Titanate-based solid electrolyte material

Abstract

The present invention provides a titanic acid-based solid electrolyte material which is free from the risk of generation of hydrogen sulfide, while containing no rare earth elements and having good lithium ion conductivity.　A titanic acid-based solid electrolyte material which is characterized by being formed of a lepidocrocite type titanate that has a structure wherein a plurality of host layers, each of which is formed of a chain of octahedrons linked in a two-dimensional direction by means of edge-sharing, each of said octahedrons being obtained by coordinating 6 oxygen atoms to a titanium atom, are stacked and lithium ions are arranged between the host layers, with some titanium sites in the host layers being substituted by monovalent to trivalent positive ions.

Description

Technical Field

[0001] The present invention relates to a titanate-based solid electrolyte material.

Background Art

[0002] A lithium-ion secondary battery is composed of a positive electrode, a negative electrode, a separator that prevents physical contact between the positive electrode and the negative electrode, and an electrolyte, and is a secondary battery that performs charge and discharge by the movement of lithium ions through the electrolyte between the positive electrode and the negative electrode. Lithium-ion secondary batteries are excellent in terms of energy density and output density, etc., and are effective for miniaturization and weight reduction, so they are used as power sources for notebook computers, tablet terminals, and smartphones. They are also attracting attention as power sources for electric vehicles.

[0003] Since conventional electrolytes use electrolytic solutions containing flammable organic solvents, liquid leakage is likely to occur, and there is a risk of short-circuiting (shorting) inside the battery and catching fire due to overcharge and overdischarge. Therefore, in recent years, in order to improve safety, research and development of all-solid-state lithium-ion secondary batteries using inorganic solid electrolyte materials instead of electrolytic solutions have been carried out.

[0004] Inorganic solid electrolyte materials used in all-solid-state lithium-ion secondary batteries are classified into two types: sulfide-based solid electrolyte materials and oxide-based solid electrolyte materials, depending on whether the main element forming the skeleton is an oxygen atom or a sulfur atom. Sulfide-based solid electrolyte materials exhibit higher lithium-ion conductivity than oxide-based solid electrolyte materials, but have a large reactivity with moisture and have safety problems such as the generation of hydrogen sulfide. Therefore, methods for improving the lithium-ion conductivity of oxide-based solid electrolyte materials such as (La, Li)TiO3 (hereinafter referred to as "LLTO"), Li6La2CaTa2O 12 , Li6La2ANb2O 12 (A = Ca, Sr), Li2Nd3TeSbO 12 etc. have been studied. For example, a method of doping LLTO with 1% to 5% by mass of sulfur has been disclosed (see Patent Document 1).

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, since the oxide-based solid electrolyte material of Patent Document 1 contains sulfur, there is a risk of generating hydrogen sulfide. In addition, since rare earths are used, there are also concerns in terms of manufacturing cost.

[0007] An object of the present invention is to provide a titanium-based solid electrolyte material that has no risk of generating hydrogen sulfide, does not contain rare earths, has good lithium ion conductivity, a method for manufacturing the same, a solid electrolyte using the titanium-based solid electrolyte material, and a lithium ion secondary battery.

Means for Solving the Problems

[0008] The present invention provides the following titanium-based solid electrolyte material, a method for manufacturing the same, a solid electrolyte, and a lithium ion secondary battery.

[0009] Item 1 A titanium-based solid electrolyte material characterized by comprising a rhabdophane-type titanate having a structure in which a plurality of host layers formed by edge-sharing octahedra in which oxygen atoms are coordinated to titanium atoms in a two-dimensional direction are stacked, and lithium ions are arranged between the layers of the host layer, and a part of the titanium sites in the host layer is substituted with monovalent to trivalent cations.

[0010] Item 2 The titanium-based solid electrolyte material according to Item 1, wherein the interlayer distance of the host layer is 5 Å or more and 10 Å or less.

[0011] Item 3 The titanium-based solid electrolyte material according to Item 1 or Item 2, wherein the rhabdophane-type titanate has crystal water.

[0012] Item 4. The titanium-based solid electrolyte material according to any one of Items 1 to 3, wherein the content of lithium ions present between the layers of the host layer is 45 mol% or more and 100 mol% or less with respect to 100 mol% of the ions present between the layers of the host layer.

[0013] Item 5. The titanium-based solid electrolyte material according to any one of Items 1 to 4, which is at least one compound selected from the group consisting of the compound represented by the following general formula (1) and the compound represented by the following general formula (2).

[0014] Li x M I y Ti 1.73 O 3.7~4 ·nH2O … Formula (1) [In the formula, M I represents an alkali metal excluding lithium, the exponent x is 0.3 to 1.0, the exponent y is 0 to 0.4, and the exponent n is 0 to 2.] Li x M I y M II z Ti 1.6 O 3.7~4 ·nH2O … Formula (2) [In the formula, M I represents an alkali metal excluding lithium, M II represents an alkaline earth metal, the exponent x is 0.3 to 1.0, the exponent y is 0 to 0.4, the exponent z is 0 to 0.4, and the exponent n is 0 to 2.]

[0015] Item 6. A method for producing a titanium-based solid electrolyte material according to any one of Items 1 to 5, the method comprising a step of mixing a rhabdophane-type titanate and a lithium salt and performing a heat treatment.

[0016] Item 7. A method for manufacturing a titanate-based solid electrolyte material according to any one of Items 1 to 5, comprising: a step of mixing a rhabdophane-type titanate and an acid to prepare rhabdophane-type titanic acid; and a step of mixing the rhabdophane-type titanic acid and a lithium salt.

[0017] Item 8. A solid electrolyte comprising the titanate-based solid electrolyte material according to any one of Items 1 to 5.

