Composite separator, method for manufacturing the same, and battery

Abstract

The application relates to the technical field of batteries, in particular to a composite diaphragm, a preparation method thereof and a battery. The composite diaphragm comprises a base film and a coating layer arranged on at least one side surface of the base film along the thickness direction; the coating layer comprises a composite material, and the composite material comprises a high-entropy alloy aerogel and a solid electrolyte. A battery comprises the composite diaphragm. In the application, a coating layer containing a solid electrolyte and a high-entropy alloy aerogel is prepared by adopting a sol-gel method, is coated on both sides of the base film, and is dried under normal pressure to obtain a composite diaphragm with excellent comprehensive performance. Compared with similar diaphragm coating materials, the multifunctional diaphragm coating structure prepared by the application is more uniform and stable, and after being coated on the surface of a lithium battery diaphragm, the high-temperature performance and cycle performance of the battery are obviously improved.

Description

Composite separator and its preparation method and battery Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a composite separator, its preparation method, and a battery. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the requirements for the safety and energy density of on-board lithium batteries are increasing. Especially under extreme operating conditions, the large amount of heat generated inside the battery can cause the temperature to rise rapidly, affecting battery life and potentially causing safety issues. The main function of the separator in the battery is to prevent physical contact between the anode and cathode electrodes, while also serving as a lithium-ion transport channel within the battery; furthermore, the separator plays a crucial role in battery safety. Therefore, developing separators with excellent thermal stability has become key to improving the thermal management of lithium batteries.

[0003] In related technologies, some diaphragms include a base membrane and a coating disposed on the base membrane. The coating can increase the diaphragm's puncture strength and high-temperature resistance. However, existing diaphragm coatings still suffer from poor thermal stability and interfacial instability. Therefore, there is an urgent need to provide a composite diaphragm to solve the problems existing in the current technology. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a composite separator, its preparation method, and a battery, which can alleviate the problems of poor thermal performance and interface instability of existing separators, improve the high-temperature performance and cycle stability of the battery, and also has the advantages of low preparation cost, simple process, and the ability to meet the technical requirements of industrialization.

[0005] To solve the above-mentioned technical problems, this application is implemented as follows:

[0006] According to one aspect of this application, an embodiment of this application provides a composite membrane, the composite membrane comprising a base membrane and a coating disposed on at least one surface of the base membrane along the thickness direction;

[0007] The coating comprises a composite material, which includes a high-entropy alloy aerogel and a solid electrolyte.

[0008] In addition, the composite diaphragm according to this application may also have the following additional technical features:

[0009] In some embodiments, the high-entropy alloy aerogel comprises at least five metallic elements selected from sodium, potassium, calcium, lead, cerium, magnesium, aluminum, zinc, strontium, barium, copper, or cobalt.

[0010] In some of these embodiments, the solid electrolyte includes at least one of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, or a polymer solid electrolyte.

[0011] In some embodiments, the coating further includes an adhesive; the adhesive includes at least one of polyvinylidene fluoride, polyacrylate, polyimide, perfluoroalkoxy, polytetrafluoroethylene, polyacrylonitrile, or polyvinyl alcohol.

[0012] In some embodiments, the mass ratio of the high-entropy alloy aerogel to the solid electrolyte in the composite material is (70-90):(10-16).

[0013] In some embodiments, the mass ratio of the high-entropy alloy aerogel, the solid electrolyte, and the binder is (70-90):(10-16):(8-11).

[0014] In some embodiments, the base film includes at least one of a polyester film, a polyethylene film, or a polypropylene film.

[0015] In some embodiments, the thickness of the base film is 7–9 μm and the porosity is 30%–40%.

[0016] In some embodiments, the coating thickness is 3–5 μm.

[0017] According to another aspect of this application, embodiments of this application provide a method for preparing a composite separator, the method comprising:

[0018] Metal salts are dissolved in a solvent, and a thickener is added to obtain a sol solution;

[0019] The sol solution was mixed with a solid electrolyte, and the pH of the system was adjusted to alkaline to obtain a composite gel.

[0020] The composite gel is post-processed to obtain a composite material containing high-entropy alloy aerogel and solid electrolyte;

[0021] A slurry containing the composite material is coated onto at least one surface of a base membrane to obtain a composite membrane;

[0022] The post-processing method includes at least one of the following: heat treatment, cyclic freeze-thaw process, chemical vapor deposition, physical vapor deposition, or electrodeposition.

[0023] In some of these embodiments, the metal salt comprises a mixture of at least five metal salts.

[0024] In some embodiments, the metal salt includes at least five mixtures selected from sodium, potassium, calcium, lead, cerium, magnesium, aluminum, zinc, strontium, barium, copper, or cobalt salts.

[0025] In some embodiments, the anion in the metal salt includes at least one of nitrate ions, acetate ions, or sulfate ions.

[0026] In some of these embodiments, the solvent includes alcohol and water.

[0027] In some of these embodiments, the volume ratio of the alcohol to water is 1:(3-4).

[0028] In some embodiments, the alcohol includes one or two of methanol, ethanol, propanol, isopropanol, and propylene glycol.

[0029] In some embodiments, the thickener includes one of polyethylene glycol, polybutane glycol, polyvinyl alcohol, or polyamide alcohol.

[0030] In some embodiments, the metal salt accounts for 35% to 45% of the mass of the solvent, based on the mass of the solvent.

[0031] In some embodiments, the thickener accounts for 1.5% to 2% of the mass of the solvent, based on the mass of the solvent.

[0032] In some of these embodiments, the solid electrolyte includes at least one of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, or a polymer solid electrolyte.

[0033] In some embodiments, the solid electrolyte accounts for 5% to 8% of the solvent mass, based on the mass of the solvent.

[0034] In some embodiments, the alkali used to adjust the pH of the system includes one or more of aluminum hydroxide, copper hydroxide, zinc hydroxide, ammonia, and sodium carbonate.

[0035] In some of these embodiments, the pH value of the adjustment system is in the range of 9 to 11.

[0036] In some embodiments, the heat treatment process is carried out in an inert gas atmosphere, the heating rate is 5-8°C / min, the holding temperature is 800-1000°C, and the holding time is 3-5 hours.

[0037] In some embodiments, a drying step is included after obtaining the composite gel and before the post-processing.

[0038] In some of these embodiments, the slurry containing the composite material comprises the composite material, a binder, and water.

[0039] In some embodiments, the mass ratio of the composite material, binder, and water in the slurry is (30-40):(3-6):100.

[0040] According to another aspect of this application, an embodiment of this application provides a battery including a separator, wherein the separator is the aforementioned composite separator or a composite separator prepared by the aforementioned preparation method.

[0041] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0042] (1) In the embodiments of this application, the provided composite separator contains high-entropy alloy aerogel. The high-entropy alloy aerogel material has severe internal lattice distortion. By increasing phonon scattering, the thermal performance of the separator can be significantly improved. Furthermore, the three-dimensional network structure of the high-entropy alloy aerogel gives the composite separator good flexibility. Therefore, the composite separator can effectively improve the overall thermal stability of the battery, thereby improving the high-temperature performance of the battery.

