All-solid-state battery

Abstract

The main object of the present disclosure is to provide an all-solid battery with good cycle characteristics. In the present disclosure, the above problem is solved by providing an all-solid battery having, in order along a thickness direction, a positive electrode (CA1), a first solid electrolyte layer, a negative electrode (AN), a second solid electrolyte layer, and a positive electrode (CA2), the first solid electrolyte layer including a first nonwoven fabric and a first solid electrolyte disposed inside the first nonwoven fabric, the second solid electrolyte layer including a second nonwoven fabric and a second solid electrolyte disposed inside the second nonwoven fabric, and an angle between a first fiber direction of the first nonwoven fabric and a second fiber direction of the second nonwoven fabric being 45° or more and 90° or less in a plan view observed along the thickness direction.

Description

Technical Field

[0001] This disclosure relates to an all-solid-state battery. Background Technology

[0002] All-solid-state batteries are batteries with a solid electrolyte layer between the positive and negative electrode layers. Compared with liquid-system batteries with electrolytes containing flammable organic solvents, they have the advantage of easily simplifying safety devices. Patent Document 1 discloses a solid electrolyte sheet for an all-solid-state secondary battery, which includes a nonwoven fabric and a solid electrolyte on and inside the surface of the nonwoven fabric.

[0003] Patent Document 2 discloses a method for manufacturing a solid electrolyte membrane for an all-solid-state battery, which includes a step of forming a nonwoven fabric having fibers made of resin. Patent Document 3 discloses an electrode assembly having a first electrode, a second electrode, and a separation membrane. The first electrode includes a plurality of fibrous first structures extending along a first direction, the second electrode includes a plurality of fibrous second structures extending along a second direction different from the first direction, and the separation membrane is disposed between the first and second structures.

[0004] Existing technical documents

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

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

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

[0008] From the viewpoint of improving battery performance, there is a demand for all-solid-state batteries with excellent cycle characteristics. This disclosure was made in view of the above situation, and its main objective is to provide an all-solid-state battery with excellent cycle characteristics.

[0009] In this disclosure, an all-solid-state battery is provided, which has a positive electrode (CA1), a first solid electrolyte layer, a negative electrode (AN), a second solid electrolyte layer and a positive electrode (CA2) sequentially along the thickness direction. The first solid electrolyte layer contains a first nonwoven fabric and a first solid electrolyte disposed inside the first nonwoven fabric. The second solid electrolyte layer contains a second nonwoven fabric and a second solid electrolyte disposed inside the second nonwoven fabric. In a plan view viewed along the thickness direction, the angle between the first fiber direction of the first nonwoven fabric and the second fiber direction of the second nonwoven fabric is 45° or more and 90° or less.

[0010] According to this disclosure, the angle between the first fiber direction and the second fiber direction is within a predetermined range, thus forming an all-solid-state battery with good cycle characteristics.

[0011] Furthermore, this disclosure provides an all-solid-state battery having, along its thickness direction, a negative electrode (AN1), a first solid electrolyte layer, a positive electrode (CA), a second solid electrolyte layer, and a negative electrode (AN2). The first solid electrolyte layer contains a first nonwoven fabric and a first solid electrolyte disposed within the first nonwoven fabric. The second solid electrolyte layer contains a second nonwoven fabric and a second solid electrolyte disposed within the second nonwoven fabric. In a plan view taken along the thickness direction, the angle between the first fiber direction of the first nonwoven fabric and the second fiber direction of the second nonwoven fabric is 45° or more and 90° or less.

[0012] According to this disclosure, the angle between the first fiber direction and the second fiber direction is within a predetermined range, thus forming an all-solid-state battery with good cycle characteristics.

[0013] In the above disclosure, the angle can be above 80° and below 90°.

[0014] In the above disclosure, the porosity of the first nonwoven fabric and the porosity of the second nonwoven fabric can be 70% or more and 90% or less, respectively.

[0015] In the above disclosure, in the first nonwoven fabric, the tensile strength in the first fiber direction can be greater than the tensile strength in the direction orthogonal to the first fiber direction, and in the second nonwoven fabric, the tensile strength in the second fiber direction can be greater than the tensile strength in the direction orthogonal to the second fiber direction.

[0016] In the above disclosure, at least one of the first solid electrolyte and the second solid electrolyte may be an inorganic solid electrolyte.

[0017] In the above disclosure, the inorganic solid electrolyte may be at least one of sulfide solid electrolyte, oxide solid electrolyte and hydride solid electrolyte.

[0018] In the above disclosure, at least one of the first solid electrolyte and the second solid electrolyte may be a molten salt (fusible salt) that is solid at 25°C.

[0019] In the above disclosure, at least one of the first solid electrolyte and the second solid electrolyte may be a plastic crystal solid electrolyte.

[0020] The all-solid-state battery disclosed herein exhibits excellent cycle performance. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure.

