A multilayer composite solid electrolyte membrane and a preparation method and application thereof

Abstract

The application provides a multilayer composite solid electrolyte film and a preparation method and application thereof, and belongs to the technical field of solid-state polymer electrolytes. The multilayer composite solid electrolyte film comprises a support film and composite electrolyte layers which are combined on both sides of the support film; the composite electrolyte layer comprises a polymer matrix, inorganic fillers and multifunctional lithium salt; the multifunctional lithium salt is obtained by compounding LiTFSI, LiDFOB and LiBOB; the mass ratio of LiTFSI, LiDFOB and LiBOB is 4: (1-3): (1-3). The multilayer composite solid electrolyte film of the application can improve ionic conductivity, generate a fluorine-containing boron interface layer to improve the stability of the positive and negative electrode interfaces, and inhibit the negative effects of fluorine elements, thereby effectively improving the high-voltage cycle performance of the solid-state battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid-state polymer electrolyte, in particular to a multilayer composite solid-state electrolyte membrane and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries play a vital role in mobile electronic devices and electric transportation due to their high energy density, long cycle life and no memory effect. The liquid electrolyte used in traditional lithium ion batteries is prone to leakage and flammable, which brings serious safety hazards to the battery. The use of non-flammable solid-state electrolyte to replace traditional liquid electrolyte is expected to fundamentally solve the safety problem of lithium ion batteries. The use of high-voltage cathode (>4.2 V) and high-capacity lithium metal anode (3860 mAh / g) can greatly improve the energy density of lithium batteries. However, the liquid electrolyte with high reactivity is prone to severe side reactions with the interface of high-voltage cathode and lithium metal, resulting in dendrite problems. Solid-state electrolyte is a potential electrolyte material that matches high-voltage cathode and lithium metal, because: (1) the mechanical rigidity of solid-state electrolyte can inhibit the growth of lithium dendrites caused by uneven deposition of lithium metal. (2) The concentration polarization problem caused by low lithium ion transference number in conventional liquid electrolyte can be solved by single-ion conducting solid-state electrolyte. (3) Solid-state electrolyte with electrochemical and thermal stability means a wider electrochemical stability window, which improves the interface of high-voltage cathode and lithium metal electrode, improves the cycle stability and full battery energy density.

[0003] Solid-state electrolyte is the core of solid-state battery. Among all solid-state electrolyte systems, solid-state polymer electrolyte (SPEs) has excellent mechanical flexibility, large interface physical contact area and compatible preparation process with the current lithium battery roll-to-roll process, and is one of the most promising solid-state electrolytes. However, due to the strong interaction between polymer backbone and lithium ions, the slow movement of polymer chain segments results in a room temperature ionic conductivity much lower than the actual requirement. The polymer composite electrolyte reported in the literature is mainly based on PEO, PVDF, PAN and other substrates, and the room temperature ionic conductivity is all below 1×10 -5 ~5×10 -5The polymer electrolyte is difficult to cycle at room temperature with a low ionic conductivity of about 10-4S / cm. In addition, the polymer electrolyte is prone to decomposition when working at high voltage, which limits the stability of the positive electrode interface and the improvement of the energy density of the full battery. The SPEs of the PVDF-based composite polymer electrolyte are promising candidates in the research of the next generation of lithium-based batteries, with strong polarity, high dielectric constant, excellent chemical stability and high affinity with liquid electrolyte, and high ionic conductivity due to high polarity. However, due to the high dielectric constant of PVDF and the strong interaction with DMF solvent, the residual DMF in the composite electrolyte system causes severe side reactions with lithium metal and high-voltage positive electrode during battery cycling, resulting in increased battery polarization and rapid performance degradation of the solid-state battery. Therefore, improving the ionic conductivity of the polymer-based electrolyte and the stability of the high-voltage positive electrode interface is the key to its application. SUMMARY

[0004] In view of the technical problems in the background art, the present application provides a multi-layer composite solid-state electrolyte film and a preparation method and application thereof, aiming to solve the technical problems of low room temperature ionic conductivity and poor high-voltage positive electrode interface stability of the existing PVDF-based solid-state polymer electrolyte.

[0005] In a first aspect, the present application provides a multi-layer composite solid-state electrolyte film, comprising a support film and a composite electrolyte layer composite on both sides of the support film.

[0006] The composite electrolyte layer comprises a polymer matrix, an inorganic filler and a multifunctional lithium salt; the multifunctional lithium salt is obtained by compounding LiTFSI, LiDFOB and LiBOB; the mass ratio of LiTFSI, LiDFOB and LiBOB is 4: (1-3): (1-3).

