JP2014094852A - Carbon material and method of producing the same, and composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon material used for a negative electrode capable of providing, at low costs and in large quantities, lithium ion secondary batteries with excellent cycle characteristics and input/output characteristics.SOLUTION: This invention provides a carbon material containing graphite, and a hardly-graphitizable carbon material that covers the graphite and has a nitrogen atom.

Description

  The present invention relates to a carbon material, a manufacturing method thereof, and a composite material.

  Lithium ion secondary batteries using lithium salt organic electrolyte as non-aqueous electrolyte secondary batteries are lightweight and have high energy density, and are used as power sources for mobile phones and laptop computers. Expected to be a power source for moving objects. Further, a carbon material is used for a negative electrode material of a lithium ion secondary battery of a mobile phone or a notebook computer, and in particular, graphite is used. Graphite is a lithium ion secondary battery in which particles are mixed with an organic binder and a solvent to form a graphite paste, and the graphite paste is applied to the surface of the copper foil and then the solvent is dried. Used as a negative electrode.

  Graphite includes expensive artificial graphite and relatively inexpensive graphite. As an example of the latter, natural graphite produced from nature or artificially produced graphite using raw materials such as coke and tar pitch is inexpensive. Such inexpensive graphite is graphite that is manufactured with relatively low energy consumption, and has already been manufactured in large quantities. A lithium ion secondary battery using graphite particles as a negative electrode material has a large capacity and relatively stable cycle characteristics. However, the battery has a difficulty in input / output characteristics for discharging and charging in a short time. The input / output characteristics are functions required for performing energy regeneration and high-speed discharge, for example, in a hybrid vehicle using a combination of an engine and a motor as a power source. As demand for such hybrid vehicles increases, negative electrode materials capable of providing batteries having excellent input / output characteristics have been desired.

  As carbon-based negative electrode materials that meet these demands, (1) a carbon material having a multilayer structure in which the surface of graphite particles is coated with a low crystalline carbonaceous material (for example, see Patent Document 1), and (2) non-graphite. Carbonizable carbon materials (see, for example, Patent Document 2) have been proposed. Further, the present inventors have found a non-graphitizable carbon material containing nitrogen at a high concentration (see Patent Document 3), and found that the carbon material is excellent in input / output characteristics and cycle characteristics. (See Patent Document 4). Patent Document 3 discloses azulmic acid as a precursor of a nitrogen-containing carbon material containing nitrogen at a high concentration, and discloses a method for producing a nitrogen-containing carbon material by carbonizing (carbonizing) azulmic acid. Yes. Furthermore, the discovery of a solvent that dissolves azulmic acid dramatically improves the processability of azulmic acid, and is expected to be applied to various new carbon materials (see Patent Documents 5 and 6).

Japanese Patent Laid-Open No. 04-368778 No. 2007-040007 Table 2007-043311 No. 2008-123380 JP 2010-260773 A JP 2011-256348 A

  Recently, the processability of azurmic acid has improved, and there is room for studying the combination of azurmic acid with other materials. An example of a useful complex is a complex of graphite and azulmic acid. By combining graphite, which is inexpensive and produced in large quantities, with azulmic acid, it is possible to impart excellent cycle characteristics and input / output characteristics to the graphite, and there is a possibility that it can be produced at low cost and in large quantities.

  However, the present inventors tried to make a composite of graphite and azulmic acid with reference to the above-mentioned literature. As a result, only a small amount of azulmic acid could be supported on graphite, or azulmic acid was supported uniformly. Therefore, the cycle characteristics and input / output characteristics of graphite were not greatly improved, and it was not possible to obtain a product having satisfactory performance.

  The present invention has been made in view of such circumstances, and a carbon material used for a negative electrode capable of providing a lithium ion secondary battery excellent in cycle characteristics and input / output characteristics at a low cost and in large quantities, and a method for producing the same, In addition, an object is to provide a composite material.

  As a result of intensive studies to achieve the above object, the present inventors, for example, if the graphite is coated with a non-graphitizable carbon material having a nitrogen atom, which is a nitrogen-containing carbon material using azulmic acid as a raw material. In addition to being able to efficiently utilize the excellent input / output characteristics of non-graphitizable carbon materials, and to occupy most of the obtained carbon material with graphite, the carbon material must be manufactured at low cost and in large quantities. Therefore, the present invention has been completed.

That is, the present invention is as follows.
[1] A carbon material containing graphite and a non-graphitizable carbon material having a nitrogen atom that covers the graphite.
[2] The above carbon material, wherein the non-graphitizable carbon material contains a carbonized product of azulmic acid.
[3] A composite material containing graphite and azulmic acid covering the graphite.
[4] A method for producing a carbon material, comprising a step of subjecting a composite material containing graphite and azulmic acid covering the graphite to a heat treatment.
[5] A step of immersing the graphite in a mixed solution containing the azulmic acid and an organic acid, and a step of removing the liquid from the mixed solution in which the graphite is immersed to obtain the composite material The manufacturing method described above.
[6] The method for producing a carbon material according to claim 5, wherein the organic acid includes formic acid.
[7] The manufacturing method described above, wherein a heat treatment temperature in the heat treatment is 600 to 1500 ° C.
[8] A carbon material produced by the above production method.
[9] A negative electrode for a lithium ion secondary battery, containing the above carbon material.

  ADVANTAGE OF THE INVENTION According to this invention, the carbon material used for the negative electrode which can provide a lithium ion secondary battery excellent in cycling characteristics and input-output characteristics at low cost and in large quantities, its manufacturing method, and a composite material can be provided. .

It is a schematic diagram which shows an example of the laser Raman spectrum figure about the carbon material of this embodiment. It is a graph which shows the charging / discharging characteristic of an Example. It is a graph which shows the charging / discharging characteristic of a comparative example. It is a graph which shows the cycling characteristics of the discharge capacity of an Example and a comparative example. It is a graph which shows the cycle characteristic of the Coulomb efficiency of an Example and a comparative example. It is a graph which shows the input-output characteristic of an Example and a comparative example. It is a laser Raman spectrum figure of the carbon material of an Example. It is a laser Raman spectrum figure of the carbon material of a comparative example.

  Hereinafter, a form for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. The present embodiment is an example for explaining the present invention, and the present invention is not limited only to the embodiment. That is, the present invention can be variously modified without departing from the gist thereof.

  The carbon material of the present embodiment contains graphite and a non-graphitizable carbon material having a nitrogen atom that covers the graphite (hereinafter referred to as “nitrogen-containing non-graphitizable carbon material”). The carbon material precursor is preferably a composite material containing graphite and azulmic acid covering the graphite.

  Since graphite is naturally produced or artificially produced from coke or tar pitch, it can be produced in large quantities with relatively low energy among carbon materials, and the production cost can be kept low. Therefore, the present inventors have considered a carbon material in which graphite, for example, graphite particles are coated with a nitrogen-containing non-graphitizable carbon material, which is a carbonized product of azulmic acid, for example. If such a carbon material can be produced, the excellent input / output characteristics of the nitrogen-containing non-graphitizable carbon material can be efficiently utilized, and most of the obtained carbon material can be occupied by graphite. It is also possible to produce the carbon material at low cost and in large quantities.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors surprisingly immerse a mixed solution containing azulmic acid and an organic acid in graphite, and then liquid components in the mixed solution It was found that the graphite coated with azulmic acid, that is, the composite material according to the present embodiment can be obtained by removing. In addition, a carbon material containing a nitrogen-containing non-graphitizable carbon material that is a carbonized product of, for example, azulmic acid, covering graphite and the graphite by subjecting the obtained composite material to heat treatment and carbonization (for example) (Hereinafter also referred to as “graphite-coated carbon material”), and the obtained graphite-coated carbon material becomes a negative electrode constituting a lithium ion secondary battery having excellent cycle characteristics, input / output characteristics, and Coulomb characteristics. I found. Furthermore, it was also found that the graphite-coated carbon material is excellent in adhesion to a copper foil as a current collector of a lithium ion secondary battery negative electrode, and is advantageous for producing a lithium ion secondary battery.

