Solid electrolyte self-supporting membrane and preparation method thereof

Abstract

The invention relates to a solid electrolyte self-supporting membrane and a preparation method thereof. The method includes mixing a sulfide-based solid electrolyte powder with a fiberizable polymer powder to produce a mixture, applying a shear stress to fiberize the polymer, and rolling the mixture to form a film. The process parameters comprise the application of shear stress at 20-125 DEG C for 3-25 minutes and the rolling at 38-125 DEG C for 3-25 minutes. The mixture comprises 0.06 to 0.6% by weight of a fiberizable polymer. Particular variations include using a polymer powder having an average diameter of 1 [mu] m to 1000 [mu] m, performing a mixing step in the absence of a solvent, selecting a polymer type, such as PTFE. In addition, the method specifies the conditions under which shear stress and rolling are applied, as well as the diameter of the resulting polymer and the consistency of the mixture. The resulting solid electrolyte self-supporting membrane (comprising a sulfide-based solid electrolyte and a fiberized polymer) demonstrates a tensile strength of at least 0.2 MPa and a lithium ion conductivity of at least 3 mS / cm. The membrane is particularly suitable for use in all-solid-state batteries.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2024-0021203, filed on February 14, 2024, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a method for preparing a self-supporting solid electrolyte membrane and the resulting membrane. Specifically, the present invention belongs to the field of solid-state batteries, focusing on the formulation and manufacture of high-performance solid electrolyte membranes. These membranes are used in various electrochemical devices (including but not limited to all-solid-state lithium-ion batteries) to improve mechanical properties and ionic conductivity. The present invention also covers various aspects of materials science, particularly the use of sulfide-based solid electrolytes and fiberizable polymers to achieve improved battery performance. Background Art

[0004] Lithium secondary batteries have been developed as small power sources for smartphones, small electronic devices, and the like, and demand therefor is increasing with the development of electric vehicles.

[0005] Lithium secondary batteries consist of anode and cathode materials that can transfer and receive lithium ions, as well as an electrolyte responsible for transporting the ions. Typical lithium secondary batteries use a liquid electrolyte composed of a lithium salt dissolved in an organic solvent and include a separator made of organic fibers that prevents physical contact between the anode and cathode to prevent short circuits. Because flammable organic solvents are used as electrolyte solvents, the potential for fire or explosion is high in the event of a short circuit caused by physical damage, and numerous accidents have occurred.

[0006] All-solid-state batteries use inorganic solid electrolytes instead of flammable liquid electrolytes. Oxide-based solid electrolytes and sulfide-based solid electrolytes are the main inorganic solid electrolytes. Sulfide-based solid electrolytes are particularly promising because their lithium-ion conductivity is sufficiently high, approaching that of liquid electrolytes.

[0007] However, sulfide-based solid electrolytes have poor mechanical properties, resulting in poor processability and battery stability. Furthermore, sulfide-based solid electrolytes tend to break when pressure is applied, making large-scale production difficult. Currently, sulfide-based solid electrolytes are used in pellet form by applying pressure to powdered solid electrolytes on a small scale.

[0008] Therefore, as a method for large-scale production of sulfide-based solid electrolytes, a method of co-coating a sulfide-based solid electrolyte with a separator used in existing lithium-ion batteries has been proposed. However, due to the increase in the resistance of the separator, the advantage of the excellent lithium ion conductivity of the sulfide-based solid electrolyte is offset. Since the thickness of the separator cannot be reduced, it is difficult to reduce the thickness of the entire membrane to a certain level or below. Moreover, since a solvent is used in the coating process, the performance of the solid electrolyte is affected.

[0009] To address these issues, a method for preparing a self-supporting membrane containing a sulfide-based solid electrolyte using a binder dissolved in a solvent has been proposed. However, in this case, the lithium ion conductivity of the sulfide-based solid electrolyte is reduced by the solvent due to the poor chemical stability of the sulfide-based solid electrolyte. Summary of the Invention

[0010] The present invention has solved the above-mentioned problems arising in the prior art while completely maintaining the advantages achieved by the prior art.

[0011] One aspect of the present invention provides a method for preparing a solid electrolyte with improved ionic conductivity by minimizing the binder content.

[0012] In some embodiments, the method for preparing a solid electrolyte self-supporting membrane comprises mixing a sulfide-based solid electrolyte powder with a fiberizable polymer powder to produce a mixture, applying shear stress to the mixture to fiberize the fiberizable polymer powder, and rolling the obtained mixture to obtain a solid electrolyte self-supporting membrane. The shear stress applying step is performed at a temperature range of about 20°C to about 125°C for about 3 minutes to about 25 minutes. The rolling step is performed at a temperature range of about 38°C to about 125°C for about 3 minutes to about 25 minutes. Based on the total weight of the mixture, the mixture comprises a fiberizable polymer powder in an amount of about 0.06 wt% to about 0.6 wt%.

[0013] The average diameter (D50) of the fiberizable polymer powder may be from about 1 μm to about 1000 μm. The mixing step may be performed without using a solvent. The rolling step may be performed at a temperature range of from about 50° C. to about 100° C. The rolling step may be performed for from about 5 minutes to about 20 minutes. The fiberizable polymer powder may include polytetrafluoroethylene (PTFE). The average diameter (D50) of the sulfide-based solid electrolyte may be from about 0.35 μm to about 4 μm. The sulfide-based solid electrolyte powder may be selected from Li2S-P2S5, Li6PS5Cl 0.5 Br 0.5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-Si S2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, Z is one of Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP2S 12 or a combination thereof. The diameter of the fiberized polymer produced in the shear stress application step may be from about 0.01 μm to about 10 μm. The shear stress application step may be performed at a temperature ranging from about 25° C. to about 100° C. The rolling step may be performed using a rolling device. After the shear stress application step, the mixture may have a clay-like consistency.

