PVDF / PI-based ultrathin composite electrolyte membrane, preparation method and application thereof

Abstract

The application discloses a PVDF / PI-based ultrathin composite electrolyte membrane and a preparation method and application thereof, and belongs to the field of lithium ion solid-state electrolytes.The PVDF / PI porous membrane is prepared by a non-solvent phase inversion method, a large number of regular holes are formed on the surface of the membrane by combining a hot stamping technology after the membrane is immersed in lithium salt, and a PVDF / inorganic solid-state electrolyte formula slurry is coated, so that the composite electrolyte membrane is obtained.The PVDF / PI composite polymer electrolyte membrane prepared by the application not only greatly improves the mechanical strength of the solid-state electrolyte membrane, but also further destroys the crystallization of PVDF, and improves the ionic conductivity of the solid-state electrolyte.The thickness of the electrolyte membrane is controllable and ultrathin, the preparation process is simple, the cost is relatively low, and the electrolyte membrane has a good application prospect in a full solid-state lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion solid electrolytes, and specifically relates to a PVDF / PI-based ultrathin composite electrolyte membrane, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have attracted much attention due to their high specific energy and long cycle life, and are widely used in portable electronic devices, automobiles, and other fields. However, during use, organic liquid electrolytes in lithium-ion batteries often pose safety issues such as leakage and flammability. Replacing the electrolyte and separator with a solid electrolyte is expected to overcome these safety problems, while also enabling further improvements in energy density when matched with a lithium metal anode.

[0003] Among the various types of solid electrolytes, polymeric electrolytes (PVDF) exhibit high dielectric constant, good thermal stability, and high electrochemical stability. However, their low room-temperature ionic conductivity limits their further applications. Furthermore, the film-forming properties of PVDF combined with lithium salts are poor, making it difficult to form stable films. Polyimide (PI) films possess high mechanical strength and are used as supports in solid electrolytes, providing both mechanical strength and improved ionic conductivity. A study (J. Wan, et al., [J], Nat. Nanotechnol., 2019, 14(7), 705-711) reported the preparation of an array of nanopores in a PI film using track etching. A PI / PEO / LiTFSI composite electrolyte was obtained by spin-coating PEO / LiTFSI solid electrolyte into the pores, achieving an ionic conductivity of 2.3 × 10⁻⁶ at 30 °C. -4 S / cm. However, this method has low pore-forming efficiency for PI membranes, and because the PI membrane itself is non-conductive, its ionic conductivity is not high. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a PVDF / PI-based ultrathin composite electrolyte membrane, its preparation method and application. The PVDF / PI-based ultrathin composite electrolyte membrane not only greatly improves the mechanical properties of solid electrolytes, but also further disrupts the crystallization of PVDF and improves lithium-ion conductivity.

[0005] This invention provides a PVDF / PI-based ultrathin composite electrolyte membrane, which is obtained by first preparing a porous PVDF / PI membrane, adsorbing lithium salt, and then filling it with PVDF / inorganic solid electrolyte components using a hot-pressing pore-forming process.

[0006] Preferably, the weight ratio of PVDF / PI is (90-95):(5-10).

[0007] Preferably, the lithium salt is one or more of lithium perchlorate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonate)imide, and lithium bis(fluorosulfonate)imide.

[0008] Preferably, the inorganic solid electrolyte is one or more of LATP, LLZO, and LLTO.

[0009] Preferably, the weight ratio of PVDF to inorganic solid electrolyte is (10-20):(80-90).

[0010] This invention also provides a method for preparing a PVDF / PI-based ultrathin composite electrolyte membrane, comprising the following steps:

[0011] Step 1: Dissolve PVDF / PI powder in dimethylacetamide to form a homogeneous solution, transfer it to a polytetrafluoroethylene mold to form a film, control the thickness of the film with a scraper, and then quickly transfer it to an ethanol / water solution coagulation bath for 5-30 minutes. Then transfer it to a new ethanol / water solution coagulation bath and leave it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in an 80℃ vacuum oven to obtain a PVDF / PI porous membrane.

[0012] Step 2: Immerse the PVDF / PI porous membrane obtained in Step 1 into an acetone solution containing lithium salt for 10-40 minutes, remove it and let it stand at room temperature until the acetone evaporates to dryness to obtain a PVDF / PI membrane containing lithium salt. After hot pressing, a lithium salt / PVDF / PI membrane with pores on the surface is obtained.

