JP2017107742A - Oxide-based negative electrode active material for secondary battery and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide-based negative electrode active material for secondary batteries, capable of effectively suppressing moisture from being adsorbed, in order to obtain high-performance lithium ion secondary batteries or sodium ion secondary batteries, and a method of producing the same.SOLUTION: An oxide-based negative electrode active material for secondary batteries comprises an oxide for a negative electrode active material carrying graphite and carbon derived from cellulose nanofibers.SELECTED DRAWING: None

Description

  The present invention relates to an oxide-based negative electrode active material for a secondary battery in which carbon derived from cellulose nanofibers and graphite are both supported on an oxide for a negative electrode active material, and a method for producing the same.

  Secondary batteries used for portable electronic devices, hybrid cars, electric cars, and the like have been developed, and secondary batteries such as lithium ion secondary batteries and sodium ion secondary batteries are widely known. In such a secondary battery, it is known that the generation of gas accompanying the charging / discharging of the battery may cause a deterioration reaction inside the battery, but if water is present, the risk is further increased.

  In order to avoid the occurrence of such a deterioration reaction, for example, as shown in Patent Document 1, it is effective to reduce the water content of the positive electrode active material used as the positive electrode material of the secondary battery. Similarly, it is effective to reduce the moisture content of the negative electrode material. For example, for a carbon-based negative electrode material, Patent Document 2 discloses moisture adsorbed by subjecting a carbon material to a specific heat treatment. A manufacturing method is disclosed in which, after removal, this is applied directly to a strip-shaped current collector. Further, Patent Document 3 discloses hard carbon (non-graphite) with a large number of closed pores that exhibits specific physical properties in differential thermal analysis. A method for reducing the amount of moisture adsorbed in the negative electrode material is disclosed.

  On the other hand, regarding the oxide-based negative electrode material, Patent Document 4 describes that in a negative electrode including a spinel-structure lithium-titanium composite oxide, the amount of water contained is preferably 0.05% by mass or less per mass of the negative electrode active material. However, no specific study has been made on how to reduce the amount of moisture.

JP2013-152911A JP 2002-190299 A International Publication No. 2007/040007 International Publication No. 2013/137272

  For these reasons, a technique for reducing the amount of adsorbed moisture of the negative electrode active material for secondary batteries using an oxide that can be used as a negative electrode material is strongly desired.

  Accordingly, an object of the present invention is to provide an oxide-based negative electrode active material for a secondary battery that can effectively suppress moisture adsorption in order to obtain a high-performance lithium ion secondary battery or a sodium ion secondary battery, and its It is to provide a manufacturing method.

  Therefore, the present inventors have intensively studied, and the surface of an oxide that can be used as a negative electrode material, that is, a so-called negative electrode active material oxide, has a high affinity with water, and therefore has a drying treatment as compared with a carbon-based negative electrode material. It has been found that it is difficult to remove moisture sufficiently by itself. Further, such oxides for negative electrode active materials often have carbides derived from water-soluble carbon materials such as glucose, which are often used for positive electrode materials, although the surface is often coated with carbon in order to improve electronic conductivity. It has also been found that it is not easy to completely cover the surface of the material only with the surface coating by. Based on such knowledge, the present inventors have further studied variously, and the oxide for the negative electrode active material is derived from a plurality of carbon sources including carbon derived from cellulose nanofibers and water-insoluble conductive carbon powder. If it is an oxide-based negative electrode active material for a secondary battery in which carbon is supported, these carbons can effectively coat the surface of the negative electrode active material oxide and effectively suppress moisture adsorption. It has been found that the ion or sodium ion is extremely useful as a negative electrode active material for a secondary battery capable of effectively carrying electric conduction, and the present invention has been completed.

That is, the present invention provides an oxide-based negative electrode active material for a secondary battery in which carbon derived from cellulose nanofibers and graphite are supported on an oxide for a negative electrode active material.
In the present invention, cellulose nanofiber and water are added to the oxide X for negative electrode active material and spray-dried to obtain the composite Y (I), and graphite is added to the obtained composite Y. The present invention provides a method for producing an oxide-based negative electrode active material for a secondary battery, which includes a step (II) of dry mixing and firing.

  According to the oxide-based negative electrode active material for a secondary battery of the present invention, carbon and graphite derived from cellulose nanofibers are effectively supported while supplementing each other as a carbon source with an oxide specific to the negative electrode active material. This effectively suppresses the exposure of the oxide without the presence of carbon in a part of the surface of the oxide for the negative electrode active material, so that the exposed portion on the surface of the oxide is effectively reduced. A negative electrode active material for a secondary battery can be obtained. Therefore, since such a negative electrode active material can effectively suppress moisture adsorption, in a lithium ion secondary battery or a sodium ion secondary battery using the negative electrode active material, lithium ions or sodium ions effectively carry electric conduction, Excellent battery characteristics such as cycle characteristics can be stably exhibited even in a different use environment.

Hereinafter, the present invention will be described in detail.
The oxide-based negative electrode active material for a secondary battery of the present invention is obtained by supporting carbon derived from cellulose nanofibers and graphite on an oxide for a negative electrode active material. That is, carbon derived from cellulose nanofibers and graphite coexist as a carbon source, and the surface of the oxide for the negative electrode active material is coated with carbon derived from one carbon source, but the negative electrode active without the presence of such carbon. The carbon derived from the other carbon source is effectively supported on the portion where the surface of the material oxide is exposed. Accordingly, the carbon derived from cellulose nanofibers and graphite are combined and firmly supported on the entire surface of the negative electrode active material oxide while effectively suppressing the exposure of the negative electrode active material oxide surface. Therefore, moisture adsorption in the oxide-based negative electrode active material for a secondary battery of the present invention can be effectively prevented.

The oxide for negative electrode active material used in the present invention is not particularly limited as long as it is an oxide generally used as a negative electrode active material of a secondary battery. Specifically, for example, Li ₄ Ti ₅ O ₁₂ , Ti ₂ Examples thereof include oxides selected from Nb ₁₀ O ₂₉ , TiNb ₂ O ₇ , brookite type TiO ₂ , and SiO.

Li ₄ Ti ₅ O ₁₂ can be obtained by firing a titanium compound and a lithium compound. Examples of the titanium compound that can be used include hydrous titanium oxides such as titanium oxide, orthotitanic acid, and metatitanic acid. These may be used alone or in combination of two or more. Among these, anatase TiO ₂ is preferable from the viewpoint of improving battery physical properties. Examples of the lithium compound that can be used include lithium oxide and lithium hydroxide, and specific examples include lithium carbonate, lithium hydroxide, and lithium nitrate. These may be used alone or in combination of two or more. Among these, lithium carbonate is preferable from the viewpoint of improving battery physical properties.
After mixing and pulverizing predetermined amounts of these titanium compound and lithium compound, Li ₄ Ti ₅ O ₁₂ is obtained by calcination at a temperature of 700 to 900 ° C. for 8 to 24 hours, and then pulverizing the obtained baked product. Can do.

