solid-state batteries

Abstract

Provided is a solid-state battery provided with a positive electrode layer comprising a solid electrolyte and a positive electrode active material that contains lithium. In a state in which the lithium desorption amount of the positive electrode active material is 40%, when the value of the maximum interplanar distance is considered to be 1 during X-ray diffraction (XRD) analysis measured while heating the positive electrode layer, the self-decomposition temperature at which a relative change in relation to the maximum interplanar distance is less than 0.995 is 215ºC or higher. Further, the solid electrolyte contains lithium borosilicate glass.

Description

[Technical Field]

[0001] The present disclosure relates to solid-state batteries. [Background technology]

[0002] Secondary batteries that can be repeatedly charged and discharged have been used for various purposes. For example, secondary batteries are sometimes used as power sources for electronic devices such as smartphones and laptop computers.

[0003] In secondary batteries, a liquid electrolyte is generally used as a medium for ion migration that contributes to charging and discharging. In other words, a so-called electrolytic solution is used in secondary batteries. However, such secondary batteries generally require safety in terms of preventing leakage of the electrolytic solution. In addition, organic solvents and the like used in the electrolytic solution are flammable, so safety is also required in this respect.

[0004] Therefore, research is being conducted on solid-state batteries that use solid electrolytes instead of liquid electrolytes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5211721 [Patent Document 2] Japanese Patent Publication No. 2021-525449 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors of the present invention have realized that conventional solid-state batteries have problems to be overcome and have newly discovered the need to take measures to address these problems. Specifically, they have found the following problems:

[0007] As the positive electrode material in a solid-state battery, a lithium transition metal oxide or a lithium composite transition metal oxide having a crystalline structure can be used (see Patent Documents 1 and 2). In this regard, solid-state batteries are sometimes used under high-temperature conditions, and under such high-temperature conditions, the crystalline structure of the positive electrode active material becomes unstable due to the desorption of lithium, which may cause deterioration in the battery characteristics of the solid-state battery under high-temperature conditions.

[0008] The present disclosure has been made in view of the above-mentioned problems. That is, a main object of the present disclosure is to provide a solid-state battery that can have more suitable battery characteristics even under high-temperature conditions. [Means for solving the problem]

[0009] In order to achieve the above object, in one embodiment of the present disclosure, a positive electrode layer including a positive electrode active material containing lithium and a solid electrolyte; The present invention relates to a solid-state battery, wherein, in an XRD analysis performed while heating the positive electrode layer when the amount of lithium desorbed from the positive electrode active material is 40%, the autodecomposition temperature at which a relative change from the maximum interplanar spacing falls below 0.995, where the maximum interplanar spacing is taken as 1, is 215°C or higher, and the solid electrolyte contains lithium borosilicate glass. [Effects of the Invention]

[0010] A solid-state battery according to an embodiment of the present disclosure can have more suitable battery characteristics even under high-temperature conditions. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view schematically illustrating an exterior of a solid-state battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view of the solid-state battery of FIG. 1 taken along the line AA when viewed in the direction of the arrow. [Figure 3]FIG. 3 is a graph showing the relative value of the interplanar spacing versus the heating temperature of the positive electrode active material in the solid state battery according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] The solid-state battery of the present disclosure will be described in detail below. While the description will be made with reference to drawings as necessary, the contents shown in the drawings are merely shown as schematic examples for the purpose of understanding the present disclosure, and the appearance, dimensional ratio, etc. may differ from the actual product.

[0013] The term "cross-sectional view" as used herein refers to the shape of a solid-state battery viewed from a direction substantially perpendicular to the stacking direction (in other words, the shape of a solid-state battery cut along a plane parallel to the thickness direction of the layers). The terms "planar view" and "planar shape" as used herein refer to a sketch of an object viewed from above or below along the thickness direction of the layers (i.e., the stacking direction).

[0014] The terms "upper and lower directions" and "left and right directions" used directly or indirectly in this specification correspond to the upper and lower directions and left and right directions in the drawings, respectively. Unless otherwise specified, the same symbols or signs indicate the same members or parts or the same meanings. In a preferred embodiment, the vertical downward direction (i.e., the direction in which gravity acts) can be considered to correspond to the "downward direction," and the opposite direction to that can be considered to correspond to the "upward direction."

[0015] In the present disclosure, the term "solid-state battery" refers in a broad sense to a battery whose components are made of solids, and in a narrow sense to an all-solid-state battery whose components (particularly preferably all components) are made of solids. In a preferred embodiment, the solid-state battery in the present disclosure is a stacked solid-state battery configured such that each layer constituting a battery unit is stacked on top of each other, and preferably each such layer is made of a sintered body. A "solid-state battery" is a so-called "secondary battery" that can be repeatedly charged and discharged. The term "secondary battery" should not be overly limited to its name, and can also include, for example, an electricity storage device.

[0016] A feature of the present disclosure relates to the positive electrode layer included in the solid-state battery. Below, we will first explain the basic configuration of the solid-state battery of the present disclosure in order to understand the overall structure of the solid-state battery. However, the configuration of the solid-state battery described here is merely an example for understanding the invention and does not limit the invention.

[0017] [Basic structure of solid-state batteries] FIG. 1 is a perspective view showing a schematic external appearance of a solid-state battery according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view of the AA section of the solid-state battery shown in FIG. 1, viewed in the direction of the arrow. The solid-state battery has at least positive and negative electrode layers and a solid electrolyte. Specifically, as shown in FIGS. 1 and 2, a solid-state battery 200 includes a solid-state battery stack 100 including battery building blocks each consisting of a positive electrode layer 10A, a negative electrode layer 10B, and a solid electrolyte 20 interposed at least therebetween.

[0018] The solid-state battery 200 according to the present disclosure typically includes: A solid-state battery stack 100 including at least one battery structural unit along a stacking direction L, the battery structural unit being composed of a positive electrode layer 10A, a negative electrode layer 10B, and a solid electrolyte layer 20 interposed therebetween; and A positive electrode terminal 40A and a negative electrode terminal 40B are provided on opposite side surfaces of the solid state battery stack 100. In the solid state battery stack 100, the positive electrode layers 10A and the negative electrode layers 10B are alternately stacked with the solid electrolyte layers 20 interposed therebetween.

[0019] The layers constituting the solid-state battery may be formed by firing, and the positive electrode layer, negative electrode layer, solid electrolyte layer, etc. may form fired layers. Preferably, the positive electrode layer, negative electrode layer, and solid electrolyte layer are each fired together, and therefore the solid-state battery stack forms a fired body.

[0020] The positive electrode layer is an electrode layer containing at least a positive electrode active material. The positive electrode layer may further contain a solid electrolyte. In a preferred embodiment, the positive electrode layer is composed of a sintered body containing at least positive electrode active material particles and solid electrolyte particles. On the other hand, the negative electrode layer is an electrode layer containing at least a negative electrode active material. The negative electrode layer may further contain a solid electrolyte. In a preferred embodiment, the negative electrode layer is composed of a sintered body containing at least negative electrode active material particles and solid electrolyte particles. A positive electrode layer and a negative electrode layer having such a configuration may also be referred to as a "composite positive electrode body" and a "composite negative electrode body", respectively.

