All Solid secondary battery and preparation method thereof

Abstract

An all-solid-state secondary battery and a method for manufacturing the same are provided, comprising an electrode assembly having a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and a porous multilayer member disposed on one or both sides of the electrode assembly, wherein the porous multilayer member comprises a porous cushioning layer; and a porous protecting layer disposed on one or both sides of the porous cushioning layer.

Description

Technology Field

[0001] This relates to an all-solid-state secondary battery and a method for manufacturing an all-solid-state secondary battery. Background Technology

[0002] Recently, driven by industrial demands, the development of batteries with high energy density and safety is actively underway. For example, lithium-ion batteries are being commercialized not only in the fields of information and communication devices but also in the automotive sector. In the automotive sector, safety is considered particularly important because it is directly related to human life.

[0003] Currently commercially available lithium-ion batteries use electrolytes containing flammable organic solvents, so there is a possibility of overheating and fire in the event of a short circuit. In response to this, all-solid-state batteries using a solid electrolyte instead of an electrolyte are being proposed.

[0004] By not using flammable organic solvents, all-solid-state batteries can significantly reduce the likelihood of fire or explosion in the event of a short circuit. Therefore, these all-solid-state batteries can offer significantly higher safety compared to lithium-ion batteries that use liquid electrolytes. The problem to be solved

[0005] One aspect is to provide a new all-solid-state secondary battery.

[0006] Another aspect is to provide a method for manufacturing an all-solid-state secondary battery. means of solving the problem

[0007] According to one embodiment

[0008] The electrode assembly comprises an anode layer; a cathode layer; and a solid electrolyte layer disposed between the anode layer and the cathode layer.

[0009] It includes a porous multilayer member disposed on one or both sides of the electrode assembly, and

[0010] An all-solid-state secondary battery is provided, wherein the porous multilayer member comprises a porous cushioning layer; and a porous protecting layer disposed on one or both sides of the porous cushioning layer.

[0011] According to another embodiment,

[0012] The method comprises the steps of: providing an electrode assembly having an anode layer; a cathode layer; and a solid electrolyte layer disposed between the anode layer and the cathode layer; and

[0013] The method includes the step of placing a porous multilayer member on one or both sides of the electrode assembly;

[0014] A method for manufacturing an all-solid-state secondary battery is provided, wherein the porous multilayer member comprises a porous cushioning layer; and a porous protecting layer disposed on one or both sides of the porous cushioning layer. Effects of the invention

[0015] According to one aspect, by placing a porous multilayer member on an electrode assembly, the ease of the manufacturing process of the all-solid-state secondary battery is improved, and the lifespan characteristics can be improved by suppressing short circuits in the all-solid-state secondary battery. Brief explanation of the drawing

[0016] FIG. 1 is a cross-sectional view of an all-solid-state secondary battery according to an exemplary embodiment. FIG. 2 is a cross-sectional view of a bi-cell all-solid-state secondary battery according to an exemplary embodiment. FIG. 3 is a cross-sectional view of an all-solid-state secondary battery according to an exemplary embodiment. FIG. 4 is a cross-sectional view of a bi-cell all-solid-state secondary battery according to an exemplary embodiment. FIG. 5a is a cross-sectional view of a porous multilayer member according to an exemplary embodiment. FIG. 5b is a cross-sectional view of a porous multilayer member according to an exemplary embodiment. FIG. 6 is a cross-sectional view of an all-solid-state secondary battery structure according to an exemplary embodiment. FIG. 7 is a cross-sectional view of an all-solid-state secondary battery structure according to an exemplary embodiment. Specific details for implementing the invention

[0017] Since the electrolyte in all-solid-state secondary batteries is solid, if sufficient contact is not maintained between the positive electrode layer and the solid electrolyte layer, and between the negative electrode layer and the solid electrolyte layer, respectively, during charging and discharging, the resistance within the battery increases, making it difficult to exhibit excellent battery characteristics.

[0018] During the charging and discharging process of an all-solid-state secondary battery, volume changes accompany the volume of the battery due to volume variations in the anode and / or cathode layers. Therefore, it is required to apply a constant pressure to the all-solid-state secondary battery to accommodate these volume changes while maintaining contact between the anode layer and the solid electrolyte layer, as well as between the cathode layer and the solid electrolyte layer. Although an elastic member can be placed on one side of the all-solid-state secondary battery to accommodate these volume changes, air pockets may form between the elastic member and the battery, preventing the application of uniform pressure. Consequently, defects may occur within the all-solid-state secondary battery due to the application of uneven pressure during the charging and discharging process. Furthermore, cracks may develop and grow within the all-solid-state secondary battery from these defects. As lithium grows through these cracks, a short circuit occurs between the anode and cathode layers, or as these cracks increase, the internal resistance of the all-solid-state secondary battery increases, and consequently, the cycle characteristics of the all-solid-state secondary battery deteriorate.

[0019] Furthermore, since elastic members generally have adhesive properties, defects occur during the process of placing the elastic members in the all-solid-state secondary battery due to unintended adhesion between the elastic members and the all-solid-state secondary battery, making it difficult to manufacture the all-solid-state secondary battery quickly and efficiently.

[0020] According to one aspect, the all-solid-state secondary battery has a new configuration that prevents short circuits during charging and discharging and improves cycle characteristics.

[0021] According to another aspect, the all-solid-state secondary battery can be manufactured quickly and efficiently by having a new configuration, thereby improving the ease of the manufacturing process.

[0022] The present inventive concept described below is subject to various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present inventive concept to specific embodiments, and it should be understood that it includes all modifications, equivalents, or substitutions that fall within the scope of the description of the present inventive concept.

[0023] The terms used below are used merely to describe specific embodiments and are not intended to limit the creative concept. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the following, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, components, materials, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, components, materials, or combinations thereof. The " / " used below may be interpreted as "and" or "or" depending on the context.

[0024] In the drawings, thicknesses have been enlarged or reduced to clearly represent various layers and regions. Throughout the specification, the same reference numerals have been used for similar parts. Throughout the specification, when a part such as a layer, film, region, or plate is described as being "on" or "above" another part, this includes not only cases where it is directly above another part but also cases where there is another part in between. Throughout the specification, terms such as "first," "second," etc., may be used to describe various components, but the components should not be limited by these terms. Terms are used solely for the purpose of distinguishing one component from another. In this specification and drawings, components having substantially the same functional configuration are referred to by the same reference numerals to avoid redundant descriptions.

[0025] In this specification, “average particle size” is the value of the median particle size (D50) when 50% is accumulated from the small particle side in volume conversion, measured, for example, using a laser scattering particle size distribution meter (e.g., Horibasa LA-920). Alternatively, in this specification, “average particle size” is the arithmetic mean value of the particle sizes of a plurality of particles shown in the image, measured manually or by software from scanning electron microscope and / or transmission electron microscope images of a cross-section of an all-solid-state secondary battery.

[0026] A solid-state secondary battery according to exemplary embodiments is described in more detail below.

[0027] [All-solid-state secondary battery]

[0028] An all-solid-state secondary battery according to one embodiment comprises an electrode assembly having a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and comprises a porous multilayer member disposed on one or both sides of the electrode assembly, wherein the porous multilayer member comprises a porous cushioning layer; and a porous protecting layer disposed on one or both sides of the porous cushioning layer. By including such a porous multilayer member, defects occurring during the charging and discharging of the all-solid-state secondary battery are suppressed, and cracks within the all-solid-state secondary battery caused by such defects are suppressed. Consequently, short circuits in the all-solid-state secondary battery are suppressed, and lifespan characteristics are improved. Furthermore, the ease of the manufacturing process of the all-solid-state secondary battery is improved.

[0029] Referring to FIGS. 1 to 4, the all-solid-state secondary battery (1) comprises an electrode assembly (40) having a positive electrode layer (10); a negative electrode layer (20); and a solid electrolyte layer (30) disposed between the positive electrode layer (10) and the negative electrode layer (20), and comprises a porous multilayer member (50, 50a, 50b) disposed on one or both sides of the electrode assembly (40). Referring to FIGS. 5a and 5b, the porous multilayer member (50) comprises a porous cushioning layer (51); and a porous protecting layer (52, 52a, 52b) disposed on one or both sides of the porous cushioning layer (51).

[0030] [Porous multilayer member]

[0031] [Porous Multilayer Member: Porous Buffer Layer]

[0032] Referring to FIGS. 5a and 5b, the porous multilayer member (50) includes a porous cushioning layer (51).

[0033] By having porosity, the porous multilayer member (50) can prevent the formation of air pockets between the electrode assembly (40) and the porous multilayer member (50). Additionally, by having porosity, the porous multilayer member (50) can more effectively accommodate volume changes of the electrode assembly (40). The porous multilayer member (50) can apply uniform pressure to one or both sides of the electrode assembly (40). Therefore, uneven deposition of lithium metal in the negative electrode layer (20) can be prevented during charging and discharging of the all-solid-state secondary battery (1). As a result, short circuits in the all-solid-state secondary battery (1) can be prevented and the lifespan characteristics of the all-solid-state secondary battery (1) can be improved.

[0034] The porous buffer layer (51) provides a buffering function to the porous multilayer member (50). The porous buffer layer (51) provides, for example, stress relaxation and restoring force. The porous buffer layer (51) effectively accommodates volume changes of the electrode assembly (40) and can apply constant pressure to the all-solid-state secondary battery (1).

[0035] Referring to FIGS. 1 to 4, a porous multilayer member (50) is disposed on the negative electrode layer (20) of the electrode assembly (40). Since the volume change of the negative electrode layer (20) during charging and discharging of the all-solid-state secondary battery (1) is relatively larger than that of the positive electrode layer (10) and the solid electrolyte layer (30), the volume change of the negative electrode layer (20) can be accommodated more effectively by placing the porous multilayer member (50) adjacent to the negative electrode layer (20). In addition, by applying a constant pressure to the negative electrode layer (50) by the porous multilayer member (50), the precipitation of lithium metal, for example, in the negative electrode layer (50) can be induced. Therefore, the formation of defects in the all-solid-state secondary battery (1) due to the non-uniform precipitation of lithium metal can be prevented more effectively.

[0036] Referring to FIGS. 5a and 5b, the elastic modulus of the porous buffer layer (51) may be smaller than the elastic modulus of the porous protective layer (52). Since the porous buffer layer (51) has a smaller elastic modulus than the porous protective layer (52), the porous buffer layer (51) can accommodate most of the volume change of the all-solid-state secondary battery (1). Thus, the porous multilayer member (50) can more effectively accommodate the volume change of the all-solid-state secondary battery (1) and apply uniform pressure to the all-solid-state secondary battery (1). The elastic modulus of the porous buffer layer may be, for example, 0.5 GPa or less, 0.3 GPa or less, or 0.1 GPa or less. The elastic modulus of the porous buffer layer may be, for example, 0.001 GPa to 0.5 GPa, 0.01 GPa to 0.3 GPa, or 0.01 GPa to 0.1 GPa. The elastic modulus of the porous protective layer (52) may be, for example, 0.1 GPa or more, 0.3 GPa or more, or 0.5 GPa or more. The elastic modulus of the porous protective layer (52) may be, for example, 0.1 GPa to 5 GPa, 0.3 GPa to 3 GPa, or 0.5 GPa to 1 GPa. The elastic modulus of the porous buffer layer (51) may be 90% or less, 80% or less, 70% or less, 50% or less, 30% or less, 20% or less, or 10% or less of the elastic modulus of the porous protective layer (52). The elastic modulus can be measured, for example, through a stress-strain test of the sample.

