A Sulfide Electrolyte Membrane with a Particle Size Gradient Distribution, Its Preparation Method and Application

Abstract

The present invention discloses a sulfide electrolyte membrane with a particle size gradient distribution, its preparation method and application, which relates to the technical field of solid-state batteries. First, a modified binder solution obtained by blending polyurethane and cis-1,4-polybutadiene rubber is prepared. Three slurries with different particle sizes are formulated with sulfide electrolyte, modified binder and organic solvent. According to the order of the average particle size of the sulfide electrolyte in the slurries from large to small, coating is carried out on the substrate in sequence. After each wet film is dried, the next layer is coated, forming a composite wet film with a particle size gradient distribution. Then, it is subjected to vacuum drying and hot roll pressing treatment to finally obtain the target electrolyte membrane. By ingeniously constructing a unique particle size gradient design, large particles form a skeleton and small particles fill the gaps, optimizing the denseness of the film layer and forming a continuous ion transport channel. This multi-layer wet film forming process is simple and highly controllable, can significantly improve the rate performance and cycle life of sulfide all-solid-state batteries, and has great potential for large-scale production and application in the field of high-energy density all-solid-state batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and particularly relates to a sulfide electrolyte membrane with a particle size gradient distribution, a preparation method thereof, and an application thereof. Background Art

[0002] All-solid-state lithium batteries are considered an important development direction for next-generation energy storage devices due to their high safety and high energy density. Among them, sulfide solid electrolytes have become a research hotspot in the field of all-solid-state batteries due to their high ionic conductivity and good interfacial contact performance. However, the wet film-forming process of sulfide electrolytes still faces many challenges in practical applications. First, during the wet film-forming process of sulfide electrolytes, the pores between particles are relatively large, resulting in a low density of the film, which in turn affects the ion transport efficiency and makes it difficult to achieve an ideal level of ionic conductivity. Second, the adhesion of traditional binders to sulfide electrolytes is insufficient, easily leading to cracks or peeling phenomena in the film layer during the film-forming process, further reducing the mechanical and electrochemical properties of the film. In addition, the particle size distribution of sulfide electrolytes has a significant impact on the ionic conductivity after film formation. Electrolyte particles of different particle sizes may lead to non-uniformity of ion transport paths after film formation, thus affecting the overall performance of the battery.

[0003] These problems not only limit the further development of the wet film-forming process of sulfide electrolytes but also have a negative impact on the energy density, cycle life, and safety of all-solid-state batteries. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a sulfide electrolyte membrane with a particle size gradient distribution, a preparation method thereof, and an application thereof.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] <First Aspect>

[0007] The present invention provides a sulfide electrolyte membrane with a particle size gradient distribution, which is a composite membrane composed of three film layers of sulfide electrolytes with different particle sizes. The average particle size of each film layer shows a gradient decreasing or increasing distribution in sequence, forming a three-layer gradient particle size structure.

[0008] As an embodiment, each film layer includes a modified binder.

[0009] As an embodiment, the modified binder is composed of a composite of polyurethane and cis-1,4-polybutadiene rubber.

[0010] As an embodiment, the mass ratio of the polyurethane to the cis-1,4-polybutadiene rubber is 1 : (2.8 - 5.4).

[0011] As an embodiment, each film layer includes a sulfide electrolyte.

[0012] As an embodiment, the mass ratio of the sulfide electrolyte to the modified binder in each film layer is 10:(0.1 - 0.5).

[0013] As an embodiment, the three - layer gradient particle size structure is three gradient layers arranged in sequence: the first gradient layer, the second gradient layer, and the third gradient layer. The particle sizes of the sulfide electrolyte in each gradient layer are respectively: for the first gradient layer, D 10 = 23 - 27 μm, D 90 = 28 - 32 μm, for the second gradient layer, D 10 = 3 - 7 μm, D 90 = 8 - 12 μm, for the third gradient layer, D 10 = 0.4 - 0.6 μm, D 90 = 0.7 - 0.9 μm;

[0014] In some embodiments, the particle sizes of the sulfide electrolyte in each gradient layer are respectively: for the first gradient layer, D 10 = 25 μm, D 90 = 30 μm, for the second gradient layer, D 10 = 5 μm, D 90 = 10 μm, for the third gradient layer, D 10 = 0.5 μm, D 90 = 0.8 μm.

