WO2015136684A1 - Negative electrode active material for lithium ion secondary batteries, method for producing negative electrode active material for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Negative electrode active material for lithium ion secondary batteries, method for producing negative electrode active material for lithium ion secondary batteries, and lithium ion secondary battery Download PDF

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Publication number
WO2015136684A1
WO2015136684A1 PCT/JP2014/056824 JP2014056824W WO2015136684A1 WO 2015136684 A1 WO2015136684 A1 WO 2015136684A1 JP 2014056824 W JP2014056824 W JP 2014056824W WO 2015136684 A1 WO2015136684 A1 WO 2015136684A1
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lithium ion
ion secondary
negative electrode
active material
electrode active
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PCT/JP2014/056824
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French (fr)
Japanese (ja)
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岡井　誠
京谷　隆
康人 干川
孝文 石井
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株式会社日立製作所
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a negative electrode active material for a lithium ion secondary battery, a method for producing a negative electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery.
  • Graphite-based carbon materials are widely used as negative electrode active materials for lithium ion secondary batteries.
  • the stoichiometric composition when graphite is filled with lithium ions is LiC 6 , and its theoretical capacity can be calculated as 372 mAh / g.
  • the stoichiometric composition when silicon is filled with lithium ions is Li 22 Si 5 , and the theoretical capacity can be calculated as 4197 mAh / g.
  • silicon is an attractive material that can be filled with 11.3 times as much lithium as graphite.
  • Patent Document 1 describes an example of doping silicon nanowires.
  • Patent Document 1 only describes a conductive inner core wire (for example, to provide conductivity necessary for electron transfer) (which may or may not be doped). There is no description about the effect on the high-speed charge / discharge of the lithium ion secondary battery in the case where silicon nanowire is used as the negative electrode active material for the secondary battery and specific electrical conductivity or electrical conductivity is imparted.
  • An object of the present invention is to provide a negative electrode active material for a lithium ion secondary battery having a desired electric conductivity.
  • a negative electrode active material for a lithium ion secondary battery having a desired electrical conductivity can be provided.
  • 1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • 1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • It is a scanning electron micrograph of the impurity doped silicon nanowire which interrupted growth. It is a scanning electron micrograph of the impurity doped silicon nanowire grown on the graphite surface.
  • 2 is a transmission electron micrograph of impurity-doped silicon nanowires grown on a graphite surface.
  • 1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • 1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • 1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. It is a scanning electron micrograph of impurity-doped silicon nanowires coated with carbon. It is a scanning electron micrograph of impurity-doped silicon nanowires coated with carbon. It is a transmission electron micrograph of impurity-doped silicon nanowires coated with carbon. It is a transmission electron micrograph of impurity-doped silicon nanowires coated with carbon.
  • FIG. 1 shows a calculation model according to an embodiment of the present invention.
  • the silicon nanowire 110 exists in contact with the surface of the carbon substrate 100, and the applied voltage at the base of the silicon nanowire 110 is V.
  • the current I flows from the root toward the tip of the silicon nanowire 110, and the voltage drop at the tip of the silicon nanowire 110 is ⁇ V. It is assumed that the voltage drop amount ⁇ V is entirely due to the electric resistance of the silicon nanowire 110.
  • the voltage drop amount ⁇ V is given by Equation (1).
  • L is the length of the silicon nanowire 110
  • ⁇ is the electrical resistivity of the silicon nanowire 110
  • R Si is the radius of the silicon nanowire 110
  • ⁇ is the circumference.
  • the current I is given by Equation (2).
  • Equation (3) D is the density of silicon
  • R is the number of lithium that can be filled per silicon
  • F is the Faraday constant
  • x is the charging rate, that is, 1 / x hours.
  • M is the atomic weight of silicon.
  • R v is expressed by Equation (4).
  • Equation (5) The results calculated using Equation (5) are shown in FIG.
  • the electrical conductivity of non-doped silicon is about 0.001 S / m, it is desirable to improve the electrical conductivity by doping the silicon nanowire 110 in order to achieve the above electrical conductivity.
  • the length of the silicon nanowire 110 depends on the growth conditions, but is considered not to exceed 5 ⁇ m. Moreover, if the charging speed is assumed to be 10 C, it is considered sufficient for most applications. From the above, it is considered practically sufficient if the electrical conductivity of the silicon nanowire 110 is 10 S / m or more, particularly 100 S / m.
  • FIG. 3 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • the negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200.
  • the diameter D si of the impurity-doped silicon nanowire 200 doped with impurities is 2 nm or more and 100 nm or less.
  • the diameter D si of the impurity-doped silicon nanowire 200 is less than 2 nm, it may be naturally oxidized in the atmosphere and become SiO 2 as a whole. In this case, it may not function as a negative electrode active material for a lithium ion secondary battery. There is.
  • the diameter D si of the impurity-doped silicon nanowire 200 is more than 100 nm, was destroyed by mechanical strain at the time of repeated charging and discharging of the lithium ion, there is a possibility that the electric capacity of the lithium ion secondary battery is depleted .
  • the diameter of the silicon nanowire sufficiently thin, such as 100 nm or less, it is possible to suppress the mechanical structural breakdown of silicon particles that occurs during repeated filling and releasing of lithium ions. And since the increase of the irreversible capacity resulting from structural destruction can be reduced significantly, the lifetime improvement of a lithium ion secondary battery is realizable.
  • the length of the impurity-doped silicon nanowire 200 is not limited, but a length of several microns to several tens of microns is considered optimal for the electrode manufacturing process.
  • High electrical conductivity can be imparted by doping silicon nanowires with impurities. Thereby, even when the silicon nanowire is broken in the middle or peeled off from the carbon substrate, electrical conduction with the current collector can be ensured and electrical isolation can be prevented. Due to this effect, the increase in irreversible capacity can be significantly reduced, and thus the life of the lithium ion secondary battery can be extended.
  • a dopant for the silicon nanowire a general dopant for a silicon substrate can be used. Among them, it is desirable to dope elements such as boron, phosphorus, arsenic, and nitrogen as dopants.
  • the doping amount is desirably 10 ⁇ 10 15 atoms / cm 3 or more, and the electric conductivity after doping is desirably 10 S / m or more, and particularly desirably 100 S / m or more. If the electrical conductivity is lower than that, it may not be possible to improve the fast charge / discharge characteristics.
  • a method of introducing ultrafine structures such as nanoparticles and nanowires is effective. This is because the specific surface area of the silicon material increases due to the introduction of the ultrafine structure, so lithium ions can be filled more quickly. This is because release is possible.
  • a method of imparting high electrical conductivity to the silicon material itself is effective. This is because the voltage drop inside the silicon material can be greatly reduced, and as a result, the diffusion rate of lithium ions in silicon can be increased.
  • FIG. 17 shows the internal structure of a lithium ion secondary battery according to an embodiment of the present invention.
  • 1401 is a positive electrode
  • 1402 is a separator
  • 1403 is a negative electrode
  • 1404 is a battery can
  • 1405 is a positive current collecting tab
  • 1406 is a negative current collecting tab
  • 1407 is an inner lid
  • 1408 is an internal pressure release valve
  • 1409 is a gasket
  • 1410 is a positive temperature coefficient (PTC) resistive element
  • 1411 is a battery lid.
  • the battery lid 1411 is an integrated part including an inner lid 1407, a pressure release valve 1408, a gasket 1409, and a positive temperature coefficient resistance element 1410.
  • the positive electrode 1401 is manufactured by the following procedure. LiMn 2 O 4 is used as the positive electrode active material. To 85.0 wt% of the positive electrode active material, 7.0 wt% and 2.0 wt% of graphite powder and acetylene black are added as conductive materials, respectively. Further, a solution dissolved in 6.0 wt% polyvinylidene fluoride (hereinafter abbreviated as PVDF) and 1-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is added as a binder, and the mixture is mixed with a planetary mixer. Further, air bubbles in the slurry are removed under vacuum to prepare a homogeneous positive electrode mixture slurry.
  • PVDF polyvinylidene fluoride
  • NMP 1-methyl-2-pyrrolidone
  • This slurry is uniformly and evenly applied to both surfaces of an aluminum foil having a thickness of 20 ⁇ m using an applicator. After the application, compression molding is performed by a roll press so that the electrode density is 2.55 g / cm 3 . This is cut with a cutting machine to produce a positive electrode 1401 having a thickness of 100 ⁇ m, a length of 900 mm, and a width of 54 mm.
  • the negative electrode 1403 can be manufactured by the following procedure.
  • the negative electrode active material the negative electrode active material for a lithium ion secondary battery in one embodiment of the present invention can be used.
  • a solution prepared by dissolving 5.0 wt% PVDF as a binder in NMP is added to 95.0 wt% of the material. It is mixed with a planetary mixer, and bubbles in the slurry are removed under vacuum to prepare a homogeneous negative electrode mixture slurry.
  • This slurry is uniformly and evenly applied to both surfaces of a rolled copper foil having a thickness of 10 ⁇ m with an applicator.
  • the electrode is compression-molded by a roll press to make the electrode density 1.3 g / cm 3 . This is cut with a cutting machine to produce a negative electrode 1403 having a thickness of 110 ⁇ m, a length of 950 mm, and a width of 56 mm.
  • the positive electrode current collecting tab 1405 and the negative electrode current collecting tab 1406 are ultrasonically welded to the positive electrode 1401 produced as described above and the uncoated part (current collector exposed surface) of the negative electrode 1403, respectively.
  • the positive electrode current collecting tab 1405 can be an aluminum lead piece
  • the negative electrode current collecting tab 1406 can be a nickel lead piece.
  • a separator 1402 made of a porous polyethylene film having a thickness of 30 ⁇ m is inserted into the positive electrode 1401 and the negative electrode 1403, and the positive electrode 1401, the separator 1402, and the negative electrode 1403 are wound.
  • the wound body is accommodated in the battery can 1404, and the negative electrode current collecting tab 1406 is connected to the bottom of the battery can 1404 by a resistance welder.
  • the positive electrode current collecting tab 1405 is connected to the bottom surface of the inner lid 1407 by ultrasonic welding.
  • a non-aqueous electrolyte is injected.
