JP2018163755A - Active material-carbon material composite, negative electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery and carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active material-carbon material composite which enables the enhancement of rate and cycle characteristics when used for a negative electrode of a nonaqueous electrolyte secondary battery.SOLUTION: An active material-carbon material composite comprises: a negative electrode active material; and a first carbon material having a graphite structure with graphite partially exfoliated, wherein the average potential of lithium ion desorption and entry in the negative electrode active material is 0.5 V or more and 2.0 V or less vs. Li/Li (a titanium-containing complex oxide including titanium and an element other than titanium when the negative electrode active material is a titanium oxide).SELECTED DRAWING: None

Description

  The present invention includes an active material-carbon material composite that is a composite of an active material and a carbon material, a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the active material-carbon material composite, The present invention also relates to a carbon material used in the active material-carbon material composite.

  In recent years, research and development of non-aqueous electrolyte secondary batteries have been actively conducted for portable devices, hybrid vehicles, electric vehicles, household power storage applications, and the like. Non-aqueous electrolyte secondary batteries used in these fields are required to have a longer life and charge / discharge performance at a large current.

  In order to meet this demand, a titanium-containing oxide disclosed in Non-Patent Document 1 has been studied as a negative electrode active material used for a negative electrode of a nonaqueous electrolyte secondary battery.

  Patent Document 1 discloses a negative electrode active material including a first layer containing a carbon material and a second layer containing lithium titanate and a conductive material. Non-Patent Document 2 discloses a composite of a titanium-containing oxide and a carbon material as a negative electrode active material.

International Publication No. 2013/014830

Journal of the Electrochemical Society, Volume 142, Issue 5, pp. 1431 (1995) GS Yuasa Technical Reart, Vol. 4, No. 2, pp. 36 (2007)

  However, the negative electrode active material of Non-Patent Document 1 has a problem that the material itself has extremely low electronic conductivity and gas is generated during cycle operation.

  Further, even when the negative electrode active material of Patent Document 1 is used, it is not a fundamental solution to the side reaction that proceeds on the surface of the negative electrode active material, and gas generation cannot be sufficiently suppressed. It was. Similarly, in the negative electrode active material of Non-Patent Document 2, although it was possible to impart conductivity, it was not possible to sufficiently suppress gas generation. Therefore, the cycle characteristics could not be sufficiently improved.

  An object of the present invention is to provide an active material-carbon material composite and an active material-carbon material composite capable of enhancing rate characteristics and cycle characteristics when used in a negative electrode of a nonaqueous electrolyte secondary battery. It is providing the negative electrode for nonaqueous electrolyte secondary batteries and the nonaqueous electrolyte secondary battery using this.

The active material-carbon material composite according to the present invention includes a negative electrode active material and a carbon material, and the carbon material has a graphite structure and is partially exfoliated with graphite. The average potential of lithium ion desorption and insertion in the negative electrode active material is 0.5 V or more and 2.0 V or less with respect to Li ⁺ / Li (provided that the negative electrode active material is titanium oxide) Is a titanium-containing composite oxide containing titanium and an element other than titanium).

  On the specific situation with the active material-carbon material composite_body | complex which concerns on this invention, a said 1st carbon material contains resin.

In another specific aspect of the active material-carbon material composite according to the present invention, the absorbance of a 10 mg / L concentration methylene blue methanol solution and the first carbon material are added to the methylene blue methanol solution, followed by centrifugation. The amount of methylene blue adsorbed per 1 g of the first carbon material (μmol / g) measured based on the difference from the absorbance of the supernatant obtained in step 1 is y, and the BET specific surface area (m ^{2 of} the first carbon material) / G) is x, the ratio y / x is 0.15 or more.

  In another specific aspect of the active material-carbon material composite according to the present invention, when the peak intensity ratio between the D band and the G band in the Raman spectrum of the first carbon material is a D / G ratio, The D / G ratio is in the range of 0.05 to 0.8.

  In still another specific aspect of the active material-carbon material composite according to the present invention, a ratio of 0.2 parts by weight or more and 10.0 parts by weight or less of the carbon material with respect to 100 parts by weight of the negative electrode active material. Contains.

  In still another specific aspect of the active material-carbon material composite according to the present invention, the negative electrode active material is a titanium-containing composite oxide.

  In still another specific aspect of the active material-carbon material composite according to the present invention, the carbon material further includes a second carbon material different from the first carbon material, When the weight is A and the weight of the second carbon material is B, 0.01 ≦ A / B ≦ 100.

  The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention includes an active material-carbon material composite configured according to the present invention.

  The nonaqueous electrolyte secondary battery according to the present invention includes a negative electrode for a nonaqueous electrolyte secondary battery configured according to the present invention.

The carbon material according to the present invention is used in a composite with a negative electrode active material, and the average potential of lithium ion desorption and insertion in the negative electrode active material is 0.5 V or more with respect to Li ⁺ / Li, 2 0.0 V or less, a carbon material having a graphite structure and partially exfoliated graphite (however, in the case where the negative electrode active material is titanium oxide, titanium and an element other than titanium are added). Including titanium-containing composite oxide).

  According to the active material-carbon material composite of the present invention, when used in the negative electrode of a non-aqueous electrolyte secondary battery, gas generation can be suppressed and cycle characteristics can be improved. Moreover, the active material-carbon material composite of the present invention can also enhance rate characteristics.

  Details of the present invention will be described below.

  The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[Active material-carbon material composite]
The active material-carbon material composite according to the present invention includes a negative electrode active material and a carbon material. The negative electrode active material is a compound having an average potential of lithium ion desorption and insertion of 0.5 V or more and 2.0 V or less with respect to Li ⁺ / Li. The carbon material includes a first carbon material having a graphite structure and a structure in which graphite is partially exfoliated.

  Since the active material-carbon material composite according to the present invention contains the above-described negative electrode active material and carbon material, when used in the negative electrode of a nonaqueous electrolyte secondary battery, the rate characteristics and cycle characteristics can be improved. it can.

(Negative electrode active material)
In the negative electrode active material used in the present invention, desorption and insertion of lithium ions proceed at 0.5 V or more and 2.0 V or less with respect to Li ⁺ / Li. Hereinafter, the average potential with respect to Li ⁺ / Li is represented by vs. It may be expressed as Li ⁺ / Li.

When the insertion reaction of lithium ions proceeds at 0.5 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less, the insertion of lithium ions into the negative electrode active material is 2.0 V (vs. .Li ⁺ / Li) or less and end at 0.5 V (vs. Li ⁺ / Li) or more. On the other hand, when the desorption reaction of lithium ions proceeds at 0.5 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less, lithium ion desorption from the negative electrode active material occurs. It starts at 0.5 V (vs. Li ⁺ / Li) or higher and ends at 2.0 V (vs. Li ⁺ / Li) or lower.

The voltage value (vs. Li ⁺ / Li) of the lithium ion desorption and insertion reaction is, for example, an operating electrode using a negative electrode active material, a charge / discharge characteristic of a half cell using lithium metal as a counter electrode, and a plateau It can be obtained by reading the voltage values at the start and end. Plateau, if more than two places, as long plateau of the lowest voltage value 0.5V (vs.Li ⁺ / Li) or more, the plateau of the highest voltage value 2.0V (vs.Li ⁺ / Li) It may be the following. The working electrode, electrolytic solution, and separator used in the half battery can be the same as those described later.

When the negative electrode active material in which the lithium ion desorption and insertion reactions proceed at 0.5 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less is titanium oxide, titanium And a titanium-containing composite oxide containing elements other than titanium. That is, in the case of titanium oxide, it is a titanium-containing composite oxide other than titanium oxide that does not contain elements other than titanium.

