JP6733248B2 - Method for producing composite active material for lithium secondary battery - Google Patents

Description

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

Along with the reduction in size and weight of electronic materials and the progress of development of HEVs or EVs, there is an increasing demand for the development of batteries having large capacity, high-speed charge/discharge characteristics, good cycle characteristics, and excellent safety. Among them, a lithium ion secondary battery (lithium secondary battery) is drawing attention as the most promising battery.

However, as a prerequisite for developing a lithium secondary battery exhibiting excellent performance, a negative electrode material, a positive electrode material, an electrolytic solution, a separator, a current collector, etc. having excellent various performances have been developed, and sufficient characteristics thereof have been developed. It is necessary to design the battery based on the above.

In particular, since the negative electrode material determines the basic battery characteristics, the development of materials having better characteristics is being actively conducted.

For example, Patent Document 1 discloses a method for producing a composite active material for a lithium secondary battery, which is capable of producing a lithium secondary battery having a large charge/discharge capacity, high-speed charge/discharge characteristics, and good cycle characteristics. ..

Japanese Patent No. 5227483

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

With reference to the Example section of Patent Document 1, ethanol is used as a solvent when mixing metal Si and expanded graphite in a procedure for producing a composite active material for a lithium secondary battery, and it is not always necessary to meet recent demands. 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, particularly the cycle characteristics, does not satisfy the recent required level.

In view of the above-mentioned circumstances, the present invention is a method for producing a composite active material for a lithium secondary battery, in which water can be used as a solvent in the production process, and a lithium secondary battery exhibiting excellent cycle characteristics can be produced. The challenge is to provide.

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

That is, the present inventors have found that the above problems can be solved by the following configurations.
(1) A mixture forming step of obtaining a mixture containing at least graphite and a battery active material capable of being combined with lithium ions,
A spheronization step of subjecting the mixture to a spheronization treatment,
And a firing step of subjecting the product obtained through the spheronization treatment to a firing treatment,
The manufacturing method of the composite active material for lithium secondary batteries which satisfy|fills at least 1 of the following requirements 1-3.
Requirement 1: In the mixture forming 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 to obtain graphite and lithium. It is a step of obtaining a mixture containing a battery active material that can be combined with ions and a water-soluble binder.
Requirement 2: Between the sphering step and the calcination step, the product obtained in the sphering step and a 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 matter, and the solid matter is baked in the firing 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, which is then converted into a solid. It further has a mixed firing step of performing firing treatment.
(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 material for a lithium secondary battery according to (1) or (2), wherein the water-soluble binder contains one kind selected from the group consisting of sugars, glycerins, and polyalkylene glycols. Method of manufacturing 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 method for producing a composite active material for a lithium secondary battery according to any one of (1) to (3), which contains a salt of these and an alkali metal or an 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) At least the battery active material that can be combined with lithium ions is selected from the group consisting of elements of Group 13 of the periodic table, elements of Group 14 of the periodic table, elements of Group 15 of the periodic table, magnesium, and manganese. The method for producing a composite active material for a lithium secondary battery according to any one of (1) to (5), which contains one element.
(7) The method for producing a composite active material for a lithium secondary battery according to any one of (1) to (6), wherein the battery active material that can be combined with lithium ions has an average particle diameter of 1 μm or less.

According to the present invention, it is possible to use water as a solvent in a manufacturing process, and to provide a method for manufacturing a composite active material for a lithium secondary battery, capable of manufacturing a lithium secondary battery exhibiting excellent cycle characteristics. You can

The method for producing the composite active material for a lithium secondary battery of the present invention (hereinafter also simply referred to as composite active material) will be described in detail below.

In addition, as a manufacturing method of a composite active material, it has a predetermined process and satisfy|fills at least one of the following requirements 1-3.
Requirement 1: In the mixture forming 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 to obtain graphite and lithium. It is a step of obtaining a mixture containing a battery active material that can be combined with ions and a water-soluble binder.
Requirement 2: Between the sphering process and the calcination process, the product obtained in the sphering process and the water-soluble binder are mixed in water, and water is removed from the resulting aqueous dispersion to obtain a solid. The method further includes a mixing step of collecting the substance, and the solid material is subjected to a firing treatment in the firing 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, which is then converted into a solid. It further has a mixed firing step of performing firing treatment.

