Niobium-containing oxide powder, electrodes using the same, energy storage devices, negative electrode active material compositions, and all-solid-state secondary batteries.

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

[Technical Field]

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

[0002] In recent years, various materials have been studied as electrode materials for energy storage devices. Among them, lithium titanate is attracting attention as an active material for energy storage devices in electric vehicles such as HEVs, PHEVs, and BEVs, due to its excellent input / output characteristics, especially in the low-temperature range, when used as an active material.

[0003] High energy density is required for energy storage devices in electric vehicles from the perspective of improving fuel efficiency or energy consumption. Although lithium titanate has excellent input / output characteristics, its energy density remains at 175 mAh / g, leaving challenges for further energy increases. Therefore, as an alternative, there is a movement to utilize niobium-containing oxides, mainly niobium titanate, which has a high energy density of 380 mAh / g, as a negative electrode material.

[0004] Patent Document 1 contains, A x TiM y Nb 2―y O 7±z A monoclinic niobium titanium composite oxide is disclosed, represented as (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 applied as an electrode material for energy storage devices, it can provide an active material with high capacity, high current discharge performance, and excellent cycle life performance.

[0005] Patent Document 2 discloses an active material including monoclinic niobium titanium composite oxide particles capable of occluding and releasing Li ions, carbon fibers having an average fiber diameter in the range of 5 nm or more and 100 nm or less which contain one or more metal elements selected from the group consisting of Fe, Co, and Ni and satisfy the following formula (2), and the average primary particle diameter of the niobium titanium composite oxide particles is in the range of 0.05 μm or more and 2 μm or less. According to Patent Document 2, it is said that a power storage device excellent in capacity, cycle life, and large current discharge performance can be obtained.

[0006] In recent years, all-solid-state secondary batteries using inorganic solid electrolytes instead of organic electrolytes have attracted attention. Since all components of an all-solid-state secondary battery, i.e., the positive electrode, the negative electrode, and the electrolyte, are made of solids, there is a possibility of greatly improving safety and reliability, and since simplification of safety devices can be achieved, high energy density can be realized, and thus application to electric vehicles, large-scale storage batteries, etc. is expected.

[0007] In an all-solid-state secondary battery, from the viewpoint of realizing excellent ion conductivity and long cycle characteristics, it is very important to form a good solid-solid interface and continuously maintain that interface. Lithium titanate has attracted attention in order to maintain a good interface between the active material and the solid electrolyte. Since the volume change associated with charge and discharge of lithium titanate is very small, it is expected that the interface between the active material and the solid electrolyte will be maintained over a long period during charge and discharge. However, although lithium titanate has excellent input / output characteristics, there are still problems for further increasing the energy density because the energy density remains at 175 mAh / g. Therefore, as an alternative candidate, there is a movement to utilize niobium-containing oxides centered on niobium titanium composite oxides having a high energy density of 387 mAh / g as a negative electrode material. Patent Document 3 discloses a sulfide solid electrolyte and D 50 (μm) / BET(m 2 / g) is 0.005 or more and 5.0 or less, and the general formula Ti 1±α Nb 2±β O 7±γAn electrode mixture containing a niobium-titanium composite oxide represented by [formula] is disclosed. According to Patent Document 3, it is disclosed that when applied as an electrode mixture for a solid-state battery, excellent charge-discharge efficiency can be obtained. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2017-224625 [Patent Document 2] Japanese Patent Publication No. 2020-149829 [Patent Document 3] International Publication No. 2021 / 049665 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the energy storage device using niobium titanate as the negative electrode material described in Patent Document 1 had the problem that the initial capacity of the battery (battery capacity) decreased when the amount of substitution element was large. The advantages of increasing battery capacity include an improvement in energy density per unit weight or per 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 described in Patent Document 2, the surface of the niobium-titanium composite oxide particles is coated with carbon fibers containing a metal element. However, since the carbon fibers do not contribute to the battery capacity, there was a problem in that the battery capacity decreased as a result, and the energy density per unit weight or per unit area decreased.

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

[0012] Furthermore, the D relative to the BET specific surface area in Patent Document 3 50Although improvements in the battery characteristics of all-solid-state secondary batteries were observed by using an electrode mixture consisting of a titanium-niobium composite oxide and a sulfide solid electrolyte with a predetermined ratio, further improvements were needed regarding the charge rate characteristics.

[0013] In its first aspect, the present invention aims to provide a niobium-containing oxide powder, a negative electrode active material composition, and an all-solid-state secondary battery 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.

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

[0015] The inventors conducted various studies to achieve the objectives of the first aspect described above, and found that when using niobium-containing oxide powder as a negative electrode active material in an all-solid-state secondary battery, it is extremely important to reduce the interfacial resistance between the solid electrolyte and the niobium-containing oxide. Therefore, after conducting research to reduce the interfacial resistance between the solid electrolyte and the niobium-containing oxide regardless of particle size or specific surface area, they discovered that by using niobium-containing oxide powder in which a specific metal element is localized on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder, the interfacial resistance can be significantly reduced, thus completing the present invention (the invention relating to the first aspect). By using the negative electrode active material composition containing the niobium-containing oxide powder and the solid electrolyte in an all-solid-state secondary battery, the initial discharge capacity, initial efficiency, and charge rate characteristics can be improved. However, the inventors' studies have shown that when a part of the Ti or Nb element described in Patent Documents 1 and 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 relating 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 containing the same.

[0016] In other words, the first aspect of the present invention provides the following (1) to (7). (1) General formula Ti 1-x / 2 Nb2O 7-x A niobium-containing oxide powder represented by (X=0~2), 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. (2) The niobium-containing oxide powder according to (1), characterized in that the content (mass%) of the metal element present on the particle surface is 0.01 or more and 1.2 or less. (3) The niobium-containing oxide powder according to (1) or (2), characterized in that the D50 of primary particles corresponding to 50% of the volume accumulation in the volume-based particle size distribution by laser diffraction scattering method is 0.6 μm or larger. (4) A negative electrode active material composition comprising a niobium-containing oxide powder and an inorganic solid electrolyte having conductivity of metal ions belonging to Group 1 of the periodic table, characterized in that the niobium-containing oxide powder comprises the niobium-containing oxide powder described in 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 inorganic solid electrolyte content is 1% by mass or more and 50% by 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 described in any one of (4) to (6).

[0017] Furthermore, the inventors conducted various studies to achieve the objectives related to the second aspect described above, and as a result, discovered a niobium-containing oxide powder in which specific metal elements are present at specific concentrations on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder, by adding a surface treatment process to the niobium-containing oxide powder. In particular, it was found that a remarkable effect is observed when metal elements with lower valences are present on the surface of the niobium-containing oxide particles, rather than when metal elements with higher valences are present. In the present invention (the invention related to the second aspect), the effect was observed even without coating the surface of the niobium-containing oxide particles with a conductive agent such as carbon fiber, making it a different technology from conventional carbon coating. The inventors found that an energy storage device to which this niobium-containing oxide powder is applied as an electrode material exhibits excellent discharge rate characteristics and cycle characteristics, and can suppress the increase in resistance after cycling, thus completing the present invention (the invention related to the second aspect).

[0018] In other words, a second aspect of the present invention provides the following (8) to (14). (8) General formula Ti 1-x / 2 Nb2O 7-x A niobium-containing oxide powder represented by (X=0~2), characterized in that M1 (M1 is a valence 3+ or 2+ metallic element other than Ti or Nb) is localized on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder. (9) The niobium-containing oxide powder according to (8), characterized in that 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 (8) or (9), characterized by containing one or more elements selected from the group of elements comprising the above. (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 or more and 1.2 or less. (12) The niobium-containing oxide powder according to any one of (8) to (11), characterized in that the D50 of primary particles corresponding to 50% of the volume cumulative size distribution by laser diffraction scattering method is 0.3 μm or larger. An electrode for an energy storage device, characterized by containing the niobium-containing oxide powder described in any one of items (13), (8), to (12). A power storage device characterized by including the electrodes described in (14)(13). [Effects of the Invention]

[0019] According to a first aspect of the present invention, by reducing the interfacial resistance with a solid electrolyte regardless of the particle size or specific surface area of ​​the niobium-containing oxide powder, it is possible to provide a niobium-containing oxide powder suitable as an electrode material for an all-solid-state secondary battery with excellent initial discharge capacity, initial efficiency, and charge rate characteristics, 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 energy storage device that has excellent discharge rate characteristics and cycle characteristics, and can suppress the increase in resistance after cycling, as well as an electrode using the same and an energy storage device. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 shows the results of the Mg1s depth profile. [Modes for carrying out the invention]

[0022] Invention relating to the first viewpoint The invention relating to the first aspect will be described below.

[0023] [Niobium-containing oxide powder according to the first aspect] The niobium-containing oxide powder according to the first aspect of the present invention has the general formula Ti 1-x / 2 Nb2O 7-x (X = 0 to 2), and 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. The niobium-containing oxide powder is characterized in that it exists. Here, X = 0 to 2 means 0 ≦ X ≦ 2 or less. The same applies hereinafter.

[0024] <General formula Ti 1-x / 2 Nb2O 7-x (X = 0 to 2) niobium-containing oxide> The niobium-containing oxide powder according to the first aspect of the present invention contains a niobium-containing oxide represented by the general formula Ti 1-x / 2 Nb2O 7-x (X = 0 to 2). Examples of specific compounds include TiNb2O7, which is a niobium-titanium composite oxide capable of occluding and releasing Li ions and Na ions, and Nb2O5, which is a niobium oxide. From the viewpoint of improving the initial discharge capacity, initial efficiency, and charge rate characteristics, TiNb2O7 is preferred. For the niobium-titanium composite oxide, a part may contain a titanium oxide phase derived from the synthesis raw material (for example, rutile-type TiO2, TiO, etc.). In the case of the 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. In this range, the electron conductivity of the niobium-containing oxide is improved, and the rate characteristics are excellent.

[0025] Regarding the niobium-containing oxide according to the first aspect of the present invention, there is no limitation on the crystal system, but it is generally monoclinic. In the case of the monoclinic form, the aspect ratio tends to be large, but from the viewpoint of improving the electrode density, it is preferably in the range of 1.0 to 4.0.

[0026] <Content of 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 the inductively coupled plasma atomic emission spectrometry (ICP-AES) or X-ray fluorescence analysis (XRF) of the niobium oxide powder according to the first aspect of the present invention. The lower limit of the detection amount by inductively coupled plasma atomic emission spectrometry is usually 0.001% by mass. Both Mo and Ce may be contained on the particle surface of the niobium-containing oxide powder. In addition, the valence of Mo and Ce is not particularly limited and may be 3+ or 2+, or may be 4+ or more. From the viewpoint of improving the initial discharge capacity, initial efficiency, and charge rate characteristics, it is preferable to contain Mo.

[0027] <Content rate of at least one metal element selected from the group consisting of Mo and Ce> The content rate (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 determined by X-ray fluorescence analysis (XRF) may be 0.01 or more and 1.2 or less. If the content rate 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 excellent in initial discharge capacity, initial efficiency, and charge rate characteristics can be obtained. It is preferably 0.01 or more and 1.0 or less, more preferably 0.015 or more and 0.9 or less, still more preferably 0.04 or more and 0.85 or less, and particularly preferably 0.07 or more and 0.75 or less from the viewpoint of further improving the charge rate characteristics. However, when Mo and Ce are simultaneously contained on the particle surface of the niobium-containing oxide powder, the content rate (mass %) is the total content rate of the two metal elements.