[0037] Referring to FIGS. 5a and 5b, the thickness of the porous buffer layer (51) may be greater than the thickness of the porous protective layer (52). Since the porous buffer layer (51) has a greater thickness than the porous protective layer (52), the porous buffer layer (51) can accommodate most of the volume change of the all-solid-state secondary battery (1). Thus, the porous multilayer member (50) can more effectively accommodate the volume change of the all-solid-state secondary battery (1). The thickness (T51) of the porous buffer layer may be, for example, 300 μm or less, 200 μm or less, 100 μm or less, 50 μm or less, 30 μm or less, or 20 μm or less. The thickness (T51) of the porous buffer layer may be, for example, 1 μm to 300 μm, 3 μm to 200 μm, 5 μm to 100 μm, 5 μm to 50 μm, 5 μm to 30 μm, or 5 μm to 20 μm.

[0038] The air permeability of the porous buffer layer (51) may be, for example, 1000 sec / 100 cc or more, 5000 sec / 100 cc or more, or 10000 sec / 100 cc or more. The air permeability of the porous buffer layer (51) may be, for example, 1000 sec / 100 cc to 50000 sec / 100 cc, 5000 sec / 100 cc to 50000 sec / 100 cc, or 10000 sec / 100 cc to 50000 sec / 100 cc. The air permeability may be measured as a Gurley value. The Gurley value may be measured by the method according to JIS P8117.

[0039] The porosity of the porous buffer layer (51) may be, for example, 5% to 95%, 10% to 90%, 20% to 80%, 30% to 70%, or 35% to 55%. By having a porosity in this range, the porous buffer layer (51) can effectively accommodate volume changes of the electrode assembly (40). The porosity can be calculated from the volume, weight, and density of the material constituting the porous protective layer of the porous buffer layer (51). Alternatively, the porosity of the porous buffer layer (51) can be measured by a liquid or gas adsorption method according to ASTM D-2873.

[0040] The size of the cells or pores included in the porous buffer layer (51) may be, for example, 0.1 μm to 50 μm, 1 μm to 30 μm, 1 μm to 10 μm, or 0.1 μm to 5 μm. The size of the cells or pores may be an average cell size or an average pore size. By including pore sizes within this range, the porous buffer layer (51) can more effectively accommodate volume changes of the electrode assembly (40). The pore size may be measured, for example, by nitrogen adsorption. The pore size may be calculated, for example, by software or by manual from a scanning electron microscope image of a cross-section of the porous buffer layer (51). The porous buffer layer (51) may have, for example, a single-layer structure or a multi-layer structure. The multi-layer structure may be, for example, a two-layer structure, a three-layer structure, or a four-layer structure.

[0041] The porous buffer layer (51) may include, for example, a porous foam, a porous sponge, or a combination thereof. The porous buffer layer (51) may include, for example, a porous foam sheet, a porous sponge sheet, or a combination thereof. By having this form, the porous buffer layer (51) can simultaneously provide porosity and buffering functions. The porous foam may include, for example, closed cells, open cells, or a combination thereof. The porous sponge may include, for example, closed cells, open cells, or a combination thereof. A closed cell refers to, for example, a closed pore, meaning a cell or pore that is not connected to the surrounding atmosphere. An open cell refers to, for example, an open pore, meaning a cell or pore that is connected to the surrounding atmosphere. The porous buffer layer (51) may include, for example, a closed-cell porous foam, an open-cell porous foam, a closed-cell porous sponge, an open-cell porous sponge, or a combination thereof. Porous foam can contain, for example, closed cells and open cells simultaneously. Porous sponge can contain, for example, closed cells and open cells simultaneously.

[0042] The porous buffer layer (51) may be, for example, an adhesive layer. Since the porous buffer layer (51) has adhesive properties, the porous protective layer (52) can be easily attached to one or both sides of the porous buffer layer (51). Since the porous buffer layer (51) is an adhesive layer, the porous protective layer (52) may not be easily detached after being attached to the porous buffer layer (51) and the porous protective layer (52). The porous adhesive layer (51) may have viscoelasticity. For example, a porous foam sheet and a porous sponge sheet may be adhesive sheets.

[0043] The porous buffer layer (51) may include a polymer material, a rubber material, or a combination thereof. By including a polymer material, a rubber material, or a combination thereof, the porous buffer layer (51) may have stress relief and resilience. The polymer material may include, for example, a polyurethane-based polymer, a polyacrylic-based polymer, a polystyrene-based polymer, a polyester-based polymer, a polyamide-based polymer, a polyolefin-based polymer, or a combination thereof. The polymer material may be, for example, a polymer resin. The polymer material may be, for example, an adhesive resin. Rubber materials may include, for example, natural rubber (NR), butadiene rubber (BR), nitrile rubber, silicone rubber, isoprene rubber (IR), styrene-butadiene rubber (SBR), isoprene-butadiene rubber, styrene-isoprene-butadiene rubber, acrylonitrile-butadiene rubber (NBR), ethylene-propylene-diene rubber, butyl halogenated rubber, chloroprene (CR), isoprene halogenated rubber, isobutylene copolymer, chloroprene rubber, butyl rubber (IIR), isobutylene-p-methylstyrene halogenated rubber, or a combination thereof. Polyurethane-based polymers may include, for example, polyester-based polyurethane, polyether-based polyurethane, or a combination thereof. Polyacrylic polymers may include, for example, polyacrylate, methyl polyacrylate, polymethacrylate, polymethyl methacrylate, or a combination thereof.Polystyrene-based polymers may include, for example, styrene-ethylene-butylene copolymer (SEB), styrene-butadiene-styrene copolymer (SBS), hydrogenated form of SBS (styrene-ethylene-butylene-styrene copolymer (SEBS)), styrene-isoprene-styrene copolymer (SIS), hydrogenated form of SIS (styrene-ethylene-propylene-styrene copolymer (SEPS)), styrene-isobutylene-styrene copolymer (SIBS), styrene-butadiene-styrene-butadiene (SBSB), styrene-butadiene-styrene-butadiene-styrene (SBSBS), polystyrene (PS), acrylonitrile-styrene copolymer (AS), acrylonitrile-butadiene-styrene copolymer (ABS), or a combination thereof. Polyester-based polymers may include, for example, polyethylene terephthalate, polybutylene terephthalate, or a combination thereof. Polyamide-based polymers may include, for example, polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, or a combination thereof. Polyolefin-based polymers include, for example, polyethylene, polypropylene, ethylene-propylene copolymer, propylene-1-hexene copolymer, propylene-4-methyl-1-pentene copolymer, propylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-4-methyl-pentene copolymer, ethylene-1-butene copolymer, 1-butene-1-hexene copolymer, 1-butene-4-methyl-pentene, ethylene methacrylic acid copolymer, ethylene ethyl methacrylate copolymer, ethylene ethyl methacrylate copolymer, ethylene butyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, propylene-methacrylic acid copolymer, propylene-methyl methacrylate copolymer, propylene-ethyl methacrylate copolymer, It may include propylene-butyl methacrylate copolymer, propylene-methyl acrylate copolymer, propylene-ethyl acrylate copolymer, propylene-butyl acrylate copolymer, ethylene-vinyl acetate copolymer (EVA), polyolefin of propylene-vinyl acetate copolymer, or a combination thereof.

[0044] [Porous multilayer component: Porous protective layer]

[0045] Referring to FIGS. 5a and 5b, a porous multilayer member (50) comprises a porous cushioning layer (51); and a porous protecting layer (52, 52a, 52b) disposed on one or both sides of the porous cushioning layer (51).

[0046] The porous protective layer (52) is disposed on one or both sides of the porous buffer layer (51) to provide a more uniform surface to the porous multilayer member (50). The porous protective layer (52) provides a protective function that prevents unnecessary contact and / or contamination between the porous buffer layer (51) and the external environment. Since the porous protective layer (52) is porous, the formation of an air pocket between the porous multilayer member (50) and the electrode assembly (40) can be prevented more effectively.

[0047] The porous protective layer (52) may be, for example, a non-adhesive layer. Since the porous protective layer (52) does not have adhesive properties, the porous multilayer member (50) having the porous protective layer (52) does not have adhesive properties. The porous multilayer member (52) can be easily wound together with, for example, the electrode assembly (40) or easily placed on one or both sides of the electrode assembly (40). The porous multilayer member (50) can be easily placed continuously between, for example, a plurality of electrode assemblies (40). Accordingly, the ease of operation or efficiency of the manufacturing process of the all-solid-state secondary battery (1) can be significantly improved.

[0048] The thickness (T52) of the porous protective layer may be, for example, 30 μm or less, 20 μm or less, or 10 μm or less. The thickness (T52) of the porous protective layer may be, for example, 0.1 μm to 30 μm, 0.5 μm to 20 μm, or 1 μm to 10 μm. The thickness (T52) of the porous protective layer may be 90% or less, 70% or less, 50% or less, 30% or less, or 20% or less of the thickness (T51) of the porous buffer layer.

[0049] The air permeability of the porous protective layer (52) may be, for example, 1000 sec / 100 cc or less, 500 sec / 100 cc or less, or 200 sec / 100 cc or less. The air permeability of the porous protective layer (52) may be, for example, 10 sec / 100 cc to 1000 sec / 100 cc, 50 sec / 100 cc to 500 sec / 100 cc, or 100 sec / 100 cc to 200 sec / 100 cc. The air permeability may be measured as a Gurley value. The Gurley value may be measured by the method according to JIS P8117. By having the porous protective layer (51) have this range of air permeability, the formation of air pockets between the porous multilayer member (50) and the electrode assembly (40) can be prevented more effectively, while the mechanical strength of the porous protective layer (52) can be maintained more effectively.

[0050] The porosity of the porous protective layer (52) may be, for example, 5% to 95%, 10% to 90%, 20% to 80%, 30% to 70%, or 35% to 55%. By having the porosity of the porous protective layer (52) within this range, the durability of the porous multilayer member (50) can be maintained more effectively while effectively preventing the formation of air pockets between the porous multilayer member (50) and the electrode assembly (40). The porosity can be calculated from the volume, weight, and density of the material constituting the porous protective layer (52). Alternatively, the porosity of the porous protective layer can be measured by the liquid or gas adsorption method according to ASTM D-2873.

[0051] The pore size included in the porous protective layer (52) may be, for example, 0.01 μm to 20 μm, 0.01 μm to 10 μm, 0.01 μm to 1 μm, or 0.01 μm to 0.5 μm. The pore size may be an average pore size. By including a pore size within this range in the porous protective layer (52), the mechanical strength of the porous protective layer (50) can be maintained more effectively while more effectively preventing the formation of air pockets between the porous multilayer member (50) and the electrode assembly (40). The pore size may be measured, for example, by a nitrogen adsorption method. The pore size can be measured by the BET 6-point method using the nitrogen gas adsorption flow method with scanning electron microscope (SEM) images, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

[0052] The porous protective layer (52) may include, for example, a polyolefin-based polymer, a cellulose-based polymer, or a combination thereof.

