JP2018206727A - All-solid battery - Google Patents

Abstract

To provide an all-solid battery in which the occurrence of peeling at the interface between a negative electrode active material and a solid electrolyte and between the negative electrode active material layer and a negative electrode current collector layer is suppressed even in a case in which a material having a large degree of expansion and shrinkage when Li ions are absorbed and released with charge and discharge is used as a negative electrode active material.SOLUTION: In an all-solid battery in which a negative electrode current collector layer 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector layer 5 are stacked in this order, the negative electrode active material layer 2 includes a negative electrode active material 2a and a solid electrolyte 2b, the solid electrolyte 2b is a sintered body having a void 2c, and the negative electrode active material 2a is disposed on a surface in contact with the void 2c of a solid electrolyte sintered body.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an all solid state battery.

  Various techniques for improving the charge / discharge characteristics of all-solid-state batteries have been studied.

For example, in Patent Document 1,
An all solid-state lithium ion battery in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are laminated in this order,
At least one of the positive electrode layer and the negative electrode layer is a sheet-like electrode in which an electrode active material layer containing a particulate electrode active material, a conductive resin layer, and a current collector layer are laminated in this order.
An all solid-state lithium ion battery is disclosed.

  Further, in Patent Document 1, the sheet-like electrode may be a negative electrode layer, the negative electrode active material in this case may be tin, tin alloy, silicon, silicon alloy, and the like, and the electrode active material layer is It is described that an oxide solid electrolyte material may be further contained.

  In Patent Document 2, as a negative electrode active material for a secondary battery that can have sufficient capacity and good cycle characteristics, a matrix composed of an oxide solid electrolyte, and specific Si particles dispersed in the matrix , A negative electrode active material for a secondary battery made of a Si-oxide solid electrolyte composite.

JP 2014-93156 A JP 2014-22319 A

  A material containing tin, silicon, or the like is used as an anode active material in an all-solid battery, specifically, a lithium all-solid battery. These materials expand and contract greatly when absorbing and releasing Li ions with charge and discharge. Therefore, an all solid state battery using a negative electrode active material containing such a material is charged and discharged at the interface between the negative electrode active material and the solid electrolyte, the interface between the negative electrode active material layer and the negative electrode current collector layer, and the like. There is a problem that peeling occurs.

  The present invention has been made to solve the above problems. Therefore, the object of the present invention is to use a negative electrode active material, a solid electrolyte, an interface, and a negative electrode active material, even when a material having a large degree of expansion and contraction when absorbing and releasing Li ions with charge and discharge is used. An object of the present invention is to provide an all-solid battery in which the occurrence of peeling at the interface between the negative electrode active material layer and the negative electrode current collector layer is suppressed.

The present invention
(1) An all-solid battery in which a negative electrode current collector layer, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are laminated in this order,
The negative electrode active material layer includes a negative electrode active material and a solid electrolyte,
The solid electrolyte is a sintered body having voids,
The negative electrode active material is disposed on a surface in contact with the void of the solid electrolyte sintered body,
It relates to an all-solid-state battery.

  Examples of non-limiting preferred embodiments of the present invention are shown below.

(2) The all-solid-state battery according to (1), wherein a porosity in the negative electrode active material layer is 10 to 50% by volume.
(3) The all-solid-state battery according to (1) or (2), wherein the negative electrode active material of the negative electrode active material layer is an active material alloyed with lithium.
(4) The all-solid-state battery according to (3), wherein the negative electrode active material contains one or more atoms of silicon and tin.
(5) Any of the above (1) to (4), wherein the negative electrode active material layer is composed of a plurality of layers, and the diameter of the void decreases from a layer closer to the solid electrolyte layer to a layer farther from the layer. Or an all solid state battery.
(6) The negative electrode active material layer is composed of a plurality of layers, and the content ratio of the negative electrode active material increases from the layer closer to the solid electrolyte layer to the layer farther from the above (1) to (5) ) All-solid battery according to any one of the above.
(7) The all-solid-state battery according to any one of (1) to (6), wherein the voids in the negative electrode active material layer are continuous from the solid electrolyte layer to the negative electrode current collector layer.
(8) The method for producing an all-solid battery according to any one of (1) to (7) above,
Attaching the negative electrode active material to the surface of the pore former;
Forming a negative electrode active material layer green sheet containing the pore former to which the negative electrode active material is adhered and the solid electrolyte, and firing the negative electrode active material layer green sheet,
In the firing process of the negative electrode active material layer green sheet, the solid electrolyte is sintered and the pore former is removed to place the negative electrode active material on the surface of the solid electrolyte sintered body in contact with the gap. Let
Manufacturing method of all solid state battery.

  The all solid state battery of the present invention has an interface between the negative electrode active material and the solid electrolyte and the interface between the negative electrode active material layer and the negative electrode current collector layer even when the negative electrode active material greatly expands and contracts with charge and discharge. The occurrence of peeling is suppressed.

FIG. 1 is a schematic cross-sectional view for explaining an example of the structure of the negative electrode active material layer in the all solid state battery of the present invention. FIG. 2 is a schematic cross-sectional view for explaining another example of the structure of the negative electrode active material layer in the all solid state battery of the present invention. FIG. 3 is a schematic cross-sectional view for explaining yet another example of the structure of the negative electrode active material layer in the all solid state battery of the present invention. FIG. 4A is a schematic cross-sectional view for explaining yet another example of the structure of the negative electrode active material layer in the all solid state battery of the present invention. FIG. 4B is a schematic cross-sectional view for explaining yet another example of the structure of the negative electrode active material layer in the all solid state battery of the present invention. FIG. 5 is a conceptual diagram for explaining an example of a method for manufacturing the all solid state battery shown in FIG. 4A. 6 is an SEM image of the negative electrode active material layer of the battery laminate obtained in Example 1. FIG. FIG. 6A is a secondary electron image, and FIG. 6B is a reflected electron image. FIG. 7 is an SEM image of the negative electrode active material layer of the battery laminate obtained in Comparative Example 1. FIG. 7A is a secondary electron image, and FIG. 7B is a reflected electron image. FIG. 8 is a diagram showing the stress in the x direction when the Si layer expands in the stacked body of the Si layer and the electrolyte layer. FIG. 9 is a graph comparing the stress applied by the expansion of the negative electrode active material layer between the case where the negative electrode active material layer of the negative electrode active material layer is a dense layer and the case where the layer is a layer having voids.

The all solid state battery of the present invention is
A negative electrode current collector layer, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are all solid-state batteries laminated in this order,
The negative electrode active material layer includes a negative electrode active material and a solid electrolyte,
The solid electrolyte is a sintered body having voids,
The negative electrode active material particles are disposed on a surface in contact with the voids of the solid electrolyte sintered body,
It is an all-solid-state battery.

<All solid battery>
The all-solid battery of the present invention is an all-solid secondary battery, and may be, for example, a lithium battery. As long as the above configuration is adopted, the specific form of the all solid state battery of the present invention is arbitrary. Specific embodiments of the all solid state battery of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following specific embodiments.

