Lithium ion conductive glass ceramics

Abstract

The present invention provides a lithium ion-conductive glass ceramic which is able to be easily produced industrially, while having low grain boundary resistivity, high lithium ion conductivity and high reduction resistance. This lithium ion-conductive glass ceramic is able to be used as a solid electrolyte for an all-solid-state secondary battery and the like. The above are achieved by means of a lithium ion-conductive glass ceramic which contains, in mol% based on oxides, from 10% to 20% of an Li2O component, from 30% to 40% of a P2O5 component, from 40% to 50% of a ZrO2 component, from 0% to 4% of a Y2O3 component, from 0% to 3% of an Al2O3 component and from 0% to 2% of a GeO2 component, while comprising a crystal phase that has a rhombohedral NASICON structure, wherein the lattice constant of the a-axis of this crystal phase as identified by means of X-ray diffractometry and Rietveld analysis is 8.872 Å or more.

Description

Technical Field

[0001] The present invention relates to lithium ion conductive glass ceramics.

Background Art

[0002] In recent years, lithium ion secondary batteries with high energy density and capable of charge and discharge have been widely used in applications such as power sources for electric vehicles and power sources for mobile phone terminals. Many of the currently commercially available lithium ion secondary batteries use a liquid electrolyte (electrolyte solution) in order to have a high energy density. And as this electrolyte solution, a solution in which a lithium salt is dissolved in an aprotic organic solvent such as a carbonic ester or a cyclic ester is used.

[0003] However, in a lithium ion secondary battery using a liquid electrolyte (electrolyte solution), there is a risk that the electrolyte solution leaks. In addition, organic solvents generally used in the electrolyte solution are volatile flammable substances, and there is a problem that it is not preferable in terms of safety.

[0004] Therefore, it has been proposed to use a solid electrolyte instead of a liquid electrolyte (electrolyte solution) such as an organic solvent as the electrolyte of a lithium ion secondary battery. Furthermore, the development of all-solid-state secondary batteries in which a solid electrolyte is used as the electrolyte and all other components are also composed of solids is underway. In addition, typical characteristics required for the solid electrolyte of an all-solid-state secondary battery include lithium ion conductivity, reduction resistance, stability during firing, and stability over time.

[0005] For example, in Patent Document 1, as a solid electrolyte interposed between a positive electrode containing an active material and a negative electrode containing an active material, Li 1+x+z M x (Ge 1-y Ti y ) 2-x Si z P 3-z O 12(However, a solid electrolyte containing glass ceramics containing a crystal phase of (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, and M is one or more selected from Al and Ga)) is disclosed. Further, in Non-Patent Document 1, NASICON-type Li having high lithium ion conductivity at room temperature, used as a solid electrolyte 1.15 Y 0.15 Zr 1.85 (PO 4 ) 3 is disclosed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, since the glass ceramics described in Patent Document 1 contain Ti as a constituent component, the reducibility resistance at 25 ° C is about 2.5 V (vs. Li), and when used as a solid electrolyte, Li 4 Ti 5 O 12 and low-potential negative electrode active materials such as TiO 2 cannot be used, which is a problem.

[0009] And, the solid electrolyte described in Non-Patent Document 1 has been improved to a reducibility resistance of 1.5 V (vs. Li) or less at 25 ° C in the investigation by the present inventors, and the lithium ion conductivity at 25 ° C is also 0.7 × 10 -4 S·cm -1It has been reported to be relatively high. However, in the production of this solid electrolyte, it is necessary to use a spark plasma sintering method (SPS) in which sintering is performed while applying current and pressure at a high temperature in order to suppress grain growth, and there are significant industrial challenges. Further, since this becomes a solid electrolyte that contains almost no amorphous material (mostly crystalline phase), it is difficult to obtain glass ceramics. In addition, when this solid electrolyte is produced without using the spark plasma sintering method, grain growth is remarkable, the grain boundary resistance (resistance of ion conduction occurring at the contact interface between particles) of the obtained solid electrolyte becomes high, and the lithium ion conductivity is 1.0×10 -5 S·cm -1 or less.

[0010] Therefore, an object of the present invention is to provide a lithium ion conductive glass ceramic that can be easily produced industrially, has low grain boundary resistance, high lithium ion conductivity, and high reduction resistance, and can be used as a solid electrolyte for all-solid-state secondary batteries and the like.

Means for Solving the Problems

[0011] In order to solve the above problems, the present inventors have intensively studied, and in terms of mol% based on oxides, Li 2 O component is 10 to 20%, P 2 O 5 component is 30 to 40%, ZrO 2 component is 40 to 50%, Y 2 O 3 component is 0 to 4%, Al 2 O 3 component is 0 to 3%, GeO 2 component is 0 to 2%, contains a crystal phase having a rhombohedral NASICON-type structure, and the a-axis lattice constant of this crystal phase identified by X-ray diffraction and Rietveld analysis is 8.872 Å or more. It has been found that the lithium ion conductive glass ceramic is a glass ceramic that can be easily produced industrially, has low grain boundary resistance, high lithium ion conductivity, and high reduction resistance, and the present invention has been completed.

[0012] That is, the present invention is as follows (1) to (10). (1) In terms of mol% based on oxides, Li 2 O component is 10 to 20%, P 2 O 5 component is 30 to 40%, ZrO 2 component is 40 to 50%, Y 2 O 3 component is 0 to 4%, Al 2 O 3 component is 0 to 3%, GeO 2 component is 0 to 2%, and it contains a crystal phase with a rhombohedral NASICON-type structure, and the a-axis lattice constant of the crystal phase identified by X-ray diffraction and Rietveld analysis is 8.872 Å or more, a lithium-ion conductive glass-ceramics. (2) The lithium-ion conductive glass-ceramics according to (1), wherein the mass sum of the crystal components identified by X-ray diffraction and Rietveld analysis is less than 97% by mass based on the total mass. (3) The lithium-ion conductive glass-ceramics according to (1) or (2), wherein the crystal phase contains LiZr 2 (PO 4 ) 3 α phase and / or LiZr 2 (PO 4 ) 3 α´ phase. (4) The lithium-ion conductive glass-ceramics according to (3), wherein the mass of the LiZr 2 (PO 4 ) 3 α phase identified by X-ray diffraction and Rietveld analysis is 80% by mass or more based on the total mass. (5) The lithium-ion conductive glass-ceramics according to any one of (1) to (4), containing 0.1 to 5% of SiO 2 component in terms of mol% based on oxides. (6) The lithium-ion conductive glass-ceramics according to (5), wherein the valence of Si contained in the entire lithium-ion conductive glass-ceramics is 3.5 or more and less than 3.9. (7) The lithium-ion conductive glass ceramics according to (5) or (6), wherein in the whole lithium-ion conductive glass ceramics, the coordination number of O to contained Si is 5 or more and 7 or less. (8) The lithium-ion conductivity at 25 °C is 1.0×10 -5 S·cm -1 or more, and the lithium-ion conductive glass ceramics according to any one of (1) to (7). (9) The lithium-ion conductivity at 25 °C is 7.0×10 -5 S·cm -1 or more and the substrate having a thickness of 300 μm or less, and the lithium-ion conductive glass ceramics according to any one of (1) to (7). (10) The lithium-ion conductive glass ceramics according to (9), wherein the maximum particle diameter of the particles in the outermost shell particle layer of the substrate is 30 μm or less, and the average particle diameter of the particles is 15 μm or less.

Advantages of the Invention

[0013] According to the present invention, lithium-ion conductive glass ceramics that can be easily manufactured industrially, have low grain boundary resistance, high lithium-ion conductivity, and high reduction resistance can be obtained. And this lithium-ion conductive glass ceramics becomes a solid electrolyte having a wide potential window on the low potential side due to its high reduction resistance, so that an electrode active material with a low potential and an electrode active material with a high potential can be combined and used, and as a result, a high-voltage battery can be obtained. Therefore, it can be suitably used as a solid electrolyte for all-solid-state secondary batteries, seawater batteries, etc.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Mode for Carrying Out the Invention

[0015] The present invention will be described. The present invention is based on oxides in mol%, with Li 2 O component being 10 to 20%, P 2 O 5 component being 30 to 40%, ZrO 2 component being 40 to 50%, Y 2 O 3 component being 0 to 4%, Al 2 O 3 component being 0 to 3%, GeO 2 component being 0 to 2%, and containing a crystal phase having a rhombohedral NASICON-type structure, and the a-axis lattice constant of this crystal phase identified by X-ray diffraction and Rietveld analysis is 8.872 Å or more, which is a lithium ion conductive glass-ceramics. Hereinafter, this may also be referred to as "the glass-ceramics of the present invention".

