WO2021132500A1

WO2021132500A1 - Solid-state battery

Info

Publication number: WO2021132500A1
Application number: PCT/JP2020/048532
Authority: WO
Inventors: 克明東; 馬場　彰
Original assignee: 株式会社村田製作所
Priority date: 2019-12-27
Filing date: 2020-12-24
Publication date: 2021-07-01

Abstract

The present invention provides a solid-state battery in which the concentration of electric field on peaks and valleys (in particular, peaks) of a positive electrode layer is suppressed, and as a result, short-circuit defects and charging defects are further suppressed even if charging and discharging are repeated under a high charging voltage (for example, 4.2 V). The present invention relates to a solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer, wherein in a cross-sectional view of the solid battery, an unevenness on the surface of the positive electrode in contact with the solid electrolyte layer is 1.0 μm or less, the unevenness being a value represented by a standard deviation of a plurality of measured values obtained by measuring the distance from a reference line to a positive electrode active material particle of the positive electrode layer, the reference line being the interface between the negative electrode layer and the solid electrolyte layer.

Description

Solid state battery

The present invention relates to a solid state battery.

Conventionally, secondary batteries that can be repeatedly charged and discharged have been used for various purposes. For example, a secondary battery may be used as a power source for electronic devices such as smartphones and notebook computers.

In secondary batteries, a liquid electrolyte is generally used as a medium for ion transfer that contributes to charging and discharging. That is, a so-called electrolytic solution is used in the secondary battery. However, in such a secondary battery, safety is generally required in terms of preventing leakage of the electrolytic solution. Further, since the organic solvent and the like used in the electrolytic solution are flammable substances, safety is also required in that respect as well.

Therefore, research is underway on a solid-state battery that uses a solid electrolyte instead of the electrolytic solution (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-035867

The inventors of the present invention have found a new problem that short-circuit defects and / or charging defects occur when charging and discharging are repeated under a high charging voltage (for example, 4.2 V) using a conventional solid-state battery. .. It is considered that such a problem occurs because the electric field is excessively concentrated on the unevenness (particularly the convex portion) of the positive electrode layer in the conventional solid-state battery.

According to the present invention, even if charging and discharging are repeated under a high charging voltage (for example, 4.2V), the electric field concentration on the unevenness (particularly the convex portion) of the positive electrode layer is sufficiently suppressed, and as a result, short-circuit defects and charging defects are further suppressed. An object of the present invention is to provide a solid-state battery that is sufficiently suppressed.

The present invention
A solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer.
The present invention relates to a solid-state battery in which the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer is 1.0 μm or less in a cross-sectional view of the solid-state battery.

A preferred embodiment of the present invention is
A positive electrode layer, a negative electrode layer, a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer, and a positive electrode current collector layer arranged on a surface of the positive electrode layer opposite to the surface in contact with the solid electrolyte layer. Is a solid-state battery containing
The positive electrode layer contains at least a lithium transition metal composite oxide and contains.
The negative electrode layer and the positive electrode current collector layer contain at least a carbon material and contain at least a carbon material.
The present invention relates to a solid-state battery in which the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer is 1.0 μm or less in a cross-sectional view of the solid-state battery.

The solid-state battery according to the present invention more sufficiently suppresses short-circuit defects and charging defects even when charging and discharging are repeated under a high charging voltage (for example, 4.2 V).

FIG. 1 is an external perspective view schematically showing a solid-state battery according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the solid-state battery of FIG. 1 when viewed in the direction of an arrow. FIG. 3 is a photomicrograph of a solid-state battery according to an embodiment of the present invention, which is a plane parallel to the stacking direction L and the width direction W and passes through a central point in the plan view shape of the solid-state battery. FIG. 4 is a photomicrograph of a cross section of a solid-state battery for explaining the “distance from the reference line to the positive electrode active material particles of the positive electrode layer” measured due to the “unevenness of the surface of the positive electrode layer” defined in the present invention. In particular, it is a micrograph for explaining the reference line (starting point) of the distance. FIG. 5 is a photomicrograph of a cross section of a solid-state battery for explaining the “distance from the reference line to the positive electrode active material particles of the positive electrode layer” measured due to the “unevenness of the surface of the positive electrode layer” defined in the present invention. In particular, it is a photomicrograph for explaining the end point of the distance.

[Solid-state battery]
Hereinafter, the "solid-state battery" of the present invention will be described in detail. Although the description will be given with reference to the drawings as necessary, the contents shown are merely schematic and exemplary for the purpose of understanding the present invention, and the appearance, dimensional ratio, and the like may differ from the actual product.

The "solid-state battery" as used in the present invention refers to a battery whose components are composed of solids in a broad sense, and in a narrow sense, its components (particularly preferably all components) are composed of solids. Refers to an all-solid-state battery. In one preferred embodiment, the solid-state battery in the present invention is a laminated solid-state battery in which the layers forming the battery building unit are laminated to each other, and preferably such layers are made of a sintered body. The "solid-state battery" includes not only a so-called "secondary battery" capable of repeating charging and discharging, but also a "primary battery" capable of only discharging. In one preferred embodiment of the invention, the "solid-state battery" is a secondary battery. The "secondary battery" is not overly bound by its name and may also include an electrochemical device such as a "storage device".

The "plan view" referred to in the present specification is based on a form in which an object is viewed from above or below along a thickness direction based on a stacking direction of each layer constituting a solid-state battery, and is a plan view (top view). (Figure and bottom view). Further, the “cross-sectional view” referred to in the present specification is a form when viewed from a direction substantially perpendicular to the thickness direction based on the stacking direction of each layer constituting the solid-state battery (in short, parallel to the thickness direction). It is based on the form when cut out on a flat surface) and includes a cross-sectional view. In particular, the "cross-sectional view" may be based on a surface parallel to the thickness direction based on the stacking direction of each layer constituting the solid-state battery, and may be based on a form cut off at a surface passing through the positive electrode terminal and the negative electrode terminal. The "vertical direction" and "horizontal direction" used directly or indirectly in the present specification correspond to the vertical direction and the horizontal direction in the drawings, respectively. Unless otherwise specified, the same reference numerals or symbols shall indicate the same members / parts or the same meanings. In one preferred embodiment, it can be considered that the vertical downward direction (that is, the direction in which gravity acts) corresponds to the "downward direction" and the opposite direction corresponds to the "upward direction".

The solid-state battery 200 according to the present invention includes, for example, a positive electrode layer 10A, a negative electrode layer 10B, and a solid electrolyte layer 20 interposed between them, as shown in FIGS. 1, 2 and 3, for example. The solid-state battery 200 according to the present invention is usually
A solid-state battery laminate 100 including at least one battery structural unit including a positive electrode layer 10A, a negative electrode layer 10B, and a solid electrolyte layer 20 interposed between them along the stacking direction L;
Positive electrode terminals 40A and negative electrode terminals 40B provided on opposite side surfaces of the solid-state battery laminate 100, respectively.
Consists of having. In the solid-state battery laminate 100, the positive electrode layer 10A and the negative electrode layer 10B are alternately laminated via the solid electrolyte layer 20. FIG. 1 is an external perspective view schematically showing a solid-state battery according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the solid-state battery of FIG. 1 when viewed in the direction of an arrow. FIG. 3 is a photomicrograph of a solid-state battery according to an embodiment of the present invention, which is a plane parallel to the stacking direction L and the width direction W and passes through a central point in the plan view shape of the solid-state battery.

