Solid-state battery

Abstract

This invention provides a solid-state battery with significantly superior cycle characteristics and leakage resistance. 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 and negative electrode layers. The negative electrode layer contains a negative electrode active material with a Li to vanadium (V) molar ratio of 2.0 or higher. The solid electrolyte layer contains a solid electrolyte having a LISICON-type structure and containing at least V. In the thickness direction of the solid electrolyte layer, the ratio γ of V in the solid electrolyte varies by an amount of 0.20 or higher.

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] As a negative electrode active material for solid-state batteries, it is known to use technologies that use oxides containing V (Patent Documents 1 and 2).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2005-11801

[0008] Patent Document 2: Japanese Patent Application Publication No. 2013-165061 Summary of the Invention

[0009] The inventors of this invention have discovered that, in the prior art described above, it is effective to combine a negative electrode layer containing a negative electrode active material containing V and a solid electrolyte layer containing a solid electrolyte having a LISICON-type structure in order to suppress side reactions during co-sintering.

[0010] The inventors of this invention have also discovered new problems with this combination, including low capacity retention during repeated charge-discharge cycles and / or high leakage current during charging. For example, if the capacity retention is too low during repeated charge-discharge cycles, the discharge capacity decreases, resulting in a reduction in the energy density of the solid-state battery. Furthermore, for example, if the leakage current is too high, the capacity of the solid-state battery gradually decreases over time after charging, causing problems with its storage characteristics. For these reasons, it is difficult to simultaneously achieve both high energy density and good storage characteristics in a solid-state battery.

[0011] The purpose of this invention is to provide a solid-state battery with significantly superior cycle characteristics and leakage resistance.

[0012] This invention relates to a solid-state battery.

[0013] 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.

[0014] The negative electrode layer contains a negative electrode active material in which the molar ratio of Li to vanadium (V) is greater than 2.0.

[0015] The solid electrolyte layer contains a solid electrolyte having a LISICON-type structure and containing at least V.

[0016] The solid electrolyte layer has a V ratio y in the solid electrolyte that varies by an amount greater than 0.20 in the thickness direction of the layer.

[0017] The inventors of this invention have discovered that when a negative electrode layer containing a negative electrode active material containing V is combined with a solid electrolyte layer containing a solid electrolyte having a LISICON-type structure and containing V, the cycle characteristics and leakage resistance are more sufficiently improved by varying the ratio of V of the solid electrolyte in the solid electrolyte layer in the thickness direction of the layer by a predetermined amount.

[0018] The inventors of this invention have discovered that by further specifying the ratio of V of the solid electrolyte layer near the negative electrode layer of the solid electrolyte layer to a specified value or higher, the cycle characteristics and leakage resistance can be further improved.

[0019] The solid-state battery of the present invention has more complete and superior cycle characteristics and leakage resistance. Attached Figure Description

[0020] Figure 1 This is an example of a SEM image of a solid-state battery showing the stacked structure of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer in the solid-state battery of the present invention.

[0021] Figure 2A This is a schematic graph illustrating a first embodiment in which the ratio of V of the solid electrolyte (particularly the first solid electrolyte) in the solid electrolyte layer of the solid battery of the present invention gradually changes along the thickness direction L of the layer.

[0022] Figure 2B This is a schematic graph illustrating a second embodiment in which the ratio of V of the solid electrolyte (particularly the first solid electrolyte) in the solid electrolyte layer of the solid battery of the present invention gradually changes along the thickness direction L of the layer.

[0023] Figure 2C This is a schematic graph illustrating a third embodiment in which the ratio of V of the solid electrolyte (particularly the first solid electrolyte) in the solid electrolyte layer of the solid battery of the present invention gradually changes along the thickness direction L of the layer.

[0024] Figure 2D This is a schematic graph illustrating a fourth embodiment in which the ratio of V of the solid electrolyte (particularly the first solid electrolyte) in the solid electrolyte layer of the solid battery of the present invention gradually changes along the thickness direction L of the layer.

[0025] Figure 2E This is a schematic graph illustrating a fifth embodiment in which the ratio of V of the solid electrolyte (particularly the first solid electrolyte) in the solid electrolyte layer of the solid battery of the present invention varies in stages along the thickness direction L of the layer.

[0026] Figure 3 This is a SEM image of a solid-state battery showing the stacked structure of the positive electrode layer, negative electrode layer, and solid electrolyte layer in the solid-state battery of Example 2.

[0027] Figure 4 This is a graph showing the analytical results of the elemental ratios in the solid electrolyte layer when line analysis was performed using energy dispersive X-ray analysis (EDX) in the solid battery of Example 2.

[0028] Figure 5 This is a graph showing the measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid battery obtained in Example 1, determined by line analysis using energy-dispersive X-ray analysis (EDX).

[0029] Figure 6 This is a graph showing the measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid battery obtained in Example 2, determined by line analysis using energy dispersive X-ray analysis (EDX).

[0030] Figure 7 This is a graph representing the measurement results of the ratio y of V in the solid electrolyte layer (particularly the first solid electrolyte) in the solid battery obtained in Example 3, determined by line analysis using energy dispersive X-ray analysis (EDX).

[0031] Figure 8 This is a graph showing the measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid battery obtained in Example 4, determined by line analysis using energy-dispersive X-ray analysis (EDX).

[0032] Figure 9This is a graph showing the measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid battery obtained in Example 5, determined by line analysis using energy-dispersive X-ray analysis (EDX).

[0033] Figure 10 This is a graph showing the measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid battery obtained in Example 6, determined by line analysis using energy-dispersive X-ray analysis (EDX).

[0034] Figure 11 This is a graph showing the measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid battery obtained in Example 7, determined by line analysis using energy-dispersive X-ray analysis (EDX).

[0035] Figure 12 This is a graph showing the measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid battery obtained in Example 8, determined by line analysis using energy-dispersive X-ray analysis (EDX).

[0036] Figure 13 It is a graph showing the measurement results related to the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid electrolyte layer of the solid battery in Examples 1 and Comparative Examples 1-2.

[0037] Figure 14 It is a graph showing the measurement results related to the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid electrolyte layer of the solid batteries of Examples 3, 5 and 6.

[0038] Figure 15 It is a graph showing the measurement results related to the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid electrolyte layer of the solid batteries of Examples 3 and 4.

[0039] Figure 16 It is a graph showing the measurement results related to the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) in the solid electrolyte layer of the solid batteries of Examples 7 and 8. Detailed Implementation

[0040] Solid-state batteries

[0041] 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.

[0042] The solid-state battery of the present invention comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, typically as follows: Figure 1 As shown, a stacked structure is formed by stacking a positive electrode layer and a negative electrode layer separated by a solid electrolyte layer. Two or more positive and negative electrode layers can be stacked, provided a solid electrolyte layer is present between them. The solid electrolyte layer is in contact with and held between the positive and negative electrode layers. 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 together by sintering. Here, it can be that both or more components (especially layers) are sintered bodies simultaneously and integrally sintered. Figure 1 This is an example of a SEM image of a solid-state battery showing the stacked structure of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer in the solid-state battery of the present invention. It should be noted that... Figure 1 The SEM photographs (physical: color photocopies) should be submitted as reference material with the case submission.

[0043] The negative electrode layer, positive electrode layer, and solid electrolyte layer constituting the solid-state battery of the present invention will be described in detail below. The following description applies only to at least one stacked structure (or stacked structure portion) formed by stacking the negative electrode layer and the positive electrode layer via the solid electrolyte layer. In the present invention, from the viewpoint of further improving cycle characteristics and leakage resistance, the following description preferably applies to all stacked structures (or stacked structure portions) formed by stacking the negative electrode layer and the positive electrode layer via the solid electrolyte layer.

[0044] (Negative electrode layer)

[0045] The negative electrode layer contains a negative electrode active material and may also contain a solid electrolyte. In the negative electrode layer, both the negative electrode active material and the solid electrolyte preferably have a sintered body morphology. For example, when the negative electrode layer contains both a negative electrode active material and a solid electrolyte, it is preferable to have a sintered body morphology in which the negative electrode active material particles are bonded together by the solid electrolyte, and the negative electrode active material particles and the negative electrode active material particles are bonded together by mutual sintering.

[0046] The negative electrode active material contains a Li (lithium) to V (vanadium) molar ratio of 2.0 or higher (particularly 2 or higher and 10 or lower). If this molar ratio is too low, the reactivity with the LISICON-type oxide in the solid electrolyte layer increases. As a battery, not only is sufficient reversible capacity not obtained, but the electrode structure is also damaged, and the cycle characteristics are reduced. Therefore, it is difficult to achieve both good cycle characteristics and leakage resistance. From the viewpoint of further improving cycle characteristics and leakage resistance, the Li to V molar ratio in the negative electrode active material is preferably 2 or higher and 6 or lower, more preferably 3 or higher and 4 or lower. In the present invention, in a solid-state battery in which the negative electrode layer contains a negative electrode active material with a Li to V molar ratio within the above 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 a constant bonding between the solid electrolyte layer and the negative electrode layer. Furthermore, side reactions during co-sintering between the negative electrode active material contained in the negative electrode layer and the LISICON-type solid electrolyte in the solid electrolyte layer can be suppressed, thereby increasing the reversible capacity of the solid-state battery. When the negative electrode layer does not contain a negative electrode active material with a Li to V molar ratio of 2 or higher, the bonding between the solid electrolyte layer and the negative electrode layer decreases, and the 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 cannot be sufficiently suppressed. As a result, the cycling performance and leakage resistance are reduced.

