All-solid-state batteries

Abstract

The main purpose of the present disclosure is to provide an all-solid-state battery with good cycle characteristics. The present disclosure solves the above-mentioned problems by providing the following all-solid-state battery, which has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer, the solid electrolyte layer has a first solid electrolyte layer and a second solid electrolyte layer, the second solid electrolyte layer is arranged on the negative electrode layer side relative to the first solid electrolyte layer, the first solid electrolyte layer contains a first non-woven fabric and a first solid electrolyte arranged inside the first non-woven fabric, the second solid electrolyte layer contains a second non-woven fabric and a second solid electrolyte arranged inside the second non-woven fabric, and in a plan view observed along the thickness direction, the angle between the first fiber direction of the first non-woven fabric and the second fiber direction of the second non-woven fabric is greater than 45° and less than 90°.

Description

Technical Field

[0001] The present disclosure relates to all-solid-state batteries. Background Art

[0002] All-solid-state batteries have a solid electrolyte layer between the positive and negative electrode layers. Compared to liquid-type batteries with an electrolyte solution containing a flammable organic solvent, they offer the advantage of simplified safety features. Patent Document 1 discloses a solid electrolyte sheet for an all-solid-state secondary battery comprising a nonwoven fabric and a solid electrolyte on and within the nonwoven fabric.

[0003] Patent Document 2 discloses a method for manufacturing a solid electrolyte membrane for an all-solid-state battery, comprising a step of forming a nonwoven fabric comprising fibers made of a resin. Patent Document 3 also discloses an electrode assembly comprising a first electrode, a second electrode, and a separator, wherein the first electrode comprises a plurality of fibrous first structures extending in a first direction, the second electrode comprises a plurality of fibrous second structures extending in a second direction different from the first direction, and the separator is disposed between the first and second structures.

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-031789

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-181758

[0007] Patent Document 3: Japanese Patent Application No. 2013-534704 Summary of the Invention

[0008] From the perspective of improving battery performance, all-solid-state batteries with excellent cycle characteristics are required. The present disclosure has been made in view of the above-mentioned situation, and its main object is to provide an all-solid-state battery with excellent cycle characteristics.

[0009] In the present disclosure, an all-solid-state battery is provided, comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer comprises a first solid electrolyte layer and a second solid electrolyte layer arranged closer to the negative electrode layer than the first solid electrolyte layer, wherein the first solid electrolyte layer comprises a first non-woven fabric and a first solid electrolyte arranged inside the first non-woven fabric, and the second solid electrolyte layer comprises a second non-woven fabric and a second solid electrolyte arranged inside the second non-woven fabric, wherein, in a plan view observed along the thickness direction, an angle between a first fiber direction of the first non-woven fabric and a second fiber direction of the second non-woven fabric is greater than 45° and less than 90°.

[0010] According to the present disclosure, the angle between the first fiber direction and the second fiber direction is within a predetermined range, thereby achieving an all-solid-state battery with excellent cycle characteristics.

[0011] In the above disclosure, the angle may be greater than or equal to 80° and less than or equal to 90°.

[0012] In the above disclosure, the porosity of the first nonwoven fabric and the porosity of the second nonwoven fabric may be 70% or more and 90% or less, respectively.

[0013] In the above disclosure, in the above-mentioned first non-woven fabric, the tensile strength in the above-mentioned first fiber direction can be greater than the tensile strength in the direction orthogonal to the above-mentioned first fiber direction, and in the above-mentioned second non-woven fabric, the tensile strength in the above-mentioned second fiber direction can be greater than the tensile strength in the direction orthogonal to the above-mentioned second fiber direction.

[0014] In the above disclosure, at least one of the first solid electrolyte and the second solid electrolyte may be an inorganic solid electrolyte.

[0015] In the above disclosure, the above-mentioned inorganic solid electrolyte may be at least one of a sulfide solid electrolyte, an oxide solid electrolyte, and a hydride solid electrolyte.

[0016] In the above disclosure, at least one of the first solid electrolyte and the second solid electrolyte may be a molten salt (meltable salt) that is solid at 25°C.

[0017] In the above disclosure, at least one of the first solid electrolyte and the second solid electrolyte may be a plastic crystalline solid electrolyte.

[0018] The all-solid-state battery disclosed herein has an effect of good cycle characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic cross-sectional view illustrating a battery in the present disclosure.

[0020] Figure 2 This is a schematic perspective view illustrating a battery in the present disclosure.

[0021] Figure 3 It is a schematic diagram explaining the first fiber direction and the second fiber direction in the present disclosure.

