Solid electrolyte and solid-state battery

Abstract

Provided is a solid electrolyte having a NASICON-type crystal structure and containing sodium (Na), zirconium (Zr), silicon (Si), phosphorus (P), and oxygen (O). A portion of Zr is substituted by one or more elements selected from the group consisting of vanadium (V), niobium (Nb), tantalum (Ta), bismuth (Bi), tungsten (W), and molybdenum (Mo).

Description

Solid electrolyte and solid battery

[0001] The present disclosure relates to a solid electrolyte and a solid battery.

[0002] Conventionally, secondary batteries capable of repeated charging and discharging have been used in various applications. For example, secondary batteries are used as power sources for electronic devices such as smartphones and notebook computers.

[0003] In secondary batteries, a liquid electrolyte is generally used as a medium for ion movement contributing to charging and discharging. That is, a so-called electrolytic solution is used in secondary batteries. However, generally, in such secondary batteries, safety is required in terms of preventing leakage of the electrolytic solution. In addition, since organic solvents and the like used in the electrolytic solution are flammable substances, safety is also required in that regard.

[0004] Therefore, research has been underway on solid batteries using solid electrolytes instead of electrolytic solutions.

[0005] J. Alamo, Solid State Ionics, Vol. 63-65 (1993) 547-561

[0006] Japanese Patent No. 3281098, Japanese Patent Application Laid-Open No. 2015-536019

[0007] The present inventor has noticed that there are problems to be overcome in conventional solid electrolytes and solid batteries using such solid electrolytes, and has newly found the necessity of taking measures therefor. Specifically, the following problems have been found.

[0008] In Non-Patent Document 1 and Patent Document 1, as a solid electrolyte having excellent ionic conductivity, a solid electrolyte having a NASICON-type crystal structure [Na ２ , ３ , ３－ｘ , ２ , １２ , ２ , １２ , ｘ Zr ２ Si ｘ P ３－ｘ O １２ (where 0 ≤ x ≤ 3)] is disclosed. Further, in Patent Document 2, Na ３ Zr ２ Si ２ PO １２In a NASICON-type solid electrolyte having the above composition, a solid electrolyte has been disclosed in which a portion of the tetravalent element Zr is replaced with an element with a lower valency. In this regard, in order to improve the capacity and charging speed of solid batteries, there is still a need for solid electrolytes with high ionic conductivity.

[0009] This disclosure has been made in view of the above issues. Specifically, the primary object of this disclosure is to provide a solid electrolyte having higher ionic conductivity, and a solid battery comprising said solid electrolyte.

[0010] To achieve the above objective, a solid electrolyte according to one embodiment of the present disclosure has a NASICON-type crystal structure and comprises Na (sodium), Zr (zirconium), Si (silicon), P (phosphorus), and O (oxygen), wherein a portion of Zr is substituted with one or more elements selected from the group consisting of V (vanadium), Nb (niobium), Ta (tantalum), Bi (bismuth), W (tungsten), and Mo (molybdenum).

[0011] Furthermore, a solid-state battery according to one embodiment of the present disclosure comprises a sintered body including a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer, wherein one or more of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer contain the above-mentioned solid electrolyte, and either the positive electrode active material or the negative electrode active material has the following compositional formula: Na ３＋ｘ V ２－ｘ (PO ４ ) ３ (II) An active material represented by the formula (wherein 0 ≤ x ≤ 1).

[0012] A solid electrolyte according to one embodiment of the present disclosure, and a solid battery comprising the solid electrolyte, may have higher ionic conductivity.

[0013] The solid electrolyte and solid battery of this disclosure will be described in detail below.

[0014] [Solid Electrolyte] The solid electrolyte of this disclosure has a NASICON-type crystal structure and contains Na (sodium), Zr (zirconium), Si (silicon), P (phosphorus), and O (oxygen). A portion of the Zr contained in the crystal phase is substituted with one or more elements selected from the group consisting of V (vanadium), Nb (niobium), Ta (tantalum), Bi (bismuth), W (tungsten), and Mo (molybdenum).

[0015] In this specification, "having a NASICON-type crystal structure" means that the main crystalline phase of the solid electrolyte is a NASICON-type crystalline phase. The crystalline phase of the solid electrolyte may be identified, for example, by obtaining a diffraction pattern obtained by XRD measurement. The proportion of the NASICON-type crystalline phase may be determined from the peak intensity ratio originating from the NASICON-type crystalline phase included in the XRD diffraction pattern.