[0021] The positive electrode active material and the negative electrode active material are substances involved in the transfer of electrons in a solid-state battery. Charging and discharging are performed by the transfer of electrons caused by the movement (conduction) of ions between the positive electrode layer and the negative electrode layer via the solid electrolyte. It is preferable that each electrode layer, the positive electrode layer and the negative electrode layer, is a layer capable of absorbing and releasing lithium ions or sodium ions in particular. In other words, the solid-state battery is preferably an all-solid-state secondary battery in which lithium ions or sodium ions move between the positive electrode layer and the negative electrode layer via the solid electrolyte to charge and discharge the battery.

[0022] (positive electrode layer) The content of the solid electrolyte in the positive electrode layer 10A is not particularly limited, and is usually 10 to 50 mass %, and particularly preferably 20 to 40 mass %, of the total amount of the positive electrode layer. The positive electrode layer may contain two or more types of solid electrolytes, in which case the total content thereof may be within the above range.

[0023] (negative electrode layer) The negative electrode active material contained in the negative electrode layer may be at least one selected from the group consisting of an oxide containing at least one element selected from the group consisting of titanium (Ti), silicon (Si), tin (Sn), chromium (Cr), iron (Fe), niobium (Nb), and molybdenum (Mo), a carbon material such as graphite, a graphite-lithium compound, a lithium alloy, a lithium-containing phosphate compound having a Nasicon structure, a lithium-containing phosphate compound having an olivine structure, and a lithium-containing oxide having a spinel structure. An example of a lithium alloy is Li-Al. An example of a lithium-containing phosphate compound having a Nasicon structure is Li3V2(PO4)3 and / or LiTi2(PO4)3. An example of a lithium-containing phosphate compound having an olivine structure is Li3Fe2(PO4)3 and / or LiCuPO4. An example of a lithium-containing oxide having a spinel structure is Li4Ti5O. 12 etc.

[0024] In addition, the negative electrode active material capable of absorbing and releasing sodium ions may be at least one selected from the group consisting of sodium-containing phosphate compounds having a Nasicon structure, sodium-containing phosphate compounds having an olivine structure, and sodium-containing oxides having a spinel structure.

[0025] The positive electrode layer and / or the negative electrode layer may contain a conductive material, which may include at least one of metal materials such as silver, palladium, gold, platinum, aluminum, copper, and nickel, and carbon.

[0026] Furthermore, the positive electrode layer and / or the negative electrode layer may contain a sintering aid, such as at least one selected from the group consisting of lithium oxide, sodium oxide, potassium oxide, boron oxide, silicon oxide, bismuth oxide, and phosphorus oxide.

[0027] There are no particular limitations on the thickness of the positive electrode layer and the negative electrode layer, but for example, they may each independently be 2 μm or more and 50 μm or less, particularly 5 μm or more and 30 μm or less.

[0028] (Positive electrode current collecting layer / Negative electrode current collecting layer) Although not essential elements of the electrode layer, the positive electrode layer and the negative electrode layer may each include a positive electrode current collecting layer and a negative electrode current collecting layer. The positive electrode current collecting layer and the negative electrode current collecting layer may each have the form of a foil. However, if emphasis is placed on improving electronic conductivity through co-firing, reducing the manufacturing cost of the solid-state battery, and / or reducing the internal resistance of the solid-state battery, the positive electrode current collecting layer and the negative electrode current collecting layer may each have the form of a sintered body.

[0029] The positive electrode current collector constituting the positive electrode current collecting layer and the negative electrode current collector constituting the negative electrode current collecting layer are preferably made of a material with high electrical conductivity, such as silver, palladium, gold, platinum, aluminum, copper, and / or nickel. The positive electrode current collector and the negative electrode current collector may each have an electrical connection part for electrical connection to the outside and may be configured to be electrically connectable to a terminal.

[0030] When the positive electrode current collecting layer and the negative electrode current collecting layer are in the form of a sintered body, they may be composed of a sintered body containing a conductive material and a sintering aid. The conductive material contained in the positive electrode current collecting layer and the negative electrode current collecting layer may be selected from, for example, the same materials as the conductive materials that may be contained in the positive electrode layer and the negative electrode layer. The sintering aid contained in the positive electrode current collecting layer and the negative electrode current collecting layer may be selected from, for example, the same materials as the sintering aids that may be contained in the positive electrode layer and the negative electrode layer.

[0031] As described above, a positive electrode current collecting layer and a negative electrode current collecting layer are not essential for a solid-state battery, and a solid-state battery that does not include such a positive electrode current collecting layer and a negative electrode current collecting layer is also conceivable.

[0032] (solid electrolyte) The solid electrolyte is a material capable of conducting lithium ions or sodium ions. In particular, the solid electrolyte layer constituting the battery structural unit of the solid-state battery may be a layer capable of conducting lithium ions between the positive electrode layer and the negative electrode layer.

[0033] The solid electrolyte layer may contain a sintering aid. The sintering aid contained in the solid electrolyte layer may be selected from the same materials as the sintering aids that may be contained in the positive electrode layer and the negative electrode layer, for example.

[0034] The thickness of the solid electrolyte layer is not particularly limited. The thickness of the solid electrolyte layer located between the positive electrode layer and the negative electrode layer may be, for example, 1 μm to 15 μm, particularly 1 μm to 5 μm.

[0035] (electrode separation part) The solid-state battery 200 of the present disclosure may further have an electrode separator (also referred to as a "blank layer" or "blank portion") 30 (30A, 30B).

[0036] The electrode separator 30A (positive electrode separator) is disposed around the positive electrode layer 10A, thereby separating the positive electrode layer 10A from the negative electrode terminal 40B. The electrode separator 30B (negative electrode separator) is also disposed around the negative electrode layer 10B, thereby separating the negative electrode layer 10B from the positive electrode terminal 40A. Although not particularly limited, the electrode separator 30 may be made of one or more materials selected from the group consisting of, for example, solid electrolytes, insulating materials, and mixtures thereof.

[0037] The solid electrolyte that can form the electrode separator 30 can be made of the same material as the solid electrolyte that can form the solid electrolyte layer.

[0038] The insulating material that can form the electrode separator 30 may be a material that does not conduct electricity, i.e., a non-conductive material. While not particularly limited, the insulating material may be, for example, a glass material or a ceramic material. For example, a glass material may be selected as the insulating material. While not particularly limited, the glass material may be at least one selected from the group consisting of soda-lime glass, potash glass, borate glass, borosilicate glass, barium borosilicate glass, zinc borate glass, barium borate glass, bismuth borosilicate glass, bismuth zinc borate glass, bismuth silicate glass, phosphate glass, aluminophosphate glass, and zinc phosphate glass. Furthermore, although not particularly limited, the ceramic material may be at least one selected from the group consisting of aluminum oxide (Al2O3), boron nitride (BN), silicon dioxide (SiO2), silicon nitride (Si3N4), zirconium oxide (ZrO2), aluminum nitride (AlN), silicon carbide (SiC), and barium titanate (BaTiO3).