[0053] Polyolefin-based polymers may be homopolymers, copolymers, or mixtures thereof, such as polyethylene and polypropylene. Polyethylene may be low-density, medium-density, or high-density polyethylene, and high-density polyethylene may be used for mechanical strength. Additionally, two or more types of polyethylene may be mixed for the purpose of imparting flexibility. For the purpose of achieving both mechanical strength and high permeability, the weight-average molecular weight of polyethylene may be, for example, 100,000 Dalton to 12 million Dalton, or 200,000 Dalton to 3 million Dalton. Polypropylene may be a homopolymer, a random copolymer, or a block copolymer, and may be used alone or in a mixture of two or more. The stereoregularity of polypropylene is not particularly limited, and isotactic, syndiotactic, or atactic may be used, but inexpensive isotactic polypropylene may be used. Additives such as polyolefins other than polyethylene or polypropylene and antioxidants may be added to the polyolefin. The porous protective layer (52) may include polyolefins such as polyethylene and polypropylene, for example, and may have a multilayer structure of two or more layers. The porous protective layer (52) may have a mixed multilayer structure such as a polyethylene / polypropylene two-layer structure, a polyethylene / polypropylene / polyethylene three-layer structure, a polypropylene / polyethylene / polypropylene three-layer structure, for example, but is not limited to these, and any material and composition that can be used in the relevant technical field is possible.

[0054] Cellulose-based polymers may include, for example, plant-based cellulose polymers, animal-based cellulose polymers, microbial cellulose polymers, or combinations thereof.

[0055] The porous protective layer (52) may be, for example, a porous film. The porous film may be, for example, a woven or nonwoven fabric. The porous film may be manufactured, for example, by wet or dry. The wet method may produce the porous film by, for example, by removing the solvent and the nonsolvent from a composition comprising a polymer, a solvent and a nonsolvent. The dry method may produce the porous film by stretching the polymer film in the machine direction (MD) and / or the transverse direction (TD). The stretching of the polymer film may be performed, for example, in a vaporized solvent atmosphere.

[0056] The porous protective layer (52) includes a porous membrane, and the porous membrane may include, for example, a cellulose-based polymer. The porous membrane may include, for example, cellulose nanofibers. The cellulose nanofibers included in the porous membrane may include microbial cellulose or bacterial cellulose nanofibers, lignocellulosic cellulose nanofibers, etc. Microbial cellulose nanofibers can be obtained directly from a culture medium containing microorganisms as a fermentation product of a culture medium containing microorganisms. In particular, the carboxyl group-containing cellulose nanofibers included in the porous membrane may be carboxyl group-containing microbial cellulose or bacterial cellulose nanofibers. That is, carboxyl group-containing microbial cellulose nanofibers are obtained directly from a culture medium containing microorganisms as a fermentation product of a culture medium containing microorganisms. Therefore, the carboxyl group-containing microbial cellulose nanofibers included in the porous membrane are distinguished from a mixture of conventional general microbial cellulose nanofibers and carboxyl group-containing compounds. Lignocellulosic cellulose nanofibers can be obtained by decomposing lignocellulosic materials. The average diameter of the cellulose nanofibers contained in the porous membrane may be 100 nm or less, 80 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, or 25 nm or less. For example, the average diameter of the cellulose nanofibers contained in the porous membrane may be 1 nm to 100 nm, 1 nm to 80 nm, 1 nm to 60 nm, 1 nm to 50 nm, 1 nm to 45 nm, or 5 nm to 45 nm. The tensile strength of the porous membrane may be improved by the porous membrane containing cellulose nanofibers having an average diameter within this range. The thermal shrinkage rate of the porous membrane after being left at 150°C for 30 minutes is 5% or less, 4.5% or less, 4% or less, 3.5% or less, 3% or less, 2.It may be 5% or less, 2% or less, 1.5% or less, or 1% or less. Since the porous membrane provides excellent thermal stability at high temperatures of 150°C or higher, the heat resistance of the porous multilayer member (50) including the porous membrane and the all-solid-state secondary battery (1) may be improved.

[0057] The porous protective layer (52) includes a porous membrane, and the porous membrane may have, for example, a single layer or a multilayer structure. Depending on the conditions required for the porous multilayer member, the porous membrane may have a single layer or a multilayer structure. The porous membrane may be a non-adhesive membrane.

[0058] [Solid Electrolyte Layer]

[0059] [Solid Electrolyte Layer: Sulfide-based Solid Electrolyte]

[0060] Referring to FIGS. 1 to 4, a solid electrolyte layer (30) is disposed between the anode layer (10) and the cathode layer (20). The solid electrolyte layer (30) may include a sulfide-based solid electrolyte.

[0061] The sulfide-based solid electrolyte included in the solid electrolyte layer (30) is, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li3PS4, Li7P3S 11 , Li 7-x PS 6-x Cl x, 0(x(2, Li 7-x PS 6-x Br x , 0(x(2, and Li 7-x PS 6-x I x , 0(x(2) is one or more selected from. Sulfide-based solid electrolytes are manufactured by processing starting materials, such as Li2S and P2S5, by methods such as melt quenching or mechanical milling. Additionally, heat treatment may be performed after such processing. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. Furthermore, the solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above, for example. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form the solid electrolyte, the mixed molar ratio of Li2S and P2S5 is, for example, in the range of Li2S : P2S5 = 50 : 50 to 90 : 10. The sulfide-based solid electrolyte is, for example, represented by the following chemical formula 1. It may include an argyrodite-type solid electrolyte:

[0062] <Chemical Formula 1>

[0063] Li + 12-n-x A n+ X 2- 6-x Y - x

[0064] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; X is S, Se, or Te; Y is Cl, Br, I, F, CN, OCN, SCN, or N3; and 1(n(5) and 0(x(2). Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Cl x, 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x It may be an argyrodite-type compound containing one or more selected from 0≤x≤2. The sulfide-based solid electrolyte may be an argyrodite-type compound containing one or more selected from, for example, Li6PS5Cl, Li6PS5Br, and Li6PS5I. The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed.

[0065] The elastic modulus of the sulfide-based solid electrolyte may be, for example, 40 GPa or less. The elastic modulus of the sulfide-based solid electrolyte may be, for example, 5 GPa to 40 GPa, 10 GPa to 40 GPa, or 15 GPa to 30 GPa.

[0066] The average particle size of the sulfide-based solid electrolyte particles included in the solid electrolyte layer (30) may be, for example, 1 µm to 50 µm, 3 µm to 30 µm, or 3 µm to 20 µm. By having the sulfide-based solid electrolyte particles have an average particle size within this range, the cycle characteristics of the all-solid-state secondary battery can be further improved.

[0067] [Solid Electrolyte Layer: Binder]

[0068] The solid electrolyte layer (30) may further include, for example, a binder. The binder included in the solid electrolyte layer (30) may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these and any binder used in the relevant technical field is possible. The binder of the solid electrolyte layer (30) may be the same as or different from the binder included in the positive electrode active material layer (12) and the negative electrode active material layer (22). The binder may be omitted.

[0069] The binder included in the solid electrolyte layer may include, for example, a conductive binder and / or a non-conductive binder.

[0070] Conductive binders are, for example, ion-conducting binders and / or electronic-conducting binders. Binders that possess both ion conductivity and electronic conductivity may belong to both ion-conducting binders and electronic-conducting binders.

[0071] Ion-conducting binders are, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polystyrene sulfonate (PSS), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinyl fluoride (PVF), poly(methylmethacrylate) (PMMA), polyethylene oxide (PEO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), polyaniline, and polyacetylene. Ion-conducting binders may include polar functional groups. Ion-conducting binders containing polar functional groups are, for example, Nafion, Aquivion, and Flemion. (Flemion), Gore, Aciplex, Morgane ADP, sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(arylene ether ketone sulfone) (SPAEKKS), sulfonated poly(aryl ether ketone) (SPAEK), poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI), polystyrene sulfonate (PSS), lithium 9,10-diphenylanthracene-2-sulfonate (DPASLi +) etc. Electronically conductive binders include, for example, polyacetylene, polythiophene, polypyrrole, poly(p-phenylene), poly(phenylenevinylene), poly(phenylenesulfide), polyaniline, etc.

[0072] The binder included in the solid electrolyte layer (30) may include, for example, a first binder. The first binder is, for example, a dry binder. A dry binder is, for example, a binder that is not impregnated, dissolved, or dispersed in a solvent. A dry binder is, for example, a binder that contains a solvent or does not come into contact with a solvent.

[0073] The first binder is, for example, a fibrillized binder. The fibrillized binder can serve as a fibrous matrix that supports and binds together a plurality of sulfide-based solid electrolyte particles and inorganic particles contained in the solid electrolyte layer. The fibrillized binder can be confirmed to have a fibrous form, for example, by scanning electron microscope images of the electrode cross-section. The fibrillized binder may have an aspect ratio of, for example, 10 or more, 20 or more, 50 or more, or 100 or more. The first binder is, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexapropylene (PVDF-HFP) copolymer, but is not necessarily limited to these, and any fibrillized binder used in the preparation of the dry composition is acceptable. The first binder may particularly include a fluorine-based binder. The fluorine-based binder is, for example, polytetrafluoroethylene (PTFE).

[0074] The binder included in the solid electrolyte layer (30) may further include, for example, a second binder. The second binder is, for example, a dry binder. The description of the dry binder is the same as that of the first binder.

[0075] The second binder is, for example, a non-fibrillized binder. The non-fibrillized binder can support the sulfide-based solid electrolyte particles and inorganic particles contained in the solid electrolyte layer and act as binding sites to bind them together. The non-fibrillized binder can be confirmed to be arranged in a particulate form rather than having a fibrous form, for example, by scanning electron microscope images of the electrode cross-section. The non-fibrillized binder may have an aspect ratio of, for example, 5 or less, 3 or less, or 2 or less. The second binder is, for example, polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or copolymers thereof, but is not necessarily limited to these, and any binder used in the manufacture of a dry electrode is acceptable. The second binder may particularly include a fluorine-based binder. The fluorine-based binder is, for example, polyvinylidene fluoride (PVDF).

[0076] The content of the binder included in the solid electrolyte layer (30) is, for example, 1 wt% to 10 wt%, 1 wt% to 5 wt%, or 1 wt% to 3 wt% with respect to the total weight of the solid electrolyte layer. By including a binder in this content range, the binding strength of the solid electrolyte layer is improved, and the all-solid-state secondary battery can maintain a high energy density.

[0077] The solid electrolyte layer (30) is, for example, a self-standing film. The solid electrolyte layer can maintain a film form without, for example, a support. Thus, the solid electrolyte layer can be prepared as a separate self-standing film and then placed between the anode layer and the cathode layer. The solid electrolyte layer may be, for example, free of residual processing solvent. For example, since the solid electrolyte layer is manufactured dry, it does not contain any intentionally added processing solvent. For example, it does not contain any residual processing solvent. Although an unintended trace amount of solvent may remain in the solid electrolyte layer, this solvent is not an intentionally added processing solvent. Thus, the solid electrolyte layer is distinguished from a wet solid electrolyte layer manufactured by mixing sulfide-based solid electrolyte particles with a processing solvent and then removing some or all of the processing solvent by drying.

