WO2018131627A1 - Electrode mix for sodium ion secondary battery and method for manufacturing same - Google Patents

Electrode mix for sodium ion secondary battery and method for manufacturing same Download PDF

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WO2018131627A1
WO2018131627A1 PCT/JP2018/000400 JP2018000400W WO2018131627A1 WO 2018131627 A1 WO2018131627 A1 WO 2018131627A1 JP 2018000400 W JP2018000400 W JP 2018000400W WO 2018131627 A1 WO2018131627 A1 WO 2018131627A1
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electrode mixture
sodium ion
powder
solid electrolyte
ion secondary
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PCT/JP2018/000400
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French (fr)
Japanese (ja)
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純一 池尻
英郎 山内
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日本電気硝子株式会社
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Publication of WO2018131627A1 publication Critical patent/WO2018131627A1/en

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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
    • H01M10/0562—Solid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to an electrode mixture for a sodium ion secondary battery used for an electricity storage device such as a sodium ion secondary battery and a method for producing the same.
  • Lithium ion secondary batteries have established themselves as high-capacity and lightweight power supplies that are indispensable for mobile devices and electric vehicles.
  • the current lithium ion secondary battery mainly uses a flammable organic electrolyte as an electrolyte, and there is a concern about the risk of ignition and the like.
  • development of a lithium ion all-solid battery using a solid electrolyte instead of an organic electrolyte has been underway (see, for example, Patent Document 1).
  • the all-solid battery as described above includes a positive electrode layer, a negative electrode layer, and a sodium ion conductive solid electrolyte layer.
  • the positive electrode layer and the negative electrode layer are generally composed of a mixture (electrode mixture) of an active material powder that occludes or releases sodium ions and electrons during charge and discharge and a solid electrolyte powder.
  • Patent Document 3 discloses an electrode mixture obtained by firing an active material precursor powder made of crystalline glass powder and a raw material powder (electrode mixture precursor) made of solid electrolyte powder, and fusing and integrating the powders. Is described.
  • the electrode mixture described in Patent Document 3 has a problem that the ion conduction path is not sufficiently formed between the active material powder and the solid electrolyte powder, and the discharge capacity is small.
  • an object of the present invention is to provide an electrode mixture for a sodium ion secondary battery in which an ion conduction path is sufficiently formed between the active material powder and the solid electrolyte powder and the discharge capacity is large. To do.
  • the electrode mixture for a sodium ion secondary battery of the present invention comprises a sintered body of an electrode mixture precursor powder containing an active material precursor powder and a sodium ion conductive solid electrolyte powder, and has a porosity of 45. % Or less.
  • the electrode mixture of the present invention has a feature that the porosity is as small as 45% or less, and the adhesiveness between the active material powder and the solid electrolyte powder is high, so that an ion conduction path is sufficiently formed and the discharge capacity is high.
  • the electrode mixture for a sodium ion secondary battery according to the present invention has an active material precursor powder (i) at least one transition metal selected from the group consisting of Cr, Fe, Mn, Co, Ni, Ti and Nb. It is preferable to contain an element, (ii) at least one element selected from P, Si and B, and (iii) O.
  • the solid electrolyte powder preferably contains at least one selected from Al, Y, Zr, Si and P, Na, and O.
  • the solid electrolyte powder preferably contains at least one selected from ⁇ -alumina, ⁇ ′′ -alumina, and NASICON type crystals.
  • the average particle diameter of the active material precursor powder and / or the solid electrolyte powder is preferably 0.01 to 15 ⁇ m. In this way, the number of ion conduction paths can be increased, and the discharge capacity can be further improved.
  • the sodium ion secondary battery of the present invention is characterized by using the above-mentioned electrode mixture for sodium ion secondary batteries.
  • the method for producing an electrode mixture for a sodium ion secondary battery comprises a step of slurrying an electrode mixture precursor powder comprising (a) an active material precursor powder and a sodium ion conductive solid electrolyte powder. (B) applying the slurry obtained on the substrate and drying it to produce an electrode mixture precursor sheet; and (c) pressing the electrode mixture precursor sheet and firing it. It is characterized by including.
  • the adhesiveness between the active material powder and the solid electrolyte powder can be effectively enhanced by pressing and firing the electrode mixture precursor sheet. Therefore, for example, even if the active material precursor powder is made of crystalline glass with low softening fluidity, it is possible to sufficiently form an ion conduction path in the electrode mixture.
  • the electrode mixture precursor sheet is preferably isotropically pressed or uniaxially pressed.
  • the electrode mixture precursor sheet is preferably pressed at a pressure of 3 MPa or more.
  • the method for producing a battery for a sodium ion secondary battery of the present invention comprises (a) slurrying an electrode mixture precursor powder containing an active material precursor powder and a sodium ion conductive solid electrolyte powder. b) A step of producing a laminate sheet in which an electrode mixture precursor layer is formed on a solid electrolyte sheet by applying and drying the obtained slurry on a solid electrolyte sheet; and (c) a laminate. And a step of firing after pressing the sheet.
  • the adhesion between the active material powder and the solid electrolyte powder in the electrode mixture can be enhanced, and at the same time, the adhesion between the electrode mixture layer and the solid electrolyte sheet can be enhanced. Therefore, it is possible to sufficiently form both ion conduction paths in the electrode mixture and between the electrode mixture and the solid electrolyte sheet.
  • the laminate sheet is isotropically pressed or uniaxially pressed.
  • the laminate sheet In the method for producing a sodium ion secondary battery of the present invention, it is preferable to press the laminate sheet at a pressure of 3 MPa or more.
  • an electrode mixture for a sodium ion secondary battery in which an ion conduction path is sufficiently formed between the active material powder and the solid electrolyte powder and the discharge capacity is large.
  • SEM 4 is a SEM (scanning electron microscope) image of a cross section of a positive electrode mixture layer in a test battery of Example 3. It is the image which binarized the SEM image of FIG. 4 is a SEM image of a cross section of a positive electrode mixture layer in a test battery of Comparative Example 3. It is the image which binarized the SEM image of FIG.
  • the electrode mixture for a sodium ion secondary battery of the present invention comprises a sintered body of an electrode mixture precursor powder including an active material precursor powder and a sodium ion conductive solid electrolyte powder.
  • the active material precursor powder becomes an active material powder by firing.
  • the active material powder includes a positive electrode active material powder and a negative electrode active material powder, and occludes and releases sodium ions during charge and discharge.
  • Examples of the active material precursor powder include glass powder.
  • the active material precursor powder is usually accompanied by crystallization by firing, but may not be crystallized. That is, the active material powder may contain crystals (crystallized glass) or amorphous.
  • the active material precursor powder is selected from (i) at least one transition metal element selected from the group consisting of Cr, Fe, Mn, Co, Ni, Ti and Nb, and (ii) P, Si and B. And (iii) those containing O.
  • the positive electrode active material precursor powder a powder containing Na 2 O 8 to 55%, CrO + FeO + MnO + CoO + NiO 10 to 70%, P 2 O 5 + SiO 2 + B 2 O 3 15 to 70% in terms of mol% in terms of oxide. Can be mentioned. The reason why each component is limited in this way will be described below. In the following description regarding the content of each component, “%” means “mol%” unless otherwise specified. “ ⁇ + ⁇ +...” Means the total amount of each corresponding component.
  • Na 2 O serves as a supply source of sodium ions that move between the positive electrode active material and the negative electrode active material during charge and discharge.
  • the content of Na 2 O is preferably 8 to 55%, 15 to 45%, particularly 25 to 35%. If the amount of Na 2 O is too small, sodium ions contributing to occlusion and release decrease, and the discharge capacity tends to decrease. On the other hand, when there is too much Na 2 O, different crystals that do not contribute to charging / discharging such as Na 3 PO 4 tend to precipitate, and the discharge capacity tends to decrease.
  • CrO, FeO, MnO, CoO, and NiO are components that act as a driving force for occlusion and release of sodium ions by causing a redox reaction by changing the valence of each transition element during charge and discharge.
  • NiO and MnO have a great effect of increasing the redox potential.
  • FeO has high structural stabilization in charge and discharge, and it is easy to improve cycle characteristics.
  • the content of CrO + FeO + MnO + CoO + NiO is preferably 10 to 70%, 15 to 60%, 20 to 55%, 23 to 50%, 25 to 40%, particularly preferably 26 to 36%.
  • P 2 O 5 , SiO 2 and B 2 O 3 form a three-dimensional network structure, they have an effect of stabilizing the structure of the positive electrode active material.
  • P 2 O 5 and SiO 2 are preferable because of excellent ion conductivity, and P 2 O 5 is most preferable.
  • the content of P 2 O 5 + SiO 2 + B 2 O 3 is 15 to 70%, preferably 20 to 60%, particularly preferably 25 to 45%. If the amount of P 2 O 5 + SiO 2 + B 2 O 3 is too small, the discharge capacity tends to decrease when the battery is repeatedly charged and discharged.
  • the content of each component of P 2 O 5 , SiO 2 and B 2 O 3 is preferably 0 to 70%, 15 to 70%, 20 to 60%, and particularly preferably 25 to 45%.
  • vitrification can be facilitated by incorporating various components in addition to the above components within a range not impairing the effects of the present invention.
  • examples of such components include MgO, CaO, SrO, BaO, ZnO, CuO, Al 2 O 3 , GeO 2 , Nb 2 O 5 , ZrO 2 , V 2 O 5 , and Sb 2 O 5 in oxide notation.
  • Al 2 O 3 serving as a network-forming oxide and V 2 O 5 serving as an active material component are preferable.
  • the total content of the above components is preferably 0 to 30%, 0.1 to 20%, particularly preferably 0.5 to 10%.
  • the active material crystals that act as the positive electrode active material powder include Na, M (M is at least one transition metal element selected from Cr, Fe, Mn, Co and Ni), sodium transition metal phosphorus containing P and O.
  • Examples include acid salt crystals. Specific examples include Na 2 FeP 2 O 7 , NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , Na 2 NiP 2 O 7 , Na 3.64 Ni 2.18 (P 2 O 7 ) 2 , Na 3. Ni 3 (PO 4) 2 ( P 2 O 7), Na 2 CoP 2 O 7, Na 3.64 Co 2.18 (P 2 O 7) 2 and the like.
  • the sodium transition metal phosphate crystal is preferable because of its high capacity and excellent chemical stability.
  • triclinic crystals belonging to the space group P1 or P1 particularly the general formula Na x M y P 2 O z (1.2 ⁇ x ⁇ 2.8,0.95 ⁇ y ⁇ 1.6,6 .5 ⁇ z ⁇ 8) is preferable because of excellent cycle characteristics.
  • Other active material crystals that act as a positive electrode active material include layered sodium transition metal oxide crystals such as NaCrO 2 , Na 0.7 MnO 2 , and NaFe 0.2 Mn 0.4 Ni 0.4 O 2. .
  • the negative electrode active material precursor powder is an oxide equivalent mol%, SnO 0 to 90%, Bi 2 O 3 0 to 90%, TiO 2 0 to 90%, Fe 2 O 3 0 to 90%, Nb 2 O 5 0 ⁇ 90%, SiO 2 + B 2 O 3 + P 2 O 5 5 ⁇ 75%, preferably contains Na 2 O 0 ⁇ 80%.
  • a structure in which Sn ions, Bi ions, Ti ions, Fe ions, or Nb ions, which are active material components, are uniformly dispersed in an oxide matrix containing Si, B, or P is formed. Moreover, it becomes a material excellent in sodium ion conductivity by containing Na 2 O. As a result, it is possible to suppress a volume change when inserting and extracting sodium ions, and it is possible to obtain a negative electrode active material having excellent cycle characteristics.
  • composition of the negative electrode active material precursor powder is limited as described above will be described below.
  • % means “mol%” unless otherwise specified.
  • SnO, Bi 2 O 3 , TiO 2 , Fe 2 O 3 and Nb 2 O 5 are active material components that serve as sites for occluding and releasing alkali ions.
  • the discharge capacity per unit mass of the negative electrode active material is increased, and the charge / discharge efficiency (ratio of the discharge capacity to the charge capacity) at the first charge / discharge is easily improved.
  • release of sodium ion at the time of charging / discharging cannot be relieved, but there exists a tendency for cycling characteristics to fall.
  • the content range of each component is preferably as follows.
  • the SnO content is preferably 0 to 90%, 45 to 85%, 55 to 75%, particularly 60 to 72%.
  • the content of Bi 2 O 3 is preferably 0 to 90%, 10 to 70%, 15 to 65%, particularly 25 to 55%.
  • the content of TiO 2 is preferably 0 to 90%, 5 to 72%, 10 to 68%, 12 to 58%, 15% to 49%, particularly preferably 15 to 39%.
  • the content of Fe 2 O 3 is preferably 0 to 90%, 15 to 85%, 20 to 80%, particularly 25 to 75%.
  • the Nb 2 O 5 content is preferably 0 to 90%, 7 to 79%, 9 to 69%, 11 to 59%, 13 to 49%, and particularly preferably 15 to 39%.
  • SnO + Bi 2 O 3 + TiO 2 + Fe 2 O 3 + Nb 2 O 5 is preferably 0 to 90%, 5 to 85%, particularly preferably 10 to 80%.
  • SiO 2 , B 2 O 3, and P 2 O 5 are network-forming oxides that surround the sodium ion occlusion and release sites in the active material component and have an effect of improving cycle characteristics. Among these, SiO 2 and P 2 O 5 not only improve cycle characteristics, but also have an effect of improving rate characteristics because of excellent sodium ion conductivity.
  • SiO 2 + B 2 O 3 + P 2 O 5 is preferably 5 to 85%, 6 to 79%, 7 to 69%, 8 to 59, 9 to 49%, particularly preferably 10 to 39%.
  • each preferred range of the content of SiO 2, B 2 O 3 and P 2 O 5 is as follows.
  • the content of SiO 2 is preferably 0 to 75%, 5 to 75%, 7 to 60%, 10 to 50%, 12 to 40%, particularly 20 to 35%.
  • the discharge capacity tends to lower.
  • the content of P 2 O 5 is preferably 5 to 75%, 7 to 60%, 10 to 50%, 12 to 40%, particularly 20 to 35%.
  • P 2 content of O 5 is too small, the above effect is difficult to obtain.
  • the content of P 2 O 5 is too large, the discharge capacity tends to decrease and the water resistance tends to decrease.
  • undesirable heterogeneous crystals are generated and the P 2 O 5 network is cut, so that the cycle characteristics are liable to deteriorate.
  • the content of B 2 O 3 is preferably 0 to 75%, 5 to 75%, 7 to 60%, 10 to 50%, 12 to 40%, particularly preferably 20 to 35%. If the B 2 O 3 content is too large, the discharge capacity tends to lower chemical durability tends to decrease.
  • x is too small, alkali ions are easily absorbed in the negative electrode active material during the initial charge, and the initial charge / discharge efficiency tends to be reduced. Further, the alkali ion conductivity is lowered, so that the resistance is increased and the discharge voltage tends to increase.
  • the operating voltage of the battery is determined by the difference between the operating voltage of the positive electrode and the operating voltage of the negative electrode, when the discharge voltage of the negative electrode increases, the operating voltage as a battery tends to decrease.
  • x is too large, a large amount of heterogeneous crystals (for example, Na 4 P 2 O 7 , NaPO 4 ) composed of alkali ions and P 2 O 5 are formed, and the cycle characteristics are likely to deteriorate.
  • the content of the active material component relatively decreases, the discharge capacity tends to decrease.
  • the range of y is 0.25 ⁇ y ⁇ 4, 1 ⁇ y ⁇ 3.8, 1.5 ⁇ y ⁇ 3.6, 2 ⁇ y ⁇ 3.4, especially 3 ⁇ y ⁇ 3.2. Is preferred. If y is too small, alkali ion conductivity tends to be lowered, and cycle characteristics tend to be lowered. On the other hand, if y is too large, the water resistance tends to decrease, and undesirable heterogeneous crystals are likely to be produced when the aqueous electrode paste is produced. As a result, the P 2 O 5 network in the negative electrode active material is cut, and the cycle characteristics are likely to deteriorate.
  • the range of z is preferably 2.5 ⁇ z ⁇ 16, 3 ⁇ z ⁇ 15, 4 ⁇ z ⁇ 14, 6 ⁇ z ⁇ 13, particularly 9 ⁇ z ⁇ 12. If z is too small, Ti is reduced and the valence is lowered, so that the redox reaction associated with charge / discharge hardly occurs. As a result, the number of occluded and released alkali ions decreases, and the capacity of the electricity storage device tends to decrease. On the other hand, if z is too large, a large amount of heterogeneous crystals (eg, Na 4 P 2 O 7 , NaPO 4 ) containing P 2 O 5 are formed, and the cycle characteristics are likely to deteriorate. Moreover, since the content of the active material component relatively decreases, the discharge capacity tends to decrease.
  • heterogeneous crystals eg, Na 4 P 2 O 7 , NaPO 4
  • Examples of the crystal phase represented by the general formula R x TiP y O z include Na 4 TiP 2 O 9 [Na 4 TiO (PO 4 ) 2 ], Na 5 TiP 3 O 12 [Na 5 Ti (PO 4 ) 3 ].
  • These crystal phases can reduce the oxidation-reduction potential of Ti 4 + / Ti 3+ associated with charging / discharging to about 1.2 V (vs. Na / Na + ), and the voltage variation associated with charging / discharging is small and constant. The operating voltage can be easily obtained.
  • Na 3.91 (TiP 2 O 9) preferably Na 4 TiP 2 O 9, Na 5 TiP 3 O 12, Na 5 TiP 3 O 12 having excellent ion conductivity are most preferred.
  • Na 3.91 TiP 2 O 9 and Na 4 TiP 2 O 9 are monoclinic crystals and belong to the space group P21 / c.
  • Na 5 TiP 3 O 12 is a hexagonal crystal and belongs to the space group R32.
  • the negative electrode active material may contain at least one selected from Nb and Ti, and crystals containing O.
  • the crystal is preferable because it has excellent cycle characteristics. Furthermore, it is preferable that the crystal contains Na because charge / discharge efficiency is increased and high discharge capacity can be maintained. In particular, if the crystal is an orthorhombic crystal, a hexagonal crystal, a cubic crystal, or a monoclinic crystal, particularly a monoclinic crystal belonging to the space group P21 / m, it is charged and discharged with a large current. However, it is preferable because the capacity is hardly lowered. Examples of orthorhombic crystals include NaTi 2 O 4 .
  • Examples of the hexagonal crystal include Na 2 TiO 3 , NaTi 8 O 13 , NaTiO 2 , LiNbO 3 , LiNbO 2 , Li 7 NbO 6 , LiNbO 2 , Li 2 Ti 3 O 7 and the like.
  • Examples of cubic crystals include Na 2 TiO 3 , NaNbO 3 , Li 4 Ti 5 O 12 , and Li 3 NbO 4 .
  • Monoclinic crystals include Na 2 Ti 6 O 13 , NaTi 2 O 4 , Na 2 TiO 3 , Na 4 Ti 5 O 12 , Na 2 Ti 4 O 9 , Na 2 Ti 9 O 19 , Na 2 Ti 3.
  • Examples include O 7 , Na 2 Ti 3 O 7 , Li 1.7 Nb 2 O 5 , Li 1.9 Nb 2 O 5 , Li 12 Nb 13 O 33 , LiNb 3 O 8, and the like.
  • Examples of the monoclinic crystal belonging to the space group P21 / m include Na 2 Ti 3 O 7 .
  • 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 have an effect of facilitating the formation of an amorphous phase together with the active material crystal and improving sodium ion conductivity.
  • the negative electrode active material includes Na metal crystals, alloy crystals containing at least Na (for example, Na—Sn alloy, Na—In alloy), at least one metal crystal selected from Sn, Bi, and Sb, Sn, Bi.
  • an alloy crystal containing at least one selected from Sb for example, Sn—Cu alloy, Bi—Cu alloy, Bi—Zn alloy, Sb—Cu alloy, Sb—Sn alloy, Sb—Si alloy, Sb—In alloy, Sb) -Zn alloy
  • glass containing at least one selected from Sn, Bi and Sb can be used. These are preferable because they have a high capacity and are unlikely to decrease in capacity even when charged and discharged with a large current.
  • the average particle diameter of the active material precursor powder is preferably 0.01 to 15 ⁇ m, 0.05 to 12 ⁇ m, and particularly preferably 0.1 to 10 ⁇ m.
  • the average particle diameter of the active material precursor powder is too small, the cohesive force between the active material precursor powders becomes strong and tends to be inferior in dispersibility when formed into a paste.
