JP2018077989A - Laminate green sheet and all-solid type secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-solid type secondary battery with a high battery performance by a simple manufacturing process.SOLUTION: A laminate green sheet comprises a first electrode layer green sheet 13 composed of one of positive and negative electrode layer green sheets, a solid electrolyte layer green sheet 12, and a second electrode layer green sheet 11 composed of the other of the positive and negative electrode layer green sheets which are laminated over one face of a metal foil current collector 14a in this order. The one face of the metal foil current collector has an uneven shape 20; a binder layer 15a is formed on the face where the uneven shape 20 is formed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laminate green sheet and an all solid state secondary battery.

With the increase in functionality of electronic devices such as personal computers and mobile phones typified by smartphones and digital cameras, the power consumption of these electronic devices is increasing. In addition, miniaturization of these electronic devices is required. For this reason, the further high energy density is calculated | required with respect to the secondary battery used for an electronic device.
High energy density is also required for household storage batteries that are stationary applications. Further, in recent years, with the expansion of demand for secondary batteries for in-vehicle applications such as hybrid vehicles and electric vehicles, it is required to achieve both higher output density and higher energy density of secondary batteries. In addition, since an organic solvent is used in the electrolyte solution for the secondary battery, there is a risk of leakage of the electrolyte solution or thermal runaway, and an improvement in the safety of the secondary battery is also required.

The most promising secondary battery that satisfies these requirements is an all-solid lithium ion secondary battery in which the entire configuration of the negative electrode layer, the electrolyte layer, and the positive electrode layer is made of a solid material. This all-solid-state lithium ion secondary battery is being developed as a battery having high energy density, high safety, and long life.
However, the all-solid-state lithium ion secondary battery currently in practical use is an all-solid-state secondary battery in which each 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 vapor deposition or sputtering, it is necessary to produce an all-solid lithium ion secondary battery in a reduced-pressure atmosphere. Is unsuitable.

Therefore, as disclosed in Patent Document 1 to Patent Document 4, a method for producing an all-solid lithium ion secondary battery by firing the green sheets of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer has been studied. Yes.
Patent Document 1 discloses that a positive electrode layer green sheet and a negative electrode layer green sheet are fired to produce a positive electrode layer fired body and a negative electrode layer fired body, and then a positive electrode layer fired body through an ion conductive inorganic material layer green sheet. It describes that a negative electrode layer fired body is sandwiched and refired to form a laminated fired body. Patent Document 1 discloses an all-solid secondary battery produced by sandwiching the laminated fired body between two current collector plates.

In Patent Document 2, a positive electrode layer green sheet, an ion conductive inorganic material layer green sheet, and a negative electrode layer green sheet are laminated in order to form a laminated body and then collectively fired to form a laminated fired body. Discloses an all-solid-state secondary battery produced by sandwiching a battery between two current collector plates.
Patent Document 3 discloses a laminate green in which a positive electrode layer green sheet and a negative electrode layer green sheet are printed on both surfaces of an ion conductive inorganic material layer green sheet, and each metal foil current collector paste is printed on the upper layer. An all-solid secondary battery produced by batch firing sheets is disclosed.

JP 2000-340255 A Japanese Patent No. 4845244 Japanese Patent No. 5430930

However, as in the invention disclosed in Patent Document 1, when a laminated fired body including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is sandwiched between a positive electrode current collector and a negative electrode current collector, the positive electrode current collector and the positive electrode current collector There is a problem that the interfacial resistance with the layer and the interfacial resistance between the negative electrode current collector and the negative electrode layer are high, and the battery performance is poor. Moreover, in order to produce an all-solid-state secondary battery, it is necessary to pass through a baking process twice, and there exists a subject that manufacturing efficiency is bad.
In addition, as in the invention disclosed in Patent Document 2, when the laminated green sheet obtained by bonding the green sheets of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer is collectively fired, the firing process is a single process. Compared with Document 1, the production efficiency is high. However, the invention disclosed in Patent Document 2 has a problem that the interface resistance between the positive electrode current collector plate and the positive electrode layer and the interface resistance between the negative electrode current collector plate and the negative electrode layer are high.

In addition, as in the invention disclosed in Patent Document 3, a laminate green sheet formed by laminating a positive electrode current collector, a positive electrode layer green sheet, a solid electrolyte layer green sheet, a negative electrode layer green sheet, and a negative electrode current collector is collectively collected. When fired, the interface resistance between the positive electrode current collector and the positive electrode layer and between the negative electrode current collector and the negative electrode layer is considered to be reduced. However, the positive electrode layer green sheet and the negative electrode layer green sheet are printed and formed on both surfaces of the solid electrolyte layer green sheet, and the metal foil current collector paste is printed and formed on the upper layer, and there is a problem that the manufacturing method is complicated. .
This invention is made | formed in view of such a point, and it aims at providing an all-solid-state secondary battery with high battery performance with a simple preparation process.

  In order to solve the problem, a laminate green sheet according to one embodiment of the present invention includes a first green sheet and a negative electrode layer green sheet on one surface of a metal foil current collector. A second electrode layer green sheet composed of the other of the electrode layer green sheet, the solid electrolyte layer green sheet, the positive electrode layer green sheet, and the negative electrode layer green sheet is laminated in this order, and one surface of the metal foil current collector is uneven. It has a shape, and a binder layer is formed on the surface on which the uneven shape is formed.

  According to one embodiment of the present invention, it is possible to provide both an easy production process and efficient decomposition and removal of a binder component in a green sheet, and an all-solid secondary battery with high battery performance can be provided.

