All-solid-state battery

Abstract

The purpose of the present invention is to provide an anodeless all-solid-state battery having improved discharge capacity and cycle characteristics. It is also an object of the present invention to provide an anodeless all-solid-state battery capable of being driven at a low limiting pressure. The present invention provides an all-solid-state battery comprising: a positive electrode comprising a positive electrode active material layer; a negative electrode current collector; and a solid electrolyte layer provided between the positive electrode and the negative electrode current collector, the all-solid-state battery not including a negative electrode active material, in which lithium ions are supplied from the positive electrode active material layer by charging, thereby forming a lithium metal layer as the negative electrode active material on the negative electrode current collector, the solid electrolyte layer contains a sulfide-based solid electrolyte that contains a Group 2 element and has an argyrodite-type crystal structure.

Description

Technical Field

[0001] This invention relates to an all-solid-state battery with an anode-less (negative electrode) structure.

[0002] This application is based on and claims priority to Japanese Patent Application No. 2023-221548, filed on December 27, 2023, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] All-solid-state batteries using solid electrolytes instead of liquid electrolytes in lithium-ion batteries have been developed to provide high safety, long lifespan, and high energy density. Among various solid electrolytes, such as Li... 10 GeP2S 12 Sulfide-based solid electrolytes possess high ionic conductivity, approaching that of liquid electrolytes, and are flexible, thus offering the advantage of readily achieving tight adhesion to active materials. Therefore, the commercialization of all-solid-state batteries using sulfide-based solid electrolytes is highly anticipated.

[0004] Meanwhile, lithium metal has attracted much attention as a negative electrode material for all-solid-state batteries due to its low weight per unit volume and high theoretical capacity, which can increase the energy density per unit weight (Wh / kg). However, lithium metal such as Li 10 GeP2S 12 Sulfide-based solid electrolytes have low stability to lithium metal, making them difficult to use with lithium metal anodes.

[0005] Furthermore, when lithium metal is used as the negative electrode in batteries, batteries are typically manufactured by adhering lithium foil to a planar current collector. However, lithium, as an alkali metal, is highly reactive, reacting explosively with water and also with oxygen in the air, making it difficult to manufacture and use under normal conditions. In particular, when lithium metal is exposed to the atmosphere, oxide films such as LiOH, Li₂O, and Li₂CO₃ form due to oxidation. When these oxide films are present on the surface, they act as insulating films, leading to reduced conductivity and inhibiting the smooth migration of lithium ions, resulting in increased resistance.

[0006] To address the aforementioned issues, Patent Documents 1 to 3 disclose an anode-free all-solid-state battery obtained by a method involving the deposition of trace amounts of a seed metal (e.g., Ag or Zn) capable of forming an alloy with lithium on the negative electrode current collector. However, such anode-free all-solid-state batteries require additional steps of coating and sputtering the metal, and suffer from high costs. Furthermore, anode-free all-solid-state batteries require the application of high confinement pressure during battery operation to prevent the growth of lithium dendrites.

[0007] To solve the above problems, the inventors of the present invention have conducted in-depth research and designed an anode-free all-solid-state battery, in which, after battery assembly, lithium ions transferred from the positive electrode active material through charging can form a lithium metal layer on the negative electrode current collector, thereby substantially blocking the contact between the lithium metal and the atmosphere during the battery assembly process. In addition, an anode-free all-solid-state battery is developed, which has excellent discharge capacity and cycle characteristics and can operate under low confinement pressure by using a sulfide-based solid electrolyte containing a polyvalent cation as the solid electrolyte used in the anode-free all-solid-state battery. Summary of the Invention

[0008] Technical Problem

[0009] The present invention aims to provide an anode-free all-solid-state battery having improved discharge capacity and cycle characteristics.

[0010] The present invention also aims to provide an anode-free all-solid-state battery capable of being driven under low confinement pressure.

[0011] Technical Solution

[0012] In one aspect of the present invention, there is provided an all-solid-state battery comprising: a positive electrode including a positive electrode active material layer; a negative electrode current collector; and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector, wherein the all-solid-state battery does not include a negative electrode active material, wherein, through charging, lithium ions are supplied from the positive electrode active material layer to form a lithium metal layer as the negative electrode active material on the negative electrode current collector, and the solid electrolyte layer includes a sulfide-based solid electrolyte containing a Group 2 element and having a thiogermanate-type crystal structure.

[0013] In an exemplary embodiment, the negative electrode current collector and the solid electrolyte layer may be in direct contact with each other. <00001`78>In an exemplary embodiment, the sulfide-based solid electrolyte is represented by the chemical formula Li 7-x-2y M y PS 6-x Ha x wherein, in this chemical formula, M represents at least one element selected from Group 2 elements, Ha is at least one element selected from halogen elements, and x and y satisfy 0 < x < 2.5 and 0 < y < 0.45.

[0015] In one exemplary implementation, M may be Ca.

[0016] In one exemplary embodiment, the all-solid-state battery may not contain the reaction products of the negative electrode current collector and the sulfide-based solid electrolyte.

[0017] In one exemplary embodiment, the all-solid-state battery can be pressurized at a pressure below 0.3 MPa in the direction in which the positive electrode, the negative electrode current collector, and the solid electrolyte layer are stacked.

[0018] In one exemplary embodiment, the positive electrode active material layer may contain the sulfide-based solid electrolyte.

[0019] In one exemplary embodiment, the average particle size of the sulfide-based solid electrolyte contained in the solid electrolyte layer may be larger than the average particle size of the sulfide-based solid electrolyte contained in the positive electrode active material layer.

[0020] In one exemplary embodiment, the Group 2 element may be present at the 48h site of the sulfide-germanium-type crystal structure.

[0021] Beneficial effects

[0022] This invention can provide an anode-free all-solid-state battery with improved discharge capacity and cycle characteristics.

[0023] Furthermore, the present invention can provide an anode-free all-solid-state battery that can be driven under low limiting pressure. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the all-solid-state batteries of Examples 1 to 3.

[0025] Figure 2 This is a schematic diagram showing the all-solid-state battery of Comparative Example 1.

[0026] Figure 3 This is a schematic diagram showing the all-solid-state battery of Comparative Example 2.

[0027] Figure 4 This is a diagram showing the X-ray diffraction (XRD) patterns of the solid electrolytes in Preparation Examples 1 and 2 and comparative preparation Examples 1 and 2.

[0028] Figure 5 The graph shows the discharge capacity retention of the all-solid-state batteries in Examples 1 to 4 and Comparative Examples 1 and 2, respectively.

[0029] Figure 6 The graph shows the discharge capacity retention of the all-solid-state batteries in Examples 1 to 4 and Comparative Examples 1 and 2, respectively.

[0030] Figure 7 This is a scanning electron microscope (SEM) image showing the calcium distribution in the all-solid-state battery of Example 1.

[0031] Figure 8 The images show SEM images (left) of the all-solid-state battery of Example 1 on the negative electrode current collector side after initial charging and a graph (right) showing the calcium line scan results. Detailed Implementation

[0032] The present invention will be described in more detail below.

[0033] Before proceeding with the description, it should be understood that the terms used in this specification and the appended claims should not be construed as limited to their general or dictionary meanings, but should be interpreted according to their meanings and concepts corresponding to the technical aspects of the invention, based on the principle that inventors are allowed to appropriately define terms for the best description.

[0034] In the accompanying drawings, parts irrelevant to the description have been omitted for clarity, and similar reference numerals are assigned to similar parts throughout the specification. Furthermore, the dimensions and relative sizes of components shown in the drawings are not proportional to actual scale and may be reduced or exaggerated for clarity.

[0035] In this specification, "D" n "" refers to particle size distribution, specifically the particle size at the n% point of the cumulative distribution of the number of particles varying with particle size. That is, D 50 It is the particle size (median particle size, average particle size) at 50% of the cumulative distribution of particle number as the particle size varies. 90 It is the particle size at 90% of the cumulative distribution of particle number as the particle size varies, and D 10 This refers to the particle size at 10% of the cumulative distribution of particle numbers varying with particle size. Simultaneously, particle size distribution can be measured using laser diffraction. Specifically, after dispersing the powder to be tested in a dispersion medium, the powder is introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns as the particles pass through the laser beam, which varies with particle size.

[0036] [All-solid-state battery]

[0037] An all-solid-state battery according to one embodiment of the present invention comprises: a positive electrode containing a positive electrode active material, a negative electrode current collector, and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector. An all-solid-state battery according to one embodiment of the present invention does not contain a negative electrode active material, and lithium ions are supplied from the positive electrode active material layer during charging, thereby forming a lithium metal layer serving as the negative electrode active material on the negative electrode current collector. In an all-solid-state battery according to one embodiment of the present invention, the solid electrolyte layer comprises a sulfide-type solid electrolyte containing a Group 2 element and having a sulfide-germanium sulfide crystal structure. An anode-free all-solid-state battery according to one embodiment of the present invention can improve discharge capacity and cycle characteristics with the above-described structure. Furthermore, an anode-free all-solid-state battery according to one embodiment of the present invention can be driven under low limiting pressure with the above-described structure.

[0038] Meanwhile, as used in this article, “all-solid-state battery” refers to the state prior to the initial lithium metal deposition (initial charging) on ​​the negative electrode current collector (also known as “all-solid-state battery precursor”).

[0039] All-solid-state batteries can also be all-solid-state lithium rechargeable batteries.

[0040] Applying confining pressure to an all-solid-state battery during charging and discharging can prevent the growth of lithium dendrites. This confining pressure can be applied in the direction of the stacking of the positive and negative current collectors and the solid electrolyte layer disposed between the positive and negative current collectors (i.e., perpendicular to the surface direction of the negative current collector). For example, the confining pressure can be achieved by using clamps to secure the battery from both sides, on the positive and negative current collector sides.

