A method for preparing a sandwich-like fiber diaphragm by triaxial electrospinning and its application

Abstract

This invention discloses a method for preparing a sandwich-like fiber membrane using triaxial electrospinning, its application, and related techniques. The preparation method includes the following steps: dissolving a substrate membrane material in a first organic solvent to obtain a middle layer solution; mixing a solid electrolyte with a binder solution to obtain a core layer solution; dissolving a flame retardant in a second organic solvent to obtain a shell layer solution; and using the middle layer solution, core layer solution, and shell layer solution, preparing a fiber membrane through triaxial electrospinning, followed by hot pressing and drying to obtain the sandwich-like fiber membrane. This sandwich-like fiber membrane has a thickness of approximately 12-14 μm and exhibits suitable porosity, excellent thermal stability, excellent closed-cell flame retardancy, high mechanical strength, high ionic conductivity, and low internal resistance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion power battery separator preparation technology. More specifically, it relates to a sandwich fiber separator prepared by triaxial electrospinning, its preparation method, and its application. Background Technology

[0002] With the continuous development of new energy technologies, lithium-ion power batteries, as a clean energy source, have attracted increasing attention. The commercial application of lithium-ion power batteries has also garnered significant attention, especially regarding their safety performance.

[0003] Many factors affect the safety of lithium batteries, and the separator, as one of the four key components of lithium-ion power batteries, primarily functions to prevent internal short circuits and provide free pathways for lithium ions. Currently, lithium-ion power battery separators on the market are mainly polyolefin separators, primarily made of polyethylene and polypropylene, including single-layer PE, single-layer PP, and three-layer PP / PE / PP composite films. However, polyolefin separators have poor thermal stability and are prone to shrinkage at high temperatures, leading to thermal runaway; furthermore, polyolefin separators have low ionic conductivity, which is unfavorable for developing high-rate performance lithium-ion power batteries. Therefore, there is an urgent need to develop high-performance lithium-ion power battery separators.

[0004] Traditionally, lithium-ion battery separators are prepared by coating a pre-mixed separator precursor solution onto a base film material. This results in a combined base film and coating thickness of approximately 20-40 μm, leading to a relatively thick separator. Increased separator thickness means a higher volume and mass percentage for the same spatial volume, while reducing the amount of active material, which is detrimental to improving battery energy density. Electrospinning, however, can accommodate nanoscale materials, offering a new approach for preparing thinner power battery separators than traditional methods. Patent CN110565269 proposes a method for preparing lithium-ion battery separators using coaxial electrospinning, employing a mixture of polyurethane prepolymer and hexafluoropropylene. However, this method only improves mechanical strength and does not truly enhance performance. Patent CN103469488A proposed a temperature difference hot-melt technology for preparing lithium-ion battery separators, which involves electrospinning two polymers with a melting temperature difference of 30°C. However, the high processing temperature negatively impacts the porosity of the separator, hindering improvements in its electrochemical performance. Therefore, in the field of lithium-ion battery separator preparation, more effective methods for producing high-performance separators are still needed. Summary of the Invention

[0005] To address the aforementioned problems, the first objective of this invention is to provide a method for preparing a sandwich-like fiber diaphragm using triaxial electrospinning. This method creatively utilizes triaxial electrospinning technology to produce a thinner diaphragm with excellent electrochemical performance, solving the problems of existing coating processes such as thick products, cumbersome processes, and poor electrochemical performance.

[0006] A second objective of this invention is to provide a sandwich-like fiber diaphragm prepared using the preparation method described above.

[0007] The third objective of this invention is to provide an application of a sandwich-like fiber separator in the preparation of lithium-ion power batteries.

[0008] The fourth objective of this invention is to provide a lithium-ion power battery.

[0009] To achieve the first objective mentioned above, the present invention adopts the following technical solution:

[0010] This invention discloses a method for preparing a sandwich-like fiber diaphragm by triaxial electrospinning, comprising the following steps:

[0011] The substrate film is dissolved in the first organic solvent to obtain the intermediate layer solution;

[0012] The solid electrolyte is mixed with the binder solution to obtain the core layer solution;

[0013] The flame retardant is dissolved in a second organic solvent to obtain a shell solution;

[0014] A fiber membrane was prepared by using a triaxial electrospinning technique with a middle layer solution, a core layer solution, and a shell layer solution. The membrane was then hot-pressed and dried to obtain a sandwich-like fiber membrane.

