Method for manufacturing solid electrolyte membrane

Abstract

The present invention relates to a method for manufacturing a solid electrolyte membrane. More specifically, a small amount of binder can be fiberized by dry rolling to prepare a solid electrolyte membrane. Since the fibrillated binder is included in the solid electrolyte membrane in a mutually entangled state, excellent ionic conductivity and strength characteristics are exhibited.

Description

Technical Field

[0001] This application claims priority to U.S. Patent Application No. 18 / 234,286, filed August 15, 2023; Korean Patent Application No. 10-2023-0124429, filed September 19, 2023; and Korean Patent Application No. 10-2024-0108292, filed August 13, 2024.

[0002] This invention relates to a method for preparing a solid electrolyte membrane, the solid electrolyte membrane thereof, and an all-solid-state battery containing the solid electrolyte membrane. Background Technology

[0003] Lithium-ion batteries have certain limitations in terms of capacity, safety, output, large size, and miniaturization. Therefore, there has always been a need for alternative battery technologies that can overcome these shortcomings.

[0004] Some alternatives to lithium-ion batteries include: metal-air batteries with very large theoretical capacity; all-solid-state batteries with no risk of explosion; supercapacitors for output; sodium-sulfur batteries (NaS batteries); redox flow batteries (RFB) for large sizes; and thin-film batteries for miniaturization.

[0005] In all-solid-state batteries, the liquid electrolyte used in conventional lithium-ion batteries is replaced by a solid electrolyte. Therefore, the use of flammable solvents in the battery can be avoided, and safety can be improved by, for example, avoiding the risk of fire or explosion caused by the decomposition or reaction of conventional electrolyte solutions. Furthermore, because all-solid-state batteries can use lithium metal or lithium alloys as the negative electrode active material, they offer the advantage of significantly higher energy density relative to mass and volume.

[0006] However, because all-solid-state batteries use solid electrolytes, the ionic conductivity may be reduced. Furthermore, when liquid electrolytes are used as a means to ensure the ionic conductivity of the solid electrolyte, there is a problem of reduced strength.

[0007] In order to ensure the safety of all-solid-state batteries while preventing the degradation of battery performance and processability, the ionic conductivity and strength of the solid electrolyte should be maintained at a certain level.

[0008] Therefore, there remains a need in the art for solid electrolytes that possess both sufficient ionic conductivity and sufficient strength, as well as suitable manufacturing methods for preparing such solid electrolytes.

[0009] [Existing Technical Documents]

[0010] [Patent Literature]

[0011] (Patent Document 1) Korean Patent Publication No. 2022-0095689 Summary of the Invention

[0012] [Technical Issues]

[0013] To address the aforementioned issues, the inventors conducted various studies, demonstrating that solid electrolyte membranes with excellent ion conductivity and strength can be prepared by controlling optimal temperature, orientation, and cycle number during calendering. The calendering process involves physically mixing a sulfide-based solid electrolyte and / or a halide-based solid electrolyte with a binder, followed by fiberization of the binder. The structure formed by the fiberized binder can vary depending on the temperature, orientation, and cycle number of the calendering process.

[0014] Therefore, one aspect of the present invention relates to providing a method for preparing a solid electrolyte membrane having improved ionic conductivity and strength.

[0015] [Technical Solution]

[0016] To achieve the above objectives, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, comprising the steps of: (S1) mixing solid electrolyte particles and a binder; and (S2) subjecting the mixture obtained in step (S1) to a calendering process to form the mixture into a membrane form, wherein the binder is fibrousized by the mixing.

[0017] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the temperature of the calendering process is 50°C to 200°C.

[0018] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the calendering process is performed for 5 to 50 cycles.

[0019] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the calendering process is performed in a uniaxial or biaxial manner.

[0020] In addition, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein steps (S1) and (S2) are carried out in the absence of solvent.

[0021] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the solid electrolyte particles comprise one or more selected from the group consisting of sulfide solid electrolyte particles and halide solid electrolyte particles.

[0022] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the solid electrolyte membrane is made of solid electrolyte particles and a fibrous binder.

[0023] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the fibrous adhesive comprises one or more selected from the group consisting of polytetrafluoroethylene (PTFE) and copolymers thereof.

[0024] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the content of the fibrous binder is less than 2% by weight, based on the total weight of the solid electrolyte membrane.

[0025] In addition, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the fibrous adhesive is contained in the solid electrolyte membrane in a dispersed state.

[0026] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the interface between the solid electrolyte particles and the fibrous binder is bonded.

[0027] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the solid electrolyte membrane has an ionic conductivity of 0.5 to 10 S / cm.

[0028] Furthermore, one aspect of the present invention provides a method for preparing a solid electrolyte membrane, wherein the tensile strength of the solid electrolyte membrane is 45 to 1000 kPa.