[0041] Typically, high confinement pressure is applied to all-solid-state batteries to prevent the growth of lithium dendrites. However, an all-solid-state battery using an embodiment of the present invention, comprising a sulfide-based solid electrolyte containing divalent cations, requires almost no confinement pressure.

[0042] During charging and discharging, the all-solid-state battery can be pressurized at pressures below 0.3 MPa, preferably below 0.1 MPa, more preferably below 0.05 MPa, and even more preferably below 0.02 MPa. Therefore, an anode-free all-solid-state battery according to one embodiment of the present invention can be driven under low limiting pressure.

[0043] In the case of the negative electrode in a lithium secondary battery, the negative electrode is typically formed on the negative electrode current collector. However, according to one embodiment of the invention, an anode-free battery structure is assembled using only a negative electrode current collector that does not contain any metal particles or coatings on its surface. Then, lithium ions released from the positive electrode active material during charging form a lithium metal layer on the negative electrode current collector, which serves as the negative electrode active material. As a result, a negative electrode with a structure having a negative electrode current collector / negative electrode active material layer is formed, thus forming the structure of a conventional lithium secondary battery.

[0044] In other words, the concept of the anodeless battery of the present invention can encompass both: an anodeless battery in which no negative electrode is formed on the negative electrode current collector during initial assembly, and a battery having a negative electrode that can be formed on the negative electrode current collector depending on use.

[0045] Furthermore, in the negative electrode of one embodiment of the present invention, the morphology of lithium metal formed on the negative electrode current collector as a negative electrode active material covers both lithium metal morphology that forms a layer and lithium metal morphology that does not form a layer (e.g., lithium metal morphology that agglomerates into particulate form).

[0046] In the following description, the invention will be explained based on the morphology of a lithium metal layer in which lithium metal is formed. However, it will be apparent to those skilled in the art that the following description does not exclude structures in which lithium metal is not formed.

[0047] <Solid Electrolyte Layer>

[0048] The solid electrolyte layer contains a solid electrolyte. The solid electrolyte layer can have insulating properties and can also act as an ion conduction channel.

[0049] The thickness of the solid electrolyte layer can be about 50 μm or less, preferably about 15 μm to 50 μm. Within the range defined above, the solid electrolyte layer can have a suitable thickness considering ionic conductivity, physical strength, and the energy density of the applicable battery. For example, in terms of ionic conductivity or energy density, the thickness can be 10 μm or more, 20 μm or more, or 30 μm or more. Meanwhile, in terms of physical strength, the thickness can be 50 μm or less, 45 μm or less, or 40 μm or less. Furthermore, although the solid electrolyte layer has the thickness range defined above, its tensile strength can be about 100 kgf / cm². 2 - Approximately 2000 kgf / cm³ 2 Furthermore, the porosity of the solid electrolyte layer can be less than 15% by volume or less than about 10% by volume. Therefore, even if the solid electrolyte layer in one embodiment of the present invention is a thin film, it can still have high mechanical strength.

[0050] (Solid electrolyte)

[0051] The solid electrolyte may include at least one of sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes. Preferably, the solid electrolyte in the all-solid-state battery of one embodiment of the present invention is a sulfide-based solid electrolyte. The solid electrolyte may be contained in the positive electrode active material layer or in the solid electrolyte layer serving as a separator.

[0052] The average particle size of solid electrolytes can be controlled according to the application. Ionic conductivity can be improved by controlling the average particle size of solid electrolytes.

[0053] The average particle size and particle size distribution of solid electrolytes can be controlled, for example, by changing the conditions of the ball milling apparatus (e.g., rotation speed or time). This allows for the preparation of coarse solid electrolyte powder with a relatively large average particle size, micro solid electrolyte powder with a relatively small average particle size, and ultra-coarse solid electrolyte powder with a wider particle size distribution compared to coarse solid electrolyte powder. For example, coarse and ultra-coarse solid electrolyte powders can be prepared separately by controlling the milling time of the ball milling apparatus.

[0054] The average particle size of the coarse solid electrolyte powder can be larger than that of the fine solid electrolyte powder. The average particle size of the coarse solid electrolyte powder can be 5 μm-50 μm, preferably 8 μm-30 μm, and more preferably 10 μm-20 μm. The average particle size of the fine solid electrolyte powder can be 0.1 μm-10 μm, preferably 0.5 μm-5 μm, and more preferably 1 μm-3 μm.

[0055] The average particle size of the ultra-coarse solid electrolyte powder can be the same as that of the coarse solid electrolyte powder. In other words, the average particle size of the ultra-coarse solid electrolyte powder is 5 μm-50 μm, preferably 8 μm-30 μm, and more preferably 10 μm-20 μm. The D0 of the ultra-coarse solid electrolyte powder... 10 D smaller than that of coarse solid electrolyte powder 10 Furthermore, the D of ultra-coarse solid electrolyte powder 90 D greater than that of coarse solid electrolyte powder 90 D of ultra-coarse solid electrolyte powder 10 The particle size is 1 μm-6 μm, preferably 2 μm-5 μm. The D0 of the coarse solid electrolyte powder... 10 The micrometer size is 3 μm-8 μm, preferably 4 μm-7 μm. The D0 of the ultracoarse solid electrolyte powder is... 90 The particle size is 100 μm-500 μm, preferably 200 μm-400 μm. The D0.05 of the coarse solid electrolyte powder... 90 The size is 30 μm-100 μm, preferably 40 μm-80 μm.

[0056] The average particle size of the sulfide-based solid electrolyte contained in the solid electrolyte layer can be larger than that of the sulfide-based solid electrolyte contained in the positive electrode active material layer. Due to the larger average particle size and fewer grain boundaries per unit volume of the coarse and ultra-coarse solid electrolyte powders, they exhibit high ionic conductivity when used in the solid electrolyte layer. When used in the positive electrode active material layer, the solid electrolyte microparticles can penetrate into the voids between the positive electrode active material particles, thus providing lithium-ion conduction pathways for the positive electrode active material. Therefore, by making the average particle size of the sulfide-based solid electrolyte contained in the solid electrolyte layer larger than that of the sulfide-based solid electrolyte contained in the positive electrode active material layer, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved.

[0057] The particle size distribution of the solid electrolyte can affect the discharge capacity and cycle characteristics of all-solid-state batteries. As the particle size distribution of the solid electrolyte becomes narrower (e.g., with (D...), the discharge capacity and cycle characteristics of the battery increase. 90 -D 10 ) / D 50 As the particle size of the solid electrolyte increases, lithium-ion conduction becomes more uniform during charge and discharge, resulting in high discharge capacity. Conversely, as the particle size of the solid electrolyte increases, lithium-ion conduction becomes less uniform during charge and discharge, leading to a decrease in discharge capacity. (D) 90 -D 10 ) / D 50 The particle size distribution is 1-30, preferably 1-10, and more preferably 1-5. In addition to the average particle size of the solid electrolyte, the discharge capacity and cycle characteristics of the all-solid-state battery can be further improved by controlling the particle size distribution within the range defined above.

[0058] There are no particular restrictions on sulfide solid electrolytes, as long as they contain sulfur (S), and any known sulfide solid electrolyte can be used.

[0059] Sulfide solid electrolytes can have a crystalline structure. Sulfide solid electrolytes with a crystalline structure enhance lithium-ion conduction to provide high lithium-ion conductivity.

[0060] Sulfide solid electrolytes can have crystal structures of the argentite, nazonite, perovskite, garnet, or LGPS type. Preferably, sulfide solid electrolytes can have an argentite crystal structure. Sulfide solid electrolytes with an argentite crystal structure exhibit high stability to lithium metal, thus allowing the use of lithium metal with high energy density per unit weight as the anode material.

[0061] Sulfide solid electrolytes can be amorphous, glassy, ​​or glass-ceramic.

[0062] Sulfide solid electrolytes can have ionic conductivity of a metal belonging to Group 1 or Group 2 in the periodic table of elements, and can include Li-P-S type glass or Li-P-S type glass ceramics. Non-limiting examples of sulfide solid electrolytes can include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, LiS-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, etc., and sulfide solid electrolytes can include more than one of them. However, the scope of the present invention is not limited thereto.

[0063] Sulfide solid electrolytes can contain a crystalline phase and an amorphous phase. Sulfide solid electrolytes can contain a crystalline phase having a thiogermanate-type crystal structure (hereinafter also referred to as "thiogermanate phase") and other phases (hereinafter also referred to as "impurity phases" or "unknown phases"). Preferably, the thiogermanate-type crystal structure is a cubic system. The other phases can be a crystalline phase or an amorphous phase. The other phases can include Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, MgS phase, CaS phase, SrS phase, BaS phase, CaBr2 phase, etc., whether crystalline phase or amorphous phase. Preferably, sulfide solid electrolytes do not contain or substantially do not contain any impurity phases other than the thiogermanate phase. In other words, sulfide solid electrolytes preferably contain only the thiogermanate phase. When sulfide solid electrolytes do not contain or substantially do not contain any impurity phases, lithium ion conduction is not easily inhibited, and thus sulfide solid electrolytes can have high lithium ion conductivity.

[0064] The ratio of the crystalline phase contained in sulfide solid electrolytes can be evaluated quantitatively or semi-quantitatively by an X-ray diffraction (XRD) pattern. As an evaluation method, the ratio of the crystalline phase can be evaluated by comparing the peak intensities (height or area) of the XRD pattern.

