Ion conductor, sheet, electrode, separator, and electricity storage device

Abstract

To provide an ion conductor in which a cubic crystal compound can be synthesized at a temperature of 1,000 °C or lower by a solid phase method, and to provide a sheet, an electrode, a separator, and a power storage device.SOLUTION: The ion conductor includes a first phase having a garnet-type crystal structure containing Li, La, Zr, and O, and a second phase containing Li, Ga, and O. The sheet, the electrode, the separator, and the electric storage device contain an ion conductor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ion conductor, a sheet, an electrode, a separator, and an electricity storage device having lithium ion conductivity. [Background technology]

[0002] Ionic conductors with garnet-type crystal structures containing Li, La, Zr, and O have been studied mainly in cubic compounds with high lithium ion conductivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2014-529327 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the synthesis of cubic compounds by the solid-phase method requires temperatures exceeding 1000°C, which is problematic.

[0005] The present invention has been made to solve this problem, and aims to provide an ionic conductor, a sheet, an electrode, a separator, and an electricity storage device that can be synthesized from a cubic compound at a temperature of 1000°C or less by a solid-phase method. [Means for solving the problem]

[0006] A first aspect to achieve this object is an ionic conductor, which includes a first phase having a garnet-type crystal structure containing Li, La, Zr, and O, and a second phase containing Li, Ga, and O.

[0007] In a second embodiment, in the first embodiment, the first phase further contains Ga and Sr.

[0008] In a third embodiment, in the second embodiment, the second phase further contains Sr.

[0009] A fourth aspect is the second or third aspect, wherein the value obtained by dividing the mole fraction of Ga by the mole fraction of Sr is less than 0.8.

[0010] A fifth aspect is the second or third aspect, wherein the value obtained by dividing the mole fraction of Ga by the mole fraction of Sr is 0.4 or less.

[0011] The sixth aspect is any one of the first to fifth aspects, further comprising at least one of Mg, Ca, and Ba.

[0012] A seventh embodiment is a sheet comprising the ion conductor of any of the first to sixth embodiments.

[0013] An eighth embodiment is an electrode comprising the ion conductor of any of the first to sixth embodiments.

[0014] A ninth embodiment is an electrode in contact with a protective layer containing the ion conductor according to any one of the first to sixth embodiments.

[0015] A tenth embodiment is a separator comprising the ion conductor of any of the first to sixth embodiments.

[0016] An eleventh embodiment is a separator, which is in contact with a protective layer containing the ion conductor according to any one of the first to sixth embodiments.

[0017] A twelfth aspect is an electricity storage device, which includes the electrode according to the eighth or ninth aspect, or the separator according to the tenth or eleventh aspect. [Effects of the Invention]

[0018] According to the ionic conductor of the present invention, the second phase containing Li, Ga, and O generates a liquid phase during compound synthesis, facilitating the diffusion of elements, and therefore, a cubic compound can be synthesized at a temperature of 1000°C or less by a solid-phase method. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a cross-sectional view of an electricity accumulation device according to a first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of an ion conductor. [Figure 3] FIG. 1 is a diagram schematically illustrating a garnet-type crystal structure. [Figure 4] FIG. 10 is a cross-sectional view of an electricity accumulation device according to a second embodiment. [Figure 5] FIG. 10 is a cross-sectional view of an electricity accumulation device according to a third embodiment. [Figure 6] 10(a) is a cross-sectional view of an insulator in the fourth embodiment, (b) is a cross-sectional view of an electrode in the fifth embodiment, and (c) is a cross-sectional view of an electrode in the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a schematic cross-sectional view of an electricity storage device 11 according to a first embodiment. The electricity storage device 11 according to this embodiment is a secondary battery that uses lithium ions as a charge carrier. The electricity storage device 11 includes, in this order, a positive electrode layer 12, a separator 15, and a negative electrode layer 16. The positive electrode layer 12, the separator 15, and the negative electrode layer 16 are housed in a case (not shown).

