TECHNICAL FIELD

The present invention relates to carbon black, a production method thereof, a composition for an electrode containing carbon black, an electrode, and a secondary battery.

BACKGROUND ART

Conventionally, carbon black has been in use as a conductive material or the like, and studies are underway to develop carbon black having a variety of characteristic values (for example, Patent Literature 1).

In addition, Patent Literature 2 describes a method for producing high-purity furnace black by a specific production method.

CITATION LIST
Patent Literature

- [Patent Literature 1] Japanese Unexamined Patent Publication No. 2009-035598
- [Patent Literature 2] Japanese Unexamined Patent Publication No. 2002-105355

SUMMARY OF INVENTION
Technical Problem

In recent years, the increasing demand for portable electronic devices has increased the demand for secondary batteries, and good ideas for reducing defect rates are in demand for materials configuring secondary batteries.

As a material that is used as a conductive material for secondary batteries, carbon black is a typical example. However, carbon black that is produced by the method described in Patent Literature 2 has a high purity but is not excellent in terms of characteristics suitable for conductive materials for secondary batteries.

Therefore, an objective of the present invention is to provide carbon black that has an extremely small nickel content and can be suitably used as a conductive material for secondary batteries. In addition, another objective of the present invention is to provide a production method of the carbon black. Still another objective of the present invention is to provide a composition for an electrode containing the carbon black, an electrode, and a secondary battery.

Solution to Problem

One aspect of the present invention relates to carbon black in which an oil absorption amount is 150 mL/100 g or more and 400 mL/100 g or less, and a nickel content that is measured by induced coupled plasma-mass spectrometry is 50 ppb or less.

In one aspect, the nickel content may be 40 ppb or less.

In the carbon black according to one aspect, a BET specific surface area may be 35 m²/g or more and 400 m²/g or less.

In the carbon black according to one aspect, the BET specific surface area may be 130 m²/g or more and 400 m²/g or less, the oil absorption amount may be 200 mL/100 g or more and 400 mL/100 g or less, and, when the BET specific surface area is represented by S (m²/g) and the oil absorption amount is represented by A (mL/100 g), a ratio S/A may be 0.3 to 2.5.

In one aspect, the ratio S/A may be 0.4 to 2.5.

In one aspect, the ratio S/A may be 0.5 to 1.5.

The carbon black according to one aspect may be acetylene black.

Another aspect of the present invention relates to a carbon black production method including a synthesis step of treating a raw material gas containing a hydrocarbon in a cylindrical cracking furnace to obtain carbon black and a purification step of removing a magnetic foreign matter from the carbon black with a magnet to obtain the carbon black according to the present invention.

In one aspect, the purification step may be a step of removing the magnetic foreign matter from the carbon black obtained in the synthesis step by bringing the carbon black into contact with the magnet or disposing the carbon black near the magnet.

In one aspect, a maximum surface magnetic flux density of the magnet may be 1000 mT or more.

Still another aspect of the present invention relates to a composition for an electrode containing the carbon black according to the present invention and an active material capable of intercalating and deintercalating lithium ions.

Far still another aspect of the present invention relates to an electrode containing the composition for an electrode.

Far still another aspect of the present invention relates to a secondary battery including the electrode.

Advantageous Effects of Invention

According to the present invention, carbon black that has an extremely small nickel content and can be suitably used as a conductive material for secondary batteries is provided. In addition, according to the present invention, a production method of the carbon black is provided. Furthermore, according to the present invention, a composition for an electrode containing the carbon black, an electrode, and a secondary battery are provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing one aspect of a cylindrical cracking furnace.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferable embodiment of the present invention will be described in detail.

(Carbon Black)

Carbon black of the present embodiment is carbon black in which the oil absorption amount is 150 mL/100 g or more and 400 mL/100 g or less and the nickel content is 50 ppb or less.

Such carbon black allows incorporation of only an extremely small amount of a nickel-based foreign matter and is capable of significantly suppressing the generation of a defect attributed to the nickel-based foreign matter. In addition, the carbon black has a sufficient oil absorption amount and thus easily retains an electrolytic solution and is capable of efficiently supplying lithium ions to active materials in the case of being used as, for example, a conductive material for an electrode in a lithium secondary battery. In addition, the carbon black has favorable dispersibility and can be dispersed uniformly between, for example, active materials. Therefore, according to the carbon black, it is possible to realize a secondary battery having excellent battery performance in which only a few defects are generated.

