Niobium-containing oxide powder, electrode using same, power storage device, negative electrode active material composition, and all-solid-state secondary battery

Abstract

A niobium-containing oxide powder represented by the general formula Ti1-x / 2Nb2O7-x (x = 0-2), the niobium-containing oxide powder being characterized in that at least one metal element selected from the group consisting of Mo and Ce is present localized on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder.

Description

Niobium-containing oxide powder, electrode using same, power storage device, negative electrode active material composition, and all-solid-state secondary battery

[0001] The present invention relates to a niobium-containing oxide powder suitable as an electrode material for an electricity storage device, an electrode using the same, an electricity storage device, a negative electrode active material composition, and an all-solid-state secondary battery.

[0002] In recent years, various materials have been studied as electrode materials for power storage devices. Among these, lithium titanate has attracted attention as an active material for power 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 and power consumption. Although lithium titanate has excellent input / output characteristics, its energy density remains at 175 mAh / g, leaving challenges for further energy enhancement. Therefore, there is a movement to use niobium-containing oxides, primarily niobium titanate, which has a high energy density of 380 mAh / g, as an alternative anode material.

[0004] In Patent Document 1, A ｘ TiM ｙ Nb ２―ｙ O ７±ｚ Patent Document 1 discloses a monoclinic niobium titanium composite oxide represented by the formula (0≦x≦5, 0≦y≦0.5, −0.3≦z≦0.3, M is at least one metal other than Ti and Nb, A is Li or Na, and M is at least one metal selected from the group consisting of Mg, Al, V, Fe, Mo, Sn, and W). According to Patent Document 1, when the oxide is used as an electrode material for an electricity storage device, it is possible to provide an active material that has high capacity and is excellent in large-current discharge performance and cycle life performance.

[0005] Patent Document 2 discloses an active material comprising: monoclinic niobium titanium composite oxide particles capable of absorbing and releasing Li ions; and carbon fibers that coat at least a portion of the surface of the niobium titanium composite oxide particles, contain one or more metal elements selected from the group consisting of Fe, Co, and Ni, and have an average fiber diameter in the range of 5 nm to 100 nm, satisfying the following formula (2): The niobium titanium composite oxide particles have an average primary particle diameter in the range of 0.05 μm to 2 μm. Patent Document 2 states that an electricity storage device having excellent capacity, cycle life, and large-current discharge performance can be obtained.

[0006] In recent years, attention has been drawn to all-solid-state secondary batteries, which use inorganic solid electrolytes instead of organic electrolytes. Because the cathode, anode, and electrolyte of all-solid-state secondary batteries are all solid, they have the potential to significantly improve safety and reliability. Furthermore, because safety devices can be simplified, high energy density is possible, and they are expected to be applied to electric vehicles, large-scale storage batteries, and other applications.

[0007] In all-solid-state secondary batteries, from the viewpoint of realizing excellent ionic conductivity and long-term cycle characteristics, it is extremely important to form a good solid-solid interface and continuously maintain that interface. Lithium titanate has attracted attention as a way to maintain a good interface between the active material and the solid electrolyte. Because lithium titanate exhibits very little volume change during charge and discharge, it is expected that the interface between the active material and the solid electrolyte will be maintained for a long period of time during charge and discharge. However, although lithium titanate has excellent input / output characteristics, its energy density remains at 175 mAh / g, leaving challenges for further energy enhancement. Therefore, as an alternative candidate, there is a movement to utilize niobium-containing oxides, primarily niobium-titanium composite oxides, which have a high energy density of 387 mAh / g, as anode materials. Patent Document 3 describes a combination of a sulfide solid electrolyte and D ５０ (μm) / BET(m ２ / g) is 0.005 or more and 5.0 or less １±α Nb ２±β O ７±γPatent Document 3 discloses an electrode mixture containing a niobium titanium composite oxide represented by the formula (1) and (2). Patent Document 3 discloses that when the electrode mixture is used as an electrode mixture for a solid-state battery, excellent charge / discharge efficiency can be obtained.

[0008] JP 2017-224625 A JP 2020-149829 A International Publication No. 2021 / 049665

[0009] However, the electricity storage device using niobium titanate as the negative electrode material of Patent Document 1 has a problem in that the initial capacity (battery capacity) of the battery decreases when the amount of substitution element is large. Note that the advantage of increasing the battery capacity is that it leads to an improvement in the energy density per unit weight or unit area, which leads to an extension of the driving range of electric vehicles and the securing of installation space for storage batteries.

[0010] In the active material of Patent Document 2, the surfaces of niobium titanium composite oxide particles are coated with carbon fibers containing a metal element. However, the carbon fibers do not contribute to the battery capacity, and as a result, there is a problem that the battery capacity decreases and the energy density per unit weight or unit area decreases.

[0011] For the reasons described above, the electricity storage devices using the negative electrode active materials and electrodes of Patent Documents 1 and 2 cannot simultaneously achieve improved energy density, improved cycle performance and discharge rate characteristics, and reduced resistance in the low temperature range.

[0012] In addition, the D ５０ Although the battery characteristics of all-solid-state secondary batteries were improved by using an electrode mixture consisting of a titanium-niobium composite oxide and a sulfide solid electrolyte with a ratio of 1 to 10% within a specified range, further improvement was required in terms of charge rate characteristics.

[0013] A first object of the present invention is to provide a niobium-containing oxide powder and a negative electrode active material composition that can be used as a negative electrode material for an all-solid-state secondary battery and can significantly improve battery characteristics, particularly initial discharge capacity, initial efficiency, and charge rate characteristics, and an all-solid-state secondary battery containing the same.

[0014] In addition, as a second aspect, the present invention aims to provide a niobium-containing oxide powder that can be used as an electrode material for an electricity storage device, has excellent discharge rate characteristics and cycle characteristics, and can suppress an increase in resistance after cycling, an electrode using the same, and an electricity storage device.

[0015] The present inventors conducted extensive research to achieve the object of the first aspect and found that when a niobium-containing oxide powder is used as a negative electrode active material for an all-solid-state secondary battery, it is very important to reduce the interfacial resistance between the solid electrolyte and the niobium-containing oxide. Therefore, they conducted extensive research to reduce the interfacial resistance between the solid electrolyte and the niobium-containing oxide regardless of particle size or specific surface area. As a result, they found that the interfacial resistance can be significantly reduced by using a niobium-containing oxide powder in which a specific metal element is localized on the surface of the niobium-containing oxide particles that constitute the niobium-containing oxide powder, and thus completed the present invention (the invention according to the first aspect). The use of a negative electrode active material composition containing the niobium-containing oxide powder and a solid electrolyte in an all-solid-state secondary battery can improve the initial discharge capacity, initial efficiency, and charge rate characteristics. Furthermore, the present inventors' research revealed that when a portion of the Ti or Nb element described in Patent Document 1 or Patent Document 2 is replaced with a different metal, the interfacial resistance with the solid electrolyte cannot be reduced, and the effects described in the present invention (the invention according to the first aspect) cannot be obtained. A first aspect of the present invention relates to a niobium-containing oxide powder, a negative electrode active material composition, and an all-solid-state secondary battery including the same.

[0016] That is, the first aspect of the present invention provides the following (1) to (7): (1) A compound represented by the general formula Ti １－ｘ／２ Nb ２ O ７－ｘ(X=0 to 2), wherein at least one metal element selected from the group consisting of Mo and Ce is present in a localized state on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder. (2) The niobium-containing oxide powder according to (1), wherein the content (mass%) of the metal element present on the particle surface in the niobium-containing oxide powder is 0.01 to 1.2. (3) The niobium-containing oxide powder according to (1) or (2), wherein the niobium-containing oxide has a D50 of 0.6 μm or more of primary particles corresponding to 50% cumulative volume in a volume-based particle size distribution measured by a laser diffraction scattering method. (4) An anode active material composition comprising a niobium-containing oxide powder and an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table, wherein the niobium-containing oxide powder comprises the niobium-containing oxide powder according to any one of (1) to (3). (5) The negative electrode active material composition according to (4), wherein the inorganic solid electrolyte is a sulfide inorganic solid electrolyte. (6) The negative electrode active material composition according to (4) or (5), wherein the content of the inorganic solid electrolyte is 1 mass % or more and 50 mass % or less. (7) An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, wherein the negative electrode layer is a layer containing the negative electrode active material composition according to any one of (4) to (6).

[0017] Furthermore, as a result of extensive investigations to achieve the object according to the second aspect, the present inventors discovered a niobium-containing oxide powder in which a specific metal element is present at a specific concentration on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder by subjecting the niobium-containing oxide powder to a surface treatment process. In particular, it was found that the presence of a metal element with a lower valence, rather than a metal element with a higher valence, on the surface of the niobium-containing oxide particles provides a significant effect. The present invention (the invention according to the second aspect) exhibits an effect even without coating the surface of the niobium-containing oxide particles with a conductive agent such as carbon fiber, and therefore is a different technology from conventional carbon coating. It was discovered that an electricity storage device using this niobium-containing oxide powder as an electrode material has excellent discharge rate characteristics and cycle characteristics and can suppress an increase in resistance after cycling, and thus the present invention (the invention according to the second aspect) was completed.

[0018] That is, the second aspect of the present invention provides the following (8) to (14): (8) A compound represented by the general formula Ti １－ｘ／２ Nb ２ O ７－ｘ (9) A niobium-containing oxide powder according to (8), characterized in that in the niobium-containing oxide powder, the element M1 present on the particle surface is a metal element of Group 2, Group 12, Group 13, or Group 14. (10) A niobium-containing oxide powder according to (8), characterized in that in the niobium-containing oxide powder, the element M1 present on the particle surface is Al ３＋ , Mg ２＋ , Ca ２＋ , Sr ２＋ , Zn ２＋ , Ga ３＋ , Ge ２＋ , and In ２＋(11) The niobium-containing oxide powder according to any one of (8) to (10), characterized in that the niobium-containing oxide powder contains one or more elements selected from the group consisting of: (11) The niobium-containing oxide powder according to any one of (8) to (10), characterized in that the content (mass%) of element M1 present on the particle surface is 0.01 to 1.2 inclusive. (12) The niobium-containing oxide powder according to any one of (8) to (11), characterized in that the niobium-containing oxide powder contains primary particles having a D50 of 0.3 μm or more, the D50 corresponding to 50% cumulative volume in a volume-based particle size distribution measured by a laser diffraction scattering method. (13) An electrode for an electricity storage device, characterized in that it contains the niobium-containing oxide powder according to any one of (8) to (12). (14) An electricity storage device, characterized in that it contains the electrode according to (13).

[0019] According to the first aspect of the present invention, it is possible to provide a niobium-containing oxide powder suitable as an electrode material for an all-solid-state secondary battery that is excellent in initial discharge capacity, initial efficiency, and charge rate characteristics by reducing the interfacial resistance with the solid electrolyte regardless of the particle size or specific surface area of ​​the niobium-containing oxide powder, a negative electrode active material composition using the same, and an all-solid-state secondary battery.

[0020] Furthermore, according to a second aspect of the present invention, it is possible to provide a niobium-containing oxide powder suitable as an electrode material for an electricity storage device that has excellent discharge rate characteristics and cycle characteristics and can suppress an increase in resistance after cycling, an electrode using the same, and an electricity storage device.

[0021] FIG. 1 shows the results of the Mg1s depth profile.

[0022] <<First Aspect of the Invention>> The first aspect of the invention will now be described.

[0023] [Niobium-containing oxide powder according to a first aspect] The niobium-containing oxide powder according to a first aspect of the present invention is a niobium-containing oxide powder represented by the general formula Ti １－ｘ／２ Nb ２ O ７－ｘ(X=0 to 2), characterized in that at least one metal element selected from the group consisting of Mo and Ce is localized on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder. Note that X=0 to 2 indicates that 0≦X≦2. The same applies hereinafter.

[0024] <General formula Ti １－ｘ／２ Nb ２ O ７－ｘ Niobium-containing oxide powder according to a first aspect of the present invention is a niobium-containing oxide powder represented by the general formula Ti １－ｘ／２ Nb ２ O ７－ｘ (X=0 to 2). Specific examples of the compound include TiNb, a niobium-titanium composite oxide capable of absorbing and releasing Li ions and Na ions. ２ O ７ , niobium oxide Nb ２ O ５ From the viewpoint of improving the initial discharge capacity, the initial efficiency, and the charge rate characteristics, TiNb ２ O ７ The niobium titanium composite oxide is preferably a titanium oxide phase (e.g., rutile-type TiO) derived from the synthesis raw material. ２ , TiO, etc.) In the case of a niobium titanium composite oxide, the ratio of the number of moles of Nb to the number of moles of Ti (Nb / Ti ratio) is preferably in the range of 1.5 to 2.5, and more preferably in the range of 1.8 to 2.0. Within this range, the electronic conductivity of the niobium-containing oxide is improved, and the rate characteristics are excellent.

[0025] The niobium-containing oxide according to the first aspect of the present invention is generally of a monoclinic crystal type, although the crystal system is not limited thereto. In the case of the monoclinic crystal type, the aspect ratio tends to be large, but from the viewpoint of improving electrode density, the aspect ratio is preferably in the range of 1.0 to 4.0.

[0026] <Containing at least one metal element selected from the group consisting of Mo and Ce> The niobium-containing oxide powder according to the first aspect of the present invention contains at least one metal element selected from the group consisting of Mo and Ce. "Containing at least one metal element selected from the group consisting of Mo and Ce" means that at least one metal element selected from the group consisting of Mo and Ce is detected in inductively coupled plasma atomic emission spectrometry (ICP-AES) or X-ray fluorescence spectrometry (XRF) of the niobium oxide powder according to the first aspect of the present invention. The lower limit of the amount detected by inductively coupled plasma atomic emission spectrometry is typically 0.001% by mass. Mo and Ce may be contained on the particle surface of the niobium-containing oxide powder. The valences of Mo and Ce are not particularly limited, and may be 3+ or 2+, or may be 4+ or higher. From the viewpoint of improving initial discharge capacity, initial efficiency, and charge rate characteristics, Mo is preferably contained.