[0016] The inventors have newly discovered that the solid electrolyte of this disclosure, having a NASICON-type crystal structure and further having a portion of Zr substituted with one or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo, exhibits higher ionic conductivity compared to solid electrolytes in which a portion of Zr is not substituted. Generally, when the content (molar ratio) of Na in a NASICON-type solid electrolyte decreases, the ionic conductivity may decrease. In the solid electrolyte of this disclosure as well, when a portion of Zr is substituted with a predetermined element, the ratio of Na may be reduced for charge compensation. However, surprisingly, it has been found that the solid electrolyte of this disclosure, when a portion of Zr is substituted with a predetermined element, can exhibit high ionic conductivity even when the Na content is lower than that of solid electrolytes in which a portion of Zr is not substituted with a predetermined element.

[0017] Although not bound by any particular theory, the solid electrolyte of this disclosure is thought to exhibit high ionic conductivity because the ionic conduction of Na ions within the crystal structure of the solid electrolyte is facilitated by substituting a portion of Zr with an element that has a higher electronegativity than Zr. More specifically, it is thought that the effect of improving ionic conductivity by the highly electronegative substitution element suppresses the decrease in ionic conductivity due to a decrease in Na content, resulting in a solid electrolyte exhibiting excellent ionic conductivity.

[0018] Furthermore, according to the solid electrolyte of this disclosure in which a portion of Zr is substituted with the aforementioned predetermined element, the composition formula is as follows: Na ３＋ｘ V ２－ｘ (PO ４ ) ３ (II) We have newly discovered that when fired together with an active material represented by the formula (wherein 0 ≤ x ≤ 1) (hereinafter also referred to as NVP), a good interface can be formed between the solid electrolyte and the active material. Generally, in solid electrolytes having a NASICON-type crystal structure and containing Na, Zr, Si, P, and O, when fired together with NVP, a change in the crystal structure may occur at the interface between the solid electrolyte and NVP due to side reactions. This change in crystal structure may lead to an increase in interfacial resistance, which may reduce the battery performance of the solid battery. On the other hand, with the solid electrolyte of this disclosure in which a portion of Zr is substituted with a predetermined element, side reactions can be suppressed when fired together with NVP. As a result, a good interface can be formed between the solid electrolyte and NVP, and a solid battery with suitable battery performance can be provided. In other words, according to this disclosure, a solid electrolyte with excellent ionic conductivity and capable of forming a good interface with the active material can be provided.

[0019] While not bound by any particular theory, the aforementioned effect is thought to be influenced by the fact that the amount of Na involved in the side reaction with NVP is reduced because some of the Zr is substituted with a predetermined element.

[0020] The valency of the element substituting for part of Zr may be 5 or greater. For example, one or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo that are substituting for part of Zr may be pentavalent or hexavalent. More specifically, part of Zr may be substituted for at least one of the following: one or more pentavalent elements selected from the group consisting of V, Nb, Ta, and Bi, and one or more hexavalent elements selected from the group consisting of W and Mo.

[0021] In solid electrolytes substituted with elements with a high valence of 5 or higher, the Na content may decrease to compensate for the charge of the solid electrolyte. However, according to this disclosure, by selecting one or more elements from the group consisting of V, Nb, Ta, Bi, W, and Mo, which have higher electronegativity than Zr, a solid electrolyte with suitable ionic conductivity can be provided despite the decrease in Na content.

[0022] In one embodiment, a portion of Zr may be substituted with two or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo. This allows for a solid electrolyte with even better ionic conductivity compared to the case where a portion of Zr is substituted with one element. Preferably, a portion of Zr may be substituted with two or more elements, each containing at least one or both of Wo and Mo. In short, a portion of Zr in a solid electrolyte may be substituted with two or more elements, each containing at least one hexavalent element. Specifically, a portion of Zr is substituted with two or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo, and it is preferable that these two or more elements contain at least one or more elements selected from the group consisting of W and Mo. This makes it possible to obtain a solid electrolyte with particularly excellent ionic conductivity.

[0023] The solid electrolyte of this disclosure is given by the following general formula (I): Na ３－（ａ＋２ｂ） Zr ２－ａ－ｂ M1 ａ M2 ｂ Si ２ P １ O １２(I) The composition may be represented by the formula (wherein M1 is one or more elements selected from the group consisting of V, Nb, Ta, and Bi, and M2 is one or more elements selected from the group consisting of W and Mo). Furthermore, the values ​​of a, b, and a+2b in the formula may be in the range of 0 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.25, and 0 < (a+2b) ≤ 1. By having a composition formula within the above numerical ranges, a solid electrolyte more suitable in terms of ionic conductivity can be provided. If M1 consists of multiple elements, their content ratios may be the same or different from each other. Similarly, if M2 consists of multiple elements, their content ratios may be the same or different from each other.

