Positive electrode for all-solid-state battery, method for manufacturing the same, and all-solid-state battery including the positive electrode

Abstract

Disclosed is a positive electrode for an all-solid-state battery, which has a granular layer composed of multiple layers having particles of different shapes, thereby increasing the electrical conductivity of the granules and at the same time having uniform surface flatness during granular sheeting and excellent adhesion to a solid electrolyte, a method for producing the same, and an all-solid-state battery including the positive electrode. The positive electrode for an all-solid-state battery includes a metal current collector, an inner granular layer located on one side of the metal current collector and containing an active material, a conductive material, and a binder in granular form, and an outer granular layer laminated on the surface side of the inner granular layer and containing an active material, a conductive material, and a binder in granular form, and the conductive material of the inner granular layer and the conductive material of the outer granular layer are different in shape from each other.

Description

【Technical Field】 【0001】 This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0067157 filed on May 31, 2022, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference. 【0002】 The present invention relates to a positive electrode for an all-solid-state battery including a granule powder composed of an active material, a conductive material, and a binder, a method for manufacturing the same, and an all-solid-state battery including the positive electrode. More specifically, the present invention relates to a positive electrode for an all-solid-state battery, a method for manufacturing the same, and an all-solid-state battery including the positive electrode, which enhance the electrical conductivity of granules and have excellent adhesion to a solid electrolyte with uniform surface flatness during sheeting of the granules by forming a granule layer with multiple layers having different forms of particles. 【Background Art】 【0003】 From the viewpoints of battery capacity, safety, output, large-scale, and ultra-small scale, various batteries that can overcome the limitations of lithium secondary batteries, which are currently widely commercialized, are being studied. Typically, in terms of capacity, a metal-air battery having a very large theoretical capacity compared to a lithium secondary battery; in terms of safety, an all-solid-state battery having no risk of explosion compared to a lithium secondary battery; in terms of output, a super capacitor; in terms of large-scale, a sodium-sulfur battery (NaS battery) or a redox flow battery (RFB); in terms of ultra-small scale, a thin film battery, etc. are continuously being studied in the academic and industrial fields. 【0004】 Among these, all-solid-state batteries refer to batteries that replace the electrolyte used in lithium secondary batteries from liquid to solid. As a result, since flammable solvents are not used, ignition and explosion due to decomposition reactions of conventional electrolytes do not occur at all, and safety can be significantly improved. In addition, all-solid-state batteries can use Li metal or Li alloy as the negative electrode material, so there is also the advantage that the energy density with respect to the mass and volume of the battery can be dramatically improved. 【0005】 On the other hand, the solid electrolytes of all-solid-state batteries can be broadly classified into organic (polymer-based) solid electrolytes and inorganic solid electrolytes. Among these, inorganic solid electrolytes can be divided into sulfide-based and oxide-based. And the solid electrolyte with the most advanced technology development currently is the sulfide-based solid electrolyte, and the development has advanced to the level where the ionic conductivity reaches a level close to that of organic electrolytes. Thus, sulfide-based solid electrolytes not only have a high ionic conductivity of 10 -3 to 10 -2 S / cm, but also have the advantages of ductility and good contact with the interface, which is advantageous for improving resistance. 【0006】 However, sulfide-based solid electrolytes are sensitive to moisture, such as generating H2S gas when in contact with moisture, so it is necessary to construct a very dry environment during the manufacture of the battery or electrodes. For these reasons, all-solid-state batteries applying sulfide-based solid electrolytes are based on the dry electrode method, and it is possible to realize a high-loading electrode compared to the wet electrode method. And the dry electrode method can be broadly classified into the PTFE fiberization method and the granule powder sheeting method using the spray drying method. Among these, the latter method can directly sheet granules with excellent sphericity, so it is advantageous for manufacturing a more uniform loading electrode compared to the PTFE fiberization method. 【0007】 In relation to this "granule sheeting method using spray drying," granules (granule powder) refer to particles consisting of an active material, a conductive material, and a binder. By stacking the granules on the current collector of the electrode using the method described above, and then applying heat and pressure to perform sheeting, an electrode can be manufactured. A solid electrolyte can then be attached to the electrode manufactured using this method and in this environment to produce an all-solid-state battery. 