Electrode material for all-solid-state batteries, electrode for all-solid-state batteries and method for manufacturing the same, and all-solid-state battery and method for manufacturing the same

Abstract

Provided is an electrode material for an all-solid battery, in which volumetric shrinkage due to crystallization of an active material precursor is unlikely to occur.　The electrode material for an all-solid battery contains an active material precursor having a non-crystalline phase, and active material crystals.

Description

Technical Field

[0001] The present invention relates to an electrode material for all-solid-state batteries, an electrode for all-solid-state batteries using the electrode material for all-solid-state batteries, a method for manufacturing the electrode for all-solid-state batteries, an all-solid-state battery, and a method for manufacturing the all-solid-state battery.

Background Art

[0002] Lithium-ion secondary batteries have established themselves as an indispensable, high-capacity and lightweight power source for mobile devices, electric vehicles, etc. However, in current lithium-ion secondary batteries, since a flammable organic electrolyte is mainly used as the electrolyte, there is concern about risks such as ignition. As a method for solving this problem, the development of all-solid-state lithium-ion batteries using a solid electrolyte instead of the organic electrolyte has been promoted. In addition, since there are concerns about problems such as the soaring of global raw materials, research on all-solid-state sodium-ion batteries has been conducted in recent years as an alternative.

[0003] In Patent Document 1 below, Na x (Fe 1-a M a ) y P2O z (M is at least one transition metal element selected from the group consisting of Cr, Mn, Co, and Ni, 1.2 ≦ x ≦ 2.8, 0.95 ≦ y ≦ 1.6, 0 ≦ a ≦ 0.9, 7 ≦ z ≦ 8) is disclosed as a cathode active material. In Patent Document 1, after applying and drying a slurry containing amorphous glass powder on one surface of a solid electrolyte layer and then firing it, a cathode layer containing the above cathode active material is formed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a method such as Patent Document 1, where an electrode material layer is formed on a solid electrolyte layer and then fired, volume shrinkage occurs when the glass crystallizes during the firing process, which can cause cracks in the resulting electrode layer.

[0006] Furthermore, in all-solid-state batteries, increasing the amount of electrode active material or the thickness of the electrode material layer to achieve higher energy density can lead to more pronounced volume contraction. Similarly, reducing the internal resistance of the battery by pulverizing the electrode material or increasing the amount of conductive additives can also lead to more pronounced volume contraction. When volume contraction becomes more pronounced, the electrode layer obtained by sintering may peel off from the solid electrolyte layer. As a result, the ion conduction contacts are lost, which may cause the battery to malfunction.

[0007] The object of the present invention is to provide an electrode material for all-solid-state batteries that is less susceptible to volume shrinkage due to crystallization of the active material precursor, an electrode for all-solid-state batteries using the electrode material, a method for manufacturing an electrode for all-solid-state batteries, an all-solid-state battery, and a method for manufacturing an all-solid-state battery. [Means for solving the problem]

[0008] This paper describes an electrode material for all-solid-state batteries that solves the above problems, an electrode for all-solid-state batteries using the electrode material, a method for manufacturing the electrode for all-solid-state batteries, an all-solid-state battery, and various embodiments of the method for manufacturing an all-solid-state battery.

[0009] The electrode material for an all-solid-state battery according to Embodiment 1 of the present invention is characterized by containing an active material precursor having an amorphous phase and an active material crystal.

[0010] In the electrode material for an all-solid-state battery according to Embodiment 2, it is preferable that the active material crystal in Embodiment 1 is a sintered body of the active material precursor.

[0011] In the electrode material for an all-solid-state battery according to Embodiment 3, it is preferable that, in Embodiment 1 or Embodiment 2, the active material crystal is contained as a composite with at least one of a solid electrolyte and a conductive additive.

[0012] In the electrode material for an all-solid-state battery according to Embodiment 4, it is preferable that the surface of the composite is covered with an amorphous layer in Embodiment 3.

[0013] In the electrode material for an all-solid-state battery according to Embodiment 5, in Embodiment 4, it is preferable that the amorphous layer contains some of the elements that constitute the active material crystal.

[0014] In the electrode material for an all-solid-state battery according to embodiment 6, in embodiment 4 or embodiment 5, the amorphous layer is preferably made of sodium phosphate.

[0015] In the electrode material for an all-solid-state battery according to embodiment 7, the amorphous layer may be made of amorphous carbon in embodiment 4.

[0016] The electrode material for all-solid-state batteries according to Embodiment 8 is preferably used in a sodium-ion secondary battery in any one embodiment of Embodiments 1 to 7.

[0017] In the electrode material for all-solid-state batteries according to Embodiment 9, in any one embodiment of Embodiments 1 to 8, the active material precursor preferably contains, in mole percent on an oxide basis, 25% to 55% of Na2O, 10% to 30% of Fe2O3+Cr2O3+MnO+CoO+NiO, and 25% to 55% of P2O5.

[0018] The electrode material for an all-solid-state battery according to embodiment 10 is, in any one embodiment from embodiment 1 to embodiment 9, the active material crystal is of the general formula Na x M y P2O z Preferably, the crystal is represented by (where M is at least one transition metal element selected from Cr, Fe, Mn, Co, and Ni, with 1.2 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, and 6.5 ≤ z ≤ 8).

[0019] In the electrode material for an all-solid-state battery according to Embodiment 11, in any one embodiment of Embodiments 3 to 10, the solid electrolyte is preferably at least one selected from the group consisting of β-alumina, β''-alumina, and NASICON crystal.

[0020] In the electrode material for an all-solid-state battery according to Embodiment 12, it is preferable that in any one embodiment of Embodiments 1 to 11, the electrode material for an all-solid-state battery contains, by mass%, 1% to 99% of the active material precursor, 1% to 99% of the active material crystal, 0% to 70% of the solid electrolyte, and 0% to 20% of the conductive additive.

[0021] The electrode for an all-solid-state battery according to aspect 13 of the present invention is characterized by comprising a sintered body of an electrode material layer containing an electrode material for an all-solid-state battery according to any one of aspects 1 to 12.

[0022] The all-solid-state battery according to aspect 14 of the present invention is characterized in that it is equipped with the electrode for the all-solid-state battery of aspect 13 as the positive electrode.

[0023] A method for manufacturing an electrode for an all-solid-state battery according to aspect 15 of the present invention is characterized by comprising the steps of forming an electrode material layer containing an active material precursor having an amorphous phase and an active material crystal, and firing the electrode material layer.

[0024] In the method for manufacturing an electrode for an all-solid-state battery in embodiment 16, it is preferable that the active material crystal in embodiment 15 is a sintered body of the active material precursor.

[0025] In the method for manufacturing an electrode for an all-solid-state battery in Embodiment 17, it is preferable that, in Embodiment 15 or Embodiment 16, the active material crystal is contained as a composite with at least one of a solid electrolyte and a conductive additive.

[0026] The method for manufacturing an electrode for an all-solid-state battery in embodiment 18 preferably includes a step in embodiment 17 of forming an amorphous layer on the surface of the composite by mixing the composite with an amorphous layer forming material.