[0027] <Content of at least one metal element selected from the group consisting of Mo and Ce> The content (mass%) of at least one metal element selected from the group consisting of Mo and Ce in the niobium-containing oxide powder according to the first aspect of the present invention, as determined by X-ray fluorescence analysis (XRF), may be 0.01 to 1.2. When the content of at least one metal element selected from the group consisting of the metal elements Mo and Ce is within this range, an all-solid-state secondary battery having excellent initial discharge capacity, initial efficiency, and charge rate characteristics can be obtained. The content is preferably 0.01 to 1.0, and from the viewpoint of further improving the charge rate characteristics, it is more preferably 0.015 to 0.9, even more preferably 0.04 to 0.85, and particularly preferably 0.07 to 0.75. However, when Mo and Ce are simultaneously contained on the particle surface of the niobium-containing oxide powder, the content (mass%) refers to the total content of the two metal elements.

[0028] Furthermore, in the niobium-containing oxide powder according to the first aspect of the present invention, the surface region of the niobium-containing oxide particles constituting the powder contains a larger amount of at least one metal element selected from the group consisting of Mo and Ce than the internal region thereof. That is, the at least one metal element selected from the group consisting of Mo and Ce is localized on the surface of the niobium-containing oxide particles, and more specifically, the surface region of the niobium-containing oxide particles contains a larger amount of the at least one metal element selected from the group consisting of Mo and Ce than the internal region thereof. As an example, in a cross-sectional analysis of the niobium-containing oxide particles using a scanning transmission electron microscope, it is sufficient that at least one metal element selected from the group consisting of Mo and Ce is contained in a large amount in the so-called near-surface region from the surface of the niobium-containing oxide particles to a depth of about 20 nm as measured by energy dispersive X-ray spectroscopy. At least one metal element selected from the group consisting of Mo and Ce is detected at a depth of 20 nm from the surface of the niobium-containing oxide particles, while at a depth of 100 nm from the surface, it is preferable that Mo and Ce are not detected. In such a state, it can be determined that at least one metal element selected from the group consisting of Mo and Ce is localized on the surface of the niobium-containing oxide particles. That is, when measured by energy dispersive X-ray spectroscopy, it means that the amount is below the amount detected by the measurement. The lower limit of the amount detected by energy dispersive X-ray spectroscopy varies depending on the element and state to be measured, but is usually 0.5 atm%. Other examples of surface analysis methods include X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). In the first aspect of the present invention, the form of the at least one metal element selected from the group consisting of Mo and Ce that is localized on the surface of the niobium-containing oxide particle is not particularly limited, and it is sufficient that the at least one metal element selected from the group consisting of Mo and Ce is localized on the surface, and the at least one metal element may be in a metallic state or in the form of a metal compound such as a metal oxide.

[0029] The niobium-containing oxide powder according to the first aspect of the present invention preferably has a peak attributable to a Mo-O bond or a Ce-O bond in a narrow spectrum of the metal element M1 in surface analysis by X-ray photoelectron spectroscopy (XPS). Here, "having a peak attributable to a Mo-O bond or a Ce-O bond" means having a peak top of Mo or a peak top of Ce in surface analysis by X-ray photoelectron spectroscopy. Furthermore, in depth profile measurement by sputtering, when the atomic concentration (atm%) of Mo or Ce at the surface (0 nm) is taken as 100%, the atomic concentration (atm%) of Mo or Ce at a depth of 100 nm from the surface is preferably less than 5%.

[0030] <Inclusion of Further Different Elements> The niobium-containing oxide powder according to the first aspect of the present invention preferably contains, as a further different element other than the at least one metal element selected from the group consisting of Mo and Ce, at least one element selected from the group consisting of elements consisting of Al, Mg, Ca, Sr, Zn, Ga, Ge, In, B, W, and S. It is presumed that the niobium-containing oxide powder according to the first aspect of the present invention contains such a different element together with Mo and Ce, thereby adjusting the electronic conductivity of the surface of the niobium-containing oxide powder and suppressing the electrical resistance more than when the element Mo or Ce is contained alone.

[0031] <Specific surface area> The specific surface area of ​​the niobium-containing oxide powder according to the first aspect of the present invention is the surface area per unit mass measured using nitrogen as an adsorption gas. The measurement method will be described in the examples below.

[0032] The niobium-containing oxide powder according to the first aspect of the present invention has a specific surface area of ​​8.0 m ２ / g or less, and an electricity storage device excellent in initial discharge capacity, initial efficiency, and charge rate characteristics can be obtained. ２ / g or less is more preferable, and 5.5m ２ / g or less is more preferable.

[0033] <D50> D50 of the niobium-containing oxide powder according to the first aspect 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.

[0034] The niobium-containing oxide powder according to the first aspect of the present invention may be primary particles or secondary particles formed by agglomeration of primary particles. When the primary particles made of niobium-containing 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.

[0035] When the niobium-containing oxide powder according to the first aspect of the present invention is in the form of secondary particles, the lower limit of the D50 of the secondary particles 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 particles 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 particles represents the D50 before the secondary particles are crushed by ultrasonic irradiation.

[0036] In the primary particles contained in the niobium-containing oxide powder according to the first aspect of the present invention, there is a gradient in the concentration of the metal elements Mo and Ce between the surface and the interior of the primary particles, and it is preferable that the concentrations of the metal elements Mo and Ce are high on the surface (for example, a so-called near-surface region extending from the surface of the primary particles to a depth of about 20 nm), and that the metal elements Mo and Ce are not present in the interior (for example, a position 100 nm from the surface of the primary particles toward the interior). When the metal elements Mo and Ce are present in such a state, an all-solid-state secondary battery having excellent initial efficiency and charge rate characteristics can be obtained.

[0037] In terms of the initial discharge capacity and charge rate characteristics, the D50 of the primary particles of the niobium-containing oxide powder according to the first aspect of the present invention has a lower limit of preferably 0.4 μm or more, more preferably 0.5 μm or more, and even more preferably 0.6 μm or more. The upper limit of D50 is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less. The D50 of the primary particles represents the D50 after a crushing treatment (using an ultrasonic device to apply ultrasound). The niobium-containing oxide powder may contain 15% to 20% of primary particles having a primary particle diameter of less than 0.4 μm, 15% to 25% of primary particles having a primary particle diameter of less than 0.5 μm, or 15% to 30% of primary particles having a primary particle diameter of less than 0.6 μm. The primary particles exceeding 3 μm may be contained in the range of 45% to 75%, the primary particles exceeding 2 μm may be contained in the range of 25% to 75%, and the primary particles exceeding 1.2 μm may be contained in the range of 25% to 80%.

[0038] <Zeta Potential by Electrophoresis> The zeta potential of the niobium-containing oxide powder according to the first aspect of the present invention is preferably less than 0 mV, more preferably less than -5 mV. The lower limit of the zeta potential is preferably greater than -60 mV, more preferably greater than -35 mV. This is because, when the zeta potential of the niobium-containing oxide powder according to the first aspect of the present invention is in the above-mentioned range, an electricity storage device can be obtained that is excellent in initial discharge rate characteristics and in suppressing resistance increase after long-term cycling. The zeta potential represents the potential difference between the sliding surface in the electric double layer and a portion sufficiently distant from the interface, and it is presumed that this potential difference affects the Li+ permeability at the surface of the niobium-containing oxide powder. The measurement method will be described in the examples below.

[0039] [Method for producing niobium-containing oxide powder according to first aspect] Hereinafter, an example of the method for producing niobium-containing oxide powder according to the first aspect of the present invention will be described, divided into a raw material preparation step, a firing step, and a surface treatment step, but the method for producing niobium-containing oxide powder according to the first aspect of the present invention is not limited thereto.

[0040] <Raw Material Preparation Step> First, the starting materials are mixed. In particular, in the case of a niobium titanium composite oxide, an oxide or salt containing Ti and Nb is used as the starting material. Furthermore, when the 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, to ensure sufficient element diffusion in the firing step described below, it is preferable to use a powder having an average particle size of 2 μm or less, preferably 0.5 μm or less, as the starting material.

[0041] 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.

[0042] <Firing Step> Next, the mixture obtained above is fired. Firing is carried out in a temperature range of 500 to 1200°C, more preferably in a range of 700 to 1000°C. By setting the firing temperature to 1000°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 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 integrated from the smallest particle size.

[0043] The calcination method is not particularly limited as long as it is a method that can perform calcination under the above conditions. Examples of calcination methods that can be used include a fixed-bed calcination furnace, a roller hearth calcination furnace, a mesh belt calcination furnace, a fluidized bed calcination furnace, and a rotary kiln calcination furnace. However, when performing efficient calcination in a short time, a roller hearth calcination furnace, a mesh belt calcination furnace, and a rotary kiln calcination furnace are preferred. In particular, a rotary kiln calcination furnace is a particularly preferred calcination furnace for producing the niobium-containing oxide powder according to the first aspect of the present invention, since it does not require a container for storing the mixture, can perform calcination while continuously adding the mixture, and can provide a uniform thermal history to the calcined material, thereby allowing for the production of a homogeneous oxide.

[0044] <Surface Treatment Step> Next, the niobium-containing oxide obtained above is subjected to a surface treatment. The niobium-containing oxide according to the first aspect of the present invention is characterized in that at least one metal element selected from the group consisting of Mo and Ce is present in a localized state on the surface of particles constituting the niobium-containing oxide powder. When used as a negative electrode material for a battery, this makes it possible to form a dense negative electrode layer and to impart excellent charge rate characteristics. In the calcination step, a compound containing at least one metal element selected from the group consisting of Mo and Ce (hereinafter, sometimes referred to as a treating agent) can be added to produce the niobium-containing oxide powder according to the first aspect of the present invention. However, more preferably, the niobium-containing oxide powder according to the first aspect of the present invention can be produced by the following surface treatment step or the like. In particular, by employing the following surface treatment step, it is possible to appropriately and relatively simply make the surface of the niobium-containing oxide particles present with at least one metal element selected from the group consisting of Mo and Ce.

[0045] There is no particular limitation on the method for mixing the niobium-containing oxide powder as the base material with the compound containing at least one metal element selected from the group consisting of Mo and Ce, and either wet mixing or dry mixing can be used. However, it is preferable to uniformly disperse the compound containing at least one metal element selected from the group consisting of Mo and Ce on the surfaces of the particles constituting the niobium-containing oxide powder as the base material, and in this respect, wet mixing is preferred.

[0046] In the wet mixing, the treatment agent and the niobium-containing oxide powder of the base material are introduced into a water or alcohol solvent and mixed in a slurry state. As the alcohol solvent, those with a boiling point of 100°C or less, such as methanol, ethanol, and isopropyl alcohol, are preferred because they are easy to remove. Furthermore, from an industrial perspective, water solvents are preferred because they are easy to recover and dispose of.

[0047] The compound (treatment agent) containing at least one metal element selected from the group consisting of Mo and Ce is not particularly limited, and examples thereof include oxides, phosphates, hydroxides, sulfates, nitrates, fluorides, chlorides, organic compounds, and metal salt compounds such as ammonium salts and phosphates. Specific examples of Mo compounds include molybdenum oxide, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum boride, molybdophosphoric acid, molybdenum disilicide, molybdenum chloride, molybdenum sulfide, molybdenum silicic acid hydrate, sodium molybdenum oxide, molybdenum carbide, molybdenum acetate dimer, lithium molybdate, sodium molybdate, potassium molybdate, calcium molybdate, magnesium molybdate, manganese molybdate, and ammonium molybdate. Among these, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum chloride, molybdenum sulfide, and lithium molybdate are preferred. Examples of Ce compounds include cerium oxide, cerium hydroxide, cerium fluoride, cerium sulfate, cerium nitrate, cerium carbonate, cerium acetate, cerium oxalate, cerium chloride, cerium boride, and cerium phosphate, and among these, cerium sulfate and its hydrates are preferred.

[0048] The amount of the compound containing at least one metal element selected from the group consisting of Mo and Ce may be any amount as long as the amount of the at least one metal element selected from the group consisting of Mo and Ce in the niobium-containing oxide falls within the range of the present invention, but it may be added in a proportion of 0.03 mass% or more, preferably 0.05 mass% or more, relative to the niobium-containing oxide powder of the substrate. Also, it may be added in a proportion of 12 mass% or less, preferably 10 mass% or less, more preferably 8 mass% or less, relative to the niobium-containing oxide powder of the substrate.

[0049] It is preferable to perform heat treatment after the surface treatment. The heat treatment temperature is a temperature at which the at least one metal element selected from the group consisting of Mo and Ce diffuses into at least the surface region of the niobium-containing oxide particles constituting the niobium-containing oxide powder of the base material, and a temperature at which a significant decrease in the specific surface area due to sintering of the niobium-containing oxide of the base material does not occur. The upper limit of the heat treatment temperature is preferably 700°C or less, more preferably 600°C or less. The lower limit of the heat treatment temperature is preferably 300°C or more, more preferably 400°C or more. The heat treatment time is preferably 0.1 to 8 hours, more preferably 0.5 to 5 hours. The temperature and time at which the at least one metal element selected from the group consisting of Mo and Ce diffuses into at least the surface region of the niobium-containing oxide powder of the base material differ in reactivity depending on the compound containing the at least one metal element selected from the group consisting of Mo and Ce, and therefore can be appropriately set. The heating method in the heat treatment is not particularly limited. Usable heat treatment furnaces include fixed-bed firing furnaces, roller hearth firing furnaces, mesh belt firing furnaces, fluidized-bed firing furnaces, and rotary kiln firing furnaces. The atmosphere during the heat treatment may be either air or an inert atmosphere such as a nitrogen atmosphere. In particular, when a metal salt compound is used for the surface treatment, air is preferred because it facilitates the removal of anionic species from the particle surface.

