A method for preparing a self-supporting sulfide electrolyte membrane using a double-layer gradient coating method

Abstract

The application discloses a method for preparing a self-supporting sulfide electrolyte membrane by adopting a double-layer gradient coating method, and the preparation method comprises the following steps: pre-wetting treatment of a skeleton membrane by using an organic solvent, and then fixing the skeleton membrane on a PET base film; sulfide solid electrolyte powders with different particle sizes are respectively mixed with a binder and an organic solvent to prepare homogeneous slurries; the fine powder slurry is applied to the surface of the PET base film and the skeleton membrane, and a dense sulfide fine powder electrolyte layer is formed after solvent volatilization; then, a sulfide coarse powder electrolyte slurry is coated, and a sulfide coarse powder electrolyte layer is formed after the solvent is completely volatilized; and roll pressing and stripping are performed, so that a self-supporting sulfide electrolyte membrane composed of a skeleton membrane and an electrolyte stack is obtained. The application further discloses a self-supporting sulfide electrolyte membrane prepared by adopting the method and a full solid-state battery comprising the sulfide electrolyte membrane. The self-supporting sulfide electrolyte membrane prepared by adopting the method of the application forms a complete three-dimensional ion conduction network with high strength, and the conductivity is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of sulfide electrolyte preparation technology, and more specifically, to a method for preparing a self-supporting sulfide electrolyte membrane using a double-layer gradient coating method. Background Technology

[0002] Traditional coating technology in lithium-ion battery manufacturing typically employs a direct coating method, where active materials are directly coated onto the surface of the negative or positive electrode. While simple and straightforward, this process has several limitations in practical applications. Particularly in multi-layer coating, the repeated solvent immersion and drying processes can easily lead to structural defects such as peeling or cracking of the electrode. Furthermore, traditional coating processes struggle to precisely control the flatness and thickness uniformity of the coating, directly impacting battery performance and safety. To address these issues, the "self-supporting sulfide electrolyte membrane" technology has emerged. The core innovation of this technology lies in pre-processing the sulfide electrolyte material into a mechanically intact and dense film. In subsequent processes, this pre-fabricated electrolyte membrane is stacked and assembled with the positive and negative electrode materials. This process route not only avoids the shortcomings of traditional coating processes but also offers better process compatibility, allowing for more flexible adaptation to existing battery manufacturing workflows. However, this technology still faces numerous challenges in practical applications, the most critical being how to fabricate a self-supporting electrolyte film that simultaneously satisfies high ionic conductivity, a uniform and dense framework structure on both sides, and sufficient mechanical strength. Solving these technical challenges will directly impact the industrialization prospects of this technology. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a method and application for preparing a self-supporting sulfide electrolyte membrane using a double-layer gradient coating method. This method relates to a coating preparation method for a self-supporting electrolyte layer with a skeleton in an all-solid-state battery. The core of this method involves pre-wetting the skeleton membrane, then coating it with fine electrolyte powder. The fine electrolyte powder, with its small particle size, completely penetrates the pores of the skeleton membrane. Finally, coarse electrolyte powder is coated to construct the main conductive structure, thereby providing the primary conductive function and improving conductivity.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] In a first aspect, the present invention provides a method for preparing a self-supporting sulfide electrolyte membrane using a two-layer gradient coating method, comprising the following steps:

[0006] S1. Pre-wet the skeleton film with an organic solvent and then fix it onto the PET base film;

[0007] S2. Sulfide solid electrolyte powders of different particle sizes are mixed with binders and organic solvents to prepare homogeneous slurries, resulting in sulfide electrolyte fine powder slurry and sulfide electrolyte coarse powder slurry.

[0008] S3, Gradient coating and drying, including:

[0009] S31. First coating: The sulfide electrolyte fine powder slurry obtained in step S2 is applied to the surface of the PET base film and skeleton film wetted by solvent in step S1 by slit coating. After the solvent evaporates, a dense sulfide electrolyte fine powder layer is formed.