<All-solid battery of the first embodiment>
The typical structure of the all-solid-state battery according to the first embodiment of the present invention is shown in the upper diagram of FIG. 1 as a schematic cross-sectional view. The all-solid battery shown in the upper diagram of FIG. 1 includes a negative electrode current collector layer 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector layer 5 stacked in this order. Is the body.

<Negative electrode active material layer>
The lower diagram of FIG. 1 is a partially enlarged sectional view showing the negative electrode active material layer 2 and the vicinity thereof in the upper diagram of FIG. In the lower diagram of FIG. 1, the negative electrode active material layer 2 includes a negative electrode active material 2a and a solid electrolyte 2b. The solid electrolyte 2b is a sintered body having a void 2c, and the negative electrode active material 2a is disposed on a surface in contact with the void 2c of the solid electrolyte 2b.

  In the all solid state battery having such a structure, the negative electrode active material 2a in the negative electrode active material layer 2 can expand in the direction of the gap 2c when it expands with charging. Therefore, it is possible to suppress excessive stress from being applied to the negative electrode current collector layer 1 and the solid electrolyte layer 3 that are in contact with the negative electrode active material layer 2 during charging. It is possible to highly suppress the peeling of the interface of the layer to be performed.

[Negative electrode active material]
The negative electrode active material 2a can be comprised from a well-known material as a negative electrode active material for all-solid-state batteries. This negative electrode active material 2a expands by storing Li ions during charging, and contracts by releasing Li ions during discharging. Specifically, the negative electrode active material 2a may be a material containing one or more atoms of silicon, tin, and the like, for example.

  The material containing a silicon atom may be a known material, and examples thereof include silicon, silicon oxide, silicon carbide, silicon nitride, silicon-containing alloy, and solid solutions thereof. Some of the silicon atoms contained in these may be substituted with one or more other atoms.

Examples of the silicon oxide include silicon oxide represented by the composition formula: SiO _a (0.05 <a <1.95). Examples of silicon carbide include silicon carbide represented by the composition formula: SiC _b (0 <b <1). Examples of the silicon nitride include silicon nitride represented by a composition formula: SiN _c (0 <c <4/3). Examples of the silicon-containing alloy include alloys of silicon and atoms other than silicon. Examples of atoms other than silicon include Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. Atoms other than silicon can be used alone or in combination of two or more.

  Examples of the material containing tin atoms include tin, tin oxide, tin nitride, tin-containing alloy, and solid solutions thereof. Some of the tin atoms contained therein may be substituted with one or more other atoms.

Examples of the tin oxide include tin oxide represented by the composition formula: SnO _d (0 <d <2), tin dioxide (SnO ₂ ), and the like. Examples of the tin-containing alloy include a Ni—Sn alloy, a Mg—Sn alloy, a Fe—Sn alloy, a Cu—Sn alloy, and a Ti—Sn alloy. Examples of the tin compound include SnSiO ₃ , Ni ₂ Sn ₄ , and Mg ₂ Sn.

  Among the above materials, silicon, silicon oxide, tin, tin oxide and the like are preferable, and silicon, silicon oxide and the like are particularly preferable. These materials can be used individually by 1 type or in combination of 2 or more types.

  The negative electrode active material 2a may be particulate. The average particle diameter of the negative electrode active material 2a in the form of particles is, for example, 10 nm or more and 20 nm or more as the median diameter from the viewpoint of effectively expressing the stress reduction effect due to the gap 2c when the negative electrode active material 2a expands. , 30 nm or more, 40 nm or more, or 50 nm or more. On the other hand, the median diameter of the negative electrode active material 2a is, for example, 500 nm or less, 400 nm or less, or 300 nm or less from the viewpoint of maintaining the density of the negative electrode active material layer 2 high and ensuring the handleability at the time of manufacturing an all-solid battery. , 200 nm or less, or 100 nm or less.

  The negative electrode active material 2a is disposed on the surface of the solid electrolyte sintered body in which the void 2c is formed, in contact with the void 2c. By disposing the negative electrode active material 2a on the surface in contact with the gap 2c of the solid electrolyte 2b, the negative electrode active material 2a can expand in the direction of the gap 2c during charging, and the negative electrode active material 2a expands. Generation of stress in the negative electrode active material layer 2 due to is suppressed.

  The phrase “the negative electrode active material 2a is“ disposed on the surface in contact with the gap 2c of the solid electrolyte 2b ”” means that, for example, the negative electrode active material 2a is in contact with the solid electrolyte 2b and in contact with the gap 2c. The negative electrode active material 2a is preferably a single layer, but some overlap may exist. The negative electrode active material 2a may be a layer composed of a continuous film of the negative electrode active material 2a. Typically, the particulate negative electrode active material 2a is scattered, adjacent to, or continuously present on the surface of the solid electrolyte 2b in contact with the gap 2c. The negative electrode active material 2a is in contact with and bound to the solid electrolyte 2b. The negative electrode active material 2a is preferably present only on the surface in contact with the gap 2c of the solid electrolyte 2b. However, the presence of a part of the negative electrode active material 2a inside the solid electrolyte 2b is allowed as long as the effect of the present invention is effectively exhibited. The negative electrode active material 2a present inside the solid electrolyte 2b is preferably 20% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less of the total negative electrode active material 2a.

[Solid electrolyte]
The solid electrolyte 2b is a sintered body having voids 2c.

  The material constituting the solid electrolyte 2b may be any known solid electrolyte material used for an all-solid battery. It may be a Li ion conductor in an all-solid battery, and may be crystalline or glass material, and may be, for example, an oxide solid electrolyte. The oxide solid electrolyte is preferable because it has reduction resistance to Li ions. Examples of the oxide solid electrolyte include a garnet-type oxide solid electrolyte and a perovskite-type oxide solid electrolyte. Of these, a garnet-type oxide solid electrolyte is particularly preferable because of its high Li ion conductivity.

The garnet-type oxide solid electrolyte has, for example, a basic formula Li _{5 + x} La ₃ Zr _x A _2−x O ₁₂ (where A is Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga) And one or more kinds of atoms selected from the group consisting of Ge, and x is a number of 1.4 or more and less than 2. The above basic formula Li _{5 + x} La ₃ Zr _x A _2−x O ₁₂ may not have a stoichiometric composition, may be partially missing, may be excessive, or may be one of the constituent atoms. The part may be substituted with another atom.

As the composition of the garnet-type oxide solid electrolyte, since Li ion conductivity is high, for example, Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li It may be ₅ La ₃ Ta ₂ O ₁₂ , Li ₅ La ₃ Nb ₂ O _12, etc., but is not limited thereto.

  The solid electrolyte 2b of the negative electrode active material layer 2 in the present embodiment is composed of a sintered body and forms voids (described later).

[Abundance ratio of negative electrode active material and solid electrolyte]
The existence ratio of the negative electrode active material 2a to the solid electrolyte 2b in the negative electrode active material layer 2 is to form a sintered body network having high ion conductivity in order to sufficiently increase the ionic conductivity of the negative electrode active material layer 2. From this viewpoint, the mass ratio of the solid electrolyte 2b to the negative electrode active material 2a of 100 parts by mass may be 50 parts by mass, 80 parts by mass, 100 parts by mass, or 120 parts by mass. On the other hand, from the viewpoint of making the output of the obtained all-solid battery sufficiently high, the mass ratio of the solid electrolyte 2b to 100 parts by mass of the negative electrode active material 2a is 200 parts by mass or less, 180 parts by mass or less, 160 parts by mass. Or less than or equal to 150 parts by weight.