[0028] Furthermore, in the niobium-containing oxide powder according to the first aspect of the present invention, at least one metal element selected from the group consisting of Mo and Ce is contained in greater quantities in the surface region than in the internal region of the niobium-containing oxide particles constituting the powder. That is, 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, at least one metal element selected from the group consisting of Mo and Ce is localized and contained in greater quantities in the surface region than in the internal region of the niobium-containing oxide particles. As an example, in cross-sectional analysis of niobium-containing oxide particles using a scanning transmission electron microscope, it is desirable that a large amount of at least one metal element selected from the group consisting of Mo and Ce is present in the so-called near-surface region up to a depth of about 20 nm from the surface of the niobium-containing oxide particles, as measured by energy-dispersive X-ray spectroscopy. Preferably, 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 Mo and Ce are not detected at a depth of 100 nm from the surface. 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. In other words, it means that the amount detected by energy-dispersive X-ray spectroscopy is below the detection limit, and the lower limit of the detection amount in energy-dispersive X-ray spectroscopy varies depending on the element and state being measured, but is usually 0.5 atm%. Other 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 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 particles is not particularly limited, and any form in which at least one metal element selected from the group consisting of Mo and Ce is localized on the surface is acceptable, and it may be in the form of a metal or 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 the 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 that in surface analysis by X-ray photoelectron spectroscopy, it has a peak top for Mo or a peak top for Ce. Furthermore, in depth profile measurement by sputtering, if the atomic concentration (atm%) of Mo or Ce at a depth of 100 nm from the surface is taken as 100%, it is preferable that the atomic concentration (atm%) of Mo or Ce at a depth of 100 nm from the surface is less than 5%.

[0030] <Further inclusion of different elements> The niobium-containing oxide powder according to the first aspect of the present invention preferably contains at least one element selected from the group consisting of Al, Mg, Ca, Sr, Zn, Ga, Ge, In, B, W, and S, as a further heterogeneous element in addition to at least one metallic element selected from the group consisting of Mo and Ce. It is presumed that the niobium-containing oxide powder according to the first aspect of the present invention, by containing such heterogeneous elements together with Mo and Ce, adjusts the electronic conductivity of the surface of the niobium-containing oxide powder, thereby suppressing electrical resistance compared to the inclusion of Mo or Ce 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 the adsorbent gas. The measurement method will be explained in the examples described later.

[0032] The niobium-containing oxide powder according to the first aspect of the present invention has a specific surface area of ​​8.0 m². 2 It is sufficient if the value is less than or equal to / g, and an energy storage device with excellent initial discharge capacity, initial efficiency, and charge rate characteristics can be obtained. 6.0m 2 More preferably less than / g, and 5.5m 2 A value of less than or equal to / g is even more preferable.

[0033] <d50> D50 in the niobium-containing oxide powder according to the first aspect of the present invention is an index of the median volume particle size. It refers to the particle size at which the cumulative volume frequency calculated from the volume fraction obtained by laser diffraction-scattering particle size distribution measurement accumulates to 50% when summed from the smallest particle size. The measurement method will be explained in the examples described later.

[0034] The niobium-containing oxide powder according to the first aspect of the present invention may consist of primary particles or secondary particles formed by aggregation of primary particles. When it contains secondary particles formed by aggregation of primary particles consisting of niobium-containing oxide particles, some of these particles may not form secondary particles but remain in the form of primary particles themselves.

[0035] When the niobium-containing oxide powder according to the first aspect of the present invention is a secondary particle, the lower limit of the D50 of the secondary particle is preferably 11 μm or more, more preferably 12 μm or more, and even more preferably 13 μm or more, from the viewpoint of improving electrode density. Furthermore, the upper limit of the D50 of the secondary particle is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 14 μm or less. Note that the D50 of the secondary particle refers to the D50 before the secondary particle is 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 metal elements Mo and Ce between the surface and the interior of the primary particles, and it is preferable that the concentration of metal elements Mo and Ce is high on the surface (for example, in the so-called near-surface region up to a depth of about 20 nm from the surface of the primary particle), and preferably that there are no metal elements Mo or Ce in the interior (for example, at a position of 100 nm from the surface of the primary particle toward the interior). This is because when metal elements Mo and Ce are present in such a state, an all-solid-state secondary battery with excellent initial efficiency and charge rate characteristics can be obtained.

[0037] In the niobium-containing oxide powder according to the first aspect of the present invention, the lower limit of the D50 of the primary particles is preferably 0.4 μm or more, more preferably 0.5 μm or more, and even more preferably 0.6 μm or more, from the viewpoint of initial discharge capacity and charge rate characteristics. The upper limit of the D50 is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less. Note that the D50 of the primary particles represents the D50 after crushing treatment (sonication with an ultrasonic device). Furthermore, the niobium-containing oxide powder may contain 15% to 20% of primary particles with a primary particle diameter of less than 0.4 μm, 15% to 25% of primary particles with a primary particle diameter of less than 0.5 μm, and 15% to 30% of primary particles with a primary particle diameter of less than 0.6 μm. The material may contain primary particles larger than 3 μm in an amount of 45% to 75%, primary particles larger than 2 μm in an amount of 25% to 75%, and primary particles larger than 1.2 μm in an amount of 25% to 80%.

[0038] <Zeta potential obtained 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, and more preferably less than or equal to -5 mV. The lower limit of the zeta potential is preferably greater than -60 mV, and 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 falls within the above range, an energy storage device with excellent initial discharge rate characteristics and suppression of resistance increase after long-term cycling can be obtained. The zeta potential represents the potential difference between the sliding surface in the electric double layer and a portion sufficiently far from the interface, and it is presumed that this potential difference affects the Li+ permeability on the surface of the niobium-containing oxide powder. The measurement method will be explained in the examples described later.

[0039] [Method for producing niobium-containing oxide powder according to the first aspect] Below, an example of a 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 calcination step, and a surface treatment step. However, the method for producing niobium-containing oxide powder according to the first aspect of the present invention is not limited thereto.

[0040] <Preparation process of raw materials> First, the starting materials are mixed. In particular, in the case of niobium-titanium composite oxides, oxides or salts containing Ti and Nb are used as starting materials. Furthermore, when other additive elements are included in the niobium-titanium composite oxide, the salt used as the starting material is preferably a salt that decomposes at a relatively low melting point to produce oxides, such as a hydroxide salt, carbonate, or nitrate salt. In addition, in order to allow sufficient elemental diffusion to proceed in the calcination process described later, it is preferable to use a powder with an average particle size of 2 μm or less, preferably an average particle size of 0.5 μm or less, as the starting material.

[0041] There are no particular restrictions on the method of mixing the raw materials; either wet or dry mixing is acceptable. For example, a Henschel mixer, ultrasonic dispersion device, homomixer, mortar and pestle, ball mill, centrifugal ball mill, planetary ball mill, vibrating ball mill, Attritor-type high-speed ball mill, bead mill, roll mill, etc., can be used.

[0042] <Firing Process> Next, the mixture obtained above is calcined. The calcination is carried out at a temperature range of 500 to 1200°C, more preferably in the range of 700 to 1000°C. By performing the calcination at a temperature of 1000°C or lower, general-purpose equipment can be used. When calcining the mixture in a short time, it is preferable to prepare the mixed powder constituting the mixture before calcination so that the D95 in the particle size distribution curve measured by a laser diffraction / scattering particle size distribution analyzer is 5 μm or less. Here, D95 is the particle size at which the cumulative volume frequency calculated by volume fraction, when accumulated from the smallest particle size, accounts for 95%.

[0043] The firing method is not particularly limited as long as it can be fired under the aforementioned conditions. Examples of usable firing methods include fixed-bed firing furnaces, roller hearth firing furnaces, mesh belt firing furnaces, fluidized bed firing furnaces, and rotary kiln firing furnaces. However, for efficient firing in a short time, roller hearth firing furnaces, mesh belt firing furnaces, and rotary kiln firing furnaces are preferred. In particular, rotary kiln firing furnaces are especially preferred for producing niobium-containing oxide powder according to the first aspect of the present invention because they do not require a container to hold the mixture, allow for firing while continuously adding the mixture, and provide a uniform thermal history to the fired material, resulting in a homogeneous oxide.

[0044] <Surface treatment process> Next, the niobium-containing oxide obtained above is subjected to 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 localized on the surface of the particles constituting the niobium-containing oxide powder, and when applied as a negative electrode material for a battery, it can form a dense negative electrode layer and provide excellent charge rate characteristics. In the firing process, a compound containing at least one metal element selected from the group consisting of Mo and Ce (hereinafter sometimes referred to as a treatment agent) can be added to produce the niobium-containing oxide powder according to the first aspect of the present invention, but more preferably, the niobium-containing oxide powder according to the first aspect of the present invention can be produced by a surface treatment process such as the following. In particular, by employing the following surface treatment process, it is possible to appropriately and relatively easily bring the surface of the niobium-containing oxide particles into a state where at least one metal element selected from the group consisting of Mo and Ce is present.

[0045] There are no particular restrictions on the method of mixing the niobium-containing oxide powder base material with a compound containing at least one metal element selected from the group consisting of Mo and Ce. Either wet mixing or dry mixing can be employed. 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 surface of the particles constituting the niobium-containing oxide powder base material, and in this respect, wet mixing is preferred.

[0046] For wet mixing, the treatment agent and the niobium-containing oxide powder of the base material are added to water or an alcohol solvent and mixed in a slurry state. As for the alcohol solvent, methanol, ethanol, isopropyl alcohol, etc., which have a boiling point of 100°C or less are preferred because they are easy to remove. Furthermore, from an industrial standpoint, water is preferred because it is easy to recover and dispose of.

[0047] The compounds (treatment agents) containing at least one metal element selected from the group consisting of Mo and Ce are not particularly limited, but examples include oxides, phosphorus oxides, hydroxides, sulfate compounds, nitrate compounds, fluorides, chlorides, organic compounds, and metal salt compounds such as ammonium salts and phosphates. Specifically, examples of Mo compounds include molybdenum oxide, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum boride, phosphate molybdic acid, molybdenum disilide, molybdenum chloride, molybdenum sulfide, silicic acid molybdic acid hydrate, sodium molybdenum oxide, molybdenum carbide, molybdenum acetate dimer, lithium molybdate, sodium molybdate, potassium molybdate, calcium molybdate, magnesium molybdate, manganese molybdate, ammonium molybdate, and 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, with cerium sulfate and its hydrate being particularly preferred.

[0048] The amount of compound containing at least one metal element selected from the group consisting of Mo and Ce can be any amount as long as the amount of at least one metal element selected from the group consisting of Mo and Ce in the niobium-containing oxide falls within the scope of the present invention. However, it is sufficient to add it in a proportion of 0.03% by mass or more relative to the base niobium-containing oxide powder, and it is preferable to add it in a proportion of 0.05% by mass or more. Alternatively, it is sufficient to add it in a proportion of 12% by mass or less relative to the base niobium-containing oxide powder, preferably 10% by mass or less, and more preferably 8% by mass or less.

[0049] It is preferable to perform heat treatment after the above surface treatment. The heat treatment temperature should be such that 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 substrate, and does not cause a significant reduction in the specific surface area due to sintering of the niobium-containing oxide of the substrate. The upper limit of the heat treatment temperature is preferably 700°C or less, and more preferably 600°C or less. The lower limit of the heat treatment temperature is preferably 300°C or higher, and more preferably 400°C or higher. The heat treatment time is preferably 0.1 hours to 8 hours, and more preferably 0.5 hours to 5 hours. The temperature and time at which 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 substrate should be set appropriately, as the reactivity differs depending on the compound containing at least one metal element selected from the group consisting of Mo and Ce. Furthermore, the heating method in the heat treatment is not particularly limited. Suitable heat treatment furnaces include fixed-bed furnaces, roller hearth furnaces, mesh belt furnaces, fluidized-bed furnaces, and rotary kilns. The atmosphere during heat treatment can be either air or an inert atmosphere such as nitrogen. In particular, when metal salt compounds are used for surface treatment, an air atmosphere is preferred as it makes it easier to remove anionic species from the particle surface.

[0050] The niobium-containing oxide powder obtained after heat treatment as described above shows slight aggregation, but does not require grinding that would destroy the particles. Therefore, after heat treatment, it is sufficient to perform crushing or classification to break down the aggregation as needed.

[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, then granulated and heat-treated to obtain a powder containing secondary particles formed by the aggregation of primary particles. Granulation can be performed by any method as long as secondary particles are produced, but a spray dryer is preferred because it can process large quantities.

