Composite powder, electrode using same, and power storage device

Abstract

Provided is a composite powder formed of carbon nanotubes and a transition metal composite oxide containing at least zinc and niobium.

Description

Composite powder, electrodes using the same, and energy storage devices

[0001] The present invention relates to a composite powder suitable as an electrode material for energy storage devices, an electrode using the same, and an energy storage device.

[0002] High energy density is required for energy storage devices in electric vehicles from the perspective of improving fuel efficiency or energy consumption, and lithium-ion batteries in particular are widely used as power sources for electric vehicles and power storage. Various materials are being researched as electrode materials for lithium-ion batteries, and although lithium titanate has excellent input / output characteristics, its energy density remains at 175 mAh / g, so further increases in energy remain a challenge. 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.

[0003] Furthermore, since currently available lithium-ion batteries use electrolytes containing flammable organic solvents, safety devices to suppress temperature rise in the event of a short circuit and structures to prevent short circuits are necessary. Under these circumstances, all-solid-state secondary batteries, which use inorganic solid electrolytes instead of organic electrolytes, are attracting attention. Because all-solid-state secondary batteries consist entirely of solids for the positive electrode, negative electrode, and electrolyte, they have the potential to significantly improve the safety and reliability issues that plague batteries using organic electrolytes. In addition, the simplification of safety devices allows for higher energy density, making them promising for applications in electric vehicles and large-scale storage batteries.

[0004] Patent Document 1 describes Zn, a niobium-containing oxide produced by a solid-phase method, with a particle size range of 3 to 5 μm. ２ Nb ３４ O ８７ Zinc niobium oxides such as the above have been disclosed, and it has been reported that when applied as electrode materials for energy storage devices, excellent battery characteristics can be obtained. Furthermore, Patent Document 2 discloses a Zn in which D50 is 5 μm or more and at least one element has been introduced. ２ Nb ３４ O ８７in, for the purpose of improving the surface electronic conductivity, pitch carbon, graphene oxide, graphene and other polyaromatic sp ２ coating with carbon is disclosed.

[0005] U.S. Patent No. 11380881 Publication of Japanese Patent National Publication of International Translation No. 2023-534759

[0006] However, when a relatively large zinc niobium oxide with a particle size of 3 μm or more as described in Patent Document 1 is applied as a negative electrode material, sufficiently satisfactory battery capacity and rate characteristics cannot be obtained. In addition, as described in Patent Document 2, pitch carbon, graphene oxide, graphene and other polyaromatic sp ２ carbon-coated Zn with a D50 of 5 μm or more and at least one element introduced therein ２ Nb ３４ O ８７ although the rate characteristics are improved compared to element-unsubstituted Zn ２ Nb ３４ O ８７ , satisfactory rate characteristics still cannot be obtained. In addition, even when coated with pitch carbon, graphene oxide, graphene and other polyaromatic sp ２ carbon, the effect of improving cycle characteristics is small, and a satisfactory cycle capacity retention rate cannot be obtained. As a result of various investigations into the cause, it was found that zinc niobium oxide has lower electronic conductivity compared to other niobium composite oxides, and it was found that when zinc niobium oxide with low electronic conductivity is applied as a negative electrode material, the contact with the conductive auxiliary agent in the electrode is extremely important. The zinc niobium oxide of 3 μm or more described in Patent Document 1 has a large volume change that occurs with the charging and discharging of the battery, and as a result, the contact with the conductive auxiliary agent cannot be maintained, and the rate characteristics are degraded. It was found that. In addition, as described in Patent Document 2, pitch carbon, graphene oxide, graphene and other polyaromatic sp ２While carbon-coated zinc niobium oxide improves the electronic conductivity of the particle surface, such coatings fail to improve the reduction in contact with conductive additives caused by volume changes during charging and discharging, and are therefore insufficient for improving cycle capacity retention. Furthermore, it was found that the molar ratio of niobium to zinc also affects volume changes within zinc niobium oxide. The advantages of increasing battery capacity include improved energy density per unit weight or unit area (unit volume), which leads to extended driving ranges for electric vehicles and frees up space for battery installation.

[0007] Based on the above, the discharge capacity, discharge rate characteristics, charge rate characteristics, and cycle capacity maintenance rate of energy storage devices using the negative electrode active material described in Patent Documents 1 and 2 are not sufficiently satisfactory and require further improvement.

[0008] Therefore, the present invention aims to provide a composite powder that can be used as an electrode material for energy storage devices, which can maintain initial discharge capacity in liquid-based energy storage devices, exhibit excellent rate characteristics and improved cycle characteristics, and improve various characteristics in all-solid-state batteries, as well as an electrode using the same and an energy storage device.

[0009] As a result of various studies to achieve the above objective, the present inventors have found that by applying a composite powder of zinc niobium oxide and carbon nanotubes as an electrode material, an energy storage device can be obtained that has excellent initial discharge capacity and rate characteristics, as well as improved cycle characteristics, and have completed the present invention. Such effects, in particular the effect of improving long-term cycle characteristics, are not described or suggested at all in the aforementioned Patent Documents 1 and 2. In other words, the present invention relates to the following matters.

[0010] [1] A composite powder comprising a transition metal composite oxide containing at least zinc and niobium and carbon nanotubes. [2] The composite powder according to [1], characterized in that the carbon nanotube content is 0.001 to 2 parts by mass per 100 parts by mass of the transition metal composite oxide. [3] The composite powder according to any one of [1] or [2], characterized in that the zinc-to-niobium molar ratio Nb / Zn in the transition metal composite oxide is 8 or more and 40 or less. [4] The composite powder according to any one of [1] to [3], characterized in that the composite powder contains secondary particles composed of primary particles of the transition metal composite oxide and carbon nanotubes, and the average particle diameter D50 of the primary particles of the transition metal composite oxide is 0.2 μm or more and 2.5 μm or less. [5] The specific surface area of ​​the composite powder is 1.2 m². ２ / g or more 10m ２ The composite powder according to any one of [1] to [4], characterized in that the amount is less than or equal to / g. [6] The transition metal composite oxide is ZnNb ８ O ２１ , Zn ２ Nb ３４ O ８７ , ZnNb ２０ O ５１ , ZnNb ４０ O １０１ or a composite powder according to any one of the following general formulas (II) to (VII) [1] to [5]. A a Zn １－ｘ M ＩＩＩ １．５ｘ＋ｖ Nb １４－０．５ｘ＋ｖ O ３６±ｚ (II) A a Zn １－ｙ M ＩＶ ３ｙ＋ｗ Nb １４－２ｙ＋ｗ O ３６±ｚ (III) A a Zn １－ｐ M ＩＩ ｐ＋ｖ Nb １４－ｑ M Ｖ ｑ＋ｗ O ３６±ｚ (IV) A a ZnMＩＩ ０．２５ｒ＋ｗ Nb １４－ｒ M ＶＩ ０．７５ｒ＋ｗ O ３６±ｚ (V) A a ZnM ＩＩＩ ０．３３ｓ＋ｗ Nb １４－ｓ M ＶＩ ０．６７ｓ＋ｗ O ３６±ｚ (VI) A a ZnM ＩＶ ０．５ｔ＋ｗ Nb １４－ｔ M ＶＩ ０．５ｔ＋ｗ O ３６±ｚ (VII) (A in the formula is at least one element selected from Li and Na, M ＩＩ Each is independently at least one divalent metallic element selected from Mg, Ca, and Cu, and M ＩＩＩ Each is independently at least one trivalent element selected from Al, Ga, Fe, and Cr, and M ＩＶ Each is independently at least one tetravalent element selected from Ti, Zr, Ge, and Sn, and M Ｖ Each is independently at least one pentavalent metallic element selected from V and Ta, and M ＶＩ ) is at least one hexavalent metallic element independently selected from Mo and W, and a, v, w, x, y, p, q, r, s, t, and z are values ​​such that 0 ≤ a ≤ 6, -0.05 ≤ v ≤ 0.05, -0.05 ≤ w ≤ 0.05, 0 < x < 0.1, 0 < y < 0.1, 0 ≤ p < 0.1, 0 ≤ q < 6, 0 < r < 6, 0 < s < 6, 0 < t < 6, 0 ≤ z ≤ 1, respectively.) An electrode for an energy storage device characterized by comprising the composite powder described in any one of [7] [1] to [6]. A negative electrode active material composition for an energy storage device characterized by comprising the composite powder described in any one of [8] [1] to [6] and an inorganic solid electrolyte. An energy storage device characterized by comprising the electrode described in [9] [7].

