Positive electrode layer for all-solid-state battery, method of manufacturing the same, and all-solid-state battery comprising the same

Abstract

A positive electrode layer for an all-solid-state battery includes a positive electrode current collector, and first and second positive electrode active material layer disposed on opposing surfaces of the positive electrode current collector. The first and second positive electrode active material layers include positive electrode active material particles. When straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first and second positive electrode active material layers, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8. A ten-point average roughness of a surface roughness of the positive electrode layer is greater than 0 μm and less than 25.2 μm, or a maximum height of a surface roughness of the positive electrode layer is greater than 0 μm and less than 24.4 μm.

Description

POSITIVE ELECTRODE LAYER FOR ALL-SOLID-STATE BATTERY, METHOD OF MANUFACTURING THE SAME, AND ALL-SOLID-STATE BATTERY COMPRISING THE SAME

[0001] The present disclosure relates to a positive electrode layer for an all-solid-state battery, a method of manufacturing the same, and an all-solid-state battery including the same.

[0002] Recently, as portable electronic devices are required to be miniaturized and used for long periods of time, higher capacity batteries are required, and with the spread of wearable electronic devices, there is a demand to ensure the safety of batteries. Therefore, the development of all-solid-state batteries using solid electrolytes instead of liquid electrolytes is actively underway.

[0003] All-solid-state batteries do not use flammable organic solvents, so additional circuits for safety can be simplified. Therefore, it is expected to be a technology that can manufacture safe batteries with high capacity per unit volume.

[0004] Oxide all-solid-state batteries using oxide electrolytes have lower ionic conductivity of the electrolyte (10-4S / cm to 10-6S / cm) than sulfide (10-2S / cm), and require a high-temperature sintering treatment process. However, they have superior stability compared to sulfide all-solid-state batteries using sulfide electrolytes that react with oxygen and moisture in the air.

[0005] Meanwhile, the development of a stacked type all-solid-state battery capable of implementing high capacity per unit volume is also being actively researched. The stacked oxide all-solid-state battery is an ultra-small battery that can be mounted on a substrate like a passive device and is stable even when exposed to high temperatures during the reflow process.

[0006] An embodiment provides a positive electrode layer for an all-solid-state battery having excellent densification and rate capability.

[0007] Another embodiment provides a method for manufacturing a positive electrode layer for an all-solid-state battery.

[0008] Another embodiment provides an all-solid-state battery including a positive electrode layer for an all-solid-state battery.

[0009] An embodiment provides a positive electrode layer for an all-solid-state battery including a positive electrode current collector, a first positive electrode active material layer disposed on one surface of the positive electrode current collector, and a second positive electrode active material layer disposed on the other surface of the positive electrode current collector. The first positive electrode active material layer and the second positive electrode active material layer include positive electrode active material particles. When straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer. An average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8. A ten-point average roughness Rz of a surface roughness of the positive electrode layer obtained by taking an average of a ten-point average roughness of a surface roughness of the first positive electrode active material layer and a ten-point average roughness of a surface roughness of the second positive electrode active material layer is greater than 0 μm and less than 25.2 μm.

[0010] A maximum height Ry of a surface roughness of the positive electrode layer, which is obtained by taking an average value of a maximum height of a surface roughness of the first positive electrode active material layer and a maximum height of a surface roughness of the second positive electrode active material layer, may be greater than 0 μm and less than 24.4 μm.

[0011] A particle size D50 of the positive electrode active material particles may be 0.01 μm to 10 μm.

[0012] The positive electrode active material particle may include two types of positive electrode active material particles having different particle sizes D50.

[0013] The first positive electrode active material layer and the second positive electrode active material layer may each have a thickness of 1 μm to 20 μm.

[0014] The first positive electrode active material layer and the second positive electrode active material layer may further include a solid electrolyte.

[0015] An interval between the straight lines may be from 5 μm to 10 μm.

[0016] An embodiment provides a positive electrode layer for an all-solid-state battery including a positive electrode current collector, a first positive electrode active material layer disposed on one surface of the positive electrode current collector, and a second positive electrode active material layer disposed on the other surface of the positive electrode current collector. The first positive electrode active material layer and the second positive electrode active material layer include positive electrode active material particles. When straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8. A maximum height Ry of a surface roughness of the positive electrode layer, which is obtained by taking an average value of a maximum height of a surface roughness of the first positive electrode active material layer and a maximum height of a surface roughness of the second positive electrode active material layer, is greater than 0 μm and less than 24.4 μm.

[0017] Another embodiment provides a method of manufacturing a positive electrode layer for an all-solid-state battery which includes: printing a first paste including positive electrode active material particles and a solid electrolyte on a substrate to form a first positive electrode active material layer; forming a positive electrode current collector on the first positive electrode active material layer; printing a second paste including positive electrode active material particles and a solid electrolyte on the positive electrode current collector to form a second positive electrode active material layer; and removing the substrate. When straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8. A ten-point average roughness Rz of a surface roughness of the positive electrode layer obtained by taking an average of a ten-point average roughness of a surface roughness of the first positive electrode active material layer and a ten-point average roughness of a surface roughness of the second positive electrode active material layer is greater than 0 μm and less than 25.2 μm.

[0018] The positive electrode active material particles and the solid electrolyte may be included in a weight ratio of 2:1 to 10:1.

[0019] Another embodiment provides a method of manufacturing a positive electrode layer for an all-solid-state battery which includes printing a first paste including positive electrode active material particles and a solid electrolyte on a substrate to form a first positive electrode active material layer; forming a positive electrode current collector on the first positive electrode active material layer; printing a second paste including positive electrode active material particles and a solid electrolyte on the positive electrode current collector to form a second positive electrode active material layer; and removing the substrate. When straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8. A maximum height Ry of a surface roughness of the positive electrode layer, which is obtained by taking an average value of a maximum height of a surface roughness of the first positive electrode active material layer and a maximum height of a surface roughness of the second positive electrode active material layer, is greater than 0 μm and less than 24.4 μm.

[0020] Another embodiment provides an all-solid-state battery including a positive electrode layer; a negative electrode layer; and a solid electrolyte layer stacked between the positive electrode layer and the negative electrode layer.

[0021] According to an embodiment, an all-solid-state battery having high densification and rate capability can be obtained.

[0022] FIG. 1 is a perspective view showing an all-solid-state battery according to an embodiment.

[0023] FIG. 2 is a cross-sectional view of the all-solid-state battery taken along line I-I' of FIG. 1.

[0024] FIG. 3 is an exploded perspective view showing the structure of a stack in the all-solid-state battery of FIG. 1.

[0025] FIG. 4 is a scanning electron microscope (SEM) image showing a method for measuring an average number of positive electrode active material particles within a positive electrode layer according to an embodiment.

[0026] FIG. 5 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 1.

[0027] FIG. 6 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 2.

[0028] FIG. 7 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 3.

[0029] FIG. 8 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 4.

[0030] FIG. 9 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 5.

[0031] FIG. 10 is a scanning electron microscope (SEM) image of the positive electrode layer according to Comparative Example 1.

[0032] FIG. 11 is a scanning electron microscope (SEM) image of the positive electrode layer according to Comparative Example 2.

[0033] FIG. 12 is a scanning electron microscope (SEM) image of the positive electrode layer according to Comparative Example 3.