[0022] Figure 2 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure.

[0023] Figure 3 This is a schematic perspective view illustrating the all-solid-state battery disclosed herein.

[0024] Figure 4 This is a schematic diagram illustrating the first fiber direction and the second fiber direction of this disclosure.

[0025] Explanation of reference numerals in the attached figures

[0026] 1… Positive electrode layer

[0027] 2… Negative electrode layer

[0028] 3… Solid electrolyte layer

[0029] 3a…First solid electrolyte layer

[0030] 3b…Second solid electrolyte layer

[0031] 4…Positive current collector

[0032] 5… Negative current collector

[0033] 10… All-solid-state batteries Detailed Implementation

[0034] The all-solid-state battery of this disclosure will now be described in detail with the aid of accompanying drawings. The figures shown below are schematic diagrams, and the size and shape of the components have been appropriately exaggerated for ease of understanding. Additionally, the shading lines representing the cross-sections of the components have been appropriately omitted in the figures.

[0035] Figure 1 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure. Figure 1 The all-solid-state battery 10 shown has, along the thickness direction DT, a positive electrode (CA1), a first solid electrolyte layer 3a, a negative electrode (AN), a second solid electrolyte layer 3b, and a positive electrode (CA2). The positive electrode (CA1) has a positive electrode layer 1 and a positive electrode current collector 4, with the positive electrode layer 1 positioned opposite the first solid electrolyte layer 3a. The negative electrode (AN) has a negative electrode current collector 5 and negative electrode layers 2 disposed on both sides of the negative electrode current collector 5. In the negative electrode (AN), one negative electrode layer 2 is positioned opposite the first solid electrolyte layer 3a, and the other negative electrode layer 2 is positioned opposite the second solid electrolyte layer 3b. Similarly, the positive electrode (CA2) has a positive electrode layer 1 and a positive electrode current collector 4, with the positive electrode layer 1 positioned opposite the second solid electrolyte layer 3b.

[0036] Figure 2 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure. Figure 2 middle, Figure 1 The positions of the positive and negative electrodes in the middle become reversed. Figure 2 The all-solid-state battery 10 shown has a thickness along the D direction. T The electrode comprises, in sequence, a negative electrode (AN1), a first solid electrolyte layer 3a, a positive electrode (CA), a second solid electrolyte layer 3b, and a negative electrode (AN2). The negative electrode (AN1) has a negative electrode layer 2 and a negative electrode current collector 5, with the negative electrode layer 2 positioned opposite the first solid electrolyte layer 3a. The positive electrode (CA) has a positive electrode current collector 4 and positive electrode layers 1 disposed on both sides of the positive electrode current collector 4. In the positive electrode (CA), one positive electrode layer 1 is positioned opposite the first solid electrolyte layer 3a, and the other positive electrode layer 1 is positioned opposite the second solid electrolyte layer 3b. Similarly, the negative electrode (AN2) has a negative electrode layer 2 and a negative electrode current collector 5, with the negative electrode layer 2 positioned opposite the second solid electrolyte layer 3b.

[0037] exist Figure 1 and Figure 2 In this structure, the first solid electrolyte layer 3a contains a first nonwoven fabric and a first solid electrolyte disposed within the first nonwoven fabric. Additionally, in... Figure 1 and Figure 2 In the second solid electrolyte layer 3b, there is a second nonwoven fabric and a second solid electrolyte disposed inside the second nonwoven fabric.

[0038] Figure 3 This is a schematic perspective view illustrating the all-solid-state battery disclosed herein. Furthermore, Figure 3 For convenience, spaces are provided between some layers. For example... Figure 3 As shown, the first fiber direction of the first nonwoven fabric contained in the first solid electrolyte layer 3a is designated as D1. Similarly, the second fiber direction of the second nonwoven fabric contained in the second solid electrolyte layer 3b is designated as D2. Along the thickness direction D... T In the plan view, the angle between D1 and D2 is within a predetermined range. For example, in Figure 4 In this disclosure, the angle θ between D1 and D2 is 90°. The angle θ between D1 and D2 refers to the angle on the acute side, and is typically less than 90°.

[0039] According to this disclosure, since the angle between the first fiber direction and the second fiber direction is within a predetermined range, it becomes an all-solid-state battery with good cycle characteristics. As described in Patent Document 1 above, a solid electrolyte sheet (solid electrolyte layer) containing a solid electrolyte inside a nonwoven fabric is known. By including the nonwoven fabric in the solid electrolyte layer, it has the advantage of being able to reduce the thickness of the solid electrolyte layer while maintaining insulation performance.