In the solid-state battery 200, where each layer constituting the solid-state battery 200 is formed by firing, the positive electrode layer 10A, the negative electrode layer 10B, the solid electrolyte layer 20, and the like form a sintered layer. Preferably, the positive electrode layer 10A, the negative electrode layer 10B, and the solid electrolyte layer 20 are integrally fired with each other, and therefore the battery constituent units form an integrally sintered body.

(Positive electrode layer)
The positive electrode layer 10A is an electrode layer 10 including at least a positive electrode active material. The positive electrode layer 10A may further contain a solid electrolyte and / or a conductive material. In one preferred embodiment, the positive electrode layer is composed of a sintered body containing at least a positive electrode active material and a solid electrolyte. As shown in FIGS. 2 and 3, the positive electrode layer 10A may or may not have the positive electrode current collecting layer 11.

The unevenness of the surface of the positive electrode layer 10A in contact with the solid electrolyte layer 20 is 1.0 μm or less in the cross-sectional view of the solid-state battery. By setting the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer 20 within the above range, the electric field concentration on the unevenness (particularly the convex portion) of the positive electrode layer 10A at the boundary between the positive electrode layer 10A and the solid electrolyte layer 20 is more sufficient. As a result, the operating rate of the solid-state battery can be significantly improved. If the unevenness exceeds 1.0 μm, the electric field concentration on the unevenness (particularly the convex portion) of the positive electrode layer at the boundary between the positive electrode layer and the solid electrolyte layer cannot be sufficiently suppressed, and the operating rate of the solid-state battery decreases. To do.

The lower limit of the unevenness on the surface of the positive electrode layer in contact with the solid electrolyte layer 20 is not particularly limited, and the unevenness is usually 0.1 μm or more, particularly 0.5 μm or more.

The unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer 20 is preferably 0.65 μm or more and 0.95 μm or less, more preferably 0.70 μm or more, from the viewpoint of more sufficiently suppressing the concentration of the electric field on the unevenness of the positive electrode layer. It is 0.82 μm or less. The unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer is usually larger than the unevenness of the surface of the negative electrode layer in contact with the solid electrolyte layer, and smaller than the unevenness of the surface of the positive electrode layer in contact with the positive electrode current collector layer.

As shown in FIGS. 4 and 5, the unevenness of the surface of the positive electrode layer 10A in contact with the solid electrolyte layer 20 is such that the negative electrode layer 10B and the solid electrolyte are formed in the solid electrolyte layer 20 arranged between the positive electrode layer 10A and the negative electrode layer 10B. The interface with the layer 20 is set as the reference line 15, and the distances (arrows in FIG. 4) from the reference line 15 to the positive electrode active material particles of the positive electrode layer 10A are measured at 1 μm intervals. It is a value expressed by the standard deviation. That is, the standard deviation (that is, variation) with respect to a plurality of measured values of the distance from the reference line 15 to the positive electrode active material particles (arrows in FIG. 4) is used as a parameter representing the unevenness of the surface of the positive electrode layer 10A. For example, the smaller the standard deviation (variation) with respect to a plurality of measured values of the distance, the smaller the unevenness on the surface of the positive electrode layer. Further, for example, the larger the standard deviation (variation), the larger the unevenness on the surface of the positive electrode layer. The reference line 15 is a line that defines the interface between the negative electrode layer 10B and the solid electrolyte layer 20 in a cross-sectional view, and is usually shown in a linear shape. FIG. 4 is a photomicrograph of a cross section of a solid-state battery for explaining the “distance from the reference line to the positive electrode active material particles of the positive electrode layer” measured due to the “unevenness of the surface of the positive electrode layer” defined in the present invention. In particular, it is a micrograph for explaining the reference line (starting point) of the distance. FIG. 5 is a photomicrograph of a cross section of a solid-state battery for explaining the “distance from the reference line to the positive electrode active material particles of the positive electrode layer” measured due to the “unevenness of the surface of the positive electrode layer” defined in the present invention. In particular, it is a photomicrograph for explaining the end point of the distance.

Specifically, the distance from the reference line 15 to the positive electrode active material particles of the positive electrode layer 10A (arrows in FIG. 4) is determined by drawing a vertical line starting from the reference line 15 toward the positive electrode layer 10A and first contacting the positive electrode active material. The distance to the particles (positive electrode layer 10A) (end point). As shown in FIG. 5, such distances are measured at 1 μm intervals, and the standard deviations of those measured values are obtained. In measuring the distance, in FIG. 5, some distances are measured relatively long as shown by arrow 16B, and some distances are measured relatively short as shown by arrow 16A. The perpendicular line starting from the reference line 15 is a line perpendicular to the surface where the positive electrode layer 10A and the solid electrolyte layer 20 are in contact with each other, and is usually perpendicular to the surface where the negative electrode layer 10B and the solid electrolyte layer 20 are in contact with each other. It may be a line and / or a line parallel to the stacking direction L.

More specifically, the distance from the reference line 15 to the positive electrode active material particles of the positive electrode layer 10A (hereinafter, may be referred to as “distance A”) is measured in the central portion of the obtained solid-state battery 200. The central portion means a central portion in a plan view, and is a central portion in the width direction W and the depth direction P. The width direction W is a direction that defines the shortest distance between the positive electrode terminal 40A and the negative electrode terminal 40B, and particularly in a direction that defines the shortest distance between the positive electrode terminal 40A and the negative electrode terminal 40B when the solid-state battery 200 has a rectangular shape. It is a parallel direction and is a direction perpendicular to the stacking direction L. The rectangular parallelepiped shape includes a so-called cubic shape. The depth direction P is a direction parallel to the positive electrode terminal 40A and the negative electrode terminal 40B, and particularly when the solid-state battery 200 has a rectangular parallelepiped shape, it is a direction perpendicular to both the stacking direction L and the width direction W. Is.

More specifically, when measuring the distance A, a cross-sectional photograph (for example, FIG.) of a surface of the solid-state battery 200 that is parallel to the stacking direction L and the width direction W and passes through the center point in the plan view shape of the solid-state battery 200. 3) is photographed. The center point means the center of gravity of the solid-state battery in the plan view shape when the solid-state battery is viewed in a two-dimensional plane from the stacking direction L. The center of gravity is the point when a homogeneous material (for example, paper) is cut out by the contour of the plan view shape of the solid-state battery and supported by points in a balanced manner. In this cross-sectional photograph, the vicinity of the central portion of the solid electrolyte layer 20 arranged between the positive electrode layer 10A and the negative electrode layer 10B is enlarged so as to have a magnification of 3000 times. In the enlarged cross-sectional photograph (for example, FIG. 5), the distance A described above was measured at 1 μm intervals of 20 μm width from the center line to the right and left to obtain a total of 41 measured values, and the standard deviation of these values was calculated. Ask. The center line is the axis of the solid-state battery, more specifically, a line parallel to the stacking direction L and a line passing through the above-mentioned center point in the plan view shape of the solid-state battery.

In the present invention, the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer described above is arranged in the center in the stacking direction L among all the solid electrolyte layers 20 arranged between the positive electrode layer 10A and the negative electrode layer 10B. It suffices if it is filled between one solid electrolyte layer 20 and the positive electrode layer 10A in contact with the solid electrolyte layer.

The one solid electrolyte layer 20 arranged in the center with respect to the stacking direction L is, for example, lower when the total number of the solid electrolyte layers 20 laminated in the stacking direction L in the solid-state battery is 2k (k is an arbitrary natural number). It is the k + 1st solid electrolyte layer from. Specifically, in the solid-state battery of FIG. 2 (total number = 2), among the two solid electrolyte layers 20, between the upper solid electrolyte layer 20 and the positive electrode layer 10A immediately below the solid electrolyte layer. It suffices if the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer described above is satisfied.
Further, for example, when the total number of the solid electrolyte layers 20 contained in the solid battery is 2k + 1 (k is an arbitrary natural number), the one solid electrolyte layer 20 arranged in the center in the stacking direction L is the k + 1th solid from the bottom. It is an electrolyte layer.
Further, for example, when the total number of the solid electrolyte layers 20 included in the solid battery is 1, one solid electrolyte layer 20 arranged at the center in the stacking direction L is the one solid electrolyte layer.

