Solid electrolyte base material, solid electrolyte, secondary battery, and method for manufacturing solid electrolyte base material

Abstract

Provided is an easy-to-handle solid electrolyte base material for obtaining a solid electrolyte that has a high ionic conductivity and suppresses short circuiting. The solid electrolyte base material to be used to manufacture a solid electrolyte has a base, a first particle part elastically held on the base by an adhesive, and a second particle part layered and held on the first particle part and containing a green compact of solid electrolyte particles.

Description

Solid electrolyte substrate, solid electrolyte, secondary battery, and method for producing solid electrolyte substrate

[0001] The present disclosure relates to a solid electrolyte substrate, a solid electrolyte, a secondary battery, and a method for manufacturing a solid electrolyte substrate.

[0002] Generally, secondary batteries are composed of electrodes (positive and negative electrodes) and an electrolyte, and charge and discharge occur through the movement of ions between the electrodes via the electrolyte. Such secondary batteries are used in a wide range of applications, from small devices such as mobile phones to large devices such as electric vehicles. Therefore, further improvement in the performance of secondary batteries is required.

[0003] In recent years, research and development of so-called all-solid-state batteries, which use inorganic solid electrolytes as the electrolyte, has progressed. By replacing conventional organic electrolytes with solid electrolytes, all-solid-state batteries are expected to improve the safety and increase the capacity and power output of secondary batteries. However, when inorganic solid electrolytes are used in secondary batteries, the contact resistance is higher than that of liquid electrolytes, which tends to result in lower ionic conductivity and a higher susceptibility to short circuits.

[0004] To solve these problems, Patent Document 1 discloses an all-solid-state battery obtained by laminating an active material on a solid electrolyte sheet, which is prepared by coating a PET film with a solid electrolyte slurry and drying it, and then heat-treating the laminate. Patent Document 2 discloses a method for producing a solid battery material in which a solid electrolyte powder is used as a starting material, and the starting material is uniformly filled to a desired thickness and pressed to form a compacted solid electrolyte layer.

[0005] JP 2014-212022 A JP 2012-221887 A

[0006] However, according to the investigations of the present inventors, when a solid electrolyte slurry is coated on a PET film and dried as in Patent Document 1, the thickness of the coating layer of the dried solid electrolyte is as thick as 250 μm, and the ionic conductivity of the solid electrolyte is insufficient. Furthermore, a press-molded, compacted solid electrolyte layer having a thickness of about 50 μm to 60 μm as in Patent Document 2 is brittle and difficult to handle, making it unsuitable for practical use. Therefore, the present disclosure aims to provide an easy-to-handle solid electrolyte substrate for obtaining a solid electrolyte with high ionic conductivity and reduced short circuiting.

[0007] According to at least one aspect of the present disclosure, there is provided a solid electrolyte substrate used in the production of a solid electrolyte, the solid electrolyte substrate having: a base; a first particle portion elastically held to the base by an adhesive; and a second particle portion including a compact of solid electrolyte particles and held in place by being stacked on the first particle portion.

[0008] According to at least one embodiment of the present disclosure, there is provided a solid electrolyte substrate used in the production of a solid electrolyte, the solid electrolyte substrate having: a base; a layer of adhesive on the base; a first particle portion dispersed and held in the adhesive; and a second particle portion including a compact of solid electrolyte particles and held in a stack on the first particle portion.

[0009] According to at least one embodiment of the present disclosure, there is provided a solid electrolyte obtained by removing at least a portion of the base from the solid electrolyte substrate.

[0010] According to at least one embodiment of the present disclosure, there is provided a secondary battery including a solid electrolyte and an electrode disposed on the solid electrolyte, wherein the solid electrolyte is the solid electrolyte described above.

[0011] Furthermore, at least one aspect of the present disclosure provides a method for manufacturing a solid electrolyte substrate in which a base, an adhesive, first particle portions, and second particle portions are laminated in this order, wherein the second particle portions include solid electrolyte particles, the method including: a preparation step of preparing the base provided with the adhesive; a first step of arranging first particles on surfaces of the adhesive; a second step of applying pressure to the first particles to form the first particle portions; a third step of arranging second particles on surfaces of the first particle portions; and a fourth step of applying pressure to the second particles to form the second particle portions and obtain the solid electrolyte substrate.

[0012] Furthermore, at least one aspect of the present disclosure provides a method for manufacturing a solid electrolyte substrate in which a base, an adhesive, and a particle portion are laminated in this order, the method including the steps of: preparing the base provided with the adhesive; arranging solid electrolyte particles on a surface of the adhesive; and applying pressure to the solid electrolyte particles to produce the particle portion and obtain the solid electrolyte substrate.

[0013] According to at least one embodiment of the present disclosure, there is provided a solid electrolyte substrate that is easy to handle and that can be used to obtain a solid electrolyte having high ionic conductivity and suppressed short circuits.

[0014] FIG. 1 is a conceptual diagram showing a solid electrolyte substrate. FIG. 2 is a conceptual diagram showing a method for producing a solid electrolyte substrate. FIG. 3 is a schematic diagram showing an apparatus using a roll in a method for producing a solid electrolyte substrate. FIG. 4 is a schematic diagram showing an apparatus using a press in a method for producing a solid electrolyte substrate. FIG. 5 is a schematic diagram showing an apparatus using a roll in a method for producing a solid electrolyte substrate, in which the same first particles and second particles are used. FIG. 6 is a schematic diagram showing an apparatus using a press in a method for producing a solid electrolyte substrate, in which the same first particles and second particles are used. FIG. 7 is a schematic diagram showing an apparatus using a base coated with adhesive in a method for producing a solid electrolyte substrate. FIG. 8 is a schematic diagram showing an apparatus using a base coated with adhesive in a method for producing a solid electrolyte substrate. FIG. 9 is a schematic diagram showing the configuration of an apparatus for removing the base and a sintering treatment apparatus. FIGS. 10A and 10B are SEM images of the substrate and binarized images. FIG. 11 is a graph showing calculated area ratios.

[0015] In the present disclosure, the expressions "XX or more and YY or less" and "XX to YY" representing a numerical range mean a numerical range including the endpoints, that is, the lower and upper limits, unless otherwise specified. When a numerical range is described in stages, any combination of the upper and lower limits of each numerical range is also disclosed. Furthermore, in the present disclosure, for example, a description such as "at least one selected from the group consisting of XX, YY, and ZZ" means any of XX, YY, ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ.

[0016] When an inorganic solid electrolyte is used as the electrolyte, the electrolyte comes into contact in a solid state, making it difficult to obtain a sufficient contact area, making it difficult to establish a conductive path at the interface and causing short circuits.In addition, while it is possible to increase the contact area by increasing the amount of solid electrolyte, this increases the thickness, resulting in a decrease in ionic conductivity (increased resistance).

[0017] To solve the above-mentioned problems, the inventors conducted detailed studies on the configuration of the solid electrolyte particles of the solid electrolyte substrate. As a result of the studies, it was found that the following configuration can provide a solid electrolyte layer that is easy to handle, suppresses short circuits, and has improved ionic conductivity. That is, the solid electrolyte substrate has a base, a first particle portion elastically held to the base by an adhesive, and a second particle portion including a compacted powder of the solid electrolyte stacked and held on the first particle portion.

