Solid electrolyte material and battery using the same

Abstract

This solid electrolyte material contains Li, Ti, M and F. Meanwhile, M is at least one element that is selected from the group consisting of Mg and Ca.

Description

Technical Field

[0001] The present disclosure relates to a solid electrolyte material and a battery using the same.

Background Art

[0002] Patent Document 1 discloses an all-solid-state battery using a sulfide solid electrolyte. Patent Document 2 discloses LiBF4 as a fluoride solid electrolyte material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide a solid electrolyte material having high lithium ion conductivity.

Means for Solving the Problems

[0005] The solid electrolyte material of the present disclosure contains Li, Ti, M, and F, where M is at least one selected from the group consisting of Mg and Ca.

Effects of the Invention

[0006] The present disclosure provides a solid electrolyte material having high lithium ion conductivity.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0009] (First Embodiment) The solid electrolyte material according to the first embodiment contains Li, Ti, M, and F. M is at least one selected from the group consisting of Mg and Ca. The solid electrolyte material according to the first embodiment has high lithium ion conductivity. Here, high lithium ion conductivity means, for example, 1×10 -8 S / cm or more. That is, the solid electrolyte material according to the first embodiment can have an ionic conductivity of, for example, 1×10 -8 S / cm or more.

[0010] The solid electrolyte material according to the first embodiment can be used to obtain a battery having excellent charge and discharge characteristics. An example of such a battery is an all-solid-state battery. The all-solid-state battery may be a primary battery or a secondary battery.

[0011] The solid electrolyte material according to the first embodiment desirably does not contain sulfur. A solid electrolyte material that does not contain sulfur is excellent in safety because hydrogen sulfide is not generated even when exposed to the atmosphere. The sulfide solid electrolyte disclosed in Patent Document 1 may generate hydrogen sulfide when exposed to the atmosphere.

[0012] Since the solid electrolyte material according to the first embodiment contains F, it can have high oxidation resistance. This is because F has a high redox potential. On the other hand, since F has a high electronegativity, its bond with Li is relatively strong. As a result, usually, the lithium ion conductivity of a solid electrolyte material containing Li and F is low. For example, LiBF4 disclosed in Patent Document 2 has a low ionic conductivity of 6.67×10 -9 S / cm. Note that LiBF4 is the solid electrolyte material used in Comparative Example 1 described later. In contrast, the solid electrolyte material according to the first embodiment can have a high ionic conductivity of, for example, 1×10 -8 S / cm or more by further containing Ti and M in addition to Li and F.

[0013] In order to increase the ionic conductivity of the solid electrolyte material, the solid electrolyte material according to the first embodiment may contain anions other than F. Examples of such anions are Cl, Br, I, O, S, or Se.

[0014] The solid electrolyte material according to the first embodiment may substantially consist of Li, Ti, M, and F. Here, "the solid electrolyte material according to the first embodiment substantially consists of Li, Ti, M, and F" means that the molar ratio (i.e., mole fraction) of the total amount of the substance of Li, Ti, M, and F to the total amount of the substance of all elements constituting the solid electrolyte material according to the first embodiment is 90% or more. As an example, the molar ratio may be 95% or more. The solid electrolyte material according to the first embodiment may consist only of Li, Ti, M, and F.

[0015] The solid electrolyte material according to the first embodiment may contain elements that are inevitably mixed in. Examples of such elements are hydrogen, oxygen, or nitrogen. Such elements may be present in the raw material powder of the solid electrolyte material or in the atmosphere for manufacturing or storing the solid electrolyte material.

[0016] In order to further enhance the ionic conductivity of the solid electrolyte material, in the solid electrolyte material according to the first embodiment, the ratio of the amount of substance of Li to the total amount of substances of Ti and M may be 0.5 or more and 4.5 or less.

[0017] In order to enhance the ionic conductivity of the solid electrolyte material, M may be Mg.

[0018] The solid electrolyte material according to the first embodiment may be represented by the following compositional formula (1). Li 6-(4-2x)b (Ti 1-x M x ) b F6 ··· Formula (1) In formula (1), the mathematical expressions: 0 < x < 1 and 0 < b ≤ 3 are satisfied. The solid electrolyte material having such a composition has high ionic conductivity.

