Composite separator, preparation method therefor and use thereof

Abstract

The present application discloses a composite separator, a preparation method therefor and a use thereof. The composite separator comprises a polyolefin separator, an adhesive layer coated on one or both sides of the polyolefin separator, and a cellulose film covering the surface of the adhesive layer, wherein the pore diameter of the cellulose film is greater than that of the polyolefin separator. According to the composite separator, the strength and thermal stability of a traditional separator can be improved, and the requirements of liquid absorption and retention are met, so that the performance and the cycle life of an energy storage device are improved.

Description

A composite diaphragm and its preparation method and application Technical Field

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

[0002] Energy storage devices, such as lithium batteries, sodium batteries, and supercapacitors, play an important role in modern energy storage and utilization. Separators, as a crucial component of energy storage devices, are primarily used to separate the positive and negative electrodes, preventing direct electron pathways while allowing the formation of ion channels, thereby enabling charge transfer and preventing short circuits.

[0003] With the rapid development of the new energy industry, the demand for various energy storage devices has increased accordingly, and at the same time, the performance requirements for these energy storage devices have become increasingly higher. As a component that is widely present in energy storage devices such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, supercapacitors, and activated carbon batteries, diaphragms have a very important impact on the performance of energy storage devices. However, traditional polyolefin diaphragms have poor thermal stability and are prone to melting or deformation under high temperature conditions, which limits the operating temperature range of energy storage devices. In addition, due to the low surface energy of polyolefin materials, traditional polyolefin diaphragms also have poor liquid absorption and liquid retention properties, which affects the cycle life and performance stability of energy storage devices.

[0004] Therefore, there is an urgent need for a composite diaphragm and a preparation method and application thereof.

[0005] Application Contents

[0006] The present application provides a composite diaphragm and a preparation method and application thereof to solve the problem of low ionic conductivity faced by existing energy storage devices at high power and high rate.

[0007] To solve the above problem, the technical solution provided by this application is as follows:

[0008] In a first aspect, the present application provides a composite membrane, comprising a composite reinforced membrane layer, the composite reinforced membrane layer comprising a polyolefin membrane and a cellulose membrane composited on one or both sides of the polyolefin membrane, wherein the polyolefin membrane and the cellulose membrane are composited by an adhesive;

[0009] Among them, the pore size of the cellulose membrane is larger than that of the polyolefin membrane.

[0010] In the composite membrane provided in the embodiment of the present application, the composite membrane also includes a nano-coating layer composited on both sides of the composite reinforced membrane layer, the pore size of the nano-coating layer is smaller than the pore size of the polyolefin membrane, and the material of the nano-coating layer includes metal halide; the binder is doped with metal hydroxide and is attached to the polyolefin membrane and the cellulose membrane.

[0011] In the composite membrane provided in the embodiment of the present application, the composite membrane also includes a ceramic membrane, the composite reinforced membrane layer in the composite membrane includes a polyolefin membrane and a cellulose membrane composited on one side of the polyolefin membrane, the ceramic membrane is composited on the side of the polyolefin membrane away from the cellulose membrane, and the ceramic membrane, the polyolefin membrane and the cellulose membrane are composited by an adhesive;

[0012] Among them, the pore size of the ceramic diaphragm is smaller than that of the polyolefin diaphragm. The pore sizes of the ceramic diaphragm, polyolefin diaphragm and cellulose membrane in the composite diaphragm are 0.01-0.1 μm, 0.05-2 μm and 0.1-5 μm respectively; the binder is doped with metal halide and attached to the ceramic diaphragm, polyolefin diaphragm and cellulose membrane.

[0013] In the composite membrane provided in the embodiment of the present application, the overall thickness of the composite membrane is 8 to 35 μm.

[0014] In the composite membrane provided in the embodiment of the present application, the polyolefin membrane is a polypropylene membrane or a polyethylene membrane, the thickness of the polyolefin membrane is 4 μm to 20 μm, and the pore size of the polyolefin membrane is 0.05 μm to 2 μm.

[0015] In the composite separator provided in the embodiment of the present application, the thickness of the cellulose membrane is 4 μm to 21 μm, and the pore size of the cellulose membrane is 0.1 μm to 15 μm.

[0016] In the composite diaphragm provided in the embodiment of the present application, the cellulose membrane is formed by interweaving nanocellulose fibers and synthetic fibers; the diameter of the nanocellulose fibers is not greater than 500 nm, and the length is 0.3 mm to 3 mm.

[0017] In the composite diaphragm provided in the embodiment of the present application, the cellulose membrane is interwoven with cotton fiber, bamboo pulp fiber, nano-aramid, and synthetic cellulose fiber; the diameters of the cotton fiber, bamboo pulp fiber, and nano-aramid are all in the range of 500 nm to 0.6 μm, and the lengths are all in the range of 0.6 mm to 6 mm.

[0018] In the composite diaphragm provided in the embodiment of the present application, the metal element in the metal halide and the metal hydroxide is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

[0019] In the composite membrane provided in the embodiment of the present application, the pore size of the ceramic membrane is 0.1 μm to 15 μm, and a layer of metal or covalent organic framework material with sub-nanometer pore size is deposited on the surface and in the pores of the ceramic membrane.

[0020] In the composite membrane provided in the embodiment of the present application, the metal or covalent organic framework material with sub-nano pore size includes any one of ZIF-8, UiO-66 and COF-Go; wherein, the pore size of ZIF-8 is 0.34nm~1.16nm, the pore size of COF-GO is 0.5nm~1.4nm, and the pore size of UiO-66 is 0.8nm~1.1nm.

[0021] In a second aspect, the present invention provides a method for preparing a composite diaphragm, the method comprising:

[0022] S10, mixing a binder and a solvent to form a binding solution;

[0023] S20, soaking the polyolefin separator and at least one cellulose membrane in a bonding solution. After sufficient soaking, the cellulose membrane is composited with both sides or one side of the polyolefin separator to obtain a composite reinforced membrane layer; the pore size of the cellulose membrane is larger than the pore size of the polyolefin separator;

[0024] S30, rolling, standing and drying the composite reinforced membrane layer in sequence to obtain a composite diaphragm.

[0025] In the composite diaphragm provided in the embodiments of the present application, the binder is one or more of polyvinylidene fluoride, sodium alginate, sodium polyacrylate, polyacrylic acid, polyvinyl alcohol, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, and styrene butadiene rubber, and the solvent is one or more of anhydrous ethanol, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, tetrahydrofuran, and cyclohexanone, and the solution concentration of the binder is 1 mg / ml to 5 mg / ml.

[0026] In the composite diaphragm provided in the embodiment of the present application, step S10 specifically includes: mixing a binder, a metal hydroxide solution, and a solvent to form a binding solution;

[0027] The concentration of the metal hydroxide solution is 0.1 mg / ml to 1 mg / ml, the solvent in the metal hydroxide solution is one of isopropyl alcohol, anhydrous ethanol, and N-methylpyrrolidone, and the metal element of the metal hydroxide is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

[0028] In the composite diaphragm provided in the embodiment of the present application, after step S30 is completed, the following steps are further included:

[0029] S40, using an atomic layer deposition device to deposit a nano-coating layer of metal halide on both side surfaces and in the pores of the composite reinforced membrane layer that has been subjected to rolling, standing and drying processes, to obtain a composite membrane.

[0030] In the composite diaphragm provided in the embodiment of the present application, step S40 specifically includes:

[0031] S401, placing the composite reinforced film layer after rolling, standing and drying in an atomic layer deposition device, introducing an inert carrier gas into the atomic layer deposition system of the atomic layer deposition device and evacuating the system, adjusting the outlet valve of the reaction chamber of the atomic layer deposition device so that the pressure in the chamber is lower than 0.01 atmospheres, and heating the system so that the deposition temperature is 1° C. to 150° C.;

[0032] S402: injecting a metal source into the reaction chamber for 5 seconds and maintaining the reaction for 60 seconds; introducing an inert carrier gas to flush out excess metal source and by-products for 30 seconds; injecting a halogen source into the reaction chamber to react with the metal source adsorbed on both sides of the composite reinforced membrane layer and depositing the reaction product on the surface of the composite reinforced membrane layer to be coated for 60 seconds; then introducing an inert carrier gas to flush out unreacted halogen source and by-products for 30 seconds;

[0033] S403 , executing step S402 cyclically, setting the number of required cycles to 50 to 100 times, until the thickness of the deposited nano-coating layer is not less than 5 nm and not more than 25 nm.