[0043] (2) The composite membrane also contains a solid electrolyte. The solid electrolyte and the high-entropy alloy aerogel can work synergistically. For example, by dispersing the solid electrolyte inside the three-dimensional skeleton of the high-entropy alloy aerogel, the microstructure morphology of the material can be adjusted to form a uniform porous structure. At the same time, the composite material can form a three-dimensional network structure with a higher specific surface area and a more uniform pore structure. It also improves the grain boundary ion transport efficiency, thereby improving the battery's electrical performance.

[0044] (3) In the embodiments of this application, a solid electrolyte / high-entropy alloy aerogel coating is prepared by using the sol-gel method. After coating both sides of the base membrane, it is dried under normal pressure to obtain a composite separator with excellent comprehensive performance. Compared with similar separator coating materials, the multifunctional separator coating prepared by the present invention has a more uniform and stable structure, and after being coated on the surface of the lithium battery separator, it has a significant effect on improving the high-temperature performance and cycle stability of the battery.

[0045] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0046] Figure 1 shows a SEM image of the surface of the composite membrane provided in Embodiment 1 of the present invention. Detailed Implementation

[0047] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0048] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0051] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0053] In related technologies, some diaphragms include a base membrane and a coating applied to the base membrane. The coating can increase the diaphragm's puncture strength and high-temperature resistance. However, existing diaphragm coatings still suffer from poor thermal performance and interface instability. For example, existing diaphragm coatings have a high thermal shrinkage rate and a low melt-rupture temperature, resulting in poor high-temperature resistance or thermal performance of the diaphragm.

[0054] In view of this, embodiments of this application provide a composite membrane, which includes a base membrane and a coating disposed on at least one surface of the base membrane along the thickness direction;

[0055] The coating includes composite materials, which include high-entropy alloy aerogels and solid electrolytes.

[0056] The provided composite membrane has a multilayer structure, which includes a base membrane and a coating layered together.

[0057] The phrase "the coating is disposed on at least one surface of the base film along its thickness direction" means that the coating can be disposed on one surface of the base film along its thickness direction, or on two surfaces of the base film along its thickness direction. Here, "surface" can be the entire area of ​​the base film or a part of the base film. As in this embodiment, the surface can be the entire area of ​​the base film. This application does not have any particular limitation in this regard, as long as the purpose of this application can be achieved.

[0058] As an example, the base film has two surfaces opposite each other in its own thickness direction, and the coating is disposed on the two opposite surfaces of the base film. It will be understood that in other embodiments, the coating may also be laminated on either of the two surfaces of the base film.

[0059] Of particular note is that in the composite separator of this application embodiment, the coating of the composite separator includes high-entropy alloy aerogel and solid electrolyte. The high-entropy alloy aerogel and solid electrolyte can form a composite material. The high-entropy alloy aerogel material has severe internal lattice distortion, which can significantly improve the thermal performance of the separator by increasing phonon scattering. Furthermore, the three-dimensional network structure of the high-entropy alloy aerogel endows the composite separator with good flexibility. Therefore, this composite separator can effectively improve the overall thermal stability and structural stability of the battery. In addition, the solid electrolyte is dispersed inside the three-dimensional framework of the high-entropy alloy aerogel. While adjusting the microstructure morphology of the material to form a uniform porous structure, it can also enable the composite material to form a three-dimensional network structure with a higher specific surface area and a more uniform porosity, and improve the grain boundary ion transport efficiency, thereby improving the electrical performance of the battery.

[0060] In this application, the composite separator provided has a low thermal shrinkage rate and a high melting and rupture temperature under the synergistic effect of the high-entropy alloy aerogel and solid electrolyte, which makes the composite separator have excellent high temperature resistance or thermal performance; and the composite separator has a high thermal conductivity, which can avoid local high temperature inside the battery, thereby improving the thermal performance of the battery and improving the battery safety.

[0061] Based on this, in the composite separator of this application, by including high-entropy alloy aerogel in the coating of the composite separator, the good flexibility of the high-entropy alloy aerogel makes the structure of the composite separator more uniform and stable. Moreover, the high-entropy alloy aerogel material itself has severe internal lattice distortion, which can effectively improve the thermal performance of the composite separator. At the same time, by adding solid electrolyte to the coating of the composite separator, the grain boundary ion transport can be improved, thereby reducing the charge and discharge internal resistance of the battery and improving the long-term cycle performance of the battery.

[0062] The term "high-entropy alloy" generally refers to an alloy material formed by mixing five or more metallic elements in equimolar or near-equimolar ratios. Alloys formed by combining at least five metallic elements exhibit superior tensile strength, corrosion resistance, and oxidation resistance. Meanwhile, aerogels, as three-dimensional porous materials, have attracted considerable attention due to their unique structural characteristics; for example, aerogels can serve as excellent heat-resistant materials and are relatively lightweight. Therefore, "high-entropy alloy aerogels" mainly refer to alloy materials in the form of aerogels formed by mixing five or more metallic elements in equimolar or near-equimolar ratios. Because different metal components have different reduction potentials and nucleation / growth kinetics, using five or more elements in a high-entropy alloy aerogel materials can combine the excellent mechanical or physicochemical properties of high-entropy alloys with the good thermal properties exhibited by the porous characteristics of aerogels.

[0063] It should be noted that this application does not limit the types of high-entropy alloy aerogels and solid electrolytes, as long as the high-entropy alloy aerogels and solid electrolytes can be mixed uniformly and used to prepare membrane coatings. Optionally, the high-entropy alloy aerogels and solid electrolytes in this application can be selected from the high-entropy alloy aerogel and solid electrolyte materials listed below.

[0064] In some embodiments, the high-entropy alloy aerogel includes, but is not limited to, at least five metallic elements selected from sodium, potassium, calcium, lead, cerium, magnesium, aluminum, zinc, strontium, barium, copper, or cobalt. For example, the high-entropy alloy aerogel may include all metals selected from sodium, potassium, calcium, lead, cerium, magnesium, aluminum, zinc, strontium, barium, copper, or cobalt; the high-entropy alloy aerogel may include six metallic elements selected from sodium, potassium, calcium, lead, cerium, magnesium, aluminum, zinc, strontium, barium, copper, or cobalt; preferably, the high-entropy alloy aerogel includes any five metallic elements selected from sodium, potassium, calcium, lead, cerium, magnesium, aluminum, zinc, strontium, barium, copper, or cobalt. Furthermore, the molar ratio of each metallic element in the high-entropy alloy aerogel is equal.

[0065] By selecting the aforementioned high-entropy alloy aerogel as a component material of the composite separator coating, the highly disordered atomic mixing of the high-entropy alloy aerogel, i.e., the severe lattice distortion within the high-entropy alloy aerogel material, can significantly improve the thermal performance of the separator by increasing phonon scattering. This includes reducing thermal shrinkage, increasing the melting and rupture temperature, improving the thermal conductivity of the separator, and preventing localized high temperatures within the battery, thereby enhancing the battery's thermal stability and safety. Simultaneously, the high-entropy alloy aerogel also possesses a three-dimensional network structure, which can improve the flexibility of the composite separator, thus enhancing the structural stability of the battery.

