All-solid-state batteries

Abstract

The main objective of the present disclosure is to provide an all-solid-state battery that exhibits excellent cycle characteristics even when the restraining pressure applied to the electrode stack is low. The present disclosure addresses the aforementioned issues by providing an all-solid-state battery comprising an electrode stack having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive and negative electrode layers; the electrode stack being restrained in the thickness direction at a restraining pressure of 0 MPa to 2 MPa; the negative electrode layer containing a negative electrode active material having a charge-induced volume expansion coefficient of 105% or greater; and the solid electrolyte layer containing a solid electrolyte and a binder, wherein the binder content in the solid electrolyte layer is 20% to 30% by volume.

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 batteries with electrolytes containing flammable organic solvents, they offer the advantage of simplified safety features. Patent Document 1 discloses a lithium all-solid-state battery comprising a battery element comprising a negative electrode layer, a positive electrode layer, and a solid electrolyte layer formed between the negative and positive electrode layers. The negative electrode layer contains a negative electrode active material, which is either a single element of Si or a Si alloy. Patent Document 1 also discloses restraining the battery element at a restraining pressure of 3 MPa to 20 MPa.

[0003] Patent Document 2 discloses a separator for an all-solid-state battery comprising a solid electrolyte layer containing a solid electrolyte and a hydrogenated rubber resin. Patent Document 3 discloses an all-solid-state battery having two or more stacked battery cells of a monopolar structure, wherein the battery cells are restrained in the stacking direction with a restraint pressure of 1.0 MPa or less.

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-092100

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-102310

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 2020-140932 Summary of the Invention

[0008] In all-solid-state batteries, ions and electrons are conducted via the solid / solid interface. From the perspective of ensuring ionic conductivity and electronic conductivity, in general all-solid-state batteries, for an electrode stack having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, a restraining member is used that is restrained along its thickness direction (stacked direction). For example, in an all-solid-state battery in which the restraining pressure applied to the electrode stack is designed to be low, there is an advantage in that the restraining member can be easily miniaturized. On the other hand, if the restraining pressure applied to the electrode stack is reduced, the cycle characteristics are easily reduced.

[0009] The present disclosure has been made in view of the above-mentioned actual situation, and a main object of the present disclosure is to provide an all-solid-state battery having excellent cycle characteristics even when the restraint pressure applied to the electrode stack is low.

[0010] In the present disclosure, an all-solid-state battery is provided, comprising an electrode stack, wherein the electrode stack 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 electrode stack is constrained in the thickness direction with a constraining pressure of not less than 0 MPa and not more than 2 MPa, the negative electrode layer contains a negative electrode active material having a volume expansion coefficient due to charging of not less than 105%, the solid electrolyte layer contains a solid electrolyte and a binder, and the proportion of the binder in the solid electrolyte layer is not less than 20 volume % and not more than 30 volume %.

[0011] According to the present disclosure, the ratio of the binder in the solid electrolyte layer is within a predetermined range, so that an all-solid-state battery having excellent cycle characteristics is achieved even when the restraint pressure applied to the electrode stack is low.

[0012] In the above disclosure, the solid electrolyte layer may have a bending elastic modulus of 5.0 GPa or less.

[0013] In addition, the present disclosure provides an all-solid-state battery comprising an electrode stack, wherein the electrode stack comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the electrode stack is constrained in a thickness direction with a constraining pressure of greater than 0 MPa and less than 2 MPa, the negative electrode layer contains a negative electrode active material having a volume expansion coefficient due to charging of greater than 105%, the solid electrolyte layer contains a solid electrolyte and a binder, and the bending elastic modulus of the solid electrolyte layer is less than 5.0 GPa.

[0014] According to the present disclosure, the flexural modulus of the solid electrolyte layer is within a predetermined range, and thus a full solid-state battery having excellent cycle characteristics is achieved even when the restraint pressure applied to the electrode stack is low.

[0015] In the above disclosure, the negative electrode active material may be a Si-based active material.

[0016] In the above disclosure, the solid electrolyte may be a sulfide solid electrolyte.

[0017] In the above disclosure, the electrode stack may include a negative electrode current collector on the opposite side of the solid electrolyte layer relative to the negative electrode layer, and a rough surface may be formed on the negative electrode current collector's surface on the negative electrode layer side.

