All-solid-state secondary battery and method for producing same

Abstract

Provided is an all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer, the mixed layer including a negative electrode layer material and a solid electrolyte layer material, the thickness ratio of the negative electrode layer to the mixed layer being 2:1 to 50:1, and the mixed volume ratio of the negative electrode layer material to the solid electrolyte in the mixed layer being 2:1 to 1:1.

Description

[Technical field]

[0001] The present invention relates to an all-solid-state secondary battery and a method for producing the same. [Background technology]

[0002] Recently, in response to industrial demands, there has been active development of batteries with high energy density and safety. For example, lithium-ion batteries are being used not only in the fields of information-related equipment and communication equipment, but also in the field of automobiles. In the field of automobiles, safety is especially important because life is at stake.

[0003] Currently available lithium-ion batteries contain flammable organic solvents and use electrolytes, which may lead to overheating and fire if a short circuit occurs. In response to this, all-solid-state batteries that use solid electrolytes instead of electrolytes have been proposed.

[0004] Since all-solid-state batteries do not use flammable organic solvents, the possibility of fire or explosion can be greatly reduced even if a short circuit occurs, and therefore such all-solid-state batteries can be significantly safer than lithium-ion batteries that use electrolytes.

[0005] In order to improve the interfacial characteristics of the anode layer / electrolyte layer of an all-solid-state battery, a pressure process is performed. Although the interfacial adhesion between the anode layer and the electrolyte layer becomes excellent through the pressure process, if pressure is applied unevenly, damage to the anode layer material or the solid electrolyte material may occur. Summary of the Invention [Problem to be solved by the invention]

[0006] One aspect of the present invention is to provide an all-solid-state secondary battery.

[0007] Another aspect of the present invention is to provide a method for producing the all-solid-state secondary battery. [Means for solving the problem]

[0008] According to one aspect, there is provided an all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer, the mixed layer including a negative electrode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer is 2:1 to 50:1, and a mixed volume ratio of the negative electrode layer material to the solid electrolyte in the mixed layer is 2:1 to 1:1.

[0009] According to another aspect, there is provided a method for manufacturing an all-solid-state secondary battery, the method including: providing an anode layer including an anode current collector and a first anode active material layer; providing a cathode layer; providing a solid electrolyte layer between the anode layer and the cathode layer to form a stack; and pressing the stack to manufacture the all-solid-state secondary battery as described above. Effect of the Invention

[0010] According to one aspect, in an all-solid-state secondary battery, when a mixed layer is formed between an anode layer and a solid electrolyte layer, the interface resistance between the anode layer and the solid electrolyte layer is reduced, thereby improving output characteristics and life characteristics. [Brief description of the drawings]

[0011] [Figure 1] 1 is a scanning electron microscope photograph of the solid electrolyte of Example 1. [Figure 2A] 1 is a diagram showing the results of SEM-EDS analysis of the solid electrolyte of Example 1. [Figure 2B] 1 is a diagram showing the results of SEM-EDS analysis of the solid electrolyte of Example 1. [Diagram 3] 1 is a diagram illustrating a schematic structure of an all-solid-state secondary battery according to an embodiment. [Figure 4] 1 is a diagram illustrating a schematic structure of an all-solid-state secondary battery according to another embodiment. [Diagram 5] 1 is a diagram illustrating a schematic structure of an all-solid-state secondary battery according to yet another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an all-solid-state secondary battery and a manufacturing method thereof according to an embodiment will be described in more detail.

[0013] Provided is an all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer, the mixed layer including a negative electrode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer being 2:1 to 50:1, and a mixed volume ratio of the negative electrode layer material to the solid electrolyte in the mixed layer being 2:1 to 1:1.

[0014] In an all-solid-state battery, a pressurizing process is performed to improve the interfacial characteristics between the anode layer and the solid electrolyte layer. However, although the pressurizing process improves the interfacial adhesion between the anode layer and the electrolyte layer, the pressurizing process may not be uniform, which may cause damage to the anode layer material or the solid electrolyte material.

[0015] In the present invention, the above-mentioned problems are solved, and a mixed layer is formed between the anode layer and the solid electrolyte layer, and the contact area between the anode layer and the solid electrolyte layer is increased, thereby reducing the interfacial resistance between the anode layer and the solid electrolyte layer, thereby making it possible to manufacture an all-solid-state secondary battery having improved output characteristics.

[0016] The mixed layer has a thickness of 2 μm or less and includes a negative electrode layer material and a solid electrolyte layer material.

[0017] According to an embodiment, the thickness ratio of the anode layer and the mixed layer is 2:1 to 50:1, 3:1 to 40:1, 3.5:1 to 35:1, 4:1 to 30:1, 5:1 to 20:1, 5:1 to 15:1, or 5:1 to 10:1. The thicknesses of the anode layer and the mixed layer refer to the thicknesses of the compressed anode layer and the compressed mixed layer, respectively, after a compression process during the preparation of the all-solid-state secondary battery, and are measured through SEM analysis, etc. If the thickness of the mixed layer relative to the anode layer is thinner than the above range, the effect of improving the interface characteristics between the anode layer and the solid electrolyte layer is insignificant, and if the thickness is thicker than the above range, the content of the anode layer material consumed as the mixed layer is relatively increased, which may partially deteriorate the characteristics of the anode.

[0018] The thickness of the mixed layer is 0.1-2 μm, 0.15-1.9 μm, 0.2-1.8 μm, 0.3-1.7 μm, 0.4-1.6 μm, or 0.5-1.5 μm. The thickness of the mixed layer refers to the thickness of the mixed layer after a pressurizing process during the preparation of the all-solid-state secondary battery, and is measured through SEM analysis, etc. If the thickness of the mixed layer exceeds 2 μm, the amount of the negative electrode consumed as the mixed layer increases, and the characteristics of the negative electrode may deteriorate.

[0019] The negative electrode layer has a thickness of 1 to 100 μm.

[0020] In the mixed layer, the mixing volume ratio of the negative electrode layer material to the solid electrolyte layer material is 2:1 to 1:2, 1.7:1 to 1:1.7, 1.8:1 to 1:1.8, 1.6:1 to 1:1.6, 1.5:1 to 1:1.5, 1.4:1 to 1:1.4, 1.3:1 to 1:1.3, or 1.2:1 to 1:1.2. When the mixing volume ratio of the negative electrode layer material to the solid electrolyte layer material in the mixed layer is within the above range, the interfacial characteristics between the negative electrode layer and the solid electrolyte layer are improved.

[0021] In this specification, the "negative electrode layer material" includes, for example, an anode active material and a binder as the solid content of the negative electrode layer, and the "solid electrolyte layer material" includes, for example, a solid electrolyte and a binder as the solid content of the solid electrolyte layer. The mixed volume ratio of the negative electrode layer material and the solid electrolyte material is calculated by measuring the volume occupied by the negative electrode layer material and the solid electrolyte layer in the mixed layer existing between the negative electrode layer and the solid electrolyte layer through SEM-EDS analysis.

[0022] SEM analysis of the mixed layer revealed that the mixed layer has unevenness on the surface, resulting in an uneven interface. If such a mixed layer is interposed between the anode layer and the solid electrolyte layer, the contact area between the anode layer and the solid electrolyte layer increases, resulting in excellent adhesion between them. Therefore, problems such as partial damage and breakage between the anode layer and the solid electrolyte layer that occur during the pressurization process when manufacturing conventional all-solid-state secondary batteries are prevented in advance, and interface characteristics are improved.

