Transition metal composite oxide powder, electrode for power storage device using same, and power storage device

Abstract

To provide a transition metal complex oxide powder that is used as an electrode material of a power storage device, has superior discharge rate characteristics, and allows for improved energy density, and a power storage device electrode and a power storage device each including the transition metal complex oxide powder.SOLUTION: A transition metal complex oxide powder includes a transition metal complex oxide that contains molybdenum, niobium, and titanium, satisfying the following formula (1): TiaMobNbcOd (a=1-x, b=16x, c=16x+2, d=86x+7, x=0.05-0.6).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a transition metal composite oxide powder suitable as an electrode material for an electricity storage device, an electrode for an electricity storage device using the same, and an electricity storage device. [Background technology]

[0002] In recent years, various materials have been studied as electrode materials for energy storage devices. Among these, lithium titanate has attracted attention as an active material for energy storage devices in electric vehicles (HEVs, PHEVs, and BEVs) due to its excellent input / output characteristics, especially at low temperatures.

[0003] Energy storage devices for electric vehicles require high energy density to improve fuel economy or power consumption. Although lithium titanate has excellent input / output characteristics, its energy density remains at 175 mAh / g, and there are still challenges in achieving higher energy density. As a result, there is a movement to use transition metal oxides containing niobium, tungsten, or molybdenum, which have high discharge capacity, as alternative anode materials.

[0004] Patent Document 1 discloses niobium molybdenum oxide for charging and / or discharging at a C rate of 5C, and a specific compound is Nb2Mo3O 14 , Nb 14 Mo3O 44 , and Nb 12 MoO 44 has been disclosed.

[0005] Patent Document 2 discloses niobium molybdenum oxide for increasing discharge capacity per volume, and reports that battery characteristics can be improved by specifying the molar ratio of niobium to molybdenum. Patent Document 3 discloses niobium molybdenum oxide in which a part of molybdenum is replaced with another metal element. 0.05 Mo 0.95 Nb 12 O 32.95, Zr 0.05 Mo 0.95 Nb 12 O 32.95 , W 0.25 Mo 0.75 Nb 12 O 32.95 It is disclosed that the rate characteristics are improved. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2021-527306 [Patent Document 2] Patent Publication No. 2021-61223 [Patent Document 3] International Publication No. 2021 / 245411 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the electricity storage devices in which oxides of niobium and molybdenum described in Patent Documents 1 to 3 are used as negative electrode materials, although high discharge capacity can be obtained, the average discharge voltage (voltage relative to Li) is high, and therefore the energy density cannot be increased significantly. Note that the advantage of increasing battery capacity is that it leads to an improvement in energy density per unit weight or unit area, which can extend the driving range of electric vehicles and secure installation space for storage batteries.

[0008] Therefore, an object of the present invention is to provide a transition metal composite oxide powder suitable as an electrode material for an electricity storage device, which is used as the electrode material for the electricity storage device and has excellent energy density and discharge rate characteristics, an electrode for the electricity storage device using the same, and an electricity storage device. [Means for solving the problem]

[0009] As a result of extensive investigations to achieve the above-mentioned object, the present inventors have found that the energy density and discharge rate characteristics of an electricity storage device can be improved by using, as an electrode material, a transition metal composite oxide powder containing molybdenum, niobium, and titanium, in which the molar ratio of molybdenum, niobium, and titanium is specified within a certain range, and have completed the present invention.

[0010] (1) A transition metal composite oxide powder, which contains molybdenum, niobium, and titanium and satisfies the following formula (1): Ti a Mo b Nb c O d (a=1―xb=16x c=16x+2 d=86x+7 x=0.05~0.6)...(1) (2) The transition metal composite oxide powder according to (1), wherein the formula (1) satisfies x=0.08 to 0.3. (3) The transition metal composite oxide powder is Ti 0.9 Mo 1.6 Nb 3.6 O 15.6 , Ti 0.88 Mo 1.92 Nb 3.92 O 17.32 , Ti 0.85 Mo 2.4 Nb 4.4 O 19.9 , Ti 0.8 Mo 3.2 Nb 5.2 O 24.2 , Ti 0.75 Mo4Nb6O 28.5 The transition metal composite oxide powder according to (1) or (2), characterized by containing at least one selected from the following: (4) The transition metal composite oxide powder according to any one of (1) to (3), wherein the D50 of primary particles corresponding to 50% cumulative volume in the volume-based particle size distribution of the transition metal composite oxide powder as determined by a laser diffraction scattering method is 0.6 μm or more. (5) The specific surface area of ​​the transition metal composite oxide powder is 2 m 2 / g or more 15m2 The transition metal composite oxide powder according to any one of (1) to (4), wherein the transition metal composite oxide powder has a viscosity of 1000 MPa or less. (6) The transition metal composite oxide powder according to any one of (1) to (5), which is an electrode material for an electricity storage device. (7) An electrode for an electricity storage device, comprising the transition metal composite oxide powder according to any one of (1) to (6) as an active material. (8) An electricity storage device comprising the electrode according to (7). [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a transition metal composite oxide powder suitable as an electrode material for an electricity storage device that has excellent energy density and discharge rate characteristics, an electrode for an electricity storage device using the same, and an electricity storage device. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Transition metal composite oxide powder] The transition metal composite oxide powder of the present invention is represented by the general formula Ti a Mo b Nb c O d This refers to a transition metal composite oxide powder expressed as (a=1-xb=16x c=16x+2 d=86x+7 x=0.05 to 0.6).