[0013] Step 3: Grind the inorganic solid electrolyte to obtain a micro-nano slurry, mix it with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry, and apply it to the lithium salt / PVDF / PI film with pores on the surface prepared in step 2 by scraping. After drying to remove the solvent, a PVDF / PI-based ultrathin composite electrolyte film is obtained.

[0014] Preferably, in step 1, the weight ratio of ethanol / water solution in the coagulation bath is (60-70):(30-40), the thickness of the film is controlled by the scraper to be 10-32 μm, and the thickness of the obtained PVDF / PI porous film is 8-28 μm.

[0015] Preferably, in step 2, the temperature of the hot embossing is 30-60℃, the pressure is 50-100MPa, the surface pore depth of the lithium salt / PVDF / PI film is 5-15μm, the spacing between adjacent pores is 5-10μm, and the shape is one or more of square, triangle, and circle.

[0016] Preferably, in step 3, the drying method is drying in a forced-air oven at a temperature of 60-80℃ for 24-48 hours.

[0017] The present invention also provides a PVDF / PI-based ultrathin composite electrolyte membrane and a method for preparing a PVDF / PI-based ultrathin composite electrolyte membrane, and their application in all-solid-state lithium-ion batteries.

[0018] The present invention has the following advantages:

[0019] (1) One of the advantages of the method of the present invention is that adding a small amount of PI to form a film with PVDF can significantly enhance the strength of the porous film. At the same time, since PI contains a large number of polar groups, it can interact with the molecular weight of PVDF through hydrogen bonding and other interactions, thereby inhibiting the crystallization of PVDF and improving the ionic conductivity.

[0020] (2) The second advantage of the method of the present invention is that the hot pressing process facilitates the penetration of lithium salt in PVDF / PI porous membrane, and constructs pores on the surface of the membrane. After filling with inorganic solid electrolyte, the inorganic solid electrolyte can be anchored. At the same time, the inorganic solid electrolyte can further improve the ionic conductivity and mechanical strength of the entire membrane. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the composite electrolyte membrane prepared in Example 1 of the present invention;

[0022] Figure 2 The XRD patterns of the composite electrolyte and PVDF powder prepared in Example 1 of this invention are shown below.

[0023] Figure 3 This is the tensile curve of the composite electrolyte prepared in Example 1 / Comparative Example 1 of the present invention;

[0024] Figure 4 This is the impedance spectrum prepared in Example 1 / Comparative Example 1 of the present invention;

[0025] Figure 5 The LSV curves of the composite electrolytes prepared in Example 1 / Comparative Example 1 of this invention are shown.

[0026] Figure 6 The constant current charge-discharge cycle curves of the composite electrolyte prepared in Example 1 / Comparative Example 1 of this invention are shown. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0028] To enable those skilled in the art to better understand the technical solutions of this application, the technical solutions of this application will be described in detail below with reference to specific embodiments. Unless otherwise specified, the experimental conditions in the embodiments are generally conventional or as recommended by the reagent company; the reagents, consumables, etc., used in the following embodiments can be obtained commercially unless otherwise specified.

[0029] Example 1

[0030] (1) Take 90 parts by weight of PVDF and 10 parts by weight of PI powder, dissolve them in dimethylacetamide to form a uniform solution, transfer them to a polytetrafluoroethylene mold to form a film, control the thickness of the film to 32 μm by scraping, and then quickly transfer it to an ethanol / water solution coagulation bath with a weight ratio of 60:40 for 5 min, then transfer it to a new ethanol / water solution coagulation bath and place it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in a vacuum oven at 80℃ to obtain a PVDF / PI porous membrane with a thickness of 28 μm.

[0031] (2) The PVDF / PI porous membrane was immersed in an acetone solution containing lithium hexafluorophosphate for 10 min, then removed and left at room temperature to allow the acetone to evaporate, resulting in a PVDF / PI membrane containing lithium salt. The hot-pressing temperature was set to 30℃ and the pressure to 100MPa. After hot-pressing, the surface pore depth of the lithium salt / PVDF / PI membrane was 5μm, the spacing between adjacent pores was 5μm, and the shape was square. A lithium salt / PVDF / PI membrane with pores on the surface was obtained.