[0040] On the other hand, when multiple fibers constituting a nonwoven fabric extend in one direction, its tensile strength is not isotropic but anisotropic. Here, the direction in which the multiple fibers primarily 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 nonwoven fabric manufacturing process. Additionally, the direction orthogonal to the MD direction is generally called the CD (Cross Direction, transverse direction). The MD and CD directions can be determined by observing the nonwoven fabric under a microscope and confirming the direction of fiber extension. When multiple fibers constituting a nonwoven fabric extend in one direction, the tensile strength in the fiber direction (MD direction) is generally greater than the tensile strength in the direction orthogonal to the fiber direction (CD direction).

[0041] If the tensile strength in the MD direction differs from that in the CD direction in a nonwoven fabric, the uniformity of the solid electrolyte layer decreases whenever stress associated with charging and discharging is applied. This leads to a higher likelihood of internal short circuits, such as micro-short circuits, and deterioration of cycle performance. In contrast, in this disclosure, the first and second solid electrolyte layers are arranged such that the first fiber direction of the first nonwoven fabric intersects with the second fiber direction of the second nonwoven fabric. This mitigates the anisotropy of tensile strength, thereby maintaining the uniformity of the solid electrolyte layer and improving cycle performance.

[0042] In addition, Figure 1 In the diagram, taking the negative current collector 5 in the negative electrode (AN) as a reference, the structures located above the negative current collector 5 and the structures located below the negative current collector 5 are symmetrical. Similarly, in Figure 2 In this embodiment, taking the positive current collector 4 in the positive electrode (CA) as a reference, the structure located above the positive current collector 1 is symmetrical with the structure located below the positive current collector 1. Thus, the all-solid-state battery of this disclosure exhibits good symmetry. In manufacturing all-solid-state batteries, very high pressures are applied to ensure electron and ion conduction paths. For example, consider a battery where a positive active material layer is disposed on one surface of the current collector (which serves as a reference), and a negative active material layer is disposed on the other surface. In this battery, due to the large difference in elongation between the positive and negative active material layers, cracks are easily generated under very high pressures. In contrast, a battery with a symmetrical structure based on the current collector has the advantage of being less prone to cracking even under very high pressures.

[0043] like Figure 3 As shown, the orientation of the first fiber of the first nonwoven fabric contained in the first solid electrolyte layer 3a is designated as D1. Similarly, the orientation of the second fiber of the second nonwoven fabric contained in the second solid electrolyte layer 3b is designated as D2. Furthermore, as... Figure 4 As shown, the angle between D1 and D2 is set as θ. Angle θ is typically 45° or higher, but can be 60° or higher, 70° or higher, or 80° or higher. On the other hand, angle θ can be 90° or less than 90°.

[0044] 1. Solid electrolyte layer

[0045] The all-solid-state battery disclosed herein has a first solid electrolyte layer and a second solid electrolyte layer as solid electrolyte layers. The solid electrolyte layer is disposed between the positive electrode layer and the negative electrode layer.

[0046] (1) First solid electrolyte layer

[0047] The first solid electrolyte layer contains a first nonwoven fabric and a first solid electrolyte disposed inside the first nonwoven fabric.

[0048] (i) First nonwoven fabric

[0049] The first nonwoven fabric typically has multiple fibers with pores formed between them. Furthermore, the multiple fibers extend along the direction of the first fiber. The multiple fibers can extend linearly along the direction of the first fiber, or they can extend in a serpentine or zigzag pattern. Examples of fiber materials include 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 aramid. Additionally, glass can be used as the fiber material. That is, the first nonwoven fabric can be a glass fiber nonwoven fabric. The fiber diameter and fiber length of the fibers constituting the first nonwoven fabric are not particularly limited.

[0050] The porosity of the first nonwoven fabric is not particularly limited; for example, it can be 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 can be, for example, 95% or less, or even 90% or less. If the porosity of the first nonwoven fabric is too large, it may not be able to function as a support. The porosity of the first nonwoven fabric can be determined, for example, by observing the cross-section of the nonwoven fabric. Furthermore, the size of the pores is not particularly limited.

[0051] In the first nonwoven fabric, the tensile strength in the first fiber direction (MD direction) is defined as TS1, and the tensile strength in the direction orthogonal to the first fiber direction (CD direction) is defined as TS2. Preferably, TS1 is greater than TS2. In this case, due to the anisotropy of tensile strength, the cycling characteristics are easily reduced. In contrast, in this disclosure, by setting the angle between the first fiber direction and the second fiber direction within a predetermined range, the anisotropy of tensile strength can be mitigated. TS1 is, for example, 1 N / cm or more, 3 N / cm or more, or 5 N / cm or more. On the other hand, TS1 is, for example, 50 N / cm or less. In addition, TS2 is, for example, 0.1 N / cm or more, 0.5 N / cm or more, or 1 N / cm or more. On the other hand, TS2 is, for example, 30 N / cm or less. In addition, the ratio of TS1 to TS2 (TS1 / TS2) is, for example, 1.1 or more, 1.5 or more, 2.0 or more, or 5.0 or more. On the other hand, TS1 / TS2 is, for example, 50 or less.

