JP6943023B2 - Laminated green sheet, all-solid-state secondary battery and its manufacturing method - Google Patents

Description

The present invention is a technique relating to an all-solid-state secondary battery laminate and a laminate green sheet used for producing an all-solid-state secondary battery laminate.

In recent years, the power consumption of small electronic devices has been increasing along with the sophistication of small electronic devices represented by personal computers (PCs) and smartphones. In addition, demand for in-vehicle applications such as hybrid vehicles and electric vehicles and stationary applications such as household storage batteries is increasing. Along with this, the demand for higher energy density for secondary batteries is accelerating.
Furthermore, the lithium-ion secondary battery currently used for the above-mentioned applications uses an organic electrolytic solution, and depending on the usage conditions, the electrolytic solution may leak or ignite, so improvement in safety is required. Has been done.

On the other hand, the all-solid-state secondary battery does not use an organic electrolyte and is composed only of a solid material, so that there is a low possibility of liquid leakage and ignition, and it is excellent in safety and post-lithium ion. It is promising as a secondary battery.
However, the only all-solid-state secondary battery currently in practical use is a thin-film all-solid-state secondary battery, which has a low energy density. Furthermore, since the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are manufactured by a vapor deposition method and a sputtering method, it is necessary to manufacture an all-solid secondary battery in a reduced pressure atmosphere, which is not suitable for large area and mass production. Is.

Further, 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 form an altered layer having a different crystal structure at the interface. This altered layer inhibits Li ion conduction across the two.
On the other hand, Patent Document 1 describes that the formation of an altered layer is suppressed by coating the surface of active material particles with a simple substance of C, a simple substance of Cu, a simple substance of Ni, a simple substance of Fe, or an _{alloy of Ni 0.9} Mg _0.1. be.

Japanese Patent No. 5551542

However, in the method described in Patent Document 1, since the coating layer itself is a substance unrelated to the battery reaction, the energy density is lowered by the amount of the coating layer. In addition, the cost increases by the amount of the coating layer. Not only that, when a general-purpose material such as lithium cobalt oxide or lithium nickel oxide is used, the method of Patent Document 1 has a problem that an altered layer is formed.
An object of the present invention is to provide an all-solid-state secondary battery having an improved energy density by suppressing a change in crystal structure during firing.

As a result of diligent studies to solve the above problems, the present inventors have conducted a laminated green sheet having a solid electrolyte layer between the positive electrode and negative electrode layers containing an active material composited with a solid electrolyte having a garnet-type crystal structure. , I came up with an all-solid secondary battery using the laminated green sheet and a method for manufacturing them.
That is, by adopting an active material (hereinafter, also referred to as composite particles) coated with an oxide solid electrolyte that does not chemically react with the active material and cause a change in crystal structure during firing, each layer and each layer during firing are used. The crystal structure does not change, and the formation of the altered layer is suppressed. It has been found that this makes it possible to manufacture an all-solid-state secondary battery in which an increase in interfacial resistance due to the altered layer is suppressed.

Not only that, the active material and the solid electrolyte are pre-combined, so that an interface advantageous for lithium ion conduction is formed. This contributes to improving the performance of the all-solid-state secondary battery.
As described above, since the composite particles have good ionic conductivity, the amount of the solid electrolyte added in addition to the composite particles for forming the ionic conductivity path between the positive electrode and negative electrode layers and the solid electrolyte layer can be reduced. Therefore, the volumetric energy density is improved.

Although the mechanism by which the formation of the altered layer is suppressed when the green sheet having the graphite negative electrode active material and the solid electrolyte having a garnet-type crystal structure is fired is not clear, the altered layer is as described in Examples described later. It has been confirmed that the production of graphite is suppressed.
Then, in order to solve the problem, the all-solid secondary battery according to one aspect of the present invention includes a positive electrode layer, a solid electrolyte layer using an oxide solid electrolyte, and a negative electrode layer containing a graphite negative electrode active material. The positive electrode layer is laminated in this order and has a positive electrode active material coated with a solid electrolyte having a garnet-type crystal structure, and the graphite negative electrode active material is coated with a solid electrolyte having a garnet-type crystal structure. And.

Further, in the laminated green sheet according to one aspect of the present invention, the solid electrolyte layer green sheet is sandwiched between the negative electrode layer green sheet containing the graphite negative electrode active material and the positive electrode layer green sheet, and the positive electrode layer green sheet is a garnet. It has a positive electrode active material coated with a solid electrolyte having a type crystal structure, and the graphite negative electrode active material is characterized by being coated with a solid electrolyte having a garnet type crystal structure.
Further, the method for producing an all-solid-state secondary battery according to one aspect of the present invention includes a step of firing the above laminated green sheet in a low oxygen atmosphere.

According to one aspect of the present invention, the composite of the active material and the solid electrolyte forms an interface advantageous for lithium ion conduction, so that an all-solid secondary battery having a high energy density and good battery performance can be provided. Can be done.

It is sectional drawing which shows the structure of the laminated body green sheet with the metal leaf current collector which concerns on embodiment based on this invention. It is sectional drawing which shows the structure of the all-solid-state secondary battery which concerns on embodiment based on this invention. It is sectional drawing which shows the structure of the laminated body green sheet with the metal leaf current collector which concerns on embodiment based on this invention. It is sectional drawing which shows the structure of the all-solid-state secondary battery which concerns on embodiment based on this invention. It is sectional drawing which shows the structure of the laminated body green sheet which concerns on embodiment based on this invention. It is sectional drawing which shows the structure of the all-solid-state secondary battery which concerns on embodiment based on this invention. It is a schematic diagram explaining the composite particle of an active material, a solid electrolyte, and a binder after an adhesion process which concerns on embodiment based on this invention. It is a schematic diagram explaining the composite particle after the softening and solidifying step which concerns on embodiment based on this invention. It is a schematic diagram explaining the state of the composite particle in the positive electrode or negative electrode layer green sheet.

Hereinafter, 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 plane dimensions, the ratio of the thickness of each layer, the shape, etc. are different from the actual ones. Further, the embodiments shown below exemplify a configuration for embodying the technical idea of the present invention, and the technical idea of the present invention describes the materials, shapes, structures, etc. of the constituent parts as follows. It is not something that is specific to something. The technical idea of the present invention may be modified in various ways within the technical scope specified by the claims stated in the claims.