[0022] Description of Reference Numerals

[0023] 1…positive electrode layer

[0024] 2…Negative electrode layer

[0025] 3…Solid electrolyte layer

[0026] 3a…1st solid electrolyte layer

[0027] 3b…Second solid electrolyte layer

[0028] 4…Positive electrode current collector

[0029] 5…Negative electrode current collector

[0030] 10…All-solid-state batteries DETAILED DESCRIPTION

[0031] The following figures illustrate the all-solid-state battery disclosed herein in detail. Each of the following figures is a schematic diagram, and the size and shape of the components are exaggerated for ease of understanding. Furthermore, hatching indicating component cross-sections is omitted in each figure.

[0032] Figure 1 This is a schematic cross-sectional view illustrating an all-solid-state battery in the present disclosure. Figure 1 The illustrated all-solid-state battery 10 includes a positive electrode layer 1, a negative electrode layer 2, a solid electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive electrode current collector 4 for collecting current from the positive electrode layer 1, and a negative electrode current collector 5 for collecting current from the negative electrode layer 2. The solid electrolyte layer 3 includes a first solid electrolyte layer 3a and a second solid electrolyte layer 3b, with the second solid electrolyte layer 3b disposed closer to the negative electrode layer 2 than the first solid electrolyte layer 3a. The first solid electrolyte layer 3a comprises a first nonwoven fabric and a first solid electrolyte disposed within the first nonwoven fabric. Furthermore, the second solid electrolyte layer 3b comprises a second nonwoven fabric and a second solid electrolyte disposed within the second nonwoven fabric.

[0033] Figure 2 This is a schematic perspective view illustrating the all-solid-state battery in the present disclosure. Figure 2 For convenience, there is space between each layer. Figure 2 As shown, the first fiber direction of the first nonwoven fabric included in the first solid electrolyte layer 3a is set to D1. Similarly, the second fiber direction of the second nonwoven fabric included in the second solid electrolyte layer 3b is set to D2. T In the plane view of the observation, the angle between D1 and D2 is within a predetermined range. Figure 3 , the angle θ between D1 and D2 is 90°. In the present disclosure, the angle θ between D1 and D2 represents an acute angle, and is usually 90° or less.

[0034] According to the present disclosure, the angle between the first fiber direction and the second fiber direction is within a predetermined range, resulting in an all-solid-state battery with excellent cycle characteristics. As described in the aforementioned Patent Document 1, a solid electrolyte sheet (solid electrolyte layer) containing a solid electrolyte within a non-woven fabric is known. By including a non-woven fabric in the solid electrolyte layer, for example, the thickness of the solid electrolyte layer can be reduced while maintaining insulation performance.

[0035] On the other hand, when the multiple fibers constituting the nonwoven fabric extend in one direction, their tensile strength is not isotropic, but anisotropic. Here, the direction in which the multiple fibers mainly extend is defined as the fiber direction. The fiber direction is usually consistent with the MD (Machine Direction, longitudinal) direction corresponding to the direction of travel (flow direction) in the manufacturing process of the nonwoven fabric. In addition, generally speaking, the direction orthogonal to the MD direction is called the CD (Cross Direction, transverse) direction. The MD direction and the CD direction can be determined by observing the nonwoven fabric with a microscope and confirming the direction in which the fibers extend. When the multiple fibers constituting the nonwoven fabric extend in one direction, the tensile strength in the fiber direction (MD direction) is usually greater than the tensile strength in the direction orthogonal to the fiber direction (CD direction).

[0036] If the tensile strength in the MD direction is different from the tensile strength in the CD direction in a non-woven fabric, the uniformity of the solid electrolyte layer decreases whenever stress associated with charge and discharge is applied to the solid electrolyte layer. As a result, internal short circuits such as micro short circuits are likely to occur, and the cycle characteristics deteriorate. In contrast, in the present disclosure, the first solid electrolyte layer and the second solid electrolyte layer are arranged in a manner such that the first fiber direction of the first non-woven fabric and the second fiber direction of the second non-woven fabric intersect. As a result, the anisotropy of the tensile strength is alleviated. As a result, the uniformity of the solid electrolyte layer can be maintained and the cycle characteristics are improved.

[0037] like Figure 2 As shown in FIG. 1 , the direction of the first fibers in the first nonwoven fabric included in the first solid electrolyte layer 3a is set to D1. Similarly, the direction of the second fibers in the second nonwoven fabric included in the second solid electrolyte layer 3b is set to D2. Figure 3 As shown, the angle between D1 and D2 is θ. The angle θ is usually greater than 45°, but may be greater than 60°, greater than 70°, or greater than 80°. On the other hand, the angle θ may be 90° or less.

[0038] 1. Solid electrolyte layer

[0039] The solid electrolyte layer in the present disclosure is a layer disposed between the positive electrode layer and the negative electrode layer. The solid electrolyte layer includes a first solid electrolyte layer and a second solid electrolyte layer disposed closer to the negative electrode layer than the first solid electrolyte layer.