  An example of the method for producing a graphite-coated carbon material of the present embodiment includes a step of performing a heat treatment on a composite material containing graphite and azulmic acid covering the graphite. The production method further includes a step of immersing graphite in a mixed solution containing azulmic acid and an organic acid, and / or a step of removing a liquid from the mixed solution in which graphite is immersed to obtain a composite material. It may be.

  Azulmic acid is a general term for polymers obtained by polymerizing hydrocyanic acid (hydrogen cyanide). What was manufactured by the well-known method can be used for cyanuric acid, and the manufacturing method is not specifically limited. For example, hydrocyanic acid is by-produced in a method for producing acrylonitrile or methacrylonitrile by a gas phase catalytic reaction in which propylene, isobutylene, tert-butyl alcohol, propane, isobutane, or the like is reacted with ammonia and an oxygen-containing gas in the presence of a catalyst. According to this method, it is possible to obtain hydrocyanic acid at a very low cost. In addition, since this type of gas phase contact reaction is a known reaction, the reaction conditions may be any known one. In order to increase the production of by-product hydrocyanic acid, for example, a raw material (such as methanol) that generates hydrocyanic acid by an ammoxidation reaction may be supplied to a reactor for synthesizing acrylonitrile or methacrylonitrile.

  Cyanic acid is also produced by the Andrewsso process in which methane, which is the main component of natural gas, is reacted with ammonia and an oxygen-containing gas in the presence of a catalyst. This method also makes it possible to obtain hydrocyanic acid at a very low cost.

  Of course, hydrocyanic acid is also produced by a laboratory production method using sodium blue soda and the like, and the product obtained in this way can also be used. However, from the viewpoint of producing a large amount of hydrocyanic acid at low cost, the hydrocyanic acid production method is preferably an industrial production method such as the production of acrylonitrile or methacrylonitrile or the Andrewsso method.

  In the step of producing azulmic acid, the raw material containing hydrocyanic acid obtained as described above is polymerized to obtain azulmic acid which is a black to brown polymer. Azulmic acid can be produced by polymerizing hydrocyanic acid and optionally a small amount of other polymerizable substances in various ways. As the polymerization method, for example, a method of heating liquefied hydrocyanic acid or an aqueous solution of hydrocyanic acid, a method of leaving them for a long time, a method of adding a base to them, a method of irradiating them with light, and radiating them with high energy The method, the method of performing various discharges in the presence thereof, and the method of electrolyzing an aqueous potassium cyanide solution are mentioned. Azulmic acid can also be obtained by recovering the deposits of the apparatus in the purifying process of cyanic acid by-produced in the ammoxidation process of propylene or the like.

  The composition of azulmic acid can be measured using a CHN analyzer. The ratio of the number of moles of nitrogen atoms to the number of moles of carbon atoms in azulmic acid ((number of moles of nitrogen atoms) / (number of moles of carbon atoms)) increases the residual ratio of nitrogen in the nitrogen-containing carbon material after carbonization. In view of the above, it is preferably 0.4 to 1.0, more preferably 0.5 to 1.0, and still more preferably 0.6 to 0.95.

Azulmic acid used in the present embodiment, the spectrogram by laser Raman spectroscopic analysis of wave number 1000～2000Cm ^-1, the Raman shift 1300～1400Cm ^-1, to exhibit peaks at any position of 1500～1600Cm ^-1 It is particularly preferable that a peak is exhibited at any position of 1360 to 1380 cm ⁻¹ and 1530 to 1550 cm ⁻¹ .

  The azulmic acid used in this embodiment preferably has a main peak at 399.0 ± 0.7 eV, more preferably 399.0 ± 0.4 eV, still more preferably 399.0 in the XPS spectrum diagram of N1s. Has a main peak at ± 0.2 eV.

  In addition, azulmic acid can be used individually by 1 type or in combination of 2 or more types from which the manufacturing method, composition, and manufacturing lot differ.

Next, a mixed solution containing azulmic acid and an organic acid (hereinafter referred to as “azurmic acid mixed solution”) will be described.
As an organic acid, the organic compound which has a carboxyl group, and the organic compound which has a sulfone group are mentioned, for example.

  More specifically, examples of the organic compound having a carboxyl group include formic acid, glycolic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caproic acid, enanthic acid, caprylic acid, and pelargonic acid. , Capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, tuberculostearic acid, arachidic acid, arachidonic acid, eicosapentaenoic acid, behenic acid, docosahexaene Acid, lignoceric acid, serotic acid, montanic acid, melicic acid, salicylic acid, trihydroxybenzoic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, cinnamic acid, melittic acid, pyruvic acid, oxalic acid, lactic acid, tartaric acid, Maleic acid, fumaric acid, malonic acid, succinic acid, phosphorus Acid, citric acid, aconitic acid, glutaric acid, adipic acid, itaconic acid, acrylic acid, and methacrylic acid.

  Examples of the organic compound having a sulfone group include methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and cyclohexanesulfonic acid.

  Of these, the preferred organic acid for dissolving azulmic acid is formic acid. An organic acid is used individually by 1 type or in combination of 2 or more types.

  Conventionally, it was considered that a nitrogen-containing carbon material using azurmic acid or azurmic acid as a raw material is hardly soluble in a solvent. The present inventors have found that azulmic acid is slightly soluble in ethylenediamine, ammonia water and concentrated sulfuric acid (see Patent Document 5 and Patent Document 6). However, according to further studies by the present inventors, even when ethylenediamine, which exhibits the most excellent solubility in the above, is coated on graphite, particularly graphite particles, the dissolving power of azulmic acid is extremely high. It turned out to be low. We also attempted to immerse a mixed solution of azulmic acid and concentrated sulfuric acid in graphite and finally coat the nitrogen-containing carbon material on the graphite, but since concentrated sulfuric acid is non-volatile, azulmic acid was added to the graphite. It was difficult to coat. On the other hand, organic acids can dissolve azulmic acid better than the above-mentioned solvents.

  The number of moles of the organic acid in the azulmic acid mixed solution is preferably 1 or more in terms of a mole ratio with respect to the number of moles of the hydrocyanic acid unit of azulmic acid. Here, the number of moles of hydrocyanic acid units of azulmic acid is a value obtained by dividing the mass (g) of azulmic acid by 27, which is the molecular weight of hydrocyanic acid. The number of moles of the organic acid is more preferably 5 or more, and still more preferably 10 or more, in the molar ratio. On the other hand, the number of moles of the organic acid is preferably 100,000 or less, more preferably 10,000 or less, and still more preferably 1,000 or less in the molar ratio.

