JP2014177389A - Lithium battery electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nano-carbon material composite in which it is difficult for the nano-carbon material to aggregate, and a Li ion battery active material and a method for producing nano-carbon material composite.SOLUTION: A nano-carbon material composite 1 is formed of Si fine particles 3 included in voids 2a of aegagropila-like carbon 2 in which a fibrous nano-carbon material 2b is radially formed from oxidation diamond catalyst fine particle 4 as core. The diameter of the aegagropila-like carbon 2 preferably is in a range of 1 μm to 100 μm and the Si fine particle 3 is polycrystalline. The nano-carbon material composite 1 comprises a step of forming aegagropila-like carbon 2 in which a fibrous nano-carbon material 2b is radially formed from oxidation diamond catalyst fine particle 4 as core, and a step of receiving the aegagropila-like carbon 2 in a reaction tank and evacuating the reaction tank, followed by crystallizing out Si fine particles 3 in voids 2a of the aegagropila-like carbon 2.

Description

  The present invention relates to a nanocarbon material composite and an active material for a Li-ion battery, and further to a method for producing a nanocarbon material composite. More specifically, the present invention relates to a nanocarbon material composite in which Si fine particles are encapsulated in a void of marimocarbon, an active material for a Li ion battery using the same, and a method for producing the nanocarbon material composite.

  In recent years, electrode materials for lithium ion batteries have been studied. Carbon is generally used as the material for the negative electrode of current lithium ion batteries, and the theoretical capacity is 370 mAh / g. In order to obtain a larger theoretical capacity, materials for negative electrodes of lithium ion batteries have been studied.

  The theoretical capacity when Si (silicon) is used for the negative electrode of a lithium ion battery (see Non-Patent Document 1) is expected to be at least four times that of when carbon is used for the negative electrode, at least 1500 mAh / g. Has been. A negative electrode made of Si is called a Si negative electrode.

  However, charging and discharging of a conventional lithium ion battery using a Si negative electrode is limited to about 100 times and has not been put into practical use.

  The reason why the number of times of charge and discharge of the lithium ion battery using the Si negative electrode is about 100 is that the Si negative electrode deteriorates due to expansion and contraction when charging and discharging. For this reason, in order to improve the charge / discharge characteristics of a lithium ion battery, research on the Si negative electrode has been actively conducted.

  Furthermore, a conductive additive is added to the electrode material of the lithium ion battery in order to improve conductivity. The conductive aid is, for example, carbon black. For this reason, when forming the electrode of a lithium ion battery, it is important to make the electrode material, carbon black, and a binder into a uniformly mixed state.

  Nano-sized carbon black tends to aggregate and is difficult to disperse uniformly. In such a state, the conductivity remains low even when carbon black is added.

  FIG. 6 is a diagram schematically showing a case where the nano-sized carbon black 102 added to the conventional electrode material 101 is not well dispersed. As shown in FIG. 6, the electrode 100 is formed by adding carbon black 102 or the like as a conductive additive to an electrode material 101. Since the carbon black 102 is aggregated, an inactive region 103 in which the carbon black 102 does not exist is generated as shown in the figure. Thus, even if carbon black 102 is added as a conductive additive to electrode material 101, carbon black 102 agglomerates, so that inactive region 103 is generated, so that the conductivity of the electrode is not readily improved.

  Patent Document 1 discloses carbon having a marimo-like shape as nano-carbon material fine particles. Marimo-like carbon has a spherical shape in which carbon nanofibers having a nanometer (nm) size diameter radiate and coconut-like growth, with oxidized diamond catalyst fine particles as nuclei.

FIG. 7 shows a configuration of a marimo-like carbon (hereinafter referred to as marimo carbon) manufacturing apparatus 110 disclosed in Patent Document 1.
The marimocarbon production apparatus 110 shown in FIG. 7 is also referred to as a fluidized gas phase synthesis apparatus, and is arranged vertically in a reaction tank 113 into which diamond oxide catalyst fine particles 112 are charged, and below and above the reaction tank 113. Passing through the introduction port 115 for introducing the gas 114 made of hydrocarbon, the discharge port 116 for discharging the gas 114, the heating device 117 disposed so as to surround the reaction tank 113, and the diamond oxide catalyst fine particles 112. The filter 118 is configured to allow the gas 114 to pass therethrough. The mixing device 120 is arranged to mix the reaction auxiliary gas and the dilution gas 119 with the gas 114 made of hydrocarbon.

