JP2011048992A - Carbon material, electrode material, and lithium ion secondary battery negative electrode material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon material which is suitable as a lithium ion secondary battery negative electrode material and can exhibit high lithium storage/release capacity. <P>SOLUTION: The carbon material contains metal doped carbon particles containing metal particles made of metal to form an alloy with lithium. In the metal particles made of metal to form the alloy with lithium, the content of an oxygen atom inside portion by 10 nm from a surface in the thickness direction is 10 wt.% or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a carbon material which is suitable as a negative electrode material for a lithium ion secondary battery and can exhibit a high lithium storage / release capacity.

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, a negative electrode material having a larger lithium storage / release capacity is required.

On the other hand, attempts have been made to improve the lithium storage / release capacity by combining a carbon material having a low charge / discharge capacity with metal particles made of a metal that forms an alloy with lithium such as silicon.
For example, Patent Document 1 discloses a carbonaceous particle for a lithium secondary battery negative electrode comprising silicon-containing carbonaceous particles and a substantially silicon-free carbonaceous layer covering the silicon-containing carbonaceous particles. ing. Patent Document 2 discloses a negative electrode material for a lithium secondary battery that includes Si particles having an average particle size (D50) of 0.05 to 5 μm and a plurality of types of carbonaceous materials, and has an oxygen content of 5% by weight or less. Is disclosed. Further, Patent Document 3 discloses particles composed of graphite, carbon obtained by firing a carbon precursor, one or more of carbon, silicon, a silicon compound, or a silicon alloy, carbon black, and voids. A negative electrode active material for a lithium ion secondary battery is disclosed which is made of graphite and is made of roughly spherical particles having an aspect ratio of 1 to 2.

However, even if these carbon materials, which are composed of metal particles that form an alloy with lithium such as silicon, are used, the lithium ion secondary battery actually has a very low lithium storage / release capacity compared to the theoretical value. There was a problem that only a negative electrode material was obtained.

JP 2001-345100 A JP 2008-1112710 A JP 2008-186732 A

An object of the present invention is to provide a carbon material that is suitable as a negative electrode material for a lithium ion secondary battery and can exhibit a high lithium storage / release capacity.

The present invention is a carbon material containing metal-encapsulated carbon particles containing metal particles made of metal that forms an alloy with lithium, the metal particles made of metal that forms an alloy with lithium in the thickness direction from the surface. It is a carbon material in which the content of oxygen atoms in the 10 nm inner portion is 10% by weight or less.
The present invention is described in detail below.

The present inventor has proposed that a negative electrode material for a lithium ion secondary battery using a carbon material in which metal particles made of metal that forms an alloy with lithium such as silicon (hereinafter also simply referred to as “metal particles”) is used. The reason why only a very low lithium storage / release capacity was obtained compared to the above value was investigated. As a result, it has been found that in the conventional carbon material, the surface of the metal particles is oxidized, and as a result, the original lithium occlusion ability of the metal that forms an alloy with lithium is not exhibited. As a result of further studies, it was found that by performing reduction firing to reduce the content of oxygen atoms on the surface of the metal particles to a certain level or less, a high lithium storage / release capacity close to the theoretical value can be exhibited, and the present invention was completed. .

The carbon material of the present invention contains metal-containing carbon particles containing metal particles made of a metal that forms an alloy with lithium.
Examples of the metal that forms an alloy with lithium include silicon, tin, magnesium, titanium, vanadium, cadmium, selenium, iron, cobalt, nickel, manganese, platinum, and boron. Among these, silicon or tin is preferable because silicon can exhibit a particularly high lithium storage / release capacity, and silicon is more preferable.

The particle diameter of the metal particles is not particularly limited, but a preferred lower limit is 10 nm and a preferred upper limit is 10 μm. If the lower limit of the particle size of the metal particles is less than 10 nm, it may be difficult to contact the metal particles with the carbon component in the carbon material, resulting in poor conductivity. If the particle size exceeds 10 μm, the metal particles in the carbon material It may be difficult to include.

The metal particles have an oxygen atom content of 10% by weight or less in the 10 nm inner portion in the thickness direction from the surface. When the content of the oxygen atom exceeds 10% by weight, a high lithium storage / release capacity cannot be exhibited. The upper limit with preferable content of the said oxygen atom is 10 weight%, and a more preferable upper limit is 7 weight%.
The content of oxygen atoms in the inner portion of 10 nm in the thickness direction from the surface of the metal particles is, for example, by embedding the metal-encapsulated carbon particles with an epoxy resin and depositing carbon, and then using a focused ion beam (FIB). A sample is prepared by cutting, and the cross section of the metal particle in the sample can be measured by elemental analysis using a field emission analytical transmission electron microscope (FE-TEM / EDS).