[0078] [Cathode layer]

[0079] [Cathode layer: Cathode active material]

[0080] Referring to FIGS. 1 to 4, the cathode layer (20) comprises a cathode current collector (21); and a first cathode active material layer (22) disposed on the cathode current collector. The first cathode active material layer (22) comprises, for example, a cathode active material and a binder.

[0081] The negative electrode active material included in the first negative electrode active material layer (22) has, for example, a particle shape. The average particle size of the negative electrode active material having a particle shape is, for example, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, or 900 nm or less. The average particle size of the negative electrode active material having a particle shape is, for example, 10 nm to 4 μm or less, 10 nm to 3 μm or less, 10 nm to 2 μm or less, 10 nm to 1 μm or less, or 10 nm to 900 nm or less. By having the negative electrode active material with an average particle size within this range, the reversible absorption and / or desorption of lithium during charging and discharging may be more facilitated. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size distribution meter.

[0082] The cathode active material included in the first cathode active material layer (22) comprises, for example, one or more selected from carbon-based cathode active materials and metal or metalloid cathode active materials.

[0083] The carbon-based cathode active material is, in particular, amorphous carbon. Amorphous carbon is, for example, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, etc., but is not necessarily limited to these, and any material classified as amorphous carbon in the relevant technical field is acceptable. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0084] The metal or metalloid cathode active material comprises one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), but is not necessarily limited to these; any metal cathode active material or metalloid cathode active material that forms an alloy or compound with lithium in the relevant technical field is acceptable. For example, nickel (Ni) is not a metal cathode active material because it does not form an alloy with lithium.

[0085] The first negative electrode active material layer (22) may include a type of negative electrode active material among these negative electrode active materials, or may include a mixture of multiple different negative electrode active materials. For example, the first negative electrode active material layer (22) may include only amorphous carbon, or one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the first negative electrode active material layer (22) may include a mixture of amorphous carbon and one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of a mixture of amorphous carbon and gold, etc., is, for example, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1 by weight ratio, but is not necessarily limited to these ranges and is selected according to the required characteristics of the all-solid-state secondary battery (1). By having the negative electrode active material have this composition, the cycle characteristics of the all-solid-state secondary battery (1) are further improved.

[0086] The negative electrode active material included in the first negative electrode active material layer (22) comprises a mixture of first particles made of amorphous carbon, for example, and second particles made of a metal or metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the metalloid is a semiconductor. The content of the second particles is 8 to 60 weight%, 10 to 50 weight%, 15 to 40 weight%, or 20 to 30 weight% based on the total weight of the mixture. By having the second particles in this range, the cycle characteristics of, for example, the all-solid-state secondary battery (1) are further improved.

[0087] [Cathode layer: Binder]

[0088] The binder included in the first negative electrode active material layer (22) may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited to these and any binder used in the relevant technical field is possible. The binder may be composed of a single binder or a plurality of different binders.

[0089] The first negative active material layer (22) is stabilized on the negative current collector (21) by including a binder. Additionally, cracking of the first negative active material layer (22) is suppressed despite volume changes and / or relative position changes of the first negative active material layer (22) during the charging and discharging process. For example, if the first negative active material layer (22) does not include a binder, it is possible for the first negative active material layer (22) to be easily separated from the negative current collector (21). As the first negative active material layer (22) is separated from the negative current collector (21), the possibility of a short circuit occurring increases in the portion of the negative current collector (21) that is exposed, as the negative current collector (21) comes into contact with the solid electrolyte layer (30). The first negative electrode active material layer (22) is manufactured by, for example, applying a slurry in which the material constituting the first negative electrode active material layer (22) is dispersed onto a negative electrode current collector (21) and drying it. By including a binder in the first negative electrode active material layer (22), stable dispersion of the negative electrode active material in the slurry is possible. For example, when applying the slurry onto the negative electrode current collector (21) using a screen printing method, it is possible to suppress clogging of the screen (for example, clogging caused by aggregates of the negative electrode active material).

[0090] [Cathode layer: Other additives]

[0091] The first negative electrode active material layer (22) may further include additives used in conventional all-solid-state secondary batteries (1), such as fillers, coating agents, dispersants, ion-conducting aids, etc.

[0092] [Cathode layer: First cathode active material layer]

[0093] The thickness of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer (12). The thickness of the first negative electrode active material layer (22) is, for example, 1 μm to 20 μm, 2 μm to 10 μm, or 3 μm to 7 μm. If the thickness of the first negative electrode active material layer (22) is excessively thin, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) cause the first negative electrode active material layer (22) to collapse, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0094] If the thickness of the first negative electrode active material layer (22) decreases, for example, the charging capacity of the first negative electrode active material layer (22) also decreases. The charging capacity of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 5% or less, or 2% or less compared to the charging capacity of the positive electrode active material layer (12). The charging capacity of the first negative electrode active material layer (22) is, for example, 0.1% to 50%, 0.1% to 40%, 0.1% to 30%, 0.1% to 20%, 0.1% to 10%, 0.1% to 5%, or 0.1% to 2% compared to the charging capacity of the positive electrode active material layer (12). If the charge capacity of the first negative electrode active material layer (22) is excessively small, the thickness of the first negative electrode active material layer (22) becomes very thin, and thus, during repeated charge and discharge processes, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) cause the first negative electrode active material layer (22) to collapse, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the charge capacity of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases, and the internal resistance of the all-solid-state secondary battery (1) caused by the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0095] The charge capacity of the positive active material layer (12) is obtained by multiplying the charge capacity density (mAh / g) of the positive active material by the mass of the positive active material in the positive active material layer (12). When multiple types of positive active materials are used, the charge capacity density × mass value is calculated for each positive active material, and the sum of these values ​​is the charge capacity of the positive active material layer (12). The charge capacity of the first negative active material layer (22) is also calculated in the same way. That is, the charge capacity of the first negative active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative active material by the mass of the negative active material in the first negative active material layer (22). When multiple types of negative active materials are used, the charge capacity density × mass value is calculated for each negative active material, and the sum of these values ​​is the capacity of the first negative active material layer (22). Here, the charge capacity density of the positive active material and the negative active material is a capacity estimated using an all-solid-state half-cell using lithium metal as the counter electrode. The charge capacity of the positive active material layer (12) and the first negative active material layer (22) is directly measured by measuring the charge capacity using an all-solid-state half-cell. By dividing the measured charge capacity by the mass of each active material, the charge capacity density is obtained. Alternatively, the charge capacity of the positive active material layer (12) and the first negative active material layer (22) may be the initial charge capacity measured during the first cycle of charging.

[0096] [Cathode layer: Second cathode active material layer]

[0097] Although not shown in the drawing, the all-solid-state secondary battery (1) further includes a second negative active material layer disposed between, for example, a negative current collector (21) and a first negative active material layer (22) by charging. The second negative active material layer is a metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the second negative active material layer is a metal layer containing lithium, it acts as, for example, a lithium reservoir. The lithium alloy is, for example, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited to these, and any alloy used as a lithium alloy in the relevant technical field is possible. The second negative active material layer may be composed of one of these alloys or lithium, or may be composed of various types of alloys. The second negative active material layer is, for example, a plated layer. For example, the second negative electrode active material layer is deposited between the first negative electrode active material layer (22) and the negative electrode current collector (21) during the charging process of the all-solid-state secondary battery (1).

[0098] The thickness of the second negative electrode active material layer is not particularly limited, but is, for example, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the second negative electrode active material layer is excessively thin, it is difficult for the second negative electrode active material layer to perform the role of a lithium reservoir. If the thickness of the second negative electrode active material layer is excessively thick, the mass and volume of the all-solid-state secondary battery (1) may increase, and the cycle characteristics may actually deteriorate. The second negative electrode active material layer may be, for example, a metal foil having a thickness within this range.

[0099] In the all-solid-state secondary battery (1), the second negative active material layer is disposed between the negative current collector (21) and the first negative active material layer (22) for example before assembly of the all-solid-state secondary battery (1), or is deposited between the negative current collector (21) and the first negative active material layer (22) by charging after assembly of the all-solid-state secondary battery (1). When the second negative active material layer (23) is disposed between the negative current collector (21) and the first negative active material layer (22) before assembly of the all-solid-state secondary battery (1), the second negative active material layer acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil is disposed between the negative current collector (21) and the first negative active material layer (22) before assembly of the all-solid-state secondary battery (1). By doing so, the cycle characteristics of the all-solid-state secondary battery (1) including the second negative active material layer are further improved. When a second negative electrode active material layer is precipitated by charging after assembly of the all-solid-state secondary battery (1), the energy density of the all-solid-state secondary battery (1) increases because the second negative electrode active material layer is not included during assembly of the all-solid-state secondary battery (1). For example, when charging the all-solid-state secondary battery (1), it is charged beyond the charging capacity of the first negative electrode active material layer (22). That is, the first negative electrode active material layer (22) is overcharged. At the beginning of charging, lithium is absorbed in the first negative electrode active material layer (22). The negative electrode active material contained in the first negative electrode active material layer (22) forms an alloy or compound with lithium ions that have moved from the positive electrode layer (10). When charging is performed beyond the capacity of the first negative electrode active material layer (22), lithium is deposited, for example, on the back surface of the first negative electrode active material layer (22), that is, between the negative current collector (21) and the first negative electrode active material layer (22), and a metal layer corresponding to the second negative electrode active material layer is formed by the deposited lithium. The second negative electrode active material layer is a metal layer composed mainly of lithium (i.e., metallic lithium). This result is obtained, for example, by the negative electrode active material included in the first negative electrode active material layer (22) being composed of a material that forms an alloy or compound with lithium.During discharge, lithium in the first negative electrode active material layer (22) and the second negative electrode active material layer, i.e., the metal layer, is ionized and moves toward the positive electrode layer (10). Therefore, it is possible to use lithium as a negative electrode active material in the all-solid-state secondary battery (1). In addition, since the first negative electrode active material layer (22) covers the second negative electrode active material layer, it acts as a protective layer for the second negative electrode active material layer, i.e., the metal layer, and at the same time, it performs the role of suppressing the precipitation growth of lithium dendrites. Therefore, short circuits and capacity degradation of the all-solid-state secondary battery (1) are suppressed, and consequently, the cycle characteristics of the all-solid-state secondary battery (1) are improved. Additionally, when a second negative electrode active material layer is disposed by charging after assembly of the all-solid-state secondary battery (1), the negative electrode current collector (21), the first negative electrode active material layer (22), and the region between them are, for example, Li-free regions that do not contain lithium (Li) in the initial state or after discharge state of the all-solid-state secondary battery.

[0100] [Cathode layer: Cathode current collector]

[0101] The negative electrode current collector (21) is composed of a material that does not react with, for example, lithium, that is, does not form any alloys or compounds. The material constituting the negative electrode current collector (21) may be, for example, copper (Cu), stainless steel (SUS), titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but is not necessarily limited to these; any material used as an electrode current collector in the relevant technical field is acceptable. The negative electrode current collector (21) may be composed of one of the metals described above, or may be composed of an alloy or coating material of two or more metals. The negative electrode current collector (21) is, for example, in the form of a plate or foil.

