Solid electrolyte sheet, method for producing same, and method for producing solid-state battery

Abstract

To provide a solid electrolyte sheet having improved performance, for example, a solid electrolyte sheet capable of suppressing the growth of dendrite of metal lithium.SOLUTION: The solid electrolyte sheet includes a solid electrolyte and a binder. The solid electrolyte sheet has a first layer and a second layer disposed adjacent to the first layer in the thickness direction. When an average particle diameter of the first solid electrolytes contained in the first layer is defined as D1 and an average particle diameter of the second solid electrolytes contained in the second layer is defined as D2, D1 is equal to or less than D2. When an amount of the first binder contained in the first layer with respect to the first solid electrode is defined as B1 and an amount of the second binder contained in the second layer with respect to the second solid electrode is defined as B2, B1 is smaller than B2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte sheet and a method for manufacturing the same, and also to a method for manufacturing a solid-state battery. [Background technology]

[0002] In recent years, secondary batteries have been attracting attention as an approach to preventing global warming by reducing CO2 emissions. Among these, solid-state batteries with a solid electrolyte layer are expected to be put into practical use as they combine safety and high energy density.

[0003] The solid electrolyte layer in solid-state batteries proposed to date has been formed from a paste containing a solid electrolyte powder. In recent years, the use of a solid electrolyte sheet as the solid electrolyte layer has been proposed. For example, the present applicant previously proposed a solid electrolyte sheet having a first solid electrolyte layer containing a first sulfide having lithium ion conductivity and a second solid electrolyte layer containing a second sulfide having lithium ion conductivity, with the aim of suppressing the growth of metallic lithium dendrites (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2023 / 190647 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] The solid electrolyte sheet described in Patent Document 1 can sufficiently suppress the growth of metallic lithium dendrites. However, recent performance requirements for solid-state batteries have become increasingly stringent, and further performance improvements are being sought for solid electrolyte sheets. Therefore, an object of the present invention is to provide a solid electrolyte sheet having improved performance compared to conventional solid electrolyte sheets. [Means for solving the problem]

[0006] The present invention provides a solid electrolyte sheet comprising a solid electrolyte and a binder, the solid electrolyte sheet has a first layer and a second layer disposed adjacent to the first layer in a thickness direction, where D1 is an average particle size of the first solid electrolyte contained in the first layer and D2 is an average particle size of the second solid electrolyte contained in the second layer, D1 is equal to or less than D2, The present invention provides a solid electrolyte sheet in which B1 is smaller than B2, where B1 is the amount of a first binder contained in a first layer for a first solid electrolyte and B2 is the amount of a second binder contained in a second layer for a second solid electrolyte.

[0007] The present invention also provides a method for producing a solid electrolyte membrane comprising: preparing a first membrane including a solid electrolyte and a binder; and preparing a second membrane including a solid electrolyte and a binder; A method for manufacturing a solid electrolyte sheet, comprising bonding a first film and a second film facing each other, where D1 is an average particle size of the first solid electrolyte contained in the first film and D2 is an average particle size of the second solid electrolyte contained in the second film, D1 is equal to or less than D2, The present invention provides a method for producing a solid electrolyte sheet in which B1 is smaller than B2, where B1 is the amount of a first binder contained in a first film for a first solid electrolyte and B2 is the amount of a second binder contained in a second film for a second solid electrolyte.

[0008] The present invention also provides a battery precursor, comprising the solid electrolyte sheet having a positive electrode layer disposed on one surface thereof and a negative electrode layer disposed on the other surface thereof, The battery precursor is pressurized, and a method for producing the solid-state battery is provided.

[0009] The present invention further provides a method for manufacturing a battery, comprising: providing a first film disposed on the negative electrode layer and including a solid electrolyte and a binder; and providing a second film disposed on the positive electrode layer and including a solid electrolyte and a binder; A method for manufacturing a solid-state battery, comprising: pressing a laminate obtained by bonding a surface of a first film on which the negative electrode layer is not disposed and a surface of a second film on which the positive electrode layer is not disposed so as to face each other; where D1 is an average particle size of the first solid electrolyte contained in the first film and D2 is an average particle size of the second solid electrolyte contained in the second film, D1 is equal to or less than D2, The present invention provides a method for manufacturing a solid-state battery in which, when the amount of a first binder contained in a first film for a first solid electrolyte is B1 and the amount of a second binder contained in a second film for a second solid electrolyte is B2, B1 is smaller than B2. [Effects of the Invention]

[0010] According to the present invention, a solid electrolyte sheet having improved performance compared to conventional solid electrolyte sheets, for example, a solid electrolyte sheet capable of suppressing the growth of metallic lithium dendrites, is provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a preferred embodiment of the solid electrolyte sheet of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the steps of a preferred method for producing a solid electrolyte sheet of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing steps of a preferred method for producing a solid electrolyte sheet of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing steps of a preferred method for producing a solid electrolyte sheet of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing steps of a preferred method for producing a solid electrolyte sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will now be described based on preferred embodiments thereof with reference to the drawings. The present invention relates to a solid electrolyte sheet. As shown in Figure 1, this solid electrolyte sheet 10 has at least a first layer 11 and a second layer 12. The first layer 11 and the second layer 12 are distinguished at least by the difference in the amount of binder contained therein. The solid electrolyte sheet 10 preferably does not have any other members between the first layer 11 and the second layer 12. That is, as shown in Fig. 1, the second layer 12 is preferably disposed adjacent to the first layer 11 in the thickness direction. A third layer (not shown) may be disposed on the outer surface of the first layer 11 and / or the second layer 12 in the thickness direction. 1 is shown schematically, and the thickness of each member does not represent the actual thickness. The same applies to FIGS. 2 to 5 shown below.

[0013] The solid electrolyte sheet 10 of the present invention includes a solid electrolyte and a binder. The solid electrolyte included in the solid electrolyte sheet 10 of the present invention may be, for example, in the form of particles. The solid electrolyte sheet 10 of the present invention is preferably configured so that the average particle size of the solid electrolyte in the first layer 11 and the second layer 12 is the same or different. Furthermore, the solid electrolyte sheet 10 of the present invention is preferably configured so that the amount of binder in the first layer 11 and the second layer 12 is different. By configuring the solid electrolyte sheet 10 in this manner, the performance of the solid electrolyte sheet 10 is improved compared to conventional solid electrolyte sheets. In particular, voids are less likely to occur in the sheet, and the growth of dendrites that may extend within the voids can be suppressed. The mechanism behind this is described in detail below. Hereinafter, the solid electrolyte contained in the first layer 11 will also be referred to as the "first solid electrolyte" for convenience, and the solid electrolyte contained in the second layer 12 will also be referred to as the "second solid electrolyte" for convenience. In addition, the binder contained in the first layer 11 will also be referred to as the "first binder" for convenience, and the binder contained in the second layer 12 will also be referred to as the "second binder" for convenience.