  • the internal resistance of the battery increases and the operating voltage tends to decrease.
  • the electrode density tends to decrease and the capacity per unit volume of the battery tends to decrease.
  • the average particle size of the active material precursor powder is too large, sodium ions are difficult to diffuse and the internal resistance tends to increase. Moreover, there exists a tendency to be inferior to the surface smoothness of an electrode.
  • the average particle diameter means D 50 (volume-based average particle diameter), and indicates a value measured by a laser diffraction scattering method.
  • Solid electrolyte powder consists of an oxide material which has sodium ion conductivity, for example.
  • the solid electrolyte powder includes a compound containing at least one selected from Al, Y, Zr, Si and P, Na, and O.
  • examples of such a compound include at least one selected from ⁇ -alumina, ⁇ ′′ -alumina, and NASICON type crystals. These are preferable because they are excellent in sodium ion conductivity.
  • the oxide material containing ⁇ -alumina or ⁇ ′′ -alumina contains Al 2 O 3 65 to 98%, Na 2 O 2 to 20%, MgO + Li 2 O 0.3 to 15% in mol%.
  • the reason for limiting the composition in this way will be described below, and “%” means “mol%” in the following description unless otherwise specified.
  • Al 2 O 3 is ⁇ - alumina and beta "- content .
  • al 2 O 3 is a main component of alumina 65 to 98% is .
  • al 2 O 3 is preferably especially 70 to 95% If the amount is too small, the ionic conductivity tends to decrease, whereas if the amount of Al 2 O 3 is too large, ⁇ -alumina having no ionic conductivity remains and the ionic conductivity tends to decrease.
  • Na 2 O is a component that imparts sodium ion conductivity to the solid electrolyte.
  • the content of Na 2 O is preferably 2 to 20%, 3 to 18%, particularly 4 to 16%.
  • Na 2 O is too small, the effect is difficult to obtain.
  • excess sodium forms a compound that does not contribute to ionic conductivity such as NaAlO 2, so that ionic conductivity tends to decrease.
  • MgO and Li 2 O are components (stabilizers) that stabilize the structure of ⁇ -alumina and ⁇ ′′ -alumina.
  • the content of MgO + Li 2 O is 0.3 to 15%, 0.5 to 10%, In particular, it is preferably 0.8 to 8% If the amount of MgO + Li 2 O is too small, ⁇ -alumina remains in the solid electrolyte and the ionic conductivity tends to decrease, whereas if the amount of MgO + Li 2 O is too large.
  • the MgO or Li 2 O that did not function as a stabilizer remains in the solid electrolyte, and the ionic conductivity tends to decrease.
  • the solid electrolyte powder preferably contains ZrO 2 or Y 2 O 3 in addition to the above components.
  • ZrO 2 and Y 2 O 3 have the effect of suppressing abnormal grain growth of ⁇ -alumina and / or ⁇ ′′ -alumina during firing and improving the adhesion of each particle of ⁇ -alumina and / or ⁇ ′′ -alumina.
  • the content of ZrO 2 is preferably 0 to 15%, 1 to 13%, particularly 2 to 10%.
  • the content of Y 2 O 3 is preferably 0 to 5%, 0.01 to 4%, particularly preferably 0.02 to 3%. If there is too much ZrO 2 or Y 2 O 3, the amount of ⁇ -alumina and / or ⁇ ′′ -alumina produced will decrease, and the ionic conductivity tends to decrease.
  • ⁇ ′′ -alumina includes trigonal (Al 10.35 Mg 0.65 O 16 ) (Na 1.65 O), (Al 8.87 Mg 2.13 O 16 ) (Na 3.13 O), Na 1.67 Mg 0.67 Al 10.33 O 17 , Na 1.49 Li 0.25 Al 10.75 O 17 , Na 1.72 Li 0.3 Al 10.66 O 17 , Na 1.6 Li 0.34 Al 10.66 O 17.
  • ⁇ -alumina examples include hexagonal (Al 10.35 Mg 0.65 O 16 ) (Na 1.65 O), (Al 10.37 Mg 0. 63 O 16 ) (Na 1.63 O), NaAl 11 O 17 , (Al 10.32 Mg 0.68 O 16 ) (Na 1.68 O).
  • a monoclinic or trigonal NASICON type crystal is preferable because of its excellent ion conductivity.
  • crystal represented by the general formula Na s A1 t A2 u O v include Na 3 Zr 2 Si 2 PO 12 , Na 3.2 Zr 1.3 Si 2.2 P 0.8 O 10. 5 , Na 3 Zr 1.6 Ti 0.4 Si 2 PO 12 , Na 3 Hf 2 Si 2 PO 12 , Na 3.4 Zr 0.9 Hf 1.4 Al 0.6 Si 1.2 P 1.8 O 12 , Na 3 Zr 1.7 Nb 0.24 Si 2 PO 12 , Na 3.6 Ti 0.2 Y 0.8 Si 2.8 O 9 , Na 3 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.12 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.6 Zr 0.13 Yb 1.67 Si 0.11 P 2.9 O 12 and the like.
  • the average particle size of the solid electrolyte powder is 0.01 to 15 ⁇ m, preferably 0.05 to 10 ⁇ m, particularly preferably 0.1 to 5 ⁇ m. If the average particle size of the solid electrolyte powder is too large, the distance required for sodium ion conduction tends to be long, and the ionic conductivity tends to decrease. In addition, the ion conduction path between the active material powder and the solid electrolyte powder tends to decrease. As a result, the discharge capacity tends to decrease. On the other hand, if the average particle size of the solid electrolyte powder is too small, the ion conductivity is likely to be lowered due to the elution of sodium ions and the deterioration due to the reaction with carbon dioxide. Moreover, since voids are easily formed, the electrode density is also likely to decrease. As a result, the discharge capacity tends to decrease.
  • the specific surface area of the solid electrolyte powder (BET specific surface area) is 1.5 ⁇ 200m 2 / g, 2 ⁇ 100m 2 / g, it is particularly preferably 2.5 ⁇ 50m 2 / g. If the specific surface area of the solid electrolyte powder is too small, the distance required for sodium ion conduction tends to be long and the ionic conductivity tends to decrease. In addition, the ion conduction path between the active material powder and the solid electrolyte powder tends to decrease. As a result, the discharge capacity tends to decrease.
  • the specific surface area of the solid electrolyte powder is too large, the ionic conductivity is likely to be lowered due to elution of sodium ions and deterioration due to reaction with carbon dioxide gas. Moreover, since voids are easily formed, the electrode density is likely to decrease. As a result, the discharge capacity tends to decrease.
  • the specific surface area is a value measured by the BET single point method using nitrogen as an adsorbate.
  • the ionic conductivity of the solid electrolyte powder at 25 ° C. is preferably 10 ⁇ 5 S / cm or more, more preferably 10 ⁇ 4 S / cm or more. If the ionic conductivity is too low, it will not function as an ionic conductive material. On the other hand, the upper limit of the ionic conductivity is not particularly limited, but is practically 10 S / cm or less, and further 1 S / cm or less.
  • the solid electrolyte powder can be produced, for example, by firing a raw material powder and subjecting it to a solid phase reaction to obtain a target product, followed by pulverization.
  • a solid electrolyte powder having a desired average particle diameter can be easily obtained.
  • Electrode composite material for sodium ion secondary battery The porosity of the electrode composite material for sodium ion secondary battery is 45% or less, preferably 40% or less, and particularly preferably 35% or less. When the porosity is too high, the adhesion between the active material powder and the solid electrolyte powder becomes insufficient, and the ion conduction path is not sufficiently formed, so that the discharge capacity tends to decrease.
  • the lower limit of the porosity is not particularly limited, but is practically 1% or more.
  • the volume ratio of the active material precursor powder to the solid electrolyte powder is preferably 20:80 to 95: 5, 30:70 to 90:10, particularly 35:65 to 88:12. If the proportion of the active material precursor powder is too small (the proportion of the solid electrolyte powder is too large), the capacity per unit electrode volume tends to decrease, and the energy density of the battery tends to decrease. On the other hand, if the proportion of the active material precursor powder is too large (the proportion of the solid electrolyte powder is too small), the ion conduction path cannot be secured and the ionic conductivity of the electrode mixture is lowered, resulting in a decrease in discharge capacity. Tend to.
  • the active material powder preferably contains an amorphous phase.
  • an amorphous phase is likely to be present at the interface between the active material powder and the solid electrolyte powder, the adhesion between the two is increased, and the porosity is easily decreased.
  • the interface resistance between the active material powder and the solid electrolyte powder tends to decrease.
  • the discharge capacity tends to increase.
  • rapid charge / discharge characteristics are expected to be improved.
  • an amorphous phase intervenes at the interface between the active material powder and the solid electrolyte powder, atomic diffusion between them is suppressed, and chemical decomposition of each powder is suppressed.
  • the electrode mixture for sodium ion secondary batteries of the present invention preferably contains conductive carbon.
  • conductive carbon highly conductive carbon black such as acetylene black or ketjen black, carbon powder such as graphite, carbon fiber, or the like can be used. Of these, acetylene black having a high electron conductivity is preferable.
  • the conductive carbon is preferably contained in the electrode mixture in an amount of 0 to 20% by mass, more preferably 1 to 10% by mass. When there is too much content of conductive carbon, battery capacity will fall easily.
  • the electrode mixture for sodium ion secondary batteries of the present invention is usually in the form of a sheet, and the thickness thereof is preferably 1 to 300 ⁇ m, more preferably 5 to 200 ⁇ m, and further preferably 12 to 90 ⁇ m. .
  • the thickness of the electrode mixture is too small, the capacity of the sodium ion secondary battery itself tends to be small, so that the energy density tends to decrease.
  • the thickness of the electrode mixture is too large, the resistance to electronic conduction increases, and the discharge capacity and operating voltage tend to decrease.
  • the capacity per unit area in the main surface of the electrode mixture for sodium ion secondary batteries of the present invention is preferably 0.03 to 1.5 mAh / cm 2 , and is 0.1 to 0.9 mAh / cm 2 . More preferably. If the capacity per unit area is too small, the battery capacity tends to decrease. On the other hand, when the capacity per unit area is too large, the internal resistance increases and the rapid charge / discharge characteristics tend to be deteriorated.
  • the electrode mixture for sodium ion secondary batteries of the present invention may be composed of a laminate of two or more layers.
  • the number of electrode mixture layers is preferably 7 layers or less, and more preferably 3 layers or less. When the number of layers is too large, the internal resistance between the electrode mixture layers tends to increase.
  • each layer of the electrode mixture composed of the laminate is preferably 3 to 90 ⁇ m, and more preferably 5 to 40 ⁇ m. If the thickness of each layer is too small, it is difficult to form a uniform electrode mixture layer, and as a result, the capacity tends to be difficult to control. On the other hand, if the thickness of each layer is too large, the amount of shrinkage associated with the firing of the electrode mixture precursor increases, cracks are generated, or the ion conductive path with the solid electrolyte sheet is cut off by peeling from the solid electrolyte sheet. It becomes easy and the capacity tends to decrease.
  • each layer of the electrode mixture composed of the laminate may be different.
  • the interface resistance between the solid electrolyte sheet and the electrode mixture can be reduced by relatively increasing the ratio of the solid electrolyte powder in the layer closer to the solid electrolyte sheet.
  • the electron conductivity between the electrode mixture and the current collector layer can be improved. it can.
  • the electrode mixture for sodium ion secondary battery of the present invention comprises: (a) a positive electrode or negative electrode active material precursor powder; and a sodium ion conductive solid electrolyte.
  • a step of slurrying an electrode mixture precursor powder containing powder (b) a step of applying and drying the obtained slurry on a substrate to produce an electrode mixture precursor sheet, and (c) It can manufacture by the method of including the process of baking after pressing an electrode compound-material precursor sheet
  • each process will be described in detail.
  • an active material precursor powder and a raw material powder containing sodium ion conductive solid electrolyte powder are mixed by dry or wet, and then a binder, a plasticizer, a solvent, etc. are added and kneaded to form a slurry.
  • the solvent may be water or an organic solvent such as ethanol or acetone.
  • water when water is used as the solvent, the sodium component is eluted from the raw material powder, the pH of the slurry is increased, and the raw material powder may be aggregated. Therefore, it is preferable to use an organic solvent, and it is particularly preferable to use an anhydrous organic solvent.
  • the obtained slurry is applied on a substrate such as PET (polyethylene terephthalate) and dried to obtain an electrode mixture precursor sheet.
  • the slurry can be applied by a doctor blade or a die coater.
  • the electrode mixture precursor sheet is pressed and then fired to obtain a positive electrode or negative electrode mixture.
  • Examples of the pressing method include a method of pressing from one direction such as a uniaxial press, a method of pressing uniformly from all directions such as an isotropic press, or a roll pressing method passing between two rolls.
  • Specific examples of the isotropic pressure press include a hydrostatic press and a hot isostatic press. Among these, an isotropic pressure press that can efficiently reduce the porosity of the electrode mixture and a uniaxial press that can be easily performed are preferable.
  • the pressing pressure is preferably 3 MPa or more, 10 MPa or more, particularly 15 MPa or more. If the pressing pressure is too low, the adhesion between the active material powder and the solid electrolyte powder becomes insufficient, and the discharge capacity tends to decrease.
  • the upper limit of the pressing pressure is not particularly limited, but is actually 500 MPa, 300 MPa, 100 MPa, or 45 MPa or less.
  • the temperature at the time of a press is 25 degreeC or more, 40 degreeC or more, 60 degreeC or more, especially 70 degreeC or more. If the temperature is too low, the binder does not soften, so the porosity of the electrode mixture is difficult to decrease.
  • the upper limit of the temperature is preferably 200 ° C. or lower, 180 ° C. or lower, 150 ° C. or lower, and 120 ° C. or lower. If the temperature is too high, evaporation of the plasticizer and thermal decomposition of the binder occur, and the sheet shape cannot be maintained.
  • the firing atmosphere examples include an air atmosphere, an inert atmosphere (such as N 2 ), and a reducing atmosphere (such as H 2 , NH 3 , CO, H 2 S, and SiH 4 ).
  • the firing temperature is preferably 400 to 900 ° C, particularly 420 to 800 ° C. If the firing temperature is too low, it becomes difficult for the desired active material crystals to precipitate, or the electrode mixture precursor powder is difficult to sinter sufficiently. On the other hand, if the firing temperature is too high, the precipitated active material crystals may be dissolved.
  • the maximum temperature holding time in firing is preferably 10 to 600 minutes, and more preferably 30 to 120 minutes. If the holding time is too short, the electrode mixture precursor powder is likely to be insufficiently sintered.
  • the active material precursor powders are excessively fused to form coarse particles, so that the specific surface area of the electrode active material is reduced and the charge / discharge capacity is likely to be reduced.
  • an electric heating furnace, a rotary kiln, a microwave heating furnace, a high-frequency heating furnace, or the like can be used.
  • the electrode mixture precursor sheet is laminated and fired. Or you may bake, after apply
  • a laminated body After producing the laminated body sheet
  • the battery for sodium ion secondary batteries it becomes possible to improve the adhesion between the electrode mixture layer and the solid electrolyte sheet.
  • the pressing method, pressure, and temperature of the laminate sheet and laminate are the same as those for the electrode mixture precursor sheet.
  • a sodium ion secondary battery has a positive electrode layer and a negative electrode layer, and a solid electrolyte layer (solid electrolyte sheet) sandwiched therebetween.
  • said electrode compound material is used as a positive electrode layer or a negative electrode layer.
  • the solid electrolyte used for the solid electrolyte layer and the solid electrolyte powder used for the electrode mixture are preferably made of the same material. In this way, the interface resistance between the solid electrolyte layer and the electrode mixture layer is reduced, and the ionic conductivity is easily improved.
  • the capacity ratio between the positive electrode and the negative electrode is preferably 3.0 to 1.0, and more preferably 1.7 to 1.2. If the capacity ratio is too small, metallic sodium tends to precipitate on the negative electrode side and the capacity tends to decrease. On the other hand, if the capacity ratio is too large, the energy density tends to decrease.
  • Table 1 shows Examples 1 to 5 and Comparative Examples 1 and 2.
  • Table 2 shows Examples 6 to 8 and Comparative Example 3.
  • Example 1 Production of solid electrolyte (a-1) Production of solid electrolyte powder Sodium carbonate (Na 2 CO 3 ), sodium hydrogen carbonate (NaHCO 3 ), magnesium oxide (MgO), aluminum oxide (Al 2 O 3 ), oxidation Zirconium (ZrO 2 ) and yttrium oxide (Y 2 O 3 ) are used in mol%, Na 2 O 14.2%, MgO 5.5%, Al 2 O 3 75.4%, ZrO 2 4.7. %, And Y 2 O 3 0.2%, the raw material powder was prepared. The raw material powder was molded by uniaxial pressing at 40 MPa using a ⁇ 20 mm mold and subjected to heat treatment at 1600 ° C. for 30 minutes to obtain ⁇ ′′ -alumina. The obtained ⁇ ′′ -alumina was rapidly dew point ⁇ 40 ° C. Moved to the following atmosphere and stored.
  • ⁇ ′′ -alumina was pulverized with an alumina mortar pestle and passed through a mesh having a mesh opening of 300 ⁇ m. And then pulverized at 300 rpm for 30 minutes, and passed through a mesh with an opening of 20 ⁇ m.After that, by classifying with an air classifier (MDS-1 type, manufactured by Nippon Pneumatic Industry Co., Ltd.), ⁇ ′′ ⁇ A solid electrolyte powder (average particle size 1.8 ⁇ m) made of alumina was obtained. All operations were performed in an atmosphere having a dew point of ⁇ 40 ° C. or lower.
  • MDS-1 type manufactured by Nippon Pneumatic Industry Co., Ltd.
  • A-2) Production of solid electrolyte sheet Sodium carbonate (Na 2 CO 3 ), sodium hydrogen carbonate (NaHCO 3 ), magnesium oxide (MgO), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), oxidation Using yttrium (Y 2 O 3 ), in mol%, Na 2 O 14.2%, MgO 5.5%, Al 2 O 3 75.4%, ZrO 2 4.7%, Y 2 O 3 0
  • the raw material powder was prepared to have a composition of 2%. Thereafter, the raw material powder was wet-mixed for 4 hours using ethanol as a medium.
  • an acrylic acid ester copolymer (Oricox 1700 manufactured by Kyoeisha Chemical Co., Ltd.) is used as a binder, and benzylbutyl phthalate is used as a plasticizer.
  • the slurry obtained above was applied using a doctor blade with a gap of 350 ⁇ m, and dried at 70 ° C. to obtain a green sheet.
  • the obtained green sheet was pressed at 90 ° C. and 40 MPa for 5 minutes using an isotropic pressure press.
  • the pressed green sheet was fired at 1600 ° C. for 30 minutes to obtain a solid electrolyte sheet made of ⁇ ′′ -alumina having a thickness of 180 ⁇ m.
  • the obtained solid electrolyte sheet was quickly transferred to an environment having a dew point of ⁇ 40 ° C. or less. Stored.
  • the obtained film-like glass was subjected to ball milling using ZrO 2 boulders with a diameter of 20 mm for 5 hours and passed through a resin sieve having an opening of 120 ⁇ m to obtain a coarse glass powder having an average particle size of 3 to 15 ⁇ m.
  • this crude glass powder was subjected to ball milling using ethanol as a grinding aid and ZrO 2 boulder with a diameter of 3 mm for 80 hours, whereby a glass powder having an average particle diameter of 0.7 ⁇ m (positive electrode active material precursor powder) )
  • Electrode mixture layer (positive electrode mixture layer) Mass%, positive electrode active material precursor powder 72%, solid electrolyte powder prepared in (a-1) 25%, acetylene black 3% (positive electrode active material) The volume ratio of the precursor powder to the solid electrolyte powder was weighed to be 76:24), and the mixture was mixed for about 2 hours using an agate mortar and pestle. 20 parts by mass of N-methylpyrrolidone (containing 10% by mass of polypropylene carbonate (manufactured by Sumitomo Seika Co., Ltd.)) is added to 100 parts by mass of the obtained mixed powder, and the mixture is sufficiently stirred using a rotation and revolution mixer. And slurried. All the above operations were performed in an environment with a dew point of ⁇ 40 ° C. or lower.
  • the obtained slurry was applied to one surface of the solid electrolyte sheet prepared in (a-2) with an area of 1 cm 2 and a thickness of 100 ⁇ m, and dried at 70 ° C. for 3 hours. Thereby, the laminated body sheet by which an electrode compound-material precursor layer was formed on the solid electrolyte sheet was obtained.
