JP7183529B2 - LAMINATED GREEN SHEET, ALL-SOLID SECONDARY BATTERY AND MANUFACTURING METHOD THEREOF - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laminate green sheet, an all-solid secondary battery, and technology for manufacturing the same.

2. Description of the Related Art As electronic devices such as personal computers, mobile phones typified by smart phones, and digital cameras become more sophisticated, the power consumption of these electronic devices is increasing. In addition, miniaturization of these electronic devices is also required. Therefore, secondary batteries used in electronic devices are required to have higher energy densities.
Higher energy densities are also required for household storage batteries, which are for stationary use. Furthermore, in recent years, with the increasing demand for secondary batteries for use in vehicles such as hybrid vehicles and electric vehicles, there has been a demand for both high power density and high energy density in secondary batteries. In addition, since organic solvents are used in the electrolyte of secondary batteries, there is a risk of electrolyte leakage and thermal runaway, so there is a need to improve the safety of secondary batteries. .

The most promising secondary battery that satisfies these requirements is an all-solid lithium ion secondary battery in which the negative electrode layer, the electrolyte layer, and the positive electrode layer are all composed of solid materials. This all-solid-state lithium-ion secondary battery is being developed as a battery that combines high energy density, high safety, and long life.
However, all-solid-state lithium ion secondary batteries currently in practical use are all-solid-state secondary batteries in which each layer of the negative electrode layer, the solid electrolyte layer, and the positive electrode layer is very thin, and the energy density is not high. Furthermore, since the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are produced by a vapor deposition method or a sputtering method, it is necessary to manufacture an all-solid-state lithium ion secondary battery under a reduced pressure atmosphere. unsuitable for

In addition, by firing the electrode layer having the active material and the solid electrolyte, the active material and the solid electrolyte react with each other to generate an altered phase having a different crystal structure at the interface. This denatured layer inhibits Li ion conduction between the two.
Therefore, as disclosed in Patent Literature 1, a method of suppressing the contact between the active material and the solid electrolyte by providing a coating layer on the surface of the active material and suppressing the formation of an altered layer during firing has been investigated. .

Japanese Patent No. 5551542

However, providing a coating layer on the surface of the active material as in the invention disclosed in Patent Document 1 requires a separate step of coating the surface of the active material, which raises the problem of increased manufacturing costs.
Furthermore, when multiple types of solid electrolytes are used, they may react with each other during sintering, and an altered phase may be generated not only on the surface of the active material and the solid electrolyte, but also on the interface between different solid electrolyte materials. Also, the altered layer inhibits the Li ion conduction between the two.

The present invention has been made in view of such points, and an object of the present invention is to provide an all-solid secondary battery with high battery performance while suppressing an increase in manufacturing cost.

In order to solve the above problems, an all-solid secondary battery that is one embodiment of the present invention has a solid electrolyte layer that includes an oxide solid electrolyte, and a negative electrode layer that includes a graphite negative electrode active material and a solid electrolyte having a garnet-type crystal structure. have
Further, in the laminate green sheet that is one aspect of the present invention, the negative electrode green sheet includes a graphite negative electrode active material, a solid electrolyte having a garnet-type crystal structure, and a binder, and the solid electrolyte layer green sheet includes an oxide solid electrolyte. have a binder.

Further, a method for manufacturing an all-solid secondary battery, which is one aspect of the present invention, includes a step of collectively firing the upper laminate green sheet in a low-oxygen atmosphere.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, it is possible to provide an all-solid secondary battery with high battery performance in which an altered layer formed at the interface between an active material and a solid electrolyte is suppressed at least on the negative electrode side.

1 is a cross-sectional view showing the configuration of a laminate green sheet with a metal foil current collector according to an embodiment of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the structure of the all-solid secondary battery which concerns on embodiment based on this invention. 1 is a cross-sectional view showing the configuration of a laminate green sheet with a metal foil current collector according to an embodiment of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the structure of the all-solid secondary battery which concerns on embodiment based on this invention. 1 is a cross-sectional view showing the configuration of a laminate green sheet according to an embodiment of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the structure of the all-solid secondary battery which concerns on embodiment based on this invention.

Next, embodiments of the present invention will be described with reference to the drawings.
The drawings are schematic, and the relationship between the thickness and the planar dimensions, the thickness ratio of each layer, the shape, etc. are different from the actual ones. Further, the embodiments shown below are examples of configurations for embodying the technical idea of the present invention. It does not specify anything. Various modifications can be made to the technical idea of the present invention within the technical scope defined by the claims.

As shown in FIG. 1 , in a laminate green sheet 16 with a metal foil current collector of this embodiment, a solid electrolyte layer green sheet 12 is sandwiched between a negative electrode green sheet 11 and a positive electrode green sheet 13 . Furthermore, a metal foil current collector 14 is adhered to the surfaces of the negative electrode green sheet 11 and the positive electrode green sheet 13 that do not face the solid electrolyte layer green sheet 12 . That is, in the laminate green sheet 16 with the metal foil current collector of this embodiment, the main body of the laminate green sheet is sandwiched between the two metal foil current collectors 14 . The metal foil current collector 14 may be formed with an antioxidant film such as a carbide coating for the purpose of preventing contact between the metal foil current collector 14 and the atmosphere.

FIG. 2 is a cross-sectional view showing the configuration of an all-solid secondary battery 26 manufactured by subjecting the laminate green sheet 16 with a metal foil current collector shown in FIG. The firing step is preferably performed in a low-oxygen atmosphere. Reference numeral 24 indicates a fired metal foil current collector.
In addition, as shown in FIG. 3, the laminate green sheet 16 with a metal foil current collector has a laminate green sheet main body in which the negative electrode green sheet 11 is laminated on the solid electrolyte layer green sheet 12, and the negative electrode green sheet is further provided. 11 , a metal foil current collector 14 may be adhered to the surface not facing the solid electrolyte layer green sheet 12 . The laminate green sheet 16 with a metal foil current collector of the present embodiment may have at least the solid electrolyte layer green sheet 12 and the negative electrode green sheet 11 as the laminate green sheet main body.

When manufacturing the all-solid secondary battery 26 from the laminate green sheet 16 with a metal foil current collector shown in FIG. After the firing process, the positive electrode layer 25 (Li foil in FIG. 4) and the metal foil current collector 14 are placed on the solid electrolyte layer 22 without the metal foil current collector 14 in the state of the laminate green sheet 16. are attached in this order to form an all-solid secondary battery 26 (see FIG. 4).

Moreover, as shown in FIG. 5, the laminate green sheet 16 may be composed only of the laminate green sheet main body without the metal foil current collector. In this case, the current collector 34 may be provided after the laminate green sheet 16 is subjected to the heat degreasing treatment and the batch firing process (see FIG. 6).
Each component will be described below.

(solid electrolyte layer green sheet)
The solid electrolyte layer green sheet 12 has an oxide solid electrolyte and a binder.
The oxide solid electrolyte is preferably an oxide solid electrolyte having a garnet-type crystal structure. The oxide solid electrolyte may contain glass that becomes an oxide solid electrolyte after firing. It may have a solid electrolyte containing at least boron and lithium elements. The solid electrolyte having a garnet-type crystal structure is preferably a composite oxide composed of at least Li, La, Zr and O. Including boron has the effect of lowering the melting point, that is, the firing temperature.
As for the binder, those described later may be used.

(Solid electrolyte layer)
The solid electrolyte layer 22 contains at least one of an oxide solid electrolyte and glass that becomes an oxide solid electrolyte after firing. The solid electrolyte contained in the solid electrolyte layer and the solid electrolyte after firing are materials with low electron conductivity and high lithium ion conductivity. In particular, a material having a garnet-type crystal structure and high lithium ion conductivity is preferable, and an oxide containing Li, La, and Zr is more preferable, and a different element may be doped in addition to Li, La, and Zr. In addition to the material having a garnet-type crystal structure and high lithium ion conductivity, a lithium ion conductive material containing Li and B may also be included. For example, Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₃ BO ₃ , or solid electrolytes obtained by doping Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ with foreign elements are most suitable.

