JP5957353B2 - Method for producing composite material, and composite material - Google Patents

Description

  The present invention relates to a composite material, particularly a negative electrode material for a lithium ion secondary battery.

  Lithium ion secondary batteries have high capacity and can be reduced in size and weight, and thus are applied to many portable devices such as mobile phones and notebook computers.

  Conventionally, carbon materials have been used as negative electrode materials for lithium ion secondary batteries. Recently, the use of silicon-based materials as negative electrode materials has been studied. For example, silicon can theoretically store and release 4.4 mol of lithium ions per mol in charge and discharge (carbon is 1/6 mol per mol), so that silicon-based materials can be used as lithium ion secondary batteries. When applied as a negative electrode material, it is expected that the capacity of the lithium ion secondary battery can be further increased.

  However, a problem with silicon-based materials is that the volume of the silicon-based material expands / shrinks with the insertion / release of lithium ions. In other words, when the negative electrode is made of a silicon-based material, the negative electrode undergoes repeated insertion / extraction cycles of lithium ions during the charge / discharge cycle of the lithium ion secondary battery, whereby the negative electrode volume expansion / contraction is repeated. The negative electrode may be deteriorated or collapsed.

  In order to prevent deterioration of the negative electrode made of a silicon-based material due to such a charge / discharge cycle of the battery, Patent Document 1 discloses that a carbon film is coated on the surface and silicon fine particles are adhered as a negative electrode material for a lithium ion secondary battery. It has been proposed to use a composite material made of graphite particles.

JP 2002-8652 A

  However, even in the composite material composed of silicon fine particles and graphite particles described in Patent Document 1, it is still difficult to say that the effect of suppressing the deterioration of the negative electrode due to the charge / discharge cycle is sufficient.

  Therefore, there is still a demand for a composite material that is a negative electrode material for a lithium ion secondary battery and that can further suppress deterioration of the negative electrode due to charge / discharge cycles.

  The present invention has been made in view of such a background, and in the present invention, when used as a negative electrode material of a lithium ion secondary battery, a composite material capable of further suppressing deterioration of the negative electrode due to a charge / discharge cycle. And a method for producing such a composite material.

In the present invention, a method for producing a composite material having graphite particles and silicon particles bonded to the surface of the graphite particles,
(A) partially oxidizing the graphite particles;
(B) surface modifying silicon particles having a primary particle size smaller than that of the graphite particles;
(C) combining the partially oxidized graphite particles and the surface-modified silicon particles;
A method for producing a composite material characterized by comprising:

Here, in the method for producing a composite material according to the present invention, the step (a) includes:
(A1) A step of oxidizing the graphite particles at a high temperature, and / or (a2) a step of wet oxidizing the graphite particles.

  In the method for producing a composite material according to the present invention, the step (b) may include a step of silane coupling treatment of silicon particles.

In the method for producing a composite material according to the present invention, the step (c) includes
(C1) mixing the graphite particles and the silicon particles in a heated non-aqueous solution, or (c2) mixing the graphite particles and the silicon particles in a non-aqueous solution containing a catalyst. You may do it.

  In the method for producing a composite material according to the present invention, the graphite particles may have a primary particle size of 1 μm to 50 μm.

  In the method for producing a composite material according to the present invention, the silicon particles may have a primary particle size of 300 nm or less.

  Moreover, in this invention, the manufacturing method of the negative electrode material of a lithium ion secondary battery which has the process of obtaining a composite material with the above-mentioned manufacturing method is provided.

Furthermore, in the present invention,
Having graphite particles and silicon particles bonded to the surface of the graphite particles;
The primary particle size of the graphite particles is 1 μm to 50 μm,
A composite material having a primary particle size of 300 nm or less is provided.

  Here, in the composite material according to the present invention, the graphite particles and the silicon particles may be amide-bonded.

  Furthermore, the present invention provides an electrode having the composite material as described above.

  Moreover, in this invention, the lithium ion secondary battery which has such an electrode is provided.