[Void]
As described above, the solid electrolyte 2b in the negative electrode active material layer of the present embodiment is composed of a solid electrolyte sintered body. The solid electrolyte forms a skeleton of the negative electrode active material layer by forming a sintered body, and has voids 2c. The voids in the negative electrode active material layer may be dispersed throughout the negative electrode active material layer 2 as shown in the lower diagram of FIG.

  The porosity of the negative electrode active material layer 2 is, for example, 10% by volume or more, 20% by volume or more, 30% by volume or more, or 40% by volume or more from the viewpoint of effectively expressing the stress reduction effect due to the gap 2c. It's okay. On the other hand, from the viewpoint of maintaining the mechanical strength of the negative electrode active material layer 2 and increasing the output of the all solid state battery, the porosity of the negative electrode active material layer 2 is, for example, 50% by volume or less, 40% by volume or less. 30 volume% or less, 20 volume% or less, 15 volume% or less, and 10 volume% or less. Here, the porosity of the negative electrode active material layer 2 is the ratio of the total volume of the voids 2 c to the total volume of the negative electrode active material layer 2. The total volume of the voids 2 c is the remaining volume obtained by subtracting the total volume of the solid electrolyte 2 b and the negative electrode active material 2 a from the total volume of the negative electrode active material layer 2.

  The shape of the gap 2c is arbitrary, for example, from a substantially spherical shape, a substantially spheroid shape, a columnar shape, a conical shape, a polygonal columnar shape, a polygonal pyramid shape, an indefinite shape, and a combination of two or more thereof. May be selected.

  From the viewpoint of effectively expressing the stress reduction effect by the gap 2c, and from the viewpoint of effectively disposing the negative electrode active material 2a on the surface in contact with the gap 2c, the gap when the negative electrode active material 2a is in the form of particles The average diameter of 2c is, for example, 0.5 times or more, 1 time or more, 2 times or more, 3 times or more, 4 times or more, 5 times or more, or 8 times based on the average diameter of the particles of the negative electrode active material 2a. It may be above. On the other hand, from the viewpoint of maintaining the mechanical strength of the negative electrode active material layer 2 and ensuring high ionic conductivity, the average diameter of the voids 2c when the negative electrode active material 2a is particulate is the particle size of the negative electrode active material 2a. For example, the average diameter may be 20 times or less, 10 times or less, 8 times or less, or 5 times or less. The average diameter of the gap 2c may vary depending on the position in the negative electrode layer, and the average diameter of the gap 2c is the average particle of the negative electrode active material 2a as long as it is far from the solid electrolyte layer 3 of the negative electrode layer 2. For example, the diameter may be 2 times or less, 1 time or less, or 0.5 times or less.

  The average diameter of the air gap 2c may be evaluated as the number average diameter of an equivalent circle by electron microscope observation. The average diameter of the air gap 2c is determined by observing the outline of the air gap for 30 or more, preferably 50 or more air gaps arbitrarily selected from one or a plurality of fields of view by observation with an electron microscope. It can be obtained as an average value of the diameter of the equivalent circle. The average diameter of the gap 2c may be, for example, 0.5 μm or more, 1.0 μm or more, 1.5 μm or more, or 2.0 μm or more, for example, 5.0 μm or less, 4.5 μm or less, or 4.0 μm. It may be the following.

<Negative electrode current collector layer>
The negative electrode current collector layer 1 in the all solid state battery of the present embodiment may have a known configuration. As a material constituting the negative electrode current collector layer 1, for example, a foil made of SUS, Cu, Ni, Fe, Ti, Co, Zn, or the like can be used.

<Solid electrolyte layer>
The solid electrolyte layer 3 may have a known configuration and may contain a solid electrolyte. The solid electrolyte may be, for example, an oxide solid electrolyte, a sulfide solid electrolyte, or the like.

<Positive electrode active material layer>
The positive electrode active material layer 4 may have a known configuration and may contain a positive electrode active material. The positive electrode active material may be selected from known positive electrode active materials such as lithium cobaltate (LiCoO ₂ ).

<Positive electrode current collector layer>
The positive electrode current collector layer 5 may have a known configuration. As a material constituting the positive electrode current collector layer 5, for example, a foil made of stainless steel (SUS), Ni, Cr, Au, Pt, Al, Fe, Ti, Zn, or the like can be used.

<The manufacturing method of the all-solid-state battery of 1st Embodiment>
The all-solid-state battery of 1st Embodiment may be manufactured by the following method, for example.

Attaching a negative electrode active material to the surface of the pore former;
Forming a negative electrode active material layer green sheet containing the pore former to which the negative electrode active material is adhered and the solid electrolyte, and firing the negative electrode active material layer green sheet,
In the firing process of the negative electrode active material layer green sheet, the solid electrolyte is sintered and the pore former is removed to place the negative electrode active material on the surface of the solid electrolyte sintered body in contact with the gap. Let
Manufacturing method of all solid state battery.

  In the negative electrode active material layer green sheet, the pore former, the negative electrode active material attached to the surface of the pore former, and the solid electrolyte may all be in the form of particles.

[Negative electrode active material layer green sheet]
The negative electrode active material layer green sheet includes a pore former having negative electrode active material particles attached to the periphery thereof and solid electrolyte particles, and may optionally further include an organic binder, a plasticizer, and the like.

  The pore former in which the negative electrode active material particles are adhered to the periphery of the negative electrode active material layer green sheet can be obtained, for example, by bringing a particulate pore former and a particulate negative electrode active material into contact with each other. .

  The pore former burns and disappears when the laminate is fired, and has a function of forming voids 2 c in the sintered body network of the solid electrolyte 2 b in the negative electrode active material layer 2. Therefore, the pore former may be made of a material that exists in the form of particles occupying a certain volume in the negative electrode active material layer green sheet and burns and disappears by firing. Such a material may be, for example, crosslinked organic polymer particles.

  The crosslinked organic polymer particles as the pore former may be particles composed of, for example, a crosslinked acrylic resin, crosslinked polystyrene, a crosslinked acrylic-styrene copolymer, and a mixture thereof. The cross-linked acrylic resin may be, for example, cross-linked polymethyl methacrylate. The crosslinked acrylic-styrene copolymer may be, for example, a crosslinked product of methyl methacrylate-styrene copolymer.

  By appropriately adjusting the particle diameter of the pore former, the size of the formed gap 2c can be controlled. Since the solid electrolyte particles in the negative electrode active material layer green sheet shrink when forming a sintered body in the firing step described later, the size of the void formed after firing is the pore formation in the negative electrode active material layer green sheet. It becomes smaller than the particle size of the material. Therefore, the particle diameter of the pore former may be larger than the desired size of the gap 2c. Quantitatively, the particle diameter of the pore former is, for example, 1 or more, 1.1 or more, 1.2 or more, 1.3 or more, or 1 with respect to the average diameter of the desired void 2c. For example, it may be 3.0 times or less, 2.9 times or less, 2.8 times or less, 2.7 times or less, or 2.6 times or less.