The thickness of the solid electrolyte layer 22 is preferably in the range of 1 μm to 1000 μm, more preferably in the range of 1 μm to 500 μm. If the thickness of the solid electrolyte layer 22 is less than 1 μm, short-circuiting between the positive electrode layer 23 and the negative electrode layer 21 is likely to occur, and not only the performance of the all-solid secondary battery 26 is reduced, but also safety may be reduced. There is In addition, when the thickness of the solid electrolyte layer green sheet 12 is thicker than 1000 μm, the movement of conductive ions such as lithium ions in the solid electrolyte layer 22 is likely to be inhibited, and the output of the all-solid secondary battery 26 may decrease. There is

(Positive electrode green sheet)
The positive electrode green sheet 13 has a positive electrode active material, a solid electrolyte and a binder. The solid electrolyte may contain glass that becomes an oxide solid electrolyte after firing.
The positive electrode active material preferably has a layered rock salt structure. The solid electrolyte is preferably a solid electrolyte having a garnet-type crystal structure. The solid electrolyte may contain glass that becomes a solid electrolyte after firing. It may have a solid electrolyte containing at least boron and lithium elements. The solid electrolyte having a garnet-type crystal structure is preferably a composite oxide composed of at least Li, La, Zr and O.
It may have an electronically conductive material as a conductive aid.
As for the binder, those described later may be used.

(positive electrode layer)
The positive electrode layer 23 contains at least one of a positive electrode active material, a solid electrolyte, and glass that becomes a solid electrolyte after firing.
The positive electrode active material contained in the positive electrode layer 23 is not particularly limited as long as it is a material containing lithium and cobalt. The positive electrode green sheet 13 contains, as a positive electrode active material, an active material exhibiting a nobler potential than the active material contained in the negative electrode green sheet 11 .
_The positive electrode active material preferably has a layered rock salt crystal structure _{. 2} ) Lithium transition metal compounds doped with different elements are the most suitable.

Further, the solid electrolyte contained in the positive electrode layer 23 may be a material having low electron conductivity and high lithium ion conductivity. In particular, a material having a garnet-type crystal structure and high lithium ion conductivity is used. An oxide containing Li, La, and Zr is preferable, and a different element other than Li, La, and Zr may be doped. In addition to the material having a garnet-type crystal structure and high lithium ion conductivity, a lithium ion conductive material containing Li and B may also be included. For example, Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₃ BO ₃ , or solid electrolytes obtained by doping Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ with foreign elements are most suitable.

The content of the solid electrolyte other than the solid electrolyte having a garnet-type crystal structure and the solid electrolyte containing Li and B is preferably less than 10% by mass. If the content is 10% or more, a resistance layer may be formed in the firing step of the method for manufacturing an all-solid-state battery, which will be described later, and the battery performance may deteriorate.
The positive electrode layer 23 may contain a conductive aid. The conductive aid is not particularly limited as long as it has conductivity, and for example, a conductive carbon material, particularly carbon black, activated carbon, carbon carbon fiber, or the like can be used.

The content of the conductive aid in the positive electrode layer 23 is preferably more than 0% by mass and less than 90% by mass with respect to the mass of the positive electrode active material. This is because if the content of the conductive aid is 90% by mass or more, the amount of the positive electrode active material in the positive electrode layer 23 may be insufficient, resulting in a decrease in the lithium storage capacity.
Any thickness of the positive electrode layer 23 can be selected according to the desired battery capacity.

A state in which at least one kind of material constituting the positive electrode layer 23 is fused with the metal foil current collector 14 is preferable.
For example, a state in which a solid electrolyte having a garnet-type crystal structure is fused with the metal foil current collector 14 is preferable.
The reason for this is that the metal foil current collector 14 and the positive electrode constituent material are fused to suppress the electron transfer resistance at the interface between the metal foil current collector 14 and the positive electrode, and the physical adhesion strength is also improved. .

(negative electrode green sheet)
The negative electrode green sheet 11 includes a graphite negative electrode active material, a solid electrolyte with a garnet-type crystal structure, and a binder. The solid electrolyte may contain glass that becomes a solid electrolyte after firing. It may have a solid electrolyte containing at least boron and lithium elements. The solid electrolyte having a garnet-type crystal structure is preferably a composite oxide composed of at least Li, La, Zr and O.

The content of the solid electrolyte other than the solid electrolyte having a garnet-type crystal structure and the solid electrolyte containing Li and B is preferably less than 10% by mass. More preferably, the solid electrolyte having a garnet-type crystal structure accounts for 90% by mass or more of the solid electrolyte.
It may have an electronically conductive material as a conductive aid.
As for the binder, those described later may be used.

(Negative electrode layer)
The negative electrode layer 21 includes a graphite negative electrode active material, and at least one of a solid electrolyte having a garnet-type crystal structure and glass that becomes a solid electrolyte having a garnet-type crystal structure after firing.
As for the graphite negative electrode active material and the garnet-type crystal structure, the mass ratio of the graphite negative electrode active material to the total mass of the graphite negative electrode active material and the solid electrolyte is preferably 30% or more and 90% or less.

The reason for this is that if the mass ratio of the graphite negative electrode active material is less than 30%, the amount of the negative electrode active material in the negative electrode layer 21 is insufficient, resulting in a decrease in lithium storage capacity. This is because if it exceeds 90%, the solid electrolyte path in the negative electrode layer 21 becomes narrow, and the ionic conductivity decreases.
The solid electrolyte having a garnet-type crystal structure is preferably a composite oxide composed of at least Li, La, Zr and O.

Here, as the solid electrolyte contained in the negative electrode layer 21, the same material as the solid electrolyte contained in the solid electrolyte layer 22 and the positive electrode layer 23 can be used. Two or more kinds of solid electrolytes contained in the negative electrode layer 21 may be mixed and used. Moreover, the solid electrolyte contained in the negative electrode layer 21 may be the same as or different from the solid electrolyte contained in the solid electrolyte layer 22 and the positive electrode layer 23 .

The solid electrolyte contained in the negative electrode layer 21 may be a material having low electron conductivity and high lithium ion conductivity, and a material having a garnet-type crystal structure and high lithium ion conductivity is particularly preferable. Further, oxides containing Li, La and Zr are preferable, and other elements other than Li, La and Zr may be doped. In addition to the material having a garnet-type crystal structure and high lithium ion conductivity, a lithium ion conductive material containing Li and B may also be included. For example, Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₃ BO ₃ , or solid electrolytes obtained by doping Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ with foreign elements are most suitable.

The content of the solid electrolyte other than the solid electrolyte having a garnet-type crystal structure and the solid electrolyte containing Li and B is preferably less than 10% by mass. If the content is 10% or more, a resistance layer may be formed in the firing step of the method for manufacturing an all-solid-state battery, which will be described later, and the battery performance may deteriorate.
The negative electrode layer 21 may contain a conductive aid. The conductive aid is not particularly limited as long as it has conductivity like the conductive aid contained in the positive electrode layer 23. For example, conductive carbon materials, particularly carbon black, activated carbon, carbon carbon fiber, etc. are used. be able to.

The content of the conductive aid in the negative electrode layer 21 is preferably more than 0% by mass and less than 90% by mass with respect to the mass of the negative electrode active material. This is because if the content of the conductive aid is 90% by mass or more, the amount of the negative electrode active material in the negative electrode layer 21 may be insufficient and the lithium storage capacity may decrease.
Any thickness of the negative electrode green sheet 11 can be selected according to the desired battery capacity.

A state in which at least one kind of material constituting the positive electrode layer 23 is fused with the metal foil current collector 14 is preferable.
For example, a state in which a solid electrolyte having a garnet-type crystal structure is fused with the metal foil current collector 14 is preferable.
The reason for this is that the metal foil current collector 14 and the positive electrode constituent material are fused to suppress the electron transfer resistance at the interface between the metal foil current collector 14 and the positive electrode, and the physical adhesion strength is also improved. .

(metal foil current collector)
The metal foil current collector 14 constitutes a positive electrode current collector or a negative electrode current collector. The positive electrode current collector and the negative electrode current collector are not particularly limited as long as they are conductive materials, but metal foil is preferable, so the metal foil current collector 14 is exemplified in this embodiment.
The material of the metal foil current collector 14 is not particularly limited as long as it is a material having conductivity. For example, metal materials such as stainless steel, nickel, aluminum, iron, titanium, copper, palladium, gold and platinum are used. be able to. In addition, it is preferable to select the material of the metal foil current collector 14 in consideration of not melting or decomposing under the firing conditions described later, and the battery operating potential and conductivity applied to the metal foil current collector 14 . Any material such as a carbon film may be used as long as it does not deteriorate in high temperature atmosphere and prevents contact between the metal foil and the atmosphere. The carbon film thickness as an antioxidant film is desirably 10 nm or more. Formation is possible.

