All-solid-state sodium-ion secondary battery

Abstract

Provided is an all-solid-state sodium-ion secondary battery which has excellent charge-discharge efficiency and can achieve high energy density.　The all-solid-state sodium-ion secondary battery 1 comprises: a solid electrolyte layer 2 having a first main surface 2a and a second main surface 2b facing each other; a positive electrode layer 3 disposed on the first main surface 2a of the solid electrolyte layer 2; and a negative electrode layer 4 disposed on the second main surface 2b of the solid electrolyte layer 2, wherein the capacity ratio (negative electrode layer / positive electrode layer) of the negative electrode layer 4 to the positive electrode layer 3 is 0.10-1.10.

Description

[Technical Field]

[0001] This invention relates to an all-solid-state sodium-ion secondary battery. [Background technology]

[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 batteries, such as all-solid-state lithium-ion batteries, which use solid electrolytes instead of organic electrolytes.

[0003] Incidentally, in all-solid-state batteries, there is a challenge in that high-rate charging and discharging is difficult due to the difficulty in forming ion paths between the active material and the solid electrolyte. For this reason, various studies have been conducted on solid electrolytes with the aim of forming ion paths. Among them, sulfide-based solid electrolytes exhibit plasticity, and it is expected that ion paths can be formed by cold-pressing them together with the active material, causing the particles to adhere closely. However, sulfide-based solid electrolytes are unstable in the atmosphere and have the problem of generating toxic gases. In contrast, oxide-based solid electrolytes are stable in the atmosphere and are therefore expected to be safer batteries. However, oxide-based solid electrolytes that have lithium-ion conductivity have low ionic conductivity, which makes low-temperature operation and high-power output difficult. Therefore, as an alternative, the development of all-solid-state sodium-ion secondary batteries using oxide-based solid electrolytes that have sodium-ion conductivity is underway (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-15782 [Overview of the project] [Problems that the invention aims to solve]

[0005] In recent years, secondary batteries used as power sources for electric vehicles have been required to have higher energy density and higher capacity in order to enable long-distance driving.

[0006] In all-solid-state sodium-ion secondary batteries, it is difficult to use graphite, which is used in lithium-ion secondary batteries, as the negative electrode material, so the use of hard carbon and other materials is being considered. However, hard carbon has a larger capacity loss due to the initial irreversible capacity compared to graphite, so using it in all-solid-state sodium-ion secondary batteries results in a decrease in energy density.

[0007] The objective of the present invention is to provide an all-solid-state sodium-ion secondary battery that has excellent charge-discharge efficiency and can achieve high energy density. [Means for solving the problem]

[0008] Various embodiments of all-solid-state sodium-ion secondary batteries that solve the above problems will be described.

[0009] A solid-state sodium-ion secondary battery according to Embodiment 1 of the present invention comprises a solid electrolyte layer having a first main surface and a second main surface facing each other, a positive electrode layer provided on the first main surface of the solid electrolyte layer, and a negative electrode layer provided on the second main surface of the solid electrolyte layer, characterized in that the capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.10 or more and 1.10 or less.

[0010] The all-solid-state sodium-ion secondary battery according to embodiment 2 is characterized in that the positive electrode layer is of the general formula Na x M y P2O zIt is preferable that the positive electrode active material consists of crystallized glass containing crystals represented by (1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, where M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr).

[0011] In the all-solid-state sodium-ion secondary battery according to Embodiment 3, in Embodiment 1 or Embodiment 2, it is preferable that the negative electrode layer contains a negative electrode active material made of hard carbon.

[0012] The all-solid-state sodium-ion secondary battery according to Embodiment 4 is, in any one embodiment from Embodiments 1 to 3, the positive electrode layer is of the general formula Na x M y P2O z The positive electrode active material is made of crystallized glass containing crystals represented by (1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, where M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr), and the negative electrode layer is made of hard carbon and contains a negative electrode active material, and it is preferable that the thickness ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.05 or more and 0.45 or less.

[0013] In the all-solid-state sodium-ion secondary battery according to Embodiment 5, it is preferable that the solid electrolyte layer, in any one embodiment from Embodiments 1 to 4, includes a solid electrolyte in which the solid electrolyte layer is at least one selected from the group consisting of β-alumina, β''-alumina, and NASICON crystal.

[0014] In the all-solid-state sodium-ion secondary battery according to embodiment 6, it is preferable that metallic sodium is deposited inside the negative electrode layer when charging is complete, in any one embodiment from embodiment 1 to embodiment 5.

[0015] A solid-state sodium-ion secondary battery according to embodiment 7 of the present invention comprises a solid electrolyte layer having a first main surface and a second main surface facing each other, a positive electrode layer provided on the first main surface of the solid electrolyte layer, and a negative electrode layer provided on the second main surface of the solid electrolyte layer, wherein the positive electrode layer is of the general formula Na x My P2O z It contains a positive electrode active material made of crystallized glass containing crystals represented by (1 ≦ x ≦ 2.8, 0.95 ≦ y ≦ 1.6, 6.5 ≦ z ≦ 8, M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr). The negative electrode layer contains a negative electrode active material made of hard carbon, and the thickness ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.05 or more and 0.45 or less.

Effects of the Invention

[0016] According to the present invention, it is possible to provide an all-solid-state sodium ion secondary battery that is excellent in charge-discharge efficiency and can achieve a high energy density.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 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] FIG. 2 is a diagram showing the results of the charge-discharge test of Example 1. [Figure 3] FIG. 3 is a diagram showing the results of the charge-discharge test of Comparative Example 7. [Figure 4] FIG. 4 is an X-ray diffraction spectrum of the negative electrode layer in the all-solid-state battery fabricated in Example 1. [Figure 5] FIG. 5 is an X-ray diffraction spectrum of the negative electrode layer in the all-solid-state battery fabricated in Comparative Example 1. [Figure 6] FIG. 6(a) is a SEM image of the cross-section of the negative electrode layer at the end of charging of the all-solid-state battery fabricated in Example 1, and FIG. 6(b) is an elemental mapping image of Na by SEM-EDX of the cross-section of the negative electrode layer at the end of charging. [Figure 7] FIG. 7(a) is a SEM image of the cross-section of the negative electrode layer at the end of discharging of the all-solid-state battery fabricated in Example 1, and FIG. 7(b) is an elemental mapping image of Na by SEM-EDX of the cross-section of the negative electrode layer at the end of discharging.

