Solid electrolyte for sodium ion secondary battery, method for manufacturing same, and all-solid sodium ion secondary battery

Abstract

Provided are a solid electrolyte for a sodium ion secondary battery excellent in ion conductivity, a method for manufacturing same, and an all-solid sodium ion secondary battery.　The solid electrolyte for a sodium ion secondary battery contains NASICON crystals expressed by a general formula NasZr2-tMtSiuP3-uO12 (M is at least one selected from Al, La, Mg, Nb, Y and Zn; 3.0 < s ≦ 4.6; 0 < t ≦ 0.3; 2.0 < u ≦ 3.0).

Description

Solid electrolyte for sodium-ion secondary batteries and method for manufacturing the same, and all-solid-state sodium-ion secondary battery

[0001] This invention relates to a solid electrolyte for sodium-ion secondary batteries, a method for producing the same, and an all-solid-state sodium-ion secondary battery using the solid electrolyte for sodium-ion secondary batteries.

[0002] Lithium-ion rechargeable batteries have established themselves as essential high-capacity, lightweight power sources for mobile devices, electric vehicles, and other applications. However, current lithium-ion rechargeable batteries primarily use flammable organic electrolytes, raising concerns about the risk of fire. To address this issue, development is underway on all-solid-state lithium-ion batteries that use a solid electrolyte instead of organic electrolytes. Furthermore, due to concerns about rising global raw material costs for lithium, development of all-solid-state sodium-ion rechargeable batteries is also progressing.

[0003] For example, Patent Document 1 describes a NASICON-type Na as a solid electrolyte. ３ Zr ２ Si ２ PO １２ An all-solid-state sodium-ion secondary battery using a sodium-ion conductive crystal composed of the above has been disclosed.

[0004] Japanese Patent Publication No. 2010-15782

[0005] NaSICON type Na ３ Zr ２ Si ２ PO １２ Solid electrolytes using sodium ion-conducting crystals composed of [a specific material] have insufficient ionic conductivity, and all-solid-state sodium-ion secondary batteries using such solid electrolytes have problems with insufficient output characteristics.

[0006] The object of the present invention is to provide a solid electrolyte for sodium-ion secondary batteries with excellent ionic conductivity, a method for producing the same, and an all-solid-state sodium-ion secondary battery.

[0007] The solid electrolyte for a sodium-ion secondary battery, its manufacturing method, and each aspect of the all-solid-state sodium-ion secondary battery for solving the above problems will be described.

[0008] The solid electrolyte for a sodium-ion secondary battery according to Aspect 1 of the present invention has the general formula Na ｓ Zr ２－ｔ M ｔ Si ｕ P ３－ｕ O １２ It is characterized by containing a NASICON crystal represented by (M is at least one selected from Al, La, Mg, Nb, Y, and Zn, 3.0 < s ≦ 4.6, 0 < t ≦ 0.3, 2.0 < u ≦ 3.0).

[0009] In the solid electrolyte for a sodium-ion secondary battery according to Aspect 2, in Aspect 1, further, in mol%, Na ２ O 10 to 80%, P ２ O ５ +B ２ O ３ +SiO ２ 10 to 85%, and Al ２ O ３ +Y ２ O ３ +Yb ２ O ３ +Nd ２ O ３ +Nb ２ O ５ +V ２ O ５ +TiO ２ +HfO ２ +ZrO ２ +MgO + CaO + BaO 0 to 55% is preferably included, containing a sodium-ion conductive glass.

[0010] In the solid electrolyte for a sodium-ion secondary battery according to Aspect 3, in Aspect 2, it is preferably composed of a sintered body containing the NASICON crystal and the sodium-ion conductive glass.

[0011] In the solid electrolyte for a sodium-ion secondary battery according to Aspect 4, in any one of Aspects 1 to 3, the NASICON crystal has the general formula Na ｓ Zr ２－ｔ Mｔ Si ｕ P ３－ｕ O １２ (It is preferable that M is represented as at least one selected from Al, La, and Zn, with 3.0 < s ≤ 4.6, 0 < t ≤ 0.3, and 2.0 < u ≤ 3.0).

[0012] In the solid electrolyte for sodium-ion secondary batteries according to Embodiment 5, it is preferable that it is for an all-solid-state sodium-ion secondary battery in any one of Embodiments 1 to 4.

[0013] The method for producing a solid electrolyte for a sodium-ion secondary battery according to aspect 6 of the present invention is based on the general formula Na ｓ Zr ２－ｔ M ｔ Si ｕ P ３－ｕ O １２ The method is characterized by including a step of calcining a raw material powder containing NASICON crystalline powder represented by (M is at least one selected from Al, La, Mg, Nb, Y, and Zn, 3.0 < s ≤ 4.6, 0 < t ≤ 0.3, 2.0 < u ≤ 3.0).

[0014] In the method for producing a solid electrolyte for a sodium-ion secondary battery according to embodiment 7, in embodiment 6, the raw material powder is further comprising, in mol%, Na ２ O 10-80%, P ２ O ５ +B ２ O ３ +SiO ２ 10-85%, and Al ２ O ３ +Y ２ O ３ +Yb ２ O ３ +Nd ２ O ３ +Nb ２ O ５ +V ２ O ５ +TiO ２ +HfO ２ +ZrO ２ It is preferable to include sodium ion conductive glass powder containing 0-55% of MgO + CaO + BaO.

[0015] The all-solid-state sodium-ion secondary battery according to aspect 8 of the present invention is characterized by comprising a solid electrolyte for a sodium-ion secondary battery according to any one of aspects 1 to 5.

[0016] According to the present invention, a solid electrolyte for sodium-ion secondary batteries with excellent ionic conductivity, a method for producing the same, and an all-solid-state sodium-ion secondary battery can be provided.

[0017] Figure 1 is a schematic cross-sectional view showing an all-solid-state sodium-ion secondary battery according to an embodiment of the present invention. Figure 2 is a schematic cross-sectional view showing the solid electrolyte layer in the all-solid-state sodium-ion secondary battery of Figure 1.

[0018] Preferred embodiments are described below. However, the following embodiments are merely illustrative, and the present invention is not limited to these embodiments. In addition, in each drawing, components having substantially the same function may be referred to by the same reference numerals.

[0019] (All-solid-state sodium-ion secondary battery) Figure 1 is a schematic cross-sectional view showing an all-solid-state sodium-ion secondary battery according to one embodiment of the present invention.

[0020] As shown in Figure 1, the all-solid-state sodium-ion secondary battery 1 comprises a solid electrolyte layer 2, a positive electrode layer 3, a negative electrode layer 4, a first current collector layer 5, and a second current collector layer 6.

[0021] The solid electrolyte layer 2 has opposing first main surface 2a and second main surface 2b. A positive electrode layer 3 is provided on the first main surface 2a of the solid electrolyte layer 2. In this embodiment, the positive electrode layer 3 and the solid electrolyte layer 2 are in contact. A first current collector layer 5 is provided on the main surface of the positive electrode layer 3 opposite to the solid electrolyte layer 2. A negative electrode layer 4 is provided on the second main surface 2b of the solid electrolyte layer 2. In this embodiment, the negative electrode layer 4 and the solid electrolyte layer 2 are in contact. The negative electrode layer 4 is provided in a position that overlaps with the positive electrode layer 3 in a plan view. Furthermore, a second current collector layer 6 is provided on the main surface of the negative electrode layer 4 opposite to the solid electrolyte layer 2. Note that the first current collector layer 5 and the second current collector layer 6 are not required.

[0022] Lead electrodes may be connected to the first current collector layer 5 and the second current collector layer 6 of the all-solid-state sodium-ion secondary battery 1. The lead electrodes electrically connect the all-solid-state sodium-ion secondary battery 1 to the outside.

[0023] The details of each layer in the all-solid-state sodium-ion secondary battery of the present invention will be described below.

[0024] (Solid Electrolyte Layer) Figure 2 is a schematic cross-sectional view showing the solid electrolyte layer in the embodiment shown in Figure 1.

[0025] The solid electrolyte layer 2 comprises a first solid electrolyte layer 7 and a pair of second solid electrolyte layers 8. The first solid electrolyte layer 7 has a third main surface 7a and a fourth main surface 7b. The third main surface 7a and the fourth main surface 7b face each other. One of the pair of second solid electrolyte layers 8 is provided on the third main surface 7a of the first solid electrolyte layer 7. The other second solid electrolyte layer 8 is provided on the fourth main surface 7b of the first solid electrolyte layer 7.

[0026] The first solid electrolyte layer 7 is specifically a dense layer. On the other hand, the second solid electrolyte layer 8 is specifically a porous layer. The second solid electrolyte layer 8 has voids that are connected in three dimensions. It is desirable that the first solid electrolyte layer 7 and the second solid electrolyte layer 8 are integrated.

[0027] The first solid electrolyte layer 7 has a denser structure than the second solid electrolyte layer 8. As a result, the first solid electrolyte layer 7 not only has the function of conducting ions, but also functions as a base layer to ensure the mechanical strength of the solid electrolyte layer 2.

[0028] As shown in Figure 2, in this embodiment, the second solid electrolyte layer 8 is provided on both the third main surface 7a and the fourth main surface 7b of the first solid electrolyte layer 7. However, the second solid electrolyte layer 8 may be provided on either the third main surface 7a or the fourth main surface 7b of the first solid electrolyte layer 7. Alternatively, the solid electrolyte layer 2 may consist only of the dense first solid electrolyte layer 7.

