Solid-state battery

Abstract

This invention provides a solid-state battery in which the utilization rate of the negative electrode active material is sufficiently high during charging and discharging even with a low content of conductive additive. The invention relates to a solid-state battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the negative electrode layer (2) contains a conductive additive (200) made of a metallic material and having an elongated shape in cross-section, the conductive additive (200) comprising 7% or more and 28% or less of the area of ​​the negative electrode layer.

Description

Technical Field

[0001] This invention relates to a solid-state battery. Background Technology

[0002] In recent years, the demand for batteries as power sources for portable electronic devices such as mobile phones and portable personal computers has increased significantly. In batteries used for such applications, electrolytes such as organic solvents have traditionally been used as the medium for ion movement.

[0003] However, batteries with the above-mentioned structure pose a risk of electrolyte leakage, and the organic solvents used in the electrolyte are flammable substances. Therefore, the use of solid electrolytes to replace liquid electrolytes has been proposed. Furthermore, the development of sintered solid-state secondary batteries that use solid electrolytes as the electrolyte and whose other components are also made of solids is underway.

[0004] From the perspective of improving electronic conductivity, it is known to add carbon materials as conductive additives to the negative electrode layer for solid-state batteries (Patent Document 1). However, in such technology, the sinterability of carbon materials is very low, which hinders the sintering of the negative electrode layer during co-sintering, thus resulting in a problem of reduced utilization of the negative electrode active material during charging and discharging.

[0005] Therefore, an attempt was made to promote the sintering of the electrode layer by using metal materials as conductive additives, thereby improving the utilization rate of the negative electrode active material (Patent Documents 2 and 3).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: WO2019 / 044901 Publication

[0009] Patent Document 2: WO2019 / 044902 Publication

[0010] Patent Document 3: Japanese Patent No. 5644951

[0011] The inventors of this invention discovered that, in the aforementioned prior art, such as Figure 5 As shown, even if the negative electrode layer 2' contains spherical conductive additives 200' made of metallic materials, it will still cause the breakage (n') of the conductive path p', making it difficult to form a continuous conductive path. Therefore, the utilization rate of the negative electrode active material is not sufficiently improved during charging and discharging. Therefore, in order to easily form conductive paths, more conductive additives need to be added. However, from the viewpoint of improving the energy density of solid-state batteries, it is not preferable to add a large amount of spherical conductive additives. Figure 5 This is a schematic cross-sectional view of the negative electrode layer used to illustrate the conductive path of the negative electrode layer in a solid-state battery of the prior art.

[0012] Under these circumstances, the inventors of this invention also discovered that when the negative electrode layer contains a negative electrode active material with a Li / V ratio of 2 or higher, significant problems related to the utilization rate of the negative electrode active material arise due to the use of the aforementioned spherical conductive additive made of metallic material. It is known that when using this negative electrode active material, spheroidization of the conductive additive is particularly easy to occur during sintering, and the breakage of the conductive path p' is particularly easy to occur. This can be attributed to the relatively low wettability of the negative electrode active material with a Li / V ratio of 2 or higher to the conductive additive (especially metal powder).

[0013] The purpose of this invention is to provide a solid-state battery in which the utilization rate of the negative electrode active material is sufficiently high during charging and discharging, even with a low content of conductive additives.

[0014] Furthermore, the present invention aims to provide a solid-state battery in which the utilization rate of the negative electrode active material during charging and discharging is sufficiently high, even when the negative electrode layer contains a negative electrode active material with a Li / V ratio of 2 or higher and the content of conductive additives is even lower. Summary of the Invention

[0015] This invention relates to a solid-state battery.

[0016] It includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer.

[0017] The negative electrode layer contains a conductive additive made of a metallic material and having an elongated shape when viewed in cross-section, the conductive additive accounting for more than 7% and less than 28% of the area of ​​the negative electrode layer.

[0018] The inventors of this invention have studied a method for forming appropriate conductive paths within the negative electrode layer with a smaller amount of conductive additive, and have found the following:

[0019] It is known that by including a conductive additive made of a metallic material and having an elongated shape in cross-section in the negative electrode layer (preferably, the conductive additive, made of a metallic material and having an elongated shape in cross-section, is moderately oriented in the in-plane direction), conductive paths can be formed efficiently. Therefore, by including a conductive additive made of a metallic material and having an elongated shape in cross-section in the negative electrode layer, even with a reduced content of the conductive additive, the utilization rate of the negative electrode active material can be improved, and high energy density of solid-state batteries can be achieved.

[0020] Furthermore, it is known that by appropriately aligning a conductive additive made of metallic material and having an elongated shape in cross-section within the negative electrode layer in the in-plane direction, a conductive path can be formed more fully and effectively even if the negative electrode layer has an end-face current-collecting structure. Therefore, by including a conductive additive made of metallic material and having an elongated shape in cross-section within the negative electrode layer, and by appropriately aligning this elongated conductive additive in the in-plane direction, the utilization rate of the negative electrode active material can be more fully improved even with a reduced content of the conductive additive. As a result, by having an end-face current-collecting structure in the negative electrode layer, a higher energy density in solid-state batteries can be achieved.

[0021] Furthermore, it is known that by including a conductive additive made of a metallic material and having an elongated shape in cross-section in the negative electrode layer (preferably, the conductive additive, made of a metallic material and having an elongated shape in cross-section, is moderately oriented in the in-plane direction), a conductive path can be effectively formed even when the negative electrode layer contains a negative electrode active material with a Li / V ratio of 2 or higher. Therefore, by including a conductive additive made of a metallic material and having an elongated shape in cross-section in the negative electrode layer, even when the negative electrode layer contains a negative electrode active material with a Li / V ratio of 2 or higher and the content of the conductive additive is reduced, the utilization rate of the negative electrode active material can be improved, and high energy density of solid-state batteries can be achieved.

[0022] Even with a low content of conductive additives, the solid-state battery of the present invention has a sufficiently high utilization rate of electrode active materials during charging and discharging. Attached Figure Description

[0023] Figure 1A This is a schematic cross-sectional view of a solid-state battery according to one embodiment of the present invention.

[0024] Figure 1B This is a schematic cross-sectional view of a solid-state battery according to another embodiment of the present invention.

[0025] Figure 2 This is a schematic cross-sectional view of the negative electrode layer used to illustrate the conductive path of the negative electrode layer in the solid-state battery of the present invention.

[0026] Figure 3A This is a schematic cross-sectional view of an example of a conductive additive contained in the negative electrode layer of the solid-state battery of the present invention, which is elongated in cross-sectional view.

[0027] Figure 3B This is a schematic cross-sectional view of another example of a conductive additive contained in the negative electrode layer of the solid-state battery of the present invention, which is elongated in cross-sectional view.

[0028] Figure 4AThis is a schematic cross-sectional view of a solid-state battery (main surface current collector structure) according to an embodiment of the present invention manufactured in the examples.

[0029] Figure 4B This is a schematic cross-sectional view of a solid-state battery (end face current collector structure) manufactured in another embodiment of the present invention.

[0030] Figure 5 This is a schematic cross-sectional view of the negative electrode layer used to illustrate the conductive path of the negative electrode layer in a solid-state battery of the prior art. Detailed Implementation

[0031] Solid-state batteries

[0032] This invention provides a solid-state battery. In a broad sense, "solid-state battery" as used in this specification refers to a battery whose constituent elements (especially the electrolyte layer) are made of solid material; in a narrow sense, it refers to an "all-solid-state battery" whose constituent elements (especially all constituent elements) are made of solid material. The term "solid-state battery" as used in this specification includes so-called "secondary batteries" capable of repeated charging and discharging, and "primary batteries" capable only of discharging. "Solid-state battery" is preferably a "secondary battery." The term "secondary battery" is not overly restrictive and may also include, for example, "energy storage device," etc.

[0033] like Figure 1A as well as Figure 1B As shown, the solid-state battery of the present invention includes a positive electrode layer 1, a negative electrode layer 2, and a solid electrolyte layer 3, typically having a stacked structure in which the positive electrode layer and the negative electrode layer are stacked with the solid electrolyte layer in between. The positive electrode layer and the negative electrode layer can each be stacked in two or more layers as long as a solid electrolyte layer is present between them. The solid electrolyte layer is in contact with and sandwiched between the positive electrode layer and the negative electrode layer. The positive electrode layer and the solid electrolyte layer are integrally sintered to form sintered bodies, and / or the negative electrode layer and the solid electrolyte layer are integrally sintered to form sintered bodies. Integral sintering to form sintered bodies means that two or more adjacent or contacting components (especially layers) are joined by sintering. Here, the two or more components (especially layers) are all sintered bodies and can also be integrally sintered. Figure 1A as well as Figure 1B These are schematic cross-sectional views of a solid-state battery according to one embodiment of the present invention.

[0034] like Figure 1A as well as Figure 1B As shown, the solid-state battery of the present invention may also have a positive electrode current collector layer 11, a negative electrode current collector layer 21, a positive electrode current collector (not shown), a negative electrode current collector 22, electrode separation portions 15 and 25, a protective layer 5, and end face electrodes 10 and 20. Figure 1B In addition to the negative electrode layer 2 having an end-face current collection structure, the solid-state battery is similar to... Figure 1A It is the same as a solid-state battery. Figure 1B The end-face current collection structure of the negative electrode layer 2 refers to, as detailed later, a structure in which the end face of the negative electrode layer 2 is in contact with the negative electrode current collection section 22, and is electrically connected to the negative terminal 20 via the negative electrode current collection section 22. On the other hand, in Figure 1A In the solid-state battery, the negative electrode layer 2 has a main surface current collector structure. Figure 1A The main surface current collection structure of the negative electrode layer 2 refers to the structure in which, as detailed later, the main surface of the negative electrode layer 2 is in contact with the negative electrode current collection layer 21, and is electrically connected to the negative terminal 20 mainly through the negative electrode current collection layer 21.

[0035] (Negative electrode layer)

[0036] The negative electrode layer 2 comprises a conductive additive and a negative electrode active material, and may also comprise a solid electrolyte. In the negative electrode layer, the conductive additive, the negative electrode active material, and the solid electrolyte are preferably in the form of a sintered body. For example, when the negative electrode layer comprises a conductive additive, a negative electrode active material, and a solid electrolyte, the negative electrode layer preferably has the form of a sintered body in which the negative electrode active material particles are bonded together by the conductive additive and the solid electrolyte, and the conductive additive, the negative electrode active material particles, and the solid electrolyte are bonded together by sintering between them.

[0037] The negative electrode layer contains a conductive additive with an elongated cross-sectional shape as a conductive additive. The conductive additive accounts for 7% to 28% of the area of ​​the negative electrode layer. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 7.5% to 25%, more preferably 10% to 23%, and even more preferably 15% to 22%. Specifically, as... Figure 2 As shown, by including a conductive additive 200 with an elongated cross-sectional shape in the negative electrode layer 2, a conductive path p can be efficiently formed. Therefore, by using a conductive additive with an elongated cross-sectional shape, even with a low content of the conductive additive, the utilization rate of the negative electrode active material can be improved, resulting in a high energy density in solid-state batteries. If the content of the conductive additive is too low, the utilization rate of the negative electrode active material decreases. If the content of the conductive additive is too high, the energy density of the solid-state battery decreases. Figure 2 This is a schematic cross-sectional view of the negative electrode layer used to illustrate the conductive path of the negative electrode layer in the solid-state battery of the present invention.

[0038] The content of the conductive additive with a slender cross-section relative to the total conductive additive is not particularly limited, but it is generally 35% or more (especially 35% or more and 100% or less) relative to the total conductive additive area. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 50% or more and 95% or less, and more preferably 70% or more and 90% or less.

[0039] The content of conductive additives exhibiting elongated cross-sectional shapes is determined using the area ratio of these conductive additives. Specifically, the content of conductive additives exhibiting elongated cross-sectional shapes is the area ratio of conductive additives exhibiting elongated cross-sectional shapes confirmed in the negative electrode layer of an SEM image (photograph) representing the stacked structure (cross-sectional structure) of the solid-state battery. More specifically, the content of conductive additives exhibiting elongated cross-sectional shapes is the average of values ​​measured at any 10 locations, representing the area ratio of the conductive additives exhibiting elongated cross-sectional shapes relative to the negative electrode layer (i.e., the total area of ​​all fields of view in the negative electrode layer) or relative to all conductive additives (i.e., the area of ​​all conductive additives in each field of view).

[0040] A conductive additive exhibiting an elongated shape in cross-sectional observation refers to a conductive additive that has an elongated shape in cross-sectional observation of the negative electrode layer. For example, a conductive additive exhibiting an elongated shape in cross-sectional observation of the negative electrode layer has a shape with an elongated direction in cross-sectional observation. As used in this specification, "cross-sectional observation" refers to the shape of a solid-state battery when viewed from a direction substantially perpendicular to the thickness direction based on the stacking direction of the active material layers constituting the solid-state battery (in short, the shape when cut with a plane parallel to the thickness direction), including cross-sectional views. In particular, "cross-sectional observation" can also refer to the shape when cut with a plane parallel to the thickness direction based on the stacking direction of each layer constituting the solid-state battery, i.e., a plane perpendicular to the positive and negative terminals; for example, examples can be listed... Figure 1A as well as Figure 1B The cross-sectional observation shown. Therefore, the "SEM image representing the stacked structure (cross-sectional structure) of a solid-state battery" used for various measurements can also be an image based on the cross-sectional observation as described above.

[0041] As a conductive additive that can be observed to have an elongated shape in cross-section, for example, flat conductive additives, fibrous conductive additives, or mixtures thereof can be used. When using simple metal powder as a conductive additive, it is difficult to obtain sufficient utilization of the negative electrode active material because the metal powder spheroidizes (especially becomes spherical) in the negative electrode layer during sintering. In this invention, since flat or fibrous conductive additives are used, spheroidization (especially becoming spherical) is suppressed during sintering, and the conductive additive can be observed to have an elongated shape in cross-section after sintering, thus easily obtaining sufficient utilization of the negative electrode active material. In the solid-state battery of this invention, the conductive additive that is observed to have an elongated shape in cross-section corresponds to any of the materials of flat conductive additives, fibrous conductive additives, or mixtures thereof, and can be easily identified by decomposing the solid-state battery.