[0018] Item 9. A lithium-ion secondary battery comprising the solid electrolyte according to Item 8.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a titanate-based solid electrolyte material that has no risk of generating hydrogen sulfide, does not contain rare earths, and has good lithium ion conductivity. By using a solid electrolyte having this titanate-based solid electrolyte material, a high-output battery with excellent safety can be obtained.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0021] Hereinafter, an example of a preferred mode for carrying out the present invention will be described. However, the following embodiments are merely illustrative, and the present invention is not limited to the following embodiments in any way.

[0022] <Titanate-based solid electrolyte material> The titanate-based solid electrolyte material of the present invention has a structure in which a plurality of host layers formed by edge-sharing of octahedrons in which oxygen atoms are coordinated to titanium atoms in a 6-fold coordination are linked in a two-dimensional direction, and lithium ions are arranged between the layers of the host layer. It is characterized by being composed of a rhabdophane-type titanate in which a part of the titanium sites in the host layer is substituted with monovalent to trivalent cations. The rhabdophane-type titanate may or may not have crystal water between the layers of the host layer. Preferably, the rhabdophane-type titanate has crystal water between the layers of the host layer.

[0023] The host layer is formed by edge-sharing of octahedrons in which oxygen atoms are coordinated to titanium atoms in a 6-fold coordination and forms a single layer that is a unit of stacking (lamination). Originally, each host layer is electrically neutral, but it has a negative charge due to substitution of a part of the tetravalent titanium sites with monovalent to trivalent cations or due to vacancies. The electrical neutrality of this compound is maintained by being compensated by positive charges such as lithium ions existing between the host layers (hereinafter referred to as "interlayer").

[0024] More specifically, FIG. 1 is a schematic diagram showing a titanate-based solid electrolyte material according to an embodiment of the present invention. As shown in FIG. 1, the titanate-based solid electrolyte material 1 has a crystal structure in which a plurality of host layers 2 are laminated, and ions 3 such as lithium ions are arranged between the layers of the host layer 2. Each host layer 2 is formed by edge-sharing of octahedrons in which oxygen atoms are coordinated to titanium atoms in a 6-fold coordination. Note that FIG. 1 is a schematic diagram as an example, and the titanate-based solid electrolyte material of the present invention is not limited to the structure of the schematic diagram of FIG. 1.

[0025] From the perspective of further enhancing the lithium ion conductivity, among the titanium sites in the host layer, it is preferable that more than 0 mol% and 40 mol% or less of the titanium sites are substituted with monovalent to trivalent cations. Examples of the cations include hydrogen ion, oxonium ion, alkali metal ion, alkaline earth metal ion, zinc ion, nickel ion, copper ion, iron ion, aluminum ion, gallium ion, manganese ion, etc. From the perspective of further enhancing the lithium ion conductivity, it is preferably at least one selected from the group consisting of hydrogen ion, oxonium ion, lithium ion, and magnesium ion, and more preferably lithium ion or magnesium ion.

[0026] A part of the titanium sites in the host layer may be pores. When there are pores, from the perspective of further enhancing the lithium ion conductivity, it is preferable that more than 0 mol% and 15 mol% or less of the titanium sites in the host layer are pores.

[0027] The interlayer distance of the host layer of the rheidite-type titanate constituting the titanium-based solid electrolyte material is preferably 5 Å or more, more preferably 6 Å or more, preferably 10 Å or less, more preferably 9 Å or less, and even more preferably 7 Å or less. The rheidite-type titanate has a layered structure in its crystal structure, and the lithium ion conductivity is exhibited by the interlayer serving as a two-dimensional lithium ion conduction path. By setting the interlayer distance within the above range, the lithium ion density in the interlayer can be increased, the activation energy of ion conduction is small, and it is considered that the lithium ion conductivity is further excellent.

[0028] In the X-ray diffraction pattern, several peaks that appear at equal intervals in the low-angle region (generally 2θ = 20° or less) are derived from the layer structure of titanic acid, and the interlayer distance can be calculated from the diffraction angle (2θ) of the first peak that appears on the lowest angle side. Specifically, it can be calculated using Bragg's equation "d = nλ / 2sinθ" (where d is the interlayer distance (Å), θ is the value obtained by dividing the diffraction angle (2θ) of the first peak by 2, λ is the wavelength of CuKα ray which is 1.5418 Å, and n is a positive integer (n = 1 in the case of the first peak)).

[0029] Only lithium ions may be arranged between the layers of the host layer, or, as long as the preferred physical properties of the present invention are not impaired, in addition to lithium ions, hydrogen ions, oxonium ions, alkali metal ions, alkaline earth metal ions, etc. may be arranged. From the viewpoint of further enhancing the lithium ion conductivity, it is preferable that at least one selected from the group consisting of hydrogen ions, oxonium ions, potassium ions, and sodium ions is arranged. More preferably, in addition to lithium ions, potassium ions or sodium ions are arranged between the layers of the host layer. From the viewpoint of further enhancing the lithium ion conductivity, the content of lithium ions present between the layers of the host layer is preferably 45 mol% or more, more preferably 60 mol% or more, still more preferably 80 mol% or more, preferably 100 mol% or less, and more preferably 90% or less, based on 100 mol% of the ions present between the layers of the host layer.

[0030] The rectorite-type titanate constituting the titanic acid-based solid electrolyte material is powdery particles in the form of spherical (including those with slightly uneven surfaces or those with a substantially spherical shape such as an elliptical cross-section), columnar (including those with a substantially columnar shape as a whole such as rod-shaped, cylindrical, prismatic, strip-shaped, substantially cylindrical shape, substantially strip-shaped, etc.), plate-shaped, block-shaped, a shape having a plurality of convex portions (such as amoeba-shaped, boomerang-shaped, cross-shaped, sugar ball-shaped, etc.), irregular shape, etc. The particle size is not particularly limited, but the average particle diameter is preferably 0.01 μm to 20 μm, more preferably 0.05 μm to 10 μm, and still more preferably 0.1 μm to 5 μm.

