Support for secondary battery, solid electrolyte sheet, and secondary battery

Abstract

The present invention constitutes a secondary battery support body capable of reducing the internal resistance of a solid electrolyte layer, the secondary battery support body having a configuration in which a plurality of layers formed by including at least one type of paper or non-woven fabric are laminated and integrated.

Description

Technical Field

[0001] The present invention relates to a support for a secondary battery that holds a solid electrolyte, a solid electrolyte sheet, and a secondary battery having the support. Background Technology

[0002] Lithium-ion secondary batteries, which utilize a liquid electrolyte (hereinafter referred to as electrolyte), are high-energy-density rechargeable batteries. A lithium-ion secondary battery utilizing an electrolyte has the following configuration: a separator is sandwiched between the positive and negative electrodes, and the electrolyte is held within the separator.

[0003] In lithium-ion secondary batteries, organic electrolytes are primarily used. However, organic electrolytes are liquids, raising concerns about leakage and flammability. Therefore, to improve the safety of lithium-ion secondary batteries, secondary batteries using solid electrolytes instead of liquid electrolytes (hereinafter referred to as all-solid-state batteries) have been developed. All-solid-state batteries use a solid electrolyte, thus eliminating leakage. Furthermore, they are more flame-retardant and heat-resistant than liquid electrolytes, making them a highly attractive option for safer secondary batteries. Due to their high safety, small all-solid-state batteries for wearable devices and other applications that come into direct contact with the body are already in mass production.

[0004] Unlike secondary batteries that use an electrolyte between the positive and negative electrodes, all-solid-state batteries have a solid electrolyte layer sandwiched between them instead of a separator that holds the electrolyte. For example, in the case of a lithium-ion all-solid-state battery, during charging, lithium ions travel from the positive electrode through the solid electrolyte layer to the negative electrode.

[0005] On the other hand, during discharge, lithium ions travel from the negative electrode to the positive electrode through the solid electrolyte layer. Therefore, in the case of all-solid-state batteries, in addition to lithium ions, various ion types such as sodium ions are studied as carrier ions, serving as the type of ion that conducts between the positive and negative electrodes, in order to avoid issues related to a stable supply of resources. Since these carrier ions travel between the positive and negative electrodes through the solid electrolyte layer, a pass line for the carrier ions must be formed relative to the thickness direction of the solid electrolyte layer.

[0006] Furthermore, to improve productivity in the mass production of all-solid-state batteries, it is desirable to form the solid electrolyte into sheets and manufacture it using the same roll-to-roll process as existing lithium-ion secondary battery manufacturing procedures. However, it is difficult to form thin, highly conductive, and self-supporting solid electrolyte sheets using only solid electrolyte and binders. Therefore, a method for forming self-supporting solid electrolyte sheets by retaining the solid electrolyte in sheets such as paper or nonwoven fabric (hereinafter referred to as supports) has been investigated.

[0007] For example, related technologies for solid electrolyte sheets using supports with a porosity of 60% or more and 95% or less, and a thickness of 5 μm or more and less than 20 μm, have been disclosed (see, for example, Patent Document 1). Furthermore, it has been disclosed that this solid electrolyte sheet, despite its thinness, possesses self-supporting properties.

[0008] In addition, a related technology for forming a solid electrolyte sheet with multiple through-holes by etching a thin film that serves as a support is disclosed (see, for example, Patent Document 2). With this technology, an all-solid-state battery with excellent energy density and power characteristics can be constructed by filling the through-holes formed by the etching process with a solid electrolyte.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2020-77488

[0012] Patent Document 2: Japanese Patent Application Publication No. 2017-103146 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] However, within the existing support, the fibers are tightly packed together, resulting in multiple overlapping areas. Consequently, even when a solid electrolyte slurry is coated onto the support, it does not penetrate to the overlapping fiber areas, leaving unfilled areas within the support.

[0015] For example, in the technology described in Patent Document 1, although the support is a support with sufficient porosity, there are areas where the fibers are closely packed and overlapping. Therefore, the formation of the carrier ion passage lines relative to the thickness direction inside the solid electrolyte sheet becomes insufficient, resulting in a solid electrolyte sheet with high internal resistance.

[0016] Furthermore, regarding the technology described in Patent Document 2, since the through-holes are formed by etching, the distribution of the through-holes is uniform, but thin film portions acting as insulating materials remain outside the through-holes. Therefore, areas without solid electrolyte are formed in the solid electrolyte sheet. Moreover, the areas in the solid electrolyte sheet capable of ion conduction are limited, resulting in a solid electrolyte sheet with high internal resistance. Consequently, the resistance of the all-solid-state battery using this support becomes high.

[0017] To solve the above problems, the present invention provides: a secondary battery support that can reduce the internal resistance of the solid electrolyte layer, a solid electrolyte sheet using the support, and a secondary battery using the solid electrolyte sheet.

[0018] Solution for solving the problem

[0019] The secondary battery support of the present invention is a support for holding a solid electrolyte of a secondary battery, the secondary battery support having multiple layers formed by laminating at least one of paper and nonwoven fabric.

[0020] In addition, the solid electrolyte sheet of the present invention comprises: a support having a plurality of layers formed by laminating at least one of paper and nonwoven fabric; and a solid electrolyte held by the support.