  The average diameter of the negative electrode active material particles may be substantially the same as the desired average diameter when the negative electrode active material 2a in the negative electrode active material layer 2 is in the form of particles.

  It is appropriate that the amount of the negative electrode active material particles around the pore former is an amount that the negative electrode active material particles cover the pore former in one layer or an amount close thereto. Quantitatively, the amount of the negative electrode active material particles is, for example, 0.5 times or more, 0.6 times or more, and 0.7 times the amount of the negative electrode active material particles covering the periphery of the pore former. For example, it may be 2.0 times or less, 1.5 times or less, 1.4 times or less, 1.3 times or less, or 1.2 times or less.

  The solid electrolyte particles in the negative electrode active material layer green sheet may be particles composed of a material selected from a desired solid electrolyte material in the negative electrode active material layer 2, for example, for lithium described above It may be a particle composed of a solid oxide having resistance to reduction. The average particle diameter of the solid electrolyte particles may be, for example, 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, 0.8 μm or more, or 1.0 μm or more as a median diameter. On the other hand, for example, it may be 10 μm or less, 8 μm or less, 5 μm or less, or 3 μm or less.

  The organic binder in the negative electrode active material layer green sheet binds the components in the negative electrode active material layer green sheet to each other, but is a component that is expected to burn and disappear when the laminate is fired. . Furthermore, from the viewpoint of appropriately controlling the diameter of the void 2c in the negative electrode active material layer 2, it is desirable that the organic binder does not leave a significant void in the negative electrode active material layer 2 even after disappearance by firing. Such an organic binder may be, for example, a non-crosslinked organic polymer. The non-crosslinked organic polymer may be composed of, for example, an acrylic resin, polystyrene, an acrylic-styrene copolymer, a fluorine atom-containing resin, and a mixture thereof. The acrylic resin may be, for example, polymethyl methacrylate. The acrylic-styrene copolymer may be, for example, methyl methacrylate-styrene copolymer. The fluorine atom-containing resin may be, for example, polyvinylidene fluoride.

  The plasticizer in the negative electrode active material layer green sheet has a function of imparting flexibility to the negative electrode active material layer green sheet and facilitating the production of the all solid state battery of the present embodiment. Such a plasticizer may be, for example, a polyvalent carboxylic acid ester or a low molecular weight polyester. Polyvalent carboxylic acid esters include, for example, phthalic acid esters such as dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, dibutyl phthalate, and butyl phthalate; adipic acid esters such as dioctyl adipate and diisononyl adipate; trimellitic acid Trimellitic acid esters such as trioctyl; citric acid esters such as tributyl acetylcitrate may be used.

  The negative electrode active material layer green sheet may be prepared by mixing the above-described components and forming into a sheet shape. Specifically, the negative electrode active material layer green sheet is prepared by, for example, applying a slurry obtained by adding and mixing each of the above components to a suitable solvent on a suitable substrate film, and then removing the solvent by heating. It may be produced by the method of: At this time, the anode active material particles and pore former particles are premixed and then mixed with other components, whereby pore former particles having active material particles attached thereto can be easily formed, which is preferable. .

  The solvent of the slurry may be a polar solvent, and may be composed of, for example, one or more selected from water, 1-butanol, 2-butanol, acetic acid, N, N-dimethylformamide, dimethyl sulfoxide, and the like.

  The base film may be a resin film having flexibility, for example, a film made of polyester, polyolefin, or the like. Here, the polyester may be, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or the like, and the polyolefin may be, for example, polyethylene, polypropylene, or the like.

  Prior to applying the slurry, an appropriate release agent may be applied on the base film.

[Solid electrolyte layer green sheet]
The solid electrolyte layer green sheet includes a solid electrolyte, and may optionally further include an organic binder, a plasticizer, and the like.

[Positive electrode active material layer green sheet]
The positive electrode active material layer green sheet includes a positive electrode active material, and may optionally further include a solid electrolyte, an organic binder, a plasticizer, and the like.

[Thickness of each green sheet]
The thickness of each green sheet may be appropriately set according to the desired thickness of each layer in the all solid state battery.

[Lamination and firing]
For example, the negative electrode active material layer green sheet, the solid electrolyte layer green sheet, and the positive electrode active material layer green sheet described above are laminated in this order to obtain a green sheet laminate. And after baking this green sheet laminated body, the negative electrode collector layer is laminated | stacked on the negative electrode active material layer side, and the positive electrode collector layer is laminated | stacked on the positive electrode active material layer side, The all-solid-state battery of this embodiment Can be obtained. The green sheets of each layer, the negative electrode current collector layer, and the positive electrode current collector layer may be fired after being previously laminated in a desired lamination order.

  When the green sheet has a base film, the lamination may be performed while peeling the base film.

  The green sheet laminate may be fired after being pressed. By pressing the green sheet laminate, the adhesion between the layers can be improved, and more excellent battery performance is exhibited. The laminate may be heated during pressing.

  The firing temperature of the green sheet laminate is such that the pore-forming material in the negative electrode active material layer green sheet is surely burned and disappeared to obtain a desired void, and the solid electrolyte in the negative electrode active material layer green sheet is fired. From the viewpoint of forming a knot, it may be, for example, 300 ° C or higher, 400 ° C or higher, 500 ° C or higher, 600 ° C or higher, or 700 ° C or higher. On the other hand, from the viewpoint of avoiding unnecessary annealing of each component in the obtained negative electrode active material layer and ensuring excellent battery performance, the firing temperature of the green sheet laminate is, for example, 1,500 ° C. or less, 1,400 It may be at most 0 ° C, at most 1,300 ° C, or at most 1,200 ° C.

  From the same viewpoint, the firing time may be 10 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 5 hours or more, or 8 hours or more, 48 hours or less, 24 hours or less, 20 hours or less, It may be 18 hours or less, or 15 hours or less.

  The ambient atmosphere when the green sheet laminate is fired can be an oxidizing atmosphere from the viewpoint that the pore former in the negative electrode active material layer green sheet surely burns and disappears, and a desired void should be obtained. For example, it may be firing in air.

<All Solid Battery of Second Embodiment>
A typical structure of a negative electrode active material layer in an all solid state battery according to another embodiment of the present invention is shown in FIG. 2 as a schematic cross-sectional view. The all solid state battery including the negative electrode active material layer 2 shown in FIG. 2 includes a negative electrode current collector layer 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector layer 5. The negative electrode active material layer 2 includes a negative electrode active material 2a and a solid electrolyte 2b, the solid electrolyte 2b is a sintered body having voids 2c, and the negative electrode active material 2a is voids 2c. It is the same as that of the all-solid-state battery of 1st Embodiment to arrange | position to the surface which touches.

  However, the negative electrode active material layer 2 in FIG. 2 is composed of a plurality of layers, and the diameter of the gap 2c decreases from the layer closer to the solid electrolyte layer 3 to the layer farther from the layer.

