All-solid-state battery and method for manufacturing the same

Abstract

To provide an all-solid-state battery and the like capable of suppressing the reduction of a battery capacity.SOLUTION: An all-solid-state battery 100 has a structure in which a positive electrode current collector 7, a positive electrode layer 20 including a positive electrode active material 2 and a solid electrolyte 1, a solid electrolyte layer 10 including a solid electrolyte 5, a negative electrode layer 30 including a negative electrode active material 3 and a solid electrolyte 4, and a negative electrode current collector 8 are laminated in this order. The negative electrode active material 3 contains a plurality of flat-shaped active material particles each of which has a structure in which a plurality of graphite small pieces are laminated. In the cross-section of the negative electrode layer 30 cut along a thickness direction of the negative electrode layer 30, some of the plurality of particles constituting the solid electrolyte 4 are embedded in at least one of the plurality of flat active material particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to all-solid-state batteries and methods for manufacturing the same, and more particularly to all-solid-state batteries using a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, as well as methods for manufacturing the same. [Background technology]

[0002] In recent years, the development of reusable batteries has become necessary due to the increasing lightness and cordless design of electronic devices such as personal computers and mobile phones. Examples of reusable batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lead-acid batteries, and lithium-ion batteries. Among these, lithium-ion batteries are attracting attention due to their characteristics such as light weight, high voltage, and high energy density.

[0003] In the automotive sector, including electric vehicles and hybrid vehicles, the development of high-capacity rechargeable batteries is considered crucial, and the demand for lithium-ion batteries is on the rise.

[0004] Lithium-ion batteries consist of a positive electrode layer, a negative electrode layer, and an electrolyte placed between them. The electrolyte is either a liquid electrolyte or a solid electrolyte, which is obtained by dissolving a supporting salt, such as lithium hexafluoride phosphate, in an organic solvent. Currently, lithium-ion batteries that are widely used are flammable because they use an electrolyte containing an organic solvent. Therefore, materials, structures, and systems are needed to ensure the safety of lithium-ion batteries. In contrast, by using a non-flammable solid electrolyte, it is expected that the above materials, structures, and systems can be simplified, leading to increased energy density, reduced manufacturing costs, and improved productivity. Hereinafter, batteries using solid electrolytes, such as lithium-ion batteries that conduct lithium (Li) ions, will be referred to as "all-solid-state batteries."

[0005] Solid electrolytes can be broadly divided into organic solid electrolytes and inorganic solid electrolytes. Inorganic solid electrolytes generally include oxide-based, sulfide-based, and halide-based solid electrolytes. Sulfide-based and halide-based solid electrolytes have lower grain boundary resistance compared to oxide-based solid electrolytes, allowing for good performance to be obtained through powder compression molding alone, without the need for a sintering process. In recent years, research has been actively conducted on coating-type all-solid-state batteries using sulfide-based solid electrolytes, which are capable of being scaled up for larger sizes and higher capacities.

[0006] Patent Document 1 discloses a method for manufacturing an all-solid-state battery, in which a negative electrode layer is produced by pressure molding a mixture of negative electrode active material particles and solid electrolyte particles. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-138724 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] This disclosure aims to provide all-solid-state batteries and the like that suppress the decrease in battery capacity. [Means for solving the problem]

[0009] A solid-state battery according to one aspect of the present disclosure has a structure in which a positive electrode current collector, a positive electrode layer containing a positive electrode active material and a first solid electrolyte, a solid electrolyte layer containing a third solid electrolyte, a negative electrode layer containing a negative electrode active material and a second solid electrolyte, and a negative electrode current collector are stacked in this order, wherein the negative electrode active material includes a plurality of flattened active material particles having a structure in which a plurality of small pieces of graphite are stacked, and in a cross-section obtained by cutting the negative electrode layer along the thickness direction of the negative electrode layer, some of the particles of the plurality of particles constituting the second solid electrolyte are embedded in at least one of the plurality of flattened active material particles.

[0010] Furthermore, a method for manufacturing an all-solid-state battery according to one aspect of the present disclosure is a method for manufacturing an all-solid-state battery, wherein the manufacturing step of the negative electrode layer includes a mixing step of the negative electrode active material and the second solid electrolyte, which includes using a negative electrode active material containing active material particles formed by folding and granulating a plurality of small pieces of graphite, and arranging aggregates formed by the aggregation of a plurality of particles constituting the second solid electrolyte on the surface of the active material particles. [Effects of the Invention]

[0011] According to the all-solid-state battery etc. related to this disclosure, it is possible to suppress the decrease in battery capacity in the all-solid-state battery. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram showing a cross-section of an all-solid-state battery in an embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view illustrating the manufacturing method of an all-solid-state battery in an embodiment. [Figure 3A] Figure 3A is a flowchart showing the method for producing the negative electrode mixture in the embodiment. [Figure 3B] Figure 3B is a flowchart showing an alternative method for producing the negative electrode mixture in the embodiment. [Figure 4] Figure 4 is a flowchart showing the method for producing the negative electrode mixture in the comparative example. [Figure 5]FIG. 5 is a schematic diagram for explaining the change in the state of the negative electrode active material and the solid electrolyte in the comparative example. [Figure 6] FIG. 6 is a schematic diagram for explaining the change in the state of the negative electrode active material and the solid electrolyte in the embodiment. [Figure 7] FIG. 7 is an electron microscope image showing a cross section of the negative electrode layer in the embodiment.

MODE FOR CARRYING OUT THE INVENTION

[0013] (Process for arriving at one aspect of the present disclosure) The present inventors have found that the following problems occur with respect to the conventional all-solid-state battery described in the "Background Art" section.

[0014] Generally, for the purpose of improving the fluidity of the active material and the like for stabilizing the battery manufacturing process, it is mainstream to handle the active material as granulated particles formed by shaping a plurality of small pieces or the like into particles. However, in the method disclosed in Patent Document 1, when using granulated particles in which a plurality of small pieces of graphite are stacked as the negative electrode active material particles, the following two problems occur.

[0015] The first problem is that it is difficult to secure a path for lithium ions to conduct to the inside of the granulated particles. Specifically, when pressure is applied by, for example, putting the mixture of negative electrode active material particles and solid electrolyte particles into a mold after mixing, the active material particles of the negative electrode active material are crushed into flat active material particles. Here, the flat active material particles are active materials in a state where small pieces of graphite are randomly folded and granulated, and then pressed and compacted into a form in which the small pieces of graphite are oriented and laminated. Hereinafter, they will be referred to as "flat active material particles". At this time, the small pieces of graphite are laminated inside the flat active material particles. In a battery, charge and discharge performance is exhibited by inserting and desorbing lithium ions, for example, from the edge portions of the small pieces of graphite. However, if the small pieces of graphite are laminated inside the flat active material particles described above, it is difficult to secure a path for lithium ions to conduct to the inside of the flat active material particles, and the battery capacity decreases. In particular, when charging and discharging at a high rate, the battery capacity is likely to decrease.