[0014] In the solid electrolyte sheet of the present invention, when the average particle size of the first solid electrolyte contained in the first layer is D1 (μm) and the average particle size of the second solid electrolyte contained in the second layer is D2 (μm), it is preferable that D1 be equal to or less than D2, from the viewpoint of improving the performance of the solid electrolyte sheet compared to conventional solid electrolyte sheets and suppressing dendrite growth. To make this effect more pronounced, the ratio of D1 to D2, D1 / D2, is preferably, for example, 1 or less, more preferably 0.8 or less, and even more preferably 0.5 or less. On the other hand, the ratio D1 / D2 may be, for example, 0.01 or more, 0.05 or more, or 0.1 or more. In this specification, the "average particle size of the solid electrolyte" refers to the volume cumulative particle size D at 50% cumulative volume by a laser diffraction scattering particle size distribution measurement method. 50 means.

[0015] In the solid electrolyte sheet of the present invention, it is preferable that the average particle diameter D1 of the first solid electrolyte is small in order to prevent voids from being formed in the first layer. From this viewpoint, provided that D1 is equal to or smaller than D2, D1 is, for example, preferably equal to or smaller than 10 μm, more preferably equal to or smaller than 5 μm, even more preferably equal to or smaller than 3 μm, and even more preferably equal to or smaller than 1.5 μm. Furthermore, from the viewpoint of improving the strength of the solid electrolyte sheet of the present invention, D1 is, for example, preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more, provided that D1 is D2 or less.

[0016] In the solid electrolyte sheet of the present invention, it is preferable that the average particle size D2 of the second solid electrolyte be within a predetermined range in order to improve the strength of the solid electrolyte sheet. From this viewpoint, provided that D1 is equal to or less than D2, D2 is, for example, preferably equal to or greater than 0.1 μm, more preferably equal to or greater than 0.3 μm, even more preferably equal to or greater than 0.6 μm, and even more preferably equal to or greater than 1 μm. Furthermore, provided that D1 is equal to or less than D2, D2 is, for example, preferably equal to or less than 20 μm, more preferably equal to or less than 10 μm, even more preferably equal to or less than 5 μm, and even more preferably equal to or less than 3 μm.

[0017] In the solid electrolyte sheet of the present invention, one or more solid electrolytes may be used in combination as the first solid electrolyte, as long as D1 is not more than D2. Similarly, one or more solid electrolytes may be used in combination as the second solid electrolyte. In the solid electrolyte sheet of the present invention, the first solid electrolyte and the second solid electrolyte may be the same or different.

[0018] In order to set the ratio D1 / D2, D1 and D2 within the above ranges, it is preferable to adjust the particle size by, for example, pulverizing the solid electrolyte when obtaining the solid electrolyte sheet of the present invention.

[0019] Volume cumulative particle size D 50 can be measured, for example, by the following method. Specifically, using an automatic sample feeder for a laser diffraction particle size distribution analyzer ("Microtrac SDC" manufactured by Microtrac-Bell Corporation), a solid electrolyte is soaked in two drops of pure water in which 0.1% polyoxyethylene octylphenyl ether is dissolved, and the pure water is added to a 0.1% aqueous solution of SN Dispersant 5468 manufactured by San Nopco. After irradiating this aqueous solution with 40 W of ultrasound for 5 minutes, the particle size distribution is measured using a laser diffraction particle size distribution analyzer "MT3300EX II" manufactured by Microtrac-Bell Corporation, and the volume cumulative particle size D is calculated from the obtained volume-based particle size distribution chart. 50At this time, the flow rate is 65%, the "solvent refractive index" is 1.33, the particle permeability condition is "reflection", the measurement range is 0.122 μm or more and 704.0 μm or less, and the measurement time is 30 seconds.

[0020] In the solid electrolyte sheet of the present invention, when the amount of the first binder contained in the first layer for the first solid electrolyte is B1 and the amount of the second binder contained in the second layer for the second solid electrolyte is B2, it is preferable that B1 be smaller than B2, from the viewpoints of improving the performance of the solid electrolyte sheet compared to conventional solid electrolyte sheets and suppressing dendrite growth. To make this effect more pronounced, the ratio of B1 to B2, B1 / B2, is preferably 0.9 or less, more preferably 0.7 or less, and even more preferably 0.5 or less, while the ratio B1 / B2 may be, for example, 0.1 or more, 0.15 or more, or 0.2 or more.

[0021] In the solid electrolyte sheet of the present invention, it is preferable that the amount B1 of the first binder contained in the first layer relative to the first solid electrolyte is small in order to prevent voids from being formed in the first layer. From this viewpoint, provided that B1 is smaller than B2, the amount B1 relative to the first solid electrolyte is, for example, preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less. Furthermore, from the viewpoint of improving the strength of the solid electrolyte sheet of the present invention, provided that B1 is smaller than B2, B1 relative to the first solid electrolyte is, for example, preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and even more preferably 0.5 mass% or more.

[0022] In the solid electrolyte sheet of the present invention, it is preferable that the amount B2 of the second binder contained in the second layer relative to the second solid electrolyte be within a predetermined range in order to improve the strength of the solid electrolyte sheet. From this viewpoint, provided that B1 is smaller than B2, B2 is, for example, preferably 0.5 mass% or more, more preferably 0.7 mass% or more, and even more preferably 1 mass% or more relative to the second solid electrolyte. Furthermore, provided that B1 is smaller than B2, B2 is, for example, preferably 20 mass% or less, more preferably 10 mass% or less, and even more preferably 8 mass% or less relative to the second solid electrolyte.

[0023] In the solid electrolyte sheet of the present invention, B1 for the first solid electrolyte and B2 for the second solid electrolyte are approximately equal to the amount of the first binder charged for the first solid electrolyte and the amount of the second binder charged for the second solid electrolyte in the manufacturing method of the solid electrolyte sheet described below.

[0024] In the solid electrolyte sheet of the present invention, one or more binders may be used in combination as the first binder, as long as B1 is smaller than B2. Similarly, one or more binders may be used in combination as the second binder. In the solid electrolyte sheet of the present invention, the first binder and the second binder may be the same or different.

[0025] In the solid electrolyte sheet of the present invention, since D1 and D2, and B1 and B2 have the above-mentioned relationship, different roles can be assigned to the first layer and the second layer, respectively, and the performance of the solid electrolyte sheet is improved compared to conventional ones. In particular, when D1 is equal to or smaller than D2 and B1 is smaller than B2, the first layer becomes denser than the second layer, thereby making it less likely that voids will form in the first layer. As a result, the growth of dendrites that can extend into voids can be suppressed. Generally, when the average particle size of the solid electrolyte contained in a layer of a solid electrolyte sheet is small, a large amount of binder is required to increase the strength of the layer. However, in the solid electrolyte sheet of the present invention, since B1 is smaller than B2, the first layer is denser than the second layer, but tends to be more fragile. Therefore, by arranging a second layer that is more flexible and stronger than the first layer adjacent to the first layer in the thickness direction, the strength of the solid electrolyte sheet as a whole is increased. Since D1 is equal to or smaller than D2 and B1 is smaller than B2, the second layer is more flexible and stronger than the first layer. The flexibility and strength of the second layer is advantageous because it facilitates deformation of the solid electrolyte contained in each layer when the first and second layers are joined to obtain a solid electrolyte sheet. As a result, voids are less likely to form between the first and second layers, which also suppresses the growth of dendrites that could extend into the voids. This effect is significant when D1 is less than D2.

