Solid electrolyte membrane and all-solid-state battery containing the same

Abstract

The present invention relates to a solid electrolyte membrane for an all-solid-state battery, which comprises a binder containing 22 to 34% by weight of styrene relative to the total weight of a styrene-butadiene-styrene copolymer, and a solid electrolyte, and to an all-solid-state battery including the same.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0153588 dated November 16, 2022, and incorporates all the contents disclosed in the said Korean Patent Application as part of this Specification.

[0002] This invention relates to a solid electrolyte membrane and an all-solid-state battery containing the same. [Background technology]

[0003] A secondary battery is a device that stores external electrical energy in the form of chemical energy and generates electricity when needed. It is also called a rechargeable battery because it can be recharged multiple times. Commonly used secondary batteries include lead-acid batteries, nickel-cadmium batteries (NiCd), nickel-metal hydride batteries (NiMH), and lithium-ion batteries. Secondary batteries offer both economic and environmental advantages compared to disposable primary batteries.

[0004] Meanwhile, with the advancement of wireless communication technology, there is a demand for lighter, thinner, and smaller portable devices and automotive accessories, and the demand for rechargeable batteries used as energy sources for these devices is increasing. In particular, from the perspective of preventing environmental pollution, hybrid and electric vehicles have become practical, and research is emerging to reduce manufacturing costs and weight and extend lifespan by using rechargeable batteries in these next-generation automotive batteries. Among the various types of rechargeable batteries, lithium-ion batteries, which are lightweight, exhibit high energy density and operating potential, and have a long cycle life, have recently been attracting attention.

[0005] Generally, lithium secondary batteries are manufactured by mounting an electrode assembly, consisting of a negative electrode, a positive electrode, and a separator membrane, inside a cylindrical or rectangular metal can or a pouch-shaped case made of aluminum laminate sheet, and then injecting an electrolyte into the electrode assembly.

[0006] However, in the case of lithium secondary batteries, a case having a certain space such as a cylindrical shape, a prismatic shape, or a pouch shape is required, so there are restrictions on developing various forms of portable devices. Therefore, a new form of lithium secondary battery that is easily deformable in form is required. In particular, as an electrolyte contained in a lithium secondary battery, an electrolyte that has no risk of liquid leakage and excellent ionic conductivity is required.

[0007] Conventionally, as an electrolyte for lithium secondary batteries, a liquid electrolyte in which a lithium salt is dissolved in a non-aqueous organic solvent has been mainly used. However, such a liquid electrolyte not only has a high possibility that the electrode material deteriorates and the organic solvent volatilizes, but also combustion, explosion, etc. may occur due to the ambient temperature and the temperature rise of the battery itself, and there is a risk of liquid leakage. Therefore, there are problems in realizing various forms of lithium secondary batteries with high safety.

[0008] On the other hand, all-solid-state batteries using solid electrolytes have the advantage that an electrode assembly can be fabricated in a safe and simple form because they eliminate organic solvents.

[0009] However, all-solid-state batteries have the limitation that their actual energy density and output are not as high as those of lithium secondary batteries using conventional liquid electrolytes. Since an electrolyte film containing a solid electrolyte is located between the positive electrode and the negative electrode in all-solid-state batteries, they are larger and heavier in volume than conventional lithium secondary batteries, and the energy density per volume and the energy density per weight decrease. If the electrolyte film is made thinner to prevent this, there is a possibility of short-circuiting between the positive electrode and the negative electrode.

[0010] However, there are limitations in the current limited slurry solvent and binder technologies. Conventionally, nitrile-butadiene rubber (NBR) has been mainly used as a binder for the solid electrolyte film of all-solid-state batteries, but there are problems in terms of moisture stability, mechanical properties, and manufacturing processability when manufacturing with a thin thickness.

[0011] As mentioned above, solid electrolyte membranes for all-solid-state batteries need to be manufactured as thin films to achieve high energy density and reduced resistance, and furthermore, they must meet the required characteristics in terms of flexibility, ionic conductivity, and the ability to be scaled up to a large area.

[0012] Therefore, there is a need to develop solid electrolyte membranes for all-solid-state batteries that can ensure not only excellent ionic conductivity but also flexibility. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Korean Published Patent Publication No. 10-2021-0098246 [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] Therefore, the present inventors conducted multifaceted research to solve the aforementioned problems and found that by adjusting the styrene content in the styrene-butadiene-styrene copolymer as a binder, the ionic conductivity and flexibility can be improved, thus completing the present invention.