[0015] In this invention, nanoscale solid electrolyte materials are used as the main raw material for the core layer solution to improve the conductivity of the separator, and flame retardants are introduced as the main raw material for the shell layer solution to improve the fire resistance of the separator. Together with the middle layer solution containing the substrate membrane material, the three materials are controlled under triaxial electrospinning technology to obtain a sandwich-like fiber separator with superior performance. This solves the problems of thick separator, complicated process and poor electrochemical performance in traditional coating processes. The resulting thinner power battery separator improves thermal stability, closed-cell flame retardancy, mechanical strength and ionic conductivity while ensuring porosity and reducing internal resistance. It is a new type of high-performance and high-safety lithium-ion power battery separator.

[0016] Traditional electrospinning processes suffer from uncontrollable jet flow, low yield, and irregular material morphology. In contrast, the triaxial process uses an external auxiliary airflow device to control the speed, and the triaxial process can simultaneously use materials with different properties to obtain membrane materials with superior performance and more stable and regular morphology.

[0017] Furthermore, the solid content of the middle layer solution is 10-25%, the solid content of the core layer solution is 20-45%, and the solid content of the shell layer solution is 1-6%.

[0018] Furthermore, the substrate membrane material is selected from one or more of polyethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyethyleneimine, polyacrylonitrile, and polyimide;

[0019] The solid electrolyte is selected from oxide solid electrolytes and / or sulfide solid electrolytes;

[0020] The adhesive solution contains an adhesive selected from one of the following: polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral.

[0021] The flame retardant is selected from inorganic flame retardants and / or organic flame retardants.

[0022] Furthermore, the oxide solid electrolyte is selected from one or more of LATP, LAGP, LLZTO, LLTO, and LLZO;

[0023] The sulfide solid electrolyte is selected from one or more of LPSBr, LPSCl, LPSI, LGePS, LSnPS, and LSiPS;

[0024] The inorganic flame retardant is selected from chlorinated paraffin and / or ammonium polyphosphate (APP);

[0025] The organic flame retardant is selected from one or more of tetrabromobisphenol A bis(2,3-dibromopropyl) ether (octabromoether), poly(2,6-dibromophenylene ether) PO-64P, FM-935, BTPAE, and triphenyl phosphate (TPP).

[0026] Furthermore, during the triaxial electrospinning process, the voltage is 10-25kV. For example, the voltage can be 10kV, 15kV, 20kV, 25kV, etc.

[0027] The injection rate of the intermediate layer solution is 0.004-0.04 mL / min. Exemplarily, the injection rate of the intermediate layer solution can be 0.004 mL / min, 0.006 mL / min, 0.008 mL / min, 0.01 mL / min, 0.012 mL / min, 0.014 mL / min, 0.016 mL / min, 0.018 mL / min, 0.02 mL / min, 0.022 mL / min, 0.024 mL / min, 0.026 mL / min, 0.028 mL / min, 0.03 mL / min, 0.032 mL / min, 0.03 mL / min, 0.036 mL / min, 0.038 mL / min, 0.04 mL / min, etc. The injection rate of the core layer solution is 0.002-0.03 mL / min. Exemplarily, the injection rate of the core layer solution can be 0.002 mL / min. The injection rates are 0.002-0.01 mL / min, 0.004 mL / min, 0.006 mL / min, 0.008 mL / min, 0.01 mL / min, 0.012 mL / min, 0.014 mL / min, 0.016 mL / min, 0.018 mL / min, 0.02 mL / min, 0.022 mL / min, 0.024 mL / min, 0.026 mL / min, 0.028 mL / min, 0.03 mL / min, etc.; the injection rate of the shell solution is 0.002-0.01 mL / min. For example, the injection rate of the shell solution can be 0.002 mL / min, 0.003 mL / min, 0.004 mL / min, 0.005 mL / min, 0.006 mL / min, 0.007 mL / min, 0.008 mL / min, 0.009 mL / min, 0.01 mL / min, etc. To ensure the stability of the membrane material framework, the injection rate of the middle layer solution should be greater than that of the core layer solution, and the injection rate of the core layer solution should be greater than that of the shell solution.