  • the laminate sheet was isostatically pressed at a pressure of 20 MPa, and then fired at 600 ° C. for 1 hour in a nitrogen gas atmosphere. As a result, a positive electrode mixture layer was formed on one surface of the solid electrolyte sheet.
  • the porosity was determined by binarizing the SEM image of the cross section of the obtained positive electrode mixture layer.
  • Example 2 A test battery was prepared in the same manner as in Example 1 except that the pressing pressure when isostatically pressing the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was 40 MPa, A charge / discharge test was conducted. The results are shown in Table 1.
  • Example 3 A test battery was produced in the same manner as in Example 1 except that the pressing method of the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was changed to uniaxial pressing, and the charge / discharge test was performed. It was. The results are shown in Table 1.
  • Example 1 A test battery was prepared in the same manner as in Example 1 except that the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was fired without isostatic pressing, and the charge / discharge test was performed. went. The results are shown in Table 1.
  • Example 4 A test battery was prepared in the same manner as in Example 1 except that the positive electrode active material precursor powder was changed to the composition shown in Table 1, and a charge / discharge test was performed. The results are shown in Table 1. Moreover, the SEM image of the cross section of a positive electrode compound material layer is shown in FIG. 1, and what binarized the SEM image is shown in FIG.
  • Example 5 A test battery was produced in the same manner as in Example 4 except that the pressing method of the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was changed to uniaxial pressing, and the charge / discharge test was performed. It was. The results are shown in Table 1.
  • Example 2 A test battery was prepared in the same manner as in Example 4 except that the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was fired without isostatic pressing, and the charge / discharge test was performed. went. The results are shown in Table 1. Moreover, the SEM image of the cross section of a positive electrode compound material layer is shown in FIG. 3, and what binarized the SEM image is shown in FIG.
  • Example 6 (Examples 6 to 8) (A) Production of solid electrolyte In the same manner as in Example 1, a solid electrolyte powder and a solid electrolyte sheet were produced.
  • Electrode mixture layer (positive electrode mixture layer) Each component was weighed and mixed so as to have the electrode mixture precursor composition shown in Table 2. 20 parts by mass of N-methylpyrrolidone (containing 10% by mass of polypropylene carbonate (manufactured by Sumitomo Seika Co., Ltd.)) is added to 100 parts by mass of the obtained mixed powder, and the mixture is sufficiently stirred using a rotation and revolution mixer. And slurried. All the above operations were performed in an environment with a dew point of ⁇ 40 ° C. or lower.
  • N-methylpyrrolidone containing 10% by mass of polypropylene carbonate (manufactured by Sumitomo Seika Co., Ltd.)
  • the slurry was applied on a solid electrolyte sheet to obtain a laminate sheet in which the electrode mixture precursor layer having the configuration shown in Table 2 was formed.
  • the one close to the solid electrolyte sheet was the first layer, and the coating thickness of each layer was 100 ⁇ m.
  • the laminate sheet was isostatically pressed at a pressure of 20 MPa, and then fired at 500 ° C. for 30 minutes in a nitrogen gas atmosphere. As a result, a positive electrode mixture layer was formed on one surface of the solid electrolyte sheet.
  • the porosity was determined by binarizing the SEM image of the cross section of the obtained positive electrode mixture layer.
  • Example 3 A test battery was prepared in the same manner as in Example 6 except that the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was fired without being isotropically pressed, and the charge / discharge test was performed. went. The results are shown in Table 1.
  • the porosity is reduced by isostatically pressing or uniaxially pressing the laminate sheet in which the electrode mixture precursor layer is formed on the solid electrolyte sheet. It was confirmed that characteristics such as discharge capacity were improved. In particular, it can be seen that the energy density can be increased by making the electrode mixture layer into a laminate structure.
  • Comparative Example 3 after firing the electrode mixture precursor, the electrode mixture was peeled from the solid electrolyte sheet, and the ion conduction path was in a cut state.

Abstract

Provided is an electrode mix for a sodium ion secondary battery having a high discharge capacity, wherein ion conduction paths are sufficiently formed between an active material powder and a solid electrolyte powder. The electrode mix for a sodium ion secondary battery is characterized by: comprising a sintered body of an electrode mix precursor powder, which contains an active material precursor powder and a solid electrolyte powder having sodium ion conductivity; and having a porosity of 45% or less.

Description

ナトリウムイオン二次電池用電極合材及びその製造方法Electrode mixture for sodium ion secondary battery and method for producing the same
　本発明は、ナトリウムイオン二次電池等の蓄電デバイスに用いられるナトリウムイオン二次電池用電極合材及びその製造方法に関する。 The present invention relates to an electrode mixture for a sodium ion secondary battery used for an electricity storage device such as a sodium ion secondary battery and a method for producing the same.
　リチウムイオン二次電池は、モバイル機器や電気自動車等に不可欠な、高容量で軽量な電源としての地位を確立している。しかし、現行のリチウムイオン二次電池には、電解質として可燃性の有機系電解液が主に用いられているため、発火等の危険性が懸念されている。この問題を解決する方法として、有機系電解液に代えて固体電解質を使用したリチウムイオン全固体電池の開発が進められている（例えば特許文献１参照）。 Lithium ion secondary batteries have established themselves as high-capacity and lightweight power supplies that are indispensable for mobile devices and electric vehicles. However, the current lithium ion secondary battery mainly uses a flammable organic electrolyte as an electrolyte, and there is a concern about the risk of ignition and the like. As a method for solving this problem, development of a lithium ion all-solid battery using a solid electrolyte instead of an organic electrolyte has been underway (see, for example, Patent Document 1).
　しかしながら、リチウムは世界的な原材料の高騰の懸念がある。そこで、リチウムに代わる材料としてナトリウムが注目されており、固体電解質としてＮＡＳＩＣＯＮ型のＮａ３Ｚｒ２Ｓｉ２ＰＯ１２からなるナトリウムイオン伝導性結晶を使用したナトリウムイオン全固体電池が提案されている（例えば特許文献２参照）。その他、β－アルミナやβ”－アルミナといったベータアルミナ系固体電解質も高いナトリウムイオン伝導性を示すことが知られており、これらの固体電解質はナトリウム－硫黄電池用固体電解質としても使用されている。 However, there is a concern that lithium will rise in raw materials worldwide. Therefore, sodium is attracting attention as a material to replace lithium, and a sodium ion all solid state battery using a sodium ion conductive crystal made of NASICON type Na 3 Zr 2 Si 2 PO 12 as a solid electrolyte has been proposed (for example, Patent Document 2). In addition, beta-alumina solid electrolytes such as β-alumina and β ″ -alumina are also known to exhibit high sodium ion conductivity, and these solid electrolytes are also used as solid electrolytes for sodium-sulfur batteries.
　上記のような全固体電池は、正極層、負極層及びナトリウムイオン伝導性固体電解質層から構成される。ここで、正極層と負極層は、充放電に伴いナトリウムイオン及び電子を吸蔵または放出する活物質粉末と、固体電解質粉末との合材（電極合材）で構成されるのが一般的である。例えば特許文献３には、結晶性ガラス粉末からなる活物質前駆体粉末と固体電解質粉末からなる原料粉末（電極合材前駆体）を焼成し、各粉末を融着一体化させてなる電極合材が記載されている。 The all-solid battery as described above includes a positive electrode layer, a negative electrode layer, and a sodium ion conductive solid electrolyte layer. Here, the positive electrode layer and the negative electrode layer are generally composed of a mixture (electrode mixture) of an active material powder that occludes or releases sodium ions and electrons during charge and discharge and a solid electrolyte powder. . For example, Patent Document 3 discloses an electrode mixture obtained by firing an active material precursor powder made of crystalline glass powder and a raw material powder (electrode mixture precursor) made of solid electrolyte powder, and fusing and integrating the powders. Is described.
特開平５－２０５７４１号公報JP-A-5-205741 特開２０１０－１５７８２号公報JP 2010-157582 A 国際公開第２０１５／０８７７３４号公報International Publication No. 2015/087734
　特許文献３に記載の電極合材は、活物質粉末と固体電解質粉末の間におけるイオン伝導パス形成が不十分であり、放電容量が小さいという問題がある。 The electrode mixture described in Patent Document 3 has a problem that the ion conduction path is not sufficiently formed between the active material powder and the solid electrolyte powder, and the discharge capacity is small.
　以上に鑑み、本発明は、活物質粉末と固体電解質粉末の間においてイオン伝導パスが十分に形成されており、放電容量が大きいナトリウムイオン二次電池用電極合材とを提供することを目的とする。 In view of the above, an object of the present invention is to provide an electrode mixture for a sodium ion secondary battery in which an ion conduction path is sufficiently formed between the active material powder and the solid electrolyte powder and the discharge capacity is large. To do.
　本発明のナトリウムイオン二次電池用電極合材は、活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末の焼結体からなり、空隙率が４５％以下であることを特徴とする。 The electrode mixture for a sodium ion secondary battery of the present invention comprises a sintered body of an electrode mixture precursor powder containing an active material precursor powder and a sodium ion conductive solid electrolyte powder, and has a porosity of 45. % Or less.
　本発明者等の調査の結果、特許文献３に記載の電極合材の放電容量が小さい理由は、活物質前駆体である結晶性ガラス粉末を焼成した際の軟化流動が不十分であるため、得られた電極合材中における活物質粉末と固体電解質粉末の間の密着性が不十分であり、イオン伝導パスが十分に形成されないためであることが原因であることがわかった。本発明の電極合材は空隙率が４５％以下と小さく、活物質粉末と固体電解質粉末の密着性が高いため、イオン伝導パスが十分に形成され、放電容量が高いという特徴を有する。 As a result of the inventors' investigation, the reason why the discharge capacity of the electrode mixture described in Patent Document 3 is small is that the softening flow when the crystalline glass powder as the active material precursor is fired is insufficient, It was found that this was because the adhesion between the active material powder and the solid electrolyte powder in the obtained electrode mixture was insufficient, and the ion conduction path was not sufficiently formed. The electrode mixture of the present invention has a feature that the porosity is as small as 45% or less, and the adhesiveness between the active material powder and the solid electrolyte powder is high, so that an ion conduction path is sufficiently formed and the discharge capacity is high.
　本発明のナトリウムイオン二次電池用電極合材は、活物質前駆体粉末が、（i）Ｃｒ、Ｆｅ、Ｍｎ、Ｃｏ、Ｎｉ、Ｔｉ及びＮｂからなる群より選ばれた少なくとも１種の遷移金属元素、（ii）Ｐ、Ｓｉ及びＢから選択される少なくとも１種の元素、並びに（iii）Ｏを含むことが好ましい。 The electrode mixture for a sodium ion secondary battery according to the present invention has an active material precursor powder (i) at least one transition metal selected from the group consisting of Cr, Fe, Mn, Co, Ni, Ti and Nb. It is preferable to contain an element, (ii) at least one element selected from P, Si and B, and (iii) O.
　本発明のナトリウムイオン二次電池用電極合材は、固体電解質粉末が、Ａｌ、Ｙ、Ｚｒ、Ｓｉ及びＰから選ばれる少なくとも１種、Ｎａ、並びにＯを含有することが好ましい。 In the electrode mixture for a sodium ion secondary battery of the present invention, the solid electrolyte powder preferably contains at least one selected from Al, Y, Zr, Si and P, Na, and O.
　本発明のナトリウムイオン二次電池用電極合材は、固体電解質粉末が、β－アルミナ、β”－アルミナ及びＮＡＳＩＣＯＮ型結晶から選ばれる少なくとも１種を含有することが好ましい。 In the electrode mixture for a sodium ion secondary battery of the present invention, the solid electrolyte powder preferably contains at least one selected from β-alumina, β ″ -alumina, and NASICON type crystals.
　本発明のナトリウムイオン二次電池用電極合材は、活物質前駆体粉末及び／または固体電解質粉末の平均粒子径が０．０１～１５μｍであることが好ましい。このようにすれば、イオン伝導パスを多くすることができ、放電容量をさらに向上させることができる。 In the sodium ion secondary battery electrode mixture of the present invention, the average particle diameter of the active material precursor powder and / or the solid electrolyte powder is preferably 0.01 to 15 μm. In this way, the number of ion conduction paths can be increased, and the discharge capacity can be further improved.
　本発明のナトリウムイオン二次電池は、上記のナトリウムイオン二次電池用電極合材を用いたことを特徴とする。 The sodium ion secondary battery of the present invention is characterized by using the above-mentioned electrode mixture for sodium ion secondary batteries.
　本発明のナトリウムイオン二次電池用電極合材の製造方法は、（ａ）活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末をスラリー化する工程、（ｂ）得られたスラリーを基材上に塗布、乾燥して電極合材前駆体シートを作製する工程、及び、（ｃ）電極合材前駆体シートをプレスした後、焼成する工程、を含むことを特徴とする。このように、電極合材前駆体シートをプレスしてから焼成することで、活物質粉末と固体電解質粉末の密着性を効果的に高めることができる。そのため、例えば、軟化流動性の低い結晶性ガラスからなる活物質前駆体粉末であっても、電極合材中のイオン伝導パスを十分に形成することが可能となる。 The method for producing an electrode mixture for a sodium ion secondary battery according to the present invention comprises a step of slurrying an electrode mixture precursor powder comprising (a) an active material precursor powder and a sodium ion conductive solid electrolyte powder. (B) applying the slurry obtained on the substrate and drying it to produce an electrode mixture precursor sheet; and (c) pressing the electrode mixture precursor sheet and firing it. It is characterized by including. Thus, the adhesiveness between the active material powder and the solid electrolyte powder can be effectively enhanced by pressing and firing the electrode mixture precursor sheet. Therefore, for example, even if the active material precursor powder is made of crystalline glass with low softening fluidity, it is possible to sufficiently form an ion conduction path in the electrode mixture.
　本発明のナトリウムイオン二次電池用電極合材の製造方法において、電極合材前駆体シートを等方圧プレスまたは一軸プレスすることが好ましい。 In the method for producing an electrode mixture for a sodium ion secondary battery of the present invention, the electrode mixture precursor sheet is preferably isotropically pressed or uniaxially pressed.
　本発明のナトリウムイオン二次電池用電極合材の製造方法において、電極合材前駆体シートを３ＭＰａ以上の圧力でプレスすることが好ましい。 In the method for producing an electrode mixture for a sodium ion secondary battery of the present invention, the electrode mixture precursor sheet is preferably pressed at a pressure of 3 MPa or more.
　本発明のナトリウムイオン二次電池用電池の製造方法は、（ａ）活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末をスラリー化する工程、（ｂ）得られたスラリーを固体電解質シート上に塗布、乾燥することにより、固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを作製する工程、及び、（ｃ）積層体シートをプレスした後、焼成する工程、を含むことを特徴とする。このようにすれば、電極合材中の活物質粉末と固体電解質粉末の密着性を高めることができると同時に、電極合材層と固体電解質シートとの密着性も高めることができる。よって、電極合材中及び電極合材－固体電解質シート間の両者のイオン伝導パスを十分に形成することが可能となる。 The method for producing a battery for a sodium ion secondary battery of the present invention comprises (a) slurrying an electrode mixture precursor powder containing an active material precursor powder and a sodium ion conductive solid electrolyte powder. b) A step of producing a laminate sheet in which an electrode mixture precursor layer is formed on a solid electrolyte sheet by applying and drying the obtained slurry on a solid electrolyte sheet; and (c) a laminate. And a step of firing after pressing the sheet. In this way, the adhesion between the active material powder and the solid electrolyte powder in the electrode mixture can be enhanced, and at the same time, the adhesion between the electrode mixture layer and the solid electrolyte sheet can be enhanced. Therefore, it is possible to sufficiently form both ion conduction paths in the electrode mixture and between the electrode mixture and the solid electrolyte sheet.
　本発明のナトリウムイオン二次電池用電池の製造方法において、積層体シートを等方圧プレスまたは一軸プレスすることが好ましい。 In the method for producing a battery for sodium ion secondary battery of the present invention, it is preferable that the laminate sheet is isotropically pressed or uniaxially pressed.
　本発明のナトリウムイオン二次電池用電池の製造方法において、積層体シートを３ＭＰａ以上の圧力でプレスすることが好ましい。 In the method for producing a sodium ion secondary battery of the present invention, it is preferable to press the laminate sheet at a pressure of 3 MPa or more.
　本発明によれば、活物質粉末と固体電解質粉末の間においてイオン伝導パスが十分に形成されており、放電容量が大きいナトリウムイオン二次電池用電極合材とを提供することが可能となる。 According to the present invention, it is possible to provide an electrode mixture for a sodium ion secondary battery in which an ion conduction path is sufficiently formed between the active material powder and the solid electrolyte powder and the discharge capacity is large.
実施例３の試験電池における正極合材層の断面のＳＥＭ（走査型電子顕微鏡）画像である。4 is a SEM (scanning electron microscope) image of a cross section of a positive electrode mixture layer in a test battery of Example 3. 図１のＳＥＭ画像を２値化した画像である。It is the image which binarized the SEM image of FIG. 比較例３の試験電池における正極合材層の断面のＳＥＭ画像である。4 is a SEM image of a cross section of a positive electrode mixture layer in a test battery of Comparative Example 3. 図３のＳＥＭ画像を２値化した画像である。It is the image which binarized the SEM image of FIG.
　本発明のナトリウムイオン二次電池用電極合材は、活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末の焼結体からなる。 The electrode mixture for a sodium ion secondary battery of the present invention comprises a sintered body of an electrode mixture precursor powder including an active material precursor powder and a sodium ion conductive solid electrolyte powder.
　以下、各構成要素について詳細に説明する。 Hereinafter, each component will be described in detail.
　（１）活物質前駆体粉末
　活物質前駆体粉末は焼成により活物質粉末となるものである。活物質粉末には正極活物質粉末と負極活物質粉末があり、充放電の際にナトリウムイオンの吸蔵及び放出を行う。活物質前駆体粉末としては例えばガラス粉末が挙げられる。活物質前駆体粉末は通常、焼成により結晶化を伴うが、結晶化しない場合もある。即ち、活物質粉末は結晶を含む場合（結晶化ガラス）と、非晶質の場合がある。活物質前駆体粉末としては、（i）Ｃｒ、Ｆｅ、Ｍｎ、Ｃｏ、Ｎｉ、Ｔｉ及びＮｂからなる群より選ばれた少なくとも１種の遷移金属元素、（ii）Ｐ、Ｓｉ及びＢから選択される少なくとも１種の元素、並びに（iii）Ｏを含むものが挙げられる。 (1) Active material precursor powder The active material precursor powder becomes an active material powder by firing. The active material powder includes a positive electrode active material powder and a negative electrode active material powder, and occludes and releases sodium ions during charge and discharge. Examples of the active material precursor powder include glass powder. The active material precursor powder is usually accompanied by crystallization by firing, but may not be crystallized. That is, the active material powder may contain crystals (crystallized glass) or amorphous. The active material precursor powder is selected from (i) at least one transition metal element selected from the group consisting of Cr, Fe, Mn, Co, Ni, Ti and Nb, and (ii) P, Si and B. And (iii) those containing O.
　正極活物質前駆体粉末としては、酸化物換算のモル％で、Ｎａ２Ｏ　８～５５％、ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯ　１０～７０％、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３　１５～７０％を含有するものが挙げられる。各成分をこのように限定した理由を以下に説明する。なお、以下の各成分の含有量に関する説明において、特に断りのない限り、「％」は「モル％」を意味する。また「○＋○＋・・・」は該当する各成分の合量を意味する。 As the positive electrode active material precursor powder, a powder containing Na 2 O 8 to 55%, CrO + FeO + MnO + CoO + NiO 10 to 70%, P 2 O 5 + SiO 2 + B 2 O 3 15 to 70% in terms of mol% in terms of oxide. Can be mentioned. The reason why each component is limited in this way will be described below. In the following description regarding the content of each component, “%” means “mol%” unless otherwise specified. “◯ + ○ +...” Means the total amount of each corresponding component.