[0042] In simple terms, a flat shape is the shape of particles that have been flattened; it is also known as a "scale-like" or "flat" shape.

[0043] Fibrous refers to shapes that include “wire-like” or “rod-like” shapes, such as those found in so-called metal nanowires.

[0044] Even when using only simple metal powder (e.g., spherical conductive additives) as conductive additives, some of the metal powder bonds together in the negative electrode layer through sintering, sometimes resulting in an elongated shape in cross-section. However, when the negative electrode layer contains only metal powder at a content of 28% or less relative to the negative electrode layer, the content of the conductive additive exhibiting an elongated shape in cross-section is typically 4% or less relative to the negative electrode layer (or 10% or less relative to the total area of ​​the conductive additives), making it impossible to achieve the elongated conductive additive content in cross-section as described in this invention.

[0045] For conductive additives that appear elongated in cross-section, specifically in the negative electrode layer, such as... Figure 3A As shown, in cross-sectional view, for one conductive additive 200a, it has a shape defined by the longest dimension a and the short side length (thickness dimension) b, and its depth length c (i.e. Figure 3A The dimensions in the inward and outward directions (not shown) are not specifically defined. The longest dimension 'a' is the dimension with the maximum length specified in the cross-sectional view. The short side length 'b' is the dimension with the maximum length (or maximum thickness) specified in the cross-sectional view in the direction perpendicular to the longest dimension 'a'. The short side length 'b' generally satisfies a > b. The depth length 'c' is the dimension with the maximum length specified in the direction perpendicular to the cross-sectional view, generally satisfying c ≥ 2b in the case of a flat shape (especially 2a ≥ c ≥ 2b), and 2b > c in the case of a fibrous shape (especially 2b > c > 0.5b). Specifically, an elongated shape in the cross-sectional view refers to a shape with a / b of 2.0 or more (especially 2.0 or more and 20.0 or less). Figure 3A This is a schematic cross-sectional view of an example of a conductive additive contained in the negative electrode layer of the solid-state battery of the present invention, which is elongated in cross-sectional view.

[0046] The cross-section shows an elongated shape, including the curved elongated shape that gives the bends. Specifically, the curved elongated shape is as follows: Figure 3B As shown, in cross-sectional view, one of the conductive additives 200b in the negative electrode layer has more than one bend 201, and its shape is defined by the longest dimension a and the short side length (thickness dimension) b, with a depth length c (i.e. Figure 3B The dimensions in the inward and outward directions (not shown) are not particularly defined. In curved slender shapes, the longest dimension 'a' is the dimension that specifies the maximum length in a cross-sectional view. The short side length 'b' is the dimension that specifies the maximum length (or maximum thickness) in a cross-sectional view in the direction perpendicular to the longest dimension 'a'. The depth length 'c' is the dimension that specifies the maximum length in a top view perpendicular to the cross-sectional view. Curved slender shapes (e.g.) Figure 3B The a, b, c, and their relationships in the text appear elongated compared to a simple cross-sectional view (e.g., Figure 3A The relationship is the same in ). Figure 3B This is a schematic cross-sectional view of another example of a conductive additive contained in the negative electrode layer of the solid-state battery of the present invention, which is elongated in cross-sectional view.

[0047] The conductive additive, which is elongated in cross-section when viewed in the negative electrode layer, typically has an average aspect ratio (the longest dimension a / short side length b) of 2.0 or more (particularly 2.0 or more and 20.0 or less). From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 2.0 or more and 15.0 or less, more preferably 2.5 or more and 10.0 or less, and even more preferably 3.0 or more and 8.0 or less.

[0048] The average aspect ratio (a / b) of the conductive additives with elongated cross-sectional shapes was determined using the average of any 100 conductive additives with elongated cross-sectional shapes identified in the negative electrode layer of an SEM image (photograph) representing the stacked structure (cross-sectional structure) of a solid-state battery.

[0049] In conductive additives that exhibit an elongated shape when viewed in cross-section within the negative electrode layer, the average short side length b is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 0.1 μm or more and 4.0 μm or less, more preferably 0.2 μm or more and 2.0 μm or less, even more preferably 0.3 μm or more and 1.5 μm or less, and particularly preferably 0.3 μm or more and 1.0 μm or less.

[0050] The average short side length b of the conductive additives with elongated cross-sectional shapes was determined using the average value of any 100 elongated conductive additives identified in the negative electrode layer of an SEM image (photograph) representing the stacked structure (cross-sectional structure) of a solid-state battery.

[0051] Regarding conductive additives that exhibit an elongated shape in cross-sectional observation within the negative electrode layer, the average depth length c is not particularly limited, and can be, for example, 0.1 μm or more and 10.0 μm or less. For example, when using a flat conductive additive, the average depth length c of the conductive additive exhibiting an elongated shape in cross-sectional observation within the negative electrode layer is typically 0.1 μm or more and 20 μm or less. Furthermore, when using a fibrous conductive additive, for example, the average depth length c of the conductive additive exhibiting an elongated shape in cross-sectional observation within the negative electrode layer is typically 0.1 μm or more and 10.0 μm or less.

[0052] The average depth length c of the conductive additive with an elongated cross-sectional shape can be obtained by using the average value of any 100 conductive additives with an elongated cross-sectional shape, which are identified in the negative electrode layer of a three-dimensional image generated from 100 SEM images taken at 0.1 μm intervals representing the stacked structure (cross-sectional structure) of the solid battery.

[0053] In conductive additives that are elongated in cross-section when viewed in the negative electrode layer, from the viewpoint of further improving the utilization rate of the negative electrode active material, the content of conductive additives with an orientation angle of 30° or less is preferably 20% or more (particularly 20% or more and 100% or less) relative to the area ratio of all conductive additives, more preferably 50% or more and 90% or less, further preferably 55% or more and 75% or less, and most preferably 61% or more and 66% or less.

[0054] The orientation angle of a conductive additive that appears elongated in cross-section is the absolute value of the angle (the angle of the smaller of the two) between the longest dimension 'a' of the conductive additive and the horizontal direction, assuming the solid-state battery is placed with the stacking direction L of the positive electrode layer, solid electrolyte layer, and negative electrode layer perpendicular to the horizontal direction. For example, assuming... Figure 3A When the vertical direction is parallel to the stacking direction L, the orientation angle of the conductive additive 200a, which appears elongated in cross-section, is 0°. Additionally, for example, assuming... Figure 3BWhen the vertical direction is parallel to the stacking direction L, the orientation angle of the conductive additive 200b, which has an elongated cross-sectional shape, is θ. The conductive additive used in this invention has an elongated cross-sectional shape, and the negative electrode layer containing the conductive additive with the elongated cross-sectional shape has an extremely thin thickness as described later. Therefore, the conductive additive with the elongated cross-sectional shape typically has a majority (e.g., an area ratio of 50% or more, especially 60% or more) of its orientation angle of less than 30° in the negative electrode layer.

[0055] The orientation angle of the elongated conductive additive observed in cross-section is a value confirmed in the negative electrode layer of an SEM image (photograph) representing the stacked structure (cross-sectional structure) of a solid-state battery.

[0056] The content of elongated conductive additives with an orientation angle of 30° or less in the cross-sectional view of the negative electrode layer, relative to the total conductive additives, is the value representing the area ratio of elongated conductive additives with an orientation angle of 30° or less in the cross-sectional view of the negative electrode layer in the SEM image (photograph) of the solid-state battery's stacked structure (cross-sectional structure), relative to the total conductive additives. More specifically, the content of elongated conductive additives with an orientation angle of 30° or less in the cross-sectional view is the average of values ​​measured at any 10 locations, representing the area ratio of elongated conductive additives with an orientation angle of 30° or less in the cross-sectional view to the total conductive additives (i.e., the area of ​​all conductive additives in each field of view).

[0057] The conductive additive, which exhibits an elongated shape in cross-sectional view, is composed of a metallic material. Examples of metallic materials suitable for constituting an elongated conductive additive in cross-sectional view include one or more metals selected from the group consisting of Ag (silver), Au (gold), Pd (palladium), Pt (platinum), Cu (copper), Sn (tin), Ni (nickel), and alloys thereof. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferable that the conductive additive exhibiting an elongated shape in cross-sectional view is composed of silver.

[0058] The negative electrode layer may also contain conductive additives other than conductive additives that have an elongated cross-sectional shape. Examples of other conductive additives include spherical conductive additives made of the same metal material as the conductive additives that have an elongated cross-sectional shape, acetylene black, Ketjen black, Super P (registered trademark), VGCF (registered trademark), and carbon materials such as carbon nanotubes.

[0059] In the negative electrode layer, from the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferable to contain all conductive additives, including conductive additives that have an elongated shape in cross-section and other conductive additives, in a content of 30% or less (especially 5% or more and 30% or less) relative to the area of ​​the negative electrode layer, more preferably 12% or more and 30% or less, and even more preferably 18% or more and 28% or less.

[0060] The content of all conductive additives is expressed as the area ratio of all conductive additives. Specifically, the content of all conductive additives is the area ratio of all conductive additives confirmed in the negative electrode layer of an SEM image (photograph) representing the stacked structure (cross-sectional structure) of the solid-state battery. More specifically, the content of all conductive additives is the average of values ​​measured at any 10 locations, representing the ratio of the area of ​​all conductive additives to the total area of ​​all fields of view in the negative electrode layer.

[0061] The negative electrode layer is a layer capable of intercalating and deintercalating metal ions, preferably a layer capable of intercalating and deintercalating lithium ions. The negative electrode active material contained in the negative electrode layer is not particularly limited, but from the viewpoint of further improving the utilization rate of the negative electrode active material and increasing the discharge capacity, a negative electrode active material containing a Li (lithium) to V (vanadium) molar ratio of 2.0 or more (particularly 2 or more and 10 or less) is preferred. From the viewpoint of further improving the utilization rate of the negative electrode active material, the Li to V molar ratio in the negative electrode active material is preferably 2 or more and 6 or less (particularly 2 or more and 4 or less). In this invention, a negative electrode active material containing such a molar ratio in the negative electrode layer is particularly effective. When the negative electrode layer contains a negative electrode active material with such a molar ratio, due to the low wettability with the conductive additive, spheroidization (e.g., balling) of the conductive additive is particularly easy to occur during sintering, which particularly easily causes the breakage of the conductive path p', further reducing the utilization rate of the negative electrode active material. However, in this invention, even when the negative electrode layer contains such a negative electrode active material, the breakage of the conductive path can be sufficiently suppressed. As a result, the utilization rate of the negative electrode active material during charging and discharging can be more fully improved with a smaller amount of conductive additive. Therefore, when the negative electrode layer contains the negative electrode active material in the above molar ratio, the effect of forming the conductive additive into a slender shape when viewed in cross-section is particularly significant in this invention.

[0062] In this invention, in a solid-state battery where the negative electrode layer contains a negative electrode active material with a Li to V molar ratio within the aforementioned range, and the solid electrolyte layer contains a solid electrolyte with a LISICON-type structure as described later, the presence of V in the LISICON-type solid electrolyte of the solid electrolyte layer allows for good bonding between the solid electrolyte layer and the negative electrode layer. Furthermore, side reactions during co-sintering between the negative electrode active material in the negative electrode layer and the LISICON-type solid electrolyte in the solid electrolyte layer can be suppressed, increasing the reversible capacity of the solid-state battery. As a result, the utilization rate of the negative electrode active material during charge and discharge can be more fully improved.

[0063] From the viewpoint of further improving the utilization rate of the negative electrode active material, the negative electrode active material preferably has an average chemical composition represented by the following general formula (1).

[0064] [Chemical Formula 1]

[0065] (Li [3-ax+(5-b)(1-y)] A x (V) y B 1-y O4 (1)

[0066] By employing such a composition, the reactivity with the LISICON-type solid electrolyte in the solid electrolyte layer can be further reduced. Furthermore, the negative electrode active material used in this invention exhibits its capacity more fully through the redox reaction of V. Therefore, to obtain sufficient reversible capacity, the amount of V, y, is preferably 0.5 ≤ y ≤ 1.0, as described later. When the negative electrode active material has the above composition, as long as the average composition described above is adopted in the thickness direction of the negative electrode layer, the chemical composition can also be varied in the thickness direction of the negative electrode layer.

[0067] In formula (1), A is one or more elements selected from the group consisting of Na (sodium), K (potassium), Mg (magnesium), Ca (calcium) and Zn (zinc).

[0068] B is one or more elements selected from the group consisting of Zn (zinc), Al (aluminum), Ga (gallium), Si (silicon), Ge (germanium), Sn (tin), P (phosphorus), As (arsenic), Ti (titanium), Mo (molybdenum), W (tungsten), Fe (iron), Cr (chromium), and Co (cobalt).

[0069] x has a relationship of 0 ≤ x ≤ 1.0, preferably a relationship of 0 ≤ x ≤ 0.5, and more preferably a relationship of 0 ≤ x ≤ 0.1.

[0070] The relationship y has 0.5≤y≤1.0, preferably 0.55≤y≤1.0, and more preferably 1.

[0071] 'a' is the average valence of A. The average valence of A, as A, for example, if we assume that there are n1 elements X with valence a+, n2 elements Y with valence b+, and n3 elements Z with valence c+, is represented by (n1×a+n2×b+n3×c) / (n1+n2+n3).

[0072] b is the average valence of B. The average valence of B, as B, for example, if we assume that there are n1 elements X with valence a+, n2 elements Y with valence b+, and n3 elements Z with valence c+, is the same value as the average valence of A mentioned above.

[0073] In formula (1), from the viewpoint of improving the ease of obtaining the negative electrode active material and further improving the utilization rate of the negative electrode active material, in the preferred embodiment, it is as follows:

[0074] A is one or more elements selected from the group consisting of Al and Zn.

[0075] B is selected from one or more elements, especially two elements, from the group consisting of Si and P.

[0076] x has the relationship 0≤x≤0.06, and is more preferably 0.

