Carbon nanotube-containing titanium-niobium composite oxide powder, and electrode and electricity storage device using the same

Abstract

To provide a carbon nanotube-containing titanium-niobium composite oxide powder which is used as an electrode material of a nonaqueous electrolyte power storage device, can achieve high volume energy density, rate characteristics, and low-temperature characteristics in a liquid-based nonaqueous electrolyte power storage device, and can improve battery characteristics in an all-solid-state battery, and to provide an electrode using the same, and a nonaqueous electrolyte power storage device.SOLUTION: The composite powder has a pH value of 5.5 or more and 7.5 or less, the pH value being measured by a pH meter after the composite powder and 5g are put into distilled and 5g and shaken for 5 minutes, and has a peak intensity ratio of two specific peaks of 10 or more in a spectrum obtained by micro-Raman spectroscopy. AaTi2-xM1xNb14 - yM2yO39 ± z (I) wherein A is at least one element selected from the group consisting of Li and Na, M1 is at least one metallic element selected from the group consisting of Al, Mg, Zr, Si, Ge and Sn, M2 is at least one metallic element selected from the group consisting of V and Ta, 0 ≤ a ≤ 6, 0 ≤ x <2, 0 ≤ y <14, and 0 ≤ z ≤ 1. (I) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a titanium-niobium composite oxide powder containing carbon nanotubes (carbon fibers) suitable as an electrode material for non-aqueous electrolyte electricity storage devices, an electrode using the same, and a non-aqueous electrolyte electricity storage device. [Background technology]

[0002] Electrical storage devices for electric vehicles require high volumetric energy density from the perspective of utilizing the vehicle's space and high operating performance at low temperatures in anticipation of use in cold regions, and lithium-ion batteries in particular are becoming widely used as power sources for electric vehicles. Various materials have been researched as electrode materials for lithium-ion batteries, and the theoretical value per unit lattice is 1,680 mAh / cm. 3 There is a trend toward using titanium-niobium composite oxides, primarily niobium titanate, which have a high volumetric energy density, as anode materials. Furthermore, because currently commercially available lithium-ion batteries use electrolytes containing flammable organic solvents, attention is being paid to all-solid-state secondary batteries, which use inorganic solid electrolytes instead of organic electrolytes, thereby enabling improvements in safety and reliability.

[0003] Patent Document 1 discloses an active material comprising carbon fibers that coat at least a portion of the surface of niobium titanium composite oxide particles, contain one or more metal elements selected from the group consisting of Fe, Co, and Ni, and have an average fiber diameter in the range of 5 nm to 100 nm. According to Patent Document 1, by uniformly dispersing and coating the surfaces of niobium titanium composite oxide particles, the electrode resistance is reduced, and the effect of the electron conduction network due to the carbon fiber coating can be maintained even when volume expansion and contraction associated with the absorption and release of lithium ions is repeated, resulting in significant improvements in the rate performance and cycle life of the battery.

[0004] Patent Document 2 discloses an active material for a battery, which includes particles of a niobium titanium composite oxide and a phase containing a carbon material formed on at least a part of the surface of the particles of the niobium titanium composite oxide. The carbon material shows a G band observed at 1530 to 1630 cm -1 in a Raman chart obtained by Raman spectroscopy, and a D band observed at 1280 to 380 cm -1 in the Raman chart. A battery active material is disclosed in which the ratio IG / ID of the peak intensity IG of the G band to the peak intensity ID of the D band is 0.8 or more and 1.2 or less. According to Patent Document 2, a carbon material in which the ratio IG / ID of the peak intensity IG of the G band to the peak intensity ID of the D band in the Raman chart is 0.8 or more and 1.2 or less has good crystallinity of graphite and excellent conductivity, and thus contributes to the improvement of the electron conductivity of the niobium titanium composite oxide particles. As a result, an active material for a non-aqueous electrolyte battery excellent in rate characteristics and cycle characteristics, and a non-aqueous electrolyte battery using the active material are obtained.

[0005] Patent Document 3 discloses an active material composite including particles of a niobium titanium composite oxide and a carbon-containing layer covering at least a part of the surface of the particles of the niobium titanium composite oxide, and the intensity ratio of the peak intensity ID of the D band appearing at 1280 to 1400 cm -1 in the Raman spectrum by Raman spectroscopy to the peak intensity IG of the G band appearing at 1530 to 1650 cm -1 satisfies 1.2 < IG / ID ≤ 5. According to Patent Document 3, when this active material composite is used for an electrode, the niobium titanium composite oxide is densely filled in the electrode. In addition, since the carbon-containing layer has high crystallinity, it is said that an electrode with a high active material filling density and excellent conductivity can be realized.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] However, in Patent Document 1, niobium-titanium composite oxide particles, at least a portion of whose surface is coated with a specific carbon fiber, are used as a negative electrode active material in an energy storage device. Only the initial capacity and 10C high-rate characteristics of the device are examined; no studies are made on the improvement of volumetric energy density or battery characteristics at low temperatures. Furthermore, there is no mention of performance when applied to all-solid-state secondary batteries. As will be described in detail later, when compounding with niobium-titanium composite oxide, unless the content and type of carbon fiber are appropriately controlled, there is a problem that the electrode density, which leads to an improvement in volumetric energy density, decreases, and the pH value also changes, making it impossible to improve low-temperature characteristics. Furthermore, Patent Document 1 does not mention the pH value or Raman peak intensity ratio.

[0008] In Patent Documents 2 and 3, active materials in which a carbon material with a Raman peak intensity ratio controlled within a specific range is formed on at least a portion of the particle surface have been investigated for their initial charge / discharge efficiency and high-rate battery characteristics, but no findings have been presented regarding changes in the pH value of the active material or battery characteristics at low temperatures. In fact, even when using carbon materials with only the Raman peak intensity ratio controlled within a specific range, no tendency has been observed to improve low-temperature characteristics while maintaining the initial battery capacity and 10C high-rate charging characteristics. In addition, Patent Documents 2 and 3 do not contain any description of performance when applied to all-solid-state secondary batteries.

[0009] For the reasons described above, in the nonaqueous electrolyte electricity storage devices using the negative electrode active materials of Patent Documents 1, 2, and 3 in the electrodes, it was not possible to improve low-temperature characteristics while maintaining high volumetric energy density and high-rate input / output characteristics, and the performance of the all-solid-state battery was not satisfactory.

[0010] Therefore, an object of the present invention is to provide a carbon nanotube-containing titanium-niobium composite oxide powder that can be used as an electrode material for a nonaqueous electrolyte electricity storage device, that can achieve both high volumetric energy density, rate characteristics, and low-temperature characteristics in a liquid-based nonaqueous electrolyte electricity storage device, and that can improve the battery characteristics of an all-solid-state battery, as well as an electrode and a nonaqueous electrolyte electricity storage device using the same. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the present inventors have investigated various mixing conditions and synthesis conditions for a composite composed of titanium-niobium oxide powder and carbon nanotubes. As a result, by mixing and compositing specific components within a specific range, they have been able to obtain a carbon nanotube-containing titanium-niobium composite oxide powder having a pH value of 5.5 to 7.5 and a controlled intensity ratio of two specific peaks in a spectrum obtained by micro-Raman spectroscopy of 10 or more. Furthermore, according to the present invention, it has been discovered that the use of carbon nanotube-containing titanium-niobium composite oxide powder as an electrode material can achieve high volumetric energy density and charge / discharge rate characteristics in nonaqueous electrolyte electricity storage devices, as well as excellent low-temperature characteristics, and further improve the battery characteristics of all-solid-state batteries, leading to the completion of the present invention. Such effects are not described or suggested in Patent Documents 1, 2, or 3. Specifically, the present invention relates to the following:

