JP6084856B2 - Method for producing carbon material, method for producing electrode material, and method for producing lithium ion secondary battery - Google Patents

Description

  The present invention relates to a carbon material and a method for producing the same, and an electrode material and a lithium ion secondary battery using the carbon material.

Carbon materials made of carbonaceous fired bodies are used for electrode materials such as lithium ion secondary batteries, electric double layer capacitors, and capacitors.
For example, in a lithium ion secondary battery, a carbon material is used as a negative electrode active material, lithium is occluded (intercalated) into the carbon material in an ionic state when the battery is charged, and released as ions (deintercalation) during discharge. It uses a “rocking chair type” battery configuration.

  As electronic devices are rapidly becoming smaller or higher in performance, there is a growing demand for higher energy density in lithium ion secondary batteries. However, since graphite constituting the carbon material has a theoretical lithium storage / release capacity limited to 372 mAh / g, an electrode material having a larger lithium storage / release capacity is required.

On the other hand, when silicon is used instead of the carbon material having a low lithium storage / release capacity, a method using a silicon material has been studied since a high capacity of 4200 mAh / g can be realized. However, the silicon material has a large volume change due to charging / discharging, and the electrode material collapses and deteriorates by performing continuous charging / discharging. Therefore, there is a problem that the capacity retention rate is low when charging / discharging is repeated.
Therefore, carbon-silicon composite materials have also been studied (for example, see Patent Documents 1 to 4).

JP 2004-259475 A JP 2003-187798 A JP 2001-160392 A JP-A-2005-123175

However, even with these carbon-silicon composite materials, the problem of material deterioration due to the volume change of silicon contained therein has not been sufficiently solved.
The present invention has been made in view of the above circumstances, is suitable for an electrode material, and a carbon material capable of exhibiting a high capacity retention rate when used as an electrode material of a lithium ion secondary battery, the carbon It is an object of the present invention to provide a material manufacturing method, an electrode material using the carbon material, and a lithium ion secondary battery using the electrode material.

In order to solve the above problems, the present invention employs the following configuration.
That is, the first aspect of the present invention has an open cell hollow structure in which a large number of fine particles made of carbon are gathered and a plurality of pores connected to each other are formed in the gaps between the fine particles. A method for producing a carbon material , the step of preparing a composite material by blending one or both of silicon and silicon monoxide and one or both of transition metal chalcogenide and metal silicide, and a raw material for polymer particles And a step of preparing a monomer-containing mixture by mixing a monomer having a low compatibility with the polymer, an organic solvent having a low compatibility with the polymer, and the composite material, and adding the monomer-containing mixture to water. A step of preparing a suspension in which oil droplets of the monomer-containing mixture are dispersed by dispersing in a phase, and polymerizing the oil droplets in the suspension to prepare the polymer particles Possess a step, a step of firing the polymer particles, wherein the transition metal chalcogenide is molybdenum sulfide (IV), there with at least one member selected from the group consisting of copper (II) sulfide and titanium sulfide (IV) The metal silicide is molybdenum disilicide, the difference between the solubility parameter of the monomer and the solubility parameter of the polymer, and the difference between the solubility parameter of the organic solvent and the solubility parameter of the polymer. is 1.5 or more, into the hole, containing the composite material through the steps of the sintering is a manufacturing method of a carbon material, characterized in that to obtain a carbon material.
In the first aspect of the present invention , the composite material is obtained by dispersing one or both of silicon and silicon monoxide and one or both of transition metal chalcogenide and metal silicide in the presence of a solvent. The solid content of the resulting dispersion is preferred.

According to a second aspect of the present invention, there is provided a method for producing an electrode material comprising a step of blending the carbon material after obtaining the carbon material by the production method .
In a second aspect of the present invention, black lead, carbon black, to have at least one conductive additive is further compounded step selected from the group consisting of carbon nanotubes, graphene and fullerene preferred.
In a second aspect of the present invention, it is preferable to have a step of further mixing the bus Indah resin.

A third aspect of the present invention, the after obtaining an electrode material in the manufacturing process, a method for manufacturing a lithium ion secondary battery, characterized by Ru with the electrode material.

  According to the present invention, a carbon material that is suitable for an electrode material and can exhibit a high capacity retention rate when used as an electrode material of a lithium ion secondary battery, a method for producing the carbon material, and the carbon material The electrode material used and a lithium ion secondary battery using the electrode material can be provided.

It is a schematic diagram which shows one Embodiment of the carbon material of this invention.

  The present invention is a carbon material having an open cell hollow structure in which a large number of fine particles made of carbon are gathered and a plurality of pores connected to each other are formed in the gaps between the fine particles, And a step of preparing a composite material by blending one or both of silicon monoxide and one or both of transition metal chalcogenide and metal silicide, a raw material for polymer particles, and compatibility with the polymer A step of preparing a monomer-containing mixture by mixing a low monomer, an organic solvent having a low compatibility with the polymer, and the composite; and dispersing the monomer-containing mixture in an aqueous phase; Preparing a suspension in which oil droplets are dispersed; polymerizing oil droplets in the suspension to prepare the polymer particles; and Obtained by the method comprising the steps of forming, a, into the hole, a carbon material characterized by containing the composite material through the steps of the firing.