[0029] In this embodiment, a positive electrode layer 3 is provided on one of the second solid electrolyte layers 8. A negative electrode layer 4 is provided on the other second solid electrolyte layer 8. In this case, an anchoring effect acts between each of the porous second solid electrolyte layers 8 and the positive electrode layer 3 and the negative electrode layer 4.

[0030] More specifically, when the positive electrode layer 3 is formed on the surface of one of the second solid electrolyte layers 8, the active material powder constituting the positive electrode layer 3 easily penetrates into the voids. Similarly, when the negative electrode layer 4 is formed on the surface of the other second solid electrolyte layer 8, the active material powder constituting the negative electrode layer 4 easily penetrates into the voids. As a result, an anchoring effect acts between each second solid electrolyte layer 8 and the formed positive electrode layer 3 and negative electrode layer 4. Therefore, the adhesion between the solid electrolyte layer 2 and the positive electrode layer 3 and negative electrode layer 4 can be improved. This makes it possible to lower the contact resistance between the solid electrolyte layer 2 and the positive electrode layer 3 and negative electrode layer 4.

[0031] The same material can be used for the first solid electrolyte layer 7 and the second solid electrolyte layer 8 in the solid electrolyte layer 2. The solid electrolyte layer 2 is mainly composed of a solid electrolyte for sodium-ion secondary batteries.

[0032] The solid electrolyte for the sodium-ion secondary battery used in the solid electrolyte layer 2 contains NASICON crystals.

[0033] The NASICON crystal in this embodiment has the general formula Na ｓ Zr ２－ｔ M ｔ Si ｕ P ３－ｕ O １２ The compound consists of (where M is at least one selected from Al, La, Mg, Nb, Y, and Zn, with 3.0 < s ≤ 4.6, 0 < t ≤ 0.3, and 2.0 < u ≤ 3.0). Here, it is preferable that M is at least one selected from Al, La, and Zn. In this way, crystals with superior ionic conductivity can be obtained.

[0034] The preferred ranges for each coefficient in the above general formula are as follows:

[0035] The upper limit of s is 4.6 or less, preferably 4.3 or less, and most preferably 4.0 or less, 3.8 or less, and especially preferably 3.6 or less. If s is too large, excess sodium forms compounds that do not contribute to ion conduction, such as sodium phosphate and sodium silicate, which tends to reduce the ionic conductivity of the solid electrolyte. On the other hand, the lower limit of s is greater than 3.0, preferably 3.05 or more, and most preferably 3.1 or more, 3.2 or more, and especially preferably 3.3 or more. If s is too small, the amount of sodium ions decreases, which tends to reduce the ionic conductivity of the solid electrolyte.

[0036] The upper limit of t is 0.3 or less, preferably 0.28 or less, preferably 0.26 or less, 0.24 or less, and particularly preferably 0.22 or less. If t is too large, the three-dimensional network structure in the crystal decreases, which tends to reduce the ionic conductivity of the solid electrolyte. On the other hand, the lower limit of t is greater than 0, preferably 0.02 or more, preferably 0.04 or more, 0.06 or more, and particularly preferably 0.08 or more. If t is too small, the ionic conductivity of the solid electrolyte tends to decrease.

[0037] The upper limit of u is 3.0 or less, preferably 2.8 or less, and more preferably 2.7 or less, 2.6 or less, and particularly preferably 2.5 or less. If u is too large, excess sodium forms compounds that do not contribute to ion conduction, such as sodium phosphate and sodium silicate, which tends to reduce the ionic conductivity of the solid electrolyte. On the other hand, the lower limit of u is greater than 2.0, preferably 2.05 or more, and more preferably 2.1 or more, 2.2 or more, and particularly preferably 2.3 or more. If u is too small, the amount of sodium ions decreases, which tends to reduce the ionic conductivity of the solid electrolyte.

[0038] The NASICON crystal is preferably a monoclinic, hexagonal, or trigonal crystal, and more preferably a monoclinic or trigonal crystal. In this case, the ionic conductivity of the solid electrolyte can be further improved.

[0039] A specific example of a NASICON crystal is Na ３．４５ Zr １．９５ Al ０．０５ Si２．４ P ０．６ O １２ 、No ３．５ Zr １．９ Al ０．１ Yes ２．４ P ０．６ O １２ 、No ３．６ Zr １．８ Al ０．２ Yes ２．４ P ０．６ O １２ 、No ３．４５ Zr １．９５ Yes ０．０５ Yes ２．４ P ０．６ O １２ 、No ３．５ Zr １．９ Yes ０．１ Yes ２．４ P ０．６ O １２ 、No ３．６ Zr １．８ Yes ０．２ Yes ２．４ P ０．６ O １２ 、No ３．５ Zr １．９５ Zn ０．０５ Yes ２．４ P ０．６ O １２ 、No ３．６ Zr １．９ Zn ０．１ Yes ２．４ P ０．６ O １２ 、No ３．８ Zr １．８ Zn ０．２ Yes ２．４ P ０．６ O １２ 、No ３．３５ Zr １．９５ N﹂ ０．０５ Yes ２．４ P ０．６ O １２ 、No ３．３ Zr １．９ N﹂ ０．１ Yes ２．４ P ０．６ O １２ 、No ３．２ Zr １．８ N﹂ ０．２ Yes ２．４ P０．６ O １２ Na ３．４５ Zr １．９５ Y ０．０５ Si ２．４ P ０．６ O １２ Na ３．５ Zr １．９ Y ０．１ Si ２．４ P ０．６ O １２ Na ３．６ Zr １．８ Y ０．２ Si ２．４ P ０．６ O １２ Na ３．５ Zr １．９５ Mg ０．０５ Si ２．４ P ０．６ O １２ Na ３．６ Zr １．９ Mg ０．１ Si ２．４ P ０．６ O １２ Na ３．８ Zr １．８ Mg ０．２ Si ２．４ P ０．６ O １２ Examples of crystals include the following. These may be used individually or in combination of multiple types. Among them, the NASICON crystal is Na ３．４５ Zr １．９５ Al ０．０５ Si ２．４ P ０．６ O １２ Na ３．５ Zr １．９ Al ０．１ Si ２．４ P ０．６ O １２ Na ３．４５ Zr １．９５ La ０．０５ Si ２．４ P ０．６ O １２ Na ３．５ Zr １．９ La ０．１ Si ２．４ P ０．６ O １２ Na ３．６ Zr １．９ Zn０．１ Si ２．４ P ０．６ O １２ Na ３．８ Zr １．８ Zn ０．２ Si ２．４ P ０．６ O １２ This is preferable. In this case, the ionic conductivity of the NASICON crystal can be further improved.

[0040] The solid electrolyte for the sodium-ion secondary battery used in the solid electrolyte layer 2 preferably further contains sodium-ion conductive glass.

[0041] In this embodiment, the sodium ion conductive glass is composed of Na ions in mol%. ２ O 10-80%, P ２ O ５ +B ２ O ３ +SiO ２ 10-85%, and Al ２ O ３ +Y ２ O ３ +Yb ２ O ３ +Nd ２ O ３ +Nb ２ O ５ +V ２ O ５ +TiO ２ +HfO ２ +ZrO ２ It is preferable that the glass composition contains 0 to 55% of MgO + CaO + BaO. The reason for limiting the glass composition in this way is explained below. In the following explanation of the content of each component, unless otherwise specified, "%" refers to "mol%".

[0042] Na ２ O is a component that forms sodium ion conduction paths. It also has the effect of lowering the melting temperature and softening point. By lowering the softening point, it becomes possible to manufacture the solid electrolyte for the sodium ion secondary battery of the present invention by low-temperature sintering (e.g., below 1200°C). ２The upper limit of the O content is preferably 80% or less, and more preferably 75% or less, 70% or less, and particularly preferably 60% or less. ２ If the O content is too high, weather resistance tends to decrease. On the other hand, Na ２ The lower limit of the O content is preferably 10% or more, and more preferably 15% or more, 20% or more, 30% or more, and especially 40% or more. ２ If the oxygen content is too low, the sodium ion conductivity tends to decrease. Furthermore, it becomes difficult to obtain a dense sintered body.

[0043] P ２ O ５ , B ２ O ３ and SiO ２ These are network-forming components and have the effect of improving chemical durability. Furthermore, by including these components, when the solid electrolyte for the sodium-ion secondary battery of the present invention is manufactured by sintering, the sodium-ion conductive glass is more easily fused to the NASICON crystal, and sodium-ion conduction paths between the NASICON crystal particles are more easily formed. The upper limit of the total content of the above components is preferably 85% or less, and is preferably 80% or less, 75% or less, 70% or less, 67% or less, 65% or less, 60% or less, 55% or less, and particularly preferably 50% or less. If the content of the above components is too high, Na ２ The O content becomes relatively low, and ionic conductivity tends to decrease. On the other hand, the lower limit of the total amount of the above components is preferably 10% or more, 15% or more, and particularly preferably 20% or more. If the amount of the above components is too low, the above effect will be difficult to obtain. Of the above components, P ２ O ５ and SiO ２ , especially P ２ O ５ This is preferable because it has a significant effect in improving sodium ion conductivity. ２ O ５ , B ２ O ３ and SiO ２The upper limit of the content of each component is preferably 85% or less, and more preferably 80% or less, 75% or less, 70% or less, 67% or less, 65% or less, 60% or less, 55% or less, and particularly preferably 50% or less. On the other hand, P ２ O ５ , B ２ O ３ and SiO ２ The lower limit of the content of each component is preferably 10% or more, 15% or more, and particularly preferably 20% or more.