[0010] S32. Second coating: A sulfide coarse powder electrolyte slurry is coated on the surface of the sulfide fine powder electrolyte layer, dried at high temperature and then dried at low temperature. After the solvent evaporates completely, a sulfide coarse powder electrolyte layer is formed.

[0011] S4. Electrolyte membrane peeling: Align the release film with the composite membrane layer obtained in step S3, and peel it off by rolling to obtain a self-supporting sulfide electrolyte membrane composed of a skeleton membrane and an electrolyte stack.

[0012] As some specific embodiments of the present invention, in step S1, the skeleton membrane comprises a non-woven fabric or a cellulose-based membrane, the thickness of the skeleton membrane is 10-15 μm, and the porosity is 85%-90%;

[0013] And / or, the organic solvent is selected from at least one of toluene, xylene, and dibutyl ether.

[0014] As some specific embodiments of the present invention, in step S1, the pre-wetting treatment includes immersing the skeleton membrane in an organic solvent and placing it in a vacuum oven (Kejing DZF-6050-53L) for vacuum drying at 100±5℃ for 3-4 hours to obtain a skeleton membrane with an organic solvent content of 900-1000ppm.

[0015] As some specific embodiments of the present invention, in step S2, the sulfide solid electrolyte is selected from Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 Li7P2S8X and Li6PS5X (X = Cl, Br, I), and at least one of the following: a sulfide solid electrolyte system composed of Li2S and P2S5.

[0016] And / or, the organic solvent is selected from at least one of toluene, xylene, and dibutyl ether;

[0017] And / or, the adhesive is selected from at least one of polyisobutylene (PIB) and styrene-butadiene rubber (BR).

[0018] As some specific embodiments of the present invention, in step S2, the particle size D50 of the sulfide solid electrolyte used to prepare the sulfide electrolyte fine powder slurry is 2-3 µm; the particle size D50 of the sulfide solid electrolyte used to prepare the sulfide electrolyte coarse powder slurry is 25-30 µm.

[0019] As some specific embodiments of the present invention, in step S2, when preparing the sulfide electrolyte fine powder slurry and the sulfide electrolyte coarse powder slurry, the mass of the organic solvent is 30%-50% of the mass of the sulfide solid electrolyte powder, and the mass of the binder is 1%-5% of the mass of the sulfide solid electrolyte powder; after mixing the sulfide solid electrolyte powder with the organic solvent and the binder, the mixture is dispersed by ball milling or high-speed shearing to form a homogeneous slurry.

[0020] As some specific embodiments of the present invention, in step S31, after coating the sulfide electrolyte fine powder slurry onto the surface of the PET base film and the skeleton film, the total thickness of the composite wet film is controlled at 45-50 μm; by drying at 80±5℃ for 23-24h to allow the solvent to evaporate, the fine powder slurry penetrates through the skeleton film to reach the base film, with a permeability of 80-90%, forming a dense sulfide fine powder electrolyte layer with a thickness of 20±5 μm.

[0021] In some specific embodiments of the present invention, in step S32, after coating the coarse sulfide electrolyte slurry onto the surface of the fine sulfide electrolyte layer, the total thickness of the composite wet film is 30-60 μm; the high-temperature drying temperature is 120±5℃, and the time is 2-3 hours; the low-temperature drying temperature is 70±5℃, and the time is 9-10 hours, forming a coarse sulfide electrolyte layer with a thickness of 20-25 μm after drying. The initial high-temperature treatment allows the solvent to evaporate quickly, preventing electrode delamination or microcracks; the subsequent long-term drying ensures complete solvent evaporation and maintains conductivity.

[0022] As some specific embodiments of the present invention, in step S4, the pressure of the roller pressing is 20-40 MPa, the temperature is 60-80℃, and the peeling rate of the roller pressing peeling is ≥95%. Thus, the self-supporting sulfide film peels off from the base film, ultimately achieving the peeling of a uniformly penetrated, uniformly thick, particle-grade coated self-supporting electrolyte double-layer structure from the substrate.