[0012] [1] A composite powder for an electrode of a nonaqueous electrolyte electricity storage device, which is composed of a titanium-niobium composite oxide powder that satisfies the following formula (I) and carbon nanotubes, characterized in that 0.5 g of the composite powder is added to 4.5 g of distilled water, the mixture is shaken for 5 minutes, and then the pH value measured with a pH meter is 5.5 or more and 7.5 or less, and in a spectrum obtained by micro-Raman spectroscopy, the intensity ratio of two peaks as represented by the following formula (II) is 10 or more. A a Ti 2-x M 1 x Nb 14-y M 2 yO 39±z (I) wherein A is at least one element selected from the group consisting of Li and Na; 1 is at least one metal element selected from the group consisting of Al, Mg, Zr, Si, Ge, and Sn, and M 2 is at least one metal element selected from the group consisting of V and Ta, and 0≦a≦6, 0≦x<2, 0≦y<14, and 0≦z≦1. IG / ID ≧ 10 (II) IG: 1570~1610cm -1 Peak intensity seen in ID: 1330~1370cm -1 Peak intensity seen in [2] The composite powder for an electrode of a non-aqueous electrolyte electricity storage device according to [1], wherein the niobium-containing oxide composite powder contains secondary particles composed of primary particles of a titanium-niobium composite oxide powder and carbon nanotubes, and the average particle diameter D50 of the secondary particles is 9 μm or more. [3] The composite powder for an electrode according to [1] or [2], characterized in that the composite powder contains secondary particles composed of primary particles of titanium-niobium composite oxide powder and carbon nanotubes, and the secondary particle crushing strength of the titanium-niobium composite oxide powder is 1 MPa or more. [4] The composite powder for an electrode of a nonaqueous electrolyte electricity storage device according to any one of [1] to [3], characterized in that the composite powder has a total pore volume measured by a nitrogen gas adsorption method of 2.5 mL / g to 3.3 mL / g. [5] An electrode for a non-aqueous electrolyte electricity storage device, comprising the composite powder according to any one of [1] to [4] as an active material. [6] A negative electrode active material composition for a non-aqueous electrolyte electricity storage device, comprising the composite powder according to any one of [1] to [4] and an inorganic solid electrolyte. [7] A non-aqueous electrolyte electricity storage device comprising the electrode according to [5]. [8] An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, wherein the negative electrode layer is a layer containing the negative electrode active material composition according to [6]. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a carbon nanotube-containing titanium-niobium composite oxide powder, an electrode for an electricity storage device using the same, and a nonaqueous electrolyte electricity storage device, which can achieve high volumetric energy density, rate characteristics, and low-temperature characteristics in a liquid-based nonaqueous electrolyte electricity storage device and further have excellent charge / discharge rate characteristics even in an all-solid-state battery. Note that the nonaqueous electrolyte may be any electrolyte other than an aqueous electrolyte, and is not particularly limited, but examples thereof include nonaqueous electrolytes such as organic electrolytes and solid electrolytes. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Electrode composite powder for non-aqueous electrolyte electricity storage device of the present invention] The composite powder for an electrode of a non-aqueous electrolyte electricity storage device of the present invention is a powder of a compound represented by general formula (I): A a Ti 2-x M 1 x Nb 14-y M 2 y O 39±z wherein A is at least one element selected from the group consisting of Li and Na; 1 is at least one metal element selected from the group consisting of Al, Mg, Zr, Si, Ge, and Sn, and M 2 is at least one metal element selected from the group consisting of V and Ta, and 0≦a≦6, 0≦x<2, 0≦y<14, 0≦z≦1.], and carbon nanotubes, and the composite powder is suitably used for electrodes of non-aqueous electrolyte electricity storage devices.

[0015] Specific examples of titanium-niobium composite oxide powder include Ti2Nb, a titanium-niobium composite oxide that can absorb and release Li ions and Na ions.14 O 39 , etc. Titanium-niobium composite oxides may contain a titanium oxide phase (e.g., rutile-type TiO2, TiO, etc.) or a niobium oxide phase (e.g., Nb2O5, NbO) derived from the synthesis raw materials. In the case of titanium-niobium composite oxides, 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 14, more preferably in the range of 1.8 to 7.0. Within this range, the electronic conductivity of the composite oxide is improved, resulting in excellent rate characteristics. In addition, M in the general formula 1 is selected from the group consisting of Al, Mg, Zr, Si, Ge, and Sn, and M 2 is at least one element selected from the group consisting of V and Ta, and titanium-niobium composite oxides substituted with these elements have improved electronic conductivity and excellent rate characteristics. Although it is not clear, it is presumed that by substituting an element with a different valence from Nb or Ti, electronic defects are formed in the crystal structure, improving electronic conductivity.

[0016] General formula (I):A a Ti 2-x M 1 x Nb 14-y M 2 y O 39±z In the formula (I), a is 0≦a≦6, preferably 0≦a≦2, more preferably 0≦a≦0.5, and even more preferably a=0. x is 0≦x<2, preferably 0≦x≦1, more preferably 0≦x≦0.5, and even more preferably x=0. y is 0≦x<14, preferably 0≦y≦3, more preferably 0≦y≦1, and even more preferably y=0. z is 0≦z≦1, preferably 0≦z≦0.5, more preferably 0≦z≦0.2, and even more preferably z=0.

[0017] The composite powder of the present invention is composed of titanium-niobium composite oxide powder and carbon nanotubes. Carbon nanotubes are a type of fibrous carbon and may be either single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs), or these may be used in combination. The carbon nanotubes are not particularly limited, and those obtained by catalytic pyrolysis, arc discharge, laser evaporation, and CVD methods such as the HiPco method and the CoMoCAT method can be used without limitation. Commercially available single-walled carbon nanotubes and multi-walled carbon nanotubes can also be used. It is preferable to use at least single-walled carbon nanotubes (SWCNTs) as the carbon nanotubes, as this can further improve the volumetric energy density, rate characteristics, and low-temperature characteristics of liquid-based nonaqueous electrolyte electricity storage devices.

[0018] In the composite powder of the present invention, the content ratio of the titanium-niobium composite oxide powder to the carbon nanotubes is not particularly limited, but the content of the carbon nanotubes is preferably 0.001 to 2.0 parts by mass, more preferably 0.01 to 1.8 parts by mass, and even more preferably 0.08 to 1.2 parts by mass, per 100 parts by mass of the titanium-niobium composite oxide powder. The carbon nanotube content can be calculated using various measurement methods, one example being simultaneous differential thermal analysis (TG-DTA), in which weight and temperature changes are continuously measured while a sample is heated at a constant rate. The physical properties of the carbon nanotubes are not particularly limited, but from the perspectives of improving conductivity and dispersibility (preventing aggregation) during electrode preparation, the average diameter should be 2 to 25 nm, the length should be 5 to 500 μm, and the specific surface area should be 50 to 600 m. 2 / g is preferred.

[0019] The composite powder of the present invention is characterized by a pH value of 5.5 to 7.5 measured using a pH meter after adding 0.5 g of the composite powder to 4.5 g of distilled water and shaking for 5 minutes. The composite powder is obtained by selecting the raw materials used to obtain the titanium-niobium composite oxide powder, adjusting the calcination temperature during synthesis, crushing conditions, and post-crushing heat treatment temperature within specific ranges, and adjusting the amount of carbon nanotubes added and the type of thickener used when mixing the titanium-niobium composite oxide powder with the carbon nanotubes. This allows the acid-base state of the composite powder surface to be controlled between neutral (weakly basic, very close to neutral) and weakly acidic, thereby suppressing reaction with non-aqueous electrolytes (non-aqueous electrolytes or solid electrolytes) and reducing the generation of decomposition products that cause interfacial resistance. In particular, the researchers found that specific pH measurement conditions are necessary to quantitatively measure the reactivity of pores present on the surface of the composite powder with non-aqueous electrolytes.

[0020] The upper limit of the pH value of the composite powder of the present invention is 7.5 or less, preferably 7 or less, and more preferably 6.5 or less. The lower limit of the pH value is 5.5 or more, and preferably 6.0 or more. As described above, by controlling the acid-base state on the surface of the composite powder, the reaction with the non-aqueous electrolyte (non-aqueous electrolytic solution or solid electrolyte) can be suppressed, and as a result, the volumetric energy density, rate characteristics, and low-temperature characteristics can be achieved in a liquid-based non-aqueous electrolyte battery, and further the charge / discharge rate characteristics of an all-solid-state battery can be improved.

[0021] The composite powder of the present invention is characterized in that it satisfies the following formula (II) in a spectrum obtained by micro-Raman spectroscopy. IG / ID ≧ 10 (II) IG: 1570~1610cm -1 Peak intensity seen in ID: 1330~1370cm -1 Peak intensity seen in Preferably, IG / ID ≧15, more preferably IG / ID ≧20. The upper limit is IG / ID ≦60. IG is a value between 1570 and 1610 cm in a Raman spectrum measured by microscopic Raman spectroscopy.-1 The G band is a peak derived from the graphite structure and indicates high electrical conductivity. The ID is the peak intensity of the G band that appears at 1330-1370 cm in the Raman spectrum obtained by micro-Raman spectroscopy. -1 The D band is a peak derived from a defect structure or metastable form of carbon, and is the peak intensity of the D band that appears in sp 3 It exhibits high intensity due to hybrid orbitals. By controlling the peak intensity ratio between these two, the electronic conductivity of the composite powder can be adjusted, but if IG / ID<10, the volumetric energy density, rate characteristics, and low-temperature characteristics will all be poor. Details of the microscopic Raman spectroscopy measurement method will be explained in the examples below.