The irregularities on the surface of the positive electrode layer in contact with the solid electrolyte layer described above are all arranged between the positive electrode layer 10A and the negative electrode layer 10B in the solid-state battery from the viewpoint of more sufficiently suppressing the electric field concentration on the irregularities of the positive electrode layer. It is preferable that the solid electrolyte layer 20 is filled between the solid electrolyte layer 20 and the positive electrode layer 10A in contact with the solid electrolyte layer.

The unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer can be controlled during the production of the positive electrode layer by adjusting the mixing conditions and the like when preparing the paste for producing the positive electrode layer, as will be described in detail later. it can.

In the positive electrode layer 10A, the average primary particle size of the positive electrode active material is not particularly limited, and is usually 1.0 μm or more and 20 μm or less, and is preferably 1 from the viewpoint of achieving the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer described above. It is 5.5 μm or more and 6 μm or less.

For the average primary particle size of the positive electrode active material in the positive electrode layer 10A, the average value calculated from the measured values of any 100 positive electrode active material particles is used in the cross-sectional photograph.

The positive electrode active material contained in the positive electrode layer 10A is a substance involved in the transfer of electrons in a solid-state battery. Charging and discharging are performed by the movement (conduction) of ions between the positive electrode layer and the negative electrode layer via the solid electrolyte and the transfer of electrons between the positive electrode layer and the negative electrode layer via an external circuit. The positive electrode layer is particularly preferably a layer capable of occluding and releasing lithium ions or sodium ions. That is, the solid-state battery of the present invention is preferably an all-solid-state secondary battery in which lithium ions or sodium ions move between the positive electrode layer and the negative electrode layer via a solid electrolyte to charge and discharge the battery. ..

The constituent material of the positive electrode active material is not particularly limited, and is, for example, a lithium-containing compound. The type of the lithium-containing compound is not particularly limited, and is, for example, a lithium transition metal composite oxide and a lithium transition metal phosphoric acid compound. Lithium transition metal composite oxide is a general term for oxides containing lithium and one or more types of transition metal elements as constituent elements. Lithium transition metal phosphoric acid compound is a general term for phosphoric acid compounds containing lithium and one or more kinds of transition metal elements as constituent elements. The type of transition metal element is not particularly limited, and is, for example, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), and the like.

The lithium transition metal composite oxide is, for example, a compound represented by _{Li x} M1O ₂ and Li _y M2O _{4, respectively.} Lithium transition metal phosphate compound, for _example, a compound represented by Li z M3PO _4, and the like. However, each of M1, M2 and M3 is one kind or two or more kinds of transition metal elements. The respective values of x, y and z are arbitrary.

Specifically, the lithium transition metal composite oxide is, for example, LiCoO ₂ (that is, lithium cobalt oxide), LiNiO ₂ , LiVO ₂ , LiCrO ₂ , LiMn ₂ O ₄ (that is, lithium manganate), LiCo _1/3 Ni _{1 / 3} Mn _1/3 O ₂ and LiNi _0.5 Mn _1.5 O ₄ and the like. Further, the lithium transition metal phosphoric acid compound is, for example, LiFePO ₄ , LiCoPO _4, LiMnPO _4, or the like.

Further, as the positive electrode active material capable of occluding and releasing sodium ions, a sodium-containing phosphoric acid compound having a pearcon-type structure, a sodium-containing phosphoric acid compound having an olivine-type structure, a sodium-containing layered oxide, and a sodium-containing material having a spinel-type structure are contained. At least one selected from the group consisting of oxides and the like can be mentioned.

The positive electrode active material is preferably a lithium transition metal composite oxide (particularly lithium cobalt oxide or lithium manganate), and more preferably lithium cobalt oxide, from the viewpoint of more sufficiently suppressing electric field concentration on the unevenness of the positive electrode layer.

The content of the positive electrode active material in the positive electrode layer 10A is usually 50% by mass or more (that is, 50% by mass or more and 99% by mass or less) with respect to the total amount of the positive electrode layer, which is more sufficient for the electric field concentration on the unevenness of the positive electrode layer. From the viewpoint of sufficient suppression, it is preferably 60% by mass or more and 90% by mass or less, and more preferably 60% by mass or more and 80% by mass or less. The positive electrode layer may contain two or more kinds of positive electrode active materials, and in that case, the total content thereof may be within the above range.

The solid electrolyte that may be contained in the positive electrode layer 10A may be selected from, for example, the same materials as the solid electrolyte that can be contained in the solid electrolyte layer described later. The positive electrode layer 10A may contain a glass-ceramic solid electrolyte as the solid electrolyte.

The content of the solid electrolyte in the positive electrode layer 10A is not particularly limited, and is usually 1 to 50% by mass, particularly 10 to 40% by mass, based on the total amount of the positive electrode layer. The positive electrode layer may contain two or more kinds of solid electrolytes, in which case the total content thereof may be within the above range.

The positive electrode layer 10A may further contain a sintering aid. As the sintering aid, at least one selected from the group consisting of lithium oxide, sodium oxide, potassium oxide, boron oxide, silicon oxide, bismuth oxide and phosphorus oxide can be mentioned.

The thickness of the positive electrode layer 10A is not particularly limited, and may be, for example, 1 μm or more and 100 μm or less, particularly 5 μm or more and 50 μm or less. When the positive electrode layer 10A has the positive electrode current collecting layer 11 and the positive electrode layer 10A is formed on both sides or one side of the positive electrode current collecting layer 11, the thickness of the positive electrode layer 10A is per one side of the positive electrode current collecting layer 11. The thickness.

As shown in FIG. 2, the positive electrode layer 10A may or may not have the positive electrode current collector layer 11. From the viewpoint of the current collecting efficiency of the positive electrode layer, the positive electrode layer preferably has a positive electrode current collecting layer. When the positive electrode layer 10A has the positive electrode current collecting layer 11, the positive electrode layer 10A may be formed on both sides of the positive electrode current collecting layer 11 or may be formed on one side as shown in FIG. In this case, the positive electrode layer 10A is preferably formed on both sides of the positive electrode current collector layer 11 as shown in FIG. 2 from the viewpoint of improving the battery capacity. The positive electrode current collector layer 11 is usually arranged on the surface of the positive electrode layer opposite to the surface in contact with the solid electrolyte layer.

The positive electrode current collecting layer 11 is a connecting layer that achieves an electrical connection between the positive electrode layer 10A and the positive electrode terminal 40A, and includes at least a conductive material. The positive electrode current collector layer 11 may further contain a solid electrolyte. In one preferred embodiment, the positive electrode current collector layer is composed of a sintered body containing at least a conductive material and a solid electrolyte.

The conductive material that may be contained in the positive electrode current collector layer 11 is usually a material having a relatively high conductivity, and is composed of, for example, a carbon material, silver, palladium, gold, platinum, aluminum, copper and nickel. At least one selected may be used. The positive electrode current collecting layer 11 preferably contains a carbon material (particularly graphite) from the viewpoint of more sufficiently suppressing the concentration of the electric field on the unevenness of the positive electrode layer. Examples of the carbon material include graphite, graphitizable carbon, non-graphitizable carbon, mesocarbon microbeads (MCMB) and highly oriented graphite (HOPG). Since the carbon material (particularly graphite) is generally softer than the positive electrode active material of the positive electrode layer and the solid electrolyte of the solid electrolyte layer, the positive electrode current collector layer 11 contains a carbon material (particularly graphite) and is solid. The unevenness of the surface of the positive electrode layer in contact with the electrolyte layer 20 can be absorbed on the positive electrode current collecting layer side. Therefore, the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer 20 can be controlled more easily within the above range.