[0066] It should be noted that the molar ratio of metal elements in high-entropy alloy aerogel materials must be equal or approximately equal; otherwise, a material with highly disordered atomic mixing cannot be formed, and the heat resistance of the final composite membrane will be poor.

[0067] Therefore, by ensuring that the molar ratios of the various metal elements in high-entropy alloy aerogels are identical, structural stability can be enhanced. For example, equimolar mixing helps eliminate the dominance of any single element, promotes uniform distribution among elements, and forms a more complex and highly mixed atomic arrangement structure, thereby improving the overall structural stability of the material. It can also promote multiple interactions. For instance, by doping different metal ions in an equimolar ratio, abundant interfacial and interfacial interactions can be induced, including electrostatic interactions and coordination interactions between metal ions. These interactions are conducive to forming a denser network structure, improving the mechanical strength and thermal stability of the aerogel. Furthermore, the high-entropy effect can lead to unique physicochemical properties, such as enhanced conductivity and optimized catalytic activity; equimolar combinations can maximize this effect, enabling the material to exhibit novel properties different from traditional single-component or simple mixtures. Additionally, in multi-component systems, different components tend to separate to reach the lowest energy state, while equimolar ratios can effectively suppress phase separation and maintain the single-phase structure of the material, which is crucial for preserving the nanoporous structure of the aerogel.

[0068] In some embodiments, the solid electrolyte includes, but is not limited to, at least one of sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes, or polymer solid electrolytes. Specifically, the sulfide solid electrolyte may be one or more of LISICON-type sulfide solid electrolytes, LGPS-type sulfide solid electrolytes, or sulfarginite-germanium ore solid electrolytes; the oxide solid electrolyte may be one or more of garnet-type oxides, perovskite-type oxides, sodium superionic conductor (NASICON)-type oxides, or sulfarginite-germanium ore oxides; the halide solid electrolyte may be one or more of lithium halides, mixed halides, or complex halides; and the polymer solid electrolyte may be one or more of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, polycarbonate, polyvinyl alcohol, polyacrylic acid, polyimide, polyurethane, or polysiloxane.

[0069] The aforementioned solid electrolyte can be well dispersed within the three-dimensional framework of high-entropy alloy aerogel. While adjusting the microstructure morphology of the material to form a uniform porous structure, it can also enable the composite material to form a three-dimensional network structure with a higher specific surface area and a more uniform porosity, and improve the grain boundary ion transport efficiency, thereby enhancing the battery's electrical performance.

[0070] In some embodiments, the coating further includes an adhesive; the adhesive includes, but is not limited to, at least one of polyvinylidene fluoride, polyacrylate, polyimide, perfluoroalkoxy (PFA), polytetrafluoroethylene, polyacrylonitrile, or polyvinyl alcohol.

[0071] In this application, the coating may primarily consist of a composite material and an adhesive. The adhesive can be used to enhance the adhesion between the composite material and the base film, thereby improving the bonding effect. The specific type of adhesive is not limited to the substances listed above; other materials that can be used to improve adhesion do not limit the purpose of this invention, and other similar adhesive materials can also be used in this invention.

[0072] In some embodiments, the mass ratio of high-entropy alloy aerogel to solid electrolyte in the composite material is (70-90):(10-16); as an example, the mass ratio of high-entropy alloy aerogel to solid electrolyte can be 70:10, 75:12, 78:15, 79:13, 80:11, 85:13, 86:15, 88:14, 89:12, 90:16, etc.

[0073] In some embodiments, the mass ratio of high-entropy alloy aerogel, solid electrolyte, and binder is (70–90):(10–16):(8–11); as examples, the mass ratio of high-entropy alloy aerogel, solid electrolyte, and binder can be 70:10:8, 75:12:9, 78:15:10, 79:13:11, 80:11:11, 85:13:10, 86:15:9, 88:14:8, 89:12:10, 90:16:11, etc.

[0074] It is understandable that the mass ratio of high-entropy alloy aerogel, solid electrolyte, and binder affects the final thermal performance, structural stability, and conductivity of the composite separator. By controlling the mass ratio of each substance in the separator coating within the aforementioned range, the combined effect of materials such as high-entropy alloy aerogel and solid electrolyte can be fully utilized, effectively improving the performance of the composite separator. For example, if the amount of solid electrolyte added is lower than the aforementioned mass ratio range, it will lead to an increase in the internal resistance of the battery during charging and discharging, reducing the battery's cycle performance. However, if the amount of solid electrolyte added exceeds the aforementioned ratio range, the permeability of the composite separator will decrease, further affecting lithium-ion transport, which will also increase the internal resistance of the battery during charging and discharging, thereby reducing the battery's cycle stability.

[0075] In some embodiments, the base film includes at least one of a polyester film, a polyethylene film, or a polypropylene film. As an example, the base film may be a polyester film, a polyethylene film, a polypropylene film, or a composite film composed of polyethylene and polypropylene.

[0076] In some embodiments, the thickness of the base film is 7–9 μm and the porosity is 30%–40%. As an example, the thickness of the base film can be 7 μm, 7.5 μm, 8 μm, 8.5 μm, or 9 μm, or other values ​​within the above range, which are not limited here. The porosity of the base film can be 30%, 31%, 33%, 35%, 36%, 37%, 38%, 39%, or 40%, or other values ​​within the above range, which are not limited here.

[0077] Firstly, by limiting the thickness of the base film within the aforementioned range, the composite separator meets the mechanical strength requirements (able to resist certain physical stress and dendrite growth) without significantly reducing ionic conductivity. This maintains the battery's low internal resistance and avoids a significant negative impact on the battery's charge / discharge efficiency and power output. Secondly, by limiting the porosity of the base film within the aforementioned range, the composite separator can absorb more electrolyte, thereby improving the uniformity of electrolyte distribution within the battery. This contributes to improving the battery's ionic conductivity and overall electrochemical performance. Simultaneously, with the base film porosity within this range, the mechanical strength of the composite separator is not too low, making it less prone to damage during battery use or assembly.

[0078] In some embodiments, the coating thickness is 3–5 μm; as examples, the coating thickness can be 3 μm, 3.5 μm, 3.6 μm, 4 μm, 4.5 μm, 5 μm, etc., or other values ​​within the above range, which are not limited here. If the coating thickness is less than 3 μm, the improvement on the heat resistance of the composite separator is limited, and the thermal stability, structural stability, and electrical performance of the battery are difficult to further guarantee and optimize, which is not conducive to the long-term cycling of the battery; if the coating thickness is greater than 5 μm, the electron transport efficiency will increase, the internal resistance of the battery will increase, and the rate performance of the battery will be further affected.