[0023] In a second aspect, the present invention provides a self-supporting sulfide electrolyte membrane, which is prepared by any of the preparation methods described above, and includes a skeleton membrane, a fine sulfide electrolyte layer, and a coarse sulfide electrolyte layer.

[0024] Thirdly, the present invention provides an all-solid-state battery, including the self-supporting sulfide electrolyte membrane described above, a silicon anode, and an NCM811 cathode; by stacking the self-supporting sulfide electrolyte membrane with the silicon anode and the NCM811 cathode and then cold-pressing it, welding and packaging it into a soft-pack cell, an all-solid-state battery is obtained.

[0025] As some specific embodiments of the present invention, the loading of the NCM811 positive electrode is 20±3 mg / cm³. 2 The pressure for cold pressing is 45-50 MPa.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) Traditional single-coating self-supporting electrolyte membrane slurry has difficulty fully penetrating the skeleton membrane to the substrate side, resulting in an asymmetrical membrane structure and affecting ionic conductivity and membrane surface condition. This invention adopts a two-layer coating strategy of fine-to-coarse coating. After pre-wetting the non-woven fabric / cellulose substrate, the electrolyte fine powder is coated first. Taking advantage of its small particle size and long-term static settling, it fully penetrates the pores of the skeleton membrane. Then, the electrolyte coarse powder is coated to build the main conductive structure, providing the main conductive function and improving conductivity. This solves the problem of poor conductivity of single-coating self-supporting electrolyte membranes due to the difficulty in achieving uniform penetration on both sides and the insufficient conductivity caused by coating only fine powder, forming a complete, high-strength three-dimensional ion conduction network.

[0028] 2) Conventional self-supporting electrolyte membranes suffer from uneven distribution of electrolyte on both sides of the skeleton, which affects mechanical strength. This invention first coats fine powder to ensure complete penetration, and then coats coarse sulfide electrolyte powder to construct the main structure and improve mechanical strength. Compared with only coating fine powder, it improves conductivity, battery performance, main structure and mechanical support. Compared with only coating coarse powder, it improves penetration capacity and membrane integrity.

[0029] 3) This invention pre-wets the framework membrane, then coats it with fine electrolyte powder. Utilizing the small particle size and prolonged settling time, this allows for 80% permeation through the framework membrane pores. Finally, coarse electrolyte powder is coated to construct the main conductive structure, providing the primary conductive function and improving conductivity. This solves the problems of poor permeability and low conductivity in self-supporting electrolyte membranes of all-solid-state batteries, making it suitable for the industrial production of high-energy-density solid-state batteries.

[0030] 4) When preparing the sulfide coarse powder electrolyte layer, the gradient drying process effectively prevents interlayer cracking, and the secondary high-temperature treatment ensures rapid solvent evaporation, prevents electrode delamination or microcracks, and avoids solvent residue.

[0031] 5) The addition of the framework membrane greatly enhances the strength of the electrolyte membrane, which helps resist deformation during cell pressure cycling. It also facilitates large-scale production and cell co-fabrication. The preparation process is simpler and more convenient, making it suitable for large-scale industrial production. Attached Figure Description

[0032] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0033] Figure 1 This is a schematic diagram of the structure of the self-supporting sulfide electrolyte membrane prepared in Example 1;

[0034] Figure 2 This is a schematic diagram of the structure of the self-supporting sulfide electrolyte membrane prepared in Comparative Example 1.

[0035] Figure 3 This is a graph showing the first charge-discharge curve of the battery assembled in Example 2;

[0036] Figure 4 The first charge-discharge curve of the battery assembled from the electrolyte membrane of Comparative Example 4 is shown. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0038] Example 1

[0039] 1. Pretreatment of the stroma membrane:

[0040] A nonwoven fabric with a thickness of 10 μm and a porosity greater than 85% was used as a skeleton membrane. It was immersed in 30 mL of toluene and placed in a vacuum oven (Kejing DZF-6050-53L) at a temperature of 100℃ for 3 hours to obtain a skeleton membrane with an organic solvent content of 1000 ppm. The skeleton membrane was then fixed onto a PET base film.