For Ti ₂ Nb ₁₀ O ₂₉ , for example, a suspension is prepared using a predetermined material such as a niobium compound and a titanium compound, a crystal is obtained by a hydrothermal reaction, and a crystal having a high degree of crystallinity is obtained by heat treatment. It can also be obtained by mixing and pulverizing a predetermined material with a ball mill or the like to obtain a solid, followed by firing. As the niobium compound, niobium hydroxide and the like can be used, and as the titanium compound, sulfates such as titanyl sulfate and titanium sulfate, nitrates, chlorides, organic acids and the like can be used. Such titanium compounds, including cases where they are inevitably mixed, are partly made of different metals M other than titanium and niobium (M is Sn, Zr, Fe, Bi, Cr, Mo, Na, Mg, Al and Si). And at least one selected from the group consisting of different metals (M) in the titanium compound from the viewpoint of securing better battery physical properties, preferably 30% by mass or less. More preferably, it is 15 mass% or less.
As a more specific production method, niobium hydroxide is used as a niobium compound, anatase TiO ₂ is used as a titanium source, a suspension is prepared with hydrogen peroxide and water, and a solid content obtained through a hydrothermal reaction is prepared. A production method in which the liquid is separated into solid and liquid and fired is preferable. In addition, the molar ratio (Nb / Ti) of niobium and titanium in the suspension is preferably 4.0 to 6.0, and more preferably 4.5 to 5.5.

TiNb ₂ O ₇ can be obtained by firing a titanium compound and a niobium compound. Examples of the titanium compound that can be used include hydrous titanium oxides such as titanium oxide, orthotitanic acid, and metatitanic acid. These may be used alone or in combination of two or more. Among these, anatase TiO ₂ is preferable from the viewpoint of improving battery physical properties. Such titanium compounds, including cases where they are inevitably mixed, are partly made of different metals M other than titanium and niobium (M is Sn, Zr, Fe, Bi, Cr, Mo, Na, Mg, Al and Si). And at least one selected from the group consisting of different metals (M) in the titanium compound from the viewpoint of securing better battery physical properties, preferably 30% by mass or less. More preferably, it is 15 mass% or less. Examples of niobium compounds that can be used include niobium oxide and niobium hydroxide. These may be used alone or in combination of two or more. Of these, niobium pentoxide (Nb ₂ O ₅ ) is preferable from the viewpoint of improving battery physical properties.
After mixing and pulverizing predetermined amounts of these titanium compound and niobium compound, TiNb ₂ O ₇ can be obtained by calcination at a temperature of 1200 to 1400 ° C. for 4 to 24 hours and then pulverizing the obtained baked product. .

Brookite-type TiO ₂ is a method of hydrothermally treating an aqueous solution containing a hydroxycarboxylic acid titanium complex in a temperature range of 100 ° C. to 300 ° C. while maintaining the pH at 8 to 13, and a titanium compound such as titanyl sulfate is oxalic acid. After peroxylation using hydrogen peroxide or the like, the obtained precipitate can be obtained by baking at a temperature of 550 to 820 ° C. Moreover, a commercial item can also be used suitably.

SiO heats the SiO ₂ and Si to 1250 to 1350 ° C. after mixing with or in a vacuum in a non-oxidizing atmosphere at a predetermined molar ratio, a method of depositing the vaporized SiO, SiO ₂ is hydrogen and the like reducing A method of heating in gas to reduce a predetermined amount, a method of heating SiO ₂ after mixing with a predetermined amount of carbon C, metal, etc. and heating to reduce a predetermined amount, and heating Si with oxygen gas or oxide to oxidize a predetermined amount It can be obtained by a method and a method in which a mixed gas of silicon compound gas such as SiH ₄ and oxygen is subjected to a heating reaction or a plasma decomposition reaction. Moreover, a commercial item can also be used suitably.

  The oxide-based negative electrode active material for a secondary battery according to the present invention is obtained by supporting carbon and graphite derived from cellulose nanofibers on the oxide for negative electrode active material. That is, it is obtained by using cellulose nanofibers and graphite as a carbon source, and both carbon obtained by carbonizing cellulose nanofibers and graphite are firmly supported on the oxide. Cellulose nanofiber is a skeletal component that occupies about 50% of all plant cell walls, and is a lightweight high-strength fiber that can be obtained by defibrating plant fibers constituting such cell walls to nano size, It also 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 carbonized and firmly supported on the oxide, so that it can be obtained in combination with graphite. A useful negative electrode active material that can effectively improve the discharge characteristics of the battery can be obtained.

  The cellulose nanofiber that can be used is not particularly limited as long as it is obtained by defibrating the plant fiber constituting the plant cell wall to nano size, for example, serish KY-100S (manufactured by Daicel Finechem), etc. Commercial products can be used. The fiber diameter of the cellulose nanofiber is preferably 4 to 500 nm, more preferably 5 to 400 nm, and still more preferably 10 to 300 nm from the viewpoint of firmly supporting the oxide on the oxide.

  The cellulose nanofibers are then carbonized, and are present in the oxide-based negative electrode active material for secondary batteries of the present invention as carbon supported on the negative electrode active material-derived cellulose nanofibers. The amount of carbon derived from cellulose nanofibers in terms of atoms is preferably 0.10 to 9% by mass, more preferably 0.15 to 8% by mass in the oxide-based negative electrode active material for secondary battery of the present invention. %, More preferably 0.15 to 6% by mass.

  In addition, the atomic conversion amount of carbon derived from cellulose nanofibers present in the oxide-based negative electrode active material for secondary batteries is the amount of graphite added later from the amount of carbon measured using a carbon / sulfur analyzer. This can be confirmed by subtracting.

The graphite that can be used may be any of artificial graphite (scale, lump, earth, graphene) and natural graphite. The BET specific surface area of such graphite is preferably 1 to 750 m ² / g, more preferably 3 to 500 m ² / g, from the viewpoint of effectively reducing the amount of adsorbed moisture. Moreover, from the same viewpoint, the average particle diameter of such graphite is preferably 0.02 to 20 μm, and more preferably 0.03 to 15 μm.

  The carbon atom equivalent of cellulose nanofiber and graphite coexists in the oxide-based negative electrode active material for secondary battery of the present invention as carbon in which carbonized cellulose nanofiber and graphite are supported on the oxide for negative electrode active material. It will be. The carbon atom equivalent amount of such cellulose nanofibers and graphite corresponds to the total supported amount of carbon and graphite derived from these cellulose nanofibers, and is preferably added in total in the oxide-based negative electrode active material for secondary batteries of the present invention. Is 0.2-18 mass%, More preferably, it is 0.3-15 mass%, More preferably, it is 0.3-12 mass%.

The oxide-based negative electrode active material for secondary battery of the present invention is formed by efficiently supporting the negative electrode active material oxide while complementing each other as carbon obtained by carbonizing cellulose nanofibers and graphite. Calcination allows carbon and graphite derived from cellulose nanofibers to be firmly supported on the negative electrode active material oxide, and the surface of the negative electrode active material oxide is exposed without the presence of carbon. It is possible to effectively avoid this.
The oxide-based negative electrode active material for a secondary battery according to the present invention is required from the viewpoint of efficiently supporting cellulose nanofibers and graphite on the oxide for negative electrode active material while complementing each other as carbonized carbon. It is preferable that graphite is supported on a composite containing an oxide for a negative electrode active material and carbon derived from cellulose nanofibers.

Specifically, the oxide-based negative electrode active material for secondary battery of the present invention is a step (I) of obtaining a composite Y by adding cellulose nanofibers and water to the oxide X for negative electrode active material, followed by spray drying. In addition, graphite can be added to the obtained composite Y, dry-mixed, and fired (II).