[0021] Furthermore, the secondary battery of the present invention includes: a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode. The solid electrolyte layer includes: a support having a plurality of layers formed by laminating at least one of paper and nonwoven fabric; and a solid electrolyte held by the support.

[0022] The effects of the invention

[0023] According to the present invention, a secondary battery support capable of reducing the internal resistance of the solid electrolyte layer, a solid electrolyte sheet using the support, and a secondary battery using the solid electrolyte sheet can be provided. Detailed Implementation

[0024] Hereinafter, examples of methods for implementing the present invention will be described, but the present invention is not limited to the following examples.

[0025] It should be noted that the explanations are presented in the following order.

[0026] 1. Embodiment of a support for a secondary battery (First Embodiment)

[0027] 2. Implementation method of secondary battery (second implementation method)

[0028] <1. Embodiment of a support for a secondary battery (First Embodiment)>

[0029] The following describes a specific implementation method for a support structure for secondary batteries.

[0030] The secondary battery support of this method (hereinafter also referred to as support) is a support for holding the solid electrolyte of the secondary battery, said secondary battery support having multiple layers formed by laminating at least one of paper and nonwoven fabric.

[0031] It should be noted that the numerical range indicated by "~" in this disclosure includes values ​​represented as upper and lower limits.

[0032] For a solid electrolyte layer sandwiched between the positive and negative electrodes, it is required that carrier ions conduct between the positive and negative electrodes during charging and discharging. To achieve this, carrier ions must form a passage line between the positive electrode and the solid electrolyte layer, within the solid electrolyte layer, and between the solid electrolyte layer and the negative electrode. In other words, by forming a uniform passage line of carrier ions within the support, the internal resistance of the solid electrolyte layer can be reduced, thereby reducing the overall resistance of the all-solid-state battery.

[0033] The inventors of this application have discovered that, in existing supports, the dispersion state of the fibers constituting the support can have an impact as one of the factors that prevents the resistance of the solid electrolyte layer from being further reduced.

[0034] In existing supports, due to the close bonding of fibers, there are multiple areas where fibers overlap and become biased. Therefore, when filling existing supports with solid electrolytes, it is impossible to fill the areas where fibers overlap with the solid electrolytes, and it is impossible to fill the solid electrolytes evenly.

[0035] Therefore, to ensure uniform filling of the solid electrolyte, the dispersion state of the fibers constituting the support must be improved. Thus, in this method, by forming a multi-layered stacked structure of the support, the dispersion state of the fibers within the support is made more uniform compared to existing supports. Compared to a single-layered support, a multi-layered support reduces fiber overlap. Therefore, the dispersion state of the fibers constituting the support can be further homogenized. By homogenizing the fiber dispersion, the internal space of the support is made more uniform, allowing the solid electrolyte to be uniformly filled throughout the support. Therefore, by having a multi-layered stacked structure, a secondary battery support capable of uniformly filling the interior with a solid electrolyte can be constructed.

[0036] For example, even with supports of the same density, a support with a heavier fiber presence (poor dispersion) will exhibit unevenness within the support compared to a support with well-dispersed fibers. This unevenness reduces the self-support of areas lacking fibers, leading to cracking. Furthermore, solid electrolytes are less likely to fill the areas of locally concentrated fibers within the support, resulting in fewer carrier ions passing through and higher resistance. Therefore, using a support with a heavier fiber presence easily leads to cracking and results in a solid electrolyte sheet with high resistance.

[0037] The multi-layered support structure of this method has more uniform fiber dispersion and equal internal space, thus allowing the solid electrolyte to be uniformly filled throughout the support. In solid electrolyte sheets using this support, the number of carrier ions passing through increases, and the resistance is less likely to rise. Furthermore, the increased number of fibers supporting the solid electrolyte in this support structure helps suppress cracking. In other words, by using a multi-layered support structure, cracking is less likely to occur compared to a single-layered support structure, resulting in lower resistance in the solid electrolyte sheet.

[0038] There are no particular limitations on the method of laminating a support into multiple layers, as long as the layers can be laminated independently without separation. For example, methods such as laminating paper using a papermaking process, or laminating the layers using a calender or laminator after fabrication, can be used. When paper is used in one of the layers, laminating using a papermaking process is preferred over lamination in a later stage. Furthermore, when using nonwoven fabrics made of chemical fibers, any method of laminating paper or lamination can be used. When laminating into multiple layers, it is important that the layers do not peel off.

[0039] The combination of materials constituting the support can be any combination of paper and non-woven fabric, and any material can be used in each layer.

[0040] Paper refers to materials made by bonding plant fibers or other fibers together. Nonwoven fabric, on the other hand, refers to sheet materials made by treating various fiber webs, such as natural, recycled, and synthetic fibers, mechanically, chemically, thermally, or in combination thereof without using a loom, and bonding the constituent fibers together using adhesives or the adhesive force of the fibers themselves.

[0041] That is, paper and nonwoven fabrics are composed of randomly arranged fibers, thus containing countless pores and through-holes of various sizes. Therefore, the coated solid electrolyte slurry can be extended not only in the thickness direction but also in the surface direction.

[0042] That is, the coated solid electrolytes include those that remain on the surface of the support, those that remain inside the support, and those that pass through the coating surface along the thickness direction of the support and reach the back side.

[0043] Therefore, for a solid electrolyte sheet made using a support structure comprising at least one of paper and nonwoven fabric in a laminated form, the solid electrolyte is naturally filled into the surface of the support and also into the interior of the support, forming a good ion-carrying flow path throughout the support.

