JP2018018578A - Solid electrolytic powder, electrode mixture material arranged by use thereof, and all-solid type sodium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide solid electrolytic powder which is superior in safety, which enables the increase in ion conduction path especially when used as an electrode mixture material and which enables the achievement of a high-capacity all-solid battery.SOLUTION: Solid electrolytic powder comprises an oxide material having sodium ion conductivity, of which the average particle diameter is 0.01-15 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solid electrolyte powder used for an electricity storage device such as a sodium ion secondary battery.

  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).

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, β-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.

  The all-solid battery as described above has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer. In general, the solid electrolyte layer is composed of a solid electrolyte powder having sodium ion conductivity. Further, the positive electrode layer and the negative electrode layer are composed of a composite material (electrode composite material) of an active material powder that occludes or releases sodium ions and electrons with charge / discharge and a solid electrolyte powder.

  In order to achieve high capacity, high output, and long life of the sodium all solid state battery, it is necessary to increase the sodium ion conductivity in the electrode layer, and the electrode mixture is required to be dense. In Patent Document 3, the contact property between the active material powder and the solid electrolyte powder is improved by using a sulfide-based solid electrolyte powder that is soft and easily deformed and press-molding the electrode mixture. Moreover, in patent document 4, the raw material powder (electrode mixture precursor) which consists of an active material precursor powder containing crystalline glass powder and a solid electrolyte powder is baked, each powder is fused, and an amorphous phase remains. It is described that a dense electrode mixture can be obtained.

JP-A-5-205741 JP 2010-15582 A JP 2014-143133 A International Publication No. 2015/087734

  The sulfide-based solid electrolyte powder used in Patent Document 3 has a problem in safety because it absorbs moisture in the atmosphere and generates hydrogen sulfide gas when exposed to the atmosphere. Although the solid electrolyte powder described in Patent Document 4 is improved in terms of safety, the electrode composite using the solid electrolyte powder has a small ion conduction path between the active material powder and the solid electrolyte powder, and the discharge capacity is small. There's a problem.

  In view of the above, the present invention provides a solid electrolyte powder that is excellent in safety, can increase the number of ion conduction paths when used as an electrode mixture, and can provide a high-capacity all-solid battery. For the purpose.

  The solid electrolyte powder of the present invention is made of an oxide material having sodium ion conductivity, and has an average particle size of 0.01 to 15 μm. As a result of the inventors' investigation, it has been found that the ion conduction path in the electrode mixture is affected by the average particle diameter of the solid electrolyte powder. Thus, it has been found that by reducing the average particle size of the solid electrolyte powder as described above, the number of ion conduction paths can be increased, and as a result, the discharge capacity can be improved. In addition, since the oxide-based solid electrolyte of the present invention is made of an oxide material, it is characterized by being stable in the atmosphere and excellent in safety.

Another form of the solid electrolyte powder of the present invention is made of an oxide material having sodium ion conductivity, and has a specific surface area of 1.5 to 200 m ² / g. By increasing the specific surface area of the solid electrolyte powder as described above, the number of ion conduction paths in the electrode mixture can be increased, and as a result, the discharge capacity can be improved.

  The solid electrolyte powder of the present invention preferably contains at least one selected from Al, Y, Zr, Si and P, Na, and O. If it does in this way, it will become easy to become a solid electrolyte powder excellent in sodium ion conductivity and safety.

  The solid electrolyte powder of the present invention preferably contains β-alumina and / or β ″ -alumina.

The solid electrolyte powder of the present invention preferably contains Al ₂ O ₃ 65 to 98%, Na ₂ O 2 to 20%, and MgO + Li ₂ O 0.3 to 15% in mol%. In this specification, “◯ + ◯ +...” Means the total amount of each component. In this case, it is not always necessary to contain each component as an essential component, and there may be a component that does not contain (0%).

  The solid electrolyte powder of the present invention is preferably for a sodium ion secondary battery.

  The electrode mixture precursor of the present invention is characterized by containing the above solid electrolyte powder and an active material precursor powder.

  The electrode mixture precursor of the present invention preferably has an average particle diameter of the active material precursor powder of 0.01 to 15 μm.

  The electrode mixture precursor of the present invention preferably has an average particle diameter of the solid electrolyte powder / an average particle diameter of the active material precursor powder of 0.5 to 25. If it does in this way, since the space | gap between active material precursor powder and solid electrolyte powder becomes small, and it becomes easy to ensure the contact area of both powder, it becomes easy to improve the ion conductivity of an electrode compound material.