[0029] [Beneficial Effects]

[0030] One aspect of the present invention provides a method for preparing a solid electrolyte membrane, which includes a structure in which fibrous adhesives are entangled in each other by fiberizing an adhesive in a dry process without the use of solvents. Therefore, even with the use of a small amount of fibrous adhesive, excellent tensile strength can be obtained.

[0031] In addition, by controlling the temperature, orientation, and number of cycles during the calendering process, the degree of fiberization of the binder after the physical mixing of solid electrolyte particles and binder, and the internal structure formed by the fiberized binder, the strength of the solid electrolyte membrane can be improved. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the internal structure of a solid electrolyte membrane according to an embodiment of the present invention.

[0033] Figure 2a These are scanning electron micrographs of solid electrolyte membranes taken at the temperature of the calendering process.

[0034] Figure 2b These are scanning electron micrographs of solid electrolyte membranes oriented according to the calendering process.

[0035] Figure 2c These are scanning electron micrographs of solid electrolyte membranes based on the number of cycles in the calendering process.

[0036] Figure 3a It is a curve showing the correlation between the temperature of the calendering process and the tensile strength.

[0037] Figure 3b It is a curve showing the correlation between the orientation of the calendering process and the tensile strength.

[0038] Figure 3c This is a graph showing the correlation between the number of calendering cycles and the ionic conductivity and tensile strength of the solid electrolyte membrane. Detailed Implementation

[0039] The invention will be described in more detail below to aid in understanding it.

[0040] As used herein, the term "three-dimensional network structure" can refer to a structure in which fibrous adhesives dispersed and contained in a solid electrolyte membrane are entangled with each other, as well as a structure comprising a framework made of fibrous adhesives and an internal space formed by the framework.

[0041] Preparation method of solid electrolyte membrane

[0042] One aspect of the present invention relates to a method for preparing a solid electrolyte membrane.

[0043] A method for preparing a solid electrolyte membrane according to one aspect of the present invention includes: (S1) mixing solid electrolyte particles and a binder; and (S2) subjecting the mixture obtained in step (S1) to a calendering process to form the mixture into a membrane form, wherein the binder is fiberized in the calendering process.

[0044] In this context, the calendering process refers to the process of forming a film using two rollers.

[0045] In one aspect of the invention, in step (S1), the solid electrolyte particles are mixed with a binder, but this can be done by a dry mixing method without the use of solvents.

[0046] Furthermore, since the solid electrolyte particles and the binder are physically mixed without any separate chemical reaction, this mixing can be called physical mixing. This mixing can be carried out using a mortar and pestle, ball mixing, or rolling.

[0047] Furthermore, the adhesive can become fibrous during physical mixing. Fiberized adhesives, also known as fibrous adhesives, can disperse and entangle themselves to form a three-dimensional network structure.

[0048] Figure 1 This is a schematic diagram illustrating the internal structure of a solid electrolyte membrane according to an embodiment of the present invention.

[0049] Reference Figure 1 Inside the solid electrolyte membrane 1, the solid electrolyte 10 exists in a particulate state, and the fibrous binder 2 can be contained in an entangled state. Specifically, the fibrous binder 2 can be dispersed and entangled to form a three-dimensional network structure. The three-dimensional network structure includes a framework composed of the fibrous binder 2 and voids serving as spaces between the framework, within which the solid electrolyte 10 particles can be located. The solid electrolyte 10 can be a sulfide-based and / or halide-based solid electrolyte.

[0050] In embodiments of the present invention, the temperature of the calendering process can be from 50°C to 200°C. Specifically, the temperature can be above 50°C, above 70°C, or above 80°C, or below 100°C, below 120°C, below 140°C, below 160°C, below 180°C, or below 200°C. When the temperature is below 50°C, less fiberization of the binder occurs, and the strength of the solid electrolyte membrane may decrease. When the temperature exceeds 200°C, even if the temperature increases, the strength of the solid electrolyte membrane may no longer increase, or the electrolyte or binder material may deteriorate.

[0051] In embodiments of the present invention, the calendering process can be performed for 5 to 50 cycles. Specifically, the number of cycles can be 5 or more, 8 or more, 10 or more, 12 or more, or 20 or less, 30 or less, 40 or less, or 50 or less. When the number of cycles is less than 5, the strength of the solid electrolyte membrane may decrease due to less fiberization of the binder, and when the number of cycles exceeds 50, even if the number of cycles increases, the strength of the solid electrolyte membrane may not increase or the processability may deteriorate.

[0052] In embodiments of the present invention, the orientation of the calendering process can be performed in a uniaxial or biaxial manner. In this case, uniaxial means calendering along one direction, while biaxial means calendering along one direction on the horizontal plane of the electrolyte membrane and then alternating calendering along the vertical direction.

[0053] When the calendering process is performed uniaxially, the fiberization of the binder is directional. On the other hand, if the calendering process is performed biaxially, the fiberization of the binder is uniformly directional, thus reducing the strength difference according to direction.