[0016] Here, in the present invention, "glass-ceramics" is obtained by precipitating a crystal phase by heat-treating a raw material glass, and includes a crystal phase and an amorphous phase formed by the heat treatment. That is, it is a mixture of ceramics and glass. In addition, the content of each component contained in the glass-ceramics of the present invention is expressed in mol% based on oxides unless otherwise specified. The composition expressed in "mol% based on oxides" means that when oxides, double salts, metal fluorides, etc. used as raw materials of the glass-ceramics of the present invention are all decomposed into oxides when melted and changed, assuming that the total number of moles of the generated oxides is 100 mol%, it is the composition in which each component contained in the glass-ceramics of the present invention is described.

[0017] <Constituent components> First, each component constituting the glass ceramics of the present invention will be described in detail.

[0018] Li 2 The O component is an essential component for imparting lithium ion conductivity to the glass ceramics of the present invention. Therefore, the Li 2 content of the O component is 10% or more, preferably 12% or more, and more preferably 14% or more as the lower limit. On the other hand, since the chemical durability of the glass ceramics of the present invention can be enhanced and the morphological stability when used as a solid electrolyte layer or the like can be improved, the Li 2 content of the O component is 20% or less, preferably 18% or less, and more preferably 16% or less as the upper limit.

[0019] P 2 O 5 The component is an essential component necessary for forming a crystal phase having a rhombohedral NASICON-type structure in the glass ceramics of the present invention. Therefore, the P 2 O 5 content of the component is 30% or more, preferably 33% or more, and more preferably 35% or more as the lower limit. On the other hand, since the formation of other crystal phases or the like can be suppressed and the lithium ion conductivity of the formed crystal phase can be made difficult to decrease, the P 2 O 5 content of the component is 40% or less, preferably 39% or less, and more preferably 38% or less as the upper limit.

[0020] ZrO 2 The component is an essential component that can make the crystal phase having lithium ion conductivity in the glass ceramics of the present invention difficult to decompose by reduction. Therefore, the ZrO 2 content of the component is 40% or more, preferably 42% or more, and more preferably 44% or more as the lower limit. On the other hand, since it can easily form a crystal phase having a rhombohedral NASICON-type structure, the ZrO 2 content of the component is 50% or less, preferably 48% or less, and more preferably 47% or less as the upper limit.

[0021] In addition, Li in the glass ceramics of the present invention 2P to the O component 2 O 5 Molar ratio of the component (P 2 O 5 component / Li 2 O component) is more preferably 2.0 to 3.0, and also, Li 2 Molar ratio of the ZrO component to the Li 2 O component (ZrO 2 component / Li 2 O component) is more preferably 2.5 to 3.5.

[0022] Y 2 O 3 The component can adjust the lithium ion conductivity of the crystal phase in the glass ceramics of the present invention, and can also adjust the mechanical strength, size, etc. of the crystal phase. Therefore, Y 2 O 3 The content of the component is preferably 0.1%, more preferably 0.5%, still more preferably 1%, and even more preferably 1.2% as the lower limit. On the other hand, since it can suppress the formation of other crystal phases and make it difficult to reduce the lithium ion conductivity of the formed crystal phase, Y 2 O 3 The content of the component is 4% as the upper limit, more preferably 3.5%, still more preferably 3.2%, even more preferably 3%, even more preferably 2.8%, and even more preferably 2.5% as the upper limit. Also, in the glass ceramics of the present invention, the molar ratio of the Y 2 O component to the Li 2 O 3 component (Y 2 O 3 component / Li 2 O component) is more preferably 0.05 to 0.26, and even more preferably 0.05 to 0.20.

[0023] Al 2 O 3 The component is also an optional component that can adjust the lithium ion conductivity of the crystal phase in the glass ceramics of the present invention, and can adjust the mechanical strength, size, etc. of this crystal phase, similar to the Y 2 O 3 component. Therefore, Al 2O 3 The content of the component is preferably 0.1%, more preferably 0.5%, still more preferably 1%, and even more preferably 1.2% as the lower limit. Also, like the Y 2 O 3 component, it can suppress the formation of other crystal phases and the like, and it is difficult to reduce the lithium ion conductivity of the formed crystal phase. Therefore, the content of the Al 2 O 3 component is preferably 3% as the upper limit, more preferably 2.8%, and still more preferably 2.5% as the upper limit.

[0024] GeO 2 component is an optional component that promotes the crystallization of the glass ceramics of the present invention. Therefore, the content of the GeO 2 component is preferably 0.1%, more preferably 0.5%, and still more preferably 1% as the lower limit. On the other hand, like the Y 2 O 3 component and the Al 2 O 3 component, it is difficult to reduce the lithium ion conductivity of the formed crystal phase, and due to the ease of coexistence with the Zr component, etc., the content of the GeO 2 component is preferably 2% as the upper limit, and preferably 1.5% as the upper limit.

[0025] SiO 2 component increases the mechanical strength of the glass ceramics of the present invention, and is an optional component that can improve the lithium ion conductivity of the glass ceramics of the present invention by partially substituting with the P 2 O 5 component. Therefore, the content of the SiO 2 component is preferably 0.1%, more preferably 0.5%, and still more preferably 0.7% as the lower limit. On the other hand, it can easily form a desired crystal phase, and the crystals are likely to be adjacent to each other, suppressing the decrease in lithium ion conductivity. Therefore, the content of the SiO 2 component is preferably 5%, more preferably 4%, still more preferably 3%, and even more preferably 2.5% as the upper limit. In addition, Li in the glass ceramics of the present invention 2 The molar ratio of the SiO 2 component to the O 2 component (SiO 2 component / Li

[0026] The CaO component and the MgO component are optional components that can increase the lithium ion conductivity by allowing Li to be contained in the crystal phase in a large amount due to the valence balance. Therefore, the content of the CaO component and the content of the MgO component are both preferably 0.5%, more preferably 1%, and even more preferably 2% as the lower limit. On the other hand, since the decrease in the lithium ion conductivity of the glass ceramics of the present invention can be suppressed, the content of the CaO component and the content of the MgO component are both preferably 5%, more preferably 4%, and even more preferably 3% as the upper limit.

[0027] Sc 2 O 3 component and Ga 2 O 3 component are optional components that can adjust the lithium ion conductivity of the crystal phase in the glass ceramics of the present invention and can also adjust the size of the crystal phase, etc., similar to the Y 2 O 3 component and the Al 2 O 3 component. Therefore, the content of the Sc 2 O 3 component and the content of the Ga 2 O 3 component are both preferably 0.1%, more preferably 0.5%, and even more preferably 1% as the lower limit. Also, similar to the Y 2 O 3 component and the Al 2 O 3 component, since the formation of other crystal phases, etc., can be suppressed and the lithium ion conductivity of the formed crystal phase can be made difficult to decrease, the content of the Sc 2 O 3 component and the content of the Ga 2 O3 The content of each component is preferably limited to 2%, more preferably 1.5% as the upper limit.

[0028] SnO 2 The component is an optional component that promotes the crystallization of the glass ceramics of the present invention, similar to the GeO 2 component. Therefore, the content of the SnO 2 component is preferably 0.1%, more preferably 0.5%, and even more preferably 1% as the lower limit. On the other hand, since it is difficult to reduce the lithium ion conductivity of the formed crystal phase, the content of the SnO 2 component is preferably limited to 2%, more preferably 1.5% as the upper limit.

[0029] Furthermore, the glass ceramics of the present invention may contain an inorganic component containing boron (B) or fluorine (F).

[0030] On the other hand, in the glass ceramics of the present invention, it is preferable to minimize the content of titanium (Ti) (for example, less than 1%, even less than 0.1%, etc.), and it is more preferable not to contain Ti. This is because reducing the Ti component can suppress the reduction of the reduction resistance. Also, not only Ti, but also transition metal components such as niobium (Nb), vanadium (V), and nickel (Ni) are preferably minimized in the same way, and it is more preferable not to contain them.