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

FIG. 2 is a cross-sectional view showing the configuration of an all-solid-state secondary battery 26 manufactured by subjecting the laminated green sheet 16 with a metal leaf current collector shown in FIG. 1 to a heat degreasing treatment and a batch firing step. The firing step is preferably performed in a low oxygen atmosphere. Reference numeral 24 indicates a fired metal leaf current collector.
Further, in the laminated green sheet 16 with a metal leaf current collector, as shown in FIG. 3, the negative electrode layer green sheet 11 is laminated on the solid electrolyte layer green sheet 12 to form the laminated green sheet main body, and further, the negative electrode layer. The metal leaf current collector 14 may be adhered to the surface of the green sheet 11 that does not face the solid electrolyte layer green sheet 12. Further, the positive electrode layer green sheet 13 may be formed on the solid electrolyte layer green sheet 12. The laminated green sheet 16 with a metal leaf current collector of the present embodiment may have at least a solid electrolyte layer green sheet 12 and a negative electrode layer green sheet 11 as the main body of the laminated green sheet.

When the all-solid secondary battery 26 is manufactured from the laminated green sheet 16 with a metal leaf current collector shown in FIG. 3, for example, the laminated green sheet 16 with a metal leaf current collector is heat-defatted and batch-treated. After the firing step, the positive electrode layer 25 (Li foil in FIG. 4) and the metal leaf current collector 14 are placed on the solid electrolyte layer 22 in which the metal foil current collector 14 is not provided in the state of the laminated green sheet 16. Are attached in this order to form an all-solid secondary battery 26 (see FIG. 4).

Further, as shown in FIG. 5, the laminated green sheet 16 may be composed of only the laminated green sheet main body having no metal leaf current collector. In this case, the current collector 34 may be provided after the laminated green sheet 16 is subjected to the heat degreasing treatment and the batch firing step (see FIG. 6).
In the present embodiment, the active material particles contained in the slurry forming the negative electrode layer green sheet 11 and the positive electrode layer green sheet 13 are contained in the state of composite particles covered with a solid electrolyte having a garnet-type crystal structure. There is. In particular, one of the features of this embodiment is that a graphite negative electrode active material is used as the negative electrode active material, and the graphite negative electrode active material is used in a state of being coated with a solid electrolyte having a garnet-type crystal structure.
Hereinafter, each component will be described.

(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 a glass body 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. The inclusion of boron has the effect of lowering the melting point, that is, the firing temperature.

(Positive electrode layer green sheet)
The positive electrode layer green sheet 13 has a positive electrode active material, a solid electrolyte, and a binder. The solid electrolyte may include a glass body that becomes an oxide solid electrolyte after firing.
The positive electrode active material is preferably a positive electrode active material having a layered rock salt structure. The solid electrolyte is preferably a solid electrolyte having a garnet-type crystal structure. The solid electrolyte may contain a glass body 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 that serves as a conductive auxiliary agent.

(Negative electrode layer green sheet)
The negative electrode layer green sheet 11 has a graphite negative electrode active material, a solid electrolyte having a garnet-type crystal structure, and a binder. The solid electrolyte may include a glass body 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, 90% by mass or more of the solid electrolyte has a garnet-type crystal structure.
It may have an electronically conductive material that serves as a conductive auxiliary agent.

(Binder used for each green sheet)
The binder is not particularly limited as long as it is a material that binds to the active material particles, the solid electrolyte particles, and the conductive auxiliary agent and decomposes under the firing conditions described later. As the binder, for example, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, polyvinyl acetal, polyvinylidene fluoride, polytetrafluoroethylene, ethyl cellulose, acrylic resin and the like can be used.

The binder in the positive electrode layer green sheet, the solid electrolyte layer green sheet and the negative electrode layer green sheet is preferably 3 parts by mass or more and 40 parts by mass or less. If it is less than 3 parts by mass, sufficient binding cannot be achieved, and if it is larger than 40 parts by mass, the capacitance per electrode volume is greatly reduced. More preferably, it is 3 parts by mass or more and 25 parts by mass or less.

(Solid electrolyte layer)
The solid electrolyte layer 22 contains an oxide solid electrolyte. The shape of the solid electrolyte is, for example, a particle shape.
The solid electrolyte contained in the solid electrolyte layer may be any material having low electron conductivity and high lithium ion conductivity. As the solid electrolyte, for example, an amorphous (glass), crystal, or glass ceramic of an oxide-based solid electrolyte or a sulfide-based solid electrolyte can be used. In particular, an oxide-based solid electrolyte capable of high-temperature firing is preferable, and NASICON-type oxides, perovskite-type oxides, LISION-type oxides, oxides having a garnet-type crystal structure, oxide glass bodies, and the like can be used. For example, 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 and the} like can be used. It is preferable to use a solid electrolyte having a garnet-type crystal structure from the viewpoint that it does not chemically react with the active material during firing to form an altered layer and has high lithium ion conductivity. That is, a material having a garnet-type crystal structure and high conductivity of lithium ions is particularly preferable, and an oxide containing Li, La, and Zr is preferable, and even if a foreign element is doped in addition to Li, La, and Zr. good. Further, in addition to a material having a garnet-type crystal structure and high lithium ion conductivity, a lithium ion conductive material containing Li and B may be included. For example, _{a solid electrolyte in which Li 7} La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ and Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ are doped with a foreign element is optimal.

The thickness of the solid electrolyte layer 22 is preferably in the range of 1 μm or more and 1000 μm or less, and more preferably in the range of 1 μm or more and 500 μm or less. If the thickness of the solid electrolyte layer 22 is thinner than 1 μm, the positive electrode layer 23 and the negative electrode layer 21 are likely to be short-circuited, which may not only reduce the performance of the all-solid-state secondary battery 26 but also reduce the safety. There is. Further, when the thickness of the solid electrolyte layer green sheet 12 is thicker than 1000 μm, the movement of conducting ions such as lithium ions in the solid electrolyte layer 22 is likely to be hindered, and the output of the all-solid secondary battery 26 may be lowered. There is.

(Positive electrode layer)
The positive electrode layer 23 contains a positive electrode active material and a solid electrolyte.
The positive electrode active material contained in the positive electrode layer 23 may be any material containing lithium and cobalt, and is not particularly limited. The positive electrode layer green sheet 13 contains an active material having a potential nobler than that of the active material contained in the negative electrode layer green sheet 11 as the positive electrode active material.
The positive electrode active material preferably has a layered rock salt type crystal structure, and is, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel cobalt manganate (Li (NiCoMn) O ₂ ), lithium nickel oxide (LiNiO). ₂ ), or a lithium transition metal compound in which a foreign element is doped in lithium manganate (Li (NiComn) O ₂ ) or lithium iron oxide (LiFePO _{4) is optimal.} At this time, it is preferable to use a general-purpose material for the lithium ion secondary battery in the all-solid-state secondary battery, and it is particularly preferable to use lithium cobalt oxide (LiCoO2).