[0077] The relationship y has 0.55≤y≤1.0, more preferably 0.8≤y≤1.0, and even more preferably 1.

[0078] a is the average price of A.

[0079] b is the average price of B.

[0080] Specific examples of negative electrode active materials include Li3VO4 and Li 3.2 (V 0.8 Si 0.2 O4、(Li 3.1 Al 0.03 (V) 0.8 Si 0.2 O4、(Li 3.1 Zn 0.05 (V) 0.8 Si 0.2 O4, Li 3.3 (V 0.6 P 0.1 Si 0.3 O4, Li 3.18 (V 0.77 P 0.05 Si 0.18 O4, Li 3.07 (V 0.90 P 0.03 Si0.07 O4, Li 3.22 (V 0.72 P 0.06 Si 0.22 O4, etc.

[0081] The chemical composition of the negative electrode active material can be considered as an average chemical composition. The average chemical composition of the negative electrode active material refers to the average value of its chemical composition along the thickness direction of the negative electrode layer. This average chemical composition can be analyzed and measured by breaking the solid-state battery and using SEM-EDX (energy dispersive X-ray spectrometry) to perform compositional analysis with the entire negative electrode layer in the thickness direction within the field of view.

[0082] In the negative electrode layer, the average chemical composition of the negative electrode active material and the average chemical composition of the solid electrolyte (described later) can be automatically distinguished and measured based on these compositions in the above composition analysis.

[0083] The negative electrode active material can be manufactured, for example, by the following method. First, a raw material compound containing a specified metal atom is weighed to achieve the specified chemical composition. Water is added and mixed to obtain a slurry. The slurry is dried and pre-calcined at a temperature of 700°C to 1000°C for 4 to 6 hours. Then, it is pulverized to obtain the negative electrode active material.

[0084] When the negative electrode active material is sintered at high speed, for example at 750°C for about 1 minute, together with the solid electrolyte layer, the chemical composition of the negative electrode active material directly reflects the chemical composition of the negative electrode active material used in manufacturing. However, when the negative electrode active material is sintered at 750°C for about 1 hour, the elements diffuse into the solid electrolyte layer, and the amount of V usually decreases.

[0085] From the perspective of further improving the utilization rate of negative electrode active materials, negative electrode active materials preferably have β II -Li3VO4 type structure or γ II -Li3VO4 type structure. This crystal structure improves charge-discharge reversibility and enables stable cycling characteristics. Furthermore, by employing γ-... II The -Li3VO4 type structure has improved binding affinity with the LISICON type solid electrolyte in the solid electrolyte layer, and is therefore preferred.

[0086] The negative electrode active material has β II The -Li3VO4 type structure refers to the fact that the negative electrode active material (especially its particles) has a β-type structure. II -Li3VO4 type crystal structure, broadly speaking, refers to a crystal structure that can be identified by those skilled in the art of solid-state batteries as β IIThe crystal structure is of the Li3VO4 type. In a narrow sense, the negative electrode active material possesses β... II The -Li3VO4 type structure refers to the fact that the negative electrode active material (especially its particles) exhibits a similarity to the so-called β-type structure in X-ray diffraction at a specified incident angle. II The crystal structure of the Li3VO4 type inherently corresponds to more than one major peak in the Miller index. As a crystal with β... II An example of a negative electrode active material with a Li3VO4-type structure is ICDD Card No. 01-073-6058.

[0087] The negative electrode active material has γ II -Li3VO4 type structure refers to the presence of γ-type in the negative electrode active material (especially its particles). II -Li3VO4 type crystal structure, broadly speaking, refers to a crystal structure that can be identified by those skilled in the art of solid-state batteries as γ II The crystal structure is of the Li3VO4 type. In a narrow sense, the negative electrode active material possesses γ... II The -Li3VO4 type structure refers to the fact that the negative electrode active material (especially its particles) exhibits a similar appearance to so-called γ-ray diffraction at a specified incident angle in X-ray diffraction. II The crystal structure of the -Li3VO4 type corresponds to more than one major peak in the Miller index. As a crystal with γ... II An example of a negative electrode active material with a Li3VO4-type structure is ICDD Card No. 01-073-2850.

[0088] The average chemical composition and crystal structure of the negative electrode active material in the negative electrode layer typically vary depending on element diffusion during sintering. In a solid-state battery where the negative electrode active material is sintered together with the positive electrode layer and the solid electrolyte layer, it preferably possesses the aforementioned average chemical composition and crystal structure.

[0089] The average particle size of the negative electrode active material is not particularly limited, for example, it can be 0.01 μm or more and 20 μm or less, preferably 0.1 μm or more and 5 μm or less.

[0090] The average particle size of the negative electrode active material can be calculated by simply averaging the particle sizes of 10 to 100 randomly selected particles from an SEM image (arithmetic mean).

[0091] Particle size is the diameter of a spherical particle assuming it is perfectly spherical. Such a particle size can be calculated, for example, as follows: cut out a cross-section of a solid-state battery, take a SEM image of the cross-section using an SEM, calculate the cross-sectional area S of the particle using image analysis software (e.g., "Azokun" (made by Asahi Kasei Engineering Co., Ltd.)), and then calculate the particle diameter R using the following formula.

[0092] [Mathematical Expression 1]

[0093] R = 2 × (S / π) 1 / 2

[0094] It should be noted that the average particle size of the negative electrode active material in the negative electrode layer can be automatically measured by assembling a specific negative electrode active material during the measurement of the average chemical composition mentioned above.

[0095] The volume ratio of the negative electrode active material in the negative electrode layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 20% or more and 80% or less, more preferably 30% or more and 75% or less, and even more preferably 30% or more and 60% or less.

[0096] The volume ratio of the negative electrode active material in the negative electrode layer can be measured from the SEM image processed by FIB cross-section. Specifically, the cross-section of the negative electrode layer is observed using SEM-EDX. The regions where V is detected by EDX are identified as negative electrode active materials. By calculating the area ratio of these regions, the volume ratio of the negative electrode active material can be measured.

[0097] The particle shape of the negative electrode active material in the negative electrode layer is not particularly limited. For example, it can be any particle shape among spherical, flat, and irregular shapes.

[0098] The negative electrode layer preferably further comprises a solid electrolyte, particularly a solid electrolyte with a garnet-type structure. By including a garnet-type solid electrolyte in the negative electrode layer, the ionic conductivity of the negative electrode layer can be increased, and a higher rate of reaction can be expected. Furthermore, since side reactions during co-firing with negative electrode active materials with a Li / V ratio of 2 or higher can be suppressed, the utilization rate of the negative electrode can be expected to be improved. As described later, the solid electrolyte layer also preferably further comprises a solid electrolyte, particularly a solid electrolyte with a garnet-type structure. This is because including a garnet-type solid electrolyte in the solid electrolyte layer improves the insulation of the solid electrolyte layer. This can be attributed to the fact that garnet-type solid electrolytes are difficult to reduce during charging and discharging, thus hindering electron injection, and the increased tortuosity and electronic resistance of the LISICON-type solid electrolyte in the solid electrolyte. Additionally, since side reactions during co-firing with negative electrode active materials with a Li / V ratio of 2 or higher can be suppressed, the utilization rate of the negative electrode can be expected to be improved. Therefore, at least one (especially both) of the negative electrode layer or the solid electrolyte layer preferably comprises a solid electrolyte with a garnet-type structure. The inclusion of a solid electrolyte with a garnet-type structure in at least one of the negative electrode layer or the solid electrolyte layer means that either the negative electrode layer or the solid electrolyte layer may contain a solid electrolyte with a garnet-type structure, or both of them may contain a solid electrolyte with a garnet-type structure.

[0099] A solid electrolyte having a garnet-type structure means that the solid electrolyte has a garnet-type crystal structure. In a broad sense, it refers to a crystal structure that can be identified as a garnet-type crystal structure by those skilled in the art of solid-state batteries. In a narrow sense, a solid electrolyte having a garnet-type structure means that, in X-ray diffraction, the solid electrolyte displays one or more major peaks corresponding to the Miller indices inherent in a so-called garnet-type crystal structure at a specified incident angle.

[0100] In the negative electrode layer, the solid electrolyte having a garnet-type structure preferably has an average chemical composition represented by the following general formula (2).

[0101] [Chemical Formula 2]

[0102] (Li [7-ax-(b-4)y] A x )La3Zr 2-y B y O 12 (2)

[0103] By including a solid electrolyte with the above-mentioned average chemical composition in the negative electrode layer, the utilization rate of the negative electrode active material can be further improved.

[0104] In formula (2), A is one or more elements selected from the group consisting of Ga (gallium), Al (aluminum), Mg (magnesium), Zn (zinc) and Sc (scandium).

[0105] B is one or more elements selected from the group consisting of Nb (niobium), Ta (tantalum), W (tungsten), Te (tellurium), Mo (molybdenum), and Bi (bismuth).

[0106] x has the relationship 0 ≤ x ≤ 0.5.

[0107] y has the relationship 0 ≤ y ≤ 2.0.

[0108] a is the average price of A, which is the same as the average price of A in equation (1).

[0109] b is the average price of B, which is the same as the average price of B in equation (1).

[0110] In equation (2), from the viewpoint of further improving the utilization rate of the negative electrode active material, in a preferred embodiment, it is as follows:

[0111] A is one or more elements selected from the group consisting of Ga and Al.

[0112] B is one or more elements selected from the group consisting of Nb, Ta, W, Mo, and Bi.

[0113] x has the relationship 0≤x≤0.3, preferably 0.

[0114] The relationship y has 0≤y≤1.0, preferably 0≤y≤0.7, more preferably 0.3≤y≤0.7, and most preferably 0.5.

[0115] a is the average price of A.

[0116] b is the average price of B.

[0117] As a specific example of a solid electrolyte represented by general formula (2), for example, (Li 6.4 Ga 0.05 Al 0.15 La3Zr2O 12 、(Li 6.4 Ga 0.2 La3Zr2O 12 Li 6.4 La3(Zr 1.6 Ta 0.4 )O 12 、(Li 6.4 Al 0.2 La3Zr2O 12 Li 6.5La3(Zr 1.5 Mo 0.25 )O 12 Li 6.5 La3(Zr 1.5 Ta 0.5 )O 12 .

[0118] The average chemical composition of the solid electrolyte (especially the solid electrolyte with a garnet-type structure) in the negative electrode layer refers to the average chemical composition of the solid electrolyte along the thickness direction of the negative electrode layer. The average chemical composition of the solid electrolyte can be analyzed and measured by breaking the solid battery and using SEM-EDX (energy dispersive X-ray spectrometry) to perform compositional analysis with the entire negative electrode layer in the thickness direction under EDX.

[0119] In the negative electrode layer, the average chemical composition of the negative electrode active material and the average chemical composition of the solid electrolyte can be automatically distinguished and measured based on these compositions in the above composition analysis.

[0120] For the solid electrolyte of the negative electrode layer, in addition to using raw material compounds containing specified metal atoms, it can be obtained by the same method as the negative electrode active material, or it can be obtained as a commercially available product.

[0121] The average chemical composition and crystal structure of the solid electrolyte in the negative electrode layer typically vary due to element diffusion during sintering. Preferably, the solid electrolyte has the aforementioned average chemical composition and crystal structure in the solid-state battery after sintering together with the positive electrode layer and the solid electrolyte layer.

[0122] The volume ratio of solid electrolyte (especially solid electrolyte with garnet structure) in the negative electrode layer is not particularly limited. From the viewpoint of further improving the utilization rate of negative electrode active material and balancing the high energy density of solid battery, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0123] The volume ratio of solid electrolyte in the negative electrode layer can be measured using the same method as the volume ratio of the negative electrode active material. Garnet-type solid electrolytes are based on the detection of Zr and / or La sites using EDX.

[0124] In addition to the negative electrode active material and the solid electrolyte, the negative electrode layer may also contain, for example, sintering aids and conductive aids.

[0125] By including sintering aids in the negative electrode layer, densification can be achieved even during sintering at lower temperatures, suppressing elemental diffusion at the interface between the negative electrode active material and the solid electrolyte layer. Sintering aids known in the field of solid-state batteries can be used. From the viewpoint of further improving the utilization rate of the negative electrode active material, the inventors conducted research and found that the composition of the sintering aid preferably contains at least Li (lithium), B (boron), and O (oxygen), with a Li / B molar ratio of 2.0 or higher. These sintering aids have low melting points, enabling densification of the negative electrode layer at lower temperatures through liquid-phase sintering. Furthermore, by employing the above composition, side reactions between the sintering aid and the LISICON-type solid electrolyte used in this invention during co-sintering can be further suppressed. Examples of sintering aids that meet these requirements include Li3BO3, (Li... 2.7 Al 0.3 )BO3, Li 2.8 (B 0.8 C 0.2 O3, etc. Among them, Li3, which has particularly high ionic conductivity, is especially preferred. 2.7 Al 0.3 )BO3.

[0126] The volume ratio of sintering aid in the negative electrode layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material and balancing the high energy density of solid-state batteries, it is preferably 0.1% or more and 10% or less, and more preferably 1% or more and 7% or less.

[0127] The volume proportion of sintering aids in the negative electrode layer can be measured using the same method as the volume proportion of the negative electrode active material. As the detection element in the EDX of the region identified as a sintering aid, B can be considered.

[0128] In the negative electrode layer, the porosity is not particularly limited, but from the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0129] The porosity of the negative electrode layer was measured using SEM images processed from the FIB cross-section.

[0130] The negative electrode layer typically has a thickness of 2 μm or more and 100 μm or less, preferably 2 μm or more and 50 μm or less.

[0131] The negative electrode layer 2 can have the following characteristics: Figure 1A The end-face collector structure shown, or may have the following characteristics: Figure 1B The main surface current collector structure is shown. From the viewpoint of further improving capacity density (e.g., energy density), the negative electrode layer preferably has an end-face current collector structure.