[0039] (Terminal) The solid-state battery 200 of the present disclosure generally has terminals (external terminals) 40 (40A, 40B). In particular, positive and negative terminals 40A, 40B are provided as a pair on the side surfaces of the solid-state battery. More specifically, the positive terminal 40A connected to the positive electrode layer 10A and the negative terminal 40B connected to the negative electrode layer 10B are provided as a pair. The terminals 40A, 40B may be provided to cover at least one side surface of the solid-state battery, and may also be referred to as "end electrodes." Such terminals 40 (40A, 40B) may be made of a material with high electrical conductivity. The material of the terminal 40 is not particularly limited, but may include at least one conductive material selected from the group consisting of silver, gold, platinum, aluminum, copper, tin, and nickel.

[0040] Terminals 40 (40A, 40B) may further contain a sintering aid. Examples of the sintering aid include the same materials as the sintering aids that may be contained in positive electrode layer 10A.

[0041] In a preferred embodiment, the terminals 40 (40A, 40B) are made of a sintered body containing at least a conductive material and a sintering aid.

[0042] (outer layer material) The solid-state battery 200 of the present disclosure typically further includes an outer layer material 60. The outer layer material 60 is generally formed on the outermost surface of the solid-state battery to electrically, physically, and / or chemically protect the solid-state battery. The material constituting the outer layer material 60 preferably has excellent insulating properties, durability, and / or moisture resistance, and is environmentally safe. For example, glass, ceramics, thermosetting resin, photocurable resin, and mixtures thereof can be used.

[0043] The glass that can be used to form the outer layer material can be the same material as the glass material that can be used to form the electrode separator, and the ceramic material that can be used to form the outer layer material can be the same material as the ceramic material that can be used to form the electrode separator.

[0044] [Features of the Solid-State Battery of the Present Disclosure] The present inventors have conducted extensive research into solutions for providing solid-state batteries with more favorable battery characteristics even under high-temperature conditions. More specifically, the present inventors focused on the positive electrode layer constituting the solid-state battery, and considered that the positive electrode active material and solid electrolyte contained in the positive electrode layer contribute to suppressing degradation of the battery characteristics of the solid-state battery under high-temperature conditions. After further research, the inventors have newly discovered that the autolysis temperature at which the lattice spacing of the positive electrode active material begins to relatively decrease with heating is correlated with the battery characteristics of the solid-state battery under high-temperature conditions (i.e., the high-temperature resistance of the solid-state battery).

[0045] FIG. 3 is a graph showing the relative change in the interplanar spacing of the (003) lattice planes of the positive electrode active material as a function of heating temperature in a positive electrode layer of a solid-state battery according to an embodiment of the present disclosure. As shown in the figure, when the positive electrode layer is heated, the interplanar spacing gradually increases with increasing temperature, eventually reaching a limit (maximum value). Further heating causes the interplanar spacing to begin to decrease. This decrease in interplanar spacing is due to autolysis (phase separation) of the positive electrode active material as it is heated. Therefore, the temperature at which the relative change with respect to the maximum interplanar spacing falls below a predetermined amount can also be referred to as the "autolysis temperature" or "phase separation temperature." In other words, in this specification, the "autolysis temperature" refers to the temperature at which the interplanar spacing of the positive electrode active material begins to decrease from its maximum value with increasing temperature and reaches a predetermined ratio (for example, when the relative change with respect to the maximum interplanar spacing falls below 0.995).

[0046] The present inventors have newly discovered that this self-decomposition temperature can be correlated with the battery characteristics of a solid-state battery under high-temperature conditions. Specifically, they have discovered that, provided that a solid electrolyte of a specific material composition is included, a positive electrode layer having a self-decomposition temperature equal to or higher than a predetermined temperature can be relatively stable under high-temperature conditions, and further, that a solid-state battery including such a positive electrode layer can be more suitably used under high-temperature conditions. Based on this discovery, they have devised the invention described in detail below.

[0047] The solid-state battery of the present disclosure includes a cathode layer that contains lithium borosilicate glass as a solid electrolyte and has a temperature (so-called "autolysis temperature") of 215°C or higher at which a relative change in the maximum interplanar spacing falls below 0.995, where the maximum interplanar spacing is measured by XRD analysis while heating the cathode layer in a state where 40% of lithium has been desorbed from the cathode active material, and the value of the maximum interplanar spacing is taken as 1. In other words, the solid-state battery of the present disclosure includes a cathode layer that has a temperature of 215°C or higher at which a decrease in the interplanar spacing falls below 0.5% based on the maximum value when the interplanar spacing is measured by X-ray powder diffraction (XRD) analysis while heating the cathode layer in a state where 40% of lithium has been desorbed from the cathode active material.

[0048] According to the present disclosure, by selecting a positive electrode layer having the above-described characteristics, a solid-state battery having more favorable battery characteristics even under high-temperature conditions can be provided. That is, according to the present disclosure, a solid-state battery having better high-temperature resistance, which can be used more favorably under high-temperature conditions, can be provided. More specifically, in a solid-state battery including a positive electrode layer having the above-described characteristics, deterioration of battery characteristics such as resistance value and / or battery capacity can be more favorably suppressed even when exposed to high-temperature conditions (e.g., a temperature range of 80°C to 200°C). Therefore, the solid-state battery according to the present disclosure can more favorably maintain its battery characteristics even under high-temperature conditions.

[0049] The phrase "a state in which the amount of desorbed lithium from the positive electrode active material is 40%" refers to a state in which the amount of desorbed lithium is 40% when expressed as a percentage of the lithium content of the positive electrode active material. In other words, the phrase "a state in which the amount of desorbed lithium from the positive electrode active material is 40%" refers to a state in which the lithium content of the positive electrode active material in an uncharged battery is 60%, with the lithium content of the positive electrode active material being 100%. For example, the phrase "a state in which the amount of desorbed lithium from the positive electrode active material is 40%" can refer to a charged state in which 40% of the lithium has been extracted from the lithium content of the positive electrode active material in a fully discharged battery.

[0050] In the present disclosure, the self-decomposition temperature of a positive electrode active material is evaluated when 40% of the lithium is desorbed from the positive electrode active material. This is to more appropriately evaluate the behavior of the positive electrode active material under high-temperature conditions, when the crystalline structure of the positive electrode active material may become unstable. Specifically, the crystalline structure of the positive electrode active material may become unstable due to lithium being extracted from the positive electrode active material during charging. This instability of the crystalline structure of the positive electrode active material may become more pronounced under high-temperature conditions. In other words, under high-temperature conditions, a solid-state battery may be more susceptible to deterioration when the amount of lithium desorbed from the positive electrode active material is approximately 40% or more. Therefore, by evaluating the self-decomposition temperature of a positive electrode layer when 40% of the lithium is desorbed from the positive electrode active material, it may be possible to more appropriately correlate the self-decomposition temperature of the positive electrode layer with the high-temperature resistance of the solid-state battery.

[0051] The amount of lithium desorption can be quantified by XRD analysis of the positive electrode layer of the charged solid-state battery. Alternatively, the amount of lithium desorption can be determined based on the initial charge / discharge efficiency and the basis weight of the positive electrode active material and the negative electrode active material. It can also be calculated from the charge amount of the solid-state battery.