[0022] [Secondary particles constituting the composite powder of the present invention] The composite powder of the present invention may contain secondary particles composed of primary particles of titanium-niobium composite oxide powder and carbon nanotubes. The secondary particles referred to here may be any secondary particle with an approximately spherical shape, including particles with partial irregularities and particles with shapes similar to spheres, such as ellipsoids. While there are no particular limitations on the method for forming the secondary particles, spray drying of a mixed slurry composed of primary particles of titanium-niobium composite oxide powder and carbon nanotubes is preferred to prevent excessive localization of carbon nanotubes on the surface of the secondary particles. A thickener may also be used to adjust the viscosity of the slurry, such as carboxyl cellulose (CMC) or 1,2-dimethylimidazole (IMD).

[0023] [D50 of secondary particles constituting the composite powder of the present invention] When the composite powder of the present invention is a secondary particle, the D50 of the secondary particle is an index of the volume median particle size. It means the particle size at which the cumulative volume frequency calculated from the volume fraction determined by laser diffraction / scattering particle size distribution measurement is 50% when calculated from the smallest particle size. From the viewpoint of improving electrode density, the D50 of the secondary particle is preferably 5 μm or more as the lower limit, more preferably 9 μm or more, and is preferably 20 μm or less as the upper limit, more preferably 18 μm or less, and even more preferably 14 μm or less.

[0024] [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 titanium-niobium composite oxide powder and carbon nanotubes, the secondary particle crushing strength of the secondary particles is preferably 1 MPa or more, more preferably 1.5 MPa or more, and even more preferably 2.0 MPa or more, with the upper limit preferably being 5.0 MPa or less. Having a secondary particle crushing strength of 1 MPa or more prevents localization of the carbon nanotubes within the electrode mixture layer when it is formed, increasing the contact area between the titanium-niobium composite oxide and the carbon nanotubes, thereby further improving the rate characteristics. The secondary particle crushing strength is the compressive strength when the secondary particles are compressed by 10% of the measured particle diameter, and the measurement method is described in the Examples below.

[0025] The titanium-niobium composite oxide constituting the composite powder of the present invention preferably contains at least one element selected from tantalum (Ta), potassium (K), and iron (Fe), and the element content is preferably 2400 ppm or less per gram of the composite powder. These elements are contained as impurities in the raw materials used to synthesize the titanium-niobium composite oxide powder constituting the composite powder of the present invention, and are often contained in the niobium source in particular. Controlling the amount of impurities in the raw materials can improve the volumetric energy density and rate characteristics of liquid-type nonaqueous electrolyte batteries. From the viewpoint of ensuring volumetric energy density, the element content is preferably 2400 ppm or less, more preferably 1700 ppm or less, and even more preferably 1500 ppm or less. Furthermore, from the viewpoint of improving rate characteristics through improved electronic conductivity, the element content is preferably 10 ppm or more, more preferably 40 ppm or more. Methods for measuring the element content include inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence spectroscopy (XRF), and X-ray photoelectron spectroscopy (XPS).

[0026] The titanium-niobium composite oxide powder constituting the composite powder of the present invention has element M on the surface of the particle. 3 (including any one or more selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo)) may be present. Two or more of these elements may be contained. Element M 3 The presence of element M means that the titanium-niobium composite oxide powder constituting the composite powder of the present invention is found to contain element M in inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence spectroscopy (XRF), or X-ray photoelectron spectroscopy (XPS). 3 The lower limit of the amount detected by inductively coupled plasma atomic emission spectrometry is usually 0.001% by mass.

[0027] In addition, the titanium-niobium composite oxide powder constituting the composite powder of the present invention contains the element M 3 When the titanium-niobium composite oxide particles constituting the powder contain element M, the surface region of the particles is more likely to contain element M than the inner region of the particles. 3are localized and exist in large quantities. 3 is present on the surface of the titanium-niobium composite oxide particles, and more specifically, the element M is more abundant in the surface region than in the inner region of the titanium-niobium composite oxide particles. 3 As an example, in a cross-sectional analysis of the titanium-niobium composite oxide particles using a scanning transmission electron microscope, the element M is found to be present in a large amount in a so-called near-surface region extending from the surface of the titanium-niobium oxide particles to a depth of about 20 nm as measured by energy dispersive X-ray spectroscopy. 3 It is sufficient that the element M is contained in a large amount at a depth of 100 nm from the surface. 3 is preferably not detected. That is, when measured by energy dispersive X-ray spectroscopy, it means that the amount is below the detectable amount by the measurement. The lower limit of the detectable amount in energy dispersive X-ray spectroscopy measurement varies depending on the element and state being measured, but is typically 0.5 atm%. Other examples include surface analysis techniques such as X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). With regard to the coating amount, from the viewpoint of improving the initial capacity and rate characteristics of liquid-based nonaqueous electrolyte batteries and the rate characteristics of 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.

[0028] The titanium-niobium composite oxide powder constituting the composite powder of the present invention contains the above-mentioned element M 3 As a further hetero element other than element M, at least one element selected from the group consisting of F, B, Mo, W, and S may be contained. Among these, F or S is particularly preferred. The titanium-niobium composite oxide powder constituting the composite powder of the present invention contains such a hetero element in the form of element M. 3 By containing together with element M 3 This is presumably because the electron conductivity of the particle surface of the titanium-niobium composite oxide powder is improved compared to when the titanium-niobium composite oxide is contained alone.

[0029] The D50 of the primary particles of the titanium-niobium composite oxide powder constituting the composite powder of the present invention is an index of the volume median particle size. It refers to the particle size at which the cumulative volume frequency calculated from the volume fraction determined by laser diffraction / scattering particle size distribution measurement reaches 50% when calculated from the smallest particle size. From the viewpoint of improving electrode density, the lower limit of the D50 of the primary particles is preferably 0.6 μm or more, more preferably 0.7 μm or more, and even more preferably 0.8 μm or more. The upper limit is preferably 2.0 μm or less, more preferably 1.8 μm or less, and even more preferably 1.6 μm or less.

[0030] <Total pore volume> The total pore volume of the composite powder of the present invention determined by nitrogen gas adsorption is calculated from the amount of gas adsorbed up to a relative pressure P / P0 of 0.99, assuming that the pores of the composite powder are filled with liquid nitrogen (P: measured internal pressure of the sample cell, P0: saturated vapor pressure of nitrogen gas). More specifically, it is the sum of the pore volume of the mesopore region of approximately 10 to 3000 Å (= pore volume by the BJH method) and the pore volume of the micropore region of 10 Å or less (= pore volume by the HK method). The measurement method will be explained in the examples below.

[0031] The lower limit of the total pore volume of the composite powder of the present invention, as determined by the nitrogen gas adsorption method, is 2.0 mL / g or more, preferably 2.5 mL / g or more, and more preferably 2.7 mL / g or more. The upper limit of the total pore volume may be 3.5 mL / g or less, preferably 3.3 mL / g or less, and more preferably 3.0 mL / g or less. The above range is preferable from the viewpoint of improving electrode density and charge / discharge rate characteristics. Although this is merely speculation, it is believed that controlling the total pore volume within a certain range can balance improved contact between the composite powder and the non-aqueous electrolyte and suppressed reactivity. Methods for adjusting the total pore volume of the composite powder as determined by the nitrogen gas adsorption method include, for example, using a titanium compound having a specific D50 diameter as the raw material or adjusting the firing conditions. The total pore volume can be adjusted by appropriately combining these methods.

[0032] [Method of manufacturing titanium-niobium composite oxide powder] An example of a method for producing the titanium-niobium composite oxide powder that constitutes the composite powder of the present invention will be described below, divided into a raw material preparation step and a firing step. However, the method for producing the titanium-niobium composite oxide powder that constitutes the composite powder of the present invention is not limited to this.

[0033] <Raw material preparation process> First, the starting materials are mixed. In addition to oxides or salt compounds containing Ti or Nb, if an additional element is included, the starting materials are mixed in a stoichiometric ratio to obtain the target composition. The salt compounds used are preferably salt compounds that have a relatively low melting point and decompose to produce an oxide, such as hydroxides, carbonates, or nitrates. To reduce the primary particle size, it is preferable to use powders with an average primary particle size of 2 μm or less, preferably 0.5 μm or less, as the starting materials.

[0034] The method for mixing the raw materials is not particularly limited, and either wet mixing or dry mixing may be used. For example, a Henschel mixer, an ultrasonic disperser, a homomixer, a mortar, a ball mill, a centrifugal ball mill, a planetary ball mill, a vibrating ball mill, an attritor-type high-speed ball mill, a bead mill, a roll mill, etc. may be used.