[0034] Hereinafter, the present disclosure will be described in detail hereinafter with reference to the accompanying drawings, in which embodiments of the present disclosure are shown. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. In the accompanying drawings, some constituent elements are exaggerated, omitted, or schematically illustrated, and the size of each constituent element does not entirely reflect the actual size.

[0035] The accompanying drawings are intended only to facilitate an understanding of the exemplary embodiments disclosed in this specification, and it is to be understood that the technical ideas disclosed herein are not limited by the accompanying drawings and include all modifications, equivalents, or substitutions that are within the range of the ideas and technology of the present disclosure.

[0036] Although terms of "first," "second," and the like are used to explain various constituent elements, the constituent elements are not limited to such terms. These terms are only used to distinguish one constituent element from another constituent element.

[0037] It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. Further, when an element is referred to as being "on" or "above" a reference element, it can be positioned above or below the reference element, and it is not necessarily referred to as being positioned "on" or "above" in a direction opposite to gravity.

[0038] Throughout the specification, the terms "comprise" or "have" are intended to specify the presence of stated features, integers, steps, operations, constituent elements, components or a combination thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, constituent elements, components, and / or groups thereof. Therefore, unless explicitly described to the contrary, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[0039] In addition, the phrase "on a plane" means a view from a position above the object (e.g., from the top), and the phrase "on a cross-section" means a view of a cross-section of the object which is vertically cut from the side.

[0040] Throughout the specification, the term "connected" does not mean only that two or more constituent components are directly connected, but may also mean that two or more constituent components are indirectly connected through another constituent component, that two or more components are electrically connected as well as physically connected, or that two or more constituent components are referred to by different names but are united by location or function.

[0041] FIG. 1 is a perspective view showing an all-solid-state battery according to an embodiment, FIG. 2 is a cross-sectional view of the all-solid-state battery taken along line I-I' of FIG. 1, and FIG. 3 is an exploded perspective view showing the structure of a stack in the all-solid-state battery of FIG. 1.

[0042] The L-axis, W-axis, and T-axis shown in FIGS. 1 to 3 represent the length direction, width direction, and thickness direction of the stack 110 of the all-solid-state battery, respectively. Here, the thickness direction (T-axis direction) may be a direction perpendicular to a wide surface (main surface) of the constituent elements in a sheet shape, and may for example be used as a same concept as the stacking direction in which the unit cells are stacked. The length direction (L-axis direction) may be a direction that extends parallel to a broad surface (main surface) of the constituent elements in the sheet shape and may be a direction approximately perpendicular to the thickness direction (T-axis direction), for example, it may be the direction in which the first external electrode 112 and the second external electrode 114 are disposed on respective sides. The width direction (W-axis direction) may be a direction that extends parallel to the broad surface (main surface) of the constituent elements in the sheet shape and may be a direction that is approximately perpendicular to the thickness direction (T-axis direction) and the length direction (L-axis direction), and the length of the constituent elements in the sheet shape in the length direction (L-axis direction) may be greater than the length in the width direction (W-axis direction).

[0043] Referring to FIGS. 1 to 3, an all-solid-state battery 100 according to an embodiment includes a stack 110 and external electrodes 112 and 114 disposed on the outside of the stack 110. The external electrodes 112 and 114 may include a first external electrode 112 and a second external electrode 114 arranged at opposite ends in the length direction (L-axis direction) of the stack 110.

[0044] For better understanding and ease of description of an embodiment, in the stack 110 of the all-solid-state battery, respective sides facing each other in the thickness direction (T-axis direction) will be defined to be a first side and a second side, respective sides connected to the first side and the second side and facing each other in the length direction (L-axis direction) will be defined to be a third side and a fourth side, and respective sides connected to the first and second sides, connected to the third and fourth sides, and facing each other in the width direction (W axis direction) will be defined to be a fifth side and a sixth side.

[0045] For example, the first side, which is a lower surface, may be the side facing a mounting direction. Additionally, the first to sixth sides may be flat, and the embodiment is not limited thereto. For example, the first to sixth sides may be curved surfaces of which central portions are convex, and edges that are boundaries of the respective sides may be round.

[0046] The stack 110 of the all-solid-state battery may have, for example, a roughly hexahedral shape.

[0047] The shape, dimensions, and number of stacked unit cells of the stack 110 of the all-solid-state battery are not limited to those shown in the drawings of the present embodiment.

[0048] A stack 110 of an all-solid-state battery 100 according to an embodiment includes a positive electrode layer 120, a negative electrode layer 140, and a solid electrolyte layer 130 disposed between the positive electrode layer 120 and the negative electrode layer 140 in the stacking direction.

[0049] For example, the electrode layer arranged at the top of the stack 110 based on the stacking direction may be a positive electrode layer 120 or a negative electrode layer 140, and the electrode layer arranged at the bottom of the stack 110 may be a negative electrode layer 140 or a positive electrode layer 120.

[0050] Positive Electrode Layer

[0051] The positive electrode layer 120 may include a positive electrode current collector 123 and positive electrode active material layers 121 and 122 disposed on at least one surface of the positive electrode current collector 123. Specifically, the positive electrode active material layers 121 and 122 may include a first positive electrode active material layer 121 disposed on one surface of the positive electrode current collector 123 and a second positive electrode active material layer 122 disposed on the other surface of the positive electrode current collector 123. For example, when the positive electrode layer 120 is disposed at the top of the stack 110 based on the stacking direction, the positive electrode layer 120 may have a structure in which a second positive electrode active material layer 122 is arranged on one surface of the positive electrode current collector 123. In addition, the positive electrode layer 120 disposed between the uppermost and lowermost layers of the stack 110 may have a structure in which a first positive electrode active material layer 121 and a second positive electrode active material layer 122 are disposed on each of both surfaces of the positive electrode current collector 123.

[0052] The positive electrode current collector 123 may be formed of, for example, a plate-shaped member or a thin member. As another example, the positive electrode current collector 123 may be a porous body, such as a reticulate or mesh shape.

[0053] The positive electrode current collector 123 may be a porous metal plate made of, for example, stainless steel, nickel (Ni), copper (Cu), tin (Sn), aluminum (Al), or an alloy thereof, but is not limited thereto. Additionally, the positive electrode current collector 133 may be coated with an oxidation-resistant metal or alloy film to prevent oxidation.

[0054] The positive electrode current collector 123 may be made of a carbon-based plate-shaped, thin-walled, or linear member. Specifically, the positive electrode current collector 123 may be made of a conductive carbon material, and the conductive carbon material may be, for example, conductive fibers such as graphite, carbon nanotubes (CNTs), vapor grown carbon fibers (VGCFs), or conductive carbon such as carbon black.

[0055] The positive electrode current collector 123 may include one or more types of solid electrolytes described below.

[0056] The first positive electrode active material layer 121 and the second positive electrode active material layer 122 include positive electrode active materials. Specifically, the positive electrode active material may be particles.

[0057] The positive electrode active material is a material including lithium ions and can reversibly intercalate and deintercalate lithium ions. That is, the positive electrode active material includes lithium ions and may play a role in providing lithium ions to the negative electrode when charging the all-solid-state battery. The positive electrode active material can affect the capacity and output of all-solid-state batteries.