Modes for Carrying Out the Invention

[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. 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.

[0020] In this embodiment, the solid electrolyte layer 2 is made of a sodium ion conductive oxide. The solid electrolyte layer 2 also has a first main surface 2a and a second main surface 2b that are opposite to each other.

[0021] A positive electrode layer 3 is provided on the first main surface 2a of the solid electrolyte layer 2. The positive electrode layer 3 contains a positive electrode active material capable of adsorbing and releasing sodium. In this embodiment, the positive electrode layer 3 is a material of the general formula Na x M y P2O z The positive electrode active material is made of crystallized glass containing crystals represented by (1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, where M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr). Furthermore, 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. Note that the first current collector layer 5 may be omitted.

[0022] A negative electrode layer 4 is provided on the second main surface 2b of the solid electrolyte layer 2. The negative electrode layer 4 contains a negative electrode active material capable of adsorbing and releasing sodium. In this embodiment, the negative electrode layer 4 contains a negative electrode active material made of hard carbon. 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. The second current collector layer 6 is optional.

[0023] In this embodiment, the capacity ratio of the negative electrode layer 4 to the positive electrode layer 3 (negative electrode layer / positive electrode layer) is 0.10 or more and 1.10 or less. Therefore, the all-solid-state sodium-ion secondary battery 1 has excellent charge-discharge efficiency and can achieve high energy density. This will be explained in detail below.

[0024] In all-solid-state sodium-ion secondary batteries, it is difficult to use graphite, which is used in lithium-ion secondary batteries, as the negative electrode material, so the use of hard carbon and other materials is expected. However, hard carbon has the problem of lowering the energy density when used in all-solid-state sodium-ion secondary batteries because it has a larger capacity loss due to the initial irreversible capacity compared to graphite.

[0025] Therefore, in all-solid-state sodium-ion secondary batteries, when the capacity of the negative electrode layer (supported capacity) is greater than the capacity of the positive electrode layer (negative electrode excess), sodium ions are consumed by the irreversible capacity of the negative electrode layer, and the energy density tends to decrease. On the other hand, when the capacity of the positive electrode layer is greater than the capacity of the negative electrode layer (positive electrode excess), the ratio of sodium ions consumed by the negative electrode layer to the amount of sodium ions released by the positive electrode layer can be reduced, thereby improving charge-discharge efficiency and increasing energy density.

[0026] Incidentally, when hard carbon is used for the negative electrode layer, sodium ions released from the positive electrode layer during charging are absorbed into the spaces between carbon layers and into the pores within the carbon particles of the hard carbon. Therefore, in the case of a positive electrode excess, some sodium ions may not be absorbed and may precipitate (electrodeposit) as metallic sodium. In this case, in liquid-based batteries, the precipitated metallic sodium can reach the positive electrode layer via the electrolyte and cause a short circuit, which poses a safety problem.

[0027] In contrast, in all-solid-state sodium-ion secondary batteries, the solid electrolyte has excellent ionic conductivity, making it easy to ionize the sodium element released from the negative electrode layer during discharge. Furthermore, metallic sodium is less likely to precipitate along the grain boundaries within the solid electrolyte, thus preventing internal short circuits in the battery. In addition, even if a short circuit occurs, the risk of ignition is small, allowing for safe use even with an excess of positive electrode material.

[0028] Furthermore, metallic sodium that does not electrodeposit within the solid electrolyte precipitates on the surface of the hard carbon, at the interface between the solid electrolyte and the negative electrode layer, or in the voids within the negative electrode layer. Because of this low reactivity with moisture, it can be used safely. In particular, when the negative electrode layer is composed of a composite of hard carbon and an oxide-based solid electrolyte, the metallic sodium is embedded and precipitated within the composite, resulting in even lower reactivity with moisture and safer use. Additionally, the metallic sodium precipitated on the surface of the hard carbon, at the interface between the solid electrolyte and the negative electrode layer, or in the voids within the negative electrode layer can undergo reversible deposition and dissolution during charging and discharging. While the exact reason is unclear, it is thought that solid electrolytes have higher reduction resistance than the electrolytes used in liquid-based batteries, thus reducing the degradation of metallic sodium, and that even when metallic sodium precipitates, the sodium ion conduction path is less likely to be interrupted. This allows for improved charge-discharge efficiency and higher energy density.

[0029] Thus, the inventors have found that in an all-solid-state sodium-ion secondary battery, by setting the capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) to 0.10 or more and 1.10 or less, it is possible to improve charge and discharge efficiency and increase energy density while ensuring safety.

[0030] In the present invention, the capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 1.10 or less, preferably 0.80 or less, and more preferably 0.60 or less. When the capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is below the above upper limit, the charge and discharge efficiency of the all-solid-state sodium-ion secondary battery can be further improved, and an even higher energy density can be achieved.

[0031] Furthermore, the capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.10 or higher, preferably 0.30 or higher, and more preferably 0.40 or higher. When the capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is equal to or higher than the above lower limit, the cycle characteristics of the all-solid-state sodium-ion secondary battery 1 can be further improved.

[0032] The capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.10 or more and 1.10 or less, preferably 0.30 or more and 0.80 or less, and more preferably 0.40 or more and 0.60 or less. In this case, the charge-discharge efficiency of the all-solid-state sodium-ion secondary battery can be further improved, and an even higher energy density can be achieved. Furthermore, since the deposition of metallic sodium in the negative electrode layer can be controlled to an appropriate amount that does not destroy the electrode structure, the cycle characteristics of the all-solid-state sodium-ion secondary battery can be easily improved. On the other hand, the deposition of metallic sodium in the solid electrolyte layer can be suppressed, making short circuits less likely.

