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

Abstract

A method for manufacturing a solid electrolyte sheet comprises a step in which a precursor (20) of a solid electrolyte sheet (40) containing a solid electrolyte powder and a binder is interposed between a pair of clamping members (11), (12), and the precursor (20) is pressed via the clamping members (11), (12). The clamping members (11, 12) each independently have a proof stress (offset method) of 100 MPa or higher as measured in conformance with JIS Z 2241. It is preferable that the clamping members (11, 12) each independently have a total elongation at break of 40% or less as measured in conformance with JIS Z 2241.

Description

Solid electrolyte sheet, method of manufacturing the same, and method of manufacturing a solid-state battery

[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.

[0002] In recent years, CO ２ Secondary batteries are 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 with 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. Instead of this type of solid electrolyte layer, the use of a solid electrolyte sheet has been proposed. For example, Patent Document 1 describes a method for obtaining a solid electrolyte sheet by roll-pressing a laminate formed by adhering an adhesive resin made of an acrylic thermoplastic resin to one side of a nonwoven fabric and then adhering a solid electrolyte material to the adhesive resin.

[0004] JP 2015-153466 A

[0005] In lithium secondary batteries, which are one type of solid-state battery, repeated charging and discharging of the battery can cause metallic lithium dendrites to form on the negative electrode. Since dendrite formation can cause short circuits in the battery, it is desirable to suppress its formation. Patent Document 1 mentioned above does not consider the formation of dendrites. An object of the present invention is to provide a solid electrolyte sheet with improved performance compared to conventional ones.

[0006] The present invention provides a method for manufacturing a solid electrolyte sheet, comprising: interposing a precursor of a solid electrolyte sheet containing a solid electrolyte powder and a binder between a pair of pressing members; and applying pressure to the precursor via the pressing members, wherein the pressing members each independently have a yield strength (offset method) of 100 MPa or more as measured in accordance with JIS Z2241.

[0007] The present invention also provides a method for manufacturing a solid state battery, which comprises pressurizing a battery precursor including a solid electrolyte sheet precursor containing a solid electrolyte powder and a binder, a positive electrode layer disposed on one surface of the precursor, and a negative electrode layer disposed on the other surface of the precursor, wherein the positive electrode layer and the negative electrode layer each independently have a proof stress (offset method) of 100 MPa or more as measured in accordance with JIS Z2241.

[0008] The present invention also provides a solid electrolyte sheet comprising a solid electrolyte powder and a binder, the solid electrolyte sheet having a three-point bending modulus of elasticity of 6 GPa or more and 40 GPa or less.

[0009] Fig. 1 is a schematic diagram showing one step in a method for manufacturing a solid electrolyte sheet of the present invention. Fig. 2 is a schematic diagram showing a step subsequent to the step shown in Fig. 1. Fig. 3 is a schematic diagram showing a step subsequent to the step shown in Fig. 2. Fig. 4 is a schematic diagram showing a step subsequent to the step shown in Fig. 3. Fig. 5 is a schematic diagram showing one step in a method for manufacturing a solid battery of the present invention. Fig. 6 is a schematic diagram showing a step subsequent to the step shown in Fig. 5.

[0010] The present invention will now be described based on preferred embodiments with reference to the drawings. First, a method for producing a solid electrolyte sheet of the present invention will be described. A solid electrolyte sheet is preferably produced by a method comprising the following steps (a) to (c) in this order: (a) preparing a precursor of a solid electrolyte sheet containing a solid electrolyte powder and a binder; (b) interposing the precursor between a pair of clamping members; (c) pressurizing the precursor via the clamping members to obtain a solid electrolyte sheet; and (d) peeling the clamping members from each side of the solid electrolyte sheet. Each step will be described below.

[0011] In step (a), a solid electrolyte powder and a binder are mixed with a volatile liquid medium, if necessary, to prepare a precursor slurry for forming a solid electrolyte sheet precursor. Examples of the volatile liquid medium include nonpolar solvents such as heptane, methylcyclohexane, and toluene, aprotic polar solvents such as methyl isobutyl ketone and cyclohexanone, and mixtures thereof. These volatile solvents can be used alone or in combination.

[0012] Examples of a method for mixing the solid electrolyte, the binder, and the volatile liquid medium used as needed include methods using 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.

[0013] Prior to preparing the precursor preparation slurry, it is preferable to pulverize the solid electrolyte to adjust the particle size, from the viewpoint of producing a solid electrolyte sheet having the desired ion conductivity. Examples of methods for pulverizing the solid electrolyte include methods using pulverization media such as a bead mill. From the viewpoint of successfully obtaining a solid electrolyte sheet having the desired ion conductivity, the particle size of the solid electrolyte is preferably, for example, 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. From the same viewpoint, the particle size of the solid electrolyte is preferably, for example, 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. In this specification, the term "particle size" refers to the volume cumulative particle size D at 50% cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method. ５０ means.

