Composition, sintered product, solid electrolyte, and power storage device

Abstract

A composition comprising an oxide and a sintering aid, wherein the oxide comprises Na, Al, Zr and P as constituent elements.

Description

Technical Field

[0001] [Cross-reference to related applications] This application claims priority based on Japanese Patent Application No. 2023-211395, filed on December 14, 2023, and Japanese Patent Application No. 2023-219373, filed on December 26, 2023, the entirety of which is incorporated herein by reference.

[0002] This disclosure relates to compositions, calcined products, solid electrolytes, and energy storage devices. Background Technology

[0003] As energy storage devices, various secondary batteries such as nickel-metal hydride batteries and lithium-ion batteries, as well as double-layer capacitors, have been put into practical use. Among them, lithium-ion batteries (LIBs) are widely used due to their high energy density and high battery capacity.

[0004] Lithium-ion secondary batteries have a negative electrode, a positive electrode, and an electrolyte. They are charged and discharged by moving lithium ions between the two electrodes via the electrolyte. Traditionally, non-aqueous electrolytes have been primarily used. However, because non-aqueous electrolytes contain flammable organic solvents, leakage of the electrolyte and short circuits inside the battery due to overcharging or over-discharging are possible.

[0005] In response, research was conducted on all-solid-state lithium-ion secondary batteries that use solid electrolytes with lithium-ion conductivity instead of non-aqueous electrolytes. However, concerns remain regarding lithium raw materials, including concerns about soaring prices and potential depletion.

[0006] Therefore, in recent years, various studies have been conducted on sodium-ion secondary batteries (NIBs) that use sodium, which is abundant and inexpensive, and charge and discharge by moving sodium ions, as a post-lithium-ion secondary battery that uses an element that replaces lithium, which is a rare metal (see, for example, Patent Document 1).

[0007] Solid electrolytes exhibiting Na-ion conductivity include sulfide-based and oxide-based solid electrolytes. Among these, oxide-based solid electrolytes demonstrate high atmospheric stability and excellent safety. Additionally, Na3Zr2Si2PO4, used by NASICON, is another known oxide-based solid electrolyte exhibiting Na-ion conductivity. 12 Various studies have been conducted on improving ionic conductivity by doping NASICON with various elements (see, for example, Non-Patent Document 1). Non-Patent Document 1 discloses improving Na ion conductivity by doping NASICON with cerium (Ce).

[0008] Existing technical documents Patent documents Patent Document 1: International Publication No. 2019 / 003846 Non-patent literature Non-patent literature 1: ACS Applied Materials & Interfaces, 2020, No. 12, pp. 3502-3509 Summary of the Invention The technical problem that the invention aims to solve To achieve high capacity and high output in all-solid-state lithium-ion secondary batteries, it is necessary to develop solid electrolytes exhibiting high Na-ion conductivity. However, oxide-based solid electrolytes, due to their inherent hardness, tend to have poor interparticle and electrode-electrolyte interface bonding, resulting in increased resistance when used as electrolytes. Therefore, to achieve high ion conductivity, it is considered, for example, to improve the interparticle and electrode-electrolyte bonding state through sintering at high temperatures exceeding 1000°C, thereby minimizing resistance.

[0009] However, in the manufacture of all-solid-state batteries, if a firing process at temperatures exceeding 1000°C is required to achieve high ion conductivity, it may be impossible to co-sinter the positive and negative electrodes with the solid electrolyte from the perspective of avoiding damage to the positive and negative electrodes. On the other hand, if the firing temperature is set to a lower temperature below 1000°C, the grain boundary resistance and interface resistance cannot be sufficiently reduced, and the Na ion conductivity may decrease.

[0010] This disclosure was made in view of the above circumstances, and one of its objectives is to provide a composition that, by firing at temperatures below 1000°C, yields a calcined product with excellent Na-ion conductivity. Furthermore, another objective is to provide a solid electrolyte comprising the calcined product and an energy storage device having the solid electrolyte.

[0011] Technical solutions for solving technical problems In order to solve the above-mentioned technical problems, the inventors conducted in-depth research and discovered that the above-mentioned technical problems can be solved by using a composition containing an oxide comprising a specific element and a sintering aid. According to this disclosure, the following composition, sintered product, solid electrolyte, and energy storage device are provided.

[0012] [1] A composition comprising an oxide and a sintering aid, wherein the oxide comprises Na, Al, Zr and P as constituent elements.

[0013] [2] The composition according to [1], wherein the oxide further comprises Si as a constituent element.

[0014] [3] The composition according to [1] or [2], wherein the sintering aid comprises at least one selected from Na, B, Bi, Zn, Nb and P as a constituent element.

[0015] [4] The composition according to any one of [1] to [3], wherein the melting point of the sintering aid is below 1000°C.

[0016] [5] The composition according to any one of [1] to [4], wherein the content of the sintering aid is 0.1 to 45.0 parts by mass relative to 100 parts by mass of the oxide.

[0017] [6] A composition according to any one of [1] to [5], wherein the composition comprises two or more of the sintering aids.

[0018] [7] A composition according to any one of [1] to [5], wherein the composition comprises one or more of the sintering aids, wherein the sintering aids contain Na and B as constituent elements in the same molecule or in different molecules.

[0019] [8] A composition according to any one of [1] to [7], wherein the composition is used for a solid electrolyte.

[0020] Calcined product of any one of the compositions in [9] [1] to [8].

[0021]

[10] The sinter according to [9], wherein the sinter has a NASICON-type crystal structure.

[0022]

[11] The sintered product according to

[10] , wherein the sintered product has the crystal structure shown in the following formula (1).

[0023] [Chemistry 1] (In formula (1), M1 contains elements that can be divalent cations, M2 contains elements other than Al that can be trivalent cations, M3 contains elements that can be tetravalent cations (excluding Zr and Si), and a, b, c, d and e satisfy "a≥0", "b>0", "c≥0", "d≥0", "0≤e<3" and "a+b+c+d<2".)

[12] The sintered product according to

[11] , wherein the sintered product satisfies b≤0.5.

[0024]

[13] The sinter according to

[11] or

[12] , wherein the sinter satisfies 1.5 ≤ e ≤ 2.8.

[0025]

[14] The sintered product according to any one of [9] to

[13] , wherein the relative density of the sintered product is 80% or more.

[0026]

[15] A solid electrolyte comprising a calcined product of any one of [9] to

[14] .

[0027]

[16] An energy storage device having the solid electrolyte of

[15] .

[0028] Invention Effects According to this disclosure, a sintered material exhibiting high Na-ion conductivity can be obtained by sintering at temperatures below 1000°C. Furthermore, by using this sintered material as an electrolyte material in energy storage devices such as secondary batteries and capacitors, energy storage devices that combine the safety benefits of electrolyte solidification with high Na-ion conductivity can be obtained. Attached Figure Description

[0029] Figure 1 This is a graph showing the DC polarization measurement results of the sintered body obtained in Example 1.

[0030] Figure 2 This is the cyclic voltammogram of the sintered body obtained in Example 1.

[0031] Figure 3 This is a graph representing the results of the critical current density measurement.

[0032] Figure 4 This is a graph showing the evaluation results of charge-discharge cycle tests on half-cells using hard carbon (HC).

[0033] Figure 5 This is a graph showing the evaluation results of charge-discharge cycle tests of a half-cell using Na3V2(PO4)3(NVP).