　Ｎａ２Ｏは、充放電の際に正極活物質と負極活物質との間を移動するナトリウムイオンの供給源となる。Ｎａ２Ｏの含有量は８～５５％、１５～４５％、特に２５～３５％であることが好ましい。Ｎａ２Ｏが少なすぎると、吸蔵及び放出に寄与するナトリウムイオンが少なくなるため、放電容量が低下する傾向にある。一方、Ｎａ２Ｏが多すぎると、Ｎａ３ＰＯ４等の充放電に寄与しない異種結晶が析出しやすくなるため、放電容量が低下する傾向にある。 Na 2 O serves as a supply source of sodium ions that move between the positive electrode active material and the negative electrode active material during charge and discharge. The content of Na 2 O is preferably 8 to 55%, 15 to 45%, particularly 25 to 35%. If the amount of Na 2 O is too small, sodium ions contributing to occlusion and release decrease, and the discharge capacity tends to decrease. On the other hand, when there is too much Na 2 O, different crystals that do not contribute to charging / discharging such as Na 3 PO 4 tend to precipitate, and the discharge capacity tends to decrease.
　ＣｒＯ、ＦｅＯ、ＭｎＯ、ＣｏＯ、ＮｉＯは、充放電の際に各遷移元素の価数が変化してレドックス反応を起こすことにより、ナトリウムイオンの吸蔵及び放出の駆動力として作用する成分である。なかでも、ＮｉＯ及びＭｎＯは酸化還元電位を高める効果が大きい。また、ＦｅＯは充放電において高い構造安定化を有し、サイクル特性が向上させやすい。ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯの含有量は１０～７０％、１５～６０％、２０～５５％、２３～５０％、２５～４０％、特に２６～３６％であることが好ましい。ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯが少なすぎると、充放電に伴うレドックス反応が起こりにくくなり、吸蔵及び放出されるナトリウムイオンが少なくなるため放電容量が低下する傾向にある。一方、ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯが多すぎると、異種結晶が析出して放電容量が低下する傾向にある。 CrO, FeO, MnO, CoO, and NiO are components that act as a driving force for occlusion and release of sodium ions by causing a redox reaction by changing the valence of each transition element during charge and discharge. Among these, NiO and MnO have a great effect of increasing the redox potential. In addition, FeO has high structural stabilization in charge and discharge, and it is easy to improve cycle characteristics. The content of CrO + FeO + MnO + CoO + NiO is preferably 10 to 70%, 15 to 60%, 20 to 55%, 23 to 50%, 25 to 40%, particularly preferably 26 to 36%. When there is too little CrO + FeO + MnO + CoO + NiO, the redox reaction accompanying charging / discharging becomes difficult to occur, and sodium ions that are occluded and released tend to decrease, so that the discharge capacity tends to decrease. On the other hand, when there is too much CrO + FeO + MnO + CoO + NiO, different crystals are deposited and the discharge capacity tends to decrease.
　Ｐ２Ｏ５、ＳｉＯ２及びＢ２Ｏ３は３次元網目構造を形成するため、正極活物質の構造を安定化させる効果を有する。特に、Ｐ２Ｏ５、ＳｉＯ２がイオン伝導性に優れるために好ましく、Ｐ２Ｏ５が最も好ましい。Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３の含有量は１５～７０％であり、２０～６０％、特に２５～４５％であることが好ましい。Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３が少なすぎると、繰り返し充放電した際に放電容量が低下しやすくなる傾向にある。一方、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３が多すぎると、Ｐ２Ｏ５等の充放電に寄与しない異種結晶が析出する傾向にある。なお、Ｐ２Ｏ５、ＳｉＯ２及びＢ２Ｏ３の各成分の含有量は各々０～７０％、１５～７０％、２０～６０％、特に２５～４５％であることが好ましい。 Since P 2 O 5 , SiO 2 and B 2 O 3 form a three-dimensional network structure, they have an effect of stabilizing the structure of the positive electrode active material. In particular, P 2 O 5 and SiO 2 are preferable because of excellent ion conductivity, and P 2 O 5 is most preferable. The content of P 2 O 5 + SiO 2 + B 2 O 3 is 15 to 70%, preferably 20 to 60%, particularly preferably 25 to 45%. If the amount of P 2 O 5 + SiO 2 + B 2 O 3 is too small, the discharge capacity tends to decrease when the battery is repeatedly charged and discharged. On the other hand, it tends to the P 2 O 5 + SiO 2 + B 2 O 3 is too large, heterogeneous crystals which does not contribute to charge and discharge, such as P 2 O 5 to precipitate. The content of each component of P 2 O 5 , SiO 2 and B 2 O 3 is preferably 0 to 70%, 15 to 70%, 20 to 60%, and particularly preferably 25 to 45%.
　また、本発明の効果を損なわない範囲で、上記成分に加えて種々の成分を含有させることでガラス化を容易にすることができる。このような成分としては、酸化物表記でＭｇＯ、ＣａＯ、ＳｒＯ、ＢａＯ、ＺｎＯ、ＣｕＯ、Ａｌ２Ｏ３、ＧｅＯ２、Ｎｂ２Ｏ５、ＺｒＯ２、Ｖ２Ｏ５、Ｓｂ２Ｏ５が挙げられ、特に網目形成酸化物として働くＡｌ２Ｏ３や活物質成分となるＶ２Ｏ５が好ましい。上記成分の含有量は、合量で０～３０％、０．１～２０％、特に０．５～１０％であることが好ましい。 In addition, vitrification can be facilitated by incorporating various components in addition to the above components within a range not impairing the effects of the present invention. Examples of such components include MgO, CaO, SrO, BaO, ZnO, CuO, Al 2 O 3 , GeO 2 , Nb 2 O 5 , ZrO 2 , V 2 O 5 , and Sb 2 O 5 in oxide notation. In particular, Al 2 O 3 serving as a network-forming oxide and V 2 O 5 serving as an active material component are preferable. The total content of the above components is preferably 0 to 30%, 0.1 to 20%, particularly preferably 0.5 to 10%.
　正極活物質粉末として作用する活物質結晶としては、Ｎａ、Ｍ（ＭはＣｒ、Ｆｅ、Ｍｎ、Ｃｏ及びＮｉからから選ばれる少なくとも１種の遷移金属元素）、Ｐ及びＯを含むナトリウム遷移金属リン酸塩結晶が挙げられる。具体例としては、Ｎａ２ＦｅＰ２Ｏ７、ＮａＦｅＰＯ４、Ｎａ３Ｖ２（ＰＯ４）３、Ｎａ２ＮｉＰ２Ｏ７、Ｎａ３．６４Ｎｉ２．１８（Ｐ２Ｏ７）２、Ｎａ３Ｎｉ３（ＰＯ４）２（Ｐ２Ｏ７）、Ｎａ２ＣｏＰ２Ｏ７、Ｎａ３．６４Ｃｏ２．１８（Ｐ２Ｏ７）２等が挙げられる。当該ナトリウム遷移金属リン酸塩結晶は、高容量で化学的安定性に優れるため好ましい。なかでも空間群Ｐ１またはＰ－１に属する三斜晶系結晶、特に一般式ＮａｘＭｙＰ２Ｏｚ（１．２≦ｘ≦２．８、０．９５≦ｙ≦１．６、６．５≦ｚ≦８）で表される結晶がサイクル特性に優れるため好ましい。その他に正極活物質として作用する活物質結晶としては、ＮａＣｒＯ２、Ｎａ０．７ＭｎＯ２、ＮａＦｅ０．２Ｍｎ０．４Ｎｉ０．４Ｏ２等の層状ナトリウム遷移金属酸化物結晶が挙げられる。 The active material crystals that act as the positive electrode active material powder include Na, M (M is at least one transition metal element selected from Cr, Fe, Mn, Co and Ni), sodium transition metal phosphorus containing P and O. Examples include acid salt crystals. Specific examples include Na 2 FeP 2 O 7 , NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , Na 2 NiP 2 O 7 , Na 3.64 Ni 2.18 (P 2 O 7 ) 2 , Na 3. Ni 3 (PO 4) 2 ( P 2 O 7), Na 2 CoP 2 O 7, Na 3.64 Co 2.18 (P 2 O 7) 2 and the like. The sodium transition metal phosphate crystal is preferable because of its high capacity and excellent chemical stability. Among them triclinic crystals belonging to the space group P1 or P1, particularly the general formula Na x M y P 2 O z (1.2 ≦ x ≦ 2.8,0.95 ≦ y ≦ 1.6,6 .5 ≦ z ≦ 8) is preferable because of excellent cycle characteristics. Other active material crystals that act as a positive electrode active material include layered sodium transition metal oxide crystals such as NaCrO 2 , Na 0.7 MnO 2 , and NaFe 0.2 Mn 0.4 Ni 0.4 O 2. .
　負極活物質前駆体粉末は、酸化物換算のモル％で、ＳｎＯ　０～９０％、Ｂｉ２Ｏ３　０～９０％、ＴｉＯ２　０～９０％、Ｆｅ２Ｏ３　０～９０％、Ｎｂ２Ｏ５　０～９０％、ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５　５～７５％、Ｎａ２Ｏ　０～８０％を含有することが好ましい。上記構成にすることにより、活物質成分であるＳｎイオン、Ｂｉイオン、Ｔｉイオン、ＦｅイオンまたはＮｂイオンがＳｉ、ＢまたはＰを含有する酸化物マトリクス中に均一に分散した構造が形成される。また、Ｎａ２Ｏを含有することによりナトリウムイオン伝導性に優れた材料となる。結果として、ナトリウムイオンを吸蔵及び放出する際の体積変化を抑制でき、サイクル特性に優れた負極活物質を得ることが可能となる。 The negative electrode active material precursor powder is an oxide equivalent mol%, SnO 0 to 90%, Bi 2 O 3 0 to 90%, TiO 2 0 to 90%, Fe 2 O 3 0 to 90%, Nb 2 O 5 0 ~ 90%, SiO 2 + B 2 O 3 + P 2 O 5 5 ~ 75%, preferably contains Na 2 O 0 ~ 80%. With the above structure, a structure in which Sn ions, Bi ions, Ti ions, Fe ions, or Nb ions, which are active material components, are uniformly dispersed in an oxide matrix containing Si, B, or P is formed. Moreover, it becomes a material excellent in sodium ion conductivity by containing Na 2 O. As a result, it is possible to suppress a volume change when inserting and extracting sodium ions, and it is possible to obtain a negative electrode active material having excellent cycle characteristics.
　負極活物質前駆体粉末の組成を上記の通り限定した理由を以下に説明する。なお、以下の説明において、特に断りのない限り、「％」は「モル％」を意味する。 The reason why the composition of the negative electrode active material precursor powder is limited as described above will be described below. In the following description, “%” means “mol%” unless otherwise specified.
　ＳｎＯ、Ｂｉ２Ｏ３、ＴｉＯ２、Ｆｅ２Ｏ３及びＮｂ２Ｏ５はアルカリイオンを吸蔵及び放出するサイトとなる活物質成分である。これらの成分を含有させることにより、負極活物質の単位質量当たりの放電容量が大きくなり、かつ、初回充放電時の充放電効率（充電容量に対する放電容量の比率）が向上しやすくなる。ただし、これらの成分の含有量が多すぎると、充放電時のナトリウムイオンの吸蔵及び放出に伴う体積変化を緩和できずに、サイクル特性が低下する傾向がある。以上に鑑み、各成分の含有量範囲は以下の通りとすることが好ましい。 SnO, Bi 2 O 3 , TiO 2 , Fe 2 O 3 and Nb 2 O 5 are active material components that serve as sites for occluding and releasing alkali ions. By containing these components, the discharge capacity per unit mass of the negative electrode active material is increased, and the charge / discharge efficiency (ratio of the discharge capacity to the charge capacity) at the first charge / discharge is easily improved. However, when there is too much content of these components, the volume change accompanying the occlusion and discharge | release of sodium ion at the time of charging / discharging cannot be relieved, but there exists a tendency for cycling characteristics to fall. In view of the above, the content range of each component is preferably as follows.
　ＳｎＯの含有量は０～９０％、４５～８５％、５５～７５％、特に６０～７２％であることが好ましい。Ｂｉ２Ｏ３の含有量は０～９０％、１０～７０％、１５～６５％、特に２５～５５％であることが好ましい。ＴｉＯ２の含有量は０～９０％、５～７２％、１０～６８％、１２～５８％、１５％～４９％、特に１５～３９％であることが好ましい。Ｆｅ２Ｏ３の含有量は０～９０％、１５～８５％、２０～８０％、特に２５～７５％であることが好ましい。Ｎｂ２Ｏ５の含有量は０～９０％、７～７９％、９～６９％、１１～５９％、１３～４９％、特に１５～３９％であることが好ましい。なお、ＳｎＯ＋Ｂｉ２Ｏ３＋ＴｉＯ２＋Ｆｅ２Ｏ３＋Ｎｂ２Ｏ５は０～９０％、５～８５％、特に１０～８０％であることが好ましい。 The SnO content is preferably 0 to 90%, 45 to 85%, 55 to 75%, particularly 60 to 72%. The content of Bi 2 O 3 is preferably 0 to 90%, 10 to 70%, 15 to 65%, particularly 25 to 55%. The content of TiO 2 is preferably 0 to 90%, 5 to 72%, 10 to 68%, 12 to 58%, 15% to 49%, particularly preferably 15 to 39%. The content of Fe 2 O 3 is preferably 0 to 90%, 15 to 85%, 20 to 80%, particularly 25 to 75%. The Nb 2 O 5 content is preferably 0 to 90%, 7 to 79%, 9 to 69%, 11 to 59%, 13 to 49%, and particularly preferably 15 to 39%. SnO + Bi 2 O 3 + TiO 2 + Fe 2 O 3 + Nb 2 O 5 is preferably 0 to 90%, 5 to 85%, particularly preferably 10 to 80%.
　ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５は網目形成酸化物であり、上記活物質成分におけるナトリウムイオンの吸蔵及び放出サイトを取り囲み、サイクル特性を向上させる作用がある。なかでもＳｉＯ２及びＰ２Ｏ５はサイクル特性を向上させるだけでなく、ナトリウムイオン伝導性に優れるため、レート特性を向上させる効果がある。ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５は５～８５％、６～７９％、７～６９％、８～５９、９～４９％、特に１０～３９％であることが好ましい。ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５が少なすぎると、充放電時のナトリウムイオンの吸蔵及び放出に伴う活物質成分の体積変化を緩和できず構造破壊を起こすため、サイクル特性が低下しやすくなる。一方、ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５が多すぎると、相対的に活物質成分の含有量が少なくなり、負極活物質の単位質量当たりの充放電容量が小さくなる傾向がある。 SiO 2 , B 2 O 3, and P 2 O 5 are network-forming oxides that surround the sodium ion occlusion and release sites in the active material component and have an effect of improving cycle characteristics. Among these, SiO 2 and P 2 O 5 not only improve cycle characteristics, but also have an effect of improving rate characteristics because of excellent sodium ion conductivity. SiO 2 + B 2 O 3 + P 2 O 5 is preferably 5 to 85%, 6 to 79%, 7 to 69%, 8 to 59, 9 to 49%, particularly preferably 10 to 39%. If there is too little SiO 2 + B 2 O 3 + P 2 O 5 , the volume change of the active material component accompanying the occlusion and release of sodium ions at the time of charge / discharge cannot be relaxed and structural destruction occurs, so the cycle characteristics are likely to deteriorate. . On the other hand, when the SiO 2 + B 2 O 3 + P 2 O 5 is too large, relatively active material component content decreases the tend charge and discharge capacity per unit mass of the negative electrode active material is reduced.
　なお、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５の各々の含有量の好ましい範囲は以下の通りである。 Incidentally, each preferred range of the content of SiO 2, B 2 O 3 and P 2 O 5 is as follows.
　ＳｉＯ２の含有量は０～７５％、５～７５％、７～６０％、１０～５０％、１２～４０％、特に２０～３５％であることが好ましい。ＳｉＯ２の含有量が多すぎると、放電容量が低下しやすくなる。 The content of SiO 2 is preferably 0 to 75%, 5 to 75%, 7 to 60%, 10 to 50%, 12 to 40%, particularly 20 to 35%. When the content of SiO 2 is too large, the discharge capacity tends to lower.
　Ｐ２Ｏ５の含有量は５～７５％、７～６０％、１０～５０％、１２～４０％、特に２０～３５％であることが好ましい。Ｐ２Ｏ５の含有量が少なすぎると、上記の効果が得られにくくなる。一方、Ｐ２Ｏ５の含有量が多すぎると、放電容量が低下しやすくなるとともに、耐水性が低下しやすくなる。また、水系電極ペーストを作製した際に、望まない異種結晶が生じてＰ２Ｏ５ネットワークが切断されるため、サイクル特性が低下しやすくなる。 The content of P 2 O 5 is preferably 5 to 75%, 7 to 60%, 10 to 50%, 12 to 40%, particularly 20 to 35%. When P 2 content of O 5 is too small, the above effect is difficult to obtain. On the other hand, when the content of P 2 O 5 is too large, the discharge capacity tends to decrease and the water resistance tends to decrease. In addition, when the aqueous electrode paste is produced, undesirable heterogeneous crystals are generated and the P 2 O 5 network is cut, so that the cycle characteristics are liable to deteriorate.
　Ｂ２Ｏ３の含有量は０～７５％、５～７５％、７～６０％、１０～５０％、１２～４０％、特に２０～３５％であることが好ましい。Ｂ２Ｏ３の含有量が多すぎると、放電容量が低下しやすくなるとともに、化学的耐久性が低下しやすくなる。 The content of B 2 O 3 is preferably 0 to 75%, 5 to 75%, 7 to 60%, 10 to 50%, 12 to 40%, particularly preferably 20 to 35%. If the B 2 O 3 content is too large, the discharge capacity tends to lower chemical durability tends to decrease.
　なお、負極活物質前駆体粉末を焼成して得られる負極活物質は、一般式Ｒｘ１Ｒ´ｘ２ＭＡｙＯｚ（ＲはＬｉ、Ｎａ及びＫから選択される少なくとも一種、Ｒ´はＭｇ、Ｃａ、Ｓｒ、Ｂａ及びＺｎから選択される少なくとも一種、ＭはＴｉ、Ｖ及びＮｂから選択される少なくとも一種、ＡはＰ、Ｓｉ、Ｂ及びＡｌから選択される少なくとも一種、０≦ｘ１≦６、０≦ｘ２≦６、０＜ｙ≦１２、０．２≦ｚ≦８７、但し、ｘ１=０．５かつｘ２＝０である場合、及び、ｘ１=１．５かつｘ２＝０である場合を含まない）で表される結晶相を含有してもよい。特に、一般式ＲｘＴｉＰｙＯｚ（ＲはＬｉ、Ｎａ及びＫから選択される少なくとも一種、０．５＜ｘ≦６、０．２５≦ｙ≦４、２．５≦ｚ≦１６、但しｘ=１．５を含まない）で表される結晶相を含有することが好ましい。以下、当該結晶相について詳細に説明する。 The negative electrode active material obtained by firing the negative electrode active material precursor powder has a general formula R x1 R ′ x2 MA y O z (R is at least one selected from Li, Na and K, R ′ is Mg, At least one selected from Ca, Sr, Ba and Zn, M is at least one selected from Ti, V and Nb, A is at least one selected from P, Si, B and Al, 0 ≦ x1 ≦ 6, 0 ≦ x2 ≦ 6, 0 <y ≦ 12, 0.2 ≦ z ≦ 87, provided that x1 = 0.5 and x2 = 0, and x1 = 1.5 and x2 = 0 It may contain a crystal phase represented by In particular, the general formula R x TiP y O z (R is at least one selected from Li, Na and K, 0.5 <x ≦ 6, 0.25 ≦ y ≦ 4, 2.5 ≦ z ≦ 16, where It is preferable to contain a crystal phase represented by: Hereinafter, the crystal phase will be described in detail.
　ｘの範囲は、０．５＜ｘ≦６、１≦ｘ≦５．８、２≦ｘ≦５．７、３≦ｘ≦５．６、４≦ｘ≦５．５、特に５≦ｘ≦５．４であることが好ましい（但し、ｘ=１．５を含まない）。ｘが小さすぎると、初回充電時にアルカリイオンが負極活物質中に吸収されやすくなり、初回充放電効率が低下しやすくなる。また、アルカリイオン伝導性が低下することで高抵抗化し、放電電圧が上昇する傾向にある。電池の作動電圧は正極の作動電圧と負極の作動電圧の差で決定されるため、負極の放電電圧が上昇すると、電池としての作動電圧が小さくなる傾向にある。一方、ｘが大きすぎると、アルカリイオンとＰ２Ｏ５からなる異種結晶（例えばＮａ４Ｐ２Ｏ７、ＮａＰＯ４）が多量に形成され、サイクル特性が低下しやすくなる。また、活物質成分の含有量が相対的に低下するため放電容量が低下する傾向にある。 The range of x is 0.5 <x ≦ 6, 1 ≦ x ≦ 5.8, 2 ≦ x ≦ 5.7, 3 ≦ x ≦ 5.6, 4 ≦ x ≦ 5.5, especially 5 ≦ x ≦. 5.4 is preferable (however, x = 1.5 is not included). When x is too small, alkali ions are easily absorbed in the negative electrode active material during the initial charge, and the initial charge / discharge efficiency tends to be reduced. Further, the alkali ion conductivity is lowered, so that the resistance is increased and the discharge voltage tends to increase. Since the operating voltage of the battery is determined by the difference between the operating voltage of the positive electrode and the operating voltage of the negative electrode, when the discharge voltage of the negative electrode increases, the operating voltage as a battery tends to decrease. On the other hand, when x is too large, a large amount of heterogeneous crystals (for example, Na 4 P 2 O 7 , NaPO 4 ) composed of alkali ions and P 2 O 5 are formed, and the cycle characteristics are likely to deteriorate. Moreover, since the content of the active material component relatively decreases, the discharge capacity tends to decrease.