[0031] Furthermore, in the glass ceramics of the present invention, it is preferable to minimize the content of the sulfur (S) component, and it is more preferable not to contain it. This is because reducing the S component can reduce the possibility of generating harmful gases such as hydrogen sulfide in all-solid-state secondary batteries, etc. Also, in order to avoid a decrease in lithium ion conductivity, it is preferable to minimize the content of alkali metal (Na, K, etc.) components other than Li, and it is more preferable not to contain them.

[0032] <Crystal phase etc.> Next, the composition of the crystal phase contained in the glass-ceramics of the present invention and the composition of the phases other than this crystal phase will be described in detail.

[0033] The glass-ceramics of the present invention contain the above-described respective components in predetermined amounts, and further contain a crystal phase having a rhombohedral NASICON-type structure composed of at least a part of these respective components. Note that it is preferable that all of the crystal phases contained in the glass-ceramics of the present invention have a rhombohedral NASICON-type structure, but other lithium-ion conductive crystal phases (for example, LISICON-type, perovskite-type, garnet-type, etc.) may be partially contained. Even in this case, among all of the crystal phases contained in the glass-ceramics of the present invention, the crystal phase having a rhombohedral NASICON-type structure is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0034] And, the glass-ceramics of the present invention containing the crystal phase having the above-described rhombohedral NASICON-type structure have an a-axis lattice constant of the crystal phase identified by X-ray diffraction (XRD) and Rietveld analysis of 8.872 Å or more. By the a-axis lattice constant of this crystal phase being extended to a predetermined value or more, glass-ceramics having high lithium-ion conductivity are obtained. Note that this a-axis lattice constant is more preferably 8.874 Å or more, even more preferably 8.876 Å or more, and even more preferably 8.878 Å or more. Also, the upper limit thereof is preferably 8.892 Å or less, more preferably 8.889 Å or less, and even more preferably 8.888 Å or less.

[0035] Furthermore, the glass ceramics of the present invention containing a crystal phase having the above-described rhombohedral NASICON-type structure preferably have a total mass of crystal components (components of the crystal phase) identified by X-ray diffraction (XRD) and Rietveld analysis of less than 97% by weight based on the total mass of the glass ceramics of the present invention. In other words, the mass of the components of the unspecified phase (phase other than the crystal phase) calculated from the difference between the total mass of the glass ceramics of the present invention and the total mass of the crystal components identified by X-ray diffraction (XRD) and Rietveld analysis is preferably 3% by weight or more based on the total mass of the glass ceramics of the present invention. This is because an increase in grain boundary resistance due to overgrowth of particles can be suppressed, and elongation of the a-axis lattice constant of the crystal phase can be stabilized. Note that this unspecified phase mainly includes an amorphous phase. And it is more preferable that the total mass of this crystal component is less than 95% by weight based on the total mass of the glass ceramics of the present invention, that is, it is more preferable that the mass of the components of the above-mentioned unspecified phase is 5% by weight or more. In addition, the lower limit of the total mass of this crystal component is not limited, but it is preferably 80% by weight or more, and more preferably 85% by weight or more based on the total mass of the glass ceramics of the present invention.

[0036] Note that the above-described X-ray diffraction (XRD) is measured using a powder X-ray diffractometer (D8 DISCOVER, manufactured by Bruker) with ZnO in the same mol% amount as the initial sample amount as a standard sample and using CuKα rays.

[0037] In addition, the above-described Rietveld analysis is performed using the Rietveld analysis software "Z-Rietveld code" with the XRD data measured under the above conditions.

[0038] And the crystal phase having the rhombohedral NASICON-type structure contained in the glass ceramics of the present invention has improved lithium ion conductivity at room temperature, so Li 1+x+y Y x Zr 2-x Si y P 3-y O 12Preferably contains a crystal phase of (0 ≦ x < 2, 0 ≦ y < 3), LiZr 2 (PO 4 ) 3 α-phase (high-temperature phase) and / or LiZr 2 (PO 4 ) 3 α'-phase (low-temperature phase). And the crystal phase having this rhombohedral NASICON-type structure is LiZr 2 (PO 4 ) 3 α-phase (high-temperature phase) and / or LiZr 2 (PO 4 ) 3 α'-phase (low-temperature phase), but in addition to this α-phase and α'-phase, LiZr 2 (PO 4 ) 3 may also contain other phases (β-phase, γ-phase, etc.). Note that when the a-axis lattice constant of LiZr 2 (PO 4 ) 3 α-phase is contained in an amount of 80% by mass or more, more preferably 85% by mass or more, based on the total mass of the lithium ion conductive glass ceramics of the present invention, the stability over time and the like are more excellent, so it is very suitable. Here, this α-phase and α'-phase refer to CSD numbers 97658 (α-LiZr 2 (PO 4 ) 3 ), CSD number 89456 (α'-LiZr 2 (PO 4 ) 3 ) in the Cambridge Structural Database CSD-System.

[0039] Furthermore, when the glass ceramics of the present invention contain a SiO 2 component, in the whole glass ceramics of the present invention (crystal phase and unspecified phase), it is more preferable that the valence of Si contained is 3.5 or more and less than 3.9, and further preferably 3.6 or more and 3.8 or less. This is because the stability of the lithium ion conductivity and the mechanical strength of the crystal structure are more excellent.

[0040] In addition, when the glass ceramics of the present invention contain SiO 2 components, in the entire glass ceramics of the present invention (crystalline phase and unspecified phase), it is more preferable that the coordination number of O to the contained Si is 5 or more and 7 or less, and it is even more preferable that this coordination number is 6. This is because the stability of lithium ion conductivity and the mechanical strength of the crystal structure are more excellent.

[0041] Note that the valence of Si described above is measured by X-ray absorption fine structure analysis (XAFS). In addition, the coordination number of O to the above-described Si is measured by extended X-ray absorption fine structure analysis (EXAFS).

[0042] <Form> Next, the form of the glass ceramics of the present invention will be described in detail.

[0043] The form of the glass ceramics of the present invention is not particularly limited, but when used in a solid electrolyte layer or electrode layer of an all-solid-state secondary battery, an electrode layer or partition layer (separator) of a seawater battery, etc., it is preferably a powder or a substrate. In particular, when the glass ceramics of the present invention and an electrode active material are mixed to form an electrode layer, the form of the glass ceramics of the present invention is preferably a powder.

[0044] And although the glass ceramics of the present invention have high lithium ion conductivity and high reduction resistance, when the glass ceramics of the present invention are in powder form, for example, the lithium ion conductivity at 25 °C is preferably 1.0×10 -5 S·cm -1 or more, more preferably 3.0×10 -5 S·cm -1 or more, even more preferably 6.0×10 -5 S·cm -1 or more, even more preferably 7.0×10 -5 S·cm -1The above is the case, and the reduction resistance at 25°C is preferably 1.5 V (vs. Li: potential with respect to lithium) or less, more preferably 1.0 V (vs. Li) or less. Note that when the lithium ion conductivity at 25°C described above is 1.0×10 -10 S·cm -1 less than this value, the conduction of lithium ions does not substantially occur. Also, although not limited, the lithium ion conductivity of this powder at 25°C may be 1.0×10 -2 S·cm -1 or less, and the reduction resistance at 25°C may be 0.3 V (vs. Li) or more. Further, the particles contained in this powder preferably have a maximum particle diameter of 30 μm or less and an average particle diameter of 15 μm or less.

[0045] Also, when the glass ceramics of the present invention is a substrate, it is preferably a substrate having a lithium ion conductivity of 7.0×10 -5 S·cm -1 or more and a thickness of 300 μm or less. Note that the thickness of this substrate is more preferably 200 μm or less. Further, although not limited, since it is easy to reduce the short circuit between the positive electrode and the negative electrode when a solid electrolyte layer is formed, the thickness of this substrate is preferably 0.5 μm or more. And further, since the lithium ion conductivity is further enhanced, it is very preferable that the maximum particle diameter of the particles in the outermost shell particle layer of this substrate is 30 μm or less and the average particle diameter of these particles is 15 μm or less. Also, the reduction resistance of this substrate is preferably 1.5 V (vs. Li) or less at 25°C, more preferably 1.0 V (vs. Li) or less, similar to the powder.