[0021] The positive electrode layer 12 is formed by stacking a current collecting layer 13 and an active material layer 14. The current collecting layer 13 is a conductive member. Examples of materials for the current collecting layer 13 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0022] The active material layer 14 includes an ion conductor 19 and an active material 20. In order to reduce the resistance of the active material layer 14, the active material layer 14 may contain a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0023] The active material 20 is exemplified by a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. The metal oxide containing a transition metal is exemplified by a metal oxide containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. The metal oxide containing a transition metal is exemplified by LiCoO2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4,LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Examples include O2 and LiFePO4.

[0024] Examples of sulfur-based active materials include S, TiS2, NiS, FeS2, Li2S, MoS3, and sulfur-carbon composites. Examples of organic active materials include radical compounds such as 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, and phenazine oxide.

[0025] The separator 15 separates the positive electrode layer 12 and the negative electrode layer 16, electrically insulating them from each other. The separator 15 contains an ion conductor 19 and an electrolyte (described below). The separator 15 may further contain a binder.

[0026] The negative electrode layer 16 is formed by stacking a current collecting layer 17 and an active material layer 18. The current collecting layer 17 is a conductive member. Examples of materials for the current collecting layer 17 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0027] The active material layer 18 includes an ion conductor 19 and an active material 21. To reduce the resistance of the active material layer 18, the active material layer 18 may contain a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag. The active material 21 may be Li, a Li-Al alloy, Li4Ti5O 12 Examples of the binder include graphite, In, Si, a Si—Li alloy, and SiO. As with the separator 15, the active material layers 14 and 18 may contain a binder.

[0028] The electricity storage device 11 is manufactured, for example, as follows: A solution in which a binder is dissolved in a solvent is mixed with an electrolyte solution in which a lithium salt is dissolved in a solvent and an ion conductor 19 to form a slurry. The slurry is formed into a sheet and then dried to obtain a green sheet (electrolyte sheet) for the separator 15.

[0029] An electrolyte solution in which a lithium salt is dissolved in a solvent is mixed with an ion conductor 19, and then an active material 20 is mixed with this, followed by a solution in which a binder is dissolved in a solvent, to form a slurry. The slurry is applied onto the current collecting layer 13 and then dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 12.

[0030] An electrolyte solution in which a lithium salt is dissolved in a solvent is mixed with an ion conductor 19, and then an active material 21 is mixed with this, followed by a solution in which a binder is dissolved in a solvent, to form a slurry. The slurry is applied onto the current collecting layer 17 and then dried to obtain a green sheet (negative electrode sheet) for the negative electrode layer 16.

[0031] The electrolyte sheet, positive electrode sheet, and negative electrode sheet are each cut to a predetermined shape, and then stacked in this order: positive electrode sheet, electrolyte sheet, negative electrode sheet, and then pressed together to form a single sheet. Terminals (not shown) are connected to the current collecting layers 13 and 17, respectively, and the device is sealed in a case (not shown), resulting in an electricity storage device 11 including a positive electrode layer 12, a separator 15, and a negative electrode layer 16. In this way, a sheet including ion conductor 19 can become an electrolyte sheet, a positive electrode sheet, and a negative electrode sheet by the ion conductor 10.

[0032] 2 is a schematic cross-sectional view of an ionic conductor 19. The ionic conductor 19 has lithium ion conductivity. The ionic conductor 19 includes a first phase 22 having a garnet-type crystal structure containing Li, La, Zr, and O, and a second phase 23 containing Li, Ga, and O. The second phase 23 is attached to the first phase 22.

[0033] Figure 3 is a diagram showing a typical garnet-type crystal structure. Garnet has the general formula C3A2B3O 12 In the garnet-type crystal structure, the C-site Sc is dodecahedrally coordinated with the oxygen atom Oa, the A-site Sa is octahedrally coordinated with the oxygen atom Oa, and the B-site Sb is tetrahedrally coordinated with the oxygen atom Oa. In the garnet-type crystal structure, Li can exist in the vacant space V, which is a position where the oxygen atom Oa is octahedrally coordinated. The vacant space V is, for example, the space sandwiched between the B-site Sb1 and the B-site Sb2. The Li present in the vacant space V is octahedrally coordinated with the oxygen atom Oa that forms an octahedron including the tetrahedral face Fb1 that forms the B-site Sb1 and the tetrahedral face Fb2 that forms the B-site Sb2. For example, in Li7La3Zr2O 12 In the garnet-type solid electrolyte having the composition above, La can occupy the C-site Sc, Zr can occupy the A-site Sa, and Li can occupy the B-site Sb and the vacant V.

