All-solid-state sodium ion secondary battery and method for producing the same

Abstract

To provide a member for a power storage device capable of performing charge and discharge even when an amount of the supported electrode active material is increased, and capable of attaining high capacity.SOLUTION: A member 6 for a power storage device includes: a solid electrolyte layer 1; and an electrode layer 2 which is provided on the solid electrolyte layer 1 and formed of a sintered body of an electrode material layer 2A including an electrode active material precursor powder whose average particle diameter is 0.01 μ m or more and less than 0.7 μ m.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electricity storage device member, an all-solid-state battery, and a method for producing an electricity storage device member. [Background technology]

[0002] Lithium-ion secondary batteries have established a position as a high-capacity, lightweight power source that is indispensable for mobile devices, electric vehicles, and the like. However, current lithium-ion secondary batteries mainly use flammable organic electrolytes as the electrolyte, raising concerns about the risk of fire and other problems. As a method for solving this problem, development of all-solid-state lithium-ion batteries that use solid electrolytes instead of organic electrolytes is underway (see, for example, Patent Document 1). In addition, because of concerns about issues with lithium, such as the worldwide rise in the price of raw materials, research has been conducted in recent years as an alternative to lithium, all-solid-state sodium-ion batteries. Patent Document 2 describes a battery with 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, and 1.2≦x≦2.8, 0.95≦y≦1.6, 0≦a≦0.9, 7≦z≦8). In Patent Document 2, a slurry containing an amorphous glass powder is applied to one surface of a solid electrolyte, dried, and then fired to form a positive electrode layer containing the above positive electrode active material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-205741 [Patent Document 2] International Publication No. 2016 / 084573 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, secondary batteries as power sources for electric vehicles are required to have a high energy density in order to extend the driving distance of the vehicle. In order to achieve a high energy density, it is necessary to increase the amount of electrode active material carried or the thickness of the electrode layer to increase the capacity. However, in the method of forming an electrode material layer on a solid electrolyte layer and sintering it as in Patent Document 2, if the amount of electrode active material carried or the thickness of the electrode material layer is increased, the positive electrode layer obtained by sintering may peel off from the solid electrolyte layer. In this case, the ion conduction contact is lost, resulting in a problem that the battery does not work.

[0005] An object of the present invention is to provide an electricity storage device member, an all-solid-state battery, and a method for producing an electricity storage device member, which are capable of charging and discharging even when the amount of electrode active material carried is increased and which enable an increase in capacity to be achieved. [Means for solving the problem]

[0006] The electricity storage device member according to the present invention is characterized by comprising: a solid electrolyte layer; and an electrode layer provided on the solid electrolyte layer and comprising a sintered body of an electrode material layer containing an electrode active material precursor powder having an average particle size of 0.01 μm or more and less than 0.7 μm.

[0007] In the present invention, the electrode layer preferably has a thickness of 20 μm or more.

[0008] In the present invention, the amount of the electrode active material carried in the electrode layer is 3 mg / cm 2 More preferably, it is equal to or greater than this.

[0009] The all-solid-state battery according to the present invention is characterized by including any one of the members for an electricity storage device described above.

[0010] The method for producing an electricity storage device member according to the present invention is characterized by comprising: a forming step of forming an electrode material layer containing an electrode active material precursor powder on a solid electrolyte layer; and a firing step of firing the electrode material layer while applying pressure.

[0011] In the present invention, it is preferable that the electrode material layer has a first main surface on the solid electrolyte layer side and a second main surface opposite to the first main surface, and that in the firing step, the second main surface is fired while being pressed in its entirety.

[0012] In the present invention, it is preferable that the electrode material layer is pressed at 1 kPa or more in the firing step.

[0013] In the present invention, the average particle size of the electrode active material precursor powder is preferably 0.01 μm or more and less than 0.7 μm.

[0014] In the present invention, the electrode active material precursor powder is preferably an amorphous oxide material.

[0015] In the present invention, the electrode material layer is preferably a positive electrode material layer.

[0016] In the present invention, the electrode active material precursor powder preferably contains, in mole percent calculated as oxides, 25% to 55% Na2O, 10% to 30% Fe2O3+Cr2O3+MnO+CoO+NiO, and 25% to 55% P2O5. Effect of the Invention

[0017] According to the present invention, it is possible to provide an electricity storage device member, an all-solid-state battery, and a method for manufacturing an electricity storage device member, which are capable of charging and discharging even when the amount of electrode active material carried is increased and which can achieve high capacity. [Brief description of the drawings]

[0018] [Figure 1] 1(a) to 1(c) are schematic cross-sectional views illustrating a method for producing an electricity storage device member according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a photograph showing a plan view of the positive electrode layer obtained in Example 5. As shown in FIG. [Figure 4] FIG. 4 is a photograph showing a plan view of the positive electrode layer obtained in Reference Example 2. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Preferred embodiments will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in the drawings, components having substantially the same functions may be referred to by the same reference numerals.

[0020] [Method of manufacturing electricity storage device components and all-solid-state batteries] 1(a) to 1(c) are schematic cross-sectional views illustrating a method for producing an electricity storage device member according to one embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention.

