JP6809473B2 - Fibrous carbon-containing lithium-titanium composite oxide powder, electrode sheet using it, and power storage device using it - Google Patents

Description

The present invention comprises a fibrous carbon-containing lithium titanium composite oxide powder suitable as an electrode material for a power storage device, and an electrode sheet for a power storage device using the fibrous carbon-containing lithium titanium composite oxide powder as an electrode mixture layer. The present invention relates to a power 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 oxide can provide a power storage device having excellent input / output characteristics when used as an active material for a negative electrode, and therefore attracts attention as an active material material for a power storage device for electric vehicles such as HEVs, PHEVs, and BEVs. ing.

However, since lithium-containing oxides such as lithium-titanium composite oxides generally have low conductivity, a conductive agent such as a carbonaceous substance is added to these lithium-containing oxides for the purpose of improving the conductivity to form a composite. Has been proposed. Carbonaceous substances include powdered carbon such as graphite powder and acetylene black, and fibrous carbon such as carbon nanotubes (CNT) and carbon nanofibers (CNF). Fibrous carbon is conductive even with a small amount of addition. It is a material suitable as such a conductive agent because it can improve the properties. Further, if spherical secondary particles are formed from an active material in which a carbonaceous substance is compounded, the powder containing such spherical secondary particles is suitable as an electrode material because it is easy to slurry and coat. .. Therefore, the 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 a power storage device.

Although it is a prior art relating to a lithium-containing oxide containing no Ti, Patent Document 1 discloses a composite material for a positive electrode composed of spherical secondary particles containing lithium manganate particles and carbon nanotubes (CNTs). The lithium ion battery to which this positive electrode composite material was applied aggregated with the positive electrode composite material composed of spherical secondary particles composited 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.

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

In this way, fibrous carbon is composited with the lithium-titanium composite oxide to form a powder containing spherical secondary particles, which is used as a negative electrode material to improve the conductivity of the negative electrode and input / output of the power storage device. The characteristics are further improved.

Japanese Patent No. 5377946 Japanese Unexamined Patent Publication No. 2014-29863

On the other hand, when lithium-titanium composite oxide is used as a negative electrode active material for a power storage device for an electric vehicle, for example, lithium titanate charges and discharges Li metal at a voltage as high as 1 V or more, so that it is rapidly charged. However, while it has the advantage that lithium metal does not easily precipitate, it has the disadvantage that the energy density is theoretically low. Therefore, when a lithium titanium composite oxide such as lithium titanate is used as a negative electrode active material, there is a demand for increasing the density of the electrode (negative electrode) as much as possible. However, if the press pressure at the time of electrode fabrication is simply increased to increase the density of the electrode mixture layer, problems such as a decrease in the capacity retention rate and a significant increase in the amount of gas generated when the charge / discharge cycle is performed at a high temperature occur. Therefore, it is difficult to apply the lithium-titanium composite oxide as an active material of a power storage device for an electric vehicle, which is strongly required not to deteriorate in performance for a long period of time, for example, 10 years or more.

Further, when a powder containing spherical secondary particles (granular composite) containing a lithium titanium composite oxide and fibrous carbon as disclosed in Patent Document 2 is used as a negative electrode material, a power storage device is inserted. 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 generated after the above-mentioned high-temperature charge / discharge cycle become more remarkable.

Therefore, the present invention uses a carbon-containing lithium-titanium composite oxide powder having excellent charge / discharge cycle characteristics in a high temperature environment and a small amount of gas generated after the charge / discharge cycle, an electrode sheet of a power storage device containing the powder, and the electrode sheet thereof. An object of the present invention is to provide a power storage device.

As a result of examining the above-mentioned 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 a power storage device. One of the causes of the decrease in capacity retention rate and the increase in gas generation amount after the high temperature charge / discharge cycle in such a power storage device is that fibrous carbon aggregates and localizes near the surface of spherical secondary particles. I found out that there was something. On the other hand, the particle size distribution of the raw material of the lithium-titanium composite oxide is set to a specific value or less, mixed with fibrous carbon, granulated into spheres, and fired to perform fibrous carbon-containing lithium-titanium composite oxidation. It has been found that by preparing a product powder, localization due to aggregation of the fibrous carbon can be eliminated.

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

(1) Spherical secondary particles containing primary particles made of a 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 and averaged. A fibrous carbon-containing lithium titanium composite oxide powder having a circularity of 90% or more, which is a lithium titanium composite oxide powder calculated from measurement by thermal weight analysis in the fibrous carbon-containing lithium titanium composite oxide powder. The mass ratio of carbon to the mass of A was defined as A, the percentage notation of A was defined as a (mass%), and the atomic ratio of carbon to titanium (carbon / titanium) calculated from the measurement by X-ray photoelectron spectroscopy was defined as B. For electrodes of power storage devices, characterized in that 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. Fibrous carbon-containing lithium titanium composite oxide powder.

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

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

(4) the specific surface area equivalent diameter _{D BET} of lithium-titanium composite oxide powder is characterized in that it is a 0.03~0.6μm (1) ~ (3) either electrode fibrous carbon of the electric storage device Containing lithium titanium composite oxide powder.

(5) The fibrous carbon is formed by stacking 2 to 30 bell-shaped structural units having a crown having a closed graphite mesh surface and an open body at the lower part, sharing a central axis. The fibrous carbon is composed of a plurality of the bell-shaped structural unit aggregates formed by connecting the plurality of the bell-shaped structural unit aggregates at intervals in a Head-to-Tail manner to form fibers. (1) to (4) A fibrous carbon-containing lithium titanium composite oxide powder for an electrode of a power storage device.

(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 _larger, and wherein the _{D BET} and _{D X} the ratio _{D BET / D X (μm /} μm) is 3 or less (1) to (5) one of the electrodes for fibrous carbon-containing lithium of the electric storage device Titanium composite oxide powder.

(7) A fibrous carbon-containing lithium titanium composite oxide powder for an electrode of any of (1) to (6), which is characterized in that the spherical secondary particles contain non-fibrous carbon.

(8) An electrode sheet of a power storage device having an electrode mixture layer on one side or both sides of a current collector, and the electrode mixture layer is a fibrous electrode for a power storage device according to any one of (1) to (7). Electrode sheet for power storage device containing carbon-containing lithium-titanium composite 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 / electrode sheet of the energy storage device, characterized in that cm is ³ (8).

(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} when the _electrode sheet of the electric storage device that L E / _{S E} is characterized in that 0.2 to 0.3 (9).

(11) A power storage device including any of the electrode sheets (8) to (10).

(12) A lithium ion secondary battery including any of the electrode sheets (8) to (10).

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

(14) 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 The power storage device according to (11), which uses a non-aqueous electrolyte solution in which an electrolyte salt containing at least one lithium salt selected from LiN (SO ₂ F) ₂ is dissolved.

(15) The non-aqueous electrolyte solution has a total electrolyte salt concentration of 0.5 M or more and 2.0 M or less, contains at least LiPF ₆ as the electrolyte salt, and further contains LiBF ₄ of 0.001 M or more and 1.0 M or less. , LiPO ₂ F ₂ , and LiN (SO ₂ F) _2, a non-aqueous electrolyte solution containing at least one lithium salt selected from (14).

(16) The non-aqueous electrolyte solution includes one or more symmetrical chain carbonates selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate, and methyl ethyl carbonate, methyl propyl carbonate, and methyl isopropyl carbonate. , Methylbutyl carbonate, and one or more asymmetric chain carbonates selected from ethylpropyl carbonate, according to (14) or (15).

According to the present invention, 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 generated after the charge / discharge cycle when applied as an electrode material of a power storage device, and the like. It is possible to provide an electrode sheet of a power storage device and a power storage device using the electrode sheet.

(Fibrous carbon-containing lithium titanium composite oxide powder)
The fibrous carbon-containing lithium titanium composite oxide powder of the present invention contains primary particles composed of lithium titanium composite oxide containing Li and Ti, and fibrous particles 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, which is obtained by thermal weight analysis of the fibrous carbon-containing lithium titanium composite oxide powder. Let A be the mass ratio of carbon to the mass of the lithium-titanium composite oxide powder calculated from the measurement, and let a (mass%) be the percentage notation of A, and the carbon and titanium calculated from the measurement by X-ray photoelectron spectroscopic analysis. When the atomic ratio (carbon / titanium) of is B, 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. It is a fibrous carbon-containing lithium titanium composite oxide powder for an electrode of a power storage device.

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). To the extent that the characteristics of the power storage device to which the fibrous carbon-containing lithium titanium composite oxide powder of the present invention is applied are not affected, components other than the spherical secondary particles, for example, fibrous carbon and lithium titanium composite oxidation Particles other than the spherical secondary particles, such as physical particles and fibrous carbon-containing lithium titanium composite oxide particles, may be included.