[0044] As a result, while the resistance of the solid electrolyte sheet decreases, the interfacial resistance between the solid electrolyte sheet and the positive and negative electrodes can also be reduced. Consequently, this leads to a reduction in the overall resistance of the all-solid-state battery.

[0045] There is no particular limit to the number of layers in the support structure. The number of layers can be adjusted according to the thickness of the support structure.

[0046] When considering the thickness of the solid electrolyte sheet, a two- or three-layer structure of the support is preferred. With more than three layers, the support tends to become thicker, which inevitably leads to a thicker solid electrolyte sheet. Consequently, the battery resistance tends to increase, and this must be carefully considered.

[0047] The density of each layer of the support is not particularly limited, but is preferably 0.15~0.8 g / cm³. 3 The range.

[0048] The density of each layer exceeds 0.8 g / cm³. 3 In such cases, the density of the support tends to increase, and the number of fibers inside the support increases, making it difficult to fill the solid electrolyte. Therefore, it is not easy to form carrier ion passage lines inside the resulting solid electrolyte sheet.

[0049] On the other hand, the density of each layer is less than 0.15 g / cm³. 3 In such cases, through-printing of solid electrolytes becomes easier, and the amount of solid electrolyte that can hold the support decreases. As a result, the number of carrier ions passing through the solid electrolyte sheet also decreases, and the internal resistance of the solid electrolyte sheet tends to increase.

[0050] Therefore, by making the density of each layer 0.15g~0.8g / cm³ 3 This allows for the easy formation of carrier ion passage lines within the solid electrolyte sheet, thereby reducing internal resistance.

[0051] The thickness of the support is not particularly limited, but is preferably 5 to 100 μm. If the thickness is less than 5 μm, the solid electrolyte sheet becomes too thin, making it difficult to prevent short circuits between the positive and negative electrodes. On the other hand, if the thickness exceeds 100 μm, the solid electrolyte sheet becomes too thick, and the resistance of the all-solid-state battery tends to increase.

[0052] Alternatively, depending on the battery design requirements, a thicker solid electrolyte layer can be formed on both sides or only one side of the support. However, since this results in a thicker solid electrolyte layer without a support structure, excessive thickness can easily lead to cracking.

[0053] There are no particular limitations on the materials that can be used in the support, as long as they are fibers that do not repel the solid electrolyte slurry and do not have adverse physical or chemical effects on the solid electrolyte. Examples include organic fibers such as cellulose fibers, polyamide fibers, polyester fibers, polypropylene fibers, and acrylonitrile fibers; and inorganic fibers such as glass fibers and alumina fibers. Furthermore, one or more fibers selected from these types can be used. By using these fibers, a support with excellent solid electrolyte filling properties can be obtained.

[0054] Furthermore, from the viewpoint of maintaining the shape and mechanical strength of the support, it is desirable for the support to contain fibers with adhesive properties. Examples of fibers with adhesive properties include: fibers with fibrils on their surface (hereinafter referred to as fibrillated fibers), synthetic resin adhesives, etc.

[0055] For example, among fibrillated fibers, cellulose fibers, polyamide fibers, and acrylonitrile fibers are examples of fibers that have physical bonds based on fiber interlacing. Furthermore, if fibrillated fibers, like cellulose fibers, contain hydroxyl groups, they also have chemical bonds based on hydrogen bonds.

[0056] Any fiber-based bonding contributes to maintaining the shape and mechanical strength of the support, and is therefore preferred.

[0057] Among synthetic resin adhesive fibers, examples include those that maintain their fiber state in a state that forms a support, and those that do not maintain their fiber state but become, for example, a membrane. Adhesive fibers that maintain their fiber state in a state that forms a support are preferred in terms of not easily hindering permeability / permeability and improving the mechanical strength of the support.

[0058] The adhesive fibers, which maintain their fiber shape in a support-like state, exert their adhesive force by thermally bonding the fiber interlacing points. Therefore, the adhesive fibers, which maintain their fiber state as a component of the support, can reduce breakage from physical impacts, and since bonding only occurs at the fiber joints, it is less likely to hinder the penetration / permeation of the solid electrolyte slurry into the support when forming a solid electrolyte layer.

[0059] On the other hand, for binder fibers that cannot maintain their fibrous state when the support is formed, heat near the melting or softening point of the resin constituting the fibers is applied during the support manufacturing process, thereby melting the resin and fusing the fiber gaps into a thin film. That is, when a binder that cannot maintain its fibrous state is used when the support is formed, the binder components form a thin film layer in the fiber gaps of the support, filling the spaces, which can sometimes hinder the penetration / permeation of solid electrolytes into the support.

[0060] The materials that can be used in binder fibers that possess adhesive strength and maintain fiber shape are not particularly limited as long as they do not repel solid electrolyte slurries and do not have adverse physical or chemical effects on solid electrolytes. Examples include: pulped cellulose fibers, pulped polyamide fibers, pulped acrylonitrile fibers, polyamide binder fibers, polyester binder fibers, polyethylene binder fibers, and polypropylene-polyethylene core-sheath type binder fibers. Furthermore, one or more fibers selected from these types can be used. In the case of using fibrillated fibers, the density of the support constituting each layer should be 0.15~0.8 g / cm³. 3 The degree of fibrillation can be adjusted by adjusting the range of fibrillation.