The nickel content of the carbon black is preferably 40 ppb or less, more preferably 30 ppb or less and still more preferably 20 ppb or less.

In the present embodiment, as the nickel content of the carbon black, a value that is measured by inductively coupled plasma-mass spectroscopy is shown. Measurement by inductively coupled plasma-mass spectroscopy is performed by, specifically, the following method.

Approximately 1 g of a carbon black sample was accurately weighed in a quartz beaker and heated at 800° C. for three hours with an electric furnace in the atmosphere. Next, 10 mL of an acid mixture (hydrochloric acid+nitric acid=7:3) and 10 mL or more of ultrapure water were added to a residue and heated and dissolved on a hot plate at 200° C. for one hour. A solution that had been left to be cooled, then, diluted and adjusted to 25 mL with ultrapure water was measured with an inductively coupled plasma-mass spectrometer (Agilent 8800 manufactured by Agilent Technologies, Inc.).

The carbon black of the present embodiment may be a carbon material having aggregates in which primary particles having diameters of several tens of nanometers fuse together in bead shapes (primary aggregates) and, furthermore, forming an agglomerate in which the aggregates physically tangle together (secondary aggregate).

The BET specific surface area of the carbon black is, for example, 35 m²/g or more, preferably 50 m²/g or more, more preferably 100 m²/g or more, still more preferably 130 m²/g or more, far still more preferably 150 m/g or more and further still more preferably 170 m²/g or more. In such a case, for example, in a case where the carbon black is used as a conductive material for an electrode of a lithium ion secondary battery, there is a tendency that the number of contact points between an active material and a current collector further increases and it becomes easy to obtain a more favorable effect of imparting conductivity. In addition, the BET specific surface area of the carbon black may be, for example, 400 m²/g or less and is preferably 350 m²/g or less. In such a case, the interaction between primary particles and the entanglement between aggregates are suppressed, the dispersibility further improves, and more uniform dispersion between, for example, active materials is realized. That is, the BET specific surface area of the carbon black may be, for example, 35 to 400 m²/g, 35 to 350 m²/g, 50 to 400 m²/g, 50 to 350 m²/g, 100 to 400 m²/g, 100 to 350 m²/g, 130 to 400 m²/g, 130 to 350 m²/g, 150 to 400 m²/g, 150 to 350 m²/g, 170 to 400 m²/g or 170 to 350 m²/g.

The BET specific surface area of the carbon black is measured by the method B described in JIS K 6217-2, Determination of Specific Surface Area—Nitrogen Adsorption Methods—Single-point Procedures.

The oil absorption amount of the carbon black is 150 mL/100 g or more, preferably 180 mL/100 g or more, more preferably 220 mL/100 g or more and still more preferably 260 m²/100 g or more. In such a case, for example, in a case where the carbon black is used as a conductive material for an electrode of a lithium ion secondary battery, the carbon black more easily retains an electrolytic solution, the supply of lithium ions to active materials becomes easier, and it becomes easy to obtain more favorable battery performance. In addition, the oil absorption amount of the carbon black is 400 mL/100 g or less, preferably 370 mL/100 g or less and more preferably 350 mL/100 g or less. In such a case, the entanglement of the agglomerate is loosened, the dispersibility further improves, and more uniform dispersion between, for example, active materials is realized. That is, the oil absorption amount of the carbon black may be, for example, 150 to 400 mL/100 g, 150 to 370 ml/100 g, 150 to 350 mL/100 g, 180 to 400 mL/100 g, 180 to 370 mL/100 g, 180 to 350 mL/100 g, 220 to 400 mL/100 g, 220 to 370 mL/100 g, 220 to 350 mL/100 g, 260 to 400 mL/100 g, 260 to 370 mL/100 g or 260 to 350 mL/100 g.

As the oil absorption amount of the carbon black, a value obtained by converting a value measured by a method described in the method B of JIS K 6221 using dibutyl phthalate (DBP) as an oil to a value corresponding to JIS K 6217-4: 2008 by the following formula (a) is shown.

DBP absorption amount=(A−10.974)/0.7833 (a)

[In the formula, A represents the value of the DBP absorption amount measured by the method described in the method B of JIS K 6221.]

