JP2017174536A - Method for producing composite active material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a composite active material for a lithium secondary battery capable of using water as a solvent in a manufacturing process and capable of producing a lithium secondary battery exhibiting excellent cycle characteristics.SOLUTION: The method for producing a composite active material for a lithium secondary battery includes: a mixture generation step of obtaining a mixture containing at least graphite and a battery active material capable of combining with lithium ions; a spheronization step of subjecting the mixture to a spheroidization treatment; a sintering step of applying a sintering treatment to the product obtained through the spheronization treatment; and a predetermined step using a water-soluble binder.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a composite active material for a lithium secondary battery.

  As electronic materials become smaller and lighter and HEV or EV development progresses, the demand for development of batteries with high capacity, high-speed charge / discharge characteristics, good cycle characteristics, and excellent safety is increasing. Among these, a lithium ion secondary battery (lithium secondary battery) has attracted attention as the most promising battery.

  However, as a premise for the development of lithium secondary batteries that exhibit excellent performance, negative electrode materials, positive electrode materials, electrolytes, separators, or current collectors that are excellent in various performances have been developed, and their characteristics are sufficient. The battery design must be made.

  Among them, since the negative electrode material determines basic battery characteristics, development of materials having more excellent characteristics is being actively conducted.

  For example, Patent Document 1 discloses a method for producing a composite active material for a lithium secondary battery that can produce a lithium secondary battery having both large charge / discharge capacity, high-speed charge / discharge characteristics, and good cycle characteristics. .

Japanese Patent No. 5227483

  On the other hand, in recent years, it has been required to refrain from using organic solvents from the viewpoint of environmental conservation and the safety of the working environment. In other words, the use of water as a solvent is required.

  Referring to the Example column of Patent Document 1, ethanol is used as a solvent for mixing metal Si and expanded graphite in the procedure for producing a composite active material for a lithium secondary battery. not filled.

  Further, the present inventors have found that when water is used instead of ethanol, the performance of the obtained composite active material for a lithium secondary battery, in particular, the cycle characteristics do not satisfy the recent required level.

  In view of the above circumstances, the present invention provides a method for producing a composite active material for a lithium secondary battery capable of using a water as a solvent in the production process and capable of producing a lithium secondary battery exhibiting excellent cycle characteristics. It is an issue to provide.

  As a result of intensive studies on the prior art, the present inventors have found that a composite active material for a lithium secondary battery exhibiting desired characteristics can be obtained by using a water-soluble binder.

That is, the present inventors have found that the above problem can be solved by the following configuration.
(1) A mixture generating step for obtaining a mixture containing at least a battery active material that can be combined with graphite and lithium ions;
A spheronization step of subjecting the mixture to a spheronization treatment;
A firing step of firing the product obtained through the spheronization treatment,
A method for producing a composite active material for a lithium secondary battery, which satisfies at least one of the following requirements 1 to 3.
Requirement 1: In the mixture generation step, graphite, a battery active material that can be combined with lithium ions, and a water-soluble binder are mixed in water, water is removed from the obtained aqueous dispersion, and graphite, lithium This is a step of obtaining a mixture containing a battery active material capable of combining with ions and a water-soluble binder.
Requirement 2: Between the spheronization step and the baking step, the product obtained in the spheronization step and the water-soluble binder are mixed in water, and water is removed from the resulting aqueous dispersion. The method further includes a mixing step of collecting the solid material, and the baking treatment is performed on the solid material.
Requirement 3: After the firing step, the fired product obtained in the firing step and the water-soluble binder are mixed in water, water is removed from the resulting aqueous dispersion, and the solid matter is recovered. It further has a mixed baking process which performs a baking process.
(2) The method for producing a composite active material for a lithium secondary battery according to (1), wherein the water-soluble binder contains a polyhydric alcohol.
(3) The composite active for a lithium secondary battery according to (1) or (2), wherein the water-soluble binder includes one selected from the group consisting of sugars, glycerins, and polyalkylene glycols. A method for producing a substance.
(4) The water-soluble binder is glucose, fructose, galactose, sucrose, maltose, lactose, starch, cellulose, glycogen, alginic acid, pectin, glycerin, diglycerin, polyethylene glycol, or an ester derivative thereof, or The manufacturing method of the composite active material for lithium secondary batteries in any one of (1)-(3) containing the salt of these, an alkali metal, or alkaline-earth metal.
(5) The method for producing a composite active material for a lithium secondary battery according to any one of (1) to (4), wherein the graphite is expanded graphite.
(6) The battery active material that can be combined with lithium ions is at least selected from the group consisting of Group 13 elements of the periodic table, Group 14 elements of the periodic table, Group 15 elements of the periodic table, magnesium, and manganese. The manufacturing method of the composite active material for lithium secondary batteries in any one of (1)-(5) containing 1 type of elements.
(7) The manufacturing method of the composite active material for lithium secondary batteries in any one of (1)-(6) whose average particle diameter of the battery active material which can be combined with lithium ion is 1 micrometer or less.

  According to the present invention, there is provided a method for producing a composite active material for a lithium secondary battery capable of producing a lithium secondary battery capable of using water as a solvent in the production process and exhibiting excellent cycle characteristics. Can do.

  Below, the manufacturing method of the composite active material for lithium secondary batteries of this invention (henceforth a composite active material only) is explained in full detail.