[0027] In the method for manufacturing an electrode for an all-solid-state battery in embodiment 19, it is preferable that the amorphous layer forming material in embodiment 18 contains some of the elements that constitute the active material crystal.

[0028] In the method for manufacturing electrodes for all-solid-state batteries of Embodiment 20, in Embodiment 18 or Embodiment 19, the amorphous material is preferably sodium phosphate.

[0029] In the method for manufacturing an electrode for an all-solid-state battery according to Embodiment 21, the amorphous layer forming material may be a surfactant in Embodiment 18.

[0030] A method for manufacturing an all-solid-state battery according to aspect 22 of the present invention is characterized by comprising the step of forming a positive electrode on a solid electrolyte layer by a method for manufacturing an all-solid-state battery electrode according to any one of aspects 15 to 21. [Effects of the Invention]

[0031] According to the present invention, it is possible to provide an electrode material for all-solid-state batteries that is less susceptible to volume shrinkage due to crystallization of the active material precursor, an electrode for all-solid-state batteries using the electrode material, a method for manufacturing an electrode for all-solid-state batteries, an all-solid-state battery, and a method for manufacturing an all-solid-state battery. [Brief explanation of the drawing]

[0032] [Figure 1] Figure 1 is a schematic diagram of an electrode material layer formed using a composite in which a sintered body containing an active material crystal, a solid electrolyte, and a conductive additive is coated with an amorphous layer. [Figure 2] Figure 2 is a schematic diagram of a modified example in which the sintered body in Figure 1 is not covered with an amorphous layer. [Figure 3] Figure 3 is a schematic diagram of an electrode material layer containing an active material precursor and an active material crystal coated with an amorphous layer. [Figure 4] Figure 4 is a schematic diagram of a modified version in which the active material crystal in Figure 3 is not covered by an amorphous layer. [Figure 5]Figure 5 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention. [Figure 6] Figure 6 is a photograph of the positive electrode layer obtained in Example 4 in plan view. [Figure 7] Figure 7 is a photograph of the positive electrode layer obtained in Comparative Example 1 in a plan view. [Modes for carrying out the invention]

[0033] 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.

[0034] [Electrode materials for all-solid-state batteries] The electrode material for all-solid-state batteries of the present invention contains an active material precursor having an amorphous phase and an active material crystal. The form of the electrode material for all-solid-state batteries is not particularly limited and may be a paste or a compacted powder.

[0035] The electrode material for all-solid-state batteries of the present invention is used as an electrode layer for an all-solid-state battery after being heated and fired. Therefore, the form of the electrode material for all-solid-state batteries may be an electrode material layer made of paste or an electrode material layer made of compacted powder.

[0036] The electrode material for all-solid-state batteries of the present invention contains active material crystals in addition to an active material precursor having an amorphous phase, so that volume shrinkage that occurs when the active material precursor crystallizes can be suppressed. Therefore, according to the electrode material for all-solid-state batteries of the present invention, cracks can be less likely to occur in the formed electrode layer. Furthermore, since the peeling of the formed electrode layer from the solid electrolyte layer can be suppressed, the ion conduction contacts can be maintained, and the battery can be operated more easily.

[0037] In all-solid-state batteries, increasing the amount of electrode active material or increasing the thickness of the electrode material layer can make the above-mentioned volume shrinkage more pronounced. Furthermore, pulverizing the electrode material or increasing the amount of conductive additive can also make the above-mentioned volume shrinkage more pronounced. However, with the electrode material for all-solid-state batteries of the present invention, volume shrinkage can be suppressed even in the above cases, and delamination of the electrode layer from the solid electrolyte layer and the like can be made less likely.

[0038] Therefore, the electrode material for all-solid-state batteries of the present invention allows for an increase in the amount of electrode active material supported and an increase in the thickness of the electrode material layer, thereby enabling a higher energy density for the battery. Furthermore, the internal resistance of the battery can be reduced by pulverizing the positive electrode mixture and increasing the amount of conductive additive added.

[0039] In this specification, whether or not an active material precursor has an "amorphous phase" can be confirmed, for example, in the case of an active material precursor used in an all-solid-state sodium-ion secondary battery described later, by whether or not an amorphous halo is observed in the X-ray diffraction spectrum (hereinafter referred to as the XRD spectrum) around 2θ = 10° to 45°.

[0040] The details of each embodiment will be described below.

[0041] (First embodiment) In the first embodiment, the active material crystal is contained as a composite with at least one of a solid electrolyte and a conductive additive. Therefore, the electrode material for an all-solid-state battery in the first embodiment includes an active material precursor having an amorphous phase and the composite. Furthermore, the electrode for an all-solid-state battery in the first embodiment can be formed by firing an electrode material layer containing an active material precursor having an amorphous phase and the composite.

[0042] As the composite, for example, a sintered body obtained by crystallizing an electrode material containing an active material precursor having an amorphous phase and at least one of a solid electrolyte and a conductive additive can be used. The electrode material may be an electrode paste, and the composite may be a sintered body obtained by drying and crystallizing the electrode paste in a lump form. Alternatively, the composite may be a sintered body powder obtained by crushing the sintered body. Below, specific examples of electrode materials for all-solid-state batteries according to the first embodiment will be described.

[0043] Figure 1 is a schematic diagram of an electrode material layer formed using a composite in which a sintered body containing an active material crystal, a solid electrolyte, and a conductive additive is coated with an amorphous layer.

[0044] In Figure 1, an electrode material layer 2 is formed on a solid electrolyte layer 1. The electrode material layer 2 is formed by applying electrode paste to the solid electrolyte layer 1. In Figure 1, the electrode material layer 2 is assumed to be unfired.

[0045] The electrode material layer 2 contains an active material precursor 3 having an amorphous phase, a solid electrolyte 4, and a conductive additive 5. The electrode material layer 2 also contains a composite 6.

[0046] The composite 6 is composed of a sintered body containing an active material crystal, a solid electrolyte, and a conductive additive. The firing temperature for forming the composite 6 can be, for example, 400°C or higher and 600°C or lower, and the firing time at that temperature can be, for example, 1 minute or higher and 10 hours or lower. The firing can be carried out under a reducing atmosphere.

[0047] In this embodiment, the active material crystals contained in the composite 6 are formed by crystallizing the same material as the active material precursor 3 through firing. Furthermore, the solid electrolyte and conductive additive are also composed of the same materials as the solid electrolyte 4 and conductive additive 5, respectively.

[0048] The electrode material layer 2 (electrode material for all-solid-state batteries) of this embodiment contains a composite 6 containing active material crystals in addition to an active material precursor 3 having an amorphous phase, so that volume shrinkage that occurs when the active material precursor 3 crystallizes can be suppressed. Furthermore, since the composite 6 is formed from the same materials as the active material precursor 3, solid electrolyte 4, and conductive additive 5, ionic conductivity can be further improved, and the battery characteristics of the all-solid-state battery can be further improved. Note that the active material crystals, solid electrolyte, and conductive additive contained in the composite 6 do not necessarily have to be formed from the same materials as the active material precursor 3, solid electrolyte 4, and conductive additive 5.