[0061] There are no particular limitations on the manufacturing method of the support; it can be manufactured using dry or wet methods. From the viewpoint of uniformity in the texture of the support, it is ideal to use a papermaking method in which fibers dispersed in water are piled onto wires, dehydrated, dried, and then formed into paper. There are no particular limitations on the papermaking form of the support; long-wire papermaking, short-wire papermaking, and cylinder papermaking can be used. Furthermore, additives such as dispersants, defoamers, and paper strength enhancers can be added during papermaking. After the paper layer is formed, post-processing such as paper strength enhancement, hydrophilic processing, calendering, hot calendering, and embossing can be performed.

[0062] Furthermore, as a method for stacking the support into multiple layers, the following methods can be used: multiple supports formed by the above-mentioned papermaking method can be stacked through post-processing such as calendering or hot calendering. Alternatively, papermaking can be performed using a combination of multiple papermaking methods such as long-wire papermaking, short-wire papermaking, and cylinder papermaking, thereby stacking the supports.

[0063] <2. Implementation Method of Secondary Battery (Second Implementation Method)>

[0064] Next, an embodiment of a secondary battery using the aforementioned support will be described. The secondary battery is, for example, an all-solid-state battery having a positive electrode, a negative electrode, and a solid electrolyte layer. In this case, the solid electrolyte layer is disposed between the positive and negative electrodes. The solid electrolyte layer is configured as a solid electrolyte sheet in which the solid electrolyte is held by the support. The solid electrolyte sheet includes a support for the secondary battery and a solid electrolyte, and the solid electrolyte is held by the support; the solid electrolyte sheet has a configuration in which the solid electrolyte and the support are integrated.

[0065] There are no particular limitations on the types of positive and negative electrodes used in all-solid-state batteries. For example, all-solid-state batteries can be composed of known positive and negative electrodes, but are not limited to these.

[0066] Furthermore, there are no particular limitations on the types of all-solid-state batteries. By selecting the materials that constitute an all-solid-state battery, it can be formed into, for example, a lithium-ion secondary battery or a sodium-ion secondary battery.

[0067] The aforementioned all-solid-state batteries can be used as batteries for, for example, mobile communication devices, portable electronic devices, electric bicycles, electric two-wheelers, electric vehicles, and small household power storage devices.

[0068] [Positive electrode, negative electrode]

[0069] In secondary batteries, there are no particular limitations on the positive electrode active material used in the positive electrode and the negative electrode active material used in the negative electrode, as long as they function as the positive and negative electrodes of the all-solid-state battery corresponding to various carrier ions.

[0070] The positive electrode is formed by having a positive electrode active material and a positive electrode current collector. For example, if an all-solid-state battery is a lithium-ion secondary battery, the positive electrode must be made of a material that can absorb, store, and release lithium ions.

[0071] As a positive current collector, aluminum can be used, for example.

[0072] Examples of positive electrode active materials include, for example, titanium sulfide (TiS2), molybdenum sulfide (MoS2), ferrous sulfide or ferric disulfide (FeS, FeS2), copper sulfide (CuS), and nickel sulfide (Ni3S2) in the sulfide system. Additionally, examples of oxide systems include bismuth oxide (Bi2O3), bismuth lead oxide (Bi2Pb2O5), copper oxide (CuO), and vanadium oxide (V6O). 13 Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), Li(NiCoMn)O2, Li(NiCoAl)O2, Li(NiCo)O2, etc. Alternatively, these can be mixed and used together.

[0073] In addition, the negative electrode is formed by having a negative electrode active material and a negative electrode current collector. For example, if an all-solid-state battery is a lithium-ion secondary battery, then a material that can absorb, store, and release metallic lithium, metallic indium, or lithium ions can be used as the negative electrode active material.

[0074] As a negative current collector, copper can be used, for example.

[0075] Examples of anode active materials include carbon materials, specifically artificial graphite, graphite carbon fibers, resin-sintered carbon, pyrolytic vapor-grown carbon, coke, mesophase carbon microspheres (MCMB), furfuryl alcohol resin-sintered carbon, polyphenylene oxide, pitch-based carbon fibers, vapor-grown carbon fibers, natural graphite, and non-graphitizable carbon. Mixtures of these materials are also possible. Additionally, examples include metals such as lithium, indium, aluminum, or silicon, or alloys combining these metals with other elements or compounds.

[0076] Two materials that can be used to form electrodes are selected to form the positive and negative electrodes of an all-solid-state battery. The charge and discharge potentials of the two compounds are compared, and the one showing a higher potential is used as the positive electrode and the one showing a lower potential is used as the negative electrode to form an arbitrary battery.

[0077] [Solid electrolyte layer]

[0078] In an all-solid-state battery, the solid electrolyte layer is formed in the form of a solid electrolyte sheet in which the solid electrolyte is held by a support. There is no particular limitation on the type of solid electrolyte constituting the solid electrolyte sheet; for example, known materials that can be used as solid electrolytes in all-solid-state batteries can be used.

[0079] Furthermore, there are no particular limitations on solid electrolytes, as long as they can facilitate the conduction of carrier ions between the positive and negative electrodes. Examples include sulfide-based solid electrolytes and oxide-based solid electrolytes. Additionally, other components such as binders can be added as needed.

