JP2015035317A - Method for producing composite graphite particle for nonaqueous secondary battery negative electrode, composite graphite particle for nonaqueous secondary battery negative electrode produced thereby, negative electrode for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an excellent negative electrode material for a nonaqueous secondary battery, being high in capacity and having both high cycle characteristics and high rate characteristics; a negative electrode for a nonaqueous secondary battery using the same; and a nonaqueous secondary battery including the negative electrode.SOLUTION: Provided is a method for producing a composite graphite particle for a nonaqueous secondary battery negative electrode containing graphite (A) and a metal particle (B) capable of being alloyed with Li. The method includes the following step 1 and step 2: step 1 of obtaining a mixture at least including a polymer containing graphite (A), a metal particle (B) capable of being alloyed with Li, and a nitrogen atom; and step 2 of imparting mechanical energy to the mixture obtained by the step 1 to be subjected to a conglobation treatment.

Description

  The present invention relates to a method for producing composite graphite particles for a nonaqueous secondary battery negative electrode, a composite graphite particle for a nonaqueous secondary battery negative electrode produced by the production method, a negative electrode for a nonaqueous secondary battery using the same, and The present invention relates to a non-aqueous secondary battery provided with the negative electrode, particularly a lithium ion secondary battery.

In recent years, demand for high-capacity secondary batteries has increased with the downsizing of electronic devices.
In particular, non-aqueous secondary batteries having higher energy density and excellent rapid charge / discharge characteristics, particularly lithium ion secondary batteries, are attracting attention as compared to nickel / cadmium batteries and nickel / hydrogen batteries.
A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions and a non-aqueous electrolyte solution in which a lithium salt such as LiPF ₆ or LiBF ₄ is dissolved has been developed and put into practical use.

Various materials have been proposed as negative electrode materials for this battery. From the high capacity and excellent discharge potential flatness, natural graphite, artificial graphite obtained by graphitization of coke, etc., Graphite carbon materials such as graphitized mesophase pitch and graphitized carbon fiber are still used today.
On the other hand, non-aqueous secondary batteries, especially lithium ion secondary batteries, have been developed recently. In addition to conventional notebook computers, mobile communication devices, portable cameras, portable game machines, etc., electric tools, There is a demand for lithium ion secondary batteries that are required for rapid charge / discharge performance that has been increased in the past, such as those for automobiles, and that have high capacity and high cycle characteristics.

However, while a high capacity is desired in this way, in a carbon-centered negative electrode, the theoretical capacity of carbon is 372 mAh, so it is impossible to desire a capacity higher than this. Therefore, application of metal particles having various theoretical capacities, especially metal particles, to the negative electrode has been studied.
For example, Patent Documents 1 and 2 propose a method for producing Si composite graphite particles by firing a mixture of fine powder of an Si compound, graphite, and a pitch of carbonaceous material precursor.

Patent Document 3 proposes Si composite graphite particles in which Si fine particles are compounded with a carbonaceous material so as to be unevenly distributed on the surface of spheroidized natural graphite.
In Patent Document 4, a granulated body obtained by pulverizing and granulating a mixture of a graphite raw material and a metal powder in a high-speed air flow, and a part of the graphite used as the raw material is pulverized to produce the graphite raw material and the pulverized product. There has been proposed Si composite graphite particles made of a granulated body in which a product is agglomerated and laminated, and a metal powder is dispersed on the surface and inside thereof.

  In Patent Document 5, a mixture of void forming agents selected from scale-like or scale-like natural graphite, fine particles of Si compound, carbon black and polyvinyl alcohol, polyethylene glycol, polycarbosilane, polyacrylic acid, cellulosic polymer, and the like is prepared. There is disclosed Si composite graphite particles composed of substantially spherical particles having fine carbon protrusions on a surface obtained by impregnating and coating a mixture of a carbon precursor and carbon black on a granulated or spherical product.

  Further, Patent Document 6 describes that it is Si composite graphite particles containing scaly natural graphite, metal particles that can be alloyed with Li, and a carbonaceous material, and the metal particles may be nitrides.

Japanese Patent Laid-Open No. 2003-223892 JP 2012-043546 A JP2012-124116A JP 2008-27897 A JP 2008-186732 A JP 2005-243508 A

  However, according to the study by the present inventors, the technique described in Patent Document 1 is Si composite graphite particles obtained by combining graphite and Si compound particles with a carbonaceous material, but the carbonaceous material responsible for binding of the Si composite graphite particles. Since the binding property of the Si compound particles was weak, the Si composite graphite particles collapsed due to the volume expansion of the Si compound particles accompanying charging and discharging, and there were problems such as cycle deterioration due to the disconnection of the conductive path.

  In the technique described in Patent Document 2, in Si composite graphite particles containing Si compound particles, scaly graphite particles, and carbonaceous material derived from coal tar pitch, firing is performed by sufficiently stirring and mixing before compositing (firing). Later, a structure in which the surface of Si compound particles and scaly graphite particles was covered with amorphous carbon was proposed (Raman R value range definition), but the binding property of the composite was weak, so it was accompanied by charging and discharging. Due to the volume expansion of the Si compound particles, the Si composite graphite particles collapsed, and there were problems such as cycle deterioration due to the disconnection of the conductive path, and the practical level was not reached.

  In the technique described in Patent Document 3, Si compound fine particles are composited with carbonaceous materials so that they are unevenly distributed on the surface of the spheroidized natural graphite, but the Si compound particles are carbonaceous materials on the graphite surface. Adhesion is insufficient just by being attached, and there is a problem such as cycle deterioration due to loss of conductive path due to volumetric expansion of Si compound particles due to charge and discharge, and the practical use level. It did not arrive.

  In the technique described in Patent Document 4, the composite particles are obtained by pulverizing a part of graphite used as a raw material in a high-speed air stream, and the pulverized product is aggregated to form a lump particle, which is a granulated body composed of a plurality of lump particles. Because it is a granulated body with metal fine particles dispersed inside and on its surface and inside, the binding between the bulk particles is weak, and the Si compound graphite particles collapse due to the volume expansion of the Si compound particles accompanying charge and discharge. There were problems such as cycle deterioration due to the path being cut, and it was not at a practical level. Moreover, the content efficiency of the metal particle of Si composite graphite particle was also low, and there was room for improvement.

  In the technique described in Patent Document 5, the spheroidized natural graphite is certainly spheroidized, but as shown in FIG. 9 in the document, it is recognized that the graphite has a folded structure. In addition, there is no suggestion of mixing polymers containing nitrogen atoms. Further, according to the study of the present inventors, even when the composite graphite particles are produced by the method described in the above document, the amount of metal particles present in the composite particles is small in addition to the above-mentioned problems, It did not satisfy the battery characteristics. Moreover, the content efficiency of the metal particle of Si composite graphite particle was also low, and there was room for improvement.

In the technique described in Patent Document 6, it is described that composite granulated particles are produced from scaly natural graphite by a mechanofusion system (Hosokawa Micron Co., Ltd.). In this manufacturing method, spherical particles can be produced, but sufficient mechanical stress cannot be applied to the flaky graphite, and the folded structure cannot be formed inside the particles. It was found that the inhibitory effect was small. In addition, there is no suggestion of mixing polymers containing nitrogen atoms. Moreover, the content efficiency of the metal particle of Si composite graphite particle was also low, and there was room for improvement.

  Therefore, the present invention has been made in view of the background art, and the problem is that the metal particles that can be alloyed with Li can be efficiently present inside the composite graphite particles. Providing a method for producing composite graphite particles, and by using metal particles that can be alloyed with Li, detachment from graphite due to volume expansion accompanying charge / discharge, which is inevitably generated, and accompanying conduction path interruptions are suppressed, and electrolysis Composite graphite particles for non-aqueous secondary battery negative electrodes (hereinafter referred to as composite graphite particles) for producing non-aqueous secondary batteries in which side reactions with the liquid are suppressed, Li addition reverse loss is reduced, and charge / discharge efficiency is improved. As a result, a non-aqueous secondary battery having a high capacity and high charge / discharge efficiency is provided.

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, a mixture of “graphite (A)”, “metal particles alloyable with Li (B)” and “polymer containing nitrogen atoms”. It was found that composite graphite particles for a non-aqueous secondary battery negative electrode in which the metal particles (B) that can be alloyed with Li were efficiently encapsulated can be produced by applying a spheroidizing treatment. .
When this composite graphite particle is analyzed, the composite graphite particle contains nitrogen atoms, and when the cross section is observed with an SEM (scanning electron microscope), a structure in which the graphite (A) is folded is observed. I understood.
By applying such composite graphite particles of the present invention to the negative electrode material of a non-aqueous secondary battery, a non-aqueous secondary battery having high capacity, high charge / discharge efficiency, and high cycle characteristics can be obtained. And found the present invention.

  Although the detailed mechanism is not known, the presence of a large amount of metal particles (B) in the gaps of the composite graphite particles having a structure in which graphite (A) is folded allows the same capacity, that is, the same amount of metal particles ( Compared with the negative electrode material containing B), the metal particles (B) and the electrolytic solution are not in direct contact with each other, so the irreversible loss of Li ions due to the reaction between the metal particles (B) and the non-aqueous electrolytic solution. Is reduced, that is, the charge / discharge efficiency is improved. In addition, comparison is made with granulated composite graphite particles containing generally known metal particles (B) or composite particles in which more metal particles (B) are attached to the outside of the graphite particles than inside the particles. Even so, in the composite graphite particles of the present invention, the graphene surfaces of the plurality of folded graphite encapsulating the metal particles (B) expand because the soft graphene layer expands and contracts during the volume expansion of the metal particles (B). Is absorbed (relaxed), so that there is an advantage that the composite graphite particles are not easily collapsed due to volume expansion and the conductive path is not easily broken.

  Moreover, the surface of a metal particle (B) can be coat | covered with this polymer or the baked product of this polymer by mixing the polymer containing a nitrogen atom. At this time, the nitrogen atoms of the polymer react with active groups (hydroxyl group, carboxylic acid group, etc.) having high reactivity on the surface of the metal particle (B), and the surface of the metal particle (B) becomes an inactive nitride. There is an advantage that the irreversible loss of Li ions due to the reaction between the metal particles (B) and the nonaqueous electrolytic solution is reduced, that is, the charge / discharge efficiency is improved. Moreover, since the polymer containing nitrogen atoms can be contained during mixing of graphite (A) and metal particles (B), many metal particles (B) can be present in the composite graphite particles. A non-aqueous secondary battery having a higher capacity than composite graphite particles produced without using this polymer can be obtained. This is considered to be because the polymer containing nitrogen atoms plays a role as a binder for holding the metal particles (B) on the graphite (A).

That is, the gist of the present invention is a method for producing composite graphite particles for a non-aqueous secondary battery negative electrode containing graphite (A) and metal particles (B) that can be alloyed with Li, comprising the following step 1 and step: 2 in a method for producing composite graphite particles for a non-aqueous secondary battery negative electrode.
Step 1: Step of obtaining a mixture containing at least a polymer containing graphite (A), Li-alloyable metal particles (B) and a polymer containing nitrogen atoms Step 2: Giving mechanical energy to the mixture of Step 1 and spheronizing treatment In addition, another aspect of the present invention is a composite graphite particle for a nonaqueous secondary battery negative electrode containing graphite (A) and metal particles (B) that can be alloyed with Li, wherein the composite graphite particle Contains a nitrogen atom, and when the cross section of the composite graphite particle is observed with an SEM (scanning electron microscope), a structure in which the graphite (A) is folded is observed. It exists in the composite graphite particle for battery negative electrodes.
Another aspect of the present invention is a non-aqueous secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte, wherein the negative electrode is the negative electrode for a non-aqueous secondary battery. Next battery.