[0007] Preferably, the support film comprises at least one of polyethylene, polypropylene and polyimide; the polymer matrix comprises at least one of PVDF-HFP and PVDF; and the inorganic filler comprises LATP.

[0008] Preferably, the mass ratio of LiTFSI, LiDFOB and LiBOB is 2:1:1.

[0009] Preferably, the mass ratio of the polymer matrix to the multifunctional lithium salt is 1:3-3:1; and the mass ratio of the inorganic filler to the multifunctional lithium salt is (0.05-0.2):1.

[0010] Preferably, the mass ratio of the polymer matrix to the multifunctional lithium salt is 1:1; and the mass ratio of the inorganic filler to the multifunctional lithium salt is 0.1:1.

[0011] Preferably, the thickness of the multi-layer composite solid-state electrolyte film is 20-200 pm; and the ratio of the thickness of the support film to the thickness of the single-layer composite electrolyte layer is 1:(0.5-2).

[0012] In a second aspect, the present application provides a method for preparing a multilayer composite solid-state electrolyte film, comprising the following steps:

[0013] The polymer matrix, inorganic filler and multifunctional lithium salt are dissolved in an organic solvent, stirred and uniformly mixed to obtain a mixed solution; the mixed solution is coated on both sides of the support film in sequence, and a multilayer composite solid-state electrolyte film is obtained after drying.

[0014] Preferably, the stirring temperature is 50-60℃, and the stirring time is 12-24h; the organic solvent is DMF.

[0015] Preferably, the drying temperature is 50-65℃.

[0016] In a third aspect, the present application provides a solid-state battery comprising a positive electrode, a negative electrode and the multilayer composite solid-state electrolyte film provided in the first aspect.

[0017] The principle of the technical scheme of the present application is that LITSFI and LiBOB, LiDFOB form a complex lithium salt, BOB - and DFOB - anions provide more lithium ion binding sites, have a competitive coordination effect with the polymer backbone, help to weaken the interaction between the polymer and lithium ions, reduce the transition energy barrier of lithium ions, and improve the ionic conductivity; LiDFOB and LiTFSI generate a LiBOFx interface layer on the positive electrode side and a lithium fluoride SEI interface layer on the negative electrode side, respectively, which can effectively inhibit the interface side reaction; further, since LiBOB does not contain fluorine element, it can produce a LiBOx interface on the positive electrode interface, which can effectively inhibit the corrosion of fluorine element to lattice oxygen, and at the same time, inhibit the corrosion of fluorine element to aluminum current collector, improve the interface stability of high-nickel ternary positive electrode or high-voltage positive electrode, and improve the high-voltage cycle performance of solid-state battery.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] (1) The multifunctional lithium salt improves the high lithium ion conductivity, and the solid-state battery can be cycled at room temperature for a long time. In the present application, the DFOB - , BOB - anion clusters of the complex lithium salt composed of LiTFSI, LiDFOB and LiBOB provide new lithium ion binding sites, have a competitive coordination effect with the polymer backbone, weaken the interaction between the polymer and lithium ions, reduce the transition energy barrier of lithium ions, and improve the room temperature ionic conductivity.

[0020] (2) Fluorine-containing boron interfacial layer improves the stability of the positive and negative electrode interface, improves the high voltage resistance, and widens the working voltage window of the full battery. In the lithium salt of the present application, LiDFOB generates in situ SEI rich in LiBOFx, LiF and other components during the cycle process, stabilizes the high-voltage positive electrode interface, inhibits the generation of lithium dendrites, and improves the working voltage window and cycle stability life of the solid-state battery.

[0021] (3) Fluorine-free LiBOB lithium salt inhibits the corrosion of fluorine elements on high-voltage positive electrode lattice oxygen and aluminum current collector. The LiBOB lithium salt in the lithium salt of the present application does not contain fluorine elements, which can further inhibit the corrosion of fluorine elements on the lattice oxygen of high-voltage oxide positive electrode (such as layered high-nickel ternary positive electrode) and the positive electrode Al current collector, further widen the electrochemical stability window of the solid-state electrolyte, and improve the energy density of the solid-state full battery. DETAILED DESCRIPTION

[0022] The embodiments of the technical solutions of the present application will be described in detail below in combination with the schemes. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0023] In the examples, the specific technology or condition not specified is carried out according to the technology or condition described in the literature in the art or according to the product instruction. The reagent or instrument not specified by the manufacturer is a conventional product or commonly used in the art, which can be obtained by market purchase.