[0023] In the all-solid-state secondary battery according to an embodiment, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer, and the negative electrode current collector, the negative electrode active material layer, and a region therebetween are Li-free regions that do not contain lithium (Li) in an initial state or a post-discharge state of the all-solid-state secondary battery.

[0024] An all-solid-state secondary battery according to an embodiment includes a lithium deposition layer between a negative electrode current collector and a negative electrode active material during or after charging.

[0025] 3, the all-solid-state secondary battery 1 includes a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 13 including a solid electrolyte disposed between the positive electrode layer 10 and the negative electrode layer 20. A mixed layer 40 is present between the negative electrode layer 20 and the solid electrolyte layer 13.

[0026] The thickness of the first negative electrode active material layer is 1 to 20 μm, for example, 1 to 10 μm, for example, 2 to 8 μm, for example, 4 to 6 μm.

[0027] The negative electrode further includes a metal or semi-metal thin film between the negative electrode current collector and the first negative electrode active material layer, the metal or semi-metal thin film including gold (Au), silver (Ag), magnesium (Mg), zinc (Zn), silicon (Si), tin (Sn), platinum (Pt), palladium (Pd), aluminum (Al), bismuth (Bi), or a combination thereof, and the metal or semi-metal thin film has a thickness of 1 to 800 nm, for example, 10 to 30 nm.

[0028] The first negative electrode active material layer has a porous structure. The porosity of the first negative electrode active material layer is 30% or less, for example, 5 to 25%. When the porosity of the first negative electrode active material layer is in the above range, it is possible to effectively prevent dendrites from growing to the positive electrode active material layer side, to prevent the occurrence of short circuits due to dendrites, and to manufacture an all-solid-state secondary battery having high voltage, high capacity, and excellent life characteristics.

[0029] The interface between the solid electrolyte layer and the negative electrode current collector may become a precipitation point for metallic lithium, and metallic lithium may be precipitated. The precipitated lithium may grow into dendrites toward the positive electrode active material layer through voids in the solid electrolyte layer, causing a short circuit in the all-solid-state secondary battery.

[0030] However, when the porosity of the first negative electrode active material layer is within the above range, the growth of dendrites to the positive electrode active material layer side is effectively suppressed, the occurrence of short circuits due to dendrites is suppressed, and an all-solid-state secondary battery having high voltage, high capacity, and excellent life characteristics can be manufactured.

[0031] In this specification, the porosity can be confirmed by mercury porosimetry or scanning electron microscope (SEM), etc. In the measurement method using a mercury porosimetry, mercury is injected into a sample, and the amount of injected mercury is measured to calculate the pore size and pore distribution.

[0032] According to an embodiment, the negative electrode layer further includes a second negative electrode active material layer. The second negative electrode active material layer may be disposed on one or more of the top of the first negative electrode active material layer and between the negative electrode current collector and the first negative electrode active material layer. The second negative electrode active material layer includes a metal, a metalloid element, or a combination thereof that forms an alloy with lithium. The second negative electrode active material layer may be, for example, a metal layer including lithium or a lithium alloy. According to an embodiment, a surface of the second negative electrode active material layer includes lithium fluoride (LiF).

[0033] The second negative electrode active material layer is also a lithium-free region that does not contain lithium metal or lithium alloy in the initial state or after discharge of the all-solid-state secondary battery. Before charging, the negative electrode layer has a structure including a negative electrode current collector, a metal or semimetal film, and a first negative electrode active material layer. After charging such a negative electrode layer, a second negative electrode active material layer may be formed on the first negative electrode active material layer. The second negative electrode active material layer is also non-porous.

[0034] A carbon layer is further included between the first negative electrode active material layer and the solid electrolyte layer. The carbon layer is formed using, for example, carbon black, carbon fiber, graphite, carbon nanotubes, graphene, or a combination thereof. By forming the carbon layer in this manner, the resistance between the first negative electrode active material layer and the solid electrolyte layer can be reduced and lithium dendrites can be suppressed. Therefore, an all-solid-state secondary battery including a negative electrode layer further formed with a carbon layer can have a further improved life characteristic compared to an all-solid-state secondary battery including a negative electrode layer not formed with a carbon layer.

[0035] Hereinafter, a method for manufacturing an all-solid-state secondary battery according to an embodiment will be described.

[0036] First, a negative electrode layer including a negative electrode current collector and a first negative electrode active material layer is provided.

[0037] A positive electrode layer is provided separately.

[0038] The method includes providing a solid electrolyte layer between the negative electrode layer and the positive electrode layer to prepare a stack, and then pressing the stack.

[0039] The solid electrolyte layer is produced by drying a composition containing a solid electrolyte, a binder, and a solvent at 25° C. to 80° C. The viscosity of the composition is controlled to about 200 cP to 10,000 cP. If a solid electrolyte layer is formed using a composition having such a viscosity, a solid electrolyte layer having excellent interfacial bonding with the negative electrode layer can be produced.

[0040] According to one embodiment, drying may be performed in a convection oven controlled at 25°C to 75°C.

[0041] According to another embodiment, the drying may be performed in multiple stages, for example, in two stages. The drying may be performed by performing a primary drying at 25 to 70° C., followed by a secondary drying at 30 to 75° C. When the primary drying is performed at a higher temperature than the secondary drying, the interfacial characteristics between the negative electrode layer and the solid electrolyte layer are improved.

[0042] The drying time is from 30 minutes to 24 hours, from 1 to 20 hours, or from 2 to 15 hours.

[0043] The laminate may be pressed by a roll press, a flat press, a hot press, a warm isostatic press (WIP), or the like, and may be pressed using, for example, isostatic pressure.

[0044] The pressurization is carried out at a temperature of room temperature (20-25°C) to 90°C. Alternatively, the pressurization is carried out at a high temperature of 100°C or more. The time for which the pressurization is applied is, for example, 30 minutes or less, 20 minutes or less, 15 minutes or less, or 10 minutes or less. The time for which the pressurization is applied is 1 ms to 30 minutes, 1 ms to 20 minutes, 1 ms to 15 minutes, or 1 ms to 10 minutes. The pressurization method is, for example, isotactic press, roll press, flat press, etc., but is not necessarily limited to such methods, and any pressurization method used in the technical field can be used. By such pressurization, for example, the solid electrolyte powder is sintered to form one solid electrolyte layer.

[0045] The pressing time varies depending on the temperature and pressure, but is, for example, less than 30 minutes, or less than 20 minutes.

[0046] After applying pressure, the positive electrode active material layer has a thickness of about 100 to 150 μm, the negative electrode active material layer has a thickness of 10 to 15 μm, and the solid electrolyte layer has a thickness of 100 to 150 μm.

[0047] According to an embodiment, the pressing is performed by WIP, and the pressure is 200-600 MPa, 300-550 MPa, 350-520 MPa, 380-500 MPa, or 400-500 MPa.