[0026] The solid electrolyte sheet of the present invention preferably has a high density, from the viewpoint of improving the performance of the solid electrolyte sheet compared to conventional solid electrolyte sheets and suppressing the growth of dendrites. In order to make this effect more pronounced, the density of the solid electrolyte sheet is, for example, 1.0 g / cm 3 It is preferable that the concentration is 1.3 g / cm or more. 3 More preferably, it is 1.5 g / cm or more. 3 More preferably, it is more than this. In order to maintain the flexibility of the solid electrolyte sheet of the present invention, the density of the solid electrolyte sheet is, for example, 2.5 g / cm 3 Preferably, it is 2.3 g / cm or less. 3 More preferably, it is 2.0 g / cm or less. 3 It is even more preferred that:

[0027] The density of a solid electrolyte sheet can be measured, for example, by the following method. First, a test piece is prepared by cutting a solid electrolyte sheet into a 10 cm x 10 cm square. The thickness and mass of the test piece are measured, and the density is calculated based on the obtained values.

[0028] In the solid electrolyte sheet of the present invention, a second layer having a low density and high rigidity is disposed adjacent to a first layer having a high density and a high flexural modulus in the thickness direction, thereby enhancing the self-supporting property of the solid electrolyte sheet. The flexural modulus is a value indicating the degree of bending that can be endured. A larger flexural modulus indicates a stronger resistance to bending, in other words, a more difficult-to-bend object. To suppress dendrite growth, a layer having a high density and a high flexural modulus is preferable. Furthermore, to ensure the self-supporting property of the solid electrolyte sheet, the solid electrolyte sheet preferably has a high density and high rigidity. A solid electrolyte sheet having an appropriate density and high resistance to bending can be determined by the flexural modulus of the solid electrolyte sheet. The reason for this is that a solid electrolyte sheet with small voids tends to have a high density and low rigidity, which in turn reduces the flexural modulus of the solid electrolyte sheet and reduces its self-supporting property. For this reason, from the viewpoint of improving the performance of the solid electrolyte sheet compared to conventional ones and suppressing the growth of dendrites, the three-point bending modulus of the solid electrolyte sheet is, for example, preferably 6.0 GPa or more, more preferably 6.5 GPa or more, and even more preferably 7.0 GPa or more. Furthermore, from the viewpoint of maintaining the flexibility of the solid electrolyte sheet of the present invention, the three-point bending modulus of the solid electrolyte sheet may be, for example, 40 GPa or less, 30 GPa or less, 20 GPa or less, or 15 GPa or less. In order to set the three-point bending modulus within the above range, it is preferable to adjust the particle sizes of the first solid electrolyte and the second solid electrolyte, and the amounts of the first binder and the second binder when obtaining the solid electrolyte sheet of the present invention. The method for measuring the three-point bending modulus will be explained in the examples below.

[0029] The solid electrolyte sheet of the present invention preferably does not include a porous support and is self-supporting. As used herein, "self-supporting" refers to the rigidity of the solid electrolyte sheet, and "having self-supporting properties" means that the solid electrolyte sheet can maintain its shape by itself without using a support member separate from the solid electrolyte sheet. In the solid electrolyte sheet of the present invention, the second layer, which has a large amount of binder, supports the first layer. For example, a test piece is prepared by cutting the solid electrolyte sheet of the present invention into a 1 cm × 1 cm square, and when adjacent corners of the test piece are gripped and the test piece is hung, if the test piece does not break under its own weight, the solid electrolyte sheet can be said to have self-supporting properties. Porous supports include those known in the art, such as woven and nonwoven fabrics made of natural or synthetic fibers, porous films made of synthetic resins, and glass fiber cloth.

[0030] The solid electrolyte sheet of the present invention is preferably thin enough to have self-supporting properties, from the viewpoint of obtaining a good battery energy density. From this viewpoint, the thickness of the solid electrolyte sheet is preferably 60 μm or less, more preferably 50 μm or less, and even more preferably 45 μm or less. From the viewpoint of maintaining self-supporting properties, the thickness of the solid electrolyte sheet is, for example, preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 5 μm or more.

[0031] As long as the solid electrolyte sheet of the present invention has self-supporting properties, it is preferable that the first layer and the second layer are each small in order to obtain a good energy density of the battery. From this viewpoint, the thickness of each of the first layer and the second layer is preferably, for example, 45 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. Furthermore, from the viewpoint of maintaining the self-supporting property of the solid electrolyte sheet of the present invention, the thickness of each of the first layer and the second layer is preferably, for example, 1 μm or more, more preferably 2 μm or more, and even more preferably 5 μm or more.

[0032] The thickness of the solid electrolyte sheet can be measured by observing the cross section of the solid electrolyte sheet under a microscope or by using a thickness gauge. The thickness of each of the first layer and the second layer can be measured, for example, by the following method. First, a cross-section of the solid electrolyte sheet is processed using a cross-section polisher, and the cross-section is observed and photographed using a scanning electron microscope (hereinafter also referred to as "SEM"). Based on the boundary line between the first layer and the second layer observed in the cross-section, the thickness of each layer is measured. Whichever measurement method is used, the thickness is measured at 10 or more different positions, and the arithmetic mean value is taken as the thickness of the solid electrolyte sheet or each layer.

[0033] In order to enhance the self-supporting property of the solid electrolyte sheet of the present invention, the basis weight is, for example, 5 g / m 2 It is preferable that the content is 10 g / m or more. 2 More preferably, it is 15 g / m or more. 2 Furthermore, from the viewpoint of maintaining a high level of electrical conductivity of the solid electrolyte sheet of the present invention, the basis weight of the solid electrolyte sheet is, for example, 80 g / m 2 Preferably, it is 75 g / m or less. 2 More preferably, it is 70 g / m or less. 2 It is even more preferred that:

[0034] In order to enhance the self-supporting property, the basis weight of the first layer and the second layer may be set independently to, for example, 1 g / m 2 It is preferable that the content is 2 g / m or more. 2 More preferably, it is 3 g / m or more. 2From the viewpoint of maintaining a high level of electrical conductivity of the solid electrolyte sheet, the basis weight of the first layer and the second layer is preferably 50 g / m or more. 2 Preferably, it is 40 g / m or less. 2 More preferably, it is 30 g / m or less. 2 It is even more preferred that:

[0035] As used herein, "basis weight" refers to the mass per unit area of ​​a solid electrolyte sheet or the mass per unit area of ​​each layer. Therefore, when two solid electrolyte sheets are made of the same material and have the same thickness but different densities (apparent densities), the solid electrolyte sheet with the higher density will have a higher basis weight. The same applies to the first and second layers. In order to set the basis weights of the solid electrolyte sheet, the first layer, and the second layer within the above ranges, it is preferable to adjust the thickness of the coating film in the method for producing the solid electrolyte sheet described below.

