JP6434555B2 - Negative electrode active material composite for lithium ion secondary battery and method for producing the same - Google Patents

Description

  The present invention relates to a negative electrode active material composite for a lithium ion secondary battery that can effectively improve cycle characteristics in a secondary battery, and a method for producing the same.

  Conventionally, the use of graphite as a negative electrode for lithium ion batteries has been widespread. Such graphite has an operating potential in the vicinity of 0.1 to 0.3 V on the basis of lithium, and plays a large role in realizing higher voltage and higher energy density of the lithium ion battery.

  On the other hand, since the working potential of graphite is near the deposition potential of metallic lithium, when the battery is overcharged, metallic lithium leaking from the immobile film on the graphite surface crystallizes toward the counter electrode, and dendrites are generated. End up. Further, in the discharge process, the dendrite root part elutes and the tip part separates from the graphite surface and remains in the battery. The metallic lithium that remains in the electrolyte and floats is also called dead lithium, and it becomes very active micro metallic lithium, which not only lowers the charge / discharge efficiency but also causes internal short circuits and heat generation in the battery. There is also a risk of causing this.

In order to avoid the generation of dendrite and the generation of dead lithium, a material whose operating potential of the negative electrode is 1 V or more on the basis of lithium is required. For example , if titanium niobium oxide (TiNb ₂ O ₇ ) is used, It is known to show a high capacity of 250 to 280 mAh / g in a potential range of 1 V or more. As a technique related to such a titanium niobium oxide, for example, Patent Document 1 discloses a composite oxide such as TiNb ₂ O ₇ having a specific BET specific surface area, and uses a solid-phase reaction or a hydrothermal reaction. It is shown that it can be obtained. Patent Document 2 discloses a production method in which niobium-based oxide fine particles are obtained as a dispersion by hydrothermal treatment using hydrogen peroxide within a specific temperature range. Furthermore, Patent Document 3 discloses excellent charge / discharge characteristics when the crystallite size of titanium niobium oxide is controlled to an appropriate range while being used as a negative electrode of a lithium ion battery while effectively suppressing the generation and residual of impurities. A negative electrode active material using a titanium niobium oxide capable of exhibiting the above and a method for producing the same are disclosed.

In such a lithium ion secondary battery using TiNb ₂ O ₇ as a negative electrode active material, lithium ions are discharged and charged by being desorbed and inserted into TiNb ₂ O _7. As the battery stacks, the capacity of the negative electrode decreases, and when the battery is used for a long time, the capacity of the battery may decrease significantly. This is thought to be caused by the expansion and contraction of the crystal structure of TiNb ₂ O ₇ accompanying the desorption and insertion of lithium ions, and the electrode mixture layer being easily collapsed. In order to solve this problem, it is essential to stabilize the crystal structure of TiNb ₂ O ₇ during charge and discharge.

Under these circumstances, Patent Document 4 discloses a titanic acid having a small volume change at the time of charging / discharging and having excellent life characteristics on an electrode mixture layer made of TiNb ₂ O ₇ as a negative electrode having high capacity and excellent life characteristics and safety. A negative electrode including a multilayer electrode composite layer in which electrode composite layers made of lithium (Li ₄ Ti ₅ O ₁₂ ) are stacked is disclosed.

JP 2010-287496 A JP 2008-81378 A JP-A-2006-219355 JP, 2006-177974, A

However, although the method described in Patent Document 4 is an effective means for improving the life characteristics of a negative electrode containing TiNb ₂ O ₇ , two types of negative electrode active materials having different life characteristics are laminated on the negative electrode. In order to improve the life characteristics of the negative electrode active material itself, there is still room for improvement.

  Therefore, the subject of this invention is providing the negative electrode active material composite for lithium ion secondary batteries which can improve cycling characteristics effectively, when it uses as a negative electrode active material of a lithium ion secondary battery.

  Therefore, as a result of intensive studies, the present inventors have determined that a specific mass with respect to the secondary particles is formed on the surface of the secondary particles containing carbon composed of monoclinic titanium niobium oxide particles and supported. When the lithium titanate particles having a ratio form a coating layer, when used as a negative electrode active material of a lithium ion secondary battery, the lithium ion secondary battery does not cause a decrease in output even after many charge / discharge cycles. It discovered that the negative electrode active material composite for secondary batteries was obtained.

That is, the present invention includes the following formula (I):
Li _a TiM _b Nb _{2 ± c} O _{7 ± d} (I)
(In Formula (I), 0 ≦ a ≦ 5, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, and 0 ≦ d ≦ 0.3, and M is Fe, V, Mo, and 1 or 2 or more elements selected from Ta.)
On the surface of titanium niobium oxide secondary particles (A) composed of monoclinic titanium niobium oxide particles represented by the following formula (II):
Li _{4 + x} Ti ₅ O ₁₂ (II)
(In the formula (II), x is 0 ≦ x ≦ 3.)
The lithium titanate particles (B) having a spinel structure represented by formula (1) form a coating layer, and the content of the titanium niobium oxide secondary particles (A) and the content of the lithium titanate particles (B) A negative electrode active material composite for a lithium ion secondary battery having a mass ratio ((A) :( B)) of 85:15 to 55:45 is provided.

  The present invention also provides a mixture of titanium niobium oxide secondary particles (A) on which carbon is supported and lithium titanate particles (B) while adding compressive force and shearing force to obtain titanium niobium oxide secondary particles. The present invention provides a method for producing the negative electrode active material composite for a lithium ion secondary battery, comprising a step of forming a coating layer of lithium titanate particles (B) on the surface of the particles (A).

  According to the negative electrode active material composite for a lithium ion secondary battery of the present invention, in the lithium ion secondary battery obtained by effectively preventing the collapse of the crystal structure of the titanium niobium oxide and using this as a negative electrode active material, Cycle characteristics can be improved effectively.

Hereinafter, the present invention will be described in detail.
The negative electrode active material composite for a lithium ion secondary battery of the present invention contains carbon that is supported and has the following formula (I):
Li _a TiM _b Nb _{2 ± c} O _{7 ± d} (I)
(In Formula (I), 0 ≦ a ≦ 5, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, and 0 ≦ d ≦ 0.3, and M is Fe, V, Mo, and 1 or 2 or more elements selected from Ta.)
On the surface of titanium niobium oxide secondary particles (A) composed of monoclinic titanium niobium oxide particles represented by the following formula (II):
Li _{4 + x} Ti ₅ O ₁₂ (II)
(In the formula (II), x is 0 ≦ x ≦ 3.)
The lithium titanate particles (B) having a spinel structure represented by formula (1) form a coating layer, and the content of the titanium niobium oxide secondary particles (A) and the content of the lithium titanate particles (B) The mass ratio ((A) :( B)) is 85:15 to 55:45.