[0048] The temperature during pressurization is 60° C. to 90° C., 65° C. to 88° C., 70° C. to 85° C., or 75° C. to 85° C. The pressurization time varies depending on the temperature and pressure during pressurization, and is 10 minutes to 6 hours, 15 minutes to 5 hours, 20 minutes to 3 hours, 20 minutes to 2 hours, or 30 minutes to 1 hour.

[0049] The above-mentioned method for manufacturing an all-solid-state secondary battery is mass-producible, and when pressure is applied after stacking, a tight interface can be easily formed between the electrode layer and the solid electrolyte layer. In addition, the method for manufacturing an all-solid-state secondary battery can reduce the interface resistance between the positive electrode layer and the solid electrolyte layer while improving battery performance such as rate characteristics and life characteristics.

[0050] In an all-solid-state secondary battery, the negative electrode layer is produced by coating and drying a composition containing a first negative electrode active material, a binder and a solvent.

[0051] The binder may be a water-based binder, an organic binder, or a combination thereof. For example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, an epoxy resin, nylon, or a combination thereof may be used as the binder.

[0052] As the water-based binder, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or a combination thereof can be used. When using a water-based binder, water is used as a solvent.

[0053] As the organic binder, polytetrafluoroethylene, polyvinylidene fluoride, or the like is used, and when such an organic binder is used, N-methylpyrrolidone (NMP) or the like is used as a solvent.

[0054] Hereinafter, the all-solid-state secondary battery according to an example embodiment will be described in more detail.

[0055] [All-solid-state secondary battery] 3, the all-solid-state secondary battery 1 includes a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30 disposed between the positive electrode layer 10 and the negative electrode layer 20, and a mixed layer 40 according to an embodiment is formed between the negative electrode layer 20 and the solid electrolyte layer 30 to have a thickness of 2 μm or less. Here, the thickness ratio of the negative electrode layer 20 to the mixed layer 40 is 2:1 to 50:1. The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on the positive electrode current collector 11, and the negative electrode layer 20 includes a negative electrode current collector 21 and a first negative electrode active material layer 22 disposed on the negative electrode current collector.

[0056] [Positive electrode layer: positive electrode current collector] The positive electrode current collector 11 is, for example, a plate or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive electrode current collector 11 is optional.

[0057] [Cathode layer: Cathode active material] The positive electrode active material layer 12 includes, for example, a positive electrode active material and a solid electrolyte. The solid electrolyte included in the positive electrode layer 10 may be similar to or different from the solid electrolyte included in the solid electrolyte layer 30. For details about the solid electrolyte, please refer to the section on the solid electrolyte layer 30.

[0058] The positive electrode active material is a positive electrode active material that can reversibly absorb and desorb lithium ions. Examples of the positive electrode active material include lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, and lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, and vanadium oxide, but are not necessarily limited thereto. Any positive electrode active material that can be used as a positive electrode active material in the art can be used. The positive electrode active material can be used alone or in a mixture of two or more kinds.

[0059] Lithium transition metal oxides include, for example, Li a A 1-b B b D 2 (wherein 0.90≦a≦1, and 0≦b≦0.5); Li a E 1-b B b O 2-c D c (wherein, 0.90≦a≦1, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B b O 4-c D c (wherein, 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b B c D α (wherein, 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Co b B c O 2-α F α(wherein, 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Co b B c O 2-α F 2 (wherein, 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b B c D α (wherein, 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Mn b B c O 2-α F α (wherein, 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b B c O 2-α F 2 (wherein, 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni b E c G d O 2 (wherein, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, and 0.001≦d≦0.1); Li a Ni b Co c Mn d GeO 2 (wherein, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li a NiG b O 2 (wherein, 0.90≦a≦1, 0.001≦b≦0.1); Li a CoG b O 2 (wherein, 0.90≦a≦1, 0.001≦b≦0.1); Li a MnGb O 2 (wherein, 0.90≦a≦1, 0.001≦b≦0.1); Li a Mn 2 G b O 4 (wherein, 0.90≦a≦1, 0.001≦b≦0.1); QO 2 ;QS 2 ;LiQS 2 ;V 2 O 5 ;LiV 2 O 5 ;LiIO 2 ;LiNiVO 4 Li (3-f) J 2 (PO 4 ) 3 (0≦f≦2);Li (3-f) Fe 2 (PO 4 ) 3 (0≦f≦2); LiFePO 4In such a compound, A is Ni, Co, Mn, or a combination thereof, B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof, D is O, F, S, P, or a combination thereof, E is Co, Mn, or a combination thereof, F is F, S, P, or a combination thereof, G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof, Q is Ti, Mo, Mn, or a combination thereof, I is Cr, V, Fe, Sc, Y, or a combination thereof, and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. It is also possible to use a compound having a coating layer added to the surface of such a compound, and it is also possible to use a mixture of the above-mentioned compound and a compound having a coating layer added thereto. The coating layer added to the surface of such a compound includes, for example, a coating element compound such as an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxide carbonate of a coating element. The compound forming such a coating layer is amorphous or crystalline. The coating element contained in the coating layer is Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The method of forming the coating layer is selected within a range that does not adversely affect the physical properties of the positive electrode active material. The coating method is, for example, spray coating, immersion, etc. The specific coating method is well understood by those engaged in the field, so a detailed description will be omitted.

[0060] The positive electrode active material includes, for example, a lithium salt of a transition metal oxide having a layered rock salt type structure among the above-described lithium transition metal oxides. The "layered rock salt type structure" is, for example, a structure in which oxygen atom layers and metal atom layers are alternately and regularly arranged in the <111> direction of a cubic rock salt type structure, whereby each atom layer forms a two-dimensional plane. The "cubic rock salt type structure" indicates a sodium chloride type (NaCl type) structure which is a kind of crystal structure. Specifically, it shows a structure in which face-centered cubic lattices (fcc) formed by each of cations and anions are displaced from each other by 1 / 2 of the ridge of a unit lattice. Such a lithium transition metal oxide having a layered rock salt type structure is, for example, LiNi x Co y Al z O 2 (NCA) or LiNi x Co y Mn z O 2 (NCM) (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1), etc., which are ternary lithium transition metal oxides. When the positive electrode active material includes a ternary lithium transition metal oxide having a layered rock salt type structure, the energy density and thermal stability of the all-solid-state secondary battery 1 are further improved.

[0061] The positive electrode active material is also covered by a coating layer as described above. Any coating layer can be used as long as it is known as a coating layer for the positive electrode active material of an all-solid-state secondary battery. The coating layer is, for example, Li 2 O-ZrO 2 (LZO), etc.

[0062] When the positive electrode active material contains nickel (Ni) as a ternary lithium transition metal oxide such as NCA or NCM, it is possible to increase the capacity density of the all-solid-state secondary battery 1 and reduce metal elution from the positive electrode active material in a charged state. As a result, the cycle characteristics of the all-solid-state secondary battery 1 in a charged state are improved.

[0063] The shape of the positive electrode active material is, for example, a particle shape such as a perfect sphere or an oval sphere. The particle size of the positive electrode active material is not particularly limited, and is within the range applicable to the positive electrode active material of a conventional all-solid-state secondary battery. The content of the positive electrode active material of the positive electrode 10 is also not particularly limited, and is within the range applicable to the positive electrode of a conventional all-solid-state secondary battery.

