JPWO2017047755A1 - Fibrous carbon-containing lithium titanium composite oxide powder, electrode sheet using the same, and electricity storage device using the same - Google Patents

Abstract

  Fibrous carbon having spherical secondary particles including primary particles made of lithium-titanium composite oxide and fibrous carbon having an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000, and an average circularity of 90% or more A lithium-titanium composite oxide powder, calculated from measurement by thermogravimetric analysis, the mass ratio of carbon to the mass of the lithium-titanium composite oxide powder is A, and the percentage notation of A is a (mass%), When the atomic ratio of carbon to titanium (carbon / titanium) calculated from measurement by X-ray photoelectron spectroscopy is B, a is 0.1 to 3% by mass, and B / A is 90 to 200. A fibrous carbon-containing lithium-titanium composite oxide powder for an electrode of an electricity storage device in which the spherical secondary particles have an average compressive strength of 1 to 25 MPa is provided.

Description

  The present invention relates to a fibrous carbon-containing lithium titanium composite oxide powder suitable as an electrode material for an electrical storage device, and an electrode sheet for an electrical storage device using the fibrous carbon-containing lithium titanium composite oxide powder in an electrode mixture layer And an electricity storage device using this electrode sheet.

  In recent years, various materials have been studied as electrode materials for power storage devices. Among them, lithium-titanium composite oxides can provide an electricity storage device with excellent input / output characteristics when used as an active material for a negative electrode, and thus are attracting attention as an active material material for electricity storage devices for electric vehicles such as HEV, PHEV, and BEV. ing.

  However, since lithium-containing oxides such as lithium-titanium composite oxides generally have low conductivity, a conductive agent such as a carbonaceous material is added to these lithium-containing oxides for the purpose of improving conductivity. It has been proposed. Examples of carbonaceous materials include powdered carbon such as graphite powder and acetylene black, and fibrous carbon such as carbon nanotubes (CNT) and carbon nanofibers (CNF). Therefore, it is a material suitable as such a conductive agent. In addition, if spherical secondary particles are formed of an active material material in which a carbonaceous material is combined, a powder containing such spherical secondary particles is suitable for an electrode material because it can be easily slurried and applied. . Therefore, fibrous carbon-containing lithium titanium composite oxide powder containing spherical secondary particles containing lithium titanium composite oxide and fibrous carbon is suitable as an electrode material for an electricity storage device.

  Although it is the prior art regarding the lithium containing oxide which does not contain Ti, in patent document 1, the composite material for positive electrodes comprised from the spherical secondary particle containing lithium manganate particle | grains and a carbon nanotube (CNT) is disclosed, A lithium ion battery to which this positive electrode composite material was applied was agglomerated with a positive electrode composite material composed of spherical secondary particles combined with carbon black instead of carbon nanotubes (CNT), and lithium manganate particles. It has been shown that the internal resistance is smaller than that of a lithium ion battery to which a positive electrode material containing fibrous carbon particles is applied.

  An electrode material including spherical secondary particles in which fibrous carbon is combined with lithium titanium composite oxide containing Li and Ti is disclosed in Patent Document 2, and an aggregate of primary particles of lithium titanate; It has been shown that spherical granular composites containing carbon nanotubes (CNT) have a lower volume resistance than granular composites that are simply carbon coated.

  Thus, by combining fibrous carbon with lithium-titanium composite oxide to form a powder containing spherical secondary particles and using it as a negative electrode material, the negative electrode conductivity is improved, and the input / output of the electricity storage device The characteristics are further improved.

Japanese Patent No. 5377946 JP 2014-29863 A

  On the other hand, when lithium titanium composite oxide is used as a negative electrode active material for an electric storage device for an electric vehicle, for example, lithium titanate is charged and discharged at a voltage higher than 1 V with respect to Li metal. However, although it has an advantage that lithium metal is difficult to precipitate, it has a weak point that its energy density is theoretically low. Therefore, when a lithium titanium composite oxide such as lithium titanate is used for the negative electrode active material, there is a demand for increasing the density of the electrode (negative electrode) as much as possible. However, when the electrode mixture layer is simply densified by increasing the press pressure during electrode production, there are problems such as a decrease in capacity retention rate and a significant increase in the amount of gas generated when a charge / discharge cycle is performed at a high temperature. Therefore, as it is, it is difficult to apply the lithium titanium composite oxide as an active material of an electric storage device for an electric vehicle that is strongly required not to deteriorate in performance for a long period of time such as 10 years or longer.

  In addition, when a powder containing spherical secondary particles (granular composite) containing lithium titanium composite oxide and fibrous carbon as disclosed in Patent Document 2 is used as the negative electrode material, Although the output characteristics are improved, it has been found that the decrease in the capacity retention rate and the increase in the amount of gas generation after the high-temperature charge / discharge cycle described above become more remarkable.

  Therefore, the present invention uses a carbon-containing lithium-titanium composite oxide powder that is excellent in charge / discharge cycle characteristics under a high-temperature environment and has a small amount of gas generation after the charge / discharge cycle, an electrode sheet of an electricity storage device including the same, and an electrode sheet thereof It is an object to provide a stored electricity storage device.

  As a result of examining the above problems, the present inventors have applied a fibrous carbon-containing lithium titanium composite oxide powder containing spherical secondary particles containing a lithium titanium composite oxide and fibrous carbon to an electricity storage device. In such electricity storage devices, one of the causes of the decrease in capacity retention rate and increase in gas generation after high-temperature charge / discharge cycles is that the fibrous carbon aggregates and localizes near the surface of the spherical secondary particles. I found out that there was. On the other hand, after making the particle size distribution of the raw material of the lithium titanium composite oxide below a specific value, it is mixed with fibrous carbon, granulated into a spherical shape and calcined, thereby producing a fibrous carbon-containing lithium titanium composite oxide. It was found that the localization due to the aggregation of the fibrous carbon can be eliminated by preparing the product powder.

  As a result of further study to solve the above-mentioned problems, the present inventors have found that a spherical secondary containing primary particles composed of a lithium titanium composite oxide and fibrous carbon having an average diameter and an average aspect ratio in a specific range. In the fibrous carbon-containing lithium-titanium composite oxide powder containing particles, the carbon content (mass%) calculated from the measurement by thermogravimetric analysis and the carbon and titanium calculated from the measurement by X-ray photoelectron spectroscopy analysis The fibrous carbon-containing lithium titanium composite oxide powder having an atomic ratio (carbon / titanium) in a specific range and an average compressive strength of the spherical secondary particles in a specific range has a long charge / discharge cycle life at high temperature, The present invention was completed by finding that the amount of gas generated after a charge / discharge cycle in a high temperature environment was small. That is, the present invention relates to the following matters.

  (1) Spherical secondary particles including primary particles made of lithium-titanium composite oxide containing Li and Ti, and fibrous carbon having an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000 are included. Lithium titanium composite oxide powder, which is a fibrous carbon-containing lithium titanium composite oxide powder having a circularity of 90% or more, calculated from thermogravimetric analysis in the fibrous carbon-containing lithium titanium composite oxide powder The mass ratio of carbon to the mass of A is A, the percentage notation of A is a (mass%), and the atomic ratio of carbon and titanium (carbon / titanium) calculated from measurement by X-ray photoelectron spectroscopy is B. Sometimes, a is 0.1 to 3% by mass, B / A is 90 to 200, and the average compressive strength of the spherical secondary particles is 1 to 25 MPa. Electrode for fibrous carbon-containing lithium-titanium composite oxide powder of the device.

(2) The lithium titanium composite oxide is lithium titanate containing Li ₄ Ti ₅ O ₁₂ as a main component, and the fibrous carbon-containing lithium titanium composite oxide for an electrode of an electricity storage device according to (1) Powder.

  (3) The fibrous carbon-containing lithium-titanium composite oxide powder for an electrode of an electricity storage device according to (1) or (2), wherein the 1-methyl-2-pyrrolidone oil absorption is 55 ml / 100 g to 160 ml / 100 g .

(4) The specific surface area equivalent diameter D _{BET of the} lithium-titanium composite oxide powder is 0.03 to 0.6 μm, (1) to (3) Fibrous carbon for electrode of any one of the electricity storage devices Containing lithium titanium composite oxide powder.

  (5) The above-mentioned fibrous carbon is formed by stacking 2 to 30 bell-like structural units having a top portion with a closed graphite mesh surface and a trunk portion with an open lower portion, sharing a central axis. A plurality of bell-shaped structural unit aggregates, and the fibrous carbon is formed by connecting a plurality of bell-shaped structural unit aggregates at intervals in a head-to-tail manner to form fibers. A fibrous carbon-containing lithium titanium composite oxide powder for an electrode of an electricity storage device according to any one of (1) to (4).

(6) said lithium-titanium composite oxide _powder, Li ₄ Ti of _{5 O 12} a crystallite size calculated from the Scherrer formula from the peak half width of the (111) plane is taken as _{D X, D X} is 80nm The fibrous carbon-containing lithium for an electrode of any one of (1) to (5), wherein the ratio is larger and the ratio D _BET / D _X (μm / μm) of D _BET to D _X is 3 or less Titanium composite oxide powder.

  (7) The fibrous secondary carbon-containing lithium titanium composite oxide powder for an electrode of any one of (1) to (6), wherein the spherical secondary particles contain non-fibrous carbon.

  (8) An electrode sheet of an electricity storage device having an electrode mixture layer on one side or both sides of a current collector, wherein the electrode mixture layer is a fibrous form for an electrode of any one of (1) to (7) The electrode sheet | seat of the electrical storage device containing carbon containing lithium titanium complex oxide powder.

(9) the electrolyte solution holding ratio of the electrode mixture layer is ^{0.7cm 3 / cm 3 ~1cm 3 /} cm 3, the electrode density of the electrode mixture layer is 1.9 g ^/ cm 3 to 2.5 g The electrode sheet of the electricity storage device according to (8), which is / cm ³ .

(10) of the electrode mixture layer, the specific surface area determined by the BET method and ^{_{S E (m 2 / g)}} , the electrolyte solution holding ratio of the electrode mixture layer ^(cm 3 / cm ³⁾ was _{L E} Sometimes, L _E / S _E is 0.2-0.3, (9) The electrode sheet of the electrical storage device characterized by the above-mentioned.

  (11) An electricity storage device comprising any one of the electrode sheets (8) to (10).

  (12) A lithium ion secondary battery comprising the electrode sheet according to any one of (8) to (10).

  (13) A hybrid capacitor including any one of the electrode sheets (8) to (10).

(14) LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , and non-aqueous solvent containing one or more cyclic carbonates selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate (11) The electrical storage device according to (11), wherein a nonaqueous electrolytic solution in which an electrolyte salt containing at least one lithium salt selected from LiN (SO ₂ F) ₂ is dissolved is used.

(15) The non-aqueous electrolyte has a total electrolyte salt concentration of 0.5 M or more and 2.0 M or less, includes at least LiPF ₆ as the electrolyte salt, and further has LiBF ₄ of 0.001 M or more and 1.0 M or less. (14) The electrical storage device according to (14), which is a non-aqueous electrolyte containing at least one lithium salt selected from LiPO ₂ F ₂ and LiN (SO ₂ F) ₂ .

  (16) The non-aqueous electrolyte is one or more symmetrical chain carbonates selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate, and methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate (14) or (15), further comprising one or more asymmetric chain carbonates selected from the group consisting of methyl butyl carbonate, and ethyl propyl carbonate.

  According to the present invention, when applied as an electrode material for an electricity storage device, a fibrous carbon-containing lithium-titanium composite oxide powder having a long charge / discharge cycle life at a high temperature and a small amount of gas generation after the charge / discharge cycle is included. An electrode sheet for an electricity storage device and an electricity storage device using the electrode sheet can be provided.

(Fibrous carbon-containing lithium titanium composite oxide powder)
The fibrous carbon-containing lithium-titanium composite oxide powder of the present invention is a primary particle composed of a lithium-titanium composite oxide containing Li and Ti, and a fibrous form having an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000. A fibrous carbon-containing lithium-titanium composite oxide powder containing spherical secondary particles containing carbon and having an average circularity of 90% or more, according to thermogravimetric analysis in the fibrous carbon-containing lithium-titanium composite oxide powder The mass ratio of carbon to the mass of the lithium titanium composite oxide powder calculated from the measurement is A, the percentage notation of A is a (mass%), and the carbon and titanium calculated from the measurement by X-ray photoelectron spectroscopy analysis When the atomic ratio (carbon / titanium) is B, a is 0.1 to 3% by mass, B / A is 90 to 200, and the average pressure of the spherical secondary particles Strength is an electrode for fibrous carbon-containing lithium-titanium composite oxide powder of the electric storage device, which is a 1～25MPa.

  The fibrous carbon-containing lithium titanium composite oxide powder of the present invention is preferably composed of the spherical secondary particles (that is, preferably substantially composed of the spherical secondary particles), Components other than the spherical secondary particles, for example, fibrous carbon, and lithium titanium composite oxidation, to the extent that the characteristics of the electricity storage device to which the fibrous carbon-containing lithium titanium composite oxide powder of the present invention is applied are not affected. Particles other than the spherical secondary particles such as product particles and fibrous carbon-containing lithium titanium composite oxide particles may also be included.