  Examples of the negative electrode active material other than the titanium-containing composite oxide include metal oxides such as tungsten oxide, niobium pentoxide, and molybdenum dioxide.

  Among these negative electrode active materials, a titanium-containing composite oxide is more preferable from the viewpoint of further improving the stability of the negative electrode active material. Titanium oxides that do not contain elements other than titanium have low reactivity of lithium ion desorption and insertion reactions. Therefore, in the case of titanium oxide, elements other than titanium are further included to improve the reactivity.

Among them, since the production is much easier, as the titanium-containing composite oxide, lithium titanate, titanium dioxide containing an element other than titanium, or H ₂ Ti ₁₂ O ₂₅ is preferable.

  Examples of elements other than titanium in titanium dioxide containing elements other than titanium include tungsten (W), niobium (Nb), boron (B), zirconia (Zr), and vanadium (V). These elements may be used alone or in combination of two or more. By including these elements, the reactivity of lithium ion desorption and insertion reaction is further improved.

For example, tungsten (W), niobium (Nb), boron (B), zirconia (Zr), or vanadium is used for lithium titanate or H ₂ Ti ₁₂ O ₂₅ from the viewpoint of further improving conductivity or stability. An element other than lithium and titanium such as (V) may further be contained. Moreover, the said negative electrode active material may use 1 type, and may use 2 or more types.

The lithium titanate preferably has a spinel structure or a ramsdellite type. Since the expansion and contraction of the negative electrode active material in the reaction of desorption and insertion of lithium ions is much smaller, a spinel structure is more preferable, and the molecular formula is represented by Li ₄ Ti ₅ O ₁₂ .

  Titanium dioxide containing an element other than titanium is preferably anatase type or B type.

  The particle diameter of the negative electrode active material used in the present invention is preferably 0.1 μm or more and 50 μm or less. From the viewpoint of further improving the handleability, it is more preferably 1 μm or more and 30 μm or less. The particle diameter is a value obtained by measuring the size of each particle from the SEM or TEM image and calculating the average particle diameter. The particle diameter may be a single crystal size or a single crystal granule size.

The specific surface area of the negative electrode active material used in the present invention is preferably 0.1 m ² / g or more and 50 m ² / g or less because a desired output density can be easily obtained. The specific surface area is preferably calculated by measurement using a mercury porosimeter or the BET method.

(Carbon material)
In the present invention, the carbon material may have a graphite structure, and may be constituted only by the first carbon material having a structure in which the graphite is partially exfoliated, and further includes a second carbon material described later. You may go out. Hereinafter, in the column of the description of “carbon material”, the first carbon material is referred to as a carbon material. However, in order to distinguish from the second carbon material, it may be referred to as the first carbon material.

  The carbon material used in the present invention has a graphite structure and a structure in which graphite is partially exfoliated. More specifically, “partially exfoliated graphite” means that in the graphene laminate, the graphene layer is open from the edge to some extent inside, that is, a part of the graphite is exfoliated at the edge. In the central part, the graphite layer is laminated in the same manner as the original graphite or primary exfoliated graphite. Therefore, the part where the graphite is partially peeled off at the edge is continuous with the central part. Further, the carbon material may include a material obtained by exfoliating and flaking graphite at the edge.

  As described above, in the carbon material of the present invention, the graphite layer is laminated in the same way as the original graphite or primary exfoliated graphite in the central portion. Therefore, the degree of graphitization is higher than that of conventional graphene oxide and carbon black, and the conductivity is excellent. Moreover, since it has a structure in which graphite is partially peeled off, the specific surface area is large. Therefore, the area of the part that contacts the negative electrode active material can be increased. Therefore, when the active material-carbon material composite containing such a carbon material is used for an electrode of a nonaqueous electrolyte secondary battery, the current distribution in the electrode can be made uniform, so that the resistance of the battery is reduced. In addition to reducing the size, side reactions can be suppressed. As a result, not only the rate characteristics can be improved, but also the generation of gas can be suppressed, and the cycle characteristics can also be improved.

  Such a carbon material is obtained by preparing a composition containing graphite or primary exfoliated graphite and a resin, in which the resin is fixed to the graphite or primary exfoliated graphite by grafting or adsorption, and pyrolyzing. Can do. The resin contained in the composition is preferably removed, but a part of the resin may remain.

  By the thermal decomposition, the distance between the graphene layers in the graphite or primary exfoliated graphite is increased. More specifically, in a graphene laminate such as graphite or primary exfoliated graphite, the graphene layer is expanded from the edge to some extent inside. That is, it is possible to obtain a structure in which a part of the graphite is exfoliated and the graphite layer is laminated in the central part in the same manner as the original graphite or primary exfoliated graphite.

  The graphite is a stack of a plurality of graphenes. As graphite, natural graphite, artificial graphite, expanded graphite and the like can be used. Expanded graphite has a larger graphene layer than normal graphite. Therefore, it can peel easily. Therefore, when expanded graphite is used, the carbon material of the present invention can be obtained more easily.

The graphite has a graphene lamination number of about 100,000 to about 1,000,000, and has a specific surface area (BET specific surface area) by BET of less than 25 m ² / g. Moreover, since the said primary exfoliated graphite is obtained by exfoliating graphite, the specific surface area should just be larger than graphite.

  In the present invention, the number of graphene layers in the carbon material where the graphite is partially peeled is preferably 5 or more and 3000 or less, and more preferably 5 or more and 1000 or less. More preferably, it is 5 layers or more and 500 layers or less.

  When the number of graphene stacks is less than the above lower limit, the number of graphene stacks in the part where the graphite is partially peeled is small, so that each negative electrode active material in the negative electrode for a non-aqueous electrolyte secondary battery described later must be connected. May not be possible. As a result, the electron conduction path in the negative electrode is interrupted, the rate characteristic and the cycle characteristic may be deteriorated, and side reactions are likely to proceed, and as a result, gas may be easily generated.

  When the number of graphene stacks is larger than the above upper limit, the size of one carbon material becomes extremely large, and the distribution of the carbon material in the negative electrode may be biased. Therefore, the electron conduction path in the negative electrode becomes undeveloped and not only the rate characteristic and the cycle characteristic may be deteriorated, but also a side reaction is likely to proceed, and as a result, gas is likely to be generated.

  The calculation method of the number of graphene layers is not particularly limited, but can be calculated by visual observation with a TEM or the like.

  The carbon material used in the present invention has a D / G ratio of 0.8 or less when the peak intensity ratio between the D band and the G band is a D / G ratio in a Raman spectrum obtained by Raman spectroscopy. It is preferable that it is 0.7 or less. When the D / G ratio is within this range, the conductivity of the carbon material itself can be further increased, and the amount of gas generated can be further reduced. Moreover, it is preferable that D / G ratio is 0.05 or more. In this case, the electrolytic solution decomposition reaction on the carbon material is suppressed, and as a result, gas generation is further suppressed and the cycle characteristics can be further improved.

The BET specific surface area of the carbon material used in the present invention is preferably 25 m ² / g or more because the contact point with the negative electrode active material can be more sufficiently secured. The BET specific surface area of the carbon material is more preferably 35 m ² / g or more, and even more preferably 45 m ² / g or more, because the contact point with the negative electrode active material can be more sufficiently secured. Moreover, it is preferable that the BET specific surface area of a carbon material is 2500 m < ² > / g or less from a viewpoint of improving the ease of handling at the time of negative electrode preparation further.