[0044] Al ２ O ３ , Y ２ O ３ Yb ２ O ３ , Nd ２ O ３ Nb ２ O ５ , V ２ O ５ , TiO ２ , HfO ２ , ZrO ２ MgO, CaO, and BaO are components that stabilize vitrification and simultaneously improve sodium ion conductivity. Furthermore, by including these components, when the raw material powder for the solid electrolyte of the present invention is sintered, the glass powder is more easily dissolved in the sodium ion conductive crystal powder, and sodium ion conduction paths are more easily formed between the sodium ion conductive crystal particles. As a result, the ionic conductivity of the solid electrolyte is also more easily improved. The upper limit of the total content of the above components is preferably 55% or less, 50% or less, and particularly preferably 40% or less. If the content of the above components is too high, vitrification tends to become unstable. On the other hand, the lower limit of the total content of the above components is preferably 0.1% or more, 0.5% or more, 1% or more, 5% or more, and particularly preferably 10% or more. Among the above components, Nb ２ O ５ , Y ２ O ３ and V ２ O ５ , especially Nb ２ O ５This is preferable because it has a high effect in improving sodium ion conductivity.

[0045] The porosity of the first solid electrolyte layer 7 is preferably smaller than that of the second solid electrolyte layer 8. The porosity is defined by the following formula (1). In formula (1), p is the bulk density and p0 is the true density.

[0046] Porosity = (1-p / p0) x 100 (%)...Formula (1)

[0047] The porosity of the first solid electrolyte layer 7 is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The lower limit of the porosity of the first solid electrolyte layer 7 is not particularly limited, but can be, for example, 0.1%.

[0048] The porosity of the second solid electrolyte layer 8 is preferably 25% or more, more preferably 30% or more, and even more preferably 40% or more. On the other hand, the porosity of the second solid electrolyte layer 8 is preferably 97% or less, more preferably 95% or less, and even more preferably 90% or less. When the porosity of the second solid electrolyte layer 8 is within the above range, three-dimensionally interconnected voids can be formed more easily, and the adhesion between the solid electrolyte layer 2 and the positive electrode layer 3 and the negative electrode layer 4 can be further improved.

[0049] The diameter of the pores constituting the voids in the second solid electrolyte layer 8 is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less. In this case, shrinkage of the solid electrolyte layer 2 can be further suppressed during the firing process when forming the solid electrolyte layer.

[0050] The pore diameter can be measured by performing 3D structural observation using X-ray CT and analyzing the images. It can also be determined by mercury intrusion or 3D reconstruction using SEM-FIB.

[0051] Furthermore, it is preferable that the second solid electrolyte layer 8 has pores with a diameter larger than the thickness of the first solid electrolyte layer 7. In this case, shrinkage of the solid electrolyte layer 2 can be further suppressed during the firing process when forming the solid electrolyte layer.

[0052] The arithmetic mean roughness Ra of the second solid electrolyte layer 8 is preferably 0.1 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. In this case, the adhesion between the solid electrolyte layer 2 and the positive electrode layer 3 or the negative electrode layer 4 can be further improved.

[0053] The second solid electrolyte layer 8 may be composed of multiple layers with different porosities. In this case, it is preferable that the multiple layers with different porosities are arranged such that the porosity decreases as the layer approaches the first solid electrolyte layer 7. The number of multiple layers with different porosities is preferably two or more, more preferably three or more, even more preferably four or more, particularly preferably five or more, preferably 200 or fewer, more preferably 150 or fewer, even more preferably 100 or fewer, particularly preferably 50 or fewer, even more preferably 20 or fewer, and most preferably 10 or fewer.

[0054] The thickness of the first solid electrolyte layer 7 is preferably 0.01 μm or more, more preferably 0.1 μm or more, even more preferably 1 μm or more, and particularly preferably 5 μm or more. On the other hand, the thickness of the first solid electrolyte layer 7 is preferably 70 μm or less, and more preferably 50 μm or less.

[0055] If the thickness of the first solid electrolyte layer 7 is too thin, the mechanical strength may decrease, warping may occur, or a short circuit may occur between the positive electrode layer 3 and the negative electrode layer 4. On the other hand, if the thickness of the first solid electrolyte layer 7 is too thick, the ionic conductivity in the first solid electrolyte layer 7 tends to decrease. In addition, the energy density per unit volume of the all-solid-state sodium-ion secondary battery 1 tends to decrease.

[0056] The thickness of the second solid electrolyte layer 8 is preferably 1 μm or more, preferably 2 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more. On the other hand, the thickness of the second solid electrolyte layer 8 is preferably 100 μm or less, and more preferably 80 μm or less.

[0057] If the thickness of the second solid electrolyte layer 8 is too thin, the amount of material constituting the positive electrode layer 3 and the negative electrode layer 4 that can penetrate the voids in the second solid electrolyte layer 8 will decrease. As a result, the contact area between the solid electrolyte layer 2 and the positive electrode layer 3 and the negative electrode layer 4 will decrease, and adhesion will tend to deteriorate. In this case, the number of ion conduction paths at the interface between the solid electrolyte layer 2 and the positive electrode layer 3 and the negative electrode layer 4 will decrease, and the internal resistance of the all-solid-state sodium-ion secondary battery 1 will tend to increase. Consequently, the rapid charge and discharge characteristics of the all-solid-state sodium-ion secondary battery 1 will tend to deteriorate.

[0058] On the other hand, if the thickness of the second solid electrolyte layer 8 is too thick, it becomes difficult to fill the entire void of the second solid electrolyte layer 8 with the material constituting the positive electrode layer 3 or the negative electrode layer 4. As a result, the energy density per unit volume of the all-solid-state sodium-ion secondary battery 1 decreases. In addition, the amount of shrinkage when forming the second solid electrolyte layer 8 increases, making the second solid electrolyte layer 8 more prone to delamination at the interface with the first solid electrolyte layer 7.

[0059] In this embodiment, when the first solid electrolyte layer 7 as a dense layer and the second solid electrolyte layer 8 as a porous layer are integrated, it is desirable that the thickness of the second solid electrolyte layer 8 be greater than the thickness of the first solid electrolyte layer 7, but this is not particularly limited.

[0060] In the solid electrolyte layer 2, the thickness ratio of the second solid electrolyte layer 8 to the first solid electrolyte layer 7 (second solid electrolyte layer 8 / first solid electrolyte layer 7) is preferably 1.01 or more, more preferably 1.1 or more, preferably 1000 or less, and more preferably 100 or less. In this case, shrinkage of the solid electrolyte layer 2 during the firing process when forming the solid electrolyte layer can be further suppressed. In addition, the adhesion between the solid electrolyte layer 2 and the electrode layer can be further improved.

[0061] The thickness of the solid electrolyte layer 2, that is, the combined thickness of the first solid electrolyte layer 7 and the second solid electrolyte layer 8, is preferably 10 μm or more, more preferably 12 μm or more, even more preferably 15 μm or more, and particularly preferably 17 μm or more. On the other hand, the combined thickness of the first solid electrolyte layer 7 and the second solid electrolyte layer 8 is preferably 170 μm or less, and more preferably 150 μm or less.

[0062] When the thickness of the solid electrolyte layer 2 is greater than or equal to the lower limit, the mechanical strength can be further improved. In addition, short circuits between the positive electrode layer 3 and the negative electrode layer 4 can be made less likely to occur. On the other hand, when the thickness of the solid electrolyte layer 2 is less than or equal to the upper limit, the distance required for ion conduction within the solid electrolyte layer 2 becomes shorter, and the ionic conductivity is further improved. In addition, the energy density per unit volume of the all-solid-state sodium-ion secondary battery 1 can be further increased.

[0063] The flatness of the solid electrolyte layer 2 is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. In this case, the handling properties of the solid electrolyte layer 2 can be further improved, and cracks during electrode formation can be made less likely to occur. The lower limit of the flatness of the solid electrolyte layer 2 is not particularly limited, but for example, it can be 0.1 μm or more.

[0064] In addition, flatness is defined in JIS B 0621-1984 as "the magnitude of the deviation of a planar feature from a geometrically correct plane." The flatness of the solid electrolyte layer 2 indicates the value of the gap created when one surface of the sheet is sandwiched between parallel planes.

[0065] The average crystal grain size of the solid electrolyte in the first solid electrolyte layer 7 is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.1 μm or more, preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, even more preferably 1 μm or less, and particularly preferably 0.6 μm or less. In this case, the uniformity and smoothness of the solid electrolyte in the first solid electrolyte layer 7 during green sheet molding can be further improved, and the adhesion during lamination and the density during firing can be improved, thereby improving the handling properties of the final solid electrolyte layer 2.

[0066] The average crystal grain size of the solid electrolyte in the second solid electrolyte layer 8 is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, particularly preferably 0.8 μm or more, most preferably 1.0 μm or more, preferably 100 μm or less, more preferably 50 μm or less, even more preferably 10 μm or less, even more preferably 5 μm or less, particularly preferably 3 μm or less, and most preferably 2 μm or less. This improves the uniformity and smoothness of the solid electrolyte in the second solid electrolyte layer 8 during green sheet molding, improves adhesion during lamination and density of the solid electrolyte skeleton during firing, and thus improves the handling of the final solid electrolyte layer 2.