[0035] <Firing process> Next, the mixture obtained above is fired. The firing is preferably carried out at a temperature range of 500 to 1200°C, more preferably 700 to 1150°C, and even more preferably 900 to 1150°C. By setting the firing temperature at 1150°C or less, general-purpose equipment can be used. When firing the mixture for a short period of time, it is preferable to prepare the mixed powder constituting the mixture before firing so that the D95 value in the particle size distribution curve measured with a laser diffraction / scattering particle size distribution analyzer is 5 μm or less. Here, D95 refers to the particle size at which the cumulative volume frequency calculated by volume fraction is 95% when calculated from the smallest particle size.

[0036] The firing method is not particularly limited as long as it can be performed under the above conditions. 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, when efficient firing is required in a short time, roller hearth firing furnaces, mesh belt firing furnaces, and rotary kiln firing furnaces are preferred.

[0037] <Crushing process> The calcined titanium-niobium composite oxide powder may be subjected to a crushing treatment to obtain the desired particle size. Methods for crushing the calcined product recovered from the calcined product recovery side include hammer mills, ball mills, jet mills, vibration mills, and bead mills, with bead mills being particularly preferred. When using a bead mill, any of the following methods can be used for crushing: wet-crushing circulation treatment, wet-crushing batch treatment, dry-crushing circulation treatment, and dry-crushing batch treatment. However, uniform crushing is preferred, and in this respect, wet-crushing circulation treatment is preferred. The circulation conditions can be determined taking into account the calcination temperature in the calcination step, and adjusting the circulation conditions can, for example, favorably control the particle size of the titanium-niobium composite oxide powder. For wet crushing, the calcined lithium titanate powder is introduced into water or an alcohol solvent and mixed in a slurry state. As the alcohol solvent, those with a boiling point of 100°C or less, such as methanol, ethanol, and isopropyl alcohol, are preferred because they are easy to remove. Moreover, from an industrial perspective, water is preferred as a solvent because of the ease of recovery and disposal.

[0038] <Surface treatment process> The titanium-niobium composite oxide obtained above may be subjected to a surface treatment. The titanium-niobium composite oxide of the present invention has a particle surface treated with an element M. 3 (M 3In the firing step, the element M may be present, which includes at least one element selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo), and when the material is used as a negative electrode material for a battery, a dense negative electrode layer can be formed and excellent charge rate characteristics can be imparted. 3 The titanium-niobium composite oxide powder of the present invention can be produced by adding a compound containing element M (hereinafter, sometimes referred to as a treating agent), but more preferably, the titanium-niobium composite oxide powder of the present invention can be produced by the following surface treatment step. In particular, by adopting the following surface treatment step, it is possible to appropriately and relatively simply coat the surface of the titanium-niobium composite oxide particles with element M. 3 can be a state in which

[0039] The titanium-niobium composite oxide powder as the substrate and the element M 3 There is no particular limitation on the method of mixing with the compound containing element M, and either wet mixing or dry mixing can be used. 3 It is preferable to uniformly disperse the compound containing the above-mentioned component (I) in the mixture, and in this respect, wet mixing is preferable.

[0040] element M 3 (M 3 The compound (treatment agent) containing one or more elements selected from the group consisting of aluminum (Al), magnesium (Mg), cerium (Ce), and molybdenum (Mo) is not particularly limited, but examples thereof include oxides, phosphates, hydroxides, sulfate compounds, nitrate compounds, fluorides, chlorides, organic compounds, and metal salt compounds such as ammonium salts and phosphates. 3When the element M is Al, examples of the aluminum oxide include aluminum oxide, aluminum phosphate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum fluoride, aluminum chloride, aluminum acetate, aluminum ammonium sulfate, and aluminum alkoxides, and among these, aluminum sulfate and its hydrates are preferred. 3 When M is Mg, examples of the element M include magnesium oxide, magnesium phosphate, magnesium hydroxide, magnesium sulfate, magnesium nitrate, magnesium fluoride, magnesium chloride, magnesium acetate, magnesium ammonium phosphate, and magnesium alkoxide, and among these, magnesium sulfate and its hydrate are preferred. 3 When the element M is Ce, examples of the element M include cerium oxide, cerium hydroxide, cerium fluoride, cerium sulfate, cerium nitrate, cerium carbonate, cerium acetate, cerium oxalate, cerium chloride, cerium boride, and cerium phosphate, and among these, cerium sulfate and its hydrates are preferred. 3 When is Mo, examples of the compound include molybdenum oxide, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum boride, molybdophosphoric acid, molybdenum disilicide, molybdenum chloride, molybdenum sulfide, molybdosilicic acid hydrate, sodium molybdenum oxide, molybdenum carbide, molybdenum acetate dimer, lithium molybdate, sodium molybdate, potassium molybdate, calcium molybdate, magnesium molybdate, manganese molybdate, and ammonium molybdate, and among these, molybdenum trioxide, molybdenum trioxide hydrate, molybdenum chloride, molybdenum sulfide, and lithium molybdate are preferred.

[0041] The element M 3 The amount of the compound containing the element M in the titanium-niobium composite oxide is 3Any amount may be used as long as it falls within the range of the present invention, but it is sufficient to add it in a proportion of 0.1% by mass or more relative to the titanium-niobium composite oxide powder substrate. It is also preferable to add it in a proportion of 12% by mass or less relative to the titanium-niobium composite oxide powder substrate, more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0042] <Heat treatment process> It is preferable to heat treat the titanium-niobium composite oxide powder after synthesis. The heat treatment temperature is preferably a temperature at which the titanium-niobium composite oxide of the base material is sintered, preventing particle size growth and a significant decrease in specific surface area. The upper limit of the heat treatment temperature is preferably 700°C or less, more preferably 650°C or less. The lower limit of the heat treatment temperature is preferably 300°C or more, more preferably 400°C or more. The heat treatment time is preferably 0.1 to 8 hours, more preferably 0.5 to 5 hours. In addition, the element M 3 When the surface treatment is carried out using a compound containing the element M 3 However, the temperature and time for diffusion into at least the surface region of the titanium-niobium composite oxide powder substrate should be appropriately set, since the reactivity differs depending on the compound containing the metal element. Furthermore, the heating method used in the heat treatment is not particularly limited. Usable heat treatment furnaces include fixed-bed calciners, roller hearth calciners, mesh belt calciners, fluidized-bed calciners, and rotary kiln calciners. The atmosphere during the heat treatment may be either air or an inert atmosphere such as a nitrogen atmosphere. In particular, when a metal salt compound is used for the surface treatment, air is preferred, as it facilitates the removal of anionic species from the particle surface.

[0043] Although the titanium-niobium composite oxide powder obtained after the heat treatment as described above has some slight agglomeration, it does not need to be pulverized to destroy the particles. Therefore, after the heat treatment, it is sufficient to perform crushing or classification to the extent that agglomerations are broken down, if necessary.

[0044] Titanium-niobium composite oxide powder is treated with a treatment agent (element M3 The resulting mixture may be mixed with a compound containing the above-mentioned (a compound containing the above-mentioned compound), granulated, and then heat-treated to form a powder containing secondary particles formed by aggregation of the primary particles. Any method for granulation may be used as long as it can produce secondary particles, but a spray dryer is preferred because it can process large quantities.

[0045] In order to reduce the amount of moisture contained in the titanium-niobium composite oxide powder, dew point control may be performed during the heat treatment process. The heat-treated powder may be classified as needed to adjust the particles to a desired maximum particle size range. Regarding the heat treatment conditions, the temperature and holding time must be within a specific range, as these have a significant effect on the secondary particle morphology and the surface treatment process. The heat treatment temperature is preferably 450°C or higher, and less than 550°C. This is because a heat treatment temperature above 550°C significantly reduces the specific surface area, resulting in a significant decrease in battery performance, particularly rate characteristics.

[0046] [Method of manufacturing the composite powder] The composite powder of the present invention can be produced by mixing carbon nanotubes with the titanium-niobium composite oxide powder obtained by the above method and compositing them. The method for mixing carbon nanotubes with the titanium-niobium composite oxide powder is not particularly limited, but examples include adding water and carbon nanotubes to the titanium-niobium composite oxide powder to prepare a mixed slurry, dispersing the mixed slurry using a paint shaker or the like, and then spray-drying it using a spray dryer or the like. When preparing the mixed slurry, a thickener such as carboxymethyl cellulose or imidazole may be used as needed. Furthermore, when the titanium-niobium composite oxide powder is subjected to a crushing treatment, the mixed slurry may be prepared by directly adding carbon nanotubes and an optional thickener such as carboxymethyl cellulose to the slurry obtained by the crushing treatment.