It is sectional drawing which shows the structure of the laminated body green sheet of 1st Embodiment based on this invention. It is sectional drawing which shows the structure of the laminated body green sheet of 2nd Embodiment based on this invention. It is sectional drawing which shows the structure of the modification of the laminated body green sheet based on this invention. It is sectional drawing which shows the structure of the modification of the laminated body green sheet based on this invention. It is sectional drawing which shows the structure of the modification of the laminated body green sheet based on this invention. It is sectional drawing which shows the structure of the laminated fired body (all-solid-state secondary battery) after baking the laminated body green sheet of 2nd Embodiment. It is sectional drawing which shows the other structure of the laminated fired body (all-solid-state secondary battery) after baking the laminated body green sheet of 1st Embodiment. It is sectional drawing which shows the other structure of the laminated fired body (all-solid-state secondary battery) after baking the laminated body green sheet of 1st Embodiment. 6 is a cross-sectional view showing a configuration of a laminate green sheet of Comparative Example 1. FIG. 6 is a cross-sectional view showing another configuration of the laminated fired body (all-solid secondary battery) of Comparative Example 1.

Embodiments according to the present invention will be described below with reference to the drawings.
Here, the laminate green sheet and all-solid secondary battery according to the present invention, and the laminate green sheet manufacturing method and all-solid secondary battery manufacturing method are not limited to the embodiments described below. It is also possible to make design changes based on the knowledge of those skilled in the art, and embodiments to which such changes are made are also included in the scope of the embodiments of the present invention.

<Configuration of laminated green sheet and all-solid secondary battery>
As shown in FIG. 1, the laminate green sheet of the first embodiment is a first electrode layer green sheet comprising a positive electrode layer green sheet 13 on one surface of a metal foil current collector 14 a, a solid electrolyte. A second electrode layer green sheet composed of the layer green sheet 12 and the negative electrode layer green sheet 11 is laminated in this order. In this embodiment, the uneven shape 20 is formed on the one surface (the surface on the first electrode layer green sheet side) of the metal foil current collector 14a, and the binder layer 15a containing the binder on the surface having the uneven shape 20 is formed. Is formed in advance.

  The laminate green sheet of the second embodiment is a laminate green sheet sandwiched between two metal foil current collectors as shown in FIG. Further, the second metal foil current collector 14b is laminated on the negative electrode layer green sheet 11 constituting the second electrode layer green sheet. An uneven shape 20 is formed on the surface of the second metal foil current collector 14 b on the negative electrode layer green sheet 11 side, and a binder layer 15 a containing a binder is formed in advance on the surface having the uneven shape 20. The metal foil current collector 14a and the second metal foil current collector 14b may be made of the same material, or may be made of different materials.

Here, in the laminate green sheet of the first embodiment, the first electrode layer green sheet laminated on one surface of the metal foil current collector 14a is the negative electrode green sheet 11, and the second electrode layer The green sheet may be the positive electrode layer green sheet 13.
Further, in the laminate green sheet of the first embodiment and the laminate green sheet of the second embodiment, the binder layer formed on the surface having the concavo-convex shape 20 as shown in FIGS. At least one layer 15a may be composed of a second binder layer 16a in which a conductive material is further blended. The second binder layer 16a includes at least a binder and a conductive material.

Here, it is good also as a laminated body green sheet for series batteries by laminating | stacking multiple layers of the laminated body green sheet of 1st Embodiment. In this case, it is preferable to provide the uneven shape 20 and the binder layer or the second binder layer on both surfaces of the metal foil current collector 14b in the middle of the lamination. In this case, the continuous laminate green sheet is the laminate green sheet of the first embodiment.
By firing such first and second laminated green sheets, a laminated fired body that is a constituent element of the all-solid-state secondary battery is obtained. For example, by firing the laminate green sheet shown in FIG. 2, a positive electrode current collector made of the fired metal foil current collector 14c and a positive electrode layer as a first electrode layer made of the fired positive electrode layer green sheet 33, an inorganic solid electrolyte layer 32 made of a fired solid electrolyte layer green sheet (hereinafter referred to as solid electrolyte layer 32), and a negative electrode layer 31 as a second electrode layer made of a fired negative electrode layer green sheet And a negative electrode current collector 14d made of the second metal foil current collector to form a laminated fired body (see FIG. 6), and the all-solid-state secondary battery itself.

Here, as shown in FIG. 6, the binder layer 15b is thermally decomposed by firing, and the negative electrode layer 31 or the positive electrode layer 33 facing each other is embedded in the concavo-convex shape by subsequent pressurization. On the other hand, when the second binder layer 16a is employed instead of the binder layer 15a, the conductive material remains by firing, so that the second binder layer 16b remains in the laminated fired body as shown in FIG. ing.
The firing treatment for producing the laminated fired body is preferably performed after the laminated green sheet is heated at a temperature lower than the firing temperature to degrease the binder component.

The all-solid secondary battery includes a positive electrode current collector made of a metal foil current collector 14b, a positive electrode layer 33, and an inorganic solid electrolyte layer 32 provided on the positive electrode layer 33 (hereinafter referred to as a solid electrolyte layer 32). And a negative electrode layer 31 provided on the solid electrolyte layer 32 and a negative electrode current collector made of a metal foil current collector provided on the negative electrode layer 31.
When the all-solid-state secondary battery is manufactured using the laminated fired body obtained by firing the laminated green sheet of the first embodiment, the second metal foil current collector is disposed on the negative electrode layer 31. May be manufactured by laminating and laminating separately. At this time, a conductive material layer made of a conductive paste may be interposed between the negative electrode layer 31 and the second metal foil current collector.