The tensile strength of the metal foil current collector 14 is preferably 10 N/10 mm or more. When the tensile strength of the metal foil current collector 14 is 10 N/10 mm or more, cracks or the like are less likely to occur in the metal foil current collector 14 in the firing process for manufacturing the all-solid secondary battery 26 . Further, when the tensile strength of the metal foil current collector 14 is 10 N/10 mm or more, the strength sufficiently supports the laminate green sheet 16 composed of the positive electrode green sheet 13, the solid electrolyte layer green sheet 12 and the negative electrode green sheet 11. is obtained.

The all-solid secondary battery 26 of the present embodiment is manufactured by laminating a positive electrode green sheet 13, a solid electrolyte layer green sheet 12, and a negative electrode green sheet 11, which will be described later, and firing them. For this reason, it is important that the metal foil current collector 14 of the all-solid secondary battery 26 has a property that cracks or the like do not occur in the firing process.
The thickness of the metal foil current collector 14 is preferably 3 μm or more and 50 μm or less. When the thickness of the metal foil current collector 14 is 3 μm or more and 50 μm or less, the metal foil current collector 14 is less likely to crack or the like during the production of the laminated sintered body, and the laminate green sheet 16 is sufficiently supported. thickness is obtained.

A method for manufacturing the laminate green sheet 16 and the all-solid secondary battery 26 having the above configuration will be described below.
The method for manufacturing the laminate green sheet 16 includes, for example, applying or printing a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector made of a metal foil current collector 14, followed by drying to form a negative electrode green sheet. a sheet forming step; a solid electrolyte layer green sheet forming step of applying or printing a solid electrolyte slurry containing a solid electrolyte on the negative electrode green sheet 11 and then drying to form the solid electrolyte layer green sheet 12; and a positive electrode green sheet forming step of forming a positive electrode green sheet 13 by applying or printing a positive electrode slurry containing a positive electrode active material and then drying the positive electrode slurry.

In the case of manufacturing the laminate green sheet 16 without the metal foil current collector 14 as shown in FIG. 5, a substrate may be used in place of the positive electrode current collector.
The substrate to which the slurry of the green sheet is applied is not particularly limited as long as it can be peeled off after the laminate green sheet 16 is produced on the substrate. Metal foil, etc. can be used.

The thickness of the base material is not particularly limited, but if it is too thin, the laminate green sheet 16 may be bent when drying each slurry constituting the laminate green sheet 16, and the laminate green sheet 16 may be destroyed. When peeled off, the laminate green sheet 16 may be destroyed. Specifically, for example, the thickness is preferably 3 μm or more and 100 μm or less, more preferably 5 μm or more and 80 μm or less.

(Manufacturing method of solid electrolyte layer green sheet 12)
The solid electrolyte layer green sheet 12 is formed by applying or printing a solid electrolyte slurry formed by mixing a binder composed of an oxide solid electrolyte and an organic substance with a solvent, and then drying the slurry. The solid electrolyte slurry is applied, for example, onto a positive electrode green sheet 13 or a negative electrode green sheet 11, which will be described later. A method for preparing the solid electrolyte slurry is not particularly limited.

(Manufacturing method of positive electrode green sheet)
The positive electrode green sheet 13 is formed by mixing a positive electrode active material, a solid electrolyte, and a binder comprising an organic substance with a solvent, applying or printing a positive electrode slurry, and then drying. The positive electrode slurry is applied onto the metal foil current collector 14 serving as a positive electrode current collector or the solid electrolyte layer green sheet 12 described later. The method for preparing the positive electrode slurry is not particularly limited.

(Manufacturing method of negative electrode green sheet)
The negative electrode green sheet 11 is formed by mixing a binder composed of a negative electrode active material, a solid electrolyte, and an organic substance with a solvent, applying or printing negative electrode slurry, and then drying. The slurry for the negative electrode is applied onto the metal foil current collector 14 serving as the negative electrode current collector or the solid electrolyte layer green sheet 12 described later. The method for preparing the negative electrode slurry is not particularly limited.

The binder contained in the positive electrode slurry, the negative electrode slurry, and the solid electrolyte slurry is not particularly limited as long as it decomposes under the firing conditions described below. Examples of binders that can be used include polyvinyl alcohol, polyvinyl butyral, polyvinyl acetal, polyvinylidene fluoride, polytetrafluoroethylene, ethyl cellulose, and acrylic resins.

In the positive electrode green sheet 13, the negative electrode green sheet 11, and the solid electrolyte layer green sheet 12, the binder content is preferably 3% by mass or more and 40% by mass or less, more preferably 3% by mass or more and 25% by mass or less. That is, the content of the binder with respect to the total solid content of each slurry excluding the solvent is preferably 3% by mass or more and 40% by mass or less, and more preferably 3% by mass or more and 25% by mass or less.

If the binder content is less than 3% by mass, for example, active materials or solid electrolytes may not be sufficiently bound together. Moreover, when the content of the binder is more than 40% by mass, the battery capacity per volume is lowered.
The positive electrode green sheet 13, the negative electrode green sheet 11, and the solid electrolyte layer green sheet 12 may contain a firing aid that promotes the formation of a matrix structure in each green sheet during firing and lowers the firing temperature. The sintering aid is not particularly limited as long as it does not react with the positive electrode active material, the negative electrode active material and the solid electrolyte, and has a softening point lower than the sintering temperature of the solid electrolyte. For example, a boron compound can be used. By adjusting the content of the sintering aid and the sintering temperature of the positive electrode green sheet 13, the negative electrode green sheet 11, and the solid electrolyte layer green sheet 12, when the laminated sintered body is formed by sintering, internal strain and internal stress of each layer can be reduced. It is possible to prevent cracks caused by the heat and promote the formation of a matrix structure.

The solvent used for the positive electrode slurry, the negative electrode slurry and the solid electrolyte slurry is not particularly limited as long as it can dissolve the binder described above. Organic solvents such as butyl, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol ethyl ether, isophorone, butyl lactate, dioctyl phthalate, dioctyl adipate, benzyl alcohol, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and water can be used. These solvents may be used alone, or two or more of them may be used in combination. The boiling point of the solvent is preferably 200° C. or less because the slurry can be easily dried.

The positive electrode slurry and the negative electrode slurry can be prepared by mixing the above-described positive electrode active material or negative electrode active material, solid electrolyte, binder, conductive aid, sintering aid, and the like with a solvent. Further, the solid electrolyte slurry can be prepared by mixing the solid electrolyte, the binder, the conductive aid, the sintering aid, and the like described above with a solvent. The method of mixing the slurry is not particularly limited, and additives such as thickeners, plasticizers, antifoaming agents, leveling agents, and adhesion imparting agents may be added as necessary.

Specific examples of methods for applying and printing the positive electrode slurry, the negative electrode slurry, and the solid electrolyte slurry include a doctor blade method, a calendar method, a spin coating method, a dip coating method, an ink jet method, an offset method, a die coating method, and a spray method. , a screen printing method, or the like can be used.
The method for drying the positive electrode slurry, the negative electrode slurry, and the solid electrolyte slurry is not particularly limited. The drying atmosphere is not particularly limited, and for example, the drying can be performed under an air atmosphere or an inert atmosphere (nitrogen atmosphere, argon atmosphere).

The positive electrode green sheet 13, the solid electrolyte layer green sheet 12 and the negative electrode green sheet 11 constitute a laminate green sheet 16 laminated in order. The laminate green sheet 16 may be composed of only the solid electrolyte layer green sheet 12 and the negative electrode green sheet.
The pressure may be applied to increase the mechanical strength of the laminate green sheet 16 and reduce voids present in the laminate green sheet 16 . The pressurization method is not particularly limited, but flat press, roll press, hot press, cold isostatic press, hot isostatic press, etc. can be used, for example. Pressurization may be performed only once, or may be divided into several times.