  The composite graphite particles for a non-aqueous secondary battery negative electrode of the present invention provide a non-aqueous secondary battery having a high capacity and high charge / discharge efficiency by using it as an active material for a non-aqueous secondary battery. be able to.

Scanning electron microscope (SEM) photograph of the cross section of the graphite particles of Example 1 An example of a method for measuring the abundance ratio in a scanning electron microscope (SEM) photograph of a cross section of composite graphite particles

Hereinafter, the contents of the present invention will be described in detail. In addition, description of the invention structural requirements described below is an example (representative example) of the embodiment of the present invention, and the present invention is not limited to these forms unless it exceeds the gist.
The composite graphite particles for a nonaqueous secondary battery negative electrode of the present invention are produced by mixing at least graphite (A), metal particles that can be alloyed with Li (B), and a polymer containing nitrogen atoms, and spheroidizing the mixture. Is done. The composite graphite particles contain nitrogen atoms, and when the cross section of the composite graphite particles is observed with an SEM (scanning electron microscope), the composite graphite particles have a structure in which the graphite (A) is folded. .

<Graphite (A)>
Graphite (A), which is one of the constituent components of the composite graphite particles of the present invention, is shown below as an example, but is not particularly limited, and any conventionally known product or commercially available product may be used, and any production method There is no problem even if it is manufactured.

(Type of graphite (A))
For example, scale-like, massive or plate-like natural graphite, or scale-like, massive or plate-like artificial graphite produced by heating petroleum coke, coal pitch coke, coal needle coke, mesophase pitch or the like to 2500 ° C. or higher. Can be obtained by performing impurity removal, pulverization, sieving and classification as required.

Among these, natural graphite is classified into flake black (FlakeGraphite), scaly graphite (CrystalLine (Vein) Graphite), and soil graphite (Amorphous Graphite) (“Granule Process Technology Assembly” ) Graphite section of Industrial Technology Center, published in 1974), and "HANDBOOKOF
CARBON, GRAPHITE, DIAMOND AND FULLLINES "(N
(see publishes oysPublications)). The degree of graphitization is highest at 100% for scaly graphite, followed by scaly graphite at 99.9%, and it is preferable to use these graphites.

The production area of scaly graphite, which is natural graphite, is Madagascar, China, Brazil, Ukraine, Canada, etc., and the production area of scaly graphite is mainly Sri Lanka. The main producers of soil graphite are the Korean Peninsula, China and Mexico.
Among these natural graphites, scaly graphite and scaly graphite have advantages such as high degree of graphitization and low amount of impurities, and therefore can be preferably used in the present invention. Visual methods for confirming that graphite is scaly include particle surface observation with a scanning electron microscope, embedding particles in a resin to produce a thin piece of resin, and cutting out the particle cross section, or coating consisting of particles Examples of the method include a method of observing a particle cross section with a scanning electron microscope after a cross-section polisher is used to produce a cross-section of the coating film and the particle cross section is cut out.
Scaly graphite and scaly graphite have natural graphite that is highly purified so that the crystallinity of graphite is almost completely crystallized, and artificially formed graphite. Natural graphite is soft and folded. It is preferable in that it is easy to fabricate the structure.

(Physical properties of graphite (A))
Graphite (A) in the present invention exhibits the following physical properties. In addition, there is no restriction | limiting in particular in the measuring method in this invention, According to the measuring method as described in an Example, unless there is a special situation.

-Volume average particle diameter (d50)
The average particle diameter (d50) of the graphite (A) before being combined with the metal particles (B) is not particularly limited, but is usually 1 μm or more and 120 μm or less, preferably 3 μm or more and 100 μm or less, more preferably 5 μm or more. 90 μm or less. If it is this range, the composite graphite particle which embeds this metal particle can be manufactured. Further, if the volume average particle diameter (d50) of graphite (A) is too large, the particle diameter of the composite graphite particles embedding the metal particles becomes large, and the electrode material mixed with the composite graphite particles is used as a binder or water. Alternatively, streaking or unevenness due to large particles may occur in the step of applying an organic solvent to form a slurry. If the flat volume average particle diameter is too small, folded graphite particles cannot be produced. The volume average particle diameter (d50) here is a volume-based median diameter measured by laser diffraction / scattering particle size distribution measurement.

Average aspect ratio The average aspect ratio, which is the ratio of the length of the major axis to the minor axis of the graphite (A) before being combined with the metal particles (B), is usually 2.1 or more and 10 or less, and 2.3 or more and 9 or less. It is preferable that it is 2.5 or more and 8 or less. When the aspect ratio is within this range, it is possible to produce composite graphite particles made of graphite having a folded structure, and minute voids are formed in the composite graphite particles, and volume expansion associated with charge / discharge Can be relaxed and contribute to the improvement of cycle characteristics.

The tap density of the tap density metallic particles (B) and graphite prior to composite (A) is generally not more than 0.1 g / cm ³ or more 1.0 g / cm ^3, preferably 0.13 g / cm ³ or more 0.8 g / cm ³ or less, more preferably 0.15 g / cm ³ or more and 0.6 g / cm ³ or less. When the tap density of graphite (A) is within the above range, minute voids are easily formed in the composite graphite particles. A tap density is measured by the method of the Example mentioned later.

· BET method using a specific surface area metal particles (B) and a specific surface area by the BET method of the graphite (A) before the composite is usually ^{1 m} 2 / g or more ^{40 m} 2 / g or less, ^2m 2 / g or more ^35m 2 / g or less it is preferably, and more preferably less ^3m 2 / g or more ^{30 m} 2 / g. The specific surface area of graphite (A) by the BET method is reflected in the specific surface area of the composite graphite particles made of graphite having a folded structure,
By setting it to 40 m ² / g or less, a decrease in battery capacity due to an increase in the irreversible capacity of the composite graphite particles can be prevented. The BET method specific surface area is measured by the method of Examples described later.

-002 plane spacing (d002) and Lc
The interplanar spacing (d002) of the 002 plane by graphite X-ray wide angle diffraction method is usually 0.337 nm or less. On the other hand, since the theoretical value of the interplanar spacing of the 002 plane of graphite is 0.335 nm, the interplanar spacing of the 002 plane of graphite is usually 0.335 nm or more. Further, Lc of graphite (A) by X-ray wide angle diffraction is 90 nm or more, preferably 95 nm or more. When the interplanar spacing (d002) of the 002 plane is 0.337 nm or less, it indicates that the crystallinity of the graphite (A) is high, and high capacity composite graphite particles for a non-aqueous secondary battery negative electrode can be obtained. Moreover, when Lc is 90 nm or more, it shows that crystallinity is high, and a negative electrode material having a high capacity can be obtained.
The interplanar spacing (d002) of the 002 surface by the X-ray wide angle diffraction method and Lc are measured by the method of the example described later.

True density The true density of the graphite (A) before being combined with the metal particles (B) is usually 2.1 g / cm ³ or more, preferably 2.15 g / cm ³ or more, more preferably 2.2 g / cm ^3. That's it. When the true density is a highly crystalline graphite having a true density of 2.1 g / cm ³ or more, composite graphite particles for a non-aqueous secondary battery negative electrode having a low capacity and a low irreversible capacity can be obtained.

-Length of particle short diameter The length of the long diameter of graphite (A) before complexing with metal particles (B) is usually 100 µm or less, preferably 90 µm or less, more preferably 80 µm or less. Further, the length of the minor axis of graphite (A) is usually 0.9 μm or more. If the length of the minor axis of graphite (A) is within the above range, minute voids are likely to be formed in the composite graphite particles, and the volume expansion associated with charge / discharge can be relaxed and cycle characteristics can be improved. it can.

<Metal particles that can be alloyed with Li (B)>
In the composite graphite particles for a nonaqueous secondary battery negative electrode of the present invention, as described above, the metal particles (B) that can be alloyed with Li are characterized in that they are at least embedded in the graphite particles.

(Types of metal particles (B) that can be alloyed with Li)
As the metal particles (B) that can be alloyed with Li (also referred to as metal particles (B) in the present specification), any conventionally known metal particles can be used. The particles are, for example, Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn, Al, Zr, Cr, P, S, V, Mn, Nb, Mo, Cu, Zn, Ge, In, Ti A metal selected from the group consisting of or the like or a compound thereof is preferable. Further, an alloy composed of two or more kinds of metals may be used, and the metal particles may be alloy particles formed of two or more kinds of metal elements. Among these, a metal selected from the group consisting of Si, Sn, As, Sb, Al, Zn, and W or a compound thereof is preferable. The metal particles (B) can be either single crystals or polycrystals regardless of their crystalline states, but are preferably polycrystalline because they can be easily reduced in particle size and have high rate characteristics.

Examples of the metal compound include metal oxides, metal nitrides, metal carbides, and the like. Moreover, you may use the metal compound which consists of 2 or more types of metals.
Among these, Si or Si compounds are more preferable as the metal particles (B) in terms of increasing the capacity. In this specification, Si or Si compounds are collectively referred to as Si compounds. Specific examples of the Si compound include SiOx, SiNx, SiCx, SiZxOy (Z = C, N) and the like, and SiOx is preferable. The general formula SiOx is obtained using Si dioxide (SiO ₂ ) and metal Si (Si) as raw materials, and the value of x is usually 0 ≦
x <2, preferably 0.2 or more and 1.8 or less, more preferably 0.4 or more and 1.6 or less, still more preferably 0.6 or more and 1,4 or less, x = 0 is particularly preferred. If it is this range, it becomes high capacity | capacitance and it becomes possible to reduce the irreversible capacity | capacitance by the coupling | bonding of Li and oxygen. SiOx has a larger theoretical capacity than graphite. Furthermore, amorphous Si or nano-sized Si crystals easily allow alkali ions such as lithium ions to enter and exit, so that a high capacity can be obtained.
The volume average particle diameter (d50) and crystallite size of the Si compound are not particularly defined, and impurities may exist in the Si compound and on the compound surface.

(Physical properties of metal particles (B) that can be alloyed with Li)
The metal particles (B) in the present invention are not particularly limited as long as they can be alloyed with Li, but preferably exhibit the following physical properties. In addition, there is no restriction | limiting in particular in the measuring method in this invention, According to the measuring method as described in an Example, unless there is a special situation.

-Volume average particle diameter (d50)
From the viewpoint of cycle life, the volume average particle diameter (d50) of the metal particles (B) in the composite graphite particles is usually 0.005 μm or more, preferably 0.01 μm or more, more preferably 0.02 μm or more, and still more preferably. It is 0.03 μm or more, usually 10 μm or less, preferably 9 μm or less, more preferably 8 μm or less. When the average particle diameter (d50) is within the above range, volume expansion associated with charge / discharge is reduced, and good cycle characteristics can be obtained while maintaining charge / discharge capacity.
The average particle diameter (d50) is determined by a laser diffraction / scattering particle size distribution measuring method or the like.