[0034] In the composite diaphragm provided in the embodiment of the present application, in step S402: the halogen source is one of tungsten hexahalide, silicon tetrahalide, boron trihalide, sulfur hexahalide, and hydrogen halide pyridine; the metal element in the metal source is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

[0035] In the composite diaphragm provided in the embodiment of the present application, step S10 specifically includes: mixing a binder, a metal halide solution, and a solvent to form a binding solution;

[0036] The concentration of the metal halide solution is 0.1 mg / ml to 1 mg / ml, and the metal element in the metal halide is selected from at least one of Ni, Al, Zn, Sn, Cu, Cr, Ti, and Mg.

[0037] The composite diaphragm provided in the embodiment of the present application also includes a ceramic diaphragm, and step S20 specifically includes:

[0038] S20, sequentially immersing the ceramic diaphragm, polyolefin diaphragm and cellulose membrane into the bonding solution. After sufficient immersion, the ceramic diaphragm and the cellulose membrane are respectively compounded on both sides of the polyolefin diaphragm to obtain a composite membrane layer; the pore size of the cellulose membrane is larger than the pore size of the polyolefin diaphragm, and the pore size of the ceramic diaphragm is smaller than the pore size of the polyolefin diaphragm. The pore size ranges of the ceramic diaphragm, polyolefin diaphragm and cellulose membrane in the composite membrane are 0.01~0.1μm, 0.05~2μm and 0.1~5μm, respectively.

[0039] In a third aspect, the present application also provides a use of any of the above composite membranes in energy storage devices including lithium / sodium / zinc metal batteries, fuel cells or supercapacitors.

[0040] Unlike existing technologies, the composite membrane of this application combines a low-thickness polyolefin membrane with a cellulose membrane via an adhesive. The cellulose membrane limits the thermal shrinkage of the polyolefin membrane, improving the thermal stability of the composite membrane and enabling it to maintain good performance even in high-temperature environments. Furthermore, the composite membrane of this application combines the polyolefin membrane and the cellulose membrane, enhancing the electrolyte wettability of the composite membrane. This improves the composite membrane's liquid retention while maintaining high liquid absorption efficiency. This not only increases the injection rate and production efficiency of battery production, but also improves the battery's cycle performance and lifespan during use.

[0041] Furthermore, the present application first uses an adhesive to composite a nano-coating layer of metal halide material on both sides of the composite reinforced membrane layer. The pore size of the nano-coating layer is smaller than the pore size of the polyolefin membrane. The halide ions in the metal halide can anchor the anions present in the electrolyte to a large extent. The halide ions of lithium-philic elements can reduce the migration energy barrier of lithium ions and improve the electrolyte affinity of the composite membrane. After coating with the metal halide, the polyolefin membrane has a nano-scale pore structure, which can well allow the ions to be desolvated. Secondly, since the binder is doped with metal hydroxide and attached to the polyolefin membrane and the cellulose membrane, the hydroxide ions and halide ions in the metal hydroxide exist in combination, which can accelerate the mobility of the ions and anchor the anions present in the electrolyte to maintain the stability and high efficiency of the battery. Finally, under the synergistic effect of multiple factors, the lithium metal negative electrode can achieve a uniform deposition and stripping process, thereby avoiding the growth of lithium dendrites and significantly improving its ionic conductivity and high-rate performance.

[0042] Furthermore, the present application uses an adhesive to composite the ceramic diaphragm onto the side of the polyolefin diaphragm away from the cellulose membrane. The pore size of the ceramic diaphragm is smaller than that of the polyolefin diaphragm. The pore sizes of the ceramic diaphragm, polyolefin diaphragm, and cellulose membrane in the composite diaphragm are 0.01-0.1 μm, 0.05-2 μm, and 0.1-5 μm, respectively. The adhesive is doped with metal halides and attached to the ceramic diaphragm, polyolefin diaphragm, and cellulose membrane. In the first aspect of the above design, pores are formed due to the different pore sizes of the ceramic diaphragm, polyolefin diaphragm, and cellulose membrane. The diameter gradient effect and the gradient pore size design can homogenize the flow of lithium ions and can quickly conduct ions under high power conditions while ensuring the accommodation of a large number of ions; secondly, since the binder is doped with metal halides and attached to the ceramic diaphragm, polyolefin diaphragm and cellulose membrane, the halide ions can anchor the anions in the electrolyte to a large extent, and the lithium-philic element fluorine can reduce the migration energy barrier of lithium ions. Compared with traditional diaphragms, the composite diaphragm has a strong affinity for the electrolyte and can desolvate the ions very well. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG1 is a schematic structural diagram of the composite diaphragm in Example 1 of the present application;

[0044] FIG2 is a schematic structural diagram of the composite diaphragm in Example 2 of the present application;

[0045] FIG3 is a schematic structural diagram of the composite diaphragm in Example 3 of the present application;

[0046] FIG4 is a SEM (scanning electron microscope) test image of the polyolefin separator in Example 3 of the present application;

[0047] FIG5 is a SEM test image of the cellulose membrane in Example 3 of the present application;

[0048] FIG6 is an EIS (electrochemical impedance spectroscopy) diagram in Example 24 of the present application;

[0049] FIG7 is a schematic structural diagram of the composite diaphragm in Example 27 of the present application;

[0050] FIG8 is a graph showing the cycling performance of Li-NCM811 batteries prepared with different membranes in Example 34 at 0.5C;

[0051] Figure 9 is a graph of the cycling performance of Li-NCM811 batteries prepared with different membranes in Example 35 at 0.5C.

[0052] Implementation Methods of the Application

[0053] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not intended to limit the present application.

[0054] In the description of this application, it should be understood that the terms "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0055] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "plurality" means two or more, and "at least one" means one, two, or more, unless otherwise specifically defined.

[0056] The following will illustrate this through specific implementation plans and product test results.

[0057] Explanation of terms

[0058] A homogenizer typically consists of two counter-rotating toothed discs: one fixed and the other moving. Material is introduced between the fixed and moving discs and subjected to high shear forces. Due to the high-speed rotation of the moving disc, the material is subjected to high friction, causing the fibers or particles to be refined or broken down into smaller sizes.

[0059] Fiber breakage and thinning occurs when fibers are subjected to mechanical forces. In a homogenizing nanomachine, fiber breakage and thinning can be controlled by controlling the distance between the blades and the rotational speed.

[0060] Fiber nanofiberization is the process of reducing fibers to the nanometer level. In a homogenizer, the pressure and speed between the toothed discs are controlled to reduce fibers to the nanometer level.

[0061] The polyolefin separator used in the following examples was sourced from Asahi KASEI. The polyolefin separator had a thickness of 4 to 20 μm, a porous structure with pore sizes of 0.05 to 0.5 μm, and good pore connectivity. Furthermore, the porosity of the polyolefin separator was 40%.

[0062] The cellulose membrane used in the following examples is the applicant's own research, and the high temperature resistant, electrochemically stable materials such as cellulose natural fibers and aramid, polyimide fibers, polyphenylene benzobisoxazole (PBO) fibers, and polyacrylonitrile are selected. The fibers are radially stripped by processing methods such as chemical enzyme catalysis, high pressure homogenization, and mechanical grinding to achieve nanofiberization in fineness, while maintaining good aspect ratio, thickness and pore characteristics, porosity, and other parameters. Then, the above-mentioned various fibers are dispersed in water and made into wet films. On the wet films composed of porous nanofibers, a cross-linking agent is introduced to polymerize the cross-linking agent in situ, further enhancing the strength of the base film fiber nodes, and then improving the mechanical properties of the diaphragm. At the same time, solvent volatilization induces cross-linking agent self-assembly, and produces a three-dimensional meshed uniform pore structure inside the diaphragm, further enhancing the porosity and pore uniformity of the diaphragm. Finally, lithium ion conductivity is improved by coating or impregnating the cellulose membrane with a polymer solid electrolyte and an inorganic ceramic solid electrolyte. The thickness of the cellulose membrane is 4 μm-21 μm, the porosity is 40%-75%, and the pore size is 0.1-15 μm.