[0041] 2. Electrolyte slurry preparation:

[0042] (1) Sulfide electrolyte fine powder slurry: Li6PS5Cl powder (D50=3μm) was mixed with toluene solvent (40% of the mass of Li6PS5Cl powder) and PIB binder (3% of the mass of Li6PS5Cl powder) and mixed in a high-speed centrifuge at 1000rpm for 2h to obtain sulfide electrolyte fine powder slurry;

[0043] (2) Sulfide electrolyte coarse powder slurry: Li6PS5Cl powder (D50=30μm) is mixed with toluene solvent (30% of the mass of Li6PS5Cl powder) and BR binder (2% of the mass of Li6PS5Cl powder) and mixed in a high-speed centrifuge at a speed of 1000rpm for 2h to obtain sulfide electrolyte coarse powder slurry.

[0044] 3. Coating and drying:

[0045] (1) First coating: The sulfide electrolyte fine powder slurry is applied to the surface of the solvent-wetted PET substrate and skeleton film by slit coating. The wet film thickness is controlled at 50 μm. It is dried at 80°C for 24 h to form a sulfide fine powder electrolyte layer with a thickness of 20 μm.

[0046] (2) Second coating: A sulfide coarse powder electrolyte slurry is coated on the surface of the sulfide fine powder layer. The wet film thickness is 40 μm. It is dried at 120℃ for 2 h to prevent interlayer cracking, and then dried at 70℃ for 10 h to form a sulfide coarse powder electrolyte layer with a thickness of 20-25 μm.

[0047] 4. Electrolyte membrane peeling:

[0048] The PET release film is aligned with the dried base film / skeleton film / electrolyte stack, and then rolled and peeled at 30 MPa pressure and 60°C to obtain a self-supporting sulfide electrolyte membrane with a gradient structure from bottom to top: "fine powder layer (permeation-formed) - cellulose / fine powder composite layer - coarse powder layer". The total thickness of the membrane is about 40-45 μm, and the electrolyte layers on both sides of the skeleton film are uniform.

[0049] The electrolyte membrane prepared in this embodiment includes a fine sulfide powder electrolyte layer and a coarse sulfide powder electrolyte layer. The fine powder layer (Li6PS5Cl, 20μm thick) serves as a buffer layer on the positive electrode side, which can suppress interfacial side reactions; the coarse powder layer (Li6PS5Cl, 25μm thick) provides a high ion conduction path.

[0050] like Figure 1 The diagram shows the structure of the self-supporting sulfide electrolyte membrane prepared in this embodiment. The solid electrolyte fine powder layer permeates through the skeleton membrane and is distributed on both sides of the skeleton membrane along with the solid electrolyte coarse powder layer, so that the electrolyte layers on both sides of the skeleton membrane are evenly distributed.

[0051] The conductivity of the self-supporting sulfide electrolyte membrane prepared in this embodiment was tested, and the result was 4.2 × 10⁻⁶. -3 S / cm.

[0052] The self-supporting sulfide electrolyte membrane prepared in this embodiment was subjected to mechanical strength testing: no cracks were found in the 180° bending test, indicating that the mechanical strength was improved.

[0053] Example 2

[0054] Assemble the self-supporting sulfide electrolyte membrane obtained in Example 1 into a battery, specifically including:

[0055] The self-supporting sulfide electrolyte membrane prepared in Example 1 was combined with a silicon anode and an NCM811 cathode (loading 20 mg / cm³). 2 The cells are stacked, cold-pressed at 50MPa, welded, and packaged into soft-pack cells to prepare an all-solid-state battery using a double-layer self-supporting electrolyte membrane.

[0056] like Figure 3 The image shows the first charge-discharge curve of the assembled all-solid-state battery, with a charge-discharge voltage of 2.5-4.3V. The assembled battery underwent a cyclic test at 0.5C, and after 10 cycles, it did not short-circuit. The open-circuit voltage of the battery is 0.7V.