[0047] From the viewpoint of further improving cycle characteristics and leakage resistance, the negative electrode active material preferably has an average chemical composition represented by the following general formula (1).

[0048] [Chemical Formula 1]

[0049] (Li [3-ax+(5-b)(1-y)] A x (V) y B 1-y O4 (1)

[0050] By employing such a composition, the reactivity with the LISICON-type solid electrolyte in the solid electrolyte layer can be reduced. Furthermore, the negative electrode active material used in this invention exhibits capacity 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.

[0051] In formula (1), A is one or more elements selected from the group consisting of Na (sodium), K (potassium), Mg (magnesium), Ca (calcium), Al (aluminum), Ga (gallium), Zn (zinc), Fe (iron), Cr (chromium) and Co (cobalt).

[0052] B is selected from one or more elements in 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), with Si being the preferred element.

[0053] x has a relationship of 0 ≤ x ≤ 1.0, preferably 0 ≤ x ≤ 0.5, more preferably 0 ≤ x ≤ 0.1, and even more preferably 0.

[0054] The relationship y has 0.5≤y≤1.0, preferably 0.55≤y≤1.0, and more preferably 0.65≤y≤0.95.

[0055] 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).

[0056] 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.

[0057] In formula (1), from the viewpoint of improving the ease of obtaining the negative electrode active material and further improving the cycle characteristics and leakage resistance, in a preferred embodiment, it is as follows:

[0058] A is one or more elements selected from the group consisting of Al and Zn.

[0059] B is selected from one or more elements in the group consisting of Si and P, with Si being the preferred choice.

[0060] x has the relationship 0≤x≤0.06, and is more preferably 0.

[0061] The relationship y has 0.55≤y≤1.0, more preferably 0.65≤y≤0.95, and even more preferably 0.70≤y≤0.90.

[0062] a is the average price of A.

[0063] b is the average price of B.

[0064] 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 Si 0.07 O4, Li 3.22 (V 0.72 P 0.06 Si 0.22 O4, etc. Li is preferred. 3.2 (V 0.8 Si 0.2 )O4.

[0065] 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 chemical composition of the negative electrode active material along the thickness direction of the negative electrode layer. The average chemical composition of the negative electrode active material can be analyzed and determined 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.

[0066] 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 determined based on their composition in the above composition analysis.

[0067] 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.

[0068] 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.

[0069] From the perspective of further improving cycle performance and leakage current resistance, the negative electrode active material preferably has β-type properties. II -Li3VO4 type structure or γ II -Li3VO4 type structure. This crystalline structure improves charge-discharge reversibility and enables stable cycling characteristics. Furthermore, by employing γ-... II The Li3VO4 structure improves the binding affinity with the LISICON-type solid electrolyte in the solid electrolyte layer, resulting in stable cycling characteristics.

[0070] The negative electrode active material has β II -Li3VO4 type structure refers to the fact that the negative electrode active material (especially its particles) has β II -Li3VO4 type crystal structure, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as β II The crystalline 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 similar appearance to the so-called β-type structure in X-ray diffraction at a specified incident angle (x-axis). II The crystalline structure of Li3VO4 inherently corresponds to more than one major peak in the Miller index. As a β-type crystal... II An example of a negative electrode active material with a Li3VO4-type structure is ICDD Card No. 01-073-6058.

[0071] The negative electrode active material has γ II -Li3VO4 type structure refers to the presence of γ in the negative electrode active material (especially its particles). II -Li3VO4 type crystalline structure, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as γ II The crystalline 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-rays at a specified incident angle (x-axis) in X-ray diffraction. II The crystalline structure of Li3VO4 inherently corresponds to more than one major peak in the Miller index. As a γ-type crystal...II An example of a negative electrode active material with a Li3VO4-type structure is ICDD Card No. 01-073-2850.

[0072] 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. Preferably, the negative electrode active material 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.

[0073] 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.

[0074] 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).

[0075] 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.

[0076] [Mathematical Expression 1]

[0077] R = 2 × (S / π) 1 / 2

[0078] It should be noted that the average particle size of the negative electrode active material in the negative electrode layer can be automatically determined by identifying the negative electrode active material through composition during the determination of the average chemical composition mentioned above.

[0079] The volume ratio of the negative electrode layer in the negative electrode active material is not particularly limited. From the viewpoint of further improving cycle characteristics and leakage resistance, 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.

[0080] The volume ratio of the negative electrode active material in the negative electrode layer can be determined based on the SEM image processed from the FIB cross-section. Specifically, the cross-section of the negative electrode layer is observed using SEM-EDX. Regions with a V-shape 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 determined.

[0081] 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.

[0082] 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 higher speeds can be expected. 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 that the increased tortuosity of the LISICON-type solid electrolyte in the solid electrolyte increases electronic resistance. 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. "At least one of the negative electrode layer or the solid electrolyte layer comprises a solid electrolyte with a garnet-type structure" means that either one of the negative electrode layer or the solid electrolyte layer comprises a solid electrolyte with a garnet-type structure, or both of them may comprise a solid electrolyte with a garnet-type structure.

[0083] A solid electrolyte having a garnet-type structure refers to a solid electrolyte having a garnet-type crystalline structure. In a broad sense, it refers to a crystalline structure that can be identified as garnet-type 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, at a specified incident angle (x-axis), the solid electrolyte displays one or more major peaks corresponding to the Miller indices inherent in a so-called garnet-type crystalline structure.

[0084] Solid electrolytes with garnet-type structures preferably have an average chemical composition represented by the following general formula (2).

[0085] [Chemical Formula 2]

[0086] (Li [7-ax-(b-4)y] A x )La3Zr 2-y B y O 12 (2)

[0087] 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).

[0088] 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).

[0089] x has the relationship 0 ≤ x ≤ 0.5.

[0090] y has the relationship 0 ≤ y ≤ 2.0.

[0091] a is the average price of A, which is the same as the average price of A in equation (1).

[0092] b is the average price of B, which is the same as the average price of B in equation (1).

[0093] In formula (2), in a preferred embodiment, it is as follows:

[0094] A is one or more elements selected from the group consisting of Ga and Al.

[0095] B is one or more elements selected from the group consisting of Nb, Ta, W, Mo, and Bi.

[0096] x has the relationship 0.1≤x≤0.3.

[0097] The relationship y has 0 ≤ y ≤ 1.0, and preferably has 0 ≤ y ≤ 0.7.

[0098] a is the average price of A.

[0099] b is the average price of B.

[0100] 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 6.5 La3(Zr 1.5 Mo 0.25 )O 12 .

[0101] 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 determined 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.

[0102] 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 determined based on these compositions in the above composition analysis.

[0103] In addition to using raw material compounds containing specified metal atoms, the solid electrolyte of the negative electrode layer can be obtained by the same method as the negative electrode active material, or it can be obtained as a commercially available product.

[0104] The average chemical composition and crystal structure of the solid electrolyte in the negative electrode layer typically vary depending on 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.

[0105] The volume ratio of solid electrolyte (especially solid electrolyte with garnet structure) in the negative electrode layer is not particularly limited, but from the viewpoint of further improving cycle characteristics and leakage resistance, it is preferably 10% or more and 50% or less, more preferably 20% or more and 40% or less.

[0106] The volume ratio of solid electrolyte in the negative electrode layer can be determined 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.

[0107] 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.

[0108] 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 cycle performance and leakage resistance, 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-temperature melting properties, 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 satisfy 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 Al0.3 )BO3.

[0109] 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, further improving the cycle characteristics and leakage resistance, it is preferably 0.1% or more and 10% or less, more preferably 1% or more and 7% or less.

[0110] The volume proportion of sintering aids in the negative electrode layer can be determined using the same method as the volume proportion of the negative electrode active material. For the EDX analysis of regions identified as sintering aids, the focus can be on element B.

[0111] The conductive additive in the negative electrode layer can be any conductive additive known in the field of solid-state batteries. From the viewpoint of further improving cycle performance and leakage resistance, preferred conductive additives include, for example, 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 (registered trademark), and VGCF (registered trademark) carbon nanotubes. There are no particular limitations on the shape of the conductive additive; materials of any shape, such as spherical, plate-like, or fibrous, can be used. Ag and / or carbon materials are preferred as conductive additives. This is because the aforementioned conductive additives are less prone to side reactions when co-sintered with the negative electrode material used in this invention, allowing for smooth charge transfer between the two.

[0112] The volume ratio of the conductive additive in the negative electrode layer is not particularly limited, but from the viewpoint of further improving cycle characteristics and leakage resistance, it is preferably 10% or more and 50% or less, more preferably 20% or more and 40% or less.