[0063] In a first aspect, the present application provides a composite membrane, comprising a composite reinforced membrane layer, the composite reinforced membrane layer comprising a polyolefin membrane and a cellulose membrane composited on one or both sides of the polyolefin membrane, wherein the polyolefin membrane and the cellulose membrane are composited by an adhesive;

[0064] Among them, the pore size of the cellulose membrane is larger than that of the polyolefin membrane.

[0065] In the composite membrane provided in the embodiment of the present application, the thickness of the polyolefin membrane is 4 μm to 10 μm.

[0066] In the composite diaphragm provided in the embodiment of the present application, the thickness of the coating formed by the adhesive is less than 2 μm.

[0067] In the composite membrane provided in the embodiment of the present application, the thickness of the cellulose membrane is 4 μm to 21 μm, and the surface density is 6 μm. 2 ~10g / m 2 .

[0068] In the composite membrane provided in the embodiment of the present application, the overall thickness of the composite membrane is 8 μm to 25 μm.

[0069] Furthermore, the cellulose membrane is interwoven with nanocellulose fibers and synthetic fibers, wherein the diameter of the nanocellulose fibers is no greater than 500 nm and the length is 0.3 mm to 3 mm;

[0070] Preferably, the surface density of the nanocellulose fibers is 8 g / m 2 .

[0071] Furthermore, the cellulose membrane is interwoven with cotton fiber, bamboo pulp fiber, nano-aramid and synthetic cellulose fiber; the diameters of the cotton fiber, bamboo pulp fiber and nano-aramid range from 500nm to 0.3μm and the length ranges from 0.6mm to 6mm.

[0072] Preferably, the surface density of the cellulose film is 10 g / m 2 .

[0073] Accordingly, the present application also provides a method for preparing a composite diaphragm, the method comprising:

[0074] S10, mixing a binder and a solvent to form a binding solution;

[0075] S20, infiltrating the polyolefin separator and at least one cellulose membrane into a bonding solution to obtain an infiltrated composite membrane layer, wherein the pore size of the cellulose membrane is larger than the pore size of the polyolefin separator;

[0076] S30, rolling, standing and drying the impregnated composite film layer in sequence.

[0077] In the composite diaphragm provided in the embodiments of the present application, the binder is one or more of polyvinylidene fluoride, sodium alginate, sodium polyacrylate, polyacrylic acid, polyvinyl alcohol, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, and styrene butadiene rubber, and the solvent is one or more of anhydrous ethanol, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, tetrahydrofuran, and cyclohexanone, and the solution concentration of the binder is 1 mg / ml to 5 mg / ml.

[0078] The above composite diaphragm will now be described with reference to specific embodiments.

[0079] Example 1:

[0080] This embodiment 1 provides a composite diaphragm for lithium batteries and sodium batteries. As shown in FIG1 , the diaphragm includes a polypropylene diaphragm, an adhesive layer adhered to both sides or one side of the polypropylene diaphragm, and a cellulose film coated on the surface of the adhesive layer.

[0081] Furthermore, a polypropylene diaphragm with a thickness of 10 μm was taken, and an adhesive solution was applied on the upper and lower surfaces of the polypropylene diaphragm to form an adhesive layer with a thickness of 2 microns. A cellulose film was set on the adhesive layer with a thickness of 10 μm. The entire composite diaphragm was then rolled and had a thickness of 20 μm.

[0082] Furthermore, the preparation method of the composite diaphragm is as follows:

[0083] Step 1: Using nanocellulose fibers as raw materials, soften them by alkaline hydrogen peroxide treatment, and then separate them into fibers and nanofibers by beating them to control the fiber diameter to less than 500nm. Add dispersant and mix with synthetic fibers at any ratio of 8g / m 2 The cellulose film with a thickness of about 10 μm is quantitatively produced.

[0084] Step 2: SBR (Styrene-Butadiene Rubber) latex, silicone defoaming agent, sodium lauryl sulfate wetting agent, and deionized water are mixed in a ratio of 100:1:1:1000 and stirred to disperse evenly, and then allowed to stand to obtain a binder solution.

[0085] Step 3: Take a 10 μm polypropylene membrane and apply the prepared adhesive solution on the polypropylene membrane by knife coating with a coating amount of 2 μm. Immediately compound it with the cellulose membrane and dry it in a hot oven at a temperature of 120°C.

[0086] Step 4: The dried composite diaphragm is hot-pressed by a hot pressing roller, the roller surface temperature is about 120°C, and the roller thickness is controlled at 20 μm to obtain the prepared composite diaphragm.

[0087] The composite separator in Example 1 has a strength of 50 MPa and an air permeability of 60 s / 100 cc. Its thermal shrinkage at 140°C does not exceed 2%, while maintaining the nanocellulose membrane's high liquid absorption efficiency, reaching a liquid absorption height of 16 mm / 10 minutes. This composite separator is suitable for various high-power batteries, improving production efficiency and operating temperature.

[0088] Example 2:

[0089] This embodiment provides a composite diaphragm for supercapacitors, activated batteries, etc. As shown in FIG2 , the diaphragm includes a polyethylene diaphragm, an adhesive layer adhered to both sides or one side of the polyethylene diaphragm, and a cellulose film coated on the surface of the adhesive layer.

[0090] Furthermore, a polyethylene diaphragm with a thickness of 5 μm is taken, and an adhesive solution is applied on the upper and lower surfaces of the polyethylene diaphragm to form an adhesive layer 2. The coating thickness is 1 micron. A cellulose film is set on the adhesive layer and has a thickness of 15 μm. The entire composite diaphragm is then rolled and has a thickness of 20 μm.

[0091] Furthermore, the preparation method of the composite diaphragm is as follows:

[0092] Step 1: Use cotton fiber, bamboo pulp fiber and nano-aramid as raw materials, prepare pulp according to the mass ratio of 7:2:1, and use a double-disc refiner to perform fiber separation and fiber nano-refining.

[0093] Add dispersant and defoamer, and the fiber mixture is 10g / m 2 A fiber-based membrane with a thickness of 15 μm was quantitatively produced.

[0094] The cellulose membrane is formed by interweaving cotton fiber, bamboo pulp fiber and nano-aramid.

[0095] Step 2: Mix the aqueous polyurethane emulsion, modified polysiloxane leveling agent, and deionized water in a mass ratio of 50:1:1000, stir and disperse evenly, and let stand to obtain an adhesive solution.

[0096] Step 3: Take a 5 μm polyethylene membrane and apply the prepared adhesive solution on the polyethylene membrane by spraying with a coating amount of 1 μm, and immediately compound it with the cellulose membrane and dry it by infrared at a temperature of 105°C.

[0097] Step 4: The dried composite diaphragm is hot-pressed by a hot pressing roller, the roller surface temperature is about 105°C, and the roller thickness is controlled at 20 μm to obtain the prepared composite diaphragm.

[0098] The composite membrane in Example 2 has a strength of 40 MPA and an air permeability of 40 s / 100 cc. Its thermal shrinkage at 140°C does not exceed 2%, while maintaining the fiber layer's high liquid absorption efficiency, reaching a liquid absorption height of 20 mm / 10 minutes. This composite membrane is suitable for various energy storage devices and can effectively improve their performance and service life.