[0049] Furthermore, the surface of the composite 6 shown in Figure 1 is covered with an amorphous layer 7. In this embodiment, the surface of the composite 6 is covered with an amorphous layer 7 that contains some of the elements constituting the active material crystal. By covering the surface of the composite 6 with the amorphous layer 7, the fluidity of the material constituting the electrode material layer 2 can be further improved, and the electrode material layer 2 can be sintered more thoroughly.

[0050] The amorphous layer 7 is not particularly limited, and when used as an electrode material for an all-solid-state sodium-ion secondary battery described later, it may consist of, for example, sodium phosphate. In this case, the amorphous layer 7 is formed as, for example, a sol-gel film of sodium phosphate. It is preferable that the amorphous layer 7 consists of a material that readily forms ion paths, such as sodium phosphate. When the amorphous layer 7 consists of sodium phosphate, for example, it can be coated onto the composite 6 by mixing the composite 6 with an aqueous solution of sodium phosphate, which is an amorphous layer forming material, and drying it. Alternatively, the amorphous layer 7 may consist of amorphous carbon. In this case, for example, the amorphous layer 7 consisting of amorphous carbon can be formed by mixing the composite 6 with a surfactant such as polyethylene oxide nonylphenyl ether and firing it. The firing temperature can be, for example, 400°C or higher and 800°C or lower, and the firing time at that temperature can be, for example, 1 minute or higher and 10 hours or lower. The firing can be carried out under an N2 atmosphere.

[0051] Furthermore, a portion of the surface of the composite 6 may be covered by the amorphous layer 7, or the entire surface of the composite 6 may be covered by the amorphous layer 7. Preferably, 50% or more of the surface of the composite 6 is covered by the amorphous layer 7, more preferably 60% or more is covered by the amorphous layer 7, and even more preferably 80% or more is covered by the amorphous layer 7.

[0052] The thickness of the amorphous layer 7 is not particularly limited and can be, for example, 0.1 nm or more and 1000 nm or less.

[0053] In this embodiment, the content of composite 6 in the electrode material layer 2 (100 mass%) is preferably 1% or more, more preferably 5% or more, even more preferably 10% or more, particularly preferably 30% or more, preferably 99% or less, more preferably 95% or less, even more preferably 90% or less, even more preferably 70% or less, and particularly preferably 50% or less. When the content of composite 6 is above the lower limit, the volume shrinkage that occurs when the active material precursor 3 crystallizes can be further suppressed. When the content of composite 6 is below the upper limit, the fluidity of the material constituting the electrode material layer 2 can be further improved, and the electrode material layer 2 can be sintered more thoroughly. Furthermore, the battery characteristics of the all-solid-state battery can be further improved.

[0054] The content of the active material precursor 3 in the electrode material layer 2 (100% by mass) can be, for example, 1% or more and 90% or less by mass. The content of the solid electrolyte 4 in the electrode material layer 2 (100% by mass) can be, for example, 0% or more and 70% or less by mass. In addition, the content of the conductive additive 5 in the electrode material layer 2 (100% by mass) can be, for example, 0% or more and 20% or less by mass.

[0055] In this embodiment, the content of active material crystals in the composite 6 (100% by mass) is preferably 10% or more, more preferably 20% or more, even more preferably 50% or more, preferably 99% or less, more preferably 98% or less, and even more preferably 95% or less, in mass%. When the content of active material crystals is within the above range, the volume shrinkage that occurs when the amorphous phase active material precursor 3 crystallizes can be further suppressed.

[0056] Furthermore, the content of the solid electrolyte contained in composite 6 (100% by mass) can be, for example, 1% or more and 70% or less by mass. Furthermore, the content of the conductive additive contained in composite 6 (100% by mass) can be, for example, 0% or more and 20% or less by mass.

[0057] The composite 6 may also be a sintered body powder obtained by crushing the above-mentioned sintered body. In this case, the average particle size of the composite 6 can be, for example, 0.1 μm or more and 100 μm or less.

[0058] In this invention, the average particle diameter refers to D50 (average particle diameter based on volume) and is a value measured by laser diffraction scattering.

[0059] Furthermore, as shown in the modified electrode material layer 2A in Figure 2, the surface of the composite 6 does not need to be covered with the amorphous layer 7. Even in this case, by using the composite 6, the volume shrinkage that occurs when the active material precursor 3 crystallizes can be suppressed. In addition, the ion conductivity of the electrode material layer 2A can be further improved, and the battery characteristics of the all-solid-state battery can be further improved.

[0060] (Second embodiment) The electrode material for an all-solid-state battery according to the second embodiment includes an active material precursor having an amorphous phase and an active material crystal. Furthermore, the electrode for an all-solid-state battery according to the second embodiment can be formed by firing an electrode material layer containing the active material precursor having an amorphous phase and the active material crystal. The active material crystal may be an active material crystal powder obtained by crushing the active material crystal. Specific examples of the electrode material for an all-solid-state battery according to the second embodiment will be described below.

[0061] Figure 3 is a schematic diagram of an electrode material layer containing an active material precursor and an active material crystal coated with an amorphous layer.

[0062] In Figure 3, an electrode material layer 12 is formed on the solid electrolyte layer 11. The electrode material layer 12 is formed by applying electrode paste to the solid electrolyte layer 11. In Figure 3, the electrode material layer 12 is assumed to have not yet been fired.

[0063] The electrode material layer 12 contains an active material precursor 13 having an amorphous phase, a solid electrolyte 14, and a conductive additive 15. The electrode material layer 12 also contains an active material crystal 16. The active material crystal 16 is formed by crystallizing the same material as the active material precursor 13 through firing. The firing temperature for forming the active material crystal 16 can be, for example, between 400°C and 600°C, and the firing time at that temperature can be, for example, between 1 minute and 10 hours. The firing can be carried out under a reducing atmosphere.

[0064] The electrode material layer 12 (electrode material for all-solid-state batteries) of this embodiment contains active material crystals 16 in addition to the active material precursor 13 having an amorphous phase, so that volume shrinkage that occurs when the active material precursor 13 crystallizes can be suppressed. The active material crystals 16 may be formed from a material different from that of the active material precursor 13.

[0065] The surface of the active material crystal 16 shown in Figure 3 is covered with an amorphous layer 17. By covering the surface of the active material crystal 16 with the amorphous layer 17, the fluidity of the material constituting the electrode material layer 12 can be further improved, and the electrode material layer 12 can be sintered more thoroughly.

[0066] The amorphous layer 17 is not particularly limited and may consist of amorphous carbon, for example. The amorphous layer 17 may also contain some of the elements that make up the active material crystal 16. When used in an all-solid-state sodium-ion secondary battery, as described later, the amorphous layer 17 may consist of sodium phosphate, for example.