[0079] Therefore, based on the above solution, a composite separator is provided. By applying a coating to at least one side of the base membrane along its thickness direction, the problems of poor thermal performance and interface instability in existing separator coatings are solved. The coating of this composite separator includes a high-entropy alloy aerogel and a solid electrolyte. The high-entropy alloy aerogel material has severe internal lattice distortion, which can significantly improve the thermal performance of the separator by increasing phonon scattering. Furthermore, the three-dimensional network structure of the high-entropy alloy aerogel gives the composite separator good flexibility. Therefore, this composite separator can effectively improve the overall thermal stability and structural stability of the battery, thereby improving battery safety. The solid electrolyte in the coating can be well dispersed inside the three-dimensional framework of the high-entropy alloy aerogel. While adjusting the microstructure morphology of the material to form a uniform porous structure, it can also enable the composite material to form a three-dimensional network structure with a higher specific surface area and a more uniform porosity, and improve the grain boundary ion transport efficiency, thereby improving the electrical performance of the battery.

[0080] Based on the same inventive concept, embodiments of this application also provide a method for preparing a composite separator, the method comprising:

[0081] Metal salts are dissolved in a solvent, and a thickener is added to obtain a sol solution;

[0082] The sol solution was mixed with a solid electrolyte, and the pH of the system was adjusted to alkaline to obtain a composite gel.

[0083] The composite gel was post-processed to obtain a composite material containing high-entropy alloy aerogel and solid electrolyte;

[0084] A composite membrane is obtained by coating a slurry containing the composite material onto at least one surface of a base membrane;

[0085] The post-processing methods include at least one of the following: heat treatment, cyclic freeze-thaw process, chemical vapor deposition, physical vapor deposition, or electrodeposition.

[0086] This application comprehensively utilizes the superior properties of high-entropy aerogel and solid electrolyte, employing a sol-gel method to prepare a coating comprising a solid electrolyte and a high-entropy alloy aerogel. After coating both sides of a base membrane, the coating is dried under normal pressure to obtain a composite separator with excellent overall performance. The prepared multifunctional separator coating has a more uniform and stable structure, and after being coated on the surface of the lithium battery base membrane, it significantly improves the high-temperature performance and electrical performance of the battery. Furthermore, the method provided in this application has low preparation cost and simple process, meeting the technical requirements for industrialization.

[0087] It should be understood that all the features and advantages described above regarding the "composite diaphragm" also apply to the "preparation method of the composite diaphragm", and will not be repeated here.

[0088] In some specific embodiments, the method for preparing the composite membrane specifically includes the following steps (a) to (b):

[0089] (a) Preparation of composite materials.

[0090] In step (a), the preparation of the composite material includes: weighing a certain amount of metal salt, adding the metal salt to a solvent, and stirring at room temperature until completely dissolved to form a transparent solution. Then, slowly adding an appropriate amount of thickener (such as a polymer thickener) to help form a more uniform gel network, resulting in a sol solution. Next, adding a solid electrolyte to the sol solution, stirring until evenly dispersed, and then slowly adding a weak alkali dropwise to the mixed sol solution while monitoring the pH value until the solution becomes strongly alkaline, forming a composite gel. The resulting composite gel is then dried and post-treated to obtain the composite material. The post-treatment can be one or more of the following processes: heat treatment, cyclic freeze-thaw process, chemical vapor deposition, physical vapor deposition, or electrodeposition. Preferably, heat treatment is used. In some embodiments, in step (a), the metal salt can be a mixture of at least five metal salts, wherein the molar ratio of the five metal salts is equal. For example, weighing a certain amount of metal salt means weighing five or more metal salts (such as metal nitrates) in an equimolar ratio.

[0091] In some embodiments, the metal salt includes, but is not limited to, at least five mixtures of sodium, potassium, calcium, lead, cerium, magnesium, aluminum, zinc, strontium, barium, copper, or cobalt salts.

[0092] In some embodiments, the anion in the metal salt includes at least one of nitrate ions, acetate ions, or sulfate ions. That is, the metal salt can be a metal nitrate, a metal acetate, or a metal sulfate.

[0093] For example, the metal salt is preferably a metal nitrate, which can be any five of the following: sodium nitrate, potassium nitrate, calcium nitrate, lead nitrate, cerium nitrate, magnesium nitrate, aluminum nitrate, zinc nitrate, strontium nitrate, barium nitrate, copper nitrate, and cobalt nitrate.

[0094] In some embodiments, the solvent comprises alcohol and water, wherein the volume ratio of alcohol to water is 1:(3-4); as an example, the volume ratio of alcohol to water may be 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, etc., or other values ​​within the above range, which are not limited here.

[0095] In some embodiments, the alcohol includes, but is not limited to, one or two of methanol, ethanol, propanol, isopropanol, and propylene glycol.

[0096] In some embodiments, the thickener may be a polymeric thickener, which includes, but is not limited to, at least one of polyethylene glycol, polybutanediol, polyvinyl alcohol, or polyamide alcohol.

[0097] In some embodiments, the mass of the metal salt accounts for 35% to 45% of the solvent mass, based on the mass of the solvent; that is, the total amount of metal salt added is 35% to 45% of the solvent mass. As an example, the mass of the metal salt can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45% of the solvent mass, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0098] In some embodiments, the thickener accounts for 1.5% to 2% of the solvent mass, based on the solvent mass; that is, the amount of thickener added accounts for 1.5% to 2% of the solvent mass. As an example, the mass of the thickener can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% of the solvent mass, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0099] By limiting the type and amount of thickener, after post-processing (such as heat treatment), the thickener decomposes, and the high-entropy alloy aerogel material eventually forms a porous structure. The resulting membrane, after coating, retains a certain degree of permeability, giving the battery lower charge-discharge internal resistance. Simultaneously, the composite membrane's permeability ensures smooth lithium-ion transport, improving the utilization efficiency of active materials and thus enhancing the battery's cycle performance. It should be noted that insufficient thickener will make it difficult to form a uniform three-dimensional gel network, while excessive thickener will result in excessively high sol viscosity, hindering uniform dispersion of the solid electrolyte.

[0100] In some embodiments, the solid electrolyte includes at least one of sulfide solid electrolyte, oxide solid electrolyte, halide solid electrolyte, or polymer solid electrolyte. It should be noted that heat treatment in the post-processing stage can cause some heat-sensitive solid electrolyte materials to decompose. Therefore, when heat treatment is selected as the post-processing stage, heat-resistant oxide solid electrolytes, such as lithium aluminum titanium phosphate (LATP) solid electrolyte, are chosen.

[0101] In some embodiments, when the post-processing method is a cyclic freeze-thaw method, chemical vapor deposition method, physical vapor deposition method, or electrodeposition method to achieve the preparation of high-entropy alloy aerogel and the mixing of solid electrolyte, the solid electrolyte that can be selected in these methods may include sulfide solid electrolyte, oxide solid electrolyte, polymer solid electrolyte or halide solid electrolyte.

[0102] In some embodiments, the solid electrolyte accounts for 5% to 8% of the solvent mass, based on the solvent mass. For example, the solid electrolyte mass can be 5%, 6%, 7%, 8%, etc., or other values ​​within the above range, which are not limited here. By limiting the amount of solid electrolyte within the above range, the battery can ultimately achieve better cycle stability. Specifically, if the amount of solid electrolyte added is lower than the above mass ratio range, the internal resistance of the battery during charging and discharging will increase, reducing the battery's cycle performance. However, if the amount of solid electrolyte added exceeds the above ratio range, the permeability of the composite separator will decrease, further affecting lithium-ion transport, which will also increase the internal resistance of the battery during charging and discharging, thereby reducing the battery's cycle stability.