[0015] Therefore, the present invention aims to provide a solid electrolyte membrane for all-solid-state batteries that exhibits excellent ionic conductivity and flexibility.

[0016] Furthermore, the present invention aims to provide an all-solid-state battery that includes the solid electrolyte membrane. [Means for solving the problem]

[0017] In order to achieve the aforementioned objective, This invention comprises a solid electrolyte and a binder. The binder comprises a styrene-butadiene-styrene copolymer. The present invention provides a solid electrolyte membrane for all-solid-state batteries, wherein styrene is contained in 22 to 34% by weight relative to the total weight of the styrene-butadiene-styrene copolymer.

[0018] Furthermore, the present invention provides an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte membrane interposed between them, wherein the solid electrolyte membrane is the solid electrolyte membrane of the present invention. [Effects of the Invention]

[0019] The solid electrolyte membrane for all-solid-state batteries of the present invention contains a styrene-butadiene-styrene copolymer as a binder, and by adjusting the styrene content in the copolymer, excellent ionic conductivity and flexibility can be achieved. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram of an all-solid-state battery containing a solid electrolyte membrane for an all-solid-state battery according to the present invention. [Figure 2] This is a photograph of the solid electrolyte membrane for the all-solid-state battery of the present invention. [Figure 3] This is a graph of the ionic conductivity of the solid electrolyte membranes for all-solid-state batteries in Examples 1-2 and Comparative Examples 1-3. [Figure 4] This is a photograph showing the measurement of the flexibility of the solid electrolyte membrane for the all-solid-state battery in Example 1. [Figure 5] This is a photograph showing the measurement of the flexibility of the solid electrolyte membrane for the all-solid-state battery in Example 2. [Figure 6] This is a photograph showing the measurement of the flexibility of the solid electrolyte membrane for all-solid-state batteries in Comparative Example 1. [Figure 7] This is a photograph showing the measurement of the flexibility of the solid electrolyte membrane for all-solid-state batteries in Comparative Example 2. [Figure 8] This is a photograph showing the measurement of the flexibility of the solid electrolyte membrane for all-solid-state batteries in Comparative Example 3. [Figure 9] This graph shows the measured charge and discharge capacities of the all-solid-state battery in Experimental Example 2. [Figure 10] This graph shows the measured life characteristics of the all-solid-state battery in Experimental Example 2. [Modes for carrying out the invention]

[0021] The present invention will be described in more detail below.

[0022] Furthermore, the terms and words used in this specification and the claims shall not be interpreted in a manner limited to their ordinary or lexicographical meanings, but rather in a manner consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0023] The terms used herein are merely illustrative for the purposes of describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “includes” or “having” specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof as described in the specification, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0024] Lithium-ion batteries have been used in small devices such as mobile phones and laptops, but recently their applications have expanded to medium and large-scale devices such as electric vehicles and energy storage systems. In these cases, unlike small devices, the operating environment is not only more demanding, but more batteries must be used, requiring both excellent performance and stability.

[0025] Most lithium-ion batteries currently on the market use a liquid electrolyte in which lithium salt is dissolved in an organic solvent. Because the organic solvent contained in the liquid electrolyte is highly volatile and flammable, there is a potential risk of ignition or explosion, and leakage may occur, resulting in a lack of long-term reliability.

[0026] Therefore, development is underway on all-solid-state batteries, which replace the liquid electrolyte of lithium-ion batteries with a solid electrolyte. All-solid-state batteries do not contain volatile organic solvents, eliminating the risk of explosion or fire, and are attracting attention as batteries that offer superior economic efficiency and productivity, as well as the ability to manufacture high-output batteries.

[0027] To achieve high energy density in all-solid-state batteries, the fabrication of thin-film solid electrolyte membranes is essential. These solid electrolyte membranes are manufactured by coating a slurry containing particulate solid electrolyte and binder onto a release film, drying it, and then removing the release film. The properties of the binder can affect the dispersibility of the solid electrolyte, the feasibility of manufacturing the solid electrolyte membrane, and even the charge-discharge characteristics of the all-solid-state battery.

[0028] Therefore, the present invention aims to provide a solid electrolyte membrane for all-solid-state batteries that minimizes the decrease in ionic conductivity, exhibits excellent ionic conductivity, and is highly flexible, facilitating the manufacture of all-solid-state batteries.