[0052] In the past, in order to improve the high-temperature resistance of lithium secondary batteries using high-nickel-based positive electrode active materials, attention has been focused on the phase transition temperature of the positive electrode active material in a fully charged state. Specifically, the high-nickel-based positive electrode active material is selected based on the phase transition temperature at which the positive electrode active material changes from a layered structure to a spinel structure in a fully charged state and the temperature at which the c-axis length of the positive electrode active material reaches a maximum value during heating (see Patent Document 2).

[0053] On the other hand, in the present disclosure, as described above, attention is focused on the autodecomposition temperature based on the relative change in the interplanar spacing of a positive electrode active material with increasing temperature. As shown in Fig. 3, after the positive electrode active material reaches the maximum interplanar spacing with increasing temperature, as the temperature continues to increase, the interplanar spacing may maintain a substantially constant value, and then the interplanar spacing may start to decrease with further increasing temperature. According to the present disclosure, the positive electrode active material is evaluated based on the autodecomposition temperature at which the interplanar spacing starts to decrease, and therefore, a positive electrode active material that can favorably maintain its crystalline structure under high temperature conditions (for example, a temperature range of 80°C to 200°C) (i.e., a higher temperature at which the interplanar spacing starts to decrease) can be more favorably selected.

[0054] Although the upper limit of the self-decomposition temperature of the positive electrode active material is not particularly limited, when emphasis is placed on battery characteristics such as initial capacity retention rate as a solid-state battery (i.e., before exposure to high-temperature conditions), the self-decomposition temperature can be, for example, 400° C. or lower, 350° C. or lower, or 330° C. or lower. When emphasis is placed on both suppressing deterioration of battery characteristics in a high-temperature environment and achieving the initial battery characteristics of the solid-state battery, the self-decomposition temperature of the positive electrode active material can be 215° C. or higher and 350° C. or lower, 215° C. or higher and 315° C. or lower, 250° C. or higher and 315° C. or lower, or 280° C. or higher and 315° C. or lower.

[0055] The lithium borosilicate glass contained in the positive electrode layer is an oxide-based glass material containing at least lithium (Li), silicon (Si), and boron (B) as constituent elements, and can be, for example, 50Li4SiO4·50Li3BO3. Because such solid electrolytes have relatively high thermal stability, their inclusion in the positive electrode layer can more effectively suppress the deterioration of the battery characteristics of the solid-state battery under high-temperature conditions.

[0056] Furthermore, lithium borosilicate-based glass may contain one or more additional elements in addition to lithium, silicon, boron, and oxygen. For example, lithium borosilicate-based glass may further contain at least one element selected from Groups 1 and 2 and Groups 14 to 17 of the Periodic Table. The content of each element contained in lithium borosilicate-based glass can be measured by analyzing the glass-ceramic solid electrolyte using, for example, inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0057] Furthermore, the solid electrolyte may include, in addition to lithium borosilicate glass, a solid electrolyte used in other known solid-state batteries. Examples of such solid electrolytes include one or more of the following: a crystalline solid electrolyte, a glass-based solid electrolyte other than lithium borosilicate glass, and a glass-ceramic solid electrolyte. Examples of crystalline solid electrolytes include oxide-based crystalline materials and sulfide-based crystalline materials. Examples of oxide-based crystalline materials include lithium-containing phosphate compounds with a Nasicon structure, oxides with a perovskite structure, oxides with a garnet or garnet-like structure, and oxide glass-ceramic lithium ion conductors.

[0058] Lithium-containing phosphate compounds with a Nasicon structure include Li x M y(PO4)3 (1≦x≦2, 1≦y≦2, M is at least one selected from the group consisting of titanium (Ti), germanium (Ge), aluminum (Al), gallium (Ga) and zirconium (Zr)). An example of a lithium-containing phosphate compound having a Nasicon structure is, for example, Li 1.2 Al 0.2 Ti 1.8 (PO4)3, etc. An example of an oxide with a perovskite structure is La 0.55 Li 0.35 Examples of oxides with garnet or garnet-like structures include Li7La3Zr2O 12 Examples of sulfide-based crystal materials include thio-LISICON, for example, Li 3.25 Ge 0.25 P 0.75 S4 and Li 10 GeP2S 12 The crystalline solid electrolyte may include a polymer material (for example, polyethylene oxide (PEO)).

[0059] Glass-based solid electrolytes include, for example, oxide-based glass materials and sulfide-based glass materials. Examples of glass-based solid electrolytes other than lithium borosilicate glass include 30Li2S 26B2S3 44LiI, 63Li2S 36SiS2 1Li3PO4, 57Li2S 38SiS2 5Li4SiO4, 70Li2S 30P2S5, and 50Li2S 50GeS2.

[0060] The glass ceramic solid electrolyte is, for example, an oxide-based glass ceramic material or a sulfide-based glass ceramic material. As the oxide-based glass ceramic material, for example, a phosphate compound containing lithium, aluminum, and titanium as constituent elements (LATP) or a phosphate compound containing lithium, aluminum, and germanium as constituent elements (LAGP) can be used. LATP is, for example, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, etc. Also, LAGP is, for example, Li1.5 Al 0.5 Ge 1.5 (PO4), etc. Examples of sulfide-based glass ceramic materials include Li7P3S 11 and Li 3.25 P 0.95 Examples include S4.

[0061] For example, the solid electrolyte may further include an oxide having a garnet-type or garnet-like structure in addition to lithium borosilicate glass. For example, the positive electrode layer of the solid-state battery of the present disclosure may include, as a solid electrolyte, lithium borosilicate glass and an oxide containing Li, La, and Zr (also referred to as LLZ or LiLaZr-based oxide). The present inventors have found that when the positive electrode layer includes at least lithium borosilicate glass as a solid electrolyte, the positive electrode active material can preferentially form an interface with the lithium borosilicate glass, which has relatively high thermal stability. Therefore, even if the positive electrode layer includes a solid electrolyte with relatively low thermal stability, the lithium borosilicate glass can suppress the reaction between the positive electrode active material and the solid electrolyte with low thermal stability under high-temperature conditions. This makes it possible to further include another solid electrolyte that has poorer thermal stability than lithium borosilicate glass but excellent lithium-ion conductivity, thereby obtaining a solid-state battery that more favorably balances high-temperature resistance and battery performance (e.g., capacity retention rate, etc.).

[0062] The content of the lithium borosilicate glass in the solid electrolyte of the positive electrode layer is not particularly limited, but may be, for example, 10% to 90% by mass, 30% to 80% by mass, or 40% to 60% by mass relative to the total amount of the solid electrolyte in the positive electrode layer. The content of the garnet-type oxide solid electrolyte in the solid electrolyte of the positive electrode layer is not particularly limited, but may be, for example, 0% to 70% by mass, 5% to 60% by mass, or 10% to 40% by mass relative to the total amount of the solid electrolyte in the positive electrode layer. When the contents of the lithium borosilicate glass and the garnet-type oxide solid electrolyte are each within the above-mentioned ranges, a solid battery that can be more suitably used even under high-temperature conditions can be provided.