The spherical secondary particles contained in the fibrous carbon-containing lithium titanium composite oxide powder of the present invention are primary particles composed of a lithium titanium composite oxide containing Li and Ti (hereinafter, may be referred to as a lithium titanium composite oxide). And fibrous carbon. Hereinafter, these will be described in the order of lithium titanium composite oxide and its physical properties, fibrous carbon, spherical secondary particles and their physical properties, and 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 an oxide containing Li and Ti, and is not particularly limited as long as it is a compound applicable to an electrode of a power storage device. For example, a spinel structure may be used. Examples thereof include a lithium titanium oxide having a lithium titanium oxide and a ramsteride type lithium titanium oxide, and a lithium titanium composite oxide in which a part of these Li and Ti sites is substituted with another metal element may be used. The lithium titanium composite oxide of the present invention is preferably lithium titanate containing Li ₄ Ti ₅ O ₁₂ as a main component. When Li ₄ Ti ₅ O ₁₂ is applied as an active material to the electrodes of a power storage device, it is excellent in maintaining the crystal structure because the volume change due to the insertion and desorption of Li ions is small, and the deterioration due to the charge / discharge cycle is relatively small. .. In addition, since the potential for insertion and desorption of lithium ions is higher than that of carbon materials, it is known that precipitation of lithium metal at low temperature and reduction decomposition of solvent by negative electrode active material are suppressed, and safety is high. Has been done. Here, assuming that 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 among the peaks measured by the X-ray diffractometry is 100. , 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 It means that the value calculated by multiplying the intensity of the peak derived from the surface by 100/80 (corresponding to the intensity of the peak on the (002) surface of Li ₂ TiO ₃ ) is 5 or less. Further, the fact that Li ₄ Ti ₅ O ₁₂ is the main component does not necessarily mean that a perfect crystal of Li ₄ Ti ₅ O ₁₂ is used.

A peak derived from the (111) plane of Li ₄ Ti ₅ O ₁₂ obtained by X-ray diffraction measurement, a peak derived from the (101) plane of anatase-type titanium dioxide, a peak derived from the (110) plane of rutile-type titanium dioxide, and Li. The peaks derived from the (002) plane of ₂ TiO ₃ are the main peaks of each crystal phase. 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 The value calculated by multiplying by is used, and this 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 is that the main peak of Li ₂ TiO ₃ is used. 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 the peak derived from other constituent phases, so that the intensity corresponding to the main peak of Li ₂ TiO ₃ can be calculated more easily. 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, in the lithium titanate of the present invention, the atomic ratio Li / Ti of Li to Ti is 0.75. It is preferably ~ 0.90. Within this range, the proportion of Li ₄ Ti ₅ O ₁₂ in lithium titanate increases, and the initial charge / discharge capacity of the power storage device to which the lithium titanate of the present invention is applied as the electrode material increases. From this viewpoint, the atomic ratio Li / Ti is more preferably 0.77 or more, further preferably 0.78 or more, and particularly preferably 0.79 or more. Further, it is more preferably 0.89 or less, still more preferably 0.88 or less.

<Diameter equivalent to specific surface area of lithium titanium composite oxide powder D _BET >
The specific surface area equivalent diameter _DBET of the lithium titanium composite oxide powder of the present invention is the lithium titanium composite oxidation after removing the carbonaceous substance containing fibrous carbon from the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. It is the specific surface area equivalent diameter calculated from the specific surface area of the powder obtained by the BET method. The method for removing the carbonaceous substance is not particularly limited, but the carbonic substance 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 will do. As the means, it is preferable to perform heat treatment under the condition that the specific surface area of the lithium titanium composite oxide powder does not change in the coexistence of oxygen such as in the atmosphere, for example, heat treatment at 450 to 550 ° C. for 1 to 4 hours. ..

The specific surface area equivalent diameter _{D BET} of lithium-titanium composite oxide powder of the present invention is not particularly limited, is preferably 0.03Myuemu～0.6Myuemu. When the D _BET is 0.03 μm to 0.6 μm, the charge / discharge capacity of the power storage device can be further increased. However, in the present invention, the value of _DBET is not particularly limited to such a range. _Further, particularly preferred that _{D BET} is 0.03～0.4Myuemu, input characteristics of the electric storage device if this range is also improved.

<Crystallite diameter D _X of the lithium-titanium composite oxide powder>
In the present invention, the crystallite diameter calculated from Scherrer equation from the peak half width of the (111) plane of _Li 4 _Ti 5 _{O 12} of the lithium-titanium composite oxide powder and _{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 be suppressed 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. Note that the crystallite diameter D _X of the lithium-titanium composite oxide powder, unlike D _BET, since the presence of the carbonaceous material does not affect the measurement result, fibrous carbon-containing lithium-titanium composite in the present invention The measurement is performed on the oxide powder.

<The ratio of _{D BET} and _{D X} the lithium-titanium composite oxide powder _{D BET / D X (μm /} μm)>
The ratio _D BET / _{D X} of _{D BET} and _{D X} the lithium-titanium composite oxide powder of the present invention (μm / μm) is not particularly limited, is preferably 2 or less, not more than 1.5 Especially preferable. More D _{BET /} D _X is smaller, the input-output characteristic of the electric storage device fibrous carbon-containing lithium titanate powder of the present invention is applied as an electrode material can be further improved. 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 the charge / discharge cycle characteristics in a high temperature environment and the gas generation after the charge / discharge cycle cannot be improved. 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. Further, when the average aspect ratio of the fibrous carbon is less than 10, the effect of improving the conductivity is small. From the viewpoint of further enhancing the effect of improving the 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 it is not possible to effectively improve the charge / discharge cycle characteristics in a high temperature environment and effectively suppress the gas generation after the charge / discharge cycle. .. The average aspect ratio of 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 enhanced and the gas generation after the charge / discharge cycle can be further reduced. It is as follows. The 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 a fibrous carbon having this average diameter and average aspect ratio, and examples thereof include single-walled and multi-walled carbon nanotubes and carbon nanofibers. A particularly preferable fibrous carbon is described in JP-A-2012-46864, in which a bell-shaped structural unit having a crown having a closed graphite mesh surface and a body having an open lower portion share a central axis. A plurality of bell-shaped structural unit aggregates formed by stacking 2 to 30 layers are provided, and the plurality of bell-shaped structural unit aggregates are connected at intervals in a Head-to-Tail manner to form fibers. It is a fibrous carbon characterized by being composed of. When the fibrous carbon of the present invention is such a fibrous carbon of a particularly preferable 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 include the primary particles made of the above-mentioned lithium titanium composite oxide and fibrous carbon. The spherical secondary particles referred to here may have a shape in which the appearance of the secondary particles approximates a spherical shape, that is, a substantially spherical shape, and is not limited to a perfect spherical shape (true spherical shape). The spherical secondary particles of the present invention also include particles having a partially uneven shape and particles having a shape close to a spherical shape such as an elliptical spherical particle.

<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 power storage device in a high temperature environment can be improved, and the amount of gas generated after the charge / discharge cycle can be suppressed. Such an effect can be 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 localized even in the electrode mixture layer. It is presumed that this is because the contact area between the lithium-titanium composite oxides or between the lithium-titanium composite oxide and the fibrous carbon becomes large. 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, still more preferably 10 MPa or less. .. The method for measuring the average compressive strength of the spherical secondary particles will be described in 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-mentioned spherical secondary particles and has an average circularity of 90% or more. If the average circularity is less than 90%, the input / output characteristics of the power storage device to which it is applied deteriorate. The reason for this is that when the fibrous carbon-containing lithium titanium composite oxide powder is mixed with other electrode constituent materials to form a paint, the dispersibility of the fibrous carbon in the paint deteriorates, and in the electrode mixture layer. It is presumed that this is due to the localization of fibrous carbon. This is probably because the fibrous carbon and lithium-titanium composite oxide primary particles near the particle surface are likely to fall off from the distorted secondary particles with low circularity during coating. From the viewpoint of further enhancing the input / output characteristics of the power 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. It is preferable to have. The method for measuring the average circularity will be described in Examples described later.

<Carbon content calculated by thermogravimetric analysis and atomic ratio of carbon to titanium calculated by X-ray photoelectron spectroscopy in fibrous carbon-containing lithium titanium composite oxide powder>
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 the measurement by thermogravimetric analysis is defined as A, and the percentage notation of A is a (mass). %), And when the atomic ratio (carbon / titanium) of carbon to titanium measured by X-ray photoelectron spectroscopy is B, a is 0.1 to 3% by mass and B / A is 90 to 90 to It is 200. If a is smaller than 0.1% by mass, the electron conductivity of the fibrous carbon-containing lithium-titanium composite oxide powder is not sufficiently improved, so that a power 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 a power storage device having good charge / discharge cycle characteristics in a high temperature environment can be obtained. However, gas generation after the charge / discharge cycle is not suppressed. From the viewpoint of further enhancing the input / output characteristics and the charge / discharge cycle characteristics in a high temperature environment, the lower limit of a is more preferably 0.3% by mass, further preferably 0.5% by mass. Further, the upper limit of a is more preferably 2.5% by mass, further preferably 2% by mass. Further, even if the B / A is smaller than 90 or larger than 200, a power storage device having good charge / discharge cycle characteristics in a high temperature environment cannot be obtained, and gas generation after the charge / discharge cycle is not suppressed. From the viewpoint that the charge / discharge cycle characteristics can be further enhanced and the gas generation after the charge / discharge cycle can be further reduced, the lower limit of B / A is more preferably 100 and further preferably 110. Further, the upper limit of B / A is more preferably 190, and even more preferably 180. In the thermal weight analysis, the entire particles of the 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 indicates the carbon content in the entire spherical secondary particles. 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 contained in the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. Of the carbon and titanium that make up the particles, only the atomic ratio (carbon / titanium) of carbon and titanium located on the surface is measured, so B is an index that replaces the carbon content on the surface of the spherical secondary particles. Is. Then, the B / A in the present invention determines the atomic ratio (carbon / titanium) of carbon and titanium located on the surface of the carbon and titanium constituting the spherical secondary particles to be fibrous carbon-containing lithium titanium composite oxidation. It is a value divided by the carbon content (mass%) of the entire material powder, and is an index showing the ratio of the carbon content of the entire spherical secondary particles to the carbon content of the surface of the spherical secondary particles. The larger the B / A, the larger the carbon content on the surface of the spherical secondary particles as compared with the carbon content of the entire fibrous carbon-containing lithium-titanium composite oxide powder.