[0019] In order to enhance the ionic conductivity of the solid electrolyte material, in formula (1), the mathematical expression: 0.05 ≤ x ≤ 0.9 may be satisfied.

[0020] When M is Mg, in order to enhance the ionic conductivity of the solid electrolyte material, in formula (1), the mathematical expression: 0.05 ≤ x ≤ 0.6 may be satisfied.

[0021] When M is Ca, in order to enhance the ionic conductivity of the solid electrolyte material, in formula (1), the mathematical expression: x = 0 may be satisfied.

[0022] The upper and lower limit values of the range of x in formula (1) may be defined by any combination selected from the numerical values of 0.05, 0.1, 0.2, 0.4, 0.5, 0.6, and 0.8.

[0023] In order to enhance the ionic conductivity of the solid electrolyte material, in formula (1), the mathematical expression: 0.80 ≤ b ≤ 1.71 may be satisfied.

[0024] The upper and lower limit values of the range of b in formula (1) can be defined by any combination selected from the numerical values of 0.8, 0.86, 0.9, 1.0, 1.1, 1.3, 1.5, and 1.71.

[0025] The solid electrolyte material according to the first embodiment may be crystalline or amorphous.

[0026] The shape of the solid electrolyte material according to the first embodiment is not limited. Examples of the shape include needle-like, spherical, or ellipsoidal. The solid electrolyte material according to the first embodiment may be particles. The solid electrolyte material according to the first embodiment may be formed to have a pellet or plate shape.

[0027] When the shape of the solid electrolyte material according to the first embodiment is, for example, particulate (e.g., spherical), the solid electrolyte material may have a median diameter of 0.1 μm or more and 100 μm or less. The median diameter means the particle diameter when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured by, for example, a laser diffraction type measuring device or an image analysis device.

[0028] The solid electrolyte material according to the first embodiment may have a median diameter of 0.5 μm or more and 10 μm or less. Thereby, the solid electrolyte material has higher conductivity. Further, when the solid electrolyte material according to the first embodiment is mixed with other materials such as an active material, the dispersion state of the solid electrolyte material according to the first embodiment and the other materials becomes good.

[0029] <Method for manufacturing solid electrolyte material> The solid electrolyte material according to the first embodiment can be manufactured, for example, by the following method.

[0030] Raw material powder is prepared and mixed so as to have the target composition. The raw material powder may be, for example, a halide.

[0031] As an example, when the target composition is Li 3.0Ti 0.5 Mg 0.5 When it is F6, LiF, TiF4, and MgF2 are mixed at a molar ratio of about 3.0:0.5:0.5. The raw material powders may be mixed at a pre-adjusted molar ratio so as to offset the compositional changes that may occur in the synthesis process.

[0032] The raw material powders are reacted with each other mechanochemically (i.e., using the method of mechanochemical milling) in a mixing device such as a planetary ball mill to obtain a reaction product. The reaction product may be fired in a vacuum or an inert atmosphere. Alternatively, a mixture of the raw material powders may be fired in a vacuum or an inert atmosphere to obtain a reaction product. The firing is preferably carried out at 100°C or higher and 300°C or lower for 1 hour or more. In order to suppress the compositional change during firing, the raw material powders are preferably fired in a sealed container such as a quartz tube.

[0033] By these methods, a solid electrolyte material according to the first embodiment is obtained.

[0034] (Second Embodiment) Hereinafter, the second embodiment will be described. Matters described in the first embodiment may be omitted.

[0035] The battery according to the second embodiment includes a positive electrode, a negative electrode, and an electrolyte layer. The electrolyte layer is provided between the positive electrode and the negative electrode. At least one selected from the group consisting of the positive electrode, the electrolyte layer, and the negative electrode contains the solid electrolyte material according to the first embodiment. Since the battery according to the second embodiment contains the solid electrolyte material according to the first embodiment, it has excellent charge and discharge characteristics. The battery may be an all-solid-state battery.

[0036] FIG. 1 shows a cross-sectional view of a battery 1000 according to the second embodiment.

[0037] The battery 1000 according to the second embodiment includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is provided between the positive electrode 201 and the negative electrode 203.