[0028] Furthermore, the injection rate ratio of the middle layer solution, the core layer solution, and the shell layer solution is 8:4:1.

[0029] Furthermore, the hot pressing temperature is 60-90℃, the hot pressing time is 2-10 min, and the hot pressing pressure is 0.4-0.8 MPa.

[0030] Furthermore, the first organic solvent is selected from one or more of N-methylpyrrolidone, n-butanol, xylene, and tetrachloroethylene;

[0031] The second organic solvent is selected from one or more of tetrahydrofuran, chloroform, acetone, methanol, ethanol, diethyl ether, carbon tetrachloride, acetic acid, etc.

[0032] To achieve the second objective mentioned above, the present invention adopts the following technical solution:

[0033] This invention discloses a sandwich-like fiber diaphragm prepared using the preparation method described above.

[0034] To achieve the third objective mentioned above, the present invention adopts the following technical solution:

[0035] This invention discloses the application of a sandwich-like fiber separator as described above in the preparation of lithium-ion power batteries.

[0036] To achieve the fourth objective mentioned above, the present invention adopts the following technical solution:

[0037] This invention discloses a lithium-ion power battery comprising a sandwich-like fiber separator as described above.

[0038] The beneficial effects of this invention are as follows:

[0039] This invention creatively employs triaxial electrospinning technology to successfully prepare a thinner, higher-performance, and safer lithium-ion power battery separator with better thermal stability, better closed-cell flame retardancy, high ionic conductivity, and low internal resistance. Specifically, nanoscale solid electrolyte materials are used as the main raw material for the core layer solution to improve the separator's conductivity, and flame retardants are introduced as the main raw material for the shell layer solution to enhance the separator's fire resistance. These materials work together with the middle layer solution containing the substrate membrane material. By precisely controlling the ratio of the three materials mentioned above, a sandwich-like fiber separator with superior performance is obtained, solving the problems of thick separators, cumbersome processes, and poor electrochemical performance in traditional coating processes. Detailed Implementation

[0040] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0041] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0042] Example 1

[0043] This invention provides a method for preparing a sandwich-like fiber diaphragm by triaxial electrospinning, the specific steps of which are as follows:

[0044] 1) Weigh 2g of polyvinylidene fluoride powder and dissolve it in N-methylpyrrolidone to obtain a middle layer solution with a solid content of 10%;

[0045] 2) Weigh 5g of solid electrolyte LLTO and mix it evenly with polyvinylidene fluoride liquid to obtain a core layer solution with a solid content of 20%.

[0046] 3) Mix 0.2g of ammonium polyphosphate flame retardant with carbon tetrachloride solution to obtain a shell solution with a solid content of 2%;

[0047] 4) Inject the core layer solution obtained in step 2 into the left needle of the micro-injection pump, inject the middle layer solution obtained in step 1 into the middle needle of the micro-injection pump, and inject the shell layer solution obtained in step 3 into the right needle of the micro-injection pump. The middle needle is connected to the main channel. Adjust the voltage of the device to 20kV, the injection speed of the middle needle to 0.008mL / min, the injection speed of the left needle to 0.004mL / min, and the injection speed of the right needle to 0.001mL / min. Keep the injection speed of the middle needle, the injection speed of the left needle, and the injection speed of the right needle constant and perform triaxial electrospinning for 150min to obtain a fiber membrane.

[0048] 5) The spun fiber membrane was hot-pressed at 65℃ and 80MPa for 5 minutes, and then dried in a vacuum environment at 105℃ to obtain a sandwich-like fiber membrane. The sandwich-like fiber membrane has a thickness of 10.5±1μm, a porosity of 56%, and a liquid absorption and retention rate of 153%.

[0049] Example 2

[0050] This invention provides a method for preparing a sandwich-like fiber diaphragm by triaxial electrospinning, the specific steps of which are as follows:

[0051] 1) Weigh 2g of polyvinylidene fluoride powder and dissolve it in N-methylpyrrolidone to obtain a middle layer solution with a solid content of 10%;

[0052] 2) Weigh 5g of solid electrolyte LLTO and mix it evenly with polyvinylidene fluoride liquid to obtain a core layer solution with a solid content of 30%.