[0016] The second problem is that in the negative electrode layer, the flat active material particles of the negative electrode active material expand and contract due to charge and discharge, resulting in peeling at the interface between the negative electrode active material and the solid electrolyte. When peeling occurs, the conduction path of lithium ions decreases, so the battery capacity decreases.

[0017] Therefore, in view of the above problems, the present disclosure provides an all-solid-state battery or the like that can suppress a decrease in battery capacity even when a negative electrode active material containing flat active material particles is used.

[0018] (Summary of the Present Disclosure) The summary of one aspect of the present disclosure is as follows.

[0019] A solid-state battery in one aspect of the present disclosure has a structure in which a positive electrode current collector, a positive electrode layer containing a positive electrode active material and a first solid electrolyte, a solid electrolyte layer containing a third solid electrolyte, a negative electrode layer containing a negative electrode active material and a second solid electrolyte, and a negative electrode current collector are stacked in this order, wherein the negative electrode active material includes a plurality of flattened active material particles having a structure in which a plurality of small pieces of graphite are stacked, and in a cross-section obtained by cutting the negative electrode layer along the thickness direction of the negative electrode layer, some of the particles of the plurality of particles constituting the second solid electrolyte are embedded in at least one of the plurality of flattened active material particles.

[0020] This allows lithium ions to be more easily transmitted to the interior of the negative electrode active material by the second solid electrolyte embedded in the flattened active material particles, thereby suppressing the decrease in battery capacity.

[0021] Furthermore, for example, in the cross-section, the depth to which some of the particles are embedded in at least one flattened active material particle may be 1 / 2 or more of the average particle diameter of the second solid electrolyte.

[0022] This makes it easier for lithium ions to be transmitted further into the negative electrode active material, further suppressing the decrease in battery capacity.

[0023] Furthermore, for example, in the cross-section, the aspect ratio, which is the ratio of the length in the long axis direction to the length in the short axis direction of at least some of the at least one flattened active material particles, may be 3 times or more.

[0024] This makes it easier for lithium ions to penetrate the graphite constituting the flattened active material particles on their surface, allowing the negative electrode active material to be effectively utilized and thus improving battery capacity.

[0025] Furthermore, for example, the volume ratio of the negative electrode active material to the total volume of the negative electrode active material and the second solid electrolyte in the negative electrode layer may be 46% or more and 96% or less, or 56% or more and 75% or less.

[0026] This makes it easier to ensure both the lithium ion conduction pathway mediated by the solid electrolyte and the electron conduction pathway mediated by the negative electrode active material within the negative electrode layer.

[0027] Furthermore, for example, the concentration of the solvent contained in the negative electrode layer may be 50 ppm or less.

[0028] As a result, the negative electrode layer contains virtually no solvent, thus suppressing the degradation of the negative electrode layer material.

[0029] Furthermore, a method for manufacturing an all-solid-state battery according to one aspect of the present disclosure is a method for manufacturing an all-solid-state battery, wherein the manufacturing step of the negative electrode layer includes a mixing step of the negative electrode active material and the second solid electrolyte, which includes using a negative electrode active material containing active material particles formed by folding and granulating a plurality of small pieces of graphite, and arranging aggregates formed by the aggregation of a plurality of particles constituting the second solid electrolyte on the surface of the active material particles.

[0030] As a result, aggregates composed of the second solid electrolyte are easily embedded in the active material particles of the negative electrode active material, thus enabling the simple manufacture of the above-mentioned all-solid-state battery.

[0031] Alternatively, for example, in the mixing step, after stirring and mixing only a portion of the second solid electrolyte used in the negative electrode layer, the remaining portion of the second solid electrolyte used in the negative electrode layer and the negative electrode active material may be added and further stirred and mixed to arrange the aggregates on the surface of the active material particles.

[0032] This allows for efficient aggregation by stirring and mixing only a portion of the second solid electrolyte, making it easier for the aggregates to be positioned on the surface of the active material particles.

[0033] The all-solid-state battery in the embodiments described below will be explained in detail. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and processes shown in the embodiments below are examples and are not intended to limit the disclosure. Furthermore, components in the embodiments below that are not described in an independent claim will be described as optional components.

[0034] Furthermore, in this specification, terms indicating relationships between elements such as parallelism, terms indicating the shape of elements such as rectangles, and numerical ranges do not represent only strict meanings, but also include substantially equivalent ranges, such as differences of a few percent.

[0035] Furthermore, each figure is a schematic diagram that has been appropriately emphasized, omitted, or had its proportions adjusted to illustrate this disclosure, and is not necessarily a strict representation of the actual shape, positional relationships, and proportions. In each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations may be omitted or simplified.

[0036] Furthermore, in this specification, the terms "upper" and "lower" in the configuration of an all-solid-state battery do not refer to the upper (vertically upward) and lower (vertically downward) directions in absolute spatial perception, but rather are terms defined by the relative positional relationship based on the stacking order in the stacked configuration.

[0037] In this specification, a cross-sectional view is a diagram showing a cross-section obtained by cutting the central part of an all-solid-state battery along the stacking direction. In this specification, the stacking direction coincides with the thickness direction of each layer of the all-solid-state battery and the normal direction of the main surface of each layer of the all-solid-state battery.

[0038] (Embodiment) <Structure> [A. All-solid-state battery] First, an overview of the all-solid-state battery in this embodiment will be described using Figure 1. Figure 1 is a schematic diagram showing a cross-section of the all-solid-state battery 100 in this embodiment. The all-solid-state battery 100 in this embodiment comprises a positive electrode current collector 7, a negative electrode current collector 8, a positive electrode layer 20 formed on the surface of the positive electrode current collector 7 closest to the negative electrode current collector 8 and containing a positive electrode active material 2 and a solid electrolyte 1, a negative electrode layer 30 formed on the surface of the negative electrode current collector 8 closest to the positive electrode current collector 7 and containing a negative electrode active material 3 and a solid electrolyte 4, and a solid electrolyte layer 10 disposed between the positive electrode layer 20 and the negative electrode layer 30 and containing a solid electrolyte 5. In other words, the all-solid-state battery 100 has a structure in which the positive electrode current collector 7, the positive electrode layer 20, the solid electrolyte layer 10, the negative electrode layer 30, and the negative electrode current collector 8 are stacked in this order.

[0039] Furthermore, the negative electrode active material 3 in this embodiment includes a plurality of flattened active material particles. Each of the plurality of flattened active material particles has a structure in which multiple small pieces of graphite are stacked. In this specification, a particle being flattened means, for example, that the aspect ratio (major axis / minor axis), which is the ratio of the length in the major axis direction (so-called major axis) to the length in the minor axis direction (so-called minor axis) of the particle, is 2 or more.