[0067] Furthermore, a portion of the surface of the active material crystal 16 may be covered by the amorphous layer 17, or the entire surface of the active material crystal 16 may be covered by the amorphous layer 17. Preferably, 50% or more of the surface of the active material crystal 16 is covered by the amorphous layer 17, more preferably 60% or more is covered by the amorphous layer 17, and even more preferably 80% or more is covered by the amorphous layer 17.

[0068] The thickness of the amorphous layer 17 is not particularly limited and can be, for example, 0.1 nm or more and 1000 nm or less.

[0069] In this embodiment, the content of active material crystals 16 contained in the electrode material layer 12 (100 mass%) is preferably 1% or more, more preferably 3% or more, even more preferably 5% or more, particularly preferably 10% or more, preferably 99% or less, more preferably 90% or less, even more preferably 80% or less, even more preferably 75% or less, and particularly preferably 40% or less. When the content of active material crystals 16 is above the lower limit, the volume shrinkage that occurs when the active material precursor 13 crystallizes can be further suppressed. When the content of active material crystals 16 is below the upper limit, the fluidity of the material constituting the electrode material layer 12 can be further improved, and the electrode material layer 12 can be sintered more thoroughly. Furthermore, the battery characteristics of the all-solid-state battery can be further improved.

[0070] The content of the active material precursor 13 contained in the electrode material layer 12 (100% by mass) can be, for example, 1% or more and 99% or less by mass. The content of the solid electrolyte 14 contained in the electrode material layer 12 (100% by mass) can be, for example, 0% or more and 70% or less by mass. In addition, the content of the conductive additive 15 contained in the electrode material layer 12 (100% by mass) can be, for example, 0% or more and 20% or less by mass.

[0071] The active material crystals 16 may also be crushed and used as active material crystal powder. In this case, the average particle size of the active material crystals 16 can be, for example, 0.1 μm or more and 100 μm or less.

[0072] Furthermore, as shown in the modified electrode material layer 12A in Figure 4, the surface of the active material crystal 16 does not need to be covered with the amorphous layer 17. Even in this case, by using the active material crystal 16, the volume shrinkage that occurs when the active material precursor 13 crystallizes can be suppressed.

[0073] The following describes specific examples of the electrode materials for all-solid-state batteries of the present invention when used as the positive electrode of an all-solid-state sodium-ion secondary battery.

[0074] (Active material precursor) The active material precursor (active material precursor powder) contains an amorphous phase. It is preferable that such an active material precursor powder is made of an amorphous oxide material that generates active material crystals upon firing. When the active material precursor powder is made of an amorphous oxide material, active material crystals are generated during firing, and softening and flowing occur, allowing for the formation of a denser electrode layer. As a result, ion conduction paths are formed more effectively, which is preferable. Furthermore, in this invention, the term "amorphous oxide material" is not limited to completely amorphous oxide materials, but also includes materials that contain some crystals (for example, with a crystallinity of 10% or less).

[0075] The active material precursor powder preferably contains, in terms of mol% of the following oxides, 25% to 55% of Na2O, 10% to 30% of Fe2O3 + Cr2O3 + MnO + CoO + NiO, and 25% to 55% of P2O5. The reasons for limiting the composition in this way will be explained below. In the following explanations of the content of each component, unless otherwise specified, "%" means "mol%".

[0076] Na2O is of the general formula Na x M y P2O z (M is at least one transition metal element selected from Cr, Fe, Mn, Co, and Ni, 1.2 ≦ x ≦ 2.8, 0.95 ≦ y ≦ 1.6, 6.5 ≦ z ≦ 8) and is the main component of the active material crystal. The content of Na2O is preferably 25% to 55%, more preferably 30% to 50%. When the content of Na2O is within the above range, the charge-discharge capacity of the all-solid-state sodium ion secondary battery can be further increased.

[0077] Fe2O3, Cr2O3, MnO, CoO, and NiO are also of 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 of the all-solid-state sodium-ion secondary battery 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 of the all-solid-state sodium-ion secondary battery, 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%.

[0078] 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 of the all-solid-state sodium-ion secondary battery can be further increased.

[0079] The 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 the high-speed charge-discharge characteristics of the electrode active material. 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 of the all-solid-state sodium-ion secondary battery can be further increased.

[0080] Furthermore, the 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-forming ability and makes it easier to obtain a more homogeneous 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.

[0081] The active material precursor powder is preferably produced by melting and molding the raw material batch. This method is preferable because it makes it easier to obtain an amorphous active material precursor powder with excellent homogeneity. Specifically, the active material precursor powder can be produced as follows.

[0082] 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.

[0083] 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.

[0084] Next, the obtained molded body is crushed to obtain active material precursor powder. The average particle size of the 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. When the average particle size of the active material precursor powder is above the lower limit, the cohesive force between particles can be weakened when used in paste form, making it easier to disperse the active material precursor powder in the paste. Also, when mixed with solid electrolyte powder, etc., the active material precursor powder can be dispersed more uniformly in the mixture, reducing internal resistance and increasing charge / discharge capacity. On the other hand, when the average particle size of the active material precursor powder is below the upper limit, the crystallization temperature can be lowered. Also, the amount of ion diffusion per unit surface area of ​​the electrode material increases, making it possible to further reduce internal resistance. Furthermore, when mixed with solid electrolyte powder, the adhesion between the active material precursor powder and the solid electrolyte powder can be further improved, thereby increasing the mechanical strength of the electrode layer. As a result, the charge and discharge capacity can be further improved. Alternatively, the adhesion between the electrode layer and the solid electrolyte layer can be further improved, making it more difficult for the electrode layer to peel off from the solid electrolyte layer.

[0085] (active material crystal) The active material crystal is preferably a sintered body of the same material as the active material precursor powder described above. Therefore, the active material crystal is of the general formula Na x M y P2O zIt is preferable that the crystal is represented by (M is at least one transition metal element selected from Cr, Fe, Mn, Co, and Ni, 1.2≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8). Examples of such active material crystals include Na2FeP2O7, Na 3.64 Fe 2.18 (P2O7)2(=Na 1.82 Fe 1.09 P2O7), Na 3.12 Fe 2.44 (P2O7)2(=Na 1.56 Fe 1.22 P2O7), Na3Fe2(PO4)P2O7(=Na2Fe 1.33 P2O 7.33 ), Na2MnP2O7, Na2CoP2O7, Na2NiP2O7, etc. can be used. Among these, Na3Fe2(PO4)P2O7 has a high capacity per unit mass and operating voltage, so it is possible to create batteries with higher energy density.

[0086] As mentioned above, the surface of the active material crystal may be coated with an amorphous layer. The active material crystal may be contained as a composite with at least one of a solid electrolyte and a conductive additive. In this case, the surface of the composite may be coated with an amorphous layer.

[0087] (solid electrolyte) Solid electrolytes (solid electrolyte powders) are components responsible for ion conduction in electrode layers such as the positive electrode layer in all-solid-state sodium-ion secondary batteries.

