An ultrathin self-supporting sulfide solid electrolyte membrane and its preparation method, and a solid-state battery.

Abstract

This invention discloses an ultrathin self-supporting sulfide solid electrolyte membrane and its preparation method, as well as a solid-state battery, relating to the field of sulfide solid electrolyte technology. The ultrathin self-supporting sulfide solid electrolyte membrane is prepared by placing sulfide electrolyte membranes on both sides of a polydopamine-cellulose nanofilm composite support and then pressing them together; wherein the sulfide electrolyte membranes are placed close to the polydopamine-cellulose nanofilm composite support. The support used has ionic conductivity, synergistically conducting ions with the sulfide electrolyte to improve the ionic conductivity of the ultrathin self-supporting sulfide solid electrolyte membrane. This invention overcomes the difficulties of poor flexibility and self-supporting film formation in inorganic solid electrolytes, producing an ultrathin, lightweight, and high mechanical strength electrolyte membrane. It effectively solves the technical problem in solid-state batteries where the brittleness and rigidity of the sulfide-based electrolyte layer hinders the thinning of the solid electrolyte in the preparation process and makes it susceptible to lithium dendrite puncture, thus promising widespread application.

Description

Technical Field

[0001] This invention relates to the field of sulfide solid electrolyte technology, and more specifically, to an ultrathin self-supporting sulfide solid electrolyte membrane, its preparation method, and a solid-state battery. Background Technology

[0002] Solid-state lithium batteries are considered one of the most promising directions in next-generation battery technology due to their superior safety performance and higher energy density. The choice of electrolyte is crucial, and sulfide solid-state electrolytes are considered the most practical due to their excellent ionic conductivity. However, sulfide electrolytes possess a certain degree of rigidity and brittleness, which is detrimental to the formation of electrolyte membranes and the suppression of lithium dendrite penetration.

[0003] Therefore, there is an urgent need to obtain a flexible and self-supporting sulfide electrolyte membrane, which can facilitate the reduction of electrolyte layer thickness and mass in solid-state batteries, improve their energy density, and ensure the safety of solid-state batteries.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an ultrathin self-supporting sulfide solid electrolyte membrane and its preparation method, as well as a solid-state battery, to solve the above-mentioned technical problems.

[0006] This invention is implemented as follows:

[0007] In a first aspect, embodiments of the present invention provide a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane, comprising the following steps:

[0008] Dopamine was mixed with nanocellulose membrane and reacted to prepare a polydopamine-nanocellulose membrane composite support.

[0009] After the sulfide electrolyte is made into a slurry, it is coated onto the surface of the substrate to obtain a sulfide electrolyte membrane.

[0010] A sulfide electrolyte membrane was placed on both sides of a polydopamine-nanocellulose membrane composite support and then pressed to obtain an ultrathin self-supporting sulfide solid electrolyte membrane; wherein the sulfide electrolyte membrane was placed close to the polydopamine-nanocellulose membrane composite support.

[0011] Secondly, embodiments of the present invention provide an ultrathin self-supporting sulfide solid electrolyte membrane, which is prepared using the preparation method described above.

[0012] Thirdly, embodiments of the present invention provide a solid-state battery, comprising an ultrathin self-supporting sulfide solid electrolyte membrane or an ultrathin self-supporting sulfide solid electrolyte membrane prepared by the aforementioned preparation method, a ternary positive electrode, and a lithium indium alloy negative electrode.

[0013] The present invention has the following beneficial effects:

[0014] The ultrathin self-supporting sulfide solid electrolyte membrane and its preparation method provided in this invention, as well as the solid-state battery, employ a support with ion conductivity to synergistically conduct ions with the sulfide electrolyte, thereby improving the ion conductivity of the self-supporting sulfide electrolyte membrane.

[0015] Ultrathin self-supporting sulfide solid electrolyte membranes overcome the difficulties of poor flexibility and self-supporting film formation in inorganic solid electrolytes, thus producing ultrathin, lightweight, and high mechanical strength electrolyte membranes. The ultrathin self-supporting sulfide electrolyte membrane contains a large amount of catechol, which initiates a carbonization process at low temperatures, resulting in a significant flame-retardant effect. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 SEM images of the polydopamine-cellulose nanofilm composite support;

[0018] Figure 2 These are the results of impedance performance tests;

[0019] Figure 3 These are the results of the cyclic performance test. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] In a first aspect, embodiments of the present invention provide a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane, comprising the following steps:

[0022] Dopamine was mixed with nanocellulose membrane and reacted to prepare a polydopamine-nanocellulose membrane composite support.