  Step (I) is a step of adding the cellulose nanofibers and water to the oxide X for negative electrode active material and then spray drying to obtain the composite Y. That is, a suspension is obtained by adding cellulose nanofibers and water to the negative electrode active material oxide X, and this is subjected to spray drying. As a result, a composite Y in which carbon derived from cellulose nanofibers is firmly supported on the oxide X for negative electrode active material can be obtained. Furthermore, from the viewpoint of favorably supporting the carbon derived from cellulose nanofibers on the surface of the oxide for negative electrode active material, the suspension A obtained by adding water to the oxide X for negative electrode active material, and water in the cellulose nanofiber It is preferable to mix with the suspension B obtained by adding and then subject the resulting suspension C to spray drying.

  The addition amount of the cellulose nanofiber in the step (I) is such that the carbon derived from the cellulose nanofiber is effectively supported on the surface of the oxide X for the negative electrode active material and the sufficient charge / discharge capacity is maintained. Preferably it is 0.2-36 mass parts with respect to 100 mass parts of oxides for substances X, More preferably, it is 0.3-32 mass parts, More preferably, it is 0.4-24 mass parts.

  In step (I), when water is added to the negative electrode active material oxide X to obtain the suspension A, the amount of water added is preferably 30 to 100 parts by mass of the negative electrode active material oxide X. 300 parts by mass, more preferably 50 to 250 parts by mass, and even more preferably 75 to 200 parts by mass. Moreover, when adding water to a cellulose nanofiber and obtaining the suspension B, the addition amount of this water becomes like this. Preferably it is 100-500 mass parts with respect to 100 mass parts of cellulose nanofibers, More preferably, it is 100- 300 parts by mass, more preferably 100 to 150 parts by mass. Furthermore, the total amount of water added in the step (I) is preferably 50 to 500 parts by mass, more preferably 75 to 400 parts by mass, and still more preferably with respect to 100 parts by mass of the oxide X for negative electrode active material. 100 to 300 parts by mass.

As the spray drying in the step (I), spray drying by a spray drying method is suitable. For example, a micro mist dryer (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) equipped with a four-fluid nozzle is used as such an apparatus. Can do. As processing conditions of the apparatus used for spray drying, the air pressure is preferably 0.3 to 0.8 MPa, more preferably 0.5 to 0.7 MPa, and the air flow rate is 20 to 60 NL / min. It is preferable that it is 50-60 NL / min. Further, it is preferable hot air amount is 0.6~1.2m ³ / min, more preferably from 0.8~1.1m ³ / min, inlet temperature, and even at 100 to 250 ° C. Preferably, it is 150-200 degreeC. Furthermore, the exhaust temperature is preferably 70 to 150 ° C, more preferably 80 to 120 ° C, and the suspension (slurry) flow rate is obtained from the point of obtaining the composite Y having a desired average particle diameter. It is preferably 20 to 70 g / min, and more preferably 50 to 70 g / min.

  The average particle size of the composite Y obtained in the step (I) is preferably 50 to 2000 nm, more preferably 50 to 1000 nm, from the viewpoint of efficiently supporting graphite.

  Step (II) is a step of adding graphite to the composite Y obtained in step (I), dry mixing, and firing. Thereby, the carbon derived from cellulose nanofibers and graphite can be firmly supported on the oxide X while effectively suppressing the exposure of the surface of the oxide X for the negative electrode active material. The amount of graphite added is preferably 0.10 to 9% by mass, more preferably 0.15 to 7% by mass, and still more preferably in the oxide-based negative electrode active material for secondary battery of the present invention. What is necessary is just the quantity used as 0.15-6 mass%.

  In addition, the composite Y and the graphite adsorb the oxide-based negative electrode active material for a secondary battery obtained by combining the cellulose with the nanofibers while the graphite efficiently and uniformly coats the surface of the oxide for the negative electrode active material. From the viewpoint of effectively reducing the water content, the mixing is preferably performed at a mass ratio (complex Y: graphite) 99: 1 to 91: 9, more preferably 98: 2 to 93: 7.

The dry mixing in the step (II) is preferably mixing by a normal ball mill, and more preferably by a planetary ball mill capable of revolving. Further, from the viewpoint of densely and uniformly dispersing graphite on the surface of the negative electrode active material oxide X and effectively supporting it as carbonized carbon, the composite Y and the graphite are added while applying compressive force and shearing force. More preferably, they are mixed. 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 / s, more preferably 27 from the viewpoint of increasing the tap density of the obtained negative electrode active material and effectively reducing the amount of adsorbed moisture by reducing the BET specific surface area. ~ 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), the processing time and / or the impeller peripheral speed when performing the mixing process while adding the compressive force and shearing force are appropriately adjusted according to the amount of the composite Y and the graphite charged into the container. There is a need to. Then, by operating the container, it is possible to perform a process of mixing the mixture Y and the graphite while the compressive force and the shearing force are applied to the mixture between the impeller and the container inner wall. Oxide-based negative electrode active material for a secondary battery that can be uniformly dispersed to efficiently support carbon and graphite derived from cellulose nanofibers on the surface of the oxide X for negative electrode active material and effectively reduce the amount of adsorbed water Can be obtained.
For example, when the mixing process is performed for 6 to 90 minutes in an airtight container equipped with an impeller rotating at a peripheral speed of 25 to 40 m / s, the total amount of the composite Y and graphite charged into the container is an effective container (impeller of the sealed container with a complex Y and container correspond to a possible site housing the graphite) 1 cm ³ per, preferably 0.1～0.7G, more preferably at 0.15~0.4g .

Examples of the apparatus equipped with a closed container that can easily perform mixing while applying 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 the processing conditions for the mixing, the processing 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.

  In step (II), the mixture obtained by the dry mixing is fired. Firing is preferably performed in a reducing atmosphere or an inert atmosphere. By such firing, carbon derived from the cellulose nanofibers is firmly supported on the surface of the oxide for negative electrode active material, and the graphite added to the composite Y also exists as carbon covering the surface of the oxide. It will be. Furthermore, since the crystallinity of both the oxide for negative electrode active material and the graphite, which has been reduced by applying compressive force and shear force, can be recovered by this firing, the conductivity in the obtained oxide-based negative electrode active material Can be effectively increased.

  The firing temperature is preferably 500 to 1000 ° C., more preferably 600 to 850 ° C., from the viewpoint of carbonizing the cellulose nanofibers more effectively and from the viewpoint of improving the crystallinity of graphite and improving the conductivity. More preferably, it is 650-750 degreeC. The firing time is preferably 10 minutes to 24 hours, more preferably 30 minutes to 12 hours.

  The oxide-based negative electrode active material for a secondary battery of the present invention thus obtained preferably has a mass ratio (graphite / cellulose nanofiber) between the amount of graphite added and the amount of carbon derived from cellulose nanofibers of 0. 0.1 to 10, more preferably 0.2 to 5, and still more preferably 0.5 to 2. As a result, the carbon and graphite derived from cellulose nanofibers supported or coated on the surface of the oxide for negative electrode active material act synergistically, and the amount of adsorbed water in the oxide negative electrode active material for secondary battery Can be effectively reduced.