<D50 of fibrous carbon-containing lithium titanium composite oxide powder>
The D50 of the fibrous carbon-containing lithium titanium composite oxide powder is preferably 1 μm or more, more preferably 3 μm or more, from the viewpoint of powder handling. 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 a particle size in which the cumulative volume frequency calculated by the volume fraction is 50% in total from the smallest 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 an oil absorption of 1-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP) 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 power storage device in 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 amount in this range, and the electrolytic solution in the electrode mixture layer in which the fibrous carbon-containing lithium titanium composite oxide powder of the present invention is used for the power storage device. It is presumed that this is because the amount of liquid retained can be adjusted appropriately. From the viewpoint that the charge / discharge cycle characteristics in a high temperature environment can be further enhanced and the gas generation after the charge / discharge cycle can be further reduced, the lower limit of the NMP oil absorption amount 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 further preferably 145 ml / 100 g. Here, the unit of ml / 100 g represents the amount of NMP absorbed per 100 g of fibrous carbon-containing lithium titanium composite oxide powder (unit is ml). The amount of NMP oil absorbed can be adjusted by adjusting the specific surface area of the lithium titanium composite oxide powder, the addition ratio of fibrous carbon, and the like.

Further, 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 it has an effect of improving charge / discharge cycle characteristics particularly in a high temperature environment. Specifically, acetylene black, Ketjen black and the like are preferable.

(Manufacturing method of fibrous carbon-containing lithium titanium composite oxide powder)
The following is an example of the method for producing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, in the case where the lithium titanium composite oxide is lithium titanate, a raw material preparation step, a drying / granulation step, and firing. Although the description will be described separately for each step, the method for producing the fibrous carbon-containing lithium titanium composite oxide powder of the present 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, the D95 of the mixture is prepared in advance so as to be in a specific range, and then the mixture and the fibrous carbon are wet-mixed and the raw material mixed slurry (hereinafter referred to as “raw material mixed slurry”). (Sometimes abbreviated as mixed slurry) is prepared. The B / A of the obtained fibrous carbon-containing lithium titanate (lithium-titanium composite oxide) powder can be adjusted to 90 to 200 by drying, granulating, and calcining the mixed slurry prepared in this manner.

<Preparation process of lithium titanium composite oxide raw material>
As the raw material of 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 the titanium raw material, it is preferable that it easily reacts with the lithium raw material in a short time, and from this viewpoint, anatase-type titanium dioxide is preferable. In particular, complete anatase-type titanium dioxide having a rutileization rate 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, but 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 by a laser diffraction / scattering type particle size distribution measuring machine is 2 μm or less. .. As a result, a fibrous carbon-containing lithium titanate (lithium-titanium composite oxide) powder having a B / A of 90 to 200 can be obtained. Here, D95 is a particle size in which the cumulative volume frequency calculated by the volume fraction is 95% in total from the smallest particle size. The state of the mixture of the titanium raw material and the lithium raw material to be mixed with the fibrous carbon is preferably in the form of 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 adopted. The first method is a method in which the raw materials are mixed and then pulverized at the same time as mixing. The second method is a method in which each raw material is pulverized until the D95 after mixing becomes 2 μm or less, and then these are mixed or mixed while being lightly pulverized. The third method is a method in which each raw material is produced into a powder composed of fine particles by a method such as crystallization, classified as necessary, and these are mixed or mixed while being lightly pulverized. Among them, in the first method, the method of pulverizing at the same time as mixing the raw materials is an industrially advantageous method because there are few steps. Regardless of the method, it is desirable that the mixing is carried out in a wet manner, and it is desirable to use polyvinyl alcohol or an ammonium polycarboxylic acid salt as the dispersant at that time.
In the present invention, a fibrous carbon-containing lithium-titanium composite oxide powder containing spherical secondary particles in which localization of fibrous carbon is suppressed on the particle surface, specifically, a fiber having a B / A of 90 to 200. The fact that it has become possible to obtain a carbon-containing lithium-titanium composite oxide powder will be considered as follows.

When fibrous carbon is composited with a lithium titanium composite oxide containing lithium titanate to form spherical secondary particles, the fibrous carbon has conventionally 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 on the particle surface of the titanium raw material, and is agglomerated. There is a possibility that the affinity of the lithium raw material for fibrous carbon and the affinity of the titanium raw material are significantly different, which is considered to be the effect.

Further, in general, a lithium raw material has a significantly larger particle size than a titanium raw material and its specific surface area is very small. Therefore, in a slurry containing a raw material having such properties, the slurry is not crushed. Even if mixed by an efficient mixing means, a dispersant having a good dispersibility of fibrous carbon is used, or the mixing time is lengthened, the fibrous carbon is present on the particle surface of a small amount of lithium raw material. It tries to coagulate and exist. As a result, the proportion of fibrous carbon that comes into direct contact with the surface of the lithium raw material, which has a good affinity for 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 the dispersion medium inside the particles moves to the particle surface accordingly, and the solid granulated particles are formed while evaporating from the particle surface. In the case of the slurry in the above state, the dispersion medium moves from the inside of the particles to the particle surface, and the fibrous carbon having a small specific gravity and not in direct contact with the particle surface of the lithium raw material is agglomerated together with the dispersion medium. Will move toward the particle surface. In the granulated particles formed in this way, fibrous carbon is localized near the surface of the granulated particles. Then, even in the spherical secondary particles obtained by firing such granulated particles, the fibrous carbon is localized on the surface of the particles.

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 with which the fibrous carbon comes into direct contact increases, and the specific surface area increases, so that the fibrous carbon Can be dispersed and come into direct contact with the surface of the lithium raw material particles. As a result, the aggregation of fibrous carbon in the slurry is suppressed, and the proportion of fibrous carbon that comes into direct contact with the surface of the lithium raw material increases. When such a slurry is sprayed and dried, the movement of the fibrous carbon to the particle surface due to the movement of the dispersion medium to the particle surface is also suppressed. As a result, the localization of fibrous carbon on the particle surface is suppressed in both the granulated particles and the spherical secondary particles obtained by firing the particles.

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

<Preparation process of fibrous carbon>
The fibrous carbon used as a raw material may be any fibrous carbon having an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000 in the obtained spherical secondary particles of fibrous carbon-containing lithium titanate powder. .. In the step of mixing the mixture of the titanium raw material and the lithium raw material and the fibrous carbon, the fibrous carbon can be cut by adjusting the conditions, so that the fibrous carbon having an average aspect ratio of more than 1000 may be used. .. In the present invention, so-called carbon nanotubes (CNTs) and carbon nanofibers (CNFs) having an average diameter of 5 to 40 nm are preferably used. Among them, a set of bell-shaped structural units formed by stacking 2 to 30 layers of bell-shaped structural units having a crown with a closed graphite net surface and a body with an open lower part sharing a central axis. Japanese Patent Application Laid-Open No. 2012-46864, which comprises a plurality of bodies, wherein the plurality of bell-shaped structural unit aggregates are connected at intervals in a Head-to-Tail manner to form fibers. The fibrous carbon described in Examples and the like is particularly preferable. By using such fibrous carbon, it becomes easy to obtain fibrous carbon-containing lithium titanate powder having a B / A of 90 to 200.

Since fibrous carbon tends to aggregate, fibers having a large average aspect ratio at the same time as being opened and dispersed using a dispersant in a liquid dispersion medium before mixing the fibrous carbon with a mixture of a titanium raw material and a lithium raw material. In the case of carbon, it is preferable to pulverize (cut) and mix the slurry with a mixture of a titanium raw material and a lithium raw material.

Examples of the dispersant include surfactants such as polyvinyl alcohol, ammonium polycarboxylic acid salt, sodium oleate, polyoxyethylene carboxylic acid ester, monoalcohol ester, and ferrocene derivative, pyrene compound (pyreneammonium), and porphyrin compound (ZnPP, Hemin, PPEt), polyfluorene, cyclic glucan, folic acid, lactam compounds (-CONH-), lactone compounds (-CO-O-) and other cyclic / polycyclic aromatic compounds, polythiophene, polyphenylene vinylene, polyphenylene ethylene and the like. Encapsulation of linear conjugated polymers, cyclic amides such as polyvinylpyrrolidone (PVP), polystyrene sulfonic acid, polymer micelles, water-soluble pyrene-containing polymers, fructose, polysaccharides (carboxymethyl cellulose, etc.), saccharides such as amylose, lactam, etc. Examples thereof include complexes and cole acids relatives, and carboxymethyl cellulose and polyvinylpyrrolidone are particularly suitable when the dispersion medium is an aqueous solution system. The dispersant is preferably added in a mass ratio of 1/100 or more and 100/100 or less with respect to the aggregate of fibrous carbon. The dispersion medium is not particularly limited, but a polar solvent such as water or alcohol is usually used from the viewpoint of handling and solubility of the lithium compound. The opening and dispersion of the agglomerates of fibrous carbon is carried out by combining the dispersion medium, the dispersant, the agglomerates of fibrous carbon, etc. and stirring with a homomixer, a trimix, etc., but it is more effective. For this purpose, ultrasonic waves due to vibration shock waves, impacts of beads, balls, etc., bead mills using shaking, and paint shakers are used. In the case of fibrous carbon having a large average aspect ratio, a method having a relatively high crushing ability such as a bead mill is preferably adopted.