[0023] After the sulfide electrolyte is made into a slurry, it is coated onto the surface of the substrate to obtain a sulfide electrolyte membrane.

[0024] The sulfide electrolyte membranes were placed on both sides of the polydopamine-nanocellulose membrane composite support and then pressed to obtain an ultrathin self-supporting sulfide solid electrolyte membrane; wherein the sulfide electrolyte membranes were placed close to the polydopamine-nanocellulose membrane composite support.

[0025] The embodiments of the present invention employ a support with ionic conductivity to synergistically conduct ions with the sulfide solid electrolyte, thereby improving the ionic conductivity of the self-supporting sulfide electrolyte membrane.

[0026] The obtained ultrathin self-supporting sulfide solid electrolyte membrane overcomes the difficulties of inorganic solid electrolytes in terms of poor flexibility and difficulty in self-supporting film formation, thus producing an ultrathin, lightweight electrolyte membrane with high mechanical strength.

[0027] It should be noted that if the sulfide electrolyte slurry is directly coated onto the surface of the polydopamine-nanocellulose membrane composite support, the slurry will seep out through the pores of the nanocellulose membrane, and the nanocellulose membrane will not be able to support the electrolyte slurry.

[0028] In an optional embodiment, the nanocellulose membrane is prepared into a nanocellulose membrane dispersion with a mass concentration of 0.3 g / L-2 g / L, and then mixed with dopamine for reaction; during the mixing reaction, dopamine is chemically bonded to the surface of the nanocellulose membrane through oxidative self-polymerization.

[0029] The mixing reaction time is 12h-48h; the nanocellulose membrane is selected from at least one of cellulose acetate membrane, cellulose nitrate membrane, mixed cellulose membrane, bacterial cellulose membrane and methylcellulose membrane.

[0030] And / or, the mass concentration of dopamine in the nanocellulose membrane dispersion is 0.2 g / L-4 g / L.

[0031] If the dopamine content is too high, it will cause PDA agglomeration, which will clog the cellulose pores and form a "barrier" for ion transport between sulfide particles. This will severely hinder the conduction of lithium ions in the electrolyte membrane, resulting in a sharp decrease in bulk ionic conductivity, an increase in battery internal resistance, and an increase in interface impedance. If the dopamine content is too low, the dopamine layer will be too thin, affecting its bonding strength with the sulfide electrolyte. The coating will be prone to powdering and will not be able to produce a synergistic transport effect.

[0032] In an optional embodiment, the process of preparing the polydopamine-cellulose nanofilm composite support also includes adjusting the pH of the system to 8-8.5 using an alkaline buffer reagent.

[0033] The alkaline buffer reagent is selected from any one of the following: tris(hydroxymethyl)aminomethane buffer (Tris alkaline buffer), glycine buffer, borate buffer, and ammonium-ammonium buffer.

[0034] It should be noted that, to ensure a more complete reaction, magnetic stirring was used to assist mixing during the preparation of the polydopamine-cellulose nanofilm composite support. Under weakly alkaline conditions, dopamine formed a dense polydopamine (PDA) coating on the cellulose nanofilm. After the reaction was complete, the membrane was washed multiple times with anhydrous ethanol and dried to obtain the polydopamine-cellulose nanofilm composite support.

[0035] In an optional embodiment, the sulfide electrolyte is selected from Li6PS5Cl, Li6PS5Br, Li6PS5I, and Li 10 SnPS 12 and Li 10 GeP2S 12 At least one of them; sulfide electrolytes are in a solid state, so they can also be written as sulfide solid electrolytes.

[0036] And / or, the particle size D50 in the sulfide electrolyte is 600 nm-15 μm.

[0037] It should be noted that a uniform particle size distribution ensures the density of the coating. Excessive particle size variation leads to uneven coating and increased porosity, which in turn affects ion transport efficiency and battery performance. Smaller sulfide electrolyte particles have a larger specific surface area, making them more prone to filling pores during coating, resulting in an actual film thickness lower than the theoretical value.