In addition, as a manufacturing method of a composite active material, while having a predetermined | prescribed process, at least 1 of the following requirements 1-requirements 3 is satisfy | filled.
Requirement 1: In the mixture generation step, graphite, a battery active material that can be combined with lithium ions, and a water-soluble binder are mixed in water, water is removed from the obtained aqueous dispersion, and graphite, lithium This is a step of obtaining a mixture containing a battery active material capable of combining with ions and a water-soluble binder.
Requirement 2: The product obtained in the spheronization step and the water-soluble binder are mixed in water between the spheronization step and the firing step, and water is removed from the resulting aqueous dispersion to form a solid. The method further includes a mixing step for recovering the product, and the baking process is performed on the solid matter.
Requirement 3: After the firing step, the fired product obtained in the firing step and the water-soluble binder are mixed in water, water is removed from the resulting aqueous dispersion, and the solid matter is recovered. It further has a mixed baking process which performs a baking process.

  As shown in the above requirements 1 to 3, it has been found that by using a water-soluble binder, a composite active material having excellent characteristics can be obtained even when manufactured using an aqueous solvent.

Hereinafter, an aspect satisfying requirement 1 will be described in detail as a first embodiment, an aspect satisfying requirement 2 as a second embodiment, and an aspect satisfying requirement 3 as a third embodiment.
<< First Embodiment >>
As a first embodiment of the method for producing a composite active material of the present invention, a mixture generating step of mixing predetermined components to obtain a mixture, a spheronizing step of subjecting the mixture to a spheronizing treatment, and a product obtained And a firing step of performing a firing treatment. In addition, the mixture production | generation process in a 1st embodiment is a process of satisfy | filling the said requirement 1.

Hereafter, the procedure of each process is explained in full detail.
<Mixture generation process>
In this step, graphite, a battery active material that can be combined with lithium ions (hereinafter also simply referred to as “battery active material”), and a water-soluble binder are mixed in water, and water is obtained from the resulting aqueous dispersion. Is removed to obtain a mixture containing graphite, a battery active material that can be combined with lithium ions, and a water-soluble binder.

Below, the component used at this process is explained in full detail first, and the procedure of a process is explained in full detail after that.
(graphite)
The specific surface area of the graphite used in this step is preferably 10 m ² / g or more. If it is in the said range, the composite active material in which the battery active material was highly disperse | distributed on the graphite surface of a high surface area (preferably thin thickness) will be obtained. As a result, the battery material using the composite active material exhibits excellent cycle characteristics.

Among these, the specific surface area is that the cycle characteristics of the lithium secondary battery using the composite active material obtained by the production method of the present invention is more excellent (hereinafter, also simply referred to as “the better effect of the present invention”). Is more preferably 20 m ² / g or more, particularly preferably 30 m ² / g or more. The upper limit is not particularly limited, but the specific surface area is preferably 200 m ² / g or less in that the production procedure is complicated and the synthesis is difficult.

  In addition, the specific surface area of graphite is measured using the BET method (JIS Z 8830, one point method) by nitrogen adsorption.

  In graphite, for example, a layer in which a plurality of graphene sheets are stacked in a direction in which the graphite surfaces overlap is included, and the graphene sheets are bonded to each other mainly by van der Waals force.

  The average thickness of the laminated graphene sheet layers contained in the above graphite is preferably 40 nm or less, more preferably 22 nm or less, from the viewpoint that the effect of the present invention is more excellent. The lower limit is not particularly limited, but is usually 4 nm or more because the production procedure becomes complicated.

  The average thickness is measured by observing graphite by electron microscope observation (TEM), measuring the thickness of 10 or more layers of graphene sheets laminated in graphite, and arithmetically averaging the values. An average thickness is obtained.

  In addition, as said graphite, what is called graphene (graphene sheet) itself can also be used.

  As graphite used at this process, a commercial item may be used and you may manufacture by a well-known method.

  As the graphite, so-called expanded graphite or flaky graphite can be used.

  As a method for producing expanded graphite, for example, after immersing graphite (for example, flaky graphite) in acid at room temperature, the obtained acid-treated graphite is subjected to heat treatment (preferably treated at 700 to 1000 ° C.). Can be manufactured. More specifically, after scaly natural graphite is immersed in a mixed acid of 9 parts by mass of sulfuric acid and 1 part by mass of nitric acid for about 1 hour, the acid is removed, washed with water and dried. Then, expanded graphite is obtained by putting the obtained acid-treated graphite into a furnace at about 850 ° C. It should be noted that an expanded black lead can also be obtained by using graphite formed with an interlayer compound such as alkali metal instead of acid-treated graphite.

  In addition, as a method for producing flaky graphite, after the expanded graphite is dispersed in a solvent, it is treated with an ultrasonic treatment or a dusting machine (for example, a stone mortar) that applies large shear stress, so that the hinge portion of the expanded graphite can be obtained. It is possible to obtain flaky graphite that is broken and laminated with about 50 (preferably 10 to 150) graphene sheets.

Note that the number of graphene sheets constituting the above expanded graphite and the number of graphene sheets constituting the flaky graphite obtained by unwinding the graphene sheets are assumed to be basically the same.
(Battery active materials that can be combined with lithium ions)
The battery active material used in this step is a battery active material (preferably a negative electrode active material) that can be combined with lithium ions. In other words, any substance that can combine with lithium ions and occlude and release lithium ions (for example, metal, metal carbide, nitride, etc.) may be used. For example, a metal or nonmetal capable of absorbing and releasing lithium ions, or a metal oxide capable of being alloyed with lithium.

  More specifically, metals such as Si, Sn, Al, Sb, Zn, Bi, Cd, Pb, In, Ag, Ga, and Ge (metals that can be alloyed with lithium) or alloys containing these metals (for example, Si alloy, Sb alloy, Sn alloy, In alloy).