[0054] In embodiments of the present invention, the pressure applied to the mixture during calendering to form a film can be from 1 to 50 kgf / cm. Specifically, the pressure can be 1 kgf / cm or more, 2 kgf / cm or more, 3 kgf / cm or more, 4 kgf / cm or more, 5 kgf / cm or more, 6 kgf / cm or more, 7 kgf / cm or more, 8 kgf / cm or more, 9 kgf / cm or more, 10 kgf / cm or more, and can be 50 kgf / cm or less, 45 kgf / cm or less, 40 kgf / cm or less, 35 kgf / cm or less, 30 kgf / cm or less, 25 kgf / cm or less, 20 kgf / cm or less. If the pressure is less than 1 kgf / cm, the degree of fiberization of the binder may decrease, requiring an increase in the number of cycles in the calendering process. If the pressure exceeds 50 kgf / cm, the uniformity of the formed film may decrease. In this case, the pressure can be a linear pressure.

[0055] In embodiments of the present invention, the solid electrolyte membrane is made of a solid electrolyte and a fibrous binder, wherein the solid electrolyte comprises one or more selected from the group consisting of sulfide solid electrolytes and halide solid electrolytes.

[0056] In embodiments of the present invention, the interface between the solid electrolyte and the fibrous adhesive can be adhesive.

[0057] Because pressure is applied during the preparation process to firmly bond the interface between the solid electrolyte and the fibrous binder, a decrease in the strength of the solid electrolyte membrane can be prevented even when using a small amount of fibrous binder. Furthermore, adhesion also occurs between the solid electrolyte molecules, which further enhances the strength of the solid electrolyte membrane.

[0058] In embodiments of the present invention, the ionic conductivity of the solid electrolyte membrane can be from 0.5 to 10 S / cm. Specifically, the ionic conductivity can be 0.5 S / cm or more, 0.6 S / cm or more, 0.8 S / cm or more, 1 S / cm or more, 1.5 S / cm or more, or 2 S / cm or more, and can be 3 S / cm or less, 5 S / cm or less, 8 S / cm or less, or 10 S / cm or less. The ionic conductivity can be measured at room temperature (25°C).

[0059] In embodiments of the present invention, the tensile strength of the solid electrolyte membrane can be from 45 to 1000 kPa. The tensile strength of the solid electrolyte membrane can be 45 kPa or more, 50 kPa or more, 80 kPa or more, 100 kPa or more, 120 kPa or more, or 150 kPa or more, and can be less than 200 kPa, less than 300 kPa, less than 500 kPa, less than 700 kPa, less than 900 kPa, or less than 1000 kPa.

[0060] In embodiments of the present invention, the solid electrolyte membrane may be solvent-free.

[0061] Since solid electrolyte membranes are prepared by a dry process of physically mixing sulfide and / or halide solid electrolytes with a binder, they do not contain any solvents. Furthermore, in the dry process, the binder is fiberized by pressure; the fibrous binder disperses and entangles with each other to form a three-dimensional network structure. Therefore, even using only a small amount of binder, a solid electrolyte membrane with improved strength can be prepared using this structure formed by the fibrous binder.

[0062] In addition, since no separate solvent is used, the crystal structure of sulfide and / or halide solid electrolytes can be prevented from being destroyed by the solvent and the ionic conductivity from decreasing.

[0063] Typically, wet processes used to prepare solid electrolyte membranes employ solvents capable of dissolving binders located between solid electrolyte particles to provide adhesion.

[0064] On the other hand, one aspect of the present invention involves a dry process in which the initial particulate binder is physically stretched into a fibrous form without the use of solvents. Therefore, the structure of the binder in the prepared solid electrolyte membrane differs from that formed by the wet process, and the physical properties of the solid electrolyte membrane or the solid electrolyte membrane prepared by the wet process can be improved. In the above, the initial particulate binder undergoes physical deformation due to shear force during the mixing step with the electrolyte particles. A mortar, ball mill, or roller press can be introduced during mixing to induce physical deformation. Furthermore, as a binder capable of effectively inducing physical deformation, a physically very weak and relatively easily fibrous binder, such as PTFE, can be used.

[0065] In embodiments of the present invention, the solid electrolyte may include sulfide solid electrolytes and / or halide solid electrolytes.

[0066] In addition, based on the total weight of the solid electrolyte membrane, the content of the solid electrolyte can be 98% by weight or more. Specifically, the content of the solid electrolyte can be 98% by weight or more, 98.5% by weight or more, or 99% by weight or more. When the content of the solid electrolyte is less than 98% by weight, the ionic conductivity of the solid electrolyte membrane may decrease. In addition, the upper limit of the content of the solid electrolyte is not particularly limited. For example, it can be 99.8% by weight or less. If the upper limit exceeds 99.8% by weight, the content of the binder will decrease relatively, so the tensile strength may decrease slightly.