The carbon material used in the present invention has a ratio y / x where y represents the methylene blue adsorption amount (μmol / g) per 1 g of the carbon material and x represents the BET specific surface area (m ² / g) of the carbon material. 0.15 or more, more preferably 0.15 or more and 1.0 or less. Moreover, since adsorption | suction with a negative electrode active material and a carbon material advances further easily at the time of the below-mentioned slurry preparation, it is still more preferable that it is 0.2 or more and 0.9 or less.

  The methylene blue adsorption amount (μmol / g) is measured as follows. First, the absorbance (blank) of a 10 mg / L concentration methylene blue methanol solution is measured. Next, a measurement object (carbon material) is put into a methanol solution of methylene blue, and the absorbance (sample) of the supernatant obtained by centrifugation is measured. Finally, the amount of methylene blue adsorbed per gram (μmol / g) is calculated from the difference between the absorbance (blank) and the absorbance (sample).

There is a correlation between the amount of methylene blue adsorbed and the specific surface area determined by BET of the carbon material. Conventionally known spherical graphite particles have a relationship of y≈0.13x, where x is the BET specific surface area (m ² / g) and y is the methylene blue adsorption amount (μmol / g). . This indicates that the larger the BET specific surface area, the larger the methylene blue adsorption amount. Therefore, the amount of methylene blue adsorption can be used as an index instead of the BET specific surface area.

  In the present invention, as described above, the carbon material ratio y / x is preferably 0.15 or more. On the other hand, in the conventional spherical graphite particles, the ratio y / x is 0.13. Therefore, when the ratio y / x is 0.15 or more, the adsorbed amount of methylene blue is increased while the conventional spherical graphite has the same BET specific surface area. That is, in this case, although it is somewhat condensed in the dry state, in the wet state such as in methanol, the graphene layer or the graphite layer can be further expanded compared to the dry state.

  The carbon material used in the present invention can be obtained through a step of first producing a composition in which a resin is fixed to graphite or primary exfoliated graphite by grafting or adsorption, and then a step of heat-treating the composition. . Note that the resin contained in the composition may be removed, or a part of the resin may remain.

  When the resin remains in the carbon material, the resin amount is preferably 1 part by weight or more and 350 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight with respect to 100 parts by weight of the carbon material excluding the resin. The content is more preferably 5 parts by weight or more and 30 parts by weight or less. If the residual resin amount is less than the above lower limit, the BET specific surface area may not be ensured. Moreover, when there are more residual resin amounts than the said upper limit, manufacturing cost may increase.

  The amount of resin remaining in the carbon material can be calculated by measuring a change in weight accompanying the heating temperature by, for example, thermogravimetric analysis (hereinafter referred to as TG).

  The carbon material used in the present invention may be removed from the resin after producing a composite with the negative electrode active material. As a method for removing the resin, a method of heat treatment at a temperature equal to or higher than the decomposition temperature of the resin and lower than the decomposition temperature of the negative electrode active material is preferable. This heat treatment may be performed in the air, in an inert gas atmosphere, in a low oxygen atmosphere, or in a vacuum.

  The resin used for preparing the composition in which the resin is fixed to graphite or primary exfoliated graphite by grafting or adsorption is not particularly limited, but is preferably a polymer of a radical polymerizable monomer. The radical polymerizable monomer may be a copolymer of a plurality of types of radical polymerizable monomers, or may be a homopolymer of one type of radical polymerizable monomer.

  Examples of such resins include polypropylene glycol, polyglycidyl methacrylate, polyvinyl acetate, polybutyral, polyacrylic acid or polyethylene glycol.

  As a manufacturing method of the said carbon material, the manufacturing method as described in international publication 2014/034156 is mentioned, for example. That is, for example, the carbon used in the present invention is obtained by passing through a step of producing a composition containing graphite or primary exfoliated graphite and a resin, and a step of thermally decomposing the produced composition (in an open system). The material is manufactured. The produced carbon material has a graphite structure and a structure in which graphite is partially exfoliated.

In the above manufacturing method, since the oxidation process is not performed, the obtained carbon material is superior in conductivity as compared with conventional graphene oxide and graphene obtained by reducing the graphene oxide. This is probably because conventional graphene oxide or redox graphene cannot sufficiently secure the sp ² structure. Since it is superior in conductivity compared to conventional graphene oxide and redox graphene, the active material-carbon material composite using the carbon material is a battery when used for an electrode of a non-aqueous electrolyte secondary battery. Resistance can be reduced, and rate characteristics and cycle characteristics can be improved. In addition, since the obtained carbon material has less active sites on the surface, the electrolytic solution is less likely to be decomposed than graphene oxide. Therefore, when the obtained carbon material is used, generation of gas can be suppressed. .

  The reason why the carbon material obtained by the above production method is difficult to decompose the electrolytic solution can be explained as follows.

  In general, graphene oxide and graphene via graphene oxide are subjected to oxidation or reduction treatment, and thus have a large number of functional groups (acidic: hydroxyl group or carboxyl group, alkaline: amino group) on the surface. Since these functional groups themselves are acidic or alkaline, they have a property of easily reacting with the electrolytic solution. In addition, since the molecules of the electrolytic solution are easily adsorbed, the chance of contact with the electrode surface is increased, and from this point, the reaction with the electrolytic solution is facilitated.

  Carbon black has defects in the crystal structure because it is not completely graphitized in addition to the above functional groups. This defect has an excess or deficiency of electrons, and works in a direction to eliminate this excess or deficiency, so that surrounding molecules are involved and the reaction with the electrolytic solution easily proceeds.

  On the other hand, the carbon material obtained by the above production method has a high degree of graphitization and has no active sites on the surface because it has not undergone an oxidation step. Therefore, the carbon material obtained by the above manufacturing method is difficult to decompose the electrolytic solution, and the generation of gas can be suppressed.

  As described above, in the present invention, when the above-described carbon material having a graphite structure and partially exfoliated graphite is used as the first carbon material, the second carbon material other than the first carbon material is used. The carbon material may be included. The second carbon material is a carbon material different from the first carbon material, and does not have a structure in which graphite is partially exfoliated. It does not specifically limit as said 2nd carbon material, A graphene, a granular graphite compound, a fibrous graphite compound, or carbon black etc. are illustrated.

  The graphene may be graphene oxide or may be graphene oxide reduced.

  The granular graphite compound is not particularly limited, and examples thereof include natural graphite, artificial graphite, and expanded graphite.

  The fibrous graphite compound is not particularly limited, and examples thereof include carbon nanohorn, carbon nanotube, or carbon fiber.

  The carbon black is not particularly limited, and examples thereof include furnace black, ketjen black, and acetylene black.

From the viewpoint of further enhancing the electrolyte solution retention of the secondary battery, the BET specific surface area of the second carbon material is preferably 5 m ² / g or more. From the viewpoint of further enhancing the electrolyte solution retention of the secondary battery, the BET specific surface area of the second carbon material is more preferably 10 m ² / g or more, and further preferably 25 m ² / g or more. Further, from the viewpoint of further enhancing the ease of handling during the production of the negative electrode, the BET specific surface area of the second carbon material is preferably 2500 m ² / g or less.

  The first carbon material having a graphite structure and a structure in which graphite is partially exfoliated and the second carbon material not having a structure in which graphite is partially exfoliated include, for example, , SEM, TEM, etc.

  The inclusion of the first carbon material and the second carbon material means that, for example, the first carbon material and the second carbon material are present in a composite body and a negative electrode described later. . The method for causing the first carbon material and the second carbon material to exist is not particularly limited, but may be mixed at the time of producing a composite body or a negative electrode described later, or a composite material described later with either one of the carbon materials. After the body is manufactured, the other carbon material may be added.

  A functional group may be present on the surface of the second carbon material. In this case, it becomes easier to produce the composite body and negative electrode described later.