【0008】 On the other hand, applying the conductive material from the granules contained in the electrodes of existing all-solid-state batteries to single-walled carbon nanotubes (SWCNTs), which are linear conductive materials, has the advantage of improving electrical conductivity and the migration phenomenon of the conductive material. However, when the conductive material contained in the granules is applied to single-walled carbon nanotubes, which are linear conductive materials, it is disadvantageous to form a uniform surface when sheeting the granules (i.e., uneven surface leveling), which inevitably leads to the problem of incomplete adhesion with the solid electrolyte in contact with the electrode. In other words, while single-walled carbon nanotubes, as linear conductive materials, are good in terms of battery performance because they exhibit excellent electrical conductivity, they have a fatal drawback (the problem of incomplete adhesion with the solid electrolyte) during electrode or battery manufacturing. 【0009】 On the other hand, in conventional all-solid-state batteries, the conductive material in the granules contained in the electrodes is sometimes applied as a point-like conductive material such as carbon black (CB). In this case, there is the advantage that a uniform surface can be formed when the granules are sheeted. However, when the conductive material contained in the granules is applied as a point-like conductive material, a problem arises in which the point-like conductive material migrates (a phenomenon in which it moves to the outer side of the granules due to density differences) during the drying process after the granules are manufactured. 【0010】 In other words, there is a trade-off between applying the conductive material contained in the electrode granules as a linear conductive material and applying it as a point-like conductive material. Therefore, a strategy is needed that can enhance the performance of batteries while simultaneously simplifying the manufacturing of electrodes and batteries by leveraging only the advantages of applying the conductive material contained in the electrode granules as a linear conductive material and the advantages of applying it as a point-like conductive material. [Overview of the project] [Problems that the invention aims to solve] 【0011】 Accordingly, the object of the present invention is to provide a positive electrode for an all-solid-state battery, a method for manufacturing the same, and an all-solid-state battery including the positive electrode, which enhances the electrical conductivity of the granules by composing the granule layer with multiple layers having particles of different shapes, while simultaneously having uniform surface flatness during granule sheeting and excellent adhesion to the solid electrolyte. [Means for solving the problem] 【0012】 To achieve the above objective, the present invention provides a positive electrode for an all-solid-state battery comprising a metal current collector, an inner granular layer located on one surface of the metal current collector and containing an active material, a conductive material, and a binder in granular form, and an outer granular layer laminated on the surface side of the inner granular layer and containing an active material, a conductive material, and a binder in granular form, wherein the conductive material of the inner granular layer and the conductive material of the outer granular layer have different shapes from each other. 【0013】 Furthermore, the present invention provides a method for manufacturing a positive electrode for an all-solid-state battery, comprising the steps of: manufacturing inner granules containing an active material, a linear conductive material, and a binder in granular form; coating them onto a positive electrode metal current collector; and rolling them to form a sheet-like inner granule layer; and manufacturing outer granules containing an active material, a point-like conductive material, and a binder in granular form; coating them onto the surface of the manufactured inner granule layer; and rolling them to form a sheet-like outer granule layer, wherein the conductive material of the inner granule layer and the conductive material of the outer granule layer have different shapes from each other. 【0014】 Furthermore, the present invention provides an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte for the all-solid-state battery. [Effects of the Invention] 【0015】 The positive electrode for an all-solid-state battery according to the present invention, its manufacturing method, and the all-solid-state battery including the positive electrode have the advantage of increasing the electrical conductivity of the granules by composing the granule layer with multiple layers having particles of different shapes, while also having uniform surface flatness during granule sheeting and excellent adhesion to the solid electrolyte. [Brief explanation of the drawing] 【0016】 [Figure 1] This is a schematic diagram of a side cross-section of a positive electrode for an all-solid-state battery according to one embodiment of the present invention. [Figure 2] This is a schematic side cross-sectional view showing that the positive electrode surface is flattened by the dot-like conductive material in the outer granular layer of a positive electrode for an all-solid-state battery according to one embodiment of the present invention. [Figure 3] This is an image of the surface of granules containing point-like conductive material, observed using a scanning electron microscope. [Figure 4] This is an image of the surface of granules containing linear conductive material, observed using a scanning electron microscope. [Modes for carrying out the invention] 【0017】 The present invention will be described in detail below. 【0018】 The positive electrode for an all-solid-state battery according to the present invention comprises a metal current collector, an inner granular layer located on one surface of the metal current collector and containing an active material, a conductive material, and a binder in granular form, and an outer granular layer laminated on the surface side of the inner granular layer and containing an active material, a conductive material, and a binder in granular form, wherein the conductive material of the inner granular layer and the conductive material of the outer granular layer have different shapes from each other. 