[0067] In addition, the solid electrolyte can be in the form of particles, and the particle size D of the solid electrolyte 50 can be from 10 nm to 10 μm. Specifically, it can be 10 nm or more, 100 nm or more, 1 μm or more, 2 μm or more, or 3 μm or more, and can be 5 μm or less, 7 μm or less, 9 μm or less, or 10 μm or less. When the particle size D of the solid electrolyte 50 is less than 10 nm, the tensile strength may decrease, and when the particle size D of the solid electrolyte 50 exceeds 10 μm, the surface of the solid electrolyte membrane is uneven, so the resistance to the electrode may increase.

[0068] In an embodiment of the present invention, the sulfide-based solid electrolyte may include one or more selected from LiPSX (X = Cl, Br or I), LiGePS, and LiPS. However, the sulfide-based solid electrolyte is not limited thereto, and sulfide-based solid electrolytes commonly used in the art can be widely used.

[0069] In some embodiments, the sulfide-based solid electrolyte particles contain a composite material or a mixture thereof shown in Formula 1:

[0070] [Formula 1]

[0071] Li a M b S c X d

[0072] Where:

[0073] M is selected from P, Sn, Sb, As, and Ge;

[0074] X is selected from Cl, Br, and I; and

[0075] where 5 ≤ a ≤ 7.5, 0.5 < b ≤ 1.5, 4 < c ≤ 6, and 0.5 < d ≤ 2.

[0076] In some embodiments, the sulfide-based solid electrolyte particles contain Li6PS5Cl.

[0077] In an embodiment of the present invention, the halide-based solid electrolyte can be represented by the following formula 2:

[0078] [Formula 2]

[0079] Li 6-3a M a Br b Cl c

[0080] Where M is a metal other than Li, a is 0 < a < 2, b is 0 ≤ b ≤ 6, c is 0 ≤ c ≤ 6, and b + c = 6. In some aspects, M is a metal other than Li. Preferably, M is selected from Sc, Y, B, Al, Ga, and In, where 0 < a < 2, 0 ≤ b ≤ 6, 0 ≤ c ≤ 6, and b + c = 6.

[0081] For example, the halide-based solid electrolyte can include one or more selected from Li3YBr6, Li3YCl6, and Li3YBr2Cl4.

[0082] In an embodiment of the present invention, in the dry process of mixing and pressing an adhesive with a sulfide-based and / or halide-based solid electrolyte, the adhesive can be fibrillated, and the fibrous adhesives can be dispersed and entangled with each other to form a three-dimensional network structure.

[0083] The adhesive can be one or more selected from polytetrafluoroethylene (PTFE) and copolymers containing it, but is not limited thereto. Such an adhesive can be widely used: it has the property of being easily stretched during the dry process due to low ductility strength and is fibrillated into a fibrous adhesive.

[0084] In addition, based on the total weight of the solid electrolyte membrane, the content of the adhesive can be 2 wt% or less. Specifically, the content of the adhesive can be 2 wt% or less, 1.5 wt% or less, or 1 wt% or less. When the content of the adhesive exceeds 2 wt%, the ionic conductivity of the solid electrolyte membrane may decrease. In addition, the lower limit of the adhesive is not particularly limited, but for example, it can be 0.2 wt% or more. If the lower limit of the adhesive is lower than 0.2 wt%, the tensile strength may slightly decrease.

[0085] Furthermore, the aspect ratio of the fibrous adhesive can range from 15 to 500. Specifically, the aspect ratio can be 15 or higher, 20 or higher, 25 or higher, 30 or higher, 35 or higher, 40 or higher, 45 or higher, 50 or higher, 55 or higher, 60 or higher, 65 or higher, 70 or higher, 75 or higher, 80 or higher, 85 or higher, 90 or higher, 95 or higher, or 100 or higher, and can be less than 500, less than 450, less than 400, less than 350, less than 300, less than 250, or less than 200. If the aspect ratio of the fibrous adhesive is less than 15, it is difficult to form a three-dimensional network structure with the fibrous adhesive, therefore, the strength of the solid electrolyte membrane may be reduced, thus worsening the processability during battery assembly. If the aspect ratio of the aforementioned fibrous adhesive exceeds 200, the manufacturing process of the fibrous adhesive with this aspect ratio may become complex, thereby reducing processability.

[0086] All-solid-state batteries

[0087] One aspect of the invention also relates to an all-solid-state battery including the solid electrolyte membrane.

[0088] The all-solid-state battery of the present invention includes: the solid electrolyte membrane; a positive electrode formed on one surface of the solid electrolyte membrane; and a negative electrode formed on the other surface of the solid electrolyte membrane.

[0089] In embodiments of the present invention, the positive electrode may comprise a positive electrode active material, a conductive material, and a binder.

[0090] In one aspect of the invention, the positive electrode of the all-solid-state battery includes a positive electrode active material layer, which may be formed on a surface of the positive electrode current collector.

[0091] The positive electrode active material layer includes the positive electrode active material, the conductive material, and the binder.