[10] An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer and a solid electrolyte layer, characterized in that the negative electrode layer is a layer containing the negative electrode active material composition described in [8].

[0011] According to the present invention, a composite powder, an electrode using the same, and a non-aqueous electrolyte energy storage device can be provided that maintain initial discharge capacity, exhibit excellent rate characteristics, and improve the capacity retention rate over long cycles in a liquid-type non-aqueous electrolyte energy storage device, and further exhibit excellent various characteristics even in an all-solid-state battery.

[0012] [Composite Powder of the Present Invention] The composite powder of the present invention is a composite powder composed of a transition metal composite oxide containing at least zinc and niobium and carbon nanotubes. The composite powder of the present invention is suitably used for electrode applications in energy storage devices. That is, the composite powder of the present invention is preferably a composite powder for electrodes in energy storage devices. The electrolyte used in the energy storage device is not particularly limited, but examples include non-aqueous electrolytes and solid electrolytes.

[0013] <Transition metal composite oxide containing zinc and niobium> The transition metal composite oxide containing zinc and niobium according to the present invention may be any composite oxide containing zinc and niobium, but from the viewpoint of improving rate characteristics and long-term cycle characteristics, it is preferable that the transition metal composite oxide satisfies the molar ratio of niobium to zinc Nb / Zn being 8 or more and 40 or less, more preferably 10 or more and 30 or less, even more preferably 10 or more and 20 or less, even more preferably 10 or more and 15 or less, and particularly preferably 12 or more and 15 or less.

[0014] The aforementioned transition metal composite oxide containing zinc and niobium is ZnNb ８ O ２１ , Zn ２ Nb ３４ O ８７ , ZnNb ２０ O ５１ , ZnNb ４０ O １０１ When it is either or at least one selected from the compounds represented by the following general formulas (II) to (VII), it is preferable because it can maintain the initial discharge capacity while exhibiting superior rate characteristics and further improving long-term cycle characteristics. a Zn １－ｘ M ＩＩＩ １．５ｘ＋ｖ Nb１４－０．５ｘ＋ｖ O ３６±ｚ (II) A a Zn １－ｙ M ＩＶ ３ｙ＋ｗ Nb １４－２ｙ＋ｗ O ３６±ｚ (III) A a Zn １－ｐ M ＩＩ ｐ＋ｖ Nb １４－ｑ M Ｖ ｑ＋ｗ O ３６±ｚ (IV) A a ZnM ＩＩ ０．２５ｒ＋ｗ Nb １４－ｒ M ＶＩ ０．７５ｒ＋ｗ O ３６±ｚ (V) A a ZnM ＩＩＩ ０．３３ｓ＋ｗ Nb １４－ｓ M ＶＩ ０．６７ｓ＋ｗ O ３６±ｚ (VI) A a ZnM ＩＶ ０．５ｔ＋ｗ Nb １４－ｔ M ＶＩ ０．５ｔ＋ｗ O ３６±ｚ (VII) (In the formula, A is at least one element selected from Li and Na, and M ＩＩ is each independently at least one divalent metal element selected from Mg, Ca and Cu, and M ＩＩＩ is each independently at least one trivalent element selected from Al, Ga, Fe and Cr, and M ＩＶ is each independently at least one tetravalent element selected from Ti, Zr, Ge and Sn, and M Ｖ is each independently at least one pentavalent metal element selected from V and Ta, and M ＶＩ(where a, v, w, x, y, p, q, r, s, t, and z are values ​​such that 0 ≤ a ≤ 6, -0.05 ≤ v ≤ 0.05, -0.05 ≤ w ≤ 0.05, 0 < x < 0.1, 0 < y < 0.1, 0 ≤ p < 0.1, 0 ≤ q < 6, 0 < r < 6, 0 < s < 6, 0 < t < 6, and 0 ≤ z ≤ 1, respectively.)

[0015] In general formulas (II) to (VII), A is not particularly limited as long as it is at least one element selected from Li and Na, but is preferably Li.

[0016] Said M ＩＩＩ The element is not particularly limited as long as it is at least one element selected from Al, Ga, Fe, and Cr, but is preferably Al, Fe, and Cr, more preferably Al and Fe, and even more preferably Al.

[0017] Said M ＩＶ The element is not particularly limited as long as it is at least one element selected from Ti, Zr, Ge, and Sn, but is preferably Ti, Zr, and Ge, more preferably Ti and Zr, and even more preferably Ti.

[0018] Said M ＩＩ The element is not particularly limited as long as it is at least one element selected from Mg, Ca, and Cu, but is preferably Mg and Cu.

[0019] Said M Ｖ The element is not particularly limited as long as it is at least one element selected from V and Ta, but is preferably Ta.

[0020] Said M ＶＩ The element is not particularly limited as long as it is at least one element selected from Mo and W, but is preferably W.

[0021] In general formulas (II) to (VII), it is preferable that 0 ≤ a ≤ 6, more preferably 0 ≤ a ≤ 2, even more preferably 0 ≤ a ≤ 0.5, and particularly preferably a = 0. Also, it is preferable that -0.05 ≤ v ≤ 0.05, more preferably -0.01 ≤ v ≤ 0.01, and particularly preferably v = 0. Also, it is preferable that -0.05 ≤ w ≤ 0.05, more preferably -0.01 ≤ w ≤ 0.01, and particularly preferably w = 0. Also, it is preferable that 0 < x < 0.1, more preferably 0 < x < 0.08, and particularly preferably 0 < x ≤ 0.06. Also, it is preferable that 0 < y < 0.1, more preferably 0 < y ≤ 0.08, and particularly preferably 0 < y ≤ 0.06. Also, it is preferable that 0 ≤ p < 0.1, more preferably 0 ≤ p ≤ 0.08, even more preferably 0 ≤ p ≤ 0.06, and particularly preferably p = 0. Furthermore, it is preferable that 0 ≤ q < 6, more preferably 0 ≤ q < 3, even more preferably 0 ≤ q < 1, and particularly preferably q = 0. Also, it is preferable that 0 < r < 6, more preferably 0 < r < 3, and particularly preferably 0 < r < 1. Also, it is preferable that 0 < s < 6, more preferably 0 < s < 3, and particularly preferably 0 < s < 1. Also, it is preferable that 0 < t < 6, more preferably 0 < t < 3, and particularly preferably 0 < t < 1. Also, it is preferable that 0 ≤ z ≤ 1, more preferably 0 ≤ z ≤ 0.5, even more preferably 0 ≤ z ≤ 0.2, and particularly preferably z = 0.