【0019】 Generally, all-solid-state batteries using sulfide-based solid electrolytes are manufactured using a dry electrode method, which allows for the realization of high-load electrodes compared to the wet electrode method. Among the dry electrode methods, the "granule powder sheeting method using spray drying," which has advantages over the PTFE fiberization method, is primarily used. Here, granules (granule powder) refer to particles consisting of active material, conductive material, and binder. Electrodes can be manufactured by stacking (or loading) these granules onto an electrode current collector using the aforementioned method, and then forming them into a sheet by applying heat and pressure. An all-solid-state battery can then be manufactured by attaching a solid electrolyte to electrodes manufactured using this method and environment. 【0020】 On the other hand, applying the conductive material from the granules contained in the electrodes of existing all-solid-state batteries to single-walled carbon nanotubes (SWCNTs), which are linear conductive materials, has the advantage of improving electrical conductivity and the migration phenomenon of the conductive material. However, when the conductive material contained in the granules is applied to single-walled carbon nanotubes, which are linear conductive materials, it is disadvantageous to form a uniform surface when sheeting the granules (i.e., uneven surface leveling), which inevitably leads to the problem of incomplete adhesion with the solid electrolyte in contact with the electrode. In other words, while single-walled carbon nanotubes, as linear conductive materials, are good in terms of battery performance because they exhibit excellent electrical conductivity, they have a fatal drawback (the problem of incomplete adhesion with the solid electrolyte) during electrode or battery manufacturing. 【0021】 On the other hand, in conventional all-solid-state batteries, the conductive material in the granules contained in the electrodes is sometimes applied as a point-like conductive material such as carbon black (CB). In this case, there is the advantage that a uniform surface can be formed when the granules are sheeted. However, when the conductive material contained in the granules is applied as a point-like conductive material, a problem arises in which the point-like conductive material migrates (a phenomenon in which it moves towards the outer surface of the granules due to density differences) during the drying process after granule manufacturing. 【0022】 In other words, there is a trade-off between applying the conductive material contained in the electrode granules as a linear conductive material and applying it as a point-like conductive material. Therefore, the applicant has made it easier to manufacture electrodes and batteries, and has also improved the performance of batteries, by bringing out only the advantages of applying the conductive material contained in the electrode granules as a linear conductive material and the advantages of applying it as a point-like conductive material (i.e., by applying both a linear conductive material and a point-like conductive material as the conductive material contained in the electrode granules). 【0023】 The present invention will be described in more detail below. 【0024】 The granules contained in the positive electrode for the all-solid-state battery are particles comprising active material, conductive material, and binder, and have a spherical shape overall. In other words, the term "spherical" here does not strictly mean a perfect sphere, but is used as a comprehensive concept that includes particles that are generally round in shape. The active material, which is a powdery fine particle, is bound together with the conductive material by a binder solution, growing into particles with a specific range of specifications. 【0025】 According to one embodiment of the present invention, the granules are point-like particles having an average diameter of 30 to 150 μm. Here, as mentioned above, spherical particles do not mean perfectly spherical particles, so the diameter refers to the largest distance between one point on the particle surface and another point. Specifically, the average diameters of the granules are 30 μm or more, 35 μm or more, 40 μm or more, 45 μm or more, 50 μm or more, 150 μm or less, 145 μm or less, 140 μm or less, 135 μm or less, 130 μm or less, 125 μm or less, and 120 μm or less. If the average diameter of the granules is less than 30 μm, there will be fewer voids within the granule layer, resulting in less sulfide-based solid electrolyte penetration and coating between the granules, which may prevent a significant improvement in battery performance. If the average diameter of the granules exceeds 150 μm, the distance between the surface in contact with the sulfide-based solid electrolyte and the center of the granules will be greater, which may also prevent a significant improvement in battery performance. 【0026】 Figure 1 is a schematic diagram of a side cross-section of a positive electrode for an all-solid-state battery according to one embodiment of the present invention. The most distinctive feature of the present invention is that the granular layer located on one surface of the positive electrode metal current collector is composed of multiple layers, preferably, as shown in Figure 1, two granular layers, namely an inner granular layer (200) and an outer granular layer (300), are sequentially stacked on one surface of the positive electrode metal current collector (100). 【0027】 Furthermore, the conductive material contained in the inner granular layer (200) and the conductive material contained in the outer granular layer (300) are different. Preferably, the conductive material contained in the inner granular layer (200) and the conductive material contained in the outer granular layer (300) have different shapes. More preferably, the conductive material contained in the inner granular layer (200) and the conductive material contained in the outer granular layer (300) have different shapes and types. 