The minimum with preferable content of the said metal particle in the said metal inclusion carbon particle is 1 weight%. When the content of the metal particles is less than 1% by weight, a high lithium storage / release capacity may not be exhibited. A more preferable lower limit of the content of the metal particles is 5% by weight.
The upper limit of the content of the metal particles is not particularly limited. The higher the amount of the metal particles, the higher the lithium storage / release capacity. However, if the content of the metal particles is too large, the carbon material is likely to be damaged due to a volume change of the metal particles during continuous charge and discharge. The upper limit with preferable content of the said metal particle is 95 weight%.

The metal-encapsulated carbon particles may be metal-encapsulated solid carbon particles having no voids inside, or metal-encapsulated hollow carbon particles having voids inside.
When the metal-encapsulated carbon particles are metal-encapsulated solid carbon particles, a high-strength electrode material or the like can be obtained.
When the metal-encapsulated carbon particles are metal-encapsulated hollow carbon particles, a lightweight carbon material can be obtained. Moreover, even if a metal particle changes in volume at the time of continuous charging / discharging, the outstanding effect that a carbon material cannot be damaged easily can also be exhibited. In the metal-encapsulated hollow carbon particles, the metal particles may be contained in the matrix part or in the void part.

When the metal-encapsulated carbon particles are metal-encapsulated hollow carbon particles, the voids present inside the metal-encapsulated hollow carbon particles may be single holes (hereinafter also referred to as “metal-encapsulated single-hole hollow carbon particles”). .), Even if it is a plurality of independent holes (hereinafter also referred to as “metal-containing porous hollow carbon particles”), a plurality of holes connected to each other (hereinafter also referred to as “metal-encapsulating hollow cell carbon particles”). It may be.
The above-mentioned metal-encapsulated continuous hollow carbon particles include those having a plurality of pores connected to each other at the molecular level as a result of the density of the matrix portion being reduced.

A schematic diagram for explaining the structure of the metal-encapsulated single-hole hollow carbon particles is shown in FIG.
FIG. 1 (a) is an example in which metal particles are contained in voids in metal-containing single-hole hollow carbon particles. The metal-encapsulated single-hole hollow carbon particle 1 includes a matrix 11 made of carbon and a single hole 12 formed inside the matrix 11. And the metal particle 13 is contained inside the single hole 12 formed inside so that the matrix 11 may be contacted.
FIG.1 (b) is an example in which metal particles are contained in the matrix portion in the metal-containing single-hole hollow carbon particles. The metal-encapsulated single-hole hollow carbon particle 1 includes a matrix 11 made of carbon and a single hole 12 formed inside the matrix 11. The metal particles 13 are contained in the matrix 11 made of carbon.

A schematic diagram illustrating the structure of the metal-encapsulated porous hollow carbon particles is shown in FIG.
FIG. 2 (a) is an example in which metal particles are contained in the voids in the metal-containing porous hollow carbon particles. The metal-encapsulated porous hollow carbon particle 2 includes a matrix 21 made of carbon and a plurality of independent holes 22 formed therein. And the metal particle 23 is contained inside the some independent hole 22 formed in the inside so that the matrix 21 which consists of carbon may be contacted.
FIG. 2B shows an example in which metal particles are contained in the matrix portion of the metal-containing porous hollow carbon particles. The metal-encapsulated porous hollow carbon particle 2 includes a matrix 21 made of carbon and a plurality of independent holes 22 formed therein. The metal particles 23 are contained in the matrix 21 made of carbon.

FIG. 3 shows a schematic diagram for explaining the structure of the above metal-encapsulating solid cell hollow carbon particles.
FIG. 3A shows an example in which metal particles are contained in the voids in the metal-encapsulating biliary hollow carbon particles. The metal-encapsulating continuous hollow carbon particles 3 are formed by gathering a large number of fine grains (matrix made of carbon) 31, and a plurality of holes 32 are formed in the gaps between the grains 31. And the metal particle 33 is contained inside the some hole 32 connected mutually so that the fine grain (matrix which consists of carbon) 31 may be contacted.
FIG.3 (b) is an example in which metal particles are contained in the matrix part in the metal-encapsulating continuous cell hollow carbon particles. The metal-encapsulating continuous hollow carbon particles 3 are formed by gathering a large number of fine grains (matrix made of carbon) 31, and a plurality of holes 32 are formed in the gaps between the grains 31. In addition, fine particles (matrix made of carbon) 31 contain metal particles 33.