[0040] In the all-solid-state battery 100, in a cross-section obtained by cutting the negative electrode layer 30 along the thickness direction of the negative electrode layer 30 (in other words, the stacking direction of the all-solid-state battery 100), some of the particles constituting the solid electrolyte 4 are embedded in at least one of the multiple flattened active material particles. Hereinafter, the cross-section obtained by cutting the negative electrode layer 30 along the thickness direction of the negative electrode layer 30 may be referred to as the "negative electrode layer cross-section." In the negative electrode layer cross-section, the number of flattened active material particles in which some of the particles constituting the solid electrolyte 4 are embedded may be one-third or more of the multiple flattened active material particles.

[0041] Furthermore, from the viewpoint of facilitating the penetration of lithium ions into the graphite constituting the flattened active material particles, the aspect ratio of at least some of the flattened active material particles among the at least one flattened particle in which a portion of the particles constituting the solid electrolyte 4 is embedded may be 3 times or more. Alternatively, this aspect ratio may be, for example, 10 times or less.

[0042] In this specification, the length in the long axis direction is the longest distance between two parallel lines tangent to the particle contour in a plan view such as a cross-section of the negative electrode layer. The long axis direction is perpendicular to the two parallel lines that make up this longest distance. The length in the short axis direction is the distance between two parallel lines tangent to the particle contour in a plan view such as a cross-section of the negative electrode layer, perpendicular to the long axis direction. The short axis direction is perpendicular to the long axis direction.

[0043] Furthermore, in this embodiment, solid electrolyte 5 is an example of a third solid electrolyte. Solid electrolyte 1 is an example of a first solid electrolyte. Solid electrolyte 4 is an example of a second solid electrolyte.

[0044] The all-solid-state battery 100 in this embodiment is formed, for example, by the following method: A positive electrode layer 20 is formed on a positive electrode current collector 7 made of metal foil, a negative electrode layer 30 is formed on a negative electrode current collector 8 made of metal foil, and a solid electrolyte layer 10 is placed between the positive electrode layer 20 and the negative electrode layer 30. Then, the all-solid-state battery 100 is manufactured by pressing the positive electrode current collector 7 and the negative electrode current collector 8 from the outside in the stacking direction. The pressing pressure is, for example, 100 MPa or more and 1000 MPa or less. Pressing makes the filling rate of at least one layer of the solid electrolyte layer 10, positive electrode layer 20 and negative electrode layer 30 60% or more and less than 100%. The detailed manufacturing method of the all-solid-state battery 100 will be described later.

[0045] By increasing the packing ratio to 60% or more, the voids within the solid electrolyte layer 10, positive electrode layer 20, or negative electrode layer 30 are reduced, resulting in increased ion and electron conduction and improved charge-discharge characteristics. Packing ratio refers to the percentage of the total volume occupied by material, excluding voids between materials.

[0046] The pressed solid-state battery 100 is then fitted with terminals and housed in a case. Examples of cases for the solid-state battery 100 include stainless steel (SUS), iron or aluminum cases, resin cases, or aluminum laminate bags.

[0047] The following describes in detail the solid electrolyte layer 10, positive electrode layer 20, and negative electrode layer 30 of the all-solid-state battery 100 in this embodiment.

[0048] [B. Solid electrolyte layer] First, the solid electrolyte layer 10 will be described. In this embodiment, the solid electrolyte layer 10 includes a solid electrolyte 5 and may also include a binder.

[0049] [B-1. Solid electrolyte] The solid electrolyte 5 in this embodiment will now be described. Examples of solid electrolyte materials used in the solid electrolyte 5 include inorganic solid electrolytes such as sulfide-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes, which are common known materials. The solid electrolyte material has, for example, lithium ion conductivity. Any of sulfide-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes may be used as the solid electrolyte material. The type of sulfide-based solid electrolyte in this embodiment is not particularly limited. Examples of sulfide-based solid electrolytes include Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, and Li2S-P2S5. In particular, from the viewpoint of having excellent lithium ion conductivity, the sulfide-based solid electrolyte may contain Li, P, and S. Furthermore, because it has high reactivity with the binder and high bonding ability with the binder, the sulfide-based solid electrolyte may contain P2S5. Furthermore, the above description of "Li2S-P2S5" refers to a sulfide-based solid electrolyte using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0050] In this embodiment, the sulfide-based solid electrolyte material is, for example, a sulfide-based glass ceramic containing Li2S and P2S5, and the ratio of Li2S to P2S5 may be in the range of 70:30 to 80:20 in molar terms, or in the range of 75:25 to 80:20. By setting the ratio of Li2S to P2S5 within this range, it is possible to achieve a crystal structure with high lithium ion conductivity while maintaining the lithium (Li) concentration that affects battery characteristics. Furthermore, by setting the ratio of Li2S to P2S5 within this range, it is easier to secure the amount of P2S5 necessary to react with and bond with the binder.

[0051] The solid electrolyte 5 is composed of, for example, multiple particles. The average particle diameter of the solid electrolyte 5 is smaller than, for example, the average particle diameter of the negative electrode active material 3. This makes it easier to secure a contact area with the negative electrode active material 3 in the negative electrode layer 30.

[0052] Furthermore, the average particle size of the solid electrolyte 5 is, for example, between 0.2 μm and 10 μm. This ensures a contact surface with the negative electrode active material 3 in the negative electrode layer 30, while reducing the particle interface within the solid electrolyte layer 10 and minimizing the resistance component at the particle interface, thereby suppressing a decrease in the overall lithium ion conductivity of the solid electrolyte layer 10.

[0053] [B-2. Binder] The binder in this embodiment will now be described. The binder is an adhesive that does not conduct lithium ions or electrons and plays the role of bonding the materials within the solid electrolyte layer 10 to each other and to other layers. The binder in this embodiment may include a thermoplastic elastomer into which a functional group that improves adhesion strength has been introduced, and the functional group may be a carbonyl group, and from the viewpoint of improving adhesion strength, the carbonyl group may be maleic anhydride. The oxygen atom of maleic anhydride reacts with the solid electrolyte 5 to bond the solid electrolytes 5 to each other via the binder, creating a structure in which the binder is positioned between the solid electrolytes 5, and as a result the adhesion strength is improved.

[0054] Examples of thermoplastic elastomers include styrene-butadiene-styrene (SBS) and styrene-ethylene-butadiene-styrene (SEBS). These are chosen because they have high adhesion strength and high durability in terms of battery cycle characteristics. Hydrogenated thermoplastic elastomers may also be used. Using hydrogenated thermoplastic elastomers improves reactivity and binding properties, as well as solubility in the solvent used to form the solid electrolyte layer 10.