(Solid electrolyte layer)
The solid electrolyte layer green sheet 12 includes at least one of a solid electrolyte and glass that becomes a solid electrolyte after firing.
At least one of the solid electrolyte contained in the solid electrolyte layer green sheet 12 and the glass that becomes the solid electrolyte after firing is not particularly limited as long as it is a material having low electron conductivity and high lithium ion conductivity. An amorphous body (glass body), a crystalline body, a glass ceramic, or the like of a physical solid electrolyte or a sulfide solid electrolyte is used. In particular, the solid electrolyte is preferably an oxide solid electrolyte that can be fired at high temperature, and it is preferable to use a NASICON type oxide, a perovskite type oxide, a LISICON type oxide, a garnet type oxide, an oxide glass, or the like. Examples of the oxide-based solid electrolyte that can be fired at such a high temperature include Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ , Li _0.29 La _0.571 TiO ₃ , Li ₄ SiO ₄ —Li ₃ PO ₄ , Li ₃ BO ₃ —Li ₃ PO ₄ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li _3.4 V _{0 .6} Si _0.4 O ₄ or the like can be used.

  The thickness of the solid electrolyte layer green sheet 12 is preferably in the range of 1 μm to 500 μm. When the thickness of the solid electrolyte layer green sheet 12 is less than 1 μm, the positive electrode layer green sheet 13 and the negative electrode layer green sheet 11 are easily short-circuited, and not only the performance of the all-solid-state secondary battery is lowered, but also safety. May also decrease. Moreover, when the thickness of the solid electrolyte layer green sheet 12 is thicker than 500 μm, the movement of conductive ions such as lithium ions in the solid electrolyte layer green sheet 12 is likely to be inhibited, and the output of the all-solid-state secondary battery may be reduced. There is sex.

(Positive electrode layer)
The positive electrode layer green sheet 13 includes a positive electrode active material, a solid electrolyte, and at least one of glass that becomes a solid electrolyte after firing.
The positive electrode active material included in the positive electrode layer green sheet 13 may be any material that can occlude and release lithium ions, and is not particularly limited. The positive electrode layer green sheet 13 contains, as a positive electrode active material, an active material that exhibits a potential more noble than the active material contained in the negative electrode layer green sheet 11.
As the positive electrode active material, for example, lithium nickel cobalt manganese oxide _{(LiNi x Co 1-y-} x Mn y O 2), lithium cobalt oxide (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate (LiMn ₂ Li transition such as O ₄ ), lithium iron phosphate (LiFePO ₄ ), lithium cobalt phosphate (LiCoPO ₄ ), lithium manganese phosphate (LiMnPO ₄ ), lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) Metal compounds can be used.

Moreover, as the solid electrolyte contained in the positive electrode layer green sheet 13, the same material as the solid electrolyte contained in the solid electrolyte layer green sheet 12 can be used. Two or more solid electrolytes contained in the positive electrode layer green sheet 13 may be mixed and used. The solid electrolyte contained in the positive electrode layer green sheet 13 may be the same as or different from the solid electrolyte contained in the solid electrolyte layer green sheet 12 and the negative electrode layer green sheet 11 described later.
The positive electrode layer green sheet 13 may contain a conductive additive. The conductive auxiliary agent is not particularly limited as long as it has conductivity. 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 additive in the positive electrode layer green sheet 13 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 auxiliary is 90% by mass or more, the amount of the positive electrode active material in the positive electrode layer green sheet 13 may be insufficient and the lithium storage capacity may be reduced.
The positive electrode layer green sheet 13 can be selected to have an arbitrary thickness according to a desired battery capacity.

(Negative electrode layer)
The negative electrode layer green sheet 11 includes a negative electrode active material, a solid electrolyte, and at least one of glass that becomes a solid electrolyte after firing.
The negative electrode active material contained in the negative electrode layer green sheet 11 may be any material that can occlude and release lithium ions, and is not particularly limited. The negative electrode layer green sheet 11 contains, as a negative electrode active material, an active material that exhibits a lower potential than the active material contained in the positive electrode layer green sheet 13.

Examples of the negative electrode active material include carbon materials such as hard carbon, soft carbon, and graphite, alloy materials such as Sn-based alloys and Si-based alloys, nitrides such as LiCoN, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). Lithium transition metal oxides such as lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) can be used. Moreover, you may use metal lithium foil as a negative electrode active material.
In addition, as the solid electrolyte contained in the negative electrode layer green sheet 11, the same material as the solid electrolyte contained in the solid electrolyte layer green sheet 12 and the positive electrode layer green sheet 13 can be used. Two or more solid electrolytes contained in the negative electrode layer green sheet 11 may be mixed and used. The solid electrolyte contained in the negative electrode layer green sheet 11 may be the same as or different from the solid electrolyte contained in the solid electrolyte layer green sheet 12 and the positive electrode layer green sheet 13.

The negative electrode layer green sheet 11 may contain a conductive additive. The conductive auxiliary agent is not particularly limited as long as it has conductivity similar to the conductive auxiliary agent contained in the positive electrode layer green sheet 13. For example, a conductive carbon material, particularly carbon black, activated carbon, carbon carbon fiber, etc. Can be used.
The content of the conductive additive in the negative electrode layer green sheet 11 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 auxiliary is 90% by mass or more, the amount of the negative electrode active material in the negative electrode layer green sheet 11 may be insufficient and the lithium storage capacity may be reduced.
The negative electrode layer green sheet 11 can be selected to have an arbitrary thickness according to a desired battery capacity.

(Metal foil current collector)
Hereinafter, when referring to the metal foil current collector of both the positive electrode current collector and the negative electrode current collector, or when not distinguishing between the positive electrode current collector and the negative electrode current collector, the positive electrode current collector and the negative electrode current collector The body may be simply referred to as “metal foil current collector”.
The material of the metal foil current collectors 14a and 14b is not particularly limited as long as it is a conductive material. For example, metal materials such as stainless steel, nickel, aluminum, iron, titanium, copper, palladium, gold, and platinum are used. Can be used. The material of the metal foil current collector is preferably selected in consideration of not being melted and decomposed under the firing conditions described later, and the battery operating potential and conductivity of the metal foil current collector.