The metal-encapsulated carbon particles preferably contain at least one conductive aid selected from the group consisting of graphite, carbon black, carbon nanotubes, graphene, and fullerene. By containing the conductive aid, the conductivity of the carbon material of the present invention can be further improved. Especially, when the said metal inclusion carbon particle contains graphite, in addition to the role as a conductive support agent, the increase effect of discharge capacity can also be anticipated.

The particle diameter of the metal-encapsulated carbon particles is not particularly limited, but a preferred lower limit is 10 nm and a preferred upper limit is 1 mm. When the particle diameter of the metal-encapsulated carbon particles is less than 10 nm, coalescence occurs during firing when producing the metal-encapsulated carbon particles, and it may be difficult to make a single particle. When forming into a desired shape and size, it may not be possible. The minimum with a more preferable particle diameter of the said metal inclusion carbon particle is 1 micrometer, and a more preferable upper limit is 500 micrometers.

In the metal-encapsulated carbon particles, the preferable upper limit of the CV value of the particle diameter is 10%. When the CV value of the particle diameter exceeds 10%, the variation between lots of the obtained carbon material may increase. A more preferable upper limit of the CV value of the particle diameter is 7%.

The metal-encapsulated carbon particles may be a mixture of two or more types of metal-encapsulated carbon particles having different particle size distributions. By using a combination of two or more kinds of metal-encapsulated carbon particles having different particle size distributions, metal-encapsulated carbon particles having a small particle size are arranged in the gaps between the metal-encapsulated carbon particles having a large particle size, and the overall is highly packed. Therefore, the conductivity of the carbon material of the present invention is improved.

The method for producing the metal-encapsulated carbon particles is not particularly limited, and the metal-encapsulated resin particles can be produced by a conventionally known method such as firing after preparing the metal-encapsulated resin particles.
However, in order to make the content of oxygen atoms in the inner portion of 10 nm in the thickness direction from the surface of the metal particles in the obtained carbon material 10 wt% or less, it is important to perform reduction firing.
Reduction firing means reaction firing while reducing oxygen atoms that oxidize the metal particles with a reducing substance, or reaction firing and carbonization firing. In an air atmosphere or a nitrogen atmosphere. It is clearly distinguished from general firing performed in (hereinafter also referred to as “normal firing”). In the reduction firing, for example, firing is performed at a temperature of 500 to 3000 ° C. in an atmosphere of 97% nitrogen volume and 3% hydrogen volume.
When the metal-encapsulated resin particles are fired to produce the metal-encapsulated carbon particles, only the reduction firing may be performed, or the normal firing may be performed and then the reduction firing may be performed.

The carbon material of the present invention preferably further contains at least one conductive additive selected from the group consisting of graphite, carbon black, carbon nanotubes, graphene, and fullerene. By mix | blending the said conductive support agent, the electroconductivity of the carbon material of this invention can be improved more.

A preferable lower limit of the blending amount of the conductive assistant is 1% by weight, and a preferable upper limit is 90% by weight. If the blending amount of the conductive aid is less than 1% by weight, a sufficient conductivity improving effect may not be obtained, and if it exceeds 90% by weight, the lithium storage capacity may be lowered.
In addition, when the said conductive support agent is mix | blended to some extent, the role of the binder which couple | bonds the said metal inclusion carbon particle can also be exhibited. In the case where the conductive auxiliary agent functions as a binder, it is not necessary to use a binder resin described later, and higher conductivity can be exhibited.

The carbon material of the present invention may further contain a binder resin. Since the binder resin serves as a binder for bonding the metal-encapsulated carbon particles, the moldability of the carbon material is improved. However, if a large amount of binder resin is added, the conductivity of the resulting carbon material may be reduced.
Examples of the binder resin include fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene, and styrene butadiene rubber.

Examples of the method for producing the carbon material of the present invention include a method in which the metal-encapsulated carbon particles, the conductive additive, and the binder resin are mixed to obtain a mixture and then molded.
The mixture may contain an organic solvent so that it can be easily molded.
The organic solvent is not particularly limited as long as it can dissolve the binder resin, and examples thereof include N-methylpyrrolidone and N, N-dimethylformamide.