[0014] In some embodiments, the solid electrolyte self-supporting membrane comprises a sulfide-based solid electrolyte and a fiberized polymer, wherein the fiberized polymer is present in an amount of about 0.1 wt % to about 0.5 wt % based on the total weight of the solid electrolyte self-supporting membrane. The tensile strength of the solid electrolyte self-supporting membrane may be equal to or greater than about 0.2 MPa. The lithium ion conductivity of the membrane may be equal to or greater than about 3 mS / cm. Based on the total weight of the solid electrolyte self-supporting membrane, the sulfide-based solid electrolyte may be present in an amount of about 99.4 wt % to about 99.9 wt %. The diameter of the fiberized polymer may be about 0.01 μm to about 10 μm. The thickness of the solid electrolyte self-supporting membrane may be about 100 μm. The sulfide-based solid electrolyte may be selected from Li2S-P2S5, Li6PS5Cl 0.5 Br 0.5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-Si S2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, Z is one of Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP2S 12 or a combination thereof. The all-solid-state battery may include a solid electrolyte self-supporting membrane. DETAILED DESCRIPTION

[0015] The present invention will be described in more detail below to help understand the present invention. In this regard, the terms or words used herein or in the claims should not be interpreted as limited to their ordinary meanings or dictionary meanings, but should be interpreted with meanings and concepts consistent with the technical ideas of the present invention based on the principle that the inventors can appropriately define the concepts of the terms to describe the present invention in the best manner.

[0016] It should be understood that the terms "vehicle" or "vehicular" or other similar terms used herein generally include motor vehicles, such as passenger cars including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft including various boats and ships, aircraft, etc., including hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum energy sources). As referred to herein, a hybrid vehicle is a vehicle that has two or more power sources, such as a vehicle that has both gasoline and electric power.

[0017] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms "one", "an" and "described" are also intended to include plural forms. These terms are only intended to distinguish one component from another component, and the terms do not limit the characteristics, order or sequence of the components. As used herein, the term "and / or" includes any combination and all combinations of one or more related enumerated items. Throughout the specification, unless clearly described to the contrary, the term "including" and variations such as "comprising" or "containing" will be understood to mean comprising the elements, but do not exclude any other elements. In addition, the terms "unit", "-device", "-part" and "module" described in this specification mean a unit for performing at least one function and operation, and can be implemented by hardware components or software components and combinations thereof.

[0018] Although the exemplary embodiments are described as using multiple units to perform the exemplary processes, it should be understood that the exemplary processes can also be performed by one or more modules. Furthermore, it should be understood that the term controller / control unit refers to a hardware device that includes a memory and a processor and is specifically programmed to perform the processes described herein. The memory is configured to store the modules, and the processor is specifically configured to execute the modules, thereby performing one or more processes described further below.

[0019] Furthermore, the control logic of the present invention may be embodied as non-transitory computer-readable media on a computer-readable medium, including executable program instructions executed by a processor, controller, or the like. Examples of computer-readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices. The computer-readable medium may also be distributed among network-connected computer systems so that the computer-readable medium is stored and executed in a distributed manner, for example, by a telematics server or a controller area network (CAN).

[0020] Unless otherwise stated or obvious from the context, as used herein, the term "about" is understood to mean within the normal tolerance range in the art, for example, within 2 standard deviations of the mean. "About" can be understood to mean within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the specified value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term "about."

[0021] In the present invention, the term "average particle diameter (D 50 )" represents the particle diameter at the 50% point of the cumulative volume distribution based on the particle diameter. The average particle diameter D50 The measurement can be performed by dispersing the powder to be measured in a dispersion medium, introducing the product into a commercially available laser diffraction particle size measuring apparatus (e.g., Microtrac's S3500), measuring the difference in diffraction patterns depending on the particle size when the particles pass through a laser beam, thereby calculating the particle size distribution, and then calculating the particle diameter at a point at which 50% of the cumulative volume distribution based on the diameters in the measuring apparatus is achieved.

[0022] <Method for producing a solid electrolyte self-supporting membrane>

[0023] The present invention provides a method for preparing a solid electrolyte self-supporting membrane.

[0024] The method for preparing a solid electrolyte self-supporting membrane of the present invention includes mixing a sulfide-based solid electrolyte powder with a fiberizable polymer powder (S1); applying shear stress to the product of step S1 to fiberize the fiberizable polymer powder (S2); and rolling the product of step S2 to obtain a solid electrolyte self-supporting membrane (S3), wherein step S3 is performed at a temperature equal to or greater than 38°C and equal to or less than 125°C for 3 minutes or more and 25 minutes or less, and the product of step S1 contains the polymer powder in an amount equal to or greater than 0.06% by weight and equal to or less than 0.6% by weight.

[0025] Generally, it is known that as the content of fibrillable polymer powder in the prepared solid electrolyte self-supporting membrane decreases, the ionic conductivity increases, but the mechanical properties (such as tensile strength) decrease. The inventors of the present invention have discovered a preparation method that can significantly improve not only the ionic conductivity of the prepared solid electrolyte self-supporting membrane but also the tensile strength, even when the content of fibrillable polymer powder is minimized, and have completed the present invention.