[0113] The volume proportion of conductive additives in the negative electrode layer can be determined using the same method as the volume proportion of the negative electrode active material. Based on SEM-EDX analysis, regions where only the signal of the used metal element is observed can be considered as conductive additives.

[0114] In the negative electrode layer, the porosity is not particularly limited, but from the perspective of further improving cycle characteristics and leakage resistance, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0115] The porosity of the negative electrode layer was determined using SEM images obtained from the FIB cross-section.

[0116] The negative electrode layer is a layer that can be called the "negative electrode active material layer". The negative electrode layer can have what is called a negative electrode current collector or a negative electrode current collector layer.

[0117] (Positive electrode layer)

[0118] In this invention, the positive electrode layer is not particularly limited. For example, the positive electrode layer may contain a positive electrode active material. Preferably, the positive electrode layer has the morphology of a sintered body containing positive electrode active material particles.

[0119] There are no particular limitations on the positive electrode active material; any positive electrode active material known 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. As a preferred example of a lithium phosphate compound with a NASICON-type structure, Li3V2(PO4)3 is an example. As a preferred example of a lithium phosphate compound with an olivine-type structure, Li3Fe2(PO4)3 and LiMnPO4 are examples. As a preferred example of lithium-containing layered oxide particles, LiCoO2 and LiCo are examples. 1 / 3 Ni 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 / Lithium-containing layered oxides such as 3O2. 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.

[0120] The term "NASICON-type structure" for the positive electrode active material in the positive electrode layer refers to the presence of a NASICON-type crystalline structure in the positive electrode active material (particularly its particles). In a broad sense, it refers to a crystalline structure that can be identified as NASICON-type by those skilled in the art of solid-state batteries. In a narrower sense, "NASICON-type structure" in the positive electrode active material in the positive electrode layer means that, in X-ray diffraction, the positive electrode active material (particularly its particles) exhibits one or more major peaks at a specified incident angle (x-axis) corresponding to the Miller index inherent in a so-called NASICON-type crystalline structure. The compounds exemplified above are examples of preferred positive electrode active materials with a NASICON-type structure.

[0121] The presence of an olivine-type structure in the positive electrode active material of the positive electrode layer refers to the positive electrode active material (especially its particles) having an olivine-type crystalline structure. In a broad sense, it refers to a crystalline structure that can be identified as olivine-type by those skilled in the art of solid-state batteries. In a narrow sense, the presence of an olivine-type structure in the positive electrode active material of 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 crystalline structure at a specified incident angle (x-axis). The compounds exemplified above can be listed as preferred positive electrode active materials with an olivine-type structure.

[0122] The spinel-type structure of the positive electrode active material in the positive electrode layer refers to the spinel-type crystalline structure of the positive electrode active material (especially its particles). In a broad sense, it refers to a crystalline 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 crystalline structure at a specified incident angle (x-axis). The compounds exemplified above are examples of preferred positive electrode active materials with a spinel-type structure.

[0123] 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 determined 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.

[0124] In addition to using raw material compounds containing specified metal atoms, positive electrode active materials can be obtained by the same methods as negative electrode active materials, or they can be obtained as commercially available products.

[0125] 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. Preferably, the positive electrode active material has the aforementioned chemical composition and crystal structure in the solid-state battery after sintering together with the negative electrode layer and the solid electrolyte layer.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] The volume ratio of the positive electrode active material in the positive electrode layer is not particularly limited, but from the viewpoint of further improving cycle performance, it is preferably 30% or more and 90% or less, and more preferably 40% or more and 70% or less.

[0131] In addition to the positive electrode active material, the positive electrode layer may also contain, for example, solid electrolyte, sintering aids, and conductive aids.

[0132] 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.

[0133] In addition to using raw material compounds containing specified metal atoms, the solid electrolyte of the positive electrode layer can be obtained by the same method as the negative electrode active material, or it can be obtained as a commercially available product.

[0134] The average chemical composition and crystal structure of the solid electrolyte in the positive electrode layer typically vary depending on 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.

[0135] The volume ratio of the solid electrolyte in the positive electrode layer is not particularly limited. From the viewpoint of further improving the cycle characteristics 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.

[0136] As a sintering aid in the positive electrode layer, the same compound as the sintering aid in the negative electrode layer can be used.

[0137] 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 further improving the cycle characteristics, it is preferably 0.1% or more and 20% or less, and more preferably 1% or more and 10% or less.

[0138] As a conductive aid in the positive electrode layer, the same compound as the conductive aid in the negative electrode layer can be used.

[0139] The volume ratio of the conductive additive in the positive electrode layer is not particularly limited, but from the viewpoint of further improving cycle performance, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0140] In the positive electrode layer, the porosity is not particularly limited, but from the viewpoint of further improving cycle performance, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0141] The porosity of the positive electrode layer is measured using the same method as that used for the porosity of the negative electrode layer.

[0142] The positive electrode layer is a layer that can be called the "positive electrode active material layer". The positive electrode layer can have what is called a positive electrode current collector or a positive electrode current collector layer.

[0143] (Solid electrolyte layer)

[0144] In this invention, the solid electrolyte layer comprises 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 form of a sintered body containing the first solid electrolyte. In this invention, as described above, 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 the first solid electrolyte, the V ratio of the first solid electrolyte in the solid electrolyte layer varies by a predetermined amount in the thickness direction of the layer. This allows for more substantial improvement in cycle characteristics and leakage current resistance. Specifically, by varying the V ratio by a predetermined amount, a region with a relatively low V ratio can be formed in the thickness direction of the layer, thus sufficiently reducing leakage current and substantially improving leakage current resistance. Furthermore, by varying the V ratio by a predetermined amount, the V ratio near the negative electrode layer in the solid electrolyte layer can be relatively high, thus allowing the V ratio to change more slowly at the interface between the solid electrolyte layer and the negative electrode layer. Therefore, the interface between the two layers bonds with sufficient strength, thus effectively suppressing interface delamination even during repeated expansion and contraction during charging and discharging, resulting in significantly improved cycle characteristics. When the solid electrolyte layer does not contain a first solid electrolyte, the bonding between the solid electrolyte layer and the negative electrode layer decreases, and / or the side reactions during co-sintering of the negative electrode active material contained in the negative electrode layer and the LISICON-type solid electrolyte in the solid electrolyte layer are not sufficiently suppressed. As a result, cycle characteristics and / or leakage current tolerance decrease. Increasing the thickness of the solid electrolyte layer can also reduce leakage current, but from the viewpoint of improving energy density, a thinner solid electrolyte layer is preferred to reduce leakage current. In this invention, by making the solid electrolyte layer relatively thin, the leakage current during charging can be reduced more sufficiently, thus this invention is more suitable for the thinning of solid-state batteries (especially solid electrolyte layers). It should be noted that the change in the ratio y of V is the value of the ratio y of V in the elemental analysis curve of the solid electrolyte layer described later, expressed as "maximum value - minimum value".

[0145] The ratio of V in a solid electrolyte (especially the first solid electrolyte) is the ratio (mole fraction) y of V when the solid electrolyte (especially the first solid electrolyte) is expressed by a chemical formula (e.g., general formula (3) described later), which varies along the thickness direction L of the solid electrolyte layer.

[0146] In a solid electrolyte layer, the ratio y of V in the chemical composition of the solid electrolyte (especially the first solid electrolyte) can be as follows along the thickness direction L of the layer: Figures 2A to 2D It can change gradually as shown, or it can also be like... Figure 2EThe ratio y of V changes in stages as shown. From the viewpoint of further improving cycle performance, the ratio y of V is preferably gradually varied in the thickness direction of the layer. Figures 2A to 2D These are schematic graphs representing the first to fourth embodiments in which the ratio of V of the solid electrolyte (particularly the first solid electrolyte) in the solid electrolyte layer of the solid battery of the present invention gradually changes along the thickness direction L of the layer. Figure 2E This is a schematic graph illustrating a fifth embodiment in which the ratio of V of the solid electrolyte (particularly the first solid electrolyte) in the solid electrolyte layer of the solid battery of the present invention varies in stages along the thickness direction L of the layer.

[0147] When the ratio y of V of the solid electrolyte in the solid electrolyte layer gradually changes, it can change in all forms (or shapes).

[0148] For example, such as Figure 2A As shown, in the solid electrolyte layer, the ratio y of V can decrease linearly from the negative electrode layer (An) side to the positive electrode layer (Ca) side in its thickness direction L.

[0149] Additionally, for example, such as Figure 2B As shown, the ratio y of V can decrease slowly from the negative electrode layer (An) side to the positive electrode layer (Ca) side in its thickness direction L within the solid electrolyte layer, then decrease sharply, and then decrease slowly again.

[0150] Additionally, for example, such as Figure 2C As shown, the ratio y of V can decrease sharply and then increase sharply in the solid electrolyte layer along its thickness direction L from the negative electrode layer (An) side to the positive electrode layer (Ca) side.