[0065] Sulfide solid electrolytes are represented by the chemical formula Li 7-x-2y M y PS 6-x Ha x In this chemical formula, M can represent at least one element selected from Group 2 elements, Ha can be at least one element selected from halogen elements, and x and y can satisfy 0 < x < 2.5 and 0 < y < 0.45. The lattice volume of sulfide solid electrolytes can be Ha can include Br. Such sulfide-based solid electrolytes can have high lithium-ion conductivity. By using a sulfide-based solid electrolyte with high lithium-ion conductivity in an anode-free all-solid-state battery, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved. Furthermore, since the sulfide-based solid electrolyte with high lithium-ion conductivity prevents lithium dendrites from growing on the negative electrode current collector, an anode-free all-solid-state battery according to one embodiment of the present invention can be driven under low limiting pressure.

[0066] In sulfide solid electrolytes, Li 7-x PS 6-x Ha x Lithium in lithium electrolytes can be partially substituted by group 2 elements (M) capable of converting into divalent cations. The group 2 element (M) substituting for lithium can be at least one selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The ionic radius (six-coordinate) of lithium (Li) is 90 pm, and the ionic radii (six-coordinate) of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) are 86 pm, 114 pm, 132 pm, and 149 pm, respectively. Based on the valence number, one group 2 element (M) can substitute for two lithium elements. Lithium site vacancies are created through the substitution of group 2 elements (M), thereby providing improved lithium-ion conductivity. Furthermore, sulfide solid electrolytes undergo changes in lattice constant and lattice volume through the substitution of group 2 elements (M), thus allowing for crystal structures suitable for lithium-ion conduction.

[0067] Furthermore, in one embodiment of the present invention, a sulfide-based solid electrolyte can be produced by infiltrating a Group 2 element (M) capable of being converted into a divalent cation into Li. 7-x PS 6-x Ha x It is formed within the crystal lattice. The Group 2 element (M) infiltrating the crystal structure can be at least one selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) can be used alone or in combination. Preferably, the Group 2 element (M) is magnesium (Mg) or calcium (Ca). Sulfide-based solid electrolytes are formed by the infiltration of the Group 2 element (M) into Li. 7-x PS 6-x Ha xThe lattice constant and lattice volume change within the crystal lattice, thus allowing sulfide-based solid electrolytes to possess crystal structures suitable for lithium-ion conduction. Sulfide-based solid electrolytes containing calcium (Ca) as a Group 2 element (M) exhibit high lithium-ion conductivity. When such sulfide-based solid electrolytes are used in anode-free all-solid-state batteries, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved. Furthermore, when such sulfide-based solid electrolytes are used, the growth of lithium dendrites on the negative electrode current collector is prevented, thus enabling the anode-free all-solid-state battery of one embodiment of the present invention to operate under low limiting pressure.

[0068] Group 2 elements (M) can be located at vacancy sites in sulfide-based solid electrolytes with a sulfhydryl-germanium oxide crystal structure. Since the Group 2 elements (M) are located at vacancy sites in the sulfhydryl-germanium oxide crystal structure, at least a portion of the Group 2 elements (M) can migrate away from the vacancy sites during the charge and discharge process of the all-solid-state battery. A portion of the Group 2 elements (M) that migrate away from the vacancy sites can be deposited at the interface between the negative electrode current collector and the solid electrolyte layer and / or at the interface between the positive electrode active material layer and the solid electrolyte layer. Furthermore, a portion of the Group 2 elements (M) that migrate away from the vacancy sites can return to the original vacancy site or another vacancy site. In an all-solid-state battery according to one embodiment of the present invention, the doping amount (y) of the Group 2 elements (M) in the sulfide-based solid electrolyte is relatively small. Therefore, even if the Group 2 elements (M) migrate away from the vacancy sites, the sulfhydryl-germanium oxide crystal structure of the sulfide-based solid electrolyte can be maintained. The Group 2 elements (M) can migrate as charge carriers in the all-solid-state battery along with lithium during the charge and discharge process. The position of a Group 2 element (M) can be measured using any technique known to those skilled in the art (e.g., neutron powder diffraction).

[0069] Preferably, the Group 2 element (M) is magnesium (Mg) and / or calcium (Ca), more preferably calcium (Ca). When the Group 2 element (M) is magnesium (Mg) and / or calcium (Ca), the sulfide solid electrolyte can have high crystallinity and therefore high ionic conductivity. This is thought to be because the ionic radius of lithium (Li) (90 pm) is close to that of magnesium (Mg) and calcium (Ca) (86 pm and 114 pm, respectively), and the sulfide-germanium ore-type crystal structure can be easily maintained even after substitution by the Group 2 element (M).

[0070] Group 2 element (M) in the chemical formula Li 7-x-2y M y PS 6-x Ha xThe doping amount (y) therein satisfies 0 < y < 0.45, preferably 0 < y < 0.1, more preferably 0.005 ≤ y ≤ 0.04, and even more preferably 0.01 ≤ y ≤ 0.03. When y satisfies the range defined above, the sulfide-based solid electrolyte can have high ionic conductivity. When y is 0, no change in the crystal structure caused by the substitution of Group 2 element (M) can be obtained, resulting in low ionic conductivity. When y is more than 0.45, the sulfide-based solid electrolyte cannot maintain the argyrodite-type crystal structure, leading to a decrease in ionic conductivity. In addition, in the sulfide-based solid electrolyte, the impurity phase that inhibits lithium ion conduction increases, resulting in a decrease in ionic conductivity.

[0071] Chemical formula Li 7-x-2y M y PS 6-x Ha x The halogen (Ha) therein is at least one element selected from halogen elements. Preferably, the halogen (Ha) includes chlorine (Cl) and bromine (Br). Since sulfur (S) as a divalent anion exhibits a stronger force to attract lithium ions than monovalent halogen ions, the migration of lithium ions can be significantly inhibited. When the halogen includes bromine (Br), the occupancy of sulfur (S) at specific sites in the argyrodite-type crystal structure decreases, and the occupancy of halogen at the corresponding sites increases. Therefore, the mobility of lithium ions around the bromine (Br) sites can become active. As a result, the lithium ion conductivity can be improved. In addition, bromine (Br) can combine with Li in the sulfide-based solid electrolyte to form lithium bromide (LiBr) as a water-absorbing substance. Lithium bromide (LiBr) absorbs water that may cause a decrease in lithium ion conductivity, thereby improving the lithium ion conductivity of the sulfide-based solid electrolyte.

[0072] Chemical formula Li 7-x-2y M y PS 6-x Ha x The ratio (x) of the halogen (Ha) therein satisfies 0 < x < 2.5, preferably 1.0 < x < 2.0, and more preferably 1.3 < x < 1.8. When x satisfies the range defined above, the argyrodite-type crystal structure is stable, and thus the sulfide-based solid electrolyte can have high ionic conductivity.

[0073] When driving a all-solid-state battery, the Group 2 element (M) contained in the sulfide-based solid electrolyte can migrate. Preferably, the Group 2 element (M) contained in the sulfide-based solid electrolyte can migrate in the form of divalent cations.

[0074] During the charging process of an all-solid-state battery, at least a portion of the Group 2 element (M) can migrate towards the negative electrode and can be deposited at the interface between the negative electrode current collector and the solid electrolyte layer. When a separate intermediate layer exists between the negative electrode current collector and the solid electrolyte layer, the Group 2 element (M) can be deposited at the interface between the negative electrode current collector and the intermediate layer. A portion of the Group 2 element (M) can be deposited inside the intermediate layer.

[0075] During the discharge process of an all-solid-state battery, at least a portion of Group 2 elements (M) can migrate towards the positive electrode and can be deposited at the interface between the positive electrode active material layer and the solid electrolyte layer. When a separate intermediate layer exists between the positive electrode active material layer and the solid electrolyte layer, Group 2 elements (M) can be deposited at the interface between the positive electrode current collector and the intermediate layer. A portion of Group 2 elements (M) can also be deposited inside the intermediate layer.

[0076] Group 2 elements (M) can be deposited on the interfaces in the form of at least one selected from the group consisting of individual Group 2 elements (M), alloys with lithium, and compounds containing Group 2 elements (M). When the Group 2 elements (M) are deposited on the interfaces during charge and discharge, the tight adhesion properties at the interfaces are improved, thus maintaining the ion conduction paths and / or conductive paths covering the interfaces. Therefore, the all-solid-state battery of one embodiment of the present invention has improved discharge capacity and cycle characteristics. Furthermore, the all-solid-state battery of one embodiment of the present invention can achieve charge and discharge without the high limiting pressure of several MPa or more required to drive conventional all-solid-state batteries.

[0077] Preferably, the Group 2 element (M) is present at the 48h site of the argyrogermanium sulfide crystal structure. A portion of the Group 2 element (M) present at the 48h site of the argyrogermanium sulfide crystal structure can migrate towards the negative electrode during the charging process of the all-solid-state battery without destroying the argyrogermanium sulfide crystal structure, and can also migrate towards the positive electrode during the discharging process of the all-solid-state battery.

[0078] Alloys of Group 2 elements (M) with lithium can include MLi. x (1≤x≤2). Preferably, the alloy of Group 2 element (M) with lithium may include CaLi. x (1≤x≤2). More preferably, the alloy of a Group 2 element (M) with lithium may include at least one selected from the group consisting of CaLi and CaLi2. The alloy may also include CaLi3 and Ca3Li.

[0079] Compounds of Group 2 elements (M) with lithium can include compounds of calcium and lithium. Additionally, these compounds can also include compounds of magnesium and lithium.

[0080] The ionic conductivity of sulfide solid electrolytes can be affected by their crystallinity. Crystallinity can be assessed by XRD patterns. In XRD patterns, sulfide solid electrolytes can exhibit high ionic conductivity when no phase other than the crystalline phase of argillium sulfide (crystalline or amorphous phases, such as Li₂S, P₂S₅, LiCl, LiBr, Li₃PS₄, MgS, CaS, SrS, BaS, etc.) is observed or substantially absent.