The content of the conductive material (particularly carbon material) in the positive electrode current collector layer 11 is usually 50% by mass or more (for example, 50 to 99% by mass), particularly 60 to 90% by mass, based on the total amount of the positive electrode current collector layer. is there. The positive electrode current collector layer may contain two or more kinds of conductive materials, and in that case, the total content thereof may be within the above range.

The solid electrolyte that may be contained in the positive electrode current collector layer 11 may be selected from, for example, the same materials as the solid electrolyte that can be contained in the solid electrolyte layer described later. The positive electrode current collector layer 11 may contain a glass-ceramic solid electrolyte as the solid electrolyte.

The content of the solid electrolyte in the positive electrode current collector layer 11 is not particularly limited, and is usually 1 to 50% by mass, particularly 10 to 40% by mass, based on the total amount of the positive electrode current collector layer. The positive electrode current collector layer may contain two or more kinds of solid electrolytes, in which case the total content thereof may be within the above range.

When the positive electrode current collector layer has the form of a sintered body, the positive electrode current collector layer 11 may further contain a sintering aid. The sintering agent contained in the positive electrode current collector layer may be selected from, for example, the same materials as the sintering aid that can be contained in the positive electrode layer.

The thickness of the positive electrode current collector layer 11 is not particularly limited, and may be, for example, 1 μm or more and 100 μm or less, particularly 3 μm or more and 20 μm or less.

(Negative electrode layer)
The negative electrode layer 10B is an electrode layer including at least a negative electrode active material. The negative electrode layer 10B may further contain a solid electrolyte. In one preferred embodiment, the negative electrode layer is composed of a sintered body containing at least a negative electrode active material and a solid electrolyte.

The negative electrode active material contained in the negative electrode layer 10B is a substance involved in the transfer of electrons in a solid-state battery. Charging and discharging are performed by the movement (conduction) of ions between the positive electrode layer and the negative electrode layer via the solid electrolyte and the transfer of electrons between the positive electrode layer and the negative electrode layer via an external circuit. The negative electrode layer is particularly preferably a layer capable of occluding and releasing lithium ions.

Examples of the negative electrode active material include carbon materials, metal-based materials, lithium alloys, and lithium-containing compounds. The negative electrode active material preferably contains a carbon material from the viewpoint of more sufficiently suppressing the concentration of the electric field on the unevenness of the positive electrode layer.

Specifically, the carbon material is, for example, graphite, graphitizable carbon, non-graphitizable carbon, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), and the like.

Metallic material is a general term for materials containing one or more of metal elements and metalloid elements capable of forming alloys with lithium as constituent elements. This metallic material may be a simple substance, an alloy, or a compound. Since the purity of the simple substance described here is not necessarily limited to 100%, the simple substance may contain a trace amount of impurities.

Metal elements and semi-metal elements include, for example, silicon (Si), tin (Sn), aluminum (Al), indium (In), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge). , Lead (Pb), Bismus (Bi), Cadmium (Cd), Titanium (Ti), Chromium (Cr), Iron (Fe), Niobium (Nb), Molybdenum (Mo), Silver (Ag), Zinc (Zn) , Hafnium (Hf), zirconium (Zr), ittrium (Y), palladium (Pd) and platinum (Pt).

Specifically, the metal-based materials include, for example, Si, Sn, SiB ₄ , TiSi ₂ , SiC, Si ₃ N ₄ , SiO _v (0 <v ≦ 2), LiSiO, SnO _w (0 <w ≦ 2). , SnSiO ₃ , LiSnO, Mg ₂ Sn, and the like.

The lithium-containing compound is, for example, a lithium transition metal composite oxide. The definition of the lithium transition metal composite oxide is as described above. Specifically, the lithium transition metal double oxides are, for example, Li ₃ V ₂ (PO ₄ ) ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , Li ₄ Ti ₅ O ₁₂ , LiTi ₂ (PO ₄ ) ₃ , And LiCuPO _{4 and the} like.

The negative electrode active material capable of occluding and releasing sodium ions is a group consisting of a sodium-containing phosphoric acid compound having a pearcon-type structure, a sodium-containing phosphoric acid compound having an olivine-type structure, a sodium-containing oxide having a spinel-type structure, and the like. At least one selected from is mentioned.

When the negative electrode active material is the above-mentioned substance, the interface between the negative electrode layer 10B and the solid electrolyte layer 20 (that is, the reference line 15) can usually be represented in a sufficiently linear shape in a cross-sectional photograph (cross-sectional view) at a magnification of 1000 times. .. When the negative electrode active material is a particularly flat powder, the interface between the negative electrode layer 10B and the solid electrolyte layer 20 can be further represented in a sufficiently linear shape. If it is difficult to represent the interface between the negative electrode layer 10B and the solid electrolyte layer 20 in a linear shape, the reference line 15 is the center line on the most solid electrolyte layer 20 side of the negative electrode layer 10B in cross-sectional view. It may be a line passing through a point in contact with (or intersecting with) the negative electrode active material and defining a surface perpendicular to the stacking direction L. If the interface between the negative electrode layer and the solid electrolyte layer is smooth, it becomes easier to accept ions (for example, lithium ions), and by using soft graphite powder for the current collecting layer, the unevenness of the positive electrode active material (for example, LCO) is collected. It can be absorbed on the layer side to improve the operating rate.

The content of the negative electrode active material (particularly carbon material) in the negative electrode layer 10B is usually 50 to 99% by mass, particularly 60 to 90% by mass, based on the total amount of the negative electrode layer. The negative electrode layer may contain two or more kinds of negative electrode active materials, and in that case, the total content thereof may be within the above range.

The solid electrolyte that may be contained in the negative electrode layer 10B may be selected from, for example, the same materials as the solid electrolyte that can be contained in the solid electrolyte layer described later. The negative electrode layer 10B may contain a glass-ceramic solid electrolyte as the solid electrolyte.

The content of the solid electrolyte in the negative electrode layer 10B is not particularly limited, and is usually 1 to 50% by mass, particularly 10 to 40% by mass, based on the total amount of the negative electrode layer. The negative electrode layer may contain two or more kinds of solid electrolytes, in which case the total content thereof may be within the above range.

The negative electrode layer 10B may further contain a sintering aid. Examples of the sintering aid include materials similar to those of the sintering aid that may be contained in the positive electrode layer 10A.

The thickness of the negative electrode layer 10B is not particularly limited, and may be, for example, 1 μm or more and 100 μm or less.

The negative electrode layer 10B may not have the negative electrode current collector layer as shown in FIG. 2, or may have the negative electrode current collector layer (not shown). From the viewpoint of the current collecting efficiency of the negative electrode layer, it is preferable that the negative electrode layer does not have the negative electrode current collecting layer. When the negative electrode layer 10B has a negative electrode current collecting layer, the negative electrode layer 10B may be formed on both sides of the negative electrode current collecting layer or may be formed on one side.

The negative electrode current collector layer is a connecting layer that achieves electrical connection between the negative electrode layer 10B and the negative electrode terminal 40B, and includes at least a conductive material. The negative electrode current collector layer may further contain a solid electrolyte. In one preferred embodiment, the negative electrode current collector layer is composed of a sintered body containing at least a conductive material and a solid electrolyte.