[0034] Figure 6 This is a graph showing the evaluation results of the charge / discharge rate characteristics of a half-cell using HC.

[0035] Figure 7 This is a graph showing the evaluation results of the charge / discharge rate characteristics of a half-cell using NVP.

[0036] Figure 8 This is a graph showing the results of a charge-discharge cycle test of a full battery. Detailed Implementation

[0037] The compositions, calcined products, solid electrolytes, and energy storage devices disclosed herein will be described in detail below.

[0038] Composition The composition disclosed herein (hereinafter also referred to as "the composition") contains oxides and sintering aids, said oxides comprising Na, Al, Zr, and P as constituent elements. By sintering the composition, a sintered product exhibiting Na ion conductivity can be obtained. This sintered product is useful as a solid electrolyte material, particularly in that it is possible to obtain sintered products exhibiting high Na ion conductivity even through a low-temperature sintering process below 1000°C. The components contained in the composition are described in detail below. Hereinafter, the oxide comprising Na, Al, Zr, and P as constituent elements will also be referred to as "oxide (X)".

[0039] <Oxide(X)> The oxide (X) only needs to contain Na, Al, Zr and P as constituent elements. It should be noted that the oxide (X) only needs to have Na ion conductivity in the state of the sintered product after being sintered with the mixture of sintering aids. Whether or not it has Na ion conductivity in the state before being sintered with the mixture of sintering aids (i.e., the oxide (X) itself) is irrelevant.

[0040] As an oxide (X), Na3Zr2Si2PO, which constitutes NASICON, can be cited as an example. 12 The oxide (also known as "NZSP") is an oxide obtained by replacing a portion of the elements with various elements (other than Al, such as B, Mg, Ca, Ba, Ga, Ge, Sc, Y, Fe, Sr, In, Ti, Hf, Sn, Pb, V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ag, Te, Tl, Ta, Sb, Bi, W, and lanthanides) that contain at least aluminum (Al). It should be noted that the oxide (X) may or may not have a NASICON-type structure in the state prior to firing with the mixture of sintering aids. From the viewpoint of obtaining a sintered product with high Na ion conductivity, the oxide (X) preferably has a composition ratio (molar ratio) determined in such a way that the sintered product containing the mixture of oxide (X) and sintering aids has a NASICON-type structure.

[0041] From the viewpoint that a sintered product with high Na ion conductivity can be obtained by sintering a mixture of oxide (X) and sintering aid, the oxide (X) is preferably an oxide in which Na, Al, Zr, Si and P satisfy the molar ratio of the following formula (1). That is, the oxide in the sintered product of this composition is preferably a substance that satisfies the following formula (1).

[0042] [Chemistry 2] (In formula (1), M1 contains elements that can be divalent cations, M2 contains elements other than Al that can be trivalent cations, and M3 contains elements that can be tetravalent cations (excluding Zr and Si). a, b, c, d, and e satisfy "a≥0", "b>0", "c≥0", "d≥0", "0≤e<3" and "a+b+c+d<2".) The sintered product containing the substance satisfying the above formula (1) is a solid electrolyte having the following crystal structure: in Na3Zr2Si2PO4 12 In the oxide with the basic framework, at least a portion of Zr is replaced by Al, and a portion of Zr can be replaced by at least one of M1 (containing elements that can be divalent cations), M2 (containing elements other than Al that can be trivalent cations), and M3 (containing elements other than Zr and Si that can be tetravalent cations).

[0043] In the above formula (1), M1 can be represented by elements from Group 2, Group 12, transition elements (groups 3 to 11) that can become divalent cations, Sn, Pb, etc.

[0044] Examples of M2 include Group 3 elements, Group 13 elements other than Al, transition elements (Groups 3-11) that can become trivalent cations, Sb, Bi, etc. Among Group 13 elements other than Al, B (boron) is preferred.

[0045] M3 refers to elements other than Zr and Si that can be tetravalent cations. Examples of M3 include elements in Group 14 other than Si, transition elements (Groups 3-11 other than Zr) that can be tetravalent cations (Ti, Ce), Pb, Se, Te, etc.

[0046] In the above formula (1), a, b, c, d, and e are not specifically limited as long as they satisfy "a≥0", "b>0", "c≥0", "d≥0", "0≤e<3", and "a+b+c+d<2". For example, in the case of a=0, b>0, c>0, d>0, and e>0, the substance is composed of "Na 1+b+c+e Al b M2 c M3 d Zr 2-b-c-d Si e P 3-e O 12 This indicates that, under the conditions of a > 0, b > 0, c > 0, d > 0, and e = 0, the substance is composed of "Na". 1+2a+b+c M1 a Al b M2 c M3 d Zr2-a-b-c-d P3O 12 "express.

[0047] Regarding a, b, c, d, and e, more specifically, in terms of obtaining a solid electrolyte exhibiting high Na ion conductivity by making it less likely to form impurity phases, it is preferable that a ≤ 0.3, more preferably that a ≤ 0.2, and even more preferably that a ≤ 0.1. When a > 0, regarding the lower limit of a, it is preferable that a ≥ 0.01, and more preferably that a ≥ 0.03.

[0048] Regarding b, in order to obtain a solid electrolyte exhibiting high Na ion conductivity through low-temperature sintering, it is preferable that b ≥ 0.01, more preferably b ≥ 0.02, even more preferably b ≥ 0.03, and even more preferably b ≥ 0.04. Regarding the upper limit of b, it is preferable that b ≤ 0.5, more preferably b ≤ 0.4, even more preferably b ≤ 0.3, even more preferably b ≤ 0.2, and even more preferably b ≤ 0.1.

[0049] Regarding c, in order to suppress the formation of impurity phases and thereby obtain a solid electrolyte with higher Na ion conductivity, it is preferable that c ≤ 0.3, more preferably that c ≤ 0.2, and even more preferably that c ≤ 0.1. Furthermore, when c > 0, regarding the lower limit of c, it is preferable that c ≥ 0.01, and more preferably that c ≥ 0.03.

[0050] Regarding d, in order to suppress the formation of impurity phases and obtain a solid electrolyte exhibiting higher Na ion conductivity, it is preferable that d ≤ 0.3, more preferably that d ≤ 0.2, and even more preferably that d ≤ 0.1. When d > 0, regarding the lower limit of d, it is preferable that d ≥ 0.01, and more preferably that d ≥ 0.03.

[0051] The preferred value for e is 1.5 ≤ e ≤ 2.8. Regarding the upper limit of e, it is considered that excessive Si substitution reduces Na ion conductivity; therefore, e ≤ 2.7 is more preferred, e ≤ 2.6 is even more preferred, and e ≤ 2.5 is even more preferred. Furthermore, regarding the lower limit of e, in order to obtain a solid electrolyte exhibiting higher Na ion conductivity, e ≥ 1.7 is more preferred, e ≥ 1.9 is even more preferred, e ≥ 2.1 is even more preferred, e ≥ 2.2 is even more preferred, and e ≥ 2.3 is even more preferred.

[0052] It should be noted that in the above formula (1), the stoichiometric ratio of O is recorded as 12, but as long as the overall electroneutrality of the oxides in the fired product can be maintained, the stoichiometric ratio of O can also be less than 12. That is, the O from the oxides in the fired product can be a value less than 12 or a value greater than 12, as long as the overall electroneutrality of the oxides in the fired product can be maintained.