The fibrous carbon can also be oxidized before it is opened and dispersed in the liquid dispersion medium. By performing the oxidation treatment, the fibrous carbon becomes more compatible with the dispersion medium, and the dispersibility in lithium titanate of the present invention is further enhanced, so that the charge / discharge cycle characteristics in a high temperature environment and the gas after the charge / discharge cycle can be achieved. It is effective in suppressing the occurrence. As the oxidation treatment method, for example, liquid phase oxidation with nitric acid / sulfuric acid, ozone, supercritical water, supercritical carbon dioxide gas, etc., or hydrophilization treatment on the carbon fiber surface by atmospheric firing, gas phase oxidation with oxygen plasma, etc. There is a method of applying.

<Mixing process of a mixture of titanium raw material and lithium raw material and fibrous carbon>
Next, the mixture of the titanium raw material and the lithium raw material obtained by the above method and the fibrous carbon were added to the obtained fibrous carbon-containing lithium titanate (lithium-titanium composite oxide) powder in terms of carbon content (mass%). Is mixed at a desired ratio of 0.1 to 3% by mass to prepare a mixed slurry to be used in the drying / granulating 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, but as described above, the slurry of the mixture of the titanium raw material and the lithium raw material and the fibrous form It is preferable to mix with the carbon slurry, for example, it can be mixed by a method of stirring with a homomixer, a trimix or the like, or a method of using impact or shaking with a bead mill, a paint shaker or the like. 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 / granulation process]
Next, the obtained mixed slurry is dried and granulated. The drying / granulating method may be any method as long as it can obtain fibrous carbon-containing lithium titanate (lithium-titanium composite oxide) powder having an average circularity of 90% or more, but is usually spray-dried (spray-dried). ) Adopt the method. A granulated powder dried and granulated by a general spray drying method has a large average circularity, and even after firing, the average circularity is usually 90% or more.

Of these, the spray drying method using a two-fluid spray dryer is preferable, and in that case, the spray drying is performed at a temperature of 190 ° C. or higher, further 210 ° C. or higher, and the slurry feeding rate range is 0.1 L / L. It is preferably carried out at 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 small, the granulated powder becomes large, and when the air pressure is large, the granulated powder becomes small. The obtained granulated powder can be used as it is for the next firing step.

[Baking process]
Then, the obtained granulated powder is calcined. In order to make the average compressive strength of the spherical secondary particles of the fibrous carbon-containing lithium titanate (lithium-titanium composite oxide) powder 1 to 25 MPa, it is preferable to calcin the granulated powder at a high temperature and in a short time. From such a viewpoint, the maximum temperature at the time of 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 at the time of firing is preferably 720 ° C. or higher. , More preferably 750 ° C. or higher, and even more preferably 780 ° C. or higher. From the same viewpoint, the holding time at the maximum temperature at the time of 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 particularly preferable to shorten the residence time from 700 ° C. to the maximum temperature in the heating process during firing.

In the present invention, the average compressive strength of the spherical secondary particles can be adjusted to 1 to 25 MPa by firing the granulated powder at a high temperature for a short time as described above. If the firing time is lengthened, the average compressive strength of the spherical secondary particles tends to be larger than 25 MPa, and the average of the spherical secondary particles is simply obtained by mixing and granulating the pre-synthesized lithium titanate powder and fibrous carbon. The compression 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 firing furnace, and a rotary kiln type firing furnace. However, in the case of efficient firing in a short time, a roller hearth type firing furnace, a mesh belt type firing furnace, and a rotary kiln type firing furnace are preferable. When using a roller hearth type firing furnace or a mesh belt type firing furnace in which the granulated powder is placed in a saggar and fired, in order to keep the quality of the obtained lithium titanate constant, the granulated powder at the time of firing is used. It is preferable to make the temperature distribution uniform, and it is preferable to reduce the amount of the granulated powder contained in the sack.

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

The atmosphere during firing is preferably an inert atmosphere such as oxygen-free nitrogen or a rare gas so that fibrous carbon or non-fibrous carbon contained in some cases is not consumed or eliminated during firing.

(Electrode sheet)
Next, the electrode sheet of the present invention will be described. The electrode sheet of the power storage device of the present invention is an electrode sheet of the power 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 the current collector. It is cut according to the design shape of 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 auxiliary agent added at the time of forming the electrode mixture layer can be contained. In the following, for convenience, the fibrous carbon contained in the fibrous carbon-containing lithium titanium composite oxide powder is used as the first conductive auxiliary agent, and in some cases, the non-fibrous carbon contained is used as the second conductive auxiliary agent. The conductive auxiliary agent added at the time of forming the mixture layer may be referred to as a third conductive auxiliary agent.

<Electrolyte retention rate of electrode mixture layer and density of electrode mixture layer>
In the electrode sheet of the power storage device of the present invention, the electrolytic 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 . Is preferable. The electrolytic solution retention rate in the present invention is an electrode mixture when the electrode sheet is immersed in a non-aqueous electrolytic solution (hereinafter, 1M LiPF ₆ / PC) in which 1M of LiPF ₆ is dissolved in a propylene carbonate solvent. It is the ratio of the volume of the non-aqueous electrolyte solution impregnated in the layer to the volume of the electrode mixture layer. The method for measuring the electrolytic solution retention rate and the electrode mixture layer density of the electrode mixture layer will be described in Examples described later. When the electrolytic solution retention rate and the electrode mixture layer density of the electrode mixture layer are within this range, the energy density is improved and the electrolytic solution is easily infiltrated, that is, the Li insertion / desorption reaction is smooth. It progresses and is effective for charge / discharge cycle characteristics in a high temperature environment and suppression of gas generation after the charge / discharge cycle. By using the fibrous carbon-containing lithium-titanium composite oxide powder of the present invention and adjusting the amount of the third conductive additive added and the electrode density of the electrode mixture layer, the electrolytic solution retention of the electrode mixture layer is maintained. 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>}
Further, the electrode sheets of the electricity storage device of the present invention, 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 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 the S E _/ L _E In this range, the electrolyte solution holding amount of the electrode mixture layer is presumed to be due to adjusted is that the range suitable for obtaining these effects. S E _/ L _E can be adjusted in such fibrous carbon-containing lithium-titanium composite oxide powder as well as the specific surface area and amount of the third conductive additive of the present invention. The method for measuring the specific surface area of the electrode mixture layer will be described in Examples.

(Power storage device)
The power storage device of the present invention is a device that stores and releases energy by utilizing intercalation and deintercalation of lithium ions on an electrode containing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention. For example, a hybrid capacitor, a lithium battery, and the like can be mentioned.

[Hybrid capacitor]
The hybrid capacitor includes an active material whose capacity is formed on the positive electrode by physical adsorption similar to that of the electrode material of an electric double layer capacitor such as activated carbon, and physical adsorption and intercalation and deintercalation such as graphite. It is a device that uses an activated carbon whose capacity is formed by redox or an active material whose capacity is formed by redox such as a conductive polymer, and uses the fibrous carbon-containing lithium titanium composite oxide powder of the present invention for the negative electrode.

[Lithium battery]
The lithium battery of the present invention is a general term for a lithium primary battery and a lithium secondary battery. Further, in the present 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, a non-aqueous electrolytic solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and the like, and 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 side or both sides of the negative electrode current collector. The electrode mixture layer may further contain a third conductive auxiliary agent.

The third conductive auxiliary agent 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 (scaly graphite, etc.), graphite such as artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, single-walled carbon nanotubes, and multi-walled carbon nanotubes. (Graphite layer is multi-layered concentric cylindrical) (non-fishbone), cup-stacked carbon nanotubes (fishbone), node-shaped carbon nanofibers (non-fishbone structure), platelet-type carbon nanofibers ( Examples thereof include carbon nanotubes (trump-shaped) and the like. 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. If the specific surface area is less than 30 m ² / g, the contact area with the active material is reduced, so that 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, which makes it more difficult to improve the electrode density and is not suitable for increasing the volume of the mixture layer. The specific surface area of graphites is preferably 30 to 600 m ² / g, and more preferably 50 to 500 m ² / g. If the specific surface area is less than 30 m ² / g, the contact area with the active material is reduced, so that 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, which makes it more difficult to improve the electrode density and is not suitable for increasing the volume 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 in one fiber is improved, but the open end of the graphite mesh surface constituting the structural unit body is a fiber. Since the frequency of exposure to the outer peripheral surface is low, 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 body of the structural unit is frequently exposed to the outer peripheral surface of the fiber, so that the conductivity between adjacent fibers is improved, but the outer peripheral surface of the fiber is the fiber. Since a large number of short graphite mesh surfaces are connected in the axial direction, the conductivity in the fiber axial direction in one fiber is impaired.