When the BET specific surface area of the carbon black is represented by S (m/g), and the oil absorption amount is represented by A (mL/100 g), the ratio S/A may be, for example, 0.2 or more and is preferably 0.3 or more, more preferably 0.4 or more and still more preferably 0.5 or more. In addition, the ratio S/A is, for example, 3.0 or less, preferably 2.0 or less, more preferably 1.5 or less and still more preferably 1.3 or less. In such a case, the balance among the number, sizes and dispersibility of the aggregates becomes more suitable for a conductive material for an electrode of a lithium ion secondary battery, it becomes easy to supply lithium ions to active materials while forming sufficient contact points between the active materials and current collectors, and it becomes easy to obtain more favorable battery performance. That is, the ratio S/A may be, for example, 0.2 to 3.0, 0.2 to 2.0, 0.2 to 1.5, 0.2 to 1.3, 0.3 to 3.0, 0.3 to 2.0, 0.3 to 1.5, 0.3 to 1.3, 0.4 to 3.0, 0.4 to 2.0, 0.4 to 1.5, 0.4 to 1.3, 0.5 to 3.0, 0.5 to 2.0, 0.5 to 1.5 or 0.5 to 1.3.

In one suitable aspect, the carbon black may have a BET specific surface area of 130 to 400 m²/g, an oil absorption amount of 200 to 400 mL/100 g and a ratio S/A of 0.3 to 2.5 (preferably 0.4 to 2.5, more preferably 0.5 to 2.5 and still more preferably 0.5 to 1.5). Such carbon black has excellent electron conduction performance, ion conduction performance and dispersibility and thus can be particularly suitably used as a conductive material. Such carbon black is produced by, for example, a method to be described below, in which an oxygen gas is sprayed.

Within the ranges of the BET specific surface area and the oil absorption amount in the present aspect, there is a tendency that the removal of a magnetic foreign matter becomes more difficult as the ratio S/A becomes larger. In the carbon black of the present aspect, the nickel content is decreased while the ratio S/A is intentionally kept within the above-described range, whereby both the above-described excellent effect as a conductive material and reduction of a disadvantage attributed to the magnetic foreign matter are satisfied.

The carbon black according to the present embodiment is preferably acetylene black.

The carbon black of the present embodiment can be produced by the following method.

(Carbon Black Production Method)

A carbon black production method of the present embodiment includes a synthesis step of treating a raw material gas containing a hydrocarbon in a cylindrical cracking furnace to obtain carbon black and a purification step of removing a magnetic foreign matter from the carbon black obtained in the synthesis step with a magnet to obtain carbon black having an oil absorption amount of 150 mL/100 g or more and 400 mL/100 g or less and a nickel content of 50 ppb or less.

In the synthesis step, a raw material gas is treated in a cylindrical cracking furnace. The cylindrical cracking furnace may be, for example, a cracking furnace including a thermal cracking portion where a thermal cracking reaction of the hydrocarbon is performed and an aging portion where a thermal cracking reaction product is reformed.

The cylindrical cracking furnace may further include a supply opening through which the raw material gas is supplied to the thermal cracking portion and a recovery opening through which carbon black generated in the aging portion is recovered.

In the cylindrical cracking furnace, from the viewpoint of more efficient removal of the magnetic foreign matter in the purification step, which will be described below, by additional homogenization of the carbon black, it is preferable that the ratio (D₁/D₂) of the diameter D₁of the thermal cracking portion to the diameter D₂of the aging portion is 1.2 to 2.2 and the ratio (L₁/L₂) of the length L₁of the thermal cracking portion to the length L₂of the aging portion is 0.4 to 1.0. In such a case, it is possible to retain the raw material gas supplied to the thermal cracking portion and thereby more reliably form carbon aerosols by the completion of the thermal cracking reaction and the development of aggregates.

The ratio (D₁/D₂) is preferably 1.3 to 1.8, and the ratio (L₁/L₂) is preferably 0.6 to 0.8. That is, the ratio (D₁/D₂) may be, for example, 1.2 to 2.2, 1.3 to 2.2, 1.2 to 1.8 or 1.3 to 1.8, and the ratio (L₁/L₂) may be, for example, 0.4 to 1.0, 0.6 to 1.0, 0.4 to 0.8 or 0.6 to 0.8.

In the thermal cracking portion, the supplied raw material gas is preferably retained at a temperature of 1900° C. or higher for 30 to 150 seconds. When the retention time is set to 30 seconds or longer, it is possible to more reliably form carbon aerosols by the completion of the thermal cracking reaction and the development of a chain structure. In addition, when the retention time is set to 150 seconds or shorter, the aggregation of carbon aerosols is suppressed, and it becomes easy to obtain carbon black from which the magnetic foreign matter is more easily removed in the purification step to be described below.