[0018] The present disclosure has the effect of being able to provide an all-solid-state battery having good cycle characteristics even when the restraint pressure applied to the electrode stack is low. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 2 This is a schematic cross-sectional view illustrating an all-solid-state battery in the present disclosure.

[0021] Figure 3 It is a graph showing the results of Examples 1 to 7 and Comparative Examples 1 to 12.

[0022] Description of Reference Numerals

[0023] 1…positive electrode layer

[0024] 2…Negative electrode layer

[0025] 30…Solid electrolyte layer

[0026] 4…Positive electrode current collector

[0027] 5…Negative electrode current collector

[0028] 6…outer body

[0029] 10…All-solid-state batteries DETAILED DESCRIPTION

[0030] Hereinafter, the all-solid-state battery in the present disclosure will be described in detail.

[0031] Figure 1 This is a schematic cross-sectional view illustrating an all-solid-state battery in the present disclosure. Figure 1 The all-solid-state battery 100 shown includes an electrode stack 10. The electrode stack 10 includes a positive electrode layer 1, a negative electrode layer 2, and a solid electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2. In addition, the electrode stack 10 includes a positive electrode current collector 4 on the surface of the positive electrode layer 1 opposite to the solid electrolyte layer 3, and a negative electrode current collector 5 on the surface of the negative electrode layer 2 opposite to the solid electrolyte layer 3. That is, the electrode stack 10 is substantially parallel to the thickness direction D. T The electrode stack 10 includes, in order, a positive electrode current collector 4, a positive electrode layer 1, a solid electrolyte layer 3, a negative electrode layer 2, and a negative electrode current collector 5. Furthermore, the electrode stack 10 includes an outer casing 6 that houses the positive electrode current collector 4, the positive electrode layer 1, the solid electrolyte layer 3, the negative electrode layer 2, and the negative electrode current collector 5.

[0032] The electrode stack 10 has a thickness direction D T The upper part is restrained with a restraining pressure of 0 MPa or more and 2 MPa or less. Figure 1 In the embodiment, the electrode stack 10 is restrained at a restraining pressure of 0 MPa. Figure 1 The electrode stack 10 in the embodiment is not subjected to a restraining pressure by the restraining fixture. Figure 2 As shown, the all-solid-state battery 100 may further include, in addition to the electrode stack 10, a plurality of electrodes in the thickness direction D of the electrode stack 10.T The restraining member 20 applies restraining pressure. Figure 1 The negative electrode layer 2 in the embodiment contains a negative electrode active material that expands in volume due to charge and contracts in volume due to discharge. Figure 1 The solid electrolyte layer 3 in the embodiment of the present invention contains a solid electrolyte and a binder. Figure 1 Among them, the solid electrolyte layer 3 is a layer that is flexible to stress.

[0033] According to the present disclosure, the solid electrolyte layer is a flexible layer, so it becomes an all-solid-state battery with good cycle characteristics even when the restraining pressure applied to the electrode stack is low. As described above, in an all-solid-state battery, ions and electrons are conducted via the solid / solid interface. From the perspective of ensuring ion conductivity and electron conductivity, in a general all-solid-state battery, a restraining member that is restrained along its thickness direction (stacking direction) is used for an electrode stack having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. For example, in an all-solid-state battery in which the restraining pressure applied to the electrode stack is designed to be low, there is an advantage of easily miniaturizing the restraining member. On the other hand, if the restraining pressure applied to the electrode stack is reduced, the cycle characteristics are easily reduced.

[0034] In contrast, in the present disclosure, by making the solid electrolyte layer a soft layer, an all-solid-state battery having good cycle characteristics is obtained even when the restraining pressure applied to the electrode stack is low. When the restraining pressure is low and the solid electrolyte layer is a rigid layer, the solid electrolyte layer is prone to cracking when the charge and discharge cycle is repeated. If the solid electrolyte layer cracks, the charge and discharge efficiency (the ratio of discharge capacity to charge capacity) is reduced due to the influence of micro-short circuits. In contrast, by making the solid electrolyte layer a soft layer, the solid electrolyte layer is difficult to crack when the charge and discharge cycle is repeated. As a result, the reduction in charge and discharge efficiency (the ratio of discharge capacity to charge capacity) can be suppressed. In addition, as shown in the comparative example described later, when the restraining pressure is 3MPa or more, good charge and discharge efficiency can be obtained regardless of the rigidity of the solid electrolyte layer. Therefore, it can be said that the problem caused by the rigidity of the solid electrolyte layer is a problem unique to the case where the restraining pressure applied to the electrode stack is low.