  According to Patent Document 1, since the diamond oxide catalyst fine particles float in the reaction tank 113 and are stirred, when the gas 114 made of hydrocarbon is introduced and the reaction tank 113 is heated in an electric furnace, the diamond oxide catalyst Catalytic reaction occurs uniformly over the entire surface of the fine particles 112. As a result, nanocarbon materials having the same length grow radially over the entire surface of the oxidized diamond catalyst fine particles 112, and marimo-like fine particles, that is, marimocarbon, are obtained.

JP 2005-335968 A, US Pat. No. 7,608,331, B2 JP 2004-277241 A JP 2005-136020 A

J. Electrochem. Soc., Volume 155, Issue 2, pp. A158-A163, 2008

  Uniformly dispersing nano-sized solid carbon in a conventional negative electrode material has a problem that it is very difficult because carbon aggregates as shown in FIG.

  In view of the above problems, an object of the present invention is to provide a nanocarbon material composite in which a nanocarbon material hardly aggregates, an active material for a Li-ion battery, and a method for producing the same.

  The present inventors diligently studied and found that Si fine particles can be encapsulated in voids formed between carbon nanofibers constituting marimocarbon, and arrived at the present invention.

  In order to achieve the above object, the nanocarbon material composite of the present invention is formed by encapsulating Si fine particles in the voids of marimocarbon in which fibrous nanocarbon materials are radially formed with oxidized diamond catalyst fine particles as nuclei. .

  In the above configuration, the diameter of marimocarbon is preferably in the range of 1 μm to 100 μm. The Si fine particles are preferably polycrystalline.

  The method for producing a nanocarbon material composite according to the present invention includes a marimocarbon forming step in which a fibrous nanocarbon material is formed radially with diamond oxide catalyst fine particles as nuclei, and the marimocarbon is accommodated in a reaction vessel. And a step of depositing Si fine particles in which the Si fine particles are precipitated in the voids of the marimocarbon after being evacuated.

  The Si fine particle deposition step is preferably performed by chemical vapor deposition.

  The lithium ion battery of the present invention is characterized by using any of the nanocarbon material composites described above.

  The active material for a Li-ion battery according to the present invention is characterized in that the nanocarbon material composite described above is used as an active material.

  According to the nanocarbon material composite of the present invention, Si fine particles can be uniformly dispersed in carbon nanofibers by encapsulating Si fine particles in the voids of carbon nanofibers constituting marimocarbon. It becomes possible to use for active materials, such as a battery, especially a negative electrode, the active material for negative electrodes, etc.

  According to the method for producing a nanocarbon material composite of the present invention, a nanocarbon material composite can be easily produced by depositing Si fine particles on marimocarbon by chemical vapor deposition (CVD). .

It is a figure which shows typically the structure of the nano carbon material composite_body | complex of this invention. It is a figure which shows typically the structure of the marimo carbon which comprises a nanocarbon material composite_body | complex. It is a figure which shows typically the structure which consists of a some nanocarbon material composite_body | complex of this invention. It is a figure which shows typically the CVD apparatus used for manufacture of the nano carbon material composite_body | complex of this invention. It is a flowchart explaining the manufacturing method of the nano carbon material composite_body | complex of this invention. It is a figure which shows typically the case where the dispersion state of the nanosized carbon added to the conventional electrode material is not favorable. It is a figure which shows the structure of the manufacturing apparatus of the marimo carbon disclosed by patent document 1. FIG.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically showing the structure of a nanocarbon material composite 1 of the present invention, and FIG. 2 schematically shows the structure of marimocarbon 2 constituting the nanocarbon material composite 1 of FIG. FIG.
As shown in FIG. 1, the nanocarbon material composite 1 of the present invention is composed of marimocarbon 2 and Si fine particles 3, and has a structure in which Si fine particles 3 are enclosed in voids 2 a of marimocarbon 2. That is, the nanocarbon material composite 1 is configured such that Si fine particles 3 are encapsulated in voids 2a of marimocarbon 2 in which fibrous nanocarbon materials are formed radially with diamond catalyst fine particles 4 as nuclei. In FIG. 1, Si fine particles 3 are dispersed in a gap 2 a whose outer shape is indicated by a dotted line.