[0033] The capacitance ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) can be adjusted, for example, by the types of materials constituting the positive and negative electrode layers, the ratio of positive and negative electrode active materials, and the thickness of the negative electrode layer relative to the positive electrode layer.

[0034] For example, as in the above embodiment, the positive electrode layer 3 is of the general formula Na x M y P2O zThe positive electrode active material is made of crystallized glass containing crystals represented by (1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, where M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr), and the negative electrode layer 4 contains a negative electrode active material made of hard carbon. In this case, the thickness ratio of the negative electrode layer 4 to the positive electrode layer 3 (negative electrode layer / positive electrode layer) is preferably 0.45 or less, more preferably 0.35 or less, and even more preferably 0.25 or less. When the thickness ratio of the negative electrode layer 4 to the positive electrode layer 3 (negative electrode layer / positive electrode layer) is less than or equal to the above upper limit, the charge-discharge efficiency of the all-solid-state sodium-ion secondary battery 1 can be further improved, and an even higher energy density can be achieved.

[0035] Furthermore, the thickness ratio of the negative electrode layer 4 to the positive electrode layer 3 (negative electrode layer / positive electrode layer) is preferably 0.025 or higher, more preferably 0.050 or higher, and even more preferably 0.150 or higher. When the thickness ratio of the negative electrode layer 4 to the positive electrode layer 3 (negative electrode layer / positive electrode layer) is equal to or greater than the above lower limit, the cycle characteristics of the all-solid-state sodium-ion secondary battery 1 can be further improved.

[0036] Furthermore, in another embodiment of the present invention, the thickness ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.05 or more and 0.45 or less. In this case as well, the all-solid-state sodium-ion secondary battery exhibits excellent charge-discharge efficiency and can achieve high energy density.

[0037] In the present invention, the thickness ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) may be 0.05 or more and 0.45 or less, preferably 0.10 or more and 0.35 or less, and more preferably 0.125 or more and 0.30 or less. In this case, the charge-discharge efficiency of the all-solid-state sodium-ion secondary battery can be further improved, and an even higher energy density can be achieved. Furthermore, it becomes easier to precipitate metallic sodium in the negative electrode layer, making it easier to improve the safety of the all-solid-state sodium-ion secondary battery. On the other hand, the precipitation of metallic sodium in the solid electrolyte layer can be suppressed, making short circuits less likely. Unless otherwise specified, the thickness and thickness ratio of the positive electrode layer and negative electrode layer refer to the thickness after sintering when manufactured by a manufacturing method such as the examples described later.

[0038] The thickness of the positive electrode layer 3 is preferably 50 μm or more, more preferably 200 μm or more, more preferably 1000 μm or less, and more preferably 600 μm or less. The thickness of the negative electrode layer 4 is preferably 10 μm or more, more preferably 40 μm or more, more preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0039] Furthermore, in the present invention, as described above, it is preferable that metallic sodium precipitates inside the negative electrode layer when charging is complete. In this case, the precipitation of metallic sodium in the solid electrolyte layer can be prevented, thereby further improving the safety of the all-solid-state sodium-ion secondary battery.

[0040] In this invention, the capacities of the positive and negative electrode layers can be calculated by multiplying the weight of the active material supported in the positive and negative electrode layers by the theoretical capacity of that active material. Alternatively, it is possible to measure the capacities of the positive and negative electrodes by creating half-cells (using metallic Na as the counter electrode) for both the positive and negative electrodes and performing charge and discharge operations on each half-cell. Furthermore, when measuring the capacities of the positive and negative electrodes in an all-solid-state sodium-ion secondary battery (finished product), the all-solid-state sodium-ion secondary battery can be disassembled to separate the positive and negative electrodes, half-cells can be created for each, and then the capacities of the positive and negative electrodes can be measured by performing charge and discharge operations on each half-cell.

[0041] Furthermore, in the present invention, the negative electrode capacity utilization rate of the negative electrode layer is preferably 80% or more, more preferably 101% or more, even more preferably 116% or more, particularly preferably 120% or more, preferably 500% or less, more preferably 400% or less, and even more preferably 300% or less. In this case, the initial charge-discharge efficiency and discharge capacity of the all-solid-state sodium-ion secondary battery can be further improved. The negative electrode capacity utilization rate of the negative electrode layer can be calculated from the battery capacity / negative electrode capacity. In addition, as in the examples described later, if the charge-discharge test is performed based on the positive electrode capacity, it can be calculated as battery capacity = positive electrode capacity.

[0042] The details of each layer constituting the all-solid-state sodium-ion secondary battery of the present invention, such as the all-solid-state sodium-ion secondary battery 1, will be described below.

[0043] (Solid electrolyte layer) The solid electrolyte constituting the solid electrolyte layer is preferably formed from a sodium ion conductive oxide. Examples of sodium ion conductive oxides include compounds containing at least one element selected from Al, Y, Zr, Si, and P, as well as Na and O. Specific examples include beta-alumina or NASICON crystals, which exhibit excellent sodium ion conductivity. Preferably, the sodium ion conductive oxide is β-alumina or β''-alumina, which exhibits even better sodium ion conductivity.

[0044] Beta-alumina exists in two crystalline forms: β-alumina (theoretical empirical formula: Na2O·11Al2O3) and β''-alumina (theoretical empirical formula: Na2O·5,3Al2O3). Since β''-alumina is a metastable substance, it is usually used with Li2O or MgO added as a stabilizer. Because β''-alumina has a higher sodium ion conductivity than β-alumina, it is preferable to use β''-alumina alone or a mixture of β''-alumina and β-alumina, and Li2O-stabilized β''-alumina (Na 1.7 Li 0.3 Al 10.7 O 17 ) or MgO-stabilized β"-alumina ((Al 10.32 Mg 0.68 O 16 )(Na 1.68 Using O)) is more preferable.