  In the present invention, when the weight of the first carbon material is A and the weight of the second carbon material is B, the ratio A / B is in the range of 0.01 to 100. It is preferable. When the ratio A / B is within the above range, the resistance of the electrode in the secondary battery can be further reduced. Therefore, when used in a secondary battery, heat generation during charging / discharging with a large current can be further suppressed.

  From the viewpoint of further reducing the resistance of the electrode in the secondary battery, the ratio A / B is preferably 0.05 or more, more preferably 0.1 or more, preferably 20 or less, more preferably 10 or less.

(Active material-carbon material composite)
The active material-carbon material composite of the present invention is produced, for example, by the following procedure.

  First, a dispersion liquid (hereinafter, a dispersion liquid of a carbon material) in which a carbon material including the first carbon material having the above-described graphite structure and partially exfoliated graphite is dispersed in a solvent is prepared. To do. Subsequently, separately from the above dispersion liquid, a negative electrode active material dispersion liquid (hereinafter, negative electrode active material dispersion liquid) in which the negative electrode active material is dispersed in a solvent is prepared. Next, the carbon material dispersion and the negative electrode active material dispersion are mixed. Finally, the composite of the negative electrode active material and the carbon material used in the negative electrode of the present invention (active material-carbon material composite) is removed by removing the solvent of the dispersion containing the carbon material and the negative electrode active material. Is produced.

  In addition to the above-described manufacturing method, a method may be used in which a negative electrode active material is added to a dispersion of a carbon material, a dispersion containing the carbon material and the negative electrode active material is prepared, and then the solvent is removed. Alternatively, a method of mixing a mixture of a negative electrode active material and a solvent with a mixer may be used. You may serve as preparation of the below-mentioned negative electrode slurry, and composite preparation.

  The solvent in which the negative electrode active material or the carbon material is dispersed may be any of aqueous, non-aqueous, a mixed solvent of aqueous and non-aqueous, or a mixed solvent of different non-aqueous solvents. The solvent used for dispersing the carbon material and the solvent for dispersing the negative electrode active material may be the same or different. If they are different, it is preferable that the solvents are compatible with each other.

  Although it does not specifically limit as a non-aqueous solvent, For example, solvents, such as alcohol system represented by methanol, ethanol, and propanol, tetrahydrofuran, or N-methyl-2-pyrrolidone, can be used from the ease of dispersion | distribution. In order to further improve dispersibility, the solvent may contain a dispersant such as a surfactant.

  The dispersion method is not particularly limited, and examples thereof include dispersion by ultrasonic waves, dispersion by a mixer, dispersion by a jet mill, and dispersion by a stirrer.

  The solid content concentration of the carbon material dispersion is not particularly limited, but when the weight of the carbon material is 1, the weight of the solvent is preferably 1 or more and 1000 or less. From the viewpoint of further improving the handleability, when the weight of the carbon material is 1, the weight of the solvent is more preferably 5 or more and 750 or less. Further, from the viewpoint of further improving dispersibility, when the weight of the carbon material is 1, the weight of the solvent is more preferably 5 or more and 500 or less.

  When the weight of the solvent is less than the above lower limit, the carbon material may not be dispersed to a desired dispersion state. On the other hand, when the weight of the solvent is larger than the above upper limit, the production cost may increase.

  The solid content concentration of the dispersion of the negative electrode active material is not particularly limited, but when the weight of the negative electrode active material is 1, the weight of the solvent is preferably 0.5 or more and 100 or less. From the viewpoint of further improving the handleability, the weight of the solvent is more preferably 1 or more and 75 or less. Further, from the viewpoint of further improving dispersibility, the weight of the solvent is more preferably 5 or more and 50 or less. In addition, when the weight of a solvent is less than the said minimum, a negative electrode active material may be unable to be disperse | distributed to a desired dispersion state. On the other hand, when the weight of the solvent is larger than the above upper limit, the production cost may increase.

  A method of mixing the dispersion of the negative electrode active material and the dispersion of the carbon material is not particularly limited, but a method of mixing each other's dispersion at a time or one dispersion into the other dispersion multiple times. A method of adding them separately is mentioned.

  Examples of the method of adding one dispersion to the other dispersion in a plurality of times include a method of dropping using a dropping device such as a spoid, a method of using a pump, or a method of using a dispenser.

  A method for removing the solvent from the mixture of the carbon material, the negative electrode active material and the solvent is not particularly limited, and examples thereof include a method of removing the solvent by filtration and then drying it in an oven or the like. The filtration is preferably suction filtration from the viewpoint of further improving productivity. Moreover, as a drying method, when drying in a vacuum oven and then drying in a vacuum, it is preferable because the solvent remaining in the pores can be removed.

  In the active material-carbon material composite of the present invention, the ratio of the negative electrode active material to the carbon material is such that the weight of the carbon material is 0.2 or more and 10.0 or less when the weight of the negative electrode active material is 100. It is preferable that From the viewpoint of further improving the rate characteristics, the weight of the carbon material is more preferably 0.3 or more and 8.0 or less. Further, from the viewpoint of further improving the cycle characteristics, the weight of the carbon material is more preferably 0.5 or more and 7.0 or less.

[Negative electrode for non-aqueous electrolyte secondary battery]
The negative electrode for a non-aqueous electrolyte secondary battery of the present invention includes the above-described active material-carbon material composite. The negative electrode for a non-aqueous electrolyte secondary battery of the present invention may be formed only from the active material-carbon material composite, but a binder may be included from the viewpoint of forming the negative electrode more easily.

  The binder is not particularly limited, but for example, at least one resin selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof. Can be used.

  The binder is preferably dissolved or dispersed in a non-aqueous solvent or water from the viewpoint of more easily producing a negative electrode for a non-aqueous electrolyte secondary battery.

  The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. You may add a dispersing agent and a thickener to these.

  The amount of the binder contained in the negative electrode for a non-aqueous electrolyte secondary battery of the present invention is preferably 0.3 parts by weight or more and 30 parts by weight or less, more preferably 0.00 parts by weight with respect to 100 parts by weight of the negative electrode active material. 5 parts by weight or more and 15 parts by weight or less. When the amount of the binder is within the above range, the adhesion between the negative electrode active material and the carbon material can be maintained, and the adhesion with the current collector can be further enhanced.

  Examples of the method for producing the negative electrode for a nonaqueous electrolyte secondary battery of the present invention include a method of producing a mixture of an active material-carbon material composite and a binder on a current collector.

  From the viewpoint of more easily producing the negative electrode for a non-aqueous electrolyte secondary battery, it is preferably produced as follows. First, a slurry is prepared by adding and mixing a binder solution or a dispersion to the active material-carbon material composite. Next, the prepared slurry is applied on a current collector, and finally the solvent is removed to prepare a negative electrode for a non-aqueous electrolyte secondary battery.

  Examples of the method for preparing the slurry include a method in which a binder solution is added to the active material-carbon material composite and mixed using a mixer or the like. Although it does not specifically limit as a mixer used for mixing, A planetary mixer, a disper, a thin film swirl-type mixer, a jet mixer, or a self-rotation type mixer etc. are mentioned.

  The solid content concentration of the slurry is preferably 30% by weight or more and 95% by weight or less from the viewpoint of further easily performing the coating described later. From the viewpoint of further improving the storage stability, the solid content concentration of the slurry is more preferably 35% by weight or more and 90% by weight or less. Further, from the viewpoint of further reducing the production cost, the solid content concentration of the slurry is more preferably 40% by weight or more and 85% by weight or less.

  The solid content concentration can be controlled by a dilution solvent. As the diluting solvent, it is preferable to use the same type of solvent as the binder solution or dispersion. Further, other solvents may be used as long as the solvents are compatible.