As shown in FIG. 2, marimocarbon 2 is a fibrous carbon nanofiber ² b (sp ² carbon formed of catalyst supported on oxidized diamond (sp ³ carbon), that is, sp ² carbon formed through oxidized diamond catalyst fine particles 4. Carbon Nano Filament (also called CNF)) extends radially from 0.1 μm to 10 μm, and the coral also has a spherical shape as a whole like Marimo. That is, the marimo carbon 2 is composed of spherical carbon nanofibers 2b.

  In the nanocarbon material composite 1 of the present invention, as shown in FIG. 1, a part 2 c of the carbon nanofibers 2 b constituting the marimocarbon 2 is exposed outside the void 2 a of the marimocarbon 2.

  The diameter of the sphere of the marimocarbon 2 can be 1 to 50 μm, and further 1 μm to 100 μm. The marimo carbon 2 has many carbon nanofibers 2b. The carbon nanofibers 2b constituting the marimo carbon 2 are entangled with each other and have a spherical structure as a whole. Many voids 2 a are formed between the carbon nanofibers 2 b of the marimo carbon 2.

The diamond oxide used for the diamond oxide catalyst fine particles 4 shown in FIG. 2 can be prepared by oxidizing diamond powder having a particle size of 500 nm or less that is commercially available for polishing (see Patent Document 2). It is preferable to use a diamond powder having a high specific surface area of 10 m ² / g or more. The diamond oxide used for the diamond oxide catalyst fine particles 4 is used as a catalyst carrier after the surface of a diamond powder is oxidized at 350 to 450 ° C. in an oxygen atmosphere or in air.

Ni, Co, Pd or the like can be used as a catalyst for the oxidized diamond catalyst fine particles 4. In order to support the catalyst on the diamond oxide, the diamond oxide is immersed in an aqueous solution of a metal salt containing a metal serving as a catalyst, left for a predetermined time, for example, 12 hours, excess water is evaporated, and 400 to 500 after drying. Baking in air at 0 ° C. causes decomposition and oxidation of the metal salt, converting the metal salt into an oxide.
Next, after air firing, diamond oxide catalyst particles 4 can be obtained by reducing a metal oxide composed of Ni or the like to a metal in a reducing atmosphere such as hydrogen to form a catalyst (see Patent Document 2).

  In order to grow the carbon nanofibers 2b on the oxidized diamond catalyst fine particles 4, a fluidized gas phase synthesizer (see Patent Document 1) shown in FIG. The carbon nanofibers 2b can be grown and manufactured. The particle diameter of the diamond oxide catalyst fine particles 4 may be 500 nm or less, and if it is too large, it is difficult to float in the reaction vessel 113 of the fluidized gas phase synthesis apparatus 110, which is not preferable. When methane is used as the source gas 16 and Ni, Co or Pd is used as the catalyst, the growth temperature is preferably in the range of 400 ° C to 600 ° C. Further, when the carbon nanofibers 2b are grown by suspending and stirring the diamond oxide catalyst fine particles 4 at a predetermined temperature, the particle diameter of the produced marimocarbon 2 increases in proportion to the stirring time, that is, the reaction time. The reaction time may be set according to the purpose of use.

  The carbon nanofibers 2b of marimocarbon 2 formed when Ni or Co is used as the catalyst are composed of single-walled carbon nanotubes having a diameter of about 18 nm, for example.

  The carbon nanofibers 2b of marimocarbon 2 formed when Pd is used as the catalyst are made of, for example, coin-laminated carbon nanographite fibers having a diameter of about 27 nm (see Patent Document 3). Coin-stacked graphite fibers are carbon fibers in which coin-type single-layer graphite having a diameter of several to several hundred nm is stacked, and the interval between coin-type single-layer graphite is 0.3 to 1 nm.

  The Si fine particles 3 are, for example, polycrystalline. The size of the Si fine particles 3 is 0.1 μm (100 nm) to 10 μm.

  FIG. 3 is a diagram schematically showing a structure composed of a plurality of nanocarbon material composites 1 of the present invention. As shown in FIG. 3, the structure composed of the plurality of nanocarbon material composites 1 of the present invention has the outermost carbon nanofibers of the marimocarbon 2 adjacent to the outermost carbon nanofibers 2c of the marimocarbon 2 shown in FIG. The fibers 2c are entangled with each other. For this reason, in the structure composed of a plurality of nanocarbon material composites 1 of the present invention, a very large number of carbon nanofibers 2b are dispersed in all directions, Si fine particles 3 are encapsulated in voids 2a therebetween, and marimocarbon 2 Are entangled with each other by the carbon nanofibers 2 c extending from the marimocarbon 2. Therefore, in the nanocarbon material composite 1, the Si fine particles 3 are uniformly dispersed in the voids 2 a of the marimocarbon 2, and the marimocarbon 2 improves the conductivity.