[0047] [Active material] The active material of the present invention contains the composite powder of the present invention. The active material of the present invention may contain one or more substances other than the composite powder of the present invention. Examples of other substances include carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers), tin and tin compounds, silicon and silicon compounds, and lithium-containing metal oxides. In particular, lithium-containing metal oxides include Li4Ti5O 12 Lithium titanate containing the above as its main component is exemplified.

[0048] [Energy storage devices] The electricity storage device of the present invention is a device that includes an electrode containing the active substance material of the present invention and stores and releases energy by utilizing the intercalation and deintercalation of lithium ions or sodium ions into such an electrode, and examples thereof include a hybrid capacitor, a lithium battery, and a sodium battery.

[0049] [Hybrid capacitor] The hybrid capacitor is a device that uses, as a positive electrode, an active material that generates capacitance by physical adsorption, such as activated carbon, similar to the electrode material of an electric double layer capacitor, an active material that generates capacitance by physical adsorption and intercalation / deintercalation, such as graphite, or an active material that generates capacitance by redox, such as a conductive polymer, and uses, as a negative electrode, the active material of the present invention. The active material of the present invention is usually used in the form of an electrode sheet for the hybrid capacitor.

[0050] [Lithium or sodium batteries] The lithium battery of the present invention is a general term for lithium primary batteries and lithium secondary batteries. In this specification, the term lithium secondary battery is used as a concept that also includes so-called lithium ion secondary batteries and all-solid-state lithium ion secondary batteries. In addition, the sodium battery of the present invention is a general term for sodium primary batteries and sodium secondary batteries. In this specification, the term sodium secondary battery is used as a concept that also includes so-called sodium ion secondary batteries and all-solid-state sodium ion secondary batteries.

[0051] The lithium or sodium battery is composed of a positive electrode, a negative electrode, and a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, or a solid electrolyte, and the active material of the present invention can be used as an electrode material. The active material of the present invention is usually used in the form of an electrode sheet for the lithium or sodium battery. This active material may be used as either a positive or negative electrode active material, but the following description will be given of its use as a negative electrode active material.

[0052] <Negative electrode> The negative electrode has a negative electrode layer containing a negative electrode active material (the active material of the present invention) and a binder on one or both sides of a negative electrode current collector. This negative electrode layer may further contain a conductive agent. This negative electrode layer is usually in the form of an electrode sheet.

[0053] The conductive agent for the negative electrode is not particularly limited as long as it is an electron-conductive material that does not undergo chemical changes. Examples thereof include graphites such as natural graphite (e.g., flake graphite) and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon nanotubes such as single-phase carbon nanotubes, multi-walled carbon nanotubes (graphite layers in a multi-layered concentric cylindrical shape) (non-fishbone-shaped), cup-stacked carbon nanotubes (fishbone-shaped), nodular carbon nanofibers (non-fishbone structure), and platelet carbon nanofibers (playing card-shaped).

[0054] The amount of conductive agent added varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents, and therefore should be optimized. However, it is preferably 0.1% to 10% by mass, and more preferably 0.5% to 5% by mass, in the negative electrode layer. If it is less than 0.1% by mass, the conductivity of the negative electrode layer cannot be ensured. If it exceeds 10% by mass, the active material ratio decreases, resulting in insufficient discharge capacity of the power storage device per unit mass and unit volume of the negative electrode layer, making it unsuitable for achieving high capacity. The conductive agent may be added during electrode preparation, or it may be coated on the active material itself. This is because coating with a conductive agent such as carbon fiber can further improve the conductivity of the negative electrode layer.

[0055] Examples of binders for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethyl cellulose (CMC).

[0056] The amount of binder added should be optimized because it varies depending on the specific surface area of ​​the active material and the type and combination of conductive agents. However, from the viewpoint of improving the binding property and ensuring the strength of the negative electrode layer, the amount of binder added in the negative electrode layer is preferably 0.2% by mass to 15% by mass.

[0057] Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, baked carbon, and those whose surfaces are coated with carbon, nickel, titanium, silver, etc. The surface of these materials may be oxidized, or the surface of the negative electrode current collector may be roughened by surface treatment.

[0058] The negative electrode can be produced by uniformly mixing a negative electrode active material (including the active material of the present invention), a conductive agent, and a binder in a solvent to form a paint, which is then applied to the negative electrode current collector, dried, and compressed.

[0059] As a method for uniformly mixing the negative electrode active material (the active material of the present invention), the conductive agent, and the binder in a solvent to prepare a paint, for example, a kneader of the type in which a stirring rod revolves while rotating within a kneading vessel such as a planetary mixer, a twin-screw extrusion kneader, a planetary stirring degassing device, a bead mill, a high-speed rotary mixer, a powder suction continuous dissolution and dispersion device, etc. Alternatively, the manufacturing process may be divided into steps depending on the solid content concentration, and these devices may be used separately.

[0060] Uniform mixing of the negative electrode active material (the active material of the present invention), conductive agent, and binder in a solvent should be optimized because it depends on the specific surface area of ​​the active material, the type of conductive agent, the type of binder, and the combination of these. However, when using a kneader such as a planetary mixer in which a stirring rod revolves while rotating on its axis within a kneading vessel, a twin-screw extrusion kneader, or a planetary stirring and degassing device, it is preferable to divide the production process into steps based on the solids concentration, knead the mixture at a high solids concentration, and then gradually reduce the solids concentration to adjust the viscosity of the paint.

[0061] The mixing procedure is not particularly limited, but examples thereof include a method of simultaneously mixing the negative electrode active material, the conductive agent, and the binder in a solvent, a method of previously mixing the conductive agent and the binder in a solvent and then adding and mixing the negative electrode active material, and a method of previously preparing a negative electrode active material slurry, a conductive agent slurry, and a binder solution and then mixing them together.

[0062] As the solvent, an organic solvent can be used, and examples of the organic solvent include aprotic organic solvents such as 1-methyl-2-pyrrolidone, dimethylacetamide, and dimethylformamide, used alone or in combination of two or more kinds, and preferably 1-methyl-2-pyrrolidone.

[0063] When an organic solvent is used as the solvent, it is preferable to dissolve the binder in the organic solvent before use.

[0064] <Positive electrode> The positive electrode has a positive electrode layer containing a positive electrode active material, a conductive agent, and a binder on one or both surfaces of a positive electrode current collector.

[0065] As the positive electrode active material, a material capable of absorbing and releasing lithium or sodium is used. For example, the active material may be a composite metal oxide containing cobalt, manganese, or nickel with lithium or sodium, or an olivine-type phosphate containing lithium or sodium. These positive electrode active materials may be used alone or in combination of two or more. Examples of such composite metal oxides include LiCoO2, LiMn2O4, LiNiO2, and LiCo 1-x Ni x O2(0.01 <x<1)、LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiNi 1 / 2 Mn 3 / 2 O4, NaMnO2, NaNiO2, NaCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, etc., and these lithium or sodium composite oxides may be partially substituted with other elements, and a portion of the cobalt, manganese, or nickel may be partially substituted with at least one element such as B, Nb, Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, or La, or a portion of the O may be substituted with S or F, or the oxide may be coated with a compound containing these other elements. Examples of lithium or sodium-containing olivine-type phosphates include LiFePO4, LiCoPO4, LiNiPO4, LiMnPO4, and LiFe 1-x Examples include MxPO4 (M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, and x is 0≦x≦0.5), NaFePO4, and NaCoPO4.

[0066] The conductive agent and binder for the positive electrode may be the same as those for the negative electrode. Examples of the positive electrode current collector include aluminum, stainless steel, nickel, titanium, baked carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The surface of these materials may be oxidized, or the positive electrode current collector surface may be roughened by surface treatment.

[0067] <Nonaqueous electrolyte> The non-aqueous electrolyte is a non-aqueous solvent in which an electrolyte salt is dissolved. There are no particular limitations on the non-aqueous electrolyte, and various types can be used.

[0068] The electrolyte salt used is one that dissolves in a non-aqueous electrolyte, and examples thereof include inorganic lithium salts such as LiPF6, LiBF4, LiPO2F2, LiN(SO2F)2, and LiClO4; chain lithium salts 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 a fluorinated alkyl group such as (CF2)2(SO2)2NLi and (CF2)3(SO2)2NLi; lithium salts with an oxalate complex as the anion such as lithium bis[oxalate-O,O']borate and lithium difluoro[oxalate-O,O']borate; and sodium salts such as NaPF6, NaBF4, NaPO2F2, NaN(SO2F)2, and NaClO4.