  The azulmic acid mixed solution may contain only an organic acid as a liquid, or may further contain a liquid other than the organic acid, for example, water or an organic solvent. When an aqueous solution containing an organic acid and water is used as the liquid, the concentration of the organic acid in the aqueous solution is not particularly limited, but is generally preferably 10 to 90% by volume, more preferably 20 to 80% by volume. .

A specific method for producing an azulmic acid mixed solution will be described below as an example.
Prior to producing the azulmic acid mixture, the azulmic acid may be in the form of a powder or a block. The powdered or massive azulmic acid is preferably pulverized in advance with a ball mill or the like and used as a raw material for the mixed solution.

  When producing an azulmic acid mixed solution, first add an organic acid and other liquids to azulmic acid in a container, or add azurmic acid to an organic acid and other liquids as needed The container containing them is preferably shaken, stirred, or subjected to ultrasonic waves. In addition, the container may be heated at this time.

  Although the temperature at the time of mixing them is not specifically limited, 0-200 degreeC is preferable, More preferably, it is 10-150 degreeC, More preferably, it is 20-80 degreeC. Moreover, the pressure in a container is not specifically limited, 2 Mpa or less is preferable, 1 MPa or less is more preferable, More preferably, it is 0.2 MPa or less. Moreover, it is although it does not specifically limit as mixing time, For example, 1 minute-10 hours may be sufficient, Preferably it is 10 minutes-3 hours, More preferably, it is 30 minutes-1 hour.

  As described above, an azulmic acid mixed solution is produced, and the obtained azulmic acid mixed solution is preferably in a state in which azurmic acid is dissolved. Moreover, you may use the filtrate obtained by performing filtration of the azulmic acid liquid mixture. However, a part of azulmic acid may not be dissolved.

  The manufacturing method of this embodiment may have the process of immersing graphite in an azulmic acid liquid mixture. Thereby, an azulmic acid-graphite dispersion is obtained.

  The graphite is not particularly limited, and for example, natural graphite, graphite on scales, artificial graphite obtained by graphitizing coke / tar pitch / organic polymer material, and graphite particles obtained by pulverizing them can be used. As a method for obtaining graphite particles by pulverizing graphite, a known method such as a jet mill, a vibration mill, a pin mill, or a hammer mill may be used. The average particle diameter of the graphite particles is preferably 10 to 30 μm.

  The manufacturing method of this embodiment may have the process of removing a liquid from the obtained azulmic acid-graphite dispersion liquid.

  The removal of the liquid can be performed by evaporating the liquid, for example. The temperature at which the liquid is removed may be any condition that allows the liquid to volatilize, but is preferably 300 ° C. or lower, more preferably 200 ° C. or lower, and even more preferably 100 ° C. or lower. The pressure of the atmosphere at the time of removing the liquid is not particularly limited, and may be normal pressure or reduced pressure, but is preferably reduced pressure.

  Thus, a composite material containing graphite and azulmic acid covering the graphite is obtained. About the mass ratio of graphite and azulmic acid in the composite material, azulmic acid is preferably 0.1 to 80 parts by mass, more preferably 0.5 to 50 parts by mass with respect to 100 parts by mass of graphite. More preferably, it is 5-40 mass parts. When the azulmic acid is 0.1 parts by mass or more with respect to 100 parts by mass of graphite, the input / output characteristics of the battery when the finally obtained graphite-coated carbon material is used as a negative electrode of a secondary battery are further improved. In addition, when the amount is 80 parts by mass or less, further cost reduction and energy saving of the secondary battery can be achieved.

  About the graphite covering carbon material of this embodiment, the raw material of nitrogen-containing non-graphitizable carbon material will not be specifically limited if a nitrogen-containing non-graphitizable carbon material is produced | generated by carbonization. The raw material preferably has a nitrogen atom and is difficult to melt during the carbonization process. The content ratio of nitrogen atoms in the raw material is preferably 35% by mass or more, more preferably 50% by mass or more, based on the entire raw material, from the viewpoint of input / output characteristics and adhesiveness with a copper foil that is generally used as an electrode. More preferably, it is 60 mass% or more. Whether or not it is melted in the process of carbonization may be confirmed visually. However, if visual inspection is difficult, the raw material is powdered, heated to 400 ° C. in an inert gas, cooled after cooling, and the heated material has a powdery form like the raw material. It can be judged by whether or not it has a powdery form. Since the powder is fused if it is melted by heating, in many cases it has a fused shape or a structure in which the fusion is partially broken after fusing. It has no shape.

  From the above viewpoint, azulmic acid is preferable as a raw material for the nitrogen-containing non-graphitizable carbon material.

Hereinafter, the method for producing a graphite-coated carbon material will be described by taking as an example the case where azulmic acid is used as the raw material.
This method for producing a graphite-coated carbon material includes a step of carbonizing the composite material obtained as described above by subjecting it to a heat treatment.

  Although the method of heat treatment is not limited to the following, for example, using a rotary furnace, tunnel furnace, tubular furnace, fluidized firing furnace, etc., the composite material is preferably 600-1500 ° C., preferably in an inert gas atmosphere, More preferably, it is performed by heating (baking) in the range of 700 to 1300 ° C, more preferably 800 to 1100 ° C, and particularly preferably 850 to 1050 ° C. When the temperature of the heat treatment is 600 ° C. to 1500 ° C., a graphite-coated carbon material that can exhibit the effect of the present invention more effectively and reliably is obtained.

  Examples of the inert gas include, but are not limited to, the following gases, and examples include inert gases such as nitrogen, argon, helium, neon, and carbon dioxide. Among these, nitrogen gas is preferable. The inert gas atmosphere may be circulated even if the inert gas is stationary, but it is circulated from the viewpoint of removing the gas generated by the heat treatment from the system and maintaining a good inert gas atmosphere. Is preferred. The oxygen concentration in the inert gas is preferably 1% or less, more preferably 0.1% or less. In addition, the pressure of the atmosphere may be reduced (vacuum) during the heat treatment in an inert gas atmosphere.

  Although it does not specifically limit as heat processing time, From a viewpoint which show | plays the effect by this invention more effectively and reliably, it is preferable that it is 10 second-100 hours, More preferably, it is 5 minutes-10 hours, More preferably, it is 15 minutes-5 Time, particularly preferably in the range of 30 minutes to 2 hours. From the same viewpoint, the pressure of the atmosphere in the heat treatment is preferably 0.01 to 5 MPa, more preferably 0.05 to 1 MPa, still more preferably 0.08 to 0.3 MPa, and particularly preferably 0.09 to 0 MPa. .15 MPa.

  In addition, the manufacturing method of the graphite covering carbon material of this embodiment may have the process of heat-processing to a composite material in oxygen-containing gas atmosphere before the said carbonization process. Various conditions in the heat treatment in this step include the following conditions, but are not limited thereto. In this step, for example, a rotary furnace, a tunnel furnace, a tubular furnace, a fluidized firing furnace, a muffle furnace or the like is used, and the composite material is preferably heat-treated in air. The heat treatment temperature is preferably 140 ° C. or higher, and more preferably 170 ° C. or higher. The temperature of the heat treatment is preferably 600 ° C. or lower, more preferably 500 ° C. or lower, further preferably 400 ° C. or lower, and particularly preferably 350 ° C. or lower.