[0064] [Positive electrode layer: solid electrolyte] The positive electrode active material layer 12 includes, for example, a solid electrolyte. The solid electrolyte included in the positive electrode layer 10 may be the same as or different from the solid electrolyte included in the solid electrolyte layer 30. For details about the solid electrolyte, please refer to the section on the solid electrolyte layer 30.

[0065] The solid electrolyte contained in the positive electrode active material layer 12 has a smaller D50 average particle size than the solid electrolyte contained in the solid electrolyte layer 30. For example, the D50 average particle size of the solid electrolyte contained in the positive electrode active material layer 12 is 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or even 20% or less of the D50 average particle size of the solid electrolyte contained in the solid electrolyte layer 30.

[0066] [Positive electrode layer: binder] The positive electrode active material layer 12 contains a binder. The binder is, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or the like.

[0067] [Positive electrode layer: conductive material] The positive electrode active material layer 12 contains a conductive material, such as graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or metal powder.

[0068] [Positive electrode layer: Other additives] The positive electrode layer 10 may further include additives such as a filler, a coating agent, a dispersant, and an ion-conductive auxiliary in addition to the above-mentioned positive electrode active material, solid electrolyte, binder, and conductive material.

[0069] The filler, coating agent, dispersant, ion-conductive auxiliary, and the like contained in the positive electrode layer 10 may be any known material that is generally used in electrodes of all-solid-state secondary batteries.

[0070] [Solid electrolyte layer] The solid electrolyte may also be a sulfide-based solid electrolyte.

[0071] [Solid electrolyte layer: sulfide solid electrolyte] 3 to 5, the solid electrolyte layer 30 includes a sulfide-based solid electrolyte disposed between the positive electrode layer 10 and the negative electrode layer 20.

[0072] The sulfide-based solid electrolyte is, for example, Li 2 SP 2 S 5 , Li 2 SP 2 S 5 -LiX (X is a halogen element), Li 2 SP 2 S 5 -Li 2 O, Li 2 SP 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 , Li 2 S-SiS 2 - LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li2 S-SiS 2 -B 2 S 3 - LiI, Li 2 S-SiS 2 -P 2 S 5 - LiI, Li 2 S.B. 2 S 3 , Li 2 SP 2 S 5 -Z m S n (m, n are positive numbers, Z is one of Ge, Zn, or Ga), Li 2 S-GeS 2 , Li 2 S-SiS 2 -Li 3 PO 4 , Li 2 S-SiS 2 -Li p MO q (p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, and In), Li 7-x P.S. 6-x Cl x (0≦x≦2), Li 7-x P.S. 6-x Br x (0≦x≦2) and Li 7-x P.S. 6-x I x (0≦x≦2). The sulfide-based solid electrolyte is, for example, Li 2 S, P 2 S 5 The solid electrolyte is prepared by processing starting materials such as those mentioned above by a melt quenching method or a mechanical milling method. After such processing, a heat treatment can be performed. The solid electrolyte may be amorphous, crystalline, or a mixture of these. The solid electrolyte may be, for example, one of the above-mentioned sulfide-based solid electrolyte materials, and may contain at least sulfur (S), phosphorus (P), and lithium (Li) as constituent elements. For example, the solid electrolyte may be Li 2 SP 2 S 5The sulfide-based solid electrolyte material that forms the solid electrolyte is Li 2 SP 2 S 5 If you use something that includes Li 2 S and P 2 S 5 The mixing molar ratio of Li 2 S:P 2 S 5 The range is approximately 50:50 to 90:10.

[0073] The sulfide-based solid electrolyte is, for example, Li 7-x P.S. 6-x Cl x (0≦x≦2), Li 7-x P.S. 6-x Br x (0≦x≦2), and Li 7-x P.S. 6-x I x (0≦x≦2). In particular, the sulfide-based solid electrolyte is an Argyrodite-type compound containing one or more of the following: Li 6 P.S. 5 Cl, Li 6 P.S. 5 Br and Li 6 P.S. 5 I is also an argyrodite-type compound containing one or more selected from the group consisting of

[0074] The density of the argyrodite-type solid electrolyte is 1.5 to 2.0 g / cc. When the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte by Li can be effectively suppressed.

[0075] The elastic modulus of the solid electrolyte is, for example, 15 to 35 GPa.

[0076] [Solid electrolyte layer: binder] The solid electrolyte layer 30 includes, for example, a binder. The binder included in the solid electrolyte layer 30 is, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited thereto, and any binder that can be used as a binder in the relevant technical field can be used. The binder of the solid electrolyte layer 30 is the same as or different from the binder included in the positive electrode active material layer 12 and the negative electrode active material layer 22.

[0077] [Negative electrode layer] [Negative electrode layer structure] The thickness of the first negative electrode active material layer 22 is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer. The thickness of the first negative electrode active material layer is, for example, 1 μm to 20 μm, 2 μm to 10 μm, or 3 μm to 7 μm. If the thickness of the first negative electrode active material layer is excessively thin, lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 collapse the first negative electrode active material layer, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. If the thickness of the negative electrode active material layer is excessively increased, the energy density of the all-solid-state secondary battery 1 decreases, and the internal resistance of the all-solid-state secondary battery 1 due to the first negative electrode active material layer increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1.

[0078] If the thickness of the first negative electrode active material layer is reduced, for example, the charge capacity of the first negative electrode active material layer is also reduced. The charge capacity of the first negative electrode active material layer 22 is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 5% or less, or 2% or less compared to the charge capacity of the positive electrode active material layer 12. The charge capacity of the first negative electrode active material layer 22 is, for example, 0.1% to 50%, 0.1% to 40%, 0.1% to 30%, 0.1% to 20%, 0.1% to 10%, 0.1% to 5%, or 0.1% to 2% compared to the charge capacity of the positive electrode active material layer 12. If the charge capacity of the first negative electrode active material layer 22 is excessively small, the thickness of the first negative electrode active material layer 22 becomes very thin, and lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 during repeated charge and discharge processes collapse the first negative electrode active material layer 22, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. If the charge capacity of the first negative electrode active material layer 22 increases excessively, the energy density of the all-solid-state secondary battery 1 decreases and the internal resistance of the all-solid-state secondary battery 1 due to the first negative electrode active material layer 22 increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1.

[0079] The charge capacity of the positive electrode active material layer 12 is obtained by multiplying the charge capacity density (mAh / g) of the positive electrode active material by the mass of the positive electrode active material in the positive electrode active material layer 12. When multiple types of positive electrode active materials are used, the charge capacity density x mass value is calculated for each positive electrode active material, and the sum of these values ​​is the charge capacity of the positive electrode active material layer 12. The charge capacity of the first negative electrode active material layer 22 is also calculated by a similar method. That is, the charge capacity of the first negative electrode active material layer 22 is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer 22. When multiple types of negative electrode active materials are used, the charge capacity density x mass value is calculated for each negative electrode active material, and the sum of these values ​​is the capacity of the first negative electrode active material layer 22. Here, the charge capacity density of the positive electrode active material and the negative electrode active material is a capacity estimated using an all-solid-state half-cell using lithium metal as a counter electrode. The charge capacities of the positive electrode active material layer 12 and the first negative electrode active material layer 22 are directly measured by measuring the charge capacity using an all-solid-state half-cell. The charge capacity density is obtained by dividing the measured charge capacity by the mass of each active material. Alternatively, the charge capacity of the positive electrode active material layer 12 and the first negative electrode active material layer 22 is also the initial charge capacity measured during the first cycle of charging.

