Composite sulfide electrolyte membrane, preparation method thereof and all-solid-state battery

Abstract

The invention provides a composite sulfide electrolyte membrane, a preparation method thereof and an all-solid-state battery. The composite sulfide electrolyte membrane comprises a matrix, a sulfide electrolyte bottom membrane and a modified sulfide electrolyte membrane which are sequentially stacked, the modified sulfide electrolyte membrane comprises at least two layers of glass fiber doped sulfide electrolyte membranes, and in the at least two layers of glass fiber doped sulfide electrolyte membranes, the doping amount of glass fibers is gradually reduced in a gradient manner along the direction far away from the sulfide electrolyte base membrane. According to the invention, the sulfide electrolyte bottom membrane is arranged to avoid sedimentation and stacking intersection of bottom glass fibers, the overall interface resistance is reduced while the membrane strength is improved, and the multi-layer membrane with gradient distribution glass fibers can increase the compaction density of the membrane in a gradient manner and reduce the porosity of the membrane in a gradient manner, so that the performance of the membrane is improved. The film strength is improved, the interface resistance is reduced, the growth of lithium dendrites is inhibited, and the battery performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries, and in particular relates to a composite sulfide electrolyte membrane and a preparation method thereof, and an all-solid-state battery. Background Art

[0002] Currently, lithium-ion batteries are widely used in portable electronics and electric vehicles, and people have higher requirements for the energy density and safety performance of lithium-ion batteries. The energy density of traditional liquid lithium-ion batteries is getting closer and closer to its theoretical upper limit, and its organic flammable electrolyte will bring a series of safety issues.

[0003] In order to solve the safety problems caused by liquid electrolytes, people began to pay attention to the development of all-solid-state batteries. All-solid-state batteries are a new generation of power sources composed of solid electrolytes instead of liquid electrolytes. The use of solid electrolytes is expected to further improve the energy of existing lithium-ion batteries. Sulfide electrolytes have relatively high lithium ion conductivity. At room temperature, the ion conductivity can reach 10-3~10-2S / cm, which is close to or even exceeds that of organic electrolytes. At the same time, they have the characteristics of high thermal stability, good safety performance, and wide electrochemical stability window, especially in high-power and high-low temperature solid-state batteries. However, despite the many advantages of sulfide electrolytes, there are still some shortcomings in the actual preparation process. The prepared sulfide electrolyte sheet is small in area, thick, brittle, and poorly flexible, making it difficult to apply in high-capacity soft-pack battery products, and the advantage of its high energy density is difficult to reflect. Moreover, the electrodes of all-solid-state batteries have large interface resistance due to the characteristics of their solid-solid contact interface, which affects the capacity of the battery.

[0004] Glass fiber, as a reinforcement, can significantly enhance the strength of the electrolyte membrane. However, the density of glass fiber is relatively high compared to sulfide. When drying, it will settle and cross-stack. When the settled side of the glass fiber contacts the electrode, the contact area between the electrolyte and the electrode will be reduced, and the ionic conductivity of the overlapping part of the glass fiber will deteriorate, increasing the interfacial resistance, further aggravating the growth of lithium dendrites, increasing the risk of lithium precipitation, increasing the probability of short circuit, and deteriorating battery performance.

[0005] Therefore, how to solve the above-mentioned problems caused by the doping of glass fibers, so as to significantly reduce the overall interface resistance and improve battery performance while improving the strength of the sulfide electrolyte membrane, is a technical difficulty that needs to be studied urgently. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a composite sulfide electrolyte membrane and a preparation method thereof and an all-solid-state battery. The present invention can effectively prevent the side of the glass fiber settling from directly contacting the electrode by arranging a sulfide electrolyte bottom membrane at the bottom of the modified sulfide electrolyte membrane, and can directly reduce the interface resistance between the membrane and the electrode. In addition, at least two layers of glass fiber-doped sulfide electrolyte membranes are used, and the doping amount of glass fiber in each layer decreases gradually along the direction away from the sulfide electrolyte bottom membrane, so that the multilayer membrane with gradient distribution of glass fiber can disperse the glass fiber throughout the membrane, significantly reducing the overall interface resistance while improving the membrane strength. At the same time, because the glass fiber has high hardness and is not easy to be compacted with the electrolyte, the gradient decreasing glass fiber content can gradually increase the compaction density of the membrane, and gradually reduce the porosity of the membrane, while improving the membrane strength and reducing the interface resistance, inhibiting the growth of lithium dendrites, and improving the battery performance.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a composite sulfide electrolyte membrane, the composite sulfide electrolyte membrane comprising a substrate, a sulfide electrolyte base membrane and a modified sulfide electrolyte membrane stacked in sequence;

[0009] The modified sulfide electrolyte membrane comprises at least two layers of glass fiber-doped sulfide electrolyte membranes, and in the at least two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of glass fiber decreases gradually along a direction away from the sulfide electrolyte base membrane.