[0067] The average crystal grain size of the solid electrolyte in the first solid electrolyte layer 7 and the second solid electrolyte layer 8 can be measured, for example, as follows.

[0068] First, a sample of the solid electrolyte layer 2 is folded to form a cross-section. Next, the sample is heat-treated. This heat treatment is preferably performed by thermal etching in an electric furnace. The heat treatment temperature can be, for example, 900°C or higher and 1600°C or lower. The heat treatment time can be, for example, 1 minute or higher and 60 minutes or lower.

[0069] Next, the cross-section of the heat-treated sample is observed using a scanning electron microscope (SEM). For example, for any 200 particles in the obtained SEM image, the size of each particle is counted using image analysis software, and the average particle size is determined. This allows the average crystal grain size of the solid electrolyte to be determined. In the image analysis, the area circle equivalent diameter of the crystal grain is used as the particle size.

[0070] Furthermore, a metal layer may be provided on the surface of the second solid electrolyte layer 8. When the negative electrode layer 4 formed on the second solid electrolyte layer 8 is made of metallic sodium or the like, the adhesion between the second solid electrolyte layer 8, the metal layer, and the negative electrode layer 4 can be increased. This reduces interfacial resistance, thereby increasing the discharge capacity.

[0071] The metals constituting the metal layer are not particularly limited, but for example, Sn, Ti, Bi, Au, Al, Cu, Sb, Pb, etc. can be used. These metals constituting the metal layer may be used individually or in combination of two or more. The metal layer may also be composed of an alloy of these metals.

[0072] The thickness of the metal layer is preferably 3 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, and particularly preferably 20 nm or more. On the other hand, the thickness of the metal layer is preferably 5 μm or less, more preferably 3 μm or less, even more preferably 1 μm or less, and particularly preferably 500 nm or less.

[0073] Methods for forming the metal layer include, for example, physical vapor phase methods such as vapor deposition or sputtering, or chemical vapor phase methods such as thermal CVD, MOCVD, or plasma CVD. Alternatively, liquid phase film deposition methods such as plating, sol-gel method, or spin coating may be used to form the metal layer. Among these, vapor deposition or sputtering is preferred for forming the metal layer. In this case, the thinning of the metal layer is easy, and the above-mentioned effects of providing a metal layer are easily obtained.

[0074] (Positive Electrode Layer) The positive electrode active material included in the positive electrode layer 3 shown in Figure 1 is not particularly limited, but includes sodium transition metal phosphate crystals containing Na, M (where M is at least one transition metal element selected from Cr, Fe, Mn, Co, V, and Ni), P, and O. A specific example is Na ２ FeP ２ O ７ Na ４ Fe ３ (PO ４ ) ２ (P ２ O ７ ), Na ４ Fe ５ (PO ４ ) ２ (P ２ O ７ ) ２ Na ３．６４ Fe ２．１８ (P ２ O ７ ) ２ Na ３ Fe ２ (PO ４ ) (P ２ O ７ ), NaFePO ４ Na ２ MnP ２ O ７ Na ４ Mn ３ (PO ４ ) ２ (P ２ O ７ ), Na ４ Mn ５ (PO ４ ) ２ (P ２ O ７ ) ２ Na ３．６４ Mn ２．１８ (P ２ O ７ ) ２ Na ３ V ２ (PO ４ ) ３ NaNiPO ４ Na ２ NiP ２ O ７ Na ４ Ni３ (PO ４ ) ２ (P ２ O ７ ), Na ４ Ni ５ (PO ４ ) ２ (P ２ O ７ ) ２ Na ３．６４ Ni ２．１８ (P ２ O ７ ) ２ Na ４ Ni ７ (PO ４ ) ６ Na ３ Ni ３ (PO ４ ) ２ (P ２ O ７ ), NaCoPO ４ Na ２ CoP ２ O ７ Na ４ Co ３ (PO ４ ) ２ (P ２ O ７ ), Na ４ Co ５ (PO ４ ) ２ (P ２ O ７ ) ２ Na ３．５ Cr １．５ Co ０．５ (PO ４ ) ３ Na ３．６４ Co ２．１８ (P ２ O ７ ) ２ Examples include the following. The sodium transition metal phosphate crystal is preferred because it has high capacity and excellent chemical stability. Among these, triclinic crystals belonging to space group P1 or P-1 are particularly preferred, especially those with the general formula Na ｘ M ｙ P ２ O ｚCrystals represented by (1.2 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8) are preferred because they have excellent cycle characteristics.

[0075] The positive electrode active material preferably consists of the above-mentioned positive electrode active material crystals and an amorphous phase. The positive electrode active material may be, for example, a crystallized glass formed by calcining a positive electrode active material precursor powder such as glass powder. By calcining the positive electrode active material precursor powder, positive electrode active material crystals are precipitated. In addition, an amorphous phase is formed together with the positive electrode active material crystals by calcination. The formation of the amorphous phase can improve the alkali ion conductivity within the electrode layer. It can also improve the adhesion between the current collector and the electrode layer.

[0076] Crystallized glass refers to a precursor glass containing an amorphous phase that has been heated to precipitate crystals. In other words, crystallized glass refers to a precursor glass containing an amorphous phase that has been fired to crystallize the amorphous phase. The entire amorphous phase may have transitioned to the crystalline phase, or some of the amorphous phase may remain. One type of crystal may be precipitated from the amorphous phase, or two or more types of crystals may be precipitated. Whether or not a glass is crystallized can be determined, for example, based on the peak angles shown by powder X-ray diffraction (XRD).

[0077] The lower limit of the content of the positive electrode active material is not particularly limited, but is preferably 30% or more by mass, preferably 40% or more, 50% or more, and especially preferably 60% or more. The upper limit of the content of the positive electrode active material is not particularly limited, but is preferably 99.9% or less by mass, preferably 95% or less, and especially preferably 90% or less. When the content of the positive electrode active material in the positive electrode layer 3 is within the above range, the battery capacity can be increased even more effectively.

[0078] The positive electrode layer 3 may contain a solid electrolyte. The solid electrolyte described in the "Solid Electrolyte Layer" section can be used. When the positive electrode layer 3 contains a solid electrolyte, the lower limit of the solid electrolyte content is preferably 0.1% or more by mass, 5% or more, and particularly preferably 10% or more. The upper limit of the solid electrolyte content is preferably 70% or less by mass, 60% or less, 50% or less, 40% or less, and particularly preferably 30% or less. When the solid electrolyte content is within the above range, integration of the positive electrode active material and the solid electrolyte can be achieved. Alternatively, when the positive electrode layer 3 is in contact with the solid electrolyte layer 2, integration of the two can be achieved. As a result, ion conductivity can be further improved, and battery characteristics can be more effectively enhanced.

[0079] The positive electrode layer 3 may contain a conductive additive. For example, conductive carbon can be used as the conductive additive. Examples of conductive carbon include acetylene black, carbon black, Ketjenblack, vapor-processed carbon fiber conductive additive (VGCF), carbon nanotubes, and graphene. The conductive additive is preferably a carbon-based conductive additive made of the above materials. When the positive electrode layer 3 contains a conductive additive, the lower limit of the conductive additive content is preferably 0.1% or more by mass, and particularly preferably 0.2% or more. The upper limit of the conductive additive content is preferably 20% or less by mass, and particularly preferably 10% or less, and particularly preferably 5% or less. When the content of the conductive additive in the positive electrode layer 3 is within the above range, it is possible to further improve ionic conductivity while ensuring high electronic conductivity in the positive electrode layer 3, and to further effectively improve battery characteristics.

[0080] The lower limit of the thickness of the positive electrode layer 3 is preferably 10 μm or more, more preferably 50 μm or more, and more preferably 100 μm or more. When the thickness of the positive electrode layer 3 is greater than or equal to the above lower limit, the charge and discharge capacity of the all-solid-state sodium-ion secondary battery 1 can be increased even further. On the other hand, the upper limit of the thickness of the positive electrode layer 3 is preferably 1000 μm or less, and more preferably 700 μm or less. If the thickness of the positive electrode layer 3 is too thick, the resistance to electron conduction increases, which may reduce the discharge capacity of the all-solid-state sodium-ion secondary battery 1. Alternatively, the operating voltage of the all-solid-state sodium-ion secondary battery 1 may decrease.

[0081] (Negative electrode layer) The negative electrode active material contained in the negative electrode layer 4 is not particularly limited, but for example, carbon electrode materials such as hard carbon and soft carbon can be used. Hard carbon is preferred as the carbon electrode material. However, the negative electrode active material may also contain alloy negative electrode active materials that can absorb sodium, such as tin, bismuth, lead, and phosphorus, or metallic sodium. It is preferable that the negative electrode layer 4 is not metallic sodium or a negative electrode layer containing metallic sodium.

[0082] The lower limit of the negative electrode active material content is not particularly limited, but is preferably 50% or more by mass, and particularly preferably 60% or more. The upper limit of the negative electrode active material content is not particularly limited, but is preferably 99.9% or less by mass, preferably 95% or less, and particularly preferably 90% or less. When the negative electrode active material content in the negative electrode layer 4 is within the above range, the battery capacity can be increased even more effectively.