  The current collector used for the negative electrode for a non-aqueous electrolyte secondary battery of the present invention is preferably copper, SUS, nickel, titanium, aluminum, or an alloy containing these metals. As the current collector, a metal material (copper, SUS, nickel, titanium, or an alloy containing these metals) coated with a metal that does not react with the potential of the negative electrode can be used.

  The thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. When the thickness of the current collector is less than 10 μm, handling may be difficult from the viewpoint of production. On the other hand, when the thickness of the current collector is thicker than 100 μm, it may be disadvantageous from an economic viewpoint.

  The method of applying the slurry to the current collector is not particularly limited. For example, the method of removing the solvent after applying the slurry with a doctor blade, die coater or comma coater, or removing the solvent after applying with a spray. And a method of removing the solvent after coating by screen printing.

  Since the method for removing the solvent is much simpler, drying using a blower oven or a vacuum oven is preferable. Examples of the atmosphere for removing the solvent include an air atmosphere, an inert gas atmosphere, and a vacuum state. The temperature for removing the solvent is not particularly limited, but is preferably 60 ° C. or higher and 250 ° C. or lower. If the temperature at which the solvent is removed is less than 60 ° C., it may take time to remove the solvent. On the other hand, if the temperature for removing the solvent is higher than 250 ° C., the binder may deteriorate.

  The negative electrode for a nonaqueous electrolyte secondary battery of the present invention may be compressed to a desired thickness and density. Although compression is not specifically limited, For example, it can carry out using a roll press, a hydraulic press, etc.

  The thickness of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention after compression is not particularly limited, but is preferably 10 μm or more and 1000 μm or less. If the thickness is less than 10 μm, it may be difficult to obtain a desired capacity. On the other hand, when the thickness is thicker than 1000 μm, it may be difficult to obtain a desired output density.

The density of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention is preferably 1.0 g / cm ³ or more and 4.0 g / cm ³ or less. When the density is less than 1.0 g / cm ³ , the contact between the negative electrode active material and the carbon material becomes insufficient, and the electronic conductivity may be lowered. On the other hand, when the density is larger than 4.0 g / cm ³ , an electrolyte solution described later hardly penetrates into the negative electrode, and lithium conductivity may be lowered.

In the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the electric capacity per 1 cm ^{2 of the} negative electrode is preferably 0.5 mAh or more and 10.0 mAh or less. When the electric capacity is less than 0.5 mAh, the size of the battery having a desired capacity may increase. On the other hand, when the electric capacity is greater than 10.0 mAh, it may be difficult to obtain a desired output density. In addition, calculation of the electric capacity per 1 cm < ² > of negative electrodes may be calculated by preparing a half battery using a lithium metal as a counter electrode after preparing a negative electrode for a non-aqueous electrolyte secondary battery, and measuring charge / discharge characteristics.

The electric capacity per 1 cm ^{2 of the} negative electrode of the negative electrode for a nonaqueous electrolyte secondary battery is not particularly limited, but can be controlled by the weight of the negative electrode formed per current collector unit area. For example, it can control by the coating thickness at the time of the above-mentioned slurry coating.

[Nonaqueous electrolyte secondary battery]
The positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery of the present invention may have a form in which the same electrode is formed on both surfaces of the current collector, and the positive electrode is formed on one surface of the current collector and the negative electrode is formed on the other surface. Alternatively, it may be a bipolar electrode.

  The nonaqueous electrolyte secondary battery of the present invention may be one obtained by winding or laminating a separator disposed between the positive electrode side and the negative electrode side. The positive electrode, the negative electrode, and the separator contain a non-aqueous electrolyte that is responsible for lithium ion conduction. Accordingly, examples of the nonaqueous electrolyte secondary battery include a lithium ion secondary battery.

  The non-aqueous electrolyte secondary battery of the present invention may be wound or laminated with a laminate film after the laminate is wound, or may be rectangular, elliptical, cylindrical, coin-shaped, button-shaped, or sheet-shaped. It may be packaged with a metal can. The exterior may be provided with a mechanism for releasing the generated gas. The number of stacked layers is not particularly limited, and the stacked body can be stacked until a desired voltage value and battery capacity are developed.

  The nonaqueous electrolyte secondary battery of the present invention can be an assembled battery that is connected in series or in parallel as appropriate depending on the desired size, capacity, and voltage. In the assembled battery, it is preferable that a control circuit is attached to the assembled battery in order to confirm the state of charge of each battery and improve safety.

(Positive electrode)
The positive electrode used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but may contain a compound having a higher average potential for lithium ion desorption and insertion than the negative electrode active material, that is, a positive electrode active material. . For example, a layered rock salt type compound represented by lithium cobaltate and lithium nickelate, a spinel type compound represented by lithium manganate, an olivine type compound represented by lithium iron olivine, or their A mixture is mentioned.

(Negative electrode)
The nonaqueous electrolyte secondary battery of the present invention includes a negative electrode for a nonaqueous electrolyte secondary battery configured according to the present invention as a negative electrode. The negative electrode for a non-aqueous electrolyte secondary battery includes an active material-carbon material composite configured according to the present invention. Therefore, the nonaqueous electrolyte secondary battery of the present invention is excellent in rate characteristics and cycle characteristics.

(Separator)
The separator used for the nonaqueous electrolyte secondary battery of the present invention may be any structure as long as it is installed between the positive electrode and the negative electrode described above and can contain an insulating nonaqueous electrolyte described later. Examples of the material for the separator include nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, polyethylene terephthalate, or a composite of two or more of these, a woven fabric, a nonwoven fabric, or a microporous membrane. Can be mentioned.

  The separator may contain various plasticizers, antioxidants, or flame retardants, and may be coated with a metal oxide or the like.

  Although the thickness of a separator is not specifically limited, It is preferable that they are 5 micrometers or more and 100 micrometers or less. When the thickness of the separator is less than 5 μm, the positive electrode and the negative electrode may contact each other. When the thickness of the separator is greater than 100 μm, the resistance of the battery may increase. From the viewpoint of further improving economy and handleability, the thickness of the separator is more preferably 10 μm or more and 50 μm or less.

(Nonaqueous electrolyte)
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but high electrolytes such as gel electrolyte, polyethylene oxide, and polypropylene oxide impregnated in a polymer with an electrolyte solution in which a solute is dissolved in a non-aqueous solvent are used. Molecular solid electrolytes or inorganic solid electrolytes such as sulfide glass and oxynitride can be used.

  As the non-aqueous solvent, it is preferable to include a cyclic aprotic solvent and / or a chain aprotic solvent because the solute described later is more easily dissolved. Examples of the cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones, and cyclic ethers. Examples of the chain aprotic solvent include chain carbonate, chain carboxylic acid ester, chain ether and the like. In addition to the above, a solvent generally used as a solvent for nonaqueous electrolytes such as acetonitrile may be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, sulfolane, dioxolane, or For example, methyl propionate can be used. These solvents may be used alone or in combination of two or more. However, it is preferable to use a solvent in which two or more kinds are mixed from the viewpoint of further easily dissolving a solute described later and further enhancing the conductivity of lithium ions.

The solute is not particularly limited, for _{example, LiClO 4, LiBF 4, LiPF} 6, LiAsF 6, LiCF 3 SO 3, LiBOB (Lithium Bis (Oxalato) Borate), or _LiN (SO 2 _{CF 3) 2} and the like are preferable . In this case, it can be dissolved more easily by a solvent.