[0010] The present invention can avoid the sedimentation of bottom glass fibers and the phenomenon of stacking and crossing by arranging a sulfide electrolyte bottom membrane at the bottom of the modified sulfide electrolyte membrane, directly reduce the interface resistance between the electrolyte and the electrode, and adopt at least two layers of sulfide electrolyte membrane doped with glass fibers, and the doping amount of glass fibers in each layer decreases gradually along the direction away from the sulfide electrolyte bottom membrane, so that the multilayer membrane with gradient distributed glass fibers can disperse the glass fibers throughout the entire interior of the membrane, significantly reduce the overall interface resistance while improving the membrane strength, and because the glass fibers have high hardness and are not easy to be compacted with the electrolyte, the gradient decreasing glass fiber content can gradually increase the compaction density of the membrane and gradually reduce the porosity of the membrane, thereby inhibiting the growth of lithium dendrites while improving the membrane strength and reducing the interface resistance, thereby improving the battery performance.

[0011] In the present invention, the doping amount of glass fiber decreases gradually along the direction away from the sulfide electrolyte base membrane. The gradient decrease can be achieved by changing the proportion of glass fiber in the sulfide electrolyte membrane slurry; or by adjusting the thickness of the sulfide electrolyte membrane. For example, the sulfide electrolyte membrane is 1-N (N≥2) layers, which are respectively recorded as the first modified layer, the second modified layer and the Nth modified layer along the direction away from the sulfide electrolyte base membrane; or the thickness of the sulfide electrolyte membrane and the proportion of glass fiber in the slurry required to prepare each layer can be changed simultaneously to achieve the gradient decrease.

[0012] If the proportion of glass fiber in the sulfide electrolyte membrane slurry is gradually decreased, the thickness of each layer of the sulfide electrolyte membrane can be consistent or inconsistent, and the number of layers is designed to be n. Then, referring to the glass fiber proportion X of the glass fiber-doped sulfide electrolyte membrane slurry, n material systems with different gradients of glass fiber proportions are designed, X1 represents the glass fiber proportion of the first modified layer, X2 represents the glass fiber proportion of the second modified layer, ..., Xn represents the glass fiber proportion of the nth layer, and at the same time, X1>X2>…>Xn, and X1+X2+…+Xn=X, (n is a natural number greater than or equal to 2); then, these modified layers are coated on the sulfide electrolyte base membrane in order from large to small according to the glass fiber proportion, to form a multi-layer glass fiber-doped sulfide electrolyte membrane, so that the glass fiber content gradient decreases in the direction away from the sulfide electrolyte base membrane.

[0013] If the thickness of the sulfide electrolyte membrane is gradually reduced, the proportion of glass fiber in the sulfide electrolyte membrane slurry required for preparing each layer is consistent or inconsistent, and the number of layers n is designed, and then n sulfide electrolyte membranes of different thicknesses are designed with reference to the thickness X of the glass fiber-doped sulfide electrolyte membrane system, X1 represents the thickness of the first modified layer, X2 represents the thickness of the first modified layer, ..., Xn represents the thickness of the nth layer, and at the same time, X1>X2>...>Xn, and X1+X2+...+Xn=X, (n is a natural number greater than or equal to 2); then these sulfide electrolyte membranes are coated on the sulfide electrolyte base membrane in order from large to small according to thickness, to form a multi-layer glass fiber-doped sulfide electrolyte membrane, so that the content of glass fiber decreases in the direction away from the sulfide electrolyte base membrane.

[0014] Preferably, the modified sulfide electrolyte membrane has a thickness of 20-100 μm, for example, 20 μm, 40 μm, 60 μm, 80 μm or 100 μm.

[0015] Preferably, the modified sulfide electrolyte membrane comprises two layers of glass fiber-doped sulfide electrolyte membranes, which are respectively marked as a first modified layer and a second modified layer along a direction away from the sulfide electrolyte base membrane, and a thickness ratio of the first modified layer to the second modified layer is (1-4):1, for example, it can be 1:1, 2:1, 3:1 or 4:1, etc.

[0016] Preferably, in the glass fiber doped sulfide electrolyte membrane, the mass ratio of glass fiber to sulfide electrolyte is (3-30):(70-97), wherein the selection range of glass fiber "3-30" can be, for example, 3, 5, 7, 10, 15, 20, 25 or 30, and the selection range of sulfide electrolyte "70-97" can be, for example, 70, 75, 80, 85, 90, 95 or 97, etc.

[0017] Preferably, the diameter of the glass fiber is 5-12 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm.

[0018] Preferably, the length of the glass fiber is 90-300 μm, for example, 90 μm, 100 μm, 150 μm, 200 μm, 250 μm or 300 μm.