  • the solvent of the electrolytic solution is composed of, for example, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and the volume ratio is 1: 1: 1.
  • the electrolyte is LiPF 6 at a concentration of 1 mol / L (about 0.8 mol / kg). Such an electrolytic solution is dropped from above the electrode group, and the battery lid 1411 is caulked and sealed in the battery can 1404 to obtain a lithium ion secondary battery.
  • FIG. 4 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • the negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200 and graphite 300.
  • impurity-doped silicon nanowires 200 were formed on the surface of graphite 300.
  • the impurity-doped silicon nanowire 200 is directly bonded to the surface of the graphite 300 and grows from the surface of the graphite 300.
  • FIG. 5 is a scanning electron micrograph of an impurity-doped silicon nanowire whose growth has been interrupted.
  • an infinite number of impurity-doped silicon nanoparticles having a diameter of several tens of nm were present on the surface of the graphite 300. From this fact, it can be inferred that silicon nanoparticles first grow on the surface of graphite 300 and the silicon nanoparticles grow into impurity-doped silicon nanowires 200.
  • FIG. 6 is a scanning electron micrograph of impurity-doped silicon nanowires grown on the graphite surface.
  • the impurity-doped silicon nanowires 200 can be manufactured very densely.
  • This sample was a composite material containing silicon and carbon, and the weight ratio of silicon measured by thermogravimetry was 23 wt%. The weight ratio of silicon can be adjusted by changing the growth conditions.
  • FIG. 7 is a transmission electron micrograph of the same sample. Since the diameter is 30 nm and the inside shows silicon lattice stripes, the silicon nanowire 200 is considered to have crystallinity, particularly a polycrystalline structure. When silicon nanowire 200 has crystallinity, the diffusion rate of lithium ions increases. As a result, the charging and discharging speed of lithium ions is fast, and the high-speed charge / discharge characteristics are improved. In addition, a natural oxide film layer of less than 3 nm exists on the surface of the impurity-doped silicon nanowire 200.
  • the impurity-doped silicon nanowire 200 is directly bonded to the surface of the graphite 300, and a chemical bond is formed between the silicon atom of the impurity-doped silicon nanowire 200 and the carbon atom on the surface of the graphite 300 at the bonding surface. It is conceivable that.
  • the graphite 300 used as the base material for the growth of the impurity-doped silicon nanowire 200 can use any kind and form of graphite such as artificial graphite, natural graphite, graphite oxide, and thermally expanded graphite. is there.
  • FIG. 8 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • the negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200 and carbon nanotubes 400.
  • the present embodiment is different from the second embodiment in that carbon nanotubes 400 are used as a carbon base material and impurity-doped silicon nanowires 200 are grown on the surface thereof.
  • the carbon nanotube 400 was used as the base material for the growth of the impurity-doped silicon nanowire 200, but it is possible to use any form of carbon-based nanostructure such as carbon nanohorn, acetylene black, ketjen black, etc. It is.
  • FIG. 9 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • the impurity-doped silicon nanowire 200 is grown on the carbon substrate, and then the carbon substrate and the impurity-doped silicon nanowire 200 are separated, and only the impurity-doped silicon nanowire 200 is used as the negative electrode material.
  • the weight ratio of silicon to the total weight can be greatly increased, so that the electric capacity can be dramatically increased.
  • FIG. 10 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
  • the negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200 and an electrically conductive carbon thin film 500.
  • the negative electrode active material 1000 has a structure in which the surface of the impurity-doped silicon nanowire 200 is partially or entirely covered with the electrically conductive carbon thin film 500.
  • the electrically conductive carbon thin film 500 is formed on the surface of the impurity-doped silicon nanowire 200.
  • the electrically conductive carbon thin film 500 has a structure in which nanographene is laminated in multiple layers, and has an electrical conductivity of 1000 S / m or more.
  • electrical conductivity can be added to the impurity-doped silicon nanowire 200. Accordingly, even when the impurity-doped silicon nanowire 200 is broken in the middle or when the impurity-doped silicon nanowire 200 is peeled off from the electrically conductive carbon thin film 500, electrical conduction with the current collector is ensured and electrical isolation is achieved. Therefore, the irreversible capacity of the lithium ion secondary battery can be reduced.
  • the film thickness L c of the electrically conductive carbon thin film 500 is not less than 0.2 nm and not more than 100 nm. Thickness L c of electrically conductive carbon film 500, is less than 0.2 nm, the coating strength is inadequate, there is a possibility that peeling partially, in which case, to ensure a sufficient electrical conductivity It may not be possible.
  • the thickness L c of electrically conductive carbon film 500 if it exceeds 100 nm, it is difficult to the weight of silicon to the total weight 20 wt%, can not be able to consequently obtain a sufficient electric capacity There is sex.
  • FIG. 11 is a scanning electron micrograph of an impurity-doped silicon nanowire coated with carbon. In this way, the carbon-coated impurity-doped silicon nanowire 200 can be grown very densely.
  • FIG. 12 is an enlarged photograph of the same sample. It is considered that the surface of the carbon-doped impurity-doped silicon nanowire 200 is uniformly covered with the electrically conductive carbon thin film 500.
  • FIG. 13 is a transmission electron micrograph of carbon-coated impurity-doped silicon nanowires.
  • an impurity-doped silicon nanowire 200 having a lattice pattern can be observed.
  • an electrically conductive carbon thin film 500 having a nanographene multilayer structure oriented along the axial direction of the impurity-doped silicon nanowire 200 can be observed. Since the electrically conductive carbon thin film 500 is oriented along the axial direction of the impurity-doped silicon nana wire 200, the electrically conductive carbon thin film 500 becomes a strong film that is difficult to peel off.
  • the diameter of the impurity-doped silicon nanowire 200 was 18 nm, and the thickness of the electrically conductive carbon thin film 500 was 6.44-8.17 nm.
  • FIG. 14 shows a transmission electron micrograph of another sample.
  • FIG. 14 is a transmission electron micrograph of impurity-doped silicon nanowires coated with carbon.
  • the diameter of the impurity-doped silicon nanowire 200 was 18 nm, and the thickness of the electrically conductive carbon thin film 500 was 10 nm.
  • FIG. 15 is a schematic diagram of a thermal vapor deposition apparatus for forming impurity-doped silicon nanowires on the surface of a carbon substrate.
  • Liquid silicon tetrachloride was used as the silicon raw material, and was introduced into the reactor by bubbling with hydrogen gas (the bottom line on the left in FIG. 15).
  • the vapor pressure of silicon tetrachloride at 20 ° C. is 30 kPa, and when bubbling is introduced, the amount of silicon tetrachloride introduced is 34%. Therefore, when introducing a smaller amount of silicon tetrachloride, it is necessary to cool the silicon tetrachloride or to provide another hydrogen gas line (middle line on the left in FIG. 15). In this example, a hydrogen line that was not bubbled was provided separately, joined with the bubbling line, and introduced into the reactor.
  • a dopant line (the uppermost line on the left in FIG. 15) was provided, and an organic compound containing elements such as boron, phosphorus, arsenic, and nitrogen as dopants was introduced as a dopant raw material.
  • the organic compound was a gas, it was introduced by mixing with an inert gas such as argon. In the case of a liquid, it was introduced by bubbling with an inert gas such as argon.
  • boron-containing organic compounds include various boronic esters
  • phosphorus-containing organic compounds include various phosphonic esters
  • various phosphoric esters include various phosphites
  • nitrogen-containing organic compounds include various amines, various amides, various types It is possible to use imine and various nitriles.
  • the procedure for growing carbon-coated impurity-doped silicon nanowires is as follows. Put the carbon substrate in the sample boat and install it near the center of the reactor. As the carbon substrate, any form of carbon material such as graphite, thermally expanded graphite oxide, graphite oxide, carbon nanotube, carbon nanohorn, etc. can be used.
  • the reactor is made of quartz and has a diameter of 5 cm and a length of 40 cm. In the middle left hydrogen line of FIG. 15, hydrogen is allowed to flow at a flow rate of 200 mL / min, and the lower bubbling hydrogen line is closed, and the growth furnace is heated from room temperature to 1000 ° C. at a rate of 10 ° C./min. did.
  • the flow rate of the upper hydrogen line was changed to 100 mL / min, and the flow rate of the hydrogen line of the lower bubbling hydrogen line was set to 100 mL / min.
  • 17% silicon tetrachloride can be introduced.
  • a dopant raw material was introduced from the dopant line.
  • the dopant line and the lower bubbling hydrogen line were closed and the flow rate of the upper hydrogen line was changed to 200 mL / min and held at 1000 ° C. for 30 minutes. Thereby, it is possible to produce the impurity-doped silicon nanowire 200 having a diameter of 20 nm on the surface of the carbon substrate.
  • the diameter and growth weight of the impurity-doped silicon nanowire 200 can be changed by changing the temperature at the time of growth of the impurity-doped silicon nanowire 200, the amount of silicon tetrachloride introduced, and the growth time. Moreover, it is possible to change the doping amount to the impurity-doped silicon nanowire 200 by changing the introduction amount of the dopant raw material.
  • both hydrogen lines were closed, and argon gas (the argon line is not shown in FIG. 15) was flowed at a flow rate of 200 mL / min, the temperature was lowered at a rate of 10 ° C./min, and the temperature was lowered to 800 ° C.
  • propylene gas (the propylene line is not shown in FIG. 15) was introduced at a flow rate of 10 mL / min, and at the same time the argon gas flow rate was set to 190 mL / min, It grew for 1 hour.
  • the production of the impurity-doped silicon nanowire 200 and the subsequent production of the electrically conductive carbon thin film 500 were continuously performed. In this way, the production of the impurity-doped silicon nanowire 200 and the subsequent production of the electrically conductive carbon thin film 500 are continuously performed, thereby preventing the formation of a natural oxide film and eliminating the process of reducing and removing the natural oxide film. become.