[0022] ZnNb ８ O ２１ , Zn ２ Nb ３４ O ８７ , ZnNb ２０ O ５１ , ZnNb ４０ O １０１Among the compounds represented by the above general formulas (II) to (VII), the compounds represented by the above general formulas (II) to (VII) are preferred from the viewpoint of being able to further improve the initial discharge capacity, rate characteristics, and long-term cycle characteristics, the compound represented by the above general formula (IV) is more preferred, and the compound represented by the above general formula (IV) is (A a Zn １－ｐ M ＩＩ ｐ＋ｖ Nb １４－ｑ M Ｖ ｑ＋ｗ O ３６±ｚ ) and a=0, p=0, q=0, v=0, w=0, z=0, i.e., ZnNb １４ O ３６ That is particularly preferable.

[0023] The composite powder of the present invention is composed of a transition metal composite oxide containing zinc and niobium, and carbon nanotubes. The carbon nanotubes are a type of fibrous carbon and may be either single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs), and these may be used in combination. The carbon nanotubes are not particularly limited and can be obtained without restriction by methods such as catalytic pyrolysis, arc discharge, laser evaporation, and CVD methods such as HiPco and CoMoCAT. Commercially available single-walled or multi-walled carbon nanotubes can also be used. As for the carbon nanotubes, it is preferable to use at least single-walled carbon nanotubes (SWCNTs) from the viewpoint of improving rate characteristics even in small amounts and further improving long-term cycle characteristics.

[0024] In the composite powder of the present invention, the content ratio of the transition metal composite oxide containing zinc and niobium to the carbon nanotube is not particularly limited, but the carbon nanotube content is preferably 0.001 to 2 parts by mass, more preferably 0.01 to 1.8 parts by mass, per 100 parts by mass of the transition metal composite oxide, and even more preferably 0.08 to 1.2 parts by mass from the viewpoint of further improving rate characteristics and long-term cycle characteristics. When single-walled carbon nanotubes (SWCNTs) are used as the carbon nanotubes, the SWCNT content is preferably 0.001 to 1.5 parts by mass, more preferably 0.01 to 1.2 parts by mass, even more preferably 0.08 to 1 part by mass, and particularly preferably 0.09 to 0.5 parts by mass, per 100 parts by mass of the transition metal composite oxide, from the viewpoint of further improving rate characteristics and long-term cycle characteristics. Furthermore, when using multi-walled carbon nanotubes (MWCNTs) as the carbon nanotubes, from the viewpoint of further improving rate characteristics and long-term cycle characteristics, the MWCNT content is preferably 0.4 to 2.0 parts by mass, more preferably 0.5 to 1.8 parts by mass, even more preferably 0.5 to 1.5 parts by mass, and particularly preferably 0.8 to 1.2 parts by mass, per 100 parts by mass of the transition metal composite oxide. The carbon nanotube content can be calculated by various measurement methods, but one example is differential thermal-thermogravimetric analysis (TG-DTA), in which weight change and temperature change are continuously measured while heating the sample at a constant rate. There are no particular restrictions on the physical properties of the carbon nanotubes, but from the viewpoint of improving conductivity and dispersibility (prevention of aggregation) during electrode fabrication, the average diameter is 1 to 25 nm, the length is 1 to 500 μm, and the specific surface area is 50 to 600 m². ２It is preferable that the amount is / g. The average diameter is more preferably 1.3 to 4 nm, even more preferably 1.4 to 2.5 nm, for single-walled carbon nanotubes (SWCNTs), and more preferably 2 to 20 nm, even more preferably 3.5 to 17 nm, for multi-walled carbon nanotubes (MWCNTs). The length is more preferably 2 to 80 μm, even more preferably 3 to 40 μm, and the specific surface area is more preferably 100 to 450 m². ２ / g, more preferably 120 to 380m ２ It is / g.

[0025] [Secondary Particles Constituting the Composite Powder of the Present Invention] The composite powder of the present invention may also contain primary particles of a transition metal composite oxide containing zinc and niobium, and secondary particles composed of carbon nanotubes. The secondary particles referred to here are those whose external appearance approximates a spherical shape, and include particles with partially uneven surfaces and particles with shapes close to spherical, such as ellipsoids. There are no particular restrictions on the method of secondary particle formation, but in order to prevent carbon nanotubes from becoming extremely localized on the surface of the secondary particles, it is preferable to employ a spray drying method in which a mixed slurry containing primary particles of the transition metal composite oxide, carbon nanotubes, and a dispersion medium is spray-dried. A thickening agent may also be used to adjust the viscosity of the slurry, and examples of thickening agents include carboxycellulose (CMC) and 1,2-dimethylimidazole (IMD). Examples of dispersion medium include water and alcohols such as methanol and ethanol.

[0026] [D50 of secondary particles constituting the composite powder of the present invention] When the composite powder of the present invention consists of secondary particles, D50 of the secondary particles 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. From the viewpoint of improving electrode density, the lower limit of D50 of the secondary particles is preferably 5 μm or more, more preferably 9 μm or more, the upper limit is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 14 μm or less.

[0027] [Average crushing strength of secondary particles constituting the composite powder of the present invention] When the composite powder of the present invention contains secondary particles composed of primary particles of a transition metal composite oxide and carbon nanotubes, the crushing strength of the secondary particles is preferably 1 MPa or more, more preferably 1.5 MPa or more, even more preferably 2.0 MPa or more, and preferably 5.0 MPa or less as the upper limit. When the crushing strength of the secondary particles is 1 MPa or more, when an electrode mixture layer is formed, the carbon nanotubes do not localize within the electrode mixture layer, the contact area between the transition metal composite oxide containing zinc and niobium and the carbon nanotubes increases, and as a result, the rate characteristics can be further improved. The crushing strength of the secondary particles is the compressive strength when the secondary particles are compressed by 10% of the measured particle diameter, and can be measured, for example, using a Shimadzu microcompression tester (MCT-510) with the added test force "1 g or less measurement mode".

[0028] The composite powder of the present invention, comprising a transition metal composite oxide containing zinc and niobium, may contain at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) on the surface of the particles. Two or more metal elements M may be present. The presence of the metal elements M means that these metal elements M are detected in inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray fluorescence spectrometry (XRF), or X-ray photoelectron spectroscopy (XPS) of the zinc and niobium-containing transition metal composite oxide comprising the composite powder of the present invention. The lower limit of the detection amount by inductively coupled plasma atomic emission spectrometry is typically 0.001% by mass.

[0029] Furthermore, when the transition metal composite oxide containing zinc and niobium that constitutes the composite powder of the present invention contains the metal element M, it is preferable that the metal element M is localized and present in greater quantities in the surface region than in the internal region of the transition metal composite oxide particles containing zinc and niobium that constitute the powder. That is, the metal element M is present on the surface of the transition metal composite oxide particles containing zinc and niobium, and more specifically, it is preferable that the element is localized and present in greater quantities in the surface region than in the internal region of the transition metal composite oxide containing zinc and niobium. As an example, in a cross-sectional analysis of the transition metal composite oxide particles containing zinc and niobium using a scanning transmission electron microscope, it is preferable that the metal element M 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 transition metal composite oxide particles containing zinc and niobium, as measured by energy-dispersive X-ray spectroscopy, and that the metal element M is not detected at a depth of 100 nm from the surface. In other words, this means that when measured by energy-dispersive X-ray spectroscopy, the amount detected by the measurement is less than or equal to the amount detected by the measurement. The lower limit of the amount detected by energy-dispersive X-ray spectroscopy varies depending on the element and state being measured, but is usually 0.5 atm%. Other surface analysis methods include X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). As for the content of the metal element M, from the viewpoint of improving the initial capacity and rate characteristics in liquid-type non-aqueous electrolyte energy storage devices, and furthermore, the rate characteristics in all-solid-state batteries, the lower limit is preferably 0.2 mass% or more, more preferably 0.5 mass% or more, even more preferably 0.7 mass% or more, and even more preferably 0.7 mass% or more. The upper limit is preferably 2.6 mass% or less, more preferably 1.8 mass% or less, even more preferably 1.5 mass% or less, and even more preferably 1.3 mass% or less.