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

In the following, a mode satisfying requirement 1 will be described as a first embodiment, a mode satisfying requirement 2 will be described as a second embodiment, and a mode satisfying requirement 3 will be described 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 forming step of obtaining a mixture by mixing predetermined components, a spheroidizing step of subjecting the mixture to a spheroidizing treatment, and the obtained product On the other hand, a method including a firing step of performing a firing treatment. The mixture generation step in the first embodiment is a step that satisfies the above requirement 1.

Hereinafter, the procedure of each step will be described in 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 the resulting aqueous dispersion is mixed with water. Is a step of removing graphite to obtain a mixture containing graphite, a battery active material capable of combining with lithium ions, and a water-soluble binder.

In the following, first, the components used in this step will be described in detail, and then the procedure of the step will be described in detail.
(graphite)
The specific surface area of the graphite used in this step is preferably 10 m ² /g or more. Within the above range, a composite active material in which a battery active material is highly dispersed on a graphite surface having a high surface area (preferably, a thin thickness) can be obtained. As a result, the battery material using the composite active material exhibits excellent cycle characteristics.

Among them, the specific surface area of the lithium secondary battery using the composite active material obtained by the production method of the present invention is more excellent in cycle characteristics (hereinafter, also simply referred to as “the effect of the present invention is more excellent”). 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 from the viewpoint that the manufacturing procedure becomes complicated and synthesis is difficult.

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

The graphite includes, for example, a layer in which a plurality of graphene sheets are stacked in the direction in which the graphite surfaces are stacked, and the graphene sheets are bonded to each other mainly by Van der Waals force.

The average thickness of the layer of the laminated graphene sheets 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 in many cases because the manufacturing procedure becomes complicated.

In addition, as a method of measuring the average thickness, by observing graphite by electron microscope observation (TEM), measuring 10 or more thicknesses of the layers of the laminated graphene sheets in graphite, and averaging the values arithmetically. , An average thickness is obtained.

Note that so-called graphene (graphene sheet) itself can be used as the above graphite.

As the graphite used in this step, a commercially available product may be used, or a known method may be used.

So-called expanded graphite or flaky graphite can be used as the graphite.

As a method for producing expanded graphite, for example, after immersing graphite (for example, flake graphite) in acid at room temperature, the acid-treated graphite obtained is subjected to heat treatment (preferably at 700 to 1000° C.). It can be manufactured. More specifically, the 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, then the acid is removed, and washing and drying are performed. Then, the obtained acid-treated graphite is put into a furnace at about 850° C. to obtain expanded graphite. In addition, the expanded black matrix can be obtained by using graphite in which an intercalation compound is formed with graphite such as an alkali metal, instead of the acid-treated graphite.

In addition, as a method for producing flaky graphite, after the expanded graphite is dispersed in a solvent, the hinge part of the expanded graphite is treated by ultrasonic treatment or a powder mill that gives a large shear stress (for example, a stone mill). It is possible to obtain flake graphite in which about 50 (preferably 10 to 150) graphene sheets are laminated and destroyed.

The number of graphene sheets forming the expanded graphite and the number of graphene sheets forming the flaky graphite obtained by disintegrating the expanded graphite are basically estimated to be substantially the same.
(Battery active material that can be combined with lithium ion)
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 to occlude and release lithium ions (eg, 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 alloying 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, in terms of the effect of the present invention being more excellent, the battery active material is selected from the group consisting of elements of Group 13 of the periodic table, elements of Group 14 of the periodic table, elements of Group 15 of the periodic table, magnesium, and manganese. 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. Is more preferable (preferably, metals of these elements or alloys containing these metals), and it is further preferable to contain elements of Si or Sn (preferably, metals of these elements or alloys containing these metals). .. Particularly, the battery active material is preferably silicon.