[0081] The lattice volume of sulfide solid electrolytes can be altered by the substitution of lithium sites by group 2 elements (M). While not bound by any particular theory, group 2 elements (M) exhibit divalent cation properties and strongly interact with other anions present in sulfide solid electrolytes, leading to changes in lattice volume (i.e., increases or decreases). This change in lattice volume produces crystal structures suitable for lithium-ion conduction, thus allowing sulfide solid electrolytes to possess high ionic conductivity.

[0082] The lattice volume of sulfide solid electrolytes can be Preferred More preferably Even better The lattice constant and lattice volume can be evaluated using XRD patterns. Even with the same composition, the lattice volume of sulfide solid electrolytes can vary depending on the calcination temperature. When the lattice volume meets the range defined above, lithium-ion conduction in sulfide solid electrolytes is accelerated, thus allowing them to exhibit high ionic conductivity.

[0083] Unless otherwise stated, the ionic conductivity (hereinafter also referred to as "lithium-ion conductivity") of the sulfide-based solid electrolyte refers to the ionic conductivity of the sulfide-based solid electrolyte at ambient pressure (1 atm) and room temperature (25°C, 298 K). When using sulfide-based solid electrolytes in all-solid-state batteries, it is practically preferred that the ionic conductivity is 4 mS / cm or higher. In one embodiment of the present invention, the conductivity of the sulfide-based solid electrolyte is 2 mS / cm or higher, preferably 4 mS / cm or higher, more preferably 10.8 mS / cm or higher, even more preferably 12 mS / cm or higher, and most preferably 13 mS / cm or higher.

[0084] A sulfide-based solid electrolyte according to one embodiment of the present invention can be obtained by a method comprising the following steps: mixing a lithium source, a Group 2 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture; and calcining the mixture at a temperature of 250°C to 600°C. The calcination step can be carried out under an inert atmosphere (e.g., argon, nitrogen, etc.).

[0085] The lithium source, group 2 element source, phosphorus source, sulfur source, and halogen source can each be a compound, such as a sulfide, oxide, or nitride. Lithium sulfide (Li₂S) can be used as a lithium source, phosphorus pentasulfide (P₂S₅) can be used as a phosphorus source, and lithium halides (LiHa), such as lithium chloride (LiCl) and lithium bromide (LiBr), can be used as halogen sources. For example, the group 2 element source can be a sulfide. In one variant, sulfur can be supplied by other element sources. In other words, at least one of the lithium source, group 2 element source, phosphorus source, and halogen source can also act as a sulfur source.

[0086] In the case of sulfide solid electrolytes with a sulfide-germanium sulfide crystal structure, the calcination temperature is preferably 350℃-550℃, more preferably 400℃-500℃, and even more preferably 410℃-470℃. When the calcination temperature meets the above-defined range, the formation of the sulfide-germanium sulfide crystal structure can be accelerated, thus the sulfide solid electrolyte can have high crystallinity. Therefore, a sulfide solid electrolyte with high ionic conductivity can be obtained.

[0087] The solid electrolyte layer may also include an adhesive for the solid electrolyte layer. The adhesive for the solid electrolyte layer can be introduced to bond the solid electrolytes to each other and to bond the solid electrolyte layer to the battery elements (e.g., positive electrode, negative electrode, etc.) stacked on both sides thereon.

[0088] There are no particular limitations on the adhesive used for the solid electrolyte layer, and it can be suitably selected from the components of adhesives used as solid electrolytes in all-solid-state lithium secondary batteries. Specific examples of adhesives for the solid electrolyte layer may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), styrene-butadiene-styrene block copolymer (SBS), nitrile rubber (NBR), fluororubber, and acrylic adhesives.

[0089] The solid electrolyte layer may not contain a binder for the solid electrolyte layer. When the solid electrolyte layer does not contain a binder for the solid electrolyte layer, the content of solid electrolyte contained in the solid electrolyte layer can be increased, thereby improving the ionic conductivity of the solid electrolyte layer.

[0090] <Negative electrode>

[0091] Before the initial lithium metal deposition (initial charging) is performed, the negative electrode does not contain negative electrode active material.

[0092] Lithium ions are supplied from the positive electrode active material contained in the positive electrode during charging, and a lithium metal layer serving as the negative electrode active material is formed on the negative electrode current collector. Specifically, when charging is performed by applying a voltage above a predetermined level to an all-solid-state battery having an anode-less battery structure, lithium ions are released from the positive electrode active material in the positive electrode, and the released lithium ions migrate through the solid electrolyte layer and toward the negative electrode current collector, forming a lithium metal layer containing pure lithium on the negative electrode current collector, thereby forming the negative electrode. The advantage of forming the lithium metal layer by charging in this way is that, compared with conventional negative electrodes formed by sputtering the lithium metal layer onto the negative electrode current collector or by stacking lithium foil with the negative electrode current collector, a thin film layer can be formed, and the interface characteristics can be easily controlled.

[0093] In particular, thanks to the anode-free battery structure, lithium metal is not exposed to the atmosphere during battery assembly, thus fundamentally avoiding the problem of oxide film formation on the surface caused by the high reactivity of lithium itself, and the resulting degradation of the lifespan of lithium secondary batteries.

[0094] The formed lithium metal layer can be a uniform and continuous or discontinuous layer on the negative electrode current collector. For example, when the negative electrode current collector has a foil shape, the lithium metal layer can have a continuous thin film shape. When the negative electrode current collector has a three-dimensional porous structure, the lithium metal layer can be formed discontinuously. That is, the discontinuous layer is a form of discontinuous distribution, meaning that regions with lithium metal layers and regions without lithium metal layers exist in specific areas, but the regions without lithium metal layers are distributed in a way that separates, breaks, or separates the regions containing lithium compounds into island-like structures, thus the regions with lithium metal layers are discontinuously distributed.

[0095] The thickness of such a lithium metal layer formed through charging and discharging is at least 50 nm to 100 μm, preferably 1 μm to 50 μm, thus enabling it to function as a negative electrode. If the thickness is less than the range defined above, the battery charging and discharging efficiency decreases rapidly. Conversely, if the thickness exceeds the range defined above, the lifespan characteristics are stable, but the battery energy density decreases.

[0096] In particular, since the lithium metal layer disclosed herein is prepared as an anode-free battery without lithium metal during battery assembly, little or no oxide layer is formed on the lithium metal layer during the assembly process, compared to existing lithium secondary batteries assembled using lithium foil. Therefore, battery life degradation caused by oxide layers can be prevented.

[0097] To form the lithium metal layer according to one embodiment of the present invention, a single charge is performed within a voltage range of 4.5 V to 2.5 V at a rate of 0.01 C to 0.2 C. If the charge is applied below the above-defined range, it is difficult to form the lithium metal layer. Conversely, if the charge is applied beyond the above-defined range, the battery is damaged due to over-discharge, and then it cannot be properly charged and discharged.

[0098] The negative electrode may include a negative electrode current collector. There are no particular limitations on the negative electrode current collector, as long as it does not cause any chemical changes in the battery and is conductive. Specific examples of negative electrode current collectors may include: iron; stainless steel; aluminum; nickel; titanium; calcined carbon; aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.; and so on.

[0099] In particular, it is preferred that the negative electrode current collector of one embodiment of the present invention does not react with the sulfide-based solid electrolyte. That is, preferably, the all-solid-state battery of one embodiment of the present invention does not contain reaction products between the negative electrode current collector and the sulfide-based solid electrolyte. The fact that the all-solid-state battery does not contain reaction products between the negative electrode current collector and the sulfide-based solid electrolyte can be determined by observing the cross-section of the all-solid-state battery using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The fact that the all-solid-state battery does not contain reaction products can also be determined by X-ray diffraction (XRD). Before the initial lithium metal deposition (initial charging) is performed, the negative electrode current collector can be in direct contact with the sulfide-based solid electrolyte. Furthermore, after the battery discharges, the lithium metal, as the negative electrode active material, migrates to the positive electrode, so there is almost no or no negative electrode active material on the negative electrode current collector. If a side reaction occurs between the negative electrode current collector and the sulfide-based solid electrolyte, byproducts such as hydrogen sulfide will be generated, which will adversely affect the performance of the all-solid-state battery. To prevent such side reactions, the negative electrode current collector preferably has high stability with the sulfide-based solid electrolyte. Because the negative electrode current collector does not react with sulfide-based solid electrolytes, an anode-free all-solid-state battery according to one embodiment of the present invention can achieve improved discharge capacity and cycle characteristics. Furthermore, because the negative electrode current collector does not react with sulfide-based solid electrolytes and therefore does not produce byproducts, an anode-free all-solid-state battery according to one embodiment of the present invention can be operated at low limiting pressures.

[0100] The thickness of the negative electrode current collector can range from 3 μm to 500 μm.

[0101] Negative current collectors can have various shapes such as sheets, foils, meshes, porous bodies, foams, and nonwovens, and have fine surface irregularities formed on their surfaces.

[0102] The negative electrode current collector can directly contact the solid electrolyte layer. Specifically, it can directly contact the sulfide-based solid electrolyte contained within the solid electrolyte layer. When the negative electrode current collector and the solid electrolyte are in direct contact without an intermediate layer, the thickness of the all-solid-state battery can be reduced and its energy density improved. Due to the increased loading of active materials in the all-solid-state battery and the prevention of lithium dendrite growth, all-solid-state batteries can achieve improved discharge capacity and cycle characteristics. Furthermore, all-solid-state batteries can be operated under low limiting pressures.

[0103] The negative electrode current collector does not need to be in direct contact with the solid electrolyte layer. An intermediate layer can be formed between the negative electrode current collector and the solid electrolyte layer. When the intermediate layer is formed, lithium ions supplied from the positive electrode active material layer pass through the intermediate layer, and a lithium metal layer is formed on the negative electrode current collector. That is, during charging, a lithium metal layer is formed between the negative electrode current collector and the intermediate layer.