[0014] From the viewpoint of successfully forming a coating film using the slurry, the proportion of the solid electrolyte contained in the precursor preparation slurry is, for example, preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. From the same viewpoint, the proportion of the solid electrolyte contained in the precursor preparation slurry is, for example, preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0015] The binder contained in the precursor preparation slurry is used for the purpose of enhancing the self-supporting property of the target solid electrolyte sheet. From this viewpoint, the proportion of the binder contained in the precursor preparation 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, relative to the mass of the solid electrolyte. The higher the proportion of the binder relative to the mass of the solid electrolyte, the higher the self-supporting property of the solid electrolyte sheet, but the ionic conductivity tends to be insufficiently improved. From this viewpoint, the proportion of the binder contained in the precursor preparation slurry is, for example, preferably 20 mass % or less, more preferably 10 mass % or less, even more preferably 8 mass % or less, and even more preferably 5 mass % or less, relative to the mass of the solid electrolyte.

[0016] From the viewpoint of successfully forming a coating film using the slurry, the proportion of the volatile liquid medium contained in the precursor preparation slurry is, for example, preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. From the same viewpoint, the proportion of the volatile liquid medium contained in the precursor preparation slurry is, for example, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0017] Once the precursor preparation slurry is prepared, the slurry is then applied to one surface of a first clamping member 11 to form a coating film 10, as shown in FIG. 1 . The coating film 10 contains the above-described solid electrolyte, a binder, and, if necessary, a volatile liquid medium. The shape of the coating film 10 in plan view is not particularly limited. For example, the coating film 10 can be formed to have a shape such as a circle, an ellipse, or a polygon in plan view. The first clamping member 11 is a sheet-like or plate-like member having two opposing main surfaces 11a and 11b. The two main surfaces 11a and 11b of the first clamping member are parallel to each other and both are flat. For example, the arithmetic mean roughness Ra of the surface of the first clamping member on which the coating film 10 is formed, as measured in accordance with JIS B0601:2001, is preferably 1.0 μm or less, more preferably 0.5 μm or less, and even more preferably 0.2 μm or less.

[0018] There are no particular limitations on the method for applying the precursor preparation slurry to one surface of the first sandwiching member 11. For example, the precursor preparation slurry can be applied to one surface of the first sandwiching member 11 by 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, or the like. Whichever coating method is used, the thickness of the coating film 10, and therefore the thickness of the solid electrolyte sheet, can be adjusted by adjusting the amount of slurry applied.

[0019] The first clamping member 11 and the coating film 10 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.

[0020] Next, the volatile liquid medium is removed from the coating film 10. Methods for removing the volatile liquid medium include, for example, warm air drying, hot air drying, infrared drying, reduced pressure drying, and dielectric heating drying. The degree of removal of the volatile liquid medium may be such that the proportion of the volatile liquid medium contained in the coating film 10 after removal is, for example, 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less. The proportion of the volatile liquid medium contained in the coating film 10 may even be 0% by mass.

[0021] A precursor 20 of a solid electrolyte sheet (hereinafter also simply referred to as "precursor") is prepared by removing the volatile liquid medium from the coating film 10. In this state, the precursor 20 is supported on one main surface 11a of the first clamping member 11.

[0022] Once the precursor 20 is prepared, the next step is step (b). In step (b), as shown in Fig. 2, a second nipping member 12 is placed on the exposed surface 20a of the precursor 20, i.e., the surface of the two main surfaces of the precursor 20 that does not face the first nipping member 11. This results in a laminate 30 in which the first nipping member 11, precursor 20, and second nipping member 12 are layered in this order. In this laminate 30, the precursor 20 is sandwiched between the pair of nipping members 11 and 12.

[0023] When the second clamping member 12 is placed on the precursor 20, it is preferable that the second clamping member 12 extend from the periphery of the precursor 20. The second clamping member 12 is a sheet-like or plate-like member having two opposing main surfaces 12a, 12b. The two main surfaces 12a, 12b of the second clamping member are parallel to each other and are both flat. The dimensions, shape, and surface roughness of the second clamping member 12 may be the same as or different from those of the first clamping member 11.

[0024] After the laminate 30 is obtained, the next step (c) is performed. In step (c), the precursor 20 is pressed via clamping members 11 and 12 as shown in Fig. 3. This step is performed for the purpose of reducing voids that may exist in the precursor 20 in the laminate 30, thereby obtaining a solid electrolyte sheet with a dense structure.

[0025] Pressurization of the precursor 20 via the clamping members 11, 12 is achieved, for example, by pressing the entire laminate 30. Specifically, the laminate 30 can be pressed in its thickness direction using a uniaxial press such as a flat press. Alternatively, the laminate 30 can be pressed in its thickness direction using a roll press. Alternatively, isostatic pressure can be applied to the precursor 20 by isostatically pressing the entire laminate 30 by CIP (cold isostatic pressing) and WIP (warm isostatic pressing).