[0102] The all-solid-state secondary battery (1) may further include a thin film containing an element capable of forming an alloy with lithium, for example, on a negative electrode current collector (21). The thin film is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22). The thin film contains, for example, an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium is, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., but is not necessarily limited to these, and any element capable of forming an alloy with lithium in the relevant technical field is possible. The thin film is composed of one of these metals or is composed of an alloy of various types of metals. By disposing of the thin film on the negative electrode current collector (21), the deposition pattern of the second negative electrode active material layer, which is deposited between, for example, the thin film (24) and the first negative electrode active material layer (22), is further flattened, and the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[0103] The thickness of the thin film is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film is less than 1 nm, it may be difficult to perform the function provided by the thin film. If the thickness of the thin film is excessively thick, the thin film itself absorbs lithium, and the amount of lithium precipitated at the negative electrode decreases, which lowers the energy density of the all-solid-state battery and may degrade the cycle characteristics of the all-solid-state secondary battery (1). The thin film may be placed on the negative electrode current collector (21) by, for example, vacuum deposition, sputtering, plating, etc., but is not necessarily limited to these methods, and any method capable of forming a thin film in the relevant technical field is possible.

[0104] [Bipolar]

[0105] [Anode layer: Anode active material]

[0106] Referring to FIGS. 1 to 4, the positive active material layer (12) includes, for example, a positive active material and a solid electrolyte.

[0107] The positive active material included in the positive active material layer (12) is a positive active material capable of reversibly absorbing and desorbing lithium ions. The positive active material may be, for example, lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited to these and any material used as a positive active material in the relevant technical field is possible. Each positive active material may be a single material or a mixture of two or more materials.

[0108] The cathode active material includes, for example, a lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium transition metal oxides described above. The "layered rock salt type structure" is, for example, a cubic rock salt type structure. <111> It is a structure in which oxygen and metal atomic layers are alternately and regularly arranged in a specific direction, thereby forming a two-dimensional plane for each layer. The "cubic rock salt type structure" represents a sodium chloride (NaCl type) structure, which is a type of crystal structure; specifically, it exhibits a structure in which the face-centered cubic lattices (fcc) formed by cations and anions, respectively, are offset from each other by half the ridge of the unit lattice. Lithium transition metal oxides having such a layered rock salt type structure are, for example, LiNi x Co y Al z O2(NCA) or LiNi x Coy Mn z It is a ternary lithium transition metal oxide such as O2(NCM) (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1). When the positive electrode active material includes a ternary lithium transition metal oxide having a layered rock salt structure, the energy density and thermal stability of the all-solid-state secondary battery (1) are further improved.

[0109] As described above, the positive electrode active material may be covered by a coating layer. The coating layer may be any material known as a coating layer for the positive electrode active material of an all-solid-state secondary battery. For example, the coating layer is Li2O-ZrO2 (LZO), etc.

[0110] When the positive electrode active material contains nickel (Ni) as a ternary lithium transition metal oxide such as NCA or NCM, for example, the capacity density of the all-solid-state secondary battery (1) is increased, and the metal leaching of the positive electrode active material in the charged state can be reduced. As a result, the cycle characteristics of the all-solid-state secondary battery (1) in the charged state are improved.

[0111] The shape of the positive active material is, for example, a particle shape such as a sphere, an elliptical sphere, etc. The particle size of the positive active material is not particularly limited and is within a range applicable to the positive active material of a conventional all-solid-state secondary battery. The content of the positive active material of the positive layer (10) is also not particularly limited and is within a range applicable to the positive layer of a conventional all-solid-state secondary battery.

[0112] [Anode layer: Solid electrolyte]

[0113] The positive electrode active material layer (12) may include, for example, a solid electrolyte. The solid electrolyte included in the positive electrode layer (10) may be the same as or different from the solid electrolyte included in the solid electrolyte layer (30). For details regarding the solid electrolyte, refer to the solid electrolyte layer (30).

[0114] The solid electrolyte included in the positive electrode active material layer (12) may have a smaller average D50 particle size compared to the solid electrolyte included in the solid electrolyte layer (30). For example, the average D50 particle size of the solid electrolyte included in the positive electrode active material layer (12) may be 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average D50 particle size of the solid electrolyte included in the solid electrolyte layer (30).

[0115] The average particle size of D50 is, for example, the median particle diameter (D50). The median particle diameter (D50) is the particle size corresponding to 50% of the cumulative volume calculated from the particle side having a small particle size in the particle size distribution measured, for example by laser diffraction.

[0116] [Bipolar layer: Binder]

[0117] The positive active material layer (12) may include a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these, and any binder used in the relevant technical field is acceptable.

[0118] [Bipolar Layer: Challenge Material]

[0119] The positive active material layer (12) may include a conductive material. The conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, etc., but is not limited to these and any material used as a conductive material in the relevant technical field is possible.

[0120] [Anode Layer: Other Additives]

[0121] The positive active material layer (12) may further include additives such as fillers, coating agents, dispersants, and ion conductivity aids in addition to the positive active material, solid electrolyte, binder, and conductive material described above.

[0122] The filler, coating agent, dispersant, ion-conducting auxiliary agent, etc. that the positive electrode active material layer (12) may include can be any known material generally used in the electrodes of all-solid-state secondary batteries.

[0123] [Bipolar layer: Bipolar current collector]

[0124] The positive current collector (11) is made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, such as a plate or foil. The positive current collector (11) may be omitted. The thickness of the positive current collector (11) is, for example, 1 µm to 100 µm, 1 µm to 50 µm, 5 µm to 25 µm, or 10 µm to 20 µm.

[0125] [Bipolar layer: Inert component]

[0126] Referring to FIGS. 3 and 4, the anode layer (10) comprises an anode current collector (11) and an anode active material layer (12) disposed on one side of the anode current collector. An inactive member (60) is disposed on one side of the anode layer (10). The inactive member (60) is disposed on one side of the anode active material layer (12) and the anode current collector (11). Alternatively, although not shown in the drawings, the inactive member (60) may be disposed on one side of the anode active material layer (12) and on one side of the anode current collector (11) facing the solid electrolyte layer. The area of ​​the porous multilayer member (50) may be larger than that of the anode active material layer (12). The area of ​​the porous multilayer member (50) may be equal to or similar to the area of ​​the cathode layer (20) and / or the solid electrolyte layer. The porous multilayer member (50) has an area equal to or similar to that of the negative electrode layer, thereby allowing for more effective capacity for volume changes in the all-solid-state secondary battery (1).

[0127] By including an inert member (60), cracking of the solid electrolyte layer (30) is prevented during manufacturing and / or charging and discharging of the all-solid-state secondary battery (1), and consequently, the cycle characteristics of the all-solid-state secondary battery (2) are improved. In an all-solid-state secondary battery (1) that does not include an inert member (60), uneven pressure is applied to the solid electrolyte layer (30) in contact with the positive electrode layer (10) during manufacturing and / or charging and discharging of the all-solid-state secondary battery (1), which increases the likelihood of cracking occurring in the solid electrolyte layer (30) and a short circuit occurring as a result.

[0128] The inert member (60) surrounds the side of the anode layer (10) and comes into contact with the solid electrolyte layer (30). By the inert member (60) surrounding the side of the anode layer (10) and coming into contact with the solid electrolyte layer (30), cracks in the solid electrolyte layer (30) caused by pressure differences during the pressing process in the solid electrolyte layer (30) that does not come into contact with the anode layer (20) can be effectively suppressed. The inert member (60) surrounds the side of the anode layer (10) and is separated from the cathode layer (20), more specifically from the first cathode active material layer (22). The inert member (60) surrounds the side of the anode layer (10), comes into contact with the solid electrolyte layer (30), and is separated from the cathode layer (20). Therefore, the possibility of a short circuit occurring due to physical contact between the anode layer (10) and the first cathode active material layer (22), or due to overcharging of lithium, is suppressed.

[0129] The inert member (60) may be, for example, a gasket. By using a gasket as the inert member (60), cracks in the solid electrolyte layer (30) caused by pressure differences during the pressurization process can be effectively suppressed.

[0130] Referring to FIG. 4, the all-solid-state secondary battery (1) comprises a positive electrode layer (10), a negative electrode layer (20), and a solid electrolyte layer (40) disposed between them; the positive electrode layer (10) comprises a positive current collector (11) and a first positive active material layer (12a) and a second positive active material layer (12b) disposed on both sides of the positive current collector (11), respectively; the solid electrolyte layer (30) comprises a first solid electrolyte layer (30a) in contact with the first positive active material layer (12a) and a second solid electrolyte layer (30b) in contact with the second positive active material layer (12b), respectively; the negative electrode layer (20) comprises a first negative electrode layer (20a) in contact with the first solid electrolyte layer (30a) and a second negative electrode layer (20b) in contact with the second solid electrolyte layer (30b), respectively; and the first solid electrolyte layer (30a) and The second solid electrolyte layer (30b) is positioned opposite each other, and includes an inert member (60) positioned between the first solid electrolyte layer (30a) and the second solid electrolyte layer (30b) to surround the side of the anode layer (10). Thus, the all-solid-state secondary battery (1) has a bi-cell structure. Since the all-solid-state secondary battery (1) has a bi-cell structure, the solid electrolyte layer (30) and the negative electrode layer (20) are symmetrically positioned opposite each other with the anode layer (10) as the center, so structural deformation caused by pressure applied during the manufacturing of the all-solid-state secondary battery (1) is more effectively suppressed. Therefore, cracking of the solid electrolyte layer (30) is suppressed during the manufacturing process and / or charging / discharging process of the all-solid-state secondary battery (1), thereby preventing a short circuit of the all-solid-state secondary battery (1) and consequently further improving the cycle characteristics of the all-solid-state secondary battery (1). In addition, since only one positive current collector (11) is used for multiple positive active material layers (12a, 12b), the energy density of the all-solid-state secondary battery (1) is increased. The area of ​​the porous multilayer member (50) may be larger than that of the first positive active material layer (12a) and / or the second positive active material layer (12b). The area of ​​the porous multilayer member (50) may be the same as or similar to the area of ​​the negative electrode layer (20) and / or the solid electrolyte layer.

[0131] [Electrode Assembly Stack]

[0132] Referring to FIGS. 6 and 7, the all-solid-state secondary battery (1) includes an electrode assembly stack (70). The electrode assembly stack (7) includes a plurality of electrode assemblies (40, 40a, 40b, 40c, 40d) spaced apart from each other along one direction, and a porous multilayer member (50) disposed between the plurality of electrode assemblies (40, 40a, 40b, 40c, 40d). By disposing of the porous multilayer member (50) between the plurality of electrode assemblies (40), volume changes during charging and discharging of the electrode assembly stack (70) can be effectively accommodated, and the structural stability of the all-solid-state secondary battery (1) can be improved. Consequently, the lifespan characteristics of the all-solid-state secondary battery (1) can be improved.

[0133] The thickness (T50) of the porous multilayer member may be smaller than the thickness (T40) of the electrode assembly. If the thickness (T50) of the porous multilayer member is larger than the thickness (T40) of the electrode assembly, the energy density of the all-solid-state secondary battery (1) may be excessively reduced. The thickness (T50) of the porous multilayer member may be 90% or less, 80% or less, 70% or less, 50% or less, 30% or less, 20% or less, or 10% or less of the thickness (T40) of the electrode assembly.