  The tensile strength of the metal foil current collector is preferably 10 N / 10 mm or more. When the tensile strength of the metal foil current collector is 10 N / 10 mm or more, cracks and the like are less likely to occur in the metal foil current collector in the firing step when the all-solid-state secondary battery 1 is manufactured. Further, when the tensile strength of the metal foil current collector is 10 N / 10 mm or more, the strength enough to support the laminate green sheet composed of the positive electrode layer green sheet 13, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 11 Is obtained.

In addition, the all-solid-state secondary battery of this embodiment is manufactured by laminating | stacking and baking the positive electrode layer green sheet 13, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 11 so that it may mention later. For this reason, it is important that the metal foil current collector of the all-solid-state secondary battery has a characteristic that cracks and the like do not occur in the firing process.
The thickness of the metal foil current collector is preferably 3 μm or more and 50 μm or less. When the thickness of the metal foil current collector is 3 μm or more and 50 μm or less, the metal foil current collector is not easily cracked at the time of manufacturing the laminated fired body, and the thickness sufficient to support the laminated green sheet is sufficient. can get.

An uneven shape 20 is formed on the surface of the metal foil current collector on which the green sheets are laminated.
The concavo-convex shape 20 is formed, for example, in a region of 50% or more, preferably 80% or more of the area of the surface.
It is preferable that the uneven shape 20 is a groove having an average roughness Ra of 0.1 μm or more and a depth of 4/15 or less of the thickness of the metal foil current collector on which the target uneven shape 20 is formed. The upper limit of the groove depth of the concavo-convex shape 20 depends on the strength of the metal foil current collector. However, if the concavo-convex shape 20 is formed from a groove having a thickness of 4/15 or less of the thickness of the metal foil current collector, the metal foil current collector is formed. The possibility that cracks and the like are generated when the electric body is fired is suppressed. In addition, when the average roughness Ra is less than 0.1 μm, the effect of providing the uneven shape 20 may not be achieved.

For example, when the film thickness of the metal foil current collector is 15 μm, the surface unevenness is desirably 0.1 to 4 μm in average roughness Ra, and when the average roughness is larger than this, the current unevenness is There is a high possibility that the foil will break.
A binder layer 15a or a second binder layer 16a is formed on the surface on which the uneven shape 20 is formed.
As a binder used for the binder layer 15a or the second binder layer 16a, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetal, polyvinylidene fluoride, polytetrafluoroethylene, ethyl cellulose, an acrylic resin, or the like can be used.

  The binder decomposition temperature of the binder layer 15a or the second binder layer 16a is preferably lower than the binder decomposition temperatures of the positive electrode layer green sheet, the solid electrolyte layer green sheet, and the negative electrode layer green sheet. When the decomposition temperature of the binder of the binder layer 15a or the second binder layer 16a is relatively low, the binder of the binder layer 15a or the second binder layer 16a is first thermally decomposed to form a degassing void. Thus, it becomes possible to effectively release the gas when the binder of the positive electrode layer green sheet, solid electrolyte layer green sheet and negative electrode layer green sheet is thermally decomposed during degreasing.

The thickness of the binder layer 15a or the second binder layer 16a is desirably a thin film as much as possible, and may be an amount that at least fills the surface irregularities of the metal foil current collector with the binder.
The electroconductive material mix | blended with the 2nd binder layer 16a will not be specifically limited if it has electroconductivity. Moreover, it does not specifically limit about the shape of an electroconductive material, A powder, a granule, a linear body etc. can be illustrated. The conductive material is made of, for example, a carbon material.
The conductive material is preferably 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the binder.

Hereinafter, the manufacturing method of a laminated body green sheet and an all-solid-state secondary battery is demonstrated.
[Method for producing laminate green sheet]
The manufacturing method of the laminated body green sheet of 1st Embodiment has the surface uneven | corrugated shape 20, and contains the binder layer 15a which contains a binder on the metal foil collector 14a, or contains the binder and an electroconductive material at least. A positive electrode layer green sheet forming step of forming a positive electrode layer green sheet 13 by applying or printing a positive electrode slurry containing a positive electrode active material on a positive electrode current collector having two binder layers 16a; A solid electrolyte layer green sheet forming step of forming a solid electrolyte layer green sheet 12 by applying or printing a solid electrolyte slurry containing a solid electrolyte on 13a and drying it, and a negative electrode active material on the solid electrolyte layer green sheet 12 A negative electrode layer green in which a negative electrode slurry is applied or printed and then dried to form a negative electrode layer green sheet 11 It comprises a chromatography preparative forming step.
In the method for producing a laminate green sheet according to the second embodiment, a metal foil current collector 14b as a negative electrode current collector having a binder layer 15a or a second binder layer 16a on the surface on which the concavo-convex shape 20 is further formed. It has the process of attaching separately.

(Method for producing solid electrolyte layer green sheet)
The solid electrolyte layer green sheet 12 is formed by applying or printing a solid electrolyte slurry formed by mixing a solid electrolyte and an organic substance binder together with a solvent and then drying. The solid electrolyte slurry is applied on, for example, a positive electrode layer green sheet 13 or a negative electrode layer green sheet 11 described later. The method for preparing the solid electrolyte slurry is not particularly limited.

(Method for producing positive electrode layer green sheet)
The positive electrode layer green sheet 13 is formed by mixing a positive electrode active material, a solid electrolyte, and an organic substance binder together with a solvent and applying or printing a positive electrode slurry, followed by drying. The positive electrode slurry is applied on the positive electrode current collector 14a or a solid electrolyte layer green sheet 12 described later. The method for preparing the positive electrode slurry is not particularly limited.