  • the impurity-doped silicon nanowire 200 is grown, the impurity-doped silicon nanowire 200 is once taken out into the air and then heat-treated in a reducing atmosphere to remove the natural oxide film on the surface of the impurity-doped silicon nanowire 200, and then the electrically conductive carbon thin film 500 is produced. It is also possible. The productivity is improved by growing the impurity-doped silicon nanowires 200 and producing the electrically conductive carbon thin film 500 in separate reactors. Further, the diameter and growth weight of the impurity-doped silicon nanowire 200 can be changed by changing the temperature at the time of growth of the impurity-doped silicon nanowire 200, the amount of silicon tetrachloride introduced, and the growth time.
  • the film thickness of the electrically conductive carbon thin film 500 can be controlled.
  • various hydrocarbon gases such as acetylene gas, propane gas, and methane gas can be used for producing the electrically conductive carbon thin film 500.
  • FIG. 16 shows the calculation result of the dependence of the negative electrode capacitance on the weight ratio Si / (Si + C) of silicon with respect to the total weight of the composite material of silicon and carbon.
  • the stoichiometric composition when filled with lithium ions was assumed to be LiC 6 and its electric capacity was 372 mAh / g.
  • the stoichiometric composition when lithium ions are filled is assumed to be Li 15 Si 4, and the electric capacity is assumed to be 3577 mAh / g, and Li 22 Si 5 is assumed, It calculated about the case where the electric capacity was 4197 mAh / g.
  • the weight ratio is 20% or more, particularly 40% or more, more preferably 80%, with respect to the negative electrode active material for lithium ion secondary battery. It is desirable to contain more than% silicon.

Abstract

A negative electrode active material for lithium ion secondary batteries, which is imparted with a desired electrical conductivity, can be provided by using a negative electrode active material for lithium ion secondary batteries containing silicon nanowires that are doped with an impurity and have an electrical conductivity of 10 S/m or more. The characteristics of a lithium ion secondary battery can be improved by using this negative electrode active material for lithium ion secondary batteries in the lithium ion secondary battery.

Description

リチウムイオン二次電池用負極活物質、リチウムイオン二次電池用負極活物質の製造方法、およびリチウムイオン二次電池Negative electrode active material for lithium ion secondary battery, method for producing negative electrode active material for lithium ion secondary battery, and lithium ion secondary battery
　本発明は、リチウムイオン二次電池用負極活物質、リチウムイオン二次電池用負極活物質の製造方法、およびリチウムイオン二次電池に関する。 The present invention relates to a negative electrode active material for a lithium ion secondary battery, a method for producing a negative electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery.
　リチウムイオン二次電池の負極活物質として、黒鉛系の炭素材料が広く用いられている。黒鉛にリチウムイオンを充填した際の化学量論的組成は、ＬｉＣ6であり、その理論容量は３７２ｍＡｈ／ｇと算出できる。これに対して、シリコンにリチウムイオンを充填した際の化学量論的組成は、Ｌｉ22Ｓｉ5であり、その理論容量は４１９７ｍＡｈ／ｇと算出できる。このように、シリコンは黒鉛に比べて、１１．３倍のリチウムを充填できる魅力的な材料である。従来技術として、特許文献１にはシリコンナノワイヤにドーピングする例が記載されている。 Graphite-based carbon materials are widely used as negative electrode active materials for lithium ion secondary batteries. The stoichiometric composition when graphite is filled with lithium ions is LiC 6 , and its theoretical capacity can be calculated as 372 mAh / g. On the other hand, the stoichiometric composition when silicon is filled with lithium ions is Li 22 Si 5 , and the theoretical capacity can be calculated as 4197 mAh / g. Thus, silicon is an attractive material that can be filled with 11.3 times as much lithium as graphite. As a prior art, Patent Document 1 describes an example of doping silicon nanowires.
特表２０１２－５２７７３５号公報Special table 2012-527735 gazette
　特許文献１には、導電性内側コアワイヤ（例えば電子移動のために必要な導電性を与えるために）（ドーピングされていてもよく、されていなくてもよい）としか記載がなく、リチウムイオン二次電池用負極活物質にシリコンナノワイヤを用いた場合の具体的な電気伝導度または電気伝導度を付与した場合のリチウムイオン二次電池の高速充放電化に対する効果については、記載されていない。本発明では、所望の電気伝導度が付与されたリチウムイオン二次電池用負極活物質を提供することを目的とする。 Patent Document 1 only describes a conductive inner core wire (for example, to provide conductivity necessary for electron transfer) (which may or may not be doped). There is no description about the effect on the high-speed charge / discharge of the lithium ion secondary battery in the case where silicon nanowire is used as the negative electrode active material for the secondary battery and specific electrical conductivity or electrical conductivity is imparted. An object of the present invention is to provide a negative electrode active material for a lithium ion secondary battery having a desired electric conductivity.
　本発明の特徴は、例えば以下の通りである。 The features of the present invention are as follows, for example.
　シリコンナノワイヤを有するリチウムイオン二次電池用負極活物質であって、シリコンナノワイヤに不純物がドーピングされ、シリコンナノワイヤの電気伝導率は１０Ｓ／ｍ以上であるリチウムイオン二次電池用負極活物質。 A negative electrode active material for a lithium ion secondary battery having a silicon nanowire, wherein the silicon nanowire is doped with impurities, and the electric conductivity of the silicon nanowire is 10 S / m or more.
　本発明により、所望の電気伝導度が付与されたリチウムイオン二次電池用負極活物質を提供できる。上記した以外の課題、構成および効果は以下の実施形態の説明により明らかにされる。 According to the present invention, a negative electrode active material for a lithium ion secondary battery having a desired electrical conductivity can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.
本発明の一実施形態に係る計算モデルである。It is a calculation model concerning one embodiment of the present invention. 本発明の一実施形態に係る計算モデルの計算結果である。It is a calculation result of the calculation model which concerns on one Embodiment of this invention. 本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. 本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. 成長を中断した不純物ドープシリコンナノワイヤの走査型電子顕微鏡写真である。It is a scanning electron micrograph of the impurity doped silicon nanowire which interrupted growth. 黒鉛表面に成長した不純物ドープシリコンナノワイヤの走査型電子顕微鏡写真である。It is a scanning electron micrograph of the impurity doped silicon nanowire grown on the graphite surface. 黒鉛表面に成長した不純物ドープシリコンナノワイヤの透過型電子顕微鏡写真である。2 is a transmission electron micrograph of impurity-doped silicon nanowires grown on a graphite surface. 本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. 本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. 本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。1 schematically illustrates the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. 炭素被覆した不純物ドープシリコンナノワイヤの走査型電子顕微鏡写真である。It is a scanning electron micrograph of impurity-doped silicon nanowires coated with carbon. 炭素被覆した不純物ドープシリコンナノワイヤの走査型電子顕微鏡写真である。It is a scanning electron micrograph of impurity-doped silicon nanowires coated with carbon. 炭素被覆した不純物ドープシリコンナノワイヤの透過型電子顕微鏡写真である。It is a transmission electron micrograph of impurity-doped silicon nanowires coated with carbon. 炭素被覆した不純物ドープシリコンナノワイヤの透過型電子顕微鏡写真である。It is a transmission electron micrograph of impurity-doped silicon nanowires coated with carbon. 炭素基材の表面に不純物ドープシリコンナノワイヤを形成するための熱気相成長装置の概略図である。It is the schematic of the thermal vapor phase growth apparatus for forming the impurity dope silicon nanowire on the surface of a carbon base material. シリコンと炭素の複合材料に関して、全体重量に対するシリコンの重量比Ｓｉ／（Ｓｉ＋Ｃ）に対する、負極電気容量の依存性を計算した結果である。It is the result of having calculated the dependence of the negative electrode electrical capacitance with respect to the weight ratio Si / (Si + C) of the silicon | silicone with respect to the whole weight regarding the composite material of silicon and carbon. 本発明の一実施形態に係るリチウムイオン二次電池の内部構造である。It is an internal structure of the lithium ion secondary battery which concerns on one Embodiment of this invention.
　以下、図面等を用いて、本発明の実施形態について説明する。以下の説明は本発明の内容の具体例を示すものであり、本発明がこれらの説明に限定されるものではなく、本明細書に開示される技術的思想の範囲内において当業者による様々な変更および修正が可能である。また、本発明を説明するための全図において、同一の機能を有するものは、同一の符号を付け、その繰り返しの説明は省略する場合がある。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.
　本発明の数値的裏付けを、図１および図２を用いて説明する。 The numerical support of the present invention will be described with reference to FIG. 1 and FIG.
　図１に本発明の一実施形態に係る計算モデルを示す。炭素基材１００の表面に接触して、シリコンナノワイヤ１１０が存在し、シリコンナノワイヤ１１０の根元における印加電圧をＶとする。シリコンナノワイヤ１１０に電流Ｉが根元から先端に向かって流れ、シリコンナノワイヤ１１０の先端における電圧降下量をΔＶとする。電圧降下量ΔＶは、すべてシリコンナノワイヤ１１０の電気抵抗に起因すると仮定する。電圧降下量ΔＶは、数式（１）により与えられる。 FIG. 1 shows a calculation model according to an embodiment of the present invention. The silicon nanowire 110 exists in contact with the surface of the carbon substrate 100, and the applied voltage at the base of the silicon nanowire 110 is V. The current I flows from the root toward the tip of the silicon nanowire 110, and the voltage drop at the tip of the silicon nanowire 110 is ΔV. It is assumed that the voltage drop amount ΔV is entirely due to the electric resistance of the silicon nanowire 110. The voltage drop amount ΔV is given by Equation (1).
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　ここで、Ｌはシリコンナノワイヤ１１０の長さ、ρはシリコンナノワイヤ１１０の電気抵抗率、ＲSiはシリコンナノワイヤ１１０の半径、πは円周率である。また、電流Ｉは数式（２）で与えられる。 Here, L is the length of the silicon nanowire 110, ρ is the electrical resistivity of the silicon nanowire 110, R Si is the radius of the silicon nanowire 110, and π is the circumference. The current I is given by Equation (2).
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　ここで、Ｄはシリコンの密度、Ｒはシリコン１個に対して充填できるリチウムの個数、Ｆはファラデー定数、ｘは充電速度、すなわち１／ｘ時間で満充電すると仮定する。また、Ｍはシリコンの原子量である。数式（１）に数式（２）を代入すると、数式（３）となる。 Here, it is assumed that D is the density of silicon, R is the number of lithium that can be filled per silicon, F is the Faraday constant, and x is the charging rate, that is, 1 / x hours. M is the atomic weight of silicon. Substituting equation (2) into equation (1) yields equation (3).