[0031] In this specification, the "average particle diameter" refers to the particle diameter at the time of cumulative 50% based on integration in the particle size distribution determined by the laser diffraction / scattering method (volume-based cumulative 50% particle diameter), that is, D 50 (median diameter), and this volume-based cumulative 50% particle diameter (D 50 ) is obtained by determining the particle size distribution based on volume, and in the cumulative curve with the total volume as 100%, the number of particles is counted from the smaller particle sizes, and it is the particle diameter at the point where the cumulative value becomes 50%. These various particle morphologies and particle sizes can be arbitrarily controlled by the shape of the raw material, the rectorite-type titanate, which will be described later.

[0032] As the rectorite-type titanate described above, at least one compound selected from the group consisting of the compound represented by the following general formula (1) and the compound represented by the following general formula (2) is preferable, and Li 0.3~1.1 K 0~0.1 Na 0~0.5 Ti 1.73 O 3.7~4 ·0~2H2O, Li 0.3~1.1 K 0~0.5 Ti 1.73 O 3.7~4 ·0~2H2O, Li 0.3~1.6 K 0~0.1 Mg 0~0.4 Ti 1.6 O 3.7~4 ·0~2H2O is more preferable, and at least one compound selected from the group consisting of Li 0.5~1.1 K 0~0.1 Na 0~0.5 Ti 1.73 O4·0~2H2O, Li 0.5~1.1 K 0~0.1 Ti 1.73 O4·0~2H2O, Li 0.5~1.6 K 0~0.1 Mg 0~0.4 Ti 1.6 O4·0~2H2O is even more preferable, and Li 0.5~1.1 K 0~0.1 Ti 1.73 O4·0.1~2H2O, Li 0.5~1.6 K 0~0.1 Mg 0~0.4 Ti1.6 At least one compound selected from the group consisting of O4·0.1~2H2O is particularly preferred.

[0033] Li x M I y Ti 1.73 O 3.7~4 ·nH2O … Formula (1) [Wherein, M I represents an alkali metal excluding lithium, the exponent x is 0.3 to 1.1, the exponent y is 0 to 0.4, and the exponent n is 0 to 2.] Li x M I y M II z Ti 1.6 O 3.7~4 ·nH2O … Formula (2) [Wherein, M I represents an alkali metal excluding lithium, M II represents an alkaline earth metal, the exponent x is 0.3 to 1.6, the exponent y is 0 to 0.4, the exponent z is 0 to 0.4, and the exponent n is 0 to 2.]

[0034] The exponent x of the general formula (1) is 0.3 to 1.1, preferably 0.5 to 1.1, more preferably 0.7 to 1.1. The exponent x of the general formula (2) is 0.3 to 1.6, preferably 0.5 to 1.6, more preferably 0.7 to 1.1.

[0035] The exponent y of the general formula (1) is 0 to 0.4, preferably 0.05 to 0.35, more preferably 0.05 to 0.1. The exponent y of the general formula (2) is 0 to 0.4, preferably 0.01 to 0.1.

[0036] The exponent z of the general formula (2) is 0 to 0.4, preferably 0.2 to 0.35.

[0037] The exponent n of the general formula (1) is 0 to 2, preferably 0.1 to 2. The exponent n of the general formula (2) is 0 to 2, preferably 0.1 to 2.

[0038] The titanium-based solid electrolyte material of the present invention has excellent lithium ion conductivity and does not contain sulfur, so it can be suitably used as a solid electrolyte material for lithium ion secondary batteries. In addition, since it does not contain sulfur, there is no risk of generating hydrogen sulfide, and since it does not use rare earths, it is excellent in terms of manufacturing cost.

[0039] (Method for manufacturing a titanium-based solid electrolyte material) The titanium-based solid electrolyte material of the present invention is not limited to a specific manufacturing method as long as the above composition can be achieved, and a manufacturing method can be mentioned in which a lithium salt is allowed to act on a rhabdophane-type titanate or rhabdophane-type titanic acid.

[0040] The manufacturing method in which a lithium salt acts on a rhabdophane-type titanate includes a step (I) of mixing a raw material rhabdophane-type titanate and a lithium salt and performing heat treatment. In the mixing in step (I), from the viewpoint of further enhancing the lithium ion conductivity, it is preferable to further mix a potassium salt or a sodium salt.

[0041] In step (I), as the raw material rhabdophane-type titanate (hereinafter, also simply referred to as "raw material titanate"), A x M y Ti (2-y) O4 [wherein, A is one or more kinds of alkali metals other than Li, M is one or more kinds selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, Mn, x is a number from 0.5 to 1.0, and y is a number from 0.25 to 1.0], A 0.5~0.7 Li 0.27 Ti 1.73 O 3.85~3.95 [wherein, A is one or more kinds of alkali metals other than Li], A 0.2~0.7 Mg 0.40 Ti 1.6 O 3.7~3.95 [wherein, A is one or more kinds of alkali metals other than Li], A 0.5~0.7 Li (0.27-x) M y Ti (1.73-z) O 3.85~3.95[wherein, A is one or more of alkali metals excluding Li, M is one or more selected from Mg, Zn, Ga, Ni, Cu, Fe, Al, Mn (however, when there are two or more, combinations of ions with different valences are excluded), when M is a divalent metal, x = 2y / 3, z = y / 3, when M is a trivalent metal, x = y / 3, z = 2y / 3, and y satisfies 0.004 ≤ y ≤ 0.4] and the like can be mentioned, and preferably A 0.5~0.7 Li 0.27 Ti 1.73 O 3.85~3.95 [wherein, A is one or more of alkali metals excluding Li], and A 0.2~0.7 Mg 0.40 Ti 1.6 O 3.7~3.95 It is at least one selected from the group consisting of [wherein, A is one or more of alkali metals excluding Li].