[0083] The negative electrode layer 4 may contain a solid electrolyte. The solid electrolyte described in the "Solid Electrolyte Layer" section can be used. When the negative electrode layer 4 contains a solid electrolyte, the lower limit of the solid electrolyte content is preferably 0.1% or more by mass, 5% or more, and particularly preferably 10% or more. The upper limit of the solid electrolyte content is preferably 40% or less by mass, 35% or less, and particularly preferably 30% or less. When the solid electrolyte content is within the above range, integration of the negative electrode active material and the solid electrolyte can be achieved. Alternatively, when the negative electrode layer 4 is in contact with the solid electrolyte layer 2, integration of the two can be achieved. As a result, ionic conductivity can be further improved, and the battery characteristics of the sodium-ion secondary battery can be more effectively enhanced.

[0084] The negative electrode layer 4 may contain a conductive additive. For example, the conductive additive described in the "positive electrode layer" section can be used. When the negative electrode layer 4 contains a conductive additive, the lower limit of the conductive additive content is preferably 0.1% or more by mass, and particularly preferably 0.2% or more. The upper limit of the conductive additive content is preferably 5% or less by mass, 3% or less, and particularly preferably 2% or less. When the content of the conductive additive in the negative electrode layer 4 is within the above range, it is possible to further improve ionic conductivity while ensuring high electronic conductivity in the negative electrode layer 4, and to further effectively improve the battery characteristics of the sodium-ion secondary battery.

[0085] The lower limit of the thickness of the negative electrode layer 4 is preferably 0.3 μm or more, more preferably 3 μm or more, and more preferably 10 μm or more. When the thickness of the negative electrode layer 4 is greater than or equal to the above lower limit, the charge and discharge capacity of the all-solid-state sodium-ion secondary battery 1 can be increased even further. On the other hand, the upper limit of the thickness of the negative electrode layer 4 is preferably 500 μm or less, and more preferably 300 μm or less. If the thickness of the negative electrode layer 4 is too thick, the resistance to electron conduction increases, which may reduce the discharge capacity of the all-solid-state sodium-ion secondary battery 1. Alternatively, the operating voltage of the all-solid-state sodium-ion secondary battery 1 may decrease.

[0086] (First current collector layer and second current collector layer) In this embodiment, the first current collector layer 5 and the second current collector layer 6 are not particularly limited as long as they are electrically conductive. Examples of current collector materials include metallic materials such as aluminum, titanium, silver, copper, stainless steel, or alloys thereof. These metallic materials may be used individually or in combination. These alloys are alloys containing at least one of the above-mentioned metals. These metallic materials have high electrical conductivity and are less prone to chemical reactions during charging and discharging of sodium-ion secondary batteries, thus effectively increasing the capacity of the sodium-ion secondary battery and exhibiting excellent cycle characteristics due to charging and discharging.

[0087] In this regard, it is preferable that the first current collector layer 5 and the second current collector layer 6 are made of aluminum or an alloy containing aluminum. Since aluminum or an alloy containing aluminum has a low density among metallic materials, it can effectively increase the capacity of the sodium-ion secondary battery. Furthermore, it is preferable that the current collector made of aluminum or an alloy containing aluminum is carbon coated on its surface. By doing so, it is possible to prevent the formation of a passive oxide film on the surface of the first current collector layer 5 and the second current collector layer 6 during electrode firing, resulting in excellent cycle characteristics due to charge and discharge of the sodium-ion secondary battery.

[0088] The first current collector layer 5 and the second current collector layer 6 are preferably made of metal foil. Because metal foil is flexible, it can increase the contact area with the electrode layer and can be integrated with the extraction electrode when used as a sodium-ion secondary battery, thereby effectively increasing the capacity of the sodium-ion secondary battery and providing excellent cycle characteristics due to charge and discharge.

[0089] Furthermore, the first current collector layer 5 and the second current collector layer 6 are preferably made of foamed metal. Because foamed metal has a high specific surface area, it can increase the contact area with the positive electrode layer 3 and the negative electrode layer 4, resulting in excellent cycle characteristics due to charging and discharging of the sodium-ion secondary battery.

[0090] The thicknesses of the first current collector layer 5 and the second current collector layer 6 are preferably 10 nm or more and 100 μm or less, respectively. The thicknesses of the first current collector layer 5 and the second current collector layer 6 are preferably 50 μm or less, and more preferably 30 μm or less, respectively. In this case, the energy density of the sodium-ion secondary battery can be further increased. Alternatively, the thicknesses of the first current collector layer 5 and the second current collector layer 6 are preferably 30 nm or more, and more preferably 50 nm or more, respectively. In this case, the decrease in internal resistance of the battery due to reduced conductivity, which reduces discharge capacity, and the resulting decrease in gravimetric energy density and volumetric energy density can be further suppressed.

[0091] The following describes an example of a manufacturing method for producing the all-solid-state sodium-ion secondary battery 1 according to the present invention.

[0092] (Formation of the solid electrolyte layer) (a) Preparation of the green sheet for forming the first solid electrolyte layer First, a slurry is prepared by adding an organic vehicle containing a binder to the first solid electrolyte powder and at least one of the raw material powders of the first solid electrolyte powder. The raw material powder referred to here is a powder that will react in the subsequent calcination process to become a solid electrolyte. The binder is a material used to bind powdered materials together.

[0093] Next, the slurry is applied to the substrate and dried to produce a first solid electrolyte layer-forming green sheet. The drying temperature of the slurry can be, for example, 40°C or higher and 100°C or lower. The drying time of the slurry can be, for example, 3 minutes or higher and 24 hours or lower. After that, the first solid electrolyte layer-forming green sheet is peeled off from the substrate.

[0094] As the first solid electrolyte powder, for example, NASICON crystals can be prepared.

[0095] For example, if the raw material powder for the first solid electrolyte powder is a raw material powder for NASICON crystals, then the amount of Na in mol% is... ２ O 17.5% to 50%, Al ２ O ３ +Y ２ O３ +La ２ O ３ +MgO+Nb ２ O ５ +ZnO+ZrO ２ 12% to 45%, SiO ２ +P ２ O ５ Products containing 24% to 54% can be prepared.

[0096] Preferably, the average particle size of at least one of the first solid electrolyte powder and the raw material powder for the first solid electrolyte powder is 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. On the other hand, preferably, the average particle size of at least one of the first solid electrolyte powder and the raw material powder for the first solid electrolyte powder is 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, even more preferably 1 μm or less, and particularly preferably 0.6 μm or less. In this case, peeling of the porous second solid electrolyte layer 8 from the first solid electrolyte layer 7 can be made less likely to occur in the subsequent firing process.

[0097] In this specification, the average particle diameter refers to the average particle diameter D measured by a laser diffraction particle size distribution analyzer. ５０ This refers to the particle size at which the cumulative amount of the volume-based cumulative particle size distribution curve, measured by laser diffraction, reaches 50% when the cumulative amount is calculated from the smallest particles upwards.

[0098] As a binder, for example, a resin binder such as polypropylene carbonate can be used. Alternatively, as a resin binder, for example, polyvinyl alcohol (PVA), polyvinyl butyral (PVB) or other polyvinyl acetals, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, acrylic resin, ethyl methylcellulose, carboxymethylcellulose, ethylcellulose, alginic acid, polyethylene glycol, polyethylene carbonate or polypropylene carbonate or other polycarbonate resins, or copolymers thereof can be used. These binders may be used individually or in combination. Among these, polyvinyl butyral (PVB), acrylic resin, polyethylene carbonate or polypropylene carbonate or other polycarbonate resins are preferred as the binder.

[0099] Alternatively, the binder may be a glass binder. For example, a sodium ion conductive glass with the above-described composition can be used as the glass binder.

[0100] Organic vehicles may contain solvents, plasticizers, and other substances in addition to binders. For example, water or organic solvents such as ethanol or acetone can be used as solvents. However, when water is used as a solvent, alkaline components such as sodium may leach from the raw material powder, increasing the pH of the slurry and potentially causing the raw material powder to aggregate. Therefore, it is preferable to use organic solvents.

[0101] Preferably, the content of at least one of the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder contained in the slurry is 10% by mass or more, and more preferably 30% by mass or more. On the other hand, preferably, the content of at least one of the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder contained in the slurry is 80% by mass or less, and more preferably 50% by mass or less. The content of the binder contained in the slurry can be, for example, 5% by mass or more and 50% by mass or less.

[0102] The substrate to which the slurry is applied is not particularly limited, but for example, a resin film such as PET (polyethylene terephthalate) film can be used.

[0103] (b) Preparation of a green sheet for forming the second solid electrolyte layer First, a slurry is prepared by adding an organic vehicle containing a binder to a mixed powder containing the second solid electrolyte powder, at least one of the raw material powders for the second solid electrolyte powder, and a polymer powder. The polymer powder is a material for forming voids within the second solid electrolyte layer 8. Specifically, the voids are formed when the polymer powder is burned off in a later firing process.

[0104] Next, a second green sheet for forming a solid electrolyte layer is prepared by applying the slurry onto the substrate and drying it. The drying temperature of the slurry can be, for example, 40°C or higher and 100°C or lower. The drying time of the slurry can be, for example, 5 minutes or higher and 24 hours or lower. After that, the second green sheet for forming a solid electrolyte layer is peeled off the substrate.

