Solid-state battery and method for manufacturing a solid-state battery

Abstract

The present invention provides a solid-state battery and a method for manufacturing the same that are less prone to the inclusion of foreign matter during manufacturing and short circuits caused by electrode expansion during charging. [Solution] The solid-state battery of this 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. The solid electrolyte layer includes a solid electrolyte, a first binder, and a second binder. The softening temperature of the first binder is higher than the softening temperature of the second binder. The content of the first binder in the solid electrolyte layer is 0.5 to 4.0 volume%, and the content of the second binder is 2.5 to 12.5 volume%. The laminated electrode body disposed between the positive electrode layer and the negative electrode layer is densified by press processing at a temperature above the softening temperature of the second binder and below the softening temperature of the first binder.

Description

[Technical Field]

[0001] This disclosure relates to a solid-state battery and a method for manufacturing a solid-state battery. [Background technology]

[0002] As a lithium-ion secondary battery with superior safety, solid-state batteries using solid electrolytes have been proposed, and one example is the all-solid-state battery equipped with a solid electrolyte layer. Patent Document 1 discloses an all-solid-state battery in which the solid electrolyte layer includes a first solid electrolyte and a second solid electrolyte. Patent Document 2 discloses a method for manufacturing an all-solid-state battery having a laminate configured such that a solid electrolyte layer made of a solid electrolyte is sandwiched between a positive electrode layer containing a positive electrode active material and a negative electrode layer containing a negative electrode active material. It is disclosed that the decomposition temperature of the binder mixed in the positive electrode layer and the negative electrode layer is higher than the decomposition temperature of the binder mixed in the solid electrolyte layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-86720 [Patent Document 2] Japanese Patent Publication No. 2015-069843 [Overview of the project] [Problems that the invention aims to solve]

[0004] Solid-state batteries are susceptible to short circuits caused by cracking of the solid electrolyte layer or other components due to contamination during the manufacturing process or electrode expansion during charging.

[0005] This disclosure is made in light of the circumstances described above. One embodiment of this disclosure aims to solve the problem of providing a solid-state battery that is less prone to the inclusion of foreign matter during manufacturing and short circuits caused by electrode expansion during charging. Other embodiments of this disclosure aim to solve the problem of providing a method for manufacturing solid batteries that is less prone to contamination by foreign matter during manufacturing and short circuits caused by electrode expansion during charging. [Means for solving the problem]

[0006] The following embodiments are included as means for solving the above problems. <1> A solid-state battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer comprises a solid electrolyte, a first binder, and a second binder, the softening temperature of the first binder being higher than that of the second binder, the content of the first binder in the solid electrolyte layer being 0.5 volume% to 4.0 volume%, and the content of the second binder being 2.5 volume% to 12.5 volume%. <2> At least one of the positive electrode layer and the negative electrode layer includes a third binder, wherein the softening temperature of the third binder is higher than that of the second binder. <1> Solid-state batteries as described above. <3> The softening temperature of the first binder is 50°C or more higher than the softening temperature of the second binder. <1> or <2> Solid-state batteries as described above. <4> The negative electrode layer includes a Si-based negative electrode active material. <1> ~ <3> A solid battery as described in any one of the following. <5> Forming a laminated electrode body 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, wherein the solid electrolyte layer comprises a solid electrolyte, a first binder, and a second binder, the softening temperature of the first binder being higher than the softening temperature of the second binder, the content of the first binder in the solid electrolyte layer being 0.5 volume% to 4.0 volume%, and the content of the second binder being 2.5 volume% to 12.5 volume%, and densifying the laminated electrode body by press-forming it at a temperature above the softening temperature of the second binder and below the softening temperature of the first binder. A method for manufacturing solid-state batteries, including the battery itself. [Effects of the Invention]

[0007] According to one embodiment of the present disclosure, there is provided a solid-state battery in which foreign matter is less likely to be mixed during manufacturing and short circuits due to electrode expansion during charging are less likely to occur. According to another embodiment of the present disclosure, there is provided a method for manufacturing a solid-state battery in which foreign matter is less likely to be mixed during manufacturing and short circuits due to electrode expansion during charging are less likely to occur.