  Specifically, the negative electrode active material layer 2 of FIG. 2 includes a negative electrode active material first layer 2 (1) and a negative electrode active material second layer 2 (2). The negative electrode active material first layer 2 (1) is in contact with the solid electrolyte layer 3. The negative electrode active material second layer 2 (2) is adjacent to the negative electrode active material first layer 2 (1) in the stacking direction and is in contact with the negative electrode current collector layer 1. The diameter of the gap 2c in the negative electrode active material second layer 2 (2) is smaller than the diameter of the gap 2c in the negative electrode active material first layer 2 (1).

  In the negative electrode active material first layer 2 (1) close to the solid electrolyte layer 3, the Li ion concentration is relatively high, and it is considered that the negative electrode active material 2 a due to charging has a large expansion coefficient. Therefore, in the negative electrode active material first layer 2 (1), it is desirable to increase the diameter of the gap 2c so that the high rate expansion of the negative electrode active material 2a can be relaxed.

  On the other hand, in the negative electrode active material second layer 2 (2) close to the negative electrode current collector layer 1, the Li ion concentration is relatively low and the expansion coefficient of the negative electrode active material 2a due to charging is considered to be small. The diameter of 2c may be small. Furthermore, when the diameter of the gap 2c is reduced, the contact area between the negative electrode active material layer 2 and the negative electrode current collector layer 1 can be increased, and the electrical resistance at the interface between the two layers can be reduced.

[Anode active material first layer]
The configuration of the negative electrode active material first layer 2 (1) may be the same as the configuration of the negative electrode active material layer 2 of the all solid state battery of the first embodiment.

[Second layer of negative electrode active material]
The abundance ratio of the negative electrode active material 2a and the solid electrolyte 2b in the negative electrode active material second layer 2 (2) may be the same as the configuration of the negative electrode active material layer 2 of the all solid state battery of the first embodiment.

  The porosity of the negative electrode active material second layer 2 (2) may be set to be relatively small, for example, may be 5% by volume or more, 10% by volume or more, or 15% by volume or more, for example, 40% by volume. % Or less, 30 volume% or less, or 20 volume% or less.

  The average diameter of the voids 2c in the negative electrode active material second layer 2 (2) is, for example, 1/20 or more, 1/18 or more as a relative value based on the thickness of the negative electrode active material second layer 2 (2). Or 1/16 or more, for example, 1/5 or less, 1/8 or less, or 1/10 or less. The quantitative value of the average diameter of the voids 2c in the negative electrode active material second layer 2 (2) is, for example, 0.3 μm or more, 0.5 μm or more, 0.8 μm or more, or 1. For example, it may be 3.0 μm or less, 3.5 μm or less, or 2.0 μm or less.

  When the negative electrode active material 2a in the negative electrode active material second layer 2 (2) is in the form of particles, the average particle diameter is from the viewpoint of ensuring contact with the relatively small-diameter voids 2c. It may be set smaller than in 2 (1). The average particle diameter of the particles of the negative electrode active material 2a in the negative electrode active material second layer 2 (2) may be, for example, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, or 25 nm or more as the median diameter. 250 nm or less, 200 nm or less, 150 nm or less, 100 nm or less, or 50 nm or less.

  The average diameter of the voids 2c in the negative electrode active material second layer 2 (2) is, for example, 2 times or more and 3 times based on the average particle diameter of the negative electrode active material 2a in the negative electrode active material second layer 2 (2). The number may be 4 times or more, or 5 times or more, for example, 20 times or less, 15 times or less, 12 times or less, or 10 times or less.

[Thickness of each layer of negative electrode active material]
The relationship between the thickness of the negative electrode active material first layer 2 (1) and the thickness of the negative electrode active material second layer 2 (2) is that of the negative electrode active material first layer 2 (1) with respect to the total thickness of both layers. The thickness ratio may be, for example, 50% or more, 60% or more, or 70% or more, for example, 90% or less, 85% or less, or 80% or less.

<The manufacturing method of the all-solid-state battery of 2nd Embodiment>
The all solid state battery of the second embodiment is, for example, the negative electrode active material layer green sheet in the method for producing the all solid state battery of the first embodiment, and the average diameter of each of the particulate negative electrode active material and the pore former, and the sheet. It may be manufactured by a method using two green sheets having different thicknesses.

<All-solid-state battery of 3rd Embodiment>
A typical structure of a negative electrode active material layer in an all solid state battery of still another embodiment of the present invention is shown in FIG. 3 as a schematic cross-sectional view. The all-solid battery including the negative electrode active material layer shown in FIG. 3 includes the negative electrode current collector layer 1, the negative electrode active material layer 2, the solid electrolyte layer 3, the positive electrode active material layer 4, and the positive electrode current collector layer 5. The negative electrode active material layer 2 includes a negative electrode active material 2a and a solid electrolyte 2b, the solid electrolyte 2b is a sintered body having voids 2c, and the negative electrode active material 2a is voids. It is the same as that of the all-solid-state battery of 1st Embodiment and 2nd Embodiment to arrange | position to the surface which touches 2c.

  However, the negative electrode active material layer 2 in FIG. 3 is composed of a plurality of layers, and the content ratio of the negative electrode active material 2a may increase from a layer closer to the solid electrolyte layer 3 to a layer farther from the layer. Also, the negative electrode active material layer 2 in FIG. 3 is composed of a plurality of layers, and the diameter of the gap 2c decreases from a layer closer to the solid electrolyte layer 3 to a layer farther from the layer.

  3 includes a negative electrode active material first layer 2 (1) and a negative electrode active material second layer 2 (2), and further includes a negative electrode active material third layer 2 (3). )including. The negative electrode active material first layer 2 (1) is in contact with the solid electrolyte layer 3. The negative electrode active material second layer 2 (2) and the negative electrode active material third layer 2 (3) are stacked in this order adjacent to the negative electrode active material first layer 2 (1) in the stacking direction. The third material layer 2 (3) is in contact with the negative electrode current collector layer 1.

[Negative electrode active material first layer and negative electrode active material second layer]
The configurations of the negative electrode active material first layer 2 (1) and the negative electrode active material second layer 2 (2) are respectively the negative electrode active material first layer 2 (1) in the negative electrode active material layer of the all-solid-state battery of the second embodiment. ) And the negative electrode active material second layer 2 (2). The content ratio of the negative electrode active material 2a in the negative electrode active material second layer 2 (2) is preferably set higher than the content ratio of the negative electrode active material 2a in the negative electrode active material second layer 2 (1).

[Negative electrode active material third layer]
The negative electrode active material third layer 2 (3) functions as a bonding layer for reducing the electrical resistance between the negative electrode active material layer 2 and the negative electrode current collector layer 1 and further improving battery performance. In order to develop the function as the bonding layer, the content of the negative electrode active material 2a having conductivity in the negative electrode active material third layer 2 (3) is set to be equal to that of the negative electrode active material first layer 2 (1) and the negative electrode. It is desired to set the content ratio of the negative electrode active material 2a in the active material second layer 2 (2) higher, that is, to set the ratio of the solid electrolyte 2b that is an insulator to the negative electrode active material 2a low.

  Specifically, in the negative electrode active material third layer 2 (3), the mass ratio of the solid electrolyte 2b to 100 parts by mass of the negative electrode active material 2a is 70 parts by mass or less, 50 parts by mass or less, or 30 parts by mass or less. It may be. However, from the viewpoint of ensuring ion conductivity in the negative electrode active material third layer 2 (3), the mass ratio of the solid electrolyte 2b to 100 parts by mass of the negative electrode active material 2a may be 50 parts by mass or more.