[0030] <D50 of primary particles of transition metal composite oxide containing zinc and niobium> In liquid-type non-aqueous electrolyte energy storage devices, the D50 of primary particles of a transition metal composite oxide containing zinc and niobium is preferably 0.2 μm or more, more preferably 0.4 μm or more, even more preferably 0.5 μm or more, and particularly preferably 0.8 μm or more, from the viewpoint of having superior rate characteristics and suppressing the rate of change in electrode thickness due to charging and discharging. The lower limit of the D50 of primary particles is preferably 0.2 μm or more, more preferably 0.4 μm or more, even more preferably 0.5 μm or more, and particularly preferably 0.8 μm or more. The upper limit of the D50 of primary particles is preferably 2.5 μm or less, more preferably 2.3 μm or less, even more preferably 2.2 μm or less, even more preferably 2.0 μm or less, especially preferably 1.8 μm or less, and particularly preferably 1.2 μm or less. Furthermore, the transition metal composite oxide containing zinc and niobium may contain primary particles with a diameter of less than 0.2 μm, and may also contain primary particles with a diameter of more than 2.5 μm.

[0031] <D90 of primary particles of transition metal composite oxide containing zinc and niobium> In liquid-type non-aqueous electrolyte energy storage devices, the D90 of primary particles is preferably 0.8 μm or more, more preferably 1.0 μm or more, even more preferably 1.2 μm or more, and particularly preferably 2 μm or more, from the viewpoint of further improving the initial discharge capacity, rate characteristics, electrode thickness change rate during charging and discharging, and in all-solid-state batteries. The lower limit of the D90 of primary particles is preferably 0.8 μm or more, more preferably 1.0 μm or more, even more preferably 1.2 μm or more, and particularly preferably 2 μm or more. The upper limit of the D90 of primary particles is preferably 15 μm or less, more preferably 10 μm or less, even more preferably 8 μm or less, even more preferably 5 μm or less, especially preferably 3 μm or less, and particularly preferably 2.4 μm or less. The D90 of primary particles of transition metal composite oxide refers to the particle size at which the cumulative volume frequency calculated using the volume fraction obtained by laser diffraction / scattering particle size distribution measurement accumulates to 90% when calculated from the smallest particle size. The measurement method will be explained in the examples described later.

[0032] <D10 of primary particles of transition metal composite oxide containing zinc and niobium> In liquid-type non-aqueous electrolyte energy storage devices, the D10 of primary particles of transition metal composite oxide is preferably 0.05 μm or more, more preferably 0.1 μm or more, even more preferably 0.2 μm or more, and particularly preferably 0.4 μm or more, from the viewpoint of further improving the initial discharge capacity, rate characteristics, and electrode thickness change rate during charging and discharging, as well as the initial discharge capacity and rate characteristics in all-solid-state batteries. The lower limit of the D10 of primary particles is preferably 0.05 μm or more, more preferably 0.1 μm or more, even more preferably 0.2 μm or more, and particularly preferably 0.4 μm or more. The upper limit of the D10 of primary particles is preferably 1.5 μm or less, more preferably 1.2 μm or less, even more preferably 1.0 μm or less, even more preferably 0.8 μm or less, and particularly preferably 0.6 μm or less. Note that the D10 of primary particles of transition metal composite oxide refers to the particle size at which the cumulative volume frequency calculated using the volume fraction obtained by laser diffraction / scattering particle size distribution measurement accumulates to 10% when calculated from the smallest particle size. The measurement method will be explained in the examples described later.

[0033] log of primary particles of transition metal composite oxides １０ (D90)-log １０ The value calculated in (D50) is preferably less than 0.6, more preferably 0.56 or less, even more preferably 0.53 or less, and even more preferably 0.5 or less, from the viewpoint of having superior initial discharge capacity and rate characteristics in liquid-type non-aqueous electrolyte energy storage devices, and further suppressing the rate of change in electrode thickness due to charging and discharging. Furthermore, the lower limit is preferably 0.03 or higher, more preferably 0.08 or higher, even more preferably 0.1 or higher, even more preferably 0.15 or higher, and particularly preferably 0.25 or higher. By setting this value within this range, the possibility of coarse transition metal composite oxide particles hindering contact with conductive materials and ion conductors in the electrode mixture, and the possibility of the electrode thickness increasing due to distortion of the entire electrode during charging and discharging is reduced. As a result, a lithium-ion secondary battery can be obtained that has superior initial discharge capacity and rate characteristics in liquid-type non-aqueous electrolyte energy storage devices, and further has a small rate of change in electrode thickness due to charging and discharging.

[0034] <Specific Surface Area> The specific surface area of ​​the composite powder is the surface area per unit mass, using nitrogen as the adsorbent gas. The measurement method will be explained in the examples below.

[0035] The composite powder has an upper limit of 10 m² in specific surface area. ２ It is preferable that the amount is less than or equal to 9.0 m ２ More preferably less than / g, and 8.0m ２ It is even more preferable to be less than or equal to 6.0 m ２ A value of less than or equal to / g is even more preferable. On the other hand, the lower limit of the specific surface area is 1.2 m². ２ It is preferable that the amount be 1.5 m or more. ２ It is more preferable that the amount is 2.0 m or more. ２ More preferably 3.5 m ２ A value of 1 / g or higher is particularly preferred. Within the above range, an excellent energy storage device can be obtained in a non-aqueous electrolyte energy storage device, from the viewpoint of further improving the rate characteristics and further suppressing the rate of change in electrode thickness due to charging and discharging.

[0036] The reason for the remarkable effect observed by using a composite powder composed of a transition metal composite oxide containing zinc and niobium and carbon nanotubes is not clear, but it is thought to be as follows. Generally, negative electrode active materials such as transition metal composite oxides such as zinc niobium oxide exhibit capacity by intercalating and releasing lithium ions via an electrolyte or solid electrolyte. Therefore, the contact area between the negative electrode active material and the non-aqueous electrolyte such as the electrolyte or solid electrolyte, as well as the diffusion of lithium ions and electrons within the active material particles, are extremely important. Furthermore, in electrodes using zinc niobium oxide active materials, which have particularly low electronic conductivity, the volume change associated with charging and discharging of the active material in the negative electrode mixture layer gradually causes the contact with the conductive additive to disappear, and the rate characteristics and other properties deteriorate significantly. The composite powder composed of a transition metal composite oxide and carbon nanotubes of the present invention can preferably suppress the rate of change in electrode thickness associated with charging and discharging by adjusting the molar ratio of niobium to zinc, and it is thought that the contact with the conductive additive and solid electrolyte in the negative electrode mixture layer can be suitably maintained. Furthermore, it is believed that the carbon nanotubes not only improve the electronic conductivity of the particle surface, but also create an electronic conduction path throughout the entire composite layer by intertwining with each other and forming a network within the composite layer, and that the strength of the composite layer is improved, thereby suppressing cracking of the entire composite layer during charging and discharging. In addition, by using the composite powder composed of the transition metal composite oxide and carbon nanotubes of the present invention, it is believed that the aggregation of carbon nanotubes, which is a problem when carbon nanotubes are used as a conductive additive, hardly occurs. As a result, the composite powder of the present invention is less likely to cause large volume changes during charging and discharging, such as pitch carbon, graphene oxide, and graphene as described in Patent Documents 1 and 2. ２ It is believed that battery characteristics that could not be achieved with carbon-coated zinc niobium oxide were obtained.

