Solid electrolyte, solid-state battery, and method for manufacturing solid-state battery

Abstract

Provided is a solid electrolyte represented by the following general formula. Formula 1: Na1+xZr2SixP3-xO12 (in the formula x conforms to 0 < x < 0.9 or 1.2 < x <2.0.

Description

Solid electrolyte, solid battery, and method for manufacturing a solid battery

[0001] This disclosure relates to a solid electrolyte, a solid battery, and a method for manufacturing a solid battery.

[0002] Rechargeable batteries, which can be repeatedly charged and discharged, have long been used in a variety of applications. For example, rechargeable batteries are 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 transfer that contributes to charging and discharging. In other words, so-called electrolyte solutions are used in secondary batteries. However, safety is generally required in such secondary batteries in terms of preventing electrolyte leakage. Furthermore, since organic solvents used in electrolyte solutions are flammable substances, safety is also required in that respect.

[0004] Therefore, research is underway on solid-state batteries that use solid electrolytes instead of liquid electrolytes.

[0005] Public Relations for Patent No. 3281098

[0006] The inventors of this application have found that there are areas for improvement in conventional solid electrolytes and solid batteries using these solid electrolytes.

[0007] Specifically, as a solid electrolyte with excellent ionic conductivity in the high-temperature range, Na is a solid electrolyte with a NASICON structure. ３ Zr ２ Si ２ PO １２ This is known. However, when manufacturing a solid battery using such a solid electrolyte, during the heat treatment (specifically during firing), the electrode active material (especially Na) ３ V ２ P ３ O １２ The reactivity of the solid electrolyte may increase in response to the active material. As a result, the crystal structure of the electrode active material may change, preventing it from functioning properly and potentially leading to a decrease in battery performance.

[0008] The present disclosure has been made in view of such circumstances. That is, an object of the present disclosure is to provide a solid electrolyte capable of reducing reactivity with an electrode active material, a solid battery including the solid electrolyte, and a method for manufacturing the solid battery.

[0009] In order to achieve the above object, in one embodiment of the present disclosure, a solid electrolyte represented by the following general formula is provided. [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２ (where x satisfies 0 < x < 0.9 or 1.2 < x < 2.0)

[0010] In order to achieve the above object, in one embodiment of the present disclosure, a solid electrolyte having a NASICON-type crystal structure containing Na, Zr, Si, P, and O is provided, and the ratio of the content of Na to the content of P (Na / P) is more than 0.3 and less than 0.9, or more than 1.2 and less than 3.

[0011] In order to achieve the above object, in one embodiment of the present disclosure, a sintered solid battery in which a positive electrode layer including a positive electrode active material and a solid electrolyte, a solid electrolyte layer including a solid electrolyte, and a negative electrode layer including a negative electrode active material and a solid electrolyte are laminated in this order, wherein the solid electrolyte in at least one of the positive electrode layer and the negative electrode layer is a solid electrolyte represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２ (where x satisfies 0 < x < 0.9 or 1.2 < x < 2.0), and at least one of the positive electrode active material and the negative electrode active material is represented by the general formula Na ３＋ｙ V ２－ｙ (PO ４ ) ３ (where 0 ≤ y ≤ 1), and a solid battery is provided.

[0012] Furthermore, in order to achieve the above objective, one embodiment of the present disclosure provides a method for manufacturing a solid battery, which includes firing an electrode layer precursor containing an electrode active material and a solid electrolyte at a temperature of 1000°C to 1300°C, wherein the solid electrolyte has a Nasicone-type crystalline structure containing Na, Zr, Si, P, and O, and is a solid electrolyte represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２ (In the equation, for x, 0 < x < 0.9 or 1.2 < x < 2.0)

[0013] According to one embodiment of the present disclosure, it is possible to provide a solid electrolyte capable of reducing reactivity with respect to electrode active materials, a solid battery equipped with this solid electrolyte, and a method for manufacturing a solid battery.

[0014] The solid electrolyte and solid battery of this disclosure will be described in detail below.

[0015] [Solid-state batteries] In this disclosure, "solid-state battery" broadly refers to a battery whose components are made of solids, and in a narrow sense refers to an all-solid-state battery whose components (particularly preferably all components) are made of solids. In one preferred embodiment, the solid-state battery in this disclosure is a stacked solid-state battery configured such that each layer constituting the battery component unit is stacked on top of each other, preferably such layers are made of a fired body. "Solid-state batteries" include not only primary batteries but also so-called "secondary batteries" that can be repeatedly charged and discharged. The term "secondary battery" is not overly restrictive and may also include, for example, energy storage devices.

[0016] The key feature of this disclosure relates to the solid electrolyte contained in the solid-state battery. Below, in order to understand the overall structure of the solid-state battery, the basic configuration of the solid-state battery of this disclosure will be described. 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] The solid-state battery of this disclosure includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, and typically has a laminated structure in which the positive electrode layer and the negative electrode layer are laminated with the solid electrolyte layer in between. The positive electrode layer and the negative electrode layer may each be laminated in two or more layers, as long as a solid electrolyte layer is provided between them. The solid electrolyte layer may be in contact with the positive electrode layer and the negative electrode layer and sandwiched between them.

[0018] The solid electrolyte of this disclosure described above is useful as a solid electrolyte for solid-state batteries. Therefore, the solid-state battery of this disclosure includes the solid electrolyte of this disclosure as a solid electrolyte. Specifically, the solid electrolyte of this disclosure is included as a solid electrolyte in one or more layers among the positive electrode layer, the negative electrode layer, and the solid electrolyte layer. This makes it possible to obtain a solid-state battery with excellent ionic conductivity.

[0019] In a solid-state battery, each of its constituent layers may be formed by firing, and the positive electrode layer, negative electrode layer, and solid electrolyte layer may form fired layers. For example, the positive electrode layer, negative electrode layer, and solid electrolyte layer may each be fired integrally with each other, and therefore the laminate containing the positive electrode layer, negative electrode layer, and solid electrolyte layer may form an integrally fired body.