  As a result of detailed investigation of the structure of the carbon material of the present invention, one or both of silicon and silicon monoxide (hereinafter sometimes referred to as “silicon etc.”), which form an alloy with lithium, and transition metal chalcogenides And a composite material (hereinafter, also referred to as “composite material”) in which one or both of metal silicide and metal silicide (hereinafter sometimes referred to as “transition metal chalcogenide” or the like) are blended. It has been found that a plurality of fine particles are gathered and formed, and has a continuous cell hollow structure in which a plurality of holes connected to each other are formed in a gap between the fine particles. A schematic diagram illustrating the hollow cell structure is shown in FIG. The carbon material in this case is in the form of particles, and may be referred to as carbon particles hereinafter.

  The carbon material 1 of the present invention is formed by gathering a large number of fine particles 11 made of carbon, and a plurality of holes 12 connected to each other are formed in gaps between the fine particles 11. And the composite material 13 which passed through the baking process so that it may contact the fine particle 11 which consists of carbon in the some hole 12 connected mutually is contained.

  The carbon material of the present invention has such an open cell hollow structure, so that it can exhibit a high lithium occlusion / desorption capacity by containing a composite material, but has an excellent performance that it is not easily damaged even if continuous charge / discharge is performed. It is thought that can be demonstrated. Even in the carbon material of the present invention, a volume change of the composite material occurs when continuous charge and discharge are performed. However, it is thought that it does not reach the point of failure because it has a solid cell hollow structure that can disperse and absorb the stress due to the volume change.

  When the carbon material of the present invention is a particle, the lower limit of the average particle diameter is 10 nm, and the upper limit is 1 mm. When the average particle diameter is less than 10 nm, coalescence occurs during firing in producing the carbon material of the present invention, and it may be difficult to make a single particle. When the average particle diameter exceeds 1 mm, the electrode material may be molded. In some cases, it cannot be formed into a desired shape or size. The preferable lower limit of the average particle diameter is 1000 nm, and the preferable upper limit is 500 μm.

The preferable lower limit of the porosity of the carbon material of the present invention is 5%, and the preferable upper limit is 95%. When the porosity is less than 5%, the volume change of the composite material during continuous charge / discharge may not be sufficiently absorbed, and the carbon material may be easily damaged. In some cases, the strength of the steel becomes low, or the conductivity is lowered due to a small amount of carbon.
The porosity can be calculated by the Archimedes method, for example, from the specific gravity measured by a pycnometer true density measuring instrument or the like.

  The composite material is obtained by blending silicon and the like and transition metal chalcogenide and the like, for example, the solid content of the dispersion obtained by dispersing silicon and the transition metal chalcogenide and the like in the presence of a solvent. Can be used.

  By using silicon or the like in the composite material, the carbon material of the present invention has a high lithium storage / release capacity. In addition, it is considered that by using a transition metal chalcogenide in the composite material, the composite material further contributes to mitigating the influence of the volume change of the carbon material during continuous charge and discharge. Then, by using metal silicide in the composite material, the electrode using the carbon material of the present invention has excellent initial Coulomb efficiency. In the present invention, the “initial Coulomb efficiency” is the ratio of the amount of discharged electricity that can be taken out with respect to the initial amount of charged electricity ([discharge capacity (mAh) in the first cycle / charge capacity (mAh) in the first cycle)]. × 100 (%)).

Silicon or the like used for preparing the composite material is preferably in the form of powder, more preferably in the form of particles, and for example, the average particle size is preferably 300 nm or less. By using such fine powdery silicon or the like, a composite material can be obtained in which the effects of the present invention can be obtained more remarkably.
The average particle diameter of silicon or the like can be obtained, for example, by measuring the particle diameter of about 100 arbitrary particles of silicon or the like using an electron microscope and calculating the average value.
For example, silicon can be pulverized by a known method using a ball mill or the like to adjust the average particle diameter to a desired value.

The transition metal chalcogenide used for the preparation of the composite material has transition metal and chalcogen as constituent elements.
The transition metal is an element from Group 3 to Group 11 of the periodic table, preferably an element of the fourth period, the fifth period, or the sixth period, and is an element of the fourth period or the fifth period More preferably, molybdenum, copper, tungsten, titanium or iron is particularly preferable. That is, the transition metal chalcogenide is particularly preferably a chalcogenide of molybdenum, copper, tungsten, titanium, or iron.

  Chalcogen is an element belonging to Group 16 of the periodic table, and examples thereof include oxygen, sulfur, selenium, and tellurium. In the present invention, sulfur or oxygen is preferable, and sulfur is more preferable. That is, the transition metal chalcogenide is preferably a transition metal sulfide or oxide, and more preferably a transition metal sulfide.

Preferred transition metal chalcogenides include molybdenum sulfide (IV) (MoS ₂ ), copper sulfide (II) (CuS), tungsten sulfide (IV) (WS ₂ ), titanium sulfide (IV) (TiS ₂ ), iron sulfide ( II) (FeS) and iron disulfide (FeS ₂ ).
The transition metal chalcogenide is preferably one that can form a layered structure such as graphite between molecules.

  The transition metal chalcogenides may be used singly or in combination of two or more. When two or more are used in combination, the combination and ratio may be appropriately selected according to the purpose. .