[0103] In some embodiments, the alkali used to adjust the pH of the system includes, but is not limited to, one or more of aluminum hydroxide, copper hydroxide, zinc hydroxide, ammonia, and sodium carbonate.

[0104] In some embodiments, the pH value of the system is adjusted to be in the range of 9 to 11; as an example, the pH value of the system can be 9, 10, 11, etc., or of course other values ​​within the above range, which are not limited here.

[0105] In some embodiments, drying can be one of atmospheric pressure drying, freeze drying, and supercritical drying; preferably, atmospheric pressure drying is selected. Specifically, the temperature for atmospheric pressure drying is 60-80°C, such as 60°C, 65°C, 66°C, 70°C, 80°C, etc., or other values ​​within the above range, which are not limited here; the air velocity is 3.5-5 m / s, such as 3.5 m / s, 3.6 m / s, 4 m / s, 4.5 m / s, 5 m / s, etc., or other values ​​within the above range, which are not limited here; the drying time is 30-40 min, such as 30 min, 32 min, 33 min, 35 min, 36 min, 38 min, 39 min, 40 min, etc., or other values ​​within the above range, which are not limited here.

[0106] In some embodiments, the post-processing employs a heat treatment process, which is carried out in an inert gas atmosphere (which can be any inert gas). The heating rate of the heat treatment is 5–8 °C / min. For example, the heating rate of the heat treatment can be 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, etc., or other values ​​within the above range, which are not limited here. The holding temperature of the heat treatment is 800–1000 °C. For example, the holding temperature of the heat treatment can be 800 °C, 830 °C, 850 °C, 900 °C, 990 °C, 1000 °C, etc., or other values ​​within the above range, which are not limited here. The holding time of the heat treatment is 3 h–5 h. For example, the holding time of the heat treatment can be 3 h, 3.5 h, 4 h, 4.5 h, 5 h, etc., or other values ​​within the above range, which are not limited here.

[0107] (b) Preparation of composite membrane.

[0108] In step (b), the preparation of the composite membrane includes: dispersing the composite material obtained in step (a) with a binder in an aqueous solution to form a membrane slurry, coating the membrane slurry on both sides of a base membrane (such as a polymer membrane), and drying it under normal pressure to obtain the composite membrane.

[0109] In some embodiments, step (b) includes a slurry containing a composite material, i.e., a diaphragm slurry comprising a composite material, a binder, and water.

[0110] In some embodiments, the mass ratio of composite material, binder and water in the diaphragm slurry is (30-40):(3-6):100; as an example, the mass ratio of composite material, binder and water in the slurry can be 30:3:100, 32:3:100, 30:5:100, 35:4:100, 38:6:100, 39:5:100, 40:4:100, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0111] Optionally, the binder is one or more of polyvinylidene fluoride, polyacrylate, polyimide, perfluoroalkoxy, polytetrafluoroethylene, polyacrylonitrile, and polyvinyl alcohol.

[0112] In some embodiments, the coating method for the diaphragm slurry includes one of spraying, dip coating, or transfer coating.

[0113] Optionally, the base film includes at least one of polyester film, polyethylene film or polypropylene film; the thickness of the base film is 7 to 9 μm and the porosity is 30% to 40%.

[0114] Optionally, the coating thickness on one side is 3–5 μm.

[0115] In some embodiments, in step (b), the atmospheric pressure drying temperature is 60–80°C, the air flow rate is 3.5–5 m / s, and the drying time is 30–40 min.

[0116] Therefore, based on the above, this invention mixes various metal compounds in a specific ratio and prepares a gel coating using a sol-gel method. Combined with atmospheric pressure drying, a heat-resistant coating comprising a high-entropy alloy aerogel and a solid electrolyte is formed on both sides of the base membrane. The high-entropy alloy aerogel material exhibits severe internal lattice distortion; by increasing phonon scattering, the thermal performance of the separator can be significantly improved, and the three-dimensional network structure of the aerogel imparts good flexibility to the separator. Simultaneously, a suitable amount of solid electrolyte is dispersed within the three-dimensional framework of the high-entropy alloy aerogel, adjusting the microstructure morphology of the material while improving grain boundary ion transport, thereby enhancing the battery's electrical performance. Compared to conventional separators, the multifunctional separator coating prepared by this invention has a more uniform and stable structure, and after being coated on the surface of a lithium battery separator, it significantly improves the battery's high-temperature performance and electrical performance. Furthermore, its application in batteries can significantly enhance the thermal performance of the separator, effectively improve the overall thermal stability of the battery, and enhance battery safety.

[0117] Based on the same inventive concept, this application also provides a battery, including a separator, wherein the separator is the aforementioned composite separator or a composite separator prepared by the aforementioned preparation method.

[0118] Because this battery contains the composite separator provided in the embodiments of this application, it has excellent thermal stability and structural stability, and has low internal resistance during charging and discharging, and good cycle stability.

[0119] In some embodiments, the battery can be a lithium-ion battery. The battery stacking type is, for example, a wound or stacked battery, and the structural type is, for example, a prismatic (aluminum, steel, etc.) battery, a pouch battery, or a cylindrical battery, etc., without specific limitations. This battery has excellent high-temperature performance and electrical performance.

[0120] In some embodiments, the battery further includes a positive electrode, an electrolyte, and a negative electrode. That is, the battery includes a positive electrode, a negative electrode, an electrolyte, and a composite separator.

[0121] In this embodiment, the materials and structures of the positive electrode current collector, the conductive agent and the binder in the positive electrode active material layer are not limited, and the positive electrode structure and composition known in the art that can be used in secondary batteries can be selected.

[0122] In this embodiment, the materials and structures of the negative electrode current collector, the conductive agent and the binder in the negative electrode active material layer are not limited, and the positive electrode structure and composition known in the art that can be used in secondary batteries can be selected.

[0123] It should also be noted that the battery in this application does not limit the specific material or type of electrolyte. Any components and types known in the art that can be used in secondary batteries can be selected, as long as the purpose of this application can be achieved.

[0124] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0125] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0126] Example 1

[0127] Weigh out 42.5g of sodium nitrate, 50.5g of potassium nitrate, 94g of copper nitrate, 82g of calcium nitrate, and 128g of magnesium nitrate. Add the five metal nitrates to 1L of an ethanol / water mixture (ethanol to water volume ratio of 1:4), then add 15g of polyethylene glycol. Stir at room temperature until completely dissolved to form a sol. Next, add 54.6g of lithium aluminum titanium phosphate solid electrolyte to the sol and stir until evenly dispersed. Slowly add ammonia water dropwise to the mixed sol, monitoring the pH value as it is added, until the pH value reaches 10, forming a composite gel. Dry the composite gel under normal pressure to obtain a composite aerogel. The normal pressure drying conditions are: drying temperature 70℃, air flow rate 4m / s, drying time 35min. Finally, heat the composite aerogel to 900℃ under nitrogen at a heating rate of 6℃ / min and hold for 4h to obtain a solid electrolyte / high entropy alloy aerogel composite material. 1.4 kg of the prepared composite material and 0.2 kg of polyvinylidene fluoride binder were added to 4 kg of water and mechanically stirred until uniformly dispersed to form a membrane slurry. The membrane slurry was sprayed onto both sides of a 9 μm polyethylene membrane with a porosity of 35% and a single-sided coating thickness of 4 μm. After drying under normal pressure, a composite membrane coated with solid electrolyte / high-entropy alloy aerogel was obtained, wherein the mass ratio of solid electrolyte to high-entropy alloy aerogel in the composite membrane was 80:11.