The carbon material of the present invention contains the metal particles. Since the content of oxygen atoms on the surface of the metal particles is below a certain level, if this is used as a negative electrode material for a lithium ion secondary battery, a high lithium storage / release capacity close to the theoretical value can be exhibited.
The carbon material of the present invention can be suitably used as an electrode material, particularly a lithium ion secondary battery negative electrode material. Moreover, it can use suitably also for the electrode material for electric double layer capacitors, and the electrode material for capacitors.

ADVANTAGE OF THE INVENTION According to this invention, it is suitable as a lithium ion secondary battery negative electrode material, and can provide the carbon material which can exhibit high lithium occlusion / release capacity | capacitance.

It is a schematic diagram explaining the structure of a metal inclusion single-hole hollow carbon particle. It is a schematic diagram explaining the structure of a metal inclusion porous hollow carbon particle. It is a schematic diagram explaining the structure of a metal inclusion encysted hollow carbon particle.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
(1) Preparation of metal-encapsulated continuous hollow carbon particles As oil phase components, 100 parts by weight of divinylbenzene as a monomer, 100 parts by weight of normal heptane as a hollow agent, silicon particles as metal particles (manufactured by Aldrich, Silicon Nano Powder, average particle diameter 50 nm) 5 parts by weight and polyvinyl pyrrolidone 5 parts by weight were mixed and ultrasonically dispersed, and then an organic peroxide was added as a polymerization initiator to prepare a monomer mixture. On the other hand, 500 parts by weight of pure water as a water phase component and 5 parts by weight of polyvinyl alcohol as a dispersant were mixed.
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 nitrogen reflux to polymerize the particles. The obtained particles were washed, classified according to the particle size, and then dried to obtain metal-encapsulated reticulated hollow resin particles.

The obtained metal-encapsulated solid cell hollow resin 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. Thereafter, reduction firing was further performed at 600 ° C. for 6 hours in an atmosphere with a nitrogen volume of 97% and a hydrogen volume of 3%, thereby obtaining metal-encapsulated continuous hollow carbon particles.
The average particle diameter and the CV value of the particle diameter are obtained by observing about 100 arbitrary particles using an electron microscope (S-4300SE / N, manufactured by Hitachi High-Technology Corporation) for the obtained metal-encapsulated continuous hollow carbon particles. As a result, the average particle size was 20 μm, and the CV value of the particle size was 5%.

(2) Production of Carbon Material 10 parts by weight of carbon black (manufactured by Mitsubishi Chemical Corporation, # 3230B) as a conductive auxiliary agent and 10 parts of polyvinylidene fluoride as a binder resin with respect to 100 parts by weight of the obtained metal-encapsulated continuous hollow carbon particles A mixed solution was prepared by mixing N-methylpyrrolidone as an organic solvent by weight.
The obtained mixed liquid was applied to one side of a Cu 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 14 mm to produce a carbon material.

(3) Production of Lithium Ion Secondary Battery A coin-type model cell was produced using the obtained carbon material as a negative electrode material for a lithium ion secondary battery.
That is, a lithium ion secondary battery negative electrode material 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.

(Example 2)
In the oil phase component, the compounding amount of silicon particles (silicon nanopowder manufactured by Aldrich) as metal particles was changed to 10 parts by weight, the compounding amount of polyvinylpyrrolidone was changed to 10 parts by weight, and graphite (manufactured by SEC Carbon Co., SNO. -3) Metal-encapsulated continuous hollow carbon particles were prepared in the same manner as in Example 1 except that 10 parts by weight and 1 part by weight of a pigment dispersant were added, and a carbon material and a lithium ion secondary battery were produced. .
The obtained metal-encapsulated solid cell hollow carbon particles had an average particle size of 20 μm and a particle size CV value of 5%.

(Example 3)
The same baking method as in Example 2 except that after heat treatment at 300 ° C. for 3 hours in the air atmosphere, reduction firing was further performed at 1000 ° C. for 3 hours in an atmosphere of 97% nitrogen volume and 3% hydrogen volume. Thus, a metal-encapsulating continuous cell hollow carbon particle was prepared, and a carbon material and a lithium ion secondary battery were produced.
The obtained metal-encapsulated solid cell hollow carbon particles had an average particle size of 20 μm and a particle size CV value of 5%.

Example 4
In the oil phase component, the metal was prepared in the same manner as in Example 1 except that the amount of silicon particles (silicon nanopowder manufactured by Aldrich) was changed to 20 parts by weight and the amount of polyvinylpyrrolidone was changed to 20 parts by weight. The encapsulated biliary hollow carbon particles were prepared, and a carbon material and a lithium ion secondary battery were produced.
The obtained metal-encapsulated solid cell hollow carbon particles had an average particle size of 20 μm and a particle size CV value of 5%.