In the aging portion, the thermal cracking reaction product supplied from the thermal cracking portion is preferably retained at a temperature of 1700° C. or higher for 20 to 90 seconds. When the retention time is set to 20 seconds or longer, it becomes easy to obtain carbon black with a higher quality by the reforming of the carbon aerosols and the strengthening of aggregates. In addition, when the retention time is set to 90 seconds or shorter, the aggregation of the carbon aerosols is suppressed, and it becomes easy to obtain carbon black from which the magnetic foreign matter is more easily removed in the purification step to be described below.

The retention velocities in the thermal cracking portion and the aging portion can be each adjusted as appropriate by adjusting the gas linear velocity of a circulating gas. The retention time in the aging portion is preferably shorter than the retention time in the thermal cracking portion. That is, the gas linear velocity in the aging portion is preferably faster than the gas linear velocity in the thermal cracking portion.

FIG. 1 is a schematic cross-sectional view showing one aspect of the cylindrical cracking furnace. A cylindrical cracking furnace 10 shown in FIG. 1 includes a thermal cracking portion 1 and an aging portion 2. In addition, the cylindrical cracking furnace further includes a nozzle (supply opening) 3 through which a raw material gas is supplied to the thermal cracking portion 1.

In the present embodiment, the raw material gas preferably contains acetylene as a first carbon source. The content of the carbon source (for example, acetylene) in the raw material gas is, for example, 10 vol % or more, preferably 20 vol % or more and more preferably 30 vol % or more and may be 100 vol %. The content of each component in the raw material gas indicates a volume ratio relative to the volume at 150° C. and one atmosphere.

The raw material gas may, furthermore, further contain one or more other carbon sources in addition to the first carbon source (for example, acetylene). Examples of the other carbon sources include saturated hydrocarbons such as methane, ethane and propane, unsaturated hydrocarbons such as ethylene, propylene and butadiene, aromatic hydrocarbons such as benzene, toluene and xylene and the like. When these carbon sources are combined together, it is possible to increase or decrease the specific surface area of carbon black by changing the reaction temperature. The carbon sources are preferably selected from the group consisting of acetylene, unsaturated hydrocarbons such as ethylene and propylene and aromatic hydrocarbons such as benzene and toluene. In addition, as the carbon source, a petroleum fraction such as gasoline, kerosene, light oil or heavy oil may also be used.

In a case where the raw material gas contains acetylene and other carbon sources, the ratio of the other carbon sources to acetylene (the volume of the other carbon sources/the volume of acetylene) may be, for example, 0.01 or more. In addition, the ratio of the other carbon sources to acetylene (the volume of the other carbon sources/the volume of acetylene) may be, for example, 99 or less and is preferably 50 or less, and more preferably 30 or less and may be 10 or less or two or less. That is, the ratio (volume ratio) of the other hydrocarbons to acetylene may be, for example, 0.01 to 99, 0.01 to 50, 0.01 to 30, 0.01 to 10 or 0.01 to 2.

The raw material gas may further contain a water vapor gas, an oxygen gas, a hydrogen gas, a carbon dioxide gas and the like. As these gases, 99.9 vol % or more of high-purity gases are preferably used. When such high-purity gases are used, there is a tendency that it becomes easy to produce carbon black in which the amount of the magnetic foreign matter is small and the BET specific surface area and the oil absorption amount are stable.

The content of the water vapor gas may be, for example, 0 to 80 parts by volume and is preferably 0.1 to 70 parts by volume, more preferably 1 to 60 parts by volume and still more preferably 3 to 55 parts by volume relative to 100 parts by volume of the carbon source (for example, acetylene) in the raw material gas. When the content of the water vapor gas is within the above-described range, there is a tendency that the BET specific surface area of the carbon black becomes larger. That is, the content of the water vapor gas may be, for example, 0 to 80 parts by volume, 0 to 70 parts by volume, 0 to 60 parts by volume, 0 to 55 parts by volume, 0.1 to 80 parts by volume, 0.1 to 70 parts by volume, 0.1 to 60 parts by volume, 0.1 to 55 parts by volume, 1 to 80 parts by volume, 1 to 70 parts by volume, 1 to 60 parts by volume, 1 to 55 parts by volume, 3 to 80 parts by volume, 3 to 70 parts by volume, 3 to 60 parts by volume or 3 to 55 parts by volume relative to 100 parts by volume of the carbon source (for example, acetylene) in the raw material gas.