[0038] In an optional embodiment, when the sulfide electrolyte is made into a slurry, a polymeric binder is also added, and the mass ratio of the sulfide electrolyte to the polymeric binder is (99.5-90):(0.5-10).

[0039] And / or, the solid content of the sulfide electrolyte slurry is 25%-65%.

[0040] It should be noted that the interfacial contact between the sulfide electrolyte and the electrode material directly affects the battery's cycle stability. The solid content of the sulfide electrolyte slurry directly affects the slurry's viscosity and the uniformity of the coated film. By controlling the solid content, the slurry viscosity can be adjusted, coating defects reduced, thereby lowering interfacial impedance and the risk of volume expansion. Setting a reasonable solid content ensures the compactness of the electrolyte membrane, preventing excessive porosity from leading to decreased ionic conductivity or increased battery internal resistance.

[0041] If the solid content is too low, the electrolyte slurry viscosity will be low, the electrolyte will settle, and the composition between the electrolyte membrane layers will be uneven, resulting in a decrease in the conductivity of the electrolyte membrane and an increase in the internal resistance of the assembled battery.

[0042] If the solid content is too high, the viscosity of the electrolyte slurry will be high, and the electrolyte particles will not disperse properly. This will cause the electrolyte and binder to agglomerate and form colloids, creating ion conduction breakpoints, which will greatly affect the performance of ion conductivity and reduce conductivity.

[0043] In an optional embodiment, the polymeric binder is selected from at least one of SBR, NBR, PIB, HNBR, SEBS, and SEPS.

[0044] Among them, SBR (Styrene-Butadiene Rubber), NBR (Nitrile Rubber), PIB (Polyisobutylene), HNBR (Hydrogenated Nitrile Rubber), SEBS (Styrene-Ethylene-Butadiene-Styrene Elastomer), and SEPS (Styrene-Ethylene-Propylene-Styrene Elastomer).

[0045] It should be noted that polymeric binders, through a synergistic polar-nonpolar strategy, are not only soluble in sulfide electrolyte solvents (such as xylene), but also form chemical bonds with sulfide electrolytes through polar functional groups, significantly enhancing adhesion and reducing the thickness of the electrolyte film. Furthermore, the polymeric binder must be compatible with the sulfide electrolyte solvent to avoid solvent residue leading to a decrease in conductivity. Simultaneously, the polymeric binder itself must possess high chemical stability to prevent decomposition and failure during battery cycling.

[0046] In an optional embodiment, the solvent used to prepare the sulfide electrolyte slurry is selected from at least one of dichloromethane, tetrahydrofuran, toluene, xylene, diethylbenzene, and anisole; the solvent is compatible with the polymer binder to avoid solvent residue.

[0047] And / or, the mixing method for preparing sulfide electrolyte slurry is degassing and stirring.

[0048] It's important to note that degassing and agitation help eliminate tiny air bubbles in the slurry, ensuring battery performance and safety. Specifically, sulfide electrolytes are sensitive to moisture, and tiny air bubbles can cause internal short circuits or thermal runaway. The degassing process reduces the surface tension of air bubbles in a vacuum environment, combined with vigorous agitation to achieve efficient degassing, reducing safety hazards caused by uneven electrolyte penetration or porosity defects. Degassing treatment reduces residual air bubbles in the slurry, preventing pinhole defects after coating, thereby reducing battery internal resistance and increasing energy density. However, the porous structure created by bubble rupture can cause active material to detach, leading to a shortened cycle life.

[0049] In an optional embodiment, after the sulfide electrolyte is made into a slurry, it is coated on the substrate surface with a thickness of 20 μm-100 μm.

[0050] And / or, the substrate is selected from any one of aluminum foil, PET film, stainless steel and copper foil;

[0051] And / or, the thickness of the ultrathin self-supporting sulfide solid electrolyte membrane is 25 μm-40 μm.

[0052] It should be noted that during the preparation of the ultrathin self-supporting sulfide solid electrolyte membrane, the substrate is located on the side away from the polydopamine-nanocellulose membrane composite support. Through pressing, the substrate and the sulfide electrolyte membrane are automatically separated, and then the sulfide electrolyte membrane is transferred to the polydopamine-nanocellulose membrane composite support, thereby preparing the ultrathin self-supporting sulfide solid electrolyte membrane.