  Among them, the battery active material is selected from the group consisting of Group 13 element of the periodic table, Group 14 element of the periodic table, Group 15 element of the periodic table, magnesium, and manganese in that the effect of the present invention is more excellent. It is preferable to contain at least one element selected (preferably a metal of these elements or an alloy containing these metals), and at least one element selected from the group consisting of Si, Sn, Al, Sb, and In It is more preferable to contain (preferably a metal of these elements or an alloy containing these metals), and even more preferable to contain an element of Si or Sn (preferably a metal of these elements or an alloy containing these metals) . In particular, the battery active material is preferably silicon.

  In addition, about this alloy, the alloy containing the metal which does not occlude and discharge | release lithium ion other than the alloy which consists of a combination of the above-mentioned metal may be sufficient. In this case, the content of the metal that can be alloyed with the lithium in the alloy is preferably larger. Judging from the uniformity of the particles and the cycle characteristics determined from the secondary electron image obtained by SEM observation, the upper limit of the metal content is preferably 70% by mass, and more preferably 60% by mass or less.

  The shape of the battery active material to be used is not particularly limited, and any shape such as powder, plate, granule, fiber, lump, and sphere can be used.

  The average particle size of the battery active material used is preferably 1 μm or less, more preferably 0.5 μm or less, and even more preferably 0.1 μm or less, from the viewpoint that the effects of the present invention are more excellent. The lower limit is not particularly limited and is preferably smaller. In a normal powder frame method, it is possible to produce a fine powder having an average particle size of about 0.01 μm, and a powder having this size can be used effectively.

  As a method for measuring the average particle size, a laser diffraction type particle size distribution measuring device is used. More specifically, D 50: 50% volume particle diameter is defined as the average particle diameter.

  In addition, as a method for obtaining the battery active material having the predetermined average particle diameter, the battery active material is powdered using a known apparatus such as a stirred tank type stirring mill (bead mill, etc.), and the like. It is possible to obtain a powder having a small particle diameter.

In particular, as the battery active material, silicon particles are preferable, and silicon particles having an average particle diameter of 100 nm or less (particularly, an average particle diameter of 50 nm or less is particularly preferable).
(Water-soluble binder (water-soluble compound))
The water-soluble binder used in this step is a material that binds the above-described graphite and the battery active material. For example, a saccharide that can be used as a water-soluble binder is carbonized in a baking step described later to become amorphous carbon in the composite active material, and plays a role of improving the properties of the composite active material. In addition, since the water-soluble binder is excellent in solubility in water, water can be used for mixing the graphite and the battery active material and the water-soluble binder described above.

  The water-soluble binder is a material that can be dissolved in water, and more specifically, a material that can be dissolved in 10 g or more in 1 L of water.

  As the water-soluble binder, a known material (for example, a surfactant) can be used. For example, a polyhydric alcohol, an amine compound, a carboxylic acid compound, a sulfuric acid compound (for example, dodecylsulfonic acid), a nitric acid compound, Or ester derivatives thereof, alkali metal salts, alkaline earth metal salts and the like can be mentioned, and polyhydric alcohols are preferable in that the effect of the present invention is more excellent. The polyhydric alcohol is a compound containing a plurality of hydroxy groups, and may be a so-called low molecular compound or a polymer compound containing a plurality of predetermined repeating units.

  Among these, saccharides, glycerins, polyalkylene glycols, and the like are mentioned in that the effects of the present invention are more excellent. As saccharides, any of monosaccharides, disaccharides, and polysaccharides can be used.

  More specifically, examples of the water-soluble binder include glucose, fructose, galactose, sucrose, maltose, lactose, starch, cellulose, glycogen, alginic acid, pectin, xylitol, sorbitol, maltotriose, erythritol and the like. Sugars, glycerins such as glycerin, diglycerin, triglycerin, polyglycerin, polyalkylene glycols such as polyethylene glycol, polypropylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, propylene glycol, dipropylene glycol , 1,2-pentanediol, glycols such as 1,2-hexylene glycol, water-soluble polymers such as polyvinyl alcohol, pentaerythritol, dipentaerythris Tall and the like. Further, these ester derivatives or salts of these with alkali metals or alkaline earth metals may be used.

  Moreover, when using saccharide | sugar as a water-soluble binder, it is preferable to use together 2 or more types of saccharides at the point which the effect of this invention is more excellent. More specifically, for example, 2 selected from the group consisting of glucose, fructose, galactose, sucrose, maltose, lactose, starch, cellulose, glycogen, alginic acid, pectin, xylitol, sorbitol, maltotriose, and erythritol. It is preferable to use more than one species.

In addition, a commercial item can be used as a water-soluble binder, For example, a honey, cake syrup, etc. can be used as a raw material of saccharides. The honey used in this step is not particularly limited, and examples thereof include honey, purified honey, sweetened honey, acacia honey, and the like.
(Process procedure)
In this step, first, the above-described graphite, battery active material, and water-soluble binder are mixed in water. That is, the various components described above are mixed in an aqueous solvent. A known stirring process can be performed as the mixing process. In addition, the organic solvent may exist at the time of mixing in the range which does not impair the effect of this invention.

  The conditions for the mixing treatment are not particularly limited, and optimum conditions are appropriately selected according to the materials used.

  Moreover, you may implement an ultrasonic treatment at the time of a mixing process as needed. That is, the graphite component, the battery active material, and the water-soluble binder may be mixed while being subjected to ultrasonic treatment.

  The mixing ratio of graphite and the battery active material is not particularly limited. However, it is preferable to mix 10 to 150 parts by mass of the battery active material with respect to 100 parts by mass of graphite because the effect of the present invention is more excellent. It is more preferable to mix 100 parts by mass.

  The mixing ratio of graphite and the water-soluble binder is not particularly limited, but 1 to 50 parts by mass of the water-soluble binder can be mixed with 100 parts by mass of graphite in terms of more excellent effects of the present invention. Preferably, 10 to 30 parts by mass are mixed.