[0032] (3) The inorganic solid electrolyte LATP was obtained by high-energy ball milling to obtain a micro-nano slurry, which was then mixed with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry with a weight ratio of PVDF to inorganic solid electrolyte of 20:80. The slurry was coated onto the porous lithium salt / PVDF / PI membrane by a blade coating method and dried in a forced-air oven at 60°C for 48 hours to obtain a PVDF / PI-based ultrathin composite electrolyte membrane with a thickness of 30 μm.

[0033] Example 2

[0034] (1) Take 95 parts by weight of PVDF and 5 parts by weight of PI powder, dissolve them in dimethylacetamide to form a uniform solution, transfer them to a polytetrafluoroethylene mold to form a film, control the thickness of the film to 10 μm by scraping, and then quickly transfer it to an ethanol / water solution coagulation bath with a weight ratio of 60:40 for 30 min, then transfer it to a new ethanol / water solution coagulation bath and place it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in a vacuum oven at 80℃ to obtain a PVDF / PI porous membrane with a thickness of 8 μm.

[0035] (2) The PVDF / PI porous membrane was immersed in an acetone solution containing lithium perchlorate for 40 min, then removed and left at room temperature to allow the acetone to evaporate, resulting in a PVDF / PI membrane containing lithium salt. The hot-pressing temperature was set to 30℃ and the pressure to 50MPa. After hot pressing, the surface pore depth of the lithium salt / PVDF / PI membrane was 5μm, the spacing between adjacent pores was 5μm, and the shape was circular. A lithium salt / PVDF / PI membrane with pores on the surface was obtained.

[0036] (3) The inorganic solid electrolyte LLZO was obtained by high-energy ball milling to obtain a micro-nano slurry, which was then mixed with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry with a weight ratio of PVDF to inorganic solid electrolyte of 20:80. The slurry was then coated onto the porous lithium salt / PVDF / PI membrane by a blade coating method and dried in a forced-air oven at 80°C for 48 hours to obtain a PVDF / PI-based ultrathin composite electrolyte membrane with a thickness of 10 μm.

[0037] The tensile strength reaches 3.5 MPa at room temperature, the elongation is 300%, the ionic conductivity at 30℃ is 0.35 mS / cm, and the electrochemical window for testing at 45℃ can reach 4.9 V.

[0038] Example 3

[0039] (1) Take 92 parts by weight of PVDF and 8 parts by weight of PI powder, dissolve them in dimethylacetamide to form a uniform solution, transfer them to a polytetrafluoroethylene mold to form a film, control the thickness of the film to 15 μm by scraping, and then quickly transfer it to an ethanol / water solution coagulation bath with a weight ratio of 65:35 for 30 min, then transfer it to a new ethanol / water solution coagulation bath and place it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in a vacuum oven at 80℃ to obtain a PVDF / PI porous membrane with a thickness of 12 μm.

[0040] (2) The PVDF / PI porous membrane was immersed in an acetone solution containing lithium difluorosulfonate imine for 25 min, then removed and left at room temperature to allow the acetone to evaporate, resulting in a PVDF / PI membrane containing lithium salt. The hot-pressing temperature was set to 35℃ and the pressure to 50MPa. After hot-pressing, the surface pore depth of the lithium salt / PVDF / PI membrane was 5μm, the spacing between adjacent pores was 7μm, and the shape was square. A lithium salt / PVDF / PI membrane with pores on the surface was obtained.

[0041] (3) The inorganic solid electrolyte LLTO was obtained by high-energy ball milling to obtain a micro-nano slurry, which was then mixed with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry with a weight ratio of PVDF to inorganic solid electrolyte of 15:85. The slurry was then coated onto the porous lithium salt / PVDF / PI membrane by a blade coating method and dried in a forced-air oven at 80°C for 36 hours to obtain a PVDF / PI-based ultrathin composite electrolyte membrane with a thickness of 15 μm.

[0042] The tensile strength at room temperature reaches 6.5 MPa, the elongation at room temperature is 210%, the ionic conductivity at 30℃ is 1.1 mS / cm, and the electrochemical window for testing at 45℃ can reach 5.35 V.

[0043] Example 4

[0044] (1) Take 90 parts by weight of PVDF and 10 parts by weight of PI powder, dissolve them in dimethylacetamide to form a uniform solution, transfer them to a polytetrafluoroethylene mold to form a film, control the thickness of the film to 15 μm by scraping, and then quickly transfer it to an ethanol / water solution coagulation bath with a weight ratio of 70:30 for 15 min, then transfer it to a new ethanol / water solution coagulation bath and place it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in a vacuum oven at 80℃ to obtain a PVDF / PI porous membrane with a thickness of 13 μm.