The oxide-based negative electrode active material for a secondary battery according to the present invention has the above-described cellulose nanofiber-derived carbon and graphite supported on the oxide for the negative electrode active material, and acts synergistically to oxidize the secondary battery. The amount of adsorbed water in the physical negative electrode active material can be effectively reduced. Specifically, the amount of adsorbed moisture of the oxide-based negative electrode active material for secondary battery of the present invention is as follows for the oxide-based negative electrode active material for secondary battery in which the oxide for negative electrode active material is Li ₄ Ti ₅ O _12. , Preferably it is 500 ppm or less, More preferably, it is 450 ppm or less. Further, in the oxide-based negative electrode active material for a secondary battery in which the oxide for the negative electrode active material is Ti ₂ Nb ₁₀ O ₂₉ , the oxide-based negative electrode active material for the secondary battery is preferably 89 ppm or less, and more Preferably, it is 87 ppm or less, and the oxide-based negative electrode active material for a secondary battery in which the oxide for the negative electrode active material is TiNb ₂ O ₇ is preferably 90 ppm or less in the oxide-based negative electrode active material for a secondary battery. Yes, more preferably 80 ppm or less, and in an oxide-based negative electrode active material for a secondary battery in which the anode active material oxide is brookite-type TiO ₂ , it is preferably 400 ppm or less, more preferably 350 ppm or less. Furthermore, in the oxide-based negative electrode active material for a secondary battery in which the oxide for the negative electrode active material is SiO, the oxide-based negative electrode active material for the secondary battery is preferably 110 ppm or less, more preferably 100 ppm or less. is there.
The amount of adsorbed water is such that moisture is adsorbed until equilibrium is reached at a temperature of 20 ° C. and a relative humidity of 50%. Measured as the amount of water volatilized from the start point to the end point, starting from when the temperature rise is resumed from 150 ° C. when held for 20 minutes and ending at the constant temperature state at 250 ° C. The amount of adsorbed water of the oxide-based negative electrode active material for a secondary battery and the amount of water volatilized between the start point and the end point are regarded as the same amount, and the amount of volatilized water is measured. The value is the amount of adsorbed water of the oxide-based negative electrode active material for secondary batteries.

Thus, since the oxide-based negative electrode active material for a secondary battery of the present invention hardly adsorbs moisture, the amount of adsorbed moisture can be effectively reduced without requiring strong drying conditions as a production environment. Both the obtained lithium ion secondary battery and sodium ion secondary battery can stably exhibit excellent battery characteristics even under various usage environments.
When water is adsorbed until equilibrium is reached at a temperature of 20 ° C. and a relative humidity of 50%, the temperature is raised to 150 ° C. and held for 20 minutes, and further raised to a temperature of 250 ° C. and held for 20 minutes. The amount of water volatilized between the start point and the end point, starting from when the temperature rise is resumed from 150 ° C. and the end point when the constant temperature state at 250 ° C. is completed, is measured using a Karl Fischer moisture meter, for example. Can be measured.

In addition, the tap density of the oxide-based negative electrode active material for secondary battery of the present invention is a secondary electrode in which the negative electrode active material oxide is Li ₄ Ti ₅ O ₁₂ from the viewpoint of stably expressing excellent battery characteristics. In the oxide type negative electrode active material for a battery, it is preferably 0.8 to 2.5 g / cm ³ , more preferably 1.2 to 2.5 g / cm ³ . Further, the anode active material for oxide Ti ₂ Nb ₁₀ O ₂₉ is a rechargeable battery for oxide-based negative electrode active material is preferably 0.9~2.7g / cm ^3, more preferably 1.3 was ~2.6g / cm ^3, the negative electrode active material for oxide is TiNb ₂ O ₇ secondary battery oxide-based negative electrode active material is preferably 0.9~2.7g / cm ^3, More preferably, it is 1.3 to 2.6 g / cm ³ , and in an oxide-based negative electrode active material for a secondary battery in which the negative electrode active material oxide is brookite-type TiO ₂ , preferably 0.9 to 3.0 g. / Cm ³ , more preferably 1.1 to 2.8 g / cm ³ . Further, in the oxide-based negative electrode active material for secondary batteries in which the oxide for negative electrode active material is SiO, it is preferably 0.6 to 2.5 g / cm ³ , more preferably 0.8 to 2.5 g / cm 2. cm ³ .

  A method for producing a secondary battery using the obtained oxide-based negative electrode active material for a secondary battery 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. Next, such a coating solution is applied onto a current collector such as a copper foil and dried to obtain a negative electrode.

  The secondary battery to which the secondary battery negative electrode containing the secondary battery oxide-based negative electrode active material of the present invention 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.

<< Production Example 1: Oxide for Negative Electrode Active Material = Li ₄ Ti ₅ O ₁₂ >>
[Example 1]
Anatase TiO ₂ (manufactured by Kanto Chemical Co., Inc.) 1.768 kg, Li ₂ CO ₃ (manufactured by Kanto Chemical Co., Ltd.) 0.654 kg, and ethanol (manufactured by Kanto Chemical Co., Ltd., grinding aid) 6 g are mixed. After pulverizing with a ball mill for 4 hours, Li ₄ Ti ₅ O ₁₂ (average particle diameter of 100 nm) was obtained by firing at 800 ° C. for 10 hours in an air atmosphere.
1000 g of the resulting Li ₄ Ti ₅ O ₁₂ was collected and mixed with 2000 g of water, and then dispersed with an ultrasonic stirrer (T25 manufactured by IKA) for 1 minute, and the suspension A ¹ was uniformly colored as a whole. Got.
Next, separately, cellulose nanofiber (Delcel Finechem Selish FD-200L, average fiber diameter of 10 to 100 nm, also referred to as “CNF”) 119.4 g of water 1250 g was mixed, and then dispersed with an ultrasonic stirrer for 5 minutes. Te, after obtaining a suspension with a whole uniform opacity, passed through a sieve having a mesh opening 150 [mu] m, to obtain a suspension a ² is a dispersion of cellulose nanofibers. In addition, the sieve residue by the said sieving was not recognized.
By mixing 1.58 g of the obtained suspension A ² with 300 g of the previous suspension A ¹ , cellulose nano-based on the total amount of carbon obtained by carbonizing Li ₄ Ti ₅ O ₁₂ and cellulose nanofibers. Suspension A ³ in which 0.15% by mass of fiber was mixed in terms of carbon amount was obtained.

The suspension A ³ obtained spray-dried (spray dryer; Fujisaki Electric Co. MDL-050M) to to give the complex ^{A 1,} it was collected 99.85g min, graphite 0.15 g ( High-purity graphite powder manufactured by Nippon Graphite Industry Co., Ltd., BET specific surface area 8.6 m ² / g, average particle size 6.1 μm, water content 150 ppm, equivalent to 0.15% by mass in terms of carbon atoms in the negative electrode active material ) together were dry mixed in a ball mill to obtain a complex a ^2.
Next, the obtained composite A ² was mixed with Nobilta NOB130 (manufactured by Hosokawa Micron) at an impeller peripheral speed of 30 m / s for 15 minutes to obtain a composite A ³ . The obtained composite A ³ was calcined at 750 ° C. for 1 hour in a reducing atmosphere, and the negative electrode active material for secondary battery (Li ₄ Ti ₅ O ₁₂ / ( CNF + C) and a carbon content of 0.3% by mass).

[Example 2]
Li ₄ Ti ₅ O ₁₂ and cellulose nanofibers were carbonized in the same manner as in Example 1 except that 27.7 g of the suspension A ² was mixed with 300 g of the suspension A ¹ obtained in Example 1. Suspension B ¹ in which 2.56% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained was obtained.
The suspension ^{B 1} obtained by spray-drying using MDL-050M in the same manner as in Example 1, after obtaining the complexes ^{B 1,} it was collected 97.5g min, with graphite 2.5g They were dry mixed in a ball mill to obtain a complex B ^2. The obtained composite B ² was mixed using Nobilta NOB 130 in the same manner as in Example 1 to obtain composite B ³ .
Next, the obtained composite B ³ was fired in the same manner as in Example 1, and a negative electrode active material for secondary battery (Li ₄ Ti ₅ O ₁₂ / (CNF + C), carbon content 5.0% by mass).