[0080] For example, sulfide-based solid electrolytes capable of lithium-ion conduction include sulfide-based amorphous solid electrolytes and sulfide-based crystalline solid electrolytes. Specific examples of sulfide-based amorphous solid electrolytes include Li₂S-SiS₂, Li₂S-GeS₂, Li₂S-P₂S₅, Li₂S-B₂S₃, Li₂S-SiS₂-Li₃PO₄, Li₂S-SiS₂-Li₂SO₄, Li₂S-P₂S₅-LiI, Li₂S-P₂S₅-P₂O₅-LiI, Li₂S-B₂S₃-LiI, Li₂S-P₂S₅-Li₂O-LiI, and Li₂S-SiS₂-B₂S₃-LiI.

[0081] It should be noted that sulfide-based amorphous solid electrolytes may also contain other elements.

[0082] Furthermore, as a specific example of a sulfide-based crystalline solid electrolyte, Li can be cited. 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12Li6PS5Cl, etc., but sulfide-based crystalline solid electrolytes are not limited to these elements.

[0083] Solid electrolytes can also be substances other than sulfide-based solid electrolytes and oxide-based solid electrolytes. Other examples include semi-solid polymer electrolytes containing carrier ions such as polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, or polyacrylonitrile. Solid electrolytes can also be so-called gel-type electrolytes that retain an electrolyte within a polymeric solid electrolyte, such as a polyethylene oxide-based polymer or a polymer containing at least one polymer selected from polyorganosiloxane chains and polyoxyethylene chains.

[0084] [Manufacturing method of solid electrolyte sheets]

[0085] There are no particular limitations on the manufacturing method of solid electrolyte sheets; common methods in this technical field can be applied.

[0086] For example, a method could be described as follows: preparing a slurry in which a solid electrolyte is dispersed in a solvent, coating the prepared slurry onto a support, and drying it. The solvent used in the preparation of the solid electrolyte slurry is not particularly limited as long as it does not adversely affect the performance of the solid electrolyte. For example, non-aqueous solvents could be used.

[0087] There are no particular limitations on the coating method of applying a slurry containing a solid electrolyte to both sides or one side of a support. Examples include slide die coat, comma die coat, comma reverse coat, gravure coating, and gravure reverse coating.

[0088] Drying after coating with a slurry containing a solid electrolyte can be carried out, for example, by using hot air, a heater, or a drying device utilizing high frequency.

[0089] It should be noted that the solid electrolyte tablets can be the dried tablets themselves, or they can be further pressurized to increase their mechanical strength and density. Examples of pressurization methods include tablet presses and roller presses.

[0090] [Manufacturing method of all-solid-state batteries]

[0091] All-solid-state batteries can be manufactured by placing a solid electrolyte layer containing a solid electrolyte sheet between the positive and negative electrodes, and bonding them together. The bonding method is not particularly limited; examples include: stacking the solid electrolyte sheet with the positive and negative electrodes and applying pressure / pressing; or releasing the components wound into rolls and continuously applying pressure / pressing (roll-to-roll), etc.

[0092] It should be noted that, in order to improve the adhesion between the solid electrolyte sheet and the positive or negative electrode, an active material with ion conductivity and an adhesive material that does not hinder ion conductivity can also be configured at the bonding interface.

[0093] Example

[0094] Hereinafter, specific embodiments of the support body according to the present invention will be described.

[0095] First, the supports for Examples 1 to 8, Existing Examples 1 to 2, and the Reference Example were manufactured using the methods described below. It should be noted that, except for Existing Example 2, the supports were manufactured using a papermaking method to produce paper or wet nonwoven fabric. Furthermore, in the following examples, for ease of explanation, in the case of two layers, one layer is referred to as layer A and the other as layer B; in the case of three layers, the middle layer is referred to as layer B, and the outer layers are referred to as layers A and C.

[0096] [Example 1]

[0097] The raw material, consisting of 100% cellulose fiber by mass, has a thickness of 2 μm and a basis weight of 1.6 g / m². 2 Density 0.80 g / cm³ 3 Layer A, made from 100% cellulose fiber raw material, has a thickness of 3 μm and a basis weight of 2.4 g / m². 2 Density 0.80 g / cm³ 3 Layer B was formed using a rotary screen-rotary screen composite machine to obtain a paper with a thickness of 5 μm and a basis weight of 4.0 g / m³. 2 Density 0.80 g / cm³ 3 The supporting structure.

[0098] [Example 2]

[0099] The material used was a mixture of 50% by mass polyester fiber and 50% by mass polyester binder fiber, with a thickness of 15 μm and a basis weight of 6.0 g / m. 2 Density 0.40 g / cm³ 3 Layer A, made from a raw material containing 50% by mass polyester fiber and 50% by mass polyester binder fiber, has a thickness of 12 μm and a basis weight of 4.0 g / m. 2 Density 0.33 g / cm³ 3 Layer B was formed using a stacked papermaking process based on a short-wire-cylinder composite machine, resulting in a paper thickness of 27 μm and a basis weight of 10.0 g / m². 2 Density 0.37 g / cm³ 3 The supporting structure.