[0026] Each step of the method for preparing a solid electrolyte self-supporting membrane according to an embodiment of the present invention will be described below.

[0027] 1. Step S1

[0028] A method for preparing a solid electrolyte self-supporting membrane according to an embodiment of the present invention may include mixing sulfide-based solid electrolyte powder with fiberizable polymer powder ( S1 ).

[0029] According to an embodiment of the present invention, the sulfide-based solid electrolyte constituting the sulfide-based solid electrolyte powder may be Li2S-P2S5, Li6PS5Cl 0.5 Br 0.5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-Si S2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, Z is one of Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP2S 12 or any combination thereof.

[0030] According to an embodiment of the present invention, the average diameter (D 50 ) may be equal to or greater than 0.35 μm and equal to or less than 4 μm. As a specific example, it may be equal to or greater than 0.4 μm, equal to or greater than 0.45 μm, equal to or greater than 0.5 μm, equal to or greater than 0.55 μm, or equal to or greater than 0.6 μm. In addition, it may be equal to or less than 3.8 μm, equal to or less than 3.6 μm, equal to or less than 3.4 μm, equal to or less than 3.2 μm, and equal to or less than 3 μm. When the average diameter of the sulfide-based solid electrolyte powder satisfies the above range, the mechanical properties of the prepared solid electrolyte self-supporting film can be improved.

[0031] According to an embodiment of the present invention, the sulfide-based solid electrolyte powder may be included in an amount equal to or greater than 99.4% by weight and equal to or less than 99.9% by weight relative to the product of step S1. As a specific example, the sulfide-based solid electrolyte powder may be included in an amount equal to or greater than 99.42% by weight, equal to or greater than 99.44% by weight, equal to or greater than 99.46% by weight, equal to or greater than 99.48% by weight, or equal to or greater than 99.5% by weight. In addition, the sulfide-based solid electrolyte powder may be included in an amount equal to or less than 99.8% by weight, equal to or less than 99.7% by weight, equal to or less than 99.6% by weight, or equal to or less than 99.5% by weight. When the content of the sulfide-based solid electrolyte powder satisfies the above range, the lithium ion conductivity and tensile strength of the prepared solid electrolyte self-supporting film can be improved. When the content of the sulfide-based solid electrolyte powder exceeds the above range, the mechanical properties of the prepared solid electrolyte self-supporting film may not be ensured, and when the content of the sulfide-based solid electrolyte powder is less than the above range, the lithium ion conductivity and tensile strength may be reduced.

[0032] According to an embodiment of the present invention, the fiberizable polymer may be any one of butadiene rubber (BR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) or a combination thereof, and as a specific example, may be PTFE.

[0033] Polytetrafluoroethylene (PTFE) is a polymer in which all hydrogen elements of polyethylene (PE) are replaced by fluorine elements. Although polytetrafluoroethylene (PTFE) is a polymer with an aliphatic main chain, PTFE has excellent thermal stability and electrical stability and is widely used in the field of electronic materials. In particular, PTFE is mainly used in anodes because the polymer has a lower highest occupied molecular orbital (HOMO) energy level and therefore has higher oxidative stability. Since polytetrafluoroethylene (PTFE) has a cylindrical structure, although PTFE has a higher glass transition temperature (Tg), it can also be fiberized, even at lower temperatures.

[0034] According to an embodiment of the present invention, the average diameter (D 50 ) may be equal to or greater than 1 μm and equal to or less than 1000 μm. As a specific example, the average diameter (D 50) may be equal to or greater than 10 μm, equal to or greater than 50 μm, equal to or greater than 100 μm, or equal to or greater than 150 μm, and may be equal to or less than 900 μm, equal to or less than 800 μm, equal to or less than 700 μm, or equal to or less than 600 μm. When the average diameter of the fibrillable polymer powder satisfies the above range, the mechanical properties of the prepared solid electrolyte self-supporting membrane can be improved.

[0035] According to an embodiment of the present invention, relative to the product of step S1, the fiberizable polymer powder may be included in an amount equal to or greater than 0.1 wt% and equal to or less than 0.6 wt%. As a specific example, the fiberizable polymer powder may be included in an amount equal to or greater than 0.15 wt%, equal to or greater than 0.2 wt%, equal to or greater than 0.25 wt%, equal to or greater than 0.3 wt%, equal to or greater than 0.35 wt%, or equal to or greater than 0.4 wt%. In addition, the fiberizable polymer powder may be included in an amount equal to or less than 0.58 wt%, equal to or less than 0.56 wt%, equal to or less than 0.54 wt%, equal to or less than 0.52 wt%, or equal to or less than 0.5 wt%. When the content of the fiberizable polymer powder satisfies the above range, the lithium ion conductivity and tensile strength of the prepared solid electrolyte self-supporting membrane can be improved. When the content of the fibrillizable polymer powder exceeds the above range, lithium ion conductivity and tensile strength may decrease, and when the content of the fibrillizable polymer powder is less than the above range, mechanical properties of the prepared solid electrolyte self-supporting membrane may not be ensured.

[0036] According to an embodiment of the present invention, in step S1 , ie, when mixing the sulfide-based solid electrolyte powder and the fiberizable polymer powder, solid-phase mixing may be performed without using a separate solvent.