[0052] To reduce the moisture content of the niobium-containing oxide powder according to the first aspect of the present invention, dew point control may be performed during the heat treatment process. Since the moisture content of the powder increases if it is exposed to the atmosphere after heat treatment, it is preferable to handle the powder in a dew point-controlled environment during cooling in the heat treatment furnace and after heat treatment. The powder after heat treatment may be classified as necessary to bring the particles into a desired maximum particle size range. When dew point control is performed during the heat treatment process, 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 expose it to an environment outside of dew point control. Even under dew point control, grinding the niobium-containing oxide powder after heat treatment makes it easier for moisture to be absorbed from the crushed surface, increasing the moisture content of the powder, so it is preferable not to grind the powder after heat treatment. The temperature and holding time within a specific range of heat treatment conditions greatly affect the secondary particle morphology and surface treatment process. The heat treatment temperature is preferably 450°C or higher, and preferably less than 550°C. This is because exceeding a heat treatment temperature of 550°C significantly reduces the specific surface area, drastically degrading battery performance, particularly rate characteristics. Furthermore, a holding time of one hour or more is preferable, as shorter holding times are thought to increase the moisture content of the powder and affect the particle surface condition.

[0053] [Negative electrode active material composition relating to the first aspect] A negative electrode active material composition according to a first aspect of the present invention is a negative electrode active material composition comprising a niobium-containing oxide powder according to a first aspect of the present invention and an inorganic solid electrolyte having conductivity of a metal ion belonging to Group 1 of the periodic table. The content of the inorganic solid electrolyte 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 higher content of the inorganic solid electrolyte is preferable because it makes it easier to obtain contact between the niobium-containing oxide powder and the solid electrolyte. However, if the content of the inorganic solid electrolyte is too high, the battery capacity of the all-solid-state secondary battery will decrease, so it may be 70% by mass or less, preferably 60% by mass or less, and more preferably 50% by mass or less. Normally, a lower content of the inorganic solid electrolyte is preferable to increase the battery capacity of the all-solid-state secondary battery, but if the content is low, it becomes difficult to obtain 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 inorganic solid electrolyte content is low. The composition may contain one or more substances other than the niobium-containing oxide powder and inorganic solid electrolyte according to the first aspect of the present invention. Other substances include, for example, carbon materials [pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion products, carbon fibers], tin and tin compounds, silicon and silicon compounds, and lithium-containing metal oxides. In particular, Li4Ti5O is used as a lithium-containing metal oxide. 12 Lithium titanate, which has as its main component, is one example.

[0054] <Periodic table> The periodic table as used herein refers to the long-period periodic table of elements as defined by IUPAC (International Union of Pure and Applied Chemistry).

[0055] [Inorganic solid electrolyte] Inorganic solid electrolytes are solid electrolytes that are inorganic, and a solid electrolyte is a solid electrolyte that can move ions within itself. Since inorganic solid electrolytes are solid in a steady state, they do not usually dissociate or become liberated into cations and anions. Inorganic solid electrolytes are not particularly limited as long as they have conductivity to metal ions belonging to Group 1 of the periodic table, and generally have little to 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. Typical examples of inorganic solid electrolytes include (A) sulfide inorganic solid electrolytes and (B) oxide inorganic solid electrolytes. In a first aspect of the present invention, sulfide inorganic solid electrolytes are preferably used because they have high ionic conductivity and a dense molded body with few grain boundaries can be formed by pressurization at room temperature alone.

[0057] (A) Sulfide inorganic solid electrolyte The sulfide inorganic solid electrolyte is preferably one that contains a sulfur atom (S), has conductivity of a metal ion belonging to Group 1 of the periodic table, and is also an electronic insulator. 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 general formula (III) may be used in combination.

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

[0059] The metal sulfide belonging to Group 1 of the periodic table is any 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 general formula (III) is preferably one of P2S5, SiS2, GeS2, B2S3, Al2S3, Ga2S3, and Sb2S5, with P2S5 being 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 sulfides belonging to Group 1 of the periodic table, the sulfides 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] The following combinations are preferred as sulfide inorganic solid electrolytes, but are not particularly limited. Li2S-P2S5, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S -GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li 10 GeP2S 12 .

[0064] Among the aforementioned combinations, LPS glass and LPS glass ceramics manufactured using a combination of Li2S-P2S5 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 it is preferable that the mixing ratio (molar ratio) of "metal sulfide:sulfide represented by general formula (III)" is 50:50 to 90:10. If the mixing ratio of the metal sulfide 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] The sulfide inorganic solid electrolyte may contain, in addition to metal sulfides belonging to Group 1 of the periodic table and sulfides represented by the general formula (III), at least one lithium halide selected from LiI, LiBr, LiCl, and LiF, or lithium salts such as lithium oxide and lithium phosphate, in order to increase ionic conductivity. However, the mixing ratio of the sulfide inorganic solid electrolyte and these lithium salts is preferably 60:40 to 95:5 in terms of the mixing ratio (molar ratio) of "sulfide inorganic solid electrolyte:lithium salt", and more preferably 80:20 to 95:5.

[0067] In addition to the above, other suitable sulfide inorganic solid electrolytes include algerodite-type solid electrolytes such as Li6PS5Cl and Li6PS5Br.

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

[0069] (B) Oxide inorganic solid electrolyte

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

[0071] Examples of oxide inorganic solid electrolytes include Li, which has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 La, which has a perovskite crystal structure, is GeO4. 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li7La3Zr2O has a garnet-type crystal structure. 12 (LLZ), lithium phosphate (Li3PO4), LiPON (Lithium Phosphate with some of the oxygen replaced by nitrogen), Li3BO3-Li2SO4, Li2O-B2O3-P2O5, Li2O-SiO2, and Li6BaLa2Ta2O 12 These are some examples of preferred materials.

[0072] The volume-average particle size of the inorganic solid electrolyte is not particularly limited, but it should be 0.01 μm or larger, and preferably 0.1 μm or larger. The upper limit should be 100 μm or less, and 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 in is not particularly limited, but it should 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 is preferable because it makes it easier to obtain contact between the niobium-containing oxide powder and the solid electrolyte. However, if the amount of inorganic solid electrolyte is too large, the battery capacity of the all-solid-state secondary battery will decrease, so it should be 70% by mass or less, and preferably 50% by mass or less. Normally, a smaller amount of inorganic solid electrolyte is preferable to increase the battery capacity of the all-solid-state secondary battery, but if the amount is small, it becomes difficult to obtain 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 amount of inorganic solid electrolyte is small.

[0074] [Other contents] The negative electrode active material composition according to the first aspect of the present invention may also include 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-conducting material that does not undergo chemical changes. Examples include graphites such as natural graphite (flaky graphite, etc.) and artificial graphite; carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; single-phase carbon nanotubes, multi-walled carbon nanotubes (multi-walled concentric cylindrical graphite layer) (non-fishbone-shaped); cup-type carbon nanotubes (fishbone-shaped); segmented carbon nanofibers (non-fishbone structure); platelet-type carbon nanofibers (playing card-shaped); and other carbon nanotubes. Furthermore, graphites, carbon blacks, and carbon nanotubes may be mixed as appropriate. While not particularly limited, the specific surface area of ​​the carbon black is preferably 30 m². 2 / g~3000m 2 / g, and more preferably 50m 2 / g~2000m 2 The specific surface area of ​​graphites is preferably 30 m². 2 / g~600m 2 / g, and more preferably 50m 2 / g~500m 2 The ratio is / g. 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 to be added should be optimized as it varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents. However, it is sufficient for the negative electrode active material composition to contain 0.1% to 10% by mass, preferably 0.5% to 5% by mass. By setting the amount in the range of 0.1% to 10% by mass, the active material ratio can be made sufficient, thereby increasing the conductivity of the negative electrode layer while ensuring sufficient initial discharge capacity of the energy 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-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethylcellulose (CMC). While not particularly limited, the molecular weight of polyvinylidene fluoride is between 20,000 and 1,000,000. From the viewpoint of further improving the binding properties of the negative electrode layer, it is preferable that the molecular weight be 25,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more. From the viewpoint of further improving conductivity without hindering contact between the active material and the conductive agent, it is preferable that the molecular weight be 500,000 or less. In particular, the specific surface area of ​​the active material is 10 m². 2 If the amount is greater than or equal to 1g, the molecular weight is preferably 100,000 or more.

[0078] The amount of binder added should be optimized as it varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, but it is sufficient if it is included in the negative electrode active material composition at a concentration of 0.2% to 15% by mass. From the viewpoint of improving binding properties and ensuring the strength of the negative electrode layer, it is preferable to have 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 not reducing the active material ratio and thus reducing the initial discharge capacity of the energy storage device per unit mass and unit volume of the negative electrode layer, it is preferable to have 10% by mass or less, and even more preferably 5% by mass or less.

[0079] [Method for preparing a negative electrode active material composition related to the 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 preferred methods include adding a specific proportion of the inorganic solid electrolyte powder to the niobium-containing oxide powder and mixing them using a mixer, stirrer, disperser, etc., or adding the niobium-containing oxide powder to a slurry containing a solid electrolyte.

[0080] The reason why the negative electrode active material composition containing a niobium-containing oxide according to the first aspect of the present invention obtained superior initial discharge capacity, initial efficiency, and charge rate characteristics compared to conventional all-solid-state secondary batteries is not entirely clear, but it is thought 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 of metal ions belonging to Group 1 of the periodic table and a niobium-containing oxide on which at least one metal element selected from the group consisting of Mo and Ce is localized on the surface of 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, and reactants with low ionic conductivity and high resistance adhere to their interface, reducing battery characteristics, especially charge rate characteristics. On the other hand, the localization 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 an all-solid-state secondary battery can be improved. In lithium-ion secondary batteries using organic electrolytes, no reaction occurs with the solid electrolyte, and therefore the problems of the present invention do not arise. When the niobium-containing oxide of the present invention was applied to lithium-ion secondary batteries using organic electrolytes, 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 as the negative electrode of an all-solid-state secondary battery. In this case, it is preferable to form a press-molded body by press-molding the negative electrode active material composition according to the first aspect of the present invention. The conditions for press-molding 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, and therefore a dense negative electrode layer with few voids can be formed. The molded body obtained using the negative electrode active material composition according to the first aspect of the present invention has a filling rate of 72.5% to 100%, preferably 73.5% to 100%. The filling rate can be measured, for example, using the density of the molded negative electrode active material composition calculated from the volume and mass of the molded 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 batteries related to the first perspective] A solid-state secondary battery according to a 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. The negative electrode active material composition according to a first aspect of the present invention, which contains niobium-containing oxide powder and an inorganic solid electrolyte having conductivity of 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 the negative electrode active material composition, or a method of adding the negative electrode active material composition to a solvent to make a slurry, then applying this negative electrode active material composition to a current collector, drying, and pressurizing it.

[0083] Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, calcined carbon, or materials coated with carbon, nickel, titanium, or silver on their surfaces. The surfaces of these materials may also be oxidized, and surface treatment may be used to create irregularities on the surface of the negative electrode current collector. Examples of the negative electrode current collector form include sheets, nets, foils, films, punched materials, laths, porous materials, foams, fiber bundles, and molded nonwoven fabrics. Porous aluminum is preferred as the form of 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 a 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 particular limitations. For example, as a positive electrode active material used in the positive electrode layer of an all-solid-state secondary battery, a composite metal oxide containing one or more elements selected from cobalt, manganese, and nickel, along with lithium, is used. These positive electrode active materials can be used individually or in combination of two or more elements. Examples of such lithium composite metal oxides include LiCoO2 and LiCo 1-x M x O2 (where M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, 0.001 ≤ x ≤ 0.05), LiMn2O4, LiNiO2, LiCo 1-x Ni x O2(0.01 <x<1)、LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiLiLi 0.5 Mn 0.3 Co 0.2 O2, LiLiLi 0.8 Mn 0.1 Co 0.1 O2, LiLiLi 0.8 Co 0.15 Al 0.05 Solid solutions of O2, Li2MnO3 and LiMO2 (where M is a transition metal such as Co, Ni, Mn, or Fe), and LiNi 1 / 2 Mn 3 / 2 One or more types selected from O4 are preferred, and two or more types are more preferred. Furthermore, combinations such as LiCoO2 and LiMn2O4, LiCoO2 and LiNiO2, and LiMn2O4 and LiNiO2 may also be used.