【0028】 First, the conductive material contained in the inner granular layer (200), which is positioned facing one surface of the positive electrode metal current collector (100), contains linear particles. Then, the conductive material contained in the outer granular layer (300), which is laminated on the surface side of the inner granular layer (200) (the side opposite to the inner granular layer (200) that does not come into contact with the positive electrode metal current collector (100)), contains dot-like particles. By including a conductive material containing linear particles (i.e., a linear conductive material) in the inner granular layer (200) and a conductive material containing dot-like particles (i.e., a dot-like conductive material) in the outer granular layer (300), it is possible to combine the advantages of using the conductive material contained in the granules as a linear conductive material and the advantages of using it as a dot-like conductive material, thereby facilitating the manufacture of electrodes and batteries while simultaneously improving the performance of the batteries. 【0029】 More specifically, the linear conductive material contained in the inner granular layer (200) is a carbon nanotube made of linear particles, and preferably a single-walled carbon nanotube (SWCNT) made of linear particles. In the case of the single-walled carbon nanotube, there is the advantage that electrical conductivity is improved and the migration phenomenon of the conductive material is improved. On the other hand, when sheeting the granules onto the positive electrode current collector, it is disadvantageous to form a uniform surface (i.e., non-uniform surface leveling), which leads to the problem of incomplete adhesion with the solid electrolyte in contact with the electrode. 【0030】 However, in this invention, since another outer granular layer (300) containing a dot-like conductive material is laminated on top of an inner granular layer (200) containing a linear conductive material, a uniform surface can be formed, which dramatically improves the adhesion strength with the solid electrolyte in contact with the electrode. In other words, not only are the granules of the outer granular layer (300) containing the dot-like conductive material impregnated into the voids between the granules of the inner granular layer (200) containing the linear conductive material, but the granules of the outer granular layer (300) containing the dot-like conductive material are also uniformly positioned on top of them, making the surface of the positive electrode flat. 【0031】 Figure 2 is a schematic side cross-section diagram showing how the positive electrode surface is flattened by the dot-like conductive material in the outer granular layer of a positive electrode for an all-solid-state battery according to one embodiment of the present invention. This diagram schematically shows how the granules of the outer granular layer (300) containing the dot-like conductive material are impregnated into the voids between the granules of the inner granular layer (200) containing the linear conductive material, and how the granules of the outer granular layer (300) containing the dot-like conductive material are uniformly positioned on top of them, flattening the positive electrode surface. Examples of such dot-like conductive materials (i.e., conductive materials composed of dot-like particles) include carbon black (CB), and other materials with similar or identical morphology and physical properties to carbon black particles can also be used as the dot-like conductive material of the present invention. 【0032】 On the other hand, the thickness ratio of the inner granule layer (200) to the outer granule layer (300) is 4:1 to 8:1. In this case, the thickness of the inner granule layer (200) refers to the thickness of the thickest part from where it contacts the positive electrode metal current collector (100) to where it contacts the outer granule layer (300), and the thickness of the outer granule layer (300) refers to the thickness of the thinnest part from the positive electrode surface (i.e., the surface of the outer granule layer that does not contact the inner granule layer) to where it contacts the inner granule layer (200). There are no special restrictions on the total thickness of the granule layer (200, 300) including the inner granule layer (200) and the outer granule layer (300), and the thickness may vary depending on the application of the battery. However, taking a typical all-solid-state battery as an example, the total thickness of the granule layer (200, 300) in this case can be 50 to 400 μm. Here, the thickness of the inner granular layer (200) can be 40 to 240 μm, and the thickness of the outer granular layer (300) can be 10 to 60 μm. 【0033】 Here, a preferred linear conductive material contained in the inner particle layer (200), that is, a single-walled carbon nanotube, will be described in more detail. The single-walled carbon nanotube has a structure that is advantageous for contacting the active material even with a smaller weight compared to multi-walled carbon nanotubes, and thus is advantageous for improving the performance of the battery. And the single-walled carbon nanotube has a single-molecule fiber structure. Further, the diameter of the single-walled carbon nanotube can be 1 to 10 nm. Here, the diameter means the largest value among the distances from one point on the outermost contour to another point based on the circular cross-section of the single-walled carbon nanotube. 