[0046] Here, in the present invention, the "outermost shell particle layer" of the substrate means a particle layer formed by the particles exposed on the substrate surface in the glass ceramics of the present invention which is the substrate. The same applies to forms other than the substrate. In the present invention, the "maximum particle diameter" and "average particle diameter" of the particles refer to the maximum value and the average value of all particle diameters (the length of the longest diagonal line) when measuring all the particles that are completely contained within a 24 μm × 19 μm field of view by scanning electron microscope (SEM) observation.

[0047] The glass ceramics of the present invention having the above-described configuration have a composition in which the particles are densified without coarsening during firing or the like, and have a composition in which the crystal structure is hardly changed even when furnace-cooled from a high temperature. And it can be easily manufactured industrially, and also has both high lithium ion conductivity and high reduction resistance. Due to this high reduction resistance, it becomes a solid electrolyte having a wide potential window on the low potential side. Therefore, a low potential electrode active material and a high potential electrode active material can be combined and used, and as a result, a high voltage battery can be obtained. And even when charging and discharging are performed at a high voltage, decomposition due to reduction hardly occurs, and the lithium ion conductivity is stable for a long time. Therefore, it can be suitably used as a solid electrolyte for all-solid-state secondary batteries, seawater batteries, and the like.

[0048] For example, when using the glass ceramics of the present invention as the solid electrolyte of an all-solid-state secondary battery, it can be used in at least one selected from the solid electrolyte layer and the electrode layer (positive electrode layer, negative electrode layer). In particular, since the glass ceramics of the present invention have high reduction resistance, it is preferably used in the solid electrolyte layer or the negative electrode layer. These will be described in detail below.

[0049] <Solid electrolyte layer> By mixing the glass ceramics of the present invention with an inorganic binder or the like as necessary and then sintering them, a solid electrolyte layer for an all-solid-state secondary battery can be formed. In particular, from the viewpoint of further enhancing the lithium ion conductivity, it is preferable that this solid electrolyte layer contains 80% by mass or more of the glass ceramics of the present invention, more preferably 90% by mass or more, and even more preferably consists of the glass ceramics of the present invention. And when it is a plate-shaped solid electrolyte layer, its thickness is preferably 0.5 μm or more and 300 μm or less, similar to the substrate described above.

[0050] In addition, when using an inorganic binder, it is preferable to use an inorganic binder having lithium ion conductivity. Examples of such an inorganic binder include amorphous or polycrystalline LiPO 3 、70LiPO 3 -30Li 3 PO 4 、Li 2 O-SiO 2 、Li 2 O-SiO 2 -P 2 O 5 -B 2 O 5 -BaO and the like. In particular, Li 2 O-P 2 O 5 -based glass, Li 2 O-P 2 O 5 -M 2 O 3 -based glass (including those in which P is substituted by Si, and M is Al or B), and one or more selected from those obtained by quenching LiPO 3 after melting to make it amorphous. A particularly preferred embodiment is LiPO 3When the material melted and then rapidly cooled to become amorphous has a low glass transition temperature (Tg) of about 280 °C and is also difficult to crystallize, by mixing this inorganic binder with the glass ceramics of the present invention and heating to 600 °C, a solid electrolyte layer having high lithium ion conductivity and high reduction resistance can be formed. And the content of the inorganic binder contained in the solid electrolyte layer is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less with respect to the total mass of the solid electrolyte layer.

[0051] <Electrode layer> By mixing the glass ceramics of the present invention with an electrode active material (a positive electrode active material or a negative electrode active material) and, if necessary, a conductive assistant, an inorganic binder, etc., and then sintering, an electrode layer for an all-solid-state secondary battery can be formed. In particular, this electrode layer preferably contains 20% by mass or more of the glass ceramics of the present invention, more preferably 40% by mass or more, and even more preferably 50% by mass or more. This is because it becomes easier to secure a migration path of lithium ions in the electrode layer, and thus it becomes easier to improve the charge and discharge characteristics and the battery capacity of the battery. On the other hand, in this electrode layer, the glass ceramics of the present invention is preferably 80% by mass or less, and more preferably 70% by mass or less. This is because the filling amount of the electrode active material can be secured and the battery capacity can be increased.

[0052] Note that, as the positive electrode active material, for example, NASICON-type LiV 2 (PO 4 ) 3 , olivine-type Li x J y MtPO 4 (where J is at least one selected from Al, Mg, W, Mt is one selected from Ni, Co, Fe, Mn, and x satisfies 0.9 ≦ x ≦ 1.5, y satisfies 0 ≦ y ≦ 0.2), layered oxides, or spinel-type oxides, etc. can be mentioned. In particular, LiMtO 2 and / or LiMt 2 O 4(However, Mt is preferably at least one selected from Fe, Ni, Co, and Mn). This is because the glass ceramics of the present invention are more likely to bond with the positive electrode active material, and lithium ions are more likely to be transferred between them, so that the charge-discharge characteristics of the all-solid-state secondary battery can be further improved. Specific examples of the positive electrode active material include, for example, LiCoPO 4 , LiCoO 2 , LiMn 2 O 4 and the like. Furthermore, by adding Mg as a trace component, the thermal decomposition of the positive electrode active material can be suppressed and the discharge capacity can be improved.

[0053] In addition, as the negative electrode active material, for example, at least one selected from oxides containing NASICON-type, olivine-type, and spinel-type crystals, rutile-type oxides, anatase-type oxides, or amorphous metal oxides, or metal alloys, etc. can be mentioned. Furthermore, low-potential negative electrode active materials such as Li 4 Ti 5 O 12 and TiO 2 can also be used. In particular, Li 1+x+z Al x Ti 2-x Si z P 3-z O 12 (where x satisfies 0 ≦ x ≦ 0.8 and z satisfies 0 ≦ z ≦ 0.6), Li 4 Ti 5 O 12 , TiO 2 is more preferably at least one selected from them. This is because the glass ceramics of the present invention are more likely to bond with the negative electrode active material, and lithium ions are more likely to be transferred between them, so that the charge-discharge characteristics of the all-solid-state secondary battery can be further improved. Specific examples of the negative electrode active material include, for example, Li 2 V 2 (PO 4 ) 3 , Li 3 Fe 2 (PO 4 ) 3 , LiFePO 4 , Li 4 Ti 5 O12 , SiO x (0.25 ≦ x ≦ 2), Cu 6 Sn 5 and the like can be mentioned.

[0054] The content of these electrode active materials is preferably 10% by mass or more and 50% by mass or less in the electrode layer. In particular, by setting this content to 10% by mass or more, the battery capacity of the all-solid-state secondary battery can be further increased. And more preferably, the lower limit is 20% by mass. On the other hand, by setting this content to 50% by mass or less, it is easy to ensure the ion conductivity of the electrode layer. And more preferably, the upper limit is 40% by mass, and even more preferably 30% by mass.

[0055] In addition, examples of the conductive assistant used in the electrode layer include carbon compounds such as graphite, activated carbon, and carbon nanotubes, metals composed of at least one selected from Ni, Fe, Mn, Co, Mo, Cr, Ag, and Cu, alloys thereof, metals such as titanium, stainless steel, and aluminum, and noble metals such as platinum, gold, ruthenium, and rhodium. By using such a material with high electronic conductivity as the conductive assistant, the amount of current that can be conducted through the narrow electronic conduction path formed in the electrode layer increases, so that the charge and discharge characteristics of the all-solid-state secondary battery can be improved.

[0056] The content rate of this conductive assistant is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 15% by mass or less, and most preferably 4% by mass or more and 10% by mass or less, considering the balance between the battery capacity and the electronic conductivity of the electrode layer, with respect to the entire electrode material (that is, the positive electrode active material or the negative electrode active material) contained in the electrode layer.

