Solid-state electrolyte and all-solid-state battery

Abstract

A NaSICON-type solid-state electrolyte that contains Na as a conducting species, Zr, M, Si, P, and O, where M is at least one element selected from Mg, V, and Nb. The NaSICON-type solid-state electrolyte has a composition in which a molar ratio of M to Zr (M/Zr) is less than 0.2.

Claims

1. A NaSICON solid-state electrolyte comprising: Na as a conducting species; Zr; M; Si; P; and O, wherein M is at least one element selected from Mg, V, and Nb, and wherein the NaSICON solid-state electrolyte has a composition in which a molar ratio of M to Zr (M/Zr) is less than 0.2.

2. The NaSICON solid-state electrolyte according to claim 1, wherein the molar ratio of M to Zr (M/Zr) is less than 0.1.

3. The NaSICON solid-state electrolyte according to claim 1, wherein the molar ratio of M to Zr (M/Zr) is more than 0.02 and less than 0.2.

4. The NaSICON solid-state electrolyte according to claim 1, wherein the molar ratio of M to Zr (M/Zr) is more than 0.05 and less than 0.2.

5. A NaSICON solid-state electrolyte comprising: Na as a conducting species; Zr; M; Si; P; O; and Y, wherein M is at least one element selected from Mg, V, and Nb, and wherein the NaSICON solid-state electrolyte has a composition in which a molar ratio of M to Zr (M/Zr) is less than 0.2.

6. The NaSICON solid-state electrolyte according to claim 5, wherein the NaSICON solid-state electrolyte is represented by the formula Na.sub.3+x(Zr.sub.1−yY.sub.y).sub.2−zM.sub.zSi.sub.2PO.sub.12, wherein x is more than −0.2 and less than 0.8, y is more than 0 and equal to or less than 0.12, and z is more than 0 and equal to or less than 0.3.

7. The NaSICON solid-state electrolyte according to claim 5, wherein z is 0.05 to 0.3.

8. The NaSICON solid-state electrolyte according to claim 5, wherein z is 0.1 to 0.3.

9. The NaSICON solid-state electrolyte according to claim 5, wherein z is 0.1 to 0.15.

10. A NaSICON solid-state electrolyte comprising: Na as a conducting species; Zr; M; Si; P; and O, wherein M is at least one element selected from Mg, V, and Nb, wherein the NaSICON solid-state electrolyte has a composition in which a molar ratio of M to Zr (M/Zr) is less than 0.2, and wherein the NaSICON solid-state electrolyte is represented by the formula Na.sub.3+x(Zr.sub.1−yY.sub.y).sub.2−zM.sub.zSi.sub.2PO.sub.12, wherein x is more than −0.2 and less than 0.8, y is more than 0 and equal to or less than 0.12, and z is more than 0 and equal to or less than 0.3.

11. The NaSICON solid-state electrolyte according to claim 10, wherein z is 0.05 to 0.3.

12. The NaSICON solid-state electrolyte according to claim 10, wherein z is 0.1 to 0.3.

13. The NaSICON solid-state electrolyte according to claim 10, wherein z is 0.1 to 0.15.

14. An all-solid-state battery comprising: a solid-state electrolyte layer which includes the NaSICON solid-state electrolyte according to claim 1; a positive electrode joined to a first surface of the solid-state electrolyte layer; and a negative electrode joined to a second surface of the solid-state electrolyte layer.

15. The all-solid-state battery according to claim 14, wherein the molar ratio of M to Zr (M/Zr) is more than 0.02 and less than 0.2.

16. An all-solid-state battery comprising: a solid-state electrolyte layer which includes the NaSICON solid-state electrolyte according to claim 5; a positive electrode joined to a first surface of the solid-state electrolyte layer; and a negative electrode joined to a second surface of the solid-state electrolyte layer.

17. An all-solid-state battery comprising: a solid-state electrolyte layer which includes the NaSICON solid-state electrolyte according to claim 10; a positive electrode joined to a first surface of the solid-state electrolyte layer; and a negative electrode joined to a second surface of the solid-state electrolyte layer.