[0045] (2) The PVDF / PI porous membrane was immersed in an acetone solution containing lithium difluorosulfonate imine for 10 min, then removed and left at room temperature to allow the acetone to evaporate, resulting in a PVDF / PI membrane containing lithium salt. The hot-pressing temperature was set to 50℃ and the pressure to 60MPa. After hot-pressing, the surface pore depth of the lithium salt / PVDF / PI membrane was 5μm, the spacing between adjacent pores was 5μm, and the shape was triangular. A lithium salt / PVDF / PI membrane with pores on the surface was obtained.

[0046] (3) The inorganic solid electrolyte LATP was obtained by high-energy ball milling to obtain a micro-nano slurry, which was then mixed with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry with a weight ratio of PVDF to inorganic solid electrolyte of 10:90. The slurry was then coated onto the porous lithium salt / PVDF / PI membrane by a blade coating method and dried in a forced-air oven at 80°C for 48 hours to obtain a PVDF / PI-based ultrathin composite electrolyte membrane with a thickness of 17 μm.

[0047] The tensile strength reaches 7.5 MPa at room temperature, the elongation is 220%, the ionic conductivity at 30℃ is 0.75 mS / cm, and the electrochemical window for testing at 45℃ can reach 5.75 V.

[0048] Comparative Example 1

[0049] (1) Take 100 parts by weight of PVDF, dissolve it in dimethylacetamide to form a uniform solution, transfer it to a polytetrafluoroethylene mold to form a film, control the thickness of the film to 32 μm by scraping, and then quickly transfer it to an ethanol / water solution coagulation bath with a weight ratio of 60:40 for 5 min, then transfer it to a new ethanol / water solution coagulation bath and place it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in a vacuum oven at 80℃ to obtain a PVDF porous membrane with a thickness of 28 μm.

[0050] (2) The PVDF porous membrane was immersed in an acetone solution containing lithium hexafluorophosphate for 10 min, then removed and left at room temperature to allow the acetone to evaporate, resulting in a PVDF membrane containing lithium salt. The hot-pressing temperature was set to 30℃ and the pressure to 100MPa. After hot pressing, the surface pore depth of the lithium salt / PVDF membrane was 5μm, the spacing between adjacent pores was 5μm, and the shape was square. A lithium salt / PVDF / PI membrane with pores on the surface was obtained.

[0051] (3) The inorganic solid electrolyte LATP was obtained by high-energy ball milling to obtain a micro-nano slurry, which was then mixed with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry with a weight ratio of PVDF to inorganic solid electrolyte of 20:80. The slurry was coated onto the porous lithium salt / PVDF membrane by a blade coating method and dried in a forced-air oven at 60°C for 48 hours to obtain a PVDF-based ultrathin composite electrolyte membrane with a thickness of 30 μm.

[0052] pass Figure 3 It can be seen that the tensile strength at room temperature is only 0.7 MPa, and the elongation at break is 80%. Figure 4 It can be seen that the ionic conductivity at 30℃ is 0.05 mS / cm. Figure 5 It can be seen that the electrochemical window for testing at 45℃ is only 3.8V. (This is followed by a continuation of the previous sentence, which is incomplete and requires further context.) Figure 6 It can be seen that the voltage polarization is large, and a micro-short circuit appears after about 130 hours. This indicates that without PI in the system, on the one hand, the structure cannot provide sufficient strength, and on the other hand, the crystallinity of PVDF cannot be reduced, resulting in low ionic conductivity.

[0053] Comparative Example 2

[0054] (1) Take 90 parts by weight of PVDF and 10 parts by weight of PI powder, dissolve them in dimethylacetamide to form a uniform solution, transfer them to a polytetrafluoroethylene mold to form a film, control the thickness of the film to 32 μm by scraping, and then quickly transfer it to an ethanol / water solution coagulation bath with a weight ratio of 60:40 for 5 min, then transfer it to a new ethanol / water solution coagulation bath and place it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in a vacuum oven at 80℃ to obtain a PVDF / PI porous membrane with a thickness of 28 μm.