[0085] Furthermore, lithium-containing olivine-type phosphates can also be used as the positive electrode active material. Lithium-containing olivine-type phosphates containing at least one selected from iron, cobalt, nickel, and manganese are particularly preferred. Specific examples include LiFePO4, LiCoPO4, LiNiPO4, and LiMnPO4. Some of these lithium-containing olivine-type phosphates may be substituted with other elements, and some of the iron, cobalt, nickel, and manganese can 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 they can be coated with compounds or carbon materials containing these other elements. Among these, LiFePO4 or LiMnPO4 is preferred. Furthermore, lithium-containing olivine-type phosphate can also be used in combination with, for example, the aforementioned positive electrode active material.

[0086] The conductive agent for the positive electrode is not particularly limited as long as it is an electron-conducting material that does not undergo chemical changes. Examples include graphite such as natural graphite (flaky graphite, etc.) 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 used in appropriate mixtures. The amount of conductive agent added to the positive electrode active material composition is preferably 1 to 10% by mass, and particularly 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), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), carboxymethylcellulose (CMC), or ethylene propylene diene polymer. The method for producing the positive electrode is not particularly limited, and suitable examples include a method of pressurizing the powder of the positive electrode active material composition, or a method of adding the powder of the positive electrode active material composition to a solvent to make a slurry, and then applying this positive electrode active material composition to an aluminum foil or stainless steel lath plate of a current collector, followed by drying and pressurizing.

[0088] The surface of the positive electrode active material may be coated with another metal oxide. Examples of surface coating agents include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specifically, Li4Ti5O 12 Examples include Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, B2O3, etc.

[0089] The solid electrolyte layer is located between the positive electrode layer and the negative electrode layer, and its thickness is not particularly limited but may be between 1 μm and 100 μm. The constituent material of the solid electrolyte layer can 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 all-solid-state rechargeable batteries; coin-type batteries, cylindrical batteries, prismatic batteries, laminated batteries, etc., can be used.

[0091] Invention relating to the second perspective Next, I will describe the invention relating to the second aspect.

[0092] [Niobium oxide powder related to the second perspective] Niobium oxide powder according to a second aspect of the present invention is of the general formula Ti 1-x / 2 Nb2O 7-x This refers to a niobium-containing oxide powder represented by (X=0~2), characterized in that M1 (M1 is a valence 3+ or 2+ metallic element other than Ti or Nb) is present on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder.

[0093] <General formula Ti 1-x / 2 Nb2O 7-x Niobium-containing oxides represented by (X=0~2) The niobium-containing oxide powder according to a second aspect of the present invention is of the general formula Ti 1-x / 2 Nb2O 7-x The material contains a niobium-containing oxide represented by (X=0~2). 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 should be 0 or greater. Specific examples of compounds include TiNb2O7, a niobium-titanium composite oxide capable of intercalating and releasing Li ions and Na ions, and Nb2O5, a niobium oxide. Niobium-titanium composite oxides may also contain a titanium oxide phase derived from the synthesis raw materials (e.g., rutile-type TiO2, TiO, etc.). In the case of niobium-titanium composite oxides, the ratio of moles of Nb to 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] Regarding the niobium-containing oxide according to the second aspect of the present invention, there are no restrictions on the crystal system, but it is generally monoclinic. In the case of monoclinic oxide, the aspect ratio tends to be large, but from the viewpoint of improving electrode density, it is preferable that it be 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 valence 3+ or 2+ metal element other than Ti or Nb) on the surface of the particles. The presence of metal element M1 means that 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 detected by inductively coupled plasma atomic emission spectrometry is usually 0.001% by mass.

[0096] <Content of metallic element M1> The content (mass%) of metal element M1 in the niobium-containing oxide powder according to the second aspect of the present invention, as 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. When the content of metal element M1 is within this range, an energy storage device with excellent discharge rate characteristics, cycle characteristics, and suppressed resistance increase after cycling can be obtained. Preferably it is 0.05 or more and 0.5 or less, 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 discharge rate characteristics and further enhancing the effect of suppressing resistance increase after cycling. Furthermore, from the viewpoint of further improving charge rate characteristics, 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 multiple metal elements are simultaneously present on the particle surface of the niobium-containing oxide powder as metal element M1, the aforementioned content (mass%) is the total content of the multiple 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 quantities 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 quantities in the surface region than in the internal region of the niobium-containing oxide particles. As an 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 present in greater quantities in the 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, and it is preferable that the metal element M1 is not detected at a depth of 100 nm from the surface. When this condition is met, it can be determined that the metal element M1 is localized on the surface of the niobium-containing oxide particles. In other words, this means that the amount detected by energy-dispersive X-ray spectroscopy is less than or equal to the detection amount obtained by that measurement. The lower limit of the detection amount in energy-dispersive X-ray spectroscopy varies depending on the element and state being measured, but is usually 0.5 atm%. Other surface analysis methods include X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).

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

[0099] <Specific examples of the 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 Al 3+ , Mg 2+ , Ca 2+ , Sr 2+ , Zn 2+ , Ga 3+ , Ge 2+ , In 2+ It is more preferable to contain any one or more selected from the group of elements consisting of (that is, when expressed in the form of a metal element, it is more preferable to contain any one or more selected from the group of elements consisting of Al, Mg, Ca, Sr, Zn, Ga, Ge, and In). Al 3+ , Mg 2+ , Ca 2+ , Zn 2+ , Ga 3+ , In 2+ It is even more preferable to contain any one or more selected from the group of elements consisting of, and it is particularly preferable to contain any one or more selected from the group of elements consisting of Al 3+ , Mg 2+ , Zn 2+ , Ga 3+ , In 2+ . These metal elements may be contained in two or more kinds. The niobium-containing oxide powder according to the second aspect of the present invention contains these elements, so that a power storage device excellent in discharge rate characteristics, cycle characteristics, and suppressing an increase in resistance after cycling can be obtained.

[0100] <Containing additional 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 an additional different element other than the metal elements having a valence of 3+ or 2+ excluding the above-mentioned Ti or Nb. Among these, S is particularly preferable. 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 electron conductivity on the surface of the niobium-containing oxide powder as compared with the case of containing only the element M1.

[0101] <Specific surface area> The specific surface area of the niobium-containing oxide powder according to the second aspect of the present invention refers to the surface area per unit mass using nitrogen as the adsorption gas. The measurement method will be described in the examples described later.

[0102] The niobium-containing oxide powder according to the second aspect of the present invention only needs to have a specific surface area of 8.0 m 2 / g or less, and a power storage device excellent in initial discharge capacity and rate characteristics can be obtained. 6.0 m 2 / g or less is preferable, and 5.5 m 2 / g or less is more preferable.

[0103] <d50> D50 in the niobium-containing oxide powder according to the second aspect of the present invention is an index of the median volume particle size. It refers to the particle size at which the cumulative volume frequency calculated from the volume fraction obtained by laser diffraction-scattering particle size distribution measurement accumulates to 50% when calculated from the smallest particle size. The measurement method will be explained in the examples described later.

[0104] The niobium-containing oxide powder according to the second aspect of the present invention may consist of primary particles or secondary particles formed by aggregation of primary particles. When it contains secondary particles formed by aggregation of primary particles consisting of niobium-containing oxide particles, some of these particles may not form secondary particles but remain in the form of primary particles themselves.

[0105] In the case of secondary particles in the niobium-containing oxide powder according to the second aspect of the present invention, 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 ultrasound with an ultrasonic device), that is, 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, in the so-called near-surface region up to a depth of about 20 nm from the surface of the primary particle), and preferably that the metal element M1 is not present in the interior (for example, at a position of 100 nm from the surface of the primary particle toward the interior). This is because when the metal element M1 is present in such a state, an energy storage device with excellent initial discharge capacity and rate characteristics can be obtained.

[0107] In 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 of the primary particles 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 preferably 3 μm or less, preferably 2 μm or less, and more preferably 1.2 μm or less. Note that the D50 of the primary particles represents the D50 after crushing treatment (sonication with an ultrasonic device). Furthermore, the niobium-containing oxide powder may contain 15% to 30% primary particles with a primary particle diameter of less than 0.6 μm, and 15% to 45% primary particles with a primary particle diameter of less than 0.7 μm. It may also contain 45% to 75% primary particles with a primary particle diameter greater than 3 μm, 25% to 75% primary particles with a primary particle diameter greater than 2 μm, and 25% to 80% primary particles with a primary particle diameter greater than 1.2 μm.

[0108] <Zeta potential obtained 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, and more preferably less than or equal to -5 mV. The lower limit of the zeta potential is preferably greater than -60 mV, and more preferably greater than -35 mV. When the zeta potential of the niobium-containing oxide powder according to the second aspect of the present invention is within the above range, an energy storage device with excellent initial discharge rate characteristics and suppression of resistance increase after long-term cycling can be obtained. The zeta potential represents the potential difference between the sliding surface in the electric double layer and a portion sufficiently far from the interface, and it is presumed that this potential difference affects the Li+ permeability on the surface of the niobium-containing oxide powder. The measurement method will be explained in the examples described later.

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

[0110] <Preparation process of raw materials> First, the starting materials are mixed. The mixing of the starting materials can be carried out in the same manner as described in the first point above. If a compound containing the metal element M1 is added before the calcination process described later, the compound may be referred to as the treatment agent or treatment agent 1 below.

[0111] <Firing Process> Next, the mixture obtained above is calcined. The calcination is carried out at a temperature range of 500 to 1200°C, more preferably in the range of 700 to 1100°C. By performing the calcination at a temperature of 1100°C or lower, general-purpose equipment can be used. When calcining the mixture in a short time, it is preferable to prepare the mixed powder constituting the mixture before calcination so that the D95 in the particle size distribution curve measured by a laser diffraction / scattering particle size distribution analyzer is 5 μm or less. Here, D95 is the particle size at which the cumulative volume frequency calculated by volume fraction, when accumulated from the smallest particle size, accounts for 95%.

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

[0113] <Surface treatment process> Next, the niobium-containing oxide obtained above is subjected to 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+ other than Ti or Nb) is localized on the surface of the particles, and when applied as a negative electrode material for a battery, it can form a dense negative electrode layer and provide excellent charge rate characteristics. In the firing process, a compound containing the metal element M1 (hereinafter sometimes referred to as 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, but more preferably, the niobium-containing oxide powder according to the second aspect of the present invention can be produced by a surface treatment process such as the following. In particular, by employing the following surface treatment process, the metal element M1 can be appropriately and relatively easily brought into a state where it is present on the surface of the niobium-containing oxide particles.

[0114] There are no particular restrictions on the method of mixing the niobium-containing oxide powder base material with the compound containing the metal element M1. 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 surface of the particles constituting the niobium-containing oxide powder base material, and in this respect, wet mixing is preferred.

[0115] For wet mixing, the treatment agent 2 and the niobium-containing oxide powder of the base material are added to water or an alcohol solvent and mixed in a slurry state. As for the alcohol solvent, methanol, ethanol, isopropyl alcohol, etc., which have a boiling point of 100°C or less are preferred because they are easy to remove. Furthermore, from an industrial standpoint, water is preferred because it is easy to recover and dispose of.

[0116] The compounds (treatment agents) containing the metal element M1 (where M1 is a metal element with a valence of 3+ or 2+, excluding Ti or Nb) are not particularly limited, but examples include oxides, phosphorus oxides, 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, or aluminum alkoxide, with aluminum sulfate and its hydrate being preferred. When the metal element M1 is Mg, there are no particular limitations, but examples include magnesium oxide, magnesium phosphate, magnesium hydroxide, magnesium sulfate, magnesium nitrate, magnesium fluoride, magnesium chloride, magnesium acetate, magnesium ammonium phosphate, or magnesium alkoxide, with magnesium sulfate and its hydrate being preferred.