[0050] The niobium-containing 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 disintegration or classification to the extent that agglomerations are broken down, as necessary.

[0051] The niobium-containing oxide powder according to the first aspect of the present invention may be mixed with a treatment agent in a surface treatment step, granulated, and then heat-treated to form a powder containing secondary particles formed by aggregation of primary particles. Any method for granulation may be used as long as secondary particles can be produced, but a spray dryer is preferred because it can process large quantities.

[0052] In order to reduce the amount of moisture contained in the niobium-containing oxide powder according to the first aspect of the present invention, dew point control may be performed in the heat treatment step. If the heat-treated powder is exposed to the atmosphere as is, the amount of moisture contained in the powder increases. 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 a desired maximum particle size range. When dew point control is performed in the heat treatment step, it is preferable to seal the niobium-containing oxide powder according to the first aspect of the present invention in an aluminum laminate 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 niobium-containing oxide powder makes it easier for moisture to be absorbed from the crushed surfaces, increasing the amount of moisture contained in the powder. Therefore, it is preferable not to pulverize the heat treatment. Regarding the heat treatment conditions, the temperature and holding time within specific ranges significantly affect the secondary particle morphology and the surface treatment step. The heat treatment temperature is preferably 450°C or higher and less than 550°C. This is because the specific surface area decreases significantly when the heat treatment temperature exceeds 550° C., resulting in a significant decrease in battery performance, particularly rate characteristics. Furthermore, the holding time is preferably 1 hour or longer, because a short holding time is thought to increase the amount of moisture contained in the powder and also affect the particle surface condition.

[0053] [Negative Electrode Active Material Composition According to a First Aspect] The negative electrode active material composition according to a first aspect of the present invention is a negative electrode active material composition comprising the niobium-containing oxide powder according to the first aspect of the present invention and an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table. The content of the inorganic solid electrolyte in the active material composition is not particularly limited, but may be 1% by mass or more, preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. A higher content of the inorganic solid electrolyte is preferred because it facilitates contact between the niobium-containing oxide powder and the solid electrolyte. Furthermore, since too much inorganic solid electrolyte reduces the battery capacity of the all-solid-state secondary battery, the content may be 70% by mass or less, preferably 60% by mass or less, and more preferably 50% by mass or less. Typically, a lower content of the inorganic solid electrolyte is preferred to increase the battery capacity of the all-solid-state secondary battery, but a lower content makes it difficult to achieve contact between the niobium-containing oxide powder and the solid electrolyte. By using the niobium-containing oxide powder used in the negative electrode active material composition according to the first aspect of the present invention, satisfactory contact between the niobium-containing oxide powder and the solid electrolyte can be obtained even when the content of the inorganic solid electrolyte is small. The negative electrode active material composition according to the first aspect of the present invention may contain one or more substances other than the niobium-containing oxide powder and the inorganic solid electrolyte. 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 include Li ４ Ti ５ O １２ Lithium titanate containing the above as its main component is exemplified.

[0054] <Periodic Table> The periodic table in this specification refers to a long-period periodic table of elements based on the provisions of IUPAC (International Union of Pure and Applied Chemistry).

[0055] [Inorganic Solid Electrolyte] An inorganic solid electrolyte is an inorganic solid electrolyte, and a solid electrolyte is a solid electrolyte that can move ions inside. Since an inorganic solid electrolyte is solid in a steady state, it is usually not dissociated or liberated into cations and anions. The inorganic solid electrolyte is not particularly limited as long as it has the conductivity of metal ions belonging to Group 1 of the periodic table, and generally has almost no electronic conductivity.

[0056] In a first aspect of the present invention, the inorganic solid electrolyte has conductivity of metal ions belonging to Group 1 of the periodic table. Representative examples of the inorganic solid electrolyte include (A) a sulfide inorganic solid electrolyte and (B) an oxide inorganic solid electrolyte. In the first aspect of the present invention, a sulfide inorganic solid electrolyte is preferably used because it has high ionic conductivity and can be formed into a dense molded body with few grain boundaries simply by applying pressure at room temperature.

[0057] (A) Sulfide Inorganic Solid Electrolyte The sulfide inorganic solid electrolyte preferably contains a sulfur atom (S), has ionic conductivity of a metal belonging to Group 1 of the periodic table, and has electronic insulation. The sulfide inorganic solid electrolyte can be produced by reacting a metal sulfide belonging to Group 1 of the periodic table with at least one sulfide represented by the following general formula (III), and two or more sulfides represented by the general formula (III) may be used in combination.

[0058] M ｘ S ｙ (III) (M represents any of P, Si, Ge, B, Al, Ga, and Sb, and x and y represent numbers that give a stoichiometric ratio depending on the type of M.)

[0059] The metal sulfide belonging to Group 1 of the periodic table is any one of lithium sulfide, sodium sulfide, and potassium sulfide, with lithium sulfide and sodium sulfide being more preferred, and lithium sulfide being even more preferred.

[0060] The sulfide represented by the general formula (III) is P ２ S ５ , SiS ２ , GeS ２ , B２ S ３ , Al ２ S ３ , Ga ２ S ３ and Sb ２ S ５ Preferably, P ２ S ５ is particularly preferred.

[0061] The composition ratio of each element in the sulfide inorganic solid electrolyte produced as described above can be controlled by adjusting the blending amounts of the metal sulfide belonging to Group 1 of the periodic table, the sulfide represented by the general formula (III), and elemental sulfur.

[0062] The sulfide inorganic solid electrolyte according to the first aspect of the present invention may be amorphous glass, crystallized glass, or a crystalline material.

[0063] Specific examples of sulfide inorganic solid electrolytes include, but are not limited to, the following combinations: Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -Al ２ S ３ , Li ２ S-GeS ２ , Li ２ S-Ga ２ S ３ , Li ２ S-GeS ２ -Ga ２ S ３ , Li ２ S-GeS ２ -P ２ S ５ , Li ２ S-GeS ２ -Sb ２ S ５ , Li ２ S-GeS ２ -Al ２ S ３ , Li ２ S-SiS ２ , Li ２ S-Al ２ S ３, Li ２ S-SiS ２ -Al ２ S ３ , Li ２ S-SiS ２ -P ２ S ５ , Li １０ GeP ２ S １２ .

[0064] Among the above combinations, Li ２ S-P ２ S ５ LPS glasses and LPS glass ceramics produced by combining the above are preferred.

[0065] The mixing ratio of the metal sulfide belonging to Group 1 of the periodic table and the sulfide represented by the general formula (III) is not particularly limited as long as it can be used as a solid electrolyte, but the mixing ratio (molar ratio) of "metal sulfide:sulfide represented by general formula (III)" is preferably 50:50 to 90:10. If the mixing ratio of the metal sulfides is 50 or more and 90 or less, the ionic conductivity can be sufficiently increased. The mixing ratio is more preferably 60:40 to 80:20, and even more preferably 70:30 to 80:20.

[0066] In order to increase ionic conductivity, the sulfide inorganic solid electrolyte may contain, in addition to the metal sulfide belonging to Group 1 of the periodic table and the sulfide represented by the general formula (III), at least one lithium halide selected from LiI, LiBr, LiCl, and LiF, or a lithium salt such as lithium oxide or lithium phosphate. However, the mixing ratio of the sulfide inorganic solid electrolyte to these lithium salts is preferably 60:40 to 95:5, and more preferably 80:20 to 95:5, in terms of the mixing ratio (molar ratio) of "sulfide inorganic solid electrolyte:lithium salt."

[0067] In addition, as sulfide inorganic solid electrolytes other than those mentioned above, Li ６ P.S. ５ Cl and Li ６ P.S. ５ Argerodite-type solid electrolytes such as Br are also suitable.

[0068] Suitable methods for producing the sulfide inorganic solid electrolyte include, but are not limited to, a solid phase method, a sol-gel method, a mechanical milling method, a solution method, and a melt quenching method.

[0069] (B) Oxide inorganic solid electrolyte

[0070] The oxide inorganic solid electrolyte preferably contains oxygen atoms, has ion conductivity of a metal belonging to Group 1 of the periodic table, and has electronic insulation properties.

[0071] Examples of oxide inorganic solid electrolytes include Lithium super ionic conductor (LISICON)-type crystalline structures. ３．５ Zn ０．２５ GeO ４ , La having a perovskite crystal structure ０．５５ Li ０．３５ TiO ３ , LiTi having a NASICON (sodium super ionic conductor) type crystal structure ２ P ３ O １２ , Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ), lithium phosphate (Li ３ P.O. ４ ), LiPON, in which some of the oxygen in lithium phosphate is replaced with nitrogen, Li ３ BO ３ -Li ２ SO ４ , Li ２ Alumni ２ O ３ -P ２ O ５ , Li ２ O—SiO ２ , and Li ６ BaLa ２ Ta ２ O １２ Suitable examples include:

[0072] The volume average particle size of the inorganic solid electrolyte is not particularly limited, but may be 0.01 μm or more, preferably 0.1 μm or more. The upper limit may be 100 μm or less, preferably 50 μm or less. The volume average particle size of the inorganic solid electrolyte can be measured using a laser diffraction / scattering particle size distribution analyzer.

[0073] The amount of inorganic solid electrolyte mixed is not particularly limited, but may be 1% by mass or more, preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more in the active material composition. A larger amount of inorganic solid electrolyte mixed is preferable because it is easier to achieve contact between the niobium-containing oxide powder and the solid electrolyte. Furthermore, since too much inorganic solid electrolyte mixed reduces the battery capacity of the all-solid-state secondary battery, the amount may be 70% by mass or less, preferably 50% by mass or less. Generally, a small amount of inorganic solid electrolyte mixed is preferable to increase the battery capacity of the all-solid-state secondary battery, but if the amount mixed is small, it becomes difficult to achieve contact between the niobium-containing oxide powder and the solid electrolyte. By using the niobium-containing oxide powder used in the negative electrode active material composition according to the first aspect of the present invention, satisfactory contact between the niobium-containing oxide powder and the solid electrolyte can be achieved even when the amount of inorganic solid electrolyte mixed is small.

[0074] [Other Ingredients] The negative electrode active material composition according to the first aspect of the present invention may contain a conductive agent and a binder in addition to the niobium-containing oxide powder and the inorganic solid electrolyte.

[0075] 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 blacks is preferably 30 m ２ / g to 3000m ２ / g, and more preferably 50m ２ / g to 2000m ２ The specific surface area of ​​the graphite is preferably 30 m ２ / g~600m ２ / g, and more preferably 50m ２ / g~500m ２ The aspect ratio of the carbon nanotubes is 2 to 150, preferably 2 to 100, and more preferably 2 to 50.

[0076] 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, but it is sufficient that the conductive agent is contained in the negative electrode active material composition in an amount of 0.1 to 10% by mass, preferably 0.5 to 5% by mass. By setting the amount within the range of 0.1 to 10% by mass, the active material ratio is made sufficient, thereby making it possible to further increase the conductivity of the negative electrode layer while ensuring sufficient initial discharge capacity of the power storage device per unit mass and unit volume of the negative electrode layer.

[0077] Examples of binders for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), styrene and butadiene copolymer (SBR), acrylonitrile and butadiene copolymer (NBR), and carboxymethyl cellulose (CMC). While not particularly limited, the molecular weight of polyvinylidene fluoride is 20,000 to 1,000,000. From the viewpoint of further enhancing the binding property 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 further enhancing conductivity without interfering with 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 When the molecular weight is 1 / g or more, the molecular weight is preferably 100,000 or more.

[0078] 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 it is sufficient that the binder is contained in the negative electrode active material composition in an amount of 0.2 to 15% by mass. From the viewpoint of improving 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 initial discharge capacity of the power storage device per unit mass and unit volume of the negative electrode layer, the amount is preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0079] [Method for Producing Negative Electrode Active Material Composition According to First Aspect] The method for producing the negative electrode active material composition according to the first aspect of the present invention is not particularly limited, and suitable examples include a method of adding a specific ratio of inorganic solid electrolyte powder to the niobium-containing oxide powder and mixing them with a mixer, a stirrer, a disperser, or the like, and a method of adding the niobium-containing oxide powder to a slurry containing a solid electrolyte.

[0080] The reason why the negative electrode active material composition containing the niobium-containing oxide according to the first aspect of the present invention exhibits better initial discharge capacity, initial efficiency, and charge rate characteristics than conventional ones in all-solid-state secondary batteries is not entirely clear, but it is believed to be as follows. The negative electrode active material composition according to the first aspect of the present invention comprises an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table and a niobium-containing oxide in which at least one metal element selected from the group consisting of Mo and Ce is localized on the surface of the niobium-containing oxide particles. Normally, when a niobium-containing oxide is mixed with an inorganic solid electrolyte, particularly a sulfide inorganic solid electrolyte, the niobium-containing oxide and the sulfide inorganic solid electrolyte chemically react, resulting in the deposition of a highly resistive reactant with low ionic conductivity at their interface, resulting in a deterioration in battery characteristics, particularly charge rate characteristics. On the other hand, the localized presence of at least one metal element selected from the group consisting of Mo and Ce on the surface of the niobium-containing oxide particles according to the first aspect of the present invention can suppress undesirable reactions with the solid electrolyte. As a result, it is believed that the characteristics of all-solid-state secondary batteries can be improved. Here, in a lithium ion secondary battery using an organic electrolyte solution, no reaction with the solid electrolyte occurs, and therefore the problem of the present application does not occur. When the niobium-containing oxide of the present application was applied to a lithium ion secondary battery using an organic electrolyte solution, no improvement in charge rate characteristics was observed.