[0020] The positive electrode layer is an electrode layer containing at least positive electrode active material. The positive electrode layer may further contain a solid electrolyte. In one embodiment, the positive electrode portion 20 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 containing at least negative electrode active material. The negative electrode layer may further contain a solid electrolyte. In one preferred embodiment, the negative electrode layer is composed of a sintered body containing at least negative electrode active material particles and solid electrolyte particles. Positive electrode layers and negative electrode layers having such configurations can also be referred to as "composite positive electrode" and "composite negative electrode," respectively.

[0021] The positive electrode active material and the negative electrode active material are materials that are involved in electron transfer in a solid-state battery. Charging and discharging occur when ions move (conduce) between the positive electrode layer and the negative electrode layer via a solid electrolyte, resulting in electron transfer. It is particularly preferable that each electrode portion of the positive electrode layer and the negative electrode layer be a layer capable of intercalating and deintercalating sodium ions. In other words, it is preferable that the solid-state battery is an all-solid-state secondary battery in which charging and discharging occur by the movement of sodium ions between the positive electrode layer and the negative electrode layer via a solid electrolyte.

[0022] The positive electrode active material contained in the positive electrode layer may be a known material capable of intercalating and deintercalating sodium ions. Examples of positive electrode active materials include at least one selected from the group consisting of sodium-containing phosphate compounds having a nasicone-type structure, sodium-containing phosphate compounds having an olivine-type structure, sodium-containing layered oxides, and sodium-containing oxides having a spinel-type structure.

[0023] For example, in the case of sodium-containing phosphate compounds, Na ３ V ２ (PO ４ ) ３ NaCoFe ２ (PO ４ ) ３ Na ２ Ni ２ Fe(PO ４ ) ３ Na ３ Fe ２ (PO ４ ) ３ Na ２ FeP ２ O ７ Na ４ Fe ３ (PO ４ ) ２ (P ２ O ７ ), and as a sodium-containing layered oxide, NaFeO ２ At least one selected from the group consisting of the following can be mentioned.

[0024] As an example, the positive electrode active material, as a sodium-containing phosphate compound, has the following compositional formula: [Formula 1] Na ３＋ｘ V ２－ｘ(PO ４ ) ３ It is preferable that the material is represented by the formula (wherein 0 ≤ x ≤ 1) (hereinafter also referred to as NVP). When the positive electrode active material is NVP, a good interface can be formed between the NVP and the solid electrolyte during integral firing. This allows for the provision of a solid-state battery with favorable battery performance.

[0025] In addition, the positive electrode active material may be, for example, an oxide, disulfide, chalcogenide, or conductive polymer. Oxides may be, for example, titanium oxide, vanadium oxide, or manganese dioxide. Disulfides may be, for example, titanium disulfide or molybdenum sulfide. Chalcogenides may be, for example, niobium selenide. Conductive polymers may be, for example, disulfide, polypyrrole, polyaniline, polythiophene, polyparastyrene, polyacetylene, or polyacene.

[0026] (Negative electrode active material) The negative electrode active material contained in the negative electrode layer may be a known material capable of intercalating and releasing sodium ions. For example, the negative electrode active material 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 sodium-containing phosphate compound having a nassycon-type structure, a sodium-containing phosphate compound having an olivine-type structure, and a sodium-containing oxide having a spinel-type structure.

[0027] For example, in the case of sodium-containing phosphate compounds, Na ３ V ２ (PO ４ ) ３ NaCoFe ２ (PO ４ ) ３ Na ２ Ni ２ Fe(PO ４ ) ３ Na ３ Fe ２ (PO ４ ) ３ Na ２ FeP ２ O７ Na ４ Fe ３ (PO ４ ) ２ (P ２ O ７ ), and as a sodium-containing layered oxide, NaFeO ２ At least one selected from the group consisting of the following can be mentioned.

[0028] As an example, the negative electrode active material has the following compositional formula: [Formula 1] Na ３＋ｘ V ２－ｘ (PO ４ ) ３ The material can be one represented by the formula (wherein 0 ≤ x ≤ 1) (hereinafter also referred to as NVP). Because the negative electrode active material is NVP, a good interface can be formed between the NVP and the solid electrolyte during integral firing. This allows for the provision of a solid-state battery with favorable battery performance.

[0029] The positive electrode layer and / or negative electrode layer may contain a conductive material. Examples of conductive materials included in the positive electrode layer and negative electrode layer include at least one of metallic materials such as silver, palladium, gold, platinum, aluminum, copper, and nickel, as well as carbon.

[0030] Furthermore, the positive electrode layer and / or negative electrode layer may contain a sintering aid. Examples of sintering aids include at least one selected from the group consisting of lithium oxide, sodium oxide, potassium oxide, boron oxide, silicon oxide, bismuth oxide, and phosphorus oxide.

[0031] In addition, in a solid-state battery, the positive electrode layer and the negative electrode layer may be made of the same material.

[0032] The thicknesses of the positive electrode layer and the negative electrode layer are not particularly limited, but for example, they may be 2 μm or more and 50 μm or less, and more particularly 5 μm or more and 30 μm or less, respectively.

[0033] (Positive electrode current collector layer / Negative electrode current collector layer) Although not essential elements of the electrode layer, the positive electrode layer and negative electrode layer may each comprise a positive electrode current collector layer and a negative electrode current collector layer. The positive electrode current collector layer and the negative electrode current collector layer may each be in the form of foil. However, if greater emphasis is placed on aspects such as improved electronic conductivity through integral sintering, reduction of manufacturing costs for solid-state batteries, and / or reduction of internal resistance of solid-state batteries, the positive electrode current collector layer and the negative electrode current collector layer may each be in the form of a sintered body.