The amount of the third conductive auxiliary agent added is optimized by the specific surface area of the active material and the type and combination of the conductive auxiliary agents, but is preferably 10% by mass or less with respect to the entire mixture layer, which is more preferable. 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, which is the first conductive auxiliary agent, and in some cases, non-fibrous carbon, which is the second conductive auxiliary agent, and is a third conductive auxiliary agent. Even if is not added, sufficient performance as a power storage device is exhibited.

Examples of the binder for the negative electrode include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), a copolymer of styrene and butadiene (SBR), and a common weight of acrylonitrile and butadiene. Coalescence (NBR), carboxymethyl cellulose (CMC) and the like can be mentioned. Although not particularly limited, the molecular weight of polyvinylidene fluoride is preferably 20,000 to 200,000. From the viewpoint of ensuring 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 auxiliary agent, 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 ensuring 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. .. The amount of the binder added should be 10% by mass or less from the viewpoint of suppressing the decrease in the active material ratio in the mixture layer and not reducing the unit mass of the mixture layer and the discharge capacity of the power storage device per unit volume. Is preferable, and 5% by mass or less is more preferable.

Examples of the negative electrode current collector include aluminum, stainless steel, nickel, copper, titanium, calcined carbon, and those whose surfaces are coated with carbon, nickel, titanium, and silver. Further, the surface of these materials may be oxidized, or the surface of the negative electrode current collector may be made uneven by surface treatment. In addition, examples of the form of the negative electrode current collector include a sheet, a net, a foil, a film, a punched body, a lath body, a porous body, a foam body, a fiber group, and a molded body of a non-woven fabric.

For the negative electrode, a solvent is added to the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, a binder, and if necessary, a third conductive auxiliary agent, and these are mixed and kneaded, and further the solvent is added. It can be obtained by adjusting the viscosity to form a paint, applying it on the negative electrode current collector, drying it, and compressing it.

The method for mixing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, the binder, and the third conductive auxiliary agent added as needed in the solvent is not particularly limited, but the present invention. The method of mixing the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, the conductive auxiliary agent and the binder at the same time in a solvent, and the fibrous carbon of the present invention after mixing the conductive auxiliary agent and the binder in the solvent in advance. A method of additionally mixing the contained 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 with each other. Can be mentioned. In order to uniformly disperse and exist these mixture layer constituent materials in the mixture layer, a method of mixing the conductive auxiliary agent and the binder in advance in a solvent and then additionally mixing the negative electrode active material and the negative electrode active material slurry It is preferable to prepare the conductive auxiliary agent slurry and the binder solution in advance and mix them.

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

When water is used as the solvent, it is preferable to add the binder at the stage of finally adjusting the viscosity to a desired value so that the binder does not aggregate. Further, when aluminum is used as the negative electrode current collector, if the pH of the paint is high, the aluminum is corroded. Therefore, it is preferable to add an acidic compound to reduce the pH to a pH at which corrosion does not occur. As the acidic compound, either an inorganic acid or an organic acid can be used. The inorganic acid is preferably phosphoric acid, boric acid, or oxalic acid, and more preferably oxalic acid. The organic acid is preferably an organic carboxylic acid. Further, as a method for preventing the 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.

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

As a device for adding a solvent to the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, a binder, and a third conductive auxiliary agent added as needed, and mixing and kneading, for example, a planetary mixer or the like. Use a kneader of the type in which the stirring rod rotates while rotating in the kneading container, a biaxial extrusion type 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 be done. Further, it is preferable to start mixing and kneading in a state where the solid content concentration is high and gradually reduce the solid content concentration to adjust the viscosity of the coating material. In that case, the viscosity is suitable according to the viscosity. It is preferable to use the mixing / kneading device properly. The solid content concentration at the stage of starting mixing / kneading is preferably 60 to 90% by mass, 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, a binder, and a third conductive auxiliary agent added as needed. It is difficult, and if it exceeds 90% by mass, the load of the device tends to increase.

<Positive electrode>
The positive electrode has a mixture layer containing a positive electrode active material, a conductive auxiliary agent, 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 occluding and releasing lithium is used, and as the active material, for example, a composite metal oxide with lithium containing cobalt, manganese, and nickel, a lithium-containing olivine-type phosphate, and the like are used. These positive electrode active materials can be used alone or in combination of two or more. Examples of such composite metal oxides include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3 Mn. Examples thereof include _1/3 O ₂ and LiNi _1/2 Mn _3/2 O ₄ , and some of these lithium composite oxides may be replaced with other elements, and some of cobalt, manganese, and nickel may be 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, it can be coated with a compound containing these other elements. The lithium-containing olivine phosphate is selected from, for example, LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ , LiFe _1-x M _x PO ₄ (M is Co, Ni, Mn, Cu, Zn, and Cd). There is at least one kind, and x is 0 ≦ x ≦ 0.5) and the like.

Examples of the conductive auxiliary agent and the 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, aluminum and stainless steel whose surface is surface-treated with carbon, nickel, titanium and silver. The surface of these materials may be oxidized, or the surface of the positive electrode current collector may be made uneven by surface treatment. In addition, examples of the form of the current collector include a sheet, a net, a foil, a film, a punched body, a lath body, a porous body, a foam body, a fiber group, and a molded body of a non-woven fabric.

<Non-aqueous electrolyte>
The non-aqueous electrolyte solution is a solution in which an electrolyte salt is dissolved in a non-aqueous solvent. The non-aqueous electrolytic solution is not particularly limited, and various ones 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 the like, 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 chain-like alkyl fluoride groups 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, lithium bis [oxalate-O, O'] lithium borate and difluoro [oxalate-O, O'] Examples thereof include a lithium salt having an oxalate complex such as 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 alone or in combination of two or more. Further, as a suitable combination of these electrolyte salts, LiPF ₆ is contained, and at least one lithium salt selected from LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO ₂ F) ₂ is contained in the non-aqueous electrolyte solution. It is preferable that it is contained in.

The concentration in which all the electrolyte salts are dissolved and used is usually preferably 0.3 M or more, more preferably 0.5 M or more, still more preferably 0.7 M or more, based on the above-mentioned non-aqueous solvent. The upper limit thereof 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, and include cyclic carbonates. Is preferable. 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, and 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 characteristic and reducing the amount of gas generated during high-temperature storage, and propylene carbonate, 1,2-. One or more cyclic carbonates having an alkylene chain selected from butylene carbonate and 2,3-butylene carbonate are more preferable. The proportion of the cyclic carbonate having an alkylene chain in the total cyclic carbonate is preferably 55% by volume to 100% by volume, more preferably 60% by volume to 90% by volume.

Therefore, the non-aqueous electrolyte solution is a non-aqueous solvent containing one or more cyclic carbonates selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate, and LiPF ₆ , LiBF ₄ , and so on. It is preferable to use a non-aqueous electrolyte 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 dissolved, and the cyclic carbonate includes propylene carbonate, 1, One or more cyclic carbonates having an alkylene chain selected from 2-butylene carbonate and 2,3-butylene carbonate are more preferable.

In particular, the total electrolyte salt concentration is 0.5 M or more and 2.0 M or less, and the electrolyte salt contains at least LiPF ₆ , and further 0.001 M or more and 1 M or less LiBF ₄ , LiPO ₂ F ₂ , and LiN. It is preferable to use a non-aqueous electrolyte solution containing at least one lithium salt selected from (SO ₂ F) ₂ . When the ratio 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 power storage device in a high temperature environment and the reduction of the amount of gas generated after the charge / discharge cycle are achieved. The effect is easily exhibited, and when it is 1.0 M or less, there is little concern that the effect of improving the charge / discharge cycle characteristics in a high temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle are reduced, which is preferable. 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 0.8 M or less, more preferably 0.6 M or less, and particularly preferably 0.4 M or less.

Moreover, it is preferable that the non-aqueous solvent is mixed and used in order to achieve appropriate physical characteristics. The combinations are, 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, and a combination of a cyclic carbonate, a chain carbonate and a chain ester. Examples thereof include a combination of a cyclic carbonate, a chain carbonate and a nitrile, a combination of a cyclic carbonate, a chain carbonate and an S = O bond-containing compound, and the like.

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 chain carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate, pivalic acid esters such as methyl pivalate, ethyl pivalate, and propyl pivalate. , One or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA) are preferred.

Among the chain esters, a chain ester 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) is preferable. In particular, a chain carbonate having a methyl group is preferable.

When chain carbonate is used, it is preferable to use two or more kinds. Further, it is more preferable that both the symmetric chain carbonate and the asymmetric chain carbonate are contained, and it is further preferable that the content of the symmetric chain carbonate is higher 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 non-aqueous solvent. If the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte solution does not become too high, and if it is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte solution decreases, so that the non-aqueous electrolyte solution is charged in a high temperature environment. 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 symmetrical chain carbonate to the chain carbonate is preferably 51% by volume or more, more preferably 55% by volume or more. The upper limit thereof is more preferably 95% by volume or less, and further preferably 85% by volume or less. It is particularly preferable that the symmetric chain carbonate contains dimethyl carbonate. Further, the asymmetric chain carbonate is more preferably having a methyl group, and methyl ethyl carbonate is particularly preferable. In the above case, it is preferable because the effect of further improving the charge / discharge cycle characteristics in a high temperature environment and the effect of reducing the amount of gas generated after the charge / discharge cycle are improved.