When the laminate green sheet 16 is formed on the base material, the base material is peeled off after the above treatment. The porosity of the laminate green sheet 16 before peeling is not particularly limited, and the pressure process may or may not be performed before peeling.
The all-solid secondary battery 26 of the present embodiment is formed, for example, by firing the laminate green sheet 16 manufactured as described above and degreasing the binder.

In the case where a current collector is not adhered to the laminate green sheet 16 in advance, a layer having a current collecting property for the exposed positive electrode surface or negative electrode surface in the laminate fired body obtained by firing the laminate green sheet 16 should be formed. The method for forming the conductive layer is not particularly limited, and for example, a metal foil can be brought into close contact with the positive electrode surface and the negative electrode surface and pressed to form a current collecting layer. In addition, the material constituting the current collecting layer is not particularly limited as long as it adheres to the positive electrode or the negative electrode and can obtain conductivity. Examples include metal foil, conductive thin film layer, conductive paste, and conductive adhesive material. etc.

The heating temperature in the firing step is a temperature equal to or higher than the thermal decomposition temperature of the binder contained in the laminate green sheet 16 and lower than the oxidation temperature of the positive electrode active material and the negative electrode active material or the combustion temperature of the metal foil current collector 14. is preferred. Specifically, the heating temperature is preferably 300° C. or higher and 1100° C. or lower, more preferably 300° C. or higher and 900° C. or lower. If the heating temperature is lower than 300° C., the binder may not be completely burned in the firing process and become a residue, which may hinder electronic conduction and ionic conduction. Moreover, if the heating temperature is higher than 1100° C., the positive electrode active material, the negative electrode active material, and the solid electrolyte may be melted and deteriorated, degrading the battery performance.

The atmosphere in the firing step is not particularly limited, and can be performed, for example, in an air atmosphere or an inert atmosphere (nitrogen atmosphere, argon atmosphere). If there is concern about the reaction between the positive electrode active material and the negative electrode active material and the metal foil current collector 14 or the decrease in conductivity of the metal foil current collector 14, it is desirable to perform the firing step in an inert atmosphere.
The firing time in the firing step is not particularly limited as long as the binder used is sufficiently decomposed.

As described above, the all-solid secondary battery 26 of the present embodiment is formed, for example, on the positive electrode green sheet 13 or the negative electrode green sheet 11 formed at the farthest position from the metal foil current collector 14 of the laminate green sheet 16. A laminated body in which the metal foil current collectors 14 are bonded together can be fired all at once to form the laminate.
Thereby, while suppressing the interfacial resistance between the metal foil current collector 14 and the positive electrode layer 23 as the positive electrode current collector, and the metal foil current collector 14 and the negative electrode layer 21 as the negative electrode current collector, one firing process is performed. It has become possible to manufacture the all-solid secondary battery 26. The method of bonding the metal foil current collector 14 is not particularly limited, but for example, flat press, roll press, hot press, cold isostatic press, hot isostatic press, etc. can be used.

The all-solid secondary battery 26 of this embodiment may be manufactured by other known manufacturing methods without using the laminate green sheet 16 as described above. For example, the all-solid-state secondary battery 26 may be manufactured by a compacting firing method in which powders are compressed and fired by compressing and firing each layer of the negative electrode layer, the solid electrolyte layer, and the positive electrode layer each having the composition described above. good.
Here, the configuration of the all-solid secondary battery 26 may be a series all-solid secondary battery. Such an all-solid secondary battery 26 includes, for example, a positive electrode layer 23, a solid electrolyte layer 22 provided on the positive electrode layer 23, and a negative electrode layer 21 provided on the solid electrolyte layer 22. A plurality of electrode stacks Prepare your body. Furthermore, the all-solid secondary battery 26 is in close contact with the positive electrode layer 23 or the negative electrode layer 21 between the stacked electrode stacks and further outside the stacking direction outer surface of the stacked electrode stacks. A plurality of metal foil current collectors 14 are provided at the same time.

The all-solid secondary battery 26 is manufactured by, for example, forming a cathode green sheet 13, a solid electrolyte layer green sheet 12, and an anode green sheet 11 on a cathode current collector, on a laminate green sheet 16, and A laminate green sheet 16 is prepared by continuously laminating a laminate green sheet 16 including a positive electrode green sheet 13, a solid electrolyte layer green sheet 12 and a negative electrode green sheet 11, and the laminate green sheet 16 prepared is collectively fired. It is realized by bonding the metal foil current collector 14 to the metal foil current collector 14 .

Here, when a green sheet having a graphite negative electrode active material and a solid electrolyte with a garnet-type crystal structure is fired, the mechanism by which the formation of an altered layer is suppressed is not clear, but as shown in Examples below, It has been confirmed that the formation of altered layers is suppressed.

Hereinafter, the all-solid secondary battery based on the present invention will be described with specific examples and comparative examples. In addition, the configuration of the all-solid secondary battery according to the present invention is not limited to the following examples.
"First embodiment"
(Example 1-1)
[Slurry preparation process]
<Preparation of slurry for inorganic solid electrolyte>
100 parts by mass of _{Li1.5Al0.5Ge1.5} ( _PO4 ) ₃ (abbreviated as _LAGP , manufactured by Toshima _Seisakusho ) powder as an inorganic solid electrolyte, 16 parts by mass of PVB as a binder, and 4 parts of dibutyl phthalate (abbreviated as DBP) as a plasticizer. 8 parts by mass and 22 parts by mass of a mixed solvent of methyl ethyl ketone and acetone (mass ratio: 1:1) as a solvent were mixed to form a slurry, and this slurry was defoamed to prepare a slurry for an inorganic solid electrolyte.

<Preparation of negative electrode slurry>
50 parts by mass _of graphite powder as a negative electrode active _material , 50 parts by mass of powder of _Li7La3Zr2O12 (abbreviated as _LLZ , manufactured by Toyoshima Seisakusho) as an inorganic solid electrolyte, 16 parts by mass of PVB as a binder, and 4.8 parts by mass of DBP as a plasticizer. 22 parts by mass of a mixed solvent of methyl ethyl ketone and acetone (mass ratio: 1:1) was mixed as a solvent to form a slurry, and the slurry was defoamed to prepare a negative electrode slurry.

<Laminate green sheet manufacturing process>
A nickel foil was used as a negative electrode current collector, and a negative electrode slurry was applied to one surface of the negative electrode current collector and dried to form a negative electrode green sheet.
Subsequently, the inorganic solid electrolyte slurry is applied to the surface of the negative electrode green sheet opposite to the surface facing the nickel foil current collector, and dried to form a solid electrolyte layer green sheet, which has a metal foil current collector. A two-layer laminate green sheet was produced.

<Cutting pressure process>
The produced two-layer laminate green sheet with a metal foil current collector was pressurized at 80° C. and 1000 kgf/cm ² and cut into a predetermined size to obtain a two-layer laminate green sheet with a metal foil current collector. .

<Degreasing process>
The cut two-layer laminate green sheet with a metal foil current collector was heated from room temperature to 500° C. at a heating rate of 20° C./min in the air, and held at 500° C. for 30 minutes for degreasing.
<Baking process>
The degreased two-layer laminate green sheet with a metal foil current collector was heated from 500° C. to 800° C. at a temperature increase rate of 20° C./min in an argon stream, held at 800° C. for 60 minutes, and fired. did. After that, the fired laminated body was cooled to room temperature by allowing it to cool in a furnace, and a Li foil was laminated on the solid electrolyte layer to fabricate an all-solid secondary battery of Example 1-1.

(Example 1-2)
In <Preparation of slurry for inorganic solid electrolyte> in Example 1-1, except that LLZ was used instead of LAGP as the solid electrolyte, the all-solid secondary of Example 1-2 was prepared under the same conditions as in Example 1-1. A battery was produced.
(Example 1-3)
[Slurry preparation process]
<Preparation of slurry for inorganic solid electrolyte>
100 parts by mass of LAGP powder as an inorganic solid electrolyte, 16 parts by mass of PVB as a binder, 4.8 parts by mass of DBP as a plasticizer, and 22 parts by mass of a mixed solvent of methyl ethyl ketone and acetone (mass ratio 1:1) as a solvent. The materials were mixed to form a slurry, and the slurry was defoamed to prepare a slurry for an inorganic solid electrolyte.

