (2) into a coagulating bath by using a pure water solution as the coagulating bath, so that the casting solution is cured for 15min at a curing temperature of 30 ℃.

(4) And (3) drying: and (3) after the film casting liquid in the step (3) is solidified, washing the composite film layer structure, and drying at 55 ℃ to prepare the lithium battery diaphragm.

In this comparative example, the total thickness of the prepared lithium battery separator was 15.3 μm, the average pore diameter was 257.4nm, and the maximum pore diameter/average pore diameter ratio was 15.68; the porosity of the PVDF coating was 70%, the average pore diameter was 257.4nm, the thickness of the PVDF coating was 3 μm, and 90% of the portion in the thickness direction was embedded in the PET nonwoven fabric. The upper surface of the lithium battery separator in comparative example 1 had a hole defect as shown in fig. 7, and there was a case where the casting solution penetrated to the back surface of the nonwoven fabric, and after the battery was assembled, the battery capacity was largely attenuated.

Comparative examples 2 to 5

Comparative examples 2 to 5 each provide a lithium battery separator comprising a non-woven fabric 3 and a polymer coating layer 4 laminated on the upper surface of the non-woven fabric 3 and embedded in the non-woven fabric 3. The preparation methods of the support films in comparative examples 2 to 5 are mainly different from example 1 in that specific parameters are different, and table 3 shows specific parameters in the preparation processes of comparative examples 1 to 5, as follows:

TABLE 3 specific parameters during the preparation of comparative examples 1 to 5

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Comparative example 6

As shown in fig. 8, the present comparative example provides a support film for a liquid separation membrane comprising a nonwoven fabric 3 and a polymer coating layer 4 laminated on the upper surface of the nonwoven fabric 3 and embedded in the nonwoven fabric 3, and is prepared as follows:

(2) Coating a casting film liquid: the casting solution was uniformly coated on the surface of the nonwoven fabric 3 to ensure that the thickness of the casting solution was 25 μm, and that 80% of the casting solution was immersed in the nonwoven fabric 3 in the thickness direction to form the composite film B. Wherein the nonwoven fabric 3 is PP nonwoven fabric with thickness of 90 μm and surface density of 70g/m ² The transverse tensile strength was 3.62kN/m and the tensile strength aspect ratio was 1.46.

(3) Curing: and (3) transferring the composite film B in the step (2) into a coagulating bath by using pure water as the coagulating bath, so that the casting film liquid is solidified, wherein the solidifying time is 10min, and the solidifying temperature is 30 ℃.

In this comparative example, the total thickness of the produced composite nonwoven fabric for a liquid separation membrane support membrane was 95 μm, the average pore diameter was 1.81 μm, and the maximum pore diameter/average pore diameter ratio was 67.4; the porosity of the polyethersulfone coating is 90%, the average pore diameter is 1.81 mu m, the thickness of the polyethersulfone coating is 25 mu m, 80% of the portion of the polyethersulfone coating, which is embedded into the PP non-woven fabric inner coating, is excessively deep in the thickness direction, so that the mass transfer resistance of liquid is increased, the roughness Ra of the surface of the polyethersulfone coating, which is far away from the PP non-woven fabric, is 103, roughness and unevenness are relatively rough, pinhole defects are generated, the method has negative influence on the subsequent preparation of an ultrathin separating layer by taking the composite non-woven fabric as a supporting film, and the thickness uniformity of an ultrathin skin layer is difficult to ensure.

Comparative examples 7 to 9

Comparative examples 7 to 9 each provide a support film of a liquid separation membrane comprising a nonwoven fabric 3 and a polymer coating layer 4 laminated on the upper surface of the nonwoven fabric 3 and embedded in the nonwoven fabric 3. The preparation methods of the support films of comparative examples 7 to 9 are mainly different from example 6 in that specific parameters are different, and table 4 shows specific parameters in the preparation processes of comparative examples 6 to 9, as follows:

table 4 specific parameters during the preparation of comparative examples 6 to 9

Application example 1

The present application example was used to measure the performance of the lithium battery separator of examples 1 to 5 and comparative examples 1 to 5, and the relevant technical index reference standards for the nonwoven fabric composite film used as the lithium battery separator were as follows:

the areal density of the nonwoven fabric 3 is determined according to the method of GB/T451.2-2002, the thickness of the nonwoven fabric 3 is determined according to the method of GB/T451.3-2002, and the density of the nonwoven fabric 3 is obtained by dividing the areal density of the nonwoven fabric 3 by the thickness of the nonwoven fabric 3.

The tensile strength of the non-woven fabric 3 is determined according to a GB/T12914-2008 method, the pore diameter of the non-woven fabric composite film is determined according to a GB/T32361-2015 method, and the air permeability and the heat shrinkage rate of the non-woven fabric composite film are determined according to a GB/T36363-2018 method.