[0015] As an embodiment, the thickness ratio of the first gradient layer, the second gradient layer, and the third gradient layer is 3:(2 - 3):(1 - 2).

[0016] <Second aspect>

[0017] The present invention provides a method for preparing a sulfide electrolyte membrane with a gradient particle size distribution, comprising the following steps:

[0018] S1. Prepare a modified binder solution, wherein the modified binder is a composite of polyurethane and cis - 1,4 - polybutadiene rubber;

[0019] S2. Prepare slurries of sulfide electrolytes with three particle sizes, and the slurries are composed of sulfide electrolytes, modified binders, and organic solvents;

[0020] S3. Coating on the substrate in sequence from the large - particle - size to the small - particle - size according to the average particle size of the sulfide electrolyte in each slurry. After the upper wet film is dried, then coat the lower wet film to obtain a composite wet film with a gradient particle size distribution;

[0021] S4. Vacuum - dry the composite wet film to obtain a dried composite film;

[0022] S5. Perform hot roll pressing on the composite film to obtain a sulfide electrolyte film with a particle size gradient distribution.

[0023] As an embodiment, the solvent in the modified binder solution is toluene.

[0024] As an embodiment, the mass ratio of the modified binder to toluene is 1 - 8 wt.%.

[0025] In some embodiments, the mass ratio of the modified binder to toluene is 5:100.

[0026] As an embodiment, the preparation method of the modified binder is: mixing a polyurethane solution and a cis - 1,4 - polybutadiene rubber solution, and then performing vacuum drying.

[0027] As an embodiment, the mass ratio of the polyurethane solution to the cis - 1,4 - polybutadiene rubber solution is 1:(3 - 6).

[0028] In some embodiments, the mass ratio of the polyurethane solution to the cis - 1,4 - polybutadiene rubber solution is 1:(3 - 5).

[0029] As an embodiment, the polyurethane solution is a homogeneous solution formed by dissolving polyurethane in a tetrahydrofuran solvent.

[0030] As an embodiment, the mass concentration of the polyurethane solution is 5 - 10 wt.%.

[0031] In some embodiments, the mass ratio of polyurethane to tetrahydrofuran is (5 - 6):80.

[0032] As an embodiment, the cis - 1,4 - polybutadiene rubber solution is a homogeneous solution formed by dissolving cis - 1,4 - polybutadiene rubber in a n - heptane solvent.

[0033] As an embodiment, the mass concentration of the cis - 1,4 - polybutadiene rubber solution is 5 - 15 wt.%.

[0034] In some embodiments, the mass ratio of cis - 1,4 - polybutadiene rubber to n - heptane is (6 - 8):100.

[0035] As an embodiment, the mass ratio of polyurethane to cis - 1,4 - polybutadiene rubber is 1:(2.8 - 5.4).

[0036] As an embodiment, the mass ratio of the sulfide electrolyte to the modified binder solution in the slurry is 10:(4.2 - 10).

[0037] In some embodiments, the mass ratio of the sulfide electrolyte, the modified binder, and the organic solvent in the slurry is 10:(4.2 - 10):(8 - 12).

[0038] In some embodiments, the sulfide electrolyte is of the Li6PS5Cl type.

[0039] In some embodiments, the organic solvent in the slurry is toluene.

[0040] As an embodiment, the mixing method of the slurry is ball milling.

[0041] In some embodiments, the grinding balls in the ball milling are zirconia balls, the ball-to-material ratio is 0.8 - 1.2, the rotation speed is 200 - 500 rpm, and the time is 1 - 4 h.