[0132] The negative electrode layer 2 having an end-face current collection structure means that the negative electrode layer 2 has a structure in which current is collected at the end face 2a (specifically, only the end face) of the negative electrode layer 2 on the side of the negative terminal 20. More specifically, the negative electrode layer 2, for example... Figure 1B As shown, the negative terminal 20 can be electrically connected to the negative electrode current collector 22 via the negative electrode current collector 22 while simultaneously contacting the negative electrode current collector 22 on the end face 2a (especially only the end face) of the negative electrode layer 2. Alternatively, the negative terminal 20 can be directly and electrically connected to the negative electrode 20 on the end face 2a (especially only the end face) of the negative electrode layer 2. From the viewpoint of more fully ensuring the electrical connection with the negative terminal 20, as... Figure 1B As shown, the negative electrode layer 2 is preferably in contact with the negative electrode current collector 22 on the negative electrode terminal 20 side at the end face 2a (especially only the end face) of the negative electrode layer 2, while the negative electrode current collector 22 is connected to the negative electrode terminal 20 via the negative electrode current collector 22.

[0133] In the end-face current collector structure of the negative electrode layer 2, when the negative electrode layer 2 is electrically connected to the negative terminal 20 via the negative electrode current collector 22, the negative electrode layer 2 and the negative electrode current collector 22 are in contact with each other at their end faces. As a result, in cross-sectional view, they have a structure that is adjacent to each other in a direction perpendicular to the stacking direction. The negative electrode layer 2 and the negative electrode current collector 22 also have a structure that is adjacent to each other in a direction perpendicular to the stacking direction in a top view.

[0134] In the end-face current collector structure of the negative electrode layer 2, when the negative electrode layer 2 is electrically connected to the negative terminal 20 via the negative electrode current collector 22, the negative electrode current collector 22 typically has an upper surface 22b flush with the upper surface 2b of the negative electrode layer 2 in the stacking direction L, and a lower surface 22c flush with the lower surface 2c of the negative electrode layer 2 in the stacking direction L. "Flush" means that there is no height difference between the two surfaces. The two surfaces refer to the upper surface 2b of the negative electrode layer 2 and the upper surface 22b of the negative electrode current collector 22, as well as the lower surface 2c of the negative electrode layer 2 and the lower surface 22c of the negative electrode current collector 22.

[0135] The negative electrode layer 2 having a main surface current collection structure means that the negative electrode layer 2 has a structure in which current is collected on the main surface of the negative electrode layer. Specifically, as follows: Figure 1A As shown, the negative electrode layer 2 is in contact with the negative electrode current collector layer 21 on its main surface 2x, and is electrically connected to the negative terminal 20 via the negative electrode current collector layer 21. In the main surface current collector structure of the negative electrode layer 2, the negative electrode current collector layer 21 can be stacked on the main surface of the negative electrode layer 2, and / or the negative electrode layer 2 can be stacked on the main surface of the negative electrode current collector layer 21. The main surface refers to a surface with a relatively large area, specifically the upper surface and / or lower surface perpendicular to the stacking direction. Current collection on the main surface mainly refers to electrons entering and exiting from the main surface. Figure 1AIn this configuration, the negative electrode layer 2 is directly electrically connected to the negative terminal 20 on the negative terminal 20 side, but it can also be electrically connected to the negative terminal 20 via a negative electrode current collector, similar to the negative electrode layer in the end-face current collector structure. When the negative electrode layer 2 has a main-face current collector structure, such as... Figure 1A As shown, the negative electrode layer 2 can be stacked on both main surfaces of the negative electrode current collector layer 21, or it can be stacked on one main surface.

[0136] The negative electrode layer 2 may include a negative electrode current collector layer 21 and a negative electrode current collector portion 22, both of which are composed of at least a conductive material. The negative electrode current collector layer 21 and the negative electrode current collector portion 22 may further include a solid electrolyte. In a preferred embodiment, the negative electrode current collector layer 21 and the negative electrode current collector portion 22 are composed of a sintered body comprising at least a conductive material and a solid electrolyte. The conductive material that may be included in the negative electrode current collector layer 21 and the negative electrode current collector portion 22 is typically a material with high conductivity, preferably at least one selected from the group consisting of carbon, silver, palladium, gold, platinum, aluminum, copper, and nickel. The solid electrolyte that may be included in the negative electrode current collector layer 21 and the negative electrode current collector portion 22 may be selected from the same solid electrolyte that may be included in the negative electrode layer described above.

[0137] From the viewpoint of reducing the manufacturing cost and internal resistance of solid-state batteries through integral sintering, the negative electrode current collector layer 21 and the negative electrode current collector portion 22 preferably have a sintered body form. When the negative electrode current collector layer 21 and the negative electrode current collector portion 22 have a sintered body form, for example, the negative electrode current collector layer 21 and the negative electrode current collector portion 22 can be composed of a sintered body containing a sintering aid in addition to the aforementioned conductive material and solid electrolyte. The sintering aid contained in the negative electrode current collector layer 21 and the negative electrode current collector portion 22 can be selected from, for example, the same material that can be contained in the negative electrode layer.

[0138] The thickness of the negative electrode current collector layer is not particularly limited. For example, it can be 1 μm or more and 10 μm or less, preferably 1 μm or more and 5 μm or less, and particularly preferably 1 μm or more and 3 μm or less.

[0139] The thickness of the negative electrode current collector can usually be the same as that of the negative electrode layer.

[0140] The negative electrode layer is a layer that can be called the "negative electrode active material layer".

[0141] As described above, the negative electrode layer is preferably a layer capable of inserting and deintercalating lithium ions, but in this invention, the negative electrode layer may also be a layer capable of inserting and deintercalating sodium ions.

[0142] (Positive electrode layer)

[0143] In this invention, the positive electrode layer 1 is not particularly limited. For example, the positive electrode layer 1 contains a positive electrode active material. The positive electrode layer 1 preferably has the morphology of a sintered body containing positive electrode active material particles.

[0144] The positive electrode layer is a layer capable of intercalating and deintercalating metal ions, preferably a layer capable of intercalating and deintercalating lithium ions. There are no particular limitations on the positive electrode active material; known positive electrode active materials in the field of solid-state batteries can be used. Examples of positive electrode active materials include lithium phosphate compound particles with a NASICON-type structure, lithium phosphate compound particles with an olivine-type structure, lithium-containing layered oxide particles, and lithium-containing oxide particles with a spinel-type structure. Specific examples of lithium phosphate compounds with a preferred NASICON-type structure include Li3V2(PO4)3. Specific examples of lithium phosphate compounds with a preferred olivine-type structure include Li3Fe2(PO4)3 and LiMnPO4. Specific examples of lithium-containing layered oxide particles that are preferred include LiCoO2 and LiCo... 1 / 3Ni 1 / 3 Mn 1 / 3 O2, etc. Specific examples of preferred lithium oxides with a spinel-type structure include LiMn2O4 and LiNi. 0.5 Mn 1.5 O4, Li4Ti5O 12 From the viewpoint of reactivity during co-sintering with the LISICON-type solid electrolyte used in this invention, LiCoO2 and LiCo are more preferably used as the positive electrode active material. 1 / 3 Ni 1 / 3 Mn 1 / 3 Lithium-containing layered oxides such as O2. It should be noted that only one type of positive electrode active material particle can be used, or multiple types can be used in combination.

[0145] The NASICON-type structure of the positive electrode active material in the positive electrode layer refers to the fact that the positive electrode active material (especially its particles) has a NASICON-type crystal structure. In a broad sense, it refers to a crystal structure that can be identified as NASICON-type by those skilled in the art of solid-state batteries. In a narrow sense, the NASICON-type structure of the positive electrode active material in the positive electrode layer means that, in X-ray diffraction, the positive electrode active material (especially its particles) displays one or more major peaks corresponding to the Miller indices inherent in a so-called NASICON-type crystal structure at a specified incident angle. The compounds exemplified above are examples of preferred positive electrode active materials with a NASICON-type structure.

[0146] The olivine-type structure of the positive electrode active material in the positive electrode layer refers to the olivine-type crystal structure of the positive electrode active material (especially its particles). In a broad sense, it refers to a crystal structure that can be identified as olivine-type by those skilled in the art of solid-state batteries. In a narrow sense, the olivine-type structure of the positive electrode active material in the positive electrode layer means that, in X-ray diffraction, the positive electrode active material (especially its particles) displays one or more major peaks corresponding to the Miller indices inherent in a so-called olivine-type crystal structure at a specified incident angle. The compounds exemplified above are examples of preferred positive electrode active materials with an olivine-type structure.

[0147] The spinel-type structure of the positive electrode active material in the positive electrode layer refers to the positive electrode active material (especially its particles) having a spinel-type crystal structure. In a broad sense, it refers to a crystal structure that can be identified as spinel-type by those skilled in the art of solid-state batteries. In a narrow sense, the spinel-type structure of the positive electrode active material in the positive electrode layer means that, in X-ray diffraction, the positive electrode active material (especially its particles) displays one or more major peaks corresponding to the Miller indices inherent in a so-called spinel-type crystal structure at a specified incident angle. The compounds exemplified above are examples of preferred positive electrode active materials with a spinel-type structure.

[0148] The chemical composition of the positive electrode active material can also be an average chemical composition. The average chemical composition of the positive electrode active material refers to the average chemical composition of the positive electrode active material along the thickness direction of the positive electrode layer. The average chemical composition of the positive electrode active material can be analyzed and measured by breaking the solid-state battery and using SEM-EDX (energy dispersive X-ray spectrometry) to perform compositional analysis with the entire thickness direction of the positive electrode layer within the field of view.

[0149] For positive electrode active materials, in addition to using raw material compounds containing specified metal atoms, they can be obtained by the same methods as negative electrode active materials, or they can be obtained as commercially available products.

[0150] The chemical composition and crystal structure of the positive electrode active material in the positive electrode layer typically change due to element diffusion during sintering. In a solid-state battery where the positive electrode active material is sintered together with the negative electrode layer and the solid electrolyte layer, it preferably possesses the aforementioned chemical composition and crystal structure.

[0151] The average particle size of the positive electrode active material is not particularly limited, for example, it can be 0.01 μm or more and 10 μm or less, preferably 0.05 μm or more and 4 μm or less.

[0152] The average particle size of the positive electrode active material can be determined using the same method as the average particle size of the negative electrode active material in the negative electrode layer.

[0153] The average particle size of the positive electrode active material in the positive electrode layer usually directly reflects the average particle size of the positive electrode active material used in manufacturing. This is especially true when LCO is used in the positive electrode particles.

[0154] The particle shape of the positive electrode active material in the positive electrode layer is not particularly limited. For example, it can be any particle shape among spherical, flat, and irregular shapes.

[0155] The volume ratio of the positive electrode active material in the positive electrode layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 30% or more and 90% or less, and more preferably 40% or more and 70% or less.

[0156] In addition to the positive electrode active material, the positive electrode layer may also contain, for example, solid electrolyte, sintering aids, and conductive aids.

[0157] There are no particular limitations on the type of solid electrolyte contained in the positive electrode layer. Examples of solid electrolytes included in the positive electrode layer include solid electrolytes with a garnet-type structure (Li₂O₃). 6.4 Ga 0.2 La3Zr2O 12 Li 6.4 La3(Zr 1.6 Ta 0.4 )O 12 、(Li 6.4 Al 0.2 La3Zr2O 12 Li 6.5 La3(Zr 1.5 Mo 0.25 )O 12 Solid electrolytes with LISICON-type structure, Li 3+x (V 1-x Si x O4, a solid electrolyte with a perovskite structure, La 2 / 3-x Li 3x TiO3, and solid electrolytes with amorphous structures such as Li3BO3-Li4SiO4. Among these, from the viewpoint of reactivity when co-sintered with the LISICON-type solid electrolyte used in the invention, solid electrolytes with garnet-type structures and solid electrolytes with LISICON-type structures are particularly preferred.

[0158] For the solid electrolyte of the positive electrode layer, in addition to using raw material compounds containing specified metal atoms, it can be obtained by the same method as the negative electrode active material, or it can be obtained as a commercially available product.

[0159] The average chemical composition and crystal structure of the solid electrolyte in the positive electrode layer typically vary due to element diffusion during sintering. Preferably, the solid electrolyte has the aforementioned average chemical composition and crystal structure in the solid-state battery after sintering together with the negative electrode layer and the solid electrolyte layer.

[0160] The volume ratio of the solid electrolyte in the positive electrode layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material and balancing the high energy density of the solid battery, it is preferably 20% or more and 60% or less, and more preferably 30% or more and 45% or less.

[0161] As a sintering aid in the positive electrode layer, the same compound as the sintering aid in the negative electrode layer can be used.

[0162] The volume ratio of sintering aid in the positive electrode layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material and balancing the high energy density of solid-state batteries, it is preferably 0.1% or more and 20% or less, and more preferably 1% or more and 10% or less.

[0163] The conductive additives in the positive electrode layer can be any conductive additives known in the field of solid-state batteries. Examples of such conductive additives include metallic materials such as Ag (silver), Au (gold), Pd (palladium), Pt (platinum), Cu (copper), Sn (tin), and Ni (nickel); and carbon materials such as acetylene black, Ketjen black, Super P (trademark), and VGCF (trademark) carbon nanotubes. Conductive additives that exhibit an elongated shape when viewed in cross-section of the negative electrode layer can also be used as conductive additives in the positive electrode layer.

[0164] The volume ratio of conductive additives in the positive electrode layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material and balancing the high energy density of solid-state batteries, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0165] In the positive electrode layer, the porosity is not particularly limited, but from the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0166] The porosity of the positive electrode layer is measured using the same method as that used for the porosity of the negative electrode layer.

[0167] like Figure 1A as well as Figure 1B As shown, the positive electrode layer 1 can have a main surface current collector structure or an end surface current collector structure. From the viewpoint of reducing manufacturing costs, the positive electrode layer preferably has a main surface current collector structure.