[0042] The lithium salt used in step (I) may have a melting point lower than that of the raw material titanate and may be melted by the heat treatment temperature in step (I). For example, lithium nitrate, lithium chloride, lithium sulfate, lithium carbonate, etc. can be mentioned, and preferably lithium nitrate.

[0043] When a sodium salt is used in step (I), the sodium salt may have a melting point lower than that of the raw material titanate and may be melted by the heat treatment temperature in step (I). For example, sodium nitrate can be mentioned.

[0044] When a potassium salt is used in step (I), the potassium salt may have a melting point lower than that of the raw material titanate and may be melted by the heat treatment temperature in step (I). For example, potassium nitrate can be mentioned.

[0045] The mixing amount of the lithium salt, the salt compound of the lithium salt and the potassium salt, or the salt compound of the lithium salt and the sodium salt is preferably 10 equivalents to 30 equivalents with respect to the exchangeable cation capacity of the raw material titanate. If it is less than 10 equivalents, sufficient ion exchange cannot be expected, and if it exceeds 30 equivalents, it is not economically advisable. "Exchangeable cation capacity" means, for example, when the layered titanate has the general formula A x My Ti (2-y) O4 (wherein A is one or more of alkali metals excluding Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, Mn, x is a number from 0.5 to 1.0, and y is a number from 0.25 to 1.0), refers to the value represented by x.

[0046] In step (I), by mixing a raw material titanate with a lithium salt, a salt compound of a lithium salt and a potassium salt, or a salt compound of a lithium salt and a sodium salt and performing heat treatment, while maintaining the layered structure of the raw material titanate, the raw material titanate reacts with the lithium salt or the salt compound, and a rheidocrase-type titanate constituting the solid electrolyte material of the present invention is formed. This mixing is preferably under dry conditions, and the heat treatment conditions can be, for example, a temperature range of 250°C to 350°C, preferably 250°C to 300°C for 24 hours to 72 hours. After the heat treatment, it is preferable to wash and remove the salt compound, which is a flux component, with deionized water, dry it, and obtain a rheidocrase-type titanate constituting the solid electrolyte material of the present invention.

[0047] The production method of allowing a lithium salt to act on rheidocrase-type titanic acid includes step (II) of mixing a raw material rheidocrase-type titanate and an acid to prepare rheidocrase-type titanic acid, and step (III) of mixing the rheidocrase-type titanic acid prepared in step (II) and a lithium salt. In the mixing in step (III), from the viewpoint of further enhancing the lithium ion conductivity, it is preferable to further mix a potassium salt or a sodium salt.

[0048] In step (II), the raw material titanate and an acid are mixed (acid treatment). The acid treatment is preferably under wet conditions. By this acid treatment, while maintaining the layered structure of the raw material titanate, metal ions substituting a part of the titanium sites in the host layer, cations such as metal ions between the host layer and the host layer are substituted with hydrogen ions or hydronium ions, and rheidocrase-type titanic acid can be obtained. The titanic acid referred to here includes hydrated titanic acid in which water molecules exist between the layers.

[0049] The acid used in step (II) is not particularly limited, and may be a mineral acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, or an organic acid. The acid treatment can be carried out, for example, by mixing an acid with an aqueous slurry of the raw material titanate, and the treatment temperature is preferably 5°C to 80°C. The cation exchange rate can be controlled by appropriately adjusting the type and concentration of the acid and the slurry concentration of the raw material titanate according to the type of the raw material titanate. However, from the viewpoint of the interlayer distance of the obtained ramsdellite-type titanate, it is preferably 70% to 100% with respect to the cation exchangeable capacity of the raw material titanate. The "cation exchangeable capacity" means, for example, when the layered titanate is represented by the general formula A x M y Ti (2-y) O4 [wherein A is one or more alkali metals other than Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, Mn, x is a number from 0.5 to 1.0, and y is a number from 0.25 to 1.0], it refers to the value represented by x + my when the valence of M is m.

[0050] In step (III), by mixing the ramsdellite-type titanic acid prepared in step (II) with a lithium salt (lithiation treatment), the lithium salt undergoes an ion exchange reaction with hydrogen ions, hydronium ions, etc. in the interlayer. In the lithiation treatment, from the viewpoint of further enhancing the lithium ion conductivity, it is preferable to further mix a potassium salt or a sodium salt. The lithiation treatment is preferably carried out under wet conditions. After this lithiation treatment, it is dried and a solvent such as water is removed to obtain the ramsdellite-type titanate constituting the solid electrolyte material of the present invention. After step (III), heat treatment may be further carried out. The heat treatment conditions can include a temperature range of 200°C to 400°C for 0.5 hour to 5 hours.

[0051] The lithium salt used in step (III) may be any salt that can introduce lithium ions into the interlayer of the rhabdophane-type titanic acid. For example, lithium hydroxide monohydrate, lithium carbonate, lithium acetate, lithium citrate, lithium chloride, lithium nitrate, lithium sulfate, lithium phosphate, lithium bromide, lithium iodide, lithium tetraborate, LiPF6, LiBF4, etc. may be mentioned, and lithium hydroxide monohydrate is preferred.