[0069] On the other hand, examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and S=O bond-containing compounds, and the non-aqueous solvent preferably contains a cyclic carbonate. Note that the term "chain ester" is used as a concept including chain carbonates and chain carboxylic acid esters.

[0070] <Structure of lithium or sodium batteries> The structure of the lithium battery or sodium battery of the present invention is not particularly limited, and examples include a coin battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and further, a cylindrical battery or a prismatic battery having a positive electrode, a negative electrode, and a roll-shaped separator.

[0071] The separator is an insulating thin film with high ion permeability and a certain mechanical strength. Examples include polyethylene, polypropylene, cellulose paper, glass fiber paper, polyethylene terephthalate, and polyimide microporous membranes. Multilayer membranes made by combining two or more types of materials can also be used. The surface of these separators can also be coated with resins such as PVDF, silicone resins, and rubber-based resins, or with particles of metal oxides such as aluminum oxide, silicon dioxide, and magnesium oxide.

[0072] <Negative electrode active material composition> The negative electrode active material composition of the present invention comprises the composite powder of the present invention and an inorganic solid electrolyte having conductivity for metal ions belonging to Group 1 of the periodic table. The content of the inorganic solid electrolyte 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 facilitates contact between the composite powder and the solid electrolyte. Furthermore, since an excessively high content of the inorganic solid electrolyte reduces the battery capacity of the all-solid-state secondary battery, the content of the inorganic solid electrolyte is preferably 70% by mass or less, preferably 60% by mass or less. Generally, a low content of the inorganic solid electrolyte is preferable to increase the battery capacity of the all-solid-state secondary battery. However, a low content of the inorganic solid electrolyte makes it difficult to achieve 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 achieved even when the content of the inorganic solid electrolyte is low. The active material composition may contain one or more substances other than the composite powder of the present invention and the inorganic solid electrolyte. Other materials that can be used include, for example, carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, and carbon fibers), tin and tin compounds, silicon and silicon compounds, and lithium-containing metal oxides. In particular, lithium-containing metal oxides such as Li4Ti5O 12 Lithium titanate containing the above as its main component is exemplified.

[0073] <Periodic table> The periodic table in this specification refers to the long-form periodic table of elements based on the rules of IUPAC (International Union of Pure and Applied Chemistry).

[0074] <Solid electrolyte> A solid electrolyte is a solid electrolyte that allows ions to move within it. In particular, inorganic solid electrolytes are solid in the steady state and are not usually dissociated or liberated into cations and anions. Inorganic solid electrolytes are not particularly limited as long as they have the conductivity of metal ions belonging to Group 1 of the periodic table, but generally have almost no electronic conductivity. Representative examples of inorganic solid electrolytes include (A) sulfide inorganic solid electrolytes, (B) oxide inorganic solid electrolytes, and (C) chloride inorganic solid electrolytes. Sulfide inorganic solid electrolytes are particularly preferred because they have high ionic conductivity and can be formed into dense compacts with few grain boundaries simply by applying pressure at room temperature. The periodic table referred to here refers to the long-period version of the periodic table.

[0075] The sulfide inorganic solid electrolyte may be amorphous glass, crystallized glass, or a crystalline material. Specific examples of the sulfide inorganic solid electrolyte include, but are not limited to, the following combinations: Li2S-P2S5, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S -GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li 10 GeP2S 12 .

[0076] Among the above combinations, LPS glass and LPS glass ceramics made by combining Li2S-P2S5 are preferred. In addition, as sulfide inorganic solid electrolytes other than those mentioned above, argerodite-type solid electrolytes such as Li6PS5Cl and Li6PS5Br, or Na3PS4 and Na 2.88 Sb 0.88 W0.12 Sulfide solid electrolytes having sodium ion conductivity such as S4 and Na3BS3 - SiO2 glass electrolyte are also preferably mentioned.

[0077] The oxide inorganic solid electrolyte contains oxygen atoms and has metal ions belonging to Group 1 of the periodic table. Those having ion conductivity and electron insulation are preferred.

[0078] Examples of the oxide inorganic solid electrolyte include, for example, LiZnGeO4 having a LISICON (Lithium super ionic conductor) type crystal structure, LaLiTiO3 having a perovskite type crystal structure, LiTi2P3O having a NASICON (Natrium super ionic conductor) type crystal structure, Li7La3Zr2O (LLZ) having a garnet type crystal structure, lithium phosphate (Li3PO4), LiPON in which a part of oxygen in lithium phosphate is substituted with nitrogen, Li3BO3 - Li2SO4, Li2O - B2O3 - P2O5, Li2O - SiO2, and Li6BaLa2Ta2O. 3.5 Zn 0.25 GeO4, LaLiTiO3 having a perovskite type crystal structure 0.55 Li 0.35 TiO3, LiTi2P3O having a NASICON (Natrium super ionic conductor) type crystal structure 12 , Li7La3Zr2O having a garnet type crystal structure 12 (LLZ), lithium phosphate (Li3PO4), LiPON in which a part of oxygen in lithium phosphate is substituted with nitrogen, Li3BO3 - Li2SO4, Li2O - B2O3 - P2O5, Li2O - SiO2, and Li6BaLa2Ta2O 12 etc. are preferably mentioned.

[0079] Examples of the chloride inorganic solid electrolyte include Li3ScCl6, LiAlCl4, LnAOCl (where Ln represents any rare earth element, A represents an alkaline earth metal, and X satisfies 0 < X < 1), etc. 1-X A X OCl 1-X (In the formula, Ln represents any rare earth element, A represents an alkaline earth metal, and X satisfies 0 < X < 1), etc. are preferably mentioned.

[0080] The volume average particle diameter of the inorganic solid electrolyte is not particularly limited, but it is preferably 0.01 μm or more, and more preferably 0.1 μm or more. As the upper limit, it is preferably 100 μm or less, and more preferably 50 μm or less.

Examples

[0081] Next, the present invention will be explained in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples and includes various combinations that can be easily inferred from the gist of the invention.

[0082] (Lithium-ion secondary battery) [Example 1] <Raw material preparation process> The starting materials were Nb2O5 (average particle size 0.2 μm) and anatase-type TiO2 (specific surface area 10 m 2 / g) were weighed out and mixed at a molar ratio of 4:1. This mixed powder was then calcined at 1,050°C for 12 hours. X-ray fluorescence analysis (XRF) of the resulting calcined powder sample confirmed that the total content of tantalum (Ta), potassium (K), and iron (Fe) as impurities derived from the raw materials was 2,400 ppm or less. Powder X-ray diffraction measurements were performed on the resulting calcined powder sample at a sampling interval of 0.01° and a scan rate of 2° / min. No peaks derived from the starting materials were observed, indicating that the reaction had progressed completely to form a titanium-niobium composite oxide (Ti2Nb 14 O 39 The calcined powder sample was confirmed to be a titanium-niobium composite oxide represented by the formula (1). Ion-exchanged water was added to the resulting sintered powder sample so that the solids concentration of the slurry was 30% by mass, and the mixture was stirred to disintegrate, yielding a powder sample composed of primary particles of titanium-niobium composite oxide. To 100 g of the resulting powder sample, 0.1% by mass (0.1 g) of single-walled carbon nanotubes (SWCNT, manufactured by OCSiAl) were added, and 0.16% by mass of carboxyl cellulose (CMC) was further added as a thickener to produce a mixed slurry. This mixed slurry was mixed for 3 hours using a paint shaker, and then spray-dried at 100°C using a spray dryer (Pris Spray Dryer "P260TN-31HOP") to produce a composite powder composed of the carbon nanotube-containing titanium-niobium composite oxide according to Example 1.

[0083] [Examples 2 to 4] The composite powders of Examples 2 to 4 were produced in the same manner as in Example 1, except that the carbon nanotube mixing ratio in the raw material preparation step was changed to satisfy the synthesis conditions shown in Table 1.

[0084] [Example 5] The composite powder of Example 5 was produced in the same manner as Example 1, except that in the raw material preparation step, 0.4 mass % (0.4 g) of single-walled carbon nanotubes (SWCNTs) was added to 100 g of crushed, fired powder so as to satisfy the synthesis conditions shown in Table 1, and 0.08 mass % of carboxyl cellulose (CMC) and 0.17 mass % of 1,2-dimethylimidazole (IMD) were further added as thickeners to prepare a mixed slurry.