[0151] Additionally, for example, such as Figure 2D As shown, the ratio y of V can increase sharply from the negative electrode layer (An) side to the positive electrode layer (Ca) side in the thickness direction L of the solid electrolyte layer, then decrease sharply, and then increase sharply again.

[0152] Additionally, for example, the ratio y of V in a solid electrolyte layer, along its thickness direction L, can be obtained from... Figures 2A to 2D The form shown can be a combination of two or more morphological changes.

[0153] The gradual change in the ratio y of V refers to the following: when elemental analysis of the solid electrolyte (especially the first solid electrolyte) in the solid electrolyte layer is performed at specified intervals along the thickness direction of the layer, and represented by a curve of ratio y (vertical axis) versus depth (depth in the thickness direction) L (horizontal axis), the difference in ratio y (vertical axis) between all any two adjacent points (i.e., all any two adjacent plotted points) is 0.50 or less, preferably 0.40 or less, more preferably 0.30 or less, and even more preferably 0.20 or less. It should be noted that in this curve, there may also be some adjacent points (i.e., adjacent plotted points) where the difference in ratio y is 0. The specified interval is, for example, an interval of 0.5 μm or more and 0.8 μm or less, preferably equal intervals. Hereinafter, the curve of ratio y (vertical axis) versus depth (depth in the thickness direction) L (horizontal axis) of V obtained from such elemental analysis is sometimes simply referred to as an "elemental analysis curve". It should be noted that... Figures 2A-2E These are two types of element analysis curves that omit plotted points.

[0154] Elemental analysis curves are plots of the ratio y (vertical axis) of V versus depth (depth in the thickness direction) L (horizontal axis) based on line analysis using energy-dispersive X-ray diffraction (EDX). For example, measurements can be performed using the Hochikage system's EMAX-Evolution. More specifically, such as... Figure 1 As shown, line analysis using energy-dispersive X-ray diffraction (EDX) along the thickness direction from the negative electrode layer through the solid electrolyte layer to the positive electrode layer yields, for example, the results obtained in Example 2. Figure 4 The analysis results of the element ratios are shown. Figure 4 In the diagram, the vertical axis represents the elemental ratio (%), and the horizontal axis represents the thickness depth (μm) of the solid electrolyte layer. The left side of the horizontal axis represents the negative electrode layer side, and the right side represents the positive electrode layer side. Based on the analysis results of these elemental ratios, the ratio y of V of the solid electrolyte (especially the first solid electrolyte) in the solid electrolyte layer is calculated, thereby obtaining, for example... Figures 2A to 2D The elemental analysis curves shown are shown. Figure 4 This is a graph illustrating an example of the elemental ratio analysis results in the solid electrolyte layer during line analysis using energy-dispersive X-ray diffraction (EDX) in the solid-state battery of the present invention, along the thickness direction from the negative electrode layer through the solid electrolyte layer to the positive electrode layer. It should be noted that... Figure 4 The curve graph (physical copy: color photocopy) shall be submitted as reference material with the case submission form.

[0155] As Figure 2A Specific examples, such as those obtained in Embodiment 1 described later, can be cited. Figure 5 The elemental analysis curves shown are shown.

[0156] As Figure 2B Specific examples, such as those obtained in embodiments 2, 3, 4, 7, and 8 described later, can be listed. Figure 6 , Figure 7 , Figure 8 , Figure 11 , Figure 12 The elemental analysis curves shown are shown.

[0157] As Figure 2C Specific examples, such as those obtained in Examples 5 and 6 described later, can be cited. Figure 9 , Figure 10 The elemental analysis curves shown are shown.

[0158] In elemental analysis plots, excessively protruding plot points [in other words, plot points that protrude upwards or downwards from their two adjacent points (i.e., the plot point between those two adjacent plot points) by more than 0.5] are omitted as noise. Specifically, in elemental analysis plots, for adjacent plot points P1(x1, y1), P2(x2, y2), and P3(x3, y3) (x1 < x2 < x3) on the horizontal axis, if the values ​​of "y2-y1" and "y2-y3" both exceed 0.5 (in the case of upward protrusion) or are less than -0.5 (in the case of downward protrusion), plot point P2 is considered noise and not counted.

[0159] In the solid electrolyte layer, the variation in the V ratio y is 0.20 or more (particularly 0.20 or more and 0.90 or less). From the viewpoint of further improving cycle performance and leakage resistance, it is preferable to be 0.30 or more and 0.90 or less, more preferably 0.60 or more and 0.90 or less, and even more preferably 0.70 or more and 0.90 or less. When the variation in the V ratio y is too small, it is difficult to simultaneously achieve good cycle performance and leakage resistance. Specifically, if the variation in the V ratio y is too small, a region with a sufficiently low V ratio cannot be formed in the thickness direction of the solid electrolyte layer, thus reducing leakage resistance. Therefore, from the viewpoint of leakage resistance, if the V ratio near the negative electrode layer in the solid electrolyte layer is relatively low, the V ratio changes drastically at the interface between the solid electrolyte layer and the negative electrode layer. As a result, the interface between the two layers cannot bond with sufficient strength, and due to repeated expansion and contraction during charging and discharging, interfacial peeling occurs, reducing cycle performance.

[0160] The change in the ratio y of V, as described above, is the value of the ratio y of V in the elemental analysis curve of the solid electrolyte layer, expressed as "maximum value - minimum value". The change in the ratio y of V can also be the average value of 10 elemental analysis curves obtained by performing line analysis at any 10 points using energy dispersive X-ray analysis (EDX).

[0161] In solid-state batteries manufactured by sintering, the change in the ratio y of V can be within the range described above.

[0162] Therefore, such a change in the ratio y of V can be achieved, for example, by one or more of the methods shown below:

[0163] Method (M1): Using V-containing LISICON-type solid electrolyte as raw material, V element diffuses from the negative electrode layer (especially the negative electrode active material therein) and / or the positive electrode layer (especially the LISICON-type solid electrolyte therein) to the solid electrolyte layer based on sintering;

[0164] Method (M2): Using a V-containing LISICON-type solid electrolyte as raw material, the V element diffuses from the solid electrolyte layer (especially the first solid electrolyte therein) to the negative electrode layer and / or positive electrode layer based on sintering;

[0165] Method (M3): Using V-free LISICON-type solid electrolyte as raw material, V element diffuses from the negative electrode layer (especially the negative electrode active material therein) and / or the positive electrode layer (especially the LISICON-type solid electrolyte therein) to the solid electrolyte layer based on sintering;

[0166] Method (M4): As described below, when manufacturing a solid electrolyte layer from multiple green sheets, the chemical composition of the solid electrolyte (especially the LISICON type solid electrolyte) contained in each of the multiple green sheets is adjusted.

[0167] The LISICON-type solid electrolyte containing V is a solid electrolyte having the same chemical composition as the general formula (3) described below, except that it satisfies 0 < y ≤ 1.0 (especially 0 < y < 1.0), preferably 0 < y ≤ 0.9, more preferably 0 < y ≤ 0.8.

[0168] A LISICON-type solid electrolyte that does not contain V is a solid electrolyte with a chemical composition that is expressed by the same general formula (3) as described below, except that it satisfies y = 0.

[0169] From the viewpoint of further improving cycle characteristics, the ratio y of V near the negative electrode layer of the solid electrolyte layer is preferably 0.40 or more (especially 0.40 or more and 0.95 or less), and preferably 0.6 or more (especially 0.6 or more and 0.9 or less).

[0170] The region near the negative electrode layer is the area within the solid electrolyte layer near the interface with the negative electrode layer; more specifically, it is the region within the solid electrolyte layer at a distance of 1 μm from the interface with the negative electrode layer. The ratio y of V in the region near the negative electrode layer can also be obtained by performing line analysis at any 10 points using energy-dispersive X-ray diffraction (EDX) to determine the average value of the 10 elemental analysis curves in the region near the negative electrode layer.

[0171] From the viewpoint of further improving leakage resistance, the solid electrolyte layer is preferably included in the portion M in the thickness direction L of the layer with a thickness of 10% or more (especially 10% or more and 100% or less) relative to the thickness of the layer, and the ratio y of V in the thickness direction L of the layer is 0.6 or less. More preferably, it is included in the portion M with a thickness of 30% or more (especially 30% or more and 100% or less) relative to the thickness of the layer.

[0172] From the viewpoint of further improving cycle characteristics and leakage resistance, the solid electrolyte layer is more preferably a portion M in the thickness direction of the layer in which the ratio y of V included in the thickness is 0.6 or less, and the thickness is 50% or more and 80% or less relative to the thickness of the layer.

[0173] For locations where the ratio y of V is less than 0.6, such as in... Figures 2A-2E The region M is represented by the oblique line. The ratio of the thickness m of this region to the thickness of the solid electrolyte layer should be within the range described above. For regions where the ratio y of V is 0.6 or less, the ratio of the thickness m of M to the thickness of the solid electrolyte layer can also be the average of this ratio obtained by performing line analysis at any 10 points using energy-dispersive X-ray diffraction (EDX) and measuring the 10 elemental analysis curves.