[0081] The negative electrode active material composition according to the first aspect of the present invention can be used in the negative electrode of an all-solid-state secondary battery. In this case, the negative electrode active material composition according to the first aspect of the present invention is preferably subjected to pressure molding to form a pressure-molded body. The pressure molding conditions are not particularly limited, but the molding temperature may be 15°C to 200°C, preferably 25°C to 150°C, and the molding pressure may be 180 MPa to 1080 MPa, preferably 300 MPa to 800 MPa. The negative electrode active material composition according to the first aspect of the present invention can form a dense molded body with few voids, thereby enabling the formation of a dense negative electrode layer with few voids. The molded body obtained using the negative electrode active material composition according to the first aspect of the present invention has a packing ratio of 72.5% to 100%, preferably 73.5 to 100%. The filling rate can be measured, for example, using the density of the molded body of the negative electrode active material composition calculated from the volume and mass of the molded body of the negative electrode active material composition and the density (true density) of each material constituting the negative electrode active material composition.

[0082] [All-Solid-State Secondary Battery According to First Aspect] The all-solid-state secondary battery according to the first aspect of the present invention is composed of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, and the negative electrode active material composition according to the first aspect of the present invention, which contains the niobium-containing oxide powder and an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table, is used for the negative electrode layer. The method for producing the negative electrode layer is not particularly limited, and suitable examples include a method of pressurizing and molding the negative electrode active material composition, and a method of adding the negative electrode active material composition to a solvent to form a slurry, and then applying the negative electrode active material composition to a current collector, drying, and pressurizing and molding.

[0083] 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 and 90% or less.

[0084] As long as the negative electrode layer includes the negative electrode active material composition according to the first aspect of the present invention, the components such as the positive electrode layer and the solid electrolyte layer can be used without any particular limitation. For example, as the positive electrode active material used as the positive electrode layer for an all-solid-state secondary battery, a composite metal oxide containing one or more elements selected from cobalt, manganese, and nickel and lithium is used. These positive electrode active materials can be used alone or in combination of two or more. Examples of such lithium composite metal oxides include LiCoO ２ , LiCo １－ｘ M ｘ O ２ (wherein M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, and 0.001≦x≦0.05), LiMn ２ O ４ , LiNiO ２ , LiCo １－ｘ Ni ｘ O ２ (0.01<x<1), LiCo １／３ Ni １／３ Mn １／３ O ２ , LiNi ０．５ Mn ０．３ Co ０．２ O ２ , LiNi ０．８ Mn ０．１ Co ０．１ O ２ , LiNi ０．８ Co０．１５ Al ０．０５ O ２ , Li ２ MnO ３ and LiMO ２ (M is a transition metal such as Co, Ni, Mn, or Fe) and LiNi solid solutions. １／２ Mn ３／２ O ４ Preferably, one or more selected from the following are listed, and more preferably two or more selected from the following: ２ and LiMn ２ O ４ , LiCoO ２ and LiNiO ２ , LiMn ２ O ４ and LiNiO ２ They may be used in combination as follows.

[0085] Furthermore, a lithium-containing olivine-type phosphate can also be used as the positive electrode active material. In particular, a lithium-containing olivine-type phosphate containing at least one selected from iron, cobalt, nickel, and manganese is preferred. A specific example thereof is LiFePO ４ , LiCoPO ４ , LiNiPO ４ , LiMnPO ４ These lithium-containing olivine-type phosphates may be partially substituted with other elements, and part of the iron, cobalt, nickel, and manganese may be substituted with one or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or may be coated with a compound or carbon material containing these other elements. ４ or LiMnPO ４ The lithium-containing olivine-type phosphate can also be used by mixing with the above-mentioned positive electrode active material, for example.

[0086] The conductive agent for the positive electrode is not particularly limited as long as it is an electron-conductive material that does not undergo chemical changes. Examples include graphite such as natural graphite (e.g., flake graphite) and artificial graphite, and carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Graphite and carbon black may also be mixed appropriately. The amount of conductive agent added to the positive electrode active material composition is preferably 1 to 10% by mass, and more preferably 2 to 5% by mass.

[0087] The positive electrode active material composition contains at least the positive electrode active material and a solid electrolyte, and may optionally contain a conductive agent such as acetylene black or carbon black, and a binder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a styrene-butadiene copolymer (SBR), an acrylonitrile-butadiene copolymer (NBR), carboxymethyl cellulose (CMC), or an ethylene propylene diene terpolymer. The method for producing the positive electrode is not particularly limited, and suitable examples include a method of pressurizing and molding a powder of the positive electrode active material composition, or a method of adding a powder of the positive electrode active material composition to a solvent to form a slurry, and then applying the positive electrode active material composition to a current collector such as aluminum foil or a stainless steel lath plate, drying, and pressurizing.

[0088] The surface of the positive electrode active material may be coated with another metal oxide. Examples of the surface coating agent include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specifically, Li ４ Ti ５ O １２ , Li ２ Ti ２ O ５ , LiTaO ３ , LiNbO ３ , LiAlO ２ , Li ２ ZrO ３ , Li ２ WO ４ , Li ２ TiO ３ , Li ２ B ４ O ７ , Li３ P.O. ４ , Li ２ MoO ４ , Li ３ BO ３ , LiBO ２ , Li ２ CO ３ , Li ２ SiO ３ , SiO ２ , TiO ２ , ZrO ２ , Al ２ O ３ , B ２ O ３ etc.

[0089] The solid electrolyte layer is located between the positive electrode layer and the negative electrode layer. The thickness of the solid electrolyte layer is not particularly limited, but may be 1 μm to 100 μm. The constituent material of the solid electrolyte layer may be the aforementioned sulfide inorganic solid electrolyte or oxide inorganic solid electrolyte, and may be different from the solid electrolyte used in the electrodes. The solid electrolyte layer may also contain a binder such as butadiene rubber or butyl rubber.

[0090] There are no particular limitations on the structure of the all-solid-state secondary battery, and coin-type batteries, cylindrical batteries, square batteries, laminated batteries, etc. can be used.

[0091] <<Second Aspect of the Invention>> Next, the second aspect of the invention will be described.

[0092] [Niobium oxide powder according to a second aspect] The niobium oxide powder according to a second aspect of the present invention is a niobium oxide powder represented by the general formula Ti １－ｘ／２ Nb ２ O ７－ｘ (X=0 to 2), characterized in that M1 (M1 is a metal element having a valence of 3+ or 2+, excluding Ti or Nb) is present on the surface of the niobium-containing oxide particle constituting the niobium-containing oxide powder.

[0093] <General formula Ti １－ｘ／２ Nb ２ O ７－ｘNiobium-containing oxide powder according to a second aspect of the present invention is a niobium-containing oxide powder represented by the general formula Ti １－ｘ／２ Nb ２ O ７－ｘ The niobium-containing oxide is represented by the formula (X = 0 to 2). The upper limit of X is preferably 2 or less, more preferably 1.5 or less, even more preferably 1 or less, and particularly preferably 0.5 or less. The lower limit of X may be 0 or more. Specific examples of the compound include TiNb, which is a niobium-titanium composite oxide capable of absorbing and releasing Li ions and Na ions. ２ O ７ , niobium oxide Nb ２ O ５ Niobium titanium composite oxides contain a titanium oxide phase (e.g., rutile-type TiO) derived from the synthesis raw materials. ２ , TiO, etc.) In the case of a niobium titanium composite oxide, the ratio of the number of moles of Nb to the number of moles of Ti (Nb / Ti ratio) is preferably in the range of 1.5 to 2.5, more preferably in the range of 1.8 to 2.2, and even more preferably in the range of 1.8 to 2.0. Within this range, the electronic conductivity of the composite oxide is improved, and the rate characteristics are excellent.

[0094] The niobium-containing oxide according to the second aspect of the present invention is generally of a monoclinic crystal type, although the crystal system is not limited thereto. In the case of the monoclinic crystal type, the aspect ratio tends to be large, but from the viewpoint of improving electrode density, the aspect ratio is preferably in the range of 1.0 to 4.0.

[0095] <Metal element M1> The niobium-containing oxide powder according to the second aspect of the present invention has a metal element M1 (M1 is a metal element having a valence of 3+ or 2+, excluding Ti or Nb) present on the particle surface. The presence of the metal element M1 means that the metal element M1 is detected in inductively coupled plasma atomic emission spectrometry (ICP-AES) or X-ray fluorescence spectrometry (XRF) of the niobium oxide powder according to the second aspect of the present invention. The lower limit of the amount detectable by inductively coupled plasma atomic emission spectrometry is usually 0.001 mass%.

[0096] <Content of Metal Element M1> The content (mass%) of the metal element M1 in the niobium-containing oxide powder according to the second aspect of the present invention, determined by X-ray fluorescence analysis (XRF), may be 0.01 or more and 1.2 or less, preferably 0.01 or more and 1.0 or less, more preferably 0.01 or more and 0.9 or less, and even more preferably 0.01 or more and 0.8 or less. If the content of the metal element M1 is within this range, an electricity storage device having excellent discharge rate characteristics and cycle characteristics and suppressing resistance increase after cycling can be obtained. The content is preferably 0.05 or more and 0.5 or less, and from the viewpoint of further improving the discharge rate characteristics and further enhancing the effect of suppressing resistance increase after cycling, the content is more preferably 0.1 or more and 0.3 or less, even more preferably 0.1 or more and 0.25 or less, and particularly preferably 0.1 or more and 0.2 or less. From the viewpoint of further improving the charge rate characteristics, the content (mass%) is more preferably 0.015 or more and 0.9 or less, even more preferably 0.04 or more and 0.85 or less, and particularly preferably 0.07 or more and 0.75 or less. However, when a plurality of metal elements are simultaneously contained on the particle surface of the niobium-containing oxide powder as the metal element M1, the content (mass%) is the total content of the plurality of metal elements.

[0097] Furthermore, in the niobium-containing oxide powder according to the second aspect of the present invention, the metal element M1 is localized and present in greater amounts in the surface region than in the internal region of the niobium-containing oxide particles constituting the powder. That is, the metal element M1 is present on the surface of the niobium-containing oxide particles, and more specifically, the metal element M1 is localized and present in greater amounts in the surface region than in the internal region of the niobium-containing oxide particles. For example, in a cross-sectional analysis of the niobium-containing oxide particles using a scanning transmission electron microscope, it is sufficient that the metal element M1 is contained in a large amount in a so-called near-surface region up to a depth of about 20 nm from the surface of the niobium oxide particles as measured by energy dispersive X-ray spectroscopy. It is preferable that the metal element M1 is not detected at a depth of 100 nm from the surface. In such a state, it can be determined that the metal element M1 is localized on the surface of the niobium-containing oxide particles. In other words, it means that when measured by energy dispersive X-ray spectroscopy, the amount is equal to or less than the amount detected by the measurement, and the lower limit of the amount detected by energy dispersive X-ray spectroscopy is usually 0.5 atm%, although the value varies depending on the element and state being measured. Other examples of surface analysis methods include X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).

[0098] The niobium-containing oxide powder according to the second aspect of the present invention preferably has a peak attributable to an M1-O bond in the narrow spectrum of the metal element M1 in surface analysis by X-ray photoelectron spectroscopy (XPS). Here, "having a peak attributable to an M1-O bond" means that the metal element M1 has a peak top in surface analysis by X-ray photoelectron spectroscopy. For example, when the metal element M1 is Mg, the Mg1s peak has a peak top at 1300-1310 eV in the narrow spectrum (1250-1350 eV) of magnesium (Mg1s) when the 2p3 peak of Ti is corrected to 458.7 eV. Furthermore, in depth profile measurement by sputtering, when the atomic concentration (atm%) of the metal element M1 at the surface (0 nm) is taken as 100%, the atomic concentration (atm%) of the metal element M1 at a depth of 100 nm from the surface is preferably less than 5%.

[0099] <Specific examples of metal element M1> In the niobium-containing oxide powder, the element M1 present on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder is a metal element with a valence of 3+ or 2+, excluding Ti or Nb. The element M1 is preferably a metal element of Group 2, Group 12, Group 13, or Group 14, and is preferably Al. ３＋ , Mg ２＋ , Ca ２＋ , Sr ２＋ , Zn ２＋ , Ga ３＋ , Ge ２＋ , In ２＋ It is more preferable that the alloy contains at least one element selected from the group consisting of Al, Mg, Ca, Sr, Zn, Ga, Ge, and In (that is, when expressed in the form of metal elements, it is more preferable that the alloy contains at least one element selected from the group consisting of Al, Mg, Ca, Sr, Zn, Ga, Ge, and In). ３＋ , Mg ２＋ , Ca ２＋ , Zn ２＋ , Ga ３＋ , In ２＋ It is more preferable that the alloy contains at least one element selected from the group consisting of Al ３＋ , Mg ２＋ , Zn ２＋ , Ga ３＋ , In ２＋ It is particularly preferable that the niobium-containing oxide powder contains one or more selected from the group consisting of: (a) and (b) above. Note that two or more of these metal elements may be contained. This is because, by containing these elements, the niobium-containing oxide powder according to the second aspect of the present invention can provide an electricity storage device that is excellent in discharge rate characteristics and cycle characteristics and that suppresses an increase in resistance after cycling.

[0100] <Inclusion of Further Different Elements> The niobium-containing oxide powder according to the second aspect of the present invention preferably contains at least one element selected from the group consisting of B, Mo, W, and S as a further different element other than the metal elements having a valence of 3+ or 2+ excluding Ti or Nb. Of these, S is particularly preferred. It is presumed that the niobium-containing oxide powder according to the second aspect of the present invention contains such a different element together with the element M1, thereby improving the electronic conductivity of the surface of the niobium-containing oxide powder compared to when the element M1 is contained alone.

[0101] <Specific Surface Area> The specific surface area of ​​the niobium-containing oxide powder according to the second aspect of the present invention is the surface area per unit mass when nitrogen is used as an adsorption gas. The measurement method will be described in the examples below.