[0055] (2) Immerse the PVDF / PI porous membrane in an acetone solution containing lithium hexafluorophosphate for 10 min, remove it and let it stand at room temperature until the acetone evaporates to dryness, and obtain a PVDF / PI membrane containing lithium salt.

[0056] (3) The inorganic solid electrolyte LATP was obtained by high-energy ball milling to obtain a micro-nano slurry, which was then mixed with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry with a weight ratio of PVDF to inorganic solid electrolyte of 20:80. The slurry was coated onto the above lithium salt / PVDF / PI membrane by a blade coating method and dried in a forced-air oven at 60°C for 48 hours to obtain a PVDF / PI-based ultrathin composite electrolyte membrane with a thickness of 30 μm.

[0057] The tensile strength at room temperature is only 2.5 MPa, the elongation at room temperature is 150%, the ionic conductivity at 30°C is 0.15 mS / cm, and the electrochemical window tested at 45°C is only 4.5 V. This indicates that without the hot-pressing process, the inorganic solid electrolyte cannot be effectively filled into the PVDF / PI substrate, leading to a decline in various properties.

[0058] Comparative Example 3

[0059] (1) Take 90 parts by weight of PVDF and 10 parts by weight of PI powder, dissolve them in dimethylacetamide to form a uniform solution, transfer them to a polytetrafluoroethylene mold to form a film, control the thickness of the film to 32 μm by scraping, and then quickly transfer it to an ethanol / water solution coagulation bath with a weight ratio of 60:40 for 5 min, then transfer it to a new ethanol / water solution coagulation bath and place it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in a vacuum oven at 80℃ to obtain a PVDF / PI porous membrane with a thickness of 28 μm.

[0060] (2) The PVDF / PI porous membrane was immersed in an acetone solution containing lithium hexafluorophosphate for 10 min, then removed and left at room temperature to allow the acetone to evaporate, resulting in a PVDF / PI membrane containing lithium salt. The hot-pressing temperature was set to 30℃ and the pressure to 100MPa. After hot-pressing, the surface pore depth of the lithium salt / PVDF / PI membrane was 5μm, the spacing between adjacent pores was 5μm, and the shape was square. A lithium salt / PVDF / PI membrane with pores on the surface was obtained.

[0061] (3) The PVDF adhesive was applied to the porous lithium salt / PVDF / PI membrane by scraping. The membrane was dried in a forced-air oven at 60°C for 48 hours to obtain a PVDF / PI-based ultrathin composite electrolyte membrane with a thickness of 30 μm.

[0062] The tensile strength at room temperature is only 3.0 MPa, the elongation at room temperature is 190%, the ionic conductivity at 30℃ is 0.15 mS / cm, and the electrochemical window for testing at 45℃ is 4.2 V. This indicates that without the addition of an inorganic solid electrolyte, the crystallinity of PVDF is difficult to reduce, resulting in a low ionic conductivity.

[0063] Experimental Tests and Results

[0064] like Figure 1 As shown, on the left Figure 1 (a) in the figure is a cross-sectional view of the PVDF / PI-based ultrathin composite electrolyte membrane, on the left. Figure 1 (b) is a top view of the PVDF / PI-based ultrathin composite electrolyte membrane.

[0065] like Figure 2 As shown, XRD tests indicate that the crystallinity of PVDF is significantly reduced, indicating that the addition of PI and inorganic solid electrolyte effectively inhibits the crystallization of PVDF.

[0066] like Figure 3 As shown, the mechanical property test results show that the composite solid electrolyte membrane has a tensile strength of 5.5 MPa and an elongation of 250% at room temperature, indicating that the solid electrolyte has good mechanical properties.

[0067] like Figure 4 As shown, the composite electrolyte membrane was cut into 10 μm diameter discs and tested with a coin cell (SS / SSE / SS) composed of two stainless steel sheets. The AC impedance spectrum of the symmetrical steel sheet cell was measured using an electrochemical workstation, with a test frequency range of 0.01-10. 6 The solid electrolyte has an ionic conductivity of 0.16 mS / cm at 30 °C.

[0068] like Figure 5As shown, the composite electrolyte membrane was assembled into a half-cell (SS / SSE / Li) consisting of a steel sheet and a lithium sheet. Linear scan voltammetry was performed using an electrochemical workstation with a voltage range of 2.5–6 V and a scan rate of 1 mV / s at 45 °C. The results show that the composite electrolyte membrane has an electrochemical window of up to 5.4 V, indicating that it effectively prevents interfacial side reactions between the electrolyte and the lithium sheet, achieving a wide and suitable electrochemical window.