(Example 5)
A stainless steel ball (diameter: 10 mm) is put into a stainless steel container (volume: 80 mL), 10 parts by weight of polybutyl acrylate, 90 parts by weight of polystyrene, 10 parts by weight of silicon particles (silicon nanopowder manufactured by Aldrich), and 80 parts by weight of graphite particles. After purging with argon gas, sealing, sealing, and mechanically alloying with planetary ball mill (P-6, manufactured by German Fritsch) for 10 hours at 400 min ⁻¹ , pulverization and classification, and metal-encapsulated resin particles Got.
The obtained metal-encapsulated resin particles were reduced and fired at 370 ° C. for 2 hours in an atmosphere with a nitrogen volume of 97% and a hydrogen volume of 3% to obtain metal-encapsulated carbon particles.
A carbon material and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the obtained metal-encapsulated carbon particles were used.

(Example 6)
As an oil phase component, 10 parts by weight of butyl acrylate as a monomer, 90 parts by weight of polystyrene, 10 parts by weight of silicon particles (silicon nanopowder manufactured by Aldrich), 80 parts by weight of graphite particles, and 5 parts by weight of polyvinylpyrrolidone are mixed. After sonic dispersion, an organic peroxide was further added as a polymerization initiator to prepare a mixed solution. On the other hand, 500 parts by weight of pure water as a water phase component and 5 parts by weight of polyvinyl alcohol as a dispersant were mixed.
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 nitrogen reflux to polymerize the particles. The obtained particles were washed, classified according to the particle size, and then dried to obtain metal-containing resin particles.
The obtained metal-encapsulated resin particles were reduced and fired at 370 ° C. for 2 hours in an atmosphere with a nitrogen volume of 97% and a hydrogen volume of 3% to obtain metal-encapsulated carbon particles.
A carbon material and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the obtained metal-encapsulated carbon particles were used.

(Example 7)
Coal tar pitch 50 parts by weight, silicon particles (Aldrich silicon nanopowder) 10 parts by weight, high molecular weight polyester acid salt 10 parts by weight, graphite particles 40 parts by weight, methylnaphthalene 40 parts by weight using a biaxial heating kneader. After mixing at 100 ° C. for 1 hour, methyl naphthalene was evaporated at 200 ° C. Next, this was calcined at 1000 ° C. for 3 hours in a nitrogen atmosphere and then crushed to obtain particles. The obtained particles were further reduced and fired at 600 ° C. for 6 hours in an atmosphere of 97% nitrogen volume and 3% hydrogen volume to obtain metal-encapsulated carbon particles.
A carbon material and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the obtained metal-encapsulated carbon particles were used.

(Example 8)
Coal tar pitch 50 parts by weight, silicon particles (Aldrich silicon nanopowder) 10 parts by weight, high molecular weight polyester acid salt 10 parts by weight, graphite particles 40 parts by weight, methylnaphthalene 40 parts by weight using a biaxial heating kneader. After mixing at 100 ° C. for 1 hour, methyl naphthalene was evaporated at 200 ° C. Next, after reducing and firing at 1000 ° C. for 3 hours in an atmosphere with a nitrogen volume of 97% and a hydrogen volume of 3%, it was crushed to obtain metal-encapsulated carbon particles.
A carbon material and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the obtained metal-encapsulated carbon particles were used.

(Comparative Example 1)
In the same manner as in Example 1 except that the firing method was heat-treated at 300 ° C. for 3 hours in an air atmosphere and then further fired at 1000 ° C. for 3 hours in a nitrogen atmosphere. Particles were prepared to produce a carbon material and a lithium ion secondary battery.

(Comparative Example 2)
In the same manner as in Example 2, except that the firing method was heat-treated at 300 ° C. for 3 hours in an air atmosphere and then further fired at 1000 ° C. for 3 hours in a nitrogen atmosphere. Particles were prepared to produce a carbon material and a lithium ion secondary battery.

(Comparative Example 3)
In the same manner as in Example 4, except that the firing method was heat-treated at 300 ° C. for 3 hours in an air atmosphere and then further fired at 1000 ° C. for 3 hours in a nitrogen atmosphere. Particles were prepared to produce a carbon material and a lithium ion secondary battery.