[0026] The pressure applied to the precursor 20 is preferably such that the particles of the solid electrolyte contained in the precursor 20 are not crushed. The hardness of the solid electrolyte varies depending on the type of solid electrolyte. When a solid electrolyte containing, for example, a crystalline phase having an argyrodite-type crystal structure is used, the pressure is preferably 1100 MPa or less, and more preferably 900 MPa or less. Furthermore, applying a high pressure of this level makes it possible to easily obtain a solid electrolyte sheet that is dense and highly self-supporting. From the viewpoint of obtaining a solid electrolyte sheet that is dense and highly self-supporting, the lower limit of the pressure is preferably, for example, 200 MPa or more, more preferably 400 MPa or more, and even more preferably 600 MPa or more.

[0027] The precursor 20 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.

[0028] When the precursor 20 is pressurized under heating, it is advantageous to use the above-mentioned WIP. In this case, the heating temperature can be, for example, 50°C or higher, or may be 75°C or higher, 100°C or higher, or 120°C or higher. The heating temperature can be, for example, 200°C or lower, or may be 190°C or lower, or may be 180°C or lower. When WIP is used, in order to avoid contact between the precursor 20 and hot water, it is preferable to place the laminate 30 in a watertight bag, degas the bag, and then seal and pressurize the bag.

[0029] When pressing the precursor 20 by pressing the laminate 30, it is also preferable to adopt pressing conditions under which the solid electrolyte sheet obtained by pressing can be peeled from the first clamping member 11 and the second clamping member 12. For example, a release treatment can be performed on the inner main surface 11a of the two main surfaces of the first clamping member 11 that faces the solid electrolyte sheet, and on the inner main surface 12a of the two main surfaces of the second clamping member 12 that faces the solid electrolyte sheet. Examples of the release treatment include application of a surface smoothing agent or a resin release agent.

[0030] The phrase "the solid electrolyte sheet can be peeled from the first and second clamping members 11 and 12" means that the solid electrolyte sheet can be peeled from the first and second clamping members 11 and 12 without destroying their respective structures. The peel strength between the solid electrolyte sheet and the first and second clamping members 11 and 12 is preferably 5 N / 10 mm or less, more preferably 4 N / 10 mm or less, and particularly preferably 2 N / 10 mm or less. Having a peel strength within this range allows the first and second clamping members 11 and 12 to be successfully peeled from the solid electrolyte sheet in step (d) described below. One method for measuring the peel strength is to cut the laminate 30 into a 10 mm-wide strip and perform a delamination test (180-degree peel, test speed 50 mm / min, chuck distance 40 mm) using a tension / compression testing machine.

[0031] By applying pressure to the precursor 20, voids that may exist within the precursor 20 are reduced or eliminated, resulting in a dense and self-supporting solid electrolyte sheet 40. From the perspective of further enhancing the density and self-supporting properties of the solid electrolyte sheet 40, the present inventors conducted extensive research and found that it is advantageous to use first and second clamping members 11, 12 having specific physical properties. Specifically, it was found that it is advantageous to use first and second clamping members 11, 12 each having a yield strength of 100 MPa or more, as measured in accordance with JIS Z2241. Clamping members 11, 12 having such yield strength are less likely to deform when subjected to pressure, which makes it easier for pressure to be transmitted to the precursor 20. In this specification, the term "yield strength" refers to a value measured in accordance with the offset method defined in JIS Z2241. In contrast, when a precursor is clamped via a clamping member with low strength, such as a sheet made of a thermoplastic resin such as polyethylene terephthalate, the clamping member deforms as pressure is applied to the precursor. When the pressure is released, the clamping member returns to its original shape. This restoration causes an external force to be applied to the precursor, which can easily cause defects such as cracks in the precursor (or, more precisely, the solid electrolyte sheet after compression). As a result, the density and self-supporting ability of the solid electrolyte sheet are impaired.

[0032] From the viewpoint of further enhancing the advantage of using first and second clamping members 11, 12 having high yield strength, the yield strengths of first and second clamping members 11, 12 are each independently more preferably 200 MPa or more, more preferably 500 MPa or more, and even more preferably 800 MPa or more. From the viewpoint of obtaining a dense and highly self-supporting solid electrolyte sheet, it is desirable that the yield strengths of first and second clamping members 11, 12 be high. However, in consideration of handleability, the yield strengths are each independently preferably 3000 MPa or less, more preferably 2000 MPa or less, and even more preferably 1500 MPa or less. Note that the first and second clamping members may have any yield strength within the above-mentioned range, and the yield strengths of the first and second clamping members may be the same or different.

