JP6259433B2 - Method for producing negative electrode active material for secondary battery - Google Patents

Description

  The present invention relates to a method for producing a negative electrode active material for a secondary battery by a solid phase method including a step of obtaining a titanium niobium oxide.

  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 such graphite is also close to 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 with respect to lithium is required. For example, in Non-Patent Document 1, it is titanium niobium oxide (TiNb ₂ O ₇ ). For example, it has been reported that a high capacity of 250 to 280 mAh / g is exhibited in a potential range of 1 V or more based on lithium. Such titanium niobium oxide production methods are roughly classified into those using hydrothermal methods, those using solid phase methods, and those using complex polymerization methods. Since it is simple, a production method by a solid phase method is widely adopted.

For example, in Patent Document 1, monoclinic TiNb ₂ O ₇ and Ti ₂ Nb ₁₀ O ₂₉ obtained by a solid phase method are heat-treated at 1000 to 1400 ° C. for 24 hours in an air atmosphere, then pulverized, and again A method of performing heat treatment at the same temperature for 24 hours is disclosed. Patent Document 2 discloses a method for producing TiNb ₂ O ₇ which is heat-treated at 1000 ° C. for 12 hours in an air atmosphere, then pulverized and heat-treated at 1100 ° C. for 12 hours.

JP 2010-287496 A JP, 2015-84321, A

Jian-Tao Han et al, “New Anode Framework for Rechargeable Lithium Batteries”, CHEMISTRY OF MATERIALS, 2011, Vol. 23, p2027-2029.

  However, in any of the production methods described in the literature, since a long-time heat treatment is required, the production method is a solid-phase method while ensuring good performance as a negative electrode active material for a secondary battery. However, it was still difficult to shorten the heat treatment.

  Therefore, the subject of this invention is providing the manufacturing method of the negative electrode active material for secondary batteries which can aim at shortening of heat processing time effectively even if it is the manufacturing method by a solid-phase method.

  Therefore, the present inventors have made various studies and prepared a suspension containing a specific raw material, and then a heat treatment, even if it is a solid phase method, as long as it is a production method through wet mixing, drying and firing. It was found that a negative electrode active material for a secondary battery capable of shortening the time and capable of expressing the performance equal to or higher than that of the negative electrode active material obtained by a conventional manufacturing method was obtained. It came to complete.

That is, the present invention provides a step (I) of preparing a suspension containing a niobium compound, a titanium compound, hydrogen peroxide, and water.
Step (II) for obtaining a mixture by wet-mixing the obtained suspension, and Step (III) for obtaining titanium niobium oxide by drying and firing the obtained mixture.
The manufacturing method of the negative electrode active material for secondary batteries by a solid-phase method is provided.

  According to the production method of the present invention, heat treatment can be effectively shortened even in the production method of a negative electrode active material for a secondary battery by a solid phase method including a step of obtaining a titanium niobium oxide. In the obtained battery, good performance can be ensured while realizing simplification of the above.

The XRD diffraction pattern figure of the titanium niobium oxide obtained in Example 1 and Comparative Example 2 is shown.

Hereinafter, the present invention will be described in detail.
The method for producing a negative electrode active material for a secondary battery according to the solid phase method of the present invention comprises a step (I) of preparing a suspension containing a niobium compound, a titanium compound, hydrogen peroxide, and water,
Step (II) for obtaining a mixture by wet-mixing the obtained suspension, and Step (III) for obtaining titanium niobium oxide by drying and firing the obtained mixture.
Is provided.