[0038] The positive electrode 201 contains positive electrode active material particles 204 and solid electrolyte particles 100.

[0039] The electrolyte layer 202 contains an electrolyte material. The electrolyte material is, for example, a solid electrolyte material.

[0040] The negative electrode 203 contains negative electrode active material particles 205 and solid electrolyte particles 100.

[0041] The solid electrolyte particles 100 are particles made of the solid electrolyte material according to the first embodiment, or particles containing the solid electrolyte material according to the first embodiment as a main component. Here, the particles containing the solid electrolyte material according to the first embodiment as a main component mean particles in which the component most contained by mass ratio is the solid electrolyte material according to the first embodiment.

[0042] The positive electrode 201 contains a material capable of occluding and releasing metal ions (for example, lithium ions). The said material is, for example, a positive electrode active material (for example, positive electrode active material particles 204).

[0043] Examples of the positive electrode active material are lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, or transition metal oxynitrides. Examples of the lithium-containing transition metal oxides are Li(Ni,Co,Al)O2, Li(Ni,Co,Mn)O2, or LiCoO2. In the present disclosure, the notation “(Ni,Co,Al)” in the chemical formula indicates at least one element selected from the group of elements within the parentheses. That is, “(Ni,Co,Al)” is synonymous with “at least one selected from the group consisting of Ni, Co, and Al”. The same applies to other elements.

[0044] The positive electrode active material particles 204 may have a median diameter of 0.1 μm or more and 100 μm or less. When the positive electrode active material particles 204 have a median diameter of 0.1 μm or more, in the positive electrode 201, the dispersion state of the positive electrode active material particles 204 and the solid electrolyte particles 100 becomes good. Thereby, the charge and discharge characteristics of the battery 1000 are improved. When the positive electrode active material particles 204 have a median diameter of 100 μm or less, the lithium diffusion rate in the positive electrode active material particles 204 is improved. Thereby, the battery 1000 can operate at high output.

[0045] The positive electrode active material particles 204 may have a median diameter larger than that of the solid electrolyte particles 100. Thereby, in the positive electrode 201, the dispersion state of the positive electrode active material particles 204 and the solid electrolyte particles 100 becomes good.

[0046] In order to increase the energy density and output of the battery, in the positive electrode 201, the ratio of the volume of the positive electrode active material particles 204 to the total volume of the positive electrode active material particles 204 and the solid electrolyte particles 100 may be 0.30 or more and 0.95 or less.

[0047] A coating layer may be formed on at least a part of the surface of the positive electrode active material particles 204. The coating layer can be formed on the surface of the positive electrode active material particles 204, for example, before mixing with the conductive assistant and the binder. Examples of the coating material contained in the coating layer are sulfide solid electrolyte, oxide solid electrolyte, or halide solid electrolyte. When the solid electrolyte particles 100 contain a sulfide solid electrolyte, in order to suppress the oxidative decomposition of the sulfide solid electrolyte, the coating material may contain the solid electrolyte material according to the first embodiment. When the solid electrolyte particles 100 contain the solid electrolyte material according to the first embodiment, in order to suppress the oxidative decomposition of the solid electrolyte material, the coating material may contain an oxide solid electrolyte. As the oxide solid electrolyte, lithium niobate excellent in stability at a high potential may be used. By suppressing the oxidative decomposition of the solid electrolyte material, an increase in the overvoltage of the battery can be suppressed.

[0048] To increase the energy density and output of the battery, the positive electrode 201 may have a thickness of 10 μm or more and 500 μm or less.

[0049] The electrolyte layer 202 contains an electrolyte material. The electrolyte material is, for example, a solid electrolyte material. The electrolyte layer 202 may be a solid electrolyte layer.

[0050] The electrolyte layer 202 may be composed only of the solid electrolyte material according to the first embodiment. Or, it may be composed only of a solid electrolyte material different from the solid electrolyte material according to the first embodiment. Examples of the solid electrolyte material different from the solid electrolyte material according to the first embodiment are Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li3(Al,Ga,In)X6, or LiI. Here, X is at least one selected from the group consisting of F, Cl, Br, and I.

[0051] Hereinafter, the solid electrolyte material according to the first embodiment is referred to as the first solid electrolyte material. The solid electrolyte material different from the solid electrolyte material according to the first embodiment is referred to as the second solid electrolyte material.