[0024] I. Preparation method

[0025] Example 1

[0026] 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium titanium aluminum phosphate), 40 parts of LiTFSI (lithium bis (trifluoromethyl sulfone) imide), 20 parts of LiDFOB (lithium difluoro (oxalato) borate), 20 parts of LiBOB (lithium difluoro (oxalato) borate), and 600 parts of DMF were mixed and placed on a magnetic stirrer for continuous stirring at 60°C for 24 hours to obtain a mixed solution. The mixed solution was transferred to an automatic coating machine, and cast coating was carried out on one side of the support film polyethylene (PE) to form a composite electrolyte layer. The coated film was moved to a vacuum drying oven and dried at 60°C for 48 hours. Subsequently, the mixture was cast coated on the other side of the support film polyethylene (PE) by an automatic coating machine to form a composite electrolyte layer. The coated film was moved to a vacuum drying oven and dried at 60°C for 48 hours. The thickness of the support film polyethylene (PE) was 10 μm, and the thickness of the single-layer composite electrolyte layer was controlled to be 10 μm during coating. Finally, the dried film was cut to obtain a multilayer composite solid-state electrolyte film.

[0027] Example 2

[0028] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 40 parts of LiTFSI (lithium bis-trifluoromethyl sulfonimide), 10 parts of LiDFOB (lithium difluoro oxalate borate), 30 parts of LiBOB (lithium bisoxalate borate), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, perform flow coating on one side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then, pass the mixture through the automatic coater to perform flow coating on the other side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10 μm, the thickness of the single-layer composite electrolyte layer is controlled to be 10 μm during coating, and finally, the dried film is cut to obtain a multi-layer composite solid-state electrolyte film.

[0029] Example 3

[0030] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 40 parts of LiTFSI (lithium bis-trifluoromethyl sulfonimide), 10 parts of LiDFOB (lithium difluoro oxalate borate), 30 parts of LiBOB (lithium bisoxalate borate), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, perform flow coating on one side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then, pass the mixture through the automatic coater to perform flow coating on the other side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10 μm, the thickness of the single-layer composite electrolyte layer is controlled to be 10 μm during coating, and finally, the dried film is cut to obtain a multi-layer composite solid-state electrolyte film.

[0031] Example 4

[0032] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 40 parts of LiTFSI (lithium bis-trifluoromethylsulfonylimide), 20 parts of LiDFOB (lithium difluoro(oxalato)borate), 20 parts of LiBOB (lithium bis(oxalato)borate), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, perform flow coating on one side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then pass the mixture through the automatic coater to perform flow coating on the other side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10 μm, the thickness of the single-layer composite electrolyte layer is controlled to be 5 μm during coating, and finally, the dried film is cut to obtain a multilayer composite solid-state electrolyte film.

[0033] Example 5

[0034] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 40 parts of LiTFSI (lithium bis-trifluoromethylsulfonylimide), 20 parts of LiDFOB (lithium difluoro(oxalato)borate), 20 parts of LiBOB (lithium bis(oxalato)borate), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, perform flow coating on one side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then pass the mixture through the automatic coater to perform flow coating on the other side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10 μm, the thickness of the single-layer composite electrolyte layer is controlled to be 5 μm during coating, and finally, the dried film is cut to obtain a multilayer composite solid-state electrolyte film.

[0035] Comparative Example 1

[0036] The difference between this comparative example and Example 1 is that the lithium salt in this comparative example is only LiTFSI.

[0037] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 80 parts of LiTFSI (lithium bis (trifluoromethyl sulfonyl imide)), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, flow coating on one side of the supporting film polyethylene (PE), form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then flow coating the mixture on the other side of the supporting film polyethylene (PE) through the automatic coater, form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10 μm, the thickness of the single-layer composite electrolyte layer is controlled to be 10 μm during coating, finally, the dried film is cut to obtain a multilayer composite solid-state electrolyte film.

[0038] Comparative Example 2

[0039] The difference between this comparative example and Example 1 is that the lithium salt in this comparative example is only LiDFOB.

[0040] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 80 parts of LiTFSI (lithium bis (trifluoromethyl sulfonyl imide)), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, flow coating on one side of the supporting film polyethylene (PE), form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then flow coating the mixture on the other side of the supporting film polyethylene (PE) through the automatic coater, form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10 μm, the thickness of the single-layer composite electrolyte layer is controlled to be 10 μm during coating, finally, the dried film is cut to obtain a multilayer composite solid-state electrolyte film.