  In the above formula (I), a is 0 ≦ a ≦ 5, and is a variable that can vary within the above range depending on the state of charge of the titanium niobium oxide. B and c are 0 ≦ b ≦ 0.3 and 0 ≦ c ≦ 0.3, preferably 0 ≦ b ≦ 0.2 and 0 ≦ c ≦ 0.2, and monoclinic titanium niobium This is a variable indicating the degree to which part of the Ti and / or Nb sites in the oxide particles is replaced with M in the formula (I). And d is 0 ≦ d ≦ 0.3, preferably 0 ≦ d ≦ 0.2, and is a variable indicating an inevitable deviation from charge compensation and / or stoichiometric ratio associated with substitution by M. is there. The monoclinic titanium niobium oxide particles represented by the formula (I) are particles having a space group C2 / m or P2 / m symmetry.

  Monoclinic titanium niobium oxide particles represented by the above formula (I) aggregate to form titanium niobium oxide secondary particles (A). The average particle diameter of the titanium niobium oxide secondary particles (A) is preferably 10 μm to 40 μm, more preferably 10 μm to 30 μm. When the average particle diameter of the titanium niobium oxide secondary particles (A) is within this range, the lithium titanate particles (B) can be efficiently coated on the surfaces of the particles (A).

The internal porosity of the titanium niobium oxide secondary particles (A) is determined from the viewpoint of allowing the expansion of the titanium niobium oxide accompanying the insertion of lithium ions within the internal voids of the secondary particles. ) Is preferably 10 to 25% by volume, more preferably 10 to 20% by volume.
The internal porosity of the titanium niobium oxide secondary particles (A) can be confirmed using a mercury intrusion porosimeter.

The average particle diameter of the monoclinic titanium niobium oxide particles as the primary particles constituting the titanium niobium oxide secondary particles (A) is the lithium titanate particles (B) on the surface of the titanium niobium oxide secondary particles (A). Is preferably 50 nm to 900 nm, more preferably 100 nm to 900 nm, from the viewpoint of efficiently covering the film. The crystallite size of the monoclinic titanium niobium oxide particles is preferably 50 nm to 500 nm, and more preferably 50 nm to 300 nm.
The crystallite diameter of the titanium niobium oxide means a value obtained by applying Scherrer's equation for an X-ray diffraction profile having a diffraction angle 2θ range of 10 ° to 80 ° by Cu-kα rays. Here, when the monoclinic titanium niobium oxide particles contain a contaminating phase such as TiO _2, an X-ray diffraction profile of those contaminating phases calculated based on the crystal structure parameters (ICDD database) is obtained. It means a value obtained by applying Scherrer's equation to the X-ray diffraction profile of TiNb ₂ O ₇ obtained by subtracting from the X-ray diffraction profile of the obtained titanium niobium oxide mixture.

The shape of monoclinic titanium niobium oxide particles serving as primary particles is preferably isotropic.
In the present specification, particles having an isotropic shape mean particles having an aspect ratio of 3 or less, and the shape of primary particles can be confirmed by a scanning electron microscope (SEM).

Chitan'niobu oxide secondary particles made of such monoclinic Chitan'niobu oxide particles (A) is preferably a specific surface area measured by the BET method is ^{1m 2 / g~20m 2 / g,} 5m 2 / g More preferably, it is -20m < ² > / g. When the BET specific surface area is 1 m ² / g or more, it is possible to sufficiently ensure the occlusion and desorption sites of lithium ions. Moreover, if a BET specific surface area is 20 m < ² > / g or less, handling on industrial production is favorable.
The BET specific surface area is a value obtained by BET analysis of an adsorption isotherm by a nitrogen adsorption method.

The titanium niobium oxide secondary particles (A) contain supported carbon. Such carbon is supported directly on the surface of monoclinic titanium niobium oxide particles, which are the primary particles constituting the titanium niobium oxide secondary particles (A), while being supported on the surface of the titanium niobium oxide secondary particles (A). Being done.
In general, titanium niobium oxide has an electronic conductivity of 1 × 10 ⁻⁸ S · cm ⁻¹ or less, which is very poor in electrical conductivity. When used as an electrode material, the titanium niobium oxide does not rapidly move electrons. In the negative electrode active material composite for a lithium ion secondary battery, a material in which carbon is supported on the surface of a titanium niobium oxide is used to compensate for this. Thus, the electrical conductivity of the titanium niobium oxide can be increased by using the titanium niobium oxide secondary particles (A) in which carbon is arranged on the primary particles or the secondary particles. In addition, the supported carbon relaxes the direct contact between the highly active particle surface of titanium niobium oxide and the electrolytic solution, the decomposition of the electrolytic solution is suppressed, and the life of the obtained secondary battery is improved. Can greatly contribute.

The supported carbon contained in the titanium niobium oxide secondary particles (A) is preferably carbon (c1) derived from cellulose nanofibers or carbon (c2) derived from a water-soluble carbon material.
The cellulose nanofiber used as the carbon source (c1) is a skeletal component that occupies about 50% of all plant cell walls, and can be obtained by defibrating the plant fibers constituting the cell walls to nano size. It is a lightweight high-strength fiber that can be produced, and carbon derived from cellulose nanofibers has a periodic structure. The fiber diameter of the cellulose nanofiber is 1 nm to 100 nm, and has good dispersibility in water. In addition, since the cellulose molecular chain constituting the cellulose nanofiber has a periodic structure formed of carbon, it is firmly supported on the surface of the primary particle or secondary particle of the titanium niobium oxide while being carbonized. Thus, a useful negative electrode active material composite for a lithium ion secondary battery that imparts electronic conductivity to these titanium niobium oxides and is excellent in cycle characteristics can be obtained.

  The water-soluble carbon material as the carbon source (c2) means a carbon material that dissolves in 100 g of water at 25 ° C. in terms of carbon atom of the water-soluble carbon material, 0.4 g or more, preferably 1.0 g or more. By being carbonized, carbon is present on the surface of the primary particle or secondary particle of the titanium niobium oxide. Examples of the water-soluble carbon material include one or more selected from saccharides, polyols, polyethers, and organic acids. More specifically, for example, monosaccharides such as glucose, fructose, galactose and mannose; disaccharides such as maltose, sucrose and cellobiose; polysaccharides such as starch and dextrin; ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol and butane Examples include polyols and polyethers such as diol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Among these, glucose, fructose, sucrose, and dextrin are preferable, and glucose is more preferable from the viewpoint of improving the solubility and dispersibility in a solvent and effectively functioning as a carbon material.