[0037] [Method for producing a transition metal composite oxide containing zinc and niobium] Below, an example of a method for producing a transition metal composite oxide containing zinc and niobium, which constitutes the composite powder of the present invention, will be described in detail, divided into raw material preparation, calcination, surface treatment, etc. However, the method for producing the transition metal composite oxide containing zinc and niobium of the present invention is not limited thereto.

[0038] <Preparation Process of Raw Materials> First, the starting materials are mixed. An oxide or salt containing Zn and Nb is used as the starting material. If the transition metal composite oxide contains other additive elements, an oxide or salt containing at least one element selected from the group consisting of Zr, Si, Ge, Sn, V, Ta, Al, Ga, Fe, Cr, Mg, Ca, Cu, Bi, Mo, and W is used as the starting material and mixed in a stoichiometric ratio to obtain the target composition of the present invention. The salt used is preferably a salt that decomposes at a relatively low melting point to produce an oxide, such as a hydroxide salt, carbonate salt, or nitrate salt. In addition, in order to reduce the primary particle size, it is preferable to use a powder with an average primary particle size of 2 μm or less, preferably an average primary particle size of 0.5 μm or less, as the starting material.

[0039] 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.

[0040] <Casturing Process> Next, the mixture obtained above is calcined. Calcination is preferably carried out in the temperature range of 500 to 1250°C, more preferably in the range of 700 to 1250°C, and even more preferably in the range of 900 to 1250°C. By performing the calcination at a temperature of 1250°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 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%.

[0041] The firing method is not particularly limited as long as it can be fired under the aforementioned conditions. Usable firing methods include fixed-bed furnaces, roller hearth furnaces, mesh belt furnaces, fluidized-bed furnaces, and rotary kilns. However, for efficient firing in a short time, roller hearth furnaces, mesh belt furnaces, and rotary kilns are preferred. In particular, rotary kilns are especially preferred for producing transition metal composite oxides because they do not require a container to hold the mixture, allow for continuous feeding of the mixture during firing, and provide a uniform thermal history to the fired material, resulting in a homogeneous oxide.

[0042] <Crushing Process> The transition metal composite oxide containing zinc and niobium after calcination is preferably subjected to crushing treatment as necessary in order to obtain the desired particle size. There are no particular limitations on the method of crushing the calcined material recovered from the calcined material recovery side, but there are hammer mills, ball mills, jet mills, vibratory mills, bead mills, etc., with bead mills being particularly preferred. When using a bead mill, any of the following methods can be used for crushing: wet crushing in a circulating system, wet crushing in a batch system, dry crushing in a circulating system, or dry crushing in a batch system. However, it is preferable to perform crushing uniformly, and in this respect, wet crushing in a circulating system is preferred. The circulation conditions should be determined considering the calcination temperature in the calcination process, etc., but for example, the particle size of the transition metal composite oxide containing zinc and niobium can be suitably controlled by adjusting the circulation conditions. For wet crushing, the transition metal composite oxide containing zinc and niobium after calcination is placed in water or an alcohol solvent and mixed in a slurry state. As the alcohol solvent, methanol, ethanol, isopropyl alcohol, etc., which have a boiling point of 100°C or lower, are preferred because they are easy to remove. Furthermore, from an industrial perspective, water is preferred because it is easy to recover and dispose of. The conditions for the crushing treatment are not particularly limited, as long as they allow the particle size to be within the above range. In addition to the crushing treatment, classification may also be performed.

[0043] <Surface Treatment Process> Surface treatment may be performed on the transition metal composite oxide containing zinc and niobium obtained above. By localizing at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) on the surface of the particles constituting the transition metal composite oxide containing zinc and niobium, a dense negative electrode layer can be formed when applied as a negative electrode material for a battery, and superior rate characteristics can be imparted. In the firing process, a compound containing the metal element M (hereinafter sometimes referred to as a treatment agent) can be added to produce a surface-treated transition metal composite oxide containing zinc and niobium, but it is more preferable to produce a surface-treated transition metal composite oxide containing zinc and niobium 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 transition metal composite oxide particles into a state where at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) is present.

[0044] There are no particular restrictions on the method of mixing the transition metal composite oxide containing zinc and niobium as a base material with the compound containing metal element M. Either wet mixing or dry mixing can be employed. However, it is preferable to uniformly disperse the compound containing at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) on the surface of the particles constituting the transition metal composite oxide containing zinc and niobium as a base material. In this respect, wet mixing is preferred.

[0045] In the wet mixing process, the treatment agent and the transition metal composite oxide of the base material are added to water or an alcohol solvent and mixed in a slurry state. As 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.

[0046] The compound (treatment agent) containing at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) is 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 element M is Al, examples include aluminum oxide, aluminum phosphate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum fluoride, aluminum chloride, aluminum acetate, aluminum ammonium sulfate, or aluminum alkoxide, among which aluminum sulfate and its hydrate are preferred. When the element M is Mg, examples include magnesium oxide, magnesium phosphate, magnesium hydroxide, magnesium sulfate, magnesium nitrate, magnesium fluoride, magnesium chloride, magnesium acetate, magnesium ammonium phosphate, or magnesium alkoxide, among which magnesium sulfate and its hydrate are preferred. When the element M is Ce, examples include cerium oxide, cerium hydroxide, cerium fluoride, cerium sulfate, cerium nitrate, cerium carbonate, cerium acetate, cerium oxalate, cerium chloride, cerium boride, cerium phosphate, and among these, cerium sulfate and its hydrate are preferred. When the element M is Mo, examples 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.

[0047] The amount of compound containing at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) added is any amount as long as the amount of at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) in the transition metal composite oxide containing zinc and niobium 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 material transition metal composite oxide containing zinc and niobium, 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 material transition metal composite oxide containing zinc and niobium, preferably 10% by mass or less, and more preferably 8% by mass or less.

[0048] Heat treatment may be performed after the above surface treatment. The heat treatment temperature should be such that at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) diffuses into at least the surface region of the zinc and niobium-containing transition metal composite oxide particles that constitute the zinc and niobium-containing transition metal composite oxide of the base material, and a significant reduction in specific surface area due to sintering of the transition metal composite oxide of the base material does not occur. 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 M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) diffuses into at least the surface region of the transition metal composite oxide containing zinc and niobium as a base material should be set appropriately, as the reactivity differs depending on the compound containing at least one metal element M selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo). Furthermore, the heating method in the heat treatment is not particularly limited. Examples of usable 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 an air atmosphere or an inert atmosphere such as a nitrogen atmosphere. In particular, when a metal salt compound is used for surface treatment, an air atmosphere is preferred as it makes it easier to remove anionic species from the particle surface.

[0049] The transition metal composite oxide containing zinc and niobium obtained after heat treatment as described above, although showing slight aggregation, 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.

[0050] To reduce the moisture content of the zinc and niobium-containing transition metal composite oxide 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 the heat-treated transition metal composite oxide is exposed to the atmosphere as is, it is preferable to handle the transition metal composite oxide in a dew point-controlled environment during cooling in the heat treatment furnace and after heat treatment. The heat-treated transition metal composite oxide 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 transition metal composite oxide 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 heat-treated transition metal composite oxide makes it easier for moisture to be absorbed from the crushed surface, increasing the moisture content of the transition metal composite oxide; therefore, it is preferable not to grind the material 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.