【0034】 Specifically, the diameter of the single-walled carbon nanotube is 1 nm or more, 2 nm or more, 3 nm or more, 10 nm or less, 9 nm or less, 8 nm or less. When the diameter of the single-walled carbon nanotube is less than 1 nm, it is difficult to form an effective structure among the active materials, such as the external area of the single-walled carbon nanotube being small and the contact area with the active material being reduced, and the degree of improvement in the battery performance may be negligible. Also, when the diameter of the single-walled carbon nanotube exceeds 10 nm, it is difficult to closely connect the active materials, and a large amount of active materials cannot be systematically covered with respect to the input weight of the single-walled carbon nanotube, and thus the degree of improvement in the battery performance may be negligible. 【0035】 Also, the single-walled carbon nanotube can have a BET specific surface area of 400 to 1,000 m 2 / g. The BET specific surface area is the specific surface area measured through the BET method. Specifically, it is desirable to calculate it by obtaining the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan. Specifically, the BET specific surface area of the single-walled carbon nanotube is 400 m 2 / g or more, 450 m 2 / g or more, 500 m 2 / g or more, and 1,000 m 2 / g or less, 950 m 2 / g or less, 900 m 2 / g or less, 850 m2 / g or less, 800m 2 / g or less, 750m 2 / g or less, 700m 2 The BET specific surface area of ​​the single-walled carbon nanotube is 400 m². 2 If the BET specific surface area of ​​the single-walled carbon nanotube is less than 1,000 m², the surface area in contact with the active material decreases relative to the weight of the single-walled carbon nanotube, and the improvement in battery performance may be minimal. 2 If the value exceeds / g, the excess specific surface area does not necessarily allow for easy contact with the active material or solid electrolyte, so the improvement in battery performance may not be significant. 【0036】 As described above, the positive electrode for an all-solid-state battery according to the present invention comprises an inner granular layer (200) and an outer granular layer (300), and the inner granular layer (200) and the outer granular layer (300) each contain an active material, a conductive material, and a binder in granular form. Of these, the active material can be used without limitation as long as it is usable as a positive electrode active material for lithium-ion secondary batteries. The active material contained in the inner granular layer (200) and the active material contained in the outer granular layer (300) can be lithium transition metal oxides containing one or more transition metals. For example, the active material contained in the inner granular layer (200) and the active material contained in the outer granular layer (300) can be LiCoO2, LiNiO2, LiMnO2, Li2MnO3, LiMn2O4, Li(Ni a Co b Mn c )O2(0 <a<1、0<b<1、0<c<1、a+b+c=1)、LiNiCo 1-y O y2 (O <y<1)、LiCo 1-y Mn y O2(O <y<1)、LiNi 1-y Mn y O2(O <y<1)、Li(Ni a Co b Mn c )O4(0 <a<2、0<b<2、0<c<2、a+b+c=2)、LiMn 2-z Ni z O4(0 <z<2)、LiMn2-z Co z It can be exemplified that it is selected from the group consisting of CoO4(0 < z < 2) and combinations thereof. 【0037】 Further, the binder is mixed with the active material and the conductive material which are fine particles in a powder state, and binds each component to assist the growth of the particles. Since the sulfide-based solid electrolyte has moisture-sensitive characteristics such as generating H2S gas when contacting with moisture, it is desirable to exclude moisture as much as possible from the time of forming the granules. The binder contained in the inner granule layer (200) and the binder contained in the outer granule layer (300) are organic binders, and the organic binder means a binder that dissolves or disperses in an organic solvent, particularly N-methylpyrrolidone (NMP), and is distinguished from an aqueous binder using water as a solvent or a dispersion medium. For example, the binder contained in the inner granule layer (200) and the binder contained in the outer granule layer (300) can be independently selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyimide, polyamideimide, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluorine rubber, but are not limited thereto. 【0038】 Also, each of the inner granule layer (200) and the outer granule layer (300) contains the active material, the conductive material, and the binder as follows. That is, each of the inner granule layer (200) and the outer granule layer (300) contains the active material at 85 to 99.8% by weight, preferably 88 to 99.5% by weight, more preferably 90 to 99.3% by weight, the binder at 0.1 to 10% by weight, preferably 0.2 to 8% by weight, more preferably 0.3 to 7% by weight, and the conductive material at 0.1 to 10% by weight, preferably 0.2 to 8% by weight, more preferably 0.3 to 7% by weight. 【0039】 The granules constituting the inner granular layer (200) and the outer granular layer (300), respectively, have a porosity of 10 to 40%. The porosity of the granules refers to the volume ratio of voids in the granules, and the porosity can be measured by, for example, the BET (Brunauer-Emmett-Teller) method or the mercury osmosis method (Hg porosimeter), but is not limited to these. Specifically, the porosity of the granules can be 10% or more, 15% or more, 20% or more, 25% or more, 40% or less, 35% or less, or 30% or less. If the porosity of the granules is less than 10%, it is difficult for the sulfide-based solid electrolyte to come into close contact with the granules, and the improvement in battery performance may be minimal. Also, if the porosity of the granules exceeds 40%, the amount of active material decreases compared to the volume of the granules, and it may be difficult to provide a high-load electrode, so the improvement in battery performance may not be significant. 