The supported amount of carbon (c1) derived from cellulose nanofibers and carbon (c2) derived from a water-soluble carbon material in the titanium niobium oxide secondary particles (A) is the titanium niobium oxide secondary particles containing the supported carbon. (A) It is 0.1-10 mass% preferably in 100 mass% of whole quantity, More preferably, it is 0.1-5 mass%. The supported amount of carbon (c1) derived from cellulose nanofibers and carbon (c2) derived from a water-soluble carbon material is preferably 0.1% in 100% by mass of the negative electrode active material composite for a lithium ion secondary battery. It is -8.5 mass%, More preferably, it is 0.1-4.3 mass%.
The supported amount of carbon (c1) derived from cellulose nanofibers and carbon (c2) derived from water-soluble carbon material, which are supported on the titanium niobium oxide secondary particles (A), was measured using a carbon / sulfur analyzer. Can be confirmed. Further, the degree of carbon support in the titanium niobium oxide secondary particles (A) can be evaluated by X-ray photoelectron spectroscopy (XPS). Specifically, when X-ray photoelectron spectroscopy is used, a peak intensity ratio ((Ti peak intensity of Ti) that compares the peak intensity of Ti and Nb derived from titanium niobium oxide with the peak intensity of C1s derived from carbon. ) + (Nb peak intensity)) / (C1s peak intensity). In the negative electrode active material for a lithium ion secondary battery of the present invention, the peak intensity ratio ((Ti peak intensity) + (Nb peak intensity)) / (C1s peak intensity) is preferably 0.1 or less, More preferably, it is 0.01 or less.

The lithium titanate particles (B) obtained by forming a coating layer on the surface of the titanium niobium oxide secondary particles (A) are represented by the following formula (II) and have a spinel structure.
Li _{4 + x} Ti ₅ O ₁₂ (II)
(In the formula (II), x is 0 ≦ x ≦ 3.)
In the above formula (II), x is 0 ≦ x ≦ 3, and is a variable that can vary within the above range depending on the state of charge of the negative electrode active material composite for a lithium ion secondary battery.

The average particle size of the lithium titanate particles (B) is preferably 600 nm to 3 μm, and more preferably 600 nm to 2 μm. The crystallite diameter of the lithium titanate constituting the lithium titanate particles (B) is preferably 20 nm to 900 nm, and more preferably 20 nm to 450 nm. Further, BET specific surface area of the lithium titanate particles (B) is ^{preferably 1m 2 / g~30m 2 / g,} 5m 2 / g~30m 2 / g is more preferable.

  The lithium titanate particles (B) need only have a coating layer formed on the surface of the titanium niobium oxide secondary particles (A), and a portion of the titanium niobium oxide secondary particles forms a coating layer. What is necessary is just to combine directly with a part of particle | grains (A).

  In the negative electrode active material composite for a lithium ion secondary battery of the present invention, the average thickness of the coating layer formed by the lithium titanate particles (B) is such that the charging / discharging capacity of the titanium niobium oxide is ensured while ensuring good charge / discharge capacity. From the viewpoint of sufficiently suppressing the volume change accompanying the discharge with lithium titanate, the thickness is preferably 0.5 μm to 3 μm, more preferably 0.7 μm to 2.5 μm.

  The average particle diameter of the negative electrode active material composite for a lithium ion secondary battery of the present invention is preferably 10 μm to 40 μm, more preferably from the viewpoint of satisfactorily applying the negative electrode slurry to the current collector in electrode preparation. 15 μm to 40 μm.

  In the negative electrode active material composite for a lithium ion secondary battery of the present invention, the mass ratio of the content of supported titanium niobium oxide secondary particles (A) containing carbon and the lithium titanate particles (B) (( A) :( B)) is 85:15 to 55:45, preferably 85:15 to 60:40, more preferably 80:20 to 60:40.

The negative electrode active material composite for a lithium ion secondary battery of the present invention is formed by forming a coating layer of lithium titanate particles (B) on the surface of titanium niobium oxide secondary particles (A). Can be evaluated by laser Raman spectroscopy. Specifically, the peak intensity value (a) of carbon derived from carbon contained in the titanium niobium oxide secondary particles (A) in the vicinity of the Raman shift of 1350 cm ⁻¹ , and the lithium titanate derived from about 430 cm ^−1. The ratio of the peak intensity values (b) of Li-O ((a) / (b)) indicates the abundance ratio of titanium niobium oxide and lithium titanate on the surface of the negative electrode active material composite for a lithium ion secondary battery. The peak intensity value ratio (a) / (b) is preferably 1.2 or less, and more preferably 1.0 or less.

  The negative electrode active material composite for a lithium ion secondary battery of the present invention adds a compressive force and a shear force between titanium niobium oxide secondary particles (A) and lithium titanate particles (B) on which carbon is supported. It can be obtained by a production method comprising a step of forming a coating layer on the surface of the titanium niobium oxide secondary particles (A) while mixing. Specifically, the production method includes compressing the step (I) for obtaining the titanium niobium oxide secondary particles (A) by granulating monoclinic titanium niobium oxide particles and the lithium titanate particles (B). It is preferable to provide the step (II) of mixing while applying force and shear force to form a coating layer on the surface of the titanium niobium oxide secondary particles (A).

  The production method of the primary particles of titanium niobium oxide used in the step (I) is not particularly limited as long as the primary particles having a desired average particle diameter and crystallite diameter can be obtained, but preferably a liquid phase reaction method. More preferably, the method is based on a hydrothermal reaction.

More specifically, the step (I) preferably includes the following (Ia) to (Ie).
(Ia): a step of preparing a suspension containing 10 to 40% by mass of niobium hydroxide, a titanium compound and hydrogen peroxide, and having a molar ratio of hydrogen peroxide to niobium of 3 to 8.
(Ib): a step of subjecting the suspension obtained in the step (Ia) to a hydrothermal reaction at 35 to 250 ° C., followed by solid-liquid separation to obtain a solid content,
(Ic): a step of washing the solid content obtained in the step (Ib) with 8 to 60 parts by mass of washing water with respect to 1 part by mass of the dry content of the solids,
(Id): a step of firing the solid content washed in step (Ic) at 600 to 1200 ° C. to obtain monoclinic titanium niobium oxide particles as primary particles,
(Ie): After granulating the monoclinic titanium niobium oxide particles obtained in step (Id) and cellulose nanofibers or a water-soluble carbon material, firing is performed in a reducing atmosphere or an inert atmosphere. The step of obtaining titanium niobium oxide secondary particles (A) containing carbon (c1) derived from cellulose nanofibers or carbon (c2) derived from a water-soluble carbon material as supported carbon.

  The niobium hydroxide used in the step (Ia) is niobium suitable for obtaining a highly dispersible suspension in the step (Ia) when obtaining monoclinic titanium niobium oxide particles as primary particles. Is the source. The niobium hydroxide content is preferably 10 to 40% by mass, more preferably 10 to 38% by mass, and still more preferably 10 to 40% by mass in the suspension obtained in the step (Ia). 35% by mass.

  The titanium compound used in the step (Ia) is a compound used as a titanium source in obtaining monoclinic titanium niobium oxide particles as primary particles, and is selected from, for example, sulfate, nitrate, chloride, and organic acid salt. 1 type, or 2 or more types. Of these, sulfates such as titanyl sulfate and titanium sulfate are preferred from the viewpoints of reactivity and operability. The content of the titanium compound is preferably 1.8 to 3 in terms of a molar ratio (Nb / Ti) with niobium in the suspension obtained in the step (Ia), and more preferably 1. It is 85-2.8, More preferably, it is 1.9-2.5.