[0036] The solid electrolyte contained in the solid electrolyte sheet of the present invention is preferably a substance having lithium ion conductivity. Examples of such solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and organic polymer electrolytes such as polymer electrolytes. From the viewpoint of further enhancing the effects of the present invention, the solid electrolyte is preferably a sulfide solid electrolyte. The sulfide solid electrolyte may be any known sulfide solid electrolyte without any particular limitation. The sulfide solid electrolyte may be, for example, one that contains Li and S and has lithium ion conductivity.

[0037] The sulfide solid electrolyte may be any of a crystalline material, a glass ceramic, and a glass. Examples of such sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (where "X" represents one or more halogen elements), Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, and Li 10 GeP2S 12 , Li3.25 Ge 0.25 P 0.75 S4, Li7P3S 11 , Li 3.25 P 0.95 S4, Li a PS b X c (wherein "X" represents one or more halogen elements). In addition, examples of sulfide solid electrolytes include those described in WO 2013 / 099834 and WO 2015 / 001818.

[0038] In particular, it is preferable that the solid electrolyte contains a crystalline phase having an argyrodite-type crystalline structure, from the viewpoint of maintaining the electrical conductivity of the solid electrolyte sheet at a higher level. The argyrodite-type crystal structure is a crystal structure possessed by a group of compounds derived from a mineral represented by the chemical formula: AgGeS. Whether or not a solid electrolyte contains a crystalline phase having the argyrodite-type crystal structure can be confirmed by measurement using X-ray diffraction (hereinafter also referred to as "XRD"). For example, in a diffraction pattern measured by XRD using CuKα1 radiation, a crystalline phase having the argyrodite-type crystal structure exhibits characteristic diffraction peaks at 2θ = 25.5° ± 1.0°, 30.0° ± 1.0°, and 30.9° ± 1.0°. Depending on the elemental species constituting the solid electrolyte, in addition to the diffraction peaks described above, characteristic diffraction peaks may also be observed at 2θ=15.3°±1.0°, 18.0°±1.0°, 44.3°±1.0°, 47.2°±1.0°, 51.7°±1.0°, 58.3°±1.0°, 60.7°±1.0°, 61.5°±1.0°, 70.4°±1.0°, and 72.6°±1.0°. The diffraction peaks attributable to the argyrodite-type crystal structure can be identified using, for example, data from PDF No. 00-034-0688.

[0039] When the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure, the solid electrolyte contains a crystalline phase represented by the composition formula (I): Li a PS b X cFrom the viewpoint of improving lithium ion conductivity, it is preferable that X is represented by the following formula: In this case, from the viewpoint of easily deforming the solid electrolyte contained in each layer when the first layer and the second layer are joined to obtain a solid electrolyte sheet, it is preferable that X contains at least iodine element.

[0040] In composition formula (I), a, which indicates the molar ratio of Li element, is preferably, for example, 3.0 or more, more preferably 4.0 or more, and particularly preferably 5.0 or more. Furthermore, a is preferably, for example, 6.5 or less, more preferably 5.9 or less, and particularly preferably 5.6 or less. When a is within this range, the cubic argyrodite-type crystal structure at around room temperature (25°C) becomes more stable, allowing sufficient lithium ion vacancies to be introduced into the structure, resulting in effectively increasing lithium ion conductivity.

[0041] In composition formula (I), b is preferably, for example, 3.5 or more, more preferably 4.0 or more, and particularly preferably 4.2 or more. Also, b is preferably, for example, 5.5 or less, more preferably 4.9 or less, and particularly preferably 4.7 or less. When b is in this range, the argyrodite-type crystal structure becomes more stable at around room temperature (25°C), and lithium ion conductivity is effectively increased.

[0042] In composition formula (I), c is preferably, for example, 0.1 or more, more preferably 1.0 or more, more preferably 1.1 or more, and particularly preferably 1.4 or more. Also, c is preferably, for example, 2.5 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0043] When the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure, the solid electrolyte has a composition formula (II): Li 7-d PS 6-d X dIn this case, X preferably contains at least iodine element from the viewpoint of easily deforming the solid electrolyte contained in each layer when the first layer and the second layer are joined to obtain a solid electrolyte sheet. The composition represented by composition formula (II) is the stoichiometric composition of an argyrodite-type crystalline phase.

[0044] In composition formula (II), d is preferably, for example, 0.4 or more, more preferably 0.8 or more, and particularly preferably 1.2 or more, and d is preferably, for example, 2.2 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0045] When the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure, the solid electrolyte has a composition formula (III): Li 7-d-2e PS 6-d-e X d In this case, from the viewpoint of easily deforming the solid electrolyte contained in each layer when the first layer and the second layer are bonded to obtain a solid electrolyte sheet, X preferably contains at least iodine element. The argyrodite-type crystalline phase having a composition represented by composition formula (III) is produced, for example, by a reaction between an argyrodite-type crystalline phase having a composition represented by composition formula (II) and P2S5 (diphosphorus pentasulfide).

[0046] In composition formula (III), e is a value indicating the deviation of the Li2S component from the stoichiometric composition represented by composition formula (II). e is, for example, preferably -0.9 or more, more preferably -0.6 or more, and particularly preferably -0.3 or more. Furthermore, e is, for example, preferably (-d+2) or less, more preferably (-d+1.6) or less, and particularly preferably (-d+1.0) or less.

[0047] The binder contained in the solid electrolyte sheet of the present invention is preferably one that has the function of binding solid electrolyte particles together and does not affect the decrease in electrical conductivity of the solid electrolyte sheet. Examples of binders include polymeric compounds obtained using at least one polymerizable monomer selected from isobutene, styrene, butadiene, ethylene, propylene, methyl methacrylate, acrylonitrile, vinylidene chloride, and vinylidene fluoride. These polymerizable monomers may have some or all of the hydrogen atoms fluorinated.

[0048] Specific examples of binders include polyisobutene, styrene-butadiene rubber, styrene-butadiene-styrene rubber, styrene-ethylene-butadiene-styrene rubber, polymethyl methacrylate, poly(acrylonitrile-butadiene), hydrogenated poly(acrylonitrile-butadiene), and polyvinylidene fluoride. These various binders may be used singly or in combination of two or more. In these various binders, some or all of the hydrogen atoms contained therein may be fluorinated. In particular, the use of a fluorine-containing polymeric compound as a binder is preferred because it can provide the solid electrolyte sheet with sufficient self-supporting properties even when used in small amounts, and can maintain the electrical conductivity of the solid electrolyte sheet at a high level. In particular, it is preferred to use a polymeric compound containing fluorine atoms in its main chain as a binder. Examples of such binders include polyvinylidene fluoride and copolymers of vinylidene fluoride with fluorinated or non-fluorinated polyolefins.