  Furthermore, in the present invention, an assembled battery having such a lithium ion secondary battery is provided.

  In the present invention, when used as a negative electrode material of a lithium ion secondary battery, it is possible to provide a composite material that can further suppress deterioration of the negative electrode due to a charge / discharge cycle, and a method for producing such a composite material. .

It is the figure which showed schematically the flow of the manufacturing method of the composite material by one Example of this invention. It is the figure which showed an example of the structure of the lithium ion secondary battery which is one Embodiment of this invention. It is the figure which showed the XPS analysis result (spectrum around 400eV) of the powder surface. It is the figure which showed the XPS analysis result (spectrum around 400eV) of the powder surface.

  The present invention will be described in detail below.

In the present invention, a method for producing a composite material,
(A) partially oxidizing the graphite particles;
(B) surface modifying silicon particles having a primary particle size smaller than that of the graphite particles;
(C) combining the partially oxidized graphite particles and the surface-modified silicon particles;
The manufacturing method characterized by having is provided.

  As described above, since silicon has a large theoretical capacity, the use of silicon as a negative electrode material for a lithium ion secondary battery may possibly further increase the capacity of the lithium ion secondary battery. is there.

  However, the silicon-based material expands / contracts greatly in volume with the insertion / release of lithium ions. Therefore, when the negative electrode is made of a silicon-based material, the negative electrode undergoes repeated insertion / extraction cycles of lithium ions during the charge / discharge cycle of the lithium ion secondary battery, thereby repeating the volume expansion / contraction of the negative electrode. The negative electrode may be deteriorated or collapsed.

  On the other hand, in this invention, a composite material is comprised by using graphite and silicon and combining both.

  Note that the graphite particles and the silicon particles cannot be combined by simply mixing them.

  For this reason, the present invention includes (a) a step of partially oxidizing graphite particles, and (b) a step of modifying the surface of silicon particles having a primary particle size smaller than that of the graphite particles. That is, graphite particles are used in a partially oxidized state, and silicon particles are used in a surface-modified state.

  There are almost no functional groups on the surfaces of graphite and silicon, and the functional groups cannot be chemically reacted.

  In the present invention, the graphite particles are partially oxidized. Generally, there are almost no functional groups on the surface of graphite. Further, when the graphite particles are heavily oxidized, they burn and change to carbon dioxide or the like. By controlling the oxidation conditions so that the graphite particles are in a partially oxidized state, some of the carbon atoms are oxidized and functional groups such as hydroxyl groups (—OH) and carboxyl groups (—COOH) are present. It is supposed to be.

  The more the partial oxidation of the graphite particles, the more functional groups, and the number of active sites of the graphite particles increases.

  In the present invention, the silicon particles are surface-modified. For example, various functional groups can be present at the terminal by surface modification with a silane coupling agent.

  Accordingly, by reacting graphite particles having many functional groups with surface-modified silicon particles under suitable conditions, functional groups on the graphite particle side (hereinafter referred to as “first functional groups”). And a functional group on the silicon particle side (hereinafter referred to as “second functional group”) are bonded, and a strong bond can be obtained between the graphite particles and the silicon particles.

  In the composite material obtained by such a manufacturing method, the graphite particles and the silicon particles are covalently bonded by a dehydration reaction between the functional groups of the two, and thus both have a strong bonded state. Therefore, when such a composite material is used for a negative electrode of a lithium ion battery, even if lithium is repeatedly stored / released in the negative electrode due to charging / discharging of the battery, the bond between the graphite particles and the silicon particles is broken. The risk of separation is significantly reduced.

  Further, since the silicon particles have a smaller primary particle size than the graphite particles, the silicon particles exist on the surface of the larger graphite particles in a so-called “dispersed” state. That is, a “gap” in which no silicon particles exist remains on the surface of the graphite particles. For this reason, when the composite material of the present invention is used for the negative electrode of a lithium ion battery, the silicon particles can expand / contract during charging / discharging without being restrained by the surrounding silicon particles. This significantly suppresses the particles from colliding with each other when the silicon particles are expanded, causing the particles to deteriorate or collapse.