[0033] From the viewpoint of obtaining a more dense and more self-supporting solid electrolyte sheet, the first and second clamping members 11 and 12 each independently have a total elongation at break measured in accordance with JIS Z2241 of preferably 40% or less, more preferably 30% or less, even more preferably 10% or less, even more preferably 5% or less, and particularly preferably 3% or less. Clamping members with a small total elongation at break are less likely to deform when pressurized. This facilitates pressure transmission to the precursor 20. Furthermore, since the shape change upon pressure release is small, external forces are less likely to be applied to the solid electrolyte sheet, and the solid electrolyte sheet is less likely to be damaged. From this viewpoint, the total elongation at break of the first and second clamping members 11 and 12 is preferably as close to zero as possible. The total elongations at break of the first and second clamping members may be the same or different.

[0034] Considering the above-mentioned yield strength and total elongation at break, it is preferable that the first and second clamping members 11, 12 are each independently made of a metal material. Examples of metal materials include, but are not limited to, copper, aluminum, stainless steel, nickel, titanium, and zinc. When stainless steel is used as the metal material, there are no particular limitations on the type of stainless steel. For example, SUS316, SUS430, and SUS444 can be used. The metal materials constituting the first clamping member 11 and the second clamping member 12 may be the same or different.

[0035] As described above, the first and second clamping members 11, 12 may be, for example, sheet-like or plate-like members. When the first and second clamping members 11, 12 have these shapes, their thicknesses are preferably independently 5 μm or more, more preferably 7 μm or more, and even more preferably 9 μm or more, from the viewpoint of applying sufficient pressure to the precursor 20. Furthermore, from the viewpoint of handleability, their thicknesses are independently preferably 100 μm or less, more preferably 90 μm or less, even more preferably 80 μm or less, even more preferably 50 μm or less, and particularly preferably 20 μm or less. The thicknesses of the first clamping member and the second clamping member may be the same or different.

[0036] Once the solid electrolyte sheet 40 is obtained by pressing the precursor 20, step (d) is then carried out as shown in FIG. 4 . That is, the first and second clamping members 11 and 12 are peeled off and removed from the solid electrolyte sheet 40. This results in a self-supporting solid electrolyte sheet 40. The solid electrolyte sheet 40 has a high density due to its dense structure. A high density of the solid electrolyte sheet 40 is preferable from the viewpoint of improving the performance of the solid electrolyte sheet 40 compared to conventional solid electrolyte sheets, particularly from the viewpoint of suppressing the growth of dendrites during charging of a solid-state battery using the solid electrolyte sheet 40. To further enhance this effect, the density of the solid electrolyte sheet 40 is preferably set to, for example, 1.0 g / cm ３ It is preferable that the density is 1.3 g / cm or more.３ More preferably, it is 1.5 g / cm or more. ３ From the viewpoint of maintaining the flexibility of the solid electrolyte sheet 40, the density of the solid electrolyte sheet 40 is preferably 2.5 g / cm or more. ３ It is preferable that the density is 2.3 g / cm or less. ３ More preferably, it is 2.0 g / cm or less. ３ It is more preferable that the density of the solid electrolyte sheet 40 is equal to or less than 10 cm. The density of the solid electrolyte sheet 40 can be measured, for example, by the following method. First, a test piece is prepared by cutting the solid electrolyte sheet 40 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. The thickness of the test piece can be measured, for example, with a thickness gauge. Alternatively, it can be measured by observing the cross section of the solid electrolyte sheet under a microscope. Whichever measurement method is used, the thickness is measured at 10 or more different positions, and the arithmetic average value thereof is taken as the thickness of the solid electrolyte sheet 40.

[0037] The solid electrolyte sheet 40 obtained by the above method is flexible in addition to being dense. The flexibility of the solid electrolyte sheet 40 can be evaluated by three-point bending modulus. From the viewpoint of maintaining the flexibility of the solid electrolyte sheet 40, the three-point bending modulus of the solid electrolyte sheet 40 may be, for example, 40 GPa or less, 30 GPa or less, or 20 GPa or less. Furthermore, from the viewpoint of suppressing dendrite growth, the three-point bending modulus of the solid electrolyte sheet 40 is preferably, for example, 6 GPa or more, more preferably 6.5 GPa or more, and even more preferably 7 GPa or more.

[0038] The three-point bending modulus of elasticity of the solid electrolyte sheet 40 is measured in accordance with JIS K7171: 2016. The dimensions of the test piece are 5 mm x 10 mm.

[0039] As long as the solid electrolyte sheet 40 has self-supporting properties, a small thickness is preferable from the viewpoint of obtaining a good battery energy density. From this viewpoint, the thickness of the solid electrolyte sheet 40 is, for example, preferably 60 μm or less, more preferably 50 μm or less, and even more preferably 45 μm or less. Furthermore, from the viewpoint of maintaining self-supporting properties, the thickness of the solid electrolyte sheet 40 is, for example, preferably 1 μm or more, more preferably 2 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and particularly preferably 20 μm or more.