[0049] The solid electrolyte sheet of the present invention preferably contains a predetermined amount of such a binder in order to enhance the self-supporting property of the solid electrolyte sheet. From this viewpoint, the amount of all binders contained in the solid electrolyte sheet may be, for example, 1 mass % or more, or 5 mass % or more. Furthermore, from the viewpoint of maintaining the electrical conductivity of the solid electrolyte sheet at a high level, the amount of all binders contained in the solid electrolyte sheet is, for example, preferably 10 mass % or less, and more preferably 7 mass % or less.

[0050] The solid electrolyte sheet of the present invention may be composed of only a solid electrolyte and a binder, or may contain other components in addition to the solid electrolyte and the binder, such as a dispersant. The amount of other components contained in the solid electrolyte sheet of the present invention, expressed as the total amount of all other components, may be, for example, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

[0051] Next, a preferred method for producing the solid electrolyte sheet of the present invention will be described with reference to the drawings. The solid electrolyte sheet of the present invention is preferably produced by a method comprising the following steps (a) to (c): (a) providing a first membrane and a second membrane; (b) bonding the first film and the second film together to obtain a laminate; and (c) A step of pressing the laminate to obtain a solid electrolyte sheet. Each step will be described below.

[0052] In step (a), the solid electrolyte particles and binder are mixed with a volatile liquid medium, if necessary, to prepare a first slurry for forming the first layer and a second slurry for forming the second layer. Examples of volatile liquid media include nonpolar solvents such as heptane, methylcyclohexane, and toluene, aprotic polar solvents such as methyl isobutyl ketone and cyclohexanone, and mixtures thereof. These solvents may be used singly or in combination. The volatile liquid media contained in the first slurry and the volatile liquid media contained in the second slurry may be the same or different. Examples of methods for mixing the solid electrolyte, binder, and volatile liquid medium include an ultrasonic homogenizer, a shaker, a thin film rotary mixer, a dissolver, a homomixer, a kneader, a roll mill, a sand mill, an attritor, a ball mill, a vibrator mill, and a high-speed impeller mill.

[0053] Prior to preparing the slurry, it is preferable to pulverize the solid electrolyte to adjust the particle size. This is to successfully obtain a solid electrolyte sheet in which the average particle size D1 of the first solid electrolyte contained in the first layer is equal to or smaller than the average particle size D2 of the second solid electrolyte contained in the second layer. Examples of methods for pulverizing the solid electrolyte include methods using pulverizing media such as a bead mill or a planetary ball mill. From the viewpoint of successfully obtaining a solid electrolyte sheet having D1 equal to or less than D2, the average particle size D1 of the first solid electrolyte contained in the first slurry is, for example, preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. Also, the average particle size D1 of the first solid electrolyte contained in the first slurry is, for example, preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. From the viewpoint of successfully obtaining a solid electrolyte sheet in which D1 is D2 or less, the average particle size D2 of the second solid electrolyte contained in the second slurry is, for example, preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.6 μm or more. Also, the average particle size D2 of the second solid electrolyte contained in the second slurry is, for example, preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less.

[0054] Furthermore, from the viewpoint of successfully obtaining a solid electrolyte sheet in which the amount B1 of the first binder contained in the first layer for the first solid electrolyte is smaller than the amount B2 of the second binder contained in the second layer for the second solid electrolyte, it is preferable to set the amount of the binder contained in the slurry within a predetermined range. From the viewpoint of successfully obtaining a solid electrolyte sheet in which B1 is smaller than B2, the amount B1 of the first binder relative to the first solid electrolyte in the first slurry is, for example, preferably 0.1 mass % or more, more preferably 0.2 mass % or more, and even more preferably 0.5 mass % or more. Also, the amount B1 of the first binder relative to the first solid electrolyte in the first slurry is, for example, preferably 10 mass % or less, more preferably 8 mass % or less, and even more preferably 5 mass % or less. From the viewpoint of successfully obtaining a solid electrolyte sheet in which B1 is smaller than B2, the amount B2 of the second binder relative to the second solid electrolyte in the second slurry is, for example, preferably 0.5 mass% or more, more preferably 0.7 mass% or more, and even more preferably 1 mass% or more. Also, the amount B2 of the second binder relative to the second solid electrolyte in the second slurry is, for example, preferably 20 mass% or less, more preferably 10 mass% or less, and even more preferably 8 mass% or less.

[0055] From the viewpoint of successfully forming a coating film from the first slurry and the second slurry, the amount of the volatile liquid medium contained in each of the first slurry and the second slurry is preferably, for example, 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. Also, the amount of the volatile liquid medium contained in each of the first slurry and the second slurry is preferably, for example, 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0056] 2, the first slurry is applied to a first base sheet 21a to form a coating film, thereby preparing a first film 21. The second slurry is applied to a second base sheet 22a to form a coating film, thereby preparing a second film 22. The first film 21 and the second film 22 each contain the above-mentioned solid electrolyte and binder. Examples of methods for applying the slurry include a doctor blade method, a die coating method, a gravure coating method, a spray coating method, an electrostatic coating method, a bar coating method, a method using a Baker-type applicator, etc. The thicknesses of the first layer, the second layer, and the solid electrolyte sheet can be adjusted by adjusting the amount of the slurry applied. The base sheets 21a and 22a to which the slurry is applied may be made of, for example, a resin, metal or glass film, cloth or foil. When the base sheets 21a, 22a are made of, for example, resin, examples of the resin that can be used include acrylic resin, polyester resin, cellulose derivative resin, polyvinyl acetal resin, polyvinyl butyral resin, vinyl chloride-vinyl acetate copolymer, chlorinated polyolefin, polyethylene terephthalate, and copolymers of these resin groups. When the base sheets 21a and 22a are made of metal, for example, the metal may be copper, stainless steel, aluminum, nickel, silver, gold, chromium, cobalt, tin, zinc, brass, or an alloy thereof.

[0057] The first base sheet 21a and the first film 21 are in direct contact with each other, and there may be no other layer between them, or there may be one or more other layers between them. In either case, it is preferable that the first base sheet 21a and the first film 21 are laminated so as to be peelable. The same applies to the second base sheet 22a and the second film 22. The base sheet and the film being peelably laminated means that they can be peeled off without destroying their respective structures. The peel strength between the base sheet and the film is preferably, for example, 5 N / 10 mm or less, more preferably 4 N / 10 mm or less, and particularly preferably 2 N / 10 mm or less. This is because a peel strength within this range allows the base sheet and the film to be peeled off well. For example, a method for measuring the peel strength may include cutting a laminate in which the target layers are laminated into a 10 mm wide strip and performing an interlayer peel test (180-degree peel, test speed 50 mm / min) using a tension and compression tester.

[0058] When the substrate sheet and the film are laminated in a peelable manner, the surface of the substrate sheet facing the film can be subjected to a peel treatment, such as smoothing the surface or applying a resinous release agent.

[0059] Next, the volatile liquid medium is removed from each of the first and second coating films. Even after this operation, voids remain between the solid electrolytes contained in the first and second films, so these films maintain their flexibility, and the first and second films easily deform in the next step (b). Examples of methods for removing the volatile liquid medium include warm air drying, hot air drying, infrared drying, reduced-pressure drying, and dielectric heating drying. The amount of volatile liquid medium removed from the coating film after removal may be, for example, 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less.