【0040】 On the other hand, the granules contained in the positive electrode for the all-solid-state battery according to the present invention, that is, the granules contained in the inner granule layer (200) and the granules contained in the outer granule layer (300), have a solid electrolyte coated on at least part or all of their surface. Furthermore, the solid electrolyte is also impregnated into the voids between the granules contained in the positive electrode for the all-solid-state battery. In other words, the positive electrode for the all-solid-state battery further includes a solid electrolyte that is coated onto the surfaces of the granules contained in the inner granule layer (200) and the granules contained in the outer granule layer (300), and a solid electrolyte that is impregnated into the spaces between the granules. 【0041】 The solid electrolyte comprises one or more selected from sulfide-based solid electrolytes, polymer-based solid electrolytes, and oxide-based solid electrolytes, and it is preferable that it comprises only sulfide-based solid electrolytes. The sulfide-based solid electrolyte is in liquid form obtained by dissolving a solid sulfide-based electrolyte, and after impregnating the granules contained in the inner granule layer (200), the granules contained in the outer granule layer (300), and the spaces between them, it is cured by drying, thereby coating the surface of the granules and being positioned between the granules. 【0042】 The aforementioned sulfide-based solid electrolyte contains a lithium salt, wherein the lithium salt is an ionizable lithium salt, Li + X - It can be expressed as follows. While there are no particular limitations on the anions of such lithium salts, F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - 、 CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - Examples include the following. 【0043】 Furthermore, the sulfide-based solid electrolyte contains sulfur (S) and has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and includes Li-PS glass and Li-PS glass ceramics. Non-limiting examples of such sulfide-based solid electrolytes include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-LiCl-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and the sulfide-based solid electrolyte may contain one or more of these. 【0044】 When a sulfide-based solid electrolyte is coated onto the granules of the positive electrode for the all-solid-state battery, the sulfide-based solid electrolyte is present in an amount of 20 to 40 parts by weight per 100 parts by weight of the total granules. If the sulfide-based solid electrolyte is present in an amount exceeding 40 parts by weight per 100 parts by weight of the total granules, the loading amount of the positive electrode active material will relatively decrease, which may have a negative impact on improving the battery's performance. 【0045】 Next, a method for manufacturing a positive electrode for an all-solid-state battery according to the present invention will be described. The method for manufacturing the positive electrode for an all-solid-state battery includes the steps of: manufacturing inner granules containing an active material, a linear conductive material, and a binder in granular form, coating them onto a positive electrode metal current collector (100), and then rolling them to form an inner granule layer (200) in sheet form; and manufacturing outer granules containing an active material, a point-like conductive material, and a binder in granular form, coating them onto the surface of the manufactured inner granule layer (200), and then rolling them to form an outer granule layer (300) in sheet form, wherein the conductive material of the inner granule layer (200) and the conductive material of the outer granule layer (300) have different shapes from each other. The method for manufacturing the positive electrode for an all-solid-state battery further includes, if necessary, the steps of injecting and drying a sulfide-based electrolyte into the inner granule layer (200), the outer granule layer (300), and the space between them. As a result, the hardened sulfide-based solid electrolyte is coated onto the surface of the granules and impregnated between the granules. 【0046】 Next, the all-solid-state battery according to the present invention will be described. The all-solid-state battery includes the positive electrode, negative electrode, and solid electrolyte described above. The solid electrolyte can be located on the surface and between the granules contained in the positive electrode (i.e., the solid electrolyte is contained in the positive electrode). In addition to being contained in the positive electrode, the solid electrolyte can also be located as a layered film between the positive and negative electrodes. Such a solid electrolyte layer can also serve a role similar to a separation membrane in a typical lithium secondary battery (i.e., electrically insulating the negative and positive electrodes while simultaneously allowing lithium ions to pass through). In some cases, the solid electrolyte may be a sulfide-based solid electrolyte. On the other hand, the all-solid-state battery can be used as a semi-solid-state battery by including a liquid electrolyte as needed, in which case another polymer separation membrane is required. 【0047】 On the other hand, the negative electrode includes a negative electrode active material that can be used in lithium-ion secondary batteries. For example, the negative electrode active material is carbon such as non-graphitizable carbon and graphite-based carbon, Li x Fe2O3 (0 ≤ x ≤ 1), Lix WO₂(0 ≦ x ≦ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge. Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 < x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8), etc. metal composite oxides, lithium metal, lithium alloy, silicon-based alloy, tin-based alloy, SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄ and Bi₂O₅, etc. metal oxides, conductive polymers such as polyacetylene, Li-Co-Ni-based materials, titanium oxides, lithium titanium oxides, etc. Any one or more selected from these are included. 