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

<Lithium battery structure>
The structure of the lithium battery of the present invention is not particularly limited, and is a coin-type battery having a positive electrode, a negative electrode and a single-layer or multi-layer separator, and a cylindrical battery or a square having a positive electrode, a negative electrode and a roll-shaped separator. A type battery and the like can be mentioned as an example.

As the separator, an insulating thin film having a large ion transmittance 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 formed by combining two or more kinds can also be used. Further, the surface of these separators can be coated with resins such as PVDF, silicon resin and rubber resin, and particles of metal oxides such as aluminum oxide, silicon dioxide and magnesium oxide. The pore diameter of the separator may be in a range generally useful for batteries, and is, for example, 0.01 to 10 μm. The thickness of the separator may be in the range for a general battery, for example, 5 to 300 μm.

Next, 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, Examples and Comparative Examples Although described in more detail with reference to the above, the present invention is not limited to the following examples, and includes various combinations that can be easily inferred from the purpose of the invention. In particular, the combination of solvents constituting the non-aqueous electrolytic solution of Examples is not limited. Details of the physical property values given in the examples and comparative examples described below will be described.

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

[2. Average diameter and average aspect ratio of fibrous carbon]
The average diameter D (nm) and 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 and the average aspect ratio of 100 fibrous carbons in the SEM image was taken as the average diameter and the average aspect ratio of the fibrous carbons. The aspect ratio is calculated as L (fiber length) / D (fiber diameter).

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

Main peak intensity of lithium titanate (peak intensity derived from (111) plane within the range of diffraction angle 2θ = 18.1 to 18.5 °), main peak intensity of anatase-type titanium dioxide (diffraction angle 2θ = 24.7 to 24.7 to) (101) plane-derived peak intensity within the range of 25.7 °), main peak intensity of rutile-type titanium dioxide ((110) surface-derived peak intensity within the range of diffraction angle 2θ = 27.2 to 27.6 °) , And the peak intensity of Li ₂ TiO ₃ (peak intensity derived from the (-133) plane in the range of diffraction angle 2θ = 43.5 to 43.8 °) was measured. 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 lithium titanate was 100, the relative values of the main peak intensities of the rutile-type titanium dioxide, anatase-type titanium dioxide, and Li ₂ TiO ₃ were calculated.

[4. Crystallite diameter of the lithium-titanium composite oxide powder (D _X)]
Crystallite diameter of the lithium titanate powder of the present invention _{(D X)} was measured using an X-ray diffraction apparatus using a CuKα ray (manufactured by Rigaku Corporation, RINT-TTR-III type). The measurement conditions are as follows: measurement angle range (2θ): 15.8 ° to 21.0 °, step interval: 0.01 °, measurement time: 1 second / step, source: CuKα ray, tube voltage: 50 kV, It was obtained from the peak half width of the (111) plane of the lithium-titanium composite oxide obtained at a current of 300 mA from Scherrer's equation, that is, the following equation (1). In calculating the full width at half maximum, it was 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) · cosθ 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: Teacher constant (0.94)
λ: CuKα _1- line wavelength (1.54059 Å)
FW (S): Sample-specific full width at half maximum (FWHM)
FW (I): Full width at half maximum (FWHM) specific to the device
D: Deconvolution parameter (1.3)
f0 = 5.108673E-02
f1 = 1.058424E-04
f2 = 6.871481E-06
θ _c : Bragg angle correction value t0 = -3.00E-03
t1 = 5.119E-04
t2 = -3.599E-06

[5. BET specific surface area of lithium titanium composite oxide powder (m ² / g)]
The BET specific surface area of the lithium titanium composite oxide powder of the present invention is measured by the method described in <Specific surface area equivalent diameter D _{BET of} lithium titanium composite oxide powder> described above, and carbonaceous substances containing fibrous carbon are removed. This was performed on the lithium titanium composite oxide powder after the above. The BET specific surface area of this lithium titanium composite oxide powder was measured by a one-point method using liquid nitrogen using a fully automatic BET specific surface area measuring device manufactured by Mountech Co., Ltd., trade name "Macsorb HM model-1208".

[6. Specific Surface Area Equivalent Diameter of Lithium Titanium Composite Oxide Powder ( _DBET )]
The specific surface area equivalent diameter ( _DBET ) was calculated from the following formula (2) on the assumption that all the particles constituting the powder were spheres having the same diameter. Here, _DBET is the diameter equivalent to the specific surface area (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]
Circularity is an index of sphericity when a particle is projected on a two-dimensional plane, and is an index that replaces sphericity. In the present invention, for the secondary particles of the fibrous carbon-containing lithium titanate powder of the present invention, the peripheral length of a perfect circle having the same area as the particle to be measured is expressed as a percentage with respect to the peripheral length of the particle to be measured. The value was calculated as the circularity of each particle, and the average value was defined as the average circularity. The peripheral length of the particle to be measured was determined by image processing the SEM image, and the circularity was determined by the following formula (3). The average value of the circularity of the 50 particles was defined as the average circularity.
Circularity = (peripheral length of a perfect circle having the same area as the particle to be measured) / (peripheral length 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 thermal-thermogravimetric simultaneous measurement device (HITACHITG / DTA7300), differential thermal-thermogravimetric simultaneous analysis measurement (TG-DTA) was performed under the following test conditions, and the fibrous carbon-containing lithium titanium composite oxide of the present invention was performed. The carbon content (mass%) of the powder was determined.
<Test conditions>
Atmosphere: Atmosphere Temperature rise rate: 20 ° C / min Measurement temperature: Room temperature to 900 ° C

[9. X-ray Photoelectron Spectroscopy (XPS)]
As an alternative to the carbon content on the particle surface of the fibrous carbon-containing lithium titanium composite oxide powder of the present invention, the fibrous carbon-containing lithium titanium composite oxide powder is subjected to X-ray photoelectron spectroscopic analysis to atomize carbon and titanium. The ratio (carbon / titanium) was measured. The measurement of the atomic ratio (carbon / titanium) between carbon and titanium by X-ray photoelectron spectroscopy was performed using a PHI1800 type X-ray photoelectron spectrometer manufactured by ULVAC-PHI under the following test conditions.
<Test conditions>
X-ray source: AlKα 400W
Analysis area: 2.0 mm x 0.8 mm

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

Then, the compressive strength (Cs [MPa]) of the spherical secondary particles was calculated by the following formula (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, 10 secondary particles having a particle size of ± 3 μm or less of D50 (μm) are measured as described above, and the average value of the measured values is the spherical secondary particle. The average compression strength of the particles was used.

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

[12. Electrolyte retention rate of electrode mixture layer]
The electrolytic 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 electrolytic solution {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 solution {1M LiPF ₆ / PC} remaining in the electrode mixture layer was measured and converted into volume. As shown in the following formula (5), the electrolytic solution retention rate was calculated by dividing the volume of the non-aqueous electrolytic solution remaining in the electrode mixture layer by the volume of the electrode mixture layer and dividing the value as a percentage. ..
Electrolyte retention rate (%) = Volume of non-aqueous electrolyte (remaining in the electrode mixture layer {1M LiPF ₆ / PC}) (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 the raw materials for lithium titanate, have been reduced to Li / Ti: 0.83, which is the atomic ratio of Li to Ti. Weighed so as to, ion-exchanged water was added so as to have a solid content concentration of 41% by mass together with 0.1% by mass of polyvinyl alcohol (PVA) with respect to TiO ₂ and stirred to prepare a slurry. This slurry is mixed with a bead mill (manufactured by Willy et Bacoffen, model: Dynomill KD-20BC type, agitator material: polyurethane, vessel inner surface material: zirconia, bead material: zirconia, bead outer diameter: 0.65 mm, bead filling in the vessel. Using a rate: 80% by volume), crushing and mixing was performed under the conditions of an agitator peripheral speed of 13 m / sec and a slurry feed speed of 55 kg / hour while controlling the internal pressure of the vessel to be 0.03 MPa or less, and titanium. A raw material slurry of lithium acid acid was prepared. When the D95 of the obtained raw material slurry of lithium titanate was measured by a laser diffraction / scattering type particle size distribution measuring machine, it was 0.9 μm.

<Synthesis of multi-walled carbon nanotubes>
In deionized water, the molar ratio of the metal elements Co: Mg: Al = 8: 66: 26 and so as to, cobalt nitrate _{[Co (NO 3) 2 · 6H} 2 O: molecular weight 291.03], magnesium nitrate [ _{mg (NO 3) 2 · 6H} 2 O: molecular weight 256.41], aluminum nitrate _{[Al (NO 3) 3 · 9H} 2 O: dissolved molecular weight 375.13], respectively, and the mixture was stirred under basic conditions. Then, the produced precipitate was filtered, washed, and dried. This was heated to 500 ° C. and calcined for 1 hour, and then pulverized in a mortar to obtain a catalyst having a spinel structure by substitution solid solution. Next, a support made of quartz wool was provided in the quartz reaction tube, and the catalyst was sprayed on the support. After heating the temperature inside the tube to 550 ° C. in a He atmosphere, a mixed gas consisting 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 yield of the obtained multi-walled carbon nanotubes was 15 times that of the mass of the catalyst.