<Preparation of negative electrode slurry>
50 parts by mass of graphite powder as a negative electrode active material, 50 parts by mass of LLZ powder as an inorganic solid electrolyte, 16 parts by mass of PVB as a binder, 4.8 parts by mass of DBP as a plasticizer, and a mixed solvent of methyl ethyl ketone and acetone as a solvent (mass ratio 1:1 ) were mixed to form a slurry, and the slurry was defoamed to prepare a negative electrode slurry.

<Preparation of positive electrode slurry>
50 parts by mass of LiCoO ₂ (abbreviated as LCO, manufactured by Toyoshima Seisakusho) powder as a positive electrode active material, 50 parts by mass of LLZ powder as an inorganic solid electrolyte, 16 parts by mass of PVB as a binder, 4.8 parts by mass of DBP as a plasticizer, and methyl ethyl ketone and acetone as solvents. 22 parts by mass of a mixed solvent (mass ratio of 1:1) was mixed to form a slurry, and the slurry was defoamed to prepare a positive electrode slurry.

<Laminate green sheet manufacturing process>
A nickel foil was used as a positive electrode current collector, and a positive electrode slurry was applied to one surface of the positive electrode current collector and dried to form a positive electrode green sheet.
Subsequently, the inorganic solid electrolyte slurry was applied to the surface of the positive electrode green sheet opposite to the surface facing the metal foil current collector and dried to form a solid electrolyte layer green sheet.
Finally, the negative electrode slurry was applied to the surface of the solid electrolyte layer green sheet opposite to the surface facing the positive electrode green sheet and dried to form a negative electrode green sheet, thereby producing a laminate green sheet.

<Cutting process>
A negative electrode current collector made of the same nickel foil as the positive electrode current collector was placed on the negative electrode green sheet of the laminate green sheet thus produced. Subsequently, the laminate composed of the laminate green sheet on which the negative electrode current collector was placed was pressed at 80° C. and 1000 kgf/cm ² and cut into a predetermined size to obtain a three-layer laminate with a bipolar metal foil current collector. Got a green sheet.

<Degreasing process>
The cut three-layer laminate green sheet with a bipolar metal foil current collector was heated from room temperature to 500° C. at a heating rate of 20° C./min in air, and held at 500° C. for 30 minutes for degreasing.
<Baking process>
The degreased three-layer laminate green sheet with a bipolar current collector was heated from 500° C. to 800° C. at a temperature elevation rate of 20° C./min in an argon stream, and was held at 800° C. for 60 minutes to perform firing. . After that, the fired stacked fired body was allowed to cool to room temperature in a furnace to produce an all-solid secondary battery of Example 1-3.

(Example 1-4)
In <Preparation of slurry for inorganic solid electrolyte> in Example 1-1, except that LLZ was used instead of LAGP as the solid electrolyte, the all-solid secondary of Example 1-4 was prepared under the same conditions as in Example 1-3. A battery was produced.
(Example 1-5)
In <preparation of positive electrode slurry> and <preparation of negative electrode slurry> of Example 1-4, 35 parts by mass of LLZ powder and 15 parts by mass of Li ₃ BO ₃ (abbreviated as LBO) powder were added as a solid electrolyte, and <inorganic solid Preparation of Slurry for Electrolyte>, except that 70 parts by mass of LLZ powder and 30 parts by mass of Li ₃ BO ₃ (abbreviated as LBO) powder were added as solid electrolytes, and the conditions of Example 1-5 were the same as in Example 1-4. An all-solid secondary battery was produced.

(Example 1-6)
In <Preparation of positive electrode slurry> and <Preparation of negative electrode slurry> in Example 1-5, except that 10 parts by mass of acetylene black (AB, Li-400, manufactured by Denki Kagaku Kogyo) was added as an electron conduction aid. An all-solid secondary battery of Example 1-6 was produced under the same conditions as in Example 1-5.
(Example 1-7)
In <preparation of positive electrode slurry><preparation of inorganic solid electrolyte slurry><preparation of negative electrode slurry> of Example 1-6, Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ ( An all-solid secondary battery of Example 1-7 was produced under the same conditions as in Example 1-6, except that the abbreviation LLZN) was used.

(Comparative Example 1-1)
An all-solid secondary battery of Comparative Example 1-1 was prepared under the same conditions as in Example 1-1, except that LAGP was used instead of LLZ as the solid electrolyte in <Preparation of negative electrode slurry> in Example 1-1. made.
(Comparative Example 1-2)
An all-solid secondary battery of Comparative Example 1-2 was prepared under the same conditions as in Example 1-2 except that LAGP was used instead of LLZ as the solid electrolyte in <Preparation of negative electrode slurry> of Example 1-2. made.

(Comparative Example 1-3)
Example 1-2 except that Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ (abbreviated as LATP, manufactured by Toshima Seisakusho) was used as the solid electrolyte instead of LLZ in <Preparation of negative electrode slurry> of Example 1-2. All-solid secondary batteries of Comparative Examples 1-3 were produced under the same conditions as in 2.
(Comparative Example 1-4)
An all-solid secondary battery of Comparative Example 1-4 was prepared under the same conditions as in Example 1-3, except that LAGP was used instead of LLZ as the solid electrolyte in <Preparation of positive electrode slurry> in Example 1-1. made.

(Comparative Example 1-5)
An all-solid secondary battery of Comparative Example 1-5 was prepared under the same conditions as in Example 1-3, except that LAGP was used instead of LLZ as the solid electrolyte in <Preparation of negative electrode slurry> in Example 1-1. made.
(Comparative Example 1-6)
Comparative Example 1-6 under the same conditions as in Example 1-3, except that LAGP was used instead of LLZ as the solid electrolyte in <Preparation of positive electrode slurry> and <Preparation of negative electrode slurry> in Example 1-1. All-solid-state secondary battery was produced.

(Comparative Example 1-7)
An all-solid secondary battery of Comparative Example 1-7 was prepared under the same conditions as in Example 1-3, except that LATP was used instead of LLZ as the solid electrolyte in <Preparation of positive electrode slurry> in Example 1-1. made.
(Comparative Example 1-8)
An all-solid secondary battery of Comparative Example 1-8 was prepared under the same conditions as in Example 1-3, except that LATP was used instead of LLZ as the solid electrolyte in <Preparation of negative electrode slurry> of Example 1-1. made.

(Comparative Example 1-9)
Comparative Example 1-9 under the same conditions as in Example 1-3, except that LATP was used instead of LLZ as the solid electrolyte in <Preparation of positive electrode slurry> and <Preparation of negative electrode slurry> in Example 1-1. All-solid-state secondary battery was produced.
(Comparative Example 1-10)
In the <slurry preparation step> of Example 1-1, lithium manganate was used instead of lithium cobaltate as the positive electrode active material. A following battery was produced.

(Comparative Example 1-11)
An all-solid secondary battery of Comparative Example 1-11 was produced under the same conditions as in Example 1-3, except that LTO was used instead of graphite as the negative electrode active material in the <slurry preparation step> of Example 1-1. did.

(evaluation)
[Crystal structure analysis]
Crystal structure analysis of the positive electrode and the negative electrode of each example and comparative example was evaluated by the following method. Table 1 shows the evaluation results.
(Evaluation method of all-solid secondary batteries of Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-11)
X Analysis was performed using a line diffractometer (XRD, Rigaku) to investigate the presence or absence of changes in the crystal structures of the positive electrode and the negative electrode. Not measured is indicated by "-".

[Battery characteristic evaluation]
The battery characteristics of the all-solid secondary battery of each example and comparative example were evaluated by the following methods. Table 1 shows the evaluation results.
(Evaluation method of all-solid secondary batteries of Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-11)
Five all-solid-state secondary batteries of each example and comparative example were prepared and evaluated.

The all-solid secondary batteries of Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-3 were charged with a constant current of 0.001 C to 0.01 V, and the charging capacity with respect to the battery design capacity was A case of 50% or more was evaluated as ◯, and a case of 50% or less was evaluated as x.
The all-solid secondary batteries of Examples 1-3 to 1-7 and Comparative Examples 1-4 to 1-11 were charged with a constant current of 0.001 C to 4.0 V, and the charge capacity with respect to the battery design capacity was A case of 50% or more was evaluated as ◯, and a case of 50% or less was evaluated as x.