[0063] The constituent material of the positive electrode active material may be a layered rock-salt metal oxide, specifically a lithium transition metal oxide. The term "a positive electrode active material is a layered rock-salt metal oxide" means that the metal oxide (particularly its particles) has a layered rock-salt crystal structure, and in a broad sense, means that the metal oxide has a crystal structure that can be recognized as a layered rock-salt crystal structure by those skilled in the field of batteries. In a narrow sense, the term "a positive electrode active material is a layered rock-salt metal oxide" means that the metal oxide (particularly its particles) is identified as having a layered rock-salt crystal structure by analyzing the X-ray diffraction pattern using Rietveld analysis or the like.

[0064] In one embodiment, the positive electrode active material includes an oxide containing Li and Co (also referred to as LiCO or LiCo-based oxide), and this LiCo-based oxide includes at least Ti. When the LiCo-based oxide includes at least Ti, the self-decomposition temperature of the positive electrode active material can be increased. In other words, the structural stability of the positive electrode active material under high-temperature conditions is improved, and a solid-state battery with better high-temperature resistance can be provided.

[0065] For example, the self-decomposition temperature of a positive electrode active material containing a Ti-containing LiCo-based oxide can be 215° C. or higher and 350° C. or lower, 250° C. or higher and 330° C. or lower, or 280° C. or higher and lower than 295° C. When the self-decomposition temperature is within the above range, a solid-state battery containing this positive electrode active material in a positive electrode layer can be suitably used even under high-temperature conditions.

[0066] The Ti-containing LiCo-based oxide may further contain at least one element selected from the group consisting of Al, Mg, Ni, Mn, Zr, Zn, Cu, B, P, Si, Ge, Nb, Au, and Pt. x Ti y α zO2(I) (wherein x+y+z≦1, 0.9≦x<1, 0.005≦y≦0.01, 0≦z≦0.05, α: at least one element selected from the group consisting of Mg, Al, Ni, Mn, Zr, Zn, Cu, B, P, Si, Ge, Nb, Au, and Pt).

[0067] In formula (I), 0.91≦x<1 is preferable, 0.93≦x≦1 is more preferable, and 0.945≦x≦0.995 is even more preferable. Furthermore, in composition formula (I), 0.003≦y≦0.015 is also acceptable, and 0.005≦y≦0.01 is more preferable. Furthermore, in composition formula (I), 0≦z≦0.08, 0.005≦z≦0.07, or 0.01≦z≦0.05 is also acceptable. Furthermore, when emphasis is placed on suppressing an increase in resistance value and capacity degradation under high-temperature conditions, α is more preferably Al and / or Mg.

[0068] In another embodiment, the positive electrode active material comprises an oxide containing Li, Ni, Co, and Mn (also referred to as NCM, or LiNiCoMn-based oxide). a Co b Mn c The metal composite oxide may include a metal composite oxide represented by the formula O2(II) (wherein a+b+c≦1, 0.3≦a≦0.8, more preferably 0.3≦a≦0.6, 0.2≦b≦0.3, 0.2≦c≦0.3).

[0069] The LiNiCoMn-based oxide may further contain Ti, Al and / or Mg. That is, the positive electrode active material has the composition formula LiNi a Co b Mn c β dThe battery may contain a metal composite oxide represented by the formula O2(II') (wherein a + b + c ≦ 1, 0.3 ≦ a ≦ 0.6, 0.1 ≦ b ≦ 0.3, 0.1 ≦ c ≦ 0.3, 0 ≦ d ≦ 0.05, and β: at least one element selected from Ti, Mg, and Al). In order to emphasize suppressing an increase in resistance and a decrease in capacity under high-temperature conditions, it is more preferable that β contains at least Ti.

[0070] In formulas (II) and (II'), 0.2≦a≦0.8 is preferred, 0.3≦a≦0.75 is more preferred, and 0.3≦a≦0.6 is even more preferred. In formulas (II) and (II'), 0.1≦b≦0.4 may be satisfied, and 0.1≦b≦0.3 or 0.2≦b≦0.3 is more preferred. In formulas (II) and (II'), 0.1≦c≦0.4 may be satisfied, and 0.1≦c≦0.3 or 0.2≦c≦0.3 is more preferred. In formula (II'), 0≦d≦0.08 may be satisfied, and 0.005≦d≦0.07 or 0.01≦d≦0.05 may be satisfied.

[0071] [Solid-state battery manufacturing method] The solid-state battery of the present disclosure can be manufactured by a printing method such as screen printing, a green sheet method using a green sheet, or a combination of these methods. Below, we will explain in detail the cases where the printing method and the green sheet method are used to understand the present disclosure, but the present disclosure is not limited to these methods. That is, the solid-state battery may be manufactured according to a conventional solid-state battery manufacturing method. Furthermore, the chronological matters, such as the order of description below, are merely for the convenience of explanation and are not necessarily bound by them.

[0072] (Solid state battery laminate precursor formation process) In this step, several types of pastes are used as inks, such as a paste for a positive electrode layer, a paste for a negative electrode layer, a paste for a solid electrolyte layer, a paste for a positive electrode current collector layer, a paste for a negative electrode current collector layer, a paste for an electrode separator, and a paste for an outer layer material, etc. In other words, the pastes are applied by a printing method and dried to form a solid battery laminate precursor having a predetermined structure on a support substrate.

[0073] In printing, a solid state battery laminate precursor corresponding to a predetermined solid state battery structure can be formed on a substrate by sequentially stacking printed layers with a predetermined thickness and pattern shape. The type of pattern formation method is not particularly limited as long as it is a method capable of forming a predetermined pattern, and may be, for example, one or more of a screen printing method, a gravure printing method, etc.

[0074] The paste can be prepared by wet mixing predetermined constituent materials for each layer appropriately selected from the group consisting of positive electrode active material particles, negative electrode active material particles, conductive material, solid electrolyte material, current collecting layer material, insulating material, sintering aid, and other materials mentioned above, with an organic vehicle in which an organic material is dissolved in a solvent. The paste for the positive electrode layer contains, for example, positive electrode active material particles, a solid electrolyte material, an organic material and a solvent, and, if desired, a sintering aid. The paste for the negative electrode layer contains, for example, negative electrode active material particles, a solid electrolyte material, an organic material and a solvent, and, if desired, a sintering aid. The paste for the solid electrolyte layer contains, for example, a solid electrolyte material, an organic material, a solvent, and, if desired, a sintering aid. The paste for the positive electrode current collector layer contains a conductive material, an organic material, a solvent, and, if desired, a sintering aid. The paste for the negative electrode current collector layer contains a conductive material, an organic material, a solvent, and, if desired, a sintering aid. The paste for the electrode separator contains, for example, a solid electrolyte material, an insulating material, an organic material, a solvent, and, if desired, a sintering aid. The paste for the outer layer material contains, for example, an insulating material, an organic material, a solvent, and, if desired, a sintering aid.

[0075] The organic material contained in the paste is not particularly limited, but at least one polymer material selected from the group consisting of polyvinyl acetal resin, cellulose resin, polyacrylic resin, polyurethane resin, polyvinyl acetate resin, and polyvinyl alcohol resin can be used.