The niobium compound used in the step (I) is a compound used as a niobium source in obtaining a titanium niobium oxide in a later step. Examples of such niobium compounds include niobium hydroxide (Nb (OH) ₅ , Nb (OH) ₂ , Nb (OH) ₄ ), niobium oxide (Nb ₂ O ₅ , NbO ₂ , Nb ₂ O ₃ , NbO, etc.), Examples thereof include one or two selected from niobium pentachloride, ammonium niobium oxalate, niobium oxychloride, niobium bromide, niobium fluoride, and niobium oxide sol. Of these, niobium hydroxide (V) (Nb (OH) ₅ ) is preferable from the viewpoint of effectively shortening the reactivity, operability, and heat treatment.
The content of the niobium compound may vary depending on the type of niobium compound, but is preferably 20 to 60% by mass, more preferably 25 to 55% by mass in the suspension obtained in the step (I). More preferably, it is 30-50 mass%.

  The titanium compound used in step (I) is a compound used as a titanium source in obtaining titanium niobium oxide in a later step. Examples of the titanium compound include titanium oxide (anatase type, rutile type, etc.), titanium complex (titanium glycolate complex, titanium citrate complex, etc.), titanium alkoxide (titanium isopropoxide, etc.), titanium salt (titanium sulfate, nitric acid, etc.). And one or more selected from titanium chloride (titanium tetrachloride, etc.), and titanium metal can also be used. Among these, titanium oxide (anatase type) is preferable from the viewpoint of effectively shortening the reactivity, operability, and heat treatment.

  In addition, such a titanium compound is inevitably mixed, and a part thereof is a different metal M other than titanium and niobium (M is Zr, Hf, V, Ta, Fe, Bi, Sb, As, P, Cr). And at least one selected from the group consisting of Mo, W, B, Na, Mg, Al, and Si. The content of the foreign metal (M) is preferably 33% by mass or less, more preferably 15% by mass or less, and further preferably 7% by mass in the titanium compound from the viewpoint of securing better battery physical properties. % Or less.

  The content of such a titanium compound is preferably 1.8 to 5.4, more preferably 1.85 in terms of a molar ratio (Nb / Ti) with niobium in the suspension obtained in the step (I). It is -5.3, More preferably, it is 1.9-5.2. More specifically, when the titanium niobium oxide obtained in the present invention is represented by the formula (1) described later, the content of the titanium compound is the mole of niobium in the suspension obtained in step (I). The ratio (Nb / Ti) is preferably 1.8 to 2.4, more preferably 1.85 to 2.3, and still more preferably 1.9 to 2.1. Moreover, when the titanium niobium oxide obtained by this invention is represented by Formula (2) mentioned later, content of a titanium compound is molar ratio (Nb / N) with the niobium in the suspension obtained in process (I). Ti) is 4.6 to 5.4, more preferably 4.7 to 5.3, and even more preferably 4.8 to 5.2.

  The hydrogen peroxide used in the step (I) may be used as an aqueous solution, and enhances the dispersibility and reactivity of each component in the suspension obtained in the step (I) and effectively promotes shortening of the heat treatment. can do. The hydrogen peroxide content is preferably 1 to 10 in terms of the molar ratio of hydrogen peroxide to niobium (hydrogen peroxide / Nb) in the suspension obtained in step (I), more preferably It is 1.5-8, More preferably, it is 2-6.

In step (I), a suspension is prepared using water in addition to the niobium compound, titanium compound, and hydrogen peroxide. As such water, hydrogen peroxide may be used as an aqueous solution, or water may be added separately.
The content of water in the suspension means the total amount of water contained in the suspension, including the amount of water contained in other components such as hydrogen peroxide solution. From the viewpoint of ensuring dispersibility and reactivity, it is preferably 10 to 90% by mass, more preferably 20 to 80% by mass in the suspension obtained in step (I).

  The pH of the suspension in the step (I) is preferably 7 to 12 from the viewpoint of favorably obtaining the target titanium niobium oxide through the steps (II) and (III) described later. Preferably it is 8-11. In addition, you may use a pH adjuster suitably.