  The spherical secondary particles contained in the fibrous carbon-containing lithium-titanium composite oxide powder of the present invention are primary particles made of lithium-titanium composite oxide containing Li and Ti (hereinafter sometimes referred to as lithium-titanium composite oxide). And fibrous carbon. Hereinafter, these will be described in the order of the lithium titanium composite oxide and its physical properties, fibrous carbon, spherical secondary particles and their physical properties, and the physical properties of the fibrous carbon-containing lithium titanium composite oxide powder.

[Lithium titanium composite oxide]
The lithium-titanium composite oxide contained in the spherical secondary particles of the present invention is not particularly limited as long as it is an oxide containing Li and Ti and can be applied to an electrode of an electricity storage device. For example, a spinel structure is used. Lithium titanium oxide, ramsteride type lithium titanium oxide, and the like, and a lithium titanium composite oxide in which a part of the sites of Li and Ti are substituted with other metal elements may be used. The lithium titanium composite oxide of the present invention is preferably lithium titanate mainly composed of Li ₄ Ti ₅ O ₁₂ . When Li ₄ Ti ₅ O ₁₂ is applied as an active material to an electrode of an electricity storage device, the volume change associated with insertion / desorption of Li ions is small, so that the crystal structure is excellent and the deterioration due to charge / discharge cycles is relatively small. . In addition, compared to carbon materials, the lithium ion insertion / desorption potential is noble, so lithium metal precipitation at low temperatures and reductive decomposition of the solvent by the negative electrode active material are suppressed, which is known to be highly safe. It has been. Here, Li ₄ Ti ₅ O ₁₂ is the main component when the intensity of the peak derived from the (111) plane of Li ₄ Ti ₅ O ₁₂ is 100 among the peaks measured by the X-ray diffraction method. The intensity of the peak derived from the (101) plane of anatase-type titanium dioxide is 5 or less, the intensity of the peak derived from the (110) plane of rutile-type titanium dioxide is 5 or less, and (-133) of Li ₂ TiO ₃ The value calculated by multiplying the intensity of the peak derived from the plane by 100/80 (corresponding to the peak intensity of the (002) plane of Li ₂ TiO ₃ ) is 5 or less. Moreover, using Li ₄ Ti ₅ O ₁₂ as a main component does not necessarily mean that a complete crystal of Li ₄ Ti ₅ O ₁₂ is used.

Peak derived from (111) plane of Li ₄ Ti ₅ O ₁₂ obtained by X-ray diffraction measurement, peak derived from (101) plane of anatase type titanium dioxide, peak derived from (110) plane of rutile type titanium dioxide, and Li peak derived from ₂ TiO ₃ of (002) plane is the main peak of each crystal phase, respectively. In the present _invention, the Li 2 TiO _{3 only,} instead of the peak derived from the main peak of Li 2 TiO ₃ (002) _plane, the intensity of the peak derived from Li 2 TiO ₃ of (-133) plane 100/80 Is used as the intensity of the peak corresponding to the (002) plane, which is the main peak of Li ₂ TiO _3. The reason for this is the main peak of Li ₂ TiO ₃ . in it (002), whereas it may be necessary to peak separation peak derived from surface overlap with the base of the peak derived from (111) plane of _{Li 4/3 Ti 5/3 O 4, Li} 2 TiO _This is because the peak derived from the (−133) plane of No. ₃ does not overlap with peaks derived from other constituent phases, and thus the intensity corresponding to the main peak of Li ₂ TiO ₃ is more easily calculated. Also, multiplying by 100/80 is based on these peak intensity ratios.

When the lithium titanium composite oxide of the present invention is lithium titanate containing Li ₄ Ti ₅ O ₁₂ as a main component, the atomic ratio Li / Ti of Li to Ti in the lithium titanate of the present invention is 0.75. It is preferable that it is -0.90. Within this range, the proportion of Li ₄ Ti ₅ O _{12 in} the lithium titanate increases, and the initial charge / discharge capacity of the electricity storage device to which the lithium titanate of the present invention is applied as an electrode material increases. From this viewpoint, the atomic ratio Li / Ti is more preferably 0.77 or more, still more preferably 0.78 or more, and particularly preferably 0.79 or more. Further, it is more preferably 0.89 or less, and still more preferably 0.88 or less.

<Specific surface area equivalent diameter D _{BET of} lithium titanium composite oxide powder>
The specific surface area equivalent diameter D _BET of the lithium-titanium composite oxide powder of the present invention is the lithium-titanium composite oxide after removing the carbonaceous material containing fibrous carbon from the fibrous carbon-containing lithium-titanium composite oxide powder of the present invention. It is a specific surface area equivalent diameter calculated from the specific surface area calculated | required by BET method of a product powder. The method for removing the carbonaceous material is not particularly limited, but the carbonaceous material containing fibrous carbon can be removed from the fibrous carbon-containing lithium titanium composite oxide powder, and the specific surface area of the lithium titanium composite oxide powder does not change. Any means can be used. As the means, it is preferable to perform a heat treatment under conditions where the specific surface area of the lithium titanium composite oxide powder does not change under the coexistence of oxygen such as in the air, for example, a heat treatment at 450 to 550 ° C. for 1 to 4 hours. .

The specific surface area equivalent diameter D _BET of the lithium titanium composite oxide powder of the present invention is not particularly limited, but is preferably 0.03 μm to 0.6 μm. When D _BET is 0.03 μm to 0.6 μm, the charge / discharge capacity of the electricity storage device can be further increased. However, in the present invention, the value of D _BET is not particularly limited to such a range. Further, D _BET is particularly preferably 0.03 to 0.4 μm, and input characteristics of the electricity storage device are further improved within this range.

<Crystal Diameter D _{X of} Lithium Titanium Composite Oxide Powder>
In the present invention, the crystallite diameter calculated from the Scherrer equation from the peak half-value width of the (111) plane of Li ₄ Ti ₅ O ₁₂ of the lithium titanium composite oxide powder is defined as D _X. D _X of the lithium-titanium composite oxide powder of the present invention is not particularly limited, it is preferably 80nm or more. When D _X is at 80nm or more, it is possible to minimize the effects of resistance when the lithium ions move grain boundary, deterioration in battery performance due to polarization increases caused by the grain boundaries lithium ion moves It can suppress more appropriately. The _{D X} is not particularly limited, it is preferably 500nm or less. D _X it is possible to minimize the influence of the diffusion resistance of the interior of the particles as long as 500nm or less, more appropriately suppress a decrease in battery performance due to polarization increases caused by the internal particles of lithium ions to move. However, in the present invention, the value of D _X is not particularly limited to this range. A method for measuring the D _X, described in detail in Examples below. In addition, regarding the crystallite diameter D _X of the lithium titanium composite oxide powder, unlike the D _BET , the presence of the carbonaceous material does not affect the measurement result. Therefore, in the present invention, the fibrous carbon-containing lithium titanium composite is used. Measurement is performed on oxide powder.

<Ratio of D _BET and D _X of lithium titanium composite oxide powder D _BET / D _X (μm / μm)>
The ratio D _BET / D _X (μm / μm) of D _BET and D _X of the lithium titanium composite oxide powder of the present invention is not particularly limited, but is preferably 2 or less, and preferably 1.5 or less. Particularly preferred. As D _BET / D _X is smaller, the input / output characteristics of the electricity storage device to which the fibrous carbon-containing lithium titanate powder of the present invention is applied as an electrode material can be further enhanced. However, in the present invention, the value of D _BET / D _X (μm / μm) is not particularly limited to the above range.

[Fibrous carbon]
The fibrous carbon of the present invention has an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000. When the average diameter of the fibrous carbon is less than 5 nm, the carbon fibers are aggregated, so that it is not possible to improve charge / discharge cycle characteristics in a high temperature environment and gas generation after the charge / discharge cycle. On the other hand, when the average diameter of the fibrous carbon is larger than 40 nm, the effect of improving the conductivity is small. Moreover, when the average aspect ratio of fibrous carbon is less than 10, the electrical conductivity improving effect is small. From the viewpoint of further enhancing the effect of improving conductivity, the average aspect ratio of the fibrous carbon is preferably 30 or more, more preferably 50 or more. On the other hand, when the average aspect ratio of the fibrous carbon is larger than 1000, the carbon fibers are aggregated, so that improvement of charge / discharge cycle characteristics under high temperature environment and generation of gas after the charge / discharge cycle cannot be effectively suppressed. . The average aspect ratio of the fibrous carbon is preferably 500 or less, more preferably 200, from the viewpoint that the charge / discharge cycle characteristics in a high temperature environment can be further improved and gas generation after the charge / discharge cycle can be further reduced. It is as follows. A method for measuring the average diameter and the average aspect ratio of the fibrous carbon will be described in detail in Examples described later. The fibrous carbon of the present invention is not particularly limited as long as it is fibrous carbon having this average diameter and average aspect ratio, and examples thereof include single-walled and multi-walled carbon nanotubes and carbon nanofibers. Particularly preferred fibrous carbon is a bell-shaped structural unit described in JP 2012-46864 A, which has a top portion with a closed graphite mesh surface and a body portion with an open bottom, sharing a central axis. A plurality of bell-like structural unit assemblies formed by stacking in layers, and a plurality of the bell-like structural unit assemblies are connected at intervals in a head-to-tail manner to form fibers. It is fibrous carbon characterized by being comprised by these. When the fibrous carbon of the present invention is such a particularly preferred embodiment, the dispersed state in the electrode is particularly good.

[Spherical secondary particles]
The fibrous carbon-containing lithium titanium composite oxide powder of the present invention contains spherical secondary particles, and the spherical secondary particles contain primary particles composed of the above-described lithium titanium composite oxide and fibrous carbon. The spherical secondary particles referred to here are not limited to perfect spheres (true spheres) as long as the appearance of the secondary particles is similar to a sphere, that is, substantially spherical. The spherical secondary particles of the present invention include particles that are partially uneven, and particles that are nearly spherical, such as elliptical spheres.

<Average compressive strength of spherical secondary particles>
The average compressive strength of the spherical secondary particles of the present invention is 1 to 25 MPa. When the average compressive strength of the spherical secondary particles is within this range, the charge / discharge cycle characteristics of the electricity storage device under a high temperature environment can be improved, and the amount of gas generated after the charge / discharge cycle can be suppressed. Such an effect is obtained when the average compressive strength of the spherical secondary particles is within this range, and when the electrode mixture layer is formed, the fibrous carbon is also localized in the electrode mixture layer. In addition, it is presumed that the contact area between the lithium titanium composite oxides or between the lithium titanium composite oxide and the fibrous carbon increases. Here, setting the average compressive strength of the spherical secondary particles to 25 MPa or less is also effective for increasing the density of the electrode mixture layer, that is, increasing the energy density. From the above viewpoint, the lower limit of the average compressive strength is preferably 2 MPa or more, more preferably 3 MPa or more, and the upper limit of the average compressive strength is preferably 20 MPa or less, more preferably 15 MPa or less, and further preferably 10 MPa or less. . A method for measuring the average compressive strength of the spherical secondary particles will be described in the examples described later.

<Average circularity of fibrous carbon-containing lithium titanium composite oxide powder>
The fibrous carbon-containing lithium titanium composite oxide powder of the present invention contains the above-described spherical secondary particles, and has an average circularity of 90% or more. When the average circularity is less than 90%, the input / output characteristics of the electricity storage device to which the average circularity is applied are deteriorated. The reason for this is that when the fibrous carbon-containing lithium-titanium composite oxide powder is mixed with another electrode constituent material to form a paint, the dispersibility of the fibrous carbon in the paint deteriorates, and the electrode mixture layer It is assumed that the fibrous carbon is localized. This is probably because the primary particles of fibrous carbon and lithium titanium composite oxide in the vicinity of the particle surface easily fall off from the irregular secondary particles with low circularity during coating. From the viewpoint of further improving the input / output characteristics of the electricity storage device, the fibrous carbon-containing lithium titanium composite oxide powder of the present invention has an average circularity of 95% or more of the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. Preferably there is. A method for measuring the average circularity will be described in Examples described later.