18. The all-solid-state battery according to claim 17, wherein z is 0.05 to 0.3.

19. The all-solid-state battery according to claim 17, wherein z is 0.1 to 0.3.

20. The all-solid-state battery according to claim 17, wherein z is 0.1 to 0.15.

Description

BRIEF EXPLANATION OF THE DRAWINGS

(1) FIG. 1 is a schematic cross-sectional view of an all-solid-state battery according to an embodiment of the present invention.

(2) FIG. 2 is a Nyquist plot of the solid-state electrolytes produced in Comparative Examples 2 and 4 and Examples 5, 6, and 9.

DETAILED DESCRIPTION OF THE INVENTION

(3) Hereinafter, an example of preferred embodiments of the present invention will be described. However, the following embodiments are merely examples. The present invention is not limited to the following embodiments at all.

(4) FIG. 1 is a schematic cross-sectional view of an all-solid-state battery 1 according to the present embodiment. As shown in FIG. 1, the battery includes a positive electrode 11, a negative electrode 12, and a solid-state electrolyte layer 13.

(5) The positive electrode 11 includes positive electrode active material particles. Examples of the positive electrode active material particles to be preferably used include sodium-containing phosphate compound particles having a NaSICON-type structure, and sodium-containing layered oxide particles. Specific examples of the sodium-containing phosphate compound having a NaSICON-type structure to be preferably used include Na.sub.3V.sub.2(PO.sub.4).sub.3. Specific examples of the sodium-containing layered oxide particles to be preferably used include NaFeO.sub.2 and NaNi.sub.1/3Co.sub.1/3Fe.sub.1/3O.sub.2. Only one kind of these positive electrode active material particles may be used, or a plurality of kinds thereof may be mixed and used.

(6) The positive electrode 11 may further include a solid-state electrolyte. The kind of solid-state electrolyte included in the positive electrode 11 is not particularly limited, and it is preferable to include the same kind of solid-state electrolyte as the solid-state electrolyte contained in the solid-state electrolyte layer 13. In this case, the adhesion strength between the solid-state electrolyte layer 13 and the positive electrode 11 can be improved.

(7) The negative electrode 12 includes negative electrode active material particles. Specific examples of the negative electrode active material particles to be preferably used include particles of a compound represented by MOx (M is at least one selected from the group consisting of Ti, Sn, and Fe, and X is equal to or more than 0.9 and equal to or less than 2.5), hardly-graphitizable carbon-sodium compound particles, sodium alloy particles, sodium-containing phosphate compound particles having a NaSICON-type structure, and lithium-containing oxide particles having a spinel-type structure. Specific examples of sodium alloys to be preferably used include Na—Sn alloys. Specific examples of the sodium-containing phosphate compound having a NaSICON-type structure to be preferably used include Na.sub.3V.sub.2(PO.sub.4).sub.3. Specific examples of the lithium-containing oxide having a spinel-type structure to be preferably used include Li.sub.4Ti.sub.5O.sub.12. Only one kind of these negative electrode active material particles may be used, or a plurality of kinds thereof may be mixed and used.

(8) The negative electrode 12 may further include a solid-state electrolyte. The kind of solid-state electrolyte included in the negative electrode 12 is not particularly limited, and it is preferable to include the same kind of solid-state electrolyte as the solid-state electrolyte contained in the solid-state electrolyte layer 13. In this case, the adhesion strength between the solid-state electrolyte layer 13 and the negative electrode 12 can be improved.