[0053] 3) Mix 0.2g of ammonium polyphosphate flame retardant with carbon tetrachloride solution to obtain a shell solution with a solid content of 2%;

[0054] 4) Inject the core layer solution obtained in step 2 into the left needle of the micro-injection pump, inject the middle layer solution obtained in step 1 into the middle needle of the micro-injection pump, and inject the shell layer solution obtained in step 3 into the right needle of the micro-injection pump. The middle needle is connected to the main channel. Adjust the voltage of the device to 20kV, the injection speed of the middle needle to 0.016mL / min, the injection speed of the left needle to 0.008mL / min, and the injection speed of the right needle to 0.002mL / min. Keep the injection speed of the middle needle, the injection speed of the left needle, and the injection speed of the right needle constant and perform triaxial electrospinning. Spin for 100min to obtain a fiber membrane.

[0055] 5) The spun fiber membrane was hot-pressed at 65℃ and 80MPa for 5 minutes, and then dried in a vacuum environment at 105℃ to obtain a sandwich-like fiber membrane. The sandwich-like fiber membrane has a thickness of 12.5±1μm, a porosity of 54%, and a liquid absorption and retention rate of 150%.

[0056] Example 3

[0057] This invention provides a method for preparing a sandwich-like fiber diaphragm by triaxial electrospinning, the specific steps of which are as follows:

[0058] 1) Weigh 2g of polyvinylidene fluoride powder and dissolve it in N-methylpyrrolidone to obtain a middle layer solution with a solid content of 10%;

[0059] 2) Weigh 5g of solid electrolyte LLTO and mix it evenly with polyvinylidene fluoride liquid to obtain a core layer solution with a solid content of 40%.

[0060] 3) Mix 0.2g of ammonium polyphosphate flame retardant with carbon tetrachloride solution to obtain a shell solution with a solid content of 1%;

[0061] 4) Inject the core layer solution obtained in step 2 into the left needle of the micro-injection pump, inject the middle layer solution obtained in step 1 into the middle needle of the micro-injection pump, and inject the shell layer solution obtained in step 3 into the right needle of the micro-injection pump. The middle needle is connected to the main channel. Adjust the voltage of the device to 20kV, the injection speed of the middle needle to 0.016mL / min, the injection speed of the left needle to 0.008mL / min, and the injection speed of the right needle to 0.002mL / min. Keep the injection speed of the middle needle, the injection speed of the left needle, and the injection speed of the right needle constant and perform triaxial electrospinning for 100min to obtain a fiber membrane.

[0062] 5) The spun fiber membrane was hot-pressed at 65℃ and 80MPa for 5 minutes, and then dried in a vacuum environment at 105℃ to obtain a sandwich-like fiber membrane. The sandwich-like fiber membrane has a thickness of 12.5±1μm, a porosity of 53%, and a liquid absorption and retention rate of 150%.

[0063] Comparative Example 1

[0064] In this example, the performance of a PE film sourced from the market will be compared. The PE film consists of a 9μm base film and two 1.5μm aluminum oxide layers coated on both sides.

[0065] Comparative Example 2

[0066] This example uses the traditional single-axis electrospinning technique to prepare the fiber membrane. The specific steps are as follows:

[0067] 1) Weigh 2g of polyvinylidene fluoride powder and dissolve it in N-methylpyrrolidone to obtain a middle layer solution with a solid content of 10%;

[0068] 2) Weigh 5g of solid electrolyte LLTO and mix it evenly with polyvinylidene fluoride liquid to obtain a core layer solution with a solid content of 40%.

[0069] 3) Mix 0.2g of ammonium polyphosphate flame retardant with carbon tetrachloride solution to obtain a shell solution with a solid content of 1%;

[0070] 4) Mix the above three solutions together and inject them into a micro-injection pump;

[0071] 5) Adjust the voltage of the device to 20kV, the injection speed of the intermediate needle to 0.016mL / min, and spin for 100min to obtain a fiber membrane;

[0072] 6) The spun fiber membrane was hot-pressed at 65℃ and 80MPa for 5 minutes, and then dried in a vacuum environment at 105℃ to obtain a sandwich-like fiber membrane. The sandwich-like fiber membrane has a thickness of 7.5±1μm, a porosity of 75%, and a liquid absorption and retention rate of 135%.