- metal particles (B) the specific surface area by the BET method of BET specific surface area of the composite graphite particles of the metal particles (B) usually 0.5 m ² / g or more 120 m ² / g or less, ^{1 m} 2 / g or more 100 m ² / g or less is preferable. It is preferable that the specific surface area by the BET method of the metal particles that can be alloyed with Li is in the above-mentioned range since the charge / discharge efficiency and discharge capacity of the battery are high, lithium can be taken in and out quickly during high-speed charge / discharge, and the rate characteristics are excellent.

-Oxygen content of metal particles (B) The oxygen content of metal particles (B) in the composite graphite particles is not particularly limited, but is usually 0.01% by mass or more and 12% by mass or less, and 0.05% by mass or more. It is preferable that it is 10 mass% or less. The oxygen distribution state in the particle may exist near the surface, may exist inside the particle, or may exist uniformly within the particle, but is preferably present near the surface. It is preferable for the oxygen content of the metal particles to be within the above-mentioned range because volume expansion associated with charge / discharge is suppressed due to strong bonding between Si and O, and cycle characteristics are excellent.

-Crystallite size of metal particles (B) The crystallite size of the metal particles (B) in the composite graphite particles is not particularly limited, but is usually 0 in the crystallite size of the (111) plane calculated from XRD. .05 nm or more, preferably 1 nm or more, and usually 100 nm or less and 50 nm or less. It is preferable that the crystallite size of the metal particles is within the above range because the reaction between Si and Li ions proceeds rapidly and is excellent in input / output.

(Method for producing metal particles (B) that can be alloyed with Li)
As long as the metal particles (B) satisfy the characteristics of the present invention, commercially available metal particles may be used. Alternatively, metal particles (B) can be produced by using metal particles having a large particle size as a raw material for the metal particles and applying a mechanical energy treatment with a ball mill or the like described later.

  The production method is not particularly limited. For example, metal particles produced by the method described in Japanese Patent No. 3952118 can be used as the metal particles (B). For example, when producing SiOx, Si dioxide powder and metal Si powder are mixed at a specific ratio, and after filling this mixture into the reactor, the pressure is reduced to normal pressure or a specific pressure, and the temperature is raised to 1000 ° C. or higher. Then, by holding it, SiOx gas is generated and cooled and precipitated to obtain general formula SiOx particles (sputtering treatment). Precipitates can be used as particles by applying mechanical energy treatment.

  As the raw material of the metal particles (B), any conventionally known material can be used. From the viewpoint of capacity and cycle life, for example, Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn A metal selected from the group consisting of Al, Zr, Cr, P, S, V, Mn, Nb, Mo, Cu, Zn, Ge, In, Ti and the like, or a compound thereof is preferable. Further, an alloy composed of two or more kinds of metals may be used, and the metal particles may be alloy particles formed of two or more kinds of metal elements. Among these, a metal selected from the group consisting of Si, Sn, As, Sb, Al, Zn, and W or a compound thereof is preferable. Note that, regardless of the crystal state of the raw material of the metal particles, single crystal / polycrystal, etc. Either can be used.

The mechanical energy treatment is performed by, for example, using a device such as a ball mill, a vibration ball mill, a planetary ball mill, a rolling ball mill, or a bead mill to put a raw material charged in the reactor and a moving body that does not react with the raw material and vibrate it. Metal particles that can be alloyed with Li satisfying the properties described below can be formed by a method that provides rotation or a combination of these.
The mechanical energy treatment time is usually 3 minutes or more, preferably 5 minutes or more, more preferably 10 minutes or more, still more preferably 15 minutes or more, usually 5 hours or less, preferably 4 hours or less, more preferably 3 hours or less, more preferably 1 hour or less. When this time is too long, it leads to a decrease in productivity, and when the time is too short, product physical properties tend to be unstable.
The mechanical energy treatment temperature is not particularly limited, but is usually a temperature not lower than the freezing point of the solvent and preferably not higher than the boiling point in terms of the process.

Also, the metal particles (B) that can be alloyed with Li are usually made as fine as possible by using a dry pulverizer such as a ball mill, vibration mill, pulverizer, jet mill, etc. The final particle size is prepared by wet milling. Further, it can be mixed and pulverized with a carbon material such as carbon black, ketjen black or acetylene black at the time of wet pulverization and used as it is.
In the case of wet pulverization, it is desirable to appropriately select a dispersion solvent to be used that is not reactive with the metal particles (B) or very small. If necessary, a small amount of a dispersant (surfactant) may be added to wet the dispersion solvent. It is desirable that the dispersing agent is appropriately selected from those having no or very little reactivity with the metal particles that can be alloyed with Li.

-Types of dispersion solvent Examples of dispersion solvents include nonpolar compounds having an aromatic ring and aprotic polar solvents. The type of nonpolar compound having an aromatic ring is not particularly limited, but metal particles (B It is more preferable if it has no reactivity with the raw materials of For example, aromatic compounds such as benzene, toluene, xylene, cumene, and methylnaphthalene that are liquid at room temperature, alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, methylcyclohexene, and bicyclohexyl, petrochemicals such as light oil and heavy oil Residual oil in coal chemistry. Among these, xylene is preferred, methylnaphthalene is more preferred, and heavy oil is more preferred because of its high boiling point. In wet pulverization, heat generation tends to occur when the pulverization efficiency is increased. A solvent having a low boiling point may volatilize and become a high concentration. On the other hand, as aprotic polar solvents, NMP (N-methyl-2-pyrrolidone), GBL (γ-butyrolactone), DMF
NNN (N-methyl-2-pyrrolidone) is preferable in that it dissolves not only water but also an organic solvent such as (NN dimethylformamide), and is particularly difficult to decompose and has a high boiling point.

The mixing ratio of the metal particles (B) and the dispersion solvent is usually 10% by mass or more, preferably 20% by mass or more, and usually 50% by mass or less, preferably 40% by mass or less with respect to the metal particles (B).
If the mixing ratio of the dispersion solvent is too high, the cost tends to increase. If the mixing ratio of the dispersion solvent is too low, uniform dispersion of the metal particles (B) tends to be difficult.

-Kind of dispersing agent You may use a dispersing agent, when manufacturing a metal particle (B). Examples of the dispersant include high molecular weight polyester acid amide amines, polyether ester amine salts, polyethylene glycol phosphate esters, primary to tertiary amines, and quaternary amine salts. Among them, high molecular weight polyester acid amides are exemplified. An amine type is preferable in that the effect of dispersion due to steric hindrance is easily obtained.

-Nitriding treatment of metal particles (B) Further, the metal particles (B) capable of being Li-alloyed have a bond with nitrogen atoms on the surface, so that the oxides of the metal particles (B) that cannot contribute to charge / discharge The presence of the metal particles (B) and nitrogen is suppressed from the point that the capacity per weight of the metal particles is suppressed, the reactivity of the surface of the metal particles (B) can be reduced, and the charge / discharge efficiency can be improved. It is preferable to form a bond with an atom.
The bond between the metal particle (B) and the nitrogen atom can be analyzed by a method such as XPS, IR, or XAFS.
In order to form a bond between the metal particle (B) and a nitrogen atom, there is a method of mixing a compound having a nitrogen atom during the sputtering process or the mechanical energy process.

<Polymer containing nitrogen atom>
The method for producing composite graphite particles for a non-aqueous secondary battery negative electrode of the present invention is characterized by mixing a polymer containing nitrogen atoms.
The polymer containing nitrogen atoms can suppress the reaction between the metal particles and the non-aqueous electrolyte by covering the periphery of the metal particles (B) capable of being Li-alloyed.
In the present specification, the polymer containing nitrogen atoms does not include coal-based heavy oil, direct-current heavy oil, and cracked heavy oil.

-Content of nitrogen atom in polymer The content (%) of nitrogen atom in the polymer containing nitrogen atom is usually 1% or more, preferably 5% or more, more preferably 10% or more, still more preferably 15% or more, particularly preferably 20% or more, most preferably 25% or more, usually 80% or less, preferably 70% or less, more preferably 60% or less, still more preferably 50% or less, particularly preferably 40% or less, Most preferably, it is 30% or less.
If the content of nitrogen atoms is too large, the bonding amount between Si and nitrogen atoms becomes excessive, and the resistance component tends to increase. If the content of nitrogen atoms is too small, the reaction between Si and oxygen atoms proceeds and the capacity decreases. Tend to.
In this specification, the content (%) of the nitrogen atom in the polymer is (molecular weight of the nitrogen atom in the monomer of the smallest repeating unit of the polymer) / (in the monomer of the smallest repeating unit of the polymer). Molecular weight of all atoms) × 100.

-Molecular weight Although the weight average molecular weight of the polymer containing a nitrogen atom is not particularly limited, usually 500 or more,
Preferably it is 1000 or more, More preferably, it is 1500 or more, More preferably, it is 2000 or more, Most preferably, it is 2500 or more. On the other hand, the weight average molecular weight is usually 1,000,000 or less, preferably 500,000 or less, more preferably 300,000 or less, further preferably 100,000 or less, particularly preferably 50,000 or less, and most preferably 10,000 or less. If the molecular weight is too small, the specific surface area increases, so the charge / discharge efficiency tends to decrease when incorporated in the particles. If the molecular weight is too large, the viscosity increases and it becomes difficult to mix and disperse uniformly. Tend.
In the present specification, the weight average molecular weight is the weight average molecular weight in terms of standard polystyrene measured by gel permeation chromatography (GPC) of the solvent tetrahydrofuran (THF), or the solvent is aqueous, dimethylformamide (DMF) or dimethyl sulfoxide. It is a weight average molecular weight in terms of standard polyethylene glycol measured by GPC of (DMSO).

Firing yield The firing yield of the polymer containing nitrogen atoms is usually 20% or more, preferably 25% or more, more preferably 30% or more, still more preferably 35% or more, while usually 90% or less, Preferably it is 70% or less, More preferably, it is 60% or less, More preferably, it is 50% or less. When the firing yield is too small, the specific surface area increases, and therefore the charge / discharge efficiency tends to decrease when the particles are contained in the particles.
The method for measuring the firing yield (%) of the resin is as follows: 10 g of a sample is weighed and baked at 720 ° C. for 1 hour in an N ² atmosphere, and then baked at 1000 ° C. for 1 hour in an N ² atmosphere. The weight of the product is measured and calculated from (weight of fired product) / (weight before firing) × 100.

Decomposition temperature The decomposition temperature of the polymer containing nitrogen atoms is usually 150 ° C. or higher, preferably 170 ° C. or higher, more preferably 200 ° C. or higher, while 500 ° C. or lower, preferably 450 ° C. or lower, more preferably 400 ° C. or lower. It is. If the decomposition temperature is too low, it may be easily decomposed. On the other hand, if it is too high, it may be difficult to dissolve in a solvent and it may be difficult to disperse uniformly.
The decomposition temperature can be measured from the thermal decomposition temperature in an inert atmosphere by using a TG-DTA apparatus.

-Types of polymers Such polymers containing nitrogen atoms include polyamide, polyimide, polyacrylonitrile, polypyrrole, polyallylamine, polyvinylamine, polyethyleneimine, poly-N-methylallylamine, poly-N, N-dimethyl. Examples include allylamine, polydiallylamine, polyN-methyldiallylamine, urethane resin, urea resin and the like. Among these, polyacrylonitrile, polyallylamine, and polyvinylamine are preferable because a cyclic structure is easily obtained during firing.