[0018] This means that the first particle portion, which is elastically maintained, and the second particle portion, which is part of the powder compact, each play a role in constituting the base material. This will be explained using FIG. 1. In FIG. 1, the particle portion (first particle portion) fixed to the base 11 by adhesive has spaces created by the adhesive. In other words, the first particle portion can have a layer structure in which particles are dispersed in the adhesive. On the other hand, the particle portion constituting the powder compact above the first particle portion has no adhesive and is therefore a particle portion (second particle portion) with little space and high density.

[0019] One example of a method for fabricating a solid electrolyte substrate is to press particles from a base to create a substrate. In this case, a pressing force is applied by the second particles to the first particles. Furthermore, this method is not limited to pressing, and a pressing force is also applied to the first particles by the mass of the second particles. Here, the adhesive may contain, for example, a resin, which is elastically deformable even in a cured state. Therefore, the pressing force transmitted by the second particles causes the first particles fixed to the adhesive to expand slightly like a spring, allowing the first particles to move in response to the pressing force. As a result, the first particles can hold the second particles as if they are biting into each other. Furthermore, the space at the interface between the first and second particles can be reduced, allowing the second particles to be firmly held. At the same time, the pressing force causes the second particles to become a compact, resulting in a high-density solid electrolyte particle.

[0020] Therefore, in the present disclosure, "elastic retention" refers to a state in which the first particle portion is fixed to the adhesive and is held so as to bite into the particles contained in the second particle portion by the pushing force transmitted from the second particle portion described above.

[0021] In the solid electrolyte substrate, the "elasticity retention" of the first particle portion can be confirmed by, for example, the fact that the first particle portion is fixed to, for example, a carbon C component derived from an adhesive in measurement using a BIB-SEM described below, and further by the fact that a compressed powder body of the second particle portion is formed thereon.

[0022] In order to "elastically maintain" the first particle portion in the solid electrolyte substrate, as described above, a layer of adhesive is formed on the base, and the first particle portion is formed so as to be dispersed and held in the adhesive. It is then preferable to stack a second particle portion including a compact of solid electrolyte particles on the first particle portion. That is, in another aspect of the present disclosure, the solid electrolyte substrate has a base, a layer of adhesive on the base, first particle portions dispersed and held in the adhesive, and a second particle portion including a compact of solid electrolyte particles stacked and held on the first particle portion.

[0023] Furthermore, in the solid electrolyte base material, the fact that the second particle portion has become a "compressed powder" can be confirmed by a high area ratio, i.e., a high density, in cross-sectional observation using a BIB-SEM, which will be described later. Preferably, in cross-sectional observation of the solid electrolyte base material using a scanning electron microscope, the area ratio (%) of the first particle portion is defined as d1, and the area ratio (%) of the second particle portion is defined as d2. It is preferable that d2 is 86% or more. d2 is more preferably 86 to 96%, and even more preferably 87 to 94%. Note that d1 is preferably 80 to 85%, and more preferably 82 to 85%.

[0024] Furthermore, with the solid electrolyte substrate of the present disclosure, only a small amount of adhesive is required to maintain the elasticity of the first particle portion, and during production of the solid electrolyte layer, for example, the resin component including the base can be removed at a low temperature, making it possible to minimize the effect of density reduction due to removal.

[0025] To produce such a solid electrolyte substrate, it is considered important to have a first particle portion elastically held by an adhesive on a base and a second particle portion constituting a powder compact. A solid electrolyte substrate having such a configuration has a high density of the first particle portion and the second particle portion, particularly the second particle portion. Therefore, by producing a solid electrolyte layer using the solid electrolyte substrate of the present disclosure, short circuits are less likely to occur and ions are more likely to conduct. Furthermore, a secondary battery using such a solid electrolyte layer can have a reduced internal resistance and improved output.

[0026] In the present disclosure, the above-described configuration is realized by using a solid electrolyte substrate in which solid electrolyte particles are arranged on a base having the characteristics of the present disclosure. The solid electrolyte substrate can also be used as a material for secondary batteries. In the present disclosure, the electronic conductivity and ionic conductivity are evaluated using the index "resistance value" for convenience.

[0027] The solid electrolyte substrate, the solid electrolyte layer, and the secondary battery using them, as well as the manufacturing method thereof, are described in detail below. The solid electrolyte substrate of the present disclosure can be used to manufacture a solid electrolyte. The solid electrolyte can be used to manufacture a secondary battery. The following description will be given taking a solid electrolyte substrate using solid electrolyte particles as an example.

[0028] The base may be any material that basically constitutes a solid electrolyte substrate. Preferably, the base contains a resin. Using a base formed of an organic material such as a resin makes it easier to remove the base by heating in the manufacturing process of the solid electrolyte layer, which will be described later.

[0029] The resin contained in the material of the base is not particularly limited, but examples thereof include polyesters such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), as well as polyamides such as nylon. Of these, it is preferable that the base contains PET from the viewpoint of the decomposition temperature and the low toxicity of gases generated during thermal decomposition. The thickness of the base is preferably 1 to 50 μm, more preferably 1 to 20 μm, and even more preferably 2 to 10 μm.

[0030] The adhesive is preferably a resin having adhesive and tackiness. The adhesive is preferably provided on a part or the entire surface of the base. Since the adhesive is intended to maintain the elasticity of the base and the first particle portion, there are no particular limitations on the method, but a method of applying the adhesive to the surface of the base is preferred.

[0031] The adhesive is not particularly limited, and known adhesives can be used. The adhesive includes, for example, a resin. The adhesive preferably has adhesiveness. Adhesion refers to the property of being able to bond temporarily. Adhesion makes it easier for the first particles to maintain their elasticity. The adhesive may be, for example, an acrylic adhesive, a rubber adhesive, or a silicone adhesive, or may be a thermoplastic resin or a photocurable resin whose adhesive strength changes in response to external disturbances such as heat or light. The adhesive is more preferably an adhesive. It is even more preferable that the adhesive is at least one selected from the group consisting of an acrylic adhesive, a rubber adhesive, and a silicone adhesive.

[0032] The solid electrolyte substrate has, for example, a base, a first particle portion held on the base by an adhesive, and a second particle portion including a compact of solid electrolyte particles stacked and held on the first particle portion.

[0033] The thickness of the adhesive (thickness after curing) is not particularly limited, but is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and even more preferably 0.5 to 3 μm.

[0034] The particles contained in the first particle portion are not particularly limited, but are preferably at least one particle selected from the group consisting of resin particles and solid electrolyte particles. If the particles are particles that disappear when heated, they can be easily removed in the manufacturing process of the solid electrolyte layer described below. The particles in this case are preferably made of an organic material, and are not particularly limited, but the particles in the first particle portion may be resin particles.

[0035] The resin particles may be particles of at least one resin selected from the group consisting of polyesters such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), polyacrylic resins, and polyamides such as nylon.

[0036] Furthermore, the particles in the first particle portion may be solid electrolyte particles that do not disappear when heated and form a solid electrolyte layer. The solid electrolyte particles are not particularly limited, and ion-conductive solids that are commonly used in all-solid-state batteries can be used. Examples of the solid electrolyte particles include Li-B oxide-based solid electrolyte particles, Li-Yb oxide-based solid electrolyte particles, and Nasicon-type solid electrolyte particles (LiAlTi(PO ４ ) ３ , LiAlGe (PO ４ ) ３ etc.), Li-P-O solid electrolyte particles (Li ３ P.O. ４ , LiPON (Li ３ P.O. ４ and the like).