<In the fibrous carbon-containing lithium titanium composite oxide powder, the carbon content calculated from the measurement by thermogravimetric analysis and the atomic ratio of carbon and titanium calculated from the measurement by X-ray photoelectron spectroscopy>
In the fibrous carbon-containing lithium-titanium composite oxide powder of the present invention, the mass ratio of carbon to the mass of the lithium-titanium composite oxide powder calculated from thermogravimetric analysis is A, and the percentage notation of A is a (mass %), And when the atomic ratio of carbon to titanium (carbon / titanium) measured by X-ray photoelectron spectroscopy analysis is B, a is 0.1 to 3% by mass and B / A is 90 to 90%. 200. When a is less than 0.1% by mass, the electronic conductivity of the fibrous carbon-containing lithium titanium composite oxide powder is not sufficiently improved, so that an electricity storage device having good input / output characteristics cannot be obtained. When a is larger than 3% by mass, the amount of fibrous carbon on the surface of the spherical secondary particles increases and aggregates on the surface of the spherical secondary particles, so that an electric storage device with good charge / discharge cycle characteristics in a high temperature environment can be obtained. Furthermore, gas generation after the charge / discharge cycle is not suppressed. From the viewpoint of further improving input / output characteristics and charge / discharge cycle characteristics in a high-temperature environment, the lower limit of a is more preferably 0.3% by mass, and further preferably 0.5% by mass. Further, the upper limit of a is more preferably 2.5% by mass, and further preferably 2% by mass. Even if B / A is smaller than 90 or larger than 200, an electricity storage device having good charge / discharge cycle characteristics under a high temperature environment cannot be obtained, and gas generation after the charge / discharge cycle is not suppressed. From the viewpoint that charge / discharge cycle characteristics can be further improved and gas generation after the charge / discharge cycle can be further reduced, the lower limit of B / A is more preferably 100, and even more preferably 110. The upper limit of B / A is more preferably 190 and even more preferably 180. In thermogravimetric analysis, the entire particles of fibrous carbon-containing lithium titanium composite oxide powder, that is, substantially the entire spherical secondary particles contained in the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, Since the mass ratio of carbon is measured, A represents the carbon content in the entire spherical secondary particle. On the other hand, in the X-ray photoelectron spectroscopic analysis, the particle surface of the fibrous carbon-containing lithium titanium composite oxide powder, that is, the spherical secondary material substantially contained in the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. Since only the atomic ratio (carbon / titanium) of carbon and titanium located on the surface of carbon and titanium constituting the particle is measured, B is an index instead of the carbon content on the surface of the spherical secondary particle. It is. In the present invention, B / A is an atomic ratio (carbon / titanium) between carbon and titanium located on the surface of carbon and titanium constituting the spherical secondary particles, and the fibrous carbon-containing lithium titanium composite oxide. It is a value divided by the carbon content (mass%) of the whole product powder, and is an index representing the ratio of the carbon content in the entire spherical secondary particle and the carbon content on the surface of the spherical secondary particle. As B / A is larger, the carbon content on the surface of the spherical secondary particles is larger than the carbon content of the entire fibrous carbon-containing lithium titanium composite oxide powder.

<D50 of fibrous carbon-containing lithium titanium composite oxide powder>
From the viewpoint of powder handling, D50 of the fibrous carbon-containing lithium titanium composite oxide powder is preferably 1 μm or more, more preferably 3 μm or more. Further, from the viewpoint of increasing the electrode mixture density and increasing the energy density, it is preferably 25 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. Here, D50 is the particle size at which the cumulative volume frequency calculated by the volume fraction is 50% when integrated from the smaller particle size.

<1-methyl-2-pyrrolidone oil absorption of fibrous carbon-containing lithium titanium composite oxide powder>
The fibrous carbon-containing lithium titanium composite oxide powder of the present invention preferably has a 1-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP) oil absorption of 55 ml / 100 g to 160 ml / 100 g. When the NMP oil absorption amount is within this range, the charge / discharge cycle characteristics of the electricity storage device under a high temperature environment are further improved, and the amount of gas generated after the charge / discharge cycle is further reduced. Such an effect can be obtained by setting the NMP oil absorption in this range so that the electrolytic solution in the electrode mixture layer of the electricity storage device using the fibrous carbon-containing lithium titanium composite oxide powder of the present invention is used. It is presumed that the amount of liquid retention can be made appropriate. From the viewpoint that the charge / discharge cycle characteristics in a high temperature environment can be further improved and the gas generation after the charge / discharge cycle can be further reduced, the lower limit of the NMP oil absorption is preferably 60 ml / 100 g, more preferably 65 ml. / 100 g, more preferably 70 ml / 100 g. The upper limit of the NMP oil absorption is preferably 155 ml / 100 g, more preferably 150 ml / 100 g, and still more preferably 145 ml / 100 g. Here, the unit of ml / 100 g represents the amount of NMP absorbed (unit: ml) per 100 g of fibrous carbon-containing lithium titanium composite oxide powder. The NMP oil absorption can be adjusted by the specific surface area of the lithium titanium composite oxide powder, the addition ratio of fibrous carbon, and the like.

The fibrous carbon-containing lithium titanium composite oxide powder of the present invention may further contain non-fibrous carbon. The non-fibrous carbon is not particularly limited, but a powder having a specific surface area of 20 to ²⁰⁰ m ² / g is preferable because an effect of improving charge / discharge cycle characteristics under a high temperature environment can be obtained. Specifically, acetylene black, ketjen black and the like are preferable.

(Method for producing fibrous carbon-containing lithium titanium composite oxide powder)
The following is an example of a method for producing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. For the case where the lithium titanium composite oxide is lithium titanate, the raw material preparation step, the drying / granulation step, and the firing Although it demonstrates and divides into a process, the manufacturing method of the fibrous carbon containing lithium titanium complex oxide powder of this invention is not limited to this.

[Preparation process of raw material mixed slurry]
In the present invention, a lithium raw material and a titanium raw material are mixed and prepared in advance such that D95 of the mixture falls within a specific range, and then the mixture and fibrous carbon are wet-mixed to prepare a raw material mixed slurry (hereinafter referred to as “mixture”). (Sometimes abbreviated as mixed slurry). The B / A of the fibrous carbon-containing lithium titanate (lithium titanium composite oxide) powder obtained can be adjusted to 90 to 200 by drying, granulating, and firing the mixed slurry thus prepared.

<Preparation process of lithium titanium composite oxide raw material>
As a raw material for lithium titanate, a titanium raw material and a lithium raw material are used. As the titanium raw material, titanium compounds such as anatase type titanium dioxide and rutile type titanium dioxide are used. As a titanium raw material, it is preferable that it reacts easily with a lithium raw material in a short time, and the anatase type titanium dioxide is preferable from the viewpoint. In particular, complete anatase-type titanium dioxide having a rutile ratio of 0% is preferable.

  As the lithium raw material, lithium compounds such as lithium hydroxide monohydrate, lithium oxide, lithium hydrogen carbonate, and lithium carbonate are used, and lithium hydroxide monohydrate and lithium carbonate are preferable.

  The above titanium raw material and lithium raw material are mixed before being mixed with fibrous carbon, and further prepared so that D95 in the particle size distribution curve measured with a laser diffraction / scattering particle size distribution analyzer is 2 μm or less. . Thereby, the fibrous carbon containing lithium titanate (lithium titanium complex oxide) powder whose B / A is 90-200 can be obtained. Here, D95 is a particle size in which the cumulative volume frequency calculated by the volume fraction is 95% when integrated from the smaller particle size. The state of the mixture of the titanium raw material and the lithium raw material used for mixing with the fibrous carbon is preferably a slurry containing the powder of the mixture.

As a method for preparing a mixture of a titanium raw material and a lithium raw material, the following methods can be employed. The first method is a method in which the raw materials are mixed and then pulverized simultaneously with mixing. The second method is a method in which each raw material is pulverized until D95 after mixing becomes 2 μm or less, and then mixed or mixed while lightly pulverizing. The third method is a method in which powders made of fine particles are produced from each raw material by a method such as crystallization, classified as necessary, and mixed while mixing or lightly pulverizing. Among them, in the first method, the method of pulverizing simultaneously with the mixing of the raw materials is an industrially advantageous method because it involves fewer steps. In any method, mixing is desirably performed in a wet manner, and it is desirable to use polyvinyl alcohol or polycarboxylic acid ammonium salt as a dispersing agent.
In the present invention, a fibrous carbon-containing lithium-titanium composite oxide powder containing spherical secondary particles in which localization of fibrous carbon on the particle surface is suppressed, specifically, a fiber having a B / A of 90 to 200 The fact that a carbon-like lithium-titanium composite oxide powder can be obtained will be considered as follows.

  In the case of forming spherical secondary particles by combining fibrous carbon with lithium titanium composite oxide containing lithium titanate, conventionally, the fibrous carbon has been extremely localized on the surface of the spherical secondary particles. The reason is considered as follows.

  When the lithium raw material, the titanium raw material and the fibrous carbon are mixed, the fibrous carbon is present more on the particle surface of the lithium raw material than the particle surface of the titanium raw material, and is present in an aggregated state. There is a possibility that the affinity of the lithium raw material for the fibrous carbon and the affinity of the titanium raw material are significantly different.

  In general, lithium raw materials have a remarkably large particle size and a very small specific surface area compared to titanium raw materials, so that in a slurry containing raw materials having such properties, the slurry does not have a grinding effect. Even if it is mixed by an efficient mixing means, or a dispersing agent having good dispersibility of fibrous carbon is used, or even if the mixing time is increased, the fibrous carbon is slightly deposited on the surface of the lithium raw material particles. Try to exist in an agglomerated manner. As a result, the proportion of fibrous carbon that is in direct contact with the surface of the lithium raw material having good affinity with fibrous carbon becomes very small.

  When the slurry is sprayed and dried, the slurry is atomized. The dispersion medium evaporates from the surface of the particles containing the dispersion medium, and accordingly, the dispersion medium inside the particles moves to the particle surface, and solid granulated particles are formed as it evaporates from the particle surface. In the case of the slurry in the state as described above, the dispersion medium moves from the inside of the particle to the particle surface, and the fibrous carbon that has a small specific gravity and is not in direct contact with the particle surface of the lithium raw material is aggregated together with the dispersion medium. Will move toward the particle surface. In the granulated particles thus formed, fibrous carbon is localized near the surface of the granulated particles. Even in the spherical secondary particles obtained by firing such granulated particles, the fibrous carbon is localized on the particle surface.

  On the other hand, if the particle size of the lithium raw material is reduced in advance before mixing with the fibrous carbon, the specific surface area of the lithium raw material in direct contact with the fibrous carbon is increased, and the specific surface area is increased. Can be dispersed and brought into direct contact with the surface of the lithium source particles. As a result, aggregation of fibrous carbon in the slurry is suppressed, and the proportion of fibrous carbon in direct contact with the surface of the lithium raw material is increased. When such a slurry is sprayed and dried, the movement of the fibrous carbon to the particle surface accompanying the movement of the dispersion medium to the particle surface is also suppressed. As a result, both the granulated particles and the spherical secondary particles obtained by firing the particles suppress the localization of fibrous carbon on the particle surface.

  As described above, in the spherical secondary particles contained in the lithium titanium composite oxide powder containing fibrous carbon, one of the causes that the fibrous carbon is likely to be localized on the surface of the spherical secondary particles is It is inferred that there is a difference in affinity and particle size between the lithium raw material and the titanium raw material. In the present invention, the particle size distribution of the raw material of the lithium titanium composite oxide is made to be a specific value or less and mixed with fibrous carbon. , Fibrous carbon-containing lithium titanium composite oxide powder containing spherical secondary particles in which localization of fibrous carbon on the particle surface is suppressed, specifically, fibrous carbon containing B / A of 90-200 It seems that the lithium titanium composite oxide powder can be obtained.

<Preparation process of fibrous carbon>
The fibrous carbon used as the raw material may be fibrous carbon having an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000 in the spherical secondary particles of the obtained fibrous carbon-containing lithium titanate powder. . Since the fibrous carbon can be cut by adjusting the conditions in the mixing step of the mixture of titanium raw material and lithium raw material and fibrous carbon, fibrous carbon having an average aspect ratio of greater than 1000 may be used. . In the present invention, so-called carbon nanotubes (CNT) and carbon nanofibers (CNF) having an average diameter of 5 to 40 nm are preferably used. In particular, a bell-shaped structural unit set in which bell-shaped structural units having a top portion with a closed graphite mesh surface and a trunk portion with an open lower portion are formed by stacking 2 to 30 layers sharing a central axis. A plurality of bell-shaped structural unit assemblies are formed by connecting fibers at intervals in a head-to-tail manner to form fibers. Fibrous carbon described in Examples and the like is particularly preferable. By using such fibrous carbon, it becomes easy to obtain a fibrous carbon-containing lithium titanate powder having a B / A of 90 to 200.

  Since fibrous carbon tends to agglomerate, the fibrous carbon is opened and dispersed with a dispersant in a liquid dispersion medium before mixing with a mixture of a titanium raw material and a lithium raw material, and at the same time a fiber having a large average aspect ratio. In the case of carbon, it is preferably pulverized (cut) and mixed with a mixture of a titanium raw material and a lithium raw material in a slurry state.