Here, as the active material particles contained in the positive electrode side and the negative electrode side, a material capable of occluding and releasing lithium ions is used, and among the active material particles, those showing a more noble potential are used as the positive electrode active material particles. Those having a lower potential can be used as the negative electrode active material particles.
The solid electrolyte contained in the positive electrode layer 23 may be any material having low electron conductivity and high lithium ion conductivity, and particularly a material having a garnet-type crystal structure and high lithium ion conductivity. Preferably, an oxide containing Li, La, and Zr is preferable, and a foreign element may be doped in addition to Li, La, and Zr. Further, in addition to a material having a garnet-type crystal structure and high lithium ion conductivity, a lithium ion conductive material containing Li and B may be included. For example, _{a solid electrolyte in which Li 7} La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ and Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ are doped with a foreign element is optimal.

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 it is contained in an amount of 10% or more, a resistance layer may be formed in the firing step in the method for manufacturing an all-solid-state battery described later, and the battery performance may be deteriorated.
The positive electrode layer 23 may contain a conductive auxiliary agent. The conductive auxiliary agent 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 auxiliary agent 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 auxiliary agent is 90% by mass or more, the amount of the positive electrode active material in the positive electrode layer 23 may be insufficient and the lithium storage capacity may decrease.
The thickness of the positive electrode layer 23 can be selected as desired according to the desired battery capacity.
It is preferable that at least one kind of material constituting the positive electrode layer 23 is fused with the metal leaf current collector 14.

For example, it is preferable that the positive electrode active material is fused with the metal leaf current collector 14.
The reason is that the positive electrode active material and the metal leaf current collector 14 are fused and the adhesion is good, so that the electron exchange between the positive electrode active material and the metal leaf current collector 14 becomes smooth, that is, the resistance. This is because the battery performance is improved.

(Negative electrode layer)
The negative electrode layer 21 contains a graphite negative electrode active material and a solid electrolyte having a garnet-type crystal structure.
Examples of the material of the graphite negative electrode active material particles include hard carbon, soft carbon, and graphite.

In the present embodiment, the main negative electrode active material particles contained in the negative electrode layer 21 are graphite negative electrode active material particles, but other negative electrode active material particles may be contained. However, among the negative electrode active material particles contained in the negative electrode layer 21, the graphite negative electrode active material particles are preferably 70% by mass or more, more preferably 90% by mass or more.
Other negative electrode active material particles include alloy materials such as Sn-based alloys and Si-based alloys, nitrides such as LiCoN, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and lithium vanadium phosphate (Li ₃ V ₂ (PO). ₄ ) Lithium transition metal oxides such as _{3) can be used.}

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. Further, 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, an oxide containing Li, La, and Zr is preferable, and a foreign element may be doped in addition to Li, La, and Zr. Further, in addition to a material having a garnet-type crystal structure and high lithium ion conductivity, a lithium ion conductive material containing Li and B may be included. For example, _{a solid electrolyte in which Li 7} La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ and Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ are doped with a foreign element is optimal.

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 it is contained in an amount of 10% or more, a resistance layer may be formed in the firing step in the method for manufacturing an all-solid-state battery described later, and the battery performance may be deteriorated.
The negative electrode layer 21 may contain a conductive auxiliary agent. 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 23, and for example, a conductive carbon material, particularly carbon black, activated carbon, carbon carbon fiber, or the like is used. be able to.

The content of the conductive auxiliary agent 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 auxiliary agent 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.
The thickness of the negative electrode layer green sheet 11 can be selected as desired according to the desired battery capacity.

It is preferable that at least one kind of material constituting the negative electrode layer 21 is fused with the metal leaf current collector 14.
For example, it is preferable that the negative electrode active material is fused with the metal leaf current collector 14.
The reason is that the negative electrode active material and the metal leaf current collector 14 are fused and the adhesion is good, so that the electron exchange between the negative electrode active material and the metal leaf current collector 14 becomes smooth, that is, the resistance. This is because the battery performance is improved.

(Metal leaf current collector)
The metal leaf 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 a metal foil is preferable. Therefore, in the present embodiment, the metal foil current collector 14 is exemplified.
The material of the metal foil current collector 14 is not particularly limited as long as it is a conductive material, and for example, metal materials such as stainless steel, nickel, aluminum, iron, titanium, copper, palladium, gold and platinum are used. be able to. Further, it is preferable that the material of the metal leaf current collector 14 is selected in consideration of not melting and decomposing under the firing conditions described later, and the battery operating potential and conductivity applied to the metal foil current collector 14. Further, the antioxidant film material may be any material such as a carbon film that does not deteriorate even in a high temperature atmosphere and prevents the metal foil from coming into contact with the atmosphere. The carbon film thickness as the antioxidant film is preferably 10 nm or more, and is formed by a vapor deposition method on a metal current collecting foil, a sputtering method, a CVD method, or an inert firing of a resin layer formed on the current collecting foil. It can be formed.

The tensile strength of the metal leaf current collector 14 is preferably 10 N / 10 mm or more. When the tensile strength of the metal leaf current collector 14 is 10 N / 10 mm or more, cracks or the like are less likely to occur in the metal leaf current collector 14 in the firing step at the time of manufacturing the all-solid-state secondary battery 26. Further, when the tensile strength of the metal foil current collector 14 is 10 N / 10 mm or more, the laminated green sheet 16 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 sufficiently supported. The strength to be obtained is obtained.

The all-solid-state secondary battery 26 of the present embodiment is manufactured by laminating the positive electrode layer green sheet 13, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 11, which will be described later, and firing them. Therefore, it is important that the metal leaf current collector 14 of the all-solid-state secondary battery 26 has a characteristic that cracks and the like do not occur in the firing step.
The thickness of the metal leaf current collector 14 is preferably 3 μm or more and 50 μm or less. When the thickness of the metal leaf current collector 14 is 3 μm or more and 50 μm or less, cracks and the like are unlikely to occur in the metal leaf current collector 14 during the production of the laminated fired body, and the laminated green sheet 16 is sufficiently supported. Thickness is obtained.