[0021] In the manufacturing method of this embodiment, first, as shown in FIG. 1(a), a cathode material layer 2A containing a cathode active material precursor powder is formed on a first main surface 1a of a solid electrolyte layer 1. Next, as shown in FIG. 1(b), the cathode material layer 2A is sintered while being pressurized. Thereby, a cathode layer 2 shown in FIG. 1(c) is formed on the first main surface 1a of the solid electrolyte layer 1, and an electricity storage device member 6 is obtained. Next, an anode layer 3 shown in FIG. 2 is formed on a second main surface 1b of the solid electrolyte layer 1. Thereby, an all-solid-state battery 10 can be obtained.

[0022] In the manufacturing method of this embodiment, as described above, the positive electrode material layer 2A formed on the solid electrolyte layer 1 is sintered while being pressurized, so that it is possible to manufacture an electricity storage device member 6 that is capable of charging and discharging even when the amount of the electrode active material carried is large, and that can increase the capacity of the all-solid-state battery 10, which is an electricity storage device. The reason for this can be explained as follows.

[0023] In the conventional method of forming a positive electrode material layer containing a positive electrode active material precursor powder on a solid electrolyte layer and firing the layer, the positive electrode layer obtained by firing may peel off from the solid electrolyte layer. This is thought to be because, when an amorphous material is used as the positive electrode active material precursor powder, the volume shrinkage is likely to occur due to crystallization during firing. In particular, when the amount of the electrode active material carried is increased or the thickness of the positive electrode layer is increased, the above-mentioned peeling problem tends to become more pronounced.

[0024] In addition, secondary batteries as power sources for electric vehicles and the like are required to have high output characteristics in order to drive motors. When the positive electrode active material precursor powder is pulverized to obtain high output, a dense positive electrode layer can be obtained, but in this case, the specific surface area of ​​the positive electrode active material precursor powder increases, so that it is necessary to increase the amount of binder added when forming the paste. However, since the binder volatilizes during firing, the number of voids in the positive electrode material layer increases, so that the volumetric shrinkage of the positive electrode material layer becomes more likely to occur. As a result, the positive electrode layer becomes more likely to peel off from the solid electrolyte layer.

[0025] In contrast, in the manufacturing method of the present embodiment, the positive electrode material layer 2A formed on the solid electrolyte layer 1 is fired while being pressurized, so that the contraction of the positive electrode material layer 2A in the planar direction can be suppressed, and the adhesion between the positive electrode layer 2 obtained by firing and the solid electrolyte layer 1 can be improved. Therefore, even when the amount of the electrode active material carried is increased, or the thickness of the positive electrode material layer 2A is increased, the positive electrode layer 2 obtained by firing is unlikely to peel off from the solid electrolyte layer 1. In this way, since the positive electrode layer 2 is unlikely to peel off from the solid electrolyte layer 1, the contact point of ion conduction is unlikely to be lost, and it is possible to obtain a power storage device member 6 and an all-solid-state battery 10 capable of charging and discharging with high output. In addition, since the amount of the positive electrode active material carried can be increased and the thickness of the positive electrode material layer 2A can be increased, the capacity can be increased, and the energy density of the all-solid-state battery can be thereby increased.

[0026] Hereinafter, as an example, each step of an all-solid-state sodium ion secondary battery using a material having sodium ion conductivity will be described in detail.

[0027] (Cathode material layer formation process) The positive electrode material layer 2A can be obtained by applying a slurry containing a positive electrode active material precursor powder onto the first main surface 1a of the solid electrolyte layer 1, and drying the slurry. The slurry may contain a solid electrolyte powder and a conductive assistant. The slurry may also contain a binder, a plasticizer, a solvent, or the like, as necessary.

[0028] Positive electrode active material precursor powder; The positive electrode active material precursor powder is preferably made of an amorphous oxide material that generates positive electrode active material crystals by firing. The amorphous oxide material generates positive electrode active material crystals during firing, and also softens and flows to form a denser positive electrode layer 2. As a result, the ion conduction path is more favorably formed, which is preferable. In the present invention, the "amorphous oxide material" is not limited to a completely amorphous oxide material, but also includes those that contain some crystals (for example, a crystallinity of 10% or less).

[0029] The positive electrode active material precursor powder preferably contains, in mole percent in terms of the following oxides, 25% to 55% Na2O, 10% to 30% Fe2O3+Cr2O3+MnO+CoO+NiO, and 25% to 55% P2O5. The reason for limiting the composition in this way is explained below. In the following explanation of the content of each component, "%" means "mol percent" unless otherwise specified.

[0030] Na2O has the general formula Na x M y P2O z (M is at least one transition metal element selected from Fe, Cr, Mn, Co, and Ni, 1.20≦x≦2.10, 0.95≦y≦1.60), and is the main component of the positive electrode active material crystal. The Na2O content is preferably 25% to 55%, and more preferably 30% to 50%. If the Na2O content is too low or too high, the charge / discharge capacity tends to decrease.

[0031] Fe2O3, Cr2O3, MnO, CoO and NiO also have the general formula Na x M y P2O z It is the main component of the positive electrode active material crystal represented by the formula: Fe2O3+Cr2O3+MnO+CoO+NiO content is preferably 10% to 30%, more preferably 15% to 25%. If the content of Fe2O3+Cr2O3+MnO+CoO+NiO is too low, the charge / discharge capacity tends to decrease. On the other hand, if the content of Fe2O3+Cr2O3+MnO+CoO+NiO is too high, undesired crystals such as Fe2O3, Cr2O3, MnO, CoO, or NiO tend to precipitate. In order to improve the cycle characteristics, it is preferable to actively contain 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 of the components Cr2O3, MnO, CoO and NiO is preferably 0% to 30%, more preferably 10% to 30%, and even more preferably 15% to 25%. When at least two components selected from Fe2O3, Cr2O3, MnO, CoO and NiO are contained, the total content thereof is preferably 10% to 30%, and more preferably 15% to 25%.