  In step (I), the order of addition of these niobium compound, titanium compound, hydrogen peroxide, and water is not particularly limited, but the dispersibility and reactivity of each component in the suspension obtained in step (I) are increased. From the viewpoint of producing a titanium niobium oxide having an appropriate crystallite diameter and promoting the shortening of the heat treatment, a niobium compound, a titanium compound, and water are mixed in advance, and hydrogen peroxide (or hydrogen peroxide) Aqueous solution) and, if necessary, a pH adjuster is preferably added. Further, before proceeding to step (II), from the viewpoint of more uniformly dispersing each component in the obtained suspension and from the viewpoint of removing the generated hydrogen peroxide gas, further mixing and degassing treatment are performed. It is preferable to apply.

  At this time, the mixing time is preferably 0.2 to 5 hours, more preferably 0.3 to 1 hour, from the viewpoint of sufficiently performing the degassing treatment. Moreover, the temperature at the time of mixing may generate heat | fever by addition of hydrogen peroxide, Preferably it is 50-100 degreeC, More preferably, it is 70-90 degreeC. From the viewpoint of favoring degassing treatment, it is desirable to perform the mixing treatment in an open system. As the mixing device, for example, a normal device capable of mixing the suspension, such as a device equipped with a magnetic stirrer or a rotating blade, can be used.

  Step (II) is a step in which the suspension obtained in step (I) is wet-mixed to obtain a mixture. The means for wet mixing is not particularly limited and can be carried out by a conventional method, but is preferably wet mixing using a ball mill.

  Examples of the container of the apparatus used in the ball mill include steel, stainless steel, and nylon, and the inner wall includes alumina brick, magnetic material, natural silica, rubber, urethane, and the like. As the ball, alumina sphere, natural silica, iron ball, zirconia ball or the like is used. The ball diameter is preferably 0.1 mm to 20 mm, and more preferably 0.5 to 5 mm. It is preferable that the filling amount of the ball is a ratio in which the filling volume of the ball occupies 5 to 50% with respect to the internal volume of the mill to be used. Moreover, when performing wet mixing with a ball mill, it is preferable to set it as conditions, for example, 50 to 800 rpm of revolution and 100 to 1,600 rpm of rotation.

  The temperature at the time of wet mixing in the step (II) is preferably 5 to 50 ° C, more preferably 10 to 30 ° C. The wet mixing time is preferably 0.5 to 24 hours, more preferably 1 to 12 hours, and further preferably 2 to 6 hours.

Step (III) is a step of obtaining a titanium niobium oxide by drying and firing the mixture obtained in step (II). That is, in this step, drying is performed before firing. Examples of the drying means include spray drying, vacuum drying, freeze drying and the like. Of these, spray drying is preferred from the viewpoint of obtaining a uniformly refined titanium niobium oxide without pulverization. When performing such spray drying, various conditions that can be usually employed may be selected as appropriate, but from the viewpoint of effectively reducing the firing time by effectively suppressing the coarsening of the crystallite diameter of the titanium niobium oxide, For example, the inlet temperature is preferably 160 to 210 ° C., the outlet temperature is preferably 75 to 95 ° C., and the spray pressure is preferably 0.5 to 0.9 kg / cm ² . Furthermore, the particle size of the titanium niobium oxide granulated by spray drying is preferably 0.5 to 20 μm, more preferably 1 to 10 μm. What is necessary is just to select the nozzle to be used suitably so that it may become this particle size.
When vacuum drying or freeze-drying is selected as the drying means, the liquid phase content is reduced as much as possible by subjecting it to solid-liquid separation using a filter press, a centrifugal filter or the like prior to drying. It is good.

  Firing in step (III) needs to be performed in an oxidizing atmosphere in order to make the valence of titanium +4, and is preferably performed in an air atmosphere from the viewpoint of simplicity and economy. From the viewpoint of effectively suppressing the coarsening of the crystallite diameter of the titanium niobium oxide, from the viewpoint of completing the solid phase reaction in a short time, and from the viewpoint of effectively shortening the firing time, the firing temperature is preferably 700 to It is 1400 degreeC, More preferably, it is 1000-1400 degreeC, More preferably, it is 1100-1400 degreeC. 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.