[0168] The positive electrode layer 1 having a main surface current collection structure means that the positive electrode layer 1 has a structure for current collection on the main surface of the positive electrode layer. More specifically, as... Figure 1A as well as Figure 1B As shown, the positive electrode layer 1 is in contact with the positive electrode current collector layer 11 on its main surface 1x, and is electrically connected to the positive terminal 10 via the positive electrode current collector layer 11. In the main surface current collector structure of the positive electrode layer 1, the positive electrode current collector layer 11 can be stacked on the main surface of the positive electrode layer 1, and / or the positive electrode layer 1 can be stacked on the main surface of the positive electrode current collector layer 11. The main surface refers to a surface with a relatively large area, specifically the upper surface and / or lower surface perpendicular to the stacking direction. Current collection on the main surface mainly refers to electrons entering and exiting from the main surface. Figure 1A In this configuration, the positive electrode layer 1 is directly electrically connected to the positive terminal 10 on the positive terminal 10 side. However, it can also be electrically connected to the positive terminal 10 via a positive electrode current collector, as described later with a positive electrode layer having a front-face current collector structure. In the case where the positive electrode layer 1 has a front-face current collector structure, as... Figure 1A as well as Figure 1B As shown, the positive electrode layer 1 can be stacked on the two main surfaces of the positive electrode current collector layer 11, or it can be stacked on one main surface.

[0169] The positive electrode layer 1 having an end-face current collection structure means that the positive electrode layer 1 has a structure that collects current on the end face (especially only the end face) of the positive electrode layer 1 on the positive terminal 10 side. In detail, the positive electrode layer 1 can be in contact with the positive electrode current collection part on the end face (especially only the end face) of the positive electrode layer 1 on the positive terminal 10 side, and be electrically connected to the positive terminal 10 through the positive electrode current collection part, or it can be directly and electrically connected to the positive terminal 10 on the end face (especially only the end face) of the positive electrode layer 1 on the positive terminal 10 side.

[0170] The positive electrode layer 1 may include a positive electrode current collector layer 11 and a positive electrode current collector portion, both of which are composed of at least a conductive material. The positive electrode current collector layer 11 and the positive electrode current collector portion may also be composed of a solid electrolyte. In a preferred embodiment, the positive electrode current collector layer 11 and the positive electrode current collector portion are composed of a sintered body comprising at least a conductive material and a solid electrolyte. The conductive material that may be included in the positive electrode current collector layer 11 and the positive electrode current collector portion is typically a material with high conductivity, for example, it can be selected from the same conductive material as that of the negative electrode current collector layer and the negative electrode current collector portion. The solid electrolyte that may be included in the positive electrode current collector layer 11 and the positive electrode current collector portion can be selected from the same solid electrolyte that may be included in the aforementioned negative electrode layer.

[0171] From the viewpoint of reducing the manufacturing cost and internal resistance of solid-state batteries through integral sintering, the positive electrode current collector layer 11 and the positive electrode current collector portion preferably have a sintered body form. When the positive electrode current collector layer 11 and the positive electrode current collector portion have a sintered body form, for example, the positive electrode current collector layer 11 and the positive electrode current collector portion can be composed of a sintered body containing a sintering aid in addition to the conductive material and solid electrolyte described above. The sintering aid contained in the positive electrode current collector layer 11 and the positive electrode current collector portion can, for example, be selected from the same material that can be contained in the negative electrode layer.

[0172] There is no particular limitation on the thickness of the positive electrode current collector layer; for example, it can be above 1 μm and below 5 μm, especially above 1 μm and below 3 μm.

[0173] The thickness of the positive current collector can usually be the same as that of the positive electrode layer.

[0174] The positive electrode layer is a layer that can be called the "positive electrode active material layer".

[0175] As described above, the positive electrode layer is preferably a layer capable of inserting and deintercalating lithium ions, but in this invention, the positive electrode layer may also be a layer capable of inserting and deintercalating sodium ions.

[0176] (Solid electrolyte layer)

[0177] In this invention, the solid electrolyte layer 3 is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material, the solid electrolyte layer 3 preferably contains a solid electrolyte (hereinafter sometimes referred to as "first solid electrolyte") having a LISICON-type structure and containing at least V. The solid electrolyte layer preferably has the morphology of a sintered body containing the first solid electrolyte.

[0178] In the solid electrolyte layer, the LISICON-type structure of the first solid electrolyte includes β I Type structure, β II Type structure, β II 'Type structure, T I Type structure, T II Type structure, γ II Type β and γ0 type structures. That is, the solid electrolyte layer can contain structures with β... I Type structure, β II Type structure, β II 'Type structure, T I Type structure, T II Type structure, γ II A solid electrolyte having one or more of the following structures: LISICON-type structure, γ0-type structure, or a combination thereof. From the viewpoint of further improving the utilization rate of the negative electrode active material, the LISICON-type structure of the first solid electrolyte layer is preferably γ0-type. IIType structure.

[0179] In the solid electrolyte layer, the first solid electrolyte has γ II The type structure refers to the solid electrolyte having γ-type structure. II A crystal structure of type γ, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as γ II A crystal structure of the type [type]. In a narrow sense, the first solid electrolyte in the solid electrolyte layer possesses γ [type]. II The type structure refers to the solid electrolyte exhibiting a similar appearance to so-called γ-ray diffraction at a specified incident angle during X-ray diffraction. II The crystal structure of the Li3VO4 type inherently corresponds to more than one major peak in the Miller index. It possesses γ II Compounds with this type of structure (i.e., solid electrolytes) are described, for example, in the literature "J. solid state chem" (ARWest et al., J. solid state chem., 4, 20-28 (1972)). As an example, ICDD Card No. 01-073-2850 can be cited.

[0180] The first solid electrolyte in the solid electrolyte layer has β I Type structure refers to the solid electrolyte having β I A β-type crystal structure, broadly speaking, refers to a crystal structure that can be identified by those skilled in the art of solid-state batteries as β. I A crystal structure of type β. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a β-type crystal structure. I The β-type structure refers to the solid electrolyte exhibiting a similar appearance to the so-called β-type structure in X-ray diffraction at a specified incident angle. I The crystal structure of the Li3VO4 type inherently contains more than one major peak corresponding to the Miller index. It possesses β... I Compounds with the following structure (i.e., solid electrolytes) are described, for example, in the literature "J. solid state chem" (ARWest et al., J. solid state chem., 4, 20-28 (1972)). As an example, the XRD data (Miller index corresponding to the surface spacing d value) described in the table below are shown.

[0181] [Table 1]

[0182]

[0183] The first solid electrolyte in the solid electrolyte layer has β II Type structure refers to the solid electrolyte having β IIA β-type crystal structure, broadly speaking, refers to a crystal structure that can be identified by those skilled in the art of solid-state batteries as β. II A crystal structure of type β. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a β-type crystal structure. II The β-type structure refers to the solid electrolyte exhibiting a similar appearance to the so-called β-type structure in X-ray diffraction at a specified incident angle. II The crystal structure of the Li3VO4 type inherently contains more than one major peak corresponding to the Miller index. It possesses β... II Compounds with this type of structure (i.e., solid electrolytes) are described, for example, in the literature "J. solid state chem" (ARWest et al., J. solid state chem., 4, 20-28 (1972)). As an example, ICDD Card No. 00-024-0675 can be cited.

[0184] The first solid electrolyte in the solid electrolyte layer has β II '-type structure refers to the solid electrolyte having β II A β-type crystal structure, broadly speaking, refers to a crystal structure that can be identified by those skilled in the art of solid-state batteries as a β-type crystal. II A crystal structure of the '-type. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a β-type crystal structure. II The 'type' structure refers to the solid electrolyte exhibiting a similar appearance to the so-called β-type structure in X-ray diffraction at a specified incident angle. II The '-Li3VO4 type crystal structure inherently contains more than one major peak corresponding to the Miller indices. It possesses β... II Compounds with a '-type structure (i.e., solid electrolytes) are described, for example, in the literature "J. solid state chem" (ARWest et al., J. solid state chem., 4, 20-28 (1972)). As an example, the XRD data (Miller index corresponding to the surface spacing d value) described in the table below are shown.

[0185] [Table 2]

[0186]

[0187] The first solid electrolyte in the solid electrolyte layer has T I Type-type structure refers to the solid electrolyte having T I A type of crystal structure, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as a T-type crystal. I A crystal structure of type T. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a T... IThe type structure refers to the solid electrolyte exhibiting a similar appearance to the so-called To structure in X-ray diffraction at a specified incident angle. I The crystal structure of the Li3VO4 type inherently contains more than one major peak corresponding to the Miller indices. It has T... I Compounds with this type of structure (i.e., solid electrolytes) are described, for example, in the literature "J. solid state chem" (ARWest et al., J. solid state chem., 4, 20-28 (1972)). As an example, ICDD Card No. 00-024-0668 can be cited.

[0188] The first solid electrolyte in the solid electrolyte layer has T II Type-type structure refers to the solid electrolyte having T II A type of crystal structure, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as a T-type crystal. II A crystal structure of type T. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a T... II The type structure refers to the solid electrolyte exhibiting a similar appearance to the so-called To structure in X-ray diffraction at a specified incident angle. II The crystal structure of the Li3VO4 type inherently contains more than one major peak corresponding to the Miller indices. It has T... II Compounds with this type of structure (i.e., solid electrolytes) are described, for example, in the literature "J. solid state chem" (ARWest et al., J. solid state chem., 4, 20-28 (1972)). As an example, ICDD Card No. 00-024-0669 can be cited.

[0189] The first solid electrolyte in the solid electrolyte layer having a γ0-type structure means that the solid electrolyte has a γ0-type crystal structure. In a broad sense, it refers to a crystal structure that can be identified as a γ0-type crystal structure by those skilled in the art of solid-state batteries. In a narrow sense, the first solid electrolyte in the solid electrolyte layer having a γ0-type structure means that the solid electrolyte, in X-ray diffraction, displays more than one major peak corresponding to the Miller index inherent to the so-called γ0-Li3VO4 type crystal structure at a specified incident angle. Compounds with a γ0-type structure (i.e., solid electrolytes) are described, for example, in the literature "J. solid state chem" (ARWest et al., J. solid state chem., 4, 20-28 (1972)). As an example, the XRD data (Miller index corresponding to the surface spacing d value) described in the following table are shown.

[0190] [Table 3]

[0191]

[0192] In the solid electrolyte layer, the first solid electrolyte more preferably has an average chemical composition represented by the following general formula (3).

[0193] [Chemical Formula 3]

[0194] (Li [3-ax+(5-b)(1-y)] A x (V) y B 1-y O4 (3)

[0195] In formula (3), A is one or more elements selected from the group consisting of Na (sodium), K (potassium), Mg (magnesium), Ca (calcium) and Zn (zinc).

[0196] B is one or more elements selected from the group consisting of Zn (zinc), Al (aluminum), Ga (gallium), Si (silicon), Ge (germanium), Sn (tin), P (phosphorus), As (arsenic), Ti (titanium), Mo (molybdenum), W (tungsten), Fe (iron), Cr (chromium), and Co (cobalt).

[0197] x has the relationship 0 ≤ x ≤ 1.0, and in particular 0 ≤ x ≤ 0.2.

[0198] The relationship y has 0 < y < 1.0, especially 0.05 ≤ y < 0.93. From the viewpoint of further improving the utilization rate of the negative electrode active material, the relationship 0.4 ≤ y ≤ 0.9 is preferred, and the relationship 0.6 ≤ y ≤ 0.9 is even more preferred.

[0199] a is the average price of A, which is the same as the average price of A in equation (1).

[0200] b is the average price of B, which is the same as the average price of B in equation (1).

[0201] In equation (3), from the viewpoint of further improving the utilization rate of the negative electrode active material, in a preferred embodiment, it is as follows:

[0202] A is Al.

[0203] B is one or more elements selected from the group consisting of Si, Ge, and P.

[0204] x has the relationship 0≤x≤0.2, especially 0≤x≤0.1, and is preferably 0.

[0205] The relationship y has 0.7≤y≤0.9, and is preferably 0.8.

[0206] The average chemical composition of the first solid electrolyte in the solid electrolyte layer refers to the average chemical composition of the first solid electrolyte in the thickness direction of the solid electrolyte layer. The average chemical composition of the first solid electrolyte can be analyzed and measured by breaking the solid battery and using SEM-EDX (energy dispersive X-ray spectrometry) to perform compositional analysis with the entire thickness direction of the solid electrolyte layer in the field of view.

[0207] The average chemical composition of the first solid electrolyte with a LISICON-type structure and the average chemical composition of the solid electrolyte with a garnet-type structure (described later) in the solid electrolyte layer can be automatically distinguished and measured based on these compositions in the above composition analysis. For example, according to SEM-EDX analysis, the sites of the first solid electrolyte (i.e., the LISICON-type solid electrolyte) can be separated by identification based on V detection, and the sites of the second solid electrolyte (e.g., the garnet-type solid electrolyte) can be separated by identification based on La and Zr.

[0208] The first solid electrolyte for the solid electrolyte layer can be obtained by the same method as the negative electrode active material, except that it can be obtained as a commercially available product, in addition to using a raw material compound containing specified metal atoms.

[0209] The chemical composition and crystal structure of the first solid electrolyte in the solid electrolyte layer typically change due to element diffusion during sintering. In a solid-state battery sintered together with the negative electrode layer and the positive electrode layer, this first solid electrolyte preferably has the aforementioned chemical composition and crystal structure. In particular, the chemical composition of the first solid electrolyte, when sintered together with the negative electrode layer at a high speed, for example, at 750°C for about 1 minute, directly reflects the chemical composition of the solid electrolyte used during manufacturing. However, when sintered at a long time, at 750°C for about 1 hour, elements from the negative electrode active material in the negative electrode layer diffuse, typically increasing the V content.

[0210] There is no particular limitation on the volume ratio of the first solid electrolyte in the solid electrolyte layer. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 10% or more and 80% or less, more preferably 20% or more and 60% or less, and even more preferably 30% or more and 60% or less.

[0211] The volume ratio of the first solid electrolyte in the solid electrolyte layer can be measured using the same method as the volume ratio of the positive electrode active material.

[0212] The solid electrolyte layer preferably further comprises a solid electrolyte having a garnet-type structure (hereinafter sometimes simply referred to as the "second solid electrolyte"). By including the second solid electrolyte in the solid electrolyte layer, as described above, the insulation of the solid electrolyte layer can be improved. This can be attributed to the fact that the second solid electrolyte is difficult to reduce during charging and discharging, thus making it difficult to inject electrons, and that the first solid electrolyte has increased tortuosity within the solid electrolyte, resulting in increased electronic resistance.