[0032] P2O5 also has the general formula Na x M y P2O z It is the main component of the positive electrode active material crystal represented by the formula: The content of P2O5 is preferably 25% to 55%, and more preferably 30% to 50%. If the content of P2O5 is too low or too high, the charge / discharge capacity tends to decrease.

[0033] In addition to the above components, the positive electrode active material precursor powder may contain V2O5, Nb2O5, MgO, Al2O3, TiO2, ZrO2, or Sc2O3. These components have the effect of increasing electrical conductivity (electronic conductivity), and the high-speed charge / discharge characteristics of the positive electrode active material are likely to be improved. The total content of the above components is preferably 0% to 25%, and more preferably 0.2% to 10%. If the content of the above components is too high, heterogeneous crystals that do not contribute to the battery characteristics are generated, and the charge / discharge capacity is likely to decrease.

[0034] In addition to the above components, SiO2, B2O3, GeO2, Ga2O3, Sb2O3, or Bi2O3 may be contained. By containing these components, glass forming ability is improved, and it becomes easier to obtain a homogeneous positive electrode active material precursor powder. The total content of the above components is preferably 0% to 25%, more preferably 0.2% to 10%. Since the above components do not contribute to the battery characteristics, if the content is too high, the charge / discharge capacity tends to decrease.

[0035] The positive electrode active material precursor powder is preferably produced by melting and molding a raw material batch. This method is preferable because it is easy to obtain an amorphous positive electrode active material precursor powder with excellent homogeneity. Specifically, the positive electrode active material precursor powder can be produced as follows.

[0036] First, the raw materials are prepared to have a desired composition to obtain a raw material batch. Next, the obtained raw material batch is melted. The melting temperature may be appropriately adjusted so that the raw material batch is homogeneously melted. For example, the melting temperature is preferably 800°C or higher, and more preferably 900°C or higher. There is no particular upper limit, but since a melting temperature that is too high leads to energy loss and evaporation of sodium components, etc., it is preferably 1500°C or lower, and more preferably 1400°C or lower.

[0037] Next, the obtained molten material is molded. The molding method is not particularly limited, and for example, the molten material may be poured between a pair of cooling rolls and molded into a film while being rapidly cooled, or the molten material may be poured into a mold and molded into an ingot.

[0038] The obtained molded body is then pulverized 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. If the average particle size of the positive electrode active material precursor powder is too small, when it is used in a paste form, the cohesive force between the particles becomes strong, making it difficult to disperse in the paste. In addition, when it is mixed with a solid electrolyte powder or the like, it becomes difficult to uniformly disperse the positive electrode active material precursor powder in the mixture, and the internal resistance increases, so that the output characteristics decrease and the charge / discharge capacity decreases. On the other hand, if the average particle size of the positive electrode active material precursor powder is too large, the crystallization temperature tends to be high. In addition, the amount of diffusion of ions and electrons per unit surface area of ​​the positive electrode material decreases, so that the internal resistance increases, so that the output characteristics decrease, and as a result, the charge / discharge capacity tends to decrease. Furthermore, when mixed with a solid electrolyte powder, the adhesion between the positive electrode active material precursor powder and the solid electrolyte powder decreases, which tends to reduce the mechanical strength of the positive electrode layer 2 and, as a result, to reduce the charge / discharge capacity. Alternatively, the adhesion between the positive electrode layer 2 and the solid electrolyte layer 1 is also poor, and there is a risk that the positive electrode layer 2 will peel off from the solid electrolyte layer 1.

[0039] In addition, if the average particle size of the positive electrode active material precursor powder is reduced, a dense positive electrode layer can be obtained, but in this case, the specific surface area of ​​the positive electrode active material precursor powder increases, so it is necessary to increase the amount of binder added when forming the paste. However, since the binder volatilizes during firing, the number of voids in the positive electrode material layer increases, so that the volumetric shrinkage of the positive electrode material layer becomes more likely to occur. As a result, the positive electrode layer becomes more likely to peel off from the solid electrolyte layer. In the manufacturing method of this embodiment, the positive electrode material layer 2A formed on the solid electrolyte layer 1 is fired while being pressed, so that even if the average particle size of the positive electrode active material precursor powder is reduced, the positive electrode layer 2 obtained by firing is less likely to peel off from the solid electrolyte layer 1.

[0040] In the present invention, the average particle size means D50 (volume-based average particle size) and indicates a value measured by a laser diffraction scattering method.

[0041] solid electrolyte powder; The solid electrolyte powder is a component responsible for ion conduction in the positive electrode layer 2 in the all-solid-state battery 10.

[0042] Examples of solid electrolyte powders include beta-alumina or NASICON crystals, which have excellent sodium ion conductivity. Beta-alumina exists in two crystal forms: β-alumina (theoretical formula: Na2O·11Al2O3) and β"-alumina (theoretical formula: Na2O·5.3Al2O3). β"-alumina is a metastable substance, so it is usually used with Li2O or MgO added as a stabilizer. β"-alumina has a higher sodium ion conductivity than β-alumina, so 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 It is more preferable to use O).