[0055] The amount of binder added is, for example, 0.01% by mass or more and 5% by mass or less, and may also be 0.1% by mass or more and 3% by mass or 0.1% by mass or more and 1% by mass or less. Adding 0.01% by mass or more of binder makes it easier for bonding via the binder to occur, and sufficient adhesion strength can be easily obtained. Furthermore, by adding 5% by mass or less of binder, it is less likely for the battery characteristics such as charge and discharge characteristics to deteriorate, and even if the physical properties of the binder such as hardness, tensile strength, and tensile elongation change in the low-temperature range, for example, the charge and discharge characteristics do not deteriorate easily.

[0056] [C. Positive electrode layer] Next, the positive electrode layer 20 in this embodiment will be described. The positive electrode layer 20 in this embodiment includes a solid electrolyte 1 and a positive electrode active material 2. The positive electrode layer 20 may further contain conductive additives such as acetylene black and Ketjenblack (registered trademark) and binders as needed to ensure electronic conductivity, but if the amount added is large, it will affect the battery performance, so it is desirable that it be in a small amount that does not affect the battery performance.

[0057] The weight ratio of the positive electrode active material 2 to the solid electrolyte 1 is, for example, in the range of 50:50 to 95:5, and may also be in the range of 70:30 to 90:10.

[0058] Furthermore, the volume ratio of the positive electrode active material 2 to the solid electrolyte 1 may be, for example, in the range of 60:40 to 90:10, or in the range of 70:30 to 85:15. This volume ratio makes it easier to ensure both lithium ion conduction paths and electron conduction paths within the positive electrode layer 20.

[0059] The positive electrode current collector 7 is made of, for example, metal foil. Examples of metal foils used include SUS, aluminum, nickel, titanium, and copper.

[0060] [C-1. Solid electrolyte] The solid electrolyte material used in solid electrolyte 1 can be arbitrarily selected from, for example, at least one of the solid electrolyte materials listed in [B-1. Solid Electrolytes] above. While there are no particular limitations on the selection of materials, a combination of materials is selected within a range that does not significantly impair lithium ion conductivity at the interface where the positive electrode active material 2 and solid electrolyte 1 come into contact, and at the interface where solid electrolyte 1 and solid electrolyte 5 come into contact. Solid electrolyte 1 is composed of, for example, multiple particles.

[0061] [C-2. Binder] Since it is the same as the binder mentioned above, it will be omitted.

[0062] [C-3. Positive electrode active material] The positive electrode active material 2 in this embodiment will now be described. As the material for the positive electrode active material 2 in this embodiment, for example, a lithium-containing transition metal oxide is used. Examples of lithium-containing transition metal oxides include LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiNiPO4, LiFePO4, LiMnPO4, and compounds obtained by substituting the transition metal of these compounds with one or two different elements. As for compounds obtained by substituting the transition metal of the above compounds with one or two different elements, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiLiLi 0.8 Co 0.15 Al 0.05 O2, LiLiLi 0.5 Mn 1.5 Known materials such as O2 are used. The positive electrode active material 2 may be used alone or in combination of two or more materials.

[0063] Furthermore, the positive electrode active material 2 is composed of multiple particles. Each particle of the positive electrode active material 2 is a granulated particle formed by the aggregation of multiple primary particles made of the above material. In this specification, these granulated particles are referred to as particles of the positive electrode active material 2.

[0064] The average particle diameter of the positive electrode active material 2 is not particularly limited, but for example, it is between 1 μm and 10 μm. Furthermore, the particle diameter distribution of the positive electrode active material 2 is such that, for example, more than 80% of the total particles are located within ±30% of the average particle diameter.

[0065] [D. Negative electrode layer] Next, the negative electrode layer 30 in this embodiment will be described. The negative electrode layer 30 in this embodiment includes a solid electrolyte 4 and a negative electrode active material 3. The negative electrode layer 30 may further contain conductive additives such as acetylene black and Ketjenblack, as well as binders, if necessary to ensure electronic conductivity. However, if the amount added is large, it will affect the battery performance, so it is desirable that it be in a small amount that does not affect the battery performance. The ratio of negative electrode active material 3 to solid electrolyte 4 may be, for example, in the range of 95:5 to 40:60 by weight, or in the range of 70:30 to 50:50. Alternatively, the ratio of negative electrode active material 3 to solid electrolyte 4 may be, for example, in the range of 96:4 to 46:54 by volume, or in the range of 75:25 to 56:44. In other words, the volume ratio of the negative electrode active material 3 to the total volume of the negative electrode active material 3 and the solid electrolyte 4 is, for example, 46% to 96%, and may also be 56% to 75%. This volume ratio makes it easier to ensure both the lithium ion conduction pathway carried out by the solid electrolyte 4 and the electron conduction pathway carried out by the negative electrode active material 3 within the negative electrode layer 30.

[0066] The negative electrode current collector 8 is made of, for example, metal foil. Examples of metal foils used include SUS, copper, and nickel.

[0067] [D-1. Solid electrolyte] The solid electrolyte material used for the solid electrolyte 4 is not particularly limited, and for example, at least one or more are arbitrarily selected from the solid electrolyte materials listed in [B-1. Solid electrolyte] described above. From the viewpoint of easily forming the aggregate 13 described later, the solid electrolyte material used for the solid electrolyte 4 may be a sulfide-based solid electrolyte or a halide-based solid electrolyte. The solid electrolyte 4 is composed of, for example, a plurality of particles.

[0068] [D-2. Binder] Since it is the same as the binder described above, it is omitted.

[0069] [D-3. Anode active material] The anode active material 3 in the present embodiment will be described. As the material of the anode active material 3 in the present embodiment, a carbon material (active material particles) granulated in a state where a plurality of small pieces of graphite are folded and overlapped is used. That is, the anode active material 3 includes a plurality of granulated active material particles. As the granulated active material particles, known materials and granulation methods are used. The granulated active material particles are, for example, non-spherical in shape having a major axis direction and a minor axis direction. Although details will be described later, the granulated active material particles become flat active material particles by being pressed in the manufacturing process of the all-solid-state battery 100.

[0070] Also, if necessary, the anode active material 3 may further contain known anode active material materials such as SiO x , lithium, indium, tin, silicon, etc.

[0071] Also, the average particle diameter of the granulated active material particles is not particularly limited, but for example, it is 1 μm or more and 15 μm or less. Here, the particle diameter is the maximum Feret diameter obtained by obtaining the maximum value of the side length of the rectangle circumscribing each active material particle in the planar image of each active material particle. The average particle diameter is the number average particle diameter obtained by obtaining the number average of the particle diameters obtained by the above method.