[0088] Examples of solid electrolyte powders include beta-alumina or NASICON crystals, which have excellent sodium ion conductivity. Beta-alumina exists in two crystalline forms: β-alumina (theoretical composition formula: Na2O·11Al2O3) and β''-alumina (theoretical composition 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 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.

[0089] As for NASICON crystals, Na3Zr2Si2PO 12 kaNa 3.2 Zr 1.3 Si 2.2 P 0.7 O 10.5 Na3Zr 1.6 Ti 0.4 Si2er 12 Na3Hf2Si2PO 12 kaNa 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 Si2er 12 kaNa 3.6 Ti 0.2 Y 0.7 Si 2.8 O9, Na3Zr 1.88 Y 0.12 Si2er 12 kaNa 3.12 Zr 1.88 Y 0.12 Si2er 12 kaNa3.6 Zr 0.13 Yb 1.67 Si 0.11 P 2.9 O 12 Examples include Na. 3.12 Zr 1.88 Y 0.12 Si2er 12 This is preferable because it has excellent sodium ion conductivity.

[0090] The average particle size of the 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. If the average particle size of the solid electrolyte powder is too small, it becomes difficult to mix it uniformly with the active material precursor powder, and hygroscopic and carbonated ionization may reduce ionic conductivity or promote excessive reaction with the active material precursor powder. As a result, the internal resistance of the electrode material layer tends to increase, and the voltage characteristics and charge / discharge capacity tend to decrease. On the other hand, if the average particle size of the solid electrolyte powder is too large, it significantly inhibits the softening flow of the active material precursor powder, which tends to result in a less smooth electrode layer with reduced mechanical strength and increased internal resistance.

[0091] (Conductive additive) Conductive additives are components that form conductive paths in electrode materials. For example, conductive carbon can be used as a conductive additive. Preferred conductive carbons are powdered or fibrous conductive carbons such as acetylene black or Ketjen black, which are highly conductive carbon blacks. When adding conductive carbon, it is preferable to add it when grinding the active material precursor powder. Conductive carbon acts as a grinding aid, enabling homogeneous mixing with the active material precursor powder, as well as suppressing excessive fusion of active material precursor powder particles during firing, making it easier to ensure conductivity and improving the rapid charge-discharge characteristics of all-solid-state sodium-ion secondary batteries.

[0092] (binder) The electrode material for all-solid-state batteries of the present invention may contain a binder. The binder is a material used to integrate the raw materials (raw material powders). 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; and polyvinylidene fluoride.

[0093] [Electrodes for all-solid-state batteries and all-solid-state batteries] Figure 5 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention. As shown in Figure 5, the all-solid-state battery 21 comprises a solid electrolyte layer 22, a positive electrode layer 23, a negative electrode layer 24, a first current collector layer 25, and a second current collector layer 26. In this embodiment, the all-solid-state battery 21 is an all-solid-state sodium-ion secondary battery.

[0094] The solid electrolyte layer 22 has opposing first main surfaces 22a and second main surfaces 22b. A positive electrode layer 23 is provided on the first main surface 22a of the solid electrolyte layer 22. A first current collector layer 25 is provided on the main surface of the positive electrode layer 23 opposite to the solid electrolyte layer 22. A negative electrode layer 24 is provided on the second main surface 22b of the solid electrolyte layer 22. A second current collector layer 26 is provided on the main surface of the negative electrode layer 24 opposite to the solid electrolyte layer 22. Note that the first current collector layer 25 and the second current collector layer 26 are optional.

[0095] (Positive electrode layer) In this embodiment, the positive electrode layer 23 is a sintered body of an electrode material layer made of the electrode material for all-solid-state batteries of the present invention described above. Therefore, volume shrinkage when the active material precursor crystallizes is less likely to occur during the firing process when forming the positive electrode layer 23. Consequently, cracks are less likely to occur in the formed positive electrode layer 23, and delamination of the positive electrode layer 23 from the solid electrolyte layer 22 is less likely to occur. Thus, an all-solid-state battery 21 equipped with such a positive electrode layer 23 can maintain ion conduction contacts and facilitate battery operation.

[0096] The thickness of the positive electrode layer 23 is preferably 20 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, particularly preferably 100 μm or more, and most preferably 120 μm or more. In this case, the capacity of the all-solid-state battery 21 can be increased even further. On the other hand, if the thickness of the positive electrode layer 23 is too thick, the resistance to electron conduction increases, which can reduce the discharge capacity and operating voltage. In addition, the stress due to shrinkage during firing increases, which can lead to delamination. Therefore, the thickness of the positive electrode layer 23 is preferably 150 μm or less.

[0097] Furthermore, the amount of positive electrode active material supported in the positive electrode layer 23 is preferably 3 mg / cm³. 2 More preferably 5 mg / cm³ 2 More preferably 7 mg / cm³ 2 In particular, 9 mg / cm³ is preferred. 2 In summary, the most preferred concentration is 12 mg / cm³. 2 This concludes the explanation. In this case, the capacity of the all-solid-state battery 21 can be further increased. The upper limit of the amount of positive electrode active material is not particularly limited, but for example, 100 mg / cm³ 2 It can be done this way.

[0098] The positive electrode layer 23 can be manufactured, for example, by the following method.

[0099] An electrode material layer made of the above-described electrode material for solid-state batteries is formed on the first main surface 22a of the solid electrolyte layer 22. The electrode material layer can be obtained, for example, by applying a slurry of the above-described electrode material for solid-state batteries and drying it. The slurry may optionally contain a binder, plasticizer, or solvent.

[0100] For mixing the raw materials, mixers such as rotary-orbit mixers and tumbler mixers, as well as general grinding machines such as mortars, pulverizers, ball mills, attritors, vibrating ball mills, satellite ball mills, planetary ball mills, jet mills, and bead mills can be used.

[0101] Furthermore, the drying temperature of the slurry is not particularly limited, but can be, for example, 30°C or higher and 100°C or lower. Also, the drying time of the slurry is not particularly limited, but can be, for example, 10 minutes or more and 600 minutes or lower.

[0102] Next, the obtained electrode material layer is fired. This allows the positive electrode layer 23 to be obtained. The atmosphere during firing is preferably a reducing atmosphere. Examples of a reducing atmosphere include an atmosphere containing at least one reducing gas selected from H2, NH3, CO, H2S, and SiH4. From the viewpoint of efficiently reducing Fe ions in the active material precursor powder from trivalent to divalent, it is preferable to contain at least one selected from H2, NH3, and CO in the atmosphere, and more preferably to contain H2 gas. When using H2 gas, it is preferable to mix in an inert gas such as N2 to reduce the risk of explosion during firing. Specifically, it is preferable that the reducing gas contains N2 90% to 99.9% and H2 0.1% to 10% by volume, more preferably N2 90% to 99.5% and H2 0.5% to 10%, and even more preferably N2 92% to 99% and H2 1% to 8%.