[0013] <General formula Ti a Mo b Nb c O d Transition metal composite oxide represented by (a=1-xb=16x c=16x+2 d=86x+7 x=0.05~0.6) The transition metal composite oxide powder of the present invention is represented by the general formula Ti a Mo b Nb c O d(a=1-xb=16x+2 c=16x d=86x+7 x=0.05-0.6) The transition metal composite oxide is represented by the formula: (a=1-xb=16x+2 c=16x d=86x+7 x=0.05-0.6). Specific examples of the compound include Ti, a molybdenum-niobium-titanium composite oxide capable of absorbing and releasing Li ions and Na ions. 0.9 Mo 1.6 Nb 3.6 O 15.6 , Ti 0.88 Mo 1.92 Nb 3.92 O 17.32 , Ti 0.85 Mo 2.4 Nb 4.4 O 19.9 , Ti 0.8 Mo 3.2 Nb 5.2 O 24.2 , Ti 0.75 Mo4Nb6O 28.5 , Ti 0.5 Mo8Nb 10 O 50 and the like. The molybdenum niobium titanium composite oxide may partially contain a titanium oxide phase (e.g., rutile-type TiO2, TiO, etc.) derived from the synthesis raw materials. In the case of the molybdenum niobium titanium composite oxide, x is preferably in the range of 0.05 to 0.45, more preferably in the range of 0.05 to 0.35, and particularly preferably in the range of 0.08 to 0.3. Within this range, the energy density of the molybdenum niobium titanium composite oxide is improved.

[0014] <Specific surface area> The specific surface area of ​​the transition metal composite oxide powder of the present invention is the surface area per unit mass when nitrogen is used as an adsorption gas. The measuring method will be explained in the examples below.

[0015] The transition metal composite oxide powder of the present invention has a specific surface area of ​​15 m 2 / g or less, and an electricity storage device excellent in energy density and discharge rate characteristics can be obtained. 2 / g or more 12m 2 / g or less is preferable, and 2.5m 2 / g or more 10m 2 / g or less is more preferable.

[0016] <d50> D50 of the transition metal composite oxide powder of the present invention is an index of the volume median particle size. It means the particle size at which the cumulative volume frequency calculated from the volume fraction determined by laser diffraction / scattering particle size distribution measurement reaches 50% when calculated from the smallest particle size. The measurement method will be explained in the examples below.

[0017] The transition metal composite oxide powder of the present invention may be in the form of primary particles or secondary particles formed by agglomeration of primary particles. When the primary particles made of transition metal composite oxide particles contain secondary particles formed by agglomeration, some of the secondary particles may not form secondary particles and may be in the form of primary particles themselves.

[0018] When the transition metal composite oxide powder of the present invention is a secondary particle, the lower limit of the D50 of the secondary particle is preferably 11 μm or more, more preferably 12 μm or more, and even more preferably 13 μm or more, from the viewpoint of improving electrode density. Furthermore, the upper limit of the D50 of the secondary particle is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 14 μm or less. Note that the D50 of the secondary particle represents the D50 before the crushing treatment (ultrasonic application with an ultrasonic device).

[0019] From the viewpoint of discharge rate characteristics, the lower limit of D50 of the primary particles of the transition metal composite oxide powder of the present invention may be 0.6 μm or more, preferably 0.7 μm or more. The upper limit of D50 may be 5 μm or less, preferably 4 μm or less, more preferably 3 μm or less. Note that D50 of the primary particles represents D50 after a crushing treatment (using an ultrasonic device to apply ultrasound).

[0020] [Method of manufacturing transition metal composite oxide powder] An example of the method for producing the transition metal composite oxide powder of the present invention will be explained below, divided into the raw material preparation step, the firing step, and the surface treatment step, but the method for producing the transition metal composite oxide powder of the present invention is not limited to this.

[0021] <Raw material preparation process> First, the starting materials are mixed. In particular, in the case of a molybdenum-niobium-titanium composite oxide, an oxide or salt containing Mo, Ti, and Nb is used as the starting material. Furthermore, when the molybdenum-niobium-titanium composite oxide contains other additive elements, the salt used as the starting material is preferably a salt that decomposes at a relatively low melting point to produce an oxide, such as a hydroxide salt, carbonate salt, or nitrate salt. Furthermore, in order to reduce the primary particle size, it is preferable to use a powder as the starting material having an average primary particle size of 2 μm or less, preferably 0.5 μm or less.

[0022] The method for mixing the raw materials is not particularly limited, and either wet mixing or dry mixing may be used. For example, a Henschel mixer, an ultrasonic disperser, a homomixer, a mortar, a ball mill, a centrifugal ball mill, a planetary ball mill, a vibrating ball mill, an attritor-type high-speed ball mill, a bead mill, a roll mill, etc. may be used.

[0023] <Firing process> Next, the mixture obtained above is fired. Firing is carried out at a temperature range of 600 to 800°C, more preferably 650 to 750°C. By keeping the firing temperature at 800°C or less, general-purpose equipment can be used. When firing the mixture for a short period of time, it is preferable to prepare the mixed powder constituting the mixture before firing so that the D95 value in the particle size distribution curve measured with a laser diffraction / scattering particle size distribution analyzer is 5 μm or less. Here, D95 refers to the particle size at which the cumulative volume frequency calculated by volume fraction is 95% when calculated from the smallest particle size.