[0045] As for NASICON crystals, Na3Zr2Si2PO 12 na 3.4 Zr2Si 2.4 P 0.6 O 12 na 3.4 Zr 1.9 Mg 0.1 Si 2.4 P 0.6 O 12 na 3.4 Zr 1.9 Zn 0.1 Si 2.4 P 0.6 O 12 na 3.4 Zr1.9 Mg 0.1 Si 2.2 P 0.8 O 12 、 Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 、 Na 3.2 Zr 1.3 Si 2.2 P 0.7 O 10.5 、 Na3Zr 1.6 Ti 0.4 Si2PO 12 、 Na3Hf2Si2PO 12 、 Na 3.4 Zr 0.9 Hf 1.4 Al 0.6 Si 1.2 P 1.8 O 12 、 Na3Zr 1.7 Nb 0.24 Si2PO 12 、 Na 3.6 Ti 0.2 Y 0.7 Si 2.8 O9、 Na3Zr 1.88 Y 0.12 Si2PO 12 、 Na 3.12 Zr 1.88 Y 0.12 Si2PO 12 、 Na 3.6 Zr 0.13 Yb 1.67 Si 0.11 P 2.9 O 12 etc. can be mentioned. As NASICON crystals, particularly Na 3.4 Zr2Si 2.4 P 0.6 O 12 、 Na3Zr 1.7 Nb 0.24 Si2PO 12 are preferable because they have excellent sodium ion conductivity.

[0046] The solid electrolyte layer can be manufactured by mixing raw material powders, molding the mixed raw material powders, and then firing them. For example, it can be manufactured by slurrying the raw material powders to produce a green sheet and then firing the green sheet. Alternatively, it may be manufactured by the sol-gel method.

[0047] The thickness of the solid electrolyte layer is preferably in the range of 5 μm to 1000 μm, and more preferably in the range of 20 μm to 200 μm. If the thickness of the solid electrolyte layer is too thin, the mechanical strength will decrease and it will be prone to breakage, making internal short circuits likely to occur. If the thickness of the solid electrolyte layer is too thick, the sodium ion conduction distance associated with charge and discharge will become long, resulting in a high internal resistance, and the discharge capacity and operating voltage will be prone to decrease. Also, the energy density per unit volume of the all-solid-state sodium ion secondary battery will be prone to decrease.

[0048] (Positive electrode layer) The positive electrode active material contained in the positive electrode layer is not particularly limited, but is preferably a positive electrode active material composed of crystallized glass containing a crystal represented by the general formula Na x M y P2O z (1 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8, and M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr). Among them, it is more preferably a positive electrode active material composed of crystallized glass containing a crystal represented by the general formula Na x MP2O7 (1 ≤ x ≤ 2, and M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr). Examples of such positive electrode active material crystals include Na2FeP2O7, Na2CoP2O 7、 Na2NiP2O7, etc. can be used.

[0049] In this disclosure, "crystallized glass" refers to a precursor glass containing an amorphous phase that has been heated (fired) to precipitate crystals (crystallize). The amorphous phase may all be transformed into a crystalline phase, or some of the amorphous phase may remain. One type of crystal may be precipitated, or two or more types of crystals may be precipitated. For example, whether or not a glass is crystallized can be determined by the peak angle shown by powder X-ray diffraction (XRD).

[0050] Furthermore, the positive electrode layer may contain a sodium ion-conducting solid electrolyte and a conductive additive. The ratio of each material in the positive electrode layer can be, for example, 60% to 99.9% by mass of the positive electrode active material, 0% to 30% of the sodium ion-conducting solid electrolyte, and 0.1% to 10% of the conductive additive.

[0051] The sodium ion conductive solid electrolyte can be, for example, the one described in the section on the solid electrolyte layer. The sodium ion conductive solid electrolyte is preferably used in powder form. The average particle size of the sodium ion conductive solid electrolyte powder is preferably 0.05 μm or more and 3 μm or less, more preferably 0.05 μm or more and less than 1.8 μm, even more preferably 0.05 μm or more and 1.5 μm or less, particularly preferably 0.1 μm or more and 1.2 μm or less, and most preferably 0.1 μm or more and 0.7 μm or less.

[0052] Furthermore, conductive carbon can be used as a conductive additive. Examples of conductive carbon include acetylene black, carbon black, Ketjenblack, vapor-processed carbon fiber conductive additive (VGCF), and carbon nanotubes. The conductive additive is preferably a carbon-based conductive additive made from the materials described above.

[0053] The positive electrode layer can be formed, for example, by forming an electrode material layer containing a positive electrode active material precursor and, optionally, sodium ion conductive solid electrolyte powder and a conductive additive on the main surface of a solid electrolyte layer, and then firing the electrode material layer. The electrode material layer can also be obtained, for example, by applying a paste containing, optionally, solid electrolyte powder and a conductive additive to the positive electrode active material precursor and drying it. The paste may optionally contain a binder, plasticizer, or solvent. The electrode material layer may also be in the form of compacted powder.

[0054] The drying temperature of the paste is not particularly limited, but for example, it can be between 30°C and 150°C. The drying time of the paste is also not particularly limited, but for example, it can be between 5 minutes and 600 minutes.

[0055] Furthermore, a reducing atmosphere is preferable during firing. The firing temperature (maximum temperature) can be, for example, 400°C to 600°C, and the holding time at that temperature can be, for example, 5 minutes to less than 3 hours. The atmosphere during firing may also be an inert atmosphere such as N2, Ar, He, or a vacuum atmosphere.