[0024] For example, if the solid electrolyte represented by general formula (I) contains M1 but does not contain M2 (i.e., b = 0), the range of a in the formula may be 0.05 ≤ a ≤ 0.3. This range allows for the provision of a solid electrolyte that is more suitable in terms of ionic conductivity.

[0025] Furthermore, if the solid electrolyte represented by general formula (I) does not contain M1 but does contain M2 (i.e., a = 0), the range of b in the formula may be 0.05 ≤ b ≤ 0.2. This range allows for the provision of a solid electrolyte that is more suitable in terms of ionic conductivity.

[0026] According to the solid electrolyte described above, side reactions with NVP during sintering are suppressed, and a good interface can be formed. This suppresses the increase in resistance at the interface between the active material and the solid electrolyte. Therefore, the solid electrolyte of this disclosure may have advantages not only in having high ionic conductivity due to a portion of Zr being substituted with a predetermined element, but also in being able to suppress the increase in interfacial resistance. When the amount of Zr substituted with the predetermined element is small and the Na content is high, the ionic conductivity tends to improve. On the other hand, when the amount of Zr substituted with the predetermined element is high and the Na content is low, the effect of suppressing side reactions with NVP tends to improve.

[0027] When considering both ionic conductivity and suppression of side reactions, the value of a+2b in general formula (I) is preferably 0.1 < (a+2b) < 0.5, more preferably 0.15 ≤ (a+2b) ≤ 0.4, and particularly preferably 0.15 ≤ (a+2b) ≤ 0.25. By having the value of a+2b within the above range, a solid electrolyte can be provided that has a good balance of both ionic conductivity and suppression of side reactions.

[0028] The crystal structure of a solid electrolyte may be analyzed by X-ray diffraction (XRD). For example, if the solid electrolyte is a sintered body, the sintered body may be pulverized into a powder and XRD analysis may be performed. The crystal structure of the solid electrolyte can be determined by determining whether or not any of the patterns of NASICON-type crystal structures are included in the diffraction pattern obtained by this analysis.

[0029] 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, 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 X-ray photoelectron spectroscopy (XPS) or secondary ion mass spectrometry (SIMS).

[0030] The composition of a solid electrolyte may be quantified, for example, by compositional analysis using inductively coupled plasma (ICP) spectrometer. 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 X-ray fluorescence (XRF) or atomic absorption spectroscopy (AAS).

[0031] The valence of elements in a solid electrolyte can be determined, for example, using X-ray absorption fine structure analysis (XFAS).

[0032] (Method for manufacturing solid electrolytes) Next, an example of a method for manufacturing solid electrolytes will be described.

[0033] First, raw materials for the Na source, raw materials for the Zr source, raw materials for the element to be partially substituted for Zr, and raw materials for the P source are weighed in the desired proportions and mixed. A calcined body is prepared by calcining the resulting mixed powder. A solid electrolyte can be obtained by calcining the obtained calcined body.

[0034] [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.

[0035] The distinguishing feature of the solid-state battery in this disclosure relates to the fact that the solid-state battery includes the solid electrolyte described above. Below, in order to understand the overall structure of the solid-state battery, the basic configuration of the solid-state battery in 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 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 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 and negative electrode layers having such configurations can also be referred to as "composite positive electrode" and "composite negative electrode," respectively.

[0040] 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 layer of the positive and negative electrode layers is 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 through the movement of sodium ions between the positive and negative electrode layers via a solid electrolyte.

[0041] 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 one or more 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. For example, in the case of a sodium-containing phosphate compound, 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 One or more selected from the group consisting of the following are examples. If the positive electrode layer and / or solid electrolyte layer contains the solid electrolyte of this disclosure, the positive electrode active material has the following compositional formula: Na ３＋ｘ V ２－ｘ (PO ４ ) ３ (II) It is particularly 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 provides a solid-state battery that is suitable in terms of battery performance.

[0042] 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.

[0043] (Negative Electrode Active Material) The negative electrode active material contained in the negative electrode layer may be a known material capable of intercalating and deintercalating sodium ions. For example, examples of negative electrode active materials include oxides containing one or more elements selected from the group consisting of titanium (Ti), silicon (Si), tin (Sn), chromium (Cr), iron (Fe), niobium (Nb), and molybdenum (Mo), carbon materials such as graphite, sodium-containing phosphate compounds having a nasicone-type structure, sodium-containing phosphate compounds having an olivine-type structure, and sodium-containing oxides having a spinel-type structure. When the negative electrode layer and / or solid electrolyte layer contains the solid electrolyte described above in this disclosure, the negative electrode active material has the following compositional formula: Na ３＋ｘ V ２－ｘ (PO ４ ) ３ (II) It is particularly preferable that the material is represented by the formula (wherein 0 ≤ x ≤ 1) (hereinafter also referred to as NVP). When the negative electrode active material is NVP, a good interface can be formed between the NVP and the solid electrolyte during integral firing. This provides a solid-state battery that is suitable in terms of battery performance.