[0051] [Method for Producing Composite Powder] The composite powder of the present invention can be produced by mixing carbon nanotubes with a transition metal composite oxide containing zinc and niobium obtained by the above method and then compounding them. The method for mixing carbon nanotubes with the transition metal composite oxide is not particularly limited, but examples include preparing a mixed slurry by adding water and carbon nanotubes to the transition metal composite oxide containing zinc and niobium, dispersing the mixed slurry using a paint shaker or the like, and then spraying and drying it using a spray dryer or the like. When preparing the mixed slurry, a thickener such as carboxymethylcellulose or imidazole may be used as needed. In addition, if the transition metal composite oxide containing zinc and niobium is subjected to a crushing treatment, a mixed slurry may be prepared by directly adding carbon nanotubes and a thickener such as carboxymethylcellulose, which may also be used as needed, to the slurry obtained by the crushing treatment.

[0052] [Active Material] The active material of the present invention contains the composite powder of the present invention. It may also contain one or more substances other than the composite powder 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, as a lithium-containing metal oxide, Li ４ Ti ５ O １２ Lithium titanate, which has as its main component, is one example.

[0053] [Energy Storage Device] The energy storage device of the present invention comprises electrodes containing the active material of the present invention, and is a device that stores and releases energy by utilizing the intercalation and deintercalation of lithium ions to such electrodes, and examples include hybrid capacitors and lithium batteries.

[0054] [Hybrid Capacitor] The hybrid capacitor 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 and 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 of the present invention. The active material of the present invention is usually used in the form of an electrode sheet for the hybrid capacitor.

[0055] [Lithium Batteries] The lithium batteries of the present invention refer collectively to lithium primary batteries and lithium secondary batteries. In this specification, the term lithium secondary battery is used to include so-called non-aqueous electrolyte lithium-ion secondary batteries and all-solid-state lithium-ion secondary batteries.

[0056] 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 of the present invention can be used as an electrode material. The active material of the present invention is usually used in the form of an electrode sheet for the lithium battery 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.

[0057] <Negative Electrode> The negative electrode has a negative electrode layer on one or both sides of the negative electrode current collector, which contains a negative electrode active material (the active material of the present invention) and a binder. The negative electrode layer may further contain a conductive agent. 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 containing the negative electrode active material (the active material of the present invention), a conductive agent, and a binder is contained within the voids.

[0058] 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; and carbon nanotubes such as single-phase carbon nanotubes, multi-walled carbon nanotubes (multi-walled concentric cylindrical graphite layers) (non-fishbone shaped), cup-type carbon nanotubes (fishbone shaped), segmented carbon nanofibers (non-fishbone structure), and platelet-type carbon nanofibers (playing card shaped).

[0059] The amount of conductive agent to be added varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, so optimization should be performed. Preferably, it is 0.1% to 10% by mass in the negative electrode layer, and more preferably 0.5% to 5% by mass. Below 0.1% by mass, the conductivity of the negative electrode layer cannot be ensured, and above 10% by mass, the active material ratio decreases, resulting in insufficient discharge capacity of the energy storage device per unit mass and unit volume of the negative electrode layer, making it unsuitable for high capacity applications. The conductive agent may be added during electrode fabrication, or the conductive agent may be coated onto the active material itself. This is because coating with a conductive agent such as carbon fiber can further improve the conductivity of the negative electrode layer.

[0060] 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).

[0061] The amount of binder added varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, and should be optimized, but is preferably 0.2% to 15% by mass in the negative electrode layer. From the viewpoint of improving binding properties and ensuring the strength of the negative electrode layer, it is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. From the viewpoint of not reducing the active material ratio and decreasing the discharge capacity of the energy storage device per unit mass and unit volume of the negative electrode layer, it is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0062] Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, calcined carbon, or materials on which carbon, nickel, titanium, or silver are coated. 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.

[0063] The negative electrode can be manufactured by uniformly mixing a negative electrode active material (including the active material of the present invention), a conductive agent, and a binder in a solvent to form a paint, which is then applied to the negative electrode current collector, dried, and compressed. In the case of a 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 (the active material of the present invention), a conductive agent, and a binder in a solvent, or by immersing the current collector having voids in the paint, diffusing it into the voids, and then drying and compressing it.

[0064] As a method for uniformly mixing the negative electrode active material (the active material 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 stages according to the solid content concentration, and these devices may be used accordingly.

[0065] To uniformly mix the negative electrode active material (the active material 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 such as a planetary mixer or 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 device, and a concentration of 80% by mass or less is even preferable.

[0066] 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.

[0067] 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.

[0068] When using an organic solvent, it is preferable to dissolve the binder in the organic solvent beforehand.

[0069] <Positive Electrode> The positive electrode has a positive electrode layer on one or both sides of the positive electrode current collector, which contains a positive electrode active material, a conductive agent, and a binder.

[0070] 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. An example of such a composite metal oxide is LiCoO ２ LiMn ２ O ４ LiNiO ２ LiCo １－ｘ Ni ｘ O ２ (0.01<x<1), LiCo １／３ Ni １／３ Mn １／３ O ２ LiNi １／２ Mn ３／２ O ４ Examples include the above, 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, or some of the oxygen may be substituted with S or F, or a compound containing these other elements may be coated. Examples of lithium-containing olivine-type phosphates include LiFePO ４ LiCoPO ４ LiNiPO ４ LiMnPO ４ LiFe １－ｘ MxPO ４ Examples include: (M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, and x is 0 ≤ x ≤ 0.5.)

[0071] Examples of conductive agents and binders for the positive electrode include 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.

[0072] <Non-aqueous 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.

[0073] As the electrolyte salt, one that dissolves in a non-aqueous electrolyte is used, for example, LiPF ６ LiBF ４ LiPO ２ F ２ , LiN (SO ２ F) ２ LiClO ４ Inorganic lithium salts such as LiN(SO4) ２ CF ３ ) ２ , LiN (SO ２ C ２ F ５ ) ２ LiCF ３ SO ３ , LiC (SO ２ CF ３ ) ３ LiPF ４ (CF ３ ) ２ LiPF ３ (C ２ F ５ ) ３ LiPF ３ (CF ３ ) ３ LiPF ３ (iso-C ３ F ７ ) ３ LiPF ５ (iso-C ３ F ７ Lithium salts containing chain-like alkyl fluorides such as (CF ２ ) ２ (SO ２ ) ２ NLi, (CF ２ ) ３ (SO ２ ) ２Examples include lithium salts containing cyclic alkylene fluoride chains such as NLi, and lithium salts using oxalate complexes such as lithium bis[oxalate-O,O']borate and lithium difluoro[oxalate-O,O']borate as anions. Among these, LiPF is a particularly preferred electrolyte salt. ６ LiBF ４ LiPO ２ F ２ , and LiN(SO ２ F) ２ The most preferred electrolyte salt is LiPF ６ These electrolyte salts can be used individually or in combination of two or more.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Furthermore, in particular, the concentration of the total electrolyte salt is 0.5 M to 2.0 M, and the electrolyte salt is at least LiPF ６ It includes, and furthermore, LiBF from 0.001M to 1M ４ LiPO ２ F ２ , and LiN(SO ２ F) ２ It is preferable to use a non-aqueous electrolyte containing at least one lithium salt selected from the following. LiPF ６ If the proportion of lithium salts other than the specified one in the non-aqueous solvent is 0.001 M or more, it is easier to improve the charge rate characteristics of the energy storage device and suppress gas generation during high-temperature operation. If it is 1.0 M or less, there is less concern that the improvement in the charge rate characteristics of the energy storage device and the suppression of gas generation during high-temperature operation will decrease, so this is preferable.

[0078] 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.

[0079] 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).

[0080] <Structure of Lithium Battery> The structure of the lithium battery 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 cylindrical batteries and prismatic batteries having a positive electrode, a negative electrode, and a roll-shaped separator.

[0081] 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.