[0092] Furthermore, there are no particular limitations on the positive electrode active material, as long as it can reversibly adsorb and release lithium ions. Examples include layered compounds such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and Li[Ni]... x Co y Mn z M v O2 (where M is one or more elements selected from Al, Ga, and In; 0.3≤x<1.0, 0≤y,z≤0.5, 0≤v≤0.1, x+y+z+v=1) and Li (Li a M b-a-b' M' b' )O 2-c A c(where 0 ≤ a ≤ 0.2, 0.6 ≤ b ≤ 1, 0 ≤ b' ≤ 0.2, 0 ≤ c ≤ 0.2; M includes one or more selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, and Ti; M' is one or more selected from Al, Mg, and B, and A is one or more selected from P, F, S, and N) or compounds substituted with one or more transition metals; lithium manganese oxides, such as Li 1+y Mn 2-y O4 (where y is 0 to 0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, LiFe3O4, V2O5 and Cu2V2O7; and LiNi 1-y M y Ni-type lithium nickel oxides represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 to 0.3); LiMn 2- y M y Lithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, y = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which a portion of the Li is replaced by alkaline earth metal ions; disulfides; and Fe2(MoO4)3, etc., but not limited thereto.

[0093] Furthermore, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be between 60% and 80% by weight. Specifically, the content of the positive electrode active material can be above 60% by weight, above 65% by weight, or above 68% by weight, and can be below 72% by weight, below 75% by weight, or below 80% by weight. When the content of the positive electrode active material is less than 60% by weight, the battery performance may decrease, and when the content of the positive electrode active material exceeds 80% by weight, the mass transfer resistance may increase.

[0094] Furthermore, the conductive material is not particularly limited, as long as it prevents side reactions in the internal environment of the all-solid-state battery, has excellent conductivity, and does not cause chemical changes in the battery. Typical conductive materials include graphite or conductive carbon. Examples of conductive materials may include graphite, such as natural and artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, Denka black, thermally cracked carbon black, channel black, furnace black, lamp black, and summer black; carbon-based materials with a crystal structure of graphene or graphite; conductive fibers, such as carbon fibers and metal fibers; fluorinated carbon; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; and conductive oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives, used alone or in combination of two or more, but not limited thereto. Preferably, the conductive material may include vapor-grown carbon fiber (VGCF).

[0095] Based on the total weight of the positive electrode active material layer, the content of conductive material can typically range from 1% to 5% by weight. Specifically, the content can be more than 1% by weight, more than 1.5% by weight, or more than 2% by weight, or less than 4% by weight, less than 4.5% by weight, or less than 5% by weight. If the content of conductive material is too low, for example less than 1% by weight, it is difficult to expect an improvement in conductivity, or the electrochemical characteristics of the battery may deteriorate. Conversely, if the content of conductive material is too high, exceeding 5% by weight, the amount of positive electrode active material is relatively small, which may result in a reduction in capacity and energy density. There are no particular limitations on the method of including conductive material in the positive electrode; commonly known methods in the art, such as mixing with and coating with the positive electrode active material, can be used.

[0096] In addition, adhesives are components that help bond the positive electrode active material to the conductive material and to the current collector. The adhesive may include one or more selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resins, phenolic resins, epoxy resins, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, cyanoethyl sucrose, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyacrylic acid, polyacrylate, lithium polyacrylate, polymethacrylic acid, polymethacrylate, polyacrylamide, polyurethane, polyvinylidene fluoride, and poly(vinylidene fluoride-co-hexafluoropropylene). Preferably, the adhesive may include polytetrafluoroethylene (PTFE).

[0097] In addition, relative to the total weight of the positive electrode active material layer, the binder content can range from 0.5% to 4% by weight. Specifically, the binder content can be more than 0.5% by weight, more than 1% by weight, or more than 1.5% by weight, or less than 3% by weight, less than 3.5% by weight, or less than 4% by weight. When the binder content is less than 0.5% by weight, the adhesion between the positive electrode active material and the positive electrode current collector may decrease. When the binder content exceeds 4% by weight, the adhesion between the positive electrode active material and the positive electrode current collector can be improved, but the content of the positive electrode active material is also reduced, so the battery capacity may decrease.

[0098] In addition, the positive current collector supports the positive active material layer and is used to transfer electrons between the outer conductor and the positive active material layer.

[0099] There are no particular restrictions on the positive electrode current collector, as long as it has high electronic conductivity and does not cause chemical changes in the all-solid-state battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon, copper or stainless steel with surfaces treated with carbon, nickel, silver, etc., and aluminum-cadmium alloys can be used as positive electrode current collectors.

[0100] To improve the adhesion strength with the positive electrode active material layer, the surface of the positive electrode current collector can have a fine uneven structure or a three-dimensional porous structure. Therefore, the positive electrode current collector can come in various forms, such as membranes, sheets, foils, screens, meshes, porous materials, foams, and nonwoven fabrics.