  As described above, the manufacturing method according to the present invention can provide a negative electrode material for a lithium ion secondary battery having high capacity because it contains silicon. Moreover, in the manufacturing method by this invention, when it uses as a negative electrode of a lithium ion secondary battery, the negative electrode material which can suppress deterioration of the negative electrode by a charging / discharging cycle more can be provided.

(Method for producing composite material according to the present invention)
Next, an example of a method for producing a composite material according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 schematically shows a flow of a method for manufacturing a composite material according to an embodiment of the present invention.

As shown in FIG. 1, a method for manufacturing a composite material according to an embodiment of the present invention includes:
(A) a step of partially oxidizing graphite particles (S110);
(B) modifying the surface of the silicon particles (S120);
(C) combining the partially oxidized graphite particles and the surface-modified silicon particles (S130);
Have

  Hereinafter, each step will be described.

(Step S110)
First, graphite particles are prepared.

  The graphite particles may be of any grade in properties such as purity and crystallinity.

  In the present application, the crystallinity of graphite is evaluated by Raman spectroscopy.

More specifically, in the present application, in the spectrum measured by Raman spectroscopy of graphite, the intensity ID of the peak near 1360 cm ⁻¹ derived from the amorphous component and the peak near 1580 cm ⁻¹ derived from the graphite component are measured. The ratio of strength IG (ID / IG) is obtained and used as an index (R value) representing the crystallinity of graphite.

  The particle size of the graphite particles is not particularly limited. The particle size of the graphite particles is, for example, in the range of 1 μm to 50 μm, and may be in the range of 1 μm to 10 μm.

  In the present application, the “particle size” of the particle means the value of the primary particle size.

The primary particle size of the particles was determined by measuring the specific surface area by the BET method and converting the particle size according to the following formula:
S = 6 / ρd
Here, S is the specific surface area, ρ is the density of the particles, and d is the primary particle size of the particles.

  Next, the prepared graphite is partially oxidized.

  Here, the “partial oxidation” treatment means a general term for treatment for oxidizing a part of the graphite particles.

  Accordingly, the “partial oxidation” treatment of graphite includes, for example, (i) a method of oxidizing graphite at a high temperature, and (ii) a wet oxidation method of oxidizing graphite in an aqueous solution or the like.

  In the case of the method of oxidizing the graphite (i) at a high temperature, the conditions for the oxidation treatment are not particularly limited. For example, the oxidation temperature is preferably in the range of 400 ° C to 700 ° C, more preferably in the range of 500 ° C to 700 ° C. Further, the treatment atmosphere may be in the air or in oxygen.

  On the other hand, in the case of the wet oxidation treatment (ii), the solution used for partial oxidation of graphite is not particularly limited. The solution used for partial oxidation of graphite may be, for example, an aqueous solution containing an oxidizing agent used in the Brodie method or the Hummers method.

  Moreover, you may implement combining the process of (i) and (ii).

  In this way, graphite is subjected to “partial oxidation” treatment under controlled oxidation conditions to make the graphite particles partially oxidized, whereby some of the carbon atoms are oxidized, and hydroxyl (—OH) and A functional group such as a carboxyl group (—COOH) is present, and the number of active sites of the graphite particles is increased.

  These functional groups provide a bond base point when the graphite particles are bonded to the silicon particles in the subsequent step S130.

  The degree of partial oxidation of graphite can be determined by measuring the oxygen concentration using an inert gas melting-infrared absorption method.

  In the present application, the degree of oxidation of graphite obtained by this method is preferably in the range of 0.1 to 5% by mass.

(Step S120)
Next, surface modification treatment is performed on the silicon particles.

  The primary particle size of the silicon particles subjected to the surface modification treatment is not particularly limited as long as it is smaller than the graphite particles. The primary particle size of the silicon particles is, for example, in the range of 1 nm to 300 nm, and may be in the range of 10 nm to 100 nm.