[0076] The type of solvent is not particularly limited, but may be, for example, one or more of organic solvents such as butyl acetate, N-methyl-pyrrolidone, toluene, terpineol, and N-methyl-pyrrolidone.

[0077] In the wet mixing, media can be used, specifically, a ball mill method, a viscomill method, etc. Alternatively, a wet mixing method without using media can be used, such as a sand mill method, a high-pressure homogenizer method, or a kneader dispersion method.

[0078] The support substrate is not particularly limited as long as it is a support capable of supporting each paste layer, and may be, for example, a release film with one surface subjected to a release treatment. Specifically, a substrate made of a polymer material such as polyethylene terephthalate can be used. When the paste layer is subjected to the firing step while being held on the substrate, a substrate that is heat resistant to the firing temperature may be used.

[0079] Alternatively, each paste may be formed into a green sheet, and the resulting green sheets may be stacked to form a solid state battery laminate precursor.

[0080] Specifically, the support base coated with each paste is dried on a hot plate heated to 30°C or higher and 90°C or lower, thereby forming a positive electrode layer green sheet, a negative electrode layer green sheet, a solid electrolyte layer green sheet, a positive electrode current collector layer green sheet, a negative electrode current collector layer green sheet, an electrode separator green sheet, and / or an outer layer material green sheet, each having a predetermined shape and thickness, on each support base (e.g., a PET film).

[0081] Next, each green sheet is peeled off from the substrate. After peeling, the green sheets of each component are stacked in order along the stacking direction to form a solid state battery laminate precursor. After stacking, a solid electrolyte layer, an insulating layer, and / or a protective layer may be provided on the side regions of the electrode green sheet by screen printing.

[0082] (Firing process) In the firing step, the solid battery laminate precursor is fired. For illustrative purposes, firing is performed by heating in an oxygen-containing nitrogen gas atmosphere or in the air, for example, at 200°C or higher to remove organic materials, and then heating in a nitrogen gas atmosphere or in the air, for example, at 300°C or higher. The firing may be performed while applying pressure to the solid battery laminate precursor in the stacking direction (and, in some cases, in the stacking direction and a direction perpendicular to the stacking direction).

[0083] Through such firing, a solid state battery stack is formed, and ultimately a desired solid state battery is obtained.

[0084] (Positive and negative electrode terminal forming process) For example, a positive electrode terminal is attached to the solid-state battery stack using a conductive adhesive, and a negative electrode terminal is attached to the solid-state battery stack using a conductive adhesive, whereby the positive electrode terminal and the negative electrode terminal are attached to the solid-state battery stack, respectively, thereby completing the solid-state battery. [Example]

[0085] A demonstration test was carried out in accordance with the present disclosure. The structure of the solid-state battery shown in Figure 2 was adopted.

[0086] Example 1 (Production process of green sheet for solid electrolyte layer) First, lithium borosilicate glass and an acrylic binder were mixed as a solid electrolyte in a mass ratio of 70:30 (lithium borosilicate glass:acrylic binder). The lithium borosilicate glass used had a composition of Li2O:SiO2:BO3 = 60:10:30 (mol %). The resulting mixture was then mixed with butyl acetate to a solid content of 30 mass %. This mixture was then stirred with 5 mm diameter zirconia balls for 4 hours to obtain a solid electrolyte layer paste. This paste was then applied to a release film and dried at 80°C for 10 minutes to produce a solid electrolyte layer green sheet as a solid electrolyte layer precursor.

[0087] (Production process of green sheet for positive electrode layer) First, titanium-containing lithium cobalt oxide (LiCoO2) was synthesized by a solid-state method in which cobalt oxide, lithium carbonate, and titanium were mixed and sintered. By controlling the mixing conditions and sintering temperature, titanium-containing lithium cobalt oxide with a 003 interplanar spacing was obtained.

[0088] Next, titanium-containing lithium cobalt oxide (LiCoO) as the positive electrode active material and lithium borosilicate glass as the solid electrolyte were mixed in a mass ratio of 75:25 (titanium-containing lithium cobalt oxide:lithium borosilicate glass). The resulting mixture was then mixed with an acrylic binder in a mass ratio of 70:30 (mixture (titanium-containing lithium cobalt oxide + lithium borosilicate glass):acrylic binder). This mixture was then mixed with butyl acetate to a solids content of 30% by mass. The resulting mixture was then stirred with 5 mm diameter zirconia balls for 4 hours to obtain a positive electrode layer paste. This paste was then applied to a release film and dried at 80°C for 10 minutes to produce a positive electrode layer green sheet as a positive electrode layer precursor.

[0089] (Production process of green sheet for negative electrode layer) First, carbon powder (KS6, manufactured by TIMCAL) as the negative electrode active material and lithium borosilicate glass as the solid electrolyte were mixed in a mass ratio of carbon powder:lithium borosilicate glass = 70:30. Next, the resulting mixture was mixed with an acrylic binder in a mass ratio of mixture (carbon powder + lithium borosilicate glass):acrylic binder = 70:30, and then this was mixed with butyl acetate so that the solid content was 30 mass%. The resulting mixture was then stirred with zirconia balls with a diameter of 5 mm for 4 hours to obtain a paste for the negative electrode layer. Next, this paste was applied to a release film and dried at 80°C for 10 minutes to produce a green sheet for the negative electrode layer as a negative electrode layer precursor.

[0090] (Process for producing green sheets for positive electrode current collecting layers) First, carbon powder (KS6, manufactured by TIMCAL) as a conductive material and lithium borosilicate glass as a solid electrolyte were mixed in a mass ratio of 70:30 (carbon powder:lithium borosilicate glass). The resulting mixture was then mixed with an acrylic binder in a mass ratio of 70:30 (mixture (carbon powder + lithium borosilicate glass):acrylic binder). This mixture was then mixed with butyl acetate to a solids content of 30% by mass. The resulting mixture was then stirred with zirconia balls with a diameter of 5 mm for 4 hours to obtain a paste for the positive electrode current collector layer. This paste was then applied to a release film and dried at 80°C for 10 minutes to produce a green sheet for the positive electrode current collector layer as a positive electrode current collector precursor.

[0091] (Process for producing green sheets for negative electrode current collecting layers) A green sheet for a negative electrode current collecting layer was prepared in the same manner as in the above-mentioned "Step of preparing a green sheet for a positive electrode current collecting layer."

[0092] (Outer layer green sheet manufacturing process) First, alumina particle powder (Nippon Light Metal Co., Ltd., AHP300) was mixed as the particle powder with lithium borosilicate glass as the solid electrolyte in a mass ratio of 50:50 (alumina particle powder:lithium borosilicate glass). The resulting mixture was then mixed with an acrylic binder in a mass ratio of 70:30 (alumina particle powder + lithium borosilicate glass:acrylic binder), and this was then mixed with butyl acetate to a solids content of 30% by mass. The resulting mixture was then stirred with 5 mm diameter zirconia balls for 4 hours to obtain a paste for the main surface exterior material. This paste was then applied to a release film and dried to produce a green sheet for the outer layer material as a precursor for the main surface outer layer material.