[0043] NASICON crystals include Na3Zr2Si2PO 12 , Na 3.2 Zr 1.3 S 2.2 P 0.7 O 10.5 , Na3Zr 1.6 Ti 0.4 SiPO 12 , Na3Hf2Si2PO 12 , Na 3.4 Zr 0.9 Hf 1.4 Al 0.6 S 1.2 P 1.8 O 12 , Na3Zr 1.7 Nb 0.24 SiPO 12 , Na 3.6 Ti 0.2 Y 0.7 S 2.8 O9, Na3Zr 1.88 Y 0.12 SiPO 12 , Na 3.12 Zr 1.88 Y 0.12 SiPO 12 , Na 3.6 Zr 0.13 Yb 1.67 S 0.11 P 2.9 O 12 In particular, Na 3.12 Zr 1.88 Y 0.12 SiPO 12 is preferred due to its excellent sodium ion conductivity.

[0044] The average particle diameter 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 diameter of the solid electrolyte powder is too small, not only is it difficult to mix it uniformly with the positive electrode active material precursor powder, but there is also a risk that the ion conductivity will decrease due to moisture absorption or carbonation, or that excessive reaction with the positive electrode active material precursor powder will be promoted. As a result, the internal resistance of the positive electrode material layer will tend to increase, and the voltage characteristics and charge / discharge capacity will tend to decrease. On the other hand, if the average particle diameter of the solid electrolyte powder is too large, the softening and flow of the positive electrode active material precursor powder will be significantly hindered, so that the smoothness of the obtained positive electrode layer 2 will tend to be poor, the mechanical strength will tend to decrease, and the internal resistance will tend to increase.

[0045] If the average particle size of the solid electrolyte powder is reduced, a dense positive electrode layer can be obtained, but in this case, the specific surface area of ​​the solid electrolyte powder increases, so it is necessary to increase the amount of binder added when forming the paste. However, since the binder volatilizes during firing, the number of voids in the positive electrode material layer increases, so that the volumetric shrinkage of the positive electrode material layer becomes more likely to occur. As a result, the positive electrode layer becomes more likely to peel off from the solid electrolyte layer. In the manufacturing method of this embodiment, the positive electrode material layer 2A formed on the solid electrolyte layer 1 is fired while being pressurized, so that even if the average particle size of the solid electrolyte powder is reduced, the positive electrode layer 2 obtained by firing is less likely to peel off from the solid electrolyte layer 1.

[0046] The solid electrolyte layer 1 is preferably made of the same material as the solid electrolyte powder. The solid electrolyte layer 1 can be manufactured by mixing raw material powders, molding the mixed raw material powder, and then firing it. For example, the solid electrolyte layer 1 can be manufactured by forming a green sheet by slurried raw material powder, and then firing the green sheet. It may also be manufactured by a sol-gel method.

[0047] Conductive additives; The conductive assistant is a component that forms a conductive path in the positive electrode material. For example, conductive carbon can be used as the conductive assistant. As the conductive carbon, powdered or fibrous conductive carbon such as highly conductive carbon black such as acetylene black or ketjen black is preferable. When conductive carbon is added, it is preferable to add it when grinding the positive electrode active material precursor powder. The conductive carbon plays the role of a grinding assistant, and not only can it be mixed homogeneously with the positive electrode active material precursor powder, but it also suppresses excessive fusion between the positive electrode active material precursor powder particles during firing, making it easier to ensure conductivity and improve rapid charge / discharge characteristics.

[0048] binder; Binders are materials for integrating raw materials (raw material powders) together. Examples of binders include cellulose derivatives such as carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose, water-soluble polymers such as polyvinyl alcohol, thermosetting resins such as thermosetting polyimide, phenol resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, and polyurethane, polycarbonate resins such as polypropylene carbonate, and polyvinylidene fluoride.

[0049] Composition of raw materials; The solid raw material preferably contains, by mass%, 30% to 100% of the positive electrode active material precursor powder, 0% to 70% of the solid electrolyte powder, and 0% to 20% of the conductive carbon, more preferably 44.5% to 94.5% of the positive electrode active material precursor powder, 5% to 55% of the solid electrolyte powder, and 0.5% to 15% of the conductive carbon, and even more preferably 50% to 92% of the positive electrode active material precursor powder, 7% to 50% of the solid electrolyte powder, and 1% to 10% of the conductive carbon. If the content of the positive electrode active material precursor powder is too low, the amount of the component that absorbs or releases sodium ions during charging and discharging in the positive electrode material decreases, and the charge and discharge capacity of the power storage device tends to decrease. If the content of the conductive carbon or solid electrolyte powder is too high, the binding property of the positive electrode active material precursor powder decreases and the internal resistance increases, and the voltage characteristics and the charge and discharge capacity tend to decrease.

[0050] The content of the binder is preferably 1 to 50 parts by mass, more preferably 5 to 40 parts by mass, relative to 100 parts by mass of the solid raw material. If the content of the binder is too low, the binding property of the solid raw material is insufficient, and the positive electrode material layer 2A may crack when dried or peel off from the solid electrolyte layer 1. If the content of the binder is too high, the binder volatilizes during firing as described above, so that the number of voids in the positive electrode material layer 2A increases and volume shrinkage is likely to occur. However, in the manufacturing method of this embodiment, the positive electrode material layer 2A formed on the solid electrolyte layer 1 is fired while being pressurized, so that the positive electrode layer 2 obtained by firing is unlikely to peel off from the solid electrolyte layer 1 even when the content of the binder is increased.