  The suspension obtained in step (Ia) further contains hydrogen peroxide. Thereby, the dispersibility and reactivity of each component in a suspension can be improved, adjusting the pH of a suspension to a suitable range. The hydrogen peroxide content is preferably 3 to 8 in terms of the molar ratio of hydrogen peroxide to niobium (hydrogen peroxide / Nb) in the suspension obtained in step (Ia). More preferably, it is 3.5-7, More preferably, it is 4-6.

  The pH of the suspension in the step (Ia) is preferably 7 to 12 and more preferably 8 to 11 from the viewpoint of favorably promoting the hydrothermal reaction in the step (Ib) described later. . In addition, you may use a pH adjuster suitably.

  In obtaining the suspension in the step (Ia), niobium hydroxide and water are used from the viewpoint of dispersing each component more uniformly and generating primary particles of titanium niobium oxide having an appropriate crystallite size. After adding hydrogen peroxide and, if necessary, a pH adjusting agent and mixing them to obtain a mixed solution, a separately prepared mixed solution of titanyl sulfate and water is added and mixed. To obtain a suspension. Further, the obtained suspension may be stirred before transferring to step (Ib). The stirring time is preferably 5 to 180 minutes, more preferably 10 to 120 minutes.

  In the step (Ib), the suspension obtained in the step (Ia) is subjected to a hydrothermal reaction at 35 to 250 ° C., and then subjected to solid-liquid separation to obtain a solid content. Thereby, monoclinic titanium niobium oxide particles are generated while using the suspension obtained in the step (Ia) without adding new water when subjected to a hydrothermal reaction, A suspension containing this can be obtained.

In subjecting to a hydrothermal reaction, the temperature of the suspension obtained in the step (Ia) is set to 35 to 250 ° C, and when the hydrothermal reaction is performed under atmospheric pressure, preferably 35 to 95 ° C, More preferably, it is 40-95 degreeC.
When the suspension obtained in the step (Ia) is stored in a pressure vessel or the like and the hydrothermal reaction is performed under pressure, the temperature of the suspension obtained in the step (Ia) is preferably set. Is 95 to 250 ° C., more preferably 110 to 200 ° C. In addition, the pressure at the time of performing a hydrothermal reaction under pressure becomes like this. Preferably it is 0.3-8.6 MPa, More preferably, it is 0.3-4.0 MPa.
The time for the hydrothermal reaction is preferably 0.5 to 8 hours, more preferably 0.5 to 4 hours.

  Next, the suspension obtained after the hydrothermal reaction is subjected to solid-liquid separation to obtain monoclinic titanium niobium oxide particles as the primary particles, which are target products, as solids. Examples of the apparatus used for solid-liquid separation include a filter press machine and a centrifugal filter machine. Especially, it is preferable to use a filter press from a viewpoint of obtaining solid content efficiently.

  In the step (Ic), the solid content obtained in the step (Ib) is washed with 8 to 60 parts by mass of washing water with respect to 1 part by mass of the dry mass of the solid. This makes it possible to control the crystallite diameter of the titanium niobium oxide obtained after firing within an appropriate range while effectively removing impurities such as anion components. The amount of the washing water is 8 to 60 parts by mass, preferably 10 to 50 parts by mass, and more preferably 10 to 40 parts by mass with respect to 1 part by mass of the dry mass of the solid content. Moreover, the temperature of the washing water is preferably 10 to 80 ° C., more preferably 10 to 70 ° C. from the viewpoint of effectively increasing the discharge capacity of a battery using the obtained composite as a negative electrode material.

  In the said process (Id), the solid content wash | cleaned in the process (Ic) is baked at 600-1200 degreeC, and a monoclinic-type titanium niobium oxide particle is obtained as a primary particle. Thereby, primary particles having high crystallinity and having a crystallite diameter controlled in an appropriate range can be obtained. The firing temperature in the step (Id) is preferably 600 to 1200 ° C., more preferably 600 to 1100, from the viewpoint of imparting an appropriate range of crystallite diameters while increasing the crystallinity of the obtained primary particles. It is 700 degreeC, More preferably, it is 700-1000 degreeC. Moreover, from the same viewpoint, the firing time is preferably 0.3 to 7 hours, and more preferably 0.5 to 6 hours. Note that the atmosphere during firing needs to be in an oxidizing atmosphere in order to make the valence of titanium +4, and is most preferably an air atmosphere from the viewpoint of simplicity and economy.

  In addition, in the said process (Ia), when sulfates, such as a titanyl sulfate and a titanium sulfate, are used as a titanium compound, the monoclinic-type titanium niobium oxidation as a primary particle obtained by passing through a process (Id) is carried out. The amount of sulfur remaining in the product particles is preferably less than 500 ppm, more preferably less than 300 ppm, and even more preferably less than 200 ppm in terms of sulfur atom. The amount of sulfur remaining in the monoclinic titanium niobium oxide particles means a value obtained from the sulfur concentration in a solution in which titanium niobium is acid-dissolved.

The monoclinic titanium niobium oxide particles obtained in the step (Id) may contain a mixed phase such as Ti ₂ Nb ₅ O ₂₉ , TiO ₂ , and an amorphous phase as long as the effects of the present invention are not impaired. good. From the viewpoint of exhibiting excellent charge / discharge characteristics, the content of these contaminated phases is preferably 5% by mass or less, more preferably 4% by mass or less, and further preferably 3% by mass or less. In addition, the content rate of these impurity phases means the quantitative value calculated | required about the obtained titanium niobium oxide by applying the X-ray diffraction-Riet belt method.

  In the step (Ie), the monoclinic titanium niobium oxide particles obtained in the step (Id) and a carbon source are granulated, and then fired in a reducing atmosphere or an inert atmosphere to be supported. To obtain titanium niobium oxide secondary particles (A) containing carbon. Thereby, the titanium niobium oxide secondary particles (A) having an appropriate particle diameter can be obtained while the electronic conductivity of the titanium niobium oxide is improved.

  In order to obtain the supported titanium niobium oxide secondary particles (A) containing carbon, the carbon may be supported, for example, the obtained monoclinic titanium niobium oxide particles and cellulose nanofibers or The process which prepares the slurry containing a water-soluble carbon material, and bakes in a reducing atmosphere or an inert atmosphere after granulation is mentioned. The slurry may appropriately contain an organic binder and an inorganic binder. By performing such a treatment, titanium-niobium oxide secondary particles (A) containing carbon supported thereon can be obtained.

  Examples of the binder include glucose, saccharose, dextrin, polyvinyl alcohol, carboxymethylcellulose, which can also be used as a water-soluble carbon material, and fructose, polyethylene glycol, starch, citric acid, and the like. Among these, glucose, saccharose, dextrin, polyvinyl alcohol, and carboxymethylcellulose are preferable, and glucose is more preferable because it functions as a carbon source by adjusting the amount used and can also be used as a conductive carbon material.