[0174] From the viewpoint of further improving cycle characteristics and leakage resistance, the solid electrolyte layer is preferably included in the portion of the thickness direction L of the layer with a thickness of 10% or more (especially 10% or more and 100% or less) relative to the thickness of the layer and a ratio y of V of 0.4 or less, and more preferably included in the portion with a thickness of 30% or more (especially 30% or more and 100% or less) relative to the thickness of the layer.

[0175] For regions where the V ratio y is below 0.4, the same method as for regions where the V ratio y is below 0.6 can be used, except that the upper limit is set to 0.4. The ratio of the thickness of the region where the V ratio y is below 0.4 to the thickness of the solid electrolyte layer can also be obtained by performing line analysis at any 10 points using energy dispersive X-ray diffraction (EDX) and measuring the average of the ratios in the 10 elemental analysis curves.

[0176] From the perspective of further improving cycling performance, the maximum value of the ratio y of V along the thickness direction L of the solid electrolyte layer is |dy / dL|.MAX Preferably, it is 0.55 or less (particularly 0.05 or more and 0.55 or less), more preferably 0.10 or more and 0.55 or less. By making the change in the ratio y of V as gradual as described above, strain is difficult to accumulate in the solid electrolyte layer, and even if expansion and contraction occur during charging and discharging, crack formation can be further effectively prevented.

[0177] |dy / dL| MAX This value is calculated by selecting the two points where the V ratio changes most significantly along the thickness direction of the solid electrolyte layer, and dividing the change in the V ratio between these two points by the distance between them. Specifically, |dy / dL| MAX The V-ratio can be calculated as follows: In the elemental analysis curve, select the two adjacent points (adjacent points in the thickness direction) where the change in V-ratio is greatest, and divide the change in V-ratio between these two points by the distance between them. |dy / dL| MAX Alternatively, it could be the |dy / dL| value when 10 elemental analysis curves are obtained by performing line analysis at any 10 points using energy-dispersive X-ray diffraction (EDX). MAX The average value.

[0178] In the solid electrolyte layer, the first solid electrolyte more preferably has an average chemical composition represented by general formula (3).

[0179] [Chemical Formula 3]

[0180] (Li [3-ax+(5-b)(1-y)] A x (V) y B 1-y O4 (3)

[0181] In formula (3), A is one or more elements selected from the group consisting of Na (sodium), K (potassium), Mg (magnesium) and Ca (calcium), preferably "none (i.e. x = 0)".

[0182] B is selected from one or more elements in 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), preferably one or more elements in the group consisting of Si, Ge, and P.

[0183] x has the relationship 0≤x≤1.0, especially 0≤x≤0.2, and is preferably 0.

[0184] The relationship y has 0 < y < 1.0 (especially 0.05 ≤ y ≤ 0.95). From the viewpoint of further improving leakage current resistance and cycle characteristics, it is preferable to have a relationship of 0.10 ≤ y ≤ 0.90, more preferably a relationship of 0.20 ≤ y ≤ 0.80, even more preferably a relationship of 0.40 ≤ y ≤ 0.80, and most preferably a relationship of 0.40 ≤ y ≤ 0.70.

[0185] a is the average price of A, which is the same as the average price of A in equation (1).

[0186] b is the average price of B, which is the same as the average price of B in equation (1).

[0187] The chemical composition (especially the ratio y of V) of the first solid electrolyte is preferably varied within the range of the average chemical composition expressed by the above general formula (3).

[0188] 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 determined 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.

[0189] The average chemical composition of the first solid electrolyte with a LISICON-type structure and the average chemical composition of the garnet-type solid electrolyte, described later, in the above compositional analysis can be automatically determined based on their composition. For example, according to SEM-EDX analysis, the portion of the first solid electrolyte (i.e., the LISICON-type solid electrolyte) can be separated by identification based on V detection, and the portion of the second solid electrolyte (e.g., the garnet-type solid electrolyte) can be separated by identification based on La and Zr.

[0190] 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 IIA 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 cycle characteristics and leakage resistance, the LISICON-type structure of the first solid electrolyte layer is preferably γ0-type. II Type structure.

[0191] 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 crystalline structure of this type, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as γ-rays. II A crystalline structure of 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 (x-axis) during X-ray diffraction. II The crystalline structure of Li3VO4 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.

[0192] 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 crystalline structure, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as a β-type crystalline structure. I A crystalline structure of type β. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a β-type crystalline 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 crystalline structure of the Li3VO4 type inherently corresponds to more than one major peak in the Miller index. It possesses β... 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, the XRD data (Miller index corresponding to the interplanar spacing d value) described in the following table are shown.

[0193] [Table 1]

[0194]

[0195] 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 crystalline structure, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as a β-type crystalline structure. II A crystalline structure of type β. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a β-type crystalline structure. II The β-structure refers to the solid electrolyte exhibiting a similar appearance to the so-called β-structure in X-ray diffraction at a specified incident angle (x-axis). II The crystalline structure of the Li3VO4 type inherently corresponds to more than one major peak in 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.

[0196] The first solid electrolyte in the solid electrolyte layer has β II '-type structure refers to the solid electrolyte having β II A '-type crystalline structure, broadly speaking, refers to a structure that can be identified by those skilled in the art of solid-state batteries as a β-type crystalline structure. II A '-type crystalline structure. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a β-type crystalline 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 (x-axis). II The '-Li3VO4 type crystal structure inherently corresponds to more than one major peak in the Miller index. 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 interplanar spacing d value) described in the following table are shown.

[0197] [Table 2]

[0198]

[0199] The first solid electrolyte in the solid electrolyte layer has T I Type-type structure refers to the solid electrolyte having T IA type of crystalline 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 crystalline structure. I A crystalline structure of type T. In a narrow sense, the first solid electrolyte in the solid electrolyte layer has a T... I 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 (x-axis). I The crystal structure of Li3VO4 inherently corresponds to more than one major peak in the Miller index. It possesses 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.

[0200] 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 crystalline 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 crystalline structure. II A crystalline 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 (x-axis). II The crystal structure of Li3VO4 inherently corresponds to more than one major peak in the Miller index. It possesses 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.

[0201] The first solid electrolyte in the solid electrolyte layer having a γ0-type structure means that the solid electrolyte has a γ0-type crystalline structure. In a broad sense, it refers to a crystalline structure that can be identified as a γ0-type crystalline 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 crystalline structure at a specified incident angle (x-axis). 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 interplanar spacing d value) described in the following table are shown.

[0202] [Table 3]

[0203]

[0204] In addition to using raw material compounds containing specified metal atoms, the first solid electrolyte of the solid electrolyte layer can be obtained by the same method as the negative electrode active material, or it can also be obtained as a commercially available product.

[0205] The chemical composition and crystal structure of the first solid electrolyte in the solid electrolyte layer typically change due to element diffusion during sintering. Preferably, this first solid electrolyte has the aforementioned chemical composition and crystal structure in the solid battery after sintering together with the negative electrode layer and the positive electrode layer. In particular, when sintering together with the negative electrode layer at a high speed, for example at 750°C for about 1 minute, the chemical composition of the first solid electrolyte directly reflects the chemical composition of the solid electrolyte used during manufacturing. However, when sintering at a long time, for about 1 hour, at 750°C, elements from the negative electrode active material of the negative electrode layer diffuse, typically increasing the V content.

[0206] 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 cycle characteristics and leakage resistance, 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.

[0207] The volume ratio of the first solid electrolyte in the solid electrolyte layer can be determined using the same method as the volume ratio of the positive electrode active material.

[0208] 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 leakage resistance of the solid electrolyte layer can be further 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.

[0209] 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.

[0210] The preferred solid electrolyte as the second solid electrolyte is a solid electrolyte having the following chemical composition in formula (2):

[0211] A is an element selected from one or more (especially two) elements in the group consisting of Ga and Al.

[0212] B is one or more elements selected from the group consisting of Nb, Ta, W, Mo, and Bi.

[0213] x has the relationship 0 ≤ x ≤ 0.3.

[0214] The relationship y has 0≤y≤1.0, preferably 0≤y≤0.7, and more preferably 0.

[0215] a is the average price of A.

[0216] b is the average price of B.

[0217] 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 determined 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.

[0218] The volume ratio of the second solid electrolyte in the solid electrolyte layer is not particularly limited, but from the viewpoint of further improving cycle characteristics and leakage resistance, 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.

[0219] The volume ratio of the second solid electrolyte in the solid electrolyte layer can be determined using the same method as the volume ratio of the positive electrode active material.

[0220] In addition to the solid electrolyte, the solid electrolyte layer may also contain, for example, sintering aids. From the viewpoint of further improving cycle characteristics and leakage resistance, 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.

[0221] As a sintering aid in the solid electrolyte layer, the same compound as the sintering aid in the negative electrode layer can be used.

[0222] The volume ratio of sintering aid in the solid electrolyte layer is not particularly limited, but from the viewpoint of further improving cycle characteristics and leakage resistance, it is preferably 0.1% or more and 20% or less, more preferably 1% or more and 10% or less.