In the synthesis step, it is preferable to supply the oxygen gas together with the raw material gas to the thermal cracking portion, and it is more preferable to supply the oxygen gas to the thermal cracking portion by spraying the oxygen gas from the circumference of the supply opening through which the raw material gas is supplied to the thermal cracking portion.

The cylindrical cracking furnace preferably has a spray opening for the oxygen gas near the supply opening of the raw material gas and more preferably has a plurality of spray openings provided at equal intervals so as to surround the supply opening. The number of the spray openings is preferably three or more and more preferably three to eight.

In addition, the cylindrical cracking furnace may also include a nozzle with a multi-tube structure (for example, a double tube structure, a triple tube structure or the like) having the supply opening of the raw material gas and the spray opening for spraying the oxygen gas from the circumference of the supply opening. In the case of a double tube structure, for example, the raw material gas may be sprayed from an air space portion on the inner cylinder side, and the oxygen gas may be sprayed from an air space portion on the outer cylinder side. In the case of a triple tube structure composed of an inner tube, a middle tube and an outer tube, for example, the oxygen gas may be sprayed from an air space portion that is formed by the outer wall of the middle tube and the inner wall of the outer tube, and the raw material gas may be sprayed from the remaining air space portion.

The amount of the oxygen gas sprayed is not particularly limited if the production yield of carbon black is not taken into account. Carbon black can be produced even when a larger amount of the oxygen gas than necessary is sprayed. From the viewpoint of obtaining carbon black having the above-described suitable oil absorption amount, the amount of the oxygen gas sprayed may be, for example, 0 to 200 parts by volume and is preferably 0.1 to 190 parts by volume, more preferably 0.5 to 180 parts by volume and still more preferably 1 to 160 parts by volume relative to 100 parts by volume of the carbon source (for example, acetylene) in the raw material gas. That is, the amount of the oxygen gas sprayed may be, for example, 0 to 200 parts by volume, 0 to 190 parts by volume, 0 to 180 parts by volume, 0 to 160 parts by volume, 0.1 to 200 parts by volume, 0.1 to 190 parts by volume, 0.1 to 180 parts by volume, 0.1 to 160 parts by volume, 0.5 to 200 parts by volume, 0.5 to 190 parts by volume, 0.5 to 180 parts by volume, 0.5 to 160 parts by volume, 1 to 200 parts by volume, 1 to 190 parts by volume, 1 to 180 parts by volume or 1 to 160 parts by volume relative to 100 parts by volume of the carbon source (for example, acetylene) in the raw material gas.

In the synthesis step, it is possible to increase or decrease the BET specific surface area and oil absorption amount of carbon black to be obtained by, for example, adjusting the addition rate of the other hydrocarbons other than acetylene, the amount of the oxygen gas to be sprayed or the like.

The nickel content in the carbon black that is obtained in the synthesis step may be, for example, more than 50 ppb, may be 60 ppb or more, may be 70 ppb or more and may be 80 ppb or more.

The purification step is a step of removing a magnetic foreign matter from the carbon black obtained in the synthesis step with a magnet.

The purification step may be, for example, a step of removing a magnetic foreign matter from the carbon black obtained in the synthesis step by bringing the carbon black into contact with the magnet or disposing the carbon black near the magnet (for example, passing the carbon black through near the magnet).

The magnet that is used is not particularly limited, and, for example, a magnet bar having a neodymium magnet packed in a stainless steel 304 tube may be used.

The maximum surface magnetic flux density of the magnet is not particularly limited, but may be, for example, 700 mT or more and is preferably 1000 mT or more and more preferably 1200 mT or more. In such a case, a fine magnetic foreign matter attached to the carbon black is more strongly adsorbed, and thus it becomes easy to obtain carbon black having a smaller nickel content. The upper limit of the maximum surface magnetic flux density of the magnet is not particularly limited and may be, for example, 1400 mT or less. That is, the maximum surface magnetic flux density of the magnet may be, for example, 700 to 1400 mT, 1000 to 1400 mT or 1200 to 1400 mT.