[0019] Preferably, the thickness of the substrate is 10-100 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0020] Preferably, the substrate includes any one of a PET (polyethylene terephthalate) film, an aluminum foil or a stainless steel foil.

[0021] Preferably, the thickness of the sulfide electrolyte base film is 10-100 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0022] Preferably, the sulfide electrolyte bottom film includes Li6PS5Cl bottom film, Li 10 SnPS 12 Base film, Li6PS5Br base film or Li 10 GeP2S 12 Any one or a combination of at least two of the base films.

[0023] Preferably, in the glass fiber-doped sulfide electrolyte membrane, the sulfide electrolyte comprises Li6PS5Cl, Li 10 SnPS 12, Li6PS5Br or Li 10 GeP2S 12 Any one or a combination of at least two of the following.

[0024] In a second aspect, the present invention provides a method for preparing the composite sulfide electrolyte membrane as described in the first aspect, the preparation method comprising the following steps:

[0025] (1) coating a sulfide electrolyte base film slurry without glass fiber on the surface of a substrate to form a sulfide electrolyte base film;

[0026] (2) preparing at least two layers of glass fiber-doped sulfide electrolyte membranes by sequentially stacking them on the sulfide electrolyte base membrane to obtain the composite sulfide electrolyte membrane;

[0027] Wherein, in the at least two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of the glass fibers decreases gradually along the direction away from the base membrane.

[0028] The preparation method provided by the invention has simple process and good development potential.

[0029] Preferably, the sulfide electrolyte base film slurry in step (1) comprises a sulfide electrolyte, a binder and a solvent.

[0030] Preferably, the solvent includes any one of n-heptane, toluene, p-xylene, anisole or isobutyl isobutyrate, or a combination of at least two thereof.

[0031] Preferably, the binder includes any one of PVDF-based binders, polyisobutylene, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, ethyl cellulose or rubber-based binders, or a combination of at least two thereof.

[0032] Preferably, the mass ratio of the sulfide electrolyte to the binder is (92-98):(2-8), wherein the selection range of the sulfide electrolyte "92-98" can be, for example, 92, 93, 94, 95, 96, 97 or 98, and the selection range of the binder "2-8" can be, for example, 2, 3, 4, 5, 6, 7 or 8.

[0033] Preferably, the solid content of the sulfide electrolyte base membrane slurry in step (1) is 30-60wt%, for example, it can be 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt% or 60wt%.

[0034] Preferably, the preparation steps of each layer of the glass fiber-doped sulfide electrolyte membrane include:

[0035] (a) mixing glass fiber, sulfide solid electrolyte, solvent and binder to obtain glass fiber-doped sulfide electrolyte slurry;

[0036] (b) coating the glass fiber-doped sulfide electrolyte slurry on the surface of a sample, and then drying the slurry to form a film, thereby obtaining a glass fiber-doped sulfide electrolyte membrane.

[0037] Preferably, the solid content of the glass fiber-doped sulfide electrolyte slurry in step (a) is 30-60wt%, for example, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt% or 60wt%.

[0038] Preferably, the drying film forming temperature in step (b) is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C, and the drying film forming time is 3-5h, for example, 3h, 3.5h, 4h, 4.5h, 5h, etc.

[0039] Preferably, the preparation method comprises the following steps:

[0040] (1) degassing, stirring and mixing a sulfide electrolyte, a solvent and a binder to prepare a sulfide electrolyte base film slurry with a solid content of 30-60 wt %; wherein the mass ratio of the sulfide electrolyte to the binder is (92-98):(2-8);

[0041] (2) applying the sulfide electrolyte base film slurry on the surface of the substrate by a doctor blade method, drying it, and then sequentially stacking at least two layers of glass fiber-doped sulfide electrolyte membranes on the dried sulfide electrolyte base film to obtain a composite sulfide electrolyte membrane;

[0042] Among them, in the at least two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of glass fiber decreases gradually along the direction away from the sulfide electrolyte bottom membrane, and the preparation steps of each layer of glass fiber-doped sulfide electrolyte membrane include:

[0043] (a) degassing and stirring glass fiber, sulfide electrolyte, solvent and binder to obtain a glass fiber-doped sulfide electrolyte slurry with a solid content of 30-60wt%; wherein the mass ratio of glass fiber to sulfide electrolyte is (3-30):(70-97);

[0044] (b) coating the glass fiber-doped sulfide electrolyte slurry on the surface of the sample, and then drying it at 70-90° C. for 3-5 hours to form a film, thereby obtaining a glass fiber-doped sulfide electrolyte membrane.

[0045] In a third aspect, the present invention provides an all-solid-state battery, comprising the composite sulfide electrolyte membrane as described in the first aspect.