[0037] Preferably, the solid electrolyte particles include oxide-based solid electrolyte particles. Among the above solid electrolyte particles, Li—B oxide-based solid electrolyte particles and Li—Yb oxide-based solid electrolyte particles can be sintered at relatively low temperatures (700°C or less), which makes it possible to suppress reaction with the positive electrode active material particles during sintering when fabricating an integrated battery, and thus makes it easy to maintain ionic conductivity. For this reason, it is preferable that the solid electrolyte particles include at least one particle selected from the group consisting of Li—B oxide-based solid electrolyte particles and Li—Yb oxide-based solid electrolyte particles.

[0038] The solid electrolyte particles may be commercially available products or may be prepared separately as materials. Examples of the Li-B oxide solid electrolyte particles include Li ３ BO ３ (Toshima Manufacturing Co., Ltd.) and Li ３ BO ３Particles in which part of O is replaced with C can be used. In addition, as the Li-Yb oxide solid electrolyte particles, compounds described in JP-A-2022-130301 can be mentioned, for example, Li ５．９ Yb ０．８１ La ０．０９ Zr ０．１ (BO ３ ) ３ These solid electrolyte particles may be made amorphous in advance by planetary ball milling or the like.

[0039] The particles in the second particle portion include solid electrolyte particles. The solid electrolyte particles are not particularly limited, and ion-conductive solids typically used in all-solid-state batteries can be used. The solid electrolyte particles used in the first particle portion described above can be used.

[0040] In cross-sectional observation of the solid electrolyte substrate using a scanning electron microscope, when the average area ratio (%) of the first particle portions is d1 and the average area ratio (%) of the second particle portions is d2, it is preferable that d1 and d2 are different. Furthermore, it is preferable that d1 and d2 satisfy the relationship d1<d2. By making d1 and d2 different in this way, gas generated from the adhesive when removing the resin by heating or the like can easily escape (preferably via the first particle portions). Therefore, cracks are less likely to occur in the solid electrolyte, making it easier to suppress short circuits.

[0041] The area ratios of the first particle portion and the second particle portion are determined by processing a cross section of the solid electrolyte substrate base, the first particle portion, and the second particle portion in the stacking direction with a broad ion beam (BIB) of Ar, and then obtaining a two-dimensional image of the cross section using a scanning electron microscope. The location of the adhesive can also be measured using an EDX method, which detects and spectroscopically analyzes characteristic X-rays generated by electron beam irradiation.

[0042] In this specification, the "first particle portion" refers to the particle portion held by the adhesive, as determined by the cross-sectional observation using the EDX method together with SEM observation. The first particle portion has a distribution in the height direction (Y direction in the image), but the position up to the maximum height of the particle held by the adhesive is defined as the first particle portion. Therefore, the second particle portion is clearly a portion free of adhesive, as determined by the cross-sectional observation using the EDX method.

[0043] The difference between d1 and d2 (preferably d2 - d1) is preferably statistically significant. The difference between d1 and d2 (preferably d2 - d1) is preferably 2% or more. By doing so, the elasticity of the first particle portions is easily maintained by the adhesive, and the second particle portions are easily fixed by the first particle portions. As a result, the second particle portions, which are solid electrolyte particles, can be formed with a sufficiently high density, thereby further improving ionic conductivity.

[0044] The difference between d1 and d2 (preferably d2-d1) is preferably 2 to 10%, and more preferably 3 to 7%. The difference between d1 and d2 can be increased by increasing the thickness of the adhesive. The difference between d1 and d2 can also be decreased by decreasing the thickness of the adhesive or decreasing the amount of change in the adhesive relative to pressure.

[0045] The thickness of the first particle portion is preferably 1 to 20 μm, more preferably 2 to 15 μm, and even more preferably 3 to 10 μm. The thickness of the second particle portion is preferably 10 μm or more and less than 100 μm, more preferably 20 to 90 μm, and even more preferably 25 to 80 μm. The total thickness of the first particle portion and the second particle portion is preferably less than 100 μm. By being in the above range, the resistance of the solid electrolyte after sintering can be reduced. The total thickness of the first particle portion and the second particle portion is preferably 20 μm or more and less than 100 μm, more preferably 25 to 90 μm, and even more preferably 30 to 80 μm.

[0046] The thickness of the adhesive, the thickness of the first particle portion, and the thickness of the second particle portion in the solid electrolyte substrate can be measured by observation using a BIB-SEM. The arithmetic average value of 10 arbitrary points is used.

[0047] <Method 1 for manufacturing a solid electrolyte substrate> An example of a method for manufacturing a solid electrolyte substrate will be described in detail below with reference to Fig. 2. Hereinafter, a solid electrolyte substrate using solid electrolyte particles for the first particle portion and the second particle portion will be described as an example, but the solid electrolyte substrate can also be manufactured in the same way by using resin particles for the first particle portion.

[0048] A method for manufacturing a solid electrolyte substrate in which a base, an adhesive, first particle portions, and second particle portions are laminated in this order preferably includes the following steps (1) to (5): (1) a preparation step of preparing a base provided with an adhesive; (2) a first step of arranging first particles on the surface of the adhesive (S101 in FIG. 2); (3) a second step of applying pressure to the first particles to form first particle portions (S102 in the figure); (4) a third step of arranging second particles on the surface of the first particle portions (S103 in the figure); and (5) a fourth step of applying pressure to the second particles to form second particle portions and obtain a solid electrolyte substrate (S104 in the figure).

[0049] (Preparation Step) In the preparation step, a base provided with an adhesive is prepared. In the present disclosure, "provided with an adhesive" means that an adhesive is provided on a part or the entire surface of the base. The base described above can be used as the base. There are no particular limitations on the method for providing the adhesive, but a method of applying an adhesive to the surface of the base is preferred.

[0050] The adhesive is not particularly limited, and known adhesives can be used. For example, it may be an acrylic adhesive, a rubber adhesive, a silicone adhesive, or a thermoplastic resin or a photocurable resin whose adhesive strength changes in response to external disturbances such as heat or light. The adhesive is as described above, and a pressure-sensitive adhesive is preferred. An adhesive with adhesive properties makes it easier to maintain elasticity.

[0051] (Steps 1, 2, 3, and 4) Step 1 is a step of arranging first particles on the surface of the adhesive on the base. It is preferable to arrange the particles so that the adhesive is not exposed. The thickness of the first particles is preferably 1 to 20 μm, more preferably 2 to 15 μm, and even more preferably 3 to 10 μm.

[0052] The second step is a step of fixing the first particles with an adhesive so that they are elastically maintained. The pressure is not particularly limited as long as it is sufficient to maintain the elasticity of the first particles. A certain level of force can easily hold the first particles in place. The pressure is preferably 5 to 300 kPa, more preferably 100 to 300 kPa.

[0053] The third step is a step of disposing second particles on the first particle portion. The second particles may be disposed to such an extent that a powder compact can be formed. The thickness of the second particles is preferably 10 μm or more and less than 100 μm, more preferably 20 to 90 μm, and even more preferably 25 to 80 μm.

[0054] The fourth step is a step of applying pressure in the same manner as in the second step to stack and hold the second particle portions on the first particle portions, thereby producing a green compact made of the second particle portions. It is sufficient to apply pressure to the extent that a green compact is formed. The pressure in the fourth step is not particularly limited, but is preferably 5 to 300 kPa, and more preferably 100 to 300 kPa.