[0080] [Negative electrode layer: negative electrode current collector] The negative electrode current collector 21 is made of a material that does not react with lithium, i.e., does not form any alloy or compound. The material constituting the negative electrode current collector 21 is, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), etc., but is not necessarily limited thereto, and any material used as an electrode current collector in the relevant technical field can be used. The thickness of the negative electrode current collector is 1 to 20 μm, for example, 5 to 15 μm, for example, 7 to 10 μm.

[0081] The negative electrode current collector 21 is made of one of the above-mentioned metals, or an alloy or coating material of two or more of the above-mentioned metals. The negative electrode current collector 21 is, for example, in the form of a plate or foil.

[0082] 4, the all-solid-state secondary battery 1 further includes a thin film 24 containing an element that forms an alloy with lithium on a negative electrode current collector 21. The thin film 24 is disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22. A mixed layer 40 according to an embodiment is disposed between the first negative electrode active material layer 22 and the solid electrolyte layer 30.

[0083] The thin film 24 includes, for example, an element that forms an alloy with lithium. The element that forms an alloy with lithium is, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., but is not necessarily limited thereto, and any element that forms an alloy with lithium in the relevant technical field can be used. The thin film 24 is made of one of these metals or an alloy of a plurality of metals. By disposing the thin film 24 on the negative electrode current collector 21, for example, the deposition form of the second negative electrode active material layer (not shown) deposited between the thin film 24 and the first negative electrode active material layer 22 can be further flattened, and the cycle characteristics of the all-solid-state secondary battery 1 can be further improved.

[0084] The thickness d24 of the thin film is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness d24 of the thin film is less than 1 nm, the function of the thin film 24 is difficult to be exerted. If the thickness d24 of the thin film is excessively thick, the thin film 24 itself absorbs lithium, the amount of lithium precipitated in the negative electrode layer decreases, the energy density of the all-solid-state battery decreases, and the cycle characteristics of the all-solid-state secondary battery 1 may decrease. The thin film 24 is disposed on the negative electrode current collector 21 by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like, but is not necessarily limited to such a method, and any method for forming the thin film 24 in the art can be used.

[0085] [Negative electrode layer: negative electrode active material] The negative electrode layer 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22 disposed on the negative electrode current collector. The negative electrode active material layer 22 includes, for example, a negative electrode active material and a binder.

[0086] The negative electrode active material contained in the negative electrode active material layer 22 has, for example, a particulate form. The average particle size of the negative electrode active material having a particulate form is, for example, 4 μm or less, 2 μm or less, 1 μm or less, or 900 nm or less. The average particle size of the negative electrode active material having a particulate form is, for example, 10 nm to 4 μm, 10 nm to 2 μm, or 10 nm to 900 nm. When the negative electrode active material has an average particle size in such a range, reversible absorbing and / or desorbing of lithium during charging and discharging is further facilitated. The average particle size of the negative electrode active material is, for example, a median diameter (D50) measured using a laser type particle size distribution meter.

[0087] The negative electrode active material may include, for example, at least one selected from a carbon-based negative electrode active material and a metal or semi-metal negative electrode active material.

[0088] The carbon-based negative electrode active material is, in particular, amorphous carbon. Examples of amorphous carbon include, but are not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, etc., and any material that is classified as amorphous carbon in the art can be used. Amorphous carbon is carbon that has no crystallinity or has very low crystallinity, and is classified as crystalline carbon or graphite-based carbon.

[0089] The metal or semi-metal negative electrode active material includes, but is not limited to, one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn) and zinc (Zn), and any material that can be used in the art as a metal or semi-metal negative electrode active material that forms an alloy or compound with lithium can be used. For example, nickel (Ni) is not a metal negative electrode active material because it does not form an alloy with lithium.

[0090] The negative electrode active material layer 22 includes one of such negative electrode active materials, or includes a mixture of a plurality of different negative electrode active materials. For example, the negative electrode active material layer 22 includes only amorphous carbon, or includes one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the first negative electrode active material layer 22 includes a mixture of amorphous carbon and one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of the mixture of amorphous carbon and gold, etc., by weight is, for example, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1, but is not necessarily limited to such ranges and is selected depending on the required characteristics of the all-solid-state secondary battery 1. When the negative electrode active material has such a composition, the cycle characteristics of the all-solid-state secondary battery 1 are further improved.

[0091] The negative electrode active material contained in the negative electrode active material layer 22 includes, for example, a mixture of first particles made of amorphous carbon and second particles made of a metal or a metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the metalloid may be a semiconductor. The content of the second particles is 8 to 60 wt%, 10 to 50 wt%, 15 to 40 wt%, or 20 to 30 wt%, based on the total weight of the mixture. When the second particles have a content in such a range, for example, the cycle characteristics of the all-solid-state secondary battery 1 are further improved.

[0092] [Negative electrode layer: binder] The binder contained in the negative electrode active material layer 22 is, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited thereto, and any binder usable in the art can be used. The binder can be composed of a single binder or a plurality of different binders.

[0093] The negative electrode active material layer 22 contains a binder, so that the negative electrode active material layer 22 is stabilized on the negative electrode current collector 21. In addition, cracks in the negative electrode active material layer 22 are suppressed despite changes in volume and / or relative position of the negative electrode active material layer 22 during charging and discharging. For example, if the negative electrode active material layer 22 does not contain a binder, the negative electrode active material layer 22 may be easily separated from the negative electrode current collector 21. When the negative electrode active material layer 22 is detached from the negative electrode current collector 21, the negative electrode current collector 21 comes into contact with the second solid electrolyte layer 23 at the exposed portion of the negative electrode current collector 21, increasing the possibility of short circuit occurrence. The negative electrode active material layer 22 is prepared, for example, by applying a slurry in which materials constituting the negative electrode active material layer 22 are dispersed onto the negative electrode current collector 21 and drying it. By including a binder in the negative electrode active material layer 22, the negative electrode active material can be stably dispersed in the slurry. For example, when the slurry is applied onto the negative electrode current collector 21 by a screen printing method, clogging of the screen (for example, clogging due to aggregates of the negative electrode active material) can be suppressed.

[0094] [Negative electrode layer: Other additives] The negative electrode active material layer 22 can further contain additives used in conventional all-solid-state secondary batteries 1, such as a filler, a coating agent, a dispersant, an ion-conductive auxiliary, and the like.

[0095] The negative electrode active material layer 22 may be a first negative electrode active material layer 22a as shown in FIG. 4, or a third negative electrode active material layer 22b as shown in FIG.