[0057] Comparative Example 1

[0058] Compared with Example 1, the only difference is that the skeleton membrane is not pre-wetted. All other steps are carried out in accordance with Example 1, and the subsequent coarse and fine powder coating work is carried out directly on the dry skeleton.

[0059] like Figure 2 The diagram shows the structure of the self-supporting sulfide electrolyte membrane prepared in this comparative example. Because the dry skeleton membrane strongly absorbs the solvent in the electrolyte slurry, the viscosity of the slurry increases instantaneously, which seriously hinders the penetration of the solid electrolyte fine powder slurry. It cannot form a uniform structure with electrolyte on both sides, but instead has a structure of "skeleton membrane + fine powder layer - coarse powder layer" from bottom to top.

[0060] Comparative Example 2

[0061] Compared to Example 1, the fine powder slurry was not coated on the skeleton membrane, and all other steps were performed in accordance with Example 1. The skeleton membrane was pre-wetted first, and the step of coating the fine powder slurry was skipped. Instead, a coarse powder slurry was directly coated, dried, and peeled off to obtain a composite membrane structure of "skeleton-coarse powder layer" with an overall membrane thickness of 40-45 μm.

[0062] Because the coarse powder particles are large and difficult to effectively penetrate the cellulose backbone, the other side of the backbone membrane has almost no electrolyte, forming a "half-membrane." Furthermore, the bonding between the backbone membrane and the coarse powder layer is poor, making it prone to delamination. Ions experience extremely high resistance when traversing the backbone region, resulting in decreased conductivity.

[0063] Comparative Example 3

[0064] Compared to Example 1, instead of coating the skeleton membrane with coarse powder slurry, only fine powder is applied, and the remaining steps are performed in accordance with Example 1. The skeleton membrane is first pre-wetted, and after coating with fine powder slurry and drying, coarse powder slurry is not coated. After peeling, a composite membrane structure of "skeleton-fine powder layer" is directly obtained, and the membrane thickness (skeleton + fine powder layer) is maintained at 40-45 μm.

[0065] The composite membrane in this comparative example has good strength and flexibility, but since the electrolyte membrane is composed entirely of fine powder, its ionic conductivity is significantly lower than that of the membrane in Example 1, which has a main conductive layer constructed from coarse powder, as shown in Table 1.

[0066] Comparative Example 4

[0067] The composite membrane layer without a framework membrane was prepared. Compared with Example 1, the only difference was that it did not contain a framework membrane; all other steps were performed in the same manner as in Example 1. That is, the fine powder and coarse powder slurry from Example 1 were directly used, coated onto a PET substrate by scraping, dried, and then peeled off by a peeling roller to form a "fine powder-coarse powder" electrolyte membrane with a thickness of about 40-45 μm.

[0068] The electrolyte membrane prepared in this comparative example is easily damaged and breaks when bent.

[0069] The electrolyte membrane is assembled into a solid-state battery, such as... Figure 4 The figure shows the first charge-discharge curve of the assembled all-solid-state battery. The open-circuit voltage of the battery assembled in this comparative example is 0.21V, significantly lower than that of Example 1, indicating a high risk of short circuit. Figure 4 It is evident that the sudden drop in voltage to 0 indicates a short circuit.

[0070] Effect Example

[0071] The ionic conductivity of the composite films from Example 1 and the comparative examples was tested, and the results are shown in Table 1 below:

[0072] Table 1. Results of Ion Conductivity Test

[0073]