<Preparation of multi-walled carbon nanotube slurry>
The obtained multi-walled carbon nanotubes, carboxymethyl cellulose (CMC) and ion-exchanged water were mixed and stirred so as to have a mass ratio of 1.0: 0.8: 98.2 to prepare a slurry. Using a bead mill (manufactured by Asada Iron Works Co., Ltd., model: PICOMILL PCM-LR type, agitator material: silicon nitride, vessel inner surface material: zirconia), a bezel made of zirconia (outer diameter: 1.0 mm) is used as a vessel. Was filled with 80% by volume and pulverized at an agitator peripheral speed of 8 m / sec and a slurry feed speed of 30 to 50 ml / min while controlling the internal pressure of the vessel to be 0.06 MPa or less.

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

<Spray / granulation by spray dry 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, spray drying was performed 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 core tube from the raw material supply side of a rotary kiln type firing furnace (core tube length: 4 m, furnace core tube diameter: 30 cm, external heating type) equipped with an adhesion prevention mechanism to create a nitrogen atmosphere. It was dried inside and fired. At this time, the inclination angle of the core tube from the horizontal direction is 2 degrees, the rotation speed of the core tube is 20 rpm, the flow velocity of nitrogen introduced into the core tube from the fired product recovery side is 20 L / min, and the heating temperature of the core tube is set. The raw material supply side: 860 ° C., the central portion: 860 ° C., the fired product recovery side: 860 ° C., and the residence time of the fired product in the heating region was set to 26 minutes. Then, the fired product recovered from the fired product recovery side of the core tube was divided into sieves (mesh roughness: 75 μm), and the fibrous carbon-containing lithium titanate powder 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 [Various physical property measurement methods]. The production conditions of Example 1 (including D95 of the raw material mixture) and the physical characteristics 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 the table is acetylene black.

<Preparation of non-aqueous electrolyte solution for characterization>
The non-aqueous electrolyte solution used for the battery for evaluating the characteristics was prepared as follows. A non-aqueous 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 prepared as an electrolyte salt. _A non-aqueous electrolyte solution was prepared by dissolving ₆ at a concentration of 1 M and LiPO ₂ F ₂ at a concentration of 0.05 M.

<Preparation of evaluation electrode sheet>
As the active material, 95% by mass of the fibrous carbon-containing lithium titanium composite oxide powder of Example 1, 2% by mass of acetylene black (third conductive auxiliary agent), and 3% by mass of polyvinylidene fluoride (binding agent). The paint contained in the ratio was prepared as follows. Polyvinylidene fluoride, acetylene black, and 1-methyl-2-pyrrolidone solvent previously dissolved in 1-methyl-2-pyrrolidone solvent are mixed by a planetary stirring and defoaming device, and then the fibrous carbon-containing lithium titanium composite oxide is mixed. The powder was added, and a 1-methyl-2-pyrrolidone solvent was further added to prepare the total solid content concentration to 56% by mass, and the mixture was mixed with a planetary stirring defoaming device to prepare a coating material. The obtained paint was applied onto an aluminum foil and dried to prepare a single-sided evaluation electrode sheet. Further, the obtained paint was applied to both sides of the aluminum foil and dried to prepare a double-sided evaluation electrode sheet.

<Making coin batteries>
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 prepared evaluation electrode and metallic lithium (molded into a circle with a thickness of 0.5 mm and a diameter of 16 mm) are opposed to each other via a glass filter (two layers of Watman GA-100 and GF / C) for evaluation. A 2030-inch coin-type battery was produced by adding and sealing each of the non-aqueous electrolytic solutions for characteristic evaluation prepared for the battery.

<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 charged in the direction in which Li is stored in the evaluation electrode in the coin-type battery manufactured by the method described in <Manufacturing a coin battery> described above. 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 to discharge. The discharge capacity at this time was defined as the initial discharge capacity (mAh / g). The results are shown in Table 2.

<Making a counter electrode sheet>
In the same production method as the above-mentioned <Production of evaluation electrode sheet>, 90% by mass of lithium cobalt oxide powder, 5% by mass of acetylene black (conductive aid), and vinylidene fluoride (binding agent) are used as active materials. The coating material contained in a proportion of 5% by mass was adjusted, applied onto the aluminum foil and dried, and then the coating material was also applied and dried on the opposite surface to prepare a counter electrode double-sided sheet.

<Making laminated batteries>
The evaluation electrode double-sided sheet was press-processed to obtain a predetermined electrode density, and then punched to prepare 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. 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 the counter electrode double-sided sheet was press-processed, a positive electrode having a lead wire connecting portion of 4 cm in length and 5 cm in width was produced by punching. 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 produced negative electrode and positive electrode are opposed to each other via a separator made of a microporous polyethylene film, laminated, the lead wires of the aluminum foil are connected together with the positive and negative electrodes, and the non-aqueous electrolytic solution for characteristic evaluation is added to the aluminum laminate. By vacuum-sealing with, a laminated battery for evaluating gas generation after a 45 ° C. charge / discharge cycle and a charge / discharge cycle was produced. The capacity of this laminated battery was 200 mAh, and the ratio of the capacity of the negative electrode to the positive electrode (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 <Manufacturing a laminated battery> described above is charged to 2.75 V at 40 mA, and further, the charging current becomes 10 mA at 2.75 V. After performing constant current constant voltage charging to charge until the battery becomes full, constant current discharge to discharge to 1.4 V with a current of 40 mA was performed for 3 cycles. The laminated battery was taken out from the constant temperature bath, and the volume of the laminated battery (volume of the laminated battery before the cycle test) was measured by the Archimedes method. After that, the temperature of the constant temperature bath is set to 45 ° C., charging is performed at 200 mA to 2.75 V, and then constant current constant voltage charging is performed at 2.75 V until the charging current reaches a current of 10 mA, and then 200 mA. A constant current discharge of up to 1.4 V with a current was performed for 500 cycles. The discharge capacity of the first cycle was divided by the discharge capacity of the 500th cycle to calculate the 500 cyc discharge capacity retention rate [45 ° C.]. Then, the temperature of the constant temperature bath was set to 25 ° C., and the mixture was stored for 1 hour. Next, the laminated battery was taken out from the constant temperature bath, and the volume of the laminated battery (volume of the laminated battery after storage) was measured by the Archimedes method. The gas generation amount [45 ° C.] was calculated by subtracting the volume of the laminated battery before the cycle test from the volume of the laminated battery after the cycle test. The results are shown in Table 2.

Based on the above characteristics evaluation results of the laminated battery using the fibrous carbon-containing lithium titanium composite oxide powder of Example 1 as the electrode sheet, the carbon-containing lithium titanium composite oxide powders of other Examples and Comparative Examples are used as electrodes. Table 2 shows the characteristics evaluation results 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 in Examples 2 and 3, the value of D95 as a raw material of lithium titanate is shown in Table 1. The fibrous carbon-containing lithium titanate powder of Examples 2 to 4 was obtained in the same manner as in Example 1 except that the raw material slurry of lithium titanate was prepared so as to be. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Example 5)
As shown in Table 1, instead of polyvinyl alcohol, the same amount of ammonium polycarboxylic acid salt was used as the dispersant, and lithium titanate was prepared so that the D95 of the raw material of lithium titanate became the value shown in Table 1. The 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. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Example 6)
Example 2 and Example 2 except that a lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the values shown in Table 1 using TiO ₂ having the specific surface area shown in Table 1 as the titanium raw material. The fibrous carbon-containing lithium titanate powder of Example 6 was obtained in the same manner. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Example 7)
Except for the fact 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, and that the maximum temperature at the time of firing of the granulated powder was changed to the temperature shown in Table 1. The fibrous carbon-containing lithium titanate powder of Example 7 was obtained in the same manner as in Example 6. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Examples 8 and 9)
Except for the fact that the lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the values shown in Table 1, and that the maximum temperature at the time of firing the granulated powder was changed to the temperature shown in Table 1. The fibrous carbon-containing lithium titanate powder of Examples 8 and 9 was obtained in the same manner as in Example 1. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Example 10)
The raw material slurry of lithium titanate was prepared so that the D95 of the raw material of lithium titanate had the values shown in Table 1, and the multi-walled carbon nanotubes, acetylene black, CMC and ion-exchanged water were mixed in a mass ratio of 0. The multi-walled carbon nanotube slurry containing acetylene black was prepared by mixing and stirring so as to be 5: 0.5: 0.8: 98.2, and the raw material slurry of lithium titanate and the multi-walled layer containing acetylene black. The mass ratio of the raw material of lithium titanate, the multi-walled carbon nanotubes, and acetylene black to the carbon nanotube slurry is "raw material of lithium titanate: total of multi-walled carbon nanotubes and acetylene black" = 99.0: 1.0. A fibrous carbon-containing lithium titanate powder of Example 10 was obtained in the same manner as in Example 1 except that the mixture was mixed as described above to prepare a mixed slurry. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Examples 11 and 12)
The raw material slurry of lithium titanate was prepared so that the D95 of the raw material of lithium titanate had the values shown in Table 1, the multi-walled carbon nanotubes and acetylene black were mixed at the ratios shown in Table 1, and titanium. The mass ratio of the lithium titanate raw material slurry and the multi-walled carbon nanotube slurry containing acetylene black to the lithium titanate raw material, the multi-walled carbon nanotubes and the acetylene black is as follows: "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 the mixed slurry was prepared by mixing so that the total was 99.0: 1.0. It was. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(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 the D95 of the lithium titanate raw material had the values shown in Table 1. Obtained. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1 except that the addition ratio of acetylene black as the third conductive auxiliary agent 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 a third conductive auxiliary agent was changed to the ratio shown in Table 1, and the electrode mixture of the evaluation electrode sheet was changed. An electrode sheet and a laminated battery using the electrode sheet 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 raw material slurry of lithium titanate was prepared so that the D95 of the raw material of lithium titanate became 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 time of firing the granulated powder was changed to the temperature shown in Table 1. Obtained. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Comparative Example 1)
A slurry prepared by mixing and stirring 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 for lithium titanate, is pulverized using a bead mill. A fibrous carbon-containing lithium titanate powder of Comparative Example 1 was obtained in the same manner as in Example 2 except that mixing was not performed. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Comparative Example 2)
Using TiO ₂ having the specific surface area shown in Table 1 as the titanium raw material, a raw material slurry of lithium titanate was prepared so that the D95 of the raw material of lithium titanate had the values shown in Table 1, and the granulated powder was prepared. Same as in Example 2 except that the mixture was filled in a high-purity alumina pot, heated at a heating rate of 200 ° C./hour using a muffle-type electric furnace, and held under the conditions shown in Table 1 for firing. To obtain fibrous carbon-containing lithium titanate powder by the above method. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Comparative Example 3)
Except for the fact that the lithium titanate raw material slurry was prepared so that the D95 of the lithium titanate raw material had the values shown in Table 1, and that the maximum temperature at the time of firing the granulated powder was changed to the temperature shown in Table 1. The fibrous carbon-containing lithium titanate powder of Comparative Example 3 was obtained in the same manner as in Example 2. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Comparative Example 4)
The raw material slurry of lithium titanate prepared by the same method as in Example 1 was not mixed with a conductive agent slurry such as a multi-walled carbon nanotube slurry, sprayed or granulated, and was used in the rotary kiln type firing furnace used in Example 1. Using the same firing furnace as above, the mixture was introduced into the core tube from the raw material supply side, dried under the same conditions as in Example 1, and fired. Then, the fired product recovered from the fired product recovery side of the core tube was crushed to collect lithium titanate powder.
Next, the collected lithium titanate powder is mixed with 0.1% by mass of polyvinyl alcohol (PVA) with respect to lithium titanate with ion-exchanged water so as to have a solid content concentration of 40% by mass, and the slurry is stirred. Made. Preparation of the mixed slurry of Example 1 so that the mass ratio of lithium titanate and the multi-walled carbon nanotubes is 99: 1.0 between this slurry and the multilayer carbon nanotube slurry prepared under the same conditions as in Example 1. Using the same bead mill as the bead mill used in the above, mixing and stirring were performed under the same conditions as for 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 using the same spray dryer as in Example 1 under the same conditions as in Example 1 to obtain lithium titanate and multi-walled carbon nanotubes. A granulated powder consisting of was obtained. Then, the recovered granulated powder was sieved by the same method as in Example 1, and the powder passed through the sieve was collected to obtain the fibrous carbon-containing lithium titanate powder of Comparative Example 4. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