[0096] [Negative electrode layer: first negative electrode active material layer] The thickness of the first negative electrode active material layer 22a is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer 12. The thickness of the first negative electrode active material layer 22a is, for example, 1 μm to 20 μm, 2 μm to 10 μm, or 3 μm to 7 μm. When the thickness of the first negative electrode active material layer 22a is within the above range, the cycle characteristics of the all-solid-state secondary battery 1 are excellent, and the charge capacity of the first negative electrode active material layer 22a is excellent. The charge capacity of the first negative electrode active material layer 22a is, for example, 50% or less, 30% or less, 10% or less, 5% or less, or 2% or less of the charge capacity of the positive electrode active material layer 12. The charge capacity of the first negative electrode active material layer 22a is, for example, 0.1% to 50%, 0.1% to 30%, 0.1% to 10%, 0.1% to 5%, or 0.1% to 2% of the charge capacity of the positive electrode active material layer 12. When the charge capacity of the first negative electrode active material layer 22a is within the above range, the thickness of the first negative electrode active material layer 22a is controlled within an appropriate range, and the all-solid-state secondary battery 1 has excellent cycle characteristics and energy density during repeated charge and discharge processes.

[0097] The charge capacity of the positive electrode active material layer 12 is obtained by multiplying the charge capacity density (mAh / g) of the positive electrode active material by the mass of the positive electrode active material in the positive electrode active material layer 12. When multiple types of positive electrode active materials are used, the charge capacity density X mass value is calculated for each positive electrode active material, and the sum of these values ​​is the charge capacity of the positive electrode active material layer 12. The charge capacity of the first negative electrode active material layer 22a is also calculated in a similar manner. That is, the charge capacity of the first negative electrode active material layer 22a is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer 22a. When multiple types of negative electrode active materials are used, the charge capacity X mass value is calculated for each negative electrode active material, and the sum of these values ​​is the capacity of the first negative electrode active material layer 22a. Here, the charge capacity density of the positive electrode active material and the negative electrode active material is a capacity estimated using an all-solid-state half-cell using lithium metal as a counter electrode. The charge capacities of the positive electrode active material layer 12 and the first negative electrode active material layer 22a are directly measured by measuring the charge capacity using an all-solid-state half-cell. The charge capacity density is obtained by dividing the measured charge capacity by the mass of each active material. Alternatively, the charge capacity of the positive electrode active material layer 12 and the first negative electrode active material layer 22a is also the initial charge capacity measured during the first cycle of charging.

[0098] [Negative electrode layer: precipitated layer] Referring to FIG. 5, the all-solid-state secondary battery 1 further includes a second negative electrode active material layer 23 disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 by charging. Although not shown, the all-solid-state secondary battery 1 may further include a second negative electrode active material layer 23 disposed between the solid electrolyte layer 30 and the first negative electrode active material layer 22 by charging, or may include only the second negative electrode active material layer 23. The second negative electrode active material layer 23 is a metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer 23 is a metal layer containing lithium, it acts as a lithium reservoir, for example. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., but is not limited thereto, and any lithium alloy used in the art may be used. Second negative electrode active material layer 23 is made of one of such alloys or lithium, or is made of a plurality of alloys.

[0099] The thickness d23 of the second negative electrode active material layer is not particularly limited, and may be, for example, 1 μm to 1000 μm, 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness d23 of the second negative electrode active material layer is too thin, it is difficult for the second negative electrode active material layer 23 to perform the role of a lithium reservoir. If the thickness d23 of the second negative electrode active material layer is too thick, the mass and volume of the all-solid-state secondary battery 1 increase, and the cycle characteristics may rather deteriorate. The second negative electrode active material layer 23 may be, for example, a metal foil having a thickness in such a range.

[0100] In the all-solid-state secondary battery 1, the second negative electrode active material layer 23 is, for example, disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the all-solid-state secondary battery 1 is assembled, or is precipitated between the negative electrode current collector 21 and the first negative electrode active material layer 22 by charging after the all-solid-state secondary battery 1 is assembled.

[0101] When the second negative electrode active material layer 23 is disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the all-solid-state secondary battery 1 is assembled, the second negative electrode active material layer 23 acts as a lithium reservoir since it is a metal layer containing lithium. The cycle characteristics of the all-solid-state secondary battery 1 including the second negative electrode active material layer 23 are further improved. For example, lithium foil is disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the all-solid-state secondary battery 1 is assembled.

[0102] When the second negative electrode active material layer 23 is disposed by charging after the all-solid-state secondary battery 1 is assembled, the energy density of the all-solid-state secondary battery 1 increases because the all-solid-state secondary battery 1 does not include the second negative electrode active material layer 23 when assembled. For example, when the all-solid-state secondary battery 1 is charged, the first negative electrode active material layer 22 is charged beyond its charge capacity. That is, the first negative electrode active material layer 22 is overcharged. At the beginning of charging, lithium is absorbed in the first negative electrode active material layer 22. That is, the negative electrode active material contained in the first negative electrode active material layer 22 forms an alloy or compound with the lithium ions that have moved from the positive electrode layer 10. If the first negative electrode active material layer 22 is charged beyond its capacity, for example, lithium is precipitated on the back surface of the first negative electrode active material layer 22, that is, between the negative electrode current collector 21 and the first negative electrode active material layer 22, and the precipitated lithium forms a metal layer corresponding to the second negative electrode active material layer 23. The second negative electrode active material layer 23 is a metal layer mainly made of lithium (i.e., metallic lithium). Such a result is obtained, for example, because the negative electrode active material contained in the first negative electrode active material layer 22 is composed of a material that forms an alloy or compound with lithium. During discharge, lithium in the first negative electrode active material layer 22 and the second negative electrode active material layer 23, i.e., the metal layer, is ionized and moves toward the positive electrode layer 10. Therefore, lithium can be used as the negative electrode active material in the all-solid-state secondary battery 1. In addition, the first negative electrode active material layer 22 covers the second negative electrode active material layer 23, and therefore serves as a protective layer for the second negative electrode active material layer 23, i.e., the metal layer, and also serves to suppress the deposition growth of lithium dendrites. Therefore, the short circuit and capacity reduction of the all-solid-state secondary battery 1 are suppressed, and as a result, the cycle characteristics of the all-solid-state secondary battery 1 are improved. In addition, when the second negative electrode active material layer 23 is disposed by charging after the all-solid-state secondary battery 1 is assembled, the negative electrode current collector 21, the first negative electrode active material layer 22, and the region therebetween are, for example, Li-free regions that do not contain lithium (Li) in the initial state or after discharge of the all-solid-state secondary battery.

[0103] The all-solid-state secondary battery according to an embodiment may be applied to a medium- to large-sized battery or an energy storage system (ESS).

[0104] The present invention will be described in more detail with reference to the following examples and comparative examples, but the examples are merely intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0105] Manufacturing Example 1 aLi 2 O-ZrO 2 The positive electrode active material having a coating film was prepared according to the method disclosed in Korean Patent Publication No. 10-2016-0064942, and the positive electrode active material prepared according to the following method was used.

[0106] Cathode active material LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NCM) was stirred and mixed for 30 minutes in a mixture of lithium methoxide, zirconium propoxide, ethanol, and ethyl acetoacetate to obtain aLi 2 O-ZrO 2 (a=1) alcohol solution (aLi 2 O-ZrO 2 The coating solution for coating was prepared. Here, the contents of lithium methoxide and zirconium propoxide were determined so that the amount of lithium methoxide and zirconium propoxide coated on the surface of the positive electrode active material was 100%. 2 O-ZrO 2 The content of (a=1) was adjusted to 0.5 mol %.

[0107] Next, the aLi 2 O-ZrO 2 The coating solution was mixed with the fine powder of the positive electrode active material described above, and the mixed solution was heated to about 40° C. while stirring to evaporate and dry the solvent such as alcohol. At this time, the mixed solution was irradiated with ultrasonic waves.