  Examples of the dispersant include surfactants such as polyvinyl alcohol, polycarboxylic acid ammonium salt, sodium oleate, polyoxyethylene carboxylic acid ester, monoalcohol ester, ferrocene derivative, pyrene compound (pyrene ammonium), porphyrin compound (ZnPP, Hemin, PPEt), polyfluorene, cyclic glucan, folic acid, lactam compound (—CONH—), lactone compound (—CO—O—) and other cyclic / polycyclic aromatic compounds, polythiophene, polyphenylene vinylene, polyphenylene ethylene, etc. Linear conjugated polymers, cyclic amides such as polyvinylpyrrolidone (PVP), polystyrene sulfonic acid, polymer micelles, water-soluble pyrene-containing polymers, fructose, polysaccharides (such as carboxymethylcellulose), saccharides such as amylose, Inclusion complex of taxane such as cholate analogue, and the like, particularly when the dispersion medium is an aqueous solution system, carboxymethyl cellulose, polyvinyl pyrrolidone are preferred. The dispersant is preferably added in a mass ratio of 1/100 to 100/100 with respect to the aggregate of fibrous carbon. The dispersion medium is not particularly limited, but polar solvents such as water and alcohols are usually used from the viewpoint of handling and solubility of the lithium compound. The opening and dispersion of the fibrous carbon aggregates are performed by combining the dispersion medium, the dispersant, the fibrous carbon aggregates, and the like, and stirring them with a homomixer, a trimix, or the like. For this purpose, a bead mill and a paint shaker are used which utilize ultrasonic waves by vibration shock waves, impact of beads, balls, etc., and shaking. In the case of fibrous carbon having a large average aspect ratio, a method having a relatively high grinding ability such as a bead mill is preferably employed.

  Before the fibrous carbon is opened and dispersed in the liquid dispersion medium, the fibrous carbon can be oxidized. By performing the oxidation treatment, the fibrous carbon is easily adapted to the dispersion medium, and the dispersibility with respect to the lithium titanate of the present invention is further increased, so that the charge / discharge cycle characteristics in a high temperature environment and the gas after the charge / discharge cycle are increased. It is effective in suppressing the occurrence. As an oxidation treatment method, for example, liquid phase oxidation with nitric acid / sulfuric acid, ozone, supercritical water, supercritical carbon dioxide gas, or the like, or hydrophilization treatment on the surface of carbon fiber by air firing, gas phase oxidation with oxygen plasma, etc. The method of giving is mentioned.

<Mixing process of titanium raw material and lithium raw material and fibrous carbon>
Next, the carbon content (mass%) in the entire fibrous carbon-containing lithium titanate (lithium titanium composite oxide) powder obtained by mixing the titanium raw material and lithium raw material obtained by the above-described method and fibrous carbon. Is mixed at a desired ratio of 0.1 to 3% by mass to prepare a mixed slurry for use in the drying and granulation step. The mixing method is not particularly limited as long as the mixture of the titanium raw material and the lithium raw material and the fibrous carbon can be uniformly mixed. As described above, the slurry of the mixture of the titanium raw material and the lithium raw material, the fibrous It is preferable to mix with a carbon slurry, and for example, it can be mixed by a method of stirring with a homomixer, a trimix or the like, or a method using impact or shaking such as a bead mill or a paint shaker. As long as the aspect ratio of the fibrous carbon is not less than 10, a mixing method in which the raw material is further pulverized may be used.

[Drying and granulating process]
Next, the obtained mixed slurry is dried and granulated. The drying / granulation method may be any method as long as it can obtain a fibrous carbon-containing lithium titanate (lithium titanium composite oxide) powder having an average circularity of 90% or more, but is usually spray-dried (spray drying). ). If the granulated powder is dried and granulated by a general spray drying method, the average circularity is large, and the average circularity is usually 90% or more even after firing.

  Of these, a spray drying method using a two-fluid spray dryer is preferable. In this case, the spray drying is performed at a temperature of 190 ° C. or higher, more preferably 210 ° C. or higher. It is preferable to carry out at 1 to 1 L / min. The size of the granulated powder can be controlled mainly by the solid content of the slurry and the pressure of the sprayed air. When the solid content of the slurry is large, the granulated powder becomes large, and when the solid content of the slurry is small, the granulated powder becomes small. Further, when the air pressure is low, the granulated powder becomes large, and when the air pressure is high, the granulated powder becomes small. The obtained granulated powder can be used for the next baking step as it is.

[Baking process]
Next, the obtained granulated powder is fired. In order to set the average compressive strength of the spherical secondary particles of the fibrous carbon-containing lithium titanate (lithium titanium composite oxide) powder to 1 to 25 MPa, the granulated powder is preferably fired at a high temperature in a short time. From such a viewpoint, the maximum temperature during firing is preferably 1000 ° C. or lower, more preferably 950 ° C. or lower, and further preferably 900 ° C. or lower. From the viewpoint of increasing the specific surface area of the spherical secondary particles of the fibrous carbon-containing lithium titanate (lithium titanium composite oxide) powder and increasing the crystallite diameter, the maximum temperature during firing is preferably 720 ° C or higher. More preferably, it is 750 degreeC or more, More preferably, it is 780 degreeC or more. From the same viewpoint, the holding time at the maximum temperature during firing is preferably 2 to 60 minutes, more preferably 5 to 45 minutes, and further preferably 5 to 30 minutes. When the maximum temperature during firing is high, it is preferable to select a shorter holding time. Similarly, from the viewpoint of increasing the crystallite diameter obtained by firing, it is preferable to particularly shorten the residence time from 700 ° C. to the highest temperature in the temperature raising process during firing.

  In this invention, the average compressive strength of spherical secondary particles can be made into 1-25 Mpa by baking granulated powder for a short time at high temperature as mentioned above. If the firing time is lengthened, the average compressive strength of the spherical secondary particles tends to be greater than 25 MPa, and the average of the spherical secondary particles can be obtained only by mixing and granulating a lithium titanate powder synthesized in advance and fibrous carbon. The compressive strength tends to be less than 1 MPa.

  The firing method is not particularly limited as long as it can be fired under such conditions. Examples of the firing furnace that can be used include a fixed bed type firing furnace, a roller hearth type firing furnace, a mesh belt type firing furnace, a fluidized bed type, and a rotary kiln type firing furnace. However, when performing efficient firing in a short time, a roller hearth firing furnace, a mesh belt firing furnace, and a rotary kiln firing furnace are preferable. When using a roller hearth-type firing furnace or mesh belt-type firing furnace in which the granulated powder is stored and fired in a mortar, in order to make the quality of the lithium titanate obtained constant, It is preferable to make the temperature distribution uniform, and it is preferable to reduce the amount of the granulated powder contained in the mortar.

  The rotary kiln-type firing furnace does not require a container to store the granulated powder, can be fired while continuously adding the granulated powder, has a uniform heat history on the material to be fired, and is a homogeneous fibrous carbon-containing titanium This is a particularly preferred firing furnace for producing the lithium titanate powder of the present invention because it is easy to obtain lithium acid powder.

  The atmosphere during firing is preferably an inert atmosphere such as nitrogen or noble gas that does not contain oxygen, so that fibrous carbon or optionally non-fibrous carbon is not consumed or lost during firing.

(Electrode sheet)
Next, the electrode sheet of the present invention will be described. The electrode sheet of the electricity storage device of the present invention is an electrode sheet of an electricity storage device having an electrode mixture layer containing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention on one side or both sides of a current collector. It is cut according to the design shape and used as a positive electrode or a negative electrode. The electrode mixture layer contains a binder in addition to the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. Further, in addition to the fibrous carbon contained in the fibrous carbon-containing lithium titanium composite oxide powder and the non-fibrous carbon contained in some cases, a conductive additive added at the time of forming the electrode mixture layer can be included. Below, for convenience, the fibrous carbon contained in the fibrous carbon-containing lithium-titanium composite oxide powder is used as the first conductive assistant, and in some cases the non-fibrous carbon contained as the second conductive assistant, the electrode The conductive auxiliary agent added at the time of forming the mixture layer may be referred to as a third conductive auxiliary agent.

<Electrolytic solution retention ratio of electrode mixture layer and density of electrode mixture layer>
In the electrode sheet of the electricity storage device of the present invention, the electrolyte solution retention rate of the electrode mixture layer is 0.7 to 1.0, and the density of the electrode mixture layer is 1.9 to 2.5 g / cm ³ . It is preferable. The electrolytic solution retention rate in the present invention is an electrode mixture when the electrode sheet is immersed in a nonaqueous electrolytic solution in which 1M LiPF ₆ is dissolved in a propylene carbonate solvent (hereinafter, 1M LiPF ₆ / PC). This is the ratio of the volume of the nonaqueous electrolyte solution impregnated in the layer to the volume of the electrode mixture layer. The method for measuring the electrolyte solution retention rate and the electrode mixture layer density of the electrode mixture layer will be described in the following examples. When the electrolyte solution retention ratio and the electrode mixture layer density of the electrode mixture layer are in this range, the energy density is improved, and the electrolyte solution is likely to penetrate, that is, the Li insertion / extraction reaction is smooth. It progresses and is effective in charge / discharge cycle characteristics in a high temperature environment and gas generation suppression after the charge / discharge cycle. After using the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, the amount of the third conductive additive added and the electrode density of the electrode mixture layer are adjusted to maintain the electrolyte solution in the electrode mixture layer. The liquid ratio and the electrode mixture layer density can be adjusted within this range.

<Specific surface area _S E of the electrode mixture layer ^(m 2 / g) and the ratio _S E _{/ L} E of the electrolyte solution holding ratio _{L E>}
Furthermore, in the electrode sheet of the electricity storage device of the present invention, the specific surface area of the electrode mixture layer determined by the BET method is S _E (m ² / g), and the electrolyte solution retention rate of the electrode mixture layer is L _E. when _a, S _E / _L E is preferably a 0.20 to 0.30. If S E _/ L _E is in this range, the charge-discharge cycle characteristics under high temperature environment of the electric storage device is particularly well, the amount of gas generated after the charge-discharge cycle is particularly reduced. By setting S _E / L _E within this range, it is presumed that the amount of electrolyte solution retained in the electrode mixture layer is adjusted to a range suitable for obtaining these effects. S _E / L _E can be adjusted not only by the fibrous carbon-containing lithium-titanium composite oxide powder of the present invention but also by the specific surface area and addition amount of the third conductive additive. A method for measuring the specific surface area of the electrode mixture layer will be described in Examples.

(Electric storage device)
The electricity storage device of the present invention is a device that stores and releases energy by utilizing intercalation and deintercalation of lithium ions to an electrode containing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. Examples thereof include a hybrid capacitor and a lithium battery.

[Hybrid capacitor]
As the hybrid capacitor, an active material having a capacity formed by physical adsorption similar to the electrode material of an electric double layer capacitor, such as activated carbon, or physical adsorption, intercalation, deintercalation, etc., such as graphite. In this device, the active material in which the capacity is formed by the active material or the active material in which the capacity is formed by redox such as a conductive polymer is used, and the fibrous carbon-containing lithium titanium composite oxide powder of the present invention is used for the negative electrode.

[Lithium battery]
The lithium battery of the present invention is a generic term for a lithium primary battery and a lithium secondary battery. In this specification, the term lithium secondary battery is used as a concept including a so-called lithium ion secondary battery.

  The lithium battery is composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent. The fibrous carbon-containing lithium titanium composite oxide powder of the present invention is used as an electrode material. be able to. The fibrous carbon-containing lithium titanium composite oxide powder of the present invention may be used as either a positive electrode active material or a negative electrode active material, but the case where it is used as a negative electrode active material will be described below.

<Negative electrode>
The negative electrode has an electrode mixture layer containing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention and a binder on one surface or both surfaces of the negative electrode current collector. The electrode mixture layer may further contain a third conductive additive.

The third conductive additive for the negative electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. For example, natural graphite (flaky graphite, etc.), graphite such as artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, single-phase carbon nanotube, multi-walled carbon nanotube (Graphite layer is multi-layer concentric cylinder) (non-fishbone), cup-stacked carbon nanotube (fishbone) (fishbone), nodal carbon nanofiber (non-fishbone structure), platelet-type carbon nanofiber ( And carbon nanotubes such as a playing card). Further, graphites, carbon blacks, and carbon nanotubes may be appropriately mixed and used. There is no particular limitation, specific surface area of the carbon blacks is preferably 30~3000m ² / g, more preferably from 50~2000m ² / g. When the specific surface area is less than 30 m ² / g, the contact area with the active material decreases, so that the electrical conductivity cannot be obtained and the internal resistance increases. When the specific surface area exceeds 3000 m ² / g, the amount of solvent required for coating increases, so it becomes more difficult to improve the electrode density, and it is not suitable for increasing the capacity of the mixture layer. The specific surface area of the graphite is preferably 30 to 600 m ² / g, more preferably 50 to 500 m ² / g. When the specific surface area is less than 30 m ² / g, the contact area with the active material decreases, so that the electrical conductivity cannot be obtained and the internal resistance increases. When the specific surface area exceeds 600 m ² / g, the amount of solvent required for coating increases, so it becomes more difficult to improve the electrode density, and it is not suitable for increasing the capacity of the mixture layer. The aspect ratio of the carbon nanotubes is preferably 10 to 1000. When the aspect ratio is large, the structure of the formed fiber approaches a cylindrical tube shape, and the conductivity in the fiber axis direction of one fiber is improved. However, the open end of the graphite network surface constituting the structural unit body is a fiber. Since the frequency of exposure to the outer peripheral surface is reduced, the conductivity between adjacent fibers is deteriorated. On the other hand, when the aspect ratio is small, the open end of the graphite mesh surface constituting the structural unit body portion is more frequently exposed to the outer peripheral surface of the fiber, so that the conductivity between adjacent fibers is improved. Since many short graphite mesh surfaces are connected in the axial direction, conductivity in the fiber axial direction of one fiber is impaired.