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　また、シリコンナノワイヤ１１０の根元と先端での拡散速度の比をＲvとすると、Ｒvは、数式（４）表される。 Further, when the ratio of the diffusion rate at the root and the tip of the silicon nanowire 110 is R v , R v is expressed by Equation (4).
Figure JPOXMLDOC01-appb-M000004
Figure JPOXMLDOC01-appb-M000004
　数式（４）に数式（３）を代入し、整理すると、数式（５）となる。 When the formula (3) is substituted into the formula (4) and rearranged, the formula (5) is obtained.
Figure JPOXMLDOC01-appb-M000005
Figure JPOXMLDOC01-appb-M000005
　数式（５）により、シリコンナノワイヤ１１０に最大許容される電気抵抗率ρの充電速度ｘ依存性を求めることができた。 From the formula (5), it was possible to obtain the charge rate x dependency of the maximum electrical resistivity ρ allowed for the silicon nanowire 110.
　数式（５）を用いて計算した結果を図２に示す。数式（５）において、定数ｋ＝１．３８×１０-23（ｍ2ｋｇｓ-2Ｋ-1）、Ｔ＝３００（Ｋ）、Ｍ＝２８．１×１０-3（ｋｇｍｏｌ-1）、ｑ＝１．６×１０-19（Ｃ）、Ｄ＝２．３３×１０3（ｋｇｍ-3）、Ｒ＝４．４、Ｆ＝９．６５×１０4（Ｃｍｏｌ-1）、また、Ｒvを１．０１とした。すなわち、根元と先端での拡散速度の差を１％以内と仮定した。 The results calculated using Equation (5) are shown in FIG. In the formula (5), constants k = 1.38 × 10 −23 (m 2 kgs −2 K −1 ), T = 300 (K), M = 28.1 × 10 −3 (kgmol −1 ), q = 1.6 × 10 −19 (C), D = 2.33 × 10 3 (kgm −3 ), R = 4.4, F = 9.65 × 10 4 (Cmol −1 ), and R v Was 1.01. That is, the difference in diffusion rate between the root and the tip was assumed to be within 1%.
　Ｌ＝１、３、５μｍの場合に計算した結果を図２に示す。図２は、本発明の一実施形態に係る計算モデルの計算結果である。図２上図の縦軸を０－０．２の領域を拡大したものが、図２下図である。これにより、１０Ｃの速度で充電する場合、Ｌ＝１μｍの場合は、シリコンナノワイヤの電気抵抗率を２．６Ωｍ以下にしなければいけないことがわかる。電気伝導率はその逆数で、０．３８Ｓ／ｍ以上にしなければならない。Ｌ＝３μｍの場合は、電気抵抗率を０．３Ωｍ以下（電気伝導率３．３Ｓ／ｍ以上）に、Ｌ＝５μｍの場合は電気抵抗率０．１Ωｍ以下（電気伝導率１０Ｓ／ｍ以上）にしなければならない。 FIG. 2 shows the calculation results when L = 1, 3, and 5 μm. FIG. 2 is a calculation result of a calculation model according to an embodiment of the present invention. 2 is an enlarged view of the region of 0-0.2 on the vertical axis in the upper diagram of FIG. This shows that when charging at a speed of 10 C and L = 1 μm, the electrical resistivity of the silicon nanowire must be 2.6 Ωm or less. The electrical conductivity is its reciprocal and must be 0.38 S / m or more. When L = 3 μm, the electrical resistivity is 0.3 Ωm or less (electric conductivity of 3.3 S / m or more), and when L = 5 μm, the electrical resistivity is 0.1 Ωm or less (electric conductivity of 10 S / m or more). Must be.
　ノンドープシリコンの電気伝導率は、０．００１Ｓ／ｍ程度であるため、上記の電気伝導率を実現するためには、シリコンナノワイヤ１１０にドーピングし、電気伝導性を向上させることが望ましい。シリコンナノワイヤ１１０の長さは、成長条件に依存するが、５μｍをこえることはないと考えられる。また、充電速度は１０Ｃを想定しておけば、大部分の用途には充分であると考えられる。以上より、シリコンナノワイヤ１１０の電気伝導率を１０Ｓ／ｍ以上、特に１００Ｓ／ｍにすれば、実用上充分であると考えられる。下記されている気相成長法でシリコンナノワイヤ１１０にドーピングする場合は、ドーピング量として５×１０18ｃｍ-3程度が限界となるので、シリコンナノワイヤ１１０の電気伝導率は１００００Ｓ／ｍ以下とすることが望ましい。
＜不純物ドープシリコンナノワイヤ＞
　本発明の一実施例について、図３を用いて説明する。図３は、本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。 Since the electrical conductivity of non-doped silicon is about 0.001 S / m, it is desirable to improve the electrical conductivity by doping the silicon nanowire 110 in order to achieve the above electrical conductivity. The length of the silicon nanowire 110 depends on the growth conditions, but is considered not to exceed 5 μm. Moreover, if the charging speed is assumed to be 10 C, it is considered sufficient for most applications. From the above, it is considered practically sufficient if the electrical conductivity of the silicon nanowire 110 is 10 S / m or more, particularly 100 S / m. When doping the silicon nanowire 110 by the vapor phase growth method described below, the doping amount is limited to about 5 × 10 18 cm −3, so the electrical conductivity of the silicon nanowire 110 should be 10000 S / m or less. Is desirable.
<Impurity-doped silicon nanowires>
An embodiment of the present invention will be described with reference to FIG. FIG. 3 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.
　負極活物質１０００は、不純物ドープシリコンナノワイヤ２００で構成される。不純物をドープした不純物ドープシリコンナノワイヤ２００の直径Ｄsiは、２ｎｍ以上、１００ｎｍ以下である。不純物ドープシリコンナノワイヤ２００の直径Ｄsiが２ｎｍ未満の場合、大気中で自然酸化されて全体がＳｉＯ2になる可能性があり、この場合、リチウムイオン二次電池用負極活物質として機能しない可能性がある。また、不純物ドープシリコンナノワイヤ２００の直径Ｄsiが１００ｎｍを超える場合、リチウムイオンの充填および放出を繰返した際の機械的歪みにより破壊し、リチウムイオン二次電池の電気容量が激減する可能性がある。シリコンナノワイヤの直径を１００ｎｍ以下と充分に細くすることにより、リチウムイオンの充填と放出を繰り返す間に起こるシリコン粒子の力学的な構造破壊を抑制できる。そして、構造破壊に起因する不可逆容量増加を大幅に低減できるため、リチウムイオン二次電池の長寿命化を実現できる。 The negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200. The diameter D si of the impurity-doped silicon nanowire 200 doped with impurities is 2 nm or more and 100 nm or less. When the diameter D si of the impurity-doped silicon nanowire 200 is less than 2 nm, it may be naturally oxidized in the atmosphere and become SiO 2 as a whole. In this case, it may not function as a negative electrode active material for a lithium ion secondary battery. There is. Further, if the diameter D si of the impurity-doped silicon nanowire 200 is more than 100 nm, was destroyed by mechanical strain at the time of repeated charging and discharging of the lithium ion, there is a possibility that the electric capacity of the lithium ion secondary battery is depleted . By making the diameter of the silicon nanowire sufficiently thin, such as 100 nm or less, it is possible to suppress the mechanical structural breakdown of silicon particles that occurs during repeated filling and releasing of lithium ions. And since the increase of the irreversible capacity resulting from structural destruction can be reduced significantly, the lifetime improvement of a lithium ion secondary battery is realizable.
　不純物ドープシリコンナノワイヤ２００の長さに制限はないが、数ミクロンから数十ミクロンぐらいの長さが、電極作製プロセスに対して、最適であると考えられる。 The length of the impurity-doped silicon nanowire 200 is not limited, but a length of several microns to several tens of microns is considered optimal for the electrode manufacturing process.
　シリコンナノワイヤに不純物をドーピングすることにより、高電気伝導性を付与できる。これにより、シリコンナノワイヤが途中で折れた場合、あるいは炭素基材から剥離した場合にも、集電体との間の電気伝導を確保し、電気的孤立を防ぐことができる。この効果により、不可逆容量増加を大幅に低減できるため、リチウムイオン二次電池の長寿命化を実現できる。 High electrical conductivity can be imparted by doping silicon nanowires with impurities. Thereby, even when the silicon nanowire is broken in the middle or peeled off from the carbon substrate, electrical conduction with the current collector can be ensured and electrical isolation can be prevented. Due to this effect, the increase in irreversible capacity can be significantly reduced, and thus the life of the lithium ion secondary battery can be extended.
　シリコンナノワイヤに対するドーパントとしては、シリコン基板に対する一般的なドーパントを用いることが可能である。その中で、ボロン、リン、ヒ素、窒素等の元素をドーパントとしてドープすることが望ましい。ドーピング量は、１０×１０15ａｔｏｍ／ｃｍ3以上であることが望ましく、ドーピング後の電気伝導度は、１０Ｓ／ｍ以上、特に１００Ｓ／ｍ以上であることが望ましい。それ以下の電気伝導度では、高速充放電特性の改善が望めない場合がある。 As a dopant for the silicon nanowire, a general dopant for a silicon substrate can be used. Among them, it is desirable to dope elements such as boron, phosphorus, arsenic, and nitrogen as dopants. The doping amount is desirably 10 × 10 15 atoms / cm 3 or more, and the electric conductivity after doping is desirably 10 S / m or more, and particularly desirably 100 S / m or more. If the electrical conductivity is lower than that, it may not be possible to improve the fast charge / discharge characteristics.