[0034] The fact that the first phase 22 has a garnet-type crystal structure can be confirmed by powder X-ray diffraction of the ionic conductor 19. The garnet-type solid electrolyte is X-ray diffraction file No. 422259 (Li7La3Zr2O) in the CSD (Cambridge Structural Database). 12 ) has an XRD pattern similar to that of No. 422259. Various elements are substituted in garnet-type solid electrolytes. For example, Ca, Sr, Ba, etc. are substituted at the C site, Nb, Ta, Sn, Hf, etc. are substituted at the A site, and Al, Ga, etc. are substituted at the B site. The amount of lithium changes with the substitution of elements, and the arrangement, occupancy rate, and occupied sites of lithium ions within the crystal structure change, which in turn changes the ionic conductivity. The diffraction angle and intensity ratio may differ compared to No. 422259 due to the substitution of elements.

[0035] The ionic conductor 19 is typically Li7La3Zr2O 12 The ion conductor 19 may have some of its constituent elements substituted with other elements, or may have a small amount of other elements added without substituting the constituent elements. Examples of the other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La).

[0036] The ionic conductor 19 is, for example, Li 7.95 Mg 0.15 Ga 0.1 La 2.75 Sr 0.25 Zr 2.0 O 12 , Li 7.95 Ga 0.1 La 2.75 Sr 0.25 Zr 2.0 O 12 , Li 7.95 Ga 0.1 La 3.0 Zr 2.0 O 12 Examples include:

[0037] The ionic conductor 19 preferably contains at least one of Mg and element A (A is at least one element selected from the group consisting of Ca, Sr, and Ba), and the molar ratio of each element satisfies all of the following (1) to (3). The element A is preferably Sr, as it increases the ionic conductivity of the ionic conductor 19. (1) 1.33≦Li / (La+A)≦3 (2) 0≦Mg / (La+A)≦0.5 (3) 0≦A / (La+A)≦0.67

[0038] Returning to Figure 2, the ionic conductor 19 is produced by a solid-state method, in which raw material powders (solids) are mixed and sintered. Sintering initiates a reaction at the contact points between solids (solid-solid or gas-solid interface), and the reaction progresses through mass transfer at the interface, synthesizing the ionic conductor 19. The second phase 23 of the ionic conductor 19 is a solidified liquid phase that is formed during the synthesis of the ionic conductor 19. The liquid phase containing Li, Ga, and O is formed at temperatures below 1000°C during the synthesis of the ionic conductor 19, promoting mass transfer. This allows the cubic first phase 22 to be synthesized at temperatures below 1000°C by a solid-state method. Because the synthesis temperature for the cubic first phase 22 can be kept below 1000°C, the amount of Li volatilized during synthesis can be reduced, facilitating the synthesis of the ionic conductor 19 with the desired composition.

[0039] The first phase 22 and the second phase 23 can be identified by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) on a cross section (a polished surface, a surface obtained by irradiating a focused ion beam (FIB), or a surface obtained by ion milling) of the ionic conductor 19. The first phase 22 and the second phase 23 can be distinguished from each other by the difference in contrast of the secondary electron image of the SEM-EDS, and the composition of the first phase 22 and the second phase 23 can be analyzed by the SEM-EDS.

[0040] According to composition analysis by SEM-EDS, the second phase 23 contains Ga and O. The first phase 22 contains La, Zr, and O, and may further contain at least one of Ga and Sr. The mole fraction of Ga in the second phase 23 according to SEM-EDS is higher than the mole fraction of Ga in the first phase 22. This is to ensure the generation of a liquid phase during the synthesis of the ionic conductor 19 and to further ensure the ionic conductivity of the first phase 22.