The alloy may be an alloy containing a combination of the above-mentioned metals or an alloy containing a metal that does not occlude and release lithium ions. In this case, it is preferable that the content of the metal capable of being alloyed with lithium in the alloy is higher. The upper limit of the metal content is preferably 70% by mass, more preferably 60% by mass or less, judging from the uniformity of particles and the cycle characteristics judged by the secondary electron image obtained by SEM observation.

The shape of the battery active material 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 further preferably 0.1 μm or less, from the viewpoint that the effect of the present invention is more excellent. The lower limit value is not particularly limited and is preferably small. With the usual powder-frame method, it is possible to produce fine powder having an average particle size of up to about 0.01 μm, and powder with a particle size of this level can be used effectively.

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

As a method of obtaining a battery active material having the above-mentioned predetermined average particle diameter, by performing powdering of the battery active material using a known device such as a stirring tank type stirring mill (bead mill etc.), It is possible to obtain a powder having a small particle size.

In particular, as the battery active material, silicon particles are preferable, and silicon particles having an average particle diameter of 100 nm or less (in particular, an average particle diameter of 50 nm or less) are particularly preferable.
(Water-soluble binder (water-soluble compound))
The water-soluble binder used in this step is a material that binds the above-mentioned graphite and the battery active material. For example, a saccharide or the like that can be used as a water-soluble binder is carbonized in the firing step described later to become amorphous carbon in the composite active material, which serves to improve the properties of the composite active material. Further, since the water-soluble binder has excellent solubility in water, water can be used to mix the above-mentioned graphite and battery active material with the water-soluble binder.

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

Known materials (for example, surfactants) can be used as the water-soluble binder, and examples thereof include polyhydric alcohols, amine compounds, carboxylic acid compounds, sulfuric acid compounds (for example, dodecylsulfonic acid), nitric acid compounds, Alternatively, ester derivatives thereof, alkali metal salts, alkaline earth metal salts and the like can be mentioned, and polyhydric alcohols are preferable from the viewpoint 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 them, saccharides, glycerins, polyalkylene glycols, and the like are listed because the effects of the present invention are more excellent. As the 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, and erythritol. Sugars, glycerins such as glycerin, diglycerin, triglycerin and polyglycerin, polyalkylene glycols such as polyethylene glycol and 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, and dipentaerythritol. In addition, these ester derivatives or salts of these with alkali metals or alkaline earth metals may be used.

When a saccharide is used as the water-soluble binder, it is preferable to use two or more saccharides in combination, because the effect of the present 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 preferred to use more than one species.

A commercially available product can be used as the water-soluble binder, and for example, honey, cake syrup, etc. can be used as the raw material of the sugar. The honey used in this step is not particularly limited, and examples thereof include honey, purified honey, sweetened honey, and acacia honey.
(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 a water solvent. As the mixing treatment, known stirring treatment can be carried out. In addition, at the time of mixing, an organic solvent may be present as long as the effect of the present invention is not impaired.

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

In addition, ultrasonic treatment may be performed during the mixing treatment, if necessary. That is, the graphite component, the battery active material, and the water-soluble binder may be mixed while performing ultrasonic treatment.

The mixing ratio of graphite and the battery active material is not particularly limited, but from the viewpoint that the effect of the present invention is more excellent, 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. It is more preferable to mix 100 parts by mass.

The mixing ratio of the graphite and the water-soluble binder is not particularly limited, but from the viewpoint that the effect of the present invention is more excellent, 1 to 50 parts by mass of the water-soluble binder may be mixed with 100 parts by mass of graphite. It is preferable to mix 10 to 30 parts by mass.

The amount of water used is not particularly limited, but as a result of achieving a higher degree of dispersion, the effect of the present invention is more excellent, and it is possible to mix water in an amount of 500 to 15,000 parts by mass with respect to 100 parts by mass of graphite. It is more preferable to mix 1000 to 7000 parts by mass.

Next, water is removed from the aqueous dispersion obtained by the above mixing treatment to obtain a mixture containing graphite, the battery active material, and the 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 of removing water is not particularly limited, and examples thereof include a method using a known device (eg, evaporator). Further, a method of separating water and solid content by filtration or the like may be carried out. In addition, in the obtained mixture, water may remain as long as the effect of the present invention is not impaired.