  If it is the manufacturing method of this invention, since shortening of heat processing can be aimed at effectively, the baking time in process (III) becomes like this. Preferably it is 0.2 to 2 hours, More preferably, it is 0.3 to 1 hour, and further 0.3 to 0.8 hours is possible.

The titanium niobium oxide obtained by the present invention is specifically a compound represented by the following formula (1) or (2) and having a monoclinic structure.
Ti _1-x M _x Nb ₂ O ₇ (1)
(In formula (1), M is at least one selected from the group consisting of Zr, Hf, V, Ta, Fe, Bi, Sb, As, P, Cr, Mo, W, B, Na, Mg, Al, and Si. X represents a number satisfying 0 ≦ x <0.1.)
_{Ti 2-y M y Nb 10} O 29 ··· (2)
(In the formula (2), M is at least one selected from the group consisting of Zr, Hf, V, Ta, Fe, Bi, Sb, As, P, Cr, Mo, W, B, Na, Mg, Al and Si. Y represents a number satisfying 0 ≦ y <0.2.)
The titanium niobium oxide may contain a mixed phase of Ti ₂ Nb ₁₀ O ₂₉ and / or TiO ₂ when represented by the formula (1) within a range that does not impair the effects of the present invention. When represented by (2), a mixed phase of TiNb ₂ O ₇ and / or TiO ₂ may be included. 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 in the titanium niobium oxide from the viewpoint of exhibiting excellent charge / discharge characteristics. It is as follows. In addition, the content rate of this contaminating phase means the quantitative value calculated | required about the obtained titanium niobium oxide by applying the X-ray diffraction-Riet belt method.

Chitan'niobu oxide obtained by the present invention, from the viewpoint of charge and discharge efficiency and the battery capacity to obtain a high battery, the BET specific surface area, is preferably 1.0 m ² / g or more, more preferably 1.2 m ² / g or more, more preferably 1.5 m ² / g or more. The upper limit of the BET specific surface area is not particularly limited, but is usually 10 m ² / g or less, preferably 7 m ² / g or less, more preferably 5 m ² / g or less.

The titanium niobium oxide obtained by the present invention has a crystallite diameter of preferably 25 to 250 nm, more preferably 25 to 220 nm, and high crystallinity. Moreover, the average particle diameter of a titanium niobium oxide is 50-900 nm, More preferably, it is 50-800 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 obtained titanium niobium oxide is expressed by, for example, the above formula (1) and contains a contaminating phase such as TiO ₂ , those contaminating phases calculated based on the crystal structure parameter (ICDD database) The value obtained by applying Scherrer's equation to the X-ray diffraction profile of TiNb ₂ O ₇ obtained by subtracting the X-ray diffraction profile from the X-ray diffraction profile of the obtained titanium niobium oxide mixture is meant.

The titanium niobium oxide can be used as a negative electrode active material for a secondary battery as it is, but carbon is supported on the surface of the titanium niobium oxide to ensure more sufficient electron conductivity and excellent battery characteristics. From the viewpoint of expression, it is preferable to add a carbon source such as glucose, saccharose, fructose, dextrin, starch, polyethylene glycol, polyvinyl alcohol, carboxymethyl cellulose, carbon black, fibrous carbon, and the like, and calcinate. Under the present circumstances, the addition amount of a carbon source is a carbon atom conversion amount, Preferably it is 1-10 mass% in the negative electrode active material for secondary batteries, More preferably, it is 3-8 mass%.
The firing conditions are preferably performed under an inert gas atmosphere or under reducing conditions, and the firing temperature is preferably 500 to 800 ° C, more preferably 550 to 750 ° C, and further preferably 600 to 750. ° C. The firing time is preferably 10 minutes to 5 hours, more preferably 30 minutes to 4 hours.