[0052] Examples of types 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 stitch-bonded nonwoven fabrics. Furthermore, the thickness of the first nonwoven fabric is not particularly limited; for example, it can be 1 μm or more, 5 μm or more, or 10 μm or more. On the other hand, the thickness of the first nonwoven fabric can be, for example, 50 μm or less.

[0053] (ii) First solid electrolyte

[0054] The first solid electrolyte layer contains a first solid electrolyte disposed within the first nonwoven fabric. The first solid electrolyte layer may contain only one type of first solid electrolyte, or it may contain two or more types. Examples of first solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes, halide solid electrolytes, and nitride solid electrolytes. Sulfide solid electrolytes preferably contain sulfur (S) as the main anionic element. Oxide solid electrolytes preferably contain oxygen (O) as the main anionic element. Hydride solid electrolytes preferably contain hydrogen (H) as the main anionic element. Halide solid electrolytes preferably contain halogen (X) as the main anionic element. Nitride solid electrolytes preferably contain nitrogen (N) as the main anionic element.

[0055] The sulfide solid electrolyte preferably contains, for example, Li, A (A being at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. Additionally, the sulfide solid electrolyte may also contain at least one of O and a halogen element. Examples of halogen elements include F, Cl, Br, and I.

[0056] Sulfide solid electrolytes preferably have anionic structures of their original composition (e.g., PS4). 3- Structure, SiS4 4- Structure, GeS4 4- Structure, AlS3 3- Structure or BS3 3- The original anionic structure is the main component of the anionic structure due to its high chemical stability. Compared to all anionic structures in sulfide solid electrolytes, the proportion of the original anionic structure is, for example, 70 mol% or more, or even 90 mol% or more.

[0057] Sulfide solid electrolytes can be amorphous or crystalline. In the latter case, the sulfide solid electrolyte has a crystalline phase. Examples of crystalline phases include the Thio-LISICON type, the LGPS type, and the sulfide-germanium type.

[0058] The composition of sulfide solid electrolytes is not particularly limited. Examples include xLi₂S·(100-x)P₂S₅ (70≤x≤80) and yLiI·zLiBr·(100-yz)(xLi₂S·(1-x)P₂S₅) (0.7≤x≤0.8, 0≤y≤30, 0≤z≤30).

[0059] Sulfide solid electrolytes can have the following composition: Li 4-x Ge 1-x P x The composition represented by S4 (0 < x < 1). In general formula (1), at least a portion of Ge can be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In general formula (1), at least a portion of P can be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In general formula (1), a portion of Li can be substituted with at least one of Na, K, Mg, Ca, and Zn. In general formula (1), a portion of S can be substituted with at least one of a halogen (F, Cl, Br, and I).

[0060] Other components of sulfide solid electrolytes include, for example, Li 7-x-2y PS 6-x-y X y Li8-x-2y SiS 6-xy 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 and 0 ≤ y.

[0061] Examples of oxide solid electrolytes include solid electrolytes containing Li, Y (where Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. A specific example of an oxide solid electrolyte is 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, and (Li,Sr)(Ta,Zr)O3; sodium superionic conductor-type solid electrolytes such as Li(Al,Ti)(PO4)3 and Li(Al,Ga)(PO4)3; Li-PO series solid electrolytes such as Li3PO4 and LIPON (a compound in which some O of Li3PO4 is replaced by N); and Li-BO series solid electrolytes such as Li3BO3 and a compound in which some O of Li3BO3 is replaced by C.

[0062] Hydride solid electrolytes, for example, contain Li and hydrogen-containing complex anions. Examples of complex anions include (BH4). - (NH2) - (AlH4) - and (AlH6) 3- As a halide solid electrolyte, Li can be cited as an example. 6-3z Y z X6 (where X is at least one of Cl and Br, and z satisfies 0 < z < 2). Li3N is an example of a nitride solid electrolyte.

[0063] Other examples of the first solid electrolyte include molten salts that are solid at 25°C. Molten salts have both cations and anions. Examples of cations include inorganic cations such as lithium ions; ammonium cations, piperidine cations, pyridine cations, imidazole cations, and pyridine cations. Cations, alicyclic amines, aliphatic amines, and aliphatic amines These are organic cations, such as cations. Examples of anions include those with a sulfonamide structure. Examples of anions with 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 typically above 25°C, but can be above 30°C or above 40°C. On the other hand, the melting point of the molten salt is, for example, below 200°C, but can be below 150°C or below 120°C.