A pressing step of pressing the obtained mixture may be included, if necessary, before the spheroidizing step of the mixture producing step, which will be described later. When the pressing step is carried out, the distance between the graphites becomes smaller, and the spheroidizing treatment described later proceeds more efficiently.

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

By carrying out this step, the graphite sheet is folded into a spherical shape so that the battery active material and the water-soluble binder are incorporated therein. At that time, the edge portion of the graphite is folded inside, and a structure in which the battery active material is not substantially exposed on the surface of the formed composite active material is obtained.

The method of spheroidizing treatment is not particularly limited and is not particularly limited as long as it is a powder mill that can mainly apply impact stress. Examples of the powder mill include a high-speed rotary impact powder mill, and more specifically, a sample mill, a hammer mill, a pin mill and the like can be used. Among them, the pin mill is preferable because the effect of the present invention is more excellent.

Examples of high-speed rotary impact type dust mills include those in which a sample is collided with a rotor that rotates at high speed to achieve miniaturization by the impact force. Mill type hammer type, pin mill type rotating disc type with pins and impact heads attached to a rotating disc, axial flow type in which a sample is crushed while being conveyed in the shaft direction, and particle refinement in a narrow annular part An annular type is used. More specifically, a hammer mill, a pin mill, a screen mill, a turbo type mill, a centrifugal classification type mill and the like can be mentioned.

When this step is performed by the high-speed rotary impact type dust mill, it is preferable to perform spheroidization at a rotation speed of usually 100 rpm or more, preferably 1500 rpm or more, and usually 2000 rpm or less. Therefore, the collision speed is preferably about 20 m/sec to 100 m/sec.

Unlike the pulverization, the spheroidizing treatment is performed with a low impact force, and therefore it is preferable to usually perform the circulation treatment in this step. The processing time varies depending on the type of powder mill used and the amount charged, but it is usually within 2 minutes, and the processing time is about 10 seconds in the case of an apparatus in which an appropriate pin or collision plate is arranged. ..

Further, the spheroidizing treatment is preferably performed in air. If the nitrogen stream is treated in the same way, there is a risk of ignition when opening to the atmosphere.
<Firing process>
The firing step is a step of subjecting the spherical mixture obtained above to a firing treatment to produce a substantially spherical composite active material for lithium secondary batteries (composite active material). The composite active material contains at least the black component derived from graphite and the battery active material. Depending on the type of the water-soluble binder, the composite active material contains components derived from the water-soluble binder. For example, when a saccharide is used as the water-soluble binder, amorphous carbon derived from the saccharide is included in the composite active material. Further, for example, when glycerin is used as the water-soluble binder, the glycerin often volatilizes by the baking treatment.

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

The firing time is preferably 0.5 hours or longer, more preferably 1 hour or longer. The upper limit is not particularly limited, but it is often 5 hours or less from the point that the effect of the invention is saturated.

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

After the firing step, if necessary, a powder frame treatment may be carried out to further miniaturize the obtained composite active material. A known method can be used as a dusting method.
<Arbitrary process>
The first embodiment of the method for producing a composite active material of the present invention may include steps other than the steps described above.

Among them, in that the effect of the present invention is more excellent, a step of mixing the calcined product obtained in the above calcining step with a precursor of amorphous carbon to obtain a mixture, and subjecting the mixture to a calcining treatment is performed. You may also have. By carrying out this step, the surface of the fired product obtained in the firing step is covered with the precursor of amorphous carbon, and by carrying out the firing treatment, composite particles covered with amorphous carbon are obtained. To be

Examples of the amorphous carbon precursor include, for example, polymer compounds (for example, thermosetting resin and thermoplastic resin), coal pitch (for example, coal tar pitch), petroleum pitch, mesophase pitch, coke, and low molecule. Examples thereof include heavy oil and derivatives thereof, and coal-based pitch (for example, coal tar pitch), petroleum-based pitch, mesophase pitch, coke, low-molecular heavy oil, and derivatives thereof are preferable. Among them, as the amorphous carbon, soft carbon obtained from a precursor such as coal-based pitch is preferable because the effect of the present invention is more excellent.