[Example 3]
Li ₄ Ti ₅ O ₁₂ and cellulose nanofibers were carbonized in the same manner as in Example 1 except that 300 g of the suspension A ¹ obtained in Example 1 was mixed with 71.7 g of the suspension A ^2. Suspension C ¹ in which 6.38% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained was obtained.
The suspension ^{C 1} obtained by spray-drying using MDL-050M in the same manner as in Example 1, after obtaining the complex ^{C 1,} it was collected 94.0g min, with graphite 6.0g They were dry mixed in a ball mill to obtain a complex C ^2. The obtained composite C ² was mixed with Nobilta NOB130 in the same manner as in Example 1 to obtain a composite C ³ .
Next, the obtained composite C ³ was fired in the same manner as in Example 1, and a negative electrode active material for a secondary battery (Li ₄ Ti ₅ O ₁₂ / (CNF + C), carbon content 12.0% by mass).

[Comparative Example 1]
95.0 g of Li ₄ Ti ₅ O ₁₂ obtained by firing in Example 1 was collected, and together with 5.0 g of graphite (corresponding to 5.0% by mass in terms of carbon atom in the negative electrode active material), Example In the same manner as in Example ¹ , the mixture was dry-mixed with a ball mill to obtain a composite D1.
Next, the composite D ¹ obtained was mixed using Nobilta NOB130 in the same manner as in Example 1 to obtain the composite D ² and then fired at 750 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material for secondary battery (Li ₄ Ti ₅ O ₁₂ / C, carbon content 5.0 mass%) carrying graphite was obtained.

[Comparative Example 2]
Li ₄ Ti ₅ O ₁₂ and cellulose nanofibers were carbonized in the same manner as in Example 1 except that 131.6 g of the suspension A ² was mixed with 300 g of the suspension A ¹ obtained in Example 1. Suspension E ^{1 in} which cellulose nanofibers were mixed 11.1% by mass in terms of carbon amount with respect to the total amount of carbon obtained was obtained.
The resulting suspension ^{E 1} was spray dried using a MDL-050M in the same manner as in Example 1, to obtain a complex ^{E 1,} this was collected 90.0g min, a ball mill together with graphite 10.0g in dry mixing to obtain a composite body E ^2. The composite E ² obtained was mixed using Nobilta NOB130 in the same manner as in Example 1 to obtain a composite E ³ .
Next, the obtained composite E ³ was fired in the same manner as in Example 1, and the negative electrode active material for secondary battery (Li ₄ Ti ₅ O ₁₂ / (CNF + C), carbon amount 20.0% by mass).

<< Production Example 2: Oxide for Negative Electrode Active Material = Ti ₂ Nb ₁₀ O ₂₉ >>
[Example 4]
In a 500 mL plastic container, 12.162 g of anatase TiO ₂ (manufactured by Kanto Chemical Co., Inc.), Nb (OH) ₅ (manufactured by HC Starck) 144.44 g, and 100 g of water, 1300 g of zirconia balls having a diameter of ₃ mm, Mixing and grinding were performed for 24 hours. Thereafter, the zirconia balls were washed and removed with a wet sieve, and then solid-liquid separated with a filter press. The obtained cake was freeze-dried at −50 ° C. for 12 hours. The obtained solid was calcined at 1100 ° C. for 12 hours in an air atmosphere to obtain Ti ₂ Nb ₁₀ O ₂₉ .

1,000 g of the obtained Ti ₂ Nb ₁₀ O ₂₉ was collected, mixed with 2000 g of water, then dispersed with an ultrasonic stirrer (T25 manufactured by IKA) for 1 minute, and the suspension F ¹ was colored uniformly throughout. Got.
Subsequently, Ti ₂ Nb ₁₀ O ₂₉ and cellulose nano were obtained in the same manner as in Example 1 except that 300 g of the obtained suspension F ¹ and 1.58 g of the suspension A ² obtained in Example 1 were mixed. Suspension F ² in which 0.15% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained by carbonizing the fiber was obtained.
The obtained suspension F ² was spray-dried using MDL-050M in the same manner as in Example ¹ to obtain a composite F ^{1, and then} 99.85 g of the composite F ¹ and 0.15 g of graphite (negative electrode) In the same manner as in Example 1, except that the carbon atom equivalent amount was 0.15% by mass in the active material, dry mixing was performed with a ball mill to obtain a composite F ² .
Next, the composite F ² obtained was mixed using Nobilta NOB130 in the same manner as in Example 1 to obtain the composite F ^3, and then fired at 750 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material for secondary battery (Ti ₂ Nb ₁₀ O ₂₉ / (CNF + C), carbon content 0.3% by mass) on which carbon and graphite derived from cellulose nanofibers were supported was obtained.

[Example 5]
Ti ₂ Nb ₁₀ O in the same manner as in Example 4 except that 300 g of the suspension F ¹ obtained in Example 4 and 27.7 g of the suspension A ² obtained in Example 1 were mixed. Suspension G ¹ in which 2.56% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained by carbonization of ₂₉ and cellulose nanofibers was obtained.
The suspension ^{G 1} obtained by spray-drying using MDL-050M in the same manner as in Example 4 to obtain a composite ^{G 1,} this was collected 97.5g min, a ball mill together with graphite 2.5g in dry mixed to obtain a complex G ^2. The obtained composite G ² was mixed using Nobilta NOB130 in the same manner as in Example 4 to obtain a composite G ³ .
Next, the obtained composite G ³ was fired in the same manner as in Example 4, and the negative electrode active material for secondary battery (Ti ₂ Nb ₁₀ O ₂₉ / (CNF + C), carbon content 5.0% by mass).

[Example 6]
In the same manner as in Example 4 except that 300 g of the suspension F ¹ obtained in Example 4 and 71.7 g of the suspension A ² obtained in Example 1 were mixed, Ti ₂ Nb ₁₀ O ₂₉ and cellulose nanofibers on the total amount of carbon cellulose nanofibers is carbonized to obtain a suspension H ¹ mixed 6.38 wt% of carbon amount conversion.
The suspension ^{H 1} obtained by spray-drying using MDL-050M in the same manner as in Example 4 to obtain a composite ^{H 1,} this was collected 94.0g min, a ball mill together with graphite 6.0g in dry mixed to obtain a complex H ^2. The obtained composite H ² was mixed using Nobilta NOB130 in the same manner as in Example 4 to obtain composite H ³ .
Next, the obtained composite H ³ was fired in the same manner as in Example 4, and the negative electrode active material for secondary battery (Ti ₂ Nb ₁₀ O ₂₉ / (CNF + C), carbon content 12.0% by mass).

[Comparative Example 3]
95.0 g of Ti ₂ Nb ₁₀ O ₂₉ obtained by firing in Example 4 was collected, and together with 5.0 g of graphite (corresponding to 5.0% by mass in terms of carbon atom in the negative electrode active material), Example In the same manner as in ^No. 4, the mixture was dry mixed with a ball mill to obtain a composite I ¹ .
Next, the obtained composite I ¹ was mixed using Nobilta NOB130 in the same manner as in Example 4 to obtain a composite I ^2, and then fired at 750 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material for secondary battery (Ti ₂ Nb ₁₀ O ₂₉ / C, carbon content 5.0 mass%) carrying graphite was obtained.