[0100] [Example 3]

[0101] Using 100% cellulose fiber as raw material, paper with a thickness of 30 μm and a basis weight of 6.0 g / m² was produced using a fourdrinier paper machine. 2 Density 0.20 g / cm³ 3 Layer A is made using a mixture of 50% by mass polyester fiber and 50% by mass polyester binder fiber, produced using a cylinder paper machine to a thickness of 30μm and a basis weight of 6.0g / m². 2 Density 0.20 g / cm³ 3 Layer B. Then, layers A and B are moistened and hot-rolled, thereby achieving a single laminated product with a thickness of 60 μm and a basis weight of 12.0 g / m³. 2 Density 0.20 g / cm³ 3 The supporting structure.

[0102] [Example 4]

[0103] The material used was a mixture of 50% by mass polyester fiber and 50% by mass polyester binder fiber, with a thickness of 30 μm and a basis weight of 5.0 g / m. 2 Density 0.17 g / cm³ 3 Layer A, made from 100% by mass cellulose fiber, has a thickness of 40 μm and a basis weight of 6.0 g / m³. 2 Density 0.15 g / cm³ 3 Layer B, made from a raw material containing 50% by mass polyester fiber and 50% by mass polyester binder fiber, has a thickness of 30 μm and a basis weight of 5.0 g / m. 2 Density 0.17 g / cm³ 3 The C layer was formed using a stacked papermaking process based on a cylinder wire-short wire-cylinder composite machine, resulting in a paper thickness of 100 μm and a basis weight of 16.0 g / m². 2 Density 0.16 g / cm³ 3 The supporting structure.

[0104] [Example 5]

[0105] The material used had a thickness of 20 μm and a basis weight of 2.5 g / m², and contained 50% by mass of polyester fiber and 50% by mass of polyester binder fiber. 2 Density 0.13 g / cm³ 3 Layer A, made from a raw material containing 50% by mass polyester fiber and 50% by mass polyester binder fiber, has a thickness of 15 μm and a basis weight of 5.0 g / m². 2 Density 0.33 g / cm³ 3 Layer B was formed using a stacked papermaking process based on a short-wire-cylinder composite machine, resulting in a paper thickness of 35 μm and a basis weight of 7.5 g / m². 2 Density 0.21 g / cm³ 3 The supporting structure.

[0106] [Example 6]

[0107] The raw material, consisting of 100% cellulose fiber by mass, has a thickness of 30 μm and a basis weight of 25.0 g / m. 2 Density 0.83 g / cm³ 3 Layer A, made from a raw material containing 50% by mass polyester fiber and 50% by mass polyester binder fiber, has a thickness of 17 μm and a basis weight of 8.0 g / m². 2 Density 0.47 g / cm³ 3 Layer B was formed using a stacked papermaking process based on a long-wire-cylinder composite machine, resulting in a paper thickness of 47 μm and a basis weight of 33.0 g / m². 2 Density 0.70 g / cm³ 3 The supporting structure.

[0108] [Example 7]

[0109] The raw material, consisting of 100% cellulose fiber by mass, has a thickness of 2 μm and a basis weight of 0.9 g / m. 2 Density 0.45 g / cm³ 3 Layer A, made from raw materials containing 100% cellulose fiber, has a thickness of 2 μm and a basis weight of 1.0 g / m³. 2 Density 0.50 g / cm³ 3 Layer B was formed using a rotary screen-rotary screen composite machine to obtain a paper with a thickness of 4μm and a basis weight of 1.9g / m³. 2 Density 0.48 g / cm³ 3 The supporting structure.

[0110] [Example 8]

[0111] The material used was a mixture of 50% by mass polyester fiber and 50% by mass polyester binder fiber, with a thickness of 32 μm and a basis weight of 13.0 g / m. 2 Density 0.41 g / cm³ 3 Layer A, made from 100% cellulose fiber raw material, has a thickness of 40 μm and a basis weight of 16.0 g / m². 2 Density 0.40 g / cm³ 3 Layer B, made from a raw material containing 50% by mass polyester fiber and 50% by mass polyester binder fiber, has a thickness of 32 μm and a basis weight of 13.0 g / m. 2 Density 0.41 g / cm³ 3 The C layer was formed using a stacked papermaking process based on a cylinder wire-short wire-cylinder composite machine, resulting in a paper thickness of 104 μm and a basis weight of 42.0 g / m². 2 Density 0.40 g / cm³ 3 The supporting structure.

[0112] [Existing Example 1]

[0113] Using a raw material mixed with 15% by mass of polyester fiber and 85% by mass of polyester binder fiber, and referring to the method for manufacturing the support described in Example 1 of Patent Document 1, cylinder papermaking was performed to obtain a thickness of 19 μm and a basis weight of 3.8 g / m². 2 Density 0.20 g / cm³ 3 The supporting structure.

[0114] [Existing Example 2]

[0115] A support was manufactured using the same method as described in Example 2 of Patent Document 1, resulting in the support of Conventional Example 2. In Conventional Example 2, the polyimide film was etched to form 200 μm square holes, resulting in a thickness of 30 μm and a basis weight of 8.8 g / m². 2 Density 0.29 g / cm³ 3 The supporting structure.

[0116] [Reference Example]

[0117] Using a raw material mixed with 50% by mass polyester fiber and 50% by mass polyester binder fiber, cylinder papermaking was performed to obtain a paper with a thickness of 60 μm and a basis weight of 12.0 g / m². 2 Density 0.20 g / cm³ 3 The supporting structure.

[0118] [The fabrication of all-solid-state batteries]

[0119] Next, a solid-state battery is fabricated using the supports described in the above embodiments, existing examples, and reference examples. The specific fabrication method is as follows.