(Method for producing negative electrode layer green sheet)
The negative electrode layer green sheet 11 is formed by mixing a negative electrode active material, a solid electrolyte, and an organic substance binder together with a solvent and applying or printing a negative electrode slurry, followed by drying. The negative electrode slurry is applied on the negative electrode current collector (in the case of the laminated green sheet of the second embodiment) 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 later. Examples of the binder that can be used include polyvinyl alcohol, polyvinyl butyral, polyvinyl acetal, polyvinylidene fluoride, polytetrafluoroethylene, ethyl cellulose, and an acrylic resin.

In the positive electrode layer green sheet 13, the negative electrode layer green sheet 11, and the solid electrolyte layer green sheet 12, the binder is preferably contained in an amount of 3% by mass to 40% by mass, and more preferably 3% by mass to 25% by mass. preferable. That is, the content of the binder with respect to the entire solid content excluding the solvent from each slurry 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.
When the content of the binder is less than 3% by mass, for example, active materials or solid electrolytes may not be sufficiently bound. On the other hand, when the content of the binder is larger than 40% by mass, the battery capacity per volume decreases.

  The positive electrode layer green sheet 13, the negative electrode layer 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 and reduces the firing temperature during firing. . The firing 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 temperature lower than the firing temperature of the solid electrolyte. For example, a boron compound can be used. By adjusting the content and firing temperature of the firing aids of the positive electrode layer green sheet 13, the negative electrode layer green sheet 11, and the solid electrolyte layer green sheet 12, when the laminated fired body is formed by firing, the internal strain of each layer While preventing cracks due to internal stress, formation of a matrix structure can be promoted.

  The solvent used for the positive electrode slurry, the negative electrode slurry, and the solid electrolyte slurry is not particularly limited as long as the above-described binder can be dissolved. For example, alcohols such as ethanol, isopropanol, and n-butanol, toluene, ethyl acetate, and acetic acid. 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. In addition, these solvents may be used independently and may use 2 or more types together. Since the slurry can be easily dried, the boiling point of the solvent is preferably 200 ° C. or lower.

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 assistant, firing assistant, and the like with a solvent. The solid electrolyte slurry can be prepared by mixing the above-described solid electrolyte, binder, conductive aid, firing aid and the like with a solvent. The method for 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 coating and printing methods for positive electrode slurry, negative electrode slurry, and 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.

Although the drying method of the slurry for positive electrodes, the slurry for negative electrodes, and a solid electrolyte slurry is not specifically limited, For example, heat drying, reduced pressure drying, heating reduced pressure drying, etc. can be used. The drying atmosphere is not particularly limited, and can be performed, for example, in an air atmosphere or an inert atmosphere (a nitrogen atmosphere or an argon atmosphere).
The positive electrode layer green sheet, the solid electrolyte layer green sheet, and the negative electrode layer green sheet constitute a laminated green sheet that is sequentially laminated.
That is, the manufacturing method of the all-solid-state secondary battery of this embodiment includes a firing step of firing the laminated green sheet formed as described above.

  The heating temperature in the firing step may be a temperature equal to or higher than the thermal decomposition temperature of the binder contained in the laminate green sheet and lower than the oxidation temperature of the positive electrode active material and the negative electrode active material or lower than the combustion temperature of the metal foil current collector. preferable. Specifically, the heating temperature is preferably 200 ° C. or higher and 1100 ° C. or lower, and more preferably 250 ° C. or higher and 900 ° C. or lower. When the heating temperature is lower than 250 ° C., the binder does not completely burn out in the baking step and becomes a residue, which may hinder electronic conduction or ionic conduction. On the other hand, when 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 / altered to deteriorate 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 (a nitrogen atmosphere or an argon atmosphere). When there is a concern about the reaction between the positive electrode active material and the negative electrode active material and the metal foil current collector or the decrease in conductivity of the metal foil current collector, 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.
Here, the firing step is preferably performed so that the laminated green sheet of the present embodiment is heated at a temperature lower than the firing temperature in an oxidizing atmosphere and degreased, and then fired. The firing in this case may be performed in any atmosphere.

By degreasing in an oxidizing atmosphere, the binder component in each green sheet is easily decomposed and removed, and the interfacial resistance can be suppressed by batch firing, resulting in the production of an all-solid secondary battery with high battery performance. I can do it.
The heating temperature in the degreasing step is preferably 250 ° C. or higher and lower than 550 ° C. When the temperature is lower than 250 ° C., the binder contained in the laminate green sheet may not be thermally decomposed and degreased. In the case of 550 ° C. or higher, there is a possibility that the residue derived from the binder is carbonized by heating at a high temperature, the conductive carbide remains in the solid electrolyte layer, and self-discharge or internal short circuit may occur.

Moreover, it is preferable that the heating temperature in a baking process is 550 degreeC or more and 1000 degrees C or less. When the temperature is lower than 550 ° C., the firing of the solid electrolyte does not proceed sufficiently, and the battery performance may be deteriorated. When the temperature is higher than 1000 ° C., the positive electrode active material and the negative electrode active material are melted and deteriorated, and the metal foil current collector is deteriorated, which may deteriorate the battery performance.
The atmosphere in the degreasing step and the firing step is preferably an inert atmosphere (nitrogen atmosphere, argon atmosphere), and a reducing gas may be mixed.
The heating time in the degreasing step is not particularly limited as long as the binder used is sufficiently decomposed. Moreover, the heating time in a baking process should just be time which baking of a solid electrolyte fully advances, and is not specifically limited.