The purification step may be a step of removing the magnetic foreign matter from the carbon black so that the nickel content reaches 50 ppb or less (preferably 40 ppb or less, more preferably 30 ppb or less and still more preferably 20 ppb or less). The lower limit of the nickel content is not particularly limited, and the nickel content in the carbon black may be, for example, 1 ppb or more, and, from the viewpoint of the cost and productivity, may be 10 ppb or more, may be 15 ppb or more and may be 50 ppb or more. That is, the nickel content in the carbon black may be, for example, 1 to 50 ppb, 1 to 40 ppb, 1 to 30 ppb, 1 to 20 ppb, 10 to 50 ppb, 10 to 40 ppb, 10 to 30 ppb, 10 to 20 ppb, 15 to 50 ppb, 15 to 40 ppb, 15 to 30 ppb or 15 to 20 ppb.

(Applications)

Since the content of a nickel-based foreign matter is significantly small, the carbon black of the present embodiment can be suitably used in applications such as conductive materials for secondary batteries and semi-conducting layers of power cables. In addition, since the oil absorption amount is within the above-described range, the carbon black of the present embodiment can be particularly suitably used as conductive materials for secondary batteries.

The carbon black of the present embodiment can be suitably used as, for example, a composition for an electrode containing carbon black and an active material capable of intercalating and deintercalating lithium ions. As the active material in the composition for an electrode, well-known active materials can be used with no particular limitations.

Examples of the active material include

- layered compounds such as lithium cobalt oxide (LiCoO₂), lithium nickel oxide (LiNiO₂), layered lithium manganese oxide (LiMnO₂) and LiMn_xNi_yCo_zO₂(x+y+z=1, 0≤y<1, 0≤z<1 and 0≤x<1), which is a complex oxide containing a plurality of transition metals;
- manganese-based compounds such as Li_1+xMn_2−xO₄(x represents 0 to 0.33), Li_1+xMn_2−x−yM_yO₄(M represents at least one metal selected from the group consisting of Ni, Co, Cr, Cu, Fe, Al and Mg, x represents 0 to 0.33, y represents 0 to 1.0, and 2−x−y>0), LiMnO₃, LiMn₂O₃, LiMnO₂, LiMn_2−xM_xO₂(M represents at least one metal selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and x represents 0.01 to 0.1) and Li₂Mn₃MO₈(M represents at least one metal selected from Co, Ni, Fe, Cr and Zn);
- copper-lithium oxide (Li₂CuO₂);
- iron-lithium oxide (LiFe₃O₄);
- olivine-based compounds such as LiFePO₄, LiMnPO₄, LiMnFePO₄and Li₂MPO₄F (M represents at least one metal selected from the group consisting of Co, Ni, Fe, Cr and Zn);
- vanadium oxides such as LiV₃O₈, V₂O₅and Cu₂V₂O₇;
- disulfide compounds;
- silicate-based compounds such as Li₂MSiO₄(M represents at least one metal selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta); and
- Li₂MO₃·LiMO₂(M represents at least one metal selected from the group consisting of Mn, Co, Ni, Fe, Cr and Zn), Fe₂(MoO₄)₃, Li₂S, S and the like.

A secondary battery of the present embodiment includes an electrode containing the composition for an electrode. In the secondary battery of the present embodiment, a positive electrode and/or a negative electrode may contain the composition for an electrode, and it is preferable that the positive electrode contains the composition for an electrode.

In the secondary battery of the present embodiment, an electrode not containing the composition for an electrode and the configuration other than the electrode are not particularly limited, and well-known electrodes and configurations in secondary batteries can be used with no particular limitations.

Hitherto, the suitable embodiment of the present invention has been described, but the present invention is not limited to the above-described embodiment.

EXAMPLES

Hereinafter, the present invention will be described in more detail with examples, but the present invention is not limited to these examples.

Example 1

The mixing ratio of a raw material gas was set to 86 vol % of an acetylene gas to 14 vol % of other carbon source (toluene gas), the raw material gas was sprayed from a nozzle installed at the furnace top of a cylindrical cracking furnace at a spraying rate of 6.5 m/s, carbon black was produced using the thermal cracking and/or combustion reaction of the acetylene gas, and the carbon black was trapped into a middle tank from a bag filter directly connected to the furnace lower portion. (Synthesis step) the trapped carbon black was passed through a transfer tube equipped with a magnet for trapping a magnetic foreign matter (magnet bar having a neodymium magnet packed in a stainless steel 304 tube having ϕ20 mm and a length of 300 mm, maximum surface magnetic flux density of 1000 mT) in the middle and trapped in a product tank (purification step), thereby obtaining carbon black (CB1). A conductive composition for an electrode and an electrode for a battery were produced by a method to be described below using the obtained CB1, and each evaluation was performed. The evaluation results are shown in Table 1.