  The amount of the cellulose nanofiber or water-soluble carbon material used when preparing the slurry is 100 parts by mass of monoclinic titanium niobium oxide particles in the slurry from the viewpoint of good charge / discharge capacity and economy. The amount is preferably 0.1 to 11.5 parts by mass in terms of carbon atom, and more preferably 0.5 to 5.3 parts by mass.

  Moreover, you may use water or an organic solvent as a solvent, and water is preferable from an economical viewpoint. The total content (slurry concentration) of the monoclinic titanium niobium oxide particles and the carbon source in the slurry is 15 to 40 masses from the viewpoint of making the particle diameter of the obtained titanium niobium oxide secondary particles (A) suitable. % Is preferable, and 15 to 35 mass% is more preferable. The slurry viscosity at 25 ° C is preferably 3 to 1000 m · Pa, more preferably 10 to 100 m · Pa.

  The granulation treatment is not particularly limited as long as a granulated product having a desired particle diameter can be obtained, but it is preferably by spray drying, and most preferably by spray drying by a spray drying method. . The average particle size of the granulated product obtained after the granulation treatment is preferably 10 μm to 50 μm, and more preferably 12 μm to 45 μm.

  The obtained granulated material can then be used as a negative electrode active material for a secondary battery by firing in a reducing atmosphere or an inert atmosphere. The firing of the secondary particles is preferably performed at 500 to 900 ° C. for 10 minutes to 24 hours, more preferably at 600 to 800 ° C. for 0.5 to 3 hours. By such treatment, secondary particles (A) in which carbon (c1) derived from cellulose nanofibers or carbon (c2) derived from a water-soluble carbon material are further firmly supported on the surface of the titanium niobium oxide can be obtained. The apparatus used for firing is not particularly limited as long as the firing atmosphere and temperature can be adjusted, and any of batch, continuous, and heating (indirect or direct) systems can be used. . Examples of such an apparatus include firing furnaces such as an external heat kiln and a roller hearth.

Next, the titanium niobium oxide secondary particles (A) and the lithium titanate particles (B) obtained in the step (I) are subjected to compressive force and shear force on the surface of the titanium niobium oxide secondary particles (A). A step of obtaining a negative electrode active material composite for a lithium ion secondary battery in which a coating layer of lithium titanate particles (B) is formed on the surface of titanium niobium oxide secondary particles (A) (II) ).
More specifically, the step (II) preferably includes the following (II-a) to (II-b).
(II-a): a step of firing the lithium compound and the titanium compound to obtain lithium titanate particles (B),
(II-b): Lithium titanate particles (B) obtained in step (II-a) are added to the titanium niobium oxide secondary particles (A) obtained in step (I), and compression force and shear A step of obtaining a negative electrode active material composite for a lithium ion secondary battery in which a coating layer of lithium titanate particles (B) is formed on the surface of titanium niobium oxide secondary particles (A) by mixing while applying force .

The said process (II-a) is a process of attaching | subjecting a lithium compound and a titanium compound to baking, and obtaining a lithium titanate particle (B).
A method for producing a lithium titanate _{(Li 4} Ti _{5 O 12)} is a titanium compound and a lithium compound. As the titanium compound, an inorganic titanium compound or an organic titanium compound such as titanium alkoxide can be used. As the inorganic titanium compound, metatitanic acid, titanic acid compound, titanium oxide, or a mixture thereof can be used. The titanium oxide is not particularly limited, and may be one or more of anatase, brookite, rutile, or bronze. Among such titanium compounds, it is preferable to use titanium oxide, particularly anatase type titanium oxide.

  A lithium compound is not specifically limited, For example, lithium hydroxide or its hydrate, lithium peroxide, lithium nitrate, lithium carbonate etc. can be used conveniently. Two or more of these may be used in combination. Among these lithium compounds, lithium hydroxide, lithium carbonate, and lithium oxide are preferably used in order to avoid remaining acidic roots in lithium titanate, and lithium hydroxide and lithium carbonate are preferably used because of easy pulverization. More preferred.

These titanium compounds and lithium compounds are mixed at a predetermined ratio and then baked to become Li ₄ Ti ₅ O ₁₂ . In order to perform such a firing reaction efficiently, the titanium compound and the lithium compound are more preferable as the particle size is smaller. The particle diameters of the titanium compound and the lithium compound are preferably 0.5 μm to 5 μm, and more preferably 0.5 μm to 3 μm.

  The pulverization of the titanium compound or the lithium compound may be performed individually or on a mixture mixed at a predetermined ratio. For the pulverization, an ordinary dry pulverizer can be used. For example, a flake crusher, a hammer mill, a pin mill, a bantam mill, a jet mill, a fret mill, a pan mill, an edge runner, a roller mill, a mix muller, and a vibration mill are used. be able to. Among these, use of a jet mill or a cyclone mill is preferable because the pulverization efficiency is high and the lithium compound can be miniaturized.

The titanium compound and the lithium compound may be mixed in such a ratio that the chemical composition of the mixture is Li ₄ Ti ₅ O ₁₂ and the titanium compound and the lithium compound are sufficiently mixed. A normal dry mixer such as a Henschel mixer can be used for mixing.

The obtained mixture of titanium compound and lithium compound is preferably formed into a compact pellet by pressure molding in order to cause a firing reaction efficiently. Such pressure molding may be performed with an applied pressure of 0.2 to 0.6 t / cm ^{2 using} a hydraulic molding machine or the like.

Next, lithium titanate particles (B) (Li ₄ Ti ₅ O ₁₂ ) can be obtained by firing the mixture of the titanium compound and the lithium compound in an oxygen atmosphere. For the firing, an electric furnace, a rotary kiln, a tubular furnace, a pusher furnace, or the like adjusted to a gas atmosphere having an oxygen concentration of 20% by mass or more, such as an oxygen atmosphere, a dry air atmosphere subjected to dehumidification and carbonation treatment, or the like can be used.
The firing temperature is preferably 700 ° C to 950 ° C, and more preferably 700 ° C to 800 ° C. A calcination temperature of less than 700 ° C. is not preferable because unreacted titanium compounds increase. On the other hand, if the firing temperature exceeds 950 ° C., a contaminated phase (Li ₂ TiO ₃ , Li ₂ Ti ₃ O ₇ or the like) is generated, which is not preferable. The firing time is preferably 3 to 10 hours, and more preferably 3 to 6 hours. Furthermore, when a hydroxide or carbonate is used for the titanium compound or lithium compound, it is preferable to perform two-stage firing in order to remove the crystal water or carbonic acid of the raw material used, and in that case, the first stage of temporary firing is performed. What is necessary is just to perform 400 degreeC-600 degreeC for 1 hour or more, and to perform 2nd step main baking at 700 degreeC-950 degreeC for 3 to 10 hours.