Battery cycling performance was tested according to the GB/T18287-2013 method.

Climbing height test of electrolyte on diaphragm sample: cutting a sample to be tested into rectangular sample strips with the length of 20cm multiplied by 1cm, fixing one end of the sample strip to be tested on a clamp vertical to a test bed, and vertically immersing the sample in an electrolyte solution (LiPF with the length of 1 mol/L) ₆ The volume ratio of EC to DEC is 1:1) of 0.5cm, and the climbing height of the electrolyte on the diaphragm sample strip is measured after standing for 1 h. The higher the height, the faster the sample absorbs electrolyte.

Electrolyte holding rate measurement: weighing the mass W1 of the non-infiltrated electrolyte of the sample to be measured, infiltrating the sample into the electrolyte for 1h, wiping off redundant electrolyte on the surface of the membrane, weighing and marking as W2, and calculating the electrolyte rate according to the following formula:

electrolyte holding ratio= (W2-W1)/w1×100%

Testing the cycle performance of the diaphragm assembled lithium ion battery, and qualitatively evaluating the attenuation condition of the capacity, wherein the evaluation standard is as follows: excellent level with a capacity decay rate of < 5%; the O-capacity attenuation rate is 5-20%, and the medium level; delta-capacity decay rate is 20-50%, worse level; x-capacity fade >50%, unusable level.

Table 5 performance parameters of lithium battery separators in examples 1 to 5

Table 6 Performance parameters of lithium battery separators in comparative examples 1 to 5

As can be seen from tables 5 and 6, the lithium battery separator of examples 1 to 5 has fine pores, small coating thickness, good thermal stability, high absorption rate of electrolyte, high electrolyte holding rate, contribution to rapid lithium ion transmission after battery assembly, good battery cycle performance after battery assembly, and capacity reduction rate of less than 5%.

Application example 2

This application example was used to measure the performance of the liquid separation membranes of examples 6 to 11 and comparative examples 6 to 9, and the relevant technical index reference standards for nonwoven fabric composite membranes used as liquid separation membranes were as follows:

The tensile strength of the non-woven fabric 3 is determined according to a GB/T12914-2008 method, the pore diameter of the non-woven fabric composite film is determined according to a GB/T32361-2015 method, the air permeability and the heat shrinkage rate of the non-woven fabric composite film are determined according to a GB/T36363-2018 method, and in the non-woven fabric composite film, the surface roughness Ra of the first pore layer is determined according to a GB/T10610-2009 method.

Evaluation criteria for "compaction resistance" of nonwoven composite films:

o: after being used for liquid separation, the dissection finds that the membrane hole structure is stable, no hole collapses or collapses, and the level is very excellent; delta: after use in liquid separation, dissection found that the membrane pore structure was essentially stable, with within 10% of the pores collapsed or depressed, moderate; x: after use for liquid separation, dissection found that the membrane pore structure was unstable, more than 10% of the pores collapsed or collapsed, and unusable levels.

TABLE 7 Performance parameters of liquid separation membranes in examples 6-11

Table 8 Performance parameters of the liquid separation membranes of comparative examples 6 to 9

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As can be seen from tables 7 and 8, the samples of examples 6 to 11 have good properties, and the membranes have high pure water flux, especially narrow pore size and pore size distribution, which is advantageous for the interfacial polymerization process for preparing ultra-thin separation layers.

The above description is only an example of the present application and is not intended to limit the scope of the present application, and various modifications and variations will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. The non-woven fabric composite film is characterized by comprising non-woven fabric and a polymer coating overlapped on the non-woven fabric, wherein the polymer coating comprises a first pore layer and a second pore layer;

the polymer coating is partially embedded in the non-woven fabric, the first pore layer is far away from the non-woven fabric relative to the second pore layer,

or the polymer coating is embedded in the non-woven fabric;

the porosity of the first pore layer is 50% -95%, the average pore diameter of the first pore layer is 10-200 nm, the average pore diameter of the second pore layer is 0.1-30 mu m, and the average pore diameter of the first pore layer is smaller than the average pore diameter of the second pore layer.

2. The nonwoven fabric composite membrane according to claim 1, wherein the nonwoven fabric composite membrane has an average pore size of not more than 0.2 μm and a maximum pore size/average pore size ratio of 1 to 50;

and/or the ratio of the longitudinal tensile strength to the transverse tensile strength of the non-woven fabric is 1.05-4;

and/or the non-woven fabric is one of PET non-woven fabric, polyester non-woven fabric, PE non-woven fabric, PP non-woven fabric, polyolefin non-woven fabric, PVC non-woven fabric, polyamide non-woven fabric, PI non-woven fabric, PTFE non-woven fabric, PPS non-woven fabric, PAN non-woven fabric, cellulose non-woven fabric or aramid non-woven fabric.