"Manufacturing method of all-solid-state secondary battery"
Hereinafter, a method for manufacturing the all-solid-state secondary battery 26 having the above-described configuration will be described.
The method for manufacturing the all-solid-state secondary battery 26 of the present embodiment includes a composite particle manufacturing step, a laminated green sheet manufacturing step, and a firing step.

(Composite particle manufacturing process)
In the composite particle preparation step, composite particles 4 for the positive electrode, which are particles in which the positive electrode active material is coated with a solid electrolyte having a garnet-type crystal structure, are produced, and particles in which the graphite negative electrode active material is coated with a solid electrolyte having a garnet-type crystal structure. This is a step of producing the composite particles 4 for the negative electrode.

In the production of the composite particles 4 in the present embodiment, the adhesion step of depositing the solid electrolyte 3 on the outer periphery of the active material 1 as shown in FIG. 7 and the solid electrolyte 3 adhered temporarily as shown in FIG. 8 are temporarily applied. It is provided with a softening and solidifying step of softening and solidifying.
Examples of the treatment in the adhesion step include a rolling flow coating method, a spray method, a dipping method, a method using a spray dryer, and the like, and these methods are used to prepare composite particles 4 of an active material 1, a solid electrolyte 3, and a binder 2. do. At this time, by making the particle size of the solid electrolyte 3 smaller than the particle size of the active material 1, the solid electrolyte 3 was adhered around the active material 1 by the binder 2 as shown in FIG. 7, which is a schematic diagram. It becomes easy to become a state.

In the softening and solidifying step, the composite particles 4 after the adhesion step are calcined to sublimate and remove the binder 2, and the solid electrolyte 3 is softened in a viscous state. By solidifying again, the active material 1 is coated with the solid electrolyte 3 to produce the desired composite particles 4. Note that FIG. 8 is a schematic diagram, and there are cases where a plurality of active materials 1 are connected in a beaded shape or a lump shape via a solid electrolyte 3.

Regarding the average particle size of the material used in the present embodiment, the particles of the active material 1 are 10 μm to several tens of μm, and the particles of the solid electrolyte 3 are several hundred nm to several μm. From the viewpoint of collectively compositing particles having different particle sizes, the spray dryer method is particularly preferable for producing the composite particles 4.
The firing temperature at which the composite particles 4 are fired to produce the composite particles 4 is preferably a temperature at which the binder 2 is decomposed and the active material and the solid electrolyte are fired, preferably 300 ° C. or higher and 1100 ° C. or lower.

(Laminated green sheet manufacturing process)
The method for manufacturing the laminated green sheet 16 is to form a negative electrode layer green sheet by applying or printing a negative electrode slurry containing a negative electrode active material on a negative electrode current collector composed of, for example, a metal foil current collector 14 and drying the negative electrode layer green sheet. A layer green sheet forming step, a solid electrolyte layer green sheet forming step of applying a solid electrolyte slurry containing a solid electrolyte on the negative electrode layer green sheet 11 or drying after printing to form a solid electrolyte layer green sheet 12, and a solid electrolyte layer. A positive electrode layer green sheet forming step of applying or printing a positive electrode slurry containing a positive electrode active material on the green sheet 12 and then drying to form the positive electrode layer green sheet 13 is provided.

In the case of manufacturing the laminated green sheet 16 which does not have the metal leaf current collector 14 as shown in FIG. 5, a base material may be used instead of the positive electrode current collector.
The base material to which the slurry of the green sheet is applied is not particularly limited, and it is sufficient that the laminated green sheet 16 can be prepared on the base material and then peeled off. Metal leaf, etc. can be used.

The thickness of the base material is not particularly limited, but if it is too thin, it may be curved when each slurry constituting the laminated green sheet 16 is dried, and the laminated green sheet 16 may be destroyed, while it is too thick. And the laminated green sheet 16 may be destroyed at the time of peeling. Specifically, for example, it is preferably 3 μm or more and 100 μm or less, and 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 oxide solid electrolyte particles and an organic substance with a solvent, and then drying the solid electrolyte layer. The solid electrolyte slurry is applied, for example, on the positive electrode layer green sheet 13 or the negative electrode layer green sheet 11, which will be described later. The method for preparing the solid electrolyte slurry is not particularly limited.

Solid Electrolyte Layer The thickness of the solid electrolyte layer formed by the green sheet is preferably in the range of 1 μm or more and 500 μm or less. If it is thinner than 1 μm, the positive electrode layer and the negative electrode layer are short-circuited, which may not only reduce the performance of the all-solid-state secondary battery but also reduce the safety. If it is thicker than 500 μm, the movement of conducting ions such as lithium ions in the solid electrolyte layer is hindered, and the output of the all-solid secondary battery may decrease.

(Manufacturing method of positive electrode layer green sheet)
The positive electrode layer green sheet 13 is formed by mixing a binder composed of composite particles 4 for positive electrodes, solid electrolyte particles, and an organic substance together with a solvent, applying or printing a slurry for positive electrodes, and then drying. The positive electrode slurry is applied onto the metal leaf current collector 14 serving as the 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 layer green sheet)
The negative electrode layer green sheet 11 is formed by mixing a binder composed of composite particles 4 for a negative electrode, solid electrolyte particles and an organic substance together with a solvent, applying or printing a slurry for a negative electrode, and then drying. The negative electrode slurry is applied onto the metal leaf 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 slurry for the negative electrode is not particularly limited.

The solid electrolyte particles in the positive electrode layer green sheet, the solid electrolyte layer green sheet, and the negative electrode layer green sheet may be the same or different, and two or more kinds may be used in combination in the same green sheet.
In the positive electrode layer green sheet and the negative electrode layer green sheet, the other solid electrolyte added to the composite particles 4 is not particularly limited as long as it is a material that does not change its crystal structure by chemically reacting with the solid electrolyte in the composite particles 4. .. The total solid electrolytic mass in the green sheet is preferably 20 parts by mass or more and 80 parts by mass or less with respect to the active material. If it is less than 20 parts by mass, the amount of solid electrolyte is too small, so that the ionic conductivity becomes small and the battery performance deteriorates. If it is more than 80 parts by mass, the amount of active material in the layer is small, and as a result. The energy density of the entire all-solid-state battery becomes low.

The binder used for 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. As the binder, for example, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetal, polyvinylidene fluoride, polytetrafluoroethylene, ethyl cellulose, acrylic resin and the like can be used.

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 or more and 40% by mass or less, and more preferably 3% by mass or more and 25% by mass or less. preferable. That is, the content of the binder with respect to the total 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.