[0108] By carrying out the above process, aLi was formed on the particle surface of the fine powder of the positive electrode active material. 2 O-ZrO 2 It was possible to support the precursor of

[0109] In addition, aLi supported on the particle surface of the positive electrode active material 2 O-ZrO 2 The precursor of (a=1) was heat-treated in an oxygen atmosphere at about 350° C. for 1 hour. During the heat treatment, the aLi 2 O-ZrO 2 The precursor of (a=1) is aLi 2 O-ZrO 2 (a=1). Li 2 O-ZrO 2 The content of (LZO) is about 0.4 parts by weight based on 100 parts by weight of NCM.

[0110] According to the above-mentioned manufacturing process, aLi 2 O-ZrO 2 LiNi with coating film 0.9 Co 0.05 Mn 0.05 O 2 (NCM) was obtained. 2 O-ZrO 2 In this case, a is 1.

[0111] Example 1 (Negative electrode layer manufacturing) A SUS foil with a thickness of 10 μm was prepared as a negative electrode current collector. A mixture was prepared by mixing Ag nanoparticles with a size of about 60 nm, carbon black, water-based binders SBR (styrene butadiene rubber) at a weight ratio of 2:1, and CMC (sodium carboxymethyl cellulose) at a weight ratio of 25:75:6:3. The SBR and CMC were used as a solvent to prepare a binder solution.

[0112] The mixture was mixed in a Thinky mixer to adjust the viscosity to an appropriate level. Then, 2 mm zirconia balls were added and mixed in a Thinky mixer to prepare a slurry. The mixed slurry was coated on a SUS foil and then vacuum dried at 100°C to prepare a 10 μm thick negative electrode layer.

[0113] (Manufacturing of solid electrolyte layer) Argyrodite-type Li solid electrolyte6 P.S. 5 Isobutylyl isobutylate (IBIB) was added as a binder solution to Cl and mixed. The mixture was stirred in a Thinky mixer to adjust the viscosity to an appropriate level. The weight ratio of the solid electrolyte to the binder was 98.5:1.5. After adjusting the viscosity of the mixture to 2,000 cP, zirconia balls with an average diameter of 2 mm were added and stirred again in the Thinky mixer to prepare a slurry. The slurry was cast on a release polyethylene terephthalate (PET) film and dried at room temperature (25°C) to prepare a solid electrolyte layer.

[0114] (Positive electrode layer manufacturing) The positive electrode active material was Li obtained by Production Example 1. 2 O-ZrO 2 (LZO) coated LiNi 0.9 Co 0.05 Mn 0.05 O 2 We prepared Li CrN2O3 (NCM) as a solid electrolyte. 6 P.S. 5 A Cl solid electrolyte (D50=1 μm or less, crystalline) was used. A polytetrafluoroethylene (PTFE) binder (DuPont's Teflon (registered trademark) binder) was prepared as a binder, and carbon nanofibers (CNF) were prepared as a conductive material. The material was mixed with xylene in a weight ratio of positive electrode active material: solid electrolyte: conductive material: binder = 85: 15: 3: 1.5 to form a positive electrode active material composition into a sheet, which was then vacuum dried at 45 ° C for 2 hours to produce a positive electrode layer having a thickness of about 150 μm.

[0115] (Manufacturing all-solid-state secondary batteries) A solid electrolyte layer was placed between the positive electrode layer and the negative electrode layer to prepare a laminate. The prepared laminate was pressurized at 80°C and 500 MPa for 60 minutes in a WIP to produce an all-solid-state secondary battery. Such a pressurization process sinters the solid electrolyte layer to improve the battery characteristics. The thickness of the sintered solid electrolyte layer was about 45 μm. The thickness of the pressed positive electrode active material layer was about 120 μm, the thickness of the negative electrode active material layer was 12 μm, the thickness of the solid electrolyte layer was 120 μm, and the thickness of the mixed layer was 2 μm.

[0116] Examples 2-5 and Comparative Examples 1-4 The same method as in Example 1 was performed, except that the manufacturing conditions of the solid electrolyte layer and the laminate pressing conditions were adjusted so that the thickness of the mixed layer disposed at the interface between the negative electrode layer and the solid electrolyte of the all-solid-state secondary battery, the ratio of the negative electrode layer material and the solid electrolyte layer material in the mixed layer, and the thickness ratio of the mixed layer and the negative electrode layer were as shown in Table 1 below.

[0117] In Table 1 below, the mixing volume ratio of the negative electrode layer material and the solid electrolyte layer material in the mixed layer was evaluated by measuring the volume of the negative electrode layer material in the mixed layer and the volume ratio of the solid electrolyte layer in the SEM analysis of the SEM-EDS analysis.

[0118] [Table 1]

[0119] Evaluation example 1: Electron scanning microscope SEM analysis was performed on the cross-sectional structure of the anode layer / mixed layer / solid electrolyte layer stack prepared in Example 1. The SEM analysis image is shown in FIG.

[0120] 1, it was found that a mixed layer exists with a thickness of about 2 μm or less by applying stress to the interface between the electrolyte layer and the anode layer through a pressurization process of the anode layer and the solid electrolyte layer, inducing mixing. As shown in FIG. 1, the mixed layer has an uneven surface, which increases the adhesion area between the anode layer and the solid electrolyte layer, improving their bonding strength.

[0121] Evaluation example 2: SEM-EDS analysis SEM-EDS analysis was performed on the cross-sectional structure of the anode layer / mixed layer / solid electrolyte layer laminate prepared in Example 1. The SEM-EDS photographs are shown in Figures 2A and 2B.

[0122] Referring to Figure 2A, the volume of the negative electrode layer material and the solid electrolyte in the mixed layer can be calculated to know the mixing ratio. Then, referring to Figure 2B, it was confirmed that two components (negative electrode: carbon and silver (Ag), electrolyte: sulfur (S), phosphorus (P), and chlorine (Cl)) are superimposed at the interface between the negative electrode layer and the solid electrolyte layer.

[0123] Evaluation example 3. Initial discharge capacity The battery life characteristics were evaluated by performing charging and discharging on the all-solid-state secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 4. When evaluating the battery life, the initial discharge capacity was evaluated by the following method under the conditions of 0.1C 4.25V CC / CV (0.05C cutoff) charging at 45°C and 1C 2.5V CC discharging.

[0124] The charge / discharge test was carried out by placing the all-solid-state secondary battery in a thermostatic chamber at 45°C.

[0125] The battery was charged at a constant current of 0.1C for about 10 hours until the battery voltage reached 4.25V, then at a constant voltage of 4.25V until the current reached 0.05C, after which it was allowed to rest for 10 minutes, and then discharged at a constant current of 1C for about 10 hours until the battery voltage reached 2.5V. After this process, the 1C initial discharge capacity was evaluated and is shown in Table 2 below.

[0126] Evaluation example 4: Capacity retention rate When evaluating the battery life, charging and discharging were performed under the conditions of 0.33C 4.25V CC / CV (0.1C cutoff) charging and 0.33C 2.5V CC discharging at 45°C. The initial capacity and the ratio of remaining capacity to the initial capacity after 100 life evaluations are shown in Table 1 below. The evaluation method is specifically described as follows.