  The obtained lithium titanate particles (B) may be crushed or pulverized as necessary after cooling in order to obtain the predetermined BET specific surface area. For the pulverization, the above-mentioned ordinary dry pulverizer can be used.

  In the step (II-b), the lithium titanate particles (B) obtained in the step (II-a) are added to the titanium niobium oxide secondary particles (A) obtained in the step (I). A negative electrode active material composite for a lithium ion secondary battery in which a coating layer of lithium titanate particles (B) is formed on the surface of titanium niobium oxide secondary particles (A) by mixing while applying compressive force and shearing force Get the body.

  In the step (II-b), it is preferable that the mixture of the titanium niobium oxide secondary particles (A) and the lithium titanate particles (B) is sufficiently dry-mixed before the composite treatment. As a dry mixing method, mixing by a normal dry mixer such as a ball mill or a V blender is preferable, and mixing by a planetary ball mill capable of revolving is more preferable.

Next, the dry-mixed mixture of the titanium niobium oxide secondary particles (A) and the lithium titanate particles (B) is mixed with lithium titanate particles (A) on the surface of the titanium niobium oxide secondary particles (A). From the viewpoint of dispersing B) densely and uniformly and effectively forming a coating layer, it is preferable to mix while applying a compressive force and a shearing force. The process of mixing while applying a compressive force and a shearing force is preferably performed in a closed container equipped with an impeller. The peripheral speed of the impeller is preferably 25 to 40 m from the viewpoint of increasing the tap density of the negative electrode active material composite obtained as a composite of the titanium niobium oxide secondary particles (A) and the lithium titanate particles (B). / S, more preferably 27 to 40 m / s. The mixing time is preferably 5 to 90 minutes, more preferably 10 to 80 minutes.
The peripheral speed of the impeller means the speed of the outermost end of the rotary stirring blade (impeller), which can be expressed by the following formula (1), and is mixed while applying compressive force and shearing force. The processing time may vary depending on the peripheral speed of the impeller so that it becomes longer as the peripheral speed of the impeller is slower.
Impeller peripheral speed (m / s) =
Impeller radius (m) × 2 × π × rotational speed (rpm) ÷ 60 (1)

In the step (II-b), the treatment time and / or the impeller peripheral speed at the time of performing the treatment of mixing while adding the compressive force and shear force are the same as the titanium niobium oxide secondary particles (A) charged into the container. It is necessary to adjust appropriately according to the amount of the mixture with the lithium titanate particles (B). Then, by operating the container, it becomes possible to perform a process of combining the mixture while applying a compressive force and a shearing force between the impeller and the inner wall of the container, and the titanium niobium oxide secondary particles. (A) The lithium titanate particles (B) can be finely and uniformly dispersed on the surface to obtain a negative electrode active material composite for a lithium ion secondary battery in which a coating layer is favorably formed.
For example, when the compounding process is performed for 6 to 90 minutes in an airtight container including an impeller rotating at a peripheral speed of 25 to 40 m / s, the amount of the mixture to be charged into the container is an effective container (an airtight container including an impeller). Among them, a container corresponding to a portion capable of accommodating the mixture) per cm ³ is preferably 0.1 to 0.7 g, more preferably 0.15 to 0.4 g.

Examples of the apparatus including a sealed container that can easily perform the compounding process while applying such compressive force and shear force include a high-speed shear mill, a blade-type kneader, and the like. Fine particle composite apparatus Nobilta (manufactured by Hosokawa Micron Corporation) can be suitably used.
As processing conditions for the above complexing treatment, the treatment temperature is preferably 5 to 80 ° C, more preferably 10 to 50 ° C. The treatment atmosphere is not particularly limited, but is preferably an inert gas atmosphere or a reducing gas atmosphere.

  A method for producing a secondary battery using the obtained negative electrode active material composite for a lithium ion secondary battery as a negative electrode active material is not particularly limited, and any known method can be used. For example, the negative electrode active material composite is mixed with additives such as a binder and a solvent to obtain a coating liquid. At this time, if necessary, a conductive additive may be further added and mixed. The binder is not particularly limited, and any known agent can be used. Specific examples include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, and ethylene propylene diene polymer. Moreover, it does not specifically limit as this conductive support agent, Any well-known agents other than graphite can be used. Specific examples include acetylene black, ketjen black, and fibrous carbon. Subsequently, this coating liquid is apply | coated on negative electrode collectors, such as copper foil, and it is made to dry and is set as a negative electrode.

  The obtained negative electrode active material composite for a lithium ion secondary battery is useful in that it exhibits extremely excellent discharge capacity and cycle specification as a negative electrode for a secondary battery of a lithium ion battery. A secondary battery to which such a negative electrode can be applied is not particularly limited as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator as essential components.

  Here, as for the positive electrode, as long as lithium ions can be released during charging and occluded during discharging, the material configuration is not particularly limited, and a known material configuration can be used. For example, it is preferable to suitably use various polyanion positive electrode active materials obtained by hydrothermal reaction of raw materials.

  The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent usually used for an electrolyte of a secondary battery such as a lithium ion battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles , Lactones, oxolane compounds and the like can be used.

The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ , LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and derivatives of the organic salts It is preferable that it is at least 1 type of these.

  The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Production Example 1: Production of secondary particles of titanium niobium oxide (TiNb ₂ O ₇ )]
Titanyl sulfate and niobium chloride are added to water in such an amount that the molar ratio of titanium to niobium (Ti: Nb) is 1: 2, so that the total content of titanyl sulfate and niobium chloride is 3.5 mol / L. A mixed liquid A1 was prepared. At this point, niobium chloride did not reach complete dissolution. Next, ammonia water was added to the mixed solution A1 to adjust the pH to 8, and it was confirmed that the mixture was cloudy.

After the obtained mixed solution A1 is transferred to the pressure vessel, the mixed solution A1 is extracted from the pressure vessel with a high-pressure compatible pump (manufactured by Teikoku Seisakusho), and the mixed solution A1 discharged from the pump is returned to the pressure vessel. Then, strong stirring was performed for 6 minutes. At this time, the temperature of the mixed liquid A1 was 30 ° C., and the flow rate of the mixed liquid A1 was adjusted to 20 cm / second on the wall surface in the pressure vessel. Next, while the pressure vessel was heated at 130 ° C. for 1 hour, the mixed solution A1 was subjected to hydrothermal reaction at a pressure of 0.3 MPa, and the above-described strong stirring was continued during the hydrothermal reaction to obtain a mixed solution A2. Thereafter, the obtained mixed liquid A2 was subjected to solid-liquid separation with a filter press, and the obtained solid content was washed with 10 parts by mass of water (20 ° C.) with respect to 1 part by mass of the solid content, Firing was performed at 850 ° C. for 4 hours in an air atmosphere to obtain monoclinic titanium niobium oxide particles (a) (TiNb ₂ O ₇ , average particle size of 300 nm) as primary particles.