[0053] From the viewpoint of being able to produce sintered products exhibiting higher Na ion conductivity, the oxide (X) preferably further comprises silicon (Si) as a constituent element. For example, when the oxide in the sintered product of this composition comprising oxide (X) and sintering aid satisfies the above formula (1), from the viewpoint of being able to improve the Na ion conductivity of the sintered body, e in the above formula (1) preferably satisfies e > 0, preferably satisfies e ≥ 0.25, more preferably satisfies e ≥ 0.5, further preferably satisfies e ≥ 1.0, and even more preferably satisfies e ≥ 1.5.

[0054] The melting point of oxide (X) can be, for example, above 1050°C, above 1100°C, above 1150°C, above 1200°C, or above 1250°C. There is no specific upper limit to the melting point of oxide (X). It should be noted that the melting point of oxide (X) is a value under atmospheric pressure.

[0055] There are no particular limitations on the method for manufacturing oxides (i.e., oxides (X)) used to obtain calcined products containing oxides satisfying the above formula (1). Oxides (X) can be manufactured, for example, by weighing and mixing raw materials in a stoichiometric ratio that satisfies the composition shown in the above formula (1) (mixing process), and calcining the resulting mixture. It should be noted that, in this specification, the calcination of raw materials for obtaining oxides (X) is referred to as "pre-calcination," and this process is referred to as the "pre-calcination process."

[0056] As raw materials for oxide (X), supply components corresponding to the elements used to obtain the target oxide (X) can be used, including Na supply components, Al supply components, M1 supply components, M2 supply components, M3 supply components, Zr supply components, Si supply components, and P supply components. For example, in the case of manufacturing an oxide for obtaining a sintered body in the above formula (1) where a = 0, b > 0, c = 0, d = 0, and e > 0, Na supply components, Al supply components, Zr supply components, Si supply components, and P supply components are used as raw materials for oxide (X). It should be noted that these supply components can also be compounds in which two or more elements from Na, Al, M1, M2, M3, Zr, Si, and P are included in the supply component.

[0057] The Na, Al, M1, M2, M3, Zr, and Si suppliers used as raw materials for oxide (X) can be inorganic or organic compounds. Each supplier can be, for example, a carbonate, bicarbonate, sulfate, sulfite, nitrate, nitrite, phosphate, acetate, citrate, ammonium salt, oxide, hydroxide, chloride, or sulfide of these metal elements. As a P supplier, phosphates are preferred, with sodium phosphate or ammonium dihydrogen phosphate being the most preferred.

[0058] In the manufacture of oxide (X), the mixing of raw materials in the mixing process can be carried out by dry mixing or by wet mixing using a liquid. Wet mixing is preferred. Water, various organic solvents, and mixtures thereof can be used as the liquid in wet mixing. The slurry obtained by wet mixing can, for example, be sieved to remove coarse particles or agglomerates.

[0059] Next, the mixture obtained through the mixing process is pre-fired (pre-firing process). The firing temperature in the pre-firing process is not particularly limited, but can be, for example, 900°C or higher, preferably 950°C or higher, more preferably 1000°C or higher. Regarding the upper limit of the firing temperature, it can be, for example, 1500°C or lower, preferably 1400°C or lower, more preferably 1350°C or lower, further preferably 1300°C or lower, and even more preferably 1250°C or lower. During pre-firing, the temperature can be gradually increased from a temperature lower than the firing temperature, ultimately maintaining the temperature required for firing.

[0060] The oxide (X) obtained through the pre-calcination process can be pulverized using any method. Pulverization of oxide (X) can be performed using pulverizers such as ball mills, planetary ball mills, bead mills, jet mills, and mixers.

[0061] Sintering aids Sintering aids are incorporated into this composition as components distinct from oxides (X) for the purpose of promoting the sintering of oxides (X). In particular, in this composition, sintering aids are used to impart excellent Na-ion conductivity to the sintered product obtained by sintering oxides (X). From the viewpoint of imparting excellent Na-ion conductivity to the sintered product obtained by sintering this composition, compounds containing at least one element selected from Na, B, Bi, Zn, Nb, and P (hereinafter also referred to as "specific elements") as constituent elements are preferably used as sintering aids. From the perspective of the availability of raw materials, sintering aids are preferably compounds having one or two elements selected from Na, B, Bi, Zn, Nb, and P.

[0062] Specific examples of sintering aids containing specific elements include oxides and carbonates containing specific elements. Further specific examples of sintering aids include Na₂O, Na₂O₂, NaHCO₃, Na₂CO₃, NaF, NaCl, NaBr, NaI, NaNO₃, Na₂SO₃, Na₂SO₄, B₂O₃, H₃BO₃, NaBH₄, Na₂B₄O₇, Na₂B₄O₇·10H₂O, Na₃BO₃, Bi₂O₃, Bi₂O₅, BiF₃, BiCl₃, BiBr₃, BiOCl, Bi(OH)₃, ZnO, ZnCl₃, Zn(OH)₂, Zn(NO₃)₂, Zn(NO₃)₂·6H₂O, ZnSO₄, ZnSO₄· 7H2O, P2O5, Na2HPO4, Na2HPO4·12H2O, NaH2PO4, NaH2PO4·2H2O, Na3PO4, Na3PO4·12H2O, 60Na2O-10Nb2O5-30P2O5, etc.

[0063] The melting point of the sintering aid is preferably lower than that of the oxide (X). From the viewpoint of obtaining a sintered product exhibiting high Na ion conductivity through sintering at the lowest possible temperature, the melting point of the sintering aid is preferably below 1000°C, more preferably below 950°C, and even more preferably below 900°C. The lower limit of the melting point of the sintering aid is not particularly limited; for example, it can be above 350°C or above, or above 400°C. It should be noted that the melting point of the sintering aid is a value at atmospheric pressure.

[0064] This composition may contain only one sintering aid or two or more. From the viewpoint of obtaining sintered products with higher Na ion conductivity, this composition preferably contains two or more sintering aids. When this composition contains two or more sintering aids, it is preferable that at least a portion of the sintering aids contained in the composition have a melting point lower than that of the oxide (X), and more preferably that the melting point of all the sintering aids is lower than that of the oxide (X).

[0065] The sintering aid incorporated in this composition, as a constituent element, preferably contains Na (sodium) and B (boron) within the same molecule, or Na and B within different molecules. By including Na and B in the composition via the sintering aid, the Na-ion conductivity of the sintered product obtained by sintering the composition at temperatures below 1000°C can be further improved, which is preferred. From the viewpoint of obtaining a sintered product exhibiting higher Na-ion conductivity, the sintering aid preferably contains Na and B within different molecules. Specifically, this composition preferably contains a first compound and a second compound different from the first compound as sintering aids, the first compound containing Na and the second compound containing B (boron). From the viewpoint of the availability of raw materials, a carbonate can preferably be used as the first compound, and an oxide can preferably be used as the second compound.

[0066] Regarding the ratio of Na to B in the sintering aids incorporated in this composition, when expressed as the molar amount of Na relative to 1 mole of B in the sintering aids (the whole of the sintering aids when two or more are included), it is preferably in the range of 0.1 to 10 moles. More preferably, the molar amount of Na relative to 1 mole of B in the sintering aids is 0.2 to 8.0 moles, further preferably 0.3 to 6.0 moles, even more preferably 0.4 to 5.0 moles, even more preferably 0.45 to 4.0 moles, and even more preferably 0.5 to 3.0 moles. By setting the ratio of Na to B in the sintering aids within the above range, the Na ion conductivity of the sintered product can be further improved.