[0105] As the second solid electrolyte powder and the raw material powder for the second solid electrolyte powder, at least one of them can be the same powder as the first solid electrolyte powder and the raw material powder for the first solid electrolyte powder described above.

[0106] Preferably, the average particle size of at least one of the powders from the second solid electrolyte powder and the raw material powder for the second solid electrolyte powder is 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, and particularly preferably 0.8 μm or more. On the other hand, preferably, the average particle size of at least one of the powders from the second solid electrolyte powder and the raw material powder for the second solid electrolyte powder is 100 μm or less, more preferably 50 μm or less, even more preferably 10 μm or less, even more preferably 5 μm or less, and particularly preferably 3 μm or less. In this case, peeling of the porous second solid electrolyte layer 8 from the first solid electrolyte layer 7 can be made less likely to occur in the subsequent firing process.

[0107] Examples of polymer powder materials include acrylic resin, polyacrylonitrile, polymethacrylonitrile, or polystyrene. A polymer powder consisting of one of these materials may be used alone, or multiple polymer powders consisting of different materials may be used in combination.

[0108] The average particle size of the polymer powder is preferably 0.1 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, and particularly preferably 10 μm or more. On the other hand, the average particle size of the polymer powder is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 70 μm or less, and particularly preferably 50 μm or less. If the average particle size of the polymer powder is too small, it becomes difficult to form three-dimensionally connected voids in the resulting second solid electrolyte layer 8. On the other hand, if the average particle size of the polymer powder is too large, the sintering of the resulting second solid electrolyte layer 8 may be insufficient, and the ionic conductivity may decrease.

[0109] The mixing ratio of the second solid electrolyte powder and at least one of the raw material powders for the second solid electrolyte powder to the polymer powder is preferably 75:25 to 3:97 by volume, more preferably 60:40 to 6:94, and even more preferably 40:60 to 9:91. If the polymer powder content is too low, it becomes difficult to form three-dimensionally connected voids in the resulting second solid electrolyte layer 8. On the other hand, if the polymer powder content is too high, the sintering of the resulting second solid electrolyte layer 8 may be insufficient, and the ionic conductivity may decrease.

[0110] Furthermore, the mixing ratio of the second solid electrolyte powder and at least one of the raw material powders for the second solid electrolyte powder to the polymer powder is preferably 95:5 to 20:80 by mass, more preferably 90:10 to 30:70, and even more preferably 80:20 to 40:60.

[0111] For the binder, solvent, plasticizer, and other components in the organic vehicle, the same components as those described in the section "Preparation of the Green Sheet for Forming the First Solid Electrolyte Layer" can be used.

[0112] Preferably, the content of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder contained in the slurry is 5% by mass or more, and more preferably 10% by mass or more. On the other hand, preferably, the content of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder contained in the slurry is 80% by mass or less, and more preferably 60% by mass or less. The content of the binder contained in the slurry can be, for example, 5% by mass or more and 30% by mass or less.

[0113] The substrate to which the slurry is applied is not particularly limited, but for example, a resin film such as PET (polyethylene terephthalate) film can be used.

[0114] (c) Preparation of laminated sheet Next, a laminated sheet is obtained by laminating the second solid electrolyte layer forming green sheet onto the main surfaces on both sides of the first solid electrolyte layer forming green sheet. Alternatively, the laminated sheet may be obtained by laminating each green sheet and then pressing it, such as by heating press. In this case, the adhesion between each green sheet can be further improved.

[0115] Alternatively, a slurry containing a second solid electrolyte powder, a mixed powder containing at least one of the raw material powders for the second solid electrolyte powder and a polymer powder, and an organic vehicle containing a binder may be applied to both main surfaces of the first solid electrolyte layer forming green sheet. A laminated sheet may then be obtained by drying the slurry.

[0116] (d) Firing of the laminated sheet Next, the obtained laminated sheet is fired. This forms a first solid electrolyte layer 7 and a second solid electrolyte layer 8. In this way, a solid electrolyte layer 2 can be obtained in which the second solid electrolyte layer 8, which is a porous layer, is provided on the main surfaces on both sides of the first solid electrolyte layer 7, which is a dense layer.

[0117] Furthermore, when forming the first solid electrolyte layer 7, it is desirable to remove the binder from the green sheet for forming the first solid electrolyte layer. When forming the second solid electrolyte layer 8, it is desirable to remove the binder and polymer powder from the green sheet for forming the second solid electrolyte layer.

[0118] The firing temperature is preferably 1200°C or higher, and more preferably 1210°C or higher. On the other hand, the firing temperature is preferably 1400°C or lower, and more preferably 1300°C or lower. If the firing temperature is too low, sintering tends to be insufficient. Alternatively, the reaction of the raw material powder becomes insufficient, making it difficult to form the desired crystals. On the other hand, if the firing temperature is too high, the amount of evaporation of sodium components, etc. increases, and heterogeneous crystals precipitate, which tends to reduce the ionic conductivity of the solid electrolyte layer 2.

[0119] The firing time is adjusted as appropriate to ensure sufficient sintering. Specifically, for example, the sintering time may be 10 minutes to 1200 minutes. It is particularly preferable that the sintering time be 20 minutes to 800 minutes.

[0120] It should be noted that a laminated sheet is not necessarily required when forming the solid electrolyte layer 2. For example, a slurry containing a second solid electrolyte powder, a mixed powder containing at least one of the raw material powders of the second solid electrolyte powder and a polymer powder, and an organic vehicle containing a binder may be applied to both main surfaces of the first solid electrolyte layer 7. The slurry may then be dried to obtain a laminate of the first solid electrolyte layer 7 and the second solid electrolyte green sheet. The solid electrolyte layer 2 may then be obtained by firing the laminate.

[0121] In this embodiment, a second solid electrolyte layer 8, which is a porous layer, is formed on both main surfaces of the first solid electrolyte layer 7, which is a dense layer. However, the second solid electrolyte layer 8 may be formed on only one main surface of the first solid electrolyte layer 7.

[0122] (Solid electrolyte precursor for sodium-ion secondary batteries and its solution) Examples of solid electrolyte precursor solutions for sodium-ion secondary batteries include solutions containing sodium elements and carbonate ions, which constitute the solid electrolyte for sodium-ion secondary batteries. In these solutions, the sodium elements are contained in the form of sodium ions. The solid electrolyte precursor for sodium-ion secondary batteries consists, for example, of a gelled or dried product of the solid electrolyte precursor solution for sodium-ion secondary batteries. The solid electrolyte for sodium-ion secondary batteries consists of a calcined product of the solid electrolyte precursor for sodium-ion secondary batteries.

[0123] As a solid electrolyte precursor solution for sodium-ion secondary batteries, a solution containing nitrate ions instead of carbonate ions can also be used.

[0124] In a solid electrolyte precursor solution for sodium-ion secondary batteries, the counterion of sodium ions is of the general formula NR ４ ＋ This is represented by the equation, where each R is independent of H and CH. ３ , C ２ H ５ and CH ２ CH ２ It is preferable that the ion contains at least one substituent selected from the group consisting of OH.

[0125] A solid electrolyte precursor solution for sodium-ion secondary batteries can be obtained, for example, by mixing water glass, sodium tripolyphosphate, and an aqueous solution of zirconium ammonia carbonate. Specifically, the water glass is sodium silicate.

[0126] (Formation of the negative electrode layer) The negative electrode layer 4 can be prepared, for example, using a paste containing a negative electrode active material precursor powder and, if necessary, a solid electrolyte powder and a conductive additive. Binders, plasticizers, solvents, etc., may be added to the paste as needed.

[0127] Furthermore, when obtaining the paste, it is preferable to use a solid electrolyte precursor solution for sodium-ion secondary batteries. Specifically, the solid electrolyte precursor solution for sodium-ion secondary batteries and the negative electrode active material precursor are mixed and then dried. This yields a powder mixture of the solid electrolyte precursor for sodium-ion secondary batteries and the negative electrode active material precursor. However, by mixing the solid electrolyte precursor for sodium-ion secondary batteries and the negative electrode active material precursor, a powder mixture of the solid electrolyte precursor for sodium-ion secondary batteries and the negative electrode active material precursor can be obtained without going through the drying process.

[0128] Next, the resulting mixture is ground into a powder and then mixed with a conductive additive and a binder in an organic solvent. If the negative electrode active material of the negative electrode layer 4 to be formed is hard carbon, hard carbon may be added to the powder mixture and mixed. For example, N-methyl-2-pyrrolidone can be used as the organic solvent. This yields a paste.

[0129] If the paste contains a binder, the binder may include, for example, cellulose derivatives such as carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose, hydroxyethylcellulose, and hydroxymethylcellulose, or water-soluble polymers such as polyvinyl alcohol; thermosetting resins such as thermosetting polyimide, phenolic resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, and polyurethane; polycarbonate resins such as polypropylene carbonate; and polyvinylidene fluoride.

[0130] The negative electrode layer 4 can be formed by applying the paste to one main surface of the solid electrolyte layer 2, drying it, and then firing it.