[0128] Example 2:

[0129] Weigh out 42.5g sodium nitrate, 50.5g potassium nitrate, 94g copper nitrate, 82g calcium nitrate, and 128g magnesium nitrate. Add the five metal nitrates to 1L of ethanol / water (ethanol to water volume ratio 1:3.5) mixed solution, then add 15g polyethylene glycol. Stir at room temperature until completely dissolved to form a sol. Next, add 60.7g lithium phosphorus sulfide chloride solid electrolyte to the sol and stir until evenly dispersed. Slowly add ammonia water dropwise to the mixed sol, monitoring the pH value as it is added, until the pH value reaches 9, forming a composite gel. Dry the composite gel under normal pressure to obtain a composite aerogel. The normal pressure drying conditions are: drying temperature 70℃, air flow rate 4m / s, drying time 35min. Finally, heat the composite aerogel to 900℃ under nitrogen at a heating rate of 6℃ / min and hold for 4h to obtain a solid electrolyte / high entropy alloy aerogel composite material. 1.4 kg of the prepared composite material and 0.2 kg of polyvinylidene fluoride binder were added to 4 kg of water and mechanically stirred until uniformly dispersed to form a membrane slurry. The membrane slurry was sprayed onto both sides of a 9 μm polyethylene membrane with a porosity of 30% and a single-sided coating thickness of 3 μm. After drying under normal pressure, a composite membrane coated with solid electrolyte / high-entropy alloy aerogel was obtained, wherein the mass ratio of solid electrolyte to high-entropy alloy aerogel in the composite membrane was 85:13.

[0130] Example 3:

[0131] Weigh out 42.5g sodium nitrate, 50.5g potassium nitrate, 94g copper nitrate, 82g calcium nitrate, and 128g magnesium nitrate. Add the five metal nitrates to 1L of an ethanol / water mixture (ethanol to water volume ratio 1:4), then add 17g polyethylene glycol. Stir at room temperature until completely dissolved to form a sol. Next, add 54.6g lithium aluminum titanium phosphate solid electrolyte to the sol and stir until evenly dispersed. Slowly add ammonia water dropwise to the mixed sol, monitoring the pH value as it is added, until the solution pH reaches 11, forming a composite gel. Dry the composite gel under normal pressure to obtain a composite aerogel. The normal pressure drying conditions are: drying temperature 70℃, air flow rate 4m / s, drying time 35min. Finally, heat the composite aerogel to 1000℃ under nitrogen at a heating rate of 8℃ / min and hold for 3h to obtain a solid electrolyte / high entropy alloy aerogel composite material. 1.4 kg of the prepared composite material and 0.2 kg of polyvinylidene fluoride binder were added to 4 kg of water and mechanically stirred until uniformly dispersed to form a membrane slurry. The membrane slurry was sprayed onto both sides of a 7 μm polyethylene membrane with a porosity of 40% and a single-sided coating thickness of 4.5 μm. After drying under normal pressure, a composite membrane coated with solid electrolyte / high-entropy alloy aerogel was obtained, wherein the mass ratio of solid electrolyte to high-entropy alloy aerogel in the composite membrane was 80:11.

[0132] Example 4:

[0133] Weigh out 42.5g sodium nitrate, 50.5g potassium nitrate, 94g copper nitrate, 82g calcium nitrate, 128g magnesium nitrate, and 182.5g strontium nitrate. Add the six metal nitrates to 1.5L of an ethanol / water mixture (ethanol to water volume ratio 1:4), then add 28g polyethylene glycol. Stir at room temperature until completely dissolved to form a sol. Next, add 90.7g lithium aluminum titanium phosphate solid electrolyte to the sol and stir until evenly dispersed. Slowly add ammonia water dropwise to the mixed sol, monitoring the pH value as it is added, until the pH value reaches 10, forming a composite gel. Dry the composite gel under normal pressure to obtain a composite aerogel. The normal pressure drying conditions are: drying temperature 70℃, air flow rate 4m / s, drying time 35min. Finally, heat the composite aerogel to 900℃ under nitrogen at a heating rate of 6℃ / min and hold for 4h to obtain a solid electrolyte / high entropy alloy aerogel composite material. 1.2 kg of the prepared composite material and 0.12 kg of polytetrafluoroethylene binder were added to 4 kg of water and mechanically stirred until uniformly dispersed to form a membrane slurry. The membrane slurry was sprayed onto both sides of a 9 μm polypropylene membrane. The porosity of the polyethylene membrane was 35%, and the coating thickness on one side was 4 μm. Finally, after drying under normal pressure, a composite membrane coated with solid electrolyte / high-entropy alloy aerogel was obtained, wherein the mass ratio of solid electrolyte to high-entropy alloy aerogel in the composite membrane was 70:16.

[0134] Example 5:

[0135] Weigh out 42.5g sodium nitrate, 50.5g potassium nitrate, 94g copper nitrate, 82g calcium nitrate, and 128g magnesium nitrate. Add the five metal nitrates to 1L of an ethanol / water mixture (ethanol to water volume ratio 1:4), then add 18g polyethylene glycol. Stir at room temperature until completely dissolved to form a sol. Next, add 56.4g lithium aluminum titanium phosphate solid electrolyte to the sol and stir until evenly dispersed. Slowly add ammonia water dropwise to the mixed sol, monitoring the pH value as it is added, until the pH value reaches 10, forming a composite gel. The composite gel is then subjected to supercritical carbon dioxide drying to obtain a composite aerogel. The drying conditions are: drying temperature 70℃, air flow rate 4m / s, drying time 35min. Finally, the composite aerogel is heated to 900℃ under nitrogen at a heating rate of 6℃ / min and held at this temperature for 4h to obtain a solid electrolyte / high entropy alloy aerogel composite material. 1.6 kg of the prepared composite material and 0.2 kg of polyvinylidene fluoride binder were added to 4 kg of water and mechanically stirred until uniformly dispersed to form a membrane slurry. The membrane slurry was then transferred and coated onto both sides of a 9 μm polyethylene membrane with a porosity of 35% and a single-sided coating thickness of 4 μm. After drying under normal pressure, a composite membrane coated with solid electrolyte / high-entropy alloy aerogel was obtained, wherein the mass ratio of solid electrolyte to high-entropy alloy aerogel in the composite membrane was 80:11.

[0136] Example 6

[0137] The difference between Example 6 and Example 1 is that the added metal nitrates are 42.5g sodium nitrate, 50.5g potassium nitrate, 106g aluminum nitrate, 82g calcium nitrate, 128g magnesium nitrate, and 182.5g strontium nitrate.