If the content of the binder is less than 3% by mass, for example, the active materials or the solid electrolytes may not be sufficiently bonded to each other. Further, when the content of the binder is larger than 40% by mass, the battery capacity per volume decreases.
The positive electrode slurry, the solid electrolyte slurry, and the negative electrode slurry are used to promote the formation of a matrix structure in each green sheet during firing of the positive electrode layer green sheet, the solid electrolyte layer green sheet, and the negative electrode layer green sheet, and to lower the firing temperature. Auxiliary agents may be further contained. The firing aid is not particularly limited as long as it does not react with the active material particles and the solid electrolyte particles and the softening point temperature is lower than the firing temperature of the solid electrolyte particles. As the firing aid, for example, a boron compound can be used. By adjusting the content of the firing aid and the firing temperature of each green sheet, cracks due to internal strain and internal stress of each layer are prevented and the formation of a matrix structure is promoted when the laminated fired body is formed by firing. can do.

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-mentioned binder can be dissolved, and for example, alcohols such as ethanol, isopropanol and n-butanol, toluene, ethyl acetate and acetic acid. Butyl, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol ethyl ether, isophorone, butyl lactate, dioctyl phthalate, dioctyl adipate, benzyl alcohol, N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), etc. Organic solvent and water can be used. These solvents may be used alone or in combination of two or more. The boiling point of the solvent is preferably 200 ° C. or lower because the slurry can be easily dried.

The positive electrode slurry and the negative electrode slurry can be produced by mixing the above-mentioned positive electrode active material or negative electrode active material, solid electrolyte, binder, conductive additive, firing aid and the like with a solvent. Further, the solid electrolyte slurry can be prepared by mixing the above-mentioned solid electrolyte, binder, conductive additive, firing aid and the like with a solvent. The method of mixing the slurry is not particularly limited, and additives such as a thickener, a plasticizer, a defoaming agent, a leveling agent, and an adhesion imparting agent may be added as needed.

Specific examples of the coating and printing methods for the positive electrode slurry, the negative electrode slurry and the solid electrolyte slurry include the doctor blade method, the calendar method, the spin coating method, the dip coating method, the inkjet method, the offset method, the die coating method and the spray method. , Screen printing method and 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, and for example, heat drying, vacuum drying, heating vacuum drying, and the like can be used. The dry atmosphere is not particularly limited, and can be performed in an atmospheric atmosphere or an inert atmosphere (nitrogen atmosphere, argon atmosphere), for example.

The positive electrode layer green sheet 13, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 11 constitute a laminated green sheet 16 that is laminated in this order. The laminated green sheet 16 may be composed of only the solid electrolyte layer green sheet 12 and the negative electrode layer green sheet.
The thickness of the positive electrode layer formed by the positive electrode layer green sheet and the thickness of the negative electrode layer formed by the negative electrode layer green sheet can be determined according to the desired battery capacity.

By applying pressure, the mechanical strength of the laminated green sheet 16 may be increased, and the voids inherent in the laminated green sheet 16 may be reduced. The pressurizing method is not particularly limited, and for example, a flat plate press, a roll press, a hot press, a cold hydrostatic press, a hot hydrostatic press, or the like can be used. Pressurization may be performed only once or may be divided into several times.
When the laminated green sheet 16 is formed on the base material, the base material is peeled off after the above treatment. The porosity of the laminated green sheet 16 before peeling is not particularly limited, and a pressurizing step may or may not be added before peeling.

(Baking process)
The all-solid-state secondary battery 26 of the present embodiment is formed by firing the laminated green sheet 16 manufactured as described above and degreasing the binder.
Here, in the laminated green sheet 16 before firing, the composite particles 4 and other solid electrolyte particles in the positive electrode layer green sheet 13 and the negative electrode layer green sheet 11 are in the state as shown in FIG. However, by firing, the solid electrolyte of the composite particles 4 and the other solid electrolyte particles 6 are temporarily softened by the heat of firing and are in a state of being attached to the solid electrolyte of the other composite particles 4 and other solid electrolyte particles. And fill the gap.

When the current collector is not adhered to the laminated green sheet 16 in advance, a layer having a current collecting property with respect to the exposed positive electrode surface or negative electrode surface in the laminated fired body obtained by firing the laminated 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. 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. For example, a metal foil, a conductive thin film layer, a conductive paste, or a conductive adhesive material. And so on.

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 laminated green sheet and lower than the oxidation temperature of the active material particles or lower than the combustion temperature of the current collector, specifically 300 ° C. or higher. It is preferably 1100 ° C. or lower, and more preferably 300 ° C. or higher and 900 ° C. or lower. If the temperature is lower than 300 ° C., the binder will not burn completely and will become a residue, which may become a resistor in the layer. If the temperature is higher than 1100 ° C., the active material particles and the solid electrolyte particles may be melted and denatured, which may deteriorate the battery performance.

The atmosphere in the firing step is not particularly limited, and for example, it can be carried out in an atmospheric atmosphere or an inert atmosphere (nitrogen atmosphere, argon atmosphere). When there is concern about the reaction between the positive electrode active material and the negative electrode active material and the metal leaf current collector 14 and 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 to be used is sufficiently decomposed.

As described above, in the present embodiment, by adopting an active material (composite particles 4) coated with an oxide solid electrolyte that does not chemically react with the active material and cause a change in crystal structure during firing, the active material (composite particles 4) is used during firing. The battery performance is good and the energy density is high because an interface advantageous for lithium ion conduction is formed by combining the active material and the solid electrolyte without causing a change in crystal structure in each layer or between layers. It has become possible to manufacture solid secondary batteries.

As a result, one firing step 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. It has become possible to manufacture the all-solid-state secondary battery 26. The method of bonding the metal foil current collector 14 is not particularly limited, and for example, a flat plate press, a roll press, a hot press, a cold hydrostatic press, a hot hydrostatic press, or the like can be used.

Here, the configuration of the all-solid-state secondary battery 26 may be a series all-solid-state secondary battery. Such an all-solid secondary battery 26 includes, for example, a plurality of electrode stacks including 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. Prepare the body. Further, the all-solid-state secondary battery 26 is in close contact with the positive electrode layer 23 or the negative electrode layer 21 between the plurality of laminated electrode laminates and further outside the outer surface of the laminated electrode laminates in the stacking direction. A plurality of metal foil current collectors 14 are provided.