  With respect to 100 parts by mass of the obtained monoclinic titanium niobium oxide particles (a), 6 parts by mass of glucose in terms of carbon atom as a binder, and a slurry concentration of 10% by mass (a1), 15% by mass (a2 ), 40% by mass (a3), and 45% by mass (a4) of water, and four types of slurries A1, A2, A3, and A4 having different slurry concentrations were prepared. Next, the slurry A1, A2, A3, and A4 were each spray-dried (spray dryer; MDL-050M manufactured by Fujisaki Electric Co., Ltd.) to obtain granules A1, A2, A3, and A4. The obtained granulated products A1, A2, A3, and A4 were each fired at 700 ° C. for 1 hour in a reducing atmosphere, and the following titanium niobium oxide secondary particles (A) ((a1) to (a4) )

Secondary particles (a1): Average particle size 8.8 μm, porosity 27.1% by volume
Secondary particles (a2): average particle size 10.1 μm, porosity 24.5% by volume
Secondary particles (a3): average particle size 18.3 μm, porosity 12.1% by volume
Secondary particles (a4): average particle size 19.1 μm, porosity 9.3% by volume

[Production Example 2: Production of lithium titanate particles (B) (Li ₄ Ti ₅ O ₁₂ )]
1.768 kg of titanium oxide powder, 0.654 kg of lithium carbonate powder, and 6 g of ethanol (grinding aid) were mixed and ground in a ball mill for 2 hours to obtain a powder mixture B1. This powder mixture B1 was calcined at 800 ° C. for 5 hours in an air atmosphere, pulverized, and then calcined at 850 ° C. for 12 hours in an air atmosphere as main firing to synthesize Li ₄ Ti ₅ O ₁₂ .

The obtained Li ₄ Ti ₅ O ₁₂ was pulverized with a ball mill or a jet mill to obtain lithium titanate particles (B) ((b1) to (b5)) having the following average particle diameter.
Li ₄ Ti ₅ O ₁₂ particles (b1): 500 nm
Li ₄ Ti ₅ O ₁₂ particles (b2): 600 nm
Li ₄ Ti ₅ O ₁₂ particles (b3): 700 nm
Li ₄ Ti ₅ O ₁₂ particles (b4): 3 μm
Li ₄ Ti ₅ O ₁₂ particles (b5): 4 μm

[Example 1]
With respect to 80 parts by mass of the secondary particles (a3) obtained in Production Example 1, 20 parts by mass of the particles (b3) obtained in Production Example 2 were added to Nobilta NOB130 (manufactured by Hosokawa Micron Corporation) with a peripheral speed of 30 m / The composite treatment was performed for 10 minutes in seconds, and the negative electrode active material composite for lithium ion secondary battery (TiNb ₂ O ₇ (carbon 6% by mass) 80% by mass + Li ₄ Ti ₅ O ₁₂ 20% by mass, average particle size: 21.0 μm) was obtained.

[Example 2]
A negative electrode active material composite for a lithium ion secondary battery (TiNb ₂ O ₇ (6% by mass of carbon) 80% by mass, in the same manner as in Example 1, except that the secondary particles (a3) were changed to secondary particles (a2). + Li ₄ Ti ₅ O ₁₂ 20% by mass, average particle size: 11.6 μm).

[Example 3]
The negative electrode active material composite for a lithium ion secondary battery was treated in the same manner as in Example 1 except that the secondary particles (a3) were secondary particles (a2) and the particles (b3) were particles (b4). TiNb ₂ O ₇ (carbon 6% by mass) 80% by mass + Li ₄ Ti ₅ O ₁₂ 20% by mass, average particle size: 13.1 μm) was obtained.

[Example 4]
The negative electrode active material composite for a lithium ion secondary battery was treated in the same manner as in Example 1 except that the secondary particles (a3) were secondary particles (a2) and the particles (b3) were particles (b2). TiNb ₂ O ₇ (carbon 6 mass%) 80 mass% + Li ₄ Ti ₅ O ₁₂ 20 mass%, average particle diameter: 11.6 μm) was obtained.

[Example 5]
The same treatment as in Example 1 was conducted except that 60 parts by mass of the secondary particles (a2) was used instead of the secondary particles (a3) and 40 parts by mass of the particles (b2) were used instead of the particles (b3). A negative electrode active material composite E for lithium ion secondary battery E (TiNb ₂ O ₇ (carbon 6% by mass) 60% by mass + Li ₄ Ti ₅ O ₁₂ 40% by mass, average particle size: 12.4 μm) was obtained.

[Reference Example 1]
A negative electrode active material for a lithium ion secondary battery consisting only of the titanium niobium oxide secondary particles (a2) was produced without being composed with Li ₄ Ti ₅ O ₁₂ particles.

[Comparative Example 1]
A negative electrode active material composite for a lithium ion secondary battery (TiNb ₂ O ₇ (carbon 6 mass%) 80) was treated in the same manner as in Example 1 except that the secondary particles (a3) were changed to secondary particles (a4). Mass% + Li ₄ Ti ₅ O ₁₂ 20 mass%, average particle diameter: 22.1 μm).

[Comparative Example 2]
A negative electrode active material composite for lithium ion secondary battery (TiNb ₂ O ₇ (carbon 6 mass%) 80) was treated in the same manner as in Example 1 except that the secondary particles (a3) were changed to secondary particles (a1). Mass% + Li ₄ Ti ₅ O ₁₂ 20 mass%, average particle diameter: 9.9 μm).

[Comparative Example 3]
The negative electrode active material composite for a lithium ion secondary battery was treated in the same manner as in Example 1 except that the secondary particles (a3) were changed to secondary particles (a2) and the particles (b3) were changed to particles (b5). TiNb ₂ O ₇ (carbon 6 mass%) 80 mass% + Li ₄ Ti ₅ O ₁₂ 20 mass%, average particle diameter: 13.4 μm) was obtained.

[Comparative Example 4]
The negative electrode active material composite for a lithium ion secondary battery was treated in the same manner as in Example 1 except that the secondary particles (a3) were secondary particles (a2) and the particles (b3) were particles (b1). TiNb ₂ O ₇ (6% by mass of carbon) 80% by mass + 20% by mass of Li ₄ Ti ₅ O ₁₂ , average particle size: 10.3 μm) was obtained.

[Comparative Example 5]
In the same manner as in Example 1 except that 85 parts by mass of the secondary particles (a2) were used instead of the secondary particles (a3) and 15 parts by mass of the particles (b2) were used instead of the particles (b3), A negative electrode active material composite for lithium ion secondary battery (TiNb ₂ O ₇ (carbon 6% by mass) 85% by mass + Li ₄ Ti ₅ O ₁₂ 15% by mass, average particle size: 10.9 μm) was obtained.