<Composite graphite particles for nonaqueous secondary battery negative electrode>
The composite graphite particles of the present invention contain graphite (A) and metal particles (B) that can be alloyed with Li, contain nitrogen atoms, and cross-section of the composite graphite particles with SEM (scanning electron microscope). ), A structure in which graphite (A) is folded is preferably observed.

-Structure in which graphite (A) is folded The composite graphite particles obtained by the production method of the present invention have a structure in which graphite (A) is folded. Although it is not limited to the type of graphite (A), for example, when scaly or scaly graphite is taken as an example, when stress is applied in a direction parallel to the graphite crystal basal surface, the scaly or scaly graphite graphite basal surface is It is known to form a sphere while taking a concentric or folded structure (Materials Integration Vol. 1).
7 No. 1 (2004)).

  More specifically, the composite graphite particles have a shape in which a plurality of scaly or scaly graphites are rounded or bent into a round shape by a spheronization process, and thus each scaly or scaly graphite is It does not have a specific orientation plane. Furthermore, when the scale-like or scale-like graphite constituting the composite graphite particles is taken as a whole, the curved or bent individual scale-like or scale-like graphite surfaces are at least in the vicinity of the surface curved or bent scale-like or scale-like graphite. The direction of the perpendicular line at each point on the surface of the surface indicates a shape that is rounded toward the substantially central portion of the composite graphite particle for a non-aqueous secondary battery negative electrode (see, for example, FIGS. 1 and 2). .

  Such a structure is obtained by observing the surface of the composite graphite particles with a scanning electron microscope, embedding the composite graphite particles in a resin or the like to produce a resin flake and cutting out the particle cross section, or preparing a coating film made of particles, A cross-section of the coating film is produced on the film by focused ion beam (FIB) or ion milling, and the cross-section of the particle is cut out, and then observed by an observation method such as particle cross-section observation using a scanning electron microscope.

  It is important that the metal particles (B) exist in the gaps in the structure in which the graphite (A) is folded. Presence or absence of the presence, observation of the particle surface with a scanning electron microscope, embedding the composite graphite particles in a resin or the like to produce a thin piece of resin and cut out the cross section of the particle, or prepare a coating film made of particles, to the film After producing a cross section of the coating film by focused ion beam (FIB) or ion milling and cutting out the cross section of the particle, it can be observed by an observation method such as a cross section of the particle by a scanning electron microscope.

  Further, the gaps present in the composite graphite particles may be voids, or substances that buffer the expansion and contraction of metal particles that can be alloyed with Li, such as amorphous carbon, graphite, and resin. May be present in the gap.

-Nitrogen atoms in composite graphite particles The composite graphite particles of the present invention contain nitrogen atoms. By containing a nitrogen atom, a highly reactive functional group present on the surface of the metal particle (B) becomes an inactive nitride, and a side reaction between the surface of the metal particle (B) and the non-aqueous electrolyte is suppressed. Therefore, an increase in irreversible capacity can be suppressed and charge / discharge efficiency can be improved. An example of the form of nitrogen atoms in the composite graphite particles is a nitrogen compound. The nitrogen compound may be a compound in which a C—N bond, a Si—N bond, an O—N bond, or the like is observed, and among them, a compound having a C—N bond or a Si—N bond is preferable. As a method for confirming these bonds, analysis can be performed by methods such as XPS, IR, and XAFS.

(Physical properties of composite graphite particles for nonaqueous secondary battery negative electrode)
The composite graphite particles for a non-aqueous secondary battery negative electrode contain nitrogen atoms, and have a structure in which the graphite (A) is folded when a cross section of the composite graphite particles is observed with an SEM (scanning electron microscope). Although it will not specifically limit if it has, The thing with the following characteristic is preferable.

-Surface functional group amount N / Si value of composite graphite particles It can be shown by the surface functional group amount N / Si value represented by the following formula (1) that the composite graphite particles contain nitrogen atoms. In the present invention, the surface functional group amount N / Si value is usually 0.05% or more, preferably 0.1%, more preferably 0.15% or more, still more preferably 0.2% or more, particularly preferably 0.8. 5% or more, most preferably 1.0% or more, while usually 50% or less, preferably 20% or less, more preferably 10% or less, more preferably 5% or less, particularly preferably 2% or less, most preferably Is 1.5% or less. If the surface functional group amount N / Si value is too small, the reactivity between the surface of the metal particles (B) and the non-aqueous electrolyte solution tends to increase, and the irreversible capacity tends to increase. The surface functional group amount N / Si value When is too large, the resistance of the surface of the metal particles (B) increases, and the output tends to decrease.

Formula 1
N / Si value (%) = N atom concentration obtained based on the peak area of the N1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / Si atom concentration obtained based on the peak area of the Si2p spectrum in XPS analysis × 100
The surface functional group amount N / Si value in the present invention can be measured as follows using X-ray photoelectron spectroscopy (XPS).

  An X-ray photoelectron spectrometer is used as an X-ray photoelectron spectroscopy measurement, and the measurement object is placed on a sample stage so that the surface is flat. An aluminum Kα ray is used as an X-ray source, and N1s (394 to 412 eV) is obtained by multiplex measurement. ) And Si2p (95-112 eV). The obtained Si2p peak of the low energy side peak was corrected to 99.5 eV, the peak areas of the N1s and Si2p spectra were obtained, and further divided by the device sensitivity coefficient to obtain the surface atomic concentrations of N and Si, respectively. calculate. The obtained N / Si atomic concentration ratio N / Si (N atomic concentration / Si atomic concentration) is defined as the surface functional group amount N / Si value of the sample (composite graphite particles).

-Abundance ratio of metal particles (B) in the composite graphite particles The abundance ratio of the metal particles (B) in the composite graphite particles, which is measured by the following measurement method, is usually 0.2 or more, preferably 0. 3 or more, more preferably 0.4 or more, still more preferably 0.5 or more, particularly preferably 0.6 or more, and usually 1.5 or less, preferably 1.2 or less, more preferably 1.0. It is as follows. The higher this number, the more metal particles (B) present inside the composite graphite particles, compared to the metal particles (B) present outside the composite graphite particles. There is a tendency that the decrease in charge / discharge efficiency due to the disconnection of the conductive path between particles can be suppressed.

  The abundance ratio of the metal particles (B) in the composite graphite particles of the present invention is calculated as follows. First, a composite graphite particle coating film or a composite graphite particle is embedded in a resin or the like to produce a thin piece of resin, and a cross section of the particle is cut out by focused ion beam (FIB) or ion milling, followed by SEM (scanning electron microscope). ) Can be observed by an observation method such as particle cross-sectional observation.

  The accelerating voltage when observing the cross section of one composite graphite particle with an SEM (scanning electron microscope) is preferably 1 kV or higher, more preferably 2 kV or higher, still more preferably 3 kV or higher, and usually 10 kV or lower. Preferably it is 8 kV or less, More preferably, it is 5 kV or less. Within this range, the graphite particles and the Si compound can be easily identified due to the difference in the reflected secondary electron image in the SEM image. The imaging magnification is usually 500 times or more, more preferably 1000 times or more, still more preferably 2000 times, and usually 10,000 times or less. If it is said range, the whole image of 1 particle | grains of a composite graphite particle is acquirable. The resolution is 200 dpi (ppi) or more, preferably 256 dpi (ppi) or more. The number of pixels is preferably evaluated at 800 pixels or more. Next, while observing the image, the elements of graphite (A) and metal particles (B) are identified by the energy dispersion type (EDX) and the wavelength dispersion type (WDX).

  One composite graphite particle is extracted from the acquired image, and the area (a) of the metal particle (B) in the particle is calculated. Next, after binarizing the extracted 1 particle and the background other than the 1 particle, the shrinking process is repeated on the particle, and a figure with an area of 70% of the extracted 1 particle is extracted. The area (b) of the existing metal particles (B) is calculated. In addition, in the area when the reduction process is repeatedly performed, when the value of 70% cannot be accurately shown, the value closest to 70% in the value of 70% ± 3% is 70% in this patent. A figure.

The extraction of one particle, the calculation of the area, the binarization process, and the reduction process can be performed by using general image processing software. For example, “Image J” “Image-Pro
software such as “plus”.
The value obtained by dividing the area (b) calculated above by the area (a) is measured with arbitrary three particles, and the value obtained by averaging the values of these three particles is the value of the metal particles (B) in the composite graphite particles. The abundance ratio.

  In addition, in the cross section of the composite graphite particles observed by the method as described above, as a condition for selecting the target composite graphite particles to be subjected to the measurement of the present invention, composite particles satisfying the following conditions (a) to (d) are selected. It is a condition to do. Note that particles not composed of graphite and / or metal particles are excluded as target particles. The target composite graphite particles satisfying such a condition, and the composite graphite particles satisfying the conditions of the present invention may be usually present in the target composite graphite particles, but preferably one or more, It is usually 30%, more preferably 50%, still more preferably 90% or more, particularly preferably 99% or more with respect to the total number of target composite graphite particles.

(A) Structure of graphite (A) in composite graphite particle The structure in which graphite (A) in composite graphite particle is folded preferably means two or more different orientations in one graphite in composite graphite particle. It is the structure which has. The graphite having at least one such structure in a particle is referred to as graphite having a folded structure in the present invention.
(B) Particle diameter of composite graphite particles Composite graphite particles having a ratio of the length of the major axis in the cross-sectional observation of the composite graphite particles to the volume average particle diameter (d50) of 0.7 to 1.3 are used as target particles. The long axis means the longest line among the lines passing through the center of gravity in one particle.

(C) Particle shape of composite graphite particles Even if the above (a) and (b) are satisfied, the composite particles that are clearly cracked and the composite particles that are torn are not suitable for the judgment of composite graphite particles. It will be excluded.
(D) Presence state of metal particles (B) In the graphite having the folded structure described in (a), the presence of the metal particles (B) in the gap between the structures having two different orientations in one graphite. The particles that can be confirmed are the target particles of the composite graphite particles.
The cross section of the target particle corresponding to the conditions (a) to (d) is observed, and the abundance ratio of the metal particles (B) in the composite graphite particles is calculated.

-Interplanar spacing (d ₀₀₂ ) of (002) plane of composite graphite particles
Since the interplanar spacing (d ₀₀₂ ) of the (002) plane of the composite graphite particles of the present invention according to the X-ray wide angle diffraction method is usually 0.337 nm or less, while the theoretical value of the interplanar spacing of the 002 plane of graphite is 0.335 nm, The interplanar spacing of the 002 plane of graphite is usually 0.335 nm or more. Further, Lc of graphite (A) by X-ray wide angle diffraction is 90 nm or more, preferably 95 nm or more. The fact that the (002) plane spacing (d ₀₀₂ ) and Lc within the above range by the X-ray wide-angle diffraction method indicate composite graphite particles for a non-aqueous secondary battery negative electrode serving as a high capacity electrode.

-Tap density of composite graphite particles The tap density of the composite graphite particles of the present invention is usually 0.5 g / cm ³ or more, preferably 0.6 g / cm ³ or more, and more preferably 0.8 g / cm ³ or more.
The fact that the tap density of the composite graphite particles of the present invention shows a large numerical value is one of the indexes showing that the composite graphite particles have a spherical shape. The smaller tap density is one index indicating that the composite graphite particles are not sufficiently spherical particles. If the tap density is small, a sufficient continuous gap is not secured in the electrode, and the mobility of Li ions in the electrolyte held in the gap tends to decrease, so that the rapid charge / discharge characteristics tend to deteriorate.