[0035] 1. Electrode stack

[0036] The all-solid-state battery disclosed herein comprises an electrode stack having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive and negative electrode layers. The electrode stack may further comprise a positive electrode current collector, a negative electrode current collector, and an exterior body.

[0037] Typically, the electrode stack is constrained in the thickness direction with a restraining pressure of 0 MPa or more and 2 MPa or less. As described above, the state of the restraining pressure of 0 MPa refers to a state in which no restraining pressure is applied to the electrode stack 10 by the restraining fixture. In addition, the restraining pressure applied to the electrode stack may be 0.05 MPa or more, or 0.1 MPa or more. On the other hand, the restraining pressure applied to the electrode stack may be 1.5 MPa or less, or 1.0 MPa or less. In addition, the electrode stack is preferably constrained with the above-mentioned restraining pressure in the uncharged state or the fully discharged state.

[0038] (1) Solid electrolyte layer

[0039] The solid electrolyte layer is a layer disposed between the positive electrode layer and the negative electrode layer, and contains a solid electrolyte and a binder. The proportion of the binder in the solid electrolyte layer is, for example, 20% by volume or more. The proportion of the binder may be greater than 20% by volume, may be 21% by volume or more, or may be 22% by volume or more. If the proportion of the binder is too small, the flexibility of the solid electrolyte layer may be reduced. On the other hand, the proportion of the binder in the solid electrolyte layer is, for example, 40% by volume or less, or may be 30% by volume or less. If the proportion of the binder is too high, the ionic conductivity of the solid electrolyte layer may be reduced, and the battery resistance may increase.

[0040] In addition, the flexural modulus of the solid electrolyte layer is, for example, less than 5.0 GPa, less than 4.9 GPa, or less than 4.8 GPa. If the flexural modulus is too large, the flexibility of the solid electrolyte layer may decrease. On the other hand, the flexural modulus of the solid electrolyte layer is, for example, more than 1.0 GPa, more than 2.0 GPa, more than 3.0 GPa, or more than 4.1 GPa. The details of the determination method of the flexural modulus are described in the Examples described below.

[0041] (i) Solid electrolyte

[0042] The solid electrolyte layer contains a solid electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide 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 nitride solid electrolyte preferably contains nitrogen (N) as the main component of the anion element. The halide solid electrolyte preferably contains a halogen (X) as the main component of the anion.

[0043] The sulfide solid electrolyte preferably contains, for example, Li element, element A (A is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S element. In addition, the sulfide solid electrolyte may further contain at least one of O element and halogen elements. As the halogen element, for example, F element, Cl element, Br element, and I element can be cited.

[0044] The sulfide solid electrolyte preferably has an anion structure of the original composition (for example, PS4 3- structure, SiS4 4- structure, GeS4 4- structure, AlS3 3- structure or BS3 <00ooo08>structure) as the main component of the anion structure. Because of its high chemical stability. The proportion of the anion structure of the original composition is, for example, 70 mol% or more, and can also be 90 mol% or more, relative to all the anion structures in the sulfide solid electrolyte.

[0045] The sulfide solid electrolyte can be amorphous or crystalline. In the latter case, the sulfide solid electrolyte has a crystalline phase. As the crystalline phase, for example, Thio-LISICON type crystalline phase, LGPS type crystalline phase, and argyrodite type crystalline phase can be cited.

[0046] The composition of the sulfide solid electrolyte is not particularly limited, and for example, xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30) can be cited.

[0047] The composition of the sulfide solid electrolyte can be represented by the general formula (1): Li 4-x Ge 1-x P x S4 (0 < x < 1). In the general formula (1), at least a part of Ge can be replaced 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 part of P can be replaced by at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the general formula (1), a part of Li can be replaced by at least one of Na, K, Mg, Ca, and Zn. In the general formula (1), a part of S can be replaced by a halogen (at least one of F, Cl, Br, and I).

[0048] As other compositions of the sulfide solid electrolyte, 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.

[0049] In addition, examples of oxide solid electrolytes include solid electrolytes containing Li element, Y element (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, S) and O element. Specific examples of oxide solid electrolytes include 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.