  In addition, the amount of water used is not particularly limited, but as a result of achieving a higher degree of dispersion, 500 to 15000 parts by mass of water may be mixed with 100 parts by mass of graphite in terms of more effective effects of the present invention. Preferably, 1000 to 7000 parts by mass are mixed.

  Next, water is removed from the aqueous dispersion obtained by the above mixing treatment to obtain a mixture containing graphite, a battery active material, and a water-soluble binder. In other words, a mixture containing graphite, a battery active material, and a water-soluble binder, which is a solid content, is recovered from the aqueous dispersion obtained by the above mixing treatment.

  The method for removing water is not particularly limited, and examples thereof include a method using a known device (for example, an evaporator). Moreover, you may implement the method of isolate | separating water and solid content by filtration etc. In the obtained mixture, water may remain as long as the effects of the present invention are not impaired.

  In addition, before the spheronization process mentioned later of the said mixture production | generation process, the press process of pressing the obtained mixture may be included as needed. If a press process is implemented, the distance between graphite will become smaller and the spheroidization process mentioned later advances more efficiently.

The pressing method is not particularly limited, and a known method can be adopted.
<Spheronization process>
The spheronization step is a step of producing a spherical mixture by subjecting the mixture containing the graphite, battery active material and water-soluble binder obtained in the mixture generation step to spheronization.

  By carrying out this step, the graphite sheet is folded into a spherical shape so as to incorporate the battery active material and the water-soluble binder therein. In that case, the edge part of graphite is folded inside, and the structure where a battery active material is not substantially exposed on the surface of the composite active material formed is obtained.

  The method of spheroidizing treatment is not particularly limited, and is not particularly limited as long as it is a dusting machine that mainly applies impact stress. Examples of the powdering machine include a high-speed rotational impact type powdering machine, and more specifically, a sample mill, a hammer mill, a pin mill, or the like can be used. Especially, a pin mill is preferable at the point which the effect of this invention is more excellent.

  Examples of high-speed rotary impact type powdering machines include those that collide a sample with a rotor that rotates at high speed and achieve miniaturization by the impact force. For example, a hammer with a fixed or swing type impactor attached to the rotor Mill type hammer type, pin mill type rotating disk type with a pin and impact head attached to a rotating disk, axial flow type that dusts while the sample is transported in the shaft direction, particle refinement in a narrow annular part Annular type to perform. More specifically, a hammer mill, a pin mill, a screen mill, a turbo mill, a centrifugal classification mill, and the like can be given.

  In addition, when performing this process with the said high-speed rotation impact type dusting machine, it is preferable to spheroidize normally at a rotational speed of 100 rpm or more, preferably 1500 rpm or more, and usually 2000 rpm or less. Therefore, the collision speed is preferably about 20 m / second to 100 m / second.

  Unlike pulverization, since the spheronization treatment is carried out with a low impact force, it is usually preferable to perform a circulation treatment in this step. The processing time varies depending on the type and amount of the dusting machine to be used, but it is usually within 2 minutes, and the processing time can be completed in about 10 seconds if the device has an appropriate pin or collision plate arrangement. .

The spheronization treatment is preferably performed in air. If the same treatment is performed with nitrogen, there is a risk of fire when released to the atmosphere.
<Baking process>
A baking process is a process of giving a baking process with respect to the spherical mixture obtained above, and manufacturing the substantially spherical composite active material (composite active material) for lithium secondary batteries. Note that the composite active material includes at least the graphite-derived black feed component and the battery active material. Depending on the type of the water-soluble binder, the composite active material contains a component derived from the water-soluble binder. For example, when saccharides are used as the water-soluble binder, saccharide-derived amorphous carbon is included in the composite active material. For example, when glycerins are used as the water-soluble binder, the glycerins are often volatilized by the baking treatment.

  As the conditions for the calcination treatment, the calcination temperature is preferably 400 ° C. or higher, more preferably 600 ° C. or higher, in that the effect of the present invention is more excellent. The upper limit is not particularly limited, but is preferably 2000 ° C. or lower, more preferably 1500 ° C. or lower, and further preferably 1000 ° C. or lower from the viewpoint of heat resistance of the composite active material.

  Moreover, as baking time, 0.5 hour or more is preferable and 1 hour or more is more preferable. The upper limit is not particularly limited, but is often 5 hours or less from the point where the effects of the invention are saturated.

  The atmosphere for performing the baking treatment is preferably an inert atmosphere from the viewpoint of preventing the oxidation of carbon.

In addition, you may implement the powder frame process for refine | miniaturizing the obtained composite active material further as needed after the said baking process. As the powdering method, known means can be implemented.
<Arbitrary process>
In the first embodiment of the method for producing a composite active material of the present invention, processes other than those described above may be included.

  Among them, in terms of more excellent effects of the present invention, a step of mixing the calcined product obtained in the calcining step with an amorphous carbon precursor to obtain a mixture, and subjecting the mixture to a calcining treatment Furthermore, you may have. By carrying out this step, the surface of the fired product obtained in the firing step is covered with an amorphous carbon precursor, and by carrying out the firing treatment, composite particles covered with amorphous carbon are obtained. It is done.

  Examples of the precursor of amorphous carbon include polymer compounds (for example, thermosetting resins, thermoplastic resins), coal-based pitches (for example, coal tar pitch), petroleum-based pitches, mesophase pitches, coke, and low molecular weights. Heavy oil, or a derivative thereof may be mentioned, and coal-based pitch (for example, coal tar pitch), petroleum-based pitch, mesophase pitch, coke, low molecular weight heavy oil, or a derivative thereof is preferable. Among these, as the amorphous carbon, soft carbon obtained from a precursor such as coal-based pitch is preferable in that the effect of the present invention is more excellent.