[0052] When a sodium salt is used in step (III), the sodium salt may be any salt that can introduce sodium ions into the interlayer of the rhabdophane-type titanic acid. For example, sodium hydroxide, sodium carbonate, sodium acetate, sodium citrate, sodium chloride, sodium nitrate, sodium sulfate, sodium phosphate, sodium bromide, sodium iodide, sodium tetraborate, NaPF6, NaBF4, etc. may be mentioned, and sodium hydroxide is preferred. These may be used alone or in combination of multiple kinds.

[0053] When a potassium salt is used in step (III), the potassium salt may be any salt that can introduce potassium ions into the interlayer of the rhabdophane-type titanic acid. For example, potassium hydroxide, potassium carbonate, potassium acetate, potassium citrate, potassium chloride, potassium nitrate, potassium sulfate, potassium phosphate, potassium bromide, potassium iodide, potassium tetraborate, KPF6, KBF4, etc. may be mentioned, and potassium hydroxide is preferred. These may be used alone or in combination of multiple kinds.

[0054] In step (III), in order to allow a lithium salt, a salt compound of a lithium salt and a potassium salt, or a salt compound of a lithium salt and a sodium salt to act on the rectorite-type titanic acid, a suspension in which the rectorite-type titanic acid is dispersed in water or an aqueous medium is mixed with a lithium salt or a salt compound directly, or a dilution of a lithium salt or a salt compound with water or an aqueous medium, and then stirred. The mixing amount of the lithium salt or the salt compound is preferably 0.2 equivalent to 3 equivalents of the lithium salt or the salt compound with respect to the exchangeable cation capacity of the rectorite-type titanic acid, more preferably 1 equivalent to 2 equivalents. If it is less than 0.2 equivalent, sufficient ion exchange cannot be expected, and if it exceeds 3 equivalents, it is not economically advantageous. The "exchangeable cation capacity" means, for example, when a layered titanate is represented by the general formula A x M y Ti (2-y) O4 [wherein A is one or more alkali metals other than Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, Mn, x is a number from 0.5 to 1.0, and y is a number from 0.25 to 1.0], it refers to the value represented by x + my when the valence of M is m.

[0055] <Solid electrolyte> The solid electrolyte of the present invention is a solid electrolyte composed of the above-described titanic acid-based solid electrolyte material, does not contain a flammable organic solvent, and is a layer capable of conducting lithium ions.

[0056] The proportion of the solid electrolyte material contained in the solid electrolyte is preferably 10% by volume to 100% by volume, more preferably 50% by volume to 100% by volume, based on 100% by volume of the total amount of the solid electrolyte. The solid electrolyte may contain a binder for binding the particles of the solid electrolyte material.

[0057] The thickness of the solid electrolyte is preferably 0.1 μm to 1000 μm, more preferably 0.1 μm to 300 μm.

[0058] Methods for forming a solid electrolyte include, for example, a method of sintering a solid electrolyte material, a method of manufacturing a solid electrolyte sheet containing a binder, and the like. As the binder, the same materials as those described for the binders used in the positive electrode and the negative electrode described later can be used. When sintering, it is preferable that the sintering temperature is set lower than the heat treatment temperature when the solid electrolyte material is manufactured so as not to change its crystal structure.

[0059] The solid electrolyte of the present invention has excellent lithium ion conductivity and does not contain sulfur, so it can be suitably used as a solid electrolyte for a lithium ion secondary battery. Further, since it does not contain sulfur, there is no risk of generating hydrogen sulfide, and since it does not use rare earths, it is excellent in terms of manufacturing cost.

[0060] <Battery> The battery of the present invention is a lithium ion secondary battery having a positive electrode, a negative electrode, and a solid electrolyte disposed between the positive electrode and the negative electrode, and the solid electrolyte has the titanium-based solid electrolyte material of the present invention, that is, it is an all-solid-state battery.

[0061] More specifically, FIG. 2 is a schematic cross-sectional view showing a lithium ion secondary battery according to an embodiment of the present invention.

[0062] As shown in FIG. 2, the lithium ion secondary battery 10 includes a solid electrolyte 11, a positive electrode 12, and a negative electrode 13. The solid electrolyte 11 has a first main surface 11a and a second main surface 11b facing each other. The solid electrolyte 11 is composed of a solid electrolyte containing the titanium-based solid electrolyte material of the present invention. The positive electrode 12 is laminated on the first main surface 11a of the solid electrolyte 11. The negative electrode 13 is laminated on the second main surface 11b of the solid electrolyte 11.

[0063] The manufacturing method of the battery of the present invention is not particularly limited as long as it can obtain the above-described battery, and a method similar to the known battery manufacturing method can be used. For example, a manufacturing method can be mentioned in which a power generation element is produced by sequentially pressing and laminating a positive electrode, a solid electrolyte, and a negative electrode, the power generation element is housed inside a battery case, and the battery case is caulked.

[0064] As the battery case used for the battery of the present invention, a general battery case can be used. Examples of the battery case include a stainless steel battery case and the like.

[0065] Since the solid electrolyte of the present invention is arranged in the battery of the present invention, there is no risk of generating hydrogen sulfide and it is excellent in safety. Since it has high lithium ion conductivity, by using a solid electrolyte, a high-output battery can be obtained. In addition, by arranging the solid electrolyte, it serves as a separator, eliminating the need for an existing separator, and the thinning of the battery can be expected.

[0066] Hereinafter, each component of the battery of the present invention will be described.

[0067] (Positive Electrode) The positive electrode constituting the battery of the present invention has a positive electrode current collector and a positive electrode active material layer.