[0046] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention provides a sulfide electrolyte bottom membrane at the bottom of the modified sulfide electrolyte membrane, which can effectively prevent the side of the glass fiber that has settled from directly contacting the electrode, and can directly reduce the interface resistance between the electrolyte and the electrode. In addition, by using at least two layers of sulfide electrolyte membrane doped with glass fibers, and the doping amount of glass fibers in each layer gradually decreases in the direction away from the sulfide electrolyte bottom membrane, the glass fibers can be dispersed throughout the entire interior of the membrane, thereby significantly reducing the overall interface resistance while improving the membrane strength, preventing the composite sulfide electrolyte membrane from being pressed through and short-circuited by the positive electrode during the assembly of the soft-pack battery, and effectively improving the battery performance.

[0049] (2) The preparation method provided by the present invention has a simple process and has good development potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of the structure of the composite sulfide electrolyte membrane provided in Example 1 of the present invention.

[0051] Figure 2 This is a SEM image of the modified sulfide electrolyte membrane provided in Comparative Example 3 of the present invention.

[0052] Among them, 1-matrix; 2-sulfide electrolyte bottom membrane; 3-modified sulfide electrolyte membrane; 31-first modified layer; 32-second modified layer; 4-glass fiber. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0054] Example 1

[0055] This embodiment provides a composite sulfide electrolyte membrane, and its structural schematic diagram is as follows: Figure 1 As shown, the composite sulfide electrolyte membrane comprises a substrate 1, a sulfide electrolyte bottom membrane 2 and a modified sulfide electrolyte membrane 3 which are stacked in sequence;

[0056] The modified sulfide electrolyte membrane 3 includes two layers of sulfide electrolyte membrane doped with glass fibers 4, and in the two layers of sulfide electrolyte membrane doped with glass fibers 4, the doping amount of the glass fibers 4 decreases gradually along the direction away from the sulfide electrolyte bottom membrane 2, which are respectively recorded as a first modified layer 31 and a second modified layer 32;

[0057] The material of the substrate 1 is PET with a thickness of 60 μm, and the sulfide electrolyte bottom film 2 is a Li6PS5Cl bottom film with a thickness of 40 μm;

[0058] The thickness of the modified sulfide electrolyte membrane 3 is 50 μm, the thickness ratio of the first modified layer 31 and the second modified layer 32 is 1.25:1, the mass ratio of the glass fiber 4 and the sulfide electrolyte in the first modified layer 31 is 9:91, the mass ratio of the glass fiber 4 and the sulfide electrolyte in the second modified layer 32 is 5:95, and the mass ratio of the glass fiber 4 in the first modified layer 31 and the glass fiber 4 in the second modified layer 32 is 2.25:1; the diameter of the glass fiber 4 is 9 μm and the length is 90 μm, and the sulfide electrolyte is Li6PS5Cl.

[0059] This embodiment also provides a method for preparing the composite sulfide electrolyte membrane, the preparation method comprising the following steps:

[0060] (1) degassing, stirring and mixing a sulfide electrolyte, a solvent and a binder to prepare a sulfide electrolyte base film slurry with a solid content of 45%; wherein the mass ratio of the sulfide electrolyte to the binder is 97:3, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li6PS5Cl;

[0061] (2) placing the substrate 1 on a coating table, adjusting the coating thickness of the scraper to 120 μm and then starting the scraping, scraping the sulfide electrolyte base membrane slurry onto the surface of the substrate, and naturally drying for 30 minutes, and then sequentially stacking two layers of sulfide electrolyte membrane doped with glass fiber 4 on the dried sulfide electrolyte base membrane 2, including a first modified layer 31 and a second modified layer 32, to obtain a composite sulfide electrolyte membrane;

[0062] Wherein, in the sulfide electrolyte membrane doped with two layers of glass fibers 4, the doping amount of the glass fibers 4 decreases gradually along the direction away from the sulfide electrolyte bottom membrane 2, and the preparation steps include:

[0063] (a) degassing, stirring and mixing glass fiber, sulfide electrolyte, solvent and binder to obtain a first modified layer slurry with a solid content of 46%; wherein the mass ratio of the glass fiber to the sulfide electrolyte and the mass of the binder is 98:3, the mass ratio of the glass fiber to the sulfide electrolyte is 9:91, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li6PS5Cl;

[0064] Degassing, stirring and mixing the glass fiber, sulfide electrolyte, solvent and binder to obtain a second modified layer slurry with a solid content of 48%; wherein the mass ratio of the glass fiber and the sulfide electrolyte to the mass of the binder is 98:3, the mass ratio of the glass fiber and the sulfide electrolyte is 5:95, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li6PS5Cl;

[0065] (b) After adjusting the thickness of the scraper coating to 80 μm, the scraper coating is started, and the first modified layer slurry is scraped on the surface of the base film. After naturally drying for 30 minutes, the scraper coating thickness is adjusted to 60 μm and the scraper coating is started. The second modified layer slurry is scraped on the surface of the first modified layer 31. After naturally drying for 30 minutes, the scraper coating is transferred to an oven at 80° C. and dried for 4 hours to obtain a composite sulfide electrolyte membrane.