Brief Description of the Drawings

[0008] [Figure 1] It is a schematic diagram showing an example of the laminated structure of the solid-state battery according to the present disclosure.

Modes for Carrying Out the Invention

[0009] In the present disclosure, the numerical range indicated by "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions. In the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, the amount of each component means the total amount of a plurality of substances when there are a plurality of substances corresponding to each component, unless otherwise specified. In the present disclosure, the term "step" includes not only an independent step but also this term even when it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0010] The solid-state battery includes a semi-solid battery having a gel layer containing an electrolytic solution and a polymer between an electrode and a solid electrolyte, and an all-solid-state battery provided with a layer of the solid electrolyte, and the all-solid-state battery is preferred.

[0011] (1) Solid-state battery The solid-state battery of this 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. The solid electrolyte layer includes a solid electrolyte, a first binder, and a second binder. The softening temperature of the first binder is higher than that of the second binder. In the solid electrolyte layer, the first binder is present in an amount of 0.5% to 4.0% by volume relative to the solid electrolyte layer. The second binder is present in an amount of 2.5% to 12.5% ​​by volume relative to the solid electrolyte layer.

[0012] The solid-state battery of this disclosure, having the above configuration, softens and fluidizes the second binder appropriately contained in the solid electrolyte layer when the laminated electrode body of the negative electrode layer, solid electrolyte layer, and positive electrode layer is densified (battery pressing) by a roll press or the like during the manufacturing of the solid-state battery, or due to the heat during charging. The softened and fluidized second binder fills in cracks in the solid electrolyte layer, negative electrode layer, and / or positive electrode layer, maintaining insulation. Therefore, it is considered that the battery resistance of the solid-state battery is suppressed, and the inclusion of foreign matter during manufacturing and short circuits due to electrode expansion during charging are less likely to occur.

[0013] The solid electrolyte layer may contain a first binder and a second binder, each within the above-mentioned ranges, and may contain three or more types of binders. However, while increasing the binder content in the solid electrolyte layer improves strength, it also increases electrical resistance. Therefore, the total amount of binder in the solid electrolyte layer is preferably less than 16.0 volume%, 15.0 volume% or less, 14.0 volume% or less, or 13.0 volume% or less. Furthermore, from the viewpoint of strength as a separator, the total amount of binder in the solid electrolyte layer is preferably more than 3.0 volume%, 4.0 volume% or more, 5.0 volume% or more, or 6.0 volume% or more.

[0014] When a set of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is considered a power generation unit, a solid-state battery may have only one power generation unit or two or more. If a solid-state battery has two or more power generation units, these units may be connected in series or in parallel. The configuration of the solid-state battery of this disclosure will be specifically described below, using an all-solid-state battery as an example.

[0015] Figure 1 is a schematic diagram showing an example of a stacked structure in an all-solid-state battery. In Figure 1, the all-solid-state battery 100 comprises a negative electrode current collector 12, a negative electrode active material layer (negative electrode layer) 10, a solid electrolyte layer 30, a positive electrode active material layer (positive electrode layer) 20, and a positive electrode current collector 22. The solid electrolyte layer 30 includes a solid electrolyte, a first binder, and a second binder. The negative electrode active material layer 10 includes a negative electrode active material 1, a conductive material, and a binder. The positive electrode active material layer 20 includes a positive electrode active material, a conductive material, and a binder. The all-solid-state battery 100 may also include an outer casing (not shown), which will be described later.

[0016] (1.1) Solid electrolyte layer The solid electrolyte layer comprises a solid electrolyte, a first binder, and a second binder having a lower softening temperature than the first binder. The first binder is present in an amount of 0.5 to 4.0 volume percent relative to the solid electrolyte layer, and the second binder is present in an amount of 2.5 to 12.5 volume percent relative to the solid electrolyte layer.