[0052] The electrolyte layer 202 may contain not only the first solid electrolyte material but also the second solid electrolyte material. In the electrolyte layer 202, the first solid electrolyte material and the second solid electrolyte material may be uniformly dispersed. A layer made of the first solid electrolyte material and a layer made of the second solid electrolyte material may be laminated along the stacking direction of the battery 1000.

[0053] FIG. 2 shows a cross-sectional view of the battery 2000 according to the second embodiment.

[0054] As shown in FIG. 2, the battery 2000 may include a positive electrode 201, a first electrolyte layer 212, a second electrolyte layer 222, and a negative electrode 203. That is, the electrolyte layer 202 may include the first electrolyte layer 212 and the second electrolyte layer 222. The first electrolyte layer 212 is disposed between the positive electrode 201 and the negative electrode 203. The second electrolyte layer 222 is disposed between the first electrolyte layer 212 and the negative electrode 203.

[0055] In the battery 2000, the first electrolyte layer 212 may contain a solid electrolyte material according to the first embodiment. Since the solid electrolyte material according to the first embodiment has high oxidation resistance, it can be used without oxidizing the solid electrolyte material contained in the second electrolyte layer 222. As a result, the charge and discharge efficiency of the battery can be improved.

[0056] In the battery 2000, the solid electrolyte material contained in the second electrolyte layer 222 may have a lower reduction potential than the solid electrolyte material contained in the first electrolyte layer 212. Thereby, the solid electrolyte material contained in the first electrolyte layer 212 can be used without being reduced. As a result, the charge and discharge efficiency of the battery can be improved. For example, when the first electrolyte layer 212 contains the solid electrolyte material according to the first embodiment, the second electrolyte layer 222 may contain a sulfide solid electrolyte in order to suppress the reductive decomposition of the solid electrolyte material.

[0057] In order to increase the energy density and output of the battery, the electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less.

[0058] The negative electrode 203 contains a material capable of occluding and releasing metal ions (for example, lithium ions). The material is, for example, a negative electrode active material (for example, negative electrode active material particles 205).

[0059] Examples of the negative electrode active material include metal materials, carbon materials, oxides, nitrides, tin compounds, or silicon compounds. The metal material may be a single metal or an alloy. Examples of the metal material include lithium metal or a lithium alloy. Examples of the carbon material include natural graphite, coke, carbon in the process of graphitization, carbon fiber, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of the capacity density, preferred examples of the negative electrode active material are silicon (i.e., Si), tin (i.e., Sn), a silicon compound, or a tin compound.

[0060] The negative electrode active material may be selected in consideration of the reduction resistance of the solid electrolyte material contained in the negative electrode 203. For example, when the negative electrode 203 contains the solid electrolyte material according to the first embodiment, the negative electrode active material may be a material capable of occluding and releasing lithium ions at 0.27 V or more with respect to lithium. Examples of such a negative electrode active material include titanium oxide, indium metal, or a lithium alloy. Examples of the titanium oxide are Li4Ti5O 12 , LiTi2O4, or TiO2. By using the above negative electrode active material, reduction decomposition of the solid electrolyte material according to the first embodiment contained in the negative electrode 203 can be suppressed. As a result, the charge-discharge efficiency of the battery can be improved.

[0061] The negative electrode active material particles 205 may have a median diameter of 0.1 μm or more and 100 μm or less. When the negative electrode active material particles 205 have a median diameter of 0.1 μm or more, in the negative electrode 203, the dispersion state of the negative electrode active material particles 205 and the solid electrolyte particles 100 becomes good. Thereby, the charge-discharge characteristics of the battery are improved. When the negative electrode active material particles 205 have a median diameter of 100 μm or less, the lithium diffusion rate in the negative electrode active material particles 205 is improved. Thereby, the battery can operate at high power.

[0062] The negative electrode active material particles 205 may have a median diameter larger than that of the solid electrolyte particles 100. Thereby, in the negative electrode 203, the dispersion state of the negative electrode active material particles 205 and the solid electrolyte particles 100 becomes good.