The metal species constituting the metal silicide used for preparing the composite material is not particularly limited as long as it can constitute a silicide (silicide). Examples of the metal silicide include general formulas “ZSi ₂ ” and “ZSi”. "Or" Z ₂ Si "(wherein Z is a metal atom). Among them, metal silicides are molybdenum (Mo), tungsten (W), iron (Fe), titanium (Ti), chromium (Cr), nickel (Ni), tantalum (Ta), vanadium (V), cobalt (Co). ), Niobium (Nb), magnesium (Mg) or calcium (Ca) silicide, molybdenum disilicide (MoSi ₂ ), tungsten disilicide (WSi ₂ ), iron disilicide (FeSi ₂ ) , titanium disilicide (TiSi _2), disilicide chromium (CrSi _2), disilicide nickel (NiSi _2), the two tantalum silicide (TaSi _2), disilicide vanadium _(VSi 2), cobalt disilicide (CoSi ₂ ), niobium disilicide (NbSi ₂ ), magnesium disilicide (MgSi ₂ ) or calcium disilicide (CaS) i ₂ ) is more preferable, and molybdenum disilicide is particularly preferable.

  One kind of the metal silicide may be used alone, or two or more kinds thereof may be used in combination. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  In the composite material, the ratio (mixing ratio) of the total blending amount of transition metal chalcogenide and metal silicide in the total blending amount of silicon, silicon monoxide, transition metal chalcogenide and metal silicide is 5 to 70% by mass. Preferably, it is 10-60 mass%.

  In the present invention, when a transition metal chalcogenide and a metal silicide are used in combination, from the viewpoint of obtaining the effects of using these components more clearly, in the composite material, [mixing amount of transition metal chalcogenide]: [mixing of metal silicide] The ratio (mass ratio) of [amount] is preferably 20:80 to 80:20, and more preferably 35:65 to 65:35.

The solvent used for the preparation of the composite material (dispersion) is one that disperses or dissolves silicon or the like and transition metal chalcogenide or the like (dispersion medium), and can be arbitrarily selected according to the type of transition metal chalcogenide or the like, which is preferable. Examples thereof include water and organic solvents.
Preferred examples of the organic solvent used in the preparation of the composite material include alcohols such as methanol, ethanol, 1-propanol, and 2-propanol; N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), and the like. Examples thereof include linear or cyclic amides; and ketones such as acetone.
The said solvent used for preparation of the said composite material may be only 1 type, 2 or more types, and when it is 2 or more types, what is necessary is just to select the combination and ratio suitably according to the objective.

The composite material (dispersion) may be obtained by blending other components not corresponding to these (silicon, transition metal chalcogenide, etc. and solvent) other than silicon, transition metal chalcogenide, etc. and solvent. . The said other component in a composite material is not specifically limited, According to the objective, it can select arbitrarily.
In the case of blending other components, in the composite material, the ratio of the blending amount of other components to the total amount of the blending components excluding the solvent (mixing ratio) is preferably 5% by mass or less, and preferably 2% by mass or less. It is more preferable that

The dispersion can be obtained by mixing and dispersing silicon, transition metal chalcogenide, etc., a solvent, and other components as required.
Each component may be mixed and dispersed while sequentially adding these components, or all components may be added and then mixed and dispersed. The blended components are uniformly mixed and the dispersoid is uniformly dispersed. It only has to be done.
For example, at least a part of the solvent may be mixed in advance with one or more selected from the group consisting of silicon and the like, transition metal chalcogenides, and other components, and blended as a solution or dispersion of these components. Good. The total amount of the solvent used for preparing such a solution or dispersion may be sufficient.

  The mixing method of each component is not particularly limited as long as a dispersion is obtained. For example, a known method using a stirrer, a stirring blade, a ball mill, a stirrer, an ultrasonic disperser, an ultrasonic homogenizer, a revolving mixer, etc. Apply. A plurality of methods may be combined.

  The solid content may be taken out from the dispersion and dried, for example, at the time of producing the carbon material described later, and only this (solid content) may be used alone as a composite material. For example, the solid content may be taken out from the dispersion and used as a solvent. You may use as a composite material in the wet state in which a part of (dispersion medium) remained.

  The method for producing a carbon material of the present invention includes a step of preparing a composite material by blending silicon or the like and a transition metal chalcogenide, a raw material for polymer particles, and a monomer having low compatibility with the polymer, The step of preparing a monomer-containing mixture by mixing an organic solvent having a low compatibility with the composite material, dispersing the monomer-containing mixture in an aqueous phase, and dispersing the oil droplets in the monomer-containing mixture. A step of preparing a suspension, a step of polymerizing oil droplets in the suspension to prepare the polymer particles, and a step of firing the polymer particles.

  The step of preparing a composite material by blending silicon or the like and a transition metal chalcogenide or the like can be performed by the composite material preparation method described above.

It is preferable that the surface of the composite material is treated with a pigment dispersant. Dispersibility in the monomer-containing mixture is improved by treating the surface with a pigment dispersant.
Examples of the pigment dispersant include amide amine salts of high molecular weight polyester acids, acrylic polymers, aliphatic polycarboxylic acids, polyester amine salts, polyvinyl alcohol, polyvinyl pyrrolidone, and methylcellulose.
The pigment dispersant may be added to the monomer mixture together with the composite material.

In this specification, “low compatibility with a polymer” means that the difference between the solubility parameter (SP value) of the monomer or organic solvent and the solubility parameter (SP value) of the polymer is 1.5 or more. To do.
In the present specification, the solubility parameter (SP value) means a value calculated by the Fedors equation.

  The said monomer comprises the carbon component of the carbon material obtained by baking after superposition | polymerization. By using the monomer in combination with an organic solvent having low compatibility, the obtained carbon material is formed by gathering a large number of fine particles composed of carbon, and a plurality of carbon materials connected to each other in the gap between the fine particles. It has a continuous cell hollow structure in which the pores are formed.

  Examples of the monomer include divinylbenzene, vinyl chloride, acrylonitrile and the like.