[0017] (1.1.1) Solid electrolyte The solid electrolyte can take the form of particulate matter, for example. The particle size of the solid electrolyte is preferably 3.0 μm or less. If the particle size of the solid electrolyte is 3.0 μm or less, the battery resistance of the solid-state battery can be reduced compared to when the particle size of the solid electrolyte is greater than 3.0 μm. The particle size of the solid electrolyte is preferably 0.2 μm to 3.0 μm. The method for measuring the particle size of the solid electrolyte is the same as that described in the examples.

[0018] Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes, halide solid electrolytes, and nitride solid electrolytes. A single type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0019] The sulfide solid electrolyte preferably contains S as the main component of the anion element. The sulfide solid electrolyte preferably contains, for example, Li, element A, and S. Element A is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The sulfide solid electrolyte may further contain at least one of O and a halogen element. Examples of the halogen element (X) include F, Cl, Br, I, etc. From the viewpoint of excellent chemical stability, the sulfide solid electrolyte preferably has an ortho-composition anion structure as the main component of the anion structure. Examples of the ortho-composition anion structure include PS4 3- structure, SiS4 4- structure, GeS4 4- structure, AlS3 3- structure or BS3 3- structure. Examples of the composition of the sulfide solid electrolyte include xLi2S·(100-x)P2S5 (70≦x≦80), yLiI·zLiBr·(100-y-z)(xLi2S·(1-x)P2S5) (0.7≦x≦0.�, 0≦y≦30, 0≦z≦30).

[0020] The sulfide solid electrolyte may have a composition 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 may be substituted with 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 may be substituted with 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 may be substituted with at least one of Na, K, Mg, Ca, and Zn. In the general formula (1), a part of S may be substituted with a halogen. The halogen is at least one of F, Cl, Br, and I. Examples of other compositions of the sulfide solid electrolyte include, for example, Li 7-x-2 Z PS 6-x-y X y 、Li 8-x-2y SIS 6-x-y X y 、Li8-z-2y GeS 6-x-y X y Examples include X. X is at least one of F, Cl, Br, and I, and x and y satisfy 0 ≦ x and 0 ≦ y.

[0021] The oxide solid electrolyte contains, for example, Li, an element Z (Z is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Examples of the oxide solid electrolyte include garnet-type solid electrolytes, perovskite-type solid electrolytes, NASICON-type solid electrolytes, Li-P-O-based solid electrolytes, Li-B-O-based solid electrolytes, and the like.

[0022] The hydride solid electrolyte has, for example, Li and a complex anion containing hydrogen. Examples of the complex anion include, for example, (BH4) - , (NH2) - , (AlH4) - , (AlH6) 3- and the like.

[0023] Examples of the halogenated solid electrolyte include Li63z Z z X6 (X is at least one of Cl and Br, and z satisfies 0 < z < 2).

[0024] Examples of the nitrided solid electrolyte include Li3N and the like.

[0025] Among them, the solid electrolyte preferably contains a sulfide solid electrolyte, and more preferably consists of a sulfide solid electrolyte. By including a sulfide solid electrolyte in the solid electrolyte, the battery resistance of the solid battery is further reduced.

[0026] (1.1.2) Binder The solid electrolyte layer contains a first binder and a second binder having different softening temperatures. The first binder has a higher softening temperature than the second binder. The softening temperature of the binder is the glass transition temperature determined from the DSC curve obtained by differential scanning calorimetry (DSC). ​Examples of binders that may be included in the solid electrolyte layer include rubber-based binders and fluoride-based binders. Examples of rubber-based binders include butadiene rubber, hydrogenated butadiene rubber, styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, and ethylene propylene rubber. Examples of fluoride-based binders include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, and fluororubber. The softening temperature of the first binder is preferably 50°C or more higher than the softening temperature of the second binder. For example, a PVDF (polyvinylidene fluoride, softening temperature 170°C) binder can be used as the first binder, and an SBR (styrene-butadiene rubber, softening temperature 120°C) binder can be used as the second binder.