[0099] Specifically, it can be seen from Examples 1 to 2 of the present application that the composite diaphragm of the present application is a composite of a low-thickness polyolefin diaphragm and a cellulose membrane by coating an adhesive layer, and the thermal shrinkage of the polyolefin diaphragm is limited by the cellulose layer, thereby improving the thermal stability of the diaphragm and enabling it to maintain good performance in a high-temperature environment. The higher baking temperature used in energy storage devices such as lithium batteries, sodium batteries, and supercapacitors shortens the baking time and improves production efficiency. The composite diaphragm of the present application overcomes the insufficient liquid absorption and liquid retention performance of traditional polyolefin diaphragms, utilizes the high liquid absorption efficiency of cellulose membranes, combines the polyolefin diaphragm and the cellulose membrane, enhances the electrolyte wettability of the diaphragm, improves the liquid absorption and liquid retention performance of the diaphragm, and enhances the performance of the energy storage device. While maintaining a high liquid absorption efficiency, the liquid retention performance of the diaphragm can be improved, which on the one hand increases the battery production injection rate and improves production efficiency; on the other hand, improves the cycle performance and life of the battery during use.

[0100] In a second aspect, the present application further provides a composite membrane comprising a polyolefin membrane, an adhesive layer coated on both sides or one side of the polyolefin membrane, and a cellulose membrane coated on the surface of the adhesive layer, wherein the pore size of the cellulose membrane is larger than the pore size of the polyolefin membrane;

[0101] A nano coating layer is deposited on the surface of the composite membrane. The material of the nano coating layer is metal halide. The pore size of the polyolefin membrane is larger than that of the nano coating layer. Metal hydroxide is also attached to the inside of the composite membrane.

[0102] In the composite membrane of the embodiment of the present application, the overall thickness of the composite membrane is 10 to 35 μm.

[0103] In the composite membrane of the embodiment of the present application, the polyolefin membrane is a polypropylene membrane or a polyethylene membrane, the thickness of the polyolefin membrane is 4 μm to 20 μm, and the pore size of the polyolefin membrane is 0.05 μm to 0.5 μm.

[0104] In the composite separator of the embodiment of the present application, the thickness of the cellulose membrane is 4 μm to 21 μm, and the pore size of the cellulose membrane is 0.1 μm to 15 μm.

[0105] In the composite diaphragm of the embodiment of the present application, the metal element in the metal halide and the metal hydroxide is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

[0106] The present application also provides a method for preparing a composite diaphragm, the method comprising:

[0107] S10, mixing a binder, a metal hydroxide solution, and a solvent to form a binding solution;

[0108] S20, infiltrating the polyolefin separator and at least one cellulose membrane into a bonding solution to obtain an infiltrated composite membrane layer, wherein the pore size of the cellulose membrane is larger than the pore size of the polyolefin separator;

[0109] S30, rolling, standing and drying the composite reinforced film layer in sequence;

[0110] S40, using an atomic layer deposition device to deposit a nano-coating layer of metal halide on both side surfaces and in the pores of the composite reinforced membrane layer that has been subjected to rolling, standing and drying processes, to obtain a composite membrane.

[0111] The concentration of the metal hydroxide solution is 0.1 mg / ml to 1 mg / ml, the solvent in the metal hydroxide solution is one of isopropyl alcohol, anhydrous ethanol, and N-methylpyrrolidone, and the metal element of the metal hydroxide is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

[0112] In the composite diaphragm provided in the embodiment of the present application, step S40 specifically includes:

[0113] S401, placing the composite reinforced film layer after rolling, standing and drying in an atomic layer deposition device, introducing an inert carrier gas into the atomic layer deposition system of the atomic layer deposition device and evacuating the system, adjusting the outlet valve of the reaction chamber of the atomic layer deposition device so that the pressure in the chamber is lower than 0.01 atmospheres, and heating the system so that the deposition temperature is 1° C. to 150° C.;

[0114] S402: injecting a metal source into the reaction chamber for 5 seconds and maintaining the reaction for 60 seconds; introducing an inert carrier gas to flush out excess metal source and by-products for 30 seconds; injecting a halogen source into the reaction chamber to react with the metal source adsorbed on both sides of the composite reinforced membrane layer and depositing the reaction product on the surface of the composite reinforced membrane layer to be coated for 60 seconds; then introducing an inert carrier gas to flush out unreacted halogen source and by-products for 30 seconds;

[0115] S403 , executing step S402 cyclically, setting the number of required cycles to 50 to 100 times, until the thickness of the deposited nano-coating layer is not less than 5 nm and not more than 25 nm.

[0116] In the composite diaphragm provided in the embodiment of the present application, in step S402: the halogen source is one of tungsten hexahalide, silicon tetrahalide, boron trihalide, sulfur hexahalide, and hydrogen halide pyridine; the metal element in the metal source is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

[0117] In the preparation method of the composite diaphragm provided in the present application, in the composite diaphragm provided in the embodiment of the present application, the binder is one or more of polyvinylidene fluoride, sodium alginate, sodium polyacrylate, polyacrylic acid, polyvinyl alcohol, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, and styrene butadiene rubber, and the solvent is one or more of anhydrous ethanol, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, tetrahydrofuran, and cyclohexanone; the concentration of the binder in the bonding solution is 1 mg / ml to 5 mg / ml.

[0118] The composite diaphragm doped with composite elements will now be described with reference to specific embodiments.

[0119] Example 3:

[0120] Preparation of composite membranes doped with composite elements: In the order of cellulose membrane, polyolefin membrane, and cellulose membrane, the three membranes are immersed in a mixture of aluminum hydroxide and PVDF (Polyvinylidene Fluoride) at the same time. The concentration of the aluminum hydroxide solution is 1 mg / ml, and the concentration of the PVDF solution is 2 mg / ml. After 8 hours of immersion, the cellulose membrane is sandwiched between the two sides of the polyolefin membrane (as shown in Figure 3), and then rolled until the thickness of the composite membrane is within 35 μm. The rolled membrane is then left undisturbed for 12 hours and placed in a 60°C oven for use. After 24 hours, the composite membrane is taken out, and a 5 nm thick AlF3 layer is evenly deposited on its surface and the inner surface of the pores using an ALD (Atomic Layer Deposition) device.

[0121] The preparation steps are as follows: Atomic layer deposition technology is used to coat aluminum fluoride on the pretreated composite membrane surface and the inner surface of the pores. The reaction temperature is 1-150°C, and each layer is coated with 1 circle (a total of 50-100 circles of aluminum fluoride are coated, and the thickness is about 5-10 nanometers).

[0122] Atomic layer deposition technology specifically includes the following steps:

[0123] Step 1: placing the prepared composite film in an atomic layer deposition device;

[0124] Step 2: Introduce inert carrier gas into the atomic layer deposition system and evacuate it, adjust the system reaction chamber outlet valve to make the pressure in the chamber lower than 0.01 atmosphere; and heat the deposition temperature to 1-150°C; this step is low-temperature coating.

[0125] Step 3: inject trimethylaluminum into the reaction chamber for 5 seconds and hold for 60 seconds; introduce an inert carrier gas to flush excess trimethylaluminum and by-products for 30 seconds; inject hydrogen fluoride pyridine into the reaction chamber to react with trimethylaluminum adsorbed on the surface of the substrate and deposit the reaction product ALF3 on the surface of the substrate to be coated for 60 seconds; then introduce an inert carrier gas to flush unreacted hydrogen fluoride pyridine and by-products for 30 seconds;

[0126] Step 4: cyclically execute step 3, setting the number of cycles to 50-100 times, until the thickness of aluminum fluoride deposited on the inner surface of the pores on the composite membrane reaches 5-10 nm.

[0127] As shown in Figures 3 and 4, they are SEM images of the polyolefin membrane and cellulose membrane used in Example 3 of the present application. It can be seen from the figures that the pore sizes of the two are between 0.05-0.5 μm and 0.1-15 μm, respectively.

[0128] The modified composite diaphragm was then combined with different battery electrodes and assembled into half-cells and full cells for electrochemical performance testing.

[0129] Example 4 to Example 7:

[0130] In Examples 4 to 7, the method steps for preparing the composite membrane are basically the same as those in Example 3, except that the types of metal fluorides deposited in the atomic layer deposition are different.