[0064] Other examples of first-order solid electrolytes include plastic crystalline solid electrolytes. Plastic crystals are composed of ordered three-dimensional lattices, exhibiting oriented, rotational disorder at the molecular or molecular ion level. Plastic crystals possess both cations and anions. Pyrrolidine is an example of a cation. Tetraalkylammonium and tetraalkyl Examples of anions include hexafluorophosphate, tetrafluoroborate, thiocyanate, bis(trifluoromethanesulfonyl)amide, bis(fluorosulfonyl)amide, bis(pentafluoroethanesulfonyl)amide, and (fluorosulfonyl)(trifluoromethane)sulfonyl)amide.

[0065] The shape of the first solid electrolyte can be, for example, granular. The average particle size (D) of the first solid electrolyte... 50 There is no particular limitation; for example, it can be 10 nm or larger, or even 100 nm or larger. On the other hand, the average particle size (D) of the first solid electrolyte... 50 For example, it can be below 50 μm, or even below 20 μm. The average particle size (D) of the first solid electrolyte... 50 Preferably, the thickness is less than that of the first nonwoven fabric. Average particle size (D) 50 The total volume of the first solid electrolyte relative to the total volume of pores in the first nonwoven fabric can be calculated, for example, by a laser diffraction particle size analyzer or a scanning electron microscope (SEM). The ratio of the total volume of the first solid electrolyte to the total volume of pores in the first nonwoven fabric is, for example, 50% or more by volume, 70% or more by volume, or 90% or more by volume.

[0066] (iii) First solid electrolyte layer

[0067] The first solid electrolyte layer may or may not contain an adhesive. Examples of adhesives include rubber-based adhesives 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 fluorinated adhesives such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, and fluororubber. The proportion of the adhesive in the first solid electrolyte layer relative to 100 parts by weight of the first solid electrolyte is, for example, 0 parts by weight or more and 3 parts by weight or less.

[0068] The shape of the first solid electrolyte layer in plan view is not particularly limited, and examples include squares, rectangles, etc. The Young's modulus of the first solid electrolyte layer is, for example, 1 GPa or more. The thickness of the first solid electrolyte layer is not particularly limited, for example, 1 μm or more, 5 μm or more, or 10 μm or more. On the other hand, the thickness of the first solid electrolyte layer is, for example, 50 μm or less.

[0069] (2) Second solid electrolyte layer

[0070] 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 the same as those described for the first nonwoven fabric and the first solid electrolyte, and therefore are omitted here. The second solid electrolyte and the first solid electrolyte are preferably, for example, sulfide solid electrolytes. Furthermore, the preferred embodiment of the second solid electrolyte layer is the same as that of the preferred embodiment of the first solid electrolyte layer.

[0071] (3) Solid electrolyte layer

[0072] The all-solid-state battery disclosed herein has a first solid electrolyte layer and a second solid electrolyte layer as solid electrolyte layers. The first nonwoven fabric in the first solid electrolyte layer can be in direct contact with the active material layers (a collective term for the positive electrode active material layer and the negative electrode active material layer). Alternatively, an intermediate solid electrolyte layer can be disposed between the first nonwoven fabric and the active material layer. Disposing of an intermediate solid electrolyte layer reduces internal resistance. The intermediate solid electrolyte layer contains at least a solid electrolyte and may contain a binder as needed. The solid electrolyte and binder are the same as described in "(1) First Solid Electrolyte Layer" above. The intermediate solid electrolyte layer is typically a layer without nonwoven fabric. Furthermore, the intermediate solid electrolyte layer may be disposed only on one side of the first solid electrolyte layer, or it may be disposed on both sides of the first solid electrolyte layer. The thickness of the intermediate solid electrolyte layer is not particularly limited, for example, it may be less than the thickness of the first nonwoven fabric.

[0073] The second nonwoven fabric in the second solid electrolyte layer can be in direct contact with the active material layer. Alternatively, an intermediate solid electrolyte layer can be disposed between the second nonwoven fabric and the active material layer. By disposing of an intermediate solid electrolyte layer, internal resistance can be reduced. The preferred embodiment of the intermediate solid electrolyte layer is the same as described above.

[0074] 2. Positive electrode

[0075] The positive electrode disclosed herein has a positive electrode layer and a positive electrode current collector. For example Figure 1 As shown in the positive electrode CA1, the positive electrode layer 1 can be disposed on only one surface of the positive electrode current collector 4. On the other hand, as... Figure 2 The positive electrode CA shown can also be configured on both sides of the positive electrode current collector 4.

[0076] (1) Positive electrode layer

[0077] 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, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other layered active substances in rock salt, LiMn2O4, Li4Ti5O 12 Li(Ni) 0.5 Mn 1.5 Spinel-type active substances such as O4, and olivine-type active substances such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0078] A protective layer containing a Li-ion-conducting oxide can be formed on the surface of the oxide active material. This is because it 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, 1 nm or more and 30 nm or less. Alternatively, Li₂S can also be used as the positive electrode active material.