From the crystal structure analysis of the positive electrode and the negative electrode, as shown in Comparative Examples 1-1 to 1-3 in Table 1, the solid electrolytes LAGP and LATP are fired in a mixed form with the negative electrode active material graphite. A different crystal structure was confirmed. On the other hand, as shown in Examples 1-1 and 1-2 in Table 1, LLZ, which is a solid electrolyte, did not change its crystal structure even when fired in a mixed form with the negative electrode active material graphite.

Furthermore, as shown in Comparative Examples 1-4 to 1-9 in Table 1, the solid electrolytes LAGP and LATP are fired in a mixed form with the positive electrode active material LCO or the negative electrode active material graphite. A different crystal structure was confirmed. On the other hand, as shown in Examples 1-3 to 1-7 in Table 1, even when LLZ and LLZN were mixed with the positive electrode active material LCO and the negative electrode active material graphite and fired in a mixed form, the crystal structure did not change.

In addition, as shown in Comparative Examples 1-10 to 1-11 in Table 1, when the positive electrode active material LMO and the solid electrolyte LLZ are fired in a mixed form, a crystal structure different from the unfired crystal structure is confirmed, and the negative electrode active material Even when the LTO and the solid electrolyte LLZ were fired in a mixed form, a crystal structure different from the unfired crystal structure was confirmed.
Next, from the battery characteristics evaluation, as shown in Comparative Examples 1-1 to 1-3 in Table 1, when using a negative electrode made of a negative electrode active material graphite, a solid electrolyte LAGP, or LATP, the charge capacity with respect to the battery design capacity was less than 50%, it was determined that the battery was malfunctioning. On the other hand, as shown in Examples 1-1 and 1-2 in Table 1, when the negative electrode composed of the negative electrode active material graphite and the solid electrolyte LLZ was used, the charge capacity was 50% or more of the battery design capacity. Therefore, it was judged that the battery operation was normal.

Further, as shown in Comparative Examples 1-4 to 1-11 in Table 1, the positive electrode made of the positive electrode active material LCO, the solid electrolyte LAGP, or LATP, or the negative electrode made of the negative electrode active material graphite, the solid electrolyte LAGP, or LATP, Alternatively, when a positive electrode composed of the positive electrode active material LMO and the solid electrolyte LLZ, or a negative electrode composed of the negative electrode active material LTO and the solid electrolyte LLZ was used, the charging capacity was 50% or less of the battery design capacity, so it was determined that the battery was malfunctioning. did. On the other hand, as shown in Examples 1-3 to 1-7 in Table 1, when using the positive electrode active material LCO, the solid electrolyte LLZ, or the mixture of LLZN, LLZ and LBO, the charge capacity with respect to the battery design capacity Since it was 50% or more, it was judged that the battery operation was normal.

From the above, it is presumed that the crystal structure of the positive electrode and the negative electrode, particularly the crystal structure of the positive electrode active material and the negative electrode active material, changed depending on the positive electrode active material type, the negative electrode active material type, and the solid electrolyte type, and the battery voltage fluctuated. . On the other hand, by using a specific positive electrode active material (LCO), negative electrode active material (graphite), solid electrolyte species (materials with a garnet-type crystal structure represented by LLZ and LLZN), the crystal structure change is suppressed, It is considered that the battery can be charged normally.

"Second embodiment"
A second embodiment will be described below.
(Example 2-1)
[Slurry preparation process]
<Preparation of positive electrode slurry>
50 parts by mass of lithium cobalt oxide (LiCoO ₂ , manufactured by Toshima Seisakusho) powder having a layered rock salt type crystal structure as the positive electrode active material, and 50 mass parts of Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ, manufactured by Toshima Seisakusho) powder as the inorganic solid electrolyte. 16 parts by mass of polyvinyl butyral (PVB) as a binder, 4.8 parts by mass of dibutyl phthalate (DBP) as a plasticizer, and 22 parts by mass of a mixed solvent of methyl ethyl ketone and acetone (mass ratio 1:1) as a solvent. This slurry was defoamed to prepare a positive electrode slurry.

<Preparation of slurry for inorganic solid electrolyte>
100 parts by mass of LLZ powder as an inorganic solid electrolyte, 16 parts by mass of PVB as a binder, 4.8 parts by mass of DBP as a plasticizer, and 22 parts by mass of a mixed solvent of methyl ethyl ketone and acetone (mass ratio 1:1) as a solvent. The materials were mixed to form a slurry, and the slurry was defoamed to prepare a slurry for an inorganic solid electrolyte.

<Preparation of negative electrode slurry>
50 parts by mass of graphite (SMG, manufactured by Hitachi Chemical) powder as a negative electrode active material, 50 parts by mass of LLZ powder as an inorganic solid electrolyte, 16 parts by mass of PVB as a binder, 4.8 parts by mass of DBP as a plasticizer, and a mixture of methyl ethyl ketone and acetone as a solvent A slurry was prepared by mixing 22 parts by mass of a solvent (mass ratio: 1:1), and the slurry was defoamed to prepare a negative electrode slurry.

<Laminate green sheet manufacturing process>
A release PET film (thickness: 25 μm) was used as a base material, and the positive electrode slurry was applied to the release surface and dried to form a positive electrode green sheet.
Subsequently, the inorganic solid electrolyte slurry was applied to the surface of the positive electrode green sheet opposite to the surface facing the release PET film, and dried to form a solid electrolyte layer green sheet.
Finally, the negative electrode slurry was applied to the surface of the solid electrolyte layer green sheet opposite to the surface facing the positive electrode green sheet and dried to form a negative electrode green sheet, thereby producing a laminate green sheet.

<Cutting process>
The produced laminate green sheet was pressurized at 80° C. and 1000 kgf/cm ² . After that, the substrate was peeled off and then cut into a predetermined area.
<Degreasing process>
The laminate green sheet described above was heated from room temperature to 500° C. at a heating rate of 20° C./min in the air, and held at 500° C. for 30 minutes for degreasing.

<Baking process>
The degreased laminate green sheet was heated from 500° C. to 800° C. at a rate of temperature increase of 20° C./min in an argon stream, and was held at 800° C. for 60 minutes for firing. After that, the sintered laminated sintered body was allowed to cool to room temperature in the furnace.
<Collecting layer attachment process>
After applying a silver paste to the positive electrode surface and the negative electrode surface of the laminated fired body, the metal foil is pressed against the silver paste so that a part of the metal foil is exposed on each different surface of the laminated body, and dried. A body was formed to produce an all-solid secondary battery of Example 2-1.

(Example 2-2)
In <Preparation of positive electrode slurry> and <Preparation of negative electrode slurry> of Example 2-1, 35 parts by mass of Li ₇ La ₃ Zr ₂ O ₁₂ powder and 15 parts by mass of Li ₃ BO ₃ (LBO) powder were used as solid electrolytes. Example 2- except that 70 parts by mass of Li ₇ La ₃ Zr ₂ O ₁₂ powder and 30 parts by mass of Li ₃ BO ₃ (LBO) powder were added as solid electrolytes in <Preparation of slurry for inorganic solid electrolyte> An all-solid secondary battery of Example 2-2 was produced under the same conditions as in 1.
(Example 2-3)
In <Preparation of positive electrode slurry> and <Preparation of negative electrode slurry> in Example 2-2, 10 parts by mass of acetylene black (AB, Li-400, manufactured by Denki Kagaku Kogyo) was added as an electron conduction aid. An all-solid secondary battery of Example 2-3 was produced under the same conditions as in Example 2-2.

(Example 2-4)
In <preparation of positive electrode slurry><preparation of inorganic solid electrolyte slurry><preparation of negative electrode slurry> in Example 2-3, Li _6.75 La ₃ Zr was used instead of Li ₇ La ₃ Zr ₂ O ₁₂ as the solid electrolyte. An all-solid secondary battery of Example 2-4 was produced under the same conditions as in Example 2-3, except that _1.75 Nb _0.25 O ₁₂ (LLZN) was used.
(Example 2-5)
In the <slurry preparation step> of Example 2-1, nickel cobalt lithium manganate (NCM, Li ₁ Ni _0.5 Co _0.2 Mn) having a layered rock salt crystal structure was used instead of lithium cobalt oxide (LiCoO ₂ ) as the positive electrode active material. An all-solid secondary battery of Example 2-5 was produced under the same conditions as in Example 2-1, except that _0.3 O ₂ ) was used.