[0041] According to time-of-flight secondary ion mass spectrometry (TOF-SIMS) of a cross section of the ionic conductor 19, the first phase 22 and the second phase 23 contain Li. TOF-SIMS confirmed that Li was also present in the portion of the second phase 23 where Ga was present, and therefore the second phase 23 contains Li, Ga, and O. The second phase 23 may further contain Sr. If the second phase 23 contains Li, Ga, Sr, and O, the temperature at which a liquid phase containing Li, Ga, Sr, and O is formed during the synthesis of the ionic conductor 19 can be further lowered, which is advantageous for lowering the temperature at which the ionic conductor 19 is synthesized.

[0042] When the second phase 23 contains Sr, the value obtained by dividing the mole fraction of Ga in the ionic conductor 19 by the mole fraction of Sr by SEM-EDS is preferably less than 0.8, and more preferably 0.4 or less, in order to increase the proportion of cubic compounds in the first phase 22.

[0043] In the cross section of the ionic conductor 19, the ratio of the area of ​​the second phase 23 to the area of ​​the ionic conductor 19 is preferably 1% or more and 10% or less, and more preferably 2% or more and 6% or less. This is to ensure the amount of liquid phase produced during the synthesis of the ionic conductor 19 and also to ensure the ionic conductivity of the first phase 22.

[0044] A second embodiment will be described with reference to Fig. 4. In the first embodiment, an electricity storage device 11 using an ion conductor 19 as the electrolyte was described. In the second embodiment, a case where an ion conductor 19 is used in a liquid-based lithium ion battery that uses an electrolytic solution as the electrolyte will be described. The same parts as those described in the first embodiment are given the same reference numerals, and the following description will be omitted. Fig. 4 is a cross-sectional view of an electricity storage device 24 in the second embodiment.

[0045] The electricity storage device 24 includes, in this order, a positive electrode layer 12, a separator 25, and a negative electrode layer 16. These are housed in a case (not shown). The separator 25 is made of a porous material that is durable against the active materials 20, 21 and the electrolyte solution contained in the positive electrode layer 12 and the negative electrode layer 16, and that allows lithium ions to pass through but does not have electronic conductivity. Examples of the separator 25 include nonwoven fabrics and porous films made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc. The electrolyte solution is the same as that described in the first embodiment, so its description will be omitted.

[0046] In the electricity storage device 24 of the second embodiment, the positive electrode layer 12 and the negative electrode layer 16 contain the ion conductor 19, and therefore, like the electricity storage device 11 of the first embodiment, the stability of operation is increased.

[0047] A third embodiment will be described with reference to Fig. 5. In the first and second embodiments, the positive electrode layer 12, separator 15, and negative electrode layer 16 contain an ion conductor 19. In the third embodiment, the protective layers 29 and 32 contain an ion conductor 19. The same parts as those described in the first and second embodiments are designated by the same reference numerals, and the following description will be omitted. Fig. 5 is a cross-sectional view of an electricity storage device 26 in the third embodiment.

[0048] The power storage device 26 includes, in order, a positive electrode layer 27, a separator 25, and a negative electrode layer 30. These are housed in a case (not shown). The power storage device 26 is a liquid-based lithium-ion battery that uses a non-aqueous electrolyte solution as the electrolyte.

[0049] The positive electrode layer 27 is formed by stacking the current collecting layer 13 and an active material layer 28. The active material layer 28 contains an active material 20. In order to reduce the resistance of the active material layer 28, the active material layer 28 may contain a conductive additive such as carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, or Ag.

[0050] A protective layer 29 is disposed between the separator 25 and the negative electrode layer 30. The protective layer 29 contains an ion conductor 19. The negative electrode layer 30 is formed by sequentially stacking an active material layer 31, a protective layer 32, and a current collecting layer 17. The active material layer 31 is made of, for example, Li, a Li-Al alloy, a Li-Sn alloy, a Li-Si alloy, a Li-Mg alloy, a Li-Si alloy, or a Si-Li alloy. The protective layer 32 contains the ion conductor 19. The protective layers 29 and 32 are disposed by laminating sheet-like compacts made of a slurry containing the ion conductor 19, or by applying a slurry containing the ion conductor 19 to the separator 25 or the current collecting layer 17.