[0027] In the solid electrolyte layer, the first binder is present in an amount of 0.5 to 4.0 volume%, and the second binder is present in an amount of 2.5 to 12.5 volume%. By including the first and second binders within these ranges in the solid electrolyte layer, short circuits are effectively suppressed. Furthermore, it functions as a separator and can suppress an increase in ion transfer resistance (electrical resistance). The content of the first binder in the solid electrolyte layer may be 1.0 volume% or more, or 3.5 volume% or less, relative to the solid electrolyte layer. The content of the second binder in the solid electrolyte layer may be 3.0 volume% or more, 4.0 volume% or more, or 5.0 volume% or more, relative to the solid electrolyte layer. The content of the second binder in the solid electrolyte layer may be 12.0 volume% or less, 11.0 volume% or less, or 10.0 volume% or less, relative to the solid electrolyte layer.

[0028] The thickness of the solid electrolyte layer is preferably 50 μm or less, and more preferably 20 μm or less, from the viewpoint of further reducing the battery resistance of the solid battery. The thickness of the solid electrolyte layer is preferably 1 μm to 50 μm. Note that the thinner the solid electrolyte layer, the more likely short circuits will occur due to cracks during manufacturing, etc. However, even if the thickness of the solid electrolyte layer is, for example, 20 μm or less, short circuits are less likely to occur if appropriate amounts of the first binder and second binder are included.

[0029] (1.2) Positive electrode layer The positive electrode layer contains a positive electrode active material. The positive electrode layer may optionally contain at least one of a solid electrolyte, a conductive material, and a binder. Examples of positive electrode active materials include oxide active materials such as rock salt layered active materials, spinel-type active materials, and olivine-type active materials.

[0030] A protective layer may be formed on the surface of the oxide active material. The protective layer preferably contains a Li-ion conductive oxide (e.g., LiNbO3). The protective layer can suppress the reaction between the oxide active material and the solid electrolyte. Its thickness is, for example, 1 nm to 30 nm.

[0031] The positive electrode active material can take the form of particulate matter, for example. The particle size of the positive electrode active material is preferably 10 nm to 50 μm. The method for measuring the particle size is the same as in the example.

[0032] The positive electrode layer may contain a conductive material. Examples of conductive materials include carbon materials, metal particles, and conductive polymers.

[0033] The solid electrolyte and binder used in the positive electrode layer are similar to those exemplified as solid electrolytes and binders that can be included in the solid electrolyte sheet. If the positive electrode layer contains a binder, for example, during densification in manufacturing, the binder in the positive electrode layer may soften and the conductive material contained in the positive electrode layer may enter the solid electrolyte layer, resulting in electrical conductivity. Therefore, it is preferable that the softening temperature of the binder contained in the positive electrode layer (third binder) is higher than the softening temperature of the second binder contained in the solid electrolyte layer. For example, the first binder contained in the solid electrolyte layer and the third binder contained in the positive electrode layer can be the same binder. The thickness of the positive electrode layer is not particularly limited, but is preferably 0.1 μm to 1000 μm.

[0034] (1.3) Positive electrode current collector Solid-state batteries may include a positive electrode current collector. The positive electrode current collector is positioned on the opposite side of the solid electrolyte layer from the positive electrode layer. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of shapes for the positive electrode current collector include foil and mesh.

[0035] (1.4) Negative electrode layer The negative electrode layer contains a negative electrode active material. The negative electrode layer may optionally contain at least one of a solid electrolyte, a conductive material, and a binder. Examples of negative electrode active materials include Li-based active materials, carbon-based active materials, oxide-based active materials, and Si-based active materials. Examples of Si-based active materials include elemental Si, Si alloys, and silicon oxide. Si-based active materials tend to expand and contract significantly during charging and discharging, making them prone to cracking in the negative electrode layer. However, by including appropriate amounts of a first binder and a second binder in the solid electrolyte layer, a repair effect can be easily obtained by the second binder, which softens and becomes fluid due to the heat generated during manufacturing and charging / discharging.

[0036] The shape of the negative electrode active material can be, for example, particulate. The particle size of the negative electrode active material is preferably 10 nm to 50 μm. The method for measuring the particle size is the same as in the example.