[0057] In addition, as the inorganic binder used for the electrode layer, the same one as the solid electrolyte layer described above can be used. Furthermore, a current collector may be provided in at least one selected from this electrode layer, that is, the positive electrode layer and the negative electrode layer. This is because it becomes easier to take out electricity through the current collector, and thus it becomes easier to charge the all-solid-state secondary battery and discharge from the all-solid-state secondary battery. As the current collector, a thin-film metal layer may be laminated or joined to the positive electrode layer and / or the negative electrode layer, or it may be obtained by laminating a metal layer or a precursor of a conductor on the raw material composition and then firing. Note that if the electron conductivity of the electrode layer itself is high, this current collector may not be provided.

[0058] An all-solid-state secondary battery can be formed using the solid electrolyte layer and the electrode layer as described above. However, for one or two of the solid electrolyte layer, the positive electrode layer, and the negative electrode layer, those known in the art may be used, and a combination of such conventionally known ones and the solid electrolyte layer or the electrode layer containing the glass ceramics of the present invention may be used. However, by making all of the solid electrolyte layer, the positive electrode layer, and the negative electrode layer contain the glass ceramics of the present invention, an all-solid-state secondary battery with higher charge-discharge characteristics can be formed.

[0059] Note that the content and composition of the glass ceramics, the electrode active material, and the conductive assistant of the present invention can be specified by scraping out the solid electrolyte layer or the electrode layer and using an energy loss analysis device or an X-ray analysis device mounted on a field emission transmission electron microscope (FE-TEM), or an X-ray analysis device mounted on a field emission scanning microscope (FE-SEM). Here, when using an X-ray analysis device, although the Li 2 O component cannot be directly analyzed, the content of the Li 2 O component can be estimated by calculating the charge from other constituent components.

[0060] <Method for manufacturing the glass ceramics of the present invention> Next, the method for manufacturing the glass ceramics of the present invention will be described in detail. The glass ceramics of the present invention can be manufactured by using general methods for manufacturing inorganic materials, such as firing, melting, and co-firing of inorganic materials, and it is a major feature that industrial manufacturing is easy. And, although not limited, it is preferable to manufacture the glass ceramics of the present invention by a solid-phase method including a mixing step of mixing a raw material composition, and a firing step of firing this mixed raw material composition or forming this raw material composition into a desired shape and then firing it to generate a desired crystal phase.

[0061] For example, as an example of the manufacturing method of the glass ceramics of the present invention, a raw material glass preparation step of dissolving and vitrifying a lithium ion conductive raw material containing an inorganic substance containing at least Li and / or P to obtain a raw material glass, and pulverizing this raw material glass and then mixing an amorphous inorganic substance containing Zr to obtain a powdery amorphous precursor, an amorphous precursor preparation step, and firing this amorphous precursor at 1100 to 1300 °C to precipitate crystals, and in terms of mol% based on oxides, Li 2 O component is 10 to 20%, P 2 O 5 component is 30 to 40%, ZrO 2 component is 40 to 50%, Y 2 O 3 component is 0 to 4%, Al 2 O 3 component is 0 to 3%, and GeO 2 component is 0 to 2%, and includes a crystal phase having a rhombohedral NASICON-type structure, and a firing step of obtaining lithium ion conductive glass ceramics in which the a-axis lattice constant of this crystal phase identified by X-ray diffraction and Rietveld analysis is 8.872 Å or more. Note that the above-mentioned firing step may be carried out in two or more stages, but from the viewpoint of manufacturing efficiency and the like, it is preferably carried out in one stage.

[0062] And in the example of the manufacturing method described above, before the firing step, a forming step of forming a powdery amorphous precursor into a substrate having a target size and thickness is included, and the formed body of the amorphous precursor obtained by this forming step is fired by the above-described firing step, whereby a substrate-shaped lithium ion conductive glass ceramic (the glass ceramic of the present invention which is a substrate) can be obtained. Even when manufacturing the glass ceramic of the present invention in a form other than a substrate, the powdery amorphous precursor may be similarly formed into a target shape by a forming step.

[0063] In addition, when manufacturing the glass ceramic of the present invention in a form other than powder, after firing the powdery amorphous precursor by the above-described firing step, a method of forming the fired powder into a target shape (a method not performing a firing step after forming, and a method of performing re-firing after forming) cannot obtain the glass ceramic of the present invention having low grain boundary resistance, high lithium ion conductivity, and high reduction resistance. The same applies to cases such as when mixing with a polymer or the like and performing sheet forming.

[0064] The embodiments described above are merely examples for facilitating the understanding of the present invention and do not limit the present invention. That is, with respect to the components and the like described above, they can be changed and improved without departing from the spirit of the present invention, and it goes without saying that equivalents thereof are included in the present invention.

[0065] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples, and various modifications are possible within the technical idea of the present invention.

Examples

[0066] <Production of a solid electrolyte (Comparative Example 1) by a solid phase method using a precursor having no amorphous composition> As raw material powders, zirconia (ZrO 2 ), lithium carbonate (Li 2 CO 3 ), ammonium dihydrogen phosphate (NH4 H 2 PO 4 ) and yttrium oxide (Y 2 O 3 ) were used, and after being formulated so as to have a stoichiometric ratio of the composition of Li 1.15 Y 0.15 Zr 1.85 P 3 O 12 , it was put into a 600 ml PP cup and mixed with a pot mill for 3 hours using a YTZ ball with an outer diameter of 10 mm. Then, the obtained mixed powder was put into a platinum pot and fired at 900 °C for 3 hours to obtain a precursor. In addition, the heating rate at this time was 300 °C / h. Furthermore, the obtained precursor was pulverized using an alumina mortar and pestle to obtain a product passing through a 106 μm mesh. Then, it was pulverized with a planetary ball mill until the cumulative 90% particle size (D90) was 1 μm or less, and dried. Then, the obtained dried powder was put into a platinum pot and fired at 1200 °C for 20 hours in a Kanthal furnace, and furnace-cooled to obtain the solid electrolyte powder of Comparative Example 1.

[0067] Also, after pulverizing the dried powder before the above firing with an agate mortar, 1.5 g of a sample passing through a 0.5 mm mesh was tablet-molded with a force of 20 kN using a mold with an outer diameter of 20 mm. The obtained molded body was placed on a platinum plate and fired at 1200 °C for 20 hours and furnace-cooled in a Kanthal furnace to obtain the solid electrolyte pellet of Comparative Example 1.

[0068] In addition, the above cumulative 90% particle size (D90) means the particle size of 90 volume% of the particles from the smaller particle size side in the particle size distribution, and was measured and calculated by a particle size distribution measuring device (manufactured by Spectris Co., Ltd., Mastersizer 3000) using the laser diffraction / scattering method in JIS R 1629 "Method for Measuring Particle Size Distribution of Fine Ceramics Raw Materials by Laser Diffraction / Scattering Method".

[0069] <Preparation of Solid Electrolytes (Examples 1 to 10) by Solid Phase Method Using Precursors Having Amorphous Compositions> An amorphous zirconium-containing inorganic raw material and a raw material glass obtained by vitrifying other raw materials were pulverized and mixed, and then dried to obtain a precursor having an amorphous composition. After firing or tableting and then firing this, the solid electrolytes of Examples 1 to 10, which are the glass ceramics of the present invention, were obtained. In the drawings described later, among these examples, Example 2 may be indicated as "LYZSP12" or "LYZSP". Hereinafter, the details of this method will be shown while following the procedure.

[0070] (Production of raw material glass) First, lithium metaphosphate (LiPO 3 ), trilithium phosphate (Li 3 PO 4 ), yttrium oxide (Y 2 O 3 ), or silicon dioxide (SiO 2 ) were prepared in the amounts shown in Table 1 or Table 2 below. Each of these prepared samples was placed in a platinum pot, melted and vitrified while stirring well at 1100 °C or higher, and cast onto a metal casting plate. The yield of the recovered raw material glass, including the raw material glass adhering to the platinum pot, was 99% or more by weight in all of Examples 1 to 10.