[0042] As an embodiment, the composite wet film is divided into three gradient layers, and the average particle sizes of the sulfide electrolyte in each gradient layer are respectively: the first gradient layer is 25 - 30 μm, the second gradient layer is 5 - 10 μm, and the third gradient layer is 0.5 - 0.8 μm.

[0043] As an embodiment, the thickness ratio of the first gradient layer, the second gradient layer, and the third gradient layer is 3 : (2 - 3) : (1 - 2).

[0044] As an embodiment, the parameters for vacuum drying of the composite wet film are a temperature of 40 - 80 °C, a vacuum degree of 0.03 - 0.08 MPa, and a constant temperature drying time of 12 - 24 h.

[0045] In some embodiments, the parameters for vacuum drying are a temperature of 50 °C, a vacuum degree of 0.05 MPa, and a time of 12 h.

[0046] As an embodiment, the parameters for hot roll pressing are a temperature of 40 - 80 °C, a pressure of 10 - 20 MPa, the roll pressing speed is controlled at 0.5 - 1 m / min, and the roll pressing is performed 3 - 5 times.

[0047] In some embodiments, the parameters for hot roll pressing are a temperature of 50 °C, a pressure of 20 MPa, the roll pressing speed is controlled at 1 m / min, and the roll pressing is performed 3 times.

[0048] <The third aspect>

[0049] The present invention provides an application of a sulfide electrolyte membrane with a particle size gradient distribution in a all-solid-state lithium battery.

[0050] As an embodiment, in the battery, the first gradient layer in the electrolyte membrane is adjacent to the negative electrode system, and the third gradient layer is adjacent to the positive electrode system.

[0051] As an embodiment, the negative electrode in the battery is a silicon-carbon negative electrode system.

[0052] As an embodiment, a ternary cathode system is selected for the positive electrode in the battery.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] Through the design of binder modification and particle size gradient layer-by-layer coating, the present invention significantly improves the density and ionic conductivity of the sulfide electrolyte membrane and reduces the porosity. The modified copolymer binder enhances the compatibility and adhesion with sulfide electrolyte particles, while the gradient layer-by-layer coating process optimizes the particle size distribution of the sulfide electrolyte and reduces the resistance of the ion transport path. This process is suitable for large-scale production and provides reliable technical support for the manufacture of high-performance all-solid-state lithium batteries. Description of the Drawings

[0055] By reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present invention will become more apparent:

[0056] Figure 1 It is a flowchart of the method for forming a multi-layer wet film of sulfide electrolyte based on particle size gradient distribution provided by the present invention. Detailed Embodiments

[0057] The present invention will be described in detail below with reference to the embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0058] The present detailed embodiment provides a method for forming a multi-layer wet film of sulfide electrolyte based on particle size gradient distribution, and the process is as Figure 1 shown, and the following is a specific introduction.

[0059] Example 1

[0060] This embodiment provides a method for forming a multi-layer wet film of sulfide electrolyte based on particle size gradient distribution, including the following steps:

[0061] S1. Prepare a modified binder solution

[0062] S11. Prepare a polyurethane solution and a cis-1,4-polybutadiene rubber solution, wherein,

[0063] The polyurethane solution is 6 g of polyurethane dissolved in 80 g of tetrahydrofuran solvent and stirred at room temperature for 10 h to form a uniform polyurethane solution, and the mass fraction of polyurethane is about 6.97 wt.%.

[0064] The cis-1,4-polybutadiene rubber solution was prepared by dissolving 8 g of cis-1,4-polybutadiene rubber in 100 g of n-heptane solvent and stirring for 24 h at room temperature to form a homogeneous cis-1,4-polybutadiene rubber solution, with the mass fraction of cis-1,4-polybutadiene rubber being approximately 7.41 wt.%.

[0065] S12. Add the polyurethane solution with a mass ratio of 1:5 to the cis-1,4-polybutadiene rubber solution, and at room temperature, stir for 12 h and then perform ultrasonic treatment for 2 h to carry out co-blending and composite modification.