[0037] Existing self-supporting film-based solid electrolyte layers are prepared by placing a separator or nonwoven fabric at the center, applying a slurry containing a solid electrolyte to one or both surfaces, and drying the slurry. However, the slurry viscosity must be low to allow the solid electrolyte to penetrate the pores of the nonwoven fabric, resulting in very poor processability. Furthermore, during the drying process of the slurry, voids are formed due to the removal of the solvent, which deteriorates the mechanical and electrochemical properties of the solid electrolyte layer. Furthermore, the nonwoven fabric not only acts as a resistor but also prevents the solid electrolyte from being evenly distributed within the solid electrolyte layer, significantly reducing lithium ion conductivity.

[0038] The present invention applies shear stress to a mixture comprising a sulfide-based solid electrolyte and a fiberizable polymer powder without a separate solvent to convert the mixture into a clay-like material, thereby achieving a solid electrolyte self-supporting film comprising a sulfide-based solid electrolyte and a fiberized polymer, thereby solving the above-mentioned problems. Since the fiberized polymer is entangled with the sulfide-based solid electrolyte, the mechanical properties are improved, and the solid electrolyte self-supporting film can maintain its shape. In addition, since the contact between the fiberized polymer and the sulfide-based solid electrolyte is minimized, the decrease in lithium ion conductivity may be significantly reduced compared to the case of using an adhesive dissolved in a solvent.

[0039] In other words, the method for preparing a solid electrolyte self-supporting film according to the present invention does not use a solvent to prevent the sulfide-based solid electrolyte from being chemically converted by the solvent, thereby preventing a decrease in lithium ion conductivity and preventing problems such as a decrease in adhesion caused by a biting phenomenon of the binder during the solvent removal process.

[0040] 2. Step S2

[0041] The method for preparing a solid electrolyte self-supporting membrane according to an embodiment of the present invention may include applying shear stress to the product of step S1 to fiberize the fiberizable polymer powder ( S2 ).

[0042] According to an embodiment of the present invention, when shear stress is applied to the mixture comprising sulfide-based solid electrolyte powder and fiberizable polymer powder (ie, the product of step S1), the fiberizable polymer powder is converted into a fiberized polymer, thereby generating a product converted into a clay-like material.

[0043] According to an embodiment of the present invention, the diameter of the fiberized polymer may be equal to or greater than 0.01 μm and equal to or less than 10 μm. As a specific example, the diameter of the fiberized polymer may be equal to or greater than 0.02 μm, equal to or greater than 0.04 μm, equal to or greater than 0.06 μm or equal to or greater than 0.1 μm. In addition, the diameter of the fiberized polymer may be equal to or less than 8 μm, equal to or less than 6 μm, equal to or less than 4 μm and equal to or less than 2 μm. The diameter of the fiberized polymer represents the diameter of the cross section cut in a direction perpendicular to the length direction of the fiberized polymer. When the diameter of the fiberized polymer is less than the above range, the mechanical properties of the solid electrolyte self-supporting membrane may be insufficient, and when the diameter exceeds the above range, the lithium ion conductivity may be reduced.

[0044] According to the embodiment of the present invention, shear stress may be applied using an apparatus or method commonly used in the technical field to which the present invention pertains.

[0045] According to an embodiment of the present invention, step S2 can be performed at a temperature equal to or greater than 20°C and equal to or less than 125°C. As a specific example, step S2 can be performed at a temperature equal to or greater than 22°C, equal to or greater than 24°C, or equal to or greater than 25°C and equal to or less than 120°C, equal to or less than 115°C, equal to or less than 110°C, equal to or less than 105°C, or equal to or less than 100°C. When step S2 is performed within the above temperature range, the fiberizable polymer powder can be easily converted into a fiberizable polymer. Therefore, even when the content of the fiberizable polymer powder is equal to or less than 0.6% by weight, the prepared solid electrolyte self-supporting membrane can also ensure excellent ionic conductivity and tensile strength at the same time.

[0046] According to an embodiment of the present invention, step S2 can be carried out for 3 minutes or longer and 25 minutes or shorter. As a specific example, step S2 can be carried out for 3.5 minutes or longer, 4 minutes or longer, 4.5 minutes or longer or 5 minutes or longer, and can be carried out for 24 minutes or shorter, 23 minutes or shorter, 22 minutes or shorter, 21 minutes or shorter or 20 minutes or shorter. When step S2 is carried out within the process time range, the fibrous polymer powder can be easily converted into a fibrous polymer. Therefore, even when the content of the fibrous polymer powder is equal to or less than 0.6 weight %, the prepared solid electrolyte self-supporting membrane can also ensure excellent ionic conductivity and tensile strength at the same time.

[0047] 3. Step S3

[0048] The method for preparing a solid electrolyte self-supporting membrane according to an embodiment of the present invention may include rolling the product of step S2 to obtain the solid electrolyte self-supporting membrane ( S3 ).

[0049] According to an embodiment of the present invention, in step S3, that is, when obtaining a solid electrolyte self-supporting film, any method of preparing a clay-like material as a solid electrolyte film by placing a roller on the product prepared in step S2 and rolling the roller can be applied to rolling, and the present invention may not be limited to any specific method. For example, rolling can be performed by placing the product prepared in step S2 (i.e., the clay-like material) and then manually rolling the roller, or it can be performed using a device such as a rolling device. Specifically, rolling can be performed by placing a roller on the clay-like material prepared in step S2 and manually rolling the roller, or it can be performed using a device such as a rolling device, thereby preparing the clay-like material as a solid electrolyte film.

[0050] Because rolling is performed directly on the clay-like material, it differs from the calendering process, which pulverizes the clay-like material into a powder and then places the powder between two rollers to form a solid electrolyte membrane through the rotation and pressure of the rollers. In other words, the rolling in step S3 is performed immediately without pulverizing the product of step S2, thereby simplifying the process and improving the degree of fiberization of the fiberizable polymer powder.