[0067] The content of the sintering aid in this composition (the total amount of two or more sintering aids) is preferably 0.1 to 45.0 parts by mass relative to 100 parts by mass of oxide (X). By setting the content of the sintering aid within the above range, a solid electrolyte exhibiting high Na ion conductivity can be obtained. From the viewpoint that the improvement effect of the Na ion conductivity in the sintered product of this composition can be sufficiently obtained by incorporating the sintering aid, the content of the sintering aid is preferably 1.0 parts by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, relative to 100 parts by mass of oxide (X). Furthermore, regarding the upper limit of the content of the sintering aid, from the viewpoint of suppressing the performance degradation caused by the incorporation of excessive sintering aid, it is preferably 40.0 parts by mass or less, more preferably 35.0 parts by mass or less, even more preferably 30.0 parts by mass or less, and even more preferably 25.0 parts by mass or less, relative to 100 parts by mass of oxide (X).

[0068] <Other Ingredients> This composition can be a combination of oxide (X) and sintering aid, or it may further contain components different from oxide (X) and sintering aid (other components). Examples of other components include polymeric solid electrolytes, polymeric gel electrolytes, inorganic fillers, conductive additives, plasticizers, binders, etc. However, considering the Na-ion conductivity and ease of manufacture of the calcined product obtained by calcining this composition, it is preferable that the content of other components is extremely low. Specifically, the content of other components relative to the total amount of this composition is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less.

[0069] This composition can be obtained by mixing oxide (X) with a sintering aid. The mixing of oxide (X) and sintering aid can be achieved by pulverizing oxide (X) into powder and then mixing it with the sintering aid, or by pulverizing the sintering aid using any method and then mixing it with oxide (X). Alternatively, the oxide (X) and sintering aid can be mixed and then pulverized into powder, or the mixing and pulverization of oxide (X) and sintering aid can be performed simultaneously. The mixing of oxide (X) and sintering aid preferably uses a method that homogenizes the oxide (X) and sintering aid. The mixing of oxide (X) and sintering aid can be performed using various equipment, such as ball mills, planetary ball mills, bead mills, mixers, homogenizers, pulverizers, homogenizing mixers, and disperser-type mixers. Furthermore, in the case of small-scale production of sintered products, a mortar and pestle can be used for mixing.

[0070] When mixing oxide (X) with sintering aids, it can be carried out by dry mixing or by wet mixing using a liquid. Wet mixing is preferred. By using wet mixing, the dispersibility of the sintering aids can be further improved, and the density of the sintered product can be increased compared to dry mixing. This also relatively improves the Na-ion conductivity of the sintered product. Water, various organic solvents, and mixtures thereof can be used as the liquid in wet mixing. The slurry obtained by wet mixing can be sieved to remove coarse particles or agglomerates. Furthermore, the mixing of oxide (X) with sintering aids can be carried out at room temperature, at low temperature, or under heating.

[0071] <Methods for manufacturing fired products> The calcined product disclosed herein can be manufactured by calcining the above-described composition. It should be noted that, in this specification, the calcination used to calcinate the composition to obtain a calcined product that can become a solid electrolyte is referred to as "formal calcination," and the process is referred to as the "formal calcination process."

[0072] In the formal firing process, the composition can be fired without being shaped, or it can be shaped before firing. There are no particular limitations on the shaping method; known methods such as extrusion molding, injection molding, pressure molding, casting, die casting, and tape casting can be used. However, considering the need to minimize the porosity of the resulting fired product and facilitate the formation of ion conduction pathways, pressure molding is preferred.

[0073] The firing temperature for firing (formal firing) of this composition is preferably below 1200°C, more preferably below 1100°C, even more preferably below 1000°C, even more preferably below 950°C, even more preferably below 900°C, even more preferably below 850°C, and particularly preferably below 800°C. According to the composition disclosed herein, even when firing at a relatively low temperature of below 1000°C, a fired product exhibiting high Na-ion conductivity can be obtained. Therefore, co-firing with positive and negative electrode materials can be achieved in the manufacturing process of an energy storage device. Regarding the lower limit of the firing temperature, from the viewpoint of sufficiently reducing interfacial resistance and improving Na-ion conductivity in the fired product, it is preferably above 500°C, more preferably above 550°C, even more preferably above 600°C, even more preferably above 650°C, even more preferably above 700°C, and even more preferably above 750°C. During the formal firing, the temperature can be gradually increased from a temperature lower than the final firing temperature (preparatory firing) and then maintained at the final firing temperature. Alternatively, for purposes such as stress relief, the fired product can be heated at a temperature lower than the final firing temperature after the formal firing.

[0074] When performing a pre-firing, the obtained pre-firing material can be pulverized before the subsequent firing process. When firing in multiple temperature zones, for example, the firing process can be carried out in three stages: a first pre-firing at a temperature zone above 300°C and below 500°C, a second pre-firing at a temperature zone above 500°C and below 700°C, and a final firing at a temperature zone above 700°C. The firing time is not particularly limited; for example, the pre-firing can be set to 1 hour or more and 100 hours or less, and the final firing can be set to 1 hour or more and 100 hours or less. The firing time for this composition is, for example, 3 to 72 hours, or 5 to 48 hours.

[0075] The sintered product thus obtained exhibits excellent ionic conductivity (more specifically, Na ion conductivity). Therefore, the sintered product of this disclosure is suitable as a solid electrolyte for energy storage devices in which sodium ions are the charge carriers for ionic conduction. Furthermore, this composition is suitable as a composition for use as a solid electrolyte.

[0076] Specifically, for sintered materials with a thickness of approximately 1000 μm (more specifically, 1000 ± 20 μm), the ionic conductivity measured using AC impedance spectroscopy at 25°C is, for example, 0.1 mS / cm or higher. From the viewpoint of obtaining a high-performance energy storage device, the ionic conductivity under the same conditions is preferably 0.5 mS / cm or higher, and more preferably 1.0 mS / cm or higher. It should be noted that the details of the method for measuring ionic conductivity are as described in the examples described later.

[0077] The phase structure of the sintered product of this composition is not particularly limited. From the viewpoint of obtaining a solid electrolyte with high Na ion conductivity, the sintered product of this composition preferably has a NASICON-type crystal structure. More specifically, the sintered product of this composition preferably contains an oxide with a NASICON-type crystal structure. The NASICON-type crystal structure differs from layered structures, etc., in that it has a wide three-dimensional space for the movement of alkali metal ions, and zirconium (Zr) is stable even at high voltages, thus it is useful as a solid electrolyte with high operating voltage. In addition, when the sintered product of this composition has the crystal structure shown in formula (1) above, the Na ion conductivity is excellent, and therefore it is particularly suitable as an electrolyte material. It should be noted that the inclusion of Al as a constituent element in the oxide (X) and the sintered product of this composition is related to the ability to maintain high Na ion conductivity in the obtained sintered product even by sintering at temperatures below 1000°C. The crystal structure of the sintered product can be determined by the diffraction pattern obtained by powder X-ray diffraction.