[0040] (1) First solid electrolyte layer

[0041] The first solid electrolyte layer includes a first nonwoven fabric and a first solid electrolyte disposed inside the first nonwoven fabric.

[0042] (i) 1st nonwoven fabric

[0043] The first non-woven fabric usually has a plurality of fibers, and pores are formed between the plurality of fibers. In addition, the plurality of fibers extend along the first fiber direction. The plurality of fibers can extend linearly along the first fiber direction, or can extend in a serpentine or zigzag manner. Examples of the material of the fiber include resins such as polyester resins, polyolefin resins, and polyamide resins. Examples of polyester resins include polyethylene terephthalate (PET). Examples of polyolefin resins include polyethylene (PE) and polypropylene (PP). Examples of polyamide resins include nylon and aromatic polyamide. In addition, glass can be used as the material of the fiber. That is, the first non-woven fabric can be a glass fiber non-woven fabric. The fiber diameter and fiber length of the fibers constituting the first non-woven fabric are not particularly limited.

[0044] The porosity of the first nonwoven fabric is not particularly limited, and may be, for example, 50% or more, 60% or more, or 70% or more. If the porosity of the first nonwoven fabric is too small, the internal resistance is likely to increase. On the other hand, the porosity of the first nonwoven fabric may be, for example, 95% or less, or 90% or less. If the porosity of the first nonwoven fabric is too large, it may not function as a support. The porosity of the first nonwoven fabric can be obtained, for example, by observing the cross-section of the nonwoven fabric. In addition, the size of the pores is not particularly limited.

[0045] In the first nonwoven fabric, the tensile strength in the first fiber direction (MD direction) is set to TS1, and the tensile strength in the direction perpendicular to the first fiber direction (CD direction) is set to TS2. Preferably, TS1 is greater than TS2. In this case, due to the anisotropy of the tensile strength, the cycle characteristics are easily reduced. In contrast, in the present disclosure, the anisotropy of the tensile strength can be alleviated by setting the angle between the first fiber direction and the second fiber direction within a predetermined range. TS1 is, for example, greater than 1 N / cm, may be greater than 3 N / cm, or may be greater than 5 N / cm. On the other hand, TS1 is, for example, less than 50 N / cm. In addition, TS2 is, for example, greater than 0.1 N / cm, may be greater than 0.5 N / cm, or may be greater than 1 N / cm. On the other hand, TS2 is, for example, less than 30 N / cm. In addition, the ratio of TS1 to TS2 (TS1 / TS2) is, for example, greater than 1.1, may be greater than 1.5, may be greater than 2.0, or may be greater than 5.0. On the other hand, TS1 / TS2 is, for example, less than 50.

[0046] Examples of the first nonwoven fabric include chemically bonded nonwoven fabrics, thermally bonded nonwoven fabrics, air-laid nonwoven fabrics, spunlace nonwoven fabrics, spunbond nonwoven fabrics, meltblown nonwoven fabrics, needle-punched nonwoven fabrics, and stitchbonded nonwoven fabrics. The thickness of the first nonwoven fabric is not particularly limited and may be, for example, 1 μm or greater, 5 μm or greater, or 10 μm or greater. Alternatively, the thickness of the first nonwoven fabric may be, for example, 50 μm or less.

[0047] (ii) First solid electrolyte

[0048] The first solid electrolyte layer contains a first solid electrolyte disposed inside the first non-woven fabric. The first solid electrolyte layer may contain only one first solid electrolyte, or may contain two or more. Examples of the first solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes, halide solid electrolytes, and nitride solid electrolytes. The sulfide solid electrolyte preferably contains sulfur (S) as the main component of the anion element. The oxide solid electrolyte preferably contains oxygen (O) as the main component of the anion element. The hydride solid electrolyte preferably contains hydrogen (H) as the main component of the anion element. The halide solid electrolyte preferably contains a halogen (X) as the main component of the anion. The nitride solid electrolyte preferably contains nitrogen (N) as the main component of the anion element.

[0049] The sulfide solid electrolyte preferably contains, for example, Li, A (A is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. Furthermore, the sulfide solid electrolyte may further contain at least one of O and a halogen element. Examples of the halogen element include F, Cl, Br, and I.

[0050] The sulfide solid electrolyte preferably has an anion structure of the original composition (e.g. PS4 3- Structure, SiS4 4- Structure, GeS4 4- Structure, AlS3 3- Structure or BS3 3- The anionic structure is the main component of the sulfide solid electrolyte. This is because of its high chemical stability. The proportion of the anionic structure in the original composition relative to the total anionic structure in the sulfide solid electrolyte is, for example, 70 mol% or more, or 90 mol% or more.