　ｙの範囲は、０．２５≦ｙ≦４、１≦ｙ≦３．８、１．５≦ｙ≦３．６、２≦ｙ≦３．４、特に３≦ｙ≦３．２であることが好ましい。ｙが小さすぎると、アルカリイオン伝導性が低下したり、サイクル特性が低下する傾向にある。一方、ｙが大きすぎると、耐水性が低下しやすくなって、水系電極ペーストを作製した際に望まない異種結晶が生じやすくなる。その結果、負極活物質中のＰ２Ｏ５ネットワークが切断されて、サイクル特性が低下しやすくなる。 The range of y is 0.25 ≦ y ≦ 4, 1 ≦ y ≦ 3.8, 1.5 ≦ y ≦ 3.6, 2 ≦ y ≦ 3.4, especially 3 ≦ y ≦ 3.2. Is preferred. If y is too small, alkali ion conductivity tends to be lowered, and cycle characteristics tend to be lowered. On the other hand, if y is too large, the water resistance tends to decrease, and undesirable heterogeneous crystals are likely to be produced when the aqueous electrode paste is produced. As a result, the P 2 O 5 network in the negative electrode active material is cut, and the cycle characteristics are likely to deteriorate.
　ｚの範囲は、２．５≦ｚ≦１６、３≦ｚ≦１５、４≦ｚ≦１４、６≦ｚ≦１３、特に９≦ｚ≦１２であることが好ましい。ｚが小さすぎると、Ｔｉが還元されて低価数化するため、充放電に伴うレドックス反応が起こりにくくなる。その結果、吸蔵及び放出されるアルカリイオンが少なくなり、蓄電デバイスの容量が低下する傾向にある。一方、ｚが大きすぎると、Ｐ２Ｏ５を含む異種結晶（例えばＮａ４Ｐ２Ｏ７、ＮａＰＯ４）が多量に形成され、サイクル特性が低下しやすくなる。また、活物質成分の含有量が相対的に低下するため放電容量が低下する傾向にある。 The range of z is preferably 2.5 ≦ z ≦ 16, 3 ≦ z ≦ 15, 4 ≦ z ≦ 14, 6 ≦ z ≦ 13, particularly 9 ≦ z ≦ 12. If z is too small, Ti is reduced and the valence is lowered, so that the redox reaction associated with charge / discharge hardly occurs. As a result, the number of occluded and released alkali ions decreases, and the capacity of the electricity storage device tends to decrease. On the other hand, if z is too large, a large amount of heterogeneous crystals (eg, Na 4 P 2 O 7 , NaPO 4 ) containing P 2 O 5 are formed, and the cycle characteristics are likely to deteriorate. Moreover, since the content of the active material component relatively decreases, the discharge capacity tends to decrease.
　一般式ＲｘＴｉＰｙＯｚで表される結晶相としては、Ｎａ４ＴｉＰ２Ｏ９［Ｎａ４ＴｉＯ（ＰＯ４）２］、Ｎａ５ＴｉＰ３Ｏ１２［Ｎａ５Ｔｉ（ＰＯ４）３］、Ｎａ３ＴｉＰ２Ｏ８．５［Ｎａ６（ＴｉＯ）Ｔｉ（ＰＯ４）４］、Ｎａ３．９１ＴｉＰ２Ｏ９［Ｎａ３．９１ＴｉＯ（ＰＯ４）２］、ＮａＴｉＰ１．６７Ｏ６．６７［Ｎａ３Ｔｉ３（ＰＯ４）５］、Ｎａ２ＴｉＰ２Ｏ８［Ｎａ２Ｔｉ（ＰＯ４）２］、ＮａＴｉＰ１．５Ｏ６［Ｎａ２Ｔｉ２（ＰＯ４）３］、ＮａＴｉＰ２Ｏ７及びＮａＴｉＰＯ５［ＮａＴｉＯＰＯ４］から選択される少なくとも一種が好ましい（［　］内は示性式を示す）。これらの結晶相は、充放電に伴うＴｉ４＋／Ｔｉ３＋の酸化還元電位を約１．２Ｖ（ｖｓ．Ｎａ／Ｎａ＋）まで低下させることができる上に、充放電に伴う電圧変動が小さく一定の作動電圧が得られやすい。なかでもＮａ３．９１（ＴｉＰ２Ｏ９）、Ｎａ４ＴｉＰ２Ｏ９、Ｎａ５ＴｉＰ３Ｏ１２が好ましく、イオン伝導性に優れるＮａ５ＴｉＰ３Ｏ１２が最も好ましい。なお、Ｎａ３．９１ＴｉＰ２Ｏ９及びＮａ４ＴｉＰ２Ｏ９は単斜晶系結晶であり空間群Ｐ２１／ｃに属する。また、Ｎａ５ＴｉＰ３Ｏ１２は六方晶系結晶であり空間群Ｒ３２に属する。 Examples of the crystal phase represented by the general formula R x TiP y O z include Na 4 TiP 2 O 9 [Na 4 TiO (PO 4 ) 2 ], Na 5 TiP 3 O 12 [Na 5 Ti (PO 4 ) 3 ]. Na 3 TiP 2 O 8.5 [Na 6 (TiO) Ti (PO 4 ) 4 ], Na 3.91 TiP 2 O 9 [Na 3.91 TiO (PO 4 ) 2 ], NaTiP 1.67 O 6 .67 [Na 3 Ti 3 (PO 4 ) 5 ], Na 2 TiP 2 O 8 [Na 2 Ti (PO 4 ) 2 ], NaTiP 1.5 O 6 [Na 2 Ti 2 (PO 4 ) 3 ], NaTiP At least one selected from 2 O 7 and NaTiPO 5 [NaTiOPO 4 ] is preferable (the inside of [] indicates a sexual formula). These crystal phases can reduce the oxidation-reduction potential of Ti 4 + / Ti 3+ associated with charging / discharging to about 1.2 V (vs. Na / Na + ), and the voltage variation associated with charging / discharging is small and constant. The operating voltage can be easily obtained. Of these Na 3.91 (TiP 2 O 9) , preferably Na 4 TiP 2 O 9, Na 5 TiP 3 O 12, Na 5 TiP 3 O 12 having excellent ion conductivity are most preferred. Na 3.91 TiP 2 O 9 and Na 4 TiP 2 O 9 are monoclinic crystals and belong to the space group P21 / c. Na 5 TiP 3 O 12 is a hexagonal crystal and belongs to the space group R32.
　さらに、負極活物質はＮｂ及びＴｉから選ばれる少なくとも１種、並びにＯを含む結晶を含有していてもよい。当該結晶はサイクル特性に優れるため好ましい。さらに、当該結晶がＮａを含むと、充放電効率が高まり、高い放電容量を維持することができるため好ましい。なかでも当該結晶が斜方晶系結晶、六方晶系結晶、立方晶系結晶または単斜晶系結晶、特に空間群Ｐ２１／ｍに属する単斜晶系結晶であれば、大電流で充放電しても容量の低下が起こりにくいため好ましい。斜方晶系結晶としては、ＮａＴｉ２Ｏ４等が挙げられる。六方晶系結晶としては、Ｎａ２ＴｉＯ３、ＮａＴｉ８Ｏ１３、ＮａＴｉＯ２、ＬｉＮｂＯ３、ＬｉＮｂＯ２、Ｌｉ７ＮｂＯ６、ＬｉＮｂＯ２、Ｌｉ２Ｔｉ３Ｏ７等が挙げられる。立方晶系結晶としては、Ｎａ２ＴｉＯ３、ＮａＮｂＯ３、Ｌｉ４Ｔｉ５Ｏ１２、Ｌｉ３ＮｂＯ４等が挙げられる。単斜晶系結晶としては、Ｎａ２Ｔｉ６Ｏ１３、ＮａＴｉ２Ｏ４、Ｎａ２ＴｉＯ３、Ｎａ４Ｔｉ５Ｏ１２、Ｎａ２Ｔｉ４Ｏ９、Ｎａ２Ｔｉ９Ｏ１９、Ｎａ２Ｔｉ３Ｏ７、Ｎａ２Ｔｉ３Ｏ７、Ｌｉ１．７Ｎｂ２Ｏ５、Ｌｉ１．９Ｎｂ２Ｏ５、Ｌｉ１２Ｎｂ１３Ｏ３３、ＬｉＮｂ３Ｏ８等が挙げられる。空間群Ｐ２１／ｍに属する単斜晶系結晶としては、Ｎａ２Ｔｉ３Ｏ７等が挙げられる。 Furthermore, the negative electrode active material may contain at least one selected from Nb and Ti, and crystals containing O. The crystal is preferable because it has excellent cycle characteristics. Furthermore, it is preferable that the crystal contains Na because charge / discharge efficiency is increased and high discharge capacity can be maintained. In particular, if the crystal is an orthorhombic crystal, a hexagonal crystal, a cubic crystal, or a monoclinic crystal, particularly a monoclinic crystal belonging to the space group P21 / m, it is charged and discharged with a large current. However, it is preferable because the capacity is hardly lowered. Examples of orthorhombic crystals include NaTi 2 O 4 . Examples of the hexagonal crystal include Na 2 TiO 3 , NaTi 8 O 13 , NaTiO 2 , LiNbO 3 , LiNbO 2 , Li 7 NbO 6 , LiNbO 2 , Li 2 Ti 3 O 7 and the like. Examples of cubic crystals include Na 2 TiO 3 , NaNbO 3 , Li 4 Ti 5 O 12 , and Li 3 NbO 4 . Monoclinic crystals include Na 2 Ti 6 O 13 , NaTi 2 O 4 , Na 2 TiO 3 , Na 4 Ti 5 O 12 , Na 2 Ti 4 O 9 , Na 2 Ti 9 O 19 , Na 2 Ti 3. Examples include O 7 , Na 2 Ti 3 O 7 , Li 1.7 Nb 2 O 5 , Li 1.9 Nb 2 O 5 , Li 12 Nb 13 O 33 , LiNb 3 O 8, and the like. Examples of the monoclinic crystal belonging to the space group P21 / m include Na 2 Ti 3 O 7 .
　Ｎｂ及びＴｉから選ばれる少なくとも１種、並びにＯを含む結晶は、さらにＢ、Ｓｉ、Ｐ及びＧｅから選ばれる少なくとも１種を含むことが好ましい。これらの成分は、活物質結晶とともに非晶質相を形成させやすくし、ナトリウムイオン伝導性を向上させる効果を有する。 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 have an effect of facilitating the formation of an amorphous phase together with the active material crystal and improving sodium ion conductivity.
　その他に、負極活物質はＮａ金属結晶、または少なくともＮａを含む合金結晶（例えばＮａ－Ｓｎ合金、Ｎａ－Ｉｎ合金）や、Ｓｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種の金属結晶、Ｓｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種を含む合金結晶（例えばＳｎ－Ｃｕ合金、Ｂｉ－Ｃｕ合金、Ｂｉ－Ｚｎ合金、Ｓｂ－Ｃｕ合金、Ｓｂ－Ｓｎ合金、Ｓｂ－Ｓｉ合金、Ｓｂ－Ｉｎ合金、Ｓｂ－Ｚｎ合金）、Ｓｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種を含有するガラスを用いることができる。これらは、高容量であり、大電流で充放電しても容量の低下が起こりにくいため好ましい。 In addition, the negative electrode active material includes Na metal crystals, alloy crystals containing at least Na (for example, Na—Sn alloy, Na—In alloy), at least one metal crystal selected from Sn, Bi, and Sb, Sn, Bi. And an alloy crystal containing at least one selected from Sb (for example, Sn—Cu alloy, Bi—Cu alloy, Bi—Zn alloy, Sb—Cu alloy, Sb—Sn alloy, Sb—Si alloy, Sb—In alloy, Sb) -Zn alloy), glass containing at least one selected from Sn, Bi and Sb can be used. These are preferable because they have a high capacity and are unlikely to decrease in capacity even when charged and discharged with a large current.
　活物質前駆体粉末の平均粒子径は０．０１～１５μｍ、０．０５～１２μｍ、特に０．１～１０μｍであることが好ましい。活物質前駆体粉末の平均粒子径が小さすぎると、活物質前駆体粉末同士の凝集力が強くなり、ペースト化した際に分散性に劣る傾向がある。その結果、電池の内部抵抗が高くなり作動電圧が低下しやすくなる。また、電極密度が低下して電池の単位体積あたりの容量が低下する傾向がある。一方、活物質前駆体粉末の平均粒子径が大きすぎると、ナトリウムイオンが拡散しにくくなるとともに、内部抵抗が大きくなる傾向がある。また、電極の表面平滑性に劣る傾向がある。 The average particle diameter of the active material precursor powder is preferably 0.01 to 15 μm, 0.05 to 12 μm, and particularly preferably 0.1 to 10 μm. When the average particle diameter of the active material precursor powder is too small, the cohesive force between the active material precursor powders becomes strong and tends to be inferior in dispersibility when formed into a paste. As a result, the internal resistance of the battery increases and the operating voltage tends to decrease. In addition, the electrode density tends to decrease and the capacity per unit volume of the battery tends to decrease. On the other hand, if the average particle size of the active material precursor powder is too large, sodium ions are difficult to diffuse and the internal resistance tends to increase. Moreover, there exists a tendency to be inferior to the surface smoothness of an electrode.
　なお、本発明において、平均粒子径はＤ５０（体積基準の平均粒子径）を意味し、レーザー回折散乱法により測定された値を指すものとする。 In the present invention, the average particle diameter means D 50 (volume-based average particle diameter), and indicates a value measured by a laser diffraction scattering method.
　（２）固体電解質粉末
　固体電解質粉末は、例えばナトリウムイオン伝導性を有する酸化物材料からなる。具体的には、固体電解質粉末は、Ａｌ、Ｙ、Ｚｒ、Ｓｉ及びＰから選ばれる少なくとも１種、Ｎａ、並びにＯを含有する化合物が挙げられる。そのような化合物としては、β－アルミナ、β”－アルミナ及びＮＡＳＩＣＯＮ型結晶から選択される少なくとも１種が挙げられる。これらはナトリウムイオン伝導性に優れるため好ましい。 (2) Solid electrolyte powder Solid electrolyte powder consists of an oxide material which has sodium ion conductivity, for example. Specifically, the solid electrolyte powder includes a compound containing at least one selected from Al, Y, Zr, Si and P, Na, and O. Examples of such a compound include at least one selected from β-alumina, β ″ -alumina, and NASICON type crystals. These are preferable because they are excellent in sodium ion conductivity.
　β－アルミナやβ”－アルミナを含有する酸化物材料としては、モル％で、Ａｌ２Ｏ３　６５～９８％、Ｎａ２Ｏ　２～２０％、ＭｇＯ＋Ｌｉ２Ｏ　０．３～１５％を含有するものが挙げられる。組成をこのように限定した理由を以下に説明する。なお、以下の説明において、特に断りのない限り、「％」は「モル％」を意味する。 The oxide material containing β-alumina or β ″ -alumina contains Al 2 O 3 65 to 98%, Na 2 O 2 to 20%, MgO + Li 2 O 0.3 to 15% in mol%. The reason for limiting the composition in this way will be described below, and “%” means “mol%” in the following description unless otherwise specified.
　Ａｌ２Ｏ３はβ－アルミナ及びβ”－アルミナを構成する主成分である。Ａｌ２Ｏ３の含有量は６５～９８％、特に７０～９５％であることが好ましい。Ａｌ２Ｏ３が少なすぎると、イオン伝導性が低下しやすくなる。一方、Ａｌ２Ｏ３が多すぎると、イオン伝導性を有さないα－アルミナが残存し、イオン伝導性が低下しやすくなる。 Al 2 O 3 is β- alumina and beta "- content .al 2 O 3 is a main component of alumina 65 to 98% is .al 2 O 3 is preferably especially 70 to 95% If the amount is too small, the ionic conductivity tends to decrease, whereas if the amount of Al 2 O 3 is too large, α-alumina having no ionic conductivity remains and the ionic conductivity tends to decrease.
　Ｎａ２Ｏは固体電解質にナトリウムイオン伝導性を付与する成分である。Ｎａ２Ｏの含有量は２～２０％、３～１８％、特に４～１６％であることが好ましい。Ｎａ２Ｏが少なすぎると、上記効果が得られにくくなる。一方、Ｎａ２Ｏが多すぎると、余剰のナトリウムがＮａＡｌＯ２等のイオン伝導性に寄与しない化合物を形成するため、イオン伝導性が低下しやすくなる。 Na 2 O is a component that imparts sodium ion conductivity to the solid electrolyte. The content of Na 2 O is preferably 2 to 20%, 3 to 18%, particularly 4 to 16%. When Na 2 O is too small, the effect is difficult to obtain. On the other hand, when there is too much Na 2 O, excess sodium forms a compound that does not contribute to ionic conductivity such as NaAlO 2, so that ionic conductivity tends to decrease.
　ＭｇＯ及びＬｉ２Ｏはβ－アルミナ及びβ”－アルミナの構造を安定化させる成分（安定化剤）である。ＭｇＯ＋Ｌｉ２Ｏの含有量は０．３～１５％、０．５～１０％、特に０．８～８％であることが好ましい。ＭｇＯ＋Ｌｉ２Ｏが少なすぎると、固体電解質中にα－アルミナが残存してイオン伝導性が低下しやすくなる。一方、ＭｇＯ＋Ｌｉ２Ｏが多すぎると、安定化剤として機能しなかったＭｇＯまたはＬｉ２Ｏが固体電解質中に残存して、イオン伝導性が低下しやすくなる。 MgO and Li 2 O are components (stabilizers) that stabilize the structure of β-alumina and β ″ -alumina. The content of MgO + Li 2 O is 0.3 to 15%, 0.5 to 10%, In particular, it is preferably 0.8 to 8% If the amount of MgO + Li 2 O is too small, α-alumina remains in the solid electrolyte and the ionic conductivity tends to decrease, whereas if the amount of MgO + Li 2 O is too large. The MgO or Li 2 O that did not function as a stabilizer remains in the solid electrolyte, and the ionic conductivity tends to decrease.
　固体電解質粉末は、上記成分以外にも、ＺｒＯ２やＹ２Ｏ３を含有することが好ましい。ＺｒＯ２及びＹ２Ｏ３は、焼成時におけるβ－アルミナ及び／またはβ”－アルミナの異常粒成長を抑制し、β－アルミナ及び／またはβ”－アルミナの各粒子の密着性を向上させる効果がある。ＺｒＯ２の含有量は０～１５％、１～１３％、特に２～１０％であることが好ましい。また、Ｙ２Ｏ３の含有量は０～５％、０．０１～４％、特に０．０２～３％であることが好ましい。ＺｒＯ２またはＹ２Ｏ３が多すぎると、β－アルミナ及び／またはβ”－アルミナの生成量が低下して、イオン伝導性が低下しやすくなる。 The solid electrolyte powder preferably contains ZrO 2 or Y 2 O 3 in addition to the above components. ZrO 2 and Y 2 O 3 have the effect of suppressing abnormal grain growth of β-alumina and / or β ″ -alumina during firing and improving the adhesion of each particle of β-alumina and / or β ″ -alumina. There is. The content of ZrO 2 is preferably 0 to 15%, 1 to 13%, particularly 2 to 10%. The content of Y 2 O 3 is preferably 0 to 5%, 0.01 to 4%, particularly preferably 0.02 to 3%. If there is too much ZrO 2 or Y 2 O 3, the amount of β-alumina and / or β ″ -alumina produced will decrease, and the ionic conductivity tends to decrease.