[0104] Here, the intermediate layer may contain any material as long as it allows for the smooth transfer of lithium ions, and may contain materials for lithium-ion conductive polymers and / or inorganic solid electrolytes, and may also include lithium salts if necessary.

[0105] The intermediate layer may contain a metal capable of forming an alloy with lithium. Metals capable of forming an alloy with lithium may include germanium, tin, zinc, indium, gallium, antimony, lead, gold, silver, aluminum, platinum, palladium, etc.

[0106] Lithium-ion conductive polymers may include, for example, any one or a mixture of two or more of the following selected from the group consisting of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), but are not limited thereto. Any polymer may be used without particular limitation, as long as it is lithium-ion conductive.

[0107] When using lithium-ion conductive polymers, the intermediate layer may also contain materials for this purpose in order to further improve lithium-ion conductivity.

[0108] For example, the intermediate layer may also contain lithium salts, such as LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborate, lower aliphatic carboxylic acids, lithium tetraphenylborate, lithium imide, etc.

[0109] Inorganic solid electrolytes are ceramic materials and can contain crystalline or amorphous materials; specific examples may include thio-LISICON (Li... 3.25 Ge 0.25 P 0.75 S4), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, Li3PS4, Li7P3S 11 , Li2O-B2O3, Li2O-B2O3-P2O5, Li2O-V2O5-SiO2, Li2O-B2O3, Li3PO4, Li2O-Li2WO4-B2O3, LiPON, LiBON, Li2O-SiO2, LiI, Li3N, Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li3PO (4-3 / 2 w) N w (w<1), Li 3.6 Si 0.6 P 0.4 O4, etc. Here, when using an inorganic solid electrolyte, the intermediate layer may also contain lithium salt if necessary.

[0110] Inorganic solid electrolytes can be mixed with known materials (e.g., binders) to be applied in the form of thick films via slurry coating. Alternatively, if necessary, inorganic solid electrolytes can be applied in the form of thin films via deposition processes (e.g., sputtering). The slurry coating process used herein can be appropriately selected based on the descriptions of coating methods, drying methods, and solvents mentioned for lithium-ion conductive polymers.

[0111] An intermediate layer containing a lithium-ion conductive polymer and / or an inorganic solid electrolyte can ensure improved lithium-ion transport rate, thus promoting the formation of a lithium metal layer, while also inhibiting or preventing the formation of lithium dendrites when the lithium metal layer / anode current collector is used as the anode.

[0112] To ensure the above effect, the thickness of the intermediate layer needs to be limited.

[0113] A thinner interlayer is advantageous for battery output characteristics. However, when the interlayer is not formed to a predetermined thickness, it cannot suppress the side reactions between lithium and electrolyte that subsequently form on the negative electrode current collector, nor can it effectively block dendrite growth. According to an embodiment of the invention, preferably, the thickness of the interlayer can be from 10 nm to 50 μm. When the thickness of the interlayer is less than the above-defined range, it cannot effectively suppress the side reactions and exothermic reactions between lithium and electrolyte, which increase under conditions such as overcharging or high-temperature storage, thus failing to improve safety. On the other hand, when the thickness exceeds the above-defined range, the increased thickness of the all-solid-state battery leads to a decrease in the volumetric energy density of the all-solid-state battery.

[0114] Positive electrode

[0115] The positive electrode may include a positive electrode active material layer and a positive electrode current collector.

[0116] There are no particular limitations on the positive electrode current collector, as long as it does not cause any chemical changes in the battery and has high conductivity. Specific examples of positive electrode current collectors may include at least one selected from the group consisting of iron, stainless steel, copper, aluminum, nickel, titanium, and calcined carbon, specifically aluminum. The positive electrode current collector may contain a carbon-based conductive material and a binder, and may also contain a base coating applied to the surface of the positive electrode current collector. This can significantly improve the adhesion and conductivity between the positive electrode active material layer and the current collector.

[0117] The positive electrode active material layer can be disposed on at least one side of the positive electrode current collector. Specifically, the positive electrode active material layer can be disposed on one or both sides of the positive electrode current collector.

[0118] The positive electrode active material layer may contain a positive electrode active material. In an embodiment of the present invention, the lithium source used to form the lithium metal layer is a positive electrode active material containing lithium. That is, lithium ions in the positive electrode active material are released when charged to a specific voltage range, thereby forming a lithium metal layer on the negative electrode current collector.

[0119] There are no particular restrictions on the positive electrode active material, as long as it can be used as a positive electrode active material for lithium-ion secondary batteries. Positive electrode active materials may include, but are not limited to: layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or these compounds substituted with one or more transition metals; lithium manganese oxide, such as those with the chemical formula Li... 1+x Mn 2- x Compounds represented by O4 (where x is 0-0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, LiV3O4, V2O5, or Cu2V2O7; and the chemical formula LiNi.1-x M x O₂ (where M is Co, Mn, Al, Cu, Fe, P, Mg, Ca, Zr, Ti, Ru, Nb, W, B, Si, Na, K, Mo, V or Ga, and x is 0.01 - 0.3) represents Ni-site type lithium nickel oxide; chemical formula LiMn 1-x M x O₂ (where M is Co, Ni, Fe, Cr, Zn or Ta, x is 0.01 - 0.1) or Li₂Mn₃MO₈ (where M is Fe, Co, Ni, Cu or Zn) represents lithium manganese composite oxide; having a spinel structure and composed of the lithium manganese composite oxide represented by the formula LiNi x Mn 2-x O₄; LiMn₂O₄ in which Li is partially replaced by alkaline earth metal ions; disulfide; LiMn x Fe 1-x PO₄ (0 ≤ x ≤ 0.9); Fe₂(MoO₄)₃, etc.

[0120] The positive electrode active material may include Li 1+x M y O 2+z , where M is at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo and V, 0 ≤ x ≤ 5, 0 < y ≤ 2, 0 ≤ z ≤ 2. Specifically, Li 1+x M y O 2+z may include at least one selected from the group consisting of LiCoO₂, LiNiO₂, LiMnO₂, Li[Ni 0.5 Co 0.3 Mn 0.2 O₂, Li[Ni 0.6 Co 0.2 Mn 0.2 O₂, Li[Ni 0.7 Co 0.1 Mn 0.2 O₂, Li[Ni 0.8 Co 0.1 Mn 0.1 O₂, Li[Ni 0.9 Co 0.05 Mn 0.05 O₂, LiMn₂O₄ and LiFePO₄, 0.5Li₂MnO₃ 0.5Li[Mn 0.4 Ni 0.3 Co 0.3 O₂. Preferably, Li 1+x M y O2+z It can include Li[Ni 0.6 Co 0.2 Mn 0.2 O2, Li[Ni 0.7 Co 0.1 Mn 0.2 O2, Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2 and Li[Ni 0.9 Co 0.05 Mn 0.05 Any of O2. Since the positive electrode active material includes Li 1+x M y O 2+z Therefore, lithium can be adequately supplied to the negative electrode. Because Li... 1+x M y O 2+z It exhibits electrochemical activity after the initial cycle without causing overall battery performance degradation, thus addressing battery capacity loss caused by irreversible capacity at the negative electrode. Li 1+x M y O 2+z It can be a secondary particle form created through the bonding or granulation of primary particles. In one variant, Li 1+x M y O 2+z It can be in single-particle form.

[0121] In the positive electrode active material layer, the content of the positive electrode active material can be 50%-95% by weight, specifically 60%-90% by weight.

[0122] Furthermore, the average particle size of the positive electrode active material can be 1 μm-30 μm, and according to one embodiment, it can be 8 μm-12 μm. When the average particle size of the positive electrode active material falls within the range defined above, the battery exhibits excellent capacity characteristics.

[0123] The positive electrode active material layer may also contain a positive electrode conductive material.

[0124] There are no particular restrictions on the positive electrode conductive material, as long as it does not undergo chemical changes in the corresponding battery and is conductive. For example, the positive electrode conductive material may include any of the following: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphene; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives, or mixtures of two or more of these.

[0125] In the positive electrode active material layer, the content of positive electrode conductive material can be 1% to 30% by weight.

[0126] The positive electrode active material layer may include a positive electrode binder.

[0127] There are no particular limitations on the positive electrode adhesive, as long as it is a component that facilitates the adhesion of the positive electrode active material, the positive electrode conductive material, and the current collector. Specifically, the positive electrode adhesive may include at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), and fluororubber.

[0128] In the positive electrode active material layer, the content of the positive electrode binder can be 1% to 30% by weight.

[0129] If necessary, the positive electrode active material layer may also contain at least one additive, such as an oxidation stabilizer, a reduction stabilizer, a flame retardant, a heat stabilizer, an anti-fogging agent, etc.

[0130] The positive electrode active material layer may also contain a sulfide-based solid electrolyte. The sulfide-based solid electrolyte contained in the positive electrode active material layer may have the same composition as the sulfide-based solid electrolyte contained in the solid electrolyte layer, or it may have a different composition.

[0131] The positive electrode active material layer may contain 5%-60% by weight, specifically 10%-40% by weight, of sulfide-based solid electrolyte.

[0132] The average particle size of the positive electrode active material can be larger than the average particle size of the solid electrolyte contained in the positive electrode active material layer. In this case, the solid electrolyte can enter the gaps between the positive electrode active material particles and thus provide a lithium-ion conduction pathway for the positive electrode active material.

[0133] This invention provides a secondary battery having the above-described structure. It also provides a battery module comprising the secondary battery as a unit cell, a battery pack comprising the battery module, and a device comprising the battery pack as a power source. Specific examples of this device may include, but are not limited to: power tools driven by an electric motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems, etc.

[0134] Preferred embodiments will be described below to facilitate understanding of the invention. However, it will be apparent to those skilled in the art that the following embodiments are merely examples of the invention, and various changes and modifications can be made within the scope of the invention, and such changes and modifications also fall within the scope of the claims.