[0127] The charge / discharge characteristics of the all-solid-state secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were evaluated by the following charge / discharge test. The charge / discharge test was performed by placing the all-solid-state secondary batteries in a thermostatic chamber at 45°C.

[0128] The battery was charged at a constant current of 0.1 C for 10 hours until the battery voltage reached 4.25 V, and then discharged at a constant current of 0.05 C for 20 hours until the battery voltage reached 2.5 V (first cycle).

[0129] Next, the battery was charged at a constant current of 0.1 C for 10 hours until the battery voltage reached 4.25 V, and then discharged at a constant current of 0.33 C for 3 hours until the battery voltage reached 2.5 V (second cycle).

[0130] Thereafter, the battery was charged at a constant current of 0.1 C for 10 hours until the battery voltage reached 4.25 V. Then, the battery was discharged at a constant current of 0.5 C for 2 hours until the battery voltage reached 2.5 V (third cycle).

[0131] Thereafter, the battery was charged at a constant current of 0.1 C for 10 hours until the battery voltage reached 4.25 V. Then, the battery was discharged at a constant current of 1 C for 1 hour until the battery voltage reached 2.5 V (fourth cycle).

[0132] Thereafter, the battery was charged at a constant current of 0.33 C for 3 hours until the battery voltage reached 4.25 V. Then, the battery was discharged at a constant current of 0.33 C for 3 hours until the battery voltage reached 2.5 V (fifth cycle).

[0133] The above cycle was repeated a total of 100 times, and the capacity change and capacity retention rate depending on the number of cycles were evaluated.

[0134] The capacity retention rate (life) characteristics were evaluated by the following formula 1, and the evaluation results are shown in Table 2 below.

[0135] <Expression 1> Capacity retention rate (%) = (discharge capacity after 100 cycles / discharge capacity of the first cycle) x 100

[0136] [Table 2]

[0137] Referring to Table 2, the all-solid-state secondary batteries of Examples 1 to 5 had improved initial discharge capacity and capacity retention rate compared to the all-solid-state secondary batteries of Comparative Examples 1 to 4. Although an illustrative embodiment has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an embodiment. It is obvious that a person having ordinary skill in the art to which the present invention pertains can derive various modifications or alterations within the scope of the technical idea described in the claims, and it goes without saying that these fall within the technical scope of the present invention. [Explanation of symbols]

[0138] 1 All-solid-state secondary battery 10 Positive electrode layer 11 Positive electrode current collector 12 Cathode active material layer 20 Negative electrode layer 21 Negative electrode current collector 22 First negative electrode active material layer 30 Solid electrolyte layer 40 mixed layer

Claims

1. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer; the mixed layer includes an anode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer is 2:1 to 50:1; In the mixed layer, the mixing volume ratio of the negative electrode layer material to the solid electrolyte is 2:1 to 1:1, The solid electrolyte layer includes a sulfide-based solid electrolyte.

2. 2. The all-solid-state secondary battery according to claim 1, wherein the negative electrode layer has a thickness of 1 to 100 μm, and the mixed layer has a thickness of 0.1 to 2 μm.

3. The all-solid-state secondary battery according to claim 1 , wherein the negative electrode layer material includes a first negative electrode active material and a binder, and the solid electrolyte layer material includes a solid electrolyte and a binder.

4. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer; the mixed layer includes an anode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer is 2:1 to 50:1; In the mixed layer, the mixing volume ratio of the negative electrode layer material to the solid electrolyte is 2:1 to 1:1, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer, and the negative electrode current collector, the first negative electrode active material layer, and a region therebetween are Li-free regions that do not contain lithium (Li) in an initial state or a post-discharge state of the all-solid-state secondary battery.

5. The all-solid-state secondary battery according to claim 4 , wherein the all-solid-state secondary battery includes a lithium deposition layer between the negative electrode current collector and the negative electrode active material during or after charging.

6. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer; the mixed layer includes an anode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer is 2:1 to 50:1; In the mixed layer, the mixing volume ratio of the negative electrode layer material to the solid electrolyte is 2:1 to 1:1, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer, and further includes a metal thin film or a semi-metal thin film between the negative electrode current collector and the first negative electrode active material layer.

7. The metal thin film or the semi-metal thin film includes gold (Au), silver (Ag), magnesium (Mg), zinc (Zn), silicon (Si), tin (Sn), platinum (Pt), palladium (Pd), aluminum (Al), bismuth (Bi), or a combination thereof; The all-solid-state secondary battery according to claim 6, wherein the metal thin film or the semi-metal thin film has a thickness of 1 to 800 nm.

8. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer; the mixed layer includes an anode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer is 2:1 to 50:1; In the mixed layer, the mixing volume ratio of the negative electrode layer material to the solid electrolyte is 2:1 to 1:1, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer, and further includes a metal layer disposed between the negative electrode current collector and the first negative electrode active material layer, the metal layer including lithium or a lithium alloy.

9. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer; the mixed layer includes an anode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer is 2:1 to 50:1; In the mixed layer, the mixing volume ratio of the negative electrode layer material to the solid electrolyte is 2:1 to 1:1, the anode layer includes a anode current collector and a first anode active material layer, a second anode active material layer is disposed on one or more of the first anode active material layer, the anode current collector, and the first anode active material layer, and the second anode active material layer includes lithium or a lithium alloy.

10. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, a mixed layer having a thickness of 2 μm or less is included between the negative electrode layer and the solid electrolyte layer; the mixed layer includes an anode layer material and a solid electrolyte layer material, a thickness ratio of the negative electrode layer to the mixed layer is 2:1 to 50:1; In the mixed layer, the mixing volume ratio of the negative electrode layer material to the solid electrolyte is 2:1 to 1:1, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer, and further includes a carbon layer between the first negative electrode active material layer and the solid electrolyte layer.

11. The sulfide-based solid electrolyte is Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -LiX (X is a halogen element), Li ２ S-P ２ S ５ -Li ２ O., Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li ２ S-P ２ S ５ -Z ｍ S ｎ (m and n are positive numbers, and Z is one of Ge, Zn, and Ga), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｐ M.O. ｑ (p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, and In), Li ７－ｘ P.S. ６－ｘ C ｘ (0≦x≦2), Li ７－ｘ P.S. ６－ｘ B ｘ (0≦x≦2), and Li ７－ｘ P.S. ６－ｘ I ｘ The all-solid-state secondary battery according to claim 1 , wherein x is one or more selected from (0≦x≦2).

12. The sulfide-based solid electrolyte is Li ６ P.S. ５ Cl, Li ６ P.S. ５ Br and Li ６ P.S. ５ 2. The all-solid-state secondary battery according to claim 1, wherein the solid electrolyte is an argyrodite-type solid electrolyte containing one or more selected from I.

13. providing a negative electrode layer including a negative electrode current collector and a first negative electrode active material layer; providing a positive electrode layer; providing a solid electrolyte layer between the anode layer and the cathode layer to form a laminate; and pressing the laminate to produce the all-solid-state secondary battery according to claim 1 .

14. The method for producing an all-solid-state secondary battery according to claim 13, wherein the solid electrolyte layer is formed by drying a composition containing a solid electrolyte, a binder, and a solvent at 25 to 40°C.

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