(9) The solid-state electrolyte layer 13 is disposed between the positive electrode 11 and the negative electrode 12. That is, the positive electrode 11 is disposed on one side of the solid-state electrolyte layer 13, and the negative electrode 12 is disposed on the other side thereof. Each of the positive and negative electrodes 11 and 12 is joined to the solid-state electrolyte layer 13 by sintering. In other words, the positive electrode 11, the solid-state electrolyte layer 13, and the negative electrode 12 are an integrated sintered body. The solid-state electrolyte layer 13 includes a NaSICON-type solid-state electrolyte having Na as a conducting species. More specifically, the solid-state electrolyte layer 13 contains Na, Zr, M, Si, P, and O (M is at least one element selected from the group consisting of Mg, V, and Nb), and contains a solid-state electrolyte having a composition in which a molar ratio of M to Zr (M/Zr) is less than 0.2. Thus, the solid-state electrolyte layer 13 according to the present embodiment has high ionic conductivity. Therefore, the all-solid-state battery 1 having the solid-state electrolyte layer 13 is excellent in battery characteristics such as power density. From the viewpoint of realizing higher ionic conductivity, it is preferable to use a solid-state electrolyte satisfying the condition that M/Zr is less than 0.1. However, when the molar ratio of M to Zr is too small, the effect of adding M may not be obtained in some cases. Accordingly, the molar ratio of M to Zr (M/Zr) is preferably more than 0.02, and more preferably more than 0.05.

(10) It is preferable that a solid-state electrolyte 13 further contain Y. In the case where the solid-state electrolyte 13 contains Y, the ionic conductivity of the solid-state electrolyte 13 can be further increased.

(11) For example, the solid-state electrolyte 13 is preferably represented by the formula Na.sub.3+x (Zr.sub.1−yY.sub.y).sub.2−zM.sub.zSi.sub.2PO.sub.12 (where M is at least one element selected from the group consisting of Mg, V, and Nb, x is more than −0.2 and less than 0.8, y is more than 0 and equal to or less than 0.12, and z is more than 0 and equal to or less than 0.3). In this case, as shown in the following examples, the ionic conductivity of the solid-state electrolyte 13 can be further increased.

(12) In the formula Na.sub.3+x (Zr.sub.1−yY.sub.y).sub.2−zM.sub.zSi.sub.2PO.sub.12, z is preferably 0.05 to 0.3, z is more preferably 0.1 to 0.3, and z is still more preferably 0.1 to 0.15. When z is in this range, the ionic conductivity can be further increased as shown in the following examples.

(13) Note that the compound represented by the formula Na.sub.3+x (Zr.sub.1−yY.sub.y).sub.2−zM.sub.zSi.sub.2PO.sub.12 has 12 oxygen atoms, but regarding the number of oxygen atoms contained in the compound represented by this formula, the stoichiometric ratio of O does not need to be strictly 12 from the viewpoint of maintaining the neutrality between the positive and negative charges. In the present invention, the compound represented by the formula includes compounds containing 7 mol or more and 15 mol or less of oxygen.

(14) Hereinafter, the present invention will be described in more detail based on specific examples; however, the present invention is not limited to the following examples at all, and may be modified as appropriate without changing the gist thereof.

Comparative Example 1

(15) Raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), and silicon dioxide (SiO.sub.2) were weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 1. Next, the raw material powders thus weighed, ethanol, and cobblestone (φ2 mm) were enclosed in a polyethylene pot made of polyethylene and rotated on a pot rack to mix the raw materials. Then, ethanol was removed by heating the mixed raw material on a hot plate heated to 90° C. Thereafter, the mixed raw material was fired in an air atmosphere at 1100° C. for 8 hours to remove volatile components, and thus a pre-fired product was obtained. Then, the pre-fired product, ethanol, and cobblestone (φ2 mm) were enclosed in a pot made of zirconia, and the pot was rotated in a planetary ball mill to pulverize the pre-fired product. Thereafter, the pre-fired product was placed on a hot plate at 90° C. and heated to remove the ethanol, and thus a pre-fired pulverized powder was obtained. Then, the resulting pre-fired pulverized powder was molded into a tablet having a diameter φ of 10 mm and a thickness of 500 μm to 1000 μm under a pressure of 50 kN/cm.sup.2. Then, the tablet was fired in an air atmosphere at 1100° C. to 250° C. for 10 hours to obtain a solid-state electrolyte tablet having the composition of Comparative Example 1 shown in Table 1 below.