[0044] 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 one or more selected from the group consisting of metallic materials such as silver, palladium, gold, platinum, aluminum, copper, and nickel, as well as carbon.

[0045] Furthermore, the positive electrode layer and / or negative electrode layer may contain a sintering aid. Examples of sintering aids include one or more selected from the group consisting of lithium oxide, sodium oxide, potassium oxide, boron oxide, silicon oxide, bismuth oxide, and phosphorus oxide.

[0046] In addition, in a solid-state battery, the positive electrode layer and the negative electrode layer may be made of the same material.

[0047] 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.

[0048] (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.

[0049] 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.

[0050] 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 or the negative electrode layer.

[0051] As mentioned above, positive electrode current collector layers and negative electrode current collector layers are not essential for 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 this disclosure may be a solid-state battery without current collector layers.

[0052] (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.

[0053] 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.

[0054] 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.

[0055] In addition to being suitable in terms of ionic conductivity, the solid electrolyte of this disclosure can suppress undesirable side reactions with the active material NVP during firing and form a good interface. For this reason, it is more preferable that the solid electrolyte of this disclosure is included in at least the electrode layer containing NVP. By including the solid electrolyte of this disclosure in the electrode layer, a good interface between NVP and the solid electrolyte can be formed over a wider area. In other words, a good interface region between NVP and the solid electrolyte of this disclosure can be formed over a wider area. This makes it possible to obtain a solid-state battery with superior battery performance.

[0056] In one embodiment, the solid electrolyte of the present disclosure may be contained in both the electrode layer containing NVP as an active material and the solid electrolyte layer. The solid electrolytes contained in the electrode layer and the solid electrolyte layer may have the same composition or different compositions. Preferably, the solid electrolyte contained in the electrode layer containing NVP may have a greater amount of substitution of a predetermined element in Zr than the solid electrolyte contained in the solid electrolyte layer.

[0057] More specifically, the solid electrolyte is given by the following general formula (I): Na ３－（ａ＋２ｂ） Zr ２－ａ－ｂ M1 ａ M2 ｂ Si ２ P １ O １２ (I) In the case where the formula is expressed as follows (wherein M1 is one or more elements selected from the group consisting of V, Nb, Ta, and Bi, and M2 is one or more elements selected from the group consisting of W and Mo, with 0 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.25, and 0 < (a + 2b) ≤ 1), the value of a + 2b of the solid electrolyte contained in the electrode layer containing NVP may be greater than the value of a + 2b of the solid electrolyte contained in the solid electrolyte layer.

[0058] As described above, the solid electrolyte of this disclosure tends to have a greater suppression effect on side reactions with NVP during firing as the amount of substitution increases (i.e., the value of (a + 2b) in general formula (I) is larger). On the other hand, the ionic conductivity tends to increase as the amount of substitution decreases. Therefore, by including a solid electrolyte with a high amount of substitution in the electrode layer, where there is a lot of contact between the solid electrolyte and NVP, a suitable interface can be formed between the NVP and the solid electrolyte, and the battery performance of the solid battery can be improved. Furthermore, in the solid electrolyte layer, where there is less contact between the solid electrolyte and NVP compared to the electrode layer, the ionic conductivity can be improved by including a solid electrolyte with a low amount of substitution. As a result, a solid battery that is more suitable in terms of ionic conductivity and battery performance can be provided.

[0059] 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.

[0060] Examples of solid electrolytes different from those disclosed herein include oxides having a perovskite structure, oxides having a garnet-type or garnet-type-like structure, etc. Examples of sodium-containing phosphate compounds having a nasicone structure include Na ｘ M ｙ (PO ４ ) ３ Examples include (1 ≤ x ≤ 2, 1 ≤ y ≤ 2, and M is one or more elements selected from the group consisting of Ti, Ge, Al, Ga, and Zr).

[0061] (Method for Manufacturing Solid-State Batteries) Solid-state batteries may be manufactured in accordance with conventional methods for manufacturing solid-state batteries (therefore, the raw materials such as organic binders, solvents, and optional additives described below may be those used in the manufacture of known solid-state batteries). Below, for the sake of better understanding of this disclosure, one manufacturing method will be described as an example, but this disclosure is not limited to this method. Furthermore, the order of description and other chronological matters below are merely for the sake of explanation and are not necessarily binding.