[0040] From the viewpoint of enhancing the self-supporting property, the solid electrolyte sheet 40 has a basis weight of, 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 the electrical conductivity of the solid electrolyte sheet 40 at a high level, the basis weight of the solid electrolyte sheet 40 is preferably 80 g / m or more. 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:

[0041] A solid-state battery can be manufactured using the solid electrolyte sheet 40 obtained by the method shown in FIGS. 1 to 4 described above. The solid-state battery may include the solid electrolyte sheet 40, a positive electrode layer (not shown) disposed on one side of the solid electrolyte sheet 40, and a negative electrode layer (not shown) disposed on the other side of the solid electrolyte sheet 40. In this specification, a solid-state battery refers to a battery having a solid electrolyte layer. A solid-state battery is a battery that does not contain any liquid or gel-like substance as an electrolyte, or a battery that contains, for example, 50% by mass or less, particularly 30% by mass or less, and particularly 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0042] The present invention also provides a method for manufacturing a solid-state battery. A preferred embodiment of the method for manufacturing a solid-state battery is as follows. For points not specifically described in the method for manufacturing a solid-state battery, the above-described description of the method for manufacturing a solid electrolyte sheet applies as appropriate. First, in the same manner as in the above-described method for manufacturing a solid electrolyte sheet, a precursor preparation slurry for forming a precursor of the solid electrolyte sheet is prepared, which contains a solid electrolyte powder, a binder, and, if necessary, a volatile liquid medium.

[0043] Once the precursor preparation slurry is prepared, the slurry is then applied to the entire surface of a first electrode layer 51 to form a coating film 10, as shown in FIG. 5 . The first electrode layer 51 is formed by forming a first electrode active material layer 51a on the entire surface of one surface of the previously described clamping member. The coating film 10 is formed on the entire surface of the first electrode active material layer 51a of the first electrode layer 51. In other words, the coating film 10 is formed on the electrode active material layer 51a so that the dimensions of the electrode active material layer 51a and the coating film 10 are the same. Note that, depending on how the coating film 10 is formed, the coating film 10 may extend beyond the periphery of the electrode active material layer 51a, but this does not affect the performance of the solid-state battery.

[0044] The first electrode active material layer 51a is a layer containing an electrode active material, a solid electrolyte, and, if necessary, a conductive additive. The electrode active material may be a positive electrode active material or a negative electrode active material. The positive electrode active material may be, for example, an oxide active material containing a lithium transition metal. Specifically, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), LiNi １／３ Co １／３ Mn １／３ O ２ rock salt layered active materials such as lithium manganese oxide (LiMn ２ O ４ ), Li(Ni ０．５ Mn １．５ ) O ４ , Li １＋ｘ Mn ２－ｘ－ｙ M ｙ O ４(M is one or more selected from the group consisting of Al, Mg, Co, Fe, Ni, and Zn), and lithium titanate (Li ｘ TiO ｙ ), LiFePO ４ , LiMnPO ４ , LiCoPO ４ , LiNiPO ４ On the other hand, examples of the negative electrode active material include materials capable of absorbing lithium, such as graphite and silicon.

[0045] After the coating film 10 is formed on the first electrode active material layer 51a of the first electrode layer 51, the volatile liquid medium is removed from the coating film 10 to form a solid electrolyte sheet precursor 20. Next, as shown in FIG. 6 , a second electrode layer 52 is overlaid on the exposed surface 20a of the precursor 20, i.e., on the surface of the two main surfaces of the precursor 20 that does not face the first electrode layer 51. The second electrode layer 52 is formed by forming a second electrode active material layer 52a over the entire area of ​​one surface of the clamping member described above. The second electrode layer 52 is overlaid on the precursor 20 so that the second electrode active material layer 52a faces the exposed surface 20a of the precursor 20. This results in a laminate in which the first electrode layer 51, the precursor 20, and the second electrode layer 52 are stacked in this order. In this laminate, i.e., a battery precursor 60, the precursor 20 is interposed between the pair of electrode layers 51 and 52.

[0046] The second electrode active material layer 52a is a layer containing an electrode active material, a solid electrolyte, and, if necessary, a conductive additive. The electrode active material may be a positive electrode active material or a negative electrode active material. When the first electrode active material layer 51a described above contains a positive electrode active material, the second electrode active material layer 52a contains a negative electrode active material, with the first electrode layer 51 functioning as a positive electrode layer and the second electrode layer 52 functioning as a negative electrode layer. Conversely, when the first electrode active material layer 51a contains a negative electrode active material, the second electrode active material layer 52a contains a positive electrode active material, with the first electrode layer 51 functioning as a negative electrode layer and the second electrode layer 52 functioning as a positive electrode layer. In either case, the battery precursor 60 includes a precursor 20, a positive electrode layer 51 (or 52) disposed on one side of the precursor 20, and a negative electrode layer 52 (or 51) disposed on the other side of the precursor 20. The second electrode active material layer 52a preferably has the same dimensions as the precursor 20 or dimensions such that the precursor 20 extends from at least a portion of the periphery of the second electrode active material layer 52a. The extension of the precursor 20 from at least a portion of the periphery of the second electrode active material layer 52a does not affect the performance of the solid state battery. Note that, for details of the clamping members used for the first electrode layer 51 and the second electrode layer 52, the above-mentioned description of the clamping members used in producing the solid electrolyte sheet applies.