[0102] The niobium-containing oxide powder according to the second aspect of the present invention has a specific surface area of ​​8.0 m ２ / g or less, and an electricity storage device excellent in initial discharge capacity and rate characteristics can be obtained. ２ / g or less is preferable, and 5.5m ２ / g or less is more preferable.

[0103] <D50> D50 of the niobium-containing oxide powder according to the second aspect 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.

[0104] The niobium-containing oxide powder according to the second aspect of the present invention may be primary particles or secondary particles formed by agglomeration of primary particles. When the secondary particles are formed by agglomeration of primary particles made of niobium-containing oxide particles, some of the secondary particles may not form secondary particles and may be in the form of primary particles themselves.

[0105] When the niobium-containing oxide powder according to the second aspect of the present invention is in the form of secondary particles, the lower limit of the D50 of the secondary particles 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 particles 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 particles refers to the D50 before the crushing treatment (applying ultrasonic waves with an ultrasonic device), i.e., the D50 before the secondary particles are crushed by ultrasonic irradiation.

[0106] In the primary particles contained in the niobium-containing oxide powder according to the second aspect of the present invention, there is a gradient in the concentration of the metal element M1 between the surface and the interior of the primary particles, and it is preferable that the concentration of the metal element M1 is high on the surface (for example, a so-called near-surface region extending to a depth of about 20 nm from the surface of the primary particles), and that the metal element M1 is not present in the interior (for example, a position 100 nm from the surface toward the interior of the primary particles). When the metal element M1 is present in such a state, an electricity storage device having excellent initial discharge capacity and rate characteristics can be obtained.

[0107] Regarding the D50 of the primary particles of the niobium-containing oxide powder according to the second aspect of the present invention, from the viewpoint of achieving both discharge rate characteristics and cycle characteristics, the lower limit of D50 is preferably 0.3 μm or more, more preferably 0.6 μm or more, and even more preferably 0.7 μm or more. The upper limit of D50 is 3 μm or less, preferably 2 μm or less, and more preferably 1.2 μm or less. The D50 of the primary particles represents the D50 after a crushing treatment (using an ultrasonic device). The niobium-containing oxide powder may contain 15% to 30% of primary particles having a primary particle diameter of less than 0.6 μm, or 15% to 45% of primary particles having a primary particle diameter of less than 0.7 μm. The niobium-containing oxide powder may contain 45% to 75% of primary particles having a primary particle diameter greater than 3 μm, 25% to 75% of primary particles having a primary particle diameter greater than 2 μm, or 25% to 80% of primary particles having a primary particle diameter greater than 1.2 μm.

[0108] <Zeta Potential by Electrophoresis> The zeta potential of the niobium-containing oxide powder according to the second aspect of the present invention is preferably less than 0 mV, more preferably less than -5 mV. The lower limit of the zeta potential is preferably greater than -60 mV, more preferably greater than -35 mV. This is because, when the zeta potential of the niobium-containing oxide powder according to the second aspect of the present invention is in the above-mentioned range, an electricity storage device can be obtained that is excellent in initial discharge rate characteristics and in suppressing resistance increase after long-term cycling. The zeta potential represents the potential difference between the sliding surface in the electric double layer and a portion sufficiently distant from the interface, and it is presumed that this potential difference affects the Li+ permeability at the surface of the niobium-containing oxide powder. The measurement method will be described in the examples below.

[0109] [Method for producing niobium-containing oxide powder according to second aspect] Hereinafter, an example of the method for producing niobium-containing oxide powder according to the second aspect of the present invention will be described, divided into a raw material preparation step, a firing step, and a surface treatment step, but the method for producing niobium-containing oxide powder according to the second aspect of the present invention is not limited thereto.

[0110] <Raw Material Preparation Step> First, the starting materials are mixed. The mixing of the starting materials may be the same as that described in the first aspect above. Note that when the compound containing the metal element M1 is added before the firing step described below, the compound may be referred to as the treatment agent or treatment agent 1 hereinafter.

[0111] <Firing Step> Next, the mixture obtained above is fired. Firing is carried out in a temperature range of 500 to 1200°C, more preferably in a range of 700 to 1100°C. By setting the firing temperature to 1100°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 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 integrated from the smallest particle size.

[0112] The firing method is not particularly limited as long as it can be performed under the above conditions, and may be the same as that described in the first aspect above.

[0113] <Surface Treatment Step> Next, the niobium-containing oxide obtained above is subjected to a surface treatment. The niobium-containing oxide according to the second aspect of the present invention is characterized in that M1 (M1 is a metal element with a valence of 3+ or 2+, excluding Ti or Nb) is present in a localized state on the surface of the particles. When used as a negative electrode material for a battery, this makes it possible to form a dense negative electrode layer and to impart excellent charge rate characteristics. In the calcination step, a compound containing the metal element M1 (hereinafter sometimes referred to as a treatment agent or treatment agent 2) can be added to produce the niobium-containing oxide powder according to the second aspect of the present invention. However, more preferably, the niobium-containing oxide powder according to the second aspect of the present invention can be produced by the following surface treatment step or the like. In particular, by employing the following surface treatment step, the metal element M1 can be present on the surface of the niobium-containing oxide particles appropriately and relatively simply.

[0114] There is no particular limitation on the method for mixing the niobium-containing oxide powder as the base material with the compound containing the metal element M1, and either wet mixing or dry mixing can be used. However, it is preferable to uniformly disperse the compound containing the metal element M1 on the surfaces of the particles constituting the niobium-containing oxide powder as the base material, and in this respect, wet mixing is preferred.

[0115] In the wet mixing, the treating agent 2 and the niobium-containing oxide powder of the substrate are introduced into a water or alcohol solvent and mixed in a slurry state. As the alcohol solvent, those with a boiling point of 100°C or less, such as methanol, ethanol, and isopropyl alcohol, are preferred because they are easy to remove. Furthermore, from an industrial perspective, water solvents are preferred because they are easy to recover and dispose of.

[0116] Compounds (treatment agents) containing the metal element M1 (M1 is a metal element with a valence of 3+ or 2+, excluding Ti and Nb) are not particularly limited, but include, for example, oxides, phosphates, hydroxides, sulfate compounds, nitrate compounds, fluorides, chlorides, organic compounds, and metal salt compounds such as ammonium salts and phosphates. Specifically, when the metal element M1 is Al, examples of Al-containing compounds include aluminum oxide, aluminum phosphate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum fluoride, aluminum chloride, aluminum acetate, aluminum ammonium sulfate, and aluminum alkoxides, with aluminum sulfate and its hydrates being preferred. When the metal element M1 is Mg, examples of Al-containing compounds include, for example, magnesium oxide, magnesium phosphate, magnesium hydroxide, magnesium sulfate, magnesium nitrate, magnesium fluoride, magnesium chloride, magnesium acetate, magnesium ammonium phosphate, and magnesium alkoxides, with magnesium sulfate and its hydrates being preferred.

[0117] The amount of the compound containing the metal element M1 to be added may be any amount as long as the amount of the metal element M1 in the niobium-containing oxide falls within the range of the present invention, but it is sufficient to add it in a proportion of 0.03 mass% or more, preferably 0.05 mass% or more, and more preferably 0.1 mass% or more, relative to the niobium-containing oxide powder of the base material. Also, it is preferably added in a proportion of 12 mass% or less, more preferably 10 mass% or less, and even more preferably 8 mass% or less, relative to the niobium-containing oxide powder of the base material.

[0118] It is preferable to carry out a heat treatment after the surface treatment, and the heat treatment conditions and method may be the same as those in the first aspect.

[0119] The niobium-containing 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 disintegration or classification to the extent that agglomerations are broken down, as necessary.

[0120] The niobium-containing oxide powder according to the second aspect of the present invention may be mixed with the treatment agent 2 in the surface treatment step, granulated, and heat-treated to form a powder containing secondary particles formed by aggregation of primary particles. Any method for granulation may be used as long as it can produce secondary particles, but a spray dryer is preferred because it can process large quantities.

[0121] In order to reduce the amount of moisture contained in the niobium-containing oxide powder according to the second aspect of the present invention, dew point control may be performed in the heat treatment step. If the heat-treated powder is exposed to the atmosphere as is, moisture from the atmosphere will be adsorbed by the powder. 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 make the particles fall within the desired maximum particle size range. These conditions may be the same as those in the first aspect described above.

[0122] [Active Material According to Second Aspect] The active material according to the second aspect of the present invention comprises the niobium-containing oxide powder according to the second aspect of the present invention. It may contain one or more substances other than the niobium-containing oxide powder according to the second aspect 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 include Li ４ Ti ５ O １２ Lithium titanate containing the above as its main component is exemplified.

[0123] [Electricity storage device according to second aspect] An electricity storage device according to a second aspect of the present invention is a device that includes an electrode containing the active substance material according to the second aspect of the present invention and stores and releases energy by utilizing intercalation and deintercalation of lithium ions into such an electrode, and examples of such a device include a hybrid capacitor, a lithium battery, and an all-solid-state secondary battery.

[0124] [Hybrid Capacitor According to a Second Aspect] A hybrid capacitor according to a second aspect of the present invention is a device that uses, in its positive electrode, an active material that forms capacitance by physical adsorption, such as activated carbon, similar to the electrode materials of electric double layer capacitors, an active material that forms capacitance by physical adsorption and intercalation / deintercalation, such as graphite, or an active material that forms capacitance by redox, such as a conductive polymer, and uses, in its negative electrode, the active material according to the second aspect of the present invention. The active material according to the second aspect of the present invention is usually used in the form of an electrode sheet for the hybrid capacitor.

[0125] [Lithium Battery According to a Second Aspect] The lithium battery according to a second aspect 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 as a concept that also includes so-called lithium ion secondary batteries and all-solid-state lithium ion secondary batteries.

[0126] 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 according to the second aspect of the present invention can be used as an electrode material. The active material according to the second aspect 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.

[0127] <Negative electrode according to a second aspect> The negative electrode according to a second aspect of the present invention has a negative electrode layer containing a negative electrode active material (the active material according to the second aspect 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 that is porous or the like and has pores, the negative electrode layer contains the negative electrode active material (the active material according to the second aspect of the present invention), a conductive agent, and a binder in the pores.

[0128] 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. The same materials as those described in the first aspect above can be used, and the amount added can also be the same. If the amount is less than 0.1% by mass, the conductivity of the negative electrode layer cannot be ensured. If the amount is more than 10% by mass, the active material ratio decreases, resulting in insufficient discharge capacity of the energy 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 the active material itself may be coated with the conductive agent. This is because coating with a conductive agent such as carbon fiber can further improve the conductivity of the negative electrode layer.

[0129] As the binder for the negative electrode, the same binder as in the first aspect can be used, and the amount of binder added can be the same.

[0130] As the negative electrode current collector, the same one as in the first aspect can be used.

[0131] The negative electrode can be produced by uniformly mixing a negative electrode active material (including the active material according to the second aspect 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 negative electrode current collector that is porous or the like and has pores, the paint is formed by uniformly mixing a negative electrode active material (including the active material according to the second aspect of the present invention), a conductive agent, and a binder in a solvent, and the paint is then pressed into the pores of the current collector to fill them, or by immersing a porous current collector in the paint to allow the paint to diffuse into the pores, followed by drying and compression.

[0132] As a method for uniformly mixing the negative electrode active material (the active material according to the second aspect 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 on its axis in 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.

[0133] Uniform mixing of the negative electrode active material (the active material according to the second aspect of the present invention), the conductive agent, and the binder in the solvent requires optimization, as it varies depending 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 manufacturing process into steps based on the solid content concentration, knead the mixture at a high solid content concentration, and then gradually reduce the solid content concentration to adjust the viscosity of the paint. A high solid content concentration is preferably 60% to 90% by mass, more preferably 60% to 80% by mass. A concentration of 60% by mass or more is preferable because shear force can be obtained, and a concentration of 90% by mass or less is preferable because the load on the device is reduced, and a concentration of 80% by mass or less is even more preferable.

[0134] 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.

[0135] 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.

[0136] When an organic solvent is used as the solvent, it is preferable to dissolve the binder in the organic solvent before use.

[0137] <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.

[0138] 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 cobalt, manganese, and nickel with lithium, 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 LiCoO ２ , LiMn ２ O ４ , LiNiO ２ , LiCo １－ｘ Ni ｘ O ２ (0.01<X<1), LiCo １／３ Ni １／３ Mn １／３ O ２ , LiNi １／２ Mn ３／２ O ４ These lithium composite oxides may be partially substituted with other elements, such as by substituting a portion of the cobalt, manganese, or nickel with at least one element such as B, Nb, Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, or La, or by substituting a portion of the O with S or F, or by coating with a compound containing these other elements. Examples of lithium-containing olivine-type phosphates include LiFePO ４ , LiCoPO ４ , LiNiPO ４ , LiMnPO ４ , LiFe １－ｘ MxPO ４ (M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, and X is 0≦X≦0.5), etc.

[0139] 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.

[0140] <Non-aqueous electrolyte> The non-aqueous electrolyte is a solution of an electrolyte salt dissolved in a non-aqueous solvent. There are no particular limitations on the non-aqueous electrolyte, and various types can be used.

[0141] The electrolyte salt used is one that dissolves in a non-aqueous electrolyte, such as LiPF ６ , LiBF ４ , LiPO ２ F ２ , LiN(SO ２ F) ２ , LiClO ４ Inorganic lithium salts such as LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiCF ３ SO ３ , LiC(SO ２ CF ３ ) ３ , LiPF ４ (CF ３ ) ２ , LiPF ３ (C ２ F ５ ) ３ , LiPF ３ (CF ３ ) ３ , LiPF ３ (iso-C ３ F ７ ) ３ , LiPF ５ (iso-C ３ F７ ) and lithium salts containing chain-like fluorinated alkyl groups such as (CF ２ ) ２ (SO ２ ) ２ NLi, (CF ２ ) ３ (SO ２ ) ２ Examples of the electrolyte salt include lithium salts containing a cyclic fluorinated alkylene chain, such as 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, a particularly preferred electrolyte salt is LiPF ６ , LiBF ４ , LiPO ２ F ２ , and LiN(SO ２ F) ２ and the most preferred electrolyte salt is LiPF ６ These electrolyte salts can be used singly or in combination of two or more. In addition, a suitable combination of these electrolyte salts is LiPF ６ and further comprising LiBF ４ , LiPO ２ F ２ , and LiN(SO ２ F) ２ It is preferable that the non-aqueous electrolyte solution contains at least one lithium salt selected from the following:

[0142] 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. The upper limit is preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

[0143] 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.