The organic solvent serves as a hollow agent in the method for producing a carbon material of the present invention.
The organic solvent is selected appropriately according to the monomer. For example, when divinylbenzene is used as the monomer, examples thereof include linear hydrocarbons such as n-heptane, and alicyclic hydrocarbons such as cyclohexane.

  In the monomer-containing mixture, the preferable lower limit of the blending amount of the organic solvent with respect to 100 parts by mass of the monomer is 5 parts by mass, and the preferable upper limit is 125 parts by mass. If the blending amount of the organic solvent is less than 5 parts by mass, sufficient voids are not formed in the obtained carbon material, and the carbon material is damaged without being able to absorb the volume change of the composite material during continuous charge and discharge. May be easier. When the blending amount of the organic solvent exceeds 125 parts by mass, the strength of the obtained carbon material may be lowered, or it may be difficult to maintain the shape. The more preferable lower limit of the blending amount of the organic solvent is 10 parts by mass, and the more preferable upper limit is 120 parts by mass.

  In the monomer-containing mixture, a preferable lower limit of the amount of the composite material to 100 parts by mass of the monomer is 1 part by mass, and a preferable upper limit is 70 parts by mass. When the compounding amount of the composite material is less than 1 part by mass, a desired high-capacity negative electrode material cannot be obtained. When the compounding amount of the composite material exceeds 70 parts by mass, it becomes difficult to obtain voids necessary for expansion relaxation. The minimum with more preferable compounding quantity of the said composite material is 5 mass parts, and a more preferable upper limit is 60 mass parts.

The monomer-containing mixture preferably contains a polymerization initiator.
As said polymerization initiator, conventionally well-known polymerization initiators, such as an organic peroxide, an azo compound, a metal ion redox initiator, a photoinitiator, a persulfate, can be used, for example.
A necessary amount of the polymerization initiator in the monomer-containing mixture may be blended. However, if the amount of the polymerization initiator is too small, the monomer may not be sufficiently polymerized and particles may not be formed. If excessively added, the molecular weight will not increase, which may hinder post-treatment of the resulting carbon material. is there.

  The monomer-containing mixture may contain other additives as necessary. For example, you may further contain the at least 1 sort (s) of conductive support agent selected from the group which consists of graphite, carbon black, a carbon nanotube, graphene, and fullerene. By containing the conductive aid, the conductivity of the obtained carbon material can be further improved. Especially, when the said monomer containing mixture contains graphite, in addition to the role as a conductive support agent, the increase effect of discharge capacity can also be anticipated.

  Examples of the method for preparing the monomer-containing mixture include a method in which the monomer, the organic solvent, the composite material, and an additive to be added as necessary are mixed and ultrasonically dispersed.

The method for producing a carbon material of the present invention includes a step of dispersing the monomer-containing mixture in an aqueous phase to prepare a suspension in which oil droplets of the monomer-containing mixture are dispersed.
Examples of the aqueous medium constituting the aqueous phase include water, alcohol, and ketone.
The aqueous medium preferably contains a dispersant such as polyvinyl alcohol, methyl cellulose, polyvinyl pyrrolidone, insoluble inorganic fine particles, and a polymer surfactant.

As a method for preparing the suspension, for example, the monomer-containing mixture is added to an aqueous medium, and a stirrer such as a homogenizer, a static static mixer, an ultrasonic mixer, an ultrasonic homogenizer, a shirasu porous filter, a stirring blade, or the like. The method of stirring with is mentioned.
The particle diameter of the carbon particles obtained can be adjusted by controlling the size of the oil droplets of the monomer-containing mixture in the suspension according to the stirring conditions.

The method for producing a carbon material of the present invention includes a step of preparing the polymer particles by polymerizing oil droplets in the suspension.
Examples of the polymerization conditions when polymer particles are prepared by polymerizing the oil droplets include a method of stirring the suspension in a nitrogen stream at 30 to 95 ° C. for about 1 to 50 hours.
The obtained polymer particles are separated from the suspension, and subjected to subsequent steps through operations such as washing with water, drying, and classification.

The method for producing a carbon material of the present invention includes a step of firing the polymer particles.
What is necessary is just to select suitably the conditions of the said baking with a polymer particle. The firing temperature may be 1000 ° C. or lower, 1000 to 2500 ° C., or 2500 ° C. or higher.
When the firing temperature is 1000 ° C. or less, when the obtained carbon material is used for a lithium ion secondary battery electrode material, an extremely high lithium storage / release capacity can be exhibited, and a high output can be obtained. However, the output of the lithium ion secondary battery may become unstable.
When the firing temperature is 1000 to 2500 ° C., stable output characteristics and cycle life can be exhibited when the obtained carbon material is used as a lithium ion secondary battery electrode material. However, the lithium storage / release capacity becomes low, and a high-power lithium ion secondary battery may not be obtained.
When the firing temperature is 2500 ° C. or higher, when the obtained carbon material is used for a lithium ion secondary battery electrode material, an extremely high lithium storage / release capacity can be exhibited, and a high output can be obtained.

  The carbon material produced by the method for producing a carbon material of the present invention has a high lithium occlusion / release capacity as compared with a conventional carbon material composed of only carbon, and is excellent in that it is not easily damaged even if continuous charge / discharge is performed. Have good performance.

The electrode material of the present invention is characterized in that the carbon material of the present invention is blended.
In addition, the electrode material of the present invention is preferably one further blended with at least one conductive aid selected from the group consisting of graphite, carbon black, carbon nanotube, graphene and fullerene. By blending the conductive assistant, the conductivity of the electrode material of the present invention is further improved.