The thermosetting resin is not particularly limited, and examples thereof include phenol resins such as novolac-type phenol resin and resol-type phenol resin; epoxy resins such as bisphenol-type epoxy resin and novolac-type epoxy resin; melamine resin; urea resin; aniline resin. Cyanate resin, furan resin, ketone resin, unsaturated polyester resin, urethane resin and the like. Further, a modified product obtained by modifying these with various components can also be used.

Further, 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, methacryl resin, polyethylene. Examples thereof include terephthalate, polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyether sulfone, polyether ether ketone, polyether imide, polyamide imide, polyimide and polyphthalamide.

These can be used alone or in combination of two or more.

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

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

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

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

In addition, the firing conditions are appropriately selected depending on the materials used, and examples include the firing process conditions described above.
<Composite active material for lithium secondary battery>
The composite active material obtained by going through the above-mentioned steps contains 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 from the viewpoint that the effect of the present invention is more excellent, it is preferably 15 to 80% by mass, more preferably 25 to 75% by mass with respect to the total amount of the composite active material. 35 to 70 mass% is 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. It is preferably 15 to 50% by mass, and more preferably.

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 in terms of more excellent effect of the present invention, the total amount of the composite active material is On the other hand, 0.1 to 60 mass% is preferable, 0.2 to 50 mass% is more preferable, and 1 to 40 mass% is further preferable.

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

The shape of the composite active material is not particularly limited, but it is preferable that the composite active material 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 mean value) obtained by obtaining the major axis/minor axis of each particle for at least 100 particles and arithmetically averaging them.

The minor axis in the above is the distance between two parallel lines that come into contact with the outside of a particle observed by a scanning electron microscope or the like and have the shortest distance among the two parallel lines that sandwich the particle. On the other hand, the major axis is two parallel lines perpendicular to the parallel line that determines the minor axis, and the distance between the two parallel lines with the longest distance among the two parallel lines in contact with the outside of the particle. Is. The rectangle formed by these four lines is the size that the particles will fit within.

The particle size (D 50: 50% volume particle size) of the composite active material is not particularly limited, but from the viewpoint that the effect of the present invention is more excellent, 2 to 40 μm is preferable, 5 to 35 μm is more preferable, and 5 to 30 μm is more preferable. preferable.

The particle size (D 90: 90% volume particle size) is not particularly limited, but is preferably 10 to 75 μm, more preferably 10 to 60 μm, and further preferably 20 to 45 μm, from the viewpoint 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 is preferably 1 to 20 μm, more preferably 2 to 10 μm from the viewpoint that the effect of the present invention is more excellent.

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

At the time of measurement, the composite active material is added to the liquid and vigorously mixed while utilizing ultrasonic waves, and the prepared dispersion liquid is introduced into the apparatus as a sample for measurement. In terms of work, it is preferable to use water, alcohol, or a low-volatile organic solvent as the liquid. At this time, it is preferable that the obtained particle size distribution chart 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. The lower limit is not particularly limited, but is preferably 0.1 m ² /g or more.

As a method for measuring the specific surface area (BET specific surface area) of the composite active material, the sample is vacuum dried at 300° C. for 30 minutes and then measured by the nitrogen adsorption single point method.
<<Second Embodiment>>
As a second embodiment of the method for producing a composite active material of the present invention, there are obtained a mixture producing step of obtaining a mixture by mixing predetermined components, a spheroidizing step of subjecting the mixture to a spheroidizing treatment, and a spheroidizing step. The mixing step of mixing the obtained product and the water-soluble binder in water, removing water from the obtained aqueous dispersion to recover the solid matter, and subjecting the obtained solid content to the baking treatment. And a firing step. In addition, 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 forming step, the mixing step is performed, and the solid content obtained in the mixing step in the firing step is On the other hand, the same procedure as in the first embodiment is carried out except that the baking treatment is performed. Therefore, the differences between the second embodiment and the first embodiment will be mainly described below in detail.
<Mixture generation process>
In the mixture producing step of the second embodiment of the present invention, the same raw materials and procedures as in the mixture producing step of the first embodiment described above are carried out except that the water-soluble binder is not used.
<Mixing process>
The mixing step is a step in which the product obtained through the spheroidizing step and the water-soluble binder are mixed in water, and water is removed from the obtained aqueous dispersion to recover a solid. By carrying out this step, a mixture of the product and the water-soluble binder can be efficiently produced.