[0144] 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 the group consisting of 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.

[0145] Therefore, the non-aqueous electrolyte solution is 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-dioxolane-2-one, and 4-ethynyl-1,3-dioxolane-2-one, and LiPF ６ , LiBF ４ , LiPO ２ F ２ , and LiN(SO ２ F) ２ It is preferable to use a non-aqueous electrolyte solution in which an electrolyte salt containing at least one lithium salt selected from the group consisting of propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate is dissolved, and the cyclic carbonate is more preferably one or more cyclic carbonates having an alkylene chain selected from the group consisting of propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate.

[0146] In particular, the concentration of the total electrolyte salt is 0.5M to 2.0M, and the electrolyte salt contains at least LiPF ６ and further comprising 0.001M to 1M LiBF ４ , LiPO ２ F ２ , and LiN(SO ２ F) ２ It is preferable to use a non-aqueous electrolyte containing at least one lithium salt selected from the group consisting of LiPF ６ When the proportion of lithium salts other than LiPF in the non-aqueous solvent is 0.001 M or more, the effect of improving the charge rate characteristics of the electricity storage device and suppressing the amount of gas generation during high-temperature operation is easily exhibited, and when the proportion is 1.0 M or less, there is little concern about a decrease in the effect of improving the charge rate characteristics of the electricity storage device and suppressing the amount of gas generation during high-temperature operation, which is preferable. ６ The proportion of lithium salts other than the above in the non-aqueous solvent is preferably 0.01 M or more, particularly preferably 0.03 M or more, and most preferably 0.04 M or more. The upper limit is preferably 0.8 M or less, more preferably 0.6 M or less, and particularly preferably 0.4 M or less.

[0147] 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.

[0148] 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).

[0149] 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.

[0150] When chain carbonates are used, it is preferable to use two or more types. It is more preferable to include both symmetric chain carbonates and asymmetric chain carbonates, and it is even more preferable that the content of the symmetric chain carbonates is higher than that of the asymmetric chain carbonates.

[0151] The content of the chain ester is not particularly limited, but is preferably in the range of 60% by volume 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 the content 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. Therefore, the above range is preferable.

[0152] The volume ratio of the symmetric chain carbonate to 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.

[0153] The ratio of the cyclic carbonate to the 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 generation during high-temperature operation.

[0154] <Structure of Lithium Battery According to Second Aspect> The structure of the lithium battery according to the second aspect 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.

[0155] 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 composed of a combination of two or more types of 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.

[0156] <Solid Electrolyte> A solid electrolyte is a solid electrolyte capable of transferring ions therein. In particular, inorganic solid electrolytes are solid in a steady state and are not usually dissociated or liberated into cations and anions. The inorganic solid electrolyte is not particularly limited as long as it has the conductivity of metal ions belonging to Group 1 of the periodic table, and generally has almost no electronic conductivity. Representative examples of inorganic solid electrolytes include (A) sulfide inorganic solid electrolytes and (B) oxide inorganic solid electrolytes. In particular, sulfide solid electrolytes are preferably used because they have high ionic conductivity and can be formed into a dense compact 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.

[0157] 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: Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -Al ２ S ３ , Li ２ S-GeS ２ , Li ２ S-Ga ２ S ３ , Li ２ S-GeS ２ -Ga ２ S ３ , Li ２ S-GeS ２ -P ２ S ５ , Li ２ S-GeS ２ -Sb ２ S ５ , Li ２ S-GeS ２ -Al ２ S ３ , Li ２ S-SiS ２ , Li ２ S-Al ２ S ３ , Li ２ S-SiS２ -Al ２ S ３ , Li ２ S-SiS ２ -P ２ S ５ , Li １０ GeP ２ S １２ .

[0158] Among the above combinations, Li ２ S-P ２ S ５ In addition, as the sulfide inorganic solid electrolyte other than the above, Li ６ P.S. ５ Cl and Li ６ P.S. ５ Argerodite-type solid electrolytes such as Br are also suitable.

[0159] The oxide inorganic solid electrolyte preferably contains oxygen atoms, has ion conductivity of a metal belonging to Group 1 of the periodic table, and has electronic insulation properties.

[0160] Examples of oxide inorganic solid electrolytes include Lithium super ionic conductor (LISICON)-type crystalline structures. ３．５ Zn ０．２５ GeO ４ , La having a perovskite crystal structure ０．５５ Li ０．３５ TiO ３ , LiTi having a NASICON (sodium super ionic conductor) type crystal structure ２ P ３ O １２ , Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ), lithium phosphate (Li ３ P.O. ４ ), LiPON, in which some of the oxygen in lithium phosphate is replaced with nitrogen, Li ３ BO ３ -Li ２ SO ４ , Li２ Alumni ２ O ３ -P ２ O ５ , Li ２ O—SiO ２ , and Li ６ BaLa ２ Ta ２ O １２ Suitable examples include:

[0161] 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.

[0162] 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.

[0163] Examples According to the Second Aspect First, examples and comparative examples according to the second aspect of the present invention will be described (Examples 1-1 to 1-10, Comparative Examples 1-1 to 1-3, Reference Example 1-1, Example 2-1, Comparative Example 2-1).

[0164] (Liquid-type lithium-ion secondary battery) [Example 1-1] <Material preparation step> Nb ２ O ５ (average particle size 0.2 μm) and anatase type TiO ２ (Specific surface area 10m ２ / g) were weighed out so that the molar ratio was 1:1 and mixed. This mixed powder was heat treated at 1000°C for 5 hours. The obtained fired powder sample was subjected to powder X-ray diffraction measurement under the conditions of a sampling interval of 0.01° and a scan rate of 2° / min. The results of crystal structure analysis by the Rietveld method confirmed that the synthesized sample was the target niobium oxide (TiNb ２ O ７ :Titanium niobium oxide, ICDD (PDF2010) PDF card 01-077-1374).

[0165] <Surface Treatment Step> Ion-exchanged water was added to the obtained fired powder sample so that the solid content concentration of the slurry was 30 mass %, and the mixture was stirred to disintegrate the powder. Aluminum sulfate hexahydrate (Al ２ (SO ４ ) ３ ・16H ２ A mixed slurry was prepared by adding 0.8% by weight of niobium-containing oxide powder (niobium titanate (hereinafter referred to as TNO)) to 100 g of the crushed fired powder. This mixed slurry was mixed for 3 hours using a paint shaker, dried at a temperature of 60°C, and then heat-treated for 1 hour using a muffle furnace at 500°C, thereby producing the niobium-containing oxide powder (niobium titanate (hereinafter referred to as TNO)) according to Example 1-1.

[0166] [Example 1-2] In the surface treatment step, aluminum sulfate hexahydrate (Al ２ (SO ４ ) ３ ・16H ２ The same procedure as in Example 1-1 was carried out except that the amounts of niobium-containing oxide powder according to Example 1-2 were changed as shown in Table 1.

[0167] [Example 1-3] In the raw material preparation step, the niobium-containing oxide powder synthesized in Example 1-1 was subjected to particle size adjustment treatment. The niobium-containing oxide powder was mixed with zirconia beads (φ2.0 mm), then subjected to ball mill treatment, and then sieved with a 75 μm sieve to obtain a niobium-containing oxide powder that had been subjected to particle size adjustment treatment. In the surface treatment step, aluminum sulfate hexahydrate (Al ２ (SO ４ ) ３ ・16H ２ The same procedure as in Example 1-1 was carried out except that the amounts of niobium-containing oxide powder according to Example 1-3 were changed as shown in Table 1.

[0168] Example 1-4 A niobium-containing oxide powder according to Example 1-4 was produced in the same manner as in Example 1-3, except that in the surface treatment step, the mixed slurry containing treatment agent 2 was not mixed using a paint shaker, but was instead lightly mixed by hand shaking for 3 minutes, dried at a temperature of 60°C, and then heat-treated at 500°C for 1 hour using a muffle furnace.

[0169] [Examples 1-5, 1-6, 1-7, 1-8, 1-9] In the surface treatment step, the same procedure as in Example 1-1 was carried out except that the type of treatment agent 2 and the amount of treatment agent 2 added were changed as shown in Table 1. ４ ・7H ２ O), Examples 1-6 (indium sulfate: In ２ (SO ４ ) ３ ), Examples 1-7 (calcium fluoride: CaF ２ ), Examples 1-8 (zinc sulfate: ZnSO ４ ), Examples 1-9 (Gallium sulfate: Ga ３ (SO ４ ) ３ A niobium-containing oxide powder was produced which was surface-treated using niobium-containing oxide powder.

[0170] [Examples 1-10] Niobium-containing oxide powder containing Nb ２ O ５ A niobium-containing oxide powder subjected to the surface treatment according to Example 1-10 was produced by carrying out the surface treatment step in the same manner as in Example 1-5, except that niobium pentoxide (Niobium (V) oxide, average particle size 0.2 μm) was used.

[0171] Comparative Example 1-1 A niobium-containing oxide powder according to Comparative Example 1-1 was produced in the same manner as in Example 1-1, except that Treating Agent 2 was not added in the surface treatment step.

[0172] Reference Example 1-1 In the surface treatment step, aluminum sulfate hexahydrate (Al ２ (SO ４ ) ３ ・16H ２The same procedure as in Example 1-1 was carried out except that the amounts of niobium-containing oxide powder according to Reference Example 1-1 were changed as shown in Table 1.

[0173] [Comparative Example 1-2] In the raw material preparation process, Nb ２ O ５ (average particle size 0.2 μm) and anatase type TiO ２ (Specific surface area 10m ２ / g) were weighed out so that the molar ratio was 1:1, and aluminum sulfate hexahydrate (Al ２ (SO ４ ) ３ ・16H ２ 1.6 mass % of niobium-containing oxide powder was mixed in the powder. This powder was heat-treated at 1000°C for 5 hours. The obtained powder sample was subjected to the surface treatment step in the same manner as in Example 1-1, except that Treating Agent 2 was not added, to produce a niobium-containing oxide powder according to Comparative Example 1-2.

[0174] Comparative Example 1-3 A niobium-containing oxide powder according to Comparative Example 1-3 was produced in the same manner as in Example 1-10, except that Treating Agent 2 was not added in the surface treatment step.

[0175] [Measurement of Metal Element M1 Content] The contents of metal elements with a valence of 3+ or 2+ excluding Ti or Nb, or molybdenum, aluminum, magnesium, indium, calcium, zinc, and gallium contained in the niobium-containing oxide powders of Examples 1-1 to 1-10, Reference Example 1-1, and Comparative Examples 1-1 to 1-3 (hereinafter, sometimes referred to as the niobium-containing oxide powders of each Example, each Reference Example, and each Comparative Example) were measured as follows.

[0176] <X-ray fluorescence analysis (XRF): Determination of content of metal element M1> Using an X-ray fluorescence analyzer (manufactured by SII Technology Inc., product name "SPS5100"), the elements contained in the niobium-containing oxide powder of each example and each comparative example were quantitatively analyzed. The content of metal element M1 with a valence of 3+ or 2+, excluding Ti or Nb, was calculated using the following formula: Content (%) = (content of metal element M1) / (mass of TNO containing metal element M1) × 100

[0177] [Measurement of Powder Physical Properties] Various physical properties of the niobium-containing oxide powders of the respective Examples and Comparative Examples were measured as follows.

[0178] <Measurement of Specific Surface Area (SSA)> The specific surface area (SSA) (m ２ / g) was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountec Co., Ltd., product name "Macsorb HM model-1208"), and nitrogen gas was used as the adsorption gas. 0.5 g of the measurement sample powder was weighed out and placed in a φ12 standard cell (HM1201-031), and after degassing under vacuum at 100°C for 0.5 hours, it was measured by the BET single-point method.

[0179] <Calculation of D50: Dry Laser Diffraction Scattering Method> The D50 of the niobium-containing oxide powders of Examples 1-1 to 1-10, Reference Example 1-1, and Comparative Examples 1-1 to 1-3 was calculated from a particle size distribution curve measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of sample was placed in a container containing 50 ml of ion-exchanged water as a measurement solvent, and the container was shaken by hand until the powder was visually uniformly dispersed in the measurement solvent. The container was then placed in a measurement cell and measured. The crushing treatment was performed by applying ultrasound (30 W, 3 s) using an ultrasonicator inside the device. Further, measurement solvent was added until the transmittance of the slurry fell within the appropriate range (the range displayed by the green bar on the device), and particle size distribution measurement was performed. The D50 of the mixed powder before and after crushing was calculated from the obtained particle size distribution curve. The D50 before crushing corresponds to the D50 of the secondary particles, and the D50 after crushing corresponds to the D50 of the primary particles.

[0180] [Evaluation of Battery Characteristics] Coin-type batteries were fabricated using the niobium-containing oxide powders of Examples 1-1 to 1-10, Reference Example 1-1, and Comparative Examples 1-1 to 1-3, and their battery characteristics were evaluated. The evaluation results are shown in Table 1.