[0072] <Manufacturing method of all-solid-state battery> Next, the manufacturing method of the all-solid-state battery 100 in this embodiment will be described with reference to Figure 2. Specifically, the manufacturing method of the all-solid-state battery 100 comprising a solid electrolyte layer 10, a positive electrode layer 20, and a negative electrode layer 30 will be described. Figure 2 is a schematic cross-sectional view illustrating the manufacturing method of the all-solid-state battery 100.

[0073] A method for manufacturing an all-solid-state battery 100 includes, for example, a negative electrode layer deposition process, a positive electrode layer deposition process, a solid electrolyte layer deposition process, a lamination process, and a pressing process. The negative electrode layer deposition process is an example of a manufacturing process for the negative electrode layer 30. In the negative electrode layer deposition process (Figure 2(a)), the negative electrode layer 30 is formed on the negative electrode current collector 8. In the positive electrode layer deposition process (Figure 2(b)), the positive electrode layer 20 is formed on the positive electrode current collector 7. In the solid electrolyte layer deposition process (Figure 2(c) and (d)), the solid electrolyte layer 10 is prepared. In the lamination and pressing processes (Figures 2(e) and (f)), the positive electrode layer 20 formed on the positive electrode current collector 7, the negative electrode layer 30 formed on the negative electrode current collector 8, and the prepared solid electrolyte layer 10 are laminated so that the solid electrolyte layer 10 is positioned between the positive electrode layer 20 and the negative electrode layer 30, and then pressed from the outside of the positive electrode current collector 7 and the negative electrode current collector 8. Details of each process are described below.

[0074] [E. Negative electrode layer deposition process] In this embodiment, the negative electrode layer 30 film formation process (negative electrode layer film formation process) can be, for example, two methods, (1) and (2) described below.

[0075] (1) In this embodiment, a method for forming the negative electrode layer 30 can be described by a film formation process that includes a mixture preparation step, a coating step, and a coating press step. Specifically, in the mixture preparation step, for example, the negative electrode active material 3 and the solid electrolyte 4 are subjected to a stirring and mixing process, which will be described in detail below, and the resulting mixed powder is dispersed in an organic solvent. If necessary, a binder and a conductive additive (not shown) are dispersed in the organic solvent to produce a slurry of the negative electrode mixture. Then, in the coating step, the obtained negative electrode mixture is applied to the surface of the negative electrode current collector 8, and the resulting coating film is heated and dried to remove the organic solvent and / or fired. Next, in the coating press step, the dried coating film formed on the negative electrode current collector 8 is pressed. The negative electrode layer 30 is produced by this film formation process.

[0076] The method of applying the slurry is not particularly limited, but examples include known application methods such as blade coaters, gravure coaters, dip coaters, reverse coaters, roll knife coaters, wire bar coaters, slot die coaters, air knife coaters, curtain coaters, or extrusion coaters, or combinations thereof.

[0077] Examples of organic solvents used for slurry formation include heptane, xylene, and toluene, but the solvent is not limited to these. Any solvent that does not chemically react with the negative electrode active material 3 and the solid electrolyte 4 should be appropriately selected.

[0078] For drying and / or firing, any known drying or firing method using a heater or the like may be used, as long as the coating is dried and the organic solvent is removed. Similarly, there are no particular limitations on the pressing method in the coating pressing process, and any known pressing method using a press machine or the like may be used.

[0079] (2) Another method for forming the negative electrode layer 30 in this embodiment is, for example, a method of production by a film formation process including a mixture preparation step, a powder lamination step, and a powder pressing step. In the mixture preparation step, a negative electrode active material 3 and a solid electrolyte 4 in powder form (not slurryed) are prepared, and a binder and a conductive additive (not shown) are prepared as needed. The prepared materials are stirred and mixed while applying appropriate compressive and shear forces to produce a negative electrode mixture in which the negative electrode active material 3 and the solid electrolyte 4 are evenly dispersed. Details of the stirring and mixing will be described later. In the powder lamination step, the obtained negative electrode mixture in powder form is uniformly laminated on the negative electrode current collector 8 using, for example, a squeegee to obtain a laminate. In the powder pressing step, the laminate obtained in the powder lamination step is pressed to form a film.

[0080] When a solid-state battery 100 is manufactured by layering powdered negative electrode mixtures, the drying process is eliminated, resulting in lower manufacturing costs. Furthermore, no solvents that contribute to the battery performance of the solid-state battery 100 remain in the negative electrode layer 30 after film formation. For example, material degradation is not caused by residual solvents during charging and discharging of the solid-state battery 100, thus suppressing a decrease in battery characteristics. In addition, the absence of solvents in the manufacturing process prevents material degradation due to solvents. Therefore, battery performance can be improved. When a solid-state battery 100 is manufactured by layering powdered negative electrode mixtures, for example, the concentration of solvent in the negative electrode layer 30 is 50 ppm or less, and the negative electrode layer 30 is substantially free of solvent components.

[0081] Here, in both methods (1) and (2) described above, it is important to undergo a mixing step in which the negative electrode active material 3 and the solid electrolyte 4 are stirred and mixed using a dry method as preparation before film formation. Here, stirring and mixing refers to a method in which compressive and shearing forces are applied while mixing the negative electrode active material 3 and the solid electrolyte 4, and is not particularly limited to any other method. Furthermore, the purpose of the stirring and mixing step is to form aggregates in which multiple particles constituting the solid electrolyte 4 are aggregated and densely pressed, and to arrange them on the surface of the negative electrode active material 3. The specific mixing procedure will be described later.

[0082] [F. Positive electrode layer deposition process] The film deposition process for the positive electrode layer 20 in this embodiment (positive electrode layer deposition process) is basically the same as the film deposition process for the negative electrode layer 30 described in [E. Negative Electrode Layer Deposition Process] above, except that the material used is changed to one suitable for the positive electrode layer 20.

[0083] The positive electrode layer 20 may be manufactured, for example, by mixing a solid electrolyte 1, a positive electrode active material 2, and optionally a binder and a conductive additive (not shown) to form a slurry of the positive electrode mixture, applying it to the positive electrode current collector 7, and then drying it (i.e., the same method as method (1) in [E. Negative Electrode Layer Formation Process]). Alternatively, the positive electrode layer 20 may be manufactured by, for example, laminating a non-slurried powder of the positive electrode mixture onto the positive electrode current collector 7 (i.e., the same method as method (2) in [E. Negative Electrode Layer Formation Process]). Furthermore, in the film formation process for the positive electrode layer 20, a stirring and mixing step may or may not be performed.

[0084] When the positive electrode mixture is manufactured by laminating the powdered material, the drying process is eliminated, resulting in lower manufacturing costs. Furthermore, no solvent that contributes to the capacity of the all-solid-state battery remains in the positive electrode layer 20 after film formation. In other words, the same effects as when the negative electrode layer 30 is manufactured by method (2) can be obtained.