  The thermosetting resin is not particularly limited. For example, a phenol resin such as a novolak type phenol resin or a resol type phenol resin; an epoxy resin such as a bisphenol type epoxy resin or a novolac type epoxy resin; a melamine resin; a urea resin; Cyanate resin; furan resin; ketone resin; unsaturated polyester resin; urethane resin; In addition, modified products obtained by modifying these with various components can also be used.

  The thermoplastic resin is not particularly limited, and examples thereof include polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, polyvinyl chloride, methacrylic resin, polyethylene. Examples include terephthalate, polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, and polyphthalamide.

  Among these, one kind or a combination of two or more kinds can be used.

  The shape of the amorphous carbon precursor is not particularly limited, and any shape such as powder, plate, granule, fiber, lump, and sphere can be used. These precursors of amorphous carbon are preferably dissolved in a solvent used when various components are mixed.

  The weight average molecular weight of the amorphous carbon precursor used is preferably 1000 or more, more preferably 1,000,000 or less, from the viewpoint that the effect of the present invention is more excellent.

  The mixing method of the calcined product and the amorphous carbon precursor is not particularly limited, and a known method can be adopted, and examples thereof include dry processing or wet processing.

  The mixing ratio of the mixture and the amorphous carbon precursor is not particularly limited, but the amorphous carbon precursor is added in an amount of 0.1 to 70 with respect to 100 parts by mass of the mixture in that the effect of the present invention is more excellent. It is preferable to mix by mass part, and it is more preferable to mix 15-50 mass parts.

Moreover, although the optimal conditions are suitably selected according to the material used for the conditions of a baking process, the conditions of the baking process mentioned above are mentioned, for example.
<Composite active material for lithium secondary battery>
The composite active material obtained through the above-described steps includes at least a graphite component and a battery active material.

  The content of the graphite component in the composite active material is not particularly limited, but is preferably 15 to 80% by mass and more preferably 25 to 75% by mass with respect to the total amount of the composite active material in that the effect of the present invention is more excellent. 35-70 mass% is still more preferable.

  Although the content of the battery active material in the composite active material is not particularly limited, it is preferably 5 to 80% by mass and more preferably 10 to 70% by mass with respect to the total amount of the composite active material in that the effect of the present invention is more excellent. Preferably, 15-50 mass% is more preferable.

  When a component derived from a water-soluble binder (for example, amorphous carbon) is contained in the composite active material, the content is not particularly limited, but the total effect of the present invention is improved in that the effect of the present invention is more excellent. On the other hand, 0.1-60 mass% is preferable, 0.2-50 mass% is more preferable, and 1-40 mass% is further more preferable.

  When the composite active material contains amorphous carbon derived from the above-mentioned amorphous carbon precursor, the content of amorphous carbon in the composite active material is not particularly limited, but the effect of the present invention is more excellent. And 5-60 mass% is preferable with respect to the composite active material whole quantity, 10-50 mass% is more preferable, 15-40 mass% is further more preferable.

The shape of the composite active material is not particularly limited, but preferably has a substantially spherical shape from the viewpoint that the effect of the present invention is more excellent. Note that the substantially spherical, the aspect ratio is the ratio of the major axis to the minor axis (major axis / ^/ minor) represents the shape of the composite active material particles of about a range of 1-3. The aspect ratio means a value (arithmetic average value) obtained by calculating the long diameter / short diameter of each particle for at least 100 particles and arithmetically averaging them.

  In addition, the minor axis in the above is the distance between two parallel lines that are in contact with the outside of the particles observed by a scanning electron microscope or the like and that are the shortest distance among the combinations of two parallel lines that sandwich the particles. On the other hand, the major axis is the two parallel lines perpendicular to the parallel line that determines the minor axis, and the distance between the two parallel lines that are the longest interval among the combination of two parallel lines in contact with the outside of the particle. It is. The rectangle formed by these four lines is the size that the particles just fit within.

  The particle size (D 50: 50% volume particle size) of the composite active material is not particularly limited, but is preferably 2 to 40 μm, more preferably 5 to 35 μm, and further more preferably 5 to 30 μm in terms of more excellent effects of the present invention. preferable.

  The particle size (D 90: 90% volume particle size) is not particularly limited, but 10 to 75 μm is preferable, 10 to 60 μm is more preferable, and 20 to 45 μm is further preferable in that the effect of the present invention is more excellent.

  Further, the particle size (D 10: 10% volume particle size) is not particularly limited, but 1 to 20 μm is preferable and 2 to 10 μm is more preferable in that the effect of the present invention is more excellent.

  D10, D50, and D90 correspond to the particle sizes of 10%, 50%, and 90% from the fine particle side of the cumulative particle size distribution measured by the laser diffraction scattering method, respectively.

  In the measurement, the composite active material is added to the liquid and mixed vigorously while utilizing ultrasonic waves, and the prepared dispersion is introduced as a sample into the apparatus for measurement. As the liquid, it is preferable to use water, alcohol, or a low-volatile organic solvent for work. At this time, the obtained particle size distribution diagram preferably shows a normal distribution.

The specific surface area of the composite active material (BET specific surface area) is not particularly limited, in terms of the effect of the present invention is more excellent, preferably ^{30 m} 2 / g or less, ^{10 m} 2 / g or less is more preferable. Although a minimum in particular is not restrict | limited, 0.1 m < ² > / g or more is preferable.