[0050] (ii) Adhesive

[0051] The solid electrolyte layer contains 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.

[0052] In addition, other examples of the above-mentioned adhesives include polyolefin-based thermoplastic resins such as polyethylene, polypropylene, and polystyrene; imide-based resins such as polyimide and polyamideimide; amide-based resins such as polyamide; acrylic resins such as polymethyl acrylate, polyethyl acrylate, polypropyl acrylate, polybutyl acrylate, polyhexyl acrylate, poly2-ethylhexyl acrylate, polydecyl acrylate, and polyacrylic acid; methacrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, poly2-ethylhexyl methacrylate, and polymethacrylic acid; and polycarboxylic acids such as polyitaconic acid, polycrotonic acid, polyfumaric acid, polyangelic acid, and carboxymethyl cellulose.

[0053] Other examples of the above-mentioned binders include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, polyvinyl acetate, polyglycidol, polysiloxane, polydimethylsiloxane, polyvinyl acetate, polyvinyl alcohol, polycarbonate, polyamine, polyalkyl carbonate, polynitrile, polydienes, polyphosphazene, unsaturated polyesters obtained by copolymerizing maleic anhydride and glycols; and polyethylene oxide derivatives having substituents. Furthermore, copolymers obtained by copolymerizing two or more monomers constituting the above-mentioned specific polymers may also be selected as the above-mentioned binders. Furthermore, polysaccharides such as glycogen, cellulose, chitin, agarose, carrageenan, heparin, hyaluronic acid, pectin, pullulan, xyloglucan, and amylose may also be used as the above-mentioned binders. Furthermore, these binders may be used as dispersions such as emulsions.

[0054] (iii) Solid electrolyte layer

[0055] The solid electrolyte layer in the present disclosure contains a solid electrolyte and a binder. The solid electrolyte layer may be composed of a single layer or a plurality of layers. The thickness of the solid electrolyte layer is, for example, not less than 0.1 μm and not more than 1000 μm. The method for forming the solid electrolyte layer is not particularly limited, and for example, a method of applying a slurry containing a solid electrolyte, a binder and a dispersion medium to a substrate (e.g., a release sheet, a positive electrode layer or a negative electrode layer) and then drying the slurry may be cited.

[0056] (2) Negative electrode layer

[0057] The negative electrode layer is a layer containing at least a negative electrode active material, and may contain at least one of a solid electrolyte, a conductive material, and a binder as necessary.

[0058] The volume expansion of the negative electrode active material is caused by charging, and the volume contraction is caused by discharging. In the negative electrode active material, the volume expansion rate caused by charging is, for example, 105% or more, 110% or more, 150% or more, or 200% or more. The volume expansion rate caused by charging refers to the ratio (V2 / V1) of the volume V2 of the negative electrode active material charged to the theoretical capacity to the volume V1 of the uncharged negative electrode active material. The volume expansion rate caused by charging can be calculated, for example, based on the change in the XRD lattice constant before and after charging. In addition, it can also be calculated based on the cross-sectional SEM images of the negative electrode active material before and after charging.

[0059] Examples of negative electrode active materials include Si-based active materials, Sn-based active materials, and carbon active materials. Si-based active materials are active materials containing Si elements. Examples of Si-based active materials include Si simple substance, Si alloys, and Si oxides. Si alloys preferably contain Si elements as the main component. The proportion of Si elements in Si alloys may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. Examples of Si alloys include Si-Al alloys, Si-Sn alloys, Si-In alloys, Si-Ag alloys, Si-Pb alloys, Si-Sb alloys, Si-Bi alloys, Si-Mg alloys, Si-Ca alloys, Si-Ge alloys, and Si-Pb alloys. Si alloys may be two-component alloys or multi-component alloys of three or more components. Examples of Si oxides include SiO.

[0060] Sn-based active materials are active materials containing the Sn element. Examples of Sn-based active materials include simple Sn and Sn alloys. The Sn alloy preferably contains the Sn element as a main component. The proportion of the Sn element in the Sn alloy may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. In addition, examples of carbon active materials include intermediate carbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon.

[0061] 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, 50 μm or less, or 20 μm or less. 50 ) can be calculated, for example, by measurement using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM).

[0062] The negative 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).