[0078] From the viewpoint of obtaining calcined products exhibiting excellent Na ion conductivity, the relative density of the calcined product of this composition is preferably 75% or more, more preferably 80% or more, further preferably 85% or more, even more preferably 90% or more, and even more preferably 95% or more. It should be noted that, in this specification, "relative density" refers to the ratio (%) of the measured density to the theoretical density. The measured density is calculated using the following method: measuring the diameter, thickness, and mass of the calcined product, determining the volume from the measured values ​​of the diameter and thickness, and calculating the value from the measured values ​​of the volume and mass.

[0079] Energy Storage Devices The energy storage device disclosed herein (hereinafter also referred to as "the device") includes a solid electrolyte comprising the sintered product of the present disclosure. Examples of specific embodiments of the device include secondary batteries and capacitors. In the case of the device being a secondary battery, one embodiment is an all-solid-state battery; considering the excellent conductivity of Na ions, a sodium-ion secondary battery is preferred.

[0080] An all-solid-state sodium-ion secondary battery, which is one embodiment of this device, will be described. The sodium-ion secondary battery is a laminate comprising electrodes including a positive electrode and a negative electrode, and a solid electrolyte layer. The solid electrolyte layer is disposed between the positive and negative electrodes in such a way that it contacts the electrodes. The materials constituting the positive and negative electrodes are not particularly limited, and can be appropriately selected from materials known as electrode materials for sodium-ion secondary batteries.

[0081] In the sodium-ion secondary battery disclosed herein, the solid electrolyte layer is formed from a sintered product obtained by firing the present composition. The solid electrolyte layer can be obtained, for example, by molding a material containing the present composition for a solid electrolyte into a desired shape and then firing it. Regarding the molding and firing methods, descriptions of the molding and firing methods for the sintered product can be referenced. The shape of the molded body is not particularly limited and can be appropriately set according to the shape of the energy storage device to which it is applied. The shape of the molded body is, for example, rectangular or circular. The thickness of the solid electrolyte layer is not particularly limited and can be appropriately set according to the application of the secondary battery, etc. The thickness of the solid electrolyte layer is, for example, 5 to 500 μm. It should be noted that a solid electrolyte layer of the energy storage device with a desired thickness can also be formed by stacking multiple molded bodies.

[0082] There are no particular limitations on the method for manufacturing sodium-ion secondary batteries, and known methods can be appropriately adopted depending on the battery structure, etc. For example, a solid electrolyte layer formed using this composition can be sandwiched between a positive electrode and a negative electrode, and preferably subjected to a heat treatment and / or pressure treatment for bonding, thereby manufacturing a laminate having a positive electrode, a solid electrolyte layer, and a negative electrode. Alternatively, an electrolyte material containing granular components of this composition can be housed in a container by sandwiching a positive electrode and a negative electrode, and the housed can be subjected to a heat treatment for firing and, preferably, a pressure treatment for bonding, thereby manufacturing a laminate having a positive electrode, a solid electrolyte layer, and a negative electrode. This composition, in particular, can produce a solid electrolyte layer exhibiting high Na-ion conductivity even through a relatively low firing process below 1000°C. Therefore, it is preferable that the electrodes and the solid electrolyte layer can be co-sintered while minimizing damage to the positive electrode and negative electrode materials. The laminate having a positive electrode, a solid electrolyte layer, and a negative electrode is typically housed in a casing and used as a secondary battery.

[0083] It should be noted that this device can also be a capacitor. One possible configuration for a capacitor is as follows: it comprises a positive electrode, a negative electrode, and a solid electrolyte layer, with the solid electrolyte layer disposed between the positive and negative electrodes in such a way that it is connected to the electrodes.

[0084] Energy storage devices incorporating the solid electrolyte of this disclosure can be applied to a variety of uses. Specifically, they can be used as power sources in various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various mobile vehicles such as electric vehicles, hybrid vehicles, robots, and drones; and various electrical and electronic devices such as digital cameras, camcorders, music players, power tools, and home appliances.

[0085] Example The present disclosure will now be described in detail based on the embodiments. It should be noted that the present disclosure is not limited to these embodiments. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0086] The manufacture of oxides [Manufacturing Example 1] Using the molar ratio of oxides shown in Table 1 (Na:Al:Zr:Si:P = 3.40:0.05:1.95:2.35:0.65), the following components were weighed as the supply components: sodium phosphate (manufactured by Kishida Chemical Company, purity 98%) 4.0607 g, sodium carbonate (manufactured by the High Purity Chemical Research Institute, purity 99%) 2.8989 g, alumina (manufactured by the High Purity Chemical Research Institute, purity 99.9%) 0.0958 g, zirconium oxide (manufactured by the High Purity Chemical Research Institute, purity 98%) 9.1565 g, and silicon dioxide (manufactured by the High Purity Chemical Research Institute, purity 99.99%) 5.2781 g. Each sample was placed into a 500 mL nylon container containing 200 g of φ4 mm zirconium oxide spheres, and 65 g of 99.5% ethanol was added. The mixture was prepared by mixing using a planetary ball mill (FRITSCH6, Puluerisette6) at 200 rpm for 120 minutes.

[0087] The resulting slurry was passed through a 250-mesh sieve and dried at 80°C for 12 hours, then granulated using a 50-mesh sieve. It was then transferred to an alumina crucible (100 mL volume) and pre-fired at 1100°C for 12 hours in atmospheric conditions. The heating rate was set at 300°C / hour. After cooling to room temperature, oxide SE-1 was obtained.

[0088] [Manufacturing Examples 2-4] As shown in Table 1, the amount of raw materials was changed, and the same operation as in Manufacturing Example 1 was performed to obtain oxides (oxide SE-2, oxide SE-3, and oxide SE-4, respectively).

[0089] [Table 1] Preparation of Compositions and Firings [Example 1] Using the mass ratio of oxide to sintering aid shown in Table 2 (SE-1:Na2CO3:B2O3 = 100:8.4:2.7), 3.6 g of oxide SE-1, 0.301 g of sodium carbonate (manufactured by the High Purity Chemical Research Institute), and 0.099 g of boron trioxide (manufactured by Kishida Chemical Company) were weighed. Each sample was added to a 500 mL nylon container containing 200 g of φ4 mm zirconia balls, and 65 g of 99.5% ethanol was further added. The mixture was stirred using a planetary ball mill at 250 rpm for 18 hours to obtain a slurry. The slurry was passed through a 250-mesh sieve, dried at 80°C for 12 hours, and then granulated using a 50-mesh sieve to obtain a composition containing oxide SE-1 and the sintering aid.

[0090] 0.36g of the obtained composition was placed in a mold with a diameter of 15cm. A hydraulic press was used to pre-form it into a cylindrical shape under a load of 40MPa. The pre-formed shape was then vacuum-sealed into a plastic bag using a vacuum sealing machine (TOSEI, V-280A). The bag was then placed in a CIP device (RIKEN, P-1B) and molded under a pressure of 200MPa in water. The resulting molded body was then covered with platinum foil. This platinum foil-covered body was then placed in a 100mL alumina crucible along with 10g of oxide SE-1 and sintered at 900°C for 12 hours. After cooling to room temperature, the platinum foil was removed, yielding the sintered product of the composition. It should be noted that the heating rate was set to 300°C / hour.

[0091] [Examples 2-14, 16-23] As shown in Table 2, the types and amounts of raw materials were changed, but the same procedures as in Example 1 were performed to obtain compositions containing oxides and sintering aids. Furthermore, using the obtained compositions, molding and formal firing were performed using the same steps as in Example 1 to obtain fired products of each composition. It should be noted that in the formal firing, the type of oxide embedded in the platinum foil-covered molded body was changed to the oxide used in the preparation of the composition, and the firing conditions were set as shown in Table 2.