(Example 2-6)
Example 2-6 was prepared under the same conditions as in Example 2-4, except that NCM was used instead of lithium cobaltate (LiCoO ₂ ) as the positive electrode active material in the <positive electrode slurry preparation step> of Example 2-4. An all-solid secondary battery was produced.
(Example 2-7)
[Mixing process]
50 parts by mass of LiCoO ₂ powder as a positive electrode active material and 50 parts by mass of LLZ powder as an inorganic solid electrolyte were mixed in an agate mortar for 15 minutes to prepare a positive electrode raw material composition. Similarly, 50 parts by mass of graphite powder as a negative electrode active material and 50 parts by mass of LLZ powder as an inorganic solid electrolyte were mixed in an agate mortar for 15 minutes to prepare a negative electrode material composition.

[Molding body manufacturing process]
The positive electrode raw material composition, the LLZ powder and the negative electrode raw material composition were successively enclosed in a pellet molding jig of φ20 mm and stacked, and then pressed at 80° C. and 1000 kgf/cm ² to produce a compact.
<Baking process>
The compact was heated to 800° C. at a rate of temperature increase of 20° C./min in an argon stream, and was held at 800° C. for 60 minutes for firing. After that, the sintered laminated sintered body was allowed to cool to room temperature in the furnace.

<Collecting layer attachment process>
A 20 μm-thick gold collector layer was formed on the positive electrode surface of the laminated fired body by magnetron sputtering, and a 20 μm-thick gold collector layer was similarly formed on the negative electrode surface. A secondary battery was produced.

(Comparative Example 2-1)
Example 2-1 except that Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ was used as the solid electrolyte instead of Li ₇ La ₃ Zr ₂ O ₁₂ in <Preparation of positive electrode slurry> of Example 2-1. An all-solid secondary battery of Comparative Example 2-1 was produced under the same conditions as in .
(Comparative Example 2-2)
Example 2-1 except that Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ was used as the solid electrolyte instead of Li ₇ La ₃ Zr ₂ O ₁₂ in <Preparation of negative electrode slurry> of Example 2-1. An all-solid secondary battery of Comparative Example 2-2 was produced under the same conditions as in .

(Comparative Example 2-3)
In <preparation of positive electrode slurry> and <preparation of negative electrode slurry> _of Example 2-1, _{Li1.5Al0.5Ge1.5} ( _PO4 ) ₃ was _{used as the} solid _electrolyte instead of _Li7La3Zr2O12 . Except for this, an all-solid secondary battery of Comparative Example 2-3 was produced under the same conditions as in Example 2-1.
(Comparative Example 2-4)
Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ (LATP, manufactured by Toshima Seisakusho) was used as the solid electrolyte in place of Li ₇ La ₃ Zr ₂ O ₁₂ in <preparation of positive electrode slurry> of Example 2-1. Except for this, an all-solid secondary battery of Comparative Example 2-4 was produced under the same conditions as in Example 2-1.

(Comparative Example 2-5)
Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ (LATP, manufactured by Toshima Seisakusho) was used as the solid electrolyte in place of Li ₇ La ₃ Zr ₂ O ₁₂ in <preparation of negative electrode slurry> of Example 2-1. Except for this, an all-solid secondary battery of Comparative Example 2-5 was produced under the same conditions as in Example 2-1.
(Comparative Example 2-6)
In <preparation of positive electrode slurry> and <preparation of negative electrode slurry> _of Example 2-1, _{Li1.5Al0.5Ge1.5} ( _PO4 ) ₃ was _{used as the} solid _electrolyte instead of _Li7La3Zr2O12 . Except for this, an all-solid secondary battery of Comparative Example 2-6 was produced under the same conditions as in Example 2-1.

(Comparative Example 2-7)
Example 2 except that lithium manganate (LiMn ₂ O ₄ ) having a spinel crystal structure was used as the positive electrode active material in place of lithium cobaltate (LiCoO ₂ ) in <slurry preparation step> of Example 2-1. An all-solid secondary battery of Comparative Example 2-7 was produced under the same conditions as in -1.
(Comparative Example 2-8)
Example 2-1 except that lithium iron phosphate (LiFePO ₄ ) having an olivine-type crystal structure was used instead of lithium cobaltate (LiCoO ₂ ) as the positive electrode active material in the <slurry preparation step> of Example 2-1. An all-solid secondary battery of Comparative Example 2-8 was produced under the same conditions as in 1.

(Comparative Example 2-9)
Comparative Example 2 was carried out under the same conditions as in Example 2-1, except that lithium titanate (Li ₄ Ti ₅ O ₁₂ ) was used instead of graphite as the negative electrode active material in the <slurry preparation step> of Example 2-1. -9 all-solid secondary battery was produced.

(evaluation)
[Crystal structure analysis]
Crystal structure analysis of the positive electrode and the negative electrode of each example and comparative example was evaluated by the following method. Table 2 shows the evaluation results.
(Evaluation method of all-solid secondary batteries of Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-9)
The positive electrode surface and the negative electrode surface of the three-layer laminate composed of the positive electrode, the solid electrolyte, and the negative electrode of the all-solid secondary battery shown in each example and comparative example were analyzed using an X-ray diffractometer (XRD, Rigaku). Then, the presence or absence of changes in the crystal structure of the positive electrode and the negative electrode was investigated.

[Battery characteristic evaluation]
The battery characteristics of the all-solid secondary battery of each example and comparative example were evaluated by the following methods. Table 2 shows the evaluation results.
(Evaluation method of all-solid secondary batteries of Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-9)
Five all-solid-state secondary batteries of each example and comparative example were prepared and evaluated.

The all-solid secondary battery of each example and comparative example was charged with a constant current of 0.001 C until the voltage reached 4.0 V. In that case, it was evaluated as ×.

From the crystal structure analysis of the positive electrode and the negative electrode, as shown in Comparative Examples 2-1 to 2-9 in Table 2, the solid electrolytes LAGP and LATP are fired in a mixed form with the positive electrode active material LCO or the negative electrode active material graphite. A crystal structure different from the unfired crystal structure was confirmed. On the other hand, as shown in Examples 2-1 to 2-7 in Table 2, even when LLZ and LLZN were fired in a mixed form with the positive electrode active materials LCO and NCM and the negative electrode active material graphite, the crystal structure did not change.

Further, as shown in Comparative Examples 2-7 and 2-8 in Table 2, the positive electrode active material is lithium manganate (LMO) or lithium iron phosphate (LFP) that does not have a layered rock salt crystal structure, and the solid electrolyte is When fired in mixed form as LLZ, a crystal structure different from the unfired crystal structure was observed. Further, as shown in Comparative Example 2-9 in Table 2, lithium titanate (LTO) as the negative electrode active material and LLZ as the solid electrolyte are fired in a mixed form, and the crystal structure is similarly different from the unfired crystal structure. Structure confirmed.

Next, from the evaluation of battery characteristics, as shown in Comparative Examples 2-1 to 2-9 in Table 2, when a positive electrode made of LCO or NCM as a positive electrode active material and a solid electrolyte LAGP or LATP is used, or the positive electrode active material When a positive electrode composed of the material LMO or LFP and a solid electrolyte LLZ was used, or when a negative electrode composed of a negative electrode active material LTO and a solid electrolyte LLZ was used, the charge capacity did not reach 50% of the battery design capacity. judged to be malfunctioning. On the other hand, as shown in Examples 2-1 to 2-7 in Table 2, when LCO or NCM is used as the positive electrode active material and LLZ or LLZN, or a mixture of LLZ and LBO is used as the solid electrolyte, the battery design capacity Since the charge capacity for the battery was 50% or more, it was determined that the battery operated normally.

From the above, it is presumed that the crystal structure of the positive electrode and the negative electrode, particularly the crystal structure of the positive electrode active material and the negative electrode active material, changed depending on the positive electrode active material type, the negative electrode active material type, and the solid electrolyte type, and the battery voltage fluctuated. . On the other hand, by using specific positive electrode active materials (LCO, NCM), negative electrode active materials (graphite), and solid electrolyte species (garnet-type crystal structure materials represented by LLZ and LLZN) having a layered rock salt crystal structure, , the crystal structure change is suppressed, and normal battery operation is possible.