　また、シリコン材料の高速充放電化を図るためには、ナノ粒子やナノワイヤ等の極微細構造を導入する方法が有効である。これは、極微細構造導入により、シリコン材料に比表面積が大きくなるため、より高速にリチウムイオンの充填？放出が可能となるからである。さらなる高速充放電化を図るためには、シリコン材料自身に高電気伝導性を付与する方法が有効である。これにより、シリコン材料内部での電圧降下を大幅に低減でき、結果としてリチウムイオンのシリコン内拡散速度を高速化できるためである。 Also, in order to achieve high-speed charge / discharge of silicon materials, a method of introducing ultrafine structures such as nanoparticles and nanowires is effective. This is because the specific surface area of the silicon material increases due to the introduction of the ultrafine structure, so lithium ions can be filled more quickly. This is because release is possible. In order to achieve further high-speed charge / discharge, a method of imparting high electrical conductivity to the silicon material itself is effective. This is because the voltage drop inside the silicon material can be greatly reduced, and as a result, the diffusion rate of lithium ions in silicon can be increased.
　図１７は、本発明の一実施形態に係るリチウムイオン二次電池の内部構造を示す。図１７で、１４０１は正極、１４０２はセパレータ、１４０３は負極、１４０４は電池缶、１４０５は正極集電タブ、１４０６は負極集電タブ、１４０７は内蓋、１４０８は内圧開放弁、１４０９はガスケット、１４１０は正温度係数（ＰＴＣ；　Ｐｏｓｉｔｉｖｅ　ｔｅｍｐｅｒａｔｕｒｅ　ｃｏｅｆｆｉｃｉｅｎｔ）抵抗素子、１４１１は電池蓋である。電池蓋１４１１は、内蓋１４０７、圧力開放弁１４０８、ガスケット１４０９、正温度係数抵抗素子１４１０からなる一体化部品である。 FIG. 17 shows the internal structure of a lithium ion secondary battery according to an embodiment of the present invention. In FIG. 17, 1401 is a positive electrode, 1402 is a separator, 1403 is a negative electrode, 1404 is a battery can, 1405 is a positive current collecting tab, 1406 is a negative current collecting tab, 1407 is an inner lid, 1408 is an internal pressure release valve, 1409 is a gasket, 1410 is a positive temperature coefficient (PTC) resistive element, and 1411 is a battery lid. The battery lid 1411 is an integrated part including an inner lid 1407, a pressure release valve 1408, a gasket 1409, and a positive temperature coefficient resistance element 1410.
　例えば、正極１４０１は以下の手順により作製される。正極活物質には、ＬｉＭｎ2Ｏ4を用いる。その正極活物質の８５．０ｗｔ％に、導電材として黒鉛粉末とアセチレンブラックをそれぞれ７．０ｗｔ％と２．０ｗｔ％を添加する。さらに、結着剤として６．０ｗｔ％のポリフッ化ビニリデン（以下、ＰＶＤＦと略記）、１－メチル－２－ピロリドン（以下、ＮＭＰと略記）に溶解した溶液を加えて、プラネタリ－ミキサーで混合し、さらに真空下でスラリー中の気泡を除去して、均質な正極合剤スラリーを調製する。このスラリーを、塗布機を用いて厚さ２０μｍのアルミニウム箔の両面に均一かつ均等に塗布する。塗布後ロールプレス機により電極密度が２．５５ｇ／ｃｍ3になるように圧縮成形する。これを切断機で裁断し、厚さ１００μｍ、長さ９００ｍｍ、幅５４ｍｍの正極１４０１を作製する。 For example, the positive electrode 1401 is manufactured by the following procedure. LiMn 2 O 4 is used as the positive electrode active material. To 85.0 wt% of the positive electrode active material, 7.0 wt% and 2.0 wt% of graphite powder and acetylene black are added as conductive materials, respectively. Further, a solution dissolved in 6.0 wt% polyvinylidene fluoride (hereinafter abbreviated as PVDF) and 1-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is added as a binder, and the mixture is mixed with a planetary mixer. Further, air bubbles in the slurry are removed under vacuum to prepare a homogeneous positive electrode mixture slurry. This slurry is uniformly and evenly applied to both surfaces of an aluminum foil having a thickness of 20 μm using an applicator. After the application, compression molding is performed by a roll press so that the electrode density is 2.55 g / cm 3 . This is cut with a cutting machine to produce a positive electrode 1401 having a thickness of 100 μm, a length of 900 mm, and a width of 54 mm.
　例えば、負極１４０３は以下の手順により作製できる。負極活物質は、本発明の一実施形態におけるチウムイオン二次電池用負極活物質を用いることができる。該材料の９５．０ｗｔ％に、結着剤として５．０ｗｔ％のＰＶＤＦをＮＭＰに溶解した溶液を加える。それをプラネタリ－ミキサーで混合し、真空下でスラリー中の気泡を除去して、均質な負極合剤スラリーを調製する。このスラリーを塗布機で厚さ１０μｍの圧延銅箔の両面に均一かつ均等に塗布する。塗布後、その電極をロールプレス機によって圧縮成形して、電極密度が１．３ｇ／ｃｍ3とする。これを切断機で裁断し、厚さ１１０μｍ、長さ９５０ｍｍ、幅５６ｍｍの負極１４０３を作製する。 For example, the negative electrode 1403 can be manufactured by the following procedure. As the negative electrode active material, the negative electrode active material for a lithium ion secondary battery in one embodiment of the present invention can be used. A solution prepared by dissolving 5.0 wt% PVDF as a binder in NMP is added to 95.0 wt% of the material. It is mixed with a planetary mixer, and bubbles in the slurry are removed under vacuum to prepare a homogeneous negative electrode mixture slurry. This slurry is uniformly and evenly applied to both surfaces of a rolled copper foil having a thickness of 10 μm with an applicator. After application, the electrode is compression-molded by a roll press to make the electrode density 1.3 g / cm 3 . This is cut with a cutting machine to produce a negative electrode 1403 having a thickness of 110 μm, a length of 950 mm, and a width of 56 mm.
　上のように作製した正極１４０１と、負極１４０３の未塗布部（集電板露出面）に、それぞれ正極集電タブ１４０５および負極集電タブ１４０６を超音波溶接する。例えば、正極集電タブ１４０５はアルミニウム製リード片とし、負極集電タブ１４０６にはニッケル製リード片を用いることができる。その後、厚み３０μｍの多孔性ポリエチレンフィルムからなるセパレータ１４０２を正極１４０１と負極１４０３に挿入し、正極１４０１、セパレータ１４０２、負極１４０３を捲回する。この捲回体を電池缶１４０４に収納し、負極集電タブ１４０６を電池缶１４０４の缶底に抵抗溶接機により接続する。正極集電タブ１４０５は、内蓋１４０７の底面に超音波溶接により接続する。 The positive electrode current collecting tab 1405 and the negative electrode current collecting tab 1406 are ultrasonically welded to the positive electrode 1401 produced as described above and the uncoated part (current collector exposed surface) of the negative electrode 1403, respectively. For example, the positive electrode current collecting tab 1405 can be an aluminum lead piece, and the negative electrode current collecting tab 1406 can be a nickel lead piece. Thereafter, a separator 1402 made of a porous polyethylene film having a thickness of 30 μm is inserted into the positive electrode 1401 and the negative electrode 1403, and the positive electrode 1401, the separator 1402, and the negative electrode 1403 are wound. The wound body is accommodated in the battery can 1404, and the negative electrode current collecting tab 1406 is connected to the bottom of the battery can 1404 by a resistance welder. The positive electrode current collecting tab 1405 is connected to the bottom surface of the inner lid 1407 by ultrasonic welding.
　上部の電池蓋１４１１を電池缶１４０４に取り付ける前に、非水電解液を注入する。電解液の溶媒は、例えば、エチレンカーボネート（ＥＣ）とジメチルカーボネート（ＤＭＣ）とジエチルカーボネート（ＤＥＣ）からなり、体積比は１：１：１である。電解質は濃度１ｍｏｌ／Ｌ（約０．８ｍｏｌ／ｋｇ）のＬｉＰＦ6である。このような電解液を電極群の上から滴下し、電池蓋１４１１を電池缶１４０４に、かしめて密封し、リチウムイオン二次電池が得られる。 Before attaching the upper battery lid 1411 to the battery can 1404, a non-aqueous electrolyte is injected. The solvent of the electrolytic solution is composed of, for example, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and the volume ratio is 1: 1: 1. The electrolyte is LiPF 6 at a concentration of 1 mol / L (about 0.8 mol / kg). Such an electrolytic solution is dropped from above the electrode group, and the battery lid 1411 is caulked and sealed in the battery can 1404 to obtain a lithium ion secondary battery.
　次に、本発明の第２の実施例について、図４を用いて説明する。図４は、本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。負極活物質１０００は、不純物ドープシリコンナノワイヤ２００および黒鉛３００で構成される。本実施例では、黒鉛３００の表面に、不純物ドープシリコンナノワイヤ２００を形成した。不純物ドープシリコンナノワイヤ２００は、黒鉛３００表面に直接結合しており、黒鉛３００の表面から成長している。 Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. The negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200 and graphite 300. In this example, impurity-doped silicon nanowires 200 were formed on the surface of graphite 300. The impurity-doped silicon nanowire 200 is directly bonded to the surface of the graphite 300 and grows from the surface of the graphite 300.
　黒鉛３００表面での不純物ドープシリコンナノワイヤ２００の成長メカニズムを明確にするために、不純物ドープシリコンナノワイヤ２００の成長の初期段階で成長を中断し、試料を取出して、走査型電子顕微鏡で観察した。図５は、成長を中断した不純物ドープシリコンナノワイヤの走査型電子顕微鏡写真である。その結果、黒鉛３００の表面に、直径が数十ｎｍの不純物ドープシリコンナノ粒子が無数に存在していた。この事実より、黒鉛３００表面に、まずシリコンナノ粒子が成長し、そのシリコンナノ粒子が、不純物ドープシリコンナノワイヤ２００へと成長すると推察できる。 In order to clarify the growth mechanism of the impurity-doped silicon nanowire 200 on the surface of the graphite 300, the growth was interrupted at the initial stage of the growth of the impurity-doped silicon nanowire 200, the sample was taken out, and observed with a scanning electron microscope. FIG. 5 is a scanning electron micrograph of an impurity-doped silicon nanowire whose growth has been interrupted. As a result, an infinite number of impurity-doped silicon nanoparticles having a diameter of several tens of nm were present on the surface of the graphite 300. From this fact, it can be inferred that silicon nanoparticles first grow on the surface of graphite 300 and the silicon nanoparticles grow into impurity-doped silicon nanowires 200.