[0024] The calcination method is not particularly limited as long as it can be performed under the above conditions. Usable calcination methods include fixed-bed calcination furnaces, roller hearth calcination furnaces, mesh belt calcination furnaces, fluidized bed calcination furnaces, and rotary kiln calcination furnaces. However, for efficient calcination in a short time, roller hearth calcination furnaces, mesh belt calcination furnaces, and rotary kiln calcination furnaces are preferred. In particular, rotary kiln calcination furnaces are particularly preferred for producing the transition metal composite oxide powder of the present invention because they do not require a container to contain the mixture, can be used to calcinate the mixture while continuously adding it, and can impart a uniform thermal history to the calcined material, thereby enabling the production of a homogeneous oxide.

[0025] The transition metal composite oxide powder obtained after the heat treatment as described above may have slight agglomerations, but does not need to be pulverized to destroy the particles. Therefore, after the heat treatment, it is sufficient to perform crushing or classification to the extent that agglomerations are broken down, if necessary.

[0026] Dew point control may be performed during the heat treatment process to reduce the moisture content of the transition metal composite oxide powder of the present invention. If the heat-treated powder is exposed to the atmosphere, it will absorb moisture from the atmosphere. Therefore, it is preferable to handle the powder in a dew point-controlled environment during cooling in the heat treatment furnace and after the heat treatment. The heat-treated powder may be classified as needed to adjust the particles to the desired maximum particle size range. When dew point control is performed during the heat treatment process, it is preferable to seal the transition metal composite oxide powder of the present invention in an aluminum-laminated bag or the like and then place it in an environment outside of dew point control. Even under dew point control, pulverization of the heat-treated transition metal composite oxide powder makes it more likely to absorb moisture from the crushed surfaces, increasing the moisture content of the powder. Therefore, it is preferable not to pulverize the heat treatment. Regarding heat treatment conditions, the temperature and holding time within specific ranges significantly affect the secondary particle morphology and surface treatment process. The heat treatment temperature is preferably 450°C or higher, but less than 550°C. This is because a heat treatment temperature above 550°C significantly reduces the specific surface area, significantly degrading battery performance, particularly rate characteristics. Furthermore, the holding time is preferably 1 hour or more, because if the holding time is short, the amount of moisture contained in the powder will increase and it is thought that this will also affect the particle surface condition.

[0027] [Active material] The active material of the present invention contains the transition metal composite oxide powder of the present invention. It may contain one or more substances other than the transition metal composite oxide powder of the present invention. Examples of other substances include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers), tin and tin compounds, silicon and silicon compounds, and lithium-containing metal oxides. In particular, lithium-containing metal oxides such as Li4Ti5O 12 Lithium titanate containing the above as its main component is exemplified.

[0028] [Energy storage devices] The electricity storage device of the present invention is a device that includes an electrode containing the active substance material of the present invention and stores and releases energy by utilizing the intercalation and deintercalation of lithium ions into such an electrode, and examples thereof include a hybrid capacitor and a lithium battery.

[0029] [Hybrid capacitor] The hybrid capacitor is a device that uses, as a positive electrode, an active material that generates capacitance by physical adsorption, such as activated carbon, similar to the electrode material of an electric double layer capacitor, an active material that generates capacitance by physical adsorption and intercalation / deintercalation, such as graphite, or an active material that generates capacitance by redox, such as a conductive polymer, and uses, as a negative electrode, the active material of the present invention. The active material of the present invention is usually used in the form of an electrode sheet for the hybrid capacitor.

[0030] [Lithium battery] The lithium battery of the present invention is a general term for lithium primary batteries and lithium secondary batteries. In this specification, the term lithium secondary battery is used to conceptually include so-called lithium ion secondary batteries and all-solid-state lithium ion secondary batteries.

[0031] The lithium battery is composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, or a solid electrolyte, and the active material of the present invention can be used as an electrode material. The active material of the present invention is usually used in the form of an electrode sheet for the lithium battery. This active material may be used as either a positive electrode active material or a negative electrode active material, but the following description will be given of its use as a negative electrode active material.

[0032] <Negative electrode> The negative electrode has a negative electrode layer containing a negative electrode active material (the active material of the present invention), a conductive agent, and a binder on one or both sides of a negative electrode current collector. This negative electrode layer is usually in the form of an electrode sheet. In the case of a negative electrode current collector having pores such as a porous body, the negative electrode layer contains the negative electrode active material (the active material of the present invention), a conductive agent, and a binder in the pores.

[0033] The conductive agent for the negative electrode is not particularly limited as long as it is an electron-conductive material that does not undergo chemical changes. Examples include graphites such as natural graphite (e.g., flake graphite) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; and carbon nanotubes such as single-phase carbon nanotubes, multi-walled carbon nanotubes (graphite layers in a multi-layered concentric cylindrical shape) (non-fishbone-shaped), cup-stacked carbon nanotubes (fishbone-shaped), nodular carbon nanofibers (non-fishbone structure), and platelet-type carbon nanofibers (playing card-shaped). Graphites, carbon blacks, and carbon nanotubes may be appropriately mixed and used. Although not particularly limited, the specific surface area of ​​the carbon black is preferably 30 m. 2 / g~3000m 2 / g, and more preferably 50m 2 / g~2000m 2 The specific surface area of ​​the graphite is preferably 30 m / g. 2 / g~600m 2 / g, and more preferably 50m 2 / g~500m 2 The aspect ratio of the carbon nanotubes is 2-150, preferably 2-100, and more preferably 2-50.