[0068] Examples of the positive electrode current collector include copper, nickel, stainless steel, iron, titanium, aluminum, aluminum alloy, etc., and aluminum is preferable. The thickness and shape of the positive electrode current collector can be appropriately selected according to the use of the battery, etc., and for example, it can have a strip-shaped planar shape. When it is a strip-shaped positive electrode current collector, it can have a first surface and a second surface as its back surface. The positive electrode active material layer can be formed on one surface or both surfaces of the positive electrode current collector.

[0069] The positive electrode active material layer is a layer containing a positive electrode active material, and may contain a conductive material and a binder as required. The positive electrode active material layer may further contain the solid electrolyte material of the present invention, and by containing the solid electrolyte material of the present invention, a positive electrode active material layer having even higher lithium ion conductivity can be obtained. The thickness of the positive electrode active material layer is preferably 0.1 μm to 1000 μm.

[0070] The positive electrode active material may be any compound that can occlude and release lithium or lithium ions. For example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMnO2), lithium nickel cobalt aluminate (LiNi 0.8 Co 0.15 Al 0.05 O2, etc.), lithium nickel cobalt manganate (LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li 1+x Ni 1 / 3 Mn 1 / 3 Co 1 / 3 O2 (0 ≦ x < 0.3), etc.), spinel-type oxides (LiM2O4, M = Mn, V), lithium metal phosphates (LiMPO4, M = Fe, Mn, Co, Ni), silicate oxides (Li2MSiO4, M = Mn, Fe, Co, Ni), LiNi 0.5 Mn 1.5 O4, S8, etc. may be mentioned.

[0071] The conductive material is blended to enhance the current collection performance and suppress the contact resistance between the positive electrode active material and the positive electrode current collector. Examples thereof include carbon-based materials such as vapor grown carbon fiber (VGCF), coke, carbon black, acetylene black, ketjen black, graphite, carbon nanofiber, and carbon nanotube.

[0072] The binder is formulated to fill the gaps between the dispersed positive electrode active materials and to bind the positive electrode active material and the positive electrode current collector. Examples include polysiloxane, polyalkylene glycol, ethyl-vinyl alcohol copolymer, carboxymethyl cellulose (CMC), hydroxypropylmethyl cellulose propyl (HPMC), cellulose acetate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), synthetic rubbers such as butadiene rubber, styrene-butadiene rubber (SBR), styrene-butadiene-styrene copolymer (SBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), ethylene-propylene rubber, butyl rubber, chloroprene rubber, acrylonitrile-butadiene rubber, acrylic rubber, silicone rubber, fluorine rubber, and urethane rubber, polyimide, polyamide, polyamideimide, polyvinyl alcohol, chlorinated polyethylene (CPE), etc.

[0073] As a method for manufacturing the positive electrode, for example, a positive electrode active material, a conductive material, and a binder are suspended in a solvent to prepare a slurry, and this slurry is applied to one or both sides of the positive electrode current collector. Then, the applied slurry is dried to obtain a laminate of the positive electrode active material-containing layer and the positive electrode current collector. Thereafter, a method of pressing this laminate can be mentioned. In another method, a positive electrode active material, a conductive material, and a binder are mixed, and the obtained mixture is formed into pellets. Then, methods such as arranging these pellets on the positive electrode current collector can be mentioned.

[0074] (Negative electrode) The negative electrode constituting the battery of the present invention has a negative electrode current collector and a negative electrode active material layer.

[0075] Examples of the negative electrode current collector include stainless steel, copper, nickel, carbon, etc., and copper is preferred. The thickness and shape of the negative electrode current collector can be appropriately selected according to the use of the battery, etc., and for example, it can have a strip-shaped planar shape. When it is a strip-shaped current collector, it can have a first surface and a second surface as its back surface. The negative electrode active material layer can be formed on one surface or both surfaces of the negative electrode current collector.

[0076] The negative electrode active material layer is a layer containing a negative electrode active material, and may contain a conductive material and a binder as required. The negative electrode active material layer may further contain the solid electrolyte material of the present invention, and by containing the solid electrolyte material of the present invention, a negative electrode active material layer with even higher lithium ion conductivity can be obtained. The thickness of the negative electrode active material layer is preferably 0.1 μm to 1000 μm.

[0077] Examples of the negative electrode active material include metal active materials, carbon active materials, lithium metal, oxides, nitrides, or mixtures thereof. Examples of the metal active material include In, Al, Si, Sn, etc. Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented pyrolytic graphite (HOPG), hard carbon, soft carbon, etc. Examples of the oxide include Li4Ti5O 12 and the like. Examples of the nitride include LiCoN, etc.

[0078] The conductive material is blended to enhance the current collection performance and suppress the contact resistance between the negative electrode active material and the negative electrode current collector. Examples of the conductive material include carbon-based materials such as vapor grown carbon fiber (VGCF), coke, carbon black, acetylene black, ketjen black, graphite, carbon nanofiber, and carbon nanotube.

[0079] The binder is compounded to fill the gaps between the dispersed negative electrode active materials and to bind the negative electrode active material and the negative electrode current collector. Examples include polysiloxane, polyalkylene glycol, polyacrylic acid, carboxymethyl cellulose (CMC), hydroxypropylmethyl cellulose propyl (HPMC), cellulose acetate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - HFP), synthetic rubbers such as butadiene rubber, styrene - butadiene rubber (SBR), styrene - butadiene - styrene copolymer (SBS), styrene - ethylene - butadiene - styrene copolymer (SEBS), ethylene - propylene rubber, butyl rubber, chloroprene rubber, acrylonitrile - butadiene rubber, acrylic rubber, silicone rubber, fluorine rubber, and urethane rubber, polyimide, polyamide, polyamideimide, polyvinyl alcohol, chlorinated polyethylene (CPE), etc.