[0223] The thickness of the solid electrolyte layer is typically 0.1–30 μm, but from the perspective of balancing the thinning of the solid electrolyte layer with further reduction of leakage current, it is preferably 20–1 μm.

[0224] The thickness of the solid electrolyte layer was calculated using the average of the thicknesses measured at any 10 points in the SEM image.

[0225] In the solid electrolyte layer, the porosity is not particularly limited, but from the viewpoint of further improving cycle characteristics and leakage resistance, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0226] The porosity of the solid electrolyte layer was determined using the same method as that used for the porosity of the negative electrode layer.

[0227] [Solid-state battery manufacturing method]

[0228] 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.

[0229] The raw slice method will be explained.

[0230] 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 first green sheet for constituting the positive electrode layer. The first green sheet may contain a solid electrolyte, conductive additives, and / or sintering aids, etc.

[0231] A paste is prepared by appropriately mixing solvents, resins, etc., into the negative electrode active material. This paste is then coated onto a sheet and dried to form a second green sheet for constituting the negative electrode. The second green sheet may contain a solid electrolyte, conductive additives, and / or sintering aids, etc.

[0232] A paste is prepared by appropriately mixing solvents, resins, etc., into a solid electrolyte. This paste is then coated and dried to create a third green sheet that forms the solid electrolyte layer. The third green sheet may contain sintering aids, etc.

[0233] Next, a laminate is prepared by appropriately layering the first to third green sheets. The prepared laminate can also be pressed. Preferred pressing methods include isostatic pressing.

[0234] Then, by sintering the laminate at a temperature of 600°C or higher and 800°C or lower for 5 minutes or more and 50 hours or less, a solid-state battery can be obtained.

[0235] In this invention, the variation of the V ratio of the solid electrolyte (especially the first solid electrolyte) in the solid electrolyte layer in the thickness direction can be controlled by the following methods (1) or (2) or a combination thereof.

[0236] Method (1): The third green sheet is composed of multiple green sheets, and the chemical composition of the solid electrolyte (especially the first solid electrolyte) contained in each green sheet and the thickness of each green sheet are adjusted;

[0237] Method (2): Adjust the sintering time.

[0238] In method (1), firstly, the chemical composition (especially the V ratio y) of the solid electrolyte (especially the first solid electrolyte) contained in each raw tablet is made different. In detail, multiple raw tablets with different chemical compositions (especially the V ratio y) of the solid electrolyte (especially the first solid electrolyte) are prepared.

[0239] Next, multiple green sheets are stacked such that the V ratio of the solid electrolyte (especially the first solid electrolyte) in the solid electrolyte layer varies in the thickness direction in a desired manner. At this point, the proportion of change in the V ratio can be controlled by adjusting the thickness. For example, by further thinning each green sheet, the difference in the chemical composition (especially the V ratio y) of the solid electrolyte (especially the first solid electrolyte) between adjacent green sheets is reduced, further decreasing the proportion of change in the V ratio.

[0240] In method (2), the longer the sintering time, the more the elemental diffusion from the negative electrode active material in the negative electrode layer proceeds, and the V content in the solid electrolyte layer increases. At this time, the longer the sintering time, the more the effect of the increase in V content in the solid electrolyte layer based on the negative electrode layer extends to regions of the solid electrolyte layer that are farther away than the negative electrode layer side (e.g., the positive electrode layer side).

[0241] When the ratio of V in the solid electrolyte of the positive electrode layer is greater than or less than the ratio of V in the first solid electrolyte in the solid electrolyte layer, elemental diffusion from the solid electrolyte of the positive electrode layer also occurs, and the amount of V in the solid electrolyte layer increases or decreases. In this case, the longer the sintering time, the more the effect of the increase or decrease in the amount of V in the solid electrolyte layer based on the positive electrode layer extends to regions of the solid electrolyte layer farther than the positive electrode layer side (e.g., the negative electrode layer side).

[0242] If the sintering time is, for example, more than 30 minutes, the effect of elemental diffusion will begin at least from the negative electrode layer, and the amount of V in the solid electrolyte layer will begin to increase.

[0243] The printing method is explained.

[0244] The printing method is the same as the raw film method, except for the following:

[0245] • Except for adjusting the amounts of solvent and resin to be suitable for use as ink, prepare inks with each layer having the same composition as the paste used to obtain each layer of green film.

[0246] • Use inks from each layer to print (and dry) and stack them to create a laminate.

[0247] 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.

[0248] Example

[0249] [Materials Manufacturing]

[0250] In steps (1) to (3) below, positive electrode active material, negative electrode active material, solid electrolyte, sintering aid, and first and second solid electrolytes and sintering aid for manufacturing the solid electrolyte layer are manufactured. In particular, Table 1, described later, shows the chemical composition of each material used to manufacture the solid electrolyte layer in each embodiment / comparative example.

[0251] (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)

[0252] The garnet-type solid electrolyte powder used in the following manufacturing examples and comparative examples.

[0253] 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).

[0254] 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%.

[0255] After evaporation and drying, the obtained slurry was pre-calcined at 900°C for 5 hours to obtain the target phase.

[0256] Add a toluene-acetone mixture to the obtained pre-calcined powder and pulverize it using a planetary ball mill for 6 hours.

[0257] The pulverized powder was dried to prepare a solid electrolyte powder. ICP analysis confirmed that the powder had no compositional deviation.

[0258] (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).

[0259] 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.

[0260] The raw materials used are lithium hydroxide monohydrate (LiOH·H2O), vanadium pentoxide (V2O5), silicon oxide (SiO2), germanium oxide (GeO2), phosphorus oxide (P2O5), aluminum oxide (Al2O3), and zinc oxide (ZnO).

[0261] 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.

[0262] After evaporation and drying, the obtained slurry is pre-fired in air at 800°C for 5 hours.

[0263] 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.

[0264] The pulverized powder was then subjected to formal sintering again at 900℃ for 5 hours.

[0265] Then, a toluene-acetone mixed solvent was added to the obtained formal sintered powder, and the mixture was pulverized in a planetary ball mill for 6 hours and dried. This powder was used as the negative electrode active material powder and the first solid electrolyte powder. The above powder was analyzed by ICP, and it was confirmed that there was no compositional deviation.

[0266] (3) Manufacturing of sintering aid powder

[0267] The sintering aid powder used in the following manufacturing examples and comparative examples.

[0268] The raw materials used are lithium hydroxide monohydrate (LiOH·H2O), boron oxide (B2O3), lithium carbonate (Li2CO3), and aluminum oxide (Al2O3).

[0269] 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.

[0270] Then, the pre-fired powder is thoroughly pulverized again in a mortar, mixed, and then formally sintered at 680°C for 40 hours.

[0271] 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 had no compositional deviation.

[0272] [Examples 1-8 and Comparative Examples 1-2]

[0273] (The manufacture of solid-state batteries)

[0274] Solid-state batteries are manufactured as follows.

[0275] • Green sheet for positive electrode layer

[0276] In all the embodiments and comparative examples, LiCoO2, as the positive electrode active material, and Li, as the solid electrolyte powder, were weighed. 3.2 V0.8 Si 0.2 O4, Li3BO3 as a sintering aid, is mixed with butyraldehyde resin, alcohol and binder to produce a slurry for the positive electrode layer.

[0277] In all the embodiments and comparative examples, the volume ratio of the positive electrode active material, the solid electrolyte, and the sintering aid was 50:45:5.

[0278] The positive electrode layer slurry sheet is formed onto a PET film using a doctor blade method, then dried and peeled off to obtain a raw sheet for the positive electrode layer.

[0279] • Raw sheet for negative electrode layer

[0280] In examples other than Example 9 and in comparative examples, Li, as the negative electrode active material, was weighed. 3.2 (V 0.8 Si 0.2 O4(γ) II Ag particles (as a conductive additive), Li3BO3 (as a sintering aid), and butyraldehyde resin, alcohol, and binder are mixed to produce a slurry for the negative electrode layer.

[0281] In the examples other than Example 9 and in the comparative examples, the volume ratio of the negative electrode active material, the conductive additive, and the sintering aid was 65:30:5.

[0282] In Example 9 only, a garnet-type solid electrolyte was mixed into the solid electrolyte layer of the negative electrode layer. At this time, Li, as the negative electrode active material, was weighed. 3.2 (V 0.8 Si 0.2 )O4(γ II (type), as a solid electrolyte powder (Li) 6.4 Ga 0.05 Al 0.15 La3Zr2O 12 (Garnet type), Ag particles as conductive additives, Li3BO3 as sintering aids, are mixed with butyraldehyde resin, alcohol, and binder to produce a slurry for the negative electrode layer.

[0283] In Example 9, the volume ratio of the negative electrode active material, solid electrolyte, conductive additive, and sintering aid is 35:30:30:5.

[0284] In all embodiments and comparative examples, a negative electrode layer slurry sheet was formed on a PET film using a doctor blade method, dried, and peeled off to obtain a green sheet for the negative electrode layer.