  In the electrode mixture precursor of the present invention, the volume ratio of the active material precursor powder to the solid electrolyte powder is preferably 20:80 to 95: 5.

  The electrode mixture of the present invention is characterized by comprising a sintered body of the above electrode mixture precursor.

  The all-solid-state sodium ion secondary battery of this invention is characterized by using said electrode compound material.

  The solid electrolyte powder of the present invention is excellent in safety, can increase the number of ion conduction paths when used as an electrode mixture, and can provide a high-capacity all-solid battery.

It is a graph which shows the discharge curve in C rates about 0.01C about Examples 1-3 and the comparative example 1. FIG.

(1) Solid electrolyte powder The solid electrolyte powder of this invention consists of an oxide material which has sodium ion conductivity. For example, the solid electrolyte powder of the present invention 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 and β ″ -alumina. These are preferable because they are excellent in sodium ion conductivity.

The oxide material containing β-alumina or β ″ -alumina contains Al ₂ O ₃ 65 to 98%, Na ₂ O 2 to 20%, and 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 β- alumina and beta "- content _.al 2 _{O 3} is a main component of alumina 65 to 98%, and _.al 2 _{O 3} is preferably especially 70% to 95% If the amount is too small, the ion conductivity tends to decrease, whereas if the amount of Al ₂ O ₃ is too large, α-alumina having no ion conductivity remains and the ion 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%. 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 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, when it is 0.8 to 8% is preferable .MgO + Li ₂ O is too small, in the solid electrolyte α- alumina remaining tends to decrease the ionic conductivity. on the other hand, if 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 of the present invention preferably contains ZrO ₂ or Y ₂ O ₃ in addition to the above components. ZrO ₂ and Y ₂ O ₃ suppress the abnormal grain growth of β-alumina and / or β ″ -alumina during firing, and improve 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%. _Further, the content of Y 2 _{O 3} 0~5% is from 0.01 to 4%, particularly preferably from 0.02 to 3%. When ZrO ₂ or Y ₂ O ₃ is too large, beta-alumina and / or beta "- the amount of the alumina is reduced, the ion conductivity tends to decrease.

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 crystal, 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.

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.

  The average particle size of the solid electrolyte powder of the present invention is 0.01 to 15 μm, preferably 0.05 to 10 μm, and 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 gas. Moreover, since voids are easily formed, the electrode density is also likely to decrease. As a result, the discharge capacity tends to decrease.

In the present invention, the average particle diameter means D ₅₀ (volume-based average particle diameter), and refers to a value measured by a laser diffraction scattering method.

Further, from a viewpoint different from the average particle diameter, the specific surface area (BET specific surface area) of the solid electrolyte powder of the present invention is 1.5 to ²⁰⁰ m ² / g, ^{2 to} 100 m ² / g, particularly 2.5 to It is preferably 50 m 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.

  In addition, a specific surface area points out the value measured by the BET single point method which uses nitrogen as an adsorbate.

The ionic conductivity at 25 ° C. of the solid electrolyte powder of the present invention is preferably 10 ⁻⁵ S / cm or more, particularly 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 of the present invention can be produced, for example, by firing a raw material powder and subjecting it to a solid phase reaction to obtain a target product, and then pulverizing it to have a predetermined average particle diameter or specific surface area. 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.
(2) Electrode mixture The electrode mixture of the present invention is characterized by comprising a sintered body of an electrode mixture precursor containing the solid electrolyte powder and the active material precursor powder. Specifically, by firing the electrode mixture precursor, the active material precursor powder is crystallized, for example, into an active material powder, and the electrode mixture is obtained by sintering with the solid electrolyte powder.

  The average particle diameter of the active material precursor powder is preferably 0.01 to 15 μm, 0.05 to 12 μm, 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.

  The ratio of the average particle size of the solid electrolyte powder to the active material precursor powder (average particle size of the solid electrolyte powder / average particle size of the active material precursor powder) is 0.5 to 25, 0.7 to 20, particularly 1.0. It is preferably ~ 15. If the average particle size ratio is too small or too large, the gap between the active material precursor powder and the solid electrolyte powder becomes large and the contact area between the two becomes small, so that the ionic conductivity tends to decrease.

  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, and particularly preferably 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.

  In the electrode mixture that 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 intervene at the interface between the active material powder and the solid electrolyte powder, the interface resistance between the active material powder and the solid electrolyte powder tends to decrease, and the ion conduction path increases. Further, since the amorphous phase is present at the interface between the electrode mixture layer and the solid electrolyte layer, the adhesive strength between the electrode mixture layer and the solid electrolyte layer is increased. 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.

