Composite lithium battery separator and preparation method therefor

Abstract

A composite lithium battery separator, comprising a polymer-based film and a coating that coats the polymer-based film, wherein the material of the coating comprises natural clay mineral nanotubes and polyphosphazene resin microspheres.

Description

Composite lithium battery separator and its preparation method

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese patent application No. 202411429051.6, filed on October 14, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to lithium batteries, and more particularly to a composite lithium battery separator and its preparation method. Background Technology

[0004] With the development of the times and technology, people's demand for consumer electronics, power batteries, and energy storage devices is increasing. Lithium-ion batteries are widely used due to their high energy density and long cycle life. The lithium battery separator is one of the core materials of lithium-ion batteries, its main function being to separate the positive and negative electrodes. While ensuring the passage of lithium ions, it separates the positive and negative active materials to prevent short circuits caused by contact between the positive and negative electrodes. The lithium battery separator is a thin film with a microporous structure. The performance of the lithium battery separator determines the battery's interface structure and internal resistance, affecting the battery's capacity and cycle life. Currently, commercially available lithium battery separators are mainly polypropylene and polyethylene separators, which are prone to shrinkage when heated. In practical use, when encountering abnormally high temperatures, the lithium battery separator is easily melted and shrunken, leading to a large-area short circuit in the lithium battery. Furthermore, because the lithium battery separator itself is flammable, the heat accumulated during a short circuit can easily ignite the separator, causing uncontrollable and serious consequences. In addition, the affinity of existing lithium battery separators for electrolytes needs to be improved. Summary of the Invention

[0005] This disclosure provides a composite lithium battery separator and its preparation method by utilizing one or more embodiments, which solves the technical problems of existing lithium battery separators being prone to shrinkage and combustion when heated, as well as having poor affinity for electrolytes.

[0006] In a first aspect, embodiments of this disclosure provide a composite lithium battery separator, comprising: a polymer base film; and a coating material applied to the polymer base film, wherein the coating material comprises natural clay mineral nanotubes and polyphosphonic nitrile resin microspheres.

[0007] Secondly, the present disclosure also provides a method for preparing a composite lithium battery separator according to the first aspect, comprising: providing natural clay mineral nanotubes; preparing polyphosphonic nitrile resin microspheres; dispersing the natural clay mineral nanotubes and polyphosphonic nitrile resin microspheres in water to form a slurry; providing a polymer base film; coating the slurry onto the polymer base film; and drying the polymer base film to obtain the composite lithium battery separator. Attached Figure Description

[0008] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0009] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0010] Figure 1 shows a scanning electron microscope image of a composite lithium battery separator according to an embodiment of the present disclosure.

[0011] Figure 2 shows a scanning electron microscope image of a polyethylene diaphragm according to a comparative example of this disclosure.

[0012] Figure 3 shows a morphological comparison of the composite lithium battery separator according to an embodiment of the present disclosure and a polyethylene separator in a comparative example before and after heating.

[0013] Figure 4 shows photographs recording the combustion phenomena of a composite lithium battery separator according to an embodiment of the present disclosure and a polyethylene separator as a comparative example.

[0014] Figure 5 shows a schematic flowchart of a method for preparing a composite lithium battery separator according to some embodiments of the present disclosure.

[0015] Figure 6 shows a schematic flowchart of the preparation of polyphosphonic nitrile resin microspheres in a method for preparing a composite lithium battery separator according to some embodiments of the present disclosure. Embodiments of the present invention

[0016] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0017] Unless otherwise specified, the terminology used herein should be understood as having the meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In case of any discrepancy, the description herein shall prevail.

[0018] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this disclosure are available on the market or can be prepared by existing methods.

[0019] Existing lithium battery separators have technical problems such as easy shrinkage when heated, easy combustion, and poor affinity for electrolyte.

[0020] The technical solution of this disclosure is to solve the above-mentioned technical problems, and the general idea is as follows.

[0021] In a first aspect, embodiments of this disclosure provide a composite lithium battery separator, comprising:

[0022] Polymer-based films; and,

[0023] The coating is applied to a polymer-based film, and the coating materials include natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres.