When the negative electrode layer 10B has the negative electrode current collector layer, the negative electrode current collector layer may be composed of the same constituent materials as the above-mentioned positive electrode current collector layer 11 in the same ratio.

(Solid electrolyte layer)
The solid electrolyte layer 20 is a layer containing at least a solid electrolyte. In one preferred embodiment, the solid electrolyte layer is composed of a sintered body containing at least the solid electrolyte.

The solid electrolyte constituting the solid electrolyte layer 20 is a material capable of conducting lithium ions or sodium ions. The solid electrolyte forms a layer in which lithium ions or sodium ions can be conducted, particularly between the positive electrode layer and the negative electrode layer. The solid electrolyte may be provided at least between the positive electrode layer and the negative electrode layer. That is, the solid electrolyte may also be present around the positive electrode layer and / or the negative electrode layer so as to protrude from between the positive electrode layer and the negative electrode layer. Specific solid electrolytes include, for example, any one or more of crystalline solid electrolytes and glass-ceramic solid electrolytes. The solid electrolyte layer 20 may contain a glass-ceramic solid electrolyte as the solid electrolyte.

The crystalline solid electrolyte is a crystalline electrolyte. Specifically, the crystalline solid electrolyte capable of conducting lithium ions is, for example, an inorganic material and a polymer material, and the inorganic material is, for example, a sulfide and an oxide. Sulfides include, for example, Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ _{-Li 3} PO ₄ , Li ₇ P ₃ S ₁₁ , Li _3.25 Ge _0.25 P _0.75 S and Li ₁₀ GeP ₂ S ₁₂ and the like. Oxides, for _{_{_{_{example, Li x M y (PO 4}}}} ) 3 (1 ≦ x ≦ 2,1 ≦ y ≦ 2, M is at least one selected from the group consisting of Ti, Ge, Al, Ga and Zr) , Li ₇ La ₃ Zr ₂ O ₁₂ , Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ , La _{2 /} _3- _x Li 3x TiO ₃ , Li _1.2 Al _0.2 Ti _1.8 (PO ₄ ) _3, La _0.55 Li _0.35 TiO ₃ and Li ₇ La ₃ Zr ₂ O ₁₂ etc. is there. The polymeric material is, for example, polyethylene oxide (PEO).

The glass-ceramic solid electrolyte is an electrolyte in which amorphous and crystalline are mixed. This glass-ceramic solid electrolyte is, for example, an oxide containing lithium (Li), silicon (Si) and boron (B) as constituent elements, and more specifically, lithium oxide (Li ₂ O) and oxidation. It contains silicon (SiO ₂ ), boron oxide (B ₂ O ₃ ) and the like. The ratio of the content of lithium oxide to the total content of lithium oxide, silicon oxide and boron oxide is not particularly limited, but is, for example, 40 mol% or more and 73 mol% or less. The ratio of the content of silicon oxide to the total content of lithium oxide, silicon oxide and boron oxide is not particularly limited, but is, for example, 8 mol% or more and 40 mol% or less. The ratio of the content of boron oxide to the total content of lithium oxide, silicon oxide and boron oxide is not particularly limited, but is, for example, 10 mol% or more and 50 mol% or less. In order to measure the respective contents of lithium oxide, silicon oxide and boron oxide, for example, inductively coupled plasma emission spectrometry (ICP-AES) or the like is used to analyze the glass-ceramic solid electrolyte.

Examples of the solid electrolyte in which sodium ions can be conducted include sodium-containing phosphoric acid compounds having a pearcon structure, oxides having a perovskite structure, oxides having a garnet type or a garnet type similar structure, and the like. The sodium-containing phosphate compound having a NASICON _{_{_{_{structure, Na x M y (PO 4}}}} ) 3 (1 ≦ x ≦ 2,1 ≦ y ≦ 2, M is, Ti, Ge, Al, from the group consisting of Ga and Zr At least one selected).

The solid electrolyte layer 20 may further contain a sintering aid. Examples of the sintering aid include materials similar to those of the sintering aid that may be contained in the positive electrode layer 10A.

The thickness of the solid electrolyte layer is not particularly limited, and may be, for example, 1 μm or more and 50 μm or less, particularly 1 μm or more and 5 μm or less.

(Electrode separation part)
The solid-state battery 200 of the present invention usually further has an electrode separation portion (also referred to as a "margin layer" or "margin portion") 30 (30A, 30B).

The electrode separating portion 30A (positive electrode separating portion) is arranged around the positive electrode layer 10A to separate the positive electrode layer 10A from the negative electrode terminal 40B. The electrode separating portion 30B (negative electrode separating portion) is also arranged around the negative electrode layer 10B to separate the negative electrode layer 10B from the positive electrode terminal 40A. Although not particularly limited, the electrode separating portion 30 may be composed of one or more materials selected from the group consisting of, for example, a solid electrolyte, an insulating material, a mixture thereof, and the like.

As the solid electrolyte that can form the electrode separation portion 30, the same material as the solid electrolyte that can form the solid electrolyte layer can be used.
The insulating material that can form the electrode separating portion 30 may be a material that does not conduct electricity, that is, a non-conductive material. Although not particularly limited, the insulating material may be, for example, a glass material, a ceramic material, or the like. As the insulating material, for example, a glass material may be selected. The glass material is not particularly limited, but the glass material is soda lime glass, potash glass, borate glass, borosilicate glass, barium borate glass, subhydrate borate glass, barium borate glass, etc. At least one selected from the group consisting of bismuth borosilicate glass, bismuth zinc borate glass, bismuth silicate glass, phosphate glass, aluminophosphate glass, and phosphate subsalt glass. Can be mentioned. Further, although not particularly limited, the ceramic material includes aluminum oxide (Al ₂ O ₃ ), boron nitride (BN), silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), and zirconium oxide (ZrO). ₂ ) At least one selected from the group consisting of aluminum nitride (AlN), silicon carbide (SiC) and barium titanate (BaTIO _{3) can be mentioned.}

(Terminal)
The solid-state battery 200 of the present invention is generally provided with terminals (external terminals) 40 (40A, 40B). In particular, positive and

negative electrode terminals

40A and 40B are provided on the side surface of the solid-state battery so as to form a pair. More specifically, the positive electrode side terminal 40A connected to the positive electrode layer 10A and the negative electrode side terminal 40B connected to the negative electrode layer 10B are provided so as to form a pair. For such terminals 40 (40A, 40B), it is preferable to use a material having a high conductivity. The material of the terminal 40 is not particularly limited, and examples thereof include at least one conductive material selected from the group consisting of silver, gold, platinum, aluminum, copper, tin, and nickel.

Terminal 40 (40A, 40B) may further contain a sintering aid. Examples of the sintering aid include materials similar to those of the sintering aid that may be contained in the positive electrode layer 10A.

Terminal 40 (40A, 40B) is, in one preferred embodiment, composed of a sintered body containing at least a conductive material and a sintering aid.

(Outer layer material)
The solid-state battery 200 of the present invention usually further includes an outer layer material 60.
The outer layer material 60 can generally be formed on the outermost side of the solid-state battery and is for electrical, physical and / or chemical protection. The material constituting the outer layer material 60 is preferably excellent in insulation, durability and / or moisture resistance, and is environmentally safe. For example, glass, ceramics, thermosetting resins, photocurable resins, and mixtures thereof may be used.

As the glass that can form the outer layer material, the same material as the glass material that can form the electrode separation portion can be used.
As the ceramic material that can form the outer layer material, the same material as the ceramic material that can form the electrode separation portion can be used.