  As the oxygen-containing gas, a gas obtained by adding an inert gas to air to dilute the oxygen concentration may be used, or a gas obtained by adding oxygen gas to the air to increase the oxygen concentration may be used. The oxygen concentration in the oxygen-containing gas is preferably 5 to 30% by volume, and more preferably 15 to 25% by volume. From the viewpoint of energy saving, it is particularly preferable to use air as the oxygen-containing gas. The oxygen-containing gas in the atmosphere may be stationary or circulated, but is preferably circulated from the viewpoint of efficiently supplying oxygen consumed with the heat treatment.

  The heat treatment time in the oxygen-containing gas atmosphere is preferably 1 minute to 100 hours, more preferably 30 minutes to 10 hours, and even more preferably 1 hour to 5 hours. Moreover, the pressure of the atmosphere at the time of the heat treatment under an oxygen-containing gas atmosphere is preferably 0.01 to 5 MPa, more preferably 0.05 to 1 MPa, and further preferably 0.08 to 0.3 MPa. Preferably, it is 0.09 to 0.15 MPa, particularly preferably.

  As described above, the graphite-coated carbon material of the present embodiment is obtained.

  From the viewpoint of more effectively and reliably achieving the effects of the present invention, the graphite-coated carbon material of the present embodiment is obtained by quantifying carbon atoms and nitrogen atoms on the surface by X-ray photoelectron spectroscopy (XPS). The ratio of the number of nitrogen atoms to N (C) is preferably 0.01 to 0.5, more preferably 0.02 to 0.4, still more preferably 0.03 to 0.35, Especially preferably, it is 0.05-0.3. XPS is an X-ray source: Al tube (Al-Kα ray), tube voltage: 15 kV, tube current: 10 mA, analysis area: 600 μm × 300 μm ellipse, capture region: N1s, C1s, Pass-Energy: 20 eV, It is defined as the value when measured at.

Graphite-coated carbon material of the present embodiment, preferably, in the laser Raman spectrum of the wave number 1000～2000Cm ^-1, a peak P1 between 1300～1390Cm ^-1, at least that the peak P2 between 1550～1620Cm ^-1 Has two major peaks. It is more preferable to have two main peaks, a peak P1 between 1320 and 1380 cm ⁻¹ and a peak P2 between 1560 and 1590 cm ⁻¹ . P1 is considered to be a peak attributed to amorphous carbon, and P2 is considered to be a peak attributed to crystalline carbon.

A preferred graphite-coated carbon material of the present embodiment is characterized in that it has a shape having a skirt larger than the base line in the laser Raman spectrum diagram between P1 and P2.
This skirt can be defined by the following ratio (L / H1) and ratio (L / H2).

  FIG. 1 shows a schematic diagram of an example of a laser Raman spectrum diagram of the graphite-coated carbon material of the present embodiment. FIG. 1 is a diagram for explaining the ratio of (L / H1) and (L / H2) used in the present embodiment, and is a laser Raman spectrum obtained from the graphite-coated carbon material of the present embodiment. The figure is not limited in any way.

  In the laser Raman spectrum diagram of the graphite-coated carbon material of the present embodiment, the (L / H1) ratio is 0.3 to 0.8, preferably 0.4 to 0.7, particularly preferably 0.8. It has a part which is 5-0.6. The ratio of (L / H1) in the laser Raman spectrum is a value related to the half width of the peak. When the half width is small, the value of (L / H1) is small, and when the half width is large, the value of (L / H1) is large.

  In the laser Raman spectrum diagram of the graphite-coated carbon material of the present embodiment, the ratio (L / H2) is preferably 0.05 to 0.3, more preferably 0.07 to 0.2, and particularly preferably. It has a part which is 0.10-0.15. Here, the ratio of (L / H2) in the laser Raman spectrum of the graphite-coated carbon material of the present embodiment is a value related to the half width of the peak. When the half width is small, the value of (L / H2) is small, and when the half width is large, the value of (L / H2) is large.

  In the laser Raman spectrum of the graphite-coated carbon material of the present embodiment, the ratio of (H1 / H2) is preferably 0.1 to 0.4, more preferably 0.15 to 0.35, and still more preferably. 0.2-0.3.

L, H1, and H2 are obtained when a green laser (wavelength: 532 nm, 100 mW) is used and measured with a beam size of 0.3 mm, an operation range of 1000 to 2000 cm ⁻¹ , an integration count of 5 minutes, and an exposure time of 5 seconds. It is measured from the laser Raman spectrum.

As shown in FIG. 1, B1 is a minimum intensity value between 1000 and 1300 cm ⁻¹ , and B2 is a minimum intensity value between 1700 and 2000 cm ⁻¹ . Note that the baseline in the laser Raman spectrum diagram used in the present embodiment is a straight line connecting B1 and B2. In addition, since the baseline has amplitude due to noise, even if it is the minimum intensity value, in consideration of the influence of noise, the middle of the line width of 1000 to 1300 cm ⁻¹ is set to the minimum value, and 1700 to 2000 cm ⁻¹ . The minimum value is the middle of the line width. Furthermore, also in the following description, when a value is obtained, a value obtained by reading an intermediate value of the line width is employed.

  Next, C1 and C2 shown in FIG. 1 are the intersections of a perpendicular line drawn from the peaks P1 and P2 to the Raman shift axis and the baseline, respectively.

  D is the intersection of the base line between the peaks P1 and P2 and the perpendicular line drawn from the lowest point M having the lowest height from the base line to the Raman shift axis. The height L of the minimum point M is the length from the minimum point M to the intersection of the perpendicular line and the baseline drawn on the Raman shift axis. Specifically, it is the length of the line segment MD in the laser Raman spectrum diagram illustrated in FIG.

  On the other hand, the height H1 is the length from the peak P1 to the intersection of the perpendicular line and the baseline that are lowered to the Raman shift axis. In the laser Raman spectrum diagram illustrated in FIG. 1, the length of the line segment P1C1 corresponds to the height H1. The height H2 is the length from the peak P2 to the intersection of the perpendicular line and the baseline drawn down to the Raman shift axis. In the laser Raman spectrum diagram illustrated in FIG. 1, the length of the line segment P2C2 corresponds to the height H2.

  Since the graphite-coated carbon material of the present embodiment contains graphite and a nitrogen-containing non-graphitizable carbon material that covers the graphite, graphitization conditions (firing in an inert gas atmosphere at 2500 to 3000 ° C.) But it satisfies the characteristics of the laser Raman spectrum. On the other hand, in the case of a carbon material containing graphite and an easily graphitizable carbon material covering the graphite, the graphitizable carbon material is graphitized, and thus does not satisfy the characteristics of the laser Raman spectrum diagram.

  In the present embodiment, the graphite-coated carbon material obtained as described above can be used for a negative electrode for a lithium ion secondary battery.

  The negative electrode for a lithium ion secondary battery according to this embodiment includes the graphite-coated carbon material, and, if necessary, a binder, a conductive additive, and a current collector. Although the graphite-coated carbon material mainly functions as an active material, the negative electrode for a lithium ion secondary battery according to the present embodiment may include an active material other than the graphite-coated carbon material.