[0062] - A slurry is prepared by mixing a solid electrolyte, an organic binder, a solvent, and any additives. Then, a sheet containing the solid electrolyte is formed from the prepared slurry by firing. - A paste for the positive electrode is prepared by mixing a positive electrode active material, a solid electrolyte, a conductive material, an organic binder, a solvent, and any additives. Similarly, a paste for the negative electrode is prepared by mixing a negative electrode active material, a solid electrolyte, a conductive material, an organic binder, a solvent, and any additives. - The paste for the positive electrode is printed on the sheet, and a current collector layer and / or negative layer is printed as needed. Similarly, the paste for the negative electrode is printed on the sheet, and a current collector layer and / or negative layer is printed as needed. - A laminate is obtained by alternately stacking sheets printed with the positive electrode paste and sheets printed with the negative electrode paste. The outermost layer (top and / or bottom layer) of the laminate may be a solid electrolyte layer, an insulating layer, or an electrode layer. - After the laminate is crimped together, it is cut to a predetermined size. The resulting cut laminate is degreased and then fired. This yields a fired laminate. Alternatively, the laminate may be degreased and fired before cutting, and then cut.

[0063] The embodiments of this disclosure have been described above, but these are merely typical examples. Therefore, those skilled in the art will easily understand that this disclosure is not limited thereto, and various embodiments are conceivable without altering the essence of this disclosure.

[0064] Furthermore, the above-described embodiment of the present disclosure encompasses the following preferred embodiments: First Embodiment: A solid electrolyte having a NASICON-type crystal structure, comprising Na (sodium), Zr (zirconium), Si (silicon), P (phosphorus), and O (oxygen), wherein a portion of Zr is substituted with one or more elements selected from the group consisting of V (vanadium), Nb (niobium), Ta (tantalum), Bi (bismuth), W (tungsten), and Mo (molybdenum). Second Embodiment: The solid electrolyte according to the first embodiment, wherein the valence of the element substituted for a portion of Zr is 5 or higher. Third Embodiment: The solid electrolyte having the following general formula: Na ３－（ａ＋２ｂ） Zr ２－ａ－ｂM1 ａ M2 ｂ Si ２ P １ O １２ A solid electrolyte according to the first or second embodiment, represented by (I) (wherein M1 is one or more elements selected from the group consisting of V, Nb, Ta, and Bi, and M2 is one or more elements selected from the group consisting of W and Mo, with 0 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.25, and 0 < (a + 2b) ≤ 1). A fourth embodiment: A solid electrolyte according to the third embodiment, wherein in the general formula (I), 0.05 ≤ a ≤ 0.3 and b = 0. A fifth embodiment: A solid electrolyte according to the third embodiment, wherein in the general formula (I), a = 0 and 0.05 ≤ b ≤ 0.2. A sixth embodiment: A solid electrolyte according to any one of the third to fifth embodiments, wherein in the general formula (I), 0.15 ≤ (a + 2b) ≤ 0.25. Seventh aspect: A solid electrolyte according to any one of the first to third aspects, wherein a portion of Zr is substituted with two or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo, and the two or more elements include at least one or more elements selected from the group consisting of W and Mo. Eighth aspect: A sintered body comprising a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer, wherein one or more of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer contain the solid electrolyte according to any one of the first to seventh aspects, and either the positive electrode active material or the negative electrode active material has the following compositional formula: Na ３＋ｘ V ２－ｘ (PO ４ ) ３ (II) A solid-state battery, wherein the active material is represented by the formula (wherein 0 ≤ x ≤ 1). Ninth aspect: The solid-state battery according to the eighth aspect, wherein at least one of the positive electrode layer and the negative electrode layer comprises the solid electrolyte and the active material. Tenth aspect: At least one of the positive electrode layer and the negative electrode layer, and the solid electrolyte layer, comprises the solid electrolyte, wherein the solid electrolyte is given by the following general formula: Na ３－（ａ＋２ｂ） Zr ２－ａ－ｂ M1 ａ M2 ｂ Si ２ P１ O １２ (I) (where M1 is one or more elements selected from the group consisting of V, Nb, Ta, and Bi, M2 is one or more elements selected from the group consisting of W and Mo, 0 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.25, 0 < (a + 2b) ≦ 1), and the value of a + 2b of the solid electrolyte contained in at least one of the positive electrode layer and the negative electrode layer is larger than the value of a + 2b of the solid electrolyte contained in the solid electrolyte layer. The solid-state battery according to the eighth or ninth aspect.