[0285] • Raw sheet for solid electrolyte layer

[0286] In each embodiment / comparative example, sheets A to B as described in Table 1 were manufactured as green sheets for the solid electrolyte layer. The manufacturing of each sheet was carried out according to the following method.

[0287] In Examples 1, 5, and 9, the solid electrolyte layer is a single-layer type formed solely from sheet A.

[0288] In Examples 2-4 and 6-8 and Comparative Examples 1-2, the solid electrolyte layer was a multilayer formed by sheet A (negative electrode layer side) and sheet B (positive electrode layer type).

[0289] Regarding Sheet A

[0290] In Examples 1-8 and Comparative Examples 1-2, the first solid electrolyte and sintering aid powder shown in Table 1 were weighed and mixed with butyraldehyde resin, alcohol and binder to prepare a slurry.

[0291] In Examples 1-8 and Comparative Examples 1-2, the volume ratio of the first solid electrolyte to the sintering aid powder was 95:5.

[0292] In Example 9, the first solid electrolyte, the second solid electrolyte, and the sintering aid powder shown in Table 1 were weighed and mixed with butyraldehyde resin, alcohol, and binder to prepare a slurry.

[0293] In Example 9, the volume ratio of the first solid electrolyte, the second solid electrolyte (garnet-type solid electrolyte), and the sintering aid powder is 47.5:47.5:5.

[0294] Regarding Sheet B

[0295] In Examples 2-4 and 6-8 and Comparative Examples 1-2, the first solid electrolyte and sintering aid powder shown in Table 1 were weighed and mixed with butyraldehyde resin, alcohol and binder to prepare a slurry.

[0296] In Examples 2-4 and 6-8 and Comparative Examples 1-2, the volume ratio of the first solid electrolyte to the sintering aid powder was 95:5.

[0297] In all embodiments and comparative examples, a doctor blade method was used to form slurry sheets onto a PET film, followed by drying and peeling to obtain the individual sheets constituting the solid electrolyte layer.

[0298] In all embodiments and comparative examples, the thickness (total thickness) of the solid electrolyte layer was 15 μm.

[0299] In Examples 2 and 6-8 and Comparative Examples 1-2, the thickness ratio of sheet A to sheet B was 1:1.

[0300] In Examples 3 and 4, the thickness ratio of sheet A to sheet B is 2:1.

[0301] Therefore, in Examples 2 and 3, the thickness ratio of the solid electrolyte layer portion based on sheet A is different from that of the solid electrolyte layer portion based on sheet B.

[0302] In Examples 3, 4, 7, and 8, the basic components and thickness are the same, but the sintering time is different.

[0303] In Examples 1 and 9, the structure of the first solid electrolyte used is the same, but in Example 9, the second solid electrolyte also includes a garnet-type solid electrolyte.

[0304] The tilted structure of the V quantity of the first solid electrolyte in the solid electrolyte layer is affected by the V quantity of the LISICON-type solid electrolyte in the positive electrode layer.

[0305] For example, when the solid electrolyte layer is a single layer, if the V amount of the first solid electrolyte in the solid electrolyte layer is different from the V amount of the first solid electrolyte in the positive electrode layer (Examples 1, 5, 9), then the V amount of the first solid electrolyte in the solid electrolyte layer is affected by the positive electrode layer.

[0306] In addition, for example, when the solid electrolyte layer is multilayered, if the V amount of the first solid electrolyte in the solid electrolyte layer portion on the positive electrode layer side is different from the V amount of the first solid electrolyte in the positive electrode layer (Examples 2 to 4), then the V amount of the first solid electrolyte in the solid electrolyte layer portion on the positive electrode layer side is affected by the positive electrode layer.

[0307] Next, the green sheet for the negative electrode layer, the green sheet for the solid electrolyte layer, and the green sheet for the positive electrode layer are stacked and pressed together in this order to obtain a laminated solid-state battery. Sheets A to B, which serve as the green sheets for the solid electrolyte layer, are stacked sequentially, so that sheet A is in contact with the green sheet for the negative electrode layer.

[0308] Next, the laminate was cut into 10mm × 10mm square shapes, clamped between two porous sintering plates, and the binder was removed at 400°C. The solid-state battery was then sintered at 750°C. The solid-state battery was then sealed using a 2032-type coin cell and evaluated.

[0309] In all the embodiments and comparative examples, the thicknesses of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer were confirmed using a scanning electron microscope, and the results were 25 μm, 15 μm, and 20 μm, respectively, in all the embodiments and comparative examples.

[0310] In addition, in any comparative example and embodiment, the porosity of the solid electrolyte layer, positive electrode layer, and negative electrode layer was less than 10%, confirming that sintering was sufficiently performed.

[0311] [Observation and Measurement]

[0312] SEM images of the solid-state battery, representing the stacked structure of the positive electrode layer, negative electrode layer, and solid electrolyte layer in Example 2, are shown below. Figure 3 . Figure 3 The SEM photographs (physical: color photocopies) should be submitted as reference material with the case submission.

[0313] In the solid-state battery of Example 2, line analysis was performed in the thickness direction from the negative electrode layer through the solid electrolyte layer to the positive electrode layer using energy dispersive X-ray analysis (EDX). Figure 3 The analytical results of the elemental ratios in the solid electrolyte layer at time ) are shown in Figure 4 . Figure 4 The analysis results (physical document: color photocopy) shall be submitted as reference material in the case submission form.

[0314] The ratio y of V in the solid electrolyte layer (particularly the first solid electrolyte) of the solid electrolyte layer in the solid batteries obtained in Examples 1-8 was determined by line analysis using energy dispersive X-ray analysis (EDX). Figures 5-12 As Figures 5-12 The graph of the measurement results (physical copy: color photocopy) shall be submitted as reference material in the case submission form.

[0315] exist Figures 5-12 In the diagram, the vertical axis "y*100" represents the ratio "y×100" in "%" units. Therefore, for example, Figures 5-12 The vertical axis "60" corresponds to "0.6" in the ratio y of V. Additionally, in Figures 5-12 In these figures, L = 0 (μm) represents the region near the negative electrode layer in the solid electrolyte layer, specifically near the interface between the solid electrolyte layer and the negative electrode layer. More specifically, it represents the region within the solid electrolyte layer that is 1 μm away from the interface with the negative electrode layer. Conversely, in these figures, L = 15 (μm) represents the region near the positive electrode layer in the solid electrolyte layer, specifically near the interface with the positive electrode layer.

[0316] In line analysis using energy dispersive X-ray analysis (EDX), specifically, the solid-state battery is broken, the cross-section is ground using ion milling, and then quantitative analysis (compositional analysis) is performed using SEM-EDX (energy dispersive X-ray spectrometry) with the entire thickness direction of each layer in the field of view. The compositional analysis was performed using the EMAX-Evolution manufactured by Horiba.

[0317] [Evaluation of Solid-State Batteries]

[0318] The solid-state batteries of each embodiment / comparative example are evaluated below.

[0319] (Cyclic Characteristics)

[0320] The following is an evaluation of solid-state batteries.

[0321] The constant current charge-discharge test was conducted at 25°C with a current density equivalent to 0.05C in a potential range of 1.0V to 3.9V, and the amount of charge obtained under these conditions was measured.

[0322] The initial discharge capacity is calculated by dividing the initial charge obtained from the constant current charge-discharge test by the weight of the negative electrode active material. The capacity retention rate after 10 cycles is calculated by dividing the discharge capacity after the 10th cycle by the initial discharge capacity.

[0323] ◎: 95% ≤ Capacity retention ≤ 100% (Very good);

[0324] ○: 85% ≤ capacity retention < 95% (good);

[0325] △: 75% ≤ capacity retention rate < 85% (qualified) (no practical problems);

[0326] ×: Capacity retention rate <75% (unacceptable) (practical issues).

[0327] (Leakage resistance)

[0328] After constant current charging and discharging to 3.9V, a constant voltage test was performed at 3.9V, and the transient current was measured. The constant current observed after a constant voltage holding time of 10,000 minutes was read as the leakage current I (A / cm) from the electronic conductivity of the solid electrolyte. 2 ).

[0329] ◎:I≤1×10 -7 (very good);

[0330] ○: 1×10 -7 <I≤5×10 -7 (good);

[0331] △: 5×10 -7 <I≤1×10 -6 (Qualified) (No practical problems);

[0332] ×:1×10 -6 <I (Unqualified) (There are practical problems).

[0333] [Inspection]

[0334] (Regarding Example 1 and Comparative Examples 1-2)

[0335] The measurement results relating to the ratio y of V in the solid electrolyte layer (particularly the first solid electrolyte) in the solid electrolyte layer of the solid batteries of Examples 1 and Comparative Examples 1-2 are shown in Figure 13 As Figure 13 The graph of the measurement results (physical copy: color photocopy) shall be submitted as reference material in the case submission form.

[0336] As can be seen from the comparison between Comparative Example 1 and Example 1, even if the average V amount in the solid electrolyte is the same, the leakage resistance and cycling characteristics of Example 1, which has a V ratio that changes by a specified amount, are significantly improved compared to Comparative Example 1, where the V ratio hardly changes.