[0034] It is preferable to use materials with high conductivity for the positive electrode current collector that constitutes the positive electrode current collector layer and the negative electrode current collector that constitutes the negative electrode current collector. For example, silver, palladium, gold, platinum, aluminum, copper, and / or nickel may be used. The positive electrode current collector and the negative electrode current collector may each have an electrical connection part for electrically connecting to the outside, and may be configured to be electrically connectable to terminals.

[0035] Furthermore, if the positive electrode current collector layer and the negative electrode current collector layer are in the form of sintered bodies, they may be composed of sintered bodies containing a conductive material and a sintering aid. The conductive material included in the positive electrode current collector layer and the negative electrode current collector layer may be selected from materials similar to those that may be included in the positive electrode layer and the negative electrode layer. The sintering aid included in the positive electrode current collector layer and the negative electrode current collector layer may be selected from materials similar to those that may be included in the positive electrode layer and the negative electrode layer.

[0036] As mentioned above, positive electrode current collector layers and negative electrode current collector layers are not essential in solid-state batteries, and solid-state batteries without such layers are also conceivable. In other words, the solid-state battery included in the package of the present invention may be a solid-state battery without current collector layers.

[0037] (Solid Electrolyte Layer) The solid electrolyte layer contains a solid electrolyte through which sodium ions can conduct. In particular, the solid electrolyte layer that forms a battery component unit in a solid-state battery may be a layer through which sodium ions can conduct between the positive electrode layer and the negative electrode layer. The solid electrolyte layer only needs to be provided between the positive electrode layer and the negative electrode layer. In other words, the solid electrolyte layer may exist around the positive electrode layer and / or the negative electrode layer so as to protrude from between the positive electrode layer and the negative electrode layer.

[0038] The solid electrolyte layer may contain a sintering aid. The sintering aid contained in the solid electrolyte layer may be selected from materials similar to those that may be contained in the positive electrode layer and / or negative electrode layer.

[0039] 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 or more and 15 μm or less, and particularly 1 μm or more and 5 μm or less.

[0040] In one embodiment, the positive electrode layer, the negative electrode layer, and / or the solid electrolyte layer may contain a solid electrolyte different from the solid electrolyte of the present disclosure described above. Examples of different solid electrolytes include crystalline solid electrolytes, glass-based solid electrolytes, and glass-ceramic solid electrolytes. The positive electrode layer, the negative electrode layer, and / or the solid electrolyte layer may contain one or more of the above-mentioned solid electrolytes.

[0041] Examples of solid electrolytes different from those disclosed herein include sodium-containing phosphate compounds having a nasicone structure, oxides having a perovskite structure, and oxides having a garnet-type or garnet-type similar structure.

[0042] [Features of this Disclosure (Solid Electrolyte)] The features of this disclosure are described below. This disclosure is characterized by a solid electrolyte, which is a component of a solid battery.

[0043] The solid electrolyte of this disclosure has a NASCON-type crystalline structure and comprises Na (sodium), Zr (zirconium), Si (silicon), P (phosphorus), and O (oxygen).

[0044] As is clear from Table 1 described later, the inventor of the present application found that, by using a solid electrolyte in which the contents (molar concentrations) of Na (sodium) and P (phosphorus) are set within a predetermined range during heat treatment (specifically, firing) in the production of a solid-state battery, the reactivity of the solid electrolyte with respect to the electrode active material (particularly, Na ３ V ２ P ３ O １２ ) can be relatively reduced.

[0045] Specifically, the decrease in the reactivity of the solid electrolyte with respect to such an electrode active material can be achieved by reducing the content (molar concentration) of Na in the solid electrolyte compared to the case where Na ３ Zr ２ Si ２ PO １２ is used as the solid electrolyte having a NASICON structure (see the comparison between Comparative Example 1 and Examples 1 to 4).

[0046] However, it has been found that simply relatively reducing the content (molar concentration) of Na in the solid electrolyte does not uniformly achieve a decrease in the reactivity of the solid electrolyte with respect to the electrode active material.

[0047] When the ratio of the content of Na (sodium) to the content of P (phosphorus) in the solid electrolyte (Na / P) is 0.9 or more and 1.2 or less, that is, when the content of P (phosphorus) in the solid electrolyte approaches the content of Na (sodium), it has been found that the reactivity of the same solid electrolyte with respect to the above electrode active material (particularly, Na ３ V ２ P ３ O １２ ) actually becomes higher (see Comparative Examples 2 to 4).

[0048] On the other hand, when the ratio of the content of Na (sodium) to the content of P (phosphorus) in the solid electrolyte (Na / P) is less than 0.9, that is, when the content of P (phosphorus) in the solid electrolyte is more than the content of Na (sodium), it has been found that the reactivity of the same solid electrolyte with respect to the above electrode active material (particularly, Na ３ V ２ P ３ O １２ ) becomes lower.

[0049] Although not bound by any particular theory, the change in crystal structure from monoclinic to hexagonal means that during the heat treatment (specifically during firing) of solid-state batteries, the electrode active material (especially Na ３ V ２ P ３ O １２ It is thought that this has made it less responsive.

[0050] Furthermore, if the ratio of sodium (Na) content to phosphorus (P) content in the solid electrolyte (Na / P) is greater than 1.2 and less than 3, the above electrode active material (especially Na ３ V ２ P ３ O １２ It was found that the reactivity of the solid electrolyte to ) was reduced.

[0051] The solid electrolyte of this disclosure is characterized in that the ratio of sodium (Na) content to phosphorus (P) content (Na / P) is greater than 0.3 and less than 0.9, or greater than 1.2 and less than 3.

[0052] Furthermore, the solid electrolyte of this disclosure is represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２ A key feature of the above equation is that for x, 0 < x < 0.9 or 1.2 < x < 2.0.