[0063] In order to increase the energy density and output of the battery, in the negative electrode 203, the ratio of the volume of the negative electrode active material particles 205 to the total volume of the negative electrode active material particles 205 and the solid electrolyte particles 100 may be 0.30 or more and 0.95 or less.

[0064] In order to increase the energy density and output of the battery, the negative electrode 203 may have a thickness of 10 μm or more and 500 μm or less.

[0065] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a second solid electrolyte material for the purpose of enhancing ion conductivity, chemical stability, and electrochemical stability.

[0066] The second solid electrolyte material may be a sulfide solid electrolyte.

[0067] Examples of sulfide solid electrolytes are Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, or Li 10 GeP2S 12 and so on.

[0068] When the electrolyte layer 202 contains the solid electrolyte material according to the first embodiment, in order to suppress the reduction decomposition of the solid electrolyte material, the negative electrode 203 may contain a sulfide solid electrolyte. By covering the negative electrode active material with an electrochemically stable sulfide solid electrolyte, it is possible to suppress the contact between the solid electrolyte material according to the first embodiment and the negative electrode active material. As a result, the internal resistance of the battery can be reduced.

[0069] The second solid electrolyte material may be an oxide solid electrolyte.

[0070] Examples of oxide solid electrolytes are (i) NASICON-type solid electrolytes such as LiTi2(PO4)3 or its element-substituted products, (ii) A perovskite-type solid electrolyte such as (LaLi)TiO3, (iii) Li 14 ZnGe4O 16 , a LISICON-type solid electrolyte such as Li4SiO4, LiGeO4 or an element-substituted body thereof, (iv) A garnet-type solid electrolyte such as Li7La3Zr2O 12 or an element-substituted body thereof, or (v) Li3PO4 or an N-substituted body thereof, is used.

[0071] As described above, the second solid electrolyte material may be a halide solid electrolyte.

[0072] Examples of the halide solid electrolyte are Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li3(Al,Ga,In)X6, or LiI. Here, X is at least one selected from the group consisting of F, Cl, Br, and I.

[0073] Another example of the halide solid electrolyte material is a compound represented by Li a Me b Y c X6. Here, a + mb + 3c = 6 and c > 0 are satisfied. Me is at least one selected from the group consisting of a metal element other than Li and Y and a semi-metal element. m represents the valence of Me. The "semi-metal element" means B, Si, Ge, As, Sb, and Te. The "metal element" means all elements included in Groups 1 to 12 of the periodic table (excluding hydrogen), and all elements included in Groups 13 to 16 of the periodic table (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0074] To increase the ionic conductivity of the halide solid electrolyte material, Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. The halide solid electrolyte may be Li3YCl6 or Li3YBr6.

[0075] The second solid electrolyte material may be an organic polymer solid electrolyte.

[0076] Examples of the organic polymer solid electrolyte are a polymer compound and a lithium salt compound.

[0077] The polymer compound may have an ethylene oxide structure. Since the polymer compound having an ethylene oxide structure can contain a large amount of lithium salt, the ionic conductivity can be further increased.

[0078] Examples of the lithium salt are LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. One kind of lithium salt selected from these may be used alone. Or, a mixture of two or more lithium salts selected from these may be used.

[0079] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a non-aqueous electrolyte solution, a gel electrolyte, or an ionic liquid for the purpose of facilitating the transfer of lithium ions and improving the output characteristics of the battery.

[0080] The non-aqueous electrolyte solution contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0081] Examples of non-aqueous solvents include cyclic carbonate solvents, chain carbonate solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, or fluorine solvents. Examples of cyclic carbonate solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of chain carbonate solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Chain ether solvents are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a chain ester solvent is methyl acetate. Examples of fluorine solvents are fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone. Or, a combination of two or more non-aqueous solvents selected from these may be used.

[0082] Examples of lithium salts are LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. One lithium salt selected from these may be used alone. Or, a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L or more and 2 mol / L or less.

[0083] As the gel electrolyte, a polymer material impregnated with a non-aqueous electrolyte can be used. Examples of the polymer material are polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0084] Examples of cations contained in the ionic liquid are (i) Aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium, (ii) Aliphatic cyclic ammonium such as pyrrolidinium, morpholinium, imidazolinium, tetrahydropyrimidinium, piperazinium, or piperidinium, or (iii) Nitrogen-containing heteroaromatic cations such as pyridinium or imidazolium, is.