[0131] Example 8:

[0132] In Example 8, the steps for preparing the composite membrane were essentially the same as those in Example 3, except that the cellulose membrane and the polyolefin membrane were simultaneously immersed in a mixture of aluminum hydroxide and PVDF. The cellulose membrane was then laminated to one side of the polyolefin membrane, and then rolled to form the composite membrane until the thickness was within 35 μm. Atomic layer deposition (ALD) nanolayer coating was then performed on the surface of the composite membrane.

[0133] Example 9:

[0134] In Example 9, the three membranes, cellulose membrane, polyolefin separator, and cellulose membrane, were simultaneously immersed in a PVDF solution at a concentration of 2 mg / ml, in this order. After 8 hours of infiltration, the cellulose membrane was sandwiched between the polyolefin separator and then roller-pressed until the composite membrane thickness was within 35 μm. In this Example 9, no metal hydroxide was added during the infiltration step, and no subsequent metal fluoride nanocoating layer was deposited.

[0135] Example 10 to Example 14:

[0136] In Examples 10 to 14, the method steps for preparing the composite membrane are basically the same as those in Example 3, except that the three membranes are immersed in a mixture of metal hydroxide and PVDF in the order of cellulose membrane, polyolefin membrane, and cellulose membrane at the same time. The types of metal hydroxides in this infiltration step are different, namely magnesium hydroxide, copper hydroxide, zinc hydroxide, nickel hydroxide, and chromium hydroxide, respectively. In atomic layer deposition, the deposited metal fluorides are all zinc fluoride.

[0137] Example 15 to Example 17:

[0138] In Examples 15 to 17, the method steps for preparing the composite membrane are basically the same as those in Example 1, except that the three membranes are prepared in the order of cellulose membrane, polyolefin membrane, and cellulose membrane, and are immersed in different metal hydroxide and PVDF mixtures at the same time. In this step, the metal hydroxides are nickel hydroxide, magnesium hydroxide, and zinc hydroxide, respectively. After the composite membranes are formed in the order of cellulose membrane, polyolefin membrane, and cellulose membrane, no nano-coating layer of metal fluoride is subsequently deposited.

[0139] Example 18 to Example 20:

[0140] In Examples 18 to 20, the method steps for preparing the composite membrane are basically the same as those in Example 1, except that in the infiltration step, only PVDF solution is used, and no metal hydroxide solution is used; in the atomic layer deposition step, the nanolayer coatings finally formed are zinc fluoride, magnesium fluoride, and nickel fluoride, respectively.

[0141] Example 21:

[0142] The method steps for preparing the composite membrane in Example 21 are basically the same as those in Example 1, except that the three membranes are immersed in the metal hydroxide and PVDF mixture in the order of cellulose membrane, polyolefin membrane, and cellulose membrane. In this step, the metal hydroxide is aluminum hydroxide. After the composite membranes are formed in the order of cellulose membrane, polyolefin membrane, and cellulose membrane, the entire membrane is subsequently immersed in an aluminum fluoride solution.

[0143] Example 22-Example 23:

[0144] Example 22 and Example 23 are single-layer polyolefin membranes and single-layer cellulose membranes, respectively, which are not immersed in a mixed solution of metal hydroxide and PVDF, and are not coated with a nano-coating layer of metal fluoride.

[0145] Specifically, in Examples 3 to 23, the coatings used in the infiltration step and the coatings deposited in the atomic layer deposition step are shown in Table 1 below. It should be noted that this application only lists some of the doping methods of metal fluorides and metal hydroxides; one or more metal fluorides and metal hydroxides fall within the scope of protection of this application.

[0146] Table 1

[0147] Example 24:

[0148] Taking the composite membrane prepared in Example 3, the cellulose membrane of Example 22, and the polyolefin membrane of Example 23 as examples, lithium metal sheet and copper foil were used to form a half-cell, 1MLiTFSIDOL / DME (volume ratio of 1:1) was used as the electrolyte, and the three membranes were used to assemble into batteries in an argon atmosphere glove box, and the interfacial impedance test was performed on the electrochemical workstation.

[0149] FIG4 shows the relevant test results of the battery in Example 24. It can be seen that the composite separator prepared in Example 3 exhibits smaller interfacial impedance.

[0150] Example 25:

[0151] This Example 25 tests the lithium ion mobility of lithium symmetric batteries based on different modified separators (Examples 3 to 21) and commercial separators (Examples 22 and 23), as well as the ionic conductivity of steel-on-steel batteries. The test results are shown in Table 2.

[0152] Table 2

[0153] Symmetrical batteries are assembled using lithium sheets (steel sheets) as both the positive and negative electrodes, with different separators used for assembly. Testing is performed using a Metrohm electrochemical workstation. The ion mobility number is used to evaluate ion migration capacity. A low ion mobility number not only reduces the electrolyte's ionic conductivity but also causes severe concentration polarization, leading to uneven lithium ion deposition and affecting battery performance. Furthermore, the separator's ability to fully contact the electrolyte reflects its affinity for the electrolyte, and its ability to deform at high temperatures reflects battery safety and stability.

[0154] Example 26:

[0155] This Example 26 tests the cycle rate performance of NCM811 batteries based on different diaphragms. Using lithium metal as the negative electrode, NCM811 as the positive electrode, 1MLiPF6EC / DEC (volume ratio of 1:1) as the electrolyte, and using different diaphragms (modified diaphragms are Examples 1 to 19, and commercial diaphragms are Examples 20 to 21), NCM811 batteries were assembled separately in an argon atmosphere glove box. The preparation method of the positive electrode sheet is as follows: NCM, SuperP, and polyvinylidene fluoride (PVDF) binder are mixed in a mass ratio of 8:1:1, ground evenly, and dispersed in polymethylpyrrolidone (NMP), then placed in a homogenizer for 20 minutes to obtain a uniform slurry, and the slurry is applied to aluminum foil with a preparation device and placed in a vacuum drying oven at 80°C for 12 hours.

[0156] Please refer to Table 3, which shows the cycling performance of the Li-NCM811 battery in this example at different rates. As can be seen from Table 3, the battery prepared using the composite separator exhibits significantly higher rate performance than the battery using the commercial separator. The full-cell voltage for this positive electrode ranged from 3V to 4.4V, and the test temperature was 25°C.

[0157] Table 3

[0158] The above data show that, in terms of effect: the three-layer composite membranes of Examples 3-7 and Examples 10-14 that have been subjected to infiltration treatment and atomic layer deposition of metal fluoride have a cycle specific capacity at high rate > the two-layer composite membrane that has been subjected to infiltration treatment and atomic layer deposition of metal fluoride in Example 8 > the three-layer composite membrane that has been subjected to infiltration treatment in Examples 15-17 and the three-layer composite membrane that has been subjected to infiltration treatment and impregnation treatment in Example 21 and the three-layer composite membrane that has been subjected to atomic layer deposition of metal fluoride in Examples 18-20 > the three-layer composite membrane in Example 9 > the single-layer membrane in Examples 22-23.

[0159] Specifically, it can be seen from Tables 1 to 3 that the -OH groups on the surface of metal hydroxides are highly lyophilic, thereby improving the wettability of the separator to the electrolyte. The introduction of metal fluoride plays the role of anchoring anions, which can make the positively charged Li + It is easier for lithium ions to move around in it, thereby improving the mobility of lithium ions.

[0160] The composite membrane's pores have good affinity for the electrolyte. The metal oxides within the pores have an affinity for lithium ions in the lithium electrolyte, allowing lithium ions to pass evenly through the membrane pores and evenly distributing the lithium electrolyte within each pore. This prevents lithium ions from only passing through a localized region of the membrane, which can lead to a decrease in ion migration rate under high currents. The metal fluoride coating reduces the pore size of the polyolefin membrane to the nanoscale. Fluoride ions and other anions within the pores of the composite membrane inhibit anions in the electrolyte from traveling through the membrane, allowing more lithium ions to pass through the pores. The nanoscale pore size of the polyolefin membrane is smaller than the molecular size of the solvent and larger than the radius of the lithium ion. This nanoscale pore size removes solvent molecules from the lithium ions, allowing lithium ions to migrate freely within the pore structure, significantly accelerating ion migration. This pore structure is ideal for high-power device applications.