[0066] S13. Subject the mixed solution to vacuum oven drying treatment at a drying temperature of 60 °C, a vacuum degree of 0.05 MPa, and a drying time of 12 h to remove the residual solvent, and finally obtain the modified binder.

[0067] S14. Dissolve 5 g of the modified binder in 100 g of toluene solvent and stir for 24 h at room temperature to form a homogeneous modified binder solution, with the mass fraction of the modified binder being 4.76 wt.%.

[0068] In this example, the stirring involved in step S1 was carried out by magnetic stirring at a rotational speed of 800 rpm.

[0069] S2. Prepare sulfide electrolyte slurries with different particle sizes

[0070] In a glove box filled with argon, add 10 g of sulfide electrolyte Li6PS5Cl to the ball milling tank, then add 10 g of the modified binder solution and 8 g of toluene solvent. After sealing, perform ball milling treatment for 2 h at room temperature. The grinding balls are 28 g of zirconia beads with a diameter of 6 mm, and the ball milling rotational speed is 300 rpm to obtain a uniformly dispersed electrolyte slurry.

[0071] In this example, according to the method of step S2, sulfide electrolytes with three different particle sizes were used to prepare slurries, namely large particle size (D 10 = 25 μm, D 90 = 30 μm), medium particle size (D 10 = 5 μm, D 90 = 10 μm) and small particle size (D 10 = 0.5 μm, D 90 = 0.8 μm). The slurries prepared correspondingly were named large particle size slurry, medium particle size slurry and small particle size slurry.

[0072] S3. Layered wet coating to form a film

[0073] In a glove box filled with argon gas, first coat the large-particle-size slurry on a copper foil substrate with a thickness controlled at 30 μm, and dry it by blowing air for 2 h; then coat the medium-particle-size slurry on it to fill the pores, with a thickness controlled at 20 μm, and dry it by blowing air for 2 h; then continue to coat the small-particle-size slurry on it to fill the pores remaining due to solvent evaporation again, with a thickness controlled at 10 μm, and dry it by blowing air for 2 h. Thus, a wet film with a three-layer particle size gradient distribution from large to small is formed on the surface of the copper foil substrate.

[0074] In this embodiment, the drying by blowing air is carried out in an argon environment.

[0075] S4. Drying treatment

[0076] Use a vacuum oven to dry the wet film. The drying temperature is 50 °C, the vacuum degree is 0.05 MPa, and the constant-temperature drying time is 12 h.

[0077] S5. Hot roll pressing treatment to improve the density of the electrolyte membrane

[0078] Perform hot roll pressing on the dried electrolyte membrane at a pressure of 50 °C and 20 MPa. Control the roll pressing speed at 0.5 - 1 m / min (0.5 m / min in this embodiment), and roll press 3 - 5 times (3 times in this embodiment) to obtain a sulfide electrolyte membrane with a three-layer particle size gradient distribution.

[0079] Example 2

[0080] This embodiment provides a method for forming a multi-layer wet film of a sulfide electrolyte based on particle size gradient distribution, including the following steps:

[0081] S1. Prepare a modified binder solution

[0082] S11. Prepare a polyurethane solution and a cis-butadiene rubber solution. Among them,

[0083] The polyurethane solution is 5 g of polyurethane dissolved in 80 g of tetrahydrofuran solvent, and stirred at a speed of 800 rpm at room temperature for 8 h to form a uniform polyurethane solution. The mass fraction of polyurethane is about 5.88 wt.%;

[0084] The cis-butadiene rubber solution is 6 g of cis-butadiene rubber dissolved in 100 g of n-heptane solvent, and stirred at a speed of 800 rpm at room temperature for 24 h to form a uniform cis-butadiene rubber solution. The mass fraction of cis-butadiene rubber is about 5.67 wt.%;

[0085] S12. Add the polyurethane solution with a mass ratio of 1:3 to the cis-butadiene rubber solution, and stir at a speed of 800 rpm at room temperature for 12 h and then perform ultrasonic treatment for 2 h for blending and modification compounding;

[0086] S13. The mixed solution is dried in a vacuum oven at a drying temperature of 60 °C, a vacuum degree of 0.05 MPa, and a drying time of 12 h to remove the residual solvent, and finally a modified binder is obtained.