[Comparative Example 4]
In the same manner as in Example 4 except that 300 g of the suspension F ¹ obtained in Example 4 and 131.6 g of the suspension A ² obtained in Example 1 were mixed, Ti ₂ Nb ₁₀ O ₂₉ and cellulose nanofibers on the total amount of carbon cellulose nanofibers is carbonized to obtain a suspension J ¹ mixed 11.1% by weight of carbon amount conversion.
The resulting suspension ^{J 1} was spray dried using a MDL-050M in the same manner as in Example 4 to obtain a composite ^{J 1,} it was collected 90.0g min, a ball mill together with graphite 10.0g in dry mixing to obtain a composite body J ^2. The obtained composite J ² was mixed using Nobilta NOB130 in the same manner as in Example 4 to obtain a composite J ³ .
Then, a complex J ³ obtained, by firing in the same manner as in Example 4, the cellulose nanofiber from carbon and graphite is carried secondary battery negative electrode active material (Ti ₂ Nb ₁₀ O ₂₉ / (CNF + C), carbon amount 20.0% by mass).

<< Production Example 3: Oxide for Negative Electrode Active Material = TiNb ₂ O ₇ >>
[Example 7]
In a 5 L plastic container, put 133.2 kg of zirconia balls with a diameter of 1 mm together with 243.2 g of anatase TiO ₂ (manufactured by Kanto Chemical Co., Ltd.), 797.4 g of Nb2O5 (manufactured by Kanto Chemical Co., Ltd.) and 1000 g of water, and mixed and pulverized. The treatment was performed for 24 hours. Thereafter, the zirconia balls were washed and removed with a wet sieve, and then solid-liquid separated with a filter press.
After adding 1 part by mass of water to 1 part by mass of the obtained cake to make a slurry, it was spray-dried using MDL-050M in the same manner as in Example 1, and the resulting granulated product was subjected to an atmospheric atmosphere. Under baking at 1300 ° C. for 12 hours, TiNb ₂ O ₇ was obtained.

1,000 g of the obtained TiNb ₂ O ₇ was collected, mixed with 2000 g of water, and then dispersed with an ultrasonic stirrer (T25 manufactured by IKA) for 1 minute to obtain a suspension K ¹ that was uniformly colored as a whole. It was.
Next, TiNb ₂ O ₇ and cellulose nanofibers were prepared in the same manner as in Example 1 except that 1.58 g of the obtained suspension K ¹ and 300 g of the suspension A ² obtained in Example 1 were mixed. cellulose nanofibers with respect to the total amount of formed by carbonizing a carbon to obtain a suspension K ² mixed 0.15 parts by weight of carbon amount conversion.
The resulting suspension ^{K 2} in the same manner as in Example 1 was spray-dried using a MDL-050M, after obtaining the complex ^{K 1,} such complexes ^K 1 99.85G graphite 0.15g except that mixed, dry-mixed in a ball mill in the same manner as in example 1 to obtain a complex K ^2.
Next, the composite K ² obtained was mixed using Nobilta NOB130 in the same manner as in Example 1 to obtain the composite K ^3, and then fired at 650 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material for secondary battery (TiNb ₂ O ₇ / (CNF + C), carbon content 0.3 mass%) on which carbon and graphite derived from cellulose nanofibers were supported was obtained.

[Example 8]
In the same manner as in Example 7, except that 300 g of the suspension K ¹ obtained in Example 7 and 27.7 g of the suspension A ² obtained in Example 1 were mixed, TiNb ₂ O ₇ and cellulose nano Suspension L ¹ in which 2.56% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained by carbonizing the fiber was obtained.
The resulting suspension ^{L 1} was spray dried using a MDL-050M in the same manner as in Example 7, to obtain a complex ^{L 1,} it was collected 97.5g min, a ball mill together with graphite 2.5g in dry mixed to obtain a complex L ^2. The obtained composite L ² was mixed using Nobilta NOB130 in the same manner as in Example 7 to obtain a composite L ³ .
Next, the obtained composite L ³ was fired in the same manner as in Example 7, and the negative electrode active material for secondary battery (TiNb ₂ O ₇ / (CNF + C) on which carbon and graphite derived from cellulose nanofibers were supported. ), And 5.0% by mass of carbon).

[Example 9]
In the same manner as in Example 7, except that 300 g of the suspension K ¹ obtained in Example 7 and 71.7 g of the suspension A ² obtained in Example 1 were mixed, TiNb ₂ O ₇ and cellulose nano A suspension M ¹ in which 6.38% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained by carbonizing the fiber was obtained.
The resulting suspension ^{M 1} was spray dried using a MDL-050M in the same manner as in Example 7, to obtain a complex ^{M 1,} this was collected 94.0g min, a ball mill together with graphite 6.0g in dry mixed to obtain a complex M ^2. The resulting composite M ² was mixed using Nobilta NOB130 in the same manner as in Example 7 to obtain a composite M ³ .
Next, the obtained composite M ³ was fired in the same manner as in Example 7, and the negative electrode active material for secondary battery (TiNb ₂ O ₇ / (CNF + C) on which carbon and graphite derived from cellulose nanofibers were supported. ), And a carbon content of 12.0% by mass.

[Comparative Example 5]
95.0 g of TiNb ₂ O ₇ obtained by firing in Example 7 was collected, and together with 5.0 g of graphite (corresponding to 5.0% by mass in terms of carbon atom in the negative electrode active material), Similarly, dry mixing was performed with a ball mill to obtain a composite N ¹ .
Next, the obtained composite N ¹ was mixed using Nobilta NOB130 in the same manner as in Example 7 to obtain a composite N ^2, and then fired at 650 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material for secondary battery (TiNb ₂ O ₇ / C, carbon content 5.0 mass%) carrying graphite was obtained.

[Comparative Example 6]
In the same manner as in Example 7, except that 300 g of the suspension K ¹ obtained in Example 7 and 131.6 g of the suspension A ² obtained in Example 1 were mixed, TiNb ₂ O ₇ and cellulose nano Suspension O ¹ in which 11.1% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained by carbonizing the fiber was obtained.
The obtained suspension O ¹ was spray-dried using MDL-050M in the same manner as in Example 7 to obtain a composite O ¹ , and 90.0 g of this was taken and ball milled with 10.0 g of graphite. And dry mixed to obtain a complex O ² . The obtained composite O ² was mixed using Nobilta NOB130 in the same manner as in Example 7 to obtain a composite O ³ .
Next, the obtained composite O ³ was fired in the same manner as in Example 7, and the negative electrode active material for secondary battery (TiNb ₂ O ₇ / (CNF + C) on which carbon and graphite derived from cellulose nanofibers were supported. ), And a carbon content of 20.0% by mass).