[0034] The amount of conductive agent added varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, and therefore should be optimized. However, it is preferably 0.1% to 10% by mass, and more preferably 0.5% to 5% by mass, in the negative electrode layer. If it is less than 0.1% by mass, the conductivity of the negative electrode layer cannot be ensured. If it exceeds 10% by mass, the active material ratio decreases, resulting in insufficient discharge capacity of the power storage device per unit mass and unit volume of the negative electrode layer, making it unsuitable for achieving high capacity. The conductive agent may be added during electrode preparation, or it may be coated on the active material itself. This is because coating with a conductive agent such as carbon fiber can further improve the conductivity of the negative electrode layer.

[0035] Examples of binders for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethyl cellulose (CMC). While not particularly limited, the molecular weight of polyvinylidene fluoride is preferably 20,000 to 1,000,000. From the viewpoint of ensuring the binding of the negative electrode layer, it is preferably 25,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more. From the viewpoint of ensuring conductivity without interfering with the contact between the active material and the conductive agent, it is preferably 500,000 or less. In particular, when the specific surface area of ​​the active material is 10 m 2 / g or more, the molecular weight is preferably 100,000 or more.

[0036] The amount of binder added varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, and therefore should be optimized, but is preferably 0.2% by mass to 15% by mass in the negative electrode layer. From the viewpoint of enhancing binding properties and ensuring the strength of the negative electrode layer, the amount is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. From the viewpoint of preventing a decrease in the active material ratio and a decrease in the discharge capacity of the electricity storage device per unit mass and unit volume of the negative electrode layer, the amount is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0037] Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, calcined carbon, and those coated with carbon, nickel, titanium, or silver. The surface of these materials may be oxidized, or the negative electrode current collector surface may be roughened by surface treatment. Examples of the negative electrode current collector include a sheet, net, foil, film, punched material, lath, porous material, foam, fiber group, and nonwoven fabric molded body. Porous aluminum is preferred as the negative electrode current collector. The porosity of the porous aluminum is 80% or more and 95% or less, preferably 85% or more.

[0038] The negative electrode can be produced by uniformly mixing a negative electrode active material (including the active material of the present invention), a conductive agent, and a binder in a solvent to form a paint, which is then applied to the negative electrode current collector, dried, and compressed. In the case of a porous negative electrode current collector having pores, the paint is prepared by uniformly mixing a negative electrode active material (including the active material of the present invention), a conductive agent, and a binder in a solvent, and is then pressed into the pores of the current collector to fill the pores, or by immersing a porous current collector in the paint to allow the paint to diffuse into the pores, followed by drying and compression.

[0039] As a method for uniformly mixing the negative electrode active material (the active material of the present invention), the conductive agent, and the binder in a solvent to prepare a paint, for example, a kneader of the type in which a stirring rod revolves while rotating within a kneading vessel such as a planetary mixer, a twin-screw extrusion kneader, a planetary stirring degassing device, a bead mill, a high-speed rotary mixer, a powder suction continuous dissolution and dispersion device, etc. Alternatively, the manufacturing process may be divided into steps depending on the solid content concentration, and these devices may be used separately.

[0040] Uniform mixing of the negative electrode active material (the active material of the present invention), conductive agent, and binder in a solvent requires optimization because it depends on the specific surface area of ​​the active material, the type of conductive agent, the type of binder, and the combination thereof. However, when using a kneader such as a planetary mixer, in which the stirring rod revolves while rotating within a kneading vessel, a twin-screw extrusion kneader, or a planetary stirring and degassing device, it is preferable to divide the production process into steps based on the solid content, knead the mixture at a high solid content, and then gradually reduce the solid content to adjust the viscosity of the coating material. A high solid content is preferably 60% to 90% by mass, more preferably 60% to 80% by mass. A solid content of 60% by mass or more is preferable because it provides sufficient shear force, while a solid content of 90% by mass or less is preferable because it reduces the load on the device, and 80% by mass or less is even more preferable.

[0041] The mixing procedure is not particularly limited, but examples include a method of simultaneously mixing the negative electrode active material, the conductive agent, and the binder in a solvent, a method of previously mixing the conductive agent and the binder in a solvent and then adding and mixing the negative electrode active material, a method of previously preparing a negative electrode active material slurry, a conductive agent slurry, and a binder solution and then mixing them, etc. Among these, in order to achieve uniform dispersion, a method of previously mixing the conductive agent and the binder in a solvent and then adding and mixing the negative electrode active material, and a method of previously preparing a negative electrode active material slurry, a conductive agent slurry, and a binder solution and then mixing them are preferred.

[0042] As the solvent, an organic solvent can be used, and examples of the organic solvent include aprotic organic solvents such as 1-methyl-2-pyrrolidone, dimethylacetamide, and dimethylformamide, used alone or in combination of two or more kinds, and preferably 1-methyl-2-pyrrolidone.

[0043] When an organic solvent is used as the solvent, it is preferable to dissolve the binder in the organic solvent before use.