In the electrode mixture which is a sintered body of the electrode mixture precursor, the distribution density of the solid electrolyte powder calculated by the following method is 5000 / mm ² or more, 10000 / mm ² or more, particularly 20000 / mm ^2. The above is preferable. If the distribution density of the solid electrolyte powder is too small, an ionic conduction path cannot be secured and the ionic conductivity of the electrode mixture is lowered, and as a result, the discharge capacity tends to be lowered. On the other hand, the upper limit of the distribution density is not particularly limited, but in reality, it is 500,000 pieces / mm ² or less, and further 300,000 pieces / mm ² or less.

The method for obtaining the distribution density of the solid electrolyte powder in the electrode mixture is as follows. The fracture surface of the electrode mixture is observed with a scanning electron microscope (SEM), and photographs are taken at random for 10 fields of view. The number of solid electrolyte powders photographed in the photograph is measured, and the distribution density (pieces / mm ² ) is calculated from the average value. The solid electrolyte powder is confirmed using, for example, a characteristic X-ray analyzer (EDX) attached to the SEM.

  Hereinafter, the active material powder will be described in detail. 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.

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) , 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. .

The negative electrode active material powder is mol% in terms of oxide, Bi ₂ O ₃ 0 to 90%, TiO ₂ 0 to 90%, Fe ₂ O ₃ 0 to 90%, Nb ₂ O ₅ 0 to 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 Bi ions, Ti ions, Fe ions, or Nb ions as 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.

  The reason why the composition of the negative electrode active material is limited as described above will be described below. In the following description, “%” means “mol%” unless otherwise specified.

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.

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%, and particularly preferably 15 to 39%. The content of Fe ₂ O ₃ is preferably 0 to 90%, 15 to 85%, 20 to 80%, particularly preferably 25 to 75%. The content of Nb ₂ O ₅ is preferably 0 to 90%, 7 to 79%, 9 to 69%, 11 to 59%, 13 to 49%, particularly 15 to 39%. Note that 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%. 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.

_{Incidentally,} 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 preferably 20 to 35%. When the content of SiO ₂ is too large, 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 preferably 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.

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.

The negative electrode active material is represented by the general formula R _x1 R ′ _x2 MA _y O _z (R is at least one selected from Li, Na and K, R ′ is at least one selected from Mg, 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, except that the case where x1 = 0.5 and x2 = 0 and the case where x1 = 1.5 and x2 = 0 are not included) Also good. 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.

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.

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.

_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.

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 P2 ₁ / m, charging / discharging with a large current is performed. However, it is preferable because the capacity is not easily 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.

(3) All-solid sodium ion secondary battery An all-solid sodium ion secondary battery has, for example, a positive electrode layer and a negative electrode layer, and a solid electrolyte layer sandwiched therebetween. In the all-solid-state sodium ion secondary battery of this invention, 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.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example.

  Tables 1 and 2 show Examples 1 to 10 and Comparative Examples 1 and 2.

(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 promptly dew point −40 ° C. Moved to the following atmosphere and stored.

  The obtained β ″ -alumina was pulverized with an alumina mortar pestle and passed through a mesh with a mesh opening of 300 μm. And then pulverized at 300 rpm for 30 minutes (pause for 15 minutes every 15 minutes) and passed through a mesh with an opening of 20 μm, and then using an air classifier (MDS-1 type, manufactured by Nippon Pneumatic Industry Co., Ltd.) By performing air classification, a solid electrolyte powder made of β ″ -alumina was obtained. In Comparative Examples 1 and 2, solid electrolyte powder obtained by pulverizing β ″ -alumina with an alumina mortar pestle and passing through a mesh having an opening of 63 μm was used. Average particle diameter of the obtained solid electrolyte powder The BET specific surface areas are shown in Tables 1 and 2. All operations were performed in an atmosphere having a dew point of −40 ° C. or lower.

(A-2) Production of solid electrolyte layer 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. Raw material powder: binder: plasticizer = 83.5: 15: 1 0.5 (mass ratio) was weighed, dispersed in N-methylpyrrolidone, and sufficiently stirred with a rotation / revolution mixer to form a slurry.

  On the PET film, the slurry obtained above was applied using a doctor blade having a gap of 350 μm 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 layer made of β ″ -alumina having a thickness of 180 μm. The obtained solid electrolyte layer was quickly transferred to an environment having a dew point of −40 ° C. or less. Stored.