[0066] Example 2

[0067] This embodiment provides a composite sulfide electrolyte membrane, which includes a substrate, a sulfide electrolyte base membrane and a modified sulfide electrolyte membrane stacked in sequence;

[0068] The modified sulfide electrolyte membrane comprises two layers of glass fiber-doped sulfide electrolyte membranes, and in the two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of glass fiber decreases gradually along the direction away from the sulfide electrolyte bottom membrane, which are respectively recorded as a first modified layer and a second modified layer;

[0069] The material of the substrate is PET with a thickness of 80 μm, and the sulfide electrolyte bottom membrane is Li 10 SnPS 12 Base film, thickness 60 μm;

[0070] The thickness of the modified sulfide electrolyte membrane is 30 μm, the thickness ratio of the first modified layer to the second modified layer is 4:1, the mass ratio of the glass fiber to the sulfide electrolyte in the first modified layer is 17:83, the mass ratio of the glass fiber to the sulfide electrolyte in the second modified layer is 10:90, and the mass ratio of the glass fiber in the first modified layer to the glass fiber in the second modified layer is 6.8:1; the diameter of the glass fiber is 8 μm and the length is 200 μm, and the sulfide electrolyte is Li 10 SnPS 12 .

[0071] This embodiment also provides a method for preparing the composite sulfide electrolyte membrane, the preparation method comprising the following steps:

[0072] (1) Degassing, stirring and mixing a sulfide electrolyte, a solvent and a binder to prepare a sulfide electrolyte base film slurry with a solid content of 60%; wherein the mass ratio of the sulfide electrolyte to the binder is 97:3, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li 10 SnPS 12 ;

[0073] (2) placing the substrate on a coating table, adjusting the coating thickness of the scraper to 150 μm and starting scraping, scraping the sulfide electrolyte base membrane slurry onto the surface of the substrate, drying it naturally for 30 minutes, and then sequentially stacking two layers of glass fiber-doped sulfide electrolyte membranes on the dried sulfide electrolyte base membrane, including a first modified layer and a second modified layer, to obtain a composite sulfide electrolyte membrane;

[0074] Wherein, in the two layers of glass fiber-doped sulfide electrolyte membrane, the doping amount of glass fiber decreases gradually along the direction away from the sulfide electrolyte bottom membrane, and the preparation steps include:

[0075] (a) degassing, stirring and mixing glass fiber, sulfide electrolyte, solvent and binder to obtain a first modified layer slurry with a solid content of 45%; wherein the mass ratio of the glass fiber and the sulfide electrolyte to the mass of the binder is 98:2, the mass ratio of the glass fiber and the sulfide electrolyte is 17:83, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li 10 SnPS 12 ;

[0076] The glass fiber, sulfide electrolyte, solvent and binder are degassed, stirred and mixed to obtain a second modified layer slurry with a solid content of 45%; wherein the mass ratio of the glass fiber and the sulfide electrolyte to the mass of the binder is 98:2, the mass ratio of the glass fiber and the sulfide electrolyte is 10:90, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li 10 SnPS 12 ;

[0077] (b) After adjusting the thickness of the scraper coating to 120 μm, the scraper coating is started, and the first modified layer slurry is scraped on the surface of the sulfide electrolyte base membrane. After naturally drying for 30 minutes, the scraper coating thickness is adjusted to 60 μm and the scraper coating is started. The second modified layer slurry is scraped on the surface of the first modified layer. After naturally drying for 30 minutes, the scraper coating is transferred to a 70° C. oven for drying for 5 hours to obtain a composite sulfide electrolyte membrane.

[0078] Example 3

[0079] This embodiment provides a composite sulfide electrolyte membrane, which includes a substrate, a sulfide electrolyte base membrane and a modified sulfide electrolyte membrane stacked in sequence;

[0080] The modified sulfide electrolyte membrane comprises two layers of glass fiber-doped sulfide electrolyte membranes, and in the two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of glass fiber decreases gradually along the direction away from the sulfide electrolyte bottom membrane, which are respectively recorded as a first modified layer and a second modified layer;

[0081] The material of the substrate is PET with a thickness of 100 μm, and the sulfide electrolyte bottom membrane is a Li6PS5Br bottom membrane with a thickness of 60 μm;

[0082] The thickness of the modified sulfide electrolyte membrane is 50 μm, the thickness ratio of the first modified layer to the second modified layer is 2:1, the mass ratio of the glass fiber to the sulfide electrolyte in the first modified layer is 5:95, the mass ratio of the glass fiber to the sulfide electrolyte in the second modified layer is 3:97, and the mass ratio of the glass fiber in the first modified layer to the glass fiber in the second modified layer is 3.3:1; the diameter of the glass fiber is 8 μm and the length is 150 μm, and the sulfide electrolyte is Li6PS5Br.