[0044] <Positive electrode> The positive electrode has a positive electrode layer containing a positive electrode active material, a conductive agent, and a binder on one or both surfaces of a positive electrode current collector.

[0045] As the positive electrode active material, a material capable of absorbing and releasing lithium is used, and examples of the active material include composite metal oxides containing lithium and containing cobalt, manganese, or nickel, and lithium-containing olivine-type phosphates. These positive electrode active materials can be used alone or in combination of two or more. Examples of such composite metal oxides include LiCoO2, LiMn2O4, LiNiO2, and LiCo 1-x Ni x O2(0.01 <x<1)、LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiNi 1 / 2 Mn 3 / 2 O4, etc., and these lithium composite oxides may be partially substituted with other elements, such as partially substituting cobalt, manganese, and nickel with at least one element such as B, Nb, Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, and La, partially substituting O with S or F, or coating with a compound containing these other elements. Examples of lithium-containing olivine-type phosphates include LiFePO4, LiCoPO4, LiNiPO4, LiMnPO4, and LiFe 1-x Examples include MxPO4 (M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, and x is 0≦x≦0.5).

[0046] The conductive agent and binder for the positive electrode may be the same as those for the negative electrode. Examples of the positive electrode current collector include aluminum, stainless steel, nickel, titanium, baked carbon, and aluminum or stainless steel surfaces treated with carbon, nickel, titanium, or silver. The surface of these materials may be oxidized, or the positive electrode current collector surface may be roughened by surface treatment. Examples of the current collector form include sheets, nets, foils, films, punched materials, laths, porous materials, foams, fiber groups, and nonwoven fabric molded bodies.

[0047] <Nonaqueous electrolyte> The non-aqueous electrolyte is a non-aqueous solvent in which an electrolyte salt is dissolved. There are no particular limitations on the non-aqueous electrolyte, and various types can be used.

[0048] The electrolyte salt used is one that dissolves in a non-aqueous electrolyte. Examples of the electrolyte salt include inorganic lithium salts such as LiPF, LiBF, LiPO, LiN(SOF), and LiClO; lithium salts containing a chain-like fluorinated alkyl group such as LiN(SOCF), LiN(SOCF) , LiCFSO, LiC(SOCF), LiPF(CF), LiPF(CF) , LiPF(CF) , LiPF(CF) , LiPF(iso-CF) , and LiPF(iso-CF); lithium salts containing a cyclic fluorinated alkylene chain such as (CF)(SO)NLi and (CF)(SO)NLi; and lithium salts having an oxalate complex as the anion, such as lithium bis[oxalate-O,O']borate and lithium difluoro[oxalate-O,O']borate. Among these, particularly preferred electrolyte salts are LiPF6, LiBF4, LiPO2F2, and LiN(SO2F)2, with LiPF6 being the most preferred. These electrolyte salts can be used alone or in combination of two or more. A preferred combination of these electrolyte salts is one in which the non-aqueous electrolyte solution contains LiPF6 and at least one lithium salt selected from LiBF4, LiPO2F2, and LiN(SO2F)2.

[0049] The concentration of all of these electrolyte salts dissolved in the nonaqueous solvent is usually preferably 0.3 M or more, more preferably 0.5 M or more, and even more preferably 0.7 M or more, with the upper limit being preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

[0050] On the other hand, examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and S=O bond-containing compounds, and the non-aqueous solvent preferably contains a cyclic carbonate. Note that the term "chain ester" is used as a concept including chain carbonates and chain carboxylic acid esters.

[0051] Examples of the cyclic carbonate include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans- or cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter, both are collectively referred to as "DFEC"), vinylene carbonate (VC), vinylethylene carbonate (VEC), and 4-ethynyl-1,3-dioxolan-2-one (EEC). One or more selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one, and 4-ethynyl-1,3-dioxolan-2-one (EEC) are more preferred from the viewpoint of improving the charge rate characteristics of the power storage device and suppressing the amount of gas generated during high-temperature operation, and one or more cyclic carbonates having an alkylene chain selected from propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate are even more preferred. The proportion of the cyclic carbonate having an alkylene chain in all cyclic carbonates is preferably 55% to 100% by volume, and more preferably 60% to 90% by volume.

[0052] Therefore, the non-aqueous electrolyte is preferably prepared by dissolving an electrolyte salt containing at least one lithium salt selected from LiPF, LiBF, LiPOF, and LiN(SOF) in a non-aqueous solvent containing one or more cyclic carbonates selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one, and 4-ethynyl-1,3-dioxolan-2-one. The cyclic carbonate is more preferably one or more cyclic carbonates having an alkylene chain selected from propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate.

[0053] In particular, it is preferable to use a non-aqueous electrolyte solution having a total electrolyte salt concentration of 0.5M to 2.0M, containing at least LiPF as the electrolyte salt, and further containing 0.001M to 1M of at least one lithium salt selected from LiBF, LiPOF, and LiN(SOF). When the proportion of lithium salts other than LiPF in the non-aqueous solvent is 0.001M or more, the charge rate characteristics of the power storage device are improved and the gas generation amount during high-temperature operation is suppressed. When the proportion is 1.0M or less, there is little concern about a decrease in the effect of improving the charge rate characteristics of the power storage device and suppressing the gas generation amount during high-temperature operation. The proportion of lithium salts other than LiPF in the non-aqueous solvent is preferably 0.01M or more, particularly preferably 0.03M or more, and most preferably 0.04M or more. The upper limit is preferably 0.8M or less, more preferably 0.6M or less, and particularly preferably 0.4M or less.