Raman R value is the peak intensity ratio in the vicinity of 1360 cm ^-1 to the peak intensity near 1580 cm ^-1 in the argon ion laser Raman spectrum of the composite graphite particles of the Raman R value present invention the composite graphite particle is usually 0.05 or more 0. 4 or less, preferably 0.1 or more and 0.35 or less. If it is this range, the crystallinity of the surface of this composite graphite particle will be in order, and a high capacity | capacitance can be anticipated.

Specific surface area of composite graphite particles by BET method The specific surface area of the composite graphite particles of the present invention by BET method is usually 40 m ² / g or less, preferably 35 m ² / g or less, more preferably 30 m ² / g or less. It is 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1 m ² / g or more. When the specific surface area is too large, the portion where the composite graphite particles and the non-aqueous electrolyte are in contact with each other increases when used as an active material for a negative electrode. There is a tendency to be difficult to be. If the specific surface area is too small, the lithium ion acceptability tends to deteriorate during charging when used as the negative electrode active material.

-Volume average particle diameter of composite graphite particles (d50)
The volume average particle diameter (d50) of the composite graphite particles of the present invention is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and usually 1 μm or more, preferably 4 μm or more, more preferably 6 μm or more. If the average particle size is too large, there will be problems such as streaking during coating, and if the average particle size is too small, a large amount of binder is required, so that resistance is high and high current density charge / discharge characteristics tend to decrease. There is.

-Content of the metal particles (B) of the composite graphite particles The content of the metal particles (B) in the composite graphite particles is usually 0.5 mass% or more, preferably 1 mass% or more, more preferably 1.5 mass%. % Or more, more preferably 2% by mass or more. Moreover, it is 99 mass% or less normally, Preferably it is 70 mass% or less, More preferably, it is 50 mass% or less, More preferably, it is less than 30 mass%, Most preferably, it is 25% or less. This range is preferable in that a sufficient capacity can be obtained. In addition, the measurement of content of the metal particle (B) of composite graphite particle is implemented by the method as described later.

-Porosity of composite graphite particles The porosity of the composite graphite particles is usually 1% or more, preferably 3% or more, more preferably 5% or more, more preferably 7% or more with respect to the graphite (A) of the composite graphite particles. is there. Further, it is usually less than 50%, preferably 40% or less, more preferably 30% or less, and still more preferably 20% or less. If the internal porosity is too small, the amount of liquid in the particles tends to be small and charge / discharge characteristics tend to deteriorate. If the porosity is too large, there is little inter-particle gap when the electrode is used, and the electrolyte does not diffuse. There is a tendency to become insufficient. In addition, the voids are filled with substances that buffer the expansion and contraction of metal particles that can be alloyed with Li, such as amorphous carbon, graphite, and resin. It may be.

<Method for producing composite graphite particles for nonaqueous secondary battery negative electrode>
The method for producing composite graphite particles for a nonaqueous secondary battery negative electrode in the present specification (also referred to as composite graphite particles in the present specification) includes at least the following Step 1 and Step 2. Step 1: Obtaining a mixture containing at least a polymer containing graphite (A), Li-alloyable metal particles (B), and a polymer containing nitrogen atoms Step 2: Giving mechanical energy to the mixture of Step 1 and spheroidizing treatment Hereinafter, the production method of the present invention will be described in detail.

(Step 1: Step of obtaining a mixture containing at least a polymer containing graphite (A), metal particles (B) that can be alloyed with Li, and a nitrogen atom)
The mixture obtained in this step may be in the form of powder, solid, lump, slurry, etc., but is preferably a lump in terms of ease of handling.

  The mixing ratio of the metal particles (B) to the total of the graphite (A), the metal particles (B) and the polymer containing nitrogen atoms is usually 1% by mass or more, preferably 3% by mass or more, more preferably 5% by mass. As mentioned above, More preferably, it is 7 mass% or more. Moreover, it is 95 mass% or less normally, Preferably it is 90 mass% or less, More preferably, it is 80 mass% or less, More preferably, it is 70 mass% or less. This range is preferable in that a sufficient capacity can be obtained.

  The mixing ratio of the polymer containing nitrogen atoms to the total of graphite (A), metal particles (B) and polymer containing nitrogen atoms is usually 0.1% by mass or more, preferably 0.3% by mass or more. More preferably, it is 0.5% by mass or more, and further preferably 0.7% by mass or more. Moreover, it is 30 mass% or less normally, Preferably it is 28 mass% or less, More preferably, it is 26 mass% or less, More preferably, it is 25 mass% or less. This range is preferable in that a sufficient capacity can be obtained.

  In this step, if a mixture containing at least a graphite (A), a metal particle (B) that can be alloyed with Li, and a polymer containing a nitrogen atom is obtained, the graphite (A), the metal particle (B), and a nitrogen atom There is no particular limitation on the method of mixing the polymer containing. As a mixing method, graphite (A), metal particles that can be alloyed with Li (B), and a polymer containing nitrogen atoms may be charged together and mixed, or each may be mixed while being charged sequentially. Also good.

A preferable method for obtaining the mixture includes, for example, a method in which wet metal particles (B) are mixed with graphite (A) so as not to dry the metal particles (B).
As the wet metal particles (B), the metal particles (B) obtained while the above-described metal particles (B) are produced by a wet method may be used, or metal particles (B) produced by a dry method may be used. ) May be dispersed and wetted in a dispersion solvent before mixing with graphite (A), or may be wetted by mixing with a polymer containing nitrogen atoms dissolved in a solvent or the like.
Since the wet metal particles (B) suppress the aggregation of the metal particles (B), they can be uniformly dispersed when mixed, and the metal particles (B) can be dispersed on the surface of the graphite (A). This is preferable because it can be easily fixed.

Moreover, you may add the dispersion solvent used when the metal particle (B) wet-grinds excessively at the time of mixing from the point which becomes easy to disperse | distribute a metal particle (B) uniformly on the surface of graphite (A).
In the present specification, when the metal particles (B) are mixed as a slurry when the metal particles (B) are mixed with the graphite (A), the solid content of the metal particles (B) is usually 10% or more, preferably It is 15% or more, more preferably 20% or more, usually 90% or less, preferably 85% or less, more preferably 80% or less. If the proportion of the solid content is too large, the fluidity of the slurry is lost, and the metal particles (B) tend to be difficult to disperse in the graphite (A). If the proportion is too small, it tends to be difficult to handle in the process.

And after mixing, it is preferable to fix the metal particles (B) on the graphite (A) by evaporating and removing the dispersion solvent using an evaporator, a dryer or the like.
Alternatively, it is preferable to fix the metal particles (B) to the graphite (A) by adding the dispersion solvent while heating in a high-speed stirrer as it is without adding an excessive dispersion solvent.

In addition, as the timing of mixing the polymer containing nitrogen atoms to obtain a mixture,
Although there is no particular limitation, for example, it may be added when mixing graphite (A) and metal particles (B), or may be added to a slurry of wet metal particles (B) or metal particles (B), You may add at the time of the wet grinding of a metal particle (B). The state at the time of mixing the polymer containing nitrogen atoms may be a powder or a solution dissolved in a solvent, but a solution is preferable because it can be uniformly dispersed.

These polymers containing nitrogen atoms not only play a role of immobilizing the metal particles (B) to the graphite (A) but also cause the metal particles (B) to be detached from the graphite (A) during the spheronization process. It is thought to play a role to prevent
Among the above, as a combination of steps for obtaining a more preferable mixture, the metal particles (from the point that the polymer containing graphite (A), metal particles (B) and nitrogen atoms can be uniformly dispersed in the mixture. More preferably, the slurry of B) and a polymer containing nitrogen atoms dissolved in a solvent are mixed, and then graphite (A) is mixed therewith.

Moreover, you may mix the carbon precursor etc. which are mentioned later from the point which can suppress the reactivity of a metal particle (B) and electrolyte solution in this case.
Furthermore, at this time, in order to relieve the destruction of the composite graphite particles due to the expansion and contraction of the metal particles (B), a resin or the like may be mixed as a void forming material.
The resin that can be used as the void forming material in this step 1 is not particularly limited, and examples thereof include polyvinyl alcohol, polyethylene glycol, polycarbosilane, polyacrylic acid, and a cellulose-based polymer. Polyvinyl alcohol and polyethylene glycol can be particularly preferably used because they have a small amount of carbon and a relatively low decomposition temperature.

  Mixing is usually carried out under normal pressure, but if desired, it can also be carried out under reduced pressure or under pressure. Mixing can be carried out either batchwise or continuously. In any case, mixing efficiency can be improved by using a combination of an apparatus suitable for rough mixing and an apparatus suitable for fine mixing. Moreover, you may utilize the apparatus which performs mixing and fixation (drying) simultaneously. Drying can usually be carried out under reduced pressure or under pressure, and preferably dried under reduced pressure.

The drying time is usually 5 minutes or longer, preferably 10 minutes or longer, more preferably 20 minutes or longer, more preferably 30 minutes or longer, and usually 2 hours or shorter, preferably 1 hour and a half or shorter, more preferably 1 hour or shorter. is there. If the time is too long, the cost increases. If the time is too short, uniform drying tends to be difficult.
Although drying temperature changes with solvents, it is preferable that it is time which can implement | achieve the said time. Moreover, it is preferable that it is below the temperature which resin does not modify | denature.

  As a batch-type mixing device, a mixer with a structure in which two frame molds rotate and revolve; a blade such as a dissolver that is a high-speed high-shear mixer and a butterfly mixer for high viscosity is placed in the tank. A device having a structure for stirring and dispersing; a so-called kneader-type device having a structure in which a stirring blade such as a sigma type rotates along the side surface of a semi-cylindrical mixing tank; a trimix type device having three stirring blades A so-called bead mill type apparatus having a rotating disk and a dispersion solvent body in a container is used.

It also has a container with a paddle that is rotated by a shaft, and the inner wall surface of the container is formed substantially along the outermost line of rotation of the paddle, preferably in a long twin cylinder shape, and the paddle has side surfaces facing each other. A device having a structure in which many pairs are arranged in the axial direction of the shaft so as to be slidably engaged (for example, KRC reactor manufactured by Kurimoto Iron Works, SC processor, TEM manufactured by Toshiba Machine Celmac, TEX-K manufactured by Nippon Steel Works) Furthermore, it has a container in which a single inner shaft and a plurality of pavement or sawtooth paddles fixed to the shaft are arranged in different phases, and the inner wall surface is the outermost line of rotation of the paddle (External heat type) apparatus (for example, a Redige mixer manufactured by Redige Co., Ltd., a flow share mixer manufactured by Taiyo Koki Co., Ltd., and Tsukishima Kikai Co., Ltd.) DT dryers, etc.) can also be used. In order to perform mixing in a continuous manner, a pipeline mixer, a continuous bead mill, or the like may be used. It is also possible to homogenize by means such as ultrasonic dispersion.
Moreover, you may carry out powder processing, such as a grinding | pulverization, crushing, and a classification process, suitably for the mixing part obtained at this process.