[0071] (Production of glass ceramic solid electrolyte) After pulverizing each of the above raw material glasses until it passed through a 106 μm mesh, for Examples 1 to 9, amorphous zirconium phosphate ((ZrO) 2 (HPO 4 ) 2 ) was used in the amounts shown in Table 1 below, and for Example 10, yttrium oxide (Y 2 O 3 ) and amorphous zirconium phosphate ((ZrO) 2 (HPO 4 ) 2( ) and were added in the amounts shown in Table 2 below, and pulverized using a planetary ball mill with 1-propanol as the dispersion medium. The pulverization media at this time were YTZ beads (manufactured by Nikkato Corporation) with an outer diameter of 2 mm. Then, the pulverized slurry was dried, and this dried powder was put into a platinum pot as an amorphous precursor, and fired at 1200 °C for 20 hours and furnace-cooled in a Kanthal furnace to obtain the solid electrolyte powders of Examples 1 to 10. Also, after each dried powder before the above firing was pulverized in an agate mortar, 1.5 g of the sample that passed through a 0.5 mm mesh was tableted with a force of 20 kN using a mold with an outer diameter of 20 mm. The obtained compact was placed on a platinum plate, fired at 1200 °C for 20 hours and furnace-cooled in a Kanthal furnace to also obtain the solid electrolyte pellets of Examples 1 to 10.

[0072]

Table 1

[0073]

Table 2

[0074] <Density and Lithium Ion Conductivity Measurement> The solid electrolyte pellets of Comparative Example 1, Example 1, and Example 2 were polished on the surface using #800 and #2000 waterproof abrasive papers and 1-propanol, and then the diameter, thickness, and weight were measured using a vernier caliper, micrometer, and electronic balance, respectively, to calculate the density. The results are shown in Table 3 below.

[0075] Furthermore, a gold electrode was formed on both sides of each solid electrolyte pellet as a blocking electrode using a magnetron sputtering apparatus (manufactured by Sunyu Electronics Co., Ltd., SC-701HMC). Then, impedance measurement was performed at 25 °C under the conditions of a frequency of 0.1 Hz to 7 MHz, an amplitude voltage of 10 mV, and an open circuit voltage using an electrochemical evaluation apparatus (manufactured by BioLogic Science Instruments, SP300), and the lithium ion conductivity was calculated. The results are also shown in Table 3 below. For reference, the Cole-Cole Plot obtained by the impedance measurement of Example 2 is shown in FIG. 1. The above-mentioned lithium ion conductivity was calculated based on the resistance at the inflection point on the low frequency side (the part indicated by the arrow in FIG. 1 in Example 2), the thickness, and the electrode area. It was shown that the solid electrolytes of Example 1 and Example 2 have a lithium ion conductivity that is one order or more higher than that of Comparative Example 1.

[0076]

Table 3

[0077] <Powder X-ray Diffraction and Rietveld Analysis> Powder X-ray diffraction and Rietveld analysis were performed to confirm the crystal structure of the solid electrolyte. First, after pulverizing the solid electrolyte powders of Comparative Example 1, Example 1, and Example 2 in an alumina mortar, 1 g of the pulverized sample and 0.1 g of zinc oxide (ZnO, manufactured by Kojundo Chemical Laboratory Co., Ltd.) as a reference were added and mixed for 5 minutes using an agate mortar and pestle, and powder X-ray diffraction measurement was performed. For the powder X-ray diffraction measurement, D8 DISCOVER manufactured by Bruker was used, and for the weighing, an electronic balance that can weigh up to 0.1 mg units was used, and weighing was performed while removing static electricity using an ionizer so that there was no weight change before and after the measurement. For ZnO, calibration was performed using α-Al 2 O 3 (STANDARD REFERANCE MATERIAL 674, manufactured by US Department of Commerce National Bureau of Standards). For the calibration of ZnO, 0.181 g of ZnO and the aforementioned α-Al 2 O3 0.122 g was mixed using an agate mortar, and this was carried out by powder X-ray diffraction measurement in the same manner as described above.

[0078] Also, the Rietveld analysis was performed by analyzing the above-described powder X-ray diffraction measurement results with the profile function "Split Pseudo Voigt function" using the Rietveld analysis software "Z-Rietveld code". The initial parameter values of the crystal structure were α-phase (LiZr 2 (PО 4 ) 3 α) with CSD number 97658, ZnO with 26170, α'-phase (LiZr 2 (PО 4 ) 3 α') with 89456, YPO 4 with 201131, and ZrO 2 with 80046. Also, the space group was fixed as it was for all phases, and the lattice constants were made variable for all phases to all values allowed by the space group.

[0079] The results of this Rietveld analysis are shown in Table 4 below. Also, the structural parameters of the α-phase of Comparative Example 1 obtained by this Rietveld analysis are shown in Table 5 below, the structural parameters of the α-phase of Example 1 are shown in Table 6 below, and the structural parameters of the α-phase of Example 2 are shown in Table 7 below. For phases other than the crystal phase (mainly unidentified phases and amorphous phases), they were calculated by the following calculation formula.

[0080] (Calculation formula for phases other than the crystal phase) Mass ratio of phases other than the crystal phase (normalized by ZnO) = (mass ratio of the evaluation sample with mixed ZnO as 1 - sum of the mass ratios of each crystal phase other than ZnO with ZnO as 1 obtained by Rietveld analysis) ÷ mass ratio of the evaluation sample with mixed ZnO as 1 (Calculation formula for the mass ratio of phases other than the crystal phase excluding ZnO) Mass ratio of phases other than the crystal phase (normalized by ZnO) / sum of the mass ratios of each crystal phase other than ZnO × 100% The correction coefficient of ZnO calibrated by Rietveld analysis was 0.879 times.

[0081] As can be seen from these results, the solid electrolyte powders of Comparative Example 1, Example 1, and Example 2 are all LiZr with a rhombohedral NASICON-type structure 2 (PO 4 ) 3 containing the crystalline phase of the α-phase. However, in Comparative Example 1, there are almost no phases other than the crystalline phase, while in Example 1 and Example 2, the phases other than the crystalline phase mainly composed of the amorphous phase are more than 3% by mass (that is, the sum of the masses of the crystalline components is less than 97% by weight with respect to the total mass). Also, it was shown that the a-axis lattice constants of these α-phases are less than 8.872 Å in Comparative Example 1, while they are more than 8.882 Å in Example 1 and Example 2.

[0082]

Table 4

[0083]

Table 5

[0084]

Table 6

[0085]

Table 7

[0086] <Secondary electron image observation> Since the state of the particles greatly affects the lithium ion conductivity, secondary electron imaging of the outermost particle layer was also performed on the solid electrolyte pellets of Comparative Example 1, Example 1, and Example 2. The secondary electron imaging was carried out using an S-3000N manufactured by Hitachi High-Technologies Corporation. The secondary electron image of Comparative Example 1 is shown in Fig. 2, the secondary electron image of Example 1 is shown in Fig. 3, and the secondary electron image of Example 2 is shown in Fig. 4 for these results. The observation conditions were as follows: for Comparative Example 1, the working distance (WD; operating distance (distance from the center of the objective lens to the sample surface)) was 16.5 mm, the acceleration voltage was 15 kV, and the magnification was 500 times. For Example 1, the WD was 15.9 mm, the acceleration voltage was 15 kV, and the magnification was 500 times. For Example 2, the WD was 11.5 mm, the acceleration voltage was 15 kV, and the magnification was 500 times. Even under the same firing conditions, significant grain growth was observed in the solid electrolyte of Comparative Example 1 obtained from a precursor having no amorphous composition (Fig. 2). On the other hand, in the solid electrolytes of Example 1 and Example 2 obtained from precursors having an amorphous composition, the formation of clear necks was confirmed and the grain boundaries were densified (Figs. 3 and 4).

[0087] <Storage test> Since solid electrolytes are mainly used for battery applications and it is also necessary for the lithium ion conductivity to be stable over a long period in battery applications, a storage test was conducted. As an evaluation method, the solid electrolyte pellets of Comparative Example 1, Example 1, and Example 2 were stored in the atmosphere at 25 °C, and powder X-ray diffraction and Rietveld analysis, as well as density and ion conductivity measurements, were performed by the same method as described above. The storage period was set to 1 year.