[0085] Examples of anions contained in the ionic liquid are PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - is.

[0086] The ionic liquid may contain a lithium salt.

[0087] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder for the purpose of improving the adhesion between particles.

[0088] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, methyl polyacrylate ester, ethyl polyacrylate ester, hexyl polyacrylate ester, polymethacrylic acid, methyl polymethacrylate ester, ethyl polymethacrylate ester, hexyl polymethacrylate ester, polyvinyl acetate, polyvinyl pyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene butadiene rubber, or carboxymethyl cellulose. Copolymers can also be used as binders. Examples of such binders are copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Mixtures of two or more materials selected from these may also be used as binders.

[0089] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive assistant to reduce the electron resistance.

[0090] Examples of conductive assistants are (i) Graphites such as natural graphite or artificial graphite, (ii) Carbon blacks such as acetylene black or ketjen black, (iii) Conductive fibers such as carbon fibers or metal fibers, (iv) Carbon fluoride, (v) Metal powders such as aluminum, (vi) Conductive whiskers such as zinc oxide or potassium titanate, (vii) Conductive metal oxides such as titanium oxide, or (viii) Conductive polymer compounds such as polyaniline, polypyrrole, or polythiophene. This is the case. For cost reduction, the conductive assistant of (i) or (ii) above may be used.

[0091] Examples of the shape of the battery according to the second embodiment include coin type, cylindrical type, square type, sheet type, button type, flat type, or laminated type.

[0092] The battery according to the second embodiment may be manufactured, for example, by preparing materials for forming a positive electrode, materials for forming an electrolyte layer, and materials for forming a negative electrode, and producing a laminate in which a positive electrode, an electrolyte layer, and a negative electrode are arranged in this order by a known method.

Examples

[0093] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0094] <Example 1> (Preparation of solid electrolyte material) In an argon atmosphere having a dew point of -60°C or lower (hereinafter referred to as "dry argon atmosphere"), LiF, TiF4, and MgF2 were prepared as raw material powders so as to have a molar ratio of LiF:TiF4:MgF3 = 3.0:0.5:0.5. These materials were ground and mixed in a mortar. The obtained mixture was milled for 12 hours at 500 rpm using a planetary ball mill. In this way, a powder of the solid electrolyte material according to Example 1 was obtained. The solid electrolyte material according to Example 1 had a composition represented by Li 3.0 Ti 0.5 Mg 0.5 F6.

[0095] (Evaluation of ionic conductivity) Figure 3 shows a schematic diagram of a pressure molding die 300 used for evaluating the ionic conductivity of a solid electrolyte material.

[0096] The pressure forming die 300 included a punch upper part 301, a frame type 302, and a punch lower part 303. The frame type 302 was formed of insulating polycarbonate. The punch upper part 301 and the punch lower part 303 were formed of electronically conductive stainless steel.

[0097] Using the pressure forming die 300 shown in FIG. 3, the ionic conductivity of the solid electrolyte material according to Example 1 was evaluated by the following method.

[0098] - In a dry atmosphere having a dew point of -30°C or lower, the powder of the solid electrolyte material according to Example 1 was filled inside the pressure forming die 300. Inside the pressure forming die 300, a pressure of 400 MPa was applied to the solid electrolyte material according to Example 1 using the punch upper part 301 and the punch lower part 303.

[0099] While the pressure was applied, the punch upper part 301 and the punch lower part 303 were connected to a potentiostat (Princeton Applied Research, VersaSTAT4) equipped with a frequency response analyzer. The punch upper part 301 was connected to the working electrode and the terminal for potential measurement. The punch lower part 303 was connected to the counter electrode and the reference electrode. The impedance of the solid electrolyte material was measured at room temperature by the electrochemical impedance measurement method.

[0100] FIG. 4 is a graph showing a Cole-Cole plot obtained by measuring the impedance of the solid electrolyte material according to Example 1.