[0134] Referring to FIG. 6, in an electrode assembly stack (70), a plurality of porous multilayer members (50b, 50c, 50d) are respectively disposed between a plurality of electrode assemblies (40a, 40b, 40c, 40d) that are spaced apart from each other, and a porous multilayer member (50a, 50e) may be additionally disposed on the outermost layer of the electrode assembly stack (70). The electrode assembly stack (70) may be prepared in a magazine manner, for example, in which a plurality of porous multilayer members (50b, 50c, 50d) are discontinuously disposed between a plurality of electrode assemblies (40a, 40b, 40c, 40d).

[0135] Referring to FIG. 7, in an electrode assembly stack (70), a porous multilayer member (50) may be folded multiple times and arranged between a plurality of electrode assemblies (40a, 40b, 40c, 40d) that are spaced apart from each other, and a porous multilayer member (50a, 50e) may be extended and arranged on the outermost layer of the electrode assembly stack (70). The electrode assembly stack (70) may be prepared in a reel manner, for example, in which a porous multilayer member (50b, 50c, 50d) is continuously arranged between a plurality of electrode assemblies (40a, 40b, 40c, 40d).

[0136] Although not shown in the drawing, pressure plates may be additionally placed on both sides of the electrode assembly stack (70) in the solid secondary battery (1). By additionally placing pressure plates, a constant pressure may be applied to the electrode assembly (40).

[0137] [Manufacturing of All-Solid State Secondary Batteries]

[0138] (Manufacturing of porous multilayer members)

[0139] A porous multilayer member is prepared by placing a porous membrane on one or both sides of a porous sheet. The porous sheet corresponds to a porous buffer layer, and the porous membrane corresponds to a porous protective layer.

[0140] The porous sheet is, for example, a porous foam sheet or a porous sponge sheet. Since the porous sheet is adhesive, a porous membrane can be easily and directly attached to one or both sides of the porous sheet. Alternatively, a binder may be additionally placed between the porous sheet and the porous membrane to enhance adhesion. The binder may be the same as the binder used in the anode layer, cathode layer, and / or solid electrolyte layer.

[0141] The porous sheet has a thickness of 10 to 200 μm and may have an air permeability of 1000 sec / 100 cc or more. For more specific details regarding the porous sheet, refer to the porous buffer layer.

[0142] The porous membrane may have a thickness of 1 to 50 μm, an air permeability of 1000 sec / 100 cc or less, a porosity of 5 to 95%, and a pore size of 0.01 μm to 20 μm. For more specific details regarding the porous membrane, refer to the porous protective layer.

[0143] The porosity and / or average pore size of porous sheets and porous membranes can be measured by the BET 6-point method using nitrogen gas adsorption flow method, for example, with scanning electron microscope (SEM) images, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

[0144] (Preparation of solid electrolyte layer)

[0145] The solid electrolyte layer can be manufactured in a dry or wet manner.

[0146] A method for manufacturing a solid electrolyte layer by dry mixing includes the step of preparing a dry mixture by dry mixing a sulfide-based solid electrolyte and a binder; the step of preparing a solid electrolyte layer by molding the dry mixture; and the step of placing the solid electrolyte layer between an anode layer and a cathode layer, wherein the average particle size of the inorganic particles is 50 nm to 5 μm or less.

[0147] First, a dry mixture is prepared by mixing a sulfide-based solid electrolyte and a binder. Dry mixing refers to mixing without the inclusion of a process solvent. A dry mixture refers to a mixture in which a process solvent has not been intentionally added. A process solvent is, for example, a solvent used in the preparation of an electrode slurry. A binder is, for example, a dry binder. A dry binder refers to a binder that does not contain a process solvent. The process solvent is, for example, water, NMP, etc., but is not limited to these, and is not limited to any process solvent used in the preparation of an electrode slurry. Dry mixing can be performed using a stirrer at a temperature of, for example, 25 to 85°C or 65 to 85°C. Dry mixing can be performed using a stirrer at a rotational speed of, for example, 10 to 10,000 rpm or 100 to 10,000 rpm. Dry mixing can be performed using a stirrer for, for example, 1 to 200 minutes. Dry mixing can be performed, for example, one or more times. A dry mixture containing a fibrillated dry binder can be obtained by dry mixing. The agitator is, for example, a mixer or a kneader. The agitator comprises, for example, a chamber; one or more rotating shafts disposed inside the chamber and rotating; and blades rotatably coupled to the rotating shafts and disposed along the longitudinal direction of the rotating shafts. The blades may be, for example, one or more selected from ribbon blades, sigma blades, jet (Z) blades, dispersion blades, and screw blades. By including the blades, the electrode active material, the dry conductive material, and the dry binder can be effectively mixed without a solvent to produce a dough-like mixture.

[0148] Next, a solid electrolyte layer can be prepared by molding the dry mixture. The prepared dry mixture can be fed into, for example, an extrusion device and extruded in the form of a sheet. The pressure during extrusion is, for example, 4 MPa to 100 MPa, or 10 MPa to 90 MPa. The resulting mixture may be in the form of a sheet. That is, the resulting sheet-shaped mixture may be the solid electrolyte layer. The extrusion device may be, for example, a roller or an extruder. Refer to the solid electrolyte layer section described above for the type and content of the sulfide-based solid electrolyte and binder. The binder may be omitted. For example, the binder may be omitted because the sulfide-based solid electrolyte particles are partially sintered by pressure.

[0149] A method for manufacturing a solid electrolyte layer according to a wet process comprises the steps of: preparing a slurry by mixing a sulfide-based solid electrolyte, a binder, and a solvent; preparing a solid electrolyte layer by molding and drying the slurry; and placing the solid electrolyte layer between an anode layer and a cathode layer.

[0150] First, a slurry is prepared by mixing a sulfide-based solid electrolyte, a binder, and a solvent. Refer to the solid electrolyte layer section described above for the sulfide-based solid electrolyte and the binder. The binder may be the same as or different from the binder used in the dry method. The binder used in the solid electrolyte layer is, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these; any binder used in the relevant technical field is acceptable. The solvent is not particularly limited and is any solvent that does not react with the sulfide-based solid electrolyte and can dissolve the binder is acceptable. For example, the solvent may be octyl acetate.

[0151] Next, the slurry is molded and dried to prepare a solid electrolyte layer. The solid electrolyte layer can be prepared by, for example, applying the slurry onto a substrate, drying it, and then separating it from the substrate. The application method and drying conditions may be performed within the range of methods and / or conditions generally used in the relevant technical field.

[0152] Next, a solid electrolyte layer is placed between the anode layer and the cathode layer. The solid electrolyte layer may be placed on the anode layer and / or cathode layer after preparing a separate solid electrolyte layer as described above, or a slurry may be applied and dried on the anode layer and / or cathode layer.

[0153] (Cathode layer manufacturing)

[0154] The cathode layer can be manufactured using a wet method, similar to conventional cathode layer manufacturing methods. For example, a cathode slurry is prepared by mixing a cathode active material, a conductive material, a binder, and a solvent. The cathode layer can be prepared by coating the cathode slurry onto a cathode current collector and then drying it. The solvent used to manufacture the cathode slurry is not particularly limited and any solvent used for cathode slurries in the relevant technical field is acceptable. For example, the solvent used for the cathode slurry is NMP. Refer to the cathode layer section described above for the types and content of the cathode current collector, cathode active material, conductive material, and binder.

[0155] (Anode layer manufacturing)

[0156] The anode layer can be manufactured using a wet or dry method.

[0157] The anode layer can be manufactured, for example, by a wet process. An anode slurry is prepared by mixing an anode active material, a sulfide-based solid electrolyte, a conductive material, a binder, and a solvent. The anode layer can be prepared by coating the anode slurry onto an anode current collector and then drying it. The solvent used in the preparation of the anode slurry is not particularly limited and any solvent used for anode slurries in the relevant technical field is acceptable. For example, the solvent used for the anode slurry is para-xylene. Refer to the anode layer section described above for the types and content of the anode current collector, anode active material, conductive material, and binder.

[0158] The anode layer can be manufactured, for example, by a dry method. First, a dry mixture is prepared by dry mixing the anode active material, the sulfide-based solid electrolyte, the conductive material, and the binder. Next, the dry mixture is molded to prepare the anode active material layer. Subsequently, the prepared anode active material layer is placed on one or both sides of an anode current collector and pressed to prepare the anode layer. The binder is, for example, a dry binder. The specific manufacturing conditions and methods for the steps of preparing the dry mixture and molding the dry mixture are substantially the same as those for the method of manufacturing the solid electrolyte layer described above. The types and contents of the anode current collector, the anode active material, the conductive material, and the binder are referenced in the anode layer section described above.

[0159] (Manufacturing of all-solid-state secondary batteries)

[0160] All-solid-state secondary batteries can be manufactured, for example, as follows.

[0161] First, an electrode assembly is provided having an anode layer; a cathode layer; and a solid electrolyte layer disposed between the anode layer and the cathode layer.

[0162] A cathode layer / solid electrolyte layer laminate is prepared by arranging a solid electrolyte layer on a cathode layer such that a cathode active material layer contacts the solid electrolyte layer. Subsequently, a cathode layer / solid electrolyte layer / anode layer laminate is prepared by arranging the solid electrolyte layer on one or both sides of an anode layer, respectively, so that it faces the anode active material layer. The prepared cathode layer / solid electrolyte layer / anode layer laminate is 50 to 100 o The solid electrolyte layer is plate-pressed at a pressure of 300 to 600 MPa for 10 to 60 minutes. Through this plate-pressing treatment, the solid electrolyte layer is partially sintered, thereby improving battery characteristics. The plated laminate is provided as an electrode assembly.

[0163] Next, a porous multilayer member is disposed on one or both sides of an electrode assembly. The porous multilayer member includes a porous cushioning layer; and a porous protecting layer disposed on one or both sides of the porous cushioning layer.

[0164] A porous multilayer member is placed on one or both sides of an electrode assembly, and the electrode assembly with the porous multilayer member placed thereon is sealed with an outer material to complete an all-solid-state secondary battery.

[0165] Alternatively, a plurality of electrode assemblies spaced apart along the thickness direction are prepared, and a plurality of porous multilayer members are placed between the spaced electrode assemblies to prepare an electrode assembly stack. The electrode assembly stack is sealed with an outer casing to complete an all-solid-state secondary battery. Alternatively, a plurality of electrode assemblies spaced apart along the thickness direction are prepared, and a single porous multilayer member is placed between the spaced electrode assemblies while folding multiple times to prepare an electrode assembly stack. The electrode assembly stack is sealed with an outer casing to complete an all-solid-state secondary battery.

[0166] The creative idea is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the creative idea and do not limit the scope of the creative idea to these examples alone.

[0167] Example 1: PE (7.7 µm) / polyacrylic foam (100 µm) / PE (7.7 µm) porous multilayer member

[0168] (Manufacturing of porous multilayer members)

[0169] A porous polyacrylic foam sheet (YT-3720BHF, Youngwoo Co. Ltd., Korea) was prepared. A porous polyethylene membrane (Cangzhou Mingzhou Plastic Co., Ltd., China) was prepared. The porous polyacrylic foam sheet is an adhesive sheet. The porous polyethylene membrane is a non-adhesive membrane. A porous multilayer member was prepared by placing the porous membrane on each side of the porous polyacrylic foam sheet and applying pressure. Since the porous polyethylene membrane does not have adhesive properties, the surface of the porous multilayer member did not have adhesive properties. The thickness of the porous polyacrylic foam sheet was 100 μm. The thickness of the porous polyethylene membrane was 7.7 μm. The air permeability of the porous polyethylene membrane was 178 sec / 100 cc, and the porosity was 38%.