[0138] Example 7

[0139] The difference between Example 7 and Example 1 is that the added metal nitrates are 42.5g sodium nitrate, 50.5g potassium nitrate, 106g aluminum nitrate, 82g calcium nitrate, 94.7g zinc nitrate, and 182.5g strontium nitrate.

[0140] Example 8

[0141] The difference between Example 8 and Example 1 is that the solid electrolyte used is Li7La3Zr2O with a garnet structure. 12 .

[0142] Comparative Example 1:

[0143] The only difference between Comparative Example 1 and Example 1 is that the amount of sodium nitrate used is 55g and the amount of potassium nitrate used is 60g; all other aspects are the same as in Example 1.

[0144] Comparative Example 2:

[0145] The only difference between Comparative Example 2 and Example 1 is that polyethylene glycol was not added; otherwise, they are the same as Example 1.

[0146] Comparative Example 3:

[0147] The only difference between Comparative Example 3 and Example 1 is that lithium aluminum titanium phosphate solid electrolyte was not added; otherwise, they are the same as Example 1.

[0148] Comparative Example 4:

[0149] The only difference between Comparative Example 4 and Example 1 is that the amount of lithium titanium aluminum phosphate solid electrolyte used is 120g, and all other aspects are the same as in Example 1.

[0150] Comparative Example 5:

[0151] The only difference between Comparative Example 5 and Example 1 is that conventional alumina ceramic material is coated on the surface of the polyethylene diaphragm. The parameters of the polyethylene diaphragm thickness, porosity, and coating thickness of the alumina ceramic material are the same as those in Example 1.

[0152] Comparative Example 6:

[0153] The only difference between Comparative Example 6 and Example 1 is that the amount of composite material added to the diaphragm slurry is 1 kg, and all other aspects are the same as in Example 1.

[0154] Performance testing

[0155] The performance of the composite separators prepared according to the above embodiments and comparative examples and the lithium batteries constructed therefrom were tested, as follows:

[0156] 1. Performance testing of composite diaphragms:

[0157] (1) Thickness test: The thickness of the diaphragm at different locations was tested using a high-precision thickness gauge, and the average value of 10 thicknesses was taken.

[0158] (2) Air permeability test: The diaphragm to be tested is placed between two air chambers, and gas is passed from one air chamber to the other air chamber through the diaphragm by a constant pressure difference. The air permeability of the diaphragm is calculated by measuring the amount of gas passing through the diaphragm per unit time.

[0159] (3) Needle penetration strength test: Referring to GB / T 36363-2018 standard, the diaphragm was placed under the sample stage fixture, and a universal tensile testing machine was used to record the maximum force value of a 1mm diameter round needle piercing the diaphragm at a speed of 100±100mm / min.

[0160] (4) Heat shrinkage test: Cut the diaphragm into 100mm*100mm samples, place the sample flat between two layers of A4 paper, and then put the sample into an oven at a test temperature of 130℃ for 1 hour; after heating, take out the sample and measure the sample size again.

[0161] Heat shrinkage rate = (size before shrinkage - size after shrinkage) / size before shrinkage * 100%

[0162] (5) Rupture temperature test: After the diaphragm is cut into appropriate sizes, it is placed in a hot press and heated and compressed under different temperatures and pressures to test the compressive strength and density of the diaphragm at different temperatures and obtain the rupture temperature.

[0163] (6) Thermal conductivity test: Place the diaphragm sample in the thermal conductivity tester, ensuring good contact between the sample and the heat and cold sources. Start the test program and wait for the system to reach steady state, i.e., after the heat flow and temperature distribution have stabilized, record key parameters such as heat flow, temperature difference, and sample thickness. Calculate the thermal conductivity using the recorded data and Fourier's law: λ = Q / (A*ΔT). Where λ is the thermal conductivity, Q is the heat flow, A is the effective area of ​​the sample, and ΔT is the temperature difference between the two sides.

[0164] The test results of the composite membranes in each embodiment and comparative example are shown in Table 1.

[0165] 2. Battery performance testing:

[0166] Preparation of lithium-ion batteries

[0167] The negative electrode (with graphite as the negative electrode active material), the prepared composite separator, and the positive electrode (with lithium nickel cobalt manganese oxide as the positive electrode active material) are stacked in sequence and wound to obtain a bare cell. After the tabs are welded, the bare cell is placed into the battery aluminum shell / soft-pack aluminum-plastic film. After liquid injection, side and top sealing, drying, formation, volume setting, and venting and sealing, a lithium-ion battery is obtained.

[0168] Electrochemical performance testing of the battery

[0169] (1) Resistance (discharge resistance and charging resistance) test: At room temperature (25℃), the charging resistance and discharging resistance of each lithium battery at 20% SOC were tested using a charge-discharge test cabinet to determine the internal resistance of the lithium battery at low SOC. The test results of each embodiment and comparative example are shown in Table 2.

[0170] (2) Capacity retention rate (capacity retention rate at 25℃ and 50℃) test: At temperatures of 25℃ and 50℃, the capacitor is charged to 4.25V at a constant current density of 1C, and the charging capacity at this point is recorded as the initial charging capacity. Then, it is charged at a constant voltage of 4.25V until the current decreases to 0.05C, and then discharged at a constant current of 0.1C to 2.8V, and the discharge capacity at this point is recorded as the initial discharge capacity. This charge-discharge cycle is repeated for 300 and 600 cycles, and the discharge capacity on the 300th and 600th cycles is recorded. The capacity retention rate after 300 and 600 cycles can be calculated using the following formula:

[0171] Capacity retention rate of the 300th cycle = Discharge capacity of the 300th cycle / Initial discharge capacity * 100%;

[0172] The capacity retention rate after the 600th cycle = (discharge capacity after the 300th cycle / initial discharge capacity) * 100%. Test results for each embodiment and comparative example are shown in Table 3.

[0173] Table 1

[0174]

[0175] Table 2

[0176]

[0177]

[0178] Table 3

[0179]

[0180] As shown in Tables 1-3, overall, compared with Comparative Examples 1-6, the solid electrolyte / high entropy alloy aerogel composite materials prepared in Examples 1-8 of the present invention can effectively improve the mechanical properties, air permeability, and temperature resistance of the separator, and improve the charge-discharge internal resistance, long-term cycle performance, and high-temperature performance of the battery.

[0181] Furthermore, Table 1 compares the mechanical properties and temperature resistance of the separators prepared in Examples 1-8 with those in Comparative Examples 1-6. Tables 2 and 3 compare the resistance, high-temperature performance, and cycle performance of the batteries prepared in Examples 1-8 with those in Comparative Examples 1-6. In Comparative Example 1, the five metal nitrates were not added in equimolar mass ratios, thus failing to form a highly entropy alloy material with highly disordered atomic mixing. In other words, the non-high-entropy alloy aerogel added in Comparative Example 1 resulted in a separator with poor thermal performance. For example, as shown in Table 1, the analysis and comparison between Example 1 and Comparative Example 1 reveals that the composite separator of Example 1 of the present invention reduces the thermal shrinkage rate, increases the melting and rupture temperature, and improves the thermal conductivity. This indicates that Example 1 of the present invention, by using high-entropy alloy aerogel, can improve the high-temperature resistance or thermal performance of the separator, effectively avoid local high temperatures inside the battery, and improve the thermal performance and safety of the battery. Furthermore, since the composite separator of Example 1 of the present invention has good thermal performance, its application in batteries is also evident in Table 3. The battery using the composite separator of Example 1 of the present invention exhibits better cycle stability at both room temperature (25°C) and high temperature (45°C) than the battery using the composite separator of Comparative Example 1.