The measurement method of the specific surface area (BET specific surface area) of the composite active material is measured by a nitrogen adsorption one-point method after vacuum drying the sample at 300 ° C. for 30 minutes.
<< Second Embodiment >>
As a second embodiment of the method for producing a composite active material of the present invention, a mixture producing step for obtaining a mixture by mixing predetermined components, a spheronizing step for subjecting the mixture to a spheronizing treatment, and a spheronizing step are obtained. The product and water-soluble binder are mixed in water, water is removed from the resulting aqueous dispersion to recover the solid, and the resulting solid is calcined. And a firing step. In the second embodiment, the above requirement 2 is satisfied in the mixing step and the firing step.

In the second embodiment of the present invention, the water-soluble binder is not used in the mixture generation step, the mixing step is carried out, and the solid content obtained in the mixing step in the firing step. On the other hand, the same procedure as that of the first embodiment is performed except that the baking treatment is performed. Therefore, in the following, differences between the second embodiment and the first embodiment will be mainly described in detail.
<Mixture generation process>
In the mixture production step of the second embodiment of the present invention, the same raw materials and procedures as those in the mixture production step of the first embodiment described above are performed except that the water-soluble binder is not used.
<Mixing process>
The mixing step is a step in which the product obtained through the spheronization step and the water-soluble binder are mixed in water, and water is removed from the obtained aqueous dispersion to recover a solid matter. By carrying out this step, a mixture of the product and the water-soluble binder can be produced efficiently.

  The procedure of a mixing process can be implemented by the same method as the mixture production | generation process of 1st embodiment.

  Further, the mixing ratio of the product obtained through the spheronization step and the water-soluble binder is not particularly limited, but the water-soluble binder is added to 100 parts by mass of the product in that the effect of the present invention is more excellent. It is preferable to mix 10-60 mass parts of an adhesive, and it is more preferable to mix 20-40 mass parts.

  Furthermore, examples of the method for removing water from the aqueous dispersion include the method described in the mixture generation step of the first embodiment.

  In the second embodiment, the <arbitrary process> described in the first embodiment may be further performed.

By performing the above procedure, a composite active material including a graphite component, a battery active material, and a component derived from a water-soluble binder can be obtained in the same manner as in the first embodiment.
<< Third Embodiment >>
As a third embodiment of the method for producing a composite active material of the present invention, a mixture generating step of mixing predetermined components to obtain a mixture, a spheronizing step of subjecting the mixture to a spheronizing treatment, and a product obtained A firing process for performing a firing process, a fired product obtained in the firing process and a water-soluble binder are mixed in water, water is removed from the obtained aqueous dispersion, and a solid is recovered. And a mixed firing step of firing the solid. In the third embodiment, the above requirement 3 is satisfied in the mixed firing step.

  In the third embodiment of the present invention, the same procedure as that of the first embodiment is performed except that the mixing step is carried out without using the water-soluble binder in the mixture generating step, and the mixed firing step is carried out. To do.

  Therefore, in the following, the mixed firing step will be mainly described in detail.

  In the mixed firing step, first, the fired product obtained in the firing step and the water-soluble binder are mixed in water. The procedure of the mixing method includes the method described in the mixture generating step of the first embodiment.

  Further, in the mixing and firing step, the mixing ratio of the product obtained through the firing step and the water-soluble binder is not particularly limited, but with respect to 100 parts by mass of the product in terms of more excellent effects of the present invention. The water-soluble binder is preferably mixed in an amount of 10 to 100 parts by mass, more preferably 20 to 80 parts by mass.

  Furthermore, examples of the method for removing water from the aqueous dispersion include the method described in the mixture generation step of the first embodiment.

  Moreover, although the optimal conditions are suitably selected according to the material used for the conditions of a baking process, the conditions of the baking process of the 1st embodiment mentioned above are mentioned, for example.

  By performing the above procedure, a composite active material including a graphite component, a battery active material, and a component derived from a water-soluble binder can be obtained in the same manner as in the first embodiment.

  Although the requirements 1 to 3 (first embodiment to third embodiment) have been described above, two or more requirements may be performed simultaneously.

  For example, requirement 1 and requirement 3 may be performed simultaneously. More specifically, in the mixture generation step, graphite, a battery active material that can be combined with lithium ions, and a water-soluble binder are mixed in water, and water is removed from the obtained aqueous dispersion, A fired product obtained in the firing step and a water-soluble binder obtained by performing a step of obtaining a mixture containing graphite, a battery active material that can be combined with lithium ions, and a water-soluble binder, and after the firing step May be mixed in water, and water may be removed from the obtained aqueous dispersion to recover a solid, and a mixed firing step of firing the solid may be further performed.

Moreover, requirement 1 and requirement 2 may be implemented simultaneously, and requirement 2 and requirement 3 may be implemented simultaneously.
<< Lithium secondary battery >>
The composite active material described above is useful as an active material used for battery materials (electrode materials) used in lithium secondary batteries.

  A method for producing a negative electrode for a lithium secondary battery using the composite active material is not particularly limited, and a known method can be used.

  For example, a composite active material and a binder can be mixed, formed into a paste using pressure molding or a solvent, and applied onto a copper foil to form a negative electrode for a lithium secondary battery.

  In addition to the copper foil, the current collector is preferably a current collector having a three-dimensional structure in that the battery cycle is more excellent. Examples of the current collector material having a three-dimensional structure include carbon fiber, sponge-like carbon (a sponge-like resin coated with carbon), metal, and the like.

  As a current collector (porous current collector) having a three-dimensional structure, a metal or carbon conductor porous body, a plain weave wire mesh, expanded metal, lath net, metal foam, metal woven fabric, metal nonwoven fabric, A carbon fiber woven fabric or a carbon fiber non-woven fabric may be used.

  As the binder to be used, a known material can be used, and for example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, SBR, polyethylene, polyvinyl alcohol, carboxymethylcellulose, glue and the like are used.