[0055] <Method for manufacturing electrolyte base material 2> When the same solid electrolyte particles are used for the first particles and the second particles, after the first step of arranging the solid electrolyte particles on the surface of the adhesive part, the second and third steps are omitted and only the fourth step is performed. As a result, a first particle part is formed by a part of the solid electrolyte particles being elastically held to the base by the adhesive, and further, a second particle part including a powder compact held by being stacked on the first particle part can be formed.

[0056] That is, the method for manufacturing a solid electrolyte substrate 2 in which a base, an adhesive, and solid electrolyte particles are laminated in this order may include the following steps (1) to (3): (1) a preparation step of preparing a base with an adhesive, (2) a step of arranging solid electrolyte particles on the surface of the adhesive, and (3) a step of applying pressure to the solid electrolyte particles to form particle portions of the solid electrolyte particles and obtain a solid electrolyte substrate.

[0057] Furthermore, the method for manufacturing a solid electrolyte substrate 2 in which a base, an adhesive, and solid electrolyte particles are laminated in this order preferably includes the following steps (1) to (3): (1) a preparation step of preparing a base provided with an adhesive, (2) a step of arranging solid electrolyte particles on the surface of the adhesive, and (3) a step of applying pressure to the solid electrolyte particles to produce a first particle portion held by the adhesive and a second particle portion including a compact of solid electrolyte particles, thereby obtaining a solid electrolyte substrate.

[0058] The thickness of the solid electrolyte particles is preferably 10 μm or more and less than 100 μm, more preferably 20 to 90 μm, and even more preferably 25 to 80 μm. The pressure in step (3) is preferably 5 to 300 kPa, and more preferably 100 to 300 kPa.

[0059] The particle size of the primary particles is not particularly limited, but for example, the cumulative 10% particle size (r10) in the volume-based particle size distribution of the primary particles is preferably 0.1 to 10.0 μm, more preferably 1.0 to 7.0 μm. Furthermore, the cumulative 50% particle size (r50) in the volume-based particle size distribution of the primary particles is preferably 0.5 to 20.0 μm, more preferably 2.0 to 10.0 μm. Furthermore, the cumulative 90% particle size (r90) in the volume-based particle size distribution of the primary particles is preferably 2.0 to 20.0 μm, more preferably 3.0 to 15.0 μm.

[0060] The second particles are solid electrolyte particles. For example, the above-described solid electrolyte particles can be used as the second particles.

[0061] The particle size of the primary particles of the second particles is not particularly limited. For example, the cumulative 10% particle size (r10) in the volume-based particle size distribution of the primary particles of the second particles is preferably 0.1 to 10.0 μm, more preferably 1.0 to 7.0 μm. Furthermore, the cumulative 50% particle size (r50) in the volume-based particle size distribution of the primary particles is preferably 0.5 to 20.0 μm, more preferably 2.0 to 10.0 μm. Furthermore, the cumulative 90% particle size (r90) in the volume-based particle size distribution of the primary particles is preferably 2.0 to 20.0 μm, more preferably 3.0 to 15.0 μm. The ratio of the first particle size to the second particle size is not particularly limited.

[0062] [Solid electrolyte substrate manufacturing apparatus 1] Figure 3 is a diagram schematically illustrating the configuration of the solid electrolyte substrate manufacturing apparatus 1. The solid electrolyte substrate manufacturing apparatus 1 is an apparatus that forms a first particle portion 14 and a second particle portion 12 on a base 11. The solid electrolyte substrate manufacturing apparatus 1 includes a storage container 21 that stores and supplies the base 11, and a belt device 22 that transports the base 11. The solid electrolyte substrate manufacturing apparatus 1 also includes a liquid application device 201 that applies a liquid to the base 11 for applying an adhesive. The belt device is provided, from the upstream side, with a first particle application device 202 that stacks first particles and a particle fixing device 25, following the liquid application device 201. Further, downstream thereof, a second particle application device 203 that stacks second particles and a particle fixing device 26 are provided.

[0063] As the liquid applying device 201, a device that ejects liquid by an inkjet method or a device that applies liquid can be used, but a plate-based method such as a flexographic plate can also be used. Among these, it is preferable to use a device that ejects liquid by an inkjet method as the liquid applying device.

[0064] As a device for discharging liquid by the inkjet method, devices using various discharging methods, such as a thermal type, a piezo type, an electrostatic type, or a continuous type, can be used.

[0065] The liquid applied by the liquid applying device 201 to provide the adhesive may be water-based or oil-based, as long as it contains a material capable of holding the first particles that can form the first particle portion. The liquid may be appropriately selected, for example, by selecting a material that does not react with the first particles. The liquid applying device 201 may also form a pattern using multiple types of liquid. For example, the liquid applying device 201 may apply two types of liquid that react with each other on the substrate 11 to increase adhesion. Examples of materials to which the first particles can adhere include resins such as acrylic resins.

[0066] The first particle applying device 202 places powder containing first particles on the base 11 on which the adhesive is laminated. As a result, the first particles are fixed by the material on the base 11.

[0067] The means for applying the powder by the first particle applying device 202 can be a means for spraying or sprinkling the powder toward the base 11. The first particle applying device 202 may further include a means for removing the first particles that have not been fixed to the base 11 by means of vibration, centrifugation, air blowing, suction, or the like.

[0068] The particle fixing device 25 has pressure rollers 223c and 223d, and the pressure roller 223d rotates drivenly. At least one of the pressure rollers 223c, 223d is preferably a soft roller having an elastic layer on its surface, such as a soft roller having an elastic layer of silicone rubber or fluororubber on the surface of a stainless steel core. At least one of the pressure rollers 223c, 223d may have a built-in heater (not shown).

[0069] The base 11 is transported by a belt device to a pressure section between the pressure rollers 223c and 223d. When the base 11 is pressed by the pressure rollers 223c and 223d, the first particles arranged on the surface of the adhesive on the base are held by the adhesive on the base, forming a first particle section. At this time, the heater described above may be used to facilitate rearrangement of the adhesive particles on the base. Furthermore, a heat source may be provided upstream of the particle fixing device 25 to heat the adhesive on the base. The pressure applied by the pressure rollers is preferably within the range described above.

[0070] The base 11 on which the first particle portion 14 is placed is transported by a belt device to the second particle applying device 203. The second particle applying device 203 places powder containing second particles on the base 11 on which the first particle portion 14 is placed.

[0071] Next, the base 11 to which the second particles have been applied is transported by the belt device 22 to the pressure section between the pressure rollers 224c and 224d. Like the particle fixing device 25, the particle fixing device 26 has pressure rollers 224c and 224d, and the pressure roller 224d is driven to rotate. When the base 11 is pressed by the pressure rollers 224c and 224d, the second particles form second particle sections 12 on the first particle sections 14 on the base.

[0072] The solid electrolyte substrate manufacturing apparatus 1 may further include a drying device that evaporates at least a portion of the liquid applied by the liquid application device 201 to control the amount, thickness, etc. of the material on the base 11. This drying device may be provided downstream of the liquid application device 201. After drying, the material on the base may be a liquid, a liquid containing solids, or only solids.

[0073] Since the pressure rollers 223c and 224c come into contact with the particles on the base, it is preferable to coat the surfaces with a material with good releasability, such as fluorine, to prevent particles from adhering to the rollers. A cleaning mechanism may be provided to remove particles adhering to the pressure rollers 223c and 224c. It is even more preferable to apply pressure while the particle layer is covered with a protective material (not shown).