[0073] Comparative Example 3

[0074] This example demonstrates the preparation of a fiber membrane under low voltage and high flow rate conditions. The specific steps are as follows:

[0075] 1) Weigh 2g of polyvinylidene fluoride powder and dissolve it in N-methylpyrrolidone to obtain a middle layer solution with a solid content of 10%;

[0076] 2) Weigh 5g of solid electrolyte LLTO and mix it evenly with polyvinylidene fluoride liquid to obtain a core layer solution with a solid content of 40%.

[0077] 3) Mix 0.2g of ammonium polyphosphate flame retardant with carbon tetrachloride solution to obtain a shell solution with a solid content of 1%;

[0078] 4) Inject the core layer solution obtained in step 2 into the left needle of the micro-injection pump, inject the middle layer solution obtained in step 1 into the middle needle of the micro-injection pump, and inject the shell layer solution obtained in step 3 into the right needle of the micro-injection pump. The middle needle is connected to the main channel. Adjust the voltage of the device to 6kV, the injection speed of the middle needle to 0.08mL / min, the injection speed of the left needle to 0.04mL / min, and the injection speed of the right needle to 0.01mL / min. Keep the injection speed of the middle needle, the injection speed of the left needle, and the injection speed of the right needle constant and perform triaxial electrospinning for 100min to obtain a fiber membrane.

[0079] 5) The spun fiber membrane is hot-pressed at 65℃ and 80MPa for 5 minutes, and then dried in a vacuum environment at 105℃ to obtain a sandwich-like fiber diaphragm. The thickness of the sandwich-like fiber diaphragm is in the range of 10-20μm, the thickness of the diaphragm is not very uniform, the porosity is 41%, and the liquid absorption and retention rate is 110%.

[0080] Comparative Example 4

[0081] This example uses a method of preparing a sandwich-like fiber membrane with high voltage and constant flow rate. The specific steps are as follows:

[0082] 1) Weigh 2g of polyvinylidene fluoride powder and dissolve it in N-methylpyrrolidone to obtain a middle layer solution with a solid content of 10%;

[0083] 2) Weigh 5g of solid electrolyte LLTO and mix it evenly with polyvinylidene fluoride liquid to obtain a core layer solution with a solid content of 30%.

[0084] 3) Mix 0.2g of ammonium polyphosphate flame retardant with carbon tetrachloride solution to obtain a shell solution with a solid content of 2%;

[0085] 4) Inject the core layer solution obtained in step 2 into the left needle of the micro-injection pump, inject the middle layer solution obtained in step 1 into the middle needle of the micro-injection pump, and inject the shell layer solution obtained in step 3 into the right needle of the micro-injection pump. The middle needle is connected to the main channel. Adjust the voltage of the device to 30kV, the injection speed of the middle needle to 0.016mL / min, the injection speed of the left needle to 0.008mL / min, and the injection speed of the right needle to 0.002mL / min. Keep the injection speed of the middle needle, the injection speed of the left needle, and the injection speed of the right needle constant and perform triaxial electrospinning. Spin for 100min to obtain a fiber membrane.

[0086] 5) The spun fiber membrane was hot-pressed at 65℃ and 80MPa for 5 minutes, and then dried in a vacuum environment at 105℃ to obtain a sandwich-like fiber diaphragm. The thickness of the sandwich-like fiber diaphragm was 7.5-10μm. The high-pressure airflow was unstable, resulting in uneven thickness of the sprayed diaphragm. The porosity was 68%, and the liquid absorption and retention rate was 140%.

[0087] Test case

[0088] The membranes of Examples 1-3 and Comparative Examples 1-4 were subjected to relevant performance tests, and the performance results are shown in the table below.

[0089] Membrane impedance was measured using the EIS electrochemical method.

[0090] Cycle life was tested using a single-chip soft-pack on the Blue Electric testing system.