[0065] An experimental test was conducted according to the present disclosure.

[0066] (Synthesis of solid electrolyte powder) As raw materials for the solid electrolyte, sodium carbonate (Na ２ CO ３ ), zirconium oxide (ZrO ２ ), ammonium dihydrogen phosphate (NH ４ H ２ PO ４ ), and silicon oxide (SiO ２ ), as well as vanadium oxide (V ２ O ５ ), bismuth oxide (Bi ２ O ３ ), niobium oxide (Nb ２ O ５ ), tantalum oxide (Ta ２ O ５ ), tungsten oxide (WO ３ ), and / or molybdenum oxide (MoO ２ ) were used. These raw materials were appropriately weighed so that a solid electrolyte having the molar ratio shown in Table 1 was obtained, enclosed in a 500 ml polyethylene polypot, and rotated on a pot stand at about 150 rpm for 16 hours to mix the raw materials.

[0067] The resulting mixture was calcined in an air atmosphere at approximately 500°C for 1 hour, and then at approximately 800°C for 6 hours to remove volatile components. Next, it was sealed in a 500 ml polyethylene poly pot with water and pebbles approximately 5 mm in diameter, and crushed by rotating it on a pot stand at approximately 150 rpm for 16 hours. After that, the moisture in the crushed material was removed on a hot plate at approximately 120°C. After moisture removal, it was calcined in an air atmosphere at approximately 900 to approximately 1200°C for 20 hours to obtain solid electrolyte powders with various compositions.

[0068] (Evaluation of the crystal structure of solid electrolytes) The crystal structure was measured using an X-ray diffractometer (Brker D8 ADVANCE). The measurement was performed on the solid electrolyte powder under the conditions of 25°C, a scan speed of 4.0°C / min, and a measurement angle range of 10°C to 60°C. As a result of the analysis, peaks corresponding to the diffraction pattern of the NASICON type crystal structure were confirmed for all solid electrolytes shown in Table 1.

[0069] (Evaluation of ionic conductivity of solid electrolytes) The ionic conductivity of the solid electrolyte powder was measured as follows.

[0070] - Preparation of sintered tablets: Solid electrolyte powder, butyral resin, and alcohol were thoroughly mixed in a weight ratio of 98:15:140. The alcohol was then removed on a hot plate at 80°C to obtain solid electrolyte powder coated with butyral resin, which served as a binder. Next, the solid electrolyte powder was pressed at 90 MPa using a tablet molding machine to form tablets. The obtained tablets were sandwiched between two porous setters to produce a sintered body. For firing, the butyral resin was removed by firing at 500°C, followed by firing in an air atmosphere at a temperature of 900 to 1300°C.

[0071] - Ion conductivity measurement: A Pt (platinum) layer, which serves as the current collector layer, was formed on both sides of a sintered tablet by sputtering. The sintered tablet was then dried at 100°C to remove moisture and sealed in a 2032 type coin cell. The ionic conductivity was calculated by measuring the AC impedance of the sealed coin cell. A frequency response analyzer (FRA) (Solartron, 1260A) was used for AC impedance measurement. Measurements were performed under conditions of a frequency range of 0.1 to 1 MHz, an amplitude of ±10 mV, and a temperature of 25°C. The ionic conductivity σ was calculated from the resistance (sum of particle and grain boundary resistance) of each solid electrolyte obtained from the cole-cole plot obtained from the AC impedance measurement, using the following equation (III): σ = (t / A) × (1 / R) (III) (wherein t: thickness of the sample, A: area of ​​the electrode, R: resistance of the solid electrolyte).

[0072] (Fabrication and evaluation of solid-state batteries) Solid-state batteries containing the solid electrolyte obtained by the method described above were fabricated according to the following procedure.

[0073] - 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, and rotated on a pot rack. After removing the media, the following slurries were prepared. - Solid Electrolyte Slurry: A solid electrolyte was used as the main material. - Cathode Slurry: A powder mixture of cathode active material, conductive agent, and solid electrolyte in a weight ratio of 40:10:50 was used as the main material. Na was used as the cathode active material. ３ V ２ (PO ４ ) ３ Ag was used as the conductive material, and the solid electrolyte was prepared by the method described above. • Negative electrode slurry: As the main material, a powder was used, which was a mixture of negative electrode active material, conductive agent, and solid electrolyte in a weight ratio of 40:10:50. The negative electrode active material was Na ３ V ２ (PO ４ ) ３ Carbon black was used as the conductive material, and the same solid electrolyte as in the positive electrode slurry was used as the solid electrolyte.