[0117] The amount of the compound containing the metal element M1 added can 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. However, it is sufficient to add it in a proportion of 0.03% by mass or more relative to the base material niobium-containing oxide powder, preferably in a proportion of 0.05% by mass or more, and more preferably in a proportion of 0.1% by mass or more. Furthermore, it is preferable to add it in a proportion of 12% by mass or less relative to the base material niobium-containing oxide powder, more preferably in a proportion of 10% by mass or less, and even more preferably in a proportion of 8% by mass or less.

[0118] It is preferable to perform heat treatment after the above surface treatment. The heat treatment conditions and methods may be the same as those described in the first aspect above.

[0119] The niobium-containing oxide powder obtained after heat treatment as described above shows slight aggregation, but does not require grinding that would destroy the particles. Therefore, after heat treatment, it is sufficient to perform crushing or classification to break down the aggregation as needed.

[0120] The niobium-containing oxide powder according to the second aspect of the present invention may be mixed with treatment agent 2 in a surface treatment step, then granulated and heat-treated to obtain a powder containing secondary particles formed by the aggregation of primary particles. Granulation can be carried out by any method as long as secondary particles are produced, but a spray dryer is preferred because it can process large quantities.

[0121] To reduce the moisture content of the niobium-containing oxide powder according to the second aspect of the present invention, dew point control may be performed during the heat treatment process. Since moisture from the atmosphere will be adsorbed onto the powder if it is exposed to the atmosphere as is after heat treatment, it is preferable to handle the powder in a dew point-controlled environment during cooling in the heat treatment furnace and after heat treatment. The powder after heat treatment may be classified as necessary to bring the particles into a desired maximum particle size range. These conditions may be the same as those described in the first aspect above.

[0122] [Active materials related to the second perspective] The active material according to the second aspect of the present invention comprises niobium-containing oxide powder according to the second aspect of the present invention. It may also contain one or more substances other than niobium-containing oxide powder according to the second aspect of the present invention. Other substances include, for example, carbon materials [pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion products, carbon fibers], tin and tin compounds, silicon and silicon compounds, and lithium-containing metal oxides. In particular, Li4Ti5O is used as a lithium-containing metal oxide. 12 Lithium titanate, which has as its main component, is one example.

[0123] [Energy storage devices related to the second perspective] A second aspect of the present invention relates to an energy storage device comprising an electrode containing an active material according to the second aspect of the present invention, which stores and releases energy by utilizing the intercalation and deintercalation of lithium ions to such an electrode, and examples include hybrid capacitors, lithium batteries, and all-solid-state secondary batteries.

[0124] [Hybrid capacitors related to the second perspective] A hybrid capacitor according to a second aspect of the present invention is a device in which the positive electrode uses an active material whose capacitance is formed by physical adsorption similar to that of an electric double-layer capacitor, such as activated carbon, or an active material whose capacitance is formed by physical adsorption, intercalation, and deintercalation, such as graphite, or an active material whose capacitance is formed by redox, such as a conductive polymer, and the negative electrode uses 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 batteries related to the second perspective] Lithium batteries according to the second aspect of the present invention refer collectively to lithium primary batteries and lithium secondary batteries. Furthermore, in this specification, the term lithium secondary battery is used to include so-called lithium-ion secondary batteries and all-solid-state lithium-ion secondary batteries.

[0126] The lithium battery described above is composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, or a solid electrolyte, etc., but 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 described above. This active material may be used as either a positive electrode active material or a negative electrode active material, but the case in which it is used as a negative electrode active material will be described below.

[0127] <Negative pole related to the second perspective> A negative electrode according to a second aspect of the present invention has a negative electrode layer on one or both sides of a negative electrode current collector, comprising a negative electrode active material (active material according to a second aspect of the present invention), a conductive agent, and a binder. This negative electrode layer is usually in the form of an electrode sheet. In the case of a negative electrode current collector having voids, such as a porous body, the negative electrode layer comprising the negative electrode active material (active material according to a second aspect of the present invention), a conductive agent, and a binder is contained within the voids.

[0128] The conductive agent for the negative electrode is not particularly limited as long as it is an electron-conducting material that does not undergo chemical changes, and the same material as 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 mass%, the conductivity of the negative electrode layer cannot be ensured, and if it exceeds 10 mass%, the active material ratio decreases, and the discharge capacity of the energy storage device per unit mass and unit volume of the negative electrode layer becomes insufficient, making it unsuitable for high capacity applications. The conductive agent may be added during electrode fabrication, 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] The binder for the negative electrode can be the same as that described in the first aspect above, and the amount added can also be the same.

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

[0131] The negative electrode can be manufactured by uniformly mixing a negative electrode active material (including an 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 having voids, such as a porous body, the negative electrode can be manufactured by filling the voids of the current collector with a paint made by uniformly mixing the negative electrode active material (an active material according to the second aspect of the present invention), a conductive agent, and a binder in a solvent under pressure, or by immersing the current collector having voids in the paint, diffusing it into the voids, and then drying and compressing it.

[0132] As a method for uniformly mixing the negative electrode active material (active material according to the second aspect of the present invention), conductive agent, and binder in a solvent to form a paint, for example, a type of kneader in which a stirring rod rotates and revolves within a kneading container such as a planetary mixer, a twin-screw extruder kneader, a planetary stirring and defoaming device, a bead mill, a high-speed swirling mixer, or a powder suction continuous dissolution and dispersion device can be used. Alternatively, the manufacturing process may be divided into steps according to the solid content concentration, and these devices may be used accordingly.

[0133] To uniformly mix the negative electrode active material (active material according to the second aspect of the present invention), conductive agent, and binder in a solvent, optimization is necessary as it varies depending on the specific surface area of ​​the active material, the type of conductive agent, the type of binder, and their combinations. However, when using a mixer of the type in which the stirring rod rotates and revolves within a mixing container such as a planetary mixer, a twin-screw extruder mixer, or a planetary stirring and defoaming device, it is preferable to divide the manufacturing process according to the solid content concentration, mix at a high solid content concentration, and then gradually decrease the solid content concentration to adjust the viscosity of the paint. The high solid content concentration is preferably 60% to 90% by mass, and more preferably 60% to 80% by mass. A concentration of 60% by mass or more is preferable because it provides shear force, a concentration of 90% by mass or less is preferable because it reduces the load on the equipment, and a concentration of 80% by mass or less is even preferable.

[0134] There are no particular limitations on the mixing procedure, but examples include mixing the negative electrode active material, conductive agent, and binder simultaneously in a solvent; mixing the conductive agent and binder in a solvent beforehand and then adding the negative electrode active material; and preparing a negative electrode active material slurry, conductive agent slurry, and binder solution in advance and then mixing them separately. Among these, the method of mixing the conductive agent and binder in a solvent beforehand and then adding the negative electrode active material, and the method of preparing a negative electrode active material slurry, conductive agent slurry, and binder solution in advance and then mixing them separately are preferred for uniform dispersion.

[0135] Organic solvents can be used as solvents. Examples of organic solvents include aprotic organic solvents such as 1-methyl-2-pyrrolidone, dimethylacetamide, and dimethylformamide, either alone or in mixtures of two or more, with 1-methyl-2-pyrrolidone being preferred.

[0136] When using an organic solvent, it is preferable to dissolve the binder in the organic solvent beforehand.

[0137] <Positive electrode> The positive electrode has a positive electrode layer on one or both sides of the positive electrode current collector, which includes a positive electrode active material, a conductive agent, and a binder.

[0138] As the positive electrode active material, a material capable of intercalating and releasing lithium is used. For example, the active material may be a composite metal oxide containing cobalt, manganese, and nickel with lithium, or a lithium-containing olivine-type phosphate. These positive electrode active materials can be used individually or in combination of two or more. Examples of such composite metal oxides include LiCoO2, LiMn2O4, LiNiO2, and LiCo 1-x Ni x O2(0.01 <X<1)、LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiLiLi 1 / 2 Mn 3 / 2 Examples include O4, and some of these lithium composite oxides may be substituted with other elements. For example, some of the cobalt, manganese, and nickel may be substituted with at least one element such as B, Nb, Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, La, etc., some of the oxygen may be substituted with S or F, or compounds containing these other elements may be coated. Examples of lithium-containing olivine-type phosphates include LiFePO4, LiCoPO4, LiNiPO4, LiMnPO4, LiFe 1-x Examples include MxPO4 (where M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, and X is 0 ≤ X ≤ 0.5).

[0139] Examples of conductive agents and binders for the positive electrode are the same as those for the negative electrode. Examples of the positive electrode current collector include aluminum, stainless steel, nickel, titanium, calcined carbon, and aluminum or stainless steel with carbon, nickel, titanium, or silver surface treatments. The surfaces of these materials may be oxidized, and surface treatments may be used to create irregularities on the surface of the positive electrode current collector. Examples of the form of the current collector include sheets, nets, foils, films, punched materials, laths, porous materials, foams, fiber groups, and molded nonwoven fabrics.

[0140] <Nonaqueous electrolyte> A non-aqueous electrolyte is prepared by dissolving an electrolyte salt in a non-aqueous solvent. There are no particular restrictions on the non-aqueous electrolyte, and various types can be used.

[0141] The electrolyte salts used are those that dissolve in non-aqueous electrolytes. Examples include inorganic lithium salts such as LiPF6, LiBF4, LiPO2F2, LiN(SO2F)2, and LiClO4; lithium salts containing linear alkyl fluoride such as LiN(SO2CF3)2, LiN(SO2C2F5)2, LiCF3SO3, LiC(SO2CF3)3, LiPF4(CF3)2, LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3(iso-C3F7)3, and LiPF5(iso-C3F7); lithium salts containing cyclic alkylene fluoride chains such as (CF2)2(SO2)2NLi and (CF2)3(SO2)2NLi; and lithium salts with oxalate complexes such as bis[oxalate-O,O']lithium borate and difluoro[oxalate-O,O']lithium borate as anions. Among these, the most preferred electrolyte salts are LiPF6, LiBF4, LiPO2F2, and LiN(SO2F)2, with LiPF6 being the most preferred. These electrolyte salts can be used individually or in combination of two or more. A preferred combination of these electrolyte salts is one in which LiPF6 is included, and at least one lithium salt selected from LiBF4, LiPO2F2, and LiN(SO2F)2 is also included in the non-aqueous electrolyte.

[0142] The concentration at which these total electrolyte salts are dissolved and used is preferably 0.3 M or higher, more preferably 0.5 M or higher, and even more preferably 0.7 M or higher, relative to the aforementioned non-aqueous solvent. The upper limit is preferably 2.5 M or lower, more preferably 2.0 M or lower, and even more preferably 1.5 M or lower.

[0143] On the other hand, examples of the non-aqueous solvent include cyclic carbonates, linear carbonates, linear esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and S=O bond-containing compounds, with the inclusion of cyclic carbonates being preferable. The term "linear ester" is used as a concept that includes linear carbonates and linear carboxylic acid esters.

[0144] Examples of cyclic carbonates 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 collectively referred to as "DFEC"), vinylene carbonate (VC), vinylethylene carbonate (VEC), and 4-ethynyl-1,3-dioxolan-2-one (EEC). One or more selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one, and 4-ethynyl-1,3-dioxolan-2-one (EEC) are more preferable from the viewpoint of improving the charge rate characteristics of the energy storage device and suppressing gas generation during high-temperature operation, and one or more cyclic carbonates having alkylene chains selected from propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate are even more preferable. The proportion of cyclic carbonates having alkylene chains in the total cyclic carbonate is preferably 55% to 100% by volume, and more preferably 60% to 90% by volume.

[0145] Therefore, as the non-aqueous electrolyte, it is preferable to use a non-aqueous electrolyte obtained by dissolving an electrolyte salt containing at least one lithium salt selected from LiPF6, LiBF4, LiPO2F2, and LiN(SO2F)2 in a non-aqueous solvent containing one or more cyclic carbonates selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one, and 4-ethynyl-1,3-dioxolan-2-one. More preferably, as the cyclic carbonate, one or more cyclic carbonates having alkylene chains selected from propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate are used.