Here, the laminated fired body obtained by firing the laminated green sheet of the second embodiment constitutes an all-solid secondary battery as it is.
Moreover, in the case of the laminated fired body obtained by firing the laminated green sheet of the first embodiment, the laminated fired body has a metal foil current collector only in one direction of the lamination. When such a laminated fired body is used as a component of an all-solid secondary battery, a step of attaching a metal foil current collector to the other surface in the lamination direction of the fired laminated fired body may be provided. . Alternatively, the conductive material layer may be formed by applying a conductive paste before attaching the metal foil current collector.
The method for attaching the metal foil current collector is not particularly limited, and for example, a flat plate press, a roll press, a hot press, a cold isostatic press, a hot isostatic press, or the like can be used.

As described above, in the present embodiment, the all-solid-state secondary battery can be obtained in a single firing step while suppressing the interface resistance between the positive electrode current collector and the positive electrode layer 33 and the negative electrode current collector and the negative electrode layer 34. Can be manufactured.
Here, if carbides generated by firing the laminated green sheet remain inside the all-solid-state secondary battery, particularly inside the solid electrolyte layer, there is a risk of causing an internal short circuit of the all-solid-state secondary battery. Therefore, it is necessary to efficiently remove the binder component contained in the positive electrode layer green sheet, the solid electrolyte layer green sheet, the negative electrode layer green sheet, and providing a path through which the decomposition gas escapes inside the laminate green sheet, It is considered effective from the viewpoint of the elimination of cracked gas. Therefore, in the present embodiment, on the metal foil current collector having an uneven surface shape, at least a binder layer using a binder that decomposes at a temperature lower than the binder in the electrode layer green sheet or a conductive material and a binder are contained. A second binder layer is provided. As a result, the binder component formed on the metal foil current collector having a surface irregularity shape is decomposed and removed at a lower temperature than the binder in the electrode layer green sheet, and the metal foil current collector and the electrode layer green sheet interface. , The gap between the surface irregularities of the metal foil current collector is formed, and the discharge of the decomposition gas of the binder component in the green sheet of the laminated body, the laminated fired body, or the electrode layer green sheet to the outside of the all-solid secondary battery is promoted. Thus, an all solid state secondary battery in which an internal short circuit is suppressed is manufactured.

  That is, the concave and convex shape 20 for degassing at the time of firing is provided on the surface on the green sheet side of the metal foil current collector, and the concave and convex shape at the time of firing is provided by providing a binder layer so as to fill the concave and convex shape 20. The binder filling 20 and the binder thereon are thermally decomposed, and a degassing passage is automatically formed when the binder in the green sheet is thermally decomposed. Even if the laminate is fired at once in order to suppress the interface resistance, the binder component in the green sheet can be efficiently decomposed and removed during firing. For this reason, if the laminate green sheet of the present embodiment is used, it is possible to achieve both a simple production process and efficient decomposition and removal of the binder component in the green sheet, and the battery performance is easily high all solid. A secondary battery can be provided.

Hereinafter, the present invention will be described with reference to specific examples and comparative examples. In addition, the structure of the laminated body green sheet which concerns on this invention, and an all-solid-state secondary battery is not restrict | limited by the following examples.
Example 1
[Slurry preparation process]
<Preparation of slurry for positive electrode>
50 parts by mass of lithium cobaltate (LiCoO ₂ ) powder as a positive electrode active material, 50 parts by mass of Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (LAGP) powder as an inorganic solid electrolyte, and acetylene as a conductive additive 20 parts by mass of black (AB), 16 parts by mass of polyvinyl butyral (PVB) as a binder, 4.8 parts by mass of dibutyl phthalate (DBP) as a plasticizer, and a mixed solvent of methyl ethyl ketone and acetone as a solvent (mass ratio 1: 1) 22 parts by mass was mixed to form a slurry, and this slurry was defoamed to prepare a positive electrode slurry.

<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 slurry was mixed to obtain a slurry, and the slurry was defoamed to prepare a slurry for an inorganic solid electrolyte.

<Preparation of slurry for negative electrode>
50 parts by mass of lithium titanate (Li ₄ Ti ₅ O ₁₂ ) powder as a negative electrode active material, 50 parts by mass of LAGP powder as an inorganic solid electrolyte, 20 parts by mass of artificial graphite as a conductive additive, 16 parts by mass of PVB as a binder, DBP4 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 prepare a slurry, and this slurry was defoamed to prepare a slurry for negative electrode.

<Process for producing metal foil current collector with binder layer>
On a nickel foil current collector (thickness 15 μm, Ra = 4 μm) as a metal foil current collector having an uneven surface, a binder solution in which polyvinyl butyral (PVB) is dissolved in a terpineol solvent as a binder is applied and dried. Thus, a binder layer was formed on the nickel foil current collector having surface irregularities.

<Laminated green sheet production process>
A positive electrode slurry was applied on the nickel foil current collector and dried to form a positive electrode layer green sheet. Then, the slurry for inorganic solid electrolyte was apply | coated and dried on the surface on the opposite side to the nickel foil collector opposing surface of a positive electrode layer green sheet, and the solid electrolyte layer green sheet was formed. Finally, on the surface of the solid electrolyte layer green sheet opposite to the surface facing the positive electrode layer green sheet, the negative electrode slurry is applied and dried to form the negative electrode layer green sheet, and the laminate as shown in FIG. A green sheet was produced.
A nickel foil current collector having a surface roughness on which a binder layer was formed was laminated on the negative electrode layer green sheet of the laminate green sheet produced above. Subsequently, the laminate green sheet comprising the laminate green sheet on which the negative electrode current collector is placed is pressurized at 80 ° C. and 1000 kgf / cm ² to have the metal foil current collector on both electrodes as shown in FIG. Was made.