[0131] When firing the laminate of the solid electrolyte layer 2 and the paste, for example, N ２ It is preferable to perform the firing at a temperature of over 600°C and 1300°C or lower under an inert atmosphere. The above firing is preferably carried out under an inert atmosphere. For example, the above firing may be carried out under an Ar, Ne or He atmosphere, or under a vacuum. Alternatively, the above firing may be carried out under an H ２ It is preferable to carry out the process in a reducing atmosphere containing [a specific substance]. When firing is performed in an inert atmosphere or a reducing atmosphere, the initial charge-discharge efficiency of the all-solid-state sodium-ion secondary battery 1 can be further improved.

[0132] Furthermore, a small amount of oxygen may be present in the atmosphere, provided that the negative electrode active material does not oxidize or decompose during firing. The oxygen concentration can be, for example, 1000 ppm or less, but is not limited to this.

[0133] Alternatively, the negative electrode layer 4 may be formed by applying the paste onto a substrate such as PET (polyethylene terephthalate), drying it to create a green sheet, and then firing this green sheet.

[0134] As described above, the negative electrode layer 4 may be a metal film or an alloy film. In this case, the negative electrode layer 4 can be formed using, for example, a physical vapor phase method such as vapor deposition or sputtering, a chemical vapor phase method such as thermal CVD, MOCVD, or plasma CVD, or a liquid phase film deposition method such as plating, sol-gel method, or spin coating. Among these, it is preferable to use vapor deposition or sputtering to form the negative electrode layer 4. In this case, it is easier to improve the adhesion of the negative electrode layer 4 to the solid electrolyte layer 2.

[0135] (Negative electrode active material precursor) When sugars are used as negative electrode active material precursors, examples include cellulose, D-glucose, sucrose, etc. When biomass is used as a negative electrode active material precursor, examples include corn stalks, sorghum stalks, pine cones, mangosteen, argan shells, rice husks, dandelions, grain straw cores, ramie fibers, cotton, kelp, coconut endocarp, etc. When polymers are used as negative electrode active material precursors, examples include polyacrylonitrile (PAN), pitch, polyvinyl chloride (PVC), nanofibers, polyaniline, sodium polyacrylate, tires (tire polymers), phosphorus-doped PAN, etc.

[0136] (Formation of the positive electrode layer) A paste is prepared containing a positive electrode active material precursor, and optionally containing solid electrolyte powder and a conductive additive. The paste may optionally contain a binder, plasticizer, or solvent.

[0137] As the binder, the binder described in the section on "Formation of the negative electrode layer" can be used.

[0138] Next, the paste is applied to one main surface of the solid electrolyte layer 2 and the paste is dried. The drying temperature of the paste is not particularly limited, but for example, it can be 30°C or higher and 150°C or lower. The drying time of the paste is not particularly limited, but for example, it can be 5 minutes or higher and 600 minutes or lower. By drying the paste, an electrode composite layer is formed on one main surface of the solid electrolyte layer 2. This gives a solid electrolyte layer with electrode composite. The electrode composite layer may be in the form of compacted powder.

[0139] Subsequently, the solid electrolyte layer with electrode composite material is fired. It is preferable that the atmosphere during firing be a reducing atmosphere. The maximum temperature during firing can be, for example, 400°C to 600°C. The holding time at this temperature can be, for example, 5 minutes or more and less than 3 hours. The positive electrode layer 3 is obtained by the above firing.

[0140] (Positive electrode active material precursor and its preparation) Specifically, the positive electrode active material precursor is, for example, a positive electrode active material precursor powder. It is preferable that the positive electrode active material precursor powder consists of an amorphous oxide material that generates active material crystals by firing. When the positive electrode active material precursor powder consists of an amorphous oxide material, active material crystals are generated during firing, and it becomes possible to form a dense positive electrode layer 3 through softening and flow.

[0141] In this invention, the term "amorphous oxide material" is not limited to completely amorphous oxide materials, but also includes oxide materials that contain some crystals. Oxide materials that contain some crystals are, for example, oxide materials with a crystallinity of 10% or less.

[0142] The positive electrode active material precursor powder contains, in the following oxide equivalent mol%, Na ２ O 25% to 55%, Fe ２ O ３ +Cr ２ O ３ +MnO+CoO+V ２ O ５ +NiO 10% to 30%, and P ２ O ５ It is preferable that the composition contains 25% to 55%. The reason for limiting the composition in this way is explained below. In the following explanation of the content of each component, unless otherwise specified, "%" means "mol%".

[0143] Na ２ O is the general formula Na ｘ M ｙ P ２ O ｚ It is represented by , where 1 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8, and M is the main component of the active material crystal, being at least one transition metal element selected from Cr, Fe, Mn, Co, V, and Ni. Na ２ The O content is preferably 25% to 55%, and more preferably 30% to 50%. ２ If the O content is within the above range, the charge and discharge capacity of the all-solid-state sodium-ion secondary battery 1 can be further increased.

[0144] Fe ２ O３ , Cr ２ O ３ , MnO, CoO, V ２ O ５ And NiO also has the general formula Na ｘ M ｙ P ２ O ｚ The main component of the above active material crystal is represented by Fe. ２ O ３ +Cr ２ O ３ +MnO+CoO+V ２ O ５ The +NiO content is preferably 10% to 30%, and more preferably 15% to 25%. Fe ２ O ３ +Cr ２ O ３ +MnO+CoO+V ２ O ５ If the +NiO content is above the above lower limit, the charge and discharge capacity of the all-solid-state sodium-ion secondary battery 1 can be further increased. On the other hand, Fe ２ O ３ +Cr ２ O ３ +MnO+CoO+V ２ O ５ If the +NiO content is below the above upper limit, unwanted Fe ２ O ３ , Cr ２ O ３ , MnO, CoO, V ２ O ５ Alternatively, it can make it difficult for crystals such as NiO to precipitate. In this specification, when the content of a+b+c+... is described, for example, it means the total amount of a, b, and c.

[0145] To further improve the cycle characteristics of the all-solid-state sodium-ion secondary battery 1, Fe ２ O ３ It is preferable to actively include Fe. ２ O ３ The content is preferably 1% to 30%, more preferably 5% to 30%, even more preferably 10% to 30%, and particularly preferably 15% to 25%. Cr２ O ３ , MnO, CoO, V ２ O ５ The content of each component, and NiO, is preferably 0% to 30%, more preferably 10% to 30%, and even more preferably 15% to 25%. ２ O ３ , Cr ２ O ３ , MnO, CoO, V ２ O ５ When at least two components selected from and NiO are included, the total amount is preferably 10% to 30%, and more preferably 15% to 25%.

[0146] P ２ O ５ Also, the general formula Na ｘ M ｙ P ２ O ｚ The main component of the above active material crystal is represented by P. ２ O ５ The content is preferably 25% to 55%, and more preferably 30% to 50%. ２ O ５ If the content of is within the above range, the charge and discharge capacity of the all-solid-state sodium-ion secondary battery 1 can be further increased.

[0147] In addition to the above components, the cathode active material precursor powder also contains Nb ２ O ５ MgO, Al ２ O ３ , TiO ２ , ZrO ２ , or Sc ２ O ３The positive electrode active material precursor powder may contain these components. These components have the effect of increasing conductivity. Conductivity, in this context, specifically refers to electronic conductivity. Therefore, the inclusion of these components in the positive electrode active material precursor powder makes it easier to improve the rapid charge and discharge characteristics of the all-solid-state sodium-ion secondary battery 1. The total content of the above components is preferably 0% to 25%, and more preferably 0.2% to 10%. When the content of the above components is below the above upper limit, heterogeneous crystals that do not contribute to the battery characteristics are less likely to form, and the charge and discharge capacity of the all-solid-state sodium-ion secondary battery 1 can be further increased.

[0148] The positive electrode active material precursor powder contains, in addition to the above components, SiO ２ , B ２ O ３ , GeO ２ Ga ２ O ３ Sb ２ O ３ , or Bi ２ O ３ It may contain these components. When the raw materials for the positive electrode active material precursor powder contain these components, the glass-forming ability is further improved when obtaining the positive electrode active material precursor powder. This makes it easier to obtain a more homogeneous positive electrode active material precursor powder. The total content of the above components in the positive electrode active material precursor powder is preferably 0% to 25%, and more preferably 0.2% to 10%. Since these components do not contribute to the battery characteristics, if their content is too high, the charge and discharge capacity of the all-solid-state sodium-ion secondary battery 1 tends to decrease.

[0149] The positive electrode active material precursor powder is preferably prepared by melting and molding a batch of raw materials. This preparation method makes it easier to obtain amorphous positive electrode active material precursor powder with excellent homogeneity. Specifically, the positive electrode active material precursor powder can be prepared as follows.

[0150] First, raw materials are prepared to obtain a raw material batch to achieve the desired composition. Next, the obtained raw material batch is melted. The melting temperature can be adjusted as appropriate to ensure that the raw material batch is melted homogeneously. For example, a melting temperature of 800°C or higher is preferable, and 900°C or higher is more preferable. There is no particular upper limit to the melting temperature. However, if the melting temperature is too high, it can lead to energy loss and evaporation of sodium components, etc. For this reason, a melting temperature of 1500°C or lower is preferable, and 1400°C or lower is more preferable.

[0151] Next, the resulting molten material is molded. The molding method is not particularly limited; for example, the molten material may be poured between a pair of cooling rolls and molded into a film while rapidly cooling. Alternatively, the molten material may be poured into a mold and molded into an ingot.