[0079] The shape of a positive electrode active material can be, for example, granular. The average particle size (D) of the positive electrode active material... 50 There is no particular limitation; for example, it can be 10 nm or larger, or even 100 nm or larger. On the other hand, the average particle size (D) of the positive electrode active material... 50 For example, it can be below 50μm, or it can be below 20μm.

[0080] The positive electrode layer may contain a conductive material. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include granular carbon materials such as acetylene black (AB) and Ketjen black (KB), as well as fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). Furthermore, the solid electrolyte and binder used in the positive electrode layer are the same as described in "1. Solid Electrolyte Layer" above, so they are omitted here. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0081] (2) Positive current collector

[0082] The positive current collector collects electricity from the positive electrode layer. The positive current collector is typically positioned on the opposite side of the solid electrolyte layer, relative to the positive electrode layer. Examples of materials used for the positive current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Furthermore, examples of shapes for the positive current collector include foil and mesh.

[0083] 3. Negative electrode

[0084] The negative electrode disclosed herein has a negative electrode layer and a negative electrode current collector. For example Figure 2 As shown in the negative electrode AN1, the negative electrode layer 2 can be disposed on only one surface of the negative electrode current collector 5. On the other hand, as... Figure 1 The negative electrode AN shown can also have a negative electrode layer 2 disposed on each of the two sides of the negative electrode current collector 5.

[0085] (1) Negative electrode layer

[0086] The negative electrode layer is a layer containing at least one negative electrode active material, and may contain at least one of a solid electrolyte, a conductive material, and a binder, depending on the requirements. Examples of negative electrode active materials include Li-based active materials such as lithium metal and lithium alloys; carbon-based active materials such as graphite, hard carbon, and soft carbon; oxide-based active materials such as lithium titanate; and Si-based active materials such as elemental Si, Si alloys, and silicon oxide.

[0087] The shape of the negative electrode active material can be granular, for example. The average particle size (D) of the negative electrode active material... 50 For example, the particle size can be 10 nm or larger, or even 100 nm or larger. On the other hand, the average particle size (D) of the negative electrode active material... 50 For example, it can be below 50μm, or it can be below 20μm.

[0088] The conductive materials, solid electrolyte, and binder used for the negative electrode layer are the same as those described in "1. Solid Electrolyte Layer" and "2. Positive Electrolyte Layer" above, so they are omitted here. The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0089] (2) Negative current collector

[0090] The negative current collector collects current in the negative electrode layer. The negative current collector is typically positioned on the opposite side of the solid electrolyte layer, relative to the negative electrode layer. Examples of materials for the negative current collector include stainless steel, copper, nickel, and carbon. Furthermore, examples of shapes for the negative current collector include foil and mesh.

[0091] 4. All-solid-state batteries

[0092] The all-solid-state battery disclosed herein comprises a positive electrode (CA1), a first solid electrolyte layer, a negative electrode (AN), a second solid electrolyte layer, and a positive electrode (CA2), or a negative electrode (AN1), a first solid electrolyte layer, a positive electrode (CA), a second solid electrolyte layer, and a negative electrode (AN2). The all-solid-state battery may have only one of the above-described components, or it may have two or more of the above-described components. When the all-solid-state battery has two or more of the above-described components, these components may be connected in series or in parallel.

[0093] All-solid-state batteries can have an outer casing that houses at least the aforementioned components. Examples of such outer casings include laminated casings and shell-type casings.

[0094] The all-solid-state battery may include a constraint member that applies a constraint pressure to the component along its thickness direction. The constraint pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. Conversely, the constraint pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0095] The all-solid-state battery disclosed herein is typically an all-solid-state lithium-ion secondary battery. The applications of all-solid-state batteries are not particularly limited; examples include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. They are particularly preferred for use as a power source for driving hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. Furthermore, the all-solid-state battery disclosed herein can be used as a power source for mobile bodies other than vehicles (e.g., railways, ships, and aircraft), and also as a power source for electronic products such as information processing equipment.

[0096] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and all solutions having the same structure and the same effect as the technical concept described in the claims of this disclosure are included within the technical scope of this disclosure.

[0097] [Example]

[0098] [Example 1]

[0099] (The production of the positive electrode)

[0100] As the positive electrode active material, the average particle size (D) determined based on laser diffraction / scattering method was used. 50 LiNi with a thickness of 5 μm 1 / 3 Co 1 / 3 Mn 1 / 3 O2 powder. Next, LiNbO3 was coated onto the surface of the positive electrode active material using a sol-gel method. Furthermore, as a sulfide solid electrolyte, the average particle size (D) determined based on laser diffraction / scattering was used. 50 The glass-ceramic is 2.5 μm thick and consists of 15LiBr·10LiI·75 (0.75Li2S·0.25P2S5) glass-ceramic.