[0047] Once the battery precursor 60 is obtained, pressure is applied to the battery precursor 60 to sandwich the precursor 20 between the first and second electrode layers 51 and 52. This step is performed for the purpose of reducing voids that may be present in the precursor 20 and obtaining a solid battery equipped with a solid electrolyte sheet having a dense structure. A solid electrolyte sheet is obtained from the precursor 20 by this pressure.

[0048] The pressurization conditions for the battery precursor 60 can be the same as those for producing the solid electrolyte sheet described above. When pressurizing the battery precursor 60, it is preferable to place the battery precursor 60 in a watertight bag, for example, a bag made of a laminate film on which aluminum is vapor-deposited, evacuate the bag, and then seal and pressurize the bag. This makes it easy to manufacture an aluminum laminate-cased solid-state battery. When manufacturing an aluminum laminate-cased solid-state battery, it is preferable to provide current-extracting tabs (not shown) on the first and second electrode layers 51, 52 in advance, and then seal the aluminum laminate bag so that the tabs are exposed to the outside of the aluminum laminate bag.

[0049] The precursor 20 is pressurized to obtain a solid electrolyte sheet, and the pressure is then released. This produces a solid-state battery, such as an aluminum laminate-cased solid-state battery. The thickness of the solid-state battery obtained by pressing (thickness excluding the aluminum laminate casing) is preferably, for example, 50 μm or more, more preferably 150 μm or more, and even more preferably 250 μm or more. The thickness of the solid-state battery obtained by pressing is preferably, for example, 400 μm or less, more preferably 350 μm or less, and even more preferably 300 μm or less.

[0050] Next, matters common to the embodiments described so far will be described. The solid electrolyte contained in the solid electrolyte sheet 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. Any conventionally known sulfide solid electrolyte can be used without any particular restrictions as the sulfide solid electrolyte. The sulfide solid electrolyte may, for example, contain Li and S and have lithium ion conductivity.

[0051] The sulfide solid electrolyte may be any of a crystalline material, a glass ceramic, and a glass. Examples of such sulfide solid electrolytes include Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -LiX (where "X" represents one or more halogen elements), Li ２ S-P ２ S ５ -P ２ O ５ , Li ２ S-Li ３ P.O. ４ -P ２ S ５ , Li ３ P.S. ４ , Li ４ P ２ S ６ , Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ , Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ , Li ａ P.S. ｂ X ｃ (wherein "X" represents one or more halogen elements). In addition, for example, sulfide solid electrolytes described in WO 2013 / 099834 and WO 2015 / 001818 can be used.

[0052] In particular, it is preferable that the solid electrolyte contains a crystalline phase having an argyrodite-type crystalline structure from the viewpoint of maintaining a higher level of electrical conductivity of the solid electrolyte sheet. The argyrodite-type crystalline structure has the chemical formula: Ag ８ GeS ６This is a crystalline structure possessed by a group of compounds derived from minerals represented by the formula: Whether or not a solid electrolyte contains a crystalline phase having an argyrodite-type crystalline 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 an argyrodite-type crystalline 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°. To identify the diffraction peaks derived from the argyrodite-type crystal structure, for example, data from PDF No. 00-034-0688 is used.

[0053] When the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure, the solid electrolyte has, as described above, a composition represented by the formula (I): Li ａ P.S. ｂ X ｃ 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, X preferably contains at least an iodine element.

[0054] 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 effective enhancement of lithium ion conductivity.

[0055] 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. Furthermore, 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 within this range, the argyrodite-type crystal structure becomes more stable near room temperature (25°C), and lithium ion conductivity is effectively increased.

[0056] 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.

[0057] 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 P.S. ６－ｄ 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 joined to obtain a solid electrolyte sheet, it is preferable that X contains at least iodine element. The composition represented by composition formula (II) is the stoichiometric composition of an argyrodite-type crystalline phase.

[0058] 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. Also, d is preferably, for example, 2.2 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0059] 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 P.S. ６－ｄ－ｅ X ｄIn 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 an iodine element. The argyrodite-type crystalline phase having a composition represented by composition formula (III) may be, for example, a mixture of an argyrodite-type crystalline phase having a composition represented by composition formula (II) and P ２ S ５ It is produced by reaction with diphosphorus pentasulfide.