[0103] The firing temperature (maximum temperature) is preferably 400°C to 600°C, more preferably 410°C to 580°C, even more preferably 420°C to 575°C, particularly preferably 425°C to 560°C, and most preferably 450°C to 530°C. If the firing temperature is too low, the crystallization of the active material precursor powder will be insufficient, and the remaining amorphous phase will become a high-resistance region, which tends to reduce the voltage characteristics and charge / discharge capacity of the all-solid-state battery 21. On the other hand, if the firing temperature is too high, the active material precursor powders will fuse excessively together, forming coarse particles, which reduces the specific surface area of ​​the active material and tends to reduce the charge / discharge characteristics of the all-solid-state battery 21. In addition, during firing, the active material precursor powder and the solid electrolyte powder may react, causing crystals that do not contribute to charging and discharging (such as maliscite-type NaFePO4 crystals) to precipitate, which may reduce the charge / discharge capacity of the all-solid-state battery 21. Alternatively, elements contained in the active material precursor powder and the solid electrolyte powder may diffuse with each other during firing, forming a partially high-resistance layer, which can degrade the rate characteristics of the all-solid-state battery 21.

[0104] The firing time (holding time at the highest temperature during firing) is preferably less than 3 hours, more preferably 2 hours or less, even more preferably 1 hour or less, particularly preferably 45 minutes or less, and most preferably 30 minutes or less. If the firing time is too long, the active material precursor powders tend to fuse excessively together, forming coarse particles, reducing the specific surface area of ​​the active material, and thus degrading the charge-discharge characteristics of the all-solid-state battery 21. In addition, in the all-solid-state battery 21, the active material precursor powder and the solid electrolyte powder react during firing, and crystals that do not contribute to charging and discharging (such as maliscite-type NaFePO4 crystals) may precipitate, potentially reducing the charge-discharge capacity. Alternatively, elements contained in the active material precursor powder and the solid electrolyte powder may diffuse with each other during firing, forming a partially high-resistance layer, which may degrade the rate characteristics of the all-solid-state battery 21. On the other hand, if the firing time is too short, the crystallization of the active material precursor powder becomes insufficient, and the remaining amorphous phase becomes a high-resistance region, which tends to degrade the voltage characteristics and charge-discharge capacity of the all-solid-state battery 21. Therefore, the baking time is preferably 1 minute or more, and more preferably 5 minutes or more.

[0105] For firing, electric heating furnaces, rotary kilns, microwave heating furnaces, high-frequency heating furnaces, etc., can be used.

[0106] (solid electrolyte layer) The solid electrolyte layer 22 is preferably composed of a sodium ion conductive oxide. In particular, the solid electrolyte layer 22 is preferably composed of a material similar to the solid electrolyte powder exemplified in the electrode material for the all-solid-state battery of the present invention described above.

[0107] The thickness of the solid electrolyte layer 22 is preferably in the range of 5 μm to 1500 μm, and more preferably in the range of 20 μm to 200 μm. If the thickness of the solid electrolyte layer 22 is too thin, the mechanical strength decreases and it becomes more prone to breakage, making internal short circuits more likely. If the thickness of the solid electrolyte layer 22 is too thick, the sodium ion conduction distance during charging and discharging increases, which increases the internal resistance and makes it easier for the discharge capacity and operating voltage to decrease. In addition, the energy density per unit volume of the all-solid-state battery 21 also tends to decrease.

[0108] (Negative electrode layer) The negative electrode layer 24 preferably contains a negative electrode active material capable of adsorbing and releasing sodium. The negative electrode active material is not particularly limited, and examples include active material crystals such as crystals containing at least one selected from Nb and Ti and O, or metal crystals containing at least one selected from Sn, Bi, and Sb. Alternatively, graphite or hard carbon may be used as the negative electrode active material. Alternatively, a metal such as metallic sodium may be used.

[0109] The thickness of the negative electrode layer 24 is preferably in the range of 0.3 μm to 300 μm, and more preferably in the range of 3 μm to 150 μm. If the thickness of the negative electrode layer 24 is too thin, the absolute capacity (mAh / g) of the negative electrode tends to decrease. If the thickness of the negative electrode layer 24 is too thick, the resistance increases, and therefore the capacity (mAh / g) tends to decrease.

[0110] The negative electrode layer 24 can be prepared, for example, using a slurry containing a negative electrode active material precursor powder and, if necessary, a solid electrolyte powder and / or a conductive additive. Binders, plasticizers, solvents, etc., are added to the slurry as needed. The negative electrode layer 24 can be prepared by coating the slurry onto the second main surface 22b of the solid electrolyte layer 22, drying it, and then firing it. Alternatively, the slurry may be coated onto a substrate such as PET (polyethylene terephthalate), dried to create a green sheet, and then fired to prepare the negative electrode layer 24. In the event that the negative electrode layer 24 is made of metal, it can be formed by sputtering, vapor deposition, or the like.

[0111] (Current collector layer) The materials for the first current collector layer 25 and the second current collector layer 26 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 thickness of the first current collector layer 25 and the second current collector layer 26 is not particularly limited, but can be in the range of 0.01 μm to 100 μm, respectively.

[0112] The method for forming the first current collector layer 25 and the second current collector layer 26 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 25 and the second current collector layer 26 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 25 and the second current collector layer 26 on the positive electrode layer 23 or the negative electrode layer 24 by sputtering because it provides excellent adhesion.

[0113] In the above embodiment, an all-solid-state sodium-ion secondary battery using a material having sodium-ion conductivity was described, but the electrode material for all-solid-state batteries of the present invention may also be used in other all-solid-state batteries, such as an all-solid-state lithium-ion secondary battery using a material having lithium-ion conductivity.

[0114] Furthermore, in the above embodiment, an electrode for a solid-state battery using the electrode material for solid-state batteries of the present invention described above was explained for the positive electrode layer 23, but a solid-state battery may also be constructed using the electrode for solid-state batteries of the present invention for the negative electrode layer 24.

[0115] 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.

[0116] (Example 1) (a) Preparation of cathode active material precursor powder Sodium metaphosphate (NaPO3), ferric oxide (Fe2O3), and orthophosphate (H3PO4) were used as raw materials. The raw material powders were blended to have a composition of 40% Na2O, 20% Fe2O, and 40% P2O in molar percentages, and melted at 1250°C for 45 minutes in an air atmosphere. The molten material was then poured between a pair of rotating rollers and molded while rapidly cooling to obtain a film-like glass with a thickness of 0.1 mm to 2 mm. The obtained film-like glass was then ground using a ball mill and a planetary ball mill to obtain glass powder (cathode active material precursor powder) with an average particle size of 0.2 μm. Powder X-ray diffraction (XRD) measurements confirmed that the obtained glass powder was amorphous (containing an amorphous phase).

[0117] (b) Preparation of active material crystal powder The film-like glass obtained in the same manner as (a) was fired at 600 °C for 1 hour in a mixed gas of 24 vol% H₂ and 96 vol% N₂. By pulverizing the fired sample with a ball mill, a powder (active material crystal powder) with an average particle diameter of 2 μm was obtained. When the powder X-ray diffraction pattern of the obtained active material crystal powder was confirmed, Na₂FeP₂O₇ crystals were confirmed.