The procedure of the mixing step can be performed by the same method as the mixture forming step of the first embodiment.

Further, the mixing ratio of the product obtained through the spheroidizing step and the water-soluble binder is not particularly limited, but the effect of the present invention is more excellent, and the water-soluble binder is added to 100 parts by mass of the product. The binder is preferably mixed in an amount of 10 to 60 parts by mass, more preferably 20 to 40 parts by mass.

Further, as a method for removing water from the aqueous dispersion, the method described in the mixture producing step of the first embodiment can be mentioned.

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

By carrying out the above procedure, a composite active material containing a graphite component, a battery active material, and a component derived from a water-soluble binder is obtained, 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 forming step of obtaining a mixture by mixing predetermined components, a spheroidizing step of subjecting the mixture to a spheroidizing treatment, and the obtained product On the other hand, a firing step of performing a firing treatment, a fired material obtained in the firing step and a water-soluble binder are mixed in water, and water is removed from the obtained water dispersion to recover a solid matter, And a firing step of performing a firing treatment on the solid matter. In addition, in 3rd Embodiment, the said requirement 3 is satisfy|filled in a mixing baking process.

In the third embodiment of the present invention, the same procedure as in the first embodiment is carried out except that the water-soluble binder is not used in the mixture forming step, the mixing step is carried out, and the mixing and firing step is carried out. To do.

Therefore, hereinafter, the mixing and firing step will be mainly described in detail.

In the mixing and firing step, first, the fired product obtained in the firing step and the water-soluble binder are mixed in water. As the procedure of the mixing method, the method described in the mixture producing step of the first embodiment can be mentioned.

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 in terms of the effect of the present invention being more excellent, with respect to 100 parts by mass of the product. 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.

Further, as a method for removing water from the aqueous dispersion, the method described in the mixture producing step of the first embodiment can be mentioned.

Further, the optimal conditions for the firing treatment are selected according to the material used, and examples thereof include the conditions for the firing process of the first embodiment described above.

By carrying out the above procedure, a composite active material containing a graphite component, a battery active material, and a component derived from a water-soluble binder is obtained, as in the first embodiment.

Although requirements 1 to 3 (first embodiment to third embodiment) have been described above, two or more requirements may be implemented at the same time.

For example, Requirement 1 and Requirement 3 may be implemented at the same time. More specifically, in the mixture forming 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, After the 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, the fired product obtained in the firing step and the water-soluble binder You may further perform the mixing baking process which mix|blends and in water, water is removed from the obtained water dispersion liquid, a solid substance is collect|recovered, and a solid substance is baked.

Further, the requirement 1 and the requirement 2 may be implemented at the same time, or the requirement 2 and the requirement 3 may be implemented at the same time.
<<Lithium secondary battery>>
The composite active material described above is useful as an active material used in a battery material (electrode material) used in a lithium secondary battery.

The method for producing the 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 may be mixed, pressure-molded or made into a paste using a solvent, and applied on a copper foil to form a negative electrode for a lithium secondary battery.

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

As a current collector (porous current collector) having a three-dimensional structure, as a porous body of a conductor of metal or carbon, a plain weave wire mesh, expanded metal, lath net, metal foam, metal woven cloth, metal nonwoven cloth, Examples include carbon fiber woven cloth and carbon fiber non-woven cloth.

As the binder to be used, known materials can be used, and examples thereof include fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene, SBR, polyethylene, polyvinyl alcohol, carboxymethyl cellulose and glue.