[0053] According to these characteristics, Na is used as the solid electrolyte in the NASCON structure. ３ Zr ２ Si ２ PO １２ Compared to cases where a solid electrolyte is used, when manufacturing a solid battery using a solid electrolyte, the electrode active material (especially Na) is affected during heat treatment (specifically during firing). ３ V ２ P ３ O １２ This can relatively reduce the reactivity of the solid electrolyte to ).

[0054] This reduction in reactivity (also referred to as a side reaction) suppresses changes in the crystal structure of the electrode active material, allowing its function to be suitably maintained. As a result, the deterioration of battery performance can be suitably suppressed. This makes it possible to improve the charge and discharge efficiency of the battery.

[0055] Preferably, in the solid electrolyte of this disclosure, x in the above formula may be 0.3 ≤ x ≤ 0.7. That is, the content of the constituent Na may be 1.3 moles or more and 1.7 moles or less. Furthermore, regarding the relationship between the content (molar concentration) of Na (sodium) and P (phosphorus), which are constituent elements of the solid electrolyte of this disclosure, preferably the above ratio (Na / P) may be 0.5 or more and 0.7 or less.

[0056] In this case, during firing when manufacturing a solid battery, Na ３ V ２ P ３ O １２ The reactivity of this solid electrolyte to the active material can be suitably reduced. This allows the function of the electrode active material to be suitably maintained, and as a result the difference between the predetermined battery capacity and discharge capacity can be reduced, and the utilization rate (corresponding to charge / discharge efficiency) can be set to approximately 94% to 98.5%.

[0057] Preferably, in the solid electrolyte of this disclosure, x in the above formula may be 1.5 ≤ x ≤ 1.7. That is, the content of the constituent Na may be 2.5 moles or more and 2.7 moles or less. Furthermore, regarding the relationship between the content (molar concentration) of Na (sodium) and P (phosphorus), which are constituent elements of the solid electrolyte of this disclosure, preferably the above ratio (Na / P) may be 1.7 or more and 2.1 or less.

[0058] In this case, during firing when manufacturing a solid battery, Na ３ V ２ P ３ O １２ The reactivity of this solid electrolyte to the active material can be suitably reduced. This allows the function of the electrode active material to be suitably maintained, and as a result the difference between the predetermined battery capacity and discharge capacity can be reduced, and the utilization rate (corresponding to charge / discharge efficiency) can be set to approximately 94%.

[0059] The crystal structure of a solid electrolyte can be analyzed by XRD analysis. If the solid electrolyte is a sintered body, the sintered body may be pulverized into a powder and then subjected to XRD analysis. The crystal structure of the solid electrolyte can be determined by determining whether or not any of the patterns of the NASCICON type crystal structure are included in the diffraction pattern obtained by such analysis.

[0060] The composition of the solid electrolyte may be determined by performing energy dispersive x-ray spectroscopy (EDS) on the solid electrolyte powder or sintered solid electrolyte body, and the elements contained in the solid electrolyte may be identified by EDS analysis. Alternatively, the elements contained in the solid electrolyte may be analyzed using bulk analysis or surface analysis techniques such as XPS or SIMS.

[0061] The composition of a solid electrolyte may be quantified, for example, by inductively coupled plasma (ICP) analysis. For instance, IPS analysis may be performed on a solid electrolyte powder to analyze the types, content, and molar ratios of elements contained in the solid electrolyte. Alternatively, quantitative analysis of the solid electrolyte may be performed using methods such as X-ray fluorescence (XRF) or atomic absorption spectroscopy (AAS).

[0062] The method for producing the solid electrolyte described above will be explained below.

[0063] First, at least the raw materials for the Na source, Zr source, Si source, and P source are weighed in the desired proportions and mixed. The resulting mixed powder is calcined to produce a calcined body. Then, the obtained calcined body is subjected to final calcination. By doing so, the solid electrolyte of this disclosure can be obtained.

[0064] For example, sodium carbonate (Na) ２ CO ３ Zirconium oxide (ZrO) ２, ammonium dihydrogen phosphate NH ４ H ２ PO ４ , and silicon dioxide SiO ２ Prepare the following: Then, weigh these appropriately and mix them. Next, in an air atmosphere, the resulting mixed powder is calcined at a temperature of 500°C to 800°C for a predetermined time (for example, 1 to 6 hours) to produce a calcined body. Then, the resulting calcined body is fired in an air atmosphere at a temperature of 1000°C to 1300°C for a predetermined time (for example, about 20 hours). By doing so, the solid electrolyte of this disclosure can be obtained.

[0065] [Method for Manufacturing Solid-State Batteries] The above-mentioned solid-state batteries can be manufactured by printing methods such as screen printing, the green sheet method using green sheets, or a combination of these methods. The following will detail the cases in which printing and green sheet methods are employed, but the method is not limited to these methods. In other words, solid-state batteries may be manufactured in accordance with conventional solid-state battery manufacturing methods. Furthermore, the order of description and other chronological matters described below are merely for explanatory purposes and are not necessarily binding.

[0066] (Solid-state battery stacking precursor formation process) In this process, several types of pastes are used as inks, such as paste for the positive electrode layer, paste for the negative electrode layer, paste for the solid electrolyte layer, paste for the positive electrode current collector layer, paste for the negative electrode current collector layer, and paste for the outer layer material. In other words, a solid-state battery stacking precursor with a predetermined structure is formed on a support substrate by applying and drying the paste using a printing method.

[0067] During printing, a solid-state battery stacking precursor corresponding to a predetermined solid-state battery structure can be formed on a substrate by sequentially stacking printed layers with 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 the predetermined pattern, but for example, it may be one or more of the following: screen printing and gravure printing.

[0068] 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 collector layer material, insulating material, and sintering aid, as well as other materials mentioned above, with an organic vehicle in which an organic material is dissolved in a solvent.