Example 2

Carbon black (CB2) was obtained by the same method as in Example 1 except that the mixing ratio of the raw material gas was changed to 100 vol % of an acetylene gas. A conductive composition for an electrode and an electrode for a battery were produced using the obtained CB2, and each evaluation was performed. The evaluation results are shown in Table 1.

Example 3

Carbon black (CB3) was obtained by the same method as in Example 1 except that the mixing ratio of the raw material gas was changed to 71 vol % of an acetylene gas, 15 vol % of an oxygen gas, 12 vol % of water vapor and 2 vol % of other carbon source (toluene gas). A conductive composition for an electrode and an electrode for a battery were produced using the obtained CB3, and each evaluation was performed. The evaluation results are shown in Table 1.

Example 4

Carbon black (CB4) was obtained by the same method as in Example 1 except that the mixing ratio of the raw material gas was changed to 69 vol % of an acetylene gas, 8 vol % of an oxygen gas, 13 vol % of water vapor and 10 vol % of other carbon source (toluene gas). A conductive composition for an electrode and an electrode for a battery were produced using the obtained CB4, and each evaluation was performed. The evaluation results are shown in Table 1.

Example 5

Carbon black (CB5) was obtained by the same method as in Example 1 except that the mixing ratio of the raw material gas was changed to 67 vol % of an acetylene gas, 3 vol % of an oxygen gas, 15 vol % of water vapor and 15 vol % of other carbon source (benzene gas). A conductive composition for an electrode and an electrode for a battery were produced using the obtained CB5, and each evaluation was performed. The evaluation results are shown in Table 1.

Example 6

Carbon black (CB6) was obtained by the same method as in Example 1 except that the mixing ratio of the raw material gas was changed to 51 vol % of an acetylene gas, 27 vol % of an oxygen gas, 20 vol % of water vapor and 2 vol % of other carbon source (toluene gas). A conductive composition for an electrode and an electrode for a battery were produced using the obtained CB6, and each evaluation was performed. The evaluation results are shown in Table 1.

Comparative Example 1

Carbon black (CB7) was obtained by the same method as in Example 1 except that the mixing ratio of the raw material gas was changed to 71 vol % of an acetylene gas, 15 vol % of an oxygen gas, 12 vol % of water vapor and 2 vol % of other carbon source (toluene gas), the sample was collected from the middle tank, and the purification step was not performed. A conductive composition for an electrode and an electrode for a battery were produced using the obtained CB7, and each evaluation was performed. The evaluation results are shown in Table 1.

Comparative Example 2

Carbon black (CB8) was obtained by the same method as in Example 1 except that the mixing ratio of the raw material gas was changed to 67 vol % of an acetylene gas, 3 vol % of an oxygen gas, 15 vol % of water vapor and 15 vol % of other carbon source (benzene gas), the sample was collected from the middle tank, and the purification step was not performed. A conductive composition for an electrode and an electrode for a battery were produced using the obtained CB8, and each evaluation was performed. The evaluation results are shown in Table 1.

Comparative Example 3

As carbon black of Comparative Example 3, SUPER P Li (manufactured by IMERYS Graphite & Carbon, trade name: SUPER P Li) was prepared.

Comparative Example 4

As carbon black of Comparative Example 4, ECP (manufactured by Lion Specialty Chemicals Co., Ltd., trade name: CARBON ECP) was prepared.

(Measurement of Nickel Content)

Approximately 1 g of a carbon black sample was accurately weighed in a quartz beaker and heated at 800° C. for three hours with an electric furnace in the atmosphere. Next, 10 mL of an acid mixture (hydrochloric acid+nitric acid=7:3) and 10 mL or more of ultrapure water were added to a residue and heated and dissolved on a hot plate at 200° C. for one hour. A solution was left to be cooled, then, diluted and adjusted to 25 mL with ultrapure water, and the nickel content was measured with an inductively coupled plasma-mass spectrometer (Agilent 8800 manufactured by Agilent Technologies, Inc.).

(Measurement of BET Specific Surface Area)

The BET specific surface area of the carbon black was measured by a BET single-point method in accordance with the method B of JIS K 6217-2 using nitrogen as an adsorption gas under a condition of a relative pressure p/p0=0.30+0.04.

(Measurement of Oil Absorption Amount)

As the oil absorption amount of the carbon black, a value obtained by converting a value measured by a method described in the method B of JIS K 6221 using dibutyl phthalate (DBP) as an oil to a value corresponding to JIS K 6217-4: 2008 by the following formula (a) is shown.