[0101] The aforementioned positive electrode can be prepared using conventional methods. Specifically, it can be prepared by coating a positive electrode active material layer forming composition prepared by mixing positive electrode active material, conductive material, and binder in a solvent, drying the mixture, and optionally compressing the composition onto a current collector to increase the electrode density. In this case, an organic solvent that can uniformly disperse the positive electrode active material, binder, and conductive material and can be easily evaporated is preferred as the organic solvent. Specifically, the organic solvent may include acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropanol, etc.

[0102] In one aspect of the invention, the negative electrode of the all-solid-state battery has a negative electrode active material layer, which can be formed on a surface of the negative electrode current collector.

[0103] Negative electrode active materials may include those capable of reversibly inserting or de-intercalating lithium (Li) + Materials that can react with lithium ions to reversibly form lithium-containing compounds, lithium metal, or lithium alloys.

[0104] Capable of reversibly inserting or de-inserting lithium ions (Li) +The material can be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. It is capable of reacting with lithium ions (Li... + Materials that reversibly form lithium-containing compounds through a reaction can be, for example, tin oxide, titanium nitrate, or silicon. Lithium alloys can be alloys of lithium (Li) with metals selected from, for example, indium (In), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

[0105] Preferably, the negative electrode active material can be lithium metal or lithium-indium alloy (Li-In), and specifically, it can be in the form of lithium metal, lithium film, lithium-indium alloy film, or powder.

[0106] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be between 40% and 80% by weight. Specifically, the content of the negative electrode active material can be above 40% or 50% by weight, and below 70% or 80% by weight. When the content of the negative electrode active material is less than 40% by weight, the connectivity between the wet and dry negative electrode active material layers may be insufficient, and when the content of the negative electrode active material exceeds 80% by weight, the mass transfer resistance may increase.

[0107] In addition, the adhesive is the adhesive used for the positive electrode active material layer as described above.

[0108] In addition, the conductive material is the conductive material used for the positive electrode active material layer as described above.

[0109] Furthermore, there are no particular limitations on the negative electrode current collector, as long as it does not cause chemical changes in the battery and is conductive. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used as negative electrode current collectors. In addition, like the positive electrode current collector, the negative electrode current collector can have fine irregularities formed on its surface and can be used in various forms such as films, sheets, foils, meshes, porous materials, foams, non-woven fabrics, etc.

[0110] There are no particular limitations on the preparation method of the negative electrode. A layer of negative electrode active material can be formed on the negative electrode current collector using methods commonly used in the art for forming layers or films. For example, methods such as compression, coating, and deposition can be used. Additionally, one aspect of the present invention includes a negative electrode in which the battery is assembled without a lithium film on the negative electrode current collector, and then a lithium metal film is formed on a metal plate through initial charging.

[0111] Methods for preparing all-solid-state batteries

[0112] Another aspect of the present invention relates to a method for preparing an all-solid-state battery.

[0113] A method for preparing an all-solid-state battery according to one aspect of the present invention includes: (P1) disposing a mixture for forming a positive electrode active material layer on one surface of a solid electrolyte membrane, and forming a positive electrode on one surface of the solid electrolyte membrane by applying pressure; and (P2) disposing a negative electrode on another surface of the solid electrolyte membrane and applying pressure.

[0114] In step (P1), a mixture for forming a positive electrode active material layer can be disposed on one surface of a solid electrolyte membrane and pressurized at a high temperature, thereby forming a positive electrode on one surface of the solid electrolyte membrane.

[0115] The mixture used to form the positive electrode active material layer may include a positive electrode active material, a conductive material, and a binder. Their specific types and weights are as described above. Additionally, the positive electrode can be prepared by attaching a current collector after the positive electrode active material layer has been formed.

[0116] Additionally, a pressurization process can be performed at a pressure of 300 MPa to 500 MPa to bond the solid electrolyte membrane to the positive electrode while reducing interfacial resistance. The pressure during the high-temperature pressurization process can be above 300 MPa, above 350 MPa, above 400 MPa, or below 450 MPa, below 460 MPa, or below 470 MPa. If the temperature and / or pressure during the high-temperature pressurization process are below the above ranges, the solid electrolyte membrane and the positive electrode may not integrate; if the temperature and / or pressure exceed the above ranges, the solid electrolyte membrane or the positive electrode may deform or be damaged.

[0117] In step (P2), an all-solid-state battery can also be prepared by placing the negative electrode on the other surface of the solid electrolyte membrane and applying pressure to the negative electrode. The negative electrode is described above.

[0118] The pressure applied can range from 40 MPa to 80 MPa. Specifically, the pressure can be above 40 MPa, above 45 MPa, above 50 MPa, or below 70 MPa, below 75 MPa, or below 80 MPa. When the pressure applied is less than 40 MPa, the interfacial resistance between the negative electrode and the solid electrolyte membrane may increase. When the pressure exceeds 80 MPa, the solid electrolyte or negative electrode may deform or be damaged.