(B) Production of active material precursor powder (b-1) Production of positive electrode active material precursor powder Sodium metaphosphate (NaPO ₃ ), ferric oxide (Fe ₂ O ₃ ) and orthophosphoric acid (H ₃ PO ₄ ) Was used as a raw material, and the raw material powder was prepared so as to have a composition of Na ₂ O 40%, Fe ₂ O ₃ 20%, and P ₂ O ₅ 40% in mol%, and in air atmosphere at 1250 ° C. for 45 minutes. Melting. Then, molten glass was poured into a pair of cooling rollers, and film-like glass was produced by forming while quenching.

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) ) In Example 4, positive electrode active material precursor powder was obtained by air-classifying the above-mentioned glass coarse powder using an air classifier.

In order to confirm the active material crystal to be precipitated, 93% of the positive electrode active material precursor powder and 7% of acetylene black (SUPAL C65 manufactured by TIMCAL) were sufficiently mixed by mass%, and then a mixed gas atmosphere of nitrogen and hydrogen (nitrogen) 96 volume%, hydrogen 4 volume%) at 550 ° C. for 1 hour. When checking powder X-ray diffraction pattern for the powder after heat treatment, triclinic crystals belonging to the space group _{P-1 (Na 2 FeP 2} O 7) diffraction line derived was confirmed. Note that the powder X-ray diffraction pattern was measured using an X-ray diffractometer (RIGAKU RINT2000).

(B-2) Production of Negative Electrode Active Material Precursor Powder Sodium carbonate (Na ₂ CO ₃ ), titanium oxide (TiO ₂ ), and boric anhydride (B ₂ O ₃ ) are used as raw materials in mol% and Na ₂ O 36. %, TiO ₂ 49%, B ₂ O ₃ 15%, and the raw material powder was prepared and melted in the air atmosphere at 1300 ° C. for 1 hour. Then, molten glass was poured into a pair of cooling rollers, and film-like glass was obtained by forming while quenching.

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, the glass coarse powder was subjected to ball milling using ethanol as a grinding aid and φ3 mm ZrO ₂ boulder for 80 hours, whereby glass powder having an average particle diameter of 0.7 μm (negative electrode active material precursor powder) ) In Example 9, a negative electrode active material precursor powder was obtained by air-classifying the above glass coarse powder using an air classifier.

In order to confirm the precipitated active material crystals, the obtained negative electrode active material precursor powder was heat-treated at 800 ° C. for 1 hour in an air atmosphere. When checking powder X-ray diffraction pattern for the powder after heat treatment, monoclinic crystals belonging to the space group _{P2 1 / m (Na 2 Ti} 3 O 7) diffraction line derived was confirmed.

(C) Preparation of electrode mixture layer (c-1) Preparation of positive electrode mixture layer 72% of positive electrode active material precursor powder by mass%, 25% of solid electrolyte powder prepared in (a-1), acetylene black 3 % (The volume ratio of the positive electrode active material precursor powder to the solid electrolyte powder is 76:24), and the mixture was mixed for about 2 hours using an agate mortar and pestle. In Example 5, mass%, positive electrode active material precursor powder 56%, solid electrolyte powder 41%, acetylene black 3% (volume ratio of positive electrode active material precursor powder to solid electrolyte powder is 60:40) Weighed and mixed. 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 having a dew point of −40 ° C. or lower.

The obtained slurry was applied to one surface of the solid electrolyte layer 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. Next, it was fired at 550 ° C. for 1 hour in a mixed gas atmosphere of nitrogen and hydrogen (nitrogen 96 volume%, hydrogen 4 volume%). As a result, a positive electrode mixture layer was formed on one surface of the solid electrolyte layer. When an X-ray diffraction pattern was confirmed for the obtained positive electrode mixture layer, a triclinic crystal (Na ₂ FeP ₂ O ₇ ) belonging to the space group P-1 which is an active material crystal, and a sodium ion conductive crystal A diffraction line derived from a trigonal crystal (β ″ -alumina [(Al _10.32 Mg _0.68 O ₁₆ ) (Na _1.68 O)]) belonging to the space group R-3m is confirmed. 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 observed in some regions, and the presence of an amorphous phase was confirmed.

(C-2) Production of negative electrode composite material layer: In mass%, negative electrode active material precursor powder 72%, solid electrolyte powder produced in (a-1) 25%, acetylene black 3% (positive electrode active material precursor powder and The volume ratio of the solid electrolyte powder was measured to be 76:24), and mixed for about 2 hours using an agate mortar and pestle. In Example 10, by mass%, positive electrode active material precursor powder 56%, solid electrolyte powder 41%, acetylene black 3% (volume ratio of positive electrode active material precursor powder to solid electrolyte powder is 60:40) Weighed and mixed so that 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 having a dew point of −40 ° C. or lower.