[0029] This invention comprises a solid electrolyte and a binder. The binder comprises a styrene-butadiene-styrene copolymer. This invention relates to a solid electrolyte membrane for all-solid-state batteries, wherein styrene is contained in an amount of 22-34% by weight relative to the total weight of the styrene-butadiene-styrene copolymer.

[0030] The solid electrolyte may include one or more selected from the group consisting of sulfide-based solid electrolytes, polymer-based solid electrolytes, and oxide-based solid electrolytes, and preferably includes a sulfide-based solid electrolyte. The solid electrolyte may be in particulate form.

[0031] The sulfide-based solid electrolyte contains sulfur (S) and has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and may include Li-PS glass or Li-PS glass ceramic.

[0032] Specifically, the sulfide-based solid electrolyte may contain one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2S5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and preferably contains one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, and Li6PS5I. The Li6PS5Cl, Li6PS5Br, and Li6PS5I mentioned above may be argyrodite-type solid electrolytes. Furthermore, the sulfide-based solid electrolyte may be in a form doped with trace amounts of elements; for example, Li6PS5Cl may be further doped with bromine (Br).

[0033] The aforementioned polymeric solid electrolyte is a composite of a lithium salt and a polymer resin, that is, a polymer electrolyte material formed by adding a polymer resin to a solventized lithium salt, and is approximately 1 x 10⁻⁶ -7 S / cm or more, preferably about 1 x 10 -5 It can exhibit ionic conductivity of S / cm or higher.

[0034] Non-limiting examples of the polymer resin include polyether-based polymers, polycarbonate-based polymers, acrylate-based polymers, polysiloxane-based polymers, phosphazene-based polymers, polyethylene derivatives, alkylene oxide derivatives such as polyethylene oxide, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, etc., and one or more of these may be included. Further, as the polymer resin, the polymer electrolyte may include a branched copolymer obtained by copolymerizing an amorphous polymer such as PMMA, polycarbonate, polysiloxane (pdms) and / or phosphazene as a comonomer with a PEO (polyethylene oxide) main chain, a comb-like polymer resin, a crosslinked polymer resin, etc., and one or more of these may be included.

[0035] In the electrolyte of the present invention, the above-described lithium salt can be represented as an ionizable lithium salt, Li + X - Although the anion of such a lithium salt is not particularly limited, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C- CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , (CF3CF2SO2)2N - These are some examples.

[0036] The oxide-based solid electrolyte may contain oxygen (O) and have the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table. For example, LLTO compounds, Li6La2CaTa2O 12 Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (Here, 0≦x≦1, 0≦y≦1), LiAl x Zr 2-x (PO4)3 (where 0≦x≦1), LiTi x Zr 2-x (PO4)3 (where 0 ≤ x ≤ 1), may contain one or more compounds selected from LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, and LLZO compounds.

[0037] The binder may contain a styrene-butadiene-styrene (SBS) copolymer, and the styrene-butadiene-styrene copolymer may be represented by the following chemical formula 1.

[0038] [Chemical formula 1] [ka]

[0039] The aforementioned l, m, and n are either identical or different integers greater than or equal to 100.

[0040] The styrene-butadiene-styrene copolymer does not react with the solid electrolyte and effectively binds the particulate solid electrolyte, thereby improving the ionic conductivity of the solid electrolyte membrane for all-solid-state batteries.

[0041] The solid electrolyte membrane for the all-solid-state battery also serves as a separator membrane and is interposed between the positive and negative electrodes during the manufacturing of the all-solid-state battery; therefore, cracks must not occur in it. Furthermore, if the solid electrolyte membrane for the all-solid-state battery is hard and easily broken, a short circuit in the all-solid-state battery could easily occur; therefore, the solid electrolyte membrane needs to be highly flexible.

[0042] The solid electrolyte membrane for all-solid-state batteries of the present invention, by containing styrene at a concentration of 22 to 34% by weight relative to the total weight of the styrene-butadiene-styrene copolymer, provides a solid electrolyte membrane for all-solid-state batteries with excellent ionic conductivity and flexibility. Furthermore, its excellent flexibility enables continuous manufacturing processes during the production of all-solid-state batteries containing it, resulting in superior processability.