[0037] The conductive material, solid electrolyte, and binder used in the negative electrode layer are the same as those exemplified as the conductive material, solid electrolyte, and binder that may be included in the positive electrode layer. When the negative electrode layer contains a binder, for the same reasons as for the binder that may be included in the positive electrode layer, it is preferable that the softening temperature of the binder (third binder) included in the negative electrode layer is higher than the softening temperature of the second binder included in the solid electrolyte layer. For example, the first binder included in the solid electrolyte layer and the third binder included in the negative electrode layer can be the same binder. When both the positive electrode layer and the negative electrode layer contain binders, the binder included in the positive electrode layer and the binder included in the negative electrode layer may be the same (same type) binder or different (different type) binders. The thickness of the negative electrode layer is not particularly limited, but is preferably 0.1 μm to 1000 μm.

[0038] (1.5) Negative electrode current collector Solid-state batteries may include a negative electrode current collector. Examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon. Examples of shapes for the negative electrode current collector include foil and mesh.

[0039] (1.6) Exterior Solid-state batteries may have an outer casing. The outer casing will house at least the power generation units described above. Examples of outer casings include laminated outer casings and case-type outer casings.

[0040] (1.7) Restraining member Solid-state batteries may include a restraining member. The restraining member applies restraining pressure in the thickness direction to the positive electrode layer, solid electrolyte layer, and negative electrode layer. The restraining pressure is preferably 0.1 MPa to 100 MPa.

[0041] (1.8) Application Solid-state batteries are used as power sources for vehicles, electronic devices, and electrical storage. In particular, the solid-state batteries of this disclosure are preferably used as power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs).

[0042] (2) Method for manufacturing solid batteries The method for manufacturing a solid battery according to this disclosure includes forming a laminated electrode body (laminated electrode body formation step) and densifying the laminated electrode body by press processing (press processing step).

[0043] (2.1) Laminated electrode formation process The laminated electrode formation process forms a laminated electrode comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive and negative electrode layers. The solid electrolyte layer comprises a solid electrolyte, a first binder, and a second binder. The softening temperature of the first binder is higher than that of the second binder, the content of the first binder in the solid electrolyte layer is 0.5 to 4.0 volume%, and the content of the second binder is 2.5 to 12.5 volume%. The solid electrolyte, first binder, and second binder contained in the solid electrolyte layer are as described above. The constituent materials of the positive electrode layer and the negative electrode layer are also as described above.

[0044] (2.2) Pressing process The press working process densifies the laminated electrode body by pressing it at a temperature above the softening temperature of the second binder and below the softening temperature of the first binder. A laminated electrode body in which the positive electrode layer, solid electrolyte layer, and negative electrode layer are stacked in this order can be densified by roll pressing. The laminated electrode body is densified (battery-forming press) by pressing it at a set temperature within the range of the softening temperature of the second binder + 10°C to the softening temperature of the first binder - 10°C. As a result, during the press working process, only the second binder of the solid electrolyte layer softens and fluidizes, repairing cracks in the solid electrolyte layer, positive electrode layer, and / or negative electrode layer. Furthermore, the manufactured solid-state battery is less prone to short circuits caused by electrode expansion during charging. [Examples]

[0045] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[0046] [1]Measurement method <Particle size> The particle sizes of the sulfide-fixed electrolyte, positive electrode active material, and negative electrode active material were measured using a laser diffraction particle size distribution analyzer. Specifically, the materials to be measured were dispersed in a dispersion medium, and the volume-based particle size distribution was measured using a particle size distribution analyzer. The particle size corresponding to 50% of the obtained volume-based integrated particle size distribution (D50) was defined as the particle size.

[0047] <Specific surface area> The specific surface areas of the positive electrode active material, negative electrode active material, positive electrode conductive material, and negative electrode conductive material were measured using the BET method (JIS R1626-1996). Vol% refers to volume percentage.