[Manufacturing method of solid-state battery]
The solid-state battery of the present invention can be produced by a printing method such as a screen printing method, a green sheet method using a green sheet, or a composite method thereof. Hereinafter, the case where the printing method and the green sheet method are adopted for understanding the present invention will be described in detail, but the present invention is not limited to this method.

(Forming process of solid-state battery laminated precursor)
In this step, for example, there are several types of pastes such as positive electrode layer paste, negative electrode layer paste, solid electrolyte layer paste, positive electrode current collector layer paste, negative electrode current collector layer paste, electrode separation part paste, and outer layer material paste. Use paste as ink. That is, a solid-state battery laminated precursor having a predetermined structure is formed on the support substrate by applying and drying the paste by a printing method.

At the time of printing, a solid-state battery lamination precursor corresponding to a predetermined solid-state battery structure can be formed on a substrate by sequentially laminating print layers having a predetermined thickness and pattern shape. The type of the pattern forming method is not particularly limited as long as it is a method capable of forming a predetermined pattern, and is, for example, any one or more of the screen printing method and the gravure printing method.

The paste is an appropriately selected layer from the group consisting of positive electrode active material particles, negative electrode active material particles, conductive material, solid electrolyte material, current collector layer material, insulating material, and sintering aid, and other materials described above. It can be produced by wet-mixing a predetermined constituent material and an organic vehicle in which an organic material is dissolved in a solvent.
The positive electrode layer paste contains, for example, positive electrode active material particles, solid electrolyte materials, organic materials and solvents, and optionally a sintering aid.
The negative electrode layer paste contains, for example, negative electrode active material particles, solid electrolyte materials, organic materials and solvents, and optionally a sintering aid.
The solid electrolyte layer paste contains, for example, solid electrolyte materials, organic materials and solvents, and optionally sintering aids.
The paste for the positive electrode current collector contains, for example, a conductive material, an organic material and a solvent, and optionally a sintering aid.
The paste for the negative electrode current collector contains, for example, a conductive material, an organic material and a solvent, and optionally a sintering aid.
The electrode separation paste contains, for example, a solid electrolyte material, an insulating material, an organic material and a solvent, and optionally a sintering aid.
The outer layer paste contains, for example, an insulating material, an organic material and a solvent, and optionally a sintering aid.

The organic material contained in the paste is not particularly limited, but at least one polymer material selected from the group consisting of polyvinyl acetal resin, cellulose resin, polyacrylic resin, polyurethane resin, polyvinyl acetate resin, polyvinyl alcohol resin and the like can be used. Can be used.
The type of solvent is not particularly limited as long as it dissolves the organic material, and for example, one or two of organic solvents such as butyl acetate, N-methyl-pyrrolidone, toluene, terpineol and N-methyl-pyrrolidone. That is all.

Any mixed dispersion method may be adopted for the preparation of the paste for the negative electrode layer, the paste for the solid electrolyte layer, the paste for the positive electrode current collector layer, the paste for the negative electrode current collector layer, the paste for the electrode separation portion, and the paste for the outer layer material. .. Specifically, a mixture containing a predetermined material is wet-mixed. For example, in wet mixing, a medium can be used, and specifically, a bead mill method, a ball mill method, a sand mill method, a visco mill method, or the like can be used. Further, for example, a wet mixing method that does not use media may be used, and a three-roll mill sand mill method, a high-pressure homogenizer method, a kneader dispersion method, or the like can be used.

The paste for the positive electrode layer is, for example, a combination of at least a "wet mixing method using media", preferably a "wet mixing method using media" and a "wet mixing method using media" (particularly, a planetary mixer dispersion method). By preparing by the bead mill method), it is possible to achieve the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer described above in the obtained solid-state battery. Specifically, first, a mixture containing a predetermined material is mixed by a wet mixing method that does not use media, and then a paste for a positive electrode layer obtained by mixing by a wet mixing method that uses media is used.

The wet mixing method without using a medium is a mixing method in which a shearing force is applied to a mixture (for example, an object to be crushed), for example, a planetary stirring mixer such as a planetary mixer or a rotation / revolution mixer, and a three-roll mill. , Use a disperser that does not use media such as a high-pressure homogenizer and kneader. The planetary mixer exerts a strong shearing force mainly by the precise spacing between the blades and between the blades and the inner surface of the tank by the planetary motion (eg planetary motion) of a plurality of (for example, two) frame-shaped blades. It is a mixing device.

The wet mixing method using media is a mixing method in which an impact force is applied to a mixture to be mixed (for example, an object to be crushed), and for example, a disperser using media such as a bead mill, a ball mill, a sand mill, or a visco mill is used. A bead mill is a mixing device in which an impact force is mainly applied by beads energized by centrifugal force generated by high-speed rotation of a stirring mechanism (disk). The constituent material of the beads is not particularly limited, and examples thereof include zirconia, alumina, steel, and glass. The particle size of the beads is as described below.

For example, even if the wet mixing method without using media is used alone, it is difficult to achieve the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer described above.

In forming the positive electrode layer, more specifically, the mixture containing a predetermined material is mixed with a planetary mixer and then dispersed by a bead mill, and the paste for producing a positive electrode layer is used to bring the mixture into contact with the above-mentioned solid electrolyte layer. The unevenness of the surface of the positive electrode layer can be achieved.
At this time, the unevenness of the surface of the positive electrode layer can be controlled by, for example, adjusting the dispersion time and rotation speed of the bead mill and the diameter of the beads used in the bead mill.
For example, the longer the dispersion time by the bead mill, the smaller the unevenness on the surface of the positive electrode layer. On the other hand, the shorter the dispersion time, the larger the unevenness on the surface of the positive electrode layer.
Further, for example, the higher the rotation speed of the bead mill, the smaller the unevenness on the surface of the positive electrode layer. On the other hand, the lower the rotation speed, the larger the unevenness on the surface of the positive electrode layer.
Further, for example, the smaller the diameter of the beads used in the bead mill, the smaller the unevenness on the surface of the positive electrode layer. On the other hand, the larger the diameter, the larger the unevenness on the surface of the positive electrode layer.

The support substrate is not particularly limited as long as it is a support capable of supporting each paste layer, but is, for example, a release film having a release treatment on one surface. Specifically, a substrate made of a polymer material such as polyethylene terephthalate can be used. When the paste layer is held on the substrate and subjected to the firing step, a substrate that exhibits heat resistance to the firing temperature may be used.

Alternatively, each green sheet can be formed from each of the above-mentioned pastes, and the obtained green sheets can be laminated to prepare a solid-state battery laminated precursor.

Specifically, a positive electrode layer green sheet having a predetermined shape and thickness on each support substrate (for example, PET film) by heating the green sheet of each paste formed on the support substrate to 80 ° C. or higher and 150 ° C. or lower. A negative electrode layer green sheet, a solid electrolyte layer green sheet, a positive electrode current collector layer green sheet, a negative electrode current collector layer green sheet, an electrode separation portion green sheet and / or an outer layer material green sheet are formed, respectively.

Next, each green sheet is peeled off from the substrate. After peeling, the green sheet of each component is laminated in order along the lamination direction to form a solid-state battery lamination precursor. After laminating, a solid electrolyte layer, an insulating layer and / or a protective layer and the like may be provided on the side region of the electrode green sheet by screen printing.