Example 1

(16) A solid-state electrolyte tablet having the composition of Example 1 described in Table 1 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), and magnesium oxide (MgO) were weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 1.

Example 2

(17) A solid-state electrolyte tablet having the composition of Example 2 described in Table 1 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), ammonium dihydrogenphosphate (NH.sub.4H.sub.2PO.sub.4), silicon dioxide (SiO.sub.2), and vanadium oxide (V.sub.2O.sub.5) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 1.

Example 3

(18) A solid-state electrolyte tablet having the composition of Example 3 described in Table 1 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), ammonium dihydrogenphosphate (NH.sub.4H.sub.2PO.sub.4), silicon dioxide (SiO.sub.2), and niobium pentoxide (Nb.sub.2O.sub.5) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 1.

Comparative Example 2

(19) A solid-state electrolyte tablet having the composition of Comparative Example 2 described in Table 2 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), and yttrium stabilized zirconia (YSZ) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 2. FIG. 1 shows the Nyquist plot of the obtained solid-state electrolyte tablet.

Example 4

(20) A solid-state electrolyte tablet having the composition of Example 4 described in Table 2 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and magnesium oxide (MgO) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 2.

Example 5

(21) A solid-state electrolyte tablet having the composition of Example 5 described in Table 2 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and vanadium pentoxide (V.sub.2O.sub.5) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 2. FIG. 1 shows the Nyquist plot of the obtained solid-state electrolyte tablet.

Example 6

(22) A solid-state electrolyte tablet having the composition of Example 6 described in Table 2 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and niobium pentoxide (Nb.sub.2O.sub.5) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 2. FIG. 1 shows the Nyquist plot of the obtained solid-state electrolyte tablet.

Example 7

(23) A solid-state electrolyte tablet having the composition of Example 7 described in Table 3 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and magnesium oxide (MgO) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 3.

Example 8

(24) A solid-state electrolyte tablet having the composition of Example 8 described in Table 3 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and magnesium oxide (MgO) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 3.

Example 9

(25) A solid-state electrolyte tablet having the composition of Example 9 described in Table 3 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and magnesium oxide (MgO) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 3. FIG. 1 shows the Nyquist plot of the obtained solid-state electrolyte tablet.

Example 10

(26) A solid-state electrolyte tablet having the composition of Example 10 described in Table 3 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and magnesium oxide (MgO) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 3.

Comparative Example 3

(27) A solid-state electrolyte tablet having the composition of Comparative Example 3 described in Table 3 below was produced in the same manner as in Comparative Example 1 except that raw materials such as sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O), sodium carbonate (Na.sub.2CO.sub.3), zirconium oxide (ZrO.sub.2), silicon dioxide (SiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), yttrium stabilized zirconia (YSZ), and magnesium oxide (MgO) were appropriately weighed so as to have the composition for obtaining the formula satisfying the conditions shown in Table 3. FIG. 1 shows the Nyquist plot of the obtained solid-state electrolyte tablet.

(28) (Evaluation of Ionic Conductivity of Solid-State Electrolyte)

(29) The ionic conductivity of the solid-state electrolyte tablet produced in each of the Examples 1 to 10 and Comparative Examples 1 to 3 was measured in the following manner.

(30) Specifically, after a platinum (Pt) layer as a current collector layer was formed on both sides of the solid-state electrolyte tablet by sputtering, the solid-state electrolyte tablet was dried at 100° C. to remove moisture, and sealed with a 2032 type coin cell. The ionic conductivity was calculated by measuring the AC impedance with respect to the sealed cell. The AC impedance was measured using a frequency response analyzer (FRA) (manufactured by Solartron) in the frequency range of 0.1 MHz to 1 MHz with an amplitude of ±10 mV at a temperature of 25° C.