  A method for producing a secondary battery using the obtained titanium niobium oxide as a negative electrode active material is not particularly limited, and any known method can be used. For example, the negative electrode active material 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 for a secondary battery is useful in that it exhibits a very excellent discharge capacity and cycle specification as a negative electrode for a secondary battery such as a lithium ion battery or a sodium 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, the positive electrode is not particularly limited in its material configuration as long as it can release a predetermined metal ion such as lithium ion or sodium ion at the time of charging and can be occluded at the time of discharging. Things can be used. For example, it is preferable to suitably use various olivine compounds obtained by hydrothermal reaction of the 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 that is usually used for an electrolyte of a secondary battery such as a lithium ion battery or a sodium 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. For example, in the case of a lithium ion secondary battery, 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 ) It is preferably at least one of an organic salt and a derivative of the organic salt. In the case of a sodium ion secondary battery, for example, an inorganic salt selected from NaPF ₆ , NaBF ₄ , NaClO ₄ and NaAsF ₆ , a derivative of the inorganic salt, NaSO ₃ CF ₃ , NaC (SO ₃ CF ₃ ) ₂ and NaN ( At least one organic salt selected from SO ₃ CF ₃ ) ₂ , NaN (SO ₂ C ₂ F ₅ ) ₂ and NaN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and a derivative of the organic salt Preferably there is.

  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.

[Example 1]
24.324 g of TiO ₂ (powder, manufactured by Kanto Chemical Co., Inc., grade 18.5% purity), Nb (OH) ₅ (powder, HC Starck, purity 92.4%) 115.552 g, and 100 g of water Was put into a beaker and mixed with a magnetic stirrer for 30 minutes to obtain a mixed solution. 58.32 g of hydrogen peroxide solution (special grade reagent manufactured by Kishida Chemical Co., Ltd., purity 35%) was added to the obtained mixed solution, and the mixture was further mixed for 30 minutes with a magnetic stirrer for deoxygenation treatment. A turbid liquid was obtained.
Next, the obtained suspension was wet-mixed at 25 ° C. for 18 hours in a ball mill (rotation speed 120 rpm, inner diameter 7.6 cm, medium φ1 mm ZrO ₂ ball, medium filling ratio 70%) to obtain a mixture.
The obtained mixture was spray-dried by a spray-drying method (spray dryer: MDL-050M manufactured by Fujisaki Electric Co., Ltd.), and the obtained powder was fired at 1200 ° C. for 20 minutes in the air atmosphere to obtain the above formula (1) in yield represented Chitan'niobu oxides of (TiNb ₂ O _7).
Then, 0.474 g of glucose, 2 g of water and 8 ml of ethanol were added to 3 g of the obtained titanium niobium oxide and mixed for 60 minutes with a ball mill (planet type, P-5 manufactured by Fritsch Japan Co., Ltd.). And calcining at 750 ° C. for 1 hour to obtain a negative electrode active material for a secondary battery.

[Example 2]
The suspension obtained by wet-mixing was performed in the same manner as in Example 1 except that the Nb source was 79.743 g of Nb ₂ O ₅ (powder, high-purity reagent manufactured by Kanto Chemical Co., Inc., purity 99.9%). The turbid liquid was spray-dried by a spray drying method. Next, the obtained powder was baked at 1150 ° C. for 50 minutes in an air atmosphere to obtain titanium niobium oxide (TiNb ₂ O ₇ ) represented by the above formula (1).
And the negative electrode active material for secondary batteries was obtained like Example 1 using the obtained titanium niobium oxide.

[Comparative Example 1]
After obtaining a mixed solution in the same manner as in Example 1, wet mixing was performed in the same manner as in Example 1 without adding aqueous hydrogen peroxide, and the resulting suspension was spray-dried by a spray drying method. . Next, the obtained powder was baked at 1100 ° C. for 12 hours in an air atmosphere to obtain titanium niobium oxide (TiNb ₂ O ₇ ) represented by the above formula (1).
And the negative electrode active material for secondary batteries was obtained like Example 1 using the obtained titanium niobium oxide.