[0058] The positive electrode active material may be, for example, compounds represented by the following chemical formulas:

[0059] LiaAl-bMbD2(where 0.90≤a≤1.8, 0≤b≤0.5); LiaEl-bMbO2-cDc(where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE2-bMbO4-cDc(where 0≤b≤0.5, 0≤c≤0.05); LiaNi1-b-cCobMcDα(where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); LiaNi1-b-cCobMcO2-αXα(where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); LiaNi1-b-cCObMcO2-αX2(where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); LiaNi1-b-cMnbMcDα(where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); LiaNi1-b-cMnbMcO2-αXα(where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); LiaNi1-b-cMnbMcO2-αX2(where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); LiaNibEcGdO2(where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); LiaNibCocMndGeO2(where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); LiaNiGbO2(where 0.90≤a≤1.8, 0.001≤b≤0.1); LiaCoGbO2(where 0.90≤a≤1.8, 0.001≤b≤0.1); LiaMnGbO2(where 0.90≤a≤1.8, 0.001≤b≤0.1); LiaMn2GbO4(where 0.90≤a≤1.8, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O2; LiRO2; LiNiVO4; Li(3-f)J2(PO4)3(0≤f≤2); Li(3-f)Fe2(PO4)3(where 0≤f≤2); and LiFePO4. In the above formula, A is Ni, Co, or Mn; M is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, or a rare-earth element; D is O, F, S, or P; E is Co or Mn; X is F, S, or P; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V; Q is Ti, Mo or Mn; R is Cr, V, Fe, Sc, or Y; and J is V, Cr, Mn, Co, Ni, or Cu.

[0060] The positive electrode active material may also be LiCoO2, LiMnxO2x(wherein x is 1 or 2), LiNi1-xMnxO2x(wherein 0<x<1), LiNi1-x-yCoxMnyO2(wherein 0≤x≤0.5, 0≤y≤0.5), LiFePO4, TiS2, FeS2, TiS3, or FeS3.

[0061] For example, the positive electrode active material may be a lithium metal compound including lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese oxide, or a combination thereof.

[0062] The positive electrode active material layers 121 and 122 may further include a solid electrolyte, for example, an oxide-based solid electrolyte.

[0063] The solid electrolyte can function as an ion conducting channel within the positive electrode layer. This can reduce the interfacial resistance. The solid electrolyte included in the positive electrode active material layers 121 and 122 is the same as the solid electrolyte included in the solid electrolyte layer 130 described later, and thus its description is omitted here.

[0064] The positive electrode active material layers 121 and 122 may further include one or more selected from a conductive material and a binder.

[0065] The conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the all-solid-state battery 100. For example, graphite, such as natural graphite or artificial graphite; a carbon-based material such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; a conductive fiber such as carbon fiber and metal fiber; carbon fluoride; a metal powder such as aluminum and nickel powder; a conductive whisker such as zinc oxide and potassium titanate; a conductive metal oxide such as titanium oxide; or a conductive material such as polyphenylene derivative may be used.

[0066] The conductive material may be included in an amount of 1 part by weight to 10 parts by weight, for example 5 parts by weight to 10 parts by weight, based on 100 parts by weight of the positive electrode active material. When the content of the conductive material is within the above range, a positive electrode layer having excellent conductivity characteristics may be obtained.

[0067] A binder can be used to improve the binding strength between positive electrode active materials and conductive materials. The binder may include acrylic, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, a styrene butadiene rubber, a fluorine rubber, and various copolymers.

[0068] The binder may be included in an amount of 1 part by weight to 50 parts by weight, for example 1 part by weight to 30 parts by weight, based on 100 parts by weight of the positive electrode active material. When the binder content is within the above range, the positive electrode active material layer can have high binding strength.

[0069] According to an embodiment, when straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector 123 in a direction of the first positive electrode active material layer 121 and in a direction of the second positive electrode active material layer 122, an average number of positive electrode active material particles crossing each straight line may be greater than 0 and less than or equal to 8, for example 0.5 to 8, 1 to 7.5, or 1.5 to 7. When the average number of positive electrode active material particles included in the first positive electrode active material layer 121 and the second positive electrode active material layer 122 is within the above range, that is, when the number of positive electrode active material particles forming the positive electrode layer 120 is within the above range, positive electrode active material particles having a small particle size are uniformly distributed and the densification is increased, so that an all-solid-state battery having excellent rate capability can be secured.

[0070] Specifically, the average number of the positive electrode active material particles may be measured as follows.

[0071] After breaking the chip of the all-solid-state battery 100, a cross-sectional sample showing the positive electrode layer 120 within the stack 110 can be obtained. Specifically, a cross-sectional sample can be obtained showing a positive electrode layer 120 composed of a positive electrode current collector 123, a first positive electrode active material layer 121 disposed on one surface of the positive electrode current collector 123, and a second positive electrode active material layer 122 disposed on the other surface of the positive electrode current collector 123. The obtained cross-sectional sample can be measured using a scanning electron microscope (SEM) at 10 kV with a reference to a length of 40 μm. In an SEM image of the obtained cross-sectional sample, at least one straight line in the first positive electrode active material layer 121 may be perpendicularly drawn to the positive electrode current collector 123 toward the first positive electrode active material layer 121 from the positive electrode current collector 123, and in addition, at least one straight line may be perpendicularly drawn to the positive electrode current collector 123 in the second positive electrode active material layer 122 from the positive electrode current collector 123 toward the second positive electrode active material layer 122 to obtain an average number of the positive electrode active material particles crossing each straight line.

[0072] FIG. 4 is a scanning electron microscope (SEM) image showing a method for measuring an average number of positive electrode active material particles within a positive electrode layer according to an embodiment. For example, as shown in FIG. 4, five straight lines in the first positive electrode active material layer 121 from the positive electrode current collector 123 toward the first positive electrode active material layer 121 and in addition, five straight lines in the second positive electrode active material layer 122 from the direction from the second positive electrode active material layer 122 toward the positive electrode current collector 123, total ten straight lines, may be drawn to obtain an average number of the positive electrode active material particles crossing the total ten straight lines.

[0073] In other to count the number of the positive electrode active material particles, at least two straight lines, if drawn in the same direction, may be drawn at a predetermined interval. For example, at least two straight lines may be spaced apart not to recross the positive electrode active material particles crossing one straight line. In other words, at least two straight lines for measuring the number of the positive electrode active material particles may be spaced apart from each other not to measure the same positive electrode active material particles. For example, at least two straight lines for measuring the positive electrode active material particles may have a space of 5 μm to 10 μm, for example, 6 μm to 9 μm.

[0074] According to an embodiment, a ten-point average roughness Rz of a surface roughness of the positive electrode layer 120 may be greater than 0 and less than 25.2 μm, for example, 0.1 μm to 24 μm, 0.5 μm to 23 μm, or 1 μm to 22 μm. The ten-point average roughness Rz of the surface roughness of the positive electrode layer 120 may be obtained as an average value of a ten-point average roughness of a surface roughness of the first positive electrode active material layer 121 and a ten-point average roughness of a surface roughness of the second positive electrode active material layer 122. When the ten-point average roughness of the surface roughness of the positive electrode layer 120 is within the ranges, an all-solid-state battery may be prevented from generation of a leakage current, resultantly securing excellent rate capability.

[0075] The ten-point average roughness Rz of the surface roughness may be obtained by extracting a region with a reference length, for example, 40 μm in length from a roughness curve in its mean line direction and then, adding an average of absolute values of the highest to fifth highest peaks and an average of absolute values of the lowest to fifth lowest valleys. In a roughness curve, the peak may be a highest top, and the valley may be a lowest bottom.