[0051] Sulfide solid electrolytes can be either amorphous or crystalline. In the latter case, the sulfide solid electrolyte has a crystalline phase. Examples of crystalline phases include Thio-LISICON, LGPS, and Argentite.

[0052] The composition of the sulfide solid electrolyte is not particularly limited, and examples thereof include xLi2S·(100-x)P2S5 (70≤x≤80), yLiI·zLiBr·(100-yz)(xLi2S·(1-x)P2S5)(0.7≤x≤0.8, 0≤y≤30, 0≤z≤30).

[0053] The sulfide solid electrolyte may have a general formula (1): Li 4-x Ge 1-x P x A composition represented by S4 (0<x<1). In the general formula (1), at least a portion of Ge may be substituted by at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the general formula (1), at least a portion of P may be substituted by at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the general formula (1), a portion of Li may be substituted by at least one of Na, K, Mg, Ca, and Zn. In the general formula (1), a portion of S may be substituted by a halogen (at least one of F, Cl, Br, and I).

[0054] Other compositions of the sulfide solid electrolyte include, for example, Li 7-x-2y PS 6-x-y X y 、Li8-x-2y SiS 6-x- y X y 、Li 8-x-2y GeS 6-x-y X y In these compositions, X is at least one of F, Cl, Br and I, and x and y satisfy 0≤x, 0≤y.

[0055] As an example of an oxide solid electrolyte, there can be mentioned a solid electrolyte containing Li element, Y element (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W and S) and O element. As a specific example of an oxide solid electrolyte, there can be mentioned Li7La3Zr2O 12 、Li 7-x La3(Zr 2-x Nb x )O 12 (0≤x≤2), Li5La3Nb2O 12 Garnet-type solid electrolytes; perovskite-type solid electrolytes such as (Li,La)TiO3, (Li,La)NbO3, (Li,Sr)(Ta,Zr)O3; sodium superion conductor-type solid electrolytes such as Li(Al,Ti)(PO4)3 and Li(Al,Ga)(PO4)3; Li-PO-based solid electrolytes such as Li3PO4 and LIPON (compounds in which part of the O in Li3PO4 is replaced by N); Li-BO-based solid electrolytes such as Li3BO3 and compounds in which part of the O in Li3BO3 is replaced by C.

[0056] The hydride solid electrolyte has, for example, Li and a complex anion containing hydrogen. As the complex anion, for example, (BH4) - NH2 - 、(AlH4) - and (AlH6) 3- As a halide solid electrolyte, for example, Li 6-3z Y z X6 (X is at least one of Cl and Br, and z satisfies 0<z<2). Examples of the nitride solid electrolyte include Li3N.

[0057] Another example of the first solid electrolyte is a molten salt that is solid at 25°C. The molten salt has cations and anions. Examples of cations include inorganic cations such as lithium ions; ammonium cations, piperidinium cations, pyridinium cations, imidazolium cations, pyridinium cations, and the like. (pyridium) cations, alicyclic amine cations, aliphatic amine cations, aliphatic An organic cation such as a cation. Examples of anions include anions having a sulfonamide structure. Examples of anions having a sulfonamide structure include bis(trifluoromethanesulfonyl)amide, bis(fluorosulfonyl)amide, bis(pentafluoroethanesulfonyl)amide, and (fluorosulfonyl)(trifluoromethanesulfonyl)amide. The melting point of the molten salt is generally above 25°C, may be above 30°C, or may be above 40°C. On the other hand, the melting point of the molten salt is, for example, below 200°C, may be below 150°C, or may be below 120°C.

[0058] As another example of the first solid electrolyte, a plastic crystal solid electrolyte can be cited. A plastic crystal is a substance composed of a regularly arranged three-dimensional lattice, and has orientational and rotational disorder at the level of molecular species or molecular ions. The plastic crystal has cations and anions. Examples of cations include pyrrolidine Tetraalkylammonium and tetraalkyl Examples of the anion include hexafluorophosphate, tetrafluoroborate, thiocyanate, bis(trifluoromethanesulfonyl)amide, bis(fluorosulfonyl)amide, bis(pentafluoroethanesulfonyl)amide, and (fluorosulfonyl)(trifluoromethanesulfonyl)amide.

[0059] The shape of the first solid electrolyte may be, for example, a granular shape. The average particle size (D 50 ) is not particularly limited, and may be, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size (D 50 ) is, for example, 50 μm or less, or 20 μm or less. The average particle size (D 50 ) is preferably smaller than the thickness of the first nonwoven fabric. Average particle size (D 50 ) can be calculated by, for example, a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM). The ratio of the total volume of the first solid electrolyte to the total volume of the pores in the first non-woven fabric is, for example, 50% by volume or more, 70% by volume or more, or 90% by volume or more.