[0054] In order to achieve suitable physical properties, the non-aqueous solvents are preferably used in combination, such as a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate, a chain carbonate and a lactone, a combination of a cyclic carbonate, a chain carbonate and an ether, a combination of a cyclic carbonate, a chain carbonate and a chain ester, a combination of a cyclic carbonate, a chain carbonate and a nitrile, or a combination of a cyclic carbonate, a chain carbonate and an S═O bond-containing compound.

[0055] Suitable examples of the chain ester include one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate; one or more symmetric chain carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate; pivalic acid esters such as methyl pivalate, ethyl pivalate, and propyl pivalate; and one or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

[0056] Among the chain esters, chain esters having a methyl group selected from dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate, and ethyl acetate (EA) are preferred, and chain carbonates having a methyl group are particularly preferred.

[0057] When chain carbonates are used, it is preferable to use two or more types. It is more preferable that both symmetric chain carbonates and asymmetric chain carbonates are contained, and it is even more preferable that the content of the symmetric chain carbonate is higher than that of the asymmetric chain carbonate.

[0058] The content of the chain ester is not particularly limited, but is preferably in the range of 60% to 90% by volume relative to the total volume of the nonaqueous solvent. If the content is 60% by volume or more, the viscosity of the nonaqueous electrolyte solution will not become too high, and if it is 90% by volume or less, the electrical conductivity of the nonaqueous electrolyte solution will decrease, which will reduce the risk of reducing the effect of improving the charge rate characteristics of the electricity storage device and reducing the amount of gas generation during high-temperature operation, so the above range is preferable.

[0059] The volume ratio of the symmetric chain carbonate in the chain carbonate is preferably 51% by volume or more, more preferably 55% by volume or more. The upper limit is more preferably 95% by volume or less, and even more preferably 85% by volume or less. It is particularly preferable that the symmetric chain carbonate contains dimethyl carbonate. Furthermore, it is more preferable that the asymmetric chain carbonate has a methyl group, and methyl ethyl carbonate is particularly preferable. In the above case, the charge rate characteristics of the electricity storage device are improved and the effect of suppressing the amount of gas generation during high-temperature operation is improved, which is preferable.

[0060] The ratio of cyclic carbonate to chain ester is preferably 10:90 to 45:55 (volume ratio), more preferably 15:85 to 40:60, and particularly preferably 20:80 to 35:65, from the viewpoint of improving the charge rate characteristics of the electricity storage device and enhancing the effect of suppressing the amount of gas generated during high-temperature operation.

[0061] <Lithium battery structure> The structure of the lithium battery of the present invention is not particularly limited, and examples include a coin battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and further, a cylindrical battery or a prismatic battery having a positive electrode, a negative electrode, and a roll-shaped separator.

[0062] The separator is an insulating thin film having high ion permeability and a predetermined mechanical strength. Examples include polyethylene, polypropylene, cellulose paper, glass fiber paper, polyethylene terephthalate, and polyimide microporous membranes. Multilayer membranes formed by combining two or more of these materials can also be used. The surface of these separators can also be coated with resins such as PVDF, silicone resins, and rubber-based resins, or particles of metal oxides such as aluminum oxide, silicon dioxide, and magnesium oxide. The pore size of the separator may be within a range generally useful for batteries, for example, 0.01 μm to 10 μm. The thickness of the separator may be within a range generally used for batteries, for example, 5 μm to 300 μm.

[0063] <Solid electrolyte> A solid electrolyte is a solid electrolyte that allows ions to move within it. In particular, inorganic solid electrolytes are solid in the steady state and are not usually dissociated or liberated into cations and anions. Inorganic solid electrolytes are not particularly limited as long as they have the conductivity of metal ions belonging to Group 1 of the periodic table, but generally have almost no electronic conductivity. Representative examples of inorganic solid electrolytes include (A) sulfide inorganic solid electrolytes and (B) oxide inorganic solid electrolytes. Sulfide inorganic solid electrolytes are particularly preferred because they have high ionic conductivity and can be formed into dense compacts with few grain boundaries simply by applying pressure at room temperature. The periodic table referred to here refers to the long-period version of the periodic table.

[0064] The sulfide inorganic solid electrolyte may be amorphous glass, crystallized glass, or a crystalline material. Specific examples of the sulfide inorganic solid electrolyte include, but are not limited to, the following combinations: Li2S-P2S5, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S -GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li 10 GeP2S 12 .

[0065] Among these combinations, LPS glass and LPS glass ceramics made by combining Li2S-P2S5 are preferred.Other sulfide inorganic solid electrolytes that are suitable include argerodite-type solid electrolytes such as Li6PS5Cl and Li6PS5Br.

[0066] The oxide inorganic solid electrolyte contains oxygen atoms and is a metal oxide belonging to Group 1 of the periodic table. Preferably, the material has both ionic conductivity and electronic insulation.