[0135] (Synthesis of solid electrolytes)

[0136] Preparation Example 1

[0137] First, lithium sulfide (Li₂S, available from Mitsuwa Chemical), phosphorus pentasulfide (P₂S₅, available from Aldrich), calcium sulfide (CaS, available from Japan Pure Chemical), lithium chloride (LiCl, available from Aldrich), and lithium bromide (LiBr, available from Aldrich) are used as raw materials. To obtain Li 5.4-2y M y PS 4.4 Cl 1.0 Br 0.6 The composition (with a doping amount of Group 2 element (M) y = 0.025) was determined by weighing the raw materials in a glove box under an argon atmosphere and mixing them with a mortar to obtain a mixed powder. The resulting mixed powder was introduced into a ZrO2 container along with ZrO2 balls to provide a sealed container. The sealed container was installed in a planetary ball mill and ball-milled at 380 rpm for 20 hours. The container was then opened in the glove box to recover the powder. The resulting powder was placed in a carbon crucible and sealed, and then calcined at 430°C for 8 hours while argon was introduced. The calcined powder was then pulverized in a mortar for 10 minutes to obtain a coarse solid electrolyte powder containing divalent cations.

[0138] Preparation Example 2

[0139] By introducing the coarse solid electrolyte powder containing divalent cations obtained from Preparation Example 1 into a ZrO2 container together with ZrO2 balls and anisole solvent, and wet pulverizing at 250 rpm for 1 hour, a micro solid electrolyte powder containing divalent cations was obtained.

[0140] Preparation Example 3

[0141] Ultracoarse powder of solid electrolyte containing divalent cations was obtained in the same manner as in Preparation Example 1, except that the calcined powder was pulverized for 1 minute using a mortar and pestle.

[0142] Comparative Preparation Example 1

[0143] A crude solid electrolyte powder free of divalent cations was obtained in the same manner as in Preparation Example 1, except that calcium sulfide (CaS, available from Japan Pure Chemical) was not used. The composition of the solid electrolyte obtained in Preparation Example 1 was compared to that obtained in Preparation Example 1, which was Li. 5.4 PS 4.4 Cl 1.0 Br 0.6 .

[0144] Comparative Preparation Example 2

[0145] By introducing the coarse solid electrolyte powder without divalent cations obtained from Comparative Preparation Example 1 into a ZrO2 container together with ZrO2 balls and anisole solvent, and wet pulverizing at 250 rpm for 1 hour, a micro solid electrolyte powder without divalent cations was obtained.

[0146] [Evaluate]

[0147] The solid electrolytes obtained as described above are evaluated as follows.

[0148] (XRD measurement)

[0149] Pre-determined amounts of each solid electrolyte were introduced into a sealed sample holder in a glove box under an argon gas flow and subjected to X-ray diffraction (XRD). The lattice constant, lattice volume, and half-width were then calculated from the resulting XRD patterns. The half-width is determined by... Figure 4 Calculation of the crystal peaks on the (311) plane of the sulfosilver-germanium type crystal structure observed near 2θ=30°.

[0150] The measurement system and conditions are as follows.

[0151] - X-ray diffraction system: Rigaku Smartlab

[0152] - Source:

[0153] - Voltage: 45 kV

[0154] - Current: 200 mA

[0155] - Scan range (2θ): 10°-60°

[0156] - Step size: 0.01°

[0157] (Determination of particle size distribution)

[0158] A solid electrolyte was introduced into a heptane solvent, and Span 80 was used as the dispersing material to prepare a solid electrolyte dispersion. The particle size distribution was determined using a Mastersizer 3000 particle size analyzer. The data were then analyzed by setting the refractive index of the solid electrolyte to 2.16.

[0159] (Determination of ionic conductivity)

[0160] Take the predetermined amount of each solid electrolyte and place it in MACOR ® The pellets were then assembled with a pellet forming fixture (upper and lower pressure pins) and pressed into shape using a uniaxial press at approximately 370 MPa. Next, a predetermined amount of gold powder was placed on both sides of the pellets and pressed into shape using a uniaxial press at approximately 554 MPa to obtain the MACOR tube cell. The resulting MACOR tube cell was then mounted onto a cell in an electrochemical measurement fixture, and pressure was applied to 80 N using a torque wrench. . m, to obtain the ionic conductivity test cell. The ionic conductivity test cell was connected to an impedance analyzer, and the resistance of the solid electrolyte pellet was measured at ambient pressure (1 atm) and room temperature (298 K) to calculate the ionic conductivity of the solid electrolyte (mS / cm).

[0161] (Neutron Powder Diffraction)

[0162] Predetermined amounts of each solid electrolyte were placed in a neutron powder diffractometer for neutron powder diffraction. The crystal structure was obtained from the resulting neutron powder diffraction pattern using the crystal structure analysis program Z-Rietveld, and the lattice constant, element positions, occupancy, and atomic displacement parameters were calculated.

[0163] The measurement system and conditions are as follows.

[0164] - Neutron Powder Diffractometer: J-PARC BL09 SPICA, a high-energy accelerator research instrument

[0165] - Neutron source: TOF (Time-of-Flight) type

[0166] - Sample amount: Approximately 0.6 g

[0167] - Measured range of d:

[0168] (Crystalline phase)

[0169] The evaluation results of the crystalline phases (crystal structures) identified by XRD patterns obtained from X-ray diffraction (XRD) measurements are shown in Table 1. Furthermore, in Figure 4 The measured XRD patterns are shown in Table 1 and... Figure 4It can be seen that virtually no impurity phases (also called "unknown phases") were observed in the solid electrolytes obtained in Preparation Examples 1 and 2, and Comparative Preparation Examples 1 and 2, and most peaks originated from the argillium sulfide phase. Sulfide-based solid electrolytes with argillium sulfide-type crystal structures containing almost no or no impurity phases were obtained. Sulfide-based solid electrolytes with high crystallinity accelerate lithium-ion hopping conduction and thus can help improve ionic conductivity.

[0170] (Lattice volume)

[0171] For the lattice constant obtained from the XRD pattern, preparation examples 1 and 2 were performed in... Within the range, while the lattice volume is Within the range. Meanwhile, in comparative preparation examples 1 and 2, where the lithium sites in sulfide-based solid electrolytes were not substituted by group 2 elements (M), the lattice constant was... And the lattice volume is This indicates that the substitution of lithium sites in a sulfide-germanium-type crystal structure with a Group 2 element (M) reduces the lattice volume by approximately 2.3%. While not bound by any particular theory, it is believed that the crystal volume of sulfide-based solid electrolytes can be altered due to the substitution of one of the two lithium sites by a Group 2 element (M) and the other becoming a lithium vacancy. It is also believed that lithium vacancies become pathways for lithium-ion hopping conduction, thus contributing to improved ionic conductivity. Furthermore, it is thought that the Group 2 element (M) substituting the lithium sites can be divalent, and the forces attracting anions around the Group 2 element (M) sites may change compared to monovalent lithium ions. Therefore, it is believed that the sulfide-based solid electrolyte undergoes a change in crystal volume, thus transforming into a structure suitable for lithium-ion hopping conduction.

[0172] For the half-width of the (311) facet of the argyrogermanium sulfide crystal structure, the half-width of Preparation Examples 1 and 2 is 0.06°. Meanwhile, the half-width of Preparation Examples 1 and 2 is 0.08°. Preparation Examples 1 and 2, as solid electrolytes containing divalent cations, exhibit smaller half-widths. It is believed that this smaller half-width corresponds to a larger crystallite size and contributes to improved ionic conductivity. Furthermore, it can be seen that the crystallinity and crystal size of the solid electrolyte are not changed by the micronization process.

[0173] [Table 1]

[0174] (Particle size distribution)

[0175] The particle size determination results are shown in Table 2 below. For the average particle size D... 50The coarse solid electrolyte powder containing divalent cations in Preparation Example 1 had a particle size of 15.1 μm, the micro solid electrolyte powder containing divalent cations in Preparation Example 2 had a particle size of 1.66 μm, and the ultrafine solid electrolyte powder containing divalent cations in Preparation Example 3 had a particle size of 14.5 μm. Furthermore, the coarse solid electrolyte powder without divalent cations in Preparation Example 1 had a particle size of 14.7 μm, and the micro solid electrolyte powder without divalent cations in Preparation Example 2 had a particle size of 1.42 μm. This indicates that coarse solid electrolyte powder can be micronized into micro solid electrolyte powder through additional wet milling.

[0176] [Table 2]

[0177] (ionic conductivity)

[0178] The results of the ionic conductivity are shown in Table 1. The coarse solid electrolyte powder containing divalent cations in Preparation Example 1 had a conductivity of 13.24 mS / cm, the micro solid electrolyte powder containing divalent cations in Preparation Example 2 had a conductivity of 4.32 mS / cm, and the ultrafine solid electrolyte powder containing divalent cations in Preparation Example 3 had a conductivity of 13.20 mS / cm. Furthermore, the coarse solid electrolyte powder without divalent cations in Preparation Example 1 had a conductivity of 9.91 mS / cm, and the micro solid electrolyte powder without divalent cations in Preparation Example 2 had a conductivity of 3.3 mS / cm. Regardless of the presence or absence of divalent cations, the coarse solid electrolyte powder exhibited higher ionic conductivity compared to the micro solid electrolyte powder. When using coarse solid electrolyte powder, it is assumed that the grain boundaries per unit volume are smaller, thus exhibiting higher ionic conductivity. Regardless of the average particle size of the solid electrolyte, the solid electrolyte containing divalent cations exhibited higher ionic conductivity compared to the solid electrolyte without divalent cations.