[0051] When mixing the raw materials, for example, a mixer such as a planetary centrifugal mixer or a tumbler mixer, or a general grinding machine such as a mortar, a mortar mixer, a ball mill, an attritor, a vibrating ball mill, a satellite ball mill, a planetary ball mill, a jet mill, or a bead mill can be used.

[0052] The drying temperature of the slurry is not particularly limited, but may be, for example, 30° C. or more and 100° C. or less. The drying time of the slurry is not particularly limited, but may be, for example, 10 minutes or more and 600 minutes or less.

[0053] (Firing process) In the firing step, the positive electrode material layer 2A formed on the solid electrolyte layer 1 is fired while being pressurized. In this embodiment, as shown in FIG. 1(b), a carbon sheet 4 is placed on the second main surface 2b of the positive electrode material layer 2A, and a weight 5 is further placed on the carbon sheet 4. As a result, the positive electrode material layer 2A is fired while being pressurized. Note that the first main surface 2a of the positive electrode material layer 2A is the main surface on the solid electrolyte layer 1 side, and the second main surface 2b is the main surface facing the first main surface 2a.

[0054] In this embodiment, pressure is applied to the entire second main surface 2b of the positive electrode material layer 2A. In this manner, in the present invention, it is desirable to apply pressure to the entire second main surface 2b, but it is sufficient to apply pressure to at least a part of the second main surface 2b, and there is no particular limitation.

[0055] The pressure applied to the positive electrode layer 2A is preferably 1 kPa or more, more preferably 5 kPa or more, and even more preferably 10 kPa or more. In this case, the positive electrode layer 2 obtained by firing is even more unlikely to peel off from the solid electrolyte layer 1. The upper limit of the pressure applied to the positive electrode layer 2A is not particularly limited, but may be, for example, 100 MPa.

[0056] The atmosphere during the firing is preferably a reducing atmosphere. Examples of the 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 the Fe ions in the positive electrode active material precursor powder from trivalent to divalent, it is preferable that the atmosphere contains at least one selected from H2, NH3, and CO, and it is more preferable that the atmosphere contains H2 gas. When H2 gas is used, it is preferable to mix an inert gas such as N2 in order to reduce the risk of explosion during firing. Specifically, the reducing gas preferably contains, by volume, 90% to 99.9% N2 and 0.1% to 10% H2, more preferably 90% to 99.5% N2 and 0.5% to 10% H2, and even more preferably 92% to 99% N2 and 1 to 8% H2.

[0057] 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 positive electrode active material precursor powder becomes insufficient, and the remaining amorphous phase becomes a high resistance part, and the voltage characteristics and charge / discharge capacity tend to decrease. On the other hand, if the firing temperature is too high, the positive electrode active material precursor powder is excessively fused to each other, and coarse particles are formed, so that the specific surface area of ​​the positive electrode active material tends to decrease, and the charge / discharge characteristics tend to decrease. In addition, the positive electrode active material precursor powder and the solid electrolyte powder react during firing, and crystals that do not contribute to charge / discharge (such as maricite-type NaFePO4 crystals) are precipitated, which may decrease the charge / discharge capacity. Alternatively, elements contained in the positive electrode active material precursor powder and the solid electrolyte powder may diffuse into each other during firing, forming a partially high-resistance layer, which may degrade the rate characteristics of the all-solid-state battery, which is an electricity storage device.

[0058] The firing time (the time to hold 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 positive electrode active material precursor powders are excessively fused to each other, coarse particles are easily formed, the specific surface area of ​​the positive electrode active material is reduced, and the charge / discharge characteristics tend to deteriorate. In addition, in the case of an all-solid-state battery, the positive electrode active material precursor powder and the solid electrolyte powder react during firing, and crystals that do not contribute to charging and discharging (such as maricite-type NaFePO4 crystals) are precipitated, which may reduce the charge / discharge capacity. Alternatively, elements contained in the positive electrode active material precursor powder and the solid electrolyte powder may diffuse mutually during firing, resulting in the formation of a partially high-resistance layer, which may reduce the rate characteristics of the all-solid-state battery. On the other hand, if the firing time is too short, the crystallization of the positive electrode active material precursor powder becomes insufficient, and the remaining amorphous phase becomes a high-resistance portion, which tends to reduce the voltage characteristics and charge / discharge capacity. Therefore, the baking time is preferably 1 minute or more, and more preferably 5 minutes or more.

[0059] For firing, an electric heating furnace, a rotary kiln, a microwave heating furnace, a high-frequency heating furnace, or the like can be used.

[0060] (Negative electrode layer formation process) The negative electrode layer 3 can be prepared, for example, by using a slurry containing a negative electrode active material precursor powder and, if necessary, a solid electrolyte powder and / or a conductive assistant. If necessary, a binder, a plasticizer, a solvent, etc. are added to the slurry. The negative electrode layer 3 can be prepared by applying the slurry onto the second main surface 1b of the solid electrolyte layer 1, drying it, and firing it. Alternatively, the negative electrode layer 3 may be prepared by applying the slurry onto a substrate such as PET (polyethylene terephthalate), drying it, preparing a green sheet, and firing the green sheet. Alternatively, the negative electrode layer 3 may be made of a metal, and in this case, the negative electrode layer 3 can be formed by a sputtering method, a vapor deposition method, or the like.