[0082] <Negative Electrode Active Material Composition> The negative electrode active material composition of the present invention is a negative electrode active material composition comprising the composite powder of the present invention and an inorganic solid electrolyte having conductivity of metal ions 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 composite 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, and preferably 60% 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 composite powder and the solid electrolyte. By using the composite powder used in the negative electrode active material composition of the present invention, satisfactory contact between the composite powder and the solid electrolyte can be obtained even when the inorganic solid electrolyte content is low. The composition may also contain one or more substances other than the composite powder and inorganic solid electrolyte of the present invention. Other materials used 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, as lithium-containing metal oxides, Li ４ Ti ５ O １２ Lithium titanate, which has as its main component, is one example.

[0083] <Periodic Table> The periodic table used herein refers to the long-period type periodic table of elements as defined by IUPAC (International Union of Pure and Applied Chemistry).

[0084] <Solid Electrolytes> 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 of 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, (B) oxide inorganic solid electrolytes, and (C) chloride inorganic solid electrolytes. In particular, sulfide inorganic solid electrolytes are preferred because they have high ionic conductivity and can form dense molded bodies with few grain boundaries by pressurization at room temperature alone.

[0085] 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. Li ２ S-P ２ S ５ Li ２ S-P ２ S ５ - Al ２ S ３ Li ２ S-GeS ２ Li ２ S-Ga ２ S ３ Li ２ S-GeS ２ -Ga ２ S ３ Li ２ S-GeS ２ -P ２ S ５ Li ２ S-GeS ２ -Sb ２ S ５ Li ２ S-GeS ２ - Al ２ S ３ Li ２ S-SiS２ Li ２ S-Al ２ S ３ Li ２ S-SiS ２ - Al ２ S ３ Li ２ S-SiS ２ -P ２ S ５ Li １０ GeP ２ S １２ .

[0086] Among the above combinations, Li ２ S-P ２ S ５ LPS glass and LPS glass ceramics manufactured by combining the above are preferred. In addition, Li is preferred as an inorganic solid electrolyte other than the above. ６ PS ５ Cl and Li ６ PS ５ Algerodite-type solid electrolytes such as Br are also preferred.

[0087] 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.

[0088] As an oxide inorganic solid electrolyte, for example, Li having a LISICON (Lithium super ionic conductor) type crystal structure. ３．５ Zn ０．２５ GeO ４ La having a perovskite-type crystal structure ０．５５ Li ０．３５ TiO ３ LiTi having a NASICON (Natrium superionic conductor) type crystal structure ２ P ３ O １２ Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ), Lithium phosphate (Li ３ PO ４), LiPON, Li, which replaces some of the oxygen in lithium phosphate with nitrogen. ３ BO ３ -Li ２ SO ４ Li ２ O-B ２ O ３ -P ２ O ５ Li ２ O-SiO ２ , and Li ６ BaLa ２ Ta ２ O １２ These are some examples of preferred materials.

[0089] As a chloride inorganic solid electrolyte, Li ３ ScCl ６ LiAlCl ４ , Ln １－Ｘ A Ｘ OCl １－Ｘ (In the formula, Ln represents any rare earth element, A represents an alkaline earth metal, and X is 0 < X ​​< 1) are examples of preferred elements.

[0090] 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.

[0091] 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.

[0092] (Liquid-based lithium-ion secondary battery) [Example 1] <Raw material preparation process> Nb ２ O ５ZnO was weighed in a molar ratio of 7:1 and mixed to obtain a mixed powder. This mixed powder was calcined at 1050°C for 12 hours to obtain a calcined powder sample. Powder X-ray diffraction measurements were performed on the obtained calcined powder sample under conditions of a sampling interval of 0.01° and a scan speed of 2° / min. No peaks originating from the starting materials were observed, confirming that the reaction proceeded completely. From the results of crystal structure analysis of the synthesized calcined powder sample and X-ray fluorescence analysis (XRF) using an X-ray fluorescence spectrometer (SII Technology Co., Ltd., product name "SPS5100"), it was confirmed that the synthesized calcined powder sample was the target transition metal composite oxide (ZnNb １４ O ３６ It was confirmed that it was a single-walled carbon nanotube (SWCNT, manufactured by OCSI Al, trade name "TUBALL", average diameter: 1.6 nm to 2.2 nm, length: 5 μm to 20 μm, specific surface area 250 m²). ２ / g to 300m ２ To 100 g of a calcined powder sample obtained by crushing ( / g), 0.1% by mass (0.1 g) was added, and then 0.15% by mass of carboxycellulose (CMC) was added as a thickener to prepare a mixed slurry. This mixed slurry was mixed in a paint shaker for 3 hours, and then sprayed and dried at a temperature of 100°C using a spray dryer to produce a composite powder consisting of carbon nanotube-containing transition metal composite oxide according to Example 1.

[0093] [Examples 2 and 3] The composite powders according to Examples 2 and 3 were produced in the same manner as in Example 1, except that the mixing ratio and type of carbon nanotubes were changed in the raw material preparation process as shown in Table 1. In Example 3, multiwalled carbon nanotubes (MWCNT, manufactured by C-Nano, average diameter: 5 nm to 15 nm, length: several μm to 20 μm, specific surface area: 150 m²) were used as carbon nanotubes. ２ / g to 300m ２ ( / g) was used.

[0094] [Comparative Example 1] A transition metal composite oxide powder according to Comparative Example 1 was produced in the same manner as in Example 1, except that carbon nanotubes were not mixed in.

[0095] [Measurement of Powder Properties] Various properties of the transition metal composite oxide powders of each example and comparative example were measured as follows.

[0096] <Measurement of specific surface area> The specific surface area (m²) of the composite powder of each example and the transition metal composite oxide powder of the comparative example. ２ The specific surface area ( / g) was measured using a fully automated BET specific surface area analyzer (Mountec Co., Ltd., product name "Macsorb HM model-1208"), with nitrogen gas used as the adsorption gas. 0.5 g of the 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 using the BET single-point method.

[0097] <Calculation of D10, D50, and D90: Dry Laser Diffraction and Scattering Method> The D50 of the primary particles of the composite powders of each example and the transition metal composite oxide powder of the comparative example was calculated from the particle size distribution curves measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.) for the composite powders of each example and the transition metal composite oxide powder of the comparative example. 50 mg of the sample was placed in a container containing 50 ml of deionized water as the measurement solvent, and the measurement solvent was added until the transmittance of the slurry was within the appropriate range (the range indicated by the green bar on the device), and the particle size distribution measurement was performed. From the obtained particle size distribution curve, the D10, D50, D90, and log of the primary particles of the transition metal composite oxide powder were calculated. １０ (D90)-log １０ (D50) was calculated. In each example, measurements were performed on the composite powder, but since the influence of carbon nanotubes was almost negligible, the measurement results can be determined to be D10, D50, and D90 of the primary particles of the transition metal composite oxide powder.

[0098] [Evaluation of Battery Characteristics] Coin-type batteries were fabricated using the composite powders of each example and the transition metal composite oxide powder of the comparative example, and their battery characteristics were evaluated. The evaluation results are shown in Tables 1 and 2.

[0099] <Preparation of Negative Electrode Sheets> Negative electrode sheets were prepared in a room controlled at 25°C and a dew point of -20°C or lower as follows. The composite powders of each example and the transition metal composite oxide powder of the comparative example were removed from aluminum laminate bags in a room controlled at 25°C and a dew point of -20°C or lower. The removed composite powders of each example and the transition metal composite oxide powder of the comparative example were mixed at a ratio of 85% by mass as the active material, 10% by mass of acetylene black as the conductive agent, and 5% by mass of polyvinylidene fluoride as the binder to prepare a coating. The obtained coating was applied to aluminum foil and dried to prepare a single-sided negative electrode sheet for use in the coin cell described later.