　次に、本実施例について、図６および図７を用いて説明する。図６は、黒鉛表面に成長した不純物ドープシリコンナノワイヤの走査型電子顕微鏡写真である。このように、不純物ドープシリコンナノワイヤ２００を非常に密に作製することが可能である。このサンプルは、シリコンと炭素を含む複合材料であり、熱重量測定法により測定したシリコンの重量比は、２３ｗｔ％であった。シリコンの重量比は、成長条件を変えることにより、調整することが可能である。 Next, this embodiment will be described with reference to FIGS. FIG. 6 is a scanning electron micrograph of impurity-doped silicon nanowires grown on the graphite surface. In this way, the impurity-doped silicon nanowires 200 can be manufactured very densely. This sample was a composite material containing silicon and carbon, and the weight ratio of silicon measured by thermogravimetry was 23 wt%. The weight ratio of silicon can be adjusted by changing the growth conditions.
　図７は、同じサンプルの透過型電子顕微鏡写真である。直径は３０ｎｍであり、内部はシリコンの格子縞がみえていることから、シリコンナノワイヤ２００は結晶性を有する、特に、多結晶構造であると考えられる。シリコンナノワイヤ２００が結晶性を有することにより、リチウムイオンの拡散速度が大きくなる。結果として、リチウムイオンの充填および放出速度が速く、高速充放電特性が向上する。また、不純物ドープシリコンナノワイヤ２００の表面には、３ｎｍ弱の自然酸化膜層が存在している。 FIG. 7 is a transmission electron micrograph of the same sample. Since the diameter is 30 nm and the inside shows silicon lattice stripes, the silicon nanowire 200 is considered to have crystallinity, particularly a polycrystalline structure. When silicon nanowire 200 has crystallinity, the diffusion rate of lithium ions increases. As a result, the charging and discharging speed of lithium ions is fast, and the high-speed charge / discharge characteristics are improved. In addition, a natural oxide film layer of less than 3 nm exists on the surface of the impurity-doped silicon nanowire 200.
　不純物ドープシリコンナノワイヤ２００は、黒鉛３００表面に直接結合しており、その接合面では、不純物ドープシリコンナノワイヤ２００のシリコン原子と、黒鉛３００表面の炭素原子との間に、化学結合が形成されていると考えられる。 The impurity-doped silicon nanowire 200 is directly bonded to the surface of the graphite 300, and a chemical bond is formed between the silicon atom of the impurity-doped silicon nanowire 200 and the carbon atom on the surface of the graphite 300 at the bonding surface. it is conceivable that.
　本実施例において、不純物ドープシリコンナノワイヤ２００成長のための基材として用いた黒鉛３００は、人造黒鉛、天然黒鉛、酸化黒鉛、熱膨張酸化黒鉛等、あらゆる種類および形態の黒鉛を用いることが可能である。 In this embodiment, the graphite 300 used as the base material for the growth of the impurity-doped silicon nanowire 200 can use any kind and form of graphite such as artificial graphite, natural graphite, graphite oxide, and thermally expanded graphite. is there.
　次に、本発明の第３の実施例について、図８を用いて説明する。図８は、本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。負極活物質１０００は、不純物ドープシリコンナノワイヤ２００およびカーボンナノチューブ４００で構成される。本実施例では、炭素基材に、カーボンナノチューブ４００を用い、その表面に不純物ドープシリコンナノワイヤ２００を成長した点が、第２の実施例と異なる。 Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 8 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. The negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200 and carbon nanotubes 400. The present embodiment is different from the second embodiment in that carbon nanotubes 400 are used as a carbon base material and impurity-doped silicon nanowires 200 are grown on the surface thereof.
　本実施例において、不純物ドープシリコンナノワイヤ２００成長のための基材として、カーボンナノチューブ４００を用いたが、カーボンナノホーン、アセチレンブラック、ケッチェンブラック等、あらゆる形態のカーボン系ナノ構造体を用いることが可能である。 In this example, the carbon nanotube 400 was used as the base material for the growth of the impurity-doped silicon nanowire 200, but it is possible to use any form of carbon-based nanostructure such as carbon nanohorn, acetylene black, ketjen black, etc. It is.
　次に、本発明の第４の実施例について、図９を用いて説明する。図９は、本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。本実施例では、まず炭素基材上に不純物ドープシリコンナノワイヤ２００を成長し、その後、炭素基材と不純物ドープシリコンナノワイヤ２００を分離し、不純物ドープシリコンナノワイヤ２００だけを負極材料として用いた点が、第２の実施例および第３の実施例と異なる。これにより、全重量に対するシリコンの重量比を大幅に増大することができるため、電気容量を飛躍的に増やすことが可能である。 Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 9 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. In this example, first, the impurity-doped silicon nanowire 200 is grown on the carbon substrate, and then the carbon substrate and the impurity-doped silicon nanowire 200 are separated, and only the impurity-doped silicon nanowire 200 is used as the negative electrode material. Different from the second and third embodiments. As a result, the weight ratio of silicon to the total weight can be greatly increased, so that the electric capacity can be dramatically increased.
　次に、本発明の第５の実施例について、図１０、図１１、図１２、図１３および図１４を用いて説明する。図１０は、本発明の一実施形態に係るリチウムイオン二次電池用負極活物質の構造を模式的に表現したものである。負極活物質１０００は、不純物ドープシリコンナノワイヤ２００および電気伝導性炭素薄膜５００で構成される。 Next, a fifth embodiment of the present invention will be described with reference to FIGS. 10, 11, 12, 13, and 14. FIG. FIG. 10 schematically represents the structure of a negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. The negative electrode active material 1000 is composed of impurity-doped silicon nanowires 200 and an electrically conductive carbon thin film 500.
　負極活物質１０００は、不純物ドープシリコンナノワイヤ２００の表面が、電気伝導性炭素薄膜５００で部分的または全体に覆われた構造である。換言すると、不純物ドープシリコンナノワイヤ２００の表面に電気伝導性炭素薄膜５００が形成されている。 The negative electrode active material 1000 has a structure in which the surface of the impurity-doped silicon nanowire 200 is partially or entirely covered with the electrically conductive carbon thin film 500. In other words, the electrically conductive carbon thin film 500 is formed on the surface of the impurity-doped silicon nanowire 200.
　電気伝導性炭素薄膜５００は、ナノグラフェンが多層に積層した構造を有し、１０００Ｓ／ｍ以上の電気伝導度を有する。不純物ドープシリコンナノワイヤ２００がナノグラフェン構造を有する電気伝導性炭素薄膜５００で部分的または全体に被覆されることにより、不純物ドープシリコンナノワイヤ２００に電気伝導性を付加することができる。これにより、不純物ドープシリコンナノワイヤ２００が途中で折れた場合、あるいは不純物ドープシリコンナノワイヤ２００が電気伝導性炭素薄膜５００から剥離した場合にも、集電体との電気伝導を確保し、電気的孤立を防ぐことができるので、リチウムイオン二次電池の不可逆容量を低減できる。 The electrically conductive carbon thin film 500 has a structure in which nanographene is laminated in multiple layers, and has an electrical conductivity of 1000 S / m or more. By electrically or partially covering the impurity-doped silicon nanowire 200 with the electrically conductive carbon thin film 500 having a nanographene structure, electrical conductivity can be added to the impurity-doped silicon nanowire 200. Accordingly, even when the impurity-doped silicon nanowire 200 is broken in the middle or when the impurity-doped silicon nanowire 200 is peeled off from the electrically conductive carbon thin film 500, electrical conduction with the current collector is ensured and electrical isolation is achieved. Therefore, the irreversible capacity of the lithium ion secondary battery can be reduced.
　電気伝導性炭素薄膜５００の膜厚Ｌcは、０．２ｎｍ以上、１００ｎｍ以下である。電気伝導性炭素薄膜５００の膜厚Ｌcが、０．２ｎｍ未満である場合、被覆強度が不十分で、部分的に剥がれる可能性があり、その場合には、十分な電気伝導性を確保することができない可能性がある。また、電気伝導性炭素薄膜５００の膜厚Ｌcが、１００ｎｍを超える場合、全体の重量に対するシリコンの重量を２０ｗｔ％にすることが困難であり、結果として十分な電気容量を得ることができない可能性がある。 The film thickness L c of the electrically conductive carbon thin film 500 is not less than 0.2 nm and not more than 100 nm. Thickness L c of electrically conductive carbon film 500, is less than 0.2 nm, the coating strength is inadequate, there is a possibility that peeling partially, in which case, to ensure a sufficient electrical conductivity It may not be possible. The thickness L c of electrically conductive carbon film 500, if it exceeds 100 nm, it is difficult to the weight of silicon to the total weight 20 wt%, can not be able to consequently obtain a sufficient electric capacity There is sex.
　図１１は、炭素被覆した不純物ドープシリコンナノワイヤの走査型電子顕微鏡写真である。このように、炭素被覆した不純物ドープシリコンナノワイヤ２００を非常に密に成長することが可能である。図１２は、同じサンプルの拡大写真である。炭素被覆した不純物ドープシリコンナノワイヤ２００の表面が、電気伝導性炭素薄膜５００で均一に覆われていると考えられる。 FIG. 11 is a scanning electron micrograph of an impurity-doped silicon nanowire coated with carbon. In this way, the carbon-coated impurity-doped silicon nanowire 200 can be grown very densely. FIG. 12 is an enlarged photograph of the same sample. It is considered that the surface of the carbon-doped impurity-doped silicon nanowire 200 is uniformly covered with the electrically conductive carbon thin film 500.