[0051] According to an embodiment of the present invention, step S3 can be performed at a temperature equal to or greater than 38°C and equal to or less than 125°C. As a specific example, step S3 can be performed at a temperature equal to or greater than 40°C, equal to or greater than 42°C, equal to or greater than 44°C, equal to or greater than 46°C, equal to or greater than 48°C, or equal to or greater than 50°C, and can be performed at a temperature equal to or less than 120°C, equal to or less than 115°C, equal to or less than 110°C, equal to or less than 105°C, or equal to or less than 100°C. When step S3 is performed within the above temperature range, a solid electrolyte self-supporting membrane can be easily obtained. Therefore, even when the content of the fiberizable polymer powder is equal to or less than 0.6% by weight, the prepared solid electrolyte self-supporting membrane can simultaneously ensure excellent ionic conductivity and tensile strength.

[0052] According to an embodiment of the present invention, step S3 can be carried out for 3 minutes or longer and 25 minutes or shorter. As a specific example, step S3 can be carried out for 3.5 minutes or longer, 4 minutes or longer, 4.5 minutes or longer or 5 minutes or longer, and can be carried out for 24 minutes or shorter, 23 minutes or shorter, 22 minutes or shorter, 21 minutes or shorter or 20 minutes or shorter. When step S3 is carried out within the process time range, the fibrous polymer powder can be easily converted into a fibrous polymer. Therefore, even when the content of the fibrous polymer powder is equal to or less than 0.6 weight %, the prepared solid electrolyte self-supporting membrane can also ensure excellent ionic conductivity and tensile strength at the same time.

[0053] <Solid Electrolyte Self-Supporting Membrane>

[0054] The present invention provides a solid electrolyte self-supporting membrane prepared using the method for preparing a solid electrolyte self-supporting membrane.

[0055] A solid electrolyte self-supporting film according to an embodiment of the present invention includes a sulfide-based solid electrolyte and a fiberized polymer, wherein the fiberized polymer is included in an amount equal to or greater than 0.06 wt % and equal to or less than 0.6 wt %.

[0056] According to an embodiment of the present invention, a sulfide-based solid electrolyte is a component corresponding to the sulfide-based solid electrolyte powder in the preparation method. Relative to the solid electrolyte self-supporting film, the sulfide-based solid electrolyte can be included in an amount equal to or greater than 99.4% by weight and equal to or less than 99.9% by weight. As a specific example, the sulfide-based solid electrolyte can be included in an amount equal to or greater than 99.42% by weight, equal to or greater than 99.44% by weight, equal to or greater than 99.46% by weight, equal to or greater than 99.48% by weight, or equal to or greater than 99.5% by weight. In addition, the sulfide-based solid electrolyte can be included in an amount equal to or less than 99.8% by weight, equal to or less than 99.7% by weight, equal to or less than 99.6% by weight, or equal to or less than 99.5% by weight. When the content of the sulfide-based solid electrolyte meets the above range, the lithium ion conductivity and tensile strength of the solid electrolyte self-supporting film can be improved. When the content of the sulfide-based solid electrolyte exceeds the above range, mechanical properties of the solid electrolyte self-supporting film may not be ensured, and when the content is less than the above range, lithium ion conductivity and tensile strength may decrease.

[0057] According to an embodiment of the present invention, a fibrillating polymer is a component corresponding to a fibrillating polymer in a preparation method. Relative to a solid electrolyte self-supporting membrane, a fibrillating polymer may be included in an amount equal to or greater than 0.1 wt % and equal to or less than 0.6 wt %, as a specific example, a fibrillating polymer may be included in an amount equal to or greater than 0.15 wt %, equal to or greater than 0.2 wt %, equal to or greater than 0.25 wt %, equal to or greater than 0.3 wt %, equal to or greater than 0.35 wt % or equal to or greater than 0.4 wt %, and furthermore, a fibrillating polymer may be included in an amount equal to or less than 0.58 wt %, equal to or less than 0.56 wt %, equal to or less than 0.54 wt %, equal to or less than 0.52 wt % or equal to or less than 0.5 wt %. When the content of the fibrillating polymer meets the above range, the lithium ion conductivity and tensile strength of the solid electrolyte self-supporting membrane can be improved. When the content of the fiberizable polymer powder exceeds the above range, lithium ion conductivity and tensile strength may decrease, and when the content is less than the above range, mechanical properties of the prepared solid electrolyte self-supporting membrane may not be ensured.

[0058] The solid electrolyte self-supporting film according to an embodiment of the present invention can ensure excellent tensile strength while satisfying excellent lithium ion conductivity.

[0059] Specifically, the solid electrolyte self-supporting membrane according to an embodiment of the present invention may have a tensile strength measured based on ASTM D638 equal to or greater than 0.2 MPa. As a specific example, the tensile strength may be equal to or greater than 0.25 MPa, equal to or greater than 0.3 MPa, equal to or greater than 0.35 MPa, or equal to or greater than 0.4 MPa.

[0060] In addition, the solid electrolyte self-supporting film according to an embodiment of the present invention can have a lithium ion conductivity measured using a PotentioStat (SP-200, Biologics) at room temperature (25° C.) with an amplitude of 10 mV and a measurement frequency range of 0.1 Hz to 7 Hz. It can be equal to or greater than 3 mS / cm. As a specific example, the lithium ion conductivity can be equal to or greater than 3.2 mS / cm, equal to or greater than 3.4 mS / cm, equal to or greater than 3.6 mS / cm, equal to or greater than 3.8 mS / cm, or equal to or greater than 4 mS / cm.