[0146] Furthermore, it is preferable to use a non-aqueous electrolyte in which the total electrolyte salt concentration is 0.5 M to 2.0 M, and the electrolyte salt contains at least LiPF6, and further contains 0.001 M to 1 M of at least one lithium salt selected from LiBF4, LiPO2F2, and LiN(SO2F)2. When the proportion of lithium salts other than LiPF6 in the non-aqueous solvent is 0.001 M or more, the effect of improving the charge rate characteristics of the energy storage device and suppressing gas generation during high-temperature operation is easily achieved, and when it is 1.0 M or less, there is less concern that the effect of improving the charge rate characteristics of the energy storage device and suppressing gas generation during high-temperature operation will decrease, so it is preferable. The proportion of lithium salts other than LiPF6 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] Furthermore, the non-aqueous solvent is preferably used in mixture to achieve appropriate physical properties. Examples of such combinations include a combination of cyclic carbonate and linear carbonate, a combination of cyclic carbonate, linear carbonate and lactone, a combination of cyclic carbonate, linear carbonate and ether, a combination of cyclic carbonate, linear carbonate and linear ester, a combination of cyclic carbonate, linear carbonate and nitrile, and a combination of cyclic carbonates, linear carbonate and S=O bond-containing compounds.

[0148] Suitable examples of chain-like esters include one or more asymmetric chain-like 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-like carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate; pivalate esters such as methyl pivalate, ethyl pivalate, and propyl pivalate; and one or more chain-like carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

[0149] Among the aforementioned linear esters, linear esters having methyl groups 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 linear carbonates having methyl groups are particularly preferred.

[0150] Furthermore, when using chain-like carbonates, it is preferable to use two or more types. It is even more preferable to include both symmetric chain-like carbonates and asymmetric chain-like carbonates, and it is even more preferable if the content of symmetric chain-like carbonates is greater than that of asymmetric chain-like carbonates.

[0151] The content of the chain-like ester is not particularly limited, but it is preferable to use it in the range of 60% to 90% by volume relative to the total volume of the non-aqueous solvent. If the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte will not become too high, and if it is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte will decrease, which may reduce the effect of improving the charge rate characteristics of the energy storage device and suppressing gas generation during high-temperature operation, so the above range is preferable.

[0152] The volume percentage of symmetrical chain carbonates within the chain carbonate is preferably 51% by volume or more, and 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 symmetrical chain carbonates include dimethyl carbonate. Furthermore, it is more preferable that the asymmetrical chain carbonates have methyl groups, and methyl ethyl carbonate is particularly preferable. The above conditions are preferable because they improve the charge rate characteristics of the energy storage device and suppress the amount of gas generated during high-temperature operation.

[0153] From the viewpoint of improving the charge rate characteristics of the energy storage device and enhancing the effect of suppressing gas generation during high-temperature operation, the ratio of cyclic carbonate to chain ester (by volume) is preferably 10:90 to 45:55, more preferably 15:85 to 40:60, and particularly preferably 20:80 to 35:65.

[0154] <Structure of lithium batteries from the second perspective> The structure of the lithium battery according to the second aspect of the present invention is not particularly limited, and examples include a coin cell having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, as well as a cylindrical battery or prismatic battery having a positive electrode, a negative electrode, and a roll-shaped separator.

[0155] As the separator, an insulating thin film with high ion permeability and a predetermined mechanical strength is used. Examples include polyethylene, polypropylene, cellulose paper, glass fiber paper, polyethylene terephthalate, and polyimide microporous films, and multilayer films composed of two or more of these materials can also be used. Furthermore, the surface of these separators can be coated with resins such as PVDF, silicone resin, and rubber-based resin, or with particles of metal oxides such as aluminum oxide, silicon dioxide, and magnesium oxide. The pore size of the separator can be within a range generally useful for batteries, for example, 0.01 μm to 10 μm. The thickness of the separator can 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 that can move ions within itself. In particular, inorganic solid electrolytes are solid in a steady state and therefore do not usually dissociate or become liberated into cations and anions. Inorganic solid electrolytes are not particularly limited as long as they have conductivity to metal ions belonging to Group 1 of the periodic table, and generally have little to no electronic conductivity. Representative examples of inorganic solid electrolytes include (A) sulfide inorganic solid electrolytes and (B) oxide inorganic solid electrolytes. Sulfide solid electrolytes are particularly preferred because they have high ionic conductivity and can form dense molded bodies with few grain boundaries by pressurizing at room temperature alone. The periodic table referred to here is the long-period type periodic table.

[0157] The sulfide inorganic solid electrolyte may be amorphous glass, crystallized glass, or a crystalline material. The following combinations are preferred as the sulfide inorganic solid electrolyte, but are not particularly limited. Li2S-P2S5, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S -GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li 10 GeP2S 12 .

[0158] Among the aforementioned combinations, LPS glass and LPS glass ceramics manufactured using the combination of Li2S-P2S5 are preferred. In addition, algerodite-type solid electrolytes such as Li6PS5Cl and Li6PS5Br are also preferred as sulfide inorganic solid electrolytes other than those mentioned above.

[0159] Oxide inorganic solid electrolytes contain oxygen atoms and are metals belonging to Group 1 of the periodic table. Materials that are both on-conductive and electronically insulating are preferred.

[0160] Examples of oxide inorganic solid electrolytes include Li, which has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 La, which has a perovskite crystal structure, is GeO4. 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li7La3Zr2O has a garnet-type crystal structure. 12 (LLZ), lithium phosphate (Li3PO4), LiPON (Lithium Phosphate with some of the oxygen replaced by nitrogen), Li3BO3-Li2SO4, Li2O-B2O3-P2O5, Li2O-SiO2, and Li6BaLa2Ta2O 12 These are some examples of preferred materials.

[0161] The volume-average particle size of the inorganic solid electrolyte is not particularly limited, but is preferably 0.01 μm or larger, and more preferably 0.1 μm or larger. The upper limit is preferably 100 μm or less, and more preferably 50 μm or less. [Examples]

[0162] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples and encompasses various combinations that can be easily inferred from the spirit of the invention.

[0163] Examples relating to the second perspective First, examples and comparative examples relating 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-based lithium-ion secondary battery) [Example 1-1] <Raw material preparation process> Nb2O5 (average particle size 0.2 μm) and anatase-type TiO2 (specific surface area 10 m²) 2 The powder was weighed ( / g) in a molar ratio of 1:1 and mixed. This mixed powder was heat-treated at 1000°C for 5 hours. Powder X-ray diffraction measurements were performed on the resulting calcined powder sample under conditions of a sampling interval of 0.01° and a scan speed of 2° / min. Crystal structure analysis results by the Rietveld method confirmed that the synthesized sample was the target niobium oxide (TiNb2O7: Titanium niobium oxide, PDF card 01-077-1374 of ICDD (PDF2010)).

[0165] <Surface treatment process> The obtained calcined powder sample was crushed by adding deionized water to the slurry so that the solid content concentration was 30% by mass and stirring. As treatment agent 2, 0.8% by weight of aluminum sulfate 16-hydrate (Al2(SO4)3·16H2O) was added per 100g of the crushed calcined powder to prepare a mixed slurry. This mixed slurry was mixed in a paint shaker for 3 hours, dried at a temperature of 60°C, and then heat-treated in a muffle furnace at 500°C for 1 hour to produce the niobium-containing oxide powder (niobium titanate (hereinafter, TNO)) according to Example 1-1.

[0166] [Examples 1-2] In the surface treatment process, the procedure was carried out in the same manner as in Example 1-1, except that the amount of aluminum sulfate 16-hydrate (Al2(SO4)3·16H2O) added as treatment agent 2 was as shown in Table 1, and the niobium-containing oxide powder according to Example 1-2 was produced.

[0167] [Examples 1-3] In the raw material preparation process, the niobium-containing oxide powder synthesized in Example 1-1 was subjected to particle size adjustment treatment. After mixing the niobium-containing oxide powder with zirconia beads (φ2.0 mm), a ball milling treatment was performed, followed by sieving with a 75 μm sieve to obtain niobium-containing oxide powder with adjusted particle size. In the surface treatment process, the procedure was carried out in the same manner as in Example 1-1, except that the amount of aluminum sulfate 16-hydrate (Al2(SO4)3·16H2O) added as treatment agent 2 was as shown in Table 1, and the niobium-containing oxide powder according to Example 1-3 was produced.

[0168] [Examples 1-4] In the surface treatment process, the mixed slurry containing treatment agent 2 was not mixed with a paint shaker, but instead lightly mixed by hand shaking for 3 minutes, then dried at a temperature of 60°C, and then heat-treated at 500°C for 1 hour using a muffle furnace. Except for these differences, the procedure was the same as in Examples 1-3 to produce the niobium-containing oxide powder according to Example 1-4.

[0169] [Examples 1-5, 1-6, 1-7, 1-8, 1-9] In the surface treatment process, the procedure was carried out in the same manner as in Example 1-1, except that the type of treatment agent 2 and the amount of treatment agent 2 added were changed as shown in Table 1. Niobium-containing oxide powders were produced by surface treatment using Example 1-5 (magnesium sulfate heptahydrate: MgSO4·7H2O), Example 1-6 (indium sulfate: In2(SO4)3), Example 1-7 (calcium fluoride: CaF2), Example 1-8 (zinc sulfate: ZnSO4), and Example 1-9 (gallium sulfate: Ga3(SO4)3).

[0170] [Examples 1-10] Except for using Nb2O5 (niobium (V) oxide, average particle size 0.2 μm) as the niobium-containing oxide powder, the surface treatment process was carried out in the same manner as in Examples 1-5 to produce the niobium-containing oxide powder with the surface treatment described in Example 1-10.

[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 treatment agent 2 was not added during the surface treatment process.

[0172] [Reference example 1-1] In the surface treatment process, the procedure was carried out in the same manner as in Example 1-1, except that the amount of aluminum sulfate 16-hydrate (Al2(SO4)3·16H2O) added as treatment agent 2 was as shown in Table 1, to produce the niobium-containing oxide powder according to Reference Example 1-1.

[0173] [Comparative Example 1-2] In the raw material preparation process, Nb2O5 (average particle size 0.2 μm) and anatase-type TiO2 (specific surface area 10 m²) are used. 2 The powder ( / g) was weighed in a molar ratio of 1:1, and then 1.6% by mass of aluminum sulfate 16-hydrate (Al2(SO4)3·16H2O) was mixed in as treatment agent 1. This powder was heat-treated at 1000°C for 5 hours. The surface treatment process was performed on the obtained powder sample in the same manner as in Example 1-1, except that treatment agent 2 was not added, to produce the niobium-containing oxide powder according to Comparative Example 1-2.

[0174] [Comparative Examples 1-3] Except for not adding treatment agent 2 during the surface treatment process, the niobium-containing oxide powder according to Comparative Example 1-3 was produced in the same manner as in Example 1-10.

[0175] [Measurement of the content of metal element M1] The content of valence 3+ or 2+ metal elements other than 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), was measured as follows.

[0176] <X-ray fluorescence analysis (XRF): Identification of the content of metal element M1> The elements contained in the niobium-containing oxide powders of each example and comparative example were quantitatively analyzed using an X-ray fluorescence spectrometer (SII Technology Co., Ltd., product name "SPS5100"). The content of metal elements 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 properties] The various physical properties of the niobium-containing oxide powders in each example and comparative example were measured as follows.