[0067] Examples of oxide inorganic solid electrolytes include Lithium super ionic conductor (LISICON) type crystal structures. 3.5 Zn 0.25 GeO4, La with perovskite crystal structure 0.55 Li 0.35 TiO3, LiTi2P3O with NASICON (sodium super ionic conductor) type crystal structure 12 , Li7La3Zr2O with a garnet-type crystal structure 12 (LLZ), lithium phosphate (Li3PO4), lithium phosphate in which some of the oxygen in the lithium phosphate is replaced with nitrogen, LiPON, Li3BO3-Li2SO4, Li2O-B2O3-P2O5, Li2O-SiO2, and Li6BaLa2Ta2O 12 Suitable examples include:

[0068] The volume average particle size of the inorganic solid electrolyte is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.1 μm or more, and the upper limit is preferably 100 μm or less, more preferably 50 μm or less. [Example]

[0069] Next, the present invention will be explained in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples and includes various combinations that can be easily inferred from the gist of the invention.

[0070] [Example 1] 5.900 g of molybdenum oxide (MoO3), 12.258 g of niobium oxide (Nb2O5), and 1.842 g of anatase TiO2 were weighed and mixed. The molar ratio was equivalent to MoO3:Nb2O5:TiO2 = 16:18:9. This mixed powder was heat-treated at 700°C for 12 hours. The resulting powder sample was crushed in an agate mortar for several minutes. Powder X-ray diffraction measurements were performed on the resulting fired powder sample at a sampling interval of 0.01° and a scan rate of 2° / min. In this way, the transition metal composite oxide of Example 1 was produced.

[0071] [Examples 2 and 3 and Comparative Examples 1 to 3] The transition metal composite oxides of Examples 2 and 3 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the metal species, blending amounts, and composition ratios of the transition metal composite oxides in Example 1 were as shown in Table 1. In Comparative Example 1, anatase-type TiO2 was not used.

[0072] [Measurement of powder properties] The various physical properties of the transition metal composite oxide powders of the examples and comparative examples were measured as follows.

[0073] <Measurement of specific surface area> The specific surface area (m 2 / g) was measured using a fully automatic BET specific surface area measurement device (manufactured by Mountech Co., Ltd., trade name "Macsorb HM model-1208"), and nitrogen gas was used as the adsorption gas. 0.5 g of the measurement sample powder was weighed, placed in a φ12 standard cell (HM1201-031), degassed under vacuum at 100 °C for 0.5 hours, and then measured by the BET single-point method.

[0074] <Calculation of D50: Dry laser diffraction scattering method> The D50 of the transition metal composite oxide powder of each example and each comparative example was calculated from the particle size distribution curve measured using a laser diffraction / scattering type particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of the sample was put into a container containing 50 ml of ion-exchanged water as the measurement solvent, and the container was shaken by hand until it was visually confirmed that the powder was uniformly dispersed in the measurement solvent. Then the container was placed in the measurement cell for measurement. The pulverization treatment was carried out by applying ultrasonic waves (30 W, 3 s) with an ultrasonic wave generator inside the device. Further, the measurement solvent was added until the transmittance of the slurry was within the appropriate range (the range indicated by the green bar of the device) to perform the particle size distribution measurement. The D50 of the mixed powder after pulverization was calculated from the obtained particle size distribution curve. Note that the D50 after pulverization corresponds to the D50 of the primary particles.

[0075] [Evaluation of battery characteristics] Coin-type batteries were fabricated using the transition metal composite oxide powders of each example and comparative example, and their battery characteristics were evaluated. The evaluation results are shown in Table 1.

[0076] [Fabrication of negative electrode sheet] The negative electrode sheet was prepared as follows in a room controlled at a room temperature of 25°C and a dew point of -20°C or less. A paint was prepared by mixing 90% by mass of the transition metal composite oxide powder of each example as the active material, 5% by mass of acetylene black as a conductive agent, and 5% by mass of polyvinylidene fluoride as a binder as follows: Polyvinylidene fluoride, acetylene black, and 1-methyl-2-pyrrolidone, which had been previously dissolved in 1-methyl-2-pyrrolidone, were mixed using a planetary agitator / deaerator, and then the transition metal composite oxide powder was added. The total solids concentration was adjusted to 64% by mass, and the mixture was mixed using a planetary agitator / deaerator. Subsequently, 1-methyl-2-pyrrolidone was added, and the total solids concentration was adjusted to 50% by mass, and the mixture was mixed using a planetary agitator / deaerator to prepare the paint. The resulting coating material was applied to aluminum foil and dried to prepare a single-sided negative electrode sheet for use in a coin battery (described later) and a double-sided negative electrode sheet for use in a laminate battery (described later). The target coating weight was 7.5 mg / cm. 2 It was decided.

[0077] <Preparation of electrolyte> The electrolyte solution used in the battery for characteristic evaluation was prepared as follows: In an argon glove box controlled at a temperature of 25°C and a dew point of -70°C or less, a non-aqueous solvent of ethylene carbonate (EC):dimethyl carbonate (DMC) = 1:2 (volume ratio) was prepared, and LiPF6 was dissolved in this as an electrolyte salt to a concentration of 1 M to prepare the coin battery electrolyte solution described below.