The electrode material of the present invention is preferably one further blended with a binder resin. The binder resin serves as a binder for bonding the carbon materials of the present invention, and plays the role of forming into an arbitrary shape. However, if a large amount of binder resin is added, the conductivity of the resulting electrode material may be reduced.
Examples of the binder resin include polyvinylidene fluoride and styrene butadiene rubber.

The electrode material of the present invention may be further blended with an organic solvent in order to facilitate molding described later.
The organic solvent may be any solvent that can dissolve the binder resin, and examples thereof include N-methylpyrrolidone and N, N-dimethylformamide.

  As a method for producing the electrode material of the present invention, for example, the carbon material of the present invention, a conductive additive, a binder resin, and an organic solvent are mixed to obtain a mixture, and then the mixture is molded. Methods and the like.

The lithium ion secondary battery of the present invention is characterized by using the electrode material of the present invention.
The lithium ion secondary battery of the present invention includes, for example, a negative electrode having a negative electrode active material layer formed using the electrode (negative electrode) material on a current collector (negative electrode current collector), a positive electrode, and an electrolysis And a liquid. Furthermore, a separator may be provided between the negative electrode and the positive electrode as necessary.
The lithium ion secondary battery of the present invention can have the same configuration as the conventional lithium ion secondary battery except that the negative electrode is used, and the negative electrode is a conventional one except that the electrode material is used. It can be set as the structure similar to a negative electrode.
The lithium ion secondary battery of the present invention exhibits a high capacity retention rate by using the electrode material.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to a following example.

Example 1
(1) Production of composite material 150 g of silicon scrap wafer (manufactured by Shin-Etsu Semiconductor Co., Ltd.) and a zirconia ball having a diameter of 20 nm are put into a dedicated zirconia container, and a planetary ball mill (Classic Line P-6, manufactured by Fritsch Japan) has a speed of 400 rpm. The silicon scrap wafer was coarsely pulverized under conditions of 30 minutes.
50 g of the coarsely pulverized silicon obtained, 50 g of molybdenum sulfide (IV) (Aldrich), 120 g of isopropyl alcohol and 1 mm diameter zirconia beads are placed in a special zirconia container, and a planetary ball mill (Classic Line P-6, manufactured by Fritsch Japan) ) At a speed of 400 rpm for 60 minutes to obtain a fine powdery composite isopropyl alcohol dispersion having an average particle size of about 200 nm.
The resulting isopropyl alcohol dispersion of the composite material was separated and collected by a centrifuge to obtain a composite material (isopropyl alcohol wet cake (solid content: 66%)).
(2) Production of carbon material As an oil phase component, 100 parts by mass of divinylbenzene as a monomer, 100 parts by mass of n-heptane as a hollow agent, 20 parts by mass of the composite material, and 5 parts by mass of polyvinylpyrrolidone are mixed, and ultrasonic waves are mixed. After the dispersion, an organic peroxide was further added as a polymerization initiator to prepare a monomer mixture. On the other hand, 500 parts by mass of pure water was mixed as an aqueous phase component, and 5 parts by mass of polyvinyl alcohol was mixed as a dispersant.
The obtained oil phase component and aqueous phase component were mixed and stirred and dispersed with a homogenizer to prepare a suspension. The resulting suspension was stirred and held at 80 ° C. for 12 hours under a nitrogen atmosphere to polymerize the particles. The obtained particles were washed, classified according to the particle size, and then dried to obtain composite material-encapsulating polymer particles.
The obtained polymer particles were heat-treated at 300 ° C. for 3 hours in an air atmosphere, and then calcined at 1000 ° C. for 3 hours in a nitrogen atmosphere to obtain a carbon material.
(3) Production of electrode material and negative electrode For 100 parts by mass of the obtained carbon material, 10 parts by mass of acetylene black (manufactured by Electrochemical Co., Ltd., HS-100) as a conductive additive and 10 parts by mass of polyvinylidene fluoride as a binder resin An electrode material was prepared by mixing N-methylpyrrolidone as an organic solvent.
The obtained electrode material was applied to one side of a copper foil having a thickness of 18 μm, dried, and then pressure-formed with a press roll to obtain a negative electrode sheet. The obtained negative electrode sheet was punched into a diameter of 16 mm to produce a negative electrode.

(Example 2)
The amount of coarsely ground silicon was changed to 80 g instead of 50 g, the amount of molybdenum sulfide (IV) was changed to 20 g instead of 50 g, and the amount of composite was changed to 12.5 parts by mass instead of 20 parts by mass. A negative electrode was produced in the same manner as Example 1 except for the above.

(Example 3)
A negative electrode was produced in the same manner as in Example 1 except that 50 g of copper sulfide (II) was used instead of 50 g of molybdenum sulfide (IV).

Example 4
A negative electrode was produced in the same manner as in Example 2 except that 20 g of copper (II) sulfide was used instead of 20 g of molybdenum sulfide (IV).

(Example 5)
A negative electrode was produced in the same manner as in Example 1 except that 50 g of titanium (IV) sulfide was used instead of 50 g of molybdenum sulfide (IV).

(Example 6)
A negative electrode was produced in the same manner as in Example 2 except that 20 g of titanium (IV) sulfide was used instead of 20 g of molybdenum sulfide (IV).

(Comparative Example 1)
A negative electrode was produced in the same manner as in Example 1 except that molybdenum (IV) sulfide was not used.