[0069] The paste for the positive electrode layer includes, for example, positive electrode active material particles, a solid electrolyte material, an organic material and a solvent, and optionally a sintering aid.

[0070] The paste for the negative electrode layer includes, for example, negative electrode active material particles, a solid electrolyte material, an organic material and a solvent, and optionally a sintering aid.

[0071] The paste for the solid electrolyte layer comprises, for example, a solid electrolyte material, an organic material, and a solvent, and optionally a sintering aid.

[0072] The paste for the positive electrode current collector layer comprises a conductive material, an organic material, and a solvent, and optionally a sintering aid.

[0073] The paste for the negative electrode current collector layer comprises a conductive material, an organic material, and a solvent, and optionally a sintering aid.

[0074] The paste for the outer layer material includes, for example, an insulating material, an organic material, and a solvent, and optionally 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 one or more of the following organic solvents: butyl acetate, N-methylpyrrolidone, toluene, terpineol, and N-methylpyrrolidone.

[0077] In wet mixing, media can be used, specifically the ball mill method or the visco mill method. On the other hand, wet mixing methods that do not use media may also be used, such as the sand mill method, high-pressure homogenizer method, or kneader dispersion method.

[0078] The support substrate is not particularly limited as long as it is a support capable of supporting each paste layer, but for example, it may be a release film with a release treatment applied to one surface. Specifically, a substrate made of a polymer material such as polyethylene terephthalate can be used. If the paste layers are to be subjected to the firing process while remaining on the substrate, the substrate may be one that exhibits heat resistance to the firing temperature.

[0079] Alternatively, a green sheet can be formed from each paste, and the resulting green sheets can be stacked to create a solid-state battery stacking precursor.

[0080] In more detail, the support substrates to which each paste is applied are dried on a hot plate heated to 30°C to 90°C, thereby forming positive electrode layer green sheets, negative electrode layer green sheets, solid electrolyte layer green sheets, positive electrode current collector layer green sheets, negative electrode current collector layer green sheets, and / or outer layer material green sheets, each having a predetermined shape and thickness, on each support substrate (e.g., PET film).

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

[0082] (Firing Process) In the firing process, the solid-state battery stacking precursor is subjected to firing. Although this is merely an example, firing is carried out by removing organic materials by heating in a nitrogen gas atmosphere containing oxygen gas or in air at, for example, 200°C or higher, and then heating in a nitrogen gas atmosphere or in air at, for example, 1000°C to 1300°C. Firing may be carried out while pressurizing the solid-state battery stacking precursor in the stacking direction (and possibly in the stacking direction and perpendicular to the stacking direction).

[0083] Through such firing, a solid-state battery stack is formed, and ultimately, the desired solid-state battery is obtained. The solid-state battery stack contains an electrode layer precursor that can ultimately become an electrode layer, and this electrode layer precursor may contain the above-mentioned electrode active material and solid electrolyte. Therefore, the electrode layer precursor can also be fired at a temperature between 1000°C and 1300°C. The solid electrolyte used here may be the solid electrolyte of the present disclosure described above. Specifically, it is a solid electrolyte having a Nasicone-type crystalline structure containing Na, Zr, Si, P, and O, and represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２ (In the equation, for x, 0 < x < 0.9 or 1.2 < x < 2.0)

[0084] (Process for forming positive and negative terminals) For example, the positive terminal is bonded to the solid battery stack using a conductive adhesive, and the negative terminal is bonded to the solid battery stack using a conductive adhesive. In this way, the positive and negative terminals are attached to the solid battery stack. As a result, the desired solid battery can be obtained.

[0085] The following describes embodiments of this disclosure.

[0086] Examples 1-7, Comparative Examples 1-4 [Preparation of Solid Electrolytes] First, sodium carbonate (Na) ２ CO ３ Zirconium oxide (ZrO) ２ , ammonium dihydrogen phosphate NH ４ H ２ PO ４ , and silicon dioxide SiO ２Prepared the mixture and weighed out the amount of each element (Na, Zr, Si, P, and O) so that its molar amount matched the values ​​shown in the formulas in Table 1. Then, the mixture was sealed in a 500 ml polyethylene poly pot and rotated on a pot stand at 150 rpm for 16 hours to mix the raw materials. Next, it was calcined in an air atmosphere at 500°C for 1 hour and then at 800°C for 6 hours to remove volatile components. Next, it was sealed in a 500 ml polyethylene poly pot with water and φ5 mm pebbles and rotated on a pot stand at 150 rpm for 16 hours to pulverize it. Afterward, the moisture was removed on a hot plate at 120°C. Finally, it was calcined in an air atmosphere at approximately 1200°C for 20 hours to obtain a solid electrolyte powder with the composition shown in Table 1.

[0087] [Evaluation of the crystal structure of solid electrolytes] The solid electrolyte powders obtained in each of Examples 1 to 7 and Comparative Examples 1 to 4 were measured using an XRD (X-ray diffractometer (Bruker D8 ADVANCE (model number))) at 25°C with a scan speed of 4.0° / min and an angle measurement range of 10° to 60°.

[0088] [Fabrication and Performance Evaluation of Solid-State Batteries] Solid-state batteries were fabricated using the solid electrolytes obtained in each of Examples 1 to 7 and Comparative Examples 1 to 4, following the steps outlined below.