[Comparative Example 6]
The same treatment as in Example 1 was conducted except that 50 parts by mass of the secondary particles (a2) was used instead of the secondary particles (a3) and 50 parts by mass of the particles (b2) were used instead of the particles (b3). A negative electrode active material composite for lithium ion secondary battery (TiNb ₂ O ₇ (carbon 6% by mass) 50% by mass + Li ₄ Ti ₅ O ₁₂ 50% by mass, average particle size: 13.3 μm) was obtained.

[Comparative Example 7]
The negative electrode active material for lithium ion secondary batteries was treated in the same manner as in Example 1 except that 90 parts by mass of the secondary particles (a3) and 10 parts by mass of the particles (b2) were used instead of the particles (b3). A composite (TiNb ₂ O ₇ (carbon 6 mass%) 90 mass% + Li ₄ Ti ₅ O ₁₂ 10 mass%, average particle diameter: 19.2 μm) was obtained.

<< Coating thickness of supported Li ₄ Ti ₅ O ₁₂ >>
The cross sections of the negative electrode active material composites for lithium ion secondary batteries obtained in Examples 1 to 5 and Comparative Examples 1 to 7 were observed with an SEM, and the thickness of the coating layer of the lithium titanate particles (B) was evaluated. . The thickness of the coating layer is the average value of the thickness of the coating layer of Li ₄ Ti ₅ O ₁₂ measured at five different locations of one negative electrode active material composite for a lithium ion secondary battery. The average value for 30 negative electrode active material composites was used. The measurement results are shown in Table 1.

"Covering ratio of _Li 4 _Ti 5 _{O 12} by laser Raman spectroscopy"
The negative electrode active material composites for lithium ion secondary batteries obtained in Examples 1 to 5 and Comparative Examples 1 to 7 were measured by laser Raman spectroscopy, and titanium niobium oxide secondary particles in the vicinity of Raman shift of 1350 cm ^−1. The peak intensity value (a) of carbon derived from C contained in (A) and the peak intensity value (b) of Li—O derived from lithium titanate in the vicinity of Raman shift of 430 cm ⁻¹ are measured. The peak intensity ratio ((a) / (b)) was determined. The measurement results are shown in Table 1.

<Evaluation of charge / discharge characteristics>
Negative electrode active material composite for lithium ion secondary battery or negative electrode active material for lithium ion secondary battery, ketjen black (conductive agent), polyfluoride obtained in Examples 1 to 5, Comparative Examples 1 to 7 and Reference Example Vinylidene (binding agent) was mixed at a mass ratio of 85: 10: 5, and N-methyl-2-pyrrolidone was added thereto and kneaded sufficiently to prepare a negative electrode slurry.
The obtained negative electrode slurry was applied to a current collector made of a copper foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80 ° C. for 12 hours. Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a negative electrode.
Next, a Li foil punched to φ15 mm was used as the counter electrode, and LiPF ₆ dissolved at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was used as the electrolyte. Using a polymer porous film (made of polypropylene) as a separator, the separator was incorporated and housed in an ordinary manner in an atmosphere having a dew point of −50 ° C. or lower to produce a coin-type lithium secondary battery (CR-2032).

For each lithium secondary battery thus produced, an initial discharge capacity of 1C (387 mA / g) and a discharge capacity after 50 cycles in an environment of 30 ° C. were measured (discharge capacity measuring device: HJ-1001SD8 (Hokuto Denko Corporation) )))), And the capacity retention rate (%) was determined by the following formula (Z). The test results are shown in Table 1.
Capacity retention (%) = (discharge capacity after 50 cycles) / (discharge capacity after 1 cycle) × 100 (Z)

  From the above results, it can be seen that the batteries obtained from the negative electrode active material composites for lithium ion secondary batteries obtained in the examples can exhibit both excellent discharge capacity and capacity retention compared to those of the comparative examples. .

Claims (10)

Under following formula (I):
Li _a TiM _b Nb ₂ ± _c O ₇ ± _d (I)
(In Formula (I), 0 ≦ a ≦ 5, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, and 0 ≦ d ≦ 0.3, and M is Fe, V, Mo, and 1 or 2 or more elements selected from Ta.)
In Ri Do from represented monoclinic Chitan'niobu oxide particles, the surface of the monoclinic form Chitan'niobu oxide particles supported Chitan'niobu oxide two containing carbon formed by primary particles (A), the following formula (II) :
Li _{4 + x} Ti ₅ O ₁₂ (II)
(In the formula (II), x is 0 ≦ x ≦ 3.)
The lithium titanate particles (B) having a spinel structure represented by formula (1) form a coating layer, and the content of the titanium niobium oxide secondary particles (A) and the content of the lithium titanate particles (B) A negative electrode active material composite for a lithium ion secondary battery having a mass ratio ((A) :( B)) of 85:15 to 55:45. Carbon supported by the titanium niobium oxide secondary particles (A) is carbon (c1) derived from cellulose nanofibers and / or carbon (c2) derived from a water-soluble carbon material, and titanium niobium oxide secondary particles 2. The lithium according to claim 1, wherein the total content of carbon (c1) derived from cellulose nanofibers and carbon (c2) derived from a water-soluble carbon material in (A) is 0.1 to 8.5% by mass. Negative electrode active material composite for ion secondary battery.   3. The negative electrode active material composite for a lithium ion secondary battery according to claim 1, wherein the titanium niobium oxide secondary particles (A) have an average particle size of 10 μm to 40 μm. The negative electrode active material composite for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the internal porosity of the titanium niobium oxide secondary particles (A) is 10 to 25% by volume. The negative electrode active material composite for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the lithium titanate particles (B) have an average particle diameter of 600 nm to 3 µm. The average thickness of the coating layer of lithium titanate particles (B) is obtained by forming the negative active material composite for a lithium ion secondary battery according to any one of claims 1 to 5 is 0.5μm~3μm body. Near the Raman shift 1350 cm ^-1, Chitan'niobu oxide secondary particle (A) carrying C of peak intensity values derived from the carbon formed by including the a (a), in the vicinity of the Raman shift 430 cm ^-1, Li from lithium titanate The ratio ((a) / (b)) to the peak intensity value (b) of -O is 1.2 or less. The negative electrode active for a lithium ion secondary battery according to any one of claims 1 to 6. Substance complex. Average particle diameter of the negative electrode active material composite for a lithium ion secondary battery according to any one of claims 1 to 7 is 10Myuemu～40myuemu.   The titanium niobium oxide secondary particles (A) containing carbon and the lithium titanate particles (B), which are supported, are mixed while applying compressive force and shearing force, and the titanium niobium oxide secondary particles (A) are mixed. The manufacturing method of the negative electrode active material composite for lithium ion secondary batteries of any one of Claims 1-8 provided with the process of forming the coating layer of lithium titanate particle (B) on the surface.   The method for producing a negative electrode active material composite for a lithium ion secondary battery according to claim 9, wherein the step of combining is a step of performing in a sealed container including an impeller rotating at a peripheral speed of 30 to 45 m / s.