[0101] Next, the positive electrode active material and the sulfide solid electrolyte were weighed at a weight ratio of positive electrode active material: sulfide solid electrolyte = 75:25, and mixed to obtain the first mixture. Then, relative to 100 parts by weight of the positive electrode active material, 3 parts by weight of SBR (styrene-butadiene rubber) binder and 10 parts by weight of conductive material (carbon nanofibers, CNF) were weighed and added to the first mixture to obtain the second mixture. Next, a dispersion medium (butyl butyrate) was added to the second mixture, and the solid component concentration was adjusted to 60% by weight. The mixture was then subjected to ultrasonic dispersion treatment for 1 minute to obtain the positive electrode slurry.

[0102] The obtained positive electrode slurry was coated with a doctor blade at a concentration of 15 mg / cm³. 2 The coating material is uniformly applied to the positive current collector (aluminum foil, 15 μm thick) and dried at 100°C for 60 minutes. This yields a positive electrode (positive electrode structure) having a positive current collector and a positive electrode layer. The same positive electrode (positive electrode structure) is then fabricated using the same procedure.

[0103] (Making the negative electrode)

[0104] As the negative electrode active material, the average particle size (D) determined by laser diffraction / scattering method was used. 50 Si powder with a particle size of 5 μm was used. Furthermore, as a sulfide solid electrolyte, the average particle size (D0) determined based on laser diffraction / scattering was used. 50 The glass-ceramic is 2.5 μm thick and consists of 15LiBr·10LiI·75 (0.75Li2S·0.25P2S5) glass-ceramic.

[0105] Next, the negative electrode active material and the sulfide solid electrolyte were weighed at a weight ratio of negative electrode active material: sulfide solid electrolyte = 50:50, and mixed to obtain the third mixture. Then, relative to 100 parts by weight of the negative electrode active material, 3 parts by weight of the SBR-based binder and 10 parts by weight of the conductive material (CNF) were weighed and added to the third mixture to obtain the fourth mixture. Next, a dispersion medium (butyl butyrate) was added to the fourth mixture, and the solid component concentration was adjusted to 40% by weight. The mixture was then subjected to ultrasonic dispersion treatment for 1 minute to obtain the negative electrode slurry.

[0106] The obtained negative electrode slurry was coated with a doctor blade at a concentration of 3 mg / cm³. 2 The coating was uniformly applied to one side surface of the negative electrode current collector (roughened copper foil, 25 μm thick, Rz = 5 μm), and dried at 100 °C for 60 minutes. Then, the negative electrode slurry was applied at a concentration of 3 mg / cm³. 2 The coating is evenly applied to the other side surface of the negative electrode current collector and dried at 100°C for 60 minutes. This yields a negative electrode (negative electrode structure) having a negative electrode layer, a negative electrode current collector, and another negative electrode layer sequentially along the thickness direction.

[0107] (Fabrication of the solid electrolyte layer)

[0108] As a sulfide solid electrolyte, the average particle size (D) determined by laser diffraction / scattering method was used. 50 The glass-ceramic material is 2.5 μm thick and consists of 15LiBr·10LiI·75 (0.75Li2S·0.25P2S5). Additionally, an SBR-based adhesive is used as the binder.

[0109] Then, the sulfide solid electrolyte and the binder were weighed at a weight ratio of 99:1 (sulfide solid electrolyte: binder) and mixed to obtain mixture 5. Next, a dispersion medium (butyl butyrate) was added to mixture 5, the concentration of the solid component was adjusted to 50% by weight, and ultrasonic dispersion was performed for 1 minute to obtain the slurry for the solid electrolyte layer.

[0110] Then, a polyester nonwoven fabric (15 μm thick, 80% porosity, tensile strength of 5 N / cm in the MD direction and 1 N / cm in the CD direction) was applied onto the aluminum foil. Next, it was coated with a solution of 5.8 mg / cm² using a doctor blade. 2 The resulting slurry (including a nonwoven fabric thickness of 30 μm) is uniformly coated onto a polyester nonwoven fabric and dried at 100°C for 60 minutes. This yields a transfer component with an aluminum foil and a solid electrolyte layer. The same transfer component is then produced by performing the same operation.

[0111] (The fabrication of an all-solid-state battery)

[0112] Two transfer components were each cut into 6.2cm × 6.2cm squares. For one transfer component, it was cut so that its fiber direction (MD direction) was parallel to one side of the square (transfer component A). For the other transfer component, it was cut so that its fiber direction (MD direction) intersects one side of the square at a 45° angle (transfer component B). Additionally, the negative electrode structure was cut into a 6.2cm × 6.2cm square. Furthermore, two positive electrode structures were each cut into a 6.0cm × 6.0cm square.