<Degreasing process>
The laminate green sheet with the bipolar metal foil current collector described above was degreased by raising the temperature in the atmosphere from room temperature to 500 ° C. at a temperature rising rate of 20 ° C./min and holding at 500 ° C. for 30 minutes.
<Baking process>
The laminated green sheet with the bipolar metal foil current collector subjected to degreasing was heated from 500 ° C. to 800 ° C. at a temperature rising rate of 20 ° C./min in an argon stream, and held at 800 ° C. for 60 minutes for firing. . Thereafter, the fired laminated fired body was cooled to room temperature by allowing it to cool in the furnace, and an all-solid secondary battery of Example 1 as shown in FIG. 6 was produced.

(Example 2)
Until the <slurry production process>, each slurry was produced by the same manufacturing method as Example 1.
<Process for producing conductive material, metal foil current collector with binder-containing layer>
A binder solution in which PVB as a binder and acetylene black as a conductive material are mixed in a terpineol solvent on a nickel foil current collector (thickness 15 μm, Ra = 4 μm) as a metal foil current collector having an uneven surface shape. By applying and drying, a second binder layer made of a conductive material and a binder was formed on a nickel foil current collector having surface irregularities.
40 parts by mass of acetylene black was added to 100 parts by mass of PVB. The same applies to the second binder layer described later.

<Laminated green sheet production process>
A positive electrode slurry was applied onto a nickel foil current collector with a conductive material and a binder-containing layer and dried to form a positive electrode layer green sheet. Then, the slurry for inorganic solid electrolyte was apply | coated and dried on the surface on the opposite side to the metal foil collector opposing surface of a positive electrode layer green sheet, and the solid electrolyte layer green sheet was formed. Finally, on the surface of the solid electrolyte layer green sheet opposite to the surface facing the positive electrode layer green sheet, the negative electrode slurry is applied and dried to form the negative electrode layer green sheet, and the laminate as shown in FIG. A green sheet was produced.
On the negative electrode layer green sheet of the produced laminate green sheet, a nickel foil current collector (thickness 15 μm, Ra = 4 μm) as a negative electrode current collector having an uneven surface shape was laminated. A second binder layer containing at least PVB as a binder and acetylene black as a conductive material was formed in advance on the surface of the laminated nickel foil current collector on which the uneven shape was formed.

Subsequently, the laminate green sheet having a bipolar metal foil current collector as shown in FIG. 4 is formed by pressing a laminate comprising a laminate green sheet carrying a negative electrode current collector at 80 ° C. and 1000 kgf / cm ² . Was made.
From the <degreasing step> to the <baking step>, an all-solid secondary battery as shown in FIG.

(Example 3)
From <slurry production process> to <laminated green sheet production process>, it was produced by the same production method as in Example 1.
On the negative electrode layer green sheet of the produced laminate green sheet, a nickel foil current collector (thickness 15 μm, Ra = 4 μm) as a negative electrode current collector having an uneven surface shape was laminated. A second binder layer containing PVB as a binder and acetylene black as a conductive aid was formed in advance on the surface of the laminated nickel foil current collector on which the uneven shape was formed.

Then, the laminated body which consists of a laminated body green sheet on which the negative electrode collector was mounted was pressurized at 80 degreeC and 1000 kgf / cm < ² >. A laminate green sheet having a bipolar metal foil current collector as shown in FIG. 5 was produced.
From the <degreasing step> to the <baking step>, an all-solid secondary battery as shown in FIG.

Example 4
It was produced by the same production method as Example 1 except that the binder used for each binder layer formed on the nickel foil current collector of both electrodes was changed from PVB to acrylic resin (SPB-K112) which is a low-temperature decomposition binder. .
(Example 5)
Production method similar to Example 2 except that the binder used for each second binder layer formed on the nickel foil current collector of both electrodes is changed from PVB to acrylic resin (SPB-K112) which is a low-temperature decomposition binder. It was produced by.

(Example 6)
The same as in Example 3 except that both the binder layer formed on each nickel foil current collector and the binder used in the second binder layer were changed from PVB to acrylic resin (SPB-K112) which is a low-temperature decomposition binder. It was produced by the manufacturing method.
(Example 7)
It was produced by the same production method as in Example 4 except that both surface irregularities formed on each nickel foil current collector (thickness 15 μm) of both electrodes were formed with a rough surface having a maximum height Ra = 2 μm.

(Example 8)
It was produced by the same production method as in Example 5, except that both the surface irregularities formed on the bipolar electrode nickel foil current collector (thickness 15 μm) were formed with a rough surface having a maximum height Ra = 2 μm.
Example 9
It was produced by the same production method as in Example 6 except that both the surface irregularities formed on the nickel foil current collector (thickness 15 μm) were formed with a rough surface having a maximum height Ra = 2 μm.

(Example 10)
It was produced by the same production method as in Example 4 except that both surface irregularities formed on the nickel foil current collector (thickness 15 μm) of both electrodes were formed with a rough surface having a maximum height Ra = 0.1 μm.
(Example 11)
It was produced by the same production method as in Example 5 except that both the surface irregularities formed on the nickel foil current collector (thickness 15 μm) were formed with a rough surface having a maximum height Ra = 0.1 μm.

(Example 12)
It was produced by the same production method as in Example 6 except that both the surface irregularities formed on the bipolar electrode nickel foil current collector (thickness 15 μm) were formed with a rough surface having a maximum height Ra = 0.1 μm.
(Comparative Example 1)
As shown in FIG. 9, the same as in the first embodiment, except that neither the surface irregularity shape, the binder layer nor the second binder layer was provided for the nickel foil current collector (thickness 15 μm) of both electrodes. An all-solid secondary battery as shown in FIG. 10 was produced.

[Battery characteristics evaluation]
The battery characteristics of the all solid state secondary batteries of each Example and Comparative Example were evaluated by the following methods.
The evaluation results are shown in Table 1.
In Table 1, the columns of “Presence / absence of positive-side binder layer” and “Presence / absence of negative-electrode-side binder layer” indicate “first” when a binder layer is provided and “second” when a second binder layer is provided. “Second” is described, and “None” is described when none is provided.