　β”－アルミナとしては、三方晶の（Ａｌ１０．３５Ｍｇ０．６５Ｏ１６）（Ｎａ１．６５Ｏ）、（Ａｌ８．８７Ｍｇ２．１３Ｏ１６）（Ｎａ３．１３Ｏ）、Ｎａ１．６７Ｍｇ０．６７Ａｌ１０．３３Ｏ１７、Ｎａ１．４９Ｌｉ０．２５Ａｌ１０．７５Ｏ１７、Ｎａ１．７２Ｌｉ０．３Ａｌ１０．６６Ｏ１７、Ｎａ１．６Ｌｉ０．３４Ａｌ１０．６６Ｏ１７が挙げられる。β－アルミナとしては、六方晶の（Ａｌ１０．３５Ｍｇ０．６５Ｏ１６）（Ｎａ１．６５Ｏ）、（Ａｌ１０．３７Ｍｇ０．６３Ｏ１６）（Ｎａ１．６３Ｏ）、ＮａＡｌ１１Ｏ１７、（Ａｌ１０．３２Ｍｇ０．６８Ｏ１６）（Ｎａ１．６８Ｏ）が挙げられる。 β ″ -alumina includes trigonal (Al 10.35 Mg 0.65 O 16 ) (Na 1.65 O), (Al 8.87 Mg 2.13 O 16 ) (Na 3.13 O), Na 1.67 Mg 0.67 Al 10.33 O 17 , Na 1.49 Li 0.25 Al 10.75 O 17 , Na 1.72 Li 0.3 Al 10.66 O 17 , Na 1.6 Li 0.34 Al 10.66 O 17. Examples of β-alumina include hexagonal (Al 10.35 Mg 0.65 O 16 ) (Na 1.65 O), (Al 10.37 Mg 0. 63 O 16 ) (Na 1.63 O), NaAl 11 O 17 , (Al 10.32 Mg 0.68 O 16 ) (Na 1.68 O).
　固体電解質粉末としては、一般式ＮａｓＡ１ｔＡ２ｕＯｖ（Ａ１はＡｌ、Ｙ、Ｙｂ、Ｎｄ、Ｎｂ、Ｔｉ、Ｈｆ及びＺｒから選択される少なくとも１種、Ａ２はＳｉ及びＰから選択される少なくとも１種、ｓ＝１．４～５．２、ｔ＝１～２．９、ｕ＝２．８～４．１、ｖ＝９～１４）で表される結晶を含有していてもよい。なお上記結晶の好ましい形態としては、Ａ１はＹ、Ｎｂ、Ｔｉ及びＺｒから選択される少なくとも１種、ｓ＝２．５～３．５、ｔ＝１～２．５、ｕ＝２．８～４、ｖ＝９．５～１２である。このようにすることでイオン伝導性に優れた結晶を得ることができる。特に、単斜晶系または三方晶系のＮＡＳＩＣＯＮ型結晶であればイオン伝導性に優れるため好ましい。 The solid electrolyte powder has a general formula Na s A1 t A2 u O v (A1 is at least one selected from Al, Y, Yb, Nd, Nb, Ti, Hf and Zr, and A2 is selected from Si and P. Or at least one kind of crystal represented by s = 1.4 to 5.2, t = 1 to 2.9, u = 2.8 to 4.1, v = 9 to 14) Good. As a preferable form of the crystal, A1 is at least one selected from Y, Nb, Ti and Zr, s = 2.5 to 3.5, t = 1 to 2.5, u = 2.8 to 4, v = 9.5-12. By doing in this way, the crystal | crystallization excellent in ion conductivity can be obtained. In particular, a monoclinic or trigonal NASICON type crystal is preferable because of its excellent ion conductivity.
　上記一般式ＮａｓＡ１ｔＡ２ｕＯｖで表される結晶の具体例としては、Ｎａ３Ｚｒ２Ｓｉ２ＰＯ１２、Ｎａ３．２Ｚｒ１．３Ｓｉ２．２Ｐ０．８Ｏ１０．５、Ｎａ３Ｚｒ１．６Ｔｉ０．４Ｓｉ２ＰＯ１２、Ｎａ３Ｈｆ２Ｓｉ２ＰＯ１２、Ｎａ３．４Ｚｒ０．９Ｈｆ１．４Ａｌ０．６Ｓｉ１．２Ｐ１．８Ｏ１２、Ｎａ３Ｚｒ１．７Ｎｂ０．２４Ｓｉ２ＰＯ１２、Ｎａ３．６Ｔｉ０．２Ｙ０．８Ｓｉ２．８Ｏ９、Ｎａ３Ｚｒ１．８８Ｙ０．１２Ｓｉ２ＰＯ１２、Ｎａ３．１２Ｚｒ１．８８Ｙ０．１２Ｓｉ２ＰＯ１２、Ｎａ３．６Ｚｒ０．１３Ｙｂ１．６７Ｓｉ０．１１Ｐ２．９Ｏ１２等が挙げられる。 Specific examples of the crystal represented by the general formula Na s A1 t A2 u O v include Na 3 Zr 2 Si 2 PO 12 , Na 3.2 Zr 1.3 Si 2.2 P 0.8 O 10. 5 , Na 3 Zr 1.6 Ti 0.4 Si 2 PO 12 , Na 3 Hf 2 Si 2 PO 12 , Na 3.4 Zr 0.9 Hf 1.4 Al 0.6 Si 1.2 P 1.8 O 12 , Na 3 Zr 1.7 Nb 0.24 Si 2 PO 12 , Na 3.6 Ti 0.2 Y 0.8 Si 2.8 O 9 , Na 3 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.12 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.6 Zr 0.13 Yb 1.67 Si 0.11 P 2.9 O 12 and the like.
　固体電解質粉末の平均粒子径は０．０１～１５μｍであり、０．０５～１０μｍ、特に０．１～５μｍであることが好ましい。固体電解質粉末の平均粒子径が大きすぎると、ナトリウムイオン伝導に要する距離が長くなりイオン伝導性が低下する傾向がある。また、活物質粉末と固体電解質粉末との間のイオン伝導パスが減少する傾向がある。結果として、放電容量が低下しやすくなる。一方、固体電解質粉末の平均粒子径が小さすぎると、ナトリウムイオンの溶出や炭酸ガスとの反応による劣化が起こってイオン伝導性が低下しやすくなる。また、空隙が形成されやすくなるため電極密度も低下しやすくなる。結果として、放電容量が低下する傾向がある。 The average particle size of the solid electrolyte powder is 0.01 to 15 μm, preferably 0.05 to 10 μm, particularly preferably 0.1 to 5 μm. If the average particle size of the solid electrolyte powder is too large, the distance required for sodium ion conduction tends to be long, and the ionic conductivity tends to decrease. In addition, the ion conduction path between the active material powder and the solid electrolyte powder tends to decrease. As a result, the discharge capacity tends to decrease. On the other hand, if the average particle size of the solid electrolyte powder is too small, the ion conductivity is likely to be lowered due to the elution of sodium ions and the deterioration due to the reaction with carbon dioxide. Moreover, since voids are easily formed, the electrode density is also likely to decrease. As a result, the discharge capacity tends to decrease.
　また、固体電解質粉末の比表面積（ＢＥＴ比表面積）は１．５～２００ｍ２／ｇであり、２～１００ｍ２／ｇ、特に２．５～５０ｍ２／ｇであることが好ましい。固体電解質粉末の比表面積が小さすぎると、ナトリウムイオン伝導に要する距離が長くなりイオン伝導性が低下する傾向がある。また、活物質粉末と固体電解質粉末との間のイオン伝導パスが減少する傾向がある。結果として、放電容量が低下しやすくなる。一方、固体電解質粉末の比表面積が大きすぎると、ナトリウムイオンの溶出や炭酸ガスとの反応による劣化が起こってイオン伝導性が低下しやすくなる。また、空隙が形成されやすくなるため電極密度が低下しやすくなる。結果として、放電容量が低下する傾向がある。 The specific surface area of the solid electrolyte powder (BET specific surface area) is 1.5 ~ 200m 2 / g, 2 ~ 100m 2 / g, it is particularly preferably 2.5 ~ 50m 2 / g. If the specific surface area of the solid electrolyte powder is too small, the distance required for sodium ion conduction tends to be long and the ionic conductivity tends to decrease. In addition, the ion conduction path between the active material powder and the solid electrolyte powder tends to decrease. As a result, the discharge capacity tends to decrease. On the other hand, if the specific surface area of the solid electrolyte powder is too large, the ionic conductivity is likely to be lowered due to elution of sodium ions and deterioration due to reaction with carbon dioxide gas. Moreover, since voids are easily formed, the electrode density is likely to decrease. As a result, the discharge capacity tends to decrease.
　なお、比表面積は、吸着質として窒素を使用したＢＥＴ一点法により測定した値を指す。 The specific surface area is a value measured by the BET single point method using nitrogen as an adsorbate.
　固体電解質粉末の２５℃におけるイオン伝導度は１０－５Ｓ／ｃｍ以上、特に１０－４Ｓ／ｃｍ以上であることが好ましい。イオン伝導度が低すぎると、イオン伝導性物質として機能しなくなる。一方、イオン伝導度の上限は特に限定されないが、現実的には１０Ｓ／ｃｍ以下、さらには１Ｓ／ｃｍ以下である。 The ionic conductivity of the solid electrolyte powder at 25 ° C. is preferably 10 −5 S / cm or more, more preferably 10 −4 S / cm or more. If the ionic conductivity is too low, it will not function as an ionic conductive material. On the other hand, the upper limit of the ionic conductivity is not particularly limited, but is practically 10 S / cm or less, and further 1 S / cm or less.
　固体電解質粉末は、例えば原料粉末を焼成して固相反応させて目的生成物を得た後、粉砕することにより作製することができる。粉砕後の粉末を空気分級機等を用いて分級することにより、所望の平均粒子径を有する固体電解質粉末が得られやすくなる。 The solid electrolyte powder can be produced, for example, by firing a raw material powder and subjecting it to a solid phase reaction to obtain a target product, followed by pulverization. By classifying the pulverized powder using an air classifier or the like, a solid electrolyte powder having a desired average particle diameter can be easily obtained.
　（３）ナトリウムイオン二次電池用電極合材
　ナトリウムイオン二次電池用電極合材の空隙率は４５％以下であり、４０％以下、特に３５％以下であることが好ましい。空隙率が高すぎると、活物質粉末と固体電解質粉末の間の密着性が不十分となり、イオン伝導パスが十分に形成されないため、放電容量が低下しやすくなる。空隙率の下限は特に限定されないが、現実的には１％以上である。 (3) Electrode composite material for sodium ion secondary battery The porosity of the electrode composite material for sodium ion secondary battery is 45% or less, preferably 40% or less, and particularly preferably 35% or less. When the porosity is too high, the adhesion between the active material powder and the solid electrolyte powder becomes insufficient, and the ion conduction path is not sufficiently formed, so that the discharge capacity tends to decrease. The lower limit of the porosity is not particularly limited, but is practically 1% or more.
　活物質前駆体粉末と固体電解質粉末の体積比は２０：８０～９５：５、３０：７０～９０：１０、特に３５：６５～８８：１２であることが好ましい。活物質前駆体粉末の割合が少なすぎる（固体電解質粉末の割合が多すぎる）と、電極単位体積あたりの容量が低下し、電池のエネルギー密度が低下する傾向にある。一方、活物質前駆体粉末の割合が多すぎる（固体電解質粉末の割合が少なすぎる）と、イオン伝導パスが確保できず電極合材のイオン伝導性が低下するため、結果的に放電容量が低下する傾向がある。 The volume ratio of the active material precursor powder to the solid electrolyte powder is preferably 20:80 to 95: 5, 30:70 to 90:10, particularly 35:65 to 88:12. If the proportion of the active material precursor powder is too small (the proportion of the solid electrolyte powder is too large), the capacity per unit electrode volume tends to decrease, and the energy density of the battery tends to decrease. On the other hand, if the proportion of the active material precursor powder is too large (the proportion of the solid electrolyte powder is too small), the ion conduction path cannot be secured and the ionic conductivity of the electrode mixture is lowered, resulting in a decrease in discharge capacity. Tend to.
　なお電極合材前駆体の焼結体である電極合材において、活物質粉末に非晶質相が含まれることが好ましい。この場合、活物質粉末と固体電解質粉末との界面に非晶質相が介在しやすくなって、両者の密着性が高まり、空隙率が低下しやすくなる。また、活物質粉末と固体電解質粉末の間の界面抵抗が低下しやすくなる。以上により、放電容量が大きくなりやすい。また、急速充放電特性の向上が期待される。なお、活物質粉末と固体電解質粉末との界面に非晶質相が介在することにより、両者の間における原子拡散が抑制され、各粉末が化学的に分解することが抑制される。 In the electrode mixture which is a sintered body of the electrode mixture precursor, the active material powder preferably contains an amorphous phase. In this case, an amorphous phase is likely to be present at the interface between the active material powder and the solid electrolyte powder, the adhesion between the two is increased, and the porosity is easily decreased. In addition, the interface resistance between the active material powder and the solid electrolyte powder tends to decrease. As a result, the discharge capacity tends to increase. In addition, rapid charge / discharge characteristics are expected to be improved. In addition, when an amorphous phase intervenes at the interface between the active material powder and the solid electrolyte powder, atomic diffusion between them is suppressed, and chemical decomposition of each powder is suppressed.
　本発明のナトリウムイオン二次電池用電極合材は、導電性炭素を含むことが好ましい。この場合、電子伝導性が高くなり、高速充放電特性が向上しやすくなる。導電性炭素としては、アセチレンブラックやケッチェンブラック等の高導電性カーボンブラック、グラファイト等のカーボン粉末、炭素繊維等を用いることができる。なかでも、電子伝導性が高いアセチレンブラックが好ましい。 The electrode mixture for sodium ion secondary batteries of the present invention preferably contains conductive carbon. In this case, electronic conductivity becomes high and high-speed charge / discharge characteristics are easily improved. As the conductive carbon, highly conductive carbon black such as acetylene black or ketjen black, carbon powder such as graphite, carbon fiber, or the like can be used. Of these, acetylene black having a high electron conductivity is preferable.
　導電性炭素は、電極合材において０～２０質量％含有することが好ましく、１～１０質量％含有することがより好ましい。導電性炭素の含有量が多すぎると、電池容量が低下しやすくなる。 The conductive carbon is preferably contained in the electrode mixture in an amount of 0 to 20% by mass, more preferably 1 to 10% by mass. When there is too much content of conductive carbon, battery capacity will fall easily.
　本発明のナトリウムイオン二次電池用電極合材は通常シート状であり、その厚みは１～３００μｍであることが好ましく、５～２００μｍであることがより好ましく、１２～９０μｍであることがさらに好ましい。電極合材の厚みが小さすぎると、ナトリウムイオン二次電池自体の容量が小さくなるためエネルギー密度が低下する傾向にある。一方、電極合材の厚みが大きすぎると、電子伝導に対する抵抗が大きくなるため放電容量及び作動電圧が低下する傾向にある。 The electrode mixture for sodium ion secondary batteries of the present invention is usually in the form of a sheet, and the thickness thereof is preferably 1 to 300 μm, more preferably 5 to 200 μm, and further preferably 12 to 90 μm. . When the thickness of the electrode mixture is too small, the capacity of the sodium ion secondary battery itself tends to be small, so that the energy density tends to decrease. On the other hand, if the thickness of the electrode mixture is too large, the resistance to electronic conduction increases, and the discharge capacity and operating voltage tend to decrease.
　本発明のナトリウムイオン二次電池用電極合材の主面における単位面積あたりの容量は、０．０３～１．５ｍＡｈ／ｃｍ２であることが好ましく、０．１～０．９ｍＡｈ／ｃｍ２であることがより好ましい。単位面積あたりの容量が小さすぎると、電池容量が低下する傾向にある。一方、単位面積あたりの容量が大きすぎると、内部抵抗が増加し急速充放電特性が低下する傾向にある。 The capacity per unit area in the main surface of the electrode mixture for sodium ion secondary batteries of the present invention is preferably 0.03 to 1.5 mAh / cm 2 , and is 0.1 to 0.9 mAh / cm 2 . More preferably. If the capacity per unit area is too small, the battery capacity tends to decrease. On the other hand, when the capacity per unit area is too large, the internal resistance increases and the rapid charge / discharge characteristics tend to be deteriorated.
　本発明のナトリウムイオン二次電池用電極合材は２層以上の積層体からなるものであってもよい。電極合材の厚みを大きくすると、電極合材前駆体の焼成に伴う収縮によりクラックが発生したり、固体電解質シートから剥離しやすくなるが、積層体構造により電極合材の厚みを大きくすることでこのような不具合の発生を抑制できる。その結果、電極合材における活物質の担持量を増加でき、高容量化できるため、高エネルギー密度のナトリウムイオン二次電池が得られやすい。電極合材の積層数は７層以下であることが好ましく、３層以下であることがより好ましい。積層数が多すぎると、各電極合材層間における内部抵抗が大きくなる傾向がある。 The electrode mixture for sodium ion secondary batteries of the present invention may be composed of a laminate of two or more layers. When the thickness of the electrode mixture is increased, cracks occur due to shrinkage associated with the firing of the electrode mixture precursor and it is easy to peel off from the solid electrolyte sheet, but by increasing the thickness of the electrode mixture by the laminate structure Generation | occurrence | production of such a malfunction can be suppressed. As a result, the amount of active material supported in the electrode mixture can be increased and the capacity can be increased, so that a high energy density sodium ion secondary battery can be easily obtained. The number of electrode mixture layers is preferably 7 layers or less, and more preferably 3 layers or less. When the number of layers is too large, the internal resistance between the electrode mixture layers tends to increase.
　積層体で構成される電極合材の各層の厚みは、３～９０μｍであることが好ましく、５～４０μｍであることがより好ましい。各層の厚みが小さすぎると、均一な電極合材層を形成することが難しく、結果として容量の制御が困難になる傾向にある。一方、各層の厚みが大きすぎると、電極合材前駆体の焼成に伴う収縮量が大きくなり、クラックが発生したり、固体電解質シートから剥離して、固体電解質シートとのイオン伝導パスが切断されやすくなり、容量が低下する傾向にある。 The thickness of each layer of the electrode mixture composed of the laminate is preferably 3 to 90 μm, and more preferably 5 to 40 μm. If the thickness of each layer is too small, it is difficult to form a uniform electrode mixture layer, and as a result, the capacity tends to be difficult to control. On the other hand, if the thickness of each layer is too large, the amount of shrinkage associated with the firing of the electrode mixture precursor increases, cracks are generated, or the ion conductive path with the solid electrolyte sheet is cut off by peeling from the solid electrolyte sheet. It becomes easy and the capacity tends to decrease.
　積層体で構成される電極合材の各層の組成は異なっていてもよい。例えば、固体電解質シートに近い方の層における固体電解質粉末の割合を相対的に多くすることにより、固体電解質シートと電極合材との界面抵抗を低減することができる。また、集電体層に近い方（固体電解質シートから遠い方）における導電性炭素の含有量を多くすることにより、電極合材と集電体層の間での電子伝導性を向上させることができる。 The composition of each layer of the electrode mixture composed of the laminate may be different. For example, the interface resistance between the solid electrolyte sheet and the electrode mixture can be reduced by relatively increasing the ratio of the solid electrolyte powder in the layer closer to the solid electrolyte sheet. Also, by increasing the content of conductive carbon in the side closer to the current collector layer (away from the solid electrolyte sheet), the electron conductivity between the electrode mixture and the current collector layer can be improved. it can.
　（４）ナトリウムイオン二次電池用電極合材の製造方法
　本発明のナトリウムイオン二次電池用電極合材は、（ａ）正極または負極の活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末をスラリー化する工程、（ｂ）得られたスラリーを基材上に塗布、乾燥して電極合材前駆体シートを作製する工程、及び、（ｃ）電極合材前駆体シートをプレスした後、焼成する工程、を含む方法により製造することができる。以下に各工程毎に詳細に説明する。 (4) Manufacturing method of electrode mixture for sodium ion secondary battery The electrode mixture for sodium ion secondary battery of the present invention comprises: (a) a positive electrode or negative electrode active material precursor powder; and a sodium ion conductive solid electrolyte. A step of slurrying an electrode mixture precursor powder containing powder, (b) a step of applying and drying the obtained slurry on a substrate to produce an electrode mixture precursor sheet, and (c) It can manufacture by the method of including the process of baking after pressing an electrode compound-material precursor sheet | seat. Hereinafter, each process will be described in detail.