[0053] In summary, the method for preparing the ultrathin self-supporting sulfide solid electrolyte membrane provided in this embodiment of the invention includes the following steps:

[0054] (1) Preparation of polydopamine (PDA)-cellulose nanofilm composite support

[0055] Nanocellulose membranes were dispersed in deionized water to prepare a nanocellulose membrane dispersion with a mass concentration of 0.3 g / L-2 g / L. After adding dopamine (the mass concentration of dopamine in the nanocellulose membrane dispersion was 0.2 g / L-4 g / L), the pH of the system was adjusted to 8.0-8.5 using an alkaline buffer solution. Polymerization was carried out at room temperature with magnetic stirring for 12-48 hours, allowing dopamine to form a dense PDA layer on the nanocellulose membrane under weakly alkaline conditions. After the reaction was complete, the membrane was washed three times with anhydrous ethanol and dried to obtain the polydopamine-nanocellulose membrane composite support.

[0056] (2) Preparation of ultrathin self-supporting sulfide solid electrolyte membrane

[0057] A slurry is formed by dispersing sulfide electrolyte and polymer binder in a corresponding solvent and coating it onto a substrate and drying it to form a film. The coating thickness of the slurry on the substrate is 20 μm-100 μm. Sulfide electrolyte membranes are placed on both sides of a polydopamine-nanocellulose membrane composite support and pressed. The solid electrolyte layer is transferred to the polydopamine-nanocellulose membrane composite support by pressing, thereby preparing an ultrathin self-supporting sulfide solid electrolyte membrane.

[0058] The sulfide electrolyte membrane is placed close to the polydopamine-nanocellulose membrane composite support, while the substrate is placed away from the polydopamine-nanocellulose membrane composite support.

[0059] Secondly, embodiments of the present invention provide an ultrathin self-supporting sulfide solid electrolyte membrane, which is prepared using the preparation method described above.

[0060] Thirdly, embodiments of the present invention provide a solid-state battery, comprising an ultrathin self-supporting sulfide solid electrolyte membrane or an ultrathin self-supporting sulfide solid electrolyte membrane prepared by the aforementioned preparation method, a ternary positive electrode, and a lithium indium alloy negative electrode.

[0061] It should be noted that the ternary cathode sheet is produced by isostatic pressing in a glove box. The environmental parameters of the glove box conform to the normal parameters for normal experimental implementation: water content ≤0.01ppm, oxygen content ≤0.01ppm, and temperature 25℃-30℃. The solid-state battery is assembled in an aluminum-plastic film and subjected to 500MPa isostatic pressing; the lithium indium alloy anode can be selected for each cell according to actual needs.

[0062] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0063] Example 1

[0064] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane, comprising the following steps:

[0065] (1) Preparation of polydopamine (PDA)-cellulose nanofilm composite support

[0066] 100 mg of bacterial cellulose membrane was dispersed in 100 mL of deionized water to prepare a bacterial cellulose membrane dispersion with a mass concentration of 1 g / L. After adding 0.02 g of dopamine, the pH of the system was adjusted to 8.5 using Tris alkaline buffer. Polymerization was carried out at room temperature with magnetic stirring for 24 h, allowing dopamine to form a dense PDA layer on the bacterial cellulose membrane under weakly alkaline conditions. After the reaction was complete, the membrane was washed three times with anhydrous ethanol and dried to obtain the polydopamine-cellulose nanofilm composite support.

[0067] (2) Preparation of ultrathin self-supporting sulfide solid electrolyte membrane

[0068] A slurry was prepared by dispersing a sulfide electrolyte (Li6PS5Cl) and a polymeric binder SBR (20g in total, with a mass ratio of 99:1; the particle size D50 of the sulfide electrolyte was 1.5μm) in 50mL of xylene. The slurry was then coated onto an aluminum foil substrate and dried to form a film with a coating thickness of 60μm. Sulfide electrolyte membranes were placed on both sides of a polydopamine-nanocellulose membrane composite support and pressed to transfer the solid electrolyte layer onto the polydopamine-nanocellulose membrane composite support, thereby preparing an ultrathin self-supporting sulfide solid electrolyte membrane with a thickness of 30μm.

[0069] The sulfide electrolyte membrane is placed close to the polydopamine-nanocellulose membrane composite support, while the substrate is placed away from the polydopamine-nanocellulose membrane composite support.