  The concentration of the solute contained in the electrolytic solution is preferably 0.5 mol / L or more and 2.0 mol / L or less. If the concentration of the solute is less than 0.5 mol / L, desired lithium ion conductivity may not be exhibited. On the other hand, if the concentration of the solute is higher than 2.0 mol / L, the solute may not dissolve further. The nonaqueous electrolyte may contain a trace amount of additives such as a flame retardant and a stabilizer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples, In the range which does not change the summary, it can change suitably.

Production example of negative electrode active material;
The negative electrode active material Li ₄ Ti ₅ O ₁₂ was produced by the method described in the literature (J. Electrochem. Soc., Volume 142, Issue 5, pp. 1431 (1995)).

  That is, first, titanium dioxide and lithium hydroxide were mixed so that the molar ratio of titanium to lithium was 5: 4 to obtain a mixture. Next, this mixture was heated at 800 ° C. for 12 hours in a nitrogen atmosphere to prepare lithium titanate as a negative electrode active material.

Carbon material production example 1;
First, expanded graphite (made by Toyo Tanso Co., Ltd., trade name “PF powder 8F”, BET specific surface area = 22 m ² / g) and thermal decomposable foaming agent (ADCA, made by Eiwa Kasei Kogyo Co., Ltd., trade name “Binihol” 20 g of AC # R-K3 ”, thermal decomposition temperature 210 ° C., 200 g of polypropylene glycol (manufactured by Sanyo Chemical Industries, trade name“ Sanix GP-3000 ”, average molecular weight = 3000) and 200 g of tetrahydrofuran are mixed, A raw material composition was prepared. Polypropylene glycol (PPG) was adsorbed on the expanded graphite by irradiating the raw material composition with ultrasonic waves at 100 W and an oscillation frequency of 28 kHz for 5 hours with an ultrasonic treatment apparatus (manufactured by Honda Electronics Co., Ltd.). In this way, a composition in which polypropylene glycol was adsorbed on expanded graphite was prepared.

  Next, after a composition in which polypropylene glycol is adsorbed on expanded graphite is formed by a solution casting method, tetrahydrofuran is heated in this order for 2 hours at 80 ° C., 1 hour at 110 ° C., and 1 hour at 150 ° C. (Hereinafter THF) was removed. Thereafter, the composition from which THF was removed was heat-treated at 110 ° C. for 1 hour, and further heat-treated at 230 ° C. for 2 hours to foam the composition.

  Furthermore, the foamed composition is heat-treated at a temperature of 450 ° C. for 0.75 hour, thereby producing a carbon material in which a part of the polypropylene glycol (resin) remains (having a graphite structure, and the graphite is partially A first carbon material that has been peeled off was produced.

  The obtained carbon material contained 15% by weight of resin with respect to the total weight. The resin amount was calculated as the amount of resin using TG (manufactured by Hitachi High-Tech Science Co., Ltd., product number “STA7300”) as the amount of resin weight decreased in the range of 350 ° C. to 600 ° C.

  It was 0.6 as a result of measuring D / G ratio which is a peak intensity ratio of D band of the Raman spectrum of the obtained carbon material, and G band. The Raman spectrum of the carbon material was measured using a Raman spectroscope (trade name “Nicolet Almega XR” manufactured by Thermo Scientific).

Further, D / G ratio is a maximum peak intensity in the range of ^{1300cm -1 ~1400cm} -1 of the obtained Raman spectrum and the peak intensity of D-band, ^also the maximum peak intensity of 1500cm ^-1 ~1600cm -1 G It was determined by taking the peak intensity of the band.

It was 120 m < ² > / g as a result of measuring the BET specific surface area of the obtained carbon material using the specific surface area measuring apparatus (Shimadzu Corporation make, product number "ASAP-2000", nitrogen gas).

  Moreover, the methylene blue adsorption amount of the obtained carbon material was 61.0 μmol / g as a result of measurement by the following procedure. Further, when the BET specific surface area was x and the methylene blue adsorption amount was y, the ratio y / x was 0.508.

  The measurement of the amount of methylene blue adsorption was performed as follows. First, a methanol solution of methylene blue (manufactured by Kanto Chemical Co., Ltd., special grade reagent) having concentrations of 10.0 mg / L, 5.0 mg / L, 2.5 mg / L, and 1.25 mg / L is prepared in a volumetric flask. Each absorbance was measured with an ultraviolet-visible spectrophotometer (manufactured by Shimadzu Corporation, product number “UV-1600”) to prepare a calibration curve. Next, 10 mg / L of methylene blue was prepared, and a carbon material to be measured (0.005 to 0.05 g, changed depending on the BET value of the sample), a methylene blue solution (10 mg / L, 50 mL), and a 100 mL eggplant flask, and After adding a stirrer bar and treating with an ultrasonic cleaner (manufactured by AS ONE) for 15 minutes, the mixture was stirred for 60 minutes in a cooling bath (25 ° C.). Further, after reaching adsorption equilibrium, the carbonaceous material and the supernatant are separated by centrifugation, and the absorbance of the blank 10 mg / L methylene blue solution and the supernatant is measured with an ultraviolet-visible spectrophotometer. The difference in absorbance with the supernatant was calculated.

  Finally, the amount of decrease in the concentration of the methylene blue solution was calculated from the difference in absorbance and the calibration curve, and the amount of methylene blue adsorbed on the surface of the carbon material to be measured was calculated from the following formula.

  Adsorption amount (mol / g) = {Amount of decrease in concentration of methylene blue solution (g / L) × Volume of measurement solvent (L)} / {Molecular blue molecular weight (g / mol) × Mass of carbon material used for measurement ( g)} ... Formula

Carbon Material Production Example 2;
First, expanded graphite (product name “PF powder 8F”, manufactured by Toyo Tanso Co., Ltd., BET specific surface area = 22 m ² / g), carboxymethylcellulose (manufactured by Aldrich, average molecular weight = 250,000), 0.48 g The mixture with 530 g of water was irradiated with ultrasonic waves for 5 hours with an ultrasonic treatment device (manufactured by SMT.CO., LTD, product number “UH-600SR”), and then polyethylene glycol (manufactured by Sanyo Chemical Industries, product number “ PG600 ") was added, and a raw material composition was prepared by mixing for 30 minutes with a homomixer (manufactured by TOKUSHU KIKA, TK HOMOMIXER MARKII).

  Next, water was removed by heat-processing the produced raw material composition at 150 degreeC. Thereafter, the composition from which water has been removed is heat-treated at a temperature of 400 ° C. for 1.5 hours, so that a carbon material (having a graphite structure, partially containing polyethylene glycol (resin) remains partially. A first carbon material from which graphite is peeled is prepared.

  The obtained carbon material contained 12% by weight of resin with respect to the total weight. The amount of resin was calculated as the amount of resin using TG (manufactured by Hitachi High-Tech Science Co., Ltd., product number “STA7300”) as the amount of weight reduction in the range of 200 ° C. to 600 ° C.

  The D / G ratio, which is the peak intensity ratio between the D band and the G band of the Raman spectrum of the carbon material obtained in Production Example 2 of the carbon material, was 0.234.

As a result of measuring the BET specific surface area of the carbon material obtained in Production Example 2 of the carbon material using a specific surface area measuring device (manufactured by Shimadzu Corporation, product number “ASAP-2000”, nitrogen gas), it is 95 m ² / g. there were.

  Moreover, the methylene blue adsorption amount of the carbon material obtained in Production Example 2 of the carbon material was 69.7 μmol / g as a result of measurement by the above procedure. Further, when the BET specific surface area was x and the methylene blue adsorption amount was y, the ratio y / x was 0.733.

Example 1
Active material-carbon material composite;
The composite of the negative electrode active material produced in the above production example and the carbon material of production example 1 was produced by the following procedure.