[0085] [G. Solid electrolyte layer deposition process] The solid electrolyte layer 10 in this embodiment can be prepared in the same manner as in [E. Negative Electrode Layer Formation Process] described above, except that a slurry is prepared by dispersing the solid electrolyte 5 and, if necessary, a binder in an organic solvent, and the resulting slurry is applied onto the positive electrode layer 20 and / or negative electrode layer 30 prepared above. Alternatively, the solid electrolyte layer 10 may be formed using the powdered material, similar to method (2).

[0086] In the examples shown in Figures 2(c) and 2(d), the solid electrolyte layer 10 is formed on the positive electrode layer 20 and the negative electrode layer 30. However, the solid electrolyte layer 10 may be formed on either the positive electrode layer 20 or the negative electrode layer 30. Alternatively, the solid electrolyte layer 10 may be fabricated on a substrate such as a polyethylene terephthalate (PET) film using the method described above, and the resulting solid electrolyte layer 10 may be laminated on the positive electrode layer 20 and / or the negative electrode layer 30.

[0087] [H. Lamination and Pressing Processes] In the lamination and pressing processes, the positive electrode layer 20 formed on the positive electrode current collector 7 obtained in each film formation process, the negative electrode layer 30 formed on the negative electrode current collector 8, and the solid electrolyte layer 10 are laminated such that the solid electrolyte layer 10 is positioned between the positive electrode layer 20 and the negative electrode layer 30 (lamination process). Then, the positive electrode current collector 7 and the negative electrode current collector 8 are pressed from the outside (pressing process) to obtain an all-solid-state battery 100.

[0088] The purpose of pressing is to increase the density of the positive electrode layer 20, the negative electrode layer 30, and the solid electrolyte layer 10. By increasing the density, lithium-ion conductivity and electronic conductivity can be improved in the positive electrode layer 20, the negative electrode layer 30, and the solid electrolyte layer 10, resulting in an all-solid-state battery 100 with good battery characteristics.

[0089] <Method for manufacturing the negative electrode layer> Detailed manufacturing method examples for the negative electrode layer 30 of the all-solid-state battery 100 according to this embodiment are described below, but the invention is not limited to these manufacturing method examples. Unless otherwise specified, each step is carried out, for example, in a glove box or dry room where the dew point is controlled to -45°C or below. Furthermore, although the method for manufacturing the negative electrode layer 30 using method (2) described above is described below, a similar negative electrode layer 30 can also be manufactured using method (1).

[0090] First, let's describe the materials used for the negative electrode layer 30. For example, a negative electrode mixture containing a negative electrode active material 3 and a solid electrolyte 4 is used in the manufacture of the negative electrode layer 30.

[0091] The material for the negative electrode active material 3 is selected from, for example, the materials listed in [D-3. Negative Electrode Active Material] as shown in the configuration of the all-solid-state battery in this embodiment described above. The material for the solid electrolyte 4 is selected from, for example, the materials listed in [B-1. Solid Electrolyte].

[0092] Furthermore, the specific details regarding the size of the materials used will be explained. For the negative electrode active material 3, for example, a material with an average particle diameter of 8.0 μm, where more than 80% of the particles fall within ±30% of the average particle diameter, is used. In addition, particulate material with an average particle diameter of 0.5 μm or more and 1.0 μm or less is used for the solid electrolyte 4.

[0093] Here, the amount of solid electrolyte 4 added is appropriately selected within the range of the overall mixing ratio of the negative electrode active material 3 and the solid electrolyte 4, where the mixing ratio of the negative electrode active material 3 and the solid electrolyte 4 is, for example, 75:25 to 56:44 by volume and 70:30 to 50:50 by weight.

[0094] An important aspect of the manufacturing of the negative electrode layer 30 is that the negative electrode mixture is prepared through a mixing process involving stirring, as described above. This allows for a configuration in which, during the manufacturing process of the final negative electrode layer 30, when the active material particles of the negative electrode active material 3 within the negative electrode layer 30 become flattened active material particles, solid electrolyte 4 particles are embedded on the surface of the flattened active material particles. To achieve this configuration, for example, appropriate material selection and manufacturing conditions are adjusted.

[0095] The manufacturing method for the negative electrode layer 30, including the mixing procedure in the preparation of the negative electrode mixture, will be described in detail below, comparing the embodiment with a comparative example.

[0096] (I) Method for fabricating the negative electrode layer in the embodiment First, the method for producing the negative electrode layer 30 in the embodiment will be described. Figure 3A is a flowchart of the method for producing the negative electrode mixture in the embodiment. Figure 3B is a flowchart of another method for producing the negative electrode mixture in the embodiment.

[0097] As shown in Figure 3A, in the manufacturing of the negative electrode mixture in this embodiment, the mixing step involves stirring and mixing the particles of the negative electrode active material 3 and the particles of the solid electrolyte 4 (step S11). In the mixing step, the negative electrode active material 3 containing multiple non-spherical active material particles is used. Here, stirring and mixing means mixing while applying compressive and shear forces to the materials. For example, the negative electrode active material 3 and the solid electrolyte 4 are put into a stirring and mixing device and stirred and mixed by the stirring and mixing device. As the stirring and mixing device, for example, a device in which a rotating blade for stirring and mixing is installed inside a container into which the materials are put is used. For example, a predetermined space is provided between the inner wall of the container of the stirring and mixing device and the rotating blade, and as the rotating blade rotates, compressive and shear forces are applied to the materials in the space. Stirring and mixing is not limited to stirring and mixing using such a stirring and mixing device, but any mixing in which compressive and shear forces are applied to the materials being mixed is acceptable.

[0098] By stirring and mixing the negative electrode active material 3 and the solid electrolyte 4, aggregates 13 can be formed in which multiple particles of the solid electrolyte 4 come together and are densely compressed. Details of the aggregates 13 will be described later. Through this mixing process, a negative electrode mixture containing active material particles of the negative electrode active material 3 with aggregates 13 arranged on its surface is obtained.

[0099] Note that the procedure for the mixing step in this embodiment is not limited to the example shown in Figure 3A. For example, as shown in Figure 3B, first, in the mixing step, only a portion of the solid electrolyte 4 used in the negative electrode layer 30 is stirred and mixed (step S21). Then, the negative electrode active material 3 and the remaining portion of the solid electrolyte 4 used in the negative electrode layer 30 are added to the stirred and mixed portion of solid electrolyte 4 and stirred and mixed further (step S22). As a result, in the stirring and mixing of step S21, aggregates 13 are efficiently formed because the negative electrode active material 3 is not present, and in the stirring and mixing of step S22, the aggregates 13 are more easily arranged on the surface of the active material particles of the negative electrode active material 3.