[0179] (Neutron Powder Diffraction)

[0180] The results of neutron powder diffraction are shown in Tables 3 and 4 below. Table 3 shows the crystal structure analysis results of the solid electrolyte coarse powder of Preparation Example 1. Table 4 shows the crystal structure analysis results of the solid electrolyte coarse powder of Preparation Example 1. In each table, the site is represented by a combination of numbers and English symbols, where the numbers represent the number of locatable positions of the element in the crystal structure, and the English symbols refer to the symmetry of the corresponding site as defined in crystallography, specified sequentially from the highest symmetry as a, b, c, d… Furthermore, g represents the occupancy of each site. Additionally, x, y, and z are parameters determined by the site and are values ​​showing the ratio of the element's position to the lattice constants in the x, y, and z directions. Furthermore, B… iso It refers to atomic displacement parameters, which represent the displacement distribution of atoms caused by thermal vibrations.

[0181] As shown in Table 3, the presence of calcium (Ca) at the 48h site of the argyrocerium sulfide crystal structure in the solid electrolyte coarse powder of Preparation Example 1 was confirmed. The occupancy (g) of calcium (Ca) at the 48h site was 0.003 ± 0.002. The doping amount of Group 2 element (M) in the solid electrolyte coarse powder of Preparation Example 1 with the crystal structure was calculated to be 0.036 ± 0.024, therefore the introduction amount (y = 0.025) falls within this range. Since calcium was not used as a raw material in the solid electrolyte coarse powder of Comparative Preparation Example 1, calcium (Ca) does not appear in the results in Table 4.

[0182] [Table 3]

[0183] Crystal structure analysis results of the solid electrolyte coarse powder prepared in Example 1

[0184] [Table 4]

[0185] Compare the crystal structure analysis results of the solid electrolyte coarse powder prepared in Example 1.

[0186] Example 1

[0187] First, 90 mg of the solid electrolyte coarse powder containing divalent cations from Preparation Example 1 was weighed, installed in a molding fixture, and pressed at 110 MPa for 1 minute to obtain solid electrolyte pellets.

[0188] Next, NCM (nickel-cobalt-manganese) positive electrode active material with a Ni content of 80 mol%, solid electrolyte micropowder containing divalent cations obtained from Preparation Example 2, and conductive material were weighed in a weight ratio of 60:35:5. These materials were mixed to obtain a positive electrode mixture.

[0189] Then, 17 mg of the positive electrode mixture was placed on one side of the solid electrolyte pellet, and planarized using a pressing needle made of SUS in a molding jig. The pressing was performed at 110 MPa for 1 minute to obtain a positive electrode active material layer formed on the solid electrolyte layer. An SUS plate serving as a positive electrode current collector was placed on the positive electrode active material layer, and another SUS plate serving as a negative electrode current collector was placed in direct contact with the solid electrolyte layer opposite the positive electrode active material layer. The resulting structure was pressed at 554 MPa for 1 minute to obtain a laminate. The resulting laminate was combined with the pressing needle made of SUS to obtain a MACOR tube cell. The obtained MACOR tube cell was installed in a cell unit, and a low-constraint pressure of approximately 0.005 MPa was applied to it to obtain an all-solid-state battery. In other words, the all-solid-state battery of Example 1 contains coarse solid electrolyte powder containing divalent cations in the solid electrolyte layer 2, and fine solid electrolyte powder containing divalent cations in the positive electrode active material layer.

[0190] Figure 1 The all-solid-state battery of Example 1 is shown. For example... Figure 1 As shown, the negative electrode current collector 1 is in direct contact with the solid electrolyte layer 2, which contains a solid electrolyte with divalent cations. The all-solid-state battery of Example 1 is in a battery precursor state before initial charging and does not contain a negative electrode active material layer. The all-solid-state battery of Example 1 is an all-solid-state battery with an anode-less structure.

[0191] Example 2

[0192] An all-solid-state battery was obtained in the same manner as in Example 1, except that in the step of preparing the solid electrolyte pellets, the solid electrolyte micropowder containing divalent cations obtained in Preparation Example 2 was used instead of the solid electrolyte coarse powder containing divalent cations obtained in Preparation Example 1. In other words, the all-solid-state battery of Example 2 contains solid electrolyte micropowder containing divalent cations in both the solid electrolyte layer 2 and the positive electrode active material layer 3.

[0193] Example 3

[0194] The all-solid-state battery was obtained in the same manner as in Example 1, except that in the step of manufacturing the all-solid-state battery, a limiting pressure of about 8 MPa was applied instead of a limiting pressure of about 0.005 MPa.

[0195] Example 4

[0196] An all-solid-state battery was obtained in the same manner as in Example 1, except that in the step of preparing the solid electrolyte pellets, the ultra-coarse solid electrolyte powder containing divalent cations obtained in Preparation Example 3 was used instead of the coarse solid electrolyte powder containing divalent cations obtained in Preparation Example 1. In other words, the all-solid-state battery of Example 4 contains ultra-coarse solid electrolyte powder containing divalent cations in the solid electrolyte layer 2 and micro solid electrolyte powder containing divalent cations in the positive electrode active material layer 3.

[0197] Comparative Example 1

[0198] A solid-state battery was obtained in the same manner as in Example 1, except that in the step of preparing the solid electrolyte pellets, the coarse solid electrolyte powder without divalent cations obtained in Comparative Preparation Example 1 was used instead of the coarse solid electrolyte powder containing divalent cations obtained in Preparation Example 1; and in the step of preparing the positive electrode mixture, the micro solid electrolyte powder without divalent cations obtained in Comparative Preparation Example 2 was used instead of the micro solid electrolyte powder containing divalent cations obtained in Preparation Example 2. In other words, as... Figure 2 As shown, the all-solid-state battery of Comparative Example 1 contains coarse solid electrolyte powder without divalent cations in the solid electrolyte layer 5, and micro solid electrolyte powder without divalent cations in the positive electrode active material layer 3.

[0199] Comparative Example 2

[0200] An all-solid-state battery was obtained in the same manner as Comparative Example 1, except that, in the steps of manufacturing the all-solid-state battery, an Ag-C interlayer was provided on the solid electrolyte layer opposite to the positive electrode active material layer, and a confinement pressure of approximately 4 MPa was applied. The Ag-C interlayer was prepared by dissolving predetermined amounts of Ag and C (carbon black) in N-methylpyrrolidone containing 7% by weight of PVDF added thereto, and coating the resulting solution onto an SUS plate. In other words, as... Figure 3 As shown, the all-solid-state battery of Comparative Example 2 contains coarse solid electrolyte powder without divalent cations in the solid electrolyte layer 5, contains micro solid electrolyte powder without divalent cations in the positive electrode active material layer 3, and provides an intermediate layer 6 between the solid electrolyte layer 5 and the negative electrode current collector 1.

[0201] [Evaluation of all-solid-state batteries]

[0202] (Charge / Discharge Test)

[0203] The obtained all-solid-state batteries were subjected to charge-discharge tests at 25°C. The voltage range was set to 4.25-3.0V, the charging conditions were set to constant current (CC) (0.05 C) - constant voltage (CV) (0.01 C cutoff), and the discharging conditions were set to CC (0.05 C). The charging and discharging capacities of each battery were obtained from the charge-discharge curves. Furthermore, the discharge capacity retention rate (%) at 25°C under the charging conditions of CC (0.05 C) - CV (0.01 C) and the discharging conditions of CC (0.05 C) was calculated using the following formula: (Discharge capacity in each cycle / Discharge capacity in the first cycle) × 100 [Evaluation Results] (Characteristics of all-solid-state batteries) Based on the capacity of the all-solid-state battery in Comparative Example 1, the relative ratio of the capacity of the all-solid-state battery in Example 1 (expressed as the relative ratio of the initial discharge capacity) is 103%.

[0204] Based on the capacity of the all-solid-state battery in Comparative Example 1, the relative ratio of the capacity of the all-solid-state battery in Example 2 (expressed as the relative ratio of the initial discharge capacity) is 103%.

[0205] Based on the capacity of the all-solid-state battery in Comparative Example 1, the relative ratio of the capacity of the all-solid-state battery in Example 3 (expressed as the relative ratio of the initial discharge capacity) is 101%.

[0206] As can be seen from the above results, compared with the all-solid-state battery of Comparative Example 1 which does not contain the sulfide solid electrolyte of the present invention, the all-solid-state batteries of Examples 1 to 3, which contain a sulfide solid electrolyte layer containing a Group 2 element and having a sulfide-germanium sulfide crystal structure, provide higher discharge capacity.

[0207] Figure 5 and Figure 6 The graph shows the discharge capacity retention of the all-solid-state batteries in Examples 1 to 4 and Comparative Examples 1 and 2, respectively. Figure 5 and Figure 6 The vertical axis scales are different from each other.

[0208] For the discharge capacity retention rate in the third cycle, Example 1 was 99.5%, Example 2 was 99.2%, Example 3 was 99.2%, Example 4 was 97.9%, Comparative Example 1 was 78.8%, and Comparative Example 2 was 92.4%.

[0209] For the discharge capacity retention rate in the 8th cycle, Example 1 had 98.6%, Example 4 had 65.5%, and Comparative Example 2 had 84.2%. In Example 4, the discharge capacity decreased after the 4th cycle. Although the ultra-coarse solid electrolyte powder used in the solid electrolyte layer of Example 4 had the same average particle size as the coarse solid electrolyte powder used in Example 1, its particle size distribution was wider. This wider particle size distribution is thought to lead to uneven lithium-ion conduction during charge and discharge, for example, due to the deterioration of the smoothness of the solid electrolyte layer surface, thus resulting in a decrease in discharge capacity. In Comparative Example 1, the discharge capacity decreased rapidly after the 4th cycle, so the discharge capacity could not be measured. In Comparative Example 2, unlike Comparative Example 1, an intermediate layer 6 was disposed between the solid electrolyte layer 5 and the negative electrode current collector. Compared with Comparative Example 1, Comparative Example 2 is considered to exhibit better cycle characteristics because the intermediate layer 6 suppresses the growth of lithium dendrites.