[0060] In step (b), as shown in FIG. 3, the first film 21 and the second film 22 are bonded together facing each other. This results in a laminate in which the first base sheet 21a, the first film 21, the second film 22, and the second base sheet 22a are laminated in this order. Because the first film 21 and the second film 22 are easily deformed due to the voids between the solid electrolytes, the voids in and between the films 21 and 22 in the laminate are small. These voids will be further reduced in the next step (c).

[0061] In step (c), as shown in Fig. 4, the laminate 23 is pressed. As described above, this step is performed for the purpose of further reducing the gaps between the films 21, 22 in the laminate, thereby obtaining a solid electrolyte sheet 10 having small gaps in the first film 21 and between the first film 21 and the second film 22. For example, the laminate 23 can be pressed in its thickness direction using a uniaxial press such as a flat press. Alternatively, the entire laminate 23 can be isotropically pressed using a roll press or CIP (cold isostatic pressing). It is preferable to pressurize the laminate at a pressure that does not crush the solid electrolyte. The hardness of the solid electrolyte varies depending on the type of solid electrolyte. However, when using a solid electrolyte containing, for example, a crystalline phase having an argyrodite-type crystal structure, whichever method is used, it is preferable to pressurize the laminate at, for example, 200 MPa or more, more preferably 400 MPa or more, and even more preferably 600 MPa or more, from the viewpoint of obtaining a solid electrolyte sheet with high self-supporting properties. There is no particular upper limit to the pressure, but it is preferable to pressurize at a pressure that does not crush the solid electrolyte. By applying a high pressure of about 900 MPa, a solid electrolyte sheet with sufficiently high self-supporting properties can be easily obtained. The laminate may be pressurized under heating. This further enhances the self-supporting property of the solid electrolyte sheet. From this viewpoint, the heating temperature may be, for example, 0°C or higher, 50°C or higher, or 100°C or higher. Furthermore, from the viewpoint of suppressing degradation of the binder, the heating temperature may be, for example, 300°C or lower, 270°C or lower, or 250°C or lower.

[0062] 5, the first base sheet 21a and the second base sheet 22a may be peeled off and removed from the solid electrolyte sheet 10. This step is preferably performed when a resin base sheet is used, but may not be performed when a metal base sheet is used. When a resin base sheet is used, peeling occurs smoothly. The reason for this is presumed to be as follows: In the pre-processing step, the first base sheet and the second base sheet expand due to pressure, and both sheets contract when the pressure is released. This is thought to result in a difference in the rate of change at the interface between the first layer and the first base sheet and the interface between the second layer and the second base sheet, which in turn makes it possible to peel the first base sheet and the second base sheet. On the other hand, when a metal sheet is used, the first base sheet and the second base sheet are less likely to elongate due to the pressure applied in the previous process. As a result, the difference in the rate of change at the interface between the first layer and the first base sheet and the interface between the second layer and the second base sheet is less likely to occur, and they are not easily peeled off. Therefore, in this case, the base sheet can be used as is in a solid-state battery as described below without peeling it off.

[0063] A solid-state battery can be manufactured using the solid electrolyte sheet obtained in this manner. The solid-state battery can include a solid electrolyte sheet, a positive electrode layer disposed on one side of the solid electrolyte sheet, and a negative electrode layer disposed on the other side of the solid electrolyte sheet. It is possible to appropriately select which of the first layer and the second layer is disposed to face the negative electrode layer. In this case, it is preferable that the first layer of the solid electrolyte sheet is disposed to face the negative electrode layer. This is because the solid electrolyte sheet of the present invention can suppress the growth of dendrites in the solid electrolyte sheet, particularly in the first layer.

[0064] The solid-state battery is preferably produced, for example, by the following method. First, a battery precursor is obtained by disposing a positive electrode layer on one side of a solid electrolyte sheet and a negative electrode layer on the other side. There are no particular restrictions on the sides of the solid electrolyte sheet on which the positive electrode layer and the negative electrode layer are disposed. From the viewpoint of further suppressing dendrite growth, it is preferable to dispose the negative electrode layer on the first layer side of the solid electrolyte sheet. The positive electrode layer contains a positive electrode active material. Examples of the positive electrode active material include oxide active materials containing lithium transition metals. Specifically, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, lithium manganese oxide (LiMn2O4), Li(Ni 0.5 Mn 1.5 )O4, Li 1+x Mn 2-x-y M ySpinel-type active materials such as O4 (wherein M is one or more selected from the group consisting of Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (Li x TiO y ), olivine-type active materials such as LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4. On the other hand, the negative electrode layer contains a negative electrode active material, such as graphite or silicon, which is capable of absorbing lithium.

[0065] Next, current collectors are placed on each side of the battery precursor, and the entire assembly is pressed and hermetically sealed in a container to obtain a solid-state battery. For example, the battery precursor can be pressed in the thickness direction using a uniaxial press such as a flat press. Alternatively, the battery precursor can be isostatically pressed using a roll press, CIP (cold isostatic pressing), or WIP (warm isostatic pressing). From the viewpoint of ease of handling, the thickness of the battery precursor after pressure application is, for example, preferably 50 μm or more, more preferably 150 μm or more, and even more preferably 250 μm or more, and the thickness of the battery precursor after pressure application is, for example, preferably 400 μm or less, more preferably 350 μm or less, and even more preferably 300 μm or less.

[0066] Alternatively, the battery precursor may be used as is without pressurization. That is, a solid-state battery can also be obtained by airtightly sealing the battery precursor itself in a container. In this case, from the viewpoint of ease of handling, the thickness of the battery precursor is preferably, for example, 100 μm or more, more preferably 150 μm or more, and even more preferably 250 μm or more. Furthermore, the thickness of the battery precursor is preferably, for example, 400 μm or less, more preferably 350 μm or less, and even more preferably 300 μm or less.

[0067] The solid-state battery can also be suitably produced by the following method. This method uses a first substrate sheet as one electrode layer and a second substrate sheet as the other electrode layer. Therefore, when obtaining a solid state battery by this method, it is preferable to use a metal substrate sheet in the above-mentioned step (a). Whether the negative electrode layer or the positive electrode layer is the first substrate sheet can be selected as appropriate. When the first substrate sheet is the negative electrode layer, a first film disposed on the negative electrode layer can be prepared by applying a first slurry to a surface of the first substrate sheet on which a mixture containing a negative electrode active material is disposed to form a coating film. When the second substrate sheet is the positive electrode layer, a second film disposed on the positive electrode layer can be prepared by applying a second slurry to a surface of the second substrate sheet on which a mixture containing a positive electrode active material is disposed to form a coating film. After removing the volatile liquid medium from each of the first film and the second film, the surface of the first film not having the negative electrode layer and the surface of the second film not having the positive electrode layer are bonded together in the same manner as in the above-mentioned step (b), thereby obtaining a laminate in which the negative electrode layer, the first film, the second film, and the positive electrode layer are stacked in this order. Next, the laminate is pressurized and airtightly sealed in a container to obtain a solid-state battery. In this method, the negative electrode layer and the positive electrode layer can be used in a solid-state battery without being peeled off from the pressed laminate. In this case, from the viewpoint of handleability, the thickness of the pressed laminate is preferably, for example, 50 μm or more, more preferably 100 μm or more, and even more preferably 150 μm or more. Furthermore, the thickness of the pressed laminate is preferably, for example, 400 μm or less, more preferably 350 μm or less, and even more preferably 300 μm or less.