  First, 5 g of ethanol was added to 0.13 g of the carbon material produced in Production Example 1, and the mixture was treated with an ultrasonic cleaner (manufactured by AS ONE) for 5 hours. A dispersion of the carbon material of Example 1 was prepared.

Next, 3 g of the negative electrode active material (Li ₄ Ti ₅ O ₁₂ ) prepared in the production example was added to 9 g of ethanol, and the mixture was stirred for 10 minutes at 600 rpm with a magnetic stirrer, thereby dispersing the negative electrode active material of Example 1 Was prepared.

  Further, the negative electrode active material dispersion of Example 1 was dropped into the carbon material dispersion of Example 1 with a dropper. In addition, at the time of dripping, the dispersion liquid of the carbon material of Example 1 continued processing with the ultrasonic cleaning machine (made by ASONE). Then, the liquid mixture of the carbon material of Example 1 and the dispersion liquid of the negative electrode active material of Example 1 was stirred for 3 hours with a magnetic stirrer.

  Finally, the mixed liquid of the dispersion liquid is subjected to suction filtration, and then vacuum-dried at 110 ° C. for 1 hour to produce a composite of the negative electrode active material and the carbon material of Example 1 (active material-carbon material composite). did. Note that the amount necessary for the production of the negative electrode was produced by repeating the above steps.

Negative electrode;
The negative electrode of Example 1 was produced as follows.

First, 100 parts by weight of the composite was mixed with a binder (PVdF, solid content concentration: 12% by weight, NMP solution) so that the solid content was 5 parts by weight to prepare a slurry. Next, this slurry was applied to an aluminum foil (20 μm), then heated in a blast oven at 120 ° C. for 1 hour to remove the solvent, and then vacuum-dried at 120 ° C. for 12 hours. Finally, it was pressed with a roll press to produce a negative electrode (single-sided coating) having an electrode density of 1.8 g · cc ⁻¹ . The electrode density was calculated from the electrode weight and thickness per unit area.

  The capacity of the negative electrode was measured by the following charge / discharge test.

First, the above-mentioned electrode was punched to 14 mmΦ, and Li metal was punched to 16 mmΦ as a counter electrode. Next, the working electrode (single-sided coating) / separator (polyolefin porous membrane, thickness 25 μm) / Li metal was laminated in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / 0.15 mL of dimethyl carbonate (1/2 vol%, LiPF ₆ 1 mol / L) was added to prepare a half-cell. Further, the half-cell was left at 25 ° C. for 12 hours, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). Finally, the above half-cell was repeatedly subjected to constant current discharge (end voltage: 1.0 V) and constant current charge (end voltage: 2.0 V) at 25 ° C. and 1.2 mA five times. did. As a result, the capacity of the negative electrode was 3.3 mAh / cm ² .

Positive electrode;
First, Li _1.1 Al _0.1 Mn _1.8 O ₄ as a positive electrode active material used in this example is described in the literature (Electrochemical and Solid-State Letters, 9 (12), A557 (2006)). Prepared by the method described.

  That is, an aqueous dispersion of manganese dioxide, lithium carbonate, aluminum hydroxide and boric acid was prepared, and a mixed powder was prepared by a spray drying method. At this time, the amounts of manganese dioxide, lithium carbonate and aluminum hydroxide were adjusted so that the molar ratio of lithium, aluminum and manganese was 1.1: 0.1: 1.8. Next, this mixed powder was heated at 900 ° C. for 12 hours in an air atmosphere, and then again heated at 650 ° C. for 24 hours. Finally, the mixed powder after heating was washed with 95 ° C. water and dried to prepare a positive electrode active material.

Next, after mixing the prepared positive electrode active material and acetylene black in a weight ratio of 95: 5, the solid content of the binder (PVdF, solid content concentration 12% by weight, NMP solution) is 5 parts by weight. The slurry was prepared by adding and mixing as described above. Furthermore, after apply | coating the produced slurry to aluminum foil (20 micrometers), it heated at 120 degreeC in the ventilation oven for 1 hour, and removed the solvent, Then, it vacuum-dried at 120 degreeC for 12 hours. Finally, it pressed with the roll press machine and produced the positive electrode (single-sided coating) whose electrode density is 3.0 g * cc- ¹ . The electrode density was calculated from the electrode weight and thickness per unit area.

  The capacity of the positive electrode was measured by the following charge / discharge test.

First, the above-mentioned electrode was punched to 14 mmΦ, and Li metal was punched to 16 mmΦ as a counter electrode. Next, the working electrode (single-sided coating) / separator (polyolefin porous membrane, thickness 25 μm) / Li metal was laminated in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / 0.15 mL of dimethyl carbonate (1/2 vol%, LiPF ₆ 1 mol / L) was added to prepare a half-cell. Further, the half-cell was left at 25 ° C. for 12 hours, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). Finally, the half-cell is charged with constant current and constant voltage at 25 ° C. and 1.2 mA (charge end voltage: 4.25 V, constant voltage charge voltage: 4.25 V, constant voltage charge end condition: 3 hours have elapsed, or the current value is 0 .12 mA) and constant current discharge (end voltage: 2.5 V) were repeated five times, and the fifth result was defined as the capacity of the positive electrode. As a result, the capacity of the positive electrode was 3.0 mAh / cm ² .

Production of non-aqueous electrolyte secondary batteries;
First, the prepared positive electrode (electrode part: 50 mm × 50 mm), negative electrode (electrode part: 55 mm × 55 mm) and separator (polyolefin-based microporous film, 25 μm, 60 mm × 60 mm) are laminated in the order of positive electrode / separator / negative electrode. did. Next, after vibration-welding aluminum tabs and nickel-plated copper tabs to the positive electrode and negative electrode at both ends, respectively, they are put into a bag-like aluminum laminate sheet and thermally welded on three sides, and the non-aqueous electrolyte secondary battery before enclosing the electrolyte solution Was made. Furthermore, after vacuum-drying the non-aqueous electrolyte secondary battery before enclosing the electrolytic solution at 60 ° C. for 3 hours, 1 mL of non-aqueous electrolyte (propylene carbonate / methyl ethyl carbonate = 3/7 vol%, LiPF ₆ 1 mol / L) The nonaqueous electrolyte secondary battery was manufactured by putting in and sealing under reduced pressure. In addition, the process so far was implemented by the atmosphere (dry box) whose dew point is -40 degrees C or less. Finally, the nonaqueous electrolyte secondary battery was charged to 2.7 V, then left at 45 ° C. for 100 hours, and discharged to 2.0 V. After removing the gas generated at this time, the nonaqueous electrolyte secondary battery of Example 1 was produced by sealing again while reducing the pressure.

(Example 2)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that the carbon material produced in Production Example 2 for carbon material was used instead of the carbon material in Production Example 1.

(Example 3)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the following active material-carbon material composite was used instead of the active material-carbon material composite in Example 1.

Active material-carbon material composite;
The composite body of the negative electrode active material of the said manufacture example, the carbon material of the manufacture example 1 as a 1st carbon material, and the 2nd carbon material was produced in the following procedure.

  First, 1 g of ethanol was added to 0.03 g of acetylene black as a second carbon material, and the mixture was treated with an ultrasonic cleaning machine (manufactured by AS ONE) for 5 hours to prepare a dispersion of the second carbon material.

  Next, 5 g of ethanol was added to 0.10 g of the carbon material of Production Example 1 as the first carbon material, and the mixture was treated with an ultrasonic cleaning machine (manufactured by AS ONE) for 5 hours to obtain a dispersion of the first carbon material. Was prepared.