  The binder used for the negative electrode for the lithium ion secondary battery of the present embodiment is not particularly limited, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene. -Perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, polyvinyl fluoride, vinylidene fluoride-hexafluoropropylene-based fluororubber, vinylidene Fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber, vinylidene fluoride-pentafluoropropylene-based fluororubber, vinylidene fluoride-pentafluoropropylene- Vinylidene fluoride fluororubbers such as trifluoroethylene fluororubber, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber, vinylidene fluoride-chlorotrifluoroethylene fluororubber, tetrafluoroethylene-propylene fluorofluorine Rubber, Tetrafluoroethylene-perfluoroalkyl vinyl ether fluorine rubber, Thermoplastic fluorine rubber, Polyethylene, Polypropylene, Styrene butadiene rubber (SBR), Isoprene rubber, Butadiene rubber, Ethylene-acrylic acid copolymer and Ethylene-methacrylic acid copolymer Examples include coalescence. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios. The content ratio of the binder in the lithium ion secondary battery electrode is preferably 1 to 20% by mass and more preferably 2 to 10% by mass with respect to the graphite-coated carbon material. When the content ratio of the binder is 1% by mass or more, the strength of the electrode becomes more sufficient, and when the content ratio of the binder is 20% by mass or less, an increase in electric resistance and a decrease in capacity can be further suppressed.

  As a conductive support agent used for the negative electrode for lithium ion secondary batteries of this embodiment, carbon black, acetylene black, and a carbon nanotube are mentioned, for example. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios. It is preferable that the content rate of a conductive support agent is 1-20 mass% with respect to a graphite covering carbon material, and it is more preferable in it being 2-10 mass%.

  The current collector used for the negative electrode for the lithium ion secondary battery of the present embodiment is not particularly limited as long as it enables electrical connection of the electrodes. Examples of the material thereof include copper, aluminum, nickel, Examples include titanium and stainless steel. Of these, copper is preferable from the viewpoint of easy processing into a thin film and cost. Examples of the shape of the current collector include a foil shape, a perforated foil shape, and a mesh shape. As the current collector, porous materials such as porous metal (foamed metal) and carbon paper can also be used.

Next, the manufacturing method of the electrode for lithium ion secondary batteries of this embodiment is demonstrated.
The manufacturing method of the negative electrode for lithium ion secondary batteries of this embodiment will not be specifically limited if it is a well-known method except using the graphite covering carbon material of this embodiment as a carbon material. For example, by adding a binder, a conductive additive and a solvent to a carbon material including a graphite-coated carbon material to form a slurry, applying the slurry to a current collector, drying and pressing to increase the density, The method of manufacturing the negative electrode for lithium ion secondary batteries is mentioned.

  The solvent used in the method for producing the lithium ion secondary battery electrode of the present embodiment may be either aqueous or non-aqueous. Examples of the non-aqueous solvent include N-methylpyrrolidone, methyl ethyl ketone, cyclohexanone, isophorone, N, N-dimethylformamide, N, N-dimethylacetamide and toluene.

  The slurry is prepared by kneading with a dispersing device such as a stirrer, a pressure kneader, a ball mill, and a super sand mill.

  Moreover, you may add the thickener for adjusting a viscosity to the said slurry. Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, and casein. These may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  The method for applying the slurry to the current collector is not particularly limited. For example, doctor blade method, metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, gravure coating method and Well-known methods, such as a screen printing method, are mentioned. After the application of the slurry, subsequent to the drying process of the slurry, a rolling process using a flat plate press, a calendar roll, or the like is performed as necessary. Thus, the electrode material slurry formed into a sheet shape, a pellet shape, or the like is integrated with a current collector by a known method such as a roll, a press, or a combination thereof, so that the lithium ion secondary battery is used. A negative electrode can be obtained.

  The negative electrode for a lithium ion secondary battery thus obtained is an advantageous negative electrode in that the graphite-coated carbon material is excellent in adhesion to the current collector, particularly in adhesion to the copper foil. Moreover, the lithium ion secondary battery provided with the negative electrode has excellent cycle characteristics, input / output characteristics, and coulomb efficiency.

  Hereinafter, an example of a lithium ion secondary battery provided with the negative electrode for lithium ion secondary batteries of this embodiment is demonstrated. However, materials and manufacturing methods that can be used for the lithium ion secondary battery are not limited to the following specific examples.

  The lithium ion secondary battery of the present embodiment is not particularly limited with respect to the configuration other than including the electrode for the lithium ion secondary battery of the present embodiment as a negative electrode, and other than the negative electrode for the lithium ion secondary battery are known. Also good. For example, this lithium ion secondary battery includes a separator, a negative electrode for a lithium ion secondary battery of the present embodiment, which is disposed to face the separator, the positive electrode, and an electrolyte solution in contact with them. This lithium ion secondary battery can be obtained by injecting an electrolytic solution into the space between the negative electrode and the positive electrode arranged as described above.

  When the graphite-coated carbon material of the present embodiment is used, the adhesion of the negative electrode for a lithium ion secondary battery to the current collector, particularly the copper foil, is improved. The reason for this has not been clarified in detail, but because nitrogen atoms have a chemical affinity with metal atoms, especially copper atoms, graphite-coated carbon materials have improved adhesion to current collectors. It is estimated that it contributes to However, the reason is not limited to this.

  The positive electrode can be produced by forming a positive electrode layer containing a positive electrode active material on a current collector in the same manner as the negative electrode.

  As the current collector of the positive electrode, for example, it is preferable to use a metal or an alloy thereof that forms a passive film on the surface by anodic oxidation in an electrolytic solution. Examples of such a current collector include aluminum, titanium, zirconium, hafnium, niobium, tantalum, and alloys containing these metals. Among these, those selected from the group consisting of aluminum, titanium, tantalum, and alloys containing these metals are preferred, and those selected from the group consisting of aluminum and alloys thereof are particularly lightweight, so that the energy density is high and preferable. . An alloy such as stainless steel can also be used as the current collector for the positive electrode. What made these metals and alloys into foil shape, perforated foil shape, mesh shape, etc. can be used as the current collector of the positive electrode.

The positive electrode active material is not particularly limited as long as it can be doped or intercalated with lithium ions, and examples thereof include such metal compounds, metal oxides, metal sulfides, and conductive polymer materials. More specifically, for example, lithium cobalt oxide (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate (LiMnO _2), and these mixed oxide _{(LiCo x Ni y Mn z O} 2, X + Y + Z = 1), lithium manganese spinel (LiMn ₂ O ₄ ), lithium vanadium compound, olivine-type LiMPO ₄ (M: Co, Ni, Mn, Fe), vanadium oxide (V ₂ O ₅ , V ₂ O ₃ ), sulfide _{(TiS 2, FeS 2, Nb} 3 S 4, Mo 3 S 4, CoS 2), chromium oxide (CrO _3), tellurium oxide (TeO _2), germanium oxide (GeO _2), phosphorus oxide (P ₂ O ₅₎ Is mentioned. Examples of the conductive polymer material that is an organic compound include polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, and conductive polymers described in known patent documents. In addition, when using a metal oxide, a metal sulfide, etc. for a positive electrode active material, it is preferable to further contain carbonaceous materials, such as a graphite, acetylene black, and ketjen black, as a electrically conductive agent.

The electrolytic solution is prepared by dissolving a lithium-containing electrolyte in a non-aqueous solvent. Examples of the lithium-containing electrolyte include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF (CF ₃ ) ₅ , LiCF ₂ (CF ₃ ) ₄ , LiCF ₃ (CF ₃ ) ₃ , and LiCF ₄ (CF ₃ ) _2. LiCF ₅ (CF ₃ ), LiCF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₂ F ₅ CO ) ₂ , LiI, LiAlCl ₄ , LiBC ₄ O ₈ . These may be used alone or in combination of two or more. Of these, LiPF ₆ is preferably used. Furthermore, the lithium salt concentration is preferably 0.1 to 3.0 mol / L, more preferably 0.5 to 2.0 mol / L.