[0068] Whichever method is adopted, the resulting solid-state battery has the advantages of improved performance compared to conventional batteries and suppressed dendrite growth.

[0069] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above-described embodiments. For example, the solid electrolyte sheet shown in FIG. 1 is composed of two layers, but it may be composed of three or more layers. For example, when the solid electrolyte sheet is composed of three layers, namely, layers A, B, and C, the first layer and second layer referred to in the present invention may be layers A and B, or layers B and C.

[0070] In relation to the above-described embodiments, the present invention discloses the following solid electrolyte sheet, a method for manufacturing the same, and a method for manufacturing a solid-state battery. [1] A solid electrolyte sheet comprising a solid electrolyte and a binder, the solid electrolyte sheet has a first layer and a second layer disposed adjacent to the first layer in a thickness direction, where D1 is an average particle size of the first solid electrolyte contained in the first layer and D2 is an average particle size of the second solid electrolyte contained in the second layer, D1 is equal to or less than D2, A solid electrolyte sheet, wherein B1 is smaller than B2, where B1 is the amount of a first binder contained in a first layer for a first solid electrolyte and B2 is the amount of a second binder contained in a second layer for a second solid electrolyte.

[0071] [2] The solid electrolyte sheet according to [1], wherein the first solid electrolyte has an average particle size D1 of 0.05 μm or more and 10 μm or less. [3] The solid electrolyte sheet according to [1] or [2], wherein the second solid electrolyte has an average particle size D2 of 0.1 μm or more and 20 μm or less. [4] [3] The solid electrolyte sheet according to any one of [1] to [3], wherein the amount B1 of the first binder contained in the first layer relative to the first solid electrolyte is 0.1 mass % or more and 10 mass % or less. [5] [4] The solid electrolyte sheet according to any one of [1] to [4], wherein the amount B2 of the second binder contained in the second layer relative to the second solid electrolyte is 0.5 mass % or more and 20 mass % or less. [6] [6] The solid electrolyte sheet according to any one of [1] to [5], which does not include a porous support and has self-supporting properties.

[0072] [7] The solid electrolyte sheet according to any one of [1] to [6], which has a three-point bending modulus of elasticity of 6.0 GPa or more. [8] [7] A solid-state battery comprising: the solid electrolyte sheet according to any one of [1] to [7]; a positive electrode layer disposed on one surface of the solid electrolyte sheet; and a negative electrode layer disposed on the other surface of the solid electrolyte sheet. [9] [9] The solid-state battery according to [8], wherein the first layer of the solid electrolyte sheet is disposed so as to face the negative electrode layer.

[10] providing a first membrane containing a solid electrolyte and a binder, and a second membrane containing a solid electrolyte and a binder; A method for manufacturing a solid electrolyte sheet, comprising bonding a first film and a second film facing each other, where D1 is an average particle size of the first solid electrolyte contained in the first film and D2 is an average particle size of the second solid electrolyte contained in the second film, D1 is equal to or less than D2, A method for producing a solid electrolyte sheet, wherein B1 is smaller than B2, where B1 is the amount of a first binder contained in a first film for a first solid electrolyte, and B2 is the amount of a second binder contained in a second film for a second solid electrolyte.

[11] A battery precursor is formed by disposing a positive electrode layer on one surface of the solid electrolyte sheet produced by the method according to

[10] and disposing a negative electrode layer on the other surface of the solid electrolyte sheet; The battery precursor is pressurized.

[12] providing a first film disposed on the negative electrode layer and including a solid electrolyte and a binder, and a second film disposed on the positive electrode layer and including a solid electrolyte and a binder; A method for manufacturing a solid-state battery, comprising: pressing a laminate obtained by bonding a surface of a first film on which the negative electrode layer is not disposed and a surface of a second film on which the positive electrode layer is not disposed so as to face each other; where D1 is an average particle size of the first solid electrolyte contained in the first film and D2 is an average particle size of the second solid electrolyte contained in the second film, D1 is equal to or less than D2, A method for manufacturing a solid-state battery, wherein B1 is smaller than B2, where B1 is the amount of a first binder contained in a first film for a first solid electrolyte, and B2 is the amount of a second binder contained in a second film for a second solid electrolyte.

[13] The manufacturing method according to

[11] or

[12] , wherein the battery precursor is pressed by hot isostatic pressing, cold isostatic pressing, roll pressing, or flat pressing. [Example]

[0073] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0074] Example 1 (a) Process The first solid electrolyte and the second solid electrolyte are each formed of a material having the composition formula Li 5.4 PS 4.4 Cl 0.8 Br 0.8 A lithium ion conductive sulfide powder was prepared, which contains a crystalline phase represented by the formula (I) and has an argyrodite-type crystal structure. The average particle size of this powder is shown in Table 1. Furthermore, a fluorine-containing polymer compound polymerized using at least vinylidene fluoride as a polymerizable monomer was used as the first binder and the second binder. Butyl butyrate was used as the volatile liquid medium. A first slurry was obtained by mixing a first solid electrolyte, a first binder, and a volatile liquid medium so that the ratio of the first binder to the first solid electrolyte in the slurry was 2%. A second slurry was obtained by mixing a second solid electrolyte, a second binder, and a volatile liquid medium so that the ratio of the second binder to the second solid electrolyte in the slurry was 7%. The amount of the volatile liquid medium in each slurry was 47%. The first slurry was applied to a 38 μm-thick polyethylene terephthalate (PET) first substrate sheet using a doctor blade with a gap of 70 μm to form a first coating film. The second slurry was similarly applied to form a second coating film. These films were then vacuum dried at 120°C.

[0075] (b) Process The first film and the second film were laminated together facing each other to obtain a laminate.

[0076] (c) Process The laminate was pressed at 700 MPa using a CIP (manufactured by Kobe Steel, Ltd.) at 25° C. After pressing, the laminate was peeled off from the first base sheet and the second base sheet to obtain a solid electrolyte sheet.

[0077] Example 2 The average particle size of the first solid electrolyte was changed as shown in Table 1. A solid electrolyte sheet was obtained in the same manner as in Example 1 except for this.

[0078] Example 3 Li as the first solid electrolyte 5.4 PS 4.4 Cl 1.5 I 0.1 The average particle size of the first solid electrolyte was changed as shown in Table 1. A solid electrolyte sheet was obtained in the same manner as in Example 1 except for this.

[0079] [Reference example 1] The average particle size of the first solid electrolyte was changed as shown in Table 1. The first solid electrolyte, the first binder, and the volatile liquid medium were mixed so that the amount of the first binder relative to the first solid electrolyte in the slurry was 7% to obtain a first slurry. A solid electrolyte sheet was obtained in the same manner as in Example 1 except for this.