(Comparative Example 2)
A negative electrode was produced in the same manner as in Example 1 except that the composite material and polyvinylpyrrolidone were not used.

(Comparative Example 3)
10 parts by mass of acetylene black (manufactured by Denki Kagaku Co., HS-100) as a conductive auxiliary agent with respect to 100 parts by mass of graphite particles (manufactured by Wako Pure Chemical Industries, average particle size 20 μm, CV value 50% of particle size), 10 parts by mass of polyvinylidene fluoride as a binder resin and N-methylpyrrolidone as an organic solvent were mixed to prepare a mixed solution.
The obtained mixed liquid was applied to one side of a copper foil having a thickness of 18 μm, dried, and then pressure-formed with a press roll to obtain a negative electrode sheet. The obtained negative electrode sheet was punched into a diameter of 16 mm to produce a negative electrode.

(Comparative Example 4)
10 parts by mass of acetylene black (manufactured by Denki Kagaku Co., HS-100) as a conductive auxiliary agent for 100 parts by mass of activated carbon particles (Norit SX Plus, manufactured by Norit Japan Ltd., average particle size 160 μm, CV value 120% of particle size) A mixture was prepared by mixing 10 parts by mass of polyvinylidene fluoride as a binder resin and N-methylpyrrolidone as an organic solvent.
The obtained mixed liquid was applied to one side of a copper foil having a thickness of 18 μm, dried, and then pressure-formed with a press roll to obtain a negative electrode sheet. The obtained negative electrode sheet was punched into a diameter of 16 mm to produce a negative electrode.

(Comparative Example 5)
For 100 parts by mass of silicon powder (Aldrich, silicon powder), 10 parts by mass of acetylene black (HS-100, manufactured by Denki Kagaku) as a conductive additive, 10 parts by mass of polyvinylidene fluoride as a binder resin, and as an organic solvent N-methylpyrrolidone was mixed to prepare a mixed solution.
The obtained mixed liquid was applied to one side of a copper foil having a thickness of 18 μm, dried, and then pressure-formed with a press roll to obtain a negative electrode sheet. The obtained negative electrode sheet was punched into a diameter of 16 mm to produce a negative electrode.

(Comparative Example 6)
(1) Preparation of carbon particles having a solid structure As an oil phase component, 100 parts by mass of divinylbenzene as a monomer, 10 parts by mass of silicon particles (silicon nanopowder manufactured by Aldrich), and high molecular weight polyester acid salt 10 as a pigment dispersant After mixing parts by mass and ultrasonically dispersing, an organic peroxide was further added as a polymerization initiator to prepare a monomer mixture. As an aqueous phase component, 500 parts by mass of pure water and 5 parts by mass of polyvinyl alcohol as a dispersant were mixed and prepared.
The obtained oil phase component and aqueous phase component were mixed and stirred and dispersed with a homogenizer to prepare a suspension. The resulting suspension was stirred and held at 80 ° C. for 12 hours under a nitrogen atmosphere to polymerize the particles. The obtained particles were washed, classified according to the particle size, and then dried to obtain polymer particles having a solid structure without containing voids and containing silicon.
The obtained polymer particles were heat-treated at 300 ° C. for 3 hours in a nitrogen atmosphere, and then calcined at 1000 ° C. for 3 hours in a nitrogen atmosphere to obtain carbon particles containing silicon and having a solid structure.
The obtained carbon particles had an average particle diameter of 20 μm and a CV value of the particle diameter of 5%. The average particle size and CV value were determined by observing about 100 arbitrary particles using an electron microscope (S-4300SE / N, manufactured by Hitachi High-Technology Corporation).

(2) Production of negative electrode For 100 parts by mass of the obtained carbon particles, 10 parts by mass of carbon nanotubes (multi-walled carbon nanotubes manufactured by Showa Denko KK) as a conductive assistant, 10 parts by mass of polyvinylidene fluoride as a binder resin, organic solvent As a mixture, N-methylpyrrolidone was mixed to prepare a mixed solution.
The obtained mixed liquid was applied to one side of a copper foil having a thickness of 18 μm, dried, and then pressure-formed with a press roll to obtain a negative electrode sheet. The obtained negative electrode sheet was punched into a diameter of 16 mm to produce a negative electrode.

(Comparative Example 7)
(1) Preparation of silicon particles 150 g of silicon scrap wafer (manufactured by Shin-Etsu Semiconductor Co., Ltd.), φ20 mm zirconia balls are put into a special zirconia container, and 400 rpm for 30 minutes using a planetary ball mill (Fritsch Japan Co., Ltd., P-6). The silicon scrap wafer was coarsely pulverized under the conditions.
100 g of the coarsely pulverized silicon obtained, 120 g of isopropyl alcohol, and 550 g of φ1 mm zirconia beads are placed in a dedicated zirconia container and pulverized using a planetary ball mill (Fritsch Japan, P-6) at 400 rpm for 120 minutes. An isopropyl alcohol dispersion of silicon particles was obtained. The average particle diameter of the dispersed silicon particles was about 100 nm.
The resulting isopropyl alcohol dispersion of silicon particles was concentrated using a centrifuge to obtain silicon particles (isopropyl alcohol wet cake, solid content 66 mass%).