【0048】 In addition, the present invention provides a battery module including the all-solid-state battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include power tools powered by an electric motor, electric vehicles (Electric Vehicle, EV), hybrid electric vehicles (Hybrid Electric Vehicle, HEV), plug-in hybrid electric vehicles (Plug-in Hybrid Electric Vehicle, PHEV), etc., electric bicycles (E-bike), electric scooters (E-scooter), electric two-wheel vehicles including electric golf carts, and power storage systems, etc., but are not limited thereto. 【0049】 Hereinafter, preferred embodiments are shown to assist in understanding the present invention, but these are merely examples of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the category and technical idea of the present invention, and it is natural that these changes and modifications belong to the scope of the appended claims. 【0050】 Example 1 Production of the positive electrode for an all-solid-state battery First, under N-methylpyrrolidone solvent conditions, LiNi is used as the active material. 0.6 Co 0.2 Mn 0.2 O2 (NCM 622), a conductive material consisting of linear single-walled carbon nanotubes (diameter: approximately 5 nm, BET specific surface area: approximately 600 m²) 2 A slurry was prepared by mixing polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 94:3:3, and then spray-drying it to produce inner granules (porosity: 30%) with an average diameter of approximately 60 μm. These granules were then applied to one surface of an aluminum current collector approximately 20 μm thick to form an inner granule layer approximately 240 μm thick, and then rolled. 【0051】 Next, under N-methylpyrrolidone solvent conditions, LiNi is used as the active material. 0.6 Co 0.2 Mn 0.2 O2 (NCM 622), and a conductive material consisting of dotted carbon black (primary particle size: approximately 35 nm, BET specific surface area: approximately 65 m²). 2 A slurry prepared by mixing polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 94:3.3 was spray-dried to produce outer granules (porosity: 30%) with an average diameter of approximately 60 μm. These granules were then applied to the surface of the formed inner granule layer to form an outer granule layer with a thickness of approximately 60 μm, and then rolled. 【0052】 Next, the formed inner and outer granular layers were impregnated with a sulfide-based electrolyte (Li2S-P2S5) at a concentration of approximately 30 parts by weight per 100 parts by weight of the total weight of the granules, and then dried and rolled to produce a positive electrode for an all-solid-state battery. 【0053】 Comparative Example 1: Manufacturing of a positive electrode for an all-solid-state battery A positive electrode for an all-solid-state battery was manufactured in the same manner as in Example 1, except that an outer granular layer was not formed on the surface of the inner granular layer. 【0054】 Comparative Example 2: Manufacturing of a positive electrode for an all-solid-state battery A positive electrode for an all-solid-state battery was manufactured in the same manner as in Example 1, except that the composition of the inner granular layer was replaced with the composition of the outer granular layer, and the outer granular layer was not formed. 【0055】 Comparative Example 3: Manufacturing of a positive electrode for an all-solid-state battery A positive electrode for an all-solid-state battery was manufactured in the same manner as in Example 1, except that the composition of the inner granular layer and the composition of the outer granular layer were swapped. 【0056】 Experimental Example 1: Observation of the positive electrode surface using a scanning electron microscope. Surface observations were performed using a scanning electron microscope (SEM) on the positive electrode for an all-solid-state battery in Comparative Example 2, which used dotted carbon black as the conductive material, and on the positive electrode for an all-solid-state battery in Comparative Example 1, which used linear single-walled carbon nanotubes as the conductive material. Figure 3 shows images of the surface of granules containing the dotted conductive material observed with a scanning electron microscope; Figure 3a is an image observed at 1,000x magnification, and Figure 3b is an image observed at 5,000x magnification. Similarly, Figure 4 shows images of the surface of granules containing the linear conductive material observed with a scanning electron microscope; Figure 4a is an image observed at 1,000x magnification, and Figure 4b is an image observed at 5,000x magnification. 【0057】 Referring to Figures 3 and 4 together, it was confirmed that the surface of granules containing linear conductive material (single-walled carbon nanotubes) was non-uniform and had a high degree of roughness (Figure 4), while the surface of granules containing dot-like conductive material (carbon black) was formed relatively smoothly compared to the surface of granules containing linear conductive material (single-walled carbon nanotubes). 【0058】 Therefore, the applicant applied a linear conductive material to the inner granular layer as in Example 1 above, and laminated an outer granular layer on top of the inner granular layer with a dot-like conductive material applied to it. In other words, with this configuration, not only are the granules of the outer granular layer containing the dot-like conductive material impregnated into the voids between the granules of the inner granular layer containing the linear conductive material, but the granules containing the dot-like conductive material are also uniformly positioned on top of them, flattening the surface of the positive electrode. This makes it possible to form a positive electrode with a uniform surface, and dramatically improves the adhesion strength with the solid electrolyte in contact with the electrode.