[Comparative Example 2]
Ethanol ( ₅ mLg) was added to TiO _{2 (} 1.622 gg) and Nb ₂ O _{5 (} 115.552 g), and after wet mixing in a mortar for 10 minutes, the mixture was calcined at 1000 ° C. for 12 hours in an air atmosphere.
The obtained mixture after calcination was pulverized in a mortar for 10 minutes and then baked at 1100 ° C. for 12 hours in an air atmosphere to obtain titanium niobium oxide (TiNb ₂ O ₇ ) represented by the above formula (1). Obtained.
And the negative electrode active material for secondary batteries was obtained like Example 1 using the obtained titanium niobium oxide.

[Comparative Example 3]
After obtaining a mixture after pre-baking in the same manner as in Comparative Example 2, the mixture was fired at 1100 ° C. for 12 hours and pulverized in a mortar for 10 minutes three times in the air atmosphere, and the above formula (1 It was obtained Chitan'niobu oxide represented (TiNb ₂ O ₇₎ in).
And the negative electrode active material for secondary batteries was obtained like Example 1 using the obtained titanium niobium oxide.

[Example 3]
A suspension was obtained in the same manner as in Example 1 except that 8.108 g of TiO ₂ , 96.293 g of Nb (OH) ₅ and 100 g of water were added, and 48.6 g of hydrogen peroxide was added. Subsequently, the obtained suspension was spray-dried in the same manner as in Example 1, and the obtained powder was calcined at 1200 ° C. for 30 minutes in the air atmosphere to obtain a titanium niobium oxide represented by the above formula (2). (Ti ₂ Nb ₁₀ O ₂₉ ) was obtained.
And the negative electrode active material for secondary batteries was obtained like Example 1 using the obtained titanium niobium oxide.

[Comparative Example 4]
After obtaining a mixed solution in the same manner as in Example 3, wet mixing was performed in the same manner as in Example 3 without adding hydrogen peroxide, and the resulting suspension was spray-dried by a spray-drying method. . Subsequently, the obtained powder was baked at 1100 ° C. for 12 hours in an air atmosphere to obtain a titanium niobium oxide (Ti ₂ Nb ₁₀ O ₂₉ ) represented by the above formula (2).
And the negative electrode active material for secondary batteries was obtained like Example 1 using the obtained titanium niobium oxide.

[Comparative Example 5]
Ethanol ( ₅ mLg) was added to TiO _{2 (} 1.622 g) and Nb ₂ O _{5 (} 13.290 g), and after wet mixing in a mortar for 10 minutes, the mixture was temporarily fired at 1100 ° C. for 12 hours in an air atmosphere.
The obtained mixture after calcination was pulverized in a mortar for 10 minutes and then baked at 1100 ° C. for 12 hours in an air atmosphere to obtain titanium niobium oxide (Ti ₂ Nb ₁₀ O ₂₉ ) represented by the above formula (2). )
And the negative electrode active material for secondary batteries was obtained like Example 1 using the obtained titanium niobium oxide.

<< Evaluation of constituent phase, contamination phase content, and crystallite size of titanium niobium oxide >>
The constituent phases of the titanium niobium oxide obtained in the examples and comparative examples were determined by X-ray diffraction analysis, and the content of each constituent phase was determined by applying the X-ray diffraction-Riet belt method. Next, by applying the Scherrer formula to the crystallite diameter of TiNb ₂ O ₇ or Ti ₂ Nb ₁₀ O ₂₉ , respectively, to the X-ray diffraction profile (full angle) (based on JIS K 0131 “X-ray diffraction analysis general rules”) Asked.
In the evaluation of the crystallite diameter, when there are a plurality of constituent phases of the titanium niobium oxide, TiNb obtained by subtracting the X-ray diffraction profile of the impurity phase other than the main phase from the X-ray diffraction profile of the obtained titanium niobium oxide. X-ray diffraction profiles of ₂ O ₇ single phase or Ti ₂ Nb ₁₀ O ₂₉ single phase were used. Note that the X-ray diffraction profile of the contaminating phase used for the calculation of the content ratio and the crystallite size was obtained by calculation using the crystal structure parameters of the ICDD database.
The results are shown in Table 1, and XRD diffraction pattern diagrams of Example 1 and Comparative Example 2 are shown in FIG.