[0161] Specifically, the metal fluoride in the above embodiment can also be replaced with a metal halide, and the halide ions can also anchor anions. The number of coils of the metal fluoride coated using ALD in the above embodiment can be increased to 100-240, which can further reduce the pore size of the polyolefin separator after coating with the metal fluoride. When the number of coils of the metal fluoride coated using ALD in the above embodiment can be increased to 240-250, the polyolefin separator after coating with the metal fluoride has a sub-nanometer pore size, which can also meet the effect of removing solvent molecules around lithium ions. This pore structure has a relatively ideal effect in the application of high-power devices.

[0162] In a third aspect, the present application further provides a composite membrane, comprising a composite reinforced membrane layer, the composite reinforced membrane layer comprising a polyolefin membrane and a cellulose membrane composited on one or both sides of the polyolefin membrane, wherein the polyolefin membrane and the cellulose membrane are composited by an adhesive;

[0163] Among them, the pore size of the cellulose membrane is larger than that of the polyolefin membrane.

[0164] Furthermore, the composite diaphragm also includes a ceramic diaphragm, the composite reinforced membrane layer in the composite diaphragm includes a polyolefin diaphragm and a cellulose membrane composited on one side of the polyolefin diaphragm, the ceramic diaphragm is composited on the side of the polyolefin diaphragm away from the cellulose membrane, and the ceramic diaphragm, the polyolefin diaphragm and the cellulose membrane are composited by an adhesive;

[0165] Among them, the pore size of the ceramic diaphragm is smaller than that of the polyolefin diaphragm, and the pore size of the composite diaphragm is 0.01-0.1 μm, 0.05-2 μm, and 0.1-5 μm according to the pore size ranges of the ceramic diaphragm, polyolefin diaphragm, and cellulose membrane, respectively; the binder is doped with metal halide and adheres to the ceramic diaphragm, polyolefin diaphragm, and cellulose membrane.

[0166] In the composite membrane provided in the embodiment of the present application, the overall thickness of the composite membrane is 10 to 35 μm.

[0167] In the composite membrane provided in the embodiment of the present application, the polyolefin membrane is a polypropylene membrane or a polyethylene membrane, the thickness of the polyolefin membrane is 4 μm to 20 μm, and the pore size of the polyolefin membrane is 0.05 μm to 2 μm.

[0168] In the composite diaphragm provided in the embodiment of the present application, the thickness of the coating layer where the binder is located is less than 2 μm.

[0169] In the composite separator provided in the embodiment of the present application, the thickness of the cellulose membrane is 4 μm to 30 μm, and the pore size of the cellulose membrane is 0.1 μm to 5 μm.

[0170] In the composite diaphragm provided in the embodiment of the present application, the metal element in the metal halide is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

[0171] In the composite membrane provided in the embodiment of the present application, the pore size of the ceramic membrane is 5μm to 15μm, and the pore size is 0.01-0.1μm. A layer of metal or covalent organic framework material with sub-nanometer pore size is deposited on the surface and pores of the ceramic membrane.

[0172] Furthermore, the metal or covalent organic framework material with sub-nanopore size includes any one of ZIF-8, UiO-66 and COF-Go; among which, the pore size of ZIF-8 is 0.34nm~1.16nm, the pore size of COF-GO is 0.5nm~1.4nm, and the pore size of UiO-66 is 0.8nm~1.1nm.

[0173] Accordingly, the present invention provides a method for preparing a composite diaphragm, the method comprising:

[0174] S10, mixing a binder, a metal halide solution, and a solvent to form a binding solution;

[0175] S20, infiltrating a ceramic diaphragm, a polyolefin diaphragm, and a cellulose membrane into a bonding solution. After sufficient infiltration, the ceramic diaphragm and the cellulose membrane are respectively composited on both sides of the polyolefin diaphragm to obtain a composite membrane layer; the pore size of the cellulose membrane is larger than the pore size of the polyolefin diaphragm, and the pore size of the ceramic diaphragm is smaller than the pore size of the polyolefin diaphragm. The pore sizes of the ceramic diaphragm, the polyolefin diaphragm, and the cellulose membrane in the composite membrane are in the range of 0.01 to 0.1 μm, 0.05 to 2 μm, and 0.1 to 5 μm, respectively;

[0176] S30, rolling, standing and drying the impregnated composite film layer in sequence.

[0177] In the composite diaphragm provided in the embodiment of the present application, the concentration of the metal halide solution is 0.1 mg / ml to 1 mg / ml, and the metal element in the metal halide is selected from at least one of Ni, Al, Zn, Sn, Cu, Cr, Ti, and Mg.

[0178] In the preparation method of the composite diaphragm provided in the present application, in the preparation method of the composite diaphragm provided in the present application, in the composite diaphragm provided in the embodiment of the present application, the binder is one or more of polyvinylidene fluoride, sodium alginate, sodium polyacrylate, polyacrylic acid, polyvinyl alcohol, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, and styrene butadiene rubber, and the solvent is one or more of anhydrous ethanol, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, tetrahydrofuran, and cyclohexanone; the concentration of the binder in the bonding solution is 1 mg / ml to 5 mg / ml.

[0179] The composite diaphragm with pore size gradient effect will now be described in detail with reference to specific embodiments.

[0180] Example 27:

[0181] Gradient battery separator preparation and battery assembly: Ceramic separators, polyolefin separators, and cellulose membranes were immersed in a mixture of zinc chloride and PVDF, with a zinc chloride concentration of 1 mg / ml and a PVDF concentration of 2 mg / ml, in that order. After 8 hours of immersion, the cellulose membrane, ceramic separator, and polyolefin separator were layered together in descending pore size order. Roll-pressing was then performed until the composite separator reached a thickness of less than 35 μm. The rolled separators were then left undisturbed for 12 hours to obtain the modified membrane, which was then placed in a 60°C oven for later use.

[0182] The modified diaphragm was then combined with different battery electrodes to form half-cells, symmetrical cells and full cells for electrochemical performance testing.

[0183] Please refer to FIG7 . In the gradient pore size battery separator design provided in Example 27 in FIG7 , the pore sizes of the various layers of separators are arranged in the following order: cellulose membrane>polyolefin separator>ceramic separator.

[0184] Example 28:

[0185] The ceramic, polyolefin, and cellulose membranes were immersed in a mixture of zinc chloride (1 mg / ml) and polyvinyl chloride (PVDF) at a concentration of 2 mg / ml. After 8 hours of immersion, the cellulose, ceramic, and polyolefin membranes were layered in order of pore size and then roller-pressed until the composite membrane reached a thickness of less than 35 μm. The rolled membranes were then left undisturbed for 12 hours before being placed in a 60°C oven for later use.

[0186] The modified composite membrane is then filtered or sprayed onto the smaller ceramic membrane side of the composite membrane, where a layer of a nanopore metal-organic framework (MOF) such as ZIF-8 is deposited. This creates a four-layer gradient effect: cellulose membrane, polyolefin membrane, ceramic membrane, and ZIF-8. The ZIF-8 pore size ranges from 0.34 to 1.16 nm.

[0187] After immersing ceramic, polyolefin, and cellulose membranes in a mixture of zinc chloride and PVDF, the pore size range remained unchanged. PVDF primarily acts as a binder, while the introduction of zinc chloride serves to anchor anions and provide a flame retardant effect. For example, when polysulfides are added to the electrolyte, chloride ions can inhibit the shuttling effect of the polysulfides. The ZIF-8 coating on the modified membrane, combined with the gradient pores of the modified membrane, creates distinct solution environments at either end. The ZIF-8 pores are separated by a large-scale external solution on one end and a micron-nanoscale composite membrane pore with zinc chloride and metal oxides on the surface on the other.

[0188] Example 29 to Example 30:

[0189] The operation is basically the same as that of Example 28, except that the halides used are fluoride-silver fluoride and bromide-magnesium bromide respectively.