[0337] A comparison of Comparative Example 1 and Example 1 shows that even with the same average V content in the solid electrolyte, Example 1, which contains a region with a V ratio of 0.6 or less, significantly reduces leakage current compared to Comparative Example 1, which does not contain this region. This can be attributed to the fact that the electronic conductivity of the electrolyte monomer decreases significantly with decreasing V content y.

[0338] As seen in Comparative Example 2, although reducing the V ratio in the solid electrolyte can sufficiently reduce leakage current, the capacity retention rate after 10 cycles is only 70%, which is insufficient. This can be attributed primarily to the significant difference between the V ratio (0.8) of the negative electrode active material in the negative electrode layer and the V ratio (0.3) in the first solid electrolyte layer. This drastic change in the chemical composition at the interface leads to insufficient interfacial bonding, resulting in delamination at the interface due to the expansion and contraction of the negative electrode during charging and discharging.

[0339] On the other hand, in Example 1, where the V ratio in the solid electrolyte near the negative electrode layer is close to the V ratio (0.8) of the negative electrode active material, the capacity retention rate after 10 cycles is 98%, exhibiting extremely excellent characteristics. This can be attributed to the similar composition of the negative electrode active material and the solid electrolyte, thereby increasing their bonding strength.

[0340] As can be seen from the above, by modulating the composition of the solid electrolyte, the V ratio near the negative electrode layer is made to be the same as that of the negative electrode active material, and there is a region with a V ratio of less than 0.6, which can further fully take into account the insulation (e.g., leakage resistance) and cycle characteristics of the solid battery.

[0341] (Regarding Examples 3, 5, and 6)

[0342] The measurement results relating to the ratio y of V in the solid electrolyte layer (particularly the first solid electrolyte) in the solid electrolyte layer of the solid batteries of Examples 3, 5, and 6 are shown in Figure 14 As Figure 14The graph of the measurement results (physical copy: color photocopy) shall be submitted as reference material in the case submission form.

[0343] A comparison of Examples 3 and 5 shows that leakage current can be sufficiently reduced in any solid-state battery having a solid electrolyte layer exhibiting any of the "variable V ratios". On the other hand, regarding capacity retention after 10 cycles, Example 3, with a higher V ratio near the negative electrode layer, achieved a significantly superior cycling characteristic of 98%. This can be attributed to the smaller variation in the V ratio at the interface between the negative electrode active material and the solid electrolyte in Example 3, resulting in a more cohesive interface.

[0344] As can be seen from Examples 3, 5, and 6, the higher the V ratio near the negative electrode layer, the better the capacity retention after 10 cycles. In particular, it can be seen that when the V ratio near the negative electrode layer is greater than 0.6, a more practically optimal capacity retention can be obtained.

[0345] (Regarding Examples 3 and 4)

[0346] The measurement results relating to the ratio y of V in the solid electrolyte layer (particularly the first solid electrolyte) in the solid electrolyte layer of the solid batteries of Examples 3 and 4 are shown in Figure 15 As Figure 15 The graph of the measurement results (physical copy: color photocopy) shall be submitted as reference material in the case submission form.

[0347] It was confirmed that both Examples 3 and 4 exhibited a tendency for the V ratio to decrease from the negative electrode layer side toward the positive electrode layer side.

[0348] The average V ratios in the solid electrolytes of Examples 3 and 4 are the same, but Example 3 shows a reduction in leakage current. This can be attributed to the smaller minimum V ratio in the solid electrolyte layer of Example 3. This can also be attributed to the significant decrease in electronic conductivity of the solid electrolyte monomers as the V content decreases.

[0349] As can be seen from Examples 1-3 and 5-6, by making the region with a minimum V ratio of 0.4 or less more than 10% of the thickness of the solid electrolyte layer, leakage current can be further reduced.

[0350] (Regarding Examples 7 and 8)

[0351] The measurement results relating to the ratio y of V in the solid electrolyte layer (particularly the first solid electrolyte) in the solid electrolyte layer of the solid batteries of Examples 7 and 8 are shown in Figure 16 As Figure 16 The graph of the measurement results (physical copy: color photocopy) shall be submitted as reference material in the case submission form.

[0352] A comparison of Examples 7 and 8 shows that in Example 8, where the V ratio changes drastically, the capacity retention rate decreases after 10 cycles. This can be attributed to the fact that, even in a solid electrolyte layer, the drastic change in the V ratio leads to the accumulation of strain in the V ratio modulation section, and the expansion / contraction of the battery cells during charging and discharging can easily cause cracks in the solid electrolyte layer.

[0353] To improve cycling performance, the maximum value of the change ratio of the V ratio in the solid electrolyte layer, |dy / dL|, is preferred. max Less than 0.55 [ / μm].

[0354] (Regarding Examples 1 and 9)

[0355] A comparison with Examples 1 and 9 shows that even though the structures of the first solid electrolyte in the solid electrolyte layer and the first solid electrolyte in the positive electrode layer are the same, the leakage current is reduced by including a garnet-type solid electrolyte in the solid electrolyte layer. This can be attributed to the fact that the garnet-type solid electrolyte is difficult to reduce during charging and discharging, thus making electron injection difficult, and the increased curvature of the LISICON-type solid electrolyte in the solid electrolyte layer leads to increased electronic resistance. The measurement results of the ratio y of V in the solid electrolyte layer (especially the first solid electrolyte) of the solid electrolyte (using energy dispersive X-ray analysis (EDX)) obtained in Example 9 are compared with the measurement results obtained in Example 1. Figure 5 )same.

[0356] [Table 4]

[0357]

[0358] [Table 5]

[0359]

[0360] Average V ratio: The average V ratio in the thickness direction of the solid electrolyte layer;

[0361] Minimum V ratio: The minimum V ratio in the thickness direction of the solid electrolyte layer;

[0362] V ratio near the negative electrode layer: The V ratio in the solid electrolyte layer near the interface with the negative electrode layer (1 μm away from the negative electrode layer).

[0363] In Comparative Examples 1 and 2, the first solid electrolyte in the solid electrolyte layer has a uniform composition.

[0364] Industrial availability

[0365] 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, and small electronic devices such as digital cameras, activity meters, arm computers, electronic paper, wearable devices, RFID tags, card-type electronic money, smartwatches, etc.); 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 contains a negative electrode active material in which the molar ratio of Li to vanadium (V) is greater than 2.

0. The solid electrolyte layer contains a solid electrolyte having a LISICON-type structure and containing at least V. In the thickness direction of the solid electrolyte layer, the ratio y of V in the solid electrolyte varies by an amount greater than 0.

20. The molar ratio of V near the negative electrode layer of the solid electrolyte layer is greater than the molar ratio of V near the positive electrode layer of the solid electrolyte layer. The ratio y of V in the solid electrolyte is the molar ratio of V when the solid electrolyte is expressed in terms of its chemical composition formula. The change in the ratio y of V is the value of the ratio y of V in the elemental analysis curve of the solid electrolyte layer, expressed as "maximum value - minimum value". The elemental analysis curve is a curve with the ratio y of V as the vertical axis and the depth L in the thickness direction as the horizontal axis, based on line analysis using energy-dispersive X-ray analysis.

2. The solid-state battery according to claim 1, wherein, The ratio y of V near the negative electrode layer of the solid electrolyte layer is 0.40 or higher.

3. The solid-state battery according to claim 1 or 2, wherein, The solid electrolyte layer includes a portion in the thickness direction of the layer in which the ratio y of V is less than 0.6, and the thickness is more than 10% of the thickness of the layer.

4. The solid-state battery according to claim 1 or 2, wherein, The solid electrolyte layer includes, in the thickness direction of the layer, a portion in which the ratio y of V is less than 0.6, and the thickness is more than 30% of the thickness of the layer.

5. The solid-state battery according to claim 1 or 2, wherein, The solid electrolyte layer includes a portion in the thickness direction of the layer in which the ratio y of V is less than 0.4, and the thickness is more than 10% of the thickness of the layer.

6. The solid-state battery according to claim 1 or 2, wherein, The maximum value of the ratio y of V in the thickness direction of the solid electrolyte layer is |dy / dL|. MAX It is below 0.

55.

7. The solid-state battery according to claim 1 or 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, Al, Ga, Zn, Fe, Cr and Co; 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.

8. The solid-state battery according to claim 1 or 2, wherein, The negative electrode active material has β II -Li3VO4 type structure or γ II -Li3VO4 type structure.

9. The solid-state battery according to claim 1 or 2, wherein, The solid electrolyte contained in the solid electrolyte layer has an average chemical composition represented by the following general formula (3). In formula (3), A is one or more elements selected from the group consisting of Na, K, Mg and Ca; 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<y<1.0; a is the average valence of A; b is the average valence of B.

10. 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 solid electrolyte having a garnet-type structure.

11. The solid-state battery according to claim 1 or 2, wherein, The negative electrode layer also contains conductive additives.

12. 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.

13. 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.

14. 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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