<< Production Example 4: Oxide for Negative Electrode Active Material = Brookite TiO ₂ >>
[Example 10]
After adding 2656 g of titanyl sulfate (manufactured by Kishida Chemical Co., Ltd.) to 4000 g of water, the solution was stirred for 24 hours while heating to 50 ° C. to obtain a solution P ¹ . Further, the water 4000 g, was added oxalic acid dihydrate (manufactured by Kanto Chemical (Co.)) 633 g, to obtain a solution ^{P 2} was dissolved under warming to 50 ° C.. Then, the solution P ^1, was added dropwise over a solution P ² 10 minutes, and stirred for 12 hours while heating at 90 ° C.. The obtained precipitate was separated by a filter press and then dried at 80 ° C. for 24 hours to obtain titanium oxyoxalate. The obtained titanium oxyoxalate was baked at 600 ° C. for 2 hours to obtain brookite type TiO ₂ .

1000 g of the resulting brookite-type TiO ₂ was collected and mixed with 2000 g of water, and then dispersed with an ultrasonic stirrer (T25 manufactured by IKA) for 1 minute to obtain a suspension P ¹ that was uniformly colored as a whole. It was. Next, brookite type TiO ₂ and cellulose nanofibers were prepared in the same manner as in Example 1 except that 300 g of the obtained suspension P ¹ and 1.58 g of the suspension A ² obtained in Example 1 were mixed. Suspension P ² in which 0.15 parts by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained by carbonization was obtained.
The obtained suspension P ² was spray-dried using MDL-050M in the same manner as in Example ¹ to obtain a composite P ^{1, and then} 99.85 g of the composite P ¹ and 0.15 g of graphite (negative electrode) except that a mixture of the corresponding) to 0.15 wt% in terms of carbon atoms content in the active material was dry mixed in a ball mill in the same manner as in example 1 to obtain a complex P ^2.
Next, the composite P ² obtained was mixed using Nobilta NOB130 in the same manner as in Example 1 to obtain the composite P ³ and then fired at 650 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material for secondary battery (Brookite TiO ₂ / (CNF + C), carbon content 0.3 mass%) on which carbon and graphite derived from cellulose nanofibers were supported was obtained.

[Example 11]
In the same manner as in Example 10 except that 300 g of the suspension P ¹ obtained in Example 10 and 27.7 g of the suspension A ² obtained in Example 1 were mixed, brookite type TiO ₂ and cellulose nano Suspension Q ¹ in which 2.56% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained by carbonizing the fiber was obtained.
The resulting suspension ^{Q 1} and spray dried using the MDL-050M in the same manner as in Example 10, to obtain a complex ^{Q 1,} this was collected 97.5g min, a ball mill together with graphite 2.5g in dry mixing to obtain a composite Q ^2. The obtained complex Q ^2, performs mixing processing using the Nobilta NOB130 in the same manner as in Example 10 to obtain a composite Q ^3.
Then, a complex Q ³ thus obtained was calcined in the same manner as in Example 10, cellulose nanofibers from carbon and graphite is carried secondary battery negative electrode active material (brookite TiO ₂ / (CNF + C ), And 5.0% by mass of carbon).

[Example 12]
In the same manner as in Example 10 except that 300 g of the suspension P ¹ obtained in Example 10 and 71.7 g of the suspension A ² obtained in Example 1 were mixed, brookite type TiO ₂ and cellulose nano Suspension R ¹ in which 6.38% by mass of cellulose nanofiber was mixed with respect to the total amount of carbon obtained by carbonizing the fiber was obtained.
The resulting suspension was spray dried to ^{R 1} in the same manner as in Example 10 using the MDL-050M, to obtain a complex ^{R 1,} it was collected 94.0g min, a ball mill together with graphite 6.0g in dry mixed to obtain a complex R ^2. The obtained composite R ² was mixed using Nobilta NOB130 in the same manner as in Example 10 to obtain a composite R ³ .
Next, the obtained composite R ³ was fired in the same manner as in Example 10, and a negative electrode active material for secondary battery (Brookite TiO ₂ / (CNF + C) on which carbon and graphite derived from cellulose nanofibers were supported. ), And a carbon content of 12.0% by mass.

[Comparative Example 7]
95.0 g of brookite-type TiO ₂ obtained by firing in Example 10 was collected, and the same as in Example 10 together with 5.0 g of graphite (corresponding to 5.0% by mass in terms of carbon atoms in the active material) to be dry mixed in a ball mill to obtain a complex S ^1.
Next, the obtained composite S ¹ was mixed using Nobilta NOB130 in the same manner as in Example 10 to obtain composite S ² and then fired at 650 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material I for secondary battery carrying graphite (Brookite type TiO ₂ / C, carbon amount 5.0 mass%) was obtained.

[Comparative Example 8]
In the same manner as in Example 10 except that 300 g of the suspension P ¹ obtained in Example 10 and 27.7 g of the suspension A ² obtained in Example 1 were mixed, brookite type TiO ₂ and cellulose nano Suspension T ^{1 in} which cellulose nanofibers were mixed in an amount of 11.1% by mass in terms of carbon amount with respect to the total amount of carbon obtained by carbonizing the fiber was obtained.
The obtained suspension T ¹ was spray-dried using MDL-050M in the same manner as in Example 10 to obtain a composite T ¹ , and 90.0 g of this was taken and ball milled with 10.0 g of graphite. in dry mixing to obtain a composite T ^2. The obtained complex ^{T 2,} performs mixing processing using the Nobilta NOB130 in the same manner as in Example 10 to obtain a composite ^{T 3.}
Next, the obtained composite T ³ was fired in the same manner as in Example 10, and the negative electrode active material for secondary battery (Brookite type TiO ₂ / (CNF + C) on which carbon and graphite derived from cellulose nanofibers were supported. ), And a carbon content of 20.0% by mass).

<< Production Example 5: Oxide for negative electrode active material = SiO >>
[Example 13]
100 g of commercially available SiO powder (manufactured by Osaka Titanium Technologies Co., Ltd.) was pulverized with a ball mill for 24 hours to obtain SiO powder having an average particle diameter of 200 nm.

100 g of the obtained SiO was collected and mixed with 200 g of water, and then dispersed with an ultrasonic stirrer (T25 manufactured by IKA) for 1 minute to obtain a suspension U ¹ that was uniformly colored as a whole.
Next, SiO and cellulose nanofibers were carbonized in the same manner as in Example 1 except that 300 g of the obtained suspension U ¹ and 1.58 g of the suspension A ² obtained in Example 1 were mixed. Suspension U ² in which 0.15 parts by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon obtained was obtained.
The obtained suspension U ² was spray-dried using MDL-050M in the same manner as in Example ¹ to obtain a composite U ^{1, and then} 99.85 g of the composite U ¹ and 0.15 g of graphite (negative electrode) except that a mixture of the corresponding) to 0.15 wt% in terms of carbon atoms content in the active material was dry mixed in a ball mill in the same manner as in example 1 to obtain a complex U ^2.
Next, the composite U ² obtained was mixed using Nobilta NOB130 in the same manner as in Example 1 to obtain the composite U ^3, and then fired at 750 ° C. for 1 hour in a reducing atmosphere. Then, a negative electrode active material for secondary battery (SiO / (CNF + C), carbon amount 0.3 mass%) on which carbon and graphite derived from cellulose nanofibers were supported was obtained.

[Example 14]
SiO and cellulose nanofibers were carbonized in the same manner as in Example 13, except that 300 g of the suspension U ¹ obtained in Example 13 and 27.7 g of the suspension A ² obtained in Example 1 were mixed. Suspension V ¹ in which 2.56% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon thus obtained was obtained.
The suspension ^{V 1} obtained by spray drying using the MDL-050M in the same manner as in Example 13, to obtain a complex ^{V 1,} it was collected 97.5g min, a ball mill together with graphite 2.5g in dry mixed to obtain a complex V ^2. The obtained composite V ² was mixed using Nobilta NOB130 in the same manner as in Example 13 to obtain composite V ³ .
Next, the obtained composite V ³ was fired in the same manner as in Example 13, and the negative electrode active material for secondary battery (SiO / (CNF + C), carbon carrying carbon derived from cellulose nanofibers and graphite was supported. Amount 5.0% by mass).