Further, the type of the second functional group formed on the surface of the silicon particle is not particularly limited as long as it has reactivity with the first functional group formed on the surface of the graphite particle. The second functional group may be, for example, an amino group (—NH ₂ ).

  The method of surface modification treatment for silicon particles is not particularly limited. For example, the silicon particle may be treated with a silane coupling agent to form a silane coupling compound on the surface of the silicon particle.

  Although the kind of silane coupling agent is not particularly limited, for example, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, 3- (2 -Aminomethyl) aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropylmethylditrimethoxysilane, alkoxysilane having an amino group such as 3-phenylaminopropyltrimethoxysilane (aminated silane coupling agent) Etc. may be used.

  In this case, the surface of the silicon particle has an amino group as a functional group.

(Step S130)
Next, the partially oxidized graphite particles prepared in step S110 described above and the surface-modified silicon particles prepared in step S120 are combined to form a composite material.

  This step S130 is performed in order to bond the first functional group of the graphite particle and the second functional group of the silicon particle. Therefore, the treatment method is not particularly limited as long as the first functional group and the second functional group can be bonded.

For example, as a method of bonding graphite particles and silicon particles,
(C1) A method of heating a non-aqueous solution containing graphite particles and silicon particles, and (c2) a method of mixing graphite particles and silicon particles in a non-aqueous solution in the presence of a catalyst.

  In any method, the non-aqueous solution is used because a dehydration reaction is used for bonding graphite particles and silicon particles. Although there is no restriction | limiting in particular in reaction, It can carry out on the heat | fever dehydration conditions in the generally known solvent.

For example, when a carboxyl group (—COOH) is present as the first functional group on the surface of the graphite particle and an amino group (—NH ₂ ) is present as the second functional group on the surface of the silicon particle, the binding site Then, the following dehydration condensation reaction occurs:

_{-COOH + -NH 2 → -CONH- + H} 2 O (1) formula

Thereby, both functional groups are amide-bonded, and the graphite particles and the silicon particles are bonded.

  As the non-aqueous solution, for example, an organic solvent is used. The non-aqueous solution may be selected from, for example, toluene, benzene, xylene, methyl acetate, propyl acetate, butyl acetate, N-methyl-2-pyrrolidinone, butanol, propanol, ethanol, dichlorobenzene, and the like. The solvent may be dehydrated with a molecular sieve or the like.

  In the method (c1), heating of the non-aqueous solution containing graphite particles and silicon particles may be performed at 50 ° C. or higher. Moreover, you may recirculate | reflux at the boiling point of a solvent. Further, it may be carried out so that moisture in the atmosphere does not enter.

  In the method (c2), the catalyst may be an acid component and / or an alkali component in the solution.

  Through the above steps, a composite material in which graphite particles and silicon particles are bonded can be manufactured.

  In such a composite material, the graphite particles and the silicon particles are bonded by a covalent bond between the functional groups of the both, and therefore both have a good bonding state. Further, it can be confirmed by SEM (scanning electron microscope), EDX (energy dispersive X-ray analysis) or the like that silicon particles are present in a “dispersed” state on the surface of graphite.

  Therefore, when such a composite material is used for the negative electrode of a lithium ion battery, even if the storage / release of lithium is repeated on the negative electrode due to charging / discharging of the battery, the bond between the graphite particles and the silicon particles is broken, The collapse of silicon particles is significantly suppressed.

  Therefore, when such a composite material is used for the negative electrode of a lithium ion battery, it becomes possible to improve the charge / discharge cycle characteristics.

  In addition, the present invention provides a lithium ion secondary battery including the composite material having the above-described characteristics as an electrode.

The lithium ion secondary battery of the present invention includes, for example, a positive electrode, an electrolyte, a separator, and a negative electrode (electrode) having a composite material as described above, and has a cylindrical shape, a rectangular shape, a coin shape,
Or it consists of various shapes, such as a sheet type. In addition, the lithium ion secondary battery by this invention is not restricted to the form quoted here, You may consist of other forms.