　まず、活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末を含む原料粉末を乾式または湿式により混合した後、バインダー、可塑剤、溶媒等を添加して混錬することによりスラリー化する。溶剤は水あるいはエタノールやアセトン等の有機溶媒のいずれでも構わない。ただし、溶剤として水を用いた場合、ナトリウム成分が原料粉末から溶出してスラリーのｐＨが上昇し、原料粉末が凝集するおそれがある。そのため、有機溶媒を用いることが好ましく、無水有機溶媒を用いることが特に好ましい。 First, an active material precursor powder and a raw material powder containing sodium ion conductive solid electrolyte powder are mixed by dry or wet, and then a binder, a plasticizer, a solvent, etc. are added and kneaded to form a slurry. The solvent may be water or an organic solvent such as ethanol or acetone. However, when water is used as the solvent, the sodium component is eluted from the raw material powder, the pH of the slurry is increased, and the raw material powder may be aggregated. Therefore, it is preferable to use an organic solvent, and it is particularly preferable to use an anhydrous organic solvent.
　次に、得られたスラリーをＰＥＴ（ポリエチレンテレフタレート）等の基材上に塗布、乾燥することにより電極合材前駆体シートを得る。スラリーの塗布はドクターブレードやダイコータ等により行うことができる。 Next, the obtained slurry is applied on a substrate such as PET (polyethylene terephthalate) and dried to obtain an electrode mixture precursor sheet. The slurry can be applied by a doctor blade or a die coater.
　さらに、電極合材前駆体シートをプレスした後、焼成することにより、正極または負極の電極合材を得る。 Furthermore, the electrode mixture precursor sheet is pressed and then fired to obtain a positive electrode or negative electrode mixture.
　プレス方法には、一軸プレスのように一軸方向からプレスする方法や、等方圧プレスのようにあらゆる方向から均一にプレスする方法、あるいは２つのロールの間を通るロールプレス方法などが挙げられる。等方圧プレスの具体例としては、静水圧プレスや熱間等方圧プレスなどが挙げられる。なかでも、電極合材の空隙率を効率よく低減できる等方圧プレスや、簡便に行える一軸プレスが好ましい。 Examples of the pressing method include a method of pressing from one direction such as a uniaxial press, a method of pressing uniformly from all directions such as an isotropic press, or a roll pressing method passing between two rolls. Specific examples of the isotropic pressure press include a hydrostatic press and a hot isostatic press. Among these, an isotropic pressure press that can efficiently reduce the porosity of the electrode mixture and a uniaxial press that can be easily performed are preferable.
　プレス圧力は３ＭＰａ以上、１０ＭＰａ以上、特に１５ＭＰａ以上であることが好ましい。プレス圧力が低すぎると、活物質粉末と固体電解質粉末の密着性が不十分となり、放電容量が低下しやすくなる。プレス圧力の上限は特に限定されないが、現実的には５００ＭＰａ、３００ＭＰａ、１００ＭＰａ、４５ＭＰａ以下である。 The pressing pressure is preferably 3 MPa or more, 10 MPa or more, particularly 15 MPa or more. If the pressing pressure is too low, the adhesion between the active material powder and the solid electrolyte powder becomes insufficient, and the discharge capacity tends to decrease. The upper limit of the pressing pressure is not particularly limited, but is actually 500 MPa, 300 MPa, 100 MPa, or 45 MPa or less.
　なお、プレス時の温度は２５℃以上、４０℃以上、６０℃以上、特に７０℃以上であることが好ましい。温度が低すぎるとバインダーが軟化しないため電極合材の空隙率が減少しにくい。一方、温度の上限は２００℃以下、１８０℃以下、１５０℃以下、１２０℃以下が好ましい。温度が高すぎると可塑剤の蒸発やバインダーの熱分解が生じるためシート形状が維持できなくなる。 In addition, it is preferable that the temperature at the time of a press is 25 degreeC or more, 40 degreeC or more, 60 degreeC or more, especially 70 degreeC or more. If the temperature is too low, the binder does not soften, so the porosity of the electrode mixture is difficult to decrease. On the other hand, the upper limit of the temperature is preferably 200 ° C. or lower, 180 ° C. or lower, 150 ° C. or lower, and 120 ° C. or lower. If the temperature is too high, evaporation of the plasticizer and thermal decomposition of the binder occur, and the sheet shape cannot be maintained.
　焼成雰囲気としては、大気雰囲気、不活性雰囲気（Ｎ２等）、還元雰囲気（Ｈ２、ＮＨ３、ＣＯ、Ｈ２Ｓ及びＳｉＨ４等）が挙げられる。焼成温度（最高温度）は４００～９００℃、特に４２０～８００℃が好ましい。焼成温度が低すぎると、所望の活物質結晶が析出しにくくなったり、電極合材前駆体粉末が十分に焼結しにくくなる。一方、焼成温度が高すぎると、析出した活物質結晶が溶解するおそれがある。焼成における最高温度の保持時間は、１０～６００分であることが好ましく、３０～１２０分であることがより好ましい。保持時間が短すぎると、電極合材前駆体粉末の焼結が不十分になりやすい。一方、保持時間が長すぎると、活物質前駆体粉末同士が過剰に融着して粗大な粒子が形成されるため、電極活物質の比表面積が小さくなって、充放電容量が低下しやすくなる。焼成には、電気加熱炉、ロータリーキルン、マイクロ波加熱炉、高周波加熱炉等を用いることができる。 Examples of the firing atmosphere include an air atmosphere, an inert atmosphere (such as N 2 ), and a reducing atmosphere (such as H 2 , NH 3 , CO, H 2 S, and SiH 4 ). The firing temperature (maximum temperature) is preferably 400 to 900 ° C, particularly 420 to 800 ° C. If the firing temperature is too low, it becomes difficult for the desired active material crystals to precipitate, or the electrode mixture precursor powder is difficult to sinter sufficiently. On the other hand, if the firing temperature is too high, the precipitated active material crystals may be dissolved. The maximum temperature holding time in firing is preferably 10 to 600 minutes, and more preferably 30 to 120 minutes. If the holding time is too short, the electrode mixture precursor powder is likely to be insufficiently sintered. On the other hand, if the holding time is too long, the active material precursor powders are excessively fused to form coarse particles, so that the specific surface area of the electrode active material is reduced and the charge / discharge capacity is likely to be reduced. . For the firing, an electric heating furnace, a rotary kiln, a microwave heating furnace, a high-frequency heating furnace, or the like can be used.
　電極合材を積層体構造にする場合は、電極合材前駆体シートを積層して焼成する。あるいは、電極合材前駆体シート上に電極合材前駆体粉末を含むスラリーを塗布、乾燥した後、焼成しても構わない。 When the electrode mixture is made into a laminate structure, the electrode mixture precursor sheet is laminated and fired. Or you may bake, after apply | coating and drying the slurry containing an electrode mixture precursor powder on an electrode mixture precursor sheet | seat.
　なお、固体電解質シート上に電極合材前駆体粉末を含むスラリーを塗布、乾燥することにより、固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを作製した後、積層体シートをプレスした後、焼成しても構わない。このようにしてナトリウムイオン二次電池用電池を製造することにより、電極合材層と固体電解質シートとの密着性を向上させることが可能となる。あるいは、固体電解質シート上に電極合材前駆体シートを貼付して得られた積層体をプレスしても構わない。 In addition, after producing the laminated body sheet | seat by which the electrode compound precursor layer is formed on a solid electrolyte sheet by apply | coating and drying the slurry containing an electrode compound precursor powder on a solid electrolyte sheet, a laminated body After the sheet is pressed, it may be fired. Thus, by manufacturing the battery for sodium ion secondary batteries, it becomes possible to improve the adhesion between the electrode mixture layer and the solid electrolyte sheet. Or you may press the laminated body obtained by sticking an electrode compound precursor sheet | seat on a solid electrolyte sheet.
　上記積層体シートや積層体のプレス方法、圧力、温度は上記電極合材前駆体シートと同様の条件で行う。 The pressing method, pressure, and temperature of the laminate sheet and laminate are the same as those for the electrode mixture precursor sheet.
　（５）ナトリウムイオン二次電池
　ナトリウムイオン二次電池は、正極層及び負極層と、その間に挟持されてなる固体電解質層（固体電解質シート）とを有する。本発明のナトリウムイオン二次電池では、正極層または負極層として、上記の電極合材を使用する。 (5) Sodium ion secondary battery A sodium ion secondary battery has a positive electrode layer and a negative electrode layer, and a solid electrolyte layer (solid electrolyte sheet) sandwiched therebetween. In the sodium ion secondary battery of this invention, said electrode compound material is used as a positive electrode layer or a negative electrode layer.
　固体電解質層に使用する固体電解質と、電極合材に使用する固体電解質粉末は同じ物質からなることが好ましい。このようにすれば、固体電解質層と電極合材層の間での界面抵抗が小さくなり、イオン伝導性が向上しやすくなる。 The solid electrolyte used for the solid electrolyte layer and the solid electrolyte powder used for the electrode mixture are preferably made of the same material. In this way, the interface resistance between the solid electrolyte layer and the electrode mixture layer is reduced, and the ionic conductivity is easily improved.
　ナトリウムイオン二次電池において、正極と負極の容量比（負極容量／正極容量）は３．０～１．０であることが好ましく、１．７～１．２であることがより好ましい。当該容量比が小さすぎると、負極側で金属ナトリウムが析出しやすく容量が低下する傾向にある。一方、当該容量比が大きすぎると、エネルギー密度が低下する傾向にある。 In the sodium ion secondary battery, the capacity ratio between the positive electrode and the negative electrode (negative electrode capacity / positive electrode capacity) is preferably 3.0 to 1.0, and more preferably 1.7 to 1.2. If the capacity ratio is too small, metallic sodium tends to precipitate on the negative electrode side and the capacity tends to decrease. On the other hand, if the capacity ratio is too large, the energy density tends to decrease.
　以下、本発明を実施例に基づいて説明するが、本発明はこれらの実施例に限定されるものではない。 Hereinafter, the present invention will be described based on examples, but the present invention is not limited to these examples.
　表１は実施例１～５及び比較例１～２を示す。また、表２は実施例６～８及び比較例３を示す。 Table 1 shows Examples 1 to 5 and Comparative Examples 1 and 2. Table 2 shows Examples 6 to 8 and Comparative Example 3.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　（実施例１）
　（ａ）固体電解質の作製
　（ａ－１）固体電解質粉末の作製
　炭酸ナトリウム（Ｎａ２ＣＯ３）、炭酸水素ナトリウム（ＮａＨＣＯ３）、酸化マグネシウム（ＭｇＯ）、酸化アルミニウム（Ａｌ２Ｏ３）、酸化ジルコニウム（ＺｒＯ２）、酸化イットリウム（Ｙ２Ｏ３）を用いて、モル％で、Ｎａ２Ｏ　１４．２％、ＭｇＯ　５．５％、Ａｌ２Ｏ３　７５．４％、ＺｒＯ２　４．７％、Ｙ２Ｏ３　０．２％の組成となるように原料粉末を調合した。原料粉末をφ２０ｍｍの金型を用いて４０ＭＰａで一軸プレスにより成型し、１６００℃、３０分間熱処理を行うことでβ”－アルミナを得た。得られたβ”－アルミナは速やかに露点－４０℃以下の雰囲気に移し、保管した。 Example 1
(A) Production of solid electrolyte (a-1) Production of solid electrolyte powder Sodium carbonate (Na 2 CO 3 ), sodium hydrogen carbonate (NaHCO 3 ), magnesium oxide (MgO), aluminum oxide (Al 2 O 3 ), oxidation Zirconium (ZrO 2 ) and yttrium oxide (Y 2 O 3 ) are used in mol%, Na 2 O 14.2%, MgO 5.5%, Al 2 O 3 75.4%, ZrO 2 4.7. %, And Y 2 O 3 0.2%, the raw material powder was prepared. The raw material powder was molded by uniaxial pressing at 40 MPa using a φ20 mm mold and subjected to heat treatment at 1600 ° C. for 30 minutes to obtain β ″ -alumina. The obtained β ″ -alumina was rapidly dew point −40 ° C. Moved to the following atmosphere and stored.
　得られたβ”－アルミナをアルミナ乳鉢乳棒で粉砕し、目開き３００μｍのメッシュを通過させた。通過した粉末を、φ５ｍｍのＹＴＺ（イットリア安定化ジルコニア）玉石を投入したＦｒｉｔｓｃｈ社製遊星ボールミルＰ６を用いて３００ｒｐｍで３０分間粉砕し、目開き２０μｍのメッシュを通過させた。その後、空気分級機（日本ニューマチック工業株式会社製　ＭＤＳ－１型）を使用して空気分級することにより、β”－アルミナからなる固体電解質粉末（平均粒子径１．８μｍ）を得た。なお、いずれの作業も露点－４０℃以下の雰囲気で行った。 The obtained β ″ -alumina was pulverized with an alumina mortar pestle and passed through a mesh having a mesh opening of 300 μm. And then pulverized at 300 rpm for 30 minutes, and passed through a mesh with an opening of 20 μm.After that, by classifying with an air classifier (MDS-1 type, manufactured by Nippon Pneumatic Industry Co., Ltd.), β ″ − A solid electrolyte powder (average particle size 1.8 μm) made of alumina was obtained. All operations were performed in an atmosphere having a dew point of −40 ° C. or lower.
　（ａ－２）固体電解質シートの作製
　炭酸ナトリウム（Ｎａ２ＣＯ３）、炭酸水素ナトリウム（ＮａＨＣＯ３）、酸化マグネシウム（ＭｇＯ）、酸化アルミニウム（Ａｌ２Ｏ３）、酸化ジルコニウム（ＺｒＯ２）、酸化イットリウム（Ｙ２Ｏ３）を用いて、モル％で、Ｎａ２Ｏ　１４．２％、ＭｇＯ　５．５％、Ａｌ２Ｏ３　７５．４％、ＺｒＯ２　４．７％、Ｙ２Ｏ３　０．２％の組成となるように原料粉末を調合した。その後、エタノールを媒体として原料粉末を４時間湿式混合した。エタノールを蒸発させた後、バインダーとしてアクリル酸エステル系共重合体（共栄社化学製オリコックス１７００）、可塑剤としてフタル酸ベンジルブチルを用い、原料粉末：バインダー：可塑剤＝８３．５：１５：１．５（質量比）となるように秤量し、Ｎ－メチルピロリドン中に分散させ、自転・公転ミキサーで十分に撹拌してスラリー化した。 (A-2) Production of solid electrolyte sheet Sodium carbonate (Na 2 CO 3 ), sodium hydrogen carbonate (NaHCO 3 ), magnesium oxide (MgO), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), oxidation Using yttrium (Y 2 O 3 ), in mol%, Na 2 O 14.2%, MgO 5.5%, Al 2 O 3 75.4%, ZrO 2 4.7%, Y 2 O 3 0 The raw material powder was prepared to have a composition of 2%. Thereafter, the raw material powder was wet-mixed for 4 hours using ethanol as a medium. After evaporating ethanol, an acrylic acid ester copolymer (Oricox 1700 manufactured by Kyoeisha Chemical Co., Ltd.) is used as a binder, and benzylbutyl phthalate is used as a plasticizer. 0.5 (mass ratio) was weighed, dispersed in N-methylpyrrolidone, and sufficiently stirred with a rotation / revolution mixer to form a slurry.
　ＰＥＴフィルム上に、間隙３５０μｍのドクターブレードを用いて上記で得られたスラリーを塗布し、７０℃で乾燥することによりグリーンシートを得た。 On the PET film, the slurry obtained above was applied using a doctor blade with a gap of 350 μm, and dried at 70 ° C. to obtain a green sheet.
　得られたグリーンシートを、等方圧プレス装置を用いて９０℃、４０ＭＰａで５分間プレスした。プレス後のグリーンシートを１６００℃で３０分間焼成することにより厚さ１８０μｍのβ”－アルミナからなる固体電解質シートを得た。得られた固体電解質シートは速やかに露点－４０℃以下の環境に移し、保管した。 The obtained green sheet was pressed at 90 ° C. and 40 MPa for 5 minutes using an isotropic pressure press. The pressed green sheet was fired at 1600 ° C. for 30 minutes to obtain a solid electrolyte sheet made of β ″ -alumina having a thickness of 180 μm. The obtained solid electrolyte sheet was quickly transferred to an environment having a dew point of −40 ° C. or less. Stored.
　（ｂ）正極活物質前駆体粉末の作製
　表１に示す各組成となるように、原料として各種酸化物、炭酸塩原料等を用いて原料粉末を調製した。原料粉末を白金ルツボに投入し、電気炉を用いて大気中にて１２００～１５００℃で９０分間の溶融を行った。次いで、溶融ガラスを一対の回転ローラー間に流し出し、急冷しながら成形し、厚み０．１～２ｍｍのフィルム状のガラス体を得た。 (B) Preparation of positive electrode active material precursor powder Raw material powders were prepared using various oxides, carbonate raw materials and the like as raw materials so as to have each composition shown in Table 1. The raw material powder was put into a platinum crucible and melted at 1200 to 1500 ° C. for 90 minutes in the air using an electric furnace. Next, the molten glass was poured out between a pair of rotating rollers, and molded while being rapidly cooled to obtain a film-like glass body having a thickness of 0.1 to 2 mm.
　得られたフィルム状ガラスについて、φ２０ｍｍのＺｒＯ２玉石を使用したボールミル粉砕を５時間行い、目開き１２０μｍの樹脂製篩に通過させ、平均粒子径３～１５μｍのガラス粗粉末を得た。次いで、このガラス粗粉末に対し、粉砕助剤にエタノールを用い、φ３ｍｍのＺｒＯ２玉石を使用したボールミル粉砕を８０時間行うことで、平均粒子径０．７μｍのガラス粉末（正極活物質前駆体粉末）を得た。 The obtained film-like glass was subjected to ball milling using ZrO 2 boulders with a diameter of 20 mm for 5 hours and passed through a resin sieve having an opening of 120 μm to obtain a coarse glass powder having an average particle size of 3 to 15 μm. Next, this crude glass powder was subjected to ball milling using ethanol as a grinding aid and ZrO 2 boulder with a diameter of 3 mm for 80 hours, whereby a glass powder having an average particle diameter of 0.7 μm (positive electrode active material precursor powder) )
　（ｃ）電極合材層（正極合材層）の作製
　質量％で、正極活物質前駆体粉末　７２％、（ａ－１）で作製した固体電解質粉末　２５％、アセチレンブラック　３％（正極活物質前駆体粉末と固体電解質粉末の体積比は７６：２４）となるように秤量し、メノウ製の乳鉢及び乳棒を用いて約２時間混合した。得られた混合粉末１００質量部に対し、Ｎ－メチルピロリドンを２０質量部（１０質量％のポリプロピレンカーボネート（住友精化株式会社製）を含有）添加して、自転公転ミキサーを用いて十分に撹拌し、スラリー化した。なお、上記の操作はすべて露点－４０℃以下の環境で行った。 (C) Preparation of electrode mixture layer (positive electrode mixture layer) Mass%, positive electrode active material precursor powder 72%, solid electrolyte powder prepared in (a-1) 25%, acetylene black 3% (positive electrode active material) The volume ratio of the precursor powder to the solid electrolyte powder was weighed to be 76:24), and the mixture was mixed for about 2 hours using an agate mortar and pestle. 20 parts by mass of N-methylpyrrolidone (containing 10% by mass of polypropylene carbonate (manufactured by Sumitomo Seika Co., Ltd.)) is added to 100 parts by mass of the obtained mixed powder, and the mixture is sufficiently stirred using a rotation and revolution mixer. And slurried. All the above operations were performed in an environment with a dew point of −40 ° C. or lower.
　得られたスラリーを、（ａ－２）で作製した固体電解質シートの一方の表面に、１ｃｍ２の面積、１００μｍの厚さで塗布し、７０℃で３時間乾燥させた。これにより、固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを得た。積層体シートを２０ＭＰａの圧力で等方圧プレスした後、窒素ガス雰囲気中６００℃にて１時間焼成した。これにより、固体電解質シートの一方の表面に正極合材層を形成した。得られた正極合材層の断面のＳＥＭ画像を２値化することにより、空隙率を求めた。 The obtained slurry was applied to one surface of the solid electrolyte sheet prepared in (a-2) with an area of 1 cm 2 and a thickness of 100 μm, and dried at 70 ° C. for 3 hours. Thereby, the laminated body sheet by which an electrode compound-material precursor layer was formed on the solid electrolyte sheet was obtained. The laminate sheet was isostatically pressed at a pressure of 20 MPa, and then fired at 600 ° C. for 1 hour in a nitrogen gas atmosphere. As a result, a positive electrode mixture layer was formed on one surface of the solid electrolyte sheet. The porosity was determined by binarizing the SEM image of the cross section of the obtained positive electrode mixture layer.