[0060] (iii) First solid electrolyte layer

[0061] The first solid electrolyte layer may or may not contain a binder. Examples of the binder include rubber-based binders such as butadiene rubber, hydrogenated butadiene rubber, styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, and ethylene-propylene rubber; and fluoride-based binders such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, and fluororubber. The proportion of the binder in the first solid electrolyte layer is, for example, 0 parts by weight or more and 3 parts by weight or less relative to 100 parts by weight of the first solid electrolyte.

[0062] The plan view shape of the first solid electrolyte layer is not particularly limited, and examples thereof include rectangular shapes such as squares and rectangles. The Young's modulus of the first solid electrolyte layer is, for example, 1 GPa or greater. The thickness of the first solid electrolyte layer is not particularly limited, and for example, it may be 1 μm or greater, 5 μm or greater, or 10 μm or greater. On the other hand, the thickness of the first solid electrolyte layer is, for example, 50 μm or less.

[0063] (2) Second solid electrolyte layer

[0064] The second solid electrolyte layer comprises a second nonwoven fabric and a second solid electrolyte disposed within the second nonwoven fabric. Details regarding the second nonwoven fabric and the second solid electrolyte are identical to those described for the first nonwoven fabric and the first solid electrolyte, respectively, and are therefore omitted here. The second solid electrolyte and the first solid electrolyte are preferably, for example, sulfide solid electrolytes. Preferred embodiments of the second solid electrolyte layer are the same as those for the first solid electrolyte layer.

[0065] (3) Solid electrolyte layer

[0066] The solid electrolyte layer disclosed in the present invention has a first solid electrolyte layer and a second solid electrolyte layer. The first non-woven fabric in the first solid electrolyte layer and the second non-woven fabric in the second solid electrolyte layer can be in direct contact. By direct contact between the two, for example, the anisotropy of tensile strength is further alleviated. On the other hand, an intermediate solid electrolyte layer can also be arranged between the first non-woven fabric and the second non-woven fabric. By arranging the intermediate solid electrolyte layer, the internal resistance can be reduced. The intermediate solid electrolyte layer contains at least a solid electrolyte and may contain an adhesive as needed. Regarding the solid electrolyte and the adhesive, the contents are the same as those described in the above-mentioned "(1) First solid electrolyte layer". The intermediate solid electrolyte layer is usually a layer that does not contain a non-woven fabric. The thickness of the intermediate solid electrolyte layer is not particularly limited, for example, it is less than the thickness of the first non-woven fabric and the thickness of the second non-woven fabric.

[0067] The first non-woven fabric in the first solid electrolyte layer can be in direct contact with the positive electrode layer. On the other hand, a positive electrode side solid electrolyte layer can also be arranged between the first non-woven fabric and the positive electrode layer. By arranging the positive electrode side solid electrolyte layer, the internal resistance can be reduced. The positive electrode side solid electrolyte layer contains at least a solid electrolyte and can contain a binder as needed. The contents regarding the solid electrolyte and the binder are the same as those described in the above-mentioned "(1) First solid electrolyte layer". The positive electrode side solid electrolyte layer usually does not have electron conductivity. In addition, the positive electrode side solid electrolyte layer usually does not contain a non-woven fabric. The thickness of the positive electrode side solid electrolyte layer is not particularly limited, for example, it is less than the thickness of the first solid electrolyte layer.

[0068] The second non-woven fabric in the second solid electrolyte layer can be in direct contact with the negative electrode layer. On the other hand, a negative electrode side solid electrolyte layer can also be arranged between the second non-woven fabric and the negative electrode layer. By arranging the negative electrode side solid electrolyte layer, the internal resistance can be reduced. The negative electrode side solid electrolyte layer contains at least a solid electrolyte and can contain a binder as needed. Regarding the solid electrolyte and the binder, the contents are the same as those described in the above "(1) First solid electrolyte layer". The negative electrode side solid electrolyte layer usually does not have electron conductivity. In addition, the negative electrode side solid electrolyte layer usually does not contain a non-woven fabric. The thickness of the negative electrode side solid electrolyte layer is not particularly limited, for example, it is less than the thickness of the second solid electrolyte layer.

[0069] The solid electrolyte layer in the present disclosure may include only the first solid electrolyte layer and the second solid electrolyte layer as a layer containing a non-woven fabric, and may also include one or more other layers (layers containing non-woven fabrics). The angle between the fiber direction of the non-woven fabric in the other layers and the first fiber direction is, for example, 30° or more. In addition, the angle between the fiber direction of the non-woven fabric in the other layers and the second fiber direction is, for example, 30° or more.

[0070] The thickness of the solid electrolyte layer is, for example, 1 μm or more, 5 μm or more, or 10 μm or more. On the other hand, the thickness of the solid electrolyte layer is, for example, 150 μm or less, or 100 μm or less.