[0076] In addition, according to an embodiment, a maximum height Ry of the surface roughness of the positive electrode layer 120 may be greater than 0 and less than 24.4 μm, for example, 0.1 μm to 24 μm, 0.5 μm to 23 μm, or 1 μm to 22 μm. The maximum height Ry of the surface roughness of the positive electrode layer 120 may be obtained as an average of a maximum height of a surface roughness of the first positive electrode active material layer 121 and a maximum height of a surface roughness of the second positive electrode active material layer 122. If the maximum height Ry of the surface roughness of the positive electrode layer 120 is within the ranges, an all-solid-state battery may be prevented from generation of a leakage current, resultantly ensuring excellent rate capability.

[0077] The maximum height Ry of the surface roughness may be obtained by extracting a region with a reference length, for example, 40 μm in length from the roughness curve in its mean line direction and then, measuring a gap between the highest peak line and the lowest valley line of the extracted region in a vertical magnification direction of the roughness curve.

[0078] Specifically, the surface roughness of the positive electrode layer 120 may be measured as follows.

[0079] The all-solid-state battery 100 may be broken into chips to obtain a cross-sectional sample in which the positive electrode layer 120 within the stack 110 is visible. Specifically, the cross-sectional sample, in which the positive electrode layer 120 consisting of the positive electrode current collector 123, the first positive electrode active material layer 121 disposed one surface of the positive electrode current collector 123, and the second positive electrode active material layer 122 disposed on the other surface of the positive electrode current collector 123, may be obtained. The obtained cross-sectional sample may be measured with a reference to a length of 40 μm by using a scanning electron microscope (SEM) under a condition of 10 kV. In the SEM image of the obtained cross-sectional sample, surface roughness of the first positive electrode active material layer may be obtained by drawing a curve along the surface of the first positive electrode active material layer to mark a peak and a valley, and in addition, surface roughness of the second positive electrode active material layer may be obtained by drawing a curve along the surface of the second positive electrode active material layer to mark a peak and a valley, which are respectively averaged to obtain surface roughness Rz and Ry.

[0080] The positive electrode active material particles included in the first positive electrode active material layer 121 and the second positive electrode active material layer 122 may have a particle size D50 of 0.01 μm to 10 μm, for example, 0.05 μm to 9.5 μm, 0.1 μm to 9 μm, 0.5 μm to 8.5 μm, or 1 μm to 8 μm. Because the positive electrode active material particles, if the particle size D50 is within the ranges, have high density, an all-solid-state battery with excellent rate capability may be secured.

[0081] The positive electrode active material particles may be a mixture of two types of positive electrode active material particles having different particle sizes D50.

[0082] The particle size D50 of the positive electrode active material particles may be measured as follows. As described above, in the scanning electron microscope (SEM) image of the obtained cross-sectional sample, at least 100 positive electrode active material particles included in the first positive electrode active material layer 121 and the second positive electrode active material layer 122 may be measured with respect to a maximum major axis to plot a cumulative size distribution curve, from which the particle size D50 may be calculated. D50 refers to a size at a point where it becomes 50% on the cumulative size distribution curve.

[0083] The first positive electrode active material layer 121 and the second positive electrode active material layer 122 may have each thickness of 1 μm to 20 μm, for example, 3 μm to 18 μm. If the first positive electrode active material layer 121 and the second positive electrode active material layer 122 have a thickness within the ranges, in which it may be possible to make the layers thin, an all-solid-state battery with excellent capacity and rate capability may be secured.

[0084] The first positive electrode active material layer 121 and the second positive electrode active material layer 122 may be measured with respect to the thickness as follows. As described above, in the scanning electron microscope (SEM) image of the obtained cross-sectional sample, the thickness may be obtained by using a length (L-axis) or width (W-axis) direction central point of the first and second positive electrode active material layers 121 and 122 as a reference point to measure thicknesses at 10 points spaced apart from the reference point at a predetermined interval and then, calculate an arithmetic mean of the thicknesses of the first and second positive electrode active material layers 121 and 122. The predetermined interval of the 10 points may be adjusted according to a scale of the scanning electron microscope (SEM) image, for example, 1 μm to 100 μm, 1 μm to 50 μm, or 1 μm to 10 μm. Herein, the 10 points should be positioned within each first and second positive electrode active material layers 121 and 122, but if the 10 points are not positioned within the first and second positive electrode active material layers 121 and 122, the position of the reference point may be changed, or the interval between the 10 points may be adjusted.

[0085] The positive electrode active material layers 121 and 122 can be formed by printing the positive electrode active material on one or both surfaces of the positive electrode current collector 123, but the method of forming the positive electrode active material layer is not limited thereto.

[0086] Specifically, the positive electrode layer 120 according to an embodiment may be manufactured by printing a first paste including positive electrode active material particles and a solid electrolyte on a substrate to form a first positive electrode active material layer; forming a positive electrode current collector on the first positive electrode active material layer; printing a second paste including positive electrode active material particles and a solid electrolyte on the positive electrode current collector to form a second positive electrode active material layer; and removing the substrate.

[0087] The substrate may include PET (polyethylene terephthalate), PEN (polyethylenenaphthalate), PES (polyethersulfone), PC (polycarbonate), PP (polypropylene), etc.

[0088] In each of the first paste and the second paste, the positive electrode active material particles and the solid electrolyte may be included in a weight ratio of 2:1 to 10:1, for example, may be included in a weight ratio of 3:1 to 9:1. When the positive electrode active material particles and the solid electrolyte are included within the above content ratio range, the number of positive electrode active material particles in the positive electrode layer and the surface roughness of the positive electrode layer are adjusted to an appropriate range, thereby increasing the densification and obtaining an all-solid-state battery with excellent rate capability.

[0089] Negative Electrode Layer

[0090] The negative electrode layer 140 may include a negative electrode current collector 143 and a negative electrode active material layers 141 and 142 disposed on at least one surface of the negative electrode current collector 143. Specifically, the negative electrode active material layers 141 and 142 may include a first negative electrode active material layer 141 disposed on one surface of the negative electrode current collector 143 and a second negative electrode active material layer 142 disposed on the other surface of the negative electrode current collector 143. For example, when the negative electrode layer 140 is disposed at the bottom of the stack 110 based on the stacking direction, the negative electrode layer 140 may have a structure in which the first negative electrode active material layer 141 is arranged on one surface of the negative electrode current collector 143. In addition, the negative electrode layer 140 disposed between the uppermost and lowermost layers of the stack 110 may have a structure in which a first negative electrode active material layer 141 and a second negative electrode active material layer 142 are disposed on each of both surfaces of the negative electrode current collector 143.

[0091] The negative electrode current collector 143 may be formed of, for example, a plate-shaped member or a thin member. As another example, the negative electrode current collector 143 may be a porous body, such as a reticulate or mesh shape.

[0092] The negative electrode current collector 143 may be a porous metal plate made of, for example, stainless steel, nickel (Ni), copper (Cu), tin (Sn), aluminum (Al), or an alloy thereof, but is not limited thereto. Additionally, the negative electrode current collector 143 may be coated with an oxidation-resistant metal or alloy film to prevent oxidation.

[0093] The negative electrode current collector 143 may be made of a conductive carbon-based material similar to the positive electrode current collector 123 and may include one or more solid electrolytes. The negative electrode current collector 143 may be identical to the negative electrode active material layers 141 and 142.

[0094] The negative electrode active material layers 141 and 142 includes a negative electrode active material.

[0095] The negative electrode active material may store lithium ions that have moved from the positive electrode layer and release them when the all-solid-state battery is discharged, thereby generating electrical energy.