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

[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 the particle size distribution curve measured using a laser diffraction / scattering type particle size distribution measuring instrument (Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd.). 50 mg of the sample was put into a container containing 50 ml of ion-exchanged water as the measurement solvent, and the container was shaken by hand until it was visually confirmed that the powder was uniformly dispersed in the measurement solvent, and then the container was placed in the measurement cell for measurement. The pulverization treatment was carried out by applying ultrasonic waves (30 W, 3 s) with the ultrasonic wave in the apparatus. Furthermore, the measurement solvent was added until the transmittance of the slurry was within the appropriate range (the range indicated by the green bar of the apparatus) for particle size distribution measurement. The D50 of the mixed powder before and after pulverization was calculated from the obtained particle size distribution curve. Note that the D50 before pulverization corresponds to the D50 of the secondary particles, and the D50 after pulverization 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] <Fabrication of Negative Electrode Sheet> The negative electrode sheets were prepared in a room controlled at 25°C and with a dew point of -20°C or lower as follows. The niobium-containing oxide powders from each example were removed from aluminum laminate bags in a room controlled at 25°C and with a dew point of -20°C or lower. The niobium-containing oxide powders from each example were mixed in the following proportions: 90% by mass as the active material, 5% by mass as acetylene black as the conductive agent, and 5% by mass as the binder, to prepare the paint. Polyvinylidene fluoride, acetylene black, and 1-methyl-2-pyrrolidone, which had been pre-dissolved in 1-methyl-2-pyrrolidone, were mixed in a planetary stirring and defoaming apparatus. Then, the niobium-containing oxide powder was added and the mixture was adjusted to a total solid content concentration of 64% by mass, and mixed in a planetary stirring and defoaming apparatus. Subsequently, 1-methyl-2-pyrrolidone was added and the mixture was adjusted to a total solid content concentration of 50% by mass, and mixed in a planetary stirring and defoaming apparatus to prepare the paint. The obtained coating was applied to aluminum foil and dried to produce a single-sided negative electrode sheet for use in the coin cell battery described later, and a double-sided negative electrode sheet for use in the laminate battery described later. The target basis weight during coating was 7.5 mg / cm². 2 That's what I decided.

[0182] <Measurement of electrode density> The negative electrode single-sided sheet coated according to the above procedure was pressed using a roll press machine (roll φ60 × 150 mm, press pressure equivalent to 40 MPa), and the density of the negative electrode layer was measured as the "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 per unit volume, resulting in an increased capacity usable as a battery.

[0183] <Preparation of Electrolyte> The electrolyte used for the characterization battery was prepared as follows: In an argon glove box controlled at a temperature of 25°C and a dew point of -70°C or lower, a non-aqueous solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:2 (volume ratio) ratio was prepared. LiPF6 was dissolved in this solvent as an electrolyte salt to a concentration of 1 M to prepare the electrolyte for the coin cell described below.

[0184] <Manufacturing of coin batteries> The negative electrode single-sided sheet produced by the method described above was punched out into a circle with a diameter of 14 mm, at 2 t / cm². 2 After pressing under pressure, the evaluation electrodes were fabricated by vacuum drying at 120°C for 5 hours. The fabricated evaluation electrodes and metallic lithium (formed into a circular shape with a thickness of 0.5 mm and a diameter of 16 mm) were placed facing each other through a glass filter (one each of ADVANTEC GA-100 and Whatman GF / C), and a non-aqueous electrolyte prepared by the method described in <Preparation of Electrolyte> above was added and sealed to create a 2032 type coin cell.

[0185] <Initial battery characteristics: Measurement of initial discharge capacity and 5C rate discharge characteristics> In a constant temperature bath at 25°C, the coin-type battery prepared using the method described above in <Fabrication of Coin Cells> was charged at 0.2 mA / cm² with the direction in which Li is absorbed into the evaluation electrode being used as the charging direction. 2 The device is charged to 1V with a current density of 0.05mA / cm², and then the charging current at 1V is 0.05mA / cm². 2 After performing constant current constant voltage charging until the current density reaches 0.2 mA / cm², 2 Three cycles of constant current discharge were performed, discharging to 2V at a current density. The initial discharge capacity (mAh / g) was determined by dividing the discharge capacity (mAh) of the third cycle by the weight of the niobium-containing oxide powder. Next, the battery was charged to 1V with a current equivalent to the initial discharge capacity of 0.3C, and then discharged to 2V with a current of 5C to determine the 5C discharge capacity. The 5C rate discharge capacity ratio (%) was calculated by dividing the 5C discharge capacity by the initial discharge capacity. The 5C rate discharge capacity ratio measured in the coin cell of Comparative Example 1-1 was set to 100, and the 5C rate discharge capacity ratios of Examples 1-1 to 1-10, as well as Comparative Examples 1-2 to 1-3 and Reference Example 1-1, were calculated as relative ratios. The results are shown in Table 1 as the 5C rate discharge characteristics (relative ratio %). When the niobium-containing oxide has high 5C rate discharge characteristics, an improvement in the charge rate characteristics of the energy storage device can be expected when it is applied as an electrode material for the energy storage device. In 1C, C represents the current value during charging and discharging. For example, 1C refers to the current value that can completely discharge (or fully charge) the theoretical capacity in 1 / 1 hour, while 0.1C refers to the current value that can completely 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 after cycles> A cycle test was performed in a constant temperature bath at 25°C using a coin-type battery fabricated using the method described above in <Fabrication of Coin Cells>. With the direction in which Li is absorbed into the evaluation electrode defined as charging, the battery was charged to 0.8V with a current value corresponding to 0.5C of the initial discharge capacity. Then, constant current constant voltage charging was performed at 0.8V until the charging current reached a value corresponding to 0.05C. Finally, a constant current discharge cycle was performed, discharging to 2V with a current value corresponding to 0.5C of the initial discharge capacity. This cycle was repeated for a total of 15 cycles. The discharge capacity retention rate (%) was calculated by dividing the discharge capacity after 15 cycles by the initial discharge capacity. The discharge capacity retention rate measured for the coin cell of Comparative Example 1-1 was set to 100, and the relative percentages of the discharge capacity retention rates for Examples 1-1 to 1-10, as well as Comparative Examples 1-2 to 1-3 and Reference Example 1-1, are shown in Table 1. Furthermore, IMP measurements were performed on the coin cell after 15 cycles at frequencies from 0.01 Hz to 1 MHz and temperatures of 0°C, and the resistance (Ω) was determined from the size of the resulting arc. The resistance measured in the coin cell of Comparative Example 1-1 was set to 100, and the results of calculating the relative resistance values ​​of Examples 1-1 to 1-10, as well as Comparative Examples 1-2 to 1-3 and Reference Example 1-1, are shown in Table 1 as the resistance values ​​after cycles (relative ratio %). A lower resistance value after cycles indicates that the increase in resistance has been suppressed.

[0187] [Table 1]

[0188] <Evaluation Results> The electrodes using the niobium-containing oxide powders of Examples 1-1 to 1-10 contain a metal element with a valence of 3+ or 2+ other than Ti or Nb on the surface of the niobium-containing oxide particles that make up the niobium-containing oxide powder. It was found that they have a high initial discharge capacity, excellent discharge rate characteristics and cycle characteristics, and can suppress the increase in resistance after cycling. In particular, Examples 1-3 in which the base material of the niobium-containing oxide was changed to a particle size preparation product and Example 1-4 in which the surface treatment method was changed to hand shaking also showed the same improvement effect. Therefore, it was confirmed that the effect of the present invention does not depend on the type of the base material or the surface treatment method of the niobium-containing oxide. Furthermore, in Example 1-5 containing a divalent metal element (Mg), the improvement effect tended to be enhanced in terms of discharge rate characteristics and cycle characteristics compared to Example 1-2 (Al) containing a trivalent metal element. Also, as in Reference Example 1-1, even when the amount of aluminum, which is a trivalent metal element, was relatively increased, the cycle characteristics were improved while maintaining good discharge rate characteristics and suppressing the increase in resistance after cycling. In Examples 1-1 to 1-10 and Reference Example 1-1, since a metal element M1 with a valence of 3+ or 2+ other than Ti or Nb was introduced by the surface treatment step, 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 did not show any improvement in the initial discharge capacity, rate characteristics, or cycle characteristics, and did not lead to an improvement in battery characteristics. In particular, in Comparative Example 1-2 in which a trivalent metal element (Al) was added during the synthesis of the base material instead of being coated, 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 primary particle surface were measured using an ULVAC-PHI Quantera II scanning X-ray photoelectron spectrometer. After sampling each sample onto an Al plate, measurements were performed using an AlKα X-ray source (monochromatic, 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 in the niobium-containing oxide powder of Comparative Example 1-1, only Ti4+ and Nb5+ were detected. Furthermore, for the niobium-containing oxide powder of Example 1-5, sputtering with Ar ions was performed under conditions of an acceleration voltage of 2 kV and an etching rate of 3.1 nm / min (SiO2 equivalent), and the Mg1s depth profile of the primary particles was measured. The Mg concentration decreased from the particle surface towards the interior of the particle. If the Mg atomic concentration at the surface (0 nm) is taken as 100%, the Mg atomic concentration at a depth of 100 nm from the surface was less than 5%. The Mg1s depth profile results are shown in Figure 1. This confirms that the introduction of a valence 3+ or 2+ metal element M1 (excluding Ti or Nb) through the surface treatment process localizes the metal element M1 on the surface of the niobium-containing oxide particles.

[0190] <Results of zeta potential measurement by electrophoresis> For the niobium-containing oxide powders of Examples 1-1, 1-2, 1-5, 1-6, and Reference Example 1-1, the zeta potential (mV) was measured by electrophoresis using a zeta potential analyzer (Malvern, instrument name "Zetasizer Nano ZS"). 0.02 g of each niobium-containing oxide powder was weighed, placed in 200 mL of deionized water, and measured at 25°C. The results are shown in Table 2 below.

[0191] [Table 2]

[0192] Regarding the niobium-containing oxide powders mentioned above, we confirmed that there were differences in zeta potential. When the zeta potential was less than 0mV and greater than -60mV, the initial 5C rate discharge characteristics were high, and the resistance value after cycling in the long-term characteristics was low, showing a good balance between both performances. Furthermore, comparing Examples 1-1 with Examples 1-2, 1-5, and 1-6, we found that when the zeta potential was greater than -35mV, the initial 5C rate discharge characteristics were further improved. Although this is speculative, it is presumed that the difference in surface coating state caused a displacement in the zeta potential, which reflects the ion diffusion layer, and as a result, 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 from Example 1-1 (a compound obtained by surface treatment with 1.6% by mass of aluminum sulfate hexahydrate (Al2(SO4)3·16H2O)) and Li6PS5Cl powder, a sulfide solid electrolyte (volume-average particle size obtained using a laser diffraction / scattering particle size distribution analyzer: 6 μm) were weighed in a mass ratio of niobium-containing oxide:Li6PS5Cl = 60:40 and mixed in an agate mortar. Next, zirconia balls (3 mm in diameter, 20 g) were placed in an 80 mL zirconia pot, and the mixed powder was added. Then, this pot was set in a planetary ball mill and stirred at a rotation speed of 200 rpm for 15 minutes to obtain the negative electrode active material composition of Example 2-1. The obtained negative electrode active material composition was pressed at room temperature for 10 minutes (360 MPa) 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, a pellet-shaped solid electrolyte layer (LPS glass with a molar ratio of Li2S:P2S5=75:25) as a separator 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 an all-solid-state secondary battery, and its battery characteristics were evaluated. The results are shown in Table 3.

[0194] [Comparative Example 2-1] All-solid-state secondary batteries were prepared in the same manner as in Example 2-1, except that the niobium-containing oxide powder was replaced with the niobium-containing oxide of Comparative Example 1-1 (a compound without treatment agent 2), and the battery characteristics were evaluated. The results are shown in Table 3.

[0195] <Measuring Rate Characteristics> In a constant temperature bath at 25°C, the all-solid-state secondary battery prepared using the method described above was charged to 0.5V with a current equivalent to 0.05C of the theoretical capacity of the niobium-containing oxide, with the direction of Li adsorption to the evaluation electrode as the charging direction. Then, constant current constant voltage charging was performed at 0.5V until the charging current was equivalent to 0.01C, followed by constant current discharge to 2V with a current equivalent to 0.05C. 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 calculated by dividing the discharge capacity by the charging capacity. Next, the battery was charged to 0.5V with a current equivalent to 0.4C of the theoretical capacity of the niobium-containing oxide, and then discharged to 2V with a current of 0.05C to determine the 0.4C charging capacity. The rate characteristic (%) was calculated by dividing this 0.4C charging capacity by the initial discharge capacity. The rate characteristic was examined relative to the value of Comparative Example 2-1, which was set to 100%. The evaluation results are shown in Table 3.