[0069] As shown in Figure 6, in the lithium battery cycle stability test, the composite electrolyte membrane was used to prevent the formation of a lithium symmetric cell (Li / SSE / Li). The battery was tested using the Blue Electric test system to ensure stable cycling at 60°C for 400 hours. The results show that the composite solid electrolyte membrane not only improves cycle stability but also inhibits the growth of lithium dendrites.

[0070] The above description of the embodiments is merely a description of preferred embodiments of the present invention and is not intended to limit the concept and scope of protection of the present invention. It should be noted that those skilled in the art can make relevant improvements and modifications to the present invention based on the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A PVDF / PI-based ultrathin composite electrolyte membrane, characterized in that: The PVDF / PI-based ultrathin composite electrolyte membrane includes a lithium salt / PVDF / PI membrane at the bottom layer, and regular pores exist on the surface of the lithium salt / PVDF / PI membrane, which are filled with the PVDF / inorganic solid electrolyte component. The PVDF / PI-based ultrathin composite electrolyte membrane is obtained by first preparing a porous PVDF / PI membrane, adsorbing lithium salt, and then using a mold imprinting pore-forming process to obtain a lithium salt / PVDF / PI porous membrane, which is then filled with PVDF / inorganic solid electrolyte components. The surface pore depth of the lithium salt / PVDF / PI membrane is 5-15 μm, the spacing between adjacent pores is 5-10 μm, and the shape is one or more of square, triangular, and circular. The weight ratio of PVDF / PI is (90-95):(5-10). The weight ratio of PVDF to inorganic solid electrolyte is (10-20):(80-90).

2. The PVDF / PI-based ultrathin composite electrolyte membrane according to claim 1, characterized in that: The lithium salt is one or more of lithium perchlorate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonate)imide, and lithium bis(fluorosulfonate)imide.

3. The PVDF / PI-based ultrathin composite electrolyte membrane according to claim 1, characterized in that: The inorganic solid electrolyte is one or more of LATP, LLZO, and LLTO.

4. A method for preparing a PVDF / PI-based ultrathin composite electrolyte membrane, characterized in that, Includes the following steps: Step 1: Dissolve PVDF / PI powder in dimethylacetamide to form a homogeneous solution, transfer it to a polytetrafluoroethylene mold to form a film, control the thickness of the film with a scraper, and then quickly transfer it to an ethanol / water solution coagulation bath for 5-30 minutes. Then transfer it to a new ethanol / water solution coagulation bath and leave it for 1 day to completely remove the dimethylacetamide. Take it out and dry it thoroughly in an 80℃ vacuum oven to obtain a PVDF / PI porous membrane. Step 2: Immerse the PVDF / PI porous membrane obtained in Step 1 into an acetone solution containing lithium salt for 10-40 minutes, remove it and let it stand at room temperature until the acetone evaporates to dryness to obtain a PVDF / PI membrane containing lithium salt. After hot pressing, a lithium salt / PVDF / PI membrane with regular pores on the surface is obtained. Step 3: Grind the inorganic solid electrolyte to obtain a micro-nano slurry, mix it with PVDF adhesive to obtain an inorganic solid electrolyte / PVDF slurry, and apply it to the lithium salt / PVDF / PI film with regular pores on the surface prepared in step 2 by a scraping method. After drying to remove the solvent, a PVDF / PI-based ultrathin composite electrolyte film is obtained. In step 2, the temperature of the hot embossing is 30-60℃, the pressure is 50-100MPa, the surface pore depth of the lithium salt / PVDF / PI film is 5-15μm, the spacing between adjacent pores is 5-10μm, and the shape is one or more of square, triangle, and circle.

5. The method for preparing a PVDF / PI-based ultrathin composite electrolyte membrane according to claim 4, characterized in that: In step 1, the weight ratio of ethanol / water solution in the coagulation bath is (60-70):(30-40), the thickness of the film is controlled by the scraper to be 10-32μm, and the thickness of the obtained PVDF / PI porous membrane is 8-28μm.

6. The application of any one of the PVDF / PI-based ultrathin composite electrolyte membranes according to claims 1-3 or the preparation method of any one of the PVDF / PI-based ultrathin composite electrolyte membranes according to claims 4 or 5 in all-solid-state lithium-ion batteries.

Images