[0092] [Example 15] In a 100 mL alumina crucible, 12.0800 g of sodium carbonate (manufactured by the High Purity Chemical Research Institute), 5.0037 g of niobium oxide (V) (manufactured by Fujifilm and Koichi Chemical Co., Ltd.), and 13.2242 g of ammonium dihydrogen phosphate (manufactured by Kishida Chemical Co., Ltd.) were weighed as raw materials for sintering aids. Each sample was placed in a platinum crucible and melted at 1300 °C. Then, the melt was spread on a copper plate to obtain the sintering aid (60Na₂O-10Nb₂O₅-30P₂O₅).

[0093] The obtained sintering aid was added to a 500 mL nylon container containing 200 g of φ4 mm zirconia balls, and 70 g of 99.5% ethanol was further added. The mixture was then pulverized at 300 rpm for 12 hours for the preparation of the composition. The melting point of the obtained sintering aid was 730 °C.

[0094] Then, the samples were weighed according to the mass ratio of oxide to sintering aid as recorded in Table 2, and the same operation as in Example 1 was performed to obtain the composition. Furthermore, using the obtained composition, molding and formal firing were performed according to the same steps as in Example 1 to obtain the fired product of the composition.

[0095] [Example 24] Using the mass ratio of oxide to sintering aid shown in Table 2 (SE-1:Na2CO3:B2O3 = 100:8.4:2.7), 3.6 g of oxide SE-1, 0.301 g of sodium carbonate, and 0.099 g of boron trioxide were weighed and placed in an agate mortar. The mixture was then mortared for 10 minutes to obtain the composition. Furthermore, using the obtained composition, molding and formal firing were performed using the same steps as in Example 1 above to obtain calcined products of each composition.

[0096] [Comparative Example 1] Without using sintering aids, the sintered product of the composition was obtained by molding and formal firing in the same manner as in Example 1 above.

[0097] [Table 2] Details of the compounds used in Table 2 are shown below.

[0098] • Na₂CO₃: Sodium carbonate, melting point 851℃ [manufactured by the High Purity Chemical Research Institute] • B2O3: Boron trioxide, melting point 450℃ [manufactured by Kishida Chemical Company] • Na₂B₄O₇: Sodium tetraborate, melting point 742℃ [manufactured by Kishida Chemical Company] Bi₂O₃: Bismuth(III) oxide, melting point 817°C [manufactured by Kishida Chemical Company] • ZnO: Zinc oxide, melting point 1975℃ [manufactured by Kanto Chemical Company] ·60Na2O-10Nb2O5-30P2O5: Sintering aid obtained in Example 15, melting point 730℃ Evaluation Methods for Fired Products (1) Determination of relative density The relative densities of the calcined products of the compositions of Examples 1-24 and Comparative Example 1 were calculated, and the results are shown in Table 2. The calculation method is as follows. The diameter, thickness, and mass of the calcined products of each composition were measured, and the measured density was calculated from the measured values ​​of volume and mass. Then, the relative density (%) was calculated by calculating the ratio (%) of the measured density to the theoretical density. It should be noted that the theoretical density is 3.27 g / cm³. 3 .

[0099] (2) Identification of crystalline phases The identification of the main crystalline phase of the calcined compositions of Examples 1-24 and Comparative Example 1 was performed using X-ray diffraction (XRD). The XRD measurement conditions are described below.

[0100] X-ray diffraction apparatus: D8 ADVANCE (manufactured by Bruker) Characteristic X-rays: CuKα Measured voltage: 40kV Measurement current: 40mA Measurement method: continuous Measurement range: 10°≤2θ≤80° Step size: 0.027° Scanning speed: 1.7° / min In the calcined products of all compositions of Examples 1 to 24 and Comparative Example 1, a NASICON-type structure with a monoclinic or trigonal crystal system as the main crystalline phase was confirmed.

[0101] (3) Evaluation of ionic conductivity (3-1) Formation of the current collector layer The sintered products of the compositions obtained in Examples 1-24 and Comparative Example 1 were shielded with silicone rubber to form a circular exposed surface with a diameter of 7 mm at the center, and sputtered on the exposed surface. The sintered products were then flipped over, shielded, and sputtered in the same manner, thereby forming current collector layers on both sides. The current collector layers were formed as gold (Au) layers with a thickness of approximately 25 nm. Sputtering was performed using a gold vapor deposition apparatus (manufactured by V Technology Co., Ltd., VTC-YAN350).

[0102] (3-2) Methods for determining AC impedance The AC impedance of the sintered material with the current collector layer formed in (3-1) above was measured, and a complex impedance diagram was prepared. The measurement was performed using a multichannel potentiostat / galvanostat (Bio-Logic SP-150e) at a frequency of 100mHz to 1MHz, a voltage of 20mV, and a temperature of 25°C.

[0103] (3-3) Calculation method of ionic conductivity The value of the right end of the arc in the complex impedance diagram obtained by (3-2) above is taken as the resistance R of each sintered object. The ionic conductivity σ (Na ion conductivity) is calculated using the following mathematical formula (1), as shown in Table 2.

[0104] σ=(t / A)×(1 / R) …(1) σ: Ionic conductivity t: thickness of the sample A: Area of ​​the current collector layer R: Resistance of the sintered material (3-4) DC polarization measurement The DC polarization of the sintered product of Example 1, in which the current collector layer was formed as described in (3-1) above, was measured. The measurement was performed using a multichannel potentiostat / galvanostat (Bio-Logic SP-150e) at a voltage of 1.0V and a temperature of 25°C.

[0105] Figure 1 This indicates the DC polarization measurement result. The stable current is read, and the electronic conductivity is calculated using the following mathematical formula (2), which is 2.0 × 10⁻⁶. -8 S / cm. This confirms that the electron conductivity of the sintered product of Example 1 is sufficiently low.

[0106] σ e =(t / A)×(I / V) …(2) σ e Electron conductivity t: thickness of the sample A: Area of ​​the current collector layer I: Stable current V: Voltage (3-5) Cyclic voltammetry determination The sample was shielded with silicone rubber to form a circular exposed surface with a diameter of 7 mm at the center of the sintered product of Example 1, and sputtering was performed on the exposed surface to form a current collector layer on only one side. The current collector layer was formed as a gold (Au) layer with a thickness of approximately 25 nm. Sputtering was performed using a gold vapor deposition apparatus.

[0107] After a current collector layer is formed on one side of the sintered material, it is moved into a glove box under an argon atmosphere. Metallic Na is placed on the side where the current collector layer has not formed, and a pressure of 0.2 MPa is applied to press it in place.

[0108] The sintered material with pressed-on metallic Na was sealed in an electrochemical measurement cell (manufactured by EC Frontier, TYS-00DM01). The cell was connected to a multichannel potentiostat / galvanostat (manufactured by Bio-Logic, SP-150e) with the gold current collector layer side as the working electrode and the metallic Na side as the reference and counter electrodes. Cyclic voltammetry (CV) was performed at 25°C to obtain a cyclic voltammogram. The scan rate was set to 1 mV / s, starting from the open-circuit voltage, with foldback voltages set to -0.1V and 5.0V, and the scan continued until the open-circuit voltage was reached. Figure 2 This represents the obtained cyclic voltammogram. It confirms that the voltage range is 0–5.0 V (vs Na). + The sintered product is stable when / Na) is present.