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

When forming a paste, a known stirrer, mixer, kneader, kneader or the like may be used for stirring and mixing as described above.

When the coating slurry is prepared using the composite active material, it is preferable to add conductive carbon black, carbon nanotubes or a mixture thereof as the conductive material. The shape of the composite active material obtained by the above process is often relatively granular (particularly, substantially spherical), and the contact between particles is likely to be point contact. In order to avoid this adverse effect, a method of adding carbon black, carbon nanotubes or a mixture thereof to 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 carbon nanotubes include single-wall carbon nanotubes and multi-wall carbon nanotubes.

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

The lithium secondary battery uses the above-mentioned negative electrode, positive electrode, separator, electrolytic solution, and other battery constituent elements (for example, current collector, gasket, sealing plate, case, etc.), and is of a cylindrical type or a rectangular type according to a conventional method. Alternatively, it may have a button type or the like.

INDUSTRIAL APPLICABILITY The lithium secondary battery of the present invention is used for various portable electronic devices, and in particular, notebook type personal computers, notebook type word processors, palmtop (pocket) personal computers, mobile phones, portable fax machines, portable printers, headphone stereos, video cameras, portable televisions. , Portable CD, portable MD, electric shaving machine, electronic notebook, transceiver, electric tool, radio, tape recorder, digital camera, portable copying machine, portable game machine, etc. In addition, it will also be used for electric vehicles, hybrid vehicles, vending machines, electric carts, power storage systems for load leveling, household power storage, distributed power storage systems (built into stationary appliances), emergency power supply systems, etc. It can also be used as a secondary battery.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
<Example 1>
(Preparation of expanded graphite)
The scale-like natural graphite having an average particle diameter of 1 mm was immersed 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, and then the mixed acid was removed with a No3 glass filter to obtain acid-treated graphite. The acid-treated graphite was washed with water and then dried. When 5 g of the dried acid-treated graphite was stirred in 100 g of distilled water and the pH was measured 1 hour later, the pH was 6.7. The dried acid-treated graphite was put into a vertical electric furnace in 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 diameter 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, and further, Honey (manufactured by Sanyo Tsusho Co., ingredient: 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 ingredients (protein, vitamins, minerals)) 25 parts by mass (5.7 parts by mass after carbonization) was added, and the mixture was stirred for 10 minutes with an in-line mixer.

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

The honey contained a plurality of types of sugar as described above.
(Press process)
The above powder mixture was pressed using a three-roller (EKAKT50). This process closes the expanded graphite layer that has been opened, shortens the interlayer distance, and also increases the density. By increasing the collision energy in the next sphering process, it becomes possible to increase the spheroidizing efficiency. ..
(Sphericalizing 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 was granulated into a spherical shape. went.
(Baking treatment (carbonization treatment))
The saccharides contained in the honey were carbonized at the same time by baking the spherical mixture at 900° C. for 1 hour while flowing nitrogen (1 L/min). As a result, a substantially spherical mixture having a graphite component content of 70 parts by mass, a silicon content of 30 parts by mass, and a saccharide-derived amorphous carbon content of 5.7 parts by mass was obtained.
(Coating with coal tar pitch)
The obtained substantially spherical mixture (100 parts by mass) was added to a solution in which coal tar pitch (carbonization degree 45%, 30 parts by mass) was dissolved in quinoline (200 parts by mass), and the mixture was stirred for 10 minutes. The coating was performed by firing using the method described in 1.
(Baking)
The coal tar pitch was modified into 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 the graphite component of 70 parts by mass, the content of silicon of 30 parts by mass, the content of the amorphous carbon derived from saccharides of 5.7 parts by mass, and the content of the soft carbon derived from coal tar pitch of 30 parts by mass. 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: approximately spherical From a secondary electron image of the composite active material using a SEM (scanning electron microscope) at a low accelerating voltage of 10 kV or less. It was found that in the composite active material, the graphite component and the battery active material had a structure 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.