[0083] This embodiment also provides a method for preparing the composite sulfide electrolyte membrane, the preparation method comprising the following steps:

[0084] (1) degassing, stirring and mixing a sulfide electrolyte, a solvent and a binder to prepare a sulfide electrolyte base film slurry with a solid content of 30%; wherein the mass ratio of the sulfide electrolyte to the binder is 97:3, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li6PS5Br;

[0085] (2) placing the substrate on a coating table, adjusting the coating thickness of the scraper to 180 μm and starting scraping, scraping the sulfide electrolyte base membrane slurry onto the surface of the substrate, drying it naturally for 30 minutes, and then sequentially stacking two layers of glass fiber-doped sulfide electrolyte membranes on the dried sulfide electrolyte base membrane, including a first modified layer and a second modified layer, to obtain a composite sulfide electrolyte membrane;

[0086] Wherein, in the two layers of glass fiber-doped sulfide electrolyte membrane, the doping amount of glass fiber decreases gradually along the direction away from the sulfide electrolyte bottom membrane, and the preparation steps include:

[0087] (a) degassing, stirring and mixing glass fiber, sulfide electrolyte, solvent and binder to obtain a first modified layer slurry with a solid content of 45%; wherein the mass ratio of the glass fiber to the sulfide electrolyte and the mass of the binder is 98:2, the mass ratio of the glass fiber to the sulfide electrolyte is 5:95, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li6PS5Br;

[0088] Degassing, stirring and mixing glass fiber, sulfide electrolyte, solvent and binder to obtain a second modified layer slurry with a solid content of 45%; wherein the mass ratio of the glass fiber to the sulfide electrolyte and the mass of the binder is 98:2, the mass ratio of the glass fiber to the sulfide electrolyte is 3:97, the solvent is p-xylene, the binder is styrene-butadiene-styrene block copolymer, and the sulfide electrolyte is Li6PS5Br;

[0089] (b) After adjusting the thickness of the scraper coating to 90 μm, the scraper coating is started, and the first modified layer slurry is scraped on the surface of the sulfide electrolyte base membrane. After naturally drying for 30 minutes, the scraper coating thickness is adjusted to 60 μm and the scraper coating is started. The second modified layer slurry is scraped on the surface of the first modified layer. After naturally drying for 3 hours, it is transferred to a 90° C. oven and dried for 3 hours to obtain a composite sulfide electrolyte membrane.

[0090] Example 4

[0091] The difference between this embodiment and Embodiment 1 is that the thickness ratio of the first modified layer to the second modified layer is 5:1.

[0092] The rest of the preparation methods and parameters were the same as those in Example 1.

[0093] Example 5

[0094] The difference between this embodiment and Embodiment 1 is that the modified sulfide electrolyte membrane includes three layers of glass fiber-doped sulfide electrolyte membranes, that is, a third modified layer is further provided on the second modified layer, the proportion of glass fiber in the sulfide electrolyte membrane slurry required for preparing the third modified layer and the sulfide electrolyte membrane slurry required for preparing the second modified layer is consistent, the thickness ratio of the second modified layer and the third modified layer is 2:1, and the mass ratio of the glass fiber in the second modified layer and the glass fiber in the third modified layer is 2:1.

[0095] The rest of the preparation methods and parameters were the same as those in Example 1.

[0096] Example 6

[0097] The difference between this embodiment and embodiment 1 is that the modified sulfide electrolyte membrane includes two layers of glass fiber-doped sulfide electrolyte membranes, that is, a third modified layer is further provided on the second modified layer, the thickness of the third modified layer is consistent with that of the second modified layer, the mass ratio of glass fiber to sulfide electrolyte in the sulfide electrolyte membrane slurry required for the third modified layer is 3:97, and the mass ratio of glass fiber in the second modified layer to glass fiber in the third modified layer is 5:3.

[0098] The rest of the preparation methods and parameters were the same as those in Example 1.

[0099] Comparative Example 1

[0100] The difference between this comparative example and Example 1 is that the modified sulfide electrolyte membrane only includes one layer of glass fiber-doped sulfide electrolyte membrane, wherein the mass ratio of glass fiber to sulfide electrolyte is 9:91.

[0101] The rest of the preparation methods and parameters were the same as those in Example 1.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that the modified sulfide electrolyte membrane consists of two layers of sulfide electrolyte membranes without glass fiber doping, that is, no glass fiber is added in step (a).

[0104] The rest of the preparation methods and parameters were the same as those in Example 1.