[0043] The upper limit of the styrene content may be 31.5% by weight, 32% by weight, 33% by weight, or 34% by weight. The lower limit of the styrene content may be 22% by weight, 23% by weight, or 23.5% by weight. The styrene content may be within a range set by combining the upper and lower limits.

[0044] If the styrene-butadiene-styrene copolymer contains less than 22% by weight of styrene, the content of rigid styrene is low, which ensures flexibility in the solid electrolyte membrane for all-solid-state batteries, but results in low ionic conductivity. On the other hand, if the styrene-butadiene-styrene copolymer contains more than 34% by weight of styrene, high ionic conductivity can be achieved due to the conjugated structure of styrene, but because styrene has a rigid structure, flexibility cannot be ensured, leading to problems such as cracking.

[0045] Therefore, by including styrene in the styrene-butadiene-styrene copolymer at a concentration of 22-34% by weight relative to the total weight of the copolymer, a solid electrolyte membrane for all-solid-state batteries with excellent ionic conductivity and flexibility can be provided.

[0046] Furthermore, the solid electrolyte may be present in an amount of 95 to 99.5% by weight of the total weight of the solid electrolyte membrane for the all-solid-state battery, and the binder may be present in an amount of 0.5 to 5% by weight. By including the solid electrolyte and binder as described above, it is possible to manufacture a solid electrolyte membrane for an all-solid-state battery that can be maintained in film form while minimizing the binder content, which acts as a resistive agent to ionic conductivity.

[0047] The solid electrolyte membrane for the all-solid-state battery may be a free-standing film (also called a "self-supporting" film). The free-standing film means one that maintains its shape without the need for a support. The free-standing film-like solid electrolyte membrane for the all-solid-state battery may be used in the manufacturing process of the all-solid-state battery without any external support requirements.

[0048] Furthermore, the thickness of the solid electrolyte membrane for the all-solid-state battery is 30 to 200 μm, preferably 50 to 100 μm. Having this thickness makes it applicable to all-solid-state batteries and allows for excellent ionic conductivity and flexibility.

[0049] The ionic conductivity of the solid electrolyte membrane for the all-solid-state battery may be 1.2 to 10 mS / cm, preferably 1.5 to 3 mS / cm.

[0050] The solid electrolyte membrane for the all-solid-state battery may be manufactured by mixing a solid electrolyte, a styrene-butadiene-styrene copolymer, and a solvent to produce a slurry, applying the slurry to one side of a release film, drying it, and then removing the release film. In this case, the solvent may be used without particular limitation as long as it does not react with the styrene-butadiene-styrene copolymer and the solid electrolyte.

[0051] Furthermore, the present invention relates to an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte membrane interposed between them, wherein the solid electrolyte membrane may be the solid electrolyte membrane of the present invention as described above.

[0052] The all-solid-state battery is a lithium secondary battery, and there are no restrictions on whether it is a positive or negative electrode. It may be a lithium-air battery, a lithium oxide battery, a lithium-sulfur battery, or a lithium metal battery.

[0053] The positive electrode may include a positive electrode current collector and a positive electrode active material coated on one or both sides of the positive electrode current collector.

[0054] The positive electrode current collector is for supporting the positive electrode active material and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the lithium secondary battery. For example, the positive electrode current collector may be any one metal selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof, and the stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and as the alloy, aluminum-cadmium alloy may be preferably used, but other materials such as calcined carbon, non-conductive polymers surface-treated with conductive materials, or conductive polymers may also be used.

[0055] The positive electrode current collector can have fine irregularities formed on its surface to strengthen its bonding force with the negative electrode active material, and may be used in various forms such as film, sheet, foil, mesh, net, porous material, foam, or nonwoven fabric.

[0056] The positive electrode active material may selectively include a conductive material and a binder.

[0057] The positive electrode active material may vary depending on the type of all-solid-state battery. For example, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (0 ≤ x ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented as O2 (M=Co, Mn, Al, Cu, Fe, Mg, B or Ga; 0.01≦x≦0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxide represented as O2 (M=Co, Ni, Fe, Cr, Zn, or Ta; 0.01≦x≦0.1) or Li2Mn3MO8 (M=Fe, Co, Ni, Cu, or Zn); LiNi x Mn 2-x Lithium manganese composite oxide with a spinel structure represented by O4; LiCoPO4; LiFePO4; elemental sulfur (S8); Li2S n (n=1), organosulfur compounds or carbon-sulfur polymers ((C2S x ) n This may include, but is not limited to, sulfur-based compounds such as (x=2.5~50, n=2).