[0024] It's easy to understand that polymer-based membranes are standard products in the field of lithium battery separators and can be obtained through commercial purchases.

[0025] It's easy to understand that the main flame-retardant principle of natural clay mineral nanotubes is that their thermal decomposition produces water, which isolates oxygen, thus achieving a flame-retardant effect. The main flame-retardant principle of polyphosphonic acid resin microspheres is that their thermal decomposition is an endothermic reaction, thus buffering temperature changes through heat absorption during the decomposition process. Simultaneously, the thermal decomposition of polyphosphonic acid resin microspheres produces non-flammable substances such as phosphoric acid, which can also contribute to flame retardancy to some extent. Natural clay mineral nanotubes contain water within their crystals. Due to the low boiling point of water, the thermal decomposition temperature of natural clay mineral nanotubes is typically high, causing the water within the crystals to directly generate water vapor. Since water vapor has a large volume, it can quickly dilute or isolate oxygen. Therefore, the flame-retardant function of natural clay mineral nanotubes takes effect rapidly at high temperatures, providing sufficient reaction time for the thermal decomposition of polyphosphonic acid resin microspheres, thereby achieving a flame-retardant effect. In other words, in the embodiments of this disclosure, the composite lithium battery separator can have a better flame retardant effect through the synergistic effect of natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres.

[0026] It is easy to understand that the chemical reaction between polyphosphonic acrylonitrile resin microspheres and natural clay mineral nanotubes at high temperatures can absorb heat, and the reaction products can be flame retardant, which is beneficial to reducing the thermal shrinkage of composite lithium battery separators.

[0027] It's easy to understand that numerous pores form between the polyphosphonic nitrile resin microspheres and between the polyphosphonic nitrile resin microspheres and clay mineral nanotubes. These pores are small in size, have high surface tension, and exhibit strong adsorption capacity for electrolyte. The clay mineral nanotubes also provide additional channels between these pores, further enhancing the adsorption capacity for electrolyte and providing additional ion pathways, which helps increase the ionic conductivity of the composite lithium battery separator. Furthermore, the total volume of the pores is relatively small compared to the total volume of the polyphosphonic nitrile resin microspheres and clay mineral nanotubes. This allows the flame-retardant substances released by the thermal decomposition of the polyphosphonic nitrile resin microspheres and clay mineral nanotubes to quickly fill the pores, effectively diluting the electrolyte and oxygen to achieve a flame-retardant effect.

[0028] The composite lithium battery separator provided in this disclosure has a coating comprising natural clay mineral nanotubes and polyphosphonic acid resin microspheres. The coating exhibits a low volume change rate at high temperatures, reducing the thermal shrinkage of the composite lithium battery separator. The synergistic flame-retardant effect of the natural clay mineral nanotubes and polyphosphonic acid resin microspheres improves the flammability of the composite lithium battery separator, enabling it to self-extinguish after ignition. The coating formed by the natural clay mineral nanotubes and polyphosphonic acid resin microspheres possesses abundant channels and pores, enabling it to absorb a large amount of electrolyte, resulting in high affinity of the composite lithium battery separator for the electrolyte and high ionic conductivity.

[0029] In some embodiments of this disclosure, the mass ratio of natural clay mineral nanotubes to polyphosphonic acrylonitrile resin microspheres in the coating is 1:(0.5~20).

[0030] The beneficial effect of using a mass ratio of natural clay mineral nanotubes to polyphosphonic acrylonitrile resin microspheres of 1:(0.5~20) is that it can significantly reduce the thermal shrinkage of the composite lithium battery separator while maintaining sufficient flexibility and processability.

[0031] As an example, in the coating, the mass ratio of natural clay mineral nanotubes to polyphosphonic acrylonitrile resin microspheres can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, or 1:20, etc., or any other value in the range of 1:(0.5~20).

[0032] In some embodiments of this disclosure, the particle size of the polyphosphazene resin microspheres satisfies: 0.05 μm ≤ D50 ≤ 5 μm; and / or,

[0033] The specific surface area of ​​natural clay mineral nanotubes is 10 m². 2 / g ~200 m 2 / g; and / or,

[0034] The natural clay mineral nanotubes are at least one of attapulgite nanotubes and halloysite nanotubes.