[0074] - Preparation of the green sheet: Using the doctor blade method, each slurry was coated onto a polyethylene terephthalate (PET) film, dried on a hot plate heated to 40°C, and formed into a sheet to the desired thickness. Then, it was cut into 25 mm x 25 mm pieces to produce sheets.

[0075] - Fabrication of the laminate: The sheet peeled from the PET film is subjected to a pressure of 1000 kgf / cm using two SUS plates heated to 60°C. ２ The sheets were heat-sealed at a pressure of 180 MPa. Next, the heat-sealed sheets were sealed in a polyethylene film container and pressed under isotropic pressure at a water pressure of 180 MPa to produce a laminate. The laminate consisted of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. A positive electrode layer consisting of one positive electrode green sheet was laminated to one side of a solid electrolyte layer consisting of five solid electrolyte green sheets, and a negative electrode layer consisting of one negative electrode sheet was laminated to one side of the solid electrolyte layer opposite to the positive electrode layer.

[0076] - Firing of the laminate - The laminate is cut into 10 mm x 10 mm pieces, sandwiched between two porous setters, and then fired at 2 kgf / cm². ２ A sintered body was produced by firing under pressurized conditions. Specifically, the process was carried out at a temperature of 500°C in a nitrogen gas atmosphere containing 1 volume% oxygen to remove the butyral resin, and then fired at a temperature of 1000°C in a nitrogen gas atmosphere.

[0077] - Fabrication of the solid-state battery: A Pt layer, which will serve as the current collector layer, was formed on the positive and negative electrode layers by sputtering. The sintered body was then dried at 100°C to remove moisture, and the solid-state battery was fabricated by sealing it with a 2032 type coin cell.

[0078] (Evaluation of the reactivity between the active material and the solid electrolyte) The solid electrolyte was extracted from the solid-state battery and pulverized to obtain solid electrolyte powder. The obtained solid electrolyte powder was subjected to XRD analysis using an XRD instrument (Brker, D8 ADVANCE) to obtain the diffraction pattern of the solid electrolyte. The reactivity between the active material and the solid electrolyte was evaluated by comparing the diffraction pattern obtained from the solid electrolyte powder extracted from the solid-state battery with the diffraction pattern of the solid electrolyte powder used as the material for the solid-state battery before integral firing, and by determining the change in crystal structure before and after integral firing.

[0079] As an evaluation criterion, if a peak that appeared in the diffraction pattern before firing did not appear in the diffraction pattern after firing, it was evaluated as "high" reactivity, indicating that the crystal structure had changed significantly due to firing. Furthermore, if a third phase peak that was not present in the diffraction pattern before firing appeared in the diffraction pattern after firing, and / or if the peak width in the diffraction pattern after firing expanded by a predetermined value compared to the peak width in the diffraction pattern before firing, it was evaluated as "medium" reactivity, indicating that there had been a slight change in the crystal structure before and after firing. In addition, if the diffraction patterns before and after firing were almost the same shape, it was evaluated as "low" reactivity, indicating that the change in crystal structure before and after firing was small. Products with "high" reactivity were rejected, and products with "medium" or "low" reactivity were accepted.

[0080] Table 1 shows the evaluation results of solid-state batteries for Examples 1 to 25 and Comparative Examples 1 to 5. In Table 1, (a + 2b) refers to the prepared solid electrolyte as given by the following general formula (I): Na ３－（ａ＋２ｂ） Zr ２－ａ－ｂ M1 ａ M2 ｂ Si ２ P １ O １２ (I) The value of a + 2b when expressed as (wherein M1 is one or more elements selected from the group consisting of V, Nb, Ta, and Bi, and M2 is one or more elements selected from the group consisting of W and Mo).

[0081]

[0082] According to the results in Table 1, the solid electrolytes of Examples 1 to 25, which have a NASICON-type crystal structure and contain Na, Zr, Si, P, and O, with a portion of Zr substituted with one or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo, were found to exhibit higher ionic conductivity compared to the solid electrolytes of Comparative Examples 1 to 5, in which Zr was not substituted. Surprisingly, the solid electrolytes of Examples 1 to 25 showed high ionic conductivity despite a decrease in the Na content in the solid electrolyte due to the substitution of a portion of Zr. From these results, it was found that a solid electrolyte exhibiting higher ionic conductivity can be provided by substituting a portion of Zr with a predetermined element. Therefore, it was confirmed that a solid electrolyte with higher ionic conductivity can be provided according to this disclosure.