[0096] The negative electrode active material may include a carbon-based material, silicon, silicon oxide, a silicon-based alloy, a silicon-carbon-based material composite, tin, a tin-based alloy, a tin-carbon composite, metal oxide, or a combination thereof, and may include a lithium metal and / or a lithium metal alloy.

[0097] The lithium metal alloy may include lithium and metal / metalloid capable of alloying with lithium. For example, the metal / metalloid capable of alloying with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, Si-M1 alloy (where M1 is an alkali metal, alkaline earth metal, Group 13 to 16 elements, transition metal, rare earth element, or a combination thereof, but does not include Si), an Sn-M2 alloy (where M2 is an alkali metal, alkaline earth metal, Group 13 to 16 elements, a transition metal, transition metal oxide of lithium titanium oxide (Li4Ti5O12), etc., a rare earth element or a combination element thereof, and does not include Sn), MnOx(0<x≤2), etc.

[0098] The elements M1 and M2 may each independently be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0099] Further, the oxide of the metal / metalloid capable of alloying with lithium may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, SnO2, SiOx(0<x<2), or the like. For example, the negative electrode active material may include one or more elements selected from Group 13 to 16 elements of the Periodic Table of Elements. For example, the negative electrode active material may include one or more elements selected from the group consisting of Si, Ge, and Sn.

[0100] The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite. In addition, the amorphous carbon may include soft carbon (low temperature calcined carbon) or hard carbon, a mesophase pitch carbonization product, calcined coke, graphene, carbon black, fullerene soot, carbon nanotubes, carbon fiber, and the like.

[0101] The silicon may be Si, SiOx(0<x<2, for example 0.5 to 1.5), Sn, SnO2, a silicon-containing metal alloy, or a mixture thereof. The silicon-containing metal alloy may include, for example, silicon and one or more of Al, Sn, Ag, Fe, Bi, Mg, Zn, In, Ge, Pb, and Ti.

[0102] The negative electrode active material layers 141 and 142 may further include a solid electrolyte.

[0103] The solid electrolyte can function as an ion conducting channel within the negative electrode layer. This can reduce the interfacial resistance. The solid electrolyte included in the negative electrode active material layers 141 and 142 is the same as the solid electrolyte included in the solid electrolyte layer 130 described later, so its description is omitted here.

[0104] The negative electrode active material layers 141 and 142 may further include one or more selected from a conductive material and a binder.

[0105] The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the all-solid-state battery 100. For example, examples of the conductive material may include: graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; fluorinated carbon; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0106] The conductive material may be included in an amount of 1 part by weight to 10 parts by weight, for example 5 parts by weight to 10 parts by weight based on 100 parts by weight of the negative electrode active material. When the content of the conductive agent is within the above range, a negative electrode layer having excellent conductivity characteristics can be obtained.

[0107] A binder can be used to improve the binding strength between positive electrode active materials and conductive materials. The binder may include acrylic, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, a styrene butadiene rubber, a fluorine rubber, and various copolymers.

[0108] The binder may be included in an amount of 1 part by weight to 50 parts by weight, for example, 1 part by weight to 30 parts by weight, based on 100 parts by weight of the negative electrode active material. When the binder content is within the above range, the negative electrode active material layer can have high binding strength.

[0109] The negative electrode active material layers 141 and 142 can be formed by printing the negative electrode active material on one side or both surfaces of the negative electrode current collector 143, but the method of forming the negative electrode active material layer is not limited thereto.

[0110] A thickness of the negative electrode layer 140 may be 4 μm to 15 μm, for example 5 μm to 12 μm.

[0111] Solid Electrolyte Layer

[0112] The solid electrolyte layer 130 may be interposed and stacked between the positive electrode layer 120 and the negative electrode layer 140. Specifically, the solid electrolyte layer 130 may be adjacently disposed between the positive electrode active material layers 121 and 122 of the positive electrode layer 120 and the negative electrode active material layers 141 and 142 of the negative electrode layer 140 in the stacking direction. In other words, within the all-solid-state battery 100, specifically, within the stack 110 of the all-solid-state battery 100, a plurality of positive electrode layers 120 and negative electrode layers 140 may be alternately arranged, and a plurality of solid electrolyte layers 130 may be interposed and stacked between them.

[0113] The solid electrolyte layer 130 includes a solid electrolyte. The solid electrolyte may act as a channel for lithium (Li) ions.

[0114] The solid electrolyte included in the solid electrolyte layer 130 may include a glass-ceramic electrolyte or a lithium borosilicate electrolyte.

[0115] The glass-ceramic electrolyte may include lithium halide (such as LiX, X=F, Br, Cl, I, etc.). The glass-ceramic or crystallized glass means a material in which amorphous and crystalline phases coexist, as shown by peaks and halos in X-ray diffraction or electron diffraction. Therefore, the glass-ceramic electrolyte is an electrolyte in a mixed state of amorphous and crystalline phases, with some crystallization occurring through firing.

[0116] The glass-ceramic electrolytes may include amorphous and two or more crystalline phases. Additionally, the crystalline phases included in the glass-ceramic electrolyte may include a lithium compound crystal phase including lithium.

[0117] When the solid electrolyte includes a glass-ceramic electrolyte, sufficient densification is achieved after firing, enabling implementation of high ionic conductivity.

[0118] The glass-ceramic electrolyte may include at least one selected from lithium (Li) oxide, boron (B) oxide, silicon (Si) oxide, aluminum (Al) oxide, gallium (Ga) oxide, phosphorus (P) oxide, germanium (Ge) oxide, magnesium (Mg) oxide, and lithium chloride (LiCl). For example, the glass-ceramic electrolyte may include Li2O, B2O3, SiO2, P2O5, GeO2, and LiCl. For example, the glass-ceramic electrolyte may be Li4B4Al3O12Cl (LCBA).

[0119] The lithium borosilicate-based electrolyte (hereinafter referred to as LBSO-based electrolyte) is a glass-like electrolyte. The glass means crystallographically amorphous, as evidenced by the observation of a halo in X-ray diffraction or electron diffraction.

[0120] When the solid electrolyte includes an LBSO-based electrolyte, the firing temperature can be lowered while maintaining an amorphous state during firing, thereby realizing high ionic conductivity, and there is an advantage of low reactivity with the electrode.

[0121] For example, the LBSO-based electrolyte may include lithium (Li), boron (B), silicon (Si), aluminum (Al), phosphorus (P), germanium (Ge), and sulfur (S).

[0122] Additionally, the solid electrolyte included in the solid electrolyte layer 130 may include an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a combination thereof.

[0123] The oxide-based solid electrolyte may be at least one selected from a garnet-type, nasicon-type, LISICON-type, perovskite-type, LiPON-type, and amorphous (glass) solid electrolyte.

[0124] The garnet-type solid electrolytes may indicate lithium-lanthanum zirconium oxide (LLZO) represented by LiaLabZrcO12, such as Li7La3Zr2O12. The nasicon-type solid electrolyte may indicate lithium-aluminum-titanium-phosphate (LATP) represented by Li1+xAlxTi2-x(PO4)3(0<x<1) in which Ti is introduced into a Li1+xAlxM2-x(PO4)3(LAMP) (0<x<2, wherein M is Zr, Ti, or Ge)-type compound, lithium-aluminum-germanium-phosphate (LAGP) represented by Li1+xAlxGe2-x(PO4)3(0<x<1), such as Li1.3Al0.3Ti1.7(PO4)3or the likein which excess lithium is introduced, and / or lithium-zirconium-phosphate (LZP) of LiZr2(PO4)3.