[0109] (3-6) Determination of critical current density In a glove box under an argon atmosphere, metallic Na was placed on both sides of the sintered product (0.13 cm thick) of the composition from Example 1, and a pressure of 10 MPa was applied to press it together, thereby forming a 0.40 cm thick product. 2 A metallic Na electrode with a surface area of ​​[area missing] was used. The resulting sintered product was sealed in an electrochemical measurement cell (manufactured by EC Frontier, TYS-00DM01), with one side serving as the working electrode and the other as the reference and counter electrode. This cell was then connected to a multichannel potentiostat / galvanostat (manufactured by Bio-Logic, SP-150e). The current flow direction was switched every 30 minutes (from working electrode to counter electrode, and from counter electrode to working electrode), and the voltage was measured. It should be noted that the measurement was performed at 25°C, with the current value increased incrementally in stages from 0.04 mA to 0.4 mA per cycle. Figure 3 This indicates the measurement result. For example... Figure 3 As shown, the current exhibits stable voltage behavior up to 0.32 mA, and no clear short-circuit behavior was observed up to 0.34 mA. The critical current density is 0.8 mA / cm². 2 Based on the above, it is confirmed that the calcined product of the composition in Example 1 has sufficient short-circuit resistance.

[0110] Evaluation Results As shown in Table 2, the compositions of Examples 1 to 24 can also produce sintered products with excellent Na ion conductivity when the firing temperature is set below 1000°C.

[0111] If the results of Examples 1 to 24 are studied in detail, it is found that when the amount of sintering aid relative to 100 parts by mass of oxide is changed (Examples 1 to 4), the Na ion conductivity is better as the amount of sintering aid approaches 11.1 parts by mass.

[0112] Furthermore, when both Na₂CO₃ and B₂O₃ are used as sintering aids, the optimal Na ion conductivity is achieved when sintering at 900°C (Examples 1, 5-8) with a Na to B molar ratio of 1:1. Additionally, when sintering at 800°C (Examples 18-22), the optimal Na ion conductivity is achieved when the Na to B molar ratio is 3:2.

[0113] When the type of oxide is changed (Examples 1, 9-11), the best result for Na ion conductivity is achieved when using oxide SE-1 (Na:Al:Zr:Si:P = 3.40:0.05:1.95:2.35:0.65).

[0114] When the types of sintering aids were changed (Examples 1, 12-15), the best Na ion conductivity was observed when Na₂CO₃ and B₂O₃ were used. Furthermore, when comparing Example 7 with Example 12, even when the molar ratio of Na to B in the sintering aids was the same, the Na ion conductivity was still better when Na₂CO₃ and B₂O₃ were used as sintering aids.

[0115] When the firing temperature of the composition is changed (Examples 6 and 17), a higher firing temperature results in better Na ion conductivity.

[0116] Furthermore, when the firing time is changed (Examples 21 and 23), a longer firing time results in better Na ion conductivity.

[0117] Comparing Example 1, which uses a different method of mixing the composition, with Example 24, the composition prepared by mixing using a planetary ball mill resulted in a higher relative density of the calcined product and better Na ion conductivity compared to the composition prepared by mixing using a mortar and pestle in Example 1.

[0118] In contrast, the sintered product of Comparative Example 1, which did not contain any sintering aids, had a lower relative density and Na ion conductivity than those of Examples 1-24, indicating poor practicality.

[0119] The results above show that, based on the composition containing oxide (X) and sintering aid, a solid electrolyte exhibiting high relative density and Na ion conductivity can be obtained even when sintering is carried out at temperatures below 1000°C.

[0120] Battery Review By evaluating the battery using the following methods, it was confirmed that the all-solid-state battery made using the composition of the example functions as a sodium-ion secondary battery.

[0121] <How to Make a Half-Battery> (1) Method for making a half-cell using hard carbon (HC) 0.0605 g of the composition prepared in Example 1 and 0.0472 g of HC were placed in a 5 mL spiral tube bottle, and 0.0204 g of polyvinyl butyral (PVB) and 2.4 g of 99.5% ethanol were added. The mixture was dispersed using an ultrasonic cleaner (SND Corporation, US103) to obtain a mixed material dispersion. Using a spin coater (Kyowa Riken Corporation, K359S1), 0.00025 g of the mixed material dispersion was dropped onto one side of the sintered product of the composition prepared in Example 1, thereby forming a negative electrode mixed material precursor layer on the sintered product. Then, the product was placed on a platinum plate with the negative electrode mixed material precursor layer facing upwards, and sintered at 950°C for 3 hours in an Ar atmosphere containing 5% hydrogen, thereby co-sintering to form a negative electrode mixed material layer on the sintered product. Then, it was moved to a glove box under an argon atmosphere, and metallic Na was placed on the surface where the current collector layer had not formed. A pressure of 0.2 MPa was applied to press it into place and seal it in an electrochemical measurement cell (manufactured by Bio-Logic, SP-150e).

[0122] (2) Method for preparing a half-cell using Na3V2(PO4)3(NVP) Using a composition ratio of Na:V:P = 3.0:2.0:3.0, 20.5315 g of disodium hydrogen phosphate (manufactured by Kishida Chemical Company) and 7.9813 g of vanadium(III) oxide (manufactured by Kishida Chemical Company) were weighed as the supply components. Each sample was placed in a platinum crucible and melted at 1300 °C, then spread onto a copper plate to prepare the NVP glass precursor. The prepared precursor was placed in a 500 mL nylon jar containing 200 g of φ4 mm zirconia spheres, and 70 g of 99.5% ethanol was added. The mixture was pulverized at 300 rpm for 12 hours to obtain a pulverized product. 0.1 g of the NVP glass precursor pulverized product and 2.4 g of 99.5% ethanol were added to a 6 mL spiral-tube flask and dispersed to obtain an NVP precursor dispersion. Using a spin coater, 0.00014 g of NVP dispersion was dropped onto one side of the sintered composition prepared in Example 1 above, thereby forming an NVP precursor layer on the sintered material. Then, the material was placed on a platinum plate with the NVP precursor layer facing upwards and sintered at 750°C for 0.5 hours in an Ar atmosphere containing 5% hydrogen, thereby co-sintering to form an NVP positive electrode layer on the sintered material, resulting in a sintered body. The sintered body was shielded with silicone rubber to form a circular exposed surface with a diameter of 7 mm on the NVP positive electrode layer, and sputtering was performed on the exposed surface of the NVP positive electrode layer to form a current collector layer only on one side. The current collector layer was a gold (Au) layer with a thickness of approximately 25 nm. Sputtering was performed using a gold vapor deposition apparatus. Then, the material was moved to a glove box under an argon atmosphere, and metallic Na was placed on the surface where the current collector layer was not formed. A pressure of 0.2 MPa was applied to press it into place, and the material was sealed in a battery for electrochemical measurement.