[0035] The beneficial effect of having a particle size of 0.05 μm≤D50≤5.00 μm for polyphosphonic nitrile resin microspheres is that it allows for sufficiently small pore structures between the microspheres, resulting in strong enough adsorption capacity for the electrolyte without easily causing aggregation.

[0036] As an example, the D50 of polyphosphonic acrylonitrile resin microspheres can be 0.05 μm, 0.20 μm, 1.00 μm, 3.00 μm or 5.00 μm, or any other value in the range of 0.05 μm to 5.00 μm.

[0037] The specific surface area of ​​natural clay mineral nanotubes is 10 m². 2 / g~200 m 2 The beneficial effect of / g is that it allows natural clay mineral nanotubes to fully adsorb electrolyte and transport ions, and also to fully support the coating, reducing the thermal shrinkage of the composite lithium battery separator.

[0038] As an example, the specific surface area of ​​natural clay mineral nanotubes can be 10 m². 2 / g, 50m 2 / g, 100m 2 / g, 150m 2 / g or 200 m 2 / g, etc., can also be 10 m 2 / g ~200 m 2 Any other value within the range / g.

[0039] The advantages of using at least one of attapulgite nanotubes and halloysite nanotubes in natural clay mineral nanotubes are that both attapulgite nanotubes and halloysite nanotubes have good flame retardant properties, provide strong support for the coating, and are inexpensive and readily available on the market.

[0040] In some embodiments of this disclosure, the coating also includes a dispersant, a wetting agent, and a binder.

[0041] In some embodiments of this disclosure, the dispersant and wetting agent are each independently selected from at least one of the following compounds: fluoroalkyl methoxyl ethers, polyoxyethylene alkylamines, sodium methylene bis(naphthalene) sulfonate, polyether-modified silicone, sodium arylnaphthalene sulfonate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium perfluorooctanoate, nonylphenol polyoxyethylene ether, sodium butylnaphthalene sulfonate, polyacrylate, polyethylene glycol, and sodium carboxymethyl cellulose; and / or,

[0042] The binder is at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, lithium polyacrylate, and polyacrylonitrile multi-component copolymer.

[0043] It is easy to understand that coatings can usually be formed by applying a slurry. In the embodiments of this disclosure, the coating can be prepared by using water as a solvent and dispersing natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres in water.

[0044] As is easily understood, the coating includes a dispersant, meaning that the slurry used to prepare the coating contains a dispersant, which can be used to increase the dispersibility of polyphosphonic acid resin microspheres in water. The coating also includes a wetting agent, meaning that the slurry used to prepare the coating contains a wetting agent, which can be used to increase the wetting ability of polyphosphonic acid resin microspheres in water.

[0045] As is easy to understand, the coating includes a binder, that is, the slurry used to prepare the coating includes a binder. The binder can be used to increase the film-forming ability of the slurry containing natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres.

[0046] In some embodiments of this disclosure, the composite lithium battery separator possesses the following properties:

[0047] The thermal shrinkage rate after baking at 180 ℃ for 30 min is ≤5%;

[0048] The air permeability is 99.6 s / 100mL~403.6 s / 100mL;

[0049] Electrolyte uptake rate was 120.6%–469.2%; and,

[0050] The ionic conductivity is 0.5 mS / cm to 3.5 mS / cm.

[0051] Figure 5 shows a schematic flowchart of a method for preparing a composite lithium battery separator according to some embodiments of the present disclosure. In a second aspect, as shown in Figure 5, an embodiment of the present disclosure also provides a method for preparing a composite lithium battery separator according to a first aspect, comprising:

[0052] S1: Provides natural clay mineral nanotubes;

[0053] S2: Preparation of polyphosphazene resin microspheres;

[0054] S3: Disperse natural clay mineral nanotubes and polyphosphonic nitrile resin microspheres in water to prepare a slurry;

[0055] S4: Provide a polymer base film, and coat the slurry onto the polymer base film; and,

[0056] S5: Dry the polymer base film to obtain a composite lithium battery separator.