(Baking process)
In the firing step, the solid-state battery laminated precursor is subjected to firing. Although it is merely an example, the firing is carried out after removing the organic material by heating in a nitrogen gas atmosphere containing oxygen gas or in the atmosphere, for example, at 200 ° C. or higher and 600 ° C. or lower for 3 hours or more and 48 hours or less. It is carried out by heating in a nitrogen gas atmosphere or in the atmosphere, for example, at 300 ° C. or higher and 500 ° C. or lower for 10 to 120 minutes. The firing may be performed while pressurizing the solid-state battery laminated precursor in the laminating direction and the direction perpendicular to the laminating direction.

By undergoing such firing, a solid-state battery laminate is formed, and finally a desired solid-state battery can be obtained.

(Forming process of positive electrode terminal and negative electrode terminal)
For example, a conductive adhesive is used to bond the positive electrode terminals to the solid-state battery laminate, and a conductive adhesive is used to bond the negative electrode terminals to the solid-state battery laminate. As a result, each of the positive electrode terminal and the negative electrode terminal is attached to the solid-state battery laminate, so that the solid-state battery is completed.

Alternatively, the positive electrode terminal and the negative electrode terminal can be formed by adhering or applying the positive electrode terminal paste and the negative electrode terminal paste to the side surfaces of the solid-state battery laminate and sintering them. The side surface of the solid-state battery laminate to which the paste for the positive electrode terminal is attached or applied is, for example, the side surface where the positive electrode current collector layer is exposed. The side surface of the solid-state battery laminate to which the paste for the negative electrode terminal is attached or applied is, for example, the side surface where the negative electrode current collector layer is exposed. Sintering can be carried out by heating in a nitrogen gas atmosphere or in the air, for example, at 150 ° C. or higher and 300 ° C. or lower for 10 minutes or longer and 120 minutes or shorter.

The positive electrode terminal paste and the negative electrode terminal paste contain a conductive material, an organic material and a solvent, and optionally a sintering aid.

Although the embodiments of the present invention have been described above, they are merely examples of typical examples. Therefore, those skilled in the art will easily understand that the present invention is not limited to this, and various aspects can be considered without changing the gist of the present invention.

<Example 1>
(Making process of green sheet for making solid electrolyte layer)
First, lithium-containing oxide glass and an acrylic binder were mixed as a solid electrolyte at a mass ratio of lithium-containing oxide glass: acrylic binder = 70:30. Next, the obtained mixture was mixed with butyl acetate so as to have a solid content of 30% by mass, and this was stirred together with zirconia beads having a diameter of 5 mm for 4 hours to obtain a slurry for preparing a solid electrolyte layer. .. Subsequently, this slurry was applied onto a release film and dried at 80 ° C. for 10 minutes to prepare a green sheet for producing a solid electrolyte layer as a precursor of the solid electrolyte layer.

(Making process of green sheet for making positive electrode layer)
First, in the tank of the planetary mixer, lithium cobalt oxide (LiCoO2) (average particle size 5 μm) as the positive electrode active material, lithium-containing oxide glass as the solid electrolyte, and lithium cobalt oxide: lithium-containing oxide glass = 70:30. After blending in the mass ratio of, the acrylic binder was mixed so that the ratio with the mixture was (lithium cobalt oxide + lithium-containing oxide glass): acrylic binder = 70:30. Further, terpineol was mixed so that the solid content became 30% by mass, and then mixed with a planetary mixer for 30 minutes. Then, the obtained mixture was dispersed in a bead mill using zirconia beads having a diameter of 5 mm for 30 minutes to obtain a paste for preparing a positive electrode layer. Subsequently, this paste was printed on a green sheet for producing a solid electrolyte layer and dried at 150 ° C. for 10 minutes to prepare a green sheet for producing a positive electrode layer as a precursor of the positive electrode layer.

(Making process of green sheet for making negative electrode layer)
First, graphite as a negative electrode active material and lithium-containing oxide glass as a solid electrolyte are mixed in a tank of a planetary mixer at a mass ratio of graphite: lithium-containing oxide glass = 70:30, and then mixed with the mixture. Acrylic binders were mixed so that the ratio was (graphite + lithium-containing oxide glass): acrylic binder = 70:30 by mass ratio. Further, terpineol was mixed so that the solid content became 30% by mass, and then mixed with a planetary mixer for 30 minutes. Then, the obtained mixture was dispersed by a three-roll mill to obtain a paste for producing a negative electrode layer. Subsequently, this paste was printed on a green sheet for producing a solid electrolyte layer and dried at 150 ° C. for 10 minutes to prepare a green sheet for producing a negative electrode layer as a precursor of the negative electrode layer.

(Making process of green sheet for making positive electrode current collector layer)
First, carbon powder as a conductive material and lithium-containing oxide glass as a solid electrolyte are mixed in a tank of a planetary mixer at a mass ratio of carbon powder: lithium-containing oxide glass = 70:30, and then mixed with the mixture. The acrylic binder was mixed so that the ratio of (carbon powder + lithium-containing oxide glass): acrylic binder = 70:30 was obtained. Further, terpineol was mixed so as to have a solid content of 30% by mass, and then mixed with a planetary mixer for 30 minutes. Then, the obtained mixture was dispersed by a three-roll mill to obtain a paste for producing a positive electrode current collector layer. Subsequently, this paste was printed on a green sheet for producing a solid electrolyte layer and dried at 150 ° C. for 10 minutes to prepare a green sheet for producing a positive electrode current collector layer as a precursor of the positive electrode current collector layer.

(Making process of green sheet for making outer layer material)
First, alumina particle powder (average particle size 1 μm) and lithium-containing oxide glass as a solid electrolyte were mixed in a tank of a planetary mixer at a mass ratio of alumina particle powder: lithium-containing oxide glass = 50:50. After that, the acrylic binder was mixed so that the ratio with the mixture was (alumina particle powder + lithium-containing oxide glass): acrylic binder = 70:30. Further, terpineol was mixed so that the solid content became 30% by mass. Then, the obtained mixture was dispersed by a three-roll mill to obtain a paste for producing a main surface exterior material. Subsequently, this paste was printed on a green sheet for producing a solid electrolyte layer and dried at 150 ° C. for 10 minutes to prepare a green sheet for producing an outer layer material as a precursor of the main surface outer layer material.

(Making process of green sheet for making electrode separation part)
In the same manner as the above-mentioned "process for producing a green sheet for producing an outer layer material", a green sheet for producing an electrode separation portion was produced as a precursor for the electrode separation portion.

(Production process of laminated body)
Using each of the green sheets obtained as described above, a laminate having the configurations shown in FIGS. 1 and 2 was produced as follows. First, each green sheet was processed into the shapes shown in FIGS. 1 and 2, and then released from the release film. Subsequently, the green sheets were sequentially laminated so as to correspond to the configurations of the battery elements shown in FIGS. 1 and 2, and then thermocompression bonded at 100 ° C. for 10 minutes. As a result, a laminated body as a battery element precursor was obtained.

(Sintering process of laminated body)
The obtained laminate was heated at 300 ° C. for 10 hours to remove the acrylic binder contained in each green sheet, and then heated at 400 ° C. for 30 minutes to remove the oxide glass contained in each green sheet. Sintered.

(Terminal manufacturing process)
First, an epoxy resin-based conductive adhesive XA-874 (Fujikura Kasei) containing Ag powder as a conductive particle powder is applied onto a release film, and then the positive electrode current collector layer and the negative electrode current collector layer are exposed. Positive electrode and negative electrode terminals were formed by adhering a conductive paste to the first and second end faces (or side surfaces) of the body and sintering at 150 ° C. for 1 hour. As a result, the target battery was obtained.