[0061] (Other embodiments) In the above embodiment, the method for manufacturing an all-solid-state sodium ion secondary battery using a material having sodium ion conductivity has been described, but the method may be used for manufacturing other all-solid-state batteries, such as an all-solid-state lithium ion secondary battery using a material having lithium ion conductivity.

[0062] In the above embodiment, the positive electrode layer 2 is fired while being pressurized when it is formed, but the negative electrode layer 3 may be fired while being pressurized when it is formed. In addition, both the positive electrode layer 2 and the negative electrode layer 3 may be fired while being pressurized when they are both formed. Both the positive electrode layer 2 and the negative electrode layer 3 may be fired simultaneously.

[0063] If necessary, a current collector layer may be formed on each of the positive electrode layer 2 and the negative electrode layer 3.

[0064] The method for forming the current collector layer is not particularly limited, and examples thereof include 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 current collector layer include liquid phase film formation methods such as plating, sol-gel method, and spin coating. However, it is preferable to form the current collector layer on the positive electrode layer 2 or the negative electrode layer 3 by a sputtering method, since this has excellent adhesion.

[0065] The material of the current collector layer is not particularly limited, and may be a metal material such as aluminum, titanium, silver, copper, stainless steel, or an alloy thereof. The above metal materials may be used alone or in combination. These alloys are alloys containing at least one of the above metals.

[0066] [All-solid battery] As shown in Fig. 2, the all-solid-state battery 10 includes a solid electrolyte layer 1, a positive electrode layer 2, and a negative electrode layer 3. The solid electrolyte layer 1 has a first main surface 1a and a second main surface 1b that face each other. A positive electrode layer 2 is provided on the first main surface 1a of the solid electrolyte layer 1. This constitutes an electricity storage device member 6. In addition, a negative electrode layer 3 is provided on the second main surface 1b of the solid electrolyte layer 1.

[0067] The positive electrode layer 2 is made of a sintered body of a positive electrode material layer containing a positive electrode active material precursor powder having an average particle size of 0.01 μm or more and less than 0.7 μm. Therefore, the positive electrode layer 2 is dense. Therefore, the energy density can be increased, and the capacity of the all-solid-state battery 10 is increased. Note that the other points can be those described in the above-mentioned manufacturing method.

[0068] The positive electrode active material contained in the positive electrode layer 2 is not particularly limited, but may be NaCrO2, Na 0.7 MnO2, NaFe 0.2 Mn 0.4 Ni 0.4 Examples of active material crystals include layered sodium transition metal oxide crystals such as O2, and sodium transition metal phosphate crystals containing Na, M (M is at least one transition metal element selected from Cr, Fe, Mn, Co, and Ni), P, and O, such as Na2FeP2O7, NaFePO4, and Na3V2(PO4)3.

[0069] In particular, crystals containing Na, M, P and O are preferred because they have high capacity and excellent chemical stability. Among them, triclinic crystals belonging to space group P1 or P-1, especially those of the general formula Na x M y P2O z A crystal represented by the formula (M is at least one transition metal element selected from Fe, Cr, Mn, Co and Ni, 1.20≦x≦2.10, 0.95≦y≦1.60) is preferred because it has excellent cycle characteristics.

[0070] The thickness of the positive electrode layer 2 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 10 can be further increased. On the other hand, if the thickness of the positive electrode layer 2 is too thick, the resistance to electronic conduction increases, which may reduce the discharge capacity and operating voltage, and the stress due to shrinkage during firing increases, which may lead to peeling, so the thickness is preferably 150 μm or less.

[0071] The amount of the positive electrode active material contained in the positive electrode layer 2 is preferably 3 mg / cm 2 More preferably, 5 mg / cm 2 More preferably, 7 mg / cm 2 More preferably, 9 mg / cm 2 More than 12 mg / cm, most preferably 12 mg / cm 2 In this case, the capacity of the all-solid-state battery 10 can be further increased. The upper limit of the amount of the positive electrode active material carried is not particularly limited, but is, for example, 100 mg / cm. 2 It can be said that:

[0072] The solid electrolyte layer 1 and the negative electrode layer 3 may be the same as the solid electrolyte layer 1 and the negative electrode layer 3 produced by the above-mentioned production method.

[0073] The thickness of the solid electrolyte layer 1 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 1 is too thin, the mechanical strength decreases and the layer is easily broken, which makes the layer more susceptible to internal short circuits. If the thickness of the solid electrolyte layer 1 is too thick, the sodium ion conduction distance during charging and discharging increases, which makes the internal resistance higher and the discharge capacity and operating voltage more likely to decrease. In addition, the energy density per unit volume of the all-solid-state battery 10 is also more likely to decrease.

[0074] Examples of the negative electrode active material include active material crystals such as crystals containing at least one selected from Nb and Ti and O, and metal crystals of at least one selected from Sn, Bi and Sb.