[0057] Figure 6 shows a schematic flowchart of the preparation of polyphosphonic nitrile resin microspheres in a method for preparing a composite lithium battery separator according to some embodiments of the present disclosure. In some embodiments of the present disclosure, as shown in Figure 6, the preparation of polyphosphonic nitrile resin microspheres includes:

[0058] S21: Disperse hexachlorotriphosphazene and monomers in a solvent to obtain an intermediate solution;

[0059] S22: A catalyst is added to the intermediate solution, and a mixture is obtained after the reaction; and,

[0060] S23: Perform solid-liquid separation on the mixture to obtain polyphosphazene resin microspheres.

[0061] In some embodiments of this disclosure, the monomer is at least one selected from 4,4-dihydroxydiphenyl sulfone, 4,4-diaminodiphenyl ether, 4,4-dihydroxybenzophenone, p-diphenylamine, 4,4-diaminodiphenyl ether, 3,4-dihydroxybenzoic acid, phloroglucinol, melamine, p-phenylenediamine, hexafluorobisphenol A, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, dopamine, phloretin, resveratrol, and isosorbide.

[0062] Those skilled in the art will understand that the catalyst can be an inorganic base or an organic base.

[0063] In some embodiments of this disclosure, the catalyst may be at least one of sodium hydroxide, triethylamine, and diisopropylethylamine.

[0064] In some embodiments of this disclosure, in step S21, the solvent is at least one selected from tetrahydrofuran, acetone, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide.

[0065] In some embodiments of this disclosure, after step S21 is performed, the concentration of hexachlorotriphosphazene in the solvent is 1 mmol / L to 20 mmol / L, and the concentration of the monomer in the solvent is 3 mmol / L to 60 mmol / L.

[0066] In some embodiments of this disclosure, after step S21 is performed, i.e. in the intermediate solution, the concentration of hexachlorotriphosphazene in the intermediate solution is 1 mmol / L to 20 mmol / L, and the concentration of the monomer in the intermediate solution is 3 mmol / L to 60 mmol / L.

[0067] As an example, the concentration of hexachlorotriphosphazene in the intermediate solution can be 1 mmol / L, 2 mmol / L, 3 mmol / L, 4 mmol / L, 5 mmol / L, 6 mmol / L, 7 mmol / L, 8 mmol / L, 9 mmol / L, 10 mmol / L, 11 mmol / L, 12 mmol / L, 13 mmol / L, 14 mmol / L, 15 mmol / L, 16 mmol / L, 17 mmol / L, 18 mmol / L, 19 mmol / L, or 20 mmol / L, or any other value within the range of 1 mmol / L to 20 mmol / L.

[0068] As an example, the concentration of the monomer in the intermediate solution is 3 mmol / L, 5 mmol / L, 10 mmol / L, 15 mmol / L, 20 mmol / L, 25 mmol / L, 30 mmol / L, 35 mmol / L, 40 mmol / L, 45 mmol / L, 50 mmol / L, 55 mmol / L, or 60 mmol / L, etc., or it can be any other value in the range of 3 mmol / L to 60 mmol / L.

[0069] In some embodiments of this disclosure, the reaction time in step S22 is 0.2 h to 2.0 h.

[0070] As an example, the reaction time can be 0.2 h, 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, or 2.0 h, or any other value within the range of 0.2 h to 2.0 h.

[0071] In some embodiments of this disclosure, after obtaining the polyphosphonic nitrile resin microspheres in step S23, the polyphosphonic nitrile resin microspheres can be washed, and the washing agent can be at least one of deionized water and ethanol. Washing removes residual solvents and catalysts, unreacted hexachlorotriphosphonic nitrile, and monomers from the polyphosphonic nitrile resin microspheres.

[0072] In some embodiments of this disclosure, while dispersing natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres in water, dispersants, wetting agents, and binders may also be added to the water.

[0073] In some embodiments of this disclosure, the total mass of the dispersant, wetting agent, and binder accounts for 1% to 10% of the slurry mass; and / or,

[0074] In the slurry, the total mass ratio of natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres to water is 1:(1.5~50.0).

[0075] As an example, the total mass of dispersant, wetting agent and binder can account for 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% of the slurry mass, or any other value in the range of 1% to 10%.