[0074] In this case, the protective material used is preferably a material with good releasability, and if it is a resin, a fluorine sheet is preferable, if it is a metal, a nichrome foil, etc. When a protective material is used, a removal mechanism (not shown) for removing the protective material is provided downstream of the particle fixing device 25 and upstream of the second particle applying device 203.

[0075] 4 is a diagram schematically illustrating the configuration of the solid electrolyte substrate manufacturing apparatus 2. Like the solid electrolyte substrate manufacturing apparatus 1, the solid electrolyte substrate manufacturing apparatus 2 is an apparatus for forming a solid electrolyte layer 12 on a base 11, and includes a storage container 21 that stores and supplies the base 11, and a belt device 22 that transports the base 11. The solid electrolyte substrate manufacturing apparatus 2 also includes a liquid application device 201 that applies a liquid for providing an adhesive portion on the base 11. The belt device is provided with, from the upstream side, a liquid application device 201, a first particle application device 202, and a particle fixing device 301, and downstream thereof, a second particle application device 203 and a particle fixing device 302.

[0076] The difference from the solid electrolyte substrate manufacturing apparatus 1 is that the particle fixing step involves fixing by pressing, but the other configurations are the same. The pressure during pressing is also preferably within the range described above. The pressure is preferably 5 kPa or more, and although it depends on the strength of the base, when a PET film is used, it is preferably 300 kPa or less to prevent damage. A pressure of 100 to 300 kPa is more preferred.

[0077] [Other solid electrolyte substrate manufacturing apparatuses] Figures 5 and 6 are diagrams illustrating solid electrolyte substrate manufacturing apparatuses when the same particles are used for the first particles and the second particles. Since the same particles are used in both cases, only one particle application device 202-2 is required. In Figure 5, the particles are fixed using a pressure roller, while in Figure 6, the particles are fixed using a press.

[0078] 7 and 8 show a solid electrolyte substrate manufacturing apparatus that uses a base that is already coated with adhesive. Because adhesive is applied to the base 11 in advance, a protective film is attached to the base. The protective film is removed by a protective film removal mechanism 401, and the apparatus moves to the next process.

[0079] In the solid electrolyte substrate, the coverage of the base surface by the solid electrolyte particles is preferably 60 area % or more, more preferably 70 area % or more, and even more preferably 80 area % or more.

[0080] In the present disclosure, the coverage of the base surface refers to the ratio (area %) of the area covered by solid electrolyte particles to the total area of ​​the base surface. The coverage of the base surface by solid electrolyte particles can be measured by photographing the area where the particle layer is formed using an optical microscope from the direction perpendicular to the substrate and calculating the area ratio of the area covered by solid electrolyte particles using image processing software. Details of the measurement method will be described later.

[0081] The upper limit of the coverage is not particularly limited, but is preferably 99 area% or less, and more preferably 98 area% or less. For example, the coverage of the resin substrate surface by the solid electrolyte particles is preferably 60 to 99 area%, 70 to 99 area%, or 80 to 99 area%, or 60 to 98 area%, 70 to 98 area%, or 80 to 98 area%. By ensuring that the coverage is within the above range, a dense particle layer is formed on the base, improving the density of the particles in the solid electrolyte layer. As a result, ionic conductivity can be further improved.

[0082] <Method for Manufacturing Solid Electrolyte Layer> An example of a method for manufacturing a solid electrolyte layer will be described in detail below with reference to Fig. 9. The method for manufacturing a solid electrolyte layer includes the following two steps (step A and step B): (step A) step A: removing a base from a solid electrolyte substrate to form a solid electrolyte integrated body; (step B) step B: sintering the solid electrolyte integrated body to obtain a solid electrolyte layer. In other words, the solid electrolyte layer manufactured by removing the base to obtain an integrated body and sintering the integrated body can be used as a solid electrolyte. Each step of the method for manufacturing a solid electrolyte layer will be described in detail below.

[0083] (Method for Manufacturing Solid Electrolyte Layer—Step A) Step A is a step of forming a solid electrolyte integrated body from a solid electrolyte substrate and removing the base. When resin particles are used for the first particle portion, it is preferable that the resin components of the resin particles and the resin components of the adhesive are also removed along with the base. Therefore, the base to be removed here refers to the resin components including the base. The base is preferably removed by heating. FIG. 9 is a diagram schematically illustrating the configuration of a sintering treatment device. The sintering treatment device includes a conveying device 41 for conveying the solid electrolyte substrate 15 and a heating furnace 42 for heating the laminate 15. Before Step A, multiple solid electrolyte substrates may be stacked. The number of stacks is not particularly limited and may be determined according to the desired capacity of the solid electrolyte.

[0084] The conveying device 41 receives the produced solid electrolyte substrate 15 and conveys it to the heating furnace 42. The conveying device 41 is preferably a device capable of conveying the solid electrolyte substrate 15. Examples of devices capable of conveying the solid electrolyte substrate 15 include a belt conveyor, a roller, and a robot arm.

[0085] The heating furnace 42 is a furnace that heats the solid electrolyte substrate 15. The heating furnace 42 has a heating means 421, a pressurizing means 422, and an atmosphere adjusting means 423. A firing furnace used for firing ceramics or the like can be used as the heating furnace 42. The pressurizing means 422 pressurizes the laminate 15 being heated in the heating furnace 42, and pressurizes the laminate 15 before and after heating.

[0086] It is preferable that the pressurizing means 422 has a pressurizing portion that pressurizes the laminate 15 and is made of a porous material that allows gas to easily pass through. The atmosphere adjusting means 423 has an atmosphere gas supplying means 423a and a pressure reducing means 423b, and adjusts the atmosphere gas in the processing space of the heating furnace 42. The atmosphere gas may be an oxidizing atmosphere (O ２ ), inert atmosphere (Ar, N ２ etc.) or reducing atmosphere (Ar-H ２ ) can be used, but sintering may also be carried out in air.

[0087] During the sintering treatment, it is preferable to heat at a temperature equal to or higher than the thermal decomposition temperature of the base 11 in the solid electrolyte substrate, and it is preferable to heat at a temperature lower than the thermal decomposition temperature of each particle layer in the solid electrolyte substrate. The temperature to which the solid electrolyte substrate is heated is preferably 200°C or higher and 1000°C or lower, and more preferably 400°C or higher and 800°C or lower. It is preferable to maintain the sintering temperature for 30 minutes or longer, and more preferably 1 hour or longer. It is sufficient to heat for a time period that allows the base to be removed, and although there is no particular upper limit, it is preferably 3 hours or shorter, more preferably 2 hours or shorter.

[0088] The thermal decomposition temperature is the temperature at which a material begins to lose weight when the temperature is gradually increased in a heating atmosphere in a sintering treatment device. Therefore, by heating the solid electrolyte substrate at a temperature equal to or higher than the thermal decomposition temperature of the base, the base of the solid electrolyte substrate can be decomposed and removed.

[0089] The heating temperature is preferably equal to or higher than the thermal decomposition temperature of the base, but is preferably even higher than the thermal decomposition temperature. Specifically, when the temperature is increased from room temperature (25°C) at a rate of 5°C / min in an atmosphere (typically air) during heating in a sintering treatment device and thermogravimetric analysis is performed, the heating temperature is preferably equal to or higher than the temperature at which the mass is reduced to 70% by mass of the initial mass. Specifically, for example, 385°C or higher is preferable.