[0051] Ion conductor 19, which has a garnet-type crystal structure containing Li, La, Zr, and O, is resistant to reduction by the metallic lithium of active material layer 31, and therefore protective layer 29 increases the operational stability of electricity storage device 26. Furthermore, protective layer 29 suppresses short circuits caused by dendrite growth of metallic lithium. Protective layer 32, interposed between active material layer 31 and current collecting layer 17, suppresses deterioration of current collecting layer 17.

[0052] Fourth to sixth embodiments will be described with reference to Fig. 6. Note that the same parts as those described in the first to third embodiments are given the same reference numerals and the description thereof will be omitted. Fig. 6(a) is a cross-sectional view of an insulator 33 in the fourth embodiment.

[0053] The insulator 33 includes a separator 25 and a protective layer 29 in contact with the separator 25. The separator 25 includes a first interface 34 and a second interface 35 opposite the first interface 34, and the protective layer 29 is disposed at the first interface 34 and the second interface 35. The protective layer 29 disposed on the separator 25 can reduce short circuits caused by dendritic growth of metallic lithium contained in the electricity storage device. Even if a short circuit occurs in the electricity storage device and the separator 25 attempts to thermally deform, the presence of the protective layer 29 allows the shape of the separator 25 to be maintained, thereby suppressing the occurrence of thermal runaway in the electricity storage device.

[0054] 6(b) is a cross-sectional view of an electrode 36 according to a fifth embodiment. The electrode 36 includes a positive electrode layer 12 and a protective layer 29 in contact with the active material layer 14 of the positive electrode layer 12. The electrode 36 has the protective layer 29 disposed at an interface 37 of the active material layer 14 opposite the surface on which the current collecting layer 13 is disposed. The protective layer 29 disposed at the interface 37 of the active material layer 14 can reduce dendrite growth from the negative electrode layer 16 of the electricity storage device.

[0055] 6(c) is a cross-sectional view of an electrode 38 according to a sixth embodiment. The electrode 38 includes a negative electrode layer 16 and a protective layer 29 in contact with the active material layer 18 of the negative electrode layer 16. The electrode 38 has the protective layer 29 disposed at an interface 39 opposite the surface of the active material layer 18 on which the current collecting layer 17 is disposed. The protective layer 29 disposed at the interface 39 of the active material layer 18 can reduce dendrite growth from the negative electrode layer 16 of the electricity storage device.

[0056] The insulator 33 is disposed in the electricity storage device in place of the separator 25 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. The insulator 33 may omit one of the two protective layers 29 disposed at the interfaces 34, 35 of the separator 25.

[0057] The electrode 36 is disposed in the electricity storage device in place of the positive electrode layers 12, 27 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. The electrode 38 is disposed in the electricity storage device in place of the negative electrode layers 16, 30 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. [Example]

[0058] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0059] Example 1 Li 7.95 Mg 0.15 Ga 0.1 La 2.75 Sr 0.25 Zr 2.0 O12 Li2CO3, MgO, Ga2O3, La(OH)3, SrCO3, and ZrO2 were weighed out so that the following would be prepared. Taking into account the volatilization of Li during firing, Li2CO3 was used in excess of about 15 mol% in elemental terms.

[0060] The weighed raw material powder and ethanol were placed in a nylon pot along with zirconia balls and milled and mixed for 15 hours in a ball mill at 105 rpm. The slurry was removed from the pot and dried, after which the powder that passed through a 250 μm mesh sieve was collected. 20 g of the powder was placed in a square mold with a side length of 33 mm and compressed using a hand press to obtain a compact.

[0061] The compact was placed on an MgO plate, heated to 850°C at a rate of 1°C / min in air, and fired at 850°C for 10 hours to obtain a rectangular block. The block was placed in a mortar and crushed with a pestle, and the powder that passed through a sieve with 250 μm openings was collected. This yielded the ionic conductor of Example 1. The value obtained by dividing the molar fraction of Ga by the molar fraction of Sr in the ionic conductor of Example 1 was 0.4.

[0062] Example 2 Li 7.95 Ga 0.1 La 2.75 Sr 0.25 Zr 2.0 O 12 The ionic conductor of Example 2 was obtained in the same manner as in Example 1, except that the raw material powders were weighed so that the following was prepared. The value obtained by dividing the molar fraction of Ga by the molar fraction of Sr in the ionic conductor of Example 2 was 0.4.