[0213] The second solid electrolyte is the same as the garnet-type solid electrolyte preferably included in the negative electrode layer, or it can be selected from the same range as the garnet-type solid electrolyte described in the description of the negative electrode layer. When both the solid electrolyte layer and the negative electrode layer contain a garnet-type solid electrolyte, the garnet-type solid electrolyte in the solid electrolyte layer and the garnet-type solid electrolyte in the negative electrode layer may have the same chemical composition, or they may have different chemical compositions.

[0214] The preferred solid electrolyte for the solid electrolyte layer is a solid electrolyte having the following chemical composition in formula (2):

[0215] A is an element selected from one or more (especially two) elements in the group consisting of Ga and Al.

[0216] B is one or more elements selected from the group consisting of Nb, Ta, W, Mo, and Bi.

[0217] x has the relationship 0≤x≤0.3, and is preferably 0.2.

[0218] The relationship y has 0≤y≤1.0, preferably 0≤y≤0.7, more preferably 0≤y≤0.3, and even more preferably 0.

[0219] a is the average price of A.

[0220] b is the average price of B.

[0221] The average chemical composition of the second solid electrolyte in the solid electrolyte layer refers to the average chemical composition of the second solid electrolyte along the thickness direction of the solid electrolyte layer. The average chemical composition of the second solid electrolyte can be analyzed and measured by breaking the solid battery and using SEM-EDX (energy dispersive X-ray spectrometry) to perform compositional analysis with the entire thickness direction of the solid electrolyte layer in the field of view.

[0222] The volume ratio of the second solid electrolyte in the solid electrolyte layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 10% or more and 80% or less, more preferably 20% or more and 70% or less, and even more preferably 40% or more and 60% or less.

[0223] The volume ratio of the second solid electrolyte in the solid electrolyte layer can be measured using the same method as the volume ratio of the positive electrode active material.

[0224] In addition to the solid electrolyte, the solid electrolyte layer may also contain, for example, sintering aids. From the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferable that at least one of the negative electrode layer or the solid electrolyte layer also contains a sintering aid, and preferably both of them also contain a sintering aid. "At least one of the negative electrode layer or the solid electrolyte layer also contains a sintering aid" means that either one of the negative electrode layer or the solid electrolyte layer may contain a sintering aid, or both of them may contain a sintering aid.

[0225] As a sintering aid in the solid electrolyte layer, the same compound as the sintering aid in the negative electrode layer can be used.

[0226] The volume ratio of sintering aid in the solid electrolyte layer is not particularly limited. From the viewpoint of further improving the utilization rate of the negative electrode active material and balancing the high energy density of solid batteries, it is preferably 0.1% or more and 20% or less, and more preferably 1% or more and 10% or less.

[0227] The thickness of the solid electrolyte layer is typically 0.1 μm or more and 200 μm or less, preferably 0.1 to 30 μm, and more preferably 20 to 1 μm from the viewpoint of thinning the solid electrolyte layer.

[0228] The thickness of the solid electrolyte layer was calculated using the average of the thickness measured at any 10 points in the SEM image.

[0229] In the solid electrolyte layer, the porosity is not particularly limited, but from the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0230] The porosity of the solid electrolyte layer is measured using the same method as that used for the porosity of the negative electrode layer.

[0231] The chemical composition of the solid electrolyte layer does not need to be homogeneous; for example, the chemical composition can vary along the thickness direction. In particular, insulation can be improved by ensuring that the average composition of the first solid electrolyte in the solid electrolyte layer meets the above conditions.

[0232] As described above, the solid electrolyte layer is preferably a layer capable of conducting lithium ions, but in this invention, the solid electrolyte layer may also be a layer capable of conducting sodium ions.

[0233] (protective layer)

[0234] like Figure 1A As shown on the paper, the protective layer 5 is formed at least on the top and bottom surfaces of the solid-state battery, and preferably also on all sides of the solid-state battery. The protective layer 5 is used to electrically, physically, and chemically protect the solid-state battery (especially battery elements such as the positive electrode layer, negative electrode layer, and solid electrolyte layer).

[0235] The protective layer 5 is typically composed of an insulating material. An insulating material is one that lacks both ionic and electronic conductivity. Therefore, an insulating material is an inorganic material that lacks both ionic and electronic conductivity. An inorganic material lacking ionic conductivity is defined as one with an ionic conductivity of 1 × 10⁻⁶. -7 Inorganic materials with an ion conductivity below S / cm. From the perspective of suppressing battery degradation over a longer period, an ion conductivity of 1×10⁻⁶ is preferred. -10 Below S / cm. Inorganic substances that do not have electronic conductivity are those with an electronic conductivity of 1×10⁻⁶. -7 Inorganic materials with an electron conductivity below S / cm. From the perspective of suppressing battery degradation over a longer period, an electron conductivity of 1×10⁻⁶ is preferred. -10 Below S / cm.

[0236] When the protective layer 5 is composed of such an insulating material, it exhibits excellent moisture resistance, environmental resistance, and durability. Specifically, compared to protective layers containing resins (e.g., polymer compounds), the protective layer 5 provides a higher bonding strength with the battery element. Consequently, compared to protective layers containing polymer compounds, the protective layer 5 more effectively prevents the expansion and contraction of the solid-state battery, thus more effectively suppressing the degradation of battery performance.

[0237] The insulating material constituting the protective layer 5 is not particularly limited, and examples include glass and ceramics. Examples of glass include quartz glass (SiO2), or composite oxide glasses composed of SiO2 combined with at least one selected from PbO, B2O3, MgO, ZnO, Bi2O3, Na2O, and Al2O3. Examples of ceramics include alumina, cordierite, mullite, talc, and forsterite. The protective layer may also be composed of one or more materials selected from the group consisting of these substances. The protective layer may also contain electronically conductive materials (e.g., metals) as long as it does not short-circuit the battery element. When the protective layer contains electronically conductive materials, the proportion of such materials may be, for example, 1% by volume or less. By including electronically conductive materials (e.g., metals) in the protective layer, heat generated by the battery reaction can be smoothly released to the outside.

[0238] The protective layer is composed of a sintered body containing the aforementioned insulating material particles. The sintered body constituting the protective layer has pores between the insulating material particles, but has a density in its thickness direction (e.g., the lamination direction L) that can suppress the adsorption, absorption, and permeation of moisture and gases (carbon dioxide).

[0239] The protective layer may contain resins such as polymers, and may also contain residues of polymers used during manufacturing and / or their thermal decomposition products. The content of polymers and their thermal decomposition products in the protective layer is typically 0.1% by weight or less relative to the total amount of the protective layer, and particularly preferably 0.01% by weight or less. It should be noted that residues may also remain in the positive electrode layer, positive current collector layer, positive current collector section, negative electrode layer, negative current collector layer, negative current collector section, solid electrolyte layer, and the electrode separation section (described later), similar to those in the protective layer. For example, the content of residues in each layer or portion of the positive electrode layer, positive current collector layer, positive current collector section, negative electrode layer, negative current collector layer, negative current collector section, solid electrolyte layer, and electrode separation section, relative to the total amount of each layer, may be within the same range as the content range of residues in the protective layer.

[0240] The porosity of the protective layer can be, for example, 0.1% by volume or more and 20% by volume or less, and particularly preferably 1% by volume or more and 10% by volume or less. The porosity is measured using methods such as gravimetric porosity, computational tomography using CT scans, and immersion methods.

[0241] The oxygen permeability in the thickness direction of the protective layer can be, for example, 10. -1 cc / m 2 / day / atmospheric pressure, preferably 10 -3 cc / m 2 / day / air pressure below.

[0242] The H2O permeability in the thickness direction of the protective layer can be, for example, 10. -2 g / m 2 For less than / day, 10 is particularly preferred. -4 g / m 2 / day or less. H2O permeability is measured at 25°C using the carrier gas method, pressurization method, and Ca corrosion method.

[0243] In addition to insulating materials, the protective layer may also contain, for example, sintering aids. Preferably, the protective layer also contains sintering aids. The same compound as the sintering aid in the negative electrode layer can be used as the sintering aid in the protective layer.

[0244] From the viewpoint of further suppressing the degradation of battery performance, the thickness of the thickest portion of the protective layer 5 is preferably 500 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, and most preferably 20 μm or less. From the viewpoint of further suppressing the degradation of battery performance caused by the adsorption, absorption, and permeation of moisture and gases (carbon dioxide), the average thickness of the protective layer is preferably 1 μm or more, more preferably 5 μm or more.

[0245] The thickness of the thickest part of the protective layer and the average thickness are respectively the maximum thickness and average thickness at any 100 points.

[0246] A protective layer covers the top and bottom surfaces of the solid-state battery. The protective layer can be like... Figure 1A as well as Figure 1B The protective layer can be in direct contact with the upper and lower surfaces of the battery element covered by the protective layer, or it can be indirectly contacted via layers other than those constituting the battery element. Direct contact between the protective layer and the upper and lower surfaces of the battery element means that layers other than those constituting the battery element are not located between the protective layer and the battery element, and the surface of the protective layer is in direct contact with the surface of the battery element.

[0247] Preferably, the protective layer is integrally sintered with the upper and lower surfaces of the battery element covered by the protective layer and the sintered body. Integral sintering of the protective layer with the upper and lower surfaces of the battery element covered by the protective layer means that the protective layer and the upper and lower surfaces of the battery element covered by the protective layer are joined together through sintering. Specifically, both the protective layer and the upper and lower surfaces of the battery element covered by the protective layer are sintered bodies and are sintered into one piece. For example, the protective layer and the battery element preferably adopt an integrally sintered structure. It should be noted that the protective layer and the upper and lower surfaces of the battery element covered by the protective layer do not necessarily have to be completely integrated; some parts may not be integrated. The protective layer and the upper and lower surfaces of the battery element covered by the protective layer need only be integrally integrated as a whole.

[0248] The top and bottom surfaces of a battery element covered by a protective layer are typically the surfaces of its outermost layer. The outermost layer refers to the highest-ranking layer and the lowest-ranking layer among the layers that make up the battery element. The surfaces of the outermost layer are the top surface of the highest layer and the bottom surface of the lowest layer.

[0249] (Electrode separation section)

[0250] The solid-state battery of the present invention typically also has an electrode separation section (also referred to as a "white layer" or "white part") 15, 25.

[0251] An electrode separation section 15 (i.e., a positive electrode separation section) is disposed around the positive electrode layer 1, thereby separating the positive electrode layer 1 from the negative electrode terminal 20. An electrode separation section 25 (i.e., a negative electrode separation section) is also disposed around the negative electrode layer 2, thereby separating the negative electrode layer 2 from the positive electrode terminal 10.

[0252] The electrode separation sections 15 and 25 are preferably made of one or more materials selected from the group consisting of solid electrolytes, insulating materials and mixtures thereof.

[0253] The solid electrolyte that can form the electrode separation sections 15 and 25 can use the same material as the solid electrolyte that can form the solid electrolyte layer.

[0254] The insulating material that can form the electrode separation parts 15 and 25 can be the same material as the insulating material that can form the protective layer.

[0255] The electrode separation section preferably also includes a sintering aid. The same compound as the sintering aid in the negative electrode layer can be used as the sintering aid in the electrode separation section.

[0256] (Electrode terminals)

[0257] The solid-state battery of the present invention has electrode terminals 10 and 20 on two opposite sides, respectively, which are electrically connected to the positive electrode layer or the negative electrode layer. The electrode terminal electrically connected to the positive electrode layer is referred to as the positive terminal, and the electrode terminal electrically connected to the negative electrode layer is referred to as the negative terminal 20. The electrode terminals are also referred to as end-face electrodes. The solid-state battery of the present invention has electrode terminals 10 and 20 that are parallel to each other and also parallel to the stacking direction L. The electrode terminals preferably contain a conductive material with high conductivity. There is no particular limitation on the specific material used to constitute the conductive terminals, but from the viewpoint of conductivity, examples include at least one conductive metal (i.e., a metal or alloy) selected from the group consisting of gold, silver, copper, platinum, tin, palladium, aluminum, titanium, nickel, oxygen-free copper, Cu-Sn alloy, Cu-Zr alloy, Cu-Fe alloy, Cu-Cr-Sn-Zn alloy, and 42 alloy (Ni-Fe alloy, Kova iron-nickel-cobalt alloy).

[0258] The thickness of electrode terminals 10 and 20 is not particularly limited; for example, it can be 1 μm or more and 1 mm or less, especially 10 μm or more and 100 μm or less.

[0259] [Solid-state battery manufacturing method]

[0260] Solid-state batteries can be manufactured, for example, by methods such as the so-called green sheet method, printing method, or a combination of these methods.

[0261] The raw slice method will be explained.

[0262] First, a paste is prepared by appropriately mixing solvents, resins, etc., into the positive electrode active material. This paste is then coated onto a sheet and dried to form a green sheet for constituting the positive electrode layer. The green sheet for the positive electrode layer may also contain solid electrolytes, conductive additives, and / or sintering aids.

[0263] A paste is prepared by appropriately mixing conductive additives, solvents, resins, etc., into the negative electrode active material. This paste is then coated onto a sheet and dried to form a green sheet for constituting the negative electrode layer. The green sheet for the negative electrode layer may also contain a solid electrolyte and / or sintering aids.

[0264] A paste is prepared by appropriately mixing solvents, resins, etc., into a solid electrolyte. This paste is then coated and dried to produce a green sheet for forming the solid electrolyte layer. The green sheet for the solid electrolyte layer may also contain sintering aids, etc.

[0265] A paste is prepared by appropriately mixing solvents, resins, etc., into an insulating material. This paste is then applied and dried to produce a green sheet that forms a protective layer. The green sheet for the protective layer may also contain sintering aids, etc.

[0266] A paste is prepared by appropriately mixing solvents, resins, etc., into a solid electrolyte and / or insulating material. This paste is then coated and dried to produce a green sheet for constituting the electrode separation section. The green sheet for the electrode separation section may also contain sintering aids, etc.