[0105] Comparative Example 3

[0106] The difference between this comparative example and Example 1 is that no sulfide electrolyte base membrane is provided, and the modified sulfide electrolyte membrane only includes a layer of glass fiber-doped sulfide electrolyte membrane, that is, a layer of glass fiber-doped sulfide electrolyte membrane is directly scraped on the substrate.

[0107] The rest of the preparation methods and parameters were the same as those in Example 1.

[0108] Figure 2 The SEM image of the modified sulfide electrolyte membrane provided in this comparative example is shown. It can be seen from the image that the modified sulfide electrolyte membrane has glass fiber sedimentation and cross-stacking phenomena.

[0109] Comparative Example 4

[0110] The difference between this comparative example and Example 1 is that the doping amount of the glass fiber increases gradually in the direction away from the sulfide electrolyte base membrane, that is, the mass ratio of the glass fiber to the sulfide electrolyte in the first modified layer is 5:95, and the mass ratio of the glass fiber to the sulfide electrolyte in the second modified layer is 25:75.

[0111] The rest of the preparation methods and parameters were the same as those in Example 1.

[0112] Comparative Example 5

[0113] The difference between this comparative example and Example 1 is that the mass ratio of the glass fiber in the first modified layer to the glass fiber in the second modified layer is 1:1.

[0114] The rest of the preparation methods and parameters were the same as those in Example 1.

[0115] Performance Testing

[0116] The composite sulfide electrolyte membrane provided in the above embodiment and comparative example is assembled with the positive electrode sheet and the negative electrode sheet into a soft package battery. The specific steps include: the positive electrode adopts NCM811 system material with a surface loading of 20 mg / cm 2 The negative electrode uses a LiCu composite tape, and both the positive and negative electrode sheets are cold pressed at 300MPa to increase the density of the electrode sheets; the positive electrode sheet with aluminum tabs, the composite sulfide electrolyte membrane and the negative electrode sheet with nickel tabs are heat-sealed in an aluminum-plastic film to form a soft-package battery.

[0117] The electrochemical performance test of the soft package battery was carried out, and the test conditions included: temperature of 45° C., test pressure of 2 MPa, and 0.055C charge and discharge.

[0118] The test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] analyze:

[0122] As can be seen from the above table, the present invention can effectively prevent the side of the glass fiber settling from directly contacting the electrode by arranging a sulfide electrolyte bottom membrane at the bottom of the modified sulfide electrolyte membrane, and can directly reduce the interface resistance between the electrolyte and the electrode. In addition, by using at least two layers of glass fiber-doped sulfide electrolyte membranes, and the doping amount of glass fiber in each layer gradually decreases along the direction away from the sulfide electrolyte bottom membrane, the glass fiber can be dispersed throughout the interior of the membrane, while improving the membrane strength and significantly reducing the overall interface resistance, preventing the composite sulfide electrolyte membrane from being pressed through and short-circuited by the positive electrode during the assembly of the soft-pack battery, and effectively improving the battery performance.

[0123] It can be seen from Example 1 and Comparative Example 1 that if the modified sulfide electrolyte membrane only includes a layer of glass fiber-doped sulfide electrolyte membrane, no gradient can be formed, resulting in a large interface resistance.

[0124] It can be seen from Example 1 and Comparative Example 2 that if the modified sulfide electrolyte membrane is composed of two layers of sulfide electrolyte membrane without glass fiber doping, the electrolyte membrane is not strong enough, causing the electrolyte membrane to be pressed through by the positive electrode and short-circuited.

[0125] It can be seen from Example 1 and Comparative Example 3 that if the sulfide electrolyte bottom membrane is not provided, the glass fiber will settle and the interface resistance will be large.

[0126] It can be seen from Example 1 and Comparative Example 4 that if the doping amount of glass fiber increases gradually along the direction away from the sulfide electrolyte substrate, the density of the sulfide electrolyte membrane decreases gradually along the direction away from the sulfide electrolyte substrate, the porosity gradient increases, the density is low, and the growth of lithium dendrites is increased.

[0127] It can be seen from Example 1 and Comparative Example 5 that if the doping amount gradient of the glass fiber is not set, the porosity of the electrolyte membrane is large and the density is low, which increases the growth of lithium dendrites.

[0128] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite sulfide electrolyte membrane, characterized in that: The composite sulfide electrolyte membrane comprises a substrate, a sulfide electrolyte base membrane and a modified sulfide electrolyte membrane which are stacked in sequence; The modified sulfide electrolyte membrane comprises at least two layers of glass fiber-doped sulfide electrolyte membranes, and in the at least two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of glass fiber decreases gradually along a direction away from the sulfide electrolyte bottom membrane.