[0063] Example 3 Li 7.95 Ga 0.1 La 3.0 Zr 2.0 O 12 The ionic conductor of Example 3 was obtained in the same manner as in Example 1, except that the raw material powders were weighed so that the following was prepared.

[0064] (Comparative Example) Li7.95 Ga 0.1 La 3.0 Zr 2.0 O 12 The ionic conductor of the comparative example was obtained in the same manner as in Example 1, except that the raw material powders were weighed so as to prepare a powder of 1000 kJ / cm2 and the compact was fired in air by increasing the temperature at a rate of 5°C / min.

[0065] (Powder X-ray diffraction) X-ray diffraction patterns of the ionic conductors in Examples 1 to 3 and the Comparative Example were obtained by powder X-ray diffraction. As a result of comparing the X-ray diffraction patterns with the ICDD (International Center for Diffraction Data) card, the X-ray diffraction pattern in Example 1 was determined to be cubic Li7La3Zr2O 12 The X-ray diffraction pattern in the comparative example is almost identical to the ICDD card corresponding to tetragonal Li7La3Zr2O 12 It was almost identical to the corresponding ICDD card.

[0066] When the volume fraction of cubic crystals in the crystalline phase of the ionic conductors was compared based on the X-ray diffraction patterns, Examples 1 and 2 were almost the same, Example 3 was smaller than Examples 1 and 2, and the Comparative Example was even smaller than Example 3. It was confirmed that the ionic conductors of Examples 1-3 contained more cubic crystal compounds than the ionic conductor of the Comparative Example. The ionic conductors of Examples 1-3 revealed that cubic crystal compounds could be synthesized at a temperature of 850°C by the solid-phase method.

[0067] (Phase 1 and Phase 2 Identification) The ionic conductors and thermosetting resins of Examples 1 to 3 and the Comparative Example were mixed, and the mixture was heated to 80° C. to solidify the thermosetting resin, thereby preparing specimens for observation. The specimens for observation were polished and then subjected to ion milling to prepare cross sections of the ionic conductors.

[0068] The cross section of the ionic conductor was analyzed by SEM-EDS to identify the first and second phases. The first and second phases, each with different contrast, were identified in the ionic conductors of Examples 1-3. However, the ionic conductors of Comparative Examples showed no difference in contrast, and it was determined that no second phase existed.

[0069] The cross section of the ionic conductor was subjected to elemental analysis of the first and second phases using SEM-EDS and TOF-SIMS. The elements contained in the first and second phases are listed in Table 1.

[0070] [Table 1]

[0071] Comparing Example 3 with the Comparative Example in Table 1, Example 3 had a second phase containing Li, Ga, and O, while the Comparative Example did not have a second phase. It is presumed that the ionic conductor in Example 3 had a second phase containing Li, Ga, and O, which allowed the proportion of cubic compounds to be increased.

[0072] Comparing Examples 1 and 2 with Example 3, Li, Ga, Sr, and O were present in the second phase in Examples 1 and 2, but Sr was not present in the second phase in Example 3. It is presumed that the presence of a second phase containing Li, Ga, Sr, and O in the ionic conductors in Examples 1 and 2 allowed the temperature at which a liquid phase was generated during synthesis to be further lowered, thereby enabling the proportion of cubic compounds to be further increased.

[0073] (Lithium ion conductivity measurement) 0.16 g of each of the ionic conductors in Example 1 and Comparative Example was placed in a mold with an inner diameter of 10 mm, and disk-shaped samples were obtained by uniaxial molding under a pressure of 10 MPa. The lithium ion conductivity of the samples was measured by an AC impedance method (7 MHz-0.1 Hz). The lithium ion conductivity of Example 1 was 3.6 × 10 -9 S / cm, and the comparative example is 1.0 × 10 -9S / cm. That is, the lithium ion conductivity of the ionic conductor in Example 1 was about three times that of the ionic conductor in the comparative example.