[0056] Cathode active material precursor; The positive electrode active material precursor (positive electrode active material precursor powder) is preferably made of an amorphous oxide material that generates active material crystals by firing. When the positive electrode active material precursor powder is made of an amorphous oxide material, active material crystals are generated during firing, and it is possible to form a dense positive electrode layer through softening and flow. Furthermore, if the positive electrode layer contains a solid electrolyte, integration of the positive electrode active material and the solid electrolyte can be achieved. Alternatively, if the positive electrode layer is in contact with a solid electrolyte layer, integration of the two can be achieved. As a result, a better ion conduction path is formed, which is preferable. In addition, in the present invention, "amorphous oxide material" is not limited to a completely amorphous oxide material, but also includes materials that contain some crystals (for example, crystallinity of 10% or less).

[0057] The positive electrode active material precursor powder preferably contains Na2O 25% to 55%, Fe2O3 + Cr2O3 + MnO + CoO + NiO 10% to 30%, and P2O 525% to 55%, in molar percentages based on the oxides listed below. The reason for this limitation of composition is explained below. In the following descriptions of the content of each component, unless otherwise specified, "%" means "molar percent".

[0058] Na2O is the general formula Na x M y P2O z The active material crystal is represented by (where M is at least one transition metal element selected from Cr, Fe, Mn, Co, and Ni, with 1 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, and 6.5 ≤ z ≤ 8). The Na2O content is preferably 25% to 55%, and more preferably 30% to 50%. When the Na2O content is within the above range, the charge and discharge capacity can be further increased.

[0059] Fe2O3, Cr2O3, MnO, CoO, and NiO also have the general formula Na x M y P2O zThis is the main component of the active material crystal represented by . The content of Fe2O3+Cr2O3+MnO+CoO+NiO is preferably 10% to 30%, and more preferably 15% to 25%. When the content of Fe2O3+Cr2O3+MnO+CoO+NiO is above the lower limit, the charge and discharge capacity can be further increased. On the other hand, when the content of Fe2O3+Cr2O3+MnO+CoO+NiO is below the upper limit, it is possible to make it difficult for unwanted crystals such as Fe2O3, Cr2O3, MnO, CoO, or NiO to precipitate. Furthermore, in order to further improve the cycle characteristics, it is preferable to actively include Fe2O3. The content of Fe2O3 is preferably 1% to 30%, more preferably 5% to 30%, even more preferably 10% to 30%, and particularly preferably 15% to 25%. The content of each component, Cr2O3, MnO, CoO, and NiO, is preferably 0% to 30%, more preferably 10% to 30%, and even more preferably 15% to 25%. Furthermore, when at least two components selected from Fe2O3, Cr2O3, MnO, CoO, and NiO are included, the total amount is preferably 10% to 30%, and more preferably 15% to 25%.

[0060] P2O5 is also a general formula Na x M y P2O z It is the main component of the active material crystal represented by [formula]. The P2O5 content is preferably 25% to 55%, and more preferably 30% to 50%. When the P2O5 content is within the above range, the charge and discharge capacity can be increased even further.

[0061] The positive electrode active material precursor powder may also contain V2O5, Nb2O5, MgO, Al2O3, TiO2, ZrO2, or Sc2O3 in addition to the above components. These components have the effect of increasing conductivity (electron conductivity), which makes it easier to improve high-speed charge-discharge characteristics. The content of the above components is preferably 0% to 25% in total, 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-discharge capacity can be increased even further.

[0062] Furthermore, the positive electrode active material precursor powder may also contain SiO2, B2O3, GeO2, Ga2O3, Sb2O3, or Bi2O3 in addition to the above components. Including these components further improves the glass formation ability and makes it easier to obtain a more homogeneous positive electrode active material precursor powder. The total content of the above components 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 tends to decrease.

[0063] The positive electrode active material precursor powder is preferably produced by melting and molding a batch of raw materials. This method is preferable because it 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 produced as follows.

[0064] 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, the melting temperature is preferably 800°C or higher, and more preferably 900°C or higher. There is no particular upper limit to the melting temperature, but if the melting temperature is too high, it can lead to energy loss and evaporation of sodium components, so it is preferably 1500°C or lower, and more preferably 1400°C or lower.

[0065] 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, or the molten material may be poured into a mold and molded into an ingot.

[0066] 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.

[0067] Binder; A binder is a material used to bind raw materials (raw material powders) together. Examples of binders include 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; acrylic resins such as polyvinylidene fluoride and polyacrylic acid, polyvinyl acetal, and polyvinyl butyral.

[0068] (Negative electrode layer) The negative electrode active material contained in the negative electrode layer 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-based 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 is not a negative electrode layer consisting of a single phase of metallic sodium.

[0069] The negative electrode layer may further contain a sodium ion-conducting solid electrolyte and a conductive additive. The ratio of each material in the negative electrode layer can be, for example, 60% to 95% by mass of the negative electrode active material, 5% to 35% of the sodium ion-conducting solid electrolyte, and 0% to 5% of the conductive additive. The sodium ion-conducting solid electrolyte can be, for example, the one described in the section on the solid electrolyte layer. The conductive additive can be, for example, the one described in the section on the positive electrode layer.

[0070] Below, as an example, a method for forming a negative electrode layer containing a carbon electrode material, which is the negative electrode active material, and a sodium ion-conducting solid electrolyte will be described.

[0071] Negative electrode layer formation method; First, a paste is prepared containing a carbon electrode material precursor and a sodium ion-conducting solid electrolyte. In preparing the paste, the sodium ion-conducting solid electrolyte precursor is prepared first. At this stage, it is preferable to prepare a solution of the sodium ion-conducting solid electrolyte precursor. Specific examples of the sodium ion-conducting solid electrolyte precursor and its solution will be described later. Furthermore, a carbon electrode material precursor (a precursor of carbon electrode material made of hard carbon) is prepared. Appropriate sugars, biomass, or polymers can be used as the carbon electrode material precursor.

[0072] Next, the sodium ion conductive solid electrolyte precursor solution and the carbon electrode material precursor are mixed and then dried. This yields a powder mixture of the sodium ion conductive solid electrolyte precursor and the carbon electrode material precursor. Next, the powder mixture is pulverized and then mixed with a conductive additive and a binder in an organic solvent. For example, N-methyl-2-pyrrolidone can be used as the organic solvent. This yields a paste.