[0083] (Evaluation of Solid-State Batteries) The solid-state batteries were 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 per gram of positive electrode active material. After holding at 3.25V for 5 hours, they were left to rest for 3 hours. Next, they were discharged to 0V with a current of 40μA and left to rest for 3 hours. After that, two charge-discharge cycles were performed at a rate of 0.01C. Table 2 shows the discharge capacity and Coulomb efficiency at a rate of 0.01C for the solid-state batteries of Comparative Example 1, Examples 1-3, 5-7, 10, 12-14, 16, 21-23, and 25.

[0084]

[0085] According to the results in Table 2, the solid-state battery of Comparative Example 1, which contained a solid electrolyte in which part of Zr was not substituted, showed high reactivity with NVP. On the other hand, the solid-state batteries of Examples 1-3, 5-7, 10, 12-14, 16, 21-23, and 25, which contained a solid electrolyte in which part of Zr was substituted with one or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo, all showed "medium" or "low" reactivity with NVP. From this, it was found that even when the solid electrolyte of this disclosure contains NVP as an active material, the side reaction between NVP and the solid electrolyte during integral firing is reduced. In other words, it was confirmed that the solid electrolyte of this disclosure can achieve both high ionic conductivity and low reactivity with NVP.

[0086] Furthermore, the solid batteries of Examples 1-3, 5-7, 10, 12-14, 16, 21-23, and 25 showed higher discharge capacity and Coulomb efficiency compared to the solid battery of Comparative Example 1. These results demonstrate that by using the solid electrolyte of this disclosure, a good interface between the solid electrolyte and NVP is formed after integral firing, resulting in a solid battery exhibiting superior battery performance.

[0087] The solid electrolytes and solid batteries of this disclosure can be used in a variety of fields where energy storage is envisioned. While these are merely examples, the solid batteries of this disclosure 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 industrial applications (e.g., power tools, golf carts, household, caregiving, and industrial robots), large 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 systems, 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 having a NASICON-type crystal structure, containing Na (sodium), Zr (zirconium), Si (silicon), P (phosphorus), and O (oxygen), wherein a portion of Zr is substituted with one or more elements selected from the group consisting of V (vanadium), Nb (niobium), Ta (tantalum), Bi (bismuth), W (tungsten), and Mo (molybdenum).

2. The solid electrolyte according to claim 1, wherein the valency of the element substituted for a portion of Zr is 5 or higher.

3. The solid electrolyte is given by the following general formula: Na ３－（ａ＋２ｂ） Zr ２－ａ－ｂ M1 ａ M2 ｂ Si ２ P １ O １２ (I) The solid electrolyte according to claim 1, represented by the formula (wherein M1 is one or more elements selected from the group consisting of V, Nb, Ta, and Bi, and M2 is one or more elements selected from the group consisting of W and Mo, with 0 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.25, and 0 < (a + 2b) ≤ 1).

4. The solid electrolyte according to claim 3, wherein in the general formula (I), 0.05 ≤ a ≤ 0.3 and b = 0.

5. The solid electrolyte according to claim 3, wherein in the general formula (I), a = 0 and 0.05 ≤ b ≤ 0.

2.

6. The solid electrolyte according to any one of claims 3 to 5, wherein in the general formula (I), 0.15 ≤ (a + 2b) ≤ 0.

25.

7. A solid electrolyte according to any one of claims 1 to 3, wherein a portion of Zr is substituted with two or more elements selected from the group consisting of V, Nb, Ta, Bi, W, and Mo, and the two or more elements include at least one or more elements selected from the group consisting of W and Mo.

8. A sintered body including a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer, wherein one or more of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer contain the solid electrolyte according to claim 1, and either one of the positive electrode active material and the negative electrode active material has the following composition formula: Na ３＋ｘ V ２－ｘ (PO ４ ) ３ (II) (where 0 ≤ x ≤ 1), and is an active material material represented by the formula, a solid battery.

9. The solid-state battery according to claim 8, wherein at least one of the positive electrode layer and the negative electrode layer comprises the solid electrolyte and the active material.

10. At least one of the positive electrode layer and the negative electrode layer, and the solid electrolyte layer, contain the solid electrolyte, wherein the solid electrolyte is given by the following general formula: Na ３－（ａ＋２ｂ） Zr ２－ａ－ｂ M1 ａ M2 ｂ Si ２ P １ O １２ (I) A solid battery according to claim 8 or 9, wherein the a+2b value of the solid electrolyte contained in at least one of the positive electrode layer and the negative electrode layer is greater than the a+2b value of the solid electrolyte contained in the solid electrolyte layer. (I) (wherein M1 is one or more elements selected from the group consisting of V, Nb, Ta, and Bi, and M2 is one or more elements selected from the group consisting of W and Mo, and 0 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.25, and 0 < (a + 2b) ≤ 1)

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