[0125] In addition, the LISICON-type solid electrolyte may indicate a solid solution oxide represented by xLi3AO4-(1-x)Li4BO4(A is P, As, V, etc. and B is Si, Ge, Ti, etc.) and including Li4Zn(GeO4)4, Li10GeP2O12(LGPO), Li3.5Si0.5P0.5O4, Li10.42Si(Ge)1.5P1.5Cl0.08O11.92, etc., and solid solution sulfide including Li2S-P2S5, Li2S-SiS2, Li2S-SiS2-P2S5, or Li2S-GeS2,etc.represented by Li4-xM1-yM'yS4(M is Si or Ge and M' is P, Al, Zn, or Ga).

[0126] The perovskite-type solid electrolyte may indicate lithium lanthanum titanate (LLTO) represented by Li3xLa2 / 3-x□1 / 3-2xTiO3(0<x<0.16, □: vacancy), such as Li1 / 8La5 / 8TiO3, and the like, and the LiPON-type solid electrolyte may refer to a nitride such as lithium-phosphorous-oxynitride, such as Li2.8PO3.3N0.46orthe like.

[0127] The amorphous solid electrolyte may be Li2O-B2O3-SiO2, Li2O-B2O3-P2O5, Li3BO3-Li2SO4, or Li3BO3-Li2CO3.

[0128] The sulfide-based solid electrolyte includes sulfur atoms among the electrolyte components and is not particularly limited to specific components, and may include one or more of a crystalline solid electrolyte, an amorphous solid electrolyte (glassy solid electrolyte), and a glass ceramic solid electrolyte.

[0129] For example, the sulfide-based solid electrolyte may include LPS-type sulfides including sulfur and phosphorus (for example, Li2S-P2S5), and Thio-LISICON type compounds, such as Li4-xGe1-xPxS4(where x may be 0.1 to 2, 3 / 4, or 2 / 3), Li10±1MP2X12(where M is Ge, Si, Sn, or Al, and X is S or Se), Li3.833Sn0.833As0.166S4, Li4SnS4, Li3.25Ge0.25P0.75S4, Li2S-P2S5, B2S3-Li2S, xLi2S-(100-x)P2S5(where x is 70 to 80), Li2S-SiS2-Li3N, Li2S-P2S5-LiI, Li2S-SiS2-LiI, Li2S-B2S3-LiI, Li10SnP2S12, and Li3.25Ge0.25P0.75S4.

[0130] The ionic conductivity of the solid electrolyte may be greater than or equal to 1X10-6S / cm. The ionic conductivity may be a value measured at a temperature of 25 °C. The ionic conductivity may be greater than or equal to 1X10-6S / cm, greater than or equal to 2X10-6S / cm, greater than or equal to 3X10-6S / cm, greater than or equal to 4X10-6S / cm, greater than or equal to 5X10-6S / cm, or greater than or equal to 1X10-3S / cm, and the upper limit is not particularly limited. When a solid electrolyte that satisfies the ionic conductivity in the above range is used, the all-solid-state battery 100 can exhibit high output.

[0131] The thickness of the solid electrolyte layer 130 may be 5 μm to 15 μm, for example 6 μm to 12 μm.

[0132] The stack 110 according to an embodiment may further include a margin insulating layer 150.

[0133] The margin insulating layer 150 fills the area on the solid electrolyte layer 130 excluding the area where the positive electrode layer 120 or the negative electrode layer 140 is arranged. When the positive electrode layer 120 is disposed on the solid electrolyte layer 130, a margin insulating layer 150 may be disposed in an area other than the area where the positive electrode layer 120 is disposed. Similarly, when a negative electrode layer 140 is disposed on a solid electrolyte layer 130, a margin insulating layer 150 may be disposed in an area other than the area where the negative electrode layer 140 is disposed. The margin insulating layer 150 may be located in the same layer of the positive electrode layer 120 and the negative electrode layer 140.

[0134] The margin insulating layer 150 can eliminate the step between the solid electrolyte layer 130 and the positive electrode layer 120 or the step between the solid electrolyte layer 130 and the negative electrode layer 140. Accordingly, the density between the solid electrolyte layer 130 and the electrode layer is increased, so that delamination or warping due to firing can be prevented during the manufacturing process of the all-solid-state battery.

[0135] The margin insulating layer 150 may include an insulating material having an ionic conductivity of less than or equal to 1.0X10-10S / cm, or less than or equal to 1.0X10-6S / cm, and for example, insulating materials such as the aforementioned solid electrolyte material or resin may be included.

[0136] For example, the insulating material may be polyolefin such as polyethylene or polypropylene; polyester such as polyethylene terephthalate (PET); polyurethane; or polyimide.

[0137] Additionally, the margin insulating layer 150 may include a ceramic material, such as, but not limited to, alumina (Al2O3), aluminum nitride (AlN), beryllium oxide (BeO), boron nitride (BN), silicon (Si), silicon carbide (SiC), silica (SiO2), silicon nitride (Si3N4), gallium arsenide (GaAs), gallium nitride (GaN), barium titanate (BaTiO3), zirconium dioxide (ZrO2), a mixture thereof, an oxide and / or a nitride of these materials, or any other suitable ceramic material.

[0138] Additionally, the margin insulating layer 150 may include the same solid electrolyte as the solid electrolyte included in the solid electrolyte layer 130 described above, but is not limited thereto.

[0139] Additionally, the stack 110 according to an embodiment may further include a protective layer disposed as an outermost layer on the top and bottom of the stack.

[0140] The protective layer may improve moisture resistance reliability by preventing moisture penetration and prevent damage caused by physical and chemical impacts.

[0141] The protective layer may be made of an insulating material that is not electrically conductive. For example, the protective layer may include a ceramic material, such as but not limited to alumina (Al2O3), aluminum nitride (AlN), beryllium oxide (BeO), boron nitride (BN), silicon (Si), silicon carbide (SiC), silica (SiO2), silicon nitride (Si3N4), gallium arsenide (GaAs), gallium nitride (GaN), barium titanate (BaTiO3), zirconium dioxide (ZrO2), a mixture thereof, an oxide and / or a nitride of such materials, or any other suitable ceramic material.

[0142] Additionally, the protective layer may include, but is not limited to, the same solid electrolyte as the solid electrolyte included in the aforementioned solid electrolyte layer 130.

[0143] An all-solid-state battery 100 may be manufactured by alternately stacking a plurality of positive electrode layers 120 and negative electrode layers 140, interposing a plurality of solid electrolyte layers 130 between them to manufacture a stack 110, and then calcining and then pressurizing / firing the stack 110.

[0144] The calcining may be performed at a temperature of 350 °C to 400 °C and in an air or nitrogen atmosphere. The firing may be performed at a temperature of 400 °C to 600 °C and in an air or nitrogen atmosphere.

[0145] The external electrodes 112 and 114 are placed on the outside of the stack 110.

[0146] On both sides of the stack 110 of the all-solid-state battery 100, the terminals of the positive electrode current collector 123 and the terminals of the negative electrode current collector 143 are exposed, and external electrodes 112 and 114 can be connected and coupled to the exposed terminals.