[0190] Example 31-Example 32:

[0191] The operation is basically the same as that of Example 28, except that the nanomaterial deposited on the ceramic diaphragm side with smaller pore size of the composite diaphragm is different. In Example 31, a layer of COF-GO covalent organic framework composite graphene oxide with sub-nanometer pore size is deposited, and the COF-GO pore size is 0.5-1.4nm. In Example 32, a layer of UiO-66 (metal organic framework-Zr) with sub-nanometer pore size is deposited, and the UiO-66 pore size is 0.8-1.1nm.

[0192] Only some examples are tested here, and other modification methods with nanopores integrated into gradient membranes are also protected by this application.

[0193] Example 33:

[0194] This Example 33 tests the composite membranes based on the pore gradient design prepared in Examples 27 and 28 (refer to the application content for the preparation method), the composite membranes prepared in Examples 29 to 32, and cellulose membranes, polyolefin membranes, ceramic membranes, composite membranes of cellulose membranes and polyolefin membranes, composite membranes of polyolefin membranes and ceramic membranes, and modified membranes in which a metal or covalent organic framework material is coated on one side of the ceramic membrane after the composite of polyolefin membrane and ceramic membrane. A total of 12 types of membranes are assembled into lithium symmetric batteries, and the ionic conductivity reflected by steel-on-steel batteries are tested.

[0195] The composite membranes of cellulose membrane and polyolefin membrane, and the composite membranes of polyolefin membrane and ceramic membrane were bonded together using an adhesive. In this embodiment, the adhesive was SBR latex, silicone defoamer, sodium lauryl sulfate wetting agent, and deionized water in a ratio of 100:1:1:1000, mixed and stirred to disperse uniformly, and allowed to stand to obtain an adhesive solution. The test results are shown in Table 4:

[0196] Table 4

[0197] Ion mobility measures the ability of ions to move within an electrolyte. Low ion mobility not only reduces the electrolyte's ionic conductivity but can also lead to severe concentration polarization. High ion mobility is crucial for accommodating a large number of ions while maintaining high ionic conductivity, enabling high-power and high-rate battery operation.

[0198] Table 4 shows that the modified composite membranes prepared in Examples 27 to 32 exhibit superior ionic conductivity and ion mobility compared to cellulose membrane, polyolefin membrane, and ceramic membranes. In particular, when a metal or covalent organic framework with a smaller pore size is introduced, the ionic conductivity of batteries prepared with composite membranes exhibiting a pore size gradient effect is even more pronounced.

[0199] Example 34:

[0200] This Example 34 tested the cycling performance of NCM811 batteries with different separators. Using lithium metal as the negative electrode, NCM811 as the positive electrode, and 1M LiPF6EC / DEC (1:1 volume ratio) as the electrolyte, NCM811 batteries were assembled in an argon atmosphere glove box using different separators. During assembly, the separators of Examples 27-32 had the smaller pore size facing the negative electrode, while the larger pore size faced the positive electrode.

[0201] The preparation method of the NCM811 positive electrode sheet is as follows: nickel cobalt manganese (NCM), SuperP (conductive carbon black), and polyvinylidene fluoride (PVDF) binder are mixed in a mass ratio of 8:1:1, ground evenly, and dispersed in polymethylpyrrolidone (NMP). Then, the mixture is placed in a homogenizer and homogenized for 20 minutes to obtain a uniform slurry. The slurry is scraped onto aluminum foil using a preparation device and placed in a vacuum drying oven at 80°C and dried for 12 hours.

[0202] Taking the CR2025 model button battery made of the above-mentioned polyolefin diaphragm, ceramic diaphragm, and composite diaphragm of Example 28 as an example, this model battery has a diameter of 20 mm and a thickness of 2.5 mm. The CR2025 model button battery is assembled in the order of negative electrode shell, lithium sheet, dripping electrolyte, diaphragm, dripping electrolyte, positive electrode sheet, gasket, and spring, and the battery pressure is 0.85 MPa.

[0203] The cycling performance diagrams of Li-NCM811 batteries prepared with the above three types of separators at 0.5C are shown in Figure 8.

[0204] Example 35:

[0205] This Example 35 tested the cycle rate performance of the NCM811 batteries prepared with different separators in Example 7. Using lithium metal as the negative electrode, NCM811 as the positive electrode, and 1MLiPF6EC / DEC (1:1 volume ratio) as the electrolyte, NCM811 batteries were assembled in an argon atmosphere glove box using different separators. When assembling the NCM811 batteries, the side with the smaller pore size of the separator in Example 1 or Example 2 faced the negative electrode, and the side with the larger pore size faced the positive electrode.

[0206] The preparation method of the positive electrode sheet is as follows: nickel cobalt manganese (NCM), SuperP (conductive carbon black), and polyvinylidene fluoride (PVDF) binder are mixed in a mass ratio of 8:1:1, ground evenly and dispersed in polymethylpyrrolidone (NMP), and then placed in a homogenizer for 20 minutes to obtain a uniform slurry. The slurry is scraped onto aluminum foil with a preparation device and placed in a vacuum drying oven at 80°C for 12 hours.

[0207] Table 5 shows the cycling performance of the Li-NCM811 battery in Example 33 at various rates. The battery using the composite separator exhibits significantly higher rate performance than the battery using the commercial separator. The full-cell voltage for the positive electrode ranged from 3V to 4.3V, and the test temperature was 25°C. Figure 9 shows the cycling performance of some of the separators in Example 35 at different rates.

[0208] Table 5

[0209] As can be seen from Table 5, the -OH and other groups on the surface of the ceramic particles in the ceramic diaphragm alone have a strong affinity for liquids, thereby improving the wettability of the diaphragm to the electrolyte. However, due to the large pore size of the polyolefin diaphragm and the small size of the ceramic ions, after the adhesive is applied, the contact between the surface of the polyolefin + ceramic composite diaphragm and the electrolyte is limited, resulting in the ionic conductivity of the polyolefin + ceramic composite diaphragm not being significantly improved. By coating the metal chloride on the surface of the cellulose membrane + polyolefin diaphragm + ceramic diaphragm through PVDF, as in Example 27, the introduction of zinc chloride plays the role of anchoring anions, which can make the positively charged Li + The composite membrane pores have good affinity with the electrolyte. The metal oxides in the composite membrane pores have affinity for the lithium ions in the lithium electrolyte, allowing lithium ions to pass through the composite membrane pores evenly, making the lithium electrolyte evenly distributed in each pore of the composite membrane. This prevents lithium ions from only passing through a local area of ​​the composite membrane, which would lead to a decrease in the rate of ion migration under high current.

[0210] The more complete the pore size gradient effect of the composite membrane's pores, the better the performance at high rate performance. For example, Example 27 is composed of a ceramic membrane, a polyolefin membrane, and a cellulose membrane with successively increasing pore sizes, while Example 28 is composed of a nano-ZIF-8 material, a ceramic membrane, a polyolefin membrane, and a cellulose membrane with successively increasing pore sizes. Compared to Example 27, the pore size gradient of the composite membrane in Example 28 is more complete, and the ion migration rate of the membrane in Example 28 is improved under high currents. This is due to the unique gradient pore size design. The larger micron-nano pores on one side of the composite membrane can accommodate more ions, and the pore diameter continuously decreases to the nanometer scale as the membrane is composited. The lithium ion radius (0.2nm-0.3nm), the hydrated lithium ion radius (0.76nm), and the hydrated anion radius (several angstroms to more than ten angstroms) in the electrolyte are at the nanometer scale, allowing the free movement of lithium ions and hydrated lithium ions.

[0211] The pore size of the ZIF-8 layer is reduced to the sub-nanometer scale. Chloride ions and other anions within the composite membrane pores inhibit the anions in the electrolyte from shuttling through the membrane, allowing more lithium ions to pass through the composite membrane pores. The sub-nanometer pore size of the ZIF-8 pores is smaller than the molecular size of the solvent and larger than the radius of the lithium ion. The ZIF-8 layer with sub-nanometer pores can remove solvent molecules around lithium ions, allowing lithium ions to migrate freely within the ZIF-8 pore structure, thereby significantly accelerating the rate of ion migration. The gradient pore structure is ideal for high-power device applications. The same applies to other materials with nanopores.