[0152] Next, the obtained molded body is crushed to obtain a positive electrode active material precursor powder. The average particle size of the positive electrode active material precursor powder is preferably 0.01 μm or more and less than 0.7 μm, more preferably 0.03 μm or more and 0.6 μm or less, even more preferably 0.05 μm or more and 0.6 μm or less, and particularly preferably 0.1 μm or more and 0.5 μm or less.

[0153] (First current collector layer and second current collector layer) The method for forming the first current collector layer 5 and the second current collector layer 6 is not particularly limited, and for example, metal foil may be used, or physical vapor phase methods such as vapor deposition or sputtering may be used, or chemical vapor phase methods such as thermal CVD, MOCVD or plasma CVD may be used. Alternatively, as a method for forming the first current collector layer 5 and the second current collector layer 6, liquid phase film formation methods such as plating, sol-gel method or spin coating may be used.

[0154] The present invention will be described in more detail below based on specific examples, but the present invention is not limited in any way to the following examples and can be implemented with appropriate modifications without changing the gist of the invention.

[0155] Table 1 shows Examples 1 to 9, Table 2 shows Examples 10 to 18 and Comparative Example 1, and Table 3 shows Examples 19 to 21.

[0156]

[0157]

[0158]

[0159] (1) Preparation of NASICON crystal powder Sodium carbonate (Na ２ CO ３ ), zirconium oxide (ZrO ２ ), silicon dioxide (SiO ２ ), sodium metaphosphate ((NaPO ３ ) ６ Using the above, etc., the general formula Na listed in Tables 1 to 3 ｓ Zr ２－ｔ M ｔ Si ｕ P ３－ｕ O １２ The raw material powders were blended to achieve the specified composition. Next, the raw material powders were wet-mixed with ethanol as a medium for 4 hours. After that, the ethanol was evaporated, and the raw material powders were calcined at 1300°C for 4 hours, then pulverized and classified using an air classifier (MDS-3 model, manufactured by Nippon Pneumatic Mfg. Co., Ltd.). The classified powders were molded using a φ30 mm mold with a uniaxial press at 11 MPa, and then heat-treated at 1300°C for 4 hours to obtain a NASICON crystal-containing compound.

[0160] The obtained NASICON crystal-containing compound was pulverized using an alumina mortar and pestle and passed through a mesh with a 300 μm opening. The resulting powder was then processed using a φ5 mm ZrO ２ The boulders were ground using a Fritsch P6 planetary ball mill at 300 rpm for 30 minutes (with 15-minute breaks every 15 minutes), and then passed through a 20 μm mesh. Subsequently, NASICON crystal powder was obtained by classification using an air classifier. The preparation of the NASICON crystal-containing compound and the NASICON crystal powder was carried out in an environment with a dew point of -40°C or lower.

[0161] (2) Preparation of sodium ion conductive glass powder In Examples 1 to 18 and Comparative Example 1, the amount of Na was in mol%. ２ O 40%, P ２ O ５ 30%, Nb ２ O ５ Sodium carbonate (Na) is added to make up 30% of the composition. ２ CO ３ ), sodium metaphosphate ((NaPO ３ ) ６ ), niobium oxide (Nb ２ O ５ ), orthophosphate (H ３ PO ４ The carbonates and other materials were weighed and the raw material batch was prepared. The raw material batch was placed in a platinum container and melted in an electric furnace at 1000°C for 30 minutes to vitrify it.

[0162] Next, the molten glass was poured between a pair of rotating rollers and molded while rapidly cooling to obtain a film-like glass with a thickness of 0.1 to 2 mm. A φ20 mm ZrO2 ２ The material was ground using a ball mill with pebbles for 5 hours, then passed through a resin sieve with a mesh size of 120 μm, and the average particle size D ５０ This yielded a coarse glass powder with a particle size of 3 to 15 μm. Furthermore, by air classification of this coarse glass powder, the average particle size D was obtained. ５０ This yielded sodium ion conductive glass powder with a particle size of 2 μm. XRD measurements confirmed that all samples were amorphous.

[0163] Furthermore, in Examples 19 to 21, Na was used in mol%. ２ O 33.3%, B ２ O ３ Sodium tetraborate (anhydrous borax), etc., was weighed to achieve a composition of 66.7%, and the raw material batch was prepared. The raw material batch was placed in a platinum container and melted in an electric furnace at 1200°C for 60 minutes in an atmospheric atmosphere. The molten material was then poured between a pair of rotating rollers and molded while rapidly cooling to obtain a film-like glass. The obtained film-like glass was then ground using a ball mill and a planetary ball mill to obtain an average particle size (D ５０A glass powder with a diameter of 5 μm was obtained. Furthermore, XRD measurements confirmed that all samples were amorphous.

[0164] (3) Preparation of solid electrolyte for sodium-ion secondary battery The NASICON crystal powder and sodium-ion conductive glass powder prepared above were weighed in a mass ratio of 90:10 in Examples 1 to 18 and Comparative Example 1, and in a mass ratio of 95:5 in Examples 19 to 21, and mixed in a centrifugal mixer to obtain the raw material powder for the solid electrolyte powder. The raw material powder for the solid electrolyte powder was heated to 500 kgf / cm². ２ After pressure molding, a sintered body (solid electrolyte for sodium-ion secondary batteries) was obtained by firing at 1200°C for 4 hours.

[0165] The sodium ion conductivity was determined as follows: Gold electrodes were formed on both sides of the sintered body processed to a thickness of 1 mm, and the conductivity was determined by the AC impedance method to a value of 1 to 10 ７ Measurements were performed in the frequency range of Hz, and the resistance value of the sample was determined from the Cole-Cole plot. The sodium ion conductivity was calculated from the obtained resistance value. The results are shown in Tables 1 to 3.

[0166] In the solid electrolytes for sodium-ion secondary batteries of Examples 1 to 21, the sodium ion conductivity was 0.68 × 10⁻⁶. －３ In the solid electrolytes for sodium-ion secondary batteries of Examples 1-9 and 19-21, where S / cm or higher, and especially where M is Al, La, or Zn, the sodium ion conductivity is 1.35 × 10⁻⁶. －３ The conductivity was S / cm or higher. On the other hand, the solid electrolyte for sodium-ion secondary batteries in Comparative Example 1 had a sodium ion conductivity of 0.59 × 10⁻⁶. －３ The value was S / cm.

[0167] 1... All-solid sodium-ion secondary battery 2... Solid electrolyte layer 2a, 2b... First and second main surfaces 3... Positive electrode layer 4... Negative electrode layer 5... First current collector layer 6... Second current collector layer 7... First solid electrolyte layer 8... Second solid electrolyte layer 7a, 7b... Third and fourth main surfaces

Claims

General formula Na ｓ Zr ２－ｔ M ｔ Si ｕ P ３－ｕ O １２ A solid electrolyte for sodium-ion secondary batteries comprising a NASICON crystal represented as (where M is at least one selected from Al, La, Mg, Nb, Y, and Zn, 3.0 < s ≤ 4.6, 0 < t ≤ 0.3, 2.0 < u ≤ 3.0). Furthermore, in mol%, Na ２ O 10 to 80%, P ２ O ５ +B ２ O ３ +SiO ２ 10 to 85%, and Al ２ O ３ +Y ２ O ３ +Yb ２ O ３ +Nd ２ O ３ +Nb ２ O ５ +V ２ O ５ +TiO ２ +HfO ２ +ZrO ２ +MgO + CaO + BaO 0 to 55%, and a sodium ion conductive glass containing the same, the solid electrolyte for a sodium ion secondary battery according to claim 1. 　 The solid electrolyte for a sodium-ion secondary battery according to claim 2, comprising the sintered body containing the NASICON crystal and the sodium-ion conductive glass. 　 The aforementioned NASICON crystal has the general formula Na ｓ Zr ２－ｔ M ｔ Si ｕ P ３－ｕ O １２ A solid electrolyte for a sodium-ion secondary battery according to any one of claims 1 to 3, wherein M is at least one selected from Al, La, and Zn, 3.0 < s ≤ 4.6, 0 < t ≤ 0.3, and 2.0 < u ≤ 3.

0. A solid electrolyte for a sodium-ion secondary battery according to any one of claims 1 to 3, for use in an all-solid-state sodium-ion secondary battery. General formula Na ｓ Zr ２－ｔ M ｔ Si ｕ P ３－ｕ O １２ A method for producing a solid electrolyte for a sodium-ion secondary battery, comprising the step of calcining a raw material powder containing NASICON crystalline powder represented by (M is at least one selected from Al, La, Mg, Nb, Y, and Zn, 3.0 < s ≤ 4.6, 0 < t ≤ 0.3, 2.0 < u ≤ 3.0). 　 The aforementioned raw material powder further contains, in mol%, Na ２ O 10-80%, P ２ O ５ +B ２ O ３ +SiO ２ 10-85%, and Al ２ O ３ +Y ２ O ３ +Yb ２ O ３ +Nd ２ O ３ +Nb ２ O ５ +V ２ O ５ +TiO ２ +HfO ２ +ZrO ２ A method for producing a solid electrolyte for a sodium-ion secondary battery according to claim 6, comprising sodium-ion conductive glass powder containing 0 to 55% of +MgO +CaO +BaO. 　 An all-solid-state sodium-ion secondary battery comprising a solid electrolyte for a sodium-ion secondary battery as described in any one of claims 1 to 3.

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