2. The composite sulfide electrolyte membrane according to claim 1, characterized in that The thickness of the modified sulfide electrolyte membrane is 20-100 μm; Preferably, the modified sulfide electrolyte membrane comprises two layers of glass fiber-doped sulfide electrolyte membranes, which are respectively marked as a first modified layer and a second modified layer along a direction away from the sulfide electrolyte base membrane, and a thickness ratio of the first modified layer to the second modified layer is (1-4):

1.

3. The composite sulfide electrolyte membrane according to claim 1 or 2, characterized in that: In the glass fiber-doped sulfide electrolyte membrane, the mass ratio of glass fiber to sulfide electrolyte is (3-30):(70-97).

4. The composite sulfide electrolyte membrane according to any one of claims 1 to 3, characterized in that: The diameter of the glass fiber is 5-12 μm; Preferably, the length of the glass fiber is 90-300 μm.

5. The composite sulfide electrolyte membrane according to any one of claims 1 to 4, characterized in that: The substrate includes any one of a PET film, an aluminum foil or a stainless steel foil; Preferably, the thickness of the substrate is 10-100 μm; Preferably, the thickness of the sulfide electrolyte bottom film is 10-100 μm; Preferably, the sulfide electrolyte bottom film includes Li6PS5Cl bottom film, Li 10 SnPS 12 Base film, Li6PS5Br base film or Li 10 GeP2S 12 Any one or a combination of at least two of the base films; Preferably, in the glass fiber-doped sulfide electrolyte membrane, the sulfide electrolyte comprises Li6PS5Cl, Li 10 SnPS 12 , Li6PS5Br or Li 10 GeP2S 12 Any one or a combination of at least two of the following.

6. A method for preparing a composite sulfide electrolyte membrane according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (1) coating a sulfide electrolyte base film slurry on the surface of a substrate to form a sulfide electrolyte base film; (2) preparing at least two layers of glass fiber-doped sulfide electrolyte membranes by sequentially stacking them on the sulfide electrolyte base membrane to obtain the composite sulfide electrolyte membrane; Wherein, in the at least two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of the glass fibers decreases gradually along the direction away from the base membrane.

7. The preparation method according to claim 6, characterized in that: The sulfide electrolyte base film slurry in step (1) comprises a sulfide electrolyte, a binder and a solvent; Preferably, the solvent comprises any one or a combination of at least two of n-heptane, toluene, p-xylene, anisole or isobutyl isobutyrate; Preferably, the binder includes any one or a combination of at least two of PVDF binders, polyisobutylene, styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, ethyl cellulose or rubber binders; Preferably, the mass ratio of the sulfide electrolyte to the binder is (92-98):(2-8); Preferably, the solid content of the sulfide electrolyte base membrane slurry in step (1) is 30-60wt%.

8. The preparation method according to claim 6 or 7, characterized in that: The preparation steps of each layer of the glass fiber-doped sulfide electrolyte membrane include: (a) mixing glass fiber, sulfide solid electrolyte, solvent and binder to obtain glass fiber-doped sulfide electrolyte slurry; (b) coating the glass fiber-doped sulfide electrolyte slurry on the surface of the sample, and then drying it to form a film to obtain a glass fiber-doped sulfide electrolyte membrane; Preferably, the solid content of the glass fiber-doped sulfide electrolyte slurry in step (a) is 30-60wt%; Preferably, the drying film forming temperature in step (b) is 70-90° C., and the drying film forming time is 3-5 h.

9. The preparation method according to any one of claims 6 to 8, characterized in that: The preparation method comprises the following steps: (1) degassing, stirring and mixing a sulfide electrolyte, a solvent and a binder to prepare a sulfide electrolyte base film slurry with a solid content of 30-60 wt %; wherein the mass ratio of the sulfide electrolyte to the binder is (92-98):(2-8); (2) applying the sulfide electrolyte base film slurry on the surface of the substrate by a doctor blade method, drying it, and then sequentially stacking at least two layers of glass fiber-doped sulfide electrolyte membranes on the dried sulfide electrolyte base film to obtain a composite sulfide electrolyte membrane; Among them, in the at least two layers of glass fiber-doped sulfide electrolyte membranes, the doping amount of glass fiber decreases gradually along the direction away from the sulfide electrolyte bottom membrane, and the preparation steps of each layer of glass fiber-doped sulfide electrolyte membrane include: (a) degassing and stirring glass fiber, sulfide electrolyte, solvent and binder to obtain a glass fiber-doped sulfide electrolyte slurry with a solid content of 30-60wt%; wherein the mass ratio of glass fiber to sulfide electrolyte is (3-30):(70-97); (b) coating the glass fiber-doped sulfide electrolyte slurry on the surface of the sample, and then drying it at 70-90° C. for 3-5 hours to form a film, thereby obtaining a glass fiber-doped sulfide electrolyte membrane.

10. An all-solid-state battery, characterized in that: The all-solid-state battery comprises the composite sulfide electrolyte membrane according to any one of claims 1 to 5.

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