According to the negative electrode and the lithium ion secondary battery, the negative electrode and the lithium secondary battery having high energy density, high discharge capacity in a flat region of the charge / discharge curve, and excellent cycle characteristics can be configured. .

Here, the positive electrode which comprises a lithium ion secondary battery can mention what contains a positive electrode active material, a conductive support material, and a binder, for example. Examples of the positive electrode active material include compounds that can occlude and release lithium, such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, and MoS.

  Moreover, as a separator, olefin type porous films, such as polyethylene and a polypropylene, can be used, for example, A polymer electrolyte etc. can also be used.

Examples of the electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl Sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate , Diethylene glycol, dimethyl ether Aprotic solvents such as Le or a mixed solvent obtained by mixing two or more of these _{solvents,, LiPF 6, LiBF 4,} LiSbF 6, LiAsF 6, LiClO 4, LiCF 3 SO 3, Li (CF 3 SO _{2) 2 N, LiC 4 F} 9 SO 3, LiSbF 6, LiAlO 4, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y + 1 SO 2) ( provided that x, y are natural numbers), LiCl, LiI It is possible to use a solution in which one or two or more electrolytes made of a lithium salt such as a mixture are dissolved.

  Hereinafter, an example of a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to the drawings. In addition, the lithium ion secondary battery of this invention is not restricted to the form demonstrated below.

  In FIG. 2, an example of the lithium ion secondary battery 1 which is embodiment of this invention is shown.

  A lithium ion secondary battery 1 shown in FIG. 2 is called a cylindrical type, and is a sheet-like negative electrode 2 (electrode), a sheet-like positive electrode 3, and between the negative electrode 2 and the positive electrode 3. Mainly composed of the arranged separator 4, the negative electrode 2, the positive electrode 3, and the electrolyte impregnated in the separator 4, the cylindrical battery container 5, and the sealing member 6 that seals the battery container 5. It is configured. The lithium ion secondary battery 1 is configured such that a negative electrode 2, a positive electrode 3, and a separator 4 are overlapped and accommodated in a battery container 5 in a state where they are wound.

  The negative electrode 2 (electrode) is configured by applying the composite material according to the present invention to a current collector made of copper foil or the like. The negative electrode 2 (electrode) includes a composite material according to the present invention which is a negative electrode active material, a conductive additive such as graphite, and a binder such as polyvinylidene fluoride that binds the composite material and the conductive additive. It may contain at least a dressing.

  A battery constituted by connecting a plurality of the lithium ion secondary batteries is particularly referred to as an “assembled battery”. Specifically, the “assembled battery” is configured by connecting at least two or more lithium ion secondary batteries in series and / or in parallel. By connecting in series and / or in parallel, the capacity and voltage of the assembled battery can be freely adjusted.

  Next, examples according to the present invention will be described.

Example 1
Graphite particles (primary particle size = 5.7 μm, R value = 0.77) were prepared. 100 g of the graphite particles were held at 600 ° C. for 2 hours in an air atmosphere to be partially oxidized (first partial oxidation).

  When the oxygen concentration of the graphite particles after the first partial oxidation treatment was measured by an active gas melting-infrared absorption method, the oxidation concentration was 0.04% by mass.

  Next, 200 ml of 5 mass% sulfuric acid aqueous solution containing 5 mass% potassium permanganate was prepared. In this aqueous solution, 20 g of graphite particles subjected to the first partial oxidation treatment were added, and the mixed solution was stirred at room temperature for 18 hours (second partial oxidation).

  Thereafter, the graphite particles in the mixed solution were collected by vacuum filtration. The recovered graphite particles were repeatedly washed with water and filtered under reduced pressure. Further, it was washed with hydrochloric acid, washed with water and filtered under reduced pressure. Then, it vacuum-dried. As a result, cleaned partially oxidized graphite particles were obtained.

  When the oxygen concentration of the obtained partially oxidized graphite particles was measured by an active gas melting-infrared absorption method, the oxygen concentration was 0.27% by mass.

  Next, surface-modified silicon particles were prepared as follows.