[0113] Then, one negative electrode layer in the negative electrode structure is overlapped with the solid electrolyte layer in transfer component A, and the other negative electrode layer in the negative electrode structure is overlapped with the solid electrolyte layer in transfer component B, at a ratio of 1 ton / cm². 2 The aluminum foil is then rolled under pressure. Next, it is peeled off from each transfer component. This yields a structure X having a first solid electrolyte layer, a negative electrode layer, a negative current collector, a negative electrode layer, and a second solid electrolyte layer. Then, the first solid electrolyte layer in structure X is overlapped with the positive electrode layer in the positive electrode structure, and the second solid electrolyte layer in structure X is overlapped with the positive electrode layer in the positive electrode structure at a pressure of 3 tons / cm². 2 The material is rolled under pressure. This yields a structure Y having a positive current collector, a positive electrode layer, a first solid electrolyte layer, a negative electrode layer, a negative current collector, a negative electrode layer, a second solid electrolyte layer, a positive electrode layer, and a positive current collector. Next, the structure Y is sealed with an outer casing (aluminum laminate) pre-installed with positive and negative terminals, thus obtaining an all-solid-state battery.

[0114] [Example 2]

[0115] Using two transfer components A, the first solid electrolyte layer and the second solid electrolyte layer were configured such 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 was 90°, otherwise a solid battery was obtained in the same manner as in Example 1.

[0116] [Comparative Example 1]

[0117] Using two transfer components A, the first solid electrolyte layer and the second solid electrolyte layer are arranged in a manner where the fiber direction (MD direction) in the first solid electrolyte layer is parallel to the fiber direction (MD direction) in the second solid electrolyte layer. Each layer is rolled in such a manner that their fiber direction (MD direction) is parallel to the rolling direction. Otherwise, an all-solid-state battery is obtained in the same manner as in Example 1.

[0118] [Comparative Example 2]

[0119] Using two transfer components A, the first solid electrolyte layer and the second solid electrolyte layer are arranged in a manner parallel to the fiber direction (MD direction) in the first solid electrolyte layer and the fiber direction (MD direction) in the second solid electrolyte layer. Each is rolled in such a manner that their fiber direction (MD direction) is orthogonal to the rolling direction. Otherwise, an all-solid-state battery is obtained in the same manner as in Example 1.

[0120] [evaluate]

[0121] Cyclic tests were conducted 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 100 MPa and charged via CCCV at a current rate of 72 mA to 4.5 V (current cutoff: 0.72 mA). Next, it was discharged via CCCV at a current rate of 72 mA to 3.0 V (current cutoff: 0.72 mA). This charge-discharge cycle was performed 100 times, and the capacity retention was determined. The results are shown in Table 1.

[0122] Capacity retention (%) = Discharge capacity at 100th cycle / Discharge capacity at 1st cycle × 100

[0123] Table 1

[0124]

[0125] As shown in Table 1, Examples 1 and 2 exhibit greater capacity retention compared to Comparative Examples 1 and 2. This is presumably because 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 mitigates the anisotropy of tensile strength.

Claims

1. An all-solid-state battery, comprising, sequentially along its thickness direction, a positive electrode, a first solid electrolyte layer, a negative electrode, a second solid electrolyte layer, and a positive electrode. The first solid electrolyte layer contains a first nonwoven fabric and a first solid electrolyte disposed within the first nonwoven fabric. The second solid electrolyte layer contains a second nonwoven fabric and a second solid electrolyte disposed within the second nonwoven fabric. In a plan view taken along the thickness direction, the angle between the first fiber direction of the first nonwoven fabric and the second fiber direction of the second nonwoven fabric is 45° or more and 90° or less. In the first nonwoven fabric, the tensile strength in the first fiber direction is greater than the tensile strength in the direction orthogonal to the first fiber direction. In the second nonwoven fabric, the tensile strength in the direction of the second fiber is greater than the tensile strength in the direction orthogonal to the direction of the second fiber.

2. A solid-state battery, comprising, sequentially along its thickness direction, a negative electrode, a first solid electrolyte layer, a positive electrode, a second solid electrolyte layer, and a negative electrode. The first solid electrolyte layer contains a first nonwoven fabric and a first solid electrolyte disposed within the first nonwoven fabric. The second solid electrolyte layer contains a second nonwoven fabric and a second solid electrolyte disposed within the second nonwoven fabric. In a plan view taken along the thickness direction, the angle between the first fiber direction of the first nonwoven fabric and the second fiber direction of the second nonwoven fabric is 45° or more and 90° or less. In the first nonwoven fabric, the tensile strength in the first fiber direction is greater than the tensile strength in the direction orthogonal to the first fiber direction. In the second nonwoven fabric, the tensile strength in the direction of the second fiber is greater than the tensile strength in the direction orthogonal to the direction of the second fiber.

3. The all-solid-state battery according to claim 1 or 2, The angle is above 80° and below 90°.

4. 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 both above 70% and below 90%.

5. 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.

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

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 molten salt that is solid at 25°C.

8. 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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