(Standard deviation of surface unevenness of positive electrode layer)
The unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer was measured for each layer of the two solid electrolyte layers 20 arranged between the positive electrode layer 10A and the negative electrode layer 10B. Specifically, in the solid-state battery 200, a cross-sectional photograph (for example, FIG. 3) of a surface parallel to the stacking direction L and the width direction W and passing through the center point in the plan view shape of the solid-state battery 200 is taken with a scanning electron microscope FlexSEM1000. Taken by (Hitachi High Technologies America). The imaging conditions of the scanning electron microscope were an acceleration voltage of 15 kV and an observation magnification of 1000 times. The center point means the center of gravity of the solid-state battery in the plan view shape when the solid-state battery is viewed in a two-dimensional plane from the stacking direction L. The center of gravity is the point when a homogeneous material (for example, paper) is cut out by the contour of the plan view shape of the solid-state battery and supported by points in a balanced manner. In this cross-sectional photograph, the vicinity of the central portion of the solid electrolyte layer 20 arranged between the positive electrode layer 10A and the negative electrode layer 10B is enlarged so as to have a magnification of 3000 times. In the enlarged cross-sectional photograph (for example, FIG. 5), the distance A was measured at 1 μm intervals of 20 μm width from the center line to the right and left, and a total of 41 measured values were obtained, and the standard deviations of these values were obtained. .. When the standard deviation was calculated for each layer of the two solid electrolyte layers 20, these values were the same. The distance A is the distance from the reference line 15 to the positive electrode active material particles of the positive electrode layer 10A. The center line is the axis of the solid-state battery, more specifically, a line parallel to the stacking direction L and a line passing through the above-mentioned center point in the plan view shape of the solid-state battery.

(Operating rate)
A charge / discharge test was performed on 18 solid-state batteries, and the ratio of solid-state batteries (non-defective products) in which short-circuit defects and charging defects did not occur was determined as the operating rate.
The charge / discharge test was performed in a temperature environment of 23 ° C. Specifically, the rated capacity of the battery is set to 1C, and the battery is charged with a constant current of 0.1C until it reaches 4.2V, and after reaching 4.2V, it is charged in the constant voltage mode until the current is reduced to 0.01C. (Constant current constant voltage charging). Then, the discharge was carried out at a constant current of 0.1 C until it reached 3.0 V (constant current discharge).
Short-circuit failure and charge failure were judged by the shape of the charge / discharge curve in the above charge / discharge test. More specifically, a short circuit failure is when the voltage hardly rises even after the start of the charge / discharge test, and a charge failure is when the voltage drops when the voltage exceeds a certain voltage and does not rise to 4.2V. Certified.
⊚; Operation rate was 90% or more (best);
◯; The operation rate was 80% or more and less than 90% (good);
Δ; The operating rate was 70% or more and less than 80% (no problem in practical use);
X; The operating rate was less than 70%.

(Measurement of average particle size)
The cross section of the positive electrode layer is observed with an optical microscope or an electron microscope, the cross section of 100 randomly selected particles is measured, and the average primary particle size is calculated. A line is drawn from one end of the cross section to the other, and the distance between two points, which is the maximum length, is defined as the particle size.

<Example 2>
In the step of producing the green sheet for producing the positive electrode layer, the solid-state battery was produced and evaluated by the same method as in Example 1 except that the dispersion time by the bead mill was doubled.

<Example 3>
In the step of producing the green sheet for producing the positive electrode layer, the solid-state battery was produced and evaluated by the same method as in Example 1 except that the dispersion time by the bead mill was quadrupled.

<Example 4>
A solid-state battery was produced and evaluated by the same method as in Example 1 except that lithium manganate (LiMnO4) (average particle size 5 μm) was used as the positive electrode active material in the process of producing the green sheet for producing the positive electrode layer. It was.

<Comparative example 1>
In the step of producing the green sheet for producing the positive electrode layer, the solid-state battery was produced and evaluated by the same method as in Example 1 except that the dispersion was performed once by the three-roll ceramics roll mill instead of the dispersion by the bead mill. ..

<Comparative example 2>
In the step of producing the green sheet for producing the positive electrode layer, the solid-state battery was produced and evaluated by the same method as in Example 1 except that the dispersion was performed twice by the three-roll ceramics roll mill instead of the dispersion by the bead mill. ..

<Comparative example 3>
In the process of producing the green sheet for producing the positive electrode layer, lithium manganate (LiMnO4) (average particle size 5 μm) was used as the positive electrode active material, and instead of the dispersion by the bead mill, the dispersion was performed twice by the three-roll ceramics roll mill. Except for the above, the solid-state battery was manufactured and evaluated by the same method as in Example 1.

Each solid-state battery of Examples 1 to 4 had the following relationship in cross-sectional view:
The unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer is larger than the unevenness of the surface of the negative electrode layer in contact with the solid electrolyte layer; It is smaller than the unevenness of.

The solid-state battery of the present invention can be used in various fields where battery use or storage is expected. Although merely an example, the solid-state battery of the present invention can be used in the field of electronics mounting. The solid-state battery of the present invention also includes electric / information / communication fields (for example, mobile phones, smartphones, laptop computers and digital cameras, activity meters, arm computers, electronic papers, wearable devices, RFID tags) in which mobile devices and the like are used. , Card-type electronic money, electrical / electronic equipment field including small electronic devices such as smart watches or mobile equipment field), household / small industrial applications (for example, electric tools, golf carts, household / nursing / industrial robots) Fields), large industrial applications (eg, forklifts, elevators, bay port cranes), transportation systems (eg, hybrid vehicles, electric vehicles, buses, trains, electrically assisted bicycles, electric motorcycles, etc.), power systems Applications (for example, various power generation, road conditioners, smart grids, general household installation type power storage systems, etc.), medical applications (medical equipment fields such as earphone hearing aids), pharmaceutical applications (fields such as dose management systems), and It can be used in the IoT field, space / deep sea applications (for example, fields such as space explorers and submersible research vessels).

10: Electrode layer 10A: Positive electrode layer 10B: Negative electrode layer 11: Positive electrode current collector layer 20: Solid electrolyte layer 30: Electrode separation part 30A: Positive electrode separation part 30B: Negative electrode separation part 40: Terminal 40A: Positive electrode terminal 40B: Negative electrode terminal 60 : Outer layer material 100: Solid-state battery laminate 200: Solid-state battery

Claims

A solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer.
In a cross-sectional view of the solid-state battery, the unevenness of the surface of the positive electrode layer in contact with the solid electrolyte layer is 1.0 μm or less.
The unevenness is represented by the standard deviation of the plurality of measured values when the distance from the reference line to the positive electrode active material particles of the positive electrode layer is measured with the interface between the negative electrode layer and the solid electrolyte layer as a reference line. A solid-state battery that is the value to be.
The positive electrode layer contains a lithium transition metal composite oxide and contains.
The solid-state battery according to claim 1, wherein the negative electrode layer contains a carbon material.
The solid-state battery according to claim 1 or 2, wherein the solid-state battery includes a positive electrode current collector layer arranged on a surface of the positive electrode layer opposite to a surface in contact with the solid electrolyte layer.
The solid-state battery according to claim 3, wherein the positive electrode current collector layer contains a carbon material.
The solid-state battery according to any one of claims 1 to 4, wherein the unevenness is 0.70 μm or more and 0.82 μm or less.
A method for producing a solid-state battery, in which a mixture containing positive electrode active material particles, a solid electrolyte material, an organic material and a solvent is mixed by a wet mixing method using a medium to prepare a paste for the positive electrode layer.
The method for manufacturing a solid-state battery according to claim 6, wherein the wet mixing method using the media is a mixing method using a bead mill.
The method for manufacturing a solid-state battery according to claim 6 or 7, wherein the solid-state battery according to any one of claims 1 to 5 is manufactured.