[0147] The external electrodes 112 and 114 may be configured to be connected to the terminal of the positive electrode current collector 123 to have a positive electrode, and to be connected to the terminal of the negative electrode current collector 143 to have a negative electrode. If the terminals of the positive electrode current collector 123 and the terminals of the negative electrode current collector 143 are configured to face opposite directions, the external electrodes 112 and 114 may also be located on both sides, respectively.

[0148] The external electrodes 112 and 114 may include conductive metal and glass.

[0149] The conductive metal may be a conductive metal including, for example, copper (Cu), nickel (Ni), tin (Sn), palladium (Pd), platinum (Pt), gold (Au), silver (Ag), tungsten (W), titanium (Ti), lead (Pb), and alloys thereof.

[0150] A glass included in the first and second external electrodes 112 and 114 may have a composition in which an oxide is mixed. The glass may include, for example, a silicon oxide, a boron oxide, an aluminum oxide, a transition metal oxide, an alkali metal oxide, an alkaline-earth metal oxide, or a combination thereof. Here, the transition metal may be at least one selected from zinc (Zn), titanium (Ti), copper (Cu), vanadium (V), manganese (Mn), iron (Fe), and nickel (Ni), the alkali metal may be at least one selected from lithium (Li), sodium (Na), and potassium (K), and the alkaline earth metal may be at least one selected from magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).

[0151] The method of forming the external electrodes 112 and 114 is not particularly limited. For example, the stack 110 may be formed by dipping it into a conductive paste including a conductive metal and glass, or by printing the conductive paste on the surface of the stack 110 using a screen printing method or a gravure printing method. In addition, external electrodes can be formed in various ways, such as by coating conductive paste on the surface of the stack 110 or by transferring a dried film of conductive paste to the stack 110.

[0152]

[0153] Hereinafter, the embodiments are illustrated in more detail with reference to examples. However, these examples are exemplary, and the present scope is not limited thereto.

[0154] (Manufacturing of All-solid-state Battery)

[0155] Examples 1 to 5 and Comparative Examples 1 to 3

[0156] A positive electrode active material prepared by mixing LiCoO2particles (A particles) with a particle size D50 of 3 μm or more and LiCoO2particles (B particles) with a particle size D50 of less than 3 μm, Li4B4Al3O12Cl (LCBA), carbon black (Li100), and an acryl binder were mixed to prepare a paste. Herein, the positive electrode active material and LCBA were mixed in each weight ratio shown in Table 1, wherein the carbon black and the acryl binder were respectively mixed in an amount of 1 part by weight and 10 parts by weight based on 100 parts by weight of a total amount of the positive electrode active material and LCBA.

[0157] A current collector was manufactured by mixing Li4B4Al3O12Cl (LCBA) and graphite in a weight ratio of 1:1.

[0158] The paste was printed on a PET film and then, dried to form a first positive electrode active material layer. Subsequently, on the first positive electrode active material layer, the current collector was formed, and the paste was printed on the current collector and then, dried to form a second positive electrode active material layer. Subsequently, the PET film was removed to form a positive electrode layer green sheet.

[0159] In addition, a negative electrode layer green sheet was formed by using artificial graphite, Li4B4Al3O12Cl (LCBA), and an acryl binder. Herein, the artificial graphite and LCBA were mixed in a weight ratio of 1:1, and the acryl binder was mixed in an amount of 30 parts by weight based on 100 parts by weight of a total amount of the artificial graphite and LCBA.

[0160] In addition, a solid electrolyte layer green sheet was formed by using Li4B4Al3O12Cl (LCBA).

[0161] The formed positive electrode layer green sheet, solid electrolyte layer green sheet, and negative electrode layer green sheet were stacked to from a stack, calcinated at 400 °C under an air or nitrogen atmosphere, and pressurized / fired at 500 °C under the air or nitrogen atmosphere, manufacturing an all-solid-state battery. In the manufactured all-solid-state battery, the first and second positive electrode active material layers were formed to have each thickness shown in Table 1.

[0162] Solid electrolytePositive electrode active materialEach thickness of first and second positive electrode active material layers (μm)LCBAA particlesB particlesExample 111.50.7514.6Example 211.51.517.4Example 312-13.0Example 412.95-13.8Example 514.5-18.0Comparative Example 11-1.939.9Comparative Example 2110.7522.9Comparative Example 310.5120.8

[0163] Evaluation 1: SEM Analysis

[0164] The all-solid-state batteries according to Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to scanning electron microscope (SEM) analysis to measure the number of positive electrode active material particles and surface roughness. The results are shown in FIGS. 5 to 12 and Table 2.

[0165] After breaking a chip of each all-solid-state battery to obtain a cross-sectional sample showing a positive electrode layer within a stack, the cross-sectional sample was subjected to the SEM analysis with a reference to a length of 40 μm under a condition of 10 kV.

[0166] FIG. 5 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 1, FIG. 6 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 2, FIG. 7 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 3, FIG. 8 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 4, and FIG. 9 is a scanning electron microscope (SEM) image of the positive electrode layer according to Example 5. In addition, FIG. 10 is a scanning electron microscope (SEM) image of the positive electrode layer according to Comparative Example 1, FIG. 11 is a scanning electron microscope (SEM) image of the positive electrode layer according to Comparative Example 2, and FIG. 12 is a scanning electron microscope (SEM) image of the positive electrode layer according to Comparative Example 3.

[0167] Referring to FIGS. 5 to 12, the positive electrode layer was composed of the positive electrode current collector in the central portion, the first positive electrode active material layer present on one surface of the positive electrode current collector, and the second positive electrode active material layer present on the other surface of the positive electrode current collector, and in the first and second positive electrode active material layers, the positive electrode active material particles were present.

[0168] In the SEM image of the cross-sectional sample of the positive electrode layer, as shown in FIGS. 5 to 12, 5 straight lines perpendicular to the positive electrode current collector in a direction from the positive electrode current collector to the first positive electrode active material layer, and another 5 straight lines perpendicular to the positive electrode current collector in a direction from the positive electrode current collector to the second positive electrode active material layer, total 10 straight lines, were drawn to count the number of positive electrode active material particles crossing the lines and then, calculate an average thereof. The five straight lines in each positive electrode active material layer were drawn at a predetermined interval not to measure the same positive electrode active material particles.

[0169] In addition, in the SEM image of the cross-sectional sample of the positive electrode layer, as shown in FIGS. 5 to 12, a curve was drawn along the surface of the first positive electrode active material layer with a reference to 40 μm in length to mark a peak and a valley, which were used to obtain surface roughness, and in addition, another curve was drawn along the surface of the second positive electrode active material layer to mark a peak and a valley, which were used to obtain surface roughness, and then, these two surface roughness were averaged to obtain surface roughness Rz and Ry.

[0170] For reference, red dots marked in each SEM image of FIGS. 5 to 12 correspond to the measured peaks and valleys.

[0171] In Table 2, Rz is ten-point average surface roughness of the surface roughness and represents an average of Rz of the first positive electrode active material layer and Rz of the second positive electrode active material layer. Each Rz of the first and second positive electrode active material layers was obtained by adding an average of absolute values of the highest peak to the fifth highest peak and another average of absolute values of the lowest to fifth lowest valley from a mean line of each roughness curve.

[0172] Ry is a maximum height of the surface roughness and represents an average of Ry of the first positive electrode active material layer and Ry of the second positive electrode active material layer. Each Ry of the first and second positive electrode active material layers was measured as an interval between the highest peak and the lowest valley from the mean line of the roughness curves.