[0088] Table 8 below shows the results of Rietveld analysis before the start of the storage test (initial product) and after 1 year of storage (after 1 year) of the examples, and Table 9 below shows the measurement results of their density and lithium ion conductivity. In the solid electrolyte of Example 1 containing no Si component, the α-phase decreased from 96.6 mass% to 28.8 mass% after 1 year of storage, and the α'-phase, YPO 4 、ZrO 2It was decomposed into etc. On the other hand, the decomposition (mass ratio decrease) of the α-phase in the solid electrolyte of Example 2 containing the Si component was suppressed to less than 10% by mass. After 1 year of storage, the lithium ion conductivity of the solid electrolyte of Example 1 without the Si component decreased by about 46%, while that of the solid electrolyte of Example 2 containing the Si component decreased by about 28%.

[0089] Also, the results of this storage test and the literature values of the same series of products (Li 1.15 Y 0.15 Zr 1.85 P 3 O 12 (JCPDS 01-083-4639), Li 1.2 Ca 0.1 Zr 1.9 P 3 O 12 (RSC Advances 2011(1)1728-1731), LiZr 2 P 3 O 12 The comparison with the rhombohedral crystal system (JCPDS 01-084-0998)) is presented in Table 10 in terms of lattice constants (a-axis (a / Å), c-axis (c / Å)) and lithium ion conductivity, and Figure 5 shows the plot of the initial values and the lithium ion conductivity after 1 year and the a-axis lattice constant of Examples 1 and 2. The a-axis lattice constants of the α-phase of Examples 1 and 2 prepared from precursors with an amorphous composition were larger than those of Comparative Example 1 prepared from precursors without an amorphous composition and the literature values of the same series of products, and in particular, Example 2 containing the Si component was the largest. From the relationship between the lithium ion conductivity and the a-axis lattice constant, it can be confirmed that as the a-axis lattice constant increases, the lithium ion conductivity tends to increase. This is presumably because lithium ions can move more freely within the lattice of the crystal phase. That is, it was confirmed that the solid electrolyte of Example 2 containing the Si component is particularly excellent in stability at room temperature (25°C). By replacing a part of P with Si, the a-axis direction of the lattice is further extended to increase the lithium ion conductivity, and it was further confirmed that the stability of the crystal structure over time and the stability of the lithium ion conductivity are further enhanced.

[0090]

Table 8

[0091]

Table 9

[0092]

Table 10

[0093] <Confirmation of Redox Potential by Cyclic Button Metrology> Regarding the reduction resistance of the solid electrolytes of Example 1 and Example 2, evaluation was performed by cyclic voltammetry (CV) using lithium as the counter electrode.

[0094] An Li metal foil (electrode) and a polymer electrolyte were attached to a copper foil serving as a current collector, and on top of them, a solid electrolyte pellet of Example 1 or Example 2 with an Au electrode sputtered on the working electrode side was placed, and current collection was taken with an aluminum foil. This evaluation sample was vacuum-packed with an aluminum laminate pack and made into a form in which only the copper foil and aluminum foil of the current collector could be taken out externally with tab films. As a pretreatment of the sealed evaluation sample, after holding at 60 °C for 2 hours or more to promote the bonding between the polymer electrolyte and the solid electrolyte, evaluation was performed. The measurement temperature was 25 °C, the starting voltage was the open circuit voltage, the scanning rate was 0.2 mV / s, and scanning was performed from 5 V to 0.2 V. The obtained cyclic voltammogram (current-potential curve: CV curve) is shown in Fig. 6. It was confirmed that the solid electrolyte of Example 2 containing the Si component had less change in current and was more excellent in reduction resistance.

[0095] <Confirmation of the Effective Valence Number of Si by X-ray Absorption Fine Structure Analysis (XAFS)> From the above results, it was confirmed that the solid electrolyte of Example 2 had high lithium ion conductivity and high reducibility. However, since the effect of the Si component and the state of Si in the solid electrolyte of this Example 2 were unknown, the valence of Si was confirmed by X-ray absorption fine structure analysis (XAFS) for the solid electrolyte pellet of Example 2. The X-ray absorption fine structure analysis was performed at BL6N1 of the Aichi Synchrotron Light Center. The results are shown in Figure 7.

[0096] The results in Figure 7 showed good agreement with the XAFS spectra (Photon Factory Activity Report 2012#30(2013)B) measured and calculated for the SiO 6 coordination. From this, it is highly likely that Si is in the SiO 6 coordination in the solid electrolyte, suggesting that it is highly likely to be present at the ZrO 6 site in the crystal or in the amorphous part of the solid electrolyte.

[0097] Note that the arrows in Figure 7 represent the parts where the difference from SiO 2 is significant. In particular, from the new peak that occurred at approximately 1845 eV indicated by the left arrow, it can be interpreted that the solid electrolyte of Example 2 contains Si with a valence lower than tetravalent. Since the difference in absorption edge energy between Si equivalent to 0 valence and SiO 2 (equivalent to tetravalent) is 9 eV, it was confirmed from the energy difference (approximately 3 eV) of the above-mentioned peak that Si with a valence of approximately 3.7 is contained.

[0098] <Confirmation of the Coordination Number of O to Si by Extended X-ray Absorption Fine Structure Analysis (EXAFS)> Furthermore, the coordination number of O to Si in the solid electrolyte of Example 2 was also confirmed by extended X-ray absorption fine structure analysis (EXAFS). The extended X-ray absorption fine structure analysis used the synchrotron radiation data measured at BL6N1 of the Aichi Synchrotron Light Center used in the above-mentioned XAFS measurement. The analysis conditions are as follows.

[0099] The K edge of Si is at E = 1847 eV, while the LIII, LII, and LI edges of Y are at E = 2080 eV, 2156 eV, and 2373 eV respectively, and the LIII, LII, and LI edges of Zr are at E = 2222 eV, 2307 eV, and 2532 eV respectively, and they exist in the EXAFS region of the K edge of Si. The data in Fig. 8 shows the mixing of the LIII edge and the LII edge of Y. Therefore, in the EXAFS analysis of the solid electrolyte in Example 2, in order to avoid these mixings, it is necessary to limit the E range (wavenumber k range) used in the analysis. Therefore, in order to improve the accuracy of the analysis as much as possible within this limitation, the following measures were taken.

[0100] The experimental data was reproduced with as few variables as possible, and the surrounding atoms were set to only the nearest neighbor O so that the nearest neighbor O coordination number could be determined. As a result, the fitting variables were the scale factor S 0 2 O coordination number (Nо), Si-O distance (r Si-O ), absorption edge (E 0 ), Debye-Waller factor (σ 0 2 ). And corresponding to the restricted E range: 1897~2061 eV, k max = 7.4, the wavenumber weighting order: 2nd order, and the fitting space: wavenumber space, the fitting variables were sequentially determined according to the following flow. (1) Analyze the reference SiO 2 in a wide E range to determine σ 0 2 . (2) Analyze the reference SiO 2 in the restricted E range (fix σ 0 2 to the value in (1)), and determine S 0 2 from this data where No = 4 can be fixed. (3) Analyze Example 2 (LYZSP12) in the restricted E range (fix σ 0 2 to the value in (1) and S 0 2 to the value in (2)), and evaluate the Nо of the target crystal phase.

[0101] The analysis results are shown in Table 11 and Figure 9 below. Figure 9 shows the "radial structure function in real space" extracted by Fourier transform. Here, the R range and k (or q) range used for extraction are shown as window functions. From the fact that the function extracted from this data matches the function of the fitting result and the R factor in Table 11, it was determined that this analysis was appropriately carried out. And the O coordination number to Si in the solid electrolyte of Example 2 was estimated to be 6 instead of 4 (Table 11). From this result, it was suggested that the inclusion of the Si component in the solid electrolyte strengthens the covalent bond in the crystal phase (especially in the α phase), and Si is arranged at the Zr site to stabilize the lattice energetically, or the amorphous phase is likely to be stabilized by 6-coordinate Si.