[0090] Similarly, when thermogravimetric analysis is performed, it is more preferable to heat the solid electrolyte particles at a temperature equal to or higher than the temperature at which the mass is reduced to 50% by mass of the initial mass, and even more preferable to heat the solid electrolyte particles at a temperature equal to or higher than the temperature at which the mass is reduced to 20% by mass of the initial mass. Specifically, for example, 400°C or higher is preferable, and 450°C or higher is more preferable. This makes it possible to shorten the time required to remove the base and increase the removal rate of the base. In this way, when the sintering treatment device removes the base by heating, it is preferable that the solid electrolyte particles have a higher thermal decomposition temperature than the base.

[0091] When multiple solid electrolyte substrates are stacked, the sintering apparatus preferably removes at least a portion of the base in the solid electrolyte substrate by heating to provide a portion where the particles of the upper and lower stacked solid electrolyte layers come into contact. Therefore, it is preferable to remove 90 mass% or more of the base in the solid electrolyte substrate 15, more preferably 95 mass% or more, and even more preferably 97 mass% or more. In this case, it is preferable that the base is burned or gasified and released to the outside as a gas. In this case, it is preferable that the gas generated by pyrolysis is released to the outside of the apparatus.

[0092] The sintering treatment device preferably exhausts the released gas to the outside of the heating furnace 42 using the pressure reducing means 423b. By creating an oxidizing atmosphere, i.e., an atmosphere containing oxygen gas such as air, inside the heating furnace 42 using the atmospheric gas supplying means 423a or the like, the base can be burned and removed. On the other hand, depending on the solid electrolyte particles, sintering in an oxidizing atmosphere may cause decomposition or composition change. In such cases, it is recommended to use an inert atmosphere (Ar, N ２ etc.) or reducing atmosphere (Ar-H ２ ) is preferably sintered.

[0093] When the base is gasified by pyrolysis from the solid electrolyte substrate 15 and released as a gas, the particle layer in the solid electrolyte substrate may be pushed up and deformed. Therefore, when heating in the heating furnace 42, the solid electrolyte substrate 15 may be pressurized by the pressurizing means 422 before or during heating.

[0094] (Method for manufacturing a solid electrolyte layer - Process B) Process B is a process in which the base is removed and the resulting solid electrolyte integrated body is sintered to sinter and bond the solid electrolyte particles together to produce a solid electrolyte layer. At this time, the solid electrolyte is heated to a sintering temperature that corresponds to the type of solid electrolyte. Furthermore, if a material with high thermal stability at high temperatures is used for the base, there is no particular effect, but if a material that is unstable to heat is used, it is better to leave only the solid electrolyte integrated body before Process B. If a resin film is used for the base, it is considered that thermal decomposition occurs in Process A, so it is possible to proceed directly to Process B.

[0095] Alternatively, pressure may be applied using a separate pressure device after removing the base before step B. Specific pressure application methods are preferably vacuum degassing, isostatic pressing, or a general hydraulic press or roller press. In particular, a combination of vacuum degassing and isostatic pressing is preferred. Pressure is preferably applied at 5 MPa to 500 MPa. This fills the voids in the solid electrolyte unit from which the base has been removed, improving the density and strength of the three-dimensional object. A solid electrolyte layer can be manufactured using a manufacturing method including the above-described steps. This configuration can reduce the resistance value of the solid electrolyte.

[0096] <Method for manufacturing a secondary battery> A secondary battery can be manufactured using the solid electrolyte layer produced by the above method, and a separate current collector or a positive electrode or a negative electrode formed by another means. The secondary battery includes at least the above-mentioned solid electrolyte layer, and, as necessary, electrodes and current collectors.

[0097] The secondary battery has a laminate of electrodes, current collectors, and a solid electrolyte layer. The laminate may be packaged with an aluminum laminate film or the like as needed, and then molded and pressurized to produce a secondary battery. That is, the method for producing a secondary battery may include a step of laminating the electrodes, current collectors, and solid electrolyte layer. The solid electrolyte may be the above-described solid electrolyte layer.

[0098] Furthermore, the method for manufacturing a secondary battery may include the steps of preparing a solid electrolyte layer by a method for manufacturing a solid electrolyte layer and providing the above-described solid electrolyte layer adjacent to an electrode. Alternatively, the method may include the steps of simultaneously providing the electrode and the solid electrolyte layer adjacent to the electrode. That is, the electrode and the solid electrolyte layer may be prepared separately in separate steps, or may be prepared simultaneously in the same step.

[0099] Here, the other means for forming the electrodes is a known means, such as forming positive electrode material particles and negative electrode material particles into pellets using a uniaxial press or the like, and sintering them in an electric furnace, etc. Sheets or the like may also be used.

[0100] The manufactured components can be stacked in the order of a positive electrode current collector, a positive electrode, a solid electrolyte layer, a negative electrode, and a negative electrode current collector to form a secondary battery. For example, these stacks can be packed in a laminate film to form a laminated secondary battery, or packed in a coin case to form a coin-type secondary battery.

[0101] The particles constituting the positive electrode, solid electrolyte, and negative electrode may differ in the appropriate temperature and atmosphere during sintering. When handling such materials, it is preferable to separately manufacture the positive electrode, solid electrolyte, and negative electrode components and assemble them into a battery. Furthermore, when lithium metal or indium is used as the negative electrode, it is preferable to use the negative electrode as a metal foil and form it into a current collector and electrolyte by a vacuum process such as sputtering. Because lithium metal has a strong reducing power, it is easily decomposed depending on the type of solid electrolyte. In this case, a buffer layer may be provided between the electrode and the solid electrolyte. It is preferable to use a polymer electrolyte or the like as the buffer layer.

[0102] The secondary battery can also be produced as a three-dimensional object by molding a laminate including two or more of a positive electrode current collector, a positive electrode, a solid electrolyte layer, a negative electrode, and a negative electrode current collector.

[0103] For example, each substrate is made of a respective particle layer. That is, a positive electrode current collector substrate, a positive electrode substrate, a solid electrolyte substrate, a negative electrode substrate, and a negative electrode current collector substrate. Each substrate may contain multiple types of particles (positive electrode active material particles and solid electrolyte particles in the case of a positive electrode substrate) or may contain only a single type of particle.

[0104] The negative electrode substrate is formed of a particle layer containing at least negative electrode active material particles. The current collector substrate is formed of a particle layer containing at least conductive particles. These substrates are stacked in the order of positive electrode current collector substrate, positive electrode substrate, solid electrolyte substrate, negative electrode substrate, and negative electrode current collector substrate using a stacking unit or the like to produce a laminate. A secondary battery can be manufactured by removing resin components from the base and performing post-treatment. Furthermore, a bipolar secondary battery can also be manufactured by stacking electrode substrates on both sides of the current collector substrate.

[0105] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the following examples, unless otherwise specified, the number of parts is based on parts by mass.

[0106] Specifically, a solid electrolyte substrate was produced using the systems shown in FIGS.