[0123] <How to Make a Full Battery> (1) Method for fabricating full cells using NVP and HC 0.0605 g of the composition prepared in Example 1 and 0.0472 g of HC were placed in a 5 mL spiral tube bottle, along with 0.0204 g of PVB and 2.4 g of 99.5% ethanol. The mixture was dispersed using an ultrasonic cleaner (SND Corporation, US103) to obtain a mixed material dispersion. Using a spin coater (Kyowa Riken Corporation, K359S1), 0.00025 g of the mixed material dispersion was dropped onto one side of the sintered product of the composition prepared in Example 1, thereby forming a negative electrode mixed material precursor layer on the sintered product. Then, the product was placed on a platinum plate with the negative electrode mixed material precursor layer facing upwards, and sintered at 950°C for 3 hours in an Ar atmosphere containing 5% hydrogen, thereby co-sintering to form a negative electrode mixed material layer on the sintered product. Then, using a spin coater, 0.00014 g of NVP glass precursor dispersion prepared according to the same steps as in <Method for Preparing a Half-Cell> (2) was dropped onto the side opposite to the side where the negative electrode mixed material layer was formed, thereby forming an NVP precursor layer on the sintered body. Then, with the NVP precursor layer facing upward, it was placed on a platinum plate and sintered at 750°C for 0.5 hours in an Ar atmosphere containing 5% hydrogen, thereby co-sintering to form an NVP positive electrode layer and obtaining a sintered body. The sintered body was shielded with silicone rubber to form a circular exposed surface with a diameter of 7 mm on the NVP positive electrode layer, and sputtering was performed on the exposed surface of the NVP positive electrode layer to form a current collector layer on only one side. The current collector layer was formed as a gold (Au) layer with a thickness of about 25 nm. Sputtering was performed using a gold vapor deposition apparatus. Then, it was transferred to a glove box under an argon atmosphere and sealed in a cell for electrochemical measurement.

[0124] <Evaluation Methods for Half-Cells> (1) Half-cell charge-discharge cycle test The aforementioned half-cell was connected to a multichannel potentiostat / galvanostat (Bio-Logic SP-150e) with the Na metal side serving as the reference electrode and counter electrode, and the negative electrode mixed material layer or NVP positive electrode layer side serving as the working electrode, and the measurements were performed at 25°C.

[0125] The negative electrode hybrid material layer was measured as follows: it was charged to the cutoff voltage of 0V at a current density equivalent to 0.1C, stopped for 10 hours, and then discharged to the cutoff voltage of 3.1V. This cycle was repeated 80 times, and the charge and discharge capacity of each cycle was measured for evaluation.

[0126] The NVP positive electrode layer side was measured as follows: it was charged to the cutoff voltage of 4V at a current density equivalent to 0.1C, stopped for 10 hours, and then discharged to the cutoff voltage of 2.8V. This cycle was repeated 80 times, and the charge and discharge capacity of each cycle was measured for evaluation.

[0127] Figure 4This indicates the evaluation results for using HC half-cells. Figure 5 This indicates the evaluation results for half-cells using NVP. Figure 4 and Figure 5 In the diagram, the solid line represents the measurement result of the first cycle, the dashed line represents the measurement result of the tenth cycle, and the single-dot dashed line represents the measurement result of the eightyth cycle.

[0128] (2) Evaluation test of charge and discharge rate characteristics of half cell The aforementioned half-cell was connected to a multichannel potentiostat / galvanostat (Bio-Logic SP-150e) with the Na metal side serving as the reference electrode and counter electrode, and the negative electrode mixed material layer or NVP positive electrode layer side serving as the working electrode, and the measurements were performed at 25°C.

[0129] The measurements on the negative electrode hybrid material layer side are as follows: The electrode is charged to a cutoff voltage of 0V at a current density equivalent to 0.1C, stopped for 10 hours, and then discharged to a cutoff voltage of 3.1V. The charge-discharge cycle is repeated 5 times at current densities equivalent to 0.1C, 0.2C, 0.3C, 0.4C, and 0.5C, respectively, and the charge-discharge capacity of each cycle is measured for evaluation.

[0130] The measurements on the positive electrode side of the NVP were as follows: The capacitor was charged to a cutoff voltage of 4V at a current density equivalent to 0.1C, stopped for 10 hours, and then discharged to a cutoff voltage of 2.8V. The charge-discharge cycle was repeated 5 times at current densities equivalent to 0.05C, 0.1C, 0.2C, 0.5C, and 1.0C, and the charge-discharge capacity of each cycle was measured for evaluation.

[0131] Figure 6 This indicates the evaluation results for using HC half-cells. Figure 7 This indicates the evaluation results for half-cells using NVP. Figure 6 and Figure 7 In the diagram, the black square marks indicate the results of the charging capacity measurement, while the hollow triangle marks indicate the results of the discharging capacity measurement.

[0132] <Evaluation Methods for Full Batteries> The aforementioned full cell was connected to a multichannel potentiostat / galvanostat (Bio-Logic SP-150e) with the negative electrode hybrid material layer side serving as the reference electrode and counter electrode, and the NVP positive electrode layer side serving as the working electrode, and measurements were performed at 25°C. The measurements were as follows: the cell was charged to a cutoff voltage of 4.0V at a current density equivalent to 0.1C and discharged to a cutoff voltage of 1.5V, and this cycle was repeated 40 times. The charge-discharge capacity of each cycle was measured for evaluation. Figure 8 This indicates the evaluation results for full-cell batteries using HC.

[0133] This invention is not limited to the embodiments described above, and includes various modifications and variations within the same scope without departing from the spirit of the invention. Therefore, it should be understood that, in accordance with the above teachings, various combinations, forms, and other combinations and forms including only one element, its superordinate concept, or its subordinate concept also fall within the scope and spirit of this invention.

Claims

1. A composition, characterized in that, It contains oxides and sintering aids, wherein the oxides contain Na, Al, Zr and P as constituent elements.

2. The composition according to claim 1, wherein, The oxide also contains Si as a constituent element.

3. The composition according to claim 1, wherein, The sintering aid comprises at least one element selected from Na, B, Bi, Zn, Nb, and P as a constituent element.

4. The composition according to claim 1, wherein, The melting point of the sintering aid is below 1000℃.

5. The composition according to claim 1, wherein, The content of the sintering aid is 0.1 to 45.0 parts by mass relative to 100 parts by mass of the oxide.

6. The composition according to claim 1, wherein, The composition contains two or more of the aforementioned sintering aids.

7. The composition according to claim 1, wherein, The composition comprises one or more of the aforementioned sintering aids. The sintering aid may contain Na and B as constituent elements within the same molecule, or may contain Na and B as constituent elements within different molecules.

8. The composition according to any one of claims 1 to 7, wherein, The composition is used for solid electrolytes.

9. A fired product, characterized in that, It is a calcined product of the composition according to any one of claims 1 to 7.

10. The fired product according to claim 9, wherein, The sintered product has a NASICON-type crystal structure.

11. The fired product according to claim 10, wherein, The sintered product has the crystal structure shown in formula (1): In equation (1), M1 contains elements that can be divalent cations, M2 contains elements other than Al that can be trivalent cations, M3 contains elements other than Zr and Si that can be tetravalent cations, and a, b, c, d and e satisfy "a≥0", "b>0", "c≥0", "d≥0", "0≤e<3" and "a+b+c+d<2".

12. The fired product according to claim 11, wherein, The fired product satisfies b ≤ 0.

5.

13. The fired product according to claim 11, wherein, The fired product satisfies 1.5≤e≤2.

8.

14. The fired product according to claim 9, wherein, The relative density of the sintered material is above 80%.

15. A solid electrolyte, characterized in that, It includes the calcined product as described in claim 9.

16. An energy storage device, characterized in that, It possesses the solid electrolyte as described in claim 15.

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