[0080] 〔evaluation〕 The thickness, density, and basis weight of the solid electrolyte sheets obtained in the Examples and Reference Examples were measured using the methods described above. The compressibility, three-point bending modulus, and ionic conductivity of the solid electrolyte sheets were also measured using the following methods. Furthermore, solid-state batteries were fabricated using the following method, and the presence or absence of short circuits was evaluated. The results are shown in Table 1.

[0081] [Compression ratio] In step (c), the compression ratio was calculated from the thickness of the laminate before and after pressing using CIP according to the following formula (1). The results are shown in Table 1. A higher compression ratio indicates fewer voids in the solid electrolyte sheet. Compression rate (%) = thickness of laminate before pressing using CIP / thickness of laminate after pressing using CIP (1)

[0082] [Three-point bending elastic modulus] Three-point bending measurements were performed based on JIS K 7171: 2016. The test specimen dimensions were 5 mm × 10 mm.

[0083] [Ionic Conductivity] The lithium ion conductivity of the solid electrolyte sheets obtained in the examples and comparative examples was measured using a high-performance electrochemical measurement system VSP-300 manufactured by Biologic Corp. The measurement conditions were an AC impedance method at a temperature of 25°C, a frequency of 100 MHz to 7 MHz, and an amplitude of 100 mV.

[0084] [Compression ratio] (1) Manufacturing of solid-state batteries NCM622 (LiNi) was used as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2) was used. The positive electrode active material and solid electrolyte (Li5.4 PS 4.4 Cl 0.8 Br 0.8 ), a conductive additive, and a binder (PTFE) were mixed in a mass ratio of 79:18:1:2 and stretched to form a film, which was then pressed onto the surface of an aluminum current collector to produce a positive electrode layer. Separately from this operation, acetylene black and silver powder were mixed in a mixing ratio of 80:20, and a solvent was added to prepare a slurry. The slurry was then applied to the surface of a current collector made of SUS to form a coating film with a thickness of 10 μm, thereby producing a negative electrode layer. A battery precursor was fabricated by placing a positive electrode layer on one side of a solid electrolyte sheet and a negative electrode layer on the other side. A CIP was used to apply a pressure of 700 MPa to this battery precursor to fabricate a solid-state battery. (2) Presence or absence of a short circuit The solid-state battery obtained in (1) was charged at a constant current of 0.1 C to 4.3 V and then discharged at a constant current of 0.1 C to 2.5 V in a 60°C environment, and the presence or absence of a short circuit was observed after three cycles. The results are shown in Table 1. The 1.0 C current was 3.5 mA / cm. 2 It was decided. [Table 1]

[0085] As is clear from the results shown in Table 1, the solid electrolyte sheets of the Examples have higher ionic conductivity than the solid electrolyte sheets of the Reference Examples. Furthermore, the battery fabricated using the solid electrolyte sheet of the Example did not short-circuit during the above-mentioned charge and discharge, whereas the battery fabricated using the solid electrolyte sheet of the Reference Example short-circuited during the first charge and discharge. [Explanation of symbols]

[0086] 10 Solid electrolyte sheet 11 First Layer 12 Second Layer 21 First membrane 21a First base sheet 22 Second membrane 22a Second base sheet 23 Laminate

Claims

1. A solid electrolyte sheet comprising a solid electrolyte and a binder, the solid electrolyte sheet has a first layer and a second layer disposed adjacent to the first layer in a thickness direction, The average particle diameter of the first solid electrolyte contained in the first layer is D １ and the average particle diameter of the second solid electrolyte contained in the second layer is D ２ When this is done, D １ D ２ is as follows: The amount of the first binder contained in the first layer for the first solid electrolyte is B １ and the amount of the second binder contained in the second layer for the second solid electrolyte is B ２ When this is done, B １ is B ２ A solid electrolyte sheet, smaller than

2. Average particle size D of the first solid electrolyte １ The solid electrolyte sheet according to claim 1, wherein the thickness is 0.05 μm or more and 10 μm or less.

3. Average particle size D of the second solid electrolyte ２ The solid electrolyte sheet according to claim 1 or 2, wherein the thickness is 0.1 μm or more and 20 μm or less.

4. Amount B of the first binder contained in the first layer for the first solid electrolyte １ The solid electrolyte sheet according to claim 1 or 2, wherein the content of SiO2 is 0.1 mass % or more and 10 mass % or less.

5. Amount B of the second binder contained in the second layer for the second solid electrolyte ２ The solid electrolyte sheet according to claim 1 or 2, wherein the content of SiO 2 is 0.5 mass % or more and 20 mass % or less.

6. 3. The solid electrolyte sheet according to claim 1, which does not include a porous support and has self-supporting properties.

7. 3. The solid electrolyte sheet according to claim 1, wherein the three-point bending modulus is 6.0 GPa or more.

8. 3. A solid state battery comprising: the solid electrolyte sheet according to claim 1; a positive electrode layer disposed on one surface of the solid electrolyte sheet; and a negative electrode layer disposed on the other surface of the solid electrolyte sheet.

9. The solid-state battery according to claim 8 , wherein the first layer of the solid electrolyte sheet is disposed so as to face the negative electrode layer.

10. providing a first membrane including a solid electrolyte and a binder, and a second membrane including a solid electrolyte and a binder; A method for manufacturing a solid electrolyte sheet, comprising bonding a first film and a second film facing each other, The average particle diameter of the first solid electrolyte contained in the first film is defined as D １ and the average particle diameter of the second solid electrolyte contained in the second film is D ２ When this is done, D １ D ２ is as follows: The amount of the first binder contained in the first membrane for the first solid electrolyte is B １ and the amount of the second binder contained in the second membrane for the second solid electrolyte is B ２ When this is done, B １ is B ２ A method for manufacturing a solid electrolyte sheet having a size smaller than 1000 nm.

11. a positive electrode layer is disposed on one surface of the solid electrolyte sheet produced by the method according to claim 10, and a negative electrode layer is disposed on the other surface of the solid electrolyte sheet to form a battery precursor; The battery precursor is pressurized.

12. providing a first film disposed on the negative electrode layer and including a solid electrolyte and a binder, and a second film disposed on the positive electrode layer and including a solid electrolyte and a binder; A method for manufacturing a solid-state battery, comprising: pressing a laminate obtained by bonding a surface of a first film on which the negative electrode layer is not disposed and a surface of a second film on which the positive electrode layer is not disposed so as to face each other; The average particle diameter of the first solid electrolyte contained in the first film is defined as D １ and the average particle diameter of the second solid electrolyte contained in the second film is D ２ When this is done, D １ D ２ is as follows: The amount of the first binder contained in the first membrane for the first solid electrolyte is B １ and the amount of the second binder contained in the second membrane for the second solid electrolyte is B ２ When this is done, B １ is B ２ How to make a solid-state battery that is smaller than

13. The method according to claim 11 or 12, wherein the battery precursor is pressed by hot isostatic pressing, cold isostatic pressing, roll pressing, or flat pressing.

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