[0080] As a method for manufacturing the negative electrode, for example, the negative electrode active material, conductive material, and binder are suspended in a solvent to prepare a slurry, and this slurry is applied to one or both sides of the negative electrode current collector. Next, the applied slurry is dried to obtain a laminate of the negative electrode active material - containing layer and the negative electrode current collector. Then, a method of pressing this laminate can be mentioned. In other methods, the negative electrode active material, conductive material, and binder are mixed, and the obtained mixture is formed into pellets. Next, methods such as arranging these pellets on the negative electrode current collector can be mentioned.

Example

[0081] Hereinafter, the present invention will be described in more detail based on specific examples. The present invention is not limited to the following examples at all, and can be appropriately modified and implemented within the scope of not changing its gist.

[0082] Regarding the raw material titanates used in the examples and comparative examples and the obtained powders, the average particle size was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, SALD-2100), and the interlayer distance was confirmed by analysis using an X-ray diffraction analyzer (manufactured by Rigaku Corporation, UltimaIV). The compositional formula was confirmed using an ICP-AES analyzer (manufactured by SII NanoTechnology Inc., SPS5100) and a thermogravimetric analyzer (manufactured by SII NanoTechnology Inc., EXSTAR6000 TG / DTA6300).

[0083] <Raw material titanate> The raw material titanates used in the examples and comparative examples are as follows.

[0084] (Raw material titanate A) As raw material titanate A, potassium lithium titanate (K 0.6 Li 0.27 Ti 1.73 O 3.9 ) having potassium ions between layers and lithium ions in the host layer was used. This potassium lithium titanate has an average particle size of 3 μm, is a white powder composed of plate-like particles, and the interlayer distance was 7.8 Å.

[0085] (Raw material titanate B) As raw material titanate B, potassium magnesium titanate (K 0.6 Mg 0.4 Ti 1.6 O 3.9 ) having potassium ions between layers and magnesium ions in the host layer was used. This potassium magnesium titanate has an average particle size of 5 μm, is a white powder composed of plate-like particles, and the interlayer distance was 7.8 Å.

[0086] (Example 1) 65 g of raw material titanate A was dispersed in 1 kg of deionized water, and 50.4 g of 95% sulfuric acid was added. After stirring for 1 hour, it was separated and washed with water. This operation was repeated twice to obtain a rhabdophane-type titanic acid in which part of the potassium ions and lithium ions were exchanged with hydrogen ions or hydronium ions. 50 g of this rhabdophane-type titanic acid was dispersed in 200 g of deionized water, heated to 70 °C, and while stirring, 324 g of a 10% aqueous solution of lithium hydroxide monohydrate was added. After stirring was continued at 70 °C for 3 hours, it was filtered out. After thoroughly washing with warm water at 70 °C, it was dried in air at 110 °C for 12 hours to obtain a powdery rhabdophane-type titanate.

[0087] The average particle size of the obtained rhabdophane-type titanate was 3 μm, the interlayer distance was 8.4 Å, and the composition formula was K 0.07 Li 1.0 Ti 1.73 O4·0.97H2O.

[0088] (Example 2) The rhabdophane-type titanate produced in Example 1 was heated at 300 °C for 1 hour to obtain a powdery rhabdophane-type titanate.

[0089] The average particle size of the obtained rhabdophane-type titanate was 3 μm, the interlayer distance was 7.0 Å, and the composition formula was K 0.07 Li 1.0 Ti 1.73 O4·0.21H2O.

[0090] (Example 3) 130 g of raw material titanate B was dispersed in 1.8 kg of deionized water, and 230.4 g of phosphoric acid was added. After stirring for 1 hour, it was separated and washed with water to obtain rectorite-type titanic acid in which part of potassium ions and magnesium ions were exchanged with hydrogen ions or hydronium ions. This rectorite-type titanic acid was dispersed in 834 g of a 10% aqueous solution of lithium hydroxide monohydrate, heated to 70 °C and stirred. After continuing stirring at 70 °C for 3 hours, it was filtered out. After thoroughly washing with warm water at 70 °C, it was dried in air at 110 °C for 12 hours to obtain powdery rectorite-type titanate.

[0091] The average particle size of the obtained rectorite-type titanate was 4 μm, the interlayer distance was 8.4 Å, and the composition formula was K 0.05 Li 1.0 Mg 0.3 Ti 1.6 O4·1.1H2O.

[0092] (Example 4) 6.0 g of raw material titanate A and 46 g of lithium nitrate were mixed, and this mixture was heated at 260 °C for 48 hours. The sample after heating was washed with water and dried at 110 °C for 12 hours to obtain powdery rectorite-type titanate.

[0093] The average particle size of the obtained rectorite-type titanate was 3 μm, the interlayer distance was 6.5 Å, and the composition formula was K 0.09 Li 0.9 Ti 1.73 O4·0.13H2O.

[0094] (Example 5) 15 g of raw material titanate A was dispersed in 220 g of deionized water, and 11.7 g of 95% sulfuric acid was added. After stirring for 1 hour, it was separated and washed with water. This operation was repeated twice to obtain rectorite-type titanic acid in which part of the potassium ions and lithium ions were exchanged with hydrogen ions or hydronium ions. 5 g of this rectorite-type titanic acid was dispersed in 142.5 g of deionized water, heated to 40 °C, and while stirring, 0.61 g of sodium hydroxide and 1.17 g of lithium hydroxide monohydrate were added. After continuing stirring at 40 °C for 3 hours, it was taken out by filtration. After thorough washing, it was dried in air at 110 °C for 12 hours to obtain powdery rectorite-type titanate.

[0095] The average particle diameter of the obtained rectorite-type titanate was 2 μm, the interlayer distance was 8.7 Å, and the composition formula was K 0.08 Na 0.28 Li 0.34 Ti 1.73 O 3.8 ·1.0H2O.