Nonaqueous solvents include, for example, carbonates, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons, esters, nitro compounds, phosphate ester compounds, It can be appropriately selected from sulfolane hydrocarbons and ionic liquids. Among these, carbonates, ethers, ketones, esters, lactones, halogenated hydrocarbons, sulfolane hydrocarbons, and ionic liquids are preferable. More specific non-aqueous solvents include, for example, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydro Pyran, 1,4-dioxane, anisole, monoglyme, 4-methyl-2-pentanone, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, 1,2-dichloroethane, γ-butyrolactone, γ-valerolactone, dimethoxy Ethane, diethoxyethane, methyl formate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl Examples include ru-sulfolane, trimethyl phosphate, triethyl phosphate, phosphazene derivatives, and mixed solvents thereof. As ionic liquids, 1-ethyl-3methylimidazolium, N-methyl-N-propylpyrrolidinium as a cation, bisfluorosulfonylimide, bistrifluorosulfonylimide, tetrafluoroborate, CF ₃ SO ₃ as anions , (CF ₃ SO ₂ ) N ₂ , (C ₂ F ₅ SO ₂ ) N ₂ . Among these, ethylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate are preferable, and these are used alone or in combination of two or more.

  In particular, it is preferable to use a mixed solvent in which ethylene carbonate is an essential component and one or more other solvents are added as the non-aqueous solvent. In general, the mixing ratio of each solvent in the mixed solvent is preferably ethylene carbonate / other solvent = 5/95 to 70/30 (volume ratio). Since ethylene carbonate has a high freezing point and is solidified at room temperature, the addition of one or more other solvents having a low freezing point lowers the freezing point of the mixed solvent and can be used. Other solvents are not particularly limited as long as the freezing point of ethylene carbonate can be lowered. For example, diethyl carbonate, dimethyl carbonate, propylene carbonate, 1,2-dimethoxyethane, methyl ethyl carbonate, γ-butyrolactone, γ- Parerolactone, γ-octanoic lactone, 1,2-diethoxyethane, 1,2-ethoxymethoxyethane, 1,2-dibutoxyethane, 1,3-dioxolanane, tetrahydrofuran, 2-methyltetrahydrofuran, 4,4- Examples include dimethyl-1,3-dioxane, butylene carbonate, and methyl formate.

  In the electrolyte, carbonates such as vinylene carbonate and butylene carbonate, benzenes such as biphenyl and cyclohexylbenzene, sulfurs such as propane sultone, ethylene sulfide, hydrogen fluoride, triazole-based cyclic compounds, fluorine-containing esters, An electrolytic solution containing at least one selected from the group consisting of hydrogen fluoride complexes of tetraethylammonium fluoride and derivatives thereof, phosphazenes and derivatives thereof, amide group-containing compounds, imino group-containing compounds, and nitrogen-containing compounds is also used. be able to.

Further, as the electrolyte, one kind of solid or gel ion conductive electrolyte can be used alone or in combination of two or more kinds. Examples of the ion conductive electrolyte include polyvinylidene fluoride, polyvinylidene fluoride, -hexafluoropropylene copolymer, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyethylene glycol or derivatives thereof, LiI, Li ₃ N, Li _{1+ x} M _x Ti _2-x (PO ₄ ) ₃ (M = Al, Sc, Y, La), Li _0.5-3x R _{0.5 + x} TiO ₃ (R = La, Pr, Nd, Sm), or Li ₄ Thiorishikon typified by _-x Ge _1-x P _x S ₄ can be used. Furthermore, oxide glasses such as LiI-Li ₂ O—B ₂ O ₅ series and Li ₂ O—SiO ₂ series, or LiI—Li ₂ S—B ₂ S ₃ series, LiI—Li ₂ S—SiS ₂ series, A sulfide glass such as Li ₂ S—SiS ₂ —Li ₃ PO ₄ can be used as the ion conductive electrolyte. Moreover, an electrolyte in which a lithium salt is dissolved in a polymer, for example, an electrolyte in which a lithium salt is dissolved in polyethylene oxide and does not contain an electrolytic solution can be used as the ion conductive electrolyte.

  If a separator is used for a normal lithium ion secondary battery, a material and a shape will not be restrict | limited in particular. This separator separates the positive electrode and the negative electrode so that they do not come into physical contact, and preferably has high ion permeability. Examples of the separator include a synthetic resin microporous membrane, a woven fabric, and a nonwoven fabric, and a synthetic resin microporous membrane is preferable. Examples of the material of the synthetic resin microporous membrane include polyolefins such as polyethylene, polypropylene, and polybutene, polyamide, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, and polyvinylidene fluoride. Among these, polyethylene and polypropylene are preferable. In addition, when it is set as the structure which does not contact the positive electrode and negative electrode of the lithium ion secondary battery to produce, it is not necessary to use a separator.

  The structure of the lithium ion secondary battery of the present embodiment is not particularly limited. Usually, a positive electrode and a negative electrode, and a separator provided as necessary, are wound in a flat spiral shape to form a wound electrode group. These are generally laminated to form a laminated electrode plate group, and the electrode plate group is sealed in an exterior body.

  The lithium ion secondary battery of this embodiment has forms such as a paper-type battery, a button-type battery, a coin-type battery, a stacked battery, and a cylindrical battery.

  Hereinafter, although an example etc. are given and the present invention is explained still in detail, these are illustrations and the present invention is not limited to these. Accordingly, those skilled in the art can implement the present invention by making various modifications to the embodiments described below, and such modifications are included in the scope of the claims of the present application.

<Production example>
(Manufacture of azulmic acid)
An aqueous solution in which 150 g of hydrocyanic acid was dissolved in 350 g of water was prepared in a container. Then, polymerization of hydrocyanic acid started and a blackish brown polymer started to precipitate, and the temperature gradually increased to 45 ° C. Two hours after the start of the polymerization, a 30% by mass aqueous solution of hydrocyanic acid was added at a rate of 200 g / hour, and 800 g was added over 4 hours. During the addition of the aqueous hydrocyanic acid solution, the vessel was cooled and controlled to maintain the reaction temperature at 50 ° C. Stir at this temperature for 100 hours. The resulting black precipitate was separated by filtration. The yield of the precipitate at this time was 96% by mass with respect to the total amount of hydrocyanic acid used. The separated precipitate was washed with water and then dried at 120 ° C. for 4 hours in a drier to obtain azulmic acid.

<Azuric acid analysis>
(CHN analysis)
Using an elemental analyzer (trade name “MICRO CORDER JM10”) manufactured by J Science Lab, a sample stage was filled with 2500 μg of azulmic acid sample, and CHN analysis was performed. The temperature of the sample furnace is 950 ° C., the temperature of the combustion furnace (copper oxide catalyst) is 850 ° C., and the temperature of the reduction furnace (consisting of a silver grain + copper oxide zone, a reduced copper zone and a copper oxide zone) is 550 ° C. Set to. The oxygen flow rate was set to 15 mL / min, and the He flow rate was set to 150 mL / min. TCD was used as a detector. Calibration was performed by the method described in the manual using Antipyrine.