[0170] (Preparation of solid electrolyte layer, dry method)

[0171] Li6PS5Cl sulfide-based solid electrolyte (D) which is an argyrodite-type crystal 50= 10 μm, crystalline). A mixture was prepared by adding 1 part by weight of a polytetrafluoroethylene (PTFE) first binder and 1 part by weight of a polyvinylidene fluoride (PVDF) second binder to 98 parts by weight of the solid electrolyte in a grind mixer and mixing. The prepared mixture was added to a mortar heated to 80°C and stirred to prepare a dough. The prepared dough was passed through a roller and formed into a sheet shape to prepare a solid electrolyte film of uniform thickness. A solid electrolyte layer was manufactured by the above process. Two solid electrolyte layers were prepared. The elastic modulus of the sulfide-based solid electrolyte was approximately 15 GPa to 30 GPa.

[0172] (Cathode layer manufacturing)

[0173] A Ni foil with a thickness of 10 μm was prepared as a negative electrode current collector. In addition, carbon black (CB) with a primary particle size of about 30 nm and silver (Ag) particles with an average particle size (D50) of about 60 nm were prepared as negative electrode active materials.

[0174] 4 g of a mixed powder, prepared by mixing carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1, was placed in a container, and 4 g of an NMP solution containing 7 wt% of PVDF binder (Kureha #9300) was added to prepare a mixed solution. Subsequently, a slurry was prepared by stirring the mixed solution while gradually adding NMP to it. The prepared slurry was applied to a SUS sheet using a bar coater and dried in air at 80°C for 10 minutes. The resulting laminate was vacuum dried at 40°C for 10 hours. The dried laminate was cold-roll-pressed to flatten the surface of the first cathode active material layer of the laminate. A cathode layer was fabricated by the above process. The thickness of the first cathode active material layer contained in the cathode layer was approximately 7 μm. The area of ​​the first cathode active material layer and the cathode current collector were the same. Two cathode layers were prepared.

[0175] (Anode layer manufacturing)

[0176] LiNi coated with Li2O-ZrO2 (LZO) as a cathode active material 0.8 Co 0.15 Mn 0.05 O2 (NCM) was prepared. The LZO-coated cathode active material was prepared according to the method disclosed in Korean Patent Publication No. 10-2016-0064942. As a solid electrolyte, Li6PS5Cl, an argyrodite-type crystal (D50 = 0.5 μm, crystalline), was prepared. As a binder, a polytetrafluoroethylene (PTFE) binder was prepared. As a conductive agent, carbon nanofibers (CNF) were prepared. A slurry was formed by mixing these materials with a xylene solvent in a weight ratio of cathode active material : solid electrolyte : conductive agent : binder = 84 : 11.5 : 3 : 1.5, molding the mixture into a sheet shape, and then vacuum drying it at 40 °C for 8 hours to produce a cathode sheet. The prepared cathode sheets were placed on each side of a cathode current collector consisting of aluminum foil coated with carbon on both sides, and 85 o The anode layer was prepared by a heated roll press of C. The total thickness of the anode layer was approximately 220 μm. The thickness of the anode active material layer was approximately 96 μm, and the thickness of the carbon-coated aluminum foil was approximately 28 μm. The area of ​​the anode active material layer and the anode current collector were the same.

[0177] (Inert component)

[0178] A flame-retardant inert member was manufactured by mixing cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder, and a solvent, forming the mixture into a gasket shape, and then removing the solvent.

[0179] The weight ratio of cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), and acrylic binder was 20:8:70:2. The thickness of the inert material was 120 μm. The manufactured flame-retardant material was left at room temperature for one week before use.

[0180] Before applying the inert material to the all-solid-state secondary battery, the inert material was vacuum heat-treated at 80°C for 5 hours to remove moisture and other substances from the inert material.

[0181] (Manufacturing of all-solid-state secondary batteries)

[0182] Referring to FIG. 4, a solid electrolyte layer was arranged on the cathode layer such that a first cathode active material layer contacted the solid electrolyte layer. Two cathode layer / solid electrolyte layer / inert member laminates were prepared by placing a flame-retardant inert member on the solid electrolyte layer under heat and pressure.

[0183] A cathode layer / solid electrolyte layer / anode layer electrode assembly was prepared by placing the inert member on each side of the anode layer so as to face the anode active material layer. The inert member was positioned around the anode layer, surrounding its sides, and in contact with the solid electrolyte layer. The inert member was used as a gasket.

[0184] The anode layer was positioned at the center of the solid electrolyte layer, and a gasket was positioned surrounding the anode layer and extending to the end of the solid electrolyte layer. The area of ​​the anode layer was approximately 90% of the area of ​​the solid electrolyte layer, and the gasket was positioned over the entire remaining 10% of the solid electrolyte layer where the anode layer was not positioned. An electrode assembly was prepared by positioning the solid electrolyte layer on the anode layer and the gasket, and positioning the cathode layer on the solid electrolyte layer.

[0185] The prepared cathode / solid electrolyte / anode electrode assembly is 85 oPlate press treatment was performed at a pressure of 500 MPa for 30 minutes. This pressurization treatment sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of one sintered solid electrolyte layer was approximately 45 μm. The area of ​​the solid electrolyte layer was equal to the area of ​​the negative electrode layer. The sintered electrode assembly was placed in a pouch and sealed to prepare a unit cell. Parts of the positive and negative current collectors were protruded outside the sealed unit cell and used as the positive and negative electrode terminals, respectively.

[0186] An electrode assembly stack was prepared using a magazine feeding method in which 10 unit cells were arranged in the thickness direction, and 11 porous multilayer members were discontinuously arranged on both sides of each unit cell.

[0187] The area and shape of the porous multilayer member were identical to the area and shape of the unit cell, i.e., the electrode assembly.

[0188] An all-solid-state secondary battery was manufactured by placing an electrode assembly stack between two pressure plates and fastening the two pressure plates with screws, thereby applying constant pressure to both sides of the electrode assembly stack.

[0189] Example 2: PE (7.7 µm) / polyacrylic foam (50 µm) / PE (7.7 µm) porous multilayer member

[0190] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the thickness of the porous polyacrylic foam sheet was changed to 50 μm.

[0191] Example 3: PE (7.7 µm) / polyacrylic foam (30 µm) / PE (7.7 µm) porous multilayer member

[0192] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the porous polyacrylic foam sheet was changed to 30 μm and the supply method of the porous multilayer member was changed to a reel supply method.

[0193] The reel supply method is a method of continuously arranging a single porous multilayer member by folding it multiple times in a zigzag shape on both sides of 10 unit cells.

[0194] Example 4: PE (7.7 µm) / polyacrylic foam (20 µm) / PE (7.7 µm) porous multilayer member

[0195] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the thickness of the porous polyacrylic foam sheet was changed to 20 μm and the supply method of the porous multilayer member was changed to a reel supply method.

[0196] Example 5: PE (7.7 µm) / polyacrylic foam (10 µm) / PE (7.7 µm) porous multilayer member

[0197] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the thickness of the porous polyacrylic foam sheet was changed to 10 μm and the supply method of the porous multilayer member was changed to a reel supply method.

[0198] Example 6: PE (5 µm) / polyacrylic foam (30 µm) / PE (5 µm) porous multilayer member

[0199] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the thickness of the porous polyacrylic foam sheet was changed to 30 μm, the supply method of the porous multilayer member was changed to a reel supply method, the thickness of the porous polyethylene film was changed to 5 μm, the air permeability was changed to 136 sec / 100 cc, and the porosity was changed to 37%.

[0200] Example 7: PE (5.4 µm) / polyacrylic foam (100 µm) / PE (5.4 µm) porous multilayer member

[0201] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the thickness of the porous polyacrylic foam sheet was changed to 30 μm, the supply method of the porous multilayer member was changed to a reel supply method, the thickness of the porous polyethylene film was changed to 5.4 μm, the air permeability was changed to 64 sec / 100 cc, and the porosity was changed to 44%.

[0202] Example 8: PE (7.7 µm) / polyacrylic foam (100 µm) / PE (7.7 µm) porous multilayer member

[0203] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the supply method of the porous multilayer member was changed to a reel supply method.

[0204] Example 9: PE (7.7 µm) / polyurethane foam (100 µm) / PE (7.7 µm) porous multilayer member

[0205] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the porous polyacrylic foam sheet was changed to a porous polyurethane foam sheet and the supply method of the porous multilayer member was changed to a reel supply method. The thickness of the porous polyurethane foam sheet was 100 μm.

[0206] Comparative Example 1: PE (7.7㎛) porous monolayer member

[0207] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the porous multilayer member was changed to a porous polyethylene membrane single-layer member with a thickness of 7.7 μm and the supply method of the porous multilayer member was changed to a reel supply method. The thickness of the porous polyurethane foam sheet was 100 μm.

[0208] Comparative Example 2: PP (11.4 μm) porous monolayer member

[0209] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the porous multilayer member was changed to a porous polypropylene membrane single-layer member with a thickness of 11.4 μm and the supply method of the porous multilayer member was changed to a reel supply method. The thickness of the porous polyurethane foam sheet was 100 μm.

[0210] Comparative Example 3: PP(CCS)(15.4㎛) porous member

[0211] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the porous multilayer member was changed to a ceramic-coated porous polypropylene separator (CCS) and the supply method of the porous multilayer member was changed to a reel supply method. The thickness of the porous polyurethane foam sheet was 100 μm. The thickness of the ceramic-coated porous polypropylene separator was 15.4 μm.

[0212] Comparative Example 4: PP(MFS) (15.4 μm) porous member

[0213] An all-solid-state secondary battery was manufactured using the same method as in Example 1, except that the porous multilayer member was changed to a porous polypropylene membrane (MFS, Multi-Functional Seprator) coated with a binder and ceramic, and the supply method of the porous multilayer member was changed to a reel supply method. The thickness of the porous polyurethane foam sheet was 100 μm. The thickness of the porous polypropylene separator coated with a binder and ceramic was 15.4 μm.

[0214] Comparative Example 5: Polyurethane foam sheet (100㎛) porous single-layer member

[0215] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the porous multilayer member was changed to a porous polyurethane foam sheet single layer member with a thickness of 100 μm.

[0216] Comparative Example 6: Polyacrylic foam sheet (100㎛) porous single-layer member

[0217] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the porous multilayer member was changed to a porous polyacrylic foam sheet single layer member with a thickness of 100 μm.

[0218] Comparative Example 7: Polytetrafluoroethylene foam sheet (100 μm) porous single-layer member

[0219] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the porous multilayer member was changed to a porous polytetrafluoroethylene foam sheet single layer member with a thickness of 100 μm.

[0220] Reference Example 1: Inactive component exclusion (free)

[0221] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that no inert member was placed around the positive active material layer.

[0222] Evaluation Example 1: Charge / Discharge Test

[0223] The charge-discharge characteristics of the all-solid-state secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 7 were evaluated by the following charge-discharge test. The charge-discharge test was performed by placing the all-solid-state secondary batteries in a constant temperature bath at 45°C.