[0119] Because all-solid-state batteries prepared in this way contain a thin solid electrolyte, the manufacturing cost can be reduced and the ionic conductivity and energy density can be improved.

[0120] In addition, the solid electrolyte and the positive electrode are integrated through a high-temperature and high-pressure process, which can improve the interface stability.

[0121] Battery Module

[0122] In addition, one aspect of the present invention relates to a battery module comprising the all-solid-state battery as a unit cell, a battery pack comprising the battery module, and an apparatus comprising the battery pack as a power source.

[0123] In this context, specific examples of the device may include: power tools driven by an electric motor; electric vehicles, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheelers, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems; and so on, but are not limited thereto.

[0124] Preferred embodiments will be provided below to aid in understanding one aspect of the invention. However, it will be apparent to those skilled in the art that the following embodiments are merely examples of one aspect of the invention, and various modifications and changes can be made within the scope and spirit of this one aspect of the invention. Furthermore, it is self-evident that these modifications and changes fall within the scope of the appended claims.

[0125] In the following examples and comparative examples, solid electrolytes and all-solid-state batteries were prepared according to the compositions and methods shown in Table 1 below.

[0126] [Table 1]

[0127]

[0128] Example 1

[0129] A mixture was prepared by mixing polytetrafluoroethylene (PTFE, Chemours) as a binder with Li6PS5Cl powder as a sulfide-based solid electrolyte in a mortar. The mixture was then subjected to 15 calendering cycles using a roller press under biaxial orientation conditions at 90°C to obtain a solid electrolyte membrane with a thickness of 300 μm. The preparation process was carried out dry without the use of solvents.

[0130] Example 2

[0131] Example 2 was carried out in the same manner as Example 1, except that the temperature was set to 23°C.

[0132] Example 3

[0133] Example 3 was carried out in the same manner as Example 1, except that the temperature was set to 60°C.

[0134] Example 4

[0135] Example 4 was carried out in the same manner as Example 1, except that the temperature was set to 120°C.

[0136] Example 5

[0137] Example 5 was carried out in the same manner as Example 1, except that the orientation condition of the calendering process was uniaxial orientation.

[0138] Example 6

[0139] Example 6 was carried out in the same manner as Example 1, except that two calendering cycles were performed.

[0140] Example 7

[0141] Example 7 was carried out in the same manner as Example 1, except that five calendering cycles were performed.

[0142] Example 8

[0143] Example 8 was carried out in the same manner as Example 1, except that 10 calendering cycles were performed.

[0144] Example 9

[0145] Example 9 was carried out in the same manner as Example 1, except that 30 rolling cycles were performed.

[0146] Experimental Example 1: Internal Structure of Solid Electrolyte Membranes

[0147] To confirm the internal structure of the solid electrolyte membrane prepared in the examples, experiments were conducted.

[0148] Figure 2a These are images of solid electrolyte membranes obtained using a scanning electron microscope (SEM, FEIApreo SEM) based on the calendering process temperature.

[0149] Reference Figure 2a It can be confirmed that in the solid electrolyte membrane of Example 2, which has the lowest temperature among Examples 1 to 4, the structure of the entangled fibrous binder is not dense. Therefore, it can be seen that if the calendering process temperature is too low, the strength of the solid electrolyte membrane will decrease.

[0150] Figure 2b These are images of solid electrolyte membranes oriented according to the calendering process, obtained by scanning electron microscopy (SEM, FEI Apreo SEM).

[0151] refer to Figure 2bAs can be seen, the three-dimensional network structure formed by the entanglement of fibrous adhesives in Example 1, which is biaxial, is denser than that in Example 5, which is uniaxially oriented during calendering. This demonstrates that the strength of the solid electrolyte membrane is further improved during calendering when the orientation is biaxial.

[0152] Figure 2c These are images of solid electrolyte membranes obtained using a scanning electron microscope (SEM, FEI Apreo SEM) based on the number of calendering cycles.

[0153] refer to Figure 2c It can be seen that the greater the number of calendering cycles, the denser the three-dimensional network structure formed by the entanglement of the fibrous binder. Therefore, it can be concluded that the strength of the solid electrolyte membrane further increases with the increase in the number of cycles in the calendering process.

[0154] Experimental Example 2: Determination of Ionic Conductivity and Tensile Strength of Solid Electrolyte Membranes

[0155] To confirm the physical properties of the solid electrolyte membrane prepared in the examples, experiments were conducted to measure its ionic conductivity and tensile strength. The methods for measuring ionic conductivity and tensile strength are as follows.

[0156] (1) Determination of ionic conductivity

[0157] To determine the ionic conductivity of a solid electrolyte membrane, the membrane was placed in a 10 mm diameter polyether ether ketone (PEEK) support, and a titanium rod was used as the blocking electrode to measure the ionic conductivity.