[0087] S14. 5 g of the modified binder is dissolved in 100 g of toluene solvent and stirred at room temperature for 24 h to form a uniform modified binder solution, and the mass fraction of the modified binder is 4.76 wt.%.

[0088] S2. Prepare sulfide electrolyte slurries with different particle sizes

[0089] In a glove box filled with argon, 10 g of sulfide electrolyte Li6PS5Cl is added to a ball milling tank, and then 4.2 g of the modified binder solution and 12 g of toluene solvent are added. After sealing, it is ball milled at room temperature for 2 h. The grinding balls are 26 g of zirconia beads with a diameter of 6 mm, and the ball milling speed is 300 rpm to obtain a uniformly dispersed electrolyte slurry.

[0090] In this example, according to the method of step S2, sulfide electrolytes with three different particle sizes are used to prepare slurries, namely large particle size (D 10 = 25 μm, D 90 = 30 μm), medium particle size (D 10 = 5 μm, D 90 = 10 μm) and small particle size (D 10 = 0.5 μm, D 90 = 0.8 μm), and the corresponding prepared slurries are named large particle size slurry, medium particle size slurry and small particle size slurry.

[0091] S3. Layered wet coating to form a film

[0092] In a glove box filled with argon, first the large particle size slurry is coated on a copper foil substrate with a thickness controlled at 25 μm and air-dried for 2 h; then the medium particle size slurry is coated on it to fill the pores with a thickness controlled at 25 μm and air-dried for 2 h; then the small particle size slurry is continuously coated on it to fill the pores remaining due to solvent evaporation again with a thickness controlled at 15 μm and air-dried for 2 h, thus forming a wet film with a three-layer particle size gradient distribution from large to small on the surface of the copper foil substrate.

[0093] S4. Drying treatment

[0094] The wet film is dried using a vacuum oven at a drying temperature of 50 °C, a vacuum degree of 0.05 MPa, and a constant temperature drying time of 12 h.

[0095] S5. Hot roll pressing treatment to improve the density of the electrolyte membrane

[0096] The dried electrolyte membrane is subjected to hot roll pressing at 50 °C and a pressure of 20 MPa. The roll pressing speed is controlled at 0.5 - 1 m / min (0.5 m / min in this embodiment), and the roll pressing is carried out 3 - 5 times (3 times in this embodiment) to obtain a sulfide electrolyte membrane with a three-layer particle size gradient distribution.

[0097] Comparative Example 1

[0098] This embodiment provides a method for preparing a multi-layer wet film of a sulfide electrolyte based on a particle size gradient distribution. The steps are basically the same as those in Example 1, except that

[0099] In step S1, an unmodified binder solution is prepared, that is, only the cis-butadiene rubber solution in step S11 is prepared, and then in step S2, the modified binder solution is replaced with the cis-butadiene rubber solution, with other parameters remaining unchanged.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing a sulfide electrolyte membrane with a uniform particle size distribution. The steps are basically the same as those in Example 1, except that

[0102] In step S2, only sulfide electrolytes with large particle sizes (D 10 = 25 μm, D 90 = 30 μm) are used to prepare the slurry;

[0103] In step S3, the method of layer-by-layer coating is cancelled, and only one-time coating is adopted, with the wet film thickness controlled at 60 μm;

[0104] Then, the drying treatment in step S4 and the hot roll pressing treatment in step S5 are carried out to obtain a sulfide electrolyte membrane with a uniform particle size distribution.

[0105] Comparative Example 3

[0106] This comparative example provides a method for preparing a sulfide electrolyte membrane with a uniform particle size distribution. The steps are basically the same as those in Comparative Example 2, except that

[0107] In step S2, only sulfide electrolytes with medium particle sizes (D 10 = 5 μm, D 90 = 10 μm) are used to prepare the slurry.