(31) TABLE-US-00001 TABLE 1 M/Zr Ionic (Molar conductivity M x y z ratio) Formula (×10.sup.−4 S/cm) Comparative Example 1 0.00 Na.sub.3Zr.sub.2Si.sub.2PO.sub.12 1.4 Example 1 Mg 0.20 0.00 0.10 0.05 Na.sub.3.20Zr.sub.1.90Mg.sub.0.10Si.sub.2PO.sub.12 4.8 Example 2 V −0.10 0.00 0.10 0.05 Na.sub.2.90Zr.sub.1.90V.sub.0.10Si.sub.2PO.sub.12 2.6 Example 3 Nb −0.10 0.00 0.10 0.05 Na.sub.2.90Zr.sub.1.90Nb.sub.0.10Si.sub.2PO.sub.12 2.9

(32) As shown in Table 1, the ionic conductivity of the solid-state electrolyte produced in each of the Examples 1 to 3 was 2.6×10.sup.−4 S/cm to 4.8×10.sup.−4 S/cm, both of which were higher than the ionic conductivity of the solid-state electrolyte produced in Comparative Example 1.

(33) TABLE-US-00002 TABLE 2 M/Zr Ionic (Molar conductivity M x y z ratio) (×10.sup.−4 S/cm) Comparative Example 2 0.12 0.06 0.00 Na.sub.3.12Zr.sub.1.88Y.sub.0.12Si.sub.2PO.sub.12 11 Example 4 Mg 0.32 0.06 0.10 0.06 Na.sub.3.32Zr.sub.1.79Y.sub.0.11Mg.sub.0.10Si.sub.2PO.sub.12 14 Example 5 V 0.02 0.06 0.10 0.06 Na.sub.3.02Zr.sub.1.79Y.sub.0.11V.sub.0.10Si.sub.2PO.sub.12 26 Example 6 Nb 0.02 0.06 0.10 0.06 Na.sub.3.02Zr.sub.1.79Y.sub.0.11Nb.sub.0.10Si.sub.2PO.sub.12 15

(34) As shown in Table 2, the ionic conductivity of the solid-state electrolyte produced in each of the Examples 4 to 6 was 1.4×10.sup.−3 S/cm to 2.6×10.sup.−3 S/cm, both of which were higher than the ionic conductivity of the solid-state electrolyte produced in Comparative Example 2.

(35) TABLE-US-00003 TABLE 3 M/Zr Ionic (Molar conductivity M x y z ratio) (×10.sup.−4 S/cm) Comparative Example 2 0.12 0.06 Na.sub.3.12Zr.sub.1.88Y.sub.0.12Si.sub.2PO.sub.12 11 Example 7 Mg 0.22 0.06 0.05 0.03 Na.sub.3.22Zr.sub.1.83Y.sub.0.12Mg.sub.0.05Si.sub.2PO.sub.12 12 Example 8 Mg 0.32 0.06 0.10 0.06 Na.sub.3.32Zr.sub.1.79Y.sub.0.11Mg.sub.0.10Si.sub.2PO.sub.12 14 Example 9 Mg 0.42 0.06 0.15 0.09 Na.sub.3.42Zr.sub.1.74Y.sub.0.11Mg.sub.0.15Si.sub.2PO.sub.12 16 Example 10 Mg 0.72 0.06 0.30 0.19 Na.sub.3.72Zr.sub.1.60Y.sub.0.10Mg.sub.0.30Si.sub.2PO.sub.12 13 Comparative Example 3 Mg 1.12 0.06 0.50 0.35 Na.sub.4.12Zr.sub.1.41Y.sub.0.09Mg.sub.0.50Si.sub.2PO.sub.12 6.3

(36) As shown in Table 3, the ionic conductivity of the solid-state electrolyte produced in each of the Examples 7 to 10 was 1.2×10.sup.−3 S/cm to 1.6×10.sup.−3 S/cm, both of which were higher than the ionic conductivity of the solid-state electrolyte produced in Comparative Example 3.

DESCRIPTION OF REFERENCE SYMBOLS

(37) 1: All-solid-state battery

(38) 11: Positive electrode

(39) 12: Negative electrode

(40) 13: Solid-state electrolyte layer