[0100] <Preparation of Electrolyte> The electrolyte used for the battery for characterization was prepared as follows: A non-aqueous solvent of ethylene carbonate (EC) : dimethyl carbonate (DMC) = 1:2 (volume ratio) was prepared in an argon glove box controlled at a temperature of 25°C and a dew point of -70°C or lower, and LiPF was added as the electrolyte salt. ６ The electrolyte for coin batteries, described later, was prepared by dissolving the compound to a concentration of 1 M.

[0101] <Manufacturing of coin cell batteries> The negative electrode single-sided sheet manufactured using the method described above is punched out into a circle with a diameter of 14 mm, at 2 t / cm 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 (molded into a circle 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.

[0102] <Initial Battery Characteristics: Initial Discharge Capacity> In a constant temperature bath at 25°C, a coin-type battery prepared using the method described in <Fabrication of Coin Cells> above was charged to the evaluation electrode in the direction in which Li is absorbed, at a discharge rate of 0.2 mA / cm². ２ The device is charged to 1V at a current density, 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 A constant current discharge was performed, discharging to 3V at a current density. The initial discharge capacity (mAh / g) was determined by dividing the obtained discharge capacity (mAh) by the mass of the transition metal composite oxide. In addition, the ratio of discharge capacity to charge capacity at this time was determined and defined as the initial efficiency.

[0103] <Measurement of 5C Rate Charge / Discharge Rate> The device was charged to 1V with a current equivalent to the initial discharge capacity of 5C, and then a constant current / constant voltage charge was performed at 1V until the charging current density reached 0.05C. After that, a constant current discharge was performed, discharging to 3V with a current of 5C. The 5C rate charge rate (%) was calculated by dividing the capacity obtained from the 5C constant current charge by the initial discharge capacity, and the 5C rate discharge rate (%) was calculated by dividing the capacity obtained from the 5C constant current discharge by the initial discharge capacity. The results are shown in Table 1. If the 5C rate characteristics of the transition metal composite oxide are high, an improvement in the discharge 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 when 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, and 0.1C refers to the current value that can completely discharge (or fully charge) the theoretical capacity in 1 / 0.1 hour.

[0104] <Capacity Retention Rate After 100 Cycles> Next, the coin cell was charged in a constant temperature bath at 25°C with a constant current and voltage of 0.5C to a cutoff voltage of 1.15V. Then, it was charged again with constant current and constant voltage until the charging current reached a current density of 0.05C at 1V. After that, it was discharged to 3V with a current of 0.05C. This constituted one cycle, and this was repeated until 100 cycles were reached. Furthermore, the discharge capacity after the cycles was determined in the same manner as the initial discharge capacity measurement. The capacity retention rate (%) after 100 cycles was calculated by dividing the obtained capacity by the initial discharge capacity. The results are shown in Table 1.

[0105]

[0106] <Evaluation Results> The electrodes using the composite powders of Examples 1 to 3, which are composites of a transition metal composite oxide containing zinc and niobium with carbon nanotubes, were found to have superior rate characteristics and cycle characteristics compared to Comparative Example 1, which is an electrode using a transition metal composite oxide powder that is not composited with carbon nanotubes.

[0107] The powder obtained by this invention, which is a composite of a transition metal composite oxide and carbon nanotubes, exhibits excellent rate characteristics and excellent cycle characteristics, making it useful as an electrode active material for lithium-ion batteries. Energy storage devices using this composite powder as an electrode active material are useful as secondary batteries for driving or backing up various devices such as automobiles and electronic devices, and for storing nighttime electricity in homes and offices. By providing society with electrode materials for lithium-ion batteries, such as non-aqueous electrolyte secondary batteries, we can contribute to achieving three of the 17 Sustainable Development Goals (SDGs) established by the United Nations: Goal 12 (Ensure sustainable consumption and production patterns), Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable and modern energy for all), and Goal 11 (Make cities and human settlements inclusive, safe, resilient and sustainable).

Claims

1. A composite powder containing a transition metal composite oxide containing at least zinc and niobium, and carbon nanotubes.

2. The composite powder according to claim 1, characterized in that the carbon nanotube content in the composite powder is 0.001 to 2 parts by mass per 100 parts by mass of the transition metal composite oxide.

3. The composite powder according to claim 1, characterized in that the molar ratio of zinc to niobium Nb / Zn in the transition metal composite oxide is 8 or more and 40 or less.

4. The composite powder according to claim 1, characterized in that the composite powder contains secondary particles composed of primary particles of the transition metal composite oxide and carbon nanotubes, and the average particle diameter D50 of the primary particles of the transition metal composite oxide is 0.2 μm or more and 2.5 μm or less.

5. The specific surface area of ​​the composite powder is 1.2 m². ２ / g or more 10m ２ The composite powder according to claim 1, characterized in that it is less than or equal to / g.

6. The aforementioned transition metal composite oxide is ZnNb ８ O ２１ , Zn ２ Nb ３４ O ８７ , ZnNb ２０ O ５１ , ZnNb ４０ O １０１ , or any one of the following general formulas (II) to (VII), the composite powder according to Claim 1. A a Zn １－ｘ M ＩＩＩ １．５ｘ＋ｖ Nb １４－０．５ｘ＋ｖ O ３６±ｚ (II) A a Zn １－ｙ M ＩＶ ３ｙ＋ｗ Nb １４－２ｙ＋ｗ O ３６±ｚ (III) A a Zn １－ｐ M ＩＩ ｐ＋ｖ Nb １４－ｑ M Ｖ ｑ＋ｗ O ３６±ｚ (IV) A a ZnM ＩＩ ０．２５ｒ＋ｗ Nb １４－ｒ M ＶＩ ０．７５ｒ＋ｗ O ３６±ｚ (V) A a ZnM ＩＩＩ ０．３３ｓ＋ｗ Nb １４－ｓ M ＶＩ ０．６７ｓ＋ｗ O ３６±ｚ (VI) A a ZnM ＩＶ ０．５ｔ＋ｗ Nb １４－ｔ M ＶＩ ０．５ｔ＋ｗ O ３６±ｚ (VII) (In the formula, A is at least one element selected from Li and Na, and M ＩＩ each independently is at least one divalent metal element selected from Mg, Ca, and Cu, and M ＩＩＩ Each is independently at least one trivalent element selected from Al, Ga, Fe, and Cr, and M ＩＶ Each is independently at least one tetravalent element selected from Ti, Zr, Ge, and Sn, and M Ｖ Each is independently at least one pentavalent metallic element selected from V and Ta, and M ＶＩ Each of the elements is independently at least one hexavalent metallic element selected from Mo and W, and a, v, w, x, y, p, q, r, s, t, and z are numerical values ​​such that 0 ≤ a ≤ 6, -0.05 ≤ v ≤ 0.05, -0.05 ≤ w ≤ 0.05, 0 < x < 0.1, 0 < y < 0.1, 0 ≤ p < 0.1, 0 ≤ q < 6, 0 < r < 6, 0 < s < 6, 0 < t < 6, and 0 ≤ z ≤ 1.

7. An electrode for an energy storage device, characterized by containing the composite powder described in any one of claims 1 to 6 as an active material.

8. A negative electrode active material composition for an energy storage device, characterized by comprising a composite powder according to any one of claims 1 to 6 and an inorganic solid electrolyte.

9. An energy storage device characterized by including the electrode described in claim 7.

10. An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, characterized in that the negative electrode layer is a layer containing the negative electrode active material composition described in claim 8.

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