[0173] Average number of positive electrode active material particlesSurface roughness Rz (μm)Surface roughness Ry (μm)Rate capability (%)(0.4C / 0.1C)Example 1318.516.670.6Example 23.820.119.676.3Example 31.516.415.688.6Example 44.417.416.184.7Example 5820.721.487.5Comparative Example 18.143.943.848.3Comparative Example 27.827.126.763.5Comparative Example 39.725.224.455.7

[0174] As shown in Table 2, according to an embodiment, the positive electrode layers of Examples 1 to 5 exhibited the average number of positive electrode active material particles of less than or equal to 8, surface roughness Rz of less than 25.2 μm, and surface roughness Ry of less than 24.4 μm. On the contrary, Comparative Examples 1 and 3 exhibited the average number of positive electrode active material particles and surface roughness all out of the ranges of an embodiment, and Comparative Example 2 exhibited surface roughness out of the range according to an embodiment.

[0175] Evaluation 2: Rate Capability

[0176] The all-solid-state batteries according to Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated with respect to rate capability, and the results are shown in Table 3.

[0177] The rate capability was expressed as a percentage of capacity at a discharge current of 0.4 C to capacity at a discharge current of 0.1 C.

[0178] Rate capability (%) (0.4C / 0.1C)Example 170.6Example 276.3Example 388.6Example 484.7Example 587.5Comparative Example 148.3Comparative Example 263.5Comparative Example 355.7

[0179] Referring to Table 3, Examples 1 to 5, compared with Comparative Examples 1 to 3, exhibited excellent rate capability. Accordingly, according to an embodiment, when the average number of positive electrode active material particles was 8 or less and when the positive electrode layer had surface roughness Rz of less than 25.2 μm or surface roughness Ry of less than 24.4 μm, density was increased, improving rate capability. It is to be understood that although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, but can be implemented in various modifications within the scope of the claims, the detailed description of the present invention, and the accompanying drawings, which also fall within the scope of the present invention.

[0180] <Description of Symbols>

[0181] 100: all-solid-state battery

[0182] 110: stack

[0183] 112, 114: external electrode

[0184] 120: positive electrode layer

[0185] 121: first positive electrode active material layer

[0186] 122: second positive electrode active material layer

[0187] 123: positive electrode current collector

[0188] 130: solid electrolyte layer

[0189] 140: negative electrode layer

[0190] 141, 142: negative electrode active material layer

[0191] 143: negative electrode current collector

[0192] 150: margin insulation layer

Claims

A positive electrode layer for an all-solid-state battery, comprising:a positive electrode current collector, a first positive electrode active material layer disposed on one surface of the positive electrode current collector, and a second positive electrode active material layer disposed on the other surface of the positive electrode current collector,wherein the first positive electrode active material layer and the second positive electrode active material layer include positive electrode active material particles,when straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8, anda ten-point average roughness Rz of a surface roughness of the positive electrode layer obtained by taking an average of a ten-point average roughness of a surface roughness of the first positive electrode active material layer and a ten-point average roughness of a surface roughness of the second positive electrode active material layer is greater than 0 μm and less than 25.2 μm.The positive electrode layer of claim 1, whereina maximum height Ry of a surface roughness of the positive electrode layer, which is obtained by taking an average value of a maximum height of a surface roughness of the first positive electrode active material layer and a maximum height of a surface roughness of the second positive electrode active material layer, is greater than 0 μm and less than 24.4 μm.The positive electrode layer of claim 1, whereina particle size D50 of the positive electrode active material particles is 0.01 μm to 10 μm.The positive electrode layer of claim 1, whereinthe positive electrode active material particles include two types of positive electrode active material particles having different particle sizes D50.The positive electrode layer of claim 1, whereinthe first positive electrode active material layer and the second positive electrode active material layer each have a thickness of 1 μm to 20 μm.The positive electrode layer of claim 1, whereinthe first positive electrode active material layer and the second positive electrode active material layer further include a solid electrolyte.The positive electrode layer of claim 1, whereinan interval between the straight lines is from 5 μm to 10 μm.A positive electrode layer for an all-solid-state battery, comprising:a positive electrode current collector, a first positive electrode active material layer disposed on one surface of the positive electrode current collector, and a second positive electrode active material layer disposed on the other surface of the positive electrode current collector,wherein the first positive electrode active material layer and the second positive electrode active material layer include positive electrode active material particles,when straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8, anda maximum height Ry of a surface roughness of the positive electrode layer, which is obtained by taking an average value of a maximum height of a surface roughness of the first positive electrode active material layer and a maximum height of a surface roughness of the second positive electrode active material layer, is greater than 0 μm and less than 24.4 μm.The positive electrode layer of claim 8, whereina particle size D50 of the positive electrode active material particles is 0.01 μm to 10 μm.The positive electrode layer of claim 8, whereinthe positive electrode active material particles include two types of positive electrode active material particles having different particle sizes D50.The positive electrode layer of claim 8, whereinthe first positive electrode active material layer and the second positive electrode active material layer each have a thickness of 1 μm to 20 μm.The positive electrode layer of claim 8, whereinthe first positive electrode active material layer and the second positive electrode active material layer further include a solid electrolyte.The positive electrode layer of claim 8, whereinan interval between the straight lines is from 5 μm to 10 μm.A method of manufacturing a positive electrode layer for an all-solid-state battery, comprising:printing a first paste including positive electrode active material particles and a solid electrolyte on a substrate to form a first positive electrode active material layer;forming a positive electrode current collector on the first positive electrode active material layer;printing a second paste including positive electrode active material particles and a solid electrolyte on the positive electrode current collector to form a second positive electrode active material layer; andremoving the substrate,wherein when straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8, anda ten-point average roughness Rz of a surface roughness of the positive electrode layer obtained by taking an average of a ten-point average roughness of a surface roughness of the first positive electrode active material layer and a ten-point average roughness of a surface roughness of the second positive electrode active material layer is greater than 0 μm and less than 25.2 μm.The method of claim 14, whereinthe positive electrode active material particles and the solid electrolyte are included in a weight ratio of 2:1 to 10:1.The method of claim 14, whereinan interval between the straight lines is from 5 μm to 10 μm.A method of manufacturing a positive electrode layer for an all-solid-state battery, comprising:printing a first paste including positive electrode active material particles and a solid electrolyte on a substrate to form a first positive electrode active material layer;forming a positive electrode current collector on the first positive electrode active material layer;printing a second paste including positive electrode active material particles and a solid electrolyte on the positive electrode current collector to form a second positive electrode active material layer; andremoving the substrate,wherein when straight lines perpendicular to the positive electrode current collector are drawn from the positive electrode current collector in a direction of the first positive electrode active material layer and in a direction of the second positive electrode active material layer, an average number of positive electrode active material particles crossing each straight line is greater than 0 and less than or equal to 8, anda maximum height Ry of a surface roughness of the positive electrode layer, which is obtained by taking an average value of a maximum height of a surface roughness of the first positive electrode active material layer and a maximum height of a surface roughness of the second positive electrode active material layer, is greater than 0 μm and less than 24.4 μm.The method of claim 17, whereinthe positive electrode active material particles and the solid electrolyte are included in a weight ratio of 2:1 to 10:1.The method of claim 17, whereinan interval between the straight lines is from 5 μm to 10 μm.An all-solid-state battery, comprisingthe positive electrode layer of claim 1;a negative electrode layer; anda solid electrolyte layer stacked between the positive electrode layer and the negative electrode layer.

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