[0060] In the composition formula (III), e is the Li from the stoichiometric composition represented by the composition formula (II). ２ e is a value indicating the deviation of the S component. 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.

[0061] 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.

[0062] 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 binders can be used singly or in combination. Furthermore, some or all of the hydrogen atoms contained in these binders may be fluorinated. In particular, the use of a fluorine-containing polymeric compound as a binder is preferred because it can provide sufficient self-supporting properties to the solid electrolyte sheet even in small amounts and maintain a high level of electrical conductivity of the solid electrolyte sheet. It is particularly 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.

[0063] Although the present invention has been described above based on preferred embodiments thereof, the present invention is not limited to these embodiments. For example, in the above-described embodiments, the solid electrolyte sheet has a single-layer structure. Alternatively, the solid electrolyte sheet may have a multilayer structure of two or more layers. In this case, a multilayer precursor of the solid electrolyte sheet may be formed on one side of a first clamping member, a second clamping member may be placed on the precursor to form a laminate, and the laminate may be compressed to produce the solid electrolyte sheet from the precursor. Alternatively, a first precursor of the solid electrolyte sheet may be formed on one side of a first clamping member, and a second precursor of the solid electrolyte sheet may be formed on one side of a second clamping member, and the first and second precursors may be placed on top of each other so as to face each other to form a laminate having a multilayer precursor. The laminate may then be compressed to produce the solid electrolyte sheet from the precursor.

[0064] In the above-described embodiment, the solid electrolyte sheet is mainly composed of a solid electrolyte and a binder. However, a porous support may be included in the solid electrolyte sheet to further enhance the self-supporting property of the solid electrolyte sheet. As the porous support, for example, a fiber sheet such as various nonwoven fabrics can be used.

[0065] In relation to the above-described embodiments, the present invention discloses the following solid electrolyte sheet, manufacturing method thereof, and manufacturing method of a solid-state battery. [1] A manufacturing method of a solid electrolyte sheet, comprising: sandwiching a precursor of a solid electrolyte sheet containing a solid electrolyte powder and a binder between a pair of clamping members; and applying pressure to the precursor via the clamping members, wherein the clamping members each have a proof stress (offset method) measured in accordance with JIS Z2241 of 100 MPa or more. [2] The manufacturing method of a solid electrolyte sheet according to [1], wherein the clamping members each have a total elongation at break measured in accordance with JIS Z2241 of 40% or less. [3] The manufacturing method according to [1] or [2], wherein the clamping members are made of a metal material. [4] The manufacturing method according to any one of [1] to [3], wherein isostatic pressure is applied to the precursor via the clamping members. [5] The manufacturing method according to [4], wherein the precursor is isostatically pressed via the clamping members. [6] A method for manufacturing a solid battery, comprising: pressing a battery precursor comprising a solid electrolyte sheet precursor containing a solid electrolyte powder and a binder, a positive electrode layer disposed on one side of the precursor, and a negative electrode layer disposed on the other side of the precursor, wherein the positive electrode layer and the negative electrode layer each independently have a proof stress (offset method) of 100 MPa or more as measured in accordance with JIS Z2241. [7] A solid electrolyte sheet comprising a solid electrolyte powder and a binder, wherein the solid electrolyte sheet has a three-point bending modulus of elasticity of 6 GPa or more and 40 GPa or less. [8] A solid battery comprising the solid electrolyte sheet according to [7], 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.

[0066] 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."

[0067] [Example 1] A lithium ion conductive sulfide powder containing a crystalline phase having an argyrodite-type crystal structure was prepared as a solid electrolyte. ５０ The thickness was 2.2 μm. The binder was a fluorine-containing polymer compound polymerized using at least vinylidene fluoride as a polymerizable monomer. Butyl butyrate was used as the volatile liquid medium. A slurry was obtained by mixing the solid electrolyte, binder, and volatile liquid medium so that the amount of binder relative to the solid electrolyte in the slurry was 2%. The amount of volatile liquid medium contained in the slurry was 47%. The slurry was applied to a first clamping member made of 10 μm-thick SUS430 foil using a doctor blade with a gap of 70 μm to form a coating. The coating was vacuum-dried at 120°C to obtain a precursor of a solid electrolyte sheet.

[0068] Next, a second clamping member made of SUS430 foil with a thickness of 10 μm was placed over the exposed surface of the precursor to obtain a laminate. This laminate was sealed in a watertight bag and pressed using a WIP. The pressing conditions were 150°C and 700 MPa. Both the first and second clamping members had a yield strength of 1040 MPa and a total elongation at break of 1.1%. After pressing was completed, the laminate was removed from the bag, and the first and second clamping members were peeled off and removed from the laminate. This resulted in the desired solid electrolyte sheet.

[0069] Example 2 A solid electrolyte sheet was obtained in the same manner as in Example 1, except that the WIP was performed at a pressure of 980 MPa.