The production of the all-solid secondary battery 26 is performed, for example, on a laminated green sheet 16 having a positive electrode layer green sheet 13, a solid electrolyte layer green sheet 12, and a negative electrode layer green sheet 11 formed on a positive electrode current collector. A laminated green sheet 16 in which a laminated green sheet 16 having a positive electrode layer green sheet 13, a solid electrolyte layer green sheet 12 and a negative electrode layer green sheet 11 formed on the body is continuously laminated is produced, and the produced laminated green sheet 16 is produced. This is achieved by firing 16 batches and laminating the metal foil current collector 14.

Hereinafter, referring to the figure, an active material (composite particles 4) coated with an oxide solid electrolyte that does not chemically react with the active material and cause a change in crystal structure during firing according to the present embodiment is used. Specific examples and comparative examples of a laminated green sheet, an all-solid secondary battery using the laminated green sheet, and a method for manufacturing them will be described. The present embodiment is not limited to the following examples.

(Example 1)
<Composite particle manufacturing process for positive electrode>
_{80 parts by mass of layered lithium cobalt oxide (LiCoO 2} , manufactured by Toyoshima Seisakusho) powder as active material particles for the positive electrode _{, and LLZ (Li 7} La ₃ Zr ₂ O ₁₂ , manufactured by Toyoshima Seisakusho) having a garnet-type crystal structure as solid electrolyte particles. ) 20 parts by mass of powder, 23 parts by mass of polyvinylpyrrolidone as a binder, and water as a solvent were used to prepare a slurry. Using the prepared slurry, composite particles 4 of an active material, a solid electrolyte and a binder as shown in FIG. 7 were prepared by a spray dryer method. By firing it, composite particles 4 for a positive electrode in which a positive electrode active material and a solid electrolyte as shown in FIG. 8 were integrated were produced.

<Composite particle manufacturing process for negative electrode>
80 parts by mass of spherical natural graphite (SMG, manufactured by Hitachi Kasei Kogyo) powder as negative electrode active material particles, _{20 parts by mass of LLZ (Li 7} La ₃ Zr ₂ O ₁₂ , manufactured by Toyoshima Seisakusho) powder as solid electrolyte particles, polyvinylpyrrolidone 23 as a binder A slurry was prepared by using water as a solvent in parts by mass. Using the prepared slurry, composite particles 4 of an active material, a solid electrolyte and a binder as shown in FIG. 7 were prepared by a spray dryer method. By firing it, composite particles 4 for the negative electrode, in which the negative electrode active material and the solid electrolyte as shown in FIG. 8 were integrated, were produced.

<Preparation of slurry for positive electrode>
95 parts by mass of the prepared composite particle 4 powder for the positive electrode, 5 parts by mass of ball mill pulverized LLZ powder as solid electrolyte particles, 16 parts by mass of polyvinyl butyral (PVB) as a binder, and a solvent (tarpineol) are mixed to form a slurry. , This slurry was defoamed to prepare a positive electrode slurry.

<Preparation of solid electrolyte slurry>
100 parts by mass of ball mill pulverized LLZ powder as solid electrolyte particles, 16 parts by mass of PVB as a binder, and a solvent (tarpineol) were mixed to form a slurry, and this slurry was defoamed to prepare a solid electrolyte slurry.

<Preparation of slurry for negative electrode>
95 parts by mass of the prepared composite particle 4 powder for the negative electrode, 5 parts by mass of LLZ powder crushed by a ball mill as a solid electrolyte, 16 parts by mass of PVB as a binder, and a solvent (tarpineol) were mixed to form a slurry, and this slurry was defoamed. To prepare a slurry for the negative electrode.

<Laminated green sheet manufacturing process>
A 15 μm nickel foil is used as the current collector, and this is used as the negative electrode current collector. A negative electrode slurry is applied onto the current collector and dried to prepare a negative electrode layer green sheet, which is then placed on the negative electrode layer green sheet. , The solid electrolyte slurry is applied and dried to prepare a solid electrolyte layer green sheet, and the positive electrode slurry is applied and dried on the solid electrolyte layer green sheet to prepare a metal positive electrode layer green sheet. A laminated green sheet with a foil current collector was produced.

<Cutting process>
The same nickel foil as above was placed on the positive electrode layer green sheet of the produced laminated green sheet as another current collector, and this was used as the positive electrode current collector, and this current collector was used at 80 ° C. and 1000 kgf / cm ² (98 MPa). ), The positive electrode current collector and the negative electrode current collector were cut into individual elements so as to be exposed on different surfaces of the laminated green sheet. The laminated green sheet with the metal leaf current collector after cutting was 30 mm × 30 mm.

<Solvent degreasing process>
The above-mentioned laminated green sheet with a metal leaf 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>
After the degreasing step, the temperature was raised from 500 ° C. to 800 ° C. at a heating rate of 20 ° C./min in an argon stream, and the temperature was maintained at 800 ° C. for 3 hours for firing. Then, the fired laminated fired body was cooled to room temperature by allowing it to cool in the furnace to prepare an all-solid-state secondary battery of Example 1.

(Example 2)
In <Preparation of Slurry for Positive Electrode> and <Preparation of Slurry for Negative Electrode> of Example 1, acetylene black (AB, Li-400, manufactured by Electrochemical Industry Co., Ltd.) was used as a conductive auxiliary agent with respect to 95 parts by mass of the active material. An all-solid-state secondary battery of Example 2 was produced under the same conditions as in Example 1 except that 5 parts by mass was added.

(Example 3)
In Example 1, <Preparation of Positive Electrode Slurry>, <Solid Electrode Slurry>, and <Preparation of Negative Electrode Slurry>, LLZN (MLZN), which is an oxide solid electrolyte having the same garnet-type crystal structure, is used instead of LLZ as the solid electrolyte. An all-solid secondary battery of Example 3 was produced under the same conditions as in Example 1 except that Li _6.75 La ₃ Zr _1.75 Nb _0.25 O _{12) was used.}
Examples 4 and 5 in which it is investigated whether the crystal structure of the active material and the solid electrolyte change before and after firing are shown below.

(Example 4)
<Preparation of calcined samples of positive electrode active material and solid electrolyte>
50 parts by mass of lithium cobalt oxide and 50 parts by mass of LLZ were mixed in an agate mortar, and 1 g of the mixture was placed in a 15φ die and pressurized to form a disk-shaped pellet. The molded pellets are placed in an alumina crucible prepared on the left and laid with a mixture of lithium cobalt oxide and LLZ, heated to 800 ° C at a heating rate of 20 ° C / min in an argon stream, and held at 800 ° C for 3 hours. The crucible was fired. The calcined pellets were crushed again in an agate mortar to prepare a sample for investigating changes in crystal structure.