[0073] Next, paste is applied to the main surface of the solid electrolyte layer. In this way, a lamination process is performed to laminate the solid electrolyte layer and the paste as the electrode material layer. Next, the laminate of the solid electrolyte layer and paste is fired, for example, in an N2 atmosphere at a temperature of over 600°C and 1300°C or less. Note that the above firing may be carried out in an inert atmosphere. For example, the above firing may be carried out in an Ar, Ne, or He atmosphere, or in a vacuum. Alternatively, the firing may be carried out in a reducing atmosphere containing H2. When firing is carried out in an inert or reducing atmosphere, it is preferable because it can further improve the initial charge-discharge efficiency of the negative electrode active material. Note that the atmosphere may contain a small amount of oxygen, as long as the carbon electrode does not oxidize or decompose during firing. The oxygen concentration can be, for example, 1000 ppm or less, but is not limited to this. The negative electrode layer can be manufactured in this manner.

[0074] Carbon electrode material precursor; When using sugars as carbon electrode material precursors, examples include sucrose, cellulose, D-glucose, etc. When using biomass as carbon electrode material precursors, 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 using polymers as carbon electrode material precursors, examples include PAN (polyacrylonitrile), pitch, PVC (polyvinyl chloride) nanofibers, polyaniline, sodium polyacrylate, tires (tire polymers), phosphorus-doped PAN, etc.

[0075] Sodium ion-conducting solid electrolyte precursors and their solutions; When the sodium-conducting solid electrolyte is beta-alumina, the sodium-conducting solid electrolyte precursor can be obtained, for example, by mixing aluminum nitrate, sodium nitrate, and lithium nitrate. At this time, the ratio of each of the above materials is adjusted to the composition ratio of the desired sodium ion-conducting solid electrolyte.

[0076] Sodium ion conductive solid electrolytes include NASICON-type crystals and Na5XSi4O 12 When the material is a type crystal (where X is at least one selected from group 3 transition metal elements, preferably rare earth elements), the sodium-conducting solid electrolyte precursor solution includes a solution containing sodium and transition metal elements that constitute the sodium-conducting solid electrolyte, and carbonate ions. In this solution, the sodium element is contained in the form of sodium ions, and the transition metal elements are contained in the form of transition metal ions. The sodium-ion-conducting solid electrolyte precursor consists, for example, of a gelled or dried product of the sodium-ion-conducting solid electrolyte precursor solution. The sodium-ion-conducting solid electrolyte consists of a calcined product of the sodium-ion-conducting solid electrolyte precursor.

[0077] Furthermore, a sodium ion-conducting solid electrolyte precursor solution can also be used that contains nitrate ions instead of carbonate ions.

[0078] Furthermore, it is preferable that carbonate ions are bidentately coordinated to the transition metal element in the sodium ion-conducting solid electrolyte precursor solution. In this case, the transition metal element is more likely to exist stably in the solution.

[0079] Also, as a counterion for sodium ions, NR 4+ It is preferable that the formula includes (wherein each R is at least one substituent independently selected from the group consisting of H, CH3, C2H5, and CH2CH2OH). This makes it easier for the transition metal element to exist stably in solution.

[0080] A sodium ion-conducting solid electrolyte precursor solution can be obtained, for example, by mixing water glass (sodium silicate), sodium tripolyphosphate, and an aqueous solution of zirconium ammonia carbonate.

[0081] The binder can be the one described in the section on the positive electrode layer.

[0082] (First current collector layer and second current collector layer) The materials for the first current collector layer and the second current collector layer are not particularly limited, but can be metallic materials such as aluminum, titanium, silver, copper, stainless steel, or alloys thereof, respectively. These metallic materials may be used individually or in combination. These alloys are alloys containing at least one of the above-mentioned metals. The thicknesses of the first current collector layer and the second current collector layer are not particularly limited, but can be in the range of 0.1 μm to 1000 μm, respectively.

[0083] The method for forming the first current collector layer and the second current collector layer is not particularly limited and includes, for example, physical vapor phase methods such as vapor deposition or sputtering, and chemical vapor phase methods such as thermal CVD, MOCVD, and plasma CVD. Other methods for forming the first current collector layer and the second current collector layer include liquid phase film deposition methods such as plating, sol-gel method, and spin coating. However, it is preferable to form the first current collector layer and the second current collector layer on the positive electrode layer and the negative electrode layer, respectively, by sputtering, as this provides excellent adhesion.

[0084] The present invention will be described in more detail below based on specific examples. The present invention is not limited in any way to the following examples, and can be implemented with appropriate modifications without changing its essence.

[0085] (Example 1) (a) Preparation of the solid electrolyte layer To obtain the composition of the solid electrolyte β''-alumina, the raw materials were calcined at 1200°C and pulverized to produce β''-alumina powder. The β''-alumina powder was pulverized in a ball mill and mixed with a binder and solvent to produce a paste. A green sheet was formed from this paste and fired at 1550°C for 30 minutes to form a solid electrolyte layer that was 12 mm square and 0.1 mm thick.

[0086] (b) Preparation of positive electrode paste A glass film was prepared by melting raw materials, which were blended to have a molar ratio of 40Na2O-20Fe2O3-40P2O5, in air at 1200°C for 1 hour and then cooling with twin rollers. The obtained glass film was then subjected to 60 hours of ball mill grinding using a mixture of φ5mm, φ3mm, and φ1mm ZrO2 pebbles in ethanol, resulting in a specific surface area of ​​11.1 m². 2 Glass powder was obtained at a concentration of / g. The obtained glass powder was further ground in ethanol with a φ0.3 mm ZrO2 boulder in a planetary ball mill at 300 rpm for 5 hours, resulting in a specific surface area of ​​32.1 m². 2 Glass powder was obtained in a quantity of / g.