[0063] The solid electrolyte and binder used in the negative electrode layer are the same as those described in the above-mentioned "(1) Solid Electrolyte Layer", so the description is omitted here. The thickness of the negative electrode layer is, for example, not less than 0.1 μm and not more than 1000 μm. The method for forming the negative electrode layer is not particularly limited. For example, a method of applying a negative electrode slurry containing a negative electrode active material and a dispersion medium to a substrate (such as a negative electrode collector) and then drying the negative electrode slurry can be cited. The negative electrode slurry may contain at least one of the above-mentioned conductive material, solid electrolyte and binder.

[0064] (3) Positive electrode layer

[0065] 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(Ni 0.5 Mn 1.5 )O4 and other spinel active materials, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4 and other olivine active materials.

[0066] 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, 1 nm to 30 nm. Alternatively, Li₂S can be used as the positive electrode active material.

[0067] 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.

[0068] The conductive material, solid electrolyte and binder used in the positive electrode layer are the same as those described in the above "(1) Solid Electrolyte Layer" and "(2) Negative Electrode Layer", 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. The method for forming the positive electrode layer is not particularly limited, and an example thereof includes a method of applying a positive electrode slurry containing a positive electrode active material and a dispersion medium to a substrate (such as a positive electrode collector) and then drying the resulting mixture. The positive electrode slurry may contain at least one of the above-mentioned conductive material, solid electrolyte and binder.

[0069] (4) Electrode stack

[0070] The electrode stack in the present disclosure comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the 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 electrode stack may comprise only one power generation unit or may comprise two or more power generation units. When the electrode stack comprises two or more power generation units, these power generation units may be connected in series or in parallel.

[0071] The electrode stack may also include a positive electrode current collector for collecting current from the positive electrode layer. Typically, the positive electrode current collector is positioned 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.

[0072] The electrode stack may also have a negative electrode collector for collecting current from the negative electrode layer. Typically, the negative electrode collector is arranged at a position opposite to the solid electrolyte layer based on the negative electrode layer. Examples of materials for the negative electrode collector include stainless steel, copper, nickel, and carbon. In addition, examples of the shape of the negative electrode collector include foil and mesh. A rough surface may be formed on the surface of the negative electrode collector on the negative electrode layer side. By forming a rough surface, the adhesion between the negative electrode collector and the negative electrode layer is improved, and as a result, the battery resistance is reduced. The so-called rough surface refers to a surface roughness R Z (Ten-point average roughness) is 0.6 μm or more. The surface roughness R of the rough surface Z The thickness may be 1.0 μm or more, 1.5 μm or more, or 2.0 μm or more.

[0073] The electrode stack may also have an outer casing that at least accommodates the above-mentioned power generation unit. Examples of the outer casing include a laminated outer casing and a shell-type outer casing. The laminated outer casing has a structure in which at least a heat-welding layer and a metal layer are laminated. The laminated outer casing may have a heat-welding layer, a metal layer, and a resin layer in that order along the thickness direction. Examples of materials for the heat-welding layer include olefin resins such as polypropylene (PP) and polyethylene (PE). Examples of materials for the metal layer include aluminum, aluminum alloys, and stainless steel. Examples of materials for the resin layer include polyethylene terephthalate (PET) and nylon.

[0074] 2. Constraint components

[0075] The all-solid-state battery disclosed herein may or may not have a restraining member. The restraining member is a member that applies restraining pressure to the electrode stack in the thickness direction. The structure of the restraining member is not particularly limited and a known structure may be adopted. Furthermore, the restraining member is usually a member different from the outer body. For example, Figure 2 The restraining member 20 includes two plate-like portions 11 disposed on both sides of the electrode stack 10 , one or more rod-like portions 12 connecting the two plate-like portions 11 , and an adjustment portion 13 connected to the rod-like portion 12 for adjusting the restraining pressure.

[0076] 3. All-solid-state batteries

[0077] Typically, the all-solid-state battery in the present disclosure is an all-solid-state lithium-ion secondary battery. The use of the all-solid-state battery is not particularly limited, and for example, power sources for vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), electric vehicles (BEV), gasoline vehicles, and diesel vehicles can be cited. It is particularly preferably used as a driving power source for hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. In addition, the all-solid-state battery in the present disclosure can be used as a power source for mobile bodies (such as railways, ships, and aircraft) other than vehicles, and can also be used as a power source for electrical products such as information processing devices.