[0041] Comparative Example 3

[0042] The difference between this comparative example and Example 1 is that the lithium salt in this comparative example is only LiBOB.

[0043] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 80 parts of LiBOB (lithium bis(oxalato)borate), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, cast coat on one side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then, cast coat the mixture on the other side of the supporting film polyethylene (PE) by an automatic coater to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10μm, the thickness of the single-layer composite electrolyte layer is controlled to be 10μm during coating, and finally, the dried film is cut to obtain a multilayer composite solid-state electrolyte film.

[0044] Comparative Example 4

[0045] The difference between this comparative example and Example 1 is that the lithium salt in this comparative example is a mixture of LiTFSI and LiDFOB.

[0046] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 80 parts of LiBOB (lithium bis(oxalato)borate), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coater, cast coat on one side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then, cast coat the mixture on the other side of the supporting film polyethylene (PE) by an automatic coater to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10μm, the thickness of the single-layer composite electrolyte layer is controlled to be 10μm during coating, and finally, the dried film is cut to obtain a multilayer composite solid-state electrolyte film.

[0047] Comparative Example 5

[0048] The difference between this comparative example and Example 1 is that the mass ratio of LiTFSI, LiDFOB and LiBOB in the lithium salt of this comparative example is 0.5:1:1.

[0049] Take 80 parts of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), 8 parts of LATP (lithium aluminum titanium phosphate), 16 parts of LiTFSI (lithium bis (trifluoromethyl sulfonyl imide)), 32 parts of LiDFOB (lithium difluoro oxalate borate), 32 parts of LiBOB (lithium bisoxalate borate), 600 parts of DMF, mix, place on a magnetic stirrer, continuously stir at 60°C for 24 hours to obtain a mixed solution, transfer the mixed solution to an automatic coating machine, perform flow coating on one side of the supporting film polyethylene (PE) to form a composite electrolyte layer, move the coated film to a vacuum drying oven, dry at 60°C for 48 hours, then, the mixture is coated on the other side of the supporting film polyethylene (PE) by an automatic coating machine to form a composite electrolyte layer, and the coated film is moved to a vacuum drying oven and dried at 60°C for 48 hours, wherein the thickness of the supporting film polyethylene (PE) is 10 μm, the thickness of the single-layer composite electrolyte layer is controlled to be 10 μm during coating, and finally, the dried film is cut to obtain a multilayer composite solid-state electrolyte film.

[0050] II. Test method

[0051] (1) Multilayer composite solid-state electrolyte film conductivity test

[0052] The multilayer composite solid-state electrolyte films prepared in Examples 1-5 and Comparative Examples 1-5 were assembled into stainless steel | solid-state electrolyte | stainless steel symmetric batteries, and an electrochemical workstation was used for alternating current impedance spectrum test, with alternating current voltage amplitude of 10 mV, frequency of 0.1 Hz-7 MHz. The room temperature ionic conductivity of the multilayer composite solid-state electrolyte film was calculated. The test results are shown in Table 1.

[0053] (2) Multilayer composite solid-state electrolyte film electrochemical window test

[0054] The multilayer composite solid-state electrolyte films prepared in Examples 1-5 and Comparative Examples 1-5 were assembled into stainless steel | solid-state electrolyte | lithium metal batteries, and the electrochemical stability window of the electrolyte was determined by cyclic voltammetry. The test results are shown in Table 1.

[0055] (3) Solid-state battery charge-discharge cycle performance test

[0056] The multilayer composite solid-state electrolyte films prepared in Examples 1-5 and Comparative Examples 1-5 were used to assemble solid-state lithium batteries, with LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), and the negative electrode was lithium metal. The assembled solid-state lithium batteries of Examples 1-5 and Comparative Examples 1-5 were tested for the first coulombic efficiency and the capacity retention rate after 200 cycles, and the test results are shown in Table 2. The specific detection method was as follows: the prepared solid-state lithium metal battery was placed in a constant temperature box at 30°C, and a high-temperature charge-discharge cycle test was performed using a charge-discharge tester. First, a 0.1C / 0.1C capacity test was performed, and then a 0.5C / 0.5C cycle test was performed, with a voltage range of 2.8-4.4V.