  The addition amount of the third conductive auxiliary agent is optimized depending on the specific surface area of the active material and the type and combination of the conductive auxiliary agent, but is preferably 10% by mass or less, more preferably based on the entire mixture layer. Is 5% by mass or less, more preferably 2% by mass or less. The fibrous carbon-containing lithium-titanium composite oxide powder contains fibrous carbon that is the first conductive aid, and in some cases non-fibrous carbon that is the second conductive aid, and the third conductive aid. Even if is not added, sufficient performance as an electricity storage device is exhibited.

Examples of the binder for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl pyrrolidone (PVP), a copolymer of styrene and butadiene (SBR), and a copolymer of acrylonitrile and butadiene. Examples include coalescence (NBR) and carboxymethyl cellulose (CMC). Although not particularly limited, the molecular weight of polyvinylidene fluoride is preferably 20,000 to 200,000. From the viewpoint of securing the binding property of the electrode mixture layer, it is preferably 25,000 or more, more preferably 30,000 or more, and further preferably 50,000 or more. From the viewpoint of ensuring conductivity without hindering contact between the active material and the conductive auxiliary agent, it is preferably 150,000 or less. In particular, when the specific surface area of the active material is 10 m ² / g or more, the molecular weight is preferably 100,000 or more.

  The amount of the binder added is optimized depending on the specific surface area of the active material and the type and combination of the conductive assistants, but is usually preferably 0.2 to 15% by mass with respect to the entire mixture layer. From the viewpoint of enhancing the binding property and securing the strength of the mixture layer, it is more preferably 0.5% by mass or more, further preferably 1% by mass or more, and particularly preferably 2% by mass or more. . From the viewpoint of suppressing the reduction of the active material ratio in the mixture layer and not reducing the unit mass of the mixture layer and the discharge capacity of the electricity storage device per unit volume, the additive amount of the binder is 10% by mass or less. Is preferable, and it is more preferable that it is 5 mass% or less.

  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, and silver. Moreover, the surface of these materials may be oxidized, and an unevenness | corrugation may be given to the negative electrode collector surface by surface treatment. Examples of the form of the negative electrode current collector include a sheet, a net, a foil, a film, a punched one, a lath body, a porous body, a foamed body, a fiber group, and a nonwoven fabric molded body.

  The negative electrode is obtained by adding a solvent to the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, a binder, and, if necessary, a third conductive additive, mixing and kneading them, and further adding a solvent. After adjusting the viscosity to form a paint, it can be obtained by applying on the negative electrode current collector, drying and compressing.

  The method of mixing the fibrous carbon-containing lithium-titanium composite oxide powder of the present invention, the binder, and the third conductive auxiliary agent added as necessary is not particularly limited. The method of mixing the fibrous carbon-containing lithium titanium composite oxide powder of the invention, the conductive additive and the binder at the same time in the solvent, the fibrous carbon of the present invention after the conductive auxiliary agent and the binder are previously mixed in the solvent A method of additionally mixing the lithium-titanium composite oxide powder, a method of preparing a slurry of the fibrous carbon-containing lithium-titanium composite oxide powder of the present invention, a conductive auxiliary agent slurry and a binder solution in advance, and mixing them. Can be mentioned. In order to make these mixture layer constituent materials uniformly disperse in the mixture layer, a method in which the conductive auxiliary agent and the binder are previously mixed in a solvent and then the negative electrode active material is additionally mixed, and the negative electrode active material slurry It is preferable to prepare a conductive auxiliary agent slurry and a binder solution in advance and mix them together.

  As the solvent, water or an organic solvent can be used. Examples of the organic solvent include aprotic organic solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide, or a mixture of two or more kinds, preferably N-methylpyrrolidone.

  When water is used as the solvent, the binder is preferably added at the stage of finally adjusting to a desired viscosity in order not to cause the binder to aggregate. Moreover, when aluminum is used as the negative electrode current collector, corrosion of aluminum occurs when the pH of the coating increases. Therefore, it is preferable to add an acidic compound to lower the pH at which corrosion does not occur. As the acidic compound, either an inorganic acid or an organic acid can be used. As the inorganic acid, phosphoric acid, boric acid and oxalic acid are preferable, and oxalic acid is more preferable. The organic acid is preferably an organic carboxylic acid. Further, as a method for preventing corrosion of aluminum, it is preferable to use an aluminum current collector in which the surface of the aluminum current collector is coated with an alkali-resistant material such as carbon.

  In the case of using an organic solvent as the solvent, it is preferable to use the binder by dissolving it in an organic solvent in advance.

  Examples of the apparatus for adding and mixing and kneading the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, a binder, and a third conductive auxiliary agent to be added as necessary, for example, a planetary mixer Use a kneader of the type in which the stirring rod revolves in the kneading vessel, a twin-screw extrusion kneader, a planetary stirring and defoaming device, a bead mill, a high-speed swirling mixer, a powder suction continuous dissolution and dispersion device, etc. Can do. In addition, it is preferable to start mixing and kneading in a state where the solid content concentration is high, and adjust the viscosity of the coating material by gradually reducing the solid content concentration. It is preferable to use the mixing / kneading apparatus properly. The solid content concentration at the stage of starting mixing and kneading is preferably 60 to 90% by mass, and more preferably 70 to 90% by mass. If it is less than 60% by mass, sufficient shearing force can be obtained to uniformly disperse the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, the binder, and the third conductive auxiliary agent added as necessary. It is difficult, and if it exceeds 90% by mass, the load on the apparatus tends to increase.

<Positive electrode>
The positive electrode has a mixture layer containing a positive electrode active material, a conductive additive and a binder on one side or both sides of the positive electrode current collector.

As the positive electrode active material, a material capable of inserting and extracting lithium is used. For example, as the active material, a composite metal oxide with lithium containing cobalt, manganese, nickel, lithium-containing olivine-type phosphate, or the like These positive electrode active materials can be used singly or in combination of two or more. Examples of such composite metal oxides include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3 Mn. _1/3 O ₂ , LiNi _1/2 Mn _3/2 O _{4 and the} like. A part of these lithium composite oxides may be substituted with other elements, and a part of cobalt, manganese, nickel may be replaced with Sn. , Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, La, etc., or a part of O is replaced with S or F Alternatively, a compound containing these other elements can be coated. Examples of the lithium-containing olivine-type phosphate include LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ , LiFe _1-x M _x PO ₄ (M is selected from Co, Ni, Mn, Cu, Zn, and Cd). At least one, and x is 0 ≦ x ≦ 0.5.

  Examples of the conductive additive and binder for the positive electrode include the same as those for the negative electrode. Examples of the positive electrode current collector include aluminum, stainless steel, nickel, titanium, calcined carbon, and aluminum or stainless steel having a surface treated with carbon, nickel, titanium, or silver. The surface of these materials may be oxidized, and the surface of the positive electrode current collector may be uneven by surface treatment. Examples of the shape of the current collector include a sheet, a net, a foil, a film, a punched one, a lath body, a porous body, a foamed body, a fiber group, and a nonwoven fabric molded body.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution is obtained by dissolving an electrolyte salt in a nonaqueous solvent. There is no restriction | limiting in particular in this non-aqueous electrolyte, A various thing can be used.

As the electrolyte salt, one that dissolves in a non-aqueous electrolyte is used. For example, an inorganic lithium salt such as LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , LiN (SO ₂ F) ₂ , LiClO _4, or LiN (SO _{2). CF 3) 2, LiN (SO} 2 C 2 F 5) 2, LiCF 3 SO 3, LiC (SO 2 CF 3) 3, LiPF 4 (CF 3) 2, LiPF 3 (C 2 F 5) 3, LiPF 3 Lithium salts containing a chain-like fluorinated alkyl group such as (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso-C ₃ F ₇ ), and (CF ₂ ) ₂ ( SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi and other lithium salts containing cyclic fluorinated alkylene chains, bis [oxalate-O, O ′] lithium borate and diflu Examples thereof include lithium salts using an oxalate complex such as oro [oxalate-O, O ′] lithium borate as an anion. Among these, particularly preferable electrolyte salts are LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO ₂ F) ₂ , and the most preferable electrolyte salt is LiPF ₆ . These electrolyte salts can be used singly or in combination of two or more. As the preferred combination of these electrolyte salts include LiPF _6, further LiBF _4, LiPO ₂ F _2, and LiN _(SO 2 _F) at least one lithium salt selected from ₂ nonaqueous solution Is preferable.

  The concentration used by dissolving all the electrolyte salts is usually preferably 0.3 M or more, more preferably 0.5 M or more, and even more preferably 0.7 M or more with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

  On the other hand, examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, S═O bond-containing compounds, and the like, including cyclic carbonates. Is preferred. The term “chain ester” is used as a concept including a chain carbonate and a chain carboxylic acid ester.

  Examples of the cyclic carbonate include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, and 2,3-butylene carbonate. Ethylene carbonate, propylene carbonate, 1, One or more selected from 2-butylene carbonate and 2,3-butylene carbonate are more preferable from the viewpoint of improving the 50C charge rate characteristics and reducing the amount of gas generated during high-temperature storage. Propylene carbonate, 1,2- One or more cyclic carbonates having an alkylene chain selected from butylene carbonate and 2,3-butylene carbonate are more preferred. The ratio of the cyclic carbonate having an alkylene chain in the total cyclic carbonate is preferably 55% by volume to 100% by volume, and more preferably 60% by volume to 90% by volume.

Therefore, as the non-aqueous electrolyte, a non-aqueous solvent containing one or more cyclic carbonates selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate, LiPF ₆ , LiBF ₄ , It is preferable to use a nonaqueous electrolytic solution in which an electrolyte salt containing at least one lithium salt selected from LiPO ₂ F ₂ and LiN (SO ₂ F) ₂ is used. As the cyclic carbonate, propylene carbonate, 1, One or more cyclic carbonates having an alkylene chain selected from 2-butylene carbonate and 2,3-butylene carbonate are more preferred.

In particular, the concentration of the total electrolyte salt is 0.5 M or more and 2.0 M or less, and the electrolyte salt includes at least LiPF ₆ and further 0.001 M or more and 1 M or less of LiBF ₄ , LiPO ₂ F ₂ , and LiN. It is preferable to use a nonaqueous electrolytic solution containing at least one lithium salt selected from (SO ₂ F) ₂ . When the proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is 0.001 M or more, the effect of improving the charge / discharge cycle characteristics of the electricity storage device in a high-temperature environment and the reduction of gas generation after the charge / discharge cycle It is preferable that the effect is easily exhibited, and that it is 1.0 M or less because there is little concern that the effect of improving the charge / discharge cycle characteristics under a high temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle are reduced. The proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is preferably 0.01 M or more, particularly preferably 0.03 M or more, and most preferably 0.04 M or more. The upper limit is preferably 0.8M or less, more preferably 0.6M or less, and particularly preferably 0.4M or less.

  The non-aqueous solvent is preferably used as a mixture in order to achieve appropriate physical properties. The combination includes, for example, a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate, a chain carbonate and a lactone, a combination of a cyclic carbonate, a chain carbonate and an ether, a cyclic carbonate, a chain carbonate and a chain ester. Combinations, combinations of cyclic carbonates, chain carbonates, and nitriles, combinations of cyclic carbonates, chain carbonates, and S═O bond-containing compounds are included.

  As the chain ester, one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate, One or more symmetrical linear 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 Preferable examples include one or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

  Among the chain esters, chain esters having a methyl group selected from dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate and ethyl acetate (EA) are preferable. In particular, a chain carbonate having a methyl group is preferred.

  Moreover, when using chain carbonate, it is preferable to use 2 or more types. Further, it is more preferable that both a symmetric chain carbonate and an asymmetric chain carbonate are contained, and it is further more preferable that the content of the symmetric chain carbonate is more than that of the asymmetric chain carbonate.

  The content of the chain ester is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. When the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte does not become too high, and when the content is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte is decreased. The above range is preferable because there is little possibility that the effect of improving the discharge cycle characteristics and the effect of reducing the amount of gas generated after the charge / discharge cycle are reduced.

  The volume ratio of the symmetric chain carbonate in the chain carbonate is preferably 51% by volume or more, and more preferably 55% by volume or more. The upper limit is more preferably 95% by volume or less, and still more preferably 85% by volume or less. It is particularly preferred that the symmetric chain carbonate contains dimethyl carbonate. The asymmetric chain carbonate preferably has a methyl group, and methyl ethyl carbonate is particularly preferable. In the above case, it is preferable because the effect of improving the charge / discharge cycle characteristics under a higher temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle are improved.