[0075] Crystals containing at least one selected from Nb and Ti and O are preferred because they have excellent cycle characteristics. Furthermore, when the crystals containing at least one selected from Nb and Ti and O contain Na and / or Li, the charge / discharge efficiency (ratio of discharge capacity to charge capacity) is increased, and a high charge / discharge capacity can be maintained, which is preferred. Among these, if the crystals containing at least one selected from Nb and Ti and O are orthorhombic crystals, hexagonal crystals, cubic crystals, or monoclinic crystals, particularly monoclinic crystals belonging to the space group P21 / m, it is preferred because the capacity is less likely to decrease even when charged and discharged at a large current. Examples of orthorhombic crystals include NaTi2O4, and examples of hexagonal crystals include Na2TiO3, NaTi8O 13 , NaTiO2, LiNbO3, LiNbO2, Li7NbO6, LiNbO2, Li2Ti3O7, etc., and cubic crystals include Na2TiO3, NaNbO3, Li4Ti5O 12 , Li3NbO4, etc., and monoclinic crystals include Na2Ti6O 13 , NaTi2O4, Na2TiO3, Na4Ti5O 12 , Na2Ti4O9, Na2Ti9O 19 , Na2Ti3O7, Na2Ti3O7, Li 1.7 Nb2O5, Li 1.9 Nb2O5, Li 12 Nb 13 O 33 , LiNb3O8, etc., and monoclinic crystals belonging to the space group P21 / m include Na2Ti3O7, etc.

[0076] The crystal containing at least one selected from Nb and Ti and O preferably further contains at least one selected from B, Si, P and Ge. These components facilitate the formation of an amorphous phase together with the active material crystal, and have the effect of improving sodium ion conductivity.

[0077] In addition, at least one metal crystal selected from Sn, Bi, and Sb, or glass containing at least one selected from Sn, Bi, and Sb can be used. These are preferred because they have high capacity and are less likely to decrease in capacity even when charged and discharged at a large current.

[0078] The thickness of the negative electrode layer 3 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 3 is too thin, the absolute capacity (mAh) of the negative electrode tends to decrease. If the thickness of the negative electrode layer 3 is too thick, the resistance increases, and the capacity (mAh / g) tends to decrease.

[0079] In the above embodiment, an all-solid-state sodium ion secondary battery using a material having sodium ion conductivity has been described. However, the present invention may 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.

[0080] In the above embodiment, the positive electrode layer 2 is made of a sintered body of the positive electrode material layer 2A containing a positive electrode active material precursor powder having an average particle size of 0.01 μm or more and less than 0.7 μm, but the negative electrode layer 3 may be made of a sintered body of the negative electrode material layer containing a negative electrode active material precursor powder having an average particle size of 0.01 μm or more and less than 0.7 μm, preferably 0.05 μm or more and 0.6 μm or less. In this case, the thickness of the negative electrode layer 3 and the amount of the negative electrode active material carried may be the thickness of the positive electrode layer 2 and the amount of the positive electrode active material carried. Both the positive electrode layer 2 and the negative electrode layer 3 may have these configurations.

[0081] Furthermore, if necessary, a current collector layer as explained in the above-mentioned section on the manufacturing method may be provided on each of the positive electrode layer 2 and the negative electrode layer 3.

[0082] The present invention will be described in more detail below with reference to specific examples. The present invention is not limited to the following examples, and can be modified as appropriate within the scope of the present invention.

[0083] (Examples 1 to 11, Reference Examples 1 to 2) (a) Preparation of positive electrode active material precursor powder Sodium metaphosphate (NaPO3), ferric oxide (Fe2O3) and orthophosphoric acid (H3PO4) were used as raw materials, and raw material powders were mixed to have a composition of 40% Na2O, 20% Fe2O3 and 40% P2O5 in mol%, and melted at 1250°C for 45 minutes in an air atmosphere. The melt was then poured between a pair of rotating rollers and molded while being quenched to obtain a film-like glass having a thickness of 0.1 mm to 2 mm. The obtained film-like glass was pulverized in a ball mill and a planetary ball mill to obtain a glass powder (positive electrode active material precursor powder) having an average particle size shown in Table 1. It should be noted that the result of powder X-ray diffraction (XRD) measurement confirmed that the obtained glass powder was amorphous.

[0084] (b) Preparation of solid electrolyte layer and solid electrolyte powder Li2O stabilized β” alumina (Ionotec, composition formula: Na 1.7 Li 0.3 Al 10.7 O 17 ) was processed into a sheet having a thickness of 0.5 mm to obtain a solid electrolyte layer. The sheet-shaped LiO-stabilized β″ alumina was pulverized in a ball mill and a planetary ball mill to obtain a solid electrolyte powder having an average particle size of 0.4 μm.

[0085] (c) Preparation of test battery In Examples 1 to 11 and Reference Examples 1 and 2, the positive electrode active material precursor powder obtained above, solid electrolyte powder, and acetylene black (SUPER C65, manufactured by TIMCAL) as conductive carbon were each weighed out in the ratios shown in Table 1 below, and mixed for 30 minutes using an agate mortar and pestle. 20 parts by mass of polypropylene carbonate and 30 parts by mass of N-methylpyrrolidone were added to 100 parts by mass of the mixed powder, and the mixture was thoroughly stirred using a planetary centrifugal mixer to form a slurry.