[0071] 2. Positive electrode layer

[0072] The positive electrode layer is a layer containing at least a positive electrode active material, and may contain at least one of a solid electrolyte, a conductive material, and a binder as needed. Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other rock salt layered active materials, LiMn2O4, Li4Ti5O 12 、Li(Ni0.5 Mn 1.5 )O4 and other spinel active materials, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4 and other olivine active materials.

[0073] A protective layer containing a Li-ion-conducting oxide can be formed on the surface of the oxide active material. This can inhibit the reaction between the oxide active material and the solid electrolyte. Examples of Li-ion-conducting oxides include LiNbO3. The thickness of the protective layer is, for example, from 1 nm to 30 nm. Alternatively, Li2S can be used as the positive electrode active material.

[0074] The shape of the positive electrode active material may be, for example, a granular shape. The average particle size (D 50 ) is not particularly limited, and may be, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size (D 50 ) is, for example, less than 50 μm, or less than 20 μm.

[0075] The positive electrode layer may contain a conductive material. Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include granular carbon materials such as acetylene black (AB) and Ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). The solid electrolyte and binder used in the positive electrode layer are the same as those described in "1. Solid Electrolyte Layer" above, so they are omitted here. The thickness of the positive electrode layer is, for example, not less than 0.1 μm and not more than 1000 μm.

[0076] 3. Negative electrode layer

[0077] The negative electrode layer contains at least a negative electrode active material and, if necessary, may contain at least one of a solid electrolyte, a conductive material, and a binder. Examples of negative electrode active materials include lithium-based active materials such as metallic lithium and lithium alloys; carbon-based active materials such as graphite, hard carbon, and soft carbon; oxide-based active materials such as lithium titanate; and silicon-based active materials such as elemental Si, Si alloys, and silicon oxide.

[0078] The shape of the negative electrode active material can be granular, for example. The average particle size (D 50 ) is, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size (D 50 ) is, for example, less than 50 μm, or less than 20 μm.

[0079] The conductive material, solid electrolyte, and binder used in the negative electrode layer are the same as those described in "1. Solid Electrolyte Layer" and "2. Positive Electrode Layer" above, so their description is omitted here. The thickness of the negative electrode layer is, for example, 0.1 μm to 1000 μm.

[0080] 4. All-solid-state batteries

[0081] The all-solid-state battery disclosed herein comprises a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. Here, when the assembly of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer serves as a power generation unit, the all-solid-state battery may comprise only one power generation unit or may comprise two or more power generation units. When the all-solid-state battery comprises two or more power generation units, these power generation units may be connected in series or in parallel.

[0082] All-solid-state batteries may include a positive electrode current collector for collecting current from the positive electrode layer. Typically, the positive electrode current collector is located on the opposite side of the solid electrolyte layer relative to the positive electrode layer. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of the shape of the positive electrode current collector include foil and mesh.

[0083] All-solid-state batteries may include a negative electrode current collector for collecting current from the negative electrode layer. Typically, the negative electrode current collector is located on the opposite side of the solid electrolyte layer relative to the negative electrode layer. Examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon. Examples of the shape of the negative electrode current collector include foil and mesh.

[0084] The all-solid-state battery may include an outer casing that houses at least the power generation unit. Examples of the outer casing include a laminated outer casing and a shell-type outer casing.

[0085] The all-solid-state battery may include a constraining member that applies a constraining pressure to the positive electrode layer, the solid electrolyte layer, and the negative electrode layer along the thickness direction. The constraining pressure is, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the constraining pressure is, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0086] The all-solid-state battery of the present disclosure is typically an all-solid-state lithium ion secondary battery. The purpose of the all-solid-state battery is not particularly limited, and for example, the power supply of vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), electric vehicles (BEV), gasoline vehicles, diesel vehicles, etc. can be cited. It is particularly preferably used as a driving power supply for hybrid electric vehicles, plug-in hybrid electric vehicles or electric vehicles. In addition, the all-solid-state battery of the present disclosure can be used as a power supply for mobile bodies (such as railways, ships, aircraft) other than vehicles, and can also be used as a power supply for electronic products such as information processing equipment.

[0087] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely illustrative, and any configuration having substantially the same structure and effect as the technical concept described in the claims of the present disclosure is encompassed within the technical scope of the present disclosure.

[0088] [Example]

[0089] [Example 1]

[0090] (Production of positive electrode)

[0091] As the positive electrode active material, the average particle size (D 50 ) is 5μm LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 powder. Then, the surface of the positive electrode active material is coated with LiNbO3 using the sol-gel method. In addition, as a sulfide solid electrolyte, an average particle size (D 50 ) is 15LiBr·10LiI·75 (0.75Li2S·0.25P2S5) glass ceramic with a thickness of 2.5 μm.