[0102]

Table 11

[0103] <Confirmation of the influence of the ratio of Y and Si on lithium ion conductivity and density> Based on Example 2, the results of confirming the influence of the ratio of Y (the value of x in the formula) of Li 1.05+x Y x Zr 2-x Si 0.05 P 2.95 O 12 in the solid electrolyte pellets of Examples 3 to 6 on lithium ion conductivity, density, and the a-axis lattice constant of the α phase are shown in Table 12 and Figure 10 below. Also, based on Examples 1 and 2, the results of confirming the influence of the ratio of Si (the value of y in the formula) of Li 1.15+y Y 0.15 Zr 1.85 Si y P 3-y O 12 in the solid electrolyte pellets of Examples 7 to 9 on lithium ion conductivity, density, and the a-axis lattice constant of the α phase are shown in Table 13 and Figure 11. Furthermore, Li 1.05+x Y x Zr 2-xSi 0.05 P 2.95 O 12 The ratio of Y (the value of x in the formula) and Li 1.15+y Y 0.15 Zr 1.85 Si y P 3-y O 12 The influence of the change in the a-axis lattice constant of the α-phase due to the variation in the ratio of Si (the value of y in the formula) on the lithium ion conductivity is shown in Fig. 12. Furthermore, Li 1+x+y Y x Zr 2-x Si y P 3-y O 12 With the ratio of Si (the value of y in the formula) being 0, the results of examining the influence of the ratio of Y (the value of x in the formula) of Li 1+x Y x Zr 2-x P 3 O 12 on the lithium ion conductivity, density, and a-axis lattice constant of the α-phase are shown in Table 14.

[0104] Note that the lithium ion conductivity, density, and a-axis lattice constant of each solid electrolyte pellet were all measured by the same method as described above. Also, for the lithium ion conductivity and density, two measurements were performed for each example (Tables 12 - 14, Figs. 10 - 12).

[0105]

Table 12

[0106]

Table 13

[0107]

Table 14

[0108] As a result, Li 1.05+x Y x Zr2-x Si 0.05 P 2.95 O 12 When the ratio of Y in it is 0.10 to 0.17, and Li 1.15+y Y 0.15 Zr 1.85 Si y P 3-y O 12 when the ratio of Si in it is 0.00 to 0.07, it was shown that its lithium ion conductivity is further increased. Also, the a-axis lattice constant of the α-phase is Li 1.05+x Y x Zr 2-x Si 0.05 P 2.95 O 12 varies from 8.880 Å to 8.8892 Å by varying the ratio of Y in it or the ratio of Si in Li 1.15+y Y 0.15 Zr 1.85 Si y P 3-y O 12 it, and it was confirmed that the value of the a-axis lattice constant of the α-phase and the value of the lithium ion conductivity are correlated. That is, as the a-axis lattice constant of the α-phase increases from 8.880 Å, the lithium ion conductivity increases, and the lithium ion conductivity is the highest when the a-axis lattice constant of the α-phase is around 8.885 Å, and it was confirmed that the lithium ion conductivity tends to decrease when the a-axis lattice constant of the α-phase exceeds 8.892 Å. Furthermore, Li 1+x+y Y x Zr 2-x Si y P 3-y O 12 even when the ratio of Y in it exceeds 0.25 and 0.2, if the ratio of Si is 0, it was confirmed that relatively high lithium ion conductivity is maintained compared to the case where the ratio of Si is 0.05. It is considered that this is affected by the fact that the a-axis lattice constant of the α-phase in Example 10 was 8.888 Å, which was below the threshold value of 8.892 Å for the a-axis lattice constant of the α-phase described above.

[0109] <Fabrication of Sintered Body by Sheet Forming Method> Regarding the solid electrolyte of Example 2 in which high lithium ion conductivity and stable performance were confirmed in pellets and powders, a sheet-shaped sintered body was produced by green sheet forming. Specifically, for the powder obtained by pulverizing the dry powder of the amorphous precursor with the composition of Example 2 to 1 μm or less in D90, 1-propanol as a solvent, a binder, and a dispersant were added. After forming a 20-μm-thick sheet, 12 sheets were laminated, vacuum-packed, and then subjected to warm water hydrostatic pressing and fired at 1200 °C. The obtained sheet-shaped sintered body (sheet-shaped substrate) was designated as Example 11.

[0110] <Measurement of Density and Lithium Ion Conductivity of Sheet-shaped Substrate> The diameter, thickness, and weight of the sheet-shaped substrate of Example 11 were measured using a vernier caliper, micrometer, and electronic balance, respectively, and the density was calculated. The density was 2.6 to 2.85 g / cm 3 Furthermore, using a magnetron sputtering apparatus (manufactured by Sunyu Electronics Co., Ltd., SC-701HMC), gold electrodes were formed on both sides of the sheet-shaped substrate of Example 11 as blocking electrodes. Then, this was placed in a constant temperature bath at 25 °C, and impedance measurement was performed at a frequency of 7 MHz to 0.1 Hz and an amplitude voltage of 10 mV using an electrochemical evaluation apparatus (manufactured by BioLogic, SP300) to measure the lithium ion conductivity. This Cole-Cole Plot is shown in Figure 13. The lithium ion conductivity at 25 °C was 8.5 to 9.3×10 -5 S·cm -1 This value was higher than the lithium ion conductivity (literature value) of the solid electrolyte (Li 1.15 Y 0.15 Zr 1.85 P 3 O 12 ) synthesized by SPS.

[0111] <Results of Secondary Electron Image Observation> Regarding the sheet-like substrate of Example 11, the same apparatus as described above was used for observation at WD 15.0 mm and acceleration voltage 15.1 kV. The magnification was set to 5000 times, and secondary electron imaging observation of the outermost shell particle layer was performed. The results are shown in FIGS. 14 and 15. From these results, the presence of grain boundaries was recognized, and it was confirmed that the grain boundaries were tightly joined. Also, regarding the particles present in the outermost shell particle layer, 27 particles that completely fit within a 24 μm × 19 μm field of view were counted. The results are shown in Table 15 below. The particle size was defined as the length of the longest diagonal (maximum value of the diagonal) (FIG. 15). From these results, it was confirmed that sintering was possible with a maximum particle size of 10.2 μm, a minimum particle size of 0.7 μm, and an average particle size of 3.7 μm, which are small particle sizes.

[0112]

Table 15

[0113] This application claims priority based on Japanese Patent Application No. 2020-076009 filed on April 22, 2020, and incorporates herein by reference all of its disclosure.

Claims

1. in terms of mol% based on oxides, Li 2 The O component is 10 to 20%, P 2 O 5 The content is 30 to 40%, ZrO 2 The component is 40 to 50%, Y 2 O 3 The content of the component is 0 to 4%, Al 2 O 3 The content of the component is 0 to 3%, GeO 2 The content is 0 to 2% containing, including a crystal phase having a rhombohedral NASICON-type structure, the crystal phase including LiZr₂(PO₄)₃ α-phase and / or LiZr₂(PO₄)₃ α'-phase, the a-axis lattice constant of the crystal phase identified by X-ray diffraction and Rietveld analysis being 8.872 Å or more, a lithium ion conductive glass ceramic.

2. The lithium ion conductive glass ceramic according to Claim 1, wherein the sum of the masses of the crystal components identified by X-ray diffraction and Rietveld analysis is less than 97% by mass based on the total mass.

3. The LiZr identified by X-ray diffraction and Rietveld analysis 2 (PO 4 ) 3 The lithium ion conductive glass ceramics according to claim 1 or 2, wherein the mass of the α-phase is 80% by mass or more based on the total mass.

4. in terms of mol% based on oxides, SiO 2 component in an amount of 0.1 to 5% containing, the lithium ion conductive glass ceramic according to any one of Claims 1 to 3.

5. The lithium ion conductive glass ceramic according to Claim 4, wherein the valence of Si contained in the entire lithium ion conductive glass ceramic is 3.5 or more and less than 3.

9.

6. The lithium ion conductive glass ceramic according to Claim 4 or 5, wherein the coordination number of O to Si contained in the entire lithium ion conductive glass ceramic is 5 or more and 7 or less.

7. The lithium ion conductivity at 25 °C is 1.0×10 -5 S·cm -1 or more, and the lithium ion conductive glass ceramics according to any one of claims 1 to 6.

8. The lithium ion conductivity at 25 °C is 7.0×10 -5 S·cm -1 or more and a substrate having a thickness of 300 μm or less, the lithium ion conductive glass ceramics according to any one of claims 1 to 6.

9. The lithium ion conductive glass ceramic according to Claim 8, wherein the maximum particle diameter of the particles in the outermost shell particle layer of the substrate is 30 μm or less, and the average particle diameter of the particles is 15 μm or less.

Images