[0087] The obtained glass powder was 83% by mass, and β''-alumina was used as a solid electrolyte (specific surface area is 45.2 m²). 2 A positive electrode mixture powder was prepared by mixing 13% by mass of (g) with 4% by mass of acetylene black (AB) as a conductive additive. To 100% by mass of the obtained positive electrode mixture powder, 15% by mass of polypropylene carbonate (PPC) was added as a binder, and N-methyl-2-pyrrolidone was added as a solvent to bring the concentration of the positive electrode mixture powder to 50% by mass. A positive electrode paste was prepared by mixing this in a rotary mixer.

[0088] (c) Preparation of negative electrode paste The composition ratio is Na3Zr2Si2PO 12 To obtain the NASICON-type crystal, water glass (sodium silicate: Na2O·3SiO2), aqueous solution of zirconium ammonium carbonate ((NH4)2Zr(OH)2(CO3)2), and sodium tripolyphosphate (Na5P3O 10 A total of 25 g of the following was weighed out. These were added to 150 g of pure water and stirred with a hot stirrer at 50°C for 24 hours. This yielded a sodium ion conductive solid electrolyte precursor solution (pH=9.7). Next, this solution was allowed to gel by standing overnight in a constant temperature bath at 5°C. The sodium ion conductive solid electrolyte precursor was thus prepared.

[0089] A mixture was obtained by mixing sucrose (table sugar), a hard carbon source and carbon electrode material precursor, and a sodium ion-conducting solid electrolyte precursor in a stirrer for 1 hour in a weight ratio of 4:1. Next, the mixture was dried in a constant temperature bath at 60°C for 12 hours, and then vacuum-dried at 100°C for 6 hours to obtain a powder mixture of the sodium ion-conducting solid electrolyte precursor and the carbon electrode material precursor. Next, the powder mixture was ground in an agate mortar to obtain a powder.

[0090] A mixture of sodium ion-conducting solid electrolyte precursor and carbon electrode material precursor powders and a conductive additive (acetylene black) were weighed in a weight ratio of 19:1 and mixed to obtain a mixed powder. To 60 parts by mass of this mixed powder, 40 parts by mass of hard carbon powder (average particle size D50: 1 μm) were mixed to obtain a negative electrode composite powder. Furthermore, 15% by mass of polypropylene carbonate (PPC) as a binder was added to 100% by mass of the negative electrode composite powder, and N-methyl-2-pyrrolidone was added as a solvent to bring the concentration of the negative electrode composite powder to 50% by mass. This was mixed in a rotary mixer to prepare a negative electrode paste. (d) Formation of the negative electrode A negative electrode paste was applied to the center of one main surface of a 12mm square, 0.1mm thick solid electrolyte layer to a thickness of 50μm and a size of 10mm square. Drying was performed in a 60°C constant temperature bath for 1 hour. Subsequently, the negative electrode was formed by firing in an N2 (99.99%) atmosphere at 800°C for 2 hours. The weight of the supported negative electrode was calculated from (weight of the laminate after negative electrode formation) - (weight of the solid electrolyte layer). The weight of the hard carbon active material was calculated by multiplying the calculated supported weight by the ratio of active material (0.8). Furthermore, the capacity of the negative electrode was calculated using a hard carbon capacity of 300mAh / g. As a result, the capacity of the negative electrode was 0.49mAh. (e) Formation of the positive electrode A positive electrode paste was applied to the center of the main surface opposite the negative electrode of the solid electrolyte layer, with a thickness of 400 μm and a square diameter of 10 mm. After drying in a 60°C constant temperature bath for 2 hours, the positive electrode was formed by firing in an N2 / H2 (96 / 4 vol%) atmosphere at 500°C for 30 minutes. The supported weight of the positive electrode was calculated from (weight of the laminate after positive electrode formation) - (weight of the laminate before positive electrode formation). The weight of the Na2FeP2O7 active material was calculated by multiplying the calculated supported weight by the ratio of the active material to 0.83. The capacity of the positive electrode was calculated using the theoretical capacity of 97 mAh / g for Na2FeP2O7 crystallized glass (Na2FeP2O7 active material) per gram. As a result, the capacity of the positive electrode was 1.4 mAh. The N / P ratio (negative electrode capacity / positive electrode capacity) was calculated by dividing the capacity of the negative electrode by the capacity of the positive electrode. (f) Formation of the current collector and assembly of the coin cell A 500 nm thick aluminum vapor-deposited film was formed on the entire surface of either the positive or negative electrode as a current collector. Then, this film was sealed in a CR2032 coin cell in an argon glove box to fabricate an all-solid-state battery. (g) Charge and discharge test Constant current charge-discharge tests were conducted in a constant temperature chamber at 30°C using a current value of 0.05C rate (20 hours of charge-discharge) based on the positive electrode capacity.

[0091] (Examples 2-8 and Comparative Examples 1-7) A charge-discharge test was conducted in the same manner as in Example 1, except that the thickness of the paste coating during negative electrode formation and positive electrode formation was changed as shown in Table 1 below.

[0092] [Evaluation Results] Figure 2 shows the results of the charge-discharge test for Example 1. Figure 3 shows the charge-discharge results for Comparative Example 7.

[0093] As shown in Figures 2 and 3, Example 1, with an N / P ratio of 0.35, achieved high initial charge-discharge efficiency, while Comparative Example 7, with an N / P ratio of 4.82, exhibited low discharge capacity and low initial charge-discharge efficiency. Initial charge-discharge efficiency was calculated by dividing the discharge capacity by the charge capacity. Similarly, the initial charge-discharge efficiency for Examples 2-8 and Comparative Examples 1-6 was determined. The results are shown in Table 1 below. Table 1 also shows the thickness of the negative electrode layer after firing, the thickness of the positive electrode layer after firing, the thickness ratio (negative electrode layer / positive electrode layer) after firing, and the negative electrode capacity utilization rate. The negative electrode capacity utilization rate was calculated from the battery capacity (positive electrode capacity) / negative electrode capacity.