[0100] In this way, by adjusting the materials and manufacturing conditions as appropriate, the negative electrode mixture can be prepared so that the aggregates 13 are arranged on the surface of the active material particles of the negative electrode active material 3.

[0101] Next, the negative electrode mixture is used to form a negative electrode layer 30, for example, using the method described in method (2) of [E. Negative Electrode Layer Formation Process] above. Then, using this negative electrode layer 30, an all-solid-state battery 100 is manufactured by the method described above. Here, the manufacturing process is not particularly limited except for the mixing procedure of the negative electrode mixture.

[0102] (II) Method for preparing the negative electrode layer in the comparative example Next, the method for producing the negative electrode layer in the comparative example will be described. Figure 4 is a flowchart showing the method for producing the negative electrode mixture in the comparative example.

[0103] In the comparative example's method for producing the negative electrode mixture, the particles of the negative electrode active material 3 and the particles of the solid electrolyte 4 are mixed (step S51). The mixing in step S51 differs from step S11 in that substantially no compressive and shear forces are applied to the negative electrode active material 3 and the solid electrolyte 4. This yields the negative electrode mixture. In the comparative example's negative electrode mixture, since the materials of the negative electrode mixture are not stirred and mixed, aggregates 13 are not formed on the surface of the active material particles of the negative electrode active material 3.

[0104] Next, the negative electrode mixture is used to form a negative electrode layer 30, for example, using the method described in method (2) of [E. Negative Electrode Layer Formation Process] above. Then, using this negative electrode layer 30, an all-solid-state battery 100 is manufactured by the method described above. Here, the manufacturing process is not particularly limited except for the mixing procedure of the negative electrode mixture.

[0105] (III) Structure of the negative electrode mixture and negative electrode layer Next, the negative electrode mixture in the embodiment and comparative example, and the structure of the negative electrode layer 30 formed using the negative electrode mixture will be described. Specifically, the state of the negative electrode active material 3, solid electrolyte 4, and aggregate 13 will be described using Figures 5 and 6. Figure 5 is a schematic diagram illustrating the change in the state of the negative electrode active material 3 and solid electrolyte 4 in the comparative example. Figure 6 is a schematic diagram illustrating the change in the state of the negative electrode active material 3 and solid electrolyte 4 in the embodiment. In detail, Figures 5(a) and 6(a) are schematic diagrams of a range of several particles of the negative electrode active material 3 in the negative electrode mixture after mixing or stirring, immediately before the powder pressing process. Figures 5(b) and 6(b) are schematic diagrams of the negative electrode mixture shown in Figures 5(a) and 6(a) during the pressing process in the powder pressing process. Figures 5(c) and 6(c) are schematic diagrams showing the state of the negative electrode active material 3 in the negative electrode layer 30 after the powder pressing process.

[0106] In the comparative example of the negative electrode mixture, as shown in Figure 5(a), the active material particles of the negative electrode active material 3 and the particles of the solid electrolyte 4 are uniformly dispersed. Here, the particle diameter of the solid electrolyte 4 is smaller than the particle diameter of the negative electrode active material 3. Therefore, as shown in Figure 5(b), during the pressing process in the powder pressing process, the particles of the solid electrolyte 4 that do not form aggregates 13 are positioned on the surface of the negative electrode active material 3, so the pressure from the press is uniformly applied to the entire surface of the active material particles of the negative electrode active material 3 via the solid electrolyte 4. As a result, as shown in Figure 5(c), within the negative electrode layer 30, the non-spherical active material particles of the negative electrode active material are compressed in the direction of the short axis of the active material particles, deforming into a flattened shape, resulting in flattened active material particles in which the particles of the solid electrolyte 4 are not substantially embedded.

[0107] In contrast, in the negative electrode mixture of the embodiment, as shown in Figure 6(a), aggregates 13, in which multiple solid electrolyte 4 particles are densely compressed together, are arranged on and near the surface of the negative electrode active material 3. Next, as shown in Figure 6(b), during the pressing process in the powder pressing process, the aggregates 13 partially contact the surface of the active material particles of the negative electrode active material 3, and the pressure from the press is concentrated and applied to a part of the surface of the active material particles of the negative electrode active material 3 via the aggregates 13. Therefore, in the negative electrode layer 30 that is finally formed after the powder pressing process, it is possible to create a negative electrode layer 30 having a structure in which the aggregates 13 are embedded in a part of the surface of the flattened active material particles formed by the compression of the active material particles in the short axis direction by pressurization, while the solid electrolyte 4 is in contact with the other parts of the surface without being embedded.

[0108] Here, the results of cross-sectional observation of the negative electrode layer 30 prepared using the negative electrode mixture prepared by the mixing procedure shown in Figure 3B above will be explained using Figure 7. Figure 7 is an electron microscope image showing a cross-section of the negative electrode layer 30 in the embodiment. As shown in Figure 7, it can be confirmed that aggregates 13 composed of solid electrolyte 4 are embedded on the surface of the flattened active material particles of the negative electrode active material 3, which was explained using Figure 6(c).

[0109] <Examples> Next, we will describe the results of evaluating the battery characteristics of the all-solid-state battery 100 in this disclosure using examples, but this disclosure is not limited to these examples. Specifically, all-solid-state batteries were fabricated in Example 1 and Comparative Example 1, and the battery characteristics of the fabricated all-solid-state batteries were evaluated.

[0110] [Fabrication of all-solid-state batteries] (I) Example 1 Among the methods described in "(I) Method for producing a negative electrode layer in the embodiment" above, the negative electrode layer 30 was formed using the negative electrode mixture produced by the mixing step shown in Figure 3B. In this case, the mixing ratio of the negative electrode active material 3 and the solid electrolyte 4 in the formed negative electrode layer 30 was 70:30 by volume.

[0111] (II) Comparative Example 1 The all-solid-state battery in Comparative Example 1 was manufactured in the same manner as the all-solid-state battery in Example 1, except that the negative electrode layer was formed using the method described in "(II) Method for manufacturing the negative electrode layer in the comparative example" above. In this case, the mixing ratio of the negative electrode active material 3 to the solid electrolyte 4 was 70:30 by volume.

[0112] [Battery capacity evaluation] Next, the battery characteristics of the all-solid-state batteries prepared in Example 1 and Comparative Example 1 described above were evaluated. Specifically, the charge-discharge efficiency, which is an indicator of battery capacity, was evaluated and the results are shown in Table 1. The charge-discharge efficiency was evaluated under two conditions: low-rate discharge and high-rate discharge. In the evaluation of charge-discharge efficiency, charging was performed under the conditions of a cutoff voltage of 3.7V, a current rate of 0.05C, and a temperature of 25°C. Discharging was performed under the conditions of a cutoff voltage of 1.9V, a charge rate of 0.05C for the low-rate discharge, a charge rate of 1C for the high-rate discharge, and a temperature of 25°C. In the evaluation of charge-discharge efficiency, charging was started first, and the ratio of discharge capacity to charge capacity (%) was calculated as the charge-discharge efficiency.