There are no particular restrictions on the apparatus used for pulverization and pulverization, for example, the coarse pulverizer includes a shearing mill, jaw crusher, impact crusher, cone crusher, etc., and the intermediate pulverizer includes roll crusher, hammer mill, etc. Examples of the pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, and a jet mill.
There is no particular limitation on the apparatus used for classification, but for example, in the case of dry sieving, a rotary sieving, a swaying sieving, a rotating sieving, a vibrating sieving, etc. can be used. In this case, gravity classifier, inertial classifier, centrifugal classifier (classifier, cyclone, etc.) can be used, wet sieving, mechanical wet classifier, hydraulic classifier, sedimentation classifier A centrifugal wet classifier or the like can be used.

(Step 2: Step of applying spheroidizing treatment by applying mechanical energy to the mixture of Step 1)
By passing through this process 2, the composite graphite particle for non-aqueous secondary battery negative electrodes of this invention can be manufactured.
That is, as a manufacturing method for obtaining the composite graphite particles for a nonaqueous secondary battery negative electrode of the present invention, the metal particles (B) and nitrogen atoms are formed on the surface of the graphite (A) before being folded obtained in the above step 1. Spheroidization treatment is performed on a mixture (also referred to as a mixture in the present specification) in which a polymer containing selenium is mixed. In particular, in the present invention, metal particles (B) within a predetermined range are folded. It is preferable to set production conditions as described later as appropriate so that they exist in the gaps in the structure.

  The spheroidizing process is basically performed using mechanical energy (mechanical action such as impact compression, friction and shearing force). Specifically, treatment using a hybridization system is preferred. The system has a rotor with a large number of blades that apply mechanical action such as impact compression, friction and shearing force, and a large air flow is generated by the rotation of the rotor, and thereby in the mixture obtained in step 1 above. A large centrifugal force is applied to the graphite (A), and the graphite (A) in the mixture obtained in the step 1 and the graphite (A) in the mixture obtained in the step 1 collide with the wall and the blade. By this, the graphite (A) in the mixture obtained at the said process 1 can be folded neatly.

  The apparatus used for the spheronization treatment has, for example, a rotor in which a large number of blades are installed inside a casing, and the rotor rotates at a high speed, whereby the graphite in the mixture obtained in step 1 introduced therein is For example, a device that performs mechanical treatment such as impact compression, friction, shearing force, etc., and performs surface treatment can be used. For example, dry ball mill, wet bead mill, planetary ball mill, vibration ball mill, mechano-fusion system, Agromaster (Hosokawa Micron Corporation), hybridization system, Micros, Miraro (manufactured by Nara Machinery Co., Ltd.), CF mill (Ube) And theta composer (manufactured by Tokuju Kogakusho Co., Ltd.) and the like. Preferred examples of the apparatus include a dry ball mill, a wet bead mill, a planetary ball mill, a vibrating ball mill, a mechano-fusion system, and an agromaster (Hosokawa Micron). Co., Ltd.), hybridization system, Micros, Miraro (manufactured by Nara Machinery Co., Ltd.), CF mill (manufactured by Ube Industries), theta composer (manufactured by Tokuju Kosakusha), pulperizer and the like. Among these, a hybridization system manufactured by Nara Machinery Co., Ltd. is particularly preferable.

In addition, the graphite (A) in the mixture obtained in the step 1 to be subjected to the spheronization treatment may have already been subjected to a certain spheronization treatment under the conditions of the conventional method. Moreover, you may give a mechanical action repeatedly by circulating the composite_body | complex obtained by the said process 1 or passing through this process in multiple times.
A spheronization treatment is performed using such an apparatus. In this treatment, the rotational speed of the rotor is usually 2000 rpm or more, preferably 4000 rpm or more, more preferably 5000 rpm or more, still more preferably 6000 rpm or more, particularly preferably. Is 6500 rpm or more, usually 9000 rpm or less, preferably 8000 rpm or less, more preferably 7500 rpm or less, and even more preferably 7200 rpm or less, usually 30 seconds or more, preferably 1 minute or more, more preferably 1 minute 30 seconds or more, still more preferably The spheronization treatment is performed in a range of 2 minutes or longer, particularly preferably 2 minutes 30 seconds or longer, usually 60 minutes or shorter, preferably 30 minutes or shorter, more preferably 10 minutes or shorter, and even more preferably 5 minutes or shorter.

  If the number of rotations of the rotor is too small, the process of spheroidizing is weak and the tapping density may not increase sufficiently, while if it is too large, the effect of pulverization becomes stronger than the process of spheroidizing, and the particles collapse As a result, the tapping density may decrease. Furthermore, if the spheronization treatment time is too short, the particle size can be made sufficiently small and a high tapping density cannot be achieved, while if too long, the graphite (A) in the mixture obtained in Step 1 above is There is a possibility that the object of the present invention cannot be achieved.

In addition, you may perform a classification process with respect to the obtained composite graphite particle. When the obtained composite graphite particles are not within the specified physical property range of the present invention, by repeating (usually 2 times or more and 10 times or less, preferably 2 times or more and 5 times or less) classification treatment, the desired physical property range is obtained. can do. Examples of the classification include dry (aerodynamic classification, sieving), wet classification, and the like, but dry classification, particularly aerodynamic classification is preferable from the viewpoint of cost and productivity.
The composite graphite particles of the present invention can be produced by the production method as described above.

<Carbonaceous material-coated composite graphite particles>
As described above, the composite graphite particles for a non-aqueous secondary battery negative electrode used in the present invention can be obtained. The composite graphite particles preferably contain a carbonaceous material. More preferably, at least a part of the surface is coated. (Hereinafter also referred to as carbonaceous material-coated composite graphite particles). In the present specification, the carbonaceous material-coated composite graphite particles are described separately from the composite graphite particles for convenience. However, in this specification, the carbonaceous material-coated composite graphite particles are also interpreted as being included in the composite graphite particles. To do.

(Method for producing carbonaceous material-coated composite graphite particles)
The carbonaceous material-coated composite graphite particles can be produced by passing through step 3 after step 2 described above.
Step 3: Step of coating the composite graphite particles spheroidized in Step 2 with a carbonaceous material Step 3 will be described in detail below.

(Step 3: Step of coating the composite graphite particles spheroidized in Step 2 with a carbonaceous material)
-Carbonaceous material As said carbonaceous material, an amorphous carbon and graphitized material are mentioned by the difference in the temperature of the heating in the manufacturing method mentioned later. Among these, amorphous carbon is preferable from the viewpoint of acceptability of lithium ions.

Specifically, the carbonaceous material can be obtained by heat-treating the carbon precursor as described later. As the carbon precursor, a carbon material described in the following (a) and / or (b) is preferable.
(A) Coal heavy oil, DC heavy oil, cracked heavy oil, aromatic hydrocarbon, N ring compound, S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and Carbonizable organic substance selected from the group consisting of thermosetting resins (b) Carbonized organic substance dissolved in low molecular organic solvent

-Coating treatment In the coating treatment, a carbon precursor for obtaining a carbonaceous material is used as a coating raw material with respect to the composite graphite particles obtained in the above-described step 2, and these are mixed and fired to obtain a coated graphite. can get.
When the firing temperature is usually 600 ° C. or higher, preferably 700 ° C. or higher, more preferably 900 ° C. or higher, usually 2000 ° C. or lower, preferably 1500 ° C. or lower, more preferably 1200 ° C. or lower, amorphous carbon is obtained as a carbonaceous material. In general, when heat treatment is performed at 2000 ° C. or higher, preferably 2500 ° C. or higher, and usually 3200 ° C. or lower, graphitized carbon is obtained as a carbonaceous material. The amorphous carbon is carbon having low crystallinity, and the graphitized carbon is carbon having high crystallinity. In the coating treatment, the above-mentioned composite graphite particles are used as a core material, a carbon precursor for obtaining a carbonaceous material is used as a coating material, and these are mixed and fired to obtain carbonaceous material-coated composite graphite particles (D). It is done.

-Mixing with metal particles and carbon fine particles The coating layer may contain metal particles and carbon fine particles that can be alloyed. The shape of the carbon fine particles is not particularly limited, and may be any of granular, spherical, chain-like, needle-like, fibrous, plate-like, and scale-like shapes.

Specifically, the carbon fine particles are not particularly limited, and examples thereof include coal fine powder, vapor phase carbon powder, carbon black, ketjen black, and carbon nanofiber. Among these, carbon black is particularly preferable. Carbon black has the advantage that the input / output characteristics are improved even at low temperatures, and at the same time, it can be obtained inexpensively and easily.
The volume average particle diameter (d50) of the carbon fine particles is usually 0.01 μm or more and 10 μm or less, preferably 0.05 μm or more, more preferably 0.07 μm or more, further preferably 0.1 μm or more, preferably It is 8 μm or less, more preferably 5 μm or less, and still more preferably 1 μm or less.

  When the carbon fine particles have a secondary structure in which primary particles are aggregated and aggregated, other physical properties and types are not particularly limited as long as the primary particle size is 3 nm or more and 500 nm or less, but the primary particle size is preferable. Is at least 3 nm, more preferably at least 15 nm, even more preferably at least 30 nm, particularly preferably at least 40 nm, preferably at most 500 nm, more preferably at most 200 nm, still more preferably at most 100 nm, particularly preferably at most 70 nm. It is. The primary particle diameter of the carbon fine particles can be measured by electron microscope observation such as SEM or a laser diffraction particle size distribution analyzer.

Other Steps The carbonaceous material-coated composite graphite particles that have undergone the above steps may be subjected to powder processing such as pulverization, pulverization, and classification as described in Step 1.
The carbonaceous material-coated composite graphite particles of the present invention can be produced by the production method as described above.

(Physical properties of carbonaceous material-coated composite graphite particles)
The carbonaceous material-coated composite graphite particles exhibit the same physical properties as those of the composite graphite particles described above. In particular, preferable physical properties of the carbonaceous material-coated composite graphite particles that change depending on the coating treatment are described below.

-(002) plane spacing (d ₀₀₂ )
The interplanar spacing (d ₀₀₂ ) of the (002) plane of the carbonaceous material-coated composite graphite particles by the X-ray wide angle diffraction method is usually 0.336 nm or more, preferably 0.337 nm or more, more preferably 0.340 nm or more, preferably 0.8. It is 342 nm or more. Moreover, it is less than 0.380 nm normally, Preferably it is 0.370 nm or less, More preferably, it is 0.360 nm or less. If the d ₀₀₂ value is too large, it indicates that the crystallinity is low, and the cycle characteristics tend to deteriorate. If the d ₀₀₂ value is too small, it is difficult to obtain the effect of combining the carbonaceous materials.

・ Cover rate Carbonaceous material-coated composite graphite particles are those coated with amorphous carbon or graphitic carbon. Among these, it is from the point of acceptability of lithium ions that it is coated with amorphous carbon. Preferably, the coverage is usually 0.5% or more, preferably 1% or more, more preferably 3% or more, still more preferably 4% or more, particularly preferably 5% or more, most preferably 6% or more, usually 30. % Or less, preferably 25% or less, more preferably 20% or less, still more preferably 15% or less, particularly preferably 10% or less, and most preferably 8% or less. If this content is too large, the amorphous carbon portion of the negative electrode material increases, and the reversible capacity when the battery is assembled tends to be small. If the content is too small, the amorphous carbon sites are not uniformly coated on the graphite particles serving as nuclei, and strong granulation is not performed, and when pulverized after firing, the particle size tends to be too small.
In addition, the content (coverage) of the carbide derived from the organic compound of the carbon material for the electrode finally obtained is measured by the amount of the raw material carbon material used, the amount of the organic compound, and a micro method based on JIS K 2270. The following equation 2 can be used to calculate the remaining charcoal rate.