[0108] Comparative Example 4

[0109] This comparative example provides a method for preparing a sulfide electrolyte membrane with a uniform particle size distribution. The steps are basically the same as those in Comparative Example 2, except that

[0110] In step S2, only sulfide electrolytes with small particle sizes (D 10 = 0.5 μm, D 90Prepare the slurry with a sulfide electrolyte (D = 0.8 μm).

[0111] Comparative Example 5

[0112] This comparative example provides a method for preparing a sulfide electrolyte membrane with a two-layer particle size gradient distribution. The steps are basically the same as those in Example 1, except that

[0113] In step S2, only sulfide electrolytes with large particle sizes (D = 25 μm, D = 30 μm) and medium particle sizes (D = 5 μm, D = 10 μm) are used to prepare the slurry separately, obtaining a large particle size slurry and a medium particle size slurry; 10 = 25 μm, D 90 = 30 μm) and medium particle sizes (D 10 = 5 μm, D 90 = 10 μm) are used to prepare the slurry separately, obtaining a large particle size slurry and a medium particle size slurry;

[0114] In step S3, first coat a 30-μm thick large particle size slurry on the copper foil substrate, and then coat a 30-μm medium particle size slurry on it to obtain a wet film;

[0115] Then perform the drying treatment in step S4 and the hot roll pressing treatment in step S5 to obtain a sulfide electrolyte membrane with a two-layer particle size gradient distribution.

[0116] Comparative Example 6

[0117] This comparative example provides a method for preparing a sulfide electrolyte membrane with a two-layer particle size gradient distribution. The steps are basically the same as those in Example 1, except that

[0118] In step S2, only sulfide electrolytes with medium particle sizes (D = 5 μm, D = 10 μm) and small particle sizes (D = 0.5 μm, D = 0.8 μm) are used to prepare the slurry separately, obtaining a medium particle size slurry and a small particle size slurry; 10 = 5 μm, D 90 = 10 μm) and small particle sizes (D 10 = 0.5 μm, D 90 = 0.8 μm) are used to prepare the slurry separately, obtaining a medium particle size slurry and a small particle size slurry;

[0119] In step S3, first coat a 30-μm thick medium particle size slurry on the copper foil substrate, and then coat a 30-μm small particle size slurry on it to obtain a wet film;

[0120] Then perform the drying treatment in step S4 and the hot roll pressing treatment in step S5 to obtain a sulfide electrolyte membrane with a two-layer particle size gradient distribution.

[0121] Detection and Analysis

[0122] Cut the electrolyte membranes prepared in each example and comparative example into small round pieces, load them into a pressure battery mold, stamp them under a pressure of 1 ton for 1 minute, and use an electrochemical workstation with the model CHI660E to perform AC impedance testing at room temperature. The test results are shown in Table 1.

[0123] Table 1

[0124]

[0125] As can be seen from Table 1, in Examples 1 and 2, the impedance of the sulfide electrolyte film using the modified binder and coated in three layers with a decreasing particle size gradient from large to small is less than that of other comparative examples, and the ionic conductivity is higher than that of other comparative examples. This is mainly because the copolymerization modification of cis-butadiene rubber with polyurethane endows the binder with both the high adhesion of polyurethane and the flexibility of cis-butadiene rubber, significantly improving the film-forming stability of the sulfide electrolyte. Moreover, the surface of the modified binder has more functional groups, better chemical compatibility with the sulfide electrolyte, reducing interfacial side reactions and lowering the interfacial resistance. And the three-level particle size gradient coating of large particle size (bottom layer), medium particle size (middle layer), and small particle size (upper layer) is adopted. The large particles provide a skeleton support, and the small particles fill the gaps. The hierarchical filling reduces pores, and the gradient particle size design optimizes the film layer density. The gradient structure forms a continuous ion transport channel, which can improve the ionic conductivity, and the ionic conductivity reaches 2.96 mS / cm.