[0113] [Table 1]

[0114] As shown in Table 1, the all-solid-state battery 100 in Example 1 has improved charge and discharge efficiency compared to the all-solid-state battery in the Comparative Example. In Example 1, the charge and discharge efficiency at high discharge rates is improved compared to Comparative Example 1. This is thought to be due to the improved battery characteristics achieved by configuring the negative electrode layer cross-section so that aggregates 13 made of solid electrolyte 4 are embedded on the surface of the flattened active material particles of the negative electrode active material 3.

[0115] Specifically, when the active material particles of the negative electrode active material 3 are pressurized and deformed into a flattened shape, the overlapping graphite fragments that make up the active material particles of the negative electrode active material 3 are crushed and rearranged. At that time, aggregates 13 can easily enter the gaps between the graphite fragments (for example, between the edges of adjacent graphite fragments). Therefore, it is thought that lithium ion conduction pathways to the edges of the graphite fragments are more easily formed. As a result, insertion and removal of lithium ions into and from the graphite fragments becomes easier even at high-rate discharges, and it is thought that the charge-discharge efficiency at high rates is improved.

[0116] Furthermore, the embedding of solid electrolyte 4 particles on the surface of the flattened active material particles of the negative electrode active material 3 has the effect of mitigating the stress of expansion and contraction of the negative electrode active material 3 due to charging and discharging, and is expected to reduce the peeling of the interface between the negative electrode active material 3 and the solid electrolyte 4.

[0117] From the viewpoint of enhancing the effects described above, the depth to which the aggregates 13 fill the surface of the flattened active material particles of the negative electrode active material 3 is, for example, 1 / 2 or more of the average particle diameter of the solid electrolyte 4. Alternatively, this depth may be 1 / 2 or more of the average particle diameter of the particles of the solid electrolyte 4 that constitute the aggregates 13.

[0118] In this embodiment, as described above, the volume ratio of the negative electrode active material 3 to the total volume of the negative electrode active material 3 and solid electrolyte 4 in the negative electrode layer 30 is, for example, 46% to 96%. By having such a volume ratio of negative electrode active material 3, the effects described using the above embodiment are easily obtained. Specifically, by having a volume ratio of 96% or less, the amount of solid electrolyte 4 relative to the negative electrode active material 3 increases, making it easier to arrange the solid electrolyte 4 across the entire surface of the negative electrode active material 3. This ensures lithium ion conduction paths within the negative electrode layer 30 and improves battery capacity at high-rate charge and discharge. Furthermore, by having a volume ratio of 46% or more, the amount of negative electrode active material 3 responsible for lithium ion insertion and removal can be ensured, thus further increasing the battery capacity. Also, from the viewpoint of further increasing the battery capacity at high-rate charge and discharge, the volume ratio may be 56% to 75%.

[0119] (Other embodiments) The all-solid-state batteries described above have been explained based on embodiments, but this disclosure is not limited to these embodiments. Without departing from the spirit of this disclosure, various modifications to the embodiments that a person skilled in the art could conceive, as well as other forms constructed by combining some of the components of the embodiments, are also included in the scope of this disclosure.

[0120] For example, in the above embodiment, an example was described in which the ions conducting in the all-solid-state battery 100 are lithium ions, but this is not limited to this. The ions conducting in the all-solid-state battery 100 may be ions other than lithium ions, such as sodium ions, magnesium ions, potassium ions, calcium ions, or copper ions. [Industrial applicability]

[0121] The all-solid-state battery described herein is expected to have various applications, such as power sources for portable electronic devices and automotive batteries. [Explanation of Symbols]

[0122] 1, 4, 5 Solid electrolytes 2 Positive active material 3. Negative active material 7 Positive current collector 8 Negative current collector 10 Solid electrolyte layer 13. Collective Cohesion 20 Positive electrode layer 30 Negative electrode layer 100 All-Solid-State Battery

Claims

1. Positive electrode current collector and A positive electrode layer comprising a positive electrode active material and a first solid electrolyte, A solid electrolyte layer containing a third solid electrolyte, A negative electrode layer containing a negative electrode active material and a second solid electrolyte, The negative electrode current collector and the other components are stacked in this order, The negative electrode active material comprises a plurality of flattened active material particles having a structure in which a plurality of small pieces of graphite are stacked, In a cross-section obtained by cutting the negative electrode layer along the thickness direction of the negative electrode layer, some of the particles among the plurality of particles constituting the second solid electrolyte are embedded in at least one of the plurality of flattened active material particles. All-solid-state battery.

2. In the cross-section, the depth to which some of the particles are embedded in at least one flattened active material particle is at least half the average particle diameter of the second solid electrolyte. The all-solid-state battery according to claim 1.

3. In the cross-section, the aspect ratio of at least a portion of the at least one flattened active material particle, which is the ratio of the length in the long axis direction to the length in the short axis direction of the flattened active material particle, is 3 times or more. The all-solid-state battery according to claim 1 or 2.

4. In the negative electrode layer, the volume ratio of the negative electrode active material to the total volume of the negative electrode active material and the second solid electrolyte is 46% or more and 96% or less. All-solid-state battery according to any one of claims 1 to 3.

5. In the negative electrode layer, the volume ratio of the negative electrode active material to the total volume of the negative electrode active material and the second solid electrolyte is 56% or more and 75% or less. The all-solid-state battery according to claim 4.

6. The concentration of the solvent contained in the negative electrode layer is 50 ppm or less. All-solid-state battery according to any one of claims 1 to 5.

7. The material of the second solid electrolyte is a sulfide-based solid electrolyte or a halogen-based solid electrolyte. All-solid-state battery according to any one of claims 1 to 6.

8. A method for manufacturing an all-solid-state battery according to any one of claims 1 to 7, The manufacturing process for the negative electrode layer is as follows: The negative electrode active material includes active material particles formed by folding multiple small pieces of graphite together, and the mixing step of the negative electrode active material and the second solid electrolyte includes a stirring and mixing process in which multiple particles constituting the second solid electrolyte are aggregated and placed on the surface of the active material particles, thereby using a negative electrode active material containing active material particles formed by folding multiple small pieces of graphite together and granulating them, and applying compressive and shearing forces. A method for manufacturing all-solid-state batteries.

9. In the mixing step, after stirring and mixing only a portion of the second solid electrolyte used in the negative electrode layer, the remaining portion of the second solid electrolyte used in the negative electrode layer and the negative electrode active material are added and further stirred and mixed to arrange the aggregates on the surface of the active material particles. A method for manufacturing an all-solid-state battery according to claim 8.

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