[0070] Example 3 A solid electrolyte sheet was obtained in the same manner as in Example 1, except that the temperature during WIP pressing was set to 190°C.

[0071] Example 4 A solid electrolyte sheet was obtained in the same manner as in Example 2, except that the temperature during WIP pressing was set to 190°C.

[0072] Examples 5 and 6: SUS316 foils with a thickness of 10 μm were used as the first and second clamping members. Both the first and second clamping members had a yield strength of 1350 MPa and a total elongation at break of 1.6%. A solid electrolyte sheet was obtained in the same manner as in Examples 3 and 4.

[0073] Comparative Example 1: 38 μm thick polyethylene terephthalate (PET) sheets were used as the first and second clamping members. Both the first and second clamping members had a yield strength of 88 MPa and a total elongation at break of 49.3%. Pressurization by WIP was performed at 500 MPa. A solid electrolyte sheet was obtained in the same manner as in Example 1, except for the above.

[0074] Comparative Examples 2 and 3 Solid electrolyte sheets were obtained in the same manner as in Comparative Example 1, except that the WIP pressure was 700 MPa and 980 MPa.

[0075] Comparative Example 4: Sheets made of 50 μm thick polyimide film (Kapton (registered trademark)) were used as the first and second clamping members. Both the first and second clamping members had a yield strength of 68 MPa and a total elongation at break of 47.3%. The pressure applied by WIP was 700 MPa, and the temperature during pressing was 190° C. A solid electrolyte sheet was obtained in the same manner as in Comparative Example 1, except for the above.

[0076] [Evaluation] The three-point bending modulus of the solid electrolyte sheets obtained in the examples and comparative examples was measured by the method described above, and the ionic conductivity was measured by the method described below. Furthermore, a solid state battery was fabricated by the method described below, and the presence or absence of a short circuit during charging was examined. The results are shown in Table 1 below.

[0077] [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.

[0078] [Presence or absence of short circuit in solid state battery] NCM622 (LiNi) was used as the positive electrode active material. ０．６ Co ０．２ Mn ０．２ O ２ ) was used. ５．４ P.S. 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. The film was then pressed onto the surface of an aluminum current collector to produce a positive electrode layer. Separately from this operation, a slurry containing acetylene black and Ag mixed in a mixing ratio of 80:20 and a solvent was applied to the surface of a SUS current collector to form a 10 μm-thick coating to produce a negative electrode layer. A laminate was produced by placing a positive electrode layer on one side of a solid electrolyte sheet and a negative electrode layer on the other side. A pressure of 700 MPa was applied to this laminate using a CIP to produce a solid-state battery. The resulting solid-state battery 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 three times at 60°C, and the presence or absence of a short circuit was observed.

[0079]

[0080] As is clear from the results shown in Table 1, the solid electrolyte sheets obtained in each Example had higher three-point bending modulus and ionic conductivity than the solid electrolyte sheets obtained in each Comparative Example. Furthermore, no short circuit occurred in the solid state batteries fabricated using the solid electrolyte sheets.

[0081] As described above in detail, the present invention provides a solid electrolyte sheet with improved performance compared to conventional solid electrolyte sheets, for example, a solid electrolyte sheet that can suppress the growth of metallic lithium dendrites.

Claims

1. A method for manufacturing a solid electrolyte sheet, comprising: placing a precursor of a solid electrolyte sheet containing a solid electrolyte powder and a binder between a pair of pressing members; and applying pressure to the precursor via the pressing members; wherein each of the pressing members independently has a yield strength (offset method) of 100 MPa or more as measured in accordance with JIS Z2241.

2. The method for manufacturing a solid electrolyte sheet according to claim 1, wherein each of the clamping members independently has a total elongation at break of 40% or less as measured in accordance with JIS Z2241.

3. The manufacturing method according to claim 1 or 2, wherein each of the clamping members is independently made of a metal material.

4. The manufacturing method according to claim 1 or 2, wherein an isotropic pressure is applied to the precursor via each of the clamping members.

5. The manufacturing method according to claim 4, wherein the precursor is isostatically pressed under hot water pressure through the clamping members.

6. A method for manufacturing a solid-state battery, comprising pressurizing a battery precursor comprising a solid electrolyte sheet precursor containing a solid electrolyte powder and a binder, a positive electrode layer disposed on one side of the precursor, and a negative electrode layer disposed on the other side of the precursor, wherein the positive electrode layer and the negative electrode layer each independently have a yield strength (offset method) of 100 MPa or more as measured in accordance with JIS Z2241.

7. A solid electrolyte sheet comprising a solid electrolyte powder and a binder, the solid electrolyte sheet having a three-point bending modulus of elasticity of 6 GPa or more and 40 GPa or less.

8. A solid-state battery comprising the solid electrolyte sheet according to claim 7, 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.

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