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

(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 ratio of the multi-walled carbon nanotubes added as the fibrous carbon was changed to the ratio shown in Table 1 to prepare a mixed slurry. Obtained. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(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 the fibrous carbon. It was. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Comparative Example 8)
The raw material slurry of lithium titanate was prepared so that the D95 of the raw material of lithium titanate had the values shown in Table 1, and the mixed slurry was directly placed in the rotary kiln type firing furnace without spraying and drying. 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, acetylene black, which is non-fibrous carbon, is used without using fibrous carbon, and the mass ratio of lithium titanate raw material and acetylene black is 99.0: 1.0. A 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 as described above. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

(Comparative Example 10)
The 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. The multi-walled carbon nanotube slurry was prepared by mixing so that the ratio was 1.0: 0.7: 0.1: 98.2. This slurry is used as a bead mill (manufactured by Asada Iron Works, 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: Using 80% by volume), the cells were pulverized under the conditions of an agitator peripheral speed of 8 m / sec and a slurry feed speed of 30 to 50 ml / min while controlling the internal pressure of the vessel to be 0.06 MPa or less. After that, 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 for lithium titanate, were added to the atomic ratio of Li to Ti Li / Ti: 0. Weighed to be .83, and mixed with the multi-layer carbon nanotube slurry so that the mass ratio of the lithium titanate raw material and the multi-layer carbon nanotube is 99.0: 1.0, and the solid content becomes 15%. Ion-exchanged water was added as described above. This slurry is mixed with a bead mill (manufactured by Willy et Bacoffen, model: Dynomill KD-20BC type, agitator material: polyurethane, vessel inner surface material: zirconia, bead material: zirconia, bead outer diameter: 0.65 mm, bead filling in the vessel. Using a rate: 80% by volume), mix while controlling the internal pressure of the vessel to be 0.05 MPa or less under the conditions of an agitator peripheral speed of 13 m / sec and a slurry feed speed of 55 kg / hour 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. An electrode sheet and a laminated battery using the electrode sheet were produced in the same manner as in Example 1.

Table 2 shows the physical characteristics of the fibrous carbon-containing lithium titanate powders of Examples 2 to 13 and Comparative Examples, the physical characteristics of the electrode sheet using the powder, and the characteristics of the lithium ion secondary battery produced using the electrode sheet. It was as shown.

By using the fibrous carbon-containing lithium titanate powder of the present invention, it is possible to obtain a power storage device having excellent charge / discharge cycle characteristics in a high temperature environment and a small amount of gas generated after the charge / discharge cycle. 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 for a long period of time, which is particularly mounted on hybrid electric vehicles, plug-in hybrid electric vehicles, battery electric vehicles, and the like. It is suitable as an electrode material.

Claims (16)

It contains primary particles made of a lithium-titanium composite oxide containing Li and Ti, and spherical secondary particles containing fibrous carbon having an average diameter of 5 to 40 nm and an average aspect ratio of 10 to 1000, and has an average circularity. A lithium-titanium composite oxide powder containing 90% or more of fibrous carbon.
The mass ratio of carbon to the mass of the lithium titanium composite oxide powder calculated from the measurement by thermogravimetric analysis in the fibrous carbon-containing lithium titanium composite oxide powder is defined as A, and the percentage notation of A is a (mass%). When the atomic ratio (carbon / titanium) of carbon to titanium calculated from the 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 a power storage device, characterized in that the average compressive strength of the spherical secondary particles is 1 to 25 MPa. The fibrous carbon-containing lithium titanium composite oxide powder for an electrode of a power 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 for an electrode of the power storage device according to claim 1 or 2, wherein the 1-methyl-2-pyrrolidone oil absorption amount of the lithium titanium composite oxide powder is 55 ml / 100 g to 160 ml / 100 g. Titanium composite oxide powder. The fibrous carbon-containing electrode for the power storage device according to any one of claims 1 to 3, wherein the lithium titanium composite oxide powder has a specific surface area equivalent diameter D _BET of 0.03 μm to 0.6 μm. Lithium-titanium composite oxide powder. The fibrous carbon is formed by stacking 2 to 30 bell-shaped structural units having a crown having a closed graphite mesh surface and an open body at the lower part in a layered manner sharing a central axis. Equipped with multiple aggregates of state structure units
Any of claims 1 to 4, wherein the fibrous carbon is composed of a plurality of the bell-shaped structural unit aggregates connected at intervals in a Head-to-Tail manner to form a fiber. The fibrous carbon-containing lithium-titanium composite oxide powder for electrodes of the power storage device according to item 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, D _BET and _D ratio of _{X D BET / D X (μm} / μm) the electrode for fibrous carbon-containing lithium titanium device according to any one of claims 1-5, characterized in that more than 3 Composite oxide powder. The fibrous carbon-containing lithium titanium composite oxide powder for an electrode of a power storage device according to any one of claims 1 to 6, wherein the spherical secondary particles contain non-fibrous carbon. An electrode sheet of a power storage device having an electrode mixture layer on one side or both sides of a current collector.
The electrode sheet of a power storage device in which the electrode mixture layer contains a fibrous carbon-containing lithium titanium composite oxide powder for an electrode of the power storage device according to any one of claims 1 to 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 of the power storage device according to claim 8, wherein the electrode sheet is characterized by the above. 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. A power storage device including the electrode sheet according to any one of claims 8 to 10. A lithium ion secondary battery comprising the electrode sheet according to any one of claims 8 to 10. A hybrid capacitor including the electrode sheet according to any one of claims 8 to 10. LiPF ₆ , LiBF ₄ , LiPO ₂ F ₂ , and LiN (SO) 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. ₂ F) The power storage device according to claim 11, wherein a non-aqueous electrolyte solution in which an electrolyte salt containing at least one lithium salt selected from ₂ is dissolved is used. The non-aqueous electrolyte solution has a total electrolyte salt concentration of 0.5 M or more and 2.0 M or less, contains at least LiPF ₆ as the electrolyte salt, and further contains LiBF ₄ and LiPO _{2 of} 0.001 M or more and 1.0 M or less. The power storage device according to claim 14, further comprising a non-aqueous electrolyte solution containing at least one lithium salt selected from F ₂ and LiN (SO ₂ F) ₂ . The non-aqueous electrolyte solution contains 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, and methyl butyl. The power storage device according to claim 14 or 15, further comprising one or more asymmetric chain carbonates selected from carbonates and ethylpropyl carbonates.