[0078] <Creating a coin battery> The negative electrode single-sided sheet prepared by the above method was punched into a circle with a diameter of 14 mm and cut into 2 t / cm 2 An electrode for evaluation was prepared by pressing the electrode at a pressure of 1000 kJ / cm2 and then vacuum drying at 120°C for 5 hours. The electrode for evaluation and metallic lithium (formed into a circle with a thickness of 0.5 mm and a diameter of 16 mm) were placed opposite each other with glass filters (one each of ADVANTEC GA-100 and Whatman GF / C) interposed between them, and the nonaqueous electrolyte prepared by the method described above in <Preparation of electrolyte> was added and sealed to prepare a 2032-type coin battery.

[0079] <Battery characteristics: Measurement of initial discharge capacity and 5C rate discharge characteristics> The coin battery fabricated by the method described in the above <Coin Battery Fabrication> was placed in a thermostatic chamber at 25°C and charged at 0.2 mA / cm in the direction in which Li was absorbed into the evaluation electrode. 2 The battery was charged to 1 V at a current density of 0.05 mA / cm at 1 V. 2 After constant current and constant voltage charging, the current density was increased to 0.2 mA / cm. 2 The battery was subjected to constant-current discharge at a current density of 0.2 C to 3 V. It was then charged to 1 V at a current equivalent to 0.2 C of the obtained discharge capacity, and further charged at 1 V until the charging current reached a current equivalent to 0.05 C. It was then discharged to 3 V at a current equivalent to 0.2 C. The initial discharge capacity (mAh / g) was calculated by dividing the discharge capacity (mAh) by the mass of the transition metal composite oxide powder. The energy density was calculated from the average discharge voltage and initial discharge capacity of the transition metal composite oxide obtained from the discharge curve when combined with a positive electrode with an average discharge voltage of 3.7 V. Next, the battery was charged to 1 V at a current equivalent to 0.3 C of the initial discharge capacity, and then discharged to 2 V at a current of 5 C to determine the 5C discharge capacity. The 5C discharge capacity was divided by the initial discharge capacity to calculate the 5C rate discharge capacity percentage (%). The 5C rate discharge capacity rate measured on the coin battery of Comparative Example 1 was set to 100, and the 5C rate discharge capacity rates of Examples 1 to 3 and Comparative Examples 1 to 3 were calculated as relative ratios, and the results are shown in Table 1 as 5C rate discharge characteristics (relative ratio %). If a transition metal composite oxide has high 5C rate discharge characteristics, when it is used as an electrode material for an electricity storage device, it can be expected to improve the charge rate characteristics of the electricity storage device. The "C" in 1C represents the current value during charging and discharging. For example, 1C refers to the current value at which the theoretical capacity can be fully discharged (or fully charged) in 1 / 1 hour, and 0.1C refers to the current value at which the theoretical capacity can be fully discharged (or fully charged) in 1 / 0.1 hour. [Table 1]

[0080] <Evaluation results> It was found that, by setting the molar ratios of Mo, Nb, and Ti in the transition metal composite oxide within specific ranges, the electrodes using the transition metal composite oxide powders of Examples 1 to 3 were able to lower the average discharge voltage, improve the energy density, and further enhance the discharge rate characteristics while maintaining the initial discharge capacity compared to Comparative Examples 1 and 3. Furthermore, Comparative Example 2, in which the molar ratio of Ti was too high, had a low initial discharge capacity and insufficient energy density. [Industrial Applicability]

[0081] The transition metal composite oxide powder obtained by the present invention can improve the energy density and discharge rate characteristics while maintaining the initial discharge capacity, and is therefore useful as an electrode active material for lithium ion secondary batteries. Furthermore, lithium ion secondary batteries using this transition metal composite oxide powder as an electrode active material are capable of stable, high-speed charging and discharging, and are therefore useful as secondary batteries for driving or backing up various devices such as automobiles and electronic devices, and for storing power at night in homes, offices, etc.

Claims

1. A transition metal composite oxide powder, which contains molybdenum, niobium, and titanium and satisfies the following formula (1): Ti ａ Mo ｂ Nb ｃ O ｄ (a=1-x b=16x c=16x+2 d=86x+7 x=0.05~0.6)・・・(1)

2. 2. The transition metal composite oxide powder according to claim 1, wherein the formula (1) satisfies x=0.08 to 0.

3.

3. The transition metal composite oxide powder is Ti ０．９ Mo １．６ Nb ３．６ O １５．６ , Ti ０．８８ Mo １．９２ Nb ３．９２ O １７．３２ , Ti ０．８５ Mo ２．４ Nb ４．４ O １９．９ , Ti ０．８ Mo ３．２ Nb ５．２ O ２４．２ , Ti ０．７５ Mo ４ Nb ６ O ２８．５ 3. The transition metal composite oxide powder according to claim 1, comprising at least one selected from the group consisting of:

4. 4. The transition metal composite oxide powder according to claim 1, wherein the D50 of primary particles corresponding to a volume cumulative 50% in a volume-based particle size distribution by a laser diffraction scattering method of the transition metal composite oxide powder is 0.6 μm or more.

5. The specific surface area of ​​the transition metal composite oxide powder is 2 m ２ / g or more 15m ２ The transition metal composite oxide powder according to any one of claims 1 to 4, wherein the transition metal composite oxide powder has a molecular weight of 1 / g or less.

6. The transition metal composite oxide powder according to any one of claims 1 to 5, which is an electrode material for an electricity storage device.

7. An electrode for an electricity storage device, comprising the transition metal composite oxide powder according to any one of claims 1 to 6 as an active material.

8. An electricity storage device comprising the electrode according to claim 7.

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