[0094] [Table 1]

[0095] As is clear from Table 1, the all-solid-state batteries in Examples 1 to 8, which have an N / P ratio of 1.10 or less, exhibit superior charge and discharge efficiency compared to the all-solid-state batteries in Comparative Examples 1 to 7, which have an N / P ratio greater than 1.10, confirming that higher energy density can be achieved.

[0096] Figure 4 shows the X-ray diffraction spectrum of the negative electrode layer in the all-solid-state battery fabricated in Example 1. Figure 5 shows the X-ray diffraction spectrum of the negative electrode layer in the all-solid-state battery fabricated in Comparative Example 1. In Figures 4 and 5, the X-ray diffraction spectrum after discharge is shown by a dashed line, and the X-ray diffraction spectrum after charging is shown by a solid line.

[0097] The X-ray diffraction spectrum of the negative electrode layer was measured using wide-angle X-ray diffraction. To prevent exposure to the atmosphere, the fully charged solid-state battery was disassembled in an argon glove box, and the battery was sealed in an air-free in-situ XRD cell with a Be window on the observation surface within the glove box for measurement. CuKα rays (wavelength 1.541 Å) were used as the X-ray source. The X-ray diffractometer used was a Rigaku "SmartLab" model.

[0098] As shown in Figure 4, the X-ray diffraction spectrum of the negative electrode layer of the all-solid-state battery fabricated in Example 1 shows a main peak of metallic sodium at 2θ = 29.3° after charging is complete, indicating that metallic sodium is deposited in the negative electrode layer. On the other hand, as shown in Figure 5, the X-ray diffraction spectrum of the negative electrode layer of the all-solid-state battery fabricated in Comparative Example 1 does not show a main peak of metallic sodium at 2θ = 29.3°, indicating that metallic sodium is not deposited in the negative electrode layer.

[0099] Figure 6(a) is an SEM image of the negative electrode layer cross-section of the all-solid-state battery fabricated in Example 1 at the completion of charging, and Figure 6(b) is an SEM-EDX elemental mapping image of Na of the negative electrode layer cross-section at the completion of charging. Furthermore, Figure 7(a) is an SEM image of the negative electrode layer cross-section of the all-solid-state battery fabricated in Example 1 at the completion of discharge, and Figure 7(b) is an SEM-EDX elemental mapping image of Na of the negative electrode layer cross-section at the completion of discharge. Note that in Figures 6 and 7, (a) the SEM image and (b) the SEM-EDX elemental mapping image of Na were observed in the same field of view.

[0100] Cross-sectional SEM observation and SEM-EDX analysis of the negative electrode layer at the completion of charging were performed after processing the cross-section by argon ion milling in an air-free environment and charging in an inert atmosphere. SEM observation was performed in an air-free environment using a Hitachi High-Tech field emission scanning electron microscope (model number "S-4800"). EDX analysis was performed using a Bruker AXS (model number "QUANTAX FlatQUAD System Xflash 5060FQ"). Subsequently, the samples were transported to a glove box in an air-free environment, discharge was performed, and cross-sectional SEM observation and SEM-EDX analysis of the negative electrode layer at the completion of discharge were repeated using the same procedure.

[0101] Figures 6(a) and (b) show that sodium metal precipitates near the solid electrolyte when charging is complete. This allows for safe handling even when exposed to the atmosphere. Figures 7(a) and (b) show that when discharge is complete, the precipitated sodium metal dissolves and disappears, demonstrating that sodium metal can be reversibly dissolved and released. This improves the initial charge-discharge efficiency, enabling the formation of a battery with high energy density. [Explanation of Symbols]

[0102] 1… All-solid-state sodium-ion secondary battery 2...Solid electrolyte layer 2a, 2b… First and second principal surfaces 3…Positive electrode layer 4…Negative electrode layer 5, 6…First and second current collector layers

Claims

1. A solid electrolyte layer having a first main surface and a second main surface facing each other, A positive electrode layer is provided on the first main surface of the solid electrolyte layer, A negative electrode layer is provided on the second main surface of the solid electrolyte layer, Equipped with, An all-solid-state sodium-ion secondary battery in which the capacity ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.10 or more and 1.10 or less.

2. The positive electrode layer is, ｘ M ｙ P ２ O ｚ The all-solid-state sodium-ion secondary battery according to claim 1, comprising a positive electrode active material made of crystallized glass containing crystals represented by (1 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8, where M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr).

3. The all-solid-state sodium-ion secondary battery according to claim 1 or 2, wherein the negative electrode layer comprises a negative electrode active material made of hard carbon.

4. The positive electrode layer is, ｘ M ｙ P ２ O ｚ The positive electrode active material comprises a crystallized glass containing crystals represented by (1 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8, where M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr), The negative electrode layer contains a negative electrode active material made of hard carbon, The all-solid-state sodium-ion secondary battery according to claim 1 or 2, wherein the thickness ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.05 or more and 0.45 or less.

5. The all-solid sodium-ion secondary battery according to claim 1 or 2, wherein the solid electrolyte layer comprises a solid electrolyte selected from the group consisting of β-alumina, β''-alumina, and NASICON crystal.

6. The all-solid-state sodium-ion secondary battery according to claim 1 or 2, wherein metallic sodium is deposited inside the negative electrode layer when charging is complete.

7. A solid electrolyte layer having a first main surface and a second main surface facing each other, A positive electrode layer is provided on the first main surface of the solid electrolyte layer, A negative electrode layer is provided on the second main surface of the solid electrolyte layer, Equipped with, The positive electrode layer contains a crystal represented by the general formula Na ｘ M ｙ P ２ O ｚ where (1 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8, and M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr), and includes a positive electrode active material composed of crystallized glass containing the crystal The negative electrode layer contains a negative electrode active material made of hard carbon, An all-solid-state sodium-ion secondary battery in which the thickness ratio of the negative electrode layer to the positive electrode layer (negative electrode layer / positive electrode layer) is 0.05 or more and 0.45 or less.

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