[0076] As an example, in the slurry, the mass ratio of the total mass of natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres to water is 1:1.5, 1:2.0, 1:3.0, 1:4.0, 1:5.0, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50, etc., or it can be any other value in the range of 1: (1.5~50.0).

[0077] The technical solutions of this disclosure are further illustrated 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 this disclosure. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0078] Example

[0079] This disclosure provides a composite lithium battery separator, which is prepared by the following method:

[0080] Methods for preparing polyphosphazene microspheres:

[0081] Anhydrous acetonitrile, used as a solvent, was added to a reaction flask. Hexachlorotriphosphazene and 4,4-dihydroxydiphenyl sulfone, used as a monomer, were added to the reaction flask in a 1:3 molar ratio. The reaction flask was then placed in an ultrasonic cleaning tank at a power of 350 W until the solid powders (hexachlorotriphosphazene and 4,4-dihydroxydiphenyl sulfone) were completely dissolved. The hexachlorotriphosphazene and 4,4-dihydroxydiphenyl sulfone dissolved in anhydrous acetonitrile, yielding an intermediate solution. In the intermediate solution, the molar concentrations of both hexachlorotriphosphazene and the monomer were set to 8 mmol / L.

[0082] Transfer the above reaction flask to a water bath, turn on the water bath and set the temperature to 30 °C, while stirring the intermediate solution in the reaction flask. After stirring the intermediate solution for 5 min, add a certain volume of triethylamine as a catalyst to the above reaction flask, with a volume ratio of triethylamine to acetonitrile of 1:50. Continue stirring the liquid in the reaction flask to allow it to react for 15 min, obtaining a mixture containing polyphosphazene microspheres, and then stop the reaction.

[0083] The mixture containing polyphosphazene microspheres in the reaction flask was transferred to a centrifuge tube and centrifuged at 13,000 rpm for 3 min using a high-speed centrifuge. The precipitate obtained by centrifugation was washed twice with deionized water and ethanol alternately. The washed precipitate was then transferred to an oven at 80 °C and dried for 12 h to obtain polyphosphazene microspheres.

[0084] Methods for preparing slurry:

[0085] A first suspension with a solid content of 11% was prepared by mixing 70 parts by weight of polyphosphazene microspheres, 30 parts by weight of halloysite nanotubes, and water. Then, 2% by weight of naphthalenesulfonic acid dispersant and 1% by weight of sodium dodecylbenzenesulfonate wetting agent were added to the first suspension to obtain a second suspension. The second suspension was then transferred to a magnetic stirrer and stirred for 24 hours. Finally, 5% by weight of polyacrylonitrile binder was added to the second suspension, and stirring was continued for 6 hours to obtain a slurry containing polyphosphazene microspheres and halloysite nanotubes.

[0086] Methods for preparing composite lithium battery separators:

[0087] The polymer base membrane is a commercial polyethylene membrane with a thickness of approximately 10 μm. No special treatment is required before coating the polyethylene membrane; simply ensuring the surface of the polyethylene membrane is clean is sufficient.

[0088] The above slurry was uniformly coated onto a polyethylene separator using an automatic coating machine to obtain a composite wet membrane. The composite wet membrane was placed at room temperature (25°C) for 30 minutes until no watermarks remained on its surface. Then, it was transferred to an 80°C forced-air drying oven for vacuum drying for 10 minutes to obtain a polyethylene composite separator with a coating containing polyphosphazene microspheres and halloysite nanotubes on one side. The above steps were repeated to obtain a polyethylene composite separator with coatings containing polyphosphazene microspheres and halloysite nanotubes on both sides, thus obtaining the composite lithium-ion battery separator. The average thickness of the obtained composite lithium-ion battery separator was 18 μm.

[0089] Comparative Example

[0090] The polyethylene diaphragm used in this comparative example is the same as the commercial polyethylene diaphragm used as the polymer base film in the examples.