　得られた正極合材層を透過型電子顕微鏡（ＴＥＭ）により観察した結果、一部の領域において結晶構造に相当する格子像は見られず、非晶質相の存在が確認された。 As a result of observing the obtained positive electrode mixture layer with a transmission electron microscope (TEM), a lattice image corresponding to the crystal structure was not seen in a part of the region, and the presence of an amorphous phase was confirmed.
　（ｄ）ナトリウムイオン二次電池の作製
　（ｃ）で得られた固体電解質固体電解質シートと電極合材層の積層体について、電極合材層の固体電解質シートとは反対側の表面に、スパッタ装置（サンユー電子株式会社製　ＳＣ－７０１ＡＴ）を用いて厚さ３００ｎｍの金電極からなる集電体層を形成した。その後、露点－６０℃以下のアルゴン雰囲気中にて、固体電解質シートの電極合材層とは反対側の表面に、対極となる金属ナトリウムを圧着し、コインセルの下蓋の上に載置した後、上蓋を被せてＣＲ２０３２型試験電池を作製した。 (D) Preparation of sodium ion secondary battery About the laminated body of the solid electrolyte solid electrolyte sheet and electrode mixture layer obtained in (c), a sputtering device is formed on the surface of the electrode mixture layer opposite to the solid electrolyte sheet. A current collector layer composed of a gold electrode having a thickness of 300 nm was formed using (SC-701AT manufactured by Sanyu Electronics Co., Ltd.). After that, in an argon atmosphere with a dew point of −60 ° C. or lower, metal sodium as a counter electrode is pressure-bonded to the surface opposite to the electrode mixture layer of the solid electrolyte sheet and placed on the lower lid of the coin cell. Then, a CR2032-type test battery was manufactured by covering the top cover.
　（ｅ）充放電試験
　得られた試験電池を用いて６０℃で充放電試験を行い、放電容量及び平均放電電圧を測定した。なお、充放電試験において、正極活物質を用いた電池については、充電（正極活物質からのナトリウムイオン放出）は、開回路電圧（ＯＣＶ）から５．５ＶまでＣＣ（定電流）充電により行い、放電（正極活物質へのナトリウムイオン吸蔵）は、５．５Ｖから２ＶまでＣＣ放電により行った。Ｃレートは０．０１Ｃとした。なお、放電容量は、正極合材層に含まれる正極活物質の単位質量当たりに対して放電された電気量（初回放電容量）とした。結果を表１に示す。 (E) Charge / Discharge Test A charge / discharge test was performed at 60 ° C. using the obtained test battery, and a discharge capacity and an average discharge voltage were measured. In the charge / discharge test, for the battery using the positive electrode active material, charging (sodium ion release from the positive electrode active material) is performed by CC (constant current) charging from an open circuit voltage (OCV) to 5.5 V, Discharge (sodium ion occlusion in the positive electrode active material) was performed by CC discharge from 5.5V to 2V. The C rate was 0.01C. The discharge capacity was the amount of electricity (initial discharge capacity) discharged per unit mass of the positive electrode active material contained in the positive electrode mixture layer. The results are shown in Table 1.
　（実施例２）
　固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを等方圧プレスする際のプレス圧力を４０ＭＰａとしたこと以外は、実施例１と同様にして試験電池を作製し、充放電試験を行った。結果を表１に示す。 (Example 2)
A test battery was prepared in the same manner as in Example 1 except that the pressing pressure when isostatically pressing the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was 40 MPa, A charge / discharge test was conducted. The results are shown in Table 1.
　（実施例３）
　固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートのプレス方法を一軸プレスに変更したこと以外は、実施例１と同様にして試験電池を作製し、充放電試験を行った。結果を表１に示す。 (Example 3)
A test battery was produced in the same manner as in Example 1 except that the pressing method of the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was changed to uniaxial pressing, and the charge / discharge test was performed. It was. The results are shown in Table 1.
　（比較例１）
　固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを等方圧プレスせずに焼成したこと以外は、実施例１と同様にして試験電池を作製し、充放電試験を行った。結果を表１に示す。 (Comparative Example 1)
A test battery was prepared in the same manner as in Example 1 except that the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was fired without isostatic pressing, and the charge / discharge test was performed. went. The results are shown in Table 1.
　（実施例４）
　正極活物質前駆体粉末を表１に記載の組成に変更したこと以外は、実施例１と同様にして試験電池を作製し、充放電試験を行った。結果を表１に示す。また、正極合材層の断面のＳＥＭ画像を図１に、ＳＥＭ画像を２値化したものを図２に示す。 Example 4
A test battery was prepared in the same manner as in Example 1 except that the positive electrode active material precursor powder was changed to the composition shown in Table 1, and a charge / discharge test was performed. The results are shown in Table 1. Moreover, the SEM image of the cross section of a positive electrode compound material layer is shown in FIG. 1, and what binarized the SEM image is shown in FIG.
　（実施例５）
　固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートのプレス方法を一軸プレスに変更したこと以外は、実施例４と同様にして試験電池を作製し、充放電試験を行った。結果を表１に示す。 (Example 5)
A test battery was produced in the same manner as in Example 4 except that the pressing method of the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was changed to uniaxial pressing, and the charge / discharge test was performed. It was. The results are shown in Table 1.
　（比較例２）
　固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを等方圧プレスせずに焼成したこと以外は、実施例４と同様にして試験電池を作製し、充放電試験を行った。結果を表１に示す。また、正極合材層の断面のＳＥＭ画像を図３に、ＳＥＭ画像を２値化したものを図４に示す。 (Comparative Example 2)
A test battery was prepared in the same manner as in Example 4 except that the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was fired without isostatic pressing, and the charge / discharge test was performed. went. The results are shown in Table 1. Moreover, the SEM image of the cross section of a positive electrode compound material layer is shown in FIG. 3, and what binarized the SEM image is shown in FIG.
　正極合材層を構成する材料について粉末Ｘ線回折パターンを確認したところ、実施例１～３及び比較例１では活物質結晶である空間群Ｐｎ２１ａに属する斜方晶Ｎａ４Ｎｉ３（ＰＯ４）２（Ｐ２Ｏ７）、実施例４、５及び比較例２は活物質結晶である空間群Ｐ－１に属する三斜晶系結晶Ｎａ３．１２Ｎｉ２．４４（Ｐ２Ｏ７）２の回折線が確認された。なお、いずれの正極合材層においても、使用した固体電解質粉末に由来する結晶性回折線が確認された。 When a powder X-ray diffraction pattern was confirmed for the material constituting the positive electrode mixture layer, in Examples 1 to 3 and Comparative Example 1, orthorhombic Na 4 Ni 3 (PO 4 ) belonging to the space group Pn21a which is an active material crystal. 2 (P 2 O 7 ), Examples 4, 5 and Comparative Example 2 are triclinic crystal Na 3.12 Ni 2.44 (P 2 O 7 ) 2 belonging to space group P-1 which is an active material crystal. Diffraction lines were confirmed. In any positive electrode mixture layer, crystalline diffraction lines derived from the used solid electrolyte powder were confirmed.
　（実施例６～８）
　（ａ）固体電解質の作製
　実施例１と同様にして、固体電解質粉末及び固体電解質シートを作製した。 (Examples 6 to 8)
(A) Production of solid electrolyte In the same manner as in Example 1, a solid electrolyte powder and a solid electrolyte sheet were produced.
　（ｂ）正極活物質前駆体粉末の作製
　表２に示す組成となるように原料粉末を調製し、石英ルツボを用いて１２５０℃で６０分間の溶融を行ったこと以外は、実施例１と同様にして平均粒子径０．７μｍのガラス粉末（正極活物質前駆体粉末）を得た。 (B) Preparation of positive electrode active material precursor powder The raw material powder was prepared so as to have the composition shown in Table 2, and was melted at 1250 ° C. for 60 minutes using a quartz crucible, as in Example 1. Thus, glass powder (positive electrode active material precursor powder) having an average particle diameter of 0.7 μm was obtained.
　（ｃ）電極合材層（正極合材層）の作製
　表２に記載の電極合材前駆体組成になるよう各成分を秤量し、混合した。得られた混合粉末１００質量部に対し、Ｎ－メチルピロリドンを２０質量部（１０質量％のポリプロピレンカーボネート（住友精化株式会社製）を含有）添加して、自転公転ミキサーを用いて十分に撹拌し、スラリー化した。なお、上記の操作はすべて露点－４０℃以下の環境で行った。 (C) Preparation of electrode mixture layer (positive electrode mixture layer) Each component was weighed and mixed so as to have the electrode mixture precursor composition shown in Table 2. 20 parts by mass of N-methylpyrrolidone (containing 10% by mass of polypropylene carbonate (manufactured by Sumitomo Seika Co., Ltd.)) is added to 100 parts by mass of the obtained mixed powder, and the mixture is sufficiently stirred using a rotation and revolution mixer. And slurried. All the above operations were performed in an environment with a dew point of −40 ° C. or lower.
　次に、上記スラリーを固体電解質シート上に塗布し、表２に記載の構成の電極合材前駆体層が形成されてなる積層体シートを得た。なお、固体電解質シートに近い方を１層目とし、各層の塗工厚は１００μｍとした。積層体シートを２０ＭＰａの圧力で等方圧プレスした後、窒素ガス雰囲気中５００℃にて３０分間焼成した。これにより、固体電解質シートの一方の表面に正極合材層を形成した。得られた正極合材層の断面のＳＥＭ画像を２値化することにより、空隙率を求めた。 Next, the slurry was applied on a solid electrolyte sheet to obtain a laminate sheet in which the electrode mixture precursor layer having the configuration shown in Table 2 was formed. The one close to the solid electrolyte sheet was the first layer, and the coating thickness of each layer was 100 μm. The laminate sheet was isostatically pressed at a pressure of 20 MPa, and then fired at 500 ° C. for 30 minutes in a nitrogen gas atmosphere. As a result, a positive electrode mixture layer was formed on one surface of the solid electrolyte sheet. The porosity was determined by binarizing the SEM image of the cross section of the obtained positive electrode mixture layer.
　得られた正極合材層を透過型電子顕微鏡（ＴＥＭ）により観察した結果、一部の領域において結晶構造に相当する格子像は見られず、非晶質相の存在が確認された。 As a result of observing the obtained positive electrode mixture layer with a transmission electron microscope (TEM), a lattice image corresponding to the crystal structure was not seen in a part of the region, and the presence of an amorphous phase was confirmed.
　（ｄ）ナトリウムイオン二次電池の作製
　実施例１と同様にして試験電池を作製した。 (D) Production of sodium ion secondary battery A test battery was produced in the same manner as in Example 1.
　（ｅ）充放電試験
　実施例１と同様にして充放電試験を行った。結果を表２に示す。なお、表２において、「平均電圧」は初回放電時の平均作動電圧、「エネルギー密度」は放電容量と平均電圧の積を電極合材の面積で除した値をそれぞれ意味する。 (E) Charge / Discharge Test A charge / discharge test was conducted in the same manner as in Example 1. The results are shown in Table 2. In Table 2, “average voltage” means the average operating voltage at the first discharge, and “energy density” means a value obtained by dividing the product of the discharge capacity and the average voltage by the area of the electrode mixture.
　（比較例３）
　固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを等方圧プレスせずに焼成したこと以外は、実施例６と同様にして試験電池を作製し、充放電試験を行った。結果を表１に示す。 (Comparative Example 3)
A test battery was prepared in the same manner as in Example 6 except that the laminate sheet in which the electrode mixture precursor layer was formed on the solid electrolyte sheet was fired without being isotropically pressed, and the charge / discharge test was performed. went. The results are shown in Table 1.
　実施例６～８及び比較例３の正極合材層を構成する材料について粉末Ｘ線回折パターンを確認したところ、活物質結晶である空間群Ｐ－１に属する三斜晶系結晶Ｎａ３．６４Ｃｏ２．１８（Ｐ２Ｏ７）２の回折線が確認された。なお、いずれの正極合材層においても、使用した固体電解質粉末に由来する結晶性回折線が確認された。 When a powder X-ray diffraction pattern was confirmed for the materials constituting the positive electrode mixture layers of Examples 6 to 8 and Comparative Example 3, triclinic crystal Na 3.64 belonging to space group P-1 which is an active material crystal. A diffraction line of Co 2.18 (P 2 O 7) 2 was confirmed. In any positive electrode mixture layer, crystalline diffraction lines derived from the used solid electrolyte powder were confirmed.
　（結果の考察）
　表１に示すように、固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを等方圧プレスまたは一軸プレスした実施例１～３では、電極合材の空隙率が４２％以下であり、放電容量が１０ｍＡｈ／ｇ以上であった。一方、積層体シートをプレスしなかった比較例１では、電極合材の空隙率が５８％以上であり、放電容量が０ｍＡｈ／ｇであった。 (Consideration of results)
As shown in Table 1, in Examples 1 to 3 in which a laminate sheet having an electrode mixture precursor layer formed on a solid electrolyte sheet was isotropically pressed or uniaxially pressed, the porosity of the electrode mixture was 42 %, And the discharge capacity was 10 mAh / g or more. On the other hand, in Comparative Example 1 in which the laminate sheet was not pressed, the porosity of the electrode mixture was 58% or more, and the discharge capacity was 0 mAh / g.
　また、実施例４、５と比較例２の比較においても、固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを等方圧プレスまたは一軸プレスすることにより、空隙率及び放電容量の向上が確認された。 Moreover, also in the comparison between Examples 4 and 5 and Comparative Example 2, the porosity and the laminate sheet formed by forming the electrode mixture precursor layer on the solid electrolyte sheet were isotropically pressed or uniaxially pressed. Improvement of discharge capacity was confirmed.
　さらに、実施例６～８と比較例３の比較においても、固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを等方圧プレスまたは一軸プレスすることにより、空隙率が向上し、放電容量等の特性の向上が確認された。特に、電極合材層を積層体構造にすることで、エネルギー密度を高めることができることがわかる。なお、比較例３では、電極合材前駆体の焼成後、電極合材が固体電解質シートから剥離しており、イオン伝導パスが切断状態にあった。 Further, also in the comparison between Examples 6 to 8 and Comparative Example 3, the porosity is reduced by isostatically pressing or uniaxially pressing the laminate sheet in which the electrode mixture precursor layer is formed on the solid electrolyte sheet. It was confirmed that characteristics such as discharge capacity were improved. In particular, it can be seen that the energy density can be increased by making the electrode mixture layer into a laminate structure. In Comparative Example 3, after firing the electrode mixture precursor, the electrode mixture was peeled from the solid electrolyte sheet, and the ion conduction path was in a cut state.

Claims (12)

  1. 　活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末の焼結体からなり、空隙率が４５％以下であることを特徴とするナトリウムイオン二次電池用電極合材。 A sodium ion secondary battery comprising a sintered body of an electrode mixture precursor powder containing an active material precursor powder and a sodium ion conductive solid electrolyte powder, and having a porosity of 45% or less Electrode composite material.
  2. 　活物質前駆体粉末が、（i）Ｃｒ、Ｆｅ、Ｍｎ、Ｃｏ、Ｎｉ、Ｔｉ及びＮｂからなる群より選ばれた少なくとも１種の遷移金属元素、（ii）Ｐ、Ｓｉ及びＢから選択される少なくとも１種の元素、並びに（iii）Ｏを含むことを特徴とする請求項１に記載のナトリウムイオン二次電池用電極合材。 The active material precursor powder is selected from (i) at least one transition metal element selected from the group consisting of Cr, Fe, Mn, Co, Ni, Ti and Nb, and (ii) P, Si and B The electrode mixture for sodium ion secondary batteries according to claim 1, comprising at least one element and (iii) O.
  3. 　固体電解質粉末が、Ａｌ、Ｙ、Ｚｒ、Ｓｉ及びＰから選ばれる少なくとも１種、Ｎａ、並びにＯを含有することを特徴とする請求項１または２に記載のナトリウムイオン二次電池用電極合材。 3. The electrode mixture for a sodium ion secondary battery according to claim 1, wherein the solid electrolyte powder contains at least one selected from Al, Y, Zr, Si and P, Na, and O. 4. .
  4. 　固体電解質粉末が、β－アルミナ、β”－アルミナ及びＮＡＳＩＣＯＮ型結晶から選ばれる少なくとも１種を含有することを特徴とする請求項３に記載のナトリウムイオン二次電池用電極合材。 4. The electrode mixture for a sodium ion secondary battery according to claim 3, wherein the solid electrolyte powder contains at least one selected from β-alumina, β ″ -alumina, and NASICON type crystals.
  5. 　活物質前駆体粉末及び／または固体電解質粉末の平均粒子径が０．０１～１５μｍであることを特徴とする請求項１～４のいずれかに記載のナトリウムイオン二次電池用電極合材。 5. The electrode mixture for a sodium ion secondary battery according to claim 1, wherein the active material precursor powder and / or the solid electrolyte powder has an average particle size of 0.01 to 15 μm.
  6. 　請求項１～５のいずれかに記載のナトリウムイオン二次電池用電極合材を用いたことを特徴とするナトリウムイオン二次電池。 A sodium ion secondary battery comprising the electrode composite material for a sodium ion secondary battery according to any one of claims 1 to 5.
  7. 　（ａ）活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末をスラリー化する工程、
    　（ｂ）得られたスラリーを基材上に塗布、乾燥して電極合材前駆体シートを作製する工程、及び、
    　（ｃ）電極合材前駆体シートをプレスした後、焼成する工程、
    を含むことを特徴とするナトリウムイオン二次電池用電極合材の製造方法。     (A) a step of slurrying an electrode mixture precursor powder containing an active material precursor powder and a sodium ion conductive solid electrolyte powder;
    (B) Applying and drying the obtained slurry on a substrate and drying to produce an electrode mixture precursor sheet; and
    (C) a step of firing after pressing the electrode mixture precursor sheet,
    The manufacturing method of the electrode compound material for sodium ion secondary batteries characterized by including these.
  8. 　電極合材前駆体シートを等方圧プレスまたは一軸プレスすることを特徴とする請求項７に記載のナトリウムイオン二次電池用電極合材の製造方法。 The method for producing an electrode mixture for a sodium ion secondary battery according to claim 7, wherein the electrode mixture precursor sheet is isotropically pressed or uniaxially pressed.
  9. 　電極合材前駆体シートを３ＭＰａ以上の圧力でプレスすることを特徴とする請求項７または８に記載のナトリウムイオン二次電池用電極合材の製造方法。 The method for producing an electrode mixture for sodium ion secondary batteries according to claim 7 or 8, wherein the electrode mixture precursor sheet is pressed at a pressure of 3 MPa or more.
  10. 　（ａ）活物質前駆体粉末と、ナトリウムイオン伝導性の固体電解質粉末と、を含む電極合材前駆体粉末をスラリー化する工程、
    　（ｂ）得られたスラリーを固体電解質シート上に塗布、乾燥することにより、固体電解質シート上に電極合材前駆体層が形成されてなる積層体シートを作製する工程、及び、
    　（ｃ）積層体シートをプレスした後、焼成する工程、
    を含むことを特徴とするナトリウムイオン二次電池用電池の製造方法。     (A) a step of slurrying an electrode mixture precursor powder containing an active material precursor powder and a sodium ion conductive solid electrolyte powder;
    (B) a step of producing a laminate sheet in which an electrode mixture precursor layer is formed on a solid electrolyte sheet by applying and drying the obtained slurry on a solid electrolyte sheet; and
    (C) a step of firing after pressing the laminate sheet,
    The manufacturing method of the battery for sodium ion secondary batteries characterized by including.
  11. 　積層体シートを等方圧プレスまたは一軸プレスすることを特徴とする請求項１０に記載のナトリウムイオン二次電池用電池の製造方法。 The method for producing a battery for a sodium ion secondary battery according to claim 10, wherein the laminate sheet is isostatically pressed or uniaxially pressed.
  12. 　積層体シートを３ＭＰａ以上の圧力でプレスすることを特徴とする請求項１０または１１に記載のナトリウムイオン二次電池用電池の製造方法。 The method for producing a battery for a sodium ion secondary battery according to claim 10 or 11, wherein the laminate sheet is pressed at a pressure of 3 MPa or more.
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