[0101] In FIG. 4, the real value of the impedance at the measurement point where the absolute value of the phase of the complex impedance is the smallest was regarded as the resistance value for the ionic conduction of the solid electrolyte material. Using the resistance value, the ionic conductivity was calculated based on the following mathematical formula (2). σ=(R SE ×S / t) -1 ···(2) Here, σ represents the ionic conductivity. S represents the contact area with the upper part 301 of the solid electrolyte material (equal to the cross-sectional area of the hollow part of the frame type 302 in FIG. 3). R SE represents the resistance value of the solid electrolyte material in the impedance measurement. t represents the thickness of the solid electrolyte material (i.e., the thickness of the layer formed from the powder 101 of the solid electrolyte material in FIG. 3).

[0102] The ionic conductivity of the solid electrolyte material according to Example 1, measured at 25 °C, was 2.33×10 -6 S / cm.

[0103] (Fabrication of the battery) In a dry argon atmosphere, the solid electrolyte material according to Example 1 and LiCoO2 as the active material were prepared so as to have a volume ratio of 30:70. These materials were mixed in an agate mortar. In this way, a positive electrode mixture was obtained.

[0104] Next, LiCl and YCl3 were prepared so as to have a molar ratio of LiCl:YCl3 = 3:1. These materials were ground and mixed in a mortar. The obtained mixture was milled using a planetary ball mill at 500 rpm for 12 hours. In this way, a halide solid electrolyte (hereinafter referred to as "LYC") having a composition represented by Li3YCl6 was obtained.

[0105] In an insulating cylinder having an inner diameter of 9.5 mm, LYC (60 mg), the solid electrolyte material according to Example 1 (26 mg), and the above-mentioned positive electrode mixture (9.1 mg) were laminated in this order. A pressure of 300 MPa was applied to the obtained laminate, and a second electrolyte layer, a first electrolyte layer, and a positive electrode were formed. That is, the first electrolyte layer formed from the solid electrolyte material according to Example 1 was sandwiched between the second electrolyte layer and the positive electrode. The thicknesses of the second electrolyte layer and the first electrolyte layer were 450 μm and 150 μm, respectively.

[0106] Next, a metal In (thickness: 200 μm) was laminated on the second electrolyte layer. A pressure of 80 MPa was applied to the obtained laminate, and a negative electrode was formed.

[0107] Next, a current collector formed of stainless steel was attached to the positive electrode and the negative electrode, and a current collecting lead was attached to the current collector.

[0108] Finally, using an insulating ferrule, the inside of the insulating cylinder was blocked from the outside air atmosphere, and the inside of the cylinder was sealed. Thus, the battery according to Example 1 was obtained.

[0109] (Charge and Discharge Test) FIG. 5 is a graph showing the initial discharge characteristics of the battery according to Example 1. The initial charge and discharge characteristics were measured by the following method.

[0110] The battery according to Example 1 was placed in a thermostat at 85°C.

[0111] 27 μA / cm 2 At a current density of, the battery according to Example 1 was charged until a voltage of 3.6 V was reached. The current density corresponds to a 0.02 C rate.

[0112] Next, at a current density of 27 μA / cm 2 the battery according to Example 1 was discharged until a voltage of 1.9 V was reached.

[0113] As a result of the charge and discharge test, the battery according to Example 1 had an initial discharge capacity of 900.76 μAh.

[0114] <Examples 2 to 16> (Preparation of Solid Electrolyte Material) In Examples 2 to 15, LiF, TiF4, and MgF2 were prepared as raw material powders so as to have a molar ratio of LiF:TiF4:MgF2 = {6-(4-2x)b}:(1-x)b:xb.

[0115] In Example 16, LiF, TiF4, and CaF2 were prepared as raw material powders so as to have a molar ratio of LiF:TiF4:CaF2 = {6-(4-2x)b}:(1-x)b:xb.

[0116] Except for the above matters, solid electrolyte materials according to Examples 2 to 16 were obtained in the same manner as in Example 1.

[0117] For the solid electrolyte materials according to Examples 2 to 16, the values of x, b, and the Li / (Ti+M) molar ratio are shown in Table 1.

[0118] (Evaluation of ionic conductivity) The ionic conductivity of the solid electrolyte materials according to Examples 2 to 16 was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

[0119] (Charge-discharge test) Using the solid electrolyte materials according to Examples 2 to 16, batteries according to Examples 2 to 16 were obtained in the same manner as in Example 1.