[0182] In Comparative Example 2, the absence of a polymer thickener prevented the formation of an aerogel porous structure in the composite material, resulting in poor permeability of the coated separator. This led to increased internal resistance during both charging and discharging. Furthermore, insufficient separator permeability may have hindered lithium-ion transport, reducing the utilization rate of active materials and slightly decreasing the battery's cycle performance. In Comparative Example 3, the absence of a solid electrolyte in the high-entropy alloy aerogel resulted in higher internal resistance and reduced cycle stability. In Comparative Example 4, the addition of an excessive amount of solid electrolyte to the high-entropy alloy aerogel slightly decreased separator permeability, leading to a slight deterioration in internal resistance and cycle performance. The experimental data from Comparative Examples 3 and 4 demonstrate that adding an appropriate amount of solid electrolyte can improve grain boundary ion transport, thereby enhancing battery performance.

[0183] The difference between Comparative Example 5 and Example 1 is that conventional alumina ceramic material was coated on the surface of the polymer separator. The thermodynamic properties of the separator and the electrical performance of the assembled battery were lower than those of all examples, indicating that the prepared solid electrolyte / high-entropy alloy aerogel composite material has an improving effect on all properties. In Comparative Example 6, adding a small amount of composite material to the separator slurry slightly reduced the mechanical and thermal properties of the composite separator, and also slightly reduced the electrical performance of the battery, indicating that adding an appropriate amount of composite material can comprehensively improve the various properties of the composite separator and the battery.

[0184] Figure 1 is a SEM image of the cross-section of the composite membrane prepared in Example 1, which has a rich pore structure with a porosity of 43.2%, providing a basis for the air permeability of the composite membrane.

[0185] In summary, this invention comprehensively utilizes the excellent properties of high-entropy alloy aerogel and solid electrolyte, employing a sol-gel method to prepare a solid electrolyte / high-entropy alloy aerogel coating. After coating both sides of the separator, it is dried under normal pressure to obtain a composite separator with excellent overall performance. Compared with similar separator coating materials, the multifunctional separator coating prepared by this invention has a more uniform and stable structure, and its coating on the surface of the lithium battery separator significantly improves the high-temperature performance and electrical performance of the battery.

[0186] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0187] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0188] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0189] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0190] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite diaphragm, characterized in that, The coating comprises a base film and a coating disposed on at least one surface of the base film along its thickness direction; the coating comprises a composite material comprising a high-entropy alloy aerogel and a solid electrolyte; the high-entropy alloy aerogel comprises at least five metallic elements selected from sodium, potassium, calcium, magnesium, aluminum, strontium, barium, or copper; the coating comprises a binder; the mass ratio of the high-entropy alloy aerogel, the solid electrolyte, and the binder is (70~90):(10~16):(8~11).

2. The composite diaphragm according to claim 1, characterized in that, The solid electrolyte includes at least one of sulfide solid electrolyte, oxide solid electrolyte, halide solid electrolyte or polymer solid electrolyte.

3. The composite diaphragm according to claim 1 or 2, characterized in that, The adhesive includes at least one of polyvinylidene fluoride, polyacrylate, polyimide, perfluoroalkoxy, polytetrafluoroethylene, polyacrylonitrile, or polyvinyl alcohol.

4. The composite diaphragm according to claim 1 or 2, characterized in that, The base film includes at least one of polyester film, polyethylene film or polypropylene film; and / or, the thickness of the base film is 7~9μm and the porosity is 30%~40%; and / or, the thickness of the coating is 3~5μm.

5. A method for preparing the composite separator according to any one of claims 1-4, characterized in that, The method includes: dissolving a metal salt in a solvent, adding a thickener to obtain a sol solution; mixing the sol solution with a solid electrolyte, adjusting the pH of the system to alkaline, to obtain a composite gel; post-treating the composite gel to obtain a composite material comprising a high-entropy alloy aerogel and a solid electrolyte; coating a slurry comprising the composite material onto at least one side surface of a base membrane to obtain a composite membrane; the post-treatment process includes at least one of a heat treatment process, a cyclic freeze-thaw process, a chemical vapor deposition process, a physical vapor deposition process, or an electrodeposition process.

6. The method for preparing the composite diaphragm according to claim 5, characterized in that, The step of obtaining the sol solution satisfies at least one of the following characteristics (1) to (5): (1) The metal salt comprises a mixture of at least five metal salts; the metal salt comprises a mixture of at least five of sodium salt, potassium salt, calcium salt, magnesium salt, aluminum salt, strontium salt, barium salt or copper salt; the anion in the metal salt comprises at least one of nitrate ion, acetate ion or sulfate ion; (2) The solvent comprises alcohol and water; the volume ratio of alcohol to water is 1:(3~4); the alcohol comprises one or two of methanol, ethanol, propanol, isopropanol and propylene glycol; (3) The thickener comprises one of polyethylene glycol, polybutylene glycol, polyvinyl alcohol or polyamide alcohol; (4) the mass of the metal salt accounts for 35% to 45% of the mass of the solvent based on the mass of the solvent; (5) the mass of the thickener accounts for 1.5% to 2% of the mass of the solvent based on the mass of the solvent.

7. The method for preparing the composite diaphragm according to claim 5, characterized in that, The step of obtaining the composite gel satisfies at least one of the following features (1) to (4): (1) The solid electrolyte includes at least one of sulfide solid electrolyte, oxide solid electrolyte, halide solid electrolyte or polymer solid electrolyte; (2) The mass fraction of the solid electrolyte to the mass of the solvent is 5% to 8% based on the mass of the solvent; (3) The alkali used to adjust the pH value of the system includes one or more of aluminum hydroxide, copper hydroxide, zinc hydroxide, ammonia water and sodium carbonate; (4) The pH value of the adjusted system is in the range of 9 to 11.

8. The method for preparing the composite diaphragm according to any one of claims 5 to 7, characterized in that, The heat treatment process is carried out in an inert gas atmosphere, with a heating rate of 5~8℃ / min, a holding temperature of 800~1000℃, and a holding time of 3h~5h; and / or, after obtaining the composite gel and before the post-treatment, a drying step is also included; and / or, the slurry containing the composite material includes the composite material, a binder, and water, wherein the mass ratio of the composite material, the binder, and the water is (30~40):(3~6):

100.

9. A battery, comprising a separator, characterized in that, The diaphragm is the composite diaphragm according to any one of claims 1 to 4 or the composite diaphragm prepared by the preparation method according to any one of claims 5 to 8.

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