[0267] A paste for electrode terminals is prepared by appropriately mixing solvents, resins, etc., into a conductive material.

[0268] Next, a laminate is produced by appropriately layering the green sheets obtained by the above method. The laminate can also be pressed. Preferred pressing methods include isostatic pressing.

[0269] Then, by applying an electrode terminal paste to a specified configuration in the laminate and sintering it at 600–800°C, a solid-state battery can be obtained.

[0270] The printing method is explained.

[0271] The printing method is the same as the raw film method, except for the following:

[0272] • Except for mixing the solvent and resin in an amount suitable for use as ink, prepare inks with each layer having the same composition as the paste used to obtain each layer of the green sheet.

[0273] • Use inks from each layer to print and layer to create a laminate.

[0274] The present invention will now be described in more detail based on specific embodiments, but the present invention is not limited to any of the following embodiments and can be implemented with appropriate modifications without changing its spirit.

[0275] Example

[0276] [Materials Manufacturing]

[0277] In (1) to (3) below, positive electrode active material, negative electrode active material, solid electrolyte and sintering aid for manufacturing positive electrode layer and negative electrode layer, and first and second solid electrolyte and sintering aid for manufacturing solid electrolyte layer are manufactured, so that they have the composition described later.

[0278] (1) Manufacturing of garnet-type solid electrolyte powder (solid electrolyte powder for the negative electrode layer and second solid electrolyte powder for the solid electrolyte layer)

[0279] The garnet-type solid electrolyte powder used in the following manufacturing examples and comparative examples.

[0280] The raw materials used are lithium hydroxide monohydrate (LiOH·H2O), lanthanum hydroxide (La(OH)3), zirconium oxide (ZrO2), gallium oxide (Ga2O3), aluminum oxide (Al2O3), niobium oxide (Nb2O5), tantalum oxide (Ta2O5), and molybdenum oxide (MoO3).

[0281] Weigh all raw materials to achieve the required chemical composition, add water, seal in a 100ml polyethylene can, and rotate on a rack at 150rpm for 16 hours to mix the materials. Additionally, considering Li loss during sintering, lithium hydroxide monohydrate (LiOH·H2O) was added as a Li source at an amount exceeding the target composition by 3wt%.

[0282] After evaporation and drying, the obtained slurry was pre-calcined at 900°C for 5 hours to obtain the target phase.

[0283] Add a toluene-acetone mixture to the obtained pre-calcined powder and pulverize it using a planetary ball mill for 6 hours.

[0284] The pulverized powder was dried to prepare a solid electrolyte powder. ICP analysis confirmed that the powder had no compositional deviation.

[0285] (2) Manufacturing of positive electrode active material powder, negative electrode active material powder and LISICON type solid electrolyte powder (the first solid electrolyte powder of the solid electrolyte layer).

[0286] The positive electrode active material powder, negative electrode active material powder, and first solid electrolyte powder used in the following manufacturing examples and comparative examples.

[0287] The raw materials used were lithium hydroxide monohydrate (LiOH·H2O), vanadium pentoxide (V2O5), silicon oxide (SiO2), germanium oxide (GeO2), phosphorus oxide (P2O5), aluminum oxide (Al2O3), and zinc oxide (ZnO).

[0288] Weigh each raw material appropriately to achieve the specified chemical composition, add water, seal in a 100ml polyethylene can, and rotate on a can rack at 150rpm for 16 hours to mix the raw materials.

[0289] After evaporation and drying, the obtained slurry is pre-fired in air at 800°C for 5 hours.

[0290] Add alcohol to the obtained pre-calcined powder, seal it again in a 100ml polyethylene can, and pulverize it by rotating it at 150rpm for 16 hours on a can rack.

[0291] The pulverized powder was then subjected to formal sintering again at 900℃ for 5 hours.

[0292] Then, a toluene-acetone mixed solvent was added to the obtained formal sintered powder, and it was pulverized in a planetary ball mill for 6 hours and dried to serve as the negative electrode active material powder and the first solid electrolyte powder. The powder was measured by ICP to confirm that there were no compositional deviations.

[0293] (3) Manufacturing of sintering aid powder

[0294] The sintering aid powder used in the following manufacturing examples and comparative examples.

[0295] The raw materials used are lithium hydroxide monohydrate (LiOH·H2O), boron oxide (B2O3), lithium carbonate (Li2CO3), and aluminum oxide (Al2O3).

[0296] Weigh each raw material appropriately to ensure the chemical composition meets the specified requirements, mix them thoroughly in a mortar, and then pre-calcine at 650°C for 5 hours.

[0297] Then, the pre-fired powder is thoroughly pulverized again in a mortar, mixed, and then formally sintered at 680°C for 40 hours.

[0298] A toluene-acetone mixture was added to the obtained sintering powder, and the mixture was pulverized in a planetary ball mill for 6 hours and then dried to obtain the sintering aid powder. ICP analysis confirmed that the powder exhibited no compositional deviation.

[0299] (4) Flat Ag powder

[0300] By bead milling spherical Ag powder (average primary particle size 2 μm, manufactured by Zhaorong Chemical Co., Ltd.), flat Ag powder A with an aspect ratio (a / b) of 4.5 and a b value of 0.9 μm was obtained.

[0301] By bead milling spherical Ag powder with an average primary particle size of 0.2 μm to 3 μm for 1 to 20 hours, flat Ag powders B to H with various aspect ratios and short side b are obtained. The longer the bead milling time, the larger the aspect ratio; the shorter the time, the smaller the aspect ratio. The larger the average primary particle size of the spherical Ag powder used, the larger the b value; the smaller the average primary particle size, the smaller the b value.

[0302] The obtained flat Ag powder B has an aspect ratio (a / b) of 4.4 and b is 0.5 μm.

[0303] The obtained flattened Ag powder C has an aspect ratio (a / b) of 4.5 and b is 1.5 μm.

[0304] The obtained flattened Ag powder D has an aspect ratio (a / b) of 4.6 and a b of 2.2 μm.

[0305] The obtained flat Ag powder E has an aspect ratio (a / b) of 2.3 and b is 0.9 μm.

[0306] The obtained flat Ag powder F has an aspect ratio (a / b) of 3.5 and b is 0.9 μm.

[0307] The obtained flat Ag powder G has an aspect ratio (a / b) of 7.0 and b is 0.8 μm.

[0308] The obtained flat Ag powder H has an aspect ratio (a / b) of 12.1 and b is 0.7 μm.

[0309] (5) Fibrous Ag powder

[0310] As fibrous Ag powder A, commercially available silver nanowires (aspect ratio (a / b) = 17, short side length b = 0.6 μm, manufactured by Aldrich) were used.

[0311] (6) Flat Cu powder

[0312] By bead milling spherical Cu powder (average primary particle size 2.8 μm, manufactured by DOWA ELECTRONICS), flat Cu powder A with an aspect ratio (a / b) of 4.5 and a b value of 1.2 μm was obtained.

[0313] [Example 1]

[0314] (The manufacture of solid-state batteries)

[0315] It was manufactured using the following method. Figure 4A The solid-state battery shown is a solid-state battery for unipolar evaluation. It should be noted that the following description of the manufacturing method of the solid-state battery in this embodiment is referenced in other embodiments / comparative examples; therefore, the methods and information in other embodiments / comparative examples are also described in the following description.

[0316] • Raw sheet for negative electrode layer

[0317] Weigh Li3VO4(β) as the negative electrode active material. Ⅱ Li3VO4 type), as a solid electrolyte powder 6.5 La3(Zr 1.5 Ta 0.5 )O 12 (Garnet type), flat Ag powder A (as a conductive additive with a slender cross-section), and Li3BO3 (as a sintering aid) are mixed with butyral resin, alcohol, and binder to prepare a slurry for the negative electrode layer. The volume ratio of the negative electrode active material, solid electrolyte, conductive additive, and sintering aid is (60-x):35:x:5 (10≤x≤25). In Example 1, x=20.

[0318] The negative electrode layer slurry sheet is formed on a PET film using a doctor blade method, then dried and peeled off to obtain a raw negative electrode layer sheet.

[0319] • Raw sheet for solid electrolyte layer

[0320] Weigh Li as the first solid electrolyte 3.2 (V 0.8 Si 0.2 O4(γ) Ⅱ (type), as the second solid electrolyte (Li) 6.4 Ga 0.05 Al 0.15 La3Zr2O 12 (Garnet type) and Li3BO3 as a sintering aid are mixed with butyral resin, alcohol, and binder to prepare a slurry for a solid electrolyte layer. The volume ratio of the first solid electrolyte, the second solid electrolyte, and the sintering aid powder is 47.5:47.5:5.

[0321] The solid electrolyte layer is formed on a PET film using a doctor blade method, then dried and peeled off to obtain a sheet for the solid electrolyte layer.

[0322] Next, the green sheet for the negative electrode layer and the green sheet for the solid electrolyte layer are stacked together and pressed together to obtain a laminate.

[0323] The laminated body is cut into square shapes with a top view dimension of 10mm × 10mm (top view shape). Then, as... Figure 4A As shown, an Ag paste coating layer for the negative electrode current collector layer 21 is formed on the surface of the green sheet for the negative electrode layer opposite to that for the green sheet for the solid electrolyte layer. The resulting laminate is sandwiched between two porous sintering plates, and after the binder is removed at 400°C, it is sintered at 750°C. Only in Examples 20, 21, and Comparative Example 6, sintering was performed in a reducing atmosphere of N2 / H2 to suppress the oxidation of conductive additives or active materials during sintering. In other examples and comparative examples, sintering was performed in an Air atmosphere.

[0324] Then, Li metal 50 was attached as a counter electrode and reference electrode to the surface of the solid electrolyte layer opposite to the negative electrode layer, and a WIP (Warm Isostatic Pressing) treatment was performed at 60°C and 200 MPa to manufacture a solid-state battery. The solid-state battery was then sealed using a 2032-type coin cell and evaluated.

[0325] The thicknesses of the solid electrolyte layer 3, the negative electrode layer 2, and the negative electrode current collector layer 21 were confirmed using a scanning electron microscope, and the results were 100 μm, 15 μm, and 5 μm, respectively. The porosity of the solid electrolyte layer and the negative electrode layer was less than 10%, confirming that sintering was complete.

[0326] Such solid-state batteries have a main surface current collector structure, such as Figure 4A As shown, current is collected from the electrode layer in the direction of the arrow. Figure 4A In the solid-state battery, the electron diffusion path in the negative electrode layer 2 is 15 μm.

[0327] In addition, the top-view dimensions (dimensions in the X and Y directions) after sintering were measured, and the result was 8mm × 8mm. The solid-state battery in this embodiment shrinks as the porosity decreases during the sintering process.

[0328] (Measurement and evaluation)

[0329] • Area ratio of all conductive additives

[0330] SEM images (photographs) representing the stacked structure (cross-sectional structure) of a solid-state battery were captured using the image analysis software "Azokun" (manufactured by Asahi Kasei Engineering Co., Ltd.). The cross-section of the solid-state battery in the SEM image is parallel to the stacking direction L of the positive electrode layer, solid electrolyte layer, and negative electrode layer, and perpendicular to the positive and negative terminals; it is a cross-section passing through the center of gravity of the solid-state battery in a top view. The center of gravity of the solid-state battery in the top view is the point at which an equal mass of material (e.g., paper) is cut along the outline of the solid-state battery (top view) and balanced with point support. The area ratio of all conductive additives identified in the negative electrode layer of the SEM image was calculated. This area ratio is the average of values ​​measured at any 10 locations, representing the ratio of the area of ​​all conductive additives to the total area of ​​all fields of view.

[0331] • The area ratio of the conductive additive with a slender shape observed in cross-section

[0332] The area ratio of elongated conductive additives in the cross-sectional observation of the negative electrode layer, as confirmed by the method of measuring the area ratio of all conductive additives, is determined in SEM images. Specifically, the content of elongated conductive additives in the cross-sectional observation is the average of values ​​measured at any 10 locations, and is calculated as the area ratio of elongated conductive additives relative to the negative electrode layer (i.e., the total area of ​​all fields of view in the negative electrode layer) and relative to all conductive additives (i.e., the area of ​​all conductive additives in each field of view).

[0333] • Area proportion of conductive additives with an orientation angle of less than 30° and an elongated shape when viewed in cross-section

[0334] The area ratio of elongated conductive additives with an orientation angle of less than 30° in the cross-section of the negative electrode layer in SEM images obtained by measuring the area ratio of all conductive additives is determined. This area ratio is the average of the values ​​measured at any 10 locations, and is the ratio of the area of ​​the elongated conductive additive observed in the cross-section with an orientation angle of less than 30° to the area of ​​all conductive additives in each field of view.

[0335] • Average aspect ratio (a / b) of conductive additives exhibiting a slender shape when viewed in cross-section.

[0336] Calculate the average aspect ratio of the elongated conductive additives observed in the cross-section of the negative electrode layer in SEM images obtained by measuring the area ratio of all conductive additives. This aspect ratio is the average of the aspect ratios of any 100 cross-sections observed at any 10 locations for the elongated conductive additives.

[0337] • The average short side length b of the conductive additive that appears elongated in cross-section

[0338] Calculate the average short side length b of the elongated conductive additives observed in cross-sections of the negative electrode layer in SEM images obtained by measuring the area ratio of all conductive additives. This average short side length b is the average of the short side lengths of the elongated conductive additives observed in any 100 cross-sections measured at any 10 locations.

[0339] • Utilization rate of negative electrode active material

[0340] For solid-state batteries, the reversible capacity is calculated by measuring the charge at a current density equivalent to 0.05C and a voltage range of 0.2V to 3.0V (vs. Li / Li+) through constant current charge-discharge tests.