The obtained slurry was applied to one surface of the solid electrolyte layer 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. Next, it baked at 800 degreeC in nitrogen atmosphere for 1 hour. As a result, a negative electrode mixture layer was formed on one surface of the solid electrolyte layer. When an X-ray diffraction pattern was confirmed for the obtained negative electrode mixture layer, monoclinic crystals (Na ₂ Ti ₃ O ₇ ) belonging to the space group P2 ₁ / m, which are active material crystals, and sodium ion conductivity A diffraction line derived from a trigonal crystal (β ″ -alumina [(Al _10.32 Mg _0.68 O ₁₆ ) (Na _1.68 O)]) belonging to the space group R-3m which is a crystal was confirmed. Further, 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) Production of all-solid-state battery About the laminated body of the solid electrolyte layer and the electrode mixture layer obtained in (c), a sputtering device (Sanyu Electronics Co., Ltd.) is formed on the surface of the electrode mixture layer opposite to the solid electrolyte layer. A current collector layer composed of a gold electrode having a thickness of 300 nm was formed using SC-701AT). 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 composite material layer of the solid electrolyte layer, and placed on the lower lid of the coin cell. Then, a CR2032-type test battery was manufactured by covering the top cover.

(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 4.3 V, Discharge (sodium ion occlusion in the positive electrode active material) was performed by CC discharge from 4.3 V to 2 V. On the other hand, for a battery using a negative electrode active material, charging (sodium ion occlusion in the negative electrode active material) is performed by CC charging from an open circuit voltage (OCV) to 0 V, and discharging (sodium ion release from the negative electrode active material). Was performed by CC discharge from 0V to 2V. C rate was set to 0.01C and 0.1C. The discharge capacity was the amount of electricity discharged per unit mass of the positive electrode active material contained in the positive electrode mixture layer. The results are shown in Tables 1 and 2. Moreover, about Examples 1-3 and the comparative example 1, the discharge curve in 0.01C is shown in FIG.

As is clear from Tables 1 and 2 and FIG. 1, the batteries of Examples 1 to 5 using the positive electrode active material had a solid electrolyte powder particle size of 1 to 4 μm and a BET specific surface area of 2.9 to 6.7 m. ^The discharge capacity was 50-72 mAh / g at 0.01 C and 20-33 mAh / g at 0.1 C. On the other hand, in Comparative Example 1, the average particle diameter of the solid electrolyte powder was 25 μm, and the discharge capacity was as small as 20 mAh / g at 0.01 C and 4 mAh / g at 0.1 C. In the batteries of Examples 6 to 10 using the negative electrode active material, the discharge capacity was as good as 48 to 60 mAh / g at 0.01 C and 17 to 25 mAh / g at 0.1 C, whereas in Comparative Example 2, the discharge capacity was good. The discharge capacity was as small as 16 mAh / g at 0.01 C and 4 mAh / g at 0.1 C.

Claims (12)

  A solid electrolyte powder comprising an oxide material having sodium ion conductivity and an average particle diameter of 0.01 to 15 μm. A solid electrolyte powder comprising an oxide material having sodium ion conductivity and having a specific surface area of 1.5 to 200 m ² / g.   3. The solid electrolyte powder according to claim 1, comprising at least one selected from Al, Y, Zr, Si, and P, Na, and O. 4.   The solid electrolyte powder according to claim 1, comprising β-alumina and / or β ″ -alumina. In _{mol%, Al 2 O 3 65~98%} , Na 2 O 2~20%, according to claim 1, characterized in that it contains 0.3~15% MgO + Li 2 O Solid electrolyte powder.   It is for sodium ion secondary batteries, The solid electrolyte powder as described in any one of Claims 1-5 characterized by the above-mentioned.   An electrode mixture precursor comprising the solid electrolyte powder according to any one of claims 1 to 6 and an active material precursor powder.   The electrode mixture precursor according to claim 7, wherein the active material precursor powder has an average particle size of 0.01 to 15 μm.   The electrode mixture precursor according to claim 7 or 8, wherein the average particle diameter of the solid electrolyte powder / the average particle diameter of the active material precursor powder is 0.5 to 25.   The electrode mixture precursor according to any one of claims 7 to 9, wherein the volume ratio of the active material precursor powder to the solid electrolyte powder is 20:80 to 95: 5.   It consists of the sintered compact of the electrode compound material precursor as described in any one of Claims 7-10, The electrode compound material characterized by the above-mentioned.   An all-solid sodium ion secondary battery comprising the electrode mixture according to claim 11.