DBP absorption amount=(A−10.974)/0.7833 (a)

[In the formula, A represents the value of the DBP absorption amount measured by the method described in the method B of JIS K 6221.]

(Preparation of Dispersion Liquid of Composition for Electrode)

N-methyl-2-pyrrolidone (manufactured by Kanto Chemical Co., Inc., hereinafter, referred to as NMP) was prepared as a solvent, LiNi_0.5Mn_0.3Co_0.2O₂(manufactured by Umicore S.A., trade name: TX10) was prepared as an active material, polyvinyl fluoride (manufactured by Arkema S.A., trade name: HSV900, hereinafter, referred to as PVdF) was prepared as a binder, the carbon black of an example or a comparative example was prepared as a conductive material, and polyvinyl alcohol (manufactured by Denka Company Limited, trade name: B05, hereinafter, referred to as polyvinyl alcohol) was prepared as a dispersant, respectively. 98 mass % of LiNi_0.5Mn_0.3Co_0.2O₂in terms of solid content, 2 mass % of PVdF in terms of solid content, 1 mass % of the carbon black in terms of solid content and 0.1 mass % of polyvinyl alcohol in terms of solid content were weighed and mixed, and NMP was added to this mixture so that the content of the solid content reached 68 mass % and mixed using a planetary centrifugal vacuum mixer (manufactured by Thinky Corporation, Thinky Mixer ARV-310) until the mixture became uniform, thereby obtaining a dispersion liquid of a composition for an electrode (composition for a positive electrode).

(Production of Positive Electrode)

A film of the prepared dispersion liquid of a composition for an electrode was formed on a 15 μm-thick aluminum foil (manufactured by UACJ Corporation) with an applicator and placed still in a dryer to be preliminarily dried at 105° C. for one hour. Next, the film was pressed with a roll pressing machine at a linear pressure of 200 kg/cm to prepare a film so that the thickness of the film including the 15 μm-thick aluminum foil reached 80 μm. In order to remove a volatile component, the film was dried in a vacuum at 170° C. for three hours, thereby obtaining a positive electrode.

(Electrode Evaluation)

A disc having a diameter of 14 mm was cut out from the produced positive electrode, the alternating current impedance was measured using an electrochemical measurement system (manufactured by Solartron Analytical, function generator 1260 and potentiostat galvanostat 1287) at an amplitude voltage of 10 mV within a frequency range of 0.1 Hz to 1 MHz in a state where the front and back were sandwiched by SUS304 plate electrodes, and the intersection point with the X axis of a Cole-Cole plot was regarded as a resistance value.

The evaluation results of the examples and the comparative examples are shown in Table 1. In Table 1, the mixing ratio of “hydrocarbon gas” means the mixing ratio of the other carbon source.

TABLE 1

Compar-
Compar-
Compar-
Compar-

ative
ative
ative
ative

Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-

ple 1
ple 2
ple 3
ple 4
ple 5
ple 6
ple 1
ple 2
ple 3
ple 4

Kind of carbon black (CB)
CB1
CB2
CB3
CB4
CB5
CB6
CB7
CB8
SUPER P Li
ECP

Raw material
Acetylene gas
86
100
71
69
67
51
71
67
—
—

gas mixing
Oxygen gas
0
0
15
8
3
27
15
3
—
—

ratio
Water vapor gas
0
0
12
13
15
20
12
15
—
—

(vol %)
Hydrocarbon gas
14
0
2
10
15
2
2
15
—
—

Kind of hydrocarbon gas
Toluene
None
Toluene
Toluene
Benzene
Toluene
Toluene
Benzene
—
—

Magnet treatment
Yes
Yes
Yes
Yes
Yes
Yes
No
No
—
—

Character-
Nichel content (ppb)
9
10
11
14
14
13
58
97
269
1172

istics of CB
BET specific surface
38
89
138
178
210
376
142
218
63
877

area (m²/g)

Oil absorption
177
192
253
257
304
318
249
316
233
390

amount (mL/100 g)

BET specific surface
0.21
0.46
0.55
0.69
0.69
1.18
0.57
0.69
0.27
2.25

area/oil absorption

amount

Electrode
Electrode plate resistance
179
151
130
96
43
97
129
46
145
218

evaluation
(Ω · cm²)

REFERENCE SIGNS LIST

- 1 Thermal cracking portion
- 2 Aging portion
- 3 Nozzle
- 10 Cylindrical cracking furnace