(Example 5)
<Preparation of calcined samples of negative electrode active material and solid electrolyte>
50 parts by mass of SMG and 50 parts by mass of LLZ were mixed in an agate mortar, and 1 g of the mixture was placed in a 15φ die and pressurized to form a disk-shaped pellet. The molded pellets are placed in an alumina crucible prepared on the left and laid with a mixture of SMG and LLZ, heated to 800 ° C. at a heating rate of 20 ° C./min in an argon stream, held at 800 ° C. for 3 hours, and fired. Was carried out. The calcined pellets were crushed again in an agate mortar to prepare a sample for investigating changes in crystal structure.

(Comparative Example 1)
In Comparative Example 1, <Preparation of positive electrode composite particle production step> and <Negative electrode composite particle production step> of Example 1 were not carried out, but <Preparation of positive electrode slurry> and <Preparation of negative electrode composite particle> were carried out as follows. bottom.
<Preparation of slurry for positive electrode>
_{76 parts by mass of lithium cobalt oxide (LiCoO 2} , manufactured by Toyoshima Seisakusho) powder as positive electrode active material particles, 24 parts by mass of ball mill pulverized LLZ powder as a solid electrolyte, 16 parts by mass of PVB as a binder, and a solvent (tarpineol) are mixed. A slurry was prepared, and this slurry was defoamed to prepare a slurry for a negative electrode.

<Preparation of slurry for negative electrode>
76 parts by mass of spherical natural graphite (SMG, manufactured by Hitachi Kasei Kogyo) powder, 24 parts by mass of LLZ powder crushed by a ball mill as a solid electrolyte, 16 parts by mass of PVB as a binder, and a solvent (tarpineol) are mixed to form a slurry. Was defoamed to prepare a slurry for the negative electrode.
Other than that, the all-solid-state secondary battery of Comparative Example 1 was produced under the same conditions as in Example 1.

(Comparative Example 2)
In Comparative Example 2, <Preparation of positive electrode composite particle production step> and <Negative electrode composite particle production step> of Example 1 were not carried out, but <Preparation of positive electrode slurry> and <Preparation of negative electrode composite particle> were carried out as follows. bottom.
<Preparation of slurry for positive electrode>
_{50 parts by mass of lithium cobalt oxide (LiCoO 2} , manufactured by Toyoshima Seisakusho) powder as positive electrode active material particles, 50 parts by mass of ball mill pulverized LLZ powder as a solid electrolyte, 16 parts by mass of PVB as a binder, and a solvent (tarpineol) are mixed. A slurry was prepared, and this slurry was defoamed to prepare a slurry for a negative electrode.

<Preparation of slurry for negative electrode>
50 parts by mass of spherical natural graphite (SMG, manufactured by Hitachi Kasei Kogyo) powder, 50 parts by mass of LLZ powder crushed by a ball mill as a solid electrolyte, 16 parts by mass of PVB as a binder, and a solvent (tarpineol) are mixed to form a slurry. Was defoamed to prepare a slurry for the negative electrode.
Other than that, the all-solid-state secondary battery of Comparative Example 2 was produced under the same conditions as in Example 1.

(Comparative Example 3)
In the <positive electrode composite particle manufacturing step> of Example 1, except that LAGP (Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ) having a NASICON type crystal structure having a different crystal structure was used instead of LLZ as the solid electrolyte. An all-solid-state secondary battery of Comparative Example 3 was produced under the same conditions as in Example 1.
(Comparative Example 4)
In the <negative electrode composite particle production step> of Example 1, the all-solid-state secondary battery of Comparative Example 4 was produced under the same conditions as in Example 1 except that LAGP was used instead of LLZ as the solid electrolyte.

(Comparative Example 5)
All-solid-state battery of Comparative Example 5 under the same conditions as in Example 1 except that the positive electrode active material of Example 1 was lithium manganate (LiMn ₂ O _{4, manufactured by Toyoshima Seisakusho) having an inverted spinel structure instead of lithium cobalt oxide.} A secondary battery was manufactured.
(Comparative Example 6)
An all-solid-state secondary battery of Comparative Example 6 was produced under the same conditions as in Example 1 except that the negative electrode active material of Example 1 was lithium titanate instead of SMG.
Below, Comparative Examples 7 to 10 are shown in which it is investigated whether the crystal structure of the active material, the solid electrolyte, and the solid electrolyte changes before and after firing.

(Comparative Example 7)
<Preparation of calcined samples of lithium cobalt oxide and LAGP>
50 parts by mass of lithium cobalt oxide and 50 parts by mass of LAGP were mixed in an agate mortar, and 1 g of the mixture was placed in a 15φ die and pressurized to form a disk-shaped pellet. The molded pellets are placed in an alumina crucible prepared on the left and laid with a mixture of lithium cobalt oxide and LAGP, heated to 800 ° C. at a heating rate of 20 ° C./min in an argon stream, and held at 800 ° C. for 3 hours. The crucible was fired. The calcined pellets were crushed again in an agate mortar to prepare a sample for investigating changes in crystal structure.

(Comparative Example 8)
<Preparation of calcined samples of SMG and LAGP>
50 parts by mass of SMG and 50 parts by mass of LAGP were mixed in an agate mortar, and 1 g of the mixture was placed in a 15φ die and pressurized to form a disk-shaped pellet. The molded pellets are placed in an alumina crucible prepared on the left and laid with a mixture of SMG and LAGP, heated to 800 ° C at a heating rate of 20 ° C / min in an argon stream, held at 800 ° C for 3 hours, and fired. Was carried out. The calcined pellets were crushed again in an agate mortar to prepare a sample for investigating changes in crystal structure.

(Comparative Example 9)
<Preparation of calcined samples of lithium manganate and LLZ>
50 parts by mass of lithium manganate and 50 parts by mass of LLZ were mixed in an agate mortar, and 1 g of the mixture was placed in a 15φ die and pressurized to form a disk-shaped pellet. The molded pellets are placed in an alumina crucible prepared on the left and laid with a mixture of lithium manganate and LLZ, heated to 800 ° C at a heating rate of 20 ° C / min in an argon stream, and held at 800 ° C for 3 hours. The crucible was fired. The calcined pellets were crushed again in an agate mortar to prepare a sample for investigating changes in crystal structure.