[0093] (Process for manufacturing green sheets for electrode separation parts) In the same manner as in the above-mentioned "process for producing green sheets for outer layer material", green sheets for electrode separators were produced as electrode separator precursors.

[0094] (Laminate manufacturing process) Using each green sheet obtained as described above, a laminate having the configuration shown in Figures 1 and 2 was produced as follows. First, each green sheet was processed into the shape shown in Figures 1 and 2, and then released from the release film. Next, each green sheet was stacked in order so as to correspond to the configuration of the battery element shown in Figures 1 and 2, and then thermocompression bonded. In this way, a laminate was obtained as a battery element precursor.

[0095] (Laminated body sintering process) The resulting laminate was heated to remove the acrylic binder contained in each green sheet, and then further heated to sinter the oxide glass contained in each green sheet.

[0096] (Terminal manufacturing process) First, Ag powder (Daiken Chemical Industry) and oxide glass (Bi-B glass, manufactured by Asahi Glass Co., Ltd., ASF1096) were mixed at a predetermined mass ratio as conductive particle powder. Next, the resulting mixture was mixed with an acrylic binder at a mass ratio of 70:30 (Ag powder + oxide glass):acrylic binder. This mixture was then mixed with a butyl acetate solvent to a solids content of 50 mass%. The resulting mixture was then stirred with zirconia balls having a diameter of 5 mm for 4 hours to obtain a conductive paste. Next, this conductive paste was applied to a release film, and then attached to the first and second end faces (or side faces) of the laminate where the positive and negative current collecting layers were exposed, respectively. The conductive paste was then sintered to form positive and negative electrode terminals. This resulted in the production of the desired battery.

[0097] <Example 2> A solid-state battery was produced in the same manner as in Example 1, except that the composition ratio of the positive electrode active material was changed.

[0098] <Examples 3 to 5> A solid-state battery was produced in the same manner as in Example 1, except that a predetermined amount of Al was further added as a positive electrode active material.

[0099] <Examples 6 to 8> A solid-state battery was produced in the same manner as in Example 1, except that a predetermined amount of Mg was further added as a positive electrode active material.

[0100] Example 9 A solid-state battery was manufactured in the same manner as in Example 1, except that a mixture of lithium borosilicate glass and LiLaZr-based oxide (lithium borosilicate glass:LiLaZr-based oxide = 60:40 (mass ratio)) was used as the solid electrolyte. The LiLaZr-based oxide was Li7La3Zr2O 12 was used.

[0101] Examples 10 and 11 A solid-state battery was produced in the same manner as in Example 1, except that a LiNiCoMn-based oxide was used as the positive electrode active material.

[0102] <Comparative Example 1> A solid-state battery was produced in the same manner as in Example 1, except that titanium-free lithium cobalt oxide was used as the positive electrode active material.

[0103] <Comparative Example 2> A solid-state battery was manufactured in the same manner as in Example 1, except that a LiLaZr-based oxide was used as the solid electrolyte. 12 was used.

[0104] (Measurement of battery characteristics) The battery was charged to a predetermined positive electrode potential at a constant current of 0.2 C with a rated capacity of 1 C. After reaching the positive electrode potential, the battery was charged in constant voltage mode until the current was reduced to 0.01 C. Impedance measurements were performed to determine the initial resistance. The battery was then stored at high temperature (105°C) for one week, slowly cooled to 25°C by air cooling, and then impedance measurements were performed at 25°C. The battery was then discharged to 2 V at a constant current of 0.2 C and the capacity was measured. The positive electrode potential varied depending on the positive electrode active material. Specifically, the battery was charged to a positive electrode potential of 4.35 V when the positive electrode active material was a LiCo-based oxide, and to 4.2 V when the positive electrode active material was a LiNiCoMn-based oxide.

[0105] The resistance increase rate was calculated by dividing the resistance value after storage under high temperature conditions by the initial resistance value obtained from the impedance measurement. In addition, the deterioration of the discharge capacity after storage under high temperature conditions was calculated from the capacity measurement results.

[0106] (X-ray diffraction measurement) The 003 interplanar spacing of the positive electrode active material was measured using an X-ray diffraction measurement device (Bruker D8 Advance). The battery was charged at a current of 0.2 C. After reaching a positive electrode potential of 4.55 V, constant-current, constant-voltage charging was performed, in which the current was reduced to 0.01 C. After the lithium desorption from the positive electrode active material reached 40%, the positive electrode layer was removed from the solid-state battery and placed in a sample holder of the X-ray diffraction measurement device. The target temperature was set in 20°C increments within the measurement temperature range of 25°C to 500°C, and the positive electrode layer was heated at a heating rate of 10°C / min. After reaching the target temperature, a 3-minute waiting period was allowed before X-ray diffraction measurement. The step width in the X-ray diffraction measurement was 0.01°, the counting time was 0.3 seconds or more, the scanning speed was 10° / min, and the angle range was 15° to 70°.

[0107] Specifically, the positive electrode layer is exposed by polishing or disassembly. After confirming that no short circuits have occurred during the work by measuring the voltage with a tester, XRD measurements are performed as described above. If there is concern that the material may be altered by exposure to the atmosphere, the entire process and measurements are performed in an inert atmosphere. The interplanar spacing at the angle showing the maximum intensity of the peaks attributed to 003 in the XRD spectrum of the positive electrode active material obtained above was calculated and defined as the interplanar spacing. The maximum value of the interplanar spacing within the measurement temperature range (i.e., the maximum interplanar spacing) was defined as 1, and the temperature at which the relative interplanar spacing to the maximum interplanar spacing fell below 0.995, which was higher than the temperature at which the maximum interplanar spacing was obtained, was defined as the autodecomposition temperature.

[0108] Table 1 shows the evaluation results of the solid state batteries of Examples 1 to 11 and Comparative Examples 1 and 2. The resistance increase rate and degradation capacity of Comparative Example 2 and Examples 1 to 11 are shown as relative values ​​when the resistance increase rate and degradation capacity of Comparative Example 1 are set to "100," respectively.

[0109] [Table 1]

[0110] According to the above results, the solid-state batteries of Examples 1 to 11 exhibited better battery characteristics even after storage at high temperatures than the solid-state battery of Comparative Example 1, which used a conventional cathode active material with a temperature below 215°C, and the solid-state battery of Comparative Example 2, which did not contain lithium borosilicate glass as the solid electrolyte but used a LiLaZr-based oxide. Specifically, the solid-state batteries of Examples 1 to 11, in which the self-decomposition temperature of the cathode active material was 215°C or higher and the solid-state electrolyte contained lithium borosilicate glass, exhibited lower values ​​for the resistance increase rate and capacity degradation than those of Comparative Examples 1 and 2, even after storage at high temperatures. In other words, the solid-state battery of the present disclosure can effectively suppress the degradation of battery characteristics even under high-temperature conditions. Therefore, the present disclosure provides a solid-state battery with more favorable battery characteristics even under high-temperature conditions.