  First, silicon powder (made by Aldrich, particle size <100 nm) was prepared.

  Next, 5 g of silicon powder was put in 200 ml of toluene, and 2 ml of 3-aminopropyltriethoxysilane was added while stirring. The mixed solution was refluxed and stirred for 1 hour.

  Next, the obtained mixed solution was filtered, and washing and filtration were repeated with toluene. The surface-modified silicon particles were collected, washed with toluene, and repeatedly filtered under reduced pressure. Then, it vacuum-dried.

  Thereby, silicon particles having an amino group on the surface were obtained.

  Next, the following treatment was performed to bond the graphite particles and the silicon particles.

  First, 18 g of partially oxidized graphite and 2 g of surface-modified silicon powder were added to 100 ml of dehydrated toluene. Next, the mixture was stirred at 80 ° C. for 6 hours while stirring.

  The obtained liquid mixture was filtered and dried with a vacuum dryer.

  As a result, a composite material in which graphite and silicon particles were bonded (hereinafter referred to as “composite material according to Example 1”) was obtained.

(Production of lithium ion battery)
Next, the negative electrode of the battery was produced using the composite material according to Example 1 produced by the above-described method.

  First, an appropriate amount of water was added to 80 parts by mass of the composite material, 10 parts by mass of the binder, and 10 parts by weight of the conductive additive, and the mixture was stirred and mixed to prepare a negative electrode paste.

  As the binder, an ethylene / vinyl acetate / acrylic acid copolymer aqueous emulsion and carboxymethyl cellulose mixed so as to have a solid content mass ratio of 1: 1 were used. Carbon black was used as the conductive assistant.

  Next, a negative electrode paste was applied to a thickness of about 100 μm on a copper foil having a thickness of 20 μm by a doctor blade method, and this was vacuum-dried at 80 ° C. overnight. Thereby, the negative electrode layer was formed. In addition, the negative electrode layer was cut into a cylindrical shape having a diameter of 15 mm by hand press and used.

  On the other hand, a lithium foil having a thickness of 0.5 mm was cut into a cylindrical shape having a diameter of 15 mm to form a positive electrode.

A film made of porous polypropylene having a thickness of 25 μm was prepared as a separator member. In addition, LiPF ₆ was dissolved at a concentration of 1 mol / dm ³ in a mixed solvent obtained by mixing 30% by volume of ethylene carbonate and 70% by volume of methyl ethyl carbonate to prepare a nonaqueous electrolytic solution.

  Using these negative electrode layer, non-aqueous electrolyte, positive electrode, and separator, a 2032 type coin cell (diameter 20 mm, thickness 3.2 mm) -shaped lithium ion battery (hereinafter referred to as “battery according to Example 1”) Was made.

  The powder surface was analyzed by XPS. FIG. 3 shows a spectrum around 400 eV.

(Example 2)
Graphite particles (primary particle size = 5.4 μm, R value = 0.06) were prepared. Moreover, 200 ml of 5 mass% sulfuric acid aqueous solution containing 5 mass% potassium permanganate was prepared. 20 g of graphite particles were added to this aqueous solution, and the mixed solution was stirred at room temperature for 18 hours.

  Thereafter, the graphite particles in the mixed solution were collected by vacuum filtration. The recovered graphite particles were repeatedly washed with water and filtered under reduced pressure. Further, it was washed with hydrochloric acid, washed with water and filtered under reduced pressure. Then, it vacuum-dried. As a result, cleaned partially oxidized graphite particles were obtained.

  When the oxygen concentration of the obtained partially oxidized graphite particles was measured by an active gas melting-infrared absorption method, the oxygen concentration was 0.24% by mass.

  Thereafter, surface-modified silicon particles were prepared by the same method as in Example 1, and graphite particles and silicon particles were bonded.

  As a result, a composite material in which graphite and silicon particles were bonded (hereinafter referred to as “composite material according to Example 2”) was obtained.