  The nanocarbon material composite 1 composed of marimocarbon 2 and Si fine particles 3 can be used for a negative electrode of a lithium ion secondary battery. The marimocarbon 2 containing the Si fine particles 3 is also referred to as Si fine particles / marimocarbon composite 1 in this specification. Specifically, the Si fine particles / marimocarbon composite 1 can be used as a negative electrode or a negative electrode active material or a conductive aid. Further, the Si fine particles / marimocarbon composite 1 can be used as an additive for a negative electrode, a negative electrode active material, or a conductive additive.

  The marimocarbon 2 used in the nanocarbon material composite 1 of the present invention is easier to handle than carbon black and carbon nanotubes, and has large voids 2a between the carbon nanofibers 2b. In the nanocarbon material composite 1 of the present invention, since the Si fine particles 3 are supported in the voids 2a, the agglomeration that occurs when carbon black or carbon nanotubes are mixed with an active material or the like does not occur. Have. For this reason, when the nanocarbon material composite 1 of the present invention is used for the negative electrode, the negative electrode active material, the conductive additive, or these additives, the conductivity can be improved, that is, the resistance can be reduced.

  Thereby, the performance of the charge / discharge characteristic of the secondary battery using the nanocarbon material composite 1 of the present invention can be improved. Further, the Si fine particles 3 encapsulated in the voids 2a of the marimocarbon 2 are configured such that the Si fine particles 3 contain carbon nanofibers in the nanocarbon material composite 1 even if the Si fine particles 3 themselves crack. As a result, the Si fine particles 3 do not collapse and fall apart. Thereby, the deterioration by the repetition of expansion | swelling and shrinkage | contraction of Si fine particle 3 accompanying the charging / discharging for the secondary battery using the nano carbon material composite_body | complex 1 of this invention or a lithium ion battery is relieved. For this reason, the repetition frequency of charging / discharging of the lithium ion battery which used the nanocarbon material composite 1 of this invention as the negative electrode can be improved.

  According to the nanocarbon material composite 1 composed of marimocarbon 2 and Si fine particles 3 of the present invention, it can be used not only as a negative electrode for a secondary battery, an active material for a negative electrode, and a conductive assistant, but also as a catalyst.

(Method for producing nanocarbon material composite)
A method for producing the nanocarbon material composite 1 of the present invention will be described.
FIG. 4 is a diagram schematically showing a CVD apparatus 10 used for manufacturing the nanocarbon material composite 1 of the present invention. As shown in FIG. 4, the CVD apparatus 10 includes a reaction tank 11, an electric furnace 12 that heats the reaction tank 11, a temperature control unit 13 that controls the temperature of the electric furnace 12, and a dilution gas 15 in the reaction tank 11. A reaction gas supply unit 18 for supplying a reaction gas 17 made of a source gas 16 and an exhaust unit 19 are included.

  The reaction gas supply unit 18 is connected to a stop valve 21 connected to a gas cylinder and a pressure regulator (not shown) of the dilution gas 15, a flow regulator 22 such as a mass flow controller, and a gas cylinder and a pressure regulator (not shown) of the source gas 16. A stop valve 21, a flow rate regulator 22 such as a mass flow controller, a flange 24 connecting the flow rate regulator 22 and the reaction tank 11, a pipe 25 made of stainless steel or the like for connecting them, and the like.

  The exhaust part 19 is composed of a flange (not shown) such as a flange connecting the vacuum pump and the reaction tank 11, a gate valve inserted between the vacuum pump and the reaction tank 11, and a vacuum gauge. As the vacuum pump, a roughing pump, an oil diffusion pump, a turbo molecular pump, an ion pump, or the like is used. These vacuum pumps can be used in appropriate combination so that the reaction tank 11 has a predetermined pressure.

  The electric furnace 12, the temperature control unit 13, the reaction gas supply unit 18, the exhaust unit 19 and the like may be further sequence-controlled by a microcomputer or the like (not shown).