[0120] (Positive electrode structure)

[0121] LiNiCoAlO2 ternary powder was used as the positive electrode active material, Li2S-P2S5 amorphous powder was used as the sulfide-based solid electrolyte, and carbon fiber was used as a conductive additive. These were then mixed together. A dehydrated xylene solution containing SBR (styrene-butadiene rubber) as a binder was added to this mixed powder to prepare the positive electrode coating solution. The positive electrode coating solution was then coated onto an aluminum foil current collector (the positive electrode current collector) and dried. Further calendering was then performed to obtain the positive electrode structure.

[0122] (Negative electrode structure)

[0123] Graphite was used as the negative electrode active material, Li2S-P2S5 amorphous powder as the sulfide-based solid electrolyte, PVdF (polyvinylidene fluoride) as the binder, and NMP (N-methyl-2-pyrrolidone) as the solvent. These were mixed to prepare the negative electrode coating solution. The negative electrode coating solution was then coated onto a copper foil current collector, which served as the negative electrode current collector, and dried. Further calendering was then performed to obtain the negative electrode structure.

[0124] (Solid electrolyte tablets)

[0125] A solid electrolyte slurry was prepared by mixing Li2S-P2S5 amorphous powder as a sulfide-based solid electrolyte, SBR as a binder, and xylene as a solvent.

[0126] Solid electrolyte slurry is coated onto the support of each of the above embodiments, existing examples and reference examples, and then dried to obtain a solid electrolyte sheet.

[0127] [Manufacturing of all-solid-state batteries]

[0128] A negative electrode structure measuring 88mm×58mm, a solid electrolyte sheet measuring 92mm×62mm, and a positive electrode structure measuring 87mm×57mm are stacked, dry-laminated, and bonded together to obtain a single cell of an all-solid-state battery.

[0129] The obtained single cell is placed into an aluminum laminate film containing terminals, degassed, and heat-sealed to form a bag.

[0130] [Methods for determining the properties of supports and all-solid-state batteries]

[0131] The properties of the fabricated support and the all-solid-state battery were determined under the following conditions and methods.

[0132] 〔thickness〕

[0133] Using a device with the measuring force of the micrometer set to 1.5 N and the diameter of the pressure surface changed to 14.3 mmφ as described in "5.1.1 Measuring device and measuring method a. When using an external micrometer" of "JIS C 2300-2 'Cellulose paper for electrical use - Part 2: Test methods' 5.1 Thickness", the thickness of the support was measured by folding 10 sheets as described in "5.1.3 When measuring thickness by folding paper".

[0134] [Base weight]

[0135] The basis weight of the support in an oven-dry state was determined according to the method specified in "JIS C 2300-2 'Cellulose paper for electrical use - Part 2: Test methods' 6 Basis weight".

[0136] 〔density〕

[0137] Calculate the density of the support using the following formula.

[0138] Density (g / cm³) 3 =W / T

[0139] W: Basis weight (g / m³) 2 T: Thickness (μm)

[0140] Porosity

[0141] The porosity of the support is calculated using the following formula. It should be noted that when multiple materials constituting the support are mixed, a calculation proportional to the mixing ratio is performed, and the average specific gravity of the constituent fibers is determined before calculating the porosity.

[0142] Porosity (%) = (1 - (D / S)) × 100

[0143] D: Support density (g / cm³) 3 S: Specific gravity of the fiber (g / cm³) 3 )

[0144] [Tensile Strength]

[0145] Using the method specified in "JIS P 8113 'Paper and board - Determination of tensile properties - Part 2: Constant rate of elongation method'" (ISO1924-2 'Paper and board - Determination of tensile properties - Part 2: Constant rate of elongation method'), the maximum tensile load in the longitudinal direction (manufacturing direction) of the support is determined with a test width of 15 mm, and this is taken as the tensile strength of the support.

[0146] [Internal resistance of all-solid-state batteries]

[0147] For all-solid-state batteries, they were charged at 0.1C current density to 4.0V at 25℃. The impedance in the frequency range of 0.1Hz to 1MHz was measured using an LCR meter. The arc portion of the resulting Cole-Cole plot was fitted to a semicircle with the x-axis as its base. The value of the portion where the right end of the semicircle intersects the x-axis was taken as the resistance value.

[0148] [Discharge capacity of all-solid-state batteries]

[0149] For all-solid-state batteries, they are charged at 0.1C current density to 4.0V at 25℃, and then discharged at 0.1C current density to 2.5V. The discharge capacity at this point is then measured.

[0150] The names and blending ratios of the fibers used in each support for Examples 1 to 8, Existing Examples 1 to 2, and the Reference Example are shown in Table 1. Furthermore, the characteristics of each support for each of the above Examples and Existing Examples, and the evaluation results of the battery characteristics of the all-solid-state battery are shown in Table 2.

[0151] [Table 1]

[0152]

[0153] [Table 2]

[0154]

[0155] The following provides a detailed description of the evaluation results of all-solid-state batteries using supports from various embodiments, existing examples, and reference examples.

[0156] As shown in Table 2, the all-solid-state batteries using the supports of Examples 1-8 exhibit superior internal resistance and discharge capacity compared to the all-solid-state batteries using the supports of Existing Examples 1-2 and the Reference Example. In particular, the all-solid-state batteries using supports with a layer density of 0.15-0.8 g / cm³ are particularly effective. 3 0.15~0.8g / cm 3 Compared with the all-solid-state batteries using supports of Examples 1-4 that have densities of each layer outside the above range, and the all-solid-state batteries using supports of Examples 7-8 that have thicknesses outside the above range, the all-solid-state batteries with supports of Examples 5-6 that have densities of each layer outside the above range have excellent internal resistance and discharge capacity.