　図１３は、炭素被覆した不純物ドープシリコンナノワイヤの透過型電子顕微鏡写真である。ワイヤの中央付近には、格子縞を有する不純物ドープシリコンナノワイヤ２００を観察することができる。また、不純物ドープシリコンナナワイヤ２００の表面には、不純物ドープシリコンナノワイヤ２００の軸方向に沿って配向したナノグラフェン多層構造を有する電気伝導性炭素薄膜５００を観察することができる。不純物ドープシリコンナナワイヤ２００の軸方向に沿って電気伝導性炭素薄膜５００が配向していることにより、電気伝導性炭素薄膜５００が剥がれにくい強固な膜に成る。不純物ドープシリコンナノワイヤ２００の直径は１８ｎｍであり、電気伝導性炭素薄膜５００の膜厚は６．４４－８．１７ｎｍであった。 FIG. 13 is a transmission electron micrograph of carbon-coated impurity-doped silicon nanowires. In the vicinity of the center of the wire, an impurity-doped silicon nanowire 200 having a lattice pattern can be observed. In addition, on the surface of the impurity-doped silicon nanowire 200, an electrically conductive carbon thin film 500 having a nanographene multilayer structure oriented along the axial direction of the impurity-doped silicon nanowire 200 can be observed. Since the electrically conductive carbon thin film 500 is oriented along the axial direction of the impurity-doped silicon nana wire 200, the electrically conductive carbon thin film 500 becomes a strong film that is difficult to peel off. The diameter of the impurity-doped silicon nanowire 200 was 18 nm, and the thickness of the electrically conductive carbon thin film 500 was 6.44-8.17 nm.
　別のサンプルの透過型電子顕微鏡写真を図１４に示す。図１４は、炭素被覆した不純物ドープシリコンナノワイヤの透過型電子顕微鏡写真である。不純物ドープシリコンナノワイヤ２００の直径は１８ｎｍであり、電気伝導性炭素薄膜５００の膜厚は１０ｎｍであった。 FIG. 14 shows a transmission electron micrograph of another sample. FIG. 14 is a transmission electron micrograph of impurity-doped silicon nanowires coated with carbon. The diameter of the impurity-doped silicon nanowire 200 was 18 nm, and the thickness of the electrically conductive carbon thin film 500 was 10 nm.
　次に、本発明の第６の実施例について、図１５を用いて説明する。図１５は、炭素基材の表面に不純物ドープシリコンナノワイヤを形成するための熱気相成長装置の概略図である。 Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 15 is a schematic diagram of a thermal vapor deposition apparatus for forming impurity-doped silicon nanowires on the surface of a carbon substrate.
　シリコン原料には、液体の四塩化シリコンを用い、水素ガスでバブリング（図１５左の一番下のライン）することにより、反応炉に導入した。四塩化シリコンの２０℃における蒸気圧は３０ｋＰａであり、バブリング導入すると、四塩化シリコンの導入量は３４％となる。そこで、それ以下の量の四塩化シリコンを導入する場合には、四塩化シリコンを冷却するか、水素ガスの別ライン（図１５左の真ん中のライン）を設ける必要がある。本実施例では、バブリングしない水素ラインを別に設け、バブリングラインと合流して、反応炉に導入した。 Liquid silicon tetrachloride was used as the silicon raw material, and was introduced into the reactor by bubbling with hydrogen gas (the bottom line on the left in FIG. 15). The vapor pressure of silicon tetrachloride at 20 ° C. is 30 kPa, and when bubbling is introduced, the amount of silicon tetrachloride introduced is 34%. Therefore, when introducing a smaller amount of silicon tetrachloride, it is necessary to cool the silicon tetrachloride or to provide another hydrogen gas line (middle line on the left in FIG. 15). In this example, a hydrogen line that was not bubbled was provided separately, joined with the bubbling line, and introduced into the reactor.
　また、ドーパントライン（図１５左の一番上のライン）を設け、ドーパントとなるボロン、リン、ヒ素、窒素等の元素を構成要素として含有する有機化合物を、ドーパント原料として導入した。上記の有機化合物が気体の場合は、アルゴン等の不活性ガスと混合して導入した。また、液体の場合は、アルゴン等の不活性ガスでバブリングすることにより導入した。例えば、ボロン含有有機化合物としては各種ボロン酸エステル、リン含有有機化合物としては、各種ホスホン酸エステル、各種リン酸エステル、各種亜リン酸エステル、窒素含有有機化合物としては、各種アミン、各種アミド、各種イミン、各種ニトリルを用いることが可能である。 Also, a dopant line (the uppermost line on the left in FIG. 15) was provided, and an organic compound containing elements such as boron, phosphorus, arsenic, and nitrogen as dopants was introduced as a dopant raw material. When the organic compound was a gas, it was introduced by mixing with an inert gas such as argon. In the case of a liquid, it was introduced by bubbling with an inert gas such as argon. For example, boron-containing organic compounds include various boronic esters, phosphorus-containing organic compounds include various phosphonic esters, various phosphoric esters, various phosphites, and nitrogen-containing organic compounds include various amines, various amides, various types It is possible to use imine and various nitriles.
　炭素被覆不純物ドープシリコンナノワイヤ成長の手順は、下記の通りである。サンプルボートに炭素基材を入れて、反応炉の中央付近に設置する。炭素基材には、黒鉛、熱膨張酸化黒鉛、酸化黒鉛、カーボンナノチューブ、カーボンナノホーン等、いかなる形態の炭素材料を用いることが可能である。反応炉は、石英製であり、直径が５ｃｍ、長さが４０ｃｍである。図１５左真ん中の水素ラインには、水素を２００ｍＬ／ｍｉｎの流速で流し、下のバブリング水素ラインは閉じた状態で、成長炉を室温から１０００℃まで、１０℃／ｍｉｎでの速度で昇温した。 The procedure for growing carbon-coated impurity-doped silicon nanowires is as follows. Put the carbon substrate in the sample boat and install it near the center of the reactor. As the carbon substrate, any form of carbon material such as graphite, thermally expanded graphite oxide, graphite oxide, carbon nanotube, carbon nanohorn, etc. can be used. The reactor is made of quartz and has a diameter of 5 cm and a length of 40 cm. In the middle left hydrogen line of FIG. 15, hydrogen is allowed to flow at a flow rate of 200 mL / min, and the lower bubbling hydrogen line is closed, and the growth furnace is heated from room temperature to 1000 ° C. at a rate of 10 ° C./min. did.
　次に、１０００℃に達したところで、上の水素ラインの流量を１００ｍＬ／ｍｉｎに変更し、下のバブリング水素ラインの水素ラインの流量を１００ｍＬ／ｍｉｎに設定した。この条件により、１７％の四塩化シリコンを導入することができる。また、同時にドーパントラインから、ドーパント原料を導入した。１０００℃で１時間成長した後、ドーパントラインおよび下のバブリング水素ラインを閉じ、上の水素ラインの流量を２００ｍＬ／ｍｉｎに変更して、１０００℃で３０分間保持した。これにより、直径が２０ｎｍの不純物ドープシリコンナノワイヤ２００を炭素基材表面に作製することが可能である。 Next, when the temperature reached 1000 ° C., the flow rate of the upper hydrogen line was changed to 100 mL / min, and the flow rate of the hydrogen line of the lower bubbling hydrogen line was set to 100 mL / min. Under this condition, 17% silicon tetrachloride can be introduced. At the same time, a dopant raw material was introduced from the dopant line. After growing at 1000 ° C. for 1 hour, the dopant line and the lower bubbling hydrogen line were closed and the flow rate of the upper hydrogen line was changed to 200 mL / min and held at 1000 ° C. for 30 minutes. Thereby, it is possible to produce the impurity-doped silicon nanowire 200 having a diameter of 20 nm on the surface of the carbon substrate.
　不純物ドープシリコンナノワイヤ２００成長時の温度、四塩化シリコン導入量、成長時間をかえることにより、不純物ドープシリコンナノワイヤ２００の直径および成長重量を変えることが可能である。また、ドーパント原料の導入量を変えることにより、不純物ドープシリコンナノワイヤ２００へのドーピング量を変えることが可能である。 The diameter and growth weight of the impurity-doped silicon nanowire 200 can be changed by changing the temperature at the time of growth of the impurity-doped silicon nanowire 200, the amount of silicon tetrachloride introduced, and the growth time. Moreover, it is possible to change the doping amount to the impurity-doped silicon nanowire 200 by changing the introduction amount of the dopant raw material.
　また、不純物ドープシリコンナノワイヤ２００の表面を、電気伝導性炭素薄膜５００で被覆するためには、引続いて、以下の手順を行う。 Further, in order to cover the surface of the impurity-doped silicon nanowire 200 with the electrically conductive carbon thin film 500, the following procedure is subsequently performed.
　まず、両水素ラインを閉じ、アルゴンガス（図１５にアルゴンラインは記載していない）を２００ｍＬ／ｍｉｎの流速で流し、１０℃／ｍｉｎの速度で降温し、８００℃まで降温した。８００℃に達したところで、プロピレンガス（図１５にプロピレンラインは記載していない）を１０ｍＬ／ｍｉｎの流速で導入し、同時にアルゴンガスの流速を１９０ｍＬ／ｍｉｎにして、電気伝導性炭素薄膜５００を１時間成長した。その後、プロピレンガスラインを閉じ、アルゴンガスを２００ｍＬ／ｍｉｎの流速で流し、３０分間保持した後、自然冷却した。これにより、不純物ドープシリコンナノワイヤ２００の表面に、ナノグラフェン多層構造を有する電気伝導性炭素薄膜５００（膜厚１０ｎｍ）を作製することが可能である。 First, both hydrogen lines were closed, and argon gas (the argon line is not shown in FIG. 15) was flowed at a flow rate of 200 mL / min, the temperature was lowered at a rate of 10 ° C./min, and the temperature was lowered to 800 ° C. When the temperature reached 800 ° C., propylene gas (the propylene line is not shown in FIG. 15) was introduced at a flow rate of 10 mL / min, and at the same time the argon gas flow rate was set to 190 mL / min, It grew for 1 hour. Thereafter, the propylene gas line was closed, and argon gas was allowed to flow at a flow rate of 200 mL / min, maintained for 30 minutes, and then naturally cooled. Thereby, it is possible to produce an electrically conductive carbon thin film 500 (thickness 10 nm) having a nanographene multilayer structure on the surface of the impurity-doped silicon nanowire 200.