[0111] (Measurement of cycle characteristics) Furthermore, the capacity retention rates of the solid-state batteries of Examples 1 to 11 and Comparative Examples 1 and 2 were measured to evaluate the initial battery characteristics before exposure to high-temperature conditions. Specifically, the rated capacity of the battery was set to 1 C, and the battery was charged at a constant current of 0.2 C to the above-mentioned positive electrode potential. After reaching the positive electrode potential, the battery was charged in a constant voltage mode until the current was reduced to 0.01 C. The battery was then discharged at a constant current of 0.2 C until the positive electrode potential reached 3 V. This cycle of charge and discharge was counted as one cycle, and the capacity retention rates relative to the initial discharge capacity were measured after 100 cycles. The measurement results are shown in Table 2.

[0112] [Table 2]

[0113] According to the above results, the solid-state batteries of Examples 10 and 11, which contained lithium borosilicate glass as a solid electrolyte and a positive electrode active material having a self-decomposition temperature of 295°C or higher, had a lower capacity retention rate than Comparative Example 1. That is, the positive electrode active material having a self-decomposition temperature of 295°C or higher was able to maintain favorable battery characteristics even under high-temperature conditions, but showed a relatively low capacity retention rate. On the other hand, the solid-state batteries of Examples 1 to 9, in which the positive electrode active material had a self-decomposition temperature of 215°C or higher but lower than 295°C, were able to maintain favorable battery characteristics even after storage under high-temperature conditions, and also showed favorable values ​​for the capacity retention rate before exposure to high-temperature conditions.

[0114] Although the embodiments of the present disclosure have been described above, they are merely typical examples. Therefore, it will be readily understood by those skilled in the art that the present disclosure is not limited thereto and that various modifications are possible within the scope of the present disclosure.

[0115] It should be noted that the embodiment of the present disclosure as described above includes the following preferred aspects. First aspect: a positive electrode layer including a positive electrode active material containing lithium and a solid electrolyte; a solid-state battery in which, in an XRD analysis performed while heating the positive electrode layer when the amount of lithium desorbed from the positive electrode active material is 40%, the autodecomposition temperature at which a relative change in the maximum interplanar spacing falls below 0.995, where the maximum interplanar spacing is defined as 1, is 215°C or higher, and the solid electrolyte comprises lithium borosilicate glass. Second aspect: In the first aspect, the positive electrode active material has a layered rock salt crystal structure. Third aspect: In the first or second aspect, the solid-state battery has a self-decomposition temperature of 215°C or higher and 315°C or lower. Fourth aspect: In any one of the first to third aspects, the solid state battery is characterized in that the positive electrode active material contains an oxide containing Li and Co, and the oxide contains at least Ti. Fifth aspect: In the fourth aspect, in the solid state battery, when the oxide in the positive electrode active material contains Ti, the self-decomposition temperature is 215°C or higher and lower than 295°C. Sixth aspect: In the fourth or fifth aspect, the solid-state battery further comprises Mg and / or Al. Seventh aspect: In any one of the fourth to sixth aspects, the positive electrode active material is LiCo x Ti y α z 1. A solid-state battery comprising: O2 (wherein x+y+z≦1, 0.9≦x<1, 0.005≦y≦0.01, 0≦z≦0.05, α: Mg and / or Al). Eighth aspect: In any one of the first to third aspects, the solid state battery comprises an oxide containing Li, Ni, Co, and Mn. Ninth aspect: In the eighth aspect, the positive electrode active material is LiNi a Co b Mn c O2 (wherein a+b+c≦1, 0.3≦a≦0.6). Tenth aspect: In any one of the first to ninth aspects, the solid state battery further comprises an oxide-based solid electrolyte having a garnet-type crystal structure. Eleventh aspect: In the tenth aspect, in the solid state battery, the oxide-based solid electrolyte is an oxide containing Li, La, and Zr. [Industrial Applicability]

[0116] The solid-state battery of the present disclosure can be used in various fields where power storage is expected. By way of example only, the solid-state battery of the present disclosure can be used in the electrical, information, and communications fields where mobile devices are used (e.g., electrical and electronic devices or mobile devices, including small electronic devices such as mobile phones, smartphones, laptops, digital cameras, activity monitors, arm computers, electronic paper, RFID tags, card-type electronic money, and smart watches), household and small industrial applications (e.g., power tools, golf carts, and household, nursing care, and industrial robots), large industrial applications (e.g., forklifts, elevators, and port cranes), transportation systems (e.g., hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (e.g., various power generation systems, road conditioners, smart grids, and general-purpose household power storage systems), medical applications (e.g., medical devices such as earphones and hearing aids), pharmaceutical applications (e.g., medication management systems), IoT applications, and space and deep-sea applications (e.g., space probes and submersible research vessels). [Explanation of symbols]

[0117] 10: Electrode layer 10A: Positive electrode layer 10B: Negative electrode layer 11: Electrode current collecting layer 11A: Positive electrode current collecting layer 11B: Negative electrode current collecting layer 20: Solid electrolyte layer 30: Electrode separation part 30A: Positive electrode separation section 30B: Negative electrode separation section 40: Terminal 40A: Positive terminal 40B: Negative terminal 60: Outer layer material 100: Solid-state battery stack 200: Solid state battery

Claims

1. a positive electrode layer including a positive electrode active material containing lithium and a solid electrolyte; a solid-state battery in which, in an XRD analysis performed while heating the positive electrode layer in a state in which the amount of lithium desorbed from the positive electrode active material is 40%, the autodecomposition temperature at which a relative change from the maximum interplanar spacing falls below 0.995, where the value of the maximum interplanar spacing is taken as 1, is 215°C or higher, and the solid electrolyte comprises lithium borosilicate glass.

2. The solid-state battery according to claim 1 , wherein the positive electrode active material has a layered rock salt type crystal structure.

3. The solid-state battery according to claim 1 , wherein the self-decomposition temperature is 215° C. or higher and 315° C. or lower.

4. The solid-state battery according to claim 1 , wherein the positive electrode active material comprises an oxide containing Li and Co, and the oxide contains at least Ti.

5. The solid-state battery according to claim 4 , wherein, in the positive electrode active material, when the oxide contains Ti, the self-decomposition temperature is 215° C. or higher and lower than 295° C.

6. The solid-state battery according to claim 4 , wherein the positive electrode active material further contains Mg and / or Al.

7. The positive electrode active material is LiCo ｘ Ti ｙ α ｚ O ２ 5. The solid-state battery of claim 4, comprising: (wherein x + y + z ≦ 1, 0.9 ≦ x < 1, 0.005 ≦ y ≦ 0.01, 0 ≦ z ≦ 0.05, and α: Mg and / or Al).

8. The solid-state battery according to claim 1 , wherein the positive electrode active material comprises an oxide containing Li, Ni, Co, and Mn.

9. The positive electrode active material is LiNi ａ Co ｂ Mn ｃ O ２ The solid-state battery according to claim 8 , wherein a+b+c≦1, 0.3≦a≦0.

6.

10. 2. The solid-state battery according to claim 1, wherein the solid electrolyte further comprises an oxide-based solid electrolyte having a garnet-type crystal structure.

11. 11. The solid-state battery according to claim 10, wherein the oxide-based solid electrolyte is an oxide containing Li, La, and Zr.

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