  The ratio of cyclic carbonate and chain ester is cyclic carbonate: chain ester (volume ratio) from the viewpoint of improving the effect of improving charge / discharge cycle characteristics in a high temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle. Is preferably 10:90 to 45:55, more preferably 15:85 to 40:60, and particularly preferably 20:80 to 35:65.

<Structure of lithium battery>
The structure of the lithium battery of the present invention is not particularly limited, and a coin-type battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery and a corner having a positive electrode, a negative electrode, and a roll separator. An example is a type battery.

  As the separator, an insulating thin film having a large ion permeability and a predetermined mechanical strength is used. For example, polyethylene, polypropylene, cellulose paper, glass fiber paper, polyethylene terephthalate, polyimide microporous film and the like can be mentioned, and a multilayer film constituted by combining two or more kinds can also be used. In addition, the surfaces of these separators can be coated with resin such as PVDF, silicon resin, rubber-based resin, particles of metal oxide such as aluminum oxide, silicon dioxide, and magnesium oxide. The pore diameter of the separator may be in a range generally useful for batteries, for example, 0.01 to 10 μm. The thickness of the separator may be in a general battery range, and is, for example, 5 to 300 μm.

Next, Examples and Comparative Examples in the case where the lithium titanium composite oxide constituting the fibrous carbon-containing lithium titanium composite oxide powder of the present invention is lithium titanate containing Li ₄ Ti ₅ O ₁₂ as a main component. 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. In particular, it is not limited to the combination of the solvent which comprises the non-aqueous electrolyte of an Example. Details of the physical property values given in the following examples and comparative examples are described.

(Various physical property measurement methods)
[1. Particle size distribution)
For measuring the particle size distribution of each powder according to the present invention, a laser diffraction / scattering particle size distribution measuring machine (Nikkiso Co., Ltd., Microtrac MT3300EXII) was used. In the preparation of the measurement sample, ethanol was used as the measurement solvent for the lithium titanate raw material slurry and mixed slurry, and ion-exchanged water was used for the fibrous carbon-containing lithium titanium composite oxide powder. About 50 mg of a sample was put into 50 ml of a measurement solvent, and 1 cc of 0.2% sodium hexametaphosphate aqueous solution as a surfactant was added, and the obtained measurement slurry was processed with an ultrasonic disperser. The measurement slurry subjected to the dispersion treatment was accommodated in a measurement cell, and a measurement solvent was added to adjust the slurry concentration. The particle size distribution was measured when the transmittance of the slurry was within an appropriate range.

[2. (Average diameter and average aspect ratio of fibrous carbon)
The average diameter D (nm) and the average fiber length L (nm) of the fibrous carbon were calculated from the SEM image of the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. The average value of the diameter of 100 fibrous carbons in the SEM image and the average value of the aspect ratio were taken as the average diameter and average aspect ratio of the fibrous carbon. The aspect ratio is calculated as L (fiber length) / D (fiber diameter).

[3. XRD]
As a measuring device, an X-ray diffractometer using CuKα ray (Rigaku Corporation, RINT-TTR-III type) was used. The measurement conditions of the X-ray diffraction measurement are: measurement angle range (2θ): 10 ° to 90 °, step interval: 0.02 °, measurement time: 0.25 seconds / step, radiation source: CuKα ray, tube voltage : 50 kV, current: 300 mA.

Main peak intensity of lithium titanate (diffraction angle 2θ = 18.1-18.5 ° -derived peak intensity in the range of (111) plane), main peak intensity of anatase titanium dioxide (diffraction angle 2θ = 24.7− (Peak intensity derived from (101) plane within a range of 25.7 °), main peak intensity of rutile titanium dioxide (peak intensity derived from (110) plane within a range of diffraction angle 2θ = 27.2 to 27.6 °) , And the peak intensity of Li ₂ TiO ₃ (diffraction angle 2θ = peak intensity derived from (−133) plane within the range of 43.5 to 43.8 °). Also the calculation of _Li 2 TiO ₃ and (-133) main peak intensity of _Li 2 TiO ₃ is multiplied by 100/80 on surface derived peak intensity ((002) intensity of the peak of the corresponding surface). Then, when the main peak intensity of the lithium titanate and 100, the rutile titanium dioxide was calculated anatase titanium dioxide, and the relative value of the main peak intensity of Li ₂ TiO _3.

[4. Crystallite diameter of lithium titanium composite oxide powder (D _X )]
The crystallite diameter (D _X ) of the lithium titanate powder of the present invention was measured using an X-ray diffractometer using CuKα rays (RINT-TTR-III type, manufactured by Rigaku Corporation). Measurement conditions were as follows: measurement angle range (2θ): 15.8 ° to 21.0 °, step interval: 0.01 °, measurement time: 1 second / step, radiation source: CuKα ray, tube voltage: 50 kV, The current was calculated from the Scherrer equation, that is, the following equation (1), from the peak half-value width of the (111) plane of the lithium titanium composite oxide obtained at 300 mA. In calculating the half width, it is necessary to correct the line width by the optical system of the diffractometer, and silicon powder was used for this correction.
D _X = K · λ / (FW (S) · cos θ _c ) (1)
FW (S) ^ D = FWHM ^ D-FW (I) ^ D
FW (I) = f0 + f1 × (2θ) + f2 × (2θ) ²
θ _c = (t0 + t1 × (2θ) + t2 (2θ) ² ) / 2
K: Scherrer constant (0.94)
λ: wavelength of CuKα ₁ line (1.54059 mm)
FW (S): Sample-specific half-width (FWHM)
FW (I): Device-specific half-width (FWHM)
D: Deconvolution parameter (1.3)
f0 = 5.108673E-02
f1 = 1.058424E-04
f2 = 6.871481E-06
θ _c : Bragg angle correction value t0 = −3,000E-03
t1 = 5.119E-04
t2 = −3.599E-06

[5. BET specific surface area of lithium titanium composite oxide powder (m ² / g)]
The measurement of the BET specific surface area of the lithium titanium composite oxide powder of the present invention is performed by removing the carbonaceous material containing fibrous carbon by the method described in the above <specific surface area equivalent diameter D _{BET of the} lithium titanium composite oxide powder>. The lithium-titanium composite oxide powder was processed. About this lithium titanium complex oxide powder, the BET specific surface area was measured with the liquid nitrogen using the full automatic BET specific surface area measuring apparatus by the mount tech Co., Ltd., and the brand name "Macsorb HM model-1208".

[6. Specific surface area equivalent diameter of lithium titanium composite oxide powder (D _BET )]
The specific surface area equivalent diameter (D _BET ) was calculated from the following formula (2) on the assumption that all particles constituting the powder were spheres having the same diameter. Here, D _BET is the specific surface area equivalent diameter (μm), ρ _S is the true density of lithium titanate (g / cc), and S is [5. A BET specific surface area of the lithium-titanium composite oxide powder ^(m 2 / g)] measured BET specific surface area method described in ^(m 2 / g).
D _BET = 6 / (ρ _S × S) (2)

[7. (Average circularity)
The circularity is an index of sphericity when a particle is projected on a two-dimensional plane, and is an index instead of sphericity. In the present invention, for the secondary particles of the fibrous carbon-containing lithium titanate powder of the present invention, the perimeter of the perfect circle having the same area as the measurement target particle is expressed as a percentage with respect to the perimeter of the measurement target particle. The value was determined as the circularity of each particle, and the average value was defined as the average circularity. The perimeter of the particles to be measured was determined by image processing of the SEM image, and the circularity was determined by the following equation (3). The average value of the circularity of 50 particles was defined as the average circularity.
Circularity = (perimeter of a perfect circle having the same area as the particle to be measured) / (perimeter of the particle to be measured) × 100 (%) (3)

[8. Thermogravimetric analysis (TG)]
The carbon content (mass%) of the fibrous carbon-containing lithium titanium composite oxide powder of the present invention was measured by thermogravimetric analysis described below. Using a differential thermothermal gravimetric simultaneous measurement device (HITACHITG / DTA7300), differential thermal-thermogravimetric simultaneous analysis (TG-DTA) is performed under the following test conditions, and the fibrous carbon-containing lithium titanium composite oxide of the present invention The carbon content (mass%) of the powder was determined.
<Test conditions>
Atmosphere: Air Temperature rising rate: 20 ° C / min Measuring temperature: Room temperature to 900 ° C

[9. X-ray photoelectron spectroscopy (XPS)]
As an index instead of the carbon content of the particle surface of the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, the carbon and titanium atoms are analyzed by X-ray photoelectron spectroscopy for the fibrous carbon-containing lithium titanium composite oxide powder. The ratio (carbon / titanium) was measured. Measurement of the atomic ratio of carbon to titanium (carbon / titanium) by X-ray photoelectron spectroscopic analysis was performed using the PHI1800 type X-ray photoelectron spectrometer manufactured by ULVAC-PHI under the following test conditions.
<Test conditions>
X-ray source: AlKα 400W
Analysis area: 2.0mm x 0.8mm

[10. (Average compressive strength of secondary particles)
The compression test of spherical secondary particles was performed under the following test conditions using a Shimadzu micro compression tester MCT-510.
<Test conditions>
Test indenter: FLAT50
Measurement mode: Compression test Test force: 4.9 [mN]
Load speed: 0.0446 [mN / sec]

And the compressive strength (Cs [MPa]) of the spherical secondary particle was computed by the following formula | equation (4).
Cs = 2.48P / πd ² (4)
P: Test force [N], d: Particle diameter (mm)

  In the present embodiment, among the obtained spherical secondary particles, the above-described measurement is performed on 10 secondary particles having a particle diameter within ± 3 μm of D50 (μm), and the average value of the measured values is determined as the spherical secondary particle. The average compressive strength of the particles was used.

[11.1-Methyl-2-pyrrolidone oil absorption]
The N-methylpyrrolidone oil absorption amount of the fibrous carbon-containing lithium titanium composite oxide powder of the present invention was based on JIS K6217-4 (2008) using NMP (1-methyl-2-pyrrolidone) as a reagent liquid. Measured by the method.

[12. Electrolyte solution retention rate of electrode mixture layer)
The electrolyte solution retention rate of the electrode mixture layer of the electrode sheet of the present invention was measured as follows. The electrode sheet was cut into a size of 16 mmφ and immersed in a non-aqueous electrolyte {1M LiPF ₆ / PC} at room temperature for 10 minutes. Thereafter, removed electrode sheet from a non-aqueous electrolyte solution {1M LiPF ₆ / PC}, quiet non-aqueous electrolyte adhering to the surface {1M LiPF ₆ / PC} so as not to damage the electrode hygroscopic nonwoven The mass of the non-aqueous electrolyte {1M LiPF ₆ / PC} remaining in the electrode mixture layer was measured and converted into a volume. The electrolyte solution retention rate was calculated by dividing the volume of the non-aqueous electrolyte remaining in the electrode mixture layer by the volume of the electrode mixture layer as a percentage as shown in the following formula (5). .
Electrolyte solution retention rate (%) = volume of nonaqueous electrolyte solution {1M LiPF ₆ / PC} (residual in electrode mixture layer) (cm ³ )) / (volume of electrode mixture layer (cm ³ )) × 100 (5)

Example 1
<Preparation of raw material slurry of lithium titanate>
Li ₂ CO ₃ (average particle size: 4.6 μm) and TiO ₂ (specific surface area: 9.2 m ² / g), which are raw materials of lithium titanate, were changed to an atomic ratio Li / Ti: 0.83 of Li to Ti. A slurry was prepared by adding ion-exchanged water to a solid content concentration of 41% by mass and stirring with 0.1% by mass of polyvinyl alcohol (PVA) with respect to TiO ₂ . This slurry is made into a bead mill (made by Willy et Bacofen, model: dyno mill KD-20BC, agitator material: polyurethane, vessel inner surface material: zirconia, bead material: zirconia, bead outer diameter: 0.65 mm, filled with beads in the vessel. Rate: 80% by volume), pulverizing and mixing while controlling the internal pressure of the vessel to be 0.03 MPa or less under the conditions of an agitator peripheral speed of 13 m / sec and a slurry feed speed of 55 kg / hr. A raw material slurry of lithium acid was prepared. It was 0.9 micrometer when D95 was measured with the laser diffraction and scattering type particle size distribution measuring machine about the obtained raw material slurry of lithium titanate.