[0157] The all-solid-state batteries using the supports of Examples 5 and 6 exhibit higher resistance and lower discharge capacity compared to the all-solid-state batteries using the supports of Examples 1-4. The support of Example 5 has a low density of only 0.13 g / cm³ due to the low density of the A-layer support. 3 Therefore, it is believed that when a solid electrolyte is coated, the amount of solid electrolyte that layer A can retain decreases. As a result, the number of carrier ions passing through the solid electrolyte sheet decreases, leading to the conclusion that it becomes an all-solid-state battery with high resistance and low discharge capacity.

[0158] The support in Example 6 has a layer A with a density as high as 0.83 g / cm³. 3 Therefore, it is considered that it becomes difficult to fill the A layer with a solid electrolyte. As a result, sufficient ion-carrying lines cannot be formed inside the obtained solid electrolyte sheet, resulting in an all-solid-state battery with high resistance and low discharge capacity.

[0159] That is, as can be seen from the comparison between Examples 1-4 and Examples 5 and 6, the density of each layer constituting the support is preferably 0.15-0.80 g / cm³. 3 The range.

[0160] The all-solid-state battery using the support of Example 7 exhibited no problems with its discharge characteristics; however, several batteries experienced short circuits during discharge testing. The support of Example 7 was only 4 μm thick, therefore, it is believed that the close proximity of the positive and negative electrodes was the primary cause of the short circuits.

[0161] When using the support of Example 8, the resistance is high and the discharge capacity is low compared to all-solid-state batteries using the supports of the various embodiments. The support of Example 8 is 104 μm thick, therefore, the thickness of the resulting solid electrolyte sheet is also increased. As a result, the resistance of the all-solid-state battery using this solid electrolyte sheet is considered to be higher.

[0162] That is, as can be seen from the comparison between Examples 1-4 and Examples 7 and 8, the thickness of the support is preferably in the range of 5-100 μm.

[0163] Compared to the all-solid-state batteries using the supports of Examples 1-8, the all-solid-state battery using the existing support of Example 1 has higher resistance and lower discharge capacity. Although the support of Existing Example 1 is a support with sufficient porosity, there are areas where the fibers are closely packed and overlapped, resulting in fewer carrier ions passing through along the thickness direction inside the solid electrolyte sheet. As a result, the all-solid-state battery using the support of Existing Example 1 has higher resistance and lower discharge capacity compared to the all-solid-state batteries using the supports of Examples 1-8.

[0164] As can be seen from the comparison of the various embodiments with the existing Example 1, in order to reduce the resistance of the all-solid-state battery, the support obtained by stacking multiple layers into one is suitable.

[0165] The support in Existing Example 2 differs from the paper or nonwoven fabric supports in Examples 1-8; it is a support with through-holes formed in a thin film. However, while a solid electrolyte can be filled into the through-holes of the support in Existing Example 2, the solid electrolyte can only be filled inside the formed through-holes. Therefore, the portion outside the through-holes retains a thin film portion belonging to the insulating material, and there are areas where no solid electrolyte exists.

[0166] The results showed that the all-solid-state battery using the support of the existing Example 2 had higher resistance and lower discharge capacity compared to the all-solid-state batteries using the supports of the various embodiments.

[0167] A comparison of Examples 1-8 with the existing Example 2 shows that paper and non-woven fabric are suitable as supports in order to reduce the resistance of all-solid-state batteries.

[0168] The support in the reference example has the same density and thickness as the support in Example 3, but it has higher resistance and lower discharge capacity. It is believed that the poor fiber dispersion in the support of the reference example caused unevenness and cracks within the support. As a result, the all-solid-state battery using the support of the reference example has higher resistance and lower discharge capacity compared to the all-solid-state batteries using the supports of Examples 1-8.

[0169] The above-described embodiments are merely examples, and those skilled in the art can appropriately modify, for example, the composition of the carrier ions, solid electrolyte, positive electrode, and negative electrode.

[0170] It should be noted that the present invention is not limited to the configuration described in the above embodiments. Furthermore, various modifications and alterations can be made without departing from the scope of the present invention.

Claims

1. A support for a secondary battery, which serves as a support for holding the solid electrolyte of the secondary battery. The secondary battery support is composed of multiple layers formed by laminating at least one of paper and nonwoven fabric.

2. The secondary battery support according to claim 1, which has a structure of being integrally stacked into two or three layers.

3. The support for a secondary battery according to claim 1, wherein, The density of each layer of the support is 0.15~0.8 g / cm³. 3 .

4. The support for a secondary battery according to any one of claims 1 to 3, wherein, The thickness of the support is 5~100μm.

5. A solid electrolyte sheet, comprising: A support for a secondary battery, comprising multiple layers integrally laminated from at least one of paper and nonwoven fabric; and, Solid electrolyte held by the support.

6. A secondary battery comprising: a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode. The solid electrolyte layer comprises: A support for a secondary battery, comprising multiple layers integrally laminated from at least one of paper and nonwoven fabric; and, Solid electrolyte held by the support.

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