11 negative electrode green sheet 12 solid electrolyte layer green sheet 13 positive electrode green sheet 14 metal foil current collector 16 laminate green sheet 21 negative electrode layer 22 solid electrolyte layer 23 positive electrode layer 24 fired metal foil current collector 25 Li metal foil 26 all solid Secondary battery 34 Current collector provided after firing

Claims (15)

A negative electrode layer, a solid electrolyte layer having an oxide solid electrolyte, and a positive electrode layer are laminated in this order and fired,
The negative electrode layer has a graphite negative electrode active material, a solid electrolyte with a garnet-type crystal structure, and a solid electrolyte composed of Li ₃ BO ₃ or a solid electrolyte in which Li ₃ BO ₃ is doped with a different element,
The content of the graphite negative electrode active material contained in the negative electrode layer is 50 parts by mass ,
The content of the solid electrolyte having the garnet-type crystal structure contained in the negative electrode layer is 35 parts by mass,
The content of the solid electrolyte composed of Li ₃ BO ₃ or the content of the solid electrolyte in which Li ₃ BO ₃ is doped with a different element in the negative electrode layer is 15 parts by mass. all-solid-state secondary battery. _The oxide _solid electrolytes of the _solid electrolyte _{layer are Li7La3Zr2O12} and Li3BO3 ,
The content _{of the Li7La3Zr2O12} contained in the solid electrolyte layer is 70 parts by mass _,
2. The all-solid secondary battery according to claim 1 , wherein _the content of said _Li3BO3 contained in said solid electrolyte layer is 30 parts by mass . The positive electrode layer includes a positive electrode active material having a layered rock salt structure, a solid electrolyte having a garnet-type crystal structure, and a solid electrolyte composed of Li ₃ BO ₃ or a solid electrolyte in which Li ₃ BO ₃ is doped with a foreign element. have
The content of the layered rock salt structure positive electrode active material contained in the positive electrode layer is 50 parts by mass ,
The content of the solid electrolyte having the garnet-type crystal structure contained in the positive electrode layer is 35 parts by mass,
The content of the solid electrolyte composed of Li ₃ BO ₃ or the content of the solid electrolyte in which the Li ₃ BO ₃ is doped with a different element contained in the positive electrode layer is 15 parts by mass. The all-solid secondary battery according to claim 1 or 2 . 4. A metal foil current collector is provided on a surface of at least one of the positive electrode layer and the negative electrode layer that does not face the solid electrolyte layer. The all-solid secondary battery described in the item. 5. The all-solid secondary battery according to claim 4 , wherein at least one kind of material constituting said positive electrode layer and said negative electrode layer is fused to said metal foil current collector. A solid electrolyte layer green sheet is laminated on the negative electrode green sheet,
The negative electrode green sheet has a graphite negative electrode active material, a solid electrolyte with a garnet crystal structure, a solid electrolyte composed of Li ₃ BO ₃ or a solid electrolyte in which Li ₃ BO ₃ is doped with a different element, and a binder,
The solid electrolyte layer green sheet has an oxide solid electrolyte and a binder,
The content of the graphite negative electrode active material contained in the negative electrode green sheet is 50 parts by mass ,
The content of the solid electrolyte having the garnet-type crystal structure contained in the negative electrode green sheet is 35 parts by mass,
The content of the solid electrolyte composed of Li ₃ BO ₃ contained in the negative electrode green sheet or the content of the solid electrolyte in which the Li ₃ BO ₃ is doped with a foreign element is 15 parts by mass .
A laminate green sheet characterized by: A solid electrolyte layer green sheet is laminated on the negative electrode green sheet, and a metal foil current collector is adhered to the surface of the negative electrode green sheet that does not face the solid electrolyte layer green sheet,
The negative electrode green sheet has a graphite negative electrode active material, a solid electrolyte with a garnet crystal structure, a solid electrolyte composed of Li ₃ BO ₃ or a solid electrolyte in which Li ₃ BO ₃ is doped with a different element, and a binder,
The solid electrolyte layer green sheet has an oxide solid electrolyte and a binder,
The content of the graphite negative electrode active material contained in the negative electrode green sheet is 50 parts by mass ,
The content of the solid electrolyte having the garnet-type crystal structure contained in the negative electrode green sheet is 35 parts by mass,
The content of the solid electrolyte composed of Li ₃ BO ₃ contained in the negative electrode green sheet or the content of the solid electrolyte in which the Li ₃ BO ₃ is doped with a foreign element is 15 parts by mass .
A laminate green sheet characterized by: 8. The laminate green sheet according to claim 6 _{or 7} , wherein the oxide solid electrolytes included _in the solid electrolyte layer _green sheet are _Li7La3Zr2O12 and _Li3BO3 . The content _{of the Li7La3Zr2O12} contained in the solid electrolyte layer green sheet _is 70 parts by mass,
9. The laminate green sheet according to claim 8 _, wherein the content of said _Li3BO3 contained in said solid electrolyte layer green sheet is 30 parts by mass . The solid electrolyte layer green sheet is sandwiched between the negative electrode green sheet and the positive electrode green sheet,
10. The laminate green sheet according to any one of claims 6 to 9 , wherein the positive electrode green sheet comprises a positive electrode active material having a layered rock salt structure, a solid electrolyte having a garnet-type crystal structure, and a binder. The positive electrode green sheet further has a solid electrolyte composed of Li ₃ BO ₃ or a solid electrolyte in which Li ₃ BO ₃ is doped with a foreign element,
The content of the positive electrode active material having the layered rock salt structure contained in the positive electrode green sheet is 50 parts by mass ,
The content of the solid electrolyte having the garnet-type crystal structure contained in the positive electrode green sheet is 35 parts by mass,
The content of the solid electrolyte composed of Li ₃ BO ₃ or the content of the solid electrolyte in which Li ₃ BO ₃ is doped with a foreign element contained in the positive electrode green sheet is 15 parts by mass. 11. The laminate green sheet according to claim 10 . The solid electrolyte layer green sheet is sandwiched between the negative electrode green sheet and the positive electrode green sheet,
12. The laminate green sheet according to any one of claims 6 to 11 , wherein at least one of the negative electrode green sheet and the positive electrode green sheet contains an electron conductive material serving as a conductive aid. A method for producing an all-solid secondary battery, comprising a step of firing the laminate green sheet according to any one of claims 6 to 12 . A negative electrode layer, a solid electrolyte layer having an oxide solid electrolyte, and a positive electrode layer are laminated in this order,
The negative electrode layer has a graphite negative electrode active material, a solid electrolyte with a garnet-type crystal structure, and a solid electrolyte composed of Li ₃ BO ₃ or a solid electrolyte in which Li ₃ BO ₃ is doped with a different element,
The content of the graphite negative electrode active material contained in the negative electrode layer is 50 parts by mass ,
The content of the solid electrolyte having the garnet-type crystal structure contained in the negative electrode layer is 35 parts by mass,
The content of the solid electrolyte composed of Li ₃ BO ₃ or the content of the solid electrolyte in which Li ₃ BO ₃ is doped with a different element in the negative electrode layer is 15 parts by mass. A method for manufacturing an all-solid secondary battery. A negative electrode layer, a solid electrolyte layer having an oxide solid electrolyte, and a positive electrode layer are laminated in this order,
The negative electrode layer has a graphite negative electrode active material, a solid electrolyte with a garnet-type crystal structure, and a solid electrolyte composed of Li ₃ BO ₃ or a solid electrolyte in which Li ₃ BO ₃ is doped with a different element,
The oxide solid electrolyte possessed by the solid electrolyte layer is a solid electrolyte having a garnet-type crystal structure,
The positive electrode layer has a positive electrode active material with a layered rock salt structure and a solid electrolyte with a garnet-type crystal structure,
The content of the graphite negative electrode active material contained in the negative electrode layer is 50 parts by mass ,
The content of the solid electrolyte having the garnet-type crystal structure contained in the negative electrode layer is 35 parts by mass,
The content of the solid electrolyte composed of Li ₃ BO ₃ or the content of the solid electrolyte in which Li ₃ BO ₃ is doped with a different element in the negative electrode layer is 15 parts by mass. A method for manufacturing an all-solid secondary battery.

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