Formula 2
Covering rate of carbide derived from organic compound (%) = (mass of organic compound × residual carbon rate × 100) / {
Mass of raw carbon material + (mass of organic compound x residual carbon ratio)}

<Other mixtures>
The composite graphite particles may be mixed with a material selected from coke, carbon black, natural graphite, artificial graphite, amorphous coated graphite, amorphous carbon, and the like. Any one of these mixtures may be used alone, or two or more thereof may be used in any combination and composition.
The mixing ratio of the composite graphite particles to the total of the composite graphite particles and the other mixture is usually 1% by mass or more, preferably 1.5% by mass or more, more preferably 2% by mass or more, and further preferably 2.5% by mass. That's it. Moreover, it is 99 mass% or less normally, Preferably it is 95 mass% or less, More preferably, it is 90 mass% or less, More preferably, it is 85 mass% or less.
If there are many composite graphite particles, the volume expansion accompanying charging / discharging will become large, capacity | capacitance deterioration will become remarkable, and it will become possible to reduce a press load. Moreover, when there are too few composite graphite particles, there exists a tendency for sufficient capacity | capacitance not to be obtained.

<Negative electrode for non-aqueous secondary battery>
In order to produce a negative electrode using the composite graphite particles according to the present invention, a composite graphite particle blended with a binder resin is made into a slurry with water or an organic solvent, and if necessary, a thickener is added thereto to collect current. Apply to the body and dry.
As the binder resin, it is preferable to use a resin that is stable with respect to the non-aqueous electrolyte and water-insoluble. For example, rubbery polymers such as styrene, butadiene rubber, isoprene rubber, ethylene / propylene rubber; synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate, and aromatic polyamide; styrene / butadiene / styrene block copolymers and hydrogenated products thereof, Thermoplastic elastomers such as styrene / ethylene / butadiene, styrene copolymer, styrene / isoprene, styrene block copolymer and hydride thereof; syndiotactic-1,2-polybutadiene, ethylene / vinyl acetate copolymer, ethylene Soft resinous polymers such as copolymers with α-olefins having 3 to 12 carbon atoms; polytetrafluoroethylene
Fluorinated polymers such as ethylene copolymer, polyvinylidene fluoride, polypentafluoropropylene, and polyhexafluoropropylene can be used. Examples of the organic medium include NMP and DMF.

  The binder resin is preferably used in an amount of 0.1% by mass or more, more preferably 0.2% by mass or more based on the composite graphite particles. By setting the ratio of the binder resin to 0.1% by mass or more with respect to the composite graphite particles, the binding force between the composite graphite particles and between the composite graphite particles and the current collector is sufficient, and the composite graphite particles are separated from the negative electrode. It is possible to prevent a decrease in battery capacity and deterioration in recycling characteristics due to peeling. The binder resin is preferably used so that it is at most 10% by mass, preferably 7% by mass or less, relative to the composite graphite particles.

  As the thickener added to the slurry, water-soluble celluloses such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, polyvinyl alcohol, polyethylene glycol, and the like may be used. Of these, carboxymethylcellulose is preferred. The thickener is preferably used in an amount of 1 to 10% by mass, more preferably 0.2 to 7% by mass with respect to the composite graphite particles.

As the negative electrode current collector, copper, copper alloy, stainless steel, nickel, titanium, carbon, or the like that is conventionally known to be used for this purpose may be used. The shape of the current collector is usually a sheet shape, and those having an uneven surface or those using a net, punching metal or the like are preferable.
After applying the composite graphite particle and binder resin slurry to the current collector and drying, pressurize to increase the density of the negative electrode active material layer formed on the current collector, so that per unit volume of the negative electrode active material layer It is preferable to increase the battery capacity. The density of the negative electrode active material layer is preferably 1.2 g / cm ³ or more, more preferably 1.3 g / cm ³ or more, and preferably 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less. It is. By setting the density of the negative electrode active material layer to 1.2 g / cm ³ or more, it is possible to prevent a decrease in battery capacity accompanying an increase in electrode thickness. By setting the density of the negative electrode active material layer to 1.8 g / cm ³ or less, the amount of electrolyte solution held in the gap decreases as the interparticle gap in the electrode decreases, and alkali ions such as lithium (Li) ions Therefore, it is possible to prevent the rapid charge / discharge characteristics from being reduced.

<Non-aqueous secondary battery>
The non-aqueous secondary battery according to the present invention can be produced according to a conventional method except that the above negative electrode is used. As the positive electrode material, a lithium cobalt composite oxide whose basic composition is represented by LiCoO ₂ , a lithium nickel composite oxide represented by LiNiO ₂ , LiMnO ₂ or LiMn ₂
Lithium transition metal composite oxides such as lithium manganese composite oxide represented by O4, transition metal oxides such as manganese dioxide, and mixtures of these composite oxides, as well as TiS ₂ , FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ O ₅ , CrO ₃ , V ₃ O ₃ , FeO ₂ , GeO ₂ , LiNi _0.33 Mn _0.33 Co _0.33 O ₂ or the like may be used.

A positive electrode can be produced by slurrying a mixture of these positive electrode materials with a binder resin with an appropriate solvent, and applying and drying to a current collector. The slurry preferably contains a conductive material such as acetylene black or ketjen black. Moreover, you may contain a thickener as desired. As the thickener and the binder resin, those well-known in this application, for example, those exemplified as those used for the production of the negative electrode may be used. The blending ratio with respect to the positive electrode material is usually 0.5% by mass or more and 20% by mass or less, preferably 1% by mass or more and 15% by mass or less, and the thickener is preferably 0.2% by mass or more and 10% by mass or less. More preferably, it is 0.5% by mass or more and 7% by mass or less, and the binder resin is preferably 0.2% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more when slurryed with water. It is 7% by mass or less, and preferably 0.5% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 15% by mass or less when slurryed with an organic solvent that dissolves a binder resin such as NMP. As the positive electrode current collector, aluminum, titanium, zirconium, hafnium, niobium, tantalum, or an alloy thereof may be used.
Of these, aluminum, titanium, tantalum or an alloy thereof is preferably used, and aluminum or an alloy thereof is most preferably used.

  As the electrolytic solution, a solution in which various lithium salts are dissolved in a conventionally known non-aqueous solvent can be used. Non-aqueous solvents include ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate and other cyclic carbonates, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate and other chain carbonates, γ-butyrolactone and other cyclic esters, crown Ether, 2-methyltetrahydrofuran, tetrahydrofuran, 1,2-dimethyltetrahydrofuran and cyclic ethers such as 1,3-dioxolane, chain ethers such as 1,2-dimethoxyethane, etc. may be used. Usually some of these are used together. Of these, it is preferable to use a cyclic carbonate and a chain carbonate, or another solvent in combination.

Further, compounds such as vinylene carbonate, vinyl ethylene carbonate, succinic anhydride, maleic anhydride, propane sultone, diethyl sulfone, difluorophosphate such as lithium difluorophosphate, and the like may be added. Furthermore, an overcharge inhibitor such as diphenyl ether or cyclohexylbenzene may be added.
Examples of the electrolyte dissolved in the non-aqueous solvent include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO _{2 ) (C 4 F 9 SO 2} ), may be used _LiC (CF 3 _{SO 2) 3} and the like. The concentration of the electrolyte in the electrolytic solution is usually 0.5 mol / liter or more and 2 mol / liter or less, preferably 0.6 mol / liter or more and 1.5 mol / liter or less.

For the separator interposed between the positive electrode and the negative electrode, it is preferable to use a porous sheet or non-woven fabric of polyolefin such as polyethylene or polypropylene.
In the non-aqueous secondary battery according to the present invention, the capacity ratio of the negative electrode / positive electrode is preferably designed to be 1.01 or more and 1.5 or less, more preferably 1.2 or more and 1.4 or less. The non-aqueous secondary battery is preferably a lithium ion secondary battery including a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte.

EXAMPLES Next, specific embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
In addition, the volume average particle diameter (d50), the BET method specific surface area, the Si content of the composite graphite particles, the cross-sectional structure of the particles, the abundance ratio, and the like in this specification were measured as follows.

  Volume average particle diameter (d50): About 1 ml of a 2% (volume)% aqueous solution of polyoxyethylene (20) sorbitan monolaurate, about 20 mg of carbon powder added and dispersed in about 200 ml of ion-exchanged water The volume particle size distribution was measured using a laser diffraction particle size distribution analyzer (LA-920, manufactured by Horiba, Ltd.), and the median diameter (d50) was determined. The measurement conditions are ultrasonic dispersion for 1 minute, ultrasonic intensity 2, circulation speed 2, and relative refractive index 1.50.

  -BET specific surface area: Measured using a Tristar II3000 manufactured by Micromeritics. Drying was performed under reduced pressure at 150 ° C. for 1 hour, and measurement was performed by a BET multipoint method (5 points in a relative pressure range of 0.05 to 0.30) by nitrogen gas adsorption.

-N / Si value of composite graphite particles The N / Si value of composite graphite particles was measured using an X-ray photoelectron spectrometer as a linear photoelectron spectroscopy measurement, and the measurement object was placed on a sample table so that the surface was flat, and the Kα of aluminum X-ray source, N1s (394-412 eV) and Si2p (95-112 eV) spectra are measured by multiplex measurement, and the peak top of the obtained Si2p low energy side peak is 99.5 eV. Then, the peak areas of the N1s and Si2p spectra are obtained, and further divided by the device sensitivity coefficient to calculate the surface atomic concentrations of N and Si, respectively, and the obtained N / Si atomic concentration ratio N / Si (N (Atom concentration / Si atom concentration) was defined as the surface functional group amount N / Si value of the sample.
N / Si value (%) = N atom concentration obtained based on the peak area of the N1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / Si atom concentration obtained based on the peak area of the Si2p spectrum in XPS analysis × 100

-Si content of composite graphite particles The Si content of composite graphite particles was determined by melting the sample (composite graphite particles) completely with alkali, then dissolving and measuring with water, and using an inductively coupled plasma emission spectrometer (HORIBA, Ltd. ULTIMA2C). ) And the Si amount was calculated from the calibration curve. Thereafter, the Si content of the composite graphite particles was calculated by dividing the Si amount by the composite graphite particle weight.

-Si abundance ratio of composite graphite particles The Si abundance ratio of composite graphite particles was measured as follows. First, the cross section polisher (JEOL IB-09020CP) was used for the processing of the electrode cross section. The processed electrode cross section was mapped with graphite and Si using EDX while observing with SEM (Hitachi High-Tech SU-70). The SEM acquisition conditions were an acceleration voltage of 3 kV and a magnification of 2000 times, and an image in a range where one particle could be acquired at a resolution of 256 dpi was obtained. Thereafter, 1 particle of composite graphite was extracted, and the area (a) of Si in the particle was calculated. Next, after binarizing the extracted one particle and the background other than the one particle using the image processing software “Image J”, the shrinking process is repeated on the particle, and the area of the extracted one particle is 70. % Figure was extracted, and the area (b) of Si of the figure was calculated. The value obtained by dividing the area (b) by the area (a) was measured with arbitrary three particles, and the value obtained by averaging the values of these three particles was defined as the abundance ratio of Si in the composite graphite particles.