[0061] <All-solid-state battery>

[0062] The present invention provides an all-solid-state battery comprising a solid electrolyte self-supporting membrane.

[0063] According to an embodiment of the present invention, the all-solid-state battery can be a stack of an anode current collector, an anode active material layer, a solid electrolyte self-supporting membrane, a cathode active material layer, and a cathode current collector. Since the description of the solid electrolyte self-supporting membrane is the same as that above, its detailed description will be omitted.

[0064] According to an embodiment of the present invention, the anode current collector may be a conductive plate-shaped substrate. Specifically, the anode current collector may be in the form of a sheet, a film, or a foil.

[0065] According to an embodiment of the present invention, the anode current collector may include a material that does not react with lithium. Specifically, the anode current collector may include at least one selected from Ni, Cu, stainless steel (SUS), and a combination thereof.

[0066] According to an embodiment of the present invention, the anode active material layer may include an anode active material, a solid electrolyte, a binder, and the like.

[0067] According to an embodiment of the present invention, the anode active material may not be particularly limited, but may be, for example, a carbon active material or a metal active material.

[0068] According to an embodiment of the present invention, the carbon active material may be graphite (eg, mesocarbon microbeads (MCMB) and highly oriented pyrolytic graphite (HOPG)) and amorphous carbon (eg, hard carbon and soft carbon).

[0069] According to an embodiment of the present invention, the metallic active material may be In, Al, Si, Sn, and an alloy containing at least one of these elements.

[0070] According to an embodiment of the present invention, the solid electrolyte may be an oxide-based solid electrolyte or a sulfide-based solid electrolyte. It is desirable to use a sulfide-based solid electrolyte having a high lithium ion conductivity. Since the sulfide-based solid electrolyte has been described above, its detailed description will be omitted hereinafter.

[0071] According to an embodiment of the present invention, the conductive material is a component that forms an electron conduction path within the electrode. The conductive material may be an sp2 carbon material such as carbon black, conductive graphite, acetylene black, carbon nanotubes, or graphene.

[0072] According to an embodiment of the present invention, the binder may be butadiene rubber (BR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc.

[0073] According to an embodiment of the present invention, the cathode active material layer may contain a cathode active material, a solid electrolyte, a conductive material, a binder, etc.

[0074] According to an embodiment of the present invention, the cathode active material may not be particularly limited, but may be, for example, an oxide active material or a sulfide active material.

[0075] According to an embodiment of the present invention, the oxide active material may be a rock salt layer type active material (such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and Li 1+x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2), a spinel type active material (such as LiMn2O4 and Li(Ni 0.5 Mn 1.5 )O)4), an inverse spinel type active material (such as LiNiVO4 and LiCoVO4), an olivine type active material (such as LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4), a silicon-containing active material (such as Li2FeSiO4 and Li2MnSiO4), a rock salt layer type active material in which a part of the transition metal is replaced by a foreign metal (such as LiNi 0.8 Co (0.2-x) Al x O2(0 < x < 0.2)), a spinel type active material in which a part of the transition metal is replaced by a foreign metal (such as Li 1+x Mn 2-x-y M yO4 (where M is at least one of Al, Mg, Co, Fe, Ni, and Zn and 0 < x + y < 2)) and lithium titanium oxide (e.g., Li4Ti5O 12 ).

[0076] According to an embodiment of the present invention, the sulfide active material may be Chevrel copper, iron sulfide, cobalt sulfide, nickel sulfide, etc.

[0077] According to an embodiment of the present invention, the solid electrolyte may be an oxide-based solid electrolyte or a sulfide-based solid electrolyte. It is desirable to use a sulfide-based solid electrolyte having a high lithium ion conductivity.

[0078] According to an embodiment of the present invention, the conductive material and the binder are the same as those described above, and thus their detailed descriptions will be omitted.

[0079] According to an embodiment of the present invention, the cathode current collector may be a conductive plate-like substrate. Specifically, the cathode current collector may have the form of a sheet or a film.

[0080] According to an embodiment of the present invention, the cathode current collector may include at least one selected from indium, copper, magnesium, aluminum, stainless steel, iron, and combinations thereof.

[0081] According to an embodiment of the present invention, the solid electrolyte self-supporting film is a component located between the anode active material layer and the cathode active material layer and responsible for lithium ion movement.

[0082] Examples of the present invention will be described in detail below so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the examples described herein.

[0083] Reference Example, Example, and Comparative Example

[0084] Reference Example 1

[0085] Using a mixer, 99.5 wt% of sulfide-based solid electrolyte Li6PS5Cl with an average diameter of 3 μm 0.5 Br 0.5 powder and 0.5 wt% of polytetrafluoroethylene powder with an average diameter of 500 μm were mixed with each other in the solid phase without using a separate solvent. Then, the mixture of the sulfide-based solid electrolyte powder and the polytetrafluoroethylene powder was placed in a mortar, and then a shear stress was applied at 100 °C for 2 minutes. Then, it was determined that the polytetrafluoroethylene powder was fibrillated and the mixture became a clay-like material.

[0086] Then, the clay-like product was placed on a steel plate at a temperature of 100 °C and manually roll-pressed for 3 minutes to prepare a 100-μm-thick solid electrolyte self-supporting film.