FIG. 5 is a flow diagram illustrating a method for producing the nanocarbon material composite 1 of the present invention.
(A) First, marimocarbon 2 is synthesized.
(B) The synthesized marimocarbon 2 is accommodated in the reaction tank 11 of the CVD apparatus 10.
(C) The reaction tank 11 of the CVD apparatus 10 containing the marimocarbon 2 is sufficiently exhausted, and the gas remaining in the fibers of the marimocarbon 2 is exhausted. Exhaust can be performed by the exhaust unit 19 connected to the reaction tank 11.
(D) The dilution gas 15 is introduced into the reaction vessel 11 and the Si fine particles 3 accommodated in the reaction vessel 11 are heated to the growth temperature. An electric furnace 12, a lamp, or a laser can be used for heating. The Si fine particles 3 may be accommodated in a carbon container or the like, and the carbon container may be induction heated by a heating coil.
(E) The raw material gas 16 for growing the Si fine particles 3 is introduced into the reaction vessel 11. As the source gas 16, a compound gas of Si and H (hydrogen), Si and Cl (chlorine), Si, Cl and H (hydrogen) can be used. The source gas 16 is, for example, SiH ₄ . These source gases 16 may be diluted with an inert gas or hydrogen gas. As the inert gas, Ar (argon) or He (helium) may be used. By flowing the raw material gas 16 at a growth temperature for a predetermined time, the Si fine particles 3 are grown in the gaps 2a between the carbon nanofibers 2b of the marimocarbon 2, and the nanocarbon material composite 1 can be formed. The polycrystalline Si fine particles 3 can be deposited in the voids 2a of the marimocarbon 2 at a growth temperature of 600 to 800 ° C., for example, by diluting the source gas 16 with Ar to make SiH ₄ .
(F) After growing for a predetermined time, the supply of SiH _{4 as} the raw material gas 16 to the reaction vessel 11 is stopped, the heating by the electric furnace 12 is stopped, and the temperature is lowered to about room temperature.
(G) The synthesized Si fine particles / marimocarbon composite 1 is recovered from the reaction vessel 11.

Next, an example of the manufacturing method of the present invention will be described.
First, marimocarbon 2 was synthesized by decomposing Ni on oxidized diamond catalyst fine particles 4 by decomposition of methane gas (see Non-Patent Document 14).
Si fine particles 3 are deposited on the marimocarbon 2 synthesized using Ni as a catalyst, using the CVD apparatus 10 shown in FIG.
First, after placing in a quartz container in the reaction vessel 11 and evacuating the residual gas in the marimocarbon 2 in the reaction vessel 11 from the exhaust unit 19, a dilution gas 15 is caused to flow into the reaction vessel 11.
Next, the reaction vessel 11 by an electric furnace 12 was raised to 600 ° C., followed by the SiH ₄ as a raw material gas 16, using Ar as a dilution gas 15, the flow rate of SiH ₄ is the flow rate at 10% 100 sccm ( sccm is cm ³ / min)). The reaction time is 60 minutes, and after 60 minutes, the energization of the electric furnace 12 is stopped, and the reaction vessel 11 is naturally cooled, whereby the Si fine particles / marimocarbon composite 1 can be produced.

  The present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention. Nor.

1: nanocarbon material composite 2: marimocarbon 2a: void 2b: carbon nanofiber 2c: outermost carbon nanofiber 3: Si fine particles 4: oxidized diamond catalyst fine particles 10: CVD apparatus 11: reaction vessel 12: electric furnace 13 : Temperature control unit 15: Dilution gas 16: Raw material gas 17: Reaction gas 18: Reaction gas supply unit 19: Exhaust unit 21: Stop valve 22: Flow rate regulator 24: Flange 25: Piping

Claims (7)

  A nanocarbon material composite in which Si fine particles are encapsulated in marimocarbon voids in which fibrous nanocarbon materials are formed radially using oxide diamond catalyst fine particles as nuclei.   2. The nanocarbon material composite according to claim 1, wherein a diameter of the marimocarbon is in a range of 1 μm to 100 μm.   2. The nanocarbon material composite according to claim 1, wherein the Si fine particles are polycrystalline. Marimocarbon formation process that forms fibrous nanocarbon material radially with oxide diamond catalyst fine particles as nuclei,
Depositing the marimocarbon in a reaction vessel, evacuating the reaction vessel, and then depositing Si fine particles in the voids of the marimocarbon;
The manufacturing method of the nanocarbon material composite containing this.   The method for producing a nanocarbon material composite according to claim 4, wherein the step of depositing the Si fine particles is performed by a chemical vapor deposition method.   A secondary battery using the nanocarbon material composite according to claim 1.   The active material for Li ion batteries using the nano carbon material composite_body | complex in any one of Claims 1-3 for the active material.