[0181] <Preparation 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 lower. The niobium-containing oxide powder of each Example was removed from the aluminum laminate bag in a room controlled at a temperature of 25°C and a dew point of -20°C or lower. The removed niobium-containing oxide powder of each Example was mixed in the following proportions as an active material: 90% by mass of acetylene black as a conductive agent, and 5% by mass of polyvinylidene fluoride as a binder, to prepare a coating material. Polyvinylidene fluoride, acetylene black, and 1-methyl-2-pyrrolidone, which had been dissolved in advance in 1-methyl-2-pyrrolidone, were mixed in a planetary stirring and defoaming device, and the niobium-containing oxide powder was added. The total solids concentration was adjusted to 64% by mass, and the mixture was mixed in a planetary stirring and defoaming device. Thereafter, 1-methyl-2-pyrrolidone was added to adjust the total solids concentration to 50% by mass, and the mixture was mixed using a planetary stirring degassing device to prepare a coating material. The resulting coating material was applied to aluminum foil and dried to prepare a single-sided negative electrode sheet for use in the coin battery described below, and a double-sided negative electrode sheet for use in the laminate battery described below. The target coating weight during application was 7.5 mg / cm. ２ It was decided.

[0182] <Measurement of electrode density> The negative electrode single-sided sheet coated as described above was pressed with a roll press (roll φ60 × 150 mm, equivalent to a press pressure of 40 MPa), and the density of the negative electrode layer was measured as "electrode density." The evaluation results are shown in Table 1. A high electrode density is preferable because it allows more active material to be packed into a given volume, resulting in an increased capacity that can be used as a battery.

[0183] <Preparation of Electrolyte> The electrolyte 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 LiPF 6 was added as an electrolyte salt to the non-aqueous solvent. ６ was dissolved to a concentration of 1 M to prepare an electrolyte solution for a coin battery, which will be described later.

[0184] <Preparation of Coin Battery> The negative electrode single-sided sheet prepared by the method described above was punched into a circle with a diameter of 14 mm, and２ An evaluation electrode was prepared by pressing the electrode at a pressure of 1000 kJ / cm2 and then vacuum drying at 120° C. for 5 hours. The evaluation electrode was placed opposite metallic lithium (molded into a circle with a thickness of 0.5 mm and a diameter of 16 mm) via glass filters (one each of GA-100 manufactured by ADVANTEC and GF / C manufactured by Whatman), 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.

[0185] <Measurement of Initial Battery Characteristics: Initial Discharge Capacity and 5C Rate Discharge Characteristics> A coin battery prepared by the method described above in <Preparation of Coin Battery> 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 ２ After constant current and constant voltage charging was performed until the current density reached 0.2 mA / cm ２ Three cycles of constant-current discharge were performed, in which the battery was discharged to 2 V at a current density of 0.3 C. The initial discharge capacity (mAh / g) was calculated by dividing the discharge capacity (mAh) at the third cycle by the weight of the niobium-containing oxide powder. 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 5 C discharge capacity. The 5 C rate discharge capacity percentage (%) was calculated by dividing the 5 C discharge capacity by the initial discharge capacity. The 5 C rate discharge capacity percentages of Examples 1-1 to 1-10, Comparative Examples 1-2 to 1-3, and Reference Example 1-1 were calculated as relative ratios, with the 5 C rate discharge capacity percentage measured using the coin battery of Comparative Example 1-1 set to 100. The results are shown in Table 1 as 5 C rate discharge characteristics (relative ratio %). When a niobium-containing oxide has high 5 C rate discharge characteristics, its application as an electrode material for an energy storage device can be expected to improve the charge rate characteristics of the energy storage device. The "C" in 1 C represents the current value during charging and discharging. For example, 1C refers to a current value that can fully discharge (or fully charge) the theoretical capacity in 1 / 1 hour, and 0.1C refers to a current value that can fully discharge (or fully charge) the theoretical capacity in 1 / 0.1 hour.

[0186] <Long-Term Battery Characteristics: Measurement of Cycle Capacity Retention Rate and Resistance Value After Cycles> A cycle test was performed in a thermostatic chamber at 25°C using coin-type batteries fabricated by the method described above in <Fabrication of Coin Batteries>. The test battery was charged to 0.8 V at a current value corresponding to 0.5 C of the initial discharge capacity, with charging in the direction in which Li was absorbed into the evaluation electrode. This was followed by constant-current, constant-voltage charging at 0.8 V until the charging current reached a current value corresponding to 0.05 C, and then constant-current discharging at a current value corresponding to 0.5 C of the initial discharge capacity to 2 V. This cycle was repeated for a total of 15 cycles. The discharge capacity after 15 cycles was divided by the initial discharge capacity to determine the discharge capacity retention rate (%). The discharge capacity retention rate measured for the coin battery of Comparative Example 1-1 was set to 100, and the results (relative ratio %) of the discharge capacity retention rates of Examples 1-1 to 1-10, Comparative Examples 1-2 to 1-3, and Reference Example 1-1 were calculated as a relative ratio. Table 1 shows the results. Furthermore, IMP measurements were performed on the coin batteries after 15 cycles at frequencies of 0.01 Hz to 1 MHz and a temperature of 0°C, and the resistance value (Ω) was calculated from the size of the resulting arc. The resistance value measured for the coin battery of Comparative Example 1-1 was set to 100, and the resistance values ​​of Examples 1-1 to 1-10, Comparative Examples 1-2 to 1-3, and Reference Example 1-1 were calculated as relative ratios, and the results are shown in Table 1 as resistance values ​​(relative ratio %) after cycling. It is considered that the lower the resistance value after cycling, the more successfully the resistance increase was suppressed.

[0187]

[0188] <Evaluation Results> It was found that the electrodes using the niobium-containing oxide powders of Examples 1-1 to 1-10 had high initial discharge capacity, excellent discharge rate characteristics, and cycle characteristics, and could suppress resistance increase after cycling by containing a metal element with a valence of 3+ or 2+, excluding Ti or Nb, on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder. In particular, Example 1-3, in which the niobium-containing oxide substrate was changed to a particle size-adjusted product, and Example 1-4, in which the surface treatment method was changed to handshake, also showed similar improvement effects. Therefore, it was confirmed that the effects of the present invention do not depend on the type of niobium-containing oxide substrate or the surface treatment method. Furthermore, Example 1-5, which contained a metal element (Mg) with a valence of 2+, tended to have a greater improvement effect in discharge rate characteristics and cycle characteristics than Example 1-2 (Al), which contained a metal element with a valence of 3+. Furthermore, even when the amount of aluminum, a metal element with a valence of 3+, was relatively high, as in Reference Example 1-1, the cycle characteristics were improved while maintaining good discharge rate characteristics and successfully suppressing resistance increase after cycling. In Examples 1-1 to 1-10 and Reference Example 1-1, a metal element M1 with a valence of 3+ or 2+, excluding Ti or Nb, was introduced by the surface treatment process, and therefore the metal element M1 was present on the surface of the niobium-containing oxide particles. On the other hand, the niobium-containing oxide powders of Comparative Examples 1-1 to 1-3 showed a decrease in initial discharge capacity, a decrease in rate characteristics, or no improvement in cycle characteristics, and did not lead to an improvement in battery characteristics. In particular, in Comparative Example 1-2, in which a metal element (Al) with a valence of 3+ was added from the time of base material synthesis rather than as a coating, there was a tendency for the electrode density, initial discharge capacity, and rate characteristics to decrease.

[0189] <Results of X-ray Photoelectron Spectroscopy (XPS) Analysis> For the niobium-containing oxide powders of Examples 1-5 and Comparative Example 1-1, elements localized near the surface of the primary particles were measured using a Quantera II scanning X-ray photoelectron spectrometer manufactured by ULVAC-PHI. Each sample was sampled on an Al plate, and then measurement was carried out using an X-ray source AlKα (monochrome, 1486.6 eV, 50 W), an analysis area of ​​200 μmφ, and a charge neutralization mechanism (electron gun + Ar ions). In the niobium-containing oxide powder of Example 1-5, Mg2+ was detected in addition to Ti4+ and Nb5+, while only Ti4+ and Nb5+ were detected in the niobium-containing oxide powder of Comparative Example 1-1. Furthermore, for the niobium-containing oxide powder of Example 1-5, the niobium-containing oxide powder was analyzed at an acceleration voltage of 2 kV and an etching rate of 3.1 nm / min (SiO ２ Sputtering with Ar ions was performed under conditions of 1000 nm (converted to 1000 nm), and the Mg1s depth profile of the primary particles was measured. The Mg concentration decreased from the particle surface toward the interior of the particle, and if the atomic concentration of Mg at the surface (0 nm) was taken as 100%, the atomic concentration of Mg at a depth of 100 nm from the surface was less than 5%. The results of the Mg1s depth profile are shown in Figure 1. From this, it was confirmed that by introducing a metal element M1 with a valence of 3+ or 2+ (excluding Ti or Nb) through the surface treatment process, the metal element M1 was localized and present on the surface of the niobium-containing oxide particles.

[0190] <Results of Zeta Potential Measurement by Electrophoresis> The zeta potential (mV) of the niobium-containing oxide powders of Examples 1-1, 1-2, 1-5, 1-6, and Reference Example 1-1 was measured by electrophoresis using a zeta potential measurement device (manufactured by Malvern, device name "Zetasizer Nano ZS"). 0.02 g of each niobium-containing oxide powder was weighed out and placed in 200 mL of ion-exchanged water, and the measurement was performed in an environment of 25°C. The results are shown in Table 2 below.

[0191]

[0192] It was confirmed that there was a difference in zeta potential for the above-mentioned niobium-containing oxide powder. It was found that when the zeta potential was less than 0 mV and greater than -60 mV, the initial 5C rate discharge characteristics were high and the long-term resistance value after cycling was low, resulting in a good balance between both performance characteristics. Furthermore, comparing Example 1-1 with Examples 1-2, 1-5, and 1-6, it was found that when the zeta potential was greater than -35 mV, the initial 5C rate discharge characteristics were further improved. Although this is only speculation, it is presumed that the difference in the surface coating state caused a shift in the zeta potential, which reflects the ion diffusion layer, and thus affected the Li+ mobility on the particle surface during rapid charging.

[0193] (All-Solid State Secondary Battery) [Example 2-1] In a glove box under an argon atmosphere, the niobium-containing oxide (aluminum sulfate hexahydrate (Al ２ (SO ４ ) ３ ・16H ２ A compound surface-treated with 1.6 mass% of LiO) and a sulfide solid electrolyte ６ P.S. ５ Cl powder (volume average particle size obtained using a laser diffraction / scattering particle size distribution analyzer: 6 μm) was mixed with niobium-containing oxide: Li ６ P.S. ５ The powders were weighed out so that the mass ratio of LiCl was 60:40, and mixed in an agate mortar. Next, zirconia balls (3 mm diameter, 20 g) were placed in an 80 mL zirconia pot, and the mixed powder was added. Thereafter, this pot was set in a planetary ball mill, and stirring was continued for 15 minutes at a rotation speed of 200 rpm, to obtain the negative electrode active material composition of Example 2-1. The obtained negative electrode active material composition was pressed (360 MPa) at room temperature for 10 minutes to produce pellets (molded bodies) with a diameter of 10 mm and a thickness of approximately 0.7 mm. A pellet-shaped electrode containing this negative electrode active material composition and a pellet-shaped solid electrolyte layer (Li ２ S:P ２ S ５A lithium-indium alloy foil was laminated in this order as a counter electrode (a lithium-indium alloy glass having a molar ratio of 75:25), and a lithium-indium alloy foil as a counter electrode. The laminate was sandwiched between stainless steel current collectors to prepare an all-solid-state secondary battery, and the battery characteristics were evaluated. The results are shown in Table 3.

[0194] [Comparative Example 2-1] An all-solid-state secondary battery shown in Table 3 below was fabricated in the same manner as in Example 2-1 above, except that the niobium-containing oxide powder was changed to the niobium-containing oxide of Comparative Example 1-1 (a compound to which treating agent 2 was not added), and the battery characteristics were evaluated. The results are shown in Table 3.

[0195] <Measurement of Rate Characteristics> In a thermostatic chamber at 25°C, the all-solid-state secondary battery prepared by the above method was charged to 0.5 V at a current equivalent to 0.05 C of the theoretical capacity of the niobium-containing oxide, with charging in the direction in which Li was absorbed into the evaluation electrode. Further, constant-current constant-voltage charging was performed at 0.5 V until the charging current reached a current equivalent to 0.01 C, and then constant-current discharging was performed at a current equivalent to 0.05 C to 2 V. The initial discharge capacity (mAh / g) was calculated by dividing the discharge capacity (mAh) by the mass of the niobium-containing oxide. The initial efficiency was also calculated by dividing the discharge capacity by the charge capacity. Next, the battery was charged to 0.5 V at a current equivalent to 0.4 C of the theoretical capacity of the niobium-containing oxide, and then discharged to 2 V at a current of 0.05 C to determine the 0.4 C charge capacity. The rate characteristic (%) was calculated by dividing the 0.4 C charge capacity by the initial discharge capacity. The rate characteristics were evaluated as relative values, with the value of Comparative Example 2-1 taken as 100%. The evaluation results are shown in Table 3.

[0196]

[0197] It was also found that in the system of an all-solid-state secondary battery, an electrode including a negative electrode layer using the niobium-containing oxide powder of Example 1-1 had excellent charge rate characteristics by containing a metal element M1 having a valence of 3+ or 2+, excluding Ti or Nb, on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder.

[0198] Examples According to the First Aspect Next, examples and comparative examples according to the first aspect of the present invention will be described (Examples 3-1 and 3-2, Comparative Example 3-1, Examples 4-1 to 4-8, Comparative Examples 4-1 and 4-2).

[0199] [Example 3-1] <Raw material preparation step> Nb ２ O ５ (average particle size 0.2 μm) and anatase type TiO ２ (Specific surface area 10m ２ / g) were weighed out so that the molar ratio was 1:1 and mixed. This mixed powder was heat treated at 1000°C for 5 hours. The obtained fired powder sample was subjected to powder X-ray diffraction measurement under the conditions of a sampling interval of 0.01° and a scan rate of 2° / min. The results of crystal structure analysis by the Rietveld method confirmed that the synthesized sample was the target niobium oxide (TiNb ２ O ７ : Titanium diniobium oxide, ICDD (PDF2010) PDF card 01-077-1374).