[0089] ■Slurry Preparation The following main materials, butyral resin, and alcohol were weighed in a weight ratio of 100:15:140. The butyral resin was dissolved in the alcohol, sealed in a pot together with the main materials and media, rotated on a pot stand, and then the media was removed. Based on the above, the following slurries were prepared. ・Solid electrolyte layer slurry: A solid electrolyte material was used as the main material. ・Positive electrode material layer slurry (corresponding to the positive electrode composite layer slurry): A powder mixture of positive electrode active material, conductive agent, and solid electrolyte material in a weight ratio of 40:10:50 was used as the main material. Na was used as the positive electrode active material. ３ V ２ P ３ O １２ The following was used: • Slurry for the negative electrode material layer (corresponding to the slurry for the negative electrode composite material layer): As the main material, a powder was used, which was a mixture of negative electrode active material, conductive agent, and solid electrolyte material in a weight ratio of 40:10:50. The negative electrode active material was Na３ V ２ P ３ O １２ The following was used. ■Method for producing green sheets Each slurry was applied to polyethylene terephthalate (PET) film using the doctor blade method, dried on a hot plate heated to 40°C, and formed into a sheet to the desired thickness. Then, each green sheet was produced by cutting so that each side length was 25 mm. ■Method for producing laminates Each sheet peeled off from the PET film was subjected to a 1000 kg / cm² load between two SUS plates heated to 60°C. ２ The layers were heat-pressed together under pressure. Next, one positive electrode material layer green sheet was laminated onto one main surface of the solid electrolyte layer, which consisted of five solid electrolyte green sheets, and one negative electrode material layer green sheet was laminated onto the other main surface. Then, the layers were sealed in a polyethylene film container and pressed under isotropic pressure at a water pressure of 180 MPa to produce a laminate. The resulting laminate has a structure in which the positive electrode material layer, solid electrolyte layer, and negative electrode material layer are laminated in this order. ■ Method of firing the laminate The laminate was cut so that each side length was 10 mm and held between two porous setters. Then, 2 kgf / cm ２ A sintered body was produced by firing under pressurized conditions. The firing process involved removing the butyral resin by firing at 500°C in a nitrogen gas atmosphere containing 1% by volume of oxygen, and then firing at 1200°C in a nitrogen gas atmosphere. Subsequently, a Pt layer (platinum layer) to serve as the current collector layer was formed on each of the positive electrode and negative electrode layers by sputtering, and then the fired laminate was dried at 100°C to remove moisture. A solid-state battery was then manufactured by sealing it with an outer casing.

[0090] [Evaluation of Solid-State Batteries 1] Each solid-state battery prepared in Examples 1 to 7 and Comparative Examples 1 to 4 was placed in a constant-temperature bath maintained at 25°C and charged to 3.25V with a current of 40μA, which corresponds to a current of approximately 0.1C relative to the weight of the positive electrode active material. After that, it was held at 3.25V for 5 hours, rested for 3 hours, discharged to 0V with a current of 40μA, and rested for 3 hours. The discharge capacity thereafter was measured, and the charge / discharge efficiency (corresponding to the utilization rate) was calculated from the predetermined capacity and discharge capacity.

[0091] [Evaluation of Solid-State Batteries 2] The solid-state batteries obtained in each of Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated based on the presence or absence of a third solid phase (corresponding to a phase having a different crystal structure from the solid electrolyte and electrode active material) that was altered from the crystal structure of the electrode active material on the electrode active material side. Specifically, the solid-state batteries after charging and discharging were crushed to extract the electrode active material, and the extracted active material was measured using an XRD (X-ray diffractometer) at 25°C with a scan speed of 4.0° / min and an angle measurement range of 10° to 60°.

[0092] The reactivity of the solid electrolyte with respect to the electrode active material was evaluated based on at least one of the above evaluations. In the evaluation, a high reactivity of the solid electrolyte with respect to the electrode active material (i.e., a high degree of degradation of the electrode active material) was indicated as "high". A moderate reactivity of the solid electrolyte with respect to the electrode active material (i.e., a moderate degree of degradation of the electrode active material) was indicated as "medium". A low reactivity of the solid electrolyte with respect to the electrode active material (i.e., a low degree of degradation of the electrode active material) was indicated as "low".

[0093] The reactivity of a solid electrolyte can be evaluated by comparing the diffraction patterns measured from the solid electrolyte powder before and after firing using XRD. If the spectral peaks appearing in the diffraction pattern before firing do not appear in the diffraction pattern after firing, the reactivity is judged to be "high". If a third phase peak that was not present in the spectrum before firing appears in the diffraction pattern after firing, and the width of the spectral peaks in the diffraction pattern widens, the reactivity is judged to be "medium". If the spectral patterns of the diffraction patterns before and after firing are almost the same shape, the reactivity is judged to be "low".

[0094] Table 1 shows the evaluation results of solid-state batteries in Examples 1-7 and Comparative Examples 1-4.

[0095]

[0096] From the results in Table 1 above, when using a solid electrolyte with a NASCON structure (containing Na, Zr, Si, P, and O), by using a solid electrolyte in which the content (molar concentration) of Na (sodium) and P (phosphorus) is set within a predetermined range during firing in the production of a solid battery, the electrode active material (especially Na ３ V２ P ３ O １２ It was found that this relatively reduces the reactivity of the solid electrolyte to ).

[0097] Specifically, the reactivity of the solid electrolyte was evaluated by comparing the diffraction patterns measured from the solid electrolyte powder before and after firing, based on results from XRD and other methods. In Comparative Examples 2 and 3, the spectral peaks that appeared in the diffraction pattern before firing did not appear in the diffraction pattern after firing, so the reactivity was evaluated as "high". On the other hand, in Comparative Examples 1 and 4, a third phase peak that was not present in the spectrum before firing appeared in the diffraction pattern after integral firing, and the width of the spectral peaks in the diffraction pattern broadened, so the reactivity was evaluated as "medium".

[0098] On the other hand, in Examples 3 to 7, the spectra of the diffraction patterns before and after firing were almost the same shape, so the reactivity was evaluated as "low". Furthermore, in Examples 1 and 2, although a third phase peak appeared in the spectrum of the diffraction pattern after integral firing that was not present in the spectrum before integral firing, the width of the peaks in the diffraction pattern spectra was about the same, so the reactivity was evaluated as "low to medium (not including medium)".