[0341] The initial reversible capacity was calculated by dividing the initial reversible charge obtained from the constant current charge-discharge test by the weight of the negative electrode active material. Furthermore, the utilization rate R was calculated by dividing the initial reversible capacity by the theoretical capacity, using the capacity of V(vanadium) in the negative electrode active material during a 2-electron reaction. It should be noted that the Li used in Comparative Example 6 and Example 21... 1.1 V 0.9 In systems where O2 is used in the negative electrode active material, the reversible capacity is calculated by measuring the charge at 0.1V to 2.5V (vs. Li / Li+V) to suppress the alloying reaction of the conductive additive Ag. The initial reversible capacity is calculated by dividing the initial reversible charge obtained from a constant current charge-discharge test by the weight of the negative electrode active material. It should be noted that the theoretical capacity, as the capacity achievable within the above voltage range, is the capacity when V in the negative electrode active material undergoes a 0.3-electron reaction.

[0342] ◎: 90% ≤ R ≤ 100% (optimal);

[0343] ○: 85% ≤ R < 90% (Good);

[0344] △: 75% ≤ R < 85% (acceptable) (no practical problems);

[0345] ×: R < 75% (not possible) (practical issues).

[0346] [Examples 2-4]

[0347] Except for changing the content of the conductive additive that appears elongated in cross-sectional view, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 1.

[0348] [Comparative Examples 1-3]

[0349] Except for using a spherical conductive additive (spherical Ag powder A, with an average primary particle size of 0.4 μm, manufactured by Zhaorong Chemical Co., Ltd.) instead of a conductive additive with a slender shape when viewed in cross-section, and changing the content of the spherical conductive additive, the solid battery was manufactured, measured, and evaluated using the same method as in Example 1.

[0350] [Table 4]

[0351]

[0352] It should be noted that in Comparative Examples 1 to 3, some of the spherical conductive additives were linked together and flat powder was observed.

[0353] In addition, in Examples 1 to 4, some of the flat powder spheroidized during sintering, resulting in a decrease in the proportion of flat powder.

[0354] In Comparative Examples 1-3, the utilization rate of active materials in solid-state batteries with varying contents of spherical conductive additives was shown. In batteries using spherical conductive additives, it was observed that the area ratio of the conductive additive decreased, and the utilization rate of the active materials significantly decreased. This can be attributed to the interruption of the conductive path of the conductive additive in the negative electrode layer, preventing the supply of electrons and resulting in the presence of active materials that do not contribute to charging and discharging.

[0355] On the other hand, as can be seen from Examples 1 to 4, by including flat powder as a conductive additive, reversible capacity can be maintained at a high level even when the content of the conductive additive is reduced. This can be attributed to the fact that by using flat powder, spheroidization during sintering can be suppressed. In addition, it has a high conductive path forming ability, so even with the same content, the conductive paths in the negative electrode composite layer are more easily connected compared to spherical powder.

[0356] Furthermore, even when flat powder is present, a decrease in reversible capacity can be observed when the area ratio of the conductive additive is 10%. Therefore, it is preferable to achieve a particularly high utilization rate when the area ratio of the conductive additive is approximately 12% or higher (especially 15% or higher).

[0357] [Examples 5, 6 and Comparative Example 4]

[0358] Except for the use of a mixture of spherical and flat conductive additives, and the alteration of their mixing ratio to change the area ratio of the flat conductive additive, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 2.

[0359] [Table 5]

[0360]

[0361] It should be noted that in Comparative Examples 2 and 4, and Examples 2, 5 and 6, the area ratio of the conductive additive is the same, while the area ratio of the flat conductive additive is different.

[0362] Comparisons of Comparative Examples 2 and 4, and Examples 2, 5, and 6 show that, with the same area ratio of conductive additive, the utilization rate of the active material increases with the increase of the area ratio of the flat conductive additive. Furthermore, it is known that, to obtain sufficient utilization, the area ratio of the aforementioned flat conductive additive is preferably 35% or more. Moreover, it is known that by making the area ratio of the aforementioned flat conductive additive 50% or more, particularly 70% or more, an active material utilization rate of 85% or more, particularly 90% or more, is particularly preferred.

[0363] [Examples 7-9]

[0364] Except for changing the type of flat Ag powder, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 2.

[0365] [Table 6]

[0366]

[0367] It should be noted that in Examples 7 to 9, the utilization rate of the active material is shown when using a flat conductive additive with the same aspect ratio and varying thickness on the short side.

[0368] It is known that the smaller the thickness 'b' of the short side of the flat conductive additive, the higher the utilization rate of the active material. This can be attributed to the fact that, for the same aspect ratio, the smaller the short side thickness 'b', the larger the contact area between the active material and the conductive additive. Furthermore, it is evident that by making 'b' below 2.0 μm, and especially below 1.5 μm, an even higher utilization rate of the active material can be obtained.

[0369] [Examples 10-13]

[0370] Except for using a flat conductive additive with the same thickness on the short side and varying aspect ratio, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 2.

[0371] [Table 7]

[0372]

[0373] As shown in Table 7, an aspect ratio of 2.5 or higher and 10 or lower, especially 3 or higher and 8 or lower, can achieve a particularly high utilization rate and is the preferred option.

[0374] It can be assumed that if the aspect ratio is too small, the percolation of the conductive additive becomes difficult, thus reducing its utilization rate.

[0375] It can be assumed that if the aspect ratio is too large, the tortuosity of the ion conduction path in the negative electrode layer will increase, thus reducing the utilization rate.

[0376] [Example 14]

[0377] Except for not forming a negative electrode current collector layer, and forming a negative electrode layer that is in contact with the negative electrode current collector while being electrically connected to the negative terminal via the negative electrode current collector, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 2.

[0378] The obtained solid-state battery has Figure 4B The cross-sectional structure shown.

[0379] In detail, such as Figure 4B As shown, in addition to forming an Ag paste coating layer for the negative electrode current collector 210 on the end face of the green sheet in the negative electrode layer, by interacting with... Figure 4A The same method used to manufacture solid-state batteries was used to manufacture... Figure 4B Solid-state batteries.

[0380] Such solid-state batteries have an end-face current-collecting structure, such as Figure 4B As shown, current is collected from the electrode layer in the direction of the arrow. Figure 4B In the solid-state battery, the electron diffusion path in the negative electrode layer 2 is 15 μm.

[0381] In addition, the top-view dimensions (dimensions in the X and Y directions) after sintering were measured, and the result was 8mm × 8mm. The solid-state battery in this embodiment shrinks as the porosity decreases during the sintering process.

[0382] [Examples 15-18]

[0383] Except for changing the slurry viscosity during the forming of the negative electrode layer and changing the area ratio of flat conductive additives with an orientation angle of less than 30°, the solid battery was manufactured, measured and evaluated using the same method as in Example 14.

[0384] [Comparative Example 5]

[0385] Except for using a spherical conductive additive (spherical Ag powder A, with an average primary particle size of 0.4 μm, manufactured by Zhaorong Chemical Co., Ltd.) instead of a conductive additive with a slender shape when viewed in cross-section, and changing the content of the spherical conductive additive, the solid battery was manufactured, measured, and evaluated using the same method as in Example 14.

[0386] [Table 8]

[0387]

[0388] In Comparative Example 5, although the same negative electrode layer as in Comparative Example 1 was used, the utilization rate of the active material was significantly reduced by forming an end-face current collector structure. This is because, in the end-face current collector structure, a conductive path needs to be continuously formed in the in-plane direction, thus making the conductive path very long and prone to interruption.

[0389] On the other hand, it can be seen that in Example 14, although the same negative electrode layer as in Example 2 was used, the utilization rate remained at a high level even when formed as an end-face current collector structure. This can be attributed to the fact that by using flat powder, it is easier to form conductive paths in the negative electrode layer, and by aligning the flat powder in the in-plane direction, it is easier to form conductive paths in the in-plane direction.

[0390] As shown in Examples 14-18, the utilization rate of the active material changes with the proportion of flat powder with an orientation angle of 30° or less. In particular, when the proportion of flat powder with an orientation angle of 30° or less is between 55% and 75%, a preferred result of over 90% utilization of the active material is obtained. This can be attributed to the fact that, with low orientation, it is difficult to obtain an in-plane conductive path, while with excessively high orientation, it is difficult to form a conductive path in the thickness direction of the negative electrode layer.

[0391] [Example 19]

[0392] Except for the use of fibrous Ag powder A as a conductive additive that appears elongated in cross-section, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 14.

[0393] Even when using fibrous Ag powder, the same or better effects can be obtained as when using the flat powder of Example 14.

[0394] [Table 9]

[0395]

[0396] [Example 20]

[0397] Except for the use of flat Cu powder A as a conductive additive that appears elongated in cross-section, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 2.

[0398] It can be seen that when Cu is used in conductive additives, the same effect as Ag can be obtained.

[0399] [Table 10]

[0400]

[0401] [Example 21]

[0402] In addition to using (Li 1.1 V 0.9 Apart from O2 as the negative electrode active material, solid-state batteries were manufactured, measured, and evaluated using the same method as in Example 2.

[0403] [Comparative Example 6]

[0404] Except that a spherical conductive additive (spherical Ag powder A, with an average primary particle size of 0.4 μm, manufactured by Zhaorong Chemical Co., Ltd.) was used instead of a conductive additive with an elongated shape when viewed in cross-section, the solid-state battery was manufactured, measured, and evaluated using the same method as in Example 21.

[0405] A comparison of Example 2 and Example 21 shows that, based on the increase in the utilization rate of the negative electrode active material, when the negative electrode layer contains a negative electrode active material with a Li / V ratio of 2 or higher, the effect of making the conductive additive appear elongated in cross-sectional view is particularly significant compared to the case where the negative electrode active material contains a negative electrode active material with a Li / V ratio of less than 2.

[0406] [Table 11]

[0407]

[0408] Industrial availability

[0409] The solid-state battery according to one embodiment of the present invention can be applied to various fields where batteries or energy storage are envisioned. Although merely illustrative, the solid-state battery according to one embodiment of the present invention can be applied to the field of electronic assembly. The solid-state battery according to one embodiment of the present invention can also be applied to the following fields: electrical / information / communication fields using mobile devices, etc. (e.g., electrical / electronic equipment fields or mobile equipment fields including mobile phones, smartphones, smartwatches, laptops, digital cameras, activity meters, arm computers, electronic paper, wearable devices, RFID tags, card-type electronic money, smartwatches, and other small electronic devices); home / small industrial applications (e.g., power tools, golf carts, home / care / industrial robots); large industrial applications (e.g., forklifts, elevators, port cranes); transportation systems (e.g., hybrid vehicles, electric vehicles, buses, trams, electric-assisted bicycles, electric motorcycles, etc.); power systems (e.g., various power generation, load regulators, smart grids, home stationary energy storage systems, etc.); medical applications (medical devices such as headphones and hearing aids); pharmaceutical applications (medical management systems, etc.); and IoT fields; space / deep-sea applications (e.g., space probes, underwater research vessels, etc.), etc.

Claims

1. A solid-state battery, It includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. The negative electrode layer includes a conductive additive made of a metallic material and having an elongated shape, the conductive additive being oriented in the negative electrode layer such that, in a cross-sectional view, the area ratio of the conductive additive to the negative electrode layer is 7% or more and 28% or less. In the cross-sectional view, the area ratio of conductive additives with an orientation angle of 30° or less relative to the stacking direction perpendicular to the positive electrode layer, the solid electrolyte layer, and the negative electrode layer is 20% or more of the total area of ​​conductive additives. The orientation angle is the absolute value of the angle between the longest dimension direction of the conductive additive and the horizontal direction, assuming the solid-state battery is placed with the stacking direction of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer perpendicular to the horizontal direction. The cross-sectional view is taken at a section parallel to the stacking direction of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer.

2. The solid-state battery according to claim 1, wherein, The negative electrode layer contains a negative electrode active material in which the molar ratio of Li to vanadium V is 2.0 or higher.

3. The solid-state battery according to claim 1 or 2, wherein, The conductive additive is a flat conductive additive, a fibrous conductive additive, or a mixture thereof.

4. The solid-state battery according to claim 1 or 2, wherein, The conductive additive has an average aspect ratio of 2.0 or higher.

5. The solid-state battery according to claim 1 or 2, wherein, The conductive additive has an average short side length of 0.1 μm or more and 4.0 μm or less.

6. The solid-state battery according to claim 1 or 2, wherein, The conductive additive is composed of one or more metallic materials selected from the group consisting of silver (Ag), gold (Au), palladium (Pd), platinum (Pt), copper (Cu), tin (Sn), nickel (Ni), and their alloys.

7. The solid-state battery according to claim 1 or 2, wherein, The area ratio of the conductive additive to all conductive additives is more than 35%.

8. The solid-state battery according to claim 1 or 2, wherein, The negative electrode layer has an end face current collection structure that contacts the negative electrode current collection part at its end face and is electrically connected to the negative terminal via the negative electrode current collection part.

9. The solid-state battery according to claim 8, wherein, The negative electrode current collector has an upper surface that is flush with the upper surface of the negative electrode layer and a lower surface that is flush with the lower surface of the negative electrode layer in the stacking direction of the positive electrode layer, the solid electrolyte layer and the negative electrode layer.

10. The solid-state battery according to claim 2, wherein, The negative electrode active material has an average chemical composition represented by the following general formula (1), In formula (1), A is one or more elements selected from the group consisting of Na, K, Mg, Ca and Zn; B is one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, Sn, P, As, Ti, Mo, W, Fe, Cr and Co; 0≤x≤1.0; 0.5≤y≤1.0; a is the average valence of A; b is the average valence of B.

11. The solid-state battery according to claim 2, wherein, The negative electrode active material has β Ⅱ -Li3VO4 type crystal structure or γ Ⅱ -Li3VO4 type crystal structure.

12. The solid-state battery according to claim 1 or 2, wherein, The negative electrode layer has a thickness of more than 2 μm and less than 50 μm.

13. The solid-state battery according to claim 1 or 2, wherein, At least one of the negative electrode layer or the solid electrolyte layer further comprises a sintering aid. The sintering aid is a compound having the following chemical composition: containing Li, B and O, and the molar ratio of Li to B, Li / B, is 2.0 or higher.

14. The solid-state battery according to claim 1 or 2, wherein, The positive electrode layer and the negative electrode layer are layers capable of inserting and de-inserting lithium ions.

15. The solid-state battery according to claim 1 or 2, wherein, The solid electrolyte layer, the positive electrode layer, and the negative electrode layer are sintered together to form a sintered body.

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