[0210] The results above show that, compared with the all-solid-state batteries of Comparative Examples 1 and 2, which do not contain the sulfide solid electrolyte of the present invention, the all-solid-state batteries of Examples 1 to 3, which contain a sulfide-based solid electrolyte with a Group 2 element and a sulfide-germanium sulfide crystal structure, provide higher cycle characteristics. Compared with the all-solid-state batteries of Comparative Examples 1 and 2, the all-solid-state battery of Example 4 exhibits higher cycle characteristics at a lower number of cycles.

[0211] The all-solid-state batteries of Examples 1 and 3 each contain coarse solid electrolyte powder containing divalent cations (i.e., the coarse solid electrolyte powder of Preparation Example 1) in the solid electrolyte layer; the all-solid-state battery of Example 2 contains micro solid electrolyte powder containing divalent cations (i.e., the micro solid electrolyte powder of Preparation Example 2) in the solid electrolyte layer; and the all-solid-state battery of Example 4 contains ultra-coarse solid electrolyte powder containing divalent cations (i.e., the ultra-coarse solid electrolyte powder of Preparation Example 3) in the solid electrolyte layer. As shown in Table 1, the ionic conductivity of the coarse solid electrolyte powder of Preparation Example 1 and the ultra-coarse solid electrolyte powder of Preparation Example 3 is approximately three times that of the micro solid electrolyte powder of Preparation Example 2. Figure 6As shown, the all-solid-state battery of Example 1 exhibits higher cycle characteristics compared to the all-solid-state battery of Example 2. This higher cycle characteristic of the all-solid-state battery of Example 1 is believed to be due to the high ionic conductivity of the coarse solid electrolyte powder containing divalent cations. Even though the all-solid-state battery of Example 4 contains ultra-coarse solid electrolyte powder with high ionic conductivity, it exhibits lower cycle characteristics compared to the all-solid-state battery of Example 2. The large particles (e.g., agglomerates) contained in the ultra-coarse solid electrolyte powder with a wide particle size distribution in Example 4 lead to a deterioration in the smoothness of the solid electrolyte layer surface, resulting in uneven lithium-ion conduction during charge and discharge. Typically, high confinement pressure is applied during the charge and discharge process of all-solid-state batteries to suppress the growth of lithium dendrites on the negative electrode current collector. However, from... Figure 6 As can be seen, compared with the all-solid-state battery of Example 3 subjected to a confinement pressure of approximately 8 MPa, the all-solid-state battery of Example 1 subjected to a confinement pressure of approximately 0.005 MPa exhibits higher discharge capacity and better cycle characteristics. This is attributed to the use of a solid electrolyte containing divalent cations in both the solid electrolyte layer and the positive electrode active material layer. As a result, the all-solid-state battery is able to operate under low confinement pressure.

[0212] Figure 7 This is a scanning electron microscope (SEM) image showing the calcium distribution in the all-solid-state battery of Example 1. Figure 7 The left figure shows a cross-sectional view of the all-solid-state battery before initial charging. Figure 7 The figure shows a cross-sectional view of the all-solid-state battery after initial charging. Figure 7 The right image shows a cross-sectional view of the all-solid-state battery after initial discharge. Calcium (Ca) is represented in white in each SEM image. The negative electrode current collector was stripped off for SEM observation.

[0213] from Figure 7 As shown in the left figure, before the initial charging of the all-solid-state battery, the calcium (Ca) contained in the solid electrolyte layer is distributed throughout the solid electrolyte layer. However, it should be noted that the white spots observed in the region where the current collector is stripped originate from the calcium (Ca) on the inner side of the solid electrolyte layer, and calcium (Ca) is not present in the region where the current collector is stripped.

[0214] from Figure 7 As can be seen from the middle figure, after the initial charging of the all-solid-state battery, some calcium (Ca) migrates to the interface between the negative electrode current collector and the solid electrolyte layer. From Figure 7As shown in the right figure, after the initial discharge of the all-solid-state battery, calcium (Ca) partially migrates to the interface between the positive electrode active material layer (also called the "positive electrode layer") and the solid electrolyte layer. After the second charge-discharge cycle, calcium migrates to the interface between the negative electrode current collector and the solid electrolyte layer during charging, and to the interface between the positive electrode active material layer and the solid electrolyte layer during discharging. This indicates that in the all-solid-state battery with the anode-less structure of Example 1, calcium (Ca) as a divalent cation migrates together with lithium as a charge carrier between the two electrodes.

[0215] Figure 8 These are SEM images (left) of the all-solid-state battery of Example 1 after initial charging, and a graph (right) showing the calcium line scan results. The negative electrode current collector was stripped for SEM observation.

[0216] from Figure 8 The left figure shows that during the initial charging process of the all-solid-state battery, precipitates form between the negative electrode current collector and the solid electrolyte layer. The calcium line scan (SEM-EDX analysis) results of the solid electrolyte layer-precipitates-negative electrode current collector are shown in... Figure 8 As shown in the right figure, calcium (Ca) is distributed throughout the solid electrolyte layer and the precipitate. In particular, calcium (Ca) is abundant at the interface between the precipitate and the negative electrode current collector. Since the precipitate forms between the solid electrolyte layer and the negative electrode current collector, it is believed that the precipitate improves the tight adhesion between the negative electrode current collector and the solid electrolyte layer.

[0217] Because lithium forms between the negative electrode current collector and the solid electrolyte layer during the charging process of an anode-free all-solid-state battery, it is believed that... Figure 8 The precipitates found contained lithium. Furthermore, SEM-EDX analysis suggests that… Figure 8 The precipitates appearing in the cells contain elemental calcium (Ca) or alloys or compounds of calcium (Ca) and lithium. In particular, since calcium (Ca) is present on the negative electrode current collector side of the precipitates, it is believed that the calcium (Ca) contained in the precipitates improves the tight adhesion / adhesion between the negative electrode current collector and the solid electrolyte layer. As a result, the all-solid-state battery is considered to have excellent discharge capacity and cycle characteristics, and is operable under low limiting pressure. Although further analysis is needed, it is believed that the precipitates formed between the positive electrode active material layer and the solid electrolyte layer during the discharge process of the all-solid-state battery have the same shape and characteristics as the precipitates formed between the negative electrode current collector and the solid electrolyte layer.

[0218] In existing anode-free batteries, the ion conduction and / or conductivity paths between the negative electrode current collector and the solid electrolyte layer are disrupted by lithium-containing deposits (e.g., lithium metal) formed between them after charging, leading to deterioration in ionic conductivity and cycle characteristics. However, in an all-solid-state battery according to one embodiment of the present invention, a Group 2 element contained in the solid electrolyte layer is deposited between the negative electrode current collector and the solid electrolyte layer during charging, improving their tight adhesion and thus maintaining high discharge capacity and cycle characteristics. Furthermore, in an all-solid-state battery according to one embodiment of the present invention, a Group 2 element contained in the solid electrolyte layer is deposited between the positive electrode current collector and the solid electrolyte layer during discharging, improving their tight adhesion and thus maintaining high discharge capacity and cycle characteristics. Moreover, in an all-solid-state battery according to one embodiment of the present invention, the improved tight adhesion between the solid electrolyte layer and the electrode through the deposit of a Group 2 element allows the all-solid-state battery to be driven at low limiting pressures (e.g., about 0.005 MPa).

[0219] The invention has been described above with respect to a limited number of embodiments and accompanying drawings, but the invention is not limited thereto, and it will be apparent to those skilled in the art that various modifications and alterations can be made to the invention within the scope of the technical aspects of the invention and the appended claims and their equivalents.

Claims

1. A all-solid-state battery, comprising: a positive electrode including a positive electrode active material layer; a negative electrode current collector; and a solid electrolyte layer disposed between the positive electrode and the negative electrode current collector, The all-solid-state battery does not include a negative electrode active material, in, Lithium ions are supplied from the positive electrode active material layer by charging, thereby forming a lithium metal layer as the negative electrode active material on the negative electrode current collector, and The solid electrolyte layer includes a sulfide-based solid electrolyte containing a Group 2 element and having a thiogermanate crystal structure.

2. The all-solid-state battery as described in claim 1, wherein, The negative electrode current collector and the solid electrolyte layer are in direct contact with each other.

3. The all-solid-state battery according to claim 1, in, The sulfide solid electrolyte is composed of the chemical formula Li 7-x-2y M y PS 6-x Ha x This indicates that in the chemical formula, M represents at least one element selected from Group 2 elements, Ha is at least one element selected from halogen elements, and x and y satisfy 0 < x < 2.5 and 0 < y < 0.

45.

4. The all-solid-state battery as described in claim 3, wherein, M is Ca.

5. The all-solid-state battery as described in claim 1, wherein, The all-solid-state battery does not include a reaction product of the negative electrode current collector and the sulfide-based solid electrolyte.

6. The all-solid-state battery as described in claim 1, wherein, The all-solid-state battery is pressurized at a pressure of 0.3 MPa or less in the direction in which the positive electrode, the negative electrode current collector, and the solid electrolyte layer are stacked.

7. The all-solid-state battery as described in claim 1, wherein, The positive electrode active material layer includes the sulfide-based solid electrolyte.

8. The all-solid-state battery as described in claim 1, wherein, The average particle size of the sulfide-based solid electrolyte contained in the solid electrolyte layer is larger than the average particle size of the sulfide-based solid electrolyte contained in the positive electrode active material layer.

9. The all-solid-state battery as described in claim 1, wherein, The Group 2 element is present at the 48h site of the thiogermanate crystal structure.

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