[0099] Furthermore, in terms of utilization rate, Examples 1 to 7 achieved a utilization rate (corresponding to charge / discharge efficiency) of over 80%, while Comparative Examples 1 to 4 had a utilization rate of less than 65%.

[0100] From the above, based on Examples 1 to 4, Na is used as the solid electrolyte in the Nasicon structure. ３ Zr ２ Si ２ PO １２ Compared to the case where (Comparative Example 1) is used, the amount of Na in the solid electrolyte (molar concentration) is reduced, resulting in a decrease in the amount of Na used as an electrode active material. ３ V ２ P ３ O １２ It was found that the reactivity of solid electrolytes to [the target substance] can be reduced.

[0101] Furthermore, from Examples 1 to 4, Na was used as the solid electrolyte in the Nasicon structure. ３ Zr ２ Si ２ PO１２ Compared to the case where (Comparative Example 1) is used, if the ratio of the sodium (Na) content to the phosphorus (P) content in the solid electrolyte (Na / P) is greater than 1.2 and less than 3, then the Na as an electrode active material ３ V ２ P ３ O １２ It was found that the reactivity of the same solid electrolyte to [the target substance] could be reduced.

[0102] On the other hand, from Comparative Examples 2-4, Na is used as the solid electrolyte in the Nasicon structure. ３ Zr ２ Si ２ PO １２ Compared to the case where (Comparative Example 1) is used, if the amount of Na in the solid electrolyte is simply relatively reduced, the Na as an electrode active material will be ３ V ２ P ３ O １２ It was found that the reactivity of solid electrolytes to [the substance] cannot be "reduced".

[0103] Specifically, from Comparative Examples 2 to 4, when the ratio of the sodium (Na) content to the phosphorus (P) content in the solid electrolyte (Na / P) is 0.9 or more and 1.2 or less, that is, when the phosphorus (P) content in the solid electrolyte approaches the sodium (Na) content, the Na as an electrode active material ３ V ２ P ３ O １２ It was found that the reactivity of the same solid electrolyte to was actually increased (see Comparative Examples 2-4).

[0104] On the other hand, from Examples 5 to 7, when the ratio of the sodium (Na) content to the phosphorus (P) content in the solid electrolyte (Na / P) is less than 0.9, that is, when the phosphorus (P) content in the solid electrolyte is greater than the sodium (Na) content, the Na as an electrode active material ３ V ２ P ３ O １２ It was found that the reactivity of the solid electrolyte to the substance was low.

[0105] Although not bound by any particular theory, the hexagonal crystal structure allows for the use of Na as an electrode active material during firing in the fabrication of solid-state batteries. ３ V ２ P ３ O １２ It is believed that the reduction in reactivity was achieved because the reaction became less frequent.

[0106] From the above, overall, when using a solid electrolyte with a NASICON structure (containing Na, Zr, Si, P, and O), if the ratio of Na (sodium) content to P (phosphorus) content (Na / P) is greater than 0.3 and less than 0.9, or greater than 1.2 and less than 3, then Na as an electrode active material ３ V ２ P ３ O １２ It was found that the reactivity of the solid electrolyte to the substance could be reduced.

[0107] As is clear from Table 1, when using the solid electrolyte of the following formula, if x in the formula is 0 < x < 0.9 or 1.2 < x < 2.0, then Na as the electrode active material ３ V ２ P ３ O １２ It was found that the reactivity of the solid electrolyte to [Equation 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２

[0108] Furthermore, regarding the battery performance (related to discharge capacity and utilization rate in Table 1), the results are not bound by any particular theory, but during the heat treatment (specifically during firing) in the solid-state battery manufacturing stage, the electrode active material (Na ３ V ２ P ３ O １２ This is understood to be due to the relative reduction in the reactivity of the solid electrolytes of Examples 1 to 7 to the ). By reducing this reactivity (also referred to as a side reaction), changes in the crystal structure of the electrode active material can be suppressed, its function can be suitably maintained, and the deterioration of battery performance can be suitably suppressed.

[0109] Compared to Examples 1 and 2, Examples 3 and 4 showed that when the content of Na, a component of the solid electrolyte, is 2.5 moles or more and 2.7 moles or less, that is, when the ratio of the content of Na (sodium) (molar concentration) to the content of P (phosphorus), a component of the solid electrolyte (Na / P), is 1.7 or more and 2.1 or less, a high utilization rate (corresponding to charge / discharge efficiency) (approximately 94%) is achieved.

[0110] Furthermore, compared to Examples 1 and 2, Examples 5 to 7 showed that when the content of Na, a component of the solid electrolyte, is 1.3 moles or more and 1.7 moles or less, that is, when the ratio of the content of Na (sodium) (molar concentration) to the content of P (phosphorus), a component of the solid electrolyte (Na / P), is 0.5 or more and 0.7 or less, a high utilization rate (corresponding to charge / discharge efficiency) (approximately 94% to 98.5%) is obtained.

[0111] Furthermore, the above electrode active material (Na ３ V ２ P ３ O １２ The effect of reducing the reactivity of the solid electrolyte in Examples 1 to 7 on the electrode layer can be evaluated in terms of the relationship between the electrode active material and the solid electrolyte within the electrode layer. Therefore, it is understood that the above effect can be similarly achieved not only in the relationship between the electrode active material and the solid electrolyte within the electrode layer, but also in the relationship between the solid electrolyte of the solid electrolyte layer adjacent to the electrode layer and the electrode active material within the electrode layer.

[0112] The embodiments described above represent typical examples. Therefore, those skilled in the art will readily understand that the present invention is not limited thereto, and various embodiments are conceivable without altering the essence of the invention.