[0096] (Example 6) 15 g of raw material titanate A was dispersed in 220 g of deionized water, and 11.7 g of 95% sulfuric acid was added. After stirring for 1 hour, it was separated and washed with water. This operation was repeated twice to obtain rectorite-type titanic acid in which part of the potassium ions and lithium ions were exchanged with hydrogen ions or hydronium ions. 5 g of this rectorite-type titanic acid was dispersed in 142.5 g of deionized water, heated to 40 °C, and while stirring, 0.81 g of potassium hydroxide and 1.17 g of lithium hydroxide monohydrate were added. After continuing stirring at 40 °C for 3 hours, it was taken out by filtration. After thorough washing, it was dried in air at 110 °C for 12 hours to obtain powdery rectorite-type titanate.

[0097] The average particle diameter of the obtained rectorite-type titanate was 2 μm, the interlayer distance was 8.6 Å, and the composition formula was K 0.30 Li 0.43 Ti 1.73 O 3.8 ·0.84H2O.

[0098] (Comparative Example 1) Li manufactured by Toyo Seisakusho 0.33 La 0.55 TiO3 (cubic) (LLTO) of the present invention was used as a comparative example. The average particle diameter was 5 μm.

[0099] <Impedance Measurement> Samples of the rapidocite-type titanates obtained in Examples 1 to 4 and LLTO of Comparative Example 1 were each placed in a Teflon (registered trademark) container having copper electrodes with a diameter of 0.8 cm at both ends, and a load of 350 kg / cm 2 was applied, the thickness of the sample was 0.04 cm, and measurement was performed in the range of 1 MHz to 1 Hz by the AC impedance method (measurement device: COMPACTSTAT manufactured by IVIUM Technologies). The Nyquist diagram is shown in FIG. 3.

[0100] Samples of 0.050 g of the rapidocite-type titanates obtained in Examples 1, 5, and 6 were each placed in a Teflon (registered trademark) container having copper electrodes with a diameter of 0.8 cm at both ends, loaded, and pressure was applied so that the thickness of the sample became 1.0 mm, and measurement was performed in the range of 1 MHz to 70 Hz by the AC impedance method (measurement device: COMPACTSTAT manufactured by IVIUM Technologies). The Nyquist diagram is shown in FIG. 4.

[0101] In the Nyquist diagram, it shows a semicircular shape on the high-frequency side and a spike shape on the low-frequency side. It is considered that the smaller the semicircle on the high-frequency side, the better the ionic conductivity. In FIG. 3, the rapidocite-type titanates obtained in Examples 1 to 4 all have a smaller arc than LLTO of Comparative Example 1, so it can be seen that they have excellent ionic conductivity. Also, in FIG. 4, which is the result of measurement under conditions more severe than those in FIG. 3, the rapidocite-type titanates obtained in Examples 5 and 6 have a smaller arc than the rapidocite-type titanate obtained in Example 1. Therefore, it can be seen that the ionic conductivity is further improved by arranging not only lithium ions but also sodium ions or potassium ions between the layers of the host layer.

Description of Reference Numerals

[0102] 1…Titanate-based solid electrolyte material 2…Host layer 3…Ion 10…Lithium-ion secondary battery 11…Solid electrolyte 11a…First main surface 11b…Second main surface 12…Positive electrode 13…Negative electrode

Claims

1. A structure in which a plurality of host layers formed by edge-sharing of octahedrons with six oxygen atoms coordinated to titanium atoms are linked in a two-dimensional direction, and lithium ions are arranged between the layers of the host layer, A titanium-based solid electrolyte material, characterized in that it is composed of a rhabdophane-type titanate in which a part of the titanium sites in the host layer is substituted with monovalent to trivalent cations.

2. The titanium-based solid electrolyte material according to claim 1, wherein the interlayer distance of the host layer is 5 Å or more and 10 Å or less.

3. The titanium-based solid electrolyte material according to claim 1 or claim 2, wherein the rhabdophane-type titanate has crystal water.

4. The titanium-based solid electrolyte material according to any one of claims 1 to 3, wherein the content of lithium ions present between the layers of the host layer is 45 mol% or more and 100 mol% or less with respect to 100 mol% of the ions present between the layers of the host layer.

5. The titanium-based solid electrolyte material according to any one of claims 1 to 4, which is at least one compound selected from the compound represented by the following general formula (1) and the compound represented by the following general formula (2). Li ｘ M I ｙ Ti １．７３ O ３．７～４ ・nH ２ O … Formula (1) [In the formula, M I represents an alkali metal excluding lithium, the exponent x is 0.3 to 1.0, the exponent y is 0 to 0.4, and the exponent n is 0 to 2. ] Li ｘ M I ｙ M II ｚ Ti １．６ O ３．７～４ ・nH ２ O … Formula (2) [In the formula, M I is an alkali metal excluding lithium, M II represents an alkaline earth metal, the exponent x is 0.3 to 1.0, the exponent y is 0 to 0.4, the exponent z is 0 to 0.4, and the exponent n is 0 to 2.

6. A method for producing a titanate-based solid electrolyte material according to any one of Claims 1 to 5, comprising a step of mixing a rhabdophane-type titanate and a lithium salt and performing heat treatment.

7. A method for producing a titanate-based solid electrolyte material according to any one of Claims 1 to 5, comprising a step of mixing a rhabdophane-type titanate and an acid to prepare rhabdophane-type titanic acid, and a step of mixing the rhabdophane-type titanic acid and a lithium salt.

8. A solid electrolyte containing the titanate-based solid electrolyte material according to any one of Claims 1 to 5.

9. A lithium-ion secondary battery having the solid electrolyte according to Claim 8.

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