[0091] Relevant experimental and effect data:

[0092] The air permeability of the composite lithium-ion battery separator in the example was tested using a Gurley 4110N air permeability tester (USA). The air permeability of a lithium-ion battery separator reflects the tortuosity of its internal pores and the actual path of ion diffusion, and is generally proportional to ionic conductivity, which can be evaluated by the Gurley value. The Gurley value refers to the time required for a certain amount of air to pass through a unit area of ​​lithium-ion battery separator at a specified pressure, measured in seconds. The composite lithium-ion battery separator in the example had an air permeability of 220 ± 10 s per 100 mL, indicating good air permeability.

[0093] The surface morphology of the composite lithium-ion battery separator of the present disclosure and the polyethylene separator of the comparative example were observed under a cold field scanning electron microscope. Referring to Figures 1 and 2, Figure 1 shows a scanning electron microscope image of the composite lithium-ion battery separator according to an embodiment of the present disclosure. Figure 2 shows a scanning electron microscope image of the polyethylene separator of the comparative example of the present disclosure. Comparing Figures 1 and 2, it can be seen that the surface morphology of the composite lithium-ion battery separator of the present disclosure and the polyethylene separator of the comparative example are completely different. On the surface of the composite lithium-ion battery separator of the present disclosure, polyphosphazene microspheres and halloysite nanotubes are interspersed, and the resulting ball-and-stick mixed coating uniformly covers the polymer base film, indicating that the slurry formulation has good coatability for polyolefin polymer base films. Furthermore, the coating contains a large number of pores, which can absorb electrolytes and provide abundant channels for lithium-ion transport.

[0094] Using a cutting machine, the composite lithium battery separator of this disclosure embodiment and the polyethylene separator of the comparative example are respectively cut into several circular pieces with a diameter of 16.5 mm. For ease of explanation later, the circular pieces cut from the composite lithium battery separator of this disclosure embodiment are denoted as PZN-HNTs@PE, and the circular pieces cut from the polyethylene separator of the comparative example are denoted as PE.

[0095] After weighing each PZN-HNTs@PE membrane individually and calculating the average value, the areal density of the composite lithium battery separator of this embodiment was calculated to be 11.5 ± 0.5 g / m³. 2 .

[0096] The thickness of the composite lithium battery separator was tested using a handheld thickness gauge, and it was found that the average thickness of the composite lithium battery separator in this embodiment of the present disclosure is 18 μm.

[0097] The liquid absorption rate of the composite lithium battery separator of this disclosure embodiment and the polyethylene separator of the comparative example were tested using a gravimetric method. Specifically, the liquid absorption rate of the lithium battery separator was calculated by the change in weight of the separator before and after liquid absorption. PZN-HNTs@PE and PE were weighed separately, then immersed in liquid electrolyte for 1 hour. After removal, the liquid on the surface of PZN-HNTs@PE and PE was gently wiped off with filter paper, and then weighed again. The liquid absorption rate EU was calculated using the following formula:

[0098] EU (%) = (W2-W1) / W1×100%

[0099] In some embodiments, W1 and W2 represent the mass of PZN-HNTs@PE and the mass of PE before and after immersion in the electrolyte. The solvent of the test electrolyte is formed by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7, and the solute of the test electrolyte is lithium hexafluorophosphate with a concentration of 1 mol / L. Tests showed that the electrolyte absorption rate of the composite lithium battery separator of this embodiment was 249%, while the electrolyte absorption rate of the comparative polyethylene separator was 164%.

[0100] The bulk impedance of the composite lithium battery separator of this disclosure embodiment and the polyethylene separator of the comparative example were measured by electrochemical impedance spectroscopy (EIS) on an electrochemical workstation (Bio-Logic VSP-300), and their respective ionic conductivity was calculated. Stainless steel symmetrical cells were assembled using PZN-HNTs@PE and PE, respectively, and the tests were conducted in a frequency range of 10 Hz. 6 ~10 -1 Hz, AC amplitude of 10 mV, the formula for calculating ionic conductivity is as follows:

[0101] σ = D / RS.

[0102] In some embodiments, σ ​​represents the ionic conductivity of the lithium battery separator; D represents the thickness of the lithium battery separator; R is the x-intercept of the Nyquist plot; and S represents the area of ​​the lithium battery separator. The ionic conductivity of the composite lithium battery separator in this embodiment is measured to be 0.64 mS / cm, while the ionic conductivity of the polyethylene separator in the comparative example is 0.29 mS / cm.