[0107] (Example 1) In Example 1, the system shown in Figure 4 was used. A 3 μm polyester (PET) sheet (Lumirror, manufactured by Toray) was used as the base. An acrylic adhesive (T-50, manufactured by Toagosei Co., Ltd.) was applied to the base as the adhesive so that the thickness would be 1 μm after drying. Furthermore, 2 μm polyacrylic resin particles (MV1002, manufactured by Nippon Shokubai) were used as the first particles, and were applied so that the thickness of the first particle portion would be 5 μm. The pressing conditions after applying the first particles were set to 250 kPa. Furthermore, Li １．５ Al ０．５ Ge １．５ P ３ O １２ (hereinafter also referred to as LAGP) powder was applied to the second particle portion to a thickness of 70 μm. After applying the second particles, the pressing conditions were 250 kPa to obtain a solid electrolyte substrate. Then, using the system shown in FIG. 9, the resin components, the base, adhesive, and resin particles, were removed from the obtained solid electrolyte substrate by heating to produce a solid electrolyte integrated body, which was then pressed and sintered again to obtain a solid electrolyte layer. The heating for removing the base was performed in an air sintering atmosphere at a temperature of 500°C (maintained for 1 h). Sintering to obtain the solid electrolyte layer was also performed at 850°C.

[0108] (Example 2) The same base and adhesive as those in Example 1 were used. The same LAGP was used for the first particles and the second particles. Therefore, the solid electrolyte substrate was produced using the system shown in Figure 8. The pressing conditions were set to 250 kPa. In addition, the total thickness of the first particle portion and the second particle portion was set to the value shown in Table 1. The other conditions were the same as those in Example 1.

[0109] (Example 3) The base and adhesive were the same as those in Example 1. The first particles and the second particles were Li５．９ Yb ０．８１ La ０．０９ Zr ０．１ (BO ３ ) ３ (manufactured by Canon Inc., hereinafter also referred to as LYbBO) was used. The other conditions were the same as in Example 2. The conditions for removing the base are shown in Table 1.

[0110] (Example 4) The base and adhesive were the same as those in Example 1. The first particles and the second particles were Li ３ BO ３ (hereinafter also referred to as LBO) was used. The other conditions were the same as in Example 2. The conditions for removing the base are shown in Table 1.

[0111] (Example 5) The base and adhesive were the same as those in Example 1. The first particles and the second particles were Li ７ La ３ Zr ２ O １３ (hereinafter also referred to as LLZ) was used. The other conditions were the same as in Example 2. The conditions for removing the base are shown in Table 1.

[0112] (Example 6) The same base and adhesive as in Example 1 were used. LYbBO was used for the first particles and second particles. Unlike Example 3, the total thickness of the first particle portion and the second particle portion was adjusted to 30 μm. The other conditions were the same as in Example 2. The conditions for removing the base, etc. are shown in Table 1.

[0113] (Comparative Example 1) The same base and adhesive as in Example 1 were used. LAGP was used for the first particles and second particles. The total thickness of the particle portions was adjusted to 5 μm. Other conditions were the same as in Example 2. The conditions for removing the base, etc. are shown in Table 1. In Comparative Example 1, the particle portions were thin, so the second particle portions were not formed.

[0114] (Comparative Example 2) The same base and adhesive as in Example 1 were used. LYbBO was used for the first particles and second particles. The total thickness of the particle portions was adjusted to 5 μm. The other conditions were the same as in Example 2. The conditions for removing the base, etc. are shown in Table 1. In Comparative Example 2, the particle portions were thin, so the second particle portions were not formed.

[0115] (Comparative Example 3) A solid electrolyte substrate was obtained by adjusting the total thickness of the particle portion to 70 μm using only LAGP without using a base or adhesive. The pressing conditions were set to 12,000 kPa. The rest were the same as in Example 2.

[0116] Comparative Example 4: No base or adhesive was used, and the total thickness of the particle portion was adjusted to 70 μm using only LYbBO. The pressing conditions were set to 12,000 kPa. The rest were the same as in Example 3.

[0117] (Comparative Example 5) The same base as in Example 2 was used, but no adhesive was used. LAGP particles were used. The pressing conditions were set to 250 kPa. The other conditions were the same as in Example 2. Therefore, in Comparative Example 5, the first particle portion was not formed, and only a compact made of LAGP was formed on the base.

[0118] (Comparative Example 6) The same base and adhesive as those in Example 2 were used. LAGP particles were used. No second particles were used, and the adhesive with the dispersed first particle portions was pressed at 250 kPa so that the thickness was 70 μm. The other conditions were the same as those in Example 2. Therefore, in Comparative Example 6, no second particle portions were formed.

[0119] (Example 7) The same base and adhesive as in Example 1 were used. LYbBO was used as the particles. The total thickness of the first particle portion and the second particle portion was adjusted to 150 μm. The conditions for removing the base and the like are shown in Table 1. The other conditions were the same as in Example 2.

[0120] (Comparative Example 7) A base and an adhesive were not used, and LYbBO was used for the first particles and the second particles. The total thickness of the particle portion was adjusted to 150 μm, and a solid electrolyte substrate was obtained. The sintering conditions and other conditions are shown in Table 1. The pressing conditions were set to 12,000 kPa. The rest were the same as in Example 3.

[0121] Regarding thickness, only the total thickness is shown for the examples produced using the system of FIG.

[0122] The evaluation results of Examples, Comparative Examples, and Reference Examples are shown in Table 2. The evaluation methods will also be described.

[0123] Handling: The center of the flat-plate-shaped solid electrolyte substrate (10 mm square) obtained before removing the base (before firing) was grasped with tweezers and evaluated to see whether cracks occurred. Those that did not crack were rated A, those that did not crack but showed warpage were rated B, and those that did crack were rated C.

[0124] Measurement of Resistance Values ​​After removing the base, gold electrodes with a diameter of 3 mm were formed on the top and bottom surfaces of the flat-plate-shaped sintered compact obtained by sintering using a magnetron sputtering device MSP-10 manufactured by Vacuum Devices, Inc., to prepare samples for AC impedance measurement. A potentio / galvanostat SI1287A and a frequency response analyzer 1255B manufactured by Solartron Analytical were used for the measurements. The measurement conditions were room temperature and a frequency of 1 MHz to 0.1 Hz. The resistance value was calculated from the complex impedance plot obtained by the impedance measurement. A resistance value (Ω) of 10,000 or less obtained using a Z-parallel circuit was rated A, a resistance value exceeding 10,000 was rated B, and a leak that could not be measured was rated C. Furthermore, samples with cracks were rated C because they could not be measured.

[0125] The difference in area ratio between the first particle layer and the second particle layer was determined by BIB-SEM photography and image processing. <BIB-SEM Photography Method> BIB-SEM images were used to determine the area ratio in the solid electrolyte substrate. The BIB-SEM photography conditions are explained below. A solid electrolyte substrate fabricated on a substrate (Al foil) was vacuum-packed and isostatically pressed to prepare a sample. The sample was cut in the stacking direction of the base, first particle portion, and second particle portion using a wire saw (DWS3400 / wire diameter 170 μm, diamond diameter 30 μm), and the cut surface was cross-sectionally processed using a broad ion beam of Ar (JEOL SM-09010 Cross Section Polisher). The cross-sectional processing conditions were a voltage of 6 kV and a current of 150 to 200 mA. A cross section in the stacking direction was obtained as a BIB-SEM image, and cross-sectional observation was performed.