  Examples of the solvent include water, isopropyl alcohol, N-methylpyrrolidone, dimethylformamide and the like.

  In addition, when making into a paste, you may stir and mix using a well-known stirrer, a mixer, a kneader, a kneader, etc. as needed as mentioned above.

  When preparing a slurry for coating using a composite active material, it is preferable to add conductive carbon black, carbon nanotube, or a mixture thereof as a conductive material. The shape of the composite active material obtained by the above process is often relatively granulated (particularly, substantially spherical), and the contact between particles tends to be point contact. In order to avoid this adverse effect, a method of blending carbon black, carbon nanotubes or a mixture thereof into the slurry can be mentioned.

  The blending amount of carbon black, carbon nanotubes or a mixture thereof is not particularly limited, but is preferably 0.2 to 4 parts by mass, and 0.5 to 2 parts by mass with respect to 100 parts by mass of the composite active material. Is more preferable. Examples of the carbon nanotube include a single wall carbon nanotube and a multi-wall carbon nanotube.

  Known materials can be used for the positive electrode, the electrolytic solution, and the separator used in the lithium secondary battery having a negative electrode obtained by using the composite active material.

  The lithium secondary battery uses the negative electrode, the positive electrode, the separator, the electrolyte, and other battery components (for example, a current collector, a gasket, a sealing plate, a case, etc.), and is cylindrical or square according to a conventional method. Or it can have forms, such as a button type.

  The lithium secondary battery of the present invention is used in various portable electronic devices, particularly notebook computers, notebook word processors, palmtop (pocket) computers, mobile phones, mobile faxes, mobile printers, headphone stereos, video cameras, and mobile TVs. , Portable CDs, portable MDs, electric shavers, electronic notebooks, transceivers, power tools, radios, tape recorders, digital cameras, portable copying machines, portable game machines, and the like. In addition, electric vehicles, hybrid vehicles, vending machines, electric carts, load leveling power storage systems, household power storage devices, distributed power storage systems (built into stationary appliances), emergency power supply systems, etc. It can also be used as a secondary battery.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.
<Example 1>
(Preparation of expanded graphite)
After immersing scaly natural graphite having an average particle diameter of 1 mm in a mixed acid of 9 parts by mass of sulfuric acid and 1 part by mass of nitric acid at room temperature for 1 hour, the mixed acid was removed with a No 3 glass filter to obtain acid-treated graphite. Further, the acid-treated graphite was washed with water and dried. When 5 g of the dried acid-treated graphite was stirred in 100 g of distilled water and the pH was measured after 1 hour, the pH was 6.7. The dried acid-treated graphite was put into a vertical electric furnace under a nitrogen atmosphere set at 850 ° C. to obtain expanded graphite. The expanded graphite had a bulk density of 0.025 g / cm ³ and a specific surface area of 24.3 m ² / g.
(Mixing process)
A methanol slurry of silicon fine powder having an average particle size of 0.3 μm (solid concentration 24.8% by mass) was added to 1600 parts by mass of water in a beaker so that the amount of silicon added was 30 parts by mass, Honey (manufactured by Sanyo Tsusho Co., Ltd., ingredients: fructose 40.94 g, glucose 35.75 g, galactose 3.1 g, maltose 1.44 g, sucrose 0.89 g, water 17.1 g, other trace components (protein, vitamins, minerals)) Was added in an amount of 25 parts by mass (5.7 parts by mass after carbonization), and stirred with an in-line mixer for 10 minutes.

  The expanded graphite (70 parts by mass) was added to an aqueous solution in which silicon fine powder and honey were dispersed to prepare a uniform mixed slurry containing expanded graphite, silicon fine powder, and honey. Water was removed from this slurry using an evaporator to obtain a powder mixture.

In addition, the honey contained multiple types of sugars as described above.
(Pressing process)
Using a three-roller (EKAKT50), the powder mixture was pressed. The expanded graphite layer opened by this treatment is closed, the distance between the layers is reduced, the density is also increased, and the impact energy in the next spheronization process is increased, so that the efficiency of spheronization can be increased. .
(Spheronization process)
Using a new power mill, PM-2005M-1380W (Osaka Chemical Co., Ltd.) (rotation speed: 20000 rpm, treatment time: 90 seconds 10 times), the powder mixture obtained above is granulated into a spherical shape. went.
(Baking treatment (carbonization treatment))
While flowing nitrogen (1 L / min), the spherical mixture was baked at 900 ° C. for 1 hour to simultaneously carbonize the saccharides contained in the honey. As a result, a substantially spherical mixture comprising 70 parts by mass of the graphite component, 30 parts by mass of silicon, and 5.7 parts by mass of saccharide-derived amorphous carbon was obtained.
(Coating with coal tar pitch)
The substantially spherical mixture obtained (100 parts by mass) was added in a solution in which coal tar pitch (carbonization degree 45%, 30 parts by mass) was dissolved in quinoline (200 parts by mass), and after stirring for 10 minutes, the following The coating was performed by firing using the method.
(Baking)
The coal tar pitch was modified to soft carbon by firing the mixture at 300 ° C. for 1 hour and at 600 ° C. for 2 hours while flowing nitrogen (1 L / min). Thereby, from the content of graphite component 70 parts by mass, silicon content 30 parts by mass, sugar-derived amorphous carbon content 5.7 parts by mass, coal tar pitch-derived soft carbon content 30 parts by mass Thus, a substantially spherical composite active material for a lithium secondary battery was obtained.