  Using the composite material according to Example 2, a lithium ion battery (hereinafter, referred to as “battery according to Example 2”) is manufactured by the method shown in the column of “Production of Lithium Ion Battery” in Example 1. did.

  The surface of the powder was analyzed by XPS. As a result, a spectrum similar to that in Example 1 was obtained.

Example 3
Graphite particles (primary particle size = 5.7 μm, R value = 0.77) were prepared. Further, 20 g of graphite particles were added to 200 ml of concentrated nitric acid solution, and this mixed solution was stirred at 60 ° C. for 1 hour.

  Thereafter, the graphite particles in the mixed solution were collected by vacuum filtration. The recovered graphite particles were repeatedly washed with water and filtered under reduced pressure to obtain purified partially oxidized graphite particles.

  When the oxygen concentration of the obtained partially oxidized graphite particles was measured by an active gas melting-infrared absorption method, the oxygen concentration was 0.20% by mass.

  Thereafter, surface-modified silicon particles were prepared by the same method as in Example 1, and graphite particles and silicon particles were bonded.

  Thereby, a composite material in which graphite and silicon particles were bonded (hereinafter referred to as “composite material according to Example 3”) was obtained.

  Using the composite material according to Example 3, a lithium ion battery (hereinafter referred to as “battery according to Example 3”) was manufactured by the method shown in the column of (Production of lithium ion battery) of Example 1. did.

  The surface of the powder was analyzed by XPS. As a result, a spectrum similar to that in Example 1 was obtained.

Example 4
After preparing graphite particles and silicon particles before bonding by the same method as in Example 2, a composite material composed of bonding of the particles was manufactured by the following treatment method as a bonding method.
That is, 5 g of cleaned graphite particles (dried) obtained by partial oxidation with 5% by mass of potassium permanganate in 5% by mass of sulfuric acid were placed in 20 ml of dehydrated toluene, and 2 g of thionyl chloride was slowly added dropwise in an ice bath. Subsequently, it was made to react at room temperature for 24 hours. Thereafter, excess thionyl chloride and toluene were carefully distilled off under reduced pressure, and 20 ml of anhydrous toluene and silicon particles modified with 3-aminopropyltriethoxysilane were added at room temperature for reaction.

  As a result, a composite material in which graphite and silicon particles were bonded (hereinafter referred to as “composite material according to Example 2”) was obtained.

  Using the composite material according to Example 4, a lithium ion battery (hereinafter, referred to as “battery according to Example 2”) was manufactured by the method shown in the column of (Production of lithium ion battery) of Example 1. did.

  The surface of the powder was analyzed by XPS. As a result, a spectrum similar to that in Example 1 was obtained.

(Comparative Example 1)
Partially oxidized graphite particles were prepared by the same method as in Example 1. In addition, surface-modified silicon particles were prepared by the same method as in Example 1.

  Next, 1.8 g of partially oxidized graphite particles and 2 g of surface-modified silicon particles were mixed with a planetary stirrer.

  As a result, a composite material containing graphite and silicon particles (hereinafter referred to as “composite material according to Comparative Example 1”) was obtained.

  Using the composite material according to Comparative Example 1, a lithium ion battery (hereinafter, referred to as “battery according to Comparative Example 1”) was manufactured by the method shown in the column of “Production of Lithium Ion Battery” in Example 1. did.

  The powder surface was analyzed by XPS. FIG. 4 shows a spectrum around 400 eV.

(Comparative Example 2)
Partially oxidized graphite particles were prepared by the same method as in Example 1. In addition, surface-modified silicon particles were prepared by the same method as in Example 1.

  Next, 18 g of partially oxidized graphite particles and 2 g of surface-modified silicon particles were added to 100 ml of dehydrated toluene. The mixture was stirred at room temperature for 6 hours.

  The obtained liquid mixture was filtered and dried with a vacuum dryer.

  As a result, a composite material containing graphite and silicon particles (hereinafter referred to as “composite material according to Comparative Example 2”) was obtained.