<Synthesis of multi-walled carbon nanotubes>
In ion-exchanged water, cobalt nitrate [Co (NO ₃ ) ₂ .6H ₂ O: molecular weight 291.03], magnesium nitrate [so that the molar ratio of metal elements is Co: Mg: Al = 8: 66: 26 Mg (NO ₃ ) ₂ · 6H ₂ O: molecular weight 256.41] and aluminum nitrate [Al (NO ₃ ) ₃ · 9H ₂ O: molecular weight 375.13] were dissolved and mixed under stirring under basic conditions. Thereafter, the produced precipitate was filtered, washed and dried. After heating this to 500 degreeC and baking for 1 hour, it grind | pulverized in the mortar and the catalyst with the spinel structure by substitution solid solution was acquired. Next, a quartz wool support was provided in the quartz reaction tube, and a catalyst was sprayed thereon. After heating the temperature in the tube to 550 ° C. in a He atmosphere, a mixed gas composed of CO and H ₂ (volume ratio: CO / H ₂ = 99.0 / 1.0) is used as a raw material gas from the bottom of the reaction tube. A multi-walled carbon nanotube was obtained by flowing at a flow rate of 28 L / min for 7 hours. The obtained multi-walled carbon nanotubes had a yield of 15 times the mass of the catalyst.

<Preparation of multi-walled carbon nanotube slurry>
The obtained multi-walled carbon nanotube, carboxymethylcellulose (CMC) and ion-exchanged water were prepared and stirred so as to have a mass ratio of 1.0: 0.8: 98.2 to prepare a slurry. Using this slurry, beads made of zirconia (outer diameter: 1.0 mm) are vesseld using a bead mill (made by Iwata Tekko Co., Ltd., model: PICOMILL PCM-LR type, agitator material: silicon nitride, vessel inner surface material: zirconia). The mixture was pulverized while controlling the internal pressure of the vessel to be 0.06 MPa or less at an agitator peripheral speed of 8 m / sec and a slurry feed speed of 30 to 50 ml / min.

<Preparation of mixed slurry>
Next, the lithium titanate raw material slurry and the multi-walled carbon nanotube slurry are mixed so that the mass ratio of the lithium titanate raw material and the multi-walled carbon nanotube is 99.5: 0.5, so that the solid content is 15%. Ion exchange water was added to and mixed and stirred. Using this slurry, beads made of zirconia (outer diameter: 0.65 mm) using a bead mill (manufactured by Willy et Bacofen, model: dyno mill KD-20BC type, agitator material: polyurethane, vessel inner surface material: zirconia). Was mixed in 80% by volume of the vessel, at an agitator peripheral speed of 13 m / sec, and a slurry feed speed of 55 kg / hr, while controlling the internal pressure of the vessel to be 0.05 MPa or less.

<Spraying and granulation by spray drying method>
The obtained mixed slurry was sprayed and dried with a two-fluid nozzle spray dryer to obtain a granulated powder. Using a spray dryer “P260TN-31HOP” manufactured by Pris, the mixture was spray-dried at an inlet temperature of 235 ° C., an outlet temperature of 110 ° C., a spray pressure of 0.5 MPa, and a slurry supply rate of 50 kg / hour to obtain granulated powder.

<Baking>
The obtained granulated powder is introduced into the furnace core tube from the raw material supply side of a rotary kiln type firing furnace (furnace core tube length: 4 m, furnace core tube diameter: 30 cm, external heating type) equipped with an adhesion prevention mechanism, and a nitrogen atmosphere Dried in and fired. At this time, assuming that the inclination angle from the horizontal direction of the core tube is 2 degrees, the rotation speed of the core tube is 20 rpm, the flow rate of nitrogen introduced into the core tube from the fired product collection side is 20 L / min, and the heating temperature of the core tube is The raw material supply side: 860 ° C., the central part: 860 ° C., the fired product collection side: 860 ° C., and the residence time of the fired product in the heating zone was 26 minutes. Thereafter, the fired product collected from the fired product recovery side of the furnace core tube was sieved (mesh roughness: 75 μm), and the fibrous carbon-containing lithium titanate powder that passed through the sieve was collected.

  The physical properties of the obtained fibrous carbon-containing lithium titanium composite oxide powder were measured by the methods described in [Methods for measuring various physical properties]. The production conditions (including D95 of the raw material mixture) of the above Example 1 and the physical properties of the fibrous carbon-containing lithium titanium composite oxide powder are shown in Tables 1 and 2 together with other examples and comparative examples. In addition, AB in a table | surface is acetylene black.

<Preparation of non-aqueous electrolyte for characteristic evaluation>
The non-aqueous electrolyte used for the battery for evaluating the characteristics was prepared as follows. A nonaqueous solvent of ethylene carbonate (EC): propylene carbonate (PC): methyl ethyl carbonate (MEC): dimethyl carbonate (DMC) (volume ratio) = 10: 20: 20: 50 was prepared, and LiPF was used as an electrolyte salt thereof. ₆ was dissolved to a concentration of 1M and LiPO ₂ F ₂ to a concentration of 0.05M to prepare a non-aqueous electrolyte.

<Production of evaluation electrode sheet>
95% by mass of the fibrous carbon-containing lithium titanium composite oxide powder of Example 1 as an active material, 2% by mass of acetylene black (third conductive additive), and 3% by mass of polyvinylidene fluoride (binder) A paint containing a proportion was prepared as follows. Polyvinylidene fluoride, acetylene black, and 1-methyl-2-pyrrolidone solvent previously dissolved in a 1-methyl-2-pyrrolidone solvent are mixed with a planetary stirring deaerator, and then a fibrous carbon-containing lithium titanium composite oxide. The powder was added, and a 1-methyl-2-pyrrolidone solvent was further added to adjust the total solids concentration to 56% by mass, and the mixture was mixed with a planetary stirring deaerator to prepare a paint. The obtained paint was applied onto an aluminum foil and dried to prepare an evaluation electrode single-sided sheet. Moreover, the obtained coating material was apply | coated on both surfaces of the aluminum foil, it was made to dry and the evaluation electrode double-sided sheet was produced.

<Production of coin battery>
The evaluation electrode single-sided sheet was punched into a circle having a diameter of 14 mm, pressed, and then vacuum-dried at 120 ° C. for 5 hours to prepare an evaluation electrode. At this time, the thickness of the mixture layer on one side was 32 μm, and the amount of the mixture was 70 g / m ² . The evaluation electrode and metal lithium (formed in a circular shape having a thickness of 0.5 mm and a diameter of 16 mm) face each other through a glass filter (two layers of Whatman GA-100 and GF / C) for evaluation. The 2030 type coin-type battery was produced by adding and sealing the said non-aqueous electrolyte for characteristic evaluation prepared for batteries, respectively.

<Measurement of initial charge / discharge efficiency (room temperature)>
In a constant temperature bath at 25 ° C., a current of 0.2 mA / cm ² is obtained by charging the coin-type battery manufactured by the method described in <Preparation of Coin Battery> with the direction in which Li is occluded in the evaluation electrode. was charged with a density up to 1V, after further charge current at 1V makes a constant-current constant-voltage charge for charging to a current density of 0.05 mA / cm ^2, to 2V at a current density of 0.2 mA / cm ² A constant current discharge was performed. The discharge capacity at this time was defined as the initial discharge capacity (mAh / g). The results are shown in Table 2.

<Preparation of counter electrode sheet>
In the same production method as in <Preparation of Evaluation Electrode Sheet>, 90% by mass of lithium cobaltate powder, 5% by mass of acetylene black (conductive aid), and polyvinylidene fluoride (binder) are used as active materials. A paint containing 5% by mass was prepared, applied onto an aluminum foil and dried, and then applied to the opposite surface and dried to prepare a counter electrode double-sided sheet.

<Production of laminated battery>
The evaluation electrode double-sided sheet was pressed to a predetermined electrode density, punched out, and a negative electrode having a mixture layer having a lead wire connecting portion of 4.2 cm in length and 5.2 cm in width was produced. At this time, the thickness of the mixture layer on one side was 32 μm, and the amount of the mixture was 70 g / m ² . After pressing the counter double-sided sheet, punching was performed to prepare a positive electrode having a mixture layer having a lead wire connecting portion of 4 cm in length and 5 cm in width. At this time, the thickness of the mixture layer on one side was 40 μm, and the amount of the mixture was 68 g / m ² . The prepared negative electrode and positive electrode are opposed to each other through a separator made of a microporous polyethylene film, laminated, the aluminum foil lead wires are connected together with the positive and negative electrodes, and the non-aqueous electrolyte for property evaluation is added to each of the aluminum laminates. The laminate type battery for gas generation evaluation after the 45 ° C. charge / discharge cycle and the charge / discharge cycle was produced by vacuum-sealing. The capacity of this laminated battery was 200 mAh, and the ratio of the negative electrode to positive electrode capacity (negative electrode capacity / positive electrode capacity ratio) was 1.1.

<Cycle test and measurement of gas generation>
In a constant temperature bath at 25 ° C., the laminated battery produced by the method described in <Preparation of laminated battery> above is charged to 2.75 V at 40 mA, and the charging current is further adjusted to 10 mA at 2.75 V. After performing constant-current constant-voltage charging until charging was performed, constant-current discharging for discharging to 1.4 V at a current of 40 mA was performed for three cycles. The laminate battery was taken out from the thermostat and the volume of the laminate battery (volume of the laminate battery before the cycle test) was measured by Archimedes method. Thereafter, the temperature of the thermostatic chamber is set to 45 ° C., the battery is charged up to 2.75 V at 200 mA, and further charged to 2.75 V until the charging current becomes 10 mA, and then the constant current and constant voltage charging is performed. 500 cycles of constant current discharge for discharging to 1.4 V with current were performed. The discharge capacity at the first cycle was divided by the discharge capacity at the 500th cycle to calculate a 500 cyc discharge capacity retention rate [45 ° C.]. Then, the temperature of the thermostat was set to 25 ° C. and stored for 1 hour. Next, the laminate battery was taken out from the thermostat, and the volume of the laminate battery (the volume of the laminate battery after storage) was measured by the Archimedes method. The gas generation amount [45 ° C.] was calculated by subtracting the volume of the laminate battery before the cycle test from the volume of the laminate battery after the cycle test. The results are shown in Table 2.

  The characteristics evaluation results of the laminate type battery using the fibrous carbon-containing lithium-titanium composite oxide powder of Example 1 as an electrode sheet as described above, and the carbon-containing lithium-titanium composite oxide powders of other examples and comparative examples as electrodes. It shows in Table 2 together with the characteristic evaluation result of the lithium ion secondary battery (laminated battery) used for the sheet.

(Examples 2 to 4)
The mixed slurry was prepared by changing the addition ratio of the multi-walled carbon nanotubes as fibrous carbon to the ratio shown in Table 1, and for Examples 2 and 3, the D95 of the lithium titanate raw material is the value shown in Table 1. The fibrous carbon-containing lithium titanate powders of Examples 2 to 4 were obtained in the same manner as in Example 1 except that a raw material slurry of lithium titanate was prepared so as to be. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Example 5)
As shown in Table 1, instead of polyvinyl alcohol, the same amount of ammonium polycarboxylate was used as a dispersant, so that the lithium titanate raw material D95 had the value shown in Table 1 as shown in Table 1. A fibrous carbon-containing lithium titanate powder of Example 5 was obtained in the same manner as in Example 2 except that the raw material slurry was prepared. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Example 6)
Example 2 with the exception that the raw material slurry of lithium titanate was prepared using TiO ₂ having a specific surface area shown in Table 1 so that D95 of the raw material of lithium titanate had the value shown in Table 1 as the titanium raw material. A fibrous carbon-containing lithium titanate powder of Example 6 was obtained in the same manner. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Example 7)
Except for changing the addition ratio of multi-walled carbon nanotubes as fibrous carbon to the ratio shown in Table 1 and preparing a mixed slurry, and changing the maximum temperature during firing of the granulated powder to the temperature shown in Table 1 A fibrous carbon-containing lithium titanate powder of Example 7 was obtained in the same manner as in Example 6. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Examples 8 and 9)
Except that the lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the value shown in Table 1, and that the maximum temperature during firing of the granulated powder was changed to the temperature shown in Table 1 The fibrous carbon-containing lithium titanate powders of Examples 8 and 9 were obtained in the same manner as in Example 1. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Example 10)
The lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the value shown in Table 1, multi-walled carbon nanotubes, acetylene black, CMC and ion-exchanged water in a mass ratio of 0.00. 5: 0.5: 0.8: 98.2 Prepared and stirred to prepare a multi-walled carbon nanotube slurry containing acetylene black, a raw material slurry of lithium titanate, and a multi-layer containing acetylene black In the carbon nanotube slurry, the mass ratio of the lithium titanate raw material, the multi-walled carbon nanotube, and acetylene black is “the raw material of lithium titanate: the total of the multi-walled carbon nanotube and acetylene black” = 99.0: 1.0. The same as in Example 1 except that a mixed slurry was prepared by mixing In to obtain a carbon fiber-containing lithium titanate powder of Example 10. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Examples 11 and 12)
The lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the value shown in Table 1, multi-walled carbon nanotubes and acetylene black were mixed in the proportions shown in Table 1, respectively, and titanium The lithium titanate raw material slurry and the multi-walled carbon nanotube slurry containing acetylene black, the mass ratio of the lithium titanate raw material, multi-walled carbon nanotubes and acetylene black is “lithium titanate raw material: multi-walled carbon nanotubes and acetylene black The fibrous carbon-containing lithium titanate powders of Examples 11 and 12 were obtained in the same manner as in Example 10 except that a mixed slurry was prepared by mixing so that “total” = 99.0: 1.0. It was. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Example 13)
The fibrous carbon-containing lithium titanate powder of Example 13 was prepared in the same manner as in Example 2 except that the lithium titanate raw material slurry was prepared so that D95 of the lithium titanate raw material had the value shown in Table 1. Obtained. An electrode sheet and a laminate battery using the same were prepared in the same manner as in Example 1 except that the addition ratio of acetylene black as the third conductive additive was changed to the ratio shown in Table 1.