Next, 3 g of the negative electrode active material (Li ₄ Ti ₅ O ₁₂ ) prepared in the above production example was added to 9 g of ethanol, and the mixture was stirred for 10 minutes at 600 rpm with a magnetic stirrer to prepare a dispersion of the negative electrode active material. .

  Furthermore, the dispersion liquid of the negative electrode active material was dropped into the dispersion liquid of the second carbon material with a dropper. In addition, at the time of dripping, the dispersion liquid of the 2nd carbon material continued to process with the ultrasonic cleaner (made by ASONE). Then, the dispersion liquid of the 1st carbon material was dripped similarly, and the liquid mixture of the dispersion liquid was stirred with the magnetic stirrer for 3 hours.

  Finally, the mixed liquid of the dispersion is subjected to suction filtration, and then vacuum-dried at 110 ° C. for 1 hour, whereby a composite of the negative electrode active material, the first carbon material, and the second carbon material of Example 3 (active Material-carbon material composite) was produced. The amount necessary for production of the negative electrode was produced by repeating the above steps.

Example 4
The first carbon material was produced in the same manner as in Example 3 except that the carbon material of Production Example 2 was used instead of the carbon material of Production Example 1.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that acetylene black (manufactured by Denka Co., Ltd., product name: Denka Black) was used instead of the carbon material of Production Example 1.

The acetylene black had a BET specific surface area of 65 m ² / g.

  Further, when the BET specific surface area of acetylene black was x and the methylene blue adsorption amount was y, the ratio y / x was 0.12, and the D / G ratio was 0.95.

(Comparative Example 2)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the negative electrode was produced using the following procedure and materials without using the active material-carbon material composite of Example 1.

The negative electrode of Comparative Example 2 was produced as follows. First, the negative electrode active material of the above production example and acetylene black were mixed at a weight ratio of 95: 5. Next, a binder (PVdF, solid content concentration of 12% by weight, NMP solution) was mixed so that the solid content was 5 parts by weight to prepare a slurry. Furthermore, after the slurry was applied to an aluminum foil (20 μm), the solvent was removed by heating in a blowing oven at 120 ° C. for 1 hour, and then vacuum dried at 120 ° C. for 12 hours. Finally, it was pressed with a roll press to produce a negative electrode (single-sided coating) having an electrode density of 1.8 g · cc ⁻¹ . The electrode density was calculated from the electrode weight and thickness per unit area.

(Rate characteristic evaluation of non-aqueous electrolyte secondary battery)
The rate characteristics were evaluated by the following method. First, the nonaqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were placed in a thermostatic bath at 25 ° C. and connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko). Next, the non-aqueous electrolyte secondary battery was charged with constant current and constant voltage (current value: 15 mA, charge end voltage: 2.7 V, constant voltage charge voltage: 2.7 V, constant voltage charge end condition: 3 hours elapsed, or Current value 1.5 mA). Further, after charging, the battery was paused for 1 minute, discharged to 2.0 V at 15 mA (small current) or 150 mA (large current), and the capacity at each current value was calculated. Finally, the rate characteristics were evaluated by dividing the discharge capacity at a large current by the discharge capacity at a small current.

(Evaluation of cycle characteristics of non-aqueous electrolyte secondary batteries)
The cycle characteristics were evaluated by the following method. First, the nonaqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were placed in a constant temperature bath at 60 ° C. and connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko). Next, constant current constant voltage charge (current value: 75 mA, charge end voltage: 2.7 V, constant voltage charge voltage: 2.7 V, constant voltage charge end condition: 3 hours elapse or current value 1.5 mA), 75 mA A cycle operation in which constant current discharge (discharge end voltage: 2.0 V) was repeated 500 times was performed. Finally, the discharge capacity retention rate (cycle characteristics) was calculated by calculating the ratio of the 500th discharge capacity when the first discharge capacity was 100.

The amount of gas generated was calculated by measuring the volume of the non-aqueous electrolyte secondary battery before and after cycle operation by the Archimedes method. The volume measurement of the nonaqueous electrolyte secondary battery by the aluminum medes method was performed as follows. First, the weight of the nonaqueous electrolyte secondary battery in an air atmosphere was measured with an electronic balance. Next, the weight in water was measured using a hydrometer (manufactured by Alpha Mirage Co., Ltd., product number “MDS-3000”). Furthermore, by calculating the buoyancy by taking the difference between the weight in the air atmosphere and the weight in water, and dividing this buoyancy by the density of water (1.0 g / cm ³ ), the non-aqueous electrolyte secondary The volume of the battery was calculated. Finally, the gas generation amount was calculated by comparing the volumes of the nonaqueous electrolyte secondary batteries before and after the cycle operation.

  The results of rate characteristics, cycle characteristics and gas generation amount are summarized in Table 1. In addition, the pass / fail judgment in Table 1 was performed according to the following criteria.

○: Rate characteristics and cycle characteristics are each 80% or more and gas generation amount is less than 0.2 mL. × ... Rate characteristics or cycle characteristics are less than 80% or gas generation amount is 0.2 mL or more.

  As is apparent from the results, the nonaqueous electrolyte secondary batteries of Examples 1 to 4 of the present invention are all better in rate characteristics, cycle characteristics and gas generation than the nonaqueous electrolyte secondary batteries of Comparative Examples 1 and 2. It was confirmed that.

Claims (10)

Including a negative electrode active material and a carbon material,
The carbon material includes a first carbon material having a graphite structure and partially exfoliated graphite;
The average potential of lithium ion desorption and insertion in the negative electrode active material is 0.5 V or more and 2.0 V or less with respect to Li ⁺ / Li (provided that the negative electrode active material is titanium oxide) , A titanium-containing composite oxide containing titanium and an element other than titanium), and an active material-carbon material composite.   The active material-carbon material composite according to claim 1, wherein the first carbon material includes a resin. The first measurement was based on the difference between the absorbance of a 10 mg / L concentration methylene blue methanol solution and the absorbance of the supernatant obtained by centrifuging the first carbon material into the methylene blue methanol solution. When the amount of methylene blue adsorbed per gram of carbon material (μmol / g) is y and the BET specific surface area (m ² / g) of the first carbon material is x, the ratio y / x is 0.15 or more. The active material-carbon material composite according to claim 1 or 2.   When the peak intensity ratio between the D band and the G band in the Raman spectrum of the first carbon material is defined as a D / G ratio, the D / G ratio is within a range of 0.05 or more and 0.8 or less. The active material-carbon material composite according to any one of claims 1 to 3.   The active material according to any one of claims 1 to 4, comprising the carbon material in a proportion of 0.2 parts by weight or more and 10.0 parts by weight or less with respect to 100 parts by weight of the negative electrode active material. Carbon material composite.   The active material-carbon material composite according to any one of claims 1 to 5, wherein the negative electrode active material is a titanium-containing composite oxide. The carbon material further includes a second carbon material different from the first carbon material;
The weight of the first carbon material is A, and the weight of the second carbon material is B, 0.01 ≦ A / B ≦ 100. Active material-carbon material composite.   The negative electrode for nonaqueous electrolyte secondary batteries containing the active material-carbon material composite of any one of Claims 1-7.   A nonaqueous electrolyte secondary battery comprising the negative electrode for a nonaqueous electrolyte secondary battery according to claim 8. A carbon material used in a composite with a negative electrode active material, wherein the average potential of desorption and insertion of lithium ions in the negative electrode active material is 0.5 V or more and 2.0 V or less with respect to Li ⁺ / Li Because
Carbon material having a graphite structure and partially exfoliated (however, when the negative electrode active material is titanium oxide, it is a titanium-containing composite oxide containing titanium and an element other than titanium). .