  Using the composite material according to Comparative Example 2, a lithium ion battery (hereinafter referred to as “battery according to Comparative Example 2”) was prepared by the method shown in the column of “Production of Lithium Ion Battery” in Example 1. did.

  The surface of the powder was analyzed by XPS. As a result, a spectrum similar to that of Comparative Example 1 was obtained.

  Table 1 below collectively shows the conditions for producing the composite materials according to Examples 1 to 4 and Comparative Examples 1 to 2.

（充放電試験）
次に、作製した各リチウムイオン電池を用いて、２５℃で充放電試験を行った。

(Charge / discharge test)
Next, a charge / discharge test was performed at 25 ° C. using each of the produced lithium ion batteries.

  The charge / discharge test was performed by charging the battery potential from the rest potential to 20 mV at a constant current, and then discharging the battery potential to 1.5 V at a constant current.

  The current value was set to be 0.1 C with respect to the negative electrode (composite material) at the time of charging / discharging (however, 1 C is a constant current discharge of a cell having a nominal capacity value, and in just one hour. This is the current value at which discharge ends.) The theoretical capacity of the composite material is calculated to be about 755 mAh / g from the theoretical capacity of silicon (4200 mAh / g) and the theoretical capacity of graphite (372 mAh / g).

  With this operation as one cycle, a total of 25 cycles of charge / discharge treatment were performed.

Further, the cycle characteristics of each battery were obtained from the discharge capacity (initial discharge capacity) of the first cycle of the battery and the discharge capacity of the 25th cycle by the following formula.

Cycle characteristics (%) =
(Discharge capacity at 25th cycle / discharge capacity at 1st cycle) × 100
(2) Formula

The results are shown in the column of “Cycle characteristics” in Table 1 above.

  From this result, it can be seen that the cycle characteristics of the batteries according to Examples 1 to 4 are significantly improved as compared with the cycle characteristics of the batteries according to Comparative Examples 1 and 2.

  Thus, it was confirmed that the cycle characteristics of the battery were improved by using the composite material produced by the production method according to the present invention as the negative electrode.

  The present invention can be used in, for example, a manufacturing technique of a negative electrode material for a lithium ion secondary battery.

1 Lithium ion secondary battery 2 Negative electrode (electrode)
3 Positive electrode 4 Separator 5 Battery container 6 Sealing member

Claims (11)

A method for producing a composite material having graphite particles and silicon particles bonded to the surface of the graphite particles,
(A) partially oxidizing the graphite particles;
(B) surface modifying silicon particles having a primary particle size smaller than that of the graphite particles;
(C) combining the partially oxidized graphite particles and the surface-modified silicon particles;
A method for producing a composite material, comprising: The step (a) includes:
The manufacturing method according to claim 1, further comprising: (a1) oxidizing the graphite particles at high temperature, and / or (a2) wet-oxidizing the graphite particles.   The manufacturing method according to claim 1, wherein the step (b) includes a step of subjecting silicon particles to a silane coupling treatment. The step (c) includes:
(C1) mixing the graphite particles and the silicon particles in a heated non-aqueous solution, or (c2) mixing the graphite particles and the silicon particles in a non-aqueous solution containing a catalyst. The manufacturing method as described in any one of Claims 1 thru | or 3.   The manufacturing method according to claim 1, wherein the graphite particles have a primary particle size of 1 μm to 50 μm.   The manufacturing method according to claim 1, wherein the silicon particles have a primary particle size of 300 nm or less.   The manufacturing method of the negative electrode material of a lithium ion secondary battery which has the process of obtaining a composite material with the manufacturing method as described in any one of Claims 1 thru | or 6. Having graphite particles and silicon particles bonded to the surface of the graphite particles;
The primary particle size of the graphite particles is 1 μm to 50 μm,
The primary particle size of the silicon particles is 300 nm or less,
A composite material in which the graphite particles and the silicon particles are amide-bonded . An electrode comprising the composite material according to claim 8 . A lithium ion secondary battery comprising the electrode according to claim 9 . The assembled battery which has a lithium ion secondary battery of Claim 10 .

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