  The other aspects of the negative electrode active material third layer 2 (3) may be the same as those of the negative electrode active material first layer 2 (1) and the negative electrode active material second layer 2 (2).

[Thickness of each layer of negative electrode active material]
In the all-solid-state battery of the third embodiment, the relationship between the thickness of the negative electrode active material first layer 2 (1) and the thickness of the negative electrode active material second layer 2 (2) is the negative electrode with respect to the total thickness of both layers. The thickness ratio of the active material first layer 2 (1) may be, for example, 50% or more, 60% or more, or 70% or more, for example, 90% or less, 85% or less, or 80% or less. It may be.

  The thickness of the negative electrode active material third layer 2 (3) in the all solid state battery of the third embodiment is the same as the thickness of the negative electrode active material first layer 2 (1) and the thickness of the negative electrode active material second layer 2 (2). And the ratio of the thickness of the negative electrode active material third layer 2 (3) to the total thickness of the negative electrode active material third layer 2 (3) is, for example, 1% or more, 5% or more, or 8% or more For example, it may be 20% or less, or 15% or less.

<The manufacturing method of the all-solid-state battery of 3rd Embodiment>
The all solid state battery of the third embodiment is, for example, in the manufacturing method of the all solid state battery of the first embodiment, as a negative electrode active material layer green sheet, the average diameter, composition ratio, and thickness of each component such as a pore former It may be manufactured by a method using three types of green sheets having different values.

<All Solid Battery of Fourth Embodiment>
A typical structure of a negative electrode active material layer of an all solid state battery according to still another embodiment of the present invention is shown in FIG. 4A as a schematic cross-sectional view. The all-solid-state battery of 4th Embodiment is a laminated body which has the negative electrode collector layer 1, the negative electrode active material layer 2, the solid electrolyte layer 3, the positive electrode active material layer 4, and the positive electrode collector layer 5 in this order. In addition, the negative electrode active material layer 2 includes a negative electrode active material 2a and a solid electrolyte 2b, the solid electrolyte 2b is a sintered body having voids 2c, and the negative electrode active material 2a is disposed on a surface in contact with the voids 2c. It is the same as that of the all-solid-state battery of 1st Embodiment-3rd Embodiment.

  However, in the all solid state battery of the fourth embodiment, the gap 2 c is continuous from the solid electrolyte layer 3 to the negative electrode current collector layer 1. The gap 2c may be continuous in parallel with the stacking direction of the all solid state battery, or may be continued obliquely with respect to the stacking direction of the all solid state battery.

  4A (b) is a cross-sectional view taken along line AA of FIG. 4A (a). The gap 2c in the all solid state battery of the fourth embodiment may be formed in a stripe shape as shown in FIG. 4A (b) when viewed from the stacking direction. That is, the plate-shaped solid electrolyte 2b having the negative electrode active material 2a on both surfaces of the plate-shaped solid electrolyte 2b, and the surface of the plate-shaped solid electrolyte 2b having the negative electrode active material 2a on it, The negative electrode active material layer 2 may be configured by extending from the electrolyte layer 3 to the negative electrode current collector layer 1 and arranging a plurality of plate-like solid electrolytes 2b in parallel.

  FIG. 4B is a schematic cross-sectional view of the all solid state battery according to another aspect of the fourth embodiment, viewed from the same direction as FIG. 4A (b). In the all solid state battery according to another aspect of the fourth embodiment, the gap 2c is continuous from the solid electrolyte layer 3 to the negative electrode current collector layer 1 as in the all solid state battery of the fourth embodiment shown in FIG. 4A. However, as shown in FIG. 4B, the gap 2c in the negative electrode active material layer 2 of the all-solid-state battery of the fourth embodiment is dot-like when viewed from the stacking direction.

  Also in the all solid state battery of the fourth embodiment, the negative electrode active material 2a in the negative electrode active material layer 2 can expand in the direction of the gap 2c along with charging, and thus constitutes an all solid state battery accompanying charge and discharge. It is possible to highly suppress peeling between layers. Moreover, in the all solid state battery of the fourth embodiment, since the negative electrode active material 2a is continuous from the solid electrolyte layer 3 to the negative electrode current collector layer 1, excellent conductivity can be exhibited.

  In the negative electrode active material layer 2 of the all-solid-state battery of the fourth embodiment, the average diameter of the particulate negative electrode active material 2a, the average diameter of the oxide solid electrolyte particles constituting the solid electrolyte 2b, and the negative electrode active material 2a The abundance ratio with respect to the solid electrolyte 2b may be the same as in the case of the all solid state battery of the first embodiment. The porosity of the negative electrode active material layer 2 may be substantially the same as or higher than that of the all solid state battery of the first embodiment.

  The negative electrode active material 2a in the negative electrode active material layer 2 of the all-solid battery of the fourth embodiment is present on the surface in contact with the void 2c of the sintered body that is a solid electrolyte. The layer thickness of the negative electrode active material 2a may be, for example, 50 nm or more and 1 μm or less.

  In the negative electrode active material layer 2 of the all-solid-state battery of the fourth embodiment, when the gaps 2c are striped when viewed from the stacking direction, the average value of the width is relative to the thickness of the negative electrode active material layer 2 As a value, it may be 1/20 or more or 1/15 or more, for example, may be 1/5 or less or 1/10 or less. The quantitative value of the average value of the width when the gap 2c is striped may be, for example, 0.5 μm or more or 1.0 μm or more, for example, 5.0 μm or less or It may be 4.0 μm or less.

  When the gap 2c is dot-like when viewed from the stacking direction, the average diameter is, for example, 1/20 or more, 1/18 or more, or 1 /, as a relative value based on the thickness of the negative electrode active material layer 2. It may be 16 or more, for example, 1/6 or less, 1/8 or less, or 1/10 or less. The quantitative value of the average diameter when the gap 2c is dot-like is, for example, 0.5 μm or more, 1.0 μm or more, 1.5 μm or more, or 2.0 μm or more as the number average diameter by electron microscope observation. For example, it may be 5.0 μm or less, 4.5 μm or less, or 4.0 μm or less.

<The manufacturing method of the all-solid-state battery of 4th Embodiment>
The all-solid-state battery according to the fourth embodiment in which the gap 2c is striped when viewed from the stacking direction may be manufactured, for example, by the following method.

A negative electrode active material-containing layer containing a negative electrode active material, a solid electrolyte-containing layer containing a solid electrolyte, and a pore-forming material-containing layer containing a pore-forming material were prepared, and these were formed into a solid electrolyte-containing layer, a negative electrode active material-containing layer, A negative electrode active material is laminated in the order of a pore material-containing layer, a negative electrode active material-containing layer, a solid electrolyte-containing layer, a negative electrode active material-containing layer, a pore former-containing layer, a negative electrode active material-containing layer, a solid electrolyte-containing layer. Obtaining a precursor laminate of layer green sheets,
Cutting the negative electrode active material layer green sheet precursor laminate in a cross section perpendicular to the stacking direction to obtain a negative electrode active material layer green sheet in which each layer is arranged in a stripe shape;
A negative electrode current collector layer, a negative electrode active material layer green sheet, a solid electrolyte layer green sheet, and a positive electrode active material layer green sheet are laminated in this order to obtain a green sheet laminate, and the green sheet laminate is fired A method for producing an all-solid battery.