(Comparative Example 4)
A metal-encapsulated carbon particle was prepared by the same method as in Example 5 except that the firing method was performed by heat treatment at 300 ° C. for 2 hours in a nitrogen atmosphere, and a carbon material and a lithium ion secondary battery were produced. did.

(Comparative Example 5)
A metal-encapsulated carbon particle was prepared by the same method as in Example 6 except that the firing method was heat treatment at 370 ° C. for 2 hours in a nitrogen atmosphere, and a carbon material and a lithium ion secondary battery were produced. did.

(Comparative Example 6)
Metal-encapsulated carbon particles were prepared in the same manner as in Example 7 except that reduction firing was not performed, and a carbon material and a lithium ion secondary battery were produced.

(Evaluation)
The metal-encapsulated carbon particles, carbon material, and lithium ion secondary battery obtained in the examples and comparative examples were evaluated as follows.
The results are shown in Tables 1 and 2.

(1) Measurement of the content of oxygen atoms on the surface of metal particles The obtained metal-encapsulated carbon particles were embedded in an epoxy resin, and after vapor deposition of carbon, a sample was prepared by cutting with a focused ion beam (FIB). About the cross section of the metal particle in the sample, the content of oxygen atoms in the inner portion of 10 nm in the thickness direction from the surface of the metal particle was measured by elemental analysis using a field emission analytical transmission electron microscope (FE-TEM / EDS). .

(2) Initial discharge capacity and initial charge / discharge efficiency The obtained lithium ion secondary battery was allowed to stand for 8 hours in a state where voltage and current were zero. After standing, the voltage first dropped to 0.002 V at a current corresponding to 0.2 C, then held for 3 hours and charged. Next, after resting for 10 minutes, the battery was discharged at a current of 0.2 C until the voltage reached 1.2V. The initial discharge capacity was determined from the amount of energization in this charge and discharge cycle (first cycle). Further, the initial charge / discharge efficiency was calculated from the following formula. In this test, the process of occluding lithium in the carbon material was charged and the process of detaching was defined as discharge.
Initial charge / discharge efficiency (%) = (first cycle discharge capacity / first cycle charge capacity) × 100

(3) Capacity maintenance rate at the 10th cycle Furthermore, the cycle of charging and discharging was repeated 10 times with a pause of 10 minutes, and the capacity maintenance rate (%) at the 10th cycle was calculated using the following formula.
10th cycle capacity retention rate (%) = (discharge capacity in the 10th cycle / discharge capacity in the 1st cycle) × 100

ADVANTAGE OF THE INVENTION According to this invention, it is suitable as a lithium ion secondary battery negative electrode material, and can provide the carbon material which can exhibit high lithium occlusion / release capacity | capacitance.

DESCRIPTION OF SYMBOLS 1 Metal inclusion | inner_cover single-hole hollow carbon particle 11 Carbon matrix 12 Single hole 13 Metal particle | grains which form metal which forms an alloy with lithium 2 Metal inclusion | inner_cover hollow carbon particle 21 Carbon matrix 22 Independent several hole 23 Lithium Particles made of metal that form an alloy with metal 3 Metal-encapsulating solid cell hollow carbon particles 31 Fine grain (matrix made of carbon)
32 A plurality of holes 33 connected to each other 33 Metal particles made of metal forming an alloy with lithium

Claims (8)

A carbon material containing metal-containing carbon particles containing metal particles made of a metal that forms an alloy with lithium,
The metal particle comprising a metal that forms an alloy with lithium is a carbon material characterized in that the content of oxygen atoms in the inner portion of 10 nm in the thickness direction from the surface is 10% by weight or less. The carbon material according to claim 1, wherein the metal-encapsulating carbon particles have a metal particle content of 1 to 95% by weight made of a metal that forms an alloy with lithium. The carbon material according to claim 1 or 2, wherein the metal that forms an alloy with lithium is silicon. The carbon material according to claim 1, 2 or 3, wherein the metal-encapsulated carbon particles contain at least one conductive aid selected from the group consisting of graphite, carbon black, carbon nanotube, graphene, and fullerene. . The carbon material according to claim 1, further comprising a binder resin. 6. The carbon material according to claim 1, further comprising at least one conductive aid selected from the group consisting of graphite, carbon black, carbon nanotube, graphene, and fullerene. An electrode material using the carbon material according to claim 1, 2, 3, 4, 5 or 6. A lithium ion secondary battery negative electrode material comprising the carbon material according to claim 1, 2, 3, 4, 5 or 6.

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