[0058] The conductive material electrically connects the electrolyte and the positive electrode active material, acting as a pathway for electrons to move from the current collector to the positive electrode active material. It can be used without limitation as long as it does not undergo chemical changes in a lithium secondary battery and is porous and conductive.

[0059] For example, the conductive material may be a porous carbon-based material, such as carbon black, graphite, graphene, activated carbon, carbon fiber, metallic fibers such as metal mesh; metallic powders such as copper, silver, nickel, and aluminum; or organic conductive materials such as polyphenylene derivatives. The conductive materials may be used individually or in combination.

[0060] Currently, commercially available conductive materials include acetylene black-based materials (such as those from Chevron Chemical Company and Gulf Oil Company), Ketjen Black EC-based materials (products from Armak Company), Vulcan XC-72 (products from Cabot Company), and Super P (products from MMM). Examples include acetylene black, carbon black, and graphite.

[0061] Furthermore, the positive electrode may further contain a binder, which enhances the bonding force between the components constituting the positive electrode and between them and the current collector, and any binder known in the industry may be used.

[0062] For example, the binder may be one, a mixture of two or more, or a copolymer selected from the group consisting of: fluororesin binders containing polyvinylidenefluoride (PVdF) or polytetrafluoroethylene (PTFE); rubber binders containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose binders containing carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyalcohol binders; polyolefin binders containing polyethylene or polypropylene; polyimide binders; polyester binders; and silane binders.

[0063] The negative electrode may include a negative electrode current collector and a negative electrode active material located on the negative electrode current collector. Furthermore, the negative electrode, like the positive electrode, may optionally include a conductive material and a binder. In this case, the negative electrode current collector, conductive material, and binder are as described above.

[0064] The aforementioned negative electrode active material is lithium ion (Li + Any substance that can reversibly intercalate or deintercalate lithium, or react with lithium ions to reversibly form lithium-containing compounds, is acceptable.

[0065] For example, the negative electrode active material is one or more carbon-based materials, Si-based materials, Li selected from the group consisting of crystalline artificial graphite, crystalline natural graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon. x Fe2O3 (0 ≤ x ≤ 1), Li x WO2(0≦x≦1), Sn x Me 1-x Me'y O z Examples of metal composite oxides such as (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0≦x≦1; 1≦y≦3; 1≦z≦8); lithium metal; lithium alloys; silicon alloys; tin alloys; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni materials; titanium oxides; lithium titanium oxide, etc. are examples, but are not limited to these.

[0066] The manufacturing of the all-solid-state battery is not particularly limited in this invention, and known methods may be used.

[0067] As an example, a solid electrolyte membrane is placed between the positive and negative electrodes, and then the cell is assembled by compression molding. After the assembled cell is placed inside an outer packaging material, it is sealed by heat compression or the like. As the outer packaging material, laminate packs made of aluminum, stainless steel, or other materials, or cylindrical or rectangular metal containers may be used.

[0068] As an example, the positive and negative electrodes are manufactured in the form of a slurry composition containing the respective electrode active material, solvent, and binder, and then coated and dried through a slurry coating process.

[0069] Methods for coating the electrode slurry onto a current collector include distributing the electrode slurry onto the current collector and then uniformly dispersing it using a doctor blade, die casting, comma coating, and screen printing. Alternatively, the electrode slurry may be molded onto another substrate and then bonded to the current collector by pressing or lamination. In this case, the thickness of the final coating can be adjusted by adjusting the concentration of the slurry solution or the number of coatings.

[0070] The drying process involves removing solvent and moisture from the slurry coated on the metal current collector in order to dry it, and may vary depending on the solvent used. For example, it is carried out in a vacuum oven at 50-200°C. Drying methods include drying with hot air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. There are no particular limitations on the drying time, but it is usually carried out in the range of 30 seconds to 24 hours.

[0071] The drying process may further include a cooling process, which may involve slow cooling to room temperature to ensure proper recrystallization of the binder.

[0072] Furthermore, if necessary, a rolling process may be performed after the drying process in which the electrodes are passed between two high-temperature heated rolls and compressed to a desired thickness in order to increase the capacitance density of the electrodes and increase the adhesion between the current collector and the active material. The rolling process is not particularly limited in this invention, and any known rolling process (pressing) is possible. For example, it may be performed by passing the electrodes between rotating rolls or by using a flat plate press.