[0212] In a fourth aspect, the present application also provides a use of any of the above composite membranes in energy storage devices including lithium / sodium / zinc metal batteries, fuel cells or supercapacitors.

[0213] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0214] The above is a detailed introduction to the technical solutions provided in the embodiments of the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core ideas of the present application. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A composite separator, characterized in that, It includes a composite reinforcing film layer, and the composite reinforcing film layer includes a polyolefin separator and a cellulose film composite on one or both sides of the polyolefin separator. The polyolefin separator and the cellulose film are composite through an adhesive; Wherein, the pore size of the cellulose film is larger than that of the polyolefin separator.

2. The composite separator according to claim 1, wherein, The composite separator further includes nano-coating layers composite on both sides of the composite reinforcing film layer. The pore size of the nano-coating layer is smaller than that of the polyolefin separator, and the material of the nano-coating layer includes metal halide; metal hydroxide is doped in the adhesive and adheres to the polyolefin separator and the cellulose film.

3. The composite separator according to claim 1, wherein The composite separator further includes a ceramic separator. The composite reinforcing film layer in the composite separator includes the polyolefin separator and a cellulose film composite on one side of the polyolefin separator. The ceramic separator is composite on the side of the polyolefin separator away from the cellulose film. The ceramic separator, the polyolefin separator and the cellulose film are composite through the adhesive; Wherein, the pore size of the ceramic separator is smaller than that of the polyolefin separator. The pore size ranges of the ceramic separator, the polyolefin separator and the cellulose film in the composite separator are 0.01-0.1μm, 0.05-2μm and 0.1-5μm respectively; metal halide is doped in the adhesive and adheres to the ceramic separator, the polyolefin separator and the cellulose film.

4. The composite separator according to any one of claims 1 to 3, characterized in that The overall thickness of the composite separator is 8-35μm.

5. The composite separator according to claim 1, characterized in that, The polyolefin separator is a polypropylene separator or a polyethylene separator. The thickness of the polyolefin separator is 4μm-20μm, and the pore size of the polyolefin separator is 0.05μm-2μm.

6. The composite separator according to claim 1, wherein The thickness of the cellulose film is 4μm-21μm, and the pore size of the cellulose film is 0.1μm-15μm.

7. The composite separator according to claim 6, characterized in that, The cellulose film is woven by nano-cellulose fibers and synthetic fibers; the diameter of the nano-cellulose fibers is not more than 500nm, and the length is 0.3mm-3mm.

8. The composite separator according to claim 6, characterized in that, The cellulose film is woven by cotton fibers, bamboo pulp fibers, nano-aramid and synthetic cellulose fibers; the diameter ranges of the cotton fibers, the bamboo pulp fibers and the nano-aramid are all 500nm-0.6μm, and the length ranges are all 0.6mm-6mm.

9. The composite separator according to claim 2 or 3, characterized in that, The metal elements in the metal halide and the metal hydroxide are selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, Li.

10. The composite separator according to claim 3, wherein, The pore size of the ceramic separator is 0.1μm-15μm, and a metal or covalent organic framework material with a sub-nano pore size is deposited on the surface and in the pores of the ceramic separator.

11. The composite separator according to claim 10, wherein, The metal or covalent organic framework material with a sub-nano pore size includes any one of ZIF-8, UiO-66 and COF-Go; wherein, the pore size of ZIF-8 is 0.34nm-1.16nm, the pore size of COF-GO is 0.5nm-1.4nm, and the pore size of UiO-66 is 0.8nm-1.1nm.

12. A method for preparing a composite separator according to any one of claims 1 to 3, characterized in that, The method includes: S10, mixing the adhesive with a solvent to form an adhesive solution; S20. Immerse the polyolefin separator and at least one of the cellulose membranes in the bonding solution. After sufficient immersion, the cellulose membranes are laminated on both sides or one side of the polyolefin separator to obtain a composite reinforced membrane layer; the pore size of the cellulose membrane is larger than that of the polyolefin separator. S30. Subject the composite reinforced membrane layer to rolling, standing, and drying treatments in sequence to obtain a composite separator.

13. The preparation method of the composite separator according to claim 12, characterized in that, In the step S10: The binder is one or more of polyvinylidene fluoride, sodium alginate, sodium polyacrylate, polyacrylic acid, polyvinyl alcohol, sodium carboxymethyl cellulose, polyvinylpyrrolidone, and styrene-butadiene rubber; the solvent is one or more of anhydrous ethanol, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, tetrahydrofuran, and cyclohexanone; the solution concentration of the binder is 1 mg / ml to 5 mg / ml.

14. The preparation method of the composite separator according to claim 13, wherein, The step S10 specifically includes: Mix the binder, the metal hydroxide solution, and the solvent to prepare the bonding solution. Among them, the concentration of the metal hydroxide solution is 0.1 mg / ml to 1 mg / ml; the solvent in the metal hydroxide solution is one of isopropanol, anhydrous ethanol, and N-methylpyrrolidone; the metal element of the metal hydroxide is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

15. The preparation method of the composite separator according to claim 14, characterized in that, After the step S30 is completed, it further includes: S40. Use an atomic layer deposition device to deposit the nano-coating layer of metal halide on both the double-sided surfaces and pores of the composite reinforced membrane layer that has undergone the rolling, standing, and drying treatments to obtain the composite separator.

16. The preparation method of the composite separator according to claim 15, characterized in that, The step S40 specifically includes: S401. Place the composite reinforced membrane layer that has undergone the rolling, standing, and drying treatments in the atomic layer deposition device. Introduce an inert carrier gas into the atomic layer deposition system of the atomic layer deposition device and evacuate. Adjust the outlet valve of the reaction chamber of the atomic layer deposition device to make the pressure in the chamber lower than 0.01 atmospheres, and heat to make the deposition temperature 1 °C to 150 °C. S402. Inject a metal source into the reaction chamber for 5 s and hold for 60 s; introduce an inert carrier gas to flush out the excess metal source and by-products for 30 s; inject a halogen source into the reaction chamber to react with the metal source adsorbed on both the double-sided surfaces of the composite reinforced membrane layer and deposit the reaction products on the surface of the composite reinforced membrane layer to be coated for 60 s; then introduce an inert carrier gas to flush out the unreacted halogen source and by-products for 30 s. S403. Repeat the step S402, and set the number of cycles to be 50 to 100 times until the thickness of the deposited nano-coating layer is not less than 5 nm and not more than 25 nm.

17. The preparation method of the composite separator according to claim 16, characterized in that, In the step S402: The halogen source is one of tungsten hexahalide, silicon tetrahalide, boron trihalide, sulfur hexahalide, and pyridine hydrogen halide; the metal element in the metal source is selected from at least one of Fe, Ni, Al, Zn, Sn, Cu, Cr, Ti, Mn, and Li.

18. The method for preparing the composite separator according to claim 13, characterized in that, The specific steps of S10 include: mixing the binder, the metal halide solution and the solvent to form the bonding solution; Among them, the concentration of the metal halide solution is 0.1 mg / ml to 1 mg / ml, and the metal element in the metal halide is selected from at least one of Ni, Al, Zn, Sn, Cu, Cr, Ti, and Mg.

19. The method for preparing the composite separator according to claim 18, wherein The composite separator further includes a ceramic separator, and the specific steps of S20 include: S20, infiltrating the ceramic separator, the polyolefin separator and the cellulose membrane into the bonding solution. After sufficient infiltration, the ceramic separator and the cellulose membrane are respectively laminated on both sides of the polyolefin separator to obtain a composite membrane layer; the pore size of the cellulose membrane is larger than that of the polyolefin separator, and the pore size of the ceramic separator is smaller than that of the polyolefin separator. The pore size ranges of the ceramic separator, the polyolefin separator, and the cellulose membrane in the composite separator are 0.01 to 0.1 μm, 0.05 to 2 μm, and 0.1 to 5 μm, respectively.

20. Application of a composite separator according to any one of claims 1 to 3 in an energy storage device including a metal battery, a fuel cell or a supercapacitor containing lithium / sodium / zinc.

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