[0091] Heat shrinkage performance: The test was conducted in a high-temperature forced-air drying oven. Specifically, the diaphragm was cut into squares with a side length of 10cm and sandwiched between glass plates. The oven was then placed at a constant temperature of 180℃ for 0.5h, and the shrinkage was measured.

[0092] Ionic conductivity: The ionic conductivity of the membrane was tested by AC impedance method on the Zenniμm electrochemical workstation. Specifically, the membrane was assembled into a "stainless steel sheet / membrane / stainless steel sheet" blocked battery (120μL electrolyte was added to the battery) and the ionic conductivity was tested (frequency range 0.01Hz-1M Hz, amplitude 5mV).

[0093] Capacity retention: Using NCM523 and graphite as the positive and negative electrodes of the pouch battery, and a separator as the decoupler, the positive and negative electrodes are stacked in a Z-shape to assemble a 350mAh pouch battery. The capacity retention was tested after 500 cycles at 1C rate.

[0094] Fire resistance: In a glass container, hold one end of the diaphragm with tweezers and burn it with a portable igniter, timing the ignition time.

[0095] Table 1

[0096]

[0097] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a sandwich-like fiber diaphragm by triaxial electrospinning, characterized in that, Includes the following steps: The substrate film is dissolved in the first organic solvent to obtain the intermediate layer solution; The solid electrolyte is mixed with the binder solution to obtain the core layer solution; The flame retardant is dissolved in a second organic solvent to obtain a shell solution; A fiber membrane was prepared by using a triaxial electrospinning technique with a middle layer solution, a core layer solution, and a shell layer solution. The membrane was then hot-pressed and dried to obtain a sandwich-like fiber membrane. The injection rate of the intermediate layer solution is 0.004-0.04 mL / min, the injection rate of the core layer solution is 0.002-0.03 mL / min, and the injection rate of the shell layer solution is 0.002-0.01 mL / min. The injection rate of the intermediate layer solution is greater than that of the core layer solution, and the injection rate of the core layer solution is greater than that of the shell layer solution.

2. The preparation method according to claim 1, characterized in that, The solid content of the middle layer solution is 10-25%, the solid content of the core layer solution is 20-45%, and the solid content of the shell layer solution is 1-6%.

3. The preparation method according to claim 1, characterized in that, The substrate membrane material is selected from one or more of polyethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyethyleneimine, polyacrylonitrile, and polyimide; The solid electrolyte is selected from oxide solid electrolytes and / or sulfide solid electrolytes; The adhesive solution contains an adhesive selected from one of the following: polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral. The flame retardant is selected from inorganic flame retardants and / or organic flame retardants.

4. The preparation method according to claim 3, characterized in that, The oxide solid electrolyte is selected from one or more of LATP, LAGP, LLZTO, LLTO, and LLZO. The sulfide solid electrolyte is selected from one or more of LPSBr, LPSCl, LPSI, LGePS, LSnPS, and LSiPS; The inorganic flame retardant is selected from chlorinated paraffin and / or ammonium polyphosphate; The organic flame retardant is selected from one or more of tetrabromobisphenol A bis(2,3-dibromopropyl) ether (octabromo ether), poly(2,6-dibromophenylene ether) PO-64P, FM-935, BTPAE, and triphenyl phosphate.

5. The preparation method according to claim 1, characterized in that, During the triaxial electrospinning process, the voltage is 10-30kV.

6. The preparation method according to claim 1, characterized in that, The injection rate ratio of the middle layer solution, core layer solution, and shell layer solution is 8:4:

1.

7. The preparation method according to claim 1, characterized in that, The hot pressing temperature is 60-90℃, the hot pressing time is 2-10 min, and the hot pressing pressure is 0.4-0.8 MPa.

8. The preparation method according to claim 1, characterized in that, The first organic solvent is selected from one or more of N-methylpyrrolidone, n-butanol, xylene, and tetrachloroethylene; The second organic solvent is selected from one or more of tetrahydrofuran, chloroform, acetone, methanol, ethanol, diethyl ether, carbon tetrachloride, and acetic acid.

9. A sandwich-like fiber diaphragm, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the sandwich-like fiber separator as described in claim 9 in the preparation of lithium-ion power batteries.

11. A lithium-ion power battery, characterized in that, Includes the sandwich-like fiber diaphragm as described in claim 9.

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