[Example 15]
SiO and cellulose nanofibers were carbonized in the same manner as in Example 13, except that 300 g of the suspension U ¹ obtained in Example 13 and 71.7 g of the suspension A ² obtained in Example 1 were mixed. Suspension W ¹ in which 6.38% by mass of cellulose nanofibers in terms of carbon amount was mixed with respect to the total amount of carbon thus obtained was obtained.
The suspension ^{W 1} obtained by spray-drying using MDL-050M in the same manner as in Example 13, to obtain a complex ^{W 1,} this was collected 94.0g min, a ball mill together with graphite 6.0g in dry mixed to obtain a complex W ^2. The obtained composite W ² was mixed using Nobilta NOB130 in the same manner as in Example 13 to obtain a composite W ³ .
Next, the obtained composite W ³ was fired in the same manner as in Example 13, and the negative electrode active material for secondary battery (SiO / (CNF + C), carbon on which carbon derived from cellulose nanofibers and graphite were supported) 12.0% by mass).

[Comparative Example 9]
95.0 g of SiO obtained by pulverization in Example 13 was collected, and 5.0 g of graphite (corresponding to 5.0% by mass in terms of carbon atom in the negative electrode active material) was used in the same manner as in Example 13. By dry mixing with a ball mill, a composite X ¹ was obtained.
Subsequently, the obtained composite X ¹ was mixed using Nobilta NOB130 in the same manner as in Example 13 to obtain the composite X ² and then calcined at 750 ° C. for 1 hour in a reducing atmosphere. A negative electrode active material for secondary battery (SiO / C, carbon content 5.0 mass%) carrying graphite was obtained.

[Comparative Example 10]
SiO and cellulose nanofibers were carbonized in the same manner as in Example 13, except that 300 g of the suspension U ¹ obtained in Example 13 and 131.6 g of the suspension A ² obtained in Example 1 were mixed. Suspension Y ^{1 in} which cellulose nanofibers were mixed 11.1% by mass in terms of carbon amount with respect to the total amount of carbon obtained was obtained.
The obtained suspension Y ¹ was spray-dried using MDL-050M in the same manner as in Example 13 to obtain a composite Y ¹ , and 90.0 g of this was taken and ball milled with 10.0 g of graphite. in dry mixed to obtain a complex Y ^2. The obtained complex ^{Y 2,} performs mixing processing using the Nobilta NOB130 in the same manner as in Example 13 to obtain a composite ^{Y 3.}
Next, the obtained composite Y ³ was fired in the same manner as in Example 13, and the negative electrode active material for secondary battery (SiO / (CNF + C), carbon on which carbon and graphite derived from cellulose nanofibers were supported. 20.0% by mass).

<Measurement of adsorbed water content>
Each obtained negative electrode active material was allowed to stand in an environment at a temperature of 20 ° C. and a relative humidity of 50% for 1 day to adsorb moisture until it reached equilibrium, heated to a temperature of 150 ° C. and held for 20 minutes, and then further heated to When the temperature is raised to 250 ° C. and held for 20 minutes, the start point is when the temperature rise is resumed from 150 ° C., the end point is when the constant temperature state at 250 ° C. is finished, and volatilization occurs between the start point and the end point. The measured moisture content was measured using a Karl Fischer moisture meter (MKC-610, manufactured by Kyoto Denshi Kogyo Co., Ltd.) and determined as the amount of adsorbed moisture in the negative electrode active material.
The results are shown in Table 1.

<< Evaluation of charge / discharge characteristics using secondary battery >>
Each obtained negative electrode active material, acetylene black (conductive agent), and polyvinylidene fluoride (binding agent) were mixed at a mass ratio of 85: 10: 5, and N-methyl-2-pyrrolidone was added thereto. The mixture was sufficiently kneaded 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 10 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 out to φ15 mm was used as a counter electrode, and a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and ethylmethyl carbonate were mixed at a volume ratio of 3: 7 was used as an electrolyte. A polymer porous film (made of polypropylene) was used as a separator, and was housed and housed in a conventional manner in an atmosphere with 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 upper limit voltage, the lower limit voltage, and the two charge / discharge rates (rate A and rate B) in the charge / discharge test were set to the values shown in Table 1, respectively, under an ambient temperature of 30 ° C. 50 cycles of repeated charge / discharge tests were performed at each rate, the initial discharge capacity (mAh / g) and the discharge capacity after 50 cycles (mAh / g) were measured, and the capacity retention rate (%) was calculated by the following formula (2). Asked.
Capacity retention (%) = (discharge capacity after 50 cycles) / (discharge capacity after 1 cycle) × 100 (2)
The results are shown in Table 1.
In addition, these values are so preferable that a numerical value is large, and the influence by the amount of moisture to adsorb | suck to a battery characteristic tends to appear in the capacity | capacitance retention rate in a quick charge / discharge rate.

  From the above results, it can be seen that the negative electrode active material of the example can surely reduce the amount of adsorbed moisture as compared with the negative electrode active material of the comparative example, and can also exhibit excellent performance in the obtained battery.

Claims (9)

  An oxide-based negative electrode active material for a secondary battery, in which carbon derived from cellulose nanofibers and graphite are supported on an oxide for a negative electrode active material.   The oxide-based negative electrode active material for a secondary battery according to claim 1, wherein graphite is supported on a composite containing an oxide for a negative electrode active material and carbon derived from cellulose nanofibers.   The oxide-based negative electrode active material for a secondary battery according to claim 1 or 2, wherein the amount of carbon derived from cellulose nanofibers is 0.10 to 9% by mass. Negative electrode active material for _{oxide, Li 4 Ti 5 O 12,} Ti 2 Nb 10 O 29, TiNb 2 O 7, brookite TiO _2, and any one of claims 1 to 3 is an oxide selected from SiO 1 An oxide-based negative electrode active material for a secondary battery according to Item.   The average particle diameter of graphite is 0.02-20 micrometers, The oxide type negative electrode active material for secondary batteries of any one of Claims 1-4. Cellulose nanofibers and water are added to the oxide X for negative electrode active material and spray-dried to obtain a composite Y (I), and graphite is added to the obtained composite Y, dry-mixed, and fired. The manufacturing method of the oxide type negative electrode active material for secondary batteries provided with process (II).   The oxide-based negative electrode for a secondary battery according to claim 6, wherein the amount of graphite added in the step (II) is an amount of 0.10 to 9% by mass in the oxide-based negative electrode active material for a secondary battery. A method for producing an active material.   The secondary battery oxide system according to claim 6 or 7, wherein the dry mixing in step (II) is a mixture in which the composite Y and graphite are premixed and then mixed while applying compressive force and shearing force. A method for producing a negative electrode active material. Negative electrode active material for _{oxide, Li 4 Ti 5 O 12,} Ti 2 Nb 10 O 29, TiNb 2 O 7, any one of the claims 6 to 8 is a brookite TiO _2, and oxides selected from SiO The manufacturing method of the oxide type negative electrode active material for secondary batteries as described in an item.