・ Polymer firing yield (%)
The firing yield of the polymer used in the present invention was measured as follows. 10 g of the sample was weighed in a bat and baked at 720 ° C. under N ² atmosphere for 1 hour. Thereafter, and baked for one hour in an N ² atmosphere of at 1000 ° C., it was weighed fired product.
(Weight of fired product) / (Weight before firing) × 100 was defined as a firing yield (%).

・ Nitrogen content in polymer (%)
The content (%) of the nitrogen atom in the polymer used in the present invention is (the molecular weight of the nitrogen atom in the monomer of the smallest repeating unit of the polymer) / (total atoms in the monomer of the smallest repeating unit of the polymer) Molecular weight) × 100.

<Example 1>
(Production of composite graphite particles)
(Process 1)
First, d50: 30 μm polycrystalline Si (manufactured by Wako) was pulverized with NMP (N-methyl-2-pyrrolidone) to a d50: 0.2 μm by a bead mill (manufactured by Ashizawa Finetech), and Si slurry (I ) Was prepared. Without drying 200 g (solid content 40%) of this Si slurry (I), 60 g of polyacrylonitrile (firing yield 37.74%, nitrogen content 26.4%) is uniformly distributed as a polymer containing nitrogen element. Dissolved NMP75
The mixture was added to 0 g and stirred using a mixing stirrer (manufactured by Dalton) to mix Si and polyacrylonitrile. Next, 1000 g of scaly natural graphite (d50: 45 μm) was added and mixed using a mixing stirrer to obtain slurry (II) in which polyacrylonitrile, Si, and graphite were uniformly dispersed. The slurry (II) was appropriately dried under reduced pressure for 3 hours at 150 ° C., which is lower than the thermal decomposition temperature of polyacrylonitrile, so that the polyacrylonitrile is not denatured. In addition, the decomposition temperature of polyacrylonitrile was 270 degree | times from the TG-DTA analysis. Subsequently, the lump of the obtained mixture was crushed with a mill having a hammer type head (manufactured by IKA).

(Process 2)
The pulverized mixture was put into a hybridization system (manufactured by Nara Machinery Co., Ltd.), and spheroidized by circulating or staying in the apparatus for 180 seconds at a rotor rotation speed of 7000 rpm to obtain composite graphite particles containing Si.
(Process 3)
The resulting composite graphite particles encapsulating Si were mixed with heavy coal oil so that the coverage after firing was 7.5%, and kneaded and dispersed with a twin-screw kneader. The obtained dispersion was introduced into a firing furnace and fired at 1000 ° C. for 1 hour in a nitrogen atmosphere. The fired lump was pulverized using the mill described above under the condition of a rotation speed of 3000 rpm, and then classified with a vibrating screen having an opening of 45 μm to obtain composite graphite particles coated with amorphous carbon.

Table 1 shows the volume average particle diameter (d50), BET specific surface area, N / Si value, Si content, and Si abundance ratio of the obtained composite graphite particles. A cross-sectional SEM image of the composite graphite particles is shown in FIG.
An example of graphic extraction for obtaining the existence ratio is shown in FIG.

(Production of battery for performance evaluation)
Kneaded 97.5% by mass of composite graphite particles, 1% by mass of carboxymethyl cellulose (CMC) and 48% by mass of styrene butadiene rubber (SBR) as an binder, 3.1% by mass of an aqueous dispersion, A slurry was obtained. This slurry was applied onto a rolled copper foil having a thickness of 10 μm by a blade method so as to have a basis weight of 7 to 8 mg / cm ² and dried.

Then, it roll-presses with a 250 mφ roll press with a load cell so that the density of the negative electrode active material layer is 1.4 to 1.5 g / cm ³ , punched into a circular shape with a diameter of 12.5 mm, and 110 ° C. for 2 hours. It vacuum-dried and set it as the negative electrode for evaluation. The negative electrode and a Li foil as a counter electrode were stacked through a separator impregnated with an electrolytic solution to produce a battery for a charge / discharge test. As an electrolytic solution, an EC / EMC = 3/7 (mass ratio) mixed solution in which LiPF6 was dissolved so as to be 1 mol / liter was used.

(Initial discharge capacity and charge / discharge efficiency)
First, the positive electrode and the negative electrode are charged to 5 mV at a current density of 0.2 mA / cm ² , further charged to a current value of 0.02 mA at a constant voltage of 5 mV, and lithium is doped into the negative electrode. The positive electrode and the negative electrode were discharged to 1.5 V at a current density of 0.2 mA / cm ² . The initial discharge capacity was determined as follows. First, the negative electrode active material mass is obtained by subtracting the mass of the copper foil punched out to the same area as the negative electrode from the negative electrode mass, and the initial discharge capacity per mass is calculated by dividing the discharge capacity at the first cycle by this negative electrode active material mass. Asked. Next, the positive electrode and the negative electrode were charged to 5 mV at a current density of 0.8 mA / cm ² , further charged to a current value of 0.08 mA at a constant voltage of 5 mV, and lithium was doped into the negative electrode Thereafter, discharging was performed to 1.5 V with respect to the positive electrode and the negative electrode at a current density of 0.8 mA / cm 2.

In the third cycle, the battery is charged to 5 mV with respect to the positive electrode and the negative electrode at a current density of 0.8 mA / cm ² and further charged to a current value of 0.08 mA at a constant voltage of 5 mV. After the lithium was doped into the negative electrode, the positive electrode and the negative electrode were discharged to 1.5 V at a current density of 0.8 mA / cm ² , and the charge / discharge efficiency was determined by the following formula 3. The negative electrode active material mass was determined by subtracting the mass of the copper foil punched out to the same area as the negative electrode from the negative electrode mass.

Formula 3
Charging / discharging efficiency (%) = {discharge capacity after 3 cycles (mAh / g) / discharge capacity at the first cycle (mAh / g)} × 100
The initial discharge capacity and charge / discharge efficiency calculated here are shown in Table 1.

<Example 2>
In order to increase the amount of Si in the composite graphite particles, the same operation as in Example 1 was performed except that the Si slurry (I) (solid content 40%) during mixing was changed to 850 g. The physical properties of the obtained composite graphite particles and the evaluation of the battery are shown in Table 1.

<Example 3>
In order to increase the amount of Si in the composite graphite particles, the same operation as in Example 1 was performed except that the amount of Si slurry (I) (solid content 40%) during mixing was changed to 1200 g. The physical properties of the obtained composite graphite particles and the evaluation of the battery are shown in Table 1.

As shown in Table 1, it was confirmed that the composite graphite particles of the present invention are excellent in initial charge capacity and charge / discharge efficiency.
This is because the Si compound can be efficiently embedded in the gaps between the plurality of scaly natural graphite particles in which the graphite (A) is folded by going through the steps 1 and 2 at the time of manufacture. This is probably because the desorption and the interruption of the conductive path associated therewith were suppressed, and the reaction between the Si compound and the electrolyte was suppressed by having composite graphite particles or nitrogen atoms.

  The non-aqueous secondary battery provided with the electrode using the composite graphite particles of the present invention has a high capacity and improves initial charge / discharge characteristics and charge / discharge efficiency. It can satisfy the characteristics required for electric vehicle applications, and is industrially useful.

(1) Solid line: One extracted particle is indicated by a solid line.
(2) Dotted line: After binarizing the extracted one particle and the background other than the one particle for the extracted one particle, the shrinking process is repeated for the particle, and the area of one particle becomes 70%. The figure is shown with a dotted line.

Claims (11)

A method for producing composite graphite particles for a non-aqueous secondary battery negative electrode containing graphite (A) and metal particles (B) that can be alloyed with Li, comprising the following steps 1 and 2 The manufacturing method of the composite graphite particle for non-aqueous secondary battery negative electrodes.
Step 1: Obtaining a mixture containing at least a polymer containing graphite (A), Li-alloyable metal particles (B), and a polymer containing nitrogen atoms Step 2: Giving mechanical energy to the mixture of Step 1 and spheroidizing treatment The process of applying Furthermore, the following process 3 is included, The manufacturing method of the composite graphite particle for non-aqueous secondary battery negative electrodes of Claim 1 characterized by the above-mentioned.
Step 3: A step of coating the spheroidized composite graphite particles in Step 2 with a carbonaceous material   The method for producing composite graphite particles for a nonaqueous secondary battery negative electrode according to claim 1 or 2, wherein the metal particles (B) that can be alloyed with Li contain SiOx (0≤x <2).   The composite graphite for a nonaqueous secondary battery negative electrode according to any one of claims 1 to 3, wherein the content of nitrogen atoms in the polymer containing nitrogen atoms is 1% or more and 80% or less. Particle production method.   The composite graphite particle for non-aqueous secondary battery negative electrodes manufactured with the manufacturing method as described in any one of Claims 1-4.   A composite graphite particle for a non-aqueous secondary battery negative electrode containing graphite (A) and metal particles (B) that can be alloyed with Li, the composite graphite particle containing nitrogen atoms, and a cross section of the composite graphite particle When observed with a SEM (scanning electron microscope), a structure in which graphite (A) is folded is observed. Composite graphite particles for a non-aqueous secondary battery negative electrode. The composite graphite particles for a nonaqueous secondary battery negative electrode according to claim 6, wherein the surface functional group amount N / Si value represented by the following formula 1 is 0.1% or more and 5% or less.
Formula 1
N / Si value (%) = N atom concentration obtained based on the peak area of the N1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / Si atom concentration obtained based on the peak area of the Si2p spectrum in XPS analysis × 100 The abundance ratio of Li and alloyable metal particles (B) in the composite carbon particles (A) calculated by the following measurement method is 0.2 or more, according to claim 6 or 7, Composite graphite particles for nonaqueous secondary battery negative electrode.
(Measuring method)
One particle is extracted when the cross section of the composite carbon particle (A) is observed with an SEM (scanning electron microscope), and the area (a) of the metal particle (B) that can be alloyed with Li in the particle is calculated. To do. Next, after binarizing the extracted 1 particle and the background other than the 1 particle, the shrinking process is repeated on the particle, and a figure with an area of 70% of the extracted 1 particle is extracted. The area (b) of the metal particles (B) that can be alloyed with the existing Li is calculated. A value obtained by dividing the area (b) by the area (a) with arbitrary three particles, and averaging the value of these three particles is a metal particle that can be alloyed with Li in the composite carbon particle (A). The existence ratio of (B).   The composite graphite particles for a nonaqueous secondary battery negative electrode according to any one of claims 6 to 8, wherein the metal particles (B) that can be alloyed with Li contain SiOx (0≤x <2).   A non-aqueous secondary battery negative electrode comprising a current collector and a negative electrode active material formed on the current collector, wherein the negative electrode active material is the non-aqueous secondary battery according to any one of claims 5 to 9. A negative electrode for a nonaqueous secondary battery, comprising composite graphite particles for a secondary battery negative electrode.   A non-aqueous secondary battery comprising a positive electrode and a negative electrode capable of occluding and releasing metal ions and an electrolyte, wherein the negative electrode is a negative electrode for a non-aqueous secondary battery according to claim 10. Water-based secondary battery.