(Examples 14 to 17)
Using the fibrous carbon-containing lithium titanate powder prepared in Example 1, the addition ratio of acetylene black as the third conductive additive was changed to the ratio shown in Table 1, and the electrode mixture of the evaluation electrode sheet An electrode sheet and a laminate battery using the same were produced in the same manner as in Example 1 except that the density was changed to the values shown in Table 1.

(Example 18)
The lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the value shown in Table 1, and the addition ratio of the multi-walled carbon nanotubes as fibrous carbon was changed to the ratio shown in Table 1. The fibrous carbon-containing lithium titanate powder of Example 18 was prepared in the same manner as in Example 1 except that the mixed slurry was prepared and the maximum temperature at the firing of the granulated powder was changed to the temperature shown in Table 1. Obtained. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 1)
Lithium titanate raw material Li ₂ CO ₃ (average particle size: 4.6 μm) and TiO ₂ (specific surface area: 9.2 m ² / g) were mixed and stirred to pulverize using a bead mill -The fibrous carbon containing lithium titanate powder of the comparative example 1 was obtained by the method similar to Example 2 except not having mixed. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 2)
Using the TiO ₂ having a specific surface area shown in Table 1 as the titanium raw material, the lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the value shown in Table 1, and the granulated powder, The same as in Example 2 except that it was filled in a high-purity alumina sagger, heated using a muffle-type electric furnace at a heating rate of 200 ° C./hour, held under the conditions shown in Table 1, and fired. Thus, fibrous carbon-containing lithium titanate powder was obtained. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 3)
Except that the lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the value shown in Table 1, and that the maximum temperature during firing of the granulated powder was changed to the temperature shown in Table 1 A fibrous carbon-containing lithium titanate powder of Comparative Example 3 was obtained in the same manner as in Example 2. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 4)
The rotary kiln-type firing furnace used in Example 1 was prepared by mixing the raw material slurry of lithium titanate prepared in the same manner as in Example 1 with a conductive agent slurry such as a multi-walled carbon nanotube slurry, and neither spraying nor granulating. Was introduced into the furnace tube from the raw material supply side, dried and fired under the same conditions as in Example 1. Thereafter, the fired product collected from the fired product recovery side of the furnace core tube was pulverized to collect lithium titanate powder.
Next, the collected lithium titanate powder is mixed with 0.1% by weight of polyvinyl alcohol (PVA) with respect to lithium titanate, and ion-exchanged water is added so as to have a solid content concentration of 40% by weight. Produced. Preparation of the mixed slurry of Example 1 so that the mass ratio of the lithium titanate and the multi-walled carbon nanotube is 99: 1.0 with this slurry and the multi-walled carbon nanotube slurry prepared under the same conditions as in Example 1. The same bead mill as that used in the above was used and mixed and stirred under the same conditions as in the preparation of the mixed slurry of Example 1. The obtained mixed slurry composed of lithium titanate and multi-walled carbon nanotubes was spray-dried under the same conditions as in Example 1 using the same spray dryer as in Example 1, and lithium titanate and multi-walled carbon nanotubes were A granulated powder consisting of Thereafter, the recovered granulated powder was sieved in the same manner as in Example 1, and the powder that passed through the sieve was collected to obtain the fibrous carbon-containing lithium titanate powder of Comparative Example 4. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 5)
The lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the value shown in Table 1, and the granulated powder was filled in a high-purity alumina sagger, and a muffle-type electric furnace was installed. The fibrous carbon-containing lithium titanate powder was obtained in the same manner as in Example 2 except that it was heated at a heating rate of 200 ° C./hour, held and fired under the conditions shown in Table 1. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 6)
The fibrous carbon-containing lithium titanate powder of Comparative Example 6 was prepared in the same manner as in Example 2 except that the mixed slurry was prepared by changing the addition ratio of multi-walled carbon nanotubes as fibrous carbon to the ratio shown in Table 1. Obtained. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 7)
As shown in Table 1, the fibrous carbon-containing lithium titanate powder of Comparative Example 7 was obtained in the same manner as in Example 2 except that single-walled carbon nanotubes were used instead of multi-walled carbon nanotubes as fibrous carbon. It was. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 8)
The lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material would be the value shown in Table 1, and the mixed slurry was directly sprayed and dried into the rotary kiln-type firing furnace without being sprayed or dried. A fibrous carbon-containing lithium titanate powder of Comparative Example 8 was obtained in the same manner as in Example 2 except that it was introduced, dried and fired.

(Comparative Example 9)
As shown in Table 1, without using fibrous carbon, only non-fibrous carbon acetylene black was used, and the mass ratio of the raw material of lithium titanate and acetylene black was 99.0: 1.0. Thus, the carbon-containing lithium titanate powder of Comparative Example 9 was obtained in the same manner as in Example 1 except that the mixed slurry was prepared. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

(Comparative Example 10)
A mass ratio of multi-walled carbon nanotubes synthesized by the same method as in Example 1, a dispersant made of a styrene-acrylic hydrophilic copolymer, a dispersant made of an acrylic hydrophobic polymer, and ion-exchanged water. Was mixed to be 1.0: 0.7: 0.1: 98.2 to prepare a multi-walled carbon nanotube slurry. This slurry was made into a bead mill (produced by Iwata Tekko Co., Ltd., model: PICOMILL PCM-LR type, agitator material: silicon nitride, vessel inner surface material: zirconia, bead material: zirconia, bead outer diameter: 1.0 mm, bead filling rate in vessel: 80 volume%), and pulverizing while controlling the internal pressure of the vessel to 0.06 MPa or less under the conditions of an agitator peripheral speed of 8 m / sec and a slurry feed speed of 30 to 50 ml / min. Thereafter, Li ₂ CO ₃ (average particle size: 4.6 μm) and TiO ₂ (specific surface area: 9.2 m ² / g), which are raw materials of lithium titanate, are used. The atomic ratio of Li to Ti Li / Ti: 0 .83, and mixed with the slurry of the multi-walled carbon nanotubes so that the mass ratio of the lithium titanate raw material to the multi-walled carbon nanotubes is 99.0: 1.0, so that the solid content becomes 15%. Ion exchange water was added as follows. This slurry is made into a bead mill (made by Willy et Bacofen, model: dyno mill KD-20BC type, agitator material: polyurethane, vessel inner surface material: zirconia, bead material: zirconia, bead outer diameter: 0.65 mm, filled with beads in the vessel. 80% by volume) and mixing under the conditions of an agitator peripheral speed of 13 m / sec and a slurry feed speed of 55 kg / hr while controlling the internal pressure of the vessel to be 0.05 MPa or less to prepare a mixed slurry did. A fibrous carbon-containing lithium titanate powder of Comparative Example 10 was obtained in the same manner as in Example 1 except that the mixed slurry was prepared as described above. In the same manner as in Example 1, an electrode sheet and a laminate battery using the electrode sheet were produced.

  Table 2 shows the physical properties of the fibrous carbon-containing lithium titanate powders of Examples 2 to 13 and the comparative example, the physical properties of the electrode sheet using the powder, and the characteristics of the lithium ion secondary battery produced using the electrode sheet. As shown.

  If the fibrous carbon-containing lithium titanate powder of the present invention is used, an electricity storage device having excellent charge / discharge cycle characteristics under a high temperature environment and a small amount of gas generated after the charge / discharge cycle can be obtained. Therefore, the fibrous carbon-containing lithium titanate powder of the present invention is a power storage device that is strongly required not to deteriorate in performance over a long period of time, particularly in a hybrid electric vehicle, a plug-in hybrid electric vehicle, a battery electric vehicle and the like. It is suitable as an electrode material.

Claims (16)

Including spherical secondary particles including primary particles made of lithium titanium composite oxide containing Li and Ti, and fibrous carbon having an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000, and the average circularity is 90% or more fibrous carbon-containing lithium titanium composite oxide powder,
The mass ratio of carbon to the mass of the lithium titanium composite oxide powder calculated from the thermogravimetric analysis in the fibrous carbon-containing lithium titanium composite oxide powder is A, and the percentage notation of A is a (mass%). And when the atomic ratio of carbon to titanium (carbon / titanium) calculated from measurement by X-ray photoelectron spectroscopy is B, a is 0.1 to 3% by mass,
B / A is 90-200,
A fibrous carbon-containing lithium titanium composite oxide powder for an electrode of an electricity storage device, wherein the spherical secondary particles have an average compressive strength of 1 to 25 MPa. 2. The fibrous carbon-containing lithium titanium composite oxide powder for an electrode of an electricity storage device according to claim 1, wherein the lithium titanium composite oxide is lithium titanate containing Li ₄ Ti ₅ O ₁₂ as a main component.   The fibrous carbon-containing lithium-titanium composite oxide powder for an electrode of an electricity storage device according to claim 1 or 2, wherein the 1-methyl-2-pyrrolidone oil absorption is 55 ml / 100 g to 160 ml / 100 g. The fibrous carbon-containing electrode for an electricity storage device according to any one of claims 1 to 3, wherein a specific surface area equivalent diameter D _{BET of the} lithium titanium composite oxide powder is 0.03 µm to 0.6 µm. Lithium titanium composite oxide powder. A bell formed by stacking two to thirty bell-like structural units, each having the top of the fibrous carbon, the top of which has a closed graphite mesh surface, and the trunk of which the lower part is open, sharing a central axis A plurality of structural unit assemblies,
The said fibrous carbon is comprised when the said some bell-shaped structural unit aggregate | assembly is connected with a space | interval in a Head-to-Tail style, and is comprised, The fiber is comprised. A fibrous carbon-containing lithium titanium composite oxide powder for an electrode of an electricity storage device according to claim 1. Wherein the lithium-titanium composite oxide _powder, Li ₄ Ti of _{5 O 12} the crystallite diameter calculated from (111) plane Scherrer formula from the peak half width of when the _{D X, D X} is larger than 80 nm, The ratio of D _BET to D _X , D _BET / D _X (μm / μm), is 3 or less, and the fibrous carbon-containing lithium titanium for electrodes of the electricity storage device according to any one of claims 1 to 5 Complex oxide powder.   The said spherical secondary particle contains non-fibrous carbon, The fibrous carbon containing lithium titanium complex oxide powder for electrodes of the electrical storage device as described in any one of Claims 1-6 characterized by the above-mentioned. An electrode sheet of an electricity storage device having an electrode mixture layer on one side or both sides of a current collector,
The electrode sheet of the electrical storage device in which the said electrode mixture layer contains the fibrous carbon containing lithium titanium complex oxide powder for electrodes of the electrical storage device as described in any one of Claims 1-7. The electrolyte solution holding ratio of the electrode mixture layer is ^{0.7cm 3 / cm 3 ~1cm 3 /} cm 3, the electrode density of the electrode mixture layer is 1.9g ^/ cm ³ ~2.5g ^/ cm 3 The electrode sheet for an electricity storage device according to claim 8, wherein: Of the electrode mixture layer, the specific surface area determined by the BET method and ^{_{S E (m 2 / g)}} , the electrolyte solution holding ratio of the electrode mixture layer ^{(cm 3} / cm 3) when the _{L E,} the electrode sheet of the electric storage device according to claim 9, wherein L _E / _{S E} is characterized in that 0.2 to 0.3.   The electrical storage device containing the electrode sheet as described in any one of Claims 8-10.   The lithium ion secondary battery containing the electrode sheet as described in any one of Claims 8-10.   The hybrid capacitor containing the electrode sheet as described in any one of Claims 8-10. In a non-aqueous solvent containing one or more cyclic carbonates selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate, LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO The electric storage device according to claim 11, wherein a nonaqueous electrolytic solution in which an electrolyte salt containing at least one lithium salt selected from ₂ F) ₂ is dissolved is used. The non-aqueous electrolyte has a total electrolyte salt concentration of 0.5 M or more and 2.0 M or less, and contains at least LiPF ₆ as the electrolyte salt, and further 0.001 M or more and 1.0 M or less of LiBF ₄ and LiPO _2. The electrical storage device according to claim 14, wherein the electrical storage device is a nonaqueous electrolytic solution containing at least one lithium salt selected from F ₂ and LiN (SO ₂ F) ₂ .   The non-aqueous electrolyte is one or more symmetrical chain carbonates selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl 16. The electricity storage device according to claim 14, further comprising one or more asymmetric chain carbonates selected from carbonate and ethylpropyl carbonate.