[0073] The shape of the all-solid-state battery is not particularly limited and may be cylindrical, stacked, coin-shaped, or in any other form.

[0074] The following are preferred embodiments to aid in understanding the present invention. These embodiments are illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that these variations and modifications fall within the scope of the appended claims.

[0075] <Manufacturing of solid electrolyte membranes for all-solid-state batteries> Example 1. A slurry was prepared by mixing argyrodite (Li6PS5Cl), styrene-butadiene-styrene copolymer, and isobutyl isobutyrate as solid electrolytes. The styrene-butadiene-styrene copolymer used contained 23.5% by weight of styrene relative to the total weight of the copolymer (molecular weight 50,000).

[0076] Polyethylene terephthalate was used as a release film, and the slurry was coated onto the release film. After drying at room temperature for 2 hours, it was dried in a vacuum oven at 70°C for 5 hours, and the release film was removed to produce a free-standing film-type solid electrolyte membrane for all-solid-state batteries.

[0077] The solid electrolyte membrane for the all-solid-state battery contained 99% by weight of argyrodite and 1% by weight of styrene-butadiene-styrene copolymer. The thickness of the solid electrolyte membrane for the all-solid-state battery was 100 μm.

[0078] Example 2. A solid electrolyte membrane for an all-solid-state battery was manufactured in the same manner as in Example 1, except that a styrene-butadiene-styrene copolymer (molecular weight 50,000) containing 31.5% by weight of styrene relative to the total weight of the styrene-butadiene-styrene copolymer was used. The thickness of the solid electrolyte membrane for the all-solid-state battery was 100 μm.

[0079] Comparative Example 1. A solid electrolyte membrane for an all-solid-state battery was manufactured in the same manner as in Example 1, except that a styrene-butadiene-styrene copolymer (molecular weight 50,000) containing 21% by weight of styrene relative to the total weight of the styrene-butadiene-styrene copolymer was used. The thickness of the solid electrolyte membrane for the all-solid-state battery was 100 μm.

[0080] Comparative Example 2. A solid electrolyte membrane for an all-solid-state battery was manufactured in the same manner as in Example 1, except that a styrene-butadiene-styrene copolymer (molecular weight 50,000) containing 40.5% by weight of styrene relative to the total weight of the styrene-butadiene-styrene copolymer was used. The thickness of the solid electrolyte membrane for the all-solid-state battery was 100 μm.

[0081] Comparative Example 3. A solid electrolyte membrane for an all-solid-state battery was manufactured in the same manner as in Example 1, except that a styrene-butadiene-styrene copolymer (molecular weight 50,000) containing 35% by weight of styrene relative to the total weight of the styrene-butadiene-styrene copolymer was used. The thickness of the solid electrolyte membrane for the all-solid-state battery was 100 μm.

[0082] Experimental Example 1. Measurement of ionic conductivity and flexibility of solid electrolyte membranes for all-solid-state batteries. The ionic conductivity and flexibility of the solid electrolyte membranes for all-solid-state batteries produced in Examples 1-2 and Comparative Examples 1-3 were measured.

[0083] Ionic conductivity was measured by placing aluminum foil on the top and bottom surfaces of the solid electrolyte membrane for all-solid-state batteries, assembling a jig cell, and then pressurizing it at 360 MPa.

[0084] Flexibility was assessed by observing the presence or absence of cracks when a solid electrolyte membrane for all-solid-state batteries was wound onto a 2 mm diameter mandrel.

[0085] The results for ionic conductivity and flexibility are shown in Table 1 and Figures 3-8 below.

[0086] [Table 1]

[0087] As shown in the results in Table 1, Examples 1 and 2, by containing styrene at a concentration of 22-34% by weight relative to the total weight of the styrene-butadiene-styrene copolymer, exhibited excellent ionic conductivity, no crack formation, and superior flexibility.

[0088] Comparative Example 1, which contained less than 22% by weight of styrene relative to the total weight of the styrene-butadiene-styrene copolymer, did not develop cracks and maintained flexibility, but showed poor ionic conductivity.

[0089] Comparative Examples 2 and 3, containing more than 34% by weight of styrene relative to the total weight of the styrene-butadiene-styrene copolymer, showed superior ionic conductivity compared to the Examples, but it was confirmed that they developed cracks and lacked flexibility.