[Negative electrode active material-containing layer]
The negative electrode active material-containing layer contains a negative electrode active material, and may optionally further contain an organic binder, a plasticizer, and the like. The negative electrode active material in the negative electrode active material-containing layer may be particulate. The negative electrode active material-containing layer may contain a solid electrolyte and a pore former, but preferably does not contain them.

  The thickness of the negative electrode active material-containing layer may be appropriately set according to the desired thickness of the negative electrode active material 2a layer in the negative electrode active material layer of the all-solid-state battery of the fourth embodiment.

[Porous material-containing layer]
The pore former-containing layer contains a pore former and optionally further contains an organic binder, a plasticizer, and the like.

  The pore former contained in the pore former-containing layer is composed of the same or similar material as the pore former in the negative electrode active material layer green sheet used when manufacturing the all solid state battery of the first embodiment. It's okay. The pore former may be an organic polymer, but need not be a crosslinked body. Here, both a crosslinked organic polymer and a non-crosslinked organic polymer can be preferably used.

  The pore former-containing layer may be formed by the same method as the negative electrode active material layer green sheet used when manufacturing the all-solid-state battery of the first embodiment, except that each component described above is used.

  The thickness of the pore former-containing layer is appropriately set according to the desired value of the width of the void 2c in the negative electrode active material layer of the all-solid-state battery of the fourth embodiment in which the void 2c is striped when viewed from the stacking direction. May be.

[Solid electrolyte-containing layer and positive electrode active material-containing layer]
Each of the solid electrolyte-containing layer and the positive electrode active material-containing layer should be appropriately adjusted in thickness, except that the solid electrolyte layer green sheet and the positive electrode active material layer green sheet in the all-solid battery of the first embodiment It may be the same.

[Example of Method for Manufacturing All-Solid Battery of Fourth Embodiment]
An example of the manufacturing method of the all-solid-state battery according to the fourth embodiment in which the gap 2c is striped when viewed from the stacking direction is schematically shown in FIG.

  First, the solid electrolyte containing layer 3 (4), the negative electrode active material containing layer 2 (4), the pore former containing layer 6 (4), the negative electrode active material containing layer 2 (4), the solid electrolyte containing layer 3 (4), The negative electrode active material containing layer 2 (4), the pore former containing layer 6 (4), the negative electrode active material containing layer 2 (4), the solid electrolyte containing layer 3 (4), etc. A layered green sheet precursor laminate 10 (4) is obtained (FIG. 5A).

  Next, the negative electrode active material layer green sheet precursor laminate 10 (4) is cut (sliced) in a cross section perpendicular to the stacking direction to obtain a negative electrode active material layer green sheet 2G in which each layer is arranged in a stripe shape ( FIG. 5B).

  Furthermore, the negative electrode current collector layer 1, the negative electrode active material layer green sheet 2G, the solid electrolyte layer green sheet 3G, and the positive electrode active material layer green sheet 4G are laminated in this order to obtain the green sheet laminate of the fourth embodiment. (FIG. 5C). The solid electrolyte layer green sheet 3G and the positive electrode active material layer green sheet 4G used here are the same as the solid electrolyte layer green sheet and the positive electrode active material layer green sheet in the all solid state battery of the first embodiment, respectively. Good.

  And after baking the green sheet laminated body of this 4th Embodiment, the all-solid-state battery of 4th Embodiment is obtained by laminating | stacking a positive electrode collector layer on the positive electrode active material layer side of the laminated body after baking. be able to.

  Alternatively, the negative electrode current collector layer 1, the negative electrode active material layer green sheet 2G, the solid electrolyte layer green sheet 3G, the positive electrode active material layer green sheet 4G, and the positive electrode current collector layer 5 are laminated in advance in a desired lamination order. In addition, it may be fired.

<Example 1>
(1) Preparation of negative electrode active material layer green sheet 8.7 g of Si particles (average particle size 80 nm) as a negative electrode active material and 16.6 g of spherical crosslinked acrylic resin particles (average particle size 0.8 μm) as a pore former Then, as a solvent, 2-butanol having the same amount as the total mass of Si particles and crosslinked acrylic resin particles was combined and mixed using a ball mill at a rotational speed of 300 rpm for 5 hours to obtain a mixture. In this mixture, Si particles adhered around the spherical crosslinked acrylic resin particles by mixing the Si particles and the crosslinked acrylic resin particles together.

To the obtained mixture, 11.8 g of Li ₇ La ₃ Zr ₂ O ₇ (LLZ) particles (average particle size 1.0 nm) and 11.8 g of 2-butanol were added as a solid electrolyte and rotated using a ball mill. The slurry A was obtained by mixing at several 300 rpm for 5 hours.

  On the other hand, a non-crosslinked acrylic resin as an organic binder, butylbenzyl phthalate as a plasticizer, and 2-butanol as a solvent are combined at a mixing ratio of a mass ratio of 18:72:10, and the rotational speed is 2,000 rpm using a ball mill. For 10 minutes to obtain a binder solution.

  Add a binder solution of the same amount as the total mass of Si particles, LLZ particles, and crosslinked acrylic resin particles in slurry A to slurry A, and mix for 5 minutes at a rotational speed of 2,000 rpm using a defoaming mixer. A slurry B was obtained.

  Using a coating machine, the slurry B was coated on a PET film coated with a release agent so that the film thickness after removal of the solvent was 15 μm, and then a dryer at room temperature for 30 minutes and at 80 ° C. The negative electrode active material layer green sheet was obtained by drying in order for 20 minutes.

(2) Preparation of solid electrolyte layer green sheet 30 g of Li ₇ La ₃ Zr ₂ O ₇ as a solid electrolyte and 30 g of 2-butanol as a solvent are mixed and mixed at a rotation speed of 300 rpm for 10 hours using a ball mill, and slurry C is obtained. Obtained. To this slurry C, 30 g of a binder solution prepared in the same manner as in the production of the negative electrode active material layer green sheet was added, and the slurry D was mixed using a defoaming mixer at 2,000 rpm for 5 minutes. Obtained.

  Using a coating machine, the slurry D was coated on a PET film coated with a release agent so that the film thickness after removal of the solvent was 20 μm, and then a dryer at room temperature for 30 minutes and at 80 ° C. The solid electrolyte layer green sheet was obtained by drying sequentially for 20 minutes.

(3) Preparation of positive electrode active material layer green sheet LiCoO ₂ 15 g as a positive electrode active material, Li ₇ La ₃ Zr ₂ O ₇ 15 g as a solid electrolyte, and 30 g of 2-butanol as a solvent were combined, and the rotation speed was 300 rpm using a ball mill. For 10 hours to obtain slurry E. To this slurry E, 30 g of a binder solution prepared in the same manner as in the production of the negative electrode active material layer green sheet was added, and the slurry F was mixed for 5 minutes at a rotational speed of 2,000 rpm using a defoaming mixer. Obtained.