The physical properties are as follows. Particle size distribution D 50: 19 μm, BET specific surface area: 7.6 m ² / g, shape: substantially spherical From secondary electron image of composite active material using SEM (scanning electron microscope) at low acceleration voltage of 10 kV or less The composite active material was found to have a structure in which the graphite component and the battery active material were covered with soft carbon.

  The area ratio of silicon exposed on the surface of the composite active material for a lithium secondary battery observed by SEM observation was 2% or less.

Further, exfoliated graphite was observed in the composite active material. The thickness of exfoliated graphite was about 20 nm (total number of graphene sheets 60).
(Negative electrode manufacturing)
95.5 parts by mass of the composite active material, 2.5 parts by mass of SBR (styrene butadiene rubber), 1.5 parts by mass of CMC (carboxymethyl cellulose), 0.5 parts by mass of carbon black for conduction, and 100 parts by mass of water are weighed. The slurry for coating was prepared by mixing for 3 minutes using a double-arm mixer. The slurry was applied to a copper foil and dried to produce a negative electrode.
(Positive electrode manufacturing)
84 parts by mass of LiNi _1-xy Co _x Al _y O _2, 66 parts by mass of PVDF-containing NMP solution (PVDF: polyvinylidene fluoride, NMP: methylpyrrolidone) (content: 12%), 8 parts by mass of conductive carbon black And 29 parts by mass of NMP were weighed and mixed for 3 minutes using a double-arm mixer to prepare a coating slurry. The slurry was applied to an aluminum foil and dried to produce a positive electrode.
(Full cell manufacturing)
Using the above negative electrode and positive electrode as electrodes, ethylene carbonate: diethyl carbonate = 1: 1, 1.2 mol / L LiPF ₆ electrolyte and 2% by volume of fluoroethylene carbonate were added to produce a full cell. Went.
(Battery evaluation: electrode expansion measurement)
A cycle test was conducted using the full cell. At that time, the charge / discharge capacity and the initial irreversible capacity were measured, and the capacity retention ratios for the first cycle at 60 cycles and 100 cycles were compared. In addition, a cycle experiment (100 times) was performed using a charge / discharge rate of 0.5 C, a cut-off voltage on the charge side of 4.0 V, and a cut-off voltage on the discharge side of 2.7 V.

  The shape of the electrode before the cycle test was a disk shape with a diameter of 14 mm and a thickness of 55 μm.

  Moreover, the maximum Coulomb efficiency “Max Coulomb efficiency” in 100 cycles was also measured.

The results are summarized in Table 1.
<Example 2>
The same as in Example 1 except that 25 parts by mass (4.43 parts by mass after carbonization) of cake syrup (manufactured by Asahi Shoji Co., Ltd., component: fructose glucose liquid sugar. Starch syrup, fragrance, caramel pigment) was used instead of honey. The composite active material was manufactured according to the procedure of, and a full cell was manufactured, and various evaluations were performed.
<Example 3>
A composite active material was produced according to the same procedure as in Example 1 except that diglycerin (manufactured by Sakamoto Yakuhin Co., Ltd., 25 parts by mass (0.3 parts by mass after carbonization)) was used instead of honey. A full cell was manufactured and subjected to various evaluations.

  As shown in Table 1 above, it was confirmed that the full cell using the composite active material for a lithium secondary battery of the present invention was excellent in cycle characteristics.

Claims (7)

A mixture generating step for obtaining a mixture containing at least a battery active material capable of being combined with graphite and lithium ions;
A spheronization step of subjecting the mixture to a spheronization treatment;
A method for producing a composite active material for a lithium secondary battery, comprising: a firing step of performing a firing treatment on a product obtained through the spheronization treatment and satisfying at least one of the following requirements 1 to 3 .
Requirement 1: In the mixture generation step, the graphite, the battery active material that can combine with the lithium ions, and the water-soluble binder are mixed in water, and water is removed from the obtained aqueous dispersion. This is a step of obtaining a mixture containing the graphite, a battery active material that can be combined with the lithium ions, and the water-soluble binder.
Requirement 2: The product obtained in the spheronization step and the water-soluble binder are mixed in water between the spheronization step and the baking step, and water is removed from the obtained aqueous dispersion. And a solidifying step for collecting the solid matter, and the solid matter is calcined in the calcining step.
Requirement 3: After the firing step, the fired product obtained in the firing step and a water-soluble binder are mixed in water, and water is removed from the obtained aqueous dispersion to recover a solid, It further has a mixed baking process which performs baking processing with respect to a solid substance.   The method for producing a composite active material for a lithium secondary battery according to claim 1, wherein the water-soluble binder contains a polyhydric alcohol.   The manufacturing method of the composite active material for lithium secondary batteries of Claim 1 or 2 in which the said water-soluble binder contains 1 type selected from the group which consists of saccharides, glycerol, and polyalkylene glycol. .   The water-soluble binder is glucose, fructose, galactose, sucrose, maltose, lactose, starch, cellulose, glycogen, alginic acid, pectin, glycerin, diglycerin, polyethylene glycol, or an ester derivative thereof, or The manufacturing method of the composite active material for lithium secondary batteries of any one of Claims 1-3 containing the salt with an alkali metal or an alkaline-earth metal.   The manufacturing method of the composite active material for lithium secondary batteries of any one of Claims 1-4 whose said graphite is expanded graphite.   The battery active material that can be combined with the lithium ions is at least one selected from the group consisting of Group 13 elements of the periodic table, Group 14 elements of the periodic table, Group 15 elements of the periodic table, magnesium, and manganese. The manufacturing method of the composite active material for lithium secondary batteries of any one of Claims 1-5 containing these elements.   The manufacturing method of the composite active material for lithium secondary batteries of any one of Claims 1-6 whose average particle diameter of the battery active material which can be combined with the said lithium ion is 1 micrometer or less.