[0196] [Table 3]

[0197] In the all-solid-state secondary battery system, the electrode including the negative electrode layer using the niobium-containing oxide powder of Example 1-1 was found to have excellent charge rate characteristics because the niobium-containing oxide powder contains a metal element M1 with a valence of 3+ or 2+ other than Ti or Nb on the surface of the niobium-containing oxide particles.

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

[0199] [Example 3-1] <Raw material preparation process> Nb2O5 (average particle size 0.2 μm) and anatase-type TiO2 (specific surface area 10 m²) 2 The powders were weighed in a molar ratio of 1:1 (per g) and mixed. This mixed powder was heat-treated at 1000°C for 5 hours. Powder X-ray diffraction measurements were performed on the resulting calcined powder sample under conditions of a sampling interval of 0.01° and a scan speed of 2° / min. Crystal structure analysis results using the Rietveld method confirmed that the synthesized sample was the target niobium oxide (TiNb2O7: Titanium diniobium oxide, PDF card 01-077-1374 of ICDD (PDF2010)).

[0200] <Surface treatment process> The obtained calcined powder sample was crushed by adding deionized water to the slurry so that the solid content concentration was 30% by mass and stirring. Lithium molybdate (Li2MoO4) was added as a treatment agent at a rate of 0.4% by mass per 100g of the crushed calcined powder to prepare a mixed slurry. This mixed slurry was mixed in a paint shaker for 3 hours, dried at a temperature of 60°C, and then heat-treated in a muffle furnace at 500°C for 1 hour to produce the 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, the amount of lithium molybdate (Li2MoO4) added as a treatment agent was as shown in Table 4, but otherwise the same procedure as in Example 3-1 was followed to produce the TNO powder according to Example 3-2.

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

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

[0204] <X-ray fluorescence analysis (XRF): Identification of the contents of metal elements Mo and Ce> Using an X-ray fluorescence spectrometer (manufactured by SII Technology Co., Ltd., trade name "SPS5100"), the elements contained in the TNO powders of each example and each comparative example were quantitatively analyzed. The contents of metal elements Mo and Ce were determined by the following calculation formula. Content (%) = (mass of metal elements Mo, Ce) / (total mass of TNO containing metal elements Mo, Ce) × 100

[0205] [Measurement of powder physical properties] The 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, 4-2 were measured as follows.

[0206] [Measurement of specific surface area] The specific surface area (m 2 / g) of the TNO powders of Examples 3-1, 3-2, 4-1 to 4-8 and Comparative Examples 3-1, 4-1, 4-2 was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountech Co., Ltd., trade name "Macsorb HM model-1208"), and nitrogen gas was used as the adsorption gas. 0.5 g of the measured sample powder was weighed, placed in a φ12 standard cell (HM1201-031), degassed under vacuum at 100 °C for 0.5 hours, and then measured by the BET single-point method.

[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, 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 the sample was put into a container containing 50 mL of ion-exchanged water as the measurement solvent, and the container was shaken by hand until the powder was visually uniformly dispersed in the measurement solvent. Then the container was placed in the measurement cell for measurement. For the disintegration treatment, ultrasonic waves (30 W, 3 s) were irradiated with an ultrasonic wave generator inside the apparatus. Further, the measurement solvent was added until the transmittance of the slurry was within the appropriate range (the range indicated by the green bar of the apparatus) for particle size distribution measurement. The D50 of the mixed powder before and after disintegration was calculated from the obtained particle size distribution curve. Note that the D50 before disintegration corresponds to the D50 of the secondary particles, and the D50 after disintegration corresponds to the D50 of the primary particles.

[0208] [Preparation of Anode Active Material Composition] In a glove box under an argon atmosphere, TNO powder of Example 3-1 and Li6PS5Cl powder, which is a sulfide inorganic solid electrolyte (volume average particle diameter obtained using a laser diffraction / scattering particle size distribution analyzer: 6 μm), were weighed so that the mass ratio of TNO:Li6PS5Cl was 60:40, and mixed in an agate mortar. Next, zirconia balls (diameter 3 mm, 20 g) were put into an 80 mL zirconia pot, and the mixed powder was put in. Then, this pot was set in a planetary ball mill, and stirring was continued at a rotation speed of 200 rpm for 15 minutes to obtain the anode active material composition of Example 3-1. [Example 3-2, Comparative Example 3-1] An anode active material composition shown in Table 4 below was prepared in the same manner as in Example 3-1, except that the TNO powder prepared by the manufacturing method described in Table 4 was used.

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

[0210] [Evaluation of Battery Characteristics] All-solid-state secondary batteries were fabricated using pellets of the negative electrode active material compositions from Examples 3-1, 3-2, 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 electrolytes] In a glove box under an argon atmosphere, lithium sulfide (Li2S) and phosphorus pentasulfide (P2S5) were weighed in a molar ratio of Li2S:P2S5 = 75:25, and mixed in an agate mortar to obtain the raw material composition. Next, zirconia balls (3 mm in 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 set in a planetary ball mill and mechanical milling was performed at a rotation speed of 510 rpm for 16 hours to obtain yellow powder sulfide inorganic solid electrolyte (LPS glass). 80 mg of the obtained LPS glass was placed over an area of ​​0.785 cm². 2 A pellet-shaped solid electrolyte layer was obtained by pressing it at a pressure of 360 MPa using a pellet molding machine having a molding section.

[0212] [Fabrication of all-solid-state secondary batteries] All-solid-state secondary batteries were fabricated by laminating pellets of the negative electrode active material composition from Examples 3-1, 3-2, 4-1 to 4-8, the pelletized solid electrolyte layer, and a lithium indium alloy foil as a counter electrode in this order, and then sandwiching the laminate with a stainless steel current collector.

[0213] <Measurement of initial discharge capacity, initial efficiency, and charge rate characteristics> In a constant temperature bath at 25°C, the all-solid-state secondary battery prepared using the method described above was charged to 0.5V with a current equivalent to 0.05C of the theoretical capacity of the TNO, with the direction of Li absorption into the evaluation electrode considered as charging. Then, constant current constant voltage charging was performed until the charging current at 0.5V was equivalent to 0.01C, followed by constant current discharge to 2V with a current equivalent to 0.05C. The initial discharge capacity (mAh / g) was calculated by dividing the discharge capacity (mAh) by the mass of the TNO. The initial efficiency was calculated by dividing the discharge capacity by the charging capacity. Next, the battery was charged to 0.5V with a current equivalent to 0.4C of the theoretical capacity of the TNO, and then discharged to 2V with a current of 0.05C to determine the 0.4C charging capacity. The charge rate characteristic (%) was calculated by dividing this 0.4C charging capacity by the initial discharge capacity. For Examples 3-1, 3-2, and Comparative Example 3-1, the initial discharge capacity and charge rate characteristics were examined relative to the values ​​of Comparative Example 3-1, with the respective values ​​set to 100%. The evaluation results are shown in Table 4. In 1C, C represents the current value during charging and discharging. For example, 1C refers to the current value that can completely discharge (or fully charge) the theoretical capacity in 1 / 1 hour, while 0.1C refers to the current value that can completely discharge (or fully charge) the theoretical capacity in 1 / 0.1 hour.

[0214] [Table 4]

[0215] Table 4 above shows that Examples 3-1 and 3-2 of the negative electrode active material composition of the present invention exhibit superior initial discharge capacity, initial efficiency, and charge rate characteristics in an all-solid-state secondary battery compared to Comparative Example 3-1. In Examples 3-1 and 3-2, the metallic element Mo was introduced through a surface treatment process, resulting in the metallic element Mo being localized on the surface of the niobium-containing oxide particles.

[0216] [Examples 4-1 to 4-8, Comparative Examples 4-1, 4-2] The negative electrode active material compositions described in Table 5 below were prepared and evaluated in the same manner as in Example 3-1, except that TNO powder produced by the manufacturing method described in Table 5 was used and the battery evaluation was performed in a constant temperature bath at 45°C. In Examples 4-1 to 4-5, the TNO powder was produced in the same manner as in Example 3-1, except that the amount of lithium molybdate (Li2MoO4) added as a treatment agent in the surface treatment step was as shown in Table 5. In Examples 4-6 and 4-7, TNO powder was produced in the same manner as in Example 3-1, except that cerium sulfate tetrahydrate was used as the treatment agent in the amount shown in Table 5, instead of lithium molybdate (Li2MoO4) in the surface treatment step. In Example 4-8, the procedure was the same as in Example 4-1, except that the conditions in the raw material preparation process were adjusted so that the specific surface area and primary particle D50 were the values ​​shown in Table 5, and TNO powder was produced. In Comparative Examples 4-1 and 4-2, TNO powder was produced in the same manner as in Examples 4-1 and 4-8, except that no treatment agent was added. For Examples 4-1 to 4-8 and Comparative Examples 4-1 and 4-2, the initial discharge capacity and charge rate characteristics were examined relative to the values ​​of Comparative Example 4-1, with the respective values ​​set to 100%.

[0217] [Table 5]

[0218] In Table 5 above, it was found that Examples 4-1 to 4-8 of the negative electrode active material composition of the present invention exhibited superior initial discharge capacity, initial efficiency, and charge rate characteristics even at 45°C compared to Comparative Examples 4-1 and 4-2. In Examples 4-1 to 4-8, since the metal elements Mo and Ce were introduced through a surface treatment process, the metal elements Mo and Ce were localized on the surface of the niobium-containing oxide particles.

[0219] [Comparative Example 4-3] Nb2O5, anatase-type TiO2, and molybdenum oxide (MoO3) were weighed and mixed so that the molar ratio became 1:1:0.1. This mixed powder was heat-treated at 1000 °C for 5 hours. When battery evaluation was carried out in the same manner as in Example 3-1 using the sample to which MoO3 was added during the production of TNO, the charge rate characteristics were 80%, and no improvement in the charge rate characteristics, which is the effect of the present invention, was observed. From this result, it was found that in order to improve the charge rate characteristics of all-solid-state secondary batteries, it is necessary for a metal element M1 such as Mo to be localized and present on the surface of niobium-containing oxide particles.

[0220] From the results of Examples 3-1, 3-2, and 4-1 to 4-8 above, the interfacial resistance between the solid electrolyte and TNO can be significantly reduced, and excellent battery characteristics are exhibited by using the negative electrode active material composition.

Claims

1. General formula Ti １－ｘ／２ Nb ２ O ７－ｘ A niobium-containing oxide powder represented by (X = 0 to 2), wherein the ratio of moles of Nb to moles of Ti (Nb / Ti ratio) is in the range of 1.5 to 2.5, and the niobium-containing oxide powder is 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.

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 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 the D50 of primary particles corresponding to 50% of the volume cumulative size distribution in the volume-based particle size distribution measured by laser diffraction scattering is 0.6 μm or larger.

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

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 inorganic solid electrolyte content is 1% by mass or more and 50% by 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 described in claim 4.

8. General formula Ti １－ｘ／２ Nb ２ O ７－ｘ A niobium-containing oxide powder for lithium batteries using a non-aqueous electrolyte or solid electrolyte, characterized in that the ratio of moles of Nb to moles of Ti (Nb / Ti ratio) is in the range of 1.5 to 2.5, and M1 (M1 is a valence 3+ or 2+ metal element other than Ti or Nb) is localized on the surface of the niobium-containing oxide particles constituting the niobium-containing oxide powder.

9. The niobium-containing oxide powder according to claim 8, characterized in that 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 by containing any one or more selected from the group of elements consisting of

11. The niobium-containing oxide powder according to claim 8 or 9, characterized in that the content (mass%) of element M1 present on the 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 the D50 of primary particles corresponding to 50% of the volume cumulative size distribution in the volume-based particle size distribution measured by laser diffraction scattering is 0.3 μm or larger.

13. An electrode for a non-aqueous electrolyte lithium-ion secondary battery or an all-solid-state lithium-ion secondary battery, characterized by containing the niobium-containing oxide powder described in claim 8 or 9.

14. A non-aqueous electrolyte lithium-ion secondary battery or an all-solid-state lithium-ion secondary battery characterized by including the electrode described in claim 13.

Images