[0092] Next, the positive electrode active material and the sulfide solid electrolyte were weighed and mixed at a weight ratio of 75:25, forming a first mixture. Next, 3 parts by weight of an SBR (styrene-butadiene rubber) binder and 10 parts by weight of a conductive material (carbon nanofiber, CNF) were weighed for 100 parts by weight of the positive electrode active material and added to the first mixture to form a second mixture. A dispersion medium (butyl butyrate) was then added to the second mixture, and the solids concentration was adjusted to 60% by weight. Ultrasonic dispersion was then performed for one minute to form a positive electrode slurry.

[0093] The obtained positive electrode slurry was coated with a doctor blade at a density of 15 mg / cm 2 The coating amount was evenly applied on a positive electrode current collector (aluminum foil, thickness 15 μm) and dried at 100° C. for 60 minutes. Thus, a positive electrode (positive electrode structure) having a positive electrode current collector and a positive electrode layer was obtained.

[0094] (Fabrication of negative electrode)

[0095] As the negative electrode active material, the average particle size (D 50 ) is 5 μm Si powder. In addition, as the sulfide solid electrolyte, the average particle size (D 50) is a glass ceramic of 15LiBr·10LiI·75 (0.75Li2S·0.25P2S5) with a thickness of 2.5μm.

[0096] Next, the negative electrode active material and the sulfide solid electrolyte were weighed and mixed at a weight ratio of 50:50, yielding a third mixture. Next, 3 parts by weight of an SBR-based binder and 10 parts by weight of a conductive material (CNF) were weighed per 100 parts by weight of the negative electrode active material and added to the third mixture to yield a fourth mixture. A dispersion medium (butyl butyrate) was then added to the fourth mixture, and the solids concentration was adjusted to 40% by weight. Ultrasonic dispersion was then performed for 1 minute to yield a negative electrode slurry.

[0097] The coating was carried out by doctor blade at a rate of 3 mg / cm 2 The obtained negative electrode slurry was evenly applied to a negative electrode current collector (roughened copper foil, thickness 25 μm, Rz=5 μm) in an amount of 100 μm and dried at 100° C. for 60 minutes. Thus, a negative electrode (negative electrode structure) having a negative electrode current collector and a negative electrode layer was obtained.

[0098] (Fabrication of Solid Electrolyte Layer)

[0099] As the sulfide solid electrolyte, the average particle size (D 50 ) is 15LiBr·10LiI·75 (0.75Li2S·0.25P2S5) glass ceramic with a particle size of 2.5 μm. In addition, an SBR-based binder was used as the binder.

[0100] Next, the sulfide solid electrolyte and binder were weighed and mixed at a weight ratio of sulfide solid electrolyte:binder = 99:1 to obtain a fifth mixture. A dispersion medium (butyl butyrate) was then added to the fifth mixture to adjust the solid content concentration to 50% by weight, followed by ultrasonic dispersion treatment for 1 minute to obtain a slurry for the solid electrolyte layer.

[0101] Then, a polyester nonwoven fabric (thickness 15 μm, porosity 80%, tensile strength 5 N / cm in MD direction, tensile strength 1 N / cm in CD direction) was placed on the aluminum foil. 2 The resulting slurry was evenly applied to a polyester nonwoven fabric in an amount of 100 μm (including the thickness of the nonwoven fabric, 15 μm) and dried at 100°C for 60 minutes. This produced a transfer member having an aluminum foil and a solid electrolyte layer. Similarly, a similar transfer member was produced by performing the same operation.

[0102] (Fabrication of all-solid-state batteries)

[0103] Cut each of the two transfer members into a 6.2 cm x 6.2 cm square. At this point, cut one transfer member so that its fiber direction (MD direction) is parallel to one side of the square (transfer member A). Cut the other transfer member so that its fiber direction (MD direction) intersects one side of the square at a 45° angle (transfer member B). Separately, cut the negative electrode structure into a 6.2 cm x 6.2 cm square. Separately, cut the positive electrode structure into a 6.0 cm x 6.0 cm square.

[0104] Then, the negative electrode layer in the negative electrode structure was overlapped with the solid electrolyte layer in the transfer member A, and the negative electrode layer was stacked at 1 ton / cm 2 The aluminum foil was peeled off from the transfer member A. The exposed solid electrolyte layer was then overlapped with the solid electrolyte layer in the transfer member B and rolled at a pressure of 1 ton / cm 2 The aluminum foil was then peeled off from the transfer member B. Thus, a structure X having a negative electrode current collector, a negative electrode layer, a second solid electrolyte layer, and a first solid electrolyte layer was obtained. Next, the first solid electrolyte layer in the structure X and the positive electrode layer in the positive electrode structure were superimposed and rolled at a pressure of 3 tons / cm. 2 The rollers were pressed at a pressing pressure of . This yielded a structure Y comprising a negative electrode current collector, a negative electrode layer, a second solid electrolyte layer, a first solid electrolyte layer, a positive electrode layer, and a positive electrode current collector. Next, the structure Y was sealed with an exterior body (aluminum laminate film) pre-equipped with a positive electrode terminal and a negative electrode terminal, thereby yielding an all-solid-state battery.