[0085] [Example 6] The composite powder of Example 6 was produced in the same manner as in Example 1, except that in the raw material preparation step, single-walled carbon nanotubes (SWCNT, manufactured by OCSIAl) and multi-walled carbon nanotubes (MWCNT, manufactured by C Nano) were added at 0.2 mass% each to 100 g of fired powder, for a total of 0.4 mass% (0.2 g each, for a total of 0.4 g), so as to achieve the synthesis conditions shown in Table 1.

[0086] [Comparative Example 1] The starting materials were Nb2O5 (average particle size 0.2 μm) and anatase-type TiO2 (specific surface area 10 m 2 / g) were weighed and mixed at a molar ratio of 4:1. This mixed powder was subjected to a calcination treatment at 1,050°C for 12 hours and then crushed to produce a powder according to Comparative Example 1. Note that this powder did not contain carbon nanotubes.

[0087] [Comparative Examples 2 to 3] The composite powders of Comparative Examples 2 and 3 were produced in the same manner as in Example 1, except that in the raw material preparation process, the type and mixing ratio of the carbon nanotube raw material were changed to achieve the synthesis conditions shown in Table 1, and the thickener (used in the same amount as in Example 1) was changed to one shown in Table 1.

[0088] Comparative Example 4 To the fired powder sample obtained in Comparative Example 1, ion-exchanged water was added so that the solid content concentration of the slurry became 30% by mass, and it was pulverized by stirring. 1% by mass of multi-walled carbon nanotubes (MWCNT, manufactured by C Nano Co., Ltd.) pulverized was added to 100 g of the fired powder, and a mixed slurry was prepared. After this mixed slurry was mixed for 3 hours with a paint shaker, it was spray-dried at a temperature of 100 °C using a blow-air thermostatic dryer (DKN302 manufactured by Yamato Scientific Co., Ltd.) to produce a composite powder composed of a carbon nanotube-containing titanium niobium composite oxide according to Comparative Example 4. Note that this synthetic powder does not take the form of secondary particles.

[0089] [Analysis of Composite Powder] Regarding the composite powders of each Example and Comparative Example, the following analysis and measurements were performed to obtain various physical property values and the like.

[0090] [Measurement of pH Value] Regarding the composite powders of each Example and each Comparative Example, 0.5 g of the composite powder was put into 4.5 g of distilled water, shaken for 5 minutes, and then measured with a pH meter (Handy type pH meter D-51 manufactured by Horiba, Ltd., waterproof plastic pH electrode 9625-10D). The results are shown in Table 1.

[0091] [Calculation of Spectral Peak Intensity Ratio in Microscopic Raman Spectroscopy] Regarding the composite powders of each Example and each Comparative Example, a Raman spectrum was measured using a laser Raman spectrometer (NRS-3300 manufactured by JASCO Corporation) under the conditions of a laser wavelength of 532 nm, a beam diameter of 4 μm, and a laser intensity of 0.7 mW. For the obtained Raman spectrum, peak separation analysis using a Lorentz function was performed. The intensity of the peak appearing at 1570 to 1610 cm -1 which is the G band derived from the graphite structure was taken as IG, and the intensity of the peak appearing at 1330 to 1370 cm -1 which is the D band derived from the disorder of the graphite structure was taken as ID, and the results of calculating the two-peak intensity ratio IG / ID are shown in Table 1.

[0092] [Calculation of D50 of Secondary Particles: Laser Diffraction Scattering Method] For the composite powders of each Example and Comparative Example, the D50 of the secondary particles was calculated from the particle size distribution curve measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). 50 mg of sample was placed in a container containing 50 ml of ion-exchanged water as the measurement solvent, and the container was shaken by hand until the powder was visually uniformly dispersed in the measurement solvent. The container was then placed in a measurement cell and measured. The D50 of the secondary particles of the powder was calculated from the obtained particle size distribution curve.

[0093] <Measurement of secondary particle crushing strength: Microcompression test> For the composite powders of each example and comparative example, the secondary particle crushing strength was measured using a Shimadzu microcompression tester (MCT-510) equipped with a test force "1 g or less measurement mode." The test mode was selected as "compression test," and the compressive strength when the particles were compressed by 10% of the measured particle diameter was taken as the measured secondary particle crushing strength. Particles that could be clearly determined to form secondary particles were randomly selected and measured one by one, and the average of 10 points was calculated, and this average was taken as the "secondary particle crushing strength."

[0094] <Measurement of total pore volume by nitrogen gas adsorption method> The total pore volume (mL / g) of the composite powders in each example and comparative example was measured using a fully automated gas adsorption analyzer (QUANTACHROME, model "NOVA touch LX4") with nitrogen gas as the adsorption gas. 0.5 g of the sample powder was weighed and placed in a measurement cell with a stem outer diameter of 6 mm. After degassing for approximately 15 hours under vacuum at 200°C, the adsorption / desorption isotherm was measured up to a relative pressure P / P = 0.99 (P: measured internal pressure of the sample cell, P: saturated vapor pressure of nitrogen gas). Subsequently, the BJH analysis method was used to analyze the mesopore region with pore diameters of 10 to 3000 Å (excluding 10 Å), and the HK analysis method was used to analyze the micropore region with pore diameters of 10 Å or less. The sum of the pore volumes measured by the BJH method and the HK method is shown in Table 1 as the "total pore volume."

[0095] <Conductivity measurement> 1 g of the composite powder of each Example and Comparative Example was weighed and packed into a metal cell with a diameter of 1 cm, and then powder-molded using a uniaxial press to obtain a powder having a relative density of 60% (2.07 g / cm). 3 ), the conductivity of the composite powder was measured by the two-probe method using a multimeter (manufactured by Toyo Corporation, product name "KEITHLEY2000 Digital Multimeter"). The results are shown in Table 1. In Table 1, the conductivity (unit: S / cm) is expressed as log 10 The value of (log 10 Electrical conductivity [S / cm]. The closer the value is to zero, the better the powder's electrical conductivity.

[0096] [Evaluation of battery characteristics] Coin-type batteries were fabricated using the composite powders of each Example and Comparative Example, and their battery characteristics were evaluated. The evaluation results are shown in Table 1.

[0097] <Production of negative electrode sheet: electrode density> The negative electrode sheet was prepared as follows in a room maintained at a room temperature of 25°C with a dew point of -20°C or lower. The composite powders of each Example and Comparative Example were removed from their aluminum-laminated bags in a room maintained at a temperature of 25°C with a dew point of -20°C or lower. The removed composite powders of each Example and Comparative Example were mixed at a ratio of 95% by mass as the active material and 5% by mass of polyvinylidene fluoride as a binder to prepare a coating material. To clarify the conductivity-enhancing effect of the composite powder, no conductive agent was intentionally added. The resulting coating material was applied to aluminum foil and dried to prepare a single-sided negative electrode sheet for use in the coin battery described below. The coated single-sided negative electrode sheet was pressed using a roll press (roll φ60 × 150 mm, press pressure equivalent to 40 MPa), after which the thickness, area, and weight of the active material layer were measured. The density of the active material layer was calculated as the "electrode density." The measurement results are shown in Table 1. A high electrode density is preferable because it allows more active material to be packed into a given volume, resulting in an increase in the capacity available for use as a battery.

[0098] <Preparation of electrolyte> The electrolyte solution used in the battery for characteristic evaluation was prepared as follows: In an argon glove box controlled at a temperature of 25°C and a dew point of -70°C or less, a non-aqueous solvent of ethylene carbonate (EC):dimethyl carbonate (DMC) = 1:2 (volume ratio) was prepared, and LiPF6 was dissolved in this as an electrolyte salt to a concentration of 1 M to prepare the coin battery electrolyte solution described below.

[0099] <Creating a coin battery> The negative electrode single-sided sheet prepared by the above method was punched into a circle with a diameter of 14 mm and cut into 2 t / cm 2 An electrode for evaluation was prepared by pressing the electrode at a pressure of 1000 kJ / cm2 and then vacuum drying at 120°C for 5 hours. The electrode for evaluation and metallic lithium (formed into a circle with a thickness of 0.5 mm and a diameter of 16 mm) were placed opposite each other with glass filters (one each of ADVANTEC GA-100 and Whatman GF / C) interposed between them, and the nonaqueous electrolyte prepared by the method described above in <Preparation of electrolyte> was added and sealed to prepare a 2032-type coin battery.

[0100] <Initial battery characteristics: initial capacity and volumetric energy density> The coin battery fabricated by the method described in the above <Coin Battery Fabrication> was placed in a thermostatic chamber at 25°C and charged at 0.2 mA / cm in the direction in which Li was absorbed into the evaluation electrode. 2 The battery was charged to 1 V at a current density of 0.05 mA / cm at 1 V. 2 After constant current and constant voltage charging, the current density was increased to 0.2 mA / cm. 2 A constant current discharge was performed, discharging the battery to 3 V at a current density of 0.05 V. The initial capacity (mAh / g) was calculated by dividing the obtained discharge capacity (mAh) by the mass of the titanium-niobium composite oxide. The volumetric energy density was calculated by multiplying this initial discharge capacity by the electrode density calculated above. The measurement results are shown in Table 1. A high volumetric energy density increases the capacity that can be used per given volume of the battery, which is desirable as it leads to a smaller battery.