[0126] The method for forming a multi-layer wet film of a sulfide electrolyte based on a particle size gradient distribution according to the present invention, and using a modified binder to form a film, can enhance the chemical compatibility with the sulfide electrolyte, effectively reduce the interfacial impedance, and optimize the lithium ion transport channel, which will improve the rate performance and cycle life of the sulfide all-solid-state battery. The preparation method of the present invention has a simple process, strong controllability, and is suitable for large-scale production, and has broad application prospects in the field of high-energy density all-solid-state batteries.

[0127] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A sulfide electrolyte membrane with a particle size gradient distribution, characterized in that, It includes the following steps: The composite membrane composed of the film layers of the sulfide electrolyte with a three-layer gradient particle size structure is obtained by hot roll pressing. Each film layer includes a modified binder composed of polyurethane and cis-1,4-polybutadiene rubber. The three-layer gradient particle size structure is three gradient layers arranged in sequence: the first gradient layer, the second gradient layer, and the third gradient layer. The particle sizes of the sulfide electrolyte in each gradient layer are respectively: the first gradient layer D 10 = 23~27 μm, D 90 = 28~32 μm, the second gradient layer D 10 = 3~7 μm, D 90 = 8~12 μm, the third gradient layer D 10 = 0.4~0.6 μm, D 90 = 0.7~0.9 μm; The mass ratio of the polyurethane to the cis-1,4-polybutadiene rubber is 1 : (2.8 - 5.4); The mass ratio of the sulfide electrolyte to the modified binder is 10 : (0.1 - 0.5); The thickness ratio of the first gradient layer, the second gradient layer and the third gradient layer is 3 : (2 - 3) : (1 - 2); One side of the first gradient layer in the electrolyte membrane is adjacent to the negative electrode system.

2. The preparation method of the sulfide electrolyte membrane according to claim 1, wherein, It includes the following steps: S1. Prepare a modified binder solution, where the modified binder is a composite of polyurethane and cis-1,4-polybutadiene rubber; S2. Prepare slurries of sulfide electrolytes with three particle sizes respectively. The slurries are composed of sulfide electrolytes, modified binders and organic solvents; S3. Coating on the substrate in order from the large particle size to the small particle size according to the average particle size of the sulfide electrolyte in each slurry. Wait for the upper wet film to dry before coating the lower wet film to obtain a composite wet film with a gradient particle size distribution; S4. Vacuum dry the composite wet film to obtain a dried composite film; S5. Thermally roll-press the composite film to obtain a sulfide electrolyte membrane with a gradient particle size distribution.

3. The preparation method according to claim 2, characterized in that, It also includes at least one of the following technical features: A1. The preparation method of the modified binder is: mixing a polyurethane solution and a cis-1,4-polybutadiene rubber solution, and then performing vacuum drying; B1. The solvent in the modified binder solution is toluene, and the mass ratio of the modified binder to toluene is 1 - 8 wt.%; C1. The mass ratio of the sulfide electrolyte to the modified binder solution in the slurry is 10 : (4.2 - 10).

4. The preparation method according to claim 2, characterized in that, It also includes at least one of the following technical features: A2. The polyurethane solution is a homogeneous solution formed by dissolving polyurethane in a tetrahydrofuran solvent; B2. The cis-1,4-polybutadiene rubber solution is a homogeneous solution formed by dissolving cis-1,4-polybutadiene rubber in a n-heptane solvent.

5. The preparation method according to claim 2, wherein, It also includes at least one of the following technical features: A3. The parameters for vacuum drying the composite wet film are: temperature is 40 - 80 °C, vacuum degree is 0.03 - 0.08 MPa, and the constant temperature drying time is 12 - 24 h; B3. The parameters for thermal roll-pressing are: temperature is 40 - 80 °C, pressure is 10 - 20 MPa, the roll-pressing speed is controlled at 0.5 - 1 m / min, and roll-press 3 - 5 times.

6. The application of the sulfide electrolyte membrane according to claim 1 in a all-solid-state lithium battery.

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