  As a result, the composition of the azulmic acid obtained as described above was 40.0% by mass of carbon element, 29.8% by mass of nitrogen element, and 4.1% by mass of hydrogen element. Here, since the adsorbed water remains under the above-described drying conditions, the difference is considered to be mainly derived from the oxygen element and the hydrogen element in the adsorbed water.

<Measurement of laser Raman spectrum>
The sample was mounted on a powder cell with an agate mortar, and the laser Raman spectrum was measured under the following conditions.
Apparatus: Product name “NRS-3100” manufactured by JASCO, Light source: Green laser (wavelength: 532 nm, 100 mW), beam size: 0.3 mm, operation range: 1000 to 2000 cm ⁻¹ , integration number: 5 minutes, exposure time: 5 Second

<Preparation of negative electrode for lithium ion secondary battery>
Styrene butadiene rubber (binder) is dissolved in pure water to prepare a 5% by mass solution, acetylene black (conducting aid) is added thereto, and then an active material (in the examples, graphite-coated carbon material) In the comparative example, graphite) was added, and then carboxymethylcellulose (thickener) was added to prepare a slurry-like negative electrode mixture. At this time, the viscosity of the slurry was adjusted by appropriately adding pure water. The mass ratio of the active material, acetylene black, carboxymethyl cellulose, and styrene butadiene rubber was adjusted to be active material: acetylene black: carboxymethyl cellulose: styrene butadiene rubber = 93: 3: 2: 2.

  The obtained negative electrode mixture was applied onto a copper foil (current collector) using a doctor blade. Then, it vacuum-dried at 80 degreeC for 24 hours. After vacuum drying, the dried product was pressure-formed through a roll press and punched into a size of 12 mm in diameter to obtain a negative electrode.

<Production of lithium ion secondary battery>
In an atmosphere having a dew point of −70 ° C. or lower, the negative electrode prepared by “Preparation of negative electrode for lithium ion secondary battery” was used as a working electrode. A lithium metal counter electrode was used as the counter electrode (positive electrode). As the electrolytic solution, a 1M-LiPF ₆ electrolytic solution using a mixed solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) = 1/1 (volume ratio) as a solvent, and vinylene carbonate with respect to the 1M-LiPF ₆ electrolytic solution are used. And 2% by mass added. A polypropylene microporous membrane (trade name “Celgard 3501”, manufactured by Celgard) was used as a separator. By using a flat cell (manufactured by Hosen) as the cell, the negative electrode, the separator, and the positive electrode are accommodated in that cell in order, and an electrolytic solution is injected, and the inside of the cell is vacuum degassed, The electrolyte solution was impregnated into each member, and an experimental lithium ion secondary battery was produced.

<Charge / discharge test>
The active material (graphite-coated carbon material in the examples and graphite in the comparative examples) was used as the working electrode. The charging mode is C.I. C. -C. V. (C.C. is a constant current, CV is an abbreviation for constant voltage). V. The mode was up to 1/10 of the set current density. When discharging, C.I. C. Mode. C. C. The set current density in the mode was 74.4 mA / g in the first cycle, and 372 mA / g in the second and subsequent cycles (hereinafter, the current density 372 mA / g is defined as 1C). The cut-off voltage had a lower limit of 5 mV and an upper limit of 2000 mV.
The capacity retention rate and coulomb efficiency were calculated by the following formula.
Capacity retention rate (%) = ((discharge capacity at the 51st cycle (mAh / g)) / (discharge capacity at the 2nd cycle (mAh / g))) × 100
Coulomb efficiency (%) = ((discharge capacity (mAh / g)) / (charge capacity (mAh / g))) × 100

<Input / output test>
The active material (graphite-coated carbon material in the examples and graphite in the comparative examples) was used as the working electrode. The charging mode is C.I. C. -C. V. (C.C. is a constant current, CV is an abbreviation for constant voltage). V. The mode was up to 1/10 of the set current density. When discharging, C.I. C. Mode. C. C. The set current density in the mode was 74.4 mA / g in the first cycle, and 372 mA / g in the second and subsequent cycles (here, the current density 372 mA / g is defined as 1C). The charging rates were 1C, 4C, 7C, and 10C, and this was performed in this order. The discharge rate was 1C. After changing the rate, charging and discharging at 1C was performed twice. Prior to the input / output test, one cycle charge / discharge was performed at 0.2C.
The rate maintenance rate was calculated by the following formula.
Rate maintenance ratio (%) = ((discharge capacity at 10 C (mAh / g)) / (discharge capacity at 1 C in the first cycle (mAh / g))) × 100

[Example 1]
<Manufacture of graphite-coated carbon material>
3 g of azulmic acid obtained by the above “production of azulmic acid” was put in a container, 300 g of formic acid was added as a solvent, and stirred at 50 ° C. for 1 hour to obtain an azulmic acid mixed solution. 20 g of scaly graphite (manufactured by Nippon Graphite Co., Ltd., trade name “PAG1”) was added to the obtained azurmic acid mixture to obtain an azulmic acid-graphite dispersion. The obtained azulmic acid-graphite dispersion was placed in an eggplant flask equipped with a refluxer and refluxed at 100 ° C. for 3 hours. Thereafter, the azulmic acid-graphite dispersion was transferred to an evaporator, and the inside of the evaporator was adjusted to a reduced pressure condition with a vacuum pump while rotating. The temperature was gradually increased from 20 ° C. so as not to bump, and finally 70 ° C. To remove formic acid. Thus, a composite material containing graphite and azulmic acid covering the graphite was obtained. The composite material was transferred to a vacuum dryer and further dried at 120 ° C. for 1 hour.

  The dried composite material was heat-treated at 170 ° C. for 5 hours in an air atmosphere. Next, 5 g of the heat-treated product is filled into a quartz tube, and heated to 900 ° C. for 1 hour in a tubular furnace while flowing nitrogen gas at 500 Ncc / min, and further maintained for 1 hour at 900 ° C. To obtain a graphite-coated carbon material.

<Production of negative electrode>
A negative electrode for a lithium ion secondary battery was prepared according to the above-mentioned “Preparation of a negative electrode for a lithium ion secondary battery”.

<Production of secondary battery>
A lithium ion secondary battery was prepared according to the above-mentioned “Preparation of lithium ion secondary battery”. When the electrolyte is immersed in the negative electrode, it is immersed in the negative electrode in the electrolyte and then vacuum deaeration. At this time, no matter how many times the vacuum deaeration is repeated, the graphite coated on the copper foil The composite containing the coated carbon material, acetylene black, carboxymethyl cellulose, and polyvinylidene fluoride was not peeled from the copper foil. Moreover, even if it took out the negative electrode from electrolyte solution with the tweezers, the composite_body | complex was not peeled from copper foil. From these things, it turned out that the adhesiveness with copper foil is improving with the graphite covering carbon material of this embodiment.

<Cycle characteristic evaluation>
The charge / discharge test of 51 cycles of the secondary battery was performed by the method of the “charge / discharge test”. The obtained results are shown in Table 1. It can be seen that the capacity retention rate and the coulomb efficiency after the second cycle are both high and charge and discharge can be performed very stably.

<Input / output characteristics>
The input / output characteristics of the secondary battery were evaluated by the above-described “input / output test”. The obtained results are shown in Table 1. It was found that the discharge capacity at 10 C was large, the rate maintenance rate was large, and the input / output characteristics were excellent.