[0120] For the batteries according to Examples 2 to 16, a charge-discharge test was conducted in the same manner as in Example 1. The batteries according to Examples 2 to 16 were charged and discharged well, just like the battery according to Example 1.

[0121] <Comparative Example 1> As the solid electrolyte material, Li 3.0 Ti 0.5 Mg 0.5 Instead of F6, LiBF4 was used.

[0122] In the same manner as in Example 1, the ionic conductivity of LiBF4 was measured. The ionic conductivity measured at 25°C was 6.67×10 -9 S / cm.

[0123] Using LiBF4 as the solid electrolyte material, a battery according to Comparative Example 1 was obtained in the same manner as in Example 1.

[0124] For the battery according to Comparative Example 1, a charge-discharge test was conducted in the same manner as in Example 1. As a result, the battery according to Comparative Example 1 had an initial discharge capacity of 0.01 μAh or less. That is, the battery according to Comparative Example 1 was neither charged nor discharged.

[0125] The solid electrolyte materials and the respective evaluation results in Examples 1 to 16 and Comparative Example 1 are shown in Table 1.

[0126]

Table 1

[0127] <Discussion> The solid electrolyte materials according to Examples 1 to 16 have a high ionic conductivity of 1×10 -8 S / cm or more at room temperature. On the other hand, the solid electrolyte material according to the comparative example has a low ionic conductivity of less than 1×10 -8 S / cm.

[0128] As is clear from comparing Examples 1 to 3 and Examples 11 to 14 with Examples 4 and 5, when 0.8 ≦ b ≦ 1.3 is satisfied, the ionic conductivity of the solid electrolyte material becomes even higher.

[0129] As is clear from comparing Example 1 with Example 16, when M is Mg rather than Ca, the ionic conductivity of the solid electrolyte material becomes higher.

[0130] The batteries according to Examples 1 to 16 were all charged and discharged at 85°C. On the other hand, the battery according to Comparative Example 1 was neither charged nor discharged.

[0131] Since the solid electrolyte materials according to Examples 1 to 16 do not contain sulfur, hydrogen sulfide is not generated.

[0132] As described above, the solid electrolyte material according to the present disclosure has a high lithium ion conductivity and is suitable for providing a battery that can be charged and discharged well.

Industrial Applicability

[0133] The solid electrolyte material of the present disclosure is used, for example, in all-solid-state lithium-ion secondary batteries.

Description of reference numerals

[0134] 100 Solid electrolyte particles 101 Powder of solid electrolyte material 201 Positive electrode 202 Electrolyte layer 212 First electrolyte layer 222 Second electrolyte layer 203 Negative electrode 204 Positive electrode active material particles 205 Negative electrode active material particles 300 Pressing die 301 Upper punch 302 Frame type 303 Lower punch 1000 Battery 2000 Battery

Claims

1. Substantially consisting of Li, Ti, M, and F, where M is Mg or Ca, represented by the following compositional formula (1), Li 6-(4-2x)b (Ti 1-x M x ) b F 6... Formula (1) In the compositional formula (1), when M is Mg, 0 < x < 1 and 0 < b ≤ 3 are satisfied, and when M is Ca, x = 0.5 and b = 1 are satisfied, A solid electrolyte material.

2. M is Mg and the mathematical formula: 0.05 ≤ x ≤ 0.8, is satisfied, The solid electrolyte material according to Claim 1.

3. M is Mg and the mathematical formula: 0.05 ≤ x ≤ 0.6, is satisfied, The solid electrolyte material according to Claim 1 or 2.

4. M is Mg and the mathematical formula: 0.80 ≤ b ≤ 1.71, is satisfied, The solid electrolyte material according to any one of Claims 1 to 3.

5. A positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, comprising, at least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer contains the solid electrolyte material according to any one of Claims 1 to 4, A battery.

6. The electrolyte layer includes a first electrolyte layer and a second electrolyte layer, the first electrolyte layer is disposed between the positive electrode and the negative electrode, the second electrolyte layer is disposed between the first electrolyte layer and the negative electrode, the first electrolyte layer contains the solid electrolyte material, The battery according to claim 5.

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