[0090] Therefore, it can be seen that a solid electrolyte membrane for all-solid-state batteries containing styrene at a concentration of 22-34% by weight relative to the total weight of the styrene-butadiene-styrene copolymer has excellent ionic conductivity and flexibility.

[0091] Experimental Example 2. Evaluation of Charge and Discharge Characteristics of All-Solid-State Batteries A positive electrode was manufactured by mixing a positive electrode active material (NCM 811), a conductive material (carbon fiber), a solid electrolyte (Li6PS5Cl), and a binder (polytetrafluoroethylene) in a weight ratio of 84:0.2:14.8:1, and then rolling the mixture.

[0092] The negative electrode was manufactured by coating a 150 μm thick mixture of negative electrode active material (carbon black) and binder (polyvinylidene fluoride) onto a 10 μm thick SUS (stainless steel) material, which served as the negative electrode current collector.

[0093] After interposing the solid electrolyte membranes for all-solid-state batteries manufactured in Examples 1-2 and Comparative Examples 1-2 between the positive and negative electrodes, a monocell-type all-solid-state battery was manufactured by applying pressure.

[0094] Each of the aforementioned solid-state batteries was repeatedly charged and discharged at 3.0 to 4.25 V and 1 C, and the charge-discharge characteristics of the solid-state batteries in Examples 1 and 2 and Comparative Examples 1 and 2 were measured. The results are shown in Figures 9 and 10.

[0095] As shown in Figure 9, the initial charge and discharge capacities of the all-solid-state batteries in Examples 1-2 and Comparative Examples 1-2 were similar.

[0096] The results in Figure 10 show that the higher the styrene content relative to the total weight of the styrene-butadiene-styrene copolymer, the better the lifespan characteristics. Specifically, Comparative Example 2, which had the highest styrene content, showed the best lifespan characteristics, while Comparative Example 1, which had the lowest styrene content, showed the worst lifespan characteristics. This result can be expected because a higher styrene content leads to higher ionic conductivity. However, Comparative Example 2 contained more than 34% by weight of styrene relative to the total weight of the styrene-butadiene-styrene copolymer, and showed poor flexibility, such as cracking, as seen in the results of Experimental Example 1. Consequently, it was not easy to manufacture an all-solid-state battery using the solid electrolyte membrane of Comparative Example 2, and even after manufacturing the all-solid-state battery, problems such as the solid electrolyte membrane failing to maintain its shape and cracking resulted in a high initial defect rate, including short circuits during initial charging.

[0097] Therefore, it can be seen that when styrene is included in a concentration of 22-34% by weight relative to the total weight of the styrene-butadiene-styrene copolymer, the solid electrolyte membrane for all-solid-state batteries can have excellent ionic conductivity and flexibility, thereby improving the charge-discharge characteristics of the all-solid-state battery.

Claims

1. It contains a solid electrolyte and a binder. The solid electrolyte includes one selected from the group consisting of sulfide-based solid electrolytes and oxide-based solid electrolytes. The binder comprises a styrene-butadiene-styrene copolymer. A solid electrolyte membrane for all-solid-state batteries, wherein styrene is contained in 22 to 34% by weight relative to the total weight of the styrene-butadiene-styrene copolymer.

2. The solid electrolyte membrane for an all-solid-state battery according to claim 1, wherein the solid electrolyte is contained in an amount of 95 to 99.5% by weight and the binder in an amount of 0.5 to 5% by weight, relative to the total weight of the solid electrolyte membrane for an all-solid-state battery.

3. The solid electrolyte membrane for an all-solid-state battery according to claim 1, wherein the solid electrolyte includes a sulfide-based solid electrolyte.

4. The solid electrolyte membrane for an all-solid-state battery according to claim 1, wherein the solid electrolyte membrane for the all-solid-state battery is a free-standing film.

5. The solid electrolyte membrane for an all-solid-state battery according to claim 1, wherein the thickness of the solid electrolyte membrane for the all-solid-state battery is 30 to 200 μm.

6. The solid electrolyte membrane for an all-solid-state battery according to claim 1, wherein the ionic conductivity of the solid electrolyte membrane for the all-solid-state battery is 1.2 to 10 mS / cm.

7. An all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte membrane interposed between the positive electrode and the negative electrode, The solid electrolyte membrane is the solid electrolyte membrane according to any one of claims 1 to 6, in this all-solid-state battery.

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