[0103] PZN-HNTs@PE and PE were heated at 180 °C for 30 min, and the morphology of the discs was recorded before and after heating. Figure 3 shows a comparison of the morphology of the composite lithium battery separator according to the embodiment of this disclosure and the polyethylene separator of the comparative example before and after heating. The circle shown in Figure 3 is a circle with a diameter of 16.5 mm, which is the diameter of PZN-HNTs@PE and PE before heating at 180 °C for 30 min. PE-180℃ is a photograph of the morphology of PE after heating at 180 °C for 30 min, and PZN-HNTs@PE-180℃ is a photograph of the morphology of PZN-HNTs@PE after heating at 180 °C for 30 min. As can be seen from Figure 3, the polyethylene separator of the comparative example obviously underwent a process of shrinkage, melting, and solidification, changing from a circle with a diameter of 16.5 mm into a small clump of light white plastic. However, the composite lithium battery separator of the embodiment of this disclosure showed almost no significant shrinkage after heating. This indicates that the composite lithium battery separator obtained in the embodiments of the present invention has excellent thermal dimensional stability.

[0104] PZN-HNTs@PE and PE were separately burned over an alcohol lamp flame. After ignition, the discs were removed from the flame area, and the combustion process of PZN-HNTs@PE and PE was recorded using a digital camera. Figure 4 shows photographs recording the combustion phenomena of the composite lithium battery separator according to an embodiment of the present disclosure and the polyethylene separator of the comparative example. As can be seen from Figure 4, the polyethylene separator of the comparative example shrinks when approaching the flame, rapidly shrinking into a clump upon contact with the flame, and then burns completely. The composite lithium battery separator of the present disclosure does not show significant shrinkage upon contact with the flame, maintaining its basic shape. After leaving the flame, the burned portion begins to carbonize, and then the flame diminishes until it extinguishes. This is due to the synergistic flame-retardant effect of natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres, which can form a protective layer with a dense structure on the surface and inside of the coating, effectively isolating oxygen and inhibiting further combustion of the polymer base film, thus exhibiting excellent flame retardancy.

[0105] In summary, compared to the comparative example, the composite lithium battery separator of this disclosure, with its coating comprising natural clay mineral nanotubes and polyphosphonic nitrile resin microspheres, exhibits a small volume change rate at high temperatures, thus reducing the thermal shrinkage of the composite lithium battery separator. The synergistic flame-retardant effect of the natural clay mineral nanotubes and polyphosphonic nitrile resin microspheres improves the flammability of the composite lithium battery separator, enabling it to self-extinguish after ignition. The coating formed by the natural clay mineral nanotubes and polyphosphonic nitrile resin microspheres possesses abundant channels and pores, enabling it to absorb a large amount of electrolyte, resulting in high affinity of the composite lithium battery separator for the electrolyte and high ionic conductivity.

[0106] Various embodiments of this disclosure may exist in the form of a range. It should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this disclosure. Therefore, it should be considered that the range description specifically discloses all possible subranges and single numerical values ​​within that range. For example, it should be considered that a range description from 1 to 6 specifically discloses subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0107] In this disclosure, unless otherwise stated, directional terms such as “upper” and “lower” specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this disclosure, the terms “comprising,” “including,” etc., mean “including but not limited to.” Moreover, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase “comprising…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this document, relational terms such as “first” and “second” are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, “and / or” describes the relationship between related objects, indicating that three relationships may exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. For relationships involving three or more related objects described using "and / or", it indicates that any one of the three related objects can exist alone, or at least two of them can exist simultaneously. For example, for A, and / or B, and / or C, it can mean that any one of A, B, and C exists alone, or any two of them exist simultaneously, or all three of them exist simultaneously. In this document, "at least one" means one or more, and "more" means two or more. "At least one", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. The "parts representation" involved in this disclosure, such as parts by weight or parts by mass, represents the proportional relationship between the components. In the proportional relationships disclosed herein, parameters that need to be described by proportion should be understood as the first term of the proportion in the order of description, and the proportion figures should be understood as the second term of the proportion. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figures in the proportion in the order of description, that is, the mass of substance A : the mass of substance B : the mass of substance C = 1 : 2 : 3.