[0087] Reference Example 2

[0088] A solid electrolyte self-supporting film was prepared in the same manner as in Reference Example 1, except that 99 wt % of sulfide-based solid electrolyte powder and 1 wt % of polytetrafluoroethylene powder were mixed with each other, and then shear stress was applied for 2 minutes and manual rolling was performed for 3 minutes.

[0089] Reference Example 3

[0090] A solid electrolyte self-supporting film was prepared in the same manner as in Reference Example 1, except that 97.5 wt % of the sulfide-based solid electrolyte powder and 2.5 wt % of the polytetrafluoroethylene powder were mixed with each other.

[0091] Example 1

[0092] A mixer was used to make 99.5 wt% of the sulfide-based solid electrolyte Li6PS5Cl with an average diameter of 3 μm. 0.5 Br 0.5 The powder was mixed with 0.5% by weight of polytetrafluoroethylene powder with an average diameter of 500 μm in a solid phase, rather than using a separate solvent. The mixture of the sulfide-based solid electrolyte powder and polytetrafluoroethylene powder was then placed in a mortar and subjected to shear stress at 100°C for 5 minutes. The polytetrafluoroethylene powder was then confirmed to be fibrillated, and the mixture transformed into a clay-like material.

[0093] Then, the clay-like product was placed on a steel plate at a temperature of 100°C and manually rolled for 3 minutes to prepare a 100 μm thick solid electrolyte self-supporting membrane.

[0094] Example 2

[0095] A solid electrolyte self-supporting membrane was prepared in the same manner as in Example 1, except that the clay-like product was manually rolled for 20 minutes.

[0096] Example 3

[0097] A solid electrolyte self-supporting film was prepared in the same manner as in Example 1, except that after the mixture of the sulfide-based solid electrolyte powder and the polytetrafluoroethylene powder was placed in a mortar, shear stress was applied for 20 minutes.

[0098] Example 4

[0099] A solid electrolyte self-supporting film was prepared in the same manner as in Example 1, except that the clay-like product was manually rolled at 50° C. for 20 minutes.

[0100] Example 5

[0101] A solid electrolyte self-supporting film was prepared in the same manner as in Example 1, except that after the mixture of the sulfide-based solid electrolyte powder and the polytetrafluoroethylene powder was placed in a mortar, shear stress was applied at 50° C. for 5 minutes.

[0102] Example 6

[0103] A solid electrolyte self-supporting film was prepared in the same manner as in Example 1, except that shear stress was applied at 25° C. after the mixture of the sulfide-based solid electrolyte powder and the polytetrafluoroethylene powder was placed in a mortar.

[0104] Example 7

[0105] A solid electrolyte self-supporting film was prepared in the same manner as in Example 1, except that the clay-like product was manually rolled at 100° C. for 5 minutes.

[0106] Comparative Example 1

[0107] A mixer was used to make 99.5 wt% of the sulfide-based solid electrolyte Li6PS5Cl with an average diameter of 3 μm. 0.5 Br 0.5 The powder was mixed with 0.5% by weight of polytetrafluoroethylene powder having an average diameter of 500 μm in a solid phase without using a separate solvent. The mixture of the sulfide-based solid electrolyte powder and the polytetrafluoroethylene powder was then placed in a mortar and subjected to shear stress at room temperature (25°C) for 5 minutes. It was then confirmed that the polytetrafluoroethylene powder was fibrillated and the mixture became a clay-like material.

[0108] The clay-like product was calendered to prepare a 100 μm thick solid electrolyte free-standing membrane.

[0109] Comparative Example 2

[0110] A solid electrolyte self-supporting membrane was prepared in the same manner as in Example 1 above, except that the clay-like product was manually rolled for 1 minute.

[0111] Comparative Example 3

[0112] A solid electrolyte self-supporting membrane was prepared in the same manner as in Example 1 above, except that the clay-like product was manually rolled at a temperature of 25° C. for 10 minutes.

[0113] Comparative Example 4

[0114] A solid electrolyte self-supporting membrane was prepared in the same manner as in Example 1 above, except that the clay-like product was manually rolled at a temperature of 150° C. for 10 minutes.

[0115] Comparative Example 5

[0116] A solid electrolyte self-supporting film was prepared in the same manner as in Example 1 above, except that a mixture of the sulfide-based solid electrolyte powder and the polytetrafluoroethylene powder was placed in a mortar and shear stress was applied for 1 minute.

[0117] Comparative Example 6

[0118] A solid electrolyte self-supporting film was prepared in the same manner as in Example 1 above, except that a mixture of the sulfide-based solid electrolyte powder and the polytetrafluoroethylene powder was placed in a mortar and shear stress was applied at 150°C.

[0119] Experimental Examples

[0120] Lithium ion conductivity (mS / cm): For the solid electrolyte self-supporting membranes prepared in the Reference Example, Examples, and Comparative Examples in a mold having a diameter of Φ13 mm, the ion conductivity was measured using a PotentioStat (SP-200, Biologics) with an amplitude of 10 mV and a measurement frequency range of 0.1 Hz to 7 Hz, and is described in Tables 1 to 3 below.

[0121] Tensile Strength (MPa): For the solid electrolyte self-supporting membranes prepared in the Reference Example, Examples, and Comparative Examples, specimens having a width of 10 mm and a length of 20 mm were obtained. The tensile strength of the specimens was measured at a crosshead speed of 10 mm / min according to ASTM D638, and is shown in Tables 1 to 3 below.