[0078] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely illustrative, and all solutions having substantially the same technical concept as that described in the claims of the present disclosure and having the same functions and effects are encompassed within the technical scope of the present disclosure.

[0079] Example

[0080] [Example 1]

[0081] (Fabrication of Positive Electrode Structure)

[0082] As the positive electrode active material, the average particle size (D 50 ) is 5μm LiNi1 / 3 Co 1 / 3 Mn 1 / 3 O2 powder. Then, the surface of the positive electrode active material is covered 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.

[0083] Next, the positive electrode active material and sulfide solid electrolyte were weighed to a weight ratio of 75:25 and mixed to form 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 to adjust the solids concentration to 60% by weight. Ultrasonic dispersion was then performed for 1 minute to form a positive electrode slurry.

[0084] The obtained positive electrode slurry was coated with a doctor blade at a pressure of 15 mg / cm 2 The coating was uniformly applied on a positive electrode current collector (aluminum foil, thickness 15 μm) with a weight per unit area of ​​15 μm and dried at 100° C. for 60 minutes. Thus, a positive electrode structure having a positive electrode current collector and a positive electrode layer was obtained.

[0085] (Fabrication of Negative Electrode Structure)

[0086] 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 15LiBr·10LiI·75 (0.75Li2S·0.25P2S5) glass ceramic with a thickness of 2.5 μm.

[0087] Next, the negative electrode active material and sulfide solid electrolyte were weighed to a weight ratio of 50:50 and mixed to obtain 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 obtain a fourth mixture. A dispersion medium (butyl butyrate) was then added to the fourth mixture to adjust the solids concentration to 40% by weight. Ultrasonic dispersion was then performed for 1 minute to obtain a negative electrode slurry.

[0088] The obtained negative electrode slurry was coated with a doctor blade at a density of 3 mg / cm 2 The weight per unit area is evenly applied to the negative electrode collector (roughened copper foil, thickness 25 μm, R Z =5 μm), and dried at 100° C. for 60 minutes. Thus, a negative electrode structure including a negative electrode current collector and a negative electrode layer was obtained.

[0089] (Fabrication of Solid Electrolyte Layer)

[0090] 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.

[0091] The sulfide solid electrolyte and binder were then weighed to a volume ratio of sulfide solid electrolyte:binder = 80:20 and mixed 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. The mixture was then ultrasonically dispersed for 1 minute to obtain a slurry for the solid electrolyte layer.

[0092] The obtained slurry was coated with a doctor blade at a density of 6 mg / cm 2 The film was evenly coated on a release film (Cerapeel WZ manufactured by Toray, thickness 25 μm) with a weight per unit area (thickness 30 μm) and dried at 100° C. for 60 minutes. Thus, a transfer member having a release film and a solid electrolyte layer was obtained.

[0093] (Fabrication of all-solid-state batteries)

[0094] The negative electrode structure and the transfer member were punched out into 1.4 cm × 1.4 cm squares. The positive electrode structure was punched out into 1 cm × 1 cm squares. Next, the negative electrode layer in the negative electrode structure was overlapped with the solid electrolyte layer in the transfer member and the negative electrode layer was stacked at 1 ton / cm 2 The first structure having a negative electrode current collector, a negative electrode layer, and a solid electrolyte layer was obtained. The solid electrolyte layer in the first structure was overlapped with the positive electrode layer in the positive electrode structure and the press was performed at a pressure of 3 tons / cm. 2The pressing pressure is 1000 psi. Thus, a second structure having a negative electrode collector, a negative electrode layer, a solid electrolyte layer, a positive electrode layer, and a positive electrode collector is obtained. Next, the second structure is sealed with an outer casing (aluminum laminate film) to which a positive electrode terminal and a negative electrode terminal are pre-attached, thereby obtaining an electrode stack. No particular restraining pressure (fixed-size restraint) is applied to the obtained electrode stack, forming an all-solid-state battery (restraining pressure = 0 MPa).