[Example 2]
<Method for producing graphite-coated carbon material>
A graphite-coated carbon material was obtained in the same manner as in “Production of graphite-coated carbon material” in Example 1 except that 3 g of azulmic acid was changed to 5 g.

<Production of negative electrode>
A negative electrode for a lithium ion secondary battery was prepared according to the above-mentioned “Preparation of a negative electrode for a lithium ion secondary battery”.

<Production of secondary battery>
A lithium ion secondary battery was prepared according to the above-mentioned “Preparation of lithium ion secondary battery”. Similar to that observed in Example 1, it was found that the adhesion with the copper foil was improved.

<Cycle characteristic evaluation>
The charge / discharge test of 51 cycles of the secondary battery was performed by the method of the “charge / discharge test”. The obtained results are shown in Table 1. A graph of charge / discharge characteristics is shown in FIG. The second and subsequent cycles all showed almost the same characteristics, and it was found that charging and discharging were extremely stable. In the first cycle, an irreversible capacity for SEI (Solid Electrolyte Interface) formation occurs, which is a basic phenomenon common to lithium ion secondary batteries.

<Input / output characteristics>
The input / output characteristics of the secondary battery were evaluated by the above-described “input / output test”. The obtained results are shown in Table 1. It was found that the discharge capacity at 10 C was large, the rate maintenance rate was large, and the input / output characteristics were excellent.

[Example 3]
<Manufacture of graphite-coated carbon material>
A graphite-coated carbon material was obtained in the same manner as in “Production of graphite-coated carbon material” in Example 1 except that 3 g of azulmic acid was changed to 7 g.

<Production of negative electrode>
A negative electrode for a lithium ion secondary battery was prepared according to the above-mentioned “Preparation of a negative electrode for a lithium ion secondary battery”.

<Production of secondary battery>
A lithium ion secondary battery was prepared according to the above-mentioned “Preparation of lithium ion secondary battery”. Similar to that observed in Example 1, it was found that the adhesion with the copper foil was improved.

<Cycle characteristic evaluation>
The charge / discharge test of 51 cycles of the secondary battery was performed by the method of the “charge / discharge test”. The obtained results are shown in Table 1. It was found that the capacity maintenance rate and the Coulomb efficiency after the second cycle were both high and charge / discharge could be performed very stably.

<Input / output characteristics>
The input / output characteristics of the secondary battery were evaluated by the above-described “input / output test”. The obtained results are shown in Table 1. It was found that the discharge capacity at 10 C was large, the rate maintenance rate was large, and the input / output characteristics were excellent.

[Example 4]
<Manufacture of graphite-coated carbon material>
A graphite-coated carbon material was obtained in the same manner as in “Production of graphite-coated carbon material” in Example 2, except that the firing at 900 ° C. in the tubular furnace was changed to 1000 ° C.

<Production of negative electrode>
A negative electrode for a lithium ion secondary battery was prepared according to the above-mentioned “Preparation of a negative electrode for a lithium ion secondary battery”.

<Production of secondary battery>
A lithium ion secondary battery was prepared according to the above-mentioned “Preparation of lithium ion secondary battery”. Similar to that observed in Example 1, it was found that the adhesion with the copper foil was improved.

<Cycle characteristic evaluation>
The charge / discharge test of 51 cycles of the secondary battery was performed by the method of the “charge / discharge test”. The obtained results are shown in Table 1. It was found that the capacity maintenance rate and the Coulomb efficiency after the second cycle were both high and charge / discharge could be performed very stably.

<Input / output characteristics>
The input / output characteristics of the secondary battery were evaluated by the above-described “input / output test”. The obtained results are shown in Table 1. It was found that the discharge capacity at 10 C was large, the rate maintenance rate was large, and the input / output characteristics were excellent.

[Comparative Example 1]
<Production of negative electrode>
A negative electrode for a lithium ion secondary battery was produced in the same manner as in Example 1 except that scaly graphite (manufactured by Nippon Graphite Co., Ltd., trade name “PAG1”) was used as it was instead of the graphite-coated carbon material as the negative electrode active material. did.

<Production of secondary battery>
A lithium ion secondary battery was prepared according to the above-mentioned “Preparation of lithium ion secondary battery”. When performing vacuum degassing, some or all of the composite containing scaly graphite, acetylene black, carboxymethylcellulose, and polyvinylidene fluoride applied on the copper foil may peel from the copper foil. It was. Moreover, when the negative electrode was taken out from the electrolytic solution with tweezers, the composite sometimes peeled off from the copper foil.

<Cycle characteristic evaluation>
The charge / discharge test of 51 cycles of the secondary battery was performed by the method of the “charge / discharge test”. The obtained results are shown in Table 1. A graph of charge / discharge characteristics is shown in FIG. It turned out that the capacity | capacitance has also deteriorated after the 2nd cycle except the influence of the irreversible capacity | capacitance in the first charge / discharge. FIG. 4 shows a graph comparing the charge / discharge capacity cycle characteristics of Example 2 and Comparative Example 4, and FIG. 5 shows a graph comparing the Coulomb efficiency cycle characteristics.

<Input / output characteristics>
The input / output characteristics of the secondary battery were evaluated by the above-described “input / output test”. The obtained results are shown in Table 1.

  From Table 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5 and FIG. 6, the graphite-coated carbon material of this embodiment has excellent cycle characteristics and Coulomb efficiency as a negative electrode for a lithium ion secondary battery compared to graphite. And it was found to show input / output characteristics. In particular, with regard to input / output characteristics, it was found that the effect at a high rate was remarkably excellent.

  FIG. 7 shows a laser Raman spectrum of the graphite-coated carbon material of Example 2, and FIG. 8 shows a laser Raman spectrum of the scaly graphite of Comparative Example 1. The graphite-coated carbon material of the present embodiment has a shape having a skirt larger than the base line between P1 and P2, L / H1 of Example 2 is 0.57, and L / H of Comparative Example 1 H1 is 0.00.

The graphite-coated carbon material of the present invention has excellent cycle characteristics, coulomb efficiency, and input / output characteristics as a negative electrode for a lithium ion secondary battery. Moreover, the adhesiveness with a collector, especially copper foil is also high, From these points, there is an industrial applicability as a negative electrode for a lithium ion secondary battery.
Moreover, the composite material of the present invention has industrial applicability as a raw material for the negative electrode for a lithium ion secondary battery.

Claims (9)

  A carbon material containing graphite and a non-graphitizable carbon material having a nitrogen atom that covers the graphite.   The carbon material according to claim 1, wherein the non-graphitizable carbon material includes a carbonized product of azulmic acid.   A composite material containing graphite and azulmic acid covering the graphite.   The manufacturing method of a carbon material which has the process of heat-processing to the composite material containing graphite and the azulmic acid which coat | covers the graphite.   A step of immersing the graphite in a mixed solution containing the azulmic acid and an organic acid, and a step of removing the liquid from the mixed solution in which the graphite is immersed to obtain the composite material. Item 5. A method for producing a carbon material according to Item 4.   The method for producing a carbon material according to claim 5, wherein the organic acid includes formic acid.   The manufacturing method of the carbon material of any one of Claims 4-6 whose heat processing temperature in the said heat processing is 600-1500 degreeC.   The carbon material manufactured with the manufacturing method of any one of Claims 4-7.   The negative electrode for lithium ion secondary batteries containing the carbon material of Claim 1 or 8.