　なお、本実施例では、不純物ドープシリコンナノワイヤ２００の表面酸化を防ぐために、不純物ドープシリコンナノワイヤ２００の作製と、それに続く電気伝導性炭素薄膜５００の作製を、連続して行った。このように、不純物ドープシリコンナノワイヤ２００の作製と、それに続く電気伝導性炭素薄膜５００の作製を、連続して行うことにより、自然酸化膜の形成を防止し、自然酸化膜の還元除去プロセスが不要になる。 In this example, in order to prevent the surface oxidation of the impurity-doped silicon nanowire 200, the production of the impurity-doped silicon nanowire 200 and the subsequent production of the electrically conductive carbon thin film 500 were continuously performed. In this way, the production of the impurity-doped silicon nanowire 200 and the subsequent production of the electrically conductive carbon thin film 500 are continuously performed, thereby preventing the formation of a natural oxide film and eliminating the process of reducing and removing the natural oxide film. become.
　不純物ドープシリコンナノワイヤ２００を成長後、一度空気中に取出し、その後還元雰囲気で熱処理して、不純物ドープシリコンナノワイヤ２００の表面の自然酸化膜を取り除いた後に、引き続いて電気伝導性炭素薄膜５００を作製することも可能である。不純物ドープシリコンナノワイヤ２００の成長と電気伝導性炭素薄膜５００の作製を別々の反応炉で行うことにより、生産性が向上する。また、不純物ドープシリコンナノワイヤ２００成長時の温度、四塩化シリコン導入量、成長時間をかえることにより、不純物ドープシリコンナノワイヤ２００の直径および成長重量を変えることが可能である。また、電気伝導性炭素薄膜５００の成長時間を変えることにより、電気伝導性炭素薄膜５００の膜厚を制御することが可能である。また、電気伝導性炭素薄膜５００作製には、プロピレンガス以外に、アセチレンガス、プロパンガス、メタンガス等の種々の炭化水素ガスを用いることが可能である。 After the impurity-doped silicon nanowire 200 is grown, the impurity-doped silicon nanowire 200 is once taken out into the air and then heat-treated in a reducing atmosphere to remove the natural oxide film on the surface of the impurity-doped silicon nanowire 200, and then the electrically conductive carbon thin film 500 is produced. It is also possible. The productivity is improved by growing the impurity-doped silicon nanowires 200 and producing the electrically conductive carbon thin film 500 in separate reactors. Further, the diameter and growth weight of the impurity-doped silicon nanowire 200 can be changed by changing the temperature at the time of growth of the impurity-doped silicon nanowire 200, the amount of silicon tetrachloride introduced, and the growth time. Further, by changing the growth time of the electrically conductive carbon thin film 500, the film thickness of the electrically conductive carbon thin film 500 can be controlled. In addition to the propylene gas, various hydrocarbon gases such as acetylene gas, propane gas, and methane gas can be used for producing the electrically conductive carbon thin film 500.
　次に、本発明の第７の実施例について、図１６を用いて説明する。図１６は、シリコンと炭素の複合材料に関して、全体重量に対するシリコンの重量比Ｓｉ／（Ｓｉ＋Ｃ）に対する、負極電気容量の依存性を計算した結果である。炭素に対しては、リチウムイオンを充填した際の化学量論的組成を、ＬｉＣ6と仮定し、その電気容量を３７２ｍＡｈ／ｇとした。また、シリコンに対しては、リチウムイオンを充填した際の化学量論的組成を、Ｌｉ15Ｓｉ4と仮定し、その電気容量を３５７７ｍＡｈ／ｇとした場合と、Ｌｉ22Ｓｉ5と仮定し、その電気容量を４１９７ｍＡｈ／ｇとした場合について、計算した。 Next, a seventh embodiment of the present invention will be described with reference to FIG. FIG. 16 shows the calculation result of the dependence of the negative electrode capacitance on the weight ratio Si / (Si + C) of silicon with respect to the total weight of the composite material of silicon and carbon. For carbon, the stoichiometric composition when filled with lithium ions was assumed to be LiC 6 and its electric capacity was 372 mAh / g. For silicon, the stoichiometric composition when lithium ions are filled is assumed to be Li 15 Si 4, and the electric capacity is assumed to be 3577 mAh / g, and Li 22 Si 5 is assumed, It calculated about the case where the electric capacity was 4197 mAh / g.
　正極電気容量とのバランスから、負極電気容量として、１０００ｍＡｈ／ｇ以上を実現できれば、当面は十分な性能であると考えられる。図１６の計算結果より、負極電気容量として、１０００ｍＡｈ／ｇ以上を実現するためには、重量比でリチウムイオン二次電池用負極活物質に対して２０％以上、特に４０％以上、更には８０％以上のシリコンを含有することが望ましい。 From the balance with the positive electrode electric capacity, if the negative electrode electric capacity is 1000 mAh / g or more, it is considered that the performance is sufficient for the time being. From the calculation result of FIG. 16, in order to realize the negative electrode electric capacity of 1000 mAh / g or more, the weight ratio is 20% or more, particularly 40% or more, more preferably 80%, with respect to the negative electrode active material for lithium ion secondary battery. It is desirable to contain more than% silicon.
１００　炭素基材
１１０　シリコンナノワイヤ
２００　不純物ドープシリコンナノワイヤ
３００　黒鉛
４００　カーボンナノチューブ
５００　電気伝導性炭素薄膜
１０００　負極活物質
１４０１　正極
１４０２　セパレータ
１４０３　負極
１４０４　電池缶
１４０５　正極集電タブ
１４０６　負極集電タブ
１４０７　内蓋
１４０８　圧力開放弁
１４０９　ガスケット
１４１０　正温度係数抵抗素子
１４１１　電池蓋 100 Carbon substrate 110 Silicon nanowire 200 Impurity doped silicon nanowire 300 Graphite 400 Carbon nanotube 500 Conductive carbon thin film 1000 Negative electrode active material 1401 Positive electrode 1402 Separator 1403 Negative electrode 1404 Battery can 1405 Positive electrode current collecting tab 1406 Negative electrode current collecting tab 1407 Inner lid 1408 Pressure release valve 1409 Gasket 1410 Positive temperature coefficient resistance element 1411 Battery cover

Claims (9)

  1. 　シリコンナノワイヤを有するリチウムイオン二次電池用負極活物質であって、
    　前記シリコンナノワイヤに不純物がドーピングされ、
    　前記シリコンナノワイヤの電気伝導率は１０Ｓ／ｍ以上であるリチウムイオン二次電池用負極活物質。     A negative electrode active material for a lithium ion secondary battery having silicon nanowires,
    The silicon nanowire is doped with impurities,
    The negative electrode active material for a lithium ion secondary battery, wherein the electrical conductivity of the silicon nanowire is 10 S / m or more.
  2. 　請求項１において、
    　前記シリコンナノワイヤの直径は、２ｎｍ以上、１００ｎｍ以下であるリチウムイオン二次電池用負極活物質。     In claim 1,
    The negative electrode active material for a lithium ion secondary battery, wherein the silicon nanowire has a diameter of 2 nm or more and 100 nm or less.
  3. 　請求項１乃至２のいずれかにおいて、
    　前記シリコンナノワイヤは、結晶性を有するリチウムイオン二次電池用負極活物質。     In any one of Claims 1 thru | or 2.
    The silicon nanowire is a negative electrode active material for a lithium ion secondary battery having crystallinity.
  4. 　請求項１乃至３のいずれかにおいて、
    　前記シリコンナノワイヤの表面に、ナノグラフェン構造を有する電気伝導性炭素薄膜が形成されるリチウムイオン二次電池用負極活物質。     In any one of Claims 1 thru | or 3,
    A negative active material for a lithium ion secondary battery, in which an electrically conductive carbon thin film having a nanographene structure is formed on the surface of the silicon nanowire.
  5. 　請求項４において、
    　前記電気伝導性炭素被覆層が、前記シリコンナノワイヤの表面に沿って配向しているリチウムイオン二次電池用負極活物質。     In claim 4,
    A negative electrode active material for a lithium ion secondary battery, wherein the electrically conductive carbon coating layer is oriented along the surface of the silicon nanowire.
  6. 　請求項４において、
    　前記電気伝導性炭素被覆層の膜厚が、０．２ｎｍ以上１００ｎｍ以下であるリチウムイオン二次電池用負極活物質。     In claim 4,
    The negative electrode active material for lithium ion secondary batteries whose film thickness of the said electroconductive carbon coating layer is 0.2 nm or more and 100 nm or less.
  7. 　請求項１乃至６のいずれかにおいて、
    　前記シリコンナノワイヤの前記リチウムイオン二次電池用負極活物質に対する重量比が２０％以上であるリチウムイオン二次電池用負極活物質。     In any one of Claims 1 thru | or 6.
    The negative electrode active material for lithium ion secondary batteries whose weight ratio with respect to the said negative electrode active material for lithium ion secondary batteries of the said silicon nanowire is 20% or more.
  8. 　請求項１乃至７のいずれかに記載のリチウムイオン二次電池用負極活物質を含むリチウムイオン二次電池。 A lithium ion secondary battery comprising the negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 7.
  9. 　シリコンナノワイヤを有するリチウムイオン二次電池用負極活物質の製造方法であって、　前記シリコンナノワイヤに不純物がドーピングされ、
    　前記シリコンナノワイヤの電気伝導率は１０Ｓ／ｍ以上であり、
    　前記シリコンナノワイヤの表面に、ナノグラフェン構造を有する電気伝導性炭素薄膜が形成され、
    　前記シリコンナノワイヤを作製後、連続して前記シリコンナノワイヤの表面に前記炭素被覆層を作製したリチウムイオン二次電池用負極活物質の製造方法。     A method for producing a negative electrode active material for a lithium ion secondary battery having silicon nanowires, wherein the silicon nanowires are doped with impurities,
    The electrical conductivity of the silicon nanowire is 10 S / m or more,
    An electrically conductive carbon thin film having a nanographene structure is formed on the surface of the silicon nanowire,
    The manufacturing method of the negative electrode active material for lithium ion secondary batteries which produced the said carbon coating layer on the surface of the said silicon nanowire continuously after producing the said silicon nanowire.
PCT/JP2014/056824 2014-03-14 2014-03-14 Negative electrode active material for lithium ion secondary batteries, method for producing negative electrode active material for lithium ion secondary batteries, and lithium ion secondary battery WO2015136684A1 (en)

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