[0095] (Preparation of Samples for Flexural Modulus Measurement)

[0096] One side of the roughened copper foil (roughened on both sides, 25 μm thick) was overlapped with the solid electrolyte layer in the transfer member. Next, the other side of the roughened copper foil was overlapped with the solid electrolyte layer in the transfer member. That is, a third structure was obtained in which the transfer members were arranged on both sides of the roughened copper foil. The obtained third structure was heated at 3 tons / cm 2 The roughened copper foil was pressed with a pressing pressure of 1000 rpm and then cut into a 4 mm x 40 mm rectangle. The release film was peeled off from the transfer member. Thus, a sample having a solid electrolyte layer disposed on each side of the roughened copper foil was obtained.

[0097] [Examples 2 to 7 and Comparative Examples 1 to 12]

[0098] A full solid-state battery was produced in the same manner as in Example 1, except that the amount of binder in the solid electrolyte layer and the restraint pressure (dimensional restraint) were changed to the values ​​listed in Table 1. Furthermore, a sample for measuring the flexural modulus was produced in the same manner as in Example 1, except that the amount of binder in the solid electrolyte layer was changed to the values ​​listed in Table 1.

[0099] [evaluate]

[0100] (Flexural elastic modulus measurement)

[0101] The flexural modulus of the solid electrolyte layer was measured using the samples prepared in Examples 1 to 7 and Comparative Examples 1 to 12. The measurement was performed according to the procedure described in JIS R 1601 (Flexural Test Methods for Fine Ceramics). The results are shown in Table 1.

[0102] (Cyclic test)

[0103] The all-solid-state batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 12 were used for cycle tests. The measurements were performed in the following order. First, the all-solid-state battery was CCCV charged to 4.5V at a current rate of 1mA (current cutoff value: 0.01mA). Next, CCCV discharged to 3.0V at a current rate of 1mA (current cutoff value: 0.01mA). The charge and discharge were performed 100 times, and the charge and discharge efficiency (discharge capacity / charge capacity) at the 100th cycle was determined. The results are shown in Tables 1 and Figure 3 .

[0104] Table 1

[0105]

[0106] As shown in Table 1 and Figure 3 As shown, when the restraining pressure was 3 MPa (Comparative Examples 9-12), the charge-discharge efficiency at the 100th cycle was high, regardless of the amount of binder in the solid electrolyte layer. This is presumably because deformation of the negative electrode layer was suppressed by the high restraining pressure. Furthermore, when the restraining pressure was between 0 MPa and 2 MPa, and the amount of binder in the solid electrolyte layer was low (Comparative Examples 1-8), the charge-discharge efficiency at the 100th cycle decreased. This is presumably because the restraining pressure applied to the electrode stack was low, causing cracks in the solid electrolyte layer during the charge-discharge cycles. In contrast, when the restraining pressure was between 0 MPa and 2 MPa, and the amount of binder in the solid electrolyte layer was high (Examples 1-7), the charge-discharge efficiency at the 100th cycle was high. Specifically, the charge-discharge efficiency in Examples 1-7 was comparable to that in Comparative Examples 9-12, which had high restraining pressures. This is presumably because the high amount of binder in the solid electrolyte layer suppressed cracks in the solid electrolyte layer during the charge-discharge cycles. Furthermore, there is a correlation between the amount of binder in the solid electrolyte layer and the flexural modulus of the solid electrolyte layer. Specifically, as shown in Examples 1 to 7, it was confirmed that good cycle characteristics (charge and discharge efficiency) were obtained when the flexural modulus was 5 GPa or less.

Claims

1. An all-solid-state battery comprising an electrode stack 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 electrode stack is restrained in the thickness direction with a restraining pressure of 0 MPa or more and 2 MPa or less. The negative electrode layer contains a negative electrode active material with a volume expansion rate of more than 105% due to charging. The solid electrolyte layer contains a solid electrolyte and a binder, The ratio of the binder in the solid electrolyte layer is 20 volume % or more and 30 volume % or less, and the flexural elastic modulus of the solid electrolyte layer is 4.1 GPa or more and 5.0 GPa or less. 2 . The all-solid-state battery according to claim 1 , wherein the negative electrode active material is a Si-based active material. The all-solid-state battery according to claim 1 , wherein the solid electrolyte is a sulfide solid electrolyte.

4. The all-solid-state battery according to any one of claims 1 to 3, The electrode stack includes a negative electrode current collector at a position opposite to the solid electrolyte layer with respect to the negative electrode layer. A rough surface is formed on the surface of the negative electrode current collector on the negative electrode layer side.

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