Furthermore, exfoliated graphite was observed in the composite active material. The exfoliated graphite had a thickness of about 20 nm (total number of graphene sheets stacked: 60).
(Manufacture of negative electrode)
95.5 parts by weight of the composite active material, 2.5 parts by weight of SBR (styrene-butadiene rubber), 1.5 parts by weight of CMC (carboxymethylcellulose), 0.5 part by weight of conductive carbon black, and 100 parts by weight of water. The slurry for coating was prepared by collecting and mixing for 3 minutes using a double-arm mixer. This slurry was applied to a copper foil and dried to produce a negative electrode.
(Production of positive electrode)
_{LiNi 1-x-y Co x} Al y O 2 84 parts by weight, PVDF-containing NMP solution (PVDF: polyvinylidene fluoride, NMP: methylpyrrolidone) (content: 12%) 66 parts by weight, the conductive carbon black 8 parts by weight , And NMP 29 parts by mass were weighed and mixed for 3 minutes using a double-arm mixer to prepare a coating slurry. This slurry was applied to an aluminum foil and dried to produce a positive electrode.
(Full cell manufacturing)
Using the above-mentioned 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 prepare a full cell, and the following battery evaluations were made. I went.
(Battery evaluation: electrode expansion measurement)
A cycle test was performed using the above full cell. At that time, the charge and discharge capacities and the initial irreversible capacities were measured, and the capacity retention ratios for the first cycle of 60 cycles and 100 cycles were compared. The charge/discharge rate was 0.5 C, the charge-side cutoff voltage was 4.0 V, and the discharge-side cutoff voltage was 2.7 V, and a cycle experiment (100 times) was performed.

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

The maximum coulombic efficiency “Max coulombic 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, perfume, caramel color) was used instead of honey. According to the procedure of 1., the composite active material was manufactured, and further, the 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, and further, A full cell was manufactured and various evaluations were performed.

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 has excellent cycle characteristics.

Claims (6)

A mixture producing step of obtaining a mixture containing at least graphite and a battery active material capable of being combined with 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 calcination step of subjecting the product obtained through the spheroidizing treatment to a calcination treatment, and satisfying at least one of requirements 1 to 3 below. ..
Requirement 1: In the mixture forming step, the graphite, the battery active material that can be combined with the lithium ions, and the polyhydric alcohol that is a water-soluble binder are mixed in water, and water is obtained from the resulting aqueous dispersion. Is removed to obtain a mixture containing the graphite, the battery active material that can be combined with the lithium ions, and the polyhydric alcohol .
Requirement 2: Between the sphering step and the calcination step, the product obtained in the sphering step and a polyhydric alcohol are mixed in water, and water is removed from the obtained aqueous dispersion. The method further includes a mixing step of collecting the solid matter, and the solid matter is subjected to a firing treatment in the firing step.
Requirement 3: After the firing step, the fired product obtained in the firing step and the polyhydric alcohol are mixed in water, water is removed from the obtained aqueous dispersion to recover a solid matter, and the solid matter is obtained. The method further includes a mixing and firing step of performing a firing treatment on. The method for producing a composite active material for a lithium secondary battery according to claim 1, wherein the polyhydric alcohol contains one selected from the group consisting of sugars, glycerins, and polyalkylene glycols. The polyhydric alcohol is glucose, fructose, galactose, sucrose, maltose, lactose, starch, cellulose, glycogen, alginic acid, pectin, glycerin, diglycerin, polyethylene glycol, or an ester derivative thereof, or an alkali metal with these. or salts with alkaline earth metals, the manufacturing method of the composite active material for lithium secondary battery according to claim 1 or 2. The graphite is expanded graphite, method for producing a lithium secondary battery composite active material according to any one of claims 1-3. The battery active material that can be combined with the lithium ion is at least one selected from the group consisting of elements of Group 13 of the periodic table, elements of Group 14 of the periodic table, elements of Group 15 of the periodic table, magnesium, and manganese. The method for producing a composite active material for a lithium secondary battery according to any one of claims 1 to 4 , containing the element of. The average particle diameter of the lithium ions can compound a battery active material is 1μm or less, the manufacturing method of a lithium secondary battery composite active material according to any one of claims 1-5.