[0158] The resistance was measured using an electrochemical impedance spectroscopy (EIS, VM3, Bio Logic Science Instrument) at 25 °C, with an amplitude of 10 mV and a scan range of 1 Hz to 0.1 MHz. The ionic conductivity of the solid electrolyte membrane was then calculated using Equation 1 below:

[0159] [Equation 1]

[0160]

[0161] Where, σ i R represents the ionic conductivity of the solid electrolyte membrane (mS / cm), R represents the resistance of the solid electrolyte membrane (Ω) measured by electrochemical impedance spectroscopy, L represents the thickness of the solid electrolyte membrane (μm), and A represents the area of ​​the solid electrolyte membrane (cm²). 2 ).

[0162] (2) Determination of tensile strength

[0163] The solid electrolyte membrane was cut into 10 mm × 50 mm pieces. To minimize damage to the solid electrolyte membrane caused by compression during the test, adhesive tape was applied to both ends of the specimen before the tensile strength was determined using a universal testing machine (UTM, MARK-10, M5-05).

[0164] Figure 3a This is a graph showing the correlation between the temperature of the calendering process and the tensile strength.

[0165] Reference Figure 3a It can be seen that the higher the temperature of the calendering process, the higher the tensile strength of the solid electrolyte membrane.

[0166] Figure 3b This is a graph showing the correlation between the orientation of the calendering process and the tensile strength. In this case, for Example 5 where the orientation of the calendering process is uniaxial, the tensile strength was measured in both the horizontal direction (uniaxial|) and the vertical direction (uniaxial┻) relative to the orientation of the calendering process.

[0167] refer to Figure 3b When the orientation of the rolling process is biaxial or uniaxial (|), the tensile strength is similar, or slightly higher with increasing rolling cycles in biaxial orientation. However, when the orientation of the rolling process is uniaxial, the tensile strength measured in the direction perpendicular to this orientation (uniaxial ┻) is significantly lower than that measured in biaxial or uniaxial (|) orientation relative to the rolling process level, and the tensile strength hardly increases even with increasing rolling cycles. This shows that when the orientation of the rolling process is uniaxial, the tensile strength is directional.

[0168] Figure 3c This is a graph showing the correlation between the number of calendering cycles and the ionic conductivity and tensile strength of the solid electrolyte membrane.

[0169] refer to Figure 3c It can be seen that even with the increase in the number of calendering cycles, the ionic conductivity of the solid electrolyte membrane did not change significantly, but the tensile strength increased.

[0170] This shows that the temperature, orientation, and number of cycles in the calendering process during the preparation of solid electrolyte membranes affect the fiberization of the binder and the structure formed by the fiberized binder, and are therefore closely related to the tensile strength of the solid electrolyte membrane.

[0171] In the foregoing, although the present invention has been described by way of limited embodiments and accompanying drawings, the present invention is not limited thereto, but can be modified and changed by those skilled in the art within the technical spirit of the present invention and the equivalent scope of the appended claims.

[0172] Key elements description:

[0173] 1: Solid electrolyte membrane

[0174] 10: Solid electrolytes (sulfide and / or halide electrolytes)

[0175] 20: Fiber-like adhesive

Claims

1. A method for preparing a solid electrolyte membrane, comprising: (S1) Mixing multiple solid electrolyte particles and a binder to form a mixture; and (S2) The mixture obtained in (S1) is subjected to a calendering process to form a solid electrolyte membrane; The adhesive is fiberized through the mixing process.

2. The method as described in claim 1, wherein, The temperature of the calendering process is 50°C to 200°C.

3. The method as described in claim 1, wherein, The calendering process is performed in 5 to 50 cycles.

4. The method of claim 1, wherein, The calendering process is performed in a single-axis or dual-axis manner.

5. The method of claim 1, wherein, (S1) and (S2) were carried out in the absence of solvent.

6. The method of claim 1, wherein, The solid electrolyte particles include one or more selected from the group consisting of sulfide solid electrolyte particles and halide solid electrolyte particles.

7. The method of claim 1, wherein, The solid electrolyte membrane is composed of solid electrolyte particles and fibrous binder.

8. The method of claim 7, wherein, The fibrous adhesive comprises one or more selected from the group consisting of polytetrafluoroethylene (PTFE) and copolymers containing PTFE.

9. The method of claim 7, wherein, Based on the total weight of the solid electrolyte membrane, the content of the fibrous adhesive is less than 2% by weight.

10. The method of claim 7, wherein, The fibrous adhesive is contained in the solid electrolyte membrane in a dispersed state.

11. The method of claim 7, wherein, The interface between the solid electrolyte particles and the fibrous adhesive is adhesive.

12. The method of claim 7, wherein, The ionic conductivity of the solid electrolyte membrane is from 0.5 S / cm to 10 S / cm.

13. The method of claim 7, wherein, The tensile strength of the solid electrolyte membrane is 45 kPa to 1000 kPa.

14. A solid electrolyte membrane prepared by the method of claim 1.

15. An all-solid-state battery comprising the solid electrolyte membrane of claim 14.

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