Claims

[Claim 1] Metal current collector, Located on one surface of the metal current collector, the inner granular layer contains an active material, a conductive material, and a binder in granular form, and The inner granular layer is laminated on the surface side and includes an outer granular layer containing an active material, a conductive material, and a binder in granular form. The conductive material of the inner granular layer and the conductive material of the outer granular layer have different shapes from each other. A positive electrode for an all-solid-state battery, characterized in that the conductive material contained in the inner granular layer contains linear particles, and the conductive material contained in the outer granular layer contains dot-shaped particles. [Claim 2] The positive electrode for an all-solid-state battery according to claim 1, characterized in that the conductive material contained in the inner granular layer and the conductive material contained in the outer granular layer differ in shape and type from each other. [Claim 3] The positive electrode for an all-solid-state battery according to claim 1, characterized in that the conductive material contained in the inner granular layer is carbon nanotubes consisting of linear particles, and the conductive material contained in the outer granular layer is carbon black consisting of dot-shaped particles. [Claim 4] The positive electrode for an all-solid-state battery according to claim 3, characterized in that the conductive material contained in the inner granular layer is a single-walled carbon nanotube consisting of linear particles. [Claim 5] The thickness ratio of the inner granular layer to the outer granular layer is 4:1 to 8:

1. The thickness of the inner granular layer is determined by the thickness of the thickest part, from where it contacts the current collector to where it contacts the outer granular layer. The positive electrode for an all-solid-state battery according to claim 1, characterized in that the thickness of the outer granule layer is the thickness of the thinnest part from the positive electrode surface to the point of contact with the inner granule layer. [Claim 6] The active material contained in the inner particle layer and the active material contained in the outer particle layer are independently of each other LiCoO 2 , LiNiO 2 , LiMnO 2 , Li 2 MnO 3 , LiMn 2 O 4 , Li(Ni a Co b Mn c )O 2 (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-y Co y O 2 (0 < y < 1), LiCo 1-y Mn y O 2 (0 < y < 1), LiNi 1-y Mn y O 2 (0 < y < 1), Li(Ni a Co b Mn c )O 4 (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni z O 4 (0 < z < 2), LiMn 2-z Co z O 4 (0 < z < 2) and are selected from the group consisting of combinations thereof, the positive electrode for an all-solid-state battery according to claim 1. [Claim 7] The positive electrode for an all-solid-state battery according to claim 1, characterized in that the binder contained in the inner granular layer and the binder contained in the outer granular layer are independently selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyimide, polyamide, polyamideimide, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butylene rubber, and fluororubber. [Claim 8] A positive electrode for an all-solid-state battery according to claim 1, characterized in that the voids between the granules of the inner granule layer containing a linear conductive material are impregnated with granules of the outer granule layer containing a point-like conductive material, and the granules of the outer granule layer containing the point-like conductive material are uniformly arranged on top of them, thereby flattening the surface of the positive electrode. [Claim 9] The positive electrode for an all-solid-state battery according to claim 1, further comprising a solid electrolyte coated on the surfaces of granules contained in an inner granule layer and granules contained in an outer granule layer, and a solid electrolyte impregnated in the voids between the granules. [Claim 10] The positive electrode for an all-solid-state battery according to claim 9, characterized in that the solid electrolyte is a sulfide-based solid electrolyte. [Claim 11] The process involves manufacturing inner granules containing an active material, a linear conductive material, and a binder in granular form, coating them onto a positive electrode metal current collector, and then rolling them to form a sheet-like inner granule layer. The process includes the steps of: manufacturing outer granules containing an active substance, a point-like conductive material, and a binder in granular form; applying these granules to the surface of the manufactured inner granule layer; and then rolling them to form a sheet-like outer granule layer. A method for manufacturing a positive electrode for an all-solid-state battery, characterized in that the conductive material of the inner granular layer and the conductive material of the outer granular layer have different shapes from each other. [Claim 12] A method for manufacturing a positive electrode for an all-solid-state battery according to claim 11, further comprising the steps of injecting and drying a sulfide-based electrolyte between the inner granule layer, the outer granule layer, and the inner granule layer and the outer granule layer. [Claim 13] An all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte, The positive electrode is, Metal current collector, Located on one surface of the metal current collector, the inner granular layer contains an active material, a conductive material, and a binder in granular form, and The inner granular layer is laminated on the surface side and includes an outer granular layer containing an active material, a conductive material, and a binder in granular form. The conductive material of the inner granular layer and the conductive material of the outer granular layer have different shapes from each other. An all-solid-state battery in which the conductive material contained in the inner granular layer contains linear particles, and the conductive material contained in the outer granular layer contains dot-like particles. [Claim 14] The all-solid-state battery according to claim 13, characterized in that the solid electrolyte is located on the surface and between the granules contained in the positive electrode for the all-solid-state battery, and is also located as a layered film between the positive electrode and the negative electrode.

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