[0118] (c) Preparation of solid electrolyte layer and solid electrolyte powder Li₂O-stabilized β''-alumina (manufactured by Ionotec, composition formula: Na 1.7 Li 0.3 Al 10.7 O 17 ) was processed into a sheet with a thickness of 0.5 mm to obtain a solid electrolyte layer. Also, the sheet-like Li₂O-stabilized β''-alumina was pulverized with a ball mill and a planetary ball mill to obtain a solid electrolyte powder with an average particle diameter of 0.3 μm.

[0119] (d) Preparation of electrode paste The positive electrode active material precursor powder, active material crystal powder, solid electrolyte powder, and acetylene black (manufactured by TIMCAL, SUPER C65) as a conductive aid obtained above were weighed at the ratios shown in Table 1, respectively, and mixed for 30 minutes using an agate mortar and pestle. To 100 parts by mass of the obtained mixed powder, 20 parts by mass of polypropylene carbonate was added, and further 110 parts by mass of N-methylpyrrolidone was added, and it was sufficiently stirred using a rotation-revolution mixer to obtain an electrode paste.

[0120] (e) Preparation of test battery (d) The electrode paste obtained was applied to one surface of the solid electrolyte layer obtained in (c) with an area of 1 cm 2 and a thickness of 80 μm, and dried at 70 °C for 4 hours to form a positive electrode material layer. In this state, by firing at 500 °C for 30 minutes in a mixed gas of 24 vol% H₂ and 96 vol% N₂, a positive electrode layer with a thickness of 100 μm was formed on one surface of the solid electrolyte layer. All the above operations were carried out in an environment with a dew point of -40 °C or lower.

[0121] Powder X-ray diffraction pattern analysis of the obtained cathode layer revealed the presence of Na2FeP2O7 crystals. Furthermore, crystalline diffraction lines originating from the solid electrolyte powder used were observed in the obtained cathode layer.

[0122] Next, a current collector consisting of a 300 nm thick gold electrode was formed on the surface of the obtained positive electrode layer using a sputtering apparatus (Sanyu Electronics Co., Ltd., model number "SC-701AT"). Then, in an argon atmosphere with a dew point of -60°C or lower, metallic sodium, which would serve as the counter electrode, was pressed onto the other surface of the solid electrolyte layer. After placing it on the lower cover of the coin cell, the upper cover was placed over it to fabricate a CR2032 type test battery.

[0123] (Example 2) 50 g of glass powder obtained in the same manner as in Example 1(a) and 5 g of surfactant (manufactured by Aoki Oil & Fat Industry Co., Ltd., product number "Brownon N510") were mixed and calcined in N2 gas at 600°C for 1 hour. The mixture after calcination was crushed using a mortar and pestle and a jet mill to obtain amorphous carbon-coated active material crystalline powder (powder of active material crystals whose surface is coated with an amorphous layer made of amorphous carbon) with an average particle size of 2 μm. When the powder X-ray diffraction pattern of the obtained amorphous carbon-coated active material crystalline powder was examined, Na2FeP2O7 crystals were confirmed.

[0124] An electrode paste was prepared in the same manner as in Example 1(d), except that the amorphous carbon-coated active material crystal powder obtained above was used instead of the active material crystal powder. A CR2032 type test battery was then prepared in the same manner as in Example 1(e).

[0125] (Example 3) The cathode active material precursor powder, solid electrolyte powder, and acetylene black (TIMCAL, SUPER C65) as a conductive additive obtained in Example 1 were weighed in a mass ratio of 83:13:4 and mixed for 30 minutes using an agate mortar and pestle. 100 parts by mass of the resulting mixed powder were mixed with 20 parts by mass of polypropylene carbonate, and then 110 parts by mass of N-methylpyrrolidone. The mixture was thoroughly stirred using a rotating / revolving mixer to obtain an electrode paste.

[0126] The obtained electrode paste was dried into a lump and calcined at 500°C for 0.5 hours in a mixed gas of 24% H and 96% N by volume. The calcined composite was then ground in a mortar and pestle and sieved to obtain a composite powder with an average particle size of 10 μm. When the powder X-ray diffraction pattern of the obtained composite powder was examined, Na2FeP2O7 crystals were confirmed.

[0127] In addition, the cathode active material precursor powder obtained in Example 1, the solid electrolyte powder, and acetylene black (TIMCAL, SUPER C65) as a conductive additive were weighed in a mass ratio of 83:13:4 and mixed for 30 minutes using an agate mortar and pestle to obtain a mixed powder.

[0128] 80 parts by mass of the mixed powder and 20 parts by mass of the composite powder were mixed to obtain a powder to which 20 parts by mass of polypropylene carbonate was added, and then 110 parts by mass of N-methylpyrrolidone was added. The mixture was thoroughly stirred using a rotation-revolution mixer to obtain an electrode paste. The composition (solid content ratio) of the mixed powder (excluding the composite powder), the composite powder, and the mixture thereof is shown in Table 1. A CR2032 type test battery was prepared in the same manner as in Example 1(e), except that the obtained electrode paste was used.

[0129] (Example 4) Ten g of the composite powder obtained in the same manner as in Example 3 was mixed with one g of a 5% by mass NaH2PO4 aqueous solution and vacuum-dried. The resulting sodium phosphate coated composite was ground in a mortar and pestle and then sieved to obtain a sodium phosphate coated composite powder (a composite powder with an amorphous layer of sodium phosphate on its surface) with an average particle size of 10 μm.

[0130] An electrode paste was prepared in the same manner as in Example 3, except that the sodium phosphate coated composite powder obtained above was used instead of the composite powder, and a CR2032 type test battery was then prepared.

[0131] (Example 5) Except for changing the composition of the positive electrode material as shown in Table 2, the electrode paste was prepared in the same manner as in Example 2, and a CR2032 type test battery was then manufactured.

[0132] (Examples 6-8) Except for changing the composition of the positive electrode material as shown in Table 2, the electrode paste was prepared in the same manner as in Example 4, and a CR2032 type test battery was then manufactured.

[0133] (Example 9) Glass powder was obtained in the same manner as in Example 1, except that sodium metaphosphate (NaPO3), ferric oxide (Fe2O3), and orthophosphate (H3PO4) were prepared to have a composition of Na2O 37.5%, Fe2O3 25%, and P2O5 37.5% in molar percentages. Using the obtained glass powder, amorphous carbon-coated active material crystalline powder with an average particle size of 2 μm was obtained in the same manner as in Example 2. When the powder X-ray diffraction pattern of the obtained active material crystalline powder was examined, it was found to be Na3Fe2(PO4)P2O7(=Na2Fe 1.33 P2O 7.33 Crystals were confirmed.

[0134] An electrode paste was prepared in the same manner as in Example 1(d), except that the amorphous carbon-coated active material crystal powder obtained in this manner was used as the active material crystal powder. Furthermore, a CR2032 type test battery was prepared in the same manner as in Example 1(e).