[0108] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A composite lithium battery separator, comprising: Polymer-based film; as well as, The coating applied to the polymer-based film comprises natural clay mineral nanotubes and polyphosphonic nitrile resin microspheres.

2. The composite lithium battery separator of claim 1, wherein, In the coating, the mass ratio of the natural clay mineral nanotubes to the polyphosphonic acrylonitrile resin microspheres is 1:(0.5~20).

3. The composite lithium battery separator of claim 1, wherein, The particle size of the polyphosphazene resin microspheres satisfies: 0.05 μm ≤ D50 ≤ 5.00 μm; and / or, The specific surface area of the natural clay mineral nanotubes is 10 m 2 / g ~ 200 m 2 / g; and / or, The natural clay mineral nanotubes are at least one of attapulgite nanotubes and halloysite nanotubes.

4. The composite lithium battery separator according to any one of claims 1 to 3, wherein, The coating also includes dispersants, wetting agents, and binders.

5. The composite lithium battery separator of claim 4, wherein, The dispersant and the wetting agent are each independently selected from at least one of the following compounds: fluoroalkyl methoxyl ethers, polyoxyethylene alkylamines, sodium methylene bis(naphthalene) sulfonate, polyether-modified silicone, sodium arylnaphthalene sulfonate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium perfluorooctanoate, nonylphenol polyoxyethylene ether, sodium butylnaphthalene sulfonate, polyacrylate, polyethylene glycol, and sodium carboxymethyl cellulose; and / or The adhesive is at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, lithium polyacrylate, and polyacrylonitrile copolymer.

6. The composite lithium battery separator according to any one of claims 1 to 5, wherein, The composite lithium battery separator has the following properties: The thermal shrinkage rate after baking at 180 ℃ for 30 min is ≤5%; The air permeability is 99.6 s / 100mL ~ 403.6 s / 100mL; Electrolyte uptake rate was 120.6%–469.2%; and, The ionic conductivity is 0.5 mS / cm ~ 3.5 mS / cm.

7. A method for preparing a composite lithium battery separator according to any one of claims 1 to 6, comprising: Provides natural clay mineral nanotubes; Preparation of polyphosphononitrile resin microspheres; The natural clay mineral nanotubes and the polyphosphononitrile resin microspheres were dispersed in water to prepare a slurry. Provide a polymer-based film, and coat the slurry onto the polymer-based film; and, The polymer-based film is dried to obtain the composite lithium battery separator.

8. The method of producing a composite lithium battery separator according to claim 7, wherein, The preparation of polyphosphononitrile resin microspheres includes: Hexachlorotriphosphazene and the monomer were dispersed in a solvent to obtain an intermediate solution; A catalyst is added to the intermediate solution, and a mixture is obtained after the reaction; and, The mixture was subjected to solid-liquid separation to obtain the polyphosphazene resin microspheres. The monomer is at least one of 4,4-dihydroxydiphenyl sulfone, 4,4-diaminodiphenyl ether, 4,4-dihydroxybenzophenone, p-diphenylamine, 4,4-diaminodiphenyl ether, 3,4-dihydroxybenzoic acid, phloroglucinol, melamine, p-phenylenediamine, hexafluorobisphenol A, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, dopamine, phloretin, resveratrol, and isosorbide.

9. The method of producing a composite lithium battery separator according to claim 7, wherein, The natural clay mineral nanotubes and polyphosphonic acrylonitrile resin microspheres are dispersed in water, and a dispersant, wetting agent and binder are added to the water to prepare the slurry.

10. The method of producing a composite lithium battery separator according to claim 9, wherein, The total mass of the dispersant, wetting agent, and binder accounts for 1% to 10% of the mass of the slurry; and / or, In the slurry, the mass ratio of the natural clay mineral nanotube and the polyphosphazene resin microsphere to water is 1: (1.5-50.0). In the slurry, the mass ratio of the natural clay mineral nanotube and the polyphosphazene resin microsphere to water is 1: (1.5-50.0).

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