[0074] It is presumed that the presence of the cubic crystal compound enabled the ionic conductor in Example 1 to have a higher lithium ion conductivity than the ionic conductor in Comparative Example. According to the Examples, it was revealed that an ionic conductor having a high lithium ion conductivity can be synthesized at a temperature of 1000°C or less by including a first phase having a garnet-type crystal structure containing Li, La, Zr, and O, and a second phase containing Li, Ga, and O.

[0075] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0076] In the embodiment, the ionic conductor 19 is a powder, but this is not necessarily limited to this. After molding the powdered ionic conductor, the sintered body can be obtained by sintering it. If a cross section of the sintered body is analyzed and the first phase 22 and the second phase 23 are confirmed, the sintered body is an ionic conductor. Therefore, the ionic conductor includes both a powder and a sintered body.

[0077] In the embodiment, the electricity storage device 11 has been described as including a positive electrode layer 12 in which an active material layer 14 is provided on one side of a current collecting layer 13, and an negative electrode layer 16 in which an active material layer 18 is provided on one side of a current collecting layer 17, but the present invention is not necessarily limited to this. For example, it is of course possible to apply each element in the embodiment to an electricity storage device including electrode layers in which an active material layer 14 and an active material layer 18 are provided on both sides of a current collecting layer 13 (so-called bipolar electrodes). If bipolar electrodes and separators 15 are alternately stacked and housed in a case (not shown), an electricity storage device with a so-called bipolar structure can be obtained.

[0078] In the embodiment, the active material layers 14, 18 and the separator 15 all contain the ion conductor 19, but this is not necessarily limited to this. The power storage device only needs to have at least one of the active material layers 14, 18 and the separator 15 contain the ion conductor 19.

[0079] In the embodiments, the power storage devices 11, 24, and 26 are described as being composed of lithium-ion batteries, but the present invention is not necessarily limited to this. It is clear that other power storage devices may include the ion conductor 19. Examples of other power storage devices include electrochemical capacitors. Examples of electrochemical capacitors include redox capacitors that utilize redox reactions and hybrid capacitors that are asymmetric cells that combine an electric double layer capacitor with the ion conductor 19.

[0080] Although not described in the embodiment, it is of course possible to dispose a protective layer 29 between the active material layer 18 and the separators 15, 25, or between the current collecting layer 17 and the active material layer 18. Disposing a protective layer 29 between the active material layer 18 and the separators 15, 25 can reduce short circuits caused by dendrites. Disposing a protective layer 29 between the current collecting layer 17 and the active material layer 18 can reduce deterioration of the current collecting layer 17. [Explanation of symbols]

[0081] 11,24,26 Energy storage devices 12 Positive electrode layer (sheet, electrode) 15 Separator (sheet) 16 Negative electrode layer (sheet, electrode) 19 Ionic Conductors 22 Phase 1 23 Phase 2 25 Separator 29,32 Protective layer

Claims

1. An ion conductor having lithium ion conductivity, a first phase having a garnet-type crystal structure containing Li, La, Zr, and O; and a second phase comprising Li, Ga, and O.

2. 2. The ionic conductor of claim 1, wherein the first phase further comprises Ga and Sr.

3. 3. The ionic conductor according to claim 2, wherein said second phase further comprises Sr.

4. 4. The ionic conductor according to claim 2, wherein the value obtained by dividing the mole fraction of Ga by the mole fraction of Sr is less than 0.

8.

5. 4. The ionic conductor according to claim 2, wherein the molar fraction of Ga divided by the molar fraction of Sr is 0.4 or less.

6. 4. The ionic conductor according to claim 1, further comprising at least one of Mg, Ca, and Ba.

7. A sheet comprising the ionic conductor according to any one of claims 1 to 3.

8. An electrode comprising the ionic conductor according to any one of claims 1 to 3.

9. An electrode in contact with a protective layer comprising the ionic conductor according to claim 1 .

10. An electricity storage device comprising the electrode according to claim 8.

11. An electricity storage device comprising the electrode according to claim 9.

12. A separator comprising the ionic conductor according to any one of claims 1 to 3.

13. A separator in contact with a protective layer comprising the ionic conductor according to claim 1 .

14. An electricity storage device comprising the separator according to claim 12.

15. An electricity storage device comprising the separator according to claim 13.

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