[0070] This embodiment also provides a solid-state battery in which a ternary cathode sheet after isostatic pressing, an ultra-thin self-supporting sulfide solid electrolyte membrane, and indium foil / lithium foil are assembled into a single battery in a glove box, encapsulated in an aluminum-plastic film, and subjected to 500 MPa isostatic pressing for later use.

[0071] Example 2

[0072] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane. The preparation steps are the same as in Example 1, with the only difference being:

[0073] (1) Preparation of polydopamine (PDA)-cellulose nanofilm composite support

[0074] The mass of dopamine is 0.03g.

[0075] Example 3

[0076] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane. The preparation steps are the same as in Example 1, with the only difference being:

[0077] (1) Preparation of polydopamine (PDA)-cellulose nanofilm composite support

[0078] The mass of dopamine is 0.04g.

[0079] Example 4

[0080] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane. The preparation steps are the same as in Example 1, with the only difference being:

[0081] (2) Preparation of ultrathin self-supporting sulfide solid electrolyte membrane

[0082] The solvent is anisole.

[0083] Example 5

[0084] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane. The preparation steps are the same as in Example 1, with the only difference being:

[0085] (2) Preparation of ultrathin self-supporting sulfide solid electrolyte membrane

[0086] The polymer binder is NBR.

[0087] Example 6

[0088] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane. The preparation steps are the same as in Example 1, with the only difference being:

[0089] (2) Preparation of ultrathin self-supporting sulfide solid electrolyte membrane

[0090] The substrate is a PET film.

[0091] Example 7

[0092] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane. The preparation steps are the same as in Example 1, with the only difference being:

[0093] (2) Preparation of ultrathin self-supporting sulfide solid electrolyte membrane

[0094] The mass ratio of sulfide electrolyte (Li6PS5Cl) to polymer binder SBR is 95:5.

[0095] Example 8

[0096] This embodiment provides a method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane. The preparation steps are the same as in Example 1, with the only difference being:

[0097] (2) Preparation of ultrathin self-supporting sulfide solid electrolyte membrane

[0098] The particle size D50 in the sulfide electrolyte is 0.8 μm.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing a sulfide solid electrolyte membrane, the only difference between the preparation steps and those in Example 1 being:

[0101] Missing step (1).

[0102] The specific steps for directly preparing sulfide solid electrolyte membranes are as follows:

[0103] A slurry was formed by dispersing a sulfide electrolyte and a polymer binder (20g in total, with a mass ratio of 99:1; the particle size D50 of the sulfide electrolyte was 1.5μm) in 50mL of xylene and coating it onto an aluminum foil substrate to dry into a film. Sulfide electrolyte membranes were placed on both sides of the bacterial cellulose membrane and pressed. The solid electrolyte layer was transferred to the polydopamine-nanocellulose membrane composite support by pressing, thereby preparing an ultrathin self-supporting sulfide solid electrolyte membrane with a thickness of 30μm.

[0104] The sulfide electrolyte membrane is placed close to the bacterial cellulose membrane, while the substrate is placed away from the bacterial cellulose membrane.

[0105] Comparative Example 2

[0106] This comparative example provides a method for preparing a sulfide solid electrolyte membrane, the only difference between this method and Comparative Example 1 being:

[0107] An ultrathin self-supporting sulfide solid electrolyte membrane with a thickness of 50 μm was prepared.

[0108] Comparative Example 3

[0109] This comparative example provides a method for preparing a sulfide solid electrolyte membrane, the only difference between this method and Comparative Example 1 being:

[0110] An ultrathin self-supporting sulfide solid electrolyte membrane with a thickness of 100 μm was prepared.

[0111] Test Example 1

[0112] This test example demonstrates SEM analysis of the polydopamine (PDA)-cellulose nanofiber membrane composite support prepared in Example 1. Test images are shown below. Figure 1 .

[0113] from Figure 1 It can be seen that polydopamine was successfully prepared on the framework of nanocellulose and formed a dense PDA layer.

[0114] Test Example 2

[0115] This test example demonstrates the impedance performance of solid-state batteries prepared in Examples 1-3 and Comparative Examples 1-3. The relevant test results are shown in [link to relevant test results]. Figure 2 .

[0116] from Figure 2 It can be seen that the solid-state battery prepared by the sulfide composite solid electrolyte membrane provided in this application has good electrochemical performance, high ionic conductivity and low impedance.