[0126] The cross section was photographed using an electron microscope (ULTRA55) under the following conditions. Examples of the photographed images (Example 2) are shown in Figures 10A and 10B. Detector: ESB (backscattered electron image) Observation conditions: Acceleration voltage 3 kV Magnification: 1000x Filter: A bias of 1500 V was applied to the ESB filter

[0127] Next, elemental and compositional analysis of each particle on the base was performed using SEM-EDX (Bruker XFlash Detector 630M), and the adhesive components and solid electrolyte particles were identified. Specifically, the base, adhesive components, and solid electrolyte particles were identified by analyzing the base and adhesive components using X-ray diffraction (XRD) or the like, and identifying the materials that make up the base and adhesive components. Thereafter, the specific elements contained in the solid electrolyte particles were detected and identified using SEM-EDX.

[0128] The first particle portion and the second particle portion are divided as follows. As mentioned above, the position of the particles held by the adhesive up to their maximum height is defined as the first particle portion. Therefore, the position of the adhesive is confirmed by observing the specific elements contained in the adhesive, specifically the carbon (C) component, using SEM-EDX. Then, particles held by the adhesive are selected, and the position of these up to their maximum height is defined as the first particle portion. Furthermore, the group of particles above the first particle portion that are not in contact with the adhesive is defined as the second particle portion.

[0129] <Method for calculating the proportion of solid electrolyte particles per unit depth> The area proportion occupied by solid electrolyte particles was detected from the BIB-SEM image taken under the above conditions. First, the BIB-SEM image was normalized to an average brightness of 100 and a standard deviation of ±30. In order to count the solid electrolyte particles on the base, an image showing only the particle layer on the base was cut out from the normalized image so as to include all particles in the image. An example of the cut-out image is shown in FIG. 10A.

[0130] The cut-out image was binarized using a brightness threshold of 70 to obtain a binarized image. For the purpose of noise removal, the area surrounded by white pixels was filled with white, and then an opening process of morphological transformation was performed with a kernel size of 3 × 3 pixels to obtain a noise-removed image. An example of the noise-removed image is shown in Figure 10B.

[0131] Next, the top and bottom positions of the white pixels in each column in the image (Figure 10B) obtained above were determined and recorded. The top position of the white pixels in each column indicates the top surface of the solid electrolyte layer, and the bottom position of the white pixels in each column indicates the bottom surface of the solid electrolyte layer. Furthermore, the thickness of the solid electrolyte layer was determined to be 70 μm from the SEM image, and the area ratio of the solid electrolyte was calculated in 5 μm increments relative to the thickness. Specifically, as shown in Figure 10B, the area ratio of the white portion (particle portion) was calculated in 300 μm increments by 5 μm increments for a solid electrolyte layer measuring 300 μm in width and 70 μm in length. Note that d1 and d2 are the average values ​​of the area ratios measured in 300 μm increments by 5 μm in length. The results are shown in Figure 11. From this, the difference in area ratio between the first particle portion and the second particle portion can be determined. In Fig. 10B, the position 70 µm (5 µm from the bottom) is the first particle portion, and the remaining positions are the second particle portion. Furthermore, the area percentage values ​​in the vertical columns in Fig. 11 multiplied by 100 are the area percentage values ​​for d1 and d2. In Fig. 11, d1 was 84%, d2 was 88%, and the difference in area percentage (second particle portion - first particle portion) was 4%.

[0132] The difference in area ratio is d2-d1.

[0133] Example 8 A secondary battery was fabricated using the solid electrolyte layer fabricated in Example 2. A positive electrode was fabricated using LCO and LAGP based on JP 2019-137060 A. An indium foil (50 μm thick) was used for the negative electrode. Aluminum foil (20 μm thick) was used as the positive electrode current collector. Copper foil (20 μm thick) was used as the negative electrode current collector. The above materials were laminated in the following order: positive electrode current collector, positive electrode, solid electrolyte layer, negative electrode, and negative electrode current collector. The laminate was then packaged in an aluminum laminate film so that a tab lead for the extraction electrode, previously welded to the current collector, was positioned outside the laminate. The laminate was then molded into a laminate cell shape using a vacuum packaging machine and pressurized (196 MPa) using an isostatic pressure device to fabricate an all-solid-state secondary battery. It was confirmed that the battery could be operated at room temperature.

[0134] Example 9 A secondary battery was produced using the solid electrolyte layer produced in Example 3. A positive electrode was produced using LCO and LYbBO based on JP 2019-137060 A. Otherwise, an all-solid-state secondary battery was produced in the same manner as in Example 7, and it was confirmed that the battery could be operated at room temperature.

[0135] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the present disclosure. Therefore, the following claims are appended to clarify the scope of the present disclosure. This application claims priority based on Japanese Patent Application No. 2023-148390, filed September 13, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A solid electrolyte substrate used in the production of a solid electrolyte, comprising: a base; a first particle portion elastically held to the base by an adhesive; and a second particle portion including a compressed powder body of solid electrolyte particles, stacked and held on the first particle portion.

2. The solid electrolyte substrate according to claim 1, wherein the solid electrolyte particles comprise oxide-based solid electrolyte particles.

3. The solid electrolyte substrate according to claim 1 or 2, wherein the total thickness of the first particle portion and the second particle portion is less than 100 μm.

4. The solid electrolyte substrate according to any one of claims 1 to 3, wherein the first particle portion includes solid electrolyte particles.

5. A solid electrolyte substrate according to any one of claims 1 to 4, wherein, in a cross-sectional observation of the solid electrolyte substrate with a scanning electron microscope, when an area ratio (%) of the first particle portion is d1 and an area ratio (%) of the second particle portion is d2, d1 and d2 are different.

6. The solid electrolyte substrate according to claim 5, wherein d1 and d2 satisfy d1<d2.

7. The solid electrolyte substrate according to claim 5 or 6, wherein the difference between d1 and d2 is 2% or more.

8. The solid electrolyte substrate according to any one of claims 1 to 7, wherein the adhesive has adhesive properties.

9. The solid electrolyte substrate according to any one of claims 1 to 8, wherein the adhesive has a thickness of 0.5 to 5 µm.

10. A solid electrolyte substrate used in the production of a solid electrolyte, comprising: a base; a layer of adhesive on the base; a first particle portion dispersed and held in the adhesive; and a second particle portion including a compressed powder of solid electrolyte particles and stacked and held on the first particle portion.

11. A solid electrolyte obtained by removing at least a part of the base from the solid electrolyte substrate according to any one of claims 1 to 10.

12. A secondary battery comprising a solid electrolyte and an electrode disposed on said solid electrolyte, said solid electrolyte being the solid electrolyte according to claim 11.

13. A method for producing a solid electrolyte substrate in which a base, an adhesive, a first particle portion and a second particle portion are laminated in this order, wherein the second particle portion includes solid electrolyte particles, the method comprising: a preparation step of preparing the base provided with the adhesive; a first step of arranging first particles on a surface of the adhesive; a second step of applying pressure to the first particles to produce the first particle portions; a third step of arranging second particles on the surfaces of the first particle portions; and a fourth step of applying pressure to the second particles to produce the second particle portions and obtain the solid electrolyte substrate.

14. A method for producing a solid electrolyte substrate in which a base, an adhesive, and a particle portion are laminated in this order, the method comprising the steps of: preparing the base provided with the adhesive; arranging solid electrolyte particles on a surface of the adhesive; and applying pressure to the solid electrolyte particles to produce the particle portion and obtain the solid electrolyte substrate.

15. The method for producing a solid electrolyte substrate according to claim 13 or 14, wherein the adhesive has adhesive properties.

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