[0135] (Example 10) Except for changing the composition of the positive electrode material as shown in Table 3, the electrode paste was prepared in the same manner as in Example 9, and a CR2032 type test battery was then manufactured.

[0136] (Comparative Example 1) The positive electrode active material precursor powder, solid electrolyte powder, and acetylene black (TIMCAL, SUPER C65) as a conductive additive obtained in Example 1 were weighed in the proportions shown in Table 1 and mixed for 30 minutes using an agate mortar and pestle. An electrode paste was prepared in the same manner as in Example 1(d), except that the mixed powder obtained in this manner was used, and a CR2032 type test battery was prepared in the same manner as in Example 1(e).

[0137] [evaluation] (Amount of shrinkage during firing) In the examples and comparative examples, the solid powder material before pasteurization was separated, placed in a φ10 mm compaction mold, and a compact was produced by uniaxial press molding. The volume of the obtained compact was measured using a Micromeritics Accupyc1330 gas displacement pycnometer. The compact was then calcined at 500°C for 30 minutes in a mixed gas of H24 vol% and N296 vol%. The volume of the sample after calcination was measured using the same gas displacement pycnometer. The amount of shrinkage was also determined from the volume change before and after calcination.

[0138] (Battery characteristics) The fabricated test batteries were subjected to charge-discharge tests at 30°C, and their battery capacity was measured. The results are shown in Tables 1 to 3. The C-rate was set to 0.02C during the charge-discharge tests.

[0139] (Appearance after firing) The presence or absence of cracks in the positive electrode layer after firing was observed visually. As shown in the photograph in Figure 6, no cracks or delamination were observed in Example 4. Similarly, no cracks or delamination were observed in Examples 2 and 3. This is thought to be due to the excellent fluidity of the positive electrode material during firing and the good degree of sintering. In Example 1, although delamination occurred, no cracks were observed. On the other hand, as shown in Figure 7, cracks were observed in the positive electrode layer of Comparative Example 1.

[0140] Furthermore, the degree of sintering of the electrodes was observed using a scanning electron microscope (SEM), and the obtained images were binarized using image analysis software to determine the porosity. The porosity was then evaluated according to the following evaluation criteria.

[0141] [Evaluation Criteria] A... Void ratio of 3% or less B...Porosity greater than 3% and less than or equal to 10% C…Porosity is more than 10% and less than 20% D...Void ratio exceeds 20%

[0142] The results are shown in Tables 1 to 3 below.

[0143] [Table 1]

[0144] [Table 2]

[0145] [Table 3]

[0146] Tables 1 to 3 show that in Examples 1 to 10, which used electrode paste containing active material crystals in addition to active material precursor powder, volume shrinkage due to crystallization of the active material precursor was suppressed. On the other hand, in Comparative Example 1, in which no active material crystals were added to the electrode paste, volume shrinkage could not be sufficiently suppressed. [Explanation of Symbols]

[0147] 1,11...Solid electrolyte layer 2,2A,12,12A…electrode material layer 3,13…Active material precursor 4,14…Solid electrolyte 5,15…Conductive additive 6…complex 7,17…Amorphous layer 16…Active material crystal 21…All-solid-state battery 22...Solid electrolyte layer 22a, 22b… First and second main surfaces 23…Positive electrode layer 24... Negative electrode layer 25, 26… First and second current collector layers

Claims

1. An electrode material for all-solid-state batteries, containing an active material precursor having an amorphous phase and an active material crystal.

2. The electrode material for an all-solid-state battery according to claim 1, wherein the active material crystal is a sintered body of the active material precursor.

3. The electrode material for an all-solid-state battery according to claim 1 or 2, wherein the active material crystal is contained as a composite with at least one of a solid electrolyte and a conductive additive.

4. The electrode material for an all-solid-state battery according to claim 3, wherein the surface of the composite is covered with an amorphous layer.

5. The electrode material for an all-solid-state battery according to claim 4, wherein the amorphous layer contains some of the elements constituting the active material crystal.

6. The electrode material for an all-solid-state battery according to claim 4, wherein the amorphous layer is made of sodium phosphate.

7. The electrode material for an all-solid-state battery according to claim 4, wherein the amorphous layer is made of amorphous carbon.

8. An electrode material for an all-solid-state battery according to claim 1 or 2, used in a sodium-ion secondary battery.

9. The aforementioned active material precursor is, in terms of oxide molar percentage, Na ２ O 25% to 55%, Fe ２ O ３ +Cr ２ O ３ +MnO+CoO+NiO 10% to 30%, and P ２ O ５ An electrode material for an all-solid-state battery according to claim 1 or 2, containing 25% to 55%.

10. The active material crystal has the general formula Na ｘ M ｙ P ２ O ｚ (M is at least one transition metal element selected from Cr, Fe, Mn, Co, and Ni, 1.2 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8), and is a crystal represented by the formula, The electrode material for all-solid-state batteries according to claim 1 or 2.

11. The electrode material for an all-solid-state battery according to claim 3, wherein the solid electrolyte is at least one selected from the group consisting of β-alumina, β''-alumina, and NASICON crystal.

12. The electrode material for an all-solid-state battery according to claim 1 or 2, wherein the electrode material for an all-solid-state battery contains, by mass%, 1% to 99% of the active material precursor, 1% to 99% of the active material crystal, 0% to 70% of the solid electrolyte, and 0% to 20% of the conductive additive.

13. An electrode for an all-solid-state battery, comprising a sintered body of an electrode material layer containing the electrode material for all-solid-state batteries described in claim 1 or 2.

14. A solid-state battery comprising the electrode for solid-state batteries described in claim 13 as the positive electrode.

15. A step of forming an electrode material layer containing an active material precursor having an amorphous phase and an active material crystal, A step of firing the electrode material layer, A method for manufacturing electrodes for all-solid-state batteries, comprising the features described above.

16. The method for manufacturing an electrode for an all-solid-state battery according to claim 15, wherein the active material crystal is a sintered body of the active material precursor.

17. The method for manufacturing an electrode for an all-solid-state battery according to claim 15 or 16, wherein the active material crystal is contained as a composite with at least one of a solid electrolyte and a conductive additive.

18. A method for manufacturing an electrode for an all-solid-state battery according to claim 17, comprising the step of forming an amorphous layer on the surface of the composite by mixing the composite with an amorphous layer forming material.

19. The method for manufacturing an electrode for an all-solid-state battery according to claim 18, wherein the amorphous layer forming material includes a portion of the elements constituting the active material crystal.

20. The method for manufacturing an electrode for an all-solid-state battery according to claim 18, wherein the amorphous layer forming material is sodium phosphate.

21. The method for manufacturing an electrode for an all-solid-state battery according to claim 18, wherein the amorphous layer forming material is a surfactant.

22. A method for manufacturing an all-solid-state battery, comprising the step of forming a positive electrode on a solid electrolyte layer by the method for manufacturing an electrode for an all-solid-state battery described in claim 15 or 16.

Images