<X-ray diffraction measurement conditions>
Sample preparation: 70 kg of pressure using a powder sample molding machine (TK-750, manufactured by Tokyo Science Co., Ltd.)
Press machine: X-ray diffractometer: Bruker AXS Co., Ltd. D8 Advance
X-ray: Cu-kα (tube voltage-current = 35 kV-350 mA)
Measurement conditions: Step scan (step size 0.023 °, 0.13 sec / step
2θ: 10 ° -80 °
Analysis software: DIFFRACplus manufactured by Bruker AXS Co., Ltd.
TOPAS (ver. 3)

<< Measurement of BET specific surface area of titanium niobium oxide >>
Using a measuring apparatus (FlowSorbIII 2305 manufactured by Shimadzu Corporation), the BET specific surface area of the titanium niobium oxide obtained in Examples and Comparative Examples was measured by a nitrogen adsorption method.
The results are shown in Table 1.

<Evaluation of charge / discharge characteristics>
The negative electrode active materials for secondary batteries, ketjen black (conductive agent), and polyvinylidene fluoride (binder) obtained in Examples and Comparative Examples were mixed at a mass ratio of 90: 3: 7, and this was mixed therewith. N-methyl-2-pyrrolidone was added and sufficiently kneaded to prepare a negative electrode slurry.
The obtained negative electrode slurry was applied to a current collector made of an aluminum 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, Li foil punched out to φ15 mm was used as the positive electrode, and an electrolyte was prepared by dissolving LiPF ₆ 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 1: 1. 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 created, the charging condition was a constant current charge of 1 CA (387 mA / g) and a voltage of 3 V under a temperature of 30 ° C., the discharge condition was a constant current of 1 CA (387 mA / g) and a final voltage of 1 V. As constant voltage discharge, discharge capacities at 0.2 CA and 3 CA were measured (measuring device: HJ-1001SD8 manufactured by Hokuto Denko Co., Ltd.).
The results are shown in Table 2.

From the result of FIG. 1, in Comparative Example 2, it is confirmed that TiNb ₂ O ₇ contains a mixed phase of Ti ₂ Nb ₁₀ O ₂₉ and TiO ₂ , whereas in Example 1, these mixed phases do not exist. it can.
Moreover, from the results of Tables 1 and 2, the negative electrode active materials for secondary batteries obtained in Examples 1 to 3 can effectively shorten the heat treatment time. An equivalent or higher discharge capacity can be ensured.

Claims (5)

A step (I) of preparing a suspension containing a niobium compound, a titanium compound, hydrogen peroxide, and water;
Step (II) for obtaining a mixture by wet-mixing the obtained suspension, and Step (III) for obtaining titanium niobium oxide by drying and firing the obtained mixture.
A method for producing a negative electrode active material for a secondary battery by a solid phase method. In suspension obtained in step (I), the molar ratio of hydrogen peroxide to niobium (hydrogen peroxide / niobium) The production of the negative electrode active material for a secondary battery according to claim 1 which is 1 to 10 Method.   The method for producing a negative electrode active material for a secondary battery according to claim 1 or 2, wherein the drying in the step (III) is spray drying.   The secondary ratio according to any one of claims 1 to 3, wherein in the suspension obtained in step (I), the molar ratio of niobium to titanium (Nb / Ti) is 1.8 to 5.4. A method for producing a negative electrode active material for a battery.   The method for producing a negative electrode active material for a secondary battery according to any one of claims 1 to 4, wherein the firing time in the step (III) is 0.2 to 2 hours.

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