[0122]

Table 1

[0123]

[0124]

[0125]

Table 2

[0126]

[0127]

Table 3

[0128]

[0129] Referring to Table 1 above, it can be seen that as the content of polytetrafluoroethylene powder decreases, the lithium ion conductivity increases, but the tensile strength decreases.

[0130] Referring to Tables 1 and 2 above, in the case of Examples 1 to 7 satisfying the appropriate shear stress application time / temperature and the appropriate manual rolling application time / temperature range, it can be seen that even if the content of polytetrafluoroethylene powder is relatively low compared to Reference Examples 2 and 3, the degree of fiberization is increased, and thus the lithium ion conductivity and tensile strength are simultaneously improved.

[0131] Referring to Tables 2 and 3 above, in the case of Comparative Examples 2 to 6, which did not meet the appropriate shear stress application time / temperature and the appropriate manual rolling application time / temperature range, it can be seen that the lithium ion conductivity and tensile strength were inferior compared to Examples 1 to 7, which met the appropriate shear stress application time / temperature and the appropriate manual rolling application time / temperature range. In particular, in the case of Comparative Example 4, which exceeded the appropriate manual rolling application temperature range, and Comparative Example 6, which exceeded the appropriate shear stress application temperature range, defects occurred in the prepared solid electrolyte self-supporting membrane, and therefore the lithium ion conductivity and tensile strength could not be measured.

[0132] Furthermore, in the case of Comparative Example 1 in which calendaring was performed instead of manual rolling, since the content of polytetrafluoroethylene powder was low and fiberization was not sufficiently performed, a solid electrolyte self-supporting membrane could not be prepared.

[0133] The solid electrolyte self-supporting membrane according to an embodiment of the present invention has excellent ion conductivity and tensile strength.

[0134] According to the method for producing a solid electrolyte self-supporting membrane according to an embodiment of the present invention, a solid electrolyte self-supporting membrane having improved lithium ion conductivity and tensile strength can be obtained.

[0135] Although the present invention has been described above with reference to exemplary embodiments, the present invention is not limited thereto but may be variously changed and modified by those skilled in the art without departing from the spirit and scope of the invention as claimed in the appended claims.

Claims

1. A method for preparing a solid electrolyte self-supporting membrane, the method comprising: a) mixing sulfide-based solid electrolyte powder and fiberizable polymer powder to produce a mixture of electrolyte powder and fiberizable polymer powder; b) applying shear stress to the mixture of step a) to fiberize the fiberizable polymer powder; and c) rolling the mixture obtained in step b) to obtain a solid electrolyte self-supporting membrane, wherein step b) is carried out at a temperature ranging from 20°C to 125°C for 3 minutes to 25 minutes, Step c) is carried out at a temperature ranging from 38°C to 125°C for 3 minutes to 25 minutes, The mixture obtained from step a) comprises the fiberizable polymer powder in an amount of 0.06% to 0.6% by weight, based on the total weight of the mixture from step a).

2. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: The average diameter D of the fiberizable polymer powder 50 1μm to 1000μm.

3. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: Step a) is carried out without using a solvent.

4. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: Step c) is carried out at a temperature ranging from 50°C to 100°C.

5. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: Step c) is performed for 5 to 20 minutes.

6. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: The fiberizable polymer powder includes polytetrafluoroethylene.

7. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: The average diameter D of the sulfide-based solid electrolyte 50 0.35μm to 4μm.

8. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: The sulfide-based solid electrolyte powder is selected from Li2S-P2S5, Li6PS5Cl 0.5 Br 0.5 , Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-Si S2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y 、Li 10 GeP2S 12 or a combination thereof, wherein m and n are positive numbers, Z is one of Ge, Zn and Ga, x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga and In.

9. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: The diameter of the fiberized polymer produced in step b) is from 0.01 μm to 10 μm.

10. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: Step b) is carried out at a temperature ranging from 25°C to 100°C.

11. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: The rolling in step c) is performed using a rolling device.

12. The method for preparing a solid electrolyte self-supporting membrane according to claim 1, wherein: After the application of the shear stress of step b), the mixture of step a) is converted to a clay-like consistency.

13. A solid electrolyte self-supporting membrane, comprising: sulfide-based solid electrolyte; and Fiberized polymer, in, The fiberized polymer is present in an amount of 0.1 wt% to 0.5 wt% based on the total weight of the solid electrolyte self-supporting membrane.

14. The solid electrolyte self-supporting membrane according to claim 13, wherein The tensile strength is equal to or greater than 0.2 MPa.

15. The solid electrolyte self-supporting membrane according to claim 13, wherein The lithium ion conductivity is equal to or greater than 3 mS / cm.

16. The solid electrolyte self-supporting membrane according to claim 13, wherein The sulfide-based solid electrolyte is present in an amount of 99.4 wt % to 99.9 wt % based on the total weight of the solid electrolyte self-supporting film.

17. The solid electrolyte self-supporting membrane according to claim 13, wherein: The fiberized polymer has a diameter of 0.01 μm to 10 μm.

18. The solid electrolyte self-supporting membrane according to claim 13, wherein The thickness of the solid electrolyte self-supporting film is 100 μm.

19. The solid electrolyte self-supporting membrane according to claim 13, wherein The sulfide-based solid electrolyte is selected from Li2S-P2S5, Li6PS5Cl 0.5 Br 0.5 , Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-Si S2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y 、Li 10 GeP2S 12 or a combination thereof, wherein m and n are positive numbers, Z is one of Ge, Zn and Ga, x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga and In.

20. An all-solid-state battery comprising the solid electrolyte self-supporting film according to claim 13.

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