[0101] <10C charge rate, 10C discharge rate measurement> The battery was charged to 1 V at a current equivalent to 10 C of the initial capacity, and then subjected to constant-current / constant-voltage charging at 1 V until the charging current reached a current density of 0.05 C. The battery was then discharged at a constant current of 10 C to 3 V. The 10 C charge rate (%) was calculated by dividing the capacity obtained from the 10 C constant-current charge by the initial capacity, and the 10 C discharge rate (%) was calculated by dividing the capacity obtained from the 10 C constant-current discharge by the initial capacity. The results are shown in Table 1. High 10 C charge / discharge rate characteristics are expected to improve the charge / discharge rate characteristics of energy storage devices when used as an electrode material. The "C" in 1 C refers to the current value during charging / discharging. For example, 1 C refers to the current value at which the theoretical capacity can be fully discharged (or fully charged) in 1 / 1 hour, while 0.1 C refers to the current value at which the theoretical capacity can be fully discharged (or fully charged) in 1 / 0.1 hour.

[0102] [Table 1] In Table 1, the amount of carbon nanotubes (CNTs) is shown in "wt %", but the amount added is the same as "parts by weight" relative to 100 parts by weight of the titanium-niobium composite oxide.

[0103] <Evaluation results> The electrodes using composite powders composed of carbon nanotube-containing titanium-niobium composite oxides in Examples 1 to 6 were found to have higher initial capacity and volumetric energy density, superior 10C charge / discharge rate characteristics, and extremely excellent 0°C low-temperature rate characteristics compared to the electrodes using composite powders in Comparative Examples 1 to 4. In particular, comparisons of Examples 1 and 2 with Comparative Examples 2 and 3 revealed that even when the composite powder conductivity was equivalent, controlling both the pH value and specific Raman peak intensity ratios resulted in excellent low-temperature characteristics. Furthermore, comparisons of Examples 1, 2, 3, and 4 with Comparative Examples 2 and 3 indicated that controlling the particle size and crushing strength of the composite secondary particles tended to further improve the 10C charge / discharge rate characteristics and low-temperature characteristics. Although this is merely speculation, it is believed that controlling the physical properties of the composite secondary particles improved the dispersion state of the carbon nanotubes and titanium-niobium composite oxide during electrode fabrication. Additionally, it was found that adjusting the total pore volume of the composite powder to 2.5 mL / g to 3.3 mL / g further improved the 10C charge / discharge rate characteristics and low-temperature characteristics.

[0104] (All-solid-state secondary battery: Active material made of titanium-niobium composite oxide containing carbon nanotubes) In a glove box under an argon atmosphere, the composite powder of the carbon nanotube-containing titanium-niobium composite oxide from Example 1 was used as the active material. The sulfide solid electrolyte Li6PS5Cl powder (volume average particle size: 6 μm, measured using a laser diffraction / scattering particle size distribution analyzer) and conductive agent were weighed out to a mass ratio of 60:40:6, and mixed in an agate mortar and a planetary ball mill to obtain a negative electrode active material composition. The resulting negative electrode active material composition was pressed (360 MPa) at room temperature for 10 minutes to produce pellets (molded bodies) with a diameter of 10 mm and a thickness of approximately 0.7 mm. A pellet-shaped electrode containing this negative electrode active material composition, a pellet-shaped solid electrolyte layer (LPS glass with a molar ratio of Li2S:PS5 = 75:25) as a separator layer, and a lithium-indium alloy foil as a counter electrode were stacked in this order, and the stack was sandwiched between stainless steel current collectors to produce an all-solid-state secondary battery. The charge / discharge efficiency of this battery was evaluated and found to be 81%. The voltage return value after discharge was measured to be 0.22V.

[0105] (All-solid-state secondary battery: active material consisting only of titanium-niobium composite oxide) Separately, in a glove box under an argon atmosphere, a powder consisting solely of the titanium-niobium composite oxide without carbon nanotubes from Comparative Example 1 was used as the active material. The sulfide solid electrolyte Li6PS5Cl powder (volume average particle size: 6 μm, measured using a laser diffraction / scattering particle size distribution analyzer) and conductive agent were weighed out to a mass ratio of active material:Li6PS5Cl:conductive agent = 60:40:6, and mixed using an agate mortar and a planetary ball mill to obtain a negative electrode active material composition. The resulting negative electrode active material composition was pressed (360 MPa) at room temperature for 10 minutes to produce pellets (molded bodies) with a diameter of 10 mm and a thickness of approximately 0.7 mm. A pellet-shaped electrode containing this negative electrode active material composition, a pellet-shaped solid electrolyte layer (LPS glass with a molar ratio of Li2S:PS5 = 75:25) as a separator layer, and a lithium-indium alloy foil as a counter electrode were stacked in this order, and the stack was sandwiched between stainless steel current collectors to produce an all-solid-state secondary battery. The charge / discharge efficiency of this battery was evaluated and found to be 79%. The voltage return value after discharge was measured to be 0.31V.

[0106] (Evaluation results of all-solid-state secondary batteries) From the above results, it was found that when the composite made of the carbon nanotube-containing titanium-niobium composite oxide of the present invention is used as an active material, the charge-discharge efficiency is high even in an all-solid-state secondary battery, and the voltage return value after the end of discharge is small, resulting in low battery resistance and improved battery characteristics.

[0107] The composite powder obtained by the present invention is useful as an electrode active material for lithium-ion batteries because it combines high volumetric energy density with rate and low-temperature characteristics. Non-aqueous electrolyte power 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 power at night in homes and offices. Providing electrode materials for lithium-ion batteries, such as non-aqueous electrolyte secondary batteries, to society can contribute to the achievement of 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 inclusive, safe, resilient, and sustainable). These are among the 17 Sustainable Development Goals (SDGs) established by the United Nations.

Claims

1. A composite powder for an electrode of a non-aqueous electrolyte electricity storage device, comprising a titanium-niobium composite oxide powder that satisfies the following formula (I) and carbon nanotubes, wherein 0.5 g of the composite powder is added to 4.5 g of distilled water, the mixture is shaken for 5 minutes, and then the pH value measured with a pH meter is 5.5 or more and 7.5 or less, and the intensity ratio of two peaks as represented by the following formula (II) is 10 or more in a spectrum obtained by micro-Raman spectroscopy. A ａ Ti ２－ｘ M １ ｘ Nb １４－ｙ M ２ ｙ O ３９±ｚ (I) [wherein A is at least one element selected from the group consisting of Li and Na; M １ is at least one metal element selected from the group consisting of Al, Mg, Zr, Si, Ge, and Sn, and M ２ is at least one metal element selected from the group consisting of V and Ta, and 0≦a≦6, 0≦x<2, 0≦y<14, and 0≦z≦1. IG / ID ≧ 10 (II) IG: 1570-1610cm －１ Peak intensity seen in ID: 1330-1370cm －１ Peak intensity seen in

2. 2. The composite powder for an electrode of a nonaqueous electrolyte electricity storage device according to claim 1, wherein the composite powder contains secondary particles composed of primary particles of a titanium-niobium composite oxide powder and carbon nanotubes, and the average particle diameter D50 of the secondary particles is 9 μm or more.

3. 2. The composite powder for an electrode of a nonaqueous electrolyte electricity storage device according to claim 1, wherein the composite powder contains secondary particles composed of primary particles of a titanium-niobium composite oxide powder and carbon nanotubes, and the secondary particles have a secondary particle crushing strength of 1 MPa or more.

4. 2. The composite powder for an electrode of a nonaqueous electrolyte electricity storage device according to claim 1, wherein the composite powder has a total pore volume measured by a nitrogen gas adsorption method of 2.5 mL / g to 3.3 mL / g.

5. An electrode for a non-aqueous electrolyte electricity storage device, comprising the composite powder according to any one of claims 1 to 4 as an active material.

6. A negative electrode active material composition for a non-aqueous electrolyte storage device, comprising the composite powder according to any one of claims 1 to 4 and an inorganic solid electrolyte.

7. A non-aqueous electrolyte electricity storage device comprising the electrode according to claim 5 .

8. An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, wherein the negative electrode layer is a layer containing the negative electrode active material composition according to claim 6.

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