(Comparative Example 10)
<Preparation of calcined samples of lithium titanate and solid electrolyte>
50 parts by mass of lithium titanate and 50 parts by mass of LLZ were mixed in an agate mortar, and 1 g of the mixture was placed in a 15φ die and pressurized to form a disk-shaped pellet. The molded pellets are placed in an alumina crucible prepared on the left and laid with a mixture of lithium titanate and LLZ, heated to 800 ° C at a heating rate of 20 ° C / min in an argon stream, and held at 800 ° C for 3 hours. Crucible firing was carried out. The calcined pellets were crushed again in an agate mortar to prepare a sample for investigating changes in crystal structure.

<Crystal structure analysis>
The crystal structure analysis was carried out as follows.
The powder samples prepared in Examples 4 and 5 and Comparative Examples 7 to 10 were subjected to crystal structure analysis using a powder X-ray diffractometer (D / teX Ultra2, manufactured by Rigaku). In the crystal structure analysis, changes in the powder X-ray diffraction peak before and after firing were observed, and those with no change in the crystal structure were rated as "none" and those with a change were rated as "yes". The evaluation results are shown in Table 1.

(evaluation)
<Electrochemical evaluation>
The electrochemical evaluation was carried out by the following method.

(Battery evaluation methods of Examples 1 to 3 and Comparative Examples 1 to 6)
Ten all-solid-state secondary batteries were evaluated. It was charged to 4.3V by the constant current method of 0.01C, and the average value of 10 pieces was calculated. After that, the average value was divided by the design capacity to obtain the capacity ratio. The evaluation results are shown in Table 2.
The evaluation was as follows.

A: Capacity rate 40% or more B: Capacity rate 20% or more and less than 40% C: Capacity rate 0% or more and less than 20% Among these, those with a capacity rate of A were considered as non-defective products.

The battery design capacity is shown in Table 3.

From Table 1, it was found that the crystal structures of the positive electrode active material, the negative electrode active material, and the oxide solid electrolyte LLZ did not change during firing, suggesting that the interfacial resistance did not increase (Examples 4 and 5). However, it was found that LAGP chemically reacted with the positive electrode active material and the negative electrode active material in firing to change the crystal structure, that is, to form an altered layer, suggesting that the interfacial resistance is increased. (Comparative Examples 7 and 8). Further, lithium manganate and lithium titanate chemically reacted with the solid electrolyte LLZ to change the crystal structure (Comparative Examples 9 and 10).
From the above, it was suggested that the batteries of Examples 1 to 3 using the solid electrolyte having a garnet-type crystal structure and graphite were good products.

From Table 2, since the battery of Comparative Example 1 does not have a composite of the active material, the ionic conductivity path formed by the active material and the solid electrolyte is not sufficient, and the compounding ratio of the active material and the solid electrolyte in the layer is the same. The result was that the battery performance was inferior to that of Example 1. Since the amount of the solid electrolyte in Comparative Example 2 was larger than that in Comparative Example 1, the ionic conductivity path formed by the active material and the solid electrolyte was large and the battery performance was B. However, as can be seen in Table 3, the implementation was carried out. There is a drawback that the energy density is low as compared with Examples 1 to 3.

From Table 3, it can be said that the batteries of Examples 1 to 3 have higher energy densities than the batteries of Comparative Example 2.
As described above, it was suggested that the compounding of particles contributes to the improvement of energy density and the improvement of battery performance, and it was confirmed that the present invention is effective in improving the performance of the all-solid-state secondary battery.

The present invention greatly contributes to the improvement of the performance of the all-solid-state secondary battery and can be widely used industrially.

1 Active material 2 Binder 3 Solid electrolyte 4 Composite particles 11 Negative electrode layer Green sheet 12 Solid electrolyte layer Green sheet 13 Positive electrode layer Green sheet 14 Metal foil current collector 16 Laminated green sheet 21 Negative electrode layer 22 Solid electrolyte layer 23 Positive electrode layer 26 All Solid secondary battery 34 Current collector provided after firing

Claims (13)

The positive electrode layer, the solid electrolyte layer using the oxide solid electrolyte, and the negative electrode layer containing the graphite negative electrode active material are laminated in this order and fired .
The positive electrode layer has a positive electrode active material coated with a solid electrolyte having a garnet-type crystal structure.
The graphite negative electrode active material is an all-solid secondary battery characterized in that it is coated with a solid electrolyte having a garnet-type crystal structure. The all-solid-state secondary battery according to claim 1, wherein the solid electrolyte having a garnet-type crystal structure is a composite oxide composed of at least Li, La, Zr, and O. The all-solid-state secondary battery according to claim 1 or 2, wherein at least one of the positive electrode layer and the negative electrode layer contains an electron conductive material serving as a conductive auxiliary agent. The all-solid-state secondary battery according to any one of claims 1 to 3, wherein the positive electrode active material has a layered rock salt structure. The all-solid state according to any one of claims 1 to 4, wherein a metal leaf current collector is provided on the surface of the positive electrode layer and the negative electrode layer that does not face the solid electrolyte layer. Secondary battery. The all-solid-state secondary battery according to claim 5, wherein at least one kind of material constituting the positive electrode layer and the negative electrode layer is fused with the metal leaf current collector. The solid electrolyte layer green sheet is sandwiched between the negative electrode layer green sheet containing the graphite negative electrode active material and the positive electrode layer green sheet.
The positive electrode layer green sheet has a positive electrode active material coated with a solid electrolyte having a garnet-type crystal structure, and has a positive electrode active material.
The graphite negative electrode active material is a laminated green sheet characterized in that it is coated with a solid electrolyte having a garnet-type crystal structure. The seventh aspect of claim 7, wherein the metal leaf current collector is provided on the surface of at least one of the negative electrode layer green sheet and the positive electrode layer green sheet that does not face the solid electrolyte layer green sheet. Laminated green sheet. The laminated green sheet according to claim 7 or 8, wherein the oxide solid electrolyte contained in the solid electrolyte layer green sheet is a solid electrolyte having a garnet-type crystal structure. The laminated green according to any one of claims 7 to 9, wherein the solid electrolyte having a garnet-type crystal structure is a composite oxide composed of at least Li, La, Zr and O. Sheet. The green sheet according to any one of claims 7 to 10, wherein at least one of the negative electrode layer green sheet and the positive electrode layer green sheet contains an electron conductive material serving as a conductive auxiliary agent. Laminated green sheet. The laminated green sheet according to any one of claims 7 to 11, wherein the positive electrode active material has a layered rock salt structure. Including the claims 7 to claim 12 or step of tempering formed a laminate green sheet according to one of method of the all-solid secondary battery.

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