[0200] <Surface Treatment Step> Ion-exchanged water was added to the obtained fired powder sample so that the solid content concentration of the slurry was 30 mass %, and the mixture was stirred to disintegrate the powder. ２ MoO ４ ) was added to 100 g of the crushed fired powder in an amount of 0.4 mass % to prepare a mixed slurry. This mixed slurry was mixed for 3 hours using a paint shaker, dried at a temperature of 60°C, and then heat-treated for 1 hour at 500°C using a muffle furnace to produce a niobium-containing oxide powder (niobium titanium composite oxide powder (hereinafter, sometimes referred to as TNO powder)) according to Example 3-1.

[0201] [Example 3-2] In the surface treatment process, lithium molybdate (Li ２ MoO ４ The same procedure as in Example 3-1 was carried out except that the amounts of the additives ) added were changed as shown in Table 4, and a TNO powder according to Example 3-2 was produced.

[0202] Comparative Example 3-1 A TNO powder according to Comparative Example 3-1 was produced in the same manner as in Example 3-1, except that no treating agent was added in the surface treatment step.

[0203] [Measurement of Contents of Metal Elements Mo and Ce] The contents of the metal elements Mo and Ce contained in the TNO powders of Examples 3-1, 3-2, 4-1 to 4-8 and Comparative Examples 3-1, 4-1, and 4-2 were measured as follows.

[0204] <X-ray Fluorescence Analysis (XRF): Identification of the Contents of Metal Elements Mo and Ce> An X-ray fluorescence analyzer (manufactured by SII Technology Inc., product name "SPS5100") was used to quantitatively analyze the elements contained in the TNO powder of each example and comparative example. The contents of the metal elements Mo and Ce were calculated using the following formula: Content (%) = (mass of metal elements Mo, Ce) / (total mass of TNO containing metal elements Mo and Ce) × 100

[0205] [Measurement of Powder Properties] Various physical properties of the TNO powders of Examples 3-1, 3-2, 4-1 to 4-8 and Comparative Examples 3-1, 4-1, and 4-2 were measured as follows.

[0206] <Measurement of specific surface area> The specific surface area (m ２ / g) was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountec Co., Ltd., product name "Macsorb HM model-1208"), and nitrogen gas was used as the adsorption gas. 0.5 g of the measurement sample powder was weighed out and placed in a φ12 standard cell (HM1201-031), and after degassing under vacuum at 100°C for 0.5 hours, it was measured by the BET single-point method.

[0207] <Calculation of D50: Dry Laser Diffraction Scattering Method> The D50 of the niobium-containing oxide powders of Examples 3-1, 3-2, 4-1 to 4-8 and Comparative Examples 3-1, 4-1, and 4-2 was calculated from the particle size distribution curve measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of sample was placed in a container containing 50 mL of ion-exchanged water as a measurement solvent, and the container was shaken by hand until the powder was visually uniformly dispersed in the measurement solvent. The container was then placed in a measurement cell and measured. The crushing treatment was performed by irradiating the sample with ultrasound (30 W, 3 s) using an ultrasonicator inside the device. Further, measurement solvent was added until the transmittance of the slurry fell within the appropriate range (the range displayed by the green bar on the device), and particle size distribution measurement was performed. The D50 of the mixed powder before and after crushing was calculated from the obtained particle size distribution curve. The D50 before crushing corresponds to the D50 of the secondary particles, and the D50 after crushing corresponds to the D50 of the primary particles.

[0208] [Preparation of Negative Electrode Active Material Composition] In a glove box under an argon atmosphere, the TNO powder of Example 3-1 and the sulfide inorganic solid electrolyte Li ６ P.S. ５ Cl powder (volume average particle size obtained using a laser diffraction / scattering particle size distribution analyzer: 6 μm) was mixed with TNO:Li ６ P.S. ５ The powders were weighed out to a mass ratio of 60:40 and mixed in an agate mortar. Next, zirconia balls (3 mm diameter, 20 g) were placed in an 80 mL zirconia pot, and the mixed powder was added. The pot was then placed in a planetary ball mill, and stirring was continued for 15 minutes at 200 rpm to obtain the negative electrode active material composition of Example 3-1. [Example 3-2, Comparative Example 3-1] The negative electrode active material compositions shown in Table 4 below were prepared in the same manner as in Example 3-1, except that the TNO powder produced by the method shown in Table 4 was used.

[0209] [Measurement of Physical Properties of Negative Electrode Active Material Composition] 100 mg of each of the above negative electrode active material compositions was weighed out, and these samples were pressed (360 MPa) at room temperature for 10 minutes to produce pellets (molded bodies) with a diameter of 10 mm and a thickness of approximately 0.7 mm.

[0210] [Evaluation of Battery Characteristics] All-solid-state secondary batteries were fabricated using pellets of the negative electrode active material compositions of Examples 3-1, 3-2, and 4-1 to 4-8 and Comparative Examples 3-1, 4-1, and 4-2, and their battery characteristics were evaluated. The evaluation results are shown in Table 4.

[0211] [Synthesis of sulfide inorganic solid electrolyte] In a glove box under an argon atmosphere, lithium sulfide (Li ２ S) and diphosphorus pentasulfide (P ２ S ５ ) to Li ２ S:P ２ S ５ The raw material composition was weighed out to a molar ratio of 75:25 and mixed in an agate mortar to obtain a raw material composition. Next, zirconia balls (3 mm diameter, 160 g) and 2 g of the obtained raw material composition were placed in an 80 mL zirconia pot, and the container was sealed under an argon atmosphere. This pot was placed in a planetary ball mill and mechanically milled at a rotation speed of 510 rpm for 16 hours to obtain a yellow powder sulfide inorganic solid electrolyte (LPS glass). 80 mg of the obtained LPS glass was placed in a 0.785 cm2 powder. ２ The mixture was pressed at a pressure of 360 MPa using a pellet molding machine having a molding section to obtain a pellet-shaped solid electrolyte layer.

[0212] [Fabrication of All-Solid-State Secondary Battery] Pellets of the negative electrode active material compositions of Examples 3-1, 3-2, 4-1 to 4-8 and Comparative Examples 3-1, 4-1, and 4-2, the pellet-shaped solid electrolyte layer, and a lithium-indium alloy foil as a counter electrode were laminated in this order, and the laminate was sandwiched between stainless steel current collectors to fabricate all-solid-state secondary batteries.

[0213] <Measurement of Initial Discharge Capacity, Initial Efficiency, and Charge Rate Characteristics> In a thermostatic chamber at 25°C, the all-solid-state secondary battery prepared by the above method was charged to 0.5 V at a current equivalent to 0.05 C of the theoretical capacity of TNO, with charging in the direction in which Li was absorbed into the evaluation electrode. Further, constant-current constant-voltage charging was performed at 0.5 V until the charging current reached a current equivalent to 0.01 C, and then constant-current discharging was performed at a current equivalent to 0.05 C to 2 V. The initial discharge capacity (mAh / g) was calculated by dividing the discharge capacity (mAh) by the mass of TNO. The initial efficiency was also calculated by dividing the discharge capacity by the charge capacity. Next, the battery was charged to 0.5 V at a current equivalent to 0.4 C of the theoretical capacity of TNO, and then discharged to 2 V at a current of 0.05 C to determine the 0.4 C charge capacity. The charge rate characteristic (%) was calculated by dividing the 0.4 C charge capacity by the initial discharge capacity. For Examples 3-1 and 3-2 and Comparative Example 3-1, the initial discharge capacity and charge rate characteristics were examined as relative values, with the value of Comparative Example 3-1 being set to 100%. The evaluation results are shown in Table 4. 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 represents the current value at which the theoretical capacity can be fully discharged (or fully charged) in 1 / 0.1 hour.

[0214]

[0215] As can be seen from Table 4 above, the negative electrode active material compositions of Examples 3-1 and 3-2 of the present invention have excellent initial discharge capacity, initial efficiency, and charge rate characteristics in all-solid-state secondary batteries compared to Comparative Example 3-1. Note that in Examples 3-1 and 3-2, the metal element Mo was introduced by the surface treatment step, and therefore the metal element Mo was localized on the surface of the niobium-containing oxide particles.

[0216] [Examples 4-1 to 4-8, Comparative Examples 4-1 and 4-2] The negative electrode active material compositions shown in Table 5 below were prepared and evaluated in the same manner as in Example 3-1, except that the TNO powder produced by the manufacturing method shown in Table 5 was used and the battery evaluation was performed in a thermostatic chamber at 45°C. In Examples 4-1 to 4-5, lithium molybdate (Li ２ MoO ４ The TNO powder was produced in the same manner as in Example 3-1, except that the amount of lithium molybdate (Li) added was changed as shown in Table 5. In Examples 4-6 and 4-7, the surface treatment step used lithium molybdate (Li ２ MoO ４ TNO powders were produced in the same manner as in Example 3-1, except that cerium sulfate tetrahydrate was used in place of the cerium sulfate tetrahydrate in the amounts shown in Table 5. In Example 4-8, TNO powders were produced in the same manner as in Example 4-1, except that the conditions in the raw material preparation step were adjusted so that the specific surface area and primary particle D50 would have the values ​​shown in Table 5. In Comparative Examples 4-1 and 4-2, TNO powders were produced in the same manner as in Examples 4-1 and 4-8, except that no treating agent was added. Note that the initial discharge capacity and charge rate characteristics of Examples 4-1 to 4-8 and Comparative Examples 4-1 and 4-2 were examined as relative values, with the respective values ​​of Comparative Example 4-1 set to 100%.

[0217]

[0218] As can be seen from Table 5 above, the negative electrode active material compositions of Examples 4-1 to 4-8 of the present invention were found to have superior initial discharge capacity, initial efficiency, and charge rate characteristics compared to Comparative Examples 4-1 and 4-2, even at 45° C. In Examples 4-1 to 4-8, the metal elements Mo and Ce were introduced by the surface treatment step, and therefore the metal elements Mo and Ce were localized and present on the surfaces of the niobium-containing oxide particles.

[0219] [Comparative Example 4-3] Nb ２ O ５ , anatase type TiO ２ , and molybdenum oxide (MoO ３) were weighed and mixed in a molar ratio of 1:1:0.1. This mixed powder was heat-treated at 1000°C for 5 hours. ３ When a battery evaluation was performed in the same manner as in Example 3-1 using a sample containing niobium, the charge rate characteristic was 80%, and the improvement in charge rate characteristic that is the effect of the present invention was not observed. From this result, it was found that in order to improve the charge rate characteristic of an all-solid-state secondary battery, it is necessary for the metal element M1 such as Mo to be localized on the surface of the niobium-containing oxide particle.

[0220] The results of Examples 3-1, 3-2, and 4-1 to 4-8 above demonstrate that the interfacial resistance between the solid electrolyte and TNO can be significantly reduced, and the use of this negative electrode active material composition exhibits excellent battery characteristics.

Claims

1. General formula Ti １－ｘ／２ Nb ２ O ７－ｘ (X=0 to 2), wherein at least one metal element selected from the group consisting of Mo and Ce is present in a localized state on the surface of a niobium-containing oxide particle constituting the niobium-containing oxide powder.

2. 2. The niobium-containing oxide powder according to claim 1, characterized in that the content (mass%) of the metal element present on the particle surface in the niobium-containing oxide powder is 0.01 or more and 1.2 or less.

3. The niobium-containing oxide powder according to claim 1 or 2, characterized in that in the niobium-containing oxide, a primary particle D50 corresponding to a volume cumulative of 50% in a volume-based particle size distribution by a laser diffraction scattering method is 0.6 μm or more.

4. A negative electrode active material composition comprising a niobium-containing oxide powder and an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table, 3. A negative electrode active material composition comprising the niobium-containing oxide powder according to claim 1 or 2.

5. 5. The negative electrode active material composition according to claim 4, wherein the inorganic solid electrolyte is a sulfide inorganic solid electrolyte.

6. The negative electrode active material composition according to claim 4 , wherein the content of the inorganic solid electrolyte is 1% by mass or more and 50% by mass or less.

7. 5. An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, the negative electrode layer being a layer containing the negative electrode active material composition according to claim 4.

8. General formula Ti １－ｘ／２ Nb ２ O ７－ｘ (X=0 to 2), wherein M1 (M1 is a metal element having a valence of 3+ or 2+, excluding Ti or Nb) is present in a localized state on the surface of a niobium-containing oxide particle constituting the niobium-containing oxide powder.

9. The niobium-containing oxide powder according to claim 8, characterized in that in the niobium-containing oxide powder, the element M1 present on the particle surface is a metal element of Group 2, Group 12, Group 13, or Group 14.

10. In the niobium-containing oxide powder, the element M1 present on the particle surface is Al ３＋ , Mg ２＋ , Ca ２＋ , Sr ２＋ , Zn ２＋ , Ga ３＋ , Ge ２＋ , and In ２＋ The niobium-containing oxide powder according to claim 8 or 9, characterized in that it contains at least one element selected from the group consisting of:

11. The niobium-containing oxide powder according to claim 8 or 9, characterized in that in the niobium-containing oxide powder, a content (mass%) of element M1 present on a particle surface is 0.01 or more and 1.2 or less.

12. The niobium-containing oxide powder according to claim 8 or 9, characterized in that in the niobium-containing oxide powder, D50 of primary particles corresponding to a volume cumulative of 50% in a volume-based particle size distribution by a laser diffraction scattering method is 0.3 μm or more.

13. An electrode for an electricity storage device, comprising the niobium-containing oxide powder according to claim 8 or 9.

14. An electricity storage device comprising the electrode according to claim 13.