(2) Preparation of copper-plated silicon particles 25 g of the obtained silicon particles (isopropyl alcohol wet cake, solid content: 66% by mass) were put into 820 g of pure water and kept at 55 ° C. while ultrasonically dispersing and stirring. Thus, a silicon particle dispersion was prepared.
On the other hand, as a copper plating solution, 110 g of copper sulfate pentahydrate and 388 g of ethylenediaminetetraacetic acid tetrasodium salt tetrahydrate (EDTA · 4Na) were dissolved in 750 g of pure water and adjusted to pH 12 with 50% aqueous sodium hydroxide solution. And aged at 55 ° C. for 2 hours.
While stirring by ultrasonic dispersion, a copper plating solution was dropped into the silicon particle dispersion at a flow rate of 10 mL / min. After the entire amount was dropped, the dispersion was kept at 55 ° C. for 3 hours while stirring by ultrasonic dispersion to obtain a dispersion of copper-plated silicon particles.
The obtained copper-plated silicon particles are recovered by separating the particles with a centrifugal separator, ultrasonically cleaning once with pure water, then separating and recovering the particles with centrifugal separator, and ultrasonically cleaning once with isopropanol. Then, the particles were separated and collected by a centrifugal separator, replaced with toluene, and centrifuged, and then the supernatant was decanted to obtain copper-plated silicon particles (toluene wet cake, solid content 50%).
The obtained copper-plated silicon particles were dried and subjected to fluorescent X-ray analysis using an energy dispersive X-ray fluorescence analyzer “EDX-800HS” manufactured by Shimadzu Corporation. The element mass ratio was 40% for silicon. Copper was 60%.

(3) Production of carbon particles As oil phase components, 100 parts by mass of divinylbenzene as a monomer, 100 parts by mass of normal heptane as a hollow agent, 10 parts by mass of the obtained copper-plated silicon particles (in terms of solid content), polyvinylpyrrolidone 5 After mixing parts by mass and ultrasonically dispersing, an organic peroxide was further added as a polymerization initiator to prepare a monomer mixture. On the other hand, 500 parts by mass of pure water was mixed as an aqueous phase component, and 5 parts by mass of polyvinyl alcohol was mixed as a dispersant.
The obtained oil phase component and aqueous phase component were mixed and stirred and dispersed with a homogenizer to prepare a suspension. The resulting suspension was stirred and held at 80 ° C. for 12 hours under a nitrogen atmosphere to polymerize the particles. The obtained particles were washed, classified according to the particle size, and then dried to encapsulate copper-plated silicon particles, thereby obtaining polymer particles having an open cell hollow structure.
The obtained polymer particles were heat-treated at 300 ° C. for 3 hours in an air atmosphere, and then fired at 1000 ° C. for 3 hours in an argon-hydrogen (hydrogen 3%) atmosphere to enclose the copper-plated silicon particles, thereby forming a continuous cell hollow. Carbon particles having a structure were obtained.
(4) Production of negative electrode For 100 parts by mass of the obtained carbon particles, 10 parts by mass of acetylene black (manufactured by Denki Kagaku Co., HS-100) as a conductive auxiliary agent, 10 parts by mass of polyvinylidene fluoride as a binder resin, an organic solvent As a mixture, N-methylpyrrolidone was mixed to prepare a mixed solution.
The obtained mixed liquid was applied to one side of a copper foil having a thickness of 18 μm, dried, and then pressure-formed with a press roll to obtain a negative electrode sheet. The obtained negative electrode sheet was punched into a diameter of 16 mm to produce a negative electrode.

(Evaluation)
The negative electrodes obtained in Examples 1 to 6 and Comparative Examples 1 to 7 were evaluated as follows. The results are shown in Tables 1-2 below.
In Comparative Example 5, the evaluation was attempted but measurement was impossible.

(1) Production of Lithium Ion Secondary Battery A coin type model cell was produced using the negative electrodes obtained in Examples and Comparative Examples.
That is, a negative electrode and a counter electrode lithium metal having a diameter of 16 mm were laminated via a separator. After impregnating the separator with the electrolytic solution, these were caulked with an upper can and a lower can through a gasket. The upper can and the lower can were brought into contact with the negative electrode and the counter electrode lithium, respectively.
As the separator, a polyethylene microporous film having a thickness of 25 μm and a diameter of 24 mm was used. As the electrolyte, a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 2 was used, and LiPF ₆ was used as the electrolyte at a concentration of 1 mol. A solution dissolved so as to be / L was used.

(2) Discharge capacity, Coulomb efficiency Charge / discharge conditions were as follows: voltage and current were 0 at rest for 4 hours, voltage dropped to 0.002 V at a current corresponding to 1 C, and held for 3 hours to charge. After resting for 10 minutes, the battery was discharged at a current of 0.2 C until the voltage reached 3V. After resting for 10 minutes, this discharging was repeated. The charge / discharge capacity was determined from the amount of electricity applied during that time.
Further, as the coulomb efficiency (charge / discharge efficiency), the first cycle coulomb efficiency (initial coulomb efficiency) (%) and the second cycle coulomb efficiency (%) were calculated from the following equations. In this test, the process of occluding lithium in the negative electrode material was charged and discharged.
Initial coulomb efficiency (%)
= (Discharge capacity at the first cycle / Charge capacity at the first cycle) × 100
Second cycle coulomb efficiency (%)
= (Discharge capacity at the second cycle / Charge capacity at the second cycle) × 100

(3) Cycle characteristics The cycle was repeated 10 times, 20 times and 100 times, and the cycle characteristics were calculated using the following formula.
Capacity maintenance rate (%) from 2nd cycle to 10th cycle
= (Discharge capacity in the 10th cycle / Discharge capacity in the 2nd cycle) × 100
Capacity maintenance rate from the 2nd cycle to the 20th cycle (%)
= (Discharge capacity at 20th cycle / discharge capacity at 2nd cycle) × 100
Capacity maintenance rate from the 2nd cycle to the 100th cycle (%)
= (Discharge capacity at 100th cycle / Discharge capacity at 2nd cycle) × 100

As is clear from the above results, the coin-type cells using the negative electrodes of Examples 1 to 6 have a high initial discharge capacity, and the capacity up to the 100th cycle as compared with the coin-type cells of Comparative Examples 1 to 7. The maintenance rate was high.
From the above, it was confirmed that the coin-type cell using the negative electrode of the present invention was excellent in capacity retention rate.