[0048] [Example 1] <Preparation of solid electrolyte sheets> As the sulfide solid electrolyte, 15LiBr·10LiI·75(0.75Li2S·0.25P2S5) glass ceramics (specific gravity 2.0) with an average particle size (D50) of 1 μm was used. For 100 parts by mass of the sulfide solid electrolyte, 1 part by mass of a PVDF-based binder (polyvinylidene fluoride, softening temperature 170°C, specific gravity 1.8) and 3 parts by mass of an SBR-based binder (styrene-butadiene rubber, softening temperature 120°C, specific gravity 0.9) were weighed. These were mixed with butyl butyrate to a solid content of 50% by mass, and ultrasonic dispersion treatment was performed for 1 minute using an ultrasonic dispersion device to obtain a solid electrolyte paste. The obtained solid electrolyte paste was then blade-coated onto a 15 μm thick aluminum foil using a commercially available applicator, with a basis weight of 3.0 mg / cm². 2 The coating was applied uniformly to achieve this result. The coating film was dried at 100°C for 60 minutes to obtain a solid electrolyte sheet on aluminum foil.

[0049] <Fabrication of the positive electrode sheet> The positive electrode active material has an average particle size (D50) of 10 μm and a specific surface area of ​​1 m². 2 / g LiLi 1 / 3 Mn 1 / 3 Co 1 / 3O2 powder was used. LiNbO3 was coated onto the surface of the positive electrode active material using the sol-gel method. The same sulfide solid electrolyte as the solid electrolyte sheet was used as the solid electrolyte. 20 parts by mass of sulfide solid electrolyte and conductive material (CNF, specific surface area 14 m²) were used per 100 parts by mass of positive electrode active material. 2 Ten parts by mass of ( / g) and one part by mass of the same PVDF-based binder as the solid electrolyte layer were weighed out. These were mixed with butyl butyrate to a solid content of 60% by mass, and ultrasonic dispersion treatment was performed for 1 minute using an ultrasonic dispersion device to obtain a composition for forming the positive electrode active material layer (positive electrode paste). Next, the obtained positive electrode paste was applied to a 15 μm thick aluminum foil positive electrode current collector by blade coating using a commercially available applicator, with a basis weight of 33 mg / cm². 2 The coating was applied uniformly to achieve this result. The coating was then dried at 100°C for 60 minutes to obtain a positive electrode sheet with a positive electrode layer formed on the aluminum foil.

[0050] <Fabrication of the negative electrode sheet> The negative electrode active material has an average particle size (D50) of 3 μm and a specific surface area of ​​4 m². 2 Si powder of / g was used, and the same sulfide solid electrolyte as the solid electrolyte sheet was used as the sulfide solid electrolyte. 50 parts by mass of sulfide solid electrolyte were used per 100 parts by mass of the above negative electrode active material, and the same conductive material (CNF, specific surface area 14 m²) as the positive electrode layer was used. 2 Ten parts by mass of ( / g) and five parts by mass of the same PVDF-based binder as the solid electrolyte sheet were weighed out. These were mixed with butyl butyrate to a solid content of 40% by mass, and ultrasonic dispersion treatment was performed for 1 minute using an ultrasonic dispersion device to obtain a composition for forming the negative electrode active material layer (negative electrode paste). The obtained negative electrode paste was then applied to a 20 μm thick surface-roughened copper foil by blade coating using a commercially available applicator to obtain a basis weight of 7.5 mg / cm². 2 The coating was applied uniformly to achieve the desired result. The coating was then dried at 100°C for 60 minutes to obtain a negative electrode sheet in which a negative electrode layer was formed on a surface-roughened copper foil.

[0051] <Fabrication of all-solid-state batteries> A 1.2 cm x 1.2 cm square was cut from the negative electrode layer, including the copper foil, and a solid electrolyte sheet cut to the same shape was placed on top of it. The solid electrolyte layer was transferred to the negative electrode by roll pressing at room temperature and a press pressure of 1 ton / cm. The aluminum foil attached to the solid electrolyte layer transferred to the negative electrode was peeled off. A 1.0 cm x 1.0 cm square was cut from the positive electrode, including the aluminum foil, and placed on top of the solid electrolyte layer transferred to the negative electrode so that the positive electrode layer and the solid electrolyte layer faced each other. The positive electrode was transferred onto the solid electrolyte layer by roll pressing at room temperature and a press pressure of 2 ton / cm, thus creating a laminated electrode body of negative electrode / solid electrolyte layer / positive electrode. The obtained laminated electrode body was roll-pressed at 150°C and 4 ton / cm to densify the electrode body. The densified laminated electrode body was sealed with an outer casing made of aluminum laminate film to which positive and negative electrode terminals were attached, and the test all-solid-state battery (all-solid-state lithium-ion secondary battery) of Example 1 was fabricated.