[0105] [Example 2]

[0106] Using two transfer components A, the first solid electrolyte layer and the second solid electrolyte layer are arranged in such a way that the angle between the fiber direction (MD direction) in the first solid electrolyte layer and the fiber direction (MD direction) in the second solid electrolyte layer is 90°. Except for this, a solid battery is obtained in the same manner as in Example 1.

[0107] [Comparative Example 1]

[0108] A slurry for a solid electrolyte layer was obtained in the same manner as in Example 1. Next, a polyester nonwoven fabric (30 μm thick) was placed on the aluminum foil. Next, a slurry was applied by doctor blade coating at a density of 5.8 mg / cm 2 The obtained slurry was evenly applied to a polyester nonwoven fabric in an amount of 100 μm (the thickness including the nonwoven fabric was 30 μm), and dried at 100° C. for 60 minutes. Thus, a transfer member having an aluminum foil and a solid electrolyte layer was obtained.

[0109] Using the obtained transfer member, a full solid-state battery was obtained in the same manner as in Example 1 except that each roll pressing was performed so that the fiber direction (MD direction) of the solid electrolyte layer was parallel to the direction of roll pressing.

[0110] [Comparative Example 2]

[0111] A full solid-state battery was obtained in the same manner as in Comparative Example 1 except that each roll pressing was performed so that the fiber direction (MD direction) of the solid electrolyte layer was perpendicular to the direction of roll pressing.

[0112] [evaluate]

[0113] A cycle test was performed using the all-solid-state batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2. The measurements were performed in the following order. First, the all-solid-state battery was constrained at a pressure of 100 MPa and CCCV charged to 4.5 V at a current rate of 36 mA (current cutoff value: 0.36 mA). Next, CCCV discharged to 3.0 V at a current rate of 36 mA (current cutoff value: 0.36 mA). The charge and discharge were performed 100 cycles to determine the capacity retention rate. The results are shown in Table 1.

[0114] Capacity retention rate (%) = discharge capacity at the 100th cycle / discharge capacity at the 1st cycle × 100

[0115] Table 1

[0116]

[0117] As shown in Table 1, Examples 1 and 2 have greater capacity retention than Comparative Examples 1 and 2. This is presumably because the anisotropy of tensile strength is mitigated by setting the angle between the fiber direction (MD direction) of the first nonwoven fabric and the fiber direction (MD direction) of the second nonwoven fabric to 45° or more and 90° or less.

Claims

1. An all-solid-state battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The solid electrolyte layer includes a first solid electrolyte layer and a second solid electrolyte layer, wherein the second solid electrolyte layer is arranged closer to the negative electrode layer than the first solid electrolyte layer. The first solid electrolyte layer includes a first nonwoven fabric and a first solid electrolyte disposed inside the first nonwoven fabric. The second solid electrolyte layer includes a second nonwoven fabric and a second solid electrolyte disposed inside the second nonwoven fabric. In a plan view observed in the thickness direction, an angle between a first fiber direction of the first nonwoven fabric and a second fiber direction of the second nonwoven fabric is greater than or equal to 45° and less than or equal to 90°. In the first nonwoven fabric, the tensile strength in the first fiber direction is greater than the tensile strength in a direction perpendicular to the first fiber direction. In the second nonwoven fabric, the tensile strength in the second fiber direction is greater than the tensile strength in a direction perpendicular to the second fiber direction.

2. The all-solid-state battery according to claim 1, The angle is greater than or equal to 80° and less than or equal to 90°.

3. The all-solid-state battery according to claim 1 or 2, The porosity of the first nonwoven fabric and the porosity of the second nonwoven fabric are respectively 70% or more and 90% or less.

4. The all-solid-state battery according to claim 1 or 2, At least one of the first solid electrolyte and the second solid electrolyte is an inorganic solid electrolyte.

5. The all-solid-state battery according to claim 4, The inorganic solid electrolyte is at least one of a sulfide solid electrolyte, an oxide solid electrolyte, and a hydride solid electrolyte.

6. The all-solid-state battery according to claim 1 or 2, At least one of the first solid electrolyte and the second solid electrolyte is a molten salt that is solid at 25°C.

7. The all-solid-state battery according to claim 1 or 2, At least one of the first solid electrolyte and the second solid electrolyte is a plastic crystalline solid electrolyte.

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