[0074] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a self-supporting sulfide electrolyte membrane using a double-layer gradient coating method, characterized in that, Includes the following steps: S1. The skeleton film is pre-wetted with an organic solvent and then fixed onto the PET base film. The pre-wetting treatment includes immersing the skeleton film in an organic solvent and vacuum drying it at 100±5℃ for 3-4 hours to obtain a skeleton film with an organic solvent content of 900-1000ppm. S2. Sulfide solid electrolyte powders of different particle sizes are mixed with binders and organic solvents to prepare homogeneous slurries, resulting in sulfide electrolyte fine powder slurry and sulfide electrolyte coarse powder slurry; the particle size D50 of the sulfide solid electrolyte used to prepare the sulfide electrolyte fine powder slurry is 2-3 µm; the particle size D50 of the sulfide solid electrolyte used to prepare the sulfide electrolyte coarse powder slurry is 25-30 µm. S3, Gradient coating and drying, including: S31. First coating: The sulfide electrolyte fine powder slurry obtained in step S2 is applied to the surface of the PET base film and skeleton film wetted by solvent in step S1 by slit coating. After the solvent evaporates, a dense sulfide electrolyte fine powder layer is formed. S32. Second coating: A coarse sulfide electrolyte slurry is coated on the surface of the fine sulfide electrolyte layer, dried at high temperature and then dried at low temperature. After the solvent evaporates completely, a coarse sulfide electrolyte layer is formed. The high temperature drying temperature is 120±5℃ and the time is 2h-3h. The low temperature drying temperature is 70±5℃ and the time is 9-10h. S4. Electrolyte membrane peeling: Align the release film with the composite membrane layer obtained in step S3, and peel it off by rolling to obtain a self-supporting sulfide electrolyte membrane composed of a skeleton membrane and an electrolyte stack.

2. The method according to claim 1, characterized in that, In step S1, the skeleton membrane comprises a nonwoven fabric or a cellulose-based membrane, the thickness of the skeleton membrane is 10-15 μm, and the porosity is 85%-90%. And / or, the organic solvent is selected from at least one of toluene, xylene, and dibutyl ether.

3. The method according to claim 1, characterized in that, In step S2, the sulfide solid electrolyte is selected from Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 Li7P2S8X (X = Cl, Br, I) and Li6PS5X (X = Br, I), and at least one of the following: a sulfide solid electrolyte system composed of Li2S and P2S5. And / or, the organic solvent is selected from at least one of toluene, xylene, and dibutyl ether; And / or, the adhesive is selected from at least one of polyisobutylene and styrene-butadiene rubber.

4. The method according to claim 1, characterized in that, In step S2, when preparing the sulfide electrolyte fine powder slurry and the sulfide electrolyte coarse powder slurry, the mass of the organic solvent is 30%-50% of the mass of the sulfide solid electrolyte powder, and the mass of the binder is 1%-5% of the mass of the sulfide solid electrolyte powder. After mixing the sulfide solid electrolyte powder with the organic solvent and binder, the mixture is dispersed by ball milling or high-speed shearing to form a homogeneous slurry.

5. The method according to claim 1, characterized in that, In step S31, after coating the sulfide electrolyte fine powder slurry onto the surface of the PET base film and the skeleton film, the total thickness of the composite wet film is controlled at 45-50 μm; by drying at 80±5℃ for 23-24 h to allow the solvent to evaporate, the fine powder slurry penetrates through the skeleton film to reach the base film, with a permeability of 80-90%, forming a dense sulfide fine powder electrolyte layer with a thickness of 20±5 μm; And / or, in step S32, after coating the coarse sulfide electrolyte slurry onto the surface of the fine sulfide electrolyte layer, the total thickness of the composite wet film is 30-60 μm; after drying, a coarse sulfide electrolyte layer with a thickness of 20-25 μm is formed.

6. The method according to claim 1, characterized in that, In step S4, the pressure of the roller pressing is 20-40 MPa, the temperature is 60-80℃, and the peeling rate of the roller pressing peeling is ≥95%.

7. A self-supporting sulfide electrolyte membrane, characterized in that, Prepared by the method of any one of claims 1-6, comprising a skeleton membrane, a sulfide fine powder electrolyte layer, and a sulfide coarse powder electrolyte layer.

8. An all-solid-state battery, characterized in that, The battery includes the self-supporting sulfide electrolyte membrane as described in claim 7, a silicon anode, and an NCM811 cathode; by stacking the self-supporting sulfide electrolyte membrane with the silicon anode and the NCM811 cathode and then cold-pressing it, welding and packaging it into a soft-pack cell, a solid-state battery is obtained.

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