[0052] [Examples 2-5 and Comparative Examples 1-4] A test all-solid-state battery was prepared using the same method as in Example 1, except that the mixing ratio (mixing ratio, Vol%) of the solid electrolyte layer was changed as shown in Table 1.

[0053] [evaluation] <Self-discharge test> The battery was held at 1 MPa, charged at a current of 2 mA, and charged with a 4.5V-CCCV upper voltage limit. The voltage change was measured from 24 hours after a period of inactivity to 48 hours after a period of inactivity.

[0054] <Cell resistance measurement> The battery (cell) was discharged at a current of 2mA under a lower voltage limit of 2.5V-CCCV, then charged under an upper voltage limit of 3.5V-CCCV, followed by a CC discharge at a current of 10mA for 10 seconds. The cell resistance was then calculated using Omega's law. "CC" indicates a constant current method. "CV" indicates a constant voltage method. "CCCV" indicates a constant current-constant voltage method.

[0055] <Durability Test> The battery was subjected to 100 cycles of charging at a current of 4mA with an upper voltage limit of 3.5V-CCCV and discharging at a lower voltage limit of 2.5V-CCCV, after which a self-discharge test was performed again.

[0056] The results are shown in Table 1. Note that the cell resistance is listed as a ratio to the cell resistance of Comparative Example 1.

[0057] [Table 1]

[0058] In Examples 1-4, the all-solid-state batteries used for testing, in which an appropriate amount of binder (SBR) with a softening temperature lower than the densification temperature of the electrode body was included in the solid electrolyte layer, showed no increase in resistance and successfully suppressed self-discharge (internal short circuit) after durability testing. It is presumed that pressing the solid electrolyte layer at a temperature above the softening temperature of the SBR during densification caused the SBR to flow inside the electrode body, filling cracks and voids and improving insulation. Furthermore, in the case of SBR alone (Comparative Example 2), self-discharge occurred in the initial stages of charging, and it is presumed that the solid electrolyte layer became too soft and deformed (crushed) during high-temperature densification, making it impossible to maintain insulation. [Explanation of Symbols]

[0059] 10: negative electrode active material layer, 12: negative electrode current collector, 20: positive electrode active material layer, 22: positive electrode current collector, 30: solid electrolyte layer, 100: all-solid battery

Claims

1. It 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, The solid electrolyte layer comprises a solid electrolyte, a first binder, and a second binder. The softening temperature of the first binder is higher than that of the second binder. A solid-state battery in which the content of the first binder in the solid electrolyte layer is 0.5% to 4.0% by volume, and the content of the second binder is 2.5% to 12.5% ​​by volume.

2. The solid-state battery according to claim 1, wherein at least one of the positive electrode layer and the negative electrode layer includes a third binder, and the softening temperature of the third binder is higher than the softening temperature of the second binder.

3. The solid battery according to claim 1, wherein the softening temperature of the first binder is 50°C or higher than the softening temperature of the second binder.

4. The solid-state battery according to claim 1, wherein the negative electrode layer includes a Si-based negative electrode active material.

5. A laminated electrode body is formed 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, wherein the solid electrolyte layer comprises a solid electrolyte, a first binder, and a second binder, the softening temperature of the first binder being higher than that of the second binder, the content of the first binder in the solid electrolyte layer being 0.5% to 4.0% by volume, and the content of the second binder being 2.5% to 12.5% ​​by volume, and The laminated electrode body is densified by press-forming it at a temperature above the softening temperature of the second binder and below the softening temperature of the first binder. A method for manufacturing solid-state batteries, including the battery itself.

Images