  Using a coating machine, the slurry F was coated on a PET film coated with a release agent so that the film thickness after removal of the solvent was 50 μm, and then a dryer at room temperature for 30 minutes and at 80 ° C. The positive electrode active material layer green sheet was obtained by drying sequentially for 20 minutes.

(4) Production of Battery Laminate Each green sheet produced above was cut into a 30 mm × 30 mm square and the PET film was peeled off while the negative electrode active material layer green sheet, solid electrolyte layer green sheet, and positive electrode active material layer green A laminate was obtained by laminating in the order of the sheets. This laminate was vacuum packed in a laminate outer package, and then hydrostatically pressed at 85 ° C. and 50 MPa for 10 minutes to obtain a laminate crimped body. Furthermore, this pressure-bonded body was carried into an electric furnace, degreased in a nitrogen atmosphere at 400 ° C. for 10 hours, and then baked in a nitrogen atmosphere at 1,000 ° C. for 10 hours to obtain a battery laminate.

(5) SEM observation SEM observation was performed about the negative electrode active material layer of the battery laminated body obtained above. FIG. 6A shows a secondary electron image, and FIG. 6B shows a reflected electron image of the same region.

<Comparative Example 1>
In “(1) Production of negative electrode active material layer green sheet”, each green sheet was produced in the same manner as in Example 1 except that the crosslinked acrylic resin particles as the pore former were not used. A battery laminate was prepared using the SEM observation of the negative electrode active material layer. FIG. 7A shows a secondary electron image, and FIG. 7B shows a reflected electron image of the same region.

<Discussion>
In the secondary electron image of SEM observation of the negative electrode active material layer, the void is observed as a black region. In the reflected electron image of SEM observation of the negative electrode active material layer, Si is observed as a dark gray tone region, and LLZ is observed as a white bright tone region.

  In the SEM image of the negative electrode active material layer obtained in Comparative Example 1 in which no pore former was used for the negative electrode active material layer green sheet, a blackened portion was seen in the secondary electron image of FIG. It can be seen that no voids are formed. Moreover, it can be seen from the secondary electron image in FIG. 7A and the reflected electron image in FIG. 7B that the sintering of Si and LLZ is progressing.

  On the other hand, in the SEM image of the negative electrode active material layer obtained in Example 1 according to this embodiment, a blackened portion is seen in the secondary electron image of FIG. I understand. Further, by comparing the secondary electron image of FIG. 6A with the reflected electron image of FIG. 6B in the same region, it was confirmed that the voids were formed in contact with the Si particles.

<Verification of stress relaxation mechanism>
In the all-solid-state battery of the present invention, the inventors have described the working mechanism that the stress caused by the active material absorbing and expanding Li ions is relieved and the problems such as peeling between layers are eliminated. It verified as follows.

  First, it was assumed that spherical Si particles as a negative electrode active material were embedded in the solid electrolyte. In this state, the stress applied to the solid electrolyte in which the Si particles were embedded when the lithium particles were absorbed by the Si particles as the negative electrode active material and expanded due to the charging was calculated. The maximum stress applied to the solid electrolyte was determined with respect to the charge ratio, assuming that the charge ratio at full discharge was 0 and the charge ratio at full charge was 1. As a result, it has been found that the maximum stress applied to the solid electrolyte in which Si particles are embedded exceeds the strength (about 100 MPa) of zirconia, which is a general ceramic, when the charge ratio is only 0.01.

  Next, a laminate in which a 5 μm × 0.5 μm Si electrode was deposited to a thickness of 1 μm on a plate-like current collector formed of a solid electrolyte was immersed in an electrolytic solution containing Li ions. In this state, a voltage was applied between the plate current collector and the electrolytic solution, and Li was absorbed by the Si electrode. As a result, the Si electrode expanded to about four times the volume in the direction opposite to the plate current collector (direction on the electrolyte side) and outward in the direction perpendicular to the stacking direction. However, the Si electrode did not peel from the plate current collector and remained attached to the plate current collector.

  Assuming that Si expands isotropically in the structure of the above laminate, the stress in the x direction on the Si electrode and the plate current collector (solid electrolyte) when the Si electrode expanded by 10 ppm was calculated. . The result is shown in FIG. According to FIG. 8, the stress in the x direction in the Si electrode and the plate current collector was maximum at the interface between the Si electrode and the plate current collector, and decreased in the direction away from the interface. Here, when the Si electrode expands by only 10 ppm, a compressive stress in the x direction is applied to the Si electrode, and a large tensile stress is applied to the solid electrolyte layer in the x direction. The maximum value of the stress is about 40 MPa. Met. According to this result, if the Si electrode isotropically expands due to charging, delamination should occur between the Si electrode and the plate current collector.

  However, as described in the expansion experiment for the above laminate, no delamination has occurred as a result of assuming that Si expands isotropically. From this, it is concluded that the Si electrode expands in the direction in which the compressive stress in the x direction is not applied, that is, in the open direction.

  Therefore, if Si, which is the negative electrode active material, is present in contact with a space that absorbs expansion (in the present invention, a void), the negative electrode active material can expand toward the space, and thereby, due to charging. It is concluded that the stress exerted on the solid electrolyte by the expansion of the negative electrode active material can be suppressed.

  Therefore, the negative electrode active material layer has voids, and the negative electrode active material is disposed on the surface in contact with the voids, whereby the expansion of the negative electrode active material is absorbed by the voids and expands in the direction in which tensile stress acts on the solid electrolyte. The maximum stress applied to the negative electrode active material layer was calculated on the assumption that the negative electrode active material layer does not. The porosity was 45% by volume. The result is shown in FIG.

  Referring to FIG. 9, it can be seen that when voids are arranged in the negative electrode active material layer according to the disclosure of the present invention, an increase in stress due to Si expansion is remarkably suppressed as compared with a conventional negative electrode having no voids. . Therefore, the all-solid-state battery of the present invention that requires that the negative electrode active material layer includes voids and the negative electrode active material is disposed on the surface in contact with the voids is affected by expansion and contraction of the negative electrode active material due to charge / discharge. Can be mitigated, and this can suppress the occurrence of peeling at the layer interface.

DESCRIPTION OF SYMBOLS 1 Negative electrode collector layer 2 Negative electrode active material layer 2 (1) Negative electrode active material 1st layer 2 (2) Negative electrode active material 2nd layer 2 (3) Negative electrode active material 3rd layer 2 (4) Negative electrode active material containing layer 2a negative electrode active material 2b solid electrolyte 2c gap 2G negative electrode active material layer green sheet 3 solid electrolyte layer 3 (4) solid electrolyte containing layer 3G solid electrolyte layer green sheet 4 positive electrode active material layer 4G positive electrode active material layer green sheet 5 positive electrode current collector Body layer 6 (4) Porous material-containing layer 10 (4) Negative electrode active material layer Precursor laminate of green sheet

Claims (1)

A negative electrode current collector layer, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are all solid-state batteries laminated in this order,
The negative electrode active material layer includes a negative electrode active material and a solid electrolyte,
The solid electrolyte is a sintered body having voids,
The negative electrode active material is disposed on a surface in contact with the void of the solid electrolyte,
All solid battery.