(Example 7)
A negative electrode was produced in the same manner as in Example 1 except that 50 g of molybdenum disilicide was used instead of 50 g of molybdenum (IV) sulfide.

(Example 8)
A negative electrode was produced in the same manner as in Example 1 except that 50 g of coarsely pulverized silicon monoxide was used instead of 50 g of coarsely pulverized silicon, and 50 g of molybdenum disilicide was used instead of 50 g of molybdenum (IV) sulfide. The coarsely pulverized silicon monoxide was obtained in the same manner as the coarsely pulverized silicon. The same applies to the following embodiments.

Example 9
A negative electrode was produced in the same manner as in Example 1 except that 25 g of molybdenum sulfide (IV) and 25 g of molybdenum disilicide were used instead of 50 g of molybdenum sulfide (IV).

(Example 10)
Example 1 except that 50 g of coarsely pulverized silicon monoxide was used instead of 50 g of coarsely pulverized silicon, and 25 g of molybdenum (IV) sulfide and 25 g of molybdenum disilicide were used instead of 50 g of molybdenum (IV) sulfide. In addition, a negative electrode was produced.

(Example 11)
As in Example 1, except that 25 g of coarsely pulverized silicon and 25 g of coarsely pulverized silicon monoxide were used instead of 50 g of coarsely pulverized silicon, and 50 g of molybdenum disilicide was used instead of 50 g of molybdenum sulfide (IV). A negative electrode was produced.

(Example 12)
Except for using 25 g of coarsely pulverized silicon and 25 g of coarsely pulverized silicon monoxide instead of 50 g of coarsely pulverized silicon, and using 25 g of molybdenum (IV) sulfide and 25 g of molybdenum disilicide instead of 50 g of molybdenum (IV) sulfide. In the same manner as in Example 1, a negative electrode was produced.

(Evaluation)
About the negative electrode obtained in Examples 7-12, it evaluated similarly to the case of Examples 1-6. The results are shown in Table 3 below.

As is clear from the results, the coin-type cells using the negative electrodes of Examples 7 to 12 have a high initial discharge capacity, and the capacity up to the 100th cycle as compared with the coin-type cells of Comparative Examples 1 to 7. The maintenance rate was high.
From the above, it was confirmed that the coin-type cell using the negative electrode of the present invention was excellent in capacity retention rate.
Furthermore, the tendency for the initial Coulomb efficiency and the second cycle Coulomb efficiency to increase by using molybdenum disilicide was confirmed. This is apparent, for example, by comparing Examples 1, 7 and 9, Examples 8 and 10, and Examples 11 and 12, respectively.

  The present invention can be used in the field of lithium ion secondary batteries.

DESCRIPTION OF SYMBOLS 1 Carbon material 11 Fine particle 12 which consists of carbon The some hole 13 mutually connected 13 The composite which passed through the baking process

Claims (6)

A method for producing a carbon material having a continuous cell hollow structure in which a large number of fine particles made of carbon are gathered and a plurality of pores connected to each other are formed in the gaps between the fine particles,
Blending one or both of silicon and silicon monoxide and one or both of transition metal chalcogenides and metal silicides to prepare a composite;
A step of preparing a monomer-containing mixture by mixing a monomer that is a raw material of polymer particles and has a low compatibility with the polymer, an organic solvent with a low compatibility with the polymer, and the composite;
Dispersing the monomer-containing mixture in an aqueous phase to prepare a suspension in which oil droplets of the monomer-containing mixture are dispersed;
Polymerizing oil droplets in the suspension to prepare the polymer particles;
Firing the polymer particles;
I have a,
The transition metal chalcogenide is at least one selected from the group consisting of molybdenum (IV) sulfide, copper (II) sulfide and titanium (IV) sulfide;
The metal silicide is molybdenum disilicide;
The difference between the solubility parameter of the monomer and the solubility parameter of the polymer, and the difference between the solubility parameter of the organic solvent and the solubility parameter of the polymer is 1.5 or more,
A method for producing a carbon material , comprising: obtaining a carbon material containing the composite material that has undergone the firing step in the hole. The composite material is a solid content of a dispersion obtained by dispersing one or both of silicon and silicon monoxide and one or both of transition metal chalcogenide and metal silicide in the presence of a solvent. The method for producing a carbon material according to claim 1 . After obtaining a carbon material in the production method according to claim 1 or 2, the manufacturing method of an electrode material and a step of blending the carbon material. Graphite, carbon black, carbon nanotubes, a manufacturing method of an electrode material according to claim 3, characterized in that it comprises at least one conductive additive further step of compounding selected from the group consisting of graphene, and fullerenes. The method for producing an electrode material according to claim 3 or 4 , further comprising a step of further blending a binder resin. After obtaining an electrode material in a process according to any one of claims 3-5, method for producing a lithium ion secondary battery, characterized in that Ru using the electrode material.

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