(Examples 1 to 6, Comparative Example 1 Evaluation Method of All Solid Secondary Battery)
Five all solid state secondary batteries of each example and comparative example were prepared and evaluated.
The all solid state secondary batteries of the examples and comparative examples were charged with a constant current of 0.02 C until the voltage reached 2.7 V, and then discharged with a constant current of 0.02 C to a voltage of 1.5 V. In addition, the average value of the discharge capacity obtained by five all solid state secondary batteries was employ | adopted for the discharge capacity of each Example.

[Short-circuit evaluation]
A short circuit test was performed on the all-solid-state secondary battery according to each of the examples and the comparative example. Moreover, when all the batteries showed a resistance value of 100 MΩ or more, it was determined that there was no short circuit.
Table 1 shows the presence / absence of the binder layer, the conductive material, the presence / absence of the binder layer, the decomposition temperature of the binder used in the binder layer or the conductive material and the binder-containing layer, the battery characteristics evaluation results, and the short-circuit evaluation results. A battery having no short circuit and having a high discharge capacity means that it is an excellent all-solid secondary battery.

  When a binder layer is provided on the bipolar nickel foil current collector as in Example 1, “Yes” is described only in the presence / absence column of the binder layer, and the bipolar nickel foil current collector is electrically conductive as in Example 2. When the material and the binder-containing layer are provided, “Yes” is described only in the presence / absence column of the conductive material and the binder-containing layer. In addition, when one nickel foil current collector is provided with a binder layer, and the other nickel foil current collector is provided with a conductive material and a binder-containing layer, the presence / absence column of the binder layer and the conductive material and the binder are included. “Yes” is described in both of the layers. The binder decomposition temperature defined the temperature at which the binder mass was reduced by 80%.

As shown in Table 1, the short circuit of the all-solid-state secondary battery first observed in Comparative Example 1 was not observed in Examples 1 to 12 based on the present invention. In Examples 1, 4, 7, and 10, the binder layer on the surface of the nickel foil current collector first decomposes and disappears in the relatively low temperature state of the degreasing process, and the nickel foil current collector and the laminate green sheet interface. It is presumed that a short circuit is suppressed by forming a void in the concave and convex portion and then discharging the binder decomposition component in the laminated green sheet to the outside through the void in a relatively high temperature state thereafter.
In Examples 2, 5, 8, and 11, in a relatively low temperature state of the degreasing process, the conductive material on the surface of the nickel foil current collector and the binder in the binder-containing layer are first decomposed and disappeared, and the conductive material having voids. It is presumed that the short circuit was suppressed because the binder decomposition component in the laminate green sheet was discharged to the outside through the voids in the conductive material layer at a relatively high temperature after that. . Furthermore, in Examples 3, 6, 9, and 12, it is presumed that short-circuiting was suppressed by the above-described combination.

In addition, also in the battery characteristic evaluation, the all solid state secondary batteries shown in Examples 1 to 12 exhibited a higher discharge capacity than the all solid state secondary battery shown in the shorted comparative example 1 because the short circuit was prevented.
As described above, a nickel foil current collector having an uneven surface is provided with a binder layer, or a conductive material, and a binder-containing layer, and a positive electrode layer green sheet, a solid electrolyte layer green sheet, and a negative electrode layer green sheet are laminated. The all-solid-state secondary battery produced using the laminate green sheet with the nickel foil current collector was found to be short-circuited and exhibit high battery characteristics.

  The scope of the present invention is not limited to the illustrated and described exemplary embodiments, but also includes all embodiments that provide equivalent effects to those intended by the present invention. Further, the scope of the invention is not limited to the combinations of features of the invention defined by the claims, but can be defined by any desired combination of specific features among all the disclosed features.

11 Negative electrode layer green sheet 12 Solid electrolyte layer green sheet 13 Positive electrode layer green sheets 14a, 14b Metal foil current collector 15a Binder layers 16a, 16b Second binder layers 17a, 17b Metal foil current collector 31 Negative electrode layer 32 Solid electrolyte layer 33 Positive electrode layer 20 Uneven shape

Claims (7)

On one surface of the metal foil current collector, a first electrode layer green sheet, a solid electrolyte layer green sheet, a positive electrode layer green sheet, and a negative electrode layer green made of one of a positive electrode layer green sheet and a negative electrode layer green sheet A second electrode layer green sheet comprising the other of the sheets is laminated in this order,
One surface of the said metal foil collector has uneven | corrugated shape, The binder layer is formed in the surface in which the uneven | corrugated shape was formed, The laminated body green sheet characterized by the above-mentioned.   The laminate green sheet according to claim 1, wherein a conductive material is blended in the binder layer. A second metal foil current collector is laminated on the second electrode layer green sheet;
The surface of the second metal foil current collector on the second electrode layer green sheet side has an uneven shape, and a binder layer is formed on the surface on which the uneven shape is formed. The laminate green sheet described in 1.   The laminate green sheet according to claim 3, wherein a conductive material is blended in at least one binder layer of the plurality of binder layers.   The binder decomposition temperature of the binder layer is lower than the decomposition temperature of each binder of the positive electrode layer green sheet, the solid electrolyte layer green sheet, and the negative electrode layer green sheet. The laminated green sheet described.   The concave / convex shape formed on the surface of the metal foil current collector is an average roughness Ra of 0.1 μm or more and a groove having a thickness of 4/15 or less of the thickness of the metal foil current collector on which the target concave / convex shape is formed. The laminate green sheet according to any one of claims 1 to 5, wherein the laminate is a green sheet.   The all-solid-state secondary battery which has a laminated fired body formed by baking the laminated body green sheet of any one of Claims 1-6.

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