[0113] Furthermore, the above-described embodiment of the present disclosure includes the following preferred embodiments: <1> A solid electrolyte represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２(wherein x is 0 < x < 0.9 or 1.2 < x < 2.0) <2> The solid electrolyte according to <1>, wherein x is 0.3 ≤ x ≤ 0.7. <3> The solid electrolyte according to <1> or <2>, wherein x is 1.5 ≤ x ≤ 1.7. <4> The solid electrolyte according to any one of <1> to <3>, wherein the Na content is 2.5 moles or more and 2.7 moles or less. <5> The solid electrolyte according to any one of <1> to <4>, wherein the Na content is 1.3 moles or more and 1.7 moles or less. <6> A solid electrolyte having a Nasicone-type crystalline structure containing Na, Zr, Si, P and O, wherein the ratio of the Na content to the P content (Na / P) is greater than 0.3 and less than 0.9, or greater than 1.2 and less than 3. <7> The solid electrolyte according to <6>, wherein the ratio (Na / P) is 0.5 or more and 0.7 or less. <8> A solid electrolyte according to <6> or <7>, wherein the ratio (Na / P) is 1.7 or more and 2.1 or less. <9> A sintered solid battery in which a positive electrode layer containing a positive electrode active material and a solid electrolyte, a solid electrolyte layer containing a solid electrolyte, and a negative electrode layer containing a negative electrode active material and a solid electrolyte are stacked in this order, wherein the solid electrolyte of at least one electrode layer of the positive electrode layer and the negative electrode layer is a solid electrolyte according to any one of <1> to <8>, and at least one of the positive electrode active material and the negative electrode active material is of the general formula Na ３＋ｙ V ２－ｙ (PO ４ ) ３ A solid battery, wherein (wherein 0 ≤ y ≤ 1) <10> The solid electrolyte of the solid electrolyte layer is the solid electrolyte described in any of <1> to <8>, and the Na content of the solid electrolyte of the electrode layer is less than the Na content of the solid electrolyte of the solid electrolyte layer, as described in <9>. <11> A method for manufacturing a solid battery, comprising at least firing an electrode layer precursor containing an electrode active material and a solid electrolyte at 1000°C or higher and 1300°C or lower, wherein the solid electrolyte is a solid electrolyte having a Nasicone-type crystalline structure containing Na, Zr, Si, P and O, and represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O１２ (In the equation, for x, 0 < x < 0.9 or 1.2 < x < 2.0)

[0114] The solid-state battery of the present invention can be used in a variety of fields where energy storage is anticipated. While these are merely examples, the solid-state battery of the present invention can be used in the electrical, information, and communication fields where mobile devices are used (e.g., the electrical and electronic equipment field or mobile device field, including small electronic devices such as mobile phones, smartphones, laptops and digital cameras, activity trackers, arm computers, electronic paper, RFID tags, card-type electronic money, and smartwatches), household and small-scale industrial applications (e.g., power tools, golf carts, household, caregiving, and industrial robots), large-scale industrial applications (e.g., forklifts, elevators, and port cranes), transportation systems (e.g., hybrid vehicles, electric vehicles, buses, trains, electric-assist bicycles, electric motorcycles, etc.), power grid applications (e.g., various power generation, road conditioners, smart grids, and general household energy storage systems), medical applications (medical equipment such as earphones and hearing aids), pharmaceutical applications (medication management systems, etc.), as well as IoT, space, and deep-sea applications (e.g., space probes, submersible research vessels, etc.).

Claims

1. A solid electrolyte represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２ (In the equation, for x, 0 < x < 0.9 or 1.2 < x < 2.0) 2. The solid electrolyte according to claim 1, wherein x satisfies 0.3 ≤ x ≤ 0.

7.

3. The solid electrolyte according to claim 1 or 2, wherein for x, 1.5 ≤ x ≤ 1.

7.

4. The solid electrolyte according to any one of claims 1 to 3, wherein the Na content is 2.5 moles or more and 2.7 moles or less.

5. The solid electrolyte according to any one of claims 1 to 4, wherein the Na content is 1.3 moles or more and 1.7 moles or less.

6. A solid electrolyte having a Nasicone-type crystalline structure containing Na, Zr, Si, P, and O, wherein the ratio of the Na content to the P content (Na / P) is greater than 0.3 and less than 0.9, or greater than 1.2 and less than 3.

7. The solid electrolyte according to claim 6, wherein the ratio (Na / P) is 0.5 or more and 0.7 or less.

8. The solid electrolyte according to claim 6 or 7, wherein the ratio (Na / P) is 1.7 or more and 2.1 or less.

9. A sintered solid battery in which a positive electrode layer containing a positive electrode active material and a solid electrolyte, a solid electrolyte layer containing a solid electrolyte, and a negative electrode layer containing a negative electrode active material and a solid electrolyte are laminated in this order, wherein the solid electrolyte in at least one of the electrode layers of the positive electrode layer and the negative electrode layer is the solid electrolyte according to any one of claims 1 to 8, and at least one of the positive electrode active material and the negative electrode active material is of the general formula Na ３＋ｙ V ２－ｙ (PO ４ ) ３ (where 0 ≦ y ≦ 1), a solid battery.

10. The solid battery according to claim 9, wherein the solid electrolyte of the solid electrolyte layer is the solid electrolyte according to any one of claims 1 to 8, and the Na content of the solid electrolyte of the electrode layer is less than the Na content of the solid electrolyte of the solid electrolyte layer.

11. A method for manufacturing a solid battery, comprising at least firing an electrode layer precursor containing an electrode active material and a solid electrolyte at a temperature of 1000°C to 1300°C, wherein the solid electrolyte has a Nasicone-type crystalline structure containing Na, Zr, Si, P, and O, and is represented by the following general formula: [Formula 1] Na １＋ｘ Zr ２ Si ｘ P ３－ｘ O １２ (In the equation, for x, 0 < x < 0.9 or 1.2 < x < 2.0)

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