[0057] III. Analysis of test results of each example and comparative example

[0058] Table 1: Test results of ionic conductivity and electrochemical window of the multilayer composite solid-state electrolyte film

[0059]

[0060] As can be seen from the results in Table 1, the composite solid-state electrolyte film prepared by the present application has good ionic conductivity at room temperature. The ionic conductivity of the solid-state electrolyte film prepared in Comparative Examples 1-4 is significantly lower than that of Example 1, indicating that the complex lithium salt composed of LiTFSI, LiDFOB and LiBOB can significantly improve the ionic conductivity of the solid-state electrolyte film. This is because the DFOB - , BOB - anion cluster provides a new lithium ion binding site, has a competitive coordination effect with the polymer backbone, weakens the interaction force between the polymer and the lithium ion, reduces the lithium ion transition energy barrier, and improves the room temperature ionic conductivity. The results of Comparative Example 5 show that the ratio of LiTFSI, LiDFOB and LiBOB has a greater effect on the electrolyte film. When LiTFSI is insufficient, the ionic conductivity decreases.

[0061] Table 2: Test results of cycle performance of solid-state batteries

[0062]

[0063] The results of Table 1 and Table 2 show that the composite solid-state electrolyte prepared in the application has excellent cycle performance and a wide electrochemical window when applied to a solid-state battery. Compared with Example 1, the cycle performance and electrochemical window of Comparative Examples 1-4 slightly decrease, because the complex lithium salt generates in-situ SEI rich in LiBOFx, LiF and other components during the cycle process, which can stabilize the high-voltage positive electrode interface, inhibit the generation of lithium dendrites, improve the working voltage window and cycle stability life of the solid-state battery. At the same time, since the LiBOB lithium salt does not contain fluorine elements, it can further inhibit the corrosion of fluorine elements on the lattice oxygen of high-voltage oxide positive electrode (such as layered high-nickel ternary positive electrode) and the positive electrode Al current collector, further widen the electrochemical stability window of the solid-state electrolyte, and improve the energy density of the solid-state battery. The results of Comparative Example 5 show that the ratio of LiTFSI, LiDFOB and LiBOB has a greater effect on the electrolyte film. When LiTFSI is insufficient, the electrochemical window becomes smaller and the cycle performance decays faster.

[0064] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A multilayer composite solid electrolyte membrane, characterized in that, It includes a support membrane and a composite electrolyte layer bonded to both sides of the support membrane; The composite electrolyte layer comprises a polymer matrix, an inorganic filler, and a multifunctional lithium salt; the multifunctional lithium salt is obtained by compounding LiTFSI, LiDFOB and LiBOB; the mass ratio of LiTFSI, LiDFOB and LiBOB is 4:(1~3):(1~3).

2. The multilayer composite solid electrolyte membrane according to claim 1, characterized in that, The supporting membrane comprises at least one of polyethylene, polypropylene, and polyimide; the polymer matrix comprises at least one of PVDF-HFP and PVDF; and the inorganic filler comprises LATP.

3. The multilayer composite solid electrolyte membrane according to claim 1, characterized in that, The mass ratio of LiTFSI, LiDFOB and LiBOB is 2:1:

1.

4. The multilayer composite solid electrolyte membrane according to claim 1, characterized in that, The mass ratio of the polymer matrix to the multifunctional lithium salt is 1:3 to 3:1; the mass ratio of the inorganic filler to the multifunctional lithium salt is (0.05 to 0.2):

1.

5. The multilayer composite solid electrolyte membrane according to claim 4, characterized in that, The mass ratio of the polymer matrix to the multifunctional lithium salt is 1:1; the mass ratio of the inorganic filler to the multifunctional lithium salt is 0.1:

1.

6. The multilayer composite solid electrolyte membrane according to claim 1, characterized in that, The thickness of the multilayer composite solid electrolyte membrane is 20~200μm; the ratio of the thickness of the support membrane to the thickness of the single-layer composite electrolyte layer is 1:(0.5~2).

7. A method for preparing a multilayer composite solid electrolyte membrane as described in any one of claims 1 to 6, characterized in that, Includes the following steps: The polymer matrix, inorganic filler, and multifunctional lithium salt are dissolved in an organic solvent and stirred to obtain a mixed solution. The mixed solution is then coated onto both sides of a support membrane and dried to obtain a multilayer composite solid electrolyte membrane.

8. The method for preparing a multilayer composite solid electrolyte membrane according to claim 7, characterized in that, The stirring temperature is 50~60℃, and the stirring time is 12~24h; the organic solvent includes DMF.

9. The method for preparing a multilayer composite solid electrolyte membrane according to claim 7, characterized in that, The drying temperature is 50~65℃.

10. A solid-state battery, characterized in that, It includes a positive electrode, a negative electrode, and a multilayer composite solid electrolyte membrane as described in any one of claims 1 to 6.

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