[0086] The obtained slurry was applied to one surface of the solid electrolyte layer obtained above to an area of ​​1 cm 2The positive electrode material layer was formed by applying the positive electrode material to a thickness of 80 μm and drying at 70° C. for 3 hours. In each of Examples 1 to 11, a carbon sheet (20 mm×20 mm×0.5 mm) was placed on the positive electrode material layer, and a weight was placed on the carbon sheet so as to apply pressure at the pressure shown in Table 1. On the other hand, in Reference Examples 1 and 2, no weight was placed.

[0087] In this state, the solid electrolyte layer was fired at 525°C for 30 minutes in a mixed gas of 4% by volume of H2 and 96% by volume of N2 to form a positive electrode layer on one surface of the solid electrolyte layer, thereby producing a member for a storage battery device. The above operations were all performed in an environment with a dew point of -40°C or less. The amount of the positive electrode active material carried (active material carried amount) is as shown in Table 1 below. The thickness of the electrode layer was measured with a micrometer.

[0088] The powder X-ray diffraction patterns of the obtained positive electrode layers were confirmed to be Na2FeP2O7 crystals. In addition, crystalline diffraction lines originating from the solid electrolyte powder used were confirmed in all positive electrode layers.

[0089] Fig. 3 is a photograph in plan view of the positive electrode layer obtained in Example 5. Fig. 4 is a photograph in plan view of the positive electrode layer obtained in Reference Example 2.

[0090] As is clear from Fig. 3, in Example 5, even though the amount of the positive electrode active material carried is large, the positive electrode layer obtained by firing is not peeled off from the solid electrolyte layer. Although not shown, it was also confirmed that the positive electrode layer obtained by firing is not peeled off from the solid electrolyte layer in Examples 1 to 4 and 6 to 11. On the other hand, as is clear from Fig. 4, it was confirmed that the positive electrode layer obtained by firing is peeled off from the solid electrolyte layer in Reference Example 2.

[0091] Next, a current collector made of a gold electrode with a thickness of 300 nm was formed on the surface of the obtained positive electrode layer using a sputtering device (manufactured by Sanyu Electronics, product number "SC-701AT") After that, metallic sodium as a counter electrode was pressed onto the other surface of the solid electrolyte layer in an argon atmosphere with a dew point of -60°C or less, and placed on the bottom lid of a coin cell, and then the top lid was placed on top to prepare a CR2032 test battery.

[0092] (d) Charge / discharge test The test battery thus fabricated was subjected to a charge-discharge test at 30° C. to measure the battery capacity. The results are shown in Table 1. In the charge-discharge test, the C rate was set to 0.1C.

[0093] [Table 1]

[0094] As is clear from Table 1, charging and discharging are possible in Examples 1 to 11 regardless of the amount of the positive electrode active material carried. Therefore, it is understood that the battery capacity is increased in Examples 2 and Examples 5 to 7, which have a large amount of the positive electrode active material carried. On the other hand, it was confirmed that charging and discharging are not possible in Reference Example 2. [Explanation of symbols]

[0095] 1...Solid electrolyte layer 1a, 2a...First main surface 1b, 2b...Second main surface 2A…Cathode material layer 2…Positive electrode layer 3...Negative electrode layer 4…Carbon sheet 5…Weight 6...Electricity storage device components 10…All-solid-state battery

Claims

1. A solid electrolyte layer; a positive electrode layer provided on the solid electrolyte layer and made of a sintered body of a positive electrode material layer containing a positive electrode active material precursor powder having an average particle size of 0.01 μm or more and less than 0.7 μm; Equipped with The thickness of the positive electrode layer is 20 μm or more, The all-solid-state sodium ion secondary battery, wherein the amount of the positive electrode active material supported in the positive electrode layer is 3 mg / cm 2 or more.

2. The all-solid-state sodium ion secondary battery according to claim 1, wherein the positive electrode active material comprises a crystal represented by the general formula Na x M y P 2 O z (M is at least one transition metal element selected from Fe, Cr, Mn, Co and Ni, 1.20≦x≦2.10, 0.95≦y≦1.60).

3. A method for producing the all-solid-state sodium ion secondary battery according to claim 1 or 2, comprising the steps of: a forming step of forming a positive electrode material layer containing a positive electrode active material precursor powder on the solid electrolyte layer; a firing step of firing the positive electrode material layer while applying pressure; A method for producing an all-solid-state sodium ion secondary battery comprising the steps of:

4. the positive electrode material layer has a first main surface on the side of the solid electrolyte layer and a second main surface opposite to the first main surface, The method for producing an all-solid-state sodium ion secondary battery according to claim 3 , wherein in the firing step, the firing is performed while applying pressure to the entire second main surface.

5. The method for producing an all-solid-state sodium ion secondary battery according to claim 3 or 4, wherein in the firing step, the positive electrode material layer is pressurized at 1 kPa or more and 90 kPa or less.

6. The method for producing an all-solid-state sodium ion secondary battery according to any one of claims 3 to 5, wherein the average particle diameter of the positive electrode active material precursor powder is 0.01 µm or more and less than 0.7 µm.

7. The method for producing an all-solid-state sodium ion secondary battery according to any one of claims 3 to 6, wherein the positive electrode active material precursor powder is an amorphous oxide material.

8. The positive electrode active material precursor powder contains, in mole percent in terms of oxide, 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 The method for producing an all-solid-state sodium ion secondary battery according to any one of claims 3 to 7, wherein the content is 25% to 55%.

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