[0224] In the first cycle, the battery was charged with a constant current of 0.1C until the battery voltage reached 4.25V, and when it reached 4.25V, constant voltage charging was performed at 4.25V with a cut-off condition of 0.05C. Subsequently, the battery was discharged with a constant current of 0.1C until the battery voltage reached 2.5V.

[0225] After the second cycle, charging and discharging were performed up to 250 cycles under the same conditions as the first cycle. This means that as the number of cycles at the point where a short circuit occurs increases, the life characteristics improve.

[0226] Stack manufacturing ease is a case where, during the stack manufacturing process, the adhesive porous member adheres to the electrode assembly, and the porous member is unevenly distributed between the electrode assemblies, making it difficult to obtain a uniform alignment state.

[0227] When a non-adhesive porous member is uniformly placed between electrode assemblies, it is easy to obtain a uniform alignment state, and when it is difficult to obtain dimensions, it was ○.

[0228] The relative speed of battery manufacturing evaluated the time required to manufacture all-solid-state secondary batteries relatively according to factors such as the method of stacking electrode assemblies and porous members.

[0229] The higher the relative speed of battery manufacturing, the shorter the time required for battery manufacturing, and the slower the relative speed, the longer the time required for battery manufacturing.

[0230] Energy density is classified according to the following criteria: if the energy density is very high (excellent), it is ◎; if the energy density is high (good), it is ○; if the energy density is average (fair), it is △; and if the energy density is low (poor), it is ×.

[0231] Stack manufacturing ease Relative speed of battery manufacturing energy density Short circuit occurrence time [times] Example 1 Magazine PE (7.7㎛) / polyacrylic foam (100㎛) / PE (7.7㎛) ○ 6 × 200 Example 2 Magazine PE (7.7㎛) / polyacrylic foam (50㎛) / PE (7.7㎛) ○ 6 △ 195 Example 3 reelPE(7.7㎛) / polyacrylic foam(30㎛) / PE(7.7㎛) ○ 8 ○ 160 Example 4 reelPE(7.7㎛) / polyacrylic foam(20㎛) / PE(7.7㎛) ○ 8 ◎ 150 Example 5 reelPE(7.7㎛) / polyacrylic foam(10㎛) / PE(7.7㎛) ○ 8 ◎ 130 Example 6 reelPE(5㎛) / polyacrylic foam(30㎛) / PE(5㎛) ○ 8 ○ 145 Example 7 reelPE(5.4㎛) / polyacrylic foam(30㎛) / PE(5.4㎛) ○ 8 ○ 120 Example 8 reelPE(7.7㎛) / polyacrylic foam(30㎛) / PE(7.7㎛) ○ 8 ○ 166 Example 9 reelPE(7.7㎛) / polyurethane foam(10㎛) / PE(7.7㎛) ○ 8 ○ 100 Comparative Example 1 reel PE (7.7㎛) ○ 8 ◎ 2 Comparative Example 2 reel PP (11.4㎛) ○ 8 ◎ 3 Comparative example reel PP(CCS)(15.4㎛) ○ 8 ◎ 10 Comparative Example 4 reel PP(MFS)(15.4㎛) ○ 8 ◎ 15 Comparative Example 5 Magazine polyurethane foam (100㎛) × 3 × 150 Comparative Example 6 Magazine polyacrylic foam (100㎛) × 2 × 200 Comparative Example 7 Magazine PTFE foam (100㎛) × 1 × 50

[0232] As shown in Table 1 above, the all-solid-state secondary batteries of Examples 1 to 9 provided excellent stack manufacturing ease, battery manufacturing speed, and lifespan characteristics.

[0233] The all-solid-state secondary batteries of Examples 3 to 9 also had improved energy density.

[0234] The all-solid-state secondary batteries of Comparative Examples 1 to 4 had poor lifespan characteristics because they did not include a porous buffer layer.

[0235] The all-solid-state secondary batteries of Comparative Examples 5 and 6 did not include a porous protective layer, which resulted in significantly poor stack manufacturing ease and battery manufacturing speed.

[0236] The all-solid-state secondary battery of Comparative Example 7 had poor processability and lifespan characteristics due to the use of a material with poor buffering function.

[0237] The all-solid-state secondary battery of Reference Example 1 did not include an inert gasket, so the number of cycles at the time of short circuit occurrence was reduced compared to the all-solid-state secondary battery of Example 1.

[0238] After the first cycle of charging was completed in the all-solid-state secondary batteries of Examples 1 to 9, SEM images of the cross-sections of these batteries were measured to confirm that a lithium metal precipitate layer corresponding to the second negative electrode active material layer was formed between the first negative electrode active material layer and the negative electrode current collector.

[0239] As described above, the all-solid-state secondary battery related to this embodiment can be applied to various portable devices or vehicles.

[0240] Although an exemplary embodiment has been described in detail above with reference to the attached drawings, the present creative idea is not limited to such examples. It is obvious that a person skilled in the art to which the present creative idea belongs can derive various variations or modifications within the scope of the technical idea described in the patent claims, and these also naturally fall within the technical scope of the present creative idea. Explanation of the symbols

[0241] 1: All-solid-state secondary battery 10: Cathode layer 11: Positive current collector 12: Positive active material layer 20: Cathode layer 21: Cathode current collector 22: First negative electrode active material layer 30: Solid electrolyte layer 40, 40a, 40b, 40c, 40d electrode assemblies 50, 50a, 50b, 50c, 50d, 50e porous multilayer member 51 Porous buffer layer 52 Porous protective layer 60 inert members 70 electrode assembly stack

Claims

Claim 1 A solid-state secondary battery comprising an electrode assembly having an anode layer; a cathode layer; and a solid electrolyte layer disposed between the anode layer and the cathode layer, and a porous multilayer member disposed on one or both sides of the electrode assembly, wherein the porous multilayer member comprises a porous cushioning layer; and a porous protecting layer disposed on one or both sides of the porous cushioning layer, wherein the elastic modulus of the porous cushioning layer is smaller than the elastic modulus of the porous protecting layer. Claim 2 A solid-state secondary battery according to claim 1, wherein the porous multilayer member is disposed on the negative electrode layer. Claim 3 delete Claim 4 An all-solid-state secondary battery according to claim 1, wherein the thickness of the porous buffer layer is greater than the thickness of the porous protective layer, the thickness of the porous buffer layer is 10 to 200 μm, and the air permeability is 1000 sec / 100 cc or more. Claim 5 A solid-state secondary battery according to claim 1, wherein the porous buffer layer comprises a porous foam, a porous sponge, or a combination thereof, and the porous foam and the porous sponge independently comprise a closed cell, an open cell, or a combination thereof. Claim 6 A solid-state secondary battery according to claim 1, wherein the porous buffer layer is an adhesive layer. Claim 7 In claim 1, the porous buffer layer comprises a polymer material, a rubber material, or a combination thereof, wherein the polymer material comprises a polyurethane-based polymer, a polyacrylic-based polymer, a polystyrene-based polymer, a polyester-based polymer, a polyamide-based polymer, a polyolefin-based polymer, or a combination thereof, and the rubber material comprises natural rubber (NR), butadiene rubber (BR), nitrile rubber, silicone rubber, isoprene rubber (IR), styrene-butadiene rubber (SBR), isoprene-butadiene rubber, styrene-isoprene-butadiene rubber, acrylonitrile-butadiene rubber (NBR), ethylene-propylene-diene rubber, butyl halogenated rubber, chloroprene (CR), isoprene halogenated rubber, isobutylene copolymer, chloroprene rubber, butyl rubber (IIR), isobutylene-p-methylstyrene halogenated rubber, or a combination thereof, all-solid Secondary battery. Claim 8 A solid-state secondary battery according to claim 1, wherein the porous protective layer is a non-adhesive layer. Claim 9 The all-solid-state secondary battery according to claim 1, wherein the thickness of the porous protective layer is 1 to 50 μm, the air permeability is 1000 sec / 100 cc or less, the porosity is 5 to 95%, and the pore size is 0.01 μm to 20 μm. Claim 10 A solid-state secondary battery according to claim 1, wherein the porous protective layer comprises a polyolefin-based polymer, a cellulose-based polymer, or a combination thereof. Claim 11 A solid-state secondary battery according to claim 1, wherein the porous protective layer is a porous membrane, the porous membrane is a woven or non-woven fabric, the porous membrane comprises cellulose nanofibers, and the porous membrane has a single-layer structure or a multi-layer structure. Claim 12 A solid-state secondary battery according to claim 1, wherein the cathode layer comprises a cathode current collector; and a first cathode active material layer disposed on the cathode current collector, wherein the first cathode active material layer comprises a cathode active material and a binder, wherein the cathode active material has a particle form and the average particle size of the cathode active material is 4 μm or less. Claim 13 A solid-state secondary battery according to claim 12, wherein the negative electrode active material comprises one or more selected from a carbon-based negative electrode active material and a metal or metalloid negative electrode active material, wherein the carbon-based negative electrode active material comprises amorphous carbon, and the metal or metalloid negative electrode active material comprises one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Claim 14 A solid-state secondary battery according to claim 12, further comprising a second negative electrode active material layer disposed between the negative electrode current collector and the first negative electrode active material layer, wherein the second negative electrode active material layer is a metal layer comprising lithium or a lithium alloy, and the second negative electrode active material layer is a plated layer. Claim 15 A solid-state secondary battery according to claim 1, wherein the positive electrode layer comprises a positive current collector and a first positive active material layer and a second positive active material layer disposed respectively on both sides of the positive current collector, the solid electrolyte layer comprises a first solid electrolyte layer and a second solid electrolyte layer in contact with the first positive active material layer and the second positive active material layer respectively, the negative electrode layer comprises a first negative electrode layer and a second negative electrode layer in contact with the first solid electrolyte layer and the second solid electrolyte layer respectively, the first solid electrolyte layer and the second solid electrolyte layer face each other, and the battery comprises an inactive member disposed between the first solid electrolyte layer and the second solid electrolyte layer, surrounding the side of the positive electrode layer, wherein the area of ​​the porous multilayer member is larger than the area of ​​one or more selected from the first positive active material layer and the second positive active material layer. Claim 16 A solid-state secondary battery according to claim 1, comprising an electrode assembly stack, wherein the electrode assembly stack comprises a plurality of electrode assemblies spaced apart from each other; and a porous multilayer member disposed between the plurality of electrode assemblies, wherein the thickness of the porous multilayer member is smaller than the thickness of the electrode assemblies. Claim 17 A solid-state secondary battery according to claim 16, wherein a plurality of porous multilayer members are each disposed between the plurality of electrode assemblies, or a single porous multilayer member is folded multiple times and disposed between the plurality of electrode assemblies, and further comprising pressure plates disposed on both sides of the electrode assembly stack. Claim 18 A method for manufacturing an all-solid-state secondary battery comprising: providing an electrode assembly having a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; and disposing of a porous multilayer member on one or both sides of the electrode assembly; wherein the porous multilayer member comprises a porous cushioning layer; and a porous protecting layer disposed on one or both sides of the porous cushioning layer, and wherein the elastic modulus of the porous cushioning layer is smaller than the elastic modulus of the porous protecting layer.

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