3. The nonwoven fabric composite membrane according to claim 1 or 2, wherein the nonwoven fabric composite membrane has a thickness of 5 to 40 μm, the first pore layer has a porosity of 70 to 95%, and the second pore layer has an average pore diameter of 0.1 to 10 μm.

4. The nonwoven fabric composite film according to claim 3, wherein not less than 10% of the polymer coating layer in the thickness direction is embedded in the nonwoven fabric;

and/or the thickness of the polymer coating is 1-25 mu m, and the thickness of the first pore layer is 1-10% of the thickness of the polymer coating;

and/or the surface density of the non-woven fabric is 5-25 g/m ² The method comprises the steps of carrying out a first treatment on the surface of the And/or the nonwoven fabric has a cross-directional tensile strength greater than 0.2kN/m.

5. The nonwoven fabric composite membrane according to claim 1 or 2, wherein the nonwoven fabric composite membrane has a thickness of more than 40 μm and not more than 210 μm, the first pore layer has a porosity of 50% to 90%, and the second pore layer has an average pore diameter of 0.5 to 30 μm.

6. The nonwoven fabric composite film according to claim 5, wherein the roughness Ra of the side of the first pore layer away from the second pore layer is 5 to 35nm.

7. The nonwoven fabric composite film according to claim 5, wherein the polymer coating layer has a portion of not less than 10% embedded in the nonwoven fabric in the thickness direction;

and/or the thickness of the polymer coating is 25-120 mu m, and the thickness of the first pore layer is 1-15% of the thickness of the polymer coating;

and/or the surface density of the non-woven fabric is 30-90 g/m ² The method comprises the steps of carrying out a first treatment on the surface of the And/or the nonwoven fabric has a cross-directional tensile strength greater than 2kN/m.

8. A method of producing the nonwoven fabric composite film according to any one of claims 1 to 7, comprising the steps of: and dissolving a polymer in a solvent to form a casting solution with the mass fraction of 5% -50%, coating the casting solution on the surface of a carrier film, covering a non-woven fabric on the liquid surface of the casting solution to obtain a composite film to be solidified, immersing the composite film to be solidified in a coagulating bath solution until the casting solution is solidified, and cleaning and stripping the carrier film.

9. The method for producing a nonwoven fabric composite film according to claim 8, wherein the carrier film is any one of a release film, an anti-sticking film, a waterproof film, and silicone paper;

Optionally, the release film is any one of a PE release film, a PET release film, an OPP release film, a PC release film, a PS release film, a PMMA release film, a BOPP release film, a TPX release film, a PVC release film, a PTFE release film, a PPS release film, or a composite release film;

and/or the polymer is at least one of polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, polyarylsulfone amide, polyetherimide, polycarbonate, polyvinyl chloride, polyimide, polyether sulfone, polysulfone, polyarylsulfone, sulfonated polysulfone, sulfonated polyether sulfone, polyacrylonitrile, polyamide, polyether ether ketone, polyarylether ketone, sulfonated polyarylether ketone, polytetrafluoroethylene, sulfonated polyphenylene ether sulfone, polyvinylidene fluoride or cellulose acetate;

and/or the solvent is at least one of N, N-dimethylformamide, dimethylacetamide, diethylformamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, acetone and tetrahydrofuran;

and/or the coagulating bath solution comprises at least one of pure water, an alcohol compound, an aqueous solution of the solvent with the mass fraction of 1-40% and acetone.

10. The method for producing a nonwoven fabric composite film according to claim 8 or 9, wherein the polymer mass fraction of the casting solution is 5 to 30%, and the thickness of the casting solution is 1 to 25 μm when the casting solution is coated on the surface of the carrier film.

11. The method of producing a nonwoven fabric composite film according to claim 10, further comprising a drying step after the composite film is cured; alternatively, the drying temperature is 40-90 ℃.

12. The method for producing a nonwoven fabric composite film according to claim 8 or 9, wherein the polymer mass fraction of the casting solution is 10% to 50%, and the thickness of the casting solution is 25 to 120 μm when the casting solution is coated on the surface of the carrier film.

13. A lithium battery separator comprising the nonwoven fabric composite film according to any one of claims 1 to 4 or comprising the nonwoven fabric composite film produced by the production method according to any one of claims 8 to 11.

14. A liquid separation membrane comprising the nonwoven fabric composite membrane according to any one of claims 1 to 2 and 5 to 7 or comprising the nonwoven fabric composite membrane produced by the production method according to any one of claims 8 to 9 and 12.

15. A lithium battery comprising the lithium battery separator of claim 13.