[0117] Test Example 3

[0118] This test example demonstrates the cycle performance testing of solid-state batteries prepared in Examples 1-3 and Comparative Examples 1-3. The relevant test results are shown in [link to relevant test results]. Figure 3 .

[0119] from Figure 3 It can be seen that the 30μm ultrathin electrolyte membranes prepared in Examples 1-3 of this invention exhibit better cycle stability when assembled into full cells. In contrast, the cycle performance of Comparative Examples 1-3 is greatly affected by the thickness.

[0120] In summary, the method for preparing an ultrathin self-supporting sulfide solid electrolyte membrane provided by the embodiments of the present invention can reduce the thickness of the solid electrolyte layer, improve the flexibility of the solid electrolyte, and prevent electrolyte brittleness during the preparation process. It effectively solves the technical problem in solid-state batteries where the brittleness and rigidity of the sulfide-based electrolyte layer hinders the thinning of the solid electrolyte in the preparation process and makes it susceptible to lithium dendrite puncture, and is expected to be widely applied.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of preparing an ultrathin self-supporting sulfide solid-state electrolyte film, characterized by, The method comprises the following steps: dopamine is mixed with nanocellulose film to prepare a polydopamine-nanocellulose film composite support; The sulfide electrolyte is made into a slurry and coated on the surface of the substrate to prepare a sulfide electrolyte film. The sulfide electrolyte film is placed on both sides of the polydopamine-nanocellulose film composite support and subjected to pressing treatment, so that the substrate is automatically separated from the sulfide electrolyte film, and the sulfide electrolyte film is transferred to the polydopamine-nanocellulose film composite support to prepare an ultrathin self-supporting sulfide solid electrolyte film; wherein the sulfide electrolyte film is placed close to the polydopamine-nanocellulose film composite support. The thickness of the ultrathin self-supporting sulfide solid electrolyte film is 25 μm-40 μm.

2. The production method according to claim 1, characterized by, The nanocellulose film is made into a nanocellulose film dispersion with a mass concentration of 0.3g / L-2g / L, and then mixed with dopamine. The mixing time is 12h-48h; the nanocellulose film is selected from at least one of cellulose acetate film, cellulose nitrate film, mixed cellulose film, bacterial cellulose film and methyl cellulose film; The mass concentration of dopamine in the nanocellulose film dispersion is 0.2g / L-4g / L.

3. The method of claim 1, wherein, During the preparation of the polydopamine-nanocellulose film composite support, an alkaline buffer reagent is used to adjust the pH of the system to 8.0-8.

5. The alkaline buffer reagent is selected from any one of tris(hydroxymethyl)aminomethane buffer pair, amino acetic acid buffer pair, borate buffer pair and ammonia-ammonium salt buffer pair.

4. The method of claim 1, wherein, The sulfide electrolyte is selected from at least one of Li6PS5CI, Li6PS5Br, Li6PS5I, Li 10 SnPS 12 and Li 10 GeP2S 12 ​ The particle size D50 of the sulfide electrolyte is 600 nm-15 μm.

5. The preparation method according to claim 1, characterized in that, When the sulfide electrolyte is made into a slurry, a high molecular binder is also added, and the mass ratio of the sulfide electrolyte to the high molecular binder is (99.5-90):(0.5-10). The solid content of the sulfide electrolyte slurry is 25%-65%.

6. The preparation method according to claim 5, characterized in that, The high molecular binder is selected from at least one of SBR, NBR, PIB, HNBR, SEBS and SEPS.

7. The preparation method according to claim 5, characterized in that, The solvent used in the preparation of the sulfide electrolyte slurry is selected from at least one of dichloromethane, tetrahydrofuran, toluene, xylene, diethylbenzene and anisole; The mixing mode for preparing the sulfide electrolyte slurry is defoaming stirring.

8. The method of claim 1, wherein, The substrate is selected from any one of aluminum foil, PET film, stainless steel and copper foil.

9. An ultrathin self-supporting sulfide solid-state electrolyte film, characterized in that, The preparation method is prepared according to any one of claims 1-8.

10. A solid-state battery, characterized by, The ultrathin self-supporting sulfide solid electrolyte film prepared by the preparation